Note: Descriptions are shown in the official language in which they were submitted.
W O 94/04752 2 1 ~ 2 3 6 7 Pc~r/US93/o~32o
ACID-TO-ALKALINE PAPERMAKING PROCESS
BAcRGRoun~D OF THE lNV ~:N-"lON
1. Field of th~ Invention
This invention relates to a fundamentally new papermaking
process, based on a fundamentally new flocculation mech~n;sm
different from charge-neutralization or polymer-bridging known
in the prior art.
Specifically, this invention relates to a process for the
manufacture of novel and improved paper, board and other wet-
laid products from furnishes comprising cellulosic and/or syn-
thetic fibers, optionally also comprising inorganic and organ-
ic filler pigments, water-soluble and water-disperse polymer
~ 15 adhesives, color dyes and other adjuvants, treated with com-
plex functional microgel cements.
The complex functional microgel cements are synthesized
in situ (in the furnish) from transient, chemically reactive
subcolloidal sodium-silico-aluminate or similar hydrosols
cross-linked with bivalent and/or multivalent inorganic salts,
optionally also using organic, cationically active chemical
compounds having at least two reactive groups in each molecule
as auxiliary (additional) cross-linking agents.
2. Discussion of th~ Releva~t Art
Paper, as a web of cellulosic fibers, is made in princi-
ple by dewatering aqueous suspensions (furnishes) of partially
crushed (refined) cellulosic fibers on stationary or moving
screens and drying the resultant screen residue.
The quality of paper products made in the above manner
would obviously be unacceptable for most of today's applica-
tions; hence, modern papermaking furnishes usually consist of
blends of selected species of cellulosic fibers, refined to
W094/04752 2 1 ~ 2 ~ 6 7 i PCT/US93/~3~
,
precisely defined standards; mineral and/or plastic filler
pigments; dyes; sizing agents; strength-enhancing polymers;
and so forth, the resultant webs being appropriately finished.
To obtain satisfactory retention of solids from such complex
furnishes on rapidly moving and vibrating forming screens of
modern paper machinec~ these furnishes must be flocculated in
a controlled manner with the aid of appropriate colloid-chem-
ical mech~n;sms. The type of flocculation-controlling mecha-
nism depends on the system of chemical agents ("wet-end chem-
icals") specific to the papermaking process employed.
As is readily understood by those skilled in the art,there can be only as many principal, fundamentally different
paperr~k;ng processes as there are principal, fll~fl~rcntally
different flocculation m~rhAn;~ms, the only two such floccula-
tion mech~nisms known in the prior art being based on eithercharqe neutrali~ation or ~olYmer ~ridginq. Accordingly, the
two principal papermaking processes at the foundation of the
entire contemporary paperma~ing industry, depending on two
flln~mentally different colloid-chemical me~h~n;cms (wet-end
chemistries) for furnish flocculation, are the "acidic" pro-
cess, known since ancient times, and the "alkaline" process,
known for just a few decades.
The flocculation of furnish ingredients in the acidic
papermaking process is induced with the aid of papermaker alum
(aluminum sulfate), which requires that the pH level in the
furnish be maintained below 5.3. It is only below the pH of
5.3 that alum dissociates into trivalent cations, Al3+, which
effectively suppress the negative charges on furnish particu-
lates causing their flocc~ tion. To maintain a precise con-
trol of the pH level in the furnish, alum is often used incombination with sulfuric acid. A dose of about 20-30 lbs. of
alum per ton of furnish solids is usually sufficient to floc-
culate the latter and obtain satisfactory solids retention on
the forming wire. High-molecular-weight organic cationic
polymers are often employed as auxiliary flocculants, in
proportions of from 1 to 4 lbs. per ton of furnish solids, to
increase the efficiency of solids retention.
?,
W094/04752 2 1 ~ 2 3 6 7 PCT/US93/~
To counter the inherent drawbacks of the acidic paper-
making process, an alkaline version of the papermaking process
was developed in the past few decades and is now replacing the
former to an ever growing extent. The most pronounced draw-
backs of the acidic papermaking process traditionally havebeen manifested in the low mechanical strength and poor aging
characteristic of paper products, along with severe adverse
environmental side effects. The alkaline papermaking process,
whose wet-end chemistry relies upon the use of special func-
tional high-molecular-weight polymers (retention aids), is
carried out as a rule at a furnish pH ranging from about 7 to
8, although somewhat higher or lower pH levels are not uncom-
mon. The fundamental colloid-chemical mech~;sm employed for
furnish flocculation in the latter process is based on "poly-
mer bridging," according to which the relatively long macro-
molecular ~h~in~ of the above-mentioned high-mol~clllAr-weight
polymeric retention aids ~ecome attached directly to receptive
sites on the surface of cellulosic fibers and/or filler parti-
cles. As the effect of polymer bridging, manifested by the
"tying" of adjacent particulates with polymer chains, ensem-
bles of flocculated mat~er are formed which can be retained
efficiently on the forming wire of a paper machine.
Although the alkaline papermaking process is free of the
major drawbacks of the acidic process, it nevertheless has
some serious drawbacks of its own. A most serious one is the
former's inherent inability to cope with the emerging techno-
logical trends and advancements taking foothold in the paper
industry. The6e new trends and advancements aim, among other
things, toward vastly increased paper machine speeds, on the
order of 6,000-8,000 ft/min; formation of webs from signifi-
cantly more concentrated furnishes than those presently used;
total closure of process-water streams on paper machines;
manufacture of "high-ash" printing papers with filler-loading
levels ranging from 25% to more than 50%, by weight; manufac-
ture of high-quality on-machine-coated papers; as well as
manufacture of ultraopaque papers (having opacities of at
least 98%) for two sided, high-resolution computer printout
W094/0~752 2 ~ ~ 2 3 ~ ~ PCT/US93/~3~
and office reproduction. It is thus fair to state that the
alkaline papermaking process of the prior art, although a
relatively very recent newcomer to the paper industry, has
been "born ~enile" at the very onset as far as its techno-
logical growth potential is concerned.
The papermaking process of the present invention relies
on an instantaneous (for all practical purposes), in~iFsrimi-
nate and complete flocculation of any and all particulates
present in papermaking furnishes with the aid of in-situ
synthesized multicomponent, functional complex microgels
disclosed by the applicant in the co-pending Patent Applica-
tion Serial No. ~7/775,025 ("Functional Complex Microgels
with Rapid Formation Kinetics"), Filed October 11, 1991,
incorporated herein by reference. The complex microgels in
question are synthesized in principle by cross-linking in-
situ-formed transient, chemically reactive sodium-silico-
aluminate and similar subcolloidal hydrosols with the aid of
bivalent and/or multivalent inorganic salts.
The above in-situ (in the papermaking furnish) synthe-
sized complex functional microgels used in practicing thepresent invention are believed to represent the most powerful
and versatile colloid-chemical systems known in the colloid
science and technology. Although many thousands of seemingly
analogous colloidal systems were described and/or patented
during the past 150 years, the applicant is not aware of any
even remotely resembling the complex functional microgels
under discussion with regard to either the chemical composi-
tion, ultrarapid formation kinetics, colloid-chemical nature
or application versatility.
The in~c~r~hle deficiency of all paper products made by
the prior-art acidic and alkaline papermaking processes is the
lack of a truly uniform distribution of the highly diversified
particulate matter present in papermaking furnishes used for
these products' manufacture. As is readily understood by
those skilled in the art, paper products with a uniform
structure (statistically uniform spatial distribution of all
particulate components) can be obtained only if all of the
W094/04752 2 ~ ~ ~3 6 7 PCT/US93/~3~
following conditions are fulfilled:
(a) starting with papermaking furnishes in which all
particulate ingredients (fibers, fiber fines, fillers) are
optimally (for all practical purposes) dispersed, the
statistically uniform distribution of the particulates in
question being sustained intact prior to flocculation;
(b) flocculating the optimally dispersed particulate
components of papermaking furnishes from step (a) instantane-
ously (for all practical purposes), indiscriminately and com-
pletely to retain an equivalent statistically uniform distri-
bution of furnish particulates in the resultant flocs; and
(c) providing an adequate r?ch~n;cal integrity to the
resultant flocs, enabling the latter to effectively withstand
the shearing forces to which they may be exposed while the
flocculated furnish is conveyed to the headbox or applied onto
the forming wire of a paper machine.
~ he meC~Ani cal integrity in question is att~; nAhle by
generating flocs with an adequate inherent tenacity or impart-
ing to these flocs the ability to reform (reconstitute) after
a transient breakup. It should be further e~ph~ized in the
above context that the use of well-dispersed, let alone opti-
mally dispersed, furnishes in the acidic and alkaline paper-
making processes of the prior art, required by condition (a)
above, is t~hnically infeasible for all practical purposes in
that the flocculation mech~nisms at the foundations of both of
the above procesC~s are too weak to override the action of the
powerful modern dispersants. Moreover, the wet-end chemistry
of an "ideal" papermaking process should also provide, in ad-
dition to the florc~ ting action, an intrinsic mechanism for
enhancing the resultant paper products' mech~nical strength,
and even for imparting desirable functional properties. As is
well known to those skilled in the art, however, the wet-end
chemistries of the acidic and alkaline papermaking processes
of the prior art have, for all practical purposes, none of the
above-mentioned "ideal" features which represent but a few of
the many attractive and important benefits provided by the
versatile papermaking process of the present invention.
w094/04752 2 1 ~ 2 ~ 6 7 PCT/US93/~ ~
Although there is no direct prior art whatsoever relating
to the acid-to-alkaline papermaking process of the present in-
vention, to the best of the applicant's knowledge, references
will be made hereinafter to any even indirectly related tech-
nical and patent literature deemed helpful to elucidating thesubject matter under discussion.
In accordance with the foregoing and disclosures to
follow, it is an object of the present invention to provide a
working description of a fundamentally novel acid-to-alkaline
papermaking process, based on a fundamentally new, hitherto
unknown flocculation mech~nism, allowing one to manufacture
improved or entirely novel paper, board and wet-laid nonwoven
products from furnishes treated with in-situ synthesized
complex functional microgels having intrinsic cementing and
surface-chemistry-modifying properties.
In particular, it is an object of the invention to
provide a working description of the wet-end chemistry of the
papermaking process under discussion, relying on the use of
the complex functional microgels disclosed in the co-pending
Patent Application Serial No. 07/775,025 ("Functional Complex
Microgels with ~apid Formation Kinetics"), Filed October 11,
1991, applicable to a whole spectrum of tasks extending from
laboratory-scale handsheet making up to full-fledged produc-
tion runs on even the fastest paper machines.
It is a further object of the invention to provide novel
approaches to the manufacture of paper, board and wet-laid
nonwoven products on paper machines utilizing essentially 100%
of the particulate matter, such as fibers or fillers, present
in the starting furni~h~c, thus obtaining effluent streams
free of particulate contaminants.
It is a still further object of the invention to provide
novel approaches to manufacturing more uniform webs at faster
paper machine speeds than is possible with the aid of the
acidic and alkaline processes of the prior art.
It is a yet further object of the invention to provide
novel approaches to manufacturing very uniform webs on paper
machines, using considerably more concentrated furnishes than
W094/04752 2 1 4 2 3 61 - PCT/US93~3~
, ~
can be employed in the acidic and alkaline papermaking proces-
ses of the prior art, hence, greatly reducing the enormous
water demand inherent to the latter processes.
It is a yet further object of the invention to provide
novel approaches to attaining the environmentally most desir-
able goal of a total closure of process-water streams on paper
machines.
It is a still further object of the invention to provide
novel approaches to the manufacture of cellulosic webs with a
superior resistance to aging.
It is a further object of the invention to provide novel
approaches to the manufacture of high-temperature-resistant
wet-laid ("nonwoven") products.
It is a yet further object of the invention to provide
novel methods of "intrinsic" sizing of cellulosic webs.
It is a still further object of the invention to provide
novel approaches to attAining filler-retention efficiencies
~Yce~ing those presently feasible with the aid of the acidic
and alkaline papermaking processes of the prior art.
It is a yet further object of the invention to provide
novel approaches to manufacturing "very-high-ash" papers with
filler-loading levels even exceeding 50%, by weight.
It is a yet further object of the invention to provide
novel approaches to manufacturing colored cellulosic and wet-
laid nonwoven webs, while utilizing essentially 100% of the
color dyes employed.
It is a still further object of the invention to provide
novel approaches to the manufacture of webs readily accepting
(disfiipating) both water and organic liquids.
A yet further object of the invention is to provide novel
approaches to the manufacture of cellulosic webs whose dry and
wet strengths surpass those attainable with similar webs made
with the aid of the acidic or alkaline papermaking processes
of the prior art.
A still further object of the invention is to provide
novel approaches to manufacturing extra-high-strength cellu-
losic and other wet-laid products from furnishes optionally
PCT/US93/~3~
2 1 ~ 2 ~;6 7 : --
comprising, besides cellulosic and/or synthetic fibers, one or
more of additional ingredients such as synthetic microfibrils,
extraneously prepared novel cellulosic microfibrils, novel
ultrafine polymer-emulsion adhesives and novel waterborne rub-
ber cements.
It is a yet further object of the invention to provide
novel approaches to manufacturing under alkaline conditions
groundwood-cont~;ni~g paper products, including newsprint, of
a quality not attainable with the aid of the papermaking
processes of the prior art.
It is a still further object of the invention to provide
novel approaches for manufacturing ultraopaque paper (with an
opacity of at least 98%) for high-resolution, two-sided com-
puter printout and office reproduction.
A yet further object of the invention is to provide a
general blueprint for custom designing novel approaches to the
manufacture of a variety of paper, board and other wet-laid
products on a paper machine, having better quality and/or
being made faster and more economically than analogous prod-
ucts made with the aid of the acidic and alkaline processes of
the prior art, as well as to provide novel approaches to mak-
ing entirely new types of paper, board and other wet-laid
products whose manufacture was hitherto not feasible with the
aid of the technologies and materials known in the prior art.
8UMMARY OF TH~ lNv~..lON
The present invention relates to a fundamentally new
acid-to-alkaline process for manufacturing paper, board and
other wet-laid products on a paper machine, from aqueous fur-
n; ~hes having a pH of from 4.5 to 12 tthe alkaline and near-
s~lh~lk~line pH range being preferred for practicing the pres-
ent invention), wherein said process comprises the following
steps:
(a) blending an aqueous solution of an alkali-metal or
quaternary ammonium silicate, and a second aqueous solution of
an alkali-metal aluminate and/or alkali-metal zincate, with a
W094/04752 2 1 4 2 ~; ~ 7 PCT/US93~3~
.
paper, board or wet-laid-nonwoven furnish to form in situ a
transient, chemically reactive subcolloidal hydrosol, wherein
each of said solutions is employed in said furnish at a con-
centration of from 0.01% to 2.0%, by weight;
(b) blending an aqueous solution of at least one cross-
linking agent selected from the group consisting of bivalent
and/or multivalent inorganic salts, said aqueous solution op-
tionally containing at least one additional (auxiliary) cross-
linking agent selected from the group consisting of organic
cationically active chemical compounds with at least two
reactive groups in each molecule, with the resultant furnish
from step ta), said cross-linking agent(s) being employed in
said furnish at a concentration of from 0.02% to 4.0~, by
weight, to cross-link said transient chemically reactive
subcolloidal hydrosol and synthesize in situ a complex func-
tional microgel cement, whereupon all particulate components
of said furnish become flocculated instantaneously, indis-
criminately and completely;
(c~ optionally purging said furnishes resulting from
step (b) of dissolved contA-;n~nts, e.g., with the aid of fil-
tration and rinsing; and
(d) recovering said furnishes resulting from steps (b)
and/or (c) to manufacture paper, board or other wet-laid (non-
woven) products on a paper machine.
The in-situ-synthesized microgels from step (b), further
in the specification and in the claims to follow referred to
in the generic terms, regardless of their specific chemical
composition, as complex functional microgels or microgel
cements, are employed in proportions of from 0.4% to 10%, by
weight, as determined by ashing, in relation to the mass of
the resultant paper, ~oard or wet-laid nonwoven products,
- wherein the constituents of said microgel cements are
(a) from 0.4% to 10%, by weight, in relation to the
total mass of paper, board or wet-laid-nonwoven
furnish solids, of transient, chemically reactive
subcolloidal hydrosols formed of
(1) at least one reagent selected from the group
wo 94/047~2 2 1 ~ 2 3 67 pCT/US93l~3 ~
consisting of alkali-metal silicates and qua-
ternary ammonium silicates; and
(2) at least one reagent selected from the group
consisting of alkali-metal aluminates and
alkali-metal zincates, the ratio of the rea-
gents of ll) to the reagents of (2) being from
1:10 to 10:1, by weight;
cross-linked by
(b) at least one cross-linking agent selected from a
first group consisting of bivalent and multivalent
inorganic salts, employed in a proportion of from
0.4% to 10.0%, by weight, in relation to the total
mass of paper, board or other wet-laid products,
and, optionally, at least one auxiliary cross-link-
lS ing agent selected from a second group consisting oforganic, cationically active chemical compounds hav-
ing at least two reactive groups in each molecule,
employed in a proportion of up to 0.5~, by weight,
in relation to the total mass of paper, board or
other wet-laid products, the ratio of said cross-
linking agents to said chemically reactive, subcol-
loidal hydrosols being from l:lo to lO:l.
In addition to cellulosic and1or synthetic fibers and
customary disperse and/or water-soluble functional adjuvants
used in papermaking, the above-mentioned furnishes for making
paper, board and other wet-laid products optionally comprise
at least one of the following materials in proportions speci-
fied below in relation to furnish solids:
(a) filler pigments, up to more than 50%, by weight;
(b) color dyes, up to 5.0%, by weight;
(c) carbon black, deagglomerated by the master-batch
method, up to 0.1~, by weight;
(d) commercial latex adhesives with an average particle
diameter larger than 70 nm, up to 5.0~, by weight;
(e) novel ultrafine acrylic polymer-emulsion adhesives
with an average particle diameter smaller than 55 nm and a
glass-transition temperature ranging from -6QC to +20C, up
W094/04752 2 1 4 2 3 ~ 7 PCTJUS93/~3~
11
to 5.0%, by weight;
(f) novel waterborne acrylic rubber cements, up to 5.0%,
by weight;
(g~ waterborne disperse thermoplastic adhesives, up to
20.0%, by weight;
(h) commercial water-soluble wet-end adhesives, up to
2.0%, by weight;
(i) synthetic microfibrils, up to 2.0%, by weight;
(j) cellulosic microfibrils with a length of from 10 ~m
to 200 ~m, prepared extraneously by the cascade microfibrilla-
tion process, up to 2.0%, by weight; and
(k) ultrafine electroconductive and/or magnetic ceramic
and/or metallic powders with particle diameters finer than
0.2 ~m, up to 20.0%, by weight.
DE8~PTPTION OF T~E PREFERRED EMBODIMENT8
In the preferred mode of practicing the present inven-
tion, novel and improved paper, board and other wet-laid prod-
ucts are manufactured on paper machines from aqueous furnishes
comprising cellulosic and/or synthetic fibers, optionally also
comprising at least one functional ingredient such as inorgan-
ic and organic pigments, organic polymer adhesives, color dyes
and other adjuvants useful in paperma~ing, dispersed and/or
dissolved in said furnishes, by flocculating all particulate
furnish ingredients instantaneously, in~i~criminately and com-
pletely with the aid of the above-mentioned, in-situ-synthe-
sized complex functional microgels which, in terms of second-
ary functions, also contribute (by virtue of their cementing
properties) to the dry and wet strengths of the resultant
cellulosic or wet-laid nonwoven webs. The microgels (microgel
cements) in question, disclosed in the previously mentioned
co-pending Patent Application Serial No. 07/775,025, Filed
October 11, 1991, are formed in two distinct process stages,
a different polymerizationmechanism beingactive in each stage.
W094/04752 2 1 ~ 23 ~7 PCT/US93/~3 ~
In the first process stage, two separate reagent solu-
tions are introduced into an aqueous furnish comprising cellu-
losic and/or synthetic fibers, optionally also containing fil-
ler pigments, water-disperse and/or water-soluble adhesives,
dyes and other water-disperse and/or water-soluble adjuvants
(auxiliary functional materials). One of these reagent solu-
tions contains an alkali-metal or quaternary ammonium sili-
cate, preferably sodium silicate. The other reagent solution
contains an alkali-metal aluminate and/or alkali-metal zinc-
ate, preferably sodium aluminate. An immediately commencingaddition polymerization of the above "primary" subcolloidal-
hydrosol-forming reagents leads to the formation of sodium-
silico-aluminate (zincate) dimers, trimers and higher-rank
oligomers. These transient, chemically reactive anionic
polymer precursors remain, for a limited period, in a very
specific state of solution, for which the ob~ectively fitting
term "subcolloidal hydrosols" has been employed herein.
In the second process stage, an aqueous solution contain-
ing at least one cross-linking agent selected from the group
consisting of essentially colorless, bivalent and/or multi-
valent salts of calcium, magnesium, barium, aluminum, zinc and
zirconium, preferably calcium chloride or nitrate, is intro-
duced into the above-mentioned furnish containing the subcol-
loidal hydrosol formed in the first process stage. The poly-
condensation reaction taking place between the transient,chemically reactive subcolloidal sodium-silico-aluminate
(zincate) hydrosols and the inorganic cross-linking salts
leads to an ultrarapid formation of complex (multicomponent)
calcium-silico-aluminate (zincate) or similar microgel
cements, made up of networks of macromolecules of a polymer-
polycondensate type.
The colloidal consequence of synthesizing the complex
microgel cements used in practicing the present invention in
in-situ, in the furnish, is an instantaneous, indiscriminate
and complete flocculation (coflocculation) of any and all par-
ticulates present in the furnish. The tenacity of the evolv-
ing flocs can often be enhanced, improving the efficiency of
W094/04752 2 1 ~ 2 3 67 PCT/US93/~3~
13
fines retention on the forming wire, by incorporating small
proportions of cationic polyelectrolytes into the solutions of
the above-mentioned inorganic bivalent and/or multivalent
cross-linking salts.
It should be emphasized that the primary reagents used in
the first stage of the process of the formation of the complex
microgels, i.e., sodium silicate and sodium aluminate (zinc-
ate), E~ first react with each other to form the transient,
chemically reactive subcolloidal sodium-silico-aluminate
(zincate) hydrosols before any complex microgels can be syn-
thesized (in the second stage of the process) by cross-linking
the subcolloidal hydrosols in question with bivalent or multi-
valent inorganic salts. Hence, the subcolloidal sodium-silico-
aluminate (zincate) hydrosols which, along with the inorganic
cross-linking ~alts, are the factual microgel-forming agents,
must be considered as "higher-rank" reagents synthesized in
situ from the primary, lower-rank reagents, i.e., sodium sili-
cate and sodium aluminate (zincate). If the latter individual
reagents reacted directly (on their own) with a cross-linking
salt, e.g., calcium chloride, the products of such reactions
would be merely suspensions, or precipitates, of solid, more
or less crystalline particles of bicom~onent calcium silicate
and calcium aluminate (zincate), respectively, but not micro-
gels, let alone complex microgels which, by definition, must
contain at least three different chemical building blocks in
their macromolecular make-up.
The complex functional microgels used in practicing the
present invention are formed virtually instantaneously, the
chemical reaction of polycondensation ~etween the above-men-
tioned low-molecular-weight subcolloidal hydrosols and the
bivalent and multivalent inorganic salts being estimated to
occur in less than one microsecond. The consequences of this
polycondensation are further manifested in a very rapid propa-
gation of association between calcium-silico-aluminate (poly-
mer-polycondensate) macromolecules, bringing about, within a
couple of milliseconds, the development of colloidal forma-
tions with useful molecular weights that may reach billions.
W094t047~2 2 1 ~ 2 3 ~ f~ PCT/US93~3~
It is primarily this rap~d continuous growth of the molecular
weights across such an enormously broad range, "sweeping"
through the entire reaction space, which is deemed responsible
for the instantaneous, indiscriminate and complete floccula-
tion of even the most heterodisperse and polydisperse colloi-
dal systems known in the art, regardless of these systems'
physical, chemical or colloidal make-up.
The quantitative aspects of the unique flocculating power
of the in-situ-synthesized complex microgels under discussion
can be readily understood considering that the efficiency of
organic polymeric flocculants, such as are routinely employed
in the acidic and alkaline papermaking processes of the prior
art, increases markedly with the increasing molec~ r weight.
As is well known to those skilled in the art, however, the use
of polymeric flocculants with a molec~ r weight higher than
about 15,000,000 i6 often difficult, if not impossible, due to
their limited solubility in water. Moreover, all organic
polymeric flocculants have relatively narrow molecular-weight
distributions and are thus incapable of satisfying "across-
the-board" the highly differentiated flocculation requirements
inherent to such pronouncedly heterodisperse and polydisperse
systems as the contemporary furnishes for making paper and
other wet-laid products. On the other hand, the complex micro-
gels under discussion possess such an across-the-board (uni-
versal) flocculating ability in that, being synthesized insitu and growing continuously from the very smallest dimen-
sions, they sweep through an enormously ~road molecular-weight
range. It would obviously be impossible to il,L~od~ce analo-
gous extraneous high-molecular-weight polymeric flocculants
into a paper (nonwoven) furnish ~ecause of insolu~ility.
While the complex tmultic~ ol-~nt) microgels used in
practicing the present invention were completely unknown here-
tofore, the transient, chemically reactive subcolloidal hydro-
sols used for synthesizing these microgels need some elabora-
tion to distinguish them from other, deceptively similar sys-
tems of the prior art. In view of the confusion and lack of
standardization in the present colloid-chemical terminology,
~ W094/04752 2 1 ~ 2 3 ~ ~ PCT/US93~3~
a fundamental treatment of the subject matter of the present
invention and a brief chronological review of the prior art
related to this subject matter is deemed necessary.
It is essential to point out in the above context that an
active worldwide interest in natural and synthetic silica and
silico-aluminates commenced with the key discoveries of
1) water-soluble sodium silicates ("water glass") by
Johann Nepomuk von Fuchs (1774-1856~, who suggested numerous
practical applications for these interesting chemicals, e.g.,
in application to the formulation of adhesives, cements, flame
retardants for paints, detergents, soap builders, dyeing adju-
vants, metal fluxes and fertilizers;
2) metallic aluminum in 1825 by Oerstedt and Woehler,
with most of the inorganic chemical compounds of this element
known today having been described in the professional litera-
ture by countless scientists within the next few decades; and
3) the phenomena of ion ~Ych~nge in soils (natural alu-
mino-silicates) by J. T. Way in 1850.
The rapidly following discoveries of many other commer-
cially valuable properties of silica and alumino-silicate
minerals, e.g., in the application to the desiccation of
gases, clarification of water, removal of color impurities
from edible and mineral oils, or manufacture of pigments and
catalysts, triggered intensive research efforts in the field
of silica and alumino-silicates. These efforts were directed
both towards improving the performance properties of naturally
occurring materials as well as producing analogous or yet
unknown synthetic materials with yet more improved or even
entirely novel properties.
Due to the similar dimensions of ionic radii of Si~+ and
Al3+ (0.41 A and 0.~0 ~, respectively), as well as an over-
whelming abundance of these two elements in the lithosphere,
a large variety of alumino-silicate minerals have been syn-
thesized in nature by geochemical processes. In contrast, the
more complex (comprising three or more components) minerals
related to alumino-silicates, exemplified by the previously
mentioned calcium-alumino-silicates, are relatively uncommon
wo 94,04,522 1 423 6 7 - PCT/US93/~3 ~
in nature. The reason for the rare occurrence of calcium-
alumino-silicate minerals, such as anorthite, Ca[Al2Si208], or
margarite, CaAl2[Al2Si2010]~OH]2, is readily understood con-
sidering that Ca++, with an ionic radius of 0.99 A, is rather
strongly rejected from an evolving alumino-silicate matrix,
making the formation of such complex minerals by the exceed-
ingly slow geochemical processes difficult.
Since no significant practical applications have yet been
found for calcium-alumino-silicate minerals, an in-depth ex-
ploration or synthesis of the latter generated thus far onlya limited interest from the standpoint of academic or indus-
trial research. On the other hand, a great number of alumino-
silicate preparations and products were synthesized in the
past 150 years because of the latters' highly diversified com-
mercial applications. That such an enormous variety of chemi-
cal compounds, characterized by distinct physical and colloid-
chemical properties, can be synthesized using just one or two
of the four simple, easily available reagents, i.e., sodium
silicate, silicic acid, sodium aluminate and alum, has abso-
lutely no precedent in the inorganic chemistry. The almostcountless patents issued in the past 150 years for a broad
variety of synthetic silica and alumino-silicate products
obtained with the aid of the above-mentioned reagents relate
essentially to only three principal colloidal systems, namely,
continuous gels and discrete sols and precipitates.
The incredible diversification of the forms and proper-
ties of products synthesized with the aid of the same few
reagents may be explained by accepting the hypothesis that
colloids are the lowest-rank systems ~nown in nature equipped
with "memory." It is the latter which makes the colloids
"remem~er" their history in chronological detail and react
accordingly, as manifested in terms of their resultant materi-
al properties and functional behavior. Hence, any intention-
al, or even accidental, deviation from established synthesis
procedures or reaction conditions will bring about inescapably
certain differences, mostly quantitative but sometimes pro-
foundly qualitative, in the constitution and/or functional
W094/04752 2 L ~ 2 3 6 7 ~cT/us93/nn3~
properties of the resultant colloidal systems. Indeed, essen-
tially all similar, or even virtually identical, patented syn-
thetic silica and alumino-silicate products differ among each
- other merely with respect to relatively minor quantitative
compositional variations, procedural modifications (such as
may pertain to the rates, order of addition and concentrations
of reagents, pH ranges, as well as thermal and aging regimes),
or with respect to the resultant products' modified physical
and physicochemical properties and new areas of application.
How even a minor processing detail may be decisive to the
very usefulness of a synthetic alumino-silicate product may be
illustrated, for example, by U.S. Patent No. 2,757,085 to
Paquin. As disclosed therein, satisfactory color-reactive
alumino-silicate pigments, synthesized in situ in a papermak-
ing furnish, were obtained only if sodium aluminate was intro-
duced into the furnish first, followed by the addition of
sodium silicate, but not vice-versa. Similarly, U.S. Patent
No. 4,213,874 to Williams et al. teaches that it was possible
to synthesize satisfactory amorphous sodium aluminosilicate
base exchange materials only if, among other things, the
proper sequence and rate of addition of the reactants were
maintained during the precipitation process.
The critical dependence of a successful preparation of
colloidal systems on maintaining strictly defined process
parameters and conditions is perhaps best summarized by S.
Voyutsky in his textbook of corro~ chEMl~y(Page 269, second
paragraph), Mir Publishers, Moscow, translated into English in
1978: "Colloidal systems can be obtained by various chemical
reactions: exchange, reduction, oxidation, hydrolysis, and so
forth. But colloidal systems are not always formed in reac-
tions capable of producing sols; they are formed only (under-
lining added by the applicant) at definite concentrations of
the initial substances, at definite order of their mixing and
- temperature, and when some other conditions are met."
The preferred transient, chemically reactive subcolloidal
hydrosols used in practicing the present invention are soluble
sodium-alumino-silicates which form spontaneously when solu-
W094/04752 2~ 6 7 PCT/US93/~3 ~
tions of sodium silicate and sodium aluminate are blended into
aqueous slurries of particulate raw materials (furnishes) used
for the manufacture of cellulosic or wet-laid nonwoven prod-
ucts by the papermaking process under discussion. As the re-
sult of an immediately commencing addition polymerization,dimers, trimers and higher-rank oligomers (polymer precursors)
evolve sequentially and continuously into very-low-molecular-
weight sodium-alumino-silicate macromolecules of an anionic
polyelectrolyte type. Due to the relatively low concentrations
of the reagents employed, but mostly due to the prompt cross-
linking of the transient subcolloidal hydrosols (terminating
their further molecular growth), the evolving sodium-alumino-
silicate macromolecules are very small, their estimated dimen-
sions being at most only slightly larger than 1 nm (10 A).
Such highly disperse systems represent special borderline
solutions classified dimensionally above solutions of crystal-
loids (simple molecules or ions), but below colloidal solu-
tions, e.g., those of starch, protein or polyacrylamides. A
scientifically appropriate term "subcolloidal hydrosols" has
been systematically used herein in referring to the above sys-
tems, which should be distinguished from aquasols (hydrosols)
of the prior art which are aqueous suspensions of solid par-
ticles with diameters of from about 5 nm to 100-200 nm.
Historically, the terminology used in colloid science and
technology evolved in connection with the basic investigative
tools available at the inception of colloidal research, name-
ly, the conventional light microscope and ultramicroscope.
Colloidal particles with diameters smaller than 200 nm could
hardly be resolved with the aid of old-fashioned light micro-
scopes equipped with low-aperture ob~ectives; hence, they were
referred to as "submicroscopic." On the other hand, ultra-
microscopes, utilizing the Tyndall effect, made it possible to
observe, though not resolve, particles as small as 5 nm in
diameter. Consequently, colloidal systems became traditional-
ly the domain of ultramicroscopical investigations and theirclassification as "ultramicroscopic," with particle dimensions
ranging from 5 nm to 200 nm, still has a great deal of valid-
W094/~4752 2 1 4 2 3 6 7 ~ PCT/US93/~3~
19
ity for most practical applications. Regrettably, some lessrigorous colloid textbooks still routinely list the colloidal
dimensions as extending from 1 nm to 500 nm, or even 1000 nm.
Modern scientific research has established unequivocally,
however, that the traditional delineation between "colloidal"
- and "noncolloidal" (crystalloid) systems, established solely
on the basis of the dimensions of particles of the disperse
phase, has no scientific foundation. Hence, contemporary doc-
trines refute the concept of "colloids" and "crystalloids,"
interpreted in the past in a rather absolute sense, accepting
instead the existence of a very specific "colloidal state"
associated with disperse systems conforming to the established
criteria of "colloid-like" behavior. The reasons for this can
be illustrated rather clearly using the example of sodium
chloride which behaves as a typical crystalloid in aqueous
solutions and a typical colloid in benzene solutions, numerous
other such systems already having been identified.
Many experimental f;n~;ngs made during studies of~highly
disperse systems attest particularly clearly to the uniqueness
of the particle-dimension interval extending from 1 nm to 5 nm
(10-50 A), in which the colloidal and crystalloid states over-
lap and deficiencies of the imperfect colloid-chemical nomen-
clature are most evident. Hence, an unambiguous treatment of
disperse systems of the above type frequently makes defining
them in fundamental terms virtually mandatory, as has been
established in dealing with many extremely important media
such as surfactants, dyes, toxins and antitoxins. For exam-
ple, the dimensions of individual molecules of some of the
above-mentioned materials are larger than 1 nm (10 A), con-
sidered as the conventional upper limit of crystalloid par-
ticles, but smaller than 5 nm (50 A), considered as a prac-
tical lower limit for typical colloidal particles. Since the
behavior of such systems overlaps the domains of both crystal-
- loids and colloids, some authors have introduced the rather
artificial term "semicolloids" to deal with these unusual
solutions. Still other authors refer to such highly disperse
systems, with particle dimensions ranging from 1 nm to 5 nm,
w094/04752 2 1 ~ 2 3 ~ 7 PCT/US931~3~
as "amicrons" (subcolloids), to be distinguished from "submi-
crons" applying to systems with particles larger than 5 nm in
diameter.
Perhaps the most unfortunate aspect of the traditional
colloid-chemical terminology is that the term "aquasol," and
the equivalent term "hydrosol," in which the suffix "sol"
stands for "solution," are used in referring to sus~ensions
of ultramicroscopic solid particles in water. Although aqua-
sols (hydrosols) do indeed appear as translucent (opalescent)
solutions to an unaided eye, the latter, fundamentally incor-
rect, terms complicate the clarity of the issue when the sci-
entific discourse revolves around boundary systems of overlap-
ping behavior (e.g., crystalloid/subcolloid or subcolloid/col-
loid) or extends beyond professional circles. It should be
pointed out, though, that many rigorous colloid scientists
systematically employ the scientifically correct term "suspen-
soids" in referring to aguasols (hydrosols~ of the prior art.
The above-mentioned, nomenclature-relatedproblems become
even more complicated in dealing with novel subject matter,
such as the subcolloidal sodium-silico-aluminate or similar
hydrosols used to synthesize the complex microgels at the
foundation of the present invention. The latter subcolloidal
hydrosols constitute borderline solutions of transient, chemi-
cally reactive polyanionic molecules. As solutions, they have
the appearance of completely clear, plain water, are totallY
devoid of any solid particles and do not exhibit the Tyndall
effect.
The transient character of these continuously changing
subcolloidal sodium-alumino-silicate hydrosols renders the
underlying oligomers and macromolecules fundamentally unde-
finable in terms of the exact physical dimensions or chemical
composition. This ic understood best when considering that
the reaction of addition polymerization, commencing with the
moment the solutions of sodium silicate and sodium aluminate
become introduced into a reactor (furnish), proceeds continu-
ously. Hence, even if it were possible to determine, at any
given instant, the dimensions, molecular weights, or chemical
W094/04752 2 ~ 4 2 3 6 ~ ~ PCT/US93/~3~
.
21
composition of the evolving macromolecules, such information
would become obsolete in the very subsequent instant.
It is possible, however, to objectively define the unique
systems mentioned above employing criteria of the philosophy
of science used in formulating scientific definitions. Accord-
ing to these criteria, the continuously changing, transient,
subcolloidal hydrosols cannot be classified as "materials" in
a conventional sense in that they have no definite (fixed)
form, mass or properties by which a material is conventionally
described or defined, e.g., in textbooks of material science.
Instead, the latter s~bcolloidal systems, representing a very
specific "material state," are defined in terms of
(a) a detailed description of the reaction medium and
conditions at the onset of the synthesis of the subcolloidal
hydrosols in question, i.e., at the point of time (t) where
t = 0; and
(b) an arbitrary subsequent fixed point of time (t = c).
The latter means that if the in-situ synthesis of an arbitrary
transient subcolloidal hydrosol is initiated at a time t = 0,
using identical reagents, reagent proportions and concentra-
tions, sequences and rates of reagent addition, temperature,
pH and all other effective reaction conditions and process
parameters, then, and only then, the resultant transient sub-
colloidal hydrosol will be exactly the same each time it pas-
ses through a subsequent fixed point of time t = x (x = c).
While the above-discussed continuously evolving (in st~u
~cendi) subcolloidal systems, e.g., the transient subcolloidal
sodium-alumino-silicate hydrosols under discussion, are unde-
finable in conventional terms used in material sciences, it is
also completely certain that they are different from any
existing natural or synthetic substances of the same nominal
chemical compofiitions. By contrast, all traditional sols are
classified as "phaseal" colloids, the latter term indicating
that the disperse phase is identical to an analogous phase
existing on a macro scale and could, in principle, be obtained
from the latter with the aid of mechanical comminution or
other preparatory methods.
w094/04752 2 1 4 ~ ~ ~ 7 Z2 PCT/U593/~3~
The transient aspects of the subcolloidal sodium-alumino-
silicate hydrosols used in practicing the present invention
must be particularly strongly emphasized since the process of
addition polymerization between sodium silicate and sodium
aluminate is a continuous one. Hence, at some advanced stage
of polymerization (aging), particles of the above-mentioned
subcolloidal hydrosols acquire sufficiently high molecular
weights to exceed the solubility limits, whereupon the subcol-
loidal hydrosols in question transform into conventional
~prior-art) aquasols, i,e., colloidal suspensions of solid
particles. The period of aging necessary to initiate such a
transformation may extend from less than a second up to sever-
al days, or even weeks or months, depending on the concentra-
tion of sodium silicate and sodium aluminate (zincate~ in the
reaction medium (furnish), and is manifested by the appearance
of the Tyndall effect.
As is readily understood by those skilled in the art, the
chemical reactivity of the transient subcolloidal hydrosols in
question, i.e., the ability to form the complex microgels at
the foundation of the present invention by a process of chemi-
cal cross-linking carried out with the aid of bivalent (multi-
valent) inorganic salts, decays with the increasing degree of
polymerization (aging). The chemical reactivity is lost almost
completely when the solute particles of the above subcolloidal
hydrosols polymerize beyond the solubility limits transforming
into solid colloidal particles of conventional sols. It is
important, therefore, that the second stage of the in-situ
synthesis of complex microgels, in which the above-mentioned
subcolloidal sodium-alumino-silicate or similar hydrosols are
chemically cross-linked with the aid of bivalent and/or multi-
valent inorganic salts, be carried out before the advent of
the Tyndall effect.
In typical paper mill installations working in a continu-
ous process mode, the above cross-linking can be carried out
within a period ranging from several seconds to a couple of
minutes, counting from the moment the solutions of sodium
silicate and sodium aluminate are added to furnishes for
W094/04752 2 1 ~ 2 3 6 ~ PCT/US93~3~
.
23
making paper, board and other wet-laid products.
The primary purpose of the in-situ synthesized complex
functional microgels under discussion is to induce an instan-
taneous, indiscriminate and complete flocculation (cofloccula-
tion) of all disperse raw materials present in paper, board orwet-laid-nonwoven furnishes. Flocculation phenomena play a
fundamental role in the manufacture of cellulosic and wet-laid
nonwoven products; however, the flocculation processes used
in the acidic and alkaline papermaking processes of the prior
art are slow, detrimentally selective (rather than indiscrimi-
nate) and incomplete. Accordingly, these processes are not
well suited for the manufacture of advanced paper, board and
wet-laid nonwoven products (especially at high paper machine
speeds) that are free of detrimental cons~quences of a selec-
tive flocculation and fractionation of furnish componentsaccording to species and size, manifested in more or less
pronounced performance deficiencies of the resultant products.
As a matter of fact, many potentially useful ultrafine colloi-
dal materials cannot, for all practical purposes, be floccu-
lated (precipitated) with the aid of the inefficient floccula-
tion processes and agents used in prior-art acidic and alka-
line papermaking processes, thus being effectively eliminated
as viable raw materials for manufacturing the above-mentioned
advanced paper, board and wet-laid nonwoven products.
Typical contemporary paper furnishes are highly hetero-
disperse and polydisperse waterborne systems con~A;n;ng cellu-
losic fibers and fiber fines, inorganic and organic fillers,
water-soluble adhesives, sizing agents, dyes, and other ad3u-
vants. All of the above furnish ingredients must be uniformly
coflocculated to be efficiently retained on the forming wire
of a paper machine and yield satisfactory (uniform) webs. As
i8 well known, however, each disperse component of a hetero-
disperse system has different surface-chemical properties,
electrical-charge density, dispersion stability, and so forth,
hence, also a different resistance to flocculation. Moreover,
virtually all particulate species used in paper furnishes are
more or less polydisperse in their own right, the process of
W094/04752 2 ~ ~ 2 3 6 7 PCT/US93/~3~
24
flocculation of dimensio~nally different component fractions of
these species being~controlled by different colloid-chemical
and other r?ch~nisms. Considerable difficulties are encoun-
tered in particular when flocculating inherently polydisperse
mineral fillers whose particle dimensions may range from about
0.1 ~m to 20 ~m e.s.d. (equivalent spherical diameter). Hence,
coarse filler fractions, e.~., those with an equivalent spher-
ical diameter larger than 2 ~m, are relatively resistant to
colloid-chemical flocculation their retention in the web being
affected primarily by mechAn;cal factors such as turbulence,
gravitational settling, or filtration. The flocculation of
intermediate-size fractions, on the other hand, is effected
mainly by the neutralization of electrical charges on filler
particles and by polymer bridging. The ultrafine filler frac-
tions, i.e., those with an equivalent spherical diameter smal-
ler than 0.1 ~m, are hardly affected by the flocculation mech-
anisms employed in the acidic and alkaline papermaking proces-
ses of the prior art. Similarly, many ultrafine particulates,
such as color dyes or polymer-emulsion adhesives, are largely
immune to flocculation by alum or organic polymers.
Another detrimental side effect of the slow and selective
flocculation of heterodisperse and polydisperse furnish compo-
nents in the acidic and alkaline papermaking processes of the
prior art is the formation of aggregates of the undesirable
segregated [...fiber/fiber...] or [...filler/filler...] types.
The latter segregation, in turn, is the reason for a reduced
retention of filler particles on the forming wire, deteriora-
tion of web-formation quality, and reduction of the optical-
performance efficacy of filler particles retained in the web.
The low and selective flocculation is particularly detrimen-
tal to the optical-performance efficacy of the expensive
titanium dioxide (Tio2) pigments, which are virtually always
employed in combination with less expensive, low-refractive-
index extender pigments intended to function as physical
spacers. The reason for this reduced optical-performance
efficacy of Tio2 is that, because of the inefficient (slow and
selective) flocculation processes of the prior art, the pre-
W094/04752 2 1 4 2 3 ~ 7 PCT/US93~3~
dominantly formed filler-particle aggregates are of the opti-
cally inferior ~...Tio2/Tio2...] and [...extender/extender...]
types instead of the desirable, optically far more efficient
[...extender/TiOJextender...] type.
It should also be borne in mind that a substantial pro-
portion of furnish ingredients dispensed from the headbox onto
the forming wire is not retained in the first pass and must be
recycled a couple of times through the papermaking process.
Since the flocculation of furnish ingredients in the conven-
tional (prior-art) acidic and alkaline papermaking processes
is also incomplete, the detrimental effects of fractionation
and selective aggregation (flocculation) of the individual
furnish components are continuously amplified during the
above-mentioned recycling.
The instantaneous, indiscriminate and complete flocculat-
ing action of the in-situ (in the furnish) synthesized complex
functional microgels used in practicing the present invention
totally eliminates the drawbacks normally associated with the
use of highly heterodisperse and polydisperse paper, board and
wet-laid-nonwoven furnishes. Hence, novel and unusual types
of paper, board and nonwoven products can be prepared from
even the most exotic, extremely heterodisperse and polydis-
perse furnishes, without incurring even a trace of selectivity
(fractionation) or incomplete flocculation. As is readily
understood by those skilled in the art, furnishes of the
above-mentioned type could not be used in the papermaking
proceCcec of the prior art without incurring unacceptable
material losses and operational difficulties, not to mention
potentially disastrous ecological consequences.
The exotic furnishes under discussion may contain, among
other things, cellulosic fibers; synthetic organic fibers;
inorganic fibers; reinforcing synthetic microfibrils and
extraneously prepared cellulosic microfibrils; magnetic and
electroconductive metal powders; mineral as well as plastic
filler pigments with particle dimensions ranging from about
0.1 ~m up to 20 ~m e.s.d.; non-film-forming (nonfusing, or
fusing only at elevated temperatures) emulsion polymers with
wo 94/04752 2 1 ~ 2 3 ~ 7 PCT/US93/~3 ~
~ 26
particles as small as 30 nm in diameter; novel ultrafine
polymer-emulsion adhesives with particles smaller than 55 nm
in diameter and glass-transition temperatures ranging between
-60OC and +20C; novel waterborne rubber cements; commer-
cial water-soluble paper adhesives; microparticulate thermo-
plastic adhesives; color pigments; and carbon black with
particles even smaller than 10 nm in diameter. Moreover, the
above particulates may have relative densities ranging from
about 1 g/cm3 for organic polymers up to 4.2 g/cm3 for-titanium
dioxide pigments, or yet considerably higher for metal pow-
ders, while their surface-chemical properties may range from
very hydrophilic to extremely hydrophobic.
Virtually no limits to potential furnish diversities,
hence also to the diversity and versatility of the resultant
paper, board and wet-laid nonwoven products, are envisaged
with the papermaking process of the present invention since,
in the applicant's extensive investigations, no waterborne
dispersion or colloidal system, regardless of how fine, com-
plex or difficult, had yet been encountered able to resist the
overpowering instantaneous, indiscriminate and complete floc-
culating action of the in-situ synthesized complex functional
microgels under discussion.
The secondary purpose of the complex functional microgels
is to provide, by virtue of their inherent cementing proper-
ties, an increased level of mech~nical strength to paper,board and wet-laid nonwoven products made by the process of
the present invention. The adhesive action of these microgels
can be controlled by both the dosage employed and a purposeful
optimization of their chemical composition, much in the same
way as i8 customary in optimizing the bonding strength of
contemporary industrial inorganic cements. With cellulosic
webs, the principal me~h~nical strength is derived from
hydrogen bonds formed between functional groups exposed at the
surface of fibrillated (refined) cellulosic fibers, the acting
range of such bonds extending merely over a distance of a few
of Angstroms. A secondary reinforcement of cellulosic webs
made by the prior-art papermaking processes is presently
W094/04752 214 2 3 G 7 PCT/US93/~3~
obtained with the aid of water-soluble polymers, mainly
starch, added directly to the papermaking furnish.
While the concept of cementing synthetic organic and
inorganic fibers by the complex functional microgels used in
practicing the present invention is rather straightforward, an
analogous cementing of cellulosic fibers is unique and
warrants further elaboration. As is obvious from elementary
chemical considerations, the in-situ (in the furnish) synthe-
sized complex microgels of calcium-silico-aluminate or similar
types leave, upon drying, an inorqanic residue embedded in the
resultant cellulosic-web structure. According to prior-art's
teachings and experience, however, any and all inorganic par-
ticulates embedded between cellulosic fibers invariably in-
hibit the formation of close-range hydrogen bonds by physical-
ly separating the fibers, thus weakening the resultant webs.
To effectively "glue" cellulosic fibers to each otherwith the aid of the microgels in question, three obvious con-
ditions must thus be met. First of all, the microgel parti-
cles must be extremely small (ultrafine), such as are indeed
obtained with the aid of the high shearing forces used in syn-
thesizing these microgels, in situ, in paper, board and wet-
laid-nonwoven furnishes. Secondly, the ultrafine microgel
particles must be "strategically" deposited at the very con-
tact areas between adjacent fibers. Thirdly, the microgel
particles must have an inherent deformability to spread in the
form of discrete, ultrathin layers between the adjacent fibers
to be cemented. Needless to say, only true microgel particles,
but not solid aquasol particles or precipitates, such as pig-
ments, are capable of such a deformation. Some quantitative
aspects of the adhesive action of the complex microgel cements
in cellulosic webs will be discussed in the context of the
examples to follow.
An additional interfiber bonding of a hitherto unknown
kind can be obtained by coflocculating, with the aid of the
complex microgels, novel ultrafine polymer-emulsion adhesives
added directly to the papermaking furnish. The subject matter
of this novel class of adhesives, developed ~y the applicant
wo 94/04752 2 1 ~ '~ 3 ~7 PCT/US93~3~
28
specially for microadhesive applications, is disclosed in the
co-pending Patent Application Serial No. 07/333/435 ("Ultra-
fine Polymer-Emulsion Adhesives for Microadhesion"), Filed
April 4, 1989, incorporated herein by reference. The latter
adhesives, encompassing primarily acrylic polymers and co-
polymers, have average particle diameters smaller than 55 nm
and glass-transition temperatures (T5) ranging from -60OC to
+20C. In comparison, the average particle diameters of even
the finest conventional (commercially available) polymer-
emulsion adhesives, known in the trade as "latexes," aresignificantly coarser, e.g., in excess of about 70 nm.
It should be pointed out in the above context that poly-
mer-emulsion adhesives have found thus far no application as
direct furnish additives in the prior-art acidic and alkaline
papermaking process, since they cannot be acceptably floccu-
lated (retained with furnish solids) by the latter. Moreover,
even the finest conventional latexes, used as wet-end addi-
tives, are too coarse to provide any measurable interfiber
bonding until the relative weight-content of latex in the web
exceeds about 15%. As a consequence, commercial latexes are
used only to saturate paper or wet-laid nonwoven webs that
have already been preformed.
The interfiber bonding of cellulosic webs by the above-
mentioned ultrafine polymer-emulsion adhesives represents a
fundamentally new discovery, which, for all practical pur-
poses, applies exclusively to the papermaking process of the
present invention but not to the acidic or alkaline paper-
making processes of the prior art. It ~hould be pointed out,
however, that the interfiber bonding in question is observed
onlv when the above-mentioned ultrafine polymer-emulsion adhe-
sives have average particle diameters smaller than 55 nm and
their content in cellulosic webs does not exceed 2~ of the
webs' mass (the interfiber-bonding action of the latter adhe-
sives ~tops increasing perceptibly beyond the 2% level until
substantially higher adhesive contents in the web, on the
order of about 10-20%, are reached).
The ternary function of the in-situ synthesized complex
W094/04752 2 1 ~ 2 ~ 6 ~ PCT/US93/~3~
functional microgels is to impart desirable functional charac-
teristics to the resultant paper, board and wet-laid nonwoven
products, important from the standpoint of the latters' end
- use applications. These functional characteristics are
derived from the microgels' own highly diversified physical
and surface-chemical properties, which can be controlled to a
large extent by a purposeful modification of the microgels'
chemical composition to suit the intended end-use applications
of the resultant paper or wet-laid nonwoven products. For
example, intrinsically sized paper can be manufactured in
accordance with the present invention by incorporating minor
proportions of organic, cationically active chemical compounds
with at least two reactive groups in each molecule into the
solutions of bivalent and multivalent inorganic cross-linking
salts. The resultant complex microgels, made up of hybrid
macromolecules of an inorganic/organic polymer-polycondensate
type, are interspersed throughout the consolidated cellulosic
webs in a statistically uniform fashion, providing a steric
matrix of discrete hydrophobic sites, thus also a controlled
level of intrinsic sizing.
The surface-chemical properties of the resultant webs can
also be modified indirectlY with the aid of the complex func-
tional microgels under discussion, by coflocculating with
other furnish ingredients such powerful surface-chemistry-
modifying agents in their own right as polymer-emulsion adhe-
sives (having a dual organophilic/hydrophilic character),
organophilic or even hydrophobic organic dyes, polar mineral
pigments, or organic polymers of controlled polarity.
The principal reagents of commercial significance for the
synthesis of the complex (multicomponent) functional microgels
used in practicing the present invention are as follows:
(1) alkali-metal silicates and quaternary ammonium sili-
cates, preferably sodium or potassium silicates;
- (2) alkali-metal aluminates, alkali-metal zincates and
blends thereof in any proportions, preferably sodium or potas-
sium aluminates and/or sodium or potassium zincates; and
(3) water-soluble, essentially colorless, bivalent and
wo 94/04752 2 1 ~ 2 3 ~7 PCT/US93/~3
multivalent salts of calcium, magnesium, barium, aluminum,
zinc, and zirconium, preferably calcium chloride or calcium
nitrate. The use of~càlcium nitrate, alone or in blends with
calcium chloride, is beneficial during hot seasons when many
paper mills encounter problems of aggravated bacterial conta-
mination and slime growth.
The pH of microgel-flocculated paper, board and wet-laid-
nonwoven furnishes usually ranges from about 8 to 12, depend-
ing to a large extent on the initial acidity of the process
water employed. The use of aluminum sulfate, alone or in a
combination with calcium chloride and/or other equivalent
cross-linking salts, may be advantageous in those instances in
which it is desirable to lower the pH of a flocculated paper
furnish, particularly one containing groundwood fibers. In
addition to, or instead of aluminum sulfate, sulfuric acid and
other common acidifying agents can also ~e used for the above
purpose. The proportions of acidifying agents needed to lower
the furnish pH to a desired level must be assessed beforehand,
e.g., by flocculating an aliquot sample of the furnish with an
unadulterated (alkaline) complex microgel and then titrating
the resultant flocculated furnish with a solution of the acid-
ifying agent(s) to be employed.
Since the primary functions of the complex functional
microgels used in practicing the present invention are limited
to flocculation, cementation, and surface-chemical modifica-
tion of particulate ingredients of paper, board and wet-laid-
nonwoven furnishes, these microgels are used as a rule only in
proportions ~eC~cs~ry to accomplish the intended tasks. In
general, a microgel content ranging from about 0.4% to 10%, by
weight, as determined by ashing, was found to be adeguate for
many types of paper, board and wet-laid nonwoven products.
The preferred microgel contents for most commercial paper,
board and wet-laid nonwoven products range from about 4% to
10%, ~y weight, as determined by ashing after washing out the
electrolyte byproducts of the cross-linking reaction, such as
NaCl, NaN03, or Na2S04.
In the majority o~ laboratory and pilot-plant trials
W094/04752 2 1 ~ 2 367 PCT/US93~3~
31
carried out with papermaking furnishes comprising cellulosic
fibers, conventional inorganic fillers, and/or novel aggregate
filler pigments (to be dealt with in more detail hereinafter),
two different dosages of the microgel-forming reagents were
employed. With furnishes having a solids content in excess of
5%, by weight, the reagent dosages encompassed 2 g of sodium
silicate, 2 g of sodium aluminate, and 4 g of calcium chloride
per 100 g of dry furnish mass. With furnishes having a solids
content of less than 5%, the reagent dosages encompassed 3 g
of sodium silicate, 3 g of sodium aluminate and 6 g of calcium
chloride per 100 g of dry furnish mass. From the standpoint
of both lowering the reagent-consumption requirements and
attaining better end results, it is advantageous to use the
highest possible furnish-solids concentrations, e.g., of up to
20% or even 30%, by weight. Furnishes with a solids concen-
tration appreciably lower than 2%, by weight, may require
higher microgel dosages than those recommended above.
There is a great latitude with regard to the quantitative
and qualitative composition of both the (intermediate) tran-
sient, chemically reactive subcolloidal sodium-silico-alumi-
nate or similar hydrosols, on the one hand, and the (final)
complex microgels, used in practicing the present invention,
on the other, without detriment to their intended functions.
For example, the acceptable ratio of sodium silicate to sodium
aluminate, sodium silicate to sodium zincate, or sodium
silicate to the combined mass of sodium aluminate and sodium
zincate employed in forming the above subcolloidal hydrosols
can be varied from 1:10 to 10:1, by weight. As had been
established in numerous trials pertaining to the manufacture
of paper, board and wet-laid nonwoven products, a preferred
such ratio is 1:1.
The preferred concentration of sodium silicate in the
furnish ranges from 0.01% to 2.0%, by weight, the same range
of concentrations being preferred with sodium aluminate,
sodium zincate or combinations thereof. When concentrations
of the above reagents in the furnish exceed 2%, by weight, an
accelerated molecular-weight growth of sodium-silico-aluminate
VO94/047S2 2 ~ q 2 3 6 ~ PCT/US93/~3~
32
(zincate) macromolecules sets in, reducing the latters' chemi-
cal reactivity toward the`inorganic cross-linking salts. To
sustain a sufficient''level of chemical reactivity necessary
for synthesizing complex functional microgels with adequate
flocculating and cementing properties, the transient subcollo-
idal hydrosols evolving from such concentrated reagent solu-
tions should be cross-linked within a period of a few s~con~s,
which, in turn, necessitates the use of special, extra-effi-
cient in-line mixers/reactors.
The ratio of calcium chloride or equivalent inorganic
cross-linking salt(s) to the combined mass of the transient,
chemically reactive subcolloidal hydrosols to ~e cross-linked
can vary from 1:10 to 10:1, by weight, but the simple ratio of
1:1 was found to be most satisfactory for synthesizing in situ
complex functional microgels with adequate flocculating effi-
cacies and for providing a subsequent marked enh~nc~ment of
the dry and wet strength of the resultant webs. While the in-
organic cross-linking salts can be used in proportions ranging
from 0.4% to 10%, by weight, of furnish solids, the amount of
calcium or equivalent bivalent and multivalent ions present in
the reaction medium should optimally exceed by at least 50%
the quantity of such ions bound chemically by the above-men-
tioned transient subcolloidal hydrosols. As was determined by
a chemical analysis of filtrates from complex microgels syn-
thesized in plain water, the above-mentioned excess of cross-
linking ions reduces the residual concentration of unreacted
silicate and aluminate (zincate) molecules to just a few parts
per million. For most practical ~Gses, it is adequate to
employ the bivalent (multivalent) inorganic cross-linking
salts at a concentration of from 0.02% to 4.0~, by weight, in
the paper, ~oard and wet-laid-nonwoven furnishes.
Although many organic, cationically active chemical com-
pounds with at least two reactive groups in each molecule are
themselves capable of cross-linking the transient, chemically
reactive subcolloidal sodium-silico-aluminate and similar
hydrosols, their use as the sole cross-linking agents is not
recommended for most practical purposes. Instead, the latter
W094/04752 2 1 4 2 3 6 ~ PCT/US93/~3~
33
organic compounds, selected from the group comprising cationic
surfactants, organometallic Werner complexes and cationic
polyelectrolytes, should be added in only relatively minor
proportions to the solutions of inorganic cross-linking salts
to the extent needed for imparting the desired surface-chemi-
cal modification to the in-situ synthesized complex microgels,
thus indirectly also to the resultant paper, board and wet-
laid nonwoven products. It is important, however, to monitor
the cementing efficacy of the evolving hybrid inorganic/or-
ganic microgels, in that the former deteriorates perceptiblywith the increasing levels of organic cationic compounds built
into the macromolecules making up the microgels in question.
The quantitative levels of the organic, cationically
active cross-linking agents with at least two reactive groups
in each molecule, necessary for a particular functional pur-
pose, e.g., surface-chemical modification of paper, board or
wet-laid nonwoven webs, must be determined empirically for
each individual agent and the intended end-product applica-
tion, e.g., with the aid of contact angle determinations,
sizing tests, and so forth. According to the present find-
ings, a pronounced modification of surface-chemical properties
of fibrous products made with the aid of complex microgels of
an inorganic/organic type was observed when the organic cross-
linking agents were present in paper, board or wet-laid non-
woven furnishes at c~oncentrations of from 0.0003% to 0.15%, by
weight. The practically useful proportions of these agents in
the resultant cellulosic or wet-laid nonwoven webs range from
about 0.001% to 0.5~, by weight.
It should be emphasized that the formation of both the
(intermediate) transient, chemically reactive subcolloidal
sodium-silico-aluminate or similar hydrosols and the (final)
complex functional microgel cements used in practicing the
present invention are not stoichiometric. Identical transient
subcolloidal hydrosols and final complex microgel cements are
synthesized each time, however, when the same compositions,
concentrations, proportions, dosages, rates and sequences of
addition of the reagents, as well as the specified reaction
wo 94/04752 2 ~ ~ ~ 3 6~ PCT/US93/~3~
34
conditions, are maintained during the synthesis process.
As is typical of ultr~fast chemical reactions in aqueous
media, the in-situ forma~ion of complex functional microgels
used in practicing the present invention is practically
independent of the temperature of the reaction medium. In
principle, therefore, the above microgels can be for~ed within
the entire temperature interval in which water remains fluid,
provided that the stability of the reagents is not affected at
elevated reaction temperatures. A special consideration, for
example, should be given to the limited thermal stability of
solutions of sodium aluminate.
The above virtual independence of the synthesis process
from thermal conditions and regimes is a unique feature of the
above complex micro~els, which becomes readily apparent when
comparisons are made with the methods of preparation of even
much simpler single-component or bicomponen~ colloidal sys-
tems, such as silica and alumino-silicate gels or aquasols
(colloidal suspensions of solid particles) known in the prior
art. For example, numerous patents disclosing various methods
of manufacturing pharmaceutical preparations, ion exchangers,
catalysts and other products based on extraneously or in-situ
prepared gels, aquasols or precipitates, sometimes of an iden-
tical chemical composition, often differ merely with respect
to some seemingly minor (though critical to these products'
successful synthesis) variations in the thermal regimes.
The broad latitudes with regard to concentrations and
chemical compositions of the reagents, or to reaction condi-
tions tolerable in synthesizing the complex functional micro-
gels under discussion, are indicative of the enormous potency
of the general colloid-chemical system used in practicing the
present invention. It is worth noting that similar latitudes
are virtually unheard-of with analogous processes of the prior
art, according to which e~en most simple monocomponent and bi-
component colloidal systems based on silica or alumino-sili-
cates must always be synthesized under rigorously maintainedprocedural and thermal regimes as well as strictly defined
concentrations, proportions and types of reagents and pH con-
W094/047s2 2 1 ~ 23~ 7 PCT/US93/~3~
ditions in the reaction medium.
A still more detailed discussion of the subject matter of
the above complex functional microgels is provided in the
specification to the previously mentioned co-pending Patent
Application Serial No. 07/775,025 ("Functional Complex Micro-
gels with Rapid Formation Kinetics"), Filed October 11, 1991.
The alkaline version of the papermaking process of the
present invention is illustrated in the example to follow.
EXAM~LE I
A set of handsheets was prepared by treating a chemical
pulp consisting of a 50:50 softwood/hardwood blend with a
brightness of 86%, using the previously described in-situ (in
the furnish) synthesized calcium-silico-aluminate microgels as
the papermaking (wet-end) chemicals. The handsheets, having
dimensions of 20 cm x 20 cm and a basis weight of 60 g/m2,
were prepared with the aid of a sheet mold, using a procedure
developed specifically for laboratory applications of the
papermaking process of the present invention.
According to the latter procedure, a "minibatch" of pulp
with a consistency of 3%, in an amount sufficient for the
preparation of just a single handsheet, was introduced into a
Waring blender with a capacity of 500 cm3. Aqueous 5%-solids
solutions of sodium silicate and sodium aluminate were inject-
ed simultaneously into the strongly agitated furnish using
plastic syringes positioned at diametrically opposite sides of
the blender, avoiding a direct contact between the ejecting
streams of reagent solutions. After about 20 seconds, the 5%-
solids aqueous solution of calcium chloride was injected intothe came strongly agitated furnish. The proportions of active
reagents used per 100 g of pulp were 3 g of sodium silicate,
3 g of sodium aluminate and 6 g of calcium chloride.
The rin;h~tch of flocculated furnish was transferred from
the blender into a 2-liter beaker and, after an aging period
ranging from a few minutes to about 2 hours, diluted with
water (under stirring) to the full capacity of the beaker and
wo 94,047s2 2 1 ~ 2 3 g ~ 36 PCT/US93/~3 ~
poured into the mold to form a handsheet. The wet handsheets
were first pressed to a solids level of about 35% and then
dried on a rotating heated drum covered with a felt. The
relative weight content of mineral residue (discrete calcium-
silico-aluminate microgel deposits) retained in the hand-
sheets, further called the "principal handsheets," was equal
to about 7~, as determined with the aid of st~n~Ard gravi-
metric methods.
Analogous h~n~cheets, further called "control hand-
sheets," were prepared with the aid of a typical acidic paper-
making process using alum and Percol 292 (a high-molecular-
weight cationic polyacrylamide flocculant) in proportions of
20 lbs. and 1 lb., respectively, per ton of pulp. Some of the
control handsheets were prepared from a furnish containing
only fibers while some additional control handsheets were pre-
pared from the same furnish to which increasing proportions of
starch were being added.
The principal h~n~cheets were characterized by a vastly
better formation quality, significantly higher dry and wet
strengths as well as stiffness, more pronounced "rattle" and
slightly higher brightness and opacity than analogous control
handsheets made without the use of web-strength-reinforcing
starch. Since a legitimate comparative assessment of the
optical properties of paper products requires that the systems
under evaluation always be of equal ~ech~nical strength, the
principal h~n~-cheets were additionally evaluated against
ap~Lopliately matched, starch-reinforced control handsheets.
Since wet-end starch markedly reduces handsheets' brightness
and opacity, the principal h~n~cheets (devoid of starch) were,
in the final balance, both brighter and more opaque by about
1.5 to 2 percentage points than the corresponding starch-
containing control handsheets of equal mechanical strength.
It is important to point out that the rather substantial
content (i.e., about 7%, by weight) of the microgel residue in
the principal handsheets only slightly increased the latters'
brightness and opacity, which is clearly indicative of the
extremely small dimensions of microgel particles (deposits)
W094/04752 2 1 4 2 3 ~7 PCT/US93~3~
.
37
retained in the sheets. In general, the undersized pigment
fractions with particles smaller than about 0.1 ~m e.s.d. are
referred to in the trade as ultrafine, or subPiqmentary, since
their inadequate light-scattering efficacy disqualifies them
as pigments in the conventional (commercial) sense. The dis-
crete microgel residues embedded in the handsheets, however,
are dimensionally yet much smaller than typical subpigmentary
particles. As is well known to those skilled in the art, the
principal handsheets would be automatically brighter by about
3-4 percentage points and more opaque by about 8-10 percentage
points if the microgel residue in the sheets were replaced
with an equivalent proportion (i.e., 7%, by weight) of an
extraneous synthetic filler pigment, such as precipitated
calcium silicate or an in-situ (in the furnish) precipitated
alumino-silicate filler pigment of the type disclosed in U.S.
Patent No. 2,757,085 to Paquin.
It is worth pointing out that results identical to those
reported above were also obtained when sodium aluminate, as
the constituent of the transient subcolloidal hydrosols, was
partially or totally replaced with sodium zincate, or when
calcium chloride, as the cross-linking agent, was partially or
totally replaced with calcium nitrate.
In analyzing the findings discussed in the above example,
the foremost emphasis should be placed on the unique sheet-
strength-reinforcing action of the in-situ-synthesized complex
microgels used in practicing the present invention. Numerous
other beneficial and unique properties of the complex micro-
gels notwithst~n~;ng, the hitherto unheard-of reinforcement of
heet strength by embedded inorganic particles unmistakably
distinguishes the above microgels from all seemingly related
inorganic colloid-chemical systems known in the prior art.
Another important finding made in evaluating paper
samples prepared in Example I was the enormous magnitude of
"wet strength" imparted to the principal handsheets by the
calcium-silico-aluminate microgels. The above performance
W094/04752 I PCT/US93/~
~142361
38
property common to the complex microgels under discussion is
particularly attractive from a commercial standpoint in that
the practical means for increasing the wet strength of paper,
known in the prior art, are quite limited. Hence, the wet
strength of handsheets dried according to the procedure des-
cribed in Example I was found to be about 100% higher with the
principal sample than with analogous control samples. However,
after an additional heating for 30 seconds at a temperature of
204C (400F), the wet strength of handsheets was found to be
600% higher with the principal sample than with the corres-
ponding control samples.
The above spectacular wet-strength increase of microgel-
containing handsheets can be explained, in principle, by the
fact that calcium-silico-aluminate microgels become essential-
ly fully cured, thus also water resistant, when heated at atemperature of about 218C. As is readily understood, the
high-wet-strength properties can be imparted to cellulosic
webs by the in-situ synthesized complex microgels only because
the discrete microgel deposits, interspersed throughout the
fibrous structure, are both ultrathin, causing no interference
with the formation of close-range hydrogen bonds between
cellulosic fibers, and strategically located at the intimate
fiber-to-fiber contact areas. In comparison, the only practi-
cally feasible ways of increasing the dry or wet strength of
cellulosic webs known in the prior art are through the addi-
tion of organic water-soluble "glues" to the fiber furnish.
An outstanding feature of the papermaking process of the
present invention, inherently related to the instantaneous,
indiscriminate and complete flocculation mechanism, is that
all particulate furnish ingredients become coflocculated in a
statistically most uniform fashion, regardless of these parti-
culates' dimensions, morphology, relative densities, surface
chemistry or colloidal characteristics. As a consequence, the
detrimental fractionation, segregation and selective aggrega-
tion (flocculation) of particulate ingredients contained inheterodisperse and polydisperse papermaking furnishes, such as
cannot be avoided in the papermaking processes of the prior
W094/04752 2 1 ~ 2 3 6 7 PCT/US93~3~
39
art, is, for all practical purposes, totally eliminated in the
papermaking process of the present invention.
Some of the instant as well as potential benefits derived
from the flocculation mechanism inherent to the papermaking
process of the present invention become apparent by way of the
following example:
BXAMPLE II
Three laboratory batches of identical furnish, each con-
taining 80~, by weight, of a 50:50 hardwood/softwood blend and
20%, by weight, of a delaminated clay filler, were prepared at
an initial consistency of 3~, by weight.
The main batch, designated as the "principal" batch, was
flocculated with the aid of the in-situ synthesized calcium-
silico-aluminate microgels according to the procedure des-
cribed in Example I and then diluted to a consistency of 0. 7%
typically used in commercial paper machine operations. The
first control batch, designated "AC" (acidic), was diluted
right away to a consistency of 0.7% and then flocculated in
accordance with typical prior-art acidic-papermaking proce-
dures, using alum and Percol 292 in proportions of 20 lbs. and
1 lb., respectively, per ton of furnish solids. Similarly,
the second control batch, designated "ALK" (alkaline), was
diluted to a consistency of 0.7% and then flocculated in
accordance with typical prior-art alkaline papermaking proce-
dures using a pair of organic polymeric retention aids (Calgon
Polymer H-7392 and Calgon Polymer H-7736 EZ), each in a pro-
portion of 2 lbs. per ton of furnish solids. The pH of the
furnish was adjusted to a level of 8 using sodium hydroxide.
Each of the above flocculated furnish samples was trans-
ferred into separate sealed glass jars for further observa-
tion. Both control batches, "AC" and "ALK," were character-
ized by decidedly nonuniform, coarsely grained floc struc-
tures, the carrier medium (water) being permanently cloudywith a substantial proportion of solid matter settling rather
promptly to the bottom of each jar. Unlike both control
w094/04752 2 1 ~ ~ 3 6 7 PCT/US93/~3
batches, the principal batch settled to the bottom of the jar
in the form of a single floc ("monofloc") resembling a large,
fluffy cotton ball surrounded by a crystal-clear supernatant,
the monofloc in question being characterized by an extremely
uniform mi~LoyLain structure.
After some period of aging, each of the above-mentioned
jars was rapidly inverted. Both of the jars containing the
control batches revealed a layer of a densified tacky residue,
consisting predo~;n~ntly of filler particles firmly adhering
to the bottom of the jar. The above separation of furnish in-
gredients, of course, provides clear evidence that the floccu-
lation mechanisms inherent to the acidic and alkaline paper-
making processes of the prior art are slow, selective, and
incomplete, leading to a predominant formation of aggregates
of the undesirable segregated t...filler/filler...] and
[...fiber/fiber...] types, instead of the desirable hetero-
aggregates of a t...fiber/filler...~ type. In contrast, the
bottom of the inverted jar containing the principal batch was
comPletely clear, indicative of the fact that the entire
filler content of the furnish was firmly and intimately
coflocculated with the cellulosic fibers.
As is readily understood ~y those skilled in the art, the
potential practical consequences of the above findings are
enormous. In accordance with the prior art, for example, pa-
per and board are made from very dilute furnishes, containing
only about 0.5-0.7%, by weight, of solid matter. The latter
cumbersome dilution requiring vast amounts of water is indis-
pensable in that the web-formation quality deteriorates rapid-
ly as the solids concentration in the furnish is increased.
In contrast, the inherent, extremely uniform micrograin struc-
ture of furnishes flocculated with the aid of the in-situ-syn-
thesized complex microgels makes it possible to use furnishes
with significantly higher solids concentrations than are
feasible in the papermaking processes of the prior art without
detriment to the resultant web-formation quality. According
,
W094/04752 2 1 4 2 3 ~ 7 PCT/US93/~
.
41
to present indications, solids concentrations in the furnish
(furnish consistencies) could be increased 2 or 3 times above
the customary levels with only minor modifications of the con-
temporary headbox designs. Yet higher furnish consistencies,
e.g., of up to 4 or 5 times higher than those currently used,
are likely to be feasible with somewhat more radically modi-
fied headbox designs.
The inescapable deterioration of web-formation quality
resulting from attempts to increase paper machine speeds be-
yond the current practical limits is also well known to thoseskilled in the art. Again, due to the extremely uniform in-
trinsic micrograin structure of fiber/fiber flocs (in filler-
less furnishes) and fiber/filler flocs (in filler-containing
furnishes) generated by the action of the in-situ-synthesized
complex microgels, it is now possible to greatly increase the
paper machine speeds without detriment to the resultant web-
formation quality. It is also possible to combine increased
furnish consistencies with higher paper machine speeds to
manufacture well-formed paper, board and wet-laid nonwoven
webs using the papermaking process of the present invention.
The total coflocculation of cellulosic fibers and mineral
filler particles by the in-situ synthesized complex microgels
is another important finding made in Example II. As is well
known to those skilled in the art, the uniformity of web for-
mation in the acidic and alkaline papermaking processes of theprior art improves with increasing filler-loading levels, up
to about 20%, by weight. As the filler-loading levels are
still further increased, however, the papermaking furnishes
must be excessively flocculated to obtain an adequate first-
pass retention of pigment particles in the web, the unavoid-
able consequence of this "overflocculation" often being
man~fested in an excessive deterioration of the web-formation
quality. In a radical contrast, the intrinsic micrograin
structure of high-ash furnishes flocculated with the in-situ
synthesized complex microgels under discussion, as well as the
quality of formation of the resultant webs, steadily improves
with the increasing filler-loading level, even if the latter
W094/047S2 21 ~ 236~ PCT/US93/~3 ~
42
exceeds 50%, by weight. As shall be discussed in more detail
hereinafter, the latter repeatedly verified finding now makes
possible to manufacture very-high-ash paper products with a
web-formation quality not attainable hitherto with the aid of
the papermaking processes of the prior art.
As is also well known to those skilled in the art, signi-
ficant proportions of valuable furnish ingredients are syste-
matically and irretrievably passed into waste-water streams
when the acidic or alkaline papermaking processes of the prior
art are employed, causing substantial material losses as well
as serious ecological problems. On the other hand, the total
(100~ complete) flocculation of particulate furnish ingre-
dients attained with the aid of the papermaking process of the
present invention enables one to recover 100% of the particu-
late matter from spent furnishes before the latter are passedto waste-water streams. The complete elimination of particu-
late contaminants from waste-water streams, using filtration,
cycloning and other easy methods for separating solids from
liquids, provides a clear economical and ecological advantage
over the papermaking processes of the prior art.
The total coflocculation of fibers and filler particles
by the in-situ-synthesized complex functional microgels offers
the attractive possibility of attaining a true "self-extin-
guishing" process loop on a paper machine. Such a self-extin-
guishing loop can be realized preferably by replacing theconventional water-soluble starch adhesives in papermaking
furnishes with particulate (polymer-emulsion) adhesives and
flocculating these furnishes at very-high solids, e.g., of up
to 10-30%, by weight, with the aid of the in-situ synthesized
complex functional microgels. By purging the resultant sys-
tems of salt byproducts of microgel formation and other solute
cont~;n~nts, e.g., by using a vacuum filtration combined with
spray rinsing, essentially solute-free and electrolyte-free
papermaking furnishes can be obtained. The above contaminant-
free furnishes, diluted subsequently with water to a desirableheadbox consistency, can be recirculated on a paper machine
until their solids are totally depleted, the portion of fur-
W094/04752 2 1 4 ~ ~ 6-71 ; PCT/US93/~3~
.
43
nish solids retained on the forming wire being continuously
replenished with a new portion of a (virgin) purified furnish.
Thus, the customary heavily polluted waste-water streams from
paper machines can be eliminated completely, with enormous
quantities of water being saved as an additional benefit. The
sole waste stream resulting from such a closed-loop papermak-
ing process is a low-volume, relatively concentrated crystal-
clear filtrate cont~;n;ng sodium and calcium salts, disper-
sants (e.g., from fillers and adhesives) and similar solutes
extracted from the flocculated high-consistency papermaking
furnishes before using them on a paper machine.
It should be emphasized that the customary laboratory
procedures for making handsheets, which rely on furnishes that
are 25-50 times less concentrated than analogous furnishes
used on paper machines, do not always provide a correct indi-
cation of the filler-retention efficiencies to be obtained in
commercial operations. For example, slightly lower filler-
retention efficiencies were sometimes observed when laboratory
h~ heets were prepared from such highly dilute furnishes
with the aid of the papermaking process of the present inven-
tion, using all-inorganic (calcium-silico-aluminate) micro-
gels, than were obtained when similar handsheets were prepared
with the aid of the acidic and alkaline processes of the prior
art. However, when analogous large-scale papermaking trials
were carried out with the aid of a pilot-plant paper machine,
using typical commercial furnish-solids concentrations of 0.5-
0.7%, by weight, the resultant filler retention efficiencies
were consistently higher with the papermaking process of the
present invention than with the acidic and alkaline paper-
ma~ing processes of the prior art.
The reason for the above-mentioned reversal of filler-
retention trends (from preliminary laboratory indications to
the actual full-scale results on a paper machine) is a better
utilization of the fiber fines generated during refining of
3S cellulosic pulps. The discrete cellulosic fiber fines gener-
ated by refining are "short-lived," reattaching themselves
readily to the comparatively much larger full-fledged fibers
~094/04752 2 ~ 4 23~7 PCT/US93/~3 ~
44
after a relatively short period of aging, or, particularly,
during the course of furnish flocculation by the slow and
inefficient flocculation mechanisms of the acidic and alkaline
papermaking processes of the prior art. As a consequence, the
latter fiber fines contribute little or nothing to reinforcing
the resultant fibrous networks or to facilitating the reten-
tion of filler particles. However, when freshly refined fiber
furnishes (still contA;n;ng freely floating, unattached fiber
fines) are treated with the in-situ synthesized complex micro-
gels inducing an instantaneous flocculation of all particu-
lates present in the furnish, the numerically abundant fiber
fines become intricately coflocculated with full-fledged
fibers, significantly contributing to the reinforcement of the
resultant fibrous networks.
Most of all, however, the unattached fiber fines cofloc-
culate predominantly, in accordance with the laws of statis-
tics, with the numerically yet more abundant filler particles
present in the furnish. The filler-laden fiber fines are
obviously heavy in relation to their geometrical dimensions
and have a low buoyancy. Hence, bearing in mind that the
principal mechanism of filler-particle retention on the
forming wire is filtration (a fibrous mat is first formed on
the forming wire, which then "filters out" the flocculated
filler particles), it is readily understood that filler-laden
fiber fines are difficult to retain on the forming screen when
making laboratory handsheets from highly dilute furnishes. On
the other hand, the fact that filler-laden fibers fines are
efficiently retained on a paper machine when typical commer-
cial furnishes with a solids content of 0.5-0.7% are being
employed clearly points to an additional, hitherto unknown
filler-retention mechanism based on the "entanglement" of
filler-laden fiber fines with consolidating fibrous networks.
As was established in numerous trials, extremely high
filler-retention efficiencies, unmatched by those typical of
the prior-art acidic and alkaline papermaking processes, were
consistently obtained, regardless of whether the furnishes
were dilute or concentrated, when relatively minor proportions
W094/0475~ 2 1 ~ 2 3 6 ~ PCT/US93/~3~
of organic cationic polyelectrolytes were added beforehand to
the solutions of inorganic cross-linking salts. For example,
by incorporating Percol 292 or Hydraid 777 in proportions of
from 0.5 to 0.75 lbs. per ton of furnish solids directly into
the solution of cross-linking salt (calcium chloride), the
resulting filler-retention efficiencies were increased by
several percentage points relative to those obtained under
similar conditions with the acidic and alkaline papermaking
processes of the prior art. It is worth noting, though, that
the above-mentioned or similar polymeric agents are custom-
arily employed in the conventional paper-making processes in
much higher proportions, usually ranging from about 2 lbs. to
4 lbs. per ton of furnish solids. Moreover, the formation
quality of sheets obtained with the aid of the above-mentioned
hybrid inorganic/organic complex functional microgels was in-
variably vastly superior to even the best commercial st~n~Ards
known to the applicant.
One of the most important tasks facing the paper industry
at the present time is to develop new lines of high-quality
printing papers in which a major portion of cellulosic fibers
is replaced with mineral fillers. Paper products of the
latter type, e.g., those having a relative filler content in
excess of 25%, by weight, are referred to in the trade as
"high-ash" papers. Regardless of the obvious ecological and
economical benefits offered by high-ash paper products, how-
ever, tangible technological advances in implementing routine
mass production of the latter are still in the state of rela-
tive infancy. The most important reasons for the above
apparent lack of success are the excessive deterioration of
sheet strength at high levels of filler loading, relatively
high abrasivity of the conventional filler pigments, as well
as the deterioration of sheet-formation quality associated
with the harsh colloid-chemical measures which must be under-
taken to effectively flocculate, retain and affix the massive
proportions of fillers contained in high-ash papers. These
harsh measures pertain, most of all, to employing high dosages
of polymeric flocculants to obtain an adequate flocculation of
W094/04752 2 1 ~ 2 3 ~ 7 PCT/US93~3
46
filler particles in high-ash furnishes along with employing
high proportions of water-soluble adhesives to compensate for
the excessive fiber debonding resulting from high filler-
loading levels. As is well known to those skilled in the art,
the increased levels of flocculants and adhesives reguired in
connection with high-ash furnishes complicate the delicate
balances of wet-end chemistr-iès of the acidic and alkaline
papermaking processes of the prior art to a point exce~;ng
the limits of these processes' objective performance capabi-
lities. As the consequence, the web-formation quality of
high-ash paper products as well as the optical-performance
efficacy of both the filler pigments and cellulosic fibers is
adversely affected.
Bearing in mind that the potential, as well as the
inherent limitations, of the prior-art acidic and alkaline
papermaking processes have already been thoroughly explored,
it is highly unlikely that the vast array of difficulties
associated with the manufacture of high-ash paper will be
resolved in the foreseeable future with the aid of materials
and technologies known in the prior art.
Novel promising approaches applicable to the manufacture
of high-ash paper products have been opened, however, by the
papermaking process of the present invention. One such
approach is applicable to the manufacture of moderately-high-
ash paper, contA;ning up to 25~, by weight, of conventionalmineral filler pigments in combination with the novel ultra-
fine polymer-emulsion adhesives discussed previously. Inter-
spersed uniformly among the flocculated furnish ingredients,
the ultrafine polymer particles form, upon drying and hot
calendering of the resultant filled webs, microadhesive joints
between individual filler particles as well as between indivi-
dual filler particles or filler aggregates, on the one hand,
and cellulosic fibers, on the other. It was indeed possible
to make filled paper of satisfactory mechanical strength
containing up to 25%, by weight, delaminated clay and 1-2%, ~y
weight, novel ultrafine polymer-emulsion adhesives using the
papermaking process of the present invention.
W094/04752 2 1 4 2 3 ~ 7 PCT/US93~3~
47
The papermaking process of the present invention is also
suitable for manufacturing very-high-ash paper with filler-
loading levels ranging from 25% to more than 50%, by weight.
The manufacture of the above paper grades requires, however,
that both the previously mentioned novel functional filler
pigments and ultrafine polymer-emulsion adhesives be simulta-
neously employed. For filler-loading levels approaching or
exc~e~;ng 50~, by weight, synthetic microfibrils and/or novel
cellulosic microfibrils (to be discussed in more detail here-
inafter) should also be employed in the papermaking furnish.
The subject matter of the above novel aggregate fillerpigments is disclosed in detail by Kaliski in U.S. Patent
Application Serial No. 07/811,623 (Low-Refractive-Index Aggre-
gate Pigment Products), Filed December 23, 1991 and in U.S.
Patent No. 5,116,418 ("Process for Making Structural Aggregate
Pigments"), incorporated herein by reference. The filler
pigments in question are made in principle by a controlled
aggregation of very-fine-particle-size kaolin clays (often
referred to in the trade as high-glossing clays) combined with
other functional ingredients, such as the novel ultrafine
polymer-emulsion adhesives, for reducing fiber debonding in
paper-filling applications, and/or with synthetic and/or
cellulosic microfibrils, for reducing fiber debonding and
increasing filler-retention efficiency. The latter filler
pigments are uniquely qualified for very-high-ash filling
applications in that, among other things, these pigments'
optical-performance efficacy does not decay at even the
highest filler-loading levels and their unusually low abra-
sivity rarely approaches 0.5 mg on the Einlehner tester.
The unique suitability of the novel ultrafine polymer-
emulsion adhesives for the manufacture of high-ash papers can
~e understood readily considering that their average particle
diameters are smaller than 55 nm. In contrast, the average
particle diameters of the overwhelming majority of polymer-
emulsion adhesives (latexes) used in the paper industry range
from about 150 to 200 nm. Hence, at any given adhesive mass,
at least 60 times more microadhesive joints (involving single
WO94/047522 I 4 2 3 6 7 PCT/US93J~3~
48
adhesive particles) can potentially be formed with the novel
ultrafine polymer-emulsion adhesives than with conventional
latexes. Moreover, as is well known in the art, the dimen-
sions of the "glue line" (adhesive between two adhints) should
be considerably smaller than the dimensions of the adhints
themselves, particles of conventional latexes being as a rule
too large to form proper microadhesive joints of fiber/filler
or filler/filler types. As was found in numerous trials, a
significant and steady web-strength increase of paper and wet-
laid nonwoven products was obtained by increasing the dosageof the novel ultrafine polymer-emulsion adhesives up to 2%, by
weight, of the web mass, whereas no corresponding web-strength
increase was observed with conventional latexes.
It is worth pointing out in the above context that both
conventional latexes as well as the novel ultrafine polymer-
emulsion adhesives are for all practical purposes unsuitable
as wet-end additives in the acidic and alkaline papermaking
processes of the prior art. Since the inefficient floccula-
tion mechanisms at the foundation of prior-art papermaking
processes are incapable of totally flocculating polymer-
emulsion adhesives of any kind, using the latter as wet-end
additives would result in many serious runnability problems
such as plugging of paper machine felts, surface picking of
paper during calendering or printing, and contamination of
waste-water streams. In contrast, both commercial latexes and
the novel ultrafine polymer-emulsion adhesives are totally
(100%) flocculated by the in-situ-synthesized complex func-
tional microgels used in practicing the present invention, the
use of such adhesives as wet-end additives presenting none of
the above-mentioned runnability problems.
The manufacture of very-high-ash, ultraopaque color-coded
paper for two-sided, high-resolution computer printout or
office reproduction, using paper furnishes containing the
previously mentioned aggregate (functional) filler pigments,
organic color dyes and the novel ultrafine polymer-emulsion
adhesives, shall be demonstrated in the example to follow.
Ultraopaque printing paper is understood herein as having an
W094/04752 2 i 1 2 ~ ~ 7 PCT/US93~3~
49
opacity of at least 98.0%, necessary to eliminate the dis-
turbing show-through of high-optical-density laser prints from
the opposite sheet side.
To comprehend the enormous magnitude of practical diffi-
culties in obtaining a conventionally machine-calendered sheet
of paper with an opacity of 98~ one should consider, for exam-
ple, that a stack of three sheets of a typical white "xerox"
paper used for office reproduction or computer printout, or a
stack of two sheets of color-coded computer printout paper,
will not always attain an opacity of 98%.
EXAMPLE III
The ultraopaque, color-coded handsheets under discussion
were prepared using the procedures and fiber-furnish compo-
sition described in Example I, except that Hydraid 777 (a
commercial polyelectrolyte retention aid) in a proportion of
0.75 lbs. per ton of furnish solids was added directly to the
solution of calcium chloride used as the cross-linking salt.
In addition to cellulosic fibers, the furnish for making
handsheets also contained the previously mentioned ultrafine
polymer-emulsion adhesive in a proportion of 1.5 g per 100 g
of furnish solids; a blue dye (Victoria blue) in a proportion
of 0.075 g per 100 g of furnish solids (equivalent to 2 lbs.
of dye per ton of furnish solids); and the previously men-
tioned aggregate filler pigment, used in such proportions as
to obtain a filler-loading level of at least 35~, by weight,
in the resultant han~che~ts.
All furnish components, including the polymer-emulsion
adhesive and dye, were coflocculated uniformly and completely
by the in-situ-synthesized hybrid inorganic/organic complex
microgels, the supernatant (filtrate) being completely clear
and colorless. The handsheets had a basis weight of 51.9 lbs.
~ per 3000 ft2; a filler-loading level of 35.0%, by weight; an
opacity of 98.0%.; a brightness of 82.3%; and a lightness of
85.0%. The handsheets had satisfactory strength, handling and
rattle, a very light pastel blue color, and a most attractive
W094/04752 2 1 A 2 3 6 7 PCT/US93/~3 ~
surface appearance resembling that of a coated paper.
The extra-high opacity of the above very-high-ash hand-
sheets made it possible to print high-optical-density images
on both sides, using a laser printer, without any print show-
through from the opposite side being noticeable. Moreover,due to the high brightness and lightness, the hAn~cheet5 were
also found to be most suitable for desktop-publishing applica-
tions requiring high-resolution, high-fidelity, high-contrast
reproduction of delicate halftone scales.
Similar very-high-ash handsheets as those described in
the above example were also prepared using Hydraid 777, in a
proportion equal to 1.5 lbs. per ton of furnish solids, by
adding it by itself (as an aftertreatment) to furnishes that
were already flocculated by an in-situ synthesized all-inor-
ganic calcium-silico-aluminate microgel. Although the hand-
sheets in question had the same filler content and optical
performance as the h~n~heets from Example III, their sheet-
formation quality was markedly poorer. The reason for thepoorer sheet-formation quality was that the polymeric reten-
tion aid, added to an already flocculated furnish, induced a
secondary, coarse flocculation pattern superimposed upon the
original, very uniform microflocculation pattern. While the
overall results, such as filler retention, optical performance
or color uniformity of the above handsheets (made with Hydraid
777 used as an aftertreatment) were still better than can be
obtained with analogous handsheets prepared with the aid of
the acidic and alkaline papermaking processes of the prior
art, the overwhelmingly preferred approach is using the paper-
making process of the present invention in which the auxiliary
organic retention aids are incorporated directly into the
solutions of calcium chloride or equivalent cross-linking
salts prior to the flocculation of the furnish.
The following example, pertaining to the preparation of
filled groundwood handsheets, illustrates particularly clearly
the benefits of adding the auxiliary organic polymeric reten-
W094/04752 2 1 4 2 ~ ~7 PCT/US93/~3~
51
tion aids directly to the solutions of the inorganic cross-
linking salts used in practicing the present invention.
~XAMPLE IV
s
A sample of a typical groundwood furnish used for news-
print manufacture, additionally containing a typical low level
of a mineral filler (mechanically delaminated clay), was aged
for several hours to intentionally deteriorate the formation
quality of the handsheets to be prepared from this furnish.
A set of newsprint handsheets, further called principal
handsheets, was prepared with the aid of procedures outlined
in Example I, except that Percol 292, used in a proportion of
0.5 lbs. per ton of furnish solids, was added directly to the
solution of calcium chloride. Two similar sets of control
handsheets were prepared from the same aged furnish using the
acidic papermaking process outlined in Example I, Percol 292
being employed in a proportion of 1 lb. per ton of furnish
solids in the first set of control handsheets and in a pro-
portion of 2 lbs. per ton of furnish solids in the second setof control handsheets.
Despite of the intentional furnish aging, such as leads
invariably to a deterioration of the web-formation quality of
handsheets made by any prior-art papermaking process, the
principal newsprint handsheets were characterized by a virtu-
ally perfect web-formation quality. As a matter of fact, a
comparable web-formation quality is, to the best of the appli-
cant's knowledge, impossible to attain with the aid of any
laboratory or cQ~^rcial newsprint-making processes of the
prior art. In contrast, the web-formation quality of both
sets of control newsprint hAn~heets was extremely poor,
coarse unsightly flocs, undispersed clumps of fibers and other
defects being clearly visible in the handsheet surface, and,
viewed in a transmitted light, also in the handsheet interior.
As was anticipated, the brightness of the principal
groundwood handsheets made under alkaline conditions (pH of
about 9.5) was lower by about 3 percentage points than the
W094/04752 2 1 ~ 7 PCT/US93/~3
52
brightness of control handsheets made by the prior-art acidic
papermaking process. The above brightness reversal can be
reduced, or even eliminated, by partially or totally replacing
calcium chloride (as the cross-linking agent) with alum and/or
adding a predetermined proportion of acid to the solution of
the cross-linking agent(s).
From the standpoint of the overall results, however, it
is still preferable to employ the alkaline version of the
papermaking process of the present invention, combined with
adding hydrogen peroxide directly into the newsprint furnish
in proportions customarily employed in groundwood bleaching.
By adding the hydrogen peroxide into the newsprint furnish
prior to, or simultaneously with, the addition of the solu-
tions of sodium silicate and sodium aluminate, the brightness
reversal of groundwood fibers can be fully eliminated.
Some of the potential benefits of making newsprint under
alkaline conditions are best evidenced by the fact that the
~rightness of the principal (alkaline) newsprint handsheets
from Example IV remained unchanged even after a prolonged
period of aging. In contrast, the originally brighter control
newsprint handsheets, made by the acidic papermaking process,
became progressively more yellow and brittle with increasing
aging. It should be emphasized that while attempts have con-
tinuously been made worldwide to manufacture newsprint under
alkaline conditions, tangible successes have thus far not been
attained to the best of the applicant's knowledge.
Additional observations made in connection with the pre-
ceding example revealed that the filler-retention efficiency
obtained with the control newsprint handsheets increased when
the proportion of Percol 292 was increased from 1 to 2 lbs.
per ton of furnish solids. The highest filler-retention effi-
ciency was obtained, however, with the principal newsprint
handsheets made from a furnish treated with the in-situ-syn-
thesized hybrid inorganic/organic complex functional microgel,
with Percol 292, in a proportion of 0.5 lb. per ton of furnish
solids, added directly to the solution of calcium chloride.
W094/04752 2 1 4 2 3 ~ 7 PCT/US93/~3~
.
53
Another important benefit derived from the instantaneous,
indiscriminate and complete flocculation of all particulates
present in paper, board and wet-laid-nonwoven furnishes is
manifested in the formation of bulky, uniformly distributed
steric configurations of filler-particle aggregates with a
vastly enhanced light-scattering efficacy. As is well under-
stood by those skilled in the art, it would be impossible to
obtain an opacity of 98.0% with a S1.9 lbs./3000 ft2 sheet
from Example III, containing exclusively low-refractive-index
fillers, if an abundance of such optically favorable aggre-
gate-pigment configurations had not been formed within the web
structure.
Still another important benefit of the papermaking pro-
cess under discussion is a complete and extremely uniform co-
flocculation of organic dyes with the particulate ingredientsof paper, board and wet-laid-nonwoven furnishes. The extra-
ordinarily high level of opacity of handsheets obtained in
Example III, of a magnitude hitherto impossible to attain with
the aid of low-refractive-index fillers, is largely the result
of an intrinsic interplay of light scattering and light ab-
sorption between the uniformly and intimately interspersed
filler particles and dyes. It should also be emphasized that
the entire dosage of the relatively low-color-intensity
Victoria Blue dye used in Example III was equivalent to only
2 lbs. per ton of furnish solids. To obtain handsheets with
a comrArable level of color intensity with the aid of the
acidic or alkaline papermaking processes of the prior art, the
dye concentration in the furnish would have to be, as a rule,
at least 10 times higher than in Example III due to the noto-
riously poor retention and unfavorable flocculation character-
istic of virtually all organic dyes in both latter processes.
Intensely colored papers can also be obtained with the
aid of the papermaking process of the present invention by
simply increasing the proportions of dyes added to the
furnish. Analogous intensely colored papers can not be made
by the acidic or alkaline papermaking processes of the prior
art without severe dye losses and the accompanying unavoidable
W094/04752 2 1 ~ 2 3 ~ ~ PCT/US93/~3
54
serious contamination of waste-water streams. Moreover, the
severe degradation of strength of intensely colored paper made
by the papermaking processes of the prior art can be curtailed
or even eliminated,with the papermaking process of the present
invention by incorporating the highly efficient novel ultra-
fine polymer-emulsion adhesives and/or novel waterborne rubber
cements into the starting furnishes.
By far the most attractive colored papers are obtained,
without exception, by combining the addition of dyes with
high-ash filling. The surface of colored papers so obtained,
particularly after supercalendering, has a unique, extremely
pleasant silky appearance that is virtually impossible to
duplicate by any other method known in the art. Moreover, the
color uniformity of the resultant products is virtually
perfect, resembling the uniformity of colored glass or ceramic
tiles. In contrast, a more or less pronounced color uneven-
ness and color two-sidedness typical of essentially all color
papers made by the papermaking processes of the prior art can
readily ~e detected by even casual evaluators.
The papermaking process of the present invention is also
particularly well-suited for a complete coflocculation of
carbon black with cellulosic fibers and filler particles
present in a paper furnish. The need for carbon black in
present-day papermaking becomes increasingly more acute in
that very substantial opacity increments can be obtained most
economically using extremely low dosages of this material.
While it is necessary to forfeit some sheet brightness to gain
an increment of the far more valuable and costly sheet
opacity, the most favorable brightness-for-opacity trade off
is obtained using carbon black dispersions prepared by the
method disclosed in U.S. Patent No. 5,116,418 to Kaliski
("Process for Making Structural Aggregate Pigments"). The
above method, referred to hereinafter and in the claims to
follow as the "master-batch" method, makes it possible to
vastly increase the opacifying power of prior-art commercial
carbon-black dispersions. In accordance with the present
industrial experience, the opacifying power of carbon black
W094/04752 2 1 4 ~ 3 6 7 PCT/US93~3~
obtained from such dispersions is about 100-150 times higher
than the opacifying power of titanium dioxide. An additional
processing of the commercial carbon-black dispersions with the
aid of the master-batch method in question still further
increases the above-mentioned opacifying power by a factor of
20 to 50.
To sustain a total immobilization of carbon black in the
resultant paper or wet-laid nonwoven products (a release of
even traces of carbon black, e.g., on the order of partC per
billion, would be unacceptable in the papermaking industry),
the former must be employed in combination with latexes or
ultrafine polymer-emulsion adhesives, or with novel waterborne
rubber cements obtained by underpolymerization of the latter
ultrafine emulsion adhesives. In contrast, as is well known
to those skilled in the art, the prior-art papermaking proces-
ses are ;ncAp~hle of a complete flocculation and immobiliza-
tion of either carbon black or polymer-emulsion adhesives.
The papermaking process of the present invention can also
be used for the manufacture of very-high-ash printing papers
with filler-loading levels approaching or even surpassing 50%,
by weight, while considerably reducing these papers' basis
weight and preserving the necessary sheet strength. The lat-
ter task can be realized by incorporating up to 2%, by weight,
of synthetic microfibrils and/or extraneously prepared novel
cellulosic microfibrils with a length ranging from about 10 ~m
to 200 ~m in combination with 1-5%, by weight, of the novel
ultrafine polymer-emulsion adhesives and/or waterborne rubber
cements into furnishes for making the above-mentioned very-
high-ash paper products.
The novel (extraneous) cellulosic microfibrils should be
distinguished from ordinary fiber fines generated (in situ)
during mec-h~n;cal refining of cellulosic pulps, the latter
fines being defined as miniature fibers passing through a 200-
mesh screen. The extraneous cellulosic microfibrils, whose
aspect ratio (the ratio of length to diameter) is 10 to 1000
times higher than that of fiber fines, can be obtained exclu-
sively by the process referred to hereinafter as well as in
W094/04752 2 1 ~6~ PCT/US93/~3
56
the claims to follow as the "cascade-microfibrillation" pro-
cess. According to the latter, cellulosic fibers derived
preferably from cotton or well-fibrillating cellulosic pulps
undergo the following consecutive processing steps:
(a) dry or wet chopping of fibers to a length preventing
a hydraulic spinning during the subsequent wet refining, the
resultant length being dependent upon both the furnish solids
and type of refining equipment to be employed in subsequent
processing;
(b) preliminary refining of chopped fibers resulting
from step (a) at the highest practically feasible solids con-
centrations, e.g., of up to 30-35%, by weight, preferably in
the presence of sodium silicate, Congo red and/or other inor-
ganic and organic fibrillation-enhancing agents;
~ (c) additional refining of the fibers resulting from
step (b) with the aid of centrifugal comminuters (exemplified
by the well-known colloidal mills); and
(d) finalizing of the fibrillation attained in step (c)
with the aid of Gmolin homogenizers or eguivalent equipment in
which the fibrous furnish is compressed at very high pressures
and then rapidly decompressed by passing through a nozzle,
causing the residual bundles of fibrils to "explosively"
separate into individual microfibrils.
The process of the present invention is also most suit-
able for the manufacture of advanced wet-laid nonwoven prod-
ucts on a paper machine. Contemporary nonwovens, as a class
of materials, are manufactured in two consecutive processing
steps. The first step involves preforming of unbounded fiber
webs (mats) using either a wet-laid approach or the currently
predominant dry-forming approach. Since the preformed webs,
made up mainly of synthetic fibers, have no cohesive strength,
suitable adhesives must be incorporated into the webs in the
second processing step to establish adhesive joints between
adjacent fibers.
The principal method of imparting the desired level of
cohesive strength to the preformed webs is by saturating them
with acrylic latexes to attain an adhesive content of up to
W094/04752 2 1 ~ 2 3 6 7 PCT/US93/nO3~
20%, by weight, followed by drying. Another method relies on
"blowing" a relatively coarse thermoplastic adhesive powder,
suspended in air, into the preformed mat using electrostatic
-assist, followed by a thermal fusing of adhesive particles
deposited between the fibers.
-As is well known to those skilled in the art, the above-
described approaches to making nonwoven products have many
inherent disadvantages. Firstly, the preforming of both wet-
laid and dry-formed nonwoven webs is several times slower than
making of analogous cellulosic webs of similar basis weights
on paper machines. Secondly, the fiber lay of raw (unbounded)
nonwoven webs is relatively poor to begin with, deteriorating
still further when webs are treated with strength-reinforcing
adhesives in the subsequent processing step. Thirdly, the
composition of furnishes for making both wet-laid and dry-
formed nonwoven webs is limited mainly to fibers, no use being
made of many valuable functional additives routinely employed
in papermaking furnishes. Fourthly, the latex and thermo-
plastic-powder adhesives used for imparting cohesive strength
to nonwoven products are utilized rather wastefully. For
example, adequate mechanical strength with latex-saturated
nonwoven webs is obtained first when the latex content in the
mat reaches about 15-20%, by weight, the powdered adhesives
not faring much better.
25The above wasteful use of adhesives is readily understood
considering that neither the wet saturation with latex nor the
electrostatically aided incorporation of adhesive powders is
amenable to directing the adhesive particles effectively into
strategic locations into, or close to, the fiber/fiber contact
areas. As a consequence, the overwhelming proportion of latex
is pasted uselessly around the fibers themselves while,
similarly, a major proportion of adhesive-powder particles is
located too far from the fiber/fiber contact areas to form
adhesive joints. Some unique problems are also associated
with the use of dry adhesive powders inasmuch as virtually all
very fine powders are agglomerating ("sticking") easily, their
flow properties being adversely affected. Moreover, as a
W094/047~2 21~ 2 ~ B 7 PCT/US93~3 ~
5~
general rule, very fine particles are not readily amenable to
electrostatic deposition. As a consequence, adhesive-powder
particles must be much larger (e.g., 20-25 ~m e.s.d.) than is
necessary for establishing individual adhesive joints between
the relatively thin synthetic fibers whose diameters typically
range between 10 and 15 ~m.
In contrast, the method of the papermaking process of the
present invention makes it possible to manufacture novel and
improved wet-laid nonwoven products with unique functional
lo properties and material characteristics, not attainable with
the aid of the nonwoven-manufacturing technologies of the
prior art. The latter advancements are realized by floccu-
lating specially designed multicomponent nonwoven furnishes
with the in-situ synthesized complex functional microgels and
forming wet-laid nonwoven webs on a paper machine. The above
multicomponent furnishes can be incomparably more diversified
and complex than furnishes used in the nonwoven-manufacturing
technologies of the prior art, comprising, among other things,
synthetic fibers; synthetic reinforcing microfibrils; polymer-
emulsion adhesives, particularly the previously mentionednovel acrylic ultrafine polymer-emulsion adhesives; novel
waterborne rubber cements; aqueous dispersions of fine-
particle-size thermoplastic adhesive powders with a preferred
average particle diameter of about 0.5 ~m; organic dyes; and
bioactive materials; the advantages of the above functional
additives being explained in more detail hereinafter.
Although, as is readily understood by those skilled in
the art, a uniform mat can be made onlY from a well-dispersed
fiber furnish, the inefficient flocculation mechanisms at the
foundation of the papermaking processes of the prior art are
incapable of overwhelming the action of the powerful modern
dispersants. As a consequence, wet-laid nonwoven webs made of
more or less nonpolar synthetic fibers, crudely (mechanically)
dispersed in aqueous furnishes, are much less uniform than
comparable webs (paper) made of distinctly polar cellulosic
fibers. Moreover, the inherently poor web-formation quality
of prior-art wet-laid nonwovens makes it difficult to increase
W094/04752 2 1 4 2 3 ~ 7 PCT/US93/~3~
59
the present low paper machine speeds, or use longer fibers
(yielding stronger webs), in making the latter nonwovens.
In contrast, the overpowering flocculation mechanism at
the foundation of the papermaking process of the present
invention allows one to use well-dispersed, highly diversified
furnish compositions, invariably generating extremely uniform
micrograin structures in the flocculated furnishes. Conse-
quently, very uniform wet-laid nonwoven webs can be preformed
at considerably higher paper machine speeds, using longer
fibers, than are feasible in the nonwoven-making technologies
of the prior art.
The manufacture of raw wet-laid nonwoven webs is greatly
facilitated by incorporating into the furnish up to 5%, by
weight, in relation to furnish solids, of the novel ultrafine
polymer-emulsion adhesives and/or novel waterborne rubber
cements with pronounced wet-tack properties. The latter adhe-
sives, along with the in-situ synthesized complex functional
microgel cements, impart a certain level of instant strength
to the raw nonwoven webs, protecting the initial uniform fiber
lay from damage during the subsequent latex saturation or
blowing-in of thermoplastic adhesive powders.
Since both the polymer-emulsion adhesives and waterborne
rubber cements are coflocculated and retained primarily with
the discrete deposits of the complex functional microgels
embedded strategically between adjacent fibers, the overall
adhesive demand in the subsequent latex saturation or
incorporation of adhesive powders is substantially reduced.
Regardless of the complete flocculation of all particulates,
however, it would be impractical to incorporate more than
about 5%, by weight, of the novel polymer-emulsion adhesives
and/or novel waterborne rubber cements into the furnish in
that an excessive concentration of tacky aggregates present in
raw wet-laid nonwoven webs could lead to a contamination of
paper-machine felts. The logical consequence of the above is
that the customary second process stage in making wet-laid
nonwoven webs cannot be eliminated as long as latex saturation
is the principal vehicle of providing the web strength.
wo 94/04752 ~ i ~ 2 3 ~ 7 PCT/US93/~3
The second process stage in making wet-laid nonwovens can
be eliminated completely with the papermaking process of the
present invention by incorporating thermoplastic adhesive pow-
ders directly into nonwoven furnishes. The adhesive powders
in question, employed in the form of fine-particle-size
aqueous dispersions, are; retained in raw wet-laid nonwoven
webs on the forming screen in exactly the same manner as
ordinary filler pigments are retained in paper webs, without
contaminating paper-machine felts.
10In addition to eliminating a second processing step, the
principal advantages of the above approach are a better
overall material and process economy as well as strategically
favorable placement of adhesive particles at the fiber/fiber
contact areas. The economic advantage in question is readily
15apparent considering that about 125,000 particles with a dia-
meter of 0.5 ~m, being potentially able of forming 125,000
microadhesive joints, can be obtained from just a single adhe-
sive-powder particle with a diameter of 25 ~m. Moreover, adhe-
sive joints between the relatively thin synthetic fibers can
be formed more readily with commensurately fine adhesive par-
ticles than with excessively coarse ones.
The above-mentioned strategic placement of adhesive par-
ticles coaggregated with microgel particles occurs because the
aggregates in question migrate with the receding water during
the dehydration (drying) of raw wet-laid nonwoven webs. Since
the very last pockets of water within dehydrating webs are
confined to capillaries formed by fiber/fiber intersections,
adhesive joints are automatically established after an appro-
priate heat treatment of the dehydrated webs.
30Another advantage of applying the papermaking process of
the present invention to the manufacture of wet-laid nonwoven
webs is that uniformly colored nonwoven products can be
obtained economically by incorporating organic dyes directly
into wet-laid-nonwoven furnishes. It is important, however,
to simultaneously incorporate the novel ultrafine acrylic
polymer-emulsion adhesives and/or waterborne rubber cements
into the latter furnishes to effectively immobilize the dyes
W094/04752 2 1 4 2 3 ~ 7 PCT/US93/~3~
61
retained in nonwoven webs. On the other hand, as is well
known to those skilled in the art, the flocculation and reten-
tion of organic dyes is largely impractical in prior-art pro-
cesses for making wet-laid nonwoven products.
Attractive, novel, uniquely strong nonwoven products can
be obtained with the aid of the papermaking process of the
present invention from furnishes containing well-dispersed
synthetic fibers, reinforcing synthetic microfibrils, ultra-
fine acrylic polymer-dispersion adhesives and/or waterborne
rubber cements, as well as the previously mentioned aqueous
dispersions of fine-particle-size thermoplastic adhesive
powders. Freshly formed (raw) nonwoven webs formulated in the
above manner, unlike raw nonwoven webs of the prior art, have
a considerable "green" strength (the latter term, borrowed
from the ceramic technology, refers to the strength of a yet
unbounded, or only partially bounded, raw mat~, thus can be
readily laminated with the aid of cylinder-board machines or
multiple-Fourdrinier machines to yield even stronger, more
versatile novel nonwoven products capable of successfully
competing with a broad range of conventional woven fabrics.
The lamination process can be facilitated by applying sprays
of aqueous dispersions of thermoplastic adhesive powders onto
the surface of freshly formed individual raw wet-laid nonwoven
webs before the latter are wound into multilayer composites.
As is well known to those skilled in the art, hygroscopic
properties are most desirable with nonwoven products intended
for body contact, while intrinsic biostatic or biocidal pro-
perties are desirable with many nonwoven products intended for
use in hospitals, biological laboratories and for related ap-
plications. In making the above products in accordance with
the prior art, the functional properties under discussion must
be imparted to nonwoven products by way of special, separate
aftertreatments. In contrast, a certain level of intrinsic
hygroscopic properties is imparted automatically to wet-laid
nonwoven products made with the aid of the in-situ synthesized
complex microgels, by virtue of these microgels' pronouncedly
polar nature, while yet higher levels of hygroscopic proper-
~094/0475~ 2 1 ~ 2 3 6 7 62 PCT/US93~3
ties are obtained by adding hydrophilic anionic or nonionicpolymers directly to wet-laid-nonwoven furnishes or by adding
hydrophilic cationic polymers to the solutions of calcium
chloride or equivalent cross-linking salts. Biostatic and/or
biocidal properties can similarly be imparted to wet-laid non-
woven products by adding suitable biostatic and/or biocidal
materials into wet-laid-nonwoven furnishes.
The papermaking process of the present invention is also
uniquely suitable for manufacturing wet-laid nonwoven webs
resistant to high temperatures, using furnishes comprising
thermally resistant inorganic fibers. In making the above
products it is often advantageous to simultaneously employ
polymer-emulsion adhesives in the furnish to improve the green
strength of the resultant raw wet-laid nonwoven webs and then
burn off the adhesives by way of calcining.
The papermaking process of the present invention is also
uniquely suited for the manufacture of novel electroconductive
and/or magnetic paper, board and wet-laid nonwoven products by
incorporating aqueous dispersions of ultrafine powders (with
particles finer than 0.2 ~m e.s.d.) of metallic or ceramic
electroconductive materials, or ceramic or metallic (alloyed)
magnetic materials (e.g., supermalloy or permalloy), into
paper, board and wet-laid-nonwoven furnishes, in proportions
of from 0.1% to 20% (active), by weight, of furnish solids.
For example, paper and wet-laid nonwoven webs containing
intrinsically deposited magnetic powders are uniquely suited
for printing of counterfeit-proof, virtually indestructible
(when made of nonwovens) banknotes, the magnetic response of
such banknotes being measurable quickly and conveniently with
the aid of inexpensive countertop detectors.
The paper (nonwoven) process of the present invention may
be executed in actual paper mill operations in several differ-
ent fashions. In a preferred approach, paper, board or wet-
laid-nonwoven furnishes are flocculated with the aid of in-
situ synthesized complex functional microgels immediatelybefore entering the chest or after leaving the chest on the
way to the headbox. To manufacture groundwood-containing
W094/047~2 2 1 ~ 2 ~ 67 PCT/US93~3~
63
paper, hydrogen peroxide is preferably incorporated into the
furnish prior to, or simultaneously with, the addition of the
highly alkaline solutions of sodium silicate and sodium alumi-
nate (zincate).
The most preferable approach is to carry out the furnish
flocculation in a fully continuous mode, using in-line mixers-
reactors, exemplified by the following consecutive steps:
(a) continuously injecting, in the first processing sta-
tion, separate streams of aqueous solutions of sodium silicate
and sodium aluminate (sodium zincate or blends of sodium alu-
minate and sodium zincate) into an in-line-agitated stream of
paper, board or wet-laid-nonwoven furnishes to form, in situ,
a transient chemically reactive subcolloidal hydrosol;
(b) continuously injecting, in the second processing sta-
tion, an aqueous solution of calcium chloride or equivalentbivalent or multivalent cross-linking salt(s), optionally con-
taining organic cationically active compound(s) with at least
two reactive groups in each molecule as the auxiliary cross-
linking salt(s), into the furnish stream resulting from step
(a) to cross-link said subcolloidal hydrosol and synthesize,
in situ, complex functional microgel cements, whereupon said
paper, board or wet-laid-nonwoven furnish becomes flocculated
instantaneously, indiscriminately and completely;
(c) optionally, continuously purging the flocculated fur-
nish resulting from step (b) of dissolved contaminants; and
(d) continuously recovering the flocculated furnish re-
sulting from steps (b) and (c) to manufacture paper, board and
other wet-laid products on a paper machine.
In another version of the above continuous process mode
the stream of furnish is first divided into two separate half-
streams, the solution of sodium silicate being injected into
one halfstream and the solution of sodium aluminate, sodium
zincate or blends thereof into the other. Both above half-
streams are recombined in the subsequent processing station
(in-line mixer-reactor) to form, in situ, the transient chemi-
cally reactive subcolloidal hydrosol, the solution of the
cross-linking agent(s) being injected into the recombined
wo 94/047s2 2 1 ~2~ ~7 PCT/US93/~3~
64
halfstreams in the subsequent processing station to form, in
situ, the complex functional microgel cements.
As is understood readily by those skilled in the art, the
sequence of the individual processing steps in the general
process of the present invention may be reversed by adding
solutions of bivalent and/or multivalent inorganic cross-
linking salts to the furnish in step (a); separately pre-
paring the transient reactive subcolloidal sodium-silico-
aluminate or similar hydrosols in step (b); and blending in
step (c) the systems resulting from steps (a) and (b) to form
in situ a complex functional calcium-silico-aluminate or simi-
lar microgel cement and flocculate the furnish instantaneous-
ly, indiscriminately and completely, thus obtaining a medium
suitable for making paper, board and other wet-laid products
on a paper machine. Such a reversal of the sequence of the
processing steps is recommended only in such instances, how-
ever, in which the colloidal stability of paper, board or wet-
laid-nonwoven furnishes is not intolerably impaired by the
action of the bivalent and/or multivalent inorganic cross-
linking salts during the interval preceding the introductionof the previously mentioned, separately prepared transient
chemically reactive subcolloidal hydrosol into the furnish.
Although the overall results obtained by the above approach
are as a rule better than can be obtained with the aid of
prior-art acidic and alkaline papermaking processes, the prin-
cipal process version of the present invention, in which the
subcolloidal hydrosols are formed in situ (in the furnish) in
the first step and then cross-linked in the second step, is
decidedly superior and preferable.
While certain preferred practices and embodiments of this
invention have been set forth in the foregoing specification,
it is understood by those skilled in the art that other vari-
ations and modifications may be employed within the scope of
the teachings of the present invention. The detailed descrip-
tion is, therefore, not to be taken in a limiting sense and
the scope of the present invention is best defined by the
claims to follow.
