Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPOSITION AND METHOD OF
~ViAKING IMPROVED HIGH BULKING CLAYS
S
BACKGROUND OF THE INVENTION
1.1 Field of the Invention _
The present invention is directed toward compositions and methods of
producing high bulking clay pigments. The pigments are demonstrated to
significantly improve paper properties such as printability, opacity, and
sheet gloss in
paper coating applications, particularly for rotogravure papers including
lightweight
coating (LWC) and ultra liehtweight coating (ULVJC) papers. The pigment can
also
be used as a filler for paper webs.
1.2 Related Art
It has been recognized that a relative narrowing of the particle size
distribution
of mechanically delaminated as well as non-delaminated kaolin particles
results in
pigments providing improved opacity in filling applications. Such pigments are
disclosed as beinb especially advantageous when used in the manufacture of
lightweight coated paper for rotogravure printinfi (see U.S. 4,948,664,
Brociner et al.).
It is well knowm to remove ultrafine kaolin particle, e.s., particles finer
than about 0.3
micrometers, e.s.d. after delamination. This contributes to the production of
a
delaminated pigment product having a nanower particle size distribution than
it
would have if the ultrafines were not removed. U.S. 4,948,664, supra, shows
that in
cases where very narrow particle size distribution was required, delamination
was
followed by a coarse fractionation and secondary fine removal steps. Patentees
did not
remove the priman~ fines prior to delamination. In illustrative examples,
there was a
3() significant amount of secondary fines that were generated during
delamination which
had to be removed latter. Removal of fines is referred to as "defining" in
U.S.
4,943,324 Bundy et al., and U.S. 5,085,707, also Bundy et al. In these
patents,
defininc is always conducted after what appears to be a mild or slight
delamination
step. Sometimes removal of the fines is termed "desliming" as is used in the
present
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patent application. The Bundy patents also disclose surface treatment of the
clay W th
such materials as aluminum sulfate and hexamethvlenediamine.
It has also been recognized that "bulking" undelaminated kaolin pigments is
an effective way of increasing the opacity of the pigment. U.S. 4,738,726, for
5 example, discloses a highly bulked kaolin pigment useful for in making
aqueous
coating colors suitable for manufacturing coating lightweight publication
papers or as
filler for paper webs. The pigment is prepared by mixing a small but effective
amount
of a water-soluble cationic polyelectrolvte flocculant with a kaolin clay
pigment in the
presence of water to prepare the bulked clay pigment. The base kaolin clay is
selected
I O to have a particle size distribution prior to flocculation wherein less
than 3~ percent
weight are finer than 0.3 micrometers.
While the foregoing pigments possess particular characteristics, there is a
continuing search for new pigments able to impart improved characteristics to
paper.
In particular, rotogravure paper applications have particular characteristics
needing to
1 ~ be satisfied such as compressibility, printability (helio), opacity, sheet
gloss,
smoothness, and low coating weight. Applicants have found a new method and
pigment compositions which surprisingly provide markedly improved paper
characteristics such as those discussed above particularly in rotogravure
paper printing
applications.
SLTMMARY OF THE INVENTION
The present invention relates to compositions and methods of producing
kaolin-based pigments which impart markedly improved characteristics to paper,
?s particularly paper used in rotogravure printing.
One embodiment of the invention relates to a method for making a kaolin-
based pigment comprising the steps of:
(a) delaminating a kaolin clay, wherein the degree of delamination of the
kaolin clav is done to the extent that increases the particle size
distribution less than
30 ~m in the range of about 5 to 40 percent over the particle size
distribution less than 2
~m before delamination;
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(b) removing a portion of particles smaller than 0.3 pm from the
delaminated clay; and
(c) adding a bulking agent;
wherein the degrees of delamination, removal of particles smaller than 0.3 um,
and
addition of bulking agent are adjusted to an extent sufficient to provide a
pigment
containing particles in the range of 5 to 30 percent equal or less than 0.3
~cm.
Advantages of the compositions of this invention include impro~~ed properties
to
coated paper. In particular for coated paper used in rotogravure applications,
significant improvements in smoothness, rotoprintability, brightness, opacity
are
obtained while maintaining desired sheet gloss. The improved properties may
allow
the reduction in use of expensive calcined clay or other more expensive
additives
without sacrificing optical and printing properties while achieving increased
sheet
gloss.
DETAILED DESCRIPTION OF
PREFERRED EMBODIMEI~'TS OF THE INVENTION
The compositions and methods of this invention relate to kaolin-based pigments
uv~hich impart improved properties to paper, particularly paper used in
rotogravure
applications. The present invention will become more apparent from the
following
definitions and accompanying discussion.
Particle size distribution, as herein reported, is based on equivalent
spherical
diameter (e.s.d.) on a weight basis as measured by conventional sedimentation
techniques using the SEDIGRAPH~ particle size analyzer supplied by
Micromeretics
Inc. It should be understood that the measurements of the size of clay
particles for an
undelaminated kaolin pigment that are 0.3 micrometer or finer are of limited
reproducibility. Thus, when a SEDIGRAPH~ analyzer is employed, the value for
weight percent may be =5% when tested by another operator or a different
SEDIGR.APH~ analyzer is employed. The limited reproducibility extends to
kaolin
clay particle sizes above 0.3 micrometer for a delaminated kaolin pigment.
This is
stressed here because delaminated pigment is one of several essential features
of this
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invention. Another essential feature of the invention is bulking. Bulking
produces
structuring of the pigment in a concentrated aqueous slurry of greater than
5~°i'o solids
as observed in the increased value for Brookfield viscosity (or lo~~ shear
viscosity).
However, in preparation of a pigment sample for SEDIGRAPH~ analysis, the clay
slurry is diluted to 6% solids and such a dilution for a bulked pigment
renders the
effect of bulking or structuring between particles not observable.
Delamination as used herein refers to the operation of subjecting-the
naturally
occurring kaolin particle ''stacks" or "booklets" in the aqueous clay slum' to
shearing
force thereby reducing the kaolin stacks to thin platelets. Delamination may
be
carried out by subjecting an aqueous slurry of stacked kaolin particles to
shearing
action in a sand grinder, ball or pebble mills, extruders or rotor-stator
colloid mills, or
other suitable devices. Reference may be made to commonly assigned U.S. Pat.
No.
~.64~,635, the disclosure of which is hereby incorporated by reference, for a
thorough
discussion of the process of delamination of kaolin clay.
1 ~ The term "desliming'~ as used herein refers to the operation of separating
and
discarding, a percentage of the fine fraction of the kaolin suspension. In
each example
presented herein, the defining operation was car:ied out in a centrifuge. The
kaolin
suspension to be "deslimed" was supplied to the centrifuge and processed
therein to
separate the suspension into a coarse fraction and a fine fraction. The fine
fraction
may be discarded in its entirety or only a selected percentage by volume of
the fine
fraction may be discarded, while the remainder of the fine fraction may be
admixed
with the coarse fraction for further processing. When discarding the selected
percentage of the fine fraction, it is conventional that the percent defining
level
expressed refers to the volume percentage of the fine fraction which is
discarded. For
?s example. defining to a level of 40 percent means that 40 percent of the
fine fraction
from the centrifuge was discarded and that the remaining 60 percent of the
fine
fraction from the centrifuge was admixed with the coarse fraction from the
centrifuge
for further processing.
The term "bulking-~ refers to a process by which clay pigments are modified to
improve light scatter, which is a property quantifiable as a scattering
coefficient, and
generally provides a measure of the opacifying power of the pigment. Reference
is
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made to commonly assigned U.S. Patent Numbers 4,640,716 and 4,738,726, the
disclosures of which is incorporated by reference, which includes a more
complete
discussion of bulking and methods and materials ("bulking agents") useful in
preparing bulked pigments.
The term "hydrous" is intended to describe a clay which has not been subjected
to calcination, i.e., a temperature at which the basic crystalline structure
of the clay
becomes altered. In the case of kaolin, maintaining the clay at temperatures
under
450°C will not alter the kaolin's crystalline structure.
Clays suitable for use in this invention include a wide variety of hydrous
kaolin
clays. While the examples of this invention may exhibit particular particle
size
distributions, the present invention is not intended to be limited to any
particular
particle size distribution.
Conventional kaolin clay crudes used as sources of pigment grades of kaolin
usually contain about 40 percent to 7~ percent by weight of particles finer
than 2
1 ~ micrometers (pm) after removal of grit and coarse impurities.
In conventional kaolin processing, the crude is fed into a blunger to separate
the
kaolin into small particles, that are mixed with water and a primary
dispersant to form
a clay-water slip or slutr~~. The primary dispersant can be sodium silicate,
sodium
polyphosphate or sodium polyacrylate and those known in the art. The amount of
?0 dispersing agent used will generally be in the range of from about 0.025 to
0.3 % by
weight based on the weight of the dry clay. The clay panicles treated with
primary
dispersant has a negative electric charge, that cause them to repel each other
when the
panicles are suspended in water. The clay-water slurry is pumped from the
blunger to
rake classifiers or hydrocyciones and screens to remove most of the grits and
very
''S coarse impurities. The degritted slurry is collected into large, agitated
storage tanks
and pumped to the processing plant. At the processing plant, the kaolin slurry
is
collected in large storage tanks at the plant before it is processed.
Generally the kaolin slurry is first scalped which separate the kaolin
particles
into a coarse and fine fraction through continuous centrifuges. The purpose of
this
30 step is to remove remaining grits and very coarse booklets. The fine
fraction is the
desired intermediate that is subjected to further processing. The degree of
scalping is
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influenced by the desired particle size distribution, theology and pigment
optical
properties of the final product. In general, the kaolin slurry is scalped to
70 to 9~ °~o
finer than 2 pm, preferably to 80 to 90 % at 2 Vim. Scalping may be performed
after
other downstream beneficiation or processing steps such as after delamination.
Delamination of the clay is conducted by conventional means such as those
described in the above definition of delamination. The degree of delamination
in
order to obtain the benefits of the present invention will vary to some extent
based on
such variables as crude clay panicle size distribution, source of crude,
amounts of
fines in the crude and smoothness of the kaolin surface.
However, for a crude clay having a particle size distribution of 50% less than
2
~m to 70% less than ? Vim, good results were achieved by delaminating to a 5
to 40%
delta at 2 Vim. preferably to a I 0 to 20% delta at 2 Vim. In other words, a
"delta" of ~
to 40% refers to increasing the particle size distribution at the 2 ~m level
by absolute
percentage points of ~ to 40°~0 over the undelaminated 2 um particle
size distribution
1 > level.
At delamination levels below 5% delta, particle size distribution
determinations
are of limited reproducibility particularly when using conventional
sedimentation
particle size distribution techniques. For example, typical sedigraphs have a
repeatabilim of about 4 to 5% at ? ~m so using this technique to measure
particle size
?0 distribution deltas below ~°ro is of limited accuracy and value.
At delamination levels above 40°~0, the rate of particle size
distribution delta for
all practical purposes levels off and no further delamination benefit is
obtained.
Therefore it is not practical to aim for a delamination delta above 40%.
In the practice of this invention, scalping is optionally performed before or
after
'_'s delamination, or further dowstream to remove the remaining grits and
excessively
coarse particles. In general, the kaolin slurry is scalped to 70 to 95 % finer
than 2 pm,
preferably to 80 to 90 °~o at ? Vim. The present invention is not
intended to be limited
to any particular scalping condition.
Desliming. of the delaminated clay can be done by any of a number of
30 conventional desliming devices or methods such as those listed in the
foregoing
definition of desliminb.
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Desliming refers to particle size separation leading to removal of the finest
panicles in the distribution of particle sizes. The finest particles are
generally
considered as particles finer than 0.3 Vim. Desliming is customarilly
accomplished by
mechanical means. While chemical desliming is an emerging technology, the
practice
5 of this invention includes any means of effective removal of very fine
panicles in a
kaolin slurry. An example of chemical removal of fine particles is disclosed
in
commonly assigned U.S. Patent Application 08/891,666, filed July 1 F, 1997,
the
disclosure of which is incorporated by reference.
Mechanical desliming of a deflocculated aqueous slurry of hydrous kaolin may
be performed by using a centrifuge such as a nozzle discharge disc centrifuge
or a
scroll discharge centrifuge. An example of a commercial unit is a horizontal
three-phase centrifuge from Alfa Laval Co. (Greenwood, Indiana). The Alfa
Laval
centrifuges apply greater much greater "g" forces (in the range of about 3,000
to
10.000 g-forces) than conventional Bird centrifuges. The high speed Alfa Laval
1 ~ centrifuge can effect a sharp separation of kaolin particles finer than
about 0.3
microns from larger kaolin particles. In the lab, desliming was accomplished
with
lower speed centrifuge, the Damon/IEC CU-X000 centrifuge at 2800 rpm and for
about 7 to I 5 minutes. In general, desliming is carried out to achieve
particle size
distribution at the 0.3 pm level of ~ to 30%, preferably in the 5 to 20 %
range.
It is believed that a wide variety of bulking agents may be used in accordance
with this invention and meet the desired application particularly regarding
rotogravure
printing properties. Such bulking agents are referred to as water soluble
cationic
polyelectrolyte flocculants described, for example, in commonly assigned U.S.
Patent
4,738.726, the disclosure of which is incorporated by reference. Cationic
'_'S polyelectrolytey refer to substances containing macromolecules carrying a
large
number of cationic changes at the pH of application.
Suitable polyelectrolytes include quaternary ammonium salt polymers,
copolymers of aliphatic secondary amines with epichlorohydrin, poly(quaternary
ammonium) polyester salts that contain quaternary nitrogen, polvamines and
30 polyimines such as polyethvieneimines and polyampholvtes having a plurality
of
cationic groups.
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One particularly useful group of polyelectrolvtes described as bulking agents
in
copending, commonly assigned U.S. Patent Application 08/936.702, filed
September 24, 1997, the disclosure of which is incorporated by reference, are
the
polyquaternary amine polymers derived from (i) reaction of secondary amines,
such as
dialkylamines, and difunctional epoxide compounds or precursors thereof or
(ii)
reaction of a lower dialkylamine (C,-C3), a difunctional epoxy type reactant
(the same
as (i)) and a third reactant selected from the group consisting of ammonia.
primary
amines, alkylenediamines of from 2-6 carbon atoms, and polyamines.
The group (i) polymers are disclosed in U.S. Pat.No. Re. 28.807 (Panzer, et.
al.).
The entire disclosure of this reissue patent is hereby incorporated by
reference herein.
As is stated in that reissue patent, the polyquaternary polymers of group (i)
are
derived from reaction of secondary amines, such as dialkylamines, and
difunctional
epoxide compounds or precursors thereof.
In accordance with the reissue patent disclosure, the water soluble or water
1 ~ dispersible polyquaternary polymers, used as the second component in the
present
invention, consist essentially of the repeat units of
R
N~ -C E 1-ox~m
R,
m
wherein R and R; are independently selected from the group consisting of lower
alkyl
( 1-3 carbon atoms). E is the residue obtained afrer bifunctional reaction of
a
compound selected from the group consisting of epihalohydrins, diepoxides,
precursors for epihalohydrins and diepoxides. and mixtures thereof. m and n
are
integers of substantially equal value. X" represents the anion forming a
portion of the
polyquaternary compound; m and n are integers both representing the molar
quantities
of amine reactants and bifunctional reactant compound. respectively. In
summary, the
polymers of group (i) involve only two reactants: a lower dialkylamine, and a
difunctional epoxy type reactant.
As to the epoxy reactant, epihalohydrins, such as epichlorohydrin and
epibromohydrin are especially useful. Epichlorohydrin is preferred. Diepoxides
such
3 ~ as 1.4-butanediol-diglycidyl ethers are also useful. Precursors for
epihalohydrins and
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diepoxides are also useful. Exemplary precursors include: 1.3-dichloropropanol-
? and
1,4-dichloro-2,3-dihydroxybutane.
As to the secondary amines which may be used as reactants, these include
dimethylamine, diethylamine, dipropylamine, and secondary amines containing
mixtwes of alkyl groups having 1 to 3 carbon atoms.
Suitable reaction parameters may be found in U.S. Pat. No. Re. 28,807 and are
not be repeated here. The preferred polymer of group (i) is formed from
dimethylamine and epichlorohydrin reaction. Such reaction is detailed in
Example 1
of the reissue patent.
The preferred polyquaternary polymers of group (i) are thought to have the
structure:
CH3
I
N='- CH,CHCH; C16
CH, OH
Suitable commercially available polymers of the group(i) type are sold under
the
trade names SHARPFLOC~ 22, SHARPFLOC~'' 23, and SHARPFLOC~' 24. The
molecular weight of these polymers are estimated to be in the range of
approximately
2,000-10,000 atomic mass units (amu). The particular molecular weights of
these
polymers are not critical as long as the polymers remains water soluble or
water
dispersible.
?5 The group (ii) polymers which may be used in accordance with the invention,
may be generically characterized as branched polyquaternary ammonium polymers
and are described in detail in U.S. Patent No. Re. ?8,808 (Panzer, et al.).
The entire
disclosure of this reissue patent is hereby incorporated by reference.
As is stated in the 28.808 reissue patent, the group (ii) water dispersible
polyquaternary polymer consists essentially of repeating units of
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R
fEl~ ' (AJ~ - ~Z
S
R,
m
wherein R, R,, E, m, and n are the same as given above for the group (i)
polymers.
A is the residue obtained after bifunctional reaction of a polyfunctional
polyamine
selected from the group consisting of ammonia. primary amines. alkylene
diamines of
'? to 6 carbon atoms, polyalkylpolyamines of the structure
R4
H,N ~-R ;-N- ~,-R,-NH:
wherein v represents an integer of about 1 to 5, R3 is an alkylene radical of
about 2 to
6 carbon atoms. and R, is selected from the group consisting of hydrogen.
alkyl of
?0 about 1 to 3 carbon atoms, and omega -aminoalkyls of about 2 to 6 carbon
atoms. a
polyglycolamine of a structure such as
CH3
'?s H,N-[-CH,CH-O -)-~CH_CH-NH,
wherein a is an integer of about 1 to ~. piperazine heteroaromatic diamines,
and
polyamine-polybasic acid condensation products of molecular weight up to about
10,000; X~' is an ion forming the anionic portion of said polyquaternary
compound; m
30 and p are integers which represent molar quantities of amine reactants, the
ratio of m
to p being from about 99:1 to 85:15; n represents the molar quantity of E
forming the
principal chain of said polyquaternary. the molar quantity represented by n
being
substantially equal to the sum of the molar quantities of m and p; said
polyfunctional
amine containing in addition to the amount of E required for difunctional
reaction
3 5 therewith an amount of E which is from zero to about the full functional
equivalency
remaining in said A; the sum of m. n and p being such as to provide a
polyquaternary
compound which as a 37% aqueous solution, by weight, based on the total weight
of
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the cationic portion of said polyquatemary has a viscosity at 25° C. of
at least = 100
centistokes and Z is an integer such as to satisfy anion requirements of the
polyquaternary compound.
In summary, the group (ii) polymers are formed from three reactants: a lower
dialkylamine (C,-C,), a difunctional epoxy type reactant (the same as in the
group (i)
polymers) and a third reactant selected from the group consisting of ammonia,
priman~
amines, alkylenediamines of from 2-6 carbon atoms, and polyamines $s defined
hereinabove for A. The preferred type of third reactant is ammonia or at least
a
trifunctional amine, i.e., an amine capable of reacting at no fewer than 3
sites on the
amine or amines. Examples of such amines are all primary amines and/or
polyfunctional amines such as ethylene diamine and diethylene triamine.
Exact reaction parameters for the group (ii) cationic polyelectrolytes are
specified in aforementioned U.S. Pat. No. Re. ?8,808. A preferred group (ii)
polymer
is a cross-linked polyquaternary polymer formed from ethylenediamine,
1 ~ dimethylamine and epichlorohydrin (see for instance Example 2 of U.S. Pat.
No. Re.
28,808).
The preferred group (ii) polymer is thought to have the structure:
CH,_ OH OH
'-0
-N~-CH_,-CH-CH,_- N~'-CH_,- CH-CH~_
CH, CH,
25 OH CH, OH CH3
-CH_,-CH-CH_,- Na-CH_,-CH-CH2- N~
CH;
30
Suitable commercially available polymers of the group (ii) type are sold under
the trade names of SHARPFLOC°" ?~, SHARPFLOC~' ?6, SHARPFLOC~' 27,
SHARPFLOC~'"'8. SHARPFLOC°~ ?9, SHAR.PFLOC~' 30, SHARPFLOC~' 31,
SHARPFLOC°' 3'_', and SHARPFLOC°'' 33. The molecular weight of
these polymers
3s arc estimated to range from approximately ?0.000 to X00.000 amu. The
particular
molecular weights of these polymers are not critical as long as the polymers
remain
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water soluble or water dispersible. Thus, the foregoing molecular weight range
and
the molecular weight ranges of other polyelectrolytes disclosed in this
invention
should not be interpreted as limitative in the present invention.
Yet another particularly useful group of polyelectrolytes are quaternary
ammonium salts. Most preferred are dialkyl, diallyl quaternary ammonium salt
polymers which contain alkyl groups of about 1 to 4 carbon atoms, preferably
methyl.
A dimethyl diallvl quaternary ammonium chloride polymer commercially
available under the trademark designation Polymer 261 LV from the Calgon
Corporation having a molecular weight estimated to be between 50,000-250.000
has
been found particularly useful in the practice of the present invention and
has FDA
approval (Code 176-170) for aqueous and fatty food use. Many reagents
heretofore
proposed to bulk clay do not have FDA approval. However, the invention is not
limited to Polymer 261 LV since other cationic flocculants appear to provide
equivalent, if not superior results.
1 ~ The amount of polyelectrolwe employed is carefully controlled to be
sufficient
to improve the opacit<~ of the clay as a result of forming a bulked
(aggregated)
structure in which the aggregates are sufficiently strong to survive
mechanical forces
exerted during manufacture and end use but is carefully limited so as to
assure that the
product can be formed into a clay-water slurry that has a solids content of at
least SS
percent or higher, which slurry has acceptable rheology. As discussed above,
while
bulking has a strong influence on rheology for a concentrated kaolin slurry.
the
panicle size distribution measured by SEDIGRAPH~ analysis does not normally
show
a significant change from that prior to bulking.
The amount of the cationic polyelectrolyte salt used to treat the kaolin clay
may
vary with characteristics of the polyelectrolyte including charge density of
the
polyelectrolyte, the particle size distribution of the clay and solids content
of the clay
slum' to which the polyelectrolyte is added. Using the presently preferred
dimethvldiallyl ammonium salt polyelectrolyte with clay having a medium size
in the
range of about 0.4 to 0.9 micrometers, preferably 0.5 to 0.7 ~tm, and having
less than
2~ percent finer than 0.3 micrometers and adding polyelectrotyte to a
previously
deflocculated clay-water suspension having a clay solids content of about 1 ~-
40
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percent by weight, useful amounts range from about 0.02 to about 0.20 percent
by
weight of the moisture free weight of the clay, most preferably about 0.06 to
about
0.12 percent by weight. When insufficient polyelectrolvte is used, the effect
on
opacity and printability in coating applications may be less than desired. On
the other
s hand. an excessive amount of the polyelectrolyte may impair other desired
properties
of the clay, especially rheology. The polyelectrolyte, which is water soluble,
is added
to the slurry as a dilute aqueous solution, e.g., I /4 -2 percent
concentration on a
weight basis, with agitation to achieve good distribution in the slum'.
Ambient
temperature can be used. It may be advantageous to heat the slurry of clay.
solution of
polyelectrolyte, or both to about 150° to 180°F.
Satisfactory results have been realized when the cationic polyelectrolyte was
added to deflocculated clay suspensions having pH values in the range of 6 to
9.
After addition of polyelectrolyte, the suspension is substantially thickened
as a result
of flocculation. The resulting thickened system is then acidified, typically
to a pH
I S below ~, usually pN 3-4, and bleached using conventional clay bleach
(hydrosulfite
salt such as sodium hydrosulfite) and aged. The bleaches used are usually
reductants
which reduce any color forming ferric ion constituents to a more water soluble
and
therefore more easily removeable ferrous state. The bleaching agents are added
to the
clay mineral slurry in an amount in the range of I to 1 S Ib of bleaching,
agent per ton
~0 of dry clay. The such treated clan suspension is dewatered by filtering to
a moist filter
cake havine a solids content of between about 50 to about 60% by weight. The
filter
cake is then washed to remove soluble material and then fluidized by addition
of a
secondary dispersing agent. such as tetrasodium pyrophosphate or sodium
poiyacrylate or a mixture of the two. To remedy possible problems encountered
when
2~ slurries of this invention are stored or exposed to high temperature during
storage,
shipment or subjected to moderate shear conditions, additives such as those
disclosed
in U.S. Patents 4,77?.332 and 4,767,466 may be beneficially used instead of
conventional secondary dispersants like tetrasodium pyrophosphate or sodium
polyacrylate.
30 The products of this invention may be shipped in slurry or in dry form.
Desirably the slum will have a total solids contern ranging from at least 5~%
solids.
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Types of additives that may be used with the present invention include those
described in U.S. Patents 4,772,332 and 4,767,466 the disclosures of which are
hereby
incorporated by reference. These additives are particularly useful for
remedying
problems encountered when aqueous slurries containing pigments of this
invention
are stored or exposed to high temperature during storage, shipment, or use for
example when slurries are prepared into coating colors while providing
acceptable
Theology.
The Theological requirements of pigments of this invention are concerned both
with acceptable high solids slurry Theology and coating color theology. The
viscosity
of the high solids suspension of the clay coating pigment must be sufficiently
low to
permit mixing and pumping. Afrer the binder is incorporated. the resulting
coating
color must also have suitable viscosity for handling and application to the
paper sheet.
In addition, it is highly desirable to obtain a coated calendered sheet which
has good
opacity, gloss, brightness and printability.
1 ~ Generally, paper makers seek to use clay coating pigments capable of
forming
high solids clay-water slurries which have a low shear viscosity below 1200
cp,
preferably below 800 cp, when measured by the Brookfield viscometer at 20
r.p.m.
High shear viscosity for these slurries should be such that they are no more
viscous
than a slurry having a Hercules endpoint viscosity of I50 r.p.m.. preferably
800
~0 r.p.m.. using the "A" bob at 16 x 105 dune-cm. Those skilled in the art are
aware that
when using the Hercules viscometer and measuring endpoints of I 100 r.p.m. or
higher. endpoint viscosities are reported in units of 105 dyne-cm at 1100
r.p.m.;
apparent viscosity decreases as the value for dyne-cm increases. It is
conventional to
use the abbreviated term "dyne" in place of 105 dune-cm. Thus, a "2 dyne" clay
slurry
25 is less viscous than a "9 dyne clay" slurry. As used hereinafter the
expressions I50
r.p.m. or higher, or 800 r.p.m. or higher, are intended to include lower
viscosities such
that endpoint measurements are at 1100 r.p.m. and the values are reported as
dynes.
Another requirement of pigments of this invention is that of durability to
survive
the various stages of production and end-use while possessing the capability
of being
30 dispersed to form high solids clay-water slurries having acceptable
viscosity. The
Leneral wet processing scheme typically employed in making pigments of this
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invention is by adding a bulking agent before filtration, and therefore the
filtered
pigment is in the filter cake containing the bulked assemblages when the
filter cake is
"made down" into a fluid slurry. 'The expressions "make dov~m'~ and "made
down' are
conventional in the industry and refer to the preparation of dispersed pigment-
water
slurries. In some cases. it may be necessary to apply mechanical work to the
filter
cake to reduce the viscosity to usable values. The pigment must be
sufficiently
tenacious to survive the mechanical forces during such treatment. Bttiking
pigments
must also be sufficiently stable under the influence of shear to maintain the
bulked
structure under the high shear rates. such as the high shear rates encountered
in
10 pumping high solids clay water slurries in centrifugal pumps. Moreover, the
pigment
must be capable of being retained when the deflocculated clay water slum is
formed
into a coating color using standard makedown equipment. Also. the pigment must
survive during the coating application and subsequent calendering. The
fragility of
the bulked structures obtained by prior art chemical treatments of hydrous
clay has
I ~ limited their commercial use. Generally. a criterion for durability of a
bulked
structure is the retention of improved opacification after the above-described
handling.
In preparing coating colors, conventional binders or mixtures of binders are
used
with the deflocculated clay slip. For example. useful coating color
compositions are
20 obtained by thoroughly mixing with the clay slip from about s to about 20
parts by
weight binder per 100 parts by weight of polyelectrolyte treated clay. Such a
coating
color, when used for coating lightweight publication paper, produces a product
which
has excellent printability, smoothness, opacity, brightness and desired level
of sheet
gloss.
The term "binder" as used herein refers to those materials known for use in
connection with paper pigments, which aid in holding the pigment particles
together
and. in turn, holding the coating to the paper surface. Such materials
include, for
example. casein, soybean proteins, starches (dextrins, oxidized starches,
enzyme-convened starches, hydroxylated starches), animal glue, polyvinyl
alcohol,
30 rubber lances, styrene-butadiene copolymer latex and synthetic polymeric
resin
emulsions such as derived from acrylic and vinyl acetates. When the binder
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comprises a starch which is jet cooked in the presence of added bulking
pigment, it
may be desirable to heat the slurry of clay into which the polyelectrolyte is
added
during preparation of the bulking pigment in order to avoid the development of
extremely viscous. unworkable coating colors. Temperatures in the range of
about
S 150° -200°F. are recommended. A temperature of about
180°F. has been used with
success. However, use of heat during preparation may decrease the scattering
ability
of the pigment.
The coating color compositions prepared in accordance with the present
invention can be applied to paper sheets in a conventional manner. The bulked
I 0 pigment may be used alone or blended with a known coating clay or other
pigments to
improve optical and printing properties of the coated paper sheet. The binders
and
additives used in the coating color are those typically used in the industry
and are
know to those skilled in the ari. The bulked pigment could also be used as
filler in
paper web.
I ~ EXAMPLES
Example I
Properties of four (4) kaolin pigments were compared. The first pigment, P-1,
was a standard fraction delaminated coating grade kaolin available under the
tradename NUCLAY supplied by Engelhard Corporation. A slurry of NUCLA1' was
20 prepared according to the PL-1 and PL-3 procedures of Engelhard Corporation
described in U.S. Patent 4.738,726 the disclosure of which having already been
incorporated by reference. The dispersant used to re-disperse the P-1 pigment
during
the make down procedure was a 18 to 21 weight % aqueous solution of soda ash,
partially neutralized polyacrylic acid, and sodium hexametaphosphate ("SAP"
dispersant) at an active weight ratio of 45.~I24.S130, respectively.
The second pigment, P-2, was prepared from a defiocculated aqueous
suspension of Georgia kaolin clay. The deflocculating agent was sodium
silicate.
Solids content was about 29%. The particle size distribution of the clay in
the
deflocculated aqeous suspensions was 68% less than 2.0 micrometers, 0.76
30 micrometers median diameter and 22% less than 0.3 micrometers diameter. The
suspension was further deflocculated with 2 Ibs./ton of sodium polyacrylate
and
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delaminated to a particle size distribution of 1 S-20 percent delta at 2 ~m in
a 6-gallon
wet grinder using a I to I volume ratio of glass beads to pigment suspension.
The
particle size distribution of the delaminated suspension was 85.8% less than 2
micrometers, 0.X5 micrometers median diameter and 25.9% less than 0.3
micrometers diameter. The delaminated suspension was then fractionated in a
centrifuge DamonlTEC CU-5000 Centrifuge to yield an overflow suspension with
particle size distribution of 87.9% less than 2.0 micrometers, 0.50
micrometers
median diameter and 28.3% less than 0.3 micrometers diameter. The resulting
suspension was passed through a magnetic separator magnet (Carpco-CC WHIMS
3x4L) to achieve above 83 brightness, actual brightness was 83.4. The
suspension
was deslimed by centrifugation with a Damon/TEC CU-5000 centrifuge to obtain
an
underflow suspension with particle size distribution of 84.0% less than 2.0
micrometers, 0.66 micrometers median diameter and 16.2% less than 0.3
micrometers
diameter. The resulting suspension was flocced using 8 lbs./ton of aluminum
sulfate
I ~ and followed by lowering in pH to 2.8 with sulfuric acid and addition of
10 Ibs.lton of
sodium hydrosulfite (commercially available as ILBrite). The flocced pigment
suspension was pan-filtered and rinsed with at least an equal volume of clean
water to
remove water soluble salts. The rinsed filter cake was redispersed with about
5 to 7
lbs./ton of SAP dispersant. Portions of this redispersed suspension was spray
dried
?0 and then added back to the suspension to raise the solids to 67.0% total
solids.
The third pigment, P-3, was a deslimed and bulked kaolin coating grade pigment
(i.e, undelaminated) available under the tradename EXSILON supplied by
Engelhard
Corporation and made down according to Engelhard's PL-1 and PL-3 methods as
described above for the make down of the P-I pigment using the C-235
dispersant
hereinafter described.
The fourth pigment, E-1, was a bulked version of P-2 pigment but with
additional differences in the redispersion package. To prepare E-1, the
deslimed
intermediate from P-2 was diluted to 20% solids and bulked with 1.6 Ibs./ton
(0.08%)
of polvdimethyldiallyl ammonium chloride (polyDADMAC). Addition of
30 polvDADMAC flocced the suspension. Further floccing was accomplished by
lowering the pH to about 3.~ with sulfuric acid. In addition. 10 lbs./ton of
sodium
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hvdrosulfite was added as bleach. The resulting dilute suspension was aged
overnight, pan-filtered and rinsed with at least an equal volume of clean
water to
remove water soluble salts. The rinsed filter cake was redispersed with a
special
dispersant stabilizer additive package sufficient to raise the pH to about 6.~
to 7Ø
S The special dispersant package used is a mixture of sodium ligno-sulfonate.
partially neutralized polyacrylic acid, pentasodium salt of
aminotri(methvlenephosphonic acid) and caustic and commercially adailable
under
the tradename Colloid 235 ("C-235") from Vinings Industries, Inc. Variations
of the
special dispersant package is disclosed in U.S. Patent 4,772.332 the
disclosure being
10 incorporated by reference. Portions of this redispersed suspension was
spray dried
and then added back to the suspension to raise the solids to about 61 to 62%
total
solids.
While pigments P-1 and P-2 used a different dispersant package than that of
pigments P-3 and E-1, such differences are not expected to affect the coating
color
1 ~ composition properties hereinafter reported except that the C-23~ package
might give
slightly lower sheet brightness than the SAP package. In any event, since C-
235 was
used with the inventive composition of this invention, the use of C-235
certainly
would not provide a brightness benefit in the coating color compositions
compared to
color compositions using the SAP dispersant package.
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Table 1. Hydrous Kaolin Pigment Properties
P-1 P-? P-3 E-1
GE Brightness 87.8 86.5 87.0 86.5
Sedigraph Avg. Particle0.71 0.66 0.56 0.6 3
Size (~tm)
at 2 wm 79 84 90 - 89
at 1 pm 60 66 70 70
at 0.3 um 22 16 22 14
Slum - % Total Solids67.2 67.0 62.6 61.4
pH 5.9 6.7 6.2 7.0
Brookfield 20 rpm 205 130 80 590
(cps)'
Brookfield 100 rpm 186 1 16 94 2S0
(cPsO
Hercules A Bob= 690 18.8 dynes'_'.5 15.7
1 100 rpm rpm dynes dynes
Notes: I - Brookfield viscosity measured by 1 AY1'1 164b-om-~8 tn tnts and
subsequent examples.
'_' - Hercules viscosiW as measured in U.S. Patent No. 4,738,726 in this and
?0 subsequent examples.
The physical properties of the four pigments and rheology of their pigment
slurries are
riven in Table 1. Within experimental error as discussed before. the particle
size
distribution for P-? and E-1 are not substantially differently despite the
fact that E-I is
''s a bulked version of P-2. Both P-2 and E-1 have lower quantities of kaolin
particle
fraction below 0.3 ~tm compared to P-1 and P-3. The influence of bulking in E-
1 vs
the unbulked P-2 was evident in their low shear rheology and the solids level
of their
suspension. P~2 can be made into 67% solids suspension while E-1 was only made
into a 61.4% solids suspension. Brookfield rheology showed that structuring
from
30 bulkint resulted in much higher low shear viscosity in E-1 even at a
significantly
lower solids level compared to P-2.
The four pigments were made into coating colors at 58 percent total solids
in a generic LWC coating formulation containing 88 pans of one of the hydrous
kaolin pigments, 12 parts of calcined clay and 6.0 pans of a styrene/butadiene
(SBR)
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latex binder, 0.8 parts of calcium stearate.
The pH of the coating colors were adjusted to 8.2. The colors were coated on
the wire side of a 28 lb lightweight paper basestock using the laboratory Dow
Coater.
The coat weight was applied at ~.5 lb/R (Ream=3300 sq.ft.) The sheets were
conditioned at 50 percent relative humidity and T_'°F and were
calendered on a lab
soft-nip calender . This condition was arrived at that which the P-1 (NUCLAY)
control achieved a gloss target of 57-58.
The following tests were performed on the coated papers: TAPPI 75°
gloss
(T480 om-8~), TAPPI Opacity (T4?~ om-91), ISO Brightness (ISO Method #2469).
l0 Parker Print Surf (at 10 kgF/cm'-) (ISO 8791/4 and TAPPI T~S~),
Compressibility and
Heliotest (rotoprintability test).
Compressibility of the coated sheet was determined by an Engelhard in-house
test based in pan on the Parker Print Surf (PPS) test. The principle of the
PPS test is
based on determining the smoothness (or roughness) of the surface of a sheet
of paper
1 ~ or board as a function of the rate at which air will pass between the
surface and a flat
circular land pressed against it at a specified pressure. Compressibility is
gauged in
this invention by testing the relative air flow at two different pressures.
The air flow
rates are measured by doing the PPS test at ~ kg/cm= and 10 kg/cm'-.
Compressibility
is then calculated as
?0
Compressibility = 100 (1-[(PPS Sk~cm= - PPS iok~°mz)/PPS S,;Ncm2j~
By this method the lower the number, the higher the compressibility and vice
versa. It
is generally accepted that good quality gravure printing requires a
compressible paper
capable of reliably contacting the printing cylinder over its entire area
thereby
ensuring that the maximum possible inl: pick-up from the cylinder is achieved.
In the Helio test, the coated sheet is printed with a gravure cylinder, which
has a
pattern of ink holding cavities that decrease in diameter from one end to the
other.
Thus. the test print has large dots at one end and small ones at the other.
Skipped dots
30 are counted starting at the large-dot end, and the print quality is
reported as the
distance in millimeters from the start of the test print to the ?0th missing
dot. For a
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given coat weight, the longer the distance in millimeters the better the
printability of
the coated paper. The results are st_mmarized in Table 2.
Table ?. Properties of Sheet Coated with Coating Color
Containing Polymer Bulked, Deslimed and Delaminated Clay
P-1 P-2 P-3 E-1
Gloss 57 59 57 -57
Tappi Opacin~ 81.3 83.7 82.5 83.0
ISO Briehtness 71.0 71.7 71.9 71.5
PPS I .20 1.27 1.20 1.16
Compressibility 79.2 76.6 79.3 74.6
Hello Printabilitv40 41 45 s4
(mm1
I ~ Note: Lower values are directionally better for compresstbtltty
and PPS (smoothness)
Data in Table '' indicate that while the delaminated and deslimed pigment
P-'_' gave significantly improved opacity and brightness over the P-I (NUCLAY)
control, no appreciable improvement in hello printability was observed.
However, by
bulking P-2 with a small amount of polyDADMAC (i.e., to make E-1 ), E-1
exhibited
similar advantages in opacity and brightness but with surprisingly marked
improvements in hello printabiliy, smoothness (from the lower PPS readings)
and
compressibility. Further Hello printability, compressibility, and smoothness
of coated
sheets treated with E-I are significantly better than P-3, the undelaminated
but bulked
pigment.
Example 2
Nev~~ batches of P-? and E-1 were prepared and are referred to P-2' and E-1',
respectively. The pigment P-?' was prepared from a deflocculated aqueous
suspension of Georgia kaolin clay. The particle size distribution of the clay
in the
def7occulated aqeous suspensions was 64% less than 2 micrometers and 15% less
than 0.3 micrometers diameter. The 30.0% solids suspension was further
deflocculated with ? Ibs./ton of sodium polyacrylate and delaminated to a
particle size
3 ~ distribution of I 5-20 percent delta at ? ~m in a 5-gallon wet grinder
using a 1 to I
volume ratio of glass beads to picment suspension. The particle size
distribution of
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the delaminated suspension was 82% less than 2 micrometers and 20°ro
less than 0. 3
micrometers diameter. The deiaminated suspension was then fractionated in a
centrifuge Damon/TEC CU-5000 Centrifuge to yield an overflow suspension with
particle size distribution of 89% less than 2 micrometers and 22% less than
0.3
micrometers diameter. The resulting suspension gave a pigment brightness of
83.s
and was not passed thru a magnet separator. The suspension was deslimed by
centrifugation with a Damon/TEC CU-5000 centrifuge to obtain an underflow
suspension with particle size distribution of 87% less than 2 micrometers.
0.65
micrometers median diameter and 15% less than 0.3 micrometers diameter. The
resulting suspension was flocced using 8 Ibs./ton of aluminum sulfate and
followed by
lowering in pH to 2.8 with sulfuric acid and addition of I O lbs./ton of
sodium
hvdrosulfite (commercially available as KBrite). The flocced pigment
suspension was
pan-filtered and rinsed with at least an equal volume of clean water to remove
water
soluble salts. The rinsed filter cake was redispersed with about 5 to 7
lbs./ton of SAP
1 ~ dispersant as described and used in Example 1. Portions of this
redispersed
suspension was spray dried and then added back to the suspension to raise the
solids
to 67.1 °~o total solids.
The pigment. E-1' was a bulked version of P-?' pigment but with additional
differences in redispersion package. To prepare E-I', the deslimed
intermediate from
~0 P-'_'' was diluted to 20°~o solids and bulked with I .6 lbs./ton
(0.08%) of
polvdimethyldiallyl ammonium chloride (polvDADMAC). Addition of
polvDADM AC flocced the suspension. Further floccing was accomplished by
lo~~ering the pH to about 3.5 with sulfuric acid. In addition, 10 lbs./ton of
soditun
hvdrosulfite was added as bleach. The resulting dilute suspension was aged
?s overnight, pan-filtered and rinsed with at least an equal volume of clean
water to
remove water soluble salts. The rinsed filter cake was redispersed with the C-
235
dispersant additive package as described and used in Example I and in an
amount
sufficient to raise the pH to about 6.~ to 7Ø Portions of this redispersed
suspension
was spray dried and then added back to the suspension to raise the solids to
about 61
30 to 6'_'°~o total solids.
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Table 3. Properties of Improved Bulked Pigment
P-1 P-2' E-1'
GE Brightness 87.8 87.2 86.0
Sedigraph, Avg. 0.71 0.65 0.70
Particle
Size ~m
at 2 ~rn 79 87 87
at 1 pm 60 66 66
%at0.3 ~m 22 15 _11
Slurry - % TS 67.1 67.1 61.~
pH 5.9 7.2 6.2
Brookfield 20 rpm 186 180 116
(cps)
Brookfield 100 rpm 169 132 106
t cps)
Hercules A Bob 687 rpm 390 ~ 759
1 ~ 1100 rpm
The physical properties of the three (3) pigments including the same P-1
(NUCLAY)
control sample as used in Example 1 and rheology of their pigment slurries are
given
in Table 3. Within experimental error as discussed before, the particle size
distribution for P-2' and E-I' are not substantially different despite the
fact that E-1' is
a bulked version of P-2'. Both P-2' and E-1' have lower quantities of kaolin
particle
fraction below 0.3 ~m compared to P-1. The influence of bulking in E-I' versus
the
unbulked P-2' was again evident in the solids level achievable for their
suspension.
P-'_'' can be made into 67.1 °~o solids suspension while E-1' was only
made into a 61.5°~0
?s solids suspension. If P-2' and E-I' suspensions were compared at 61.x%
solids, the
low shear viscosity of P-2' is expected to be extremely low compared to E-1'.
This
expectation is based on the structuring effects from bulking.
The three (3) pigments were formulated into 57 percent total solids coating
colors using substantially the same formulation as in Example 1. The coating
color
was applied to a 28 lb.. weight basestock using the CLC coater (a high speed
pilot
batch Boater). Coat weight was ~.0 Ib/3300 sq.ft. Conditioning of the coated
sheets
was identical to that in Example l . Calendering conditions were selected to
achieve a
gloss target of ~6 for the Nuclay control. The properties of the coated sheet
are given
in Table 4 based on an equal calendering conditions as noted below in Table 4.
;;
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Table 4. Coated Sheet Properties
Equal
Calendering
P-1 (NUCLAY) 88
P-2' 88
E-1' 88 94
Calcined Clay 12 12 12 6
Sheet Gloss 56 63 58 63
ISO Brightness 71.1 72.0 71.9 71.8
-
Tappi Opacity 84.7 85.8 8~.8 85.8
Hello Printability 74 79 89 86
PPS 10 Kgf/cm2 0.99 0.92 0.88 0.89
Compressibility 72.2 72.0 70.8 72.5
CLC Runnabilitv BetterBetter Good Better
1 ~ Calenderin~ conditions: Equal Calendenng
Pli (lbs./linear inch) 1093
Temp (F) 17~
Speed (ft/min) 3~
Passes
At equal calendering conditions, E-I' gave better to much better coating and
print properties than the control P-1 at equal calcined clay content (12
parts). E-1' had
a significant advantage over the unbulked version, P-2' as well. Hello
printability,
smoothness (PPS). opacity, brightness and compressibility were significantly
improved over the P-I control. Also at equal pans of calcined clay (I2 parts),
E-1'
outperformed P-'?' with marked improvements in hello printability, smoothness
(PPS)
and compressibility. Sheet gloss for E-I' can be improved dramatically by
reducing
calcined clay from 1 ~' pans to 6 pans while maintaining hello printability,
smoothness, brightness and opacity. By reducing the amount of calcined clay,
CLC
runnability was also improved.
Example 3
This example demonstrates the use of another bulking agent described as a
copolymer of aliphatic secondary amines with epichlorhydrin commercially
available
under the tradename SHARPFLOC'" 26 ("SF-26") available from Sharpe Speciality
Chemical Company and compares results against the bulking agent polyDADMAC
CA 02316998 2000-06-28
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used in making E-1 and E-I'. This time, another deslimed and delaminated
kaolin
clay intermediate was used from tfat used in Examples 1 and 2 and identified
as P-4
in Table ~ below. The intermediate was derived from a crude having a particle
size
distribution range of approximately 50 to 75 % less than 2 Vim. P-4 was also
re-
s dispersed with the SAP dispersant of Example 1 after having been filtered
and rinsed.
Pigment E-2 was bulked with 1.6 lbs/ton of poly(DADMAC) while E-3 was bulked
with 2.0 lbs/ton of SF-26 polymer. After bulking, both pigment suspensions
were
filtered and rinsed with clean water of remove soluble salts. The E-1 and E-2
pigment
suspensions were redispersed with 6 lbs/ton of SAP dispersant as described and
used
10 in Example 1 and passed through a 32~ mesh screen and spray dried. Thus in
this
example, pigments P-1, P-4. E-2, and E-3 all used the SAP dispersant. The
pigment
and slum properties of P-4, E-2, E-3 and the previous control P-1 (NUCLAY)
pigment are given in Table 5. Both E-2 and E-3 have slightly lower kaolin
particle
fraction below 0.3 ~m than P-l and P-4. Both pigments were made down to
1 s significantly lower solids than the P-1 control and P-4 pigments.
Table ~. Hydrous Kaolin Pigment Properties
P- I P-4 E-2 E-3
GE Brichtness 87.8 90.7 90.5 90.6
20 ~o at 2 um 79 88 88 88
at 1 ~m 6U 69 70 68
at 0.3 urn _ ~~ 20 17 16
Slurry - ro Total 67.1 68.1 61.1 61.0
Solids
pH _ 5.8 6.9 6.8 6.8
25 Brookfield 20 rpm 200 280 170 120
(cps)
Brookfield 100 rpm 156 176 150 120
(cps)
Hercules A Bob 82~ rpm 40~ rpm 14.8 dynes234 rpm
I 100 rpr~
30 Pigments P-1, E-2, and E-3 were made into coating colors at 57 percent
total solids in
the same generic LWC coating formulation discussed in Example I. The coating
color was applied to a 28 lb., weight basestock using the CLC coater (a high
speed
pilot batch coater). Coat weight was S.5 1bI3300 sq.ft. Conditioning of the
coated
sheets was identical to that in Example 1. Calendering conditions were
selected to
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WO 00/26306 _ 26 _ PCT/US99!25208
achieve a gloss target of ~4 for the Nuclay control. The properties of the
coated sheet
are given in Table 6 based on equal calendering conditions as noted below in
Table 6.
Table 6. Coated Sheet Properties
P-I (Nuclav) 88
88
E_3 88
Calcined Clav 12 12 12
~o Sheet Gloss 54 52 52
ISO Brightness 68.8 70.0 70.2
Tappi Opacity 81.4 81.7 82.9
PPS at 10 Kuf/cm2 0.91 0.86 0.80
1 ~ Hello Printabilitv~7 70 8?
Calendering conditions: Equal calendenng
Pli (lbs/linear inch) 1407
Temp (F) 150
Speed (ftlmin) 36.5
Passes 2
E-'?. the polv(D.ADMAC) bulked pigment, gave better print properties and
smoothness than the control P-1. E-3. the copolymer of aliphatic secondary
amines
with epichlorhvdrin, gave significantly better print properties, smoothness
and
opacim than E-?. the poly(D.ADMAC) bulked pigment.
Separately. P-1 and P-4 were made into coating colors at X8.0 percent total
solids in a generic LWC coating formulation containing 100% hydrous kaolin
clay
(i.e., without calcincd clays). 6.0 parts of a styrene/butadiene (SBR) latex
and 0.5
parts of calcium stearate. The colors were coated unto the wire side of a
commercial
LV~'C basestock at ~.~ lb,'3300 ft'-. The properties of the coated sheet are
given in
Table 7.
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WO 00/26306 _ 27 - PCT/US99/25208
Table 7
P-1 P-4
Sheet Gloss 57 61
Brightness 69.7 71.0
Tappi Opacity 83.3 83.8
PPS at 10 Kgf/cm? 0.90 0.83
Helio Printability 71 74
While P-4 gave better smoothness, brightness and slightly improved opacity
over P-1,
helioprintability was not improved within variability of the helio test in
contrast with
the significant improvement show b~~ E-2 and E-3 over P-1 in Table 6.
The principles, preferred embodiments, and modes of operating of this
invention
have been described in the foregoing specification. However, the invention
which is
1 ~ intended to be protected herein is not to be construed as limited to the
particular forms
disclosed, since thev are to be regarded as illustrative rather than
restrictive.
t% ariations and changes may be made by those skilled in the art without
departing
from the spirit of the invention.
