Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LATEX TREATED CATIONIC CELI,ULOSE PRODUCT
AND METHOD FOR ITS PREPARATION
BACKGROUND OF THE INVENTION
The present invention is a fibrous eellulosic product containing a
uniformly dispersed polymeric material wl~ch has been deposites~ in an
aqueous suspension from an anionic latex. The invention further comprises
the method of making the products. These products are especially advar~
5 tageous for making air laid webs wherein the polymer serves as a heat
activatable bonding agent.
Treatmen$ of cellulosic products with polymers o~ various types
has a long history in the p~p and papermaking art. Depending on the
particular polymeric system being used, and the ultimate effect desired, this
10 treatment may take place either before or after formation of the sheet at
the wet end of a paper machine. OFten it is desired to retain the polymer on
or near the surface or surfaces of the sheet. In this case, it can be applied
by any of the conventional coating technigues. For other applications, it is
desirable for the polymer to be distributed uniformly throughout the sheet.
15 Where large amounts of polymer are desired, this can be accomplished by
dipping or impregnating the sheet after the papermaking process. ~Iowever,
where uniform distrib1~ion of smaller Mmolmts of polymer is desired, it is
usually preferred to include the additive with the stock prior to the
papermak ng process. Unfortunately, this is not always possible. Many
20 polymeric materials must be used in the form of aqueous emulsions. These
emulsions are usually anionic in nature and, almost universally~ will have
water as the continuous phase. Within the papermaking industry? these
polymer emulsions are typically referred to as "latexes or latices." In the
present application the term "Iatex" refers to very broadly to any anionic
25 aqueous emulsion of a polymeric material. These polymers can range from
hard vitreous types to those which are soft and rubbery. They may be either
thermoplastic or thermosetting in nature. In the case of therrnoplastic
polymers they rnay ~e materials which remain permanently thermop~astic or
they m~y be types which are partially or f~ly crosslinkable, with or withollt
3U an extern~l catnlyst, into therrnosetting types.
Because of their anionic nature, very few latices can be added
directly to a pldp making slurry with the e~pectation of having satisfactory
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retention. The cellulosic ~ibers are also anionic and they will repel the r esinparticles unless the fiber surface is modi-fied in some means to make it less
negative in character. Cal:ionic retention aids are sometimes used to
accomplish this purpose. Examples of this practice are fow~d in recent U.S.
PRtents to Jukes, et al., 4,125,645 and 4,256,807. A paper by Latimer and
Gill, ~ 56(4): 66-69 (1973), describes the beater deposition of an acrylic
latex onto wood pulp using a cationic deposition aid. Another approach
ou~lined in Japnnese Kokai 85,374l74 has been to c~eate a cationic latex.
However, this approach is possible vvith only a very limited number of
polymeric rnaterials.
The use of cationic retention or depos;tion ai~s is not without
problems in its own right. Retention aids tend to be quite expensive and any
given retention material may be totally ineffective with the latex of choice.
Rarely do retention efficiencies exceed 60-70~6. For these reasons, it has
not been the usual practice to date to employ wet addition of latices except
in very selective circurnstances.
Another approach has been to precipitate the polymer particles
on the fibers by p~ change or by chemieal additives. Tl~is method can cause
the latex to agglomerate and form relatively large globules rather than
producing a ~iform fiber coating.
()ne problem with the use of retention aids has been the inability
of the papermaker to precisely control the electrical charge of the fibers.
An approach that h~s received some study over the years has bsen to
chemically modify the fiber surface to make it less negative. Uwatoko~
2S ~@~ (Japan~ 25(3): 360-362 (1974), briefly summarizes the state of
art in regard to cationie fibers and lists six major approache~ thQt have been
taken. The first method introduces side chains containing a tertiary
nitrogen atom. These side chains are attached to the cellulose molecule at
the hydroxyl groups as ethers. One product of this type which has received
considerable study is the quaterr~zed diethylaminoethyl derivative OI
cellulose. A second route to the preparation of cationic cellulose is the
reaction of cellu~ose in the presence of sodium hydroxide with ethanolamine?
aqueolJs ammonia, or melamine. A third process is the reaction between
cellulose and a material such as 2-aminoethyl s~furic acid in the presence
of sodium hydroxide. Another product has been formed by iminating an
aminated cellulose by reaction between the aminated cellulose and ethylene
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imlne. ~n approach which has received considerable st~ldy is the reaction
of various trimethyl ammonium salts. Of particular import~nce has been
glycidyl trimethyl ammonium chloride reacted with cel]ulose in the presence
of a catalytie amount of sodium hydroxide. A related approach has been the
reaction of 2-chloroethyldiethyl amune with aIkali eellulose. The product
is then quaternized ~ith methyl iodide in anhydrous a]cohol. Finally, Uwa-
toko comments on a process wnere cellulose is reacted with a solution of
sodium acid cyanamide at a concentration of 50-200 g/L at a pH in the range
of 10-13 and tel~erature of 10-40C for 4-24 hours.
McKelvey and senerito, J. Appl. Polymer Sci. 11:1693-1701 (1967),
show the reaction of cellulose with a mi~ture of epichlorohydrin and a
tertiary amine in the presence of aqueous sodium hydroxide.
The references cited are exemplary only since the preparation of
cationic cellulose is not the subject of the present invention. The reader
interested in a more detailed literature survey of cationie celluloses
might refer to the present assigne~'s U.S. Patent No. 4,505,775. m is pat-
ent, of whieh the present inventor is a eoinventor, deseribes a very inex-
pensive and greatly simplified proeess for manufacturing a eationie eellu-
lose. ~his is done by adding either a linear or partially crosslinked
water soluble eondensate of epichlorohydrin and dimethylamine to an aqueous
suspension of eellulose under alkaline conditions. The preferred coneen-
trations of epichlorohydrin and dimethylamine will be approximately equi-
molar in proportion. Amm~nia and primary aliphatie diamines serve to aet
as eross-linking agents for the eondensates. Further, their use inereases
the number of tertiary nitrogen atoms which may be quaternized to provide
sites for positive eharges. Up to 30 molar percent of the dimethylamine
may be replaeed by ammonia or the aliphatie diamine in the eondensation
proeess. In general, it is preferred that the molar pereentage of the
erosslinking material should be in the range of 10-20%. Preparation of
suitable eondensates is deseribed in U.S. Patent No. 3,930,877 to Aitken.
It has been found that a eationie eellulose of the types deseribed
in -the foregoing patent applieation can effeetively bond a wide variety of
anionie latiees under the processing eonditions normally used prior to the
wet end of a paper maehine. The products thus prepared have a wide v æiety
of uses, partic~ æly in areas where the fibers are later formed into air
laid we~hs of væ ious types.
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SUMMARY OF THE INVENTIC~N
The present inventiorl comprises a new cornposition of matter
and the method for making it. In its broadest form, the composition
comprises a cat;onized cellulose and from 0.1-30%, on a dry weigh~ basis, of
5 a polymer capable of being emulsified into an anionic dispersion. The
ca~ionized cellulose is an additive of cellulose with a material from the
group consisting of a condensate of epichlorohydrin and dimetllylamine, said
condensate further modified by a crosslinking agent, and mixtures thereof
wherein the cross linking agent, if present, is selected from the group
ln consisting of ammonia and a primary aliphatic diamine of the type
H2N-R-NH2 llvherein E~ is an alkylene rad;cal of from 2 8 carbon atoms.
The product is made by first preparing the cationic cellulose by
treating celll~ose under aqueous alkaline conditions with a material selected
from the aforementioned group of condensates. The cationi~ed cellulose is
15 then treated in an aqueous suspension with an anionic polymer em~sion
within the range of usage noted above. The cationic cellulose may be
prepared aforehand and conventionally dried, as by sheeting, or it can be
prepared, washed, and immediately treated with the appropriate latex. The
term "latex" is considered in i$s broadest sense as being any aqueous based
20 anionic polymer emulsion in which ~ter is the continuous phase.
A preferred cationic additive is made using an approximately
equimolar condensate of epic~orhy~rin and dimethylamine in which up to 30
molar percent of the dieth~lamine has been replaced by hexamethylene
diamine. The cationizing condensate will normally be used in the range of
25 0.5-20 kg/t based on the dry weight of the cellulose. More typically it will
be used within the range of 1-10 kgjt.
A wide range OI polymer emulsions or latices can be successfldly
bonded to the cationic cell~ose. These can be polymers based on acryl~
nitrile9 styren~butadiene, styrene-acrylonitrile, acrylonitril~butadien~
30 styrene, acrylic and methacr~lic ethers, vinylacrylics, vinylaeetate~
vinylchloride, and p~lyolefins such as polyethylene, polypropylene~ and
various polymers based on polybutene. Mixtures of two or more types of
these polymers are considered to be within the scope of the invention as are
block and graft copolymers of tWQ or more of the monomeric species just
35 noted. The abovs list should be considered as exernplary rather than
limiting.
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Among the preferred polymers are the various types broadly
identified as polyvinyl acetate and polyacrylates and rnethacrylates.
Polyvinyl acetates are generally partially hydrolyzed materials and may be
chemically modified so they can be crosslinked by applying heat, with or
without the need for an external catalyst. l`he polyacrylate and
methacrylate resins likewise are considered in a generic sense since there
are many versions which may be either permanently thermsplastic or which
can be crosslirlked with or without the need for an external calalyst. The
resin treated products of the invention may be prepared in sheeted form, as
loose fibrous materials, or in other of the forms well known in the
papermaking industry. The products a~e particularly useful for making such
absorbent materials as air laid paper towelling or indllstrial wipes. These
products are currently made by spraying on as much as 30% latex binder
after formation of an air laid feltO The large amount of water added at this
time necessitates an adclitional drying step which is not required using the
products of the present invention.
It is an object of the present invention to provide a fibrous,
polyme~treated cellulosic product in which the polymer is uniformly
distributed over the fiber surface.
It is another object to provide a simple method for adding a
polymeric latex to cell~dosic fibers.
It is a further object to provide a method for treating cellulosic
fibers in aqueous suspension with an anionic polymeric latex without the
necessity ~or using a cationic retention or deposition aid.
These and many o~her objects will become immediately apparent
to those skilled in the art upon reading the following detailed description.
DETA.ILED DESCRIPTION OF THE PREFERRED EM 3ODIMENTS
The products of the present invention are made by first
preparing a cationic cellulose. This is made by treating a dilute aqueous
suspension of the ce~lulose with a condensate of epichlorohydrin and
dimethylamine (Epi-DMA) or a eondensate of these materials which has
been modified by a crosslinking ~gent w}~ch may be ammonia or a primary
aliphatic diamine of the type H2N-R-NH2 wherein R is an ~lkylene radical
OI from 2-8 earbon atoms. This treatment may be carried out at the end of
a bleaching sequence. Alternativ~ly, it can be carried out during any
alkaline bleaching step at which the pH is 10 or above, as long as this step is
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not followed by a c~orin~tion or hypochlorite stage. The temperature and
ffme for the preparation of the catiorlic cellulose are not criticHl. The
addition and/or reaction product be$ween celludose and the Epi-DMA
condenstate appears to form very rapidly. The cationized cellulose product
5 may then be dried by convention~l sheeting, as loose fiber, or in other
physical forms. It may be also used without further drying wherein it is
suspended in w ater and the appropriate latex simply added 7vith gentle
agitation.
The following examples will serve to show specific embodiments
10 of the present invention.
Example 1
Bleached Douglas-fir kraft pulp was obtained from a
northwestern pulp mill. Samples having 15.5 g of dry fiber wele slurried in
760 mL of water to produce a suspension having 2% consistency. The pH
was adjusted to 1û.5 with Na~H and 0.16 g of a 50% aqueous solution (5 kg/t
on an active materi~l basis~ of an epichlorohydri~dimethylamine condensate
partially crosslinked with hexamethylene diamine was added with stirring.
The condensate is av~ilable as Nalco ~-7135 frorn Nalco Chemic~l Co., Oak
Brook, ~linois. Aîter gen'de agitation for 30 minutes the pulp was drained
on a Buelmer funnel and washed lmtil the washings were essentially neutral.
This cationic product was stor d for furthe~ use without drying~ Kil~da~il
nitrogen determinations made on the treated product showed a retention
efficiency for the additive in the range ~ 85-90%. The procedure was
readily sc~led up for preparation of larger quantities of c~tionic fiber
without any loss of retention efficiency.
Exam~
C~tionic fiber prepared as in Ex~mple 1 was reslurried in water
to give a suspension at 2% eonsistency. Using continuous gentle egitation,
varying arnounts of a crosslinkable polyvinyl acetate em~sion having 50%
solids content were added. Samples were made using 5, 10, and 30%
emulsion solids based on cationized fiber. One suitable emulsion is available
as Airflex 105 from hir Products and Chemicals, Inc., Allentown,
Pennsylvania. Agitation was continued for 30 seconds after completion of
latex addi Ition. Additional dilution water was added and the fi~er suspension
was formed into hand sheets in ~ standard 8 x 8 inch (20.3 x 20.3 ~m) Noble
and Wood laboratory sheet former. The sheets were drum dried to about
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80% moisture and then conditioned. Standard Mullen burst tests were run on
the sheets after air drying and before further processing.
After checking burst values, the sheets were refiberiæed dry in a
high shear blender and air felted into sheets 6 inches (15.9 cm) in diameter
5 with a basis weight averaging 50 g/m2. The air ormed felts were pressed
for 15 seconds at 150C and 300 psi (2,068 kPa) to consolidate the~n into
handleable tissue sheets.
An additional sample was made using 1û% of the polyvinyl
acetate latex. A~ter the dry felted sheets were formed, but before pressing,
10 one sample set was sprayed with a water solution containing 0.74%, based on
latex solidsJ of citric acid. Citric acid serves as a catalyst to induce
crosslinking of the polymer.
Dry tensile strength values were determined for the tissues using
a constant rate of elongation tester having a head speed of 2 in./min. with R
15 3 in. span between clamps and 1 in. wide samples. Test results are shown in
the following table.
Table I
Resin U~e2 %~Iandsheet M~len, kPa 8
0 90~1100 ~-10
112~ 18
lû 150~ 45
10 ~ catalyst 1530 88
1180 30
The dramatic improvement in dry laid tissue tensile strength
30 using up to 1û% latex is immediately apparent.
Products made a¢cording to the p~esent invention have potential
applications in many areas. Among these are uses where strength must be
combined with so~tness to the touch. Paper towe3ing and facial tissues are
35 ex~mples as are wrapper tissues for diaper and sanitary napkin fillers. In
many of these uses rapid water absorption is also important.
Latex treated samples were made as in Example 2, using 10%
latex solids based on cationized pulp. In addition to the polyYinyl acetate
latex used previously, a sample set was made using Airflex 4500 polyvinyl
40 c~oride crosslinking latex. This is available from the supplier noted
previously.
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One sarnple with ea~h latex was further treated with
surfactant to promote rapid wetting. Th;s was added as an aqueous solution
at the time of lAtex addition to the cationized pulp slurry, using 0.74% based
on latex solids. Many types of surfflctants are suitable. The specific
S rnaterial used for the products in this example was Aerosol OT, a dioct~l
ester of sodium s~f~succinic acid, available from Amer;can Cyanamid Co.
Wayne, New Jersey.
The produc~s were made into dry laid sheets a~ before with the
exception that basis weight WAS increased to an average of 200 g/m2 to
1a simulate pQper toweling. On selected samples a citric ~cid catalyst solution
was sprayed on the air felted fiber~ ~s described in Example 2, to promote
crosslinking of the resin. An amount equivalent to 0.74% based on latex
solids was used.
Wet and dry tensile strengths were determined as was the time
15 to completely wet out a 5.1 x 501 cm sampls free floating on a water
surfaee. In order to avoid handling damage to strip6 intended for wet tensile
tests, the strips were placed dry in the jaws oE the tester an~ then water
sprayed until thoroug}~y wet. Results of the tests follow,
TABLE ~
Resin Wetting Agellt Tersile Strength9 N/m WettingTime,
:E mldsion Present ~ Wet sec.
PVAc A-105(1) No - - 52
P~Ac ~ Cat~l~st No 251 38. 7 34
PVAc + Catalyst Yes 283 39. 3 1. 6
30 PV~ A-45oo(2j No - - 3. 2
PVC + Cat~lyst No 112 .36. 3 3 . 2
PVC ~ Cat~lyst Yes 81 32~0 1.4
None No ~10 - 0. ~1.0
(1) Polyvinyl acetate
(2) Polyvinyl cl~oride
The effectiYeness of the surfactant in reducing wetting time is
40 immediat~ly apparent. This may in part be due to the cationic nature of the
fiber which serv~ to retain the anior~ic surfa~tant.
After the above labor~tory tests had been complete, trials were
.~ ~ made on a continuous pilot scale paper machine using cataonized fiber as the
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cellulosic furnish. In the first trial, the resin emulsion was added to the
fiber at the machine chest. This is an area of vigorous agitat;on which
caused foaming, resulting in numerous sheet breaks. In a later trial, the
latex was added just prior to the headbox. Running conditions on the paper
5 machine and product quality were excellent.
The optimum point for adding the surfactant in a paper machine
run has not yet been determined. Adding the surfactant following latex
addition and immediately prior to the machine headbox failed to achieve
results equal to those reached in laboratory trialsO
A set of samples si:nilar to those described earlier in the
example was made using uneationized fiber. Latex usage was 10% solids
based on dry fiber. Son some samples 10 kg/t of alum was used at the time
of latex addition.
Table III
Resin Catalyst AlumI:)ry Tensile
Emulsion Present Present_trength, N/m
___ __._
20 PYAc A-105 No No 37
PVAc A-105 No Yes 83
PVAc A-105 Yes No 50
PVAc A-180 No No 52
PVAcA-180 No Yes 111
25 PVAc A-180 Yes No 50
PVC A-450U No No 56
PVC A-4500 No Yes 144
The tensile strength superiority of the samples .nade with
30 cationized fiber is immediately evident with the exeeption of the one
sample made with PVC and alum.
Example 4
The cationized fiber of Example 1 is effective in retaining a
wide variety of anionic polymer dispersions (latices) having significantly
35 differing ehemical properties. As might be expected, ~his array of latices
produces Idtimate products which may differ significantly in physical and
chemical properties. However, most of the resin systems testecl produced a
very significant increase in the tensile strength of a dry felted tissue
product, made as described in ~xample 2. Tests were made with the
40 following polymer emulsions: Airflex 105 and 120 ~polyvinyl acetate),
Airflex 4500 (polyvinyl chloride, all available from Air Products and
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Chemicels Co., Allentown, Pennsylvani~ Hycar 267:L and 26170 (acrylic) and
Hycar 1572 and 1572X64 (acrylonitrile), all products of B.F. Goodrich
Company, Cleveland, Ohio; and Surlyn 56220 (polyethylene) available from
E.l. duPont de Nemours ~ Co.~ Wilmington, Delaware~ Each was added as
5 described in Example 2 using 10% polymer solids ~sed on cationized fiber.
The following tensile tests were run on air laid tissues having a 50 glm2
basis weight. No catalyst was llsed for any samples.
Table IV
Tensile Strength
Polymer Emulsion Resin T~ N/m
Airflex 105 Polyvinyl acetate 4S
Airflex 120 Polyvinyl acetate 19
Airflex 4500 Polyvinyl cldoride45
Hycar 4671 Acrylic 38
Hycar 26170 Acrylic 26
Elycar 1572 Acrylonitrile 22
~0 Hycar 1572X64 Acrylonitrile 20
Surlyn 56220 Polyethylene 10
None 6-10
The irnprovement i~ tensile strengths over an untreated control
25 is immediately apparent.
The above tests are not shown as a comparison of the rEilative
me~its ~f the products tested. Ma~y p~operties besides dry tensile strength
are irnportant ~nd these will vary greatly between different resin types.
Further, it is ur~ikely that all, or even any, were slsed under opffmum
30 conditions~ Nor are the tests to be regarded as any endorsement of the
products of the a~ve manufacturers since many competing products are
considered to work equally well. rrhe purpose of the tests was solely to show
the effectiveness of the cationized Iiber at retair~ing various generic types
OI latlces without the need ~or external retention aidsO
Analytical methods are not available for precise determination
of the amounts of dif~erent types of latices retained by cationized fiber. By
using a saponification method, it is estimated that about 82% of the A~105
polyvinyl acetate is re~ained. Other test methods indicate retention of
various latex types in the range of. 60 ~o 90~9~. The use of small quantities
40 of alum; e.g., 2.5 -10 kg/t with the cationi~ed fiber can improYe retention of
some types of latex as is shown in the following examples.
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A cationic cellulose is made as in Example 1 except that an
uncrosslinked epic~orohydrin~dimethylamine condensate (Nalco N-7655)
(Epi-DMA) was used in place OI the hexameth~lene diamine (HMDA~
5 modified material of the previous example. Usage in the present case was
higher, 10 kg/t, in contrast to 5 kg/t for the earlier material. Retention
efficiency of the condensate was measured by Kjeldal~ nitro~en determina-
tion as about 87%.
The cationized fibers of ~xamples 1 and 5 were slurried in water
and varying amounts of a self-crosslinking acrylic emulsion latex (UCAR
872, Union Carbide Corp., New York, New York) were added. Handsheets
were then made from the fiber latex mixtures. In addition to the two
treated materials, trials were run on untreated pulp and untreated pulp with
15 alum in ranges from 2.5 to 5 kg/t alum.
Untreated fiber, untreated fiber with alum and the fiber treated
with 10 kg/t 13pi-DMA were inefEective at retaining this latex, which was
essentially all lost with the white water. Fiber treated with HMDA
modified condensate showed exeellent latex retention7 as measured by
20 increase in sheet weight.
When small amounts OI alum were added to the mixture of
Epi-DMA treated fiber and latex, the latex was effectively retained at alum
usages of 5 k~/t and greater. Alum at usages of about 2.5 kg/t also
improved latex retention of fiber treated with HMDA modified polymer
25 although not to the same extent as with the Epi-DMA treated fib~r. With
the HMDA modified sample, there did not appear to be significant
advantage in using alum in amounts greater than 2.5 kg/t.
It is apparent that the partic~ar cationi~ing agent used will
affect the finul fiber properties. Some age~ts will be optimum for certain
30 latices but will be less effective with others. There does not appear to be
any way to predict this relationship and it must, to a large degree, be
determined experimentally.
It will be eviden~ to those skilled in the art that many variations
can be made without departing from the spirit of the present invention. The
3~ invention is to be considered as limited or~y by the ~ollowing claims.
