U.S. patent application number 11/493794 was filed with the patent office on 2006-11-23 for anionic-cationic polymer blend for surface size.
This patent application is currently assigned to Georgia-Pacific Resins, Inc.. Invention is credited to Cornel Hagiopol, Augusto Rodriguez.
Application Number | 20060260774 11/493794 |
Document ID | / |
Family ID | 34103400 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060260774 |
Kind Code |
A1 |
Rodriguez; Augusto ; et
al. |
November 23, 2006 |
Anionic-cationic polymer blend for surface size
Abstract
A composition for surface sizing and strengthening of paper and
other cellulosic products and the related sizing method and
resulting sized product, wherein the composition is an aqueous
mixture of a film-forming binder, such as starch and an anionic
polymer and a cationic polymer.
Inventors: |
Rodriguez; Augusto;
(Lilburn, GA) ; Hagiopol; Cornel; (Lilburn,
GA) |
Correspondence
Address: |
BANNER & WITCOFF
1001 G STREET N W
SUITE 1100
WASHINGTON
DC
20001
US
|
Assignee: |
Georgia-Pacific Resins,
Inc.
Atlanta
GA
|
Family ID: |
34103400 |
Appl. No.: |
11/493794 |
Filed: |
July 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10628577 |
Jul 29, 2003 |
|
|
|
11493794 |
Jul 27, 2006 |
|
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Current U.S.
Class: |
162/135 ;
162/164.1; 162/164.3; 162/175 |
Current CPC
Class: |
D21H 17/44 20130101;
D21H 17/42 20130101; D21H 21/16 20130101; D21H 17/28 20130101; D21H
17/72 20130101; D21H 23/22 20130101 |
Class at
Publication: |
162/135 ;
162/175; 162/164.3; 162/164.1 |
International
Class: |
D21H 21/16 20060101
D21H021/16 |
Claims
1. A method of sizing a cellulosic web for improving surface size
and surface strength comprising applying to a surface of the
cellulosic web an aqueous sizing mixture of a film-forming binder,
a cationic polymer and an anionic polymer, wherein the film-forming
binder is a starch, wherein the cationic polymer is a
polyamidoamine-epichlorohydrin resin and wherein the anionic
polymer is a hydrolyzed copolymer of styrene-maleic anhydride.
2. The method of claim 1 wherein the hydrolyzed copolymer of
styrene-maleic anhydride has a copolymer of styrene-acrylic ester
dispersed therein.
3. The method of claim 2 wherein said hydrolyzed copolymer of
styrene-maleic anhydride is prepared by forming an ammonium salt of
said styrene-maleic anhydride copolymer.
4. The method of claim 3 wherein said hydrolyzed copolymer of
styrene-maleic anhydride having a copolymer of styrene-acrylic
ester dispersed therein is NovaCote PS2.
5. A sized cellulosic web made by the method of claim 1.
6. A sized cellulosic web made by the method of claim 2.
7. A sized cellulosic web made by the method of claim 3.
8. A sized cellulosic web made by the method of claim 4.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of prior application Ser.
No. 10/628,577 filed Sep. 29, 2003, the entire disclosure of which
is hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to a surface size composition
for cellulosic products, such as paper. The composition also
improves paper surface strength. In particular, the invention
relates to a surface size composition comprising a mixture of
film-forming binder, such as starch, and a blend of an anionic
polymer and a cationic polymer.
DESCRIPTION OF RELATED ART
[0003] Paper and other cellulosic products often are sized, i.e.,
are treated with a composition in order to improve those
characteristics of the paper important for printing, such as
surface porosity and hydrophobicity. Sizing typically influences
absorption by the substrate of water, water-borne compositions, and
inks. This effect, in turn, generates higher ink penetration time
values, reduced lateral spread of printing inks, as well as
improved imaging and contrast with various printing technologies.
Thus, hydrophobic surface size agents improve printability
primarily by decreasing paper sheet absorbency and enhancing
surface resistance to liquid (ink) penetration.
[0004] There are two principal ways for sizing paper, internal
sizing (also known as bulk sizing) and surface sizing. Internal
sizing involves mixing a sizing agent or composition with the
aqueous suspension of paper pulp at the wet-end of a paper machine
and then forming a sheet, or web, having a uniform distribution of
sizing agent and pulp. Most of the internal sizing agents are small
molecules (AKD, ASA, rosin, etc.). Surface sizing involves applying
the sizing agent to the surface of a previously formed web. Surface
sizing typically increases the hydrophobic character, improves
product quality and is less expensive than internal sizing because
almost the entire sizing agent is retained on the surface of the
treated paper product. Most of the surface-sizing agents are
macromolecular compounds.
[0005] A variety of natural and synthetic resins have been used as
surface sizing agents. Surface sizing agents may be anionic,
cationic, or amphoteric, and may be used in combination with other
agents of the same electrical charge type. The effectiveness of a
particular sizing agent is influenced by the
hydrophilic-hydrophobic balance in its molecule. Illustrative of
such known sizing agents are modified starches, modified petroleum
resins, and synthetic copolymers, such as copolymers of an
ethylenically unsaturated monomer with an acrylate, styrene-maleic
anhydride (SMA) copolymers, and the like. In sizing compositions
made from such materials, the surface-sizing agent is dissolved or
dispersed in water.
[0006] Exemplary of the prior art of surface sizing agents can be
mentioned the following issued U.S. Pat. Nos. 3,941,736; 4,109,053;
4,112,155; 4,115,331; 4,835,212; 4,855,343; 5,139,614; 5,258,466;
5,290,849; 5,525,661; 5,591,489; 5,795,932; 5,824,190; 6,051,107;
6,087,457; 6,114,417; 6,171,444; 6,284,099 and 6,310,132.
[0007] The performance of many of these known sizing agents often
is not entirely satisfactory for certain applications. Various
printing technologies continue to require paper surfaces with high
integrity and resistance to the abrasive effects of the printing
processes. Fiber picking, linting and filler dusting all contribute
to decreased runnability of paper in various printing processes.
The accumulation of lint degrades the quality of the print job and
lowers productivity as more frequent cleaning in required. Thus,
there exists a need for surface sizing agents that overcome or
ameliorate these surface defects. In particular, regardless of
their ability to reduce surface absorption, often measured by the
Hercules Sizing Test (HST), almost all sizing agents show
relatively high values for the Adams Wet Rub test. For paper to be
used in offset printing applications especially, a satisfactory
(i.e., lower) result in the Adams Wet Rub test is important.
[0008] Thus, there remains a need in the art for new surface sizing
compositions that are easily prepared and easy to use, particularly
size compositions that can be used both in the acidic pH range, in
the case of alum-containing papers, and in the neutral to weakly
alkaline pH range in the case of alum-free and chalk-containing
papers and which give an outstanding sizing effect.
[0009] U.S. Patent Application 20020100567 describes a process for
internally sizing paper comprising adding to an aqueous suspension
of paper fibers, and optional fillers, an anionic or cationic
sizing dispersion of AKD, and a sizing promoter comprising a
cationic organic polymer having an aromatic group; and an anionic
polymer having an aromatic group selected from step-growth
polymers, polysaccharides and naturally occurring aromatic
polymers, wherein the sizing dispersion and sizing promoter are
added separately to the aqueous suspension.
[0010] Dasgupta U.S. Pat. No. 5,338,407 describes a process for
enhancing the dry strength of paper without reducing its softness,
in which a mixture of an anionic carboxymethyl guar or a
carboxymethyl hydroxyethyl guar and a cationic guar, which may be
prepared by reacting a natural guar with caustic and subsequently
with quaternary ammonium chloride, is added to a bleached pulp
furnish (wet end).
[0011] Allen et al., U.S. Pat. No. 6,294,645 describes a
composition useful for imparting dry-strength to paper without
substantially increasing the paper's wet-strength wherein the resin
system comprises a cationic component and an anionic component. The
cationic component comprises a reaction product of an intralinker
and a polyamidoamine. The anionic component comprises an anionic
component consisting of copolymers of acrylamide and at least one
member selected from the group consisting of acrylic acid, itaconic
acid, methacrylic acid and 2-acrylamido-2-methyl-1-propanesulfonic
acid and salts thereof. Alternatively, the anionic component
comprises an anionic component selected from the group consisting
of carboxylmethylcellulose, carboxymethyl guar, alginic acid,
pectin, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), and
salts thereof. Preferably, the salts of the anionic component are
the sodium salts thereof. The composition is added at the wet end
of a paper machine.
BRIEF DESCRIPTION OF THE INVENTION
[0012] The present invention is directed to a composition of matter
for surface sizing of paper and other cellulosic products and to
the related surface sizing method and to the sized substrate. The
composition according to the present invention will provide size
and impart surface strength to cellulosic substrates such as paper.
In particular, the surface sizing composition of the present
invention is a mixture of a film-forming binder, such as starch,
and an anionic polymer and a cationic polymer.
[0013] The present invention is directed to imparting surface size
and surface strength via surface application to cellulosic
substrates and should be distinguished from compositions and
processes for internally sizing and strengthening paper.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The invention is directed to a composition of matter for
surface sizing and strengthening paper and other cellulosic
products, to the related process of surface sizing and to the
resulting product. The composition is a mixture of an anionic
polymer and a cationic polymer with a film-forming binder such as
starch.
[0015] The term "polymer" is used throughout this application in
its conventional sense to refer to compounds having about ten or
more monomer units, and is intended to include homopolymers as well
as copolymers. The term "monomer" is used herein to refer to
compounds that are not polymeric.
[0016] Paper sized with the composition of the present invention
will typically exhibit acceptable resistance to penetration of ink
and aqueous liquids, adequate surface smoothness and surprisingly
improved surface strength, such that linting is reduced.
[0017] As noted above, a key feature of the present invention
resides in the discovery that by combining an anionic polymeric
sizing agent with a cationic polymeric sizing agent in the presence
of a film-forming binder, especially starch, one obtains a surface
sizing composition that results is a sized cellulosic product
having satisfactory surface absorbance performance, while
exhibiting surprisingly improved surface strength as indicated by
the Adams Wet Rub test. While not wishing to be bound by any theory
of operation, applicants believe that the surface strength
improvement flows from the interaction of the anionic and cationic
components on the paper surface to provide a reinforced crosslinked
layer.
[0018] As used herein, "crosslinked" and similar terms are intended
to embrace the structural and/or morphological change that occurs,
for example, by covalent chemical reaction, ionic interaction or
clustering, improved adhesion to the substrate, phase
transformation or inversion, and hydrogen bonding, in the sizing
composition of the present invention as it is dried and set to
modify the surface properties (size and strength) of a flexible,
porous cellulosic substrate, such as paper, to which an effective
amount of the sizing composition has been applied.
[0019] Suitable anionic polymers for use in the composition as the
anionic polymeric agent of the invention include hydrolyzed
copolymers of maleic anhydride with another unsaturated comonomer
such as styrene, as well as salts (e.g., ammonium, potassium or
sodium salts) of such copolymers. The anionic (co)-polymer can be
in a solution or in a dispersion.
[0020] Also included within the group of anionic polymers suitable
for use in the present invention are the other well known, alkali
soluble, acid-containing copolymers. Examples of such alkali
soluble, acid containing copolymers useful in this invention are:
styrene-acrylic acid (SAA) copolymers, styrene-methacrylic acid
copolymers, styrene-acrylonitrile-acrylic acid copolymers,
styrene-butyl acrylate-acrylic acid copolymers, acrylamide-acrylic
acid copolymers and the like. Instead of styrene, other hydrophobic
monomers may be contained in the acid containing copolymers, such
as alpha-methylstyrene; alkyl substituted styrenes, such as vinyl
toluene; acrylonitrile; vinyl chloride, acrylic- and (meth)acrylic
esters, such as butyl acrylate, methyl methacrylate; or the like,
or mixtures thereof; vinyl esters, such as vinyl acetate or vinyl
laurate; fumarate esters, such as dibutyl fumarate; maleate esters,
such as dibutyl maleate; itaconate esters, such as dibutyl
itaconate; olefins, such as ethylene, and the like, or mixtures
thereof.
[0021] In addition, instead of acrylic- or methacrylic acid, other
copolymerizable, unsaturated acids also may be used in the alkali
soluble, acid-containing copolymers. Examples are: maleic acid,
fumaric acid, crotonic acid; itaconic acid; monoalkyl maleates,
such as monoethyl maleate; aconitic acid; and the like. Unsaturated
sulfonic acids, such as vinyl sulfonic acid or styrene sulfonic
acid and the like may also be used. The weight average molecular
weight of the alkali soluble, acid-containing copolymer is
generally from 3,000 to 1,000,000, preferably from about 10,000 to
150,000 Mw (weight average molecular weight). Again, these
copolymers can be used as their salts, such as their ammonium
salts.
[0022] One specific anionic polymeric agent is a solublized
styrene-maleic acid (also referred to as "SMA") copolymer. The
styrene/maleic acid copolymer may comprise 50-80 weight % styrene
and 50-20 weight % maleic acid and may have a molecular weight of
between about 3,000 and about 300,000. This copolymer can be
solubilized by forming its ammonium salt in any manner known to the
skilled practitioner. Such anionic copolymers are commercially
available from G-P Resins, Inc. under the trade name NovaCote.RTM.
1936 and NovaCote.RTM. 2000. A suitable anionic compound also might
be a polymeric latex having sulfonic or carboxylic moieties such as
NovaCote.RTM. 1934, also available from G-P Resins, Inc. Also
commercially available is another G-P product suitable for use as
the anionic polymer, Ambond 1500, which is an acrylamide-acrylic
acid copolymer grafted on starch. One advantage of using such a
material in the preparation of the sizing composition of the
present invention is that a single component provides the
composition with both the required anionic agent as well as the
film-forming binder component, described below in more detail.
Finally, a hybrid anionic component such as an ammonium SMA
solution and a styrene-acrylate copolymer (SAE) dispersion,
available from G-P Resins, Inc. as NovaCote.RTM. PS2, or an anionic
guar gum such as a carboxymethyl guar, obtained by reacting a
natural guar with caustic and then with monochloroacetate, can also
be used as the anionic polymer.
[0023] Examples of suitable cationic polymers useful as the
cationic polymeric agent include polyamines, polyethylene imines,
polyamidoamine-epichlorohydrin resins (such as AMRES 25HP available
from G-P Resins, Inc.), dialkylamine-epichlorohydrin resins, homo-
and copolymers based on monomers selected from
diallyldimethyl-ammonium chloride, vinyl amines, (meth)acrylamides
and (meth)acrylates. The use of the term (meth)acrylamide and
similar terms is a shorthand notation meant to embrace both
acrylamide and methacrylamide. The cationic monomers can be acid
addition salts and/or quaternary ammonium salts. Examples of
suitable (meth)acrylamides and (meth)acrylates include
dialkylaminoalkyl (meth) acrylamides and dialkylaminoalkyl
(meth)acrylates, preferably their quaternary ammonium salts. The
molecular weight of the cationic polymer may depend on the type of
polymer and its charge density. Suitably the molecular weight is
below 1,000,000 and preferably below 600,000. The lower molecular
weight limit is usually 2,000 and preferably about 5,000.
[0024] One suitable cationic polymer can be prepared by
polymerizing a cationic monomer such as a diallyl quaternary
monomer (generally diallyl dimethyl ammonium chloride, DADMAC); but
may also be a dialkylaminoalkyl (meth)-acrylate or -acrylamide
wherein the alkyl and alkylene groups are usually C.sub.1-3,
generally as an acid addition or quaternary ammonium salt, possibly
with a small amount of acrylamide. For instance it may be
dimethylaminoethyl acrylate or methacrylate usually as a quaternary
ammonium salt or dimethylaminopropyl--acrylamide or
-methacrylamide, again generally as quaternary salt. The
quaternizing group is usually methyl chloride or another aliphatic
group. In such polymers, the amount of cationic monomer can be from
5 to 45% and the amount of acrylamide can be from 95 to 55%. If
desired small amounts of other ethylenically unsaturated monomers
can be included in the monomer blend but this is usually
unnecessary and the polymer conveniently is formed from the binary
blend. Cationic homopolymers of water soluble ethylenically
unsaturated cationic monomer optionally with a comonomer,
preferably not more than 90% by weight acrylamide, are generally
suitable. The ethylenically unsaturated cationic monomers can be
any of those cationic monomers discussed above but the monomer is
preferably diallyl dimethyl ammonium chloride (DADMAC). Generally
it is a homopolymer or a copolymer of at least 5 and usually at
least 10% DA DMAC with the balance being acrylamide.
[0025] Another class of cationic polymers that can be used as the
cationic polymeric agent are the co-polyhydroxyaminoethers of
bis-phenol (BLOX.RTM. product type available from Dow). Again, the
polymers can be provided as their acid addition salts and/or
quaternary ammonium salts. Also suitable are hydroxyethyl
acrylate-co-2-methacryloyloxyethyldimethylammonium chloride and a
cationic guar prepared by reacting natural guar with caustic and
then with a quaternary ammonium chloride.
[0026] One particularly useful cationic polymer is a
DADMAC-acrylamide copolymer grafted on starch (Ambond 1520). Such
grafted starch polymers are prepared by the graft polymerization of
the acrylamide vinyl monomer on to a starch substrate. As is well
known in the art, there are various free radical polymerization
methods useful for grafting vinyl monomers to starch, e.g.,
radiation, redox-based free radical polymerization and mechanical
fission. One particularly preferred method involves preparing a
solution of the starch and acrylamide, adding thereto an
appropriate free radical catalyst, and then carrying out the
polymerization below the pasting temperature of the starch. Typical
free radical catalysts that may be used are hydrogen peroxide,
solution soluble organic peroxides and hydroperoxides, and
persulfates. An activator, which is typically a mild reducing agent
can also be added along with the catalyst. All of these methods are
well-known to those skilled in the art and require no further
discussion herein.
[0027] Styrene-maleic anhydride copolymers in imide form
(3-propyl-dimethyl ammonium chloride) are also suitable as a
cationic surface size. They may also provide a surface strength in
conjunction with an anionic water-soluble or water dispersible
polymer. The styrene content ranges between 50% and 80% based on
weight. The imide SMA can be dissolved in acetic acid or in
hydrochloric acid solutions.
[0028] A cationic surface size also can be a cationic latex
obtained by emulsion copolymerization of styrene with butyl
acrylate and having cationic charges on the particle surface. The
styrene content may range from 30% to 75% and the cationic charge
is anywhere between 0.2-1.0 meq/gram.
[0029] Starches useful in preparing such grafted starch polymers
include for example, indian corn starch, rice starch, waxy maize
starch, waxy sorghum starch, tapioca starch, wheat starch, potato
starch, pearl starch and sweet potato starch, and derivatives
thereof. The derivatives include oxidized starches,
hydroxyalkylated starches, carboxyalkylated starches, various
solubilized starches, enzyme modified starches, and the like.
Generally, any starch can be used from which the vinyl monomer can
be polymerized thereupon.
[0030] A polymer of this type is available from G-P Resins, Inc.
under the Ambond.RTM. designation. One advantage of using such a
material in the preparation of the sizing composition of the
present invention is that a single component can provide the
composition with both the required cationic agent as well as the
film-forming binder component, described below in more detail.
[0031] The anionic and cationic polymers used to prepare the sizing
composition of the present invention are generally aqueous
solutions or aqueous dispersions of water-insoluble polymers. In
the case of aqueous dispersions, the dispersed polymer particles or
droplets of the anionic and cationic polymers generally are
obtained by polymerizing the corresponding monomers in the presence
of water. The polymerization is generally carried out according to
well-known techniques. The resulting product typically is an
aqueous dispersion (e.g., a latex) comprised of finely divided
dispersed water-insoluble anionic or cationic polymer particles in
aqueous solution, often containing a stabilizing agent.
[0032] Another important component of the sizing composition of the
present invention is a film-forming binder, such as a
polysaccharide. Any film-forming binder that is compatible with the
blend of anionic and cationic polymers can be used. Exemplary
film-forming binders include, but are not necessarily limited to:
polysaccharides and derivatives thereof, e.g., starches, cellulosic
polymers, dextran and the like; polypeptides (e.g., collagen and
gelatin); and synthetic polymers, particularly synthetic vinyl
polymers such as poly(vinyl alcohol), poly(vinyl phosphate),
poly(vinyl pyrrolidone), vinyl-pyrrolidone-vinyl acetate
copolymers, vinyl acetate-acrylic acid copolymers, vinyl
alcohol-vinyl acetate copolymers, vinyl pyrrolidone-styrene
copolymers, and poly(vinylamine), synthetic acrylate polymers and
copolymers such as poly(acrylic acid-co-methacrylate),
poly(vinyl-co-acrylate), and the like.
[0033] Generally, based on cost considerations the film-forming
binder will be a polysaccharide such as a water-soluble alginate
(sodium or potassium), carboxymethyl cellulose, hydroxyethyl
cellulose, or a starch. The polysaccharide is preferably a starch.
Suitable starches may be any of a variety of natural, converted,
and synthetically modified starches. Suitable starches include:
barley, wheat, potato, corn, waxy maize, rice, tapioca, sorghum,
and wheat. The starch may be converted or modified, e.g. treated
with enzyme, acid, thermochemical treatment or oxidized. The starch
may also be pregelatinized. The starch may also be chemically
treated, e.g. by etherification, esterification, crosslinking,
etc., to make it cationic, anionic or amphoteric. Starches that
have been treated by a combination of the aforementioned processes
also can be used, as can mixtures of the aforementioned starches. A
preferred starch is a slightly anionic or slightly cationic
starch.
[0034] As noted above, a particularly preferred source of the
film-forming binder is a grafted starch, especially starches having
a graft of a cationic polymer.
[0035] The various components of the sizing composition are added
to form the size press solution or dispersion in a sequence to
prevent any reciprocal interaction in the starch dispersion. For
example, in order to make a size-press composition using a slightly
cationic starch according the present invention, the anionic
polymer additive is first added to the slightly cationic starch
solution followed by the cationic polymer additive. If the starch
is slightly anionic, then the cationic polymer additive is added
prior to adding the anionic polymer additive. A suitable sequencing
of the addition of the various constituents of the sizing
composition to prevent any reciprocal interaction can be determined
by a skilled worker using only routine experimentation. Generally,
the various components can be combined a short time before using
the composition to size paper.
[0036] The anionic and cationic polymers are present in the sizing
composition in an amount sufficient to provide an essentially
balanced charge. Generally, an essentially balanced charge can be
obtained by providing the anionic and cationic polymers in a weight
ratio of anionic polymer to cationic polymer of between about 0.2:1
to about 2.5:1, more usually the weight ratio is in the range of
0.4:1 to 2:1.
[0037] The film-forming polymer is generally present in the sizing
composition in an amount of about 1 to about 18 percent by weight
of the sizing composition, preferably in an amount of about 2 to
about 12 percent by weight. Thus, a typical sizing composition for
use as a size press solution will generally contain about 1 to
about 18% by weight starch, often about 2 to about 12% by weight
starch, in water with a pH between about 6 and 9.
[0038] The sizing composition will generally be provided in an
aqueous liquid vehicle, as an aqueous solution or dispersion,
although small amounts of a water-soluble or water miscible organic
solvent may also be present. It may on occasion be necessary to add
a solubilizing compound during preparation of the sizing
composition so that the components dissolve in the aqueous liquid
vehicle, e.g., an inorganic base such as ammonia and/or an organic
amine. Suitable organic amines include lower alkyl-substituted
amines such as methylamine, dimethylamine, ethylamine, and
trimethylamine, as well as ethanolamine, diethanolamine,
triethanolamine, and substituted ethanolamines, typically lower
alkyl-substituted ethanolamines such as N-methyl and N,N-dimethyl
ethanolamines, and morpholine. Such compounds are also useful for
bringing the pH into the desired range for basic formulations, and,
if present, will generally represent not more than about 1.0 wt. %
of the composition, and in most cases will represent not more than
about 0.5 wt. % of the composition.
[0039] The solids content of the aqueous solution or dispersion is
influenced by the method selected for applying the size composition
to the cellulosic substrate. In the case of conventional size
presses, the size composition will typically have a solids content
of about 1 to about 20 weight percent, i.e., an amount of water
between about 80 and about 99 weight percent. Suitable solids
concentrations for the size compositions in other applications can
be selected based on routine testing.
[0040] Thus, the amount of the anionic and cationic polymers added
to the mixture to form the size press composition is preferably
from about 0.05 to about 50 wt. %, more usually 0.05 to 25 wt. %,
based on the total solids of the size press composition. More
preferably the polymer solids level will be from about 0.1 to about
20 wt. % based on the total solids. Usually, the polymer solids
level will be from about 0.1 to about 15 wt. % based on the total
solids and most often between about 0.5 and about 10 wt. %.
[0041] The specific techniques used to size paper and other
cellulosic products such as cardboard, by means of the present
invention are similar to those that are commonly employed in
papermaking to apply the sizing composition to the cellulose-based
product. For instance, the aqueous sizing composition may be
applied to the surface of the paper using a size press by a
calender or a doctor knife blade. Alternatively, the size
composition may be sprayed onto the paper web or be applied by
dipping the paper into the aqueous composition. The sizing
composition also may be applied as part of the paper conversion
process using conventional coating techniques. Paper treated with
the sizing solution is then dried at elevated temperatures. Drying
the paper web is sufficient to bring the surface size and surface
strength to full development.
[0042] Thus, surface size treatment can be applied to paper as
either a post-production operation or as a portion of the
papermaking process itself. Surface size is applied typically in
the papermaking process after the paper sheet has been formed and
dried but not passed through a calendar stack. The formed and dried
sheet (web) is conducted through a size press (actually a
nip-coater of various configurations), which re-wets the sheet to
some degree (depending on the type of size press) with the sizing
composition. Upon the wetting or coating of the web, it is again
dried and subsequently passed through a series of nips at the
calendar to control caliper and smooth the finished sheet prior to
wind-up and slitting or sheeting.
[0043] The size press composition is applied at the size press in
an amount such that the level of starch and polymer solids applied
to the surface is preferably about 0.02 wt. % to about 4.5 wt. % on
a dry basis based on the weight of the dry sheet of paper. Usually,
the level is about 0.025 wt. % to about 4.0 wt. %, and most often
from about 0.05 wt. % to about 3.5 wt. %.
[0044] The sizing composition of this invention also may be used in
conjunction with or serially with other additives conventionally
used in the production of cellulose-based products. Such additional
additives may include, but are not necessarily limited to,
inorganic fillers, anti-curl agents, or additional conventional
components such as a surfactant, plasticizer, humectant, defoamer,
UV absorber, light fastness enhancer, polymeric dispersant, dye
mordant, optical brightener, or leveling agent, as are commonly
known in the art.
[0045] The paper onto which the sizing composition is applied may
vary widely and is independent of the kind of pulp used to make the
paper. The paper may be a paper base produced by sheeting under the
wide pH ranges of 4 to 9. Thus, the invention is suitable for the
preparation of sized paper of any thickness and of any kind and
thus applies to papers or cardboards obtained from mechanical,
chemical, soda, sulphite, sulphate, semichemical, wood, natural
vegetable, rag or old paper pulp and mixtures thereof.
[0046] The paper also may contain additives such as fillers,
dyestuffs, paper strengthening agents, drainage rate improvers, and
internal sizing agents. The surface sizing of previously internally
sized paper is specifically contemplated. In particular, by using
the invention in connection with a sheet that has been internally
sized, that is, certain sizing agents have been added to the pulp
suspension before it is converted to a paper sheet, one may obtain
higher levels of surface sizing. Internal sizing tends to prevent
or retard the surface size from soaking into the sheet, thus
allowing it to remain on the surface where it has maximum
effectiveness and may permit a lower surface size application rate
at equivalent surface properties.
[0047] Internal sizing agents may include any of those commonly
used at the wet end of a fine paper machine. These include rosin
sizes, ketene dimers and multimers, alkenylsuccinic anhydrides and
the like. The internal sizes are generally used at levels of from
about 0.05 wt. % to about 0.25 wt. % based on the weight of the dry
paper sheet.
[0048] When paper is sized in accordance with the present invention
(a mixture of a film-forming binder and anionic polymer and
cationic polymer additives), the paper has a degree of sizing that
is equivalent to that when a starch-based sizing agent that
contains either an anionic or a cationic polymer is used. The
sizing is typically manifested by an observation of improved
surface hydrophobic properties (i.e., higher HST test results).
[0049] When paper is processed in accordance with the present
invention, the paper has a degree of surface strength that is
greater than when a starch-based sizing agent that does not contain
the blend of the anionic and cationic polymers is used. Improved
surface strength is typically manifested by an observation of
improved surface integrity (i.e., lower Adam's Wet Rub test
results).
[0050] In many cases one or more improved properties may be
obtained simultaneously in a given product, but even if one only
obtains a sized product having improved properties in one area and
equivalent or even decreased properties in another area that result
is often satisfactory. Those skilled in the art recognize the
necessity or desirability of balancing the benefits of various
improvements against costs, depending on particular
circumstances.
[0051] It will be understood that while the invention has been
described in conjunction with specific embodiments thereof, the
foregoing description and following examples are intended to
illustrate, but not limit the scope of the invention. Other
aspects, advantages and modifications will be apparent to those
skilled in the art to which the invention pertains, and these
aspects and modifications are within the scope of the invention.
Thus, the following examples are to be considered as exemplifying
the invention, rather than limiting it in any way.
[0052] Throughout the specification and in the examples, "parts"
means parts by weight.
[0053] Throughout the specification and in the examples, molecular
weights are weight average, as measured by conventional, high
pressure, size exclusion chromatography techniques using suitable
molecular weight standards e.g. Pullulan polysaccharide
standards.
[0054] The Hercules Sizing Test (HST) measures the rate of
penetration of a 1 percent formic acid dye solution, read at 80%
reflectance, as the solution penetrates through the sized paper.
Skilled practitioners recognize that the HST test, results reported
as seconds, is a well-established test protocol for gauging the
performance of a sized product. The test provides a relative
evaluation of the hydophobicity of a sized substrate.
[0055] The Adams Wet Rub test provides a measure of the amount of
coating loss in a set time from a sample, as indicated by the
turbidity of a water suspension. In the Adams Wet Rub Test, a
moistened rubber roll, which passes through a moisturizing bath of
fixed volume (formic acid solution of 1%), is rubbed against the
sample (mounted on a backing roll) for a specified time and at a
known pressure. The bath solution is collected and amount of
coating removed from the sample is determined by measuring the
turbidity of a given volume of water containing the abraded
coating. Lower values indicate a higher level of surface integrity
or strength.
EXAMPLE 1
[0056] A base size press-solution includes 5.4% of a slightly
anionic starch (Penford 280). In one case, an anionic polymer
additive (NovaCote 1934) was added to the base solution. In another
case, to the base starch solution was first added under stirring a
cationic polymer additive (Amres 25 HP) and after 2 minutes the
anionic polymer additive (NovaCote 1934) was added. The base paper
used for sizing with each of the three compositions was a
communication grade paper (15% ash) having a porosity (Gurley) of
16 seconds and an internal size (estimated by HST) of 2 seconds.
The total pick up for each of the sizing compositions was 70
lb/ton. Based on this total pick-up, the calculated pick-ups for
each of the sizing compositions are shown in Table 1. The drying
temperatures were 103.degree. C. Results of HST and Adams Wet Rub
testing for each of the three samples are summarized in Table 1
below. TABLE-US-00001 TABLE 1 Adams Wet Rub SAMPLE HST (sec.)
(Turbidity units) Starch only (70 lbs/ton) 10 32 NovaCote .RTM.
1934 (2 lb/ton) + starch 28 45 (68 lbs/ton) NovaCote .RTM. 1934 (2
lb/ton) with 36 4.6 AMRES (1 lb/ton) + starch (67 lbs/ton)
EXAMPLE 2
[0057] Size-press compositions were obtained by repeating the
procedures of Example 1 except that NovaCote PS2 anionic polymer
was substituted for NovaCote 1934 and Ambond 1520 was substituted
for Amres. Again, the total pick up for each of the sizing
compositions was 70 lb/ton. Based on this total pick-up, the
calculated pick-ups for each of the sizing compositions are shown
in Table 2. Results of HST and Adams Wet Rub testing are summarized
in Table 2 below. TABLE-US-00002 TABLE 2 Adams Wet Rub SAMPLE HST
(sec.) (Turbidity units) Starch only (70 lbs/ton) 10 32 Starch (68
lbs/ton) + NovaCote PS2 50 13 (2.0 lb/T) Starch (68 lbs/ton) +
Ambond 1520 11 35 (2.0 lb/T) Starch (66 lbs/ton) + NovaCote PS2 74
10 (2.0 lb/T) + Ambond 1520 (2.0 lb/T)
EXAMPLE 3
[0058] A base size press composition was prepared which contained
3.5% of a slightly anionic starch (Penford 280). In one case, a
size press composition was prepared by additionally adding an
anionic polymer additive (NovaCote 1934). In another case, to this
base starch solution was first added under stirring a cationic
polymer additive (Amres 25 HP) and after 2 minutes an anionic
polymer additive (NovaCote 1934) was added. The base paper used
with each of the three sizing compositions was a newsprint grade
paper having a porosity (Gurley) of 40 seconds and an internal size
(estimated by water drop method) of less than 1 second. The total
solids pick-up from each of the sizing compositions was 55 lb/ton.
Based on this total pick-up, the calculated pick-ups for each of
the sizing compositions are shown in Table 3. The drying
temperatures were 103.degree. C. Results of sizing (water drop
method) and of Adams Wet Rub testing for each of the sizing
compositions are summarized in Table 3 below. TABLE-US-00003 TABLE
3 Water drop Adams Wet Rub SAMPLE (sec.) (Turbidity units) Starch
only (55 lbs/Ton) <1.0 16 NovaCote .RTM. 1934 (1.7 lbs/Ton) plus
16 7.0 starch (53.3 lbs/Ton) NovaCote .RTM. 1934 (1.7 lbs/Ton) with
16 1.6 AMRES (1 lb/Ton) plus starch (52.3 lbs/Ton)
EXAMPLE 4
[0059] A size-press composition was obtained by repeating the
procedures of Example 3 except that NovaCote PS2 was substituted
for NovaCote 1934. Test results are summarized in Table 4 below.
TABLE-US-00004 TABLE 4 Water drop Adams Wet Rub SAMPLE (sec.)
(Turbidity units) Starch only (55 lbs/Ton) <1.0 16 NovaCote
.RTM. PS2 (1.7 lbs/ton) + starch 259 3.5 (53.3 lbs/Ton) NovaCote
.RTM. PS2 (1.7 lbs/ton) with 237 1.2 AMRES (1 lb/ton) + starch
(52.3 lbs/Ton)
[0060] The present invention has been described with reference to
specific embodiments. However, this application is intended to
cover those changes and substitutions that may be made by those
skilled in the art without departing from the spirit and the scope
of the invention. Unless otherwise specifically indicated, all
percentages are by weight. Throughout the specification and in the
claims the term "about" is intended to encompass + or -5%.
* * * * *