U.S. patent application number 10/266992 was filed with the patent office on 2004-04-08 for latex paper sizing composition.
This patent application is currently assigned to Kemira Chemicals, Inc.. Invention is credited to Boardman, Delos E., Cotter, Terrence Edward, Irwin, Vaughn L..
Application Number | 20040065425 10/266992 |
Document ID | / |
Family ID | 32042770 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065425 |
Kind Code |
A1 |
Irwin, Vaughn L. ; et
al. |
April 8, 2004 |
Latex paper sizing composition
Abstract
Methods of sizing paper using a latex as a surface sizing agent
are described, in which the latex is defined by acid number or
particle size. Further described are methods of improving toner
adhesion of papers that are surface sized with alkenylsuccinic
anhydrides by employing latexes that have a glass transition
temperature of from about 25 to about 65. Still further described
are low shear methods of dispersing alkenylsuccinic anhydrides in
sizing compositions using latexes as dispersing aids.
Inventors: |
Irwin, Vaughn L.; (Mableton,
GA) ; Cotter, Terrence Edward; (Kennesaw, GA)
; Boardman, Delos E.; (Marietta, GA) |
Correspondence
Address: |
KING & SPALDING
191 PEACHTREE STREET, N.E.
ATLANTA
GA
30303-1763
US
|
Assignee: |
Kemira Chemicals, Inc.
|
Family ID: |
32042770 |
Appl. No.: |
10/266992 |
Filed: |
October 7, 2002 |
Current U.S.
Class: |
162/168.1 ;
162/158; 162/169; 162/175 |
Current CPC
Class: |
G03G 7/0073 20130101;
G03G 7/006 20130101; D21H 21/16 20130101; G03G 7/008 20130101; D21H
17/28 20130101; D21H 17/72 20130101; D21H 17/37 20130101; G03G
7/0066 20130101; D21H 21/52 20130101; D21H 17/16 20130101 |
Class at
Publication: |
162/168.1 ;
162/169; 162/158; 162/175 |
International
Class: |
D21H 017/37; D21H
017/28; D21H 017/14 |
Claims
What is claimed is:
1) A method of making paper comprising: a) providing an aqueous
pulp suspension; b) sheeting and drying the aqueous suspension to
obtain paper; c) contacting the paper with a size composition
comprising a latex having an acid number less than 30; and d)
drying the paper to obtain sized paper.
2) The method of claim 1 wherein the latex has an acid number of
less than 20.
3) The method of claim 1 wherein the latex has an acid number of
less than 10.
4) The method of claim 1 wherein the latex has an acid number of
less than 5.
5) The method of claim 1 wherein the latex particles have an
average particle size of from about 30 to about 90 nanometers.
6) The method of claim 1 wherein the latex has a glass transition
temperature of from about 35 to about 55.degree. C.
7) The method of claim 1 wherein the surface size composition
comprises an alkenylsuccinic anhydride and a latex mixed in a low
shear process.
8) The method of claim 1 wherein the latex comprises monomeric
residues of styrene, alkyl acrylate or methacrylate, and an
ethylenically unsaturated carboxylic acid.
9) A method of making paper comprising: a) providing an aqueous
pulp suspension; b) sheeting and drying the aqueous suspension to
obtain paper; c) contacting the paper with a size composition
comprising a dispersion of latex particles having an average
particle size of from about 20 to about 100 nanometers, and a
surfactant contribution from the latex of less than about 20% (w/w)
based on the weight of the latex; and d) drying the paper to obtain
sized paper.
10) The method of claim 9 wherein the latex particles have an
average particle size of from about 30 to about 90 nanometers.
11) The method of claim 9 wherein the latex particles have an
average particle size of from about 40 to about 80 nanometers.
12) The method of claim 9 wherein the latex has an acid number of
less than about 20.
13) The method of claim 9 wherein the latex has a glass transition
temperature of from about 35 to about 55.degree. C.
14) The method of claim 9 wherein the surface size composition
comprises an alkenylsuccinic anhydride and a latex mixed in a low
shear process.
15) The method of claim 9 wherein the latex comprises monomeric
residues of styrene, alkyl acrylate or methacrylate, and an
ethylenically unsaturated carboxylic acid.
16) A method of making paper sized with an alkenylsuccinic
anhydride having improved toner fusion comprising: a) providing an
aqueous pulp suspension; b) sheeting and drying the aqueous
suspension to obtain paper; c) contacting the paper with a surface
size composition comprising an alkenylsuccinic anhydride and a
latex having a glass transition temperature of from about 25 to
about 65.degree. C.; and d) drying the paper to obtain sized
paper.
17) The method of claim 16 wherein the latex has a glass transition
temperature of from about 35 to about 55.degree. C.
18) The method of claim 16 wherein the latex has a glass transition
temperature of from about 40 to about 50.degree. C.
19) The method of claim 16 wherein the latex has an acid number of
less than about 20.
20) The method of claim 16 wherein the latex particles have an
average particle size of from about 30 to about 90 nanometers.
21) The method of claim 16 wherein the alkenylsuccinic anhydride
and latex are mixed in a low shear process.
22) The method of claim 16 wherein the latex comprises monomeric
residues of styrene, alkyl acrylate or methacrylate, and an
ethylenically unsaturated carboxylic acid.
23) A method of making paper sized with an alkenylsuccinic
anhydride comprising: a) providing an aqueous pulp suspension; b)
sheeting and drying the aqueous suspension to obtain paper; c)
contacting the aqueous suspension or paper with an internal or
surface size composition comprising an alkenylsuccinic anhydride
and a latex; and d) drying the paper to obtain sized paper; wherein
(i) the alkenylsuccinic anhydride and latex are mixed in a low
shear process, (ii) the alkenylsuccinic anhydride and latex are
mixed in an in-line mixer, or (iii) the surfactant contribution
from the latex in the surface size composition is less than 20%
(w/w) based upon the weight of the latex.
24) The method of claim 23 wherein the latex has a glass transition
temperature of from about 35 to about 55.degree. C.
25) The method of claim 23 wherein the latex has an acid number of
less than about 20.
26) The method of claim 23 wherein the latex particles have an
average particle size of from about 30 to about 90 nanometers.
27) The method of claim 23 wherein the latex comprises monomeric
residues of styrene, alkyl acrylate or methacrylate, and an
ethylenically unsaturated carboxylic acid.
28) A method of making a size composition comprising providing an
aqueous latex dispersion and mixing ASA with the aqueous latex
dispersion, wherein: a) the ASA is mixed with the latex dispersion
in an in-line mixer, or b) the ASA is mixed with the latex
dispersion under low shear; or c) the surfactant contribution from
the latex in the surface size composition is less than 20% (w/w)
based upon the weight of the latex.
29) A surface sizing composition comprising: a) starch; and b) a
latex selected from: i) a latex having an acid number less than 30;
ii) a latex having an average particle size of from about 20 to
about 100 nanometers, and a surfactant contribution from the latex
of less than about 20% (w/w) based on the weight of the latex; iii)
a latex having a glass transition temperature of from about 25 to
about 65.degree. C., wherein the surface sizing composition further
comprises an alkenylsuccinic anhydride; or iv) a latex, wherein the
surface sizing composition further comprises an alkenylsuccinic
anhydride and wherein (A) the alkenylsuccinic anhydride and latex
are mixed in a low shear process, (B) the alkenylsuccinic anhydride
and latex are mixed in an in-line mixer, or (C) the surfactant
contribution from the latex in the surface size composition is less
than 20% (w/w) based upon the weight of the latex.
30) A paper coated by a surface sizing composition comprising: a)
starch; and b) a latex selected from: i) a latex having an acid
number less than 30; ii) a latex having an average particle size of
from about 20 to about 100 nanometers, and a surfactant
contribution from the latex of less than about 20% (w/w) based on
the weight of the latex; iii) a latex having a glass transition
temperature of from about 25 to about 65.degree. C., wherein the
surface sizing composition further comprises an alkenylsuccinic
anhydride; or iv) a latex, wherein the surface sizing composition
further comprises an alkenylsuccinic anhydride and wherein (A) the
alkenylsuccinic anhydride and latex are mixed in a low shear
process, (B) the alkenylsuccinic anhydride and latex are mixed in
an in-line mixer, or (C) the surfactant contribution from the latex
in the surface size composition is less than 20% (w/w) based upon
the weight of the latex.
Description
FIELD OF THE INVENTION
[0001] This invention relates to latexes for sizing paper in
surface sizing processes, and to the use of latexes to improve the
performance of alkenylsuccinic anhydrides when used as internal and
surface sizing agents.
BACKGROUND OF THE INVENTION
[0002] Fine papers produced for use in office printers and high
speed photocopiers must meet demanding physical and aesthetic
criteria. The paper must have a good appearance and feel, and at
the same time it must be durable and provide a receptive surface
for receiving ink from such printers and copiers. The process by
which the paper is sized during production can have a tremendous
impact on the performance of the paper. Paper sizing typically is
accomplished in one of two methods: (1) "internal sizing" or "wet
end" sizing accomplished by mixing the sizing composition with a
pulp slurry before sheet formation, and (2) "surface sizing" which
is accomplished by adding sizing agents to a surface of a paper
sheet that has been formed and at least partially dried.
[0003] Sizing agents are typically categorized either as reactive
sizing agents or non-reactive sizing agents, depending on whether
they form covalent bonds by reaction with the hydroxyl groups in
cellulose. Non-reactive sizing agents that are commonly applied in
surface sizing operations include starch and other polymeric sizes
such as copolymers of styrene and vinyl monomers. Reactive sizing
agents that are commonly applied in internal sizing processes
include alkenylsuccinic anhydrides, alkyl ketene dimers, and
rosin.
[0004] Varnell, in U.S. Pat. No. 6,051,107, discloses a process for
surface sizing paper using size compositions that contain polymer
latexes. The latexes have a glass transition temperature of
-15.degree. C. to 50.degree. C., an acid number of 30 to 100, and
an average particle size of 50 to 200 nanometers, preferably 80 to
150 nanometers. The patent does not disclose the concentrations of
surfactant used in the production of these latexes. The examples in
the patent disclose various commercially available latexes that are
at least 100 nanometers in size. The patent indicates that the
paper is preferably internally sized with one of various known
internal sizing agents, and that the latex is preferably admixed
with a starch or starch derivative before being applied to the
surface of the paper.
[0005] Cenisio et. al. in U.S. Pat. No. 6,162,328, discloses a
process for surface sizing paper by applying a surface sizing
composition comprising starch, a non-reactive sizing agent, and a
reactive sizing agent. Useful reactive sizing agents identified in
the patent include ketene dimers and multimers, alkenylsuccinic
anhydrides, organic epoxides, acyl halides, fatty acid anhydrides
and organic isocyanates. The patent identifies two groups of
non-reactive sizes that are used in the process: (1) those that are
insoluble in water at pH less than about 6, and soluble at a pH
above 6, and (2) those insoluble in water at pH's greater than
about 6 and preferably having a primary glass transition
temperature (T.sub.G) of less than about 100.degree. C.
[0006] Alkenylsuccinic anhydrides (sometimes hereinafter denoted
"ASA") are widely used paper sizing agents. However, they do not
disperse well and typically require significant make-down
conditions in a high energy mixer before being converted into
aqueous emulsions that can be applied to paper, which increases the
capital and operating costs of the system. In addition, make-down
emulsification must typically be performed in the presence of a
surfactant which is detrimental to the ultimate sizing performance.
Indeed, an alkenylsuccinic anhydride sold by Bayer Chemicals, sold
under the trade name Baysize I, is sold with surfactant already
present to aid in this mixing. Alkenylsuccinic anyhdrides are
generally not used in surface sizing operations because they
interfere with toner fusion onto the paper.
[0007] EP 0 644 205 of Brinkley et al. discloses a method of
producing nanolatexes that are less than 100 nanometers in size in
reduced-surfactant environments. The document proposes numerous
uses for the nanolatexes, including wood preservatives, polymer and
metal coatings, water proofing textile sizes, inks, and paper
making. EP 0 659 929 of Brinkley discloses similarly sized
nanolatexes specifically designed for textile sizing
operations.
[0008] It is an object of the invention to provide novel
non-reactive sizes giving improved sizing performance in paper
surface sizing processes.
[0009] It is another object of the invention to provide novel
latexes in the nanoparticle size range exhibiting improved sizing
performance.
[0010] Another object of the present invention is to improve the
sizing performance of fine papers in terms of water absorbance and
ink penetration.
[0011] Yet another object of the present invention is to provide
improved processes for internal and surface sizing of paper by
reducing the amount of surfactant present in chemical sizing
agents.
[0012] Still another object of the invention is to improve the
adhesion of toner that is applied to paper that has been surface
sized by the addition of alkenylsuccinic anyhdride to the surface
of the paper.
SUMMARY OF THE INVENTION
[0013] It has surprisingly been discovered that latexes having a
low acid number exhibit improved sizing performance when applied to
paper in surface sizing operations. In particular, it has
surprisingly been discovered that latexes that have an acid number
below 30, when applied to paper in a surface sizing operation,
improve the performance of the paper by decreasing the water
absorption of the paper, and by decreasing the penetration of ink
into the paper. Thus, in one embodiment the invention provides a
method of making paper comprising (a) providing an aqueous pulp
suspension; (b) sheeting and drying the aqueous suspension to
obtain paper; (c) contacting the paper with a size composition
comprising a latex having an acid number less than 30; and (d)
drying the paper to obtain sized paper.
[0014] It has further been discovered that the performance of
latexes as surface sizing agents can be improved by reducing the
size of the latex to below about 100 nanometers. The improved
performance can be seen especially when the latex is prepared in a
low-surfactant environment, that minimizes the quantity of
surfactant that is introduced to the surface sizing composition.
Thus, in another embodiment the invention provides a method of
making paper comprising: (a) providing an aqueous pulp suspension;
(b) sheeting and drying the aqueous suspension to obtain paper; (c)
contacting the paper with a size composition comprising a
dispersion of latex particles having an average particle size of
from about 20 to about 100 nanometers, and a surfactant
contribution from the latex of less than about 20% (w/w) based on
the weight of the latex; and (d) drying the paper to obtain sized
paper.
[0015] It has further been discovered that when a latex and
alkenylsuccinic anhydride are both applied as surface sizing
agents, the toner fusion of the resulting paper can be improved by
employing a latex having a glass transition temperature within a
preferred range. Thus, in still another embodiment the invention
provides a method of making paper sized with an alkenylsuccinic
anhydride having improved toner fusion comprising: (a) providing an
aqueous pulp suspension; (b) sheeting and drying the aqueous
suspension to obtain paper; (c) contacting the paper with a surface
size composition comprising an alkenylsuccinic anhydride and a
latex having a glass transition temperature of from about 25 to
about 65.degree. C.; and (d) drying the paper to obtain sized
paper.
[0016] It has further been discovered that the required make-down
of alkenylsuccinic anhydrides into an aqueous emulsion can be
reduced by dispersing the alkenylsuccinic anhydrides in the
presence of a latex. The reduced make-down requirements decrease
the amount of shear that must be applied to the alkenylsuccinic
anyhdrides to effect the make-down, allow the alkenylsuccinic
anhydrides to be mixed in a sizing composition in an in-line mixer,
and also reduce the amount of surfactant that must be added to the
alkenylsuccinic anyhdrides to accomplish the make-down. Latexes can
thus improve the process economics of any process in which an
alkenylsuccinic anhydride is applied as a sizing agent, as well as
the performance of the alkenylsuccinic anhydride due to the reduced
concentration of surfactant in the alkenylsuccinic anhydride,
whether the alkenylsuccinic anhydride is applied as a surface
sizing agent or an internal sizing agent. Thus, in another
embodiment the invention provides a method of making paper sized
with an alkenylsuccinic anhydride comprising: (a) providing an
aqueous pulp suspension; (b) sheeting and drying the aqueous
suspension to obtain paper; (c) contacting the aqueous suspension
or paper with an internal or surface size composition comprising an
alkenylsuccinic anhydride and a latex; and (d) drying the paper to
obtain sized paper, wherein (i) the alkenylsuccinic anhydride and
latex are mixed in a low shear process, (ii) the alkenylsuccinic
anhydride and latex arc mixed in an in-line mixer, or (iii) the
surfactant contribution from the latex in the surface size
composition is less than 20% (w/w).
[0017] In another embodiment the invention provides a method of
making a size composition comprising (a) providing an aqueous latex
dispersion, and (b) mixing ASA with the aqueous latex dispersion in
an in-line mixer and/or under low shear.
[0018] Further embodiments relate to surface sizing compositions,
and to paper coated with such surface sizing compositions, in which
the surface sizing composition comprises:
[0019] a) starch; and
[0020] b) a latex selected from:
[0021] i) a latex having an acid number less than 30;
[0022] ii) a latex having an average particle size of from about 20
to about 100 nanometers, and a surfactant contribution from the
latex of less than about 20% (w/w) based on the weight of the
latex;
[0023] iii) a latex having a glass transition temperature of from
about 25 to about 65.degree. C., wherein the surface sizing
composition further comprises an alkenylsuccinic anhydride; or
[0024] iv) a latex, wherein the surface sizing composition further
comprises an alkenylsuccinic anhydride and the alkenylsuccinic
anhydride and latex are mixed in an in-line mixer or a low shear
process.
[0025] The polymer latexes may be made from a variety of monomers
and combinations of monomers known to form latexes through emulsion
polymerization, but preferably comprise a blend of residues from
the following three monomers: (1) styrene, (2) an alkyl acrylate or
methacrylate, and (3) an ethylenically unsaturated carboxylic
acid.
BRIEF DESCRIPTION OF THE FIGURES
[0026] FIG. 1 is a graphical plot of data from the surface sizing
experiments of example 4 illustrating the effect of nanolatex
particle size on HST.
[0027] FIG. 2 is a graphical plot of data from the surface sizing
experiments of example 4 illustrating the effect of nanolatex
particle size on Cobb absorption.
[0028] FIG. 3 is a graphical plot of data from the surface sizing
experiments of example 5 illustrating the effect of nanolatex acid
number on HST.
[0029] FIG. 4 is a graphical plot of data from the surface sizing
experiments of example 5 illustrating the effect of nanolatex acid
number on Cobb absorption.
DEFINITIONS
[0030] The term nanolatex, when used in this document, means a
dispersion or emulsion of latex particles having an average
particle size of from about 10 nanometers to about 100 nanometers.
The term "latex" refers to an aqueous emulsion of natural or
synthetic rubber or plastic capable of forming a film when dried on
a surface, having properties that are characteristic of colloidal
dispersions obtained through emulsion polymerization such as
particle sphericity and Gaussian size distributions. Latexes useful
in the present invention preferably have a particle size of less
than about 1000 nanometers, more preferably less than about 500
nanometers, still more preferably less than about 200 nanometers,
and most preferably are within the nanolatex size range.
[0031] A "surface size" or "surface sizing agent" means a size or
agent that provides, upon addition to paper at a size press in
combination with a starch typically used as a surface size, at the
levels disclosed herein, an increase of sizing as measured by the
Hercules Sizing Test (HST) method over the same paper treated with
only starch at the same level.
[0032] The term alkyl, as used herein, unless otherwise specified,
refers to a saturated straight, branched, or cyclic, primary,
secondary, or tertiary hydrocarbon, typically of C.sub.1 to
C.sub.12, and specifically includes methyl, ethyl, propyl,
isopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl,
isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl,
cyclohexylmethyl, 3-methylpentyl, 2,2-dimethylbutyl, and
2,3-dimethylbutyl. The alkyl group can be optionally substituted
with one or more moieties selected from the group consisting of
hydroxyl, carboxy, carboxamido, carboalkoxy, acyl, amino,
alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic
acid, sulfate, phophonic acid, phosphate, or phosphonate, either
unprotected, or protected as necessary, as known to those skilled
in the art, for example, as taught in Greene, et al., "Protective
Groups in Organic Synthesis," John Wiley and Sons, Second Edition,
1991, hereby incorporated by reference.
[0033] The term lower alkyl, as used herein, and unless otherwise
specified, refers to a C.sub.1 to C.sub.5 saturated straight,
branched, or if appropriate, a cyclic (for example, cyclopropyl)
alkyl group. The lower alkyl group can be optionally substituted in
the same manner as described above for the alkyl group.
[0034] The term "alkenyl," as referred to herein, and unless
otherwise specified, refers to a straight, branched, or cyclic
hydrocarbon of C.sub.2 to C.sub.12 with at least one double bond.
The alkenyl group can be optionally substituted in the same manner
as described above for the alkyl group.
[0035] The term aryl, as used herein, and unless otherwise
specified, refers to phenyl, biphenyl, or naphthyl, and preferably
phenyl. The aryl group can be optionally substituted with one or
more moieties selected from the group consisting of hydroxyl, acyl,
amino, halo, carboxy, carboxamido, carboalkoxy, alkylamino, alkoxy,
aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid,
phosphate, or phosphonate, either unprotected, or protected as
necessary, as known to those skilled in the art, for example, as
taught in Greene, et al., "Protective Groups in Organic Synthesis,"
John Wiley and Sons, Second Edition, 1991.
[0036] The term aralkenyl, as used herein, and unless otherwise
specified, refers to an aryl group as defined above linked to the
molecule through an alkyenl group as defined above. The aralkyl
group can be optionally substituted with one or more moieties
selected from the group consisting of hydroxyl, carboxy,
carboxamido, carboalkoxy, acyl, amino, halo, alkylamino, alkoxy,
aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid,
phosphate, or phosphonate, either unprotected, or protected as
necessary, as known to those skilled in the art, for example, as
taught in Greene, et al., "Protective Groups in Organic Synthesis,"
John Wiley and Sons, Second Edition, 1991.
[0037] "Particle size" means the volume average median size of
particles in an emulsion or dispersion as measured by photon
correlation spectroscopy. The standard deviation of the particle
size is preferably within about 50%, 40%, or 30%.
DETAILED DISCUSSION
[0038] In one aspect the invention provides latexes and their use
as surface sizing agents. They are applied to paper in a paper
making process that comprises: (a) providing an aqueous pulp
suspension; (b) sheeting and drying the aqueous suspension to
obtain paper; (c) contacting the paper with a surface size
composition that comprises a latex of the present invention; and
(d) drying the paper to obtain sized paper. In preferred
embodiments the latex of the present invention is defined by one or
more of the following three criteria, in any combination: (1) acid
number, (2) glass transition temperature, and/or (3) particle size
and surfactant concentration.
[0039] In one particular embodiment the surface sizing composition
comprises a latex having an acid number less than 30. In various
embodiments, the acid number can be from 0 to about 25, 0 to about
20, to about 10, 0 to about 7, 0 to about 5, or 0 to about 3.
[0040] While the pH of the aqueous pulp suspension is important to
the ultimate performance of the sizing composition in most paper
making operations, a distinct advantage of the present invention is
that the sizing process can be practiced over a wide range of pH
systems. This is a consequence of the low acid number of the
latexes and their reduced dependence on pH for effectiveness. Thus,
the invention can be practiced in systems in which the pH ranges
from about 3 to about 9, from about 4 to about 5, from about 5 to
about 6, from about 6 to about 7, and from about 7 to about 8, or
any combination thereof.
[0041] In another particular embodiment, which has been found
especially useful for improving toner adhesion, the latex has a
glass transition temperature of from about 25.degree. C. to about
65.degree. C. This embodiment is preferred when surface sizing
compositions that also include an ASA are employed in the paper
making process. In various embodiments the glass transition
temperature of the latexes of the present invention is from about
25 to about 65.degree. C., from about 30 to about 60.degree. C.,
from about 35 to about 55.degree. C., from about 40 to about
50.degree. C., or about 45.degree. C.
[0042] In another particular embodiment the latex has an average
particle size of from about 20 to about 100 nanometers. In other
embodiments the average particle size of the latexes is from about
25 to about 90 nanometers, from about 30 to about 90 nanometers,
from about 30 to about 80 nanometers, from about 40 to about 80
nanometers, or from about 40 to about 70 nanometers.
[0043] These particle sizes are preferably present in the presence
of minimal surfactant concentrations. In this context, the
surfactant concentration refers to the quantity of surfactant that
is employed in the emulsion polymerization process to manufacture
the latex, relative to the quantity of latex produced in the
polymerization step. The latex is preferably prepared in a solution
comprising from about 1 to about 20% (w/w) surfactant, from about 1
to about 12% (w/w), from about 1 to about 8% (w/w) surfactant, from
about 1 to about 5% (w/w) surfactant, or from about 1 to about 3%
(w/w) surfactant, based upon the weight of latex produced in the
polymerization step. The sizing compositions of the present
invention are frequently described as having a "surfactant
contribution from the latex." This means that the latex is emulsion
polymerized in the presence of the recited quantity or proportion
of surfactant. Exemplary processes for producing nanolatexes in the
presence of low concentrations of surfactant are disclosed in the
examples herein below, and in EP 0 644 205 of Brinkley et al., the
disclosure of which is hereby incorporated by reference.
[0044] It has further been discovered that the required make-down
of alkenylsuccinic anhydrides into aqueous emulsions can be reduced
by dispersing the alkenylsuccinic anhydrides in the presence of a
latex. The reduced make-down requirements decrease the amount of
energy or shear that must be applied to the ASAs to effect the
make-down, and also reduce the amount of surfactant that must be
added to the ASAs, whether the ASA is applied as a surface sizing
agent or an internal sizing agent. A typical high shear mixing
system for a pure ASA would employ a rotor-stator type mixing head
operating in either batch or in-line style mixing modes at radial
tip speeds in excess of 4,000 feet per minute which accordingly
have very high horsepower demands dependent on the commercial
throughput requirements. Alternatively, a pressurized plate
homogenizer may be used when high mixing shear is needed. In the
presence of a latex, the make down of ASA can be performed in a
low-shear environment such as an in-line mixer, and/or in the
presence of low surfactant concentrations. Exemplary in-line mixers
include static mixers, in-line homogenizers, and the like which can
be fed with a standard centrifugal pump.
[0045] For purposes of this document, the term "low shear" means
the amount of shear imparted by an impeller-type mixer operating at
a radial tip speed of less than about 2,000 feet per minute, 1,500
feet per minute, or 1,000 feet per minute, and greater then about
250 or 500 feet per minute. Low shear mixing according to the
present invention is typically performed using an impeller-type
mixer at from about 500 to about 1,000 feet per minute.
[0046] Thus in another embodiment the invention provides a method
of making paper sized with an alkenylsuccinic anhydride comprising:
(a) providing an aqueous pulp suspension; (b) sheeting and drying
the aqueous suspension to obtain paper; (c) contacting the aqueous
suspension or paper with an internal or surface size composition
comprising an alkenylsuccinic anhydride and a latex; and (d) drying
the paper to obtain sized paper, wherein (i) the alkenylsuccinic
ahnydride and latex are mixed in a low shear mixer, (ii) the
alkenylsuccinic ahnydride and latex are mixed in an in-line mixer,
and/or (iii) the surfactant contribution from the latex is less
than about 20% (w/w) based on the weight of the latex.
[0047] In yet another embodiment the invention provides a method of
making a size composition comprising (a) providing an aqueous latex
dispersion, and (b) mixing ASA with the aqueous latex dispersion in
an in-line mixer. In another embodiment the invention provides a
method of making a size composition comprising (a) providing an
aqueous latex dispersion, and (b) mixing ASA with the aqueous latex
dispersion under low shear, thereby eliminating the need for using
a high shear rotor-stator mixer. In still another embodiment the
invention provides a method of making a size composition comprising
(a) providing an aqueous latex dispersion, and (b) mixing ASA with
the aqueous latex, wherein the surfactant contribution from the
latex is less than about 20% (w/w) based on the weight of the
latex. In a preferred embodiment, the aqueous latex dispersion
comprises starch, and is produced by mixing the latex dispersion
with a starch solution or dispersion, preferably in a continuous
mixing process that precedes the ASA mixing process.
[0048] When the latex is used as a dispersing aid as discussed
above, it generally is not limited by the technical specifications
that define the latex in other embodiments of the invention such as
acid number or particle size. Indeed, the only preferred
requirements are that the latex have an average particle size of
from about 10 nanometers to about 100 nanometers, or from about 30
to about 80 nanometers. Nevertheless, it will be understood that
the latex can further be characterized by any combination of (1)
acid number, (2) glass transition temperature, (3) particle size,
or (4) surfactant concentration, as discussed above.
[0049] The latexes of the present invention may be made from a
variety of monomers and combinations of monomers known to form
latexes through emulsion polymerization, but preferably comprise
copolymers (ternary, or higher) of styrene or substituted styrenes
with vinyl monomers and ethylenically unsaturated carboxylic acids.
Examples of such vinyl monomers include, but are not restricted to
maleic anhydride, acrylic acid or its alkyl esters, methacrylic
acid or its alkyl esters, itaconic acid, divinyl benzene,
acrylamide, acrylonitrile, cyclopentadiene and mixtures thereof.
Examples of ethylenically unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid or anhydride, fumaric
acid, itaconic acid and mixtures thereof. Latexes also include
polyurethanes and copolymers of ethylene with comonomers such as
vinyl acetate, acrylic acid and methacrylic acid.
[0050] The latexes of the present invention preferably comprise a
ternary blend of monomers selected from (1) styrene, (2) alkyl
acrylate or methacrylate, and (3) ethylenically unsaturated
carboxylic acids. The alkyl group of the alkyl acrylate or
methacrylate preferably comprises from 1 to 12 carbon atoms, more
preferably from about 1 to about 8 carbon atoms. Preferred alkyl
acrylates or methacrylates are methyl methacrylate, ethyl acrylate,
ethyl methacrylate, propyl acrylate, butyl acrylate, butyl
methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,
lauryl acrylate, lauryl methacrylate, and mixtures thereof.
[0051] Preferred ethylenically unsaturated carboxylic acids are
alpha, beta unsaturated carboxylic acids having a carbon number of
from about 3 to about 12, more preferably from about 3 to about 6
carbons. Exemplary ethylenically unsaturated carboxylic acids
include acrylic acid, methacrylic acid, maleic acid, fumaric acid
and itatonic acid. Preferred acids are acrylic acid and methacrylic
acid, with methacrylic acid being most preferred.
[0052] In various preferred embodiments the latex comprises:
[0053] a) From about 65 to about 45 monomeric parts alkyl acrylate
or methacrylate, from about 0 to about 10 monomeric parts
ethylenically unsaturated carboxylic acid, and from about 40 to
about 45 monomeric parts styrene;
[0054] b) From about 60 to about 50 monomeric parts alkyl acrylate
or methacrylate, and from about 0 to about 7 monomeric parts
ethylenically unsaturated carboxylic acid, and from about 40 to
about 45 monomeric parts styrene;
[0055] c) From about 58 to about 52 monomeric parts alkyl acrylate
or methacrylate, and from about 0 to about 5 monomeric parts
ethylenically unsaturated carboxylic acid, and from about 40 to
about 45 monomeric parts styrene; or
[0056] d) From about 57 to about 54 monomeric parts alkyl acrylate
or methacrylate, and from about 0 to about 3 monomeric parts
ethylenically unsaturated carboxylic acid, and from about 41 to
about 44 monomeric parts styrene.
[0057] In each of the foregoing embodiments, the monomeric parts of
ethylenically unsaturated carboxylic acid is preferably greater
than about 0.5, 1, or 2.
[0058] Alkenylsuccinic anhydrides, or "ASAs" useful in the
invention are composed of unsaturated hydrocarbon chains containing
pendant succinic anhydride groups. They are usually made in a
two-step process starting with an alpha olefin. The olefin is first
isomerized by randomly moving the double bond from the alpha
position. In the second step the isomerized olefin is reacted with
maleic anhydride. Typical olefins used for the reaction with maleic
anhydride include alkenyl, cycloalkenyl and aralkenyl compounds
containing from about 8 to about 22 carbon atoms. Specific examples
are isooctadecenylsuccinic anhydride, n-octadecenylsuccinic
anhydride, n-hexadecenylsuccinic anhydride, n-dodecylsuccinic
anhydride, i-dodecenylsuccinic anhydride, n-decenylsuccinic
anhydride and n-octenylsuccinic anhydride.
[0059] Alkenylsuccinic anhydrides are disclosed in U.S. Pat. No.
4,040,900, which is incorporated herein by reference in its
entirety, and by C. E. Farley and R. B. Wasser in The Sizing of
Paper, Second Edition, edited by W. F. Reynolds, Tappi Press, 1989,
pages 51-62. A variety of alkenylsuccinic anhydrides are
commercially available from Kemira OY under the trade name HYDRORES
AS 1000, from Bayer Chemicals under the trade name BAYSIZE or
ACCOSIZE, and from Nalco as NALSIZE. In addition, Albemarle
Corporation provides ASA to relabelers for sale under a variety of
trade names. Alkenylsuccinic anhydrides for use in the invention
are preferably liquid at 25.degree. C. More preferably they are
liquid at 20.degree. C.
[0060] When applied as surface sizing agents, the latexes of the
present invention typically will be applied along with starch or a
starch derivative in an aqueous solution or dispersion. Suitable
starches include oxidized, ethylated, cationic and pearl
starches.
[0061] The aqueous size composition preferably contains from about
1 to about 20 wt. % starch, more preferably from about 2 to about
15 wt. % starch, and even more preferably from about 3 to about 8
wt. % starch. The latex is preferably present in an amount of from
about 0.05 to about 2.5 wt. %, and more preferably from about 0.10
to about 2.0 wt. % (based on dry latex to dry starch). When ASA is
present, it is preferably present in an amount of from about 0.01
to about 5.0 wt. %, and more preferably from about 0.02 to about
4.0 wt. % (based on dry starch). The pH of the composition is
preferably from about 6 to about 9, preferably above about 7. Small
amounts of other additives may be present as well, such as optical
brighteners and defoamers. In a preferred embodiment EDTA is
present in the sizing composition to improve the physical pumping
stability of the latex, in an amount of from about 2 to about 10
wt. % (based upon the weight of the latex particles).
[0062] The amount of aqueous size composition applied to the paper
is preferably sufficient to yield paper coated by from about 0.02
wt. % to about 0.8 wt. % latex, on a dry basis based on the weight
of the dry sheet of paper, more preferably from about 0.03 wt. % to
about 0.5 wt. %, and most preferably from about 0.05 wt. % to about
0.1 wt. %. The amount of starch applied to the sheet is generally
from about 0.5 to about 8 wt. %, more preferably from about 1 to
about 6 wt. %, and most preferably from about 2 to about 5 wt. %,
on a dry basis based on the weight of the dry sheet of paper. When
ASA is applied either as an internal or surface sizing agent, it is
preferably present in an amount of from about 0.01 to about 1.0 wt.
%, more preferably from about 0.02 to about 0.5 wt. %, and most
preferably from about 0.03 to about 0.3 wt. %, on a dry basis based
on the weight of the dry sheet of paper.
[0063] The aqueous pulp suspension of step (a) of the process is
obtained by means well known in the art, such as known mechanical,
chemical and semichemical, etc., pulping processes. Normally, after
the mechanical grinding and/or chemical pulping step, the pulp is
washed to remove residual pulping chemicals and solubilized wood
components. Either bleached or unbleached pulp fiber may be
utilized in the process of this invention. Recycled pulp fibers are
also suitable for use.
[0064] The sheeting and drying of the pulp suspension is carried
out by methods well known in the art. A variety of materials can be
added to the aqueous pulp suspension before it is converted into
paper, including wet strength resins, internal sizes, dry strength
resins, alum, fillers, pigments and dyes. In a preferred embodiment
the sheet is internally sized with any conventional internal sizing
agent before being sheeted and dried. Exemplary internal sizing
agents include rosin sizes, ketene dimers and multimers, and
alkenylsuccinic anhydrides. In a preferred embodiment the internal
size is cured before surface sizing agents are applied to the
paper. ASAs are preferred because of their high curing ability.
[0065] Methods and materials utilized for internal sizing are
discussed by E. Strazdins in The Sizing of Paper, Second Edition,
edited by W. F. Reynolds, Tappi Press, 1989, and C. E. Farley and
R. B. Wasser in The Sizing of Paper, Second Edition, edited by W.
F. Reynolds, Tappi Press, 1989.
EXAMPLES
[0066] Standard Methods
[0067] Cobb is a measure of water absorption and is actually the
quantity of water absorbed by one square meter of the treated
paper. Lower Cobb values are better since they indicate less water
absorption. This test method is described in TAPPI Standard T
441.
[0068] The Hercules Size Test, an art-recognized test for measuring
sizing performance, is described in Pulp and Paper Chemistry and
Chemical Technology, J. P. Casey, Ed., Vol. 3, p. 1553-1554 (1981)
and in TAPPI Standard T530. The Hercules Size Test determines the
degree of water sizing obtained in paper by measuring the change in
reflectance of the paper's surface as an aqueous solution of dye
penetrates from the opposite surface side. The aqueous dye
solution, e.g., naphthol green dye in 1% formic acid, is contained
in a ring on the top surface of the paper, and the change in
reflectance is measured photoelectrically from the bottom
surface.
[0069] For all of the examples below, the paper used for sizing was
prepared in advance, stored, and then treated on a laboratory
puddle size press with the materials described. In all cases the
base paper had no treatment applied at the size press during its
manufacture. The application of materials at the size press
consisted of dissolving starch in water by stirring and heating to
about 95.degree. C. for at least 20 minutes or alternating heating
in a sealed container in a microwave oven then stirring on a
magnetic stirrer until homogeneous. The starch solution was then
kept at 60.degree. C. until used, usually within one hour. The
sizing materials were mixed with the starch for a few minutes and
then added to the nip of two rollers on the puddle size press.
[0070] The untreated paper was fed through the rollers twice to
apply the solution in the nip to the paper. The amount of solution
applied to the paper by a specific starch solution under specific
conditions was determined and used to set the level of additives in
the starch solution to give the desired level of paper
treatment.
[0071] Immediately following the application of the size press
composition, the papers were dried on a drum dryer heated at
120-130.degree. C. The papers were then conditioned and tested.
Example 1
[0072] In a glass polymerization reactor equipped with
heating/cooling source and controls, stirrer, metering device for
liquid substances, input opening for N.sub.2 sparge addition, and
reflux condenser, 16.3 gm of sodium laurel sulfate (30% solids) is
placed in 443.3 gm demineralized water. This mixture, stirred and
under a constant N.sub.2 sparge, is heated to 182.degree. F. and
the temperature allowed to stabilize at this set point. A solution
of 0.0333 gm ammonium persulfate in 36.09 gm demineralized water is
added to the reaction media, which is held 10 minutes while the
temperature re-stabilizes at 182.degree. F. Starting
simultaneously, two solutions are dosed into this preparation over
a period of 2.25 hours. Solution 1 consists of 0.100 gm ammonium
persulfate dissolved in 41.9 gm demineralized water. Solution 2
consists of 84.1 gm styrene, 1.39 gm n-dodecyl mercaptan, 58.8 gm
methyl methacrylate, 49.17 gm butyl acrylate, and 3.92 gm
methacrylic acid. 1.0 hours after the start of these concurrent
solutions being fed into the reaction zone, a third solution of
122.7 gm demineralized water is started to finish simultaneously
with the other two additions. After termination of the dosages,
stirring is continued at 182.degree. F. for an additional 30
minutes. Cooling is applied to the reactor, and 32.84 gm
demineralized water is added. When the reactor contents are at
<75.degree. F., sufficient ammonium hydroxide diluted with
demineralized water is added to adjust the solution pH to 7.0-7.5.
The final product is a microlatex with a solids content of
.about.22.4%, acid value of .about.2.85, Tg of .about.45.degree. C.
(.about.113.degree. F.) and a particle size of .about.50 NM as
measured by light scattering methods.
Example 2
[0073] The method of example 1 was followed except that Feed
Solution 2 contained 84.1 gm styrene, 1.38 gm n-dodecyl mercaptan,
53.69 gm methyl methacrylate, 54.28 gm butyl acrylate, and 3.93 gm
methacrylic acid. The final product is a microlatex with a solids
content of .about.22.4%, acid value of .about.2.85, Tg of
.about.40.degree. C. (.about.104.degree. F.) and a particle size of
.about.50 NM as measured by light scattering methods.
Example 3
[0074] The method of example 1 was followed except that Feed
Solution 2 contained 84.1 gm styrene, 1.38 gm n-dodecyl mercaptan,
63.69 gm methyl methacrylate, 44.28 gm butyl acrylate, and 3.93 gm
methacrylic acid. The final product is a microlatex with a solids
content of .about.22.4%, acid value of .about.2.85, Tg of
.about.50.degree. C. (.about.122.degree. F.) and a particle size of
.about.50 NM as measured by light scattering methods.
Example 4
[0075] In this example the effect of nanolatex particle size on
surface sizing performance was determined. A series of experiments
was performed using a nanolatex produced according to the
procedures set forth in examples 1-3. The nanolatex was applied to
paper in the surface sizing process described above. The acid
number of the nanolatexes was held constant at 2.9. Particle sizes
ranging from 20 to 160 nanometers were applied at 1, 2, 4, and 8
wet pounds per ton (wherein a wet pound is the equivalent of about
one fourth of a dry pound).
[0076] Sizing performance was evaluated according to HST and Cobb
absorption test protocol. Experimental results are tabulated in
Table 1. The effect of particle size on HST is plotted in FIG. 1.
The effect of particle size on Cobb absorption is plotted in FIG.
2.
Example 5
[0077] In this example the effect of nanolatex acid number on
surface sizing performance was determined. A series of experiments
was performed using a nanolatex produced according to the
procedures set forth in examples 1-3. The nanolatex was applied to
paper in the surface sizing process described above. The size of
the nanolatexes varied from about 35 to about 60 nanometers. The
acid number of the nanolatexes varied from about 0 to about 30. The
particles were applied at 1, 2, 4, and 8 wet pounds per ton
(wherein a wet pound is the equivalent of about one fourth of a dry
pound).
[0078] Sizing performance was evaluated according to HST and Cobb
absorption test protocol. Experimental results are tabulated in
Table 1. The effect of acid number on HST is plotted in FIG. 3. The
effect of acid number on Cobb absorption is plotted in FIG. 4.
1TABLE 1 Particle 0.25 lb per ton 0.5 lb per ton 1 lb per ton 2 lb
per ton Size (nm) Acid # Cobb60 Cobb30 HST HST Cobb .sub.45 Cobb
.sub.60 HST Cobb .sub.45 HST Cobb .sub.60 Starch 61.36 41.59 21.1
23 2.9 43.5 37.76 28.5 29.15 45.00 41.04 32.30 32.93 50.25 29.26 28
2.9 44.9 40.7 31.9 36.98 31.25 45.44 40.10 41.13 66.13 24.57 59 2.9
39.23 26.31 44.6 34.03 30.18 42.78 56.98 24.48 69.13 23.69 87 2.9
57.05 31.82 27.8 29.98 40.43 44.09 34.83 36.94 47.65 26.05 164 2.9
61.64 55.15 14.8 14.55 54.03 68.73 19.03 62.18 28.00 59.87 60 0.04
32.47 31.88 39.2 31.63 27.54 42.02 45.08 26.69 66.35 24.15 46 10
45.44 31.89 30.5 33.03 42.98 43.28 38.48 33.13 60.38 29.25 35 30
57.02 50.48 10.5 16.58 59.02 58.12 21.73 59.95 33.28 58.38
[0079] The present invention may be embodied in other specific
forms without departing from the spirit or essential attributes
thereof and accordingly reference should be made to the appended
claims rather than the foregoing specifications as indicating the
scope of the invention.
* * * * *