STARCH/LATEX CAST COATINGS FOR PAPER

COUCHES A BASE D'AMIDON ET DE LATEX POUR COUCHAGE A HAUT BRILLANT DU PAPIER

English Abstract

ABSTRACT OF THE DISCLOSURE
A non-proteinaceous binder for cast coating of paper
which is made up of three primary components: modified starch
and two latexes of carboxylated styrene-butadiene polymeric
materials. Paper coated with the binder, as well as a process
employing the binder in the cast coating of paper are described.

Claims

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:
1. A non-proteinaceous binder for cast surface
coating of paper which comprises from about 3-5 parts of a
modified starch selected from an ethylated, a cationic or a
high amylopectin modified starch and from two carboxylated
styrene-butadiene latexes which differ in the type and/or
amount of carboxylation, one of which is present in an amount
of 6 to 8 parts while the other is present in an amount of
5 to 12 parts, all parts being on a dry weight basis.
2. The binder of Claim 1 which in addition contains
an insoluble filler, an inorganic polyphosphate dispersant, an
organic dispersant, an oleaginous release material and a
pentaerythritol ester of rosin.
3. The binder of Claim 1, wherein about 5 parts of
modified starch and wherein 6 parts of one and 8 parts of the
other of the two carboxylated styrene-butadiene latexes are
present, calculated on the dry weight basis.
4. The binder of Claim 3, wherein the modified
starch is an ethylated starch.
5. Paper cast surface coated with the binder of
Claim 1.
6. In a process of making cast surface coated paper
the improvement which comprises employing the binder of
Claim 1.

7. A binder as claimed in Claim 1, comprising about
85 parts of calcium carbonate, about 15 parts of clay, about
0.5 part of inorganic polyphosphate dispersant, about 0.7 part
of organic dispersant, about 3-5 parts of modified starch,
about 6-8 parts of a butadiene-styrene latex, about 5-12 parts
of another butadiene-styrene latex, about 1.5 parts of an
oleaginous release agent and about 1.0 part of the sodium salt
of a pentaerythritol ester of rosin, said binder composition
having a pH of about 9.5-10.
8. The binder of Claim 7, wherein the modified
starch is an acid hydrolyzed hydroxyethyl ether cornstarch,
and the oleaginous release agent is oleic acid.

Description

09Z~736
The present invention relates to a non-proteinaceous
binder composition adapted for the cast coating of paper as
described, for example, in U.S. Patent Nos. 1,719,166 and
2,568,288 (Reissue No. 23,637).
Casein, a proteinaceous material, has been the
chief adhesivelcomponent in binder compositions for cast coating
of paper since the inception of this process. Attempts have
been made to circumvent the use of casein because of its high
cost and, at times, limited availability. Up to now, however,
3 lo because of the stringent requirements of a suitable binder for
cast coating of paper a suitable substitute for casein has not
been available. For example, one of the mzin requirements for
a suitable binder in the cast coating operation is sustained
drum release. In its simplest form the cast coating operation
compriseg applying an aqueous coating to a paper substrate.
The coating is pressed against a rotating heated chromium
surface. In the process, the coating must stick and conform
to the chromium surface while wet, but on drying must have auto-
releasing properties.
The binder composition should also yield a commercial
quality paper sheet of outstanding print quality, press perform-
ance, sheet gloss; water-resistance, fold, and freedom from
c~rling. It should also permit maximum drum speed in the coating
operation.
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With the foregoing in mind, we provide in accordance
with the invention a non-proteinaceous binder composition
adapted for cast surface coating of paper, characterized in
that the binder composition ~omprises modified starch, and two
carboxylated styrene-butadiene latexes which differ in the type
and/or amsunt of carboxylation.
The binder composition of the invention eliminates
~' the need for casein and thereby overcomes the problems inherent
in the use of casein as the adhesive component.
More specifically, the binder composition of the
~ invention may advantageously include the following ingredients
i in an aqueous medium, the parts being on a dry weight basis.
An insoluble filler such as a mineral filler
of about 85 parts calcium carbonate and
about 15 parts #2 coating clay;
about 0.5 parts of an inorganic polyphosphate
dispersant; ?
about 0.7 parts of an organic dispersan,t;
`, about 3-5 parts of a modified starch;
1 20 about 6-8 parts of Dow 650 Latex;
; about 5-12 parts of Dow XD-8388.02 Latex;
.f sufficient ammonia to impart a pH of 9.5-10;
about 1.5 parts to 1.75 of an oleaginous
release agent;
B 25 about 1.0 parts do ~ um salt of Pentalyn 856
The coating composition has a pH of about 9.5
to 10 and a total solids content of about 55 - 60%.
The calcium carbonate employed in the composition
advantageously comprises precipitated calcium carbonate with a
specific surface of 35,000 to 40,000 sq. centimeters/gram.
The No. 2 coating clay is of the kaolin type having a particle
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- size of 82% less than 2 microns. The inorganic polyphosphate
employed as a dispersant is sold under the trademark Calgon
and Calgon T by Merck and Company. Organic dispersants are
sold under the trad~mark Tamol 850 by Rohm & Haas, Dow XD-7321
by Dow Chemical Company, and Dispex N-40 by allied Colloids.
The modified starch is of the ethylated, cationic
or high amylopectin type, as for example,
1) Acid hydrolyzed hydroxyethyl ether cornstarch sold
under the trademarks Penford Gum and Pencote by
Penick and Ford, and Amizo 745-D by American Maize
Products Co., as an ethylated modified starch
2) Starch sold under the trademark Cato-Bond 485 by
National Starch as a cationic modified starch
gi 3) Starch sold under the trademark Amioca 85 by
National Starch as a high amylopectin modified
starch.
Carboxylated styrene-butadiene polymeric latexes
are sold under the trademarks Dow 650 I.atex and Dow
XD-8388.02 Latex. They differ in types and/or amounts of
carboxylation.
The oleaginous release agent is an oleaginous
~ material such as disclosed in U.S. Patent No. 2,568,288,
; issued September 18, 1951, and in column 3 line 39, to column
4, line 54, of Reissue Patent No. 23,637 and in the Examples
of said patent.
Pentalyn 856 is a pentaerythritol ester of rosin
sold by Hercules Chemical Company.
It is a feature of the invention that the
disadvantages attributable to the individual components
; 30 of the binder composition are offset or avoided by the
synergistic effect obtained by admixing the individual
binder components. Thus, while starch functions like
a thermosetting binder and aids casting drum release
and imparts ink attack resistance, it is not easily
.
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109Z736
waterproofed (a property a cast coating must have). On the
other hand, while Dow 650 has less than desired drum release
i properties, when combined with starch, it increases ink
attack resistance and also aids in waterproofing starch. As
to Dow XD-8388.02 while its sheet surface is poor, when combined
with starch and Dow 650, it imparts desirable release properties.
3 Accordingly, by using the three components within the range
specified, the undesirable properties of each component are
offset or avoided and the desired properties enhanced.
In the general preparation of the coating composition,
the above mentioned components are merely added to a sufficient
amount of water to give the desired total solids contents and
r pH of the finished coating preparation.
m e following are examples of specific embodiments
of the invention.
EXAMPLE I
In the formula set forth in the specification above
there are employed 3 parts Pencote ethylated starch sold by
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Penick and Fort (or the same amount of Amaizo 745-D ethylated
atarch sold by kmerican Maize Products Co.); 8 parts of Dow 650
Latex and 8 parts of Dow XD-8388.02 Latex.
EXAMPLE II
In the formula set forth in the specification above
there are employed 4 parts of Pencote ethylated starch (or the
same amount of Amaizo 745-D ethylated starch); 8 parts Dow 650
Latex and 6 parts of Dow XD-8388.02 Latex.
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EXAMPLE III
In the formula set forth in the specification above
there are employed 5 parts of Pencote ethylated starch (or
the same amount of Amaizo 745-D ethylated starch); 6 parts
of Dow 650 Latex, and 8 parts of Dow XD-8388.02 Latex.
The preferret formulation i8 that of Example III.
With this formulation the drum release of the coatings is at
maximum efficiency.
In employing the formulations in the cast coating
of paper, the aqueous coating composition is applied to a
paper substrate and pressed against a rotating heated chromium
surface and then dried in the manner described in the above
mentioned patents. By means of the above described coating
compositions there are obtained cast coated papers of high
~ 15 printing quality, press performance, sheet gloss, water
3 resistance, fold, and freed~m from curling.
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