REVETEMENTS COULES LATEX/AMIDON POUR PAPIER

STARCH/LATEX CAST COATINGS FOR PAPER

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A non-proteinaceous binder is provided for cast coating
of paper which comprises three primary components; a modified
starch; a styrene-butadiene latex characterized by a particle
size of about 800 to about 1300 angstroms, a solids content of
between about 45.0 and about 47.0%, a maximum 200 mesh residue of
about 0.075 gms./900 mls., a pH of between about 3.8 and 4.8, a
maximum Brookfield viscosity of about 100, and a surface tension of
between about 43.0 and about 49.0; and a second styrene-butadiene
latex characterized by a particle size of about 1350 to about 1650
angstroms, a solids content of between about 47.0 and about 49.0%,
a maximum 200 mesh residue of about 0.05 gms./900 mls., a pH of be-
tween about 5.5 and 6.5, a maximum Brookfield viscosity of about
300 cps., and a surface tension of between about 49.0 and 55Ø
An aqueous aliquot portion of the composition is coated on a paper
substrate, pressed against a chromium heat roll and dried, thereby
providing a cast coating paper according to the invention.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composition of matter comprising a modified starch
of an acid hydrolyzed hydroxyethyl ether cornstarch, a dis-
persed styrene-butadiene polymer having a particle size of
from 800 to about 1300 angstroms and a solids content of be-
tween about 45.0 and about 47.0%, a maximum 200 mesh residue
of about 0.075 gms./900 mls., a pH of about 3.8 to about 4.8,
a maximum Brookfield viscosity of about 100 cps. and a surface
tension of about 43.0 to about 49.0, and a dispersed styrene-
butadiene polymer having a particle size of from about 1350
to about 1650 angstroms and a solids content of between about
47.0 and about 49.0%, a maximum 200 mesh residue of about 0.05
gms./900mls., a pH of between about 5.5 and about 6.5, a maxi-
mum Brookfield viscosity of about 300 cps., and a surface ten-
sion of from about 49.0 to about 55.0; said starch and said two
latexes being included in relative proportions of about 1:2:2
dry weight basis on said composition.
2. The improved composition of claim 1, which includes
0.5 parts of a hexametaphosphate as an inorganic dispersant.
3. The improved composition of claim 2, wherein said
hexametaphosphate is sodium hexametaphosphate or zinc substi-
tuted sodium hexametaphosphate.
4. The improved composition of any of claims 1 to 3,
which includes 0.7 parts of an aqueous sodium polyacrylate as
an organic dispersant.
5. The improved composition according to any one of
claims 1 to 3, which includes from 1.5 to 1.7 parts of sulfonated
castor oil as the release agent.

Description

1092737 CANADA
The present application is directed to an improvement
over the binder composition disclosed and claimed in our earlier
. application Serial Number 251,795 filed May 4, 1976.
. . .
. In our mentioned application, we have broadly dis-
closed components which when combined resulted in a binder com-
position particul~rly useful for cast surface coating of paper.
.
The present application discloses specific formNlations of
various components w~ich when admixed in the parts by weight
. hereinafter disclosed enhances the paper coating process by en- .
~ 10 suring drum release of the coatings without impairing the print-
~ ing quality of the paper, its press performance, its sheet
.,~ .
. gloss, its water resistance or folding properties.
`~ With the foregoing in mind, we provide in accordance
with the invention a composition of matter comprising a modified
~ lS starch of an acid hydrolyzed hydroxyethyl ether cornstarch, à
- dispersed styrene-butadiene polymer having a particle size of
from 800 to about 1300 angstroms and a solids content of between
` about 45.0 and about 47.0%, a maximum 200 mesh residue of about
0.075 gms./900 mls., a pH of about 3.8 to about 4.8, a maximum
Brookfield viscosity of about 100 cps. and a surface tension of
about 43.0 to about 49.0, and a dispersed styrene-buta-
diene polymer having a particle size of from about 1350 to
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lO9Z73'7
about 1650 angstroms and a solids content of between about
47.0 and about 49.0%, a maximum 200 mesh residue of about
0.05 gms./ 900 mls., a pH of between about 5.5 and about 6.5,
a maximum Brookfield viscosity of about 300 cps., and a sur-
face tension of from about 49.0 to about 55.0; said starch
and said two latexes being included in relative proportions
of about 1:2:2 dry weight basis on said composition.
We have now determined that an acid hydrolyzed
` hydroxyethyl ether cornstarch is suited to a cast coating
composition because it has reduced tendency to gel or retro-
; grade and because of its hydrophilic character. Preferably,
between about 3 and about 5 parts of the starch are included
i in the composition, calculated on a dry weight basis. The
starch is commercially available from American Maize Products
.~ .
Co.
Both latexes employed in the coating composition
include dispersed styrene-butadiene polymer. The particle
size of styrene-butadiene in one latex varies from about 800
to about 1300 angstroms, and the latex is characterized by a
solids content of between about 45.0 and about 47.0%, a maxi-
mum 200 mesh residue of about 0.075 gms./900 mls., a pH of
~` about 3.8 to about 4.8, a maximum Brookfield viscosity of about
-100, and a surface tension of about 43.0 to about 49Ø Styrene-
~ butadiene latices and their preparation are well known, and one
;- 25 such latex having the character and properties described herein
~ is a commercially available product of Dow Chemical Company.
s~ Preferably, from about 6 to about 8 parts of this latex are
employed in the coating composition, calculated on a dry weight basis.
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lO9'~q37
Tlle other latex includes dispersed styrene-butadiene
; polymer having a particle size varying from about 1350 to about
1650 angstroms. This latex is characterized by a solids content
of about 47.0 to about 49.0%, a maximum 200 mesh residue of about
0.05 gms./900 mls., a pH of between about 5.5 and about 6.5, a
maximum Broo~field viscosity of about 300 cps., and a surface
tension of from about 49.0 to about 55Ø The coating composition
preferably includes from about 6 to about 8 parts of this latex,
calculated on the dry weight basis.
As in our earlier application, the preferred form of
the coating composition includes an insoluble filler, an inorganic
polyphosphate dispersant, an organic dispersant; i.e. a poly-
acrylate dispersant, an oleaginous release agent and rosin
which promotes adhesion of the coating to a paper web, without
deleterious effect. The preferred insoluble filler is described
in our earlier application as constituting about 85 parts calcium
carbonate and about 15 parts #2 coating clay.
Preferred inorganic polyphosphate dispersants employed
herein are the hexametaphosphates. Among the st preferred hexa-
metaphosphates are sodium hexametaphosphate and zinc substituted
sodium hexametaphosphate which are respectively commercially avail-
able from Calgon Corporation and from Merck & Company. Preferably,
.~ . .
-` about 0.5 parts, calculated on the dry weight basis, of the in-
organic polyphosphate dispersant are employed in the composition.
As the .! ' organic dispersant we use an aqueous solution
of sodium polyacrylate which is the preferred polyacrylate.
Preferably about 0.7 parts, calculated on the dry weight basis,
; are employed. The sodium polyacrylate dispersants herein contem-
` plated are available from Rohm & Haas Company, Dow Chemical Com-
pany and Allied Colloids.
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lO9Z737
The preferred oleaginous release agent for our im-
proved composition is sulfonated castor oil. From about 1.5
to about 1.75 parts, calculated on the dry weight basis, of
the oleaginous release agent are preferably employed in the
coating composition.
The preferred rosin is an acidic thermoplastic
pentaerythritol rosin ester, and particularly the sodium salt
thereof. Such rosinsare commercially available from Hercules
Incorporated. In the most preferred embodiment of the inven-
tion about 1.0 parts of the rosin are employed in the composi-
tion.
As in our earlier application, the pH of the composi-
tion may be adjusted to the desired range by the addition of
ammonia thereto. As formulated, the coating composition prefer-
ably has a solids content of 55 to about 60%.
In the general preparation of the coating composition,the heretofore disclosed constituents may be added in any appro-
priate sequence to a sufficient amount of water to give the
desired total solids content and pH thereof.
'I ' .
-;/ 20 The examples that follow are merely exemplary of
specific embodiments of the invention, and are not otherwise in-
tended to limit the scope thereof. All parts are by dry weight
on the composition.
EXAMPLE I
A coating composition is formulated including 3 parts
~ acid hydrolyzed hydroxyethyl ether cornstarch, 8 parts of the
¦ latex including dispersed styrene-butadiene polymer of particle
size between 800 and 1300 angstroms, and 8 parts of the latex in-
3 cluding dispersed styrene-butadiene polymer of particle size be-
j 30 tween 1350 and 1650 angstroms.

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109;~737
EXAMPLE II
A coating composition is formulated including 4 parts
- acid hydrolyzed hydroxyethyl ether cornstarch, 8 parts of the
. latex including dispersed styrene-butadiene polymer of particle
size between 800 and 1300 angstroms, and 6 parts of the latex in-
cluding dispersed styrene-butadiene polymer of particle size be-
~ tween 1350 and 1650 angstroms.
`~ EXAMPLE III
~' A coating composition is formulated including 5 parts
^ 10 acid hydrolyzed hydroxyethyl ether cornstarch, 6 parts of the
:
latex including dispersed styrene-butadiene polymer of particle
'~ -~ size between 800 and 1300 angstroms, and 8 parts of the latex in-
i.~ ~ cluding dispersed styrene-butadiene polymer of particle size be-
. tween 1350 and 1650 angstroms.
The preferred formulation is that of Example III. With
that formulation, the drum release of the coatings is at maximum
efficiency.
` ~ In employing the formulations in the cast coating of
`~ papers, the aqueous coating composition is applied to a paper web
and pressed against a rotating heated chromium surface and then
dried in the manner described in the above incorporated patents.
By means of the above described coating compositions there are
obtained cast coated papers of high printing quality, press per-
formance, sheet gloss, water resistance, fold, and freedom from
curling.
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