Note: Descriptions are shown in the official language in which they were submitted.
113~84'~8
S P E C I F I C A T I 0 N
The present invention is concerned with aqueous
compositions for the coating of paper and cardboard for
photogravure printing, and the paper and cardboard coated
with such compositions.
It is well known that aqueous compositions for the
coating of papex and ca~dboard mainly contain pigments and
binding agents~ The most frequently used pigment is
mineral clay. Use may also be made, in small proportions
in relation to the mineral clay, of other pigments such
as calcium carbonate, titanium oxide, hydrargillite, talc
and barium sulphate. These pigments are dispersed in water,
generally in an alkaline medium and in the presence of
dispersing agents, the most prominent of which are
tetrasodium pyrophosphate, sodium hexametaphosphate and
polyacrylates of low molecular weight, in amounts of
between 0.2 and 0.5% by weight based on the pigments.
These pigments are fixed on the paper or cardboard by means
of binding agents. The binding agent generally used is an
aqueous dispersion of a synthetic polymer such as a co-
polymer of styrene and butadiene, an acrylic polymer or
a polymer of vinyl acetate, used either alone or mixed
with natural binding agents such as starches, proteins,
and casein, or synthetic binding agents such as polyvinyl
alcohols. It is also possible to use the aqueous disper-
sions in conjunction with products capable of improving
the water-retaining properties of the coating compositions,
examples of such products being carboxymethyl cellulose or
alginates.
Finally, the coating compositions may contain
various other ingredients: in particular, cross-linking
3 agents, anti-foaming agents, slip-inducing agents, bluing
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agents and coloran~s.
The paper or cardboard is coated with the aqueous
compositions by means of a coating machine based on any
one of various known techniques and involving various
arrsngements, among which may be mentioned those known
i~dus~rially under the names: air blade, size press,
Champion coating machine, Massey coating machine and the
t.railing spreader apparatus. After the paper or card-
board has been coated, it is dried.
Photogravure printing, in which the ink used is
liquid, does not require the use of a paper or cardboard
having a high dry-tear strength; the quantity of binding
agent to be used is smaller than in offset printing, and
generally lies within the range of 5 to 7 parts by weight
per 1-0 parts by weight of pigment.
The quality of the photogravure printing depends
upon the quantity of points missing on the print. In the
photogravure printing process, the ink in fact is con-
tained in small cavities, and it transfers to the paper
or cardboard by capillary action, which can take place
only if the zone surrounding each cavity is in perfect
contact with the paper or cardboard. It is therefore
important to use a paper or cardboard having very great
smoothness. A good method of evaluating the aptitude of
a paper or cardboard for receiving a photogravure print, .
and particularl~ of determining the risk of the occurrence
of missing points, is constituted by the heliotest which
will hereinafter be described.
The lower the qu~ntity of binding agent contained
in the paper or cardboard, the higher will be the gloss
3 obtained in calandering. It is therefore advantageous
1~684Z8
to use a film-forming constituent, the binding capacity
of which is as high as possible so that this constituent
can be used in the lowest possible quantity, it being
understood that it is necessary to use enough of the
constituent to prevent the paper or cardboard from
suffering the phenomenon of dusting during calandering,
printing or preparation of the prints.
According to the invention, the compositions
contain, as the principal film-forming constituent, an
aqueous latex of a copolymer of butadiene and of carboxy-
lized styrene, consisting of 41 to 45% by weight ofbutadiene, 45 to 57% by weight of styrene, and 2 to 10%
by weight of at least one unsaturated carboxylic ethylenic
acid, the particles of which have a diameter of between
0.08 and 0.14 microns.
By using the minimum quantity of film-form.ng
constituent, which performs the function of a binding
agent, the compositions forming the subject matter of the
invention enable coated paper or cardboard to be obatined
that has an adequate dry tear strength and is very suitable
for use in photogravure printing.
To enable the compositions of the invention to be
used in an efficient manner, the quantity of carboxylic
acid in the copolymer is in the range from 3 to 6% by
weight. The unsaturated carboxylic ethylenic acids used
in accordance with the invention include in particular
acrylic acid, methacrylic acid, itaconic acid and fum~ric
acid .
The following Examples are given to illustrate
the invention and provide comparative data.
,:
, - 3-
1~1684Z8
Examples l to 12
Aqueous coating compositions were prepared, and
a coating of 10 g/m2,in terms o~ dry substancè (dry solids
by weight), of each of the said composi~ions was applied
to a paper weighing 52 g/m2 with the aid of a coating
machine of the trailing spreader type. The coated paper
was dried in a drying tunnel ae a temperature of 100C and
then was calandered by four successive passes through two
rolls under a pressure of 80 kg/cm.
After drying and calandering, the coated paper was
conditioned at a temperature of 20C in an atmosphere having
a relative humidity of 65%, and the paper was then examined
for dry tear strength and suitability for use in photo-
gravure printing (heliotest), with the aid of the following
methods:
Dry-tear strength was determined on the IGT apparatus
designed by the Institute von Grafische Technik, ln which
the paper is adjusted to a selected value, and the speed
of which is increased until incipient tearing of the inked
coating was observed. Dry-tear strength was determined by
the value for the speed at which tearing begins. The ink
was the graduated absorption "3800" ink sold by Etablisse-
ments Lorilleux Lefranc.
Suitability for use in photogravure printing
(heliotest). Use was made of a half-tone roller on which
were provided caviti~s of varying sizes, and by means of
which, using the IGT apparatus, printing was carried out
on the paper under examination. The cavity size below
which transfer did not occur was then determined. The
smaller the size, the better is the printing. Since the
3 size of the cavities diminishes uniformly over the roller,
-4-
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the result of the measurement corresponds t~ a distance
over the printing zone. The greater the distance indicated,
the greater the suitability of the material for printing.
The distance is indicated in mm.
The following Table 1 gives the details of the
la~exes A, B, C, D, E, F, G, H, I, J, K and L at 50% dry
solids by weight of butadiene copolymers and of carboxylized
styrene, as used in Examples 1 to 12 respectively.
TABLE 1
_ . Butadienel Acids Styrenë Particle
1~ Example Latex by weightlby weight by weight diameter
% I % % micron
1 ~ . A 32 4 64 0.18 .
2 B 32 4 64 0.15
3 C 1 32 4 64 0.12 .
4 D ¦ 32 4 64 0 10
E ¦ 37 4 S9 0.18
6 F 37 4 59 _0.15 .
7 G 37 ¦ 4 59 0.12
8 H 37 4 59 0.10
.. .
I 43 4 _ 53 ~0.18
J 43 ~ 4 53 0.15
! .
11 K 43 ¦ 4 53 0.12 .
12 L ¦ 43 1 4 ¦ 53 0.1
.
1~8428
Table 2 shows the nature and the quantity by weight
of the solid constituents of the coating compositions
corresponding to each of the Examples. The coating compo-
sitions were adjusted to a pH-value of 8.5 by the addition
of ammonia. They were adjusted to contain 60% by weight
of dry substance. For each example, five tests were
carried out, corresponding to five different contents of
copolymer of butadiene and of carobylized styrene.
TABLE 2
1 ~ Test 1 Test 2 Test 3 Test 4
Kao in 100 100 100 100 100
Sodium pyrophosphaee 0.4 0.4 0.4 0.4 0.4
Copolymer o uta lene
and carboxylized styrene 3 4 5 6 7
Tables 3 and 4 below show the properties of th~
coated paper for each of the five tests on each of the
Examples 1 to 6 and each of the Examples 7 to 12 respec-
tively.
106~3428
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1(~684Z8
The aqtleous coating compositions that enable a
satisfactory quality of coated paper for use in photo-
gravure printing to be obtained are those for which, under
the test conditions herein used, the dry tear strength
is at least 40 cm/s, and the suitability for printing
(heliotest) is the best.
Examples 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 are
given for comparison purposes, Examples 11 and 12 are
in accordance with the invention. It will be seen that,
of the various latexes studied, only the latexes K and
L, used in Examples 11 and 12, enable aqueous compositions
to be obtained that result in a coated paper of satisfac-
tory quality for photogravure printing, even when only
three parts by weight of binding agent per 100 par~s by
weight of pigment is used.
