Note: Descriptions are shown in the official language in which they were submitted.
vCA 02269648 1999-04-22
Ref. No. 5011 ; ' .~ ' .
Coated Printing Paper and Method of Manufacture
Technical Fietd
This invention relates to a coating composition for a novel high brightness,
high
gloss printing paper and to a method of manufacturing the novel high gloss
printing
paper.
Background of the Invention
The use of calcium carbonate, both natural ground and precipitated) to
increase
brightness in coating compositions far printing paper is well known in the
art. In Europe,
relatively high levels of calcium carbonate are routinely used in coating
compositions.
High levels of calcium carbonate, however, can lead to a variety of printing
problems
such as ink rub off, sheet marking and tail picking. Most coating compositions
use 80%
by weight or less in an effort to minimize these problems. Precipitated
calcium
carbonates are also used to reduce these printing problems because they are
less
abrasive than ground calcium carbonates. In addition, coatings containing high
levels of
calcium carbonate are generally restricted to matte, lightweight coated or
rotogravure
papers. In the United States, size press solutions are formulated for use with
clay
coatings and tend to worsen the printing problems when used with coatings
containing
high levels of calcium carbonate.
Hollow sphere plastic pigments, each particle containing a single distinct
internal
void, are promoted by the manufacturers as useful for improving a wide variety
of paper
properties, such as paper gloss, print gloss, opacity and smoothness. They can
also be
used to increase bulk with reduced coat weights. The use of hollow sphere
plastic
pigments with high levels of calcium carbonate is not known.
It is an object of the invention to provide a printing paper that exhibits
high
brightness and high gloss coupled with minimized printing problems.
It is still another object of the invention to provide a method of
manufacturing a high
gloss printing paper.
Summary of the Invention
The invention provides a glossy printing paper comprising a paper substrate
coated
on at least one surface with a layer of coating composition comprising at
least 80 parts
precipitated calcium carbonate and at least 5 parts hollow sphere plastic
pigment, parts
based on 100 parts by weight of total pigment. Preferably the coating
composition
comprises 80 to 92 parts precipitated calcium carbonate and 6 to 12 parts
hollow
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sphere plastic pigment. The invention further provides a glossy printing paper
wherein
the layer of coating composition includes titanium dioxide pigment. The
invention also
provides a glossy printing paper wherein the layer of coating composition
comprises
less than 6 parts clay pigment. Preferably the dried coat weight of the
coating
composition is 8.9 to 16.3 g/m2 (6 to 11 1b/3300 ft2)) the hollow sphere
plastic pigment is
composed of an acrylic styrene copolymer with an average diameter of
approximately
1.0 Nm and a void volume of 55%, and the precipitated calcium carbonate has a
median particle size of approximately 0.6 Nm, a surtace area of approximately
10 mZ/g,
and an aspect ratio of 2:1 to 3:1.
The invention further provides a method of making a glossy printing paper by
applying a layer of coating composition to at least one surface of a paper
substrate, the
coating composition comprising at least 80 parts precipitated calcium
carbonate and at
least 5 parts hollow sphere plastic pigment, drying the coated substrate, and
calendering the dried coated substrate. The method may also incorporate the
other
coating compositions described.
Other objects and advantages of the invention will be apparent to those
skilled in
the art from the following detailed description of preferred embodiments of
the
invention.
Description of Preferred Embodiments of the Invention
The glossy printing paper of the present invention is made by coating a paper
substrate with a coating composition comprising at least 80 parts precipitated
calcium
carbonate (hereinafter PCC) and at least 5 parts hollow sphere plastic
pigment, based
on 100 parts by weight of total pigment.
The use in combination, in accordance with the invention, of at least 80 parts
PCC
and at least 5 parts hollow plastic pigment unexpectedly produced a printing
paper with
superior quality characteristics and with substantially improved printability.
The
combination provides improved coating-ink interaction, ink absorption)
fountain solution
absorption as well as a smooth uniform surface with high gloss and high
brightness.
The resulting printed image has high ink gloss, high ink uniformity and low
microgloss.
The printing paper of the invention also exhibits excellent blister
resistance. The
improved runnability and printability of the paper is demonstrated in the
substantially
eliminated tail picking, marking and scuffing.
The coating composition of the invention comprises at least 80 parts by weight
of
PCC and at least 5 parts by weight of hollow sphere plastic pigment. Examples
of
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suitable PCC's include Albaglos L and Albaglos S, manufactured by Specialty
Minerals,
Inc. The PCC preferably has a median particle size of approximately 0.6 Nm and
a
surface area of approximately 10 m2/g. Most preferably, the PCC has an aspect
ratio
range of 2:1 to 3:1.
Suitable hollow sphere plastic pigments, each particle containing a single
distinct
internal void, are available from Rohm & Haas Company, such as Ropaque HP-1055
(with an average particle size of 1.0 Nm, a void diameter of 0.82 Nm, and a
void volume
of 55%), OP-96 (average particle size 0.5 Nm, void diameter 0.38 Nm, and void
volume
43%) and HP-91 96 (average particle size 1.0 Nm, void diameter 0.80 Nm, and
void
volume 50%). Preferably, the hollow sphere plastic pigment has an average
particle
diameter of approximately 1.0 Nm and a void volume of approximately 55%. Most
preferably, the hollow sphere plastic pigment is composed of an acrylic
styrene
copolymer.
The coating composition of the invention can further comprise less than 6
parts by
weight clay. Those skilled in the art will know that the use of clay in
coating
compositions will decrease the brightness while improving other properties. In
contrast,
addition of clay in the present invention unexpectedly also decreased paper
gloss and
other final product attributes. The desired final product attributes will
determine the
quantity of clay used in these coating formulations. Examples of suitable
clays include
2o Astra-Plus, available from ECC1, and Ansilex 93, available from Engelhard
Corporation.
Preferably, the coating compositions of the invention further comprise natural
or
synthetic non-clay pigments, alone or in a mixture. Examples of suitable
pigments
include titanium dioxide, both anatase or rutile forms, aluminum hydroxide,
satin white,
silica, organic pigments etc. It is to be understood that these pigments are
listed by way
of example and the pigments used for this invention are not limited to those
listed. Most
preferably, the non-clay pigment is titanium dioxide. An example of a suitable
anatase
titanium dioxide is TiONA-A2000, available from SCM Chemicals.
The preferred coating composition comprises 80 to 92 parts PCC and 6 to 12
parts
hollow sphere plastic pigment, parts based by weight of total pigment. For
products
requiring high opacity, the most preferred coating composition comprises 80 to
84 parts
PCC, 6 to 12 parts hollow sphere plastic pigment and 9 to 12 parts titanium
dioxide,
parts based by weight of total pigment. Otherwise, the most preferred coating
composition, balancing both final product quality and cost of production,
comprises 85
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CA 02269648 1999-04-22
to 92 parts PCC, 8 to 12 parts hollow sphere plastic pigment and less than 6
parts
titanium dioxide, parts based by weight of total pigment.
The coating compositions of the invention are suitable for both sheet and web
printing grades without modifications. Practitioners skilled in the art know
that coating
compositions generally must be modified for web grades because of the speeds
and
high temperatures involved in web printing. Web printing papers tend to have
lower
moisture and more porous coating layers to reduce blistering during drying.
The coating composition of the invention further comprises a binder system,
required for all paper coatings. Those skilled in the art will know that a
binder system
with starch will decrease brightness. It is preferred to use a latex binder
system with
minimum quantities of starch. Latex binders that can be used in the invention
include
acrylic, styrene-butadiene, styrene-acrylate, urethane, acrylonitrile,
carboxylated latices)
etc. It is to be understood that these binders are listed by way of example
and the
binders used for this invention are not limited to those listed. Preferably, a
blend of two
latex types, styrene-butadiene and styrene-acrylate, is used in the invention.
Practitioners skilled in the art know that coating formulations can include a
variety of
additives, such as dyes, fluorescent brighteners, dispersants, thickeners,
lubricants, pH
control agents, etc. The use of coating additives is determined by the final
product
attributes. It is to be understood that the invention is not limited to the
additive
2o components listed.
The paper substrate of the invention is obtained by conventional papermaking
techniques using any papermaking fibers. Preferably, the paper substrate will
be
woodfree. Those skilled in the art will understand that final product
attributes and
productivity factors will determine the particular mixture of papermaking
fibers used. In
addition, the substrate is preferably sized with a starch precoat.
The coating composition of the invention can be applied by a variety of
coating
technologies. Examples of coating applications include bent blade, bevel
blade, rod)
short dwell, curtain coating, air knife etc. Practitioners skilled in the art
will know that the
invention is not limited to these techniques. In addition, those skilled in
the art know that
3o modifications to the theology of the coating compositions of the invention
will be
necessary depending on the coating technique employed.
The most preferred method of applying the coating composition of the invention
is
with a bent blade coater at a dried coat weight of 8.9 to 16.3 g/mz (6 to 11
1b/3300 ftz)
per side. The invention, however, includes paper products coated on only one
side as
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well as products double-coated on one or both sides. Practitioners skilled in
the art will
know that both the rheology and applied coat weights will vary depending on
the final
product attributes desired. In addition, the coating operation can be in a
continuous in-
line operation with the papermaking operation.
The invention includes the finishing step of calendering the dried coated
paper. The
method of calendering the paper of the invention is not restrictive. The paper
can be
calendered as a separate step, on a stand alone calender or supercalender) or
can be
calendered in a continuous in-line operation with the papermaking operation
and/or the
coating operation.
1 o The following examples illustrate the invention and enable those skilled
in the art to
understand the invention. It shall be understood that the invention is not
limited to the
particular examples given below. Unless otherwise stated, all parts and
percentages are
by weight.
Table 1 lists the formulations and final product attributes of both invention
and
comparative examples. Examples 1 through 5 illustrate the present invention.
Examples
C 1 through C3 are listed for comparison. All coating compositions were mixed
in
laboratory size batches, with a final coating solids of 58-60%. Bodystock with
a basis
weight of 71.0 g/m2 (48 1b/3300 ftz) was coated on one side with each coating.
The final
coat weight was approximately 14.8 g/mZ (10 1b/3300 ftz). The coated and dried
2o samples were calendered in a laboratory calender, through one nip at high
temperature
and pressure. The tests were performed after the samples had conditioned for
24 hours
in a constant humidity of 50%.
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Table 1
1 2 3 4 5 C1 C2 C3
Formulations:
PCC 81 88 86 88 90 100 96.5 0
Hollow sphere8 6 8 8 6 0 3.5 0
lastic i
ment
TiOz 11 6 6 4 0 0 0 0
Clay 0 0 0 0 4 0 0 75
Ground 0 0 0 0 0 0 0 25
Calcium
Carbonate
Properties:
Brightness 92.8 94.0 93.8 92.0 91.3 93.5 94.4 86.3
75 Paper 80.7 76.0 81.0 81.0 73.1 50.0 50.0 81.1
Gloss
20 Ink Gloss66.0 69.0 68.5 73.0 57.3 30.4 28.0 60.5
Microgloss 273 272 270 320 400 189 230 505
Microgloss is a measure of point to point variation in gloss, which relates to
image
quality. It is measured using a 1.5 mm microgloss head in the Tobias Mottle
tester. The
lower the value, the more uniform the gloss of the surface.
The embodiments of the invention illustrated by the examples balance the
desired
final product attributes of high brightness, high paper gloss, high ink gloss
and low
microgloss.
While the preferred forms of the invention have been described and illustrated
in the
examples, variations will be apparent to those skilled in the art. The
invention is not
limited to these embodiments and modifications may be made without departing
from
the spirit of the invention or the scope of the appended claims.
It is claimed:
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