Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02038511 2000-11-22
40004-1088A
DEIONIZED CLAY AND CALCIUM CARBONATE AND
PAPER COATINGS CONTAINING THE SAME
Background of the Invention
The present invention relates to a paper coating
composition which exhibits improved rheology and which is
capable of providing higher gloss. The compositions of the
present invention are characterized in that they are prepared
using a deionized clay and/or deionized calcium carbonate and
other low ionic strength components.
Paper coating compositions are widely used in the
paper industry to provide high grade printing surfaces. Among
the compositions which have been used are compositions
comprised essentially of a major proportion of a mineral or
organic pigment and a minor proportion of a binder in the form
of a latex of a film-forming polymer. Suitable pigments have
included finely divided clay, calcium sulfoaluminate also
known as satin white, oxides of titanium, aluminum, silicon
and zinc, calcium carbonate and microsized particles of high
softening point polymers which are insoluble in the binder.
Suitable binder polymers have been those which are film-
forming at ambient and higher temperatures. The coating is
spread over the paper surface by a roll coater, trailing
blade, air knife, brush or other known means, after which it
is dried and calendered.
Summary of the Invention
The invention is a low ionic strength kaolin clay or
ground calcium carbonate pigment that has been highly washed
to remove free salt, coatings containing these pigments, and
coating compositions containing the same. The resulting low
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40004-1088A
ionic strength pigment slurry has a reduced degree of
flocculation, smaller median particle size and increased
colloidal stability of the particles. The low ionic strength
pigment slurries have substantially improved rheology.
Coatings containing only low ionic strength pigments
and coatings using low ionic strength pigments as a
substantial component of the pigment portion (i.e., greater
than 30% based on pigment) display unique properties.
Compared to analogous compositions that do not contain low
ionic strength pigments, the coatings of the present invention
have substantially reduced viscosities that give them similar
rheological properties at 3 to 4% higher solids. Compared to
analogous compositions that do not contain low ionic strength
pigments, the coatings of the present invention when applied
to paper have substantially higher sheet gloss and porosity.
It has been found that coating compositions having
improved rheology and glossability can be obtained by using a
deionized clay or calcium carbonate in the coating
composition. The term "deionized" refers to a low ionic
strength clay or calcium carbonate which has been treated to
remove at least a portion of the ions it contains. The clay or
calcium carbonate starting material from which the ions are
removed is herein referred to as "untreated". It is important
to emphasize that in this context commercially available clays
are considered untreated. Typically the materials of the
present invention are deionized by the use of an ion exchange
resin or by multiple washes with deionized or distilled water.
It is well known that clay particle size
distribution, shape, and state of aggregation have a major
effect on the performance of a paper coating composition. It
was in an effort to understand more fully the effect of the
state of clay aggregation on paper coatings that the present
invention was discovered. This work involved an analysis of
the particle size distribution of the clay and required that
very dilute slurries (7% solids) of clays be prepared (more
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90009-1088A 2 ~ _:; ~ ,: a
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concentrated slurries could not be analyzed). In order to
determine whether the method of dilution from normal shipping
solids of 70% to the measurement solids of 7% affected the
particle size of the clay, samples were prepared which had
been diluted with deionized water or with the supernatant from
the suspended clay. This lead to the discovery that the
particle size distribution of a clay diluted with deionized
water was substantially different than that of a clay diluted
with its original suspending liquid (supernatant) containing
all the salts and dispersants present in the clay as supplied
by the manufacturer. Clays diluted with deionized water had a
much higher population of smaller particles, a narrower
particle size distribution and greater colloidal stability.
Part of the effect of deionizing the clay is to
eliminate or reduce flocculation and thereby reduce particle
size, however, it is only part of the effect. When coatings
are prepared from clays having comparable particle size which
are not deionized, gloss is not as high as it is for the paper
coatings of the present invention and theology is not as good.
In addition reducing particle size often decreases opacity and
brightness and increases viscosity; this does not occur in the
coating compositions of the present invention. Viscosity
decreases~and in many cases no decrease in opacity or
brightness is observed.
The low ionic strength clay of the present invention
is a kaolin clay slurry which has been highly washed to give
it substantially lower dissolved salt content than a
conventional clay. Slurries of this clay range from about 60
to 75% solids with a preferred range of about 70 to 72%. Clay
slurries in accordance with this invention are characterized
by a conductivities less than 1500 micromhos at 70% solids and
more preperably conductivities less than 1300 micromhos at 70%
solids. The conventional analog to this clay slurry has a
conductivity of greater than 3000 micromhos at 70% solids.
The low ionic strength of the liquid phase gives the clay
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40009-1088A ~ ~' ~~ ~~ ;:' -' ,i
slurry unique properties. The particles have a higher degree
of colloidal stability as measured by their zeta potential.
This increase in zeta potential causes aggregates that exist
in the parent clay slurry to dissociate, resulting in a more
monodispersed system of particles with a substantially reduced
median particle size. The low ionic strength clay slurry has
improved rheology as shown by substantially reduced high shear
viscosity and dilatancy. The improved rheology allows a low
ionic strength clay slurry to contain about 2% higher solids
than its conventional counterpart but have comparable
rheology. A dried clay made from the slurry is included in
this invention.
The low ionic strength ground calcium carbonate of
the present invention has been highly washed to give it
substantially lower dissolved salt content than a conventional
ground calcium carbonate slurry. Slurries of this material
contain 70 to 80% solids with the preferred range being 75 to
80% solids. Calcium carbonate slurries in accordance with the
invention are characterized by conductivities less than ?00
micromhos at 70% solids and preferably less than 500
micromhos. The low ionic strength of the liquid phase gives
the ground calcium carbonate slurry unique properties. The
particles have a higher degree of colloidal stability as
measured by zeta potential. This increase in zeta potential
causes aggregates that exist in the parent calcium carbonate
slurry to dissociate. resulting in a more monodispersed system
of particles with a substantially reduced median particle
size. The low ionic strength ground calcium carbonate slurry
has improved rheology as shown by substantially reduced high
shear viscosity and dilatancy. The improved rheology allows a
low ionic strength ground calcium carbonate slurry to contain
1 to 2% higher solids than its conventional counterpart but
have comparable rheology. A dried calcium carbonate made from
the slurry is included in this invention.
The coating compositions of the present invention are
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CA 02038511 2000-11-22
40004-1088
advantageous because for comparable clay or calcium carbonate
concentrations, they provided higher gloss and they can be
used at higher solids. When applied to optically flat black
glass plates, which are used as an ideal substrate to reflect
the properties of a pigment or a coating without interference
from surface roughness, up to a 20 point improvement in gloss
was obtained. On paper, not only can higher gloss be
achieved, but comparable gloss levels can be obtained with
less calendering.
Accordingly, the present invention provides a coating
composition which, in its simplest form comprises deionized
clay or deionized calcium carbonate and a latex. The
compositions of the present invention will also generally
include those additives commonly used in paper coatings such
as dispersants, defoamers, pH modifiers, lubricants and other
binders like starch.
In accordance with a preferred embodiment of the
invention the deionized clay or deionized calcium carbonate is
used in combination with a latex having a low ionic strength.
Such latexes can be manufactured to have low salt and free
surfactant content, or can be prepared by treating
commercially available latexes with an ion exchange resin to
remove ions therefrom.
The present invention also provides slurries of
deionized clays and deionized calcium carbonates and the
deionized clays and calcium carbonate itself.
Detailed Description of the Invention
Clays may be provided as calcined, non-calcined,
predispersed, non-predispersed or physically delaminated
clays. Representative clays for use in the present invention
include Ultragloss*90 and Ultrawhite*90 sold by Engelhard
Minerals & Chemicals Corporation, Edison, N.J. 08817;
Hydragloss 90, Hydratex, and Hydrafine sold by J.M. Huber
Corporation, Menlo Park, N.J. 08837; and Nuclay; and Lustra
* Trademark
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40004-1088A ~ ~~'' ~' fv ~' v
Clay sold by Freeport Kaolin Company, a division of Freeport
Sulphur Company, New York, N.Y. 10017. No. 1, No. 2 and fine
and delaminated clays may be used.
Other conventional pigments can also be employed
along with the paper coating clay. These include titanium
dioxide, talc, Satin White, hydrated alumina commonly employed
as an extender for titanium dioxide, and calcium carbonate
(which is preferably deionized). These pigments are used in
amounts up to 305 by weight.
These clays and calcium carbonate may be deionized by
suspending a normal process clay filtercake or calcium
carbonate in deionized water, filtering the suspension,
followed by 0-3 repetitions of the suspension-filtration
process and finally deflocculation with about .3~ sodium
polyacrylate having a molecular weight between 1000 and 5000.
Alternatively other traditional dispersants can be used. It
is anticipated that other techniques for deionization will
also be useful.
The clays and calcium carbonate can also be deionized
by preparing a slurry of the clay, water and an ion exchange
resin and screening out the ion exchange resin after the clay
is deionized. This is shown in Example 9.
About 7 parts by weight water per 3 parts clay or
calcium carbonate are used. Washing is typically conducted at
room temperatures but higher or lower temperatures are also
effective. Washing is continued until the desired level of
deionization is achieved.
The deionized clays are characterized by both the
median particle size, modal particle size, and the size
distribution. These measurements are made by sedimentation
and expressed as a mass distribution using the Sedigraph 5100
particle sizer. Samples are diluted to test solids of 7$
using their own supernatant. Further, deionized clays are
defined by changes in particle size and distribution relative
to the non-deionized clays. Typical results are shown in
Table 1.
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40004-1088A
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Table 1
Typical Change in Clay Particle Size
Due to Deionization
Fine Delaminated
#1 Clav#2 Clay Clav Clay
Median Particle Size
Microns
Nondeionized 1.15 1.10 0.56 1.55
Deionized 0.38 0.45 0.26 0.60
Percent Reduction 67 53 54 60
Percent Less than
0.5 Microns
Nondeionized 17 15 45 9
Deionized 60 59 75 45
Percent Increase 253 260 67 400
The latexes used in the present invention may also be
selected from among those latexes commonly used in this art.
Particularly preferred are the resins which exhibit primarily
elastomeric properties, often described as the rubbery
polymers, such as the copolymers styrene-butadiene and
styrene-isoprene. or either of them slightly carboxylated by
incorporation of from 3 to 10% acrylic acid. Suitable
commercial examples are the latexes sold by Dow Chemical
Company No. 316, 620, and 690. More generally, the latexes
may be latexes of homopolymers or copolymers of C4-C10 dienes
such as butadiene, 2-methylbutadiene, pentadiene-1.3, etc.
The copolymers may be copolymers of vinyl monomers such as
styrene, acrylic acid and its esters, methacrylic acid and its
esters, nitriles and amides. If desired, rubbery polymer
latices may be blended with minor proportions of latices of
hard or resinous polymers having a high MFT such as
polystyrene, polyacrylonitrile, polymethyl methacrylate,
copolymers of the monomers of these resinous polymers such as
styrene-acrylonitrile resins and resinous copolymers of these
monomers with other copolymerizable monomers such as
copolymers of styrene with butadiene in which styrene forms
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40004-1088A
more than 70 weight % of the polymer. Preferred are latices
in which the copolymer is composed of about 0-60 weight % of a
C4-C6 conjugated diolefin, 40 to 99% of a styrene and 0.1-5%
of a polymerizable unsaturated monomer having a polar group
such as a carboxyl group in its structure. The solid content
of the latex is generally 20 to 55% by weight.
These latexes can be manufactured using additives
which are designed to minimize ionic strength or they can be
prepared by treating commercially available latexes to reduce
their ionic strength.
A technique which may be used to deionize or reduce
the ionic strength of a commercial latex involves diluting the
latex to about 34% solids with deionized water and adding a
mixed anionic and cationic ion exchange resin such as Dow MR3
or Rohm and Haas Amberlite 150 at a dry weight ratio between
0.1:1 and 2:1 to the latex. After about 1 to 2 hours the ion
exchange resin can be strained from the latex.
It has been found the pH of the latex is preferably
about 6.0 to 10Ø
Paper coating compositions in accordance with the
invention may also contain a hydrocolloid. The hydrocolloid
may be deionized as well. Conventional paper coating
hydrocolloids may be used such as starch, polyvinyl alcohol,
proteins.
The starch optionally used in the present invention
may also be selected from those starches commonly used in this
art. Suitable commercial examples include all commercial
starches praduced for the paper industry. These starches are
preferably deionized by diluting to 5% with deionized water
and filtering once or diluting to 10-20% and filtering 2 or 3
times. The slurry need only be mixed for 5-10 minutes before
filtering or can be separated by gravity settling. The starch
or hydrocolloid has a preferred conductivity of less than 0.5
millimhos at 20% solids and 23°C.
Addition of 1-10% deionized starch to the deionized
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40009-1088A
clay has been found to partially protect the clay from
reflocculation by later additives.
The deionized clay may be treated with a dispersing
agent to disperse the deionized clay in the latex.
Conventional non-ionic dispersing agents such as polyacrylates
may be used for this purpose.
The compositions of the present invention may contain
about 60 to 85% by weight pigment (of which 50 to 100% is
deionized clay and/or calcium carbonate), about 1 to 40 and
preferably 3 to 20% latex and about 0 to 5% of starch or other
hydrocolloid. Clay and calcium carbonate are often used
together in a ratio of clay to calcium carbonate of about 7:1
to 1:3.
In addition to the pigment and latex binder
components, other usual and known additives may be included in
the paper coating composition as required. Other binders,
e.g., proteins, viscosity modifiers, e.g., sodium
polyacrylates, defoamers, pH modifiers (preferred coatings
have a pH of 6 to 10), lubricants, and other film-forming
latices, etc. may be included.
Clay containing coating compositions in accordance
with this invention (i.e., the combination of clay, latex, and
any pigment, starch, or other additive) preferably have a
conductivity less than 1.3 millimhos at 23°C and 60% total
solids. Calcium carbonate containing coating compositions
preferably have a conductivity less than 0.8 millimhos at 23°C
and 60% solids.
Desirable properties are achieved when the latex and
hydrocolloid as well as the clay and calcium carbonate are
deionized. However, because deionization of the latex and
hydrocolloid adds expense to the composition this may not
always be desirable commercially. Accordingly, in the most
typical embodiments of the invention the clay and calcium
carbonate will be deionized, however, further improvements in
Theology and gloss may be achieved if commercially desirable
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40009-1088A
by deionizing the latex and hydrocolloid.
The compositions of the present invention can be
applied to conventional base stocks using known paper coating
techniques and optionally calendered. The compositions can be
applied in conventional coat weights.
The present invention .is illustrated in more detail
by the following non-limiting examples.
Example 1
Three samples of deionized clay were prepared.
Sample A was a regular #1 clay which was centrifuged then the
sediment was resuspended in deionized water. The
centrifugation-resuspension process was repeated twice. A
polyacrylate dispersant was added to the resulting clay until
minimum low shear viscosity was reached.
Sample B was prepared by triple washing a regular #1
clay with deionized water. A polyacrylate dispersant was
added to the resulting clay until minimum low shear viscosity
was reached.
Sample C was prepared by mixing a high brightness #1
clay with a mixed ion exchange resin at a 1:0.1 dry-on-dry
ratio. The mixture was blended for 2 hours then screened
through a 65 mesh screen to remove the beads. A polyacrylate
dispersant was added to the resulting clay until minimum low
shear viscosity was reached. The conductivity, Hercules and
Brookfield viscosity of each clay is shown in Tables 2 and 3.
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40004-losaA
Table 2
Clav Sample A
Conductivity Hercules Visc. Hrookfield Visc.
(millimhos) (1100 RPM) (100 RPM)
Solids Regular DeionizedRegular Deionized Regular Deionized
75.0 2.25 .130 5457 2465 910 1360
74.5 2.25 .122 3697 1200 363 960
74.0 2.25 .122 3757 1118 292 798
73.5 2.25 .122 2122 104 245 694
73.0 2.22 .122 1592 83 217 592
72.5 2.22 .122 1226 52 192 482
72.0 2.22 .122 160 42 170 404
71.5 2.22 .122 118 35 152 350
71.0 2.20 .122 76 28 140 298
70.5 2.20 .122 49 28 120 250
70.0 2.20 .122 42 28 109 222
This example clearly shows that deionized clay has
greatly reduced high shear viscosity and this difference is
increased as solids level is raised. Since high shear
viscosity is the parameter most important to pumpability of a
slurry, the deionized clay can be shipped and handled at 2%
higher solids without detrimentally affecting the pumpability.
Table 3
Clay Samp le B Clay Samp le C
UndeionizedDeionizedUndeionized Deionized
Solids 70. 1 70.1 70.0 70.0
Conductivity 1.65 0.61 1.41 0.59
Brookfield Viscosity 146 268 106 188
(100 RPM)
Hercules Viscosity 278 222 3016 1190
(1100 RPM and ABOB)
The results in Table 2 and 3 clearly show that high
shear viscosity is reduced by deionizing a clay whether the
clay is deionized by multiple centrifugation and resuspension,
multiple washing, or by use of an ion exchange resin.
Example 2
Clay
Hydrafine clay, a No. 1 kaolin clay from J.M. Huber
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CA 02038511 2000-11-22
40004-1088A
Corporation, was deionized by washing twice with deionized
water.
Latex
x
Dow RAP316 latex (a styrene butadiene latex available
from Dow Chemical Company) was diluted to 34% solids and
blended with an ion exchange resin (Dow MR3, a mixed cationic
and anionic resin available from Dow Chemical Company) in a
dry weight ratio of 1:1. The mixture was mixed for 4 hours
and filtered through a 65 mesh screen to remove the ion
exchange resin. The resulting latex contained 30~ solids and
the pH was adjusted to 8.5 with ammonia.
Starch
Coating compositions were prepared by preparing a
clay suspension containing 74~ solids and blending this with
the starch before the latex addition to provide the coating
compositions shown in Table 4:
Table 4
Sample No. (wt.~)
1 2
Control Invention
Clay (Hydrofine) g7 _
Deionized Clay (Hydrofine) - g7
Latex (Dow RAP 316) 10 5
Deionized Latex (Dow RAP 316) - 5
Starch (PG 250) 3 3
Solids 61.4 61.4
The conductivity of each coating was measured using a
YSI Model 32 conductance meter having a range of 0.01 to
20,000 microohms. All testing was done at room temperature.
The coatings were drawn down on an optically smooth black
glass to measure the optical properties. Gloss was measured
using a Hunter 75 degree gloss meter.
The results obtained are provided in Table 5.
* Trademark
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40004-108$A
Table 5
Sample #
1 2
Conductivity 1.97 1.26
Brookfield Viscosity 960 830
Hercules Viscosity 43.8 36.8
Gloss 36.2 46.0
The foregoing results clearly show that the paper
coating compositions of the present invention prepared with
deionized clay and deionized latex and deionized starch
exhibit higher gloss and better rheology than coatings
prepared without deionizing the clay and latex. The deionized
coating can be prepared at 4% higher solids and maintain equal
or better rheology.
Example 3
The coatings described in Example 3 were applied to
paper using a rigid blade coater. The rawstock was a wood-
free sheet, and the coater speed was 2000 feet per minute. A
precoat made up of a 50:50 blend of #2 clay and coarse calcium
carbonate was used. The resulting calendered and uncalendered
glosses are recorded in Table 6.
Table 6
Uncalendered Calendered
Control
As 8 lb/rm single coat 21.3 57.0
As 6 lb/rm topcoat 27.1 63.8
Sample #1
As 8 lb/rm single coat 25.3 60.4
As 6 lb/rm topcoat 35.5 69.8
Sample #2
As 8 lb/rm single coat 30.0 65.0
As 6 lb/rm topcoat 92.8 73.3
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40004-1088A
It can clearly be seen from these results that a
deionized coating (Sample ~2) gives an increase from 3-8
points of gloss when applied to uncoated or precoated paper.
Example 4
In the lab, 2000 g of a commercial spray dried ~1
clay was added to 857 grams of distilled water and mixed on a
Cowles mixer for 10 minutes. The resulting 70% solids slurry
was blended in a high speed blender 'for 2 minutes. A second
batch of slurry was made in an identical manner.
The first batch was diluted to 40% solids while under
a mixer and 200 g of a mixed cationic and anionic ion exchange
resin was added. The clay and resin were mixed for 2 hours.
After this time, the mixture was poured through a 100 mesh
screen to remove the resin. A polyacrylate dispersant was
added to the resulting slurry at a level of .3% based on dry
clay. About half of the resulting dispersed deionized clay
slurry was dried and added back to the remaining slurry to
create a 73% solids deionized clay slurry. This slurry was
used for comparison to the second batch of 70% ~1 clay slurry.
Two ground calcium carbonate slurries (90% less than
2 microns) were made at 76% solids using the method described
above. One of the slurries was diluted to 50% and the same
ion exchange resin was added on a 1:10 basis dry resin: dry
carbonate. After 2 hours of mixing, the slurry was screened
to remove the resin. A polyacrylate dispersant was added at
.015% based an dry carbonate.
A portion of the resulting dispersed deionized
calcium carbonate slurry was dried and added back to the
remaining slurry to produce a 78% solids deionized calcium
carbonate slurry. This slurry was compared to the other 76%
slurry of undeionized calcium carbonate.
These slurries were tested and the results are shown
in Tables 7 and 8. Particle size was measured using the
Sedigraph Model 5100. Zeta potential was measured using a
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40009-1088A
Lazer Z instrument. Samples for zeta
particle size and
potential measurement were diluted ng their
usi own
supernatant. These results show the deionized
that pigments
have reduced high shear viscosity can be increased in
and
solids and have comparable rheologythe conventional
to
pigment slurries. The reduction indicates
in particle size
deflocculation of the pigment slurries. occulation
This defl
is due to the increase in colloidalability cated by the
st indi
changes in zeta potential.
I0 Table 7
Evaluation of Deionized and ConventionalClay
and Calcium Carbonate Slurries
Hercules
Brookfield Visc. (cP)
Lcw Shear High Sheer
Visc. (cP) (A bob, Conductivity
Solids (100 rpmD 4000 rpm) (micromhos>
Commercial #1 Clay 70.1 153 198 1650
Deioniaed #1 Clay 70.0 222 43 650
71.0 4i7 69 710
72.0 539 198 750
73.0 832 1018 830
Ground
Calcium Carbonate 76.0 301 996 780
Deionized
Calcium Carbonate 76.0 263 167 600
77.0 359 465 630
78.0 553 1093 650
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40004-1088A
Table 8
Evaluation of Deionized and Convention Clav
and Calcium Carbonate Slurries
Zeta
Particle Size (u) Potential
% Solids (Modal) (Median) (mV)
Commercial #1 Clay 70.0 0.79 0.76 -50.8
Deionized #1 Clay 70.0 0.37 0.42 -63.3
Ground
Calcium Carbonate 76.0 1.18 0.94 -45.5
Deionized
Calcium Carbonate 76.0 1.07 0.83 -53.3
Example 5
Deionized clay and calcium carbonate slurries were
produced by the method described in Example 1. Deionized
latex was produced by diluting a styrene-butadiene latex to
40% solids and adding an ion exchange resin to latex at a 1:10
ratio. This mixture was stirred for one hour and filtered
through cheesecloth to remove the ion exchange resin. A
deionized polystyrene 3 plastic pigment was produced by the
same process. A deionized starch was produced by diluting an
uncooked commercial ethylated starch to 5% solids with
distilled water and then removing the water by filtration.
The resulting deionized starch was cooked by conventional
methods.
Five different coating formulations containing
various combinations of clay, titanium dioxide, calcium
carbonate, plastic pigment, latex and starch were made with
deionized and convention components. These coatings were
applied to optically smooth glass (an ideal substrate) and the
gloss of the dried films was measured. The results in Tables
9 and 10 show that in all cases, the coatings containing
deionized components had lower low shear viscosity and higher
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90004-1088A
gloss than their conventional analogs. Generally, high shear
viscosities were comparable. Coatings B, D, H and K show that
coatings with pigment systems that are only partially
deionized also show the described benefits.
Table 9
Evaluation of Deionized and
Coatings
Their Conventional Analogs gmentBlends
Containing Pi
A B C D E F
Commercial #1 Clay 82 62 80
Deionized #1 Clay 82 62 80
Titanium Dioxide 5 5 25 25
Plastic Pigment 7
Deionized Plastic Pigment 7
Styrene/Butadiene Latex 10 10 10
Deionized Styrene/
Butadiene Latex 10 10 10
Corn Starch 3 3 3
Deionized Corn Starch 3 3 3
Solids (%) 60 60 60 60 60 60
Conductivity (millimhos) 1.88 0.82 2.18 1.022.13 0.56
Brookfield Visc. (100 rpm) 912 509 1000 665 824 335
Hercules Visc.
(E bob, 6000 rpm) 31.3 32.7 28.9 59.133.3 26.2
Coating Gloss
(Ct Wt = 15 lb/rm) 28.2 54.6 30.3 51.238.0 63.4
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40004-1088A '~ 9~ ~ ~ ~ 4
Table 10
Evaluation of Deionized Coatings and
Their Analogs Containing Calcium Carbonate
G H I J K L
Commercial #1 Clay 77 27
Deionized #1 Clay 77 77 27 27
Ground Carbonate (90%<2 u> 10 10 60 60
Deionized Ground Carbonate
(90%<2 u) 10 60
Styrene/Butadiene Latex 10 10
Deionized Styrene/
Butadiene Latex 10 10 10 10
Corn Starch 3 3
Deionized Corn Starch 3 3 3 3
Solids (%) 60 60 60 60 60 60
Conductivity (millimhos) 2.05 0.85 0.74 1.08 0.77 0.59
Brookfield Visc. (100 rpm) 720 489 5?5 1174 691 424
Hercules Visa.
(E bob, 6000 rpm) 33.4 38.3 36.9 31.2 45.4 37.7
Coating Gloss
(Ct Wt = 15 lb/rm) 29.1 47.0 44.3 18.6 28.5 36.0
Example 6
A conventional clay based paper coating and its
deionized analog were prepared using the formulations
shown in
Table 11. These two coatings were applied to a wood-free
base
sheet with a rigid blade at 1500 feet per minute on
a high
speed pilot coater. Sheets of the coated paper were
supercalendered on a handsheet supercalender. The test
results in Table 11 show that the deionized coating
at 64%
solids has higher shear viscosity equivalent to its
convention
analog at 60.5% solids. In addition, the supercalendered
paper with the deionized coating has higher gloss with
improved smoothness and porosity.
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40004-1088A
Table 11
Comparison of a Deionized Clav Based
Coating and Its Conventional Analog
Values in the Table are percent of total dry weight
(coat weight of about 9 lb/rm)
Commercial Fine Clay 65
Deionized Commercial Fine Clay 65
Commercial #2 Clay 11
Deionized Commercial #2 Clay 11
Titanium Dioxide 4 4
Plastic Pigment 7
Deionized Plastic Pigment 7
Styrene/Butadiene Latex 12.7
Deionized Styrene/Butadiene Latex 12.7
Polyvinyl Alcohol 0.3 0.3
Lubricant 1.0 1.0
Crosslinker 0.15 0.15
Coating Solids (%) 60.6 64.2
Conductivity (micromhos) 2370 1060
Brookfield Viscosity, 100 rpm (cP) 688 2164
Hercules Viscosity, E bob. 6000 rpm (cP)18.9 19.4
Sheet Gloss 68.9 73.1
Smoothness (microns) 1.04 0.76
(Parker Print Surf, 20 kg)
High Pressure Porosity (sec/100 cc) 201.2 170.5
Example 7
A conventional calcium carbonate based paper coating
and its deionized analog were prepared using the formulations
shown in Table 12. These two coatings were applied to a wood-
free base sheet with a bent blade at 1500 feet per minute on a
high speed pilot coater. Sheets of the coated paper were
supercalendered on a handsheet supercalender. The test
results in Table 12 show that the deionized coating at 69%
solids has lower low shear viscosity and equivalent high shear
viscosity to its conventional analog at 67% solids. In
addition, the supercalendered coated sheet with the deionized
coating has higher gloss.
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40004-1088A ~'.~' .; ;.;i ~:~_
Table 12
Comparison of a Deionized
Calcium Carbonate
Based Coating and Its Conventional
Analog
Values in the Table are of total dry weight
percent
(coat weight of about 10 lb/rm)
Calcium Carbonate 50
Deionized Calcium Carbonate 50
Commercial #1 Clay 25
Deionized Commercial ~1 25
Clay
Titanium Dioxide 5 5
Plastic Pigment 7
Deionized Plastic Pigment 7
Styrene/Butadiene Latex 10
Deionized Styrene/Butadiene 10
Latex
Corn Starch 3.0
Deionized Corn Starch 3.0
Lubricant 1.0 1.0
Crosslinker 0.25 0.25
Solids (~) 67 69
Conductivity (micromhos) 2170 650
Brookfield Viscosity (100 2400 480
rpm)
Hercules Viscosity (E bob, 46.0 48.7
6000 rpm)
Sheet Gloss 60.5 63.7
Having described the invention
in detail and by
reference to preferred
embodiments thereof, it
will be apparent
that modifications and possible without
variations are
departing from the scope
of the invention defined
in the
appended claims.
What is claimed is:
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