Note: Descriptions are shown in the official language in which they were submitted.
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RECORDING MEDIUM WITH GLOSSY COATING CONTAINING ALUMINA
TECHNICAL FIELD OF THE INVENTION
The present invention relates to recording media
comprising alumina particles in the coating thereof,
compositions comprising such particles, and production
methods therefor.
BACKGROUND OF THE INVENTION
A surface coating is sometimes applied to a
recording medium in order to improve its printing
properties. For example, the coating can improve the
appearance, ink absorption, and/or image smear resistance
of the medium.
Surface coatings can be classified into two general
categories -- glossy coatings and non-glossy (matte or
dull) coatings. Glossy coatings are highly desirable, as
they are very smooth, and can impart a superior feel and
a photograph-like quality to a recorded image. However,
it remains a challenge to provide a glossy medium that
imparts superior printing properties to the medium (e.g.,
good ink absorption, good dye-fixing ability, good
waterfastness, and/or good resistance to image smear), in
addition to superior smoothness and gloss.
Gloss and dye immobilization (i.e., dye-fixing) can
sometimes be achieved by incorporating different types of
polymeric resins into a coating. For example, a gelatin,
a polyvinyl alcohol, a polyolefin resin, polyester resin,
polyamide resin, and/or polycarbonate resin can be used
to produce glossiness, while a cationic polymer (e.g.,
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polyvinylpyrrolidone) can be used to promote the surface
immobilization of an anionic dye. However, inks applied
to resin-coated recording media dry relatively slowly,
and often have an undesirable tendency to smear and rub
off. While some pigments such as certain treated kaolin
clays or treated calcium carbonates can immobilize dyes,
the overall absorptivity and rate of absorption are often
compromised.
Using a metal oxide pigment such as silica or
alumina can be advantageous in that they have good
absorptivity and also can produce an excellent coating.
Alumina is particularly advantageous in that its
particles naturally have a cationic surface (i.e., a
positive zeta potential). Since the vast majority of ink
dyes are anionic in nature, the cationic surface of
alumina imparts superior dye immobilizing properties to
coatings derived therefrom. Moreover, alumina also
imparts good ink absorption, good waterfastness, and good
image smear resistance, in addition to superior gloss,
smoothness, and brightness, to the coating.
Despite its advantages, the use of alumina presents
significant challenges in the recording medium coating
industry in that alumina is very difficult to process.
Unlike silica, which is typically amorphous, alumina is
crystalline, and can exist in various crystalline phases,
for example, alpha, or the transitional phases, for
example, gamma, delta, and theta phases. In addition,
long drying times are typically required in recording
medium coating which utilize low solids alumina
dispersions, making the overall coating process costly
and inefficient. Moreover, some forms of alumina require
a relatively high binder ratio (about 3:1 pigment to
binder ratio). The high binder demand of alumina
restricts the ratio of alumina particles (relative to
binder) that can be achieved in the coating, sacrificing
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desirable properties that could otherwise be imparted to
the coating by the alumina particles (e.g., drying time,
dye immobilization, waterfastness, image quality, and the
like). As such, the overall quality of the recording
medium can be limited.
Poor colloidal stability of alumina also seriously
limits the solids content that can be attained in coating
compositions used to make the recording media, thereby
placing an upper limit on coater productivity
(throughput), as drier demand can be excessive in order
to adequately dry the coating on the substrate. In a
commercial setting, such coating compositions are
produced from an initial alumina dispersion. The initial
dispersion is often manufactured in a separate facility
and shipped to the end user. Typically, the end user
processes the initial dispersion into a coating
composition, which is normally applied to a substrate
shortly after its production.
As dispersions with higher alumina solids content
have a greater tendency to gel or separate (i.e., the
solid settles out of the dispersion), low solids initial
dispersions are used. As such, the overall quality of
recording media is limited by the low alumina solids
content (e.g., in terms of porosity, dye immobilization,
image quality, or the like).
Accordingly there remains a need for an improved
recording medium comprising alumina particles, desirably
having a low binder demand and high porosity, as well as
an alumina-based coating composition and a method of
producing such a composition and recording medium. The
present invention provides such a recording medium,
coating composition, and methods of making them. These
and other advantages of the present invention, as well as
additional inventive features, will be apparent from the
description of the invention provided herein.
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BRIEF SUMMARY OF THE INVENTION
The present invention provides a recording medium
comprising a substrate having a glossy coating thereon,
wherein the glossy coating comprises a binder and alumina
particles that are aggregates of primary particles. The
coating of the recording medium of the present invention
comprises alumina particles that are aggregates of
primary particles, with pyrogenic or fumed alumina being
preferred.
The present invention further provides a coating
composition comprising alumina particles and a binder,
wherein the alumina particles are aggregates of primary
particles and the solids content of the alumina in the
coating composition is at least about 20 wt.%.
The present invention also provides a method of
preparing a coating composition. The inventive method of
preparing a coating composition comprises providing a
colloidally stable dispersion comprising water and alumina
particles, wherein the alumina particles are aggregates of
primary particles and the solids content of the alumina
particles in the dispersion is at least about 30 wt.%;
adding a binder to and, optionally, diluting the
colloidally stable dispersion, until a desired pigment to
binder ratio and overall solids content are obtained; and
optionally adjusting the pH with a suitable acid or base.
The present invention additionally provides a method
of preparing a recording medium. The inventive method of
preparing a recording medium comprises providing a
substrate; coating the substrate with the coating
composition of the present invention to produce a
substrate coated with a coating; optionally calendering
the coated substrate; and drying the coated substrate.
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In accordance with one aspect of the present invention
there is provided a recording medium comprising a substrate
having a glossy coating thereon, the glossy coating
comprising fumed alumina particles and a binder, wherein
the fumed alumina particles are aggregates of primary
particles and the glossy coating has a 75 specular gloss
of at least 15%.
In accordance with another aspect of the present
invention there is provided a method of preparing a coating
composition, the method comprising: providing a colloidally
stable dispersion comprising water and fumed alumina
particles, wherein the fumed alumina particles are
aggregates of primary particles and the solids content of
the fumed alumina particles in the dispersion is greater
than 20 wt.%; adding a binder to and, optionally, diluting
the colloidally stable dispersion; and optionally adjusting
the pH with a suitable acid or base.
In accordance with still another aspect of the present
invention there is provided a method of preparing a
recording medium, the method comprising: providing a
substrate; coating the substrate with the coating
composition of any of claims 10-15, to produce a substrate
coated with a coating; optionally calendering the coated
substrate; and drying the coated substrate.
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The coating composition of the present invention
dries quickly when applied to a substrate, to form a non-
tacky glossy coating.
5 BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates the electron micrograph of fumed
alumina aggregate particles used in the recording medium of
the present invention.
Fig. 2 illustrates a rheogram of an alumina dispersion
useful in preparing the coating composition and recording
medium of the present invention.
Fig. 3 illustrates two rheograms (A and B) of coating
compositions useful in preparing the recording medium of
the present invention.
Fig. 4 illustrates the change in contact angle over
time for a distilled water droplet applied to the recording
medium of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a recording medium
comprising a substrate having a glossy coating thereon,
wherein the glossy coating comprises a binder and alumina
particles that are aggregates of primary particles.
The inventive recording medium comprises a
substrate, which can be either transparent or opaque, and
which can be made of any suitable material. Examples of
such materials include, but are not limited to, films or
sheets of polymer resins (e.g., poly(ethylene
terephthalate)), diacetate resins, triacetate resins,
acrylic resins, polycarbonate resins, polyvinyl chloride
resins, polyimide resins, cellophane and celluloid, glass
sheets, metal sheets, plastic sheets, paper (e.g.,
cellulose paper, synthetic paper), coated paper (e.g.,
resin-coated paper), pigment-containing opaque films, and
foamed films. Polyester sheets and cellulose paper are
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preferred, with poly(ethylene terephthalate) sheets being
a preferred polyester.
The substrate used in the recording medium of the
present invention has a glossy coating thereon, which can
be of any suitable thickness. In particular, the coating
is preferably from about 1 m to about 50 m in
thickness, more preferably from about 5 m to about 40 m
in thickness, and most preferably from about 10 m to
about 30 pm in thickness. The recording medium of the
present invention provides excellent gloss and also has
good ink absorption, dye immobilization, a high rate of
liquid absorption, and overall liquid absorption
capacity. Moreover, the recording medium of the present
invention provides excellent image quality, particularly
when used in ink jet printing applications.
In certain embodiments of the present invention the
inventive recording medium comprises a substrate having
more than one layer of coating, which can be the same or
different. However, at least one of the coating layers
comprises alumina particles with properties as described
herein. For example, the recording medium of the present
invention can comprise a substrate coated with one or
more ink-receptive layers (e.g., comprising anionic
silica) and/or one or more resinous layers (e.g., a
glossy, laminated surface layer). Even when the
recording medium of the present invention comprises such
additional layers of coating, it has been found that the
above-described glossy coating comprising the alumina
particles described herein provides sufficient ink
absorption, dye immobilization, and gloss for the vast
majority of printing applications.
The coating of the recording medium of the present
invention comprises alumina particles that are aggregates
of primary particles, with pyrogenic or fumed alumina
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being preferred. Particles of pyrogenic alumina are
aggregates of smaller, primary particles. Although the
primary particles are not porous, the aggregates contain
a significant void volume, and are capable of rapid
liquid absorption. These void-containing aggregates
enable a coating to retain a significant capacity for
liquid absorption even when the aggregate particles are
densely packed, which minimizes the inter-particle void
volume of the coating.
The size of the alumina particles of which the
coating is comprised impacts the glossiness of the
coating. It should be noted that when the alumina
particles used in the present invention comprise
aggregates of fused (i.e., aggregated) primary particles,
the diameter values refer to the diameters of the
aggregates. Particle diameter can be determined by any
suitable technique, for example, by a light scattering
technique, (e.g., using a Brookhaven 90Plus Particle
Scanner, available from Brookhaven Instruments
Corporation, Holtsville, New York).
In order to maximize glossiness, it is preferred
that the mean diameter of the alumina particles (i.e.,
the aggregates) is less than about 1 m. More
preferably, the mean diameter of the alumina particles is
less than about 500 nm, still more preferably the mean
diameter of the alumina particles is less than about 400
nm, and most preferably the mean diameter of the alumina
particles is less than about 300 nm.
It is highly preferred that at least about 80%
(e.g., at least about 90%) or substantially all of the
alumina particles have diameters smaller than the mean
diameter values set forth above. In other words, it is
highly preferred that at least about 80% (e.g., at least
about 90%) or substantially all of the particles have
diameters of less than about 1 m, more highly preferred
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that at least about 80% (e.g., at least about 90%) or
substantially all of the particles have diameters of less
than about 500 nm, still more highly preferred that at
least about 80% (e.g., at least about 90%) or
substantially all of the particles have diameters of less
than about 400 nm, and most highly preferred that at
least about 80% (e.g., at least about 90%) or
substantially all of the particles have diameters of less
than about 300 nm.
In certain preferred embodiments, the mean diameter
of the alumina particles is at least about 40 nm (e.g.,
particles having a mean diameter from about 40 nm to
about 300 nm, more preferably from about 100 nm to about
200 nm, still more preferably from about 120 to about 190
nm, and most preferably from about 140-180 nm (e.g., from
about 150-170 nm)). In certain of these embodiments, at
least about 80% (e.g., at least about 90%) or
substantially all of the alumina particles have diameters
of at least about 100 nm (e.g., from about 100 nm to
about 200 nm, more preferably from about 120 to about 190
nm, and most preferably from about 140-180 nm (e.g., from
about 150-170 nm)).
In other embodiments of the present invention, the
alumina particles preferably have a mean diameter of less
than about 300 nm, more preferably less than about 200
nm, still more preferably less than about 190 nm, and
most preferably less than about 180. In certain
embodiments it is preferred that at least about 80%
(e.g., at least about 90%) or substantially all of the
alumina particles have diameters of less than about 300
nm, more preferably less than about 200 nm, still more
preferably less than about 190 nm, and most preferably
less than about 180 nm.
The coating can comprise alumina particles having
any suitable range of individual particle diameters, such
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as a relatively broad range or a relatively narrow range.
The particles also can be monodispersed. By
monodispersed is meant that the individual particles have
diameters that are substantially identical. For example,
substantially all monodispersed 150 nm particles have
diameters in the range of from about 140 nm to about 160
nm.
With respect to the primary particles that make up
these alumina aggregates, in certain embodiments of the
present invention, such as when a glossy coating having a
relatively high rate of and capacity for liquid
absorption is desired, it is preferred that the primary
particles have a mean diameter of less than about 100 nm
(e.g., from about 1 nm to about 100 nm). More
preferably, the primary particles have a mean diameter of
less than about 80 nm (e.g., from about 1 nm to about 80
nm), even more preferably less than about 50 nm (e.g.,
from about 1 nm to about 50 nm), and most preferably less
than about 40 nm (e.g., from about 5 nm to about 40 nm).
In certain of these embodiments it is preferred that
at least about 80% (e.g., at least about 90%) or
substantially all of the primary particles have diameters
smaller than the mean diameter values set forth above.
In other words, it is preferred that at least about 80%
(e.g., at least about 90%) or substantially all of the
primary particles have diameters of less than about 100
nm (e.g., from about 1 nm to about 100 nm), more
preferred that at least about 80% (e.g., at least about
90%) or substantially all of the primary particles have
diameters of less than about 80 nm (e.g., from about 1 nm
to about 80 nm), even more preferred that at least about
80% (e.g., at least about 900) or substantially all of
the primary particles have diameters of less than about
50 nm (e.g., from about 1 nm to about 50 nm), and most
preferred that at least about 80% (e.g., at least about
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90%) or substantially all of the primary particles have
diameters of less than about 40 nm (e.g., from about 5 nm
to about 40 nm).
It will be appreciated that the surface area of the
5 alumina particles of the recording medium of the present
invention is largely a function of the mean diameter of
the primary particles, rather than the mean diameter of
the aggregates. The alumina particles of the recording
medium of the present invention can have any suitable
10 surface area. While the alumina particles of the
recording medium of the present invention can have a
surface area of up to about 400 m2/g, it is preferred
that the surface area of the alumina particles of the
recording medium of the present invention have a surface
area of less than about 200 m2/g, more preferably less
than about 150 m2/g. In a particularly preferred
embodiment, the alumina particles of the recording medium
of the present invention have a surface area of less than
about 400 m2/g (e.g., about 15-300 m2/g, more preferably
about 20-200 m2/g, more preferably about 30-80 m2/g, and
most preferably about 40-60 m2/g).
The glossiness of the recording medium of the
present invention can be measured using any suitable
technique. For example, the glossiness of the present
invention can be measured in terms of the 75 specular
gloss, e.g., according to JIS P 8142, or an equivalent
U.S. standard, using a gloss photometer, for example, a
VGS-1001, manufactured by Nihon Denshoku Kogyosha, a
Hunter 75 Gloss Meter, a Technidyne Glossmeter (e.g.,
Model T480A), or the like. Other suitable test methods
can be used to determine glossiness, for example, ASTM,
TAPPI, or the like. When TAPPI is used, it is preferably
TAPPI T480. When ASTM is used, it is preferably ASTM
D1223.
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It is preferred that the recording medium of the
present invention has a 75 specular gloss of at least
about 15%. More preferably, the recording medium of the
present invention has a glossiness of at least about 25%,
even more preferably at least about 35%, still more
preferably at least about 45%. In some instances, the
glossiness is least about 55%, and even at least about
650.
Desirably, the recording medium of the present
invention is calendered to provide a glossier coating.
cpreferably has a 75 specular gloss of at least about
15%, more preferably at least about 25%, even more
preferably at least about 35%, and still more preferably
at least about 45%. In a preferred embodiment, the
recording medium of the present invention, when
calendered, has a 75 specular gloss of at least about
50%. In some instances, depending on the substrate, the
coating compostion, the nature of the coating
composition, and the method of applying the coating to
the substrate, the recording medium of the present
invention, when calendered, can have glossiness is least
about 55%, and even at least about 65%.
The coating of the recording medium of the present
invention has good dye immobilization properties and
waterfastness. Organic dyes, such as those used in ink-
jet inks, often contain ionizable functional groups
(e.g., SO3H, COOH, P03H2r etc.), which increase the water
solubility of the dyes. The dyes become negatively
charged when these functional groups ionize in water
(e . g . , to S03-, COO-, P032-, etc .) . As the alumina used in
the glossy coating of the recording medium of the present
invention has a cationic surface, the alumina particles
enhances the ability of the coating to immobilize (i.e.,
adsorb) and display dye molecules at the surface of the
coating. This is due to the strong electrostatic
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attraction of the dye toward the alumina particles in the
glossy coating of the recording medium of the present
invention.
Therefore, even though the ink can be rapidly
absorbed into the coating via the pores of the alumina
particles, the anionic dye molecules can be separated
from the ink, and immobilized at the coating surface. As
such, the coating of the recording medium of the present
invention has excellent dye immobilizing ability, which
promotes desirable qualities, for example, superior image
quality and high optical density.
It is desirable for the alumina particles in the
coating of the the recording medium of the present
invention to have a high positive zeta potential. The
net charge on the alumina particles of the recording
medium of the present invention can be qualitatively
determined by measuring the zeta potential of the
dispersion (e.g., using a Matec MBS 8000 or a Brookhaven
Zeta Plus instrument). A negative zeta potential is
indicative of a net negative charge, while a positive
zeta potential indicates a net positive charge. The
magnitude of the zeta potential is proportional to the
magnitude of the charge.
Dye adhesion to the surface of a recording medium
can be quantified by measuring the optical density and
waterfastness of a test sample of the recording medium to
which an aqueous ink-jet ink comprising an anionic dye
has been applied. For example, a test sample having an
ink coverage of about 12 g/m2 over an area of about 90 cm2
can be cut in half and tested in the following manner.
One minute after applying the ink, one of the halves is
soaked in deionized water for one minute and then
repeatedly dipped in and out of the water to remove all
dissolved ink from the sample. After drying, a
densitometer (e.g., a MacBeth 512 densitometer) can be
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used to measure the image intensity at a number of
positions (e.g., at ten random positions) on each half of
the test sample, and the values for each half averaged.
The optical density of the recording medium is the
average image intensity of the half of the test sample
that was not soaked in water. The waterfastness can be
reported as:
r (ave. I.I. of unsoaked)-(ave. I.I. of soaked)
1 L
(ave. I.I. of unsoaked)
wherein ave. I.I. is the average image intensity of each
half of the test sample (i.e., the half that was soaked
in water and the half that was not soaked in water).
Waterfastness values that are less than one, when
calculated in this fashion, generally indicate loss of
ink from the coating.
Alternatively, waterfastness can be evaluated in
terms of retained optical density. For example, a test
print can be evaluated by immersing a sample in deionized
water for 5 minutes with light agitation, drying the
sample, and comparing the color density of the dry soaked
sample with that of an unsoaked sample (as indicated
above) by measuring color density with a suitable
densitomer (e.g., X-Rite 938 Spectrodensitometer).
Waterfastness can then be expressed in terms of the
percentage of optical density retained by the soaked
sample relative to the unsoaked sample.
The recording medium of the present invention
exhibits excellent waterfastness. For example, the
recording medium of the present invention typically
retains at least about 50% of the optical density after
immersion in deionized water for 5 minutes with light
agitation. Preferably, after it is immersed in deionized
water for 5 minutes with light agitation, the recording
medium of the present invention retains at least about
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60% of the optical density of the printed image, more
preferably at least about 70% of the optical density,
still more preferably at least about 80% of the optical
density, and most preferably at least about 90% of the
optical density is retained (e.g., about 95% or even 100%
of the optical density).
The recording medium of the present invention also
has a good rate of liquid absorption and good capacity
for liquid absorption. The rate of liquid absorption can
be measured by any suitable method, for example, by
applying a droplet of a liquid (e.g., distilled water) to
the coating surface and measuring the change in the angle
of the droplet with respect to the surface (contact
angle) over time. Preferably, the contact angle of
distilled water, when applied to the glossy coating of
the recording medium of the present invention, decreases
by at least about 5 over the first five minutes. More
preferably, the contact angle decreases by at least about
7 over the first five minutes. Most preferably, the
contact angle of distilled water, when applied to the
glossy coating of the recording medium of the present
invention, decreases by at least about 10 over the first
five minutes.
The capacity for liquid absorption of the coating of
the recording medium of the present invention can be
measured by any suitable technique. For example, the
capacity for liquid absorption can be measured by
contacting a liquid, for example, water, or a 1:1
solution of polyethylene glycol (e.g., PEG 400) and
water, or the like, with a predetermined area of the
glossy coating of the recording medium of the present
invention for 10 seconds at 22 C, followed by contacting
the medium with a blotting paper to remove excess
solution, measuring the weight of the solution absorbed
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by the glossy coating, and expressing that weight in
terms of g/m2.
Alternatively, the liquid absorption capacity of the
coating can be measured as a function of porosity.
5 Porosity can be measured by any suitable method, for
example, by measuring the total intrusion volume of a
liquid (e.g., mercury) into the glossy coating applied to
a non-porous substrate (e.g., polyethylene). It will be
appreciated that the total intrusion volume of a liquid
10 for a particular coating (and, therefore, the porosity)
can be a function of variables that influence the
structure of the coating, for example, binder type,
pigment-to-binder ratio, pigment particle size,
calendering, and the like. Preferably, the porosity is
15 determined by measuring the total intrusion volume of
mercury. In this regard, the glossy coating of the
recording medium of the present invention, when the
substrate is a non-porous substrate, preferably has a
total mercury intrusion volume of at least about 0.3
ml/g, more preferably at least about 0.5 ml/g, still more
preferably at least about 0.8 ml/g, most preferably about
1 ml/g or greater.
The properties of the inventive recording medium
promote high image quality when used in the vast majority
of printing applications. Any suitable printing method
can be used to apply an image to the inventive recording
medium. Such printing methods include, but are not
limited to gravure, letterpress, collotype, lithography
(e.g., offset lithography), ink-jet, and printing with
hand-held implements (e.g., pens), with ink-jet printing
being preferred.
Any suitable binder can be used in the coating of
the recording medium of the present invention. Preferred
binders include, but are not limited to, polyvinyl
alcohol (PVOH), polyvinyl acetate, polyvinyl acetal,
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polyvinyl pyrrolidone, oxidized starch, etherified
starch, cellulose derivatives (e.g., carboxymethyl
cellulose (CMC), hydroxyethyl cellulose, etc.), casein,
gelatin, soybean protein, silyl-modified polyvinyl
alcohol, conjugated diene copolymer latexes (e.g., maleic
anhydride resin, styrene-butadiene copolymer, methyl
methacrylate-butadiene copolymers, etc.), acrylic polymer
-Latexes (e.g., polymers and copolymers of acrylic esters
and methacrylic esters, polymers and copolymers of
acrylic acid and methacrylic acid, etc.), vinyl polymer
latexes (e.g., ethylene-vinyl acetate copolymer),
functional group-modified polymer latexes obtained by
modifying the above-mentioned various polymers with
monomers containing functional groups (e.g., carboxyl
groups), aqueous binders such as thermosetting resins
(e.g., melamine resin, urea resin, etc.), synthetic resin
binders such as polymethyl methacrylate, polyurethane
resin, polyester resin (e.g., unsaturated polyester
resin), amide resin, vinyl chloride-vinyl acetate
copolymer, polyvinyl butyral, and alkyd resin, with
polyvinyl alcohol being most preferred.
The alumina particles in the coating of the
recording medium of the present invention have a low
binder demand. As such, a higher pigment to binder ratio
can be utilized in the coating of the recording medium of
the present invention. The high pigment to binder ratio
is advantageous in that a greater number of alumina
particles per unit volume can exist in the coating of the
recording medium of the present invention, improving the
properties thereof (e.g., gloss and porosity).
Preferably, the pigment to binder ratio of the coating of
the recording medium of the present invention is at least
about 2:1 by weight. More preferably the pigment to
binder ratio of the coating of the recording medium of
the present invention is at least about 5:1 by weight,
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still more preferably at least about 7:1 by weight, and
most preferably at least about 8:1 by weight. In some
embodiments, the pigment to binder ration of the coating
of the recording medium of the present invention is at
least about 9:1 by weight (e.g., at least about 10:1 by
weight).
The total amount of binder (i.e., dry binder) can be
any suitable amount, but is preferably from about 1% to
about 50% of the composition (i.e., dry binder and
particles combined) by weight. More preferably, the
total amount of binder is from about 1% to about 40% of
the composition by weight, even more preferably from
about 1% to about 30% by weight, still more preferably
from about 3% to about 25% by weight, yet more preferably
from about 5% to about 15% by weight, and most preferably
from about 5% to about 10% by weight (e.g., about 9% by
weight).
When PVOH is used as a binder, the total amount of
PVOH is preferably from about 1% to about 50% of the
composition by weight, more preferably from about 1% to
about 40% by weight, even more preferably from about 1%
to 30% by weight, yet more preferably from about 3% to
about 25% by weight, still more preferably from about 5%
to about 15% by weight, and most preferably from about 5%
to about 10% by weight (e.g., about 9% by weight).
In certain embodiments of the present invention, the
glossy coating of the inventive recording medium
comprises one or more pigments in addition to alumina
particles, such as calcium carbonate, clays, aluminum
silicates, urea-formaldehyde fillers, and the like.
Other suitable pigments include silica (e.g., colloidal
silica, precipitated silica, silica gel, pyrogenic
silica, or cationically modified analogs thereof),
alumina (e.g., alumina sols, colloidal alumina, cationic
aluminum oxide or hydrates thereof, pseudoboehmite,
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boehmite, Al(OH)31 etc.), magnesium silicate, magnesium
carbonate, kaolin, talc, calcium sulfate, barium sulfate,
titanium dioxide, zinc oxide, zinc sulfide, zinc
carbonate, satin white, diatomaceous earth, calcium
silicate, aluminum hydroxide, lithopone, zeolite,
hydrated halloycite, magnesium hydroxide, polyolefins
(e.g., polystyrene, polyethylene, polypropylene, etc.),
plastics (e.g., acrylic), urea resin, and melamine resin.
The glossy coating of the recording medium of the
present invention also can comprise one or more other
additives, such as surfactants (e.g., cationic
surfactants, anionic surfactants such as long-chain
alkylbenzene sulfonate salts and long-chain, preferably
branched chain, alkylsulfosuccinate esters, nonionic
surfactants such as polyalkylene oxide ethers of long-
chain, preferably branched-chain alkyl group-containing
phenols and polyalkylene oxide ethers of long-chain alkyl
alcohols, and fluorinated surfactants), silane coupling
agents (e.g., y-aminopropyltriethoxysilane, N-(3
(aminoethyl) y-aminopropyltrimethoxysilane, etc.),
hardeners (e.g., active halogen compounds, vinylsulfone
compounds, aziridine compounds, epoxy compounds, acryloyl
compounds isocyanate compounds, etc.), pigment
dispersants, thickeners (e.g., carboxymethyl cellulose
(CMC)), flowability improvers, antifoamers (e.g., octyl
alcohol, silicone-based antifoamers, etc.), foam
inhibitors, releasing agents, foaming agents,
pentetrants, coloring dyes, coloring pigments, whiteners
(e.g., fluorescent whiteners), preservatives (e.g., p-
hydroxybenzoate ester compounds, benzisothiazolone
compounds, isothiazolone compounds, etc.), antifungal
agents, yellowing inhibitors (e.g., sodium
hydroxymethanesulfonate, sodium p-toluenesulfinate,
etc.), ultraviolet absorbers (e.g., benzotriazole
compounds having a hydroxy-dialkylphenyl group at the 2-
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position), antioxidants (e.g., sterically hindered phenol
compounds), antistatic agents, pH regulators (e.g.,
sodium hydroxide, sodium carbonate, sulfuric acid,
hydrochloric acid, phosphoric acid, citric acid, etc.),
water-resisting agents, wet strengthening agents, and dry
strengthening agents.
The present invention further provides a coating
composition comprising alumina particles and a binder,
wherein the alumina particles are aggregates of primary
particles and the solids content of the alumina in the
coating composition greater than about 10,wt.o.
Any suitable alumina particles can be used in the
coating composition of the present invention. Suitable
alumina particles include the alumina particles described
herein with respect to the coating of the recording
medium of the present invention. The alumina particles
used in the coating composition of the present invention
can be of any suitable diameter and surface area.
Suitable particle diameters and surface areas of the
particles include the particle diameters and surface
areas described herein with respect to the coating of the
recording medium of the present invention.
Any suitable binder can be used in coating
composition of the present invention, including those
described herein with respect to the coating of the
recording medium of the present invention. Likewise, any
suitable pigment to binder ratio can be used in the
coating composition of the present invention.
Preferably, the pigment to binder ratio is at least about
2:1 by weight. More preferably the pigment to binder
ratio of the coating composition of the present invention
is at least about 5:1 by weight, still more preferably at
least about 7:1 by weight, and most preferably at least
about 8:1 by weight. In some embodiments, the pigment to
binder ration of the coating composition of the present
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invention is at least about 9:1 by weight (e.g., at least
about 10:1 by weight).
The coating composition of the present invention
typically includes a suitable carrier. The carrier can
5 be any suitable fluid or combination of fluids (e.g.,
solvents) in which the first and second groups of
particles, and any other additives (e.g., one or more
binders), can be mixed and applied to a substrate.
Preferred carriers have a relatively high vapor pressure
10 to accelerate drying of the coating after application,
and preferred examples include, but are not limited to,
organic solvents (e.g., methanol) and water, with water
being most preferred.
In certain embodiments, coating composition of the
15 present invention comprises one or more pigments in
addition to alumina particles, including those described
herein with respect to the coating of the recording
medium of the present invention. The coating composition
of the present invention also can comprise one or more
20 other additives, for example, surfactants, silane
coupling agents, hardeners, pigment dispersants,
thickeners, flowability improvers, antifoamers, foam
inhibitors, releasing agents, foaming agents,
pentetrants, coloring dyes, coloring pigments, whiteners,
antifungal agents, yellowing inhibitors, ultraviolet
absorbers, antioxidants, water-resisting agents, wet
strengthening agents, and dry strengthening agents,
including those described herein with respect to the
coating of the recording medium of the present invention.
The present invention further provides a method of
preparing a coating composition. The method comprises:
providing a colloidally stable dispersion comprising
water and alumina particles, wherein the alumina
particles are aggregates of primary particles and the
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solids content of the alumina particles in the dispersion
is at greater than about 20 wt.%;
adding a binder to and, optionally, diluting the
colloidally stable dispersion, until a desired pigment to
binder ratio and overall solids content are obtained; and
optionally adjusting the pH with a suitable acid or
base.
Any suitable alumina particles can be used in the
inventive method of preparing a coating composition.
Suitable alumina particles include the alumina particles
described herein with respect to the coating of the
recording medium of the present invention. The alumina
particles used in the inventive method of preparing a
coating composition can be of any suitable diameter and
surface area. Suitable particle diameters and surface
areas of the particles include the particle diameters and
surface areas described herein with respect to the
coating of the recording medium of the present invention.
Any suitable binder can be used in the inventive
method of preparing a coating composition, including
those described herein with respect to the coating of the
recording medium of the present invention. Likewise, any
suitable pigment to binder ratio can be used in preparing
the coating composition in accordance with the method of
the present invention. Preferred pigment to binder
ratios include those described herein with respect to the
coating of the recording medium of the present invention.
A suitable carrier can be employed in the method of
preparing a coating composition of the present invention.
The carrier can be present in the dispersion or can be
added to the dispersion to produce the final coating
composition. Suitable carriers include those described
herein with respect to the coating of the recording
medium of the present invention, with water being most
preferred.
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In accordance with the inventive method of preparing
a coating composition, one or more pigments can be added
to the dispersion in addition to the alumina particles,
including those described herein with respect to the
coating of the recording medium of the present invention.
One or more other additives also can be added, including
those described herein with respect to the coating of the
recording medium of the present invention.
The colloidally stable dispersion (i.e., the initial
dispersion) used to prepare the coating composition in
accordance with the present invention has,a high solids
content (i.e., greater than about 20 wt.% alumina solids)
and also is colloidally stable. The high alumina solids
content of the initial dispersion is highly advantageous
in that a higher solids content of the coating
composition can be achieved (e.g., at least about 20 wt.%
total solids taking the binder and other additives into
account). As a result, drying time in coating operations
is significantly diminished, making the overall process
less costly and more efficient. The initial dispersion
can be prepared by any suitable method, but is preferably
prepared according to the method described in U.S. Patent
5,527,423.
Preferably, the alumina solids content of the
initial dispersion is at least about 25 wt.%, more
preferably at least about 30 wt.%, still more preferably
at least about 35 wt.%, even more preferably at least
about 40 wt.%, and most preferably al least about 50
wt.%. In certain embodiments, the alumina solids content
of the colloidally stable dispersion is about 25-50 wt.%
or 30-50 wt.%, but is more preferably about 30-50 wt.%,
most preferably about 40-50 wt.%.
The alumina particles in the initial dispersion used
in the method of the present invention can have any
suitable positive zeta potential. Desirably, the
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positive zeta potential is sufficiently high to promote
colloidal stability in the initial dispersion.
Preferably, the zeta potential of the alumina particles
in the initial dispersion is at least about +20 mV. More
preferably, the zeta potential of the alumina particles
in the initial dispersion dispersion is at least about
+30 mV. Most preferably, the zeta potential of the
alumina particles in the initial dispersion dispersion is
at least about +40 mV.
The initial dispersion can be of any suitable pH.
Preferably, the pH of the initial dispersion is about 3-
5, and more preferably is about 3.5-4.5, but most
preferably is about 4-4.5. While the initial dispersion
can have a range of specific gravity values, the specific
gravity of the initial dispersion preferably is in the
range of about 1-2 kg/1.
The initial dispersion used to prepare the coating
composition of the present invention has excellent
rheological properties, making the dispersion and coating
compositions derived therefrom highly amenable to large
scale coating operations. For example, the initial
dispersion exhibits low viscosity at a high shear rate,
e.g., as measured in a Hercules High-Shear Viscometer at
4400 RPM, FF Bob measuring geometry. Preferably, the
initial dispersion, at an alumina solids content of about
40 wt.%, has an apparent viscosity of less than about 20
cp at high shear rate (e.g., as measured in a Hercules
High-Shear Viscometer at 4400 RPM, FF Bob measuring
geometry). More preferably, the initial dispersion (at
about 40 wt.% alumina solids) has an apparent viscosity
of less than about 15 cp, as measured in a Hercules
High-Shear Viscometer at 4400 RPM, FF Bob measuring
geometry. Most preferably, the initial dispersion (at
about 40 wt.% alumina solids) has an apparent viscosity
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of less than about 10 cp, as measured in a Hercules
High-Shear Viscometer at 4400 RPM, FF Bob measuring
geometry.
The initial dispersion used to prepare the coating
composition of the present invention also exhibits low
viscosity at a low shear rate, e.g., as measured in a
Brookfield Model RV viscometer, spindle #1, after about
30 seconds at 60 RPM. Preferably, the initial dispersion
(at about 40 wt.% alumina solids) has an apparent
viscosity of less than about 100 cp at low shear rate
(e.g., as measured in a Brookfield Model RV viscometer,
spindle #1, after about 30 seconds at 60 RPM). More
preferably, the initial dispersion (at about 40 wt.=
alumina solids) has an apparent viscosity of less than
about 80 cp, as measured in a Brookfield Model RV
viscometer, spindle #1, after about 30 seconds at 60 RPM.
Most preferably, the initial dispersion (at about 40 wt.%
alumina solids) has an apparent viscosity of less than
about 50 cp, as measured in a Brookfield Model RV
viscometer, spindle 41, after about 30 seconds at 60 RPM.
The initial dispersion used to prepare the coating
composition of the present invention can be very high in
alumina solids content (e.g., 30-50 wt.% alumina solids),
yet maintain long-term colloidal stability (e.g., 1
year). Coating compositions prepared from the initial
dispersion in accordance with the method of the present
invention have a significantly lower binder demand and
have greater runnability than conventional alumina
coating compositions. Moreover, when applied to a
substrate as a coating, the coating composition prepared
from the initial dispersion in accordance with the
present invention require significantly less drying time
than conventional coatings. The coatings on the
recording media thus produced have high porosity,
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excellent gloss, dye-immobilizing ability, and
waterfastness, and provide superior image quality.
The present invention further provides a method of
preparing a recording medium. The inventive method of
5 preparing a recording medium comprises:
providing a substrate;
coating the substrate with the coating composition
of the present invention to produce a substrate coated
with a coating;
10 optionally calendering the coated substrate; and
drying the coated substrate.
As indicated above, the coating composition of the
present invention provides fast drying times, drying
quickly to form a non-tacky glossy coating. The coating
15 composition can be applied using any suitable method or
combination of methods. Suitable methods include, but
are not limited to, roll coating, blade coating, air
knife coating, rod coating, bar coating, cast coating,
gate roll coating, wire bar coating, short-dowel coating,
20 slide hopper coating, curtain coating, flexographic
coating, gravure coating, Komma coating, size press
coating in the manner of on- or off-machine, and die
coating, with rapid, inexpensive methods such as rod
coating and air knife coating being preferred.
25 The coated substrate can be dried using any suitable
method. Suitable drying methods include, but are not
limited to, air or convection drying (e.g., linear tunnel
drying, arch drying, air-loop drying, sine curve air
float drying, etc.), contact or conduction drying, and
radiant-energy drying (e.g., infrared drying and
microwave drying).
Many physical properties of a glossy coating
prepared with the coating composition of the present
invention, can be rationally optimized by varying the
relative quantity of particles from each group contained
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therein. It will be appreciated that materials other
than the alumina particles (e.g., binders, thickeners,
and the like) can be varied to alter or optimize the
physical properties of the coating composition of the
present invention.
The primary features of the inventive method of
preparing a recording medium are as previously described
with respect to the recording medium and coating
composition of the present invention. For example, the
preferred substrates, coating methods, coating
composition (e.g., solids content, binder content,
apparent density, additives, etc.), properties of the
alumina particles (i.e., materials, diameters, surface
area, etc.), coating properties (i.e., thickness, number
and constitution of coating layers, glossiness, rate and
capacity of liquid absorption, packing density,
adhesiveness, etc.), are as described herein with respect
to the recording medium and coating composition of the
present invention.
The following examples further illustrate the present
invention but, of course, should not be construed as in any
way limiting its scope.
Example 1
This example illustrates the preparation of a coating
composition of the present invention. An initial
dispersion of fumed alumina was prepared in accordance with
U.S. Patent 5,527,423. The fumed alumina had a surface
area of about 55 m2/g. The fumed alumina was greater than
95 crystalline, of which about 70% was theta phase,
about 20% was delta phase, and about 10% was gamma phase,
the fraction of alpha phase having been below the
detection limit.
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The dispersion had an alumina solids content of 40.0
wt.%, a pH of 4-4.4, and a specific gravity of 1.4 kg/l.
The viscosity of the final dispersion was less than 50 cp
when measured using a Brookfield Model LV viscometer,
spindle #1, after 60 seconds at 60 RPM. The mean
diameter of the alumina particles in the final dispersion
was 154 nm as measured in a Brookhaven 90Plus Particle
Scanner (Brookhaven Instruments Corporation, Holtsville,
New York). An electron micrograph of the alumina
particles in the initial dispersion is illustrated in
Fig. 1.
The initial dispersion had excellent rheological
properties. The apparent viscosity of the initial
dispersion, as measured in a Hercules High-Shear
Viscometer at 4400 RPM, FF Bob measuring geometry, was
8.8 cp (centipoise). The rheogram of the initial
dispersion, as generated in a Hercules High-Shear
Viscometer from 0-4400 RPM, FF Bob measuring geometry, is
illustrated in Fig. 2.
The zeta potential of the particles in the
dispersion was +40 mV. The dispersion was colloidally
stable in that there was no appreciable increase in
viscosity or gellation after one year at a storage
temperature ranging from 40-110 F (4-43 C).
A coating composition was prepared by adding
sufficient polyvinyl alcohol binder (PVOH) to the initial
dispersion to give a pigment to binder ratio of 7:1, HEC
(1.55 wt.%), and diluting to an overall solids content
(including binder) of 24.28 wt.%. The final pH was 4.20.
The coating composition had excellent rheological
properties. The viscosity of the composition was 888 cp
when measured using a Brookfield Model RV viscometer,
spindle #5, after 30 seconds at 100 RPM. The apparent
viscosity of the composition was 24.1 cp as measured in a
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Hercules High-Shear Viscometer at 4400 RPM, FF Bob
measuring geometry. The rheogram of the coating
composition, as generated in a Hercules High-Shear
Viscometer from 0-4400 RPM, FF Bob measuring geometry, is
illustrated in Fig. 3 (curve B).
The coating composition produced excellent coatings
with an unusually low pigment to binder ratio of 7:1.
The coating composition prepared in this example had
significantly lower binder demand than conventional
alumina coating compositions, which typically use a 3:1
pigment to binder ratio.
Example 2
This example illustrates a coating composition
prepared from the initial dispersion prepared in Example
1. A coating composition was prepared by adding
sufficient polyvinyl alcohol binder (PVOH) to the
dispersion prepared in Example 1 to give a pigment to
binder ratio of 7:1, and diluting to an overall solids
content (including binder) of 22.27 wt.%. The pH was
adjusted to about 7.97 with ammonium hydroxide.
The coating composition had excellent Theological
properties. The viscosity of the composition was 2076 cp
when measured using a Brookfield Model RV viscometer,
spindle #5, after 30 seconds at 100 RPM. The apparent
viscosity of the composition was 14.0 cp as measured in a
Hercules High-Shear Viscometer at 4400 RPM, FF Bob
measuring geometry. The rheogram of the coating
composition, as generated in a Hercules High-Shear
Viscometer from 0-4400 RPM, FF Bob measuring geometry, is
illustrated in Fig. 3 (curve A).
The coating composition produced excellent coatings
with low pigment to binder ratio of 7:1. The coating
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composition prepared in this example had a low binder
demand.
Example 3
This example illustrates the preparation of a
recording medium of the present invention. An uncoated
paper substrate base was coated with the coating
composition of Example 1, except that the coating
composition had a total solids content of 26.3 wt.%, no
HEC added was added, the pH of the coating composition
was 4.45, and the pigment to binder ratio was 4:1.
Coating was performed on a CLC (Cylindrical Laboratory
Coater) blade coating apparatus at high speed. The CLC
simulates conditions that are characteristic of
commercial manufacture. The performance of a particular
coating composition in the CLC at high speed is
indicative of how the coating composition is expected to
perform under high speed commercial manufacturing
conditions. The coating was preformed at a rate of 2000
feet per minute (610 meters per minute) using a flexible
blade, and the coating was dried (infrared). The coating
dried quickly.
The dry coat weight in grams per square meter (g/m2)
for each recording medium (i.e., coated substrate) was
determined, and the dry recording media (uncalendered)
were analyzed. Optical and surface properties were
measured for each recording medium and also for the
uncoated substrate.
Samples were calendered on one side with 3 nips at 6
pli (pounds per linear inch) (1.25 kg/linear cm) and 60
C. The optical, surface and printing properties were
measured for the calendered samples, and the results were
compared to the uncalendered samples.
The uncoated paper substrate had the following
properties: basis weight: 77.5 g/m2; pH: 6.6; ash: 8.31%;
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caliper 3.62/1000" (91.9 m) ; brightness: 82.70; gloss:
6.4%; smoothness: 3.93 m; Hercules sizing test: 109
sec; and PPS porosity: 2.77 ml/min. The recording media
obtained by coating the substrate in accordance with this
5 example had excellent gloss, brightness, and porosity.
The coating had an excellent appearance and superior
feel, and did not crack or exhibit brittleness.
Moreover, the recording media produced an excellent
printed image.
10 Brightness was measured using a Technidyne
Brightness Meter Tappi Procedure T 452 OM-92. Gloss was
measured using a Hunter 75 degree gloss meter according
to TAPPI standard procedure T 4800M-92. The surface
smoothness and porosity of the sheets were measured using
15 a Parker Print Surf (PPS) tester (TAPPI T555 PM-94). The
rate of liquid absorption of the papers was measured
using a First 10 Angstrom Dynamic Contact Angle measuring
device.
The properties of the recording media (uncalendered
20 and calendered) are shown below in Table 1.
Table 1
Medium Brightness 75 Specular PPS Porosity
(o) Gloss Smoothness (ml/min. )
(%) (Fm)
Uncoated
Substrate 82.7 6.4 3.93 2.77
Coated
Substrate 86.7 13.0 3.68 82.6
(8 g/m2)
Calendered 83.9 66.3 1.16 20.0
(8 g/m2)
The samples were printed on Epson Stylus Pro
25 Photorealistic and Hewlett Packard 820C ink jet printers
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using a test pattern created with ADOBE software. The
print gloss and print density of the samples was then
measured. Print gloss was measured using a Gardener 60
degree Micro-Gloss meter. Print density was measured
using a BYK Gardner densitometer. The properties of the
image as printed using the Epson Stylus Pro
Photorealistic and the Hewlett Packard 820C are shown in
Tables 2A and 2B, respectively.
Table 2A
Epson Stylus Pro ES Wide Format
Coating
Medium Black Cyan Magenta Yellow Ink Gloss
Gloss
Coated
Substrate 1.44 0.69 0.91 0.79 1.82 13.0
(8 g/m2)
Calendered 1.64 0.73 1.02 0.98 14.8 66.3
(8 g/m2)
Table 2B
Hewlett Packard 820C
Coating
Medium Black Cyan Magenta Yellow Ink Gloss
Gloss
Coated
Substrate 1.57 1.18 1.23 0.86 9.40 13.0
(8 g/m2)
Calendered 1.64 0.73 1.02 0.98 11.7 66.3
(8 g/m2)
These results demonstrate that the recording media
produced in accordance with this example exhibited
excellent optical, physical, and textural properties, as
indicated by the high measured values for gloss (low PPS
smoothness), and the high measured values for brightness
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and porosity. These results also demonstrate the
excellent quality of printed images attainable using such
recording media, as indicated by the high values for ink
density using several representative colors, as well as
high ink gloss values.
Example 4
Using the CLC apparatus described in Example 3, one
side of a cellulose paper substrate was coated with the
composition prepared according to Example 1, except that
the total solids content of the coating composition was
26.4 wt.%, the pH was 4.5, the amount of HEC added was
3.0 wt.%, and the pigment to binder ratio was 5:1.
Coating was performed at a rate of 3000 feet per minute
(914 meters per minute) and the samples dried (infrared).
The coatings were applied at three different coating
weights, and the coatings dried quickly after they were
applied to the substrate.
The dry coat weight in grams per square meter (g/m2)
for each recording medium was determined, and the dry
recording media (uncalendered) were analyzed. Optical
and surface properties were measured for each recording
medium and also for the uncoated substrate. PPS (Parker
Print Surf) roughness and brightness were measured.
Brightness was measured in accordance with TAPPI
brightness standard. Glossiness was measured in terms of
the 75 specular gloss according to JIS P 8142 using a
gloss photometer.
The recording media were calendered, and the 75
specular gloss measurements were determined for the
calendered media. The results are shown in Table 3.
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Table 3
Coat 75 Specular PPS PPS
Wt. Brightness Gloss Smoothness Porosity
(g/m2) ($) (o) [Calendered] (uncalendered) (uncalendered)
( m) (ml/min)
5.67 92.6 26.1 [N/A] 4.4 69.2
7.59 91.9 21.74 [69.6] 4.2 70.6
10.85 92.2 24.92 [N/A] 4.3 67.4
These data demonstrate that the coating composition
of the present invention exhibits excellent performance
at high speed and produces a glossy recording medium with
excellent optical and surface properties under such
conditions. These data demonstrate that the composition
of the present invention possesses rheological properties
desirable for producing high quality coatings under high
speed manufacturing operations.
Example 5
Using the CLC apparatus described in Example 3, one
side of a cellulose paper substrate was coated with the
composition prepared according to Example 1, except that
the total solids content of the coating composition was
33.3 wt.%, the pH was 4.5, the amount of HEC added was
3.0 wt.%, and the pigment to binder ratio was 5:1.
Coating was performed at a rate of 3000 feet per minute
(914 meters per minute) and the samples dried (infrared).
The coatings were applied at three different coating
weights, and the coatings dried quickly after they were
applied to the substrate.
The dry coat weight in grams per square meter (g/m2)
for each recording medium was determined, and the dry
recording media (uncalendered) were analyzed. Optical
and surface properties were measured for each recording
medium and also for the uncoated substrate. PPS (Parker
Print Surf) roughness and brightness were measured.
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Brightness was measured in accordance with TAPPI
brightness standard. Glossiness was measured in terms of
the 75 specular gloss according to JIS P 8142 using a
gloss photometer.
The recording media were calendered, and the 75
specular gloss measurements were determined for the
calendered media. The results are shown in Table 4.
Table 4
Coat 75 Specular PPS PPS
Wt. Brightness Gloss Smoothness Porosity
(g/m2) ( ) (o) [Calendered] (uncalendered) (uncalendered)
( m) (ml/min)
5.00 85.1 18.0 [N/A] 4.2 17.1
14.4 86.9 20.6 [69.4] 4.3 20.1
15.0 86.9 22.0 [N/A] 4.3 18.3
18.0 85.1 19.80 [N/A] 4.3 17.5
These data demonstrate that the coating composition
of the present invention exhibits excellent performance
at high speed and produces a glossy recording medium with
excellent optical and surface properties under such
conditions. These data demonstrate that the composition
of the present invention possesses rheological properties
desirable for producing high quality coatings under high
speed manufacturing operations.
Example 6
This example illustrates the rate of liquid
absorption of the recording medium of the present
invention. A coating composition was prepared in
accordance with Example 1 (pigment to binder ratio 7:1),
except that the coating composition had a total solids
content of 29 wt.%, the pH of the composition was 4.5,
and the amount of HEC added was 3.0 wt.%. Recording
media were prepared by coating a cellulose paper
CA 02385878 2007-02-12
substrate using the CLC coating apparatus as described in
Example 4, except that the applied coating weights were
5.3 g/mz, 8.0 g/m2, and 13.6 g/mz, respectively.
The change in contact angle (for a distilled water
5 droplet) was measured over time for recording medium
samples of each coating weight, and the results were
plotted and are graphically depicted in Fig. 4.
As shown in Fig. 4, each sample exhibited a sharp
initial decrease over the first few minutes, indicating a
10 good rate liquid absorption for a range of coating
weights.
While this invention has been described with an
emphasis upon preferred embodiments, it will be obvious to
those of ordinary skill in the art that variations of the
preferred embodiments may be used and that it is intended
that the invention may be practiced otherwise than as
specifically described herein. Accordingly, this invention
includes all modifications encompassed within the spirit
and scope of the invention as defined by the following
claims.
