Title: Recording medium
Abstract: 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.
Patent Number: 6,887,559 Issued on 05/03/2005 to Darsillo, et al.
| Inventors:
|
Darsillo; Michael S. (Clifton Park, NY);
Fluck; David J. (Bel Aire, MD);
Laufhutte; Rudiger (Tuscola, IL)
|
| Assignee:
|
Cabot Corporation (Boston, MA)
|
| Appl. No.:
|
670118 |
| Filed:
|
September 26, 2000 |
| Current U.S. Class: |
428/206; 428/323; 428/402 |
| Intern'l Class: |
G11B 005//18 |
| Field of Search: |
428/143,206,694. SL,694. SG,323,402
|
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|
Primary Examiner: Bernatz; Kevin M.
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
This patent application claims priority to provisional U.S. patent application
Ser. No. 60/157,462 filed on Oct. 1, 1999.
Claims
1. An ink-jet recording medium comprising a substrate having a glossy coating
thereon, the glossy coating comprising furned alumina particles and a binder, wherein
the fumed alumina particles have a surface area of about 30-80 m
2/g,
and the glossy coating un calendered has a 75° specular gloss of about 15%
or more and the glossy coating has a total mercury intrusion volume of about 0.3
ml/g or more.
2. The ink-jet recording medium of claim 1, wherein the substrate comprises a
polymer or cellulose paper.
3. The ink-jet recording medium of claim 1, wherein the substrate comprises poly(ethylene terephthalate).
4. The ink-jet recording medium of claim 1, wherein the glossy coating has a
75° specular gloss of about 65% or more.
5. The ink-jet recording medium of claim 1, wherein the glossy coating has a
total mercury intrusion volume of about 0.8 ml/g or more.
6. The ink-jet recording medium of claim 1, wherein the fumed alumina particles
have a surface area of about 40-60 m
2/g.
7. The ink jet recording medium of claim 1, wherein the fumed alumina particles
comprise aggregates of primary particles, and the aggregate have a mean diameter
of about 1 μm or less.
8. The ink-jet recording medium of claim 7, wherein the fumed alumina particles
comprise aggregates of primary particles, and the aggregates have a mean diameter
of about 80-300 nm.
9. The ink-jet recording medium of claim 8, wherein the fumed alumina particles
comprise aggregates of primary particles, and the aggregates have a mean diameter
of about 100-200 nm.
10. The ink-jet recording medium of claim 7, wherein at least about 80% of the
aggregates have a mean diameter of about 1 μm or less.
11. The ink-jet recording medium of claim 10, wherein at least about 90% of the
aggregates have a mean diameter of about 1 μm or less.
12. The ink-jet recording medium of claim 1, wherein the alumina to binder ratio
is about 2:1 by weight or more.
13. The ink-jet recording medium of claim 12, wherein the alumina to binder ratio
is about 7:1 by weight or more.
14. The ink-jet recording medium of claim 13, wherein the alumina to binder ratio
is about 9:1 by weight or more.
15. The ink-jet recording medium of claim 1, wherein the fumed alumina particles
comprise aggregates of primary particles, and the primary particles have a mean
diameter of about 1-100 nm.
16. The ink-jet recording medium of claim 15, wherein at least about 80% of the
primary particles have a mean diameter of about 1-100 nm.
17. The ink-jet recording medium of claim 15, wherein the primary particles have
a mean diameter of about 1-80 nm.
18. The ink-jet recording medium of claim 17, wherein at least about 80% of the
primary particles have a mean diameter of about 1-80 nm.
19. The ink-jet recording medium of claim 17, wherein the primary particles have
a mean diameter of about 1-50 nm.
20. The ink-jet recording medium of claim 19, wherein at least about 80% of the
primary particles have a mean diameter of about 1-50 nm.
21. The ink-jet recording medium of claim 19, wherein the primary particles have
a mean diameter of about 5-40 nm.
22. The ink-jet recording medium of claim 21, wherein at least about 80% of the
primary particles have a mean diameter of about 5-40 nm.
Description
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., 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 ration (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
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
dispersion 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.
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.
The coating composition of the present invention dries quickly when applied to
a substrate, to form a non-tacky glossy coating.
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 aggregate 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 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 μm to about 50 μm in thickness, more preferably
from about 5 μm to about 40 μm in thickness, and most preferably from
about 10 μm to about 30 μm 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
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, N.Y.).
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 μm. 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 μm, 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 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, preferably from about 80 nm to about 300 nm, more preferably from
about 100 nm to about 200 nm, still more preferably from about 120 nm 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
nm 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 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 90%) 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 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 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
surface area. While the alumina particles of the recording medium of the present
invention can have a surface area of up to about 400 m
2/g (e.g., about
20-400 m
2/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 m
2/g, more preferably less than about 150 m
2/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 m
2g/
(e.g., about 15-300 m
2/g, more preferably about 20-200 m
2/g,
more preferably about 30-80 m
2/g, and most preferably about 40-60 m
2/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, 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.
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 65%.
Desirably, the recording medium of the present invention is calendered
to provide a glossier coating. The recording medium epreferably 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 composition, 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 a glossiness of at 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-jets inks,
often contain ionizable functional groups (e.g., SO
3H, COOH, PO
3H
2,
etc.), which increase the water solubility of the dyes. The dyes become negatively
charged when these functional groups ionize in water (e.g., to SO
3-,
COO
-, PO
32-, 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 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 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 zeto 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 and anionic dye has been applied. For
example, a test sample having an ink coverage of about 12 g/m
2 over
an area of about 90 cm
2 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 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:
##EQU1##
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 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 by the glossy coating, and expressing that weight in terms
of g/m
2.
Alternatively, the liquid absorption capacity of the coating can be
measured as a function of porosity. Porosity can be measured by any suitable method,
for example, by measuring the total intrusions 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 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 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, 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-butadine copolymers, etc.), acrylic
polymer latextes (e.g., polymers and copolymers of acrylic esters and methacrylate
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 polymer 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, still more preferably at least about 7:1 by weight, and most preferably
at least about 8:1 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 filters,
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, boehmite, Al(OH)
3, 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, aluminate 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,
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., γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-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-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. %.
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 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
