WO2001081078A1

WO2001081078A1 - Glossy printing media

Info

Publication number: WO2001081078A1
Application number: PCT/US2001/012233
Authority: WO
Inventors: Yuying Tang
Original assignee: Rexam Graphics Inc.
Priority date: 2000-04-20
Filing date: 2001-04-16
Publication date: 2001-11-01

Abstract

Provided is a glossy medium useful for colored printing applications, particulary for ink jet printing. The medium comprises a substrate coated with a mixture of different submicron pigment particles. The pigment particles preferably comprise at least acicular or plate-like particles, and equiaxed or spherical submicron pigment particles.

Description

GLOSSY PRINTING MEDIA

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention provides glossy media for color printing applications, particularly for ink jet printing. More particularly, the media prepared using the coatings have the combination of good imaging characteristics, fast ink drying time, good mechanical strength of the coating, good waterfastness , and wide compatibility with different inks and different printers . Description of the Related Art

Ink jet printing is a printing technology in which color dots are formed on a substrate from the ink droplets ejected from nozzles in the print head. The inks are composed of solvent, molecular dyes (or pigmented dyes) , one or more cosolvents, and one or more surfactants. In most of the applications, water is the primary solvent. The substrate (ink jet media) can be plain paper, coated paper, plastic film, cloth, and any other media which can absorb ink and form a good image. The maximum amount of ink laid on the media in a solid composite black area depends on the printer type and resolution required, and usually ranges from 10g/m² to 60g/m².

In order to absorb the inks quickly and form a high resolution image, the substrate is usually coated with a specially formulated ink jet coating. These coatings can be divided into two major categories: fully dense coatings and porous coatings. The characteristics of these two types of coatings differ significantly. The dense coatings are mainly composed of film- forming polymers, at least one of the polymers is hydrophilic. This hydrophilic polymer is either water soluble or water swellable. Sometimes a small amount of pigment is incorporated into these coatings, but the amount of pigment is usually far below the critical pigment volume concentration. This type of coating gives a glossy surface and it is usually transparent.

The dense coatings absorb ink and form image through rapid swelling of the coating itself. The coating composition needs to be carefully tailored to ensure compatibility between the coating, the dye molecules, and the ink vehicles. Therefore, it is extremely difficult to design a dense polymeric coating which performs well on two different inks with different type and quantity of cosolvents, such as the inks used in Epson piezotype printers and the inks used in Hewlett Packard bubblejet printers. Other major disadvantages of dense coatings are the long ink dry time, low water resistivity of both the coating and the printed image, sensitivity of the image quality to the environment, and low dimensional stability of the coating when environmental conditions change. A polymeric coating is saturated with ink immediately after printing. This ink plasticizes the polymer coating and lowers the glass transition temperature of the coating. The coatings are tacky for a certain amount of time, usually from 30 seconds to 10 minutes, until enough solvent is evaporated from the coating to bring the glass transition temperature of the coating to near or above room temperature. During this time period, the image would smear if touched and it would block to another sheet of paper or film.

The polymeric coating needs to absorb a high amount of water rapidly to obtain a high quality image without bleeding and coalescence. On the other hand, it needs to be waterfast to provide durability. These two requirements frequently conflict with each other. It is very difficult to achieve good waterfastness and high water absorbency at the same time. The coating also needs to anchor the dye molecules in order to achieve image waterfastness . The dye molecules are water- soluble or at least water-dispersible in an aqueous ink and these same molecules need to be completely insolubilized once they are deposited and diffused into the coating. A complete insolubilization of the dye is difficult to achieve. The polymeric ink jet coating always contains moisture and the amount of moisture depends on the environment. The imaging characteristics and ink dry time is, therefore, a function of temperature and humidity. For example, under cold and dry conditions, the equilibrium moisture in the coating is low; the free volume is also low. The initial diffusion coefficient of ink in the coating is lower than in the same media which is exposed to a hot and humid atmosphere. Color bleeding and coalescence can occur. In a hot and humid environment, the equilibrium moisture in the coating is high. The free volume of the coating is higher than the dry and cold conditions. Dye molecules in the ink can easily diffuse into the coating. However, the image is likely to be tacky for a long time after printing and blocking resistance of the image is expected to be low. Different environmental conditions also affect the dimensional stability of the coating due to the moisture change in the polymer. An anticurl coating is generally needed in order to balance out the dimensional change of the coating with the atmosphere. This anticurl layer adds cost to the production process.

The second type of coating noted above for ink jet applications is a porous coating. This type of coating is usually composed of inorganic or organic particles bonded together by a binder. The amount of pigment particles in this type of coating is often far above the critical pigment volume concentration, which results in high porosity in the coating. During the ink jet printing process, ink droplets are rapidly absorbed into the coating through capillary action and the image is dry-to-touch right after it comes out of the printer. Therefore, a porous coating allows fast "drying" of the ink and produces a smear-resistant image. The dye molecules adsorb on the surface of the particles and form an image. High water resistance of both the coating and the image can be achieved with the porous coating. The performance of the porous ink jet coating is less sensitive to the compositions of the ink. Therefore, a universal media that performs well on all printers can be designed. The performance of a porous coating is also much less sensitive to the temperature and humidity of the environment, so consistent imaging characteristics and dry time can be expected. The disadvantages of this type of coating, however, include difficulties in achieving high gloss due to the high porosity in the coating.

The pigments used in nonglossy porous coatings are usually clay (US Patent 4,732,786), calcium carbonate (US Patent 4,474,847), magnesium carbonate (US Patent 5,338,597, 5227962, 5246774), silica (UK patent GB2129333, 2166063), surface modified silica (US Patent 5,372,884), zeolite, and alumina (US Patent 5,182,175). A combination of two or more of the above mentioned pigments can also be used. These porous coatings are composed of pigment particles or its aggregates in the size of 1 to 20 μm. Therefore, both the pigment particles and the large interstitial pores scatter light and result in a matte and opaque coating. Dye molecules should be kept on the top surface layer in order to achieve high optical density. Pigments with high surface area are desirable in order to keep the dye molecules on the surface layer.

Silica pigments are especially preferred in ink jet applications due to the availability of a variety of silica gels and precipitated silica with high surface area and high internal pore volume. US Patent No. 4780356 describes a coating composed of porous silica bonded by a water-soluble binder such as polyvinyl alcohol. The particles have a pore volume of 0.05-3.00 cc/g, a particle size of 0.1 to 5 μm, and a pore size of 1 to 500 nm. US Patent 5352503 describes a coating based on silica gel with polyvinyl alcohol as the binder, polyethylene glycol as curl -reducing agent, and a polyquartenary amine as a dye mordant.

The binders for these coatings are usually hydrophilic binders such as polyvinyl alcohol. The waterfastness of the coating is a function of the pigment to binder ratio. If the amount of binder is low enough so that all the polymer binder is adsorbed on the particle surface, good waterfastness can be achieved. However, the coating would have very little flexibility. This type of coating can be used for a plain paper coating, where a thinner coating layer is required since the base paper can absorb some of the ink vehicle. In the case of impermeable substrates such as polyester and polyvinyl chloride, or low permeability substrates such as highly sized glossy paper, a thick coating (10-80μm) is required to accommodate all the ink since the coating is the sole ink absorbent. This type of coating is not suitable due to its brittleness.

When the pigment to binder ratio decreases, the toughness of the coating increases and the porosity of the coating decreases. After the particle surface is fully covered with adsorbed binder, any additional binder occupies the interstitial space. The binders adsorbed on the particle surface has limited configuration and mobility, and it is water insoluble. The other part of the binder is free polymer and it dissolves in water. As the amount of free polymer increases, the coating loses its waterfastness . The ink jet media described in US Patent No. 5352503 falls into this category.

Porous and matte inkjet coatings are suitable for display purpose such as in the case of banners and billboard display. However, they are unsuitable for the applications when a glossy and photographic quality paper or a glossy film is needed.

A glossy porous media can be made by using very small particles so neither the pigment particles nor the pores formed between them would scatter light. A glossy surface can also be obtained by drying a wet or semiwet surface against a high gloss surface, i.e., cast coating.

US Patent Nos. 4879155, 5104730, 5264275, 5275867 and US Patent Nos. 5707716 and 5738932 disclose a type of porous coating which is composed of colloidal boehmite particles bonded together by a water-soluble binder such as polyvinyl alcohol and gelatin. The pore size in these coatings is controlled, so that the radius of the majority of pores lies between 1 and 10 nm.

Unlike the porous matte coating, these porous coatings are transparent or at least translucent due to the small particle size and pore size. High optical density can be achieved even when the dye molecules are not all kept on the surface layer. Good water fastness of both coating layer and printed image are achieved in this type of coating, because the polymer binder in the coating and the anionic dye in the inks are adsorbed on the surface of boehmite particles. Colloidal silica or its fine aggregates or agglomerates are also used to produce glossy porous coating. This is partially due to the wide availability and affordability of various types of silica: colloidal silica derived from sodium silicate, fine silica particles made from flame hydrolysis, and the fine agglomerations of these particles. EP patent 813978 (Konica) describes a porous glossy ink jet media based on flame silica. Polyvinyl alcohol is the major binder and liquid paraffin wax or phthalate are used as a plasticizer to reduce cracks in the coating. The described coating exhibits reasonable gloss (40-70% at 70°) . However, coating crack and low pore volume are still the major problems. EP patent 803374 describes a semigloss porous coating composed of fine silica gel particles and polyvinyl alcohol as a binder. These fine silica particles are made from large porous silica gel. A glossy porous coating can also be achieved through cast coating. Cast coated paper is prepared by pressing and drying a wet coated surface against a heated metal drum with a highly polished mirror- finish surface. The dried coating surface then copies the mirror-like surface of the drum. The cast coating technique has been practiced in the paper making industry for over 30 years and is described in US Patent Nos. 2678890, 2819184 and US Patent Nos. 3829325, 4109056. This technique has been recently modified to get a cast coated coating suitable for ink jet application. The major requirements of a glossy porous ink jet coating are high surface area of the pigment and high porosity of the coating. The high surface area is necessary to anchor the dye molecules close to the top surface in order to achieve high image density. The high porosity of the coating is necessary to rapidly transport and absorb the large amount of ink during printing in order to prevent bleeding between colors and to provide rapid ink dry time. EP707977 describes a coating where a non- film- forming styrene acrylate and colloidal silica particles are cast coated on top of an alumina coated paper. EP806301 describes casting a blend of silica gel and calcium carbonate particles along with organic binders on paper to achieve good gloss and good imaging properties. US Patent Nos. 5576088 and 5750200 describes a cast coated ink jet paper where colloidal particles were cast with a latex binder on top of a paper with a pigment-binder precoat; the pigment and binder precoat provides ink absorption and imaging properties while the cast -coated top coat provides gloss to the coating. EP879709 describes cast- coating a finely ground porous silica gel on paper to form a glossy ink jet coating. US Patent No. 5281467 describes a cast coated ink jet sheet composed of calcium carbonate-compounded silica and a binder. This coating composition and coating method is alleged to provide good gloss and good water resistance.

A porous coating composed of pseudoboehmite colloidal particles provides high gloss and good imaging properties. The disadvantage of this type of coating is the low mechanical strength of the coating. Boehmite crystal is soft, and a coating based on boehmite crystal is therefore, prone to mechanical damage such as scratching. An additional thin silica layer is sometimes coated on the top of the boehmite surface to improve the durability of the coating, such as described in U.S. Patent Nos. 5,463,178 and 5,472,773. This extra coating adds a processing step to the final product. A porous glossy coating based on colloidal silica or its fine agglomerates is hard and brittle. Therefore, this type coating is very prone to cracking. Plasticizers are sometimes used to minimize cracks in ^■ l i ¬

the coating and provide the coating with some flexibility. However, plasticizers reduce the strength of the coating and it also lowers the porosity of the coating. The cast coated glossy media has the advantages of utilizing the base paper as an ink vehicle reservoir and, therefore, less coating is needed to achieve the same goal of absorbing the maximum amount of ink per unit area. However, the cast coated media usually has low mechanical strength, there is usually cracks in the coating, and the printed sheets usually cockles in the heavy ink load area.

It is clear, therefore, that a porous glossy ink jet medium which can overcome the short-comings of the existing technology as discussed above is needed. It is, therefore, an object of the present invention to provide ink jet media which possesses good mechanical properties, fast ink drying time, superb imaging quality, good waterfastness, consistent performance in different environments, and wide compatibility with different printers and different inks. It has been discovered that these objectives can be achieved through the invention described herein.

Other objects will also become apparent to the skilled artisan upon a review of the following specification and the claims appended thereto. SUMMARY OF THE INVENTION The present invention provides printing media having a glossy and porous coating which exhibits good mechanical strength, high gloss, instant ink dry time, and good imaging density. The above properties are achieved by utilizing at least two different types of submicron pigment particles in the coating. The particles can be different in shape, e.g., at least one type of pigment particles are acicular or plate-like and the other kind of particles are equiaxed or spherical, and/or the particles can be a blend of particles with different surface chemistry, e.g., silicon and alumina or boehmite. An example of a porous glossy coating in accordance with the present invention is one composed of platelet shaped pseudoboehmite particles and equiaxed submicron porous silica gel particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating layer of the ink jet media of the present invention comprises a blending of submicron pigment particles, generally of different shape, and sometimes of different surface chemistry. The use of two different types of submicron particles is important. The use of particles with a different shape has been found to provide a higher porosity than either one alone can achieve. Particles of different surface chemistry provides better mechanical strength to the coating since, e.g., silica and alumina would act as a binder for each other in that they carry opposite surface charges. An example of the blended pigment particles is a blend of submicron porous silica gel with platelet pseudoboehmite particles where the silica gel particles increase the porosity and hardness of the coating and the pseudoboehmite particles increase the gloss of the coating and minimizes its tendency to crack.

The coating can be one layer or multilayers. In a one layer design, the majority of the pigment particles, i.e., greater than half, have to be smaller than 0.5μm in order to achieve suitable gloss. With a multilayer design, however, only the topmost layer needs to have the majority of the particles to be smaller than 0.5μm; while the layer below the topmost layer only needs to be smooth and porous. The size of the pores in this design generally falls into the mesopore region, i.e., 2-200nm. If the pore diameter falls below 2nm, they are considered micropores . Micropores are undesirable because they are smaller than most dye molecules and therefore, they filter out the dye molecules instead of adsorbing the dye molecules on the surface of the pores . If the pore diameter is greater than 200nm, they are considered macropores . Macropores are also undesirable in the topmost layer because they scatter light, which reduces the gloss and reduces transparency of the coating.

In the topmost coating layer, at least one type of pigment should be acicular or platelike in shape and at least one type of pigment should be equiaxed or spherical shape. Both types of pigment can be either porous or nonporous . It is preferred that at least 80% of the total pigment particles is smaller than 0.5μm in either diameter or in its length, in order to achieve good gloss. It is more preferred that at least 80% of the total pigment particles is smaller than 0.3μm. The size of the pigments, if necessary, can be measured by conventional techniques, e.g., X-ray diffraction, transmission electron microscope (TEM) and/or laser methods, as is well known in the art.

The acicular or plate-like particles are preferably comprised of one or more of the following materials: boehmite, pseudo-boehmite, elongated silica sol such as Snowtex-UP from Nissan Chemical, silicates such as

Attagel 50 --a needle-like hydrous magnesium aluminum silicate, aluminum trihydrate, clay, calcium carbonate, and other acicular or plate-like particles whose longest dimension is equal or greater than 1.5 times of the shortest dimension of the particle. The exact function of this type of particles is not entirely clear. However, it is speculated that the acicular or platelike shape helps film forming, reduces the cracking tendency, and improves the gloss of the coating. The amount of this type of pigment should be 10 to 96% of the total pigment .

The equiaxed or spherical particles are preferably comprised of one or more of the following materials: unmodified or surface modified colloidal silica, unmodified or surface modified porous silica gel or fine silica aggregates, fine silica particles made from flame hydrolysis, titanium oxide, aluminum oxide, mullite and non- film forming organic pigments or latex particles.

It is found that this type of pigment disturbs the dense packing of the acicular or plate-like type of particles and therefore, increases porosity of the coating. Most of these particles also increase the hardness and durability of the coating. The amount of this type of pigment should be 4 to 90% of the total pigment. If the amount is lower than 4%, the effect of increasing porosity and improving coating durability is minimal. If the amount is higher than 90%, there might be problems such as cracking and low coating gloss.

A small amount of organic binder is preferred to provide flexibility to this system. This binder can be water-soluble polymer or polymer latex. Examples of these polymers are polyvinyl alcohol, anionically or cationically modified polyvinyl alcohol, starch and modified starch, polyvinyl pyrrolidone, hydroxyethyl cellulose, carboxymethyl cellulose, casein, gelatin, polyethylene imine, polyethylene oxide, polyethylene glycol; SBR latex, NBR latex, polyacrylate emulsion, polyvinyl acetate latex, ethyl vinylacetate latex, and polyurethane dispersion. The amount of binder used should be 3 to 40 volume percentage based on the volume of the particles. Polyvinyl alcohol and modified polyvinyl alcohol are especially preferred as the binder for the submicron particles. Crosslinkers can be used with polyvinyl alcohol to further improve the wet strength of the coating. For example, boric acid, borate, or glyoxal can be used to crosslink partially hydrated polyvinyl alcohol. Polyaminoepichlorohydrin resin can be used to crosslink an acetoacetylated or carboxylated polyvinyl alcohol . In the case where all the pigment particles have an anionic surface, a small amount of dye- fixing agent should be used to provide the image with waterfastness . Both inorganic and organic materials can be used for this purpose. Inorganic materials include aluminum salt, calcium and magnesium salt, aluminum complex, zirconium oxychloride, zirconium hydroxychloride, and zirconium nitrate. Organic dye mordants include cationic monomers, oligomers, and polymers. Examples of cationic polymers are polyquaternary amine , polyethylene imine, copolymer of vinyl pyrrolidone and di ethylaminoethyl methacrylate, copolymer of vinyl pyrrolidone and methylvinylimidazole chloride. The cationic polymer is not necessary when the media is used in combination with a waterfast pigmented ink, such as the pigmented ink described in US Patent No. 5,503,664, which patent is incorporated by reference herein. If the cationic dye mordants coagulate the coating fluid and causes the coating to lose its gloss, it can be coated on the porous and glossy coating separately as a wash coat .

The substrate for this coating can be sized papers, papers with glossy barrier layer, polyester films, and polyvinyl chloride films. The glossy paper can be polyolefin coextruded paper, paper with a UV cured glossy layer, paper with an acrylic layer, a SBR layer, or a polyurethane barrier layer. The coating thickness ranges from 5μm to lOOμm, depending on the drop size and resolution of the printers. For each printer and resolution combination, there is a critical thickness of the coating below which ink coalescence and color bleeds occur. The coating thickness should be l-5μm above the critical thickness in order to achieve high resolution image and fast drying properties.

This invention is further illustrated by the following examples. In these examples, the shape of the pigment particles is equiaxed or spherical unless otherwise indicated. Gloss of the coated sheets was measured using a HunterLab ProGloss meter and the gloss at 60° is reported. Then color blocks of cyan, magenta, yellow, black, red, green and blue were printed using an Epson Stylus Photo (Epson 700) printer. Bleed between red and green was visually inspected and described in the Table below.

The ink dry time was measured as follows: a black strip and a blue strip (heightxwidth=lcmx20cm) were printed side by side on the tested samples, after the samples have been conditioned at 23 °C and 50% RH for 4 hours. Immediately after printing, the sample was placed on a flat surface and an area of black was smeared into the unimaged area with one finger tip while applying moderate pressure. The same procedure was applied to the blue color area. The above steps were repeated every 15 seconds until the ink did not smear beyond the printed area. This was recorded as the ink dry time. The waterfastness was tested in two different ways : drip test and wet -rub resistance. In the drip test, four strips (4x30mm) of cyan, magenta, yellow, and black were printed in the same column with 10mm unprinted area between each strip. The image was allowed to air dry for one hour. It was then clamped to a hard board and held at a 45° angle. Then 0.05cc distilled water was dispensed right above the topmost strip and the water was allowed to run down the color strips naturally. The water resistance of the image was then visually observed and rated on a scale of 1 to 10. A rating of 10 indicates perfect waterfastness of all colors, while a rating of 1 indicates massive color running. When the waterfastness is lower than 10, the specific colors which exhibits inferior waterfastness are indicated in the parenthesis in the Table below. For example, (C, K) indicates that the cyan and black color exhibit less than perfect waterfastness in the drip test . In the wet rub resistance test, color blocks of cyan, magenta, yellow, and black were printed and allowed to air dry for an hour. These blocks were then immersed in distilled water for ten minutes. The image was then pad dried and rubbed under moderate pressure with a 100% cotton wiper (TexWipe TX309, a double-sided twill- pattern cotton wiper woven in a cross section of 118x60 threads per squared inch) . The images were rubbed back and forth 3 times. The wet rub resistance of the image was visually inspected and rated on a scale of 1 to 10. A rating of 10 means no damage occurred to either the image or the coating after a wet-dry rub. A rating of 1 means the image was completely ruined.

Example 1

The following components were gathered: (a) 13.33 g 0.5μm porous alumina (Ceralox APA-0.5G from Condea Vista Company, 30% dispersion in water)

(b) 22.22 g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g) (c) 43.38 g water

(d) 24g acetoacetylated polyvinyl alcohol solution (10% solution, Gohsefimer Z-320 from Nippon Gohsei)

(e) 106.67g platelet boehmite slurry (Dispal 14N4- 25 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 13nm, crystallite size (120) : 26nm ) (f) 6.4g polyaminoepichlorohydrin resin solution (K ene 557H from Hercules, 12.5% solution)

First, (a), (b) and (c) were mixed together, then (d) was slowly added to the above mix. This mix was slowly stirred for ten minutes and then (e) and (f) were added to the mix and mixed for five more minutes. The mixed lacquer was then coated on a polyethylene coextruded paper (a 115 g/m² base paper with 24 g/m² polyethylene coextruded on both sides of the base paper) with a #120 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated. The results are reported in the Table below.

Example 2

The following components were gathered:

(a) 5 g of 0.3μm silica gel slurry (Grace Davison, 20%solid, pH=8.5, internal pore volume 0.8cc/g)

(b) IN nitric acid (c) 16.67 g of 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(d) 8.94 g water

(e) 22.86 g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed) (f) 53.33g boehmite slurry (Dispal 11N7-80 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 20nm, crystallite size (120) : 38nm)

(g) 1.6g boric acid solution (5% solution in warm water)

IN nitric acid was added dropwise to (a) until the pH of (a) was lowered to the range of 2.8-3.5. Then (c) and (d) were added to it and mixed. Then (e) was slowly added to the above mix and this mix was slowly stirred for ten minutes, and then (f) was added to the mix and mixed for five more minutes. Then (g) was added slowly to the mix and mixed for five more minutes. The mixed lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #120 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated. The results are reported in the Table below.

Example 3

The following components were gathered: (a) 33.33g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g) (b) 46.67g boehmite slurry (Dispal 11N7-80 from

Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 20nm, crystallite size (120) : 38nm) (c) 3.94 g water

(d) 22.86 g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed) (e) 1.6g boric acid solution (5% solution in warm water)

(a) , (b) , and (c) were added together and mixed. To this mix, (d) was added slowly and mixed for ten minutes. Then (e) was added slowly and mixed for five minutes. The mixed lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #120 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated, with the results being reported in the Table below.

Example 4

The following components were gathered: (a) 16.67 g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(b) 10 g Iμm cationic modified silica gel slurry (Grace Davison, WSSG 1CA, 20% solid, pH=3-4, internal pore volume 0.8cc/g)

(c) 15.23g water (d) 50g boehmite slurry (Dispal 11N7-80 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 20nm, crystallite size (120) : 38nm)

(e) 12g acetoacetylated polyvinyl alcohol solution (10% solution, Gohsefimer Z-320 from Nippon Gohsei)

(f) 3.2g polyaminoepichlorohydrin resin solution (Kymene 557H from Hercules, 12.5% solution)

(a) , (b) , (c) , and (d) were added together and mixed. To this mix, (e) was added slowly and mixed for ten minutes. Then (f) was added slowly and mixed for five minutes. The mixed lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #120 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated. The results are reported in the Table below.

Comparative Example 1 ; Only plate- like boehmite particles are used as pigment The following components were collected:

(a) 66.67g boehmite slurry (Dispal 11N7-80 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size

(020) : 20nm, crystallite size (120) : 38nm)

(b) 21.29g distilled water (c) 17.14g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed) (d) 1.20 g boric acid solution (5% solution in warm water)

(a) and (b) were combined and then (c) was added slowly and mixed for 10 minutes. Then (d) was added and mixed for five more minutes. The lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #120 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated, with the results being reported in the Table below.

Comparative Example 2 : Only equiaxed or spherical particles are used as pigment The following components were gathered:

(a) 88.89g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(b) 11.76g colloidal silica (Nalco 1034A from Nalco Chemical Company, pH=2.8 , particle size: 20nm,

34%solid)

(c) 25g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 8% solution, 88% hydrolyzed) (d) 2g boric acid solution (5% solution in warm water) (a) and (b) were combined and then (c) was added slowly and mixed for ten minutes. Then (d) was added slowly and mixed for five more minutes. The lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #130 Myer rod and dried at 110°C for 3 minutes to achieve a 37 g/m² coating. The gloss of the coating was then measured and the coating was imaged with an Epson Stylus Photo printer. The dry time and color bleed were evaluated. The results are reported in the Table below.

Examples 5, 6, and 7 are of a two layer design medium. Each medium was tested for waterfastness, dry time, color bleed and cracking, with the results reported in the Table below.

Example 5

A base-coat layer was prepared using the following slurries and solutions :

(a) 33.33g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(b) 20g boehmite slurry (Dispal 14N4-25 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 13nm, crystallite size (120) : 26nm)

(c) 5.06 g distilled water (d) 60g lμm cationic modified silica gel slurry

(Grace Davison, WSSG 1CA, 20% solid, pH=3-4, internal pore volume 0.8cc/g) (e) 34.29 partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed)

(f) 8.83g colloidal silica (Nalco 1034A from Nalco Chemical Company, pH=2.8 , particle size: 20nm, 34%solid)

(g) 0. lg glyoxal

(a) , (b) , (c) , and (d) were combined and stirred. Then (e) was added slowly and mixed for 10 minutes. (f) was then added to the above mix and mixed for 5 minutes . Then (g) was added slowly and mixed for 5 minutes. The mixed lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #50 Myer rod and dried at 110°C for 3 minutes to achieve a 18 g/m² coating . A topcoat layer was prepared using the following slurry and solutions :

(a) 26.67g boehmite slurry (Dispal 14N4-25 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 13nm, crystallite size (120) : 26nm) (b) 26.96g distilled water

(c) 8g acetoacetylated polyvinyl alcohol solution (10% solution, Gohsefimer Z-320 from Nippon Gohsei)

(d) 5.88g colloidal silica (Nalco 1034A from Nalco Chemical Company, pH=2.8 , particle size: 20nm, 34%solid) (e) 1.6g polyaminoepichlorohydrin resin solution (Kymene 557H from Hercules, 12.5% solution) (a) and (b) were combined and then (c) was added slowly and stirred for 10 minutes. Then (d) was added and mixed for 5 minutes. (e) was then added and mixed for 5 more minutes . The lacquer was then coated on the top of the above basecoat which was prewetted with water, to achieve a coating weight of 12 g/m².

Example 6

A topcoat layer was prepared using the following slurry and solutions: (a) lOg chain-like silica (Snowtex-UP from Nissan Chemical Industries, 20% solid, width: 5-20nm, length: 40-300nm, pH=9-10

(b) 17.35 g distilled water

(c) IN nitric acid (d) 20g boehmite slurry (Dispal 14N4-25 from

Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 13nm, crystallite size (120) : 26nm)

(e) 4.65g cationic modified colloidal silica (Nyacol IJ222 from Akzo Nobel, 43% solid, pH=4 , particle diameter: 70nm)

(f) 8g acetoacetylated polyvinyl alcohol solution (10% solution, Gohsefimer Z-320 from Nippon Gohsei)

(g) 1.6g polyaminoepichlorohydrin resin solution (Kymene 557H from Hercules, 12.5% solution) (a) and (b) were combined and then (c) was added dropwise until pH was lowered to 2.5-3. Then (d) and (e) were added and mixed for 2 minutes. Then (f) was added slowly and mixed for 10 minutes. (g) was then added and mixed for five more minutes . The lacquer was then coated on the top of the same basecoat as in Example 5, to achieve a coating weight of 12g/m².

Example 7

A base coat layer was prepared using the following slurries and solution:

(a) 40g 0.5μm porous alumina (Ceralox APA-0.5G from Condea Vista Company, 30% dispersion in water) (b) 22.22g 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(c) 13.33g boehmite slurry (Dispal 14N4-25 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 13nm, crystallite size (120) : 26nm)

(d) 7.99 g distilled water

(e) 22.86 g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed) (f) 2g boric acid solution (5% solution in warm water)

(a) , (b) , (c) , and (d) were combined and mixed for

2 minutes. (e) was then added slowly into it and mixed for 10 minutes. Then (f) was added slowly and mixed for 5 minutes. The lacquer was then coated on the same polyethylene coextruded paper used in Example 1 with a #50 Myer rod and dried at 110°C for 2 minutes to achieve a 18 g/m² coating.

A topcoat layer was prepared using the following slurries and solution: (a) 12.65g distilled water

(b) 26.67g boehmite slurry (Dispal 11N7-80 from Condea Vista Chemical, 30% solid, pH=4 , crystallite size (020) : 20nm, crystallite size (120) : 38nm)

(c) ll.llg 0.3μm cationic modified silica gel slurry (Grace Davison, SMSG 3CS, 18% solid, pH=3-4, internal pore volume 0.7cc/g)

(d) 8.57g partially hydrolyzed polyvinyl alcohol solution (Airvol 540 from Air Product and Chemicals, 7% solution, 88% hydrolyzed) (e) l.OOg cationic dispersion of styrene acrylic copolymer (Basoplast 265D from BASF, 20% solid, Tg=37°C, particle size: 70nm)

(a) , (b) , and (c) were combined and mixed for 2 minutes. Then (d) was added slowly and mixed for 10 minutes. Then (e) was added and mixed for 5 more minutes. The lacquer was then coated on the top of the above basecoat which was prewetted with water, to achieve a coating weight of 12 g/m². Table; Durability and Performance of the Coatings

Based upon a review of the results of the foregoing examples, it is clear that when the coating only contains the elongated particles, such as in the case of Comparative Example 1, it has lower porosity than the coating on the medium of the present invention. This lower porosity is reflected in the high bleed level between the red and the green color. The coatings which contain only equiaxed or spherical particles also has lower porosity, such as illustrated in Comparative Example 2. The coatings contain only equiaxed or spherical particles also has lower gloss and has severe cracking tendency. In Examples 1 through 7, the pigment particles involved a blend of different shaped particles, i.e., equiaxed particles and elongated particles, in accordance with the present invention. The coatings exhibited higher porosity than when either one of them was used alone. The cracking tendency of the coatings were also greatly reduced or eliminated. A glossy coating with instant ink dry time, good water- resistance, good mechanical strength, and wide compatibility with different types of printers and inks is, therefore, provided by the present invention.

While the invention has been explained in the relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reviewing the specification. Therefore, it is to be understood that the invention disclosed to you and is intended to cover such modifications has fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An ink jet medium comprised of a substrate and an ink receptive coating, with the ink receptive coating comprising a mixture of different shape submicron pigment particles.

2. The ink jet medium of claim 1, wherein the mixture of submicron pigment particles comprises a mixture of acicular or plate-like particles, and equiaxed or spherical particles.

3. The ink jet medium of claim 2, wherein the mixture of particles is comprised of platelet shaped pseudoboehmite particles and equiaxed submicron porous silica gel particles.

4. The ink jet medium of claim 1, wherein the mixture of particles further comprises a mixture of particles having different surface chemistry.

5. The ink jet medium of claim 4, wherein the particles of different surface chemistry comprise silica and alumina .

6. The ink jet medium of claim 2, wherein the mixture of particles further comprises a mixture of particles having different surface chemistry.

7. The ink jet medium of claim 6, wherein the particles of different surface chemistry comprise silica and alumina.

8. The ink jet medium of claim 1, wherein the majority of particles are smaller than 0.5 μm.

9. The ink jet medium of claim 2, wherein the majority of particles are smaller than 0.5 μm.

10. The ink jet medium of claim 1, wherein the ink receptive coating further comprises a binder.

11. The ink jet medium of claim 10, wherein said binder comprises polyvinyl alcohol .

12. The ink jet medium of claim 11, wherein polyvinyl alcohol is crosslinked.

13. The ink jet medium of claim 2, wherein the ink receptive coating further comprises a binder.

14. The ink jet medium of claim 13, wherein said binder comprises polyvinyl alcohol .

15. The ink jet medium of claim 12, wherein polyvinyl alcohol is crosslinked.

16. The ink jet medium of claim 1, wherein the ink receptive coating comprises more than one layer, with the topmost layer containing the mixture of different shape pigment particles.

17. The ink jet medium of claim 16, wherein at least 80% of the total pigment particles in the topmost layer are smaller than 0.5 μm in either diameter or its length.

18. The ink jet medium of claim 17, wherein at least 80% of the total pigment particles in the topmost layer are smaller than 0.3 μm.

19. The ink jet medium of claim 12, wherein the ink receptive coating comprises more than one layer, with the topmost layer containing the mixture of different shape pigment particles.

20. The ink jet medium of claim 19, wherein at least 80% of the total pigment particles in the topmost layer are smaller than 0.5 μm in either diameter or its length.

21. The ink jet medium of claim 20, wherein at least 80% of the total pigment particles in the topmost layer are smaller than 0.3 μm.

22. The ink jet medium of claim 16, wherein the topmost layer of the ink receptive coating further comprises a binder.

23. The ink jet medium of claim 22, wherein said binder comprises polyvinyl alcohol .

24. The ink jet medium of claim 23, wherein polyvinyl alcohol is crosslinked.

25. The ink jet medium of claim 19, wherein the topmost layer of the ink receptive coating further comprises a binder.

26. The ink jet medium of claim 25, wherein said binder comprises polyvinyl alcohol .

27. The ink jet medium of claim 26, wherein polyvinyl alcohol is crosslinked.

28. A process for preparing the ink receptive coating of the ink jet medium of claim 1, comprising mixing an unmodified silica slurry with boehmite, with the pH of the silica slurry being lowered to the range of 2-4 before adding the boehmite.