INK-JET PRINTING MEDIA

Abstract: A printing medium which may be ink jet printed to provide images of improved quality comprises a substrate having at least one surface, and a substantially nonporous coating on the surface wherein the coating comprises transparent, colorless alumina monohydroxide and water-soluble organic polymer, and wherein the water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. A printing medium which may be ink jet printed eliminates or reduces coalescence of a wide variety of ink jet printing inks and often provides fast drying times. This embodiment comprises: (a) a substrate having at least one surface; and (b) a coating on the surface wherein the coating comprises: (1) a binder comprising organic polymer, wehrein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 20 percent by weight of the organic polymer; and (2) discrete particles dispersed in the binder, which particles have a number average particle size in the range of from 1 to 500 nanometers.

Description: INK-JET PRINTING MEDIA The present invention is in respect of printing media which may be ink jet printed and to coating compositions which may be used to form the printing media. The invention comprises several principal embodiments, or Parts, and various embodiments within each Part. Except aε noted below, the descriptions of the various Parts are substantially autonomous. Other than in the operating examples or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about" . PART I Ink-jet printing produces little noise and can be used to print single color images or multicolor images on various substrates. Plain paper or paper having a low degree of sizing can be used as the printing substrate, but these suffer from the disadvantage that a clear image cannot be obtained because of the diffusion of the ink into the paper. More particularly, the image lacks sharp resolution, and in the case of color printing, the image lacks good optical density. In order to achieve ink-jet printed images of improved quality, coated papers have been employed as the printing substrates. The image quality varies depending upon the type of coating employed. In most instances image quality is better than that obtained using uncoated paper, but it is still less than desired. Similarly, ink-jet printing has been used to print single color images or multicolor images on organic polymer media, but spreading of the ink on organic polymer surfaces presents many problems, including lack of sharp image resolution, and in the case of color printing, the image lacks good optical density. Coatings have provided some improvement, but image quality is still far less than desired. Ink jet printing inks contain large amounts of solvents. In order to form high quality images, it iε necessary for the printing media to quickly remove most of the solvent from the surface of the printing medium and yet retain the colorants within localized areas. One coating used m the past is a porous coating comprising substantially transparent, colorless alumina monohydroxide, e.g., pseudo-boehmite, and organic polymer. Such coatings were porous because it was believed that coating porosity was necessary to accomplish rapid solvent removal. Images of somewhat improved quality were obtained using these coatings, but image quality was still less than desired. It has now been found that image quality is considerably improved if the coating is substantially nonporous, rather than porous. This is surprising since the solvents of the inks must still be quickly removed from the surface. It has also been found that image quality is improved if water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer are both present. Accordingly, one embodiment of Part I of the invention is a printing medium comprising: (a) a substrate having at least one surface; and (b) a substantially nonporous coating on the surface wherein the coating comprises transparent, colorless alumina monohydroxide and water-soluble organic polymer, and wherein the water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. As used herein and in the claims, a coating is substantially nonporous when the pore volume of the coating is less than 0.01 cubic centimeters per gram (cm 3 /g) . Often the pore volume of the coating is less than 0.005 cm /g. Preferably the pore volume iε less than 0.001 cm /g. Also as used herein and in the claims, the pore volume of the coating is determined using a Micromeritics Model ASAP 2400 Accelerated Surface Area and Porosimetry Instrument (Micromeritics Instrument Corporation) and nitrogen as the adsorbate in accordance with the accompanying operating manual in which the following choices and modifications are followed: (a) samples are prepared by drying for 6 hours under vacuum at ambient room temperature, (b) a dried sample weight of approximately 0.2 gram is used, (c) 40 adsorption points are used, (d) 40 desorption points are used, and (e) the BJH cumulative desorption pore volume of the pores having diameters between 1.7 nanometers and 300 nanometers reported by the instrument is taken as the pore volume. Transparent, colorless alumina monohydroxide, AlO(OH) , is known. Its preparation and properties are described by B. E. Yoldas in The American Ceramic Society Bulletin. Vol. 54, No. 3, (March 1975), pages 289-290, in Journal of Applied Chemical Biotechnology, Vol. 23 (1973), pages 803-809, and in Journal of Materials Science. Vol. 10 (1975) , pages 1856-1860. Briefly, aluminum isopropoxide or aluminum secondary-butoxide are hydrolyzed in an excess of water with vigorous agitation at from 75 C to 80°C to form a slurry of aluminum monohydroxide. The aluminum monohydroxide is then peptized at temperatures of at least 80°C with an acid to form a clear alumina monohydroxide sol which exhibits the Tyndall effect when illuminated with a narrow beam of light. Since the alumina monohydroxide of the sol is neither white nor colored, it iε not a pigment and does not function as a pigment in the present invention. The acid employed is noncomplexing with aluminum, and it has sufficient strength to produce the required charge effect at low concentration. Nitric acid, hydrochloric acid, perchloric acid, acetic acid, chloroacetic acid, and formic acid meet these requirements. The acid concentration is usually in the range of from 0.03 to 0.1 mole of acid per mole of aluminum alkoxide. Although it is desired not to be bound by any theory, it iε believed that the alumina monohydroxide produced in this manner iε pseudo-boehmite. Pseudo-boehmite is indeed the preferred transparent, colorless alumina monohydroxide for use in the present invention. The amount of transparent, colorless alumina monohydroxide in the coating may vary widely. Often the transparent, colorless alumina monohydroxide constitutes from 10 to 87 percent by weight of the coating. In many cases the transparent, colorless alumina monohydroxide constitutes from 50 to 85 percent by weight of the coating. From 70 to 85 percent by weight is preferred. The water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. Organic polymer of either or both classes may or may not be insolubilized as desired. As used herein and in the claimε, insolubilized water-soluble organic polymer is organic polymer which is water-soluble when applied to the substrate and which iε completely or partially insolubilized after such application. Preferably the insolubilizer reacts with water-soluble noncellulosic organic polymer to provide the desired degree of insolubilization to the total organic polymer of the coating. There are many widely varying types of water-soluble cellulosic organic polymers which may be employed in the present invention. Of these, the water-soluble cellulose ethers are preferred water-soluble cellulosic organic polymers. Many of the water-soluble cellulose ethers are also excellent water retention agents. Examples of the water-soluble cellulose ethers include water-soluble methylcellulose [CAS 9004-67-5] , water-soluble carboxymethylcellulose, water-soluble sodium carboxymethylcellulose [CAS 9004-32-4] , water-εoluble ethylmethylcelluloεe, water-soluble hydroxyethylmethylcellulose [CAS 9032-42-2] , water-soluble hydroxypropylmethylcellulose [CAS 9004-65-3] , water-soluble hydroxyethylcellulose [CAS 9004-62-0] , water-soluble ethylhydroxyethylcellulose, water-soluble sodium carboxymethylhydroxyethylcellulose, water-soluble hydroxypropylcellulose [CAS 9004-64-2] , water-soluble hydroxybutylcellulose [CAS 37208-08-5] , water-soluble hydroxybutylmethylcellulose [CAS 9041-56-9] and water-soluble cellulose sulfate sodium salt [CAS 9005-22-5] . Water-soluble hydroxypropylcellulose is preferred. Water-soluble hydroxypropylcellulose is a known material and is available commercially in εeveral different average molecular weights . The weight average molecular weight of the water-soluble hydroxypropylcellulose used in the present invention can vary widely, but usually it is in the range of from 100,000 to 1,000,000. Often the weight average molecular weight is in the range of from 100,000 to 500,000. From 200,000 to 400,000 is preferred. Two or more water-soluble hydroxypropylcelluloses having different average molecular weights may be admixed to obtain a water-soluble hydroxypropyl cellulose having a differing average molecular weigh . Similarly, there are many widely varying kinds of water-soluble noncellulosic organic polymers which may be employed in the present invention. Examples of the water-soluble noncellulosic organic polymers include water-soluble poly(vinyl alcohol), water-soluble poly(vinylpyrrolidone) , water-soluble poly(vinylpyridine) , water-soluble poly(ethylene oxide), water-soluble poly(ethylenimine) , water-soluble ethoxylated poly(ethyleni ine) , water-soluble poly(ethylenimine) - epichlorohydrin, water-soluble polyacrylate, water-soluble sodium polyacrylate, water-soluble poly(acrylamide) , water-soluble carboxy modified poly(vinyl alcohol) , water-εoluble poly(2-acrylamido-2-methylpropane sulfonic acid) , water-soluble poly(styrene sulfonate) , water-soluble vinylmethyl ether/maleic acid copolymer, water-soluble styrene-maleic anhydride copolymer, water-soluble ethylene- maleic anhydride copolymer, water-soluble acrylamide/acrylic acid copolymer, water-soluble poly(diethylene triamine-co- adipic acid) , water-soluble poly[ (dimethylamino) ethyl methacrylate hydrochloride] , water-soluble quatemized poly(imidazoline) , water-εoluble poly(N,N-dimethyl-3 , 5- dimethylene piperidinium chloride) , poly(dimethyldiallylammonium chloride) , poly(vinylbenzyltrimethylammonium chloride) , water-soluble poly(vinylpyridinium halide) , water-soluble poly[ (methacryloyloxyethyl) (2-hydroxyethyl) dimethylammonium chloride] , water-soluble poly(alkylenepolyaminedicyandiamide ammonium condensate), water-soluble poly( (meth)acrylamidealkyl quaternary salts, water-soluble starch, water-soluble oxidized starch, water-soluble cationized starch, water-soluble casein, water-soluble gelatin, water-soluble sodium alginate, water-soluble carrageenan, water-soluble dextran, water-soluble gum arabic, water-soluble pectin, water-soluble albumin, and water-soluble agar-agar. Water-soluble poly(vinyl alcohol) is preferred. Water-soluble poly(vinyl alcohol) may be broadly classified as one of two typeε. The firεt type iε fully hydrolyzed water-soluble poly(vinyl alcohol) in which less than 1.5 mole percent acetate groups are left on the molecule. The second type is partially hydrolyzed water-soluble poly(vinyl alcohol) in which from 1.5 to as much as 20 mole percent acetate groups are left on the molecule. The water-εoluble organic polymer may comprise either type or a mixture of both. The fully hydrolyzed water-soluble poly(vinyl alcohol) is preferred. The amount of water-soluble organic polymer in the coating may vary widely. Often the water-soluble organic polymer constitutes from 13 to 90 percent by weight of the coating. In many cases the water-soluble organic polymer constitutes from 15 to 50 percent by weight of the coating. From 15 to 30 percent by weight is preferred. The water-soluble organic polymer of the coating comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. Usually the water-soluble cellulosic organic polymer constitutes from 5 to 95 percent by weight of the water-soluble organic polymer and the water-soluble noncellulosic organic polymer constitutes from 5 to 95 percent by weight of the water-soluble organic polymer. Frequently the water-soluble cellulosic organic polymer constitutes from 30 to 90 percent by weight of the water-soluble organic polymer and the water-soluble noncellulosic organic polymer constitutes from 10 to 70 percent by weight of the water-soluble organic polymer. Preferably the water-soluble cellulosic organic polymer constitutes from 60 to 80 percent by weight of the water-soluble organic polymer and the water-soluble noncellulosic organic polymer constitutes from 20 to 40 percent by weight of the water-soluble organic polymer. The coating comprising transparent, colorless alumina monohydroxide and organic polymer may itself be substantially transparent, substantially opaque, or of intermediate transparency. It may be subεtantially colorless, it may be highly colored, or it may be of an intermediate degree of color. Preferably the coating comprising transparent alumina monohydroxide and organic polymer is itself substantially transparent and subεtantially colorleεε. Aε used herein and in the claims, the coating is substantially transparent if the luminous transmission in the visible region is at least 80 percent of the incident light. Often the luminous transmisεion is at least 85 percent of the incident light. Preferably the luminous transmission iε at leaεt 90 percent. Also as used herein and in the claims, the coating is substantially colorless if the transmission is subεtantially the same for all wavelengths in the visible region. The subεtrate may be any substrate at least one surface of which is capable of bearing the coating discussed above. In most instances the subεtrate iε in the form of an individual sheet or in the form of a roll, web, strip, film, or foil of material capable of being cut into sheets. The substrate may be porous throughout, but it is preferred that printing medium comprise: (a) a substrate having at least one substantially nonporous surface; and (b) a subεtantially nonporous coating on the surface wherein the coating comprises transparent, colorless alumina monohydroxide and organic polymer, and wherein the water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. An example of a porous substrate is paper. Another example is cloth. When, as is preferred, the substrate has at least one subεtantially nonporouε εurface, the εubεtrate may be εubstantially nonporous throughout or the surface may be subεtantially nonporouε irrespective of how much of the remainder of the substrate is porous. Examples of substrateε which are εubstantially nonporouε throughout and hence have at least one εubstantially nonporous surface, include sheetε or films of organic polymer such as poly(ethylene terephthalate) , polyethylene, polypropylene, cellulose acetate, and copolymers εuch aε saran. Additional examples include metal foilε εuch as aluminum foil. Yet another example is a porous or microporous foam comprising thermoplastic organic polymer which foam has been compressed to such an extent that the resulting deformed material is substantially nonporous. The subεtrate may or may not include one or more coatingε or laminations between the base stock and the subεtantially nonporouε coating which compriεeε alumina monohydroxide and organic polymer and which is deεcribed above. Baεe εtocks which are normally porous such as for example paper, cloth, nonwoven fabric, felt, porous foam, or microporouε foam may be coated or laminated to render one or more surfaceε substantially nonporous and thereby provide substrates having at least one substantially nonporous surface. The substrate may be substantially tranεparent, it may be substantially opaque, or it may be of intermediate transparency. For some applications such aε ink-jet printed overhead slides, the substrate must be sufficiently transparent to be useful for the application. For other applications such as ink-jet printed paper, transparency of the substrate iε not so important. The printing media of Part I of the invention may be made by coating a substantially nonporous surface of the substrate with a coating composition comprising: (a) transparent, colorless alumina monohydroxide; (b) aqueous solvent; and (c) water-soluble organic polymer disεolved in the aqueous solvent; wherein the water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. The discussionε above in respect of the alumina monohydroxide, the water-soluble cellulosic organic polymer, and the water-soluble noncellulosic organic polymer, are applicable here. The weight ratio of the alumina monohydroxide to water-soluble organic polymer in the coating composition may vary considerably, but it is usually in the range of from 11:100 to 670:100. Often the weight ratio is in the range of from 100:100 to 567:100. Preferably it is in the range of from 233:100 to 567:100. The discussions above in respect of the proportions of water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer water-soluble organic polymer in - li ¬ the water-soluble organic polymer, are applicable to the coating composition as well as to the coating. In most instances the aqueous solvent is water. Organic cosolvents miscible with water may optionally be present when desired. The amount of aqueous solvent present in the coating composition may vary widely. The minimum amount is that which will produce a coating composition having a viscoεity low enough to apply as a coating. The maximum amount is not governed by any theory, but by practical considerations such as the coεt of the solvent, the minimum desired thickness of the coating to be deposited, and the cost and time required to remove the solvent from the applied wet coating. Uεually, however, the aqueous solvent constitutes from 80 to 98 percent by weight of the coating composition. Often the aqueous solvent constitutes from 85 to 95 percent by weight of the coating composition. Preferably aqueous solvent constitutes from 85 to 90 percent by weight of the composition. A material which may optionally be present in the coating composition is insolubilizer. Insolubilizers are materials which react with functional groups of water-soluble organic polymerε, especially those of water-εoluble noncellulosic organic polymers, and generally function as crosslinking agents. There are many available insolubilizers which may be used. Examples of suitable insolubilizers include, but are not limited to, Curesan ® 199 insolubilizer (PPG Industries, Inc., Pittsburgh, PA), Curesan ® 200 insolubilizer (PPG Industries, Inc.), Sequarez ® 700C insolubilizer (Sequa Chemicals, Inc., Chester, SC) , Sequarez ® 700M insolubilizer (Sequa Chemicals, Inc.), Sequarez ® 755 insolubilizer (Sequa Chemicals, Inc.), Sequarez ® 770 insolubilizer (Sequa Chemicals, Inc.), Berset ® 39 insolubilizer (Bercen Inc., Cranston, RI), Berset ® 47 insolubilizer (Bercen Inc.), Berset ® 2185 insolubilizer (Bercen Inc.), and Berset ® 2586 insolubilizer (Bercen Inc. ) . When used, the amount of insolubilizer preεent in the coating composition may vary considerably. In such instances the weight ratio of the insolubilizer to the water-soluble noncellulosic organic polymer is usually in the range of from 0.05:100 to 25:100. Often the weight ratio is in the range of from 2:100 to 10:100. From 4:100 to 6:100 is preferred. These ratios are on the basiε of inεolubilizer dry εolidε and water-εoluble noncelluloεic organic polymer dry εolid . There are many other materials which may optionally be present in the coating composition. These include such materialε aε lubricants, waxes, antioxidants, organic solvents, mordants, lakes, and pigments. The listing of such materialε iε by no meanε exhaustive. These and other ingredients may be employed in their customary amounts for their customary purposes so long as they do not seriously interfere with good coating composition formulating practice. The coating compositions are usually prepared by simply admixing the various ingredients. The ingredients may be mixed in any order, but it is preferred to mix the dry ingredients together before mixing with liquid. Although the mixing of liquid and solids iε uεually accomplished at room temperature, elevated temperatures are sometimes used. The maximum temperature which is usable depends upon the heat stability of the ingredients. The coating compositions are generally applied to the surface of the substrate using substantially any technique known to the art. These include spraying, curtain coating, dipping, rod coating, blade coating, roller application, εize preεε, printing, brushing, drawing, die-slot coating, and extrusion. The coating is then formed by removing the solvent from the applied coating composition. This may be accomplished by any conventional drying technique. Coating composition may be applied once or a multiplicity of times. When the coating composition is applied a multiplicity of times, the applied coating is usually but not necessarily dried, either partially or totally, between coating applications. Once the coating composition has been applied to the paper, the solvent is εubstantially removed, uεually by drying. Optionally the substantially nonporous coating containing the transparent alumina monohydroxide and water-soluble organic polymer may be overlaid with an overcoating comprising ink-receptive organic polymer. The overcoating may be formed by applying an overcoating composition comprising solvent and ink-receptive organic polymer dissolved in the solvent and removing the solvent, as for example, by drying. Preferably the solvent is an aqueous solvent and the ink-receptive organic polymer iε water-εoluble celluloεic organic polymer, both of which have been described above in respect of the alumina monohydroxide-containing coating. Water is an especially preferred aqueous solvent and hydroxypropylcellulose is an especially preferred water-soluble cellulosic organic polymer. The relative proportions of aqueous solvent and organic polymer present in the overcoating composition may vary widely. The minimum proportion is that which will produce an overcoating composition having a viscoεity low enough to apply as an overcoating. The maximum proportion is not governed by any theory, but by practical conεiderations such as the cost of the solvent and the cost and time required to remove the solvent from the applied wet overcoating. Usually, however, the weight ratio of aqueous solvent to organic polymer is from 18:1 to 50:1. Often the weight ratio is from 19:1 to 40:1. Preferably weight ratio is from 19:1 to 24:1. Optional ingredients such as those discussed above may be present when desired. The overcoating composition may be prepared by admixing the ingredients. It may be applied and dried using any of the coating and drying techniques discussed above. When an overcoating composition is to be applied, it may be applied once or a multiplicity of times. After the coating has been substantially dried, the coated substrate may optionally be calendered. In most cases calendering iε accomplished between two rolls. Preferably, but not necessarily, the roll contacting the coating of the coated substrate is a metal-surfaced roll. The other roll is preferably, but not necessarily, surfaced with a somewhat resilient material such as an elastomer of medium hardness. When calendering is employed, the roll temperature may be widely varied, but usually the roll temperature is in the range of from 20°C to 100°C. Often the roll temperature is in the range of from 30°C to 80°C. From 40°C to 60°C is preferred. Similarly, the force per unit length of the nip may be widely varied. Frequently the force per unit length of the nip is in the range of from 85 to 350 kilonewtonε per meter (kN/m) . In many inεtanceε the force per unit length of the nip is in the range of from 120 to 275 kN/m. Preferably it is in the range of from 155 to 200 kN/m. The gloss of the coated subεtrate may vary widely. Although lower gloεses are acceptable for many purposes , it is preferred that the gloss be at least 20. As used herein gloss is determined according to TAPPI Standard T480 om-92. Part I of the invention is further described in conjunction with the following examples which are to be considered illustrative rather than limiting, and in which all parts are parts by weight and all percentages are percentages by weight unless otherwise specified. EXAMPLE 1 With stirring, 248 grams of aluminum tri - sec- butoxide [CAS 2269-22-9] was added to 2 literε of water at 70°C in a glaεs container. To this mixture 6 grams of 60 percent concentrated nitric acid was added. The reaction mixture was stirred for 15 minutes on a hot plate. The glasε container containing the reaction mixture was then sealed with a lid and placed in an oven at 95°C for 2 days. During the two-day period in the oven the precipitate in the reaction mixture was peptized. The resulting colloidal dispersion was concentrated in an unsealed container to 600 grams by boiling to produce a colloidal dispersion (sol) containing 10 percent by weight colloidal alumina monohydroxide. F.XAMPLE 2 To 300 grams of alumina monohydroxide sol prepared as in Example 1 was added 6 grams of hydroxypropyl cellulose (HPC) having a weight average molecular weight of 370,000 (Aldrich Chemical Company, Inc.), and 3 grams of Airvol ® 205S poly(vinyl alcohol) (Air Products and Chemicals Inc.) . The mixture was stirred until the HPC and the poly(vinyl alcohol) (PVA) had completely dissolved giving a coating composition containing about 13 percent solids. The coating composition waε applied to poly(ethylene terephthalate) (PET) transparencies with a Meyer Rod (13.7 g/m ) and allowed to dry at room temperature. The coating waε about 20 μm thick and clear. The coated transparencies were then printed by an HP- 350 ink jet printer. The ink jet printed transparencieε exhibited excellent ability to maintain the edge acuity of ink patternε, excellent color fidelity, and resistance against scratches . Example 2 waε repeated except that one gram of 3-methacryloxypropyltrimethoxysilane [CAS 2530-85-0] was added to each 100 grams of coating composition prepared as in Example 2. The dry coating and ink jet printed transparencies showed excellent water resistance after being soaked in water for one hour. EXAMPLE 4 One gram of tetramethyl orthosilicate [CAS 681-84-5] was added to each 100 grams of coating composition prepared as in Example 2. After several hours the resulting coating composition was applied to PET transparencieε in a manner similar to that of Example 2. After the coating had dried, the coated transparencies were ink jet printed. The ink jet printed transparencies exhibited water fastness when soaked in water for a period of hours. EXAMPLE 5 To 100 grams of alumina monohydroxide sol prepared as in Example 1 was added 5 grams of HPC having a weight average molecular weight of 370,000, 2 grams of Airvol ® 205S PVA, and 70 grams of water. The mixture was stirred until the HPC and PVA had diεεolved. The reεulting coating compoεition was applied to PET transparencies in a manner similar to that of Example 2. After the coating had dried, the coated transparencies were ink jet printed on an Epson ink jet printer. The quality of the ink jet printed transparencies was excellent. .XAMPLE 6 To 100 grams of alumina monohydroxide sol prepared as in Example 1 waε added 2 gramε of HPC having a weight average molecular weight of 370,000, 2 gramε of Airvol ® 205S PVA, 2 gramε of poly(vinyl pyrrolidone) [CAS 9003-39-8] (Aldrich Chemical Company, Inc.) (PVP) having a weight average molecular weight of 10,000, and 50 grams of water. The mixture was stirred until the HPC, PVA, and PVP had disεolved. The resulting coating composition was applied to PET transparencieε in a manner similar to that of Example 2. After the coating had dried, the coated transparencieε were ink jet printed on an Epson ink jet printer. Not only waε the quality of the ink jet printed transparencies excellent, but the inks dried much faster than on many commercially available transparencieε . KXAMPLE 7 To 100 grams of alumina monohydroxide sol prepared as in Example 1 was added 3.5 grams of Airvol ® 205S PVA, 1.5 grams of PVP having a weight average molecular weight of 10,000, and one gram of 3-methacryloxypropyltrimethoxysilane. The mixture waε stirred until the PVA and PVP had disεolved and then allowed to stand overnight. The resulting coating composition was applied to PET transparencieε in a manner εimilar to that of Example 2. After the coating had dried, the coated transparencies were ink jet printed by an HP-855 ink jet printer which is a heaterless printer. The ink dried within 30-60 seconds and the ink jet printed transparencies were of excellent quality. EXAMPLE 8 To 150 grams of alumina monohydroxide sol prepared as in Example 1 was added one gram of HPC having a weight average molecular weight of 370,000, 2 grams of Airvol ® 205S PVA, one gram of PVP having a weight average molecular weight of 10,000, and 1.5 grams of 3-methacryloxypropyltrimethoxysilane mixed in 10 grams of ethanol. The mixture was stirred until the HPC, PVA, and PVP had dissolved. The resulting coating composition was applied to PET transparencies in a manner similar to that of Example 2. After the coating had dried, the coated transparencies were ink jet printed by an HP-855 ink jet printer. The ink dried quickly and the ink jet printed tranεparencieε were water resistant and of excellent quality. EXAMPLE 9 A solution waε prepared by dissolving 10 grams of HPC having a weight average molecular weight of 370,000 and 5 grams of Airvol ® 205S PVA in 285 gramε of water. Portionε of this solution were admixed with portions of alumina monohydroxide sol prepared as in Example 1 to form a series of coating compositions having varying organic polymer to alumina monohydroxide ratios. These coating compositions were applied to glass subεtrateε and to PET transparencieε. The wet coatings were then dried at room temperature. The dried coatings were peeled from the glasε substrates with a blade and the pore volumes were ascertained using the procedure earlier described. The weight percents of organic polymer in the dry coatings and the corresponding pore volumes are shown in Table 1. TABLE 3- Organic Polymer, Pore Volume, Sample No. weight percent (cm 3 /g) 1 0 0.2240 2 3 0.2008 3 7 0.1519 4 11 0.0797 5 13 0.0096 6 14 0.0008 7 18 0.0007 The data show that when the organic polymer constitutes 13 weight percent or more of the dry coating, the coating is subεtantially nonporouε with a common εtandard of diεcernment. Similar coating compositions containing no alumina monohydroxide provide dry coatings having pore volumes of from 0.0005 to 0.0010 cm 3 /g- EXAMPLE 10 To 300 gramε of alumina monohydroxide εol prepared aε in Example 1 waε added 9 grams of HPC having a weight average molecular weight of 370,000, 6 grams of Airvol ® 205S PVA. The mixture was stirred until the HPC and PVA had disεolved. The product was a first coating composition. Nine grams of HPC having a molecular weight of 370,000, nine grams of Airvol ® 205S PVA, and 16.7 grams of 45 weight percent solids Luviskol ® K 60 poly(vinyl pyrrolidone) (BASF Corp.) were diεsolved in 220 grams of water to form a second coating composition. The first coating composition waε applied to photographic resin coated basestock at a coating weight of 11.8 g/m using a hand drawn Meyer Rod applicator and air dried at room temperature to form a first coating. The second coating composition was applied to the first coating at a coating weight of 11.8 g/m using a hand drawn Meyer Rod applicator and air dried at room temperature to form a εecond coating. The resulting articles were high glosε printing sheets . The above high gloss sheets were printed on an Epson Color Stylist Ink Jet Printer and a Canon BJC 610 Ink Jet Printer. The print densitieε are εhown in Table 2. TABLE 2 Printer Black Cyan Magenta Yellow Epson 2.38 1.97 1.67 0.87 Canon 2.40 1.86 1.55 1.08 The data show that the print densitieε were exceptionally good. Edge acuity, wicking, and bleed were eεtimated visually. The results were also exceptionally favorable in each of these categories. PART II A considerable problem that has arisen from the use of coatings for ink jet printing media is that many of the inks used for ink jet printing coalesce on many of the coatings. There are, unfortunately, many different kinds of inks which are used for ink jet printing and a coated subεtrate which performε εatiεfactorily with inks of one type frequently performs less than satisfactorily with inks of another type. Another problem that has arisen from the use of coated substrates as ink jet printing media is the long drying time of the water-based inks after they have been applied to the coated substrates. A coated substrate has now been found which eliminates or reduces coalescence of a wide variety of ink jet printing inks when applied to the coated substrate and which often provides fast drying times. Accordingly, one embodiment of Part II of the invention iε a printing medium comprising: (a) a substrate having at least one surface; and (b) a coating on the surface wherein the coating comprises: (1) a binder comprising mainly organic polymer, wherein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 20 percent by weight of the organic polymer; and (2) discrete particles dispersed in the binder, which particles have a number average particle size in the range of from 1 to 500 nanometers. In this embodiment the coating may be substantially nonporous or it may be porous . The number average particle size of the particles is in the range of from 1 to 500 nanometers. Often the number average particle size is in the range of from 1 to 100 nanometers. Frequently the number average particle size is in the range of from 1 to 50 nanometers. Preferably the number average particle size iε in the range of from 1 to 20 nanometers. As used herein and in the claims number average particle size is determined by transmission electron microscopy. The amount of the diεcrete particleε in the coating may vary widely. Often the particleε constitute from 20 to 70 percent by weight of the coating. In many caseε the particleε constitute from 40 to 60 percent by weight of the coating. From 45 to 55 percent by weight is preferred. The discrete particles may be discrete inorganic particles, discrete crosslinked organic particles, or a mixture thereof . The discrete particles are often discrete particles of metal oxide. The metal oxide constituting the particles may be a simple metal oxide (i.e., the oxide of a single metal) or it may be a complex metal oxide (i.e., the oxide of two or more metals) . The particles of metal oxide may be particles of a single metal oxide or they may be a mixture of different particles of different metal oxideε. Exampleε of suitable metal oxides include alumina, silica, and titania. Other oxides may optionally be present in minor amount. Examples of such optional oxides include, but are not limited to, zirconia, hafnia, and yttria. Other metal oxides that may optionally be present are those which are ordinarily present as impurities such aε for example, iron oxide. For purposes of the present specification and claims, silicon is considered to be a metal. When the particles are particles of alumina, most often the alumina iε alumina monohydroxide. Particles of alumina monohydroxide, AlO(OH) , and their preparation are known. The preparation and properties of alumina monohydroxide are deεcribed by B. E. Yoldaε in The American Ceramic Society Bulletin, Vol. 54, No. 3, (March 1975), pageε 289-290, in Journal of Applied Chemical Biotechnology. Vol. 23 (1973), pageε 803-809, and in Journal of Materialε Science, Vol. 10 (1975) , pageε 1856-1860. Briefly, aluminum isopropoxide or aluminum secondary-butoxide are hydrolyzed in an excesε of water with vigorouε agitation at from 75 C to 80°C to form a slurry of aluminum monohydroxide. The aluminum monohydroxide is then peptized at temperatures of at leaεt 80°C with an acid to form a clear alumina monohydroxide sol which exhibits the Tyndall effect when illuminated with a narrow beam of light. Since the alumina monohydroxide of the sol is neither white nor colored, it is not a pigment and does not function aε a pigment in the preεent invention. The acid employed is noncomplexing with aluminum, and it has sufficient strength to produce the required charge effect at low concentration. Nitric acid, hydrochloric acid, perchloric acid, acetic acid, chloroacetic acid, and formic acid meet these requirements. The acid concentration is usually in the range of from 0.03 to 0.1 mole of acid per mole of aluminum alkoxide. Although it is desired not to be bound by any theory, it iε believed that the alumina monohydroxide produced in thiε manner iε pseudo-boehmite. Pseudo-boehmite is indeed the preferred alumina monohydroxide for use in the present invention. The alumina monohydroxide is not a pigment and does not function aε a pigment in the present invention. In most instanceε the alumina monohydroxide is transparent and colorless. Colloidal silica is also known. Its preparation and properties are described by R. K. Her in The Chemistry of Silica, John Wiley & Sons, Inc., New York (1979) ISBN 0-471-02404-X, pages 312-337, and in United States Patents No. 2,601,235; 2,614,993; 2,614,994; 2,617,995; 2,631,134; 2,885,366; and 2,951,044, the disclosureε of which are, in their entireties, incorporated herein by reference. Exampleε of commercially available colloidal εilica include Ludox® HS, LS, SM, TM and CL-X colloidal silica (E. I. du Pont de Nemours & Company, Inc.) in which the counter ion is the sodium ion, and Ludox® AS colloidal silica (E. I. du Pont de Nemourε & Company, Inc.) in which the counter ion is the ammonium ion. Another example is Ludox® AM colloidal silica (E. I. du Pont de Nemours & Company, Inc.) in which some of the silicon atoms have been replaced by aluminum atoms and the counter ion is the sodium ion. Colloidal titania iε also known. Its preparation and properties are described in United States Patent No. 4,275,118. Colloidal titania may alεo be prepared by reacting titanium iεopropoxide [CAS 546-68-9] with water and tetramethyl ammonium hydroxide. The discrete particles are frequently discrete particles of crosslinked organic polymer. Examples of such crosslinked organic polymer include crosslinked melamine- formaldehyde polymer, crosslinked resorcinol-formaldehyde polymer, crosslinked phenol-resorcinol-formaldehyde polymer, crosslinked (meth) acrylate polymer, and crosslinked styrene- divinylbenzene polymer. The binder functions as a matrix for the diεcrete particles dispersed therein. The binder comprises mainly organic polymer but it may optionally contain minor amounts of conventional adjuvants as will be discussed more fully later in connection with the coating composition used to form the coating of the printing medium. The binder of the coating comprises film-forming organic polymer or insolubilized film-forming organic polymer. The film-forming polymer may be water-soluble or water-disperεible organic polymer. Poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 is known. Such materials are ordinarily formed by polymerizing ethylene oxide [CAS 75-21-8] , usually in the presence of a small amount of an initiator such as low molecular weight glycol or triol . Examples of such initiators include ethylene glycol [CAS 107-21-1] , diethylene glycol [CAS 111-46-6] , triethylene glycol [CAS 112-27-6] , tetraethylene glycol [CAS 112-60-7] , propylene glycol [CAS 57-55-6] , trimethylene glycol [CAS 504-63-2] , dipropylene glycol [CAS 110-98-5] , glycerol [CAS 56-81-5] , trimethylolpropane [CAS 77-99-6] , and α,ω-diaminopoly(propylene glycol) [CAS 9046-10-0] . One or more other lower alkylene oxides such as propylene oxide [CAS 75-56-9] and trimethylene oxide [CAS 503-30-0] may alεo be employed aε comonomer with the ethylene oxide, whether to form random polymers or block polymers, but they should be used only in those small amounts aε will not render the resulting polymer both water-insoluble and nondisperεible in water. As used herein and in the claimε, the term "poly(ethylene oxide)" iε intended to include the foregoing copolymers of ethylene oxide with small amounts of lower alkylene oxide, as well aε homopolymers of ethylene oxide. The configuration of the poly(ethylene oxide) can be linear, branched, comb, or star-shaped. The preferred terminal groups of the poly(ethylene oxide) are hydroxyl groups, but terminal lower alkoxy groups such as methoxy groups may be present provided their types and numbers do not render the poly(ethylene oxide) polymer unsuitable for its purpose. In most cases the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 is water-insoluble. The preferred poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 is a water-soluble homopolymer of ethylene oxide produced using a small amount of ethylene glycol as an initiator. The weight average molecular weight of the poly(ethylene oxide) is in the range of from 100,000 to 3,000,000. Often the weight average molecular weight of the poly(ethylene oxide) is in the range of from 150,000 to 1,000,000. Frequently the weight average molecular weight of the poly(ethylene oxide) is in the range of from 200,000 to 1,000,000. From 300,000 to 700,000 is preferred. The amount of organic polymer of the binder in the coating may vary widely. Often the organic polymer of the binder constitutes from 30 to 80 percent by weight of the coating. In many cases the organic polymer of the binder constitutes from 40 to 60 percent by weight of the coating. From 45 to 55 percent by weight is preferred. The organic polymer of the binder may optionally also comprise additional organic polymer other than poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000. Such additional organic polymers are film-forming organic polymers or insolubilized film-forming organic polymers. Examples of additional film-forming organic polymers include, but are not limited to, water-soluble poly(ethylene oxide) having a weight average molecular weight below 100,000, water-soluble poly(ethylene oxide) having a weight average molecular weight above 3,000,000, water-soluble cellulosic organic polymers such as those heretofore described in respect of Part I, water-soluble noncellulosic organic polymers such aε thoεe heretofore deεcribed in reεpect of Part I, water dispersible polymers such as poly(ethylene-co-acrylic acid) , or a mixture of two or more thereof. Both of such Part I descriptions are, in their entireties, incorporated herein by reference. Examples of water-εoluble polyacrylates which can advantageously be used include the water-soluble anionic polyacrylates and the water-soluble cationic polyacrylates. Water-soluble anionic polyacrylates are themselves well known. Usually, but not necessarily, they are copolymers of one or more (meth) acrylic esters and enough (meth) acrylic acid and/or (meth) acrylic acid salt to provide sufficient carboxylate anions to render the polymer water-soluble. Similarly, water-soluble cationic polyacrylates are themselves well known. Usually, but not necessarily, they are copolymers of one or more (meth)acrylic esters and enough amino-functional ester of (meth) acrylic acid to provide sufficient ammonium cations to render the acrylic polymer water-soluble. Such ammonium cations may be primary, secondary, tertiary, or quaternary. Usually the water soluble cationic polyacrylate iε a primary, secondary, tertiary, or quaternary ammonium εalt, or it iε a quaternary ammonium hydroxide. After application of the coating compoεition to the εubstrate surface, the film-forming organic polymer may optionally be reacted with crosεlinking agent (alεo known aε inεolubilizer) to form inεolubilized organic polymer. Examples of crosεlinking agentε and their amounts are discloεed in Part I and such disclosures are, in their entireties, incorporated herein by reference. Usually the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 20 percent by weight of the organic polymer of the binder. Generally the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at leaεt 51 percent by weight of the organic polymer of the binder. In many instances the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at leaεt 60 percent by weight of the organic polymer of the binder. Often the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 90 percent by weight of the organic polymer of the binder. Frequently the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at least 95 percent by weight of the organic polymer of the binder. In many cases the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 99 percent by weight of the organic polymer of the binder. In some cases the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes 100 percent by weight of the organic polymer of the binder. When optional additional organic polymer is preεent in the binder, it usually constituteε from 1 to 80 percent by weight of the organic polymer of the binder. Frequently the optional additional organic polymer conεtitutes from 1 to 49 percent by weight of the organic polymer of the binder. In many caseε the optional additional organic polymer constitutes from 1 to 40 percent by weight of the organic polymer of the binder. Often the optional additional organic polymer constitutes from 1 to 10 percent by weight of the organic polymer of the binder. Frequently the optional additional organic polymer constitutes from 1 to 5 percent by weight of the organic polymer of the binder. The coating may be subεtantially transparent, substantially opaque, or of intermediate transparency. It may be subεtantially colorless, it may be highly colored, or it may be of an intermediate degree of color. Preferably the coating iε substantially transparent and εubεtantially colorless. As used herein and in the claims, a coating is substantially transparent if its luminous transmisεion in the viεible region iε at least 80 percent of the incident light. Often the luminous transmission of the coating is at least 85 percent of the incident light. Preferably the luminous transmisεion of the coating is at leaεt 90 percent. Also as uεed herein and in the claimε, a coating is substantially colorless if the luminous transmission is substantially the same for all wavelengths in the visible region, viz., 400 to 800 nanometers. The thicknesε of the coating may vary widely, but in most instances the thicknesε of the coating iε in the range of from 1 to 40 μm. In many caseε the thickneεs of the coating iε in the range of from 5 to 40 μm. Often the thickness is in the range of from 8 to 30 μm. From 12 to 18 μm iε preferred. The εubstrate may be any subεtrate at leaεt one surface of which iε capable of bearing the coating discussed above. In most instanceε the εubstrate is in the form of an individual sheet or in the form of a roll, web, εtrip, film, or foil of material capable of being cut into εheets. The subεtrate may be porouε throughout, it may be nonporouε throughout, or it may comprise both porous regions and nonporous regions. Examples of porous substrates include paper, paperboard, wood, cloth, nonwoven fabric, felt, unglazed ceramic material, polymer membranes, porous foam, and microporous foam. Examples of substrates which are subεtantially nonporous throughout include sheets or films of organic polymer such as poly(ethylene terephthalate) , polyethylene, polypropylene, cellulose acetate, poly(vinyl chloride), and copolymers such as εaran. The εheetε or filmε may be metallized or unmetallized aε deεired. Additional examples include metal substrates including but not limited to metal foils such as aluminum foil and copper foil. Yet another example is a porous or microporous foam comprising thermoplastic organic polymer which foam has been compresεed to εuch an extent that the resulting deformed material is substantially nonporous. Still another example is glass. Base stocks which are normally porous such as for example paper, paperboard, wood, cloth, nonwoven fabric, felt, unglazed ceramic material, polymer membranes, porous foam, or microporous foam may be coated or laminated to render one or more surfaces subεtantially nonporous and thereby provide substrates having at least one substantially nonporous surface. The substrate may be subεtantially tranεparent, it may be substantially opaque, or it may be of intermediate transparency. For some applications εuch aε ink jet printed overhead slides, the substrate must be sufficiently transparent to be useful for that application. For other applications such as ink jet printed paper, transparency of the substrate is not so important. The printing media of one embodiment Part II of the invention may be made by coating a surface of the subεtrate with a coating composition compriεing: (a) diεcrete particleε having a number average particle εize in the range of from 1 to 500 nanometers; (b) an aqueous liquid medium; and (c) film-forming organic polymer disεolved or diεpersed in the aqueous liquid medium wherein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 20 percent by weight of the organic polymer; and thereafter εubstantially removing the aqueous liquid medium. The coating composition can be in the form of an aqueous solution in which case the aqueous liquid medium is an aqueous solvent, or the coating composition can be in the form of an aqueous dispersion in which instance the aqueous liquid medium is an aqueous dispersion liquid. The discussions above in respect of the particles, the film-forming organic polymer, the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000, and the additional film-forming organic polymer which may optionally alεo be preεent are applicable here. The weight ratio of the particles to organic film-forming polymer in the coating composition may vary considerably, but it is usually in the range of from 54:100 to 233:100. Often the weight ratio is in the range of from 67:100 to 150:100. Preferably it is in the range of from 82:100 to 122:100. Usually the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 20 percent by weight of the film-forming organic polymer of the coating composition. Generally the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at leaεt 51 percent by weight of the film-forming organic polymer of the coating composition. In many instances the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at least 60 percent by weight of the film-forming organic polymer of the coating composition. Often the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 90 percent by weight of the film-forming organic polymer of the coating composition. Frequently the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 95 percent by weight of the film-forming organic polymer of the coating composition. In many cases the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 99 percent by weight of the film-forming organic polymer of the coating composition. Often the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes 100 percent by weight of the film-forming organic polymer of the coating composition. When additional organic film-forming polymer is preεent, it usually constitutes from 1 to 80 percent by weight of the organic film-forming polymer of the coating composition. Generally the additional organic film-forming polymer constituteε from 1 to 49 percent by weight of the organic film-forming polymer of the coating composition. Often the additional organic film-forming polymer constituteε from 1 to 40 percent by weight of the organic film- orming polymer of the coating composition. In many cases the additional organic film-forming polymer constitutes from 1 to 10 percent by weight of the organic film-forming polymer of the coating composition. Frequently the additional organic film-forming polymer constitutes from 1 to 5 percent by weight of the organic film-forming polymer of the coating composition. In moεt instances the aqueous liquid medium is water. Organic cosolventε miεcible with water may optionally be present when desired. The amount of aqueous liquid medium present in the coating composition may vary widely. The minimum amount is that which will produce a coating composition having a viscosity low enough to apply as a coating. The maximum amount is not governed by any theory, but by practical considerations such as the cost of the liquid medium, the minimum desired thicknesε of the coating to be depoεited, and the cost and time required to remove the aqueous liquid medium from the applied wet coating. Usually, however, the aqueous liquid medium constitutes from 75 to 98 percent by weight of the coating composition. In many caseε the aqueous liquid medium conεtitutes from 85 to 98 percent by weight of the coating composition. Often the aqueous liquid medium constitutes from 86 to 96 percent by weight of the coating composition. Preferably aqueous liquid medium conεtitutes from 88 to 95 percent by weight of the composition. As a corollary, the particles having a number average particle size in the range of from 1 to 500 nanometers and the film-forming organic polymer together usually constitute from 2 to 25 percent by weight of the coating composition. Frequently such particles and the film-forming organic polymer together constitute from 2 to 15 percent by weight of the coating composition. Often such particles and the film-forming organic polymer together constitute from 4 to 14 percent by weight of the coating composition. Preferably such particles and the film-forming organic polymer together constitute from 5 to 12 percent by weight of the coating composition. A material which may optionally be present in the coating composition is mordant. For purposeε of the preεent specification and claims mordant iε considered not to be a part of the film-forming organic polymer of the binder. Mordants, also known as ink-fixing agents, are materials which interact, usually by reaction or absorption, with binder, dye, and/or pigment of the ink applied to the coated substrate. There are many available mordants which may be used. Suitable mordants include, but are not limited to, the poly(ethylenimines) , the ethoxylated poly(ethylenimines) , and other derivativeε of poly(ethylenimine) . Examples include Lupasol™ SC-61B ink-fixing agent (BASF Aktiengesellschaft) , Lupasol™ SC-62J mordant (BASF Aktiengesellschaft) , and Lupasol™ SC-86X mordant (BASF Aktiengesellschaft) , Lupasol™ PS mordant (BASF Aktiengesellschaft) , Lupasol™ G-35 mordant (BASF Aktiengeεellεchaft) , and Lupasol™ FG mordant (BASF Aktiengesellschaft) . When used, the amount of mordant present in the coating composition may vary considerably. In such instanceε the weight ratio of the mordant to the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 is usually in the range of from 0.5:100 to 30:100. Frequently the weight ratio is in the range of from 0.5:100 to 20:100. Often the weight ratio is in the range of from 1:100 to 10:100. From 2:100 to 5:100 is preferred. These ratios are on the basiε of mordant dry solids and poly(ethylene oxide) dry solids. Another material which may optionally be present in the coating composition is εurfactant . For purposes of the present specification and claims surfactant is considered not to be a part of the organic film-forming polymer of the binder. There are many available surfactants and combinations of surfactants which may be used. Examples of suitable surfactants include, but are not limited to, Fluorad ® FC-170-C surfactant (3M Company) , and Triton ® X-405 surfactant (Union Carbide Corporation) . When used, the amount of εurfactant present in the coating composition may vary considerably. In such instanceε the weight ratio of the surfactant to the poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 is usually in the range of from 0.01:100 to 10:100. In many instanceε the weight ratio iε in the range of from 0.1:100 to 10:100. Often the weight ratio iε in the range of from 0.2:100 to 5:100. From 0.5:100 to 2:100 is preferred. These ratios are on the basiε of surfactant dry solids and poly(ethylene oxide) dry solids. There are many other conventional adjuvant materialε which may optionally be preεent in the coating composition. These include such materials as lubricants, waxes, plasticizers, antioxidants, organic solventε, lakes, and pigments. The listing of such materials is by no means exhaustive. These and other ingredients may be employed in their customary amounts for their customary purposeε εo long aε they do not seriously interfere with good coating composition formulating practice. The pH of the coating composition may vary considerably. In most instanceε the pH iε in the range of from 3 to 10. Often the pH is in the range of from 3 to 6. Frequently the pH is in the range of from 3 to 5.5. In many instanceε the pH is in the range of from 3.5 to 4.5. In other instances the pH is in the range of from 7 to 9. The coating compositions are usually prepared by simply admixing the various ingredients. The ingredients may be mixed in any order. Although the mixing of liquid and solidε is usually accomplished at room temperature, elevated temperatures are sometimes used. The maximum temperature which is usable depends upon the heat stability of the ingredients. The coating compositions are generally applied to the surface of the substrate using any conventional technique known to the art. These include spraying, curtain coating, dipping, rod coating, blade coating, roller application, size press, printing, brushing, drawing, slot-die coating, and extrusion. The coating is then formed by removing the solvent from the applied coating composition. This may be accomplished by any conventional drying technique. Coating composition may be applied once or a multiplicity of times. When the coating composition is applied a multiplicity of times, the applied coating is usually but not necessarily dried, either partially or totally, between coating applications. Once the coating composition has been applied to the substrate, the solvent iε εubεtantially removed, usually by drying. Optionally the above-described coatings may be overlaid with an overcoating comprising ink-receptive organic film-forming polymer. The overcoating may be formed by applying an overcoating composition comprising a liquid medium and ink-receptive organic film-forming polymer dissolved or dispersed in the liquid medium and removing the liquid medium, as for example, by drying. Preferably the liquid medium iε an aqueous εolvent and the ink-receptive organic film-forming polymer iε water-εoluble poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000, both of which have been described above in respect of earlier described embodiments of the invention. Water is an especially preferred aqueous solvent. The relative proportions of liquid medium and organic film-forming polymer present in the overcoating composition may vary widely. The minimum proportion is that which will produce an overcoating composition having a viscosity low enough to apply as an overcoating. The maximum proportion is not governed by any theory, but by practical considerations such as the cost of the liquid medium and the cost and time required to remove the liquid medium from the applied wet overcoating. Usually, however, the weight ratio of liquid medium to film-forming organic polymer is from 18:1 to 50:1. Often the weight ratio iε from 19:1 to 40:1. Preferably weight ratio is from 19:1 to 24:1. Optional ingredients such as those discussed above may be present in the overcoating composition when desired. The overcoating composition may be prepared by admixing the ingredients. It may be applied and dried using any of the coating and drying techniques discusεed above. When an overcoating compoεition iε to be applied, it may be applied once or a multiplicity of timeε. The gloss of the coated substrate may vary widely. Although lower glosseε are acceptable for many purpoεeε, it iε preferred that the gloss be at least 20. As used herein gloss is determined according to TAPPI Standard T653 pm-90. Part II of the invention is further described in conjunction with the following examples which are to be considered illustrative rather than limiting, and in which all parts are parts by weight and all percentages are percentageε by weight unless otherwise specified. XAMPT.F π One liter of deionized water was heated to 80°C with vigorous stirring in a large open beaker. While continuing the stirring, 71 grams of titanium isopropoxide was slowly added. A white precipitate formed immediately. Stirring at 80°C was continued for 90 minutes during which period the volume boiled down to approximately 750 milliliters. The slurry was poured into a one-liter round bottom flask. Twenty-three gramε of a 10 percent by weight solution of tetramethyl ammonium hydroxide solution was added and the contentε of the flask were refluxed overnight to form a colloidal dispersion (sol) containing 7.8 percent by weight colloidal titania. A poly(ethylene oxide) (PEO) solution waε formed by diεsolving 150 grams poly(ethylene oxide) having a weight average molecular weight of about 400,000 in 2850 grams of deionized water. The mixture was stirred until all poly(ethylene oxide) was dissolved giving a composition containing 5.0 percent solids. To 55 grams of the above PEO solution was added 28.8 grams of the above titania sol. Into this mixture was added with stirring 50 milligrams Fluorad™ FC-170-C surfactant to form a coating composition. The coating composition was applied to commercially available gloεεy polyethylene-coated paper with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating waε about 20 micrometerε thick. The coated paper waε then printed on the coated εide by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed paper εhowed excellent print quality. EXAMPLE 12 To 120 gramε of a poly(ethylene oxide) solution prepared as described in Example 11 were added 20 grams of a colloidal εilica sol (Ludox ® HS-40; E.I. Dupont de Nemours & Co.) containing 40 percent by weight of silica and 16 grams of a poly(ethylene-co-acrylic acid) diεperεion (Adcote ® 50T4983; Morton Adheεiveε) containing 25 percent by weight of polymer. Into thiε mixture was added with stirring 78 milligrams Fluorad™ FC-170-C surfactant ' to form a coating composition. The coating composition was applied to poly(ethylene terephthalate) transparencies with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating was about 20 micrometers thick and it was clear. The coated transparencies were then printed on the coated side by a Hewlett-Packard 1600C ink jet printer. The ink jet printed transparencies exhibited excellent ability to maintain the edge acuity of ink patterns, excellent color fidelity, and were dry to touch as they came out of the printer. A test with a roller εhowed no color tranεfer to paper after 5 seconds. A water test εhowed excellent water faεtneεε of the ink dyes in all colors. Pigmented black ink in the test patterns showed no cracking. EXAMPLE 13 To 120 grams of a poly(ethylene oxide) solution prepared aε deεcribed in Example 11 were added 7.5 gramε of a colloidal εilica sol (Ludox ® HS-40; E.I. Dupont de Nemours & Co.) containing 40 percent by weight of silica. Into thiε mixture was added with stirring 64 mg Fluorad™ FC-170-C surfactant to form a coating composition. The coating compoεition waε applied to poly(ethylene terephthalate) transparencies with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating was about 20 micrometers thick and it was clear. The coated transparencieε were then printed on the coated εide by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed tranεparencieε showed excellent print quality. EXAMPLE 14 Sixty-five grams of a low molecular weight, partially methylated melamine-formaldehyde resin (Resimene ® AQ-7550; Monsanto Co.) containing 78% solids was added to 435 grams of deionized water. The mixture was stirred at room temperature until a homogeneous solution was formed. Next, concentrated hydrochloric acid was added while stirring to lower the pH to a value of 3.2. The acidified solution was then covered and placed in an oven at 85°C for 3 hours. The resultant melamine-formaldehyde sol had a light blue haze reεulting from Rayleigh εcattering indicating a number average particle εize less than 500 nanometers. The sol contained approximately 10 percent by weight of a partially crosεlinked melamine-formaldehyde (MF) polymer. To 55 grams of a poly(ethylene oxide) solution prepared as described in Example 11 were added 30 grams of colloidal alumina monohydroxide sol prepared as described in Example 1 of Part I and 15 gramε of the above melamine- formaldehyde sol. Into this mixture was added with εtirring 50 milligrams Fluorad™ FC-170-C surfactant to form a coating composition. The coating composition was applied to poly(ethylene terephthalate) transparencies with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating was about 20 micrometers thick and it was clear. The coated transparencies were then printed on the coated side by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed transparencieε εhowed excellent print quality. EXAMPLE 15 To 70 gramε of a poly(ethylene oxide) solution prepared as described in Example 11 were added 30 gramε of a melamine-formaldehyde sol prepared as described in Example 14. Into this mixture waε added with stirring 50 milligrams Fluorad™ FC-170-C surfactant to form a coating composition. The coating composition was applied to poly(ethylene terephthalate) transparencies with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating was about 20 micrometers thick and it was clear. The coated tranεparencieε were then printed on the coated εide by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed tranεparencieε εhowed excellent print quality. EXAMPLE 16 The following initial charge and feedε εhown in Table 3 were uεed in the preparation of aqueous εecondary amine and hydroxyl functional acrylic polymer via εolution polymerization technique. TABLE 3 Ingredients Weiσht. grams Initial Charge Iεopropanol 130.0 Feed 1 Isopropanol 113 . . 0 n-Butyl acrylate 69 . . 2 Methyl methacrylate 153 . . 0 2 - (tert-Butylamino)ethyl methacrylate [CAS 3775-90-4] 73 . . 0 Styrene 69 . . 2 VAZO Φ 67 Initiator 1 18 , . 2 Feed 2 Glacial acetic acid 17.7 Feed 3 Deionized water 1085.0 1 2, 2 ' -Azobis (2-methylbutanenitrile) initiator commercially available from E.I. du Pont de Nemourε and Company, Wilmington, Delaware. The initial charge waε heated in a reactor with agitation to reflux temperature (80°C) . Then Feed 1 waε added in a continuous manner over a period of 3 hours. At the completion of Feed 1 addition, the reaction mixture was held at reflux for 3 hours. The resultant acrylic polymer solution had a total solids content of 61.7 percent (determined by weight difference of a sample before and after heating at 110°C for one hour) and number average molecular weight of 4792 as determined by gel permeation chromatography using polystyrene as the standard. Thereafter, Feed 2 was added over five minutes at room temperature with agitation. After the completion of the addition of Feed 2, Feed 3 was added over 30 minutes while the reaction mixture was heated for azeotropic distillation of isopropanol. When the distillation temperature reached 99°C, the distillation was continued about one more hour and then the reaction mixture was cooled to room temperature. The total distillate collected was 550.6 grams. The product, which was a cationic acrylic polymer aqueous solution, had a solids content of 32.6 percent (determined by weight difference of a sample before and after heating at 110°C for one hour) , and a pH of 5.25. To 50 grams of a poly(ethylene oxide) solution prepared as described in Example 11 were added 12.5 grams of colloidal alumina sol prepared as described in Example 1 of Part I and 4.3 grams of the above cationic acrylic polymer aqueous solution. Into this mixture was added with stirring 50 milligramε Fluorad™ FC-170-C εurfactant to form a coating composition. The coating composition was applied to poly(ethylene terephthalate) transparencieε with a Meyer Rod #150 and allowed to dry under an infrared heating lamp. The dry coating waε about 20 micrometerε thick and it was clear. The coated transparencies were then printed on the coated side by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed transparencies showed excellent print quality. EXAMPLE 17 With stirring, 248 grams of aluminum tri- εec-butoxide [CAS 2269-22-9] waε added to 2 liters of water at 75°C in a glaεε container. To this mixture 5.5 grams of 60 percent concentrated nitric acid was added. The reaction mixture was stirred 5 minutes on a hot plate. The glaεε container containing thiε mixture waε then εealed with a lid and placed in an oven at 95°C for 3 dayε . During thiε period the precipitate of the mixture was peptized to a colloidal dispersion of AlO(OH) . The resultant colloidal dispersion was concentrated to 1200 grams by boiling on a hot plate under stirring to produce a 5 percent by weight colloidal sol of colloidal alumina monohydroxide, AlO(OH) . To 100 grams of above prepared colloidal εol waε added 4 grams of poly(ethylene oxide) having a weight average molecular weight of about 400,000. The mixture was stirred vigorously until all poly(ethylene oxide) was dissolved giving a composition containing 8.7 percent solids. Into this mixture were added with stirring 20 mg Fluorad™ FC-170-C εurfactant and 0.5 gram of 5 percent Lupasol™ SC 61-B concentrated hydroxyethylated poly(ethylenimine) to form a coating composition. The coating composition was applied to poly(ethylene terephthalate) transparencies with a Meyer Rod #150 and allowed to dry at room temperature. The dry coating was about 20 μm thick and it was clear. The coated transparencies were then printed on the coated side by a Hewlett-Packard 1600C ink jet printer. The ink jet printed transparencies exhibited excellent ability to maintain the edge acuity of ink patterns, excellent color fidelity, and were dry to touch as it came out of the printer. A test with a roller showed no color transfer to paper after 5 seconds. A water test showed excellent water fastneεs of the ink dyes in all colors. Pigmented black ink in the teεt patternε εhowed no cracking. EXAMPLE 18 The coating compoεition prepared in Example 12 waε applied εimilarly onto commercially available glossy polyethylene-coated paper and onto commercially available gelatine-coated paper and dried. When theεe paperε were printed on the coated side using a Hewlett-Packard 850C ink jet printer, they εhowed photographic quality prints with high gloss, about 90%, again with excellent color fidelity, edge acuity, and water and light fastness. The coating composition prepared in Example ll was applied similarly onto cloth, and aluminum foil. After the coating had dried, these coated subεtrateε were ink jet printed with excellent results. EXAMPLE 19 To 100 grams of colloidal alumina sol prepared in Example 12, 7 grams of poly(ethylene oxide) with a weight average molecular weight of about 200,000 waε added. An additional 43 grams of water was alεo added to facilitate complete dissolution of the poly(ethylene oxide) . The mixture was stirred until complete dissolution of the poly(ethylene oxide) took place yielding 150 grams of solution containing 12 grams of solids (8 percent solids) . With stirring, one gram of Lupasol™ SC ® -J 5 percent poly(ethylenimine) solution, was added to form a coating composition. Similarly to Example 12, the coating composition was applied to transparencies and dried with a hot air blower for several minutes until the coatings were dry. The coated transparencieε were printed on the coated εide by a Hewlett-Packard 1600C ink jet printer and a Hewlett-Packard 850C ink jet printer. The printed transparencieε showed excellent print quality. EXAMPLE 20 Two solutions were prepared as follows: Solution A: A poly(ethylene oxide) (PEO) solution was formed by disεolving 150 grams poly(ethylene oxide) having a weight average molecular weight of about 400,000 in 2850 grams of water. Solution B: 408 grams of aluminum isopropoxide was introduced to 4 liters of water at 70°C with stirring. To this mixture was added 11 grams of 60 percent concentrated nitric acid with stirring. The resulting mixture was εealed with a lid and placed in an oven at 95°C to be peptized. After 3 days, the lid was opened and the colloidal εol waε allowed to evaporate to a final total weight of 800 gramε and an AlO(OH) concentration of 15% by weight. Variouε coating compositions were made by mixing these two solutions as shown in Table 4 : TABLE 4 Coating Solution A, Solution B, Composition grams grams 1 200 100 2 300 100 3 400 100 4 500 100 These coating compositions were coated on poly(ethylene terephthalate) (PET) transparencies with a Meyer Rod so as to deposit films which, after drying, were approximately 20 μm thick. All four coated transparencies were transparent with excellent ink jet printability. EXAMPLE 21 A 600 gram quantity of Coating Composition No. 2 of Example 20 was prepared. This was divided into six 100 gram portions. Six coating solutions were formed by introducing a mordant to each portion as shown in Table 5: TABLE 5 Coating Solution Number 1 _2_ _3_ _4_ ___ __ Coating Composition No. 2, gramε 100 100 100 100 100 100 5% Aqueous Lupasol™ SC 61-B Mordant, gramε 1 5 0 0 0 0 5% Aqueouε Lupaεol™ SC 62-J Mordant, gramε 0 0 1 5 0 0 5% Aqueous Lupasol™ SC 86-X Mordant, grams 0 0 0 0 1 5 Theεe solutions were each coated on a separate poly(ethylene terephthalate) transparency approximately 20-25μm thick. After drying, the coated transparencieε were printed on the coated εide by a Hewlett-Packard 1600C ink jet printer. The quality of the print waε excellent on all of them and all showed excellent water fastness of all colors. EXAMPLE 22 With stirring 22.35 kg. of aluminum tri-secondary butoxide waε charged with εtirring into a reactor containing 75 kg of water at about 78°C. Four hundred twenty grams of 70% nitric acid was diluted in 1110 grams of water and added into the same reactor immediately after the charging of aluminum tri-secondary butoxide. The system was closed when the reactor waε heated to about 120°C gaining pressure to about 276 kilopascals, gauge. The reactor was held at this temperature for 5 hours then cooled to 70°C and opened. Then the reactor was heated to boil off the alcohol and water-alcohol azeotrope of the hydrolyεiε reaction until the concentration of the sol reached about 10 weight percent AlO (OH) , about 54 kg. total, having a pH of 3.8-4.0 and a turbidity of 112. Into 90 grams of this colloidal alumina sol, 11 grams of poly(ethylene oxide) having a weight average molecular weight of about 400,000 and 150 grams of water were added and stirred until the poly(ethylene oxide) was completely dissolved. Into this εufficient nitric acid waε added to lower the pH to within a range of 3.5 to 4.0. Then 12.5 grams of 5% Lupasol™ SC 61-B mordant was added followed by the addition of 0.075 gram of Fluorad™ FC-170-C surfactant. After mixing, the solution was coated on poly(ethylene terephthalate) transparencies using a Meyer Rod #150. The coating was heat dried. No haze waε observed. The coated transparencies were printed on the coated side by a Hewlett-Packard 1600C ink jet printer to produce printed transparencies having excellent print quality, edge acuity, and color fidelity. Ink drying time waε leεε than 5 εecondε. The printed tranεparencieε were free from observed scratches and ink cracking. Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded aε limitations upon the scope of the invention except insofar as they are included in the accompanying claims.

Claims: CLAIMS 1. A printing medium comprising: (a) a substrate having at least one surface, and (b) a substantially nonporous coating on said surface wherein said coating comprises transparent, colorless alumina monohydroxide and water-soluble organic polymer, and wherein said water-soluble organic polymer compriseε water-soluble cellulosic organic polymer and water-soluble noncellulosic organic polymer. 2. The printing medium of claim 1 wherein said surface of said substrate is substantially nonporous. 3. The printing medium of claim 1 wherein said transparent, colorlesε alumina monohydroxide conεtitutes from 10 to 87 percent by weight of the coating. 4. The printing medium of claim 1 wherein said tranεparent, colorless alumina monohydroxide is transparent, colorless pseudo-boehmite. 5. The printing medium of claim 1 wherein said water-soluble organic polymer constitutes from 13 to 90 percent by weight of said coating. 6. The printing medium of claim 1 wherein said substrate is coated paper. 7. The printing medium of claim 1 wherein said coating iε substantially transparent. 8. The printing medium of claim 7 wherein said subεtrate is substantially transparent. 9. The printing medium of claim 8 wherein said subεtantially tranεparent substrate is a sheet or film of subεtantially transparent organic polymer. 10. The printing medium of claim 9 wherein said subεtantially tranεparent organic polymer of εaid εubεtantially tranεparent εubεtrate iε poly(ethylene terephthalate) or cellulose acetate. 11. The printing medium of claim 1 wherein said water-soluble cellulosic organic polymer constitutes from 5 to 95 percent by weight of said water-soluble organic polymer and said water-soluble noncellulosic organic polymer constitutes from 5 to 95 percent by weight of said water-εoluble organic polymer. 12. The printing medium of claim 1 wherein: (a) εaid water-soluble cellulosic organic polymer comprises water-soluble hydroxypropylcellulose, and (b) εaid water-εoluble noncelluloεic organic polymer compriεeε water-εoluble poly(vinyl alcohol) . 13. The printing medium of claim 12 wherein the weight average molecular weight of said water-soluble hydroxypropylcelluloεe iε in the range of from 200,000 to 400,000. 14. The printing medium of claim 12 wherein εaid water-soluble poly(vinyl alcohol) is fully hydrolyzed water-soluble poly(vinyl alcohol) . 15. The printing medium of claim 1 wherein said coating is overlaid with an overcoating comprising ink-receptive organic polymer. 16. The printing medium of claim 15 wherein said ink-receptive organic polymer comprises water-soluble hydroxypropylcellulose. 17. A printing medium comprising: (a) a substrate having at least one surface, and (b) a substantially nonporous coating on said surface wherein said coating compriseε tranεparent, colorleεs alumina monohydroxide and partially or completely inεolubilized water-εoluble organic polymer. 18. The printing medium of claim 17 wherein εaid surface of said substrate is εubεtantially nonporouε. 19. The printing medium of claim 17 wherein said coating is overlaid with an overcoating comprising ink-receptive organic polymer. 20. The printing medium of claim 19 wherein said ink-receptive organic polymer comprises water-soluble hydroxypropylcellulose. 21. A coating composition comprising: (a) transparent, colorlesε alumina monohydroxide; (b) aqueous solvent; and (c) water-soluble organic polymer dissolved in said aqueous solvent; wherein said water-soluble organic polymer comprises water-soluble cellulosic organic polymer and water-εoluble noncelluloεic organic polymer. 22. The coating composition of claim 21 wherein: (a) the weight ratio of said alumina monohydroxide to said water-soluble organic polymer is in the range of from 11:100 to 670:100, and (b) said water-soluble cellulosic organic polymer constitutes from 5 to 95 percent by weight of said water-soluble organic polymer and said water-soluble noncellulosic organic polymer constitutes from 5 to 95 percent by weight of said water-soluble organic polymer. 23. The coating composition of claim 21 wherein said aqueous solvent constitutes from 80 to 98 percent by weight of said coating composition. 24. The coating composition of claim 21 wherein: (a) said water-soluble cellulosic organic polymer compriseε water-εoluble hydroxypropylcellulose, and (b) said water-soluble noncellulosic organic polymer comprises water-soluble poly(vinyl alcohol) . 25. The coating composition of claim 24 wherein the weight average molecular weight of said water-soluble hydroxypropylcellulose is in the range of from 200,000 to 400,000. 26. The coating composition of claim 24 wherein said water-soluble poly(vinyl alcohol) is fully hydrolyzed water-soluble poly(vinyl alcohol) . 27. The coating composition of claim 21 which further compriseε inεolubilizer. 28. The coating composition of claim 27 wherein the weight ratio of said insolubilizer to said water-soluble noncellulosic organic polymer is in the range of from 0.05:100 to 25:100. 29 . A printing medium comprising : (a) a substrate having at least one surface; and (b) a coating on said surface wherein said coating comprises : (1) a binder comprising organic polymer, wherein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at leaεt 20 percent by weight of εaid organic polymer; and (2) diεcrete particleε dispersed in said binder, which particleε have a number average particle εize in the range of from 1 to 500 nanometers. 30. The printing medium of claim 29 wherein the number average particle size of said discrete particles iε in the range of from 1 to 100 nanometers. 31. The printing medium of claim 29 wherein the number average particle size of said discrete particles is in the range of from 1 to 50 nanometers. 32. The printing medium of claim 29 wherein the number average particle size of said diεcrete particleε iε in the range of from 1 to 20 nanometerε. 33. The printing medium of claim 29 wherein said diεcrete particles constitute from 20 to 70 percent by weight of said coating. 34. The printing medium of claim 29 wherein said discrete particleε are discrete inorganic particles, diεcrete croεslinked organic particles, or a mixture thereof. 35. The printing medium of claim 29 wherein said discrete particles are discrete particles of crosslinked organic polymer. 36. The printing medium of claim 29 wherein said discrete particles are discrete particles of metal oxide. 37. The printing medium of claim 36 wherein said metal oxide comprises at least one member selected from the group comprising alumina, silica, and titania. 38. The printing medium of claim 36 wherein said metal oxide comprises alumina. 39. The printing medium of claim 38 wherein said alumina is alumina monohydroxide. 40. The printing medium of claim 39 wherein said alumina monohydroxide is pseudo-boehmite. 41. The printing medium of claim 39 wherein said alumina monohydroxide is transparent and colorless. 42. The printing medium of claim 36 wherein said metal oxide compriεeε colloidal silica. 43. The printing medium of claim 36 wherein said metal oxide comprises colloidal titania. 44. The printing medium of claim 29 wherein said organic polymer constituteε from 30 to 80 percent by weight of said coating. 45. The printing medium of claim 29 wherein said organic polymer compriseε additional organic polymer other than said poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000. 46. The printing medium of claim 45 wherein said additional organic polymer iε water-soluble poly(ethylene oxide) having a weight average molecular weight below 100,000, water-soluble poly(ethylene oxide) having a weight average molecular weight above 3,000,000, water-soluble cellulosic organic polymer, water-soluble noncellulosic organic polymer, and water dispersible polymer 47. The printing medium of claim 45 wherein said additional organic polymer is water-soluble anionic poly(meth) acrylate or water-soluble cationic poly(meth) acrylate. 48. The printing medium of claim 45 wherein: (a) said water-soluble poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 60 percent by weight of εaid organic polymer of said binder; and (b) said additional organic polymer constitutes from 1 to 40 percent by weight of said organic polymer of said binder. 49. The printing medium of claim 29 wherein: said poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at leaεt 99 percent by weight of said organic polymer of said binder. 50. The printing medium of claim 29 wherein said substrate is coated paper. 51. The printing medium of claim 29 wherein said coating is subεtantially transparent. 52. The printing medium of claim 29 wherein εaid coating iε overlaid with an overcoating compriεing ink-receptive organic polymer. 53. The printing medium of claim 52 wherein said ink-receptive organic polymer comprises water-soluble poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000. 54. The printing medium of claim 29 wherein the thicknesε of said coating is in the range of from 5 to 40 micrometers. 55. A coating composition comprising: (a) discrete particles having a number average particle size in the range of from 1 to 500 nanometers; (b) an aqueous liquid medium; and (c) film-forming organic polymer dissolved or dispersed in said aqueous liquid medium wherein water-soluble poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constituteε at leaεt 20 percent by weight of said organic polymer. 56. The coating composition of claim 55 wherein the number average particle size of said discrete particles is in the range of from 1 to 100 nanometers. 57. The coating composition of claim 55 wherein the number average particle εize of said discrete particleε iε in the range of from 1 to 50 nanometers. 58. The coating composition of claim 55 wherein the number average particle εize of said discrete particles is in the range of from 1 to 20 nanometers. 59. The printing medium of claim 55 wherein said discrete particles constitute from 20 to 70 percent by weight of said coating. 60. The printing medium of claim 55 wherein said discrete particles are discrete inorganic particles, discrete crosεlinked organic particleε, or a mixture thereof. 61. The printing medium of claim 55 wherein εaid discrete particles are discrete particles of crosslinked organic polymer. 62. The coating composition of claim 55 wherein said discrete particles are discrete particles of metal oxide. 63. The coating composition of claim 62 wherein said metal oxide comprises at least one member selected from the group comprising aluminia, silica, and titania. 64. The coating composition of claim 62 wherein said metal oxide comprises alumina. 65. The coating composition of claim 64 wherein said alumina is alumina monohydroxide. 66. The coating composition of claim 65 wherein said alumina monohydroxide is pseudo-boehmite. 67. The coating composition of claim 65 wherein said alumina monohydroxide is tranεparent and colorless. 68. The coating composition of claim 62 wherein said metal oxide compriseε colloidal silica. 69. The coating composition of claim 62 wherein said metal oxide comprises colloidal titania. 70. The coating composition of claim 55 wherein said organic polymer constitutes from 30 to 80 percent by weight of said coating. 71. The coating compoεition of claim 55 wherein εaid organic polymer comprises additional organic polymer other than said poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000. 72. The printing medium of claim 71 wherein said additional organic polymer is water-εoluble poly(ethylene oxide) having a weight average molecular weight below 100,000, water-εoluble poly(ethylene oxide) having a weight average molecular weight above 3,000,000, water-εoluble cellulosic organic polymer, water-soluble noncellulosic organic polymer, water disperεible polymer, or a mixture of two or more thereof. 73. The printing medium of claim 71 wherein said additional organic polymer is water-εoluble anionic polyacrylate or water-εoluble cationic polyacrylate. 74. The coating composition of claim 71 wherein: (a) said water-soluble poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 60 percent by weight of said organic polymer of said binder; and (b) said additional organic polymer constituteε from 1 to 40 percent by weight of εaid organic polymer of said binder. 75. The coating composition of claim 55 wherein said poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes at least 99 percent by weight of said organic polymer of said binder.

Inventors: ALDERFER GEORGE E, HILL CHARLES T JR, PEKALA RICHARD W, YOLDAS BULENT E, ALDERFER, GEORGE, E., HILL, CHARLES, T., JR., PEKALA, RICHARD, W., YOLDAS, BULENT, E.
Applicants: PPG INDUSTRIES INC, PPG INDUSTRIES, INC.
Application year: 1996
Main classification: B41J
IPC codes: B41M5, C09D101