IMAGE RECORDING MEDIA

Abstract: An ink image recording medium is provided having excellent color developability and which can effectively prevent a coloring component in ink from transferring to micropores in a medium. The image recording medium comprises (i) a substrate layer containing permeable micropores and (ii) an ink image receptive layer containing water-soluble salts as a coagulating agent disposed on the surface of the substrate layer, characterized in that a surface of the substrate layer and an inner surface of the micropores are hydrophilized with a surfactant. The ink image receptive layer contains a polar organic polymer.

Description: IMAGE RECORDING MEDIA Field of the Invention The present invention relates to an image recording medium and, more particularly, to an image recording medium used for recording an ink image by using a printing method such as inkjet recording method. Particularly, the present invention relates to an image recording medium capable of forming or recording an image having high ink drying property (water-fastness) and high water resistance. Background of the Invention It has hitherto been known that materials having a porous substrate layer containing a plurality of permeable micropores are useful as ink image recording mediums such as inkjet recording paper. For example, International Publication No. W099/03685 discloses an ink image recording medium comprising a substrate layer made of a porous film, wherein surfactant and a polyvalent metal salt are contained in micropores of the substrate layer. The polyvalent metal salt is fixed in the micropores by hydrophilizing an inner wall (inner surface) of the micropores of the substrate layer using a surfactant, and coating a liquid containing the polyvalent metal salt. Ink is printed (recorded) so as to be fixed onto the surface of this substrate layer. However, in the case of this ink image recording medium, since a portion of a pigment contained in ink does not remain on the surface of the recording medium and transfers into the micropores, it is difficult to improve the color developability and water-fastness. Further, U.S. Patent No. 5,605,750 discloses an ink image recording medium wherein an image forming layer (ink receptive layer) made of a porous pseudo-boehmite is disposed on the surface of a porous substrate layer containing water-insoluble filler particles (e.g. silica) dispersed therein. Specific examples of a material for substrate layer include porous stretched resin film "Teslin™" manufactured by PPG Industries Co. In the case of this recording medium, since the image forming layer described above was provided on the substrate layer, it is possible to easily form and record an image having high color developability. In the ink image recording medium described above, the ink receptive layer to be disposed on the substrate layer may also be a layer containing a polymer. For example, the ink receptive layer in this case is a layer containing a polymer and an inorganic pigment. The inorganic pigment is that for imparting porosity to the ink receptive layer, and water-insoluble particles such as porous synthetic silica, alumina hydrosol, etc. are usually used. The polymer includes, for example, water- soluble polymer, cationically modified polymer (polyurethane) or the like. The cationically modified polymer is particularly useful for enhancement of the ink setting property, thereby easily realizing an image having high color developability. However, still some room for improvement in water-fastness is left in such an ink receptive layer. Summary of the Invention The present invention provides an image recording medium comprising (i) a substrate layer containing permeable micropores and (ii) an ink image receptive layer containing water-soluble salts as a coagulating agent disposed on the surface of the substrate layer. A surface of the substrate layer and an inner surface of the micropores are hydrophilized with a surfactant. The ink image receptive layer contains a polar organic polymer. Detailed Description of the Invention In order to enhance the color developability and image quality in the ink image recording medium as described above, it is advantageous to provide an ink receptive layer, in addition to a porous substrate layer. In order to enhance the ink drying property (water-fastness), it is advantageous that the permeability (i.e. porosity) of the ink receptive layer is not deteriorated. However, even if the porosity of the ink receptive layer is improved, the coloring component in ink, particularly pigment tended to transfer to the ink receptive layer, or the ink receptive layer and the micropores in the substrate layer, retards drying of the ink after printing. Accordingly, the present invention provides a novel ink image recording medium, which can realize excellent color developability and can effectively prevent a coloring component (e.g. pigment, etc.) in ink from transferring to micropores in a medium, thereby enhancing the water-fastness. The image recording medium of the present invention is characterized in that said image recording medium comprises an ink image receptive layer on a substrate layer containing permeable micropores, and the ink image receptive layer contains water-soluble salts (i.e. salts of organic acid and/or inorganic acid) as a coagulating agent. The coagulating agent has an operation of quickly coagulating the coloring component such as pigment when ink is applied on the surface of the recording medium by printing. Accordingly, the coagulating agent can effectively prevent the pigment from transferring into to micropores in the recording medium, thereby enhancing the water- fastness of the ink. The ink image receptive layer preferably contains an organic polymer, in addition to the coagulating agent. The water resistance of the ink image fixed onto the surface of the ink image receptive layer is further enhanced by a synergistic effect of the coagulation action described above and binding action of the polymer. Assuming that the air permeability of the substrate layer is specified with reference to the Gurley-air-permeability, it ranges usually from 10 to 3,000 seconds per 100 ml, preferably from 50 to 2,500 seconds per 100 ml, more preferably from 100 to 2,000 seconds per 100 ml. Note that the "Gurley-air-permeability" used herein is the value measured by using a Gurley densometer in accordance with the Japanese Standard, JIS P-8117-1980, and is expressed in time taken for air with a volume of 100 ml to pass the substrate layer. The above coagulation action of the water-soluble salts can be effectively enhanced by ionization of the salts. Accordingly, ink to be applied onto the surface of the image recording medium (ink image receptive layer) is preferably ink containing water, i.e. water-based ink. The fact that the salts are "water-soluble" (that is, having a property which is soluble in water) means that the salts can react with water thereby to generate ionic chemical species. In addition, if the solubility of the salts is expressed with its quantity capable of being dissolved in lOOg of water at 20°C, it ranges usually from 0.001 to lOOg, preferably from 0.01 to 90g, more preferably from 0.1 to 80g. As these salts, polyvalent metal salts of organic or inorganic acid are preferred. These salts have comparatively high coagulation action are superior in effect of simultaneously enhancing the water-fastness and water resistance of the fixed ink image. The thickness of the ink image receptive layer can vary widely, but is comparatively small. When the thickness is, for example, within a range from 0.01 to 5 μm, the substrate layer advantageously contains amorphous silica. This is because, even if the pigment has passed through the ink image receptive layer, the ink coagulation action on the surface of the substrate layer or in the vicinity of the surface is effectively enhanced by the synergistic effect of the coagulating agent and amorphous silica. The ink coagulation action is effectively enhanced by the synergistic effect of the coagulating agent and polar polymer, in the same manner as described above. As such a polar polymer, a basic polymer such as cationically modified polyurethane, polyvinyl pyrrolidone and the like is preferred. On the other hand, when the thickness of the ink image receptive layer is comparatively large, smudge of the ink image can be easily prevented, which is advantageous. From such a point of view, the thickness of the ink image receptive layer is usually from 5 to 200 μm, and preferably from 10 to 100 μm. The upper limit of the thickness does not exert an influence on characteristics of the ink image, but is likely to more increase the thickness of the image recording medium than it needs. Therefore, the above range is preferred. The micropores on the surface of the substrate layer and those in the substrate layer are hydrophilized with a surfactant to improve water-fastness. A hydrophilization treatment can also be conducted, simultaneously with formation of the ink image receptive layer, by adding a surfactant to a coating solution for forming an ink image receptive layer, and coating the coating solution onto the surface of a substrate layer. If necessary, the hydrophilization treatment can also be conducted before formation of the ink image receptive layer. That is, the ink image receptive layer is preferably formed by coating a liquid containing a surfactant onto the surface of the substrate layer first, or impregnating the substrate layer with the liquid, subjecting to a hydrophilization treatment, and then coating a coating solution containing a polymer and a coagulating agent onto the surface of the hydrophilized substrate layer. According to the latter method, an image recording medium having high water-fastness can be produced more easily. Embodiments for Carrying Out the Invention Preferred embodiments of the present invention will be described hereinafter with reference to the respective constituent elements of the image recording medium of the present invention and method of using it. Substrate layer The substrate layer comprises a film or sheet containing a plurality of micropores (hereinafter referred generically to as a "porous film"), thereby to quickly absorb a solvent (dispersion medium) such as water in ink to be applied to the recording medium, thus making it possible to enhance water-fastness. The porous film is not specifically limited as far as it exerts the above effect, and it is possible to use those which have hitherto been used as a base in the ink image recording medium. For example, various stretched resin films including the above- described porous stretched film "Teslin™" manufactured by PPG Industries are preferred. Specific examples of the resin film include polyolefin such as polyethylene, polypropylene and polymethylpentene-1; polyamide such as polyvinyl chloride, polyvinylidene chloride, polystyrene, styrenebutadiene-acrylonitrile copolymer, nylon 6 and nylon 66; polyester such as copolymerized polyamide, polycarbonate, polymethyl methacrylate, polysulfone, polyethylene terephthalate and polybutylene phthalate; copolymerized polyester; polyether ester; polyether amide; and polyester amide. These materials may be used alone or in combination. Among these materials, general-purpose resin, for example, polyolefin resin such as polypropylene and high-density polyethylene is preferred in view of the water resistance and cost. The resin film may also contain inorganic fine powders, if necessary. As the inorganic fine powders, for example, powders of calcium carbonate, alumina, calcined clay, silica (including amorphous silica), diatomaceous earth, talc, titanium oxide and barium sulfate can be used, if necessary. The particle diameter of the fine powders is usually from 0.3 to 10 μm, and preferably from 0.8 to 5 μm. Other additives such as heat stabilizers, ultraviolet absorbers, dispersants, antistatic agents, antioxidants and oils (e.g. mineral oil) can also be mixed. Specific examples of a stretching equipment used for stretching the above resin film (also including those prepared by adding inorganic fine powders and additives, if necessary) include inflation film molding equipment, inflation film molding equipment with an inner mandrel, and T-die film molding equipment with a tenter or a group of longtitudinal stretching rolls and the tenter. The stretching direction may be a monoaxial or biaxial direction. The stretching percent is at least 1.3 times or higher, preferably from 1 to 10 times in both longitudinal and lateral directions, and more preferably from 1.3 to 9 times. The stretching temperature is from 140 to 155°C when the resin is a homopolymer of propylene (melting point: 164-167°C while it is from 110 to 120°C when the resin is a high-density polyethylene (melting point: 121-134°C). The stretching rate is usually from 10 to 350 rn/min. The porosity (volume occupied by pores compared with the total volume of the film) of the porous film is usually from 10 to 90% by volume, and preferably from 20 to 80% by volume. When the porosity of the porous film is too small, there is a fear that the drying property of ink is lowered. On the other hand, when the porosity is too large, nerve (mechanical strength) of the substrate layer is lowered and, therefore, there is a fear that supply and delivery of the recording medium can not be smoothly conducted. The pore diameter of pores of the porous film is usually from 0.01 to 3 μm, preferably from 0.02 to 2 μm, and particularly preferably from 0.03 to 1 μm, when the film was cut in the direction perpendicular (horizontal to the porous film) to the thickness sectional direction and measured. When the pore diameter of the pores is too small, there is a fear that the drying property of ink is lowered. On the other hand, when the pore diameter is too large, there is a fear that the color developability (color density) after applying ink is lowered and uniformity of the ink image receptive layer to be formed by coating thereon is lowered. The total thickness of the substrate layer is from 30 to 500 μm, and preferably from 50 to 300 μm. when the substrate layer is too thin, there is a fear that the ink drying property is lowered. On the other hand, when the substrate layer is too thick, there is a fear that handling of the recording medium becomes inconvenient. The image recording medium of the present invention can be preferably used in various types of printing equipments such as inkjet printer. When the recording medium is too large, there is a fear that some printer can not be used. The image recording medium of the present invention can be preferably used in such a manner that an adhesive layer is disposed on an opposite surface to a surface of the substrate layer on which the ink image receptive layer is disposed, and the image recording medium is attached to an adherend such as wall. When the recording medium is too thick, the recording medium can not follow curve or irregularity of the surface of the adherend and there is a fear that it becomes difficult to attach. In the preferred embodiments of the present invention, the micropores on the surface of the substrate layer and those in the substrate layer are hydrophilized with a surfactant. As the surfactant, any of anionic, cationic, amphoteric and nonionic surfactants can be used. As the anionic surfactant, for example, carboxylate, sulfonate and phosphate surfactants can be used. As the cationic surfactant, for example, amine salt and quaternary salt surfactants can be used. As the amphoteric surfactant, for example, betain and sulfobetain surfactants can be used. As the nonionic surfactant, for example, polyoxyalkylene (e.g. polyethylene glycol), sorbitan and sorbitol surfactants can be used. When the hydrophilization treatment is conducted by coating a liquid containing a surfactant and drying, for example, water and alcohol such as ethanol are preferably used as the solvent. The concentration of the surfactant in the liquid containing the surfactant is usually from 1 to 30% by weight, and preferably from 5 to 25% by weight. As the coating equipment, for example, a normal coater such as bar coater, knife coater, roll coater and die coater can be used. Ink image receptive layer The ink image receptive layer of the image recording medium according to the present invention comprises a polar organic polymer, and a coagulating agent containing water-soluble salts. As the organic polymer, for example, there can be used polyolefin, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene-butadiene- acrylonitrile copolymer, polyamide, acrylic polymer, polyester and normal unmodified polyurethane provided that the polymer contains polar functionality. The coagulating agent is not specifically limited as far as it has water solublility and can quickly coagulate a coloring component such as pigment on the surface of the ink image receptive layer when ink is applied (e.g. printing) onto the surface of the recording medium. The coagulating agent contains organic or inorganic salts as an essential component. As described above, salts are preferably polyvalent metal salts of organic or inorganic acid. In the film obtained after applying ink and drying, ink coagulates an ink component once on the surface of the fixed layer, thereby making it possible to effectively fix polyvalent metal ions and counter ions of an acid. As the polyvalent metal ion, for example, one or more sorts of aluminum, gallium, titanium, zirconium, hafnium, zinc, magnesium, calcium, niobium, tantalum, iron, copper, tin and cobalt can be used in combination. As the organic acid, for example, aromatic carboxylic acid, sulfonic acid, sulfocarbonic acid, hydroxysulfocarboxylic acid or hydroxycarboxylic acid can be used. Typical aromatic acid is not specifically limited to those listed below, but includes the following aromatic acids (I) to (VI). Metal sulfocarbolates ••• ( I ) M = Cu,Mg, Co (x:y = 1:2); M = Al.Ga (x:y = 1:3,2:3) Metal hydroquinonesulfonates (II) M - Cu,Mg,Co(x:y = 1:2,2:2); M = Al, Ga, Ti, Zr (x:y = 1:3,2:3,2:2) Metal dihydroxybenzenedisulfonates (HI) M - Cu,Mg, Co(x:y = 1:1,1:2); M = Al,Ga,Ti,Zr(x:y = 1:1,2:2,4:3) Metal sulfosalicylates (IV) M = Cu,Mg, Co(x:y = 1:2,1:1); M = Al,Ga,Ti,Zr(x:y = 1:3,2:3,3:3) R - -COOH Metal sulfophthalates M = Cu, Mg, Co (χ:y = 1:1, 2:2, 3:2); M = Al, Ga, Ti, Zr (x:y = 1:3, 2:2, 2:3) R = -COOH (Li + , Na + , K + ) Metal carboxylates ( VI ) M = Cu, Co (x:y = 1:1, 2:2, 3:2); M = Al. Ga (x:y = 1:3, 2:2, 2:3) R 1 = -COOH, R 2 = -OH The aromatic acids described above may be used alone, or two or more kinds of them may also be used in combination. In the case of the metal salt of the organic acid, an oligomer acid salt wherein two or more monomer units are combined (e.g. bis-, tris- and tetra-compounds) can also be used, in addition to a monomer acid salt, but the monomer acid salt is preferred in view of an enhancement in coagulating force, water-fastness and water resistance. Referring to the metal salt of sulfophthalic acid, a metal salt of sulfophthalic acid is better than a metal salt of bis-sulfophthalic acid and a metal salt of tris-sulfophthalic acid. The above organic acid metal salt is particularly preferred when amorphous silica is contained in the substrate layer. Because the coagulating force (fixing force) of ink can be effectively enhanced. From such a point of view, it is also preferred to add amorphous silica in the ink image receptive layer. Amorphous silica is usually made of silicon dioxide wherein the silicon center is tetrahedrally bound to the oxygen atoms which are bridged between the silicon centers. In an aqueous environment, there is certain percentage of silanol (Si-OH) on the silica surface. In an acidic environment, the percentage of the silanol group increases. That is, the presence of acidic counter ions, particularly organic acid ions enhance the concentration of silanol, thereby making it possible to enhance an ink fixing force. Such an ink fixing force is further enhanced by the presence of a surfactant. The metal ion is preferably an aluminum ion (Al 3+ ). Because the aluminum ion is strongly bound to a silanol group and coagulation of a coloring component such as pigment is effectively caused by the aluminum ion. On the other hand, preferred examples of the inorganic acid include sulfuric acid, nitric acid or hydrochloric acid. When the polar organic polymer is a cationically modified polymer, such as cationically modified polyurethane, an inorganic acid salt is generally preferred as compared to an organic acid salt. This is because the inorganic acid salt can more effectively enhance the water- fastness and water resistance in cooperation with the cationically modified polymer. The inorganic acid salt is preferably aluminum sulfate. Although details of the reason are not apparent, it is considered that the ink fixing force is enhanced by an interaction between a cation portion of the polymer and sulfuric and aluminum ions, which is reflected in the water-fastness and water resistance. By using the inorganic acid salt in combination with the organic acid (e.g. sulfophthalic acid, phthalic acid, etc.), the interaction between the inorganic acid salt and amorphous silca can be enhanced to effectively improve the water resistance. In this case, a mixing molar ratio of the inorganic acid salt (In) to the organic acid (Or), i.e. In:Or is usually from 1:10 to 10:1, and preferably from 1 :5 to 5:1. The amount of the coagulating agent contained in the ink image receptive layer is usually from 1 to 70 parts by weight, preferably from 3 to 50 parts by weight, and particularly preferably from 5 to 30 parts by weight, based on 100 parts by weight of the organic polymer. When the amount of the coagulating agent is too small, the ink fixing force is lowered and, therefore, there is a fear that the water resistance and color developability are deteriorated. On the other hand, when the amount is too large, there is a fear that smudge of the ink image occurs. If necessary, inorganic fine powders can also be contained in the ink image receptive layer so as to enhance the porosity of the receptive layer. As the inorganic fine powders, for example, calcium carbonate, alumina, calcined clay, silica (including amorphous silica), diatomaceous earth, talc, titanium oxide and barium sulfate can be used. The particle diameter of the fine powders is usually from 0.3 to 10 μm, and preferably from 0.8 to 5 μm. Other additives such as heat stabilizers, ultraviolet absorbers, dispersants, antistatic agents and antioxidants can also be mixed. The ink image receptive layer can be formed, for example, by coating a coating solution containing a coagulating agent and an organic polymer and drying. In this case, water or alcohol is preferably used as a solvent. As the coating equipment, for example, a normal coater such as bar coater, knife coater, roll coater and die coater can be used. Method of using image recording medium The image recording medium of the present invention is used for recording an ink image by a printing equipment such as inkjet printer. Ink to be used for forming an image usually comprises a colorant such as pigment, dye, etc. and a solvent such as water, alcohol, etc. The recording medium of the present invention particularly exerts an effect in recording by an inkjet printer using water base ink (the solvent includes water), thereby effectively enhancing both the water-fastness and water resistance. The print conditions can be the same as those in the case of a normal recording paper. The recording medium of the present invention is also superior in that printing under special conditions is not particularly required as described above. The image recording medium of the present invention can also be used as a constituent material of a decorative adhesive sheet. For example, an adhesive layer containing a tackifϊer or an adhesive is disposed on an opposite surface to a surface of a substrate layer on which an ink image receptive layer is disposed, and then a liner for protecting the adhesive surface of the adhesive layer, thereby forming a laminate comprising an image recording medium, an adhesive layer and a liner. This laminate is subjected to a printer in the same manner as in the case of the recording medium alone and the ink receptive/fixing surface on the surface of the recording medium (ink image receptive layer) is provided with decorative printing, thereby making a decorative adhesive sheet. The adhesive sheet according to the present invention is capable of decorating an adherend by applying onto the surface of the adherend such as wall, vehicle body, glass-paned window, etc. in the same manner as in the case of a conventional decorative adhesive sheet. As a matter of course, this adhesive sheet can also be used for purposes other than the above decorative purpose. Other purposes include, for example, advertising and displaying purposes. Examples The present invention will be described below with reference to the following examples. It is appreciated that the present invention is not limited by the following examples. Example 1 An amorphous silica-containing porous film "Teslin™" manufactured by PPG Co. was prepared as a substrate layer. This porous film had a thickness of 180 μm, a porosity of 65% by volume and a pore diameter of 0.01 to 1 μm. An acrylic adhesive layer (thickness = 30 μm) with a liner was laminated on one surface of the substrate layer. On the surface having no adhesive layer of the resulting substrate layer with the adhesive layer, a hydrophilization treatment solution of the following composition was coated and dried. Composition of hydrophilization treatment solution Surfactant (Pelex™ TR, 13 parts by weight manufactured by Kao Corp.) Deionized water 61 parts by weight Ethanol 26 parts by weight After the completion of the hydrophilization treatment, a coating solution 1 for forming ink image receptive layer of the following composition was coated on the hydrophilized surface of the substrate layer, using a bar coater. Composition of coating solution 1 for forming ink image receptive layer Coating agent (see below) 95 parts by weight Aqueous solution of 5 parts by weight aluminum sulfate* 14-18H 2 O The coating agent used is a coating agent comprising a cationically modified polyurethane and inorganic fine powders Pateracoal™ IJ-170, which is commercially available from Dainippon Ink and Chemicals, Inc. The coated film of the coating solution 1 was dried at 100°C for 3 minutes. As a result, an ink image receptive layer having a thickness of 20 μm has been completed, thereby to obtain an image recording medium (embodiment capable of being used as a constituent material of a decorative adhesive sheet) of this example. Printing test 1 On the surface (ink receptive/fixing surface) of the ink image recording medium of this example, full-color printing was conducted by using an inkjet printer Navajet™ III manufactured by Encad Co and printing characteristics were evaluated. The printing conditions applied are as follows. Printing direction: single direction Ink jetting rate: 5000 Hz Ink to be used: pigment ink 8500 series, Cyan #8551, Magenta #8553, Yellow #8552 and Black #8554, manufactured by 3M Co. Printing characteristics (evaluation items) (1) Drying time A drying time of the portion (amount of ink: 400% parts) where all four colors (cyan, magenta, yellow and black) are mixed was measured and evaluated. As a result, the drying time was 75 seconds. Accordingly, it has been proved that the drying property of ink is sufficiently high, that is, ink has a water- fastness. (2) Smudge at boundary Smudge of the color at the boundary between the portion (amount of ink: 300% parts) where all four colors (cyan, magenta, yellow and black) are mixed and the other color portion adjacent to the above portion was visually observed and evaluated. As a result, smudge of the color was hardly observed. (3) Color developability (color concentration) With respect to four colors (cyan, magenta, yellow and black), the color developability of the portion of each single color and that of the color-mixed portion were visually observed. As a result, it has been confirmed that the color developability of any portion is very high. Printing test 2 In the same manner as in the printing test 1, full-color printing was conducted and printing characteristics were evaluated. In this printing test, however, an inkjet printer manufactured by Canon Co. was used in place of the inkjet printer manufactured by Encad Co. and exclusive four color dye inks (cyan, magenta, yellow and black) were used. In the case of this printing test, the drying property of ink (400% parts) was excellent and the drying had been completed until the print came out from the printer. Smudge at the boundary (300% parts) was hardly observed. Furthermore, the color developability was also high. Example 2 (Comparative Example) The procedure described in Example 1 was repeated, except that aluminum sulfate was not added to the coating solution for forming ink image receptive layer for comparison in this example. The printing test 1 was conducted. The results are as follows. The drying time was 80 seconds and ink exhibited sufficient water-fastness, but smudge at the boundary (300% parts) occurred to a large extent, it is considered that this smudge is caused by lowering of the ink fixing force. The color developability was not clear compared with Example 1. Example 3 The procedure described in Example 1 was repeated, except that the step of the hydrophilization treatment to be subjected to the surface of the substrate layer was omitted in this example. The printing test 1 was conducted. The results are as follows. The drying time was 40 minutes and it was evaluated that ink was dried comparatively slowly. However, smudge .at the boundary (300% parts) was hardly observed and the color developability was good enough to compare with Example 1. Example 4 The procedure described in Example 1 was repeated, except that the step of the hydrophilization treatment to be subjected to the surface of the substrate layer was omitted and a thin top coat having a thickness of smaller than 0.1 μm was provided on the surface on which an ink image receptive layer of an amorphous silica-containing porous film prepared as a substrate layer is to be disposed in place of the step of the hydrophilization treatment in this example. The top coat is made of silica and a copolymer of polyvinyl pyrrolidone (PNP) and acrylic acid (AA) (polymerization ratio of PNP to AA = 75:25). On the top coat provided on the substrate layer, a coating solution 2 for forming ink image receptive layer having the following composition was coated in place of the coating solution 1 for forming ink image receptive layer used in Example 1, using a Meyer Rod #4. Composition of coating solution 2 for forming ink image receptive layer Coagulating agent 10 parts by weight (aluminum (III) sulfophthalate) Surfactant 6 parts by weight (dihexylsulfosuccinate-Νa salt) Organic polymer 2 parts by weight (PNP:AA = 75:25) Isopropyl alcohol 25 parts by weight Deionized water 57 parts by weight The organic polymer is made of a copolymer of polyvinyl pyrrolidone (PNP) and acrylic acid (AA) (polymerization ratio of PNP to AA = 75:25). The coated film of the coating solution 2 was dried at 120-130°C for about 1 to 2 minutes. As a result, an ink image receptive layer having a thickness of 20 μm has been completed to obtain an image recording medium of this example. Printing test 3 Test 1: In the same manner as in the printing test 1 , full-color printing was conducted and printing characteristics were evaluated. In this printing test, however, printing characteristics were evaluated with respect to the following items using two inkjet printers HP-2500cp and HP-3500cp manufactured by Huelet Packard Co. were used in place of the inkjet printer manufactured by Encad Co. and using exclusive four color dye inks (cyan, magenta, yellow and black). As a result of the printing test, both printers provided an ink image with very high density and high quality. The resulting ink image was free from smudge and feathering and was superior in water-fastness. Test 2: An amorphous silica-containing porous film "Teslin™" manufactured by PPG Co. was cut to prepare a substrate layer having a width of 16 inch (about 40 cm) and a length of 24 inch (about 61 cm). In the same manner as described above, the coating solution 2 for forming ink image receptive layer was coated on half of the surface of the substrate layer to form an ink image receptive layer having a thickness of 20 μm. An ink image receptive layer was not formed on the remaining half of the surface of the substrate layer. As a result, an image recording medium having an ink image receptive layer provided on half of the surface was obtained. On the surface of the resulting image recording medium, full-color printing was conducted by using an inkjet printer HP-2500cp manufactured by Huelet Packard Co. and exclusive four pigment inks (cyan, magenta, yellow and black) and then printing characteristics were evaluated with respect to the following items. As a result of the printing test, it has been found that an ink image with very high density can be formed regardless of the presence or absence of the ink image receptive layer. However, the ink image in the portion with the ink image receptive layer showed higher density than that in the portion free from the ink image receptive layer. Test 3: In the same manner as in test 2, full-color printing was conducted and the image recording medium after printing was laminated face up onto an aluminum poster board. The resulting laminate was subjected to a water-wash test by strongly spraying water at 25-30°C to the printed surface thereof. At least 90% (original area of the ink image being 100%) of the wet image at the portion free from the ink image receptive layer was washed away only by rubbing with a paper towel. To the contrary, in the case of the ink image with the ink image receptive layer, only a small loss in color (1% or less) was observed at a very small portion of the ink image because the drying was quickly completed. Example 5 The procedure described in Example 4 was repeated, except that the surfactant (dihexylsulfosuccinate-Na salt) was removed from the coating solution 2 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed slightly lower drying property than in Example 4, but showed similar good characteristics as in Example 4 in other points except for test 3 (water- wash test). In the test 3, a portion of black and green colors was lost after washing but the amount was about 5-10% of the original area of the ink image. Example 6 The procedure described in Example 4 was repeated, except that the organic polymer (PVA:AA = 75:25) was removed from the coating solution 2 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. It seemed that the amount of the black color observed on the surface was larger than that of the other colors and color development was not clear in the resulting image. In the test 3, a portion of the black color and a portion of the green color were lost. As is apparent from these results, the ink image receptive layer preferably contains an organic polymer. Example 7 The procedure described in Example 4 was repeated, except that both of the surfactant (dihexylsulfosuccinate-Na salt) and organic polymer (PVA:AA = 75:25) were removed from the coating solution 2 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed slightly lower drying property than in Example 4. It seemed that the amount of the black color observed on the surface was larger than that of the other colors and color development was not clear. Furthermore, a zonal group wherein pigments are coagulated in the form of beads was observed. In the test 3, a portion of the black color and a portion of the green color were lost. Example 8 The procedure described in Example 4 was repeated, except that bis- aluminum (III) sulfophthalate was used as the coagulating agent in place of aluminum (III) sulfophthalate in the coating solution for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed slightly lower drying property than in Example 4. In the test 3, a portion of the red color and a portion of the green color were lost. Example 9 The procedure described in Example 4 was repeated, except that tris- aluminum (III) sulfophthalate was used as the coagulating agent in place of aluminum (III) sulfophthalate in the coating solution for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed slightly lower drying property than in Example 4. In the test 3, a portion of black, red and green colors was lost. Example 10 The procedure described in Example 1 was repeated, except that a coating solution 3 for forming ink image receptive layer having the following composition was coated in place of the coating solution 2 for forming ink image receptive layer. Composition of coating solution 3 for forming ink image receptive layer Coagulating agent 9 parts by weight (zirconiumtetrakis(sulfophthalate)) Surfactant 6 parts by weight (dihexylsulfosuccinate-Na salt) Isopropyl alcohol 25 parts by weight Deionized water 58 parts by weight The printing test 3 was conducted. The results are as follows. Test l: Both printers provided an ink image with very high density and high quality. The resulting ink image was free from smudge and feathering and was superior in water- fastness. Test 2: As a result of the printing test, it has been found that an ink image with very high density can be formed regardless of the presence or absence of the ink image receptive layer. However, the ink image in the portion with the ink image receptive layer showed higher density than that in the portion free from the ink image receptive layer. Test 3: Almost all of the wet image at the portion free from the ink image receptive layer was washed away only by rubbing with a paper towel. To the contrary, in the case of the ink image with the ink image receptive layer, only a small loss in color (3-5%) was observed at a very small portion of the ink image because the drying was quickly completed. This fact proves that zirconium tetrakis(sulfophthalate) used as the coagulating agent in this example imparts excellent water resistance to the ink image receptive layer and contributes to a further improvement in water- fastness than an organic acid aluminum salt. Example 11 The procedure described in Example 10 was repeated, except that titanium tetrakis(sulfophthalate) was used as the coagulating agent in place of zirconium tetrakis(sulfophthalate) in the coating solution 3 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 10. In the test 3, a portion (10-20%) of the image was lost in the ink image with the ink image receptive layer. Example 12 The procedure described in Example 10 was repeated, except that copper (II) tetrakis(sulfophthalate) was used as the coagulating agent in place of zirconium tetrakis(sulfophthalate) in the coating solution 3 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water- fastness as in Example 10. In the test 3, a portion (5-10%) of the image was lost in the ink image with the ink image receptive layer. Example 13 The procedure described in Example 4 was repeated, except that magnesium sulfophthalate was used as the coagulating agent in place of aluminum (III) sulfophthalate in the coating solution 2 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 4. In the test 3, a portion (10-15%) of the image was lost in the ink image with the ink image receptive layer. Example 14 The procedure described in Example 4 was repeated, except that a coating solution 4 for forming ink image receptive layer having the following composition was coated in place of the coating solution 2 for forming ink image receptive layer. Composition of coating solution 4 for forming ink image receptive layer Coagulating agent 3 parts by weight (aluminum sulfate- 14 hydrate) Surfactant 6 parts by weight (dihexylsulfosuccinate-Na salt) Organic polymer 2 parts by weight (PVP:AA = 75:25) Isopropyl alcohol 25 parts by weight Deionized water 64 parts by weight The printing test 3 was conducted. The results are as follows. The resulting ink image showed lower water- fastness than in Example 4, but was in a level enough to put to practical use. In the test 3, a portion of the image was lost in the ink image with the ink image receptive layer. Example 15 The procedure described in Example 14 was repeated, except that 9.6 parts by weight of sulfophthalic acid was further added as the coagulating agent in the coating solution 4 for forming ink image receptive layer in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 14. In the test 3, a portion of the image was lost in the ink image with the ink image receptive layer, but the image was more improved than in Example 14. Example 16 The procedure described in Example 14 was repeated, except that 4.5 parts by weight of phthalic acid was further added as the coagulating agent in the coating solution 4 for forming ink image receptive layer in this example so that a molar ratio of aluminum sulfate- 14 hydrate to phthalic acid becomes 1:3. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 14. In the test 3, a portion of the image was lost in the ink image with the ink image receptive layer, but the image was more improved than in Examples 14 and 15. Example 17 The procedure described in Example 14 was repeated, except that 5.7 parts by weight of l,2,4benzenetricarboxylic acid was further added as the coagulating agent in the coating solution 4 for forming ink image receptive layer in this example so that a molar ratio of aluminum sulfate* 14 hydrate to 1,2,4- benzenetricarboxylic acid becomes 1:3. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 14. In the test 3, a portion of the image was lost in the ink image with the ink image receptive layer, but the image was more improved than in Example 14. Example 18 The procedure described in Example 4 was repeated, except that a silica filling type porous high-density polyethylene film (Texwipe™ Mp-10, manufactured by Texwipe Co.) was used as the substrate layer in place of the amorphous silica-containing porous film in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good water-fastness as in Example 4. In the test 3, only a portion (5-7%) of the image was lost in the ink image with the ink image receptive layer. Example 19 The procedure described in Example 4 was repeated, except that it was eliminated to dispose a thin top coat on the surface on which an ink image receptive layer of a substrate layer is to be disposed in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good ink developability and good water-fastness as in Example 4. The results of the test 3 were also good as in Example 4. Example 20 The procedure described in Example 10 was repeated, except that it was eliminated to dispose a thin top coat on the surface on which an ink image receptive layer of a substrate layer is to be disposed in this example. The printing test 3 was conducted. The results are as follows. The resulting ink image showed similar good ink developability and good water-fastness as in Example 10. The results of the test 3 were also good as in Example 10. Effect of the Invention As described above, according to the present invention, there can be provided an excellent image recording medium, which can realize excellent color developability and can effectively prevent coloring components (e.g. pigment) in ink from transferring to micropores in the medium, thereby to enhance water- fastness, and which has never been obtained. In particular, when using the image recording medium of the present invention, the printing time can be markedly reduced and, at the same time, the workability and productivity after printing can also be markedly improved because of its excellent drying property of ink, in other words, water-fastness of the ink image. The image recording medium of the present invention can also be applied to a high-speed printer by making use of its water-fastness. In the image recording medium of the present invention, since coloring component such as pigment and dye are quickly coagulated by multivalent metal salts contained in the ink image receptive layer and the resulting large coagulum can be fixed onto the surface of the ink image receptive layer, there can be obtained an high-quality ink image which has very high color concentration, in other words excellent color developability, and is free from smudge. Accordingly, the image recording medium can be advantageously used in wide applications. Furthermore, in the image recording medium of the present invention, sufficiently satisfactory results can be expected even under an outdoor environment exposed to wind and rain because of its good water resistance in addition to the water-fastness of the ink image. Although the kind of the printer and ink to be used for each recording medium in a conventional image recording medium was heretofore limited, such a limitation is removed in the image recording medium of the present invention because of its excellent ink receptive property. Therefore, similar good printing characteristics can be obtained even when using various printers and inks.

Claims: What is claimed is: 1. An image recording medium comprising (i) a substrate layer containing permeable micropores and (ii) an ink image receptive layer containing water- soluble salts as a coagulating agent disposed on the surface of the substrate layer, characterized in that a surface of the substrate layer and an inner surface of the micropores are hydrophilized with a surfactant, wherein the ink image receptive layer contains a polar organic polymer. 2. The image recording medium according to claim 1, wherein the polar organic polymer is a cationically modified polymer. 3. The image recording medium according to claim 2, wherein the cationically modified polymer is a cationically modified polyurethane polymer. 4. The image recording medium according to claim 1, which further comprises an adhesive layer on an opposite surface to a surface of the substrate layer on which the ink image receptive layer is disposed. 5. The image recording medium according to claim 1, wherein the coagulating agent comprises a polyvalent metal salt of an inorganic acid. 6. The image recording medium according to claim 1, wherein the substrate layer contains amorphous silica.

Inventors: TAKEDA YASUYUKI, TAKEDA, YASUYUKI
Applicants: 3M INNOVATIVE PROPERTIES CO, TAKEDA YASUYUKI, 3M INNOVATIVE PROPERTIES COMPANY, TAKEDA, YASUYUKI
Application year: 2000
Main classification: B41M5
IPC codes: B41J2, B41M5