Ink jet recording material and process for producing the same

Abstract: An ink jet recording material having high gloss, a good ink-absorbing property, and high color density of the ink image includes at least one under recording layer and at least one upper recording layer formed on a support and each containing fine pigment particles having an average primary particle size of 3 to 40 nm and an average secondary particle size of 10 to 400 nm, the pigment particles in the under recording layer having a larger primary particle size than those in the upperrecording layer.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording material and processes for producing the same. More particularly, the present invention relates to an ink jet recording material having excellent gloss and ink-absorption and capable of recording ink images with excellent color density, and processes for producing the same. 2. Description of the Related Art The ink jet recording system is an ink image recording system wherein ink droplets are jetted through an ink-jetting nozzle toward a recording material at a high speed, and ink jetted droplets are absorbed in and fixed on the recording material, to form ink images. This ink jet recording system is advantageous in that full colored images can be easily formed and the printing noise is low. The ink usable for the ink jet recording system contains a large amount of a solvent in which a coloring material is dissolved or dispersed and thus, to obtain a high color density of the recorded ink images, a large amount of the ink must be absorbed in the recording material. For the complete absorption of the ink droplets which have reached the recording material, a certain length of time is necessary. This feature of the ink jet recording system causes such a disadvantage that when the ink droplets are continuously jetted imagewise to form ink dots on the recording material surface, sometimes the ink droplets reach a target dot before an ink dot adjacent to the target dot has been completely absorbed in the recording material, and the target ink dot is connected to the adjacent ink dot so that the resultant ink image becomes unclear. Accordingly if the recording material for the ink jet recording system is to have such an advantage that the ink dots formed thereon have high color density and brightness and a high clarity, the ink droplets must be rapidly absorbed therein and even if the ink dots are overlapped on each other, substantially no blotting of the ink may occur. Currently, due to the rapid spread of ink jet printers, various ink jet prints with a high gloss are demanded for publications and packing paper sheets. Particularly, in colored prints, film type or coated sheet type ink jet recording sheets which have an appropriate dot form (true circle), a high dot sharpness, and high ink-receiving properties such as high ink-absorbing and fixing rates and a high ink absorption are in great demand. To meet to the above-mentioned demands, a large number of types of ink jet recording sheets in which a coating layer containing an ink-absorbing pigment, for example, silica and alumina, and a binder is formed on a surface of a support sheet, are available. In these recording sheets, the pigments have the very small particle size of several µm, and thus the surface of the resultant recording sheet is rough and a high gloss in the resultant prints is difficult to obtain. Also, since the coating layer is quite opaque, the applied ink is easily embedded in the coating layer and thus the color density of the resultant ink images is low. Namely, the droplets of ink easily spread between the fine pigment particles over a wide area and the color density in the image decreases with an increase in the distance from the center of the image. Also, the ink-spread area becomes unnecessarily large. Therefore, the color density of the ink image becomes low as a whole and the sharpness and clearness of the image decrease. Thus, undesirable unevenness and blotting of the image occur. To solve the above-mentioned problems, Japanese Unexamined Patent Publication No. 62-111,782 proposed an ink jet recording material in which upper and under porous coating layers, different in porosity from each other, are formed on a support sheet, to control the ink-spread and to prevent unevenness and blotting of ink images. However, since the upper and under coating layers contain pigments having a relatively large particle size, in the µm order, the resultant recording sheet was unsatisfactory in gloss and the color density of ink image. Also, Japanese Unexamined Patent Publication No. 62-244,689 discloses an ink jet recording material in which a support is coated with an under coating layer containing a while pigment having a refraction of 1.50 or more and then with an upper coating layer containing a silicon pigment having a refraction of 1.43 to 1.48. This ink jet recording sheet-can record ink images having a bright color and a high clarity. However, in this type of recording material, the pigments have a large particle size of 1 µm or more, and thus the recording material exhibits an unsatisfactory gloss and the resultant ink images have an unsatisfactory color density. Further, Japanese Unexamined Patent Publication No. 63-104,878 discloses an ink jet recording material in which a support is coated with a two-layered recording layer. In this recording layer, the pigments contained in an upper layer and a under layer are different in particle size, and one of the upper and under coating layers contains spherical silica particles, to enhance the ink-coloring property and the dot properties, for example, the true circle form of dots. However, the ink jet recording material is still unsatisfactory in gloss and color density of ink images. For the purpose of enhancing the gloss of ink images and the ink-absorbing property of the ink jet recording material, currently, for example, Japanese Unexamined Patent Publication No. 7-101,142 and No. 7-117,335 disclose a two layered recording layer in which an upper coating layer serves as a high gloss-exhibiting layer. In these publications, since the high gloss-exhibiting layer contains primary particles of a pigment, the porosity of the high gloss-exhibiting layer is very low. Therefore, the high gloss-exhibiting layer has very small or substantially no space for receiving and fixing the ink, and thus can serve only as an ink-passing layer. Almost all of the applied ink can be fixed only in the coating layer. The under coat layer contains pigment particles having a particle size of a µm order. Thus, the resultant under coating layer has a poor transparency, and thus cannot record ink images having a high color density. Therefore, this type of ink jet recording material substantially cannot record photographic image-like ink images having a high gloss and color density. Further, EP-A-803374 discloses an ink jet recording material in which a support is coated with an ink receiving layer containing secondary particles having an average secondary particle size of 10 to 300 nm and consisting of primary particles having an average particle size of 3 to 40 nm and agglomerated with each other. This ink jet recording material can record photographic image-like ink images having a high gloss and a high color density. However, in the current ink jet printers, since the printing speed and ink-jetting rate are greatly increased, the blotting and unevenness of the printed ink images must be further prevented. EP-A-0759365 discloses an ink jet recording material comprising a support and at least one recording layer containing colloidal primary particles and a water-soluble resin. EP-A-0450540 discloses an ink jet recording medium comprising a substrate and a pigment layer formed on the substrate. The pigment layer comprises an upper layer containing alumina particles having a primary particle size of 50 nm and a secondary particle size of 1800 nm. The lower layer comprises primary alumina particles having a size of 200 nm. SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording material having a high gloss, a high ink-absorbing property and a high resistance to blotting of ink and capable of recording clear ink images having excellent color density and sharpness, and processes for producing the same. The above-mentioned object can be attained by the ink jet recording material of the present invention as defined in claim 1. The process for producing an ink jet recording material of the present invention as defined by claim 7 comprises the following steps: forming at least one first coating layer corresponding to the at least one upperrecording layer on a casting surface; forming at least one second coating layer corresponding to the at least one underrecording layer on the first coating layer; laminating a support on the first and second coating layers formed on the casting surface; and separating the resultant laminate from the casting surface. Preferred embodiments of the claimed ink jet recording material and of the claimed process are disclosed and claimed in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an explanatory cross-sectional profile of an embodiment of the ink jet recording material of the present invention, and Fig. 2 shows an explanatory cross-sectional profile of another embodiment of the ink jet recording material of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors of the present invention have extensively studied an ink jet recording materials to solve the above-mentioned problems of the conventional ink jet recording material and have found that when a multi-layered ink receiving layer which comprises at least one underrecording layer and at least one upperrecording layer each containing secondary particles of a pigment, each consisting essentially of a plurality of primary particles agglomerated with each other, is formed on a support, the average secondary particles size of the secondary particles is controlled within the range of from 10 to 400 nm, the average primary particle size of the primary particles is controlled within the range of from 3 to 40 nm, and the average primary particle size of the primary particles in the underrecording layer is controlled to be larger than the average primary particle size of the primary particles in the upperrecording layer, the resultant ink jet recording material exhibits a high gloss, a high ink-absorbing property and a high resistance to blotting of ink, and can record clear ink images having a high color density. The present invention according to the present claims was completed on the basis of the above-mentioned finding. When the particle size of the primary particles, from which secondary particles of a pigment having an average secondary particle size of 10 to 400 nm, are formed, is small, the resultant recording layer exhibits a high transparency and the pores formed between the particles are relatively small. Also, the specific surface area of the small particles is large, and thus the ink dye is easily fixed on the particle surfaces and a printed material having a high gloss and a high color density of printed ink images can be easily obtained. However, the small size of the primary particle causes the film-forming property of the primary particles to be low and a binder must be employed in a large amount to obtain a recording layer having a satisfactory basis weight. When the content of the binder in the recording layer is too high, the resultant recording layer exhibits a significantly decreased ink-absorbing rate and capacity. Current ink jet printers exhibit a high ink-jetting rate and capacity. Therefore, the decreased ink-absorbing rate and capacity may cause the ink droplets applied to the recording material to flow or blot to the outside of the ink dots. To solve the above-mentioned problems, in the ink jet recording material of the present invention, the ink receiving layer is formed in a two or more layered form and the average particle size of the primary particles in the underrecording layer is controlled to be larger than that in the upperrecording layer. When the size of the primary particles, from which the secondary particles in the upper recording layer are formed, is small, the resultant ink receiving layer exhibits a high gloss and is capable of recording ink images having a high color density. When the size of the primary particles, from which the primary particles in the underrecording layer are formed, is large, the underrecording layer exhibits an enhanced film-forming property and can be formed in a large basis weight. Also, it becomes.possible to control the ink absorbing rate of the underrecording layer to be higher than that of the upperrecording layer. In this case, an ink jet recording material having a high ink-absorbing capacity and a significantly high resistance to blotting of the ink, is obtained. In the ink jet recording material, when a cationic compound is contained in the ink receiving layer, an anionic dye of the ink can be easily fixed in the ink receiving layer, and the resultant prints exhibit a significantly enhanced water resistance and durability in storage. Further, when at least the upperrecording layer is formed on a casting surface and then transferred to a support or an underrecording layer formed on the support, the resultant ink jet recording material has a photographic paper-like high gloss. The ink jet recording material of the present invention comprises a support and a multi-layered ink-receiving layer comprising at least one underrecording layer formed on the support and at least one upperrecording layer formed on the underrecording layer, wherein, the under and upperrecording layers comprise secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm, and the average primary particle size of-the primary particles contained in the underrecording layer is larger than the average primary particle size of the primary particles contained in the upperrecording layer. According to an embodiment of the present invention the average secondary particle size of the secondary particles is controlled within the range of from 10 to 300 nm. In the ink jet recording material of the present invention, the average primary particle size of the primary particles contained in the underrecording layer may be 1.2 to 10 times the average primary particle size of the primary particles contained in the upperrecording layer. In the ink jet recording material of the present invention, the upperrecording layer optionally further comprises a cationic compound. In the ink jet recording material of the present invention, the ink-receiving layer optionally further comprises an additional recording layer comprising, as a principal component, a polymeric material. The additional layer is arranged between the support and the underrecording layer. In the ink jet recording material of the present invention, the upperrecording layer may be one provided in such a manner that a first coating layer corresponding to the upperrecording layer is formed on a casting surface, a second coating layer corresponding to the under recording layer is formed on the first coating layer, a support is superposed on and bonded to the second coating layer, and the resultant laminate is separated from the casting surface. In the ink jet recording material of the present invention, the pigment comprises amorphous silica. In the ink jet recording material of the present invention, at least one recording layer other than an uppermost recording layer of the ink-receiving layer may have cracks formed to an extent such that when an ink jet dot printing is applied to the crack-formed recording layer, and printed ink dots having a diameter of 50 µm are observed through an optical microscope at a magnification of 150, a crack proportion, which is represented by a ratio in % of the number of printed dots in which cracks are formed to the total number of the printed dots, is 30% or more. In the ink jet recording material of the present invention, the uppermost recording layer may have a crack proportion smaller than that of the other recording layers. In the ink jet recording material of the present invention, the uppermost recording layer may have a pore volume of 0.2 to 3.0 ml/g. In the ink jet recording material of the present invention, at least the uppermost recording layer may be one formed on a casting surface, integrated with the remaining recording layers of which at least one layer has the cracks and the support, and then separated from the casting surface. The ink jet recording material of the present invention may be produced by a procedure in which at least one recording layer other than the uppermost recording layer is formed on a surface of a support and dried; during the formation of the other recording layer, at least one surface of the at least one other recording layer is wetted with water or a solvent; and then the uppermost recording layer is coated on the at least one other recording laver and dried. In the ink jet recording material of the present invention, there is no limitation to the type, form and size of the support. The support may be transparent or opaque. For example, the support can be formed from at least one member selected from cellulose films, plastic film, for example polyethylene, polypropylene, soft polyvinyl chloride, hard polyvinyl chloride and polyester films, paper sheets, for example, woodfree paper sheets, neutral paper sheets, photographic paper support sheets, art paper sheets, coated paper sheets, cast-coated paper sheets, metallic foil-laminated paper sheets, kraft paper sheets, polyethylene-laminated paper sheets, impregnated paper sheets, metallized paper sheets and water-soluble paper sheets, metal foils and synthetic paper sheets. The multi-layered ink receiving layer of the present invention will be explained in detail below. The ink receiving layer comprises at least one underrecording layer and at least one upperrecording layer. Each recording layer comprises a binder and a pigment. The pigment comprises amorphous silica. However, to obtain the ink jet recording material of the present invention having high gloss and ink-absorbing property and capable of recording ink images having a high color density, the pigment secondary particles having an average secondary particle size of 10 to 400 nm and constituted from a plurality of primary particles having an average primary particle size of 3 to 40 nm must be used. To obtain the secondary particle of a pigment having an average secondary particle size of 10 to 400 nm, trade pigment particle having a particle size in µm order are subjected to a high mechanical force, namely, a cracking down method or a breaking down method is applied to the pigment particles. The cracking down method is utilized to finely pulverize a lump-shaped material. The mechanical means include ultrasonic homogenizers, pressure-type homogenizers, nanomizers, high speed revolution mills, roller mills, container-drived medium mills, medium-stirring mills, jet mills, mortars, and sand grinders. The fine particles of the pigment usable for the present invention may be colloidal particles and in the state of a slurry. To attain the effect of the present invention as much as possible, the pigment is preferably selected from silica, alumina silicate, alumina (including pseudo-boehmite) and calcium carbonate pigments, more preferably amorphous silica and alumina silicate. Particularly, the amorphous silica is preferred. Unless specifically mentioned, the average particle size used in the present invention is a particle diameter (Martin size) determined by using an electron microscope (both SEM and TEM) (Asakura Shoten, "Fine Particle Handbook" page 52). In the upperrecording layer, the primary particles from which the secondary particles are formed have an average particle size of 3 to 40 nm, preferably 3 to 25 nm, more preferably 5 to 20 nm. When the average particle size of the primary particles is small, the gaps formed between the primary particles are small, and the absorbing capacity of the recording layer for solvent or water in the ink is significantly small. Also, when the particle size of the primary particles is large, the resultant secondary particles formed from the primary particles agglomerated with each other are large, the resultant recording layer exhibits a reduced transparency and thus there is a risk that the ink images having a high color density cannot be formed. The average particle size of the primary particles from which the secondary particles for the underrecording layer are formed is larger than the average particle size of the upperrecording layer. Preferably, the average primary particle size in the underrecording layer is 1.2 to 10 times, more preferably 1.5 to 5 times, that in the upperrecording layer. When the average primary particle size in the underrecording layer is too close to the average primary particle size in the upperrecording layer, the color density of the ink images and the ink-absorbing property of the ink-receiving layer are difficult to balance. When the average particle size of the primary particles in the underrecording layer is too large, the resultant underrecording layer exhibits a low mechanical strength and is not preferred. In the present invention, the average particle size of the secondary particles in the underrecording layer is preferably larger than the average particle size of the secondary particles in the upperrecording layer. In the present invention, the particles size of the secondary particles in the under-and upper-recording layers is in the range of from 10 to 400 nm, preferably 10 to 300 nm, more preferably 15 to 200 nm, still more preferably 20 to 150 nm. When the particle size of the secondary particles is too small, the ink-absorption rate of the resultant recording layer is low. Also, when the average particle size of the secondary particles is too large, the resultant recording layer surface is rough and exhibits a low gloss. Conventional pigments which are commonly known and widely used in the general coated paper sheet field, and have a particle size of an µm order, can be employed together with the specific pigment particles of the present invention, to increase the ink-absorbing property, unless the gloss and color density of the ink images are decreased. The under- and upper-recording layers of the present invention contain a binder. The binder comprises at least one member selected from, for example, water-soluble polymeric material, for example, polyvinyl alcohol which will be referred to as PVA hereinafter, modified polyvinyl alcohols such as silyl-modified polyvinyl alcohols, cation-modified polyvinyl alcohols, casein, soybean protein, synthetic proteins, starch, and cellulose derivatives such as carboxymethyl cellulose and methylcellulose; and water-dispersible or emulsionizable polymeric materials, for example, conjugated diene polymer latices such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer latices, acrylic polymer latices, and vinyl copolymer latices such as styrene-vinyl acetate copolymer latices, and acrylic polymer latices, which are usually used for the conventional coated paper sheets. The binder materials as mentioned above may be employed alone or in a mixture of two or more thereof. To enhance the adhesion between the support and the ink-receiving layer or between the recording layers, the water-soluble polymeric materials are preferably employed. Particularly, when a polyvinyl alcohol having a degree of polymerization of 2000 or more is employed, the adhesion between the ink receiving layer and the support is high, and thus the resultant ink jet recording material exhibits a high gloss, a high ink absorbing property and a high water resistance and can record ink images having a high color density. In each of the under-and upper-recording layers, a solid weight ratio of the pigment to the binder is controlled preferably to a level of 100/5 to 100/200, more preferably 100/10 to 100/100,. When the proportion of the binder is too high, the pores formed between the pigment particles may be small, and the ink-absorbing rate of the resultant recording layer may be low. Also, when the proportion of the binder is too low, the resultant recording layer may be easily cracked and may exhibit a low gloss. In the present invention, when the solid weight ratio of the pigment to the binder in the upperrecording layer is controlled between 100/10 and 100/60, small cracks having a length of 0.02 mm or less are formed in the resultant upperrecording layer. The small cracks contribute to enhancing the ink-absorbing rate of the layer and substantially do not cause the gloss of the layer to decrease. Thus the resultant ink jet recording material exhibits a high gloss and a very high ink-absorbing rate and can record ink images having a high color density. In the ink jet recording material of the present invention, the ink-receiving layer optionally contains a cationic resin which contributes to enhancing the ink-fixing property of the ink-receiving layer. Particularly, the cationic resin is preferably contained in the upperrecording layer. The cationic resin is preferably selected from polyalkylenepolyamines, for example, polyethylenepolyamine and polypropylenepolyamine, and derivatives thereof, acrylic resins having tert-amino groups and/or quatanary ammonium groups; and diacrylamino compounds which are known compounds and are available as trade chemicals. In the ink-receiving layer, the cationic resin is preferable contained in an amount of 1 to 30 parts by weight, more preferably 5 to 20 parts by weight, per 100 parts by weight of the pigment. The cationic resin may be mixed into the fine pigment particle dispersion produced, for example, by the breaking down method. When the fine pigment particles are anionic, the mixing of the cationic resin with the anionic fine pigment particles results in an agglomeration of the fine pigment particles. Therefore, the mixing of the cationic resin with the anionic pigment particles is preferably carried out in such a manner in that fine pigment particles having a particle size in a µm order is mixed with a cationic resin, and the resultant mixture is dispersed and further mechanically pulverized and dispersed. Otherwise, secondary particles of a pigment prepared by a disperse-pulverizing procedure and having a secondary particle size of 10 to 400 nm are mixed with a cationic resin, to provide a coagulated mixture having an increased viscosity, and the coagulated mixture is mechanically pulverized and dispersed. Also, the ink-receiving layer optionally contains a conventional additive comprising at least one member selected from dispersants, thickening agents, defoaming agents, coloring materials, antistatics and preservatives. There are no limitations to the amounts of the upperrecording layer and the underrecording layer. Preferably, the amount of the upperrecording layer is controlled to 1 to 50 g/m 2 , more preferably 2 to 20 g/m 2 . Also, the amount of the underrecording layer is preferably controlled to 2 to 80 g/m 2 , more preferably 5 to 70 g/m 2 . When the amount of the upper- or under-recording layer is small, the layer may be difficult to form uniformly. Also, when the layer amount is large, the resultant layer may have large cracks. To increase the ink-absorbing capacity, for example, the upperrecording layer may be formed in two or more layers. Also, the ink receiving layer may have an additional recording layer comprising, as a principal component, an ink-absorbing resin, and may be located between the support and the underrecording layer. The ink-absorbable resin may comprise at least one member selected from, for example, polyalkyleneoxides, PVA, modified polyvinyl alcohols, cellulosic derivatives, casein, gelatin, and polyvinyl pyrrolidone. Among these resins, cross-linked thermoplastic polyalkyleneoxide resins are preferably utilized. Compared with other resins, the thermoplastic polyalkyleneoxide resins are advantageous in high processability, high ink absorbing capacity, and high sharpness of resultant ink images. Particularly, the cross-linked polyalkyleneoxide resin is advantageously mixed with a polyamide resin. In this mixture, a high ink-absorbing performance derived from the cross-linked polyalkyleneoxide resin and high heat resistance and water resistance derived from the polyamide resin are not lost and a synergistic effect can be attained. In an embodiment of the process of the ink jet recording material of the present invention, at least the upperrecording layer, namely the upperrecording layer alone or both the upper- and under-recording layers, are formed on a casting surface, and are transferred onto the underrecording layer formed on a support or onto the support (when the underrecording layer is formed on the upperrecording layer on the casting layer), and the resultant laminate is separated from the casting surface. In this process, the resultant upperrecording layer surface has a high gloss. The casting surface can be selected from high smoothness surfaces of polymeric films, for example, regenerated cellulosic films, polyethylene films, polypropylene films, soft polyvinyl chloride films, hard polyvinyl chloride films, and polyester films surface-smoothed paper sheets, for example, polyethylene laminated paper sheets, glassine paper sheets, impregnated paper sheets, and metallized paper sheets, metal foils, and thermoplastic sheets, for example, synthetic paper sheets, inorganic glass plates and surface-smoothed metallic and plastic drums and plates. In consideration of ease in production and in separation of the resultant recording layer from the casting surface, a polymer film, for example, a polyethylene, polypropylene or polyester film, or a metallic drum having a high surface smoothness is used as a casting surface. For the purpose of imparting a high gloss to the upperrecording layer, the casting surface preferably has a high smoothness. Namely, the surface roughness Ra of the casting surface is preferably 0.5 µm or less, more preferably 0.05 µm or less, determined in accordance with JIS B 0601. Also, the surface of the upperrecording layer may be semi-gloss or mat. The gloss or mat surface of the upperrecording layer can be obtained by controlling the surface roughness Ra of the casting surface. The casting surface may be a non-treated one. However, to control the bonding strength between the casting surface and the upperrecording layer to a level lower than the bonding strength between the support and the ink-receiving layer, the casting surface may be coated with a releasing agent, for example, a silicone or a fluorine-containing resin. The bonding method between the upperrecording layer formed on the casting surface and the underrecording layer formed on the support, or between the underrecording layer formed on the upperrecording layer formed on the casting surface and the support is not limited to a specific method as long as they are firmly bonded to each other. The bonding method can be selected from direct bonding method in which they are directly press-bonded to each other under pressure, and indirect bonding method in which the surface of the support or of the underrecording layer formed on the support is coated with an intermediate layer (including an adhesive layer, a adhesive recording layer or a tacky or adhesive ink-absorbable resin layer), and then laminated to the coating layer formed on the casting surface through the intermediate layer. Otherwise, the intermediate layer is coated on the coating layer formed on the casting layer and then, the support or the underrecording layer-coated support is laminated to the coating layer on the casting surface through the intermediate layer. After the lamination is completed, the resultant laminate is separated from the casting surface. The recording layers and intermediate layer can be formed by using conventional coating means, for example, a die coater, blade coater, air knife coater, roll coater, bar coater, gravure coater, rodblade coater, lip coater, or curtain coater. The ink usable for the ink jet recording material of the present invention comprises, as indispensable components, a coloring material for forming colored images and a liquid medium for dissolving or dispersing the coloring material, and as optional components, a dispersant, surfactant, viscosity modifier, specific resistance-modifier, pH-adjuster, mildewcide, and a solution or a dispersion-stabilizer for a recording agent. The recording agent for the ink comprises at least one member selected from direct dyes, acid dyes, basic dyes, reactive dyes, food coloring matters, disperse dyes, oil dyes and pigments. Conventional recording agents can be used for the ink without any restriction. The content of the coloring material in the ink is established in response to the type of the liquid medium and the properties required to the coloring material. In the ink usable for the ink jet recording material of the present invention, the content of the coloring material is about 0.1 to 20% by weight which is quite usual for conventional inks. In a preferred embodiment of the present invention, an ink jet recording material having a high surface smoothness and gloss, and a high ink-absorbing capacity and capable of recording ink images having a high color density and grade and a process for producing the same are provided. Generally, a dispersion containing particles having a particle size of 300 nm or more causes a resultant recording layers formed therefrom to exhibit an unsatisfactory transparency and a poor surface smoothness and thus is not suitable for producing an ink jet recording material having a high gloss and capable of recording ink images with a high color density. When the upperrecording layer is formed on a casting surface, there are no specifically severe limitations to the viscosity and particle concentration of the coating liquid for the upperrecording layer. The upperrecording layer having a high surface smoothness and gloss can be obtained by forming it from a coating liquid containing a binder and secondary particles of a pigment having an average secondary particle size of 10 to 400 nm, preferably 10 to 300 nm, and each consisting essentially a plurality of primary particles having an average particle size of 3 to 40 nm. When the casting surface has a high smoothness, a high smoothness of the upperrecording layer surface can be obtained. Also, when the secondary pigment particles having an average secondary particle size of 10 to 400 nm are used, the resultant upperrecording layer exhibit a high transparency and can record ink images having a high color density. Also, when the upperrecording layer is bonded to the underrecording layer by a wet laminating method, no bubble or pore is formed in the surface portion of the upperrecording layer. Further, when the upperrecording layer is bonded, after drying, to the underrecording layer, there is no risk of mixing the coating liquid for the upperrecording layer with the coating liquid for the underrecording layer. By increasing the total amount of the ink receiving layer, the ink-absorbing capacity of the resultant ink jet recording material can be increased. In the ink jet recording material of the present invention, since the under and upper-recording layers contain very fine pigment secondary particles having an average secondary particle size of 10 to 400 nm preferably 10 to 300 nm, and consisting essentially of primary particles having an average primary particle size of 4 to 40 nm and agglomerated with each other, the ink-receiving layer exhibits a high gloss and can record ink images with a high color density. When a cationic resin is contained in the upperrecording layer, anionic dyes can be easily fixed in the upperrecording layer and the resultant ink images exhibit an enhanced water resistance and durability in storage. The present invention includes the embodiments as shown below. To fix the dye in the ink in the uppermost recording layer, the uppermost recordinglayer preferably has a pore volume of 0.2 to 3.0 ml/g, more preferably 0.5 to 2.5 ml/g. The pore volume was determined by forming the recording layer on a plastic film to prevent an influent of the support, removing the film from the recording layer by using, for example, a cutter, and measuring the pore volume of the recording layer by a mercury penetration method using Poresizer 9320 made by SHIMAZU SEISAKUSHO. The present invention will be further illustrated by the following examples which are merely representative and do not restrict the scope of the present invention in any way. In the examples and comparative examples, the "part" and "%" are --part by solid weight-- and --% by solid weight", unless specifically indicated otherwise. In the group I of examples and comparative examples, the following pigments were employed. It should be noted that the pulverizing and dispersing procedure did not cause the average primary particle size of the pigment to be changed. [Silica sol I-A] A synthetic amorphous silica (NIPSIL® HD-2, made by NIPPON SILICA INDUSTRIAL CO., LTD.) having an average secondary particle size of 3 µm and an average primary particle size of 11 nm was pulverized and dispersed by a sand grinder, and then by a pressure type homogenizer, and then a pulverizing and dispersing procedure with a sand grinder and ultrasonic homogenizer was repeatedly applied to the silica pigment until the average secondary particle size reached 70 nm, to provide a dispersion having a pigment solid content of 7%. [Silica sol I-B] A synthetic amorphous silica (NIPSIL® E-1011, made by NIPPON SILICA INDUSTRIAL CO., LTD.) having an average secondary particle size of 1.5 µm and an average primary particle size of 24 nm, was pulverized and dispersed by a sand grinder and then by a pressure-type homogenizer; and then a pulverizing and dispersing procedure with a sand grinder and then with an ultrasonic homogenizer was repeatedly applied to the silica pigment until the average secondary particle size reached 100 nm, to provide a silica sol I-B having a solid pigment content of 10%. Example I-1 A 10% aqueous coating liquid containing a mixture of 100 parts of silica sol I-B with 40 parts of a polyvinyl alcohol (trademark: PVA-135H, made by KURARAY CO., LTD.) having a degree of polymerization of 3500 and a degree of saponification of 99% or more, was prepared. As a support, an polyethylene-laminated paper sheet which was produced by laminating polyethylene in a thickness of 25 µm on a surface of a trade coated paper sheet (trademark: OK COAT, made by OJI PAPER CO., LTD.) having a basis weight of 127.9 g/m 2 , by an extrusion lamination method, and will be referred to as a laminated paper sheet hereinafter, was employed. The 10% aqueous coating liquid was coated on the laminate surface of the laminated paper sheet and dried, to form an underrecording layer in an amount of 30 g/m 2 . Then, a 7% aqueous coating liquid containing a mixture of 100 parts of silica sol I-A with 30 parts of PVA (PVA-135H) was prepared and coated on the underrecording layer and dried, to form an upperrecording layer in an amount of 10 g/m 2 . An ink jet recording material of the present invention was obtained. Example I-2 An ink jet recording material of the present invention was produced by the same procedures as in Example I-1 with the following exceptions. On the underrecording layer containing silica sol I-B and formed on the laminated paper sheet, an upperrecording layer was coated by the following procedures. When 100 parts of silica sol I-A were mixed with 15 parts of a cationic resin consisting of a diallyldimethyl-ammonium chloride-acrylamide copolymer (trademark: PAS-J-81, made by NITTO BOSEKI CO., LTD.), the silica sol particles were agglomerated. The agglomerated silica particles were pulverized and dispersed by a pressure type homogenizer until the average secondary particle size reached 120 nm. The average primary particle size was kept at 11 nm. The resultant cationic resin-containing silica sol was mixed with 25 parts of a polyvinyl alcohol (trademark: PVA-135H, made by KURARAY CO., LTD.), and the resultant coating liquid was coated on the underrecording layer and dried to form an upperrecording layer in an amount of 10 g/m 2 . Example I-3 The same cationic resin containing silica sol as in Example I-2 was added with 25 parts of a polyvinyl alcohol (trademark: PVA-135H, made by KURARAY CO., LTD.) to prepare a coating liquid for an upperrecording layer. As a casting surface, a surface of a PET film (trademark: LUMILAR T, made by TORAY INDUSTRIES INC.) having a thickness of 50 µm and a surface roughness Ra of 0.02 µm, was employed. The coating liquid was coated in a dry coating amount of 10 g/m 2 on the casting surface, and dried to form a coating layer corresponding to an upperrecording layer. After water was applied to the coating layer on the casting surface, the same silica sol I-B-containing coating liquid as in Example I-1 was coated on the water-wetted coating layer and dried to form an coating layer corresponding to an undercoating layer and in an amount of 30 g/m 2 . Then, the same laminated paper sheet was laminated and bonded, at the laminate surface thereof, to the coating layer at a calendering temperature of 75°C under a calendering linear pressure of 20 kg/cm. Then the PET film was removed from the resultant laminate. An ink jet recording material of the present invention was obtained. Example I-4 On the laminate surface of the same laminated paper sheet as in Example I-1, an acrylic ester adhesive (trademark: A-02, made by NIPPON CARBIDE INDUSTRIES CO., LTD.) was coated in an amount of 15 g/m 2 , and dried. A coating liquid was prepared by mixing the same cationic resin-containing silica sol as in Example I-2 with 25 parts of a polyvinyl alcohol (trademark: PVA-135H, made by KURARAY CO., LTD.). The coating liquid was coated on the same casting surface as in Example I-3 (the PET film, trademark: LUMILAR T, made by TORAY INDUSTRIES INC.) having a thickness of 50 µm and a surface roughness of 0.02 µm and dried, to form a coating layer in an amount of 10 g/m 2 , corresponding to an upperrecording layer. After applying water to the dried coating layer, the same coating liquid containing the silica sol I-B as in Example I-1 was coated on the water-applied coating liquid and dried, to form a coating layer in an amount of 30 g/m 2 corresponding to an underrecording layer. The adhesive layer on the laminated paper sheet was laminated and bonded to the coating layer corresponding to the underrecording layer. The resultant laminate was separated from the PET film. An ink jet recording material of the present invention was obtained. Example I-5 A surface of a trade coated paper sheet (trademark: OK COAT, made by OJI PAPER CO., LTD.) having a basis weight of 127.9 g/m 2 was laminated with a cross-linked thermoplastic polyethyleneoxide (trademark: AQUACOK, made by SUMITOMO SEIKA CHEMICALS CO., LTD.) in an amount of 25 g/m 2 . Separately, a coating liquid prepared by mixing the same cationic resin-containing silica sol as in Example I-2 with 25 parts of PVA (trademark: PVA-135H, made by KURARAY CO., LTD.), was coated on a casting surface consisting of a surface of a PET film (trademark: LUMILAR T, made by TORAY INDUSTRIES INC.) having a thickness of 50 µm and a surface roughness Ra of 0.02 µm, and dried to form a coating layer having a weight of 10 g/m 2 and corresponding to an upperrecording layer. After applying water to the coating layer, the same silica sol I-B-containing coating liquid as in Example I-1 was coated on the water-wetted coating layer and dried to form a coating liquid in an amount of 30 g/m 2 corresponding to an underrecording layer. The coating layer was laminated and bonded to the laminated polyethyleneoxide layer on the coated paper sheet. The resultant laminate was separated from the PET film. An ink jet recording material of the present invention was obtained. Comparative Example I-1 A 7% aqueous coating liquid containing a mixture of 100 parts of silica sol I-A with 30 parts of PVA (trademark: PVA-135H, made by KURARAY CO., LTD.) was coated on a surface of the same laminated paper sheet as in Example I-1, and dried, to form a coating layer in an amount of 10 g/m 2 . A comparative ink jet recording material was obtained. Comparative Example I-2 A 7% aqueous coating liquid containing a mixture of 100 parts of silica sol I-A with 30 parts of PVA (trademark: PVA-135H, made by KURARAY CO., LTD.) was coated on a surface of the same laminated paper sheet as in Example I-1, and dried, to form a coating layer in an amount of 40 g/m 2 . A comparative ink jet recording material was obtained. Comparative Example I-3 A 10% aqueous coating liquid containing a mixture of 100 parts of silica sol I-B with 40 parts of PVA (trademark: PVA-135H, made by KURARAY CO., LTD.) was coated on a surface of the same laminated paper sheet as in Example I-1, and dried, to form a coating layer in an amount of 40 g/m 2 . A comparative ink jet recording material was obtained. Comparative Example I-4 A 7% aqueous coating liquid containing a mixture of 115 parts of the same cationic resin-containing silica sol as in Example I-2 with 25 parts of PVA (trademark: PVA-135H, made by KURARAY CO., LTD.) was coated on a surface of the same laminated paper sheet as in Example I-1, and dried, to form a coating layer in an amount of 30 g/m 2 . On the coating layer, a 10% aqueous coating liquid containing a mixture of 100 parts by weight of silica sol I-B with 40 parts of a PVA (trademark: PVA-135H) was coated and dried to form a coating layer in an amount of 10 g/m 2 . A comparative ink jet recording material was obtained. Comparative Example I-5 A trade gloss paper sheet (trademark: KONICA PHOTOJET PAPER, made by KONICA) in which a hydrophilic resin is coated on a support paper sheet was employed as a comparative ink jet recording material. [Evaluation] The ink-absorbing property, gloss and color density of ink images of the ink jet recording materials of Examples I-1 to I-5 and Comparative Examples I-1 to I-5 were tested and evaluated by the methods as shown below. In the testings on the gloss, ink-absorbing property and color density of ink images, a record was made in each ink jet recording material by a trade ink jet printer (trademark: PM-700 C, made by EPSON CORP., LTD.), and a gloss, ink-absorbing property and color density of a solid printed portion were measured. [Ink-absorbing property] A solid print was provided by overlapping a yellow-colored ink, a magenta-colored ink and a cyan-colored ink on each other. Each 5 seconds immediately after the printing, a woodfree paper sheet was superposed on the solid print to check whether the ink in the solid print is transferred to the paper sheet. The ink drying time, after which no transfer of the ink occured, was determined. The ink-absorbing property of the ink jet recording material was evaluated in the following four classes. class Ink-drying time 4 Less than 5 seconds 3 5 seconds or more but less than 15 seconds 2 15 seconds or more but less than 30 seconds 1 30 seconds or more When the ink-drying time is less than 15 seconds (class 4 or 3), the ink jet recording material is evaluated to be excellent or satisfactory in the ink-absorbing rate and capacity. [Gloss (luster) of printed portion] The gloss of printed portion was evaluated by observing each of black, yellow, cyan and magenta-colored images at an inclined angle by the naked eye, in the following four classes. class Gloss 4 Excellent and similar to silver salt type photographic colored images 3 Satisfactory but slightly lower than silver salt type photographic colored images 2 Similar to trade coated paper sheets or art paper sheets 1 No gloss [Color density of ink image] A solid black-colored ink image was subjected to a measurement of color density by MACBETH REFLECTION COLOR DENSITY TESTER (model: RD-920). The color density was represented by an average of five measurement data. [Moisture resistance for storage] The print was stored in a constant temperature constant humidity vessel at a temperature of 40°C at a humidity of 90% for 48 hours. After the storage, the print was removed from the vessel and checked on whether blotting of the ink occurs. The test results were evaluated in the following four classes. class Moisture resistance 4 No ink-blotting 3 Slight ink-blotting Usable in practice 2 Certain ink-blotting Sometimes unusable in practice 1 Severe ink-blotting Unusable in practice [Water resistance of ink-receiving layer] A water drop was placed on an ink-receiving layer, and 5 minutes after the water-dropping, the water-wetted portion was lightly rubbed and the change occurred in the ink-receiving layer was checked and evaluated in the following three classes. class Water resistance 3 No change 2 A portion of the ink-receiving layer is removed. 1 The ink receiving layer is completely removed. The test results are shown in Table 1. Table 1 clearly shows that the ink jet recording materials in accordance with the present invention are excellent or satisfactory in ink-absorbing property, gloss, color density of ink image, moisture resistance and water resistance. In the group of Examples III-1 to III-6 and Comparative Examples III-1 and III-2, the cracks formed in the ink receiving layer were checked in the following manner. For each ink jet recording material, ten samples were collected and each was printed with 100 ink dots per mm 2 . The dots were evenly distributed, each of the dots had a diameter of 50 µm, and the dots were produced by a trade ink jet printer (model: PM-700C, made by EPSON CORP., LTD.) having a dot density of 720 dots/2.54 cm × 720 dots/2.54 cm. The printed ink dots were observed by an optical microscope at a magnification of 150. When cracks were found in the dots in the number corresponding to 60% or more of the total number of the dots printed in the 10 samples, the ink jet recording material was recognized to have sufficient cracks formed in at least one recording layer. When, for example, cracks were formed in the dots in the number corresponding to 50% of the total number of the dots printed in the 10 samples, the degree of cracks of the ink jet recording material is 50%. In Examples III-1 to III-6 and Comparative Examples III-1 and III-2, the following pigments were employed. [Silica sol III-A] Synthetic amorphous silica particles (trademark: NIPSIL HD-2, made by NIPPON SILICA INDUSTRIAL CO., LTD.) having an average secondary particle size of 3 µm and an average primary particle size of 11 nm were pulverized and dispersed by a sand grinder and then by a pressure type homogenizer, and pulverizing and dispersing procedures with a sand grinder and then with a pressure type homogenizer were repeately applied to the silica particles until the average secondary particle size reached 60 nm. A 7% silica particle dispersion was prepared. [Silica sol III-B] Synthetic amorphous silica particles (trademark: NIPSIL LP, made by NIPPON SILICA INDUSTRIAL CO., LTD.) having an average secondary particle size of 3 µm and an average primary particle size of 16 nm were pulverized and dispersed by a sand grinder and then by a pressure type homogenizer, and pulverizing and dispersing procedures with a sand grinder and then with a pressure type homogenizer were repeately applied to the silica particles until the average secondary particle size reached 100 nm. A 9% silica particle dispersion was prepared. [Silica sol III-C] Synthetic amorphous silica particles (trademark: NIPSIL E-1011, made by NIPPON SILICA INDUSTRIAL CO., LTD.) having an average secondary particle size of 1.5 µm and an average primary particle size of 24 nm were pulverized and dispersed by a sand grinder and then by a pressure type homogenizer, and pulverizing and dispersing procedures with a sand grinder and then with a pressure type homogenizer were repeately applied to the silica particles until the average secondary particle size reached 150 nm. A 12% silica particle dispersion was prepared. Example III-1 As a support, a laminated paper sheet prepared by laminating polyethylene layer, at a thickness of 25 µm by an extrusion-lamination method onto a trade coated paper sheet (trademark: OK COAT, made by OJI PAPER CO., LTD.) having a basis weight of 127.9 g/m 2 , was employed. This laminated paper sheet will be referred to as a "laminate sheet" hereinafter. A 10% aqueous coating liquid comprising a mixture of 100 parts of silica sol III-C with 35 parts of a polyvinyl alcohol (trademark: PVA-135H, made by KURARAY CO., LTD.) having a degree of polymerization of 3500 and a degree of saponification of 99% or more, was coated on the polyethylene-coated surface of the laminate sheet and dried at a temperature of 120°C, to form an underrecording layer having a dry weight of 20 g/m 2 . The resultant underrecording layer had a degree of cracks of 80%. The underrecording layer was wetted with water in an amount of 20 g/m 2 , and then coated with a 7% aqueous coating liquid prepared from a mixture of 100 parts of silica sol III-A with 30 parts of a PVA (PVA-135H), and dried at a temperature of 50°C to form an upperrecording layer having a degree of cracks of 30% and a pore volume of 0.9 ml/g. An ink jet recording material of the present invention was obtained. Example III-2 Silica sol III-A in an amount of 100 parts was mixed with 15 parts of cationic resin consisting of diallyl-dimethyl ammonium chloride-acrylamide copolymer (trademark: PAS-J-81, made by NITTO BOSEKI CO., LTD.). The resultant mixture exhibited an increased viscosity and silica particles were agglomerated. The mixture was pulverized and dispersed by a pressure type homogenizer until the average agglomerated particle size reached 100 nm. Then, the resultant cationic resin-containing silica sol was further mixed with 20 parts of a polyvinyl alcohol (PVA-135H), to provide an 8% aqueous coating liquid. The same support as in Example III-1 was coated with the same silica sol III-C-containing underrecording layer as in Example III-1. After wetting the underrecording layer with water in an amount of 20 g/m 2 , the above-mentioned coating liquid was coated on the water-wetted underrecording layer, and dried at a temperature of 50°C, to form an upperrecording layer having a dry weight of 8 g/m 2 , a degree of cracks of 30%, and a pore volume of 0.83 ml/g. Example III-3 The same diallyl-dimethyl ammonium chloride-acrylamide copolymer-containing silica sol III-A as in Example III-2 and in an amount of 115 parts was mixed with 20 parts of a polyvinyl alcohol (PVA-135H), to provide an aqueous coating liquid having a solid content of 8%. The coating liquid was coated on a surface of a PET film (trademark: LUMILAR T, made by TORAY INDUSTRIES INC.) having a thickness of 50 µm and a surface roughness Ra of 0.02 µm, used as a casting surface, and dried at a temperature of 40°C, to form a coating layer corresponding to an upperrecording layer having a weight of 8 g/m 2 and a degree of cracks of 10% or less. Separately, a 10% aqueous coating liquid containing a mixture of 100 parts of silica sol III-C with 30 parts of a polyvinyl alcohol (PVA-135H) was coated on a surface of a trade woodfree paper sheet having a basis weight of 157 g/m 2 , and dried at a temperature of 120°C, to form an underrecording layer having a weight of 20 g/m 2 and a degree of cracks of 90%. After the cationic resin-containing coating layer formed on the PET film was wetted with 5 g/m 2 of water, the underrecording layer was laminated and bonded to the wetted coating layer at a calendering temperature of 75°C under a calendering linear pressure of 20 kg/cm. After drying, the resultant laminate was separated from the PET film. An ink jet recording material of the present invention was obtained. In the recording material, the upper-recording layer had a pore volume of 0.76 ml/g. Example III-4 The same diallyl-dimethyl ammonium chloride-acrylamide copolymer-containing silica sol III-A as in Example III-2 and in an amount of 115 parts was mixed with 20 parts of a polyvinyl alcohol (PVA-135H), to provide an aqueous coating liquid having a solid content of 8%. The coating liquid was coated on a surface of a PET film (trademark: LUMILAR T, made by TORAY INDUSTRIES INC.) having a thickness of 50 µm, used as a casting surface, and dried at a temperature of 40°C to form a coating layer corresponding to an upperrecording layer having a weight of 8 g/m 2 and a degree of cracks of 10% or less. The coating layer was coated with a 10% aqueous coating liquid containing a mixture of 100 parts of silica sol III-B with 35 parts of a polyvinyl alcohol (PVA-135H) and dried at a temperature of 80°C to form an intermediate recording layer having a dry weight of 10 g/m 2 and a degree of cracks of 20%. Separately, a 10% aqueous coating liquid containing a mixture of 100 parts of silica sol III-C with 25 parts of a polyvinyl alcohol (PVA-135H), was coated on a surface of a trade woodfree paper sheet having a basis weight of 157 g/m 2 , to form a coating liquid layer in a dry amount of 10 g/m 2 . The coating liquid layer was superposed on and bonded to the intermediate recording layer, and dried at a temperature of 130°C, to form an underrecording layer. The resultant laminate was separated from the PET film. An ink jet recording material of the present invention was obtained. In the obtained recording material, the silica sol III-C-containing underrecording layer had a degree of cracks of 95% which was measured by the method as mentioned above, after the upperrecording layer and the intermediate recording layer were removed by shaving and printed with the ink. The upperrecording layer had a pore volume of 0.76 ml/g. Example III-5 The polyethylene-laminated surface of the same laminate sheet in Example III-1 was coated with a 10% aqueous coating liquid containing a mixture of 100 parts of silica sol III-C with 35 parts of a polyvinyl alcohol (PVA-135H) and dried at a temperature of 100°C, to form an underrecording layer having a dry weight of 20 g/m 2 and a degree of cracks of 65%. The underrecording layer was wetted with 15 g/m 2 of water and then coated with a 7% aqueous coating liquid containing 100 parts of silica sol III-A with 25 parts of a polyvinyl alcohol (PVA-135H) and dried at a temperature of 80°C, to form an upperrecording layer having a dry weight of 8 g/m 2 and a degree of cracks of 80%. An ink jet recording material of the present invention was obtained. Comparative Example III-1 The polyethylene-laminated surface of the same laminate sheet as in Example III-1 was coated with a 10% aqueous coating liquid containing a mixture of 100 parts of silica sol III-B with 45 parts of a polyvinyl alcohol (PVA-135H), and dried at a temperature of 100°C, to form an ink receiving layer having a dry weight of 28 g/m 2 and a degree of cracks of 10% or less. A comparative ink jet recording material was obtained. Example III-6 A 10% of aqueous coating liquid containing a mixture of 100 parts of silica sol III-C with 40 parts of a polyvinyl alcohol (PVA-135H) was coated on the polyethylene-laminated surface of the same laminate sheet as in Example III-1, and dried at a temperature of 100°C, to form an underrecording layer having a dry weight of 20 g/m 2 and a degree of cracks of 20%. The underrecording layer was wetted with water in an amount of 20 g/m 2 , and then coated with a 7% aqueous coating liquid containing a mixture of 100 parts of silica sol III-A with 30 parts of a polyvinyl alcohol (PVA-135H), and dried at a temperature of 50°C, to form an upperrecording layer having a dry weight of 8 g/m 2 , a degree of cracks of 30% and a pore volume of 0.91 ml/g. An ink jet recording material of the present invention was obtained. Comparative Example III-2 A trade gloss paper sheet (trademark: GP-101, made by CANON) having a coating layer with a degree of cracks of 100%, was employed as a comparative ink jet recording material. [Evaluation] Each of the ink jet recording materials of Examples III-1 to III-6 and Comparative Examples III-1 and III-2 was subjected to evaluations of ink-absorbing rate, ink-absorbing capacity, gloss, and color density of ink image by the methods as shown below. In the evaluations of the gloss and color density of image, solid ink prints were formed by a trade ink jet printer (model: PM-700C, made by EPSON CORP., LTD.), and the gloss and color density of the solid prints were determined. [Ink-absorbing rate] An yellow-colored ink, a magenta-colored ink and a cyan-colored ink were printed and overlapped on each other to form a black-colored solid print on an ink jet recording material. Every five seconds after the printing, a woodfree paper sheet was superposed on the solid print, to determining an ink-drying time after which time no ink was transferred from the solid print to the paper sheet. The ink-absorbing rate was evaluated in four classes as shown below. class Ink drying time 4 Less than 5 seconds 3 Five seconds or more but less than 10 seconds 2 Ten seconds or more but less than 30 seconds 1 Thirty seconds or more [Ink-absorbing capacity] A sample of an ink jet recording material in dimensions of 10 cm × 10 cm was attached to a center portion of an A4 size PPC paper sheet, and a black-colored ink was jetted toward the sample at an ink-extrusion amount of 40 g/m 2 to form a black-colored solid print. Every 10 seconds after the printing, a woodfree paper sheet was superposed on the solid print on the sample, and an ink-drying time after which time no ink was transferred from the solid print from the woodfree paper sheet, was determined. The ink-absorbing capacity was evaluated in the four classes as shown below. class Ink-drying time 4 Less than 10 seconds 3 Ten seconds or more but less than 30 seconds 2 Thirty seconds or more but less than one minute 1 One minute or more [Gloss (luster) of ink image] Black-colored images, yellow-colored images, cyan-colored images and magenta-colored images formed on an ink jet recording material were observed by the naked eye at an inclined angle and gloss of the images was evaluated in the following four classes. class Gloss 4 Excellent and similar to silver salt type photographic colored images 3 Satisfactory but slightly lower than silver salt type photographic colored images 2 Similar to trade coated paper sheets or art paper sheets 1 No gloss [Color density of image] A black-colored solid print formed on an ink jet recording material was subjected to a color density measurement by MACBETH REFLECTION COLOR DENSITY TESTER (model RD-920). The color density was shown by an average of five measurement data. [Moisture resistance for storage] An ink-printed sample was stored in a constant temperature, constant humidity vessel at a temperature of 40°C at a humidity of 90% for 48 hours. Then, the blotting of ink on the sample was checked and evaluated in the following four classes. class Moisture resistance 4 No ink-blotting 3 Slight ink-blotting Usable in practice 2 Certain ink-blotting Sometimes unusable in practice 1 Severe ink-blotting Unusable in practice [Corrugation] On a sample of an ink jet recording material, a black-colored solid print was formed by overlapping yellow, cyan and magenta-colored inks, and a corrugation of the solid printed sample was checked and evaluated in the following three classes. class Water resistance 3 No change 2 A portion of the ink-receiving layer is removed. 1 The ink receiving layer is completely removed. The test results are shown in Table 3. Table 3 shows that the ink jet recording materials in accordance with the present invention exhibited excellent ink-absorbing property and satisfactory gloss and color density of an ink image.

Claims: An ink jet recording material comprising a support and a multi-layered ink-receiving layer comprising at least one underrecording layer formed on the support and at least one upperrecording layer formed on the underrecording layer, wherein the under and upperrecording layers comprise secondary particles of a pigment comprising amorphous silica and having an average secondary particle size of 10 to 400 nm, each of the secondary particles consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm, the average primary and secondary particle sizes being measured by an electron microscope, and a binder; and the average primary particle size of the primary particles contained in the underrecording layer is larger than the average primary particle size of the primary particles contained in the upper-recording layer. The ink jet recording material as claimed in claim 1, wherein the average primary particle size of the primary particles contained in the underrecording layer is 1.2 to 10 times the average primary particle size of the primary particles contained in the upperrecording layer. The ink jet recording material as claimed in claim 1, wherein the upperrecording layer further comprises a cationic compound. The ink jet recording material as claimed in claim 1, wherein the ink receiving layer further comprises an additional recording layer comprising, as a principal component, a polymeric material and is arranged between the support and the underrecording layer. The ink jet recording material as claimed in claim 1, wherein the upperrecording layer is one obtainable by a procedure in which a coating layer corresponding to the upperrecording layer is formed on a casting surface; a underrecording layer formed on a support is superposed on and bonded to the coating layer located on the casting surface, and the resultant laminate is separated from the casting surface. The ink jet recording material as claimed in claim 1, wherein the upperrecording layer is one obtainable by a procedure in which a first coating layer corresponding to the upperrecording layer is formed on a casting surface; a second coating layer corresponding to the underrecording layer is formed on the first coating layer; a support is superposed on and bonded to the second coating layer; and the resultant laminate is separated from the casting surface. The ink jet recording material as claimed in claim 1, wherein the average secondary particle size of the secondary particles of the pigment is 10 to 300 nm. The ink jet recording material as claimed in claim 1, wherein the average secondary particle size of the secondary particles of the amorphous silica pigment in the underrecording layer is larger than the average secondary particle size of the secondary particles of the amorphous silica pigment in the upperrecording layer. A process for producing an ink jet recording material as defined in claim 1, comprising the steps of forming at least one first coating layer corresponding to the at least one upperrecording layer on a casting surface; forming at least one second coating layer corresponding to the at least one underrecording layer on the first coating layer; laminating a support on the first and second coating layers formed on the casting surface; and separating the resultant laminate from the casting surface. The process as claimed in claim 9, wherein the average secondary particle size of the secondary particles of the pigment is 10 to 300 nm.

Inventors: KITAMURA RYU, MUKOYOSHI SHUNICHIRO, TAKAHASHI TOMOMI, KITAMURA, RYU, MUKOYOSHI, SHUNICHIRO, TAKAHASHI, TOMOMI
Applicants: OJI PAPER CO, OJI PAPER COMPANY LIMITED
Application year: 1998
Main classification: B41M5
IPC codes: B41M5