Ink jet recording sheet and ink jet recording method

Abstract: A recording medium is provided which enables a good print to be formed on both surfaces thereof and, when printing on one surface of the recording medium is performed under conditions different from that in the printing on the other surface of the recording medium, causes neither curling nor strike through of the print. The recording medium comprises: a substrate having two faces; and an ink-receptive layer or a coat layer provided on both faces of the substrate to form a first sruface and a second surface opposite the first surface, wherein when a droplet of an ink in an identical amount is deposited onto the first and second surfaces of the recording medium, the diameter of a dot formed on the first surface is different from that of a dot formed on the second surface.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a recording medium for ink jet recording having the features of the preamble of claim 1, and an ink jet recording method using the same and, more specifically, an ink jet recording medium and an ink jet recording method which enable an image to be printed on both surfaces of the recording medium. Background Art Water-base inks are mainly used for ink jet recording method from the viewpoints of odor, safety, and recording properties. For example, inks are used which comprise: various water-soluble dyes dissolved in water or a solvent mixture, of water with a water-soluble organic solvent such as a polyhydric alcohol; and optionally various additives. Regarding recording materials for ink jet recording, wood free papers, bond papers, PPCs, postal cards, greeting cards, envelopes, labels, specialty papers which have been coated with special ink-receptive layers, films for OHP (overhead projector) have been used. In particular, widespread use of color ink jet printers has resulted in an ever-increasing demand for simple printing on business cards and postal cards. On the other hand, ink jet recording with higher resolution are enhancing property requirements for recording materials, and, in particular, the following properties are demanded for business cards and postal cards where high-resolution, high-quality color images are required. Specifically, a color image having a quality comparable to a photograph should be formed on one surface of the recording material with a letter having good sharpness being formed on the other surface of the recording material (for example, surface for address). Further, the recording material should have good water resistance for its both surfaces, should be free from deformation of the sheet by ink absorption, should have certain nerve, i.e., should be strong, and should have good carriability. Further, a recent trend is such that an increase in resolution reduces the weight of an ink droplet per dot while the demand for a higher quality leads to increased amount of an ink printed on the recording medium. This trend poses a problem that when printing on both surfaces of a recording medium is performed under different conditions, for example, when the resolution of a print formed on one surface of the recording medium is different from that of a print formed on the other surface of the recording medium, there is fear of creating unfavorable phenomena such as curling, due to a difference in the amount of absorbed ink between the two surfaces, and print through. A recording medium having the features of the preamble of claim 1 is known from JP 02 270 588 A. In particular, JP 02 270 588 A, JP 62 225390 A, EP 0 600 245 A; and WO 94 20303 A, disclose recording media having ink receptive layers on both surfaces, wherein said recording media have different ink receptive layers on both surfaces. Moreover, JP 08 002089 A, and EP 0 444 950 A disclose recording media having ink receptive layers on both surfaces. Summary of the Invention The object of the present invention is to provide a recording medium and a corresponding recording method which enables a good print to be formed on both surfaces thereof and which causes neither curling nor print-through when printing on one surface thereof and printing on the other surface thereof are performed with different resolutions. This object is solved by the recording media of claim 1 and the method of claim 7. Preferred embodiments are disclosed in the dependent claims. DETAILED DESCRIPTION OF THE INVENTION Recording Medium According to the recording medium of the present invention, an ink-receptive layer or a coat layer is provided on both surfaces thereof so as to enable recording on both the surfaces. The terms "ink-receptive layer" and "coat layer" used herein mean a layer, provided on a substrate, which functions to receive and fix an ink thereon. Therefore, in the present invention, both the above terms are used as synonymous with each other so far as the layers have the above function. According to a preferred embodiment of the present invention, the ink-receptive layer or the coat layer may be composed mainly of a pigment and a binder. Pigments usable herein include, for example, silica, clay, mica, swellable mica, talc, kaolin, diatomaceous earth, calcium carbonate, barium sulfate, aluminum silicate, synthetic zeolite, alumina, zinc oxide, lithopone, satin white, and organic and inorganic colored pigments. Binders usable herein include, for example, water-soluble resins and aqueous emulsion resins, such as acrylic resin, polyester resin, polyurethane resin, styrene/butadiene copolymer resin, acrylonitrile/butadiene copolymer resin, polyvinyl alcohol resin, water-soluble polyvinyl acetal resin, polyvinyl butyral resin, and other vinyl resins, amide resin, oxidized starch, casein, polyethylene oxide, polyvinyl pyrrolidone, silicone resin, rosin-modified maleic resin, rosin-modified phenolic resin, alkyd resin, and coumarone-indene resin. According to a preferred embodiment of the present invention, the ink-receptive layer or the coat layer contains silica. The composition of the silica-containing ink-receptive layer or coat layer may be suitably determined from the viewpoints of ink absorption, drying of printed ink, sharpness of a recorded image and the like. According to a preferred embodiment of the present invention, the use of a water-soluble resin, such as polyvinyl alcohol resin, water-soluble polyvinyl acetal resin, or polyvinyl pyrrolidone, as the binder in combination with silica as the pigment is preferred. In this case, the mixing ratio of the resin to silica is preferably 1 : 1 to 1 : 15, particularly preferably 1 : 2 to 1 : 10. According to a further preferred embodiment of the present invention, the average particle diameter of silica is preferably about 1 to 30 µm (in terms of volume average particle diameter as measured by means of Coulter counter), particularly preferably 5 to 25 µm. The ink-receptive layer or the coat layer may comprise a plurality of layers. For example, it may comprise a first layer, provided on the substrate face, responsible mainly for the function of receiving an ink, and a second layer, provided on the surface of the first layer, responsible mainly for the function of improving the surface glossiness or brightness. The ink-receptive layer or the coat layer in the recording medium according to the present invention may contain other component(s) for improving the properties of the recording medium. For example, a waterproofing agent, such as a melamine-formaldehyde resin, urea-formaldehyde, an acrylamide resin, glyoxal, zirconium carbonate, or ammonium, may be added in order to improve the water resistance of the ink-receptive layer and to impart a function of preventing an ink from being blotted. Further, a dispersant, a fluorescent dye, a pH adjustor, an antifoaming agent, a wetting agent, a preservative and the like may be added from the viewpoint of further enhancing the productivity, recording properties, or storage stability of the ink jet recording sheet. Further embodiments of the ink-receptive layer or the coat layer in the recording medium according to the present invention will be described. A preferred embodiment of the ink-receptive layer provided on both surfaces of the recording medium according to the present invention is, for example, an ink-receptive layer, described in Japanese Patent Laid-Open No. 222281/1985, wherein a fluorine-containing synthetic amorphous silica is used as a void forming material. In the ink-receptive layer described in this publication, regulation of the fluorine content of the synthetic amorphous silica to a value falling within a specific range enables the dot diameter to be regulated and, at the same time, blotting to be effectively prevented. Another preferred embodiment of the ink-receptive layer is, for example, an ink-receptive layer described in Japanese Patent Laid-Open No. 89082/1986. The ink-receptive layer described in this publication is formed by coating a pigment and a water-soluble binder and, in addition, a silicone emulsion or a water-soluble silicone compound on a substrate. According to this ink-receptive layer, good development can be achieved even when color ink compositions in ink jet recording are superimposed in different sequences. Further, the addition of a silicone emulsion or a water-soluble silicone compound enables the dot diameter to be regulated. Still another embodiment of the ink-receptive layer is, for example, an ink-receptive layer described in Japanese Patent Laid-Open No. 95285/1987. In the ink-receptive layer described in this publication, amorphous silica is used as a part of the pigment and is prepared by cast coating. This ink-receptive layer has high smoothness and offers a print of dots having a sharp outline. A further preferred embodiment of the ink-receptive layer is, for example, an ink-receptive layer described in Japanese Patent Laid-Open No. 186372/1989. This ink-receptive layer comprises a polyacrylamide having a molecular weight of 10000 to 500000, a synthetic amorphous silica, and polyvinyl alcohol and can offer a recorded image having excellent storage stability. A still further preferred embodiment of the ink-receptive layer is described, for example, in Japanese Patent Laid-Open Nos. 276670/1990, 139275/1990, and 297831/1994. The ink-receptive layers described in these publications have a porous layer formed of a specific alumina hydrate, and the advantages of these ink-receptive layers are to provide high circularity of ink dots and excellent fixability of dyes and to realize a print having high color density. An ink-receptive layer described in Japanese Patent Laid-Open No. 151476/1988, is also usable. This ink-receptive layer is formed by coating a composition composed mainly of a pigment and a binder, semi-drying the coating, putting a transfer sheet having a desired surface form onto the coating, drying the laminate, and removing the transfer sheet. The advantage of this ink-receptive layer is to offer high ink absorption and to realize a high-quality image. Specific examples of a preferred embodiment of the coat layer provided on both surfaces of the recording medium according to the present invention include those described in Japanese Patent Laid-Open Nos. 82085/1982 and 135190/1982. The coat layer described in these publications contains a plastic pigment and is formed by hot calendering. This coat layer offers high resolution. Further, coat layers described in Japanese Patent Laid-Open Nos. 264391/1988, 113986/1990, and 274587/1990, may be preferably used. These coat layers are formed by coating a mixture of a pigment, an aqueous binder, and a silicone emulsion or a water-soluble silicone compound on a substrate. They are excellent in ink absorption and surface gloss and smoothness. Furthermore, a coat layer, as described in Japanese Patent Laid-Open No. 79967/1994, also may be preferably used wherein an ink-receiving layer as the outermost layer has been pressed in a wet state against a heated specular surface to dry the layer. Furthermore, ink-receptive layers formed by casting as described in Japanese Patent Laid-Open Nos. 158084/1987, 305237/1994, 89220/1995, and 117335/1995, also may be preferably utilized. In addition, an ink-receptive layer, having high glossiness, described in Japanese Patent Laid-Open No. 189985/1986, and an ink-receptive layer, which is glossy and offers high print density and excellent resistance to cracking on bending, described in Japanese Patent Laid-Open No. 101142/1995, also may be preferably utilized. Further, ink-receptive layers having a crack on its surface, for example, those described in Japanese Patent Laid-Open Nos. 198250/1985, 198251/1985, and 198252/1985, also may be preferably utilized. Any of the ink-receptive layer and the coat layer may have a surface which has been treated to render it glossy. For example, a composition containing silica or a resin, which is dissolved in or swollen with an ink, may be coated to impart gloss. Silica is generally available as colloidal silica. The form of silica, however, is not particularly limited so far as the effect of the present invention is provided. The colloidal silica is usually in the form of an anionic colloidal dispersion which is a stable dispersion of ultrafine particles of silicic anhydride (silica) in water and may be produced, for example, by the following method. At the outset, an aqueous sodium silicate solution is passed through an cation exchange resin layer to prepare a sol having an SiO 2 /Na 2 O ratio of 60 to 130. The sol is then heated and fired at 60°C or above to grow particles into discrete dispersed particles, and a sol which has been passed through an ion exchange resin is added thereto to conduct polymerization deposition. Thus, colloidal silica can be prepared as a stable sol of which the particles have been grown to an average diameter of 3 nm to 200 nm. In the present invention, commercially available colloidal silica may be used, and examples thereof include Ludox manufactured by Du Pont, Syton manufactured by Monsanto, Nalcoag manufactured by Nalco, and Snowtex manufactured by Nissan Chemical Industry Ltd. According to a preferred embodiment of the present invention, the glossiness on the surface having a higher ink absorption capacity is higher than that on the surface having a lower ink absorption capacity. This construction can enhance the quality of an image formed on the surface that realizes higher resolution. Further, it offers an additional advantage that the first surface can be easily distinguished from the second surface. The glossiness on the surface having a higher ink absorption capacity is preferably not less than 30 in terms of 60° specular glossiness specified in any one of JIS Z 8741, ISO 2813, ASTM D 523, and DIN 67530. For both the ink-receptive layer and the coat layer, the surface brightness is preferably high. The high brightness can be realized by incorporating, for example, a fluorescent dye or a fluorescent pigment as a white dye or pigment into the ink-receptive layer. According to a preferred embodiment of the present invention, the brightness on the surface having a higher ink absorption capacity is higher than that on the surface having a lower ink absorption capacity. This construction can enhance the quality of an image formed on the surface that realizes higher resolution. Further, it offers an additional advantage that the first surface of the recording medium can be easily distinguished from the second surface of the recording medium. The brightness on the surface having a higher ink absorption capacity is preferably not less than 80 as measured by the procedure set forth in any one of Brightness by Hunter JIS P 8123, ISO Brightness JIS P 8148, and ISO 2470-1977. The substrate for the recording medium of the present invention is not particularly limited so far as it can support the ink-receptive layer or the coat layer and has satisfactory strength to be usable in the recording medium, and preferred examples thereof include papers and plastic films. In order to effectively prevent the so-called "print through" of the image and other unfavorable phenomena, the substrate preferably has a basis weight of about 80 to 200 g/m 2 . The thickness of paper as a preferred substrate is about 90 to 220 µm. In the case of a plastic film, the thickness is preferably about 75 to 200 µm. According to the present invention, when a droplet of an ink in an identical amount is deposited onto the first and second surfaces of the recording medium, the diameter of a dot formed on the first surface is different from that of a dot formed on the second surface. One preferred means for regulating the dot diameter is to regulate the ink absorption capacity of the ink-receptive layer or the coat layer provided on the first and second surfaces of the recording medium. The term "ink absorption capacity" used herein means, for example, ink absorption capacity in the thicknesswise direction of the recording medium or the maximum amount of the ink absorbed which causes neither feathering nor bleeding. According to an embodiment of the present invention, the ink absorption capacity means the rate at which a surface of the recording medium absorbs an ink composition. In particular, the rate at which one surface of the recording medium absorbs an ink composition is made larger than that at which the other surface of the recording medium absorbs the ink composition. As a result, even when a droplet of an ink in an identical amount is deposited onto the first and second surfaces of the recording medium, the diameter of a dot formed on the first surface is different from that of a dot formed on the second surface. When an ink droplet is deposited on the surface having a higher ink absorption capacity, the ink is immediately absorbed in the thicknesswise direction of the recording medium, forming a relatively small dot. On the other hand, when an ink droplet is deposited on the other surface having a lower ink absorption capacity, the time taken for the ink to be absorbed is longer than that for the surface having a higher ink absorption capacity, causing the ink composition to be spread in the lateral direction on the surface of the recording medium, resulting in the formation of a relatively larger dot than the dot formed on the surface having a higher ink absorption capacity. According to a preferred embodiment of the present invention, the diameter of the dot formed on the surface having a higher ink absorption capacity is 50 to 90 µm, with the diameter of the dot formed on the surface having a lower ink absorption capacity being 90 to 120 µm. Further, preferably, the above dot diameter is obtained in an ink droplet weight of about 0.01 to 0.05 µg. Further, the present invention would advantageously improve the carriability of the recording medium in a printer. Preferably, the coefficient of friction also is regulated for the ink-receptive layer and the coat layer on both surfaces of the recording medium. According to the present invention, the ink-receptive layer or the coat layer provided on both surface of the recording medium contributes to the strength of the recording medium to some extent, advantageously creating greater freedom in selection of the substrate for the recording medium. Further, according to a preferred embodiment of the present invention, the maximum amount of an ink absorbed which causes neither feathering nor bleeding on the surface having a higher ink absorption capacity is 3 to 60 µl/mm 2 . The maximum amount of an ink absorbed which creates neither feathering nor bleeding on the surface having a lower ink absorption capacity is 1 to 20 µl/mm 2 . In the recording medium according to the present invention, the ink-receptive layer or the coat layer may be formed on each surface by a standard method for the formation of the ink-receptive layer or the coat layer. According to a preferred embodiment of the present invention, the ink-receptive layer or the coat layer on the first surface of the recording medium and the ink-receptive layer or the coat layer on the second surface of the recording medium may be separately formed (the so-called "off-machine) or alternatively may be simultaneously formed (the so-called "on-machine). Further, two media each having an ink-receptive layer or a coat layer formed on one surface thereof may be laminated onto each other to form the recording medium of the present invention. When the ink-receptive layer is formed by coating of a precursor composition, the coverage may be suitably determined by taking into consideration the ingredients of the precursor composition, desired ink absorption and the like. Preferably, however, the coverage of the ink-receptive layer on the surface having a lower ink absorption capacity is 1 to 10 g/m 2 , the coverage of the ink-receptive layer on the surface having a higher ink absorption capacity is 10 to 30 g/m 2 , and the thickness of the substrate is 100 to 200 µm. The recording medium according to the present invention may be used in various forms. Specifically, it may be used as a standard-size recording medium, and, in addition, may be used in the form of postal cards and business card sheets on which perfect printing (printing on both surfaces thereof) may be performed. Ink Jet Recording Method According to another aspect of the present invention, there is provided an ink jet recording method which permits printing to be made on both surfaces of the recording medium in accordance with claim 7. In the present invention, printing is made so that the resolution of an image printed on one surface of the recording medium is different from that of an image printed on the other surface of the recording medium. Specifically, an image with a higher resolution is printed on the surface having a higher ink absorption capacity and an image with a lower resolution is printed on the surface having a lower ink absorption capacity. According to the recording medium of the present invention, even when the amount of the ink deposited on one surface of the recording medium is identical to that of the ink deposited on the other surface of the recording medium, the diameter of the dot formed on the surface having a higher ink absorption capacity is smaller than that of the dot formed on the surface having a lower ink absorption capacity. Thus, two images with two respective resolutions can be advantageously realized by using an identical recording head and varying only the resolution without varying the amount of the ink deposited. In this connection, it is needless to say that, in the recording medium according to the present invention, the regulation of the amount of ink deposited results in the formation of more advantageously regulated dots. The above embodiment of the present invention, which, despite the deposition of an ink in an identical amount, permits the diameter of the dot formed on the first surface of the recording medium to be made different from that of the dot formed on the second surface of the recording medium, can be realized, for example, by selecting the ink composition and the recording medium according to the following criteria and using the selected ink composition in combination with the selected recording medium. Specifically, an ink composition having a static contact angle with the recording medium, as measured 5 s after dropping of the ink composition on the recording medium, of not more than 10° in terms of the contact angle of the ink composition with one surface of the recording medium and more than 10° in terms of the contact angle of the ink composition with the other surface of the recording medium. In such a combination of the ink composition with the recording medium, the ink composition is rapidly absorbed into the one surface of the recording medium while it is slowly absorbed into the other surface of the recording medium. The diameter of dots formed on the surface with the ink composition being rapidly absorbed is smaller than the diameter of dots formed on the surface with the ink composition being slowly absorbed. According to a preferred embodiment of the present invention, the resolution of a print on the surface having a higher ink absorption capacity is about 600 to 1440 dpi, while the resolution of a print on the surface having a lower ink absorption capacity is about 300 to 600 dpi. The ink composition used in the ink jet recording method according to the present invention may comprise conventional colorant and organic solvent and the like. Suitable solvents used in the present invention include ion-exchanged water with the contents of Ca and Mg ions being not more than 5 ppm and high-boiling, low-volatile polyhydric alcohols such as glycerin, ethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,3-propane diol, and 1,5-pentanediol. It is also possible to use lower alkyl ethers of polyhydric alcohols, such as diethylene glycol monobutyl ether and triethylene glycol monobutyl ether, and nitrogen-containing organic solvents, such as N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, monoethanolamine, diethanolamine, and triethanolamine. Further, the utilization of highly hygroscopic additives, such as urea and saccharides, is also preferred from the viewpoint of preventing nozzles of a recording head from being clogged. Although the amount of the polyhydric alcohol or the lower alkyl ether of polyhydric alcohol may be suitably determined, it is preferably about 4 to 30% by weight, more preferably about 7 to 20% by weight. Further, according to a preferred embodiment of the present invention, the ink composition contains a surfactant for regulating the penetration of the ink into the recording medium. Preferred surfactants usable herein include, for example, acetylene glycols, and those commercially available from the Nisshin Chemical Industry Co., Ltd. under the tradename designations Surfynol 465, TG, 104, and 82. The term "ink composition" used herein means a black ink composition in the case of monochrome printing and, in the case of color printing, color ink compositions, specifically a yellow ink composition, a magenta ink composition, a cyan ink composition and, in some cases, a black ink composition. Further, the recording medium according to the present invention may be used in a recording method using ink compositions of six colors in total, specifically a yellow ink composition, two magenta ink compositions different from each other in color density, two cyan ink compositions different from each other in color density, and a black ink composition. A combination of the above ink compositions of six colors with the recording medium of the present invention can realize a printed image, comparable to a photograph, having excellent gradation and free from particulate spots. In an area where the image density is low, particulate spots are often observed. The use of an ink composition having a high color density in combination with an ink composition having a low color density for each of a magenta ink composition and a cyan ink composition can effectively prevent the creation of the particulate spots and, at the same time, can realize a print with excellent gradation. According to a preferred embodiment of the present invention, the colorant concentration of the ink composition having a low color density is preferably 5 to 50% by weight, more preferably about 10 to 30% by weight, of the colorant concentration of the ink composition having a high color density. The use of the ink composition having a high color density in combination with the ink composition having a low color density can realize an image with better gradation. EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples, though it is not limited to these examples only. In the following examples and comparative examples, all "parts" are by weight unless otherwise specified. Example 1 and Comparative Examples 1 and 2:Preparation of recording media A recording paper having a basis weight of 180 g/m 2 was provided as a substrate, and the following ink-receptive layers were formed respectively on the front and back sides. Side A: A coating liquid having the following composition was prepared. Synthetic amorphous silica 100 parts Polyvinyl alcohol 30 parts Colloidal silica 30 parts Cationic dye fixing agent 20 parts The coating liquid was diluted with water to a solid content of 15% by weight and then coated by means of an air knife coater on one side (side A) of the substrate to form a coat layer at a coverage on a dry weight basis of 12 g/m 2 . Thereafter, a coating liquid having the following composition was prepared. Organic particles of styrenic polymer resin 100 parts Styrene-butadiene latex 30 parts Release agent 2 parts The coating liquid was diluted with water to a solid content of 25% by weight and then cast coated on the dried coat layer to form a coat layer at a coverage on a dry weight basis of 3 g/m 2 . Side B: A coating liquid having the following composition was prepared. Kaolin 100 parts Polyvinyl alcohol 5 pars Styrene-butadiene latex 20 parts Waterproofing agent 2 parts This coating liquid was coated on the other side (side B) of the substrate, and the coating was dried to form an ink-receptive layer at a coverage on a dry basis of 5 g/m 2 . The recording medium thus obtained was cut into size A4 and a size of a postal card. This recording medium will be hereinafter referred to as "Example 1." A comparative recording medium was prepared in the same manner as described above, except that only one side of the substrate was treated as described above in connection with the treatment of the side A. Another comparative recording medium was prepared in the same manner as described above, except that only one side of the substrate was treated as described above in connection with the treatment of the side B. These comparative recording media were cut into size A4 and a size of a postal card. The comparative recording medium with only the side A being treated and the comparative recording medium with only the side B being treated will be hereinafter referred to as "Comparative Example 1" and "Comparative Example 2," respectively. Example 2 A wood-free paper having a basis weight of 90 g/m 2 was provided as a substrate, and the following ink-receptive layer was formed on the front and back sides of the substrate. Side A: A coating liquid, for a first ink-receptive layer, having the following composition was coated on one side (side A) of the substrate, and the coating was dried to from an ink-receptive layer at a coverage on a dry basis of 15 g/m 2 . Silica (average particle diameter: 5.3 µm) 150 parts Polyvinyl alcohol (10% dissolved) 500 parts Melamine crosslinking agent (solid content 80%) 4 parts Fluorescent dye 5 parts A coating liquid, for a second ink-receptive layer, having the following composition was then coated on the first ink-receptive layer, and the coating was dried to form an ink-receptive layer at a coverage on a dry basis of 7 g/m 2 . Silica (average particle diameter: 19.3 µm) 150 parts Polyvinyl alcohol (10% dissolved) 400 parts Polyvinyl pyrrolidone (10% dissolved) 600 parts Fluorescent dye 10 parts Side B: A coating liquid having the following composition was prepared. Amorphous silica 100 parts Polyvinyl alcohol 80 parts Polyamide epoxy resin 10 parts Waterproofing agent 10 parts This coating liquid was coated on the other side (side B) of the substrate, and the coating was dried to form an ink-receptive layer at a coverage on a dry basis of 5 g/m 2 . Example 3 A coating liquid, for a gloss layer, composed of 250 parts of colloidal silica (Snowtex C, solid content 20%, manufactured by Nissan Chemical Industry Ltd.) and 50 parts of polyvinyl alcohol (Gosenol T330, 10% dissolved, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was coated on a polyethylene film, and the coated polyethylene film was laminated onto the recording medium prepared in Example 2 so that the coated side of the polyethylene film faced the second ink-receptive layer. After the coating for a gloss layer was fully dried, the polyethylene film was peeled off followed by further drying to prepare a recording medium having a gloss layer, at a coverage on a dry basis of 5 g/m 2 , the surface of which had a 60° specular glossiness of 30. Printing test The following ink composition was prepared and used for a printing test. Colorant 2% by weight Glycerin 10% by weight Diethylene glycol monobutyl ether 10% by weight Ion-exchanged water 77.2% by weight Surfynol TG 0.8% by weight Colorant: Yellow ink composition - C.I. Direct Yellow 86 Magenta ink composition - C.I. Acid Red 52 Cyan ink composition - C.I. Direct Blue 199 Black ink composition - C.I. Direct Black 19 Printing was carried out using an ink jet recording printer MJ700V2C (manufactured by Seiko Epson Corporation). The recording media were evaluated for the following items and according to the following criteria. Test 1: Print through An identical image was printed on the recording media, having size A4 of Examples 1, 2 and 3 and Comparative Examples 1 and 2. For the side A, the image was printed with a resolution of 720 dpi, and, for the side B, the image was printed with a resolution of 360 dpi. The recording media were then inspected for the so-called "print through" which is a phenomenon wherein the printed image is seen also through the backside of the medium. As a result, no print through phenomenon was observed for the recording media of Examples 1, 2 and 3, whereas the print through phenomenon was observed for both the recording media of Comparative Examples 1 and 2. Test 2: Anticurling property 2-1 . Environment curling The prints obtained in the test 1 were allowed to stand under conditions of temperature 10°C and humidity 20% and under conditions of temperature 32°C and humidity 80%. The recording media with the ink-receptive layer provided on only one side thereof were allowed to stand with the surface of the ink-receptive layer up. Twenty four hr after the initiation of standing, the height of the four corners of each of the recording medium from a plane, that is, the degree of upward warpage, was measured. The results were as follows. Degree of upward warpage (mm) 10°C/20% humidity 32°C/80% humidity Example 1 0 0 Example 2 0 0 Example 3 0 0 Comparative Example 1 10 8 Comparative Example 2 8 6 2-2 . Curling upon printing An identical image was printed on the recording media having size A4 of Example 1 and Comparative Examples 1 and 2 over the whole printable area. For the side A, the image was printed with a resolution of 720 dpi, and, for the side B, the image was printed with a resolution of 360 dpi. Upon printing, the height of the four corners of each of the recording medium from a plane, that is, the degree of upward warpage, was measured. The results were as follows. Degree of upward warpage (mm) Example 1: Printed on both sides 0 Printed on side A alone 1 - 2 Printed on side B alone 0 - 1 Example 2: Printed on both sides 0 Printed on side A alone 0 Printed on side B alone 0 Example 3: Printed on both sides 0 Printed on side A alone 0 Printed on side B alone 0 Comparative Example 1: Printed on both sides 6 Printed on side A alone 8 Printed on side B alone 7 Comparative Example 2: Printed on both sides 5 Printed on side A alone 7 Printed on side B alone 5 Test 3 : Carriability 3-1 . Evaluation under low temperature and low humidity conditions Fifty sheets of the recording medium were continuously passed through a printer under an environment of temperature 10°C and humidity 20%. When none of double feed, non-feed, and a failure of the front end of the sheet to be successfully delivered were observed for all the sheets, the carriability was evaluated as "○", and, when at least one of the above phenomena was observed for at least one sheet, the carriability was evaluated as "×." 3-2 . Evaluation under high temperature and high humidity conditions Fifty sheets of the recording medium were continuously passed through a printer under an environment of temperature 32°C and humidity 80%. When none of double feed, non-feed, and a failure of the front end of the sheet to be successfully delivered were observed for all the sheets, the carriability was evaluated as "○", and, when at least one of the above phenomena was observed for at least one sheet, the carriability was evaluated as "×." The results were as tabulated in the following Table 3. 10°C/20% humidity 32°C/80% humidity Example 1 ○ ○ Example 2 ○ ○ Example 3 ○ ○ Comparative Example 1 × × Comparative Example 2 × × Test 4: Static contact angle of recording medium with ink composition The above black ink composition was dropped on each of the side A and the side B of the recording media of Examples 1 to 3 to determine the static contact angle. The contact angle was measured 5 s after dropping of a droplet of the black ink composition onto the recording medium in an environment of 25°C by a droplet method using a contact angle goniometer (model CA-Z contact angle goniometer, manufactured by Kyowa Interface Science Co., Ltd.). The results were as tabulated in the following Table 4. Static contact angle (° ) Side A Side B Example 1 0 15 Example 2 5 20 Example 3 0 20 Test 5: Dot diameter For the images formed in the test 1, the equivalent circular diameter per dot was measured for 100 samples. The results were as tabulated in the following Table 5. Dot diameter (µm) Side A Side B Example 1 75 110 Example 2 80 120 Example 3 85 120 Test 6: Brightness The brightness of the recording media prepared in Examples 1 to 3 were measured with a brightness meter (manufactured by Kumagai Riki Kogyo Co., Ltd.) according to ISO-2470. The results were tabulated in the following Table 6. Brightness Side A Side B Example 1 82 78 Example 2 85 82 Example 3 88 82

Claims: An ink jet recording medium, comprising: a substrate having two faces; and an ink-receptive and fixing layer provided on both faces of the substrate to form a first surface and a second surface opposite the first surface, said respective ink-receptive and fixing layers being different from each other, the diameter of a dot formed on the first surface is different from that of a dot formed on the second surface when a droplet of an ink in an identical amount is deposited onto the first and second surfaces of the recording medium, characterized in that the ink-receptive and fixing layer provided on the surface on which a dot having a smaller diameter is to be formed having cracks on its surface and having a higher maximum amount of ink absorbed than that one on the surface on which a dot having a larger diameter is to be formed. The recording medium according to claim 1, wherein the maximum amount of an ink which does not create feathering or bleeding on the surface having a higher maximum amount of the ink absorbed thereon is 3 to 60 µl/mm 2 and the maximum amount of an ink which does not create feathering or bleeding on the surface having a lower maximum amount of the ink absorbed thereon is 1 to 20 µl/mm 2 . The recording medium according to any one of claims 1 and 2, wherein the ink-receptive and fixing layer provided on the surface having a higher maximum amount of the ink absorbed thereon contains fluorine or a silicone compound. The recording medium according to any one of claims 1 to 3, wherein the glossiness on the surface having a higher maximum amount of the ink absorbed thereon is 30 or more in terms of 60° specular glossiness specified in any one of JIS Z8741, ISO 2813, ASTM D523, and DIN 67530. The recording medium according to any one of claims 1 to 4, wherein the brightness on the surface having a higher maximum amount of the ink absorbed thereon is higher than that on the surface having a lower maximum amount of the ink absorbed thereon. The recording medium according to claim 5, wherein the brightness on the surface having a higher maximum amount of the ink absorbed thereon is 80 or more as measured by Hunter JIS P8123, ISO Brightness JIS P8148, or ISO 2470-1977. An ink jet recording method comprising the steps of: forming droplets of an ink composition; and depositing the droplets onto a recording medium to perform printing, wherein the recording medium used comprises: a substrate having two faces; and an ink-receptive and fixing layer provided on both faces of the substrate to form a first surface and a second surface opposite the first surface, (a) the diameter of a dot formed on the first surface is different from that of a dot formed on the second surface when a droplet of an ink in an identical amount is deposited onto the first and second surfaces of the recording medium, (b) the maximum amount of the ink absorbed on the surface on which a dot having a smaller diameter is to be formed is higher than that one on the surface on which a dot having a larger diameter is to be formed, and an image with a higher resolution is printed on the surface having a higher maximum amount of the ink absorbed thereon and image with a lower resolution is printed on the surface having a lower maximum amount of the ink absorbed thereon. The ink jet recording method according to claim 7, wherein the ink composition used has a static contact angle, as measured 5 s after dropping of the ink composition onto the recording medium, of not more than 10° in terms of the contact angle of the ink composition with one surface of the recording medium and more than 10° in terms of the contact angle of the ink composition with the other surface of the recording medium. The ink jet recording method according to claim 7 or 8, wherein the ink composition contains acetylene glycol. The ink jet recording method according to any one of claims 7 to 9, wherein the higher resolution is 600 to 1440 dpi and the lower resolution is 300 to 600 dpi. The ink jet recording method according to any one of claims 7 to 10, wherein a yellow ink composition, a magenta ink composition, a cyan ink composition, and optionally a black ink composition are used as the ink composition. The ink jet recording method according to any one of claims 7 to 10, wherein ink compositions of six colors in total which are a yellow ink composition, a high color density magenta ink composition, a low color density magenta ink composition, a high color density cyan ink composition, a low color density cyan ink composition, and a black ink composition, are used. The ink jet recording method according to claim 12, wherein the colorant concentration of the low color density magenta ink composition is 5 to 50% by weight of that of the high color density magenta ink composition with the colorant concentration of the low color density cyan ink composition being 5 to 50% by weight of that of the high color density cyan ink composition. The ink jet recording method according to claim 7, wherein with the recording medium used the maximum amount of an ink which does not create feathering or bleeding on the surface having a higher maximum amount of the ink absorbed thereon is 3 to 60 µl/mm 2 and the maximum amount of an ink which does not create feathering or bleeding on the surface having a lower maximum amount of the ink absorbed thereon is 1 to 20 µl/mm 2 . The ink jet recording method according to any one of claims 7 and 14, wherein with the recording medium used the ink-receptive and fixing layer provided on the surface having a higher maximum amount of the ink absorbed thereon contains fluorine or a silicone compound. The ink jet recording method according to any one of claims 7, 14, and 15, wherein with the recording medium used the ink-receptive and fixing layer provided on the surface having a higher maximum amount of the ink absorbed thereon has cracks on its surface. The ink jet recording method according to any one of claims 7 and 14 to 16, wherein with the recording medium used the glossiness on the surface having a higher maximum amount of the ink absorbed thereon is 30 or more in terms of 60° specular glossiness specified in any one of JIS Z8741, ISO 2813, ASTM D523, and DIN 67530. The ink jet recording method according to any one of claims 7 and 14 to 17, wherein with the recording medium used the brightness on the surface having a higher maximum amount of the ink absorbed thereon is higher than that on the surface having a lower maximum amount of the ink absorbed thereon. The ink jet recording method according to claim 18, wherein the brightness on the surface having a higher maximum amount of the ink absorbed thereon is 80 or more as measured by Hunter JIS P8123, ISO Brightness JIS P8148, or ISO 2470-1977.

Inventors: ONISHI HIROYUKI, ONISHI, HIROYUKI
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1997
Main classification: B41M5
IPC codes: B41J2, B41M5, D21H27