Double-side recording medium

Abstract: A double-side recording medium comprises a base material for paper mainly comprising pulp, one side of which has an ink jet recording ability and the other side of which has a heat-sensitive recording ability, wherein the time required for the penetration of 0.5 ml of a 10% polyethylene glycol aqueous solution dropped, using a micro-syringe, on the side, to which the ink jet recording ability is imparted into the side to which the heat-sensitive recording ability is imparted, is adjusted to not less than 30 seconds. The recording medium permits high-speed double-side recording and at least one side of the recording medium is favorable for color ink jet recording, while the other side has a heat-sensitive recording ability. The recording medium is one that permits both ink jet recording and heat-sensitive recording. The medium never causes any bleeding on the ink jet recording side, any graying of the heat-sensitive recording layer due to the action of the solvent present in the ink jet ink and never undergoes any discoloration of the printed matter on the heat-sensitive recording layer.

Description: Background of the Invention The present invention relates to a recording medium, more particularly to a double-side recording medium, one side of which has an ink jet recording ability and the other side of which has a heat-sensitive recording ability. The ink jet recording system which makes use of a water-base ink has been applied to printers for terminal devices, facsimiles, plotters, ledger paper printing devices or the like, because of such reasons that the system does not generate so much noises during recording operations, makes it easy to carry out color printing or recording and permits high-speed recording. Since the wood free paper and coated paper used in the usual printing are inferior in ink-absorptive capacity, printed ink remains on the paper surface over a long period of time without being dried, this in turn leads to the contamination of the printing device and printed sheets and/or the contamination of printed images and therefore, such paper is less practicable. To solve these problems, there have been proposed, for instance, the use of recording paper having a low degree of sizing (Japanese UnExamined Patent Publication (hereunder referred to as "J.P. KOKAI") No. Sho 52-53012); and the impregnation of base paper in which an urea-formalin resin is incorporated with a water-soluble polymer (J.P. KOKAI No. Sho 53-49113). Moreover, there has also been disclosed recording paper whose surface is coated with a variety of porous inorganic pigments including amorphous silica in order to improve the color-developing ability of an ink and reproducibility of images (J.P. KOKAI Nos. Sho 55-51583 and Sho 56-148585). In addition, there has also been proposed an improvement such as those in which physical properties of these porous pigments are specified for the purpose of obtaining images whose bleeding is controlled and which have high fineness (J.P. KOKAI Nos. Sho 58-110287; Sho 59-185690; and Sho 61-141584). As the ink jet recording system has widely been used, there has been desired for the development of recording paper which can simultaneously satisfy the requirements for properties as office paper such as writing quality with a pencil and recording ability. Thus, J.P. KOKAI No. Hei 4-16379 proposes the use of at least two porous pigments, which have different fine pore sizes, in combination and this would be successful to some extent. In recent years, the ink jet printing technique has rapidly been developed and there have recently been developed ink jet printers whose image quality is almost comparable to those observed for silver salt photographs. However, demands, which had heretofore been neglected have attracted special interest lately, one of which is high-speed double-side recording technique. The ink jet recording method is one in which recording is performed by impacting ejected ink drops against the surface of a recording medium. Accordingly, the impact precision should be improved in order to obtain recorded materials having high precision and excellent reproducibility. For this reason, the direction, in which an ink is discharged from a printer head, is limited to that along which the gravity acts on it, i.e., the direction from upward to downward. Thus, it is difficult to simultaneously record the both sides of a recording medium. In addition, it is possible to once record one side of a recording medium, to have then the recording medium turned over and to thus record the other side of the medium. However, this never allows the speeding-up of the printing or recording operations and rather makes the mechanism of the printer more complicated and also makes the size of the printer larger. Therefore, this method is not practically acceptable. Incidentally, the high-speed recording technique is badly needed in cases where a large quantity of double-side printed materials should be printed, while taking into consideration the practical method of using printers. This corresponds to the cases where New Year's cards, letters of inquiry after health in the hot season, invitation cards, and greeting cards are printed in general family. In these cases, various designs and/or letters are recorded on the back side thereof, but only addresses are printed on the front face thereof and therefore, monochromatic printing is sufficient in most of the cases. If these printing operations are carried out simply by an existing ink jet printer, however, all the printing medium should be reset on the printer after the completion of the printing operation on one side of the medium to thus record images on the other side thereof. Summary of the Invention Accordingly, it is an object of the present invention to solve the foregoing problems and more specifically to provide a recording medium, which permits high-speed double-side recording and at least one side of which is suited for color recording methods. Another object of the present invention is to provide a double side recording medium, which does not cause any bleeding on a heat-sensitive recording layer due to the solvent present in an ink jet ink, which does not cause any discoloration of the printed letters on the heat-sensitive recording layer and which permits both heat-sensitive recording and ink jet recording. The inventors of this invention have conducted various studies to achieve the foregoing objects, have found a recording medium, which can satisfy the foregoing requirements. The present invention provides a double-side recording medium, according to claims 1 to 9 of this document. Description of the Preferred Embodiments As the pulp for paper used in the present invention as the substrate, there may be listed. For instance, chemical pulp such as soft-wood bleached kraft pulp (hereunder referred to as "NBKP") and hardwood bleached kraft pulp (hereunder referred to as "LBKP"); mechanical pulp such as GP, BCTMP and MP; pulp obtained from raw materials other than wood such as kenaf; and paper-making pulp represented by DIP pulp or the like. These principal components may be mixed with polyolefinic fibers such as polyethylene, polypropylene, ethylene-propylene copolymer, polystyrene and ethylene-vinyl acetate copolymer; halogen atom-containing polymers such as polyvinyl chloride and polyvinylidene chloride; polyamide type fibers such as 6-nylon and 66-nylon; aliphatic polyester fibers such as polyethylene succinate, polycaprolactone, polylactic acid and polyhydroxy butyrate-valylate copolymer; and/or vinylon fibers. In addition, it is also possible to optionally incorporate, into the substrate, fillers, for instance, inorganic pigments such as talc, kaolin, calcined kaolin, calcium carbonate, white carbon, amorphous silica, diatomaceous earth, titanium oxide, activated china clay and barium sulfate; and/or organic pigments such as urea-formalin resin, nylon powder and polyethylene powder and the substrate can be prepared by the acidic or neutral paper-making process according to the usual method. Furthermore, it is also possible to appropriately use base paper which contains or is provided thereon with a sizing agent represented by rosin type sizes, alkenyl succinic acid anhydride and alkyl ketene dimers; starches such as oxidized starch, enzyme-modified starch, cation-modified starch, esterified starch and etherified starch; cellulose derivatives such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, methoxy cellulose and hydroxy cellulose; polyvinyl alcohols such as completely or partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol and silicon-modified polyvinyl alcohol; water-soluble polymers such as polyacrylamide, polyvinyl pyrrolidone, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, alkali salts of styrene-maleic anhydride copolymer, alkali salts of isobutylene-maleic anhydride copolymer and casein; and adhesives represented by latexes such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, polybutyl methacrylate, styrene-butadiene copolymer, vinyl chloride-vinyl acetate copolymer, and styrene-butadiene-acrylic copolymer. To impart the ink jet recording ability to the recording medium, an inkjet receiving layer containing dialkylamine epichlorohydrin polycondensate is provided. A base material for paper is coated with or impregnated with a cationic resin and/or a water-soluble resin or a water-dispersible resin (wood free paper type one). In this respect, however, it is preferred to apply a pigment-containing layer to the base material from the viewpoint of the ink-absorbing ability. In particular, to impart an excellent ink jet recording ability, it is preferred to apply, to one side of the recording medium, an ink-receiving layer containing a xerogel type porous pigment. The order of the ink-receiving layer and the heat-sensitive layer to be applied is not restricted to any specific one, but it is preferred that the ink-receiving layer be first applied to the base material before the step for the application of the heat-sensitive layer since contamination upon color development due to, for instance, rubbing of the heat-sensitive layer can be reduced to a level of as low as possible. Examples of the pigments to be incorporated into the ink-receiving layer include inorganic pigments such as amorphous silica, alumina, calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, white carbon, alumina and aluminum hydroxide; and organic pigments such as styrenic, acrylic, urea resin type, melamine resin type and benzoguanamine type ones. Among the pigments to be incorporated into the ink-receiving layer, preferred are xerogel type porous pigments, which can be prepared using a variety of known methods such as those listed below and have already been put on the market: (1) A method comprises the steps of drying a hydrogel-forming substance as a raw material such as aluminum hydroxide, alumina, silica or magnesium oxide into a xerogel, followed by pulverization and classification thereof; (2) A method comprises the steps of granulation of the hydrogel per se into secondary or tertiary agglomerates having an appropriate size, then drying the agglomerates and further heating them to thus proceed, for instance, sintering and/or crystallization thereof and to hence enhance the bonds between primary particles of the oxides; and (3) A method comprises the steps of adjusting conditions for forming a resin such as an urea-formalin resin or melamine-formalin resin in the stage for the formation of such a resin in a suspension of fine particles of, for instance colloidal silica or colloidal alumina to thus form fine particles having a desired secondary particle size, followed by drying and optionally sintering the fine particles. Among these, preferably used in the ink jet recording medium are silica type pigments, because they are excellent in the ink receiving ability and can ensure a high recording density due to their characteristic properties such as relatively low refractive index, and easy controllability of the porous structure. Moreover, the use of a pigment having a particle size of not more than 1µm as a pigment to be incorporated into the ink-receiving layer permits the preparation of an ink-receiving layer having excellent surface gloss. In particular, it is preferred to use, as a principal pigment component, fine silica having an average secondary particle size of not more than 500 nm and produced by the agglomeration of primary particles having a particle size ranging from 3 to 40 nm, for applications which require recorded images excellent in glossiness. In addition, the resins (which serve as binders) may appropriately be selected from any known ones. Examples thereof are aqueous solutions or aqueous dispersions of, for instance, starch and derivatives thereof; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; natural or semisynthetic polymers such as casein, gelatin and soybean protein; polyvinyl alcohol derivatives such as polyvinyl alcohol, silyl-modified polyvinyl alcohol and cation-modified polyvinyl alcohol; vinylic copolymer resins such as polyvinyl butyral resin, polyethyleneimine type resin, polyvinyl pyrrolidone type resin, poly(meth)acrylic resin, acrylic acid ester type resin, polyamide type resin, polyacrylamide type resin, polyester resin, urea resin, melamine resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer and ethylene-vinyl acetate copolymer; or modified polymers such as those obtained by introducing anionic or cationic residues into the foregoing resins. As for the resins, it is also preferable to use sell-emulsifiable cationic resins containing no emulsifier. By employment of the self-emulsifiable cationic resins, both anti-graying of background properties of heat sensitive recording layer and reduction of the color forming ability are small, and there can be obtained superior effects in terms of water resistance and recorded image quality of the ink jet recording portion. When an emulsion polymerization type latex is used as the resin, there are some cases where an anionic, cationic or nonionic emulsifier reduces adhesion properties and water resistance of ink jet recording portion or where bleedings occur on ink jet recording portion. Furthermore, there are some possibilities in that such an emulsifier lowers anti-graying of background and color formation properties of heat-sensitive recording layer. Examples of the self-emulsifiable cationic resins include copolymers obtained by soap free polymerization of monomers such as styrene butadiene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethyl-hexyl acrylate, a cationic functional group being bonded to at least one part of the monomers. Examples of the cationic functional groups include thirdly amino group, quaternary ammonium group and the like but are not limited to them. An amount of the self-emulsifiable cationic resins is not limited but preferably 1 to 30 wt %, more preferably, 3 to 15 wt % relative to an amount of an aqueous ink receiving layer. The method for the production of the sell-emulsifiable cationic resins is not limited, but includes, for example, seed polymerization method, reactive emulsion method or oligomer method. Moreover, it is also possible to use, in combination with the foregoing materials, for instance, cationic polymer compounds such as polyethyleneimine type resin, polyamine type resin, polyamide type resin, polyamide epichlorhydrin type resin, polyamine epichlorhydrin type resin, polyamide polyamine epichlorhydrin type resin, polydiallylamine type resin, and dicyan-diamide condensate, in order to improve the water resistance of images printed with a water-based ink. Among these, dialkylamine • epichlorohydrin polycondensate is incorporated into the ink receiving layer. As the dialkylamine in the polycondensate, alkyl group having 1 to 4 carbon atoms is preferable and in particularly, dimethylamine • epichlorohydrin polycondensate is preferable. Use of dialkylamine • epichlorohydrin polycondensate improves water resistance of ink jet recorded parts and does not lower the color formation properties of the heat sensitive recording layer even if it is subjected to high temperature and high humidity condition. Molecular weight of the polycondensates is not limited but preferably about 3.0 × 10 3 ∼about 1.0 × 10 5 , more preferably about 5.0 × 10 3 ∼ about 5.0 × 10 4 . It is preferable that the ink receiving layer contain at least 0.1 wt %, more preferably 1 to 50 wt %, most preferably 3 to 30 wt % of dialkylamine · epichlorohydrin polycondensate. Furthermore, for the purpose of ink fixing, there may be added thereto a cationic substance such as polyvinyl pyridine, polydialkyl aminoethyl methacrylate, polydialkyl aminoethyl acrylate, polydialkyl aminoethyl methacrylamide, polydialkyl aminoethyl acrylamide, polyepoxy amine, polyamideamine, dicyanediamide • formalin condensate, dicyanediamide polyalkyl • polyalkylene polyamine condensate, polydiallyldimethylammonium chloride, polyvinyl amine, polyallylamine, acrylamide • diallylamine hydrochloric acid copolymer and modified product thereof. It is also possible to use, if necessary, a pigment dispersant, a thickening agent, an anti-foaming agent, a foam-inhibitor, a foaming agent, a releasing agent, a penetrating agent, a wetting agent, a thermal gelling agent, a lubricant and/or other various kinds of auxiliary agents known in the art. The means for applying an ink-receiving layer to the base material for paper may be appropriately be selected from those usually employed such as size press, gate roll, roll coater, bar coater, air-knife coater, rod blade coater and blade coater. A heat-sensitive recording ability is imparted to the side opposite to the side to which the ink jet recording ability is imparted. The heat-sensitive recording in general comprises the steps of heating a heat-sensitive recording layer, which mainly comprises a colorless or pale colored leuco dye and a developer, which can cause the coloration of the dye upon heating, through a heating head to thus cause a reaction between the leuco dye and the developer and to thus perform recording through the coloration of the dye. Such a method has suitably been used in, for instance, various kinds of printers and facsimiles, since the maintenance of these apparatuses is quite easy. Moreover, the heat-sensitive recording is not limited in the relative positions of the recording head and the recording layer, unlike the ink jet recording system and thus, the device can be miniaturized. As the leuco dyes to be incorporated into the heat-sensitive recording layer, there may be listed, for instance, triphenylmethane type, fluoran type and diphenylmethane type compounds and can be selected from those conventionally known in this art. For instance, the leuco dye may be at least one member selected from the group consisting of 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, Crystal Violet Lactone, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(o,p-dimethylanilino) fluoran, 3-(N-ethyl-N-p-toluidino)-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-7-(o-chloroanilino) fluoran, 3-diethylamino-7-(m-trifluoromethylanilino) fluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6-methylfluoran, 3-cyclohexylamino-6-chlorofluoran, 3-(N-ethyl-N-cyclohexyl)-6-methyl-7-(p-chloroanilino) fluoran, and 3-butylamino-7-(o-chloroanilino) fluoran. The developer to be incorporated into the heat-sensitive recording layer may be, for instance, at least one member selected from the group consisting of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl)-1-phenylethane, 1,4-bis (1-methyl-1-(4'-hydroxyphenyl) ethyl) benzene, 1,3-bis (1-methyl-1-(4'-hydroxyphenyl) ethyl) benzene, dihydroxy diphenyl ether, benzyl p-hydroxy benzoate, bisphenol S, 4-hydroxy-4'-isopropyloxy diphenyl sulfone, 1,1-di-(4-hydroxyphenyl) cyclohexane, 1,7-di-(4-hydroxyphenylthio)-3,5-dioxaheptane, 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone, N-(p-toluenesulfonyl)-N'-phenyl urea, N-(p-toluenesulfonyl)-N'-(p-methoxyphenyl) urea, N-(p-toluenesulfonyl)-N'-(o-tolyl) urea, N-(p-toluenesulfonyl)-N'-(m-tolyl) urea, N-(p-toluenesulfonyl)-N'-(p-tolyl) urea, N-(p-toluenesulfonyl)-N'-benzyl urea, 4,4'-bis (p-toluenesulfonylaminocarbonylamino)-diphenyl methane, 4,4'-bis (o-toluenesulfonylaminocarbonylamino)-diphenyl methane, 4,4'-bis (benzenesulfonylaminocarbonylamino)-diphenyl methane, 1,2-bis [4'-(p-toluenesulfonylaminocarbonylamino) phenyloxy] ethane, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenyl ether and 3,3'-bis (p-toluenesulfonylaminocarbonylamino) diphenyl sulfone. There can be also used organic acid substances, for example, phenol compounds such as 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxyphenylsulfide, hydroguinone monobenzylether, 2,4'-dihydroxybenzophenone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 2,4-bis(phenylsulphonyl) phenol, bis(p-hydroxyphenyl) methyl acetate, 1,4-bis[ α -methyl- α -(4'-hydroxyphenyl) ethyl]benzene, 1,3-bis[ α -methyl- α -(4'-hydroxyphenyl) ethyl]benzene, di(4-hydroxy-3-methylphenyl) sulfide, 2,2'-thiobis(3-tert-octyl phenol); thiourea comounds such as N,N'-di-m-chlorophenyl thiourea; compounds having a SO 2 NH-bond in their molecule such as N-(p-trylsulfonyl) carbamoic acid p-cmylphenyl ester, N-(p-trylsulfonyl) carbamoic acid p-benzyloxyphenyl ester, N-(o-toruoyl)-p-torylsulfonamide; zinc aromatic carboxylates such as zinc p-chlorobenzoate, zinc 4-[2-(P-methoxyphenoxy)ethyloxy] salicylate, zinc 4-[3-(tolylsulfonyl) propyloxy] salicylate, zinc 5-[p-(2-p-methoxyphenoxyethoxy) cmyl] salicylate; and inorganic acid substances such as activated clay, attapulgite and aluminum silicate. Among these, preferred are compounds having sulfonyl group in their molecule such as 4-hydroxy-4'-isopropyloxy diphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 2,4-bis(phenylsulfonyl) phenol, N-(p-trylsulfonyl) carbamoic acid p-cmylphenylester, N-(p-trylsulfonyl) carbamoic acid p-benzyloxyphenyl ester, N-(o-toluoyl)-p-torylsulfonamide, N-(p-toluenesulfonyl)-N'-(p-tolyl) urea. In particular, 4-hydroxy-4'-isopropyloxy diphenyl sulfone and 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone are preferable since storability and recording sensitivity of heat sensitive recording portion becomes good by use of one of these. A ratio of leuco dye and developer is optimally determined based on the kind of the using leuco dye and developer, and is not limited. However, it is preferable that the weight ratio of leuco dye to developer be 1:1 to 1:10, more preferably 1:2 to 1:6. In addition, binders usable herein are, for instance, polyvinyl alcohols having a variety of molecular weights; starch and derivatives thereof; cellulose derivatives such as methoxy cellulose, carboxymethyl cellulose, methyl cellulose and ethyl cellulose; water-soluble polymer materials such as sodium polyacrylate, polyvinyl pyrrolidone, acrylic acid amide/acrylic acid ester copolymers, acrylic acid amide/acrylic acid ester/methacrylic acid terpolymers, alkali salts of styrene/maleic anhydride copolymers, polyacrylamide, sodium alginate, gelatin and casein; and latexes such as polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer, and styrene/butadiene/acrylic copolymers. Moreover, the heat-sensitive recording layer may comprise heat-fusible substance (so-called sensitizer) in combination with the foregoing components. The sensitizers usable herein may be heat-fusible organic compounds having a melting point ranging from 50 to 150°C and specific examples thereof include 1-hydroxy-2-naphthoic acid phenyl ester, benzyl naphthyl ether, dibenzyl terephthalate, benzyl p-benzyloxy benzoate, diphenyl carbonate, ditolyl carbonate, m-terphenyl, 1,2-bis (phenoxy) ethane, 1,2-bis (m-tolyloxy) ethane, 1,5-bis (p-methoxyphenoxy)-3-oxapentane, oxalic acid diesters, 1,4-bis (p-tolyloxy) benzene, benzene-sulfoanilide, 2-chloroacetoacetoanilide, 4-ethoxymethylsulfonyl benzene, 4-methoxy acetoacetoanilide, o-methyl acetoanilide, 4-methoxybenzene sulfoanilide, 3,4-dimethyl acetoanilide and 2-methoxybenzene sulfoanilide. Furthermore, the heat-sensitive recording layer of the present invention may likewise comprise a pigment and/or waxes. Such pigments may be, for instance, inorganic fine powder such as calcium carbonate, silica, zinc carbonate, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated calcium carbonate and silica; and organic fine powder such as urea-formalin resin, styrene/methacrylic acid copolymer and polystyrene resin. Among these, preferred are oil-absorptive pigments whose oil absorption is not less than 70 ml/100 g. The waxes usable herein may be, for instance, known ones such as paraffins, amide type waxes, bisimide type waxes, and metal salts of higher fatty acids. Further the heat-sensitive recording layer according to the present invention may if necessary comprise a storage stabilizer, a coloring agent and/or other auxiliary agents. A primer coating layer may be arranged below the heat-sensitive recording layer in order to improve the sensitivity of the recording layer and to prevent any formation of scum on the printer head and it is also possible to apply a protective layer on the heat-sensitive recording layer for the purpose of improving the storability and printability of the resulting recording medium. The printer used in the present invention is preferably one that possesses two recording units, i.e., an ink jet recording unit and a heat-sensitive recording unit. Each of these recording units may be a usual separate recording unit. More specifically, the ink jet recording unit may be a commercially available usual recording unit for the ink jet printer and the heat-sensitive recording unit may likewise be the usual recording unit for the heat-sensitive recording printer. That is, they are not necessarily specially designed ones, respectively. In this respect, however, the head of the heat-sensitive recording unit is desirably arranged upwardly or faces sideways and further the heat-sensitive recording unit is preferably positioned in front of the ink jet recording unit. This is because if the heat-sensitive recording unit faces downward, it is necessary to have the recording paper turned inside out for the ink jet recording, for the reason described above. If the ink jet recording unit is positioned in front of the heat-sensitive recording unit, the heat-sensitive recording is carried out after the ink jet recording operations. In case of heat-sensitive recording, it is necessary to arrange a platen roll at the position against which the head of the recording unit is pressed and the nipping of the recording paper immediately after the ink jet recording between the platen roll and the head of the heat-sensitive unit may cause contamination of the platen roll with the undried ink on the paper. In addition, if the recording paper gets swollen as it absorbs water-based ink and as a result, the surface thereof is not smooth, the paper may, for instance, wrinkle. The recording heads of the both ink jet and heat-sensitive recording units may be a serial head or a line head, with the line head being desirable for high-speed recording operations. The ink jet recording unit of the printer used in the present invention may be one similar to those of the presently commercially available ink jet printers, as has been discussed above. The recording head may be either a serial head or a line head, with the line head being preferred for high-speed recording operations. Moreover, the ink used is not limited to any specific one. The water-based ink used in the present invention comprises, as a dye, at least one member selected from the group consisting of water-soluble direct dyes, water-soluble acid dyes and colored pigments and other optional components such as a wetting agent, a dye-solubilizing agent, an antiseptic and/or an anti-fungus agent. Examples of water-soluble direct dyes include, but are not limited to, CI. Direct Black, CI. Direct Yellow, CI. Direct Blue, and Ci. Direct Red and examples of water-soluble acid dyes include, but are not limited to, CI. Acid Black, CI. Acid Yellow, CI. Acid Blue, and CI. Acid Red. As the wetting agents and dye-solubilizing agents, there may be listed, for instance, alcohols and derivatives thereof such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol and glycerin; nitrogen atom-containing compounds such as formamide, dimethyl acetamide and N-methyl-2-pyrrolidone; and sulfur atom-containing compounds such as dimethyl sulfoxide and sulfolane. In these compounds, substances capable of inducing color development of the heat-sensitive recording layer may be included and therefore, the wetting agent, dye-solubilizing agent or the like present in the ink penetrate into the heat-sensitive recording layer to thus induce the color development of the recording layer and, in turn, sometimes results in the so-called phenomenon: fog, if the base material is susceptible, to the penetration of the foregoing components of the ink. In addition, some of the components of the ink such as the wetting agent and the dye-solubilizing agent may induce the discoloration of the color-developed portion of the heat-sensitive recording layer and thus they may often induce the discoloration of images developed on the heat-sensitive recording layer. Therefore, it is necessary to inhibit any penetration of the solvents for these wetting agent and dye-solubilizing agent or the like into the heat-sensitive recording layer. If adjusting the time required for a 10% polyethylene glycol aqueous solution dropped on the side to which the ink jet recording ability is imparted to penetrate into the side to which the heat-sensitive recording ability is imparted to not less than 30 seconds, any penetration of the solvent can substantially be inhibited. The time is preferably not less than 35 seconds. The complete inhibition of the penetration of the solvent is not attended any adverse effect and therefore, the upper limit of the time is not important and is not, therefore, particularly specified. A 10% polyethylene glycol aqueous solution (0.5 ml) is dropwise added to the side to which the ink jet recording ability is imparted using a micro-syringe, followed by observing the droplet from the side of the heat-sensitive recording layer and then determining the time required till three transparent spots appear. The time is defined to be its resistance to solvent-permeation. To control the penetration time to a level of not less than 30 seconds, there can be used various means such as an increase in the thickness of the base material (basis weight is preferably 30 to 300 g/m 2 ), improvement of the degree of sizing, and appropriate selection of the kind and amount of the resin incorporated into the ink-receiving layer (the first embodiment of the present invention). Alternatively, it is also possible to use a base material free of any solvent-penetration, but such a recording medium may cause bleeding. However, in cases of using a base material having a basis weight of about 50 to 200 g/m 2 , said penetrating time can be controlled in 30 seconds or more by adjusting the Stockigt sizing degree (specified by JIS P 8122) of the base paper to 30 seconds or more. Alternatively, it is also possible to control penetrating time in 30 seconds or more by adjusting the oil absorption of pigment contained in the ink jet receiving layer to the range of 80 to 300 cc/100 g (JIS K 5101) and using the pigment contained in the layer in an amount of 70 wt % or less. The present invention positions or arranges an intermediate layer free of any solvent-penetration between the heat-sensitive recording layer and the base material. If the intermediate layer is arranged between the ink jet recording layer and the substrate, the resulting recording medium often has a reduced ink jet ink-absorptive capacity and accordingly, ink jet-recorded images may be accompanied by bleeding. For this reason, the intermediate layer is between the substrate and the heat-sensitive recording layer in the recording medium of the present invention. The resin included in the intermediate layer may be appropriately selected from those.known ones, for instance, aqueous solutions or aqueous dispersions of, for instance, starch and derivatives thereof; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; naturally occurring or semisynthetic polymers such as casein, gelatin and soybean protein; polyvinyl alcohol derivatives such as polyvinyl alcohol, silyl-modified polyvinyl alcohol and cation-modified polyvinyl alcohol; vinylic copolymer resins such as polyvinyl butyral resin, polyethyleneimine type resin, polyvinyl pyrrolidone type resin, poly(meth)acrylic resin, acrylic acid ester type resin, polyamide type resin, polyacrylamide type resin, polyester resin, urea resin, melamine resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer and ethylene-vinyl acetate copolymer; or modified polymers such as those obtained by introducing anionic or cationic residues into the foregoing resins. Among these, those excellent in the solvent-penetration-inhibitory effect are polyvinyl butyral resin, styrene-butadiene copolymer and polyvinyl alcohols, preferably having an average degree of polymerization of not less than 500 and they can preferably be used in the invention. The intermediate layer of the present invention may if necessary comprise a pigment and examples thereof usable herein are inorganic pigments such as calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, white carbon, alumina and aluminum hydroxide; and organic pigments such as styrenic, acrylic, urea resin type, melamine resin type and benzoguanamine resin type pigments. The amount of the intermediate layer to be applied ranges, in terms of the weight of the solid content, from 2 to 15 g/m 2 , preferably 4 to 8 g/m 2 . This is because if the coated amount is less than 2 g/m 2 , it is difficult to achieve the intended effect of inhibiting solvent-penetration, while if the amount exceeds 15 g/m 2 , the resistance to solvent-penetration is satisfied, but the resulting recording medium is often unfavorable from the viewpoint of recording operations or preparation operations and production cost. In cases of using the intermediate layer, it is preferable that the base paper have a basis weight of 30 to 300 g/m 2 , more preferably 50 to 250 g/m 2 . In cases of using the intermediate layer, there can be obtain advantages in that it is not necessary to adjust the sizing degree of the base paper or the oil absorption of pigment contained in the ink jet recording layer. In this connection, the Stockigt sizing degree of the base paper may be 30 seconds or less, and it is preferable that the oil absorption of the ink jet recording layer be in the range of about 200 to 350. The application of a resin-containing protective layer onto the heat-sensitive recording layer would serve to inhibit any possible adverse effect of the ink, present on the ink jet recording layer on the neighboring heat-sensitive recording layer even when the recording mediums are put in layers after recording operations. Preferably, an acetoacetyl-modified polyvinyl alcohol or a polyvinyl alcohol, more preferably having an average degree of polymerization of not less than 500 is incorporated into the protective layer. This permits the achievement of quite excellent resistance to ink jet ink and therefore, the heat-sensitive recording layer is never adversely affected by the high-speed double-side recording operations. If the recording mediums are put in layers immediately after recording mediums are subjected to ink jet recording operations, the ink solvent may sometimes undergo the inter-recording medium transfer from the surface of the ink jet recording layer to that of the heat-sensitive recording layer and this would leads to graying of the heat-sensitive recording layer and/or discoloration of recorded images. In particular, if the recording medium is set on a recording apparatus in the form of a roll and then wound up in a roll immediately after ink jet recording operations, the heat-sensitive recording layer undergoes conspicuous graying and/or discoloration. To prevent such graying and discoloration due to the action of the ink solvent, it is quite effective to apply a protective layer onto the heat-sensitive recording layer. Materials effective for use as such a protective layer include, for instance, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; casein; gum arabic; starches such as oxidized starch, etherified starch, dialdehyde starch and esterified starch; completely or partially saponified polyvinyl alcohol; polyvinyl alcohols or those modified with a variety of functional groups such as acetoacetyl-modified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol and silicon-modified polyvinyl alcohol, with acetoacetyl-modified polyvinyl alcohol and polyvinyl alcohol, preferably having an average degree of polymerization of not less than 500 being most preferred. Furthermore, preferred is a polyvinyl alcohols selected from the group consisting of acetoacetyl-modified polyvinyl alcohols, carboxyl-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, and polyvinyl alcohol. Moreover, to improve the ink solvent transfer-inhibitory effect, a curing agent may be incorporated into the coating solution for forming a protective layer. As such curing agents, there may be listed, for instance, glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, alum and ammonium chloride. To further improve the printability and sticking properties, a pigment may if necessary be added to the protective layer. Specific examples of such pigments are inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined kaolin and colloidal silica; and organic pigments such as styrene micro-balls, nylon powder, polyethylene powder, urea-formalin resin filler and raw starch particles. Moreover, the protective layer may if necessary comprise various kinds of auxiliary agents, for instance, a lubricant such as zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax or ester wax; a surfactant such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium salt of lauryl alcohol sulfate, alginic acid salts or metal salts of fatty acids; a UV absorber such as benzophenone type or triazole type one; an anti-foaming agent, a fluorescent dye, and/or a colored dye. The amount of the protective layer to be applied ranges, in terms of the solid content, from 0.1 to 10 g/m 2 and preferably 0.5 to 5 g/m 2 . This is because if it is less than 0.1 g/m 2 , the intended effect, i.e., the resistance to solvent-penetration is insufficient, while if it exceeds 10 g/m 2 , the resulting recording medium may cause a decrease in the sensitivity upon heat-sensitive recording operations. Incidentally, the recording medium of the present invention can be used not only for the simultaneous high-speed ink jet recording and heat-sensitive recording, but also in the recording operations wherein an ink jet printer and a heat-sensitive printer are used independently. In this connection, the recording medium of the present invention can be used as papers for ballot, tickets, tags, papers for printer, postcards, paper for various forms, cards, postal matters and the likes. For example, words or marks are, in advance, printed on the surface of ink jet recording layers of the recording medium of the present invention and then figures or other marks are printed on the surface of heat sensitive layer. As has been discussed above in detail, the recording medium of the present invention permits high-speed double-side recording and at least one side of the recording medium is favorable for color ink jet recording, while the other side has a heat-sensitive recording ability. The recording medium of the present invention is one that permits both ink jet recording and heat-sensitive recording. The medium never causes any bleeding on the ink jet recording side, any graying of the heat-sensitive recording layer due to the action of the solvent present in the ink jet ink and never undergoes any discoloration of the printed matter on the heat-sensitive recording layer.

Claims: A double-side recording medium which comprises a base material for paper mainly comprising pulp, one side of which has an ink jet receiving layer and the other side of which has a heat-sensitive recording layer containing a leuco dye and a developer, wherein (i) an intermediate layer containing a resin is arranged between the base material for paper and the heat-sensitive recording layer and (ii) the ink jet receiving layer contains dialkylamine • epichlorohydrin polycondensate. The double-side recording medium of claim 1, wherein the base material has a basis weight of between 50 and 300 g/m 2 . The double-side recording medium of claim 1, wherein the base material has a basis weight of between 50 and 100 g/m 2 The double-side recording medium of claim 1, wherein the base material has a binder contained therein and the Stockigt sizing degree of the base material is 30 seconds or more. The double-side recording medium of claim 1, wherein the resin included in the intermediate layer comprises one member selected from the group consisting of polyvinyl alcohol, silyl-modified polyvinyl alcohol, polyvinyl butyral resins, polyvinyl pyrrolidone, styrene-butadiene copolymers, carboxymethyl cellulose and starch. The double-side recording medium of claim 1, wherein the weight of the solid content of the intermediate layer is in the range 2 to 15 g/m 2 . The double-side recording medium of claim 1, wherein a protective layer containing a resin is formed on the heat-sensitive recording layer. The double-side recording medium of claim 7, wherein the resin included in the protective layer comprises a polyvinyl alcohol selected from the group consisting of acetoacetyl-modifled polyvinyl alcohols, carboxyl-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, olefin-modifled polyvinyl alcohol, nitrile-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, and polyvinyl alcohol. The double-side recording medium of claim 7, wherein the weight of the solid content of the protective layer is in the range 0.1 to 10 g/m 2 .

Inventors: ISHIDA KOICHI, KONDO HIROMASA, KORO TAKAAKI, MANDO RITSUO, NISHIMURA MASAKI, SUZUKI HIDEYUKI, ISHIDA, KOICHI, KONDO, HIROMASA, KORO, TAKAAKI, MANDO, RITSUO, NISHIMURA, MASAKI, SUZUKI, HIDEYUKI
Applicants: OJI PAPER CO, OJI PAPER CO., LTD.
Application year: 2000
Main classification: B41M3
IPC codes: B41M5, B41M3