FR2805204A1 - Recording sheet or film for use in ink jet printing showing improved image sharpness and color reproduction with improved water-resistance, contains an organic acid with specified water-solubility - Google Patents

Abstract

A recording sheet or film comprises a porous layer containing an organic acid with a solubility of 0.01-2g in 100g water at 20[deg]C.

Description

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 The present invention relates to an image-receiving sheet suitable for ink-jet recording, a method for its production, and a method of recording an image using such a sheet.

 Recently, the ink-jet recording system has been a great success and has been adopted for desktop or personal printers and wide-format printers for banner printing because it is easily applied to the printing industry. production of true color images, it is quiet, gives excellent print quality and is inexpensive. Ink jet printing requires the use of a low drying rate ink so that the ink injection nozzles do not become clogged. In addition, for reasons of security and general recording ability, essentially a water-based ink is used. Ink droplets are projected from an injection nozzle head to a recording sheet, so that it is essential that the sheet rapidly absorbs the ink to record an image.

 For example, in the case of an image receiving sheet having poor ink absorption so that after recording, the ink remains for a long time on the surface of the ink receiving material, without drying or being fixed, and the recorded image is stained because its own ink is in contact with a roll ahead of the recording apparatus or an operator or other sheets placed on it. In addition, in high-density image regions, inks applied in large quantities are not absorbed and mixed together, so that they deteriorate the image quality or recorded characters or inks may flow along. the surface of the image-receiving material.

 Several proposals have been made for the solution of these problems in the prior art. For example, Japanese Patent Laid-open Applications Nos. 174,381 / 1984 and 224,578 / 1985 (JP-A-59-174,381 and JP-A-60-224,578) provide for the formation of a diaper

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 receiving ink on a support using a hydrophilic polymer, such as starch, a water-soluble cellulose derivative and polyvinyl alcohol. Although this image-receiving sheet is satisfactory from the point of view of ink absorption, the water resistance of the ink-receiving layer itself is poor, so that the ink-receptive layer or the recorded regions dissolve in the water, or the surface of the material becomes viscous, thereby causing the sheets to stick together when stacked.

 In addition, Japanese Patent Application Laid-open No. 72,460 / 1991 (JP-B-3-72,460) proposes a method for improving the bond strength, wherein a sheet is made of a surface layer permeable to the ink and an ink-absorbing underlayer. The underlay absorbs the ink so that the surface of the sheet does not stick. However, as the ink passes through the surface layer and is absorbed by the underlayer, this infiltration of the ink deeply into the recording sheet not only makes it difficult to obtain deep colors in the recorded regions, but also causes easy separation of the surface layer and the underlayment at their interface. In addition, the water resistance of the underlayer is also bad.

 The provision of a porous layer on an ink absorption layer has also been proposed so that it can absorb the ink by a capillary phenomenon. For example, Japanese Patent Application Nos. 110 287/1983 and 51 470/1993 (JP-A-58-110 287 and JP-A-5-51 470) provide registration sheets consisting of a support and a porous layer formed thereon, the porous layer being an aggregate of fine particles, for example silica, whose pores are formed by the spaces between the particles. These recording sheets have good ink absorption properties, but have poor transparency or surface gloss properties due to scattering of light by the particles. As a result, these leaves are not suitable

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 to overhead projectors that require slides or for high quality image printing, for example photographs, requiring a very bright surface on the recording material. In addition, their ink absorption capacity is also insufficient. Japanese Patent Application Laid-Open No. 278 417/1998 (JP-A-10-278417) has proposed a recording sheet in which a porous layer is disposed on an ink absorbing layer formed on a medium, but this sheet also does not give satisfaction in the printing of high quality images.

 In addition, Japanese Patent Application Laid-Open No. 233,569 / 2000 (JP-A-2000-233,569) discloses a porous film recording sheet having a three-dimensional network structure made up of parts granular and bonding portions analogous to wires connected thereto, and a water-soluble polycarboxylic acid, such as maleic acid, is incorporated into the porous film and / or an ink-absorbing layer, but the definition of image or sharpness of this recording sheet is still insufficient.

 Japanese Patent Application Laid-open No. 86251/1986 (JP-A-61-86251) proposes a recording sheet composed of an ink absorption layer associated with a thin layer of material. porous plastic.

This thin layer of porous plastic material is formed of a hydrophobic plastic material, such as polyethylene or polypropylene, and the ink permeability of this recording sheet is not sufficient for it to be used in ink jet printing in which a water-based ink is generally used. In addition, since the thin layer of porous plastic is adhered to the ink-absorbing layer by thermocompression, its pores can be crushed or deformed.

 On the other hand, in the case of ink-jet printing of an image on a fabric, such as a fabric, usually an image is printed by ink jets.

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 on the surface of the fabric provided with the aforesaid layer of ink absorption. Alternatively, after an image has been printed on an ink absorbing layer, containing a hot melt adhesive resin, of a recording sheet, the layer is thermally transferred to the fabric. However, these techniques are problematic because the ink absorbing layer soil the texture of the fabric.

 Thus, an object of the invention is to provide an image-receiving sheet having excellent ink-absorbing and stick-resistance properties and having excellent surface gloss, sharpness and color reproducibility of recorded images, as well as a method for its production.

 The invention also relates to an image-receiving sheet having excellent properties not only of ink absorption and stickiness, but also of texture, as well as a process for its production.

 The invention also relates to an image-receiving sheet which imparts an image having excellent water and weather resistance properties, as well as a process for its production.

 The invention also relates to an image-receiving sheet having a suitable adhesion strength between an ink-receptive layer and a substrate, as well as excellent dissociation properties, as well as a process for its production.

 The invention also relates to a method of forming a recorded image with excellent properties of sharpness and color reproducibility.

 The inventors have devoted extensive and extensive studies to solving the aforementioned problems and have finally discovered that the incorporation of a particular organic acid into a porous layer of an image-receiving sheet made of the porous layer significantly increases not only the absorption and bonding properties of the image-bearing material, but also the surface gloss and

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 sharpness of recorded images. The invention was carried out on the basis of this discovery.

Thus, the image-receiving sheet according to the invention comprises at least one porous layer which contains an organic acid whose solubility is between 0.01 and 2 g per 100 g of water at 20 ° C. The receiving sheet of image may be a laminate composed of a substrate and a porous layer placed on at least one side of the substrate, or may consist of a porous support. It is preferable to use as organic acid an aromatic polycarboxylic acid, especially an aromatic dicarboxylic acid. The average pore size of the porous layer is about 0.005 to 10 m. The image-receiving sheet may have a porous layer formed of a hydrophilic polymer (particularly a cellulosic derivative, a polymer of the series of vinyl products, and a polymer of the series of polysulfones), on at least one side of the substrate. In the case where the porous layer contains the organic acid, the proportion of acid per 100 parts by weight of the hydrophilic polymer is about 1 to 100 parts by weight and preferably about 2 to 100 parts by weight. . The porous layer may be separable from the substrate, and the adhesion strength between the porous layer and the substrate may be from about 0.01 to 4.9 N / 15 mm. The image-receiving sheet, after printing, can correspond to the following formula (1):
Fp - Fn # <1.47 N / 15 mm Fn being the adhesion strength between the porous layer and the substrate in a region having no image and Fp being this resistance in the region bearing the image.

 The image-receiving sheet described above may be of a type composed of a porous support which is itself used as a porous layer, on at least one side of which the organic acid may be applied. The amount of organic acid applied thereto, as determined on the solids, is usually about 0.05 g / m 2 and more, and preferably about 0.05 to 1 g / m 2. The porous support can

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 be a porous plastic sheet or fabric (for example a fabric or a nonwoven fabric).

 The invention also relates to a method for producing an image-receiving sheet comprising at least one porous layer, wherein an organic acid having a solubility of between 0.01 and 2 g in 100 g of water at 20 ° C. is incorporated in the porous layer of the image-receiving sheet. In this method of manufacture, the porous layer may be formed by coating a doping agent containing a hydrophilic polymer, good and bad solvents of the hydrophilic polymer, and the aforementioned organic acid, on at least one side of the sheet of the substrate, the resulting layer being then subjected to a phase conversion.

Alternatively, the method comprises forming the porous layer by depositing a doping agent containing a hydrophilic polymer and the hydrophilic polymer on at least one side of a substrate sheet, applying to the resulting layer of a phase conversion, the deposition on the phase-converted layer of a coating agent containing the aforementioned organic acid, and the extraction of the solvent from the coating agent. In addition, the organic acid having the aforementioned solubility can be applied (by coating or dipping) on at least one side of the porous support.

 The invention also relates to a method of forming an image to be recorded in which the image (in particular an image printed with a water-based ink) is recorded on the porous layer of the image-receiving sheet (a material of in which the porous layer is formed on at least one side of a substrate), then the porous layer is separated from the substrate, and a method in which an image is recorded on the porous layer of the receiving sheet. In the abovementioned image, a cover sheet is bonded to the porous layer and the cover sheet and the porous layer are separated from the substrate or dissociated.

 The image-receiving sheet according to the invention must only comprise at least one porous sheet. By

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 for example, the image-receiving sheet according to the invention may be a laminate comprising a substrate and a porous layer placed on at least one side of the substrate, or may consist of a porous substrate.

Laminate substrate
The substrate material is not subject to any particular restriction. Examples of substrates are paper, coated paper, synthetic paper, nonwoven, and plastic films or sheets, although the substrate used is preferably paper, coated paper or a film or sheet of plastic material, for reasons of mechanical strength and convenience in practice.

 Examples of paper and coated paper are woodfree paper, "Kent" paper and drawing paper.

 Examples of the polymer constituting the synthetic paper or plastic film or sheet are olefinic polymers (eg polypropylene), halogen-containing polymers (eg polyvinyl chloride), styrene resins (e.g. polystyrene, rubber-reinforced polystyrene, ABS resins), cellulosic resins (cellulose derivatives, such as cellulose acetate), polyester resins (such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate), polycarbonate series resins (for example a bisphenol-A-based polycarbonate), and polyamide series resins (for example, polyamides). aromatic compounds such as "nylon 6"). Copolymers, mixtures and corresponding crosslinked products may also be used. Among them, and for reasons of, for example, mechanical strength and convenience of use, it is preferable to use the resins of the series of polyesters, especially polyalkylene arylate series resins such as polyethylene terephthalate. Such resins may be used alone or in combination, or in the form of a single layer film or a laminated film.

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 If desired, an antioxidant, a heat stabilizer, a lubricant, a pigment, an ultraviolet absorbing agent and other adjuvants may be added to the plastic film or sheet. In addition, the substrate may be subjected to discharge treatment by corona discharge or by application of an undercoat so that the adhesion of the porous layer is better.

 If it is considered that the production of an image usually involves inserting the resulting recording material into an inkjet printer, the thickness of the substrate should be, for example, about 20 to 200 m and preferably about 50 to 170 m, and most preferably about 80 to 150 m.

Porous layer of laminate
The porous layer-forming polymer is not subject to any particular restrictions, since the resulting porous layer provides high wettability to the ink, and various resins (thermoplastics or thermosets) can be used. A thermoplastic resin is usually used. The following resins and polymers are examples of thermoplastic resins.

(1) Cellulosic resins (derived from cellulose)
Cellulose esters [e.g. organic acid esters, such as cellulose acetate, propionate, butyrate, acetopropionate and acetobutyrate, esters of mineral acid, such as nitrate, sulfate or cellulose phosphate, and mixed acid esters, such as cellulose acetate nitrate]
Cellulose ethers [eg methylcellulose, ethylcellulose, isopropylcellulose, butylcellulose, benzylcellulose, hydroxyethylcellulose, carboxymethylcellulose, carboxyethylcellulose, cyanoethylcellulose] (2) Polymers of the vinyl series
Olefinic polymers [e.g. homopolymers or copolymers of olefins (for example polyethylene, polypropylene, poly-1-butene, polyisobutene, polybutadiene, polyisoprene, polyallene, copolymer

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ethylene-propylene), copolymers of olefins with copolymerizable monomers (for example a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and an ester of acrylic or methacrylic acid, and modified polyolefins)]
Halogen-containing vinyl polymers [for example homopolymers or copolymers of vinyl monomers containing halogen (eg polyvinyl chloride), copolymers of vinyl monomers containing halogen with copolymerizable monomers (for example a copolymer of vinyl chloride and vinyl acetate, a copolymer of vinylidene chloride and vinyl acetate, a copolymer of vinylidene chloride and acrylic or methacrylic acid, and a copolymer of vinylidene chloride and an acrylic acid ester or methacrylic)]
Polymers of the series of vinyl esters and their derivatives [for example vinyl acetate, polyvinyl alcohol, a copolymer of ethylene and vinyl alcohol, polymers of the series of polyvinyl acetals (for example formai, acetal or polyvinyl butyral)]
Polymers of the heterocyclic vinyl series [for example polyvinylpyrrolidone and polyvinylpyridine]
Polymers of the aromatic vinyl series [eg styrene polymers (eg polystyrene, rubber-reinforced polystyrene, ABS resins), copolymers of vinyl aromatic monomers with copolymerizable monomers (for example copolymers of styrene and alkyl methacrylate having 1 to 10 carbon atoms, a copolymer of styrene and maleic anhydride or a copolymer of styrene and maleimide)]
Polymers of the allylic alcohols series (for example copolymers of allyl alcohol and of an alkylvinyl ether having 1 to 6 carbon atoms)
Polyvinyl ketones [for example polyvinyl methyl ketone, polyvinyl methyl isobutyl ketone, and polymethyl isopropenyl ketone]

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Polymers of the vinyl ether series [e.g. polymethylvinylether, and a copolymer of methylvinylether and maleic anhydride]
Acrylic or methacrylic polymers [for example homopolymers or copolymers of acrylic or methacrylic monomers (for example acrylonitrile and methacrylonitrile, acrylate and methacrylate monomers), copolymers of acrylic or methacrylic monomers with copolymerizable monomers ( monomers of the vinyl series such as monomers of the vinyl ester series, monomers of the heterocyclic vinyl series such as vinylpyrrolidone, vinyl aromatic monomers, polymerizable unsaturated dicarboxylic acids and derivatives thereof]] (3) Polymers of the series polysulfones
Polysulfones (for example polyhexamethylenesulfone), sulfonated polysulfone, polyethersulphone, polymers having the -SO2- linking group in their molecule (4) Polymers of the series of polyesters
Polyalkylene terephthalates (for example homopolyesters and copolyesters, containing 1,4-cyclohexanedimethylene terephthalate, ethylene terephthalate or butylene terephthalate), polyalkylene naphthalates (for example homopolymers and copolymers of esters containing ethylene or butylene naphthalate), and others (5) Polymers of the polyamide series
Aliphatic polyamides (eg "nylon" 6,66, 610,612, 11 and 12) (6) Polymers of the polycarbonate series
Polymers which can be obtained by reaction between a dihydroxy compound, such as 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) and phosgene or a carbonic diester such as dimethyl carbonate

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(7) Polymers of the polyurethane series
Polymers which can be obtained by reaction between a polyisocyanate, such as tolylene diisocyanate, with a polyol, such as a polyethylene glycol (8) Polymers derived from epoxides
Polyalkyleneglycol (for example polyethylene glycol, polypropylene glycol) and epoxy resins (for example epoxy resins of the ether series, such as bisphenol-based epoxy resins and epoxy resins of the novolac series, and epoxy resins from the amines series)
These polymers can be used alone or in combination.

 The polymer constituting the porous layer is not subject to particular restrictions insofar as the wettability of the surface of the layer or pores vis-à-vis the ink is high, and the polymer is selected depending on the type of the ink to use. The inks used in general are water based. In this case, among the stated polymers, the hydrophilic polymers are particularly advantageous. On the other hand, the polymers to which the expression "hydrophilic polymers" refers are those having a contact angle with water of less than 80 (preferably about 0 to 60 and in particular about 0 to 40). Assuming a drop of water is placed on the surface of the polymer at room temperature, the contact angle is that of the angles separated by the tangent to the surface of the water at the point where the drop of water water stops spreading with the intersection of the polymer surface, which is on the side of the drop of water.

 Examples of such hydrophilic polymers are cellulosic derivatives [eg cellulosic esters such as cellulose acetate (eg cellulose diacetate, cellulose triacetate), cellulose propionate and cellulose nitrate, and cellulose ethers). such as ethylcellulose], polymers of the vinyl series [e.g. acrylic and methacrylic polymers and acrylates and methacrylates such as

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 polymethyl methacrylate, polyacrylonitrile, copolymers of acrylonitrile and vinylpyrrolidone (for example copolymers having an acrylonitrile content of between about 50 and 99.9%), polyacrylamide, poly-N-methylacrylamide], polyvinylpyrrolidone, polymers of the series of vinyl ethers (such as polymethylvinylether, methylvinylether and maleic anhydride copolymer), polymers of the vinyl acetate series and their derivatives (for example polyvinyl acetate and its products partially saponified polyvinyl alcohol, a copolymer of ethylene and vinyl acetate and its partially saponified products), polymers of the polysulfone series (for example polysulfone, polyethersulfone), polyethylene glycol, polyethyleneimine, polyamide and a copolymer of styrene and maleic anhydride. Among these, cellulose derivatives, polymers of the vinyl series and polymers of the polysulfone series are particularly advantageous.

 Although polytetrafluoroethylene, polyethylene and polystyrene are hydrophobic according to the definition indicated above, they can be incorporated into the polymers considered hydrophilic according to the invention when their surface is rendered hydrophilic by addition or coating, for example by a surfactant. or a wetting agent, or by plasma treatment.

 The porous layer may have separation or peelability properties to facilitate separation of the porous layer from the substrate. In addition, a release agent, intended to increase the possibilities of separation or peelability, can be added to the porous layer.

 Mention may be made, for example, as separating or demolding agent, of silicone compounds (for example a silicone oil, a silicone resin, a polyorganosiloxane having a polyoxyalkylene unit), higher fatty acids and their salts, higher fatty acids, waxes (for example a vegetable wax, such as carnauba wax, an animal wax such as lanolin,

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 paraffin such as paraffin wax and polyethylene wax) and fluorine-containing compounds (e.g., a fluorinated oil or polytetrafluoroethylene). These release or separation agents can be used in the form of emulsions, alone or in combination.

 The amount of demoulding agent used, per 100 parts by weight of polymer constituting the porous layer, is, for example, between 0.01 and 10 parts by weight and preferably between approximately 0.01 and 5 parts by weight (especially between 0.1 and 2 parts), determined on solids.

 Fine particles can be incorporated into the porous layer to increase its possibilities of separation. Examples of the powder are mineral powders (for example mineral powders such as silica, calcium silicate, aluminum silicate, magnesium silicate, zeolites, magnesium aluminosilicates, diatomaceous earth, earth calcined diatomaceous earth, magnesium carbonate, alumina, silica, talc, kaolin, kaolin, clay, zinc oxide, heavy calcium carbonate, light calcium carbonate, carbonate magnesium, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, calcium sulfate, barium sulfate, sericite, bentonite and smectite) and organic powders (For example, crosslinked or non-crosslinked organic powders or finely divided hollow particles of polystyrene resin, acrylic resin, urea resin, melamine resin and benzoguanamine resin). These powders can be used alone or in combination. The average particle size of the powder is about 1 to 30 m, and preferably about 2 to 25 m (for example 2 to 20 m), usually 5 to 25 m (for example 10 to 25 m) .

 The amount of fine particles to be used is, for example, from about 0.05 to 10 parts by weight, preferably from about 0.1 to 5 parts by weight and most preferably from about 0.15 to 3 parts by weight, determined on the

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 solids per 100 parts by weight of the polymer constituting the porous layer.

 According to the invention, the porous layer is separable from the substrate. Depending on the intended application, the adhesion strength between the porous layer and the substrate is preferably selected in the range of about 0.01 to 4.9 N / 15 mm (for example 0.02 to 4.9 N / 15 mm), preferably about 0.01 to 1.96 N / 15 mm (for example 0.07 to 1.96 N / 15 mm), very advantageously about 0.02 to 1.47 N / 15 mm (for example 0.02 to 1.37 N / 15 mm), and usually about 0.03 to 0.98 N / 15 mm (for example 0.1 to 0.59 N / 15 mm).

 According to the invention, the image-receiving sheet, after imaging, can correspond to the following formula (1), preferably to the following formula (2) and very advantageously to the following formula (3). In these formulas, the adhesion strength between the porous layer and the substrate in the non-image area is called Fn, and that of the image area is called Fp. The printing conditions of the images are the same as in the ink absorption test of the examples described later.

#Fp - Fnl <1.47 N / 15 mm (1) #Fp - Fnl <1.18 N / 15 mm (2)
Fp - Fnl <0.89 N / 15 mm (3)
The average pore size at the surface and in the porous layer may be selected from about 0.005 to 10 m, preferably from about 0.01 to 8 m, and most preferably from about 0.01 to 5 m (for example 01 and 3 m). An average pore size of less than 0.005 m can give insufficient ink absorption, while an average size greater than 10 tends to degrade water resistance or print quality.

 The degree of porosity also influences the ink absorption capacity of the porous layer. The porosity of the porous layer can be selected from about 40 to 80% and preferably from about 42 to 75%. If the porosity is less than 40%, the possibilities

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 ink absorption of the layer are worse. If it exceeds 80%, the mechanical strength of the porous layer itself is reduced.

 The thickness of the porous layer is not subject to any specific restriction and is selected according to the intended use. The thickness is selected in the range, for example, from about 1 to 100 μm and preferably from about 3 to 50 μm (for example, 5 to 30 μm). If the thickness of the porous layer is less than 1 m, its water resistance is unsatisfactory. If it exceeds 100 m, its properties of transparency, ink absorption or other are deteriorated.

 The porous layer may also contain various conventional adjuvants such as crosslinking, curing, antifoam, increasing coating properties, thickeners, lubricants, stabilizers (eg antioxidants, ultraviolet absorption, stabilization at the heat, stabilizing the light resistance), colorants, pigments, antistatic agents, antiblocking agents, fillers, gelling agents and others.

Porous support
The porous support is not subject to any particular restriction. Examples are porous plastic sheets and fibrous supports.

 The polymer constituting the porous plastic sheet is not subject to any particular restriction as it has high wettability by the ink, and various resins (thermoplastic and thermosetting) can be used. A thermoplastic resin is usually used. Examples of thermoplastic resin are listed in the sections relating to the porous layer, and are for example the polymers of the series of polyesters, the vinyl series, the cellulosic series (cellulose derivatives), the series of polycarbonates, the the polyamide series, the polysulfone series, the polyurethane series and those derived from epoxides.

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 It is also possible to use copolymers, polymer blends and corresponding crosslinked products. Among these, it is preferable to use, for reasons of mechanical strength and workability of the porous support, polymers of the series of polyesters and in particular polymers of the polyalkylene arylate series, for example polyethylene terephthalate. These polymers may be used alone or in combination and in the form of a single layer sheet or laminated where appropriate.

 The porous plastic sheet may be manufactured by a phase separation process in which a polymer is microphase separated with good and bad solvents, a foaming operation in which a polymer constitutes foams for forming pores, stretching operation in which the polymer film is stretched, an irradiating operation in which a polymer film is exposed to radiation for pore formation, an extraction operation in which a film of a polymer or a solvent-soluble organic salt and solvent-insoluble polymer is extracted from the soluble ingredient in the solvent to form pores, a sintering operation in which polymer particles are partially fused or attached by a binder, the spaces between the particles forming pores, or other methods.

 Examples of fibrous support are a fabric (fabric or nonwoven) and a paper. The fibrous support has a shape in which fibers are entangled randomly or orderly. A paper or nonwoven usually has a web structure.

 Insofar as ink absorption is not reduced, the nature (of the material) of the fabric or nonwoven is not particularly restricted, and the fabric or nonwoven may be formed of fibers (eg natural, regenerated, semi-synthetic, synthetic) with a conventional process (for example, in the case of

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 woven, by a process in which fibers are formed into a web and bonded by thermocompression or with the aid of an adhesive or by needling).

 Examples of natural fibers are cotton, linen, silk, wool, and cellulosic fibers. Examples of regenerated fibers are rayon (eg viscous rayon). Examples of semisynthetic fibers are cellulosic ester series fibers (e.g., cellulose acetate fibers) and cellulosic ethers series fibers (e.g., methylcellulose fibers). Examples of synthetic fibers are thermoplastic resins such as polyesters (for example polyethylene or polybutylene terephthalate), acrylic and methacrylic resins (for example polyacrylates and polymethacrylates and polyacrylonitrile), polycarbonates, polyethers, polyether esters, polyamides (for example "nylon" 6 and 66), polyimides, polyamideimides, polyolefins (for example polyethylene and polypropylene), halogenated vinyl resins (for example polyvinyl chloride and chloride). polyvinylidene) and polystyrene, as well as those obtainable from copolymers which are combinations of the constituent units of these resins, their crosslinked products, and mixtures thereof. Fibers are cellulosic ester (for example cellulose acetate), polyester (for example polyethylene terephthalate and polybutylene), polyolefin (for example polyethylene or polypropylene) and polyamide fibers. Polyester fibers are particularly advantageous.

 The weight per unit area of the fabric or nonwoven is, for example, greater than or equal to approximately 50 g / m 2, preferably approximately 100 g / m 2 (for example between 100 and 1000 g / m 2 and preferably between approximately 200 and 800 m 2). g / m2). The average diameter of the fibers is, for example, from about 0.01 to 100 μm and preferably from about 0.1 to 50 μm (especially from 1 to 10 μm). The air permeability is between about

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0.1 and 100 cm3 / cm2 .s and preferably between about 0.1 and 50 cm3 / cm2.
Examples of paper are coated paper (eg woodfree paper, Kent paper or drawing paper) and synthetic paper.

 The average pore size on or in the surface of the porous support may be selected in the range of about 0.005 to 10 m, preferably 0.01 to 8 m, and most preferably 0.01 to 5 m. (for example between 0.01 and 3 m). The average pore size, when it is less than 0.005 m, can give insufficient ink absorption while, when it exceeds 10 m, it tends to cause degradation of the water resistance or the print quality.

 The porosity of the porous support also has an influence on the possibilities of ink absorption or on the absorption itself. The porosity of the porous support can be chosen between about 40 and 80% and preferably between about 42 and 75%. If the porosity of the support is less than 40%, since the absorption area is small, the absorption ability becomes poor, whereas if the porosity exceeds 80%, the mechanical strength of the porous support itself is deteriorated.

 It is considered that the production of an image usually comprises the insertion of the resulting recording material into an ink jet printer, and the thickness of the porous support should then be, for example, about 20 to 200 m, and preferably from about 50 to 170 m and most preferably from about 80 to 150 m.

 The porous support must have at least one porous surface, and it may be formed of a laminate comprising a sheet of paper or plastic as a substrate and a porous layer adhered to the sheet.

 The porous support may also comprise various conventional adjuvants such as crosslinking, hardening, antifoaming agents, increasing coating properties, thickeners, lubricants, stabilizers (eg

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 examples are antioxidants, ultraviolet absorption, heat stabilization, stabilizing the light resistance), dyes, pigments, antistatic agents, anti-scaling agents, fillers, gelling agents and others.

Organic acid
The image-receiving sheet (image-forming material) according to the invention contains an organic acid whose solubility, in 100 g of water at 20 ° C., is between approximately 0.1 and 2 g and preferably between about 0.01 and 1.5 g. The incorporation of this organic acid increases the sharpness (print quality) of the images.

 When the porous layer consists of the aforementioned porous support, the organic acid can be applied to at least one side of the support. The application of the organic acid to the porous support not only increases the sharpness (print quality of the images), but also ensures the production of image-receiving materials of good texture.

 Examples of organic acids are organic polycarboxylic acids (for example organic polycarboxylic acids having 8 to 12 carbon atoms and their anhydrides, such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid terephthalic acid, trimellitic acid and pyrromellitic acid), aromatic sulphonic acids (for example, aromatic sulphonic acids having 6 to 10 carbon atoms, such as benzenesulphonic acid, o-toluenesulphonic acid, m-toluenesulphonic acid, p-toluenesulfonic, naphthalene-α-sulfonic, and naphthalenesulfonic), alicyclic polycarboxylic acids (e.g. alicyclic polycarboxylic acids having 8 to 10 carbon atoms such as 1,4-cyclohexanedicarboxylic acid and tetrahydrophthalic acid), heterocyclic polycarboxylic acids (e.g., pyridinecarboxylic, pyridinetricarboxylic and pyridinetetracarboxylic acids), and aliphatic polycarboxylic acids (such as saturated aliphatic polycarboxylic acids having 2 to 10 carbon atoms, such as

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 glutaric, adipic, suberic and sebacic, and unsaturated aliphatic polycarboxylic acids such as itaconic acid). Among these organic acids, aromatic polycarboxylic acids, especially aromatic dicarboxylic acids (for example phthalic acids such as phthalic acid, phthalic anhydride, isophthalic acid and their derivatives, especially phthalic acid) are preferable.

 The organic acid can be used as a salt, and some or all of the carboxyl or sulfonic acid group can form a salt with a base. Organic acid salts are salts with inorganic bases (eg ammonium or alkali metals, such as potassium and sodium), and salts with organic bases (eg tertiary amine).

 The organic acid may be incorporated in the porous layer or applied to at least one surface of the porous layer. When the porous layer contains the organic acid, the organic acid content, per 100 parts by weight of the hydrophilic polymer, is between about 1 and 100 parts by weight (for example between 2 and 100 parts by weight) and preferably between 5 and 50 parts by weight and very advantageously between 10 and 30 parts by weight approximately.

 In the case where the organic acid is applied to the surface of the porous layer (for example porous support such as a nonwoven), its amount after drying can be about 0.05 g / m 2 or more ( for example between 0.05 and 1 g / m 2) and preferably about 0.1 g / m 2 or more (for example between 0.1 and 1 g / m 2) and very advantageously about 0.2 to 0 , 8 g / m2.

 The organic acid can be used with conventional adjuvants, such as dye-fixing agents, stabilizers (e.g. antioxidants, ultraviolet absorbers, heat stabilizers, light stabilizers) binders (especially water-insoluble hydrophilic resins such as cellulose esters, polyesters,

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 acrylic resins, polyamides, polysulfones, or polyurethanes), coloring agents, antistatic, antifoam, coating enhancers, thickeners, lubricants, dyes, pigments, antiblocking agents, fillers, and gelling agents .

Production process
The image-receiving sheet according to the invention is manufactured using a porous layer of the material of the image-receiving sheet which contains the indicated organic acid. For example, the incorporation of organic acid into the porous layer can be carried out in a process in which the porous layer is formed using a doping agent containing the organic acid, or a process in which the organic acid is applied to the porous layer.

 The method in which the porous layer is formed using a doping agent containing the organic acid is useful for the manufacture of an image-receiving sheet which is a laminate composed of a substrate and a substrate. porous layer.

 The organic acid is applied to the porous layer by, for example, depositing a coating agent which contains the organic acid on at least one side of the porous layer (the porous layer of a laminate or the porous support) and by drying or dipping the porous layer in the coating agent before drying.

 The porous layer of the laminate can be fabricated in a phase separation process in which a polymer is microphase separated using good and bad solvents, a method of forming a polymer foam, a method of forming a polymer stretching of a polymer film, an irradiation process in which a polymer film is exposed to radiation intended to form pores, an extraction process in which a film of a polymer or a soluble organic salt is a solvent and a solvent-insoluble polymer is extracted from a solvent-soluble ingredient for pore formation, a sintering process in which the polymer particles are partially fused or attached

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 by a binder for use of the spaces formed between the particles in the form of pores, or by other methods.

 Among these methods, the phase separation method in which a polymer undergoes microphase separation with good and bad solvents is preferably used, which method comprises a dry phase conversion process (process in which a substantially compound doping agent a polymer, a good solvent of the polymer and a poor solvent of the polymer having a boiling point higher than that of the good solvent, is deposited on a substrate and dried so that it forms a porous layer) and a wet-phase conversion process (a process in which a doping agent containing at least the above-mentioned polymer and a good solvent thereof is cast or deposited on a substrate, and the resulting substrate is immersed in a poor polymer solvent to cause phase separation and form a porous layer). The dry phase conversion process is preferably used because it is suitable for mass production.

 Further details of the production process by conversion to the dry phase are given below. A doping agent, composed of a polymer, a good solvent thereof, and a bad solvent, having a boiling point higher than that of the good solvent, is deposited on a substrate. After drying, the good solvent whose boiling point is low evaporates before the bad solvent. At this time, when the evaporation of the good solvent proceeds, the solubility of the polymer decreases and the polymer forms micelles and separates from the phase of the bad solvent. In addition, as the evaporation of the poor solvent progresses, the micelles are brought into contact with each other to form a network or web structure, and at the end of the evaporation of the bad solvent, the porous layer is formed.

 The good solvent is selected depending on the nature of the polymer. Examples of good solvents are ketones (for example dialkyl ketones having 3 to 6 carbon atoms).

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 carbon, such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone and methyl isobutyl ketone and cyclohexanone), esters (for example alkyl formates having 1 to 4 carbon atoms, such as ethyl formate, alkyl acetates having 1 to 4 carbon atoms such as methyl, ethyl and butyl acetates, as well as ethyl propionate and ethyl butyrate), ethers (for example, ethers having 4 to 4 carbon atoms); to 6 carbon atoms in cyclic or chain form, such as 1,4-dioxane, tetrahydrofuran, tetrahydropyran, diethyl ether, diisopropyl ether and dimethoxyethane), "Cellosolves" (e.g. Cellosolves "alkylic with 1 to 4 carbon atoms, in particular methyl, ethyl and butyl), acetates of" Cellosolve "(such as acetates of" Cellosolve "alkyl having 1 to 4 carbon atoms, such as acetates of methyl- "Cellosolve" and ethyl- "Cel losolve "), aromatic hydrocarbons (eg benzene, toluene and xylene), halogenated hydrocarbons (eg methylene chloride and ethylene chloride), amides (eg formamide, acetamide, N-methylformamide, N-methylacetamide, N, N-dimethylformamide, N, N-dimethylacetamide), sulfoxides (for example dimethylsulfoxide), nitriles (for example acetonitrile, propionitrile, butyronitrile, benzonitrile), organic acids (such as formic, acetic and propionic acids), organic acid anhydrides (for example maleic and acetic anhydrides) and mixtures thereof. Moreover, the good solvent [for example a lower alcohol (for example alkyl alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, isopropanol, and butanol as well as diacetone alcohol), cycloalkanols (e.g. cycloalkanols having 4 to 8 carbon atoms which may be substituted with an alkyl group having 1 to 4 carbon atoms, such as cyclopentanol, cyclohexanol, methylcyclohexanol, dimethylcyclohexanol)] is a poor solvent for some

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 resins. The good solvent may contain a nitrated compound (eg nitromethane, nitroethane, nitropropane).

 More concretely, in the case of the use of cellulose acetate as a polymer, a good, preferred solvent is selected from acetone, methyl ethyl ketone, ethyl acetate, dioxane, dimethoxyethane, methyl and the like. Cellosolve ", Methyl acetate" Cellosolve "and mixtures thereof. Acetone is particularly advantageous.

 The term "bad solvent" refers to a solvent whose solubility in the polymer to be used is low or zero, and no specific restriction applies to the solvent provided that its boiling temperature is higher than that of the good solvent. Examples of a bad solvent are water, esters (eg alkyl formates having 5 to 8 carbon atoms such as amyl formate and isoamyl formate, alkyl esters having 6 to 10 carbon atoms, and the like). carbon of aliphatic carboxylic acid having 2 to 4 carbon atoms, which may comprise an alkoxylated group having 1 to 4 carbon atoms, such as amyl acetate, hexyl acetate, octyl acetate , 3-methoxybutyl acetate, 3-methoxybutyl acetate, butylpropionate and 3-methoxybutylpropionate, alkyl benzoates having 1 to 4 carbon atoms, such as methyl, ethyl and propyl), alcohols (for example alcohols having 6 to 10 carbon atoms such as amyl alcohol or a heterocyclic alcohol), aliphatic polyols (for example ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol and glycerol). ), and their mixtures.

 More concretely, when cellulose acetate is used as polymer, the preferred poor solvent is amyl formate, cyclohexanone, methylcyclohexanone, ethyl benzoate or mixtures thereof. Cyclohexanone is particularly advantageous.

 The proportions of the good solvent and the bad solvent in the doping agent present no particular restriction insofar as a homogeneous solution of the polymer is formed, and the proportions are advantageously

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 selected according to, for example, the porosity of the desired porous layer. Usually, the proportion of the bad solvent is selected in the range of about 100 parts by weight of the good solvent from about 0 to 300 parts by weight and preferably from about 3 to 250 parts by weight, and most preferably from about 5 to 250 parts by weight.

 Depending on the degree of polymerization of the polymer, the polymer content of the doping agent is selected in the range of about 1 to about 30% by weight and preferably about 1 to 25% by weight, and in particular between 3 and About 20% by weight (for example between 3 and 15% by weight).

 Conventional additives, such as antifoaming agents, coating enhancers, thickeners, heat stabilizers, lubricants, ultraviolet absorbers, antistatic agents and anti-stick agents may be added. to the doping agent, unless the necessary characteristics of the invention are adversely affected.

 The polymer, the good solvent and the bad solvent are mixed in a conventional manner so that the polymer is added and dissolved in the good solvent, then the bad solvent is added and mixed with the resulting mixture by stirring.

 The application of the porous layer to the substrate does not present any particular restriction, and a well-known method such as cylinder coating, air knife coating, blade coating or rod or bar can be used. or coating.

 The drying process of the porous layer is not subject to any particular restriction. When using the dry phase conversion process, the temperature and the water vapor pressure must be adjusted so that the good solvent first evaporates so that the polymer forms micelles, then the bad solvent

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 evaporates so that the micelles are brought into mutual contact and form a network structure.

 In the image-receiving sheet, the porous layer may be formed on only one side or both sides of the substrate. The porous layer may be formed by coating the substrate with a polymer-containing doping agent and by pore-forming in the resulting layer in a film forming step or the substrate may be adhered to the separately prepared porous layer, for example by a conversion to the dry phase.

 When a transparent substrate is used for the production of the image-receiving sheet, it is preferable that the substrate be transparent to the visible rays, and the light transmittance can be selected at a wavelength of 400 nm between a value which is not less than 45% (for example between 45 and 100%) and preferably between approximately 60 and 100% (for example between 70 and 100%). Depending on the intended application, a non-transparent substrate may be used.

 In the application of an organic acid to the porous layer, the coating agent containing the organic acid is deposited in the same manner as the porous layer is applied or by a technique known as spray deposition. The organic acid can be applied to the porous layer by immersion. The solvent of the coating agent is not subject to any particular restriction, and its selection depends on the nature of the organic acid, etc. Examples of the solvent are alcohols (for example alkyl alcohols having 1 to 4 carbon atoms such as methanol, ethanol, isopropanol and butanol), ketones (for example dialkyl ketones having 1 to 4 atoms). carbon, such as acetone and methyl ethyl ketone), esters (for example alkyl formates having 1 to 4 carbon atoms such as ethyl formate), ethers (such as cyclic ethers or 4 to 6 carbon atoms, in particular 1,4-dioxane and tetrahydrofuran, "Cellosolves", (for example alkyl "Cellosolves" having 1 to 4 carbon atoms,

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 carbon, such as methyl-Cellosolve and ethyl Cellosolve) and aromatic hydrocarbons (such as benzene, toluene and xylene). The solvents can be used in the form of a mixture. In addition, the solvent of the coating agent may contain water. The organic acid concentration of the coating agent is such that the organic acid / solvent weight ratio is between about 0.1 / 99.9 and 10/90 (e.g. / 80) and preferably between 1/99 and 10/90.

Image-receiving sheet and imaging method
Since the image-receiving sheet according to the invention has excellent moisture-absorbing properties, it can be used as an image-forming material or an image-receiving sheet for ink-jet printing in which droplets of ink (for example aqueous pigment or dye) are projected against the material. Although the image-receiving sheet according to the invention can be used indoors or outdoors, when used outdoors, generally water-based pigment inks are used because of the fact that their durability.

 The image-receiving sheet formed by the above-described laminate in particular gives good quality images because the inks applied to the surface of the recording material are easily and safely absorbed by and retained by the porous layer. so that the inks do not stagnate on the surface, remaining sticky for a long time, and the inks can not flow or mix. Accordingly, the image-receiving sheet made of the aforementioned laminate is particularly useful as an overhead projector sheet or high-quality image sheet which must be transparent or have a glossy surface.

 The image-receiving sheet comprising the porous support described above is suitable for applications that require a certain texture (softness), such as flags, banners and store curtains.

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 Images are produced by recording images or characters on the porous layer of the image-receiving sheet formed by the laminate and then by separating the porous layer from the substrate by peeling. When recording images according to the invention, the porous layer can be separated from the substrate, and the dissociation of the porous layer of the substrate increases the sharpness, the reproducibility of the colors and the transparency of the images recorded on the porous layer.

 The production of an image can be performed by recording the image or characters on the porous layer of the image-receiving sheet by gluing a coating sheet onto the porous layer, and separating these two elements. of the substrate. The film of the substrate described above, in particular a transparent film, can be used as a cover sheet. In the image recording operation according to the invention, since the porous layer can be separated from the substrate, a regular transfer of the porous layer can be provided. In particular, a sheet having a small difference in adhesion strength between the image forming region and the non-image forming region exhibits excellent dissociation properties. In addition, the use of the porous layer separated from a substrate having a relatively low water resistance by peeling with the cover sheet (for example a cover sheet having a porous layer bonded so that the porous layer is turned inwardly) makes the resulting image-receiving sheet suitable for outdoor applications that require high water resistance.

 Provided is a recording image receiving sheet having excellent surface gloss and excellent sharpness properties of recorded images and color reproducibility, with excellent ink absorption and resistance properties. to collage. Further, the invention relates to an image receiving material which has excellent properties not only of ink absorption and bonding but also of

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 texture. In addition, according to the invention, an image-receiving sheet can be obtained which gives images having excellent water and weather resistance properties. The invention also relates to an image-receiving sheet having a suitable adhesion strength between the porous layer and a substrate and having excellent separability (ease of dissociation).

EXAMPLES
The following examples allow a more detailed description of the invention and should not be considered as limiting the scope of the invention.

 The term "part" and the sign "%" refer to the proportion by weight unless otherwise indicated. The recording sheets obtained in the examples and comparative examples were evaluated for their ink absorption properties, water resistance, image definition (sharpness of the images), stickiness resistance and adhesion resistance by the following methods.

Ink absorption
Each of the cyan, yellow and magenta raster images formed of water-based inks of the corresponding pigment type were printed individually on the recording sheets obtained in the Examples and Comparative Examples using an inkjet printer ("Master Jet-JC2008" manufactured by Graphtech, Co.

Ltd. ). After printing, a sheet of PPC copy paper was placed on the printed portion at synchronized intervals, and a load (2.45 N / cm 2) was applied to the paper for 10 seconds. Then, the copy paper was peeled off and examined visually for the determination of the degree of transfer and the time required for the copy paper to be cleared of the deferred portion was measured.

Water resistance-1
Images were printed in the same manner as for the ink absorption test on the recording (or imaging) sheets obtained in the Examples and Comparative Examples. Then the part

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printed was wiped with a sufficiently water impregnated buffer on three alternative runs at 25 C, and the degree of soiling by the ink of the buffer was evaluated with the following criteria:
A: the pad has not been stained
B: the stamp was slightly stained with the ink and the printed part was attenuated
D: complete removal of the wiped area layer Water resistance-2
Images were printed in the same manner as in the ink absorption test on the recording sheets obtained in the Examples and Comparative Examples. After immersion in water at room temperature for 24 h, the appearance was visually examined with the following criteria:
B: no effect
C: the printed part is slightly dissolved
D: most of the printed area is dissolved Sharpness of images (image definition)
Using an inkjet printer ("Master Jet-JC2008", manufactured by Graphtech, Co. Ltd.), a magenta line (width 100 m) was printed on a yellow base on each of the sheets recording (imaging) examples and comparative examples, and these points were observed under a microscope with a magnification of 50 and were evaluated with the following criteria:
A: low smearing of points
B: slight smudging of points, actual dimension of points exceeding 120 m
D: smudging of points, the boundary between the neighboring points yellow and magenta can not be discerned Resistance to gluing
Two recording sheets obtained in at least the examples and comparative examples were stacked and were able to rest one day under a load of 0.392 N / cm 2 at a temperature of 40 C and a humidity of 90% humidity.

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relative. Resistance to bonding was evaluated with the following criteria:
A: no matting or collage
B: matage observed but without bonding
D: bonding adhesion resistance
An adhesive tape of "Cellophane" was adhered to the porous layer of each of the recording sheets obtained in the Examples and Comparative Examples, and the sheet was cut into 15 mm wide samples. The adhesion strength was determined for a peel strength of 200 mm / min with a tensile tester "Tensilon UCT-5T" from Orientech Co. Ltd.

Example 1
The following solution of resin was deposited on one side of a sheet of PPC paper which can be adapted to ink jet printing ("FC dream" manufactured by Kishu Seishi KK) and dried at 70 ° C. C for 5 min to give a porous layer of 8 m in which pores of average size equal to 1 m were present in dense form. The evaluation results of the resulting recording sheet are shown in Table 1.

Resin solution a
The resin solution was prepared by adding 2 parts of phthalic acid and 100 parts of cyclohexanol in 100 parts of a solution in acetone containing cellulose acetate (average degree of acetylation 55%, average degree polymerization 170) at a concentration of 10%.

Example 2
The following solution of resin ba was deposited on one side of a sheet of paper "Kent"("White Excel Kent" manufactured by Tokushuseishi KK) and dried at 70 C with a relative humidity of 90% for 1.5 min, then at 120 ° C for 3 minutes to obtain a porous layer 7 m thick in which the pores had a mean dimension of 0.3 m and were present in dense form. The

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 Evaluation results of the resulting recording sheet are shown in Table 1.

Resin solution b
The resin solution b was prepared by adding 2 parts of phthalic acid and 15 parts of 3-methoxybutyl acetate to 100 parts of a solution in N, N-dimethylformamide containing an acrylonitrile (AN) copolymer and of vinylpyrrolidone (VP) ("DUY", molar ratio AN / VP = 0.98 / 0.02 manufactured by Daicel Chemical Industries, Ltd.) at a concentration of 10%.

Example 3
The following solution of resin was deposited on one side of a sheet of drawing paper ("Npi Dullart" manufactured by Tokushuseishi KK) and dried at a temperature of 60 ° C. and at a relative humidity of 95% for 1.5 minutes. , then at 120 ° C. for 3 minutes to obtain a porous layer 11 m thick in which pores of average size equal to 0.6 m were present in dense form. The evaluation results of the resulting recording sheet are shown in Table 1.

Resin solution c
The resin solution was prepared by adding 1.2 parts of p-toluenesulfonic acid and 15 parts of 3-methoxybutyl acetate to 100 parts of a solution in N, N-dimethylformamide containing polymethyl methacrylate ( manufactured by Scientific Polymer Products) at a concentration of 10%
Comparative Example 1
An 18% aqueous solution of modified polyvinyl alcohol ("OKS-7158G" manufactured by Nippon Gosei Kagaku) was deposited on one side of a 100 m thick polyethylene terephthalate film ("Merinex 339"). manufactured by Dupon Japan) and dried at 120 ° C. for 5 minutes for the formation of a 15 m image-receiving layer. The evaluation results of the resulting recording sheet are shown in Table 1.

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Table 1

<Tb>
<tb> Ex. <SEP> 1 <SEP> Ex. <SEP> 2 <SEP> Ex. <SEP> 3 <SEP> Ex. <SEP> comp.
<Tb>

1
<tb> Absorption <SEP> ink <SEP> 1 <SEP> min <SEP> or <SEP> 1 <SEP> min <SEP> or <SEP> 1 <SEP> min <SEP> or <SEP> 3 <SEP> min <SEP>
<tb> less <SEP> less <SEP> less
<tb> Resistance <SEP> to <SEP> water-1 <SEP> A <SEP> A <SEP> A <SEP> D
<tb> Image <SEP> Definition <SEP> A <SEP> A <SEP> A <SEP> B
<tb> Resistance <SEP> to <SEP> Paste <SEP> A <SEP> A <SEP> A <SEP> D
<tb> Resistance <SEP> between <SEP><SEP> 0.3 <SEP> N <SEP> 0.5 <SEP> N <SEP> 0.4 <SEP> N <SEP> layers <SEP> / <SEP> mm <SEP> / <SEP> 15 <SEP> mm <SEP> / 15 <SEP> mm <SEP>
<Tb>

Example 4
Adhesion resistance (Fp) was measured after the image recording on the recording sheet obtained in Example 1, in the same manner as in the ink absorption test. The result is shown in Table 2 with the previously measured adhesion strength (Fn). The cyan, magenta and yellow images all showed the same trend, so we used representative cyan color image data (in the following, the same applies unless otherwise stated) ).

 The printed porous layer of the sheet was then bonded to a surface protective sheet ("LAG Protect G055AV50", to which an adhesive, manufactured by Sakurai K.K.) is applied. Then, the surface protection sheet combined with the porous layer was peeled off from the recording sheet. After peeling, the porous layer was clearly separated from the substrate with almost no resistance. The result of the water resistance test 2 is shown in Table 2.

Example 5
After printing images on the recording sheet obtained in Example 2 in the same manner as for the ink absorption test, the adhesion strength (Fp) was measured. The result is shown in Table 2 with the previously measured adhesion strength (Fn).

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 Next, the printed porous layer of the sheet was adhered to a surface protection surface ("LAG Protect G055AV50" to which an adhesive, manufactured by Sakurai K.K.) is applied. Then, the surface protection sheet combined with the porous layer was peeled off from the recording sheet. After peeling, the porous sheet was clearly separated from the substrate with almost no resistance. The result of the water resistance test 2 is shown in Table 2.

Example 6
After printing images on the recording sheet obtained in Example 3 in the same manner as for the ink absorption test, the adhesion strength (Fp) was measured. The result is shown in Table 2 with the previously measured adhesion strength (Fn).

 Next, the printed porous layer of the sheet was adhered to a surface protection surface ("LAG Protect G055AV50" to which an adhesive, manufactured by Sakurai K.K.) is applied. Then, the surface protection sheet combined with the porous layer was peeled off from the recording sheet. After peeling, the porous sheet was clearly separated from the substrate with almost no resistance. The result of the water resistance test 2 is shown in Table 2.

Table 2

<Tb>
<tb> Fp / Fn / Fp-Fn <SEP> (N / 15 <SEP> mm) <SEP> Resistance <SEP> to <SEP> water <SEP> 2
<tb> Ex. <SEP> 1 <SEP> 0.7 / 0.3 / 0.4 <SEP> D
<tb> Ex. <SEP> 2 <SEP> 0.5 / 0.5 / 0 <SEP> D
<tb> Ex. <SEP> 3 <SEP> 0.5 / 0.4 / 0.1 <SEP> D
<tb> Ex. <SEP> 4 <SEP> 0.7 / 0.3 / 0.4 <SEP> B
<tb> Ex. <SEP> 5 <SEP> 0.5 / 0.5 / 0 <SEP> B
<tb> Ex. <SEP> 6 <SEP> 0.5 / 0.4 / 0.1 <SEP> B
<Tb>

Table 2 shows the results of the water resistance test 2 carried out on the recording sheets obtained in Examples 1 to 3. In the comparison of these recording sheets, the results

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 obtained with Examples 4 to 6 indicate remarkably high water resistance. Thus, the recording sheets obtained in Examples 4 to 6 had a water resistance sufficiently high to be used outdoors as billboard materials.

Comparative Example 2
A coating agent composed of 100 parts of an aqueous solution, containing a modified polyvinyl alcohol ("OKS-7158G" from Nippon Gosei Kagaku K. K) at a concentration of 15% and 1.5 parts of maleic acid, was deposited on one side of a sheet of 100 μm thick polyethylene terephthalate paper (Toyo Boseki KK "Crysper") and dried at 120 ° C. for 5 minutes for the formation of an absorption layer 15 m thick ink.

Then, a doping agent composed of 100 parts of a solution in acetone, containing cellulose acetate (average degree of acetylation 55%, average degree of polymerization 170) at a concentration of 10% and 100 parts of cyclohexanol, was deposited and dried for 3 min in an atmosphere at 80 ° C and 90% relative humidity for the formation of a porous layer with a thickness of 8 .mu. in which pores of average size equal to 0, 9 were present in dense form.

 The measurement showed that the adhesion strength (Fn) between the porous layer and the ink absorption layer was 0.7 N / 15 mm.

 The ink absorption of the recording sheet was evaluated, and it was found that the ink dried in 1 min.

Attempting to bond the porous layer to a protective film, as indicated in Example 4, gave a break in the cohesion of the porous layer, the printed image being thinned. As a result, it was impossible to measure the adhesion strength Fp. This is probably due to the fact that, after printing, the solvent of the inks containing the pigment and the fluid of the modified polyvinyl alcohol flowed into the porous layer, without distinction between the porous layer and the ink absorption layer.

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Example 7
The following coating agent was deposited on one side of a 150 m thick polyester fabric (92.3 g / m2 basis weight) and dried at 80 ° C for 5 minutes for the formation of a receiving material. image, 2.1 g / m 2 of phthalic acid being applied (determined on dry matter). The evaluation results of the image-receiving material are shown in Table 3.

Coating agent
A coating agent was prepared from 2 parts of phthalic acid and 98 parts of isopropanol forming a solvent.

Example 8
The coating agent as prepared above was deposited on one side of a 100 m thick polyester fleece ("05-TH48" from Hirose Seishi KK, surface density 46.0 g / m 2) and dried at 80 ° C. for 5 minutes for the formation of an image-receiving material with application of 1.9 g / m 2 of phthalic acid (determined on the solids). The evaluation results of the sheet are shown in Table 3.

Example 9
A following resin solution was deposited on one side of a sheet of PPC paper for ink jet printing ("FC Dream" manufactured by Kishu Seishi KK) and dried at 70 ° C for 5 min. forming a sheet having a porous layer of plastic 8 m thick, having pores of 1 m average size, present in dense form. The plastic sheet was coated with the coating agent and dried at 80 ° C for 5 minutes to form an image receiving material on which 0.5 g / m 2 of phthalic acid was applied, determined on dry matter. The evaluation results of the recording sheet are shown in Table 3.

Resin solution b
The resin solution b was prepared by adding 100 parts of cyclohexanol, constituting a bad solvent, to 100 parts of a 10% solution of sodium acetate.

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 cellulose, which is a derivative of cellulose (degree of acetylation 55, degree of polymerization 170) and acetone constituting a good solvent.

Comparative Example 3
The coating agent was deposited on one side of a 100 m polyethylene terephthalate film ("Merinex 339" manufactured by Dupon Japan Co.) and dried at 80 ° C. for 5 minutes to form a material with application of 0.5 g / m 2 of phthalic acid, determined on the solids. The evaluation results of the sheet are shown in Table 3.

Comparative Example 4
An aqueous solution containing 18% polyvinyl alcohol ("OKS7158G" manufactured by Nippon Gosei Kagaku KK) was deposited on the polyester fabric used in Example 7 and dried at 120 ° C. for 5 minutes for the formation of a polyvinyl alcohol. image-receiving layer of 15 m. The material evaluation results are shown in Table 3.

Table 3

<Tb>
<tb> Ex. <SEP> Ex.
<Tb>

Ex. <SEP> 7 <SEP> Ex. <SEP> 8 <SEP> Ex. <SEP> 9 <SEP> Comp. <SEP> comp.
<tb> comp. <SEP> 3 <SEP> comp. <SEP> 4
<tb> Absorption <SEP> of <SEP> ink <SEP> 1 <SEP> min <SEP> or <SEP> 1 <SEP> min <SEP> or <SEP> 1 <SEP> min <SEP> or <SEP> 3 <SEP> min <SEP> 3 <SEP> min
<tb> minus <SEP> minus <SEP> minus <SEP> or <SEP> plus <SEP> or <SEP> plus
<tb> Resistance <SEP> to <SEP> water <SEP> 2 <SEP> A <SEP> A <SEP> A- <SEP> D
<tb><SEP> Image Definition <SEP> A <SEP> A <SEP> A <SEP> D <SEP> B
<tb><SEP> Resistance <SEP><SEP> A <SEP> A <SEP> A <SEP> - <SEP> D
<Tb>

The recording sheet of Comparative Example 3 did not absorb the ink so that no image was recorded on it. The texture of the image-receiving materials of the examples after treatment remained unchanged.

 Of course, various modifications can be made by those skilled in the art to the sheets and processes that have just been described by way of non-limiting example without departing from the scope of the invention.

Claims (25)

An image-receiving sheet having at least one porous layer, characterized in that the porous layer contains an organic acid having a solubility of 0.01 to 2 g in 100 g of water at 20 C.  2. Sheet according to claim 1, characterized in that it is selected from a laminate in which the porous layer is formed on at least one side of a substrate, and a porous support.  3. Sheet according to claim 1, characterized in that the organic acid is an aromatic polycarboxylic acid.  4. Sheet according to claim 1, characterized in that the average pore size of the porous layer is between 0.005 and 10 m.  5. Sheet according to claim 1, characterized in that the porous layer contains a hydrophilic polymer and is disposed on at least one side of a substrate.  6. Sheet according to claim 5, characterized in that it contains 1 to 100 parts by weight of the organic acid per 100 parts by weight of the hydrophilic polymer.  7. Sheet according to claim 5, characterized in that the hydrophilic polymer is formed of at least one polymer selected from the group consisting of a cellulose derivative, a polymer of the vinyl series and a polymer of the polysulfone series.  8. Sheet according to claim 1, characterized in that the porous layer has a structure formed by separation of microphases following a phase conversion.  An image-receiving sheet of the type which comprises a substrate and a porous layer formed on at least one side of the substrate, characterized in that the porous layer comprises at least one polymer selected from the group consisting of a cellulose derivative , a polymer of the vinyl series and a polymer of the polysulfone series, and has a microphase separation structure from a phase conversion and contains 2 to 100 <Desc / Clms Page number 39>  parts by weight of an aromatic dicarboxylic acid, per 100 parts by weight of the polymer.  10. Sheet according to claim 5, characterized in that the porous layer can be separated from the substrate.  11. Sheet according to claim 5, characterized in that the adhesion strength existing between the porous layer and the substrate is between 0.01 and 4.9 N / 15 mm.  12. Sheet according to claim 5, characterized in that it corresponds to the following formula (1): # Fp-Fnl <1.47 N / 15 mm (1) Fn being the adhesion resistance between the porous layer and the substrate in a non-image area and Fp being the adhesion strength between the porous layer and the substrate in an image forming area.  13. Sheet according to claim 1, characterized in that the porous layer consists of a porous support, and at least one side of the porous support contains the organic acid.  14. Sheet according to claim 1, characterized in that the amount of organic acid is not less than 0.05 g / m2, determined on the solids.  15. Sheet according to claim 13, characterized in that the porous support is selected from the group which comprises a porous plastic sheet and a fabric.  16. Sheet according to claim 15, characterized in that the fabric is selected from the group consisting of fabrics and nonwovens.  An image-receiving sheet, characterized in that at least one side of a polyester fabric, selected from fabrics and nonwovens, contains an aromatic dicarboxylic acid in an amount of 0.05 to 1 g / m2, determined on dry matter.  18. A process for producing an image-receiving sheet which comprises at least one porous layer, characterized in that it comprises the incorporation, at the porous layer of an image-receiving sheet, of an acid <Desc / Clms Page number 40>  organic such that the solubility of the organic acid is between 0.01 and 2 g in 100 g of water at 20 C.  19. The method of claim 18, characterized in that it comprises the application of a doping agent which contains a hydrophilic polymer, a good solvent and a poor solvent of the hydrophilic polymer, and an organic acid having a solubility between 0.01 and 2 g in 100 g of water at 20 C, on at least one side of a substrate, and the formation of the porous layer by phase conversion.  20. The method of claim 18, characterized in that it comprises, after the application of a doping agent containing a hydrophilic polymer, a good solvent and a poor solvent of the hydrophilic polymer, on at least one side of the substrate, the formation of the porous layer by phase conversion of the doping agent, the application of a coating agent containing the organic acid having a solubility of between 0.01 and 2 g in 100 g of water at 20.degree. C on the porous layer, and extracting a solvent from the coating agent.  21. The method of claim 18, characterized in that it comprises the application of the organic solubility acid of between 0.01 and 2 g in 100 g of water at 20 C on at least one side of a porous support.  22. The method of claim 21, characterized in that the organic acid is applied to the porous support by a method selected from a method of applying a coating agent containing the organic acid and a method of immersing the support porous in the coating agent.  A method of forming an image, characterized in that it comprises forming an image on a porous layer of an image receiving sheet according to claim 5, and separating the porous layer from a substrate.  24. A method of forming an image, characterized in that it comprises forming an image on a porous layer of an image receiving sheet according to claim 5, adhering a coating sheet to the <Desc / Clms Page number 41>  porous sheet, and separating the coating sheet and the porous layer from a substrate.  25. Method according to one of claims 23 and 24, characterized in that the image is recorded by a water-based ink.