JP5113707B2 - Inkjet recording medium - Google Patents

Description

  The present invention relates to an ink jet recording medium, and more particularly to an ink jet recording medium having glossiness similar to that of a silver salt photograph, particularly excellent in discoloration resistance during processing and storage, close to photographic image quality and high in print quality.

The ink jet recording method is a method for recording by ejecting ink droplets and depositing them on a recording medium to form dots. In recent years, recording with high print quality has become possible due to technological advances in inkjet printers, inks, and recording media. As an element required for an inkjet recording medium,
(A) fast ink absorption and drying;
(B) high print density;
(C) no dot spread and / or whiskers,
Etc. If ordinary plain paper has a certain size or more, it can be expected to have a certain level of print quality with little blurring. On the other hand, when a higher print quality is required, a dedicated medium in which an ink receiving layer suitable for the ink of an ink jet printer is provided on various media on the medium is used. Many of these ink-jet recording media have paper and / or film as a support and a pigment coating layer mainly composed of a pigment and a binder or a resin coating layer not containing a pigment provided on the surface. used.

The ink jet dedicated medium is further classified into a matte medium and a glossy medium on the basis of the surface state. The latter glossy medium is used when image quality closer to silver halide photography is required. In addition to the properties described above, the properties required for glossy media
(D) the roundness of the dots is high and the image reproducibility is good,
(E) good water resistance and light resistance;
(F) The glossiness of the image area and the blank paper portion is high,
Etc.

  Various methods have been proposed for producing glossy media in order to maintain the properties (b) to (f) while maintaining the ink absorbability and drying properties of (a). Is a method of forming an ink receiving layer by a casting method to give gloss to the surface, or a method of forming an ink receiving layer and a gloss developing layer by a multilayer coating method on a photographic paper substrate.

  In general, the former method is easier to control the ink absorptivity of (a) than the latter method, but (d) the dot roundness and image reproducibility, (f) the gloss of the image area and the blank paper portion. The feeling and quality are inferior to the latter method. When the ink-receiving layer is formed on the surface of the photographic paper base, since the polyethylene film layer is formed on the paper base as generally called RC paper (resin-coated paper), the film surface Is smooth, the surface of the ink receiving layer is also smooth, and a glossy surface is easily formed.

  However, in the latter method using a photographic paper substrate, it is necessary to increase the amount of coating in order to increase ink absorbency, and since the substrate itself is more expensive than paper, the former casting method is used. Compared to glossy media, the overall cost is high. In addition, when it is discarded, there is a problem that it cannot be recycled because it is a composite material.

  The latter glossy paper for ink-jet recording by the casting method is advantageous in this respect, but has the above-mentioned problems in quality, and various proposals have been made to solve these problems.

  For example, there is a proposal that an inkjet recording paper having high surface smoothness and excellent image quality can be obtained by defining the average roughness, glossiness and air permeability of the recording paper on the surface of the recording layer (for example, , See Patent Document 1). There is also a proposal that an inkjet recording paper having excellent gloss and ink receptivity can be obtained by defining the size and number of cracks on the surface of the recording layer (see, for example, Patent Document 2). However, in this case, if the number of cracks is too small, there is a problem that glossiness increases while ink absorbability decreases. Furthermore, there is also a proposal of an ink jet recording sheet containing a pearl necklace-shaped colloidal silica (see, for example, Patent Document 3). In this case, it is said that the use of pearl necklace-shaped colloidal silica is effective in improving printing quality, particularly ink absorbability. Furthermore, recently, a paper coated with a mixture of alumina hydrate and a water-soluble binder has been proposed as a glossy paper for ink-jet recording having a high ink absorption rate and a glossiness similar to a silver salt photograph (for example, patents). (Ref. 4).

  An ink jet recording medium having glossiness very close to that of a silver salt photograph as in the above document has been proposed as an alternative to the silver salt photograph. Normally, it is assumed that it is natural to store these inkjet recording media in an album, a clear file, etc. after printing an image, as well as storing a silver halide photograph in an album, a clear file, etc. Based on such preservation, a technique for suppressing discoloration by defining the surface pH of the ink receiving layer surface (see, for example, Patent Document 5) or a technique for suppressing discoloration by using an organic titanium compound ( For example, see Patent Document 6).

Japanese Patent Laid-Open No. 06-72017 Japanese Patent Laid-Open No. 11-348416 JP 2000-108506 A Japanese Patent Laid-Open No. 06-055829 JP 2001-246833 A JP 2000-43403 A

  The reason why the technique for suppressing discoloration in Patent Document 5 or Patent Document 6 is studied is as follows. That is, generally, an antioxidant or a plasticizer is kneaded into a film used for a commercially available clear file, album, etc., and the ink is received by adsorbing the antioxidant to the ink receiving layer. The surface of the layer may change color. Further, when processing the ink jet recording medium as a postcard paper, offset printing is often performed on the surface opposite to the ink receiving layer, and these offset inks are often mixed with an antioxidant. When the printing portion comes into contact with the ink receiving layer, the antioxidant may be adsorbed on the ink receiving layer and the surface of the ink receiving layer may be discolored. For the same reason, discoloration may occur due to contact with a substance containing an antioxidant, such as rubber bands and cellophane tape, which is often a problem.

  The color change phenomenon as described above tends to be more conspicuous in an ink jet recording medium having a glossy layer aiming for a silver salt photographic substitute as compared with a so-called matte ink jet recording medium. This is because the pigment used for the glossy layer has a smaller specific particle size and a higher specific surface area than the pigment used for the so-called matte ink jet recording medium, so that the molecule adsorption ability is further enhanced. Because. Therefore, it can be said that the problem of discoloration during processing and storage is more serious in the ink jet recording medium having the glossy expression layer than in other ink jet recording media.

  However, the technique for suppressing discoloration disclosed in Patent Document 5 does not solve the discoloration problem of an ink jet recording medium having a glossy layer only by this method, even if the matte ink jet recording medium has a certain effect. . Further, the technique for suppressing discoloration disclosed in Patent Document 6 is also unsatisfactory in the case of an ink jet recording medium having a glossy expression layer for the reasons specific to the ink jet recording medium having a glossy expression layer as described above. There is a point.

  As described above, for inkjet recording media with high glossiness intended to replace silver salt photography, the specific surface area increases because the particle size of the pigment used in the glossy layer is very small. Since it tends to be easily adsorbed, discoloration due to an antioxidant or the like tends to be more prominent when compared to an inkjet recording medium having a low gloss such as a matte inkjet medium. Therefore, it is very difficult to achieve both glossiness similar to silver salt photography and prevention of discoloration during processing and storage, and it remains as a technical problem.

  Therefore, the results of research on the color change suppression technology by the present inventors have led to the conclusion that the above proposals cannot be completely satisfied with respect to the request for solving the color change problem of the inkjet recording medium having the glossy expression layer. . In view of such a current situation, there is no recording medium that has excellent image quality and uniform glossiness and has both excellent anti-discoloration performance in an inkjet recording medium having a glossy expression layer. Currently.

  Therefore, an object of the present invention is to solve the problems of the prior art in an inkjet recording medium having a glossy expression layer, and has a high gloss feeling similar to a silver salt photograph while having good ink absorbability, Furthermore, it is to provide a medium having very excellent discoloration resistance.

In the ink jet recording medium, the inventors set the base material to acid paper, the glossy layer has a surface pH of 5.0 to 6.4, and sodium contained in the ink jet recording medium is a predetermined amount or less. As a result, the inventors have found that the above problems can be solved, and have completed the present invention. That is, the ink jet recording medium according to the present invention is provided with one or more ink receiving layers on at least one side of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink receiving layer. In the inkjet recording medium, the base material is acidic paper, the gloss developing layer is provided by a cast coating method, the cast coating method is a coagulation method, and the gloss developing layer is polyvinyl as the binder. The mass of sodium that contains alcohol, contains sodium borate as a coagulant, has a surface pH of the glossy layer of 5.0 to 6.4, and is contained in the inkjet recording medium. The ratio is 600 mass ppm or less. By providing the gloss developing layer by the cast coating method, the glossiness is particularly excellent. Further, since the base material is necessarily paper, it becomes a relatively inexpensive and recyclable inkjet recording medium. Furthermore, since the cast coating method is a coagulation method, it is particularly excellent in productivity, and excellent in glossiness and image sharpness. Further, since the gloss developing layer contains polyvinyl alcohol and sodium borate, the gloss developing layer is particularly excellent in surface strength and image sharpness.

  In the ink jet recording medium according to the present invention, the surface pH of the substrate is preferably in the range of 3.0 to 5.5. When the surface pH of the substrate is in the range of 3.0 to 5.5, it is possible to achieve both better ink absorbability and better discoloration resistance.

  In the inkjet recording medium according to the present invention, it is preferable that the glossy layer contains a cationic polymer. In particular, the water resistance of the printed part is excellent. In addition, by selecting a cationic polymer having a low pH, it is possible to lower the surface pH of the glossy layer and improve the discoloration resistance.

In the inkjet recording medium according to the present invention, the glossy layer preferably contains silica having an average secondary particle diameter of 500 nm or less, alumina having an average secondary particle diameter of 500 nm or less, or both. In particular, it has excellent gloss and ink absorbability.

Further, the ink jet recording medium according to the present invention is preferably processed into a postcard shape. A medium in which discoloration is suppressed at a high level is particularly suitable for use as a postcard application.

The method for producing an inkjet recording medium according to the present invention is an inkjet in which one or more ink receiving layers are provided on at least one side of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink receiving layer. In the method for producing a recording medium, the base material is acidic paper, the gloss developing layer is provided by a cast coating method, the cast coating method is a coagulation method, and the gloss developing layer is polyvinyl as the binder. It contains alcohol and sodium borate as a coagulant, the concentration of sodium borate in the coagulation liquid is less than 3% by mass, and the glossy layer has a surface pH of 5.0 to 6.4. And the mass ratio of sodium contained in the ink jet recording medium is 600 ppm by mass or less.

  The ink jet recording medium of the present invention has a good gloss resistance layer discoloration resistance performance while achieving a high level of surface gloss and ink absorbency. In particular, since inkjet recording media with high glossiness are intended to replace silver salt photography, it is easily guessed that the level of resistance to discoloration during processing and storage will increase more and more. . Therefore, the significance of the present invention is great.

  Next, the present invention will be described in detail. The present invention is not construed as being limited to these descriptions, and the embodiment may be modified as long as the effects of the invention are achieved.

  Examples of the pigment contained in the coating liquid for the glossy layer of the glossy inkjet recording medium include, for example, spherical colloidal silica, aggregated colloidal silica in which a plurality of spherical colloidal silicas are combined, gas phase method silica, alumina, or the like. A combination of is used. Since these pigments are used for the purpose of increasing gloss, the selected pigments are very often small particles having an average secondary particle diameter of less than 1 μm. On the other hand, since the pigment used for the ink receiving layer of a non-glossy ink jet recording medium, that is, a so-called matte ink jet recording medium, does not need to have a high gloss, the average secondary particle diameter is about 1 μm to 30 μm. Large particles are used. Therefore, the coating layer of the ink jet recording medium that necessarily has gloss has a high specific surface area compared with the ink receiving layer of the matte medium, and has an increased ability to adsorb molecules, such as an antioxidant and a plasticizer. It tends to adsorb molecules that cause discoloration. Further, having gloss means that the smoothness is inevitably high, and it is presumed that the coating layer is likely to adsorb discoloration-causing molecules because the contact area tends to be high when contacting with a substance. .

  Examples of antioxidants contained in albums, clear files, and the like include phenolic antioxidants such as dibutylhydroxytoluene (BHT), but these molecules change to a quinone structure when adsorbed on the ink receiving layer. In addition, the coating layer is colored and discoloration occurs. These antioxidants and plasticizers are often contained in rubber bands, cellophane tapes, etc. in addition to films such as clear files for paper preservation. Further, it is often contained in ink for offset printing.

  In order to prevent these discoloration, the present inventors have recognized as an empirical rule that lowering the surface pH of the surface of the glossy layer has a certain effect, but this method alone is a really satisfactory result. It is the present condition that it does not lead to.

  Therefore, regarding an ink jet recording medium having a glossy expression layer, it has been extremely difficult to improve the discoloration resistance performance of the glossy expression layer, and thus the establishment of a technique for suppressing discoloration has inevitably remained as a problem.

  In order to achieve the above object, according to the configuration of the present invention, at least one ink receiving layer is provided on at least one side of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink receiving layer. In the obtained inkjet recording medium, the base material is acid paper, the surface pH of the gloss developing layer is in the range of 5.0 to 6.4, and the mass ratio of sodium contained in the inkjet recording medium is 600 mass. ppm or less.

  When the surface pH of the glossy layer exceeds 6.4, the discoloration deteriorates, and when it is less than 5.0, the image sharpness decreases due to a decrease in color development. Preferably, the glossy layer has a surface pH in the range of 5.2 to 6.3.

  In the case of an ink jet recording medium having a glossy layer, control of the surface pH of the substrate is also very important. As a result of examination by the inventors of the present invention on the discoloration suppressing technique, it has been found that the surface pH of the base material affects the surface pH and discoloration resistance performance of the surface of the coating layer coated on the base material surface. Since the one where the surface pH of the substrate is as low as possible is excellent in resistance to discoloration, the substrate needs to be acid paper. When the substrate is not acidic paper, for example, when it is neutral paper, discoloration tends to deteriorate. The acidic paper described here refers to paper that is made by adding an acidic filler such as talc or kaolin clay and an acidic chemical such as a sulfuric acid band. On the other hand, the neutral paper described here refers to paper made in a neutral to weakly alkaline region. In general, neutral paper often uses calcium carbonate as a filler.

  As the base material used in the present invention, paper base materials such as fine paper, medium paper, and white paperboard can be used as long as they are acidic paper. In the present invention, it is desirable to use ECF (Elemental Chlorine Free) pulp or TCF (Totally Chlorine Free) pulp having a low chlorine content as a raw material pulp in consideration of the case of being recycled as fuel. Further, when the base material is paper, it is economical because it can be recycled as used paper. As the paper substrate, either single-layer paper or multi-layer paper can be used as long as it is within the scope of the present invention.

  As the base material filler, known pigments such as titanium oxide, synthetic silica, alumina, talc, calcined kaolin clay, kaolin clay and the like can be used.

  In this invention, since the surface pH of a base material is the range of 3.0-5.5, since there exists a further inhibitory effect with respect to discoloration, it is preferable. As described above, the surface pH of the substrate affects the surface pH and discoloration resistance of the coating layer surface coated on the substrate surface. When the surface pH of the substrate exceeds 5.5, discoloration may be deteriorated. When the surface pH of the substrate is less than 3.0, there is a possibility that the image sharpness is lowered due to a decrease in color development. Preferably, the surface pH of the substrate is in the range of 3.2 to 5.4.

  In the present invention, the mass ratio of sodium contained in the ink jet recording medium is 600 ppm by mass or less, and the mass of sodium can be accurately measured by ICP (Inductively Coupled Plasma) emission spectroscopy. Sodium is empirically mixed as a substance that raises the surface pH, that is, counter ions of alkaline substances, so in order to improve discoloration resistance, the mass ratio of sodium as an indicator of alkaline substances is extremely limited. Need to be lowered. Even if the surface pH of the base material and gloss developing layer is controlled within the scope of the present invention, if the absolute amount of sodium, which is an indicator of the amount of alkali, exceeds 600 ppm by mass, the discoloration resistance performance is unsatisfactory. It will occur. Preferably, the mass ratio of sodium is 580 mass ppm or less. More preferably, it is 560 mass ppm or less. The reason for measuring the mass of sodium in all layers including the base material of the ink jet recording medium is that the components of the coating liquid for the ink receiving layer and the gloss developing layer may penetrate into the base material. As described above, the alkali component that has penetrated into the base material also has an adverse effect on the discoloration, so that it is difficult to grasp the discoloration resistance performance of the entire medium by measuring only the coating layer. The mass ratio of sodium is controlled mainly by selecting pigments, borax and other materials from the viewpoint of low sodium content.

  The glossy layer preferably contains polyvinyl alcohol as a binder and a boron compound. By containing polyvinyl alcohol and a boron compound, it is easy to achieve both color developability and surface strength. The content of polyvinyl alcohol in the glossy expression layer is preferably 1 part by mass to 30 parts by mass with respect to 100 parts by mass of the pigment in the glossy expression layer. If it is less than 1 part by mass, the surface strength may be inferior, and if it exceeds 30 parts by mass, the ink absorbency may be inferior. More preferably, it is 3 mass parts-20 mass parts. The polyvinyl alcohol of the present invention includes modified polyvinyl alcohols such as carboxyl-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, and cation-modified polyvinyl alcohol. Further, the content of the boron compound is preferably 5% by mass or more with respect to polyvinyl alcohol. If it is less than 5% by mass, the surface strength may be lowered. More preferably, it is 10 mass% or more. Further, the upper limit content of the boron compound is preferably 300% by mass with respect to polyvinyl alcohol. Although the kind of boron compound is not specifically limited, Sodium borate or boric acid or both are preferable.

  Furthermore, the binder that can be used in combination with the polyvinyl alcohol that is the binder includes polyvinyl acetal, oxidized starch, etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soybean protein, and polyethyleneimide. Resin, polyvinyl pyrohydrin resin, polyacrylic acid or copolymer thereof, maleic anhydride copolymer, acrylamide resin, acrylate ester resin, polyamide resin, polyurethane resin, polyester resin, polyvinyl butyral Resin, alkyd resin, epoxy resin, epichlorohydrin resin, urea resin, melamine resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic ester or methacrylic acid Acrylic polymer latexes such as stealth polymers or copolymers, vinyl polymer latexes such as ethylene-vinyl acetate copolymers, colloidal silica and acrylic copolymer resins, colloidal silica and styrene-acrylic Resins such as copolymer resins can be exemplified, but are not particularly limited as long as the effects of the present invention are not impaired.

  The glossy layer preferably further contains a cationic polymer. By containing a cationic polymer, it is possible to improve the water resistance of the printed portion. Examples of such cationic polymers include polyethyleneimine, epichlorohydrin-modified polyalkylamine, polyamine, polyamine polyamide epichlorohydrin, dimethylamine ammonia epichlorohydrin, polyvinylbenzyltrimethylammonium halide, polydiacryldimethylammonium halide, polydimethylaminoethyl methacrylate hydrochloride, Polyvinylpyridium halide, cationic polyacrylamide, cationic polystyrene copolymer, diallyldimethylammonium chloride polymer, diallyldimethylammonium chloride sulfur dioxide copolymer, diallyldimethylammonium chloride amide copolymer, dicyandiamide formalin polycondensate, dicyandiamide Diethylenetriamine polycondensate, Reallyamine, polyallylamine hydrochloride, polyacrylamide resin, polyamide epoxy resin, melamine resin acid colloid, urea resin, cation-modified polyvinyl alcohol, amino acid type amphoteric surfactant, betaine type compound, other quaternary ammonium salts, etc. Used. The content of the cationic polymer is preferably 1 part by mass to 50 parts by mass with respect to 100 parts by mass of the pigment. If the amount is less than 1 part by mass, the water resistance of the printed part may be reduced, and if it exceeds 50 parts by mass, the ink absorbability may be reduced. Moreover, it is preferable that pH of the cationic polymer contained in the glossy layer is 6.5 or less. When pH exceeds 6.5, the surface pH of a glossiness expression layer may go up and a discoloration suppression effect may fall. More preferably, the pH is 6.0 or less. The pH of the cationic polymer is determined by measuring pH as a 10% by mass aqueous solution.

  The gloss developing layer is preferably provided by a cast coating method. In the case of the cast coating method, glossiness is further improved, which is preferable. Moreover, since the base material needs to be a gas-permeable paper on the manufacturing principle, it is preferable from the viewpoint of recyclability.

  Here, as the cast coating method, a wet method, a solidification method, and a rewetting method are known, and a solidification method is more preferable. When the cast coating method is a coagulation method, it is possible to achieve both glossiness, ink absorbability, and image sharpness at a high level. The coagulation method is a method in which a gloss developing layer is applied and a coagulating liquid is applied to the cast drum while being in a wet state and subjected to coagulation treatment. In the coagulation treatment, it is important to select a coagulant that effectively coagulates with the binder component of the coating layer. In the present invention, the boron compound is preferable. More preferably, sodium borate or boric acid or both. A high concentration of the coagulating liquid is preferable because the coagulation force is increased and the surface strength is further improved. Furthermore, it is possible to add the cationic polymer for fixing the ink to the coagulation liquid. High glossiness is achieved by adjusting the time from application to application of the coagulant, the time from application of the coagulant to reaching the cast drum, the temperature of the cast drum, the pressure during pressure bonding, and the line speed. A glossy layer can be formed. About these various conditions, it optimizes by calculating | requiring optimal conditions according to the equipment and coating material to be used.

  Depending on the components and / or pH of the coagulant, the surface pH of the glossy layer after drying may be affected. As described above, in the present invention, it is necessary to control the surface pH of the glossy layer in the range of 5.0 to 6.4.

  Moreover, you may perform calendar processes, such as a machine calendar, a soft calendar, and a super calendar, after gloss formation layer formation. Further, for curl adjustment, the curl can be adjusted by applying water, a curling adjuster, or the like on the back surface, or by humidifying.

  The glossy layer preferably contains silica having an average secondary particle diameter of 500 nm or less, alumina having an average secondary particle diameter of 500 nm or less, or both. By containing these fine particles, it is possible to achieve both glossiness, ink absorbability and image sharpness at a higher level. In order to further improve the glossiness, it is more preferable to contain silica having an average secondary particle diameter of 450 nm or less, alumina having an average secondary particle diameter of 450 nm or less, or both. When both silica and alumina are used, for example, the mass ratio is silica: alumina = 95: 5 to 5:95, preferably silica: alumina = 90: 10 to 10:90. In the present invention, the average secondary particle diameter is a value measured by a dynamic light scattering method (for example, DLS-6500, manufactured by Otsuka Electronics Co., Ltd.). In addition, since spherical colloidal silica (excluding aggregate colloidal silica) exists as primary particles without forming secondary particles, in the present invention, when spherical colloidal silica is used as silica, average secondary particles are used. The concept of silica having a diameter of 500 nm or less is treated as including spherical colloidal silica having an average primary particle diameter of 500 nm or less.

  Furthermore, the ink jet recording medium of the present invention is preferably used for postcard use. This is because the medium in which discoloration during storage and processing is suppressed as much as possible is preferably used for postcard use.

  For the glossy layer, release agents, dispersants, thickeners, preservatives, antifoaming agents, coloring dyes, coloring pigments, fluorescent whitening agents, water resistance agents, leveling agents, antioxidants, UV absorbers, etc. These additives can be appropriately selected and added.

As coating methods of the coating liquid for forming the glossy layer, known coating machines such as an air knife coater, roll coater, reverse roll coater, bar coater, comma coater, blade coater, curtain coater, simultaneous multilayer coater, etc. Is used and there is no particular limitation. Amount of coating is, 3 to 20 g / ^{m 2} in terms of solid content, preferably in the range of 5 to 15 g / ^{m 2.} When the coating amount exceeds 20 g / m ² , the productivity is inferior, and when the coating amount is less than 3 g / m ² , it is difficult to form a sufficiently glossy surface.

  Further, according to JIS H 8686-2: 1999 “Image clarity test method of aluminum and aluminum alloy anodic oxide coating” of the gloss developing layer, the image clarity of the condition with an optical comb width of 2 mm and an incident reflection angle of 60 ° is 50% or more. It is preferable from the viewpoint of glossiness. More preferably, the image clarity is 55% or more. If the image clarity is 60% or more, it can be said that the glossiness is further improved. Here, the reason for changing the incident / reflective angle from 45 ° described in JIS to 60 ° is to facilitate evaluation of the difference in glossiness.

  In the ink jet recording medium of the present invention, one or more ink-receiving layers are provided on at least one surface of a substrate, and a gloss developing layer is provided thereon. Here, the ink receiving layer contains a white pigment and a binder component as main components. The ink receiving layer may be a single layer or two or more layers in order to obtain a thickness. Even if two or more ink receiving layers are provided, there is no difference in performance from the single layer except for the influence on the thickness. In addition, an ink receiving layer and a glossy expression layer may be provided on both sides in order to support double-sided printing.

  The pigment used in the ink receiving layer contains at least one known white pigment, such as kaolin, talc, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, and carbonate. White inorganic pigments such as zinc, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, magnesium hydroxide, satin white, synthetic silica, colloidal silica, alumina, or organic such as acrylic-styrene, ethylene, vinyl chloride, nylon Pigment.

  The binder used in the ink receiving layer is polyvinyl alcohol, polyvinyl acetal, oxidized starch, etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soybean protein, polyethylene imide resin, polyvinyl pyrohydrin resin, poly Acrylic acid or its copolymer, maleic anhydride copolymer, acrylamide resin, acrylate ester resin, polyamide resin, polyurethane resin, polyester resin, polyvinyl butyral resin, alkyd resin, epoxy resin, epichlorohydrin Resin, urea resin, melamine resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic acid ester or methacrylic acid ester polymer or copolymer Acrylic polymer latex such as an ethylene - resins of the vinyl polymer latexes such as vinyl acetate copolymer and the like, used alone or in combination. The amount of the binder used is determined in consideration of the printability of the recording medium, the strength of the ink receiving layer, and the paint liquid property. Usually, it is added in the range of 1 to 200 parts by mass with respect to the mass of the pigment contained in the ink receiving layer. Preferably, it is added in the range of about 5 to 100 parts by mass. If the amount is less than 1 part by mass, the coating layer strength may decrease. If it exceeds 200 parts by mass, the ink absorbability may decrease.

  In the present invention, it is preferable to add the cationic polymer exemplified above to the ink receiving layer in addition to the pigment and the binder. As an action of the cationic polymer, it reacts with an anionic component in the dye used in the ink to form a water-insoluble salt, so that the ink is more firmly fixed on the ink receiving layer, Water resistance is improved. Although content in an ink receiving layer is not specifically limited, It is used in 1-50 mass parts with respect to 100 mass parts of pigments in an ink receiving layer. Preferably, it is added in the range of about 5 to 40 parts by mass. If it is less than 1 part by mass, the water resistance of the printed part may be lowered. If it exceeds 50 parts by mass, the ink absorbability may be inferior.

  Other additives to be included in the ink receiving layer include antifoaming agents, lubricants, dispersants, wetting agents, fluorescent whitening agents, colored dyes, colored pigments, thickeners, preservatives, and water resistance as necessary. Agents, ultraviolet absorbers, antioxidants and the like can be used.

As a coating method of the coating liquid for forming the ink receiving layer of the present invention, a known coating machine such as an air knife, a roll coater, a bar coater, a comma coater, a blade coater or a simultaneous multilayer coater is used. The coating amount is not particularly limited, but when the coating amount is too small, the ink absorbability is inferior, so that it is preferably 5 g / m ² or more in terms of solid content. Moreover, when there is too much coating amount, since binder migration generate | occur | produces at the time of glossiness expression layer coating and the surface intensity | strength of a glossiness expression layer may fall, 25 g / m < ² > or less is preferable. More preferably 6~20g / ^{m 2.}

  Further, in order to obtain a certain smoothness after coating, the ink receiving layer can be processed by a known calendar device such as a super calendar, a machine calendar, or a soft calendar.

  In the present invention, the surface pH of the outermost surface of the ink receiving layer is preferably 3.0 to 6.4. By controlling the surface pH of the outermost surface of the ink receiving layer in the range of 3.0 to 6.4, it becomes easier to improve the color fastness. When the surface pH of the outermost surface of the ink receiving layer exceeds 6.4, discoloration may be deteriorated. Further, when the surface pH of the outermost surface of the ink receiving layer is less than 3.0, there is a possibility that the image sharpness is lowered due to a decrease in color development. More preferably, it is the range of 3.0-6.3.

  In order to suppress excessive penetration of the glossy layer coating liquid, it is preferable to use a substrate coated with a known water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide by a size press.

  EXAMPLES Next, although an Example is given and this invention is further explained in full detail, this invention is not limited to these examples. Further, “parts” and “%” shown in the examples indicate solid mass parts and solid mass% unless otherwise specified.

Example 1:
As acidic paper as the base material, 100 parts of L-BKP (hardwood bleached kraft pulp) beaten in Canadian Standard Freeness (CSF) 530 ml, talc (trade name: T-Lite 83, manufactured by Taihei Talc Co., Ltd.) as an internal filler ) 5 parts, and further 3% sulfate band, 0.25 parts of acidic rosin sizing agent (trade name: AL-120, manufactured by Seiko PMC), cationized starch (trade name: Mermaid C-50, Shikishima Starch Co., Ltd.) (Manufactured) 1.0 part was added, the pH was adjusted to 3.4 with dilute sulfuric acid, paper was made, surface treatment was performed with oxidized starch, and paper with a basis weight of 220 g / m ² was made. Next, 100 parts by mass of synthetic silica (Mizukasil P-78A, manufactured by Mizusawa Chemical Co., Ltd.), 10 parts by mass of polyvinyl alcohol (PVA117: manufactured by Kuraray Co., Ltd.) as a binder, ethylene-vinyl acetate (Polysol EVA AD-10: Showa High) (Molecular Co., Ltd.) 40 parts by mass and cationic polymer (Papiogen P-105: Senka Co., Ltd.) 30 parts by mass were used to prepare a coating solution having a solid content of 22%, and this coating solution was completely removed with an air knife coater. The ink receiving layer was coated by applying and drying the fine paper so that the dry coating amount was 12 g / m ² . Next, 100 parts by mass of spherical colloidal silica (SYLOJET 4000C, cationic, average primary particle size 30 to 40 nm: manufactured by Grace Devison Co., Ltd.) as a pigment to be included in the glossy layer coating liquid, and styrene-acrylic resin (Pascol) as a binder 10 parts by mass of JK718: manufactured by Meisei Chemical Co., Ltd., 10 parts by mass of polyvinyl alcohol (PVA-105: manufactured by Kuraray Co., Ltd.), 10 parts by mass of a cationic polymer (Smileys resin 1001: manufactured by Sumitomo Chemical Co., Ltd.), release agent A coating liquid having a solid content of 20% was obtained using 1 part by mass of a polyethylene emulsion (SN coat 287: manufactured by San Nopco). This coating solution was applied to the surface of the ink receiving layer with an air knife coater so that the dry coating amount was 10 g / m ² . Next, after applying a 0.5% aqueous solution of sodium borate as a coagulation solution and coagulating, the resulting coating layer surface was pressed onto a cast drum having a surface temperature of 105 ° C. while being wet, and ink jet recording was performed. A working medium was prepared.

Example 2:
In Example 1, 50 parts by mass of alumina (PG-003, average secondary particle size 150 nm, crystal form-γ, θ mixture: manufactured by CABOT), gas phase method silica, is included in the glossy layer coating liquid. (Leoroseal QS-102, average secondary particle size 160 nm: manufactured by Tokuyama Co., Ltd.) An ink jet recording medium was produced under the same conditions as described in Example 1 except that the amount was 50 parts by mass.

Example 3:
In Example 1, colloidal silica (Snowtex HS-M-20, average secondary particle diameter of 278 nm) having an aggregate shape in which a plurality of primary particles are randomly combined with the pigment to be contained in the glossy layer coating liquid. (Manufactured by Nissan Chemical Co., Ltd.) An ink jet recording medium was produced under the same conditions as described in Example 1 except that the amount was 100 parts by mass.

Example 4:
An ink jet recording medium was produced under the same conditions as described in Example 1 except that the coagulation liquid was a mixed aqueous solution of 0.5% sodium borate and 3.0% boric acid.

Example 5:
In Example 1, 100 parts of L-BKP beaten to 530 ml of Canadian Standard Freeness (CSF) as acidic paper as a base material, calcined kaolin (trade name: Ansilex 90, Engel Hard Minerals, Inc.) as an internal additive pigment 5 parts of sulfuric acid band, acid rosin sizing agent (trade name: AL-120, manufactured by Seiko PMC) 0.25 part, cationized starch (trade name: Mermaid C-50, Shikishima Starch) 1.0 part), adjusted to pH 5.0 with dilute sulfuric acid, made paper, further surface-treated with oxidized starch, and made high-quality paper with a basis weight of 150 g / m ² . Except for the above, an ink jet recording medium was produced under the same conditions as described in Example 1.

Example 6:
In the same manner as in Example 1, acid paper (high-quality paper having a basis weight of 220 g / m ² which was surface-treated with oxidized starch) was made, and an ink receiving layer was applied in the same manner as in Example 1. . Subsequently, 100 parts by mass of spherical colloidal silica (Adelite AT-20Q, anionic, average primary particle size 10 nm: manufactured by ADEKA) as a pigment of the coating liquid for the glossy layer, and an acrylic resin emulsion (Likabond ES-63 as a binder) , Glass transition temperature 90 ° C: manufactured by Chuo Rika Kogyo Co., Ltd.) 10 parts by mass, silanol-modified polyvinyl alcohol (PVA-R1130: manufactured by Kuraray Co., Ltd.), 3 parts by mass, polyethylene emulsion as a release agent (SN coat 287: manufactured by San Nopco) 1 A coating solution having a solid content of 18% was obtained using parts by mass. This coating solution was applied to the surface of the ink receiving layer with an air knife coater so that the dry coating amount was 10 g / m ² . Next, a coagulation treatment was performed by applying a mixed aqueous solution of 0.5% sodium borate as a coagulation liquid and 3% of a cationic polymer (Smileze Resin 1001: manufactured by Sumitomo Chemical Co., Ltd.). While the layer surface was in a wet state, it was pressure-bonded to a cast drum having a surface temperature of 105 ° C. to produce an ink jet recording medium.

Example 7:
In Example 6, as a coagulation liquid, a mixed aqueous solution of 0.5% sodium borate, 3.0% boric acid, and 3% cationic polymer (Smileze Resin 1001: manufactured by Sumitomo Chemical Co., Ltd.) was applied. An ink jet recording medium was produced under the same conditions as described in Example 6 except that the coagulation treatment was performed.

Reference Example 8:
In the same manner as in Example 2, acidic paper as a base material was made, and in the same manner as in Example 2, an ink receiving layer was applied. Next, after adjusting and applying the glossy layer coating liquid as in Example 2, the coating layer was once dried with an air dryer, and then a 0.5% aqueous solution of sodium borate was applied as a rewetting liquid. While the surface of the coating layer was wet, it was pressure-bonded to a cast drum having a surface temperature of 110 ° C. to produce an ink jet recording medium.

Comparative Example 1:
As neutral paper as a base material, 5 parts of light calcium carbonate (trade name: TP-121, manufactured by Okutama Kogyo Co., Ltd.) as an internal pigment to 100 parts of L-BKP beaten in 530 ml of Canadian Standard Freeness (CSF) Add 0.25 parts of neutral rosin sizing agent (Brander R-10, manufactured by Toho Chemical Co., Ltd.), 1.0 part of cationized starch (Product name: Mermaid C-50, manufactured by Shikishima Starch Co., Ltd.) An ink jet recording medium was prepared under the same conditions as described in Example 1 except that paper was added and paper was made, and a high-quality paper having a basis weight of 220 g / m ² surface-treated with oxidized starch was made.

Comparative Example 2:
In Comparative Example 1, an ink jet recording medium was produced under the same conditions as described in Comparative Example 1 except that a solidification solution was applied with a 3.0% aqueous solution of sodium borate to perform a solidification treatment.

Comparative Example 3:
In Example 1, an ink jet recording medium was produced under the same conditions as described in Example 1, except that a 3.0% aqueous solution of sodium borate was applied as the coagulation liquid to perform the coagulation treatment.

Comparative Example 4:
In Example 1, an ink jet recording medium was used under the same conditions as described in Example 1, except that a solid solution of 3.5% sodium borate and 3.0% boric acid was applied as a coagulation solution to perform the coagulation treatment. Was made.

Comparative Example 5:
In Example 1, an ink jet recording medium was produced under the same conditions as described in Example 1 except that the ink receiving layer was not provided.

(1) Surface pH of substrate surface and glossy layer surface:
Using a pH meter for paper quality inspection (model MPC) manufactured by Kyoritsu Riken, the surface pH of the substrate surface and the glossy layer surface was measured. The measuring method is Japan Tappi No. 49-2 (2000 version; coating method).

(2) Sodium mass ratio of ink jet recording medium:
The mass of sodium contained in the obtained inkjet recording medium was measured by ICP (Inductively Coupled Plasma) emission spectroscopy (manufactured by Thermo Fisher Scientific, IRIS-Intrepid II), and the mass ratio with respect to the obtained medium was determined. .

(3) Image clarity on the surface of the glossy layer:
In order to evaluate the specularity of the glossy layer surface of the obtained ink jet recording paper, image clarity was measured. The image clarity is in accordance with JIS H 8686-2: 1999 “Image quality test method for anodized films of aluminum and aluminum alloys” with an optical comb width of 2 mm and an incident / reflection angle of 60 °. 1T: Suga Test Instruments Co., Ltd.). As an evaluation, when the image clarity is 50% or more, the reflected image is clearly visible and the glossiness is excellent (no problem in practical use). If it is less than 50%, the reflected image is unclear and inferior in gloss (practically problematic). Here, the reason for changing the incident / reflective angle from 45 ° described in JIS to 60 ° is to facilitate evaluation of the difference in glossiness.

(4) Image clarity:
Inkjet obtained by using ISO standard image (ISO / JIS-SCID high-definition color digital standard image data, image name: portrait, image identification number: N1) using a Seiko Epson inkjet printer “PM-G820” Printed on a recording medium. The printed image was visually evaluated.
(Double-circle): The recorded image is very clear and contrast is clear, and it can be used practically.
○: The recorded image is clear and the contrast is clear, and can be used practically.
(Triangle | delta): The recorded image is clear, but contrast is not clear, the color is sinking, and there exists a problem in practical use.
X: The recorded image is unclear and the color is sinking, impractical.

(5) Ink absorbability:
Using an ink jet printer “PM-G820” manufactured by Seiko Epson Corporation, solid (100% density) and characters were obtained for solid colors of each of CMYK inks and the three primary colors of RGB (Red-Green-Blue). Printed on. The boundary of each color of the solid part and the degree of blurring of the characters were evaluated visually.
(Double-circle): A boundary is clear, there is no blur, a character is clear, and it can be used practically.
○: The blur of the boundary is not conspicuous, the characters are clear, and can be used practically.
(Triangle | delta): The blur of a boundary is conspicuous, a character is unclear, and there exists a problem practically.
X: The blurring of the boundary is severe, and the characters cannot be distinguished, so that it is not practical.

(6) Discoloration resistance of the glossy layer surface:
Dibutylhydroxytoluene (BHT) was dissolved in isopropyl alcohol (IPA) to prepare a 1% by mass BHT solution. 20 μl of this BHT solution was dropped on the surface of the glossy layer of each sample and allowed to stand in an environment of 23 ° C. and 50% RH. After 24 hours, the degree of discoloration on the glossy layer surface was observed and evaluated visually.
A: Very little discoloration and no problem at all.
○: Slight discoloration is observed, but there is no practical problem.
(Triangle | delta): Discoloration is seen and there is a problem in practical use.
X: Discoloration is remarkable and impractical.

As is apparent from Table 1, one or more ink-receiving layers are provided on at least one surface of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink-receiving layer. A medium, the base material is acid paper, the surface pH of the glossy layer is in the range of 5.0 to 6.4, and the mass ratio of sodium contained in the ink jet recording medium is or less 600 mass ppm example 1-7 is excellent in printing performance and gloss compared to Comparative example 1-5, and was found to have excellent discoloration resistance of the glossy layer.

  In Comparative Example 1, since the base material was neutral paper, the color change resistance of the glossy layer surface was inferior. In Comparative Example 2, the base material is neutral paper, the surface pH of the glossy layer is as high as 6.8, and the mass ratio of sodium is as high as 780 ppm by mass. It was inferior to. In Comparative Example 3, since the surface pH of the glossy layer was as high as 6.6 and the mass ratio of sodium was as high as 780 ppm by mass, the surface of the glossy layer was inferior in discoloration resistance. In Comparative Example 4, since the mass ratio of sodium to the inkjet recording medium was as high as 900 ppm by mass, the gloss resistance layer surface was inferior in discoloration resistance. Comparative Example 5 was inferior in image clarity and printing performance on the surface of the glossy layer because no ink receiving layer was provided.

Claims (6)

In an ink jet recording medium in which at least one ink receiving layer is provided on at least one side of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink receiving layer.
The substrate is acid paper;
The gloss developing layer is provided by a cast coating method, and the cast coating method is a coagulation method,
The gloss developing layer contains polyvinyl alcohol as the binder, and contains sodium borate as a coagulant,
An ink jet recording medium, wherein the glossy layer has a surface pH in the range of 5.0 to 6.4, and a mass ratio of sodium contained in the ink jet recording medium is 600 mass ppm or less. .   2. The ink jet recording medium according to claim 1, wherein the surface pH of the substrate is in the range of 3.0 to 5.5. Ink jet recording medium of claim 1 or 2 wherein the glossy layer is characterized by containing a cationic polymer. Wherein said glossy layer is inkjet according to claim 1, 2 or 3 average secondary particle diameter, characterized in that the following silica or average secondary particle diameter 500nm containing less alumina or both 500nm Recording medium. The inkjet recording medium according to claim 1, 2, 3 or 4, characterized in that it is processed into a postcard form. In the method for producing an ink jet recording medium, one or more ink receiving layers are provided on at least one surface of a substrate, and a glossy expression layer containing a pigment and a binder is provided on the ink receiving layer.
The substrate is acid paper;
The gloss development layer is provided by a cast coating method, and the cast coating method is a solidification method,
The gloss developing layer contains polyvinyl alcohol as the binder, and contains sodium borate as a coagulant,
The concentration of sodium borate in the coagulation liquid is less than 3% by weight,
An ink jet recording medium, wherein the glossy layer has a surface pH in the range of 5.0 to 6.4, and a mass ratio of sodium contained in the ink jet recording medium is 600 mass ppm or less. Manufacturing method.