JP2006306108A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recording medium which eliminates bleeding with elapse of time in images, while maintaining a better glossiness and print toner concentration. <P>SOLUTION: The inkjet recording medium has an ink receiving layer on a substrate. The ink receiving layer contains at least a cationic urethane resin and the mean particle diameter of the aqueous dispersion is not larger than 0.05 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording medium, and more particularly, to an ink jet recording medium in which image blurring is improved while maintaining good gloss and high print density.

  In recent years, with the rapid development of the information technology (IT) industry, various information processing systems have been developed, and a recording method and a recording apparatus suitable for each information processing system have been developed and put into practical use. Among such recording methods, the inkjet recording method is advantageous in that it can be recorded on various recording materials, the hardware (device) is relatively inexpensive, is compact, and is excellent in low noise. It has been widely used not only in offices but also in so-called home use.

In addition, with the recent increase in resolution of inkjet printers, it is also possible to obtain so-called photographic-like high-quality recorded materials, and along with the further development of hardware (device), various recording sheets for inkjet recording are also available. Improvements have been made.
The characteristics required for a recording sheet for ink jet recording are generally (1) fast drying (fast ink absorption speed), and (2) proper and uniform ink dot diameter (bleeding). (3) Good graininess, (4) High roundness of dots, (5) High color density, (6) High saturation (no dullness) ), (7) The light resistance and water resistance of the print portion are good, (8) The whiteness of the recording sheet is high, (9) The recording sheet has good storage stability (yellowing coloration during long-term storage) (10) hard to deform, good dimensional stability (curl is sufficiently small), (11) good running performance of hardware, Etc. Furthermore, in the use of photo glossy paper used for the purpose of obtaining so-called photographic-like high-quality recorded matter, in addition to the above characteristics, glossiness, surface smoothness, texture of photographic paper similar to silver salt photography, etc. Required.

  In recent years, an ink jet recording medium having a porous structure in an ink receiving layer has been developed and put into practical use for the purpose of improving the above-mentioned various characteristics. Such an ink jet recording medium has a porous structure, so that it has excellent ink receptivity (fast drying property) and high glossiness.

  For example, there has been proposed an ink jet recording medium containing fine inorganic pigment particles and a water-soluble resin and having an ink receiving layer having a high porosity on a support (see, for example, Patent Documents 1 and 2). . These recording media, particularly ink jet recording media provided with an ink-receiving layer having a porous structure using silica as inorganic pigment fine particles, are excellent in ink absorptivity and can form high-resolution images due to the structure. It has ink receptive performance and can exhibit high gloss.

  In addition, compounds having tertiary amino groups or quaternary ammonium salts, particularly polymer compounds having these, have been widely added to inkjet recording sheets for the purpose of fixing the dye component of the ink. For example, (co) polymers of diallylammonium salt derivatives (see, for example, Patent Documents 3, 4, and 5), allylamine salt copolymers (see, for example, Patent Documents 6 and 7), (meth) acrylates having ammonium salts , (Meth) acrylamide (co) polymers, vinyl (co) polymers such as vinylbenzylammonium salt (co) polymers (for example, see Patent Documents 8 to 14), modified polyvinyl alcohol (for example, see Patent Document 15) ), Amine-epichlorohydrin polyadduct (see, for example, Patent Documents 16 and 17), and polyamidine (see, for example, Patent Documents 18 and 19). By using these compounds to fix the dye, aging blur is prevented.

  However, all of these compounds are basically water-soluble polymers, and water-soluble dyes cannot be completely immobilized, and improvement in aging due to high temperature and high humidity is still insufficient. . Also, if the ink is stored in a clear file immediately after printing, the ink moisture and high-boiling solvents (such as glycerin and diethylene glycol derivatives) contained in a small amount remain in the ink. End up.

  On the other hand, those containing a base latex that has a similar tertiary amino group or quaternary ammonium salt but is insoluble in water are also known (see, for example, Patent Document 20, Patent Document 21, Patent Document 22, and Patent Document 23). .) And improvement of water resistance is achieved by using these hydrophobic latexes.

  In addition, in order to impart sufficient water resistance, it is necessary to add a large amount of these compounds. As a result, problems such as deterioration in image light resistance and reduction in miscibility with pigments are caused. Many of these are crosslinkable monomers (that is, monomers having two or more polymerizable functional groups in the molecule) in order to make a hydrophobic monomer unit such as a tertiary amino group or a quaternary ammonium salt into a latex. Is used. For this reason, it is difficult for water-soluble ink to penetrate into the pigment particles, and the ink acceptability is not sufficient. In addition, when used in a receiving layer made of a porous film in order to add a particulate compound, the pores of the porous film are blocked and the ink absorbability is inhibited.

  Furthermore, even when the above-described means are used, when the printed image is stored in a clear file immediately after printing, or when it is stored for a long period of time particularly under high humidity conditions. However, there is also a problem that aging blur of the image occurs.

  In addition, an example using a hydrophobic vinylbenzylammonium salt-based cationic polymer that is water-insoluble but solvent-soluble is disclosed instead of latex (see, for example, Patent Document 24). However, even when this is used, there is a problem that the light fastness of the image is lowered although the effect of improving the aging blur is high.

  To prevent the above problems, for example, the use of a cationic polymer having both a (meth) acrylate and / or (meth) acrylamide-based cation moiety and a vinylbenzylammonium salt-based cation moiety prevents aging blurring. However, even in these cases, the effect of improving the aging blur is still insufficient (see, for example, Patent Document 25).

  Further, it is described that aging blurring can be improved by using a (co) polymer of a vinylbenzylammonium salt-based water-soluble polymer (cation content is 40 mol% or more) (for example, patents) Reference 26). However, with this polymer, the aging blur is improved, but it causes a decrease in ink absorbency and a decrease in print density. Further, when silica is used as the fine particles, the dispersibility may be deteriorated.

In this way, it is possible to form a high-resolution and high-density image with good ink absorbability, excellent image-storability (light resistance, ozone resistance, etc.), and especially for a long time in a high-temperature and high-humidity environment. At present, an ink jet recording medium that does not cause aging even when stored has not yet been developed.
JP 10-119423 A Japanese Patent Laid-Open No. 10-217601 JP 60-83882 A JP-A 64-75281 JP 59-20696 A JP-A-61-61887 JP-A 61-72581 JP-A-6-340163 JP-A-4-288283 Japanese Patent Laid-Open No. 7-242055 Japanese Patent Laid-Open No. 9-300180 JP-A-8-318672 Japanese Patent Laid-Open No. 10-272830 JP 63-115780 A Japanese Patent Laid-Open No. 10-44588 JP-A-6-234268 JP 11-277888 A JP-A-11-58934 Japanese Patent Laid-Open No. 11-28860 JP 57-36692 A Japanese Patent Laid-Open No. 11-180034 Japanese Patent Laid-Open No. 11-20302 JP-A-8-244336 JP 2000-239014 A JP 11-348409 A International Publication No. 99/64248 Pamphlet

  The present invention has been made in view of the above circumstances, and can form a high-resolution and high-density image having good ink absorptivity and glossiness, and storage stability (light resistance, ozone resistance) of the image area. Etc.) and to provide an ink jet recording medium that does not generate aging even when stored in a high temperature and high humidity environment for a long time, and to achieve the object. .

Means of the present invention for solving the above-mentioned problems are as follows. That is,
<1> An ink jet recording medium having an ink receiving layer on a support, wherein the ink receiving layer contains at least a cationic urethane resin.
<2> The inkjet recording medium according to <1>, wherein the cationic urethane resin has a glass transition temperature of 50 ° C. or higher.
<3> The ink jet recording medium according to <1> or <2>, wherein the ink receiving layer further contains a water-soluble resin.
<4> The water-soluble resin is at least one selected from a polyvinyl alcohol resin, a cellulose resin, a resin having an ether bond, a resin having a carbamoyl group, a resin having a carboxy group, and gelatins. The inkjet recording medium according to <3> above.
<5> The ink jet recording medium according to any one of <3> and <4>, wherein the ink receiving layer contains a crosslinking agent capable of crosslinking the water-soluble resin.
<6> The ink jet recording medium according to any one of <1> to <5>, wherein the ink receiving layer further contains fine particles.
<7> The inkjet recording medium according to <6>, wherein the fine particles are at least one selected from silica fine particles, colloidal silica, alumina fine particles, and pseudoboehmite.
<8> The ink jet recording medium according to any one of <1> to <7>, wherein the ink receiving layer further contains a mordant.

  According to the present invention, it is possible to provide an ink jet recording medium in which the aging of an image is improved while maintaining good glossiness and printing density.

The ink jet recording medium of the present invention is characterized in that the ink receiving layer provided on the support contains at least a cationic urethane resin. Furthermore, the ink receiving layer of the ink jet recording medium of the present invention may contain a water-soluble resin, a crosslinking agent, fine particles, a mordant, other additives, and the like, if necessary or necessary. Further, another layer may be provided on the support. In the present invention, the ink receiving layer is preferably formed on the support by the WOW method described later.
Hereinafter, the main configuration and production of the present invention will be described in detail.

(Cationic urethane resin)
The ink receiving layer of the ink jet recording medium of the present invention contains at least a “cationic urethane resin”. The cationic urethane resin according to the present invention is preferably a urethane resin having a cationic group such as a tertiary amine and a quaternary ammonium salt from the viewpoint of production suitability and excellent viewpoint.

Examples of the polyurethane applicable as the cationic urethane resin include polyurethanes synthesized by a polyaddition reaction using various combinations of the following diol compounds and diisocyanate compounds. The diol compound and diisocyanate compound that can be used for the synthesis of the polyurethane may be used alone or in various ways (for example, adjustment of the glass transition temperature (Tg) of the polymer and improvement of solubility, Depending on the compatibility with the binder, improvement of the stability of the dispersion, etc., two or more of them can be used in any proportion.
Specific examples of the diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 2,2 -Dimethyl-1,3-propanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 3,3-dimethyl-1,2-butanediol, 2 -Ethyl-2-methyl-1,3-propanediol, 1,2-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol 2,2-diethyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 1,7-heptane All, 2-methyl-2-propyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, 1, 8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, hydroquinone, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol (average molecular weight = 200,300,400,600,1000,1500,4000), polypropylene glycol (average molecular weight = 200,400,1000), polyester polyol, 4,4′-dihydroxy-diphenyl-2,2-propane, 4,4 ′ -Dihydroxyphenyls Luhon etc. are mentioned.

  Examples of the diisocyanate compound include methylene diisocyanate, ethylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylylene diisocyanate, 1, 5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, 3,3′-dimethylbiphenylene diisocyanate, 4,4′-biphenylene diisocyanate, dicyclohexylmethane diisocyanate , Methylenebis (4-cyclohexylisocyanate) and the like.

  The cationic group-containing polyurethane according to the present invention can be obtained, for example, by using a diol having a hydrophilic group during the synthesis of polyurethane. In that case, the hydrophilic group is introduced into the polyurethane as a substituent from the polymer main chain. The diol compound and diisocyanate compound that can be used for the synthesis of the polyurethane may be used alone or for various purposes (for example, adjustment of glass transition temperature (Tg) of polyurethane and improvement of solubility, Depending on the compatibility with the binder, improvement of the stability of the dispersion, etc., two or more of them can be used in any proportion.

  The cationic group can be introduced into the polyurethane by various methods. For example, during the synthesis of polyurethane, a diol containing a cationic group can be used as a substituent from the polymer main chain. Furthermore, after the polyurethane is produced by polymerization, a cationic group may be introduced by reacting a reactive group such as an —OH group or amino group remaining at the terminal with a tertiary amine, quaternary ammonium salt-containing compound or the like. it can.

  0.1-3 mmol / g is preferable and, as for content of the cationic group in the said cationic group containing polymer, 0.2-2 mmol / g is more preferable. In addition, when there is too little content of the said cationic group, the dispersion stability of a polyurethane will become small, and when too large, compatibility with a binder will fall.

The exemplary compounds of polyurethane used for the cationic urethane resin are listed below. The numbers in parentheses represent the molar composition ratio of each structural unit. The present invention is not limited to these compounds.
(P-1) 4,4′-diphenylmethane diisocyanate / hexamethylene diisocyanate / tetraethylene glycol / ethylene glycol / 2,2-bis (hydroxymethyl) propionic acid (40/10/20/20/10)
(P-2) 4,4′-diphenylmethane diisocyanate / hexamethylene diisocyanate / butanediol / polyethylene glycol (Mw = 400) / 2,2-bis (hydroxymethyl) propionic acid (40/10/20/10/20)
(P-3) 1,5-naphthylene diisocyanate / butanediol / 4,4′-dihydroxy-diphenyl-2,2′-propane / polypropylene glycol (Mw = 400) / 2,2-bis (hydroxymethyl) propion Acid (50/20/5/10/15)
(P-4) 1,5-naphthylene diisocyanate / hexamethylene diisocyanate / 2,2-bis (hydroxymethyl) butanoic acid / polybutylene oxide (Mw = 500) (35/15/25/25)
(P-5) Isophorone diisocyanate / diethylene glycol / neopentyl glycol / 2,2-bis (hydroxymethyl) propionic acid (50/20/20/10)
(P-6) Toluene diisocyanate / 2,2-bis (hydroxymethyl) butanoic acid / polyethylene glycol (Mw = 1000) / cyclohexanedimethanol (50/10/10/30)

  When the cationic urethane resin of the present invention is used in the ink receiving layer, the glass transition temperature is particularly important. In order to suppress blurring of the image over time after the image is formed by inkjet recording, it is preferable that the cationic urethane resin has a glass transition temperature of 50 ° C. or higher. Furthermore, the glass transition temperature of the cationic urethane resin is more preferably 55 ° C. or higher, and the glass transition temperature is more preferably 60 ° C. or higher. If the glass transition temperature is less than 50 ° C., aging blur may not be effectively suppressed over a long period of time. In addition, although there is no restriction | limiting in particular in the upper limit of this glass transition temperature, in normal use, 150 degreeC is enough, and when it exceeds this, there exists a possibility that the manufacturability at the time of preparing an aqueous dispersion may fall.

  As a mass average molecular weight (Mw) of the said cationic urethane resin used for this invention, 1000-200000 are preferable normally and 2000-50000 are more preferable. If the molecular weight is less than 1000, it tends to be difficult to obtain a stable aqueous dispersion. If the molecular weight exceeds 200000, the solubility becomes poor and the liquid viscosity increases, and the average particle size of the aqueous dispersion increases. There is a tendency that it is difficult to control the diameter, in particular, to 0.05 μm or less.

  In the ink receiving layer of the present invention, the content of the cationic urethane resin is preferably from 0.1 to 30% by mass, more preferably from 0.3 to 20% by mass, based on the total solid content constituting the ink receiving layer. In particular, 0.5 to 15% by mass is most preferable. When the content is less than 0.1% by mass, the effect of improving aging blurring tends to be insufficient. On the other hand, when the content exceeds 30% by mass, the proportion of fine particles and binder components decreases. In addition, the ink absorptivity to high-quality recording paper tends to decrease.

Next, a method for adjusting the aqueous dispersion of the cationic urethane resin according to the present invention will be described.
The above cationic urethane resin is mixed with an aqueous solvent, additives are mixed as necessary, and the mixture is finely divided using a disperser, thereby dispersing water in an average particle size of 0.05 μm or less. A liquid can be obtained. Dispersers used for obtaining the aqueous dispersion include conventionally known high-speed rotary dispersers, medium stirring dispersers (ball mill, sand mill, bead mill, etc.), ultrasonic dispersers, colloid mill dispersers, high pressure dispersers, and the like. Various dispersers can be used. From the viewpoint of efficiently dispersing the formed fine particles, a medium stirring type disperser, a colloid mill disperser, or a high pressure disperser is preferable.

  The high-pressure disperser (homogenizer) is described in detail in US Pat. No. 4,533,254, JP-A-6-47264, etc., but as a commercially available apparatus, a Gorin homogenizer (APV GAULIN) is used. INC.), A microfluidizer (MICROFLUIDEX INC.), An optimizer (Sugino Machine Co., Ltd.) and the like can be used. In recent years, a high-pressure homogenizer having a mechanism for atomizing in an ultrahigh-pressure jet stream as described in US Pat. No. 5,720,551 is particularly effective for emulsification dispersion of the present invention. DeBEE2000 (BEE INTERNIONAL LTD.) Is an example of an emulsifying apparatus using this ultra-high pressure jet stream.

  Water, an organic solvent, or a mixed solvent thereof can be used as the aqueous solvent in the dispersion step. Examples of the organic solvent that can be used for the dispersion include alcohols such as methanol, ethanol, n-propanol, i-propanol, and methoxypropanol, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, acetonitrile, ethyl acetate, and toluene. It is done.

  The cationic urethane resin of the present invention itself can be a naturally stable emulsified dispersion, but a small amount of a dispersing agent (surfactant) is added to make the emulsified dispersion more quickly or more stable. It may be used. Surfactants used for such purposes include, for example, fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensates. , Anionic surfactants such as polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene Nonionic surfactants such as alkylamines, glycerin fatty acid esters and oxyethyleneoxypropylene block copolymers are preferred. Further, SURFYNOLS (Air Products & Chemicals), which is an acetylene-based polyoxyethylene oxide surfactant, is also preferably used. An amine oxide type amphoteric surfactant such as N, N-dimethyl-N-alkylamine oxide is also preferred. Further, pages (37) to (38) of JP-A-59-157,636, Research Disclosure No. Those listed as surfactants described in 308119 (1989) can also be used.

  In order to stabilize immediately after emulsification, a water-soluble polymer can be added in combination with the surfactant. As the water-soluble polymer, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, polyacrylic acid, polyacrylamide or a copolymer thereof is preferably used. It is also preferable to use natural water-soluble polymers such as polysaccharides, casein, and gelatin.

  When the cationic urethane resin of the present invention is dispersed in an aqueous medium by the emulsification dispersion method, it is particularly important to control the particle size. In order to increase color purity and color density when an image is formed by inkjet, it is necessary to reduce the average particle diameter of the cationic urethane resin in the aqueous dispersion. Specifically, in the ink receiving layer of the present invention, the volume average particle size of the cationic urethane resin needs to be 0.05 μm or less, and the average particle size is preferably 0.04 μm or less, Furthermore, 0.03 μm or less is more preferable.

(Fine particles)
In general, the ink receiving layer according to the present invention preferably contains fine particles.
The fine particles are preferably inorganic pigment fine particles. Examples of the inorganic pigment fine particles include silica fine particles, colloidal silica, titanium dioxide, barium sulfate, calcium silicate, zeolite, kaolinite, halloysite, mica, talc, calcium carbonate, Examples thereof include magnesium carbonate, calcium sulfate, boehmite, and pseudo boehmite. Among these, silica fine particles are particularly preferable.

  Since the silica fine particles have a particularly large specific surface area, the ink absorption and retention efficiency is high, and the refractive index is low. Therefore, if the dispersion is carried out to an appropriate fine particle diameter, transparency can be imparted to the ink receiving layer, There is an advantage that high color density and good color developability can be obtained. Thus, the fact that the receiving layer is transparent means that not only for applications that require transparency such as OHP, but also when applied to recording media such as photo glossy paper, high color density and good color developability and This is important from the viewpoint of obtaining glossiness.

  The average primary particle diameter of the inorganic pigment fine particles is preferably 20 nm or less, more preferably 15 nm or less, and particularly preferably 10 nm or less. When the average primary particle diameter is 20 nm or less, the ink absorption characteristics can be effectively improved, and at the same time, the glossiness of the ink receiving layer surface can be enhanced.

  In particular, the silica fine particle has a silanol group on the surface thereof, and the particles are likely to adhere to each other due to the hydrogen bond of the silanol group, and because of the adhesion effect between the particles via the silanol group and the water-soluble resin, Similarly, when the average primary particle size is 20 nm or less, the ink-receiving layer has a high porosity and a highly transparent structure can be formed, and the ink absorption characteristics can be effectively improved.

  Generally, silica fine particles are roughly classified into wet method particles and dry method (gas phase method) particles depending on the production method. In the above wet method, a method is mainly used in which activated silica is produced by acid decomposition of a silicate, and this is appropriately polymerized and agglomerated and precipitated to obtain hydrous silica. On the other hand, the gas phase method is a method by high-temperature gas phase hydrolysis of silicon halide (flame hydrolysis method), a method in which silica sand and coke are heated and reduced by an arc in an electric furnace and oxidized with air. The method of obtaining anhydrous silica by the (arc method) is the mainstream, and the “gas phase method silica” refers to anhydrous silica fine particles obtained by the gas phase method.

Vapor phase method silica is different from the above hydrous silica in the density of silanol groups on the surface, the presence or absence of vacancies, etc., and shows different properties, but is suitable for forming a three-dimensional structure with high porosity. The reason for this is not clear, but in the case of hydrous silica, the density of silanol groups on the surface of the fine particles is as high as 5 to 8 / nm ^2, and the silica fine particles tend to agglomerate closely (aggregate). In the case of the method silica, the density of silanol groups on the surface of the fine particles is as small as ² to 3 / nm ² , so that it becomes sparse soft agglomeration (flocculate), and as a result, it is estimated that the structure has a high porosity. The
In the present invention, vapor phase silica fine particles (anhydrous silica) obtained by the dry method are preferable, and silica fine particles having a density of 2 to 3 silanol groups / nm ² on the surface of the fine particles are more preferable.

(Water-soluble resin)
The ink receiving layer according to the present invention preferably further contains a water-soluble resin.
Examples of the water-soluble resin include resins having a hydroxyl group as a hydrophilic structural unit, such as polyvinyl alcohol (PVA), cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, polyvinyl acetal, and cellulose resin [ Methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), etc.], chitins, chitosans, starch; polyethylene oxide (PEO), polypropylene which is a resin having a hydrophilic ether bond Oxide (PPO), Polyethylene glycol (PEG), Polyvinyl ether (PVE); Polyacrylamid, which is a resin having a hydrophilic amide group or amide bond (PAAM), polyvinyl pyrrolidone (PVP) and the like. In addition, polyacrylic acid salts, maleic acid resins, alginic acid salts, gelatins and the like having a carboxyl group as a dissociable group can also be mentioned.
Among the above, polyvinyl alcohol (PVA) is particularly preferable.

As the content of the water-soluble resin, the decrease in the film strength and cracking at the time of drying due to the insufficient content, and the excessive content makes the voids easily blocked by the resin, From the viewpoint of preventing the ink absorbency from decreasing due to the decrease in the porosity, the amount is preferably 9 to 40% by mass, and more preferably 12 to 33% by mass with respect to the total solid mass of the ink receiving layer.
The fine particles and the water-soluble resin mainly constituting the ink receiving layer may be a single material or a mixed system of a plurality of materials.

  The polyvinyl alcohol (PVA) has a number average degree of polymerization of preferably 1800 or more, more preferably 2000 or more, from the viewpoint of preventing cracks. When combined with silica fine particles, the type of water-soluble resin is important from the viewpoint of transparency. In particular, when anhydrous silica is used, it is preferable to use PVA as the water-soluble resin, and more preferable is a PVA resin having a saponification degree of 70 to 99%.

  Examples of the polyvinyl alcohol include cation-modified PVA, anion-modified PVA, silanol-modified PVA and other polyvinyl alcohol derivatives in addition to polyvinyl alcohol (PVA). Polyvinyl alcohol may be used alone or in combination of two or more.

The PVA has a hydroxyl group in its structural unit, and this hydroxyl group and a silanol group on the surface of the silica fine particle form a hydrogen bond, and it is easy to form a three-dimensional network structure in which the secondary particle of the silica fine particle is a chain unit. To do. By forming such a three-dimensional network structure, it is considered that an ink receiving layer having a porous structure with a high porosity can be formed.
In the ink jet recording medium, the porous ink receiving layer obtained as described above can rapidly absorb ink by capillary action and form dots with good roundness without ink bleeding.

(Content ratio of fine particles to water-soluble resin)
The content ratio of the fine particles (preferably silica fine particles; x) to the water-soluble resin (y) [PB ratio (x / y), the mass of inorganic pigment fine particles relative to 1 part by mass of the water-soluble resin] is the film structure of the ink receiving layer. It also has a big impact. That is, as the PB ratio increases, the porosity, pore volume, and surface area (per unit mass) increase. Specifically, as the PB ratio (x / y), a decrease in film strength and cracking during drying caused by the PB ratio being too large are prevented, and the PB ratio is too small. From the viewpoint of preventing the gap from being easily blocked by the resin and preventing the ink absorbability from being lowered due to a decrease in the void ratio, 1.5 / 1 to 10/1 is preferable.

  Since stress may be applied to the recording medium when passing through the transport system of the ink jet printer, the ink receiving layer needs to have sufficient film strength. Further, when cutting into a sheet, the ink receiving layer needs to have sufficient film strength to prevent cracking and peeling of the ink receiving layer. From such a viewpoint, the PB ratio (x / y) is preferably 5/1 or less, and preferably 2/1 or more from the viewpoint of securing high-speed ink absorbability with an inkjet printer.

For example, a coating solution in which anhydrous silica fine particles having an average primary particle size of 20 nm or less and a water-soluble resin are completely dispersed in an aqueous solution with a PB ratio (x / y) of 2/1 to 5/1 is coated on a support. When the coating layer is dried, a three-dimensional network structure in which the secondary particles of silica fine particles are chain units is formed, the average pore diameter is 30 nm or less, the porosity is 50% to 80%, and the pore specific volume is 0. A translucent porous film having a surface area of 5 ml / g or more and a specific surface area of 100 m ² / g or more can be easily formed.

(Crosslinking agent)
The ink receiving layer according to the present invention is a porous layer in which a layer containing inorganic fine particles and a water-soluble resin further contains a crosslinking agent capable of crosslinking the water-soluble resin, and is cured by a crosslinking reaction of the water-soluble resin by the crosslinking agent. The aspect which is a quality layer is preferable.

As the cross-linking agent, a suitable one may be appropriately selected in relation to the water-soluble resin contained in the ink-receiving layer. Among them, a boron compound is preferable in that the cross-linking reaction is rapid, and examples thereof include borax and boric acid. , borates (eg, _{orthoborate, InBO 3, ScBO 3, YBO} 3, LaBO 3, Mg 3 (BO 3) 2, Co 3 (BO 3) 2, two borates (e.g., Mg ₂ B ₂ O ₅ , Co ₂ B ₂ O ₅ ), metaborate (for example, LiBO ₂ , Ca (BO ₂ ) ₂ , NaBO ₂ , KBO ₂ ), tetraborate (for example, Na ₂ B ₄ O ₇ .10H ₂ O), And pentaborates (for example, KB ₅ O ₈ .4H ₂ O, Ca ₂ B ₆ O ₁₁ .7H ₂ O, CsB ₅ O ₅ ), etc. Of these, borax, boric acid, and borate are preferable, and boric acid is particularly preferable. Most preferably, it is used in combination with polyvinyl alcohol, which is a functional resin.

  In the present invention, the crosslinking agent is preferably contained in an amount of 0.05 to 0.50 parts by mass, and 0.08 to 0.30 parts by mass with respect to 1.0 part by mass of the water-soluble resin. More preferably. When the content of the crosslinking agent is within the above range, the water-soluble resin can be effectively crosslinked to prevent cracks and the like.

When gelatin is used as the water-soluble resin, the following compounds other than boron compounds can also be used as a crosslinking agent.
For example, aldehyde compounds such as formaldehyde, glyoxal and glutaraldehyde; ketone compounds such as diacetyl and cyclopentanedione; bis (2-chloroethylurea) -2-hydroxy-4,6-dichloro-1,3,5- Active halogen compounds such as triazine and 2,4-dichloro-6-S-triazine sodium salt; divinylsulfonic acid, 1,3-vinylsulfonyl-2-propanol, N, N′-ethylenebis (vinylsulfonylacetamide) ), Active vinyl compounds such as 1,3,5-triacryloyl-hexahydro-S-triazine; N-methylol compounds such as dimethylolurea and methyloldimethylhydantoin; melamine resins (for example, methylolmelamine, alkylated methylolmelamine) ;Epoxy resin;

  Isocyanate compounds such as 1,6-hexamethylene diisocyanate; aziridine compounds described in US Pat. Nos. 3,017,280 and 2,983611; carboximide compounds described in US Pat. No. 3,100,704; glycerol triglycidyl Epoxy compounds such as ether; Ethyleneimino compounds such as 1,6-hexamethylene-N, N′-bisethyleneurea; Halogenated carboxaldehyde compounds such as mucochloric acid and mucophenoxycyclolic acid; 2,3-dihydroxy Dioxane compounds such as dioxane; Titanium lactate, aluminum sulfate, chromium alum, potassium alum, metal-containing compounds such as zirconyl acetate and chromium acetate, polyamine compounds such as tetraethylenepentamine, hydrazide compounds such as adipic acid dihydrazide It is a small molecule or polymer or the like containing an oxazoline group two or more. The above crosslinking agents may be used alone or in combination of two or more.

  In the present invention, the cross-linking agent may be added to the ink receiving layer coating solution and / or the coating solution for forming the adjacent layer of the ink receiving layer when forming the ink receiving layer, or The above-mentioned coating solution for ink-receiving layer is coated on a support on which a coating solution containing a crosslinking agent has been applied in advance, or a coating solution for ink-receiving layer that does not contain a crosslinking agent is coated and dried, and then the coating solution is overcoated. For example, a crosslinking agent can be supplied to the ink receiving layer. Preferably, from the viewpoint of production efficiency, it is preferable to add a crosslinking agent to the ink receiving layer coating solution or the coating solution for forming the adjacent layer, and supply the crosslinking agent simultaneously with the formation of the ink receiving layer. In particular, it is preferably contained in the ink receiving layer coating solution from the viewpoint of improving the image printing density and glossiness. Further, the concentration of the crosslinking agent in the ink receiving layer coating solution is preferably 0.05 to 10% by mass, and more preferably 0.1 to 7% by mass.

  For example, the crosslinking agent can be suitably applied as follows. Here, a boron compound will be described as an example. That is, when the ink receiving layer is a layer obtained by crosslinking and curing the coating layer coated with the ink receiving layer coating liquid (first coating liquid), the crosslinking curing is performed by (1) coating the coating layer by applying the coating liquid. (2) During the dry coating of the coating layer formed by coating the coating solution and before the coating layer exhibits a reduced rate of drying, the pH is 8 or more. This is performed by applying a basic solution (second coating solution) to the coating layer. The boron compound as the crosslinking agent may be contained in either the first coating liquid or the second coating liquid, or may be contained in both the first coating liquid and the second coating liquid.

(mordant)
In the present invention, a mordant is preferably contained in the ink receiving layer in order to improve the water resistance and aging resistance of the formed image. As the mordant, any of an organic mordant such as a cationic polymer (cationic mordant) and an inorganic mordant such as a water-soluble metal compound can be used. Of these, organic mordants are preferable, and cationic mordants are particularly preferable.

  The presence of the mordant in at least the upper layer of the ink receiving layer causes an interaction with an ink-jet liquid ink having an anionic dye as a coloring material, which stabilizes the coloring material, thereby improving water resistance and resistance. The aging blur can be further improved.

  In this case, the ink receiving layer coating liquid (first coating liquid) and the basic solution (second coating liquid) may be contained, but a liquid containing inorganic fine particles (particularly, vapor phase silica) Is preferably contained in a second coating liquid that is a separate liquid. That is, when a mordant is added directly to a coating solution for an ink receiving layer, aggregation may occur in the presence of vapor phase silica having an anionic charge. Can be prepared independently and applied separately, there is no need to worry about agglomeration of inorganic fine particles, and the range of mordant species can be selected.

  Among these, it is particularly preferable to use a basic mordant (for example, polyallylamine). When a basic mordant is used, it plays a role as a mordant and also functions as a basic substance, and a basic solution can be prepared without using a basic substance.

As the cationic mordant, a polymer mordant having a primary to tertiary amino group or a quaternary ammonium base as a cationic group is preferably used, but a cationic non-polymer mordant may also be used. it can.
Examples of the polymer mordant include a homopolymer of a monomer having a primary to tertiary amino group and a salt thereof, or a monomer having a quaternary ammonium base (hereinafter referred to as “mordant monomer”), or the mordant monomer. And those obtained as a copolymer or a condensation polymer of the other monomer (hereinafter referred to as “non-mordant polymer”) are preferable. These polymer mordants can be used in any form of a water-soluble polymer or water-dispersible latex particles.

  Examples of the mordant monomer include trimethyl-p-vinylbenzylammonium chloride, trimethyl-m-vinylbenzylammonium chloride, triethyl-p-vinylbenzylammonium chloride, triethyl-m-vinylbenzylammonium chloride, N, N-dimethyl- N-ethyl-Np-vinylbenzylammonium chloride, N, N-diethyl-N-methyl-Np-vinylbenzylammonium chloride, N, N-dimethyl-Nn-propyl-Np-vinylbenzyl Ammonium chloride, N, N-dimethyl-Nn-octyl-Np-vinylbenzylammonium chloride, N, N-dimethyl-N-benzyl-Np-vinylbenzylammonium chloride, N, N-diethyl-N Benzyl-Np-vinylbenzylammonium chloride, N, N-dimethyl-N- (4-methyl) benzyl-Np-vinylbenzylammonium chloride, N, N-dimethyl-N-phenyl-Np-vinyl Benzylammonium chloride;

  Trimethyl-p-vinylbenzylammonium bromide, trimethyl-m-vinylbenzylammonium bromide, trimethyl-p-vinylbenzylammonium sulfonate, trimethyl-m-vinylbenzylammonium sulfonate, trimethyl-p-vinylbenzylammonium acetate, trimethyl-m-vinyl Benzylammonium acetate, N, N, N-triethyl-N-2- (4-vinylphenyl) ethylammonium chloride, N, N, N-triethyl-N-2- (3-vinylphenyl) ethylammonium chloride, N, N-diethyl-N-methyl-N-2- (4-vinylphenyl) ethylammonium chloride, N, N-diethyl-N-methyl-N-2- (4-vinylphenyl) ethylammonium chloride Tate;

  N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N- Methyl chloride, ethyl chloride, methyl bromide of dimethylaminoethyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N-diethylaminopropyl (meth) acrylamide , Quaternized products of ethyl bromide, methyl iodide or ethyl iodide, or sulfonates, alkyl sulfonates, acetates or alkyl carboxylates substituted with their anions.

  Specific examples of the compound include monomethyl diallylammonium chloride, trimethyl-2- (methacryloyloxy) ethylammonium chloride, triethyl-2- (methacryloyloxy) ethylammonium chloride, trimethyl-2- (acryloyloxy) ethylammonium chloride, Triethyl-2- (acryloyloxy) ethylammonium chloride, trimethyl-3- (methacryloyloxy) propylammonium chloride, triethyl-3- (methacryloyloxy) propylammonium chloride, trimethyl-2- (methacryloylamino) ethylammonium chloride, triethyl- 2- (methacryloylamino) ethylammonium chloride, trimethyl-2- (acryloylua) C) ethylammonium chloride, triethyl-2- (acryloylamino) ethylammonium chloride, trimethyl-3- (methacryloylamino) propylammonium chloride, triethyl-3- (methacryloylamino) propylammonium chloride, trimethyl-3- (acryloylamino) Propylammonium chloride, triethyl-3- (acryloylamino) propylammonium chloride;

N, N-dimethyl-N-ethyl-2- (methacryloyloxy) ethylammonium chloride, N, N-diethyl-N-methyl-2- (methacryloyloxy) ethylammonium chloride, N, N-dimethyl-N-ethyl- 3- (acryloylamino) propylammonium chloride, trimethyl-2- (methacryloyloxy) ethylammonium bromide, trimethyl-3- (acryloylamino) propylammonium bromide, trimethyl-2- (methacryloyloxy) ethylammonium sulfonate, trimethyl-3- And (acryloylamino) propylammonium acetate.
Other examples of the copolymerizable monomer include N-vinylimidazole and N-vinyl-2-methylimidazole.

In addition, allylamine, diallylamine, derivatives thereof, salts and the like can also be used. Examples of such compounds are allylamine, allylamine hydrochloride, allylamine acetate, allylamine sulfate, diallylamine, diallylamine hydrochloride, diallylamine acetate, diallylamine sulfate, diallylmethylamine and salts thereof (for example, Hydrochloride, acetate, sulfate, etc.), diallylethylamine and salts thereof (for example, hydrochloride, acetate, sulfate, etc.), diallyldimethylammonium salt (chloride, acetic acid as counter anions of the salt) Ion sulfate, etc.). In addition, since these allylamines and diallylamine derivatives are inferior in polymerizability in the amine form, it is a general production method to polymerize in the form of a salt and desalting as required.
In addition, a polymerization unit such as N-vinylacetamide, N-vinylformamide or the like, which is converted into a vinylamine unit by hydrolysis after polymerization, and a salt thereof can be used.

The non-mordant monomer does not contain a basic or cationic moiety such as a primary to tertiary amino group and a salt thereof, or a quaternary ammonium base, and does not interact with a dye in an inkjet ink. Or a monomer having a substantially small interaction.
Examples of the non-mordant monomer include (meth) acrylic acid alkyl ester; (meth) acrylic acid cycloalkyl ester such as cyclohexyl (meth) acrylate; (meth) acrylic acid aryl ester such as phenyl (meth) acrylate; Aralkyl esters such as (meth) benzyl acrylate; Aromatic vinyls such as styrene, vinyl toluene and α-methylstyrene; Vinyl esters such as vinyl acetate, vinyl propionate and vinyl versatic acid; Allyl esters such as allyl acetate Halogen-containing monomers such as vinylidene chloride and vinyl chloride; vinyl cyanide such as (meth) acrylonitrile; olefins such as ethylene and propylene; and the like.

  The (meth) acrylic acid alkyl ester is preferably a (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl moiety, specifically, for example, methyl (meth) acrylate or ethyl (meth) acrylate. Propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, (meth) Examples include octyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and the like. Among these, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and hydroxyethyl methacrylate are preferable. The non-mordant monomers can be used alone or in combination of two or more.

  Further, as a polymer mordant, polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polyethylenimine, polyallylamine and its modified product, polyallylamine hydrochloride, polyamide-polyamine resin, cationized starch, Dicyandiamide formalin condensate, dimethyl-2-hydroxypropylammonium salt polymer, polyamidine, polyvinylamine, or acrylic silicon described in JP-A-10-264511, JP-A-2000-43409, JP-A-2000-343811, JP-A-2002-120452 Cationic acrylic emulsion of latex (trade name “Aquabrid series ASi-781, ASi-784, manufactured by Daicel Chemical Industries, Ltd.” ASi-578, ASi-903 ") and the like can also be mentioned as preferred, and polyallylamine and polyallylamine-modified products are particularly preferred.

  The polyallylamine-modified product is obtained by adding 2 to 50 mol% of acrylonitrile, chloromethylstyrene, TEMPO, epoxy hexane, sorbic acid or the like to polyallylamine, and preferably 5 to 5 of acrylonitrile, chloromethylstyrene, and TEMPO. It is a 10 mol% adduct, and 5 to 10 mol% TEMPO adduct of polyallylamine is particularly preferable from the viewpoint of exhibiting the effect of preventing ozone fading.

  The molecular weight of the mordant is preferably 2000 to 300,000 in terms of mass average molecular weight. When the molecular weight is within this range, the water resistance and aging resistance can be further improved.

(Other ingredients)
The ink receiving layer of the present invention comprises the following components as necessary.
That is, for the purpose of suppressing the deterioration of the ink coloring material, various ultraviolet absorbers, antioxidants, anti-fading agents such as singlet oxygen quenchers may be included.
Examples of the ultraviolet absorber include cinnamic acid derivatives, benzophenone derivatives, benzotriazolylphenol derivatives, and the like. For example, α-cyano-phenyl cinnamate butyl, o-benzotriazole phenol, o-benzotriazole-p-chlorophenol, o-benzotriazole-2,4-di-t-butylphenol, o-benzotriazole-2,4 -Di-t-octylphenol etc. are mentioned. A hindered phenol compound can also be used as an ultraviolet absorber, and specifically, a phenol derivative in which one or more of at least 2-position or 6-position is substituted with a branched alkyl group is preferable.

  Moreover, a benzotriazole type ultraviolet absorber, a salicylic acid type ultraviolet absorber, a cyanoacrylate type ultraviolet absorber, an oxalic acid anilide type ultraviolet absorber, etc. can be used. For example, JP-A-47-10537, 58-111942, 58-21284, 59-19945, 59-46646, 59-109055, 63-53544. No. 36, Japanese Patent Publication No. 36-10466, No. 42-26187, No. 48-30492, No. 48-31255, No. 48-41572, No. 48-54965, No. 50-10726. No. 2,719,086, US Pat. No. 3,707,375, US Pat. No. 3,754,919, US Pat. No. 4,220,711, and the like. .

  A fluorescent brightening agent can also be used as an ultraviolet absorber, and examples thereof include a coumarin fluorescent brightening agent. Specifically, it is described in Japanese Patent Publication Nos. 45-4699 and 54-5324.

  Examples of the antioxidant include European Patent Publication No. 223739, Publication No. 309401, Publication No. 309402, Publication No. 310551, Publication No. 310552, Publication No. 4594416, Publication of German Patent No. 3435443, JP-A-54-48535, JP-A-60-107384, JP-A-60-107383, JP-A-60-125470, JP-A-60-125471, JP-A-60-125472, JP-A-60-287485. 60-287486, 60-287487, 60-287488, 61-160287, 61-185483, 61-2111079, 62-146678, 62-146680, 62-146679, 62-282885, JP same 62-262047, JP-same 63-051174, JP-same 63-89877, JP-same 63-88380, JP-same 66-88381, JP-same 63-113536 JP;

  JP-A-63-163351, JP-A-63-203372, JP-A-63-224989, JP-A-63-251282, JP-A-63-267594, JP-A-63-182484, JP-A-1-239282, JP-A-2-262654, JP-A-2-71262, JP-A-3-121449, JP-A-4-29185, JP-A-4-291684, JP-A-5-61166, JP-A-5-119449, 5-188687, 5-188686, 5-110490, 5-110437, 5-170361, JP 48-43295, 48-33212, Examples thereof include those described in U.S. Pat. Nos. 4,814,262 and 4,980,275.

  Specifically, 6-ethoxy-1-phenyl-2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2-dihydroquinoline 6-ethoxy-1-phenyl-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2,3 4, -tetrahydroquinoline, nickel cyclohexane acid, 2,2-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) -2-ethylhexane, 2-methyl-4-methoxy-diphenylamine, Examples include 1-methyl-2-phenylindole.

  These anti-fading agents may be used alone or in combination of two or more. The anti-fading agent may be water-solubilized, dispersed, emulsified, or contained in microcapsules. The addition amount of the anti-fading agent is preferably 0.01 to 10% by mass of the ink receiving layer coating solution.

  In the present invention, the ink receiving layer preferably contains a high boiling point organic solvent for curling prevention. The high-boiling organic solvent is preferably a water-soluble one. Examples of the water-soluble high-boiling organic solvent include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerin, diethylene glycol monobutyl ether (DEGMBE), Triethylene glycol monobutyl ether, glycerin monomethyl ether, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,4-pentanetriol, 1,2,6-hexanetriol, thiodiglycol, Examples include alcohols such as triethanolamine and polyethylene glycol (weight average molecular weight of 400 or less). Diethylene glycol monobutyl ether (DEGMBE) is preferred.

The content of the high-boiling organic solvent in the ink-receiving layer coating solution is preferably 0.05 to 1% by mass, particularly preferably 0.1 to 0.6% by mass.
In addition, for the purpose of improving the dispersibility of the inorganic pigment fine particles, various inorganic salts, pH adjusting agents, and the like may contain acids and alkalis.
Further, for the purpose of suppressing surface frictional charge and peeling charge, the metal oxide fine particles having electronic conductivity may contain various matting agents for the purpose of reducing the surface frictional characteristics.

(Support)
As the support used in the present invention, either a transparent support made of a transparent material such as plastic or an opaque support made of an opaque material such as paper can be used. In order to make use of the transparency of the ink receiving layer, it is preferable to use a transparent support or a highly glossy opaque support. Further, a read-only optical disk such as a CD-ROM or DVD-ROM, a write-once optical disk such as a CD-R or DVD-R, or a rewritable optical disk may be used as a support to provide an ink receiving layer on the label surface side. it can.

The material that can be used for the transparent support is preferably a material that is transparent and can withstand radiant heat when used in an OHP or a backlight display. Examples of such materials include polyesters such as polyethylene terephthalate (PET); polysulfone, polyphenylene oxide, polyimide, polycarbonate, polyamide and the like. Of these, polyesters are preferable, and polyethylene terephthalate is particularly preferable.
Although there is no restriction | limiting in particular as thickness of the said transparent support body, 50-200 micrometers is preferable at the point of the ease of handling.

  As the highly glossy opaque support, one having a glossiness of 40% or more on the surface on which the ink receiving layer is provided is preferable. The glossiness is a value determined according to the method described in JIS P-8142 (75-degree specular gloss test method for paper and paperboard). Specifically, the following supports are mentioned.

For example, high gloss paper support such as art paper, coated paper, cast coated paper, baryta paper used for silver salt photographic support, etc .; polyesters such as polyethylene terephthalate (PET), nitrocellulose, cellulose acetate , Cellulose esters such as cellulose acetate butyrate, and plastic films such as polysulfone, polyphenylene oxide, polyimide, polycarbonate, and polyamide are made opaque by adding a white pigment or the like (surface calendering may be applied). Glossy film; or a support in which a polyolefin coating layer containing or not containing a white pigment is provided on the surface of a highly glossy film containing the various paper supports, the transparent support or the white pigment. Etc.
A white pigment-containing foamed polyester film (for example, foamed PET containing polyolefin fine particles and forming voids by stretching) can also be suitably exemplified. Furthermore, resin-coated paper used for silver salt photographic printing paper is also suitable.

Although there is no restriction | limiting in particular also about the thickness of the said opaque support body, 50-300 micrometers is preferable at the point of the ease of handling.
In addition, it is preferable to use a surface of the support that has been subjected to corona discharge treatment, glow discharge treatment, flame treatment, ultraviolet irradiation treatment or the like in order to improve wettability and adhesion.

Next, a base paper used for a paper support such as resin-coated paper will be described.
The base paper is made from wood pulp as a main raw material and, if necessary, paper using synthetic pulp such as polypropylene or synthetic fibers such as nylon or polyester in addition to wood pulp. As the wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, NUKP can be used, but it is preferable to use more LBKP, NBSP, LBSP, NDP, LDP with a lot of short fibers. preferable. However, the ratio of LBSP and / or LDP is preferably 10% by mass to 70% by mass.

As the above-mentioned pulp, chemical pulp (sulfate pulp or sulfite pulp) with few impurities is suitably used, and a pulp whose whiteness is improved by performing a bleaching treatment is also useful.
In the base paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength enhancing agents such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, polyethylene glycols A water retaining agent such as a dispersant, a softening agent such as a quaternary ammonium, and the like can be appropriately added.

  The freeness of the pulp used for papermaking is preferably 200 to 500 ml as defined by CSF, and the fiber length after beating is a 24 mesh residual mass% and a 42 mesh residual as defined in JIS P-8207. 30 to 70% of the sum with the mass% of is preferable. The 4 mesh residue is preferably 20% by mass or less.

The basis weight of the base paper is preferably 30 to 250 g, and particularly preferably 50 to 200 g. The thickness of the base paper is preferably 40 to 250 μm. The base paper can be given a high smoothness by calendering at the paper making stage or after paper making. The density of the base paper is generally 0.7 to 1.2 g / m ² (JIS P-8118). Furthermore, the base paper stiffness is preferably 20 to 200 g under the conditions specified in JIS P-8143.

A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, a sizing agent similar to the size that can be added to the base paper can be used.
The pH of the base paper is preferably 5 to 9 when measured by a hot water extraction method defined in JIS P-8113.

  The polyethylene covering the front and back surfaces of the base paper is mainly low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE), but some other LLDPE, polypropylene, etc. can also be used.

  In particular, the polyethylene layer on the side on which the ink receiving layer is formed is obtained by adding rutile or anatase type titanium oxide, fluorescent whitening agent, ultramarine blue to polyethylene, as is widely done in photographic paper, Those having improved whiteness and hue are preferred. Here, as a titanium oxide content, about 3-20 mass% is preferable with respect to polyethylene, and 4-13 mass% is more preferable. Although the thickness of a polyethylene layer does not have limitation in particular, 10-50 micrometers is suitable for both front and back layers. Further, an undercoat layer can be provided on the polyethylene layer in order to provide adhesion to the ink receiving layer. As the undercoat layer, aqueous polyester, gelatin and PVA are preferable. Moreover, as thickness of this undercoat layer, 0.01-5 micrometers is preferable.

  Polyethylene-coated paper can be used as glossy paper, or matte or silky surface that can be obtained with ordinary photographic printing paper by applying a so-called molding process when polyethylene is melt-extruded and coated on the base paper surface. Can also be used.

A back coat layer can be provided on the support, and examples of components that can be added to the back coat layer include a white pigment, an aqueous binder, and other components.
Examples of white pigments contained in the backcoat layer include light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, and aluminum silicate. , Diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, colloidal alumina, pseudoboehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrous halloysite, magnesium carbonate, magnesium hydroxide, white inorganic pigment, styrene And organic pigments such as polyethylene plastic pigments, acrylic plastic pigments, polyethylene, microcapsules, urea resins, and melamine resins.

Examples of the aqueous binder used in the back coat layer include styrene / maleate copolymer, styrene / acrylate copolymer, polyvinyl alcohol, silanol-modified polyvinyl alcohol, starch, cationized starch, casein, gelatin, carboxy Examples thereof include water-soluble polymers such as methyl cellulose, hydroxyethyl cellulose, and polyvinyl pyrrolidone, and water-dispersible polymers such as styrene butadiene latex and acrylic emulsion.
Examples of other components contained in the backcoat layer include an antifoaming agent, an antifoaming agent, a dye, a fluorescent brightening agent, a preservative, and a water-proofing agent.

(Preparation of inkjet recording medium)
The ink receiving layer of the ink jet recording medium of the present invention comprises, for example, a coating liquid (first coating liquid) containing at least a water dispersion of a cationic urethane resin according to the present invention and fine particles and a water-soluble resin on a support. A coating layer is formed by coating, and a crosslinking agent is further added to the coating solution (first coating solution) and / or the following basic solution (second coating solution), and (1) the coating solution (first coating solution). (2) the coating layer formed by applying the coating solution (first coating solution) is being dried, and the coating layer has a reduced drying rate. At any time before showing, a method of applying a basic solution (second coating solution) having a pH of 8 or more to the coating layer and crosslinking and curing the coating layer (this is referred to as “Wet on Wet method”) .).

  The cross-linking agent capable of cross-linking the water-soluble resin is preferably contained in at least one or both of the first coating liquid and the second coating liquid. As described above, the ink receiving layer obtained by applying a basic solution (second coating solution) to the first coating solution at the same time as (1) or during (2) drying is crosslinked and cured. In addition to having advantages such as ink absorbability and prevention of film cracking, it is particularly preferable for improving the appearance of repelling failure and the like.

  Here, the aqueous dispersion of the cationic urethane resin of the present invention contained in the ink receiving layer is used by being added to at least one of the first coating liquid and the second coating liquid (basic solution). From the viewpoint of being sufficiently mixed with the fine particles and the water-soluble resin in the first coating liquid and capable of effectively preventing aging blur over a long period of time, the aqueous dispersion of the cationic urethane resin according to the present invention is the first coating liquid ( A mode of inclusion in a coating solution containing fine particles and a water-soluble resin is preferred. At this time, it is not always necessary to include the entire aqueous dispersion of the cationic urethane resin according to the present invention in the first coating liquid, and at least a part of the aqueous dispersion of the cationic urethane resin according to the present invention is added to the first coating liquid. It is also effective to make it contained in two coating liquids, and this can prevent aging blur effectively. Moreover, the aspect which contains at least one part of the aqueous dispersion of the said cationic urethane resin which concerns on this invention in both a 1st coating liquid and a 2nd coating liquid is also preferable.

  The mordant is preferably present so that the thickness of the portion where the mordant is present from the surface of the ink receiving layer is 10 to 60% with respect to the total thickness of the ink receiving layer. For example, (1) a method of forming a coating layer containing fine particles, a water-soluble resin and a crosslinking agent, and applying a mordant-containing solution thereon, (2) a coating solution containing the fine particles and a water-soluble resin, and a mordant-containing solution. It can be formed by any method such as a method of applying multiple layers. The mordant-containing solution may contain inorganic fine particles, a water-soluble resin, a crosslinking agent, and the like. When configured as described above, since a large amount of mordant is present in a required portion of the ink receiving layer, the ink color material of the ink jet is sufficiently mordanted, and the color density, aging blur, gloss of the printed portion, characters and images after printing are printed. It is preferable because water resistance and ozone resistance are further improved. Part of the mordant may be contained in the layer initially provided on the support, and in that case, the mordant to be applied later may be the same or different.

In the present invention, the coating liquid containing the inorganic pigment fine particles, the water-soluble resin, and the boron compound (crosslinking agent) as the first coating liquid can be prepared, for example, as follows.
That is, silica fine particles having an average primary particle size of 20 nm or less are added to water (for example, 10 to 20% by mass), and a high-speed rotating wet colloid mill (for example, “Clairemix” manufactured by M Technique Co., Ltd.) is used. For example, after being dispersed for 20 minutes (preferably 10 to 30 minutes) under the condition of high-speed rotation at a rotation speed of 10,000 rpm (preferably 5000 to 20000 rpm), a boron compound (for example, 0.5 to 20 of silica) (Mass%) and dispersion under the same conditions as above, an aqueous polyvinyl alcohol solution (for example, PVA having a mass of about 1/3 of silica), and further dispersion under the same rotation conditions as above. Can be prepared. The obtained coating solution is a uniform sol, and this is applied to a support by the following coating method to form an ink-receiving layer having a porous structure having a three-dimensional network structure.
If necessary, a pH adjuster, a dispersant, a surfactant, an antifoaming agent, an antistatic agent and the like can be further added to the first coating liquid.

  As the dispersing machine used for the above dispersion, various conventionally known dispersing machines such as a high-speed rotary dispersing machine, a medium stirring type dispersing machine (ball mill, sand mill, etc.), an ultrasonic dispersing machine, a colloid mill dispersing machine, and a high-pressure dispersing machine are used. However, in order to efficiently disperse the generated fine particles, a medium stirring type disperser, a colloid mill disperser or a high pressure disperser is preferable.

  Moreover, water, an organic solvent, or these mixed solvents can be used as a solvent used for preparation of each coating liquid. Examples of organic solvents that can be used in the coating solution include alcohols such as methanol, ethanol, n-propanol, i-propanol, and methoxypropanol, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, acetonitrile, ethyl acetate, and toluene. Can be mentioned.

  Moreover, the 2nd coating liquid (basic solution) containing surfactant can be prepared as follows, for example. That is, a mordant (for example, 0.1 to 5.0% by mass) and a surfactant (for example, a total amount of 0.01 to 1.0% by mass) in ion-exchanged water and a crosslinking agent (0 to 0 as necessary). 5.0% by mass) and sufficiently stirred. The pH of the second coating liquid is preferably 8.0 or more, and pH adjustment is performed using ammonia water, sodium hydroxide, calcium hydroxide, amino group-containing compounds (ethylamine, ethanolamine, diethanolamine, polyallylamine, etc.) and the like. It can be appropriately performed at 0.0 or more.

  Application of the first coating liquid (ink receiving layer coating liquid) is, for example, a known coating such as an extrusion die coater, air doctor coater, bread coater, rod coater, knife coater, squeeze coater, reverse roll coater, bar coater, etc. It can be done by the method.

  At the same time as or after the application of the first coating liquid (ink-receiving layer coating liquid), the second coating liquid (basic solution) is applied to the coating layer. It may be applied before the coating layer exhibits reduced rate drying. That is, after the application liquid for the ink receiving layer is applied, it is preferably manufactured by introducing a basic solution while the applied layer exhibits constant rate drying. The second coating liquid may contain a mordant.

  Here, “before the coating layer comes to show reduced drying” usually refers to a process for several minutes immediately after the coating of the coating liquid for the ink-receiving layer. This shows a phenomenon of “constant rate drying” in which the content of the solvent (dispersion medium) of the ink decreases in proportion to time. The time indicating “constant rate drying” is described in, for example, “Chemical Engineering Handbook” (pages 707 to 712, published by Maruzen Co., Ltd., October 25, 1980).

  As described above, after the application of the first coating liquid, the coating layer is dried until the coating layer exhibits reduced-rate drying. This drying is generally performed at a temperature of 50 to 180 ° C. for 0.5 to 10 minutes (preferably, 0.5 to 5 minutes). The drying time naturally varies depending on the coating amount, but the above range is usually appropriate.

  As a method of applying the second coating liquid before the reduced rate of drying is exhibited, (1) a method of further applying the second coating liquid on the coating layer, and (2) a method of spraying by a method such as spraying (3) A method of immersing the support on which the coating layer is formed in the second coating liquid.

  In the above method (1), examples of the application method for applying the second coating liquid include curtain flow coaters, extrusion die coaters, air doctor coaters, bread coaters, rod coaters, knife coaters, squeeze coaters, reverse roll coaters, A known coating method such as a bar coater can be used. However, it is preferable to use a method in which the coater does not directly contact the first coating layer that has already been formed, such as an extrusion die coater, a curtain flow coater, or a bar coater.

The coating amount of the second coating solution, 5 to 50 g / m ² is generally, 10 to 30 g / m ² is preferred.

  After the application of the second coating liquid, it is generally heated at a temperature of 40 to 180 ° C. for 0.5 to 30 minutes, and dried and cured. Especially, it is preferable to heat at a temperature of 40 to 150 ° C. for 1 to 20 minutes. For example, when the cross-linking agent contained in the first coating liquid is borax or boric acid, heating at a temperature of 60 to 100 ° C. is preferably performed for 5 to 20 minutes.

  Further, when the basic solution (second coating solution) is applied simultaneously with the application of the ink receiving layer coating solution (first coating solution), the first coating solution supports the first coating solution and the second coating solution. The ink receiving layer can be formed by simultaneous application (multilayer application) on the support so as to come into contact with the body, followed by drying and curing.

  The simultaneous coating (multilayer coating) can be performed by a coating method using, for example, an extrusion die coater or a curtain flow coater. After the simultaneous coating, the formed coating layer is dried. In this case, the drying is generally performed by heating the coating layer at a temperature of 40 to 150 ° C. for 0.5 to 10 minutes, preferably at a temperature of 40 It is carried out by heating at -100 ° C for 0.5-5 minutes.

  When the above simultaneous coating (multilayer coating) is performed by, for example, an extrusion die coater, the two types of coating liquid discharged at the same time are close to the discharge port of the extrusion die coater, that is, before moving onto the support. A multilayer is formed, and in that state, the multilayer is applied on the support. Since the two-layer coating liquid layered before coating is likely to cause a cross-linking reaction at the interface between the two liquids when transferred to the support, the two liquids to be ejected are mixed in the vicinity of the discharge port of the extrusion die coater. As a result, thickening is likely to occur, which may hinder the application operation. Therefore, when applying simultaneously as described above, it is preferable to apply a triple layer simultaneously with the application of the first coating liquid and the second coating liquid, with a barrier layer liquid (intermediate layer liquid) interposed between the two liquids. .

  The barrier layer solution can be selected without particular limitation. For example, an aqueous solution containing a trace amount of water-soluble resin, water, and the like can be given. The water-soluble resin is used in consideration of applicability for the purpose of a thickener and the like. For example, a cellulose resin (for example, hydroxypropylmethylcellulose, methylcellulose, hydroxyethylmethylcellulose) And polymers such as polyvinylpyrrolidone and gelatin. Here, the mordant may be contained in the barrier layer solution.

  After the ink receiving layer is formed on the support, the ink receiving layer is subjected to, for example, super calender, gloss calender, etc., and is subjected to calender treatment through the roll nip under heat and pressure, so that surface smoothness, glossiness, It is possible to improve transparency and coating strength. However, the calendering process may cause a decrease in the porosity (that is, the ink absorbability may be decreased), so it is necessary to set the conditions under which the decrease in the porosity is small.

  As roll temperature in performing the said calendar process, 30-150 degreeC is preferable and 40-100 degreeC is more preferable. Moreover, as a linear pressure between rolls at the time of a calendar process, 50-400 kg / cm is preferable and 100-200 kg / cm is more preferable.

The layer thickness of the ink receiving layer of the present invention needs to be determined in relation to the porosity in the layer since it needs to have an absorption capacity sufficient to absorb all droplets in the case of inkjet recording. For example, if the ink amount is 8 nL / mm ² and the porosity is 60%, a film having a layer thickness of about 15 μm or more is required. Considering this point, in the case of ink jet recording, the layer thickness of the ink receiving layer is preferably 10 to 50 μm.

  The pore diameter of the ink receiving layer is preferably 0.005 to 0.030 μm, more preferably 0.01 to 0.025 μm in terms of median diameter. The porosity and pore median diameter can be measured using a mercury porosimeter “Bore Sizer 9320-PC2” manufactured by Shimadzu Corporation.

  In addition, the ink receiving layer is preferably excellent in transparency, as a guide, the haze value when the ink receiving layer is formed on a transparent film support is preferably 30% or less, More preferably, it is 20% or less. The haze value can be measured using a haze meter “HGM-2DP” manufactured by Suga Test Instruments Co., Ltd.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the examples, “parts” and “%” all represent “parts by mass” and “% by mass”.

(Production of support)
Wood pulp composed of 100 parts of LBKP is beaten to 300 ml Canadian freeness with a double disc refiner, 0.5 parts of epoxidized behenamide, 1.0 part of anionic polyacrylamide, 0.1 part of polyamide polyamine epichlorohydrin, 0.5 part of cationic polyacrylamide All parts were added at an absolutely dry mass ratio with respect to the pulp, and weighed with a long net paper machine to produce a base paper of 170 g / m ² .

In order to adjust the surface size of the base paper, 0.04% of a fluorescent whitening agent (“Whiteex BB” manufactured by Sumitomo Chemical Co., Ltd.) was added to a 4% aqueous solution of polyvinyl alcohol, and this was converted to 0 in terms of absolute dry weight. The base paper was impregnated to a density of 0.5 g / m ² , dried, and then subjected to a calendering process to obtain a base paper adjusted to a density of 1.05.

After the corona discharge treatment was performed on the wire surface (back surface) side of the obtained base paper, high-density polyethylene was coated to a thickness of 19 μm using a melt extruder to form a resin layer composed of a mat surface. (Hereinafter, this resin layer surface is referred to as “back surface”). The back side resin layer is further subjected to a corona discharge treatment, and thereafter, as an antistatic agent, aluminum oxide (“Alumina Sol 100” manufactured by Nissan Chemical Industries, Ltd.) and silicon dioxide (“Snow manufactured by Nissan Chemical Industries, Ltd.”) are used. Tex O ") the mass ratio of 1: a dispersion dispersed in water at 2, dry weight was applied as a 0.2 g / m ^2.

  Furthermore, after the corona discharge treatment is applied to the felt surface (surface) side where the resin layer is not provided, anatase-type titanium dioxide 10%, a trace amount of ultramarine blue, and a fluorescent whitening agent 0.01% (vs. polyethylene) Low-density polyethylene containing MFR (melt flow rate) 3.8 is melt-extruded to a thickness of 29 μm using a melt extruder, and a high-gloss thermoplastic resin layer is formed on the surface side of the base paper. (Hereinafter, this highly glossy surface is referred to as “front side”), and used as a support for this example.

[Example 1]
(Preparation of coating solution for ink receiving layer)
(1) Silica fine particles, (2) Dispersant, and (3) Ion-exchanged water in the following composition are mixed, and using a high-speed rotating colloid mill ("CLEAMIX" manufactured by M Technique Co., Ltd.) After being dispersed for 20 minutes at a rotational speed of 10,000 rpm, the following (4) cross-linking agent, (5) polyvinyl alcohol, (6) diethylene glycol monobutyl ether, (7) additive (cationic urethane aqueous dispersion), and ( The surfactants 8) and (9) were added, and further dispersed under the same conditions as described above to prepare the intended ink-receiving layer coating solution.

<Composition of coating liquid for ink receiving layer>
(1) Silica fine particles (inorganic pigment fine particles) ………… 100kg
("Reorosil QS-30" manufactured by Tokuyama Corporation, average primary particle size: 7 nm)
(2) Dispersant …… 15.0kg
("Chemistat 7005" manufactured by Sanyo Chemical Industries, 40%)
(3) Ion-exchanged water ... 575.3kg
(4) Boric acid (crosslinking agent, 5.3%) ............ 77.4kg
(5) Water-soluble resin (polyvinyl alcohol) ... 317.2kg
("PVA124" manufactured by Kuraray Co., Ltd., 7% aqueous solution)
(6) Diethylene glycol monobutyl ether (100%) ………… 3.6kg
(7) Additive (cationic urethane resin aqueous dispersion) ... 24.9kg
(“Superflex 600” manufactured by Daiichi Kogyo Seiyaku Co., Ltd., average particle size: 0.01 μm, Tg = 70 ° C., 25% dispersion)
(8) Surfactant (Polyoxyethylene oleyl ether) ………… 9.3kg
("Emulgen 109P" manufactured by Kao Corporation, 10%)
(9) Surfactant (Fluorine Surfactant) ……… 6.0kg
(Dainippon Ink Chemical Co., Ltd. “Megafac F-1405”, 10%)

(Preparation of inkjet recording medium)
After the corona discharge treatment was applied to the front surface of the support, the ink receiving layer coating solution obtained above was applied to the front surface of the support at an application amount of 170 ml / m ² using an extrusion die coater. It was applied (application process), and dried with a hot air dryer at a temperature of 40 ° C. (wind speed 5 m / sec) until the solid content concentration of the application layer reached 18%. During this time, the coating layer exhibited a constant rate of drying. Immediately after that, it is immersed in a basic solution (pH = 9.6) having the following composition, and 20 g / m ² is deposited on the coating layer (solution application step), and further dried at a temperature of 80 ° C. for 10 minutes. (Drying process). As a result, an ink jet recording medium (1) of the present invention provided with an ink receiving layer having a dry film thickness of 35 μm was obtained.

<Composition of basic solution>
(1) Boric acid (cross-linking agent, 100%) …… 6.5kg
(2) Ion exchange water ... 723.5kg
(3) Basic mordant …………… 150kg
("PAA-03" manufactured by Nittobo Co., Ltd., 20% aqueous solution)
(4) Surface pH adjuster (ammonium chloride, 100%) ……… 1.0kg
(5) Surface pH adjuster (p-toluenesulfonic acid, 100%) ............ 18.0 kg
(6) Surfactant …………… 100.0kg
("Emulgen 109P" manufactured by Kao Corporation, 2%)
(7) Surfactant (Fluorine surfactant) ……… 2.0kg
("MegaFuck F-1405" manufactured by Dainippon Ink and Chemicals, 100%)

[Comparative Example 1]
In Example 1, a comparison was made in the same manner as in Example 1 except that 9.3 kg of (7) additive (cationic urethane aqueous dispersion) in <Composition of coating liquid for ink receiving layer> was not used. The ink jet recording medium (2) of Example 1 was obtained.

[Comparative Example 2]
In Example 1, instead of (7) additive (cationic urethane aqueous dispersion) in <Ink-Receptive Coating Liquid Composition>, (7) Additive (styrene-acrylic emulsion “Polymalon 1602” (Arakawa) An inkjet recording medium (3) of Comparative Example 2 was obtained in the same manner as in Example 1 except that Chemical Industries, Ltd. (average particle size: 0.15 μm) was used.

(Evaluation test)
The ink jet recording media (1) to (3) obtained above were subjected to the following evaluation tests. The results are shown in Table 1 below.
(1) Time-lapse Niimi Using an inkjet printer “BJF-900” manufactured by Canon Inc., a magenta and yellow ink are adjacent to each inkjet recording medium to form a grid-like linear pattern (width 0.28 mm). Printed. The print sample is inserted into a transparent PP file and stored in an environment of 35 ° C. and 80% RH for 3 days. The width of the linear magenta is measured, and the magenta line width with respect to the width immediately after the print is measured. The rate of increase (%) was calculated and used as an evaluation index for aging blur.

(2) Print Density Using the inkjet printer “BJF-900” manufactured by Canon Inc., a black solid image was printed on each ink jet recording medium, and the reflection density of the print screen after being left for 3 hours. Was measured with a reflection densitometer “X-rite 938” manufactured by X-rite.

(2) Glossiness The 60 ° glossiness on the ink receiving layer surface of each inkjet recording medium was measured using a digital variable angle glossiness meter “UGV-50DP” manufactured by Suga Test Instruments Co., Ltd.

  As shown in Table 1 above, the inkjet recording medium (1) of the present invention containing an aqueous dispersion of a self-emulsifying polymer having an average particle size of 0.05 μm or less is an inkjet recording medium of a comparative example ( As compared with 2) and (3), it was found that the aging blur was improved while maintaining the same or higher in print density and gloss.

Claims (8)

  An ink jet recording medium having an ink receiving layer on a support, wherein the ink receiving layer contains at least a cationic urethane resin.   The inkjet recording medium according to claim 1, wherein the cationic urethane resin has a glass transition temperature of 50 ° C. or higher.   The ink jet recording medium according to claim 1, wherein the ink receiving layer further contains a water-soluble resin.   The water-soluble resin is at least one selected from polyvinyl alcohol resins, cellulose resins, resins having an ether bond, resins having a carbamoyl group, resins having a carboxy group, and gelatins. Item 4. The ink jet recording medium according to Item 3.   The inkjet recording medium according to claim 3, wherein the ink receiving layer contains a crosslinking agent capable of crosslinking the water-soluble resin.   6. The ink jet recording medium according to claim 1, wherein the ink receiving layer further contains fine particles.   The ink jet recording medium according to claim 6, wherein the fine particles are at least one selected from silica fine particles, colloidal silica, alumina fine particles, and pseudoboehmite.   The ink jet recording medium according to claim 1, wherein the ink receiving layer further contains a mordant.