JP2005219429A - Inkjet recording medium and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium for pigment ink, which can bring about a sense of uniform gloss over a white background and an image part when printing is done in the pigment ink and which can bring about a highly scratch-resistant image making a scratch hardly conspicuous even if the scratch is made, and an inkjet recording method. <P>SOLUTION: In this inkjet recording medium, a surface layer containing a binder and inorganic particulates with a mean refractive index of 2.1-2.9, and a porous layer containing inorganic particulates and a binder are provided on a substrate. The inkjet recording medium is characterized in that an absorption coefficient based on the Bristow's method is 17 ml/m<SP>2</SP>ms<SP>1/2</SP>or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inkjet recording medium and an inkjet recording method.

  In recent years, with the widespread use of digital cameras or computers, hard copy image recording technology for recording these images on paper or the like has been rapidly developed. The ultimate goal of these hard copies is to bring the image quality closer to that of a silver halide photograph. In particular, the color reproducibility, color density, texture, resolution, glossiness, light resistance, etc. should be closer to that of a silver halide photograph. It is a development goal.

  As such hard copy recording methods, various recording methods such as sublimation type thermal transfer method, ink jet method, electrostatic recording method, etc. are proposed in addition to direct photographing of a display displaying an image with a silver salt photograph. Has been put to practical use. Among these recording methods, ink jet printers have the advantage of being easy to achieve full color and having less printing noise, and have been rapidly spreading in recent years.

  The ink jet recording method is capable of recording high-definition images with a relatively simple apparatus, and has been rapidly developed in various fields. In addition, there are various uses, and a recording medium or ink suitable for each purpose is used.

  The recording medium used in the ink jet recording method has an ink receiving layer in which an ink absorbing layer is coated on a supporting body such as plain paper such as plain paper or a supporting body that also serves as an absorbing body such as coated paper. Or an ink-absorbing layer coated on a non-absorbing support such as a resin-coated paper or a polyester film. Among them, the recording medium of the type in which an ink absorbing layer is coated on a non-absorbing support is a silver salt such as gloss, gloss, and depth because the support has a high surface smoothness and little swell. It is preferably used for an output that requires a high quality texture such as a photograph. Furthermore, as a glossy recording medium having high gloss and gloss, a swelling type recording medium in which a water-soluble binder such as polyvinyl pyrrolidone or polyvinyl alcohol is coated as an ink absorbing layer on a non-absorbent support, As the ink absorbing layer, a so-called void type recording medium is used in which a fine void structure is formed with inorganic fine particles and a binder, and the ink is absorbed into the void.

  On the other hand, an ink jet recording method using an ink liquid using a pigment as a color material has been proposed aiming at a highly durable image. This is an ink using a dispersion liquid in which a pigment is dispersed as a color material, and the durability of an image using the same is greatly improved as compared with that using a dye. However, in the ink using the pigment, the pigment does not soak into the recording medium and deposits on the surface. As a result, the gloss of the image portion made of the pigment is different from that of the white background on which the ink is not placed. A major problem in image quality, such as roughening of the surface at high density parts, and a problem related to scratching such as scratching when rubbed have emerged.

  In order to solve this problem, an ink jet recording medium having an uneven surface and diffusing reflected light to make the difference in gloss inconspicuous and reducing the contact area has been used for pigment ink. . However, as a result of making the surface uneven, there was a drawback that only a rough image with low gloss was obtained.

  As an attempt to obtain uniform gloss, there is a method of functionally separating the pigment fixing layer and the solvent absorbing layer (see, for example, Patent Documents 1 and 2). Further, an inkjet recording medium having a high 60 ° gloss is disclosed by arranging spherical particles having a refractive index of 1.65 or more on the surface (see, for example, Patent Document 3). There is also an attempt to increase image color and coating strength by putting titanium oxide and colloidal silica in the protective layer with a two-layer structure of a protective layer and an ink receiving layer (see, for example, Patent Document 4). However, even in these methods, there is a difference in gloss in the image obtained using the pigment ink, particularly a difference in gloss between the white background and the image portion, so that a non-uniform gloss is given and a uniform gloss image is obtained. It did not come.

The present inventors have found that uniform glossiness can be achieved by forming the surface layer with inorganic fine particles having a specific high refractive index and a binder. In particular, it has been found that an ink jet recording medium having excellent ink absorptivity can be obtained by providing a void-type ink absorbing layer comprising a porous layer as a lower layer of the surface layer. However, if the ink absorption speed is not more than a certain value, the pigment will aggregate when the ink overflows on the surface, and the printed part will have a metallic gloss (so-called bronzing), resulting in the gloss of the white background and the image part. The problem became clear that the difference was particularly large.
JP 2000-127613 A Japanese Patent Laid-Open No. 2002-211113 JP 2001-328341 A JP 2001-10212 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a uniform gloss feeling over a white background and an image portion when printed with pigment ink, and has high scratch resistance, An object of the present invention is to provide an ink jet recording medium for a pigment ink and an ink jet recording method capable of obtaining an image that is hardly noticeable even if scratched.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
An inkjet recording medium having a surface layer containing inorganic fine particles having an average refractive index of 2.1 to 2.9 and a binder on a support, and a porous layer containing inorganic fine particles and a binder, according to the Bristow method An ink jet recording medium having an absorption coefficient of 17 ml / m ² · ms ^1/2 or more.

(Claim 2)
2. The ink jet recording medium according to claim 1, wherein a product of the surface roughness Ra (μm) of the surface layer and the average refractive index is 1.7 μm or less.

(Claim 3)
3. The ink jet recording medium according to claim 1, wherein the inorganic fine particles in the surface layer are at least one selected from titanium oxide, cerium oxide and zirconium oxide.

(Claim 4)
The ink jet recording medium according to claim 1, wherein the surface layer contains a cationic polymer.

(Claim 5)
The inkjet according to any one of claims 1 to 4, wherein the inorganic fine particles of the porous layer have an average refractive index of 1.3 to 1.7 and an average particle diameter of 1 to 200 nm. recoding media.

(Claim 6)
The inkjet recording medium according to claim 1, wherein the inorganic fine particles of the porous layer are silica or alumina.

(Claim 7)
The inkjet recording medium according to any one of claims 1 to 6, wherein the support is a non-absorbent support.

(Claim 8)
An ink jet recording method comprising: recording an image by ejecting an ink containing at least a water-soluble solvent and a pigment onto the ink jet recording medium according to claim 1.

  According to the present invention, when printed with pigment ink, an inkjet for pigment ink that can obtain a uniform glossy feeling over a white background and an image portion, and has a high scratch resistance, for example, an image that is not noticeable even if scratched. A recording medium and an ink jet recording method can be provided.

As a result of diligent research, the present inventor has an inkjet having a surface layer containing inorganic fine particles having an average refractive index of 2.1 to 2.9 and a binder, and a porous layer containing inorganic fine particles and a binder on the support. The inkjet recording medium support, which is a recording medium and has an absorption coefficient by Bristow method of 17 ml / m ² · ms ^1/2 or more, provides a uniform glossy feeling over a white background and an image area. It has been found that an ink jet recording medium is obtained that has a high resistance to scratches and produces an image that is not noticeable even if it is scratched.

  By arranging inorganic fine particles having a high refractive index in a specific range on the surface of the ink jet recording medium, the gloss of the white background is increased, and the difference in gloss from the printed portion is eliminated. Further, it was found that the scratch resistance is improved by the fine particles. Although details of this reason have not been elucidated, since inorganic fine particles with a high refractive index tend to have high crystallinity, when the image is rubbed, the inorganic fine particles with a high refractive index bite into the lower layer and generate a so-called anchor effect. I think that.

In addition, by setting the absorption coefficient by the Bristow method of the ink jet recording medium having the above configuration to 17 ml / m ² · ms ^1/2 or more, it is possible to reduce the time that the ink stays on the surface during printing, and the aggregation of the pigment As a result, the gloss difference between the white background and the printed portion can be reduced.

  The present invention will be described in detail below.

[Surface layer]
(Inorganic fine particles)
The inorganic fine particles (also referred to as inorganic filler) used for the surface layer are inorganic fine particles having an average refractive index of 2.1 to 2.9.

  In the present invention, the average refractive index means the refractive index when the inorganic fine particles are composed of one kind. In the case of a plurality of types, the refractive index is averaged by the mass fraction of each inorganic fine particle, and can be calculated by the mass fraction from the refractive index of each individual inorganic fine particle and the composition ratio of the inorganic fine particles. For example, the average refractive index of inorganic fine particles having a composition of titanium oxide (refractive index = 2.76): silica (refractive index = 1.44) = 2: 1 (mass ratio) is (2.76 × 2/3). ) + (1.44 × 1/3) = 2.32. Regarding the refractive index of inorganic fine particles, many measured values are published in publicly known literature.

  Examples of such inorganic fine particles include titanium oxide (rutile type, refractive index = 2.76), titanium oxide (anatase type, 2.52), zirconium oxide (2.40), cerium oxide (2.21), three Examples thereof include ferric oxide (2.9) and antimony oxide (2.19). Among these, one selected from titanium oxide, tin oxide, cerium oxide and zirconium oxide is preferable from the viewpoint of securing a white background on the surface of the recording medium. In particular, titanium oxide is particularly preferable from the viewpoint of cost because it has a high refractive index and brings about a large effect in a small amount. If the average refractive index is in the range of 2.1 to 2.9, the inorganic fine particles having a refractive index lower than that of the individual fine inorganic particles, such as zinc oxide (2.02), tin oxide (2. 093), α-alumina (1.8), γ-alumina (1.7), alumina (1.56), magnesium hydroxide (1.52), and silica (1.44) can be used in combination.

  The product of the surface roughness Ra (μm) of the surface layer and the average refractive index is preferably 1.7 μm or less. Even if the product is larger than 1.7 μm, a uniform gloss can be obtained on a white background and an image, but if it is 1.7 μm or less, the 60 ° gloss value is increased, and a better gloss can be obtained. The surface roughness in the present invention can be measured using RST / PLUS manufactured by WYKO. The surface roughness is preferably as small as possible from the viewpoint of preventing light scattering. Although light scattering is affected by the surface roughness and the refractive index of the surface layer, in the present invention, it is preferable to make the surface roughness particularly small because fine particles having a high refractive index are used for the surface layer as described above. It is preferable that the product has a constant value of 1.7 μm or less.

  The average primary particle diameter of the inorganic fine particles having an average refractive index of 2.1 to 2.9 is preferably 1 to 200 nm. If the average primary particle size is within this range, there is no particular limitation, but the range of 5 to 80 nm is particularly preferable. When the average primary particle size is less than 5 nm, the gap through which the surface ink passes becomes small, so that ink absorption deteriorates and ink leakage occurs. Will occur. This is because when the thickness is larger than 80 nm, the surface roughness increases, and the gloss deteriorates.

(binder)
A conventionally known hydrophilic resin is used as the binder for the surface layer. Examples of known hydrophilic resins include gelatin, polyvinyl pyrrolidone, pullulan, polyvinyl alcohol or derivatives thereof, polyethylene glycol, hydroxyethyl cellulose, dextran, dextrin, water-soluble polyvinyl butyral, and the like.

  The amount of the binder added is not limited as long as it does not desorb the inorganic particles in the surface layer, but it is used in the range of 1 to 200% by mass with respect to the inorganic fine particles. Preferably, it is 5 to 50%. If the amount of the binder is too much, the ink absorptivity is deteriorated.

Various additives can be added to the coating solution for forming the surface layer. Such additives include, for example, cationic mordants, crosslinking agents, surfactants (cations, nonions, anions, amphoterics), white color tone adjusting agents, fluorescent whitening agents, antifungal agents, viscosity adjusting agents, low boiling points. Organic solvents, high-boiling organic solvents, latex emulsions, anti-fading agents, UV absorbers, polyvalent metal compounds (water-soluble or water-insoluble), matting agents, silicone oils, etc., among which cationic mordants are used after printing It is preferable for improving the water resistance and fixability of the resin.
.

A cationic polymer is preferably used as the cationic mordant. Examples of cationic polymers include polyethyleneimine, polyallylamine, polyvinylamine, dicyandiamide polyalkylene polyamine condensate, polyalkylene polyamine dicyandiamide ammonium salt condensate, dicyandiamide formalin condensate, epichlorohydrin-dialkylamine addition polymer, diallyldimethylammonium chloride Polymer, diallyldimethylammonium chloride / SO ₂ copolymer, polyvinyl imidazole, vinyl pyrrolidone / vinyl imidazole copolymer, polyvinyl pyridine, polyamidine, chitosan, cationized starch, vinyl benzyl trimethyl ammonium chloride polymer, (2-methacryloyl) Oxyethyl) trimethylammonium chloride polymer, dimethylaminoethyl methacrylate Over preparative polymer and the like. Examples include the cationic polymers described in Chemical Industry Times, August 15 and 25, 1998, and polymer dye fixing agents described in “Introduction to Polymer Drugs” issued by Sanyo Chemical Industries, Ltd.

  The dry film thickness of the surface layer is preferably 0.01 to 0.3 μm or 1.2 to 20 μm from the viewpoint of preventing light interference fringes. If it is less than 0.01 μm, the effect of gloss difference is not sufficiently exhibited, and if it exceeds 20 μm, the surface layer is cracked and the gloss is lowered.

(Porous layer)
Next, the porous layer (also referred to as an ink absorbing layer) will be described.

  The ink jet recording medium of the present invention has one or more porous layers, so-called ink absorbing layers. In general, the ink absorption layer is roughly divided into a swelling type and a void type. However, in order to support continuous high-speed printing, a void type composed of a porous layer having a high ink absorption rate is preferable.

  The porous layer is mainly formed by soft aggregation of a hydrophilic binder and inorganic fine particles. Conventionally, various methods for forming voids in a film are known. For example, a uniform coating solution containing two or more kinds of polymers is coated on a support, and these polymers are phase-separated from each other in the drying process. A method of forming voids, applying a coating liquid containing solid fine particles and a hydrophilic or hydrophobic resin on a support, and after drying, immersing the inkjet recording medium in water or a liquid containing a suitable organic solvent, A method for producing voids by dissolving solid fine particles, a method for forming voids in a film by applying a coating liquid containing a compound having a property of foaming during film formation, and then foaming this compound in a drying process, porous A method in which a coating liquid containing solid fine particles and a hydrophilic binder is coated on a support and voids are formed in or between the porous fine particles. Solid particles and or a coating solution containing a particulate oil and a hydrophilic binder is coated on a support, and a method of forming an air gap between the solid particles are known to. In the present invention, it is particularly preferable that the void layer is formed by containing various inorganic solid fine particles having an average particle diameter of 400 nm or less.

(Inorganic fine particles)
Examples of the inorganic fine particles used for the above purpose include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide. , Zinc carbonate, hydrotalcite, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, magnesium hydroxide, etc. A white inorganic pigment etc. can be mentioned. The average particle size of the inorganic fine particles is determined by observing the particles themselves or particles appearing on the cross section or surface of the porous layer with an electron microscope, measuring the particle size of 1,000 arbitrary particles, and calculating the simple average value (number Average). Here, the particle diameter of each particle is represented by a diameter assuming a circle equal to the projected area. As the inorganic fine particles, it is preferable that the inorganic fine particles have an average refractive index of 1.3 to 1.7 and an average particle diameter of 1 to 200 nm. As such inorganic fine particles, silica, alumina or alumina hydrate can be used. It is preferable to use selected inorganic fine particles. Examples of the silica that can be used in the present invention include silica synthesized by an ordinary wet method, colloidal silica, silica synthesized by a gas phase method, and the like, but the fine particle silica particularly preferably used in the present invention is colloidal. Silica or fine particle silica synthesized by a gas phase method is preferred, and among these, fine particle silica synthesized by a gas phase method can provide a high porosity. Alumina or alumina hydrate may be crystalline or amorphous, and any shape such as amorphous particles, spherical particles, and acicular particles can be used. The inorganic fine particles are preferably in a state where the fine particle dispersion is dispersed to the primary particles. The inorganic fine particles preferably have a particle size of 200 nm or less. For example, in the case of the above vapor phase method fine particle silica, the average particle size of primary particles of inorganic fine particles dispersed in a primary particle state (particle size in a dispersion state before coating) is preferably 100 nm or less, More preferably, it is 4-50 nm, Most preferably, it is 4-20 nm. As silica most preferably used and synthesized by a vapor phase method in which the average particle size of primary particles is 4 to 20 nm, for example, Aerosil manufactured by Nippon Aerosil Co., Ltd. and Leolosil manufactured by Tokuyama Co., Ltd. are commercially available. The vapor phase fine particle silica can be dispersed to primary particles relatively easily by sucking and dispersing in water using, for example, a jet stream inductor mixer manufactured by Mitamura Riken Kogyo Co., Ltd.

  The ratio of the fine particles to the hydrophilic binder in the porous layer is preferably 3 to 30 times by mass ratio. If the mass ratio is 3 times or more, the porosity of the porous layer is good, it is easy to obtain a sufficient void volume, and excessive hydrophilic binder can be prevented from swelling and closing the void during ink jet recording. On the other hand, when this ratio is 30 times or less, it is preferable that cracks hardly occur when the porous layer is applied as a thick film. The ratio of the fine particles to the particularly preferred hydrophilic binder is 3 to 15 times from the viewpoint of breakage of the dried coating film.

(Hydrophilic binder)
Examples of the hydrophilic binder that can be used in the present invention include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, dextran, dextrin, color ginnan (κ, ι, λ, etc.), agar , Pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose and the like. Two or more of these water-soluble binders can be used in combination.

The amount of inorganic fine particles used in the ink absorption layer (porous layer) depends largely on the required ink absorption capacity, the porosity of the porous layer, the type of inorganic pigment, and the type of water-soluble binder. The amount is usually 5 to 30 g, preferably 10 to 25 g per 1 m ^{2 of} recording paper.

  In the porous layer according to the present invention, a cationic polymer can be used as a dispersant for inorganic fine particles. As the cationic polymer, the same polymer as the surface layer can be used.

In the porous layer, the total amount of voids (void volume) is preferably 20 ml or more per 1 m ² of the inkjet recording medium. When the void volume is less than 20 ml / m ² , the ink absorbency is good when the amount of ink at the time of printing is small, but when the amount of ink increases, the ink is not completely absorbed and the image quality deteriorates, Problems such as delay in drying are likely to occur. The void volume is the volume of bubbles generated when a unit volume of the coating film is immersed in water, the volume of water that can be absorbed by the coating film, or the recording paper finally obtained. It is defined as the amount of liquid transfer when the contact time is 2 seconds as measured by the liquid absorbency test method (Bristow method) of paper and paperboard specified in TAPPI 51.

  In the porous layer having ink holding ability, the void volume relative to the solid content volume is referred to as a void ratio. In the present invention, it is preferable to set the porosity to 50% or more because the voids can be efficiently formed without unnecessarily increasing the film thickness.

  Various additives other than those described above can be used in the porous layer of the inkjet recording medium of the present invention and other layers provided as necessary. For example, organic latex fine particles such as polystyrene, polyacrylic acid esters, polymethacrylic acid esters, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, urea resin, or melamine resin , Anionic, cationic, nonionic and amphoteric surfactants, UV absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, No. 57-87989, 60-72785, 61-146591, JP-A-1-95091, JP-A-3-13376, etc., JP-A-59-42993, 59- Nos. 52689, 62-280069, 61-242871 and JP-A-4-21 Optical brighteners described in No. 266, etc., pH adjusters such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, antifoaming agents, preservatives, thickeners, antistatic agents Various known additives such as an agent and a matting agent can also be contained.

  The ink absorbing layer (porous layer) may be composed of two or more layers. In this case, the structures of the ink absorbing layers may be the same or different from each other.

[Support]
As the support that can be used in the present invention, those conventionally known for inkjet recording media can be used as appropriate, and may be a water-absorbing support, but is preferably a non-water-absorbing support.

  In the case of an absorptive support, so-called cockling that causes the support to be distorted due to water absorption occurs, not only the quality is lowered, but also the gloss difference between the white background and the image area, which is the object of the present invention, is not sufficient. This is because the apparent glossiness changes due to cockling.

  Examples of the water-absorbing support that can be used in the present invention include sheets and plates having general paper, cloth, wood, and the like. In particular, paper is excellent in water absorption of the substrate itself and It is most preferable because of its excellent cost. As the paper support, the main raw materials are chemical pulps such as LBKP and NBKP, mechanical pulps such as GP, CGP, RMP, TMP, CTMP, CMP, and PGW, and wood pulp such as waste paper pulp such as DIP. It is. In addition, various fibrous materials such as synthetic pulp, synthetic fiber, and inorganic fiber can be appropriately used as raw materials as necessary. If necessary, various conventionally known additives such as sizing agents, pigments, paper strength enhancers, fixing agents, fluorescent whitening agents, wet paper strength agents, cationizing agents and the like are added to the paper support. be able to. The paper support can be produced by mixing various fibrous materials such as wood pulp and various additives and using various paper machines such as a long net paper machine, a circular net paper machine, and a twin wire paper machine. Further, if necessary, the paper can be subjected to size press treatment with starch, polyvinyl alcohol or the like, various coating treatments, or calendar treatment on a paper making stage or a paper machine.

  Non-water-absorbing supports that can be preferably used in the present invention include transparent supports and opaque supports. Examples of the transparent support include films having materials such as polyester resins, diacetate resins, triatesate resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polyimide resins, cellophane, and celluloid. Among them, those having a property of resisting radiant heat when used for overhead projectors (OHP) are preferable, and polyethylene terephthalate is particularly preferable. The thickness of such a transparent support is preferably 50 to 200 μm. Further, as the opaque support, for example, resin-coated paper (so-called RC paper) having a polyolefin resin coating layer in which white pigment or the like is added to at least one of the base paper, white pigment such as barium sulfate is added to polyethylene terephthalate. A so-called white pet is preferable. For the purpose of increasing the adhesive strength between the various supports and the ink absorbing layer, the support is preferably subjected to corona discharge treatment, subbing treatment or the like prior to application of the ink absorbing layer. Furthermore, the inkjet recording medium of the present invention is not necessarily colorless, and may be a colored recording sheet.

  In the ink jet recording medium of the present invention, it is particularly preferable to use a paper support obtained by laminating both sides of a base paper support with polyethylene because the recorded image is close to photographic image quality and a high quality image can be obtained at low cost.

  Such a paper support laminated with polyethylene will be described below. The base paper used for the paper support is made from wood pulp as a main raw material, and if necessary, paper is made using synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester in addition to wood pulp. As wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, and NUKP can be used, but it is preferable to use more LBKP, NBSP, LBSP, NDP, and LDP with a large amount of short fibers. . However, the ratio of LBSP or LDP is preferably 10 to 70% by mass. The pulp is preferably a chemical pulp (sulfate pulp or sulfite pulp) with few impurities, and a pulp having a whiteness improved by bleaching 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 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 the mass% of the 24 mesh residue defined by JIS-P-8207 and the 42 mesh residue. The sum of the mass% of the minute is preferably 30 to 70%. In addition, it is preferable that the mass% of 4 mesh remainder is 20 mass% or less. The basis weight of the base paper is preferably 30 to 250 g, particularly preferably 50 to 200 g. The thickness of the base paper is preferably 40 to 250 μm. The base paper can be given 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. 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 ink absorbing layer side preferably has an improved opacity and whiteness by adding rutile or anatase type titanium oxide to the polyethylene as is widely done in photographic paper. The titanium oxide content is usually 3 to 20% by mass, preferably 4 to 13% by mass, based on polyethylene. Polyethylene-coated paper can be used as glossy paper, or when the polyethylene is melt-extruded onto the surface of the base paper and coated, a so-called molding process is performed to form a matte or silky surface that can be obtained with ordinary photographic paper These can also be used in the present invention. In the polyethylene-coated paper, the water content in the paper is particularly preferably maintained at 3 to 10% by mass.

  The method for applying various ink absorbing layers, which are appropriately provided as necessary, such as the porous layer and the undercoat layer of the ink jet recording medium of the present invention on the support, can be appropriately selected from known methods. A preferred method is obtained by coating a coating liquid constituting each layer on a support and drying. In this case, two or more layers can be applied simultaneously. As the coating method, for example, a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, or an extrusion coating method using a hopper described in US Pat. No. 2,681,294 is preferable. Used.

  The method for applying the surface layer of the ink jet recording medium of the present invention can be appropriately selected from known methods.

The absorption coefficient according to the Bristow method in the present invention is described in J. Org. It conforms to the paper and paperboard liquid absorptivity test method specified in TAPPI 51. The unit of the absorption coefficient is ml / m ² · ms ^1/2 . In order to increase the absorption coefficient to 17 ml / m ² · ms ^1/2 or more, the ratio of the inorganic fine particles to the binder in the surface layer, the particle size of the inorganic fine particles in the surface layer, the film thickness of the surface layer, the degree of swelling of the surface layer Optimum ratio of inorganic fine particles to binder in porous layer, particle size of inorganic fine particles in porous layer, additive of porous layer, degree of swelling of porous layer (depending on cross-linking agent, etc.) This can be achieved. It is also possible to increase the absorption coefficient by applying and drying the surface layer and then performing post-treatment such as heating and humidification.

〔ink〕
In the ink jet recording method of the present invention, an image is formed by discharging ink containing at least water, a water-soluble solvent and a color material onto the ink jet recording medium of the present invention.

  In the present invention, it is particularly preferable to use a pigment ink as a coloring material from the viewpoint of image storage stability. As the pigment used in the pigment ink, insoluble pigments, organic pigments such as lake pigments, carbon black and the like can be preferably used.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  A pigment dispersant may be used for these pigments as necessary. Examples of pigment dispersants that can be used include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates. Activators such as acid salts, polyoxyalkylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene glycols, glycerin esters, sorbitan esters, polyoxyethylene fatty acid amides, amine oxides, or styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, Block copolymers, random copolymers, and random copolymers composed of two or more monomers selected from acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives Mention may be made of these salts.

  As a method for dispersing the pigment, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  The average particle size of the pigment particles in the pigment ink is selected in consideration of stability in the ink, image density, glossiness, light resistance, etc. In addition, the inkjet recording method of the present invention improves glossiness, textures. It is preferable to select the particle size as appropriate from the viewpoint of improvement. In the present invention, the reason for improving the glossiness or texture is not clear at this stage, but in the formed image, the pigment is in a desirable state dispersed in the film in which the thermoplastic resin is melted. I guess it is related. For the purpose of high-speed processing, the thermoplastic resin must be melted and formed into a film in a short time, and the pigment must be sufficiently dispersed in the film. At this time, it is considered that the surface area of the pigment has a great influence, and therefore there is an optimum region for the average particle diameter.

  The water-based ink composition which is a preferable form as the pigment ink preferably uses a water-soluble organic solvent in combination. Examples of the water-soluble organic solvent that can be used in the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl). Alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol Etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol) Ether monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, mole) Phosphorus, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N , N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides ( For example, dimethyl sulfoxide etc.), sulfones (for example, sulfolane etc.), urea, acetonitrile, acetone etc. are mentioned. Preferable water-soluble organic solvents include polyhydric alcohols. Furthermore, it is particularly preferable to use a polyhydric alcohol and a polyhydric alcohol ether in combination.

  One or more water-soluble organic solvents may be used in combination. The total amount of the water-soluble organic solvent added to the ink is 5 to 60% by mass, preferably 10 to 35% by mass.

  The ink composition may be prepared by adding various known additives such as viscosity according to the purpose of improving ejection stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Adjusting agents, surface tension adjusting agents, specific resistance adjusting agents, film forming agents, dispersants, surfactants, ultraviolet absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. are appropriately selected and used. For example, polystyrene, polyacrylic acid esters, polymethacrylic acid esters, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, urea resin, melamine resin, etc. Organic latex fine particles, liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil and other oil droplet fine particles, Various surfactants of thione or nonion, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988 and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, 60-72785, 61-146591, anti-fading agents described in JP-A-1-95091 and 3-13376, JP-A-59-42993, 59-52689, 62- 280069, 61-242871, and JP-A-4-219266, etc., optical brighteners, pH adjusters such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, etc. Can be mentioned.

  The ink composition has a viscosity at the time of flight of preferably 40 mPa · s or less, and more preferably 30 mPa · s or less. The ink composition has a surface tension during flight of preferably 20 mN / m or more, and more preferably 30 to 45 mN / m.

  The printer that can be used in the present invention is not particularly limited as long as it has a recording paper storage unit, a transport unit, an ink cartridge, and an inkjet print head, such as a commercially available printer.

  The inkjet head to be used may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (R) type, and the like, an electrostatic suction type (for example, an electric field control type, a slit jet type, etc.), a discharge type (for example, a spark jet type, etc.), and the like. However, any discharge method may be used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. Unless otherwise specified, “%” in the examples represents “mass%”.

Example 1
[Preparation of inkjet recording medium]
(Preparation of silica dispersion S-1)
Gas phase method silica (Japan) having an average primary particle size of about 12 nm uniformly dispersed in 120 g of an aqueous solution of 10% cationic polymer P-1 (containing 10% n-propanol and 2% ethanol). 400 g of silica dispersion (pH 2.6, containing 0.5% ethanol) containing 25% of Aerosil 200, Aerosil 200), 3.6 g of boric acid, and 0.8 g of borax were added at room temperature with stirring at 3000 rpm. did.

Subsequently, it disperse | distributed by the pressure of 3000 N / cm < ² > with the high-pressure homogenizer by Sanwa Kogyo Co., Ltd., the whole quantity was finished with a pure water so that a silica content might be 18%, and silica dispersion liquid S-1 was obtained. The obtained dispersion was filtered using a TCP-10 type filter manufactured by Advantex Toyo. It was 46 nm when the silica average secondary particle diameter was measured.

  The average secondary particle size is a value measured by diluting the dispersion 50 times and using a dynamic light scattering method particle size measuring device Zetasizer 1000HS (Malvern).

(Preparation of coating solution 1)
The following additives were sequentially mixed with 555 g of the above dispersion S-1 while stirring at 40 ° C., and finally the total amount was adjusted to 1000 g with pure water to prepare a coating solution 1.

8% aqueous solution of polyvinyl alcohol with a polymerization degree of 3500 (manufactured by Kuraray, PVA235)
192g
8% aqueous solution of polyvinyl alcohol with a polymerization degree of 4500 (manufactured by Kuraray, PVA245)
60g
(Preparation of coating solution 2)
The following additives were sequentially mixed with 555 g of the above dispersion S-1 while stirring at 40 ° C., and finally the total amount was adjusted to 1000 g with pure water to prepare a coating solution 2.

8% aqueous solution of polyvinyl alcohol with a polymerization degree of 3500 (manufactured by Kuraray, PVA235)
320g
8% aqueous solution of polyvinyl alcohol with a polymerization degree of 4500 (manufactured by Kuraray, PVA245)
100g
(Preparation of porous layer 1)
The coating solution 1 is a polyethylene-coated paper in which both sides of a base paper having a thickness of 170 g / m ² are coated with polyethylene (containing 8% anatase-type titanium oxide in polyethylene on the ink receiving layer side, 0.05 g on the ink receiving layer side). / G ² gelatin subbing layer, latex polymer having Tg of about 80 ° C. on the opposite side as back layer 0.2 g / m ² ), using a bar coater, the amount of silica applied is 18 g / m ² After coating, the substrate was dried with warm air to prepare a porous layer 1.

(Preparation of porous layer 2)
A porous layer 2 was produced in the same manner as the porous layer 1 except that the coating solution 1 was changed to the coating solution 2.

(Preparation of inkjet recording medium 1)
An ink jet recording medium 1 was prepared by storing in a constant temperature bath at 40 ° C. and 80% RH without applying a surface layer to the porous layer 1.

(Preparation of surface layer coating solution 1)
While stirring to 333 g of titanium oxide aqueous dispersion (Ishihara Sangyo, TSK-5), 250 g of an 8% aqueous solution of polyvinyl alcohol with a polymerization degree of 2400 (Kuraray, PVA224) was added, and the total amount was adjusted to 1000 g with pure water. A surface layer coating solution 1 was prepared.

(Preparation of surface layer coating solution 2)
250 g of titanium oxide aqueous dispersion (Ishihara Sangyo Co., Ltd., TSK-5) and 125 g of colloidal silica (Nissan Chemical Co., Snowtex OS) are mixed. A surface layer coating solution 2 was prepared by adding 250 g of an aqueous solution and adjusting the total amount to 1000 g with pure water.

(Preparation of surface layer coating solution 3)
A surface layer coating solution 3 was prepared by adding 250 g of an 8% aqueous solution of polyvinyl alcohol having a polymerization degree of 2400 (manufactured by Kuraray, PVA224) to 1000 g of colloidal silica (Nissan Chemical, Snowtex OS) while stirring.

(Preparation of surface layer coating solution 4)
While stirring 333 g of titanium oxide aqueous dispersion (Ishihara Sangyo, TSK-5), add 625 g of 8% aqueous solution of polyvinyl alcohol with a polymerization degree of 2400 (Kuraray, PVA224) and adjust the total amount to 1000 g with pure water. A surface layer coating solution 4 was prepared.

(Preparation of inkjet recording medium 2)
On the porous layer 1, the surface layer coating solution 1 is applied with a wire bar while controlling the film thickness so that the dry film thickness becomes 2 μm, dried with warm air, and then a constant temperature bath at 40 ° C. and 80% RH. The ink-jet recording medium 2 was produced by storing for 12 hours.

(Preparation of inkjet recording medium 3)
An ink jet recording medium 3 was produced in the same manner as the ink jet recording medium 2 except that the pH of the surface layer coating solution 1 was changed to Ra in Table 1.
A kjet recording medium 3 was produced.

(Preparation of inkjet recording medium 4)
An ink jet recording medium 4 was produced in the same manner as the ink jet recording medium 2 except that the surface layer coating liquid 1 was changed to the surface layer coating liquid 2.

(Preparation of inkjet recording medium 5)
An ink jet recording medium 5 was produced in the same manner as the ink jet recording medium 2 except that the surface layer coating liquid 1 was changed to the surface layer coating liquid 3.

(Preparation of inkjet recording medium 6)
An ink jet recording medium 6 was produced in the same manner as the ink jet recording medium 2 except that the porous layer 1 was changed to the porous layer 2.

(Preparation of inkjet recording medium 7)
An ink jet recording medium 7 was produced in the same manner as the ink jet recording medium 2 except that the surface layer coating liquid 1 was changed to the surface layer coating liquid 4.

[Preparation of ink]
The pigment particles were dispersed so that the average particle diameter of the pigment particles was 0.2 to 0.3 μm with the following composition to prepare pigment dispersions of respective colors.

(Yellow pigment dispersion 1)
C. I Pigment Yellow-12 10 parts Polymer dispersant 5 parts Stearyl acrylate 85 parts (Magenta pigment dispersion 1)
C. I Pigment Red-57: 1 15 parts Polymer dispersant 5 parts Stearyl acrylate 80 parts (Cyan pigment dispersion 1)
C. I Pigment Red-15: 3 20 parts Polymer dispersant 5 parts Stearyl acrylate 75 parts (White pigment dispersion 1)
Titanium oxide (anatase type: particle size 0.2 μm) 20 parts Polymer dispersant 5 parts Stearyl acrylate 85 parts An ink having the following formulation was prepared using the above dispersion.

(Yellow ink)
Yellow pigment dispersion 1 20 parts Stearyl acrylate 60 parts Bifunctional aromatic urethane acrylate (molecular weight 1500) 10 parts Hexafunctional aliphatic urethane acrylate (molecular weight 1000) 5 parts Photopolymerization initiator (Ciba, Irgacure 184) 5 parts ( Magenta ink)
Magenta pigment dispersion 1 20 parts Stearyl acrylate 60 parts Bifunctional aromatic urethane acrylate (molecular weight 1500) 10 parts Hexafunctional aliphatic urethane acrylate (molecular weight 1000) 5 parts Photopolymerization initiator (Ciba, Irgacure 184) 5 parts (Cyan ink)
Cyan pigment dispersion 1 15 parts Stearyl acrylate 65 parts Bifunctional aromatic urethane acrylate (molecular weight 1500) 10 parts Hexafunctional aliphatic urethane acrylate (molecular weight 1000) 5 parts Photopolymerization initiator (Ciba, Irgacure 184) 5 parts (White ink)
White pigment dispersion 1 15 parts Stearyl acrylate 65 parts Bifunctional aromatic urethane acrylate (molecular weight 1500) 10 parts Hexafunctional aliphatic urethane acrylate (molecular weight 1000) 5 parts Photopolymerization initiator (Ciba, Irgacure 184) 5 parts [Measurement and evaluation of inkjet recording medium]
(Absorption coefficient)
J. et al. The absorption coefficient was measured according to the liquid absorptivity test method for paper and paperboard specified in TAPPI 51. The used ink is PM-9000C magenta manufactured by Seiko Epson Corporation.

  The ink prepared above is mounted on an ink jet printer MC-2000 (manufactured by Seiko Epson). The ink jet recording media 1 to 7 have a solid cyan image and high-definition color digital standard image data “Bride” published by the Japan Standards Association. Is printed. This image was dried in an environment of 23 ° C. and 55% RH for 1 hour. Each inkjet recording medium was printed using what was stored at 23 ° C. for 1 day. This sample was evaluated for the following gloss difference and scratch resistance.

(Gloss difference)
Visual evaluation was performed by 15 people to determine whether there was a difference in gloss between the white background in the dress of the high-definition color digital standard image data “Bride” and the image of the other dress, and the following three-level evaluation was performed.

◎: The number of people who felt that there was a difference in gloss 0-2 people ○: The number of people who felt that there was a difference in gloss 3-5 people △: The number of people who felt that there was a difference in gloss 6-10 people ×: 11-15 people who feel that there is a difference in gloss (Scratch resistance)
The image was rubbed 5 times with Kimwipe S-200 (manufactured by Crecia), visually evaluated for the degree of surface scratches and the color fading of the image, and the following four grades were evaluated.

◎: Scratches and color fading are not observed ○: Scratches are scarce and no color fading is observed △: Scratches are slight and color fading is observed ×: Scratches are observed and color fading is also greatly recognized The results obtained are shown in Table 1.

  As is apparent from Table 1, the inkjet recording medium of the present invention is superior in gloss difference and scratch resistance as compared with the comparative inkjet recording medium.

Claims (8)

An inkjet recording medium having a surface layer containing inorganic fine particles having an average refractive index of 2.1 to 2.9 and a binder on a support, and a porous layer containing inorganic fine particles and a binder, according to the Bristow method An ink jet recording medium having an absorption coefficient of 17 ml / m ² · ms ^1/2 or more. 2. The ink jet recording medium according to claim 1, wherein a product of the surface roughness Ra (μm) of the surface layer and the average refractive index is 1.7 μm or less. 3. The ink jet recording medium according to claim 1, wherein the inorganic fine particles in the surface layer are at least one selected from titanium oxide, cerium oxide and zirconium oxide. The ink jet recording medium according to claim 1, wherein the surface layer contains a cationic polymer. The inkjet according to any one of claims 1 to 4, wherein the inorganic fine particles of the porous layer have an average refractive index of 1.3 to 1.7 and an average particle diameter of 1 to 200 nm. recoding media. The inkjet recording medium according to claim 1, wherein the inorganic fine particles of the porous layer are silica or alumina. The inkjet recording medium according to any one of claims 1 to 6, wherein the support is a non-absorbent support. An ink jet recording method comprising: recording an image by ejecting an ink containing at least a water-soluble solvent and a pigment onto the ink jet recording medium according to claim 1.