JP2004299378A - Ink jet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recording medium which causes no significant cockling after recording and has excellent ink absorption. <P>SOLUTION: This ink jet recording medium comprises base paper composed mainly of wood pulp and, provided on the base paper, at least an anchor layer and an ink receiving layer and is characterized in that an olefin-based surface sizing agent is contained in the surface of the base paper in its side where the anchor layer and the ink receiving layer are provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording medium, and more specifically, an ink receiving layer is provided on a base paper mainly composed of wood pulp to enable formation of a high quality image by an ink jet recording method, and a sheet after recording. The present invention relates to an ink jet recording medium having little cockling and excellent ink absorbability.

  The ink jet recording system records fine images and characters by flying small droplets of ink and attaching them to recording paper such as paper according to various operating principles. It is easy to use, has great flexibility in recording patterns, and does not require development-fixing, and is rapidly spreading in various applications as a recording device for various figures including Chinese characters and color images. Furthermore, an image formed by the multi-color ink jet method can obtain a record comparable to multi-color printing by a plate making method or printing by a color photographic method. In addition, in applications where the number of copies required is small, it is being widely applied to the field of full-color image recording because it is cheaper than the photographic technique.

  One of the drawbacks of the ink jet recording system is its slow printing speed. In recent years, technical improvements have progressed with the spread of the ink jet recording method, and the printing speed has been remarkably increased. However, as a printer performs high-speed printing, cockling becomes a problem, in which a printed portion is wavy by ink injected into an ink jet recording medium. If the cockling becomes severe, the impact point of the ink on the ink jet recording medium will be shifted, so the image will be blurred or the printer ink head will rub on the raised part of the ink jet recording medium, and the printed image will not be printed. In some cases, the sheet may be contaminated, or the ink jet recording medium may be broken, so that the paper cannot be passed.

  Inks are classified into a solvent type and an aqueous type. However, in terms of price, safety, ease of handling, etc., there are many aqueous inks, and ink jet inks also belong to the aqueous inks. Improvement of cockling by the solvent of the aqueous ink that has reached the base paper has become an important issue. At present, this problem has not been sufficiently addressed. In the case of an inkjet recording medium having a support mainly composed of wood pulp having a function as an ink absorber, it is more important and earlier. It is an issue that needs to be solved.

  As a means for avoiding this phenomenon, a method of making the base paper sufficiently thick or a method of providing a back coat layer on the opposite side of the base paper from the ink receiving layer to suppress expansion and contraction of the base paper are known. However, with these methods, it is difficult to completely avoid cockling in a printing apparatus in which the amount of ejected ink has recently increased. Further, in order to make the base paper thicker and to cope with the rigidity of the base paper, a considerable thickness is required, which is much larger than the thickness (for example, 280 μm or less) of the recording paper normally used. As a result, the rigidity of the base paper is increased, the flexibility of the recording paper is lacking, and the base paper is thick, so that the transportability in the ink jet recording apparatus is reduced.

  Further, a method of increasing the absorption capacity of the ink receiving layer so that the ink does not reach the base paper can be considered. However, in order to increase the absorption capacity of the ink receiving layer, it is necessary to reduce the binder component in the ink receiving layer or increase the coating amount of the ink receiving layer. However, it is difficult to say that this is a preferable means because the adhesive strength of the toner and the reproducibility of the image due to the thinning of the dots forming the image are reduced.

  Further, a method of providing a barrier layer between the base paper and the ink receiving layer so as to prevent the printed ink from penetrating to the base paper, or a method of providing water resistance so that the base paper does not expand and contract even when the ink permeates may be considered. However, according to these methods, the ink absorption capacity of the ink jet recording medium is reduced, and ink overflow or bleeding occurs, making it difficult to obtain a good image.

Several proposals have been made for such problems. For example, an ink jet recording medium provided with a back coat (for example, see Patent Document 1) and an ink jet recording medium in which the value of the air permeability / density of the ink jet recording medium is within a specific range (for example, Patent Document 2) (See, for example, Japanese Patent Application Laid-Open Publication No. H11-157572) in which a support wood pulp is impregnated with a specific ionizing radiation-curable compound and then irradiated with ionizing radiation and cured. Further, an ink jet recording medium having a starch particle layer between a support and an ink receiving layer (see, for example, Patent Document 4), and an ink jet recording medium having a support layer provided on the opposite surface of the ink receiving layer surface through the base paper. A recording medium (for example, see Patent Document 5) is disclosed. However, the ink receptivity and cockling have not been sufficiently improved at the same time.
JP-A-5-221115 (page 4) JP-A-6-143796 (pages 2 to 3) JP-A-8-169174 (pages 3 to 5) JP-A-8-258396 (pages 2 to 3) JP-A-11-301101 (pages 3 and 4)

  The present invention is directed to an ink jet recording medium in which an ink receiving layer is provided on a base paper mainly composed of wood pulp, with little cockling after recording, and an ink jet recording medium having excellent ink absorbability. To provide. Another object of the present invention is to provide an ink jet recording medium having a higher glossiness.

The above object of the present invention has been achieved by the following inventions.
(1) An ink jet recording medium having at least an anchor layer and an ink receiving layer on a base paper mainly composed of wood pulp, wherein an olefin-based surface is provided on the surface of the base paper on which the anchor layer and the ink receiving layer are provided. An ink jet recording medium comprising a sizing agent.
(2) The ink jet recording medium according to (1), wherein the water immersion elongation after 2 minutes of water immersion in a direction (CD direction) orthogonal to a papermaking direction (MD direction) of the base paper is 2.0% or less.
(3) The inkjet recording medium according to the above (1), wherein the anchor layer has a 30-second Cobb water absorbency of 5 to 15 g / m ² in distilled water specified by JIS-P-8140.
(4) The ink jet recording medium according to the above (1), wherein the anchor layer contains an inorganic pigment and a polymer latex.
(5) The ink jet recording medium according to the above (1), wherein the ink receiving layer contains an inorganic pigment and a hydrophilic binder.
(6) The olefin-based surface sizing agent is selected from the group consisting of an olefin maleic acid copolymer, an olefin (meth) acrylic acid copolymer, an olefin styrene maleic acid copolymer, and an olefin styrene (meth) acrylic acid copolymer. The inkjet recording medium according to the above (1), which is at least one kind of the recording medium.
(7) The ink jet recording medium according to (1), wherein the base paper has a surface pH defined by TAPPI T529 of 4 to 6.
(8) The ink jet recording medium according to the above (1), further comprising a glossy layer on the ink receiving layer.

  The ink jet recording medium of the present invention has little cockling after recording, has excellent ink absorbability, and has a higher glossiness.

  As the wood pulp used in the base paper of the present invention, hardwood bleached sulphite pulp (LBSP), hardwood bleached kraft pulp (LBKP), softwood bleached sulphite pulp (NBSP), softwood bleached kraft pulp (NBKP) and the like are advantageous. Used for If necessary, non-wood pulp, synthetic pulp, synthetic fiber or recycled pulp may be used in addition to wood pulp. The base paper of the present invention is one in which wood pulp accounts for 60% by mass or more of the entire base paper.

  The pulp is usually beaten with a beater in order to improve the papermaking suitability and various properties of the paper such as strength, smoothness, formation uniformity and the like.

  The beaten pulp slurry is made by a paper machine such as a fourdrinier paper machine, a twin wire paper machine, or a round net paper machine. At this time, various additives such as a dispersing aid, a dry paper strength enhancer, a filler, a sizing agent, and a fixing agent can be added as needed. Further, if necessary, a pH adjuster, a dye, a colored pigment, a fluorescent whitening agent and the like can be added.

  In the present invention, an olefin-based surface sizing agent is added to the surface of the base paper formed as described above. The olefin surface sizing agent is applied or impregnated on the surface of the base paper on which at least the anchor layer and the ink receiving layer are provided.

  Examples of the method of coating or impregnating the base paper surface with an olefin surface sizing agent include, for example, an air knife coater, a curtain coater, a slide lip coater, a die coater, a blade coater, a gate roll coater, a bar coater, a rod coater, and a roll coater. , A bill blade coater, a short dwell blade coater, a size press and the like are used. In the present invention, it is preferable to impregnate or apply the olefin-based surface sizing agent continuously on-machine after papermaking the base paper, and more preferably to impregnate it with a size press device.

  The base paper coated or impregnated with the olefin surface sizing agent is preferably subjected to a calendering treatment such as a machine calender, a TG calender or a soft calender for the purpose of smoothing the base paper surface before providing the anchor layer.

  Examples of the olefin surface sizing agent used in the present invention include an olefin maleic acid copolymer, an olefin (meth) acrylic acid copolymer, an olefin styrene maleic acid copolymer, and an olefin styrene (meth) acrylic acid copolymer. Can be

  The olefin surface sizing agent used in the present invention will be described in detail. The olefin-based surface sizing agent is a surface sizing agent composed of a copolymer having at least an olefin-based monomer as a constituent component. Such olefin monomers include, for example, ethylene, propylene, n-butylene, isobutylene, octene, decene and the like. Other components of the copolymer include anionic monomers (hydrophilic monomers), for example, acrylic monomers such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, methylmaleic acid, and phenylmaleic acid. Maleic acid monomers such as acid, chloromaleic acid, fumaric acid, itaconic acid and the like can be mentioned.

  Specifically, ethylene / acrylic acid copolymer, isobutylene / acrylic acid copolymer, ethylene / maleic acid copolymer, n-butylene / (meth) acrylic acid copolymer / (meth) acrylic acid ester copolymer Copolymer, ethylene / maleic acid copolymer and propylene / maleic acid copolymer are exemplified. These copolymers may be a sodium salt, a potassium salt, or an ammonium salt.

  The olefin-based surface sizing agent of the present invention contains a styrene-based monomer, such as styrene, α-methylstyrene, chlorostyrene, and cyanostyrene, as a copolymer component in addition to the olefin-based monomer and the anionic monomer described above. Copolymers can also be used.

  The weight average molecular weight of the olefin surface sizing agent used in the present invention is preferably 10,000 to 100,000. The olefin surface sizing agent of the present invention may be a water-soluble type or an emulsion type, but is preferably a water-soluble type.

  The content of the olefin surface sizing agent of the present invention in the base paper is preferably in the range of 0.1 to 3% by mass, and particularly preferably in the range of 0.2 to 2% by mass based on the wood pulp.

  In the present invention, it is preferable to use a binder such as starch or polyvinyl alcohol together with the olefin-based surface sizing agent as a coating liquid (size press liquid) when the olefin-based surface sizing agent is coated or impregnated on the base paper surface. . The coating liquid may further contain a dimensional stabilizer such as an ethylene-urea resin, an inorganic conductive agent such as sodium chloride and potassium chloride, an organic conductive agent, a surfactant, a pigment, and a dye.

The base paper used in the present invention preferably has a water immersion elongation of 2.0% or less after 2 minutes of water immersion in a direction (CD direction) orthogonal to a papermaking direction (MD direction) in a paper machine. The base paper used for the measurement of water immersion elongation in the present invention is one coated or impregnated with an olefin surface sizing agent. Here, the water immersion elongation after 2 minutes of immersion refers to the elongation percentage of the paper piece 2 minutes after immersing a piece of paper obtained by cutting the base paper into a predetermined size in water and immersing the same. Is calculated.
A = (L ₁ −L ₀ ) / L ₀ × 100
In the formula, A represents the water immersion elongation (%), L ₀ represents the initial length (mm), and L ₁ represents the length after immersion (mm).

  The measurement of the water immersion elongation in the present invention is carried out according to JAPAN TAPPI Paper Pulp Test Method No. Although the measurement can be performed according to the measurement principle of 27B, in the present invention, the measurement was performed by an apparatus in which a dynamic dimensional displacement measurement module was attached to a dynamic permeability tester DPM manufactured by emco.

A measurement method using an apparatus in which a dynamic dimensional displacement measurement module is attached to the dynamic permeability tester DPM manufactured by emco will be described in detail. The sample paper piece of the base paper is cut so that the initial measurement length (L ₀ ) in the CD direction is 50 mm and the length in the width direction (MD direction) is 50 mm. However, the length in the CD direction is set to 70 mm so that a holding margin (about 10 mm) is provided at each end of the paper piece.

  A thin stainless steel plate of about 10 mm is adhered to each end of the sample paper piece of the predetermined size prepared as described above in the CD direction with a double-sided adhesive tape so that the measurement length becomes 50 mm. The plate attached to both ends of the paper piece is gripped and immersed in water while applying a low tension (0.5 N) to the paper piece, and the dimensional displacement of the paper piece is continuously measured by a sensor, and then immersed. Calculate the dimensional displacement after one minute. Here, the tension of 0.5 N applied to the sample piece is for keeping the sample piece uniformly stretched in order to accurately measure the dimensional displacement of the sample piece with a sensor, and does not stretch the sample piece. Is set as follows. The tension is adapted to the basis weight of the base paper preferably used in the present invention.

  The base paper used for the measurement needs to be seasoned in advance at 23 ° C. and 50% (RH) for 10 hours or more. The temperature of the water in which the sample paper piece is immersed during the measurement is 23 ° C.

The basis weight of the base paper used in the present invention is preferably in the range of 80 to 280 g / m ² , more preferably 80 to 200 g / m ² . More preferably, it is in the range of 80 to 150 g / m ² .

  The base paper of the present invention preferably has a surface pH in the range of 4 to 6 as defined in JAPAN TAPPI paper pulp test method T512. For that purpose, when a base paper made from a slurry containing wood pulp as a main component is used, an acidic paper is preferable. Here, the base paper used for the measurement of the surface pH is coated or impregnated with an olefin-based surface sizing agent. By using a base paper having a surface pH of 4 to 6, cockling is further suppressed.

  In the ink jet recording material of the present invention, an anchor layer and an ink receiving layer are coated on a base paper coated or impregnated with an olefin surface sizing agent. The anchor layer of the present invention preferably contains a pigment and a polymer latex. As the pigment, an inorganic pigment is preferable.

  Examples of the pigment used for the anchor layer include light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc carbonate, tissan white, aluminum silicate, diatomaceous earth, and calcium silicate. , Magnesium silicate, synthetic amorphous silica, colloidal silica, colloidal alumina, pseudoboehmite, fumed silica, aluminum oxide such as α, β, γ, δ-, aluminum hydroxide, alumina, lithopone, zeolite, hydrohaloisite One or more types of white pigments, such as white inorganic pigments such as magnesium carbonate and magnesium hydroxide, styrene plastic pigments, acrylic plastic pigments, and organic pigments such as polystyrene, urea resin, and melamine resin can be used. It preferably contains at least one inorganic pigment selected from the group consisting of kaolin, talc, calcium carbonate, magnesium carbonate and amorphous silica. In particular, kaolin, calcium carbonate, and magnesium carbonate are preferable, and these pigments are preferably contained in an amount of 50% by mass or more based on all the pigments in the anchor layer.

  As the polymer latex used for the anchor layer, a wide range of polymer latex can be used. For example, a latex containing an ethylenically unsaturated monomer as a constituent component is exemplified. Suitable ethylenically unsaturated monomers include acrylates (methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, t-butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, etc.), α-substituted acrylates (methyl methacrylate) , Ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexylhexyl methacrylate, etc.), acrylamide (butylacrylamide, hexylacrylamide, etc.), vinyl ester (vinyl acetate, etc.), vinyl halide (vinyl chloride, etc.), vinylidene halide (chloride Vinylidene, etc.), vinyl ether (vinyl methyl ether, vinyl octyl ether, etc.), styrene, ethylene, butadiene And acrylonitrile.

  The polymer latex used in the present invention may be a homopolymer or a copolymer of the above-described vinyl monomer, and may include the above-mentioned vinyl monomer and other monomers such as acrylic acid, methacrylic acid, itaconic acid, or sulfonic acid. A copolymer with a vinyl monomer having a group can be exemplified.

  In the anchor layer, the content ratio of the polymer latex is preferably from 5 to 30% by mass, more preferably from 5 to 20% by mass, and even more preferably from 7 to 15% by mass in terms of the solid content mass ratio to the inorganic pigment.

  The anchor layer may further contain a hydrophilic binder such as polyvinyl alcohol, silanol or cation-modified polyvinyl alcohol, starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, casein, gelatin and the like. When these hydrophilic binders are used, they are preferably contained at 50% by mass or less based on the polymer latex.

The coating amount (dry coating amount) of the anchor layer is preferably in the range of 5 to 30 g / m ² , particularly preferably in the range of 6 to ²⁰ g / m ² , and more preferably in the range of 7 to 15 g / m ² .

  The applied and dried anchor layer may be smoothed by calendering. Examples of the calendering device at that time include a gloss calender, a super calender, a soft calender, and a heat calender.

In the present invention, the anchor layer provided on the base paper preferably has a 30-second Cobb water absorption of 5 to 15 g / m ² in distilled water specified by JIS-P-814. By providing an anchor layer having a Cobb water absorption in this range between the base paper and the ink receiving layer, cockling can be further suppressed. In the present invention, the Cobb water absorption of the anchor layer is a value obtained by subtracting the Cobb water absorption of the base paper before the anchor layer is applied from the Cobb water absorption in a state where the anchor layer is applied on the base paper.

  The ink receiving layer of the present invention preferably contains an inorganic pigment and a hydrophilic binder. As inorganic pigments, for example, light calcium carbonate, heavy calcium carbonate, calcium silicate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc carbonate, tissan white, aluminum silicate, diatomaceous earth, magnesium silicate, carbonate Examples include magnesium, magnesium hydroxide, synthetic amorphous silica, alumina, alumina hydrate, lithopone, zeolite, hydrohaloysite, and the like. Among these, calcium carbonate, magnesium carbonate, kaolin, and synthetic amorphous silica are preferably used. The average secondary particle diameter of these inorganic pigments is preferably 0.5 to 15 μm, and particularly preferably 1 to 10 μm.

  Examples of the hydrophilic binder used in the ink receiving layer include polyvinyl alcohol, silanol-modified or cation-modified polyvinyl alcohol, polyvinylpyrrolidone, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, casein, gelatin, starch, soybean, agar, and chitosan. And the like. Among these, polyvinyl alcohol or modified polyvinyl alcohol is preferably used.

  The content ratio of the hydrophilic binder to the inorganic pigment in the ink receiving layer is preferably in the range of 5 to 80% by mass, and particularly preferably in the range of 10 to 50% by mass. The ink receiving layer may contain the polymer latex as described above in addition to the hydrophilic binder, and the content ratio of the polymer latex is preferably 50% by mass or less based on the hydrophilic binder. It is. It is preferable that the ink receiving layer further contains a cationic polymer.

Dry coating amount of the ink receiving layer is preferably in the range of 1 to 30 g / m ^2, in particular in the range of 5 to 20 g / m ² is preferred.

  In the present invention, it is preferable to further provide a gloss developing layer on the ink receiving layer. The glossiness of the inkjet recording medium can be increased by providing the glossy layer on the ink receiving layer. However, when cockling occurs, the gloss improving effect of the gloss developing layer cannot be sufficiently enjoyed. Therefore, the technical significance of the present invention is high in an embodiment in which a gloss developing layer is provided on the ink receiving layer. The glossy layer is a layer containing inorganic ultrafine particles having an average secondary particle diameter of 1 μm or less, preferably 10 to 400 nm, in an amount of 55% by mass or more based on the total solid content of the layer. Preferably, it is a layer containing 60 to 90% by mass of the inorganic ultrafine particles.

  As the inorganic ultrafine particles, at least one selected from colloidal silica, fumed silica, alumina, and alumina hydrate can be used. The glossy layer of the present invention preferably contains alumina hydrate as inorganic ultrafine particles in an amount of 50% by mass or more based on the total inorganic ultrafine particles.

  As the colloidal silica, besides the conventional general-purpose unmodified colloidal silica, any of the modified colloidal silicas whose silica surface is coated with ions or compounds such as calcium and alumina and whose behavior with respect to ionicity and pH fluctuation is changed can be used. it can. Examples of commercially available colloidal silica according to the present invention include, for example, Nissan Chemical Industries Snowtex 20, Snowtex N, Snowtex O, Snowtex S, Snowtex 20L, Snowtex AK, and Snowtex UP. Such as silica doll 20, silica doll 20A, silica doll 20G, and silica doll 20P, such as Adelite AT-20, Adelite AT-20N, Adelite AT-30A, and Adelite AT-20Q manufactured by Asahi Denka Kogyo; -30, Ludox LS, Ludox SM-30, Ludox AS, and Ludox AM.

  The fumed silica is called dry silica, and is amorphous silica fine particles synthesized by a gas phase method. Above all, the average secondary particle diameter in which the average primary particle diameter of 5 nm to 30 nm is aggregated is preferably 10 nm to 400 nm. Aerosil (Texa) is a commercially available product as fumed silica.

  The fumed silica is dispersed with a high-pressure homogenizer, a media mill, or the like, and dispersed to have an average secondary particle diameter of 400 nm or less, preferably 200 nm or less.

  The alumina fine particles used in the present invention are aluminum oxide crystal fine particles, and can be broadly classified into two types, α-type and γ-type, which are thermodynamically stable among various crystal types. The group preferably used in the present invention can be further divided into a γ group and a δ group. Fine particles having a crystal form of the δ group are more preferable.

  The alumina of the γ-type crystal fine particles can reduce the average particle diameter of the primary particles to about 10 nm, but generally, the primary particles form a secondary aggregated form (secondary particles).

  In order to obtain γ-type alumina crystal fine particles, usually, γ-type alumina crystals, which are secondary particles of several thousands to tens of thousands of nm, have an average particle diameter of pulverizing means such as a bead mill, an ultrasonic homogenizer, and a high-pressure homogenizer. Pulverization is performed until ultrafine particles of 400 nm or less, preferably 200 nm or less, more preferably 100 nm or less are obtained. As a pulverizing means, a method using an ultrasonic homogenizer or a high-pressure homogenizer is preferable. γ-type alumina crystal fine particles are excellent in ink absorbency, good in printing quality such as drying property and ink fixing property, and are made into ultra-fine particles. A recording medium can be obtained.

  The γ-type alumina crystal fine particles are commercially available as aluminum oxide C belonging to δ group (manufactured by Nippon Aerosil Co., Ltd.), AKP-G015 belonging to γ group (manufactured by Sumitomo Chemical Co., Ltd.), and the like.

The alumina hydrate used in the present invention can be represented by the following general formula.
Al ₂ O ₃ .nH ₂ O
Alumina hydrate is classified into gypsite, vialite, norstrandite, boehmite, boehmite gel (pseudo-boehmite), diaspore, amorphous amorphous and the like according to the difference in composition and crystal form. Above all, when the value of n in the above formula is 1, the alumina hydrate has a boehmite structure, and when n is more than 1 and less than 3, the alumina hydrate has a pseudo-boehmite structure. In the above, alumina hydrate having an amorphous structure is represented. In particular, the alumina hydrate preferred for the present invention is an alumina hydrate in which at least n is more than 1 and less than 3.

  In order for the alumina hydrate to have a sufficient ink absorption rate, the average pore radius of the alumina hydrate is preferably from 1 to 10 nm, and particularly preferably from 3 to 7 nm. If the pore radius is too small, it becomes difficult to absorb the ink. If the pore radius is too large, fixing of the dye in the ink becomes poor, and image bleeding occurs.

In order for the alumina hydrate to have a sufficient ink absorption capacity, the pore volume of the alumina hydrate is preferably in the range of 0.3 to 0.8 ml / g, and particularly preferably 0.4 to 0.6 ml. / G is preferable. The solvent absorption amount of the ink receiving layer per unit area is preferably 5 ml / m ² or more, particularly preferably 10 ml / m ² or more.

For the alumina hydrate to sufficiently absorb and fix the dye in the ink, the BET specific surface area is preferably in the range of 70 to 300 m ² / g.

  The shape of the alumina hydrate may be any of a flat plate shape, a fibrous shape, a needle shape, a spherical shape, a rod shape, and the like, and a preferable shape is a flat plate shape from the viewpoint of ink absorbability. The plate-like alumina hydrate has an average aspect ratio of 3 to 8, preferably an average aspect ratio of 3 to 6. The aspect ratio is expressed as the ratio of “diameter” to “thickness” of a particle. Here, the diameter of the particle represents the diameter of a circle equal to the projected area of the particle when the alumina hydrate is observed with an electron microscope.

  Alumina hydrate can be produced by a known method such as hydrolysis of aluminum alkoxide such as aluminum isopropoxide, neutralization of aluminum salt with alkali, and hydrolysis of aluminate. The physical properties of alumina hydrate, such as particle diameter, pore diameter, pore volume, and specific surface area, should be controlled by conditions such as precipitation temperature, aging temperature, aging time, liquid pH, liquid concentration, and coexisting compounds. Can be.

  As a method for obtaining an alumina hydrate from an alkoxide, JP-A-57-88074, JP-A-62-56321, JP-A-4-275917, JP-A-6-64918, JP-A-7-10535, No. 7,267,633 and U.S. Pat. No. 2,656,321 disclose a method of hydrolyzing aluminum alkoxide. These aluminum alkoxides include isopropoxide, 2-butoxide and the like.

  JP-A-54-116398, JP-A-55-23034, JP-A-55-27824 and JP-A-56-120508 disclose a method using an inorganic salt of aluminum or a hydrate thereof as a raw material. It has been disclosed. Examples of the raw material include inorganic salts such as aluminum chloride, aluminum nitrate, aluminum sulfate, polyaluminum chloride, ammonium alum, sodium aluminate, potassium aluminate, and aluminum hydroxide, and hydrates thereof.

  Still another method is disclosed in JP-A-56-120508, in which the pH is alternately changed from an acidic side to a basic side to grow alumina hydrate crystals. As described in JP-A-33728, there is a method of mixing alumina hydrate obtained from an inorganic salt of aluminum with alumina obtained by a Bayer method, and rehydrating the alumina.

  The glossy layer preferably contains a hydrophilic binder together with the inorganic ultrafine particles described above. As the hydrophilic binder, those similar to the above-described hydrophilic binder of the ink receiving layer are used, and preferably polyvinyl alcohol or modified polyvinyl alcohol. The content ratio of the hydrophilic binder in the gloss developing layer is preferably in the range of 5 to 50% by mass, particularly preferably in the range of 8 to 40% by mass, based on the inorganic ultrafine particles. The glossy layer preferably further contains a cationic polymer.

  The anchor layer, the ink-receiving layer, and the gloss-developing layer of the present invention further include, as other additives, a pigment dispersant, a thickener, a leveling agent, a coloring dye, a coloring pigment, a fluorescent whitening agent, an antioxidant, Surfactants, defoamers, foam inhibitors, foaming agents, penetrants, release agents, preservatives, anti-binders, waterproofing agents, wet paper strength agents, dry paper strength agents, pH regulators, etc. Various additives may be added in appropriate combination.

  On the surface of the support opposite to the side on which the ink receiving layer is provided, various types of back coat layers can be applied for antistatic properties, transport properties, curling prevention, writing properties, gluing properties, and the like. An inorganic antistatic agent, an organic antistatic agent, a hydrophilic binder, a latex, a curing agent, a pigment, a lubricant, a matting agent, a surfactant and the like may be added to such a back coat layer as appropriate. Further, the above-mentioned anchor layer, ink receiving layer, or gloss developing layer can also be provided on the opposite surface.

  The method of applying a coating layer such as an ink receiving layer in the present invention is performed by turning on various devices such as various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters, curtain coaters, short dwell coaters, and size presses. It can be used in a machine or off-machine. After coating and drying, the ink receiving layer can be flattened by using a calender such as a machine calender, TG calender, super calender, and soft calender, and can be gloss-finished to form a flatter ink receiving layer.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. Further, "parts" and "%" shown in Examples are parts by mass and% by mass unless otherwise specified.

<Preparation of base paper 1>
To 100 parts of wood pulp consisting of 70 parts of LBKP having a freeness of 450 ml CSF and 30 parts of NBKP having a freeness of 450 ml CSF, 20 parts of talc, 3 parts of a sulfuric acid band, 0.2 parts of a commercially available rosin sizing agent, and 0.3 parts of a commercially available cationized starch were used. After preparing the slurry and adjusting the pH of the slurry to 5, papermaking was performed using a fourdrinier paper machine with a basis weight of 100 g / m ² , and then 6 parts of oxidized starch and an olefin-based surface sizing agent (olefin / maleic acid copolymer) were added. A size press liquid containing 5 parts and 94 parts of water was subjected to an ink-inline size press so that the dry adhesion amount was 5 g / m ^2, and dried to obtain a base paper 1. The pH of the base paper surface was 5.3.

<Preparation of anchor layer 1 coating solution>
100 parts of light calcium carbonate as a pigment and 10 parts of a styrene-butadiene copolymer latex as an adhesive in a solid content of 10 parts were mixed and dispersed in water to prepare a coating solution for anchor layer 1 having a solid concentration of 45%.

<Preparation of ink receiving layer 1 coating liquid>
100 parts of amorphous silica (average particle diameter: 3.5 μm), 30 parts of polyvinyl alcohol, and 15 parts of a cationic polymer (Smileds Resin 1001: manufactured by Sumitomo Chemical Co., Ltd.) were mixed and dispersed in water to give a solid content of 15 parts. % To obtain an ink receiving layer 1 coating solution.

After applying the coating liquid of the anchor layer 1 on the base paper 1 with a rod coater at a dry coating amount of 10 g / m ^{2, the} coating liquid of the ink receiving layer 1 is dried at a dry coating amount of 10 g / m ² with an air knife coater. Then, the resultant was subjected to a super calender treatment to prepare an ink jet recording medium of Example 1.

An ink jet recording medium was manufactured in the same manner as in Example 1 except that the base paper 1 of Example 1 was changed to the following base paper 2.
<Preparation of base paper 2>
The base paper 1 was prepared in the same manner as the base paper 1 except that the olefin surface sizing agent was changed to an olefin / styrene / acrylic acid copolymer. The pH of the base paper surface was 5.5.

An ink jet recording medium was produced in the same manner as in Example 1, except that the base paper 1 of Example 1 was changed to the following base paper 3.
<Preparation of base paper 3>
The base paper 1 was prepared in the same manner as the base paper 1 except that the olefin surface sizing agent was changed to 0.2 part. The pH of the base paper surface was 4.8.

An ink jet recording medium was manufactured in the same manner as in Example 1 except that the base paper 1 of Example 1 was changed to the following base paper 4.
<Preparation of base paper 4>
To 100 parts of wood pulp consisting of 90 parts of LBKP having a freeness of 450 ml CSF and 10 parts of NBKP having a freeness of 450 ml CSF, 20 parts of pigment having a ratio of light calcium carbonate / heavy calcium carbonate of 1: 1 and 0.10 part of commercially available alkyl ketene dimer , 0.03 parts of cationic acrylamide, 1.0 part of cationized starch, and 0.5 part of sulfuric acid band were adjusted to adjust the slurry pH to 8, and then formed using a fourdrinier paper machine at a basis weight of 100 g / m ² . After that, a size press liquid containing 6 parts of oxidized starch, 0.5 part of an olefin-based surface sizing agent (olefin / maleic acid copolymer), and 94 parts of water was ink-coated so that the dry adhesion amount was 5 g / m ^2. It was subjected to line size press and dried to obtain a base paper 4. The pH of the base paper surface was 9.0.

An ink jet recording medium was produced in the same manner as in Example 1 except that the dry coating amount of the anchor layer in Example 1 was changed to 5 g / m ² .

An ink jet recording medium was produced in the same manner as in Example 1, except that the base paper 1 of Example 1 was changed to the following base paper 5.
<Preparation of base paper 5>
Base paper 1 was prepared in the same manner as base paper 1 except that the basis weight was changed to 120 g / m ² . The pH of the base paper surface was 5.5.

(Comparative Example 1)
An ink jet recording medium was manufactured in the same manner as in Example 1 except that the base paper 1 of Example 1 was changed to the following base paper 6.
<Preparation of base paper 6>
The base paper 1 was prepared in the same manner as the base paper 1 except that the olefin-based surface sizing agent was removed from the size press liquid. The pH of the base paper surface was 4.5.

(Comparative Example 2)
An ink jet recording medium was manufactured in the same manner as in Example 1 except that the base paper 1 in Example 1 was changed to the following base paper 7.
<Preparation of base paper 7>
The base paper 1 was prepared in the same manner as the base paper 1 except that the olefin surface sizing agent was changed to a rosin sizing agent. The pH of the base paper surface was 5.7.

(Comparative Example 3)
An ink jet recording medium was manufactured in the same manner as in Example 1. However, without providing an anchor layer, only the ink receiving layer was coated so that the dry coating amount was 20 g / m ² .

(Comparative Example 4)
An ink jet recording medium was manufactured in the same manner as in Example 1. However, without the ink receiving layer, only the anchor layer was coated so that the dry coating amount was 20 g / m ² .

  With respect to the recording medium produced as described above, ink acceptability and cockling were evaluated. Table 1 shows the results.

<Evaluation of ink acceptability>
A photographic image was recorded on a recording medium using an inkjet printer (PM10000: manufactured by Seiko Epson Corporation), and the degree of ink overflow and the degree of bleeding of the image were visually determined and evaluated according to the following criteria.
A: There is no overflow of the ink and there is no blur of the image.
B: The image is slightly blurred.
C: Both ink overflow and image bleeding are recognized, but the degree is small.
D: The degree of occurrence of both ink overflow and image bleeding is large.

<Evaluation of cockling>
Cockling was evaluated based on the surface elongation measured using a laser displacement meter.
The surface elongation is a means for evaluating macroscopic irregularities caused by local elongation of the ink jet recording sheet caused by absorbing the ink, and specifically, arbitrarily determined for the ink jet recording sheet. Between the two points (linear distance A), the length (B) of the surface of the ink receiving layer along the unevenness of the surface of the recording sheet caused by the extension of the recording sheet was measured.
(BA) / A × 100 (%) is defined as the surface elongation. The greater the elongation, the greater the cockling (undulation).
The measurement was performed using a device in which a laser displacement meter using a triangulation method and an XY stage capable of collecting accurate positional information from the laser displacement meter were used.
The relationship between the evaluation grade and the elongation is shown below.
A: The elongation is 0.45% or less, and there is almost no cockling.
B: The elongation is greater than 0.45% and 0.6% or less, and the cockling is slight but not so noticeable.
C: The elongation is larger than 0.6%, and cockling is conspicuous.

  As is clear from the results in Table 1, Examples 1 to 6 of the present invention have good ink receptivity and cockling. In addition, it can be seen that, among Examples 1 to 6, the lower the surface pH of the base paper is, the better the cockling is (the cockling of Example 1 is more excellent than that of Example 4). On the other hand, Comparative Examples 1 to 4 cannot simultaneously satisfy the ink receptivity and cockling.

  Two types of base papers having different water immersion elongations were prepared. One base paper was the base paper 1 of Example 1, and its water immersion elongation was 1.6%. Another base paper (base paper 8) was prepared in the same manner except that the wood pulp of base paper 1 was changed to wood pulp having a freeness of 350 ml CSF. The water immersion extension of the base paper 8 was 2.5%. These two types of base papers were coated with the anchor layer and the ink receiving layer of Example 1 in the same manner as in Example 1 to produce two types of ink jet recording media.

  The two types of ink jet recording materials were evaluated for ink receptivity and cockling in the same manner as described above. As a result, the recording medium using the base paper 1 obtained the same results as in Example 1, while the recording medium using the base paper 8 had B for cockling and A for ink receptivity. . From this result, it is understood that the cockling suppressing effect is further improved by setting the water immersion elongation of the base paper to 2.0% or less.

Two types of anchor layers having different Cobb's water absorption are prepared, and each of the anchor layers is applied on the base paper 1 of Example 1 at a dry coating amount of 10 g / m ² , and the ink receiving layer of Example 1 is further coated. Coating was performed at a dry coating amount of 10 g / m ² to prepare two types of ink jet recording media. One anchor layer was the anchor layer 1 of Example 1, and the Cobb water absorption was 9 g / m ² . Another anchor layer (anchor layer 2) had the following composition, and had a Cobb water absorption of 25 g / m ² .
<Preparation of anchor layer 2 coating solution>
100 parts of amorphous silica (average secondary particle diameter 4 μm) as a pigment and 10 parts of a styrene-butadiene copolymer latex as an adhesive in a solid content of 10 parts are mixed and dispersed in water, and the anchor layer 2 having a solid concentration of 35% is applied. A liquid was prepared.

The two types of ink jet recording materials were evaluated for ink receptivity and cockling in the same manner as described above. As a result, the recording medium using the anchor layer 1 obtained the same results as in Example 1, while the recording medium using the anchor layer 2 had B for cockling and A for ink receptivity. . From this result, it can be seen that the cockling suppression effect is further improved by using the anchor layer having a Cobb water absorption of 5 to 15 g / m ² .

On the ink receiving layer of the ink jet recording medium prepared in Example 1 and Comparative Example 3, the following gloss-developing layer was further applied at a dry coating amount of 8 g / m ² to obtain Examples 9 and Comparative Example 5. Two types of ink jet recording media were produced.
<Glossy layer>
60 parts of alumina hydrate (tabular pseudo-boehmite-type alumina hydrate having an aspect ratio of 5 and an average secondary particle diameter of 100 nm), cationic colloidal silica (ST-AK manufactured by Nissan Chemical Industries, Ltd., average primary particles) 40 parts of polyvinyl alcohol (15 to 20 nm in diameter), 15 parts of polyvinyl alcohol, and 1 part of a cationic polymer (PolyFix 601: manufactured by Showa Polymer Co., Ltd.) are mixed and dispersed in water to form a glossy layer having a solid concentration of 14%. A liquid was obtained.

  The two types of ink jet recording materials were evaluated for ink receptivity and cockling in the same manner as described above. As a result, the recording medium of Example 9 was A for both cockling and ink receptivity, whereas the recording medium of Comparative Example 5 was C for cockling and A for ink receptivity.

Furthermore, the glossiness by visual observation was evaluated. Example 9 enjoyed the original effect of improving the glossiness of the glossy layer and had a high glossiness. However, Comparative Example 5 was unable to obtain the effect of the glossy layer sufficiently due to the influence of cockling. It was inferior.

Claims (8)

  An ink jet recording medium having at least an anchor layer and an ink receiving layer on a base paper mainly composed of wood pulp, wherein an olefin-based surface sizing agent is coated on the surface of the base paper on which the anchor layer and the ink receiving layer are provided. An ink jet recording medium characterized by containing.   2. The ink jet recording medium according to claim 1, wherein a water immersion elongation after 2 minutes of water immersion in a direction (CD direction) orthogonal to a papermaking direction (MD direction) of the base paper is 2.0% or less. Inkjet recording medium of claim 1 30 seconds Cobb water absorption in distilled water defined by JIS-P-8140 of the anchor layer is 5 to 15 g / m ^2.   The ink jet recording medium according to claim 1, wherein the anchor layer contains an inorganic pigment and a polymer latex.   2. The ink jet recording medium according to claim 1, wherein the ink receiving layer contains an inorganic pigment and a hydrophilic binder.   The olefin-based surface sizing agent is at least one selected from the group consisting of an olefin maleic acid copolymer, an olefin (meth) acrylic acid copolymer, an olefin styrene maleic acid copolymer, and an olefin styrene (meth) acrylic acid copolymer. The inkjet recording medium according to claim 1, which is a seed.   2. The ink jet recording medium according to claim 1, wherein the base paper has a surface pH defined by TAPPI T529 of 4 to 6. 2. The ink jet recording medium according to claim 1, further comprising a glossy layer on the ink receiving layer.