JP2020097230A - Recording medium for inkjet - Google Patents

Abstract

To provide a recording medium for inkjet excellent in folding cracking resistance and ink absorption property.SOLUTION: There is provided a recording medium for inkjet having a substrate, an undercoat layer arranged on the substrate, and an ink receiving layer arranged on the undercoat layer. The ink receiving layer contains an inorganic particle and a binder, the undercoat layer contains cellophane, thickness of the ink receiving layer is 20 μm or less, and H1/H2 is 0.50 to 1.00, wherein Martens hardness of the ink receiving layer is H1 (N/mm), and Martens hardness of the undercoat layer is H2 (N/mm).SELECTED DRAWING: None

Description

The present invention relates to an inkjet recording medium.

A recording medium is known in which an ink receiving layer having a porous structure mainly composed of inorganic particles such as silica and alumina is provided on a substrate. In recent years, there is a service that provides a photo book, a photo album, or the like obtained by printing a favorite photograph or a photograph in which characters and figures are mixed on such a recording medium and binding the photograph. Photobooks and photo albums are produced, for example, by making creases in advance on a recording medium having an image recorded on only one side by an ink jet recording method, and bonding the surfaces on which no image is recorded with the folds as boundaries. .. With such a method, a photo book or a photo album in which a large image that extends over pages is arranged can be manufactured.

When a photobook is produced by the above method, the ink receiving layer may be cracked or peeled off at the folds. Since the folds where the ink receiving layer is peeled off become white, the image quality is degraded. Further, since the ink receiving layer having a porous structure is formed mainly of inorganic particles, the ink receiving layer is brittle and is particularly liable to break at the folds. Therefore, there is a demand for a recording medium having excellent resistance to folding cracks.

In order to improve the folding resistance of the recording medium, for example, an inkjet recording medium has been proposed in which an intermediate layer containing a resin having a glass transition temperature of 50° C. or less is provided between a substrate and an ink receiving layer. (Patent Document 1). Further, as a recording medium capable of recording an image with good color developability and having improved ink absorbency, a recording medium provided with a coating layer containing a water-soluble polysaccharide between a substrate and an ink receiving layer has been proposed. (Patent Document 2). Further, there is proposed a recording medium in which a resin layer containing a biodegradable resin and a wax is formed on one surface of a base paper and which has improved glossiness and flatness (Patent Document 3).

JP 2008-183807 A JP-A-8-108617 JP, 2005-189541, A

The folding resistance of the recording media proposed in Patent Documents 1 to 3 was good to some extent. However, when a large load is applied to the folds during the bookbinding process, an excessive compressive force is applied to the ink receiving layer on the inner side of the folds, so that a part of the ink receiving layer peels or is missing, resulting in image defects. Occasionally, problems such as occurrences occurred. For this reason, it has been difficult to obtain an inkjet recording medium having improved folding crack resistance while ensuring ink absorbability.

Therefore, an object of the present invention is to provide an inkjet recording medium that is excellent in folding crack resistance and ink absorbency.

The above object is achieved by the present invention described below. That is, according to the present invention, there is provided an inkjet recording medium having a base material, an undercoat layer provided on the base material, and an ink receiving layer provided on the undercoat layer. The layer contains inorganic particles and a binder, the undercoat layer contains cellophane, the thickness of the ink receiving layer is 20 μm or less, and the Martens hardness of the ink receiving layer is H1 (N/mm. ² ) and the Martens hardness of the undercoat layer is H2 (N/mm ² ), H1/H2 is 0.50 or more and 1.00 or less, and an inkjet recording medium is provided. It

According to the present invention, it is possible to provide an inkjet recording medium that is excellent in folding crack resistance and ink absorbency.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. Hereinafter, the inkjet recording medium may be simply referred to as a “recording medium”. In a general inkjet recording medium, an ink receiving layer is provided on a base material. The ink receiving layer has a function of keeping ink droplets near the surface of the ink receiving layer to improve the color developability of an image, and a function of quickly absorbing a liquid medium in the ink to reduce bleeding. The main components of the ink receiving layer are usually an inorganic pigment and a binder. By using an inorganic pigment having a particle size of about 100 nm, the surface of the recording medium can have a glossy feeling.

As a result of the study, the present inventors have arranged an undercoat layer containing cellophane, preferably composed of cellophane, between the substrate and the ink receiving layer, so that the ink receiving layer has good crease resistance and ink resistance. It was found that the absorbability was improved. The present inventors have speculated as follows regarding the mechanism of improving the resistance to fold cracking and the ink absorption by such a configuration.

In order to prevent defects such as peeling or missing in the ink receiving layer, it is necessary to make the ink receiving layer thin, specifically, to make the thickness of the ink receiving layer 20 μm or less. However, when the ink receiving layer is made thin, the ink absorbency is lowered. Cellophane is a transparent film produced by using viscose prepared from cellulose as a raw material. Cellophane has a large number of nano-order voids, and it is considered that the absorbed water can be retained in these voids. Therefore, by using cellophane as a constituent material of the ink receiving layer, the ink can be absorbed and held to some extent. However, since the density of the voids is not necessarily high, a great amount of time is required to hold all the ink with cellophane alone.

Therefore, by arranging an undercoat layer containing cellophane between the substrate and the ink receiving layer, the ink immediately after being applied is absorbed by the ink receiving layer while all the ink including the ink after a certain time has passed It can also be absorbed by the coat layer. It is considered that this makes it possible to ensure sufficient ink absorbency while making the ink receiving layer thin.

Further, when the Martens hardness (N/mm ² ) of the ink receiving layer is H1 (N/mm ² ) and the Martens hardness of the undercoat layer is H2 (N/mm ² ), H1/H2 is 0. It is necessary to be 50 or more and 1.00 or less. Usually, when a film having a two-layer structure formed by stacking two films is bent, strain is generated at the boundary between the layers due to the different hardness of each layer. Then, when the generated strain is large, it is considered that a fold crack occurs in one of the layers. Here, by controlling the Martens hardness of the ink receiving layer and the undercoat layer so that H1/H2 is 0.50 or more and 1.00 or less, the occurrence of strain at the boundary between layers is suppressed. It is considered that the cracking resistance is improved and the crease resistance is improved. When H1/H2 is more than 1.00, the ink receiving layer, which is harder than the undercoat layer, receives the resistance to bending, so that the ink receiving layer is likely to be broken. On the other hand, when H1/H2 is less than 0.50, the strain generated at the boundary between the ink receiving layer and the undercoat layer becomes large, and the ink receiving layer is likely to be broken.

The Martens hardness of the ink receiving layer and the undercoat layer is measured according to ISO14577. The Martens hardness measuring method based on ISO14577 is a method of measuring the depth and hardness of an indentation formed by applying a load to an indenter in situ. As a measuring device for measuring the Martens hardness, a micro hardness tester (trade name “Picodenter (registered trademark) HM500”, manufactured by Fisher Instruments) is used. The Martens hardness of the undercoat layer is measured for the surface of the undercoat layer after being provided on the substrate and before the ink receiving layer is formed. Specifically, the value measured when the indenter was pushed in with a load of 3 mN for 60 seconds from the surface of the undercoat layer to a depth of 1 μm in the thickness direction, the Martens hardness H2(N /Mm ² ).

The Martens hardness of the ink receiving layer is measured by using the surface of the ink receiving layer formed on the undercoat layer as a target. Specifically, the value measured when the indenter was pushed in from the surface of the ink receiving layer to a depth of 1 μm in the thickness direction with a load of 3 mN for 60 seconds was calculated as Martens hardness H1 (N/N) of the ink receiving layer. mm ² ).

From the viewpoint of ink absorbency, the Cobb water absorption of the recording medium is preferably 20 g/m ² or more. In the present specification, the “cobb water absorption” is a physical property value measured with the surface of the recording medium on the side where the ink receiving layer is provided as a measurement target. The Cobb water absorption of the recording medium is measured in accordance with JIS P 8140:1998 under the condition that the contact time between the surface of the recording medium (the surface of the ink receiving layer) and water is 30 seconds.

<Recording medium>
The recording medium of the present invention has a base material, an undercoat layer provided on the base material, and an ink receiving layer provided on the undercoat layer. That is, at least two layers including the undercoat layer and the ink receiving layer are provided on the base material. The recording medium of the present invention is an inkjet recording medium applied to an inkjet recording method.

(Base material)
Examples of the base material include a base paper only, a plastic film only, and a cloth only. It is also possible to use a base material having a multilayer structure. As the base material having a multilayer structure, a so-called resin-coated base material in which a base paper and a resin layer are laminated can be used. The resin layer constituting the resin-coated substrate may be provided on only one side of the base paper, or may be provided on both sides of the base paper. The base material is preferably a resin-coated base material, a plastic film, or a cloth.

The thickness of the substrate is preferably 50 μm or more and 400 μm or less, more preferably 70 μm or more and 200 μm or less. The thickness of the base material is measured and calculated according to the method described below. The cross section of the recording medium cut out by a microtome is observed with a scanning electron microscope, and the thickness at arbitrary 100 points or more is measured. Next, the average value of the measured thicknesses of 100 points or more is calculated, and the calculated average value is used as the thickness of the base material.

[Resin coated substrate]
[1] Base paper The base paper is made from wood pulp as a main raw material, and if necessary, synthetic pulp such as polypropylene and synthetic fibers such as nylon and polyester are added to make the paper. As the wood pulp, hardwood bleached kraft pulp (LBKP), hardwood bleached sulfite pulp (LBSP), softwood bleached kraft pulp (NBKP), softwood bleached sulphite pulp (NBSP), hardwood dissolved pulp (LDP), softwood dissolved pulp (NDP) ), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), and the like. Among wood pulp, it is preferable to use LBKP, NBSP, LBSP, NDP, and LDP, which have many short fiber components. As the pulp, a chemical pulp containing few impurities (sulfate pulp or sulfite pulp) is preferable. Pulp that has been bleached to improve whiteness is also preferred. A sizing agent, a white pigment, a paper strength enhancer, a fluorescent whitening agent, a water retention agent, a dispersant, a softening agent and the like may be appropriately added to the base paper.

The thickness of the base paper is preferably 50 μm or more and 130 μm or less, and more preferably 90 μm or more and 120 μm or less. The paper density of the base paper specified by JIS P 8118:2014 is preferably 0.6 g/cm ³ or more and 1.2 g/cm ³ or less, and 0.7 g/cm ³ or more and 1.2 g/cm ³ or less. Is more preferable.

[2] Resin layer The resin layer constituting the resin-coated substrate is provided on the surface of the base paper so as to cover at least a part of the surface of the base paper. The coverage of the resin layer (surface area of the base paper coated with the resin layer/total surface area of the base paper) is preferably 70% or more, more preferably 90% or more, and further preferably 100%. .. That is, it is particularly preferable that the entire surface of the base paper is covered with the resin layer.

The thickness of the resin layer is preferably 20 μm or more and 60 μm or less, and more preferably 35 μm or more and 50 μm or less. When resin layers are provided on both sides of the base paper, the thickness of each resin layer is preferably within the above range.

A thermoplastic resin is preferable as the resin forming the resin layer. Examples of the thermoplastic resin include acrylic resin, acrylic silicone resin, olefin resin, and styrene-butadiene copolymer. Among them, olefin resins which are homopolymers or copolymers of ethylene, propylene, isobutylene and the like are preferable, and polyethylene is more preferable. Examples of polyethylene include low density polyethylene (LDPE) and high density polyethylene (HDPE).

The resin layer may contain a white pigment, a fluorescent whitening agent, ultramarine blue or the like in order to adjust opacity, whiteness and hue. Above all, it is preferable to contain a white pigment because the opacity can be improved. Examples of white pigments include rutile type titanium oxide and anatase type titanium oxide. The content of the white pigment in the resin layer is preferably 3 g/m ² or more and 30 g/m ² or less. When the resin layers are provided on both sides of the base paper, the total content of the white pigment in each resin layer is preferably within the above range. The content of the white pigment in the resin layer is preferably 0.25 times or less in terms of mass ratio with respect to the content of the resin. When the content ratio of the white pigment in the resin layer is more than 0.25 times the mass ratio of the resin content, the dispersion stability of the white pigment may be insufficient.

[Plastic film]
The plastic film is formed by processing plastic into a film. As the plastic, one containing a polymer component having a molecular weight of 10,000 or more in an amount of 50% by mass or more based on the total mass of the plastic can be used. Examples of the plastics include thermoplastics such as vinyl plastics, polyester plastics, cellulose ester plastics, polyamide plastics and heat resistant engineering plastics.

Examples of vinyl plastics include polyethylene, polyvinyl chloride, polyvinyl chloride, polyvinyl alcohol, polystyrene, polypropylene, and fluororesins. Examples of polyester plastics include polycarbonate and polyethylene terephthalate. Examples of cellulose ester plastics include cellulose diacetate, cellulose triacetate, and cellulose acetate butyrate. Examples of polyamide-based plastics include nylon 6, nylon 66, nylon 12 and the like. Examples of heat-resistant engineering plastics include polyimide, polysulfone, polyether sulfone, polyphenylene sulfide, polyether ether ketone, and polyether imide. From the viewpoint of durability and cost, it is preferable to use polyvinyl chloride, polypropylene, polycarbonate, or polyethylene terephthalate.

It is possible to use a plastic film which has been subjected to treatments such as chemical treatment, surface coating and internal addition to increase the opacity. Examples of the chemical treatment include a method in which the swelling layer formed by contacting the surface of the plastic film with an organic solvent such as acetone or methyl isobutyl ketone is treated with another organic solvent such as methanol and dried and solidified. Examples of the surface coating include a method of forming a layer containing a white pigment such as calcium carbonate or titanium oxide and a binder on the surface of the plastic film. Examples of the internal addition include a method in which a pigment such as calcium carbonate, titanium oxide, zinc oxide, white carbon, clay, talc, barium sulfate is contained in the plastic film as a filler. Further, it is possible to use a foamed plastic film in which polybutylene terephthalate fine particles, polycarbonate fine particles, polyester resin, polycarbonate resin or the like is added to form voids to increase opacity.

The thickness of the plastic film is preferably 50 μm or more and 300 μm or less, and more preferably 75 μm or more and 135 μm or less. The glass transition point of the plastic is preferably −20° C. or higher and 150° C. or lower, and more preferably −20° C. or higher and 80° C. or lower. The glass transition point of plastics can be measured, for example, by a differential scanning calorimetry method (DSC method).

The plastic density of the plastic film specified by JIS K 7112:1999 is preferably 0.6 g/cm ³ or more and 1.5 g/cm ³ or less, and 0.7 g/cm ³ or more and 1.4 g/cm ³ or less. Is more preferable. The water absorption of the plastic film specified in JIS K 7209:2000 is preferably 5% or less, more preferably 1% or less.

By subjecting the plastic film to a surface oxidation treatment, it is possible to improve the adhesion between the plastic film and a layer disposed adjacent to the plastic film. Examples of the surface oxidation treatment include corona discharge treatment, flame treatment, plasma treatment, glow discharge treatment, ozone treatment and the like, of which ozone treatment is preferable.

[cross]
The cloth is obtained by processing a large number of fibers into a thin and wide sheet. Examples of the fibers include natural fibers, materials having the properties of natural fibers, recycled fibers regenerated from plastics, and synthetic fibers made from a polymer such as petroleum. Examples of the natural fiber include cotton, silk, hemp, mohair, wool, cashmere and the like. Examples of the recycled fiber include acetate, cupra, rayon, recycled polyester and the like. Examples of synthetic fibers include nylon, polyester, acrylic, vinylon, polyethylene, polypropylene, polyamide and polyurethane.

(Ink receiving layer)
The ink receiving layer contains inorganic particles and a binder. The ink receiving layer can be formed, for example, by preparing a coating liquid containing the material contained in the ink receiving layer, and applying and drying the prepared coating liquid. The ink receiving layer may be a single layer or a multilayer of two or more layers. The ink receiving layer may be provided on only one side of the substrate, or may be provided on both sides.

The thickness of the ink receiving layer is 20 μm or less, preferably 15 μm or less. If the thickness of the ink receiving layer is more than 20 μm, the crease resistance is lowered. The undercoat layer containing cellophane provided under the ink receiving layer is a layer capable of absorbing ink. Therefore, even when the ink receiving layer is thin to some extent (20 μm or less), the decrease in ink absorbability is compensated by the undercoat layer. From the viewpoint of ink absorbency, the thickness of the ink receiving layer is preferably 5 μm or more. The thickness of the ink receiving layer is measured according to the following procedure. First, a cross section formed by cutting a recording medium with a microtome is observed with a scanning electron microscope (trade name “SU-70”, manufactured by Hitachi Ltd.). Then, the thickness of the observed ink receiving layer at any 10 points or more is measured, and the average value thereof is used as the thickness of the ink receiving layer.

[Inorganic particles]
The ink receiving layer contains inorganic particles. The average primary particle diameter of the inorganic particles is preferably 50 nm or less, more preferably 1 nm or more and 30 nm or less, and particularly preferably 3 nm or more and 10 nm or less. If the average primary particle size of the inorganic particles exceeds 50 nm, sufficient ink absorbency may not be obtained. The average primary particle diameter of the inorganic particles is the number average particle diameter (average value of 100 points or more) of the diameter of a circle having an area equal to the projected area of the primary particles of the inorganic particles when observed with an electron microscope.

The content (% by mass) of the inorganic particles in the ink receiving layer is preferably 50.0% by mass or more and 98.0% by mass or less, and 70.0% by mass or more and 96% by mass, based on the total mass of the ink receiving layer. More preferably, it is not more than 0.0% by mass.

As the inorganic particles, alumina hydrate, alumina, silica, colloidal silica, titanium dioxide, zeolite, kaolin, talc, hydrotalcite, zinc oxide, zinc hydroxide, aluminum silicate, calcium silicate, magnesium silicate, zirconium oxide, water. Examples thereof include zirconium oxide. Among them, silica, alumina, and alumina hydrate, which can form a porous structure having excellent ink absorption, are preferable, and silica having a large ink absorption capacity per coating amount is more preferable.

[1] Silica Silica is roughly classified into a wet method and a dry method (gas phase method) depending on its production method. Any silica can be preferably used. Among them, the use of wet process silica is preferable because the resistance to folding cracks can be further improved. The wet process silica can be used to form an ink receiving layer having a higher porosity. Therefore, it is presumed that the ink receiving layer is more likely to be deformed by the compression generated at the time of bending, and the resistance of the ink receiving layer to tearing or peeling is further increased.

As the wet method silica, precipitation method silica and gel method silica are preferable. Precipitated silica can be produced by reacting sodium silicate and sulfuric acid under alkaline conditions. After the silica particles that have grown in the manufacturing process are aggregated and settled, the silica particles are commercialized through steps such as filtration, washing with water, drying, crushing, and classification. The secondary particles of precipitated silica produced by such a method are gradual aggregated particles and are relatively easy to grind. Examples of commercially available precipitated silica include Nipseal (made by Tosoh Silica); Tokuseal and Fineseal (made by Tokuyama) under the following trade names.

The gel method silica can be produced by reacting sodium silicate and sulfuric acid under acidic conditions. Since the small silica particles dissolved during aging are re-precipitated so as to bond the primary particles of the large silica particles to each other, the distinct primary particles disappear and relatively hard agglomerated particles having an internal void structure are formed. Examples of commercially available gel method silica include Mizukasil (manufactured by Mizusawa Chemical Co., Ltd.) and Silojet (manufactured by Grace Japan) under the trade names below.

As a dry method (gas phase method), a method by high-temperature gas phase hydrolysis of silicon halide (flame hydrolysis method), or silica sand and coke are heated and reduced and vaporized by an arc in an electric furnace, and this is air-cooled. There is known a method (arc method) of oxidizing with. Examples of commercially available fumed silica include Aerosil (manufactured by Nippon Aerosil); Reorosil QS type (manufactured by Tokuyama) under the trade names below.

Examples of the dispersant for dispersing the vapor grown silica include a cationic resin and a polyvalent metal salt. Examples of the cationic resin include polyethyleneimine resin, polyamine resin, polyamide resin, polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, polyamide polyamine epichlorohydrin resin, polydiallylamine resin, dicyandiamide condensate and the like. Examples of the polyvalent metal salt include aluminum compounds such as polyaluminum chloride, polyaluminum acetate, and aluminum polylactic acid.

[2] Alumina Examples of alumina include γ-alumina, α-alumina, δ-alumina, θ-alumina, and χ-alumina. Among them, γ-alumina is preferable from the viewpoint of optical density of an image and ink absorbability. As the γ-alumina, vapor phase method alumina is preferably used. Examples of commercial products of vapor-phase process alumina include AEROXIDE; Alu C, Alu 130, Alu 65 (above, manufactured by EVONIK) and the like under the trade names.

[3] Alumina hydrate The alumina hydrate is preferably represented by the following general formula (X).
_{Al 2 O 3-n (OH} ) 2n · mH 2 O ··· (X)

In general formula (X), n is an integer of 0 to 3 and m is 0 to 10, preferably 0 to 5. However, m and n are not 0 at the same time. mH ₂ O often represents a detachable aqueous phase that does not participate in the formation of the crystal lattice. Therefore, m need not be an integer. When alumina hydrate is heated, m may become zero.

The crystal structure of alumina hydrate includes amorphous, gibbsite type, and boehmite type, depending on the temperature of heat treatment. The crystal structure of alumina hydrate can be analyzed by an X-ray diffraction method. As the alumina hydrate, boehmite type alumina hydrate or amorphous alumina hydrate is preferable. Specific examples of the alumina hydrate are described in JP-A-7-232473, JP-A-8-132731, JP-A-9-66664, and JP-A-9-76628. I can list things. Examples of commercially available products of alumina hydrate include Disperal HP14 and HP18 (above, manufactured by Sasol) under the trade names.

The alumina hydrate is preferably a plate-shaped alumina hydrate having an aspect ratio of 2 or more. The aspect ratio of the sheet-shaped alumina hydrate can be determined by the method described in Japanese Patent Publication No. 5-16015. That is, the aspect ratio is represented by the ratio of the "diameter" to the "thickness" of the particle. “Diameter” is the diameter of a circle having an area equal to the projected area of particles when observing an alumina hydrate with an electron microscope (equivalent circle diameter).

Alumina hydrate is a method for hydrolyzing aluminum alkoxide or hydrolyzing sodium aluminate as described in US Pat. Nos. 4,242,271 and 4,202,870. It can be produced by a known method such as It can also be produced by a known method such as a method of neutralizing by adding an aqueous solution of aluminum sulfate, aluminum chloride or the like to an aqueous solution of sodium aluminate or the like.

Alumina and alumina hydrate may be used in combination. When alumina and alumina hydrate are used together, alumina and alumina hydrate may be mixed and dispersed in a powder state to form a dispersion liquid (sol), or an alumina dispersion liquid and an alumina hydrate dispersion liquid may be mixed. May be.

Alumina hydrate and alumina are preferably mixed with the coating liquid for the ink receiving layer in the state of an aqueous dispersion liquid dispersed with a dispersant, and an acid is preferably used as the dispersant. As the acid, it is preferable to use a sulfonic acid represented by the following general formula (Y) because the effect of suppressing image bleeding can be obtained.
R-SO ₃ H (Y)

In general formula (Y), R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkenyl group having 1 to 4 carbon atoms. R may be substituted with an oxo group, a halogen atom, an alkoxy group, and an acyl group. The content of the acid is preferably 1.0% by mass or more and 2.0% by mass or less, and 1.3% by mass or more and 1.6% by mass with respect to the total content of the alumina hydrate and the alumina. The following is more preferable.

[Binder]
The ink receiving layer contains a binder. A hydrophilic binder is preferably used as the binder. As the binder, starch derivatives such as oxidized starch, etherified starch and phosphoric acid esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein, gelatin, soybean protein, polyvinyl alcohol, and their derivatives; polyvinyl pyrrolidone, etc. Can be mentioned.

Among them, it is preferable to use polyvinyl alcohol (PVA) or polyvinyl alcohol derivative (PVA derivative) as the binder. Examples of PVA derivatives include cation-modified PVA, anion-modified PVA, silanol-modified PVA, and polyvinyl acetal. As the cation-modified PVA, for example, those having an amino group or the like in the main chain or side chain of polyvinyl alcohol as described in JP-A No. 61-10483 are preferable.

When polyvinyl alcohol containing a large number of hydroxyl groups in its molecular structure is used as a binder, the adhesion between the undercoat layer containing cellophane and the ink receiving layer can be improved, and the folding resistance of the recording medium can be further improved. Preferred for.

Polyvinyl alcohol can be synthesized by saponifying polyvinyl acetate. The saponification degree of polyvinyl alcohol is preferably 80.0 mol% or more and 100.0 mol% or less, and more preferably 98.0 mol% or more and 100.0 mol% or less. The saponification degree of polyvinyl alcohol is the ratio (mol%) of hydroxy groups to the total of acetyloxy groups and hydroxy groups in polyvinyl alcohol. The saponification degree of polyvinyl alcohol in the present specification is a value measured by a method according to JIS K 6726:1994.

The polymerization degree of polyvinyl alcohol is preferably 2,000 or more, more preferably 2,000 or more and 5,000 or less. By using polyvinyl alcohol having a degree of polymerization of 2,000 or more as a binder, it is possible to improve the adhesion between the undercoat layer containing cellophane and the ink receiving layer, and further improve the crease resistance of the recording medium. .. The degree of polymerization of polyvinyl alcohol in the present specification is a viscosity average degree of polymerization measured by a method according to JIS K 6726:1994.

When preparing the coating liquid for the ink receiving layer, it is preferable to use polyvinyl alcohol or a polyvinyl alcohol derivative in the form of an aqueous solution. The solid content of polyvinyl alcohol and the polyvinyl alcohol derivative in the aqueous solution is preferably 3.0% by mass or more and 20.0% by mass or less based on the total mass of the aqueous solution.

[Crosslinking agent]
The ink receiving layer preferably contains a crosslinking agent. Examples of the crosslinking agent include aldehyde compounds, melamine compounds, isocyanate compounds, zirconium compounds, amide compounds, aluminum compounds, boric acid, and borate salts. When polyvinyl alcohol or a polyvinyl alcohol derivative is used as the binder, boric acid or borate is preferably used as the crosslinking agent.

Examples of boric acid include orthoboric acid (H ₃ BO ₃ ), metaboric acid, and diboric acid. The borate is preferably a water-soluble boric acid salt. Examples of the water-soluble salts of boric acid include alkali metal salts of boric acid such as sodium salts and potassium salts of boric acid; alkaline earth metal salts of boric acid such as magnesium salts and calcium salts of boric acid; ammonium salts of boric acid. And so on. Among them, it is preferable to use orthoboric acid because the stability of the coating liquid over time is improved and the occurrence of cracks is suppressed.

The amount of the cross-linking agent can be appropriately adjusted according to the production conditions and the like. The content of the crosslinking agent in the ink receiving layer is preferably 1.0% by mass or more and 50.0% by mass or less, and 5.0% by mass or more and 40.0% by mass or less with respect to the content of the binder. Is more preferable.

When the binder is polyvinyl alcohol and the crosslinking agent is at least one of boric acid and borate, the total content of boric acid and borate with respect to the content of polyvinyl alcohol in the ink receiving layer is It is preferably 5% by mass or more and 30% by mass or less.

[Other additives]
The ink receiving layer may contain other additives than the above-mentioned various components. Other additives include pH adjusters, thickeners, fluidity improvers, defoamers, foam suppressors, surfactants, release agents, penetrants, coloring pigments, coloring dyes, optical brighteners, Examples thereof include ultraviolet absorbers, antioxidants, antiseptics, antifungal agents, water resistant agents, dye fixing agents, curing agents, and weather resistant materials.

(Method of forming ink receiving layer)
The ink receiving layer can be formed on the undercoat layer by applying the coating liquid for the ink receiving layer on the undercoat layer and then drying the coating liquid. The coating liquid can be applied to the undercoat layer by a known coating method. Examples of the coating method include a slot die method, a slide bead method, a curtain method, an extrusion method, an air knife method, a roll coating method and a rod bar coating method. The ink receiving layer may have a multilayer structure including a first ink receiving layer, a second ink receiving layer,..., An nth ink receiving layer. The coating liquid for forming each layer may be applied sequentially or simultaneously in multiple layers. Among them, simultaneous multi-layer coating by the slide bead method is preferable because of high productivity.

The coating layer formed by applying the coating liquid is, for example, a straight tunnel dryer; hot air dryer such as arch dryer, air loop dryer, sine curve air float dryer; infrared ray, heating dryer, microwave, etc. Dryer, etc. Thereby, an ink receiving layer can be formed on the undercoat layer.

(Undercoat layer)
The undercoat layer is a layer containing cellophane, and preferably a layer containing cellophane as a main component. More specifically, the undercoat layer is a layer containing 50% by mass or more and 100% by mass or less of cellophane based on the total mass of the undercoat layer. The thickness of the undercoat layer is preferably 10 μm or more, more preferably 10 μm or more and 40 μm or less, and particularly preferably 20 μm or more and 30 μm or less. By setting the thickness of the undercoat layer to 10 μm or more, ink absorbency can be improved. Further, the undercoat layer having a thickness of 10 μm or more functions as a buffer layer for the pressure generated at the time of bending, so that the folding resistance of the recording medium can be further improved. The thickness of the undercoat layer is measured according to the following procedure. First, a cross section formed by cutting a recording medium with a microtome is observed with a scanning electron microscope (trade name “SU-70”, manufactured by Hitachi Ltd.). Then, the thickness of the observed undercoat layer is measured at arbitrary 10 points or more, and the average value thereof is taken as the thickness of the undercoat layer.

Cellophane is produced by desulfurizing, washing with water and drying viscose obtained by sulfiding and dissolving pulp as a raw material with carbon disulfide, and shaping it into a film or sheet. The degree of polymerization of cellulose is preferably 100 or more and 1,000 or less. When the degree of polymerization of cellulose is less than 100, the function as a buffer layer may be deteriorated, and the effect of improving the folding crack resistance may be slightly insufficient. On the other hand, cellulose having a degree of polymerization of more than 1,000 does not easily swell, so that the effect of improving the ink absorbency may be slightly insufficient.

The undercoat layer preferably further contains a polyhydric alcohol. By including the polyhydric alcohol, the flexibility of the undercoat layer is improved, and thus the folding resistance of the recording medium can be further improved. Examples of the polyhydric alcohol include glycerin, diethylene glycol, triethylene glycol and the like. Among them, glycerin is preferable as the polyhydric alcohol. The content of the polyhydric alcohol in the undercoat layer is preferably 2% by mass or more and 20% by mass or less based on the total mass of the undercoat layer. To add polyhydric alcohol to cellophane for forming the undercoat layer, for example, by impregnating the polyhydric alcohol immediately before the final drying step when forming cellophane, polyfunctional alcohol is formed in the formed cellophane. A polyhydric alcohol can be included. The Martens hardness H2 of the undercoat layer is preferably 50 N/mm ² or more and 100 N/mm ² or less.

Examples of the method of providing the undercoat layer on the substrate include a method of directly coating viscose on the substrate to form cellophane; a method of laminating film-shaped cellophane on the substrate. As the film-shaped cellophane, a commercially available cellophane film can be used. Examples of commercially available cellophane films include cellophane #300 (manufactured by Rengo); PL series (manufactured by Futamura Chemical Co., Ltd.) under the trade names below. When laminating the film-shaped cellophane on the substrate, an adhesive layer containing a binder may be formed between the substrate and cellophane. As the binder, a water-soluble polymer such as polyvinyl alcohol, an acrylic resin, a urethane resin, a polyester resin, or the like can be used.

(Backcoat layer)
It is preferable to provide a back coat layer on the surface of the base material opposite to the surface on which the ink receiving layer is provided in order to improve handling properties, transportability, and transport scratch resistance during continuous printing when stacking a large number of sheets. The back coat layer preferably contains a white pigment, a binder and the like. The thickness of the back coat layer is preferably such that the dry coating amount is 1 g/m ² or more and 25 g/m ² or less.

(Top coat layer)
In order to improve scratch resistance, it is preferable to provide a top coat layer containing colloidal silica as a main component on the surface of the ink receiving layer. The average primary particle diameter of colloidal silica is preferably 20 nm or more and 200 nm or less. If the average primary particle size of the colloidal silica is less than 20 nm, the effect of improving scratch resistance may be insufficient. On the other hand, when the average primary particle diameter of the colloidal silica is more than 200 nm, the glossiness and the optical density may be easily reduced due to the scattering.

The top coat layer can be formed, for example, by applying and drying a coating liquid containing colloidal silica. The dry coating amount of the coating liquid is preferably 0.01 g/m ² or more and 2 g/m ² or less. By setting the dry coating amount of the coating liquid to 0.01 g/m ² or more, appropriate scratch resistance can be obtained. Further, by setting the dry coating amount of the coating liquid to 2 g/m ² or less, it is possible to effectively prevent the decrease in ink absorbency.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Regarding the component amounts, those described as “part” and “%” are based on mass unless otherwise specified.

<Preparation of Inorganic Particle Dispersion>
(Alumina hydrate sol)
1.5 parts of methanesulfonic acid, which is a peptic acid, was dissolved in 333 parts of ion-exchanged water to obtain a methanesulfonic acid aqueous solution. While stirring the obtained aqueous solution of methanesulfonic acid at 3,000 rpm using a disperser (trade name "Homomixer MARKII 2.5 type" manufactured by PRIMIX), alumina hydrate (trade name "DISPERAL HP14" manufactured by Sasol) ) 100 parts were added in small portions. After the addition of the alumina hydrate was completed, the mixture was further stirred for 30 minutes to obtain an alumina hydrate sol having a solid content of 23.0%.

(Vapor-phase method silica sol)
An aqueous solution of a cationic resin was obtained by dissolving 4.0 parts of a cationic resin (trade name "Charol DC902P", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) in 333 parts of ion-exchanged water. While stirring the obtained aqueous solution of the cationic resin at 3,000 rpm using a disperser (trade name "Homomixer MARKII 2.5 type", manufactured by PRIMIX), 100 parts of vapor phase method silica was added little by little. As the vapor phase method silica, a trade name “AEROSIL300” (manufactured by EVONIK, primary particle diameter: 7 nm) was used. After the addition of the vapor phase silica was completed, it was diluted with ion-exchanged water. A high-pressure homogenizer (trade name “Nanomizer”, manufactured by Yoshida Kikai Co., Ltd.) was used for two treatments to obtain a vapor-phase process silica sol having a solid content of 20.0%.

<Preparation of coating liquid for ink receiving layer>
(Coating liquid A)
An aqueous polyvinyl alcohol solution was added to the alumina hydrate sol in an amount such that polyvinyl alcohol (trade name "PVA120", manufactured by Kuraray) was 10 parts with respect to 100 parts of the solid content of the alumina hydrate. Next, a coating solution A was obtained by adding and mixing an aqueous solution of 5% orthoboric acid in an amount such that 1 part of orthoboric acid was added to 100 parts of the solid content of the alumina hydrate.

(Coating liquid B)
An aqueous polyvinyl alcohol solution was added to the vapor phase silica sol in an amount such that polyvinyl alcohol (trade name "PVA120", manufactured by Kuraray Co., Ltd.) was 25 parts per 100 parts of the solid content of the vapor phase silica. Next, a coating solution B was obtained by adding and mixing an aqueous 5% orthoboric acid solution in an amount such that 3 parts of orthoboric acid was added to 100 parts of the solid content of the vapor phase silica.

(Coating liquid C)
An aqueous polyvinyl alcohol solution was added to the alumina hydrate sol in an amount such that polyvinyl alcohol (trade name "PVA120", manufactured by Kuraray) was 10 parts with respect to 100 parts of the solid content of the alumina hydrate. Next, a coating solution C was obtained by adding and mixing an aqueous solution of 5% orthoboric acid in an amount such that 3 parts of orthoboric acid was added to 100 parts of the solid content of the alumina hydrate.

Table 1 shows the composition of the prepared coating liquid.

<Manufacture of recording medium>
(Example 1: Recording medium 1)
As a base material, a film made of polyethylene terephthalate (PET) (trade name “Lumirror 50”, manufactured by Toray, thickness 50 μm) was prepared. Acrylic resin particles (trade name "Movinyl 7820", manufactured by Nihon Gosei) were applied on the surface of the base material so that the solid content was 2 g/m ^2, and then transparent cellophane (containing 5% glycerin) having a thickness of 20 μm was placed. did. A roller heated to 80° C. was used to pressurize to 5 N/m ² , and cellophane was laminated on the substrate to form an undercoat layer. The coating liquid A was applied to the formed undercoat layer so that the dry coating amount was 15 g/m ^2, and then dried with hot air at 90° C. to form an ink receiving layer, and a recording medium 1 was obtained. The thickness of the undercoat layer (cellophane) measured by observing the cross section of the obtained recording medium 1 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.60, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorbency of the recording medium 1 was 33 g/m ² .

(Example 2: Recording medium 2)
A recording medium 2 was obtained in the same manner as in Example 1 except that the coating liquid A was applied to the undercoat layer so that the dry coating amount was 20 g/m ² . The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 2 was 20 μm, and the thickness of the ink receiving layer was 20 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.55, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorption of the recording medium 2 was 38 g/m ² .

(Example 3: Recording medium 3)
A recording medium 3 was obtained in the same manner as in Example 1 except that the coating liquid A was applied to the undercoat layer so that the dry coating amount was 10 g/m ² . The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 3 was 20 μm, and the thickness of the ink receiving layer was 10 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.65, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorption of the recording medium 3 was 28 g/m ² .

(Example 4: Recording medium 4)
A recording medium 4 was obtained in the same manner as in Example 1 except that the coating liquid B was applied to the undercoat layer so that the dry coating amount was 15 g/m ² . The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 4 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.58, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorption of the recording medium 4 was 25 g/m ² .

(Example 5: recording medium 5)
A recording medium 5 was obtained in the same manner as in Example 1 except that milky cellophane (containing 5% glycerin) was used as the undercoat layer. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 5 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.51, and the Martens hardness H2 of the undercoat layer was 101 N/mm ² . Further, the Cobb's water absorbency of the recording medium 5 was 32 g/m ² .

(Example 6: Recording medium 6)
A recording medium 6 was obtained in the same manner as in Example 1 except that transparent cellophane (containing 0% glycerin) was used as the undercoat layer. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 6 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.50, and the Martens hardness H2 of the undercoat layer was 103 N/mm ² . Further, the Cobb's water absorption degree of the recording medium 6 was 34 g/m ² .

(Example 7: recording medium 7)
The same procedure as described above except that transparent cellophane with a thickness of 10 μm (containing 5% glycerin) was used as the undercoat layer, and that the coating liquid A was applied at a dry coating amount of 10 g/m ^2. A recording medium 7 was obtained in the same manner as in Example 1. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 7 was 10 μm, and the thickness of the ink receiving layer was 10 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.92, and the Martens hardness H2 of the undercoat layer was 61 N/mm ² . Further, the Cobb's water absorption of the recording medium 7 was 19 g/m ² .

(Comparative Example 1: Recording medium 8)
A recording medium 8 was obtained in the same manner as in Example 1 above, except that the coating liquid A was applied so that the dry coating amount was 25 g/m ² . The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 8 was 20 μm, and the thickness of the ink receiving layer was 25 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.50, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorption of the recording medium 8 was 43 g/m ² .

(Comparative Example 2: Recording medium 9)
The same procedure as described above except that a transparent cellophane with a thickness of 30 μm (containing 5% glycerin) was used as the undercoat layer, and that the coating liquid A was applied at a dry coating amount of 15 g/m ^2. A recording medium 9 was obtained in the same manner as in Example 1. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 9 was 30 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.45, and the Martens hardness H2 of the undercoat layer was 114 N/mm ² . Further, the Cobb's water absorption of the recording medium 9 was 61 g/m ² .

(Comparative Example 3: Recording medium 10)
A recording medium 10 was obtained in the same manner as in Example 1 except that the coating liquid C was applied so that the dry coating amount was 15 g/m ² . The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 10 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 1.20, and the Martens hardness H2 of the undercoat layer was 86 N/mm ² . Further, the Cobb's water absorption of the recording medium 10 was 30 g/m ² .

(Comparative Example 4: Recording medium 11)
A cationic urethane resin (trade name "Superflex 650-5", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was applied to the surface of the substrate so as to have a dry coating amount of 20 g/m ² and dried to form an undercoat layer. .. A recording medium 11 was obtained in the same manner as in Example 1 except for the above. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 11 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.50, and the Martens hardness H2 of the undercoat layer was 103 N/mm ² . The Cobb's water absorption of the recording medium 11 was 15 g/m ² .

(Comparative Example 5: Recording medium 12)
Carboxy-modified SBR (styrene-butadiene rubber) particles (trade name "JSR-0695", manufactured by JSR, polymer adhesive) are applied to the surface of the base material so as to have a dry coating amount of 20 g/m ² and dried. An undercoat layer was formed. A recording medium 12 was obtained in the same manner as in Example 1 except for the above. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 12 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.37, and the Martens hardness H2 of the undercoat layer was 141 N/mm ² . Further, the Cobb's water absorption of the recording medium 12 was 15 g/m ² .

(Comparative Example 6: Recording medium 13)
The biodegradable resin particles and the modified wax particles were mixed at a ratio of 5:2 (mass ratio of solid content), and the resulting dispersion was applied to the surface of the base material so that the dry coating amount was 20 g/m ^2. And dried to form an undercoat layer. As the biodegradable resin particles, trade name "Randy PL-1000" (manufactured by Miyoshi Yushi) was used. As the modified wax particles, a trade name "WR984" (manufactured by Seiko PMC) was used. A recording medium 13 was obtained in the same manner as in Example 1 except for the above. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 13 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.16, and the Martens hardness H2 of the undercoat layer was 321 N/mm ² . In addition, the Cobb's water absorption of the recording medium 13 was 15 g/m ² .

(Comparative Example 7: recording medium 14)
Polyvinyl alcohol (trade name "PVA117", manufactured by Kuraray) was applied to the surface of the substrate so as to have a dry coating amount of 20 g/m ² and dried to form an undercoat layer. A recording medium 14 was obtained in the same manner as in Example 1 except for the above. The thickness of the undercoat layer measured by observing the cross section of the obtained recording medium 14 was 20 μm, and the thickness of the ink receiving layer was 15 μm. The ratio (H1/H2) of the Martens hardness H1 of the ink receiving layer and the Martens hardness H2 of the undercoat layer was 0.48, and the Martens hardness H2 of the undercoat layer was 108 N/mm ² . The Cobb's water absorption of the recording medium 14 was 55 g/m ² .

(Comparative Example 8: recording medium 15)
A recording medium 15 was obtained in the same manner as in Example 1 except that the ink receiving layer was directly formed on the base material without forming the undercoat layer. The thickness of the ink receiving layer measured by observing the cross section of the obtained recording medium 15 was 15 μm. Further, the Cobb's water absorption of the recording medium 15 was 15 g/m ² .

Table 2 shows the configuration of the manufactured recording medium.

<Evaluation>
In the evaluation criteria of each item shown below, "A" and "B" were set as preferable levels, and "C" was set as an unacceptable level.

(Crack resistance)
Using an inkjet recording device (trade name "MP990", manufactured by Canon Inc.), a black solid image (100% duty) was recorded on the entire recording surface (surface of the ink receiving layer) of the recording medium cut into A4 size. After the recording medium was folded in half so that the recorded image was on the inside, a load of 500 kg was applied using a press machine and held for 5 minutes. The folded recording medium was opened and the folds were visually observed, and the crease resistance was evaluated according to the following evaluation criteria. The results are shown in Table 3.
A: White streaks cannot be seen.
B: Some white streaks are visible.
C: White streaks are clearly visible.

(Ink absorption)
An inkjet recording device (trade name "MP990", manufactured by Canon Inc.) was used to record a solid green image (150% duty) on the recording surface (surface of the ink receiving layer) of the recording medium. The recording conditions were "photo paper gloss gold" and "no color correction mode". The recorded image was visually observed and the ink absorbency was evaluated according to the following evaluation criteria. The results are shown in Table 3.
A: Almost no ink overflow was seen.
B: Ink overflow was seen.
C: Ink overflow was noticeable.

Claims (9)

A recording medium for inkjet having a substrate, an undercoat layer provided on the substrate, and an ink receiving layer provided on the undercoat layer,
The ink receiving layer contains inorganic particles and a binder,
The undercoat layer contains cellophane,
The thickness of the ink receiving layer is 20 μm or less,
When the Martens hardness of the ink receiving layer is H1 (N/mm ² ) and the Martens hardness of the undercoat layer is H2 (N/mm ² ), H1/H2 is 0.50 or more and 1.00 or less. A recording medium for inkjet, characterized in that The inkjet recording medium according to claim 1, wherein the Martens hardness H2 of the undercoat layer is 50 N/mm ² or more and 100 N/mm ² or less. The inkjet recording medium according to claim 1, wherein the undercoat layer further contains a polyhydric alcohol. The inkjet recording medium according to claim 3, wherein the polyhydric alcohol is glycerin. The inkjet recording medium according to claim 1, wherein the undercoat layer has a thickness of 10 μm or more. The inkjet recording medium according to any one of claims 1 to 5, having a Cobb water absorption of 20 g/m ² or more. The inkjet recording medium according to any one of claims 1 to 6, wherein the binder is polyvinyl alcohol. The inkjet recording medium according to claim 7, wherein the saponification degree of the polyvinyl alcohol is 98.0 mol% or more. The inkjet recording medium according to claim 7, wherein the degree of polymerization of the polyvinyl alcohol is 2,000 or more.