JP2020082448A - Recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording medium having excellent folding resistance and ink absorption. An ink receiving layer including a base material and a receiving layer (A) provided on the base material and arranged on the upper layer side of the receiving layer (A). It is a recording medium having and. The receiving layer (A) contains the first inorganic particles and the water-soluble resin, and the receiving layer (B) contains the second inorganic particles having an average particle diameter of 300 nm or less, the water-soluble resin, and the average particle diameter of 0. It contains a resin containing resin particles having an elongation of 3 μm or more and an elongation of 550% or more, and the content of the water-soluble resin in the receiving layer (B) is 0.10 times the mass ratio to the content of the second inorganic particles. It is 0.50 times or more, and the content of the resin particles in the receiving layer (B) is 0.10 times or more and 0.80 times or less in terms of the mass ratio to the content of the second inorganic particles, and is accepted. The thickness of the layer (B) is 10% or more and 50% or less of the thickness of the ink receiving layer. [Selection diagram] None

Description

The present invention relates to a recording medium.

In recent years, there is an increasing demand for photo books manufactured using a recording medium for inkjet recording. The photobook is produced, for example, by previously forming a crease on a recording medium having an image recorded on only one side by an ink jet recording method, and adhering the surfaces on which no image is recorded with the fold as a boundary. By such a method, it is possible to produce a photo book in which a large image laid across pages is arranged.

When creating a photo book by the above method, when the crease is made on the recording medium (recorded matter) on which the image is recorded, the ink receiving layer of the recording medium is cracked, and a part of the image is cracked or peeled off. Sometimes occurred. Further, even if the creases are not positively made, the recorded matter may be unintentionally bent during storage, and a part of the image may be cracked or peeled off. Therefore, even if a crease is formed, a demand for a recorded material excellent in so-called crease resistance, in which a defect such as cracking or peeling of an image hardly occurs, is increasing.

In order to improve the resistance to breakage of the recording medium, for example, the flexibility of the ink receiving layer having an ink receiving layer containing a resin having an average particle size of 0.3 μm or more and an elongation of 550% or more is improved. Another recording medium has been proposed (Patent Document 1). Further, a recording medium has been proposed in which an intermediate layer containing a resin having a glass transition temperature of 50° C. or lower is provided between an ink receiving layer and a substrate (Patent Document 2).

JP, 2016-165890, A JP 2008-183807 A

The folding resistance of the recording media proposed in Patent Documents 1 and 2 was good to some extent. However, when a crease is positively made like in the case of making a photo book, problems such as cracking and peeling of the image may occur. In addition, the ink absorbency may be lowered, and the quality of the image may be lowered, or the recording speed may be lowered.

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

The above object is achieved by the present invention described below. That is, according to the present invention, the base material, the receiving layer (A) provided on the base material and arranged on the base material side, and the receiving layer (a) arranged on the upper layer side of the receiving layer (A) ( An ink receiving layer containing B), wherein the receiving layer (A) contains first inorganic particles and a water-soluble resin, and the receiving layer (B) has an average particle diameter of 300 nm. The following second inorganic particles, the water-soluble resin, and a resin containing resin particles having an average particle size of 0.3 μm or more and an elongation of 550% or more, and the water-soluble resin in the receiving layer (B). Content (parts by mass) is 0.10 times or more and 0.50 times or less in terms of mass ratio (times) to the content (parts by mass) of the second inorganic particles, and in the receiving layer (B). The content (parts by mass) of the resin particles is 0.10 times or more and 0.80 times or less in mass ratio (times) to the content (parts by mass) of the second inorganic particles, and the receiving layer The mass ratio (times) of the content (parts by mass) of the resin to the content (parts by mass) of the second inorganic particles in (B) is the first inorganic content in the receiving layer (A). It is larger than the mass ratio (times) of the content (parts by mass) of the water-soluble resin to the content (parts by mass) of particles, and the thickness of the receiving layer (B) is 10 times the thickness of the ink receiving layer. There is provided a recording medium characterized by being 50% or more and 50% or less.

According to the present invention, it is possible to provide a recording medium excellent in folding resistance and ink absorption.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. By satisfying the following requirements (i) to (vii), the present inventors are less likely to cause defects such as cracking and peeling in a part of the recorded image even when repeatedly bent, and It has been found that the ink absorbency is improved.
(I) a base material, and an ink receiving layer provided on the base material and including the receiving layer (A) arranged on the base material side and the receiving layer (B) arranged on the upper layer side of the receiving layer (A) And a recording medium having.
(Ii) The receiving layer (A) contains the first inorganic particles and the water-soluble resin.
(Iii) The receiving layer (B) contains second inorganic particles having an average particle diameter of 300 nm or less, a water-soluble resin, and a resin containing resin particles having an average particle diameter of 0.3 μm or more and an elongation of 550% or more. ..
(Iv) In the receptor layer (B), the content (parts by mass) of the water-soluble resin is 0.10 times or more and 0.50 times the content (parts by mass) of the content (parts by mass) of the second inorganic particles. It is less than twice.
(V) In the receptor layer (B), the content (parts by mass) of the resin particles is 0.10 times or more and 0.80 times the mass ratio (times) with respect to the content (parts by mass) of the second inorganic particles. It is below.
(Vi) The mass ratio (times) of the content (parts by mass) of the resin to the content (parts by mass) of the second inorganic particles in the reception layer (B) is larger than that in the first layer in the reception layer (A). It is larger than the mass ratio (times) of the content (parts by mass) of the water-soluble resin to the content (parts by mass) of the inorganic particles.
(Vii) The thickness of the receiving layer (B) is 10% or more and 50% or less of the thickness of the ink receiving layer.

The present inventors presume as follows regarding the mechanism that the folding crack resistance and the like are improved by satisfying the above requirements. Since the object has a thickness, when folded, a compressive force is generated inside the fold and a stretching force is generated outside. When the recording medium is bent with the ink receiving layer inside, the ink receiving layer is compressed and plastically deformed. Then, when the folded recording medium is opened, a stretching force is relatively generated in the ink receiving layer released from the compression, and it is considered that the ink receiving layer is easily broken. As a result of examination, the present inventors have found that the vicinity of the surface layer of the ink receiving layer is particularly greatly compressed. That is, when the ink receiving layer has a laminated structure, it is considered important that the layer existing on the surface (recording surface) side can withstand the compressive force and the stretching force generated when the recording medium is opened and closed.

By satisfying the requirements (iii) and (iv) among the above requirements (i) to (vii), the flexibility of the entire ink receiving layer is improved, and the compression force and stretching that occur when the recording medium is opened and closed. Can bear the force. Further, among the requirements (i) to (vii) above, satisfying the requirement (vi) can greatly improve the ink absorbency.

Since the amount of resin in the receiving layer (A) arranged on the lower layer side is smaller than the amount of resin in the receiving layer (B) arranged on the upper layer side, the flexibility of the ink receiving layer as a whole is lowered. Seem.
However, as described above, the layer existing on the surface (recording surface) side is subjected to the compression/stretching force at the time of opening and closing, whereas the layer existing on the substrate side is less compressed/stretching force. It is believed that the layers are less likely to break. Further, by arranging the receiving layer (A), which has relatively low flexibility and is less likely to be deformed, on the base material side (lower layer side), the effect of alleviating the compression of the receiving layer (B) arranged on the upper layer side It is considered that the folding crack resistance and the ink absorbency are compatible with each other.

<Recording medium>
The recording medium of the present invention is a recording medium having a base material and an ink receiving layer provided on the base material, and is suitable for inkjet, for example. The ink receiving layer includes a receiving layer (A) arranged on the substrate side and a receiving layer (B) arranged on the upper layer side of the receiving layer (A). The receiving layer (A) contains the first inorganic particles and a water-soluble resin. The receiving layer (B) contains second inorganic particles having an average particle diameter of 300 nm or less, a water-soluble resin, and a resin containing resin particles having an average particle diameter of 0.3 μm or more and an elongation of 550% or more. Hereinafter, each component constituting the recording medium of the present invention will be described.

(Base material)
As the base material, when the base material is composed of one layer, a base material and the like can be mentioned. When the base material is laminated with a plurality of layers, examples include those having a base paper and a resin layer, that is, a resin-coated paper in which the base paper is coated with a resin, and a resin film. Of these, a base material having a base paper and a resin layer provided on the base paper is preferable. The resin layer may be provided on only one side of the base paper, but it is preferable to provide the resin layer on both sides of the base paper because curling of the recording medium can be suppressed.

The arithmetic average roughness Ra of the surface of the base material defined by JIS B 0601:2001 is preferably 1.0 μm or more and 5.0 μm or less. By setting the arithmetic average roughness Ra of the surface of the base material within the above range, the adhesive strength between the base material and the ink receiving layer is improved, and the folding resistance can be further improved. The thickness of the base material is preferably 25 μm or more and 500 μm or less, more preferably 50 μm or more and 300 μm or less. When the thickness of the base material is 25 μm or more, the rigidity of the recording medium is improved, so that a good feel and texture can be obtained when the recording medium is held by the hand. Further, when the thickness of the substrate is 500 μm or less, the paper feeding run in the inkjet recording device can be smoothly performed. The basis weight of the base material is preferably 25 g/m ² or more and 500 g/m ² or less.

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 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. Further, a pulp having a whiteness improved by a bleaching treatment is also preferable. 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.

When the base paper is a coated paper coated with a resin, the coverage of the resin layer (area of the surface of the base paper coated with the resin layer/total area of the surface of the base paper) is 70% or more. It is preferably 90% or more, and more preferably 90% or more. Further, it is particularly preferable that it is 100% (that is, 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 the 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, polyolefin resin, and styrene-butadiene copolymer. Of these, polyolefin resins are preferred. The polyolefin resin means a polymer obtained by using olefin as a monomer. More specifically, homopolymers and copolymers of ethylene, propylene, isobutylene and the like can be mentioned. Of these, polyethylene is preferable. As polyethylene, it is preferable to use low density polyethylene (LDPE) or 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, or hue. Above all, it is preferable to include a white pigment because the opacity of the resin layer 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 pigments in the two resin layers is preferably within the above range. From the viewpoint of the dispersion stability of the white pigment, the content of the white pigment in the resin layer is preferably 25% by mass or less with respect to the content of the resin.

(Ink receiving layer)
The ink receiving layer has a laminated structure in which two or more layers are laminated, including a receiving layer (A) arranged on the base material side and a receiving layer (B) arranged on the upper layer side of the receiving layer (A). Have. The thickness of the receiving layer (B) is 10% or more and 50% or less of the thickness of the ink receiving layer. If the thickness of the receptive layer (B) is less than 10% of the thickness of the ink receptive layer, the folding resistance is insufficient. On the other hand, if the thickness of the receiving layer (B) is more than 50% of the thickness of the ink receiving layer, the ink absorbency becomes insufficient.

The thickness of the ink receiving layer (the total thickness of the ink receiving layer including the receiving layer (A) and the receiving layer (B)) is preferably 15 μm or more and 35 μm or less, and more preferably 20 μm or more and 30 μm or less. .. If the thickness of the ink receiving layer is less than 15 μm, the ink absorbency becomes insufficient. On the other hand, if the thickness of the ink receiving layer is more than 35 μm, the folding crack resistance becomes insufficient. The "thickness" of a layer in the present specification is a thickness when dried, and is an average value of thicknesses measured by observing cross sections at four points using a scanning electron microscope.

[Inorganic particles]
The receiving layer (A) contains the first inorganic particles. The average particle size of the first inorganic particles is preferably 300 nm or less. Further, the receiving layer (B) contains second inorganic particles having an average particle diameter of 300 nm or less. The average 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 observed by an electron microscope. The first inorganic particles and the second inorganic particles may be the same or different. Hereinafter, the first inorganic particles and the second inorganic particles will be collectively referred to simply as “inorganic particles”. Further, the receiving layer (A) and the receiving layer (B) are collectively referred to simply as "ink receiving layer".

The ink receiving layer is formed, for example, by applying a coating liquid for the ink receiving layer on a substrate and drying the coating. The inorganic particles in the coating liquid are preferably dispersed with a dispersant. The average secondary particle diameter of the inorganic particles in a dispersed state is preferably 300 nm or less, and more preferably 10 nm or more and 250 nm or less. The average secondary particle diameter of the inorganic particles in a dispersed state can be measured by the dynamic light scattering method.

As the inorganic particles, alumina hydrate, vapor phase alumina, vapor phase silica, colloidal silica, titanium dioxide, zeolite, kaolin, talc, hydrotalcite, zinc oxide, zinc hydroxide, aluminum silicate, calcium silicate, silicic acid Examples thereof include magnesium, zirconium oxide, zirconium hydroxide and the like. Among them, alumina hydrate, vapor-phase method alumina, and vapor-phase method silica, which can form a porous structure having excellent ink absorbency, are preferable.

[1] Silica Silica is roughly classified into a wet method and a dry method (gas phase method) depending on its production method. As a wet method, there is known a method in which activated silica produced by acid decomposition of silicate is appropriately polymerized and coagulated and precipitated. On the other hand, as a dry method (gas phase method), a method by high temperature gas phase hydrolysis of silicon halide (flame hydrolysis method), or heat reduction vaporization of silica sand and coke by an arc in an electric furnace, A method (arc method) of oxidizing air with air is known. As the silica, vapor phase method silica obtained by a dry method (gas phase method) is preferable. Since vapor-phase method silica has a particularly large specific surface area, it has a particularly high ink absorptivity. Further, since vapor-phase method silica has a low refractive index, transparency can be imparted to the ink receiving layer, and good color developability can be obtained. Examples of commercially available vapor phase silica include Aerosil (manufactured by Nippon Aerosil); Reorosil QS type (manufactured by Tokuyama) and the like under the following trade names.

The specific surface area of the vapor phase silica by the BET method is preferably 50 m ² /g or more and 400 m ² /g or less, and more preferably 200 m ² /g or more and 350 m ² /g or less.

The vapor phase silica is preferably mixed with the coating liquid for the ink receiving layer in a state of being dispersed with a dispersant. The particle size of the vapor phase silica in the dispersed state is more preferably 50 nm or more and 300 nm or less. The particle size of the vapor phase method silica in a dispersed state can be measured by a dynamic light scattering method.

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 polyvalent metal salts include aluminum compounds such as polyaluminum chloride, polyaluminum acetate, and polyaluminum lactate.

[2] 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 does not have to be an integer. When alumina hydrate is heated, m may become zero.

The crystal structure of hydrated alumina includes amorphous, gibbsite type, and boehmite type, depending on the heat treatment temperature. The crystal structure of alumina hydrate can be analyzed by an X-ray diffraction method. The alumina hydrate is preferably boehmite-type alumina hydrate or amorphous alumina hydrate. Specific examples of the alumina hydrate include alumina hydrates 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 alumina hydrates include Disperal HP14 and HP18 (above, manufactured by Sasol) with the following trade names.

The number average particle diameter of the primary particles of the alumina hydrate is preferably 5 nm or more and 50 nm or less. The alumina hydrate is preferably a plate-shaped alumina hydrate having an aspect ratio of 2 or more. The aspect ratio of the plate-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 the particles when observing the alumina hydrate with an electron microscope (equivalent circle diameter).

The specific surface area of the alumina hydrate obtained by the BET method is preferably 100 m ² /g or more and 200 m ² /g or less, and more preferably 125 m ² /g or more and 175 m ² /g or less. The BET method is a method in which molecules or ions of known size are adsorbed on the sample surface, and the specific surface area of the sample is measured from the adsorbed amount. As a molecule to be adsorbed on the sample surface, for example, nitrogen gas is used.

[3] Vapor phase alumina As the vapor phase alumina, γ-alumina, α-alumina, δ-alumina, θ-alumina, χ-alumina and the like can be mentioned. Of these, γ-alumina is preferable from the viewpoint of image optical density and ink absorbability. Examples of commercially available vapor phase alumina include AEROXIDE; Alu C, Alu 130, Alu 65 (all manufactured by EVONIK) and the like under the following trade names.

The specific surface area of the vapor phase alumina obtained by the BET method is preferably 50 m ² /g or more and 150 m ² /g or less, and more preferably 80 m ² /g or more and 120 m ² /g or less.

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) since an 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.

[Water-soluble resin]
The receiving layer (A) and the receiving layer (B) each contain a water-soluble resin. The water-soluble resin is a resin capable of binding inorganic particles to form a film, which functions as a so-called binder. The content (parts by mass) of the water-soluble resin in the receptor layer (A) is a mass ratio (times) with respect to the content (parts by mass) of the first inorganic particles, and is 0.05 times or more and 0.30 times or less. It is preferable that it is 0.07 times or more and 0.20 times or less. By setting the mass ratio to be 0.05 times or more, folding crack resistance can be further improved. Further, by setting the mass ratio to 0.30 times or less, the ink absorbency can be further improved.

The content (parts by mass) of the water-soluble resin in the receiving layer (B) is a mass ratio (times) to the content (parts by mass) of the second inorganic particles, and is 0.10 times or more and 0.50 times or less. Yes, it is preferably 0.30 times or less. By setting the mass ratio to be 0.10 times or more, folding crack resistance can be improved. By setting the mass ratio to 0.50 times or less, the ink absorbency can be improved.

Examples of the water-soluble resin include 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, polyvinylpyrrolidone, polyacrylic acid, Examples thereof include polyacrylamide, polyvinyl acetamide, and derivatives thereof.

Among them, polyvinyl alcohol and polyvinyl alcohol derivatives are preferably used as the water-soluble resin from the viewpoints of preventing cracks during coating and drying and film water resistance. Examples of the polyvinyl alcohol derivative include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, and polyvinyl acetal. Examples of the cation-modified polyvinyl alcohol include polyvinyl alcohols having a primary to tertiary amino group or a quaternary ammonium group in the main chain or side chain thereof, as described in JP-A No. 61-10483. preferable.

Polyvinyl alcohol can be synthesized, for example, by saponifying polyvinyl acetate. The saponification degree of polyvinyl alcohol is preferably 80 mol% or more and 100 mol% or less, and more preferably 85 mol% or more and 98 mol% or less. As the saponification degree of polyvinyl alcohol, a value measured by a method according to JIS K 6726:1994 is used.

The average degree of polymerization of polyvinyl alcohol and the polyvinyl alcohol derivative is preferably 2,500 or more, more preferably 3,000 or more and 5,000 or less. As the average degree of polymerization of polyvinyl alcohol and a polyvinyl alcohol derivative, a viscosity average degree of polymerization obtained by a method according to JIS K 6726:1994 is used.

When preparing the coating liquid for the ink receiving layer, it is preferable to use polyvinyl alcohol and a polyvinyl alcohol derivative in the form of an aqueous solution. The content of solids in the aqueous solution of polyvinyl alcohol or polyvinyl alcohol derivative is preferably 5% by mass or more and 20% by mass or less.

[Resin particles]
The receiving layer (B) contains resin particles having an average particle diameter of 0.3 μm or more and an elongation of 550% or more. The flexibility of the receiving layer (B) can be increased by including resin particles having an average particle size of 0.3 μm or more and an elongation of 550% or more. As a result, even when the recording medium is folded in half and repeatedly opened and closed, it is possible to effectively prevent the ink receiving layer from cracking. The average particle size of the resin particles is preferably 0.5 μm or more from the viewpoint of further improving the resistance to folding cracks. The average particle diameter of the resin particles means the average particle diameter in the emulsion state dispersed in water, and can be measured by the dynamic light scattering method. The elongation of the resin particles means the elongation at break measured by the method according to JIS K6251:2010. The shape of the test piece when measuring the elongation can be dumbbell-shaped No. 3 shape, thickness 2.0 mm, and the tensile speed can be 500 mm/min.

The content (parts by mass) of the resin particles in the receiving layer (B) is a mass ratio (times) to the content (parts by mass) of the second inorganic particles, and is 0.10 times or more and 0.80 times or less. , Preferably 0.20 times or more and 0.50 times or less. By setting the mass ratio to be 0.10 times or more, folding crack resistance can be improved. Also, by setting the mass ratio to 0.80 times or less, it is possible to improve ink absorbency.

The receiving layer (A) may further contain resin particles. However, it is preferable that the receiving layer (A) has low flexibility and does not easily deform. Therefore, the content (parts by mass) of the resin particles in the receiving layer (A) is a mass ratio (times) to the content (parts by mass) of the first inorganic particles, and is 0.30 times or less. preferable. Further, it is particularly preferable that the receiving layer (A) does not contain resin particles.
When the receiving layer (A) contains resin particles, the following is preferable. That is, the mass ratio (times) of the resin content (parts by mass) to the content (parts by mass) of the second inorganic particles in the receiving layer (B) is the first inorganic content in the receiving layer (A). It is preferably larger than the mass ratio (times) of the resin content (parts by mass) to the particle content (parts by mass). Here, the content of the resin is the total content of the water-soluble resin and the resin particles.

The resin particles are preferably cationic or nonionic resin particles from the viewpoint of color developability of an image. From the viewpoint of miscibility, the resin particles are preferably mixed with the coating liquid for the ink receiving layer in the state of an emulsion dispersed in water.

The resin particles are preferably present nonuniformly in the ink receiving layer in the form of a resin mass in which a plurality of particles are bonded to each other, rather than being present in the ink receiving layer in a uniformly dispersed state. By allowing the resin particles to be non-uniformly distributed in the ink receiving layer, the mechanical properties of the resin particles can be more effectively expressed in the ink receiving layer. By selectively compressively deforming the resin lumps of the resin particles when the ink receiving layer is deformed by compression, the compression of the entire ink receiving layer can be relieved and the cracking of the ink receiving layer can be more effectively suppressed.

The presence state of the resin particles in the ink receiving layer can be confirmed by observing a sample including a cross section of the ink receiving layer prepared by using a microtome or the like using an apparatus such as SEM. When preparing a sample including the cross section of the ink receiving layer, it is preferable to use a freezing method such as a cryomicrotome method in order to avoid deformation of the resin as much as possible. The average particle diameter of the resin particles, which is measured by observing the cross section of the ink receiving layer, shows a value that is substantially the same as the average particle diameter measured by the dynamic light scattering method described above.

By using the water-soluble resin and the resin particles, the resin particles can be nonuniformly present in the ink receiving layer in the state of a resin block. Since the water-soluble resin and the resin particles have low compatibility, phase separation occurs during the coating and drying process of the coating liquid for the ink receiving layer, and resin lumps of resin particles are formed and distributed unevenly in the ink receiving layer. Will be done.

The size of the resin mass of the resin particles in the ink receiving layer is preferably 0.3 μm or less. If the resin mass is too large, the compression relaxation effect becomes insufficient. The size of the resin lump of the resin particles is substantially the same as the dispersed particle size of the resin particles in the coating liquid for the ink receiving layer. Therefore, the average dispersed particle diameter of the resin particles is preferably 0.3 μm or less. The elongation of the resin particles is preferably 550% or more in order to effectively exert the compression relaxation effect by the resin lumps of the resin particles in the ink receiving layer.

As the resin constituting the resin particles, a conjugated diene polymer such as polyester resin, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methylmethacrylate-butadiene copolymer, etc.; Acrylic polymers such as polymer and copolymer; vinyl acetate-maleic acid ester copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-acrylic copolymer, vinyl acetate-ethylene-acrylic copolymer, vinyl acetate -Vinyl polymers such as vinyl chloride copolymers; modified polymers obtained by incorporating functional groups such as carboxy groups and cationic groups into these various polymers; synthesis of thermosetting resins such as melamine resins and urea resins Resin-based water-based adhesives; synthetic resin-based adhesives such as maleic anhydride copolymer resin-based, polyacrylamide-based, polymethylmethacrylate-based, polyurethane resin-based, unsaturated polyester resin-based, polyvinyl butyral-based, alkyd resin-based adhesives, etc. Can be mentioned. Among them, urethane resin is preferable from the viewpoint of further improving the folding crack resistance.

[Crosslinking agent]
The ink receiving layer preferably contains a crosslinking agent. Examples of the cross-linking 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. As the borate, a water-soluble salt of boric acid is preferable. 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 depending on the production conditions and the like. The content (mass %) of the cross-linking agent in the ink receiving layer is preferably 0.01 times or more and 0.50 times or less in terms of mass ratio (times) with respect to the content (mass %) of the binder. It is more preferable that the ratio is 05 times or more and 0.40 times or less.

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 relative 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, fluorescent whitening agents, Examples thereof include an ultraviolet absorber, an antioxidant, an antiseptic agent, a fungicide, a water resistance agent, a dye fixing agent, a curing agent, and a weather resistant material.

(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 a large number of sheets are stacked. 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)
It is preferable to provide a topcoat layer containing colloidal silica as a main component on the surface of the ink receiving layer in order to improve scratch resistance. The average primary particle diameter of colloidal silica is preferably 20 μm or more and 200 μm or less. The dry coating amount of the top coat layer is preferably 0.01 g/m ² or more and 2 g/m ² or less.

<Method of manufacturing recording medium>
The recording medium can be manufactured, for example, by a manufacturing method including the following steps. That is, the method for producing a recording medium includes a step of preparing a coating liquid for forming an ink receiving layer (coating liquid preparing step), and a step of applying the coating liquid on at least one surface of the substrate, and then applying the coating liquid. And a step of drying the applied coating liquid (ink receiving layer forming step). The method of manufacturing the recording medium will be described below.

(Coating liquid preparation process)
In the coating liquid preparation step, a coating liquid containing inorganic particles is prepared. The inorganic particles are preferably used in the coating liquid in a so-called dispersion state in which they are dispersed in a liquid medium by a dispersant. When the inorganic particles are dispersed in the liquid medium, a homomixer, an agitator, a ball mill, an ultrasonic disperser or the like can be used.

In order to disperse the inorganic particles easily and uniformly, it is preferable to add peptizing acid. Peptic acids include formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, malonic acid, succinic acid, adipic acid, maleic acid, malic acid, tartaric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid. , Organic acids such as glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, pimelic acid, suberic acid and methanesulfonic acid; and inorganic acids such as hydrochloric acid, nitric acid and phosphoric acid. Of these, organic acids such as formic acid, acetic acid, glycolic acid and methanesulfonic acid; inorganic acids such as hydrochloric acid and nitric acid are preferable.

By mixing the inorganic particle dispersion liquid prepared as described above, the water-soluble resin (binder), the resin particles, and other components, a coating liquid for the ink receiving layer can be obtained. The solid content of the coating liquid can be 10% by mass or more and 30% by mass or less based on the total mass of the coating liquid. In addition, the coating liquid may include a pH adjuster, a thickener, a fluidity improver, an antifoaming agent, a foam suppressor, a surfactant, a release agent, a penetrant, a coloring pigment, a coloring dye, if necessary. A fluorescent whitening agent, an ultraviolet absorber, an antioxidant, an antiseptic, an antifungal agent, a water resistance agent, a dye fixing agent, a curing agent, a weather resistant material and the like can be contained.

(Ink receiving layer forming step)
In the ink receiving layer forming step, the prepared coating liquid is applied to at least one surface of the substrate, and then the applied coating liquid is dried. As a result, the ink receiving layer containing the inorganic particles is formed, and the intended recording medium can be obtained.

The coating amount (g/m ² ) of the inorganic particles applied to the substrate is preferably 8 g/m ² or more and 45 g/m ² or less. By setting the coating amount of the inorganic particles within the above range, the ink receiving layer having a preferable thickness can be formed.

A known coating method can be used to coat the surface of the substrate with the coating liquid. Known coating methods include a slot die method, a slide bead method, a curtain method, an extrusion method, an air knife method, a roll coating method, a rod bar coating method and the like.

The ink receiving layer can be formed by drying the coating liquid applied to the surface of the base material. For drying the coating liquid, for example, a hot air dryer such as a straight tunnel dryer, an arch dryer, an air loop dryer, a sine curve air float dryer can be used. Further, a dryer using infrared rays, a heating dryer, a microwave, or the like can also be used. These dryers can be appropriately selected and used.

The content (% by mass) of the inorganic particles in the ink receiving layer is preferably 50% by mass or more and 98% by mass or less, and 70% by mass or more and 96% by mass or less, based on the total mass of the ink receiving layer. Is more preferable.

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 unless it exceeds the gist. Regarding the component amounts, those described as “part” and “%” are based on mass unless otherwise specified.

<Substrate>
To 100 parts of hardwood bleached kraft pulp (LBKP) slurry, 20 parts of light calcium carbonate, 2 parts of cationized starch, and 0.3 part of neutral alkenylsuccinic acid neutral sizing agent are added and mixed sufficiently to produce paper The raw material was obtained. The papermaking raw material obtained using a Fourdrinier multi-cylinder paper machine was dried until the water content was 10%. A 7% solution of oxidized starch was applied to both sides of the papermaking raw material by a size press at a coating amount of 4 g/m ² , and then dried until the water content became 7%, and a basis weight of 110 g/m ² was applied. Paper was made. A resin composition consisting of 20 parts of high-density polyethylene and 70 parts of low-density polyethylene was melt-extruded and coated on both sides of the obtained base paper so that the coating amount was 30 g/m ² per side. Immediately after the melt extrusion coating, a cooling roll having irregularities on the surface was used to mold the polyethylene surface while cooling the base paper to obtain a base material having a basis weight of 170 g/m ² .

<Inorganic particles>
Inorganic particles of the types shown in Table 1 were prepared.

<Preparation of Inorganic Particle Dispersion>
(Inorganic particle A dispersion liquid (alumina hydrate sol))
1.5 parts of methanesulfonic acid, which is a peptic acid, was dissolved in 333.0 parts of ion-exchanged water to obtain a methanesulfonic acid aqueous solution. 100.0 parts of the inorganic particles A were added little by little while stirring the obtained aqueous methanesulfonic acid solution at 3,000 rpm using a disperser (trade name "Homomixer MARKII 2.5 type", manufactured by Primix). After the addition of the inorganic particles A was completed, the mixture was further stirred for 30 minutes to obtain an inorganic particle A dispersion liquid (alumina hydrate sol) having a solid content of 23.0%.

(Inorganic particle B dispersion liquid (gas phase method silica sol))
An aqueous polymer solution was obtained by dissolving 4.0 parts of a cationic polymer (trade name “Charol DC902P”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) in 333.0 parts of ion-exchanged water. The obtained polymer aqueous solution was stirred at 3,000 rpm using a disperser (trade name "Homomixer MARKII 2.5 type", manufactured by PRIMIX), and 100.0 parts of inorganic particles B were added little by little. After the addition of the inorganic particles B was completed, the particles were diluted with ion-exchanged water. Furthermore, a high-pressure homogenizer (trade name “Nanomizer”, manufactured by Yoshida Kikai Kogyo) was used for two treatments to obtain an inorganic particle B dispersion liquid (vapor phase silica sol) having a solid content of 20.0%. ..

<Water-soluble resin>
Water-soluble resins of the types shown in Table 2 were prepared.

<Preparation of liquid containing water-soluble resin>
(Liquid containing water-soluble resin A)
100 parts of water-soluble resin A was added to 1,150 parts of ion-exchanged water while stirring. After the addition was completed, the mixture was heated to 90° C. to dissolve the water-soluble resin A to obtain a liquid containing the water-soluble resin A having a solid content of 8.0%.

(Liquid containing water-soluble resin B)
100 parts of water-soluble resin B was added to 2,400 parts of ion-exchanged water while stirring. After completion of the addition, the water-soluble resin B was dissolved by heating at 90° C. to obtain a liquid containing the water-soluble resin B having a solid content of 4.0%.

(Liquid containing water-soluble resin C)
100 parts of water-soluble resin C was added to 1,010 parts of ion-exchanged water while stirring. After completion of the addition, the water-soluble resin C was dissolved by heating at 90° C. to obtain a liquid containing the water-soluble resin C having a solid content of 9.0%.

<Resin particles>
Resin particles of the types shown in Table 3 were prepared.

<Manufacture of recording medium>
(Examples 1 to 23, Comparative examples 1 to 15)
Table 4-1 shows the types of inorganic particles, the type and content (parts) of the water-soluble resin, and the type and content (parts) of the resin particles for the inorganic particle dispersion liquid, the liquid containing the water-soluble resin, and the resin particles. Mix as shown in ~4-4. Further, 5% orthoboric acid aqueous solution was added and mixed at a ratio of 0.75 parts orthoboric acid to 100 parts of the inorganic particles to prepare each coating solution. Each coating liquid prepared was applied onto one surface of the substrate and then dried to form a receiving layer (A) having a thickness (μm) shown in Tables 4-1 to 4-4.

Table 4-1 shows the types of inorganic particles, the type and content (parts) of the water-soluble resin, and the type and content (parts) of the resin particles for the inorganic particle dispersion liquid, the liquid containing the water-soluble resin, and the resin particles. Mix as shown in ~4-4. Further, 5% orthoboric acid aqueous solution was added and mixed at a ratio of 0.75 parts orthoboric acid to 100 parts of the inorganic particles to prepare each coating solution. After coating the prepared coating liquid on the surface of the above-mentioned receiving layer (A), it is dried to form a receiving layer (B) having a thickness (μm) shown in Tables 4-1 to 4-4. A recording medium was obtained.

<Evaluation>
In the evaluation criteria of each item shown below, "5", "4", "3", and "2" were set as preferable levels, and "1" was set as an unacceptable level.

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

(Ink absorption)
An inkjet recording device (trade name "MP990", manufactured by Canon Inc.) was used to record a solid green image on the recording surface (surface of the ink receiving layer) of the recording medium. The recording conditions were a temperature of 30° C., a humidity of 80%, “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 5.
5: Almost no unevenness is recognized in the image.
4: The image is slightly uneven.
3: Some unevenness is observed in the image.
2: The image is considerably uneven.
1: Overflow of ink is recognized in the image.

Claims (9)

A base material; and an ink receiving layer provided on the base material, the ink receiving layer including a receiving layer (A) arranged on the base material side and a receiving layer (B) arranged on the upper layer side of the receiving layer (A). A recording medium having,
The receiving layer (A) contains first inorganic particles and a water-soluble resin,
The receiving layer (B) contains second inorganic particles having an average particle diameter of 300 nm or less, the water-soluble resin, and a resin containing resin particles having an average particle diameter of 0.3 μm or more and an elongation of 550% or more,
In the receiving layer (B), the content (parts by mass) of the water-soluble resin is 0.10 times or more and 0.50 times or more as a mass ratio (times) with respect to the content (parts by mass) of the second inorganic particles. Less than twice
In the receiving layer (B), the content (parts by mass) of the resin particles is 0.10 times or more and 0.80 times as a mass ratio (times) with respect to the content (parts by mass) of the second inorganic particles. Is less than
The mass ratio (times) of the content (parts by mass) of the resin with respect to the content (parts by mass) of the second inorganic particles in the receiving layer (B) is larger than that in the receiving layer (A). 1 is greater than the mass ratio (times) of the content (parts by mass) of the water-soluble resin to the content (parts by mass) of the inorganic particles,
A recording medium, wherein the thickness of the receiving layer (B) is 10% or more and 50% or less of the thickness of the ink receiving layer. The recording medium according to claim 1, wherein the water-soluble resin in the receiving layer (B) is at least one of polyvinyl alcohol and a polyvinyl alcohol derivative. The recording medium according to claim 2, wherein the polyvinyl alcohol and the polyvinyl alcohol derivative have an average degree of polymerization of 2,500 or more. The recording medium according to claim 1, wherein the resin forming the resin particles is a urethane resin. The receiving layer (A) further contains the resin particles,
In the receiving layer (A), the content (parts by mass) of the water-soluble resin is a mass ratio (times) with respect to the content (parts by mass) of the first inorganic particles, and is 0.05 times or more and 0.30 or more. Less than twice
The content (parts by mass) of the resin particles in the receiving layer (A) is 0.30 times or less in mass ratio (times) with respect to the content (parts by mass) of the first inorganic particles. The recording medium according to any one of 1 to 4. The mass ratio (times) of the content (parts by mass) of the resin with respect to the content (parts by mass) of the second inorganic particles in the receiving layer (B) is larger than that in the receiving layer (A). The recording medium according to claim 5, which is larger than a mass ratio (times) of the content (parts by mass) of the resin to the content (parts by mass) of the inorganic particles of 1. The recording medium according to claim 1, wherein the thickness of the ink receiving layer is 15 μm or more and 35 μm or less.
The recording medium according to claim 1, wherein the resin particles have an average particle diameter of 0.5 μm or more. The recording medium according to claim 1, wherein the recording medium is for inkjet.