Inkjet recording paper

Abstract

The present invention provides an inkjet recording paper that does not use resin-coated paper as a support, has print image quality equivalent to or close to that of inkjet recording paper with an ink-receiving layer on resin-coated paper, suppresses curling, and exhibits excellent pulp fiber separation from the inkjet recording paper for reuse. [Solution] The base paper has at least one sealing layer on the surface of the base paper, at least one ink receiving layer, and at least one moisture absorption adjusting layer on the back surface of the base paper. The Cobb water absorption of the aforementioned moisture-absorbing adjustment layer, measured in accordance with ISO 535:2023, after 30 seconds of contact with water at 23°C, is 0.1 g / m². 2 More than 1.0g / m 2 The following is inkjet recording paper.

Description

[Technical Field]

[0001] This invention relates to paper used in inkjet recording systems. [Background technology]

[0002] Inkjet recording paper has long been used as printing paper for images taken with digital cameras. Among these, inkjet recording photographic paper is popular among photography enthusiasts as an alternative to conventional photographic printing paper. Similar to conventional photographic printing paper, the aforementioned inkjet recording photographic paper uses resin-coated paper as its support material for its texture, smoothness, and gloss. Generally speaking, resin-coated paper refers to paper in which both sides of the base paper are coated with a polyolefin-based resin layer. Inkjet photographic paper with an ink-receiving layer on top of resin-coated paper offers excellent resistance to cockling (warping) after printing. However, given the current environmental concerns, resource reuse is desirable. Resin-coated paper is a composite material with a coating layer of polyolefin resin or similar material on both sides of the base paper, making it less recyclable than ordinary recycled paper. In other words, it is difficult to separate resin-coated paper for reuse of its pulp fibers. Similarly, it is difficult to separate inkjet photographic paper made from resin-coated paper for reuse of its pulp fibers. Therefore, considering the environmental impact, there is a need for inkjet photographic paper that does not use resin-coated paper as a support.

[0003] There is a known inkjet recording material that has cockling suppression ability, smoothness, gloss, and texture equivalent to that of an inkjet recording material using resin-coated paper as a support, is particularly suitable for glossy photographic printing, and is recyclable (see, for example, Patent Document 1). In the inkjet recording material described in Patent Document 1, an ink receiving layer is provided on a support, and an undercoat consisting of multiple layers is provided between the support and the ink receiving layer, wherein any undercoat layer (A) constituting the undercoat, excluding the layer furthest from the support, contains hollow particles with a higher void ratio and a binder, and an undercoat layer (B) adjacent to the undercoat layer (A) on the side opposite to the support contains hollow particles with a lower void ratio and a smaller average particle diameter and a binder, and the surface of the undercoat layer (B) is smoothed by calendering, the mass ratio of the binder to the amount of hollow particles with a higher void ratio in the undercoat layer (A) is greater than the mass ratio of the binder to the amount of hollow particles in the undercoat layer (B), and the hollow particles in the undercoat layer (A) are characterized in that the calendering process makes the undercoat layer (A) easier to deform so as to fill in the irregularities of the support and flatten it. Furthermore, there is a known inkjet recording medium that has image quality comparable to silver halide photographic paper, excellent suitability for pigment inks, and good prevention of curling in the environment (see, for example, Patent Document 2). The inkjet recording medium described in Patent Document 2 has at least one ink-receiving layer on one side of a permeable support, the outermost layer of which is given gloss by a casting process, and a back coating layer on the side of the support opposite to the ink-receiving layer. The back coating layer composition mainly consists of pigment and binder. Furthermore, Patent Document 2 states that if the amount of pigment added to the back coating layer composition is 70 to 95% by mass relative to the total solid content of the back coating layer composition, environmental curling is good prevented. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-233851 [Patent Document 2] Japanese Patent Publication No. 2010-184364 [Overview of the Initiative] [Problems to be Solved by the Invention]

[0005] Unlike inkjet recording paper provided with an ink receiving layer on resin-coated paper, inkjet recording paper provided with an ink receiving layer on base paper which is non-resin-coated paper is liable to curl due to the difference in moisture content between the front and back of the base paper. Generally, in inkjet recording paper having an ink receiving layer on the surface of the base paper, in order to prevent the occurrence of curl of the inkjet recording paper, as described in Patent Document 2, a coating layer is often provided on the back surface of the base paper. However, when there is a coating layer on the back surface of the base paper, it becomes difficult to separate pulp fibers from the inkjet recording paper for reuse.

[0006] An object of the present invention is to provide an inkjet recording paper that does not employ resin-coated paper as a support, has printing image quality equivalent to or nearly equivalent to that of inkjet recording paper provided with an ink receiving layer on resin-coated paper, suppresses the occurrence of curl, and is excellent in the separation of pulp fibers from the inkjet recording paper for reuse. [Means for Solving the Problems]

[0007] As a result of intensive studies, the inventors of the present invention have invented the inkjet recording paper according to the present invention. The above problems of the present invention are achieved by the following forms. [1] An inkjet recording paper having a base paper, at least one layer of a blocking layer on the surface of the base paper, at least one layer of an ink receiving layer, and at least one layer of a moisture absorption adjustment layer on the back surface of the base paper, and having a Cobb water absorption of 0.1 g / m 2 or more and 1.0 g / m 2 or less, measured according to ISO 535:2023 for contact time of 30 seconds with water at a water temperature of 23°C with respect to the moisture absorption adjustment layer.

[0008] Moreover, the present invention includes the following forms. [2] The water absorption of the edge surface of the inkjet recording paper, as determined by the following method, is 0.13 mg / mm². 2 More than 0.45mg / mm 2 The inkjet recording paper described in [1] above is as follows: (method) A sample of inkjet recording paper was cut to 80mm on the MD side and 140mm on the CD side. Both sides of the sample were laminated with a 100μm thick laminate film, and then cut to 50mm on the MD side and 125mm on the CD side so that the edge of the inkjet recording paper was exposed, and this was used as the measurement sample (n=5). The measurement sample was immersed in water at a temperature of 23℃±1℃ for 10 minutes, and the water absorption of the edge surface (mg / mm) was measured. 2 ) is calculated using the following formula.

number

[0009] Furthermore, the present invention includes the following embodiments. [3] The inkjet recording paper according to [1] or [2] above, wherein the moisture absorption adjustment layer contains a flat inorganic pigment and a water-dispersible resin, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment.

[0010] Furthermore, the present invention includes the following embodiments. [4] The inkjet recording paper according to [3] above, wherein the sealing layer located furthest from the base paper contains a flat inorganic pigment and a water-dispersible resin, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment. [Effects of the Invention]

[0011] The present invention provides an inkjet recording paper that does not use resin-coated paper as a support, and has print image quality equivalent to or close to that of inkjet recording paper with an ink-receiving layer on resin-coated paper, while suppressing curling and exhibiting excellent separation of pulp fibers from the inkjet recording paper for reuse. [Modes for carrying out the invention]

[0012] In this specification, the terms "front" and "back" of the base paper are for convenience to indicate the location of the base paper surface, and do not refer to a distinction between the "front" and "back" based on specific chemical or physical differences on the base paper surface. Furthermore, in this specification, "at least one layer" means "one or two or more layers."

[0013] The present invention will be described in detail below. The inkjet recording paper of the present invention comprises a base paper, at least one sealing layer on the surface of the base paper, at least one ink receiving layer, and at least one moisture absorption adjusting layer on the back surface of the base paper.

[0014] The above base paper consists of chemical pulps such as LBKP (Leaf Bleached Kraft Pulp) and NBKP (Needle Bleached Kraft Pulp), mechanical pulps such as GP (Groundwood Pulp), PGW (Pressure Groundwood Pulp), RMP (Refiner Mechanical Pulp), TMP (ThermoMechanical Pulp), CTMP (ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp), and CGP (ChemiGroundwood Pulp), and DIP (DeInked This paper basically consists of paper produced by papermaking using a pulp mixture that is dispersed with one or more types of pulp selected from the group consisting of recycled paper pulp such as Pulp and pulp obtained by disintegrating spoilage generated at paper mills, and, as necessary, one or more conventionally known fillers selected from heavy calcium carbonate, light calcium carbonate, talc, clay, silica, and kaolin, binders, sizing agents, fixing agents, yield improvers, cationizing agents, paper strength agents, pigment dispersants, thickeners, flow improvers, defoaming agents, antifoaming agents, release agents, foaming agents, penetrating agents, coloring dyes, coloring pigments, fluorescent whitening agents, ultraviolet absorbers, antioxidants, preservatives, anti-bifacement agents, printability improvers, and water-resistant agents. Furthermore, the paper produced is subjected to a size press treatment with a size press liquid containing a surface sizing agent. The base paper also includes paper that has undergone calendering after papermaking, and plain paper that has undergone calendering after size pressing.

[0015] The above papermaking process can be achieved using papermaking machines that are conventionally known in the papermaking field. Examples of such papermaking machines include wire screen machines, twin-wire paper machines, combination paper machines, cylinder screen machines, and Yankee paper machines. Papermaking machines generally consist of a wire section that forms wet paper from pulp slurry, a press section that performs dewatering by mechanical watering using press rolls, and a dryer section that performs dewatering by heating and evaporation.

[0016] The calendering process described above is a process that equalizes the smoothness and thickness of paper by passing it between rolls. The equipment used for calendering is conventionally known in the papermaking field, and examples include machine calenders, soft nip calenders, supercalenders, multi-stage calenders, and multi-nip calenders.

[0017] In some embodiments, the base paper includes a surface sizing agent. The base paper can be made to contain a surface sizing agent by undergoing a sizing press treatment with a sizing press liquid containing a surface sizing agent. The surface sizing agents are those conventionally known in the papermaking field. Examples of surface sizing agents include starches such as oxidized starch, alkyl ketene dimer-based sizing agents, cellulose-based sizing agents, polyvinyl alcohol-based sizing agents, styrene-acrylic-based sizing agents, olefin-based sizing agents, styrene-maleic acid-based sizing agents, and acrylamide-based sizing agents. Inkjet recording paper, by containing a surface sizing agent in the base paper, acts on the moisture-regulating layer described below, thereby somewhat adjusting the Cobb water absorption rate relative to the moisture-regulating layer. For example, in inkjet recording materials, when the sizing effect increases due to the surface sizing of the base paper, the hydrophilicity of the surface decreases, and as a result, the Cobb water absorption rate relative to the moisture-regulating layer tends to decrease.

[0018] Size pressing can be achieved using size pressing devices conventionally known in the papermaking field. Examples of size pressing devices include inclined size presses, horizontal size presses, and, as film transfer methods, rod metering size presses, roll metering size presses, and blade metering size presses. The rod metering size press may further include shim sizers, opti sizers, speed sizers, and film presses, while the roll metering size press may further include gate roll coaters, etc. Other examples include bill blade coaters, twin blade coaters, velvapa coaters, tab size presses, and calender size presses.

[0019] The inkjet recording paper of the present invention has at least one layer of moisture absorption adjustment layer on the back surface of the base paper, and the Cobb water absorption at a contact time of 30 seconds with water at a water temperature of 23°C measured in accordance with ISO 535:2023 "Paper and board--Determination of water absorptiveness--Cobb method" for the moisture absorption adjustment layer is 0.1 g / m 2 or more and 1.0 g / m 2 or less. If the Cobb water absorption is less than 0.1 g / m 2 , it becomes difficult to separate pulp fibers from the inkjet recording paper. If the Cobb water absorption is 1.0 g / m 2 or more, curling is likely to occur in the inkjet recording paper even though a moisture absorption adjustment layer is provided on the back surface of the base paper.

[0020] The moisture absorption adjustment layer is not a layer that completely blocks moisture absorption or water absorption, nor is it a layer that does not block moisture absorption or water absorption at all, but is a layer that achieves moisture absorption or water absorption within a certain range. The moisture absorption adjustment layer is not particularly limited as long as it can appropriately suppress the absorption of moisture, humidity, or water vapor into the moisture absorption adjustment layer and the base paper. The moisture absorption adjustment layer can be formed by applying and drying a coating liquid containing a predetermined material. The coating liquid for the moisture absorption adjustment layer can be prepared by blending a predetermined material, mixing and dispersing it with water, and adjusting it to an appropriate concentration. In some embodiments, the moisture absorption adjustment layer contains an inorganic pigment and a water-dispersible resin. The inorganic pigment contributes to moisture absorption, and the water-dispersible resin contributes to the suppression of moisture absorption. The hygroscopicity of the moisture absorption adjustment layer can be adjusted by the type of inorganic pigment, the type of water-dispersible resin, and the content ratio of the inorganic pigment and the water-dispersible resin.

[0021] The inorganic pigments mentioned above are those conventionally known in the field of coated paper. Examples of inorganic pigments include heavy calcium carbonate, light calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, activated clay, diatomaceous earth, silica, alumina, aluminum hydroxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide, as well as mica, plate-shaped clay, plate-shaped talc, pyrophyllite, bentonite, montmorillonite, vermiculite, chlorite, septe-chlorite, serpentine, and stilpnomelane. The inorganic pigment is one or more selected from the group consisting of these. In some embodiments, the inorganic pigment includes plate-shaped inorganic pigments. In this specification, "plate-shaped" means a shape having a flat surface and a thin thickness in the direction intersecting the direction of the surface. That is, a shape in which the ratio of the diameter of the flat surface (equivalent to a circle) to the thickness (aspect ratio) is large, and the aspect ratio is greater than 1. In some embodiments, the aspect ratio of the plate-shaped inorganic pigment is between 2 and 1500. Examples of plate-shaped inorganic pigments include mica, kaolin, plate-shaped clay, plate-shaped talc, pyrophyllite, bentonite, montmorillonite, vermiculite, chlorite, septe-chlorite, serpentine, and stilpnomelane. The plate-shaped inorganic pigment is one or more selected from the group consisting of these. In addition, in some embodiments, in the moisture-regulating layer, the content of plate-shaped inorganic pigment is 70% by mass or more per 100 parts by mass of inorganic pigment contained in the moisture-regulating layer. The reason for these reasons is that it is easy to set the Cobb water absorption rate for the moisture absorption adjustment layer within the above range. In at least one embodiment, the inorganic pigment contains at least kaolin. This is because it is easier to set the Cobb water absorption level for the moisture absorption adjustment layer within the above range. Here, "kaolin" is a concept that includes ordinary kaolin such as first-grade kaolin, and processed kaolin such as delaminated kaolin, calcined kaolin, and engineered kaolin.

[0022] The above-mentioned water-dispersible resin is conventionally known in the field of coated paper as a water-dispersible binder. A water-dispersible resin is a resin that is not water-soluble but can be dispersed in water. In this specification, "not water-soluble" in a water-dispersible resin means that its solubility in water at 25°C is less than 10 g / L. Water-dispersible resins are distinguished from water-soluble resins in that, once dried from their water-dispersed state, they are substantially insoluble even in hot water. Examples of water-dispersible resins include conjugated diene copolymer resins such as styrene-butadiene copolymer resins, acrylonitrile-butadiene copolymer resins, and styrene-butadiene-acrylonitrile copolymer resins; water-dispersible acrylic resins such as (meth)acrylic acid ester copolymer resins, styrene-(meth)acrylic acid ester copolymer resins, and (meth)acrylic acid ester-butadiene copolymer resins; vinyl copolymer resins such as vinyl chloride vinyl acetate copolymer resins and vinylidene chloride acrylonitrile copolymer resins; polyurethane resins; alkyd resins; polyester resins; and various modified copolymer resins thereof; thermosetting synthetic resins such as melamine resins and urea resins; and natural rubber. Water-dispersible resins are one or more selected from the group consisting of these. In some embodiments, the water-dispersible resin includes a styrene-butadiene copolymer resin. This is because it makes it easier to set the Cobb water absorption of the moisture-regulating layer within the specified range. Styrene-butadiene copolymer resins are those in which the total amount of styrene monomers and butadiene constituting the main chain of the resin exceeds 50 mol%. Examples of styrene monomers include styrene and styrene derivatives having substituents on the vinyl group, such as α-methylstyrene, and derivatives having substituents on the benzene ring, such as vinyltoluene and p-chlorostyrene. In some embodiments, the moisture-regulating layer contains 70% by mass or more of styrene-butadiene copolymer resin per 100 parts by mass of water-dispersible resin. This is because it makes it easier to set the Cobb water absorption of the moisture-regulating layer within the specified range.

[0023] In some embodiments, the moisture-regulating layer contains an inorganic pigment and a water-dispersible resin, the inorganic pigment includes a plate-shaped inorganic pigment, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment. In at least one embodiment, the moisture-regulating layer contains an inorganic pigment and a water-dispersible resin, the inorganic pigment includes a plate-shaped inorganic pigment, the content of the plate-shaped inorganic pigment is 70% by mass or more per 100 parts by mass of the inorganic pigment contained in the moisture-regulating layer, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment. In at least one embodiment, the moisture-regulating layer contains an inorganic pigment and a water-dispersible resin, the inorganic pigment includes a plate-shaped inorganic pigment, the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment, and the plate-shaped pigment contains kaolin. Furthermore, in at least one embodiment, the moisture-regulating layer contains an inorganic pigment and a water-dispersible resin, the inorganic pigment includes a plate-shaped inorganic pigment, the content of the plate-shaped inorganic pigment is 70% by mass or more per 100 parts by mass of the inorganic pigment contained in the moisture-regulating layer, the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment, and the plate-shaped pigment contains kaolin. The reason for these reasons is that it is easy to set the Cobb water absorption rate for the moisture absorption adjustment layer within the above range.

[0024] The moisture-absorbing and adjusting layer may contain a water-soluble resin as a water-soluble binder. Examples of water-soluble resins include starches such as oxidized starch, etherified starch, phosphate-esterified starch, and urea-phosphate-esterified starch; celluloses such as methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose; polyvinyl alcohols such as polyvinyl alcohol and silanol-modified polyvinyl alcohol; casein, gelatin and their modified products; natural polymer resins such as soy protein, pullulan, acacia gum, karaya gum, and albumin and their modified products; vinyl copolymers such as polyacrylamide and polyvinylpyrrolidone; alginic acid, polyethyleneimine, polypropylene glycol, polyethylene glycol; and maleic anhydride and its copolymers. In this specification, "water-soluble" of a water-soluble resin means that its solubility in water at 25°C is 10 g / L or more.

[0025] The moisture-regulating layer may contain various additives as needed. These additives are conventionally known in the field of coated paper and include, for example, dispersants, organic pigments, thickeners, flow improvers, defoamers, foaming agents, lubricants, water-retaining agents, penetrating agents, coloring pigments, coloring dyes, ultraviolet absorbers, antioxidants, preservatives, anti-bifacement agents, and printability improvers.

[0026] The moisture-regulating layer is one or more layers on the back surface of the base paper. In some embodiments, the moisture-regulating layer is one layer from the viewpoint of manufacturing cost. Also, if there are two or more moisture-regulating layers, the materials and proportions of each moisture-regulating layer may be the same or different.

[0027] The inkjet recording paper of the present invention has a Cobb water absorption rate of 0.1 g / m² on the back side of the base paper. 2 More than 1.0g / m 2 It is preferable that there be no coating layers other than the moisture-absorbing adjustment layer that satisfy the following conditions.

[0028] The inkjet recording paper of the present invention has at least one sealing layer on the surface of the base paper. In this specification, the sealing layer is a layer for sealing voids and depressions present on the surface of the base paper. This makes it possible to obtain print image quality equivalent to or close to that of inkjet recording paper with an ink receiving layer on resin-coated paper. The sealing layer is not particularly limited as long as it is a sealing layer other than a resin laminate layer formed by laminating a resin film and has the effect of sealing voids and depressions present on the surface of the base paper. The sealing layer can be formed by coating and drying a coating liquid containing a predetermined material. The coating liquid for the sealing layer can be prepared by blending a predetermined material, mixing and dispersing it with water, and adjusting it to an appropriate concentration. The sealing layer is, for example, a layer having an inorganic pigment and a binder, or a layer that does not contain an inorganic pigment and contains a binder. Inorganic pigments can be the same as those used in the moisture-regulating layer, so a detailed explanation is omitted here. The binders are conventionally known in the field of coated paper, and examples include water-soluble resins as water-soluble binders and water-dispersible resins as water-dispersible binders. Examples of water-soluble resins include starches such as oxidized starch, etherified starch, phosphate-esterified starch, and urea-phosphate-esterified starch; celluloses such as methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose; polyvinyl alcohols such as polyvinyl alcohol and silanol-modified polyvinyl alcohol; casein, gelatin, and their modified products; natural polymer resins such as soy protein, pullulan, acacia gum, karaya gum, and albumin, and their modified products; vinyl copolymers such as polyacrylamide and polyvinylpyrrolidone; alginic acid, polyethyleneimine, polypropylene glycol, polyethylene glycol; and maleic anhydride and its copolymers. Examples of water-dispersible resins include latex binders such as conjugated diene copolymer latexes like styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, acrylic copolymer latexes such as polymers and copolymers thereof of (meth)acrylic acid esters, vinyl copolymer latexes such as ethylene vinyl acetate copolymer and vinyl chloride vinyl acetate copolymer, polyurethane resin latex, alkyd resin latex, unsaturated polyester resin latex, and functional group-modified copolymer latexes using monomers containing functional groups such as carboxyl groups of these copolymers, as well as thermosetting synthetic resins such as melamine resin and urea resin. The binder is one or more types selected from the group consisting of these water-soluble resins and water-dispersible resins.

[0029] The sealing layer may contain various additives as needed. These additives are conventionally known in the field of coated paper and include, for example, dispersants, organic pigments, thickeners, flow improvers, defoamers, foaming agents, lubricants, water-retaining agents, penetrating agents, coloring pigments, coloring dyes, UV absorbers, antioxidants, preservatives, anti-bifacement agents, and printability improvers.

[0030] The sealing layer is one or more layers on the surface of the base paper. In some embodiments, the sealing layer is one layer from the viewpoint of manufacturing cost. In some embodiments, the sealing layer consists of two layers to enhance the glossiness of the inkjet recording paper. Furthermore, when there are two or more sealing layers, the materials and proportions of each sealing layer may be the same or different.

[0031] In some embodiments, the sealing layer located furthest from the base paper contains a plate-shaped inorganic pigment as an inorganic pigment and a water-dispersible resin as a binder, with the water-dispersible resin content being 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment. The reason for these is that the print image quality and the separation of pulp fibers from the inkjet recording paper are improved. Specifically, when the water-dispersible resin content is 65 parts by mass or more per 100 parts by mass of the plate-shaped inorganic pigment, it is easier to obtain print image quality equivalent to or close to that of inkjet recording paper with an ink-receiving layer on resin-coated paper, and when the water-dispersible resin content is 200 parts by mass or less per 100 parts by mass of the plate-shaped inorganic pigment, the separation of pulp fibers from the inkjet recording paper is further improved. If the sealing layer is a single layer, that sealing layer will be the one located furthest from the base paper. The plate-shaped inorganic pigment and water-dispersible resin of the sealing layer are the same as those used in the moisture-regulating layer, and therefore their explanation is omitted here.

[0032] The inkjet recording paper of the present invention has at least one ink-receiving layer. The ink-receiving layer is, for example, a layer containing inorganic fine particles and a binder, which are conventionally known for inkjet recording paper used as printing paper for images captured by a digital camera. The ink-receiving layer can be formed by coating and drying a coating solution containing predetermined materials. The coating solution for the ink-receiving layer can be prepared by blending predetermined materials, mixing and dispersing them with water, and adjusting to an appropriate concentration.

[0033] The inorganic fine particles in the ink receiving layer are inorganic particles whose average particle diameter, based on volume, is 500 nm or less when dispersed. Examples of inorganic fine particles include alumina hydrate, boehmite pseudo, aluminum hydroxide, alumina, colloidal alumina, alumina sol, vapor-phase silica, precipitated silica, gel-phase silica, colloidal silica, and titanium dioxide. The inorganic fine particles are one or more selected from the group consisting of these. In some embodiments, from the viewpoint of glossiness of the inkjet recording paper, the inorganic fine particles of the ink-receiving layer contain alumina hydrate. In some embodiments, the ink-receiving layer contains 70 parts by mass or more of alumina hydrate per 100 parts by mass of inorganic fine particles in the ink-receiving layer. In some embodiments, the inorganic fine particles of the ink-receiving layer are alumina hydrate.

[0034] The binder used in the ink-receiving layer is the same material as that used in the sealing layer, and therefore its explanation is omitted here. In some embodiments, the binder contains polyvinyl alcohols from the viewpoint of glossiness of the inkjet recording paper. In some embodiments, the ink receiving layer contains 70 parts by mass or more of polyvinyl alcohols per 100 parts by mass of the binder in the ink receiving layer. In some embodiments, the binder of the ink receiving layer is polyvinyl alcohols.

[0035] The ink receiving layer may contain various additives as needed. These additives are conventionally known in the field of coated paper and include, for example, dispersants, crosslinking agents, organic pigments, thickeners, flow improvers, defoamers, foaming agents, lubricants, water-retaining agents, penetrating agents, coloring pigments, coloring dyes, ultraviolet absorbers, antioxidants, preservatives, anti-bifacement agents, and printability improvers.

[0036] The ink receiving layer is one or more layers, relative to the sealing layer or, if necessary, the resin coating layer described below. In some embodiments, the ink receiving layer is one layer from the viewpoint of manufacturing cost. Also, if there are two or more ink receiving layers, the materials and proportions of each ink receiving layer may be the same or different.

[0037] Inkjet recording paper can be calendered after it has been coated with an ink-receiving layer, a sealing layer, a moisture-regulating layer, and, if necessary, a resin coating layer as described below. This is because it improves the smoothness of the final inkjet recording paper. The smoothness of the ink-receiving layer and sealing layer affects the print image quality. The smoothness of the moisture-regulating layer affects handling. On the other hand, excessive calendering may adversely affect the separation of pulp fibers from the inkjet recording paper.

[0038] The inkjet recording paper has an edge water absorption rate of 0.13 mg / mm², as determined by the following method. 2 More than 0.45mg / mm 2 The following is preferable: When the water absorption of the edge surface of the inkjet recording paper is within the aforementioned range, the print image quality and the separation of pulp fibers from the inkjet recording paper are further improved. Specifically, the water absorption of the edge surface is 0.13 mg / mm². 2 As a result, the separation of pulp fibers from the inkjet recording paper is improved, and the water absorption of the edge surface is 0.45 mg / mm². 2 The following conditions result in a more pronounced suppression of curling in inkjet recording paper due to the application of a coating layer to the back surface of the base paper. In this specification, "edge" refers to the side or cut surface of the inkjet recording paper. The water absorption of the edge surface can be increased by methods such as using pulp with short fiber length, increasing the degree of pulp beating, reducing the amount of internal sizing agent in the base paper, increasing the amount of filler in the base paper, lowering the press pressure in the press part during the papermaking process, and lowering the pressure during the calendering process on the base paper. In particular, since voids tend to be present in the base paper, lowering the press pressure in the press part during the papermaking process and lowering the pressure during the calendering process on the base paper are effective.

[0039] Edge surface water absorption (mg / mm 2 ) is a value measured by the following method. (method) A sample of inkjet recording paper was cut to 80mm on the MD side and 140mm on the CD side. Both sides of the sample were laminated with a 100μm thick laminate film, and then cut to 50mm on the MD side and 125mm on the CD side so that the edge of the inkjet recording paper was exposed, and this was used as the measurement sample (n=5). The measurement sample was immersed in water at a temperature of 23℃±1℃ for 10 minutes, and the water absorption of the edge surface (mg / mm) was measured. 2 ) is calculated using the following formula.

number

number

[0040] Inkjet recording paper can be manufactured by coating a base paper or existing layers with a coating solution containing predetermined materials and then drying the mixture. The coating solution for each layer can be prepared by blending predetermined materials, mixing and dispersing them with water, and adjusting the concentration to an appropriate level. Coating and drying can be carried out, for example, by using coating and drying equipment conventionally known in the field of coated paper. Coating equipment can include, for example, comma coaters (registered trademark), film press coaters, air knife coaters, rod blade coaters, bar coaters, blade coaters, gravure coaters, curtain coaters, E-bar coaters, and film transfer coaters. Furthermore, experimental coating methods using hand-applied wire bars can also be mentioned. Examples of drying equipment include various types of drying devices such as straight tunnel dryers, arch dryers, air loop dryers, sine curve air float dryers, and other hot air dryers, as well as infrared heating dryers and microwave dryers.

[0041] In inkjet recording paper having an ink-receiving layer on the surface of the base paper, there is a method of applying a coating layer to the back of the base paper to prevent curling. However, in the case of conventional inkjet recording paper having an ink-receiving layer on the surface of the base paper and a coating layer on the back of the base paper, these layers hinder the disintegration process, which is carried out to recover and reuse the pulp fibers of the base paper after use. This is because the ink-receiving layer on the surface of the base paper, the coating layer between the base paper and the ink-receiving layer, and the coating layer on the back of the base paper prevent water from penetrating the base paper during disintegration. The inventors focused on the water absorption of the coating layer on the back of the base paper and discovered a coating layer on the back of the base paper that has an appropriate water absorption, which suppresses curling while not hindering the disintegration of pulp fibers from the inkjet recording paper, i.e., the moisture-regulating layer of the present invention.

[0042] Furthermore, the inventors focused on water absorption from the edge surface of inkjet recording paper and found that the water absorption rate of the edge surface of inkjet recording paper is 0.13 mg / mm². 2 More than 0.45mg / mm 2 We found that the following conditions do not affect the occurrence of curl and improve the disintegration of pulp fibers from inkjet recording paper. In other words, when separating the pulp fibers from the inkjet recording paper, the separation of pulp fibers from the inkjet recording paper is improved by compensating for the penetration of water from the edge surface of the inkjet recording material into the base paper.

[0043] In some embodiments, the coating amounts of the ink-receiving layer, sealing layer, and moisture-regulating layer of the inkjet recording paper are each 25 g / m² as dry solids.2 More than 45g / m 2 Below 10g / m 2 More than 30g / m 2 The following and 8g / m 2 More than 20g / m 2 The reasons are as follows: These are because they suppress curling and improve the separation of the base paper from the inkjet recording paper. The coating amount for each quantity refers to the total coating amount when each is present in two or more layers.

[0044] In some embodiments, inkjet recording paper has a resin coating layer between the ink-receiving layer and the furthest sealing layer relative to the base paper to obtain a higher gloss. The resin coating layer can seal any small voids and depressions that may exist on the surface of the furthest sealing layer. The resin coating layer is a layer that can be formed by applying and drying a coating liquid for forming the resin coating layer to the furthest sealing layer, and is different from a resin laminate layer formed by laminating a resin film. The coating liquid for the resin coating layer can be prepared by blending predetermined materials, mixing and dispersing them with water, and adjusting to an appropriate concentration. The resin constituting the resin coating layer is a resin conventionally known in the field of coated paper. The resin can be, for example, the binder used in the sealing layer, and is one or more types selected from the group consisting of water-soluble resins and water-dispersible resins. The water-soluble resin and water-dispersible resin of the resin coating layer are the same as those used in the sealing layer, and therefore their explanation is omitted here. The resin coating layer may contain various additives as needed. These additives are conventionally known in the field of coated paper and include, for example, inorganic pigments, organic pigments, thickeners, flow improvers, defoamers, foaming agents, lubricants, water-retaining agents, penetrating agents, coloring pigments, coloring dyes, ultraviolet absorbers, antioxidants, preservatives, anti-bifacement agents, and printability improvers. In some embodiments, the amount of resin coating layer applied is 5 g / m² in terms of dry solids. 2 More than 20g / m 2 The reason is as follows: This method reduces the material cost of the resin coating layer while increasing the glossiness of the inkjet recording paper.

[0045] Inkjet recording paper does not contain a resin laminate layer formed by laminating a resin film.

[0046] In some embodiments, the inkjet recording paper comprises a base paper, at least one sealing layer on the surface of the base paper, at least one ink receiving layer, and at least one moisture-regulating layer on the back surface of the base paper, wherein the moisture-regulating layer has a Cobb water absorption of 0.1 g / m² after 30 seconds of contact with water at 23°C, as measured according to ISO 535:2023. 2 More than 1.0g / m 2 The following conditions must be met, and the water absorption of the edge surface of the inkjet recording paper obtained by the above method must be 0.13 mg / mm². 2 More than 0.45mg / mm 2 The following applies:

[0047] In at least one embodiment, the inkjet recording paper comprises a base paper, at least one sealing layer on the surface of the base paper, at least one ink receiving layer, and at least one moisture-regulating layer on the back surface of the base paper, wherein the moisture-regulating layer has a Cobb water absorption of 0.1 g / m² after 30 seconds of contact with water at 23°C as measured in accordance with ISO 535:2023. 2 More than 1.0g / m 2 The following conditions must be met, and the water absorption of the edge surface of the inkjet recording paper obtained by the above method must be 0.13 mg / mm². 2 More than 0.45mg / mm 2 The following conditions apply: the moisture-absorbing adjustment layer contains a flat inorganic pigment and a water-dispersible resin, with the water-dispersible resin content being 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment; and in the sealing layer, the sealing layer located furthest from the base paper contains a flat inorganic pigment and a water-dispersible resin, with the water-dispersible resin content being 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment. [Examples]

[0048] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Here, "parts by mass" and "mass%" represent "parts by mass" and "mass%" of the dry solid content and substantial component content, respectively. The coating amount of the coating layer represents the dry solid content.

[0049] <Base paper> A pulp slurry consisting of 800 parts by mass of LBKP with a CSF filtration rate of 430 ml and 200 parts by mass of NBKP with a CSF filtration rate of 570 ml was mixed with 5 parts by mass of a rosin-based sizing agent, 10 parts by mass of cationized starch as a paper strength agent, 10 parts by mass of an aluminum sulfate fixing agent, and 0.1 parts by mass of an acrylamide-based yield agent to prepare the paper stock. The aforementioned pulp was manufactured using a wire screen paper machine to obtain paper. Both sides of the paper were subjected to sizing with a sizing solution containing oxidized starch and an acrylamide-based sizing agent as surface sizing agents, and then calendered using a supercalender to obtain a base paper to be used as a substrate. The mixing ratio (mass ratio) of oxidized starch and acrylamide-based sizing agent for the sizing press fluid is oxidized starch:acrylamide-based sizing agent = 7.0:0.3, and the total amount of surface sizing agent applied is 1 g / m² per side. 2 That's what I decided. The pressure of the press section during papermaking and the pressure of the calendering process were adjusted so that the water absorption of the inkjet recording paper reached a predetermined value.

[0050] <Coating liquid for moisture-regulating layer> The coating solution for the moisture absorption adjustment layer was prepared according to the following specifications. Inorganic pigment (kaolin) 100 parts by mass 0.07 parts by mass of acrylic dispersant Water-dispersible resins (styrene-butadiene copolymer resins) are listed in Table 1. Water-soluble binder (urea phosphate esterified starch) 5 parts by mass Antifoaming agent (hydrocarbon-based) 0.02 parts by mass The above ingredients were combined and mixed and dispersed with water to adjust the concentration to 50% by mass.

[0051] <Sealing layer coating liquid - 1> The sealing layer coating solution-1 was prepared according to the following specifications. Inorganic pigment (heavy calcium carbonate) 100 parts by mass Water-soluble binder (fully saponified polyvinyl alcohol with an average degree of polymerization of 400) 4 parts by mass Water-dispersible binder (styrene-butadiene copolymer resin) 7 parts by mass Lubricant (calcium stearate) 0.4 parts by mass Printability enhancer (modified polyamide) 0.3 parts by mass The above ingredients were combined and mixed and dispersed with water to adjust the concentration to 60% by mass.

[0052] <Sealing layer coating liquid - 2> The sealing layer coating solution-2 was prepared according to the following specifications. Inorganic pigment (kaolin) 100 parts by mass 0.07 parts by mass of acrylic dispersant Water-dispersible binder (styrene-butadiene copolymer resin) Listed in Table 1 Water-soluble binder (urea phosphate esterified starch) 5 parts by mass Antifoaming agent (hydrocarbon-based) 0.02 parts by mass The above ingredients were combined and mixed and dispersed with water to adjust the concentration to 50% by mass.

[0053] <Coating liquid for resin coating layer> Water-soluble resin (polyvinyl alcohol with partial saponification degree and average degree of polymerization of 3500) 1.5 parts by mass Water-dispersible resin (ethylene vinyl acetate copolymer resin) 100 parts by mass The above ingredients were combined and mixed and dispersed with water to adjust the concentration to 35% by mass.

[0054] <Ink-receiving layer coating solution> The coating solution for the ink-receiving layer was prepared according to the following specifications. Inorganic pigment (alumina hydrate) 100 parts by mass Dispersant for alumina hydrate (nitric acid) 0.6 parts by mass Binder (fully saponified polyvinyl alcohol with an average degree of polymerization of 3500) 8 parts by mass Crosslinking agent (boric acid) 0.2 parts by mass Lubricant (calcium stearate) 0.3 parts by mass Antifoaming agent (nonionic surfactant) 0.3 parts by mass The above ingredients were combined and mixed and dispersed with water to adjust the concentration to 23% by mass.

[0055] The inkjet recording papers for the examples and comparative examples were manufactured as follows.

[0056] The moisture-absorbing coating liquid was applied to the back surface of the base paper using an air knife coater and then dried. The amount of moisture-absorbing coating liquid applied was 15 g / m². 2 I adjusted the coater so that it would look like this.

[0057] A moisture-absorbing adjustment layer was provided on the back surface of the base paper, and a sealing layer, and optionally a resin coating layer, was applied to the surface of the base paper with the following layer configurations (1) to (5). (1) Apply the coating liquid for sealing layer-2 using an air knife coater and allow it to dry. (2) Apply the coating liquid for sealing layer-1 using an air knife coater and allow it to dry. (3) Apply the coating liquid of sealing layer-1 with a blade coater and dry it. Next, apply the coating liquid of sealing layer-2 to sealing layer-1 using an air knife coater. Coating and drying. (4) Apply the coating liquid of sealing layer-1 with a blade coater and dry it. Next, apply the coating liquid of sealing layer-1 to sealing layer-1 using an air knife coater. Coating and drying again. (5) Apply the coating liquid of sealing layer-1 with a blade coater and allow it to dry. Next, apply the coating liquid of sealing layer-2 to sealing layer-1 using an air knife coater. Coating and drying, Next, the resin coating liquid is applied to the sealing layer-2 using an air knife coater. Coating and drying. The adopted layer configurations (1) to (5) are shown in Table 1. The coating amount for each layer is 15g / m² for the sealing layer-1. 2 Therefore, the sealing layer-2 is 10g / m 2 Therefore, the resin coating layer is 15 g / m². 2 I adjusted the coater to achieve this result.

[0058] The sealant layer or resin coating layer obtained as described above was coated with the ink-receiving layer coating solution using an air knife coater and dried to obtain each inkjet recording paper. Here, the amount of ink-receiving layer coating was 35 g / m². 2 I adjusted the coater so that it would look like this.

[0059] Regarding the obtained inkjet recording paper, the Cobb water absorption (g / m²) of the moisture-adjusting layer of the inkjet recording paper was determined. 2 ) and the water absorption of the edge surface of inkjet recording paper (mg / mm²) 2 The following method was used to measure the following:

[0060] <Cobb water absorption> The Cobb water absorption of the moisture-regulating layer of inkjet recording paper was measured in accordance with ISO 535:2023. The water temperature used was 23°C, and the contact time between the moisture-regulating layer and the water was 30 seconds.

[0061] <Water absorption of the edge surface> The water absorption of the edge surface of inkjet recording paper was measured using the following method. A laminator (Iris Ohyama Co., Ltd.) and commercially available laminating film (164mm x 100mm and 100μm thick) were used as the laminating equipment. For visibility, a immersion tray was prepared containing water at a temperature of 23°C ± 1°C mixed with a small amount of red ink, to a depth of 50 mm or more. Inkjet recording paper was cut to 80mm on the MD side and 140mm on the CD side of the original paper to be used as a sample for measurement. Five samples were prepared. The thickness (μm) of each sample was measured to one decimal place. The average value (μm) was calculated from the individual thicknesses of the five samples. The thickness (μm) was rounded to one decimal place. Using the aforementioned laminating apparatus and laminating film, each sample was passed through the laminating apparatus twice to perform lamination, thereby preparing samples for measurement. Laminated sample sheets were cut to 50mm on the MD side and 125mm on the CD side so that the edge of the inkjet recording paper was exposed. The mass (g) of each sample sheet was measured using an electronic balance. The mass (g) of each sample sheet was measured using an electronic basis scale capable of measuring to three decimal places, and the value was rounded to the third decimal place. The average value (g) was calculated from the individual masses of five sample sheets. The average value (g) was calculated by rounding to the third decimal place (mass A (g)). Each sample for measurement was placed in the immersion tray so that its entire edge was submerged in water. After 10 minutes of immersion, the sample was removed from the water, and any moisture adhering to the surface of the sample was quickly wiped off with commercially available filter paper. Immediately afterward, the mass of each sample was measured using the same method as before immersion, and the average value was calculated (mass B (g)). Edge surface water absorption (mg / mm 2 The value is calculated using the following formula. The result is rounded to the third decimal place.

number

[0062] Cobb water absorption (g / m²) measured for the moisture-regulating layer of inkjet recording paper. 2 ) and the water absorption of the edge surface of inkjet recording paper (mg / mm²) 2 ) are listed in Table 1.

[0063] [Table 1]

[0064] <Print image quality> For evaluating print image quality, a commercially available inkjet printer ("Colorio Printer EP-884AR" / Seiko Epson Corporation) was used as the printing device. For printing, the photo quality setting was selected. As inkjet recording paper with a resin-coated paper support, commercially available inkjet recording photographic paper ("Gakusai Photo Finish Pro" / Fujifilm Corporation) was used as the standard for print image quality. Ten subjects observed the printed materials of each example and comparative example against the print image quality standard from the perspectives of color development and sharpness, and evaluated the print image quality of each example and comparative example according to the following criteria. The final evaluation result adopted was the evaluation that received the most votes from the ten subjects. If the most votes were the same for two types, the result with the worse votes was adopted. In the present invention, if the inkjet recording paper is evaluated as A or B, it shall have the same print image quality as inkjet recording paper provided with an ink receiving layer on resin-coated paper. A: I feel that the color rendering and sharpness are exactly the same as the comparison. B: I feel that the color rendering and sharpness are roughly equivalent to those of the comparison product. C: Color development and sharpness are inferior compared to the comparison.

[0065] <Paper curling occurs> A4-sized, unprinted inkjet recording paper was prepared and placed horizontally on a smooth surface in two configurations: with the ink-receiving layer facing upwards and with the ink-receiving layer facing downwards. The environment for placement was set to a temperature of 23°C and a humidity of 20% RH. After 24 hours of placement to allow for humidity adjustment, inkjet recording paper that had curled and lifted was selected, and the degree to which the four corners lifted from the surface was measured with a ruler. The average height of the four corners was calculated from the measured values, and the occurrence of paper curl was evaluated according to the following criteria. In this invention, inkjet recording paper is considered to have suppressed curling if it receives an evaluation of A or B. A: The average value is 3 mm or less. B: The average value is between 3mm and 10mm. C: The average value is over 10 mm.

[0066] <Disintegration of pulp fibers from paper> <Dissociability> Using a standard pulp dissociator (2L capacity / Toyo Seiki Co., Ltd.), 50g of inkjet recording paper cut to 30mm x 30mm was placed in 1.95L of water and stirred at 3000rpm for 10 minutes. After stirring, the dissociability was evaluated according to the following criteria by visually observing the state of the pulp fibers of the base paper in the dissociated material, as well as the separation state between each layer of the inkjet recording paper and the pulp fibers of the base paper. In the present invention, the inkjet recording paper is provided to have excellent pulp fiber separation properties if it receives an evaluation of A or B. A: No undissociated fragments with a maximum diameter of 1 mm or more were observed. There are no unseparated particles from the layers. B: Although there are a small number of disintegrated pieces with a maximum diameter of 1 mm to 3 mm, No undissolved material larger than 3 mm exists, nor does any material remain unseparated from the layers. C: Undissociated material with a maximum diameter of 1 mm to 3 mm exists. Undissolved material larger than 3 mm is present, or material that has not separated from the layer is present.

[0067] Table 1 shows that Examples 1 to 15, which correspond to the inkjet recording paper of the present invention, have print image quality equivalent to or close to that of inkjet recording paper with an ink receiving layer on resin-coated paper, and despite having a coating layer on the back surface, the pulp fibers from the inkjet recording paper separate well and curling is suppressed. The Cobb water absorption of the moisture-regulating layer of the inkjet recording paper is 0 g / m². 2Comparative Example 1, an inkjet recording paper, exhibited insufficient pulp fiber separation from the paper, similar to conventional inkjet recording papers with a coating layer on the back. The Cobb water absorption of the moisture-regulating layer of the inkjet recording paper was 1.0 g / m². 2 In Comparative Example 2, the inkjet recording paper exceeding the specified value exhibited curling.

[0068] Mainly, by comparing Examples 2, 5, and 6 with Examples 4 and 7, the water absorption on the edge of the inkjet recording paper was found to be 0.13 mg / mm². 2 More than 0.45mg / mm 2 The following conditions can be observed to further suppress curling in inkjet recording paper and to improve the separation of pulp fibers from inkjet recording paper.

[0069] Furthermore, mainly from a comparison between Example 2 and Example 12, or between Examples 2 and 13 and Example 14, it can be seen that if the moisture absorption adjustment layer contains a flat inorganic pigment and a water-dispersible resin, with the water-dispersible resin content being 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment, or if the sealing layer located furthest from the base paper contains a flat inorganic pigment and a water-dispersible resin, with the water-dispersible resin content being 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment, then the print image quality and separation of the base paper from the inkjet recording paper are good.

Claims

1. The material comprises a base paper, at least one sealing layer on the surface of the base paper, at least one ink receiving layer, and at least one moisture absorption adjusting layer on the back surface of the base paper. The Cobb water absorption of the aforementioned moisture-absorbing adjustment layer, measured in accordance with ISO 535:2023, after 30 seconds of contact with water at 23°C, is 0.1 g / m². ２ 1.0g / m or more ２ The following is inkjet recording paper.

2. The water absorption rate of the edge surface of the inkjet recording paper, as determined by the method below, is 0.13 mg / mm². ２ 0.45mg / mm or more ２ The inkjet recording paper according to claim 1, which is as follows: (method) After cutting the inkjet recording paper to a size of 80 mm on the MD side and 140 mm on the CD side, both sides of the sample were laminated with a 100 μm thick laminate film. Then, the sample was cut to 50 mm on the MD side and 125 mm on the CD side so that the edge of the inkjet recording paper was exposed, and this was used as the measurement sample (n=5). After immersing the sample in water at a temperature of 23°C ± 1°C for 10 minutes, the water absorption of the edge surface (mg / mm²) was measured. ２ ) is calculated using the following formula. [Math 1] Here, Mass A is the average mass value (g) of the measurement samples (n=5) before immersion in water. Mass B is the average mass value (g) of the measurement samples (n=5) after immersion in water for 10 minutes. The thickness is the average thickness (μm) of the samples (n=5) before lamination. The circumference of the sample used for measurement is 350 mm (50 + 125 + 50 + 125).

3. The inkjet recording paper according to claim 1 or 2, wherein the moisture absorption adjustment layer contains a flat inorganic pigment and a water-dispersible resin, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment.

4. The inkjet recording paper according to claim 3, wherein the sealing layer located furthest from the base paper contains a flat inorganic pigment and a water-dispersible resin, and the content of the water-dispersible resin is 65 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the flat inorganic pigment.

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