Leather manufacturing method

Abstract

Provided is a method for producing leather, comprising the steps of: applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water to a leather substrate by means of ink jet recording; applying an outer coating liquid containing polyurethane resin particles and water to the leather base material to which the ink is applied; and drying the coating liquid, the solid content concentration of the coating liquid being 20% by mass or more, and in the step of applying the coating liquid, the applied mass per unit area of the solid content contained in the coating liquid being 5 g / cm2 to 20 g / cm2.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing leather. Background Art

[0002] In recent years, various studies have been conducted on the decoration of leather.

[0003] For example, Japanese Unexamined Patent Application Publication No. 2019-77070 discloses an inkjet printing method for leather whose surface is made of synthetic resin. The inkjet printing method includes the following steps: heating the surface of leather whose surface is made of synthetic resin to 40°C or higher; ejecting the ink contained in the aqueous inkjet ink set onto the leather surface by an inkjet method; and heating the leather surface onto which the ink has been ejected to 60°C or higher. The inkjet printing method is characterized in that the ink contained in the aqueous inkjet ink set contains at least water (A), pigment (B), water-soluble organic solvent component (C), surfactant (D), and resin particles (E), the glass transition temperature of the resin particles (E) is 0°C or lower, the ink contains at least one substituted butanol selected from the group consisting of 3-methoxy-1-butanol and 3-methoxy-3-methyl-1-butanol in an amount of 8% by mass or more and 23% by mass or less as the water-soluble organic solvent component (C), and the aqueous inkjet ink set includes a white ink containing a white pigment as the pigment (B) and a colored ink containing a pigment other than white as the pigment (B). Japanese Unexamined Patent Application Publication No. 2022-22084 discloses a printing method for printing on leather using an ink set having a color ink and a transparent ink. The printing method is characterized in that the color ink contains a coloring agent, an organic solvent, and a resin, the transparent ink contains an organic solvent, an acrylic resin, and a polyurethane resin, and the printing method includes: a first transparent ink application step of applying a transparent ink onto the leather in the area where the color ink is applied; a color ink application step of applying a color ink onto the applied first transparent ink; and a second transparent ink application step of applying a transparent ink onto the applied color ink. Summary of the Invention

[0004] Technical Problem to be Solved by the Invention

[0005] In leather, it is sometimes required to satisfy all of alcohol resistance, rubbing resistance, bending resistance, and stretchability.

[0006] A problem in one embodiment of the present invention is to provide a method for manufacturing leather, in which leather having excellent alcohol resistance, rubbing resistance, bending resistance, and stretchability is manufactured using an ink containing water.

[0007] Means for Solving the Technical Problem

[0008] The present invention includes the following aspects.

[0009] <1>

[0010] A method for manufacturing leather, comprising the following steps:

[0011] Applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water onto a leather substrate by an inkjet recording method;

[0012] Applying an overcoat liquid containing polyurethane resin particles and water onto the leather substrate having the ink applied thereon; and

[0013] Drying the overcoat liquid,

[0014] The solid content concentration of the overcoat liquid is 20% by mass or more,

[0015] In the step of applying the overcoat liquid, the application mass per unit area of the solid content contained in the overcoat liquid is 5 g / cm 2 ~20 g / cm 2 .

[0016] <2>

[0017] The method for manufacturing leather according to <1>, wherein,

[0018] The viscosity of the overcoat liquid is 200 mPa·s or more.

[0019] <3>

[0020] The method for manufacturing leather according to <1> or <2>, wherein,

[0021] In the step of applying the ink, when the application mass per unit area of the solid content contained in the ink is set as W I g / cm 2 , and the application mass per unit area of the solid content contained in the overcoat liquid is set as W O g / cm 2 in the case, W O / W I is 5 or more.

[0022] <4>

[0023] The method for manufacturing leather according to any one of <1> to <3>, wherein,

[0024] The overcoat liquid further contains an ultraviolet absorber.

[0025] <5>

[0026] The method for manufacturing leather according to any one of <1> to <4>, further comprising the following step: applying a pretreatment liquid containing a coagulant and water onto the leather substrate,

[0027] After applying the pretreatment liquid, ink is applied to the leather substrate to which the pretreatment liquid has been applied.

[0028] <6>

[0029] The method for manufacturing leather according to any one of <1> to <5>, wherein

[0030] In the step of applying the ink, an inkjet head with a nozzle density of 600 nozzles or more per 1 inch is used to apply the ink.

[0031] <7>

[0032] The method for manufacturing leather according to any one of <1> to <6>, wherein

[0033] In the step of applying the ink, the ink is applied by a single-pass method.

[0034] <8>

[0035] The method for manufacturing leather according to any one of <1> to <7>, wherein

[0036] The solid content concentration of the topcoat liquid is 30% by mass or more.

[0037] <9>

[0038] The method for manufacturing leather according to any one of <1> to <8>, wherein

[0039] In the step of drying the topcoat liquid, heating is performed at a temperature of 80°C or higher.

[0040] <10>

[0041] The method for manufacturing leather according to any one of <1> to <9>, wherein

[0042] The leather substrate is a plant-derived substrate.

[0043] <11>

[0044] The method for manufacturing leather according to any one of <1> to <10>, wherein

[0045] The pigment contained in the ink is at least one selected from the group consisting of C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 184, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, and C.I. Pigment Yellow 155.

[0046] <12>

[0047] The method for manufacturing leather according to <11>, wherein

[0048] The pigment contained in the ink is at least one selected from the group including C.I. Pigment Yellow 110 and C.I. Pigment Yellow 184.

[0049] <13>

[0050] According to the method for manufacturing leather according to any one of <1> to <12>, wherein,

[0051] The resin particles contained in the ink are polyurethane resin particles.

[0052] Advantages of the Invention

[0053] According to an embodiment of the present invention, a method for manufacturing leather can be provided, wherein leather excellent in alcohol resistance, rubbing resistance, bending resistance, and stretchability is manufactured using an ink containing water. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a diagram showing the character image used in the examples. DETAILED DESCRIPTION

[0055] In the present invention, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0056] In the numerical ranges described stepwise in the present invention, the upper limit value or the lower limit value described in a certain numerical range can be replaced with the upper limit value or the lower limit value of other stepwise described numerical ranges. And, within the numerical ranges described in the present invention, the upper limit value or the lower limit value described in a certain numerical range can be replaced with the value shown in the examples.

[0057] In the present invention, regarding the amounts of the respective components in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0058] In the present invention, the combination of two or more preferred modes is a more preferred mode.

[0059] In the present invention, the term "process" includes not only an independent process, but also, even in a case where it cannot be clearly distinguished from other processes, as long as the intended purpose of the process can be achieved, it is also included in this term.

[0060] In the present invention, "image" means the entire film formed by the ink, and "image recording" means the formation of an image (i.e., a film).

[0061] Furthermore, the concept of "image" in the present invention also includes a solid image.

[0062] In the present invention, “(meth)acrylate” is a concept including both acrylate and methacrylate. “(Meth)acrylic acid” is a concept including both acrylic acid and methacrylic acid.

[0063] In the present invention, “synthetic leather” is different from natural leather made from animal skins and refers to an artificially manufactured material. The concept of “synthetic leather” in the present invention also includes artificial leather, artificial hide, and imitation leather.

[0064] [Method for manufacturing leather]

[0065] The method for manufacturing leather according to the present invention includes the following steps: a step of applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water to a leather substrate by an inkjet recording method (hereinafter, also referred to as “ink application step”); a step of applying an overcoat liquid containing polyurethane resin particles and water to the leather substrate to which the ink has been applied (hereinafter, also referred to as “overcoat liquid application step”); and a step of drying the overcoat liquid (hereinafter, also referred to as “overcoat liquid drying step”). The solid content concentration of the overcoat liquid is 20% by mass or more, and in the step of applying the overcoat liquid, the application mass per unit area of the solid content contained in the overcoat liquid is 5 g / cm 2 ~20 g / cm 2 .

[0066] According to the method for manufacturing leather of the present invention, it is possible to manufacture decorated leather having excellent alcohol resistance, rub resistance, bend resistance, and stretchability.

[0067] Conventionally, synthetic leather has been manufactured by attaching a texture pattern to a leather substrate and then applying an overcoat liquid. In the method for manufacturing leather of the present invention, by applying ink to the leather substrate before applying the overcoat liquid, it is possible to simply obtain decorated synthetic leather. No special manufacturing process is required, and it is useful as a method for manufacturing decorated synthetic leather.

[0068] Moreover, natural leather can generally be manufactured by treating animal skins such as cow, horse, and pig skins by “tanning” or the like. However, in the method for manufacturing leather of the present invention, by applying ink to the leather substrate before applying the overcoat liquid, it is possible to simply obtain decorated natural leather.

[0069] In addition, in the method for manufacturing leather of the present invention, both the ink and the overcoat liquid are aqueous systems, having high safety and low environmental impact.

[0070] Furthermore, in the method for manufacturing leather of the present invention, the solid content concentration of the overcoat liquid is 20% by mass or more, and in the step of applying the overcoat liquid, the application mass per unit area of the solid content contained in the overcoat liquid is 5 g / cm 2 ~20 g / cm 2, and thus can satisfy all of alcohol resistance, rub resistance, bend resistance, and stretchability.

[0071] In the methods described in Japanese Patent Laid-Open No. 2019-77070 and Japanese Patent Laid-Open No. 2022-22084, it is difficult to balance all of these properties.

[0072] Hereinafter, each process of the method for manufacturing leather of the present invention will be described.

[0073] <Ink application process>

[0074] The ink application process is a process of applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water to a leather substrate by an inkjet recording method.

[0075] (Leather substrate)

[0076] In the present invention, the leather substrate can be appropriately selected from substrates commonly used in the manufacture of natural leather or synthetic leather. The leather manufactured by the method for manufacturing leather of the present invention can be natural leather or synthetic leather, but synthetic leather is preferred.

[0077] In recent years, substrates manufactured without using raw materials derived from animals, such as "vegan leather", have received attention. The leather substrate is preferably vegan leather. Vegan leather includes substrates derived from petroleum and substrates derived from plants.

[0078] From the viewpoint of environmental suitability, the leather substrate is preferably a resin substrate used in the manufacture of synthetic leather, and more preferably a substrate derived from plants. A substrate derived from plants means a substrate manufactured from plants. As plants, for example, pineapple, apple, grape, and mushroom can be cited. A substrate derived from plants may contain components derived from petroleum.

[0079] As a preferred example of the leather substrate, pineapple leather (Pinatex) manufactured by Ananas Anam can be cited. Pineapple leather is a plant-derived substrate containing about 72% by mass of pineapple leaf fibers.

[0080] It is preferable to perform texture processing on the surface of the leather substrate. Texture refers to a concavo-convex wrinkled pattern.

[0081] The shape of the leather substrate is not particularly limited, and for example, it is sheet-like.

[0082] As the thickness of the leather substrate, it is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0083] (Ink)

[0084] The ink applied through the ink application process contains a pigment, resin particles, a water-soluble organic solvent, and water.

[0085] - Water

[0086] The ink contains water. That is, the ink is a water-based ink.

[0087] Conventionally, a method of recording an image by applying an ultraviolet (UV) curable ink (UV ink) to a leather substrate has been known. A polymerizable monomer is usually contained in the UV ink. If there are many monofunctional polymerizable monomers, flexibility can be obtained, but the rub resistance tends to be insufficient. If there are many polyfunctional polymerizable monomers, rub resistance can be obtained, but flexibility tends to be insufficient, and it is difficult to balance flexibility and rub resistance. Further, when using a UV ink, sometimes a part of the polymerizable monomer contained in the UV ink does not polymerize even when irradiated with ultraviolet rays and remains, and the polymerizable monomer may remain in the final product. Moreover, when a UV ink is applied to a leather substrate and cured, the texture formed on the surface of the leather substrate may sometimes be crushed.

[0088] On the other hand, the manufacturing method of leather of the present invention is a manufacturing method using a water-based ink, which is highly safe and has a low environmental load. Further, by using a water-based ink, an image can be recorded while maintaining the texture formed on the surface of the leather substrate.

[0089] The content of water is preferably 30% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more, relative to the total amount of the ink.

[0090] The content of water is preferably 90% by mass or less, more preferably 80% by mass or less, relative to the total amount of the ink.

[0091] - Pigment

[0092] The ink contains at least one pigment.

[0093] The type of the pigment is not particularly limited, and it may be an organic pigment or an inorganic pigment.

[0094] Examples of the organic pigment include azo pigments, polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, violanthrone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates, nitro pigments, nitroso pigments, and aniline black.

[0095] Examples of the inorganic pigment include white inorganic pigments, iron oxides, barium yellow, cadmium red, chrome yellow, and carbon black. Preferred embodiments of the white inorganic pigment will be described later.

[0096] Examples of the pigment include the pigments described in paragraphs 0096 to 0100 of JP-A-2009-241586.

[0097] Inks in the form of containing colored pigments or black pigments can be used as coloring inks (e.g., cyan ink, magenta ink, yellow ink, black ink, etc.).

[0098] Inks in the form of containing white pigments (e.g., white inorganic pigments) can be used as white inks (hereinafter, also referred to as "white inks").

[0099] As white inorganic pigments, for example, titanium dioxide (TiO 2 ), barium sulfate, calcium carbonate, aluminum hydroxide, silicon dioxide, zinc oxide, zinc sulfide, mica, talc, pearl, etc. Among white inorganic pigments, titanium dioxide, barium sulfate, calcium carbonate or zinc oxide is also preferred, and titanium dioxide is more preferred.

[0100] The average primary particle diameter of the white inorganic pigment is, for example, 150 nm to 400 nm.

[0101] If the average primary particle diameter is 150 nm or more, the hiding power is further improved. Here, the hiding power refers to the property of covering a substrate by an image (e.g., a white image).

[0102] If the average primary particle diameter is 400 nm or less, the ejection property of the ink is further improved.

[0103] As the average primary particle diameter of the white inorganic pigment, it is preferably 250 nm to 350 nm, and more preferably 250 nm to 300 nm.

[0104] The average primary particle diameter of the white inorganic pigment is a value measured using a transmission electron microscope (TEM). In the measurement, a transmission electron microscope 1200EX manufactured by JEOL Ltd. can be used.

[0105] Specifically, after dropping and drying the ink diluted 1,000 times on a Cu200 mesh (manufactured by JEOL Ltd.) attached with a carbon film, the circular equivalent diameter of 300 non-overlapping and independent particles is measured based on an image magnified 100,000 times by TEM, and the value obtained by simply averaging the obtained measurement values is used as the average primary particle diameter.

[0106] In the case of imparting yellow ink, the pigment is preferably at least one selected from the group consisting of C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 184, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, and C.I. Pigment Yellow 155.

[0107] Among them, from the viewpoint of light fastness, the pigment is more preferably at least one selected from the group consisting of C.I. Pigment Yellow 110 and C.I. Pigment Yellow 184.

[0108] In particular, the fading of the leather is suppressed in an environment exposed to light.

[0109] The content of the pigment is preferably 1% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 1% by mass to 10% by mass, relative to the total amount of the ink.

[0110] - Resin particles -

[0111] The ink contains at least one kind of resin particles.

[0112] The resin particles are particles containing a resin, which are different from the pigment dispersion resin described later.

[0113] As the resin constituting the resin particles, a water-insoluble resin is preferred.

[0114] There is no particular limitation on the glass transition temperature of the resin particles (that is, the glass transition temperature of the resin in the resin particles).

[0115] From the viewpoint of further improving the strength of the image, the glass transition temperature (Tg) of the resin particles is preferably 20°C or higher, more preferably 50°C or higher, and further preferably 80°C or higher.

[0116] From the viewpoint of the manufacturing applicability of the resin particles, the glass transition temperature (Tg) of the resin particles is preferably 150°C or lower, more preferably 130°C or lower.

[0117] As the resin particles, particles containing an acrylic resin (hereinafter, also referred to as acrylic resin particles), particles containing a styrene-acrylic resin (hereinafter, also referred to as styrene-acrylic resin particles), particles containing a polyester resin (hereinafter, also referred to as polyester resin particles), particles containing a urethane (hereinafter, also referred to as polyurethane resin particles), or particles containing a polyolefin resin (hereinafter, also referred to as polyolefin resin particles) are preferred.

[0118] Among them, from the viewpoint of rub resistance, the resin particles are preferably polyurethane resin particles. The preferred form of the polyurethane resin particles that can be contained in the ink is the same as the preferred form of the polyurethane resin particles contained in the overcoat liquid described later.

[0119] As the resin particles, self-dispersible resin particles are preferred.

[0120] As the self-dispersible resin particles, for example, self-dispersible polymer particles described in paragraphs 0062 to 0076 of Japanese Patent Application Laid-Open No. 2016-188345, paragraphs 0109 to 0140 of International Publication No. 2013 / 180074, etc. can be cited.

[0121] The weight-average molecular weight of the resin in the resin particles is preferably 1,000 to 300,000, more preferably 2,000 to 200,000, and still more preferably 5,000 to 100,000.

[0122] In the present invention, the weight-average molecular weight refers to the value measured by gel permeation chromatography (GPC). When measuring by gel permeation chromatography (GPC), as the measuring device, HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) is used. As the column, three TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation) are used. As the eluent, THF (tetrahydrofuran) is used. For the measurement, the sample concentration is set to 0.45 mass%, the flow rate is set to 0.35 ml / min, the sample injection volume is set to 10 μl, and the measurement temperature is set to 40°C, and it is carried out using an RI detector. The calibration curve is prepared from eight samples of "standard sample TSKstandard, polystyrene (polystyrene)" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000" and "n-propylbenzene".

[0123] The volume-average particle diameter of the resin particles is preferably 1 nm to 200 nm, more preferably 3 nm to 200 nm, and still more preferably 5 nm to 50 nm.

[0124] When the ink contains resin particles, the content of the resin particles relative to the total amount of the ink is preferably 1 mass% to 25 mass%, more preferably 2 mass% to 20 mass%, still more preferably 2 mass% to 15 mass%, and particularly preferably 2 mass% to 10 mass%.

[0125] - Pigment-dispersing resin -

[0126] The ink preferably contains a pigment-dispersing resin as a pigment dispersant.

[0127] As the pigment-dispersing resin, a water-insoluble resin is preferred.

[0128] As the pigment-dispersing resin, an acrylic resin is preferred.

[0129] Examples of the pigment dispersion resin include those described in International Publication No. 2013 / 180074, Japanese Patent No. 5863600, Japanese Unexamined Patent Application Publication No. 2018-28080, Japanese Unexamined Patent Application Publication No. 2017-149906, and Japanese Unexamined Patent Application Publication No. 2016-193981. The pigment dispersion resin is also referred to as a "resin dispersant" or the like.

[0130] As a combination of a pigment and a pigment dispersion resin, for example, a resin-coated pigment in which a pigment is coated with a crosslinked water-soluble resin as described in Japanese Patent No. 5404669 or the like can be applied. In this case, as the water-soluble resin of the resin-coated pigment, an acrylic resin having a carboxyl group can be used, and a polyfunctional epoxide having two or more functional groups can be used as a crosslinking agent.

[0131] From the viewpoint of the adsorptivity to the pigment, the pigment dispersion resin preferably contains an alicyclic structure or an aromatic ring structure, and more preferably contains an aromatic ring structure.

[0132] As the alicyclic structure, an alicyclic hydrocarbon structure having 5 to 10 carbon atoms is preferred, and a cyclohexane ring structure, a dicyclopentanyl ring structure, a dicyclopentenyl ring structure, a norbornane ring structure, an isobornane ring structure, a norbornene ring structure, an isobornene ring structure, or an adamantane ring structure is more preferred.

[0133] As the aromatic ring structure, a naphthalene ring or a benzene ring is preferred, and a benzene ring is more preferred.

[0134] As the amount of the alicyclic structure or the aromatic ring structure, for example, per 100 g of the resin contained in the resin particles, it is preferably 0.01 mol to 1.5 mol, and more preferably 0.1 mol to 1 mol.

[0135] From the viewpoint of the performance of dispersing the pigment, the pigment dispersion resin preferably has an ionic group in the structure.

[0136] As the ionic group, it can be an anionic group or a cationic group, but an anionic group is preferred.

[0137] As the anionic group, there is no particular limitation, but a carboxyl group, a salt of a carboxyl group, a sulfo group, or a salt of a sulfo group is preferred.

[0138] From the viewpoints of pigment dispersibility and storage stability, the acid value of the pigment dispersion resin is preferably 30 mgKOH / g to 300 mgKOH / g, more preferably 30 mgKOH / g to 200 mgKOH / g, and further preferably 50 mgKOH / g to 200 mgKOH / g.

[0139] Here, the acid value is defined as the mass (mg) of KOH required to completely neutralize 1 g of the resin, and is measured by the method described in the JIS standard (JIS K 0070, 1992).

[0140] The weight-average molecular weight (Mw) of the pigment-dispersing resin is preferably 30,000 or more, more preferably 30,000 to 150,000, still more preferably 30,000 to 100,000, and even more preferably 30,000 to 80,000.

[0141] When the ink contains a pigment-dispersing resin, the content of the pigment-dispersing resin relative to the total amount of the ink is preferably 1% by mass to 25% by mass, more preferably 1% by mass to 20% by mass, still more preferably 1% by mass to 15% by mass, and particularly preferably 1% by mass to 10% by mass.

[0142] The ratio of the pigment-dispersing resin (D) to the pigment (P) (i.e., the D / P ratio) is preferably 0.05 to 3, more preferably 0.05 to 2, still more preferably 0.05 to 1, and even more preferably 0.05 to 0.7.

[0143] As a dispersing device for dispersing the pigment, a known dispersing device can be used. For example, a ball mill, a sand mill, a bead mill, a roll mill, a jet mill, a paint stirrer, a grinder, an ultrasonic disperser, and a disperser can be mentioned.

[0144] The form of the pigment-dispersing resin is not particularly limited, and may be any of a random polymer, a block polymer, and a graft polymer, and may be a polymer having a crosslinked structure.

[0145] The pigment-dispersing resin is preferably a polymer having a crosslinked structure or a block polymer.

[0146] Hereinafter, preferred forms of the polymer having a crosslinked structure and the block polymer, which are preferred pigment-dispersing resins, are shown.

[0147] In the present invention, a polymer means a compound having a weight-average molecular weight of 1000 or more.

[0148] --Polymer having a crosslinked structure--

[0149] The polymer having a crosslinked structure is not particularly limited as long as it is a polymer having at least one crosslinked structure in the molecule.

[0150] Regarding whether the polymer contained in the ink has a crosslinked structure, for example, it can be determined by the following method. First, a separation method such as solvent extraction is used for the ink to separate the polymer. For the separated polymer, various analysis methods such as nuclear magnetic resonance method (NMR), infrared spectroscopy (IR), and thermal analysis method are used for analysis, whereby the presence or absence of a crosslinked structure can be comprehensively determined.

[0151] A polymer having a crosslinked structure (hereinafter, also referred to as "crosslinked polymer") is formed, for example, by crosslinking an uncrosslinked polymer (hereinafter, also referred to as "uncrosslinked polymer") using a crosslinking agent. The uncrosslinked polymer is preferably a water-soluble polymer.

[0152] In the present invention, "water-soluble" means a property of dissolving 1 g or more in 100 g of water at 25°C. As "water-soluble", a property of dissolving 3 g or more (more preferably 10 g or more) in 100 g of water at 25°C is preferred.

[0153] In addition, even if the uncrosslinked polymer is water-soluble, the crosslinked polymer is not necessarily water-soluble.

[0154] Examples of the uncrosslinked polymer include vinyl resins, acrylic resins, polyurethane resins, and polyester resins. Among them, the uncrosslinked polymer is preferably an acrylic resin.

[0155] The uncrosslinked polymer is preferably a polymer having a functional group that can be crosslinked using a crosslinking agent. Examples of the functional group that can be crosslinked include a carboxyl group or its salt, an isocyanate group, and an epoxy group. Among them, from the viewpoint of improving the dispersibility of the pigment, the functional group that can be crosslinked is preferably a carboxyl group or its salt, and particularly preferably a carboxyl group. That is, the uncrosslinked polymer is preferably a polymer containing a carboxyl group.

[0156] The uncrosslinked polymer is preferably a copolymer containing a structural unit derived from a carboxyl group-containing monomer (hereinafter, referred to as "carboxyl group-containing monomer"). The structural unit derived from the carboxyl group-containing monomer contained in the copolymer may be only one kind, or may be two or more kinds. The copolymer may be a random copolymer or a block copolymer, but a random copolymer is preferred.

[0157] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0158] From the viewpoints of crosslinkability and dispersibility, the carboxyl group-containing monomer is preferably (meth)acrylic acid or β-carboxyethyl acrylate, and more preferably (meth)acrylic acid.

[0159] The content of the structural unit derived from the carboxyl group-containing monomer is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 35% by mass, and further preferably 10% by mass to 30% by mass with respect to the total amount of the uncrosslinked polymer.

[0160] The uncrosslinked polymer preferably contains, in addition to the structural unit derived from the carboxyl group-containing monomer, a structural unit derived from a hydrophobic monomer. The structural unit derived from the hydrophobic monomer contained in the copolymer may be only one kind, or may be two or more kinds.

[0161] As the hydrophobic monomer, examples thereof include (meth)acrylates having an alkyl group with 1 to 20 carbon atoms, (meth)acrylates having an aromatic ring (for example, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc.), styrene, and styrene derivatives.

[0162] The content of the structural unit derived from the hydrophobic monomer is preferably 60% by mass to 95% by mass, more preferably 65% by mass to 90% by mass, and still more preferably 70% by mass to 90% based on the total amount of the uncrosslinked polymer.

[0163] The uncrosslinked polymer is preferably a random copolymer containing at least one of a structural unit derived from a carboxyl group-containing monomer, a structural unit derived from a (meth)acrylate having an alkyl group with 1 to 20 carbon atoms, and a structural unit derived from a (meth)acrylate having an aromatic ring, more preferably a random copolymer containing a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylate having an aromatic ring, and still more preferably a copolymer containing a structural unit derived from (meth)acrylic acid and a structural unit derived from benzyl (meth)acrylate.

[0164] The weight average molecular weight (Mw) of the uncrosslinked polymer is not particularly limited, but from the viewpoint of the dispersibility of the white pigment, it is preferably 3,000 to 300,000, more preferably 5,000 to 200,000, and still more preferably 7,000 to 100,000.

[0165] The preferred range of the weight average molecular weight of the crosslinked polymer is the same as the preferred range of the weight average molecular weight of the uncrosslinked polymer.

[0166] The crosslinking agent used for crosslinking the uncrosslinked polymer is preferably a compound having two or more reaction sites with the uncrosslinked polymer (for example, a polymer having a carboxyl group). The crosslinking agent may be used alone or in combination of two or more.

[0167] A preferred combination of the crosslinking agent and the uncrosslinked polymer is a combination of a compound having two or more epoxy groups (i.e., a polyfunctional epoxy compound) and a polymer having a carboxyl group. In this combination, a crosslinked structure is formed by the reaction of the epoxy group and the carboxyl group. The formation of the crosslinked structure using the crosslinking agent is preferably carried out after dispersing the pigment using the uncrosslinked polymer.

[0168] Examples of the polyfunctional epoxy compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

[0169] Among them, the epoxy compounds having two or more functional groups are preferably polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether or trimethylolpropane triglycidyl ether.

[0170] The crosslinking agent can be a commercially available product.

[0171] As commercially available products, for example, Denacol EX-321, EX-821, EX-830, EX-850 and EX-851 (manufactured by Nagase ChemteX Corporation) can be cited.

[0172] From the viewpoints of the crosslinking reaction rate and the dispersion stability after crosslinking, the molar ratio of the reactive sites (for example, epoxy groups) in the crosslinking agent to the reactive sites (for example, carboxyl groups) in the uncrosslinked polymer is preferably 1:1.1 to 1:10, more preferably 1:1.1 to 1:5, and further preferably 1:1.1 to 1:3.

[0173] -- Block polymer --

[0174] The block polymer is also called a block copolymer and is a copolymer in which at least two polymers are bonded in the molecule.

[0175] The block polymer preferably contains a structural unit derived from a hydrophobic monomer and a structural unit derived from a monomer containing an anionic group (hereinafter referred to as "anionic group-containing monomer").

[0176] The structural unit derived from the hydrophobic monomer contained in the block polymer may be only one kind or two or more kinds. The structural unit derived from the anionic group-containing monomer contained in the block polymer may be only one kind or two or more kinds.

[0177] As the structural unit derived from the hydrophobic monomer, there can be cited an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure and a (meth)acrylate having an alkyl group with 1 to 20 carbon atoms.

[0178] The content of the structural unit derived from the hydrophobic monomer relative to the total amount of the block polymer is preferably 35% by mass to 95% by mass, more preferably 50% by mass to 95% by mass, and further preferably 70% by mass to 90% by mass.

[0179] From the viewpoint of the adsorptivity to the pigment, the hydrophobic monomer preferably contains an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure, more preferably contains an ethylenically unsaturated compound having an alicyclic structure, and further preferably contains an ethylenically unsaturated compound having an alicyclic structure with 6 or more carbon atoms.

[0180] The content of the structural unit derived from an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 80% by mass, still more preferably 30% by mass to 70% by mass, and still more preferably 30% by mass to 60% by mass, relative to the total amount of the block polymer.

[0181] The structural unit derived from a hydrophobic monomer preferably further contains a (meth)acrylate having an alkyl group with 1 to 20 carbon atoms. The alkyl group may be either linear or branched.

[0182] Examples of the (meth)acrylate having an alkyl group with 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate.

[0183] The content of the structural unit derived from a (meth)acrylate having an alkyl group with 1 to 20 carbon atoms is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 80% by mass, still more preferably 30% by mass to 70% by mass, and particularly preferably 40% by mass to 60% by mass, relative to the total amount of the block polymer.

[0184] In the structural unit derived from a monomer containing an anionic group, examples of the anionic group include a carboxyl group, a salt of a carboxyl group, a sulfo group, a salt of a sulfo group, a phosphoric acid group, a salt of a phosphoric acid group, a phosphonic acid group, and a salt of a phosphonic acid group.

[0185] Examples of the counter ion in the salt include alkali metal ions such as sodium ion, potassium ion, and lithium ion; alkaline earth metal ions such as calcium ion and magnesium ion; and ammonium ion.

[0186] Among them, the anionic group is preferably a carboxyl group or a salt of a carboxyl group. Examples of the monomer containing an anionic group include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid. Among them, the monomer containing an anionic group is preferably (meth)acrylic acid.

[0187] The content of the structural unit derived from a monomer containing an anionic group is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 25% by mass, and still more preferably 3% by mass to 20% by mass, relative to the total amount of the block polymer.

[0188] Whether the polymer contained in the ink is a block polymer can be determined, for example, by the following method. First, a separation method such as solvent extraction is used for the ink to separate the polymer. For the separated polymer, various analysis methods such as nuclear magnetic resonance method (NMR), infrared spectroscopy method (IR), and thermal analysis method are used for analysis, and physical properties such as glass transition temperature are measured, whereby it is possible to comprehensively determine whether it is a block polymer.

[0189] The weight average molecular weight (Mw) of the block polymer is not particularly limited, but from the viewpoint of pigment dispersibility, it is preferably 3,000 to 100,000, more preferably 5,000 to 80,000, and further preferably 10,000 to 60,000.

[0190] -Water-soluble organic solvent-

[0191] The ink contains at least one water-soluble organic solvent. From the viewpoint of balancing the drying property and ink ejection property of the ink, the ink preferably contains a water-soluble organic solvent with a boiling point less than 220°C (hereinafter, also referred to as "low-boiling solvent").

[0192] In the present invention, the boiling point refers to the boiling point under 1 atmospheric pressure (101325 Pa).

[0193] Examples of the low-boiling solvent include 1,2-propanediol (also known as propylene glycol) (boiling point 188°C), 1,3-propanediol (boiling point 213°C), propylene glycol monomethyl ether (boiling point 121°C), ethylene glycol (boiling point 197°C), ethylene glycol monomethyl ether (boiling point 124°C), propylene glycol monoethyl ether (boiling point 133°C), ethylene glycol monoethyl ether (boiling point 135°C), propylene glycol monopropyl ether (boiling point 149°C), ethylene glycol monopropyl ether (boiling point 151°C), propylene glycol monobutyl ether (boiling point 170°C), ethylene glycol monobutyl ether (boiling point 171°C), 2-ethyl-1-hexanol (boiling point 187°C), dipropylene glycol monomethyl ether (boiling point 188°C), diethylene glycol dimethyl ether (boiling point 162°C), diethylene glycol diethyl ether (boiling point 188°C), and dipropylene glycol dimethyl ether (boiling point 175°C).

[0194] When the ink contains a low-boiling solvent, the content of the low-boiling solvent relative to the total amount of the ink is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, further preferably 10% by mass to 40% by mass, and particularly preferably 15% by mass to 35% by mass.

[0195] From the viewpoint of balancing the drying property and ink ejection property of the ink, the content of the organic solvent with a boiling point of 220°C or higher (hereinafter, also referred to as "high-boiling solvent") in the ink is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 1% by mass or less. The content of the high-boiling solvent can be 0% by mass.

[0196] As high-boiling solvents, for example, glycerin (boiling point: 290°C), 1,2-hexanediol (HDO) (boiling point: 223°C), diethylene glycol (boiling point: 245°C), diethylene glycol monobutyl ether (boiling point: 230°C), triethylene glycol (boiling point: 285°C), dipropylene glycol (boiling point: 232°C), tripropylene glycol (boiling point: 267°C), trimethylolpropane (boiling point: 295°C), 2-pyrrolidone (boiling point: 245°C), tripropylene glycol monomethyl ether (boiling point: 243°C), and triethylene glycol monomethyl ether (boiling point: 248°C) can be cited.

[0197] The content of the water-soluble organic solvent is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, still more preferably 10% by mass to 40% by mass, and particularly preferably 15% by mass to 35% by mass, relative to the total amount of the ink.

[0198] - Surfactant -

[0199] The ink may contain at least one surfactant.

[0200] As the surfactant, nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants can be cited.

[0201] As a preferred surfactant, an acetylene glycol-based surfactant, which is a kind of nonionic surfactant, can be cited.

[0202] As the acetylene glycol-based surfactant, for example, the acetylene glycol-based surfactants described in paragraphs 0070 to 0080 of International Publication No. 2017 / 149917 can be used.

[0203] Examples of the acetylene glycol-based surfactant include

[0204] Polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,4,7,9-tetramethyl-5-decyn-4,7-diol,

[0205] Polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 3,6-dimethyl-4-octyn-3,6-diol,

[0206] Polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol, and

[0207] Polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,5-dimethyl-3-hexyn-2,5-diol.

[0208] Examples of commercially available acetylenediol surfactants include the Surfynol series (e.g., Surfynol 420, Surfynol 440, Surfynol 465, Surfynol 485) manufactured by Air Products Ltd. or Nissin Chemical co., ltd., the OLFINE series (e.g., OLFINE E1010, OLFINE E1020), the Dynol series (e.g., Dynol 604), and ACETYLENOL manufactured by Kawaken Fine Chemicals Co., Ltd.

[0209] Commercially available acetylenediol surfactants are also provided by The Dow Chemical Company, General Aniline & Film Corp., etc.

[0210] Examples of surfactants also include the compounds cited as surfactants on pages 37 - 38 of Japanese Patent Laid-Open No. 59-157636 and Research Disclosure No. 308119 (1989). Further, examples include fluorine (fluorinated alkyl-based) surfactants, silicone surfactants, etc. described in each of Japanese Patent Laid-Open Nos. 2003-322926, 2004-325707, and 2004-309806.

[0211] When the ink contains a surfactant, the content of the surfactant in the ink can be appropriately adjusted in consideration of the surface tension of the ink.

[0212] The content of the surfactant is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 3% by mass, and still more preferably 0.1% by mass to 2% by mass based on the total amount of the ink.

[0213] - Other Components -

[0214] The ink may contain other components in addition to the above components.

[0215] Examples of other components include known additives such as silicate compounds (e.g., the silicate compounds described in paragraphs 0058 - 0075 of Japanese Patent No. 5430316), urea, urea derivatives, wax, anti-fading agents, emulsion stabilizers, penetration promoters, ultraviolet absorbers, preservatives, fungicides, pH regulators, defoaming agents, viscosity regulators, dispersion stabilizers, chelating agents, etc.

[0216] - Physical Properties of Ink -

[0217] The viscosity of the ink (at 25 °C) is preferably 1.2 mPa·s or more and 15.0 mPa·s or less, more preferably 2 mPa·s or more and less than 13 mPa·s, and still more preferably 2.5 mPa·s or more and less than 10 mPa·s.

[0218] Regarding the viscosity, it is measured at 25 °C using a viscometer. For example, it is measured using a TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.

[0219] The surface tension of the ink (at 25 °C) is preferably 25 mN / m to 50 mN / m, more preferably 30 mN / m to 45 mN / m, and still more preferably 30 mN / m to 40 mN / m.

[0220] Regarding the surface tension, it is measured at 25 °C using a surface tensiometer. For example, it is measured using an automatic surface tensiometer (product name “CBVP-Z”) manufactured by Kyowa InterfaceScience Co., Ltd. and by the plate method.

[0221] The pH of the ink (at 25 °C) is preferably pH 6 to 11, more preferably pH 7 to 10, and still more preferably pH 7 to 9.

[0222] Regarding the pH, it is measured at 25 °C using a pH meter. For example, it is measured using a pH meter (model “HM-31”) manufactured by DKK-TOA CORPORATION.

[0223] (Application of the ink)

[0224] In the ink application step, the above-mentioned ink is applied to the leather substrate by an inkjet recording method.

[0225] There is no particular limitation on the ink ejection method in the inkjet recording method, and it can be a known method. For example, a charge control method that ejects ink using electrostatic induction force, a drop-on-demand inkjet method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam and irradiates the ink and uses the radiation pressure to eject the ink, and a thermal inkjet (Bubble Jet (registered trademark)) method that heats the ink to form bubbles and uses the generated pressure, etc.

[0226] As the inkjet recording method, in particular, the inkjet method in the method described in Japanese Patent Laid-Open No. 54-59936 can be effectively used. In this inkjet method, the ink under the action of heat energy undergoes a rapid volume change, and the ink is ejected from the nozzle by the acting force generated by this state change.

[0227] As an inkjet recording method, the method described in paragraphs 0093 to 0105 of Japanese Patent Laid-Open No. 2003-306623 can also be applied.

[0228] The application of ink based on the inkjet recording method is performed by ejecting ink from the nozzles of an inkjet head.

[0229] As a method of the inkjet head, there are a reciprocating method (multiple pass method) in which a short-size serial head is scanned in the width direction of a substrate while recording; and a line method (single pass method) using a line head in which recording elements are arranged corresponding to the entire area of one side of the substrate.

[0230] In the line method, by scanning the substrate in a direction crossing the arrangement direction of the recording elements, image recording can be performed on the entire surface of the substrate. In the line method, a conveyance system such as a carriage for scanning the short-size head in the reciprocating method is not required. And, in the line method, compared with the reciprocating method, complicated scanning control of the carriage and the substrate is not required, and only the substrate is moved. Therefore, compared with the reciprocating method, high-speed image recording can be achieved according to the line method.

[0231] Therefore, in the ink application step, it is preferable to apply ink by the line method (single pass method).

[0232] And, in the ink application step, it is preferable to apply ink using an inkjet head having a nozzle density of 600 nozzles or more per inch. The nozzle density is more preferably 900 nozzles or more per inch, and further preferably 1200 nozzles or more. In addition, instead of an inkjet head having 600 nozzles, inkjet heads having 300 nozzles may be staggeredly arranged to substantially set the nozzle density to 600 or more per inch.

[0233] From the viewpoint of obtaining a high-definition image, the droplet volume of the ink ejected from the nozzles of the inkjet head is preferably 1 pL (picoliter) to 10 pL, and more preferably 1.5 pL to 6 pL.

[0234] And, from the viewpoint of improving image non-uniformity and connection of continuous gradations, it is also effective to eject by combining different droplet volumes.

[0235] In the ink application step, from the viewpoint of balancing ejectability and the required application amount of the solid component on the substrate, the application mass per unit area of the solid component contained in the ink is preferably 5 g / cm 2 ~20 g / cm 2 . The solid component of the ink refers to the component obtained by removing liquid components (for example, water and water-soluble organic solvents) from all components contained in the ink.

[0236] The mass per unit area of the solid components contained in the ink (unit: g / m 2 ) is calculated by multiplying the mass per unit area of the ink applied by the concentration of the solid components in the ink (mass %).

[0237] In the ink application process, two or more inks can be applied to the leather substrate.

[0238] In the ink application process, when two or more colors of inks are successively applied to the leather substrate, the ink of the nth color (n is an integer of 1 or more. The same applies hereinafter) applied to the leather substrate can be heated and dried, and the (n + 1)th color ink can be applied on the heated and dried ink of the nth color, or the ink of the nth color applied to the leather substrate can be not heated and dried, and the (n + 1)th color ink can be applied on the ink of the nth color.

[0239] (Heating and drying of the ink)

[0240] After the ink application process, the ink applied to the leather substrate can be heated and dried.

[0241] As the mechanism for heating and drying, known heating mechanisms such as infrared heaters, known air supply mechanisms such as dryers, and mechanisms formed by combining two or more of these mechanisms can be cited.

[0242] As the method for heating and drying, for example, the following can be cited: a method of blowing warm air or hot air onto the surface of the leather substrate to which the ink is applied; a method of applying heat from the surface of the leather substrate to which the ink is applied and / or the side opposite to the surface to which the ink is applied using an infrared heater or the like; and a method formed by combining these various methods.

[0243] The heating temperature during heating and drying is preferably 55 °C or higher, more preferably 60 °C or higher, and further preferably 65 °C or higher. The upper limit value of the heating temperature is not particularly limited. For example, 100 °C can be cited, and preferably 90 °C.

[0244] The time for heating and drying is not particularly limited, but is preferably 3 seconds to 60 seconds, more preferably 5 seconds to 30 seconds, and further preferably 5 seconds to 20 seconds.

[0245] <Topcoat liquid application process>

[0246] The topcoat liquid application process is a process of applying a topcoat liquid containing polyurethane resin particles and water to the leather substrate to which the ink has been applied.

[0247] (Topcoat liquid)

[0248] The coating liquid applied in the coating liquid application step contains polyurethane resin particles and water.

[0249] - Water -

[0250] The coating liquid contains water.

[0251] As described above, the method for manufacturing leather of the present invention is a manufacturing method using water-based ink. In addition to the water-based ink, the coating liquid is also water-based, so it has high safety and low environmental load.

[0252] The content of water is preferably 30% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more with respect to the total amount of the coating liquid.

[0253] The content of water is preferably 90% by mass or less, more preferably 80% by mass or less with respect to the total amount of the coating liquid.

[0254] - Polyurethane resin particles -

[0255] The coating liquid contains polyurethane resin particles. By including polyurethane resin particles, leather with excellent softness can be obtained.

[0256] The polyurethane resin constituting the polyurethane resin particles is preferably at least one selected from the group consisting of self-emulsifying polyurethane resin and forced-emulsifying polyurethane resin. The self-emulsifying polyurethane resin is preferably a polyurethane resin having an anionic group. The forced-emulsifying polyurethane resin is preferably a polyurethane resin that does not have an anionic group and can be dispersed in water by an emulsifier.

[0257] The polyurethane resin particles can be commercially available products or can be obtained as an aqueous dispersion containing polyurethane resin particles.

[0258] As the aqueous dispersion containing polyurethane resin particles, for example, polyurethane emulsions manufactured by NICCA CHEMICAL CO., LTD., such as the EVAFANOL series (for example, EVAFANOL HA-55), can be cited.

[0259] The average particle size of the polyurethane resin particles is, for example, 10 nm to 10 μm.

[0260] From the viewpoint of improving rub resistance, the content of the polyurethane resin particles is preferably 15% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more with respect to the total amount of the coating liquid.

[0261] From the viewpoint of coatability, the content of the polyurethane resin particles is preferably 70% by mass or less, more preferably 60% by mass or less, and further preferably 50% by mass or less, relative to the total amount of the outer coating liquid. From the above viewpoints, the content of the polyurethane resin particles is preferably 15% by mass to 70% by mass.

[0262] - Other components -

[0263] The outer coating liquid may contain other components in addition to the polyurethane resin particles and water. Examples of the other components include ultraviolet absorbers, crosslinking agents, lubricants, and surfactants.

[0264] The outer coating liquid preferably contains an ultraviolet absorber. If an ultraviolet absorber is included, fading during use in a location susceptible to sunlight can be suppressed.

[0265] The ultraviolet absorber is not particularly limited as long as it is a compound having absorption in the ultraviolet region and little absorption in the visible region.

[0266] Examples of the ultraviolet absorber include compounds having a benzotriazole skeleton, a triazine skeleton, a benzophenone skeleton, or an oxanilide skeleton, and metal oxide particles. Examples of the metal oxide particles include titanium oxide particles, zinc oxide particles, and cerium oxide particles.

[0267] Examples of commercially available products of the ultraviolet absorber include CHIGUARD 5400WB and 5582WB (manufactured by Kusumoto Chemicals, Ltd.).

[0268] When the outer coating liquid contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 1% by mass to 10% by mass or more, and more preferably 2% by mass to 8% by mass, relative to the total amount of the outer coating liquid.

[0269] - Solid component concentration of the outer coating liquid -

[0270] The solid component concentration of the outer coating liquid is 20% by mass or more. The solid components of the outer coating liquid refer to the components obtained by removing the liquid components (e.g., water and water-soluble organic solvents) from all the components contained in the outer coating liquid.

[0271] If the solid component concentration is 20% by mass or more, the drying time in the subsequent drying process of the outer coating liquid can be reduced, and leather can be effectively manufactured. Also, if the solid component concentration is 20% by mass or more, the alcohol resistance and rub resistance are improved. From the above viewpoints, the solid component concentration of the outer coating liquid is preferably 25% by mass or more, more preferably 35% by mass or more. The upper limit value of the solid component concentration of the outer coating liquid is not particularly limited, but from the viewpoint of easy application, it is preferably 70% by mass. From the above viewpoints, the solid component concentration is preferably 20% by mass to 70% by mass.

[0272] -Physical properties of the outer coating liquid-

[0273] From the viewpoint of the amount of solid components contained, the viscosity (25 °C) of the outer coating liquid is preferably 200 mPa·s or more, more preferably 220 mPa·s or more. The upper limit value of the viscosity of the outer coating liquid is not particularly limited, but from the viewpoint of easy application, it is preferably 10,000 mPa·s.

[0274] Regarding the viscosity, it is measured at 25 °C using a viscometer. For example, it is measured using a TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.

[0275] (Application of the outer coating liquid)

[0276] The method of applying the outer coating liquid is not particularly limited, and known methods such as a coating method, an immersion method, and an inkjet recording method can be cited.

[0277] As the coating method, known coating methods such as using a bar coater, an extrusion die coater, an air knife coater, a blade coater, a rod coater, a doctor blade coater, an extrusion coater, and a reverse roll coater can be cited. Also, the outer coating liquid can be applied using analog printing methods such as a screen printing method, a gravure printing method, a flexographic printing method, and a lithographic printing method. Among them, from the viewpoint of the amount of ink that can be applied, the outer coating liquid is preferably applied using the screen printing method.

[0278] The application mass per unit area of the solid components contained in the outer coating liquid is 5 g / cm 2 ~20 g / cm 2 . If the above application mass is 5 g / cm 2 or more, the alcohol resistance and rub resistance are excellent. If the above application mass is 20 g / cm 2 or less, the bending resistance and stretchability are excellent.

[0279] The application mass per unit area of the solid components contained in the outer coating liquid (unit: g / m 2 ) is calculated by multiplying the application mass per unit area of the outer coating liquid by the solid component concentration (% by mass) of the outer coating liquid.

[0280] When the mass per unit area of the solid component contained in the ink is set as W I g / cm 2 and the mass per unit area of the solid component contained in the overcoat liquid is set as W O g / cm 2 in the case, W O / W I is preferably 3 or more. If W O / W I is 5 or more, the alcohol resistance and rub resistance are excellent. From the above viewpoints, W O / W I is preferably 6 or more. The upper limit value of W O / W I is not particularly limited, for example, it is 100.

[0281] <Overcoat liquid drying process>

[0282] The overcoat liquid drying process is a process of drying the overcoat liquid after the overcoat liquid application process.

[0283] As a drying method of the overcoat liquid, for example, a method of heating a substrate applied with the overcoat liquid in an oven can be cited.

[0284] From the viewpoint of rub resistance, the heating temperature is preferably 80 °C or more, more preferably 100 °C or more, and further preferably 120 °C or more. The upper limit value of the heating temperature is not particularly limited, for example, it can be cited as 180 °C, and preferably 150 °C.

[0285] The heating time is not particularly limited, but from the viewpoint of rub resistance, it is preferably 30 seconds to 20 minutes, more preferably 1 minute to 10 minutes, and further preferably 1 minute to 5 minutes.

[0286] <Pretreatment liquid application process>

[0287] The manufacturing method of the leather of the present invention preferably further includes a process of applying a pretreatment liquid containing a coagulant and water on a leather substrate, and after applying the pretreatment liquid, an ink is applied on the leather substrate applied with the pretreatment liquid.

[0288] The components in the ink are coagulated by the coagulant in the pretreatment liquid, and thus an image with more excellent image quality can be obtained.

[0289] (Pretreatment liquid)

[0290] The pretreatment liquid contains a coagulant and water.

[0291] - Water -

[0292] The pretreatment liquid contains water.

[0293] The content of water is preferably 50% by mass or more, more preferably 60% by mass or more, relative to the total amount of the pretreatment liquid.

[0294] The content of water is preferably 90% by mass or less relative to the total amount of the pretreatment liquid.

[0295] - Coagulant -

[0296] Regarding the pretreatment liquid, a coagulant is prepared, and the coagulant is at least one selected from the group consisting of organic acids, organic acid salts, polyvalent metal compounds, and metal complexes.

[0297] The coagulant is a component that causes components (e.g., resin) in the ink to coagulate.

[0298] - Organic acid -

[0299] As the organic acid, organic compounds having acidic groups can be cited.

[0300] As the acidic group, phosphoric acid group, phosphonic acid group, hypophosphorous acid group, sulfuric acid group, sulfonic acid group, sulfinic acid group, and carboxyl group can be cited.

[0301] From the viewpoint of the coagulation rate of the ink, the above acidic group is preferably a phosphoric acid group or a carboxyl group, more preferably a carboxyl group.

[0302] In addition, it is preferred that at least a part of the above acidic group dissociates in the pretreatment liquid.

[0303] As the organic compound having a carboxyl group, polyacrylic acid, acetic acid, formic acid, benzoic acid, glycolic acid, malonic acid, malic acid (preferably DL - malic acid), maleic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, phthalic acid, adipic acid, pimelic acid, 4 - methylphthalic acid, lactic acid, pyrrolidonecarboxylic acid, pyranonecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, pimelic acid, etc. are preferred. These compounds can be used alone or in combination of two or more.

[0304] As the organic compound having a carboxyl group, from the viewpoint of the coagulation rate of the ink, carboxylic acids having a valence of 2 or more (hereinafter, also referred to as polycarboxylic acids) are preferred.

[0305] As the polycarboxylic acid, dicarboxylic acids or tricarboxylic acids are preferred, more preferably glutaric acid, malonic acid, succinic acid, adipic acid, pimelic acid, malic acid, maleic acid, fumaric acid, tartaric acid or citric acid, further preferably glutaric acid, malonic acid, succinic acid, adipic acid, pimelic acid, malic acid, fumaric acid, tartaric acid or citric acid, and particularly preferably glutaric acid, malonic acid, succinic acid, adipic acid or pimelic acid.

[0306] The pKa of the organic acid is preferably low (e.g., 1.0 to 5.0).

[0307] Thus, by contacting with an organic acidic compound having a lower pKa, the surface charge of particles such as pigments and polymer particles in an ink dispersed and stabilized by a weakly acidic functional group such as a carboxyl group can be reduced, thereby decreasing the dispersion stability.

[0308] The organic acid preferably has a low pKa, high solubility in water, and a valence of 2 or more, and more preferably is a divalent or trivalent acidic substance having a high buffering capacity in a pH region lower than the pKa of the functional group (e.g., carboxyl group, etc.) that stabilizes the dispersion of the particles in the ink.

[0309] -Organic acid salts-

[0310] Examples of the organic acid salts include the salts of the organic acids exemplified above.

[0311] Examples of the organic acid salts include organic acid salts containing alkaline earth metals of Group 2 of the periodic table (e.g., magnesium, calcium), transition metals of Group 3 of the periodic table (e.g., lanthanum), cations from Group 13 of the periodic table (e.g., aluminum), and lanthanides (e.g., neodymium).

[0312] As the organic acid salts, organic acid salts containing alkaline earth metals are preferred, and organic acid salts containing calcium (e.g., calcium lactate, calcium acetate, etc.) or organic acid salts containing magnesium (e.g., magnesium lactate, magnesium acetate, etc.) are more preferred.

[0313] -Polyvalent metal compounds-

[0314] Examples of the polyvalent metal compounds include salts containing at least one selected from the group consisting of alkaline earth metals of Group 2 of the periodic table (e.g., magnesium, calcium), transition metals of Group 3 of the periodic table (e.g., lanthanum), cations from Group 13 of the periodic table (e.g., aluminum), and lanthanides (e.g., neodymium) (however, excluding organic acid salts).

[0315] As the polyvalent metal compounds, nitrates, chlorides, or thiocyanates are preferred.

[0316] As the polyvalent metal compounds, calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, or calcium salts or magnesium salts of thiocyanic acid are particularly preferred.

[0317] It is preferred that at least a part of the polyvalent metal compound dissociates into polyvalent metal ions and counter ions in the pretreatment liquid.

[0318] -Metal complexes-

[0319] As the metal complexes, metal complexes containing at least one selected from the group consisting of zirconium, aluminum, and titanium as metal elements are preferred.

[0320] As the metal complex, a metal complex preferably containing at least one selected from the group consisting of acetate, acetylacetonate, methyl acetoacetate, ethyl acetoacetate, octyleneglycolate, butoxyacetylacetonate, lactate, ammonium lactate, and triethanol aminate as a ligand is used.

[0321] As the metal complex, various metal complexes are commercially available, and in the present invention, commercially available metal complexes can be used. Further, various organic ligands, particularly various polydentate ligands capable of forming a metal chelate catalyst, are commercially available. Therefore, a metal complex prepared by combining a commercially available organic ligand and a metal can be used.

[0322] The content of the flocculant is not particularly limited.

[0323] From the viewpoint of the flocculation rate of the ink, the content of the flocculant is preferably 0.1% by mass to 40% by mass, more preferably 0.1% by mass to 30% by mass, still more preferably 1% by mass to 20% by mass, and particularly preferably 1% by mass to 10% by mass, relative to the total amount of the pretreatment liquid.

[0324] - Resin -

[0325] The pretreatment liquid preferably contains at least one resin.

[0326] Examples of the resin include an acrylic resin, a polyester resin, a polyolefin resin, a polyurethane resin, a polyurea resin, a polyamide resin, a polycarbonate resin, and a polystyrene resin.

[0327] The pretreatment liquid preferably contains at least one resin particle which is a particle containing a resin.

[0328] When preparing the pretreatment liquid, commercially available aqueous dispersions of resin particles can be used.

[0329] Examples of commercially available aqueous dispersions of resin particles include Pesthresin A124GP, Pesthresin A645GH, Pesthresin A615GE, Pesthresin A520 (manufactured by TAKAMATSU OIL & FAT CO., LTD.), Eastek 1100, Eastek 1200 (manufactured by Eastman Chemical Company), plascoat RZ570, plascoat Z687, plascoat Z565, plascoat RZ570, plascoat Z690 (manufactured by GOO CHEMICAL CO., LTD.), Vylonal MD1200 (manufactured by TOYOBO CO., LTD.), EM57DOC (manufactured by Daicel Fine Chem Ltd.), Superflex M500 (manufactured by DKS Co., Ltd.), and the like.

[0330] When the pretreatment liquid contains resin particles, the content of the resin particles is preferably 0.5% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and particularly preferably 1% by mass to 15% by mass, relative to the total amount of the pretreatment liquid.

[0331] -Water-soluble organic solvent-

[0332] The pretreatment liquid may contain at least one water-soluble organic solvent.

[0333] As the water-soluble organic solvent, known water-soluble organic solvents can be used without particular limitation.

[0334] Examples of the water-soluble organic solvent include the same water-soluble organic solvents as those contained in the ink.

[0335] When the pretreatment liquid contains a water-soluble organic solvent, the content of the water-soluble organic solvent is preferably 0.5% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and particularly preferably 1% by mass to 15% by mass, relative to the total amount of the pretreatment liquid.

[0336] -Other components-

[0337] Optionally, the pretreatment liquid may contain other components in addition to the above.

[0338] As other components that can be contained in the pretreatment liquid, surfactants, solid wetting agents, silicate compounds (e.g., colloidal silica), inorganic salts, anti-fading agents, emulsion stabilizers, penetration promoters, ultraviolet absorbers, preservatives, mildew-proof agents, pH adjusters, viscosity adjusters, rust inhibitors, chelating agents, water-soluble polymer compounds other than water-soluble cationic polymers (e.g., water-soluble polymer compounds described in paragraphs 0026 to 0080 of Japanese Patent Laid-Open No. 2013-001854), and other known additives can be mentioned.

[0339] (Application of the pretreatment liquid)

[0340] The method for applying the pretreatment liquid is not particularly limited, and known methods such as coating methods, dipping methods, and inkjet recording methods can be mentioned.

[0341] As coating methods, known coating methods such as using a bar coater, an extrusion die coater, an air knife coater, a blade coater, a rod coater, a doctor blade coater, an extrusion coater, and a reverse roll coater can be mentioned.

[0342] In the pretreatment liquid application step, the application mass per unit area of the solid components contained in the pretreatment liquid is preferably 0.1 g / cm 2 ~1 g / cm 2 . The solid components of the pretreatment liquid refer to the components obtained by removing the liquid components (e.g., water and water-soluble organic solvents) from all the components contained in the pretreatment liquid.

[0343] (Heating and drying of the pretreatment liquid)

[0344] After the pretreatment liquid application step, the pretreatment liquid applied to the leather substrate can be heated and dried.

[0345] As the mechanism for heating and drying, the same mechanism as that for heating and drying of ink can be mentioned.

[0346] The heating temperature during heating and drying is preferably 55°C or higher, more preferably 60°C or higher, and further preferably 65°C or higher. There is no particular limitation on the upper limit of the heating temperature. For example, 100°C can be mentioned, and preferably 90°C.

[0347] The time for heating and drying is not particularly limited, but is preferably 3 seconds to 60 seconds, more preferably 5 seconds to 30 seconds, and further preferably 5 seconds to 20 seconds.

[0348] The leather produced by the manufacturing method of the leather of the present invention is excellent in alcohol resistance, rubbing resistance, bending resistance, and stretchability. According to the manufacturing method of the leather of the present invention, desired characters and patterns can be displayed on the leather, and it can be applied to various uses. The leather produced by the manufacturing method of the leather of the present invention can be applied to vehicle seats, for example. Both the ink and the overcoating liquid are water-based, with high safety and low environmental load, so they are suitable for vehicle seats that are directly contacted by people. Moreover, since it has excellent alcohol resistance, it is also useful from the viewpoints of disinfection and sterilization.

[0349] Examples

[0350] Hereinafter, examples of the present invention are shown, but the present invention is not limited to the following examples.

[0351] [Example 1-1]

[0352] <Preparation of pretreatment liquid>

[0353] The following components were mixed to prepare a pretreatment liquid.

[0354] · Glutaric acid [coagulant]... 6.1% by mass

[0355] · Propylene glycol [solvent]... 5.0% by mass

[0356] · OLFINE E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) [surfactant]... 0.5% by mass

[0357] · SUPERFLEX M500 (DKS Co., Ltd.) [aqueous dispersion of polyurethane resin particles]... 7.0% by mass

[0358] · Triisopropanolamine [pH regulator]... 0.2% by mass

[0359] · BYK024 (BYK-Chemie GmbH) [defoamer]... 0.01% by mass

[0360] · Ultrapure water... The balance to make the total pretreatment liquid 100% by mass

[0361] <Preparation of cyan ink>

[0362] (Synthesis of pigment dispersant P1)

[0363] 965 g of dipropylene glycol was added to a 5000 mL three-necked flask equipped with a stirrer and a cooling tube, and the mixture was heated to 85 °C under a nitrogen atmosphere. The following solutions were prepared separately: Solution I obtained by dissolving 640 g of benzyl methacrylate, 340 g of methacrylic acid, and 19.94 g of 2-mercaptopropionic acid in 370.28 g of dipropylene glycol; and Solution II obtained by dissolving 17.69 g of tert-butyl peroxy-2-ethylhexanoate (product name “PERBUTYL O”, manufactured by NOF CORPORATION) in 221.17 g of dipropylene glycol.

[0364] Solution I was added dropwise to the above three-necked flask over 4 hours, and Solution II was added dropwise over 5 hours. After the addition was completed, the reaction was further carried out for 2 hours. By 1 1H-NMR, the disappearance of the monomers was confirmed.

[0365] The obtained reaction solution was heated to 70 °C, 248.02 g of a 50 mass% aqueous potassium hydroxide solution was added thereto, and then 107.48 g of dipropylene glycol and 75.52 g of pure water were added and stirred to obtain a 37 mass% solution of the random polymer. This random polymer was used as the pigment dispersant P1.

[0366] By 1 1H-NMR, the structural units constituting the obtained random polymer were confirmed. Further, the weight-average molecular weight (Mw) was determined by GPC. The weight-average molecular weight (Mw) of the obtained pigment dispersant P1 was 8400, and the acid value was 221.7 mgKOH / g.

[0367] (Preparation of Cyan Pigment Dispersion Liquid)

[0368] 150 parts by mass of the pigment dispersant P1 was dissolved in water to prepare an aqueous polymer solution such that the concentration of the pigment dispersant P1 was approximately 25 mass%. 180 parts by mass of this aqueous polymer solution, 90 parts by mass of a cyan pigment (C.I. Pigment Blue 15:3, product name “PB15:3”, manufactured by Dainichiseika Color&Chemicals Mfg.Co.,Ltd.), and 171.9 parts by mass of water were mixed to obtain a mixed liquid. An aqueous potassium hydroxide solution was added to the obtained mixed liquid and adjusted so that the pH after neutralization became 8.7.

[0369] Next, the neutralized mixed liquid was subjected to a dispersion treatment for 3 hours using a bead mill (bead diameter: zirconia beads). Thus, a cyan pigment dispersion liquid (uncrosslinked dispersion liquid) in which the cyan pigment was dispersed by the pigment dispersant P1 was obtained. Water was added to this cyan pigment dispersion liquid to obtain an uncrosslinked dispersion liquid C1 (pigment concentration 15 mass%).

[0370] Next, with respect to 136 parts by mass of the uncrosslinked dispersion (C1), 3.77 parts by mass of trimethylolpropane polyglycidyl ether (product name “Denacol EX-321”, manufactured by Nagase ChemteX Corporation) and 41.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4 mass%) were added as crosslinking agents, and after reacting at 70°C for 6 hours, it was cooled to 25°C.

[0371] Thereby, the pigment dispersant P1 was crosslinked to obtain a cyan pigment dispersion (crosslinked dispersion) in which the cyan pigment was dispersed by the pigment dispersant P1a. Here, the pigment dispersant P1a is a polymer obtained by crosslinking the pigment dispersant P1, which is an uncrosslinked polymer, with a crosslinking agent.

[0372] Next, ion-exchanged water was added to the above crosslinked dispersion so that the concentration of the pigment became 15 mass%. The obtained liquid was passed through an ultrafiltration device (crossflow ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (size of fine pores: 0.1 μm) at a flow rate of 600 mL per minute for ultrafiltration. At this time, the liquid temperature was adjusted to 25°C, and ultrafiltration was performed 8 times with a volume multiple of the charged liquid as 1 time. Ion-exchanged water was added to the obtained liquid so that the concentration of the pigment became 15 mass%. Thereby, a cyan pigment dispersion was obtained. The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the cyan pigment dispersion was 75 mgKOH / g.

[0373] (Preparation of Cyan Ink)

[0374] The following components were mixed to prepare a cyan ink.

[0375] · The above cyan pigment dispersion... the content as the pigment was 4.0 mass%

[0376] · Propylene glycol (water-soluble organic solvent)... 30.0 mass%

[0377] · Propylene glycol monomethyl ether (water-soluble organic solvent)... 1.0 mass%

[0378] · Neocryl A-1105 (acrylic resin particle dispersion) (manufactured by DSM)... the content as the resin particles was 5.0 mass%

[0379] · Olfine E1010 (acetylene glycol-based surfactant manufactured by Nissin Chemical co.,ltd.)... 1.0 mass%

[0380] · BYK3450 (a silicone surfactant manufactured by BYK-Chemie GmbH) …… 1.0% by mass

[0381] · PVP K15 (polyvinylpyrrolidone K15) …… 0.15% by mass

[0382] · ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Corporation) …… The content of colloidal silica particles is 0.05% by mass

[0383] · Water …… The balance to make the whole ink 100% by mass

[0384] <Preparation of overcoat liquid>

[0385] As the overcoat liquid, an aqueous dispersion of polyurethane resin (product name “EVAFANOL HA-55”, manufactured by NIPPON CARBIDE INDUSTRIES CO., INC.) was prepared. The solid content concentration of the overcoat liquid is 40% by mass, and the viscosity at 25 °C is 250 mPa·s.

[0386] <Manufacture of leather>

[0387] (Preparation of inkjet recording device)

[0388] An inkjet recording device was prepared, which has a conveying mechanism for conveying a substrate, and successively has 4 ink-jet heads for ink application (hereinafter, also simply referred to as “nozzles”) from the upstream side in the conveying direction of the substrate (hereinafter, also simply referred to as the “upstream side”).

[0389] The 4 nozzles are arranged along the conveying direction of the substrate. Hereinafter, the nozzles from the upstream side are sometimes successively referred to as the 1st nozzle, the 2nd nozzle, the 3rd nozzle, and the 4th nozzle. The nozzle is a piezoelectric full-width type nozzle of 1200 dpi / 20 inches wide. The nozzle density is 1200 nozzles per 1 inch. Here, dpi is the abbreviation of dot per inch (dots per inch). All the nozzles are line heads with nozzles arranged in a direction orthogonal to the conveying direction of the substrate (i.e., the width direction of the substrate). As each of the above nozzles, Samba (registered trademark) G3L (manufactured by FUJIFILM DIMATIX, Inc.) was used. The droplet volume of the ink is 2.2 pL.

[0390] (Image recording)

[0391] -Pre-treatment liquid application process-

[0392] Using a corona processor (manufactured by KASUGA DENKI, INC., corona surface modification evaluation device TEC-4AX), corona discharge was carried out on a leather substrate (product name "Cuppuccino CP-830", manufactured by YAMAPLAS CO., LTD.) under the conditions of a discharge gap of 1 mm, 100 W, and 4 m / min, and surface treatment was performed. A pretreatment liquid was applied to the leather substrate after surface treatment using a wire bar. The application mass per unit area of the pretreatment liquid was set to 1.5 g / m 2 ². The coating speed was set to 50 m / min. Here, the application mass of the pretreatment liquid is the value obtained by dividing the mass of the applied pretreatment liquid by the area of the region to which the pretreatment liquid was applied. At the position where the application of the pretreatment liquid was completed, 2 seconds after the completion of the application of the pretreatment liquid to that position, a dryer was used to dry the pretreatment liquid to dry the pretreatment liquid. The drying of the pretreatment liquid was carried out under the conditions of 60 °C for 3 seconds. If measured using a Karl Fischer moisture meter, the residual water content in the pretreatment liquid is 0.01 g / m 2 ² or less.

[0393] - Ink application process, ink drying process -

[0394] Cyan ink was introduced into the nozzle of an inkjet recording device, and the substrate to which the pretreatment liquid was applied was set.

[0395] While moving the substrate to which the pretreatment liquid was applied at a constant speed of 50 m / min, cyan ink was ejected from the nozzle onto the surface of the substrate to which the pretreatment liquid was applied, thereby recording a solid image and the character images shown at 4 points and 8 points. Figure 1 At this time, the droplet volume of the ink was set to 2.1 ng, the Duty ratio was set to 100%, and the ejection frequency was set to 39.37 kHz.

[0396] Then, 2 seconds after the completion of ink application, an infrared (IR) irradiation device (product name "PLC-328", manufactured by Noritake Co., Ltd.) was used to perform infrared (IR) drying on the cyan ink applied to the substrate under the condition that the surface temperature of the ink became 75 °C. Then, a dryer was used to dry with warm air at 80 °C for 20 seconds.

[0397] - Overcoat liquid application process, overcoat liquid drying process -

[0398] While moving the substrate to which the ink was applied at a constant speed of 50 m / min, an overcoat liquid was applied to the surface of the substrate to which the ink was applied using a wire bar coater. The application mass per unit area of the overcoat liquid was set to 25 g / m 2 ². The application mass per unit area of the solid component contained in the overcoat liquid was 10 g / m².2 The substrate with the outer coating liquid was heated in an oven at 130 °C for 2 minutes, thereby obtaining leather.

[0399] In Table 1, the solid content concentration of the outer coating liquid, the application mass per unit area of the solid components contained in the outer coating liquid (in Table 1, "W" o ", unit: g / cm 2 ), the solid content concentration of the ink, the application mass per unit area of the solid components contained in the ink (in Table 1, "W" I ", unit: g / cm 2 ), the solid content concentration of the pretreatment liquid, and the application mass per unit area of the solid components contained in the pretreatment liquid (in Table 1, "W" P ", unit: g / cm 2 ) are recorded.

[0400] [Examples 1-2 to 1-4, Comparative Examples 1-1 to 1-6]

[0401] The solid content concentration of the outer coating liquid and the application mass per unit area of the solid components contained in the outer coating liquid were changed to the values recorded in Table 1. Otherwise, leather was obtained by the same method as in Example 1-1. In addition, the solid content concentration of the outer coating liquid was adjusted by adding water to the outer coating liquid in Example 1-1.

[0402] [Example 1-5]

[0403] The pretreatment liquid was not applied to the leather substrate. Otherwise, leather was obtained by the same method as in Example 1-1.

[0404] [Example 1-6]

[0405] In the ink application step, the dot percentage of the solid image was changed, and the application mass per unit area of the solid components contained in the cyan ink was adjusted to the value recorded in Table 1. Otherwise, leather was obtained by the same method as in Example 1-1.

[0406] Using the obtained leather, evaluations of alcohol resistance, rub resistance, bend resistance, stretchability, and character reproducibility were carried out. The evaluation methods are as follows.

[0407] <Alcohol resistance>

[0408] A cotton swab was wetted with 100% by mass ethanol.

[0409] The solid image was wiped 10 times with the above cotton swab. After wiping 10 times, the surface state of the solid image and the surface state of the cotton swab were visually observed. The evaluation criteria are as follows.

[0410] A: The surface of the solid image has no change and the cotton swab is not colored.

[0411] B: The surface of the solid image has no change, but the cotton swab is colored.

[0412] C: The solid image fades and the cotton swab is colored.

[0413] <Rub resistance>

[0414] Using cotton canvas No. 6, a reciprocating rubbing test of 100 cycles was carried out on the solid image with a weight of 500 g. After the test, the surface state of the solid image and the surface state of the cotton canvas were visually observed. The evaluation criteria are as follows.

[0415] A: The surface of the solid image has no change and the cotton canvas is not colored.

[0416] B: The surface of the solid image has no change, but the cotton canvas is colored.

[0417] C: The solid image fades and the cotton canvas is colored.

[0418] <Bending resistance>

[0419] A 500-cycle 180-degree bending test was carried out on the obtained leather. After the 500-cycle bending test, visual confirmation of cracks was carried out. In the case where no cracks were generated, a further 500-cycle 180-degree bending test (total of 1000 cycles) was carried out. After the 1000-cycle bending test, visual confirmation of cracks was carried out. The evaluation criteria are as follows.

[0420] A: After the 1000-cycle bending test, no cracks were generated.

[0421] B: No cracks were generated after the 500-cycle bending test, but cracks were generated after the 1000-cycle bending test.

[0422] C: Cracks were generated after the 500-cycle bending test.

[0423] <Tensility>

[0424] Using a tensile testing machine (Shimadzu Precision Universal Testing Machine “AUTOGRAPH AGS-J”, manufactured by SHIMADZU CORPORATION), a tensile test was carried out on the obtained leather at 25 °C. For the tensile direction, the test was carried out in such a way that the length of the leather was elongated by 20%. After the 20% tensile test, visual confirmation of cracks was carried out. In the case where no cracks were generated, the test was carried out in such a way that the length of the leather was elongated by 40%. After the 40% tensile test, visual confirmation of cracks was carried out. The evaluation criteria are as follows.

[0425] A: After the 40% tensile test, no cracks occurred.

[0426] B: No cracks occurred after the 20% tensile test, but cracks occurred after the 40% tensile test.

[0427] C: Cracks occurred after the 20% tensile test.

[0428] <Character reproducibility>

[0429] Visually observed the character images shown at 4 o'clock and 8 o'clock. Figure 1 The evaluation criteria are as follows.

[0430] A: The character images at 4 o'clock and 8 o'clock can be reproduced.

[0431] B: The character image at 8 o'clock can be reproduced, but there are parts of the character image at 4 o'clock that cannot be reproduced.

[0432] C: There are parts of the character images at 4 o'clock and 8 o'clock that cannot be reproduced.

[0433] The evaluation results are shown in Table 1.

[0434] [Table 1]

[0435]

[0436] As shown in Table 1, it is known that in Examples 1-1 to 1-6, the following steps are included: applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water to a leather substrate by an inkjet recording method; applying an overcoat liquid containing polyurethane resin particles and water to the leather substrate to which the ink has been applied; and drying the overcoat liquid. The solid content concentration of the overcoat liquid is 20% by mass or more, and in the step of applying the overcoat liquid, the application mass per unit area of the solid components contained in the overcoat liquid is 5 g / cm 2 ~20 g / cm 2 , so leather with excellent alcohol resistance, rubbing resistance, bending resistance, and stretchability can be obtained.

[0437] On the other hand, in Comparative Examples 1-1 to 1-5, the application mass per unit area of the solid components contained in the overcoat liquid is less than 5 g / cm 2 , and the alcohol resistance and rubbing resistance are poor.

[0438] It is known that in Comparative Example 1-6, the application mass per unit area of the solid components contained in the overcoat liquid exceeds 20 g / cm 2 , and the bending resistance and stretchability are poor.

[0439] [Examples 2-1, Examples 2-2]

[0440] <Preparation of Black Ink>

[0441] By the same method as in Example 1-1, a pigment dispersant P1 was obtained.

[0442] (Preparation of Black Pigment Dispersion Liquid)

[0443] 150 parts by mass of the pigment dispersant P1 was dissolved in water to prepare an aqueous polymer solution such that the concentration of the pigment dispersant P1 became approximately 25% by mass. 180 parts by mass of this aqueous polymer solution, 110.0 parts by mass of carbon black (product name "FW182", manufactured by Orion), and 240.0 parts by mass of water were mixed to obtain a mixed liquid. An aqueous potassium hydroxide solution was added to the obtained mixed liquid and adjusted so that the pH after neutralization became 8.7.

[0444] Next, a bead mill (bead diameter: zirconia beads) was used to perform a dispersion treatment on the neutralized mixed liquid for 3 hours. Thereby, a black pigment dispersion liquid (uncrosslinked dispersion liquid) in which the black pigment was dispersed by the pigment dispersant P1 was obtained. Water was added to the black pigment dispersion liquid to prepare an uncrosslinked dispersion liquid K1 (pigment concentration 15% by mass).

[0445] Next, with respect to 136 parts by mass of the uncrosslinked dispersion liquid (K1), 2.40 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 26.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) were added as crosslinking agents, and after reacting at 70°C for 6 hours, it was cooled to 25°C. As a result, the pigment dispersant P1 was crosslinked to obtain a black pigment dispersion liquid (crosslinked dispersion liquid) in which the black pigment was dispersed by the pigment dispersant P1a. Here, the pigment dispersant P1a is a polymer obtained by crosslinking the pigment dispersant P1, which is an uncrosslinked polymer, with a crosslinking agent.

[0446] Next, with respect to the above crosslinked dispersion liquid, ion-exchanged water was added so that the concentration of the pigment became 15% by mass. The obtained liquid was passed through an ultrafiltration device (cross-flow type ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (size of fine pores: 0.1 μm) at a flow rate of 600 mL per minute for ultrafiltration. At this time, the liquid temperature was adjusted to 25°C, and ultrafiltration was performed 8 times with 1 time being 1 times the volume multiple of the charged liquid. With respect to the obtained liquid, ion-exchanged water was added so that the concentration of the pigment became 15% by mass. Thereby, a black pigment dispersion liquid was obtained. The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the black pigment dispersion liquid was 105 mgKOH / g.

[0447] (Preparation of Black Ink K1)

[0448] Black Ink K1 was prepared by mixing the following components.

[0449] · The above black pigment dispersion... The content of the pigment is 5.0% by mass

[0450] · Propylene glycol (water-soluble organic solvent)... 30.0% by mass

[0451] · Propylene glycol monomethyl ether (water-soluble organic solvent)... 1.0% by mass

[0452] · Neocryl A-1105 (acrylic polymer resin particle dispersion) (manufactured by DSM Corporation)... The content of the resin particles is 5.0% by mass

[0453] · Olfine E1010 (acetylene glycol-based surfactant manufactured by Nissin Chemical co.,ltd.)... 1.0% by mass

[0454] · BYK3450 (silicone-based surfactant manufactured by BYK-Chemie GmbH)... 1.0% by mass

[0455] · PVPK15 (polyvinylpyrrolidone K15)... 0.15% by mass

[0456] · ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Corporation)... The content of the colloidal silica particles is 0.05% by mass

[0457] · Water... The balance to make up 100% by mass

[0458] <Preparation of Magenta Ink>

[0459] (Preparation of Magenta Pigment Dispersion 1)

[0460] The following points were changed, and except for this, Magenta Pigment Dispersion 1 was prepared by the same method as the preparation of the black pigment dispersion.

[0461] The operation of "mixing 180 parts by mass of the polymer aqueous solution, 110.0 parts by mass of carbon black, and 240.0 parts by mass of water" was changed to the operation of "mixing 180 parts by mass of the polymer aqueous solution, 90 parts by mass of magenta pigment (C.I. Pigment Red 122, FUJI Fast Red (registered trademark), manufactured by FujiPigment Co.,Ltd.), and 171.9 parts by mass of water".

[0462] Change the operation of "adding 2.40 parts by mass of crosslinking agent and 26.2 parts by mass of boric acid aqueous solution" to the operation of "adding 3.00 parts by mass of crosslinking agent and 32.8 parts by mass of boric acid aqueous solution".

[0463] The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the magenta pigment dispersion liquid 1 is 105 mgKOH / g.

[0464] (Preparation of magenta pigment dispersion liquid 2)

[0465] Change the magenta pigment to C.I. Pigment Red 150, and except for this, the magenta pigment dispersion liquid 2 was prepared by the same method as the preparation of the magenta pigment dispersion liquid 1.

[0466] The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the magenta pigment dispersion liquid 2 is 105 mgKOH / g.

[0467] (Preparation of magenta ink M3)

[0468] Mix the following components to prepare magenta ink M3.

[0469] · The above magenta pigment dispersion liquid 1... the content as a pigment is 4.5% by mass

[0470] · The above magenta pigment dispersion liquid 2... the content as a pigment is 1.5% by mass

[0471] · Propylene glycol (water-soluble organic solvent)... 30.0% by mass

[0472] · Propylene glycol monomethyl ether (water-soluble organic solvent)... 1.0% by mass

[0473] · Neocryl A-1105 (acrylic polymer resin particle dispersion liquid) (manufactured by DSM Corporation)... the content as resin particles is 5.0% by mass

[0474] · Olfine E1010 (acetylene glycol-based surfactant manufactured by Nissin Chemical co.,ltd.)... 1.0% by mass

[0475] · BYK3450 (silicone-based surfactant manufactured by BYK-Chemie GmbH)... 1.0% by mass

[0476] · PVPK15 (polyvinylpyrrolidone K15)... 0.15% by mass

[0477] · ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Corporation) …… The content of colloidal silica particles is 0.05% by mass

[0478] · Water… The balance to make up 100% by mass

[0479] <Preparation of yellow ink>

[0480] (Preparation of yellow pigment dispersion y1)

[0481] The following points were changed, and except for these, the yellow pigment dispersion y1 was prepared by the same method as the preparation of the black pigment dispersion.

[0482] The operation of "mixing 180 parts by mass of the aqueous polymer solution, 110.0 parts by mass of carbon black, and 240.0 parts by mass of water" was changed to the operation of "mixing 180 parts by mass of the aqueous polymer solution, 75 parts by mass of a yellow pigment (C.I. Pigment Yellow 74, FUJI Fast Red (registered trademark), manufactured by Fuji Pigment Co., Ltd.), and 140 parts by mass of water".

[0483] The operation of "adding 2.40 parts by mass of a crosslinking agent and 26.2 parts by mass of an aqueous boric acid solution" was changed to the operation of "adding 3.60 parts by mass of a crosslinking agent and 39.4 parts by mass of an aqueous boric acid solution".

[0484] The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the yellow pigment dispersion y1 is 105 mgKOH / g.

[0485] (Preparation of yellow ink Y1)

[0486] The following components were mixed to prepare yellow ink Y1.

[0487] · The above yellow pigment dispersion y1… The content of the pigment is 4.0% by mass

[0488] · Propylene glycol (water-soluble organic solvent) … 30.0%

[0489] · Propylene glycol monomethyl ether (water-soluble organic solvent) … 1.0%

[0490] · Neocryl A-1105 (acrylic resin particle dispersion) (manufactured by DSM) … The content of resin particles is 5.0% by mass

[0491] · Olfine E1010 (acetylene glycol-based surfactant manufactured by Nissin Chemical co., ltd.) … 1.0%

[0492] · BYK3450 (a silicone surfactant manufactured by BYK-Chemie GmbH) …… 1.0% by mass

[0493] · PVP K15 (polyvinylpyrrolidone K15) …… 0.15% by mass

[0494] · ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Corporation) …… 0.05% by mass as the content of colloidal silica particles

[0495] · Water …… the balance to make up 100% by mass

[0496] <Manufacture of leather>

[0497] Cyan ink, black ink, magenta ink, and yellow ink were respectively introduced into the first nozzle, second nozzle, third nozzle, and fourth nozzle of the inkjet recording apparatus used in Example 1-1.

[0498] The solid content concentration of the overcoat liquid and the mass per unit area of the solid content contained in the overcoat liquid and each ink were changed to the values described in Table 2. Otherwise, leather was obtained by the same method as in Example 1-1.

[0499] In Example 2-1, a solid image was recorded in the order of cyan ink and magenta ink.

[0500] In Example 2-2, a solid image was recorded in the order of cyan ink, magenta ink, yellow ink, and black ink.

[0501] Similar to Example 1-1, evaluations of alcohol resistance, rub resistance, bend resistance, and stretchability were performed.

[0502] The evaluation results are shown in Table 2.

[0503] [Table 2]

[0504]

[0505] As shown in Table 2, it is known that even when recording an image using multiple inks, leather with excellent alcohol resistance, rub resistance, bend resistance, and stretchability can be obtained.

[0506] [Examples 3-1 to 3-6, Comparative Examples 3-1 to 3-6]

[0507] The leather substrate was changed to pineapple leather (white) manufactured by Ananas Anam Co., Ltd., and the leather was obtained by the same method as in Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-6 except for this.

[0508] Similar to Example 1-1, evaluations of alcohol resistance, rub resistance, bend resistance, and stretchability were conducted. It is known that in Examples 3-1 to 3-6, the same rub resistance as in Examples 1-1 to 1-6 was shown. On the other hand, it is known that in Comparative Examples 3-1 to 3-6, the rub resistance decreased significantly.

[0509] [Example 4-1]

[0510] <Preparation of topcoat liquid>

[0511] 80 parts by mass of an aqueous dispersion of a polyurethane resin (product name “EVAFANOL HA-55”, manufactured by NICCA CHEMICAL CO., LTD.) and 20 parts by mass of an aqueous dispersion of a triazine-type ultraviolet absorber (product name “CHIGUARD 5400WB”, manufactured by Kusumoto Chemicals, Ltd., concentration of ultraviolet absorber 30 mass%) were mixed to obtain a topcoat liquid. The solid content concentration of the topcoat liquid was 38 mass%, and the viscosity at 25 °C was 300 mPa·s.

[0512] The topcoat liquid was changed to contain an ultraviolet absorber, and the leather was obtained by the same method as in Example 1-1 except for this. The mass per unit area of the solid components contained in the topcoat liquid was 9.5 g / m 2 .

[0513] Similar to Example 1-1, evaluations of alcohol resistance, rub resistance, bend resistance, stretchability, and character reproducibility were conducted. Similar to Example 1-1, all the evaluation results were A.

[0514] [Examples 5-1 to 5-8]

[0515] <Preparation of yellow inks Y2 to Y7>

[0516] (Preparation of yellow pigment dispersions y2 to y7)

[0517] The pigments used in the preparation of the yellow pigment dispersion in Example 2-1 were changed to the pigments shown below, and yellow pigment dispersions y2 to y7 were prepared by the same method as in the preparation of the yellow pigment dispersion in Example 2-1 except for this.

[0518] · Pigment of Pigment Dispersion Liquid y2: C.I. Pigment Yellow 109 (Product Name “Irgazin Yellow L 1030”, manufactured by BASF)

[0519] · Pigment of Pigment Dispersion Liquid y3: C.I. Pigment Yellow 110 (Product Name “Irgazin Yellow D 1999”, manufactured by BASF)

[0520] · Pigment of Pigment Dispersion Liquid y4: C.I. Pigment Yellow 184 (Product Name “Hostaperm Oxide Yellow BV02”, manufactured by Clariant)

[0521] · Pigment of Pigment Dispersion Liquid y5: C.I. Pigment Yellow 120 (Product Name “Ink Jet Yellow H2G”, manufactured by Clariant)

[0522] · Pigment of Pigment Dispersion Liquid y6: C.I. Pigment Yellow 151 (Product Name “Hostaperm Yellow H4G”, manufactured by Clariant)

[0523] · Pigment of Pigment Dispersion Liquid y7: C.I. Pigment Yellow 155 (Product Name “NOVOPERM YELLOW 4G”, manufactured by Clariant)

[0524] (Preparation of Yellow Inks Y2 - Y7)

[0525] Yellow inks Y2 - Y7 were prepared by using yellow pigment dispersion liquids y2 - y7 to replace yellow pigment dispersion liquid y1, and in other respects, by the same method as the preparation of yellow ink Y1.

[0526] The inks in Example 4 - 1 were changed to yellow inks Y1 - Y7, and in other respects, the leathers of Examples 5 - 1 to 5 - 8 were obtained by the same method as Example 4 - 1.

[0527] In Examples 5 - 1 to 5 - 8, evaluations of alcohol resistance, rub resistance, bend resistance, stretchability, and character reproducibility were carried out in the same manner as in Example 1 - 1.

[0528] Moreover, in Example 4 - 1, Examples 5 - 1 to 5 - 8, evaluations of light resistance were carried out. The evaluation method is as follows.

[0529] <Light Resistance>

[0530] Using a weather resistance testing machine (product name "Eye Super UV Tester SUV-W161", manufactured by Iwasaki Electric Co., Ltd.), a light irradiation test was conducted on the image recording surface of each leather. Regarding the irradiation conditions, the UV illuminance was set to 100 mW / cm 2 , the light source was set to a metal halide lamp, the wavelength range was set to 300 nm to 400 nm (filtered out wavelengths outside 300 nm to 400 nm), and the irradiation time was set to 50 hours. In the image recording objects before and after light irradiation, a fluorescence spectrophotometer (product name "FD-7", manufactured by Konica Minolta, Inc.) was used to measure L * , a * , b * values, and ΔE was calculated using the following formula. The evaluation criteria are as follows.

[0531] △E = 〔(△L * ) 2 +(△a * ) 2 +(△b * ) 2 〕 1 / 2

[0532] △L * refers to the difference in L * between the image recording objects before and after light irradiation.

[0533] △a * refers to the difference in a * between the image recording objects before and after light irradiation.

[0534] △b * refers to the difference in b * between the image recording objects before and after light irradiation.

[0535] A: ΔE is 1 or less.

[0536] B: ΔE exceeds 1 and is 3 or less.

[0537] C: ΔE exceeds 3.

[0538] The evaluation results are shown in Table 3. In Table 3, "PB" refers to C.I. Pigment Blue. "PY" refers to C.I. Pigment Yellow.

[0539] [Table 3]

[0540]

[0541] As shown in Table 3, in Examples 5-2 to 5-7 where yellow ink was used, the pigment was at least one selected from the group consisting of C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 184, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, and C.I. Pigment Yellow 155. Therefore, compared with Example 5-1, the lightfastness was excellent.

[0542] Moreover, it is known that the pigment is at least one selected from the group consisting of C.I. Pigment Yellow 110 and C.I. Pigment Yellow 184. Therefore, the lightfastness is even more excellent. In vehicle seats, high lightfastness is required. Therefore, the leather manufactured by the manufacturing method of the leather of the present invention is suitable for vehicle seats.

[0543] [Example 6-1]

[0544] In Example 1-1, an aqueous dispersion of a polyurethane resin (product name "EVAFANOL HA-55", manufactured by NICCACHEMICAL CO., LTD.) was used to replace the acrylic resin particles in the cyan ink. Except for this, the cyan ink was prepared in the same manner. In addition, it was assumed that the content of the polyurethane resin particles in Example 6-1 was the same as the content of the acrylic resin particles in Example 1-1.

[0545] Using the prepared cyan ink, leather was produced by the same method as in Example 1-1, and the alcohol resistance, bend resistance, stretchability, and character reproducibility were evaluated in the same manner as in Example 1-1.

[0546] Regarding the rub resistance, different from Example 1-1, the evaluation was carried out by the following evaluation method.

[0547] <Rub resistance 2>

[0548] Using No. 6 cotton canvas, a 500 g weight was applied to the image recording surface of each leather for 500 reciprocating Taber abrasion tests. After the abrasion test, the surface state of the image recording surface and the surface state of the cotton canvas were visually observed. The evaluation criteria are as follows.

[0549] A: The image recording surface has no change, and the cotton canvas is not colored.

[0550] B: The image recording surface has no change, but the cotton canvas is colored.

[0551] C: The image recording surface fades, and the cotton canvas is colored.

[0552] The evaluation results are shown in Table 4.

[0553] [Table 4]

[0554]

[0555] As shown in Table 4, in Example 6-1 where the resin particles are polyurethane resin particles, all evaluation results are A, and the rub resistance is more excellent compared to Example 1-1.

[0556] In addition, regarding the inventions of Japanese Patent Application No. 2022-176770 filed on November 2, 2022 and Japanese Patent Application No. 2023-081903 filed on May 17, 2023, the whole of them is incorporated herein by reference. And all documents, patent applications, and technical specifications described in this specification are incorporated herein by reference to the same extent as the case where each of the documents, patent applications, and technical specifications incorporated by reference is specifically and individually described.

Claims

1. A method for manufacturing leather, which comprises the following steps: Applying an ink containing a pigment, resin particles, a water-soluble organic solvent, and water to a leather substrate by an inkjet recording method; Applying an overcoat liquid containing polyurethane resin particles and water to the leather substrate to which the ink has been applied; and Drying the overcoat liquid, The solid content concentration of the overcoat liquid is 20% by mass or more, In the step of applying the outer coating liquid, the application mass per unit area of the solid component contained in the outer coating liquid is 5 g / cm 2 to 20 g / cm 2 .

2. The method for manufacturing leather according to claim 1, wherein, The viscosity of the overcoat liquid is 200 mPa·s or more.

3. The method for manufacturing leather according to claim 1 or 2, wherein, In the step of applying the ink, when the application mass per unit area of the solid component contained in the ink is W I g / cm 2 and the application mass per unit area of the solid component contained in the overcoat liquid is W O g / cm 2 , W O / W I is 5 or more.

4. The method for manufacturing leather according to claim 1 or 2, wherein, The overcoat liquid further contains an ultraviolet absorber.

5. The method for manufacturing leather according to claim 1 or 2, which further comprises the following steps: Applying a pretreatment liquid containing a coagulant and water to the leather substrate, After applying the pretreatment liquid, applying the ink to the leather substrate to which the pretreatment liquid has been applied.

6. The method for manufacturing leather according to claim 1 or 2, wherein, In the step of applying the ink, an inkjet head with a nozzle density of 600 nozzles or more per 1 inch is used to apply the ink.

7. The method for manufacturing leather according to claim 1 or 2, wherein, In the step of applying the ink, the ink is applied by a single-pass method.

8. The method for manufacturing leather according to claim 1 or 2, wherein, The solid content concentration of the overcoat liquid is 30% by mass or more.

9. The method for manufacturing leather according to claim 1 or 2, wherein, In the step of drying the overcoat liquid, heating is performed at a temperature of 80°C or higher.

10. The method for manufacturing leather according to claim 1 or 2, wherein, The leather substrate is a plant-derived substrate.

11. The method for manufacturing leather according to claim 1 or 2, wherein, The pigment contained in the ink is at least one selected from the group consisting of C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 184, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, and C.I. Pigment Yellow 155.

12. The method for manufacturing leather according to claim 11, wherein, The pigment contained in the ink is at least one selected from the group consisting of C.I. Pigment Yellow 110 and C.I. Pigment Yellow 184.

13. The method for manufacturing leather according to claim 1 or 2, wherein, The resin particles contained in the ink are polyurethane resin particles.

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