Leather manufacturing method

Abstract

Provided is a method for producing leather, comprising: a step in which a stealth ink containing an infrared-absorbing compound, a fluorescent compound, or a photochromic compound is applied to a leather base material to record a code image; and a step for forming an overcoat layer on the leather substrate on which the code image is recorded.

Description

Technical Field

[0001] This invention relates to a method for manufacturing leather. Background Technology

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

[0003] For example, Japanese Patent Application Publication No. 2019-77070 discloses an inkjet printing method for printing on leather with a surface made of synthetic resin. This inkjet printing method includes the following steps: heating the surface of the leather, at least the surface of which is made of synthetic resin, to at least 40°C; spraying ink contained in a water-based inkjet ink group onto the leather surface by inkjet spraying; and heating the leather surface with the sprayed ink to at least 60°C. The inkjet printing method is characterized in that the ink contained in the water-based inkjet ink group contains at least water (A) and pigment. The ink comprises a material (B), a water-soluble organic solvent component (C), a surfactant (D), and resin microparticles (E), wherein the glass transition temperature of the resin microparticles (E) is below 0°C, and the ink contains at least 8% by mass and 23% by mass of at least one substituted butanol selected from the group consisting of 3-methoxy-1-butanol and 3-methoxy-3-methyl-1-butanol as a water-soluble organic solvent component (C). The water-based inkjet ink group includes white ink containing a white pigment as pigment (B) and colored ink containing pigments other than white as pigment (B).

[0004] Furthermore, in recent years, anti-counterfeiting measures have been required for products using leather. As an anti-counterfeiting measure, methods using infrared-absorbing ink to record coded images are known.

[0005] For example, Japanese Patent Application Publication No. 2008-144004 discloses inkjet recording inks containing infrared-absorbing oxocyanine compounds. Summary of the Invention

[0006] The technical problem to be solved by the invention For anti-counterfeiting purposes, when coded images are recorded on leather, it is required to ensure invisibility, readability after wiping, and readability after wiping with alcohol.

[0007] The present invention was made in view of this situation, and the objective of one embodiment of the present invention is to provide a method for manufacturing leather that records a code image with excellent visibility, readability after wiping and readability after alcohol wiping.

[0008] means for solving technical problems The present invention includes the following methods.

[0009] <1> A method for manufacturing leather, comprising: A process of applying invisible ink containing infrared absorbing compounds, fluorescent compounds, or photochromic compounds to a leather substrate with a water contact angle of less than 100° to record coded images; and The process of forming an outer coating on a leather substrate containing coded images.

[0010] <2> According to the leather manufacturing method described in <1>, wherein, The code image is a barcode, QR code (registered trademark), or dot code.

[0011] <3> According to the leather manufacturing method described in <1> or <2>, wherein, The code image is dotted code.

[0012] <4> The method for manufacturing leather according to any one of <1> to <3>, wherein, Invisible ink contains infrared-absorbing compounds.

[0013] <5> The method for manufacturing leather according to any one of <1> to <4>, wherein, The infrared absorbing compound is selected from at least one of the groups consisting of compounds represented by the following formulas (1) and (2).

[0014] [Chemical Formula 1] [Chemical Formula 2] In Equation 1, Y 1 and Y 2 Each group of nonmetallic atoms that forms an aliphatic ring or heterocycle is represented independently, M + L represents a proton, a monovalent alkali metal cation, or an organic cation. 1 This indicates a methine chain consisting of 5 or 7 methine groups, with the central methine group having a substituent represented by formula A below. -S A -T A Formula A In equation A, S A Represents single bond, alkylene, alkenylene, ynylene, -O-, -S-, -NR L1 -, -C(=O)-, -C(=O)O-, -C(=O)NR L1 -、-S(=O)2-、-OR L2- or a group consisting of at least two of these, R L1 R represents a hydrogen atom, halogen atom, alkyl, aryl, or monovalent heterocyclic group. L2 Indicates alkylene, arylene, or divalent heterocyclic group, T A The following groups are represented: halogen, alkyl, cycloalkyl, aryl, monovalent heterocyclic, cyano, hydroxyl, formyl, carboxyl, amino, thiol, sulfonyl, phosphoryl, boronyl, vinyl, ethynyl, trialkylsilyl, or trialkoxysilyl. A Indicates a single bond or alkylene group, and T A When representing an alkyl group, S A and T A The total number of carbon atoms contained therein is 3 or more. This indicates the bonding site with the methylene group in the center of the methylene chain.

[0015] In equation (2), ring A and ring B independently represent aromatic rings or heteroaromatic rings, respectively, and X A and X B Each of the following independently represents a monovalent substituent, G A and G B Each of these groups represents a monovalent substituent independently, and kA represents 0 to n. A Integers, kB represents 0 to n B an integer, n A and n B They represent G that can be substituted on ring A or ring B, respectively. A and G B The largest integer, X A With G A They can bond together to form a ring, X B With G B They can bond together to form a ring, G A and G B When multiple G exist, A Each other and G B They can bond with each other to form a ring structure.

[0016] <6> The method for manufacturing leather according to any one of <1> to <5>, wherein, Invisible ink is applied using an inkjet recording method.

[0017] <7> The method for manufacturing leather according to any one of <1> to <6>, wherein, The process of forming the outer coating includes the process of applying the outer coating liquid.

[0018] <8> According to the leather manufacturing method described in <7>, wherein, The topical coating contains silicone compounds.

[0019] <9> The method for manufacturing leather according to any one of <1> to <8> further includes a step of applying visible ink containing a colorant to a leather substrate to record a colored image. Record coded images on a leather substrate on which colored images have been recorded.

[0020] <10> According to the leather manufacturing method described in <9>, wherein, It is evident that the colorants contained in the ink do not absorb infrared light.

[0021] <11> According to the leather manufacturing method described in <9> or <10>, wherein, Visible ink is applied through inkjet recording.

[0022] <12> The method for manufacturing leather according to any one of <9> to <11>, wherein, Invisible inks, visible inks, and topcoats all contain urethane resin particles.

[0023] <13> The method for manufacturing leather according to any one of <9> to <12>, wherein, Invisible inks, visible inks, and topcoats all contain water.

[0024] Invention Effects According to the present invention, a method for manufacturing leather is provided, which produces leather containing code images that are invisible, readable after wiping, and readable after wiping with alcohol. Detailed Implementation

[0025] The method for manufacturing leather according to the present invention will be described in detail below.

[0026] In this invention, the numerical range indicated by “~” represents the range included by taking the values ​​before and after “~” as the minimum and maximum values, respectively.

[0027] In the numerical ranges described in stages in this invention, the upper or lower limit value recorded within a certain numerical range can be replaced with the upper or lower limit value of other numerical ranges described in stages. Furthermore, in the numerical ranges described in this invention, the upper or lower limit value recorded within a certain numerical range can also be replaced with the values ​​shown in the embodiments.

[0028] In this invention, the amount of each component in the composition, when there are multiple substances corresponding to each component in the composition, unless otherwise specified, refers to the total amount of the multiple substances present in the composition.

[0029] In this invention, a combination of two or more preferred methods is a more preferred method.

[0030] In this invention, the term "process" includes not only independent processes, but also processes that can achieve their intended purpose, even if they cannot be clearly distinguished from other processes.

[0031] In this invention, "image" refers to the entire film formed by ink, and "image recording" refers to the formation of an image (i.e., the film).

[0032] Furthermore, the concept of "image" in this invention also includes solid images.

[0033] In this invention, "synthetic leather" differs from natural leather made from animal hides; it refers to artificially manufactured materials. The concept of "synthetic leather" in this invention also includes artificial leather, synthetic leather, and imitation leather.

[0034] [Leather manufacturing methods] The leather manufacturing method of the present invention includes: a step of applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound to a leather substrate to record a coded image; and a step of forming an outer coating on the leather substrate on which the coded image is recorded.

[0035] In the leather manufacturing method of the present invention, leather with recorded coded images can be easily obtained by recording coded images on a leather substrate and forming an outer coating on the leather substrate with recorded coded images. The leather manufacturing method of the present invention does not require special manufacturing steps and is useful as a method for manufacturing leather with recorded coded images.

[0036] Furthermore, since the coded images are recorded using invisible ink containing infrared-absorbing compounds, fluorescent compounds, or photochromic compounds, their invisibility is excellent. Moreover, by forming an outer coating on the leather substrate containing the coded images, readability after wiping and after wiping with alcohol is excellent.

[0037] In contrast, Patent Document 1 does not describe a method for recording code images. Furthermore, Patent Document 2 does not focus on the leather substrate as the base material. Neither Patent Document 1 nor Patent Document 2 describes any process related to forming the outer coating.

[0038] The following describes each step of the leather manufacturing method of the present invention.

[0039] <Invisible Ink Application Process> The leather manufacturing method of the present invention includes a step of applying an invisible ink containing an infrared absorbing compound, a fluorescent compound or a photochromic compound to a leather substrate to record a coded image (hereinafter referred to as the "invisible ink application step").

[0040] (Leather substrate) In this invention, the leather substrate can be appropriately selected from substrates commonly used in the manufacture of natural or synthetic leather. The leather manufactured by the leather manufacturing method of this invention can be either natural or synthetic leather, but is preferably synthetic leather.

[0041] Furthermore, from the viewpoint of improving stain resistance and abrasion resistance, synthetic leather that is commonly available sometimes has an outer coating containing a silicone-based lubricant on its surface. It is also preferable to use the material before applying the outer coating as the leather substrate.

[0042] In recent years, "vegan leather," a type of base material manufactured without the use of animal-derived raw materials, has attracted attention. Vegan leather is preferred as a leather base material. Vegan leather can contain both petroleum-derived and plant-derived base materials.

[0043] From an environmental suitability perspective, the leather substrate is preferably a resin substrate used in the manufacture of synthetic leather, and more preferably a plant-derived substrate. A plant-derived substrate refers to a substrate made from plants. Examples of plants include pineapple, apple, grape, and mushroom. Plant-derived substrates may contain petroleum-derived components.

[0044] As a preferred example of a leather substrate, pineapple leather (Pinatex) manufactured by Ananas Anam is an example. Pineapple leather is a plant-derived substrate containing approximately 72% by weight of pineapple leaf fiber.

[0045] Preferably, the surface of the leather substrate is textured. Texture refers to a raised or recessed pattern of wrinkles.

[0046] The shape of the leather substrate is not particularly limited; for example, it can be sheet-like.

[0047] The thickness of the leather substrate is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0048] From a readability point of view, the water contact angle of the leather substrate is 100° or less, preferably 90° or less.

[0049] The lower limit of the contact angle is, for example, 50°.

[0050] Regarding the water contact angle, approximately 2 μL of distilled water was dropped onto the surface of the leather substrate to be measured, and the result was measured using a contact angle meter after 1000 microseconds. The water contact angle was measured, for example, using a contact angle meter (product name "Drop MasterDMo-501", manufactured by Kyowa Interface Science Co.,LTD.).

[0051] (Invisible ink) The invisible ink applied during the invisible ink application process contains infrared absorbing compounds, fluorescent compounds, or photochromic compounds.

[0052] Invisible inks may contain only one of the infrared absorbing compound, fluorescent compound, and photochromic compound, or may contain two or more of them.

[0053] -Infrared absorbing compounds- In this invention, the term "infrared absorbing compound" refers to a compound that has a maximum absorption wavelength in the range of 750 nm to 1,400 nm.

[0054] From the viewpoint of invisibility, the infrared absorbing compound is preferably selected from at least one of the groups consisting of compounds represented by the following formulas (1) and (2).

[0055] [Chemical Formula 3] [Chemical Formula 4] In equation (1), Y 1 and Y 2 Each group of nonmetallic atoms that forms an aliphatic ring or heterocycle is represented independently, M + L represents a proton, a monovalent alkali metal cation, or an organic cation. 1 This indicates a methine chain containing 5 or 7 methines, wherein the central methine of the methine chain has a substituent represented by the following formula A.

[0056] -S A -T A Formula A In equation A, S A Represents single bond, alkylene, alkenylene, ynylene, -O-, -S-, -NR L1 -, -C(=O)-, -C(=O)O-, -C(=O)NR L1 -、-S(=O)2-、-OR L2 - or a group consisting of at least two of these, R L1R represents a hydrogen atom, halogen atom, alkyl, aryl, or monovalent heterocyclic group. L2 Indicates alkylene, arylene, or divalent heterocyclic group, T A The following groups are represented: halogen, alkyl, cycloalkyl, aryl, monovalent heterocyclic, cyano, hydroxyl, formyl, carboxyl, amino, thiol, sulfonyl, phosphoryl, boronyl, vinyl, ethynyl, trialkylsilyl, or trialkoxysilyl. A Indicates a single bond or alkylene group, and T A When representing an alkyl group, S A and T A The total number of carbon atoms contained therein is 3 or more. This indicates the bonding site with the methylene group in the center of the methylene chain.

[0057] In equation (2), ring A and ring B independently represent aromatic rings or heteroaromatic rings, respectively, and X A and X B Each of the following independently represents a monovalent substituent, G A and G B Each of these groups represents a monovalent substituent independently, and kA represents 0 to n. A Integers, kB represents 0 to n B an integer, n A and n B They represent G that can be substituted on ring A or ring B, respectively. A and G B The largest integer, X A With G A They can bond together to form a ring, X B With G B They can bond together to form a ring, G A and G B When multiple G exist, A Each other and G B They can bond with each other to form a ring structure.

[0058] For details regarding the compounds represented by formulas (1) and (2), please refer to International Publication No. 2021 / 065151.

[0059] <<Compounds represented by formula (1)>> [Y] 1 and Y 2 ] Y 1 and Y 2 The atoms can be the same or different sets of non-metallic atoms, but from the perspective of synthetic suitability, the same set of non-metallic atoms is preferred.

[0060] In equation (1), Y 1and Y 2 Preferably, each group of nonmetallic atoms forming the heterocycle is represented independently; more preferably, groups of nonmetallic atoms forming the same heterocycle are used. From the viewpoint of invisibility, Y 1 and Y 2 The heterocycle formed is preferably a barbiturate ring.

[0061] [M] + ] M + This represents a proton, a monovalent alkali metal cation, or an organic cation. From the viewpoint of improving the lightfastness and damp heat resistance of the obtained code image, M... + The preferred form is a monovalent alkali metal cation.

[0062] Among them, the monovalent alkali metal cation is preferably Li + Na + K + 、Rb + or Cs + Li is preferred. + Na + K + 、Rb + or Cs + Li is further preferred. + Na + or K + .

[0063] [L] 1 ] L 1 This indicates a methine chain consisting of 5 or 7 methines, with the methine at the center of the chain having a substituent represented by formula A.

[0064] L 1 It indicates a methine chain consisting of 5 or 7 methines, preferably a methine chain consisting of 5 methines.

[0065] The methines in the above-mentioned methine chain, except for the central methine, may be substituted, but are preferably unsubstituted.

[0066] The methine chain can have cross-linked structures at any position. For example, adjacent carbon atoms of the methine can cross-link to form a ring structure. Furthermore, by introducing a ring structure, the lightfastness and other properties of the coded images obtained using invisible ink can be controlled. The ring structure can be appropriately determined according to the intended use of the invisible ink. There are no particular limitations on the aforementioned ring structure; an aliphatic ring is preferred, especially a 5-membered or 6-membered aliphatic ring.

[0067] Specifically, L 1Preferably, the group is represented by the following formula L1-1, L1-2, L2-1 or L2-2, and more preferably, the group is represented by the following formula L1-1 or L1-2.

[0068] [Chemical Formula 5] In formulas L1-1, L1-2, L2-1, and L2-2, A represents the substituent represented by formula A, and the wavy lines independently represent L in formula (1). 1 Bonding sites outside of the structure.

[0069] Y L This represents the group of nonmetallic atoms that form aliphatic rings or heterocycles, preferably the group of nonmetallic atoms that form aliphatic rings. L Alkyl groups are preferred, and examples of alkyl groups include -CH2CH2- and -CH2C(Z)2-CH2-. The aliphatic ring is preferably a 5-membered or 6-membered aliphatic ring.

[0070] -Substituents represented by formula A- In formula A, S A Represents single bond, alkylene, alkenylene, ynylene, -O-, -S-, -NR L1 -, -C(=O)-, -C(=O)O-, -C(=O)NR L1 -、-S(=O)2-、-OR L2 - or a group consisting of at least two of these. From the perspective of improving the invisibility of the obtained code image, S A Preferably, it is a single bond, an alkylene group, an alkenyl group, or an alkyne group, and more preferably a single bond.

[0071] In equation A, T A The group can be represented by halogen, alkyl, aryl, monovalent heterocyclic, cyano, hydroxyl, formyl, carboxyl, amino, thiol, sulfonyl, phosphoryl, boroalkyl, vinyl, ethynyl, trialkylsilyl or trialkoxysilyl, preferably aryl, monovalent heterocyclic or trialkylsilyl.

[0072] From the perspective of dispersion, in equation A, T A Preferably, it contains a heterocyclic group, aryl group, or halogen atom.

[0073] From the viewpoint of further improving invisibility, the compound represented by formula (1) is preferably the compound represented by the following formula (1A).

[0074] [Chemical Formula 6] In equation (1A), M +L represents a proton, a monovalent alkali metal cation, or an organic cation. 1 This indicates a methine chain consisting of 5 or 7 methines, with the central methine having a substituent represented by formula A above.

[0075] R 1 R 2 R 3 and R 4 Each of these groups can independently represent a hydrogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group. X can independently represent an O atom, a S atom, or a Se atom.

[0076] [L] 1 and M + ] In equation (1A), L 1 and M + L in equation (1) 1 and M + The meanings are the same, and the preferred selection methods are also the same.

[0077] [R] 1 R 2 R 3 and R 4 ] In equation (1A), R 1 R 2 R 3 and R 4 Each of the hydrogen atom, alkyl group, aryl group, or monovalent heterocyclic group is independently represented. From the viewpoint of the lightfastness and invisibility of the obtained code image, hydrogen atom or aryl group is preferred, and hydrogen atom or phenyl group is even more preferred.

[0078] R 1 R 2 R 3 and R 4 The aryl group is preferably an aryl group with 6 to 20 carbon atoms, more preferably phenyl or naphthyl, and even more preferably phenyl.

[0079] The aryl group may be unsubstituted, but it is preferred to have substituents. From the viewpoint of dispersibility and associative stability, the substituent placement is preferably meta or para, and more preferably meta, relative to the bonding sites with other structures in formula (1A). More preferably, the meta position has a polar group.

[0080] From the viewpoint of lightfastness and resistance to damp heat in the code image, the substituents are preferably hydrogen-bonded groups. Hydrogen-bonded groups are groups that interact via hydrogen atoms. Examples of hydrogen-bonded substituents listed above include -OH, -C(=O)OH, and -NHC(=O)R. L3 -C(=O)N(R) L32. -NHC (=O) OR L3 -OC(=O)N(R) L3 2. -NHC(=O)N(R) L3 )2、-NHS(=O)2R L3 and -S(=O)2N(R) L3 2. The hydrogen-bonding group is more preferably -NHC(=O)OR L3 .

[0081] R L3 Each can be independently represented by a hydrogen atom, alkyl group, alkenyl group, aryl group, or monovalent heterocyclic group, preferably a hydrogen atom, alkyl group, or aryl group.

[0082] As R L3 The alkyl group in the form of the alkyl group is preferably an alkyl group with 1 to 10 carbon atoms, more preferably an alkyl group with 1 to 4 carbon atoms, and even more preferably methyl or ethyl.

[0083] Furthermore, from the viewpoint of improving the lightfastness and damp heat resistance of the obtained code image, R is preferred. 1 R 2 R 3 and R 4 At least one atom in the group is a hydrogen atom, more preferably free R. 1 R 2 R 3 and R 4 At least two of the constituent atoms are hydrogen atoms, and further selection is made from R. 1 R 2 R 3 and R 4 Two of the atoms in the group are hydrogen atoms.

[0084] Choose freely R 1 R 2 R 3 and R 4 When two of the constituent atoms are hydrogen atoms, R is preferred. 1 and R 2 1 in and R 3 and R 4 One of them is a hydrogen atom.

[0085] Furthermore, considering the invisibility of the obtained code image, R 1 and R 2 One of them and R 3 and R 4 One of them is a hydrogen atom, more preferably R 1 and R 2 Another one and R 3 and R 4The other one is phenyl. As mentioned above, the phenyl group is further preferably substituented.

[0086] [X] In formula (1A), X independently represents O atom, S atom or Se atom, preferably O atom or S atom, more preferably O atom.

[0087] From the viewpoint of further improving invisibility, the compound represented by formula (1A) is preferably the compound represented by the following formula (1B).

[0088] [Chemical Formula 7] In equation (1B), M + This indicates a proton, a monovalent alkali metal cation, or an organic cation. L 1 This represents a methine chain consisting of 5 or 7 methine groups. The central methine group in the methine chain has a substituent represented by formula A above.

[0089] R 5 and R 7 Each can independently represent a hydrogen atom, alkyl group, aryl group, or monovalent heterocyclic group. R 6 and R 8 Each can be independently represented by an alkyl group, halogen atom, alkenyl group, aryl group, monovalent heterocyclic group, nitro group, cyano group, or -OR group. L3 -C(=O)R L3 -C (=O) OR L3 -OC (=O)R L3 -N(R) L3 2. -NHC(=O)R L3 -C(=O)N(R) L3 2. -NHC (=O) OR L3 -OC(=O)N(R) L3 2. -NHC(=O)N(R) L3 2. -SR L3 -S(=O)2R L3 -S(=O)2OR L3 -NHS(=O)2R L3 or -S(=O)2N(R) L3 2. R L3 Each of the following groups can be independently represented by a hydrogen atom, alkyl group, alkenyl group, aryl group, or monovalent heterocyclic group; n can be independently represented by an integer from 1 to 5; and X can be independently represented by an O atom, S atom, or Se atom.

[0090] [L] 1 M + and X] In equation (1B), L1 M + and X and L in equation (1A) 1 M + The meanings of X and X are the same, and the preferred selection methods are also the same.

[0091] [R] 5 R 6 R 7 and R 8 ] R 5 and R 7 Each of the following can be independently represented: hydrogen atom, alkyl group, aryl group, or monovalent heterocyclic group, with hydrogen atom being preferred.

[0092] R 5 and R 7 The alkyl, aryl, or monovalent heterocyclic group in the above R 1 and R 3 The alkyl, aryl, or monovalent heterocyclic groups in them are the same, and the preferred methods are also the same.

[0093] R 6 and R 8 Each can be independently represented by an alkyl group, halogen atom, alkenyl group, aryl group, monovalent heterocyclic group, nitro group, cyano group, or -OR group. L3 -C(=O)R L3 -C (=O) OR L3 -OC (=O)R L3 -N(R) L3 2. -NHC(=O)R L3 -C(=O)N(R) L3 2. -NHC (=O) OR L3 -OC(=O)N(R) L3 2. -NHC(=O)N(R) L3 2. -SR L3 -S(=O)2R L3 -S(=O)2OR L3 -NHS(=O)2R L3 or -S(=O)2N(R) L3 2, the above R L3 With R 1 ~R 4 R in L3 The meanings are the same, and the preferred selection methods are also the same.

[0094] R 6 and R 8 Each group is preferably a hydrogen-bonded group. Examples of hydrogen-bonded groups include -OH, -C(=O)OH, and -NHC(=O)R. L3 -C(=O)N(R)L3 2. -NHC (=O) OR L3 -OC(=O)N(R) L3 2. -NHC(=O)N(R) L3 )2、-NHS(=O)2R L3 and -S(=O)2N(R) L3 )2, Preferred -NHC(=O)OR L4 .

[0095] The above R L3 With R 1 ~R 4 R in L3 The meanings are the same, and the preferred methods are also the same.

[0096] The above R L4 The alkyl group is preferred, with alkyl groups having 1 to 4 carbon atoms, and methyl groups are more preferred.

[0097] From the viewpoint of the preservation stability of invisible ink, the compound represented by formula (1B) preferably has one of each of the following: R 6 The group represented by R and the group represented by R 8 The group represented by R. At this time, in the presence of R... 6 or R 8 In the benzene ring bonded by the group indicated, R 6 The group represented by R or R 8 The bonding position of the indicated group is preferably meta position relative to the bonding position with the barbituric acid ring.

[0098] In equation (1B), the preferred choice is R. 5 R 6 R 7 and R 8 At least one of the constituent groups is a hydrogen-bonded group, more preferably selected from R. 5 R 6 R 7 and R 8 At least two of the groups are hydrogen-bonded groups.

[0099] Furthermore, from the perspective of synthetic suitability, R is preferred. 5 With R 7 and R 6 With R 8 They are the same group.

[0100] Moreover, R is preferred 5 and R 7 They are hydrogen atoms, and R 6 and R 8 They are the same hydrogen-bonded groups.

[0101] [n] n represents an integer from 1 to 5 independently. From the viewpoint of ease of distribution, it is preferably an integer from 1 to 3, more preferably 1 or 2, and even more preferably 1.

[0102] <<Compounds represented by formula (2)>> [G] A and G B ] G A and G B Each can be represented independently as a monovalent substituent. Examples of monovalent substituents include halogen atoms, cyano groups, nitro groups, alkyl groups, alkenyl groups, ynyl groups, aryl groups, heteroaryl groups, aralkyl groups, and -OR groups. 10 -COR 11 -COOR 12 -OCOR 13 -NR 14 R 15 -NHCOR 16 -CONR 17 R 18 -NHCONR 19 R 20 -NHCOOR 21 -SR 22 -SO2R 23 -SO2OR 24 -NHSO2R 25 or SO2NR 26 R 27 .

[0103] R 10 ~R 27 Each can independently represent a hydrogen atom, an aliphatic group, an aromatic group, or a heterocyclic group. Additionally, -COOR 12 R 12 In the case of hydrogen (i.e., carboxyl group), the hydrogen atom can dissociate (i.e., carbonate group) or remain in a salt state. Furthermore, -SO2OR 24 R 24 When the hydrogen atom is a hydrogen atom (i.e., a sulfonyl group), the hydrogen atom can dissociate (i.e., a sulfonate group) or be in a salt state.

[0104] [X] A and X B ] X A and X B Each substituent is represented independently. The substituent is preferably a group having an active hydrogen atom, more preferably -OH, -SH, -COOH, -SO3H, or -NR. X1 R X2 -NHCOR X1 -CONRX1 R X2 -NHCONR X1 R X2 -NHCOOR X1 -NHSO2R X1 -B(OH)2 and PO(OH)2, more preferably -OH, -SH and NR X1 R X2 .

[0105] R X1 and R X2 Each can be represented independently by a hydrogen atom or a monovalent substituent. Examples of substituents include alkyl, alkenyl, ynyl, aryl, and heteroaryl groups. Alkyl groups are preferred. Alkyl groups are preferably straight-chain or branched. For detailed information on alkyl, alkenyl, ynyl, and heteroaryl groups, please refer to G. A and G B The meaning of the scope described in the text is the same.

[0106] [Ring A and Ring B] Ring A and ring B represent aromatic rings or heteroaromatic rings independently, respectively.

[0107] Aromatic rings and heteroaromatic rings can be monocyclic or fused rings.

[0108] Among them, the aromatic ring and heteroaromatic ring are preferably benzene ring or naphthalene ring.

[0109] The aromatic ring may be unsubstituted or substituented. G is an example of a substituent. A and G B The substituents described in the text.

[0110] X A With G A They can bond together to form a ring, X B With G B They can bond together to form a ring, in G A and G B When multiple cases exist, G A Each other and G B They can bond with each other to form a ring.

[0111] The ring is preferably a 5-membered or 6-membered ring. The ring can be a single ring or multiple rings.

[0112] X A With G A X B With G B G A Each other or G BWhen these bonds together to form a ring, they can form a ring directly, or they can form a ring by bonding with a divalent linker selected from the group consisting of alkylene groups, -CO-, -O-, -NH-, -BR-, and combinations thereof. A With G A X B With G B G A Each other or G B They are preferably bonded together to form a ring.

[0113] R represents a hydrogen atom or a monovalent substituent. G is an example of a substituent. A and G B The substituents described herein. The substituents are preferably alkyl or aryl.

[0114] [kA and kB] kA represents 0~n A Integers, kB represents 0 to n B an integer, n A Let n represent the largest integer that can be replaced by ring A. B This represents the largest integer that can be replaced by ring B.

[0115] kA and kB are each preferably 0 to 4, more preferably 0 to 2, and especially preferably 0 to 1.

[0116] From the viewpoint of improving lightfastness, the compound represented by formula (2) is preferably the compound represented by formula (2A).

[0117] [Chemical Formula 8] In equation (2A), R 1 and R 2 Each independently represents a monovalent substituent, R 3 and R 4 Each can be represented independently by a hydrogen atom or an alkyl group. Examples of substituents include G. A and G B The substituents described in the text.

[0118] X 1 and X 2 Each can be used independently to represent an oxygen atom or -N (R) 5 )-, X 3 and X 4 They can be used to represent carbon atoms or boron atoms independently.

[0119] t and u in X 3 and X 4 When it is a boron atom, it represents 1; in X... 3 and X 4When it represents a carbon atom, it is represented as 2.

[0120] R 5 Y represents a hydrogen atom, alkyl group, aryl group, or heteroaryl group. 1 Y 2 Y 3 and Y 4 Each of the substituents, Y, represents a monovalent substituent independently. 1 With Y 2 They can bond together to form a ring, Y 3 With Y 4 They can bond together to form a ring. When Y 1 Y 2 Y 3 and Y 4 When multiple substituents exist separately, they can also bond together to form a ring. G can be cited as an example of a substituent. A and G B The substituents described in the text.

[0121] p and s independently represent integers from 0 to 3, and q and r independently represent integers from 0 to 2.

[0122] R 1 R 2 Y 1 Y 2 Y 3 and Y 4 The substituents represented can be similarly exemplified by G. A and G B The substituents described in the text.

[0123] R 3 and R 4 Preferably, it contains hydrogen atoms, methyl or ethyl groups, especially hydrogen atoms or methyl groups, and most preferably hydrogen atoms.

[0124] X 1 With X 2 They can be the same or different, but the same is preferred.

[0125] R 5 Hydrogen atoms, alkyl groups, or aryl groups are preferred, with hydrogen atoms or alkyl groups being more preferred.

[0126] The molecular weight of the compound represented by formula (2A) is preferably 100 to 2,000, more preferably 150 to 1,000.

[0127] The compounds represented by formula (2) are described in detail in Japanese Patent Application Publication No. 2011-2080101. The compounds described in Japanese Patent Application Publication No. 2011-2080101 are preferably used as infrared absorbing compounds in this invention. Specific examples of compounds represented by formula (2) include, for example, the compounds described in Japanese Patent Application Publication No. 2011-208101 and the compounds described in paragraphs 0076 and 0077 of Japanese Patent Application Publication No. 2018-154672. However, the specific examples of compounds represented by formula (2) are not limited to those described.

[0128] The content of the infrared absorbing compound relative to the total mass of the invisible ink is preferably 0.3% to 5% by mass, more preferably 0.5% to 2% by mass.

[0129] -Fluorescent compounds- In this invention, fluorescent compound refers to a compound that produces fluorescence.

[0130] Fluorescent compounds can be inorganic compounds, organic compounds, or organic-inorganic complexes.

[0131] Examples of red fluorescent inorganic compounds include YVO4:Eu, Y2O3:Eu, Y2SiO5:Eu, and Y3AlO4. 12 :Eu, Y2O2S:Eu, Bi, Zn3(PO4)2:Mn, YBO3:Eu, CaLa2S4:Ce, (Y,Gd)BO3:Eu, SrS:Eu, (Ca,Sr)S:Eu, GdBO3:Eu, ScBO3:Eu, LuBO3:Eu, YVO4:Bi, Eu, YVO4:Pb, Eu, etc.

[0132] Regarding blue phosphors that are inorganic compounds, examples include Y₂SiO₅:Ce, CaWO₄:Pb, and BaMgAl. 14 O 23 Eu, BaMgAl 10 O 17 :Eu,Mn, Zn2GeO4:Mn, MgAl2O4:Ce, etc.

[0133] Examples of green phosphors that are inorganic compounds include Zn₂SiO₄:Mn and BaAl. 12 O 19 Mn, BaMgAl 14 O 23 Mn, SrAl 13 O 19 Mn, CaAl 12 O 19:Mn, YBO3:Tb, YBO3:Ce,Tb, LaPO4:Ce,Tb, LuBO3:Tb, GdBO3:Tb, ScBO3:Tb, Sr6Si3O3C 14 Eu, YVO4:Tb, etc.

[0134] Examples of organic fluorescent compounds include, for example, fluorescein, eosin, rhodamine B, rhodamine 6G, thioflavin, diaminostilbene disulfonic acid, imidazole, coumarin, triazole, carbazole, pyridine, naphthalene dicarboxylic acid, imidazole one, anthracene, and derivatives of these compounds.

[0135] As an organic-inorganic complex, the organic-inorganic complex described in Japanese Patent No. 5630752 can be cited as an example.

[0136] From the viewpoint of further improving invisibility and readability, the fluorescent compound is preferably an organic fluorescent compound.

[0137] The content of fluorescent compound relative to the total mass of invisible ink is preferably 1% to 8% by mass, more preferably 2% to 6% by mass.

[0138] -Photochromic compounds- In this invention, a photochromic compound refers to a compound whose chemical bonding state changes reversibly through the action of light, generating two isomers. The absorption spectra of the two isomers are different. Photochromic compounds possess properties such as coloring upon exposure to ultraviolet light and then reverting to colorless state upon exposure to visible light.

[0139] Examples of photochromic compounds include photo-opening / closing ring type compounds that change from an open-ring form to a closed-ring form or from a closed-ring form to an open-ring form through the action of light, and photo-geometric isomerization type compounds that change from a trans form to a cis form. From the viewpoint of repeated durability, compounds that change from an open-ring form to a closed-ring form or from a closed-ring form to an open-ring form through the action of light are preferred as photochromic compounds; that is, photo-opening / closing ring type photochromic compounds.

[0140] Examples of photochromic compounds of the open / closed ring type include spiro compounds, naphthopyran compounds, diarylethylene compounds, fulgide compounds, and fulgimide compounds. Examples of spiro compounds include spiropyran compounds, spirothiran compounds, and spiroxazine compounds. In this invention, from the viewpoint of thermal stability, the photochromic compound is preferably at least one selected from the group consisting of spiropyran compounds, spiroxazine compounds, naphthopyran compounds, and diarylethylene compounds.

[0141] Furthermore, in this invention, "system compound" refers to a compound whose molecule has a skeleton or structure labeled "system compound". For example, "spiro-system compound" refers to a compound having a spiro skeleton.

[0142] For a preferred method of photochromic compound, reference can be made to International Publication No. 2021 / 095372.

[0143] <<Helical Compounds>> For example, spiro compounds are represented by the following formula (3).

[0144] [Chemical Formula 9] In equation (3), X represents NR 1 、O or S. R 1 This indicates an aliphatic or aromatic group. Aliphatic and aromatic groups may have substituents.

[0145] X is preferably NR 1 .

[0146] In equation (3), Q represents O, S, or CR. 2 R 3 R 2 and R 3 They can be used to represent aliphatic or aromatic groups independently.

[0147] Q is preferably CR 2 R 3 .

[0148] In equation (3), Y represents N, O, or S. Y is preferably O.

[0149] In equation (3), Z represents CH, N, or P. Z is preferably CH or N.

[0150] In equation (3), A represents the group of atoms that form a ring bonded to Q and X.

[0151] As a ring structure formed by A, Q and X, examples include a 5- or 6-element single-ring structure; and a multi-ring structure composed of two or more 5- or 6-element single-ring structures; preferably a 2-ring structure.

[0152] Among them, the ring formed by A, Q and X is preferably a two-ring consisting of an aromatic ring and a heterocyclic ring, and more preferably an indole ring.

[0153] In equation (3), V 1 This indicates a substituent bonded to a ring formed by A, Q, and X.

[0154] In equation (3), m1 represents an integer from 0 to 4.

[0155] In equation (3), R 4 and R 5 Each of these groups independently represents a hydrogen atom, a halogen atom (e.g., fluorine, chlorine, bromine, and iodine), a cyano group, a nitro group, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aryl group with 6 to 19 carbon atoms, a heterocyclic group, or -OR. 10 -COR 11 -COOR 12 -OCOR 13 -NR 14 R 15 -NHCOR 16 -CONR 17 R 18 -NHCONR 19 R 20 -NHCOOR 21 -SR 22 -SO2R 23 -SO2OR 24 -NHSO2R 25 or SO2NR 26 R 27 R 10 ~R 27 Each of the following groups independently represents a hydrogen atom, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aralkyl group with 7 to 20 carbon atoms, or an aryl or heterocyclic group with 6 to 19 carbon atoms. R 4 and R 5 They can bond with each other to form rings with 3 to 20 carbon atoms.

[0156] R 4 and R 5 When they bond together to form a ring, examples of ring structures include 5- or 6-membered single-ring structures; and multi-ring structures composed of two or more 5- or 6-membered single-ring structures. 4 and R 5 The rings formed by mutual bonding are preferably aromatic hydrocarbon rings, and more preferably benzene rings or naphthalene rings.

[0157] In formula (3), the ring formed by A, Q and X is more preferably an indole ring, and R is preferred. 4 and R 5 They bond together to form a ring with 3 to 20 carbon atoms. Specifically, the spiro compounds are preferably represented by the following formula (3A).

[0158] [Chemical Formula 10] In equation (3A), Y, Z, R 1 V 1 And m1 is the same as in equation (3).

[0159] In formula (3A), B represents the set of atoms required to form an aromatic hydrocarbon ring. Examples of aromatic hydrocarbon rings include the benzene ring and the naphthalene ring.

[0160] In equation (3A), V 2 This indicates a substituent bonded to the ring formed by B. As V 2 This indicates hydrogen atoms, halogen atoms (e.g., fluorine, chlorine, bromine, and iodine), cyano, nitro, alkyl with 1 to 20 carbon atoms, alkenyl with 2 to 20 carbon atoms, alkynyl with 2 to 20 carbon atoms, aralkyl with 7 to 20 carbon atoms, aryl with 6 to 19 carbon atoms, heterocyclic groups, and -OR. 10 -COR 11 -COOR 12 -OCOR 13 -NR 14 R 15 -NHCOR 16 -CONR 17 R 18 -NHCONR 19 R 20 -NHCOOR 21 -SR 22 -SO2R 23 -SO2OR 24 -NHSO2R 25 or SO2NR 26 R 27 R 10 ~R 27 Each of the following groups can be independently represented: hydrogen atom, alkyl group with 1 to 20 carbon atoms, alkenyl group with 2 to 20 carbon atoms, alkynyl group with 2 to 20 carbon atoms, aralkyl group with 7 to 20 carbon atoms, aryl group or heterocyclic group with 6 to 19 carbon atoms.

[0161] In equation (3A), m2 represents an integer from 0 to 4.

[0162] <<Naphthopyran compounds>> Naphthopyran compounds are represented, for example, by the following formula (4A) or formula (4B).

[0163] [Chemical Formula 11] In equations (4A) and (4B), V 3 R represents a substituent bonded to the naphthalene ring. 30 R 31 R32 and R 33 This indicates a substituent bonded to the pyran ring.

[0164] In equations (4A) and (4B), R 30 R 31 R 32 R 33 and V 3 Each of these groups independently represents a hydrogen atom, a halogen atom (e.g., fluorine, chlorine, bromine, and iodine), a cyano group, a nitro group, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aryl group with 6 to 19 carbon atoms, a heterocyclic group, or -OR. 10 -COR 11 -COOR 12 -OCOR 13 -NR 14 R 15 -NHCOR 16 -CONR 17 R 18 -NHCONR 19 R 20 -NHCOOR 21 -SR 22 -SO2R 23 -SO2OR 24 -NHSO2R 25 or SO2NR 26 R 27 R 10 ~R 27 Each of these groups independently represents a hydrogen atom, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aralkyl group with 7 to 20 carbon atoms, or an aryl or heterocyclic group with 6 to 19 carbon atoms. Examples of these groups include alkyl, alkenyl, alkynyl, aralkyl, aryl, and heterocyclic groups. Alkyl, alkenyl, alkynyl, aralkyl, aryl, and heterocyclic groups may have substituents.

[0165] In equations (4A) and (4B), m3 represents an integer from 0 to 6.

[0166] <<Diarylethylene compounds>> Diarylethylene compounds are represented, for example, by the following formula (5).

[0167] [Chemical Formula 12] In equation (5), Z 1 and Z 2 NR are represented independently. 48 、O or S. R48 This indicates an aliphatic or aromatic group. The aliphatic and aromatic groups may have substituents. The preferred embodiments of the aliphatic and aromatic groups are the same as those described above. Furthermore, the preferred embodiments of the substituents are the same as those described above.

[0168] Z 1 and Z 2 S is preferred to be independent of each other.

[0169] In equation (5), R 40 R 41 R 42 R 43 R 44 R 45 R 46 and R 47 Each of these groups independently represents a hydrogen atom, a halogen atom (e.g., fluorine, chlorine, bromine, and iodine), a cyano group, a nitro group, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aryl group with 6 to 19 carbon atoms, a heterocyclic group, or -OR. 10 -COR 11 -COOR 12 -OCOR 13 -NR 14 R 15 -NHCOR 16 -CONR 17 R 18 -NHCONR 19 R 20 -NHCOOR 21 -SR 22 -SO2R 23 -SO2OR 24 -NHSO2R 25 or SO2NR 26 R 27 R 10 ~R 27 Each of these groups independently represents a hydrogen atom, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkynyl group with 2 to 20 carbon atoms, an aralkyl group with 7 to 20 carbon atoms, or an aryl or heterocyclic group with 6 to 19 carbon atoms. Examples of these groups include alkyl, alkenyl, alkynyl, aralkyl, aryl, and heterocyclic groups. Alkyl, alkenyl, alkynyl, aralkyl, aryl, and heterocyclic groups may have substituents.

[0170] R 41 With R 42 R 43 With R 44 and R 45 With R46 They can bond with each other to form rings with 3 to 20 carbon atoms. R 41 With R 42 and R 45 With R 46 When they bond together to form a ring, the ring structure can be exemplified by a 5- or 6-element single ring structure; and a multi-ring structure composed of two or more 5- or 6-element single ring structures.

[0171] R 40 and R 47 Preferably, each alkyl group is independently composed of 1 to 20 carbon atoms, more preferably alkyl groups of 1 to 10 carbon atoms, and even more preferably methyl groups.

[0172] R 41 R 42 R 45 and R 46 Preferred R 41 With R 42 and R 45 With R 46 They bond together to form a ring with 3 to 20 carbon atoms, or are independently hydrogen atoms, alkyl groups with 1 to 20 carbon atoms, or aryl groups with 6 to 19 carbon atoms. R 41 With R 42 and R 45 With R 46 The rings formed by mutual bonding are more preferably benzene rings or cyclohexane rings. Furthermore, R 41 R 42 R 45 and R 46 More preferably, each is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0173] Preferred R 43 and R 44 They bond together to form a ring represented by any of the following structures.

[0174] [Chemical Formula 13] The content of photochromic compound relative to the total mass of invisible ink is preferably 0.3% to 5% by mass, more preferably 0.5% to 2% by mass.

[0175] The invisible ink preferably contains an infrared-absorbing compound. Because the infrared-absorbing compound does not show color under black light or sunlight, it can be used on leather in a wide range of environments.

[0176] In addition to infrared absorbing compounds, fluorescent compounds, or photochromic compounds, invisible inks preferably also contain ingredients commonly known to be found in inks.

[0177] Invisible inks can be either water-based or UV-curable. Water-based inks typically contain water. UV-curable inks typically contain polymerizable monomers and polymerization initiators.

[0178] The invisible ink is preferably a water-based ink containing water. In the case of a water-based ink, unlike UV-curable inks, it is possible to record coded images while maintaining the texture formed on the surface of the leather substrate.

[0179] -water- When the invisible ink contains water, the water content relative to the total amount of the invisible ink is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more.

[0180] The water content relative to the total amount of invisible ink is preferably 90% by mass or less, more preferably 80% by mass or less.

[0181] -Resin particles- Invisible inks preferably contain at least one type of resin particle.

[0182] Resin particles are particles composed of resin.

[0183] Water-insoluble resins are preferred as the resins constituting the resin particles.

[0184] In this invention, "water insoluble" refers to the property that the amount of water that can be dissolved in 100g of water at 25°C is less than 1g.

[0185] There are no particular restrictions on the glass transition temperature of the resin particles (i.e., the glass transition temperature of the resin in the resin particles).

[0186] From the viewpoint of further improving image intensity, the glass transition temperature (Tg) of the resin particles is preferably 20°C or higher, more preferably 50°C or higher, and even more preferably 80°C or higher.

[0187] From the viewpoint of suitability for manufacturing resin particles, the glass transition temperature (Tg) of the resin particles is preferably 150°C or less, and more preferably 130°C or less.

[0188] As resin particles, it is preferred to include particles containing acrylic resin (hereinafter also referred to as acrylic resin particles), particles containing styrene acrylic resin (hereinafter also referred to as styrene acrylic resin particles), particles containing polyester resin (hereinafter also referred to as polyester resin particles), particles containing urethane (hereinafter also referred to as urethane resin particles), or particles containing polyolefin resin (hereinafter also referred to as polyolefin resin particles).

[0189] From the perspective of adhesion, the resin particles are preferably urethane resin particles.

[0190] The urethane resin constituting the urethane resin particles is preferably at least one selected from the group consisting of self-emulsifying urethane resins and forced emulsifying urethane resins. The self-emulsifying urethane resin is preferably a urethane resin having anionic groups. The forced emulsifying urethane resin is preferably a urethane resin that does not have anionic groups and can be dispersed in water by an emulsifier.

[0191] The urethane resin particles can be commercially available or obtained as an aqueous dispersion containing the urethane resin particles.

[0192] As an aqueous dispersion containing urethane resin particles, examples include polyurethane emulsions manufactured by NICCA CHEMICAL CO.,LTD., namely the EVAFANOL series (e.g., EVAFANOL HA-55).

[0193] The average particle size of the urethane resin particles is, for example, 10 nm to 10 μm.

[0194] From the viewpoint of adhesion, the content of resin particles relative to the total amount of invisible ink is preferably 1% to 10% by mass, more preferably 3% to 8% by mass.

[0195] -Other ingredients- Invisible inks may contain other ingredients besides those mentioned above, depending on the need.

[0196] Other components include, for example, colloidal silica, organic solvents, water-soluble resins, and surfactants.

[0197] (Methods for applying invisible ink) There are no particular limitations on the method of applying invisible ink, but from the viewpoint of recording detailed code images, it is preferable to apply it by inkjet recording.

[0198] There are no particular limitations on the way ink is ejected in inkjet recording. It can be any of the known methods, such as charge control methods that use electrostatic induction to eject ink, on-demand inkjet methods (pressure pulse methods) that use the vibration pressure of piezoelectric elements, acoustic inkjet methods that convert electrical signals into sound beams that irradiate the ink and use radiation pressure to eject the ink, and thermal inkjet methods (Bubble Jet (registered trademark)) that heat the ink to form bubbles and use the resulting pressure.

[0199] As an inkjet recording method, it is particularly effective to utilize the inkjet method described in Japanese Patent Application Publication No. 54-59936, in which ink subjected to heat undergoes a rapid volume change, and ink is ejected from the nozzle by the force generated by this change in state.

[0200] As an inkjet recording method, the method described in paragraphs 0093 to 0105 of Japanese Patent Application Publication No. 2003-306623 can also be applied.

[0201] Ink application based on inkjet recording is achieved by ejecting ink from the nozzles of the inkjet head.

[0202] As for inkjet head types, there are reciprocating methods (multiple pass methods) that record while scanning along the width of the substrate with a short serial head; and line methods (single pass methods) that use a line head that arranges recording elements in an area corresponding to one side of the substrate.

[0203] In line mode, by scanning the substrate in a direction intersecting the arrangement direction of the recording elements, images can be recorded across the entire surface of the substrate. In line mode, the transport system, such as the carriage with the short scanning head used in reciprocating mode, is unnecessary. Furthermore, compared to reciprocating mode, line mode eliminates the need for carriage movement and complex scanning control of the substrate; only the substrate moves. Therefore, compared to reciprocating mode, line mode enables higher speeds of image recording.

[0204] Therefore, in the invisible ink application process, it is preferable to apply the ink in a row-by-row manner (single pass).

[0205] Furthermore, in the invisible ink application process, it is preferable to use an inkjet head with a nozzle density of 600 nozzles per inch or more to apply the ink. A nozzle density of 900 nozzles per inch or more is more preferable, and 1200 nozzles per inch or more is even more preferable. Alternatively, an inkjet head with 300 nozzles can be used instead of an inkjet head with 600 nozzles, effectively setting the nozzle density to 600 nozzles per inch or more.

[0206] From the viewpoint of obtaining high-definition coded images, the amount of ink droplets ejected from the nozzle of the inkjet head is preferably 1 pL (picoliter) to 10 pL, more preferably 1.5 pL to 6 pL.

[0207] (Code image) In the invisible ink application process, coded images are recorded on the leather substrate.

[0208] A code image is an image whose pre-embedded information can be read using a corresponding code reader.

[0209] The preferred code image is a barcode, QR code, or dotted code. A barcode, for example, is an image formed by multiple lines of varying thicknesses arranged in a stripe pattern. A QR code, for example, is an image formed by multiple squares of varying sizes arranged in a lattice pattern. A dotted code, for example, is an image with extremely small dots arranged within an area of ​​approximately 2mm square. Dotted codes are provided by Apollo Japan Co., Ltd. as "Screen Code".

[0210] When combining a code image with a coloring image (described later), from the viewpoint of further maintaining the appearance of the coloring image, the code image is preferably a dotted code.

[0211] <Visible Ink Application Process> The leather manufacturing method of the present invention preferably further includes a step of applying visible ink containing a colorant to record a colored image, and includes recording a code image on the leather substrate on which the colored image is recorded (hereinafter, "visible ink application step").

[0212] That is, preferably, visible ink, invisible ink, and outer coating liquid are sequentially applied to a leather substrate.

[0213] By recording colored images, it is possible to obtain decorated leather. Recording invisible coded images allows for anti-counterfeiting measures while maintaining the appearance of the colored image.

[0214] -Coloring agents- It is evident that the colorant contained in ink is not particularly limited; it can be either dye or pigment.

[0215] From the viewpoint of improving readability, the colorant preferably does not have absorption in the infrared region. For example, a black colorant is preferably lactam black.

[0216] In this invention, "no absorption in the infrared region" means that the absorbance at 800 nm, measured by a spectrophotometer (product name "V770", manufactured by JASCO Corporation) of the colorant coating, is 0.5 or less. In this case, the difference between the absorption in the code image and the absorption in the visible light image near 800 nm, which serves as the reading wavelength for the infrared detector, becomes sufficient to read the code. Furthermore, when measuring absorbance, the colorant coating is manufactured by applying 2 μm of ink to a substrate using an inkjet printhead at a resolution of 1200 dpi × 1200 dpi.

[0217] The content of colorant relative to the total amount of visible ink is preferably 1% to 15% by mass, more preferably 2% to 10% by mass.

[0218] It is evident that, in addition to colorants, inks preferably also contain other components commonly known to be present in inks.

[0219] It is evident that inks can be either water-based or UV-curable. Water-based inks typically contain water. UV-curable inks typically contain polymerizable monomers and polymerization initiators.

[0220] It is evident that the ink is preferably a water-based ink containing water. In the case of a water-based ink, unlike UV-curable inks, it is possible to record a colored image while maintaining the texture formed on the surface of the leather substrate.

[0221] -water- The water content relative to the total amount of visible ink is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more.

[0222] The water content relative to the total amount of visible ink is preferably 90% by mass or less, more preferably 80% by mass or less.

[0223] -Resin particles- It is evident that the ink preferably contains at least one resin particle. Examples of resin particles contained in visible ink include those identical to those contained in invisible ink.

[0224] From the viewpoint of adhesion, the resin particles are preferably urethane resin particles. The preferred method for urethane resin particles is as described above.

[0225] If both the visible and invisible inks contain urethane resin particles, the adhesion between the leather substrate and the colored image, as well as the adhesion between the colored image and the coded image, is excellent.

[0226] From the viewpoint of adhesion, the content of resin particles relative to the total amount of invisible ink is preferably 1% to 10% by mass, more preferably 3% to 8% by mass.

[0227] -Other ingredients- It is evident that ink can contain other components besides those mentioned above, depending on the requirements.

[0228] Other components include, for example, colloidal silica, organic solvents, water-soluble resins, and surfactants. Furthermore, when using pigments as colorants, the ink preferably contains a pigment dispersant for dispersing the pigments.

[0229] (The method of applying ink is visible) It is clear that there are no particular limitations on the method of applying ink, but from the viewpoint of recording detailed colored images, it is preferable to apply ink by inkjet recording.

[0230] The details of inkjet recording are as described above.

[0231] The visible ink applied to the leather substrate can be heated and dried after the visible ink application process.

[0232] Examples of mechanisms for heating and drying include known heating mechanisms such as infrared heaters, known air supply mechanisms such as dryers, and mechanisms that combine two or more of these mechanisms.

[0233] Examples of methods for heating and drying include: blowing warm air or hot air onto the ink-covered side of a leather substrate; applying heat to the ink-covered side of the leather substrate and / or the side opposite to the ink-covered side using an infrared heater or the like; and methods combining these methods.

[0234] The heating temperature during heat drying is preferably 55°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. There is no particular limitation on the upper limit of the heating temperature; for example, 100°C is possible, but 90°C is preferred.

[0235] There is no particular limitation on the heating and drying time, but it is preferably 3 to 60 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 20 seconds.

[0236] In the visible ink application process, two or more visible inks can be applied to the leather substrate.

[0237] In the visible ink application process, when two or more colors of ink are sequentially applied to the leather substrate, the nth color (n is an integer greater than or equal to 1, and the same applies below) of ink applied to the leather substrate can be heated and dried, and the (n+1)th color of ink can be applied on top of the heated and dried nth color of ink. Alternatively, the nth color of ink applied to the leather substrate can be left unheated and dried, and the (n+1)th color of ink can be applied on top of the nth color of ink.

[0238] <External coating formation process> The leather manufacturing method of the present invention includes a step of forming an outer coating on a leather substrate on which a code image is recorded (hereinafter also referred to as the "outer coating forming step").

[0239] The method of forming the outer coating can be either by applying an outer coating liquid to a leather substrate on which a coded image is recorded, or by bonding an outer coating film to a leather substrate on which a coded image is recorded.

[0240] From an energy-saving perspective, the process of forming the outer coating preferably includes the process of applying an outer coating liquid (hereinafter also referred to as the "outer coating liquid application process").

[0241] (External coating liquid application process) -Topical Liquid- There are no particular restrictions on the ingredients contained in the topical liquid.

[0242] The coating liquid can be water-based or UV-curable. In the case of an aqueous coating, it typically contains water. And in the case of a UV-curable coating, it typically contains polymerizable monomers and polymerization initiators.

[0243] The preferred external coating solution is water-based.

[0244] That is, invisible ink, visible ink and coating liquid are preferably all water-containing.

[0245] Since invisible ink, visible ink, and coating liquid are all water-based, they are highly safe and have a low environmental impact.

[0246] -water- The external coating solution preferably contains water.

[0247] The water content relative to the total amount of the external coating liquid is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more.

[0248] The water content relative to the total amount of the external coating liquid is preferably 90% by mass or less, more preferably 80% by mass or less.

[0249] -Resin particles- The coating liquid preferably contains at least one resin particle. Examples of resin particles contained in the coating liquid include resin particles that are the same as those contained in invisible ink.

[0250] From the viewpoint of adhesion, the resin particles are preferably urethane resin particles. The preferred method for urethane resin particles is as described above.

[0251] The preferred invisible inks, visible inks, and coatings all contain urethane resin particles.

[0252] If the invisible ink, visible ink, and coating liquid all contain urethane resin particles, the adhesion between the leather substrate and the colored image, the adhesion between the colored image and the coded image, and the adhesion between the coded image and the coating are excellent.

[0253] From the viewpoint of adhesion, the content of resin particles relative to the total amount of the external coating liquid is preferably 1% to 10% by mass, more preferably 3% to 8% by mass.

[0254] -Silicone compounds- The coating liquid preferably contains at least one silicone compound. If the coating liquid contains a silicone compound, the abrasion resistance of the obtained leather is improved.

[0255] Examples of silicone compounds include amine-modified silicones, alcohol-modified silicones, polyether-modified silicones, and long-chain alkyl-modified silicones.

[0256] From the perspective of improving abrasion resistance, polyether-modified silicone compounds are preferred.

[0257] From the viewpoint of abrasion resistance, the content of silicone compound relative to the total amount of the topcoat liquid is preferably 0.1% to 5% by mass, more preferably 0.3% to 2% by mass.

[0258] -Other ingredients- Topical solutions may contain other ingredients besides those mentioned above, depending on the need.

[0259] Other components include, for example, ultraviolet absorbers and crosslinking agents.

[0260] (Method for applying topical solution) The method of applying the external coating is not particularly limited, and well-known methods such as coating, immersion, and inkjet recording can be cited.

[0261] As for coating methods, known coating methods include rod coating machines, extrusion coating machines, air knife coating machines, blade coating machines, bar coating machines, doctor blade coating machines, extrusion coating machines, and reverse roller coating machines. Furthermore, the coating liquid can also be applied using simulated printing methods such as screen printing, gravure printing, flexographic printing, and offset printing. Among these, considering the amount of ink that can be applied, screen printing is preferred for the coating liquid.

[0262] The external coating liquid can be heated and dried after the external coating liquid application process.

[0263] As a method for drying the coating liquid, for example, heating the substrate to which the coating liquid has been applied in an oven can be cited.

[0264] From the viewpoint of abrasion resistance, the heating temperature is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. There is no particular limitation on the upper limit of the heating temperature; for example, 180°C is possible, and 150°C is preferred.

[0265] There is no particular limitation on the heating time, but from the point of view of abrasion resistance, it is preferred to be 30 seconds to 20 minutes, more preferably 1 minute to 10 minutes, and even more preferably 1 minute to 5 minutes.

[0266] (Method for applying the outer coating film) In the outer coating process, the outer coating film can be bonded to the leather substrate with the coded image instead of applying an outer coating liquid.

[0267] The outer coating is preferably a polyurethane-containing film.

[0268] There are no particular limitations on the method of applying the outer coating film. For example, one method is to form the outer coating film on the release paper, then transfer it, and finally peel off the release paper.

[0269] <Pretreatment solution application process> The leather manufacturing method of the present invention preferably further includes a step of applying a pretreatment liquid containing a coagulant and water to a leather substrate (hereinafter also referred to as the "pretreatment liquid application step"), and after applying the pretreatment liquid, applying visible ink to the leather substrate on which the pretreatment liquid has been applied.

[0270] It is evident that the components in the ink are coagulated by the coagulant in the pretreatment solution, thereby obtaining images with superior image quality.

[0271] (Pretreatment solution) The pretreatment solution contains coagulant and water.

[0272] -water- The pretreatment solution contains water.

[0273] The water content relative to the total amount of the pretreatment liquid is preferably 50% by mass or more, and more preferably 60% by mass or more.

[0274] The water content relative to the total amount of the pretreatment liquid is preferably 90% by mass or less.

[0275] -Flocculant- Regarding the pretreatment solution, a coagulant is prepared, which is at least one selected from the group consisting of organic acids, organic acid salts, polyvalent metal compounds and metal complexes.

[0276] A coagulant is a component that causes components (such as resins) in an ink to coagulate.

[0277] There is no particular limit to the amount of coagulant.

[0278] From the viewpoint of visible ink coagulation rate, the coagulant content relative to the total amount of pretreatment liquid is preferably 0.1% to 40% by mass, more preferably 0.1% to 30% by mass, even more preferably 1% to 20% by mass, and especially preferably 1% to 10% by mass.

[0279] -Resin particles- The pretreatment solution preferably contains at least one resin particle. Examples of resin particles contained in the pretreatment solution include resin particles identical to those contained in invisible ink.

[0280] From the viewpoint of adhesion, the resin particles are preferably urethane resin particles. The preferred method for urethane resin particles is as described above.

[0281] Preferred pretreatment solutions, invisible inks, visible inks, and topcoat solutions all contain urethane resins.

[0282] If the pretreatment liquid, invisible ink, visible ink, and topcoat all contain urethane resin, the adhesion between the leather substrate and the colored image, the adhesion between the colored image and the code image, and the adhesion between the code image and the topcoat are excellent.

[0283] From the viewpoint of adhesion, the content of resin particles relative to the total amount of invisible ink is preferably 1% to 10% by mass, more preferably 3% to 8% by mass.

[0284] -Other ingredients- Depending on the requirements, the pretreatment solution may contain other components besides those mentioned above.

[0285] Other components that may be contained in the pretreatment solution include known additives such as organic solvents, surfactants, solid wetting agents, silica compounds (e.g., colloidal silica), inorganic salts, anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, mildew inhibitors, pH adjusters, viscosity adjusters, rust inhibitors, chelating agents, and water-soluble polymers other than water-soluble cationic polymers (e.g., water-soluble polymers described in paragraphs 0026 to 0080 of Japanese Patent Application Publication No. 2013-001854).

[0286] (Pretreatment solution application method) The method of applying the pretreatment solution is not particularly limited, and well-known methods such as coating, immersion, and inkjet recording can be cited.

[0287] As a coating method, known coating methods include those using rod coaters, extrusion die coaters, air knife coaters, scraper coaters, bar coaters, doctor blade coaters, extrusion coaters, and reverse roller coaters.

[0288] The pretreatment solution applied to the leather substrate can be heated and dried after the pretreatment solution application process.

[0289] As a mechanism for performing heat drying, an example is the same mechanism used for heat drying of ink.

[0290] The heating temperature during heat drying is preferably 55°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. There is no particular limitation on the upper limit of the heating temperature; for example, 100°C is an example, but 90°C is preferred.

[0291] There is no particular limitation on the heating and drying time, but it is preferably 3 to 60 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 20 seconds.

[0292] The leather manufactured using the method of the present invention contains a coded image, but due to its excellent invisibility, it can be used in the same way as ordinary leather without a coded image. Furthermore, the coded image serves as an anti-counterfeiting measure.

[0293] Furthermore, the leather manufactured using the leather manufacturing method of the present invention can be applied, for example, to vehicle seats. Vehicle seats have a high frequency of contact with people, but the leather manufactured using the leather manufacturing method of the present invention exhibits excellent readability after wiping, thus enabling long-term reading of coded images. Moreover, while leather is sometimes wiped with alcohol when soiled, the leather manufactured using the leather manufacturing method of the present invention exhibits excellent readability after alcohol wiping, thus suppressing any decrease in coded image readability.

[0294] Example The following are embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0295] [Example 1-1] <Preparation of Pretreatment Solution> The pretreatment solution was prepared by mixing the following components.

[0296] • Glutaric acid (coagulant) ... 6.1% by mass • Propylene glycol (solvent) … 5.0% by mass • OLFINE E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) [surfactant] ... 0.5% by mass • SUPERFLEX M500 (DKS Co. Ltd.) [Aqueous dispersion of urethane resin particles]... 7.0% by mass • Triisopropanolamine [pH adjuster]... 0.2% by mass • BYK024 (BYK-Chemie GmbH) [Defoamer]...0.01% by mass • Ultrapure water… ensures the pretreatment solution is 100% by mass. <Preparation of Black Ink> (Synthesis of pigment dispersant P1) 965 g of dipropylene glycol was added to a 5000 mL three-necked flask equipped with a stirrer and cooling tube, and heated to 85 °C under a nitrogen atmosphere. The following solutions were prepared: 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 peroxide-2-ethylhexanoate (product name "PERBUTYL O", manufactured by NOF CORPORATION) in 221.17 g of dipropylene glycol.

[0297] Solution I was added dropwise to the three-necked flask over 4 hours, followed by solution II over 5 hours. After the addition was complete, the reaction was allowed to proceed for an additional 2 hours. 1 H-NMR confirmed the disappearance of the monomer.

[0298] The obtained reaction solution was heated to 70°C, and 248.02 g of 50% potassium hydroxide aqueous solution was added. Then, 107.48 g of dipropylene glycol and 75.52 g of pure water were added and stirred to obtain a 37% (by mass) solution of the random polymer. This random polymer was used as pigment dispersant P1.

[0299] pass 1 ¹H-NMR confirmed the structural units constituting the obtained random polymer. Furthermore, the weight-average molecular weight (Mw) was determined by GPC. The obtained pigment dispersant P1 had a weight-average molecular weight (Mw) of 8400 and an acid value of 221.7 mg KOH / g.

[0300] (Preparation of black pigment dispersion) A polymer aqueous solution was prepared by dissolving 150 parts by weight of pigment dispersant P1 in water to achieve a pigment dispersant P1 concentration of approximately 25% by weight. This 25% by weight polymer aqueous solution was then mixed with 180 parts by weight of black pigment (product name "Irgaphor (registered trademark) Black S0100CF", lactam black, manufactured by BASF) and 171.9 parts by weight of water to obtain a mixture. A potassium hydroxide aqueous solution was added to the obtained mixture to adjust the pH to 8.7 after neutralization.

[0301] Next, a bead mill (bead diameter: 0.1mm) was used. The neutralized mixture was dispersed for 3 hours using zirconia beads. This yielded a black pigment dispersion (uncrosslinked dispersion) containing black pigment dispersed in pigment dispersant P1. Water was then added to this black pigment dispersion to adjust the uncrosslinked dispersion DK1 (pigment concentration 15% by mass).

[0302] Next, relative to 136 parts by mass of the uncrosslinked dispersion (DK1), 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% by mass) were added as crosslinking agents, and the mixture was reacted at 70°C for 6 hours, then cooled to 25°C. Thus, pigment dispersant P1 was crosslinked to obtain a black pigment dispersion (crosslinked dispersion) in which black pigment was dispersed by pigment dispersant P1a. Here, pigment dispersant P1a is a polymer obtained by crosslinking pigment dispersant P1, which is an uncrosslinked polymer, using a crosslinking agent.

[0303] Next, ion-exchanged water was added to the above crosslinked dispersion to bring the pigment concentration to 15% by mass. The resulting liquid was then ultrafiltered at a flow rate of 600 mL per minute through an ultrafiltration apparatus (cross-flow ultrafiltration unit (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (micropore size: 0.1 μm). The liquid temperature was adjusted to 25°C, and ultrafiltration was performed eight times, with each cycle defined as one volume ratio of the liquid being filtered. Ion-exchanged water was then added to the resulting liquid to bring the pigment concentration to 15% by mass. This yielded a black pigment dispersion DK1. The pigment dispersant P1a (crosslinked polymer) contained in the black pigment dispersion has an acid value of 75 mg KOH / g.

[0304] (Preparation of black ink K1) Black ink K1 was prepared by mixing the components described below.

[0305] • Black pigment dispersion DK1… contains 4.0% by mass as pigment. • Propylene glycol (water-soluble organic solvent) … 30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) … 1.0% by mass ·EVAFANOL HA-55 (Polyurethane Resin Particle Dispersion) (manufactured by Nikka Chemical Co., Ltd.)...The content of resin particles is 5.0% by mass. •Olfine E1010 (acetylene glycol surfactant manufactured by Nissin Chemical Co., Ltd.)…1.0% by mass • BYK3450 (a silicone surfactant manufactured by BYK-Chemie GmbH) … 1.0% by mass •PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass •ST-XS (Colloidal Silica Dispersion) (manufactured by Nissan Chemical Corporation)...The content of colloidal silica particles is 0.05% by mass. • Water…makes the ink a 100% mass surplus. <Preparation of Cyan Ink C1> The black pigment was changed to a cyan pigment (product name "PB15:3", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and the cyan pigment dispersion DC1 was obtained by the same method as the preparation of the black pigment dispersion DK1.

[0306] The black pigment dispersion DK1 was replaced with the cyan pigment dispersion DC1. Otherwise, the cyan ink C1 was obtained by the same method as the preparation of the black ink K1.

[0307] <Preparation of Magenta Ink M1> (Preparation of magenta pigment dispersion DM1-1) The black pigment was changed to a magenta pigment (product name "FUJI Fast Red (registered trademark) 9800", Pigment Red 122, manufactured by Fuji Pigment Co., Ltd.), and the amount of crosslinking agent was changed to 3.00 parts by mass, and the amount of boric acid aqueous solution was changed to 32.8 parts by mass. Otherwise, a magenta pigment dispersion DM1-1 was obtained using the same method as the preparation of the black pigment dispersion DK1. The pigment dispersant P1a (crosslinking polymer) contained in the magenta pigment dispersion DM1-1 has an acid value of 105 mg KOH / g.

[0308] (Preparation of magenta pigment dispersion DM1-2) The magenta pigment was changed to magenta pigment (product name "LIONOGEN RED LX10231", Pigment Red 150, manufactured by TOYOCOLOR CO., LTD.). Otherwise, magenta pigment dispersion DM1-2 was obtained using the same method as that used in preparing magenta pigment dispersion DM1-1. The pigment dispersant P1a (crosslinking polymer) contained in magenta pigment dispersion DM1-2 has an acid value of 105 mg KOH / g.

[0309] (Preparation of magenta ink M1) Magenta ink M1 was prepared by mixing the components described below.

[0310] • Magenta pigment dispersion DM1-1… The pigment content is 4.5% by mass. • Magenta pigment dispersion DM1-2… The pigment content is 1.5% by mass. Propylene glycol…30.0% by mass Propylene glycol monomethyl ether…1.0% by mass ·EVAFANOL HA-55… contains 5.0% by mass as resin particles. • OLFINE E1010…1.0% of mass • BYK 3450…1.0% of mass ·PVPK15…0.15% quality •ST-XS… contains 0.05% by mass as colloidal silica particles. Water...totaling as a 100% mass surplus <Preparation of Yellow Ink Y1> (Preparation of yellow pigment dispersion DY1) In obtaining the mixture, 180 parts by mass of a 25% polymer aqueous solution, 75 parts by mass of a yellow pigment (product name "HANSABRILLIANT YELLOW 5GX 03, Pigment Yellow 74, manufactured by Clariant) and 140 parts by mass of water were mixed, and the amount of crosslinking agent was changed to 3.60 parts by mass and the amount of boric acid aqueous solution was changed to 39.4 parts by mass. Otherwise, the yellow pigment dispersion DY1 was obtained by the same method as the preparation of the black pigment dispersion DK1. The pigment dispersant P1a (crosslinking polymer) contained in the yellow pigment dispersion DY1 has an acid value of 105 mg KOH / g.

[0311] (Preparation of yellow ink Y1) The black pigment dispersion DK1 was replaced with a yellow pigment dispersion DY1, and the yellow ink Y1 was obtained by the same method as the preparation of the black ink K1.

[0312] <Preparation of Invisible Ink IR1> As infrared absorbing compounds, the following compounds were prepared, wherein L in formula (1A) 1 Let L1-1, L 1 In this context, A is A-1, R. 1 and R 3 For hydrogen atoms, R 2 and R 4 Let R-1 be the following, where X is an oxygen atom and M is potassium.

[0313] [Chemical Formula 14] [Chemical Formula 15] Four parts by mass of the infrared absorbing compound were added to 96 parts by mass of ultrapure water and dispersed using a bead mill for 3 hours to obtain an aqueous dispersion A of the infrared absorbing compound.

[0314] The following components were mixed to prepare the invisible ink IR1.

[0315] • Aqueous dispersion A of infrared absorbing compound (solid concentration 4% by mass) ... 25% by mass Propylene glycol…30.0% by mass Propylene glycol monomethyl ether…1.0% by mass ·EVAFANOL HA-55… contains 5.0% by mass as resin particles. • OLFINE E1010…1.0% of mass • BYK 3450…1.0% of mass ·PVPK15…0.15% quality •ST-XS… contains 0.05% by mass as colloidal silica particles. Water... makes the ink a 100% mass surplus. <Preparation of Topical Coating Solution OC1> The following components were mixed to prepare the external coating liquid OC1.

[0316] • EVA VANOL HA-55 (solid content concentration 40% by mass) ... 96% by mass ·NK Assist CI-22 (manufactured by Nikka Chemical Co., Ltd.; crosslinking agent)…3% by mass Silicone compounds (product name "DOWSIL (registered trademark) 404LS Additive", lubricant, manufactured by Dow Toray Co., Ltd.) ... 1% by mass <Leather Manufacturing> (Preparation of the inkjet recording device) An inkjet recording device is provided, which has a transport mechanism for transporting a substrate and has four ink-applying inkjet heads (hereinafter also referred to as "printheads") sequentially arranged on the upstream side (hereinafter also referred to as "upstream side") from the transport direction of the substrate.

[0317] Four printheads are arranged along the substrate transport direction. Hereinafter, the printheads from the upstream side are sometimes referred to as printhead 1, printhead 2, printhead 3, and printhead 4, respectively. The printheads are 1200 dpi / 20 inch wide piezoelectric full-line printheads. The nozzle density is 1200 nozzles per inch. Here, dpi is an abbreviation for dots per inch. All printheads are row-type heads with nozzles arranged orthogonally to the substrate transport direction (i.e., the width direction of the substrate). The printheads used are Samba G3L (manufactured by FUJIFILM DIMATIX, Inc.). The ink droplet volume is 2.2 pL.

[0318] (Image Recording) -Pretreatment solution application process- Corona discharge was applied to a leather substrate (product name "Foregord 2 #300", manufactured by Kyowa LifeTechno Co., Ltd.) using a corona treatment machine (KASUGA DENKI, INC., TEC-4AX corona surface modification evaluation device) at a discharge gap of 1 mm, 100 W, and a discharge rate of 4 m / min, followed by surface treatment. A pretreatment solution was then applied to the surface-treated leather substrate using a wire rod. The application mass of the pretreatment solution per unit area was set to 1.5 g / m². 2 The coating speed was set to 50 m / min. Here, the mass of the pretreatment solution applied is calculated by dividing the mass of the applied pretreatment solution by the area of ​​the region to which it was applied. At the end of the pretreatment solution application, drying of the pretreatment solution using a dryer begins 2 seconds after the application ends at that location. Drying of the pretreatment solution is performed at 60°C for 3 seconds. If measured using a Karl Fischer moisture meter, the residual water content in the pretreatment solution is 0.01 g / m³. 2 the following.

[0319] -Visible ink application process- Visible ink (black ink K1, cyan ink C1, magenta ink M1, and yellow ink Y1) and invisible ink IR1 are introduced into the printhead of the inkjet recording device, and a substrate is provided with a pretreatment solution.

[0320] While the substrate, which has been treated with a pretreatment solution, is moved at a constant speed of 50 m / min, black ink K1, cyan ink C1, magenta ink M1, and yellow ink 1 are ejected from the printhead onto the surface of the substrate that has been treated with the pretreatment solution, thereby recording a solid image. At this time, the ink droplet volume is set to 2.2 pL, the duty ratio is set to 100%, and the ejection frequency is set to 39.37 kHz.

[0321] Next, two seconds after ink application was completed, the visible ink applied to the substrate was dried using an infrared (IR) irradiation device (product name "PLC-328", manufactured by Noritake Co., Ltd.) at a surface temperature of 75°C. Then, it was dried for 20 seconds using a dryer with warm air at 80°C.

[0322] -Invisible ink application process- Invisible ink IR1 was sprayed onto solid images of various colors to record screen codes (dot codes), QR codes, and barcodes made by APOLLO JAPAN CO.,LTD.

[0323] -Topical coating application process- While the substrate to be coated with invisible ink is moved at a constant speed of 50 m / min, an external coating liquid is applied to the ink-coated surface of the substrate using a wire bar coater. The applied mass of the solid components in the external coating liquid is 10 g / m². 2 The substrate coated with the external coating was heated in an oven at 130°C for 2 minutes to obtain leather.

[0324] [Examples 1-2] Instead of the silicone compound in the topcoat OC1, water was added, and the topcoat OC1a was prepared using the same method as the topcoat OC1.

[0325] Leather was obtained using the same method as in Examples 1-1, except that an external coating liquid OC1a was used.

[0326] [Comparative Example 1-1] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, leather was obtained using the same method as in Example 1-1.

[0327] [Examples 1-2] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, leather was obtained using the same method as in Examples 1-2.

[0328] The obtained leather was used to evaluate its invisibility, initial readability, readability after wiping, readability after alcohol wiping, alcohol resistance, and abrasion resistance. The evaluation methods are as follows.

[0329] <Invisibility> -Dot Code- Leather with a serial number was presented to 10 test subjects who were unaware of the serial number, and an experiment was conducted to determine whether they noticed it. The evaluation criteria are as follows.

[0330] -QR code- Leather bearing a QR code was presented to 10 test subjects who were unaware that a QR code was present, and an experiment was conducted to determine whether the QR code was detected. The evaluation criteria are as follows.

[0331] -Barcode- Leather with barcodes was presented to 10 test subjects who were unaware that QR codes were present, and an experiment was conducted to determine whether the QR codes were detected. The evaluation criteria are as follows.

[0332] A: No one has been found.

[0333] B: Discovered by 1 to 3 people.

[0334] C: 4 to 9 people were found.

[0335] D: Everyone has noticed.

[0336] <Initial readability> -Dot Code- Ten areas with dotted markings were selected for a reading test using a voice pen manufactured by Apollo Japan Co., Ltd. The evaluation criteria are as follows: A through D represent levels where there are no issues in practical applications.

[0337] -QR code- Ten locations with QR codes were selected and photographed using an APIS Detector S3B. A QR code reader was then used to perform reading tests. The evaluation criteria are as follows: A through D represent levels where there are no issues in practical applications.

[0338] -Barcode- Ten locations with barcodes were selected for recording. Images were taken using an APIS Detector S3B, and barcode readers were used for reading tests. The evaluation criteria are as follows: A through D represent levels where there are no issues in practical applications.

[0339] A: All were read.

[0340] B: 8 or 9 locations were read.

[0341] C: 3 to 7 locations were read.

[0342] D: One or two locations are read.

[0343] E: None of them could be read.

[0344] <Readability after wiping> A 500-cycle reciprocating vibrational abrasion test was conducted on the leather surface using cotton canvas No. 6, weighted at 500g. Following the abrasion test, the leather was evaluated using the same method as the initial readability assessment. The evaluation criteria are as follows.

[0345] A: The number of readings after 500 reciprocating friction tests is the same as the number of readings before the friction tests.

[0346] B: No readings were obtained after 500 cycles of reciprocating friction test.

[0347] <Readability after alcohol wiping> A cotton swab was moistened with 100% ethanol. The leather surface was then wiped 10 times with the swab. Following the wiping test, the leather was evaluated using the same method as the initial readability assessment. The evaluation criteria are as follows.

[0348] A: All were read.

[0349] B: 8 or 9 locations were read.

[0350] C: 3 to 7 locations were read.

[0351] D: One or two locations are read.

[0352] E: None of them could be read.

[0353] <Alcohol Resistance> A cotton swab was moistened with 100% ethanol. The leather surface was then wiped 10 times with the swab. After 10 wipings, the surface condition of both the solid image and the cotton swab was visually observed. The evaluation criteria are as follows.

[0354] A: The surface of the solid image remains unchanged, and the swab is not stained.

[0355] B: The surface of the solid image remains unchanged, but there is slight staining on the swab.

[0356] C: The surface of the solid image remains unchanged, but the swab is stained.

[0357] D: The solid image has faded, and the cotton swab is stained.

[0358] <Abrasion Resistance> A 500-cycle reciprocating vibrational friction test was conducted on the leather surface using cotton canvas No. 6, with a weighted average of 500g. After the friction test, the surface condition of both the solid image and the cotton canvas was visually observed. The evaluation criteria are as follows.

[0359] A: The surface of the solid image remains unchanged, and the cotton canvas is not colored.

[0360] B: The surface of the solid image remains unchanged, but there is slight coloration on the cotton canvas.

[0361] C: The surface of the solid image remains unchanged, but the cotton canvas is colored.

[0362] D: The solid image has faded, and the cotton canvas is stained.

[0363] The evaluation results are shown in Table 1.

[0364] [Table 1]

[0365] As shown in Table 1, it can be seen that in Examples 1-1 and 1-2, the process of applying invisible ink containing an infrared absorbing compound to a leather substrate to record code images and the process of forming an outer coating on the leather substrate with the recorded code images have excellent invisibility, readability after wiping, and readability after wiping with alcohol.

[0366] In Comparative Examples 1-1 and 1-2, it was found that after applying the external coating liquid, the invisible ink was applied, resulting in poor readability after wiping.

[0367] [Example 2-1] <Preparation of Cyan Ink C2, Magenta Ink M2, Yellow Ink Y2, and Black Ink K2> (Preparation of cyan pigment dispersion DC2, magenta pigment dispersion DM2, yellow pigment dispersion DY2, and black pigment dispersion DK2) The following pigments have been prepared.

[0368] • Cyan pigment (product name "HELIOGEN BLUE D 7110 F", pigment blue 15:4, manufactured by BASF) • Magenta pigment (product name "CINQUASIA MAGENTA L 4540", mixed quinacridone, manufactured by BASF) • Yellow pigment (product name "INKJET YELLOW 4GC", pigment yellow 155, manufactured by Clariant) • Black pigment (product name "Irgaphor (registered trademark) Black S0100CF", lactam black, manufactured by BASF) Using the above-mentioned pigments, cyan pigment dispersion DC2, magenta pigment dispersion DM2, yellow pigment dispersion DY2 and black pigment dispersion DK2 were prepared respectively.

[0369] The components other than the pigment were mixed and stirred at 2000-3000 rpm for 10-15 minutes using a mixer manufactured by SILVERSON. The pigment was then added, and the mixture was further stirred at 2000-3000 rpm for 10-20 minutes to obtain 500 parts by weight of a pre-dispersion. This was then dispersed using a circulating bead mill (product name "SL-012C1") manufactured by DISPERMAT. Under the dispersion conditions, 200 parts by weight of 0.65 mm diameter zirconia beads were filled, and the circumferential speed was set to 15 m / s. The dispersion time was set to 1-6 hours. • Pigment…30% by weight • Dispersant (product name "SOLS PERSE32000", manufactured by Lubrizol) ... 10% by mass • Diethylene glycol diethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) …60% by mass (Preparation of Cyan Ink C2) By mixing the following components and stirring at 2000-3000 rpm for 10-15 minutes using a mixer manufactured by SILVERSON, cyan ink C2 was obtained.

[0370] • Cyan pigment dispersion DC2…6% by mass ·Butyl 3-methoxyacetate (manufactured by Tokyo Chemical Industry Co., Ltd.)…79.9% by mass • Carbamate acrylate oligomer (product name "CN9001", manufactured by Sartomer Company, Inc.) ... 7% by mass • Vinyl chloride-vinyl acetate copolymer (product name "vinnol H14 / 36", manufactured by Wacker Chemie AG) ... 3% by mass • Polymerization inhibitor: Tris(N-nitroso-N-phenylhydroxylamine) aluminum salt (product name "FLORSTAB UV12", manufactured by Kromachem)...1% by mass • Polymerization initiator: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV) ... 2% by mass • Polymerization initiator: 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxymethylacetone (product name "Omnirad 2959", manufactured by IGM Resins BV)...1% by mass Surfactant: Product name "BYK-331", manufactured by BYK Corporation... 0.1% by mass (Preparation of magenta ink M2, yellow ink Y2, and black ink K2) The 6% by mass cyan pigment dispersion DC2 and 79.9% by mass 3-methoxyethyl acetate were replaced with 11.2% by mass magenta pigment dispersion DM2 and 74.7% by mass 3-methoxyethyl acetate. Otherwise, magenta ink M2 was obtained by the same method as the preparation of cyan ink C2.

[0371] The 6% by mass cyan pigment dispersion DC2 and 79.9% by mass 3-methoxyethyl acetate were replaced with 10% by mass yellow pigment dispersion DY2 and 75.9% by mass 3-methoxyethyl acetate. Otherwise, yellow ink Y2 was obtained by the same method as that used to prepare cyan ink C2.

[0372] The 6% by mass cyan pigment dispersion DC2 and 79.9% by mass 3-methoxyethyl acetate were replaced with 7.5% by mass black pigment dispersion DK2 and 78.4% by mass 3-methoxyethyl acetate. Otherwise, black ink K2 was obtained by the same method as the preparation of cyan ink C2.

[0373] <Preparation of Invisible Ink IR2> Compound B-1 was prepared as an infrared absorbing compound.

[0374] [Chemical Formula 16] A dispersion B of an infrared absorbing compound was prepared by mixing the components described below.

[0375] Compound B-1…4% by mass • Polymer dispersant (product name "SOLS PERSE 35000", manufactured by Lubrizol) ... 4% by mass • Polymer dispersant (product name "SOLSPERSE 5000S", manufactured by Lubrizol)...0.01% by mass · 3-Methyl-1,5-pentanediol diacrylate (product name "SR341", manufactured by Sartomer) ... 91.99% by mass The following components were mixed and stirred at 2000-3000 rpm for 10-15 minutes using a mixer manufactured by SILVERSON to obtain the invisible ink IR2.

[0376] • Dispersion of infrared absorbing compound B…25 parts ·3-Methyl-1,5-pentanediol diacrylate…66.8% by mass • Polymerization initiator: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV)...4% by mass • Pigment sensitizer: (Product name "SPEEDCURE 7010L", manufactured by Lambson) ... 4% by mass • Polymerization inhibitor: Tris(N-nitroso-N-phenylhydroxylamine) aluminum salt (product name "FLORSTAB UV12", manufactured by Kromachem)...0.1% by mass • Silicone-based surfactants: Product name "BYK307", BYK)...0.1% by mass <Preparation of External Coating Solution OC2> The following components were mixed and stirred at 2000-3000 rpm for 10-15 minutes using a mixer manufactured by SILVERSON to prepare the external coating liquid OC2.

[0377] ·3-Methoxyethylbutyrate…81% by mass • Carbamate acrylate oligomer (product name "CN9001", manufactured by Sartomer Company, Inc.) ... 5% by mass • Carbamate acrylate oligomer (product name "UV-7600B", manufactured by Mitsubishi Chemical Corporation) ... 5% by mass • Vinyl chloride-vinyl acetate copolymer (product name "vinnol H14 / 36", manufactured by Wacker Chemie AG) ... 2% by mass • Polymerization inhibitor: Tris(N-nitroso-N-phenylhydroxylamine) aluminum salt (product name "FLORSTAB UV12", manufactured by Kromachem)...1% by mass • Polymerization initiator: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV) ... 3% by mass • Polymerization initiator: 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxymethylacetone (product name "Omnirad 2959", manufactured by IGM Resins BV)...1% by mass • Silicone compound (product name "KP109", manufactured by Shin-Etsu Silicone Co., Ltd.) ... 2% by mass <Leather Manufacturing> -Visible ink application process- Cyan ink C2 was introduced into the cyan slot of the inkjet printer (product name "SUVJ-160", manufactured by Mimaki Engineering Co., Ltd.), magenta ink M2 was introduced into the magenta slot, yellow ink Y2 was introduced into the yellow slot, black ink K2 was introduced into the black slot, and external coating liquid OC2 was introduced into the transparent slot.

[0378] A solid image of cyan ink C1, magenta ink M1, yellow ink 1, and black ink K1 was recorded on a leather substrate (product name "Folegoard 2 #300", manufactured by Kyowa LifeTech Co., Ltd.). The resolution was 900 dpi × 1200 dpi, and the platen temperature was 70°C.

[0379] -Invisible ink application process- Using an inkjet printer (product name "DMP-2831", manufactured by FUJIFILM Dimatix, Inc.), invisible ink IR2 was ejected onto solid images of various colors to record screen codes (dot codes), QR codes, and barcodes manufactured by APOLO JAPAN CO.,LTD. An LED light source (wavelength 385nm) was positioned directly below the printhead and irradiated with ultraviolet light after image recording.

[0380] -Topical coating application process- A transparent PET film (product name "Viewful UV TP-100N", thickness 100μm, manufactured by Mimaki Engineering Co., Ltd.) was applied to an inkjet printer (product name "SUVJ-160"). A leather substrate with a recorded coded image was attached to the transparent PET film. An external coating liquid OC2 was ejected from a transparent throttle valve, recording a solid image over the entire surface of the coded image. The resolution was 900dpi × 1200dpi, and the pressure plate temperature was 70°C. After image recording was complete, the transparent PET film was peeled off.

[0381] [Comparative Example 2-1] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, the leather was obtained using the same method as in Example 2-1.

[0382] The obtained leather was evaluated in the same manner as in Examples 1-1. The evaluation results are shown in Table 2.

[0383] [Table 2]

[0384] As shown in Table 2, it can be seen that in Example 2-1, the process of applying invisible ink containing an infrared absorbing compound to a leather substrate to record code images and the process of forming an outer coating on the leather substrate with the recorded code images have excellent invisibility, readability after wiping, and readability after wiping with alcohol.

[0385] In Comparative Example 2-1, it can be seen that after applying the external coating liquid, the invisible ink was applied, resulting in poor readability after wiping.

[0386] [Example 3-1] <Preparation of Invisible Ink F1> (Preparation of the dispersion of fluorescent compound DF1) The black pigment was replaced with a fluorescent compound (4-methylumbelliferone (coumarin derivative)), and the amount of crosslinking agent was changed to 3.60 parts by mass, and the amount of boric acid aqueous solution was changed to 39.4 parts by mass. Otherwise, the dispersion of the fluorescent compound DF1 was obtained by the same method as the preparation of the black pigment dispersion DK1.

[0387] (Preparation of Invisible Ink F1) Invisible ink F1 was prepared by mixing the following components.

[0388] The dispersion of the fluorescent compound DF1… contains 4.0% by mass as a pigment. Propylene glycol…30.0% by mass Propylene glycol monomethyl ether…1.0% by mass ·EVAFANOL HA-55… contains 5.0% by mass as resin particles. • OLFINE E1010…1.0% of mass • BYK 3450…1.0% of mass ·PVPK15…0.15% quality •ST-XS… contains 0.05% by mass as colloidal silica particles. Water...totaling as a 100% mass surplus <Leather Manufacturing> Leather was obtained in the same manner as in Example 1-1, except that invisible ink F1 was used instead of invisible ink IR1.

[0389] [Example 3-2] Instead of the silicone compound in the topcoat OC1, water was added, and the topcoat OC1a was prepared using the same method as the topcoat OC1.

[0390] Leather was obtained using the same method as in Example 3-1, except that an external coating liquid OC1a was used.

[0391] [Comparative Example 3-1] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, leather was obtained using the same method as in Example 3-1.

[0392] [Example 3-2] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, leather was obtained using the same method as in Examples 3-2.

[0393] The obtained leather was evaluated in the same manner as in Examples 1-1. Additionally, regarding dotted codes, reading tests were conducted using a code reader application manufactured by Apollo Japan Co., Ltd., under black light. Regarding QR codes, reading tests were conducted using a QR code reader under black light. Regarding barcodes, reading tests were conducted using a barcode reader under black light.

[0394] The evaluation results are shown in Table 3.

[0395] [Table 3]

[0396] As shown in Table 3, it can be seen that in Examples 3-1 and 3-2, the steps of applying invisible ink containing fluorescent compounds to a leather substrate to record code images and forming an outer coating on the leather substrate with the recorded code images have excellent invisibility, readability after wiping, and readability after wiping with alcohol.

[0397] In Comparative Examples 3-1 and 3-2, it was found that after applying the external coating liquid, the invisible ink was applied, resulting in poor readability after wiping.

[0398] [Example 4-1] <Preparation of Invisible Ink Ph1> (Preparation of an aqueous dispersion of resin particles DPh1 containing photochromic compounds) A 1-liter three-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet was filled with 250 g of water, 1.84 g of 12-methylacrylamide dodecanoic acid, 0.68 g of potassium bicarbonate, and 20 g of isopropanol, and heated to 85°C under a nitrogen atmosphere. A mixed solution consisting of V-501 (free radical polymerization initiator, manufactured by FUJIFILM Wako Pure Chemical Corporation) (0.57 g), potassium bicarbonate (0.43 g), and water (9 g) was added and stirred for 10 minutes. Then, a solution consisting of methyl methacrylate (54 g), 2-ethylhexyl methacrylate (36 g), and a spiropyran compound (product name "TPC-0024", manufactured by YAMADA CHEMICAL CO.,LTD.) (10 g) was added dropwise to the flask at a constant rate over a period of 3 hours. Furthermore, a mixed solution consisting of V-501 (0.28 g), potassium bicarbonate (0.21 g), and water (6 g) was added in two batches, one immediately after the initial addition of the monomer solution and the other 1.5 hours later. After the initial addition of the monomer solution, the mixture was stirred for 1 hour, and then the mixed solution consisting of V-501 (0.28 g), potassium bicarbonate (0.21 g), and water (6 g) was added, followed by further stirring for 3 hours. The reaction mixture was filtered through a sieve with a mesh width of 50 μm to obtain an aqueous dispersion of resin particles DPh1 containing photochromic compounds. The resin particles DPh1 contain structural units derived from methyl methacrylate, structural units derived from 2-ethylhexyl methacrylate, and structural units derived from potassium 12-methacrylamide dodecanoate (59:39:2 (mass ratio)), and also contain spiropyran compounds.

[0399] The aqueous dispersion of resin particles DPh1 has a pH of 7.5, a solids concentration of 25% by mass, and a volume average particle size of 121 nm. Furthermore, the resin of DPh1 has a weight-average molecular weight (Mw) of 200,000 and a glass transition temperature of 70°C.

[0400] (Preparation of invisible ink Ph1) The following components were mixed to prepare the invisible ink Ph1.

[0401] • An aqueous dispersion of resin particles DPh1 containing photochromic compounds…40.0% by mass Propylene glycol…30.0% by mass Propylene glycol monomethyl ether…1.0% by mass • OLFINE E1010…1.0% of mass • BYK 3450…1.0% of mass ·PVPK15…0.15% quality •ST-XS… contains 0.05% by mass as colloidal silica particles. Water...totaling as a 100% mass surplus <Leather Manufacturing> Leather was obtained in the same manner as in Examples 1-1, except that invisible ink Ph1 was used instead of invisible ink IR1.

[0402] [Example 4-2] Instead of the silicone compound in the topcoat OC1, water was added, and the topcoat OC1a was prepared using the same method as the topcoat OC1.

[0403] Leather was obtained using the same method as in Example 4-1, except that an external coating liquid OC1a was used.

[0404] [Comparative Example 4-1] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, the leather was obtained using the same method as in Example 4-1.

[0405] [Example 4-2] After the visible ink application process, the outer coating liquid application process and the invisible ink application process were performed in sequence. Otherwise, leather was obtained using the same method as in Example 4-2.

[0406] The obtained leather was evaluated in the same manner as in Examples 1-1. Additionally, regarding dotted codes, reading tests were conducted using a code reader application manufactured by Apollo Japan Co., Ltd., under black light. Regarding QR codes, reading tests were conducted using a QR code reader under black light. Regarding barcodes, reading tests were conducted using a barcode reader under black light.

[0407] The evaluation results are shown in Table 4.

[0408] [Table 4]

[0409] As shown in Table 4, it can be seen that in Examples 4-1 and 4-2, the steps of applying invisible ink containing a photochromic compound to a leather substrate to record code images and forming an outer coating on the leather substrate with the recorded code images have excellent invisibility, readability after wiping, and readability after wiping with alcohol.

[0410] In Comparative Examples 4-1 and 4-2, it was found that after applying the external coating liquid, the invisible ink was applied, resulting in poor readability after wiping.

[0411] [Comparative Example 5-1] The leather substrate was changed to a leather substrate (product name "EL-200#201", manufactured by Shoko Co., Ltd.), and the leather was otherwise obtained using the same method as in Examples 1-1.

[0412] Approximately 2 μL of distilled water was dropped onto the surface of the leather substrate used in Examples 1-1 and 5-1. After 1000 microseconds, the contact angle of the water was measured using a contact angle meter (product name "Drop Master DMo-501", manufactured by Kyowa Interface Science Co., Ltd.).

[0413] The obtained leather was evaluated in the same manner as in Example 1-1.

[0414] The evaluation results are shown in Table 5.

[0415] [Table 5]

[0416] As shown in Table 5, in Comparative Example 5-1, it can be seen that the readability after wiping is poor because the water contact angle in the leather substrate exceeds 100°.

[0417] [Example 6-1] The solid content of the release paper for synthetic leather (product name "DN-TP (registered trademark)", manufactured by Nippon Printing Co., Ltd.) is coated with a thread roller to a solid content of 10 g / m². 2 The external coating liquid OC1 was dried at 130°C for 2 minutes to prepare the external coating film 1.

[0418] In Example 1-1, instead of performing the external coating liquid application process, after the visible ink application process, the external coating film 1 was adhered to the code image using a synthetic leather adhesive (product name "DIABOND kc-da888", manufactured by DIABOND CORPORATION). Then, the synthetic leather release paper was peeled off to obtain leather.

[0419] The obtained leather was evaluated in the same manner as in Example 1-1, and the results were the same as in Example 1-1.

[0420] Furthermore, the entire disclosure of Japanese Patent Application No. 2023-150289, filed on September 15, 2023, is incorporated herein by reference. Moreover, all documents, patent applications, and technical specifications described in this specification are incorporated herein by reference to the same extent that each document, patent application, and technical specification specifically and individually described and incorporated herein by reference.

Claims

1. A method for manufacturing leather, comprising: A process of applying invisible ink containing infrared absorbing compounds, fluorescent compounds, or photochromic compounds to a leather substrate with a water contact angle of less than 100° to record coded images; and The process of forming an outer coating on a leather substrate on which the code image is recorded.

2. The method for manufacturing leather according to claim 1, wherein, The code image is a barcode, a QR code that is a registered trademark, or a dotted code.

3. The method for manufacturing leather according to claim 1 or 2, wherein, The code image is a dotted code.

4. The method for manufacturing leather according to claim 1 or 2, wherein, The invisible ink contains the infrared-absorbing compound.

5. The method for manufacturing leather according to claim 1 or 2, wherein, The infrared absorbing compound is selected from at least one compound chosen from the group consisting of compounds represented by formulas (1) and (2) below. In equation (1), Y 1 and Y 2 Each group of nonmetallic atoms that forms an aliphatic ring or heterocycle is represented independently, M + L represents a proton, a monovalent alkali metal cation, or an organic cation. 1 This indicates a methine chain consisting of 5 or 7 methine groups, wherein the central methine group has a substituent represented by the following formula A. -S A -T A Formula A In equation A, S A Represents single bond, alkylene, alkenylene, ynylene, -O-, -S-, -NR L1 -, -C(=O)-, -C(=O)O-, -C(=O)NR L1 -、-S(=O)2-、-OR L2 - or a group consisting of at least two of these, R L1 R represents a hydrogen atom, halogen atom, alkyl, aryl, or monovalent heterocyclic group. L2 Indicates alkylene, arylene, or divalent heterocyclic group, T A The following groups are represented: halogen, alkyl, cycloalkyl, aryl, monovalent heterocyclic, cyano, hydroxyl, formyl, carboxyl, amino, thiol, sulfonyl, phosphoryl, boronyl, vinyl, ethynyl, trialkylsilyl, or trialkoxysilyl. A Indicates a single bond or alkylene group, and T A When representing an alkyl group, S A and T A The total number of carbon atoms contained therein is 3 or more. This indicates the bonding site with the central methine group of the methine chain. In equation (2), ring A and ring B independently represent aromatic rings or heteroaromatic rings, respectively, and X A and X B Each of the following independently represents a monovalent substituent, G A and G B Each of these groups represents a monovalent substituent independently, and kA represents 0 to n. A Integers, kB represents 0 to n B an integer, n A and n B They represent G that can be substituted on ring A or ring B, respectively. A and G B The largest integer, X A With G A They can bond together to form a ring, X B With G B They can bond together to form a ring, G A and G B When multiple G exist, A Each other and G B They can bond with each other to form a ring structure.

6. The method for manufacturing leather according to claim 1 or 2, wherein, The invisible ink is applied using an inkjet recording method.

7. The method for manufacturing leather according to claim 1 or 2, wherein, The process of forming the outer coating includes the process of applying an outer coating liquid.

8. The method for manufacturing leather according to claim 7, wherein, The external coating liquid contains a silicone compound.

9. The method for manufacturing leather according to claim 1 or 2, wherein, It also includes the process of applying visible ink containing colorant to the leather substrate to record a colored image. The code image is recorded on a leather substrate on which the coloring image is recorded.

10. The method for manufacturing leather according to claim 9, wherein, The colorants contained in the visible ink do not absorb infrared light.

11. The method for manufacturing leather according to claim 9, wherein, The visible ink is applied by inkjet recording.

12. The method for manufacturing leather according to claim 9, wherein, The process of forming the outer coating includes the process of applying an outer coating liquid.

13. The method for manufacturing leather according to claim 12, wherein, The external coating liquid contains a silicone compound.

14. The method for manufacturing leather according to claim 12, wherein, The invisible ink, the visible ink, and the external coating all contain urethane resin particles.

15. The method for manufacturing leather according to claim 12, wherein, The invisible ink, the visible ink, and the topcoat all contain water.

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