Method for producing leather

Abstract

The present invention provides a method for producing leather, comprising the steps of: applying invisible ink containing an infrared-absorbing compound, a fluorescent compound, or a photochromic compound onto a leather substrate to record a code image; and forming an overcoat layer on the leather substrate on which the code image is recorded.

Description

Leather manufacturing method

[0001] The present disclosure relates to a method for manufacturing leather.

[0002] In recent years, various studies have been conducted on the decoration of leather. For example, Japanese Patent Application Laid-Open No. 2019-77070 describes an inkjet printing method for leather having a surface made of synthetic resin, which includes the steps of heating the surface of leather, at least the surface of which is made of synthetic resin, to 40°C or higher, ejecting inks contained in an aqueous inkjet ink set onto the surface of the leather using an inkjet system, and heating the surface of the leather onto which the ink has been ejected to 60°C or higher, wherein the inks contained in the aqueous inkjet ink set contain at least water (A), a pigment (B), a water-soluble organic solvent component (C), a surfactant (D), and resin fine particles (E), and the glass transition temperature of the resin fine particles (E) is 0°C or lower, the ink contains, as the water-soluble organic solvent component (C), 8% by mass or more and 23% by mass or less of at least one substituted butanol selected from the group consisting of 3-methoxy-1-butanol and 3-methoxy-3-methyl-1-butanol, and the aqueous inkjet ink set includes a white ink containing a white pigment as the pigment (B) and a colored ink containing a pigment other than white as the pigment (B).

[0003] Furthermore, in recent years, there has been a demand for counterfeit prevention measures for leather-based products. As a counterfeit prevention measure, a method of recording a code image using infrared-absorbing ink is known. For example, Japanese Patent Application Laid-Open No. 2008-144004 describes an inkjet recording ink containing an infrared-absorbing oxonol compound.

[0004] For the purpose of preventing counterfeiting, when a code image is recorded on leather, it is required to ensure invisibility, readability after rubbing, and readability after wiping with alcohol.

[0005] The present disclosure has been made in consideration of the above circumstances, and an object of one embodiment of the present disclosure is to provide a method for manufacturing leather that produces leather on which a code image is recorded that is excellent in invisibility, readability after rubbing, and readability after wiping with alcohol.

[0006] The present disclosure includes the following aspects. <1> A method for producing leather, comprising the steps of applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound to a leather substrate having a water contact angle of 100° or less to record a code image, and forming an overcoat layer on the leather substrate on which the code image has been recorded. <2> A method for producing leather according to <1>, in which the code image is a barcode, a QR code (registered trademark), or a dot code. <3> A method for producing leather according to <1> or <2>, in which the code image is a dot code. <4> A method for producing leather according to any one of <1> to <3>, in which the invisible ink contains an infrared absorbing compound. <5> A method for producing leather according to any one of <1> to <4>, in which the infrared absorbing compound is at least one selected from the group consisting of compounds represented by the following formulas (1) and (2): In formula (1), Y １ and Y ２ each independently represents a non-metallic atomic group forming an aliphatic ring or a heterocycle; M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation; L １ represents a methine chain consisting of 5 or 7 methine groups, and the central methine group of the methine chain has a substituent represented by the following formula A: Ａ -T Ａ Formula A In formula A, S Ａ represents a single bond, an alkylene group, an alkenylene group, an alkynylene group, —O—, —S—, —NR Ｌ１ -, -C(=O)-, -C(=O)O-, -C(=O)NR Ｌ１ -, -S(=O) ２ -, -OR Ｌ２ - or a group formed by combining at least two of these, R Ｌ１represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group; R Ｌ２ represents an alkylene group, an arylene group, or a divalent heterocyclic group; T Ａ represents a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, a monovalent heterocyclic group, a cyano group, a hydroxy group, a formyl group, a carboxy group, an amino group, a thiol group, a sulfo group, a phosphoryl group, a boryl group, a vinyl group, an ethynyl group, a trialkylsilyl group, or a trialkoxysilyl group; S Ａ represents a single bond or an alkylene group, and T Ａ When represents an alkyl group, S Ａ and T Ａ In formula (2), the sum of the carbon atoms contained in the rings A and B is 3 or more, and * represents a bonding site with the central methine group of the methine chain. Ａ and X Ｂ each independently represents a monovalent substituent; G Ａ and G Ｂ each independently represents a monovalent substituent, and kA is 0 to n Ａ , kB is 0 to n Ｂ represents an integer of Ａ and n Ｂ each represents a G that can be substituted on ring A or ring B Ａ and G Ｂ represents the largest integer in Ａ and G Ａ may be bonded to each other to form a ring, and X Ｂ and G Ｂ may be bonded to each other to form a ring, G Ａ and G Ｂ If there are multiple of each, G Ａ Comrades and G ＢThey may be bonded to each other to form a ring structure. <6> A method for producing leather according to any one of <1> to <5>, in which the invisible ink is applied by an inkjet recording system. <7> A method for producing leather according to any one of <1> to <6>, in which the step of forming an overcoat layer includes a step of applying an overcoat liquid. <8> A method for producing leather according to <7>, in which the overcoat liquid includes a silicone compound. <9> A method for producing leather according to any one of <1> to <8>, further including a step of applying a visible ink containing a colorant onto a leather substrate to record a colored image, and recording a code image on the leather substrate on which the colored image has been recorded. <10> A method for producing leather according to <9>, in which the colorant contained in the visible ink does not absorb in the infrared region. <11> A method for producing leather according to <9> or <10>, in which the visible ink is applied by an inkjet recording system. <12> The method for producing leather according to any one of <9> to <11>, wherein the invisible ink, the visible ink, and the overcoat liquid all contain urethane resin particles. <13> The method for producing leather according to any one of <9> to <12>, wherein the invisible ink, the visible ink, and the overcoat liquid all contain water.

[0007] According to the present disclosure, there is provided a method for manufacturing leather that produces leather on which a code image is recorded that is highly invisible, readable after rubbing, and readable after wiping with alcohol.

[0008] The leather manufacturing method of the present disclosure will be described in detail below.

[0009] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in an example.

[0010] In the present disclosure, the amount of each component in a composition means the total amount of the components in the composition unless otherwise specified, when the composition contains multiple substances corresponding to each component. In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect. In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0011] In this disclosure, the term "image" refers to a film formed by ink in general, and "image recording" refers to the formation of an image (i.e., a film). The concept of "image" in this disclosure also includes a solid image.

[0012] In this disclosure, "synthetic leather" refers to an artificially produced material, as distinguished from natural leather, which is produced using animal hide as a raw material. The concept of "synthetic leather" in this disclosure also encompasses artificial leather, man-made leather, and fake leather.

[0013] [Method for manufacturing leather] The method for manufacturing leather of the present disclosure includes a step of applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound onto a leather substrate to record a code image, and a step of forming an overcoat layer on the leather substrate on which the code image has been recorded.

[0014] In the leather manufacturing method of the present disclosure, a code image is recorded on a leather substrate, and an overcoat layer is formed on the leather substrate on which the code image has been recorded, thereby easily obtaining leather on which the code image has been recorded. The leather manufacturing method of the present disclosure does not require any special manufacturing steps and is useful as a method for manufacturing leather on which a code image has been recorded.

[0015] The code image is recorded by applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound, which provides excellent invisibility. Furthermore, by forming an overcoat layer on the leather substrate on which the code image is recorded, the code image has excellent readability after rubbing and after wiping with alcohol.

[0016] In contrast, Patent Document 1 does not describe a method for recording a code image. Patent Document 2 does not describe anything that focuses on leather as a substrate. Neither Patent Document 1 nor Patent Document 2 describes a process for forming an overcoat layer.

[0017] Each step of the leather manufacturing method of the present disclosure will be described below.

[0018] <Invisible Ink Application Step> The method for producing leather according to the present disclosure includes a step of applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound onto a leather substrate to record a code image (hereinafter referred to as the "invisible ink application step").

[0019] (Leather substrate) In the present disclosure, the leather substrate can be appropriately selected from substrates commonly used in the production of natural leather or synthetic leather. The leather produced by the leather production method of the present disclosure may be natural leather or synthetic leather, but synthetic leather is preferred. In addition, commonly available synthetic leather may have an overcoat layer containing a silicone-based slip agent on the surface to improve stain resistance and abrasion resistance. It is also preferred to use the material before this overcoat layer is applied as the leather substrate. In recent years, "vegan leather," a substrate produced without using animal-derived materials, has been attracting attention. The leather substrate is preferably vegan leather. Vegan leather includes petroleum-derived substrates and plant-derived substrates.

[0020] From the viewpoint of environmental friendliness, the leather substrate is preferably a resin substrate used in the production of synthetic leather, and more preferably a plant-derived substrate. Plant-derived substrates refer to substrates manufactured from plants. Examples of plants include pineapple, apple, grape, and mushroom. Plant-derived substrates may also contain petroleum-derived components.

[0021] A preferred example of a leather substrate is Piñatex, manufactured by Ananas Anam S.A. Piñatex is a plant-derived substrate containing approximately 72% by weight of pineapple leaf fiber.

[0022] The surface of the leather substrate is preferably subjected to a graining process. Graining is an uneven wrinkle pattern.

[0023] The shape of the leather substrate is not particularly limited, and may be, for example, a sheet. The thickness of the leather substrate is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0024] From the viewpoint of readability, the leather substrate has a water contact angle of 100° or less, preferably 90° or less. The lower limit of the contact angle is, for example, 50°. The water contact angle is measured using a contact angle meter after dropping approximately 2 μL of distilled water onto the surface of the leather substrate to be measured and waiting 1000 microseconds. The water contact angle is measured, for example, using a contact angle meter (product name "Drop Master DMo-501", manufactured by Kyowa Interface Science Co., Ltd.).

[0025] (Invisible Ink) The invisible ink applied in the invisible ink application step contains an infrared absorbing compound, a fluorescent compound, or a photochromic compound. The invisible ink may contain only one type of infrared absorbing compound, one type of fluorescent compound, and one type of photochromic compound, or two or more types of infrared absorbing compound, one type of fluorescent compound, and one type of photochromic compound.

[0026] Infrared-Absorbing Compound In the present disclosure, an infrared-absorbing compound refers to a compound having a maximum absorption wavelength in the wavelength range of 750 nm to 1,400 nm.

[0027] In particular, from the viewpoint of invisibility, the infrared absorbing compound is preferably at least one selected from the group consisting of compounds represented by the following formula (1) and formula (2):

[0028]

[0029]

[0030] In formula (1), Y １ and Y ２ each independently represents a non-metallic atomic group forming an aliphatic ring or a heterocycle; M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation; L １represents a methine chain consisting of 5 or 7 methine groups, and the central methine group of the methine chain has a substituent represented by the following formula A: Ａ -T Ａ Formula A In formula A, S Ａ represents a single bond, an alkylene group, an alkenylene group, an alkynylene group, —O—, —S—, —NR Ｌ１ -, -C(=O)-, -C(=O)O-, -C(=O)NR Ｌ１ -, -S(=O) ２ -, -OR Ｌ２ - or a group formed by combining at least two of these, R Ｌ１ represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group; R Ｌ２ represents an alkylene group, an arylene group, or a divalent heterocyclic group; T Ａ represents a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, a monovalent heterocyclic group, a cyano group, a hydroxy group, a formyl group, a carboxy group, an amino group, a thiol group, a sulfo group, a phosphoryl group, a boryl group, a vinyl group, an ethynyl group, a trialkylsilyl group, or a trialkoxysilyl group; S Ａ represents a single bond or an alkylene group, and T Ａ When represents an alkyl group, S Ａ and T Ａ The total number of carbon atoms contained in is 3 or more, and * represents the bonding site with the central methine group of the methine chain.

[0031] In formula (2), ring A and ring B each independently represent an aromatic ring or a heteroaromatic ring; Ａ and X Ｂ each independently represents a monovalent substituent; G Ａ and G Ｂ each independently represents a monovalent substituent, and kA is 0 to n Ａ , kB is 0 to n Ｂ represents an integer of Ａ and n Ｂ each represents a G that can be substituted on ring A or ring B Ａ and G Ｂ represents the largest integer in Ａ and G Ａ may be bonded to each other to form a ring, and XＢ and G Ｂ may be bonded to each other to form a ring, G Ａ and G Ｂ If there are multiple of each, G Ａ Comrades and G Ｂ They may be bonded to each other to form a ring structure.

[0032] For details of the compounds represented by formula (1) and formula (2), refer to WO 2021 / 065151.

[0033] <<Compound represented by formula (1)>> [Y １ and Y ２ 〕 Y １ and Y ２ may be the same nonmetallic atomic group or different nonmetallic atomic groups, but from the viewpoint of synthesis suitability, they are preferably the same nonmetallic atomic group.

[0034] In formula (1), Y １ and Y ２ are each independently preferably a group of non-metal atoms forming a heterocycle, and more preferably a group of non-metal atoms forming the same heterocycle. １ and Y ２ The hetero ring formed by the formula (I) is preferably a barbituric acid ring from the viewpoint of invisibility.

[0035] [M ＋ 〕 M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation. From the viewpoint of improving the light fastness and moist heat resistance of the resulting code image, M ＋ is preferably a monovalent alkali metal cation.

[0036] Among them, the monovalent alkali metal cation is Li ＋ , Na ＋ , K. ＋ , Rb ＋ , or Cs ＋ is preferred, and Li ＋ , Na ＋ , K. ＋ , Rb ＋ , or Cs ＋ is more preferred, and Li ＋ , Na ＋, or K ＋ is more preferable.

[0037] [L １ 〕 L １ represents a methine chain consisting of 5 or 7 methine groups, and the central methine group of the methine chain has a substituent represented by formula A. １ represents a methine chain consisting of 5 or 7 methine groups, and preferably represents a methine chain consisting of 5 methine groups. Methine groups other than the central methine group of the methine chain may be substituted, but are preferably unsubstituted. The methine chain may have a crosslinked structure at any position. For example, carbons on both sides of a methine group may be crosslinked to form a ring structure. The introduction of a ring structure can control the light resistance, etc. of a code image obtained using an invisible ink. The ring structure may be appropriately determined depending on the purpose of use of the invisible ink. The ring structure is not particularly limited, but is preferably an aliphatic ring, and a 5-membered aliphatic ring or a 6-membered aliphatic ring is preferred. Specifically, L １ is preferably a group represented by the following formula L1-1, L1-2, L2-1, or L2-2, and more preferably a group represented by the following formula L1-1 or L1-2.

[0038]

[0039] In formulas L1-1, L1-2, L2-1, and L2-2, A represents a substituent represented by formula A, and the wavy lines each independently represent L in formula (1). １ Each represents a bonding position with a structure other than Ｌ represents a non-metallic atomic group forming an aliphatic ring or a hetero ring, and preferably represents a non-metallic atomic group forming an aliphatic ring. Ｌ is preferably an alkyl group, and examples of the alkyl group include —CH ２ CH ２ - and -CH ２ C(Z) ２ -CH ２ The aliphatic ring is preferably a five-membered aliphatic ring or a six-membered aliphatic ring.

[0040] -Substituent represented by formula A- In formula A, SＡ represents a single bond, an alkylene group, an alkenylene group, an alkynylene group, —O—, —S—, —NR Ｌ１ -, -C(=O)-, -C(=O)O-, -C(=O)NR Ｌ１ -, -S(=O) ２ -, -OR Ｌ２ -, or a group formed by combining at least two of these. Ａ From the viewpoint of improving the invisibility of the resulting code image, is preferably a single bond, an alkylene group, an alkenylene group, or an alkynylene group, and more preferably a single bond.

[0041] In formula A, T Ａ represents a halogen atom, an alkyl group, an aryl group, a monovalent heterocyclic group, a cyano group, a hydroxy group, a formyl group, a carboxy group, an amino group, a thiol group, a sulfo group, a phosphoryl group, a boryl group, a vinyl group, an ethynyl group, a trialkylsilyl group, or a trialkoxysilyl group, and is preferably an aryl group, a monovalent heterocyclic group, or a trialkylsilyl group.

[0042] Among these, from the viewpoint of dispersibility, T Ａ is preferably a nitrogen atom-containing heterocyclic group, an aryl group, or a halogen atom.

[0043] From the viewpoint of further improving invisibility, the compound represented by formula (1) is preferably a compound represented by the following formula (1A):

[0044]

[0045] In formula (1A), M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation; L １ represents a methine chain consisting of 5 or 7 methine groups, and the central methine group of the methine chain has a substituent represented by the above formula A.

[0046] R １ , R ２ , R ３ and R ４ each independently represents a hydrogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group. Each X independently represents an O atom, a S atom, or a Se atom.

[0047] [L １ and M ＋ ] In formula (1A), L １ and M ＋ is L in formula (1) １ and M ＋ The same applies to the preferred embodiments.

[0048] [R １ , R ２ , R ３ and R ４ ] In formula (1A), R １ , R ２ , R ３ , and R ４ each independently represents a hydrogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group, and from the viewpoint of the light fastness and invisibility of the resulting code image, a hydrogen atom or an aryl group is preferred, and a hydrogen atom or a phenyl group is more preferred.

[0049] R １ , R ２ , R ３ and R ４ The aryl group in the formula (1A) is preferably an aryl group having 6 to 20 carbon atoms, more preferably a phenyl group or a naphthyl group, and even more preferably a phenyl group. The aryl group may be unsubstituted, but preferably has a substituent. From the viewpoints of dispersibility and association stability, the position at which the substituent is introduced is preferably the meta or para position relative to the bonding site with other structures in formula (1A), more preferably the meta position. Among these, an embodiment having a polar group at the meta position is more preferred.

[0050] From the viewpoint of the light resistance and moist heat resistance of the code image, the substituent is preferably a hydrogen-bonding group. A hydrogen-bonding group is a group that interacts via a hydrogen atom. Among the substituents exemplified above, examples of the hydrogen-bonding group include -OH, -C(=O)OH, -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) ２ R Ｌ３ , and -S(=O) ２ N (R Ｌ３ ) ２ Among these, the hydrogen-bonding group is —NHC(═O)OR Ｌ３ is more preferred.

[0051] R Ｌ３ R each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or a monovalent heterocyclic group, and is preferably a hydrogen atom, an alkyl group, or an aryl group. Ｌ３ The alkyl group in is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and further preferably a methyl group or an ethyl group.

[0052] In addition, from the viewpoint of improving the light resistance and moist heat resistance of the resulting code image, R １ , R ２ , R ３ , and R ４ Preferably, at least one selected from the group consisting of is a hydrogen atom, and R １ , R ２ , R ３ , and R ４ It is more preferable that at least two selected from the group consisting of are hydrogen atoms, and R １ , R ２ , R ３ , and R ４ It is more preferable that two selected from the group consisting of R are hydrogen atoms. １ , R ２ , R ３ , and R ４ When two selected from the group consisting of are hydrogen atoms, R １ and R ２ One of the two and R ３ and R ４ and R are preferably hydrogen atoms. １ and R ２ One of the two and R ３ and R ４ and one of R is a hydrogen atom, １ and R ２ and the other one of R３ and R ４ and the other of the two is preferably a phenyl group. As described above, the phenyl group more preferably has a substituent.

[0053] [X] In formula (1A), each X independently represents an O atom, an S atom, or an Se atom, and is preferably an O atom or an S atom, and more preferably an O atom.

[0054] From the viewpoint of further improving invisibility, the compound represented by formula (1A) is preferably a compound represented by the following formula (1B):

[0055]

[0056] In formula (1B), M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation. １ represents a methine chain consisting of 5 or 7 methine groups, the central methine group of which has a substituent represented by the above formula A.

[0057] R ５ and R ７ R each independently represents a hydrogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group. ６ and R ８ each independently represents an alkyl group, a halogen atom, an alkenyl group, an aryl group, a monovalent heterocyclic group, a nitro group, a cyano group, or —OR 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) ２ R Ｌ３ , -S(=O) ２ ORＬ３ , -NHS(=O) ２ R Ｌ３ , or -S(=O) ２ N (R Ｌ３ ) ２ Represents R Ｌ３ each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or a monovalent heterocyclic group; each independently represents an integer of 1 to 5; and each independently represents an O atom, a S atom, or a Se atom.

[0058] [L １ , M ＋ and X] In formula (1B), L １ , M ＋ and X is L in formula (1A). １ , M ＋ and X have the same meanings, and preferred embodiments are also the same.

[0059] [R ５ , R ６ , R ７ and R ８ 〕 R ５ and R ７ R each independently represents a hydrogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group, and a hydrogen atom is preferred. ５ and R ７ The alkyl group, aryl group, or monovalent heterocyclic group in １ and R ３ The preferred embodiments are the same as those of the alkyl group, aryl group, or monovalent heterocyclic group in R. ６ and R ８ each independently represents an alkyl group, a halogen atom, an alkenyl group, an aryl group, a monovalent heterocyclic group, a nitro group, a cyano group, or —OR 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) ２ R Ｌ３ , -S(=O) ２ OR Ｌ３ , -NHS(=O) ２ R Ｌ３ , or -S(=O) ２ N (R Ｌ３ ) ２ represents the above R Ｌ３ is R １ ~R ４ R in Ｌ３ The same applies to the preferred embodiments. ６ and R ８ are each independently preferably a hydrogen-bonding group. Examples of the hydrogen-bonding group 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) ２ R Ｌ３ , and -S(=O) ２ N (R Ｌ３ ) ２ and -NHC(=O)OR Ｌ４ The above R Ｌ３ is R １ ~R ４ R in Ｌ３ The same definitions and preferred embodiments are also the same. Ｌ４ represents an alkyl group, preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group.

[0060] From the viewpoint of storage stability of the invisible ink, the compound represented by formula (1B) is ６ and a group represented by R ８ In this case, it is preferable that R ６ or a group represented by R ８The bonding position of the group represented by R ６ or R ８ In the benzene ring to which the group represented by the following formula (I) is bonded, it is preferably at the meta position relative to the bonding position to the barbituric acid ring.

[0061] In formula (1B), R ５ , R ６ , R ７ , and R ８ Preferably, at least one selected from the group consisting of is a hydrogen-bonding group, and R ５ , R ６ , R ７ , and R ８ It is more preferable that at least two selected from the group consisting of R ５ and R ７ , and R ６ and R ８ are preferably the same groups. ５ and R ７ are each a hydrogen atom, and R ６ and R ８ are preferably the same hydrogen-bonding groups.

[0062] [n] Each n independently represents an integer of 1 to 5, and from the viewpoint of ease of dispersion, an integer of 1 to 3 is preferred, 1 or 2 is more preferred, and 1 is even more preferred.

[0063] <<Compound represented by formula (2)>> [G Ａ and G Ｂ 〕 G Ａ and G Ｂ each independently represents a monovalent substituent. Examples of the monovalent substituent include a halogen atom, a cyano group, a nitro group, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heteroaryl group, an aralkyl group, -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 , -SO ２ R ２３ , -SO ２ OR ２４ , -NHSO ２ R ２５ , or SO ２ NR ２６ R ２７ Examples include: R １０ ~R ２７ each independently represents a hydrogen atom, an aliphatic group, an aromatic group, or a heterocyclic group. １２ R １２ When —SO 3 is a hydrogen atom (i.e., a carboxyl group), the hydrogen atom may dissociate (i.e., a carbonate group) or may be in the form of a salt. ２ OR ２４ R ２４ When is a hydrogen atom (i.e., a sulfo group), the hydrogen atom may be dissociated (i.e., a sulfonate group) or may be in the form of a salt.

[0064] [X Ａ and X Ｂ 〕 X Ａ and X Ｂ Each independently represents a monovalent substituent. The substituent is preferably a group having an active hydrogen, such as —OH, —SH, —COOH, or —SO ３ H, -NR Ｘ１ R Ｘ２ , -NHCOR Ｘ１ , -CONR Ｘ１ R Ｘ２ , -NHCONR Ｘ１ R Ｘ２ , -NHCOOR Ｘ１ , -NHSO ２ R Ｘ１ , -B(OH) ２ and PO(OH) ２ is more preferred, and —OH, —SH, and NR Ｘ１ R Ｘ２ is more preferable.

[0065] R Ｘ１ and R Ｘ２Each of the groups independently represents a hydrogen atom or a monovalent substituent. Examples of the substituent include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, and a heteroaryl group. Among these, the substituent is preferably an alkyl group. The alkyl group is preferably linear or branched. For details of the alkyl group, the alkenyl group, the alkynyl group, the aryl group, and the heteroaryl group, see G Ａ and G Ｂ This has the same meaning as the range explained above.

[0066] [Ring A and Ring B] Ring A and ring B each independently represent an aromatic ring or a heteroaromatic ring. The aromatic ring and heteroaromatic ring may be a monocyclic ring or a fused ring.

[0067] Among these, the aromatic ring and heteroaromatic ring are preferably a benzene ring or a naphthalene ring. The aromatic ring may be unsubstituted or may have a substituent. Examples of the substituent include G Ａ and G Ｂ Examples of the substituents include those described above.

[0068] X Ａ and G Ａ may be bonded to each other to form a ring, and X Ｂ and G Ｂ may be bonded to each other to form a ring, G Ａ and G Ｂ If there are multiple of each, G Ａ Comrades and G Ｂ They may be bonded to each other to form a ring. The ring is preferably a 5-membered or 6-membered ring. The ring may be a monocyclic ring or a polycyclic ring. Ａ and G Ａ , X Ｂ and G Ｂ , G Ａ Comrades or G Ｂ When X are bonded to each other to form a ring, they may be bonded directly to form the ring, or may be bonded via a divalent linking group selected from the group consisting of an alkylene group, -CO-, -O-, -NH-, -BR-, and combinations thereof to form the ring. Ａ and G Ａ , X Ｂ and G Ｂ , G ＡComrades or G Ｂ It is preferable that they are bonded to each other via -BR- to form a ring. R represents a hydrogen atom or a monovalent substituent. Examples of the substituent include G Ａ and G Ｂ The substituent is preferably an alkyl group or an aryl group.

[0069] [kA and kB] kA is 0 to n Ａ represents an integer from 0 to n Ｂ represents an integer of Ａ represents the maximum integer that can be substituted on ring A, and n Ｂ represents the maximum integer that can be substituted on ring B. kA and kB each independently represent preferably 0 to 4, more preferably 0 to 2, and particularly preferably 0 or 1.

[0070] From the viewpoint of improving light resistance, the compound represented by formula (2) is preferably a compound represented by formula (2A).

[0071]

[0072] In formula (2A), R １ and R ２ each independently represents a monovalent substituent, R ３ and R ４ each independently represents a hydrogen atom or an alkyl group. Ａ and G Ｂ Examples of the substituents are those described above. １ and X ２ are each independently an oxygen atom or —N(R ５ )-, and X ３ and X ４ each independently represents a carbon atom or a boron atom; ３ and X ４ represents 1 when X is a boron atom; ３ and X ４ When R is a carbon atom, it represents 2. ５ represents a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group; Y １ , Y ２ , Y ３ , and Y４ each independently represents a monovalent substituent; Y １ and Y ２ may be bonded to each other to form a ring, and Y ３ and Y ４ may be bonded to each other to form a ring, and Y １ , Y ２ , Y ３ , and Y ４ When a plurality of each of these groups are present, they may be bonded to each other to form a ring. Ａ and G Ｂ p and s each independently represent an integer of 0 to 3, and q and r each independently represent an integer of 0 to 2. R １ , R ２ , Y １ , Y ２ , Y ３ , and Y ４ The substituent represented by is G Ａ and G Ｂ The same substituents as those described above are also included.

[0073] R ３ and R ４ is preferably a hydrogen atom, a methyl group, or an ethyl group, particularly preferably a hydrogen atom or a methyl group, and most preferably a hydrogen atom. １ and X ２ may be the same or different, but are preferably the same. ５ is preferably a hydrogen atom, an alkyl group or an aryl group, more preferably a hydrogen atom or an alkyl group.

[0074] The molecular weight of the compound represented by formula (2A) is preferably from 100 to 2,000, more preferably from 150 to 1,000.

[0075] The compound represented by formula (2) is described in detail in JP 2011-2080101 A. The compound described in JP 2011-2080101 A can be suitably used as the infrared absorbing compound in the present disclosure. Specific examples of the compound represented by formula (2) include the compounds described in JP 2011-208101 A and the compounds described in paragraphs 0076 and 0077 of JP 2018-154672 A. However, specific examples of the compound represented by formula (2) are not limited to these descriptions.

[0076] The content of the infrared absorbing compound is preferably 0.3% by mass to 5% by mass, and more preferably 0.5% by mass to 2% by mass, relative to the total mass of the invisible ink.

[0077] -Fluorescent Compound- In the present disclosure, a fluorescent compound refers to a compound that emits fluorescence. The fluorescent compound may be an inorganic compound, an organic compound, or an organic-inorganic composite. Examples of inorganic red phosphors include YVO4, ４ : Eu, Y ２ O ３ : Eu, Y ２ SiO ５ : Eu, Y ３ AlO １２ : Eu, Y ２ O ２ S: Eu, Bi, Zn ３ (P.O. ４ ) ２ : Mn, YBO ３ : Eu, CaLa ２ S ４ :Ce, (Y, Gd)BO ３ :Eu, SrS:Eu, (Ca,Sr)S:Eu, GdBO ３ : Eu, ScBO ３ : Eu, LuBO ３ : Eu, YVO ４ : Bi, Eu, YVO ４ Examples of inorganic blue phosphors include: Pb, Eu, etc. ２ SiO ５ : Ce, CaWO ４ :Pb, BaMgAl １４O ２３ :Eu, BaMgAl １０ O １７ : Eu, Mn, Zn ２ GeO ４ : Mn, MgAl ２ O ４ Examples of inorganic green phosphors include Zn, ２ SiO ４ : Mn, BaAl １２ O １９ :Mn, BaMgAl １４ O ２３ : Mn, SrAl １３ O １９ : Mn, CaAl １２ O １９ : Mn, YBO ３ : Tb, YBCO ３ :Ce, Tb, LaPO ４ :Ce, Tb, LuBO ３ :Tb, GdBO ３ : Tb, ScBO ３ : Tb, Sr ６ Si ３ O ３ C １４ : Eu, YVO ４ :Tb and the like.

[0078] Examples of organic fluorescent compounds include fluorescein, eosin, rhodamine B, rhodamine 6G, thioflavin, diaminostilbenedisulfonic acid, imidazole, coumarin, triazole, carbazole, pyridine, naphthalic acid, imidazolone, anthracene, and derivatives of these compounds.

[0079] An example of the organic-inorganic composite is the organic-inorganic composite described in Japanese Patent No. 5630752.

[0080] From the viewpoint of further improving invisibility and readability, the fluorescent compound is preferably an organic fluorescent compound.

[0081] The content of the fluorescent compound is preferably 1% by mass to 8% by mass, and more preferably 2% by mass to 6% by mass, relative to the total mass of the invisible ink.

[0082] Photochromic Compound: In the present disclosure, a photochromic compound is a compound whose chemical bonding state changes under the action of light, reversibly generating two isomers. The two isomers have different absorption spectra. Photochromic compounds have the property of becoming colored when irradiated with ultraviolet light, for example, and then returning to their colorless state when irradiated with visible light.

[0083] Examples of photochromic compounds include photo-opening / closing compounds that change from an open-ring form to a closed-ring form or from a closed-ring form to an open-ring form under the action of light, and photo-induced geometric isomerization compounds that change from a trans form to a cis form. Among these, from the viewpoint of repeated use 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 under the action of light, i.e., photo-opening / closing type photochromic compounds, are preferred.

[0084] Examples of photochromic compounds of the photo-opening / closing type include spiro compounds, naphthopyran compounds, diarylethene compounds, fulgide compounds, and fulgimide compounds. Examples of spiro compounds include spiropyran compounds, spirothiopyran compounds, and spirooxazine compounds. In the present disclosure, from the viewpoint of thermal stability, the photochromic compound is preferably at least one selected from the group consisting of spiropyran compounds, spirooxazine compounds, naphthopyran compounds, and diarylethene compounds.

[0085] In the present disclosure, the term "type compound" refers to a compound having in its molecule a skeleton or structure with the name "type compound." For example, the term "spiro type compound" refers to a compound having a spiro skeleton.

[0086] As a preferred embodiment of the photochromic compound, reference can be made to WO 2021 / 095372.

[0087] <<Spiro Compound>> The spiro compound is represented by, for example, the following formula (3).

[0088]

[0089] In formula (3), X is NR １ , O or S. １ represents an aliphatic group or an aromatic group. The aliphatic group and the aromatic group may have a substituent.

[0090] X is NR １ It is preferable that:

[0091] In formula (3), Q is O, S, or CR ２ R ３ Represents R ２ and R ３ each independently represents an aliphatic group or an aromatic group.

[0092] Q is CR ２ R ３ It is preferable that:

[0093] In formula (3), Y represents N, O or S. Y is preferably O.

[0094] In formula (3), Z represents CH, N, or P. Z is preferably CH or N.

[0095] In formula (3), A represents a group of atoms that constitute a ring formed by bonding to Q and X.

[0096] Examples of the ring structure formed by A, Q, and X include a 5- or 6-membered monocyclic structure and a polycyclic structure formed by combining two or more 5- or 6-membered monocyclic structures, and a bicyclic structure is preferred.

[0097] Among these, the ring formed by A, Q and X is preferably a bicyclic ring consisting of an aromatic ring and a heterocyclic ring, and more preferably an indole ring.

[0098] In formula (3), V １ represents a substituent bonded to the ring formed by A, Q and X.

[0099] In formula (3), m1 represents an integer of 0 to 4.

[0100] In formula (3), R ４ and R ５each independently represents a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), a cyano group, a nitro group, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, a heterocyclic group, -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 , -SO ２ R ２３ , -SO ２ OR ２４ , -NHSO ２ R ２５ or SO ２ NR ２６ R ２７ Represents R １０ ~R ２７ R each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, or a heterocyclic group. ４ and R ５ may be bonded to each other to form a ring having 3 to 20 carbon atoms.

[0101] R ４ and R ５ When R are bonded to each other to form a ring, examples of the ring structure include a 5- or 6-membered monocyclic structure and a polycyclic structure in which two or more 5- or 6-membered monocyclic structures are combined. ４ and R ５ The ring formed by bonding together is preferably an aromatic hydrocarbon ring, more preferably a benzene ring or a naphthalene ring.

[0102] In formula (3), the ring formed by A, Q, and X is more preferably an indole ring, and R４ and R ５ are preferably bonded to each other to form a ring having 3 to 20 carbon atoms. Specifically, the spiro compound is preferably represented by the following formula (3A):

[0103]

[0104] In formula (3A), Y, Z, R １ , V １ and m1 are the same as in formula (3).

[0105] In formula (3A), B represents an atomic group necessary to form an aromatic hydrocarbon ring, such as a benzene ring or a naphthalene ring.

[0106] In formula (3A), V ２ represents a substituent bonded to the ring formed by B. ２ Examples of the alkyl group include a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), a cyano group, a nitro group, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, a heterocyclic group, -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 , -SO ２ R ２３ , -SO ２ OR ２４ , -NHSO ２ R ２５ or SO ２ NR ２６ R ２７ Represents R １０ ~R ２７each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, or a heterocyclic group.

[0107] In formula (3A), m2 represents an integer of 0 to 4.

[0108] <<Naphthopyran Compound>> The naphthopyran compound is represented by, for example, the following formula (4A) or (4B).

[0109]

[0110] In formula (4A) and formula (4B), V ３ represents a substituent bonded to the naphthalene ring, and R ３０ , R ３１ , R ３２ and R ３３ represents a substituent bonded to the pyran ring.

[0111] In formula (4A) and formula (4B), R ３０ , R ３１ , R ３２ , R ３３ and V ３ each independently represents a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), a cyano group, a nitro group, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, a heterocyclic group, -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 , -SO ２ R ２３ , -SO ２ OR ２４ , -NHSO ２ R ２５or SO ２ NR ２６ R ２７ Represents R １０ ~R ２７ each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, or a heterocyclic group. Examples of the alkyl group, alkenyl group, alkynyl group, aralkyl group, aryl group, and heterocyclic group include those described above. The alkyl group, alkenyl group, alkynyl group, aralkyl group, aryl group, and heterocyclic group may have a substituent.

[0112] In formula (4A) and formula (4B), m3 represents an integer of 0 to 6.

[0113] <<Diarylethene Compound>> The diarylethene compound is represented by, for example, formula (5) below.

[0114]

[0115] In formula (5), Z １ and Z ２ are each independently NR ４８ , O or S. ４８ represents an aliphatic group or an aromatic group. The aliphatic group and the aromatic group may have a substituent. Preferred embodiments of the aliphatic group and the aromatic group are the same as the preferred embodiments described above. In addition, preferred embodiments of the substituent are the same as the preferred embodiments described above.

[0116] Z １ and Z ２ are each independently preferably S.

[0117] In formula (5), R ４０ , R ４１ , R ４２ , R ４３ , R ４４ , R ４５ , R ４６ and R ４７each independently represents a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), a cyano group, a nitro group, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, a heterocyclic group, -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 , -SO ２ R ２３ , -SO ２ OR ２４ , -NHSO ２ R ２５ or SO ２ NR ２６ R ２７ Represents R １０ ~R ２７ each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an aryl group having 6 to 19 carbon atoms, or a heterocyclic group. Examples of the alkyl group, alkenyl group, alkynyl group, aralkyl group, aryl group, and heterocyclic group include those described above. The alkyl group, alkenyl group, alkynyl group, aralkyl group, aryl group, and heterocyclic group may have a substituent.

[0118] R ４１ and R ４２ , R ４３ and R ４４ , and R ４５ and R ４６ may be bonded to each other to form a ring having 3 to 20 carbon atoms. ４１ and R ４２ , and R ４５ and R ４６When these are bonded to each other to form a ring, examples of the ring structure include a 5- or 6-membered monocyclic structure and a polycyclic structure in which two or more 5- or 6-membered monocyclic structures are combined.

[0119] R ４０ and R ４７ are each independently preferably an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and even more preferably a methyl group.

[0120] R ４１ , R ４２ , R ４５ and R ４６ is R ４１ and R ４２ , and R ４５ and R ４６ and R are preferably bonded to each other to form a ring having 3 to 20 carbon atoms, or each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 19 carbon atoms. ４１ and R ４２ , and R ４５ and R ４６ The ring formed by bonding together is more preferably a benzene ring or a cyclohexane ring. ４１ , R ４２ , R ４５ and R ４６ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0121] R ４３ and R ４４ are preferably bonded to each other to form a ring represented by any of the following structures:

[0122]

[0123] The content of the photochromic compound is preferably 0.3% by mass to 5% by mass, and more preferably 0.5% by mass to 2% by mass, relative to the total mass of the invisible ink.

[0124] In particular, the invisible ink preferably contains an infrared absorbing compound, which does not develop color under black light or sunlight, allowing the ink to be used on leather in a wide range of environments.

[0125] The invisible ink preferably contains components that can be contained in commonly known inks in addition to the infrared absorbing compound, the fluorescent compound, or the photochromic compound.

[0126] The invisible ink may be a water-based ink or a UV-curable ink. Water-based inks typically contain water, while UV-curable inks typically contain a polymerizable monomer and a polymerization initiator.

[0127] The invisible ink is preferably a water-based ink containing water. Unlike UV-curable ink, water-based ink can record a code image while preserving the grain formed on the surface of the leather substrate.

[0128] -Water- When the invisible ink contains water, the water content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the invisible ink. The water content is preferably 90% by mass or less, and more preferably 80% by mass or less, based on the total amount of the invisible ink.

[0129] Resin Particles The invisible ink preferably contains at least one type of resin particle. The resin particles are particles made of resin. The resin constituting the resin particles is preferably a water-insoluble resin. In the present disclosure, "water-insoluble" means that the amount of the resin that dissolves in 100 g of water at 25°C is less than 1 g.

[0130] The glass transition temperature of the resin particles (i.e., the glass transition temperature of the resin in the resin particles) is not particularly limited. From the viewpoint of further improving the strength of the image, the glass transition temperature (Tg) of the resin particles is preferably 20°C or higher, more preferably 50°C or higher, and even more preferably 80°C or higher. From the viewpoint of the manufacturing suitability of the resin particles, the glass transition temperature (Tg) of the resin particles is preferably 150°C or lower, more preferably 130°C or lower.

[0131] The resin particles are preferably particles made of an acrylic resin (hereinafter also referred to as acrylic resin particles), particles made of a styrene-acrylic resin (hereinafter also referred to as styrene-acrylic resin particles), particles made of a polyester resin (hereinafter also referred to as polyester resin particles), particles made of a urethane resin (hereinafter also referred to as urethane resin particles), or particles made of a polyolefin resin (hereinafter also referred to as polyolefin resin particles).

[0132] Among these, from the viewpoint of adhesion, the resin particles are preferably urethane resin particles. 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 an anionic group. The forced emulsifying urethane resin is preferably a urethane resin having no anionic group and capable of being dispersed in water by an emulsifier.

[0133] The urethane resin particles may be commercially available and may be available as an aqueous dispersion containing urethane resin particles. Examples of aqueous dispersions containing urethane resin particles include the Evaphanol series (e.g., Evaphanol HA-55), which is a polyurethane emulsion manufactured by Nicca Chemical Co., Ltd.

[0134] The average particle size of the urethane resin particles is, for example, 10 nm to 10 μm.

[0135] From the viewpoint of adhesion, the content of the resin particles is preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass, relative to the total amount of the invisible ink.

[0136] Other Components The invisible ink may contain other components in addition to those described above, as necessary. Examples of other components include colloidal silica, organic solvents, water-soluble resins, and surfactants.

[0137] (Method of Applying Invisible Ink) The method of applying the invisible ink is not particularly limited, but from the viewpoint of recording a fine code image, it is preferable to apply the invisible ink by an inkjet recording method.

[0138] The ink ejection method in the inkjet recording method is not particularly limited, and may be any of known methods, such as a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink with it, thereby ejecting the ink using radiation pressure, and a thermal inkjet (Bubble Jet (registered trademark)) method that heats the ink to form bubbles and uses the resulting pressure.

[0139] As an inkjet recording method, in particular, the method described in JP-A-54-59936 can be effectively used, in which ink subjected to the action of thermal energy undergoes a sudden change in volume, and the ink is ejected from a nozzle by the force resulting from this state change.

[0140] As an inkjet recording method, the method described in paragraphs 0093 to 0105 of JP-A No. 2003-306623 can also be applied.

[0141] Ink application by the inkjet recording method is performed by ejecting ink from the nozzles of an inkjet head.

[0142] Inkjet head methods include a shuttle method (multi-pass method) in which a short serial head is scanned across the width of the substrate to perform printing, and a line method (single-pass method) in which a line head has printing elements arranged to cover the entire area of ​​one side of the substrate.

[0143] In the line method, an image can be recorded on the entire surface of a substrate by scanning the substrate in a direction intersecting the arrangement direction of the recording elements. The line method does not require a transport system such as a carriage that scans a short head, as in the shuttle method. Furthermore, compared to the shuttle method, the line method does not require complex scanning control of the carriage movement and the substrate, and only the substrate moves. Therefore, the line method achieves faster image recording than the shuttle method.

[0144] Therefore, in the invisible ink application step, it is preferable to apply the ink by a line method (single pass method).

[0145] In addition, in the invisible ink application step, it is preferable to apply the ink using an inkjet head having a nozzle density of 600 nozzles per inch or more. The nozzle density is more preferably 900 nozzles per inch or more, and even more preferably 1200 nozzles per inch or more. Note that instead of an inkjet head having 600 nozzles, an inkjet head having 300 nozzles may be arranged at a staggered position, thereby substantially achieving a nozzle density of 600 nozzles per inch or more.

[0146] The amount of ink droplets ejected from the nozzles of the inkjet head is preferably 1 pL (picoliter) to 10 pL, and more preferably 1.5 pL to 6 pL, from the viewpoint of obtaining a high-definition code image.

[0147] (Code Image) In the invisible ink application process, a code image is recorded on the leather substrate. The code image is an image that can be read using a corresponding code reader.

[0148] The code image is preferably a barcode, a QR code, or a dot code. A barcode is, for example, an image in which a plurality of lines of different thicknesses are arranged in a striped pattern. A QR code is, for example, an image in which a plurality of squares of different sizes are arranged in a vertical and horizontal mosaic pattern. A dot code is, for example, an image in which extremely small dots are arranged in an area of ​​approximately 2 mm square. Dot codes are provided by Apollo Japan as "Screen Codes."

[0149] When the code image is combined with a colored image described later, the code image is preferably a dot code, from the viewpoint of maintaining the appearance of the colored image.

[0150] <Visible Ink Application Step> The leather manufacturing method of the present disclosure preferably further includes a step of applying a visible ink containing a colorant to record a colored image, and further includes recording a code image on the leather substrate on which the colored image has been recorded (hereinafter referred to as the "visible ink application step").

[0151] That is, it is preferable to apply the visible ink, the invisible ink, and the overcoat liquid in this order onto the leather substrate.

[0152] By recording a colored image, it is possible to obtain decorated leather. An invisible code image is recorded, which can prevent counterfeiting while maintaining the appearance of the colored image.

[0153] Colorant The colorant contained in the visible ink is not particularly limited, and may be a dye or a pigment.

[0154] From the viewpoint of improving readability, it is preferable that the colorant does not have absorption in the infrared region. For example, a black colorant is preferably lactam black.

[0155] In this disclosure, "having no absorption in the infrared region" means that the absorbance of the colorant-coated product at 800 nm measured using a spectrophotometer (product name "V770" manufactured by JASCO Corporation) is 0.5 or less. In this case, the difference between the absorption in the code image and the absorption in the visible image is sufficient at around 800 nm, the reading wavelength of the infrared detector, making the code readable. Note that, when measuring the absorbance, the colorant-coated product is prepared by applying 2 pl of ink to a substrate using an inkjet head at a resolution of 1200 dpi x 1200 dpi.

[0156] The content of the colorant is preferably 1% by mass to 15% by mass, and more preferably 2% by mass to 10% by mass, based on the total amount of the visible ink.

[0157] The visible ink preferably contains, in addition to the colorant, components that can be contained in commonly known inks.

[0158] The visible ink may be a water-based ink or a UV-curable ink. Water-based inks typically contain water, while UV-curable inks typically contain a polymerizable monomer and a polymerization initiator.

[0159] The visible ink is preferably a water-based ink containing water. Unlike UV-curable inks, water-based inks can record colored images while preserving the grain formed on the surface of the leather substrate.

[0160] -Water- The water content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the visible ink. The water content is preferably 90% by mass or less, and more preferably 80% by mass or less, based on the total amount of the visible ink.

[0161] Resin Particles The visible ink preferably contains at least one type of resin particles, which may be the same as those contained in the invisible ink.

[0162] In particular, from the viewpoint of adhesion, the resin particles are preferably urethane resin particles. Preferred embodiments of the urethane resin particles are as described above. When both the visible ink and the invisible ink contain urethane resin particles, excellent adhesion is achieved between the leather substrate and the colored image, and between the colored image and the code image.

[0163] From the viewpoint of adhesion, the content of the resin particles is preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass, relative to the total amount of the invisible ink.

[0164] Other Components The visible ink may contain other components in addition to those described above, as necessary. Examples of other components include colloidal silica, organic solvents, water-soluble resins, and surfactants. Furthermore, when a pigment is used as the colorant, the visible ink preferably contains a pigment dispersant for dispersing the pigment.

[0165] (Method of applying visible ink) The method of applying the visible ink is not particularly limited, but from the viewpoint of recording a fine colored image, it is preferable to apply the visible ink by an inkjet recording method. Details of the inkjet recording method are as described above.

[0166] After the visible ink application step, the visible ink applied to the leather substrate may be dried by heating. Examples of means for drying by heating include known heating means such as an infrared heater, known air blowing means such as a dryer, and a combination of two or more of these means. Examples of methods for drying by heating include a method of applying warm or hot air to the ink-applied surface of the leather substrate; a method of applying heat using an infrared heater or the like from the ink-applied surface of the leather substrate and / or the side opposite to the ink-applied surface; and a combination of these methods. The heating temperature during drying by heating is preferably 55°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. The upper limit of the heating temperature is not particularly limited, but examples include 100°C, with 90°C being preferred. The drying time is not particularly limited, but is preferably 3 to 60 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 20 seconds.

[0167] The visible ink application step may apply two or more types of visible ink onto the leather substrate.

[0168] In the visible ink application step, when two or more colors of ink are applied sequentially onto the leather substrate, the nth color (n is an integer of 1 or more; the same applies hereinafter) ink applied onto the leather substrate may be heated and dried, and the (n+1)th color ink may be applied onto the heated and dried nth color ink, or the (n+1)th color ink may be applied onto the nth color ink without heating and drying the nth color ink applied onto the leather substrate.

[0169] <Overcoat Layer Forming Step> The method for producing leather according to the present disclosure includes a step of forming an overcoat layer on the leather substrate on which the code image has been recorded (hereinafter also referred to as "overcoat layer forming step").

[0170] The method for forming the overcoat layer may be a method of applying an overcoat liquid onto a leather substrate on which a code image has been recorded, or a method of laminating an overcoat film onto a leather substrate on which a code image has been recorded.

[0171] In particular, from the viewpoint of energy saving, the step of forming the overcoat layer preferably includes a step of applying an overcoat liquid (hereinafter also referred to as an "overcoat liquid applying step").

[0172] (Overcoat Liquid Application Step) —Overcoat Liquid— The components contained in the overcoat liquid are not particularly limited.

[0173] The overcoat liquid may be water-based or ultraviolet-curable. If it is water-based, it usually contains water. If it is ultraviolet-curable, it usually contains a polymerizable monomer and a polymerization initiator.

[0174] The overcoat liquid is preferably water-based. That is, the invisible ink, the visible ink, and the overcoat liquid all preferably contain water. When the invisible ink, the visible ink, and the overcoat liquid are all water-based, they are highly safe and have a low environmental impact.

[0175] -Water- The overcoat liquid preferably contains water.

[0176] The water content of the overcoat solution is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the overcoat solution, and is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total amount of the overcoat solution.

[0177] Resin Particles The overcoat liquid preferably contains at least one type of resin particles, which may be the same as the resin particles contained in the invisible ink.

[0178] Among these, from the viewpoint of adhesiveness, the resin particles are preferably urethane resin particles. Preferred embodiments of the urethane resin particles are as described above.

[0179] It is preferable that the invisible ink, the visible ink, and the overcoat liquid all contain urethane resin particles. When the invisible ink, the visible ink, and the overcoat liquid all contain urethane resin particles, 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 overcoat layer are excellent.

[0180] From the viewpoint of adhesion, the content of the resin particles is preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass, based on the total amount of the overcoat liquid.

[0181] Silicone Compound The overcoat liquid preferably contains at least one silicone compound, which improves the abrasion resistance of the resulting leather.

[0182] Examples of the silicone compound include modified silicone compounds such as amine-modified silicone, alcohol-modified silicone, polyether-modified silicone, and long-chain alkyl-modified silicone. Among these, from the viewpoint of improving abrasion resistance, the silicone compound is preferably polyether-modified silicone.

[0183] From the viewpoint of abrasion resistance, the content of the silicone compound is preferably 0.1% by mass to 5% by mass, and more preferably 0.3% by mass to 2% by mass, based on the total amount of the overcoat liquid.

[0184] Other Components The overcoat liquid may contain other components in addition to those described above, as necessary. Examples of other components include an ultraviolet absorber and a crosslinking agent.

[0185] (Method of Applying Overcoat Liquid) The method of applying the overcoat liquid is not particularly limited, and examples thereof include known methods such as a coating method, a dipping method, and an inkjet recording method.

[0186] Examples of the application method include known application methods using a bar coater, extrusion die coater, air doctor coater, blade coater, rod coater, knife coater, squeeze coater, reverse roll coater, etc. The overcoat liquid can also be applied using analog printing methods such as screen printing, gravure printing, flexographic printing, and offset printing. Among these, from the viewpoint of the amount of ink that can be applied, it is preferable to apply the overcoat liquid using the screen printing method.

[0187] After the overcoat liquid application step, the overcoat liquid may be dried by heating.

[0188] The overcoat liquid can be dried, for example, by heating the substrate to which the overcoat liquid has been applied in an oven.

[0189] 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. The upper limit of the heating temperature is not particularly limited, but examples include 180° C., and 150° C. is preferred. The heating time is not particularly limited, but from the viewpoint of abrasion resistance, it is preferably 30 seconds to 20 minutes, more preferably 1 minute to 10 minutes, and even more preferably 1 minute to 5 minutes.

[0190] (Method of Laminating Overcoat Film) In the overcoat layer forming step, instead of applying an overcoat liquid, an overcoat film may be laminated to the leather substrate on which the code image has been recorded.

[0191] The overcoat film is preferably a film containing polyurethane. The method for laminating the overcoat film is not particularly limited, and examples thereof include a method in which the overcoat film is formed on a release paper, then transferred, and the release paper is peeled off.

[0192] <Pretreatment Liquid Application Step> The method for producing leather according to the present disclosure further includes a step of applying a pretreatment liquid containing a flocculant and water onto a leather substrate (hereinafter also referred to as a "pretreatment liquid application step"). After applying the pretreatment liquid, it is preferable to apply a visible ink onto the leather substrate to which the pretreatment liquid has been applied.

[0193] The components in the visible ink are aggregated by the aggregating agent in the pretreatment liquid, thereby obtaining an image with superior image quality.

[0194] (Pretreatment liquid) The pretreatment liquid contains a flocculant and water.

[0195] -Water- The pretreatment liquid contains water. The water content is preferably 50% by mass or more, and more preferably 60% by mass or more, based on the total amount of the pretreatment liquid. The water content is preferably 90% by mass or less, based on the total amount of the pretreatment liquid.

[0196] The pretreatment liquid contains at least one flocculant selected from the group consisting of organic acids, organic acid salts, polyvalent metal compounds, and metal complexes. The flocculant is a component that aggregates components (e.g., resins) in the ink.

[0197] The content of the aggregating agent is not particularly limited. From the viewpoint of the aggregation rate of the visible ink, the content of the aggregating agent is preferably 0.1% by mass to 40% by mass, more preferably 0.1% by mass to 30% by mass, even more preferably 1% by mass to 20% by mass, and particularly preferably 1% by mass to 10% by mass, relative to the total amount of the pretreatment liquid.

[0198] Resin Particles The pretreatment liquid preferably contains at least one type of resin particles. Examples of the resin particles contained in the pretreatment liquid include the same resin particles as those contained in invisible ink.

[0199] Among these, from the viewpoint of adhesiveness, the resin particles are preferably urethane resin particles. Preferred embodiments of the urethane resin particles are as described above.

[0200] It is preferable that the pretreatment liquid, the invisible ink, the visible ink, and the overcoat liquid all contain a urethane resin. When the pretreatment liquid, the invisible ink, the visible ink, and the overcoat liquid all contain a urethane resin, excellent adhesion is achieved between the leather substrate and the colored image, between the colored image and the code image, and between the code image and the overcoat layer.

[0201] From the viewpoint of adhesion, the content of the resin particles is preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass, relative to the total amount of the invisible ink.

[0202] Other Components The pretreatment liquid may contain other components in addition to those described above, as necessary. Examples of other components that can be contained in the pretreatment liquid include known additives such as organic solvents, surfactants, solid wetting agents, silicic acid compounds (e.g., colloidal silica), inorganic salts, anti-fading agents, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, antifungal agents, pH adjusters, viscosity adjusters, rust inhibitors, chelating agents, and water-soluble polymer compounds other than water-soluble cationic polymers (e.g., the water-soluble polymer compounds described in paragraphs 0026 to 0080 of JP 2013-001854 A).

[0203] (Method of Applying Pretreatment Liquid) The method of applying the pretreatment liquid is not particularly limited, and examples thereof include known methods such as a coating method, a dipping method, and an inkjet recording method.

[0204] Examples of the coating method include known coating methods using a bar coater, extrusion die coater, air doctor coater, blade coater, rod coater, knife coater, squeeze coater, reverse roll coater, and the like.

[0205] After the pretreatment liquid application step, the pretreatment liquid applied to the leather substrate may be dried by heating. Examples of means for drying by heating include the same means as those used for drying ink by heating. The heating temperature during drying by heating is preferably 55°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. There is no particular upper limit to the heating temperature, but examples include 100°C, and 90°C is preferred. The time for drying by heating is not particularly limited, but is preferably 3 to 60 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 20 seconds.

[0206] Although a code image is recorded on leather produced by the leather manufacturing method of the present disclosure, the code image is highly invisible and can be used in the same way as regular leather without a recorded code image. Furthermore, the recorded code image is useful as a countermeasure against counterfeiting. Furthermore, leather produced by the leather manufacturing method of the present disclosure can be applied to, for example, vehicle seats. Vehicle seats are frequently in contact with people, but leather produced by the leather manufacturing method of the present disclosure has excellent readability after abrasion, allowing the code image to be read for a long period of time. Furthermore, leather is sometimes wiped with alcohol when it becomes dirty, but leather produced by the leather manufacturing method of the present disclosure has excellent readability after wiping with alcohol, thereby suppressing a decrease in the readability of the code image.

[0207] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.

[0208] Example 1-1 Preparation of Pretreatment Liquid The following components were mixed to prepare a pretreatment liquid: Glutaric acid (flocculant)...6.1% by mass Propylene glycol (solvent)...5.0% by mass Olfine E1010 (manufactured by Nissin Chemical Co., Ltd.) (surfactant)...0.5% by mass Superflex M500 (Dai-ichi Kogyo Seiyaku) (aqueous dispersion of urethane resin particles)...7.0% by mass Triisopropanolamine (pH adjuster)...0.2% by mass BYK024 (BYK Corporation) (antifoaming agent)...0.01% by mass Ultrapure water...the balance to make the total pretreatment liquid 100% by mass

[0209] <Preparation of Black Ink> (Synthesis of Pigment Dispersant P1) 965 g of dipropylene glycol was added to a 5000 mL three-neck flask equipped with a stirrer and a condenser and heated to 85°C under a nitrogen atmosphere. Solution I was prepared 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 was prepared by dissolving 17.69 g of t-butylperoxy-2-ethylhexanoate (product name "Perbutyl O," manufactured by NOF Chemical Industries, Ltd.) in 221.17 g of dipropylene glycol. Solution I was added dropwise to the three-neck flask over 4 hours, and Solution II was added dropwise over 5 hours. After the completion of the addition, the mixture was allowed to react for an additional 2 hours. The disappearance of the monomer was confirmed by 1H-NMR. The resulting reaction solution was heated to 70°C, and 248.02 g of a 50% by mass aqueous solution of potassium hydroxide was added thereto. Then, 107.48 g of dipropylene glycol and 75.52 g of pure water were added thereto and stirred to obtain a 37% by mass solution of a random polymer. This random polymer was designated as pigment dispersant P1. The structural units constituting the resulting random polymer were １ The polymer was confirmed by H-NMR. The weight average molecular weight (Mw) was determined by GPC. The weight average molecular weight (Mw) of the obtained pigment dispersant P1 was 8,400, and the acid value was 221.7 mgKOH / g.

[0210] (Preparation of Black Pigment Dispersion) 150 parts by mass of pigment dispersant P1 was dissolved in water to prepare a polymer aqueous solution so that the concentration of pigment dispersant P1 was approximately 25% by mass. 180 parts by mass of this 25% by mass polymer aqueous solution, 90 parts by mass of black pigment (product name "Irgaphor (registered trademark) Black S0100CF", lactam black, manufactured by BASF), and 171.9 parts by mass of water were mixed to obtain a mixed solution. A potassium hydroxide aqueous solution was added to the obtained mixed solution, and the pH after neutralization was adjusted to 8.7. Next, the neutralized mixed solution was subjected to a dispersion treatment for 3 hours using a bead mill (bead diameter: 0.1 mmφ, zirconia beads). This resulted in a black pigment dispersion (uncrosslinked dispersion) in which the black pigment was dispersed using pigment dispersant P1. Water was added to this black pigment dispersion to prepare uncrosslinked dispersion DK1 (pigment concentration 15% by mass). Next, 3.77 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) as a crosslinking agent and 41.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) were added to 136 parts by mass of the uncrosslinked dispersion (DK1), and the mixture was allowed to react at 70°C for 6 hours, followed by cooling to 25°C. This resulted in a black pigment dispersion (crosslinked dispersion) in which the pigment dispersant P1 was crosslinked and the black pigment was dispersed by the pigment dispersant P1a. Here, the pigment dispersant P1a is a polymer in which the pigment dispersant P1, which is an uncrosslinked polymer, has been crosslinked by a crosslinking agent. Next, ion-exchanged water was added to the crosslinked dispersion so that the pigment concentration was 15% by mass. The obtained liquid was ultrafiltered by passing it through an ultrafiltration device (cross-flow ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (pore size: 0.1 μm) at a flow rate of 600 mL per minute. The liquid temperature was adjusted to 25°C, and ultrafiltration was performed eight times, with each run being equal to the volumetric expansion of the liquid charged. Ion-exchanged water was added to the obtained liquid so that the pigment concentration was 15% by mass. This resulted in black pigment dispersion DK1. The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the black pigment dispersion was 75 mgKOH / g.

[0211] (Preparation of Black Ink K1) The components shown below were mixed to prepare Black Ink K1. Black pigment dispersion DK1... 4.0% by mass as pigment content Propylene glycol (water-soluble organic solvent)... 30.0% by mass Propylene glycol monomethyl ether (water-soluble organic solvent)... 1.0% by mass Evaphanol HA-55 (polyurethane-based resin particle dispersion) (manufactured by Nicca Chemical Co., Ltd.)... 5.0% by mass as resin particle content Olfine E1010 (acetylene glycol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd.)... 1.0% by mass BYK3450 (silicone-based surfactant manufactured by BYK Corporation)... 1.0% by mass PVPK15 (polyvinylpyrrolidone K15)... 0.15% by mass ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Industries, Ltd.)... 0.05% by mass as colloidal silica particle content Water... the remaining amount to make the total ink 100% by mass

[0212] <Preparation of Cyan Ink C1> Cyan pigment dispersion DC1 was obtained in the same manner as for preparing black pigment dispersion DK1, except that the black pigment was changed to a cyan pigment (product name "PB15:3", manufactured by Dainichiseika Color & Chemicals). Cyan ink C1 was obtained in the same manner as for preparing black ink DK1, except that the black pigment dispersion DK1 was changed to cyan pigment dispersion DC1.

[0213] <Preparation of Magenta Ink M1> (Preparation of Magenta Pigment Dispersion DM1-1) Magenta pigment dispersion DM1-1 was obtained in the same manner as for preparing black pigment dispersion DK1, except that the black pigment was changed to a magenta pigment (product name "FUJI Fast Red (registered trademark) 9800", Pigment Red 122, manufactured by Fuji Color 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. The acid value of the pigment dispersant P1a (crosslinked polymer) contained in magenta pigment dispersion DM1-1 was 105 mgKOH / g.

[0214] (Preparation of Magenta Pigment Dispersion DM1-2) Magenta pigment dispersion DM1-2 was obtained in the same manner as in the preparation of magenta pigment dispersion DM1-1, except that the magenta pigment was changed to a magenta pigment (product name "LIONOGEN RED LX10231", Pigment Red 150, manufactured by Toyocolor Co., Ltd.). The acid value of the pigment dispersant P1a (crosslinked polymer) contained in magenta pigment dispersion DM1-2 was 105 mgKOH / g.

[0215] (Preparation of Magenta Ink M1) Magenta ink M1 was prepared by mixing the following components: Magenta pigment dispersion DM1-1: 4.5% by mass as pigment content Magenta pigment dispersion DM1-2: 1.5% by mass as pigment content Propylene glycol: 30.0% by mass Propylene glycol monomethyl ether: 1.0% by mass Evaphanol HA-55: 5.0% by mass as resin particle content Olfine E1010: 1.0% by mass BYK3450: 1.0% by mass PVPK15: 0.15% by mass ST-XS: 0.05% by mass as colloidal silica particle content Water: balance to make the total 100% by mass

[0216] <Preparation of Yellow Ink Y1> (Preparation of Yellow Pigment Dispersion DY1) Yellow pigment dispersion DY1 was obtained in the same manner as in the preparation of Black Pigment Dispersion DK1, except that when obtaining the mixed liquid, 180 parts by mass of a 25% by mass aqueous polymer solution, 75 parts by mass of a yellow pigment (product name "HANSA BRILLIANT 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. The acid value of the pigment dispersant P1a (crosslinked polymer) contained in Yellow Pigment Dispersion DY1 was 105 mgKOH / g.

[0217] (Preparation of Yellow Ink Y1) Yellow ink Y1 was obtained in the same manner as in the preparation of black ink DK1, except that black pigment dispersion DK1 was changed to yellow pigment dispersion DY1.

[0218] <Preparation of invisible ink IR1> As an infrared absorbing compound, L １ is L1-1, and L １ A in the formula is A-1 below, and R １ and R ３ is a hydrogen atom, and R ２ and R ４ A compound was prepared in which R-1 below was used, X was an oxygen atom, and M was potassium.

[0219]

[0220]

[0221] 4 parts by mass of the infrared absorbing compound was added to 96 parts by mass of ultrapure water, and the mixture was dispersed for 3 hours using a bead mill, thereby obtaining an aqueous dispersion A of the infrared absorbing compound.

[0222] The components of the following composition were mixed to prepare invisible ink IR1: Aqueous dispersion A of infrared absorbing compound (solid content: 4% by mass) 25% by mass; Propylene glycol 30.0% by mass; Propylene glycol monomethyl ether 1.0% by mass; Evaphanol HA-55 5.0% by mass as resin particle content; Olfine E1010 1.0% by mass; BYK3450 1.0% by mass; PVPK15 0.15% by mass; ST-XS 0.05% by mass as colloidal silica particle content; Water remaining to make the total ink 100% by mass.

[0223] <Preparation of Overcoat Solution OC1> Overcoat solution OC1 was prepared by mixing the following components: Evaphanol HA-55 (solid content concentration 40% by mass)... 96% by mass NK Assist CI-22 (manufactured by Nicca Chemical Co., Ltd.; crosslinking agent)... 3% by mass Silicone compound (product name "DOWSIL (registered trademark) 404LS Additive", slip agent, manufactured by Dow Toray Industries, Inc.)... 1% by mass

[0224] <Leather Manufacturing> (Preparation of Inkjet Recording Apparatus) An inkjet recording apparatus was prepared, which included a transport mechanism for transporting the substrate and four inkjet heads (hereinafter simply referred to as "heads") for applying ink, arranged in this order from the upstream side of the substrate transport direction (hereinafter simply referred to as the "upstream side"). The four heads were arranged along the substrate transport direction. Hereinafter, the heads will be referred to as head 1, head 2, head 3, and head 4, starting from the upstream side. The heads were 1200 dpi / 20-inch wide piezo full-line heads. The nozzle density was 1200 nozzles per inch. Here, dpi stands for dots per inch. Each head was a line head with nozzles arranged in a direction perpendicular to the substrate transport direction (i.e., the width direction of the substrate). Samba (registered trademark) G3L (manufactured by FUJIFILM DIMATIX) was used for each of the heads. The ink droplet volume was 2.2 pL.

[0225] (Image Recording) - Pretreatment Liquid Application Step - A leather substrate (product name "Foregold 2 #300", manufactured by Kyowa Life Techno Co., Ltd.) was subjected to corona discharge using a corona treatment machine (Kasuga Electric Co., Ltd., Corona Surface Modification Evaluation Device TEC-4AX) under conditions of a discharge gap of 1 mm, 100 W, and 4 m / min, thereby carrying out surface treatment. The pretreatment liquid was applied to the surface-treated leather substrate using a wire bar. The applied mass of the pretreatment liquid per unit area was 1.5 g / m. ２ The coating speed was 50 m / min. The applied mass of the pretreatment liquid was the mass of the applied pretreatment liquid divided by the area of ​​the region to which the pretreatment liquid was applied. At the location where application of the pretreatment liquid had been completed, drying of the pretreatment liquid with a dryer was started 2 seconds after application of the pretreatment liquid to this location was completed, and the pretreatment liquid was dried. The pretreatment liquid was dried at 60°C for 3 seconds. When measured with a Karl Fischer moisture meter, the amount of residual water in the pretreatment liquid was 0.01 g / m ２ It was as follows.

[0226] Visible Ink Application Process—Visible inks (black ink K1, cyan ink C1, magenta ink M1, and yellow ink Y1) and invisible ink IR1 were introduced into the head of an inkjet recording device, and a substrate to which a pretreatment liquid had been applied was set. While the substrate to which the pretreatment liquid had been applied was moved at a constant speed of 50 m / min, black ink K1, cyan ink C1, magenta ink M1, and yellow ink 1 were ejected from the head onto the surface of the substrate to which the pretreatment liquid had been applied, thereby recording a solid image. The ink droplet volume was 2.2 pL, the duty ratio was 100%, and the ejection frequency was 39.37 kHz. Next, two seconds after the completion of ink application, the visible ink applied to the substrate was subjected to infrared (IR) drying using an infrared (IR) irradiation device (product name "PLC-328", manufactured by Noritake Company Limited) under conditions where the ink surface temperature reached 75°C. Then, a dryer was used to dry the film with hot air at 80° C. for 20 seconds.

[0227] -Invisible Ink Application Step- The invisible ink IR1 was ejected onto the solid image of each color, and a screen code (dot code), a QR code, and a bar code manufactured by Apollo Japan Co., Ltd. were recorded.

[0228] - Overcoat liquid application step - The substrate to which the invisible ink had been applied was moved at a constant speed of 50 m / min, and the overcoat liquid was applied to the ink-applied surface of the substrate using a wire bar coater. The applied mass per unit area of ​​the solid content of the overcoat liquid was 10 g / m. ２ The substrate to which the overcoat liquid had been applied was heated in an oven at 130° C. for 2 minutes to obtain leather.

[0229] Example 1-2 An overcoat solution OC1a was prepared in the same manner as for the overcoat solution OC1, except that water was added instead of the silicone compound in the overcoat solution OC1. Leather was obtained in the same manner as in Example 1-1, except that the overcoat solution OC1a was used.

[0230] Comparative Example 1-1 Leather was obtained in the same manner as in Example 1-1, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0231] Example 1-2 Leather was obtained in the same manner as in Example 1-2, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0232] The obtained leather was evaluated for invisibility, initial readability, readability after rubbing, readability after wiping with alcohol, alcohol resistance, and abrasion resistance. The evaluation methods were as follows.

[0233] <Invisibility> - Dot code - Leather with a recorded dot code was presented to 10 test subjects who were unaware that a dot code had been recorded on it, and a test was conducted to see if they noticed that a dot code had been recorded on it. The evaluation criteria were as follows. - QR code - Leather with a recorded QR code was presented to 10 test subjects who were unaware that a QR code had been recorded on it, and a test was conducted to see if they noticed that a QR code had been recorded on it. The evaluation criteria were as follows. - Bar code - Leather with a recorded bar code was presented to 10 test subjects who were unaware that a QR code had been recorded on it, and a test was conducted to see if they noticed that a QR code had been recorded on it. The evaluation criteria were as follows. A: None of the subjects noticed. B: 1 to 3 subjects noticed. C: 4 to 9 subjects noticed. D: All of the subjects noticed.

[0234] <Initial readability> - Dot code - Ten locations where dot codes were recorded were selected, and a reading test was conducted using a voice pen manufactured by Apollo Japan Co., Ltd. The evaluation criteria are as follows. A to D are levels where there are no practical problems. - QR code - Ten locations where QR codes were recorded were selected, and images were taken with a Detector S3B manufactured by APIS Co., Ltd., and a reading test was conducted using a QR code reader. The evaluation criteria are as follows. A to D are levels where there are no practical problems. - Bar code - Ten locations where bar codes were recorded were selected, and images were taken with a Detector S3B manufactured by APIS Co., Ltd., and a reading test was conducted using a bar code reader. The evaluation criteria are as follows. A to D are levels where there are no practical problems. A: All were readable. B: Eight or nine locations were readable. C: Three to seven locations were readable. D: One or two locations were readable. E: Not readable at all.

[0235] <Readability after rubbing> A Gakushin-type rub test was conducted on the leather surface using cotton canvas No. 6, with a load of 500 g, 500 times. After the rub test, evaluation was performed in the same manner as for the evaluation of initial readability. The evaluation criteria are as follows: A: The number of readable marks after 500 rub tests was the same as the number of readable marks before the rub test. B: Unreadable after 500 rub tests.

[0236] <Readability after wiping with alcohol> A cotton swab was wetted with 100% by mass of ethanol. The cotton swab was rubbed against the leather surface 10 times. After the rubbing test, evaluation was performed in the same manner as for the evaluation of initial readability. The evaluation criteria are as follows: A: All readable. B: Readable in 8 or 9 locations. C: Readable in 3 to 7 locations. D: Readable in 1 or 2 locations. E: Not readable at all.

[0237] <Alcohol resistance> A cotton swab was wetted with 100% by mass of ethanol. The cotton swab was rubbed against the leather surface 10 times. After rubbing 10 times, the surface condition of the solid image and the cotton swab were visually observed. The evaluation criteria are as follows: A: No change in the surface of the solid image, and no color was transferred to the cotton swab. B: No change in the surface of the solid image, but slight color transfer to the cotton swab. C: No change in the surface of the solid image, but color transfer to the cotton swab. D: The solid image faded, and color transfer to the cotton swab.

[0238] <Abrasion Resistance> A Gakushin-type abrasion test was conducted on the leather surface using No. 6 cotton canvas, with 500g of weight applied, 500 times. After the abrasion test, the surface condition of the solid image and the cotton canvas were visually observed. The evaluation criteria are as follows: A: No change in the surface of the solid image, and no color transfer to the cotton canvas. B: No change in the surface of the solid image, but slight color transfer to the cotton canvas. C: No change in the surface of the solid image, but slight color transfer to the cotton canvas. D: The solid image faded, and the cotton canvas was colored.

[0239] Table 1 shows the evaluation results.

[0240]

[0241] As shown in Table 1, Examples 1-1 and 1-2 included a step of applying an invisible ink containing an infrared absorbing compound onto a leather substrate to record a code image, and a step of forming an overcoat layer on the leather substrate on which the code image had been recorded, and were found to be excellent in invisibility, readability after rubbing, and readability after wiping with alcohol. In Comparative Examples 1-1 and 1-2, the invisible ink was applied after applying the overcoat liquid, and it was found that the readability after rubbing was poor.

[0242] 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 were prepared. 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)

[0243] Using the above pigments, cyan pigment dispersion DC2, magenta pigment dispersion DM2, yellow pigment dispersion DY2, and black pigment dispersion DK2 were each prepared. The components other than the pigments in the following compositions were mixed and stirred for 10 to 15 minutes at 2,000 to 3,000 revolutions per minute using a Silverson mixer. The pigment was added, and the mixture was further stirred for 10 to 20 minutes at 2,000 to 3,000 revolutions per minute using the mixer, yielding 500 parts by mass of a preliminary dispersion. Thereafter, a dispersion treatment was carried out using a circulation type bead mill device (product name "SL-012C1") manufactured by Dispermat Co., Ltd. The dispersion conditions were 200 parts by mass of zirconia beads with a diameter of 0.65 mm filled, and a peripheral speed of 15 m / s. The dispersion time was 1 to 6 hours. Pigment... 30 mass% Dispersant (product name "SOLSPERSE32000", manufactured by Lubrizol Corporation)... 10 mass% Diethylene glycol diethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.)... 60 mass%

[0244] (Preparation of Cyan Ink C2) The components of the following composition were mixed and stirred for 10 to 15 minutes at 2000 to 3000 rpm using a Silverson mixer to obtain cyan ink C2. Cyan pigment dispersion DC2...6% by mass 3-Methoxybutyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.)...79.9% by mass Urethane acrylate oligomer (product name "CN9001", manufactured by Sartomer)...7% by mass Vinyl chloride-vinyl acetate copolymer (product name "vinnol H14 / 36", manufactured by Wacker Chemie)...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 B.V.)...2% by mass Polymerization initiator: 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxymethylpropanone (product name "Omnirad 2959", manufactured by IGM Resins B.V.) ... 1 mass% Surfactant: product name "BYK331", manufactured by BYK ... 0.1 mass%

[0245] (Preparation of Magenta Ink M2, Yellow Ink Y2, and Black Ink K2) Magenta ink M2 was obtained in the same manner as for the preparation of cyan ink C2, except that 6% by mass of cyan pigment dispersion DC2 and 79.9% by mass of 3-methoxybutyl acetate were replaced with 11.2% by mass of magenta pigment dispersion DM2 and 74.7% by mass of 3-methoxybutyl acetate. Yellow ink Y2 was obtained in the same manner as for the preparation of cyan ink C2, except that 6% by mass of cyan pigment dispersion DC2 and 79.9% by mass of 3-methoxybutyl acetate were replaced with 10% by mass of yellow pigment dispersion DY2 and 75.9% by mass of 3-methoxybutyl acetate. Black ink K2 was obtained in the same manner as in the preparation of cyan ink C2, except that 6% by mass of cyan pigment dispersion DC2 and 79.9% by mass of 3-methoxybutyl acetate were changed to 7.5% by mass of black pigment dispersion DK2 and 78.4% by mass of 3-methoxybutyl acetate.

[0246] <Preparation of Invisible Ink IR2> The following compound B-1 was prepared as an infrared absorbing compound.

[0247]

[0248] The components having the following composition were mixed to prepare a dispersion B of an infrared absorbing compound: Compound B-1... 4 mass% Polymer dispersant (product name "SOLSPERSE 35000", manufactured by Lubrizol)... 4 mass% Polymer dispersant (product name "SOLSPERSE 5000S", manufactured by Lubrizol)... 0.01 mass% 3-methyl-1,5-pentanediol diacrylate (product name "SR341", manufactured by Sartomer)... 91.99 mass%

[0249] The components of the following composition were mixed and stirred for 10 to 15 minutes at 2,000 to 3,000 revolutions per minute using a Silverson mixer to obtain invisible ink IR2. Infrared absorbing compound dispersion 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 B.V.)... 4% by mass Dye 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 surfactant: product name "BYK307", manufactured by BYK)... 0.1% by mass

[0250] <Preparation of Overcoat Solution OC2> The components shown below were mixed and stirred for 10 to 15 minutes at 2000 to 3000 rpm using a Silverson mixer to prepare overcoat solution OC2. 3-Methoxybutyl acetate...81% by mass Urethane acrylate oligomer (product name "CN9001", manufactured by Sartomer)...5% by mass Urethane acrylate oligomer (product name "Shikoh UV-7600B", manufactured by Mitsubishi Chemical Corporation)...5% by mass Vinyl chloride-vinyl acetate copolymer (product name "vinnol H14 / 36", manufactured by Wacker Chemie)...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 B.V.)...3% by mass Polymerization initiator: 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxy-methylpropanone (product name "Omnirad 2959", manufactured by IGM Resins B.V.) ... 1 mass% Silicone compound (product name "KP109", manufactured by Shin-Etsu Silicones Co., Ltd.) ... 2 mass%

[0251] <Leather Manufacturing> - Visible Ink Application Process - Cyan ink C2 was applied to the cyan throttle of an inkjet printer (product name "SUJV-160", manufactured by Mimaki Engineering Co., Ltd.), magenta ink M2 to the magenta throttle, yellow ink Y2 to the yellow throttle, black ink K2 to the black throttle, and overcoat liquid OC2 to the clear throttle. A leather substrate (product name "Foregold 2 #300", manufactured by Kyowa Life Techno Co., Ltd.) was set, and solid images of cyan ink C1, magenta ink M1, yellow ink 1, and black ink K1 were recorded. The resolution was 900 dpi x 1200 dpi, and the platen temperature was 70°C.

[0252] -Invisible Ink Application Step- Using an inkjet printer (product name "DMP-2831", manufactured by FUJIFILM Dimatix Corporation), invisible ink IR2 was ejected onto the solid image of each color to record a screen code (dot code), a QR code, and a barcode manufactured by Apollo Japan Co., Ltd. An LED light source (wavelength 385 nm) was set directly below the inkjet head, and ultraviolet light was irradiated immediately after image recording.

[0253] - Overcoat liquid application process - A transparent PET film (product name "Viewful UV TP-100N", thickness 100 μm, manufactured by Kimoto Co., Ltd.) was set in an inkjet printer (product name "SUJV-160", manufactured by Mimaki Engineering Co., Ltd.). A leather substrate on which a code image had been recorded was attached to the set transparent PET film. Overcoat liquid OC2 was ejected from the clear throttle, and a solid image was recorded over the entire code image. The resolution was 900 dpi x 1200 dpi, and the platen temperature was 70°C. After image recording was completed, the transparent PET film was peeled off.

[0254] Comparative Example 2-1 Leather was obtained in the same manner as in Example 2-1, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0255] The leather thus obtained was subjected to the same evaluation as in Example 1-1. Table 2 shows the evaluation results.

[0256]

[0257] As shown in Table 2, Example 2-1 included a step of applying an invisible ink containing an infrared absorbing compound onto a leather substrate to record a code image, and a step of forming an overcoat layer on the leather substrate on which the code image was recorded, and was found to be excellent in invisibility, readability after rubbing, and readability after wiping with alcohol. In Comparative Example 2-1, the invisible ink was applied after applying the overcoat liquid, and it was found to be inferior in readability after rubbing.

[0258] [Example 3-1] <Preparation of invisible ink F1> (Preparation of fluorescent compound dispersion DF1) A fluorescent compound dispersion DF1 was obtained in the same manner as in the preparation of black pigment dispersion DK1, except that the black pigment was changed to a fluorescent compound (4-methylumbelliferone (a coumarin derivative)), and the amount of crosslinker was changed to 3.60 parts by mass, and the amount of boric acid aqueous solution was changed to 39.4 parts by mass.

[0259] (Preparation of invisible ink F1) The components of the following composition were mixed to prepare invisible ink F1. Fluorescent compound dispersion DF1: 4.0% by mass as pigment content; Propylene glycol: 30.0% by mass; Propylene glycol monomethyl ether: 1.0% by mass; Evaphanol HA-55: 5.0% by mass as resin particle content; Olfine E1010: 1.0% by mass; BYK3450: 1.0% by mass; PVPK15: 0.15% by mass; ST-XS: 0.05% by mass as colloidal silica particle content; Water: remaining amount to make the total 100% by mass.

[0260] <Production of Leather> Leather was obtained in the same manner as in Example 1-1, except that invisible ink F1 was used instead of invisible ink IR1.

[0261] Example 3-2 An overcoat solution OC1a was prepared in the same manner as for the overcoat solution OC1, except that water was added instead of the silicone compound in the overcoat solution OC1. Leather was obtained in the same manner as in Example 3-1, except that the overcoat solution OC1a was used.

[0262] Comparative Example 3-1 Leather was obtained in the same manner as in Example 3-1, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0263] Example 3-2 Leather was obtained in the same manner as in Example 3-2, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0264] The obtained leather was subjected to the same evaluation as in Example 1-1. For the dot code, a reading test was performed using a code reader application manufactured by Apollo Japan Co., Ltd. under black light. For the QR code, a reading test was performed using a QR code reader under black light. For the barcode, a reading test was performed using a barcode reader under black light. The evaluation results are shown in Table 3.

[0265]

[0266] As shown in Table 3, Examples 3-1 and 3-2 included a step of applying an invisible ink containing a fluorescent compound onto a leather substrate to record a code image, and a step of forming an overcoat layer on the leather substrate on which the code image was recorded, and were found to be excellent in invisibility, readability after rubbing, and readability after wiping with alcohol. In Comparative Examples 3-1 and 3-2, the invisible ink was applied after applying the overcoat liquid, and it was found that the readability after rubbing was poor.

[0267] Example 4-1 Preparation of Invisible Ink Ph1 Preparation of Aqueous Dispersion of Resin Particles DPh1 Containing Photochromic Compound Water (250 g), 12-methacrylamidodecanoic acid (1.84 g), potassium bicarbonate (0.68 g), and isopropanol (20 g) were placed in a 1-liter three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 85° C. under a nitrogen stream. To this was added a mixed solution consisting of V-501 (radical polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (0.57 g), potassium bicarbonate (0.43 g), and water (9 g), and the mixture was stirred for 10 minutes. Next, a solution consisting of methyl methacrylate (54 g), 2-ethylhexyl methacrylate (36 g), and a spiropyran-based compound (product name "TPC-0024", manufactured by Yamada Chemical Co., Ltd.) (10 g) was added dropwise to the three-neck flask at a constant rate so that the addition was completed within 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 portions, immediately after the start of the addition of the monomer solution and 1.5 hours after the start of the addition. After the addition of the monomer solution was completed, the mixture was stirred for 1 hour, and then a mixed solution consisting of V-501 (0.28 g), potassium bicarbonate (0.21 g), and water (6 g) was added and stirred for an additional 3 hours. The resulting reaction mixture was filtered using a mesh filter with a lattice width of 50 μm to obtain an aqueous dispersion of resin particles DPh1 containing a photochromic compound. 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-methacrylamidodecanoate (59:39:2 (mass ratio)), and also contain a spiropyran compound. The aqueous dispersion of the resin particles DPh1 had a pH of 7.5, a solids concentration of 25 mass%, and a volume average particle diameter of 121 nm. The weight average molecular weight (Mw) of the resin of the resin particles DPh1 was 200,000, and the glass transition temperature was 70°C.

[0268] (Preparation of invisible ink Ph1) The components shown below were mixed to prepare invisible ink Ph1.

[0269] Aqueous dispersion of resin particles DPh1 containing a photochromic compound... 40.0% by mass; Propylene glycol... 30.0% by mass; Propylene glycol monomethyl ether... 1.0% by mass; Olfine E1010... 1.0% by mass; BYK3450... 1.0% by mass; PVPK15... 0.15% by mass; ST-XS... 0.05% by mass as the content of colloidal silica particles; Water... the balance to make the total 100% by mass.

[0270] <Production of Leather> Leather was obtained in the same manner as in Example 1-1, except that invisible ink Ph1 was used instead of invisible ink IR1.

[0271] Example 4-2 An overcoat solution OC1a was prepared in the same manner as for the overcoat solution OC1, except that water was added instead of the silicone compound in the overcoat solution OC1. Leather was obtained in the same manner as in Example 4-1, except that the overcoat solution OC1a was used.

[0272] Comparative Example 4-1 Leather was obtained in the same manner as in Example 4-1, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0273] Example 4-2 Leather was obtained in the same manner as in Example 4-2, except that the visible ink application step was followed by the overcoat liquid application step and the invisible ink application step in this order.

[0274] The obtained leather was subjected to the same evaluation as in Example 1-1. For the dot code, a reading test was performed using a code reader application manufactured by Apollo Japan Co., Ltd. under black light. For the QR code, a reading test was performed using a QR code reader under black light. For the barcode, a reading test was performed using a barcode reader under black light. The evaluation results are shown in Table 4.

[0275]

[0276] As shown in Table 4, Examples 4-1 and 4-2 included a step of applying an invisible ink containing a photochromic compound onto a leather substrate to record a code image, and a step of forming an overcoat layer on the leather substrate on which the code image was recorded, and were found to be excellent in invisibility, readability after rubbing, and readability after wiping with alcohol. In Comparative Examples 4-1 and 4-2, the invisible ink was applied after applying the overcoat liquid, and it was found that the readability after rubbing was poor.

[0277] Comparative Example 5-1 Leather was obtained in the same manner as in Example 1-1, except that the leather substrate was changed to a leather substrate (product name "EL-200#201", manufactured by Shoko Co., Ltd.) Approximately 2 μL of distilled water was dropped onto the surface of the leather substrate used in Examples 1-1 and 5-1, and after 1000 microseconds, the contact angle of water was measured using a contact angle meter (product name "Drop Master DMo-501", manufactured by Kyowa Interface Science Co., Ltd.).

[0278] The leather thus obtained was subjected to the same evaluation as in Example 1-1. Table 5 shows the evaluation results.

[0279]

[0280] As shown in Table 5, in Comparative Example 5-1, the contact angle of water on the leather substrate was more than 100°, and therefore it was found that the readability after rubbing was poor.

[0281] Example 6-1: Overcoat liquid OC1 was applied to a release paper for synthetic leather (product name "DN-TP (registered trademark)", manufactured by Dai Nippon Printing Co., Ltd.) at a solid content of 10 g / m ２ The resulting mixture was coated with a wire bar so that the coating became a uniform layer, and then dried at 130°C for 2 minutes to produce overcoat film 1. Instead of carrying out the overcoat liquid application step in Example 1-1, after the visible ink application step, overcoat film 1 was attached to the code image using an adhesive for synthetic leather (product name "Diabond KC-DA888", manufactured by Diabond Co., Ltd.). The release paper for synthetic leather was then peeled off to obtain leather.

[0282] The obtained leather was subjected to the same evaluation as in Example 1-1, and the same results as in Example 1-1 were obtained.

[0283] The disclosure of Japanese Patent Application No. 2023-150289, filed on September 15, 2023, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A method for manufacturing leather, comprising the steps of: applying an invisible ink containing an infrared absorbing compound, a fluorescent compound, or a photochromic compound onto a leather substrate having a water contact angle of 100° or less to record a code image; and forming an overcoat layer on the leather substrate on which the code image has been recorded.

2. The method for manufacturing leather according to claim 1, wherein the code image is a barcode, a QR code (registered trademark), or a dot code.

3. A method for manufacturing leather according to claim 1 or 2, wherein the code image is a dot code.

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

5. The method for producing leather according to claim 1 or 2, wherein the infrared absorbing compound is at least one selected from the group consisting of compounds represented by the following formula (1) and formula (2): In formula (1), Y １ and Y ２ each independently represents a non-metallic atomic group forming an aliphatic ring or a heterocycle; M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation; L １ represents a methine chain consisting of 5 or 7 methine groups, the central methine group of the methine chain having a substituent represented by the following formula A, Ａ -T Ａ Formula A In formula A, S Ａ represents a single bond, an alkylene group, an alkenylene group, an alkynylene group, -O-, -S-, -NR Ｌ１ -, -C(=O)-, -C(=O)O-, -C(=O)NR Ｌ１ -, -S(=O) ２ -, -OR Ｌ２ - or a group formed by combining at least two of these, R Ｌ１ represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, or a monovalent heterocyclic group; R Ｌ２ represents an alkylene group, an arylene group, or a divalent heterocyclic group; T Ａ represents a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, a monovalent heterocyclic group, a cyano group, a hydroxy group, a formyl group, a carboxy group, an amino group, a thiol group, a sulfo group, a phosphoryl group, a boryl group, a vinyl group, an ethynyl group, a trialkylsilyl group, or a trialkoxysilyl group; S Ａ represents a single bond or an alkylene group, and T Ａ When represents an alkyl group, S Ａ and T Ａ In formula (2), the sum of the carbon atoms contained in X is 3 or more, and * represents a bonding site with the central methine group of the methine chain. Ａ and X Ｂ each independently represents a monovalent substituent; G Ａ and G Ｂ each independently represents a monovalent substituent; kA is an integer of 0 to n Ａ , kB is 0 to n Ｂ represents an integer of n Ａ and n Ｂ Each of the rings A and B is a substitutable G Ａ and G Ｂ represents the integer that is the largest number in Ａ and G Ａ may be bonded to each other to form a ring, X Ｂ and G Ｂ may be bonded to each other to form a ring, G Ａ and G Ｂ If there are multiple of each, G Ａ Comrades and G Ｂ They may be bonded to each other to form a ring structure.

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

7. The method for producing leather according to claim 1 or 2, wherein the step of forming the overcoat layer includes a step of applying an overcoat liquid.

8. The method for producing leather according to claim 7, wherein the overcoat liquid contains a silicone compound.

9. A method for producing leather according to claim 1 or 2, further comprising the step of applying a visible ink containing a colorant onto the leather substrate to record a colored image, and recording the code image on the leather substrate on which the colored image has been recorded.

10. The method for producing leather according to claim 9, wherein the colorant contained in the visible ink has no absorption in the infrared region.

11. The method for producing leather according to claim 9, wherein the visible ink is applied by an ink-jet recording method.

12. The method for producing leather according to claim 9, wherein the step of forming the overcoat layer includes a step of applying an overcoat liquid.

13. The method for producing leather according to claim 12, wherein the overcoat liquid contains a silicone compound.

14. The method for producing leather according to claim 12, wherein the invisible ink, the visible ink, and the overcoat liquid all contain urethane resin particles.

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

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