Laser marking composition, resin film, and laminate

Abstract

To provide a laser marking composition capable of forming a two-dimension film which is excellent in heat resistance and readability when a one dimensional code or a resinous code is printed, and in which generation of gas during printing is suppressed.SOLUTION: The laser marking composition contains at least one (meth) acrylic resin, a bismuth-containing compound, and a crosslinking agent having a triazine ring skeleton, wherein the total proportion of a methacrylic acid-derived structural unit and a methacrylic acid alkyl ester-derived structural unit in all structural units of the (meth) acrylic resin is less than 45 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laser marking composition, a resin film, and a laminate. [Background technology]

[0002] Various packaging for food, pharmaceuticals, etc., and various components such as electronic components, require the printing of variable information for traceability, such as production lot numbers and production dates. Laser marking is one of the marking methods used for this purpose. In particular, color-developing laser marking, which uses a laser to change the color of resins or pigments, is used in a variety of places in recent years because it can be done without generating odors or dust.

[0003] The following compositions are known as labels and inks for laser marking. For example, Patent Document 1 discloses an adhesive that contains an adhesive resin (A) and a bismuth-based laser coloring agent (B) and that can form an adhesive layer that has good contrast after printing and suppresses coloration. Furthermore, Patent Document 2 discloses an ink composition for laser marking that has sufficient laser printability (visibility), blocking resistance, adhesion, and lamination strength, and that contains a binder resin, a white pigment, and an organic solvent, wherein the binder resin contains a polyurethane resin and a cellulose derivative, the cellulose derivative is a lower acyl group-substituted cellulose derivative and / or a lower alkyl-substituted cellulose derivative, and the white pigment is titanium oxide having an average particle size of 0.26 μm or less.

[0004] Patent Document 1: Patent No. 6292429 Patent document 2: Patent No. 7057236 Summary of the Invention [Problem to be solved by the invention]

[0005] Resin compositions that can turn black when irradiated with laser light achieve this color by utilizing the reduction reaction of inorganic oxides caused by the laser light. The heat generated during reduction carbonizes the resin and generates gas. This carbonization can spread beyond the intended range, causing the laminate to swell, leading to poor readability when printing one-dimensional and two-dimensional codes. For example, the adhesive using a bismuth-based laser coloring agent disclosed in Patent Document 1 may cause the print to deform due to heat during printing, which may make the print difficult to read depending on the content. Furthermore, in the laser marking ink composition disclosed in Patent Document 2, the urethane resin is easily carbonized, so the resin surrounding the inorganic oxide is also easily carbonized, which can make the printed content difficult to read. Furthermore, the (meth)acrylic copolymer given as a comparative example in Patent Document 2 is mainly composed of methacrylic resin, which can cause problems such as gas generation and swelling during printing. On the other hand, bismuth-based laser colorants, such as bismuth oxide, produce bismuth through a reduction reaction induced by a laser. Bismuth-based laser colorants develop color due to the color difference between bismuth oxide and bismuth. Because bismuth loses its color when it becomes a carboxylate or bismuth hydroxide, it is expected that the absorbance in the visible light range will decrease when a carboxyl group or hydroxyl group coordinates with bismuth. Because the (meth)acrylic resin contained in the laser marking composition contains a hydroxyl group or carboxyl group as a crosslinking point, bismuth loss of color due to the (meth)acrylic resin may occur. In particular, bismuth loss of color is more likely to occur with increasing temperature, and laser marking using a bismuth-based laser colorant may result in poor heat resistance in the printed area. The present disclosure has been made in consideration of the above-mentioned conventional circumstances, and aims to provide a laser marking composition that can form a resin film that has excellent heat resistance and readability when one-dimensional or two-dimensional codes are printed, and that suppresses gas generation during printing, as well as a resin film and a laminate that use this laser marking composition. [Means for solving the problem]

[0006] Specific means for achieving the above object are as follows. <1> The composition contains at least one (meth)acrylic resin, a bismuth-containing compound, and a crosslinking agent having a triazine ring skeleton, A laser marking composition, wherein the total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester in all structural units of the (meth)acrylic resin is less than 45 mass %. <2> The crosslinking agent having a triazine ring skeleton includes at least one of an isocyanate-based crosslinking agent and a melamine-based crosslinking agent having a triazine ring skeleton. <1> 10. The laser marking composition according to claim 9. <3> The isocyanate-based crosslinking agent having a triazine ring skeleton includes at least one selected from the group consisting of an isocyanurate-based crosslinking agent for an aromatic aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an alicyclic polyisocyanate compound, and an isocyanurate-based crosslinking agent for an aromatic polyisocyanate compound. <2> 10. The laser marking composition according to claim 9. <4> Further containing a urethane resin, <1> ~ <3> 10. The laser marking composition according to claim 9, wherein the laser marking composition is a fluororesin. <5> Further containing a filler, <1> ~ <4> 10. The laser marking composition according to claim 9, wherein the laser marking composition is a fluororesin. <6> <1> ~ <5> A resin film obtained by using the laser marking composition according to any one of the preceding claims. <7> <6> A laminate having the resin film according to claim 1. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a laser marking composition capable of forming a resin film that has excellent heat resistance and readability when one-dimensional or two-dimensional codes are printed, and that suppresses gas generation during printing, as well as a resin film and a laminate that use this laser marking composition. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of a cross-sectional structure of a laminate according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0010] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one 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 this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain multiple types of particles. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable. In the present disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate. In the present disclosure, the average thickness of a layer or film is a value obtained by measuring the thickness of the layer or film at five points and calculating the arithmetic mean value. The thickness of a layer or film can be measured using a micrometer or the like. In the present disclosure, when the thickness of a layer or film can be measured directly, it is measured using a micrometer. On the other hand, when measuring the thickness of a single layer or the total thickness of multiple layers, it may be measured by observing the cross section of the object to be measured using an electron microscope. In this disclosure, the solid content refers to the components excluding the organic solvent in the laser marking composition or sample solution.

[0011] <Laser marking composition> The laser marking composition of the present disclosure contains at least one (meth)acrylic resin, a bismuth-containing compound, and a crosslinking agent having a triazine ring skeleton, and the total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester in all structural units of the (meth)acrylic resin is less than 45 mass%. The laser marking composition of the present disclosure makes it possible to form a resin film that has excellent heat resistance and readability when one-dimensional or two-dimensional codes are printed, and that suppresses gas generation during printing. The reason for this is not clear, but is presumed to be as follows. When comparing structural units derived from alkyl acrylate esters and structural units derived from alkyl methacrylate esters that can be contained in (meth)acrylic resins, the difference lies in whether a methyl group is directly bonded to a carbon atom that constitutes the main chain of the (meth)acrylic resin. The carbon atom directly bonded to a methyl group becomes a tertiary carbon. Decomposition of the (meth)acrylic resin is likely to occur upon laser irradiation at locations where tertiary carbons that constitute the main chain of the (meth)acrylic resin are present. If the (meth)acrylic resin contains a large amount of structural units derived from methacrylic acid and alkyl methacrylate esters, gas derived from the decomposition products is more likely to be generated. In the present disclosure, since the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylate esters in the total structural units of the (meth)acrylic resin is less than 45% by mass, the proportion of tertiary carbons among the carbon atoms constituting the main chain of the (meth)acrylic resin can be kept relatively low, which is thought to facilitate the suppression of gas generation derived from decomposition products. Furthermore, as gas generation is suppressed, the occurrence of blistering of the resin film made of the laser marking composition is also easily suppressed. Furthermore, because (meth)acrylic resins contain hydroxyl and carboxyl groups as crosslinking points, the hydroxyl and carboxyl groups may coordinate with the bismuth generated by the laser reduction reaction, resulting in the discoloration of the bismuth. However, in a resin film formed by the crosslinking reaction between a crosslinker having a triazine ring skeleton and a (meth)acrylic resin, molecular movement is easily inhibited due to the rigidity of the triazine ring skeleton, which in turn inhibits the coordination of hydroxyl and carboxyl groups with bismuth. In particular, even when molecular movement becomes more intense due to an increase in temperature, the coordination of hydroxyl and carboxyl groups contained in the (meth)acrylic resin with bismuth is easily inhibited, which is presumably improving the heat resistance of the printed area produced by laser marking. Furthermore, the rigidity of the triazine ring skeleton is likely to inhibit deformation of the resin film due to gas and heat that may be generated during printing, which is presumably improving the readability of printed one-dimensional and two-dimensional codes.

[0012] Each component constituting the laser marking composition of the present disclosure will be described below.

[0013] ((Meth)acrylic resin) The laser marking composition of the present disclosure contains at least one (meth)acrylic resin. The total proportion of structural units derived from methacrylic acid and structural units derived from methacrylic acid alkyl esters to all structural units of the (meth)acrylic resin is less than 45% by mass. The total proportion of structural units derived from methacrylic acid and structural units derived from methacrylic acid alkyl esters to all structural units of the (meth)acrylic resin is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 5% by mass or less. The total proportion of structural units derived from methacrylic acid and structural units derived from methacrylic acid alkyl esters to all structural units of the (meth)acrylic resin may be 0% by mass. The total proportion of structural units derived from methacrylic acid and structural units derived from methacrylic acid alkyl esters to all structural units of the (meth)acrylic resin is preferably 0% by mass or more and less than 45% by mass.

[0014] When the laser marking composition of the present disclosure contains one type of (meth)acrylic resin, so long as the (meth)acrylic resin satisfies the above conditions, it may be a homopolymer consisting of structural units derived from a single (meth)acrylic monomer, or a copolymer consisting of structural units derived from two or more types of (meth)acrylic monomers. Furthermore, when the laser marking composition of the present disclosure contains two or more types of (meth)acrylic resins, two or more types of homopolymers having different structural units may be used in combination, or at least one type of homopolymer and at least one type of copolymer may be used in combination, or two or more types of copolymers having different structural units may be used in combination, as long as the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylate esters to all structural units contained in the two or more types of (meth)acrylic resins is less than 45 mass%. Furthermore, when the laser marking composition of the present disclosure contains two or more types of (meth)acrylic resins, at least one type of (meth)acrylic resin having a total proportion of structural units derived from methacrylic acid and alkyl methacrylate esters to all structural units of the (meth)acrylic resin may be used in combination with at least one type of (meth)acrylic resin having the above proportion of 45 mass% or more.

[0015] Here, the (meth)acrylic monomer refers to at least one of acrylic acid, derivatives of acrylic acid such as alkyl acrylate esters, and derivatives of methacrylic acid such as alkyl methacrylate esters. The derivatives of acrylic acid and the derivatives of methacrylic acid may have a substituent such as a hydroxyl group, an amino group, a carboxyl group, or a glycidyl group. In addition, the (meth)acrylic resin may contain other monomers than the (meth)acrylic monomer.

[0016] Specific examples of (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, glycidyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate.

[0017] Specific examples of (meth)acrylic monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) mono(meth)acrylate, and pentaerythritol tri(meth)acrylate.

[0018] Other monomers that contain a carboxy group include crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, and citraconic acid.Other monomers that do not contain a carboxy group include vinyl acetate, vinyl ether, acrylonitrile, and styrene.

[0019] In the present disclosure, the proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in all structural units of the (meth)acrylic resin is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more. The proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in all structural units of the (meth)acrylic resin may be 99% by mass or less. The proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in all structural units of the (meth)acrylic resin is preferably 55% to 99% by mass.

[0020] Preferred examples of the alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms include ethyl acrylate, methyl acrylate, butyl acrylate such as n-butyl acrylate, i-butyl acrylate and t-butyl acrylate, and 2-hydroxyethyl acrylate.

[0021] In one embodiment of the present disclosure, the total proportion of ethyl acrylate-derived structural units, methyl acrylate-derived structural units, and 2-hydroxyethyl acrylate-derived structural units relative to all structural units in the (meth)acrylic resin is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 65% ​​by mass or more. The total proportion of ethyl acrylate-derived structural units, methyl acrylate-derived structural units, and 2-hydroxyethyl acrylate-derived structural units relative to all structural units in the (meth)acrylic resin may be 99% by mass or less. The total proportion of ethyl acrylate-derived structural units, methyl acrylate-derived structural units, and 2-hydroxyethyl acrylate-derived structural units relative to all structural units in the (meth)acrylic resin is preferably 20% by mass to 99% by mass. Ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate have high glass transition temperatures when made into homopolymers. Therefore, it is thought that the main chain of the (meth)acrylic resin is less likely to move in the structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate in the (meth)acrylic resin, even when heat is generated by the reduction of inorganic oxides. As a result, printing tends to be easier and more accurate. In another embodiment of the present disclosure, the total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate in all structural units of the (meth)acrylic resin may be 1 mass% or less.

[0022] The total proportion of structural units derived from monomers containing a carboxy group in the molecule, such as acrylic acid, methacrylic acid, and other monomers containing a carboxy group, in all structural units of the (meth)acrylic resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The total proportion of structural units derived from monomers containing a carboxy group in the molecule in all structural units of the (meth)acrylic resin may be 0.5% by mass or more. The total proportion of structural units derived from monomers containing a carboxy group in the molecule in all structural units of the (meth)acrylic resin is preferably 0.5% by mass to 20% by mass. When the total proportion of structural units derived from monomers containing a carboxy group in the molecule in all structural units of the (meth)acrylic resin is 20% by mass or less, visibility tends to be improved.

[0023] When the (meth)acrylic resin is a copolymer, the polymerization mode is not particularly limited, and may be random copolymerization, alternating copolymerization, block copolymerization, or graft copolymerization.

[0024] The weight-average molecular weight (Mw) of the (meth)acrylic resin is preferably within the range of 5,000 to 1,000,000, more preferably within the range of 10,000 to 800,000, and even more preferably within the range of 100,000 to 750,000. If the weight-average molecular weight (Mw) of the (meth)acrylic resin is 5,000 or more, the resin film tends to be less brittle. Furthermore, if the weight-average molecular weight (Mw) of the (meth)acrylic resin is 1,000,000 or less, the film-forming properties tend to be excellent. When the laser marking composition of the present disclosure uses two or more (meth)acrylic resins in combination, the weight average molecular weight (Mw) of the mixture of two or more (meth)acrylic resins preferably falls within the above range.

[0025] In the present disclosure, the weight average molecular weight (Mw) of the (meth)acrylic resin is a value measured by the following method. Specifically, it is measured according to the following (1) to (3). (1) A solution of (meth)acrylic resin is applied to a release paper and dried at 100°C for 1 minute to obtain a film of (meth)acrylic resin. (2) Using the (meth)acrylic resin film obtained in (1) above and tetrahydrofuran, a sample solution with a solid content concentration of 0.2% by mass is obtained. (3) Using gel permeation chromatography (GPC), the weight average molecular weight (Mw) of the (meth)acrylic resin is measured in terms of standard polystyrene under the following conditions.

[0026] ~Conditions~ Measurement equipment: High-speed GPC (Model: HLC-8220 GPC, Tosoh Corporation) Detector: Differential refractometer (RI) (built into HLC-8220, Tosoh Corporation) Column: Four TSK-GEL GMHXL (Tosoh Corporation) columns connected in series Column temperature: 40℃ Eluent: tetrahydrofuran Sample concentration: 0.2% by mass Injection volume: 100μL Flow rate: 0.6mL / min

[0027] The glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C or higher, more preferably 0°C or higher, and even more preferably 10°C or higher, in order to suppress deformation of the printed area due to heat or gas during printing and enable one-dimensional or two-dimensional codes to be printed with high precision. The glass transition temperature Tg of the (meth)acrylic resin may be 100°C or lower, in order to improve workability of the resin film and prevent it from becoming brittle. The glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C to 100°C. The glass transition temperature Tg of a (meth)acrylic resin refers to the value determined as the inflection point of the DSC curve obtained by measuring 10 mg of a measurement sample in a nitrogen gas flow at a heating rate of 10°C / min using a differential scanning calorimeter (DSC) (e.g., EXSTAR6000 manufactured by Seiko Instruments Inc.). When two or more inflection points are observed in the DSC curve using the differential scanning calorimeter (DSC), the temperature at the highest inflection point is taken as the glass transition temperature Tg of the (meth)acrylic resin.

[0028] In addition, when the structural units constituting the (meth)acrylic resin are known, the Tg of the (meth)acrylic resin may be a value obtained by converting the absolute temperature (K) calculated by the following formula into Celsius temperature (°C).

[0029]

number

[0030] In the formula, Tg1, Tg2, ... and Tg n are the glass transition temperatures of the homopolymers of monomer 1, monomer 2, and monomer n, expressed in absolute temperature (K). n is the mole fraction of each monomer.

[0031] The "glass transition temperature of a homopolymer expressed in absolute temperature (K)" refers to the glass transition temperature of a homopolymer produced by polymerizing the monomer alone, expressed in absolute temperature (K). The glass transition temperature of a homopolymer can be measured by the above-mentioned method using a differential scanning calorimeter (DSC).

[0032] The "glass transition temperatures of homopolymers expressed in Celsius degrees (°C)" of representative monomers are as follows: 10°C for methyl acrylate, −22°C for ethyl acrylate, −54°C for n-butyl acrylate, −70°C for 2-ethylhexyl acrylate, −15°C for 2-hydroxyethyl acrylate, −80°C for 4-hydroxybutyl acrylate, 43°C for t-butyl acrylate, 32°C for vinyl acetate, 106°C for acrylic acid, 105°C for methyl methacrylate, and 85°C for 2-hydroxyethyl methacrylate. For example, by using these representative monomers, it is possible to appropriately adjust the glass transition temperatures described above. For the "glass transition temperature when made into a homopolymer" of a monomer other than the above-mentioned monomers, the value described in the Polymer Handbook (4th edition, Wiley-Interscience; the same applies hereinafter) is adopted, and if there is no description in the Polymer Handbook, the value of the glass transition temperature of the homopolymer obtained by the above-mentioned measurement method is adopted. Note that absolute temperature (K) can be converted to Celsius temperature (°C) by subtracting 273 from it, and Celsius temperature (°C) can be converted to absolute temperature (K) by adding 273 to it.

[0033] When two or more types of (meth)acrylic resins are used in combination, the glass transition temperature Tg of the (meth)acrylic resin exhibiting the highest glass transition temperature Tg is preferably within the above range.

[0034] The method for producing the (meth)acrylic resin is not particularly limited, and the resin can be produced by polymerizing monomers using methods such as solution polymerization, emulsion polymerization, suspension polymerization, etc. Note that, when preparing a laser marking composition after producing the (meth)acrylic resin, solution polymerization is preferred because the processing steps are relatively simple and can be completed in a short time.

[0035] Solution polymerization can generally be carried out by charging a predetermined organic solvent, monomers, a polymerization initiator, and an optional chain transfer agent into a polymerization vessel, and then heating the mixture for several hours under stirring in a nitrogen stream or at the reflux temperature of the organic solvent. The weight-average molecular weight of the (meth)acrylic resin can be adjusted to a desired value by adjusting the reaction temperature, reaction time, amount of solvent, and type and amount of catalyst.

[0036] Examples of organic solvents used in the polymerization reaction of the (meth)acrylic resin include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds, etc. These organic solvents may be used alone or in combination of two or more.

[0037] More specifically, examples of organic solvents used in the polymerization reaction include aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon organic solvents such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine; ester organic solvents such as ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl ether, methyl ... Examples of the organic solvent include ketone-based organic solvents typified by chiroketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether-based organic solvents typified by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol-based organic solvents typified by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

[0038] Examples of the polymerization initiator include organic peroxides and azo compounds that can be used in ordinary polymerization methods.

[0039] The (meth)acrylic resin may be a commercially available product. Examples of commercially available (meth)acrylic resins include KP-1876E (trade name: Nissetsu (registered trademark), manufactured by Nippon Carbide Industries Co., Ltd.) and H-4002 (manufactured by Negami Chemical Industrial Co., Ltd.).

[0040] The (meth)acrylic resin content of the solid content of the laser marking composition is preferably 15% to 98% by mass, more preferably 20% to 95% by mass, and even more preferably 40% to 90% by mass. If the (meth)acrylic resin content is 15% to 98% by mass, the heat resistance of the printed portion tends to be improved.

[0041] (bismuth-containing compounds) The laser marking composition of the present disclosure contains a bismuth-containing compound. The bismuth-containing compound functions as a color-developing pigment. The bismuth-containing compound is preferably bismuth(III) oxide (BiO), as it exhibits excellent black color upon color development. In this case, a metal oxide with many oxygen vacancies is more preferred in order to improve laser marking properties.

[0042] The volume average particle diameter of the bismuth-containing compound is not particularly limited, but is preferably 0.05 μm to 30 μm, more preferably 0.1 μm to 15 μm, and even more preferably 0.3 μm to 1.5 μm. When the volume average particle diameter of the bismuth-containing compound is 0.05 μm or more, the bismuth-containing compound tends to absorb laser light and generate heat more easily, which tends to further improve color development. On the other hand, when the volume average particle diameter of the bismuth-containing compound is 30 μm or less, dispersibility during film formation tends to be good. The volume average particle diameter of the bismuth-containing compound refers to a value measured by a laser diffraction / light scattering method. The specific method for the laser diffraction / light scattering method is as follows: 5 mL of an aqueous dispersion of a bismuth-containing compound is placed in a glass cell measuring 5 mm in length, 65 mm in width, and 80 mm in height using a Pasteur pipette, and this is then placed in a laser diffraction / light scattering particle size distribution analyzer (e.g., HORIBA, Ltd.'s LA-960A (trade name)). The concentration of the aqueous dispersion of the bismuth-containing compound is adjusted so that the transmittance of laser light (red) is 80% to 90%, and the results are measured at a temperature of 25°C ± 1°C and processed by computer to determine the average particle size of the bismuth-containing compound particles in the aqueous dispersion. The volume average value is used as the average particle size.

[0043] The content of the bismuth-containing compound in the solid content of the laser marking composition is preferably 0.2% by mass to 4.0% by mass, more preferably 0.5% by mass to 2.5% by mass, and even more preferably 1.0% by mass to 2.0% by mass. If the content of the bismuth-containing compound is 0.2% by mass or more, appropriate color development occurs during laser marking, and the readability of the laser-marked area tends to be good. If the content of the bismuth-containing compound is 4.0% by mass or less, dust generation during laser marking is suppressed, and the readability of the laser-marked area tends to be good. The laser marking composition of the present disclosure may contain, as another color-forming pigment, a metal oxide containing at least one metal selected from the group consisting of antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium.

[0044] (Crosslinking agent) The laser marking composition of the present disclosure contains a crosslinking agent having a triazine ring skeleton. The crosslinking agent having a triazine ring skeleton is not particularly limited as long as it contains a functional group that can react with a hydroxyl group or a carboxyl group contained in the (meth)acrylic resin to crosslink the (meth)acrylic resin. Examples of crosslinking agents having a triazine ring skeleton include isocyanate-based crosslinking agents, melamine-based crosslinking agents, benzoguanamine-based crosslinking agents, and epoxy-based crosslinking agents having a triazine ring skeleton. In this disclosure, "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in the molecule (so-called polyisocyanate compound) and its derivatives. Also, "melamine-based crosslinking agent" refers to a melamine derivative having one or more methylol groups in the molecule. Also, "benzoguanamine-based crosslinking agent" refers to benzoguanamine and its derivatives. Also, "epoxy-based crosslinking agent" refers to a compound having at least one epoxy group in the molecule (so-called epoxy compound) and its derivatives. Among these, at least one of an isocyanate-based crosslinking agent having a triazine ring skeleton and a melamine-based crosslinking agent is preferred, as it can further suppress the discoloration of bismuth that has been reduced by irradiation with laser light. The reason why the discoloration of bismuth can be further suppressed by using at least one of an isocyanate-based crosslinking agent having a triazine ring skeleton and a melamine-based crosslinking agent is further not clear, but is presumed to be as follows. Isocyanate groups contained in isocyanate-based crosslinking agents and amino groups, imino groups, methylol groups, alkyl ether groups, etc. contained in melamine-based crosslinking agents are highly reactive with hydroxyl groups and carboxyl groups contained in (meth)acrylic resins, so the amount of hydroxyl groups and carboxyl groups in the resin film is likely to decrease due to the crosslinking reaction between these crosslinking agents and the (meth)acrylic resin. Therefore, it is presumed that the coordination of hydroxyl groups and carboxyl groups to bismuth generated by the reduction reaction using a laser is suppressed, thereby suppressing the attenuation of the absorbance of bismuth in the visible light region and making it less likely for the bismuth to fade. Furthermore, urethane bonds are formed by reactions between hydroxyl groups and isocyanate groups, and amino groups and urea groups are formed by reactions between carboxyl groups and isocyanate groups. Melamine-based crosslinking agents typically contain imide groups. When these functional groups are present in the resin film, they tend to coordinate with the reduced bismuth upon irradiation with laser light, resulting in a darker color.

[0045] -Isocyanate-based crosslinking agent with a triazine ring skeleton- Examples of isocyanate-based crosslinking agents having a triazine ring skeleton include derivatives in which an isocyanurate ring is formed from a polyisocyanate compound, that is, isocyanurate-based crosslinking agents having an isocyanurate ring. In the present disclosure, an isocyanate-based crosslinking agent having an isocyanurate ring is referred to as an "isocyanurate-based crosslinking agent." Examples of the polyisocyanate compound include araliphatic polyisocyanate compounds, aliphatic or alicyclic polyisocyanate compounds, and aromatic polyisocyanate compounds.

[0046] In the present disclosure, the term "aromatic aliphatic polyisocyanate compound" refers to a compound having a structure in which an isocyanate group and an aromatic ring are bonded via an alkylene group in the molecule. Examples of such an aromatic aliphatic polyisocyanate compound include compounds having a structure in which an isocyanate group and an aromatic ring are bonded via a methylene group in the molecule. Examples of the aromatic aliphatic polyisocyanate compound having a structure in which an isocyanate group and an aromatic ring are bonded via a methylene group in the molecule include o-xylene diisocyanate (XDI), m-xylene diisocyanate (XDI), p-xylene diisocyanate (XDI), etc.

[0047] In the present disclosure, the "aliphatic or alicyclic polyisocyanate compound" may be an aliphatic or alicyclic compound having about 1 to 1,000 carbon atoms to which an isocyanate group is bonded. Examples of such aliphatic polyisocyanate compounds include hexamethylene diisocyanate (HDI) and heptamethylene diisocyanate. Examples of such alicyclic polyisocyanate compounds include isophorone diisocyanate (IPDI), hydrogenated xylylene diisocyanate (hydrogenated XDI) such as 1,4-cyclohexane bismethyl isocyanate, and hydrogenated diphenylmethane diisocyanate (hydrogenated MDI) such as 4,4-methylene biscyclohexyl isocyanate.

[0048] In the present disclosure, the "aromatic polyisocyanate compound" may be an aromatic compound having approximately 6 to 1000 carbon atoms to which an isocyanate group is bonded. Examples of such aromatic polyisocyanate compounds include polymeric MDIs such as diphenylmethane diisocyanate (MDI) and triphenylmethane triisocyanate, and aromatic polyisocyanate compounds such as tolylene diisocyanate (TDI).

[0049] In the present disclosure, from the viewpoint of printing accuracy, it is preferable that the isocyanate-based crosslinking agent having a triazine ring skeleton includes at least one selected from the group consisting of an isocyanurate-based crosslinking agent for an aromatic aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an alicyclic polyisocyanate compound, and an isocyanurate-based crosslinking agent for an aromatic polyisocyanate compound. In the present disclosure, among these, from the viewpoint of suppressing yellowing of the resin film, isocyanurate crosslinking agents of aliphatic or alicyclic polyisocyanate compounds are preferred as the crosslinking agent among isocyanurate crosslinking agents, and from the viewpoint of improving printing accuracy, isocyanurate crosslinking agents of alicyclic polyisocyanate compounds are even more preferred.

[0050] The isocyanurate crosslinking agent can be obtained by a standard method from a polyisocyanate compound using an isocyanurate catalyst such as a quaternary ammonium salt, a tertiary amine, or a metal salt of an organic acid.

[0051] The isocyanurate crosslinking agent may be a commercially available product, such as Takenate D-140N, Takenate D-127N, Takenate D-268, or Takenate D-131N manufactured by Mitsui Chemicals, Inc., Coronate HX or Coronate HK manufactured by Tosoh Corporation, Duranate TKA-100 manufactured by Asahi Kasei Corporation, or Desmodur N4470BA, Desmodur RC, or Desmodur N3300A manufactured by Sumika Covestro Urethane Co., Ltd.

[0052] -Melamine-based crosslinking agent- Examples of melamine-based crosslinking agents include melamine, methylolated melamine derivatives obtained by condensing melamine with formaldehyde, compounds obtained by reacting methylolated melamine with a lower alcohol to partially or completely etherify it, and mixtures thereof. Furthermore, the melamine-based crosslinking agent may be a condensate of a monomer or a dimer or higher polymer, or a mixture thereof. More specific examples include imino group-type methylated melamine resins, methylol group-type melamine resins, methylol group-type methylated melamine resins, and fully alkylated methylated melamine resins.

[0053] The melamine-based crosslinking agent is, for example, represented by the following general formula (I).

[0054] [ka]

[0055] where R 1 ~R 5 are each independently a hydrogen atom, R 7 -OCH2- or a melamine residue represented by formula (II) or formula (III), and R 7 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group. 6 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. n1 is an integer of 1 to 8.

[0056] [ka]

[0057] where R 11 ~R 15 are each independently a hydrogen atom, R 16 OCH2- or a melamine residue represented by formula (III), and R 16 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group.

[0058] [ka]

[0059] where R 21 ~R 25 are each independently a hydrogen atom, R 26 OCH2- or a melamine residue represented by formula (II), R 26 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group. The melamine-based crosslinking agent is also represented by the following general formula (IV).

[0060] [ka]

[0061] where R 31 ~R 35 is a hydrogen atom, R 37 -OCH2- or a melamine residue represented by formula (II) or formula (III), and R 37 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group. 36 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. n2 is an integer of 1 to 8. The melamine-based crosslinking agent is also represented by the following general formula (V).

[0062] [ka]

[0063] where R 41 ~R 45 , R 51 ~R 54 is a hydrogen atom, R 47 -OCH2- or a melamine residue represented by formula (II) or formula (III), and R 47 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group. 55 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. n3 and n4 are integers, and n3+n4 is 2 to 8. Among the compounds represented by general formulas (I) to (V), preferred melamine-based crosslinking agents include Nikalac (registered trademark) MS-11 and MS-001 (both manufactured by Nippon Carbide Industries Co., Ltd.), and Mycoat 715 (manufactured by Nippon Cytec Industries Co., Ltd.).

[0064] -Benzoguanamine-based crosslinking agent- Examples of benzoguanamine-based crosslinking agents include benzoguanamine, methylolated benzoguanamine derivatives obtained by condensing benzoguanamine with formaldehyde, compounds obtained by reacting methylolated benzoguanamine with a lower alcohol to partially or completely etherify it, and mixtures thereof. Benzoguanamine-based crosslinking agents may also be condensates of monomers or dimers or higher polymers, or mixtures thereof. More specific examples include butylated benzoguanamine resins and methylolated benzoguanamine resins.

[0065] -Epoxy crosslinking agent with triazine ring structure- Examples of epoxy crosslinking agents having a triazine ring skeleton include the TEPIC series manufactured by Nissan Chemical Industries, Ltd.

[0066] The content of the crosslinking agent having a triazine ring skeleton in the laser marking composition (equivalent (amount of functional groups in the crosslinking agent / amount of functional groups in the (meth)acrylic resin)) is preferably 0.1 to 10 equivalents relative to the total of the hydroxyl groups and carboxyl groups in the (meth)acrylic resin. By setting the content of the crosslinking agent to 0.1 equivalents or more, molecular movement can be suppressed, thereby improving printing accuracy. By setting the content of the crosslinking agent to 10 equivalents or less, discoloration of the (meth)acrylic resin can be suppressed. It is more preferable that the content of the crosslinking agent is 0.3 to 3.0 equivalents, as this facilitates film formation.

[0067] The laser marking composition of the present disclosure may contain a crosslinking agent other than the crosslinking agent having a triazine ring skeleton. Other crosslinking agents include dimers (uretdiones) of the above-mentioned polyisocyanate compounds; prepolymers of the above-mentioned isocyanate compounds and polyol resins; adducts of (a) the above-mentioned polyisocyanate compounds and (b) polyhydric alcohol compounds such as propylene glycol (difunctional alcohol), butylene glycol (difunctional alcohol), trimethylolpropane (TMP, trifunctional alcohol), glycerin (trifunctional alcohol), and pentaerythritol (tetrafunctional alcohol), urea compounds, and the like; isocyanate-based crosslinking agents that do not have a triazine ring skeleton, such as biuret derivatives of the above-mentioned polyisocyanate compounds, urea-based crosslinking agents, metal chelate-based crosslinking agents, organosilane-based crosslinking agents, epoxy-based crosslinking agents that do not have a triazine ring skeleton, and acid anhydride-based crosslinking agents. When the laser marking composition of the present disclosure contains other crosslinking agents, the proportion of crosslinking agents having a triazine ring skeleton in the total crosslinking agents is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more. Since bismuth is a Group 15 element, it tends to coordinate with Lewis acids. Bismuth also has a low tendency to ionize. Therefore, when aluminum chelate is used as a crosslinking agent, heating can cause ligand exchange between aluminum and bismuth, potentially resulting in discoloration of the bismuth, similar to the case of hydroxyl and carboxylic acid groups. Therefore, to prevent discoloration of the bismuth, the content of aluminum chelate crosslinking agent in the total crosslinking agent is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0068] (white pigment) The laser marking composition of the present disclosure may contain a white pigment to further improve visibility by increasing the contrast between the black of the printed area and the white of the non-printed area. Various inorganic pigments can be used as the white pigment. Examples include titanium oxide (TiO2), titanium oxide-coated mica, zinc oxide (zinc white), basic lead sulfate, zinc sulfide, and antimony oxide. Other examples of white pigments include barium sulfate, barium carbonate, precipitated calcium carbonate, diatomaceous earth, talc, clay, basic magnesium carbonate, and alumina white. Among these, titanium oxide (TiO2) is preferred as the white pigment because of its excellent whiteness. Furthermore, the above-mentioned white pigments and aluminum may be included because they can reflect transmitted laser light, thereby increasing the efficiency of the reduction reaction of the bismuth-containing compound and improving color development. The volume average particle diameter of the white pigment is not particularly limited, but is preferably 0.01 μm to 50 μm, more preferably 0.05 μm to 30 μm, and even more preferably 0.1 μm to 15 μm. The volume average particle diameter of the white pigment refers to a value measured by a laser diffraction / light scattering method.

[0069] When the laser marking composition of the present disclosure contains a white pigment, the content of the white pigment relative to the solid content of the laser marking composition is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and even more preferably 1% by mass to 20% by mass. When the content of the white pigment relative to the solid content of the laser marking composition is 0.01% by mass or more, the reduction efficiency of the color-forming pigment can be improved, and visibility tends to be further improved. When the content of the white pigment relative to the solid content of the laser marking composition is 50% by mass or less, a decrease in the color development of the bismuth-containing compound tends to be prevented.

[0070] (urethane resin) The laser marking composition of the present disclosure may contain a urethane resin to improve printability when printing on the surface of a resin film. By containing a urethane resin in the laser marking composition, the fixation of the printed layer formed on the surface of the resin film becomes good. The type of urethane resin is not particularly limited, and conventionally known urethane resins can be used, such as polycarbonate-based urethane resins, polyester-based urethane resins, polyether-based urethane resins, etc. The urethane resins may be used alone or in combination of two or more. When the laser marking composition of the present disclosure contains a urethane resin, the content of the urethane resin in the solid content of the laser marking composition is preferably 2% by mass to 75% by mass, more preferably 5% by mass to 20% by mass, and even more preferably 10% by mass to 15% by mass, from the viewpoint of improving printability. By keeping the content of the urethane resin in the solid content of the laser marking composition at 75% by mass or less, laser markability can be maintained. By keeping the content of the urethane resin in the solid content of the laser marking composition at 20% by mass or less, suitability for lamination can be maintained.

[0071] As the urethane resin, commercially available products can be used. Examples of commercially available urethane resins include "NE-8836 (polycarbonate-based)," "NE-8811 (polycarbonate-based)," and "NE-8850 (polycarbonate-based)" (all manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), as well as "Superflex 420 (polycarbonate-based)," "Superflex 460 (polycarbonate-based)," and "Superflex 210 (polyester-based)" (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and "Pandex T-5275 (polyester-based)," "Pandex T-9280 (polycarbonate-based)," "Pandex T-9290 (polycarbonate-based)," "Pandex T-1190 (polyester-based)," and "Pandex T-8190 (polyether-based)" (all manufactured by DIC Covestro Polymer Co., Ltd.).

[0072] (filler) The laser marking composition of the present disclosure may contain a filler to improve printability when printing on the surface of a resin film. By containing a filler in the laser marking composition, the slipperiness on the surface of the resin film is improved, and operability when printing on the surface of the resin film is improved, resulting in good printability. As the filler, known fillers such as inorganic particles such as silica particles, resin particles such as acrylic beads, melamine beads, etc. The fillers may be used alone or in combination of two or more. The volume average particle diameter of the filler is not particularly limited, and from the viewpoint of improving lubricity, it is preferably 0.5 μm to 25 μm, more preferably 1 μm to 15 μm, and even more preferably 2 μm to 10 μm. The volume average particle diameter of the filler is measured by the same method as the volume average particle diameter of the metal oxide described above. When the laser marking composition of the present disclosure contains a filler, the content of the filler in the solid content of the laser marking composition is preferably 0.2% by mass to 30.0% by mass, more preferably 0.5% by mass to 20% by mass, and even more preferably 2% by mass to 10% by mass, from the viewpoint of improving slipperiness.

[0073] (Other ingredients) The laser marking composition of the present disclosure may contain other resins and various additives, such as dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants, as long as the heat resistance, readability of printed one-dimensional and two-dimensional codes, and the effect of suppressing gas generation during printing are not impaired.

[0074] (organic solvent) The laser marking composition of the present disclosure may contain an organic solvent to improve coating workability. The organic solvent is not particularly limited as long as it dissolves or disperses the various components contained in the laser marking composition. Examples of organic solvents include alcohol-based organic solvents such as methanol, ethanol, n-propanol, isopropanol, and butanol; ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-based organic solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; aliphatic hydrocarbon-based organic solvents such as n-hexane, n-heptane, and n-octane; alicyclic hydrocarbon-based organic solvents such as cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, and cyclooctane; and aromatic hydrocarbon-based organic solvents such as toluene and xylene. The organic solvents may be used alone or in combination of two or more.

[0075] When the laser marking composition of the present disclosure contains an organic solvent, the content of the organic solvent in the laser marking composition is preferably 40% by mass to 90% by mass.

[0076] <Resin film> The resin film of the present disclosure is formed using the laser marking composition of the present disclosure. The method for producing a resin film using the laser marking composition of the present disclosure is not particularly limited, and the resin film can be formed by a known method using a single-layer T-die extruder, a multi-layer T-die extruder, a calendar molding machine, or the like. Alternatively, a resin film can be formed by applying the laser marking composition of the present disclosure containing an organic solvent to one side of a substrate film described below and drying it. Examples of such application methods include screen printing, gravure printing, bar coating, knife coating, roll coating, comma coating, blade coating, die coating, and spray coating. When the laser marking composition contains a crosslinking agent, the resin film may be cured by drying with hot air or by heating with a heating device such as an oven or a hot plate. The average thickness of the resin film is not particularly limited, and may be, for example, 2 μm to 100 μm.

[0077] <Laminate> The laminate of the present disclosure has a resin film of the present disclosure. The disclosed laminate may be a laminate used in a laser marking label. The layer configuration of the laminate is not particularly limited, and may be a laminate in which a first layer that transmits laser light, a second layer that develops color in response to laser light, and an optionally provided third layer having adhesive properties are stacked in this order. Alternatively, the laminate may be a laminate in which a first layer that transmits laser light, and a second layer that develops color in response to laser light and has adhesive properties are stacked in this order. When the laminate has such a configuration, it is preferable to use the resin film of the present disclosure as the second layer.

[0078] The laminate of the present disclosure, having the resin film of the present disclosure, tends to suppress gas generation in the second layer during laser marking, thereby suppressing odor generation, and also tends to improve the readability of printed one-dimensional and two-dimensional codes.

[0079] The application of the laminate of the present disclosure to a three-layer laser-marking label will be described below with reference to Fig. 1. Fig. 1 is a diagram schematically illustrating an example of the cross-sectional structure of a laminate 1 according to an embodiment of the present disclosure. As shown in Fig. 1, the laminate 1 has a first layer 10, a second layer 20, and a third layer 30, which are stacked in this order. The second layer 20 is in contact with the first layer 10.

[0080] Here, laser marking of the laminate 1 will be described. First, laser light is irradiated from the first layer 10 side of the laminate 1. The irradiated laser light passes through the first layer 10 and acts on the second layer 20. Since the second layer 20 is formed from the resin layer of the present disclosure, the bismuth-containing compound develops color in the area of ​​the second layer 20 irradiated with the laser light, and the resin is carbonized by the heat of the laser light. The colored and carbonized area of ​​the second layer 20 becomes the printed area of ​​the laser marking label. The printed area is the area of ​​the second layer 20 that has turned black. A laser marking label of this type, which includes a resin layer containing a bismuth-containing compound inside the film and causes the resin layer to develop color upon laser irradiation, is sometimes referred to as an internal coloring type laser marking label. In this disclosure, "laser marking" is not limited to the act of writing meaningful information such as letters or symbols on the laminate 1, but refers to the general act of coloring at least a portion of the second layer 20 of the laminate 1 by irradiating it with laser light.

[0081] Each layer of the laminate will be described below using the laminate 1 according to one embodiment of the present disclosure as an example.

[0082] [First layer 10] The first layer 10 is a layer that transmits laser light. In the present disclosure, the first layer 10 may also be referred to as a surface layer.

[0083] An optically transparent film is used as the first layer 10. In the present disclosure, "optically transparent" means, for example, that the transmittance of laser light is 50% or more and the transmittance of visible light is 80% or more. If the transmittance of visible light through the first layer 10 is sufficiently high, when the laminate 1 after laser marking is viewed in plan from the first layer 10 side, the second layer 20, which is the underlying layer, can be sufficiently seen through the first layer 10. The transmittance of laser light and the transmittance of visible light through the substrate film can be measured, for example, using a known spectrophotometer.

[0084] The resin used as the material of the substrate film as the first layer 10 may be either a thermoplastic resin or a thermosetting resin. More specifically, the resin used as the material of the substrate film as the first layer 10 is, for example, a (meth)acrylic copolymer, a vinyl butyral resin, a vinyl chloride resin, a fluorine-containing resin, a polyester resin, a polystyrene resin, or a thermoplastic polyurethane resin (TPU). These resins are excellent in transparency, heat resistance, and handleability. These resins may be used alone or in combination of two or more.

[0085] Among the resins mentioned above, polyester resins are particularly suitable for use as the material for the substrate film because they can sufficiently transmit laser light and have good handleability and heat resistance. By using a polyester resin for the substrate film as the first layer 10, the versatility of the laminate 1 can be improved and precise laser marking can be achieved.

[0086] The polyester resin is preferably an aromatic ester resin from the viewpoint of suppressing deformation due to heat during laser marking, and the aromatic ester resin is more preferably a transparent resin from the viewpoint of suppressing deformation due to heat during laser light irradiation.

[0087] Examples of aromatic ester-based resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate, and polyethylene naphthalate (PEN). Among these, from the above-mentioned viewpoint, polyethylene terephthalate is more preferable as the aromatic ester-based resin.

[0088] There are no particular restrictions on the thickness of the first layer 10, but a thicker thickness is preferable from the viewpoints of chemical resistance and abrasion resistance. The upper limit of the thickness of the first layer 10 may be set appropriately from the viewpoints of workability and cost. For example, from the viewpoint of improving workability (e.g., handleability) when bonding the laminate 1 to an adherend, the thickness of the first layer 10 is preferably in the range of 10 μm to 200 μm.

[0089] The resin used as the material of the base film as the first layer 10 may contain various additives to the extent that print readability and adhesion are not impaired. Examples of such additives include dispersants, light stabilizers, heat stabilizers, plasticizers, fillers, and colorants. Furthermore, the surface of the first layer 10 on the side where the second layer 20 is provided may be subjected to a corona treatment or provided with an easy-adhesion layer.

[0090] [Second layer 20] The second layer 20 develops color when exposed to laser light. In the present disclosure, the second layer 20 may also be referred to as a color-developing layer 20. The second layer 20 is composed of the resin layer of the present disclosure.

[0091] The thickness of the second layer 20 is not particularly limited, but is preferably 2 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 15 μm to 50 μm. If the thickness of the second layer 20 is 2 μm or more, the printing can be sufficiently recognized. Furthermore, if the thickness of the second layer 20 is 15 μm or more, penetration resistance to laser light and printability are improved. Furthermore, if the thickness of the second layer 20 is 100 μm or less, the productivity of the second layer 20 is improved. [Third layer 30] The third layer 30 has adhesive properties. In the present disclosure, the third layer 30 may be referred to as an adhesive layer 30.

[0092] The adhesive used in the third layer 30 should be capable of adhering to an adherend such as a resin plate, a metal plate, or a glass plate, and of being releasable from the adherend. Specifically, the adhesive strength of the adhesive used in the third layer 30 is preferably 0.1 N / 25 mm to 40 N / 25 mm, and more preferably 0.3 N / 25 mm to 30 N / 25 mm. An adhesive strength of 0.1 N / 25 mm or greater ensures good adhesion to the adherend. An adhesive strength of 40 N / 25 mm or less ensures good releasability. The adhesive strength of the adhesive is measured by attaching a 10 mm wide laminate to an aluminum plate with a 2 kg load, leaving it at 23°C for 24 hours, and then peeling the laminate from the aluminum plate at a peel angle of 180°, a peel speed of 300 mm / min, and a measurement temperature of 23°C.

[0093] The third layer 30 is made of a resin composition. Examples of the resin composition used for the third layer 30 include a (meth)acrylic adhesive, a silicone adhesive, and a synthetic rubber adhesive, and from the viewpoint of improving the adhesion between the second layer 20 and the third layer 30, a (meth)acrylic adhesive is more preferable.

[0094] There are no particular restrictions on the thickness of the third layer 30, but it is preferably in the range of 5 μm to 100 μm. When the thickness of the third layer 30 is in the above range, workability (for example, handleability) when bonding the laminate 1 to an adherend is improved.

[0095] The resin composition used for the third layer 30 may contain various additives to the extent that print readability and adhesion are not impaired. Examples of such additives include dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants. Metal oxide pigments are preferred as the colorant used in the third layer 30. The use of metal oxide pigments tends to improve the hiding power of the base and reduce the penetration of the laser. Furthermore, the laser light is reflected by the metal oxide pigment, which increases the efficiency of the reduction reaction of the bismuth-containing compound present in the second layer 20, and as a result, the color development tends to be improved. Examples of metal oxide pigments include, but are not limited to, metal oxides containing at least one metal selected from the group consisting of titanium, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium.

[0096] [Laser marking method for laminate 1] Laser marking on the laminate 1 can be carried out by irradiating the laminate 1 with laser light from the first layer 10 side.

[0097] The laser used for laser marking may be, for example, a near-infrared laser with a wavelength of about 1000 nm, such as a YVO4 laser, a YAG laser, or a fiber laser. Alternatively, a UV laser with a wavelength of 300 nm to 400 nm may also be used.

[0098] Laser marking on the laminate 1 is usually performed before the laminate 1 is attached to the adherend. Laser marking can also be performed after the laminate 1 is attached to the adherend, but in this case, it is preferable that the laminate 1 has sufficient penetration resistance so that the adherend to which the laminate 1 is attached is not damaged by laser irradiation.

[0099] [Method for manufacturing laminate 1] The laminate 1 can be produced by forming a first layer 10, a second layer 20, and a third layer 30 stacked in this order. For example, the laminate 1 can be produced by a production method including at least a second layer forming step of forming the second layer 20 on one surface of the first layer 10, and a third layer forming step of forming the third layer 30 on the surface of the second layer 20 that is not in contact with the first layer 10 after the second layer forming step.

[0100] The second layer formation step may be a step of applying the laser marking composition used in the second layer 20 to one surface of the substrate film serving as the first layer 10, and curing it as necessary to form the second layer 20. The method for forming the second layer 20 may be the same as the method for producing a resin film according to the present disclosure described above.

[0101] The third layer formation step may be a step of applying a resin composition used for the third layer 30 to the surface of the second layer 20 after the second layer formation step, the surface not in contact with the first layer 10, and curing the composition to form the third layer 30. In another embodiment, the third layer formation step may be a step of applying a resin composition used for the third layer 30 to the surface of the second layer 20 after the second layer formation step, the surface not in contact with the first layer 10, and then bonding the third layer 30 to the surface of the second layer 20 after the second layer formation step, the surface not in contact with the first layer 10. The resin composition used for the third layer 30 is as described in the section "Third Layer 30." In the method for producing the laminate 1, the method for applying the resin composition used for the third layer 30 and the method for curing the resin composition used for the third layer 30 may also be performed by known application and curing methods, as described above.

[0102] The method for producing the laminate 1 may further include a first layer forming step of forming the first layer 10 before the second layer forming step, as necessary.

[0103] Other Embodiments The laminate of the present disclosure is not limited to the laminate 1 applied to a laser-markable label having a three-layer structure having a first layer, a second layer, and a third layer. The laminate of the present disclosure may be a laminate consisting of the second and third layers without the first layer, a laminate having the second, third, and other layers without the first layer, or a laminate having the first, second, third, and other layers.

[0104] Examples of other layers include a colored layer, a printed layer, and an easy-adhesion layer. The colored layer is provided, for example, between the second layer and the third layer, and is a layer that imparts a color, pattern, etc. to the entire laminate. By providing a colored layer, the design of the laminate is improved. The colored layer may be a layer containing a resin and a colorant. The resin contained in the colored layer is not particularly limited, and may be the same resin as the resin used in the first layer. The colorant contained in the colored layer is not particularly limited, and may be a pigment, a dye, or the like. The thickness of the colored layer is not particularly limited, and may be in the range of 1 μm to 50 μm, for example. The colored layer may be formed by applying a resin composition for forming a colored layer to the surface of the second layer facing the third layer, or may be formed separately and then attached to the surface of the second layer facing the third layer. When the colored layer is attached to the surface of the second layer, a pressure-sensitive adhesive layer may further be provided between the colored layer and the second layer.

[0105] The printed layer is, for example, a layer provided between the second layer and the third layer and formed by a printer. Specifically, for example, a resin composition containing a resin, a colorant, a solvent, etc. is applied to the surface of the layer adjacent to the printed layer in the shape of a desired pattern, character, etc., and then, if necessary, undergoes processes such as drying and curing to form the printed layer. The provision of the printed layer improves the design of the laminate. The printed layer may be provided only on a portion of the laminate surface or on the entire surface. Examples of printing methods include inkjet printer printing, screen printing, gravure printing, and flexographic printing.

[0106] The printed layer is formed, for example, by printing on the surface of the second layer on the third layer side. When the laminate has a colored layer, the printed layer may be provided, for example, between the second layer and the colored layer, and may be formed by printing on the surface of the second layer facing the colored layer, or may be formed by printing on the surface of the colored layer facing the second layer. When the printed layer is formed by printing on the surface of the second layer, it is preferable that the laser marking composition used to form the second layer contains at least one of a urethane resin and a filler. [Example]

[0107] The present disclosure will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0108] [Polymerization Example 1] In a reaction vessel of a reaction apparatus equipped with a stirrer, a reflux condenser, a successive dropping device, and a thermometer, 70.0 parts by mass of ethyl acetate (organic solvent) was charged. In a separate vessel, 100.0 parts by mass of a monomer mixture consisting of 65.0 parts by mass of ethyl acrylate [EA; an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms], 21.0 parts by mass of methyl methacrylate [MMA; a methacrylic acid alkyl ester monomer], and 14.0 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; a methacrylic acid alkyl ester monomer having a hydroxyl group] was prepared. 20.0% by mass of this prepared monomer mixture was charged into the reaction vessel, and then heated and refluxed at reflux temperature for 10 minutes. Next, under reflux temperature conditions, the remaining 80.0 mass% of the monomer mixture, 50.0 mass parts of ethyl acetate, and 0.026 mass parts of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) were successively added dropwise to the reaction vessel over 120 minutes, and after the completion of the addition, the reaction was continued for an additional 150 minutes to complete the reaction. After the reaction was completed, the solution was diluted with ethyl acetate to a solids concentration of 35.0 mass%, thereby obtaining a (meth)acrylic resin solution of Polymerization Example 1. The term "solid content concentration" used herein means the mass proportion of the (meth)acrylic resin in the (meth)acrylic resin solution. Table 1 also lists the weight-average molecular weight (Mw) and glass transition temperature (Tg) of the (meth)acrylic resin of Polymerization Example 1, as well as the proportion (A, % by mass) of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms, the total proportion (A-1, % by mass) of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate, and the total proportion (B, % by mass) of structural units derived from an alkyl methacrylate ester, all of which account for all structural units of the (meth)acrylic resin. The weight-average molecular weight of the (meth)acrylic resin solution is a value measured by the method described above. The glass transition temperature (Tg) of the (meth)acrylic resin is a value obtained by converting the absolute temperature (K) calculated by the above formula into Celsius temperature (°C).

[0109] [Synthesis of Polymer 6 from Polymerization Example 2] In the synthesis of Polymer 1, (meth)acrylic resin solutions of Polymerization Examples 2 to 6 were obtained in the same manner as in Polymerization Example 1, except that the monomers listed in Table 1 were used. In Table 1, MA represents methyl acrylate (an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms), BA represents butyl acrylate (an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms), 2HEA represents 2-hydroxyethyl acrylate (an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms and a hydroxyl group), and AA represents acrylic acid.

[0110] [Table 1]

[0111] [Examples 1 to 33 and Comparative Examples 1 to 7] The components shown in Tables 2 to 4 were blended in the ratios (parts by mass) shown in Tables 2 to 4, and the solids concentration was adjusted to 20% by mass with ethyl acetate to obtain the laser marking compositions of Examples 1 to 33 and Comparative Examples 1 to 7. In Tables 2 to 4, for Polymerization Examples 1 to 6, the solid content means the content of the (meth)acrylic resin. In Tables 2 to 4, "equivalent weight" indicates the content of the crosslinking agent contained in the crosslinking agent relative to the total of the hydroxyl groups and carboxyl groups in the (meth)acrylic resin (amount of functional groups in the crosslinking agent / amount of functional groups in the (meth)acrylic resin). The details of each component listed in Tables 2 to 4 are as follows. Crosslinker 1: Isocyanurate crosslinker of IPDI (Takenate D140N-60, manufactured by Mitsui Chemicals, Inc.) Crosslinker 2: HDI isocyanurate crosslinker (Coronate HK, manufactured by Tosoh Corporation) Crosslinker 3: XDI isocyanurate crosslinker (Takenate D-131N, manufactured by Mitsui Chemicals, Inc.) Crosslinker 4: TMP adduct of HDI (Duranate E402-80B, manufactured by Asahi Kasei Corporation) Crosslinker 5: TMP adduct of TDI (Takenate D101A, manufactured by Mitsui Chemicals, Inc.) Crosslinker 6: Melamine-based crosslinker (Nicalac MS-11, manufactured by Nippon Carbide Industries Co., Ltd.) Crosslinking agent 7: Aluminum chelate crosslinking agent (CK-401, manufactured by Nippon Carbide Industries Co., Ltd.) Bismuth-containing compounds: bismuth oxide color pigment (42-970A, TOMATEC Corporation) Urethane resin 1: Lezamin NE-8836 (Dainichiseika Color & Chemicals Mfg. Co., Ltd.) Urethane resin 2: Pandex T-5275N (DIC Covestro Polymer Co., Ltd.) Catalyst: Polyphosphate ester (CT-198, Tokusiki Co., Ltd.) White pigment 1: Titanium oxide coated mica (Iriodin 103, Merck Ltd.) Filler 1: Silica (Sylysia 445, Fuji Silysia Chemical Ltd.) Filler 2: Acrylic beads (Art Pearl GR-300, Negami Chemical Industrial Co., Ltd.)

[0112] Corona treatment was performed on both sides of a 50 μm thick PET film (surface layer), and the laser marking composition was applied to one side of the PET film so that the film thickness after drying would be as shown in Tables 2 to 4. The composition was then dried at 70°C for 3 minutes and then at 150°C for 3 minutes to form a laser marking layer (color-developing layer). 100 parts by mass of acrylic resin PE-121 (manufactured by Nippon Carbide Industries Co., Ltd.) was blended with 0.53 parts by mass of crosslinking agent CK-401 (manufactured by Nippon Carbide Industries Co., Ltd.), mixed with ethyl acetate to an appropriate viscosity, and then coated to a thickness of 20 μm on release-treated PET (75E0010GT, manufactured by Fujimori Kogyo Co., Ltd.) and heated at 100° C. for 1 minute to form a pressure-sensitive adhesive layer on the release-treated PET. The adhesive surface of this pressure-sensitive adhesive layer was bonded to the laser marking layer to produce a laser-marking laminate for each of the Examples and Comparative Examples. The obtained laser marking laminate was subjected to the following evaluations. In the evaluation of the seal printability and inkjet printability described below, the evaluation was carried out using a sample before the pressure-sensitive adhesive layer was attached to the laser marking layer.

[0113] [Printability] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), laser light was irradiated onto the surface layer of the laser marking laminate under conditions of 25% output (printing intensity), 50 Hz pulse cycle, 0.07 mm line width, and 2000 mm / sec to print a 15 mm square fill pattern. The laser marking laminate was then attached to a glass plate, and a hiding power test paper specified in JIS K 5600-4-1:1999 was placed on the back of the glass, and the color difference between the laminate itself and the printed area was measured using a colorimeter (trade name "Spectrophotometer CM-3600A", manufactured by Konica Minolta, Inc.), and ΔE * ab1 (color difference before heating) was calculated. The results are shown in Tables 2 to 4. ΔE * If ab1 is 5 or more, there is no problem in practical use. * The larger ab1 is, the better the visibility is.

[0114] [Heat resistance] A laser-markable laminate printed with a 15 mm square fill pattern, obtained by the same method as described in the [Printability] section, was attached to a glass plate and heated at 120°C for 168 hours. Thereafter, a hiding power test paper specified in JIS K 5600-4-1:1999 was placed on the back of the glass, and the color difference between the laminate itself and the printed area was measured using a colorimeter (trade name "Spectrophotometer CM-3600A", manufactured by Konica Minolta) to determine ΔE * ab2 (color difference after heating) was calculated. ΔE after printability test * ab1 and ΔE after heating * The absolute value of the difference from ab2 was taken as the color difference before and after heating (ΔE*ab), and was evaluated according to the following criteria: If the evaluation was B or higher, it was acceptable for practical use. SS: When ΔE*ab is 0 or ΔE*ab is 3 or less, the density of the printed area becomes darker after heating. S: When ΔE*ab is 3 or less, the density of the printed area becomes lighter after heating. A: ΔE*ab exceeds 3 and the density of the printed area becomes dark. B: ΔE*ab is greater than 3 and ΔE*ab is 5 or less, and the density of the printed area becomes lighter after heating. C: ΔE*ab exceeds 5, and the density of the printed area becomes light.

[0115] [2D code readability] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), laser light was irradiated onto the surface layer of the laminate under conditions of output (printing intensity) of 20%, 30%, and 50%, a pulse cycle of 50 Hz, a line width of 0.07 mm, and 2000 mm / sec, to print 4 mm square and 8 mm square two-dimensional codes. A code reader (Keyence Corporation, product name SR-H60W) was then used to conduct a reading test 100 times and evaluate the codes according to the following criteria. A rating of B or higher indicates that the code is suitable for practical use. S: The success rate of reading 8mm squares is 80% or more. A: The reading success rate for 8mm squares is 50% or more. B: The success rate of reading 4mm squares is 90%. C: The success rate of reading 4mm squares is 50% or more. D: The success rate of reading 4mm squares is less than 50%.

[0116] [Bulge] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), laser light was irradiated onto the surface layer of the laminate at output (printing intensity) of 20%, 30%, and 50%, with a pulse frequency of 50 Hz, a line width of 0.07 mm, and a speed of 2000 mm / sec, to print 4 mm square and 8 mm square two-dimensional codes. During this process, the occurrence of blisters between the release-treated PET and the adhesive layer was observed visually and by touch, and the results were evaluated according to the following criteria. A rating of B or higher indicated practical suitability. It can be said that the less swelling occurs, the more gas generation during printing is suppressed. A: It does not swell even when the print strength is 50%. B: Swells at 50% print intensity. C: Swells regardless of print strength.

[0117] [Seal printability] Before laminating the adhesive layer, the two-dimensional code printing area (10 mm 2 ) the entire surface except for the white areas was printed with ink (UV161J black ink, manufactured by T&K TOKA) in 10-point Gothic font with a thickness of 1 mm using a sticker printing machine, with the words "NIPPON CARBIDE INDUSTRIES" printed in solid color except for the white-out areas, and the print was then hardened by irradiating it with UV light from a 2kW metal halide lamp for 5 seconds to form a printed layer. On the other hand, a mixture of the (meth)acrylic resin solution of Polymerization Example 3 (100 parts by mass in terms of solid content), rosin ester (Pensel D-125, manufactured by Arakawa Chemical Industries, Ltd., 8.27 parts by mass), the crosslinker 5 (3.36 parts by mass), and white pigment 2 (NX-501 White, manufactured by Dainichiseika Color & Chemicals Co., Ltd., 27.80 parts by mass) was applied to a release paper (KH10 White GM, manufactured by Lintec Corporation) so that the film thickness after drying would be 40 μm, and the mixture was dried to form an adhesive layer. The adhesive surface of the obtained pressure-sensitive adhesive layer was attached to the printed surface of the laser marking layer to obtain a laser-markable laminate. A 9 mm square two-dimensional code was printed by laser in the center of the non-printed part of the obtained laser-markable laminate, and this was used as the initial sample. Thereafter, the laminate serving as the initial sample was folded in half, and the pressure-sensitive adhesive layers were bonded together, and then the laminate was peeled back to the state before bonding, which was used as a peeled sample. The initial sample was visually inspected for ink repellency and bleeding, and the peeled sample was visually inspected for distortion and peeling of the printed layer, and evaluated according to the following criteria. A: No ink repellency or bleeding is observed on the initial sample, and no distortion or peeling of the printed layer is observed on the sample after peeling. B: No ink repellency or bleeding was observed on the initial sample, and distortion of the printed layer was observed on the sample after peeling. C: No ink repellency or bleeding was observed on the initial sample, and peeling of the printed layer was observed on the sample after peeling. D: At least one of ink repellency and bleeding is observed on the initial sample.

[0118] [Inkjet printability] Before laminating the adhesive layer, the two-dimensional code printing area (10 mm 2 ) on the entire surface except for the white areas, "NIPPON CARBIDE INDUSTRIES" was printed in 10-point Gothic font with a thickness of 1 mm using an inkjet printer (JV-300-130, manufactured by Mimaki Engineering Co., Ltd.) in a solid color in the hue of PTN311 except for the white areas, forming a printed layer. On the other hand, an adhesive layer was formed on a release paper in the same manner as in the evaluation of the seal printability. The adhesive surface of the obtained pressure-sensitive adhesive layer was attached to the printed surface of the laser marking layer to obtain a laser-markable laminate. A 9 mm square two-dimensional code was printed by laser in the center of the non-printed part of the obtained laser-markable laminate, and this was used as the initial sample. Thereafter, the laminate serving as the initial sample was folded in half, and the pressure-sensitive adhesive layers were bonded together, and then the laminate was peeled back to the state before bonding, which was used as a peeled sample. The initial sample was visually inspected for ink repellency and bleeding, and the peeled sample was visually inspected for distortion and peeling of the printed layer, and evaluated according to the following criteria. A: No ink repellency or bleeding is observed on the initial sample, and no distortion or peeling of the printed layer is observed on the sample after peeling. B: No ink repellency or bleeding was observed on the initial sample, and distortion of the printed layer was observed on the sample after peeling. C: No ink repellency or bleeding was observed on the initial sample, and peeling of the printed layer was observed on the sample after peeling. D: At least one of ink repellency and bleeding is observed on the initial sample.

[0119] [Lamination suitability] The two-dimensional code printing area (10 mm) on the surface of the acrylic film (A0800, manufactured by Nippon Carbide Industries Co., Ltd.) 2 In addition to the above, a 10 mm square filled with purple, blue, light blue, green, yellow-green, yellow, orange, red, and black was printed using an inkjet printer (JV-300-130, manufactured by Mimaki Engineering Co., Ltd.) along with the words "NIPPON CARBIDE" in 8-point font to form a printed layer. The release-treated PET of the laser-marking laminate of each Example and Comparative Example was peeled off to expose the adhesive layer. The adhesive layer of the laser-marking laminate was attached to the printed surface of the acrylic film on which the printing layer was formed, thereby laminating the acrylic film with the laser-marking laminate. A 9 mm square two-dimensional code was then printed with a laser in the center of the non-printed area, and the code was visually inspected from the laser-marking laminate side and evaluated according to the following criteria. A: The color tone of the printed layer remains the same before and after lamination. B: The printed layer after lamination appears slightly whitish compared to before lamination. C: The printed layer appears whiter after lamination than before lamination.

[0120] [Table 2]

[0121] [Table 3]

[0122] [Table 4]

[0123] The evaluation results shown in Tables 2 to 4 show that the laser marking laminate having a color-forming layer (resin film) obtained from the laser marking composition of the example achieves high levels of heat resistance, readability, and suppression of gas generation compared to the laser marking laminate having a color-forming layer (resin film) obtained from the laser marking composition of the comparative example. Furthermore, among the evaluations of the examples, laser marking laminates that exhibited excellent heat resistance were also considered to exhibit excellent resistance to fading due to immersion in water (water resistance) and fading due to light irradiation (weather resistance).

[0124] The disclosure of Japanese Patent Application No. 2022-159100, filed on September 30, 2022, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are incorporated herein by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0125] 1. Laminate 10 First layer (surface layer) 20 Second layer (coloring layer) 30 Third layer (adhesive layer)

Claims

1. The composition contains at least one (meth)acrylic resin, a bismuth-containing compound, and a crosslinking agent having a triazine ring skeleton, the total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester in all structural units of the (meth)acrylic resin is less than 45 mass%; Further containing urethane resin, A laser marking composition, wherein the content of the urethane resin in the solid content of the laser marking composition is 2% by mass to 75% by mass.

2. 2. The laser marking composition according to claim 1, wherein the crosslinking agent having a triazine ring skeleton comprises at least one of an isocyanate-based crosslinking agent and a melamine-based crosslinking agent having a triazine ring skeleton.

3. 3. The laser marking composition according to claim 2, wherein the isocyanate-based crosslinking agent having a triazine ring skeleton comprises at least one selected from the group consisting of an isocyanurate-based crosslinking agent for an aromatic aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an aliphatic polyisocyanate compound, an isocyanurate-based crosslinking agent for an alicyclic polyisocyanate compound, and an isocyanurate-based crosslinking agent for an aromatic polyisocyanate compound.

4. 10. The laser marking composition of claim 1, further comprising a filler.

5. A resin film obtained by using the laser marking composition according to any one of claims 1 to 4.

6. A laminate comprising the resin film according to claim 5 .

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