Laser marking compositions, resin films, and laminates

Abstract

To provide a laser marking composition capable of forming a resin film which has excellent heat resistance and readability when one-dimensional or two-dimensional codes are printed, and which suppresses gas generation during printing. [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, 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%.

Description

[Technical Field]

[0001] This disclosure relates to laser marking compositions, resin films, and laminates. [Background technology]

[0002] Various packaging materials for food, pharmaceuticals, and other products, as well as various components such as electronic parts, require the printing of variable information for traceability, such as manufacturing lot numbers and manufacturing dates. Laser marking is one method used for this purpose. In particular, color-changing laser marking methods, which use a laser to change the color of resin or pigment, are being used in various places in recent years because they can be printed without generating odors or dust.

[0003] The following compositions are known for use as labels and inks for laser marking. For example, Patent Document 1 discloses an adhesive that provides good contrast after printing and forms an adhesive layer with suppressed discoloration, comprising an adhesive resin (A) and a bismuth-based laser coloring agent (B). Furthermore, Patent Document 2 discloses a laser marking ink composition that has sufficient laser printability (visibility), blocking resistance, adhesion, and lamination strength, comprising a binder resin, a white pigment, and an organic solvent, wherein the binder resin comprises 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 dioxide with an average particle size of 0.26 μm or less.

[0004] Patent Document 1: Patent No. 6292429 Patent Document 2: Patent No. 7057236 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Resin compositions that can turn black when irradiated with laser light utilize the reduction reaction of inorganic oxides caused by laser light to produce color. During this process, the heat generated causes carbonization of the resin and the generation of gases. If the carbonization of the resin spreads more than intended, or if the laminate swells, it is prone to reading errors when printing one-dimensional or two-dimensional codes. For example, the adhesive using a bismuth-based laser colorant disclosed in Patent Document 1 may cause deformation of the printed text due to the heat generated during printing, which may make it difficult to read the printed content. Furthermore, in the laser marking ink composition disclosed in Patent Document 2, the urethane resin is prone to carbonization, which can cause the resin surrounding the inorganic oxide to carbonize, making it difficult to read the printed content depending on the content. In addition, the (meth)acrylic copolymer listed as a comparative example in Patent Document 2 has methacrylic resin as its main component, which can lead to 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 with a laser. In bismuth-based laser colorants, color is produced by the color difference between bismuth oxide and bismuth. Since bismuth decolorizes when it becomes a carboxylate salt or bismuth hydroxide, it is expected that the absorbance in the visible light region will decrease when carboxyl or hydroxyl groups coordinate to bismuth. The (meth)acrylic resin contained in the laser marking composition contains hydroxyl and carboxyl groups as crosslinking points, so decolorization of bismuth due to the (meth)acrylic resin may occur. In particular, decolorization of bismuth is more likely to occur with rising temperatures, and laser marking using bismuth-based laser colorants may have poor heat resistance in the printed area. This disclosure is made in view of the above-mentioned conventional circumstances, and aims to provide a laser marking composition capable of forming a resin film that has excellent heat resistance and readability when printing one-dimensional or two-dimensional codes, and that suppresses gas generation during printing, as well as a resin film and laminate using this laser marking composition. [Means for solving the problem]

[0006] The specific means for achieving the aforementioned objectives are as follows: <1> It contains at least one (meth)acrylic resin, a bismuth-containing compound, and a crosslinking agent having a triazine ring skeleton. A laser marking composition in which the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylate to the total structural units of the (meth)acrylic resin is less than 45% by mass. <2> 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. <1> The laser marking composition described above. <3> The isocyanate crosslinking agent having a triazine ring skeleton includes at least one selected from the group consisting of isocyanurate crosslinking agents for aromatic aliphatic polyisocyanate compounds, isocyanurate crosslinking agents for aliphatic polyisocyanate compounds, isocyanurate crosslinking agents for alicyclic polyisocyanate compounds, and isocyanurate crosslinking agents for aromatic polyisocyanate compounds. <2> The laser marking composition described above. <4> Further containing urethane resin, <1> ~ <3> A laser marking composition according to any one of the following items. <5> It further contains fillers, <1> ~ <4> A laser marking composition according to any one of the following items. <6> <1> ~ <5> A resin film made using the laser marking composition described in any one of the items. <7> <6> A laminate having the resin film described above. [Effects of the Invention]

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

[0008] [Figure 1] It is a figure which shows typically an example of the cross-sectional structure of the laminated body which concerns on one Embodiment of this indication.

FORM FOR CARRYING OUT 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, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and they do not limit the present disclosure.

[0010] In the present disclosure, the term "step" includes not only a step independent of other steps but also the step even if it cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range shown by using "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types of particles. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for the mixture of the plurality of types of particles present in the composition unless otherwise specified. In the present disclosure, the term "layer" or "film" includes not only the case where it is formed over the entire region where the layer or film exists but also the case where it is formed only in a part of the region when observing the region where the layer or film exists. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable. In this disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate. In this disclosure, the average thickness of a layer or film is given as the arithmetic mean of measuring the thickness of five points on the layer or film in question. The thickness of a layer or film can be measured using a micrometer or the like. In this disclosure, if 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, the measurement may be performed by observing the cross-section of the object to be measured using an electron microscope. In this disclosure, "solids" refers to the components of the laser marking composition or sample solution excluding the organic solvent.

[0011] <Laser marking composition> The laser marking composition of this disclosure 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 structural units derived from methacrylic acid and structural units derived from alkyl methacrylate to the total structural units of the (meth)acrylic resin is less than 45% by mass. The laser marking composition disclosed herein makes it possible to form a resin film that exhibits excellent heat resistance and readability when printing one-dimensional or two-dimensional codes, and suppresses gas generation during printing. The reason for this is not clear, but it is presumed to be as follows. Comparing structural units derived from alkyl acrylates and alkyl methacrylates that may be contained in (meth)acrylic resin, the difference lies in whether or not a methyl group is directly bonded to the carbon atoms constituting the main chain of the (meth)acrylic resin. Carbon atoms directly bonded to a methyl group become tertiary carbons. Decomposition of (meth)acrylic resin is more likely to occur by laser irradiation at locations where tertiary carbons constituting 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, gases derived from decomposition products are more likely to be generated. In this disclosure, since the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylate to the total structural units of the (meth)acrylic resin is less than 45% by mass, it is possible to maintain a relatively low proportion of tertiary carbons among the carbon atoms constituting the main chain of the (meth)acrylic resin, and it is thought that the generation of gases derived from decomposition products can be easily suppressed. Furthermore, as gas generation is suppressed, the occurrence of blistering of the resin film made of the laser marking composition can be easily suppressed. Furthermore, because (meth)acrylic resin contains hydroxyl and carboxyl groups as crosslinking points, there is a possibility that these groups may coordinate to the bismuth produced by the laser reduction reaction, causing the bismuth to decolorize. However, in resin films produced by the crosslinking reaction between a crosslinking agent having a triazine ring skeleton and (meth)acrylic resin, the rigidity of the triazine ring skeleton makes it easier to suppress molecular movement, thus suppressing the coordination of hydroxyl and carboxyl groups to bismuth. In particular, even if molecular motion becomes more vigorous due to rising temperatures, the coordination of hydroxyl and carboxyl groups contained in the (meth)acrylic resin to bismuth is easily suppressed, and it is presumed that the heat resistance of the printed area produced by laser marking will improve. In addition, due to the rigidity of the triazine ring skeleton, deformation of the resin film due to gases and heat that may be generated during printing is easily suppressed, and it is presumed that the readability of one-dimensional and two-dimensional codes when printed will improve.

[0012] The following describes each component constituting the laser marking composition of this disclosure.

[0013] ((meth)acrylic resin) The laser marking composition of this disclosure contains at least one (meth)acrylic resin Furthermore, the total proportion of structural units derived from methacrylic acid and alkyl methacrylate in the total structural units of the (meth)acrylic resin is less than 45% by mass. The total proportion of structural units derived from methacrylic acid and alkyl methacrylate in the total 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 alkyl methacrylate in the total structural units of the (meth)acrylic resin may be 0% by mass. The total proportion of structural units derived from methacrylic acid and alkyl methacrylate in the total structural units of the (meth)acrylic resin is preferably 0% by mass or more and less than 45% by mass.

[0014] If the laser marking composition of this disclosure contains one type of (meth)acrylic resin, any (meth)acrylic resin that satisfies the above conditions 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, if the laser marking composition of this disclosure contains two or more (meth)acrylic resins, two or more homopolymers with different structural units may be used in combination, or at least one homopolymer and at least one copolymer may be used in combination, or two or more copolymers with 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 to all structural units contained in the two or more (meth)acrylic resins is less than 45% by mass.

[0015] Here, (meth)acrylic monomer means at least one of acrylic acid, derivatives of acrylic acid such as alkyl acrylates, or derivatives of methacrylic acid such as methacrylic acid and alkyl methacrylates. Derivatives of acrylic acid and derivatives of methacrylic acid may have substituents such as hydroxyl groups, amino groups, carboxyl groups, and glycidyl groups. Furthermore, other monomers besides (meth)acrylic monomers may be used in the (meth)acrylic resin.

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

[0019] In this disclosure, the proportion of structural units derived from alkyl acrylates containing alkyl groups having 1 to 4 carbon atoms to the total 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 alkyl acrylates containing alkyl groups having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin may be 99% by mass or less. The proportion of structural units derived from alkyl acrylates containing alkyl groups having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin is preferably 55% by mass to 99% by mass.

[0020] Preferred alkyl acrylates containing alkyl groups with 1 to 4 carbon atoms include ethyl acrylate, methyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, and other butyl acrylates, as well as 2-hydroxyethyl acrylate.

[0021] In this disclosure, in some embodiments, the total proportion of structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate to the total structural units of 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 structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate to the total structural units of the (meth)acrylic resin may be 99% by mass or less. The total proportion of structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate to the total structural units of 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 homopolymerized. Therefore, in (meth)acrylic resins, the main chain of the (meth)acrylic resin is less likely to move even if heat is generated by the reduction of inorganic oxides in the structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate. As a result, it tends to be easier to print with high precision. Furthermore, in other embodiments of this disclosure, the total proportion of structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate to the total structural units of the (meth)acrylic resin may be 1% by mass or less.

[0022] The total proportion of structural units derived from monomers containing a carboxyl group in their molecule, such as acrylic acid, methacrylic acid, and other monomers containing a carboxyl group, to the total 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 carboxyl group in their molecule to the total 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 carboxyl group in their molecule to the total 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 carboxyl group in the molecule to the total structural units of (meth)acrylic resin is 20% by mass or less, visibility tends to improve.

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

[0025] In this 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 (1) to (3) below. (1) Apply a solution of (meth)acrylic resin to release paper and dry it at 100°C for 1 minute to obtain a film-like (meth)acrylic resin. (2) Using the film-like (meth)acrylic resin 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 as a standard polystyrene equivalent under the following conditions.

[0026] ~Conditions~ Measurement device: High-speed GPC (Model number: HLC-8220 GPC, Tosoh Corporation) Detector: Differential Refractometer (RI) (integrated into HLC-8220, Tosoh Corporation) Columns: Four TSK-GEL GMHXL columns (Tosoh Corporation) 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 (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 and gas during printing and to enable accurate printing of one-dimensional and two-dimensional codes. The glass transition temperature Tg of (meth)acrylic resin may be 100°C or lower from the viewpoint of good workability of the resin film and less brittleness. The glass transition temperature Tg of (meth)acrylic resin is preferably -20°C to 100°C. The glass transition temperature (Tg) of (meth)acrylic resin is determined by measuring the temperature using a differential scanning calorimetry (DSC) (e.g., EXSTAR6000, manufactured by Seiko Instruments Inc.) in a nitrogen atmosphere with a 10 mg sample and a heating rate of 10°C / min, and finding the inflection point of the resulting DSC curve. If two or more inflection points are observed in the DSC curve using a differential scanning calorimetry (DSC), the temperature at the inflection point with the highest temperature is defined as the glass transition temperature (Tg) of the (meth)acrylic resin.

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

[0029]

number

[0030] In the formula, Tg1, Tg2, ... and Tg n m1, m2, ..., and m n These represent the mole fractions of each monomer.

[0031] Furthermore, "glass transition temperature expressed as the absolute temperature (K) of a homopolymer" refers to the glass transition temperature expressed as the absolute temperature (K) of a homopolymer produced by polymerizing the monomers individually. The glass transition temperature of a homopolymer can be measured by the method described above using a differential scanning calorimetry (DSC).

[0032] The glass transition temperatures (expressed in Celsius temperature (°C)) of representative monomers are as follows: methyl acrylate is 10°C, ethyl acrylate is -22°C, n-butyl acrylate is -54°C, 2-ethylhexyl acrylate is -70°C, 2-hydroxyethyl acrylate is -15°C, 4-hydroxybutyl acrylate is -80°C, t-butyl acrylate is 43°C, vinyl acetate is 32°C, acrylic acid is 106°C, methyl methacrylate is 105°C, and 2-hydroxyethyl methacrylate is 85°C. For example, by using these representative monomers, it is possible to adjust the aforementioned glass transition temperatures as appropriate. For monomers other than those mentioned above, the "glass transition temperature when used as a homopolymer" is based on the values ​​listed in the Polymer Handbook (4th edition, Wiley-Interscience; hereafter the same). If the value is not listed in the Polymer Handbook, the glass transition temperature of the homopolymer obtained by the measurement method described above is used. Furthermore, absolute temperature (K) can be converted to Celsius temperature (°C) by subtracting 273 from it, and Celsius temperature (°C) can be converted back to absolute temperature (K) by adding 273 to it.

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

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

[0035] Solution polymerization generally involves placing a predetermined organic solvent, monomer, polymerization initiator, and a chain transfer agent (if necessary) into a polymerization tank and heating the mixture for several hours under a nitrogen atmosphere or at the reflux temperature of the organic solvent while stirring. The weight-average molecular weight of the (meth)acrylic resin can be adjusted to the desired value by controlling the reaction temperature, reaction time, amount of solvent, and type and amount of catalyst.

[0036] Organic solvents used in the polymerization reaction of (meth)acrylic resins include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. These organic solvents may be used individually or in mixtures of two or more.

[0037] More specifically, organic solvents used in polymerization reactions include, for example, aromatic hydrocarbon organic solvents represented by benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon organic solvents represented by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirits, petroleum naphtha, and turpentine oil; ester organic solvents represented by ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl ester Examples include ketone-based organic solvents such as tyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether-based organic solvents such as 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 such as 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 polymerization initiators include organic peroxides and azo compounds that can be used in conventional polymerization methods.

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

[0040] The content of (meth)acrylic resin in 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. When the (meth)acrylic resin content is 15% to 98% by mass, the heat resistance of the printed area tends to improve.

[0041] (Bismuth-containing compounds) The laser marking composition of this disclosure contains a bismuth-containing compound. The bismuth-containing compound functions as a coloring pigment. As the bismuth-containing compound, bismuth(III) oxide (Bi2O3) is preferred because it exhibits excellent blackness when colored. In this case, a metal oxide with many oxygen vacancies is more preferred in order to improve laser printability.

[0042] The volume-average particle size 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 size 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, thus improving color development. On the other hand, when the volume-average particle size of the bismuth-containing compound is 30 μm or less, the dispersibility during film formation tends to be good. The volume-average particle size of the bismuth-containing compound refers to the value measured by laser diffraction / light scattering. The specific method for laser diffraction / light scattering is as follows: A 5 mL aqueous dispersion of a bismuth-containing compound is collected using a Pasteur pipette into a glass cell measuring 5 mm x 65 mm x 80 mm square, and this is placed in a laser diffraction / light scattering particle size distribution analyzer (for example, LA-960A (product name) from Horiba, Ltd.). After adjusting the concentration of the aqueous dispersion of the bismuth-containing compound so that the transmittance of the laser light (red) is 80% to 90%, the average particle size of the bismuth-containing compound particles in the aqueous dispersion is determined by computer processing of the results measured under conditions of a measurement temperature of 25°C ± 1°C. The volume average value of the average particle size is used.

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

[0044] (Crosslinking agent) The laser marking compositions of this disclosure contain 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 functional groups that can react with hydroxyl groups and carboxyl groups 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 having a triazine ring skeleton, 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" means a compound having two or more isocyanate groups in its molecule (so-called polyisocyanate compound) and its derivatives. Furthermore, "melamine-based crosslinking agent" means a melamine derivative having one or more methylol groups in its molecule. Furthermore, "benzoguanamine-based crosslinking agent" means benzoguanamine and its derivatives. Furthermore, "epoxy-based crosslinking agent" means a compound having at least one epoxy group in its 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 they can more effectively suppress the decolorization of bismuth that has been reduced by laser irradiation. The reason why using at least one of an isocyanate-based crosslinking agent having a triazine ring skeleton and a melamine-based crosslinking agent can more effectively suppress the decolorization of bismuth is not clear, but it can be inferred as follows. The isocyanate groups contained in isocyanate-based crosslinking agents and the amino groups, imino groups, methylol groups, and alkyl ether groups contained in melamine-based crosslinking agents are highly reactive with the hydroxyl and carboxyl groups contained in (meth)acrylic resins. Therefore, the amount of hydroxyl and carboxyl groups in the resin film is easily reduced by the crosslinking reaction between these crosslinking agents and (meth)acrylic resins. As a result, it is presumed that the coordination of hydroxyl and carboxyl groups to bismuth produced by the laser reduction reaction is suppressed, thereby reducing the attenuation of bismuth's absorbance in the visible light region and making bismuth less likely to decolorize. Furthermore, urethane bonds are formed by the reaction of hydroxyl groups with isocyanate groups, and amino groups and urea groups are formed by the reaction of carboxyl groups with isocyanate groups. In addition, melamine-based crosslinking agents usually contain imide groups. When these functional groups are present in the resin film, they tend to coordinate with bismuth reduced by laser irradiation, making the film more prone to darkening.

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

[0046] In this disclosure, "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 aromatic aliphatic polyisocyanate compounds include those having a structure in which an isocyanate group and an aromatic ring are bonded via a methylene group in the molecule. Examples of aromatic aliphatic polyisocyanate compounds 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), and the like.

[0047] In this disclosure, "aliphatic or alicyclic polyisocyanate compound" refers to any aliphatic or alicyclic compound having approximately 1 to 1000 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 such as 1,4-cyclohexanebismethylisocyanate (hydrogenated XDI), and hydrogenated diphenylmethane diisocyanate such as 4,4-methylenebiscyclohexyl isocyanate (hydrogenated MDI).

[0048] In this disclosure, an "aromatic polyisocyanate compound" is defined as 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 this disclosure, from the viewpoint of printing accuracy, it is preferable that the isocyanate crosslinking agent having a triazine ring skeleton includes at least one selected from the group consisting of isocyanurate crosslinking agents for aromatic aliphatic polyisocyanate compounds, isocyanurate crosslinking agents for aliphatic polyisocyanate compounds, isocyanurate crosslinking agents for alicyclic polyisocyanate compounds, and isocyanurate crosslinking agents for aromatic polyisocyanate compounds. In this disclosure, among these, from the viewpoint of suppressing yellowing of the resin film, isocyanurate-based crosslinking agents of aliphatic or alicyclic polyisocyanate compounds are preferred as crosslinking agents. Furthermore, from the viewpoint of improving printing accuracy, isocyanurate-based crosslinking agents of alicyclic polyisocyanate compounds are even more preferred.

[0050] Isocyanurate-based crosslinking agents can be obtained from polyisocyanate compounds by conventional methods using isocyanuration catalysts such as quaternary ammonium salts, tertiary amines, and metal salts of various organic acids.

[0051] Commercially available isocyanurate crosslinking agents may be used. Examples of commercially available isocyanurate crosslinking agents include Takenate D-140N, Takenate D-127N, Takenate D-268, and Takenate D-131N from Mitsui Chemicals, Inc., Coronate HX and Coronate HK from Tosoh Corporation, Duranate TKA-100 from Asahi Kasei Corporation, and Desmodur N4470BA, Desmodur RC, and Desmodur N3300A from Sumika Covestro Urethane Co., Ltd.

[0052] -Melamine-based crosslinking agent- As the melamine-based crosslinking agent, for example, melamine, a methylolated melamine derivative obtained by condensing melamine and formaldehyde, a compound obtained by reacting methylolated melamine with a lower alcohol to be partially or completely etherified, or a mixture thereof, etc. are used. Further, the melamine-based crosslinking agent may be any condensate composed of a monomer or a multimer of dimer or higher, or a mixture thereof. More specifically, an imino group type methylated melamine resin, a methylol group type melamine resin, a methylol group type methylated melamine resin, a completely alkyl type methylated melamine resin, etc. can be mentioned.

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

[0054]

Chemical formula

[0055] Here, 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 carbons, or a glycidyl group. R 6 is a hydrogen atom or an alkyl group having 1 to 3 carbons. n1 is an integer of 1 to 8.

[0056]

Chemical formula

[0057] Here, 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 carbons, or a glycidyl group.

[0058]

Chemical formula

[0059] Here, R 21 ~R 25 These are, independently, hydrogen atoms and R 26 OCH2-, or a melamine residue represented by formula (II), R 26 This is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a glycidyl group. Furthermore, melamine-based crosslinking agents can also be represented by the following general formula (IV).

[0060] [ka]

[0061] Here, R 31 ~R 35 is a hydrogen atom, R 37 -OCH2-, or a melamine residue represented by formula (II) or formula (III), R 37 R is a hydrogen atom, a C1-C4 alkyl group, or a glycidyl group. 36 n2 is a hydrogen atom or a carbon-1 to carbon-3 alkyl group. n2 is an integer from 1 to 8. Furthermore, melamine-based crosslinking agents can also be represented by the following general formula (V).

[0062] [ka]

[0063] Here, 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), R 47 R is a hydrogen atom, a C1-C4 alkyl group, or a glycidyl group. 55 n is a hydrogen atom or an alkyl group with 1 to 3 carbon atoms. n3 and n4 are integers, and n3 + n4 is between 2 and 8. Among the compounds represented by general formulas (I) to (V), preferred melamine-based crosslinking agents include Nikalac® MS-11 and MS-001 (both manufactured by Nippon Carbide Industries, Ltd.), and Mycoat 715 (manufactured by Nippon Scitec Industries, Ltd.).

[0064] -Benzoguanamine-based crosslinking agent- Examples of benzoguanamine-based crosslinking agents include benzoguanamine, methylolated benzoguanamine derivatives obtained by condensing benzoguanamine with formaldehyde, compounds partially or completely etherified by reacting methylolated benzoguanamine with a lower alcohol, or mixtures thereof. Furthermore, the benzoguanamine-based crosslinking agent may be a condensate consisting of a monomer or a polymer of two or more monomers, or a mixture thereof. More specifically, examples include butylated benzoguanamine resin and methylolated benzoguanamine resin.

[0065] -Epoxy crosslinking agent having a triazine ring skeleton- An example of an epoxy crosslinking agent having a triazine ring skeleton is the TEPIC series from Nissan Chemical Industries, Ltd.

[0066] The amount of crosslinking agent having a triazine ring skeleton in the laser marking composition (equivalent amount (amount of functional groups of the crosslinking agent / amount of functional groups of the (meth)acrylic resin) is preferably 0.1 to 10 equivalents relative to the total amount of hydroxyl and carboxyl groups of the (meth)acrylic resin. A crosslinking agent content of 0.1 equivalents or more suppresses molecular movement and improves printing accuracy. A crosslinking agent content of 10 equivalents or less suppresses discoloration of the (meth)acrylic resin. A crosslinking agent content of 0.3 to 3.0 equivalents is more preferable because it facilitates film formation.

[0067] The laser marking compositions of this disclosure may contain other crosslinking agents besides those having a triazine ring skeleton. Other crosslinking agents include dimers (uretdiones) of the polyisocyanate compounds mentioned above; prepolymers of the isocyanate compounds and polyol resins mentioned above; adducts of (a) the polyisocyanate compounds mentioned above and (b) polyhydric alcohol compounds such as propylene glycol (bifunctional alcohol), butylene glycol (bifunctional alcohol), trimethylolpropane (TMP, trifunctional alcohol), glycerin (trifunctional alcohol), pentaerythritol (tetrafunctional alcohol), urea compounds, etc.; isocyanate-based crosslinking agents that do not have a triazine ring skeleton, such as biuret forms of the polyisocyanate compounds mentioned above, 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, acid anhydride-based crosslinking agents, etc. If the laser marking composition of this disclosure contains other crosslinking agents, the proportion of the crosslinking agent having a triazine ring skeleton to the total crosslinking agent is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more. Furthermore, since bismuth is a group 15 element, Lewis acids tend to coordinate easily to it. Also, bismuth has a low ionization tendency. Therefore, when aluminum chelate is used as a crosslinking agent, ligand exchange occurs between aluminum and bismuth upon heating, and the bismuth may decolorize, similar to the case of hydroxyl groups and carboxylic acid groups. For this reason, from the viewpoint of suppressing the decolorization of 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 disclosed herein may contain a white pigment to further improve visibility by increasing the contrast between the black color of the printed area and the white color of the non-printed area. Various inorganic pigments can be used as white pigments. For example, white pigments such as titanium dioxide (TiO2), titanium dioxide-coated mica, zinc oxide (zinc oxide), basic lead sulfate, zinc sulfide, and antimony oxide can be used. Alternatively, barium sulfate, barium carbonate, precipitated calcium carbonate, diatomaceous earth, talc, clay, basic magnesium carbonate, and alumina white may also be used as white pigments. Among these, titanium dioxide (TiO2) is preferred as a white pigment because of its excellent whiteness. Furthermore, the above-mentioned white pigments and aluminum may also be included, as 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 size 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 size of the white pigment refers to the value measured by laser diffraction / light scattering.

[0069] When the laser marking composition of this 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% to 50% by mass, more preferably 0.1% to 30% by mass, and even more preferably 1% to 20% by mass. If 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-developing pigment can be improved, and visibility tends to be further improved. If the content of the white pigment relative to the solid content of the laser marking composition is 50% by mass or less, it tends to prevent a decrease in the color development of the bismuth-containing compound.

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

[0071] Commercially available urethane resins can be used. Examples of commercially available urethane resins include, for example, "NE-8836 (polycarbonate type)", "NE-8811 (polycarbonate type)", "NE-8850 (polycarbonate type)" [all manufactured by Dainichi Seika Kogyo Co., Ltd.], as well as "Superflex 420 (polycarbonate type)", "Superflex 460 (polycarbonate type)", "Superflex 210 (polyester type)" [all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], "Pandex T-5275 (polyester type)", "Pandex T-9280 (polycarbonate type)", "Pandex T-9290 (polycarbonate type)", "Pandex T-1190 (polyester type)", and "Pandex T-8190 (polyether type)" [all manufactured by DIC Covestro Polymer Co., Ltd.].

[0072] (Filler) The laser marking composition of this disclosure may contain a filler to improve printability when printing on the surface of a resin film. The inclusion of a filler in the laser marking composition improves the slipperiness on the surface of the resin film, thereby improving operability when printing on the surface of the resin film and resulting in good printability. As fillers, known fillers such as inorganic particles like silica particles, and resin particles like acrylic beads and melamine beads can be used. Fillers may be used individually or in combination of two or more types. The volume-average particle size of the filler is not particularly limited, but 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 size of the filler is measured by the same method as the volume-average particle size of the metal oxide described above. If the laser marking composition of this disclosure contains a filler, the filler content in the solid content of the laser marking composition is preferably 0.2% to 30.0% by mass, more preferably 0.5% to 20% by mass, and even more preferably 2% to 10% by mass, from the viewpoint of improving lubricity.

[0073] (Other ingredients) The laser marking compositions of this disclosure may contain other resins and various additives, to the extent that they do not impair heat resistance, readability when printing one-dimensional or two-dimensional codes, and the effect of suppressing gas generation during printing. Such additives include, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants.

[0074] (Organic solvents) The laser marking compositions of this disclosure may contain organic solvents 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. One type of organic solvent may be used alone, or two or more types may be used in combination.

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

[0076] <Resin film> The resin film of this disclosure is made using the laser marking composition of this disclosure. The method for producing a resin film using the laser marking composition of this disclosure is not particularly limited, and the resin film can be formed by known methods using a single-layer T-die extruder, a multi-layer T-die extruder, a calendering machine, etc. Furthermore, a resin film can be formed by applying the laser marking composition of this disclosure, which contains an organic solvent, to one side of a substrate film described later 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. If the laser marking composition contains a crosslinking agent, the resin film may be cured. Methods for curing the resin film include drying with hot air, heating with a heating device such as an oven or hot plate, etc. 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 comprises the resin film of the present disclosure. The laminate of the disclosure may be a laminate used for laser marking labels. The layer configuration of the laminate is not particularly limited, and may consist of a first layer that transmits laser light, a second layer that changes color when exposed to laser light, and an optional third layer that is adhesive, stacked in this order. Alternatively, the first layer that transmits laser light and the adhesive second layer that changes color when exposed to laser light may be 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 this disclosure, having the resin film of this disclosure, tends to suppress gas generation in the second layer during laser marking. Consequently, odor generation is suppressed. Furthermore, the readability of one-dimensional and two-dimensional codes printed on it also tends to improve.

[0079] The following describes the application of the laminate of this disclosure to a three-layer laser marking label with reference to Figure 1. Figure 1 is a schematic diagram showing an example of the cross-sectional structure of a laminate 1 according to one embodiment of this disclosure. As shown in Figure 1, the laminate 1 has a first layer 10, a second layer 20, and a third layer 30, and the first layer 10, second layer 20, and third layer 30 are stacked in this order. The second layer 20 is in contact with the first layer 10.

[0080] Here, we will explain laser marking on the laminate 1. First, laser light is irradiated onto the laminate 1 from the first layer 10 side. 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 this disclosure, the bismuth-containing compound changes color in the area of ​​the second layer 20 irradiated with laser light, and the resin carbonizes due to the heat of the laser light. The colored and carbonized areas in the second layer 20 become the printed areas in the laser marking label. The printed areas are the regions in the second layer 20 that have turned black. A laser marking label of this type, which contains a resin layer containing a bismuth-containing compound inside the film and causes the resin layer to change color by laser irradiation, is sometimes specifically referred to as an internally colored type laser marking label. In this disclosure, "laser marking" is not limited to the act of writing meaningful information such as letters or symbols onto the laminate 1, but rather refers to any act of coloring at least a portion of the second layer 20 of the laminate 1 by irradiating it with laser light.

[0081] The following describes each layer of the laminate, using laminate 1 according to one embodiment of this disclosure as an example.

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

[0083] As the first layer 10, an optically transparent film is used. In this 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 in the first layer 10 is sufficiently high, when the laminate 1 after laser marking is viewed from the first layer 10 side, the lower layer, the second layer 20, can be clearly seen through the first layer 10. The transmittance of laser light and visible light of the substrate film can be measured, for example, using a known spectrophotometer.

[0084] The resin used as the material for the base film as the first layer 10 may be either a thermoplastic resin or a thermosetting resin. More specifically, resins used as the material for the base film as the first layer 10 include, for example, (meth)acrylic copolymers, vinyl butyral resins, polyvinyl chloride resins, fluororesins, polyester resins, polystyrene resins, and thermoplastic polyurethane resins (TPU). These resins have excellent transparency, heat resistance, and handling properties. These resins may be used individually or in combination of two or more types.

[0085] Among the resins mentioned above, polyester resins are particularly suitable as the material for the base film because they can sufficiently transmit laser light and have good handling and heat resistance. By making the base film as the first layer 10 a polyester resin, the versatility of the laminate 1 can be increased and fine laser marking can be achieved.

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

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

[0088] There are no particular restrictions on the thickness of the first layer 10, but a thicker layer is preferable from the viewpoint of chemical resistance and abrasion resistance. The upper limit of the thickness of the first layer 10 can be set as appropriate from the viewpoint of workability and cost. For example, from the viewpoint of good workability (e.g., handling) when bonding the laminate 1 to the substrate, the thickness of the first layer 10 is preferably in the range of 10 μm to 200 μm.

[0089] Furthermore, the resin used as the material for the base film as the first layer 10 may contain various additives, to the extent that they do not impair print readability and adhesion. Such additives include, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, fillers, and colorants. Furthermore, the first layer 10 may be subjected to corona treatment on the side having the second layer 20, or an easy-adhesion layer may be provided.

[0090] [Second layer 20] The second layer 20 is colored by laser light. In this disclosure, the second layer 20 may be referred to as the coloring layer 20. The second layer 20 is composed of the resin layer of this disclosure.

[0091] The thickness of the second layer 20 is not particularly restricted, 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 clearly recognized. Furthermore, if the thickness of the second layer 20 is 15 μm or more, the resistance to laser light penetration 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 is adhesive. In this disclosure, the third layer 30 may be referred to as the adhesive layer 30.

[0092] The adhesive used in the third layer 30 should be able to adhere to a substrate such as a resin plate, metal plate, or glass plate, and should also be able to be peeled off from the substrate. 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. If the adhesive strength of the adhesive is 0.1 N / 25 mm or more, good adhesion to the substrate can be obtained. Furthermore, if the adhesive strength of the adhesive is 40 N / 25 mm or less, the peelability of the adhesive will be good. The adhesive strength of the adhesive is measured by attaching a 10 mm wide laminate to an aluminum plate with a load of 2 kg, leaving it at 23°C for 24 hours, and then peeling the laminate from the aluminum plate at a peeling angle of 180°, a peeling 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 resin compositions used in the third layer 30 include (meth)acrylic adhesives, silicone adhesives, and synthetic rubber adhesives, and a (meth)acrylic adhesive is more preferable from the viewpoint of improving the adhesion between the second layer 20 and the third layer 30.

[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. If the thickness of the third layer 30 is within the above range, the workability (e.g., handling) when bonding the laminate 1 to the adherend will be improved.

[0095] Furthermore, the resin composition used in the third layer 30 may contain various additives, to the extent that they do not impair print readability and adhesion. Examples of such additives include dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants. Metal oxide pigments are preferred as colorants for the third layer 30. Using metal oxide pigments tends to increase the opacity of the substrate and reduce laser penetration. Furthermore, the laser light is reflected by the metal oxide pigment, increasing the efficiency of the reduction reaction of the bismuth-containing compound present in the second layer 20, which tends to improve color development. 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 performed by irradiating the laminate 1 with laser light from the first layer 10 side.

[0097] Lasers used for laser marking include, for example, near-infrared lasers with a wavelength of around 1000 nm; YVO4 lasers, YAG lasers, and fiber lasers. UV lasers with a wavelength of 300 nm to 400 nm can also be used.

[0098] Laser marking on the laminate 1 is usually performed before attaching the laminate 1 to the substrate. It is also possible to perform laser marking after attaching the laminate 1 to the substrate, but in this case, it is preferable that the laminate 1 has sufficient penetration resistance so as not to damage the substrate to which the laminate 1 is attached by laser irradiation.

[0099] [Method for manufacturing laminate 1] The laminate 1 can be manufactured by forming the first layer 10, the second layer 20, and the third layer 30 in that order. For example, the laminate 1 can be manufactured by a manufacturing method that includes at least a second layer forming step of forming the second layer 20 on one side of the first layer 10, and a third layer forming step of forming the third layer 30 on the side 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 a laser marking composition used for the second layer 20 to one side of the base film 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 manufacturing a resin film described above.

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

[0102] In the method for manufacturing the laminate 1, a first layer formation step for forming the first layer 10 may be included before the second layer formation step, if necessary.

[0103] [Other embodiments] The laminates of this disclosure are not limited to laminate 1 applied to a laser marking label having a three-layer structure having a first layer, a second layer, and a third layer. The laminates of this disclosure may be laminates consisting of a second layer and a third layer without a first layer, or laminates having a second layer, a third layer, and other layers without a first layer, or laminates having a first layer, a second layer, a third layer, and other layers.

[0104] Other layers include coloring layers, printing layers, and easy-adhesion layers. A colored layer, for example, is placed between the second and third layers, and is a layer that gives color, patterns, etc., to the entire laminate. The addition of a colored layer improves the aesthetic appeal of the laminate. The colored layer may include a layer containing a resin and a coloring agent. The resin contained in the colored layer is not particularly limited and may include resins similar to those used in the first layer. The coloring agent contained in the colored layer is not particularly limited and may include pigments, dyes, etc. The thickness of the colored layer is not particularly limited, and can range from 1 μm to 50 μm, for example. The colored layer may be formed by applying a resin composition for colored layer formation to the surface of the second layer facing the third layer, or it may be formed separately and then bonded to the surface of the second layer facing the third layer. When bonding the colored layer to the surface of the second layer, an adhesive layer may be further provided between the colored layer and the second layer.

[0105] The printed layer is, for example, a layer provided between the second and third layers and formed by a printing press. Specifically, for example, a resin composition containing resin, colorants, solvents, etc., is applied to the surface of a layer adjacent to the printed layer in accordance with the desired pattern, characters, etc., and the printed layer is formed by drying, curing, etc., as necessary. Providing a printed layer improves the design of the laminate. The printed layer may be provided only on a part of the laminate surface direction, or it may be provided on the entire surface. Printing methods include inkjet 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 that is on the side facing the third layer. If 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 colored layer side of the second layer, or by printing on the second layer side of the colored layer. When forming a printed layer 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. [Examples]

[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] 70.0 parts by mass of ethyl acetate [organic solvent] was charged into the reaction vessel of a reaction apparatus equipped with a stirrer, reflux condenser, sequential dropper, and thermometer. In addition, 100.0 parts by mass of a monomer mixture consisting of 65.0 parts by mass of ethyl acrylate [EA; alkyl acrylate monomer having an alkyl group with 1 to 4 carbon atoms], 21.0 parts by mass of methyl methacrylate [MMA; alkyl methacrylate monomer], and 14.0 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; alkyl methacrylate monomer having a hydroxyl group] was prepared in a separate container. 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 conditions, the remaining 80.0% by mass of the monomer mixture, 50.0 parts by mass of ethyl acetate, and 0.026 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were sequentially added dropwise to the reaction vessel over 120 minutes. After the addition was complete, the reaction was allowed to continue for another 150 minutes to complete the reaction. The solution after the reaction was diluted with ethyl acetate to a solid content concentration of 35.0% by mass to obtain the (meth)acrylic resin solution of Polymerization Example 1. In this context, "solid content concentration" refers to the mass ratio of (meth)acrylic resin to the (meth)acrylic resin solution. Table 1 also lists the weight-average molecular weight (Mw), glass transition temperature (Tg) of the (meth)acrylic resin in polymerization example 1, as well as the percentage of structural units derived from alkyl acrylates containing alkyl groups with 1 to 4 carbon atoms (A, mass%), the total percentage of structural units derived from ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate (A-1, mass%), and the total percentage of structural units derived from alkyl methacrylate (B, mass%), out of the total structural units of the (meth)acrylic resin. The weight-average molecular weight of the (meth)acrylic resin solution is the value measured by the method described above. The glass transition temperature Tg of the (meth)acrylic resin is the value obtained by converting the absolute temperature (K) calculated by the above formula to Celsius temperature (°C).

[0109] [Synthesis of Polymerization Examples 2 to Polymer 6] In the synthesis of Polymer 1, the (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 (alkyl acrylate monomer having an alkyl group with 1 to 4 carbon atoms), BA represents butyl acrylate (alkyl acrylate monomer having an alkyl group with 1 to 4 carbon atoms), 2HEA represents 2-hydroxyethyl acrylate (alkyl acrylate monomer having an alkyl group having a hydroxyl group with 1 to 4 carbon atoms), and AA represents acrylic acid.

[0110] [Table 1]

[0111] [Examples 1-33 and Comparative Examples 1-7] The components listed in Tables 2 to 4 were blended in the proportions (parts by mass) listed in Tables 2 to 4, and the mixture was prepared with ethyl acetate to obtain the laser marking compositions of Examples 1 to 33 and Comparative Examples 1 to 7, with a solid content concentration of 20% by mass. In Tables 2 to 4, Polymerization Examples 1 to 6 refer to the solid content of (meth)acrylic resin. In Tables 2 to 4, "equivalent weight" indicates the amount of crosslinking agent contained in the crosslinking agent relative to the total number of hydroxyl 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: • Crosslinking agent 1: IPDI's isocyanurate-based crosslinking agent (Takenate D140N-60, manufactured by Mitsui Chemicals, Inc.) • Crosslinking agent 2: Isocyanurate-based crosslinking agent of HDI (Coronate HK, manufactured by Tosoh Corporation) • Crosslinking agent 3: Isocyanurate-based crosslinking agent of XDI (Takenate D-131N, manufactured by Mitsui Chemicals, Inc.) • Crosslinking agent 4: HDI TMP adduct body (Duranate E402-80B, manufactured by Asahi Kasei Corporation) • Crosslinking agent 5: TDI TMP adduct (Takenate D101A, manufactured by Mitsui Chemicals, Inc.) • Crosslinking agent 6: Melamine-based crosslinking agent (Nicalac MS-11, manufactured by Nippon Carbide Industries, Ltd.) • Crosslinking agent 7: Aluminum chelate crosslinking agent (CK-401, manufactured by Nippon Carbide Industries Co., Ltd.) • Bismuth-containing compound: Bismuth oxide-based color pigment (42-970A, TOMATEC Corporation) • Urethane resin 1: Rezamin NE-8836 (Dainichi Seika Kogyo Co., Ltd.) • Urethane resin 2: Pandex T-5275N (DIC Covestro Polymer Co., Ltd.) • Catalyst: Polyphosphate ester (CT-198, Tokushiki Co., Ltd.) • White pigment 1: Titanium oxide coated mica (Iriodin 103, Merck KGaA) • Filler 1: Silica (Silysia 445, Fuji Silysia Chemical Co., Ltd.) • Filler 2: Acrylic beads (Art Pearl GR-300, Negami Kogyo Co., Ltd.)

[0112] A 50 μm thick PET film (surface layer) was subjected to corona treatment on both sides. A laser marking composition was applied to one side of the PET film so that the film thickness after drying was as shown in Tables 2 to 4. The laser marking layer (coloring layer) was then formed by drying at 70°C for 3 minutes and then at 150°C for 3 minutes. 100 parts by mass of acrylic resin PE-121 (manufactured by Nippon Carbide Industries Co., Ltd.) was mixed with 0.53 parts by mass of crosslinking agent CK-401 (manufactured by Nippon Carbide Industries Co., Ltd.), and after mixing with ethyl acetate to an appropriate viscosity, the mixture was coated to a thickness of 20 μm onto release-treated PET (75E0010GT, manufactured by Fujimori Industries Co., Ltd.), and heated at 100°C for 1 minute to form an adhesive layer on the release-treated PET. The adhesive side of this adhesive layer was bonded to the laser marking layer to obtain the laser marking laminates for each example and comparative example. The following evaluations were performed on the resulting laminate for laser marking. In the evaluation of the sticker printability and inkjet printability described below, the evaluation was performed using samples before the adhesive layer was bonded to the laser marking layer.

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

[0114] [Heat resistance] A laser marking laminate, on which a 15mm square filled pattern obtained by the same method as described in the [Printability] section was printed, was attached to a glass plate and heated at 120°C for 168 hours. Afterward, an opacity test paper specified in JIS K 5600-4-1:1999 was placed on the back of the glass plate, and the color difference between the laminate itself and the printed area was measured using a colorimeter (product name "Spectrophotometer CM-3600A", manufactured by Konica Minolta). ΔE * ab2 (color difference after heating) was calculated. ΔE after printability test * ab1 and ΔE after heating * The absolute value of the difference between ab2 and the color difference before heating (ΔE*ab) was defined as the color difference before and after heating, and evaluated according to the following criteria. If the evaluation is B or higher, it is 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. If S:ΔE*ab is 3 or less, the density of the printed area will become lighter after heating. A: ΔE*ab exceeds 3, resulting in increased density in the printed area. B: When ΔE*ab is greater than 3 and ΔE*ab is 5 or less, the density of the printed area becomes lighter after heating. If C:ΔE*ab exceeds 5, the density of the printed area becomes lighter.

[0115] [2D barcode readability] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), 4mm square and 8mm square two-dimensional codes were printed on the surface layer of a laminate by irradiating it with laser light under the following conditions: output (print intensity) of 20%, 30%, and 50%, pulse period of 50Hz, line width of 0.07mm, and speed of 2000mm / second. Subsequently, a code reader (product name SR-H60W, manufactured by Keyence Corporation) was used to perform 100 reading tests, and the results were evaluated according to the following criteria. A rating of B or higher indicates that the product is practically acceptable. S: The success rate for reading 8mm square objects is over 80%. A: The success rate for reading 8mm square objects is 50% or higher. B: The success rate for reading 4mm square objects is 90%. C: The success rate for reading 4mm square objects is 50% or higher. The success rate for reading 4mm square objects (D) is less than 50%.

[0116] [Fukure] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), laser light was irradiated onto the surface layer of a laminate to print 4mm square and 8mm square two-dimensional codes under the following conditions: output (print intensity) of 20%, 30%, and 50%, pulse period of 50Hz, line width of 0.07mm, and speed of 2000mm / second. During this process, the occurrence of blistering between the release-treated PET and adhesive layers was observed visually and by touch, and evaluated according to the following criteria. A rating of B or higher indicates that the product is practically acceptable. The less blistering occurs, the more gas is suppressed during printing. A: It doesn't swell even at 50% print intensity. B: It swells at 50% print intensity. C: It swells regardless of print intensity.

[0117] [Printability of labels] On the surface of the laser marking layer before bonding the adhesive layer, the two-dimensional code printing area (10mm) 2 On all surfaces except the white areas, the words "NIPPON CARBIDE INDUSTRIES" were printed in solid color using a sticker printing machine with 1mm thick, 10-point Gothic ink (UV161J black, manufactured by T&K TOKA), except for the white areas. The printed layer was then cured by irradiating it with UV light from a 2kW metal halide lamp for 5 seconds. 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 (Pencel D-125, manufactured by Arakawa Chemical Industries, Ltd., 8.27 parts by mass), the crosslinking agent 5 (3.36 parts by mass), and white pigment 2 (NX-501 White, manufactured by Dainichi Seika Co., Ltd., 27.80 parts by mass) was applied to release paper (KH10 Shiro GM, manufactured by Lintec Corporation) so that the film thickness after drying was 40 μm, and the mixture was dried to form an adhesive layer. The adhesive side of the obtained adhesive layer was bonded to the printed surface of the laser marking layer to obtain a laser marking laminate. A 9mm square two-dimensional code was laser-printed in the center of the non-printed area of ​​the obtained laser marking laminate, and this was used as the initial sample. Subsequently, the initial laminated sample was folded in half, the adhesive layers were bonded together, and then the layers were separated back to their original state. This resulting piece was designated as the post-separation sample. For the initial samples, the presence or absence of ink repellency and bleeding was visually checked, and for the samples after delamination, the presence or absence of distortion and peeling of the printed layer was visually checked, and evaluated according to the following criteria. A: No ink repellency or bleeding was observed in the initial sample, and no distortion or peeling of the printed layer was observed in the sample after delamination. B: No ink repellency or bleeding was observed in the initial sample, and distortion of the printed layer was observed in the sample after peeling. C: No ink repellency or bleeding was observed in the initial sample, and peeling of the printed layer was observed in the sample after delamination. D: At least one of the following is observed in the initial sample: ink repellency and ink bleeding.

[0118] [Inkjet printability] On the surface of the laser marking layer before bonding the adhesive layer, the two-dimensional code printing area (10mm) 2 On all areas except the white areas, the words "NIPPON CARBIDE INDUSTRIES" were printed in a 1mm thick, 10-point Gothic font using an inkjet printer (JV-300-130, manufactured by Mimaki Engineering Co., Ltd.), with the color being PTN311, except for the white areas, to form a printed layer. On the other hand, an adhesive layer was formed on the release paper in the same manner as the evaluation of the seal printability described above. The adhesive side of the obtained adhesive layer was bonded to the printed surface of the laser marking layer to obtain a laser marking laminate. A 9mm square two-dimensional code was laser-printed in the center of the non-printed area of ​​the obtained laser marking laminate, and this was used as the initial sample. Subsequently, the initial laminated sample was folded in half, the adhesive layers were bonded together, and then the layers were separated back to their original state. This resulting piece was designated as the post-separation sample. For the initial samples, the presence or absence of ink repellency and bleeding was visually checked, and for the samples after delamination, the presence or absence of distortion and peeling of the printed layer was visually checked, and evaluated according to the following criteria. A: No ink repellency or bleeding was observed in the initial sample, and no distortion or peeling of the printed layer was observed in the sample after delamination. B: No ink repellency or bleeding was observed in the initial sample, and distortion of the printed layer was observed in the sample after peeling. C: No ink repellency or bleeding was observed in the initial sample, and peeling of the printed layer was observed in the sample after delamination. D: At least one of the following is observed in the initial sample: ink repellency and ink bleeding.

[0119] [Lamination suitability] On the surface of the acrylic film (A0800, manufactured by Nippon Carbide Industries, Ltd.), the 2D code printing area (10mm) 2 In addition to the above, an inkjet printer (JV-300-130, manufactured by Mimaki Engineering Co., Ltd.) was used to print 10mm squares filled with purple, blue, light blue, green, yellow-green, yellow, orange, red, and black, along with the words "NIPPON CARBIDE" in 8-point font, to form a printed layer. The PET release agent of the laser marking laminate in each example and comparative example was peeled off to expose the adhesive layer. The adhesive layer of the laser marking laminate was applied to the printed surface of the acrylic film on which the printed layer was formed, thereby laminating the acrylic film with the laser marking laminate. Subsequently, a 9mm square two-dimensional code was laser-printed in the center of the non-printed area and visually inspected from the laser marking laminate side, and evaluated according to the following criteria. A: The color tone of the printed layer does not change before and after lamination. B: The printed layer after lamination appears slightly whiter compared to before lamination. C: The printed layer after lamination appears whiter compared to before lamination.

[0120] [Table 2]

[0121] [Table 3]

[0122] [Table 4]

[0123] From the evaluation results shown in Tables 2 to 4, it can be seen that the laser marking laminate having a color-developing layer (resin film) obtained from the laser marking composition of the example achieves higher levels of heat resistance, readability, and suppression of gas generation compared to the laser marking laminate having a color-developing layer (resin film) obtained from the laser marking composition of the comparative example. Furthermore, among the examples evaluated, the laser marking laminate exhibiting excellent heat resistance is considered to also exhibit excellent 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 30 September 2022, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted as being incorporated by reference. [Explanation of Symbols]

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

Claims

1. It 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 alkyl methacrylate in the total structural units of the (meth)acrylic resin is less than 45% by mass. The content of the (meth)acrylic resin in the solid content of the laser marking composition is 15% by mass or more and 98% by mass or less. It further contains urethane resin, A laser marking composition in which the content of the urethane resin in the solid content of the laser marking composition is 2% by mass to 75% by mass.

2. The laser marking composition according to claim 1, wherein the content of the (meth)acrylic resin in the solid content of the laser marking composition is 40% by mass or more and 90% by mass or less, and the content of the urethane resin is 5% by mass or more and 20% by mass or less.

3. The laser marking composition according to claim 1, wherein the total proportion of structural units derived from monomers containing a carboxyl group in the molecule to the total structural units of the (meth)acrylic resin is 0.5% by mass or more and 5% by mass or less.

4. The laser marking composition according to claim 1, further comprising a filler.

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

6. A laminate having a resin film as described in claim 5.

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