LASER MARKING COMPOSITION, RESIN FILM AND LAYER

Abstract

A laser marking composition includes at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium and neodymium, wherein a proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more.

Description

Technical field

[0001] The present disclosure relates to a laser marking composition, a resin film and a laminated body. State of the art

[0002] Various types of packaging for food, pharmaceuticals, etc., as well as various types of components such as electronic components, require the printing of variable information for traceability, such as production batch numbers and production dates. Laser marking can sometimes be used as a marking method for this purpose. In particular, color development laser marking, which changes the color of a resin or pigment through laser irradiation, has been used in a variety of applications in recent years because it enables printing without generating odors or dust.

[0003] The following compositions are known as labels or laser marking inks.

[0004] For example, Patent Document 1 discloses a pressure-sensitive adhesive including a pressure-sensitive adhesive resin (A) and a bismuth-based laser color developing agent (B), the pressure-sensitive adhesive capable of forming a discoloration-suppressed pressure-sensitive adhesive layer with favorable contrast after printing.

[0005] Patent Document 2 discloses an ink composition for laser marking having sufficient laser printability (visibility), blocking resistance, adhesiveness, and lamination strength, the composition including a binder resin, a white pigment, and an organic solvent, wherein the binder resin includes a polyurethane resin and a cellulose derivative, the cellulose derivative is a cellulose derivative substituted with a lower acyl group and / or a cellulose derivative substituted with a lower alkyl group, and the white pigment is titanium oxide having an average particle diameter of 0.26 μm or less. Patent Document 1: Japanese Patent (JP-B) No. 6292429 Patent Document 2: Japanese Patent (JP-B) No. 7057236 SUMMARY OF THE INVENTIONTechnical problem

[0006] A resin composition capable of turning black upon laser irradiation typically utilizes a reduction reaction of an inorganic oxide by laser light. During the reduction, heat is generated, leading to carbonization of the resin or gas generation. Consequently, the carbonization of the resin can spread further than intended and can lead to blistering in the laminate, which often results in read errors when printing with one-dimensional or two-dimensional codes.

[0007] For example, the pressure-sensitive adhesive using the bismuth-based laser color developing agent disclosed in Patent Document 1 may experience deformation of the print due to heat generated during printing, which may make reading difficult depending on the printed content.

[0008] Furthermore, in the ink composition for laser marking disclosed in Patent Document 2, since the urethane resin is easily carbonized, the resin around the inorganic oxide is also easily carbonized, which may make reading difficult depending on the printed content. Furthermore, (meth)acrylic copolymers mentioned in the comparative examples of Patent Document 2 contain methacrylic resins as a main component, which may lead to problems of easy gas generation and blistering during printing.

[0009] The present disclosure has been made in view of the aforementioned conventional circumstances, and its object is to provide a laser marking composition capable of forming a resin film having excellent visibility and readability upon printing with one-dimensional or two-dimensional codes while suppressing gas generation during printing, and to provide a resin film and a laminated body using the laser marking composition. Solution to the task

[0010] Specific means to achieve the above objective are the following: <1> A laser marking composition including at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium and neodymium, wherein a proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms is 55 mass% or more with respect to all structural units of the (meth)acrylic resin. <2> The laser marking composition according to <1> , wherein a total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester with respect to all structural units of the (meth)acrylic resin is less than 45% by mass. <3> The laser marking composition according to <1> or <2> wherein a total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate and structural units derived from 2-hydroxyethyl acrylate with respect to all structural units of the (meth)acrylic resin is 20 mass% or more. <4> The laser marking composition according to one of <1> until <3> , wherein the metal oxide includes a bismuth-containing compound. <5> A resin film formed using the laser marking composition according to any one of <1> until <4> . <6> A laminated body containing the resin film according to <5> includes. Advantageous effects of the invention

[0011] According to the present disclosure, there can be provided a laser marking composition capable of forming a resin film having excellent visibility and readability when printing with one-dimensional or two-dimensional codes while suppressing gas generation during printing, as well as a resin film and a laminated body using the laser marking composition. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a schematic diagram illustrating an example of the cross-sectional structure of a laminated body according to an embodiment of the present disclosure. MODES FOR CARRYING OUT THE INVENTION

[0012] The embodiments in the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including elementary steps and the like) are not essential unless explicitly stated otherwise. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0013] In the present disclosure, the term “step” includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0014] In the present disclosure, a numerical range expressed using “to” includes numerical values described before and after “to” as minimum value and maximum value, respectively.

[0015] For numerical value ranges described step by step in this disclosure, the upper limit or lower limit of a numerical value range may be replaced by the upper limit or lower limit of another numerical value range described step by step. The upper limit or lower limit of a numerical value range described in this disclosure may also be replaced by a value described in the examples.

[0016] In the present disclosure, each component may include multiple substance types corresponding to it. In a case where multiple substance types corresponding to a component of interest are present in a composition, the content proportion or amount of the component refers to a total content proportion or amount of the multiple substance types present in the composition, unless otherwise specified.

[0017] In the present disclosure, particles corresponding to the respective component may include multiple particle types. In a case where multiple particle types corresponding to a component of interest are present in the composition, the particle diameter of the respective component refers to a value for the mixture of the multiple particle types in the composition, unless otherwise specified.

[0018] In the present disclosure, the term “layer” or “film” includes not only a case where a layer or film is formed over an entire region, but also a case where a layer or film is formed only in a portion of a region when the region in which the layer or film is present is considered.

[0019] In the present disclosure, the term "layers" refers to the stacking of layers, where two or more layers can be bonded together and two or more layers can be detachable from each other.

[0020] In the present disclosure, “(meth)acrylic” means at least one of acrylic or methacrylic, and “(meth)acrylate” means at least one of acrylate or methacrylate.

[0021] In the present disclosure, the average thickness of a layer or film is defined as the arithmetic mean of thickness measurements at five points on the layer or film.

[0022] The thickness of a layer or film can be measured using a micrometer or the like. In the present disclosure, in a case where the thickness of a layer or film can be directly measured, it is measured using a micrometer. In the case of measuring the thickness of a single layer or the total thickness of multiple layers, the measurement can be performed by observing the cross section of the measurement target using an electron microscope.

[0023] In the present disclosure, “solid content” refers to components other than the organic solvent in the laser marking composition or a sample solution. <lasermarkierungszusammensetzung>

[0024] The laser marking composition includes at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium and neodymium, wherein a proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more.

[0025] The laser marking composition of the present disclosure is capable of forming a resin film that exhibits excellent visibility and readability when printing one-dimensional or two-dimensional codes while suppressing gas generation during printing. Although the reason for this is not clear, it is believed as follows.

[0026] When comparing structural units derived from an alkyl acrylate and a structural unit derived from an alkyl methacrylate that may be present in the (meth)acrylic resin, the difference is that a methyl group is directly bonded to the carbon atoms that form the main chain of the (meth)acrylic resin. The carbon atom directly bonded to the methyl group becomes a tertiary carbon. At sites where tertiary carbons are present in the main chain of the (meth)acrylic resin, decomposition of the (meth)acrylic resin is likely to occur upon laser irradiation. If the (meth)acrylic resin contains a higher proportion of structural units derived from an alkyl methacrylate, gas is likely to be generated from the decomposition products.

[0027] In the present disclosure, since the proportion of structural units derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms is 55 mass% or more with respect to all structural units of the (meth)acrylic resin, it is believed that the proportion of tertiary carbons among the carbons constituting the main chain of the (meth)acrylic resin can be kept relatively low, which facilitates the suppression of gas generation derived from decomposition products. Since gas generation is suppressed, the suppression of blistering in the resin film composed of the laser marking composition is also facilitated.

[0028] Furthermore, since the number of carbon atoms of an alkyl group contained in the structural units derived from an alkyl acrylate is 1 to 4, the glass transition temperature of the (meth)acrylic resin is less likely to decrease. Therefore, deformation of the resin film due to heat generated by the reduction of the inorganic oxide under laser irradiation is more easily suppressed.

[0029] As a result, it is believed that visibility and readability will improve when printing one-dimensional or two-dimensional codes.

[0030] Each component constituting the laser marking composition of the present disclosure will be described below. ((Meth)acrylic resin))

[0031] The laser marking composition of the present disclosure includes at least one (meth)acrylic resin, wherein a proportion of structural units derived from an alkyl acrylic acid ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more. The proportion of structural units derived from an alkyl acrylic acid ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is preferably 56 mass% or more, more preferably 60 mass% or more, and even more preferably 90 mass% or more. The proportion of structural units derived from an alkyl acrylic acid ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin may be 99 mass% or less.The proportion of structural units derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is preferably 55% by mass to 99% by mass.

[0032] In a case where the laser marking composition of the present disclosure includes a (meth)acrylic resin, as 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 (meth)acrylic monomers.

[0033] In a case where the laser marking composition of the present disclosure includes two or more (meth)acrylic resins, as long as the proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more, it is further possible to use two or more homopolymers different from each other in structural units in combination, or to use at least one homopolymer and at least one copolymer in combination, or to use two or more copolymers different from each other in structural units in combination.Furthermore, in a case where the laser marking composition of the present disclosure includes two or more (meth)acrylic resins, it is also possible to use at least one (meth)acrylic resin in which a proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more in combination together with at least one (meth)acrylic resin in which the aforementioned proportion is less than 55 mass%.

[0034] The (meth)acrylic monomer means at least one of acrylic acid, a derivative of acrylic acid such as an alkyl acrylate, methacrylic acid, or a derivative of methacrylic acid such as an alkyl methacrylate. The derivative of acrylic acid and methacrylic acid may have a substituent group such as a hydroxy group, an amino group, a carboxyl group, a glycidyl group, and the like.

[0035] Furthermore, monomers other than (meth)acrylic monomers can also be used for the (meth)acrylic resin.

[0036] Spezifische Beispiele für (Meth)acrylmonomere schließen Methyl(meth)acrylat, Ethyl(meth)acrylat, n-Propyl(meth)acrylat, i-Propyl(meth)acrylat, n-Butyl(meth)acrylat, i-Butyl(meth)acrylat, t-Butyl(meth)acrylat, n-Hexyl(meth)acrylat, 2-Ethylhexyl(meth)acrylat, Octyl(meth)acrylat, Cyclohexyl(meth)acrylat, Phenyl(meth)acrylat, Benzyl(meth)acrylat, Phenoxyethyl(meth)acrylat, Isobornyl(meth)acrylat, 2-Methoxyethyl(meth)acrylat, 2-Ethoxyethyl(meth)acrylat, Glycidyl(meth)acrylat und Tetrahydrofurfuryl(meth)acrylat ein.

[0037] Specific examples of hydroxyl-containing (meth)acrylic monomers 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.

[0038] Examples of other monomers containing a carboxyl group include crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, and citraconic acid. Examples of other monomers not containing a carboxyl group include vinyl acetate, vinyl ether, acrylonitrile, and styrene.

[0039] Preferred examples of the acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms include ethyl acrylate, methyl acrylate, butyl acrylates such as n-butyl acrylate, i-butyl acrylate and t-butyl acrylate, and 2-hydroxyethyl acrylate.

[0040] In the present disclosure, a total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate with respect to all structural units of the (meth)acrylic resin in one aspect is preferably 20 mass% or more, more preferably 30 mass% or more, even more preferably 40 mass% or more, and particularly preferably 65 mass% or more. The total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate with respect to all structural units of the (meth)acrylic resin may be 99 mass% or less.The total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate and structural units derived from 2-hydroxyethyl acrylate with respect to all structural units of the (meth)acrylic resin is preferably 20 mass% to 99 mass%.

[0041] Ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate exhibit high glass transition temperatures when polymerized as homopolymers. Therefore, at the portions composed of ethyl acrylate-derived structural units, methyl acrylate-derived structural units, and 2-hydroxyethyl acrylate-derived structural units in the (meth)acrylic resin, the main chain of the (meth)acrylic resin is believed to be resistant to movement even when heat is generated by laser irradiation. As a result, this tends to facilitate more accurate printing.

[0042] In the present disclosure, in another aspect, the total proportion of ethyl acrylate-derived structural units, methyl acrylate-derived structural units, and 2-hydroxyethyl acrylate-derived structural units with respect to all structural units of the (meth)acrylic resin in another aspect may be 1 mass % or less.

[0043] In the present disclosure, a total proportion of structural units derived from methacrylic acid and structural units derived from an alkyl methacrylate with respect to all structural units of the (meth)acrylic resin is preferably less than 45 mass %, more preferably 40 mass % or less, even more preferably 35 mass % or less, and particularly preferably 5 mass % or less. The total proportion of structural units derived from methacrylic acid and structural units derived from an alkyl methacrylate with respect to all structural units of the (meth)acrylic resin may be 0 mass %. The total proportion of structural units derived from methacrylic acid and structural units derived from an alkyl methacrylate with respect to all structural units of the (meth)acrylic resin is preferably 0 mass % or more and less than 45 mass %.

[0044] When the total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester with respect to all structural units of the (meth)acrylic resin is less than 45 mass%, the generation of gas originating from decomposition products that may be generated by decomposition of the (meth)acrylic resin is more easily suppressed.

[0045] A total proportion of structural units derived from monomers containing a carboxyl group in the molecule, such as acrylic acid, methacrylic acid, and other monomers containing a carboxyl group, with respect to all structural units of the (meth)acrylic resin is preferably 20 mass% or less, more preferably 10 mass% or less, and still more preferably 5 mass% or less. The total proportion of structural units derived from monomers containing a carboxyl group in the molecule with respect to all structural units of the (meth)acrylic resin may be 0.5 mass% or more. The total proportion of structural units derived from monomers containing a carboxyl group in the molecule with respect to all structural units of the (meth)acrylic resin is preferably 0.5 mass% to 20 mass%.

[0046] When the total proportion of structural units derived from monomers containing a carboxyl group in the molecule with respect to all structural units of the (meth)acrylic resin is 20 mass% or less, it is possible to suppress the occurrence of attenuation of absorption due to the reaction of the metal oxide reduced by the laser light irradiation with the carboxyl group, and the visibility tends to be improved.

[0047] In a case where 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.

[0048] The weight-average molecular weight (Mw) of the (meth)acrylic resin is preferably in a range of 5,000 to 1,000,000, more preferably in a range of 10,000 to 800,000, and even more preferably in a range of 100,000 to 750,000. When 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, when 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.

[0049] In a case where the laser marking composition of the present disclosure includes 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 in the aforementioned range.

[0050] In the present disclosure, the weight-average molecular weight (Mw) of the (meth)acrylic resin is a value measured by the following method. Specifically, the measurement is performed according to (1) to (3) below. (1) A solution of the (meth)acrylic resin is applied to a release paper, then dried at 100°C for 1 minute to obtain a film-like (meth)acrylic resin. (2) The film-like (meth)acrylic resin obtained in the above (1) and tetrahydrofuran are used to prepare a sample solution with a solid concentration of 0.1 mass%. (3) The weight-average molecular weight (Mw) of the (meth)acrylic resin is measured by gel permeation chromatography (GPC) under the conditions described below as a converted value with respect to polystyrene standard. - Conditions - Measuring instrument: High-speed GPC (Model: HLC-8220 GPC, TOSOH Corporation) Detector: Differential refractometer (RI) (built into HLC-8220, TOSOH Corporation) Column: TSK-GEL GMHXL (TOSOH Corporation), four columns connected in series Column temperature: 40°C Eluent: Tetrahydrofuran Sample concentration: 0.2 mass% Injection volume: 100 µL Flow rate: 0.6 mL / min

[0051] To suppress deformation of the printed area caused by heat or gas during printing and enable accurate printing of one-dimensional or two-dimensional codes, the glass transition temperature 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 view of good processability of the resin film and resistance to embrittlement, the glass transition temperature Tg of the (meth)acrylic resin may be 100°C or lower. The glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C to 100°C.

[0052] The glass transition temperature Tg of the (meth)acrylic resin refers to a value obtained as the inflection point of the DSC curve obtained from a measurement under conditions of nitrogen flow, a measurement sample of 10 mg, and a heating rate of 10°C / min using a differential scanning calorimeter (DSC) (for example, EXSTAR 6000, manufactured by Seiko Instruments Inc.). In a case where two or more inflection points are observed in the DSC curve using a differential scanning calorimeter (DSC), the temperature of the inflection point at the highest temperature is taken as the glass transition temperature Tg of the (meth)acrylic resin.

[0053] In a case where 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) determined by the following formula into the Celsius temperature (°C). 1Tg=m1Tg1+m2Tg2+⋯⋯+m2Tgn

[0054] In the formula, Tg1, Tg2, ... and Tg n Glass transition temperatures as absolute temperature (K) of homopolymers from the respective monomer 1, monomer 2, ... and monomer n. Furthermore, m1, m2, ... and m n Mole fractions of the respective monomers.

[0055] The "glass transition temperature as absolute temperature (K) of the homopolymer" refers to a glass transition temperature as absolute temperature (K) of a homopolymer produced by polymerizing the monomer alone. The glass transition temperature of the homopolymer can be measured by the aforementioned method using a differential scanning calorimeter (DSC).

[0056] The "glass transition temperature as Celsius temperature (°C) of the homopolymer" of typical monomers is as follows: for methyl acrylate 10°C, for ethyl acrylate -22°C, for n-butyl acrylate -54°C, for 2-ethylhexyl acrylate -70°C, for 2-hydroxyethyl acrylate -15°C, for 4-hydroxybutyl acrylate -80°C, for t-butyl acrylate 43°C, for vinyl acetate 32°C, for acrylic acid 106°C, for methyl methacrylate 105°C, and for 2-hydroxyethyl methacrylate 85°C. By using these representative monomers, for example, it is possible to appropriately adjust the glass transition temperature described above. Regarding the "glass transition temperature of a homopolymer" of monomers other than those mentioned above, the value described in Polymer Handbook (4th edition, Wiley-Interscience, hereinafter the same) is adopted. If no value is described in Polymer Handbook, the glass transition temperature of the homopolymer obtained by the measurement method described above is adopted.

[0057] An absolute temperature (K) can be converted to a Celsius temperature (°C) by subtracting 273 from the absolute temperature (K), and a Celsius temperature (°C) can be converted to an absolute temperature (K) by adding 273 to the Celsius temperature (°C).

[0058] In a case where two or more (meth)acrylic resins are used in combination, it is preferable that the glass transition temperature Tg of the (meth)acrylic resin having the highest glass transition temperature Tg is in the aforementioned range.

[0059] The method for producing the (meth)acrylic resin is not particularly limited, and it can be produced by polymerizing monomers using methods such as solution polymerization, emulsion polymerization, or suspension polymerization. Notably, when the laser marking composition is prepared after the preparation of the (meth)acrylic resin, solution polymerization is preferred because it allows for relatively simple and short processing steps.

[0060] Generally, solution polymerization can be carried out by adding an organic solvent, a monomer, a polymerization initiator, and, if necessary, a chain transfer agent to a polymerization vessel. The mixture is then heated and reacted with stirring for several hours, either under a nitrogen stream or at the reflux temperature of the organic solvent. Furthermore, the weight-average molecular weight of the (meth)acrylic resin can be set to a desired value by adjusting the reaction temperature, reaction time, solvent amount, and type or amount of catalyst.

[0061] Examples of organic solvents used in the polymerization reaction for the (meth)acrylic resin include aromatic hydrocarbon compounds, aliphatic or cycloaliphatic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. The organic solvent can be used singly or in combination with two or more of them.

[0062] Specifically, examples of organic solvents used during the polymerization reaction include: aromatic hydrocarbon-based organic solvents represented by benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or cycloaliphatic hydrocarbon-based organic solvents represented by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum benzine, petroleum naphtha, and turpentine; ester-based organic solvents represented by ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; ketone-based organic solvents represented by acetone, methyl ethyl ketone, Methyl i-butyl ketone, isophorone, cyclohexanone and methylcyclohexanone, organic solvents based on glycol ethers,represented 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 represented by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol and t-butyl alcohol.

[0063] Examples of polymerization initiators include organic peroxides and azo compounds that can be used in conventional polymerization processes.

[0064] The (meth)acrylic resin can be a commercially available product. Examples of commercially available (meth)acrylic resins include KP-1876E (product name: Nissetsu (registered trademark), manufactured by Nippon Carbide Industries Co., Inc.) and H-4002 (manufactured by Negami Chemical Industrial Co., Ltd.).

[0065] The content of the (meth)acrylic resin relative to the solid content of the laser marking composition is preferably 15 mass% to 99.5 mass%, more preferably 20 mass% to 99 mass%, and even more preferably 40 mass% to 98.5 mass%. When the content of the (meth)acrylic resin is 15 mass% to 99.5 mass%, the heat resistance of the printed part tends to be improved. (metal oxide)

[0066] The laser marking composition of the present disclosure includes a metal oxide containing at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium. The metal oxide serves as a color developing agent.

[0067] Among these metals, a bismuth-containing compound is preferred, and bismuth(III) oxide (Bi2O3) is particularly preferred due to its excellent blackness in color development. To improve laser printability, a metal oxide with many oxygen vacancies is preferred in this case.

[0068] The volume-average particle diameter of the metal oxide is not particularly limited and 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 metal oxide is 0.05 µm or more, the metal oxide absorbs laser light and easily generates heat, so color development during printing tends to be further improved. On the other hand, when the volume-average particle diameter of the metal oxide is 30 µm or less, dispersibility during film formation tends to be favorable. The volume-average particle diameter of the metal oxide refers to a value measured by a laser diffraction / light scattering method.

[0069] The specific procedure of the laser diffraction / light scattering method is as follows: 5 mL of an aqueous dispersion of the metal oxide is placed into a glass cell with a length of 5 mm, a width of 65 mm, and a height of 80 mm using a Pasteur pipette and placed in a laser diffraction / light scattering particle diameter distribution measuring device (for example, LA-960A (product name), manufactured by Horiba, Ltd.). The concentration of the aqueous dispersion of the metal oxide is adjusted so that the transmittance of laser light (red) is 80% to 90%, and the measurement results obtained at a measurement temperature of 25°C ± 1°C are then processed by a computer to determine the average particle diameter of the metal oxide particles in the aqueous dispersion. The volume-average value is used as the average particle diameter value.

[0070] The content of the metal oxide relative to the solid content of the laser marking composition is preferably 0.2 mass% to 50.0 mass%, more preferably 0.5 mass% to 25.0 mass%, and even more preferably 1.0 mass% to 5.0 mass%. When the content of the metal oxide is 0.2 mass% or more, color develops appropriately during laser marking, and the readability of the laser-marked part tends to be favorable. When the content of the metal oxide is 50.0 mass% or less, dust generation during laser marking can be suppressed, so the readability of the laser-marked part tends to be favorable. (crosslinking agent)

[0071] The laser marking composition of the present disclosure may include a crosslinking agent to improve the strength of the resin film. Examples of crosslinking agents include isocyanate-based crosslinking agents, aluminum chelate-based crosslinking agents, and epoxy-based crosslinking agents. When the laser marking composition includes a crosslinking agent, the (meth)acrylic resin preferably includes structural units derived from a (meth)acrylic monomer containing a hydroxy group or another monomer containing a carboxyl group.

[0072] In a case where the laser marking composition includes a crosslinking agent, the content of the crosslinking agent is preferably 0.1 equivalent to 10 equivalents with respect to the total hydroxyl groups and carboxyl groups of the (meth)acrylic resin. By setting the content of the crosslinking agent to 0.1 equivalent or more, the effect of the molecules can be suppressed and the printing accuracy can be improved. By setting the content of the crosslinking agent to 10 equivalents or less, the discoloration of the (meth)acrylic resin can be suppressed. The content of the crosslinking agent is more preferably 0.3 equivalents to 3.0 equivalents because it is easy to form a film. (white pigment)

[0073] 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 part and the white of the non-printed part.

[0074] Various inorganic pigments can be used as the white pigment. Examples of the white pigment include titanium oxide (TiO2), titanium oxide-coated mica, zinc oxide (zinc white), basic lead sulfate, zinc sulfide, and antimony oxide. In addition, the white pigment can be barium sulfate, barium carbonate, precipitated calcium carbonate, diatomaceous earth, talc, clay, basic magnesium carbonate, or alumina white. Among them, titanium oxide (TiO2) is preferred as the white pigment due to its excellent whiteness. Titanium oxide-coated mica can also be included because it reflects transmitted laser light, increasing the efficiency of the reduction reaction of the metal oxide and consequently improving color development.

[0075] The volume-average particle diameter of the white pigment is not particularly limited and is preferably 0.01 µm to 50 µm, more preferably 0.05 µm to 30 µm, and still more preferably 0.1 µm to 20 µm. The volume-average particle diameter of the white pigment is a value measured by a laser diffraction / light scattering method.

[0076] In a case where the laser marking composition of the present disclosure includes a white pigment, the content of the white pigment relative to the solid content of the laser marking composition is preferably 0.01 mass% to 50 mass%, more preferably 0.1 mass% to 30 mass%, and even more preferably 1 mass% to 20 mass%. When the content of the white pigment is 0.01 mass% or more, the reduction efficiency of the color-developing pigment can be improved, and visibility tends to be further improved. When the content of the white pigment is 50 mass% or less, the decrease in color development of the metal oxide tends to be prevented. (Urethane resin)

[0077] The laser marking composition of the present disclosure may include a urethane resin to improve printability when printing on the surface of a resin film. When the laser marking composition includes a urethane resin, the fixation of the printing layer formed on the surface of a resin film is improved.

[0078] 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 can be used singly or in combination with two or more of them.

[0079] In a case where the laser marking composition of the present disclosure includes a urethane resin, the content of the urethane resin with respect to the solid content of the laser marking composition is preferably 2 mass % to 75 mass %, more preferably 5 mass % to 20 mass %, and even more preferably 10 mass % to 15 mass % from the viewpoint of improving printability. By setting the content of the urethane resin with respect to the solid content of the laser marking composition to 75 mass % or less, laser printability can be maintained. By setting the content of the urethane resin with respect to the solid content of the laser marking composition to 20 mass % or less, lamination suitability can be maintained.

[0080] Commercially available products can be used as the urethane resin.

[0081] 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 Co., Ltd.), as well as "Superflex 420 (polycarbonate-based)", "Superflex 460 (polycarbonate-based)", and "Superflex 210 (polyester-based)" (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "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 Inc.). (Filler)

[0082] The laser marking composition of the present disclosure may include a filler to improve printability when printing on the surface of a resin film. When the laser marking composition includes a filler, lubricity on the surface of a resin film is improved and workability when printing on the surface of a resin film is improved, resulting in favorable printability.

[0083] Common fillers such as inorganic particles such as silica particles, resin particles such as acrylic beads, and melamine beads can be used as fillers. The filler can be used singly or in combination with two or more of them.

[0084] 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.

[0085] In a case where the laser marking composition of the present disclosure includes a filler, the content of the filler with respect to the solid content of the laser marking composition is preferably 0.2 mass% to 30.0 mass%, more preferably 0.5 mass% to 20 mass%, and even more preferably 2 mass% to 10 mass% in view of improving the lubricity. (Additional component)

[0086] The laser marking composition of the present disclosure may include other resins or various additives to an extent that does not impair the visibility, readability of printed 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. (Organic solvent)

[0087] The laser marking composition of the present disclosure may include an organic solvent to improve coating processability. The organic solvent is not particularly limited as long as it dissolves or disperses each component 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 solvent can be used singly or in combination of two or more thereof.

[0088] In a case where the laser marking composition of the present disclosure includes an organic solvent, the content of the organic solvent contained in the laser marking composition is preferably 40 mass% to 90 mass%. <harzfolie>

[0089] The resin film of the present disclosure is formed using the laser marking composition of the present disclosure.

[0090] 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 calender molding machine, or the like.

[0091] Furthermore, the 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, doctor blade coating, die coating, and spray coating.

[0092] In a case where the laser marking composition includes a crosslinking agent, the resin film can be cured. Examples of methods for curing the resin film include drying with hot air and heating with a heating device such as an oven or hot plate.

[0093] The average thickness of the resin film is not particularly limited and can be, for example, 2 µm to 100 µm. <Schichtkörper>

[0094] The laminated body of the present disclosure includes the resin film of the present disclosure. The laminated body of the present disclosure may be a laminated body used for a laser marking label. The layered structure of the laminated body is not particularly limited and may be a layered structure in which a first layer that transmits laser light, a second layer that develops color by laser light, and a third layer having pressure-sensitive adhesiveness, which is present as needed, are layered in this order. Furthermore, the layered structure may be a layered structure in which a first layer that transmits laser light and a second layer having pressure-sensitive adhesiveness that develops color by laser light are layered in this order.In a case where the laminated body has such a structure, it is preferable to use the resin film of the present disclosure as the second layer.

[0095] The laminated body of the present disclosure includes the resin film of the present disclosure and therefore tends to suppress gas evolution in the second layer during laser marking. This also suppresses odor generation. Furthermore, visibility and readability tend to improve when printing one-dimensional or two-dimensional codes.

[0096] The following is based on reference to Fig. 1, a case where the laminated body of the present disclosure is used for a laser marking label having a three-layer structure is described. Fig. 1 is a diagram illustrating a schematic example of a cross-sectional structure of a laminated body 1 according to an embodiment of the present disclosure. As shown in Fig. As shown in Figure 1, the laminated body 1 comprises a first layer 10, a second layer 20, and a third layer 30, wherein the first layer 10, the second layer 20, and the third layer 30 are layered in this order. The second layer 20 is in contact with the first layer 10.

[0097] Here, laser marking on the laminated body 1 will be described. First, laser light is irradiated from the first layer 10 side of the laminated body 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 film of the present disclosure, the metal oxide in a portion of the second layer 20 irradiated with the laser light develops color, and the resin is carbonized by the heat of the laser light. The colored and carbonized portion of the second layer 20 becomes a printed portion of the laser marking label. The printed portion is a portion of the second layer 20 that has turned black.Thus, a laser marking label type that encloses a resin layer containing a metal oxide inside the film and causes the resin layer to develop color upon laser irradiation may be specifically referred to as an internal coloring type laser marking label. In the present disclosure, "laser marking" is not limited to the act of writing meaningful information such as letters or symbols on the laminated body 1; rather, the general act of coloring at least a portion of the layer 20 of the laminated body 1 by irradiating it with laser light is referred to as "laser marking."

[0098] Each layer of the laminated body will be described below using the laminated body 1 according to an embodiment of the present disclosure as an example. [First Layer 10]

[0099] The first layer 10 is a layer that transmits laser light. In the present disclosure, the first layer 10 may be referred to as a surface layer.

[0100] An optically transparent film is used as the first layer 10. In the present disclosure, "optically transparent" means, for example, that the laser light transmittance is 50% or more and the visible light transmittance is 80% or more. When the visible light transmittance of the first layer 10 is sufficiently high, the second layer 20, which is the lower layer, can be sufficiently seen through the first layer when viewed from the first layer 10 side of the laminated body 1 after laser marking. The laser light transmittance and the visible light transmittance of the substrate film can be measured, for example, using a known spectrophotometer.

[0101] The resin used as the material for the substrate film as the first layer 10 can be either a thermoplastic resin or a thermosetting resin. 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-based resin, a polyester-based resin, a polystyrene resin, and a thermoplastic polyurethane (TPU)-based resin. These resins are excellent in transparency, heat resistance, and handling properties. These resins can be used singly or in combination of two or more of them.

[0102] Among the resins described above, polyester-based resins are particularly preferred as the material for the substrate film because they sufficiently transmit laser light and have favorable handling properties and heat resistance. By forming the substrate film as the first layer 10 from a polyester-based resin, the versatility of the laminated body 1 can be increased and fine laser marking can be achieved.

[0103] The polyester-based resin is preferably an aromatic ester-based resin in view of suppressing deformation due to heat during laser marking. In view of suppressing deformation due to heat during laser light irradiation, it is particularly preferable that the aromatic ester-based resin is a transparent resin.

[0104] Examples of aromatic ester-based resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexylenedimethylene terephthalate, and polyethylene naphthalate (PEN). Among them, it is particularly preferable that the aromatic ester-based resin be polyethylene terephthalate in view of the above.

[0105] The thickness of the first layer 10 is not particularly limited, and a larger thickness is more preferable in terms of chemical resistance and wear resistance. The upper limit of the thickness of the first layer 10 can be appropriately determined in consideration of processability and cost. In view of improving processability (e.g., handling property) when attaching the laminated body 1 to an adhesive surface, the thickness of the first layer 10 is preferably in a range of 10 μm to 200 μm.

[0106] Furthermore, the resin used as the material for the substrate film as the first layer 10 may include various additives to an extent that does not impair print legibility and adhesion. Such additives may include, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, fillers, and colorants.

[0107] In addition, the surface of the first layer 10 on the side having the second layer 20 may be subjected to a corona treatment or be provided with a slightly adhesive layer. [Second Layer 20]

[0108] The second layer 20 develops color through laser light. In the present disclosure, the second layer 20 may be referred to as a color-developing layer 20. The second layer 20 is composed of the resin film of the present disclosure.

[0109] The thickness of the second layer 20 is not particularly limited, and is preferably 2 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 15 μm to 50 μm. When the thickness of the second layer 20 is 2 μm or more, the print can be sufficiently recognized. Furthermore, when the thickness of the second layer 20 is 15 μm or more, the laser light penetration resistance and printability are improved. Furthermore, when the thickness of the second layer 20 is 100 μm or less, the productivity of the second layer 20 is improved. [Third Layer 30]

[0110] The third layer 30 has pressure-sensitive adhesive properties. In the present disclosure, the third layer 30 may be referred to as a pressure-sensitive adhesive layer 30.

[0111] Any pressure-sensitive adhesive capable of adhering to an adherend such as a resin plate, a metal plate, or a glass plate and peeling from the adherend can be used for the third layer 30. Specifically, the adhesive strength of the pressure-sensitive adhesive used for 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. When the adhesive strength of the pressure-sensitive adhesive is 0.1 N / 25 mm or more, adhesion to the adherend is obtained. When the adhesive strength of the pressure-sensitive adhesive is 40 N / 25 mm or less, peelability of the pressure-sensitive adhesive is advantageous.The adhesive strength of the pressure-sensitive adhesive refers to a value measured by applying 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 at a peel angle of 180°, a peel speed of 300 mm / min, and a measuring temperature of 23°C.

[0112] The third resin layer 30 is made of a resin composition. Examples of resin compositions used for the third layer 30 include (meth)acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, and synthetic rubber-based pressure-sensitive adhesives. In view of increasing the adhesion between the second layer 20 and the third layer 30, a (meth)acrylic-based pressure-sensitive adhesive is more preferable.

[0113] The thickness of the third layer 30 is not particularly limited and is preferably in a range of 5 μm to 100 μm. When the thickness of the third layer 30 is in the aforementioned range, the processability (e.g., handling property) when attaching the laminated body 1 to the adhesive surface is improved.

[0114] The resin composition used for the third layer 30 may include various additives to an extent that does not compromise print legibility and adhesion. Examples of such additives include dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants.

[0115] The colorant used in the third layer 30 is preferably a metal oxide-based pigment. Using a metal oxide-based pigment tends to improve base concealment and reduce laser penetration. Furthermore, the laser light is reflected by the metal oxide-based pigment, increasing the efficiency of the reduction reaction of the metal oxide present in the second layer 20, resulting in a tendency to improve color development. Examples of metal oxide-based 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. [Method for laser marking on laminated body 1]

[0116] The laser marking on the layered body 1 can be carried out by irradiating the layered body 1 with laser light from the side of the first layer 10.

[0117] The laser used for laser marking can be, for example, a near-infrared laser with a wavelength of approximately 1,000 nm, a YVO4 laser, a YAG laser, or a fiber laser. A UV laser with a wavelength of 300 nm to 400 nm can also be used.

[0118] The laser marking on the laminated body 1 is usually performed before the laminated body 1 is attached to an adhesive surface. It is also possible to perform the laser marking after the laminated body 1 is attached to an adhesive surface. However, in this case, it is preferred that the laminated body 1 has sufficient penetration resistance so that the adhesive surface to which the laminated body 1 is attached is not damaged by the laser irradiation. [Method for producing the laminated body 1]

[0119] The laminated body 1 can be manufactured by laminating the first layer 10, the second layer 20, and the third layer 30 in this order. For example, the laminated body 1 can be manufactured by a manufacturing method including at least a second layer forming step in which the second layer 20 is formed on the side of the first layer 10, and a third layer forming step in which, after the second layer forming step, a third layer 30 is formed on the side of the second layer 20 that is not in contact with the first layer 10.

[0120] The second layer forming step may be a step of applying a laser marking composition used for the second layer 20 to one side of a substrate film as the first layer 10 and curing the laser marking composition as needed to form the second layer 20. The method for forming the second layer 20 may be the same as the above-described manufacturing method for the resin film of the present disclosure.

[0121] The third layer forming 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 forming step on a side not in contact with the first layer 10, and curing the resin composition to form the third layer 30. In another embodiment, the third layer forming step may be a step of applying a resin composition used for the third layer 30, curing the resin composition to form the third layer 30, and then attaching the third layer 30 to the surface of the second layer 20 after the second layer forming step on a side not in contact with the first layer 10. The resin composition used for the third layer 30 is described in the "Third Layer 30" section.In the method for producing the laminated body 1, the method for applying a resin composition used for the third layer 30 and the method for curing the resin composition used for the third layer 30 can also be carried out by the known application methods and curing methods described above.

[0122] Depending on the need, the method for producing the laminated body 1 may further include a first layer forming step in which the first layer 10 is formed before the second layer forming step. [Other embodiments]

[0123] The laminated body of the present disclosure is not limited to the laminated body 1 used for a laser marking label having a three-layer structure of the first layer, the second layer, and the third layer. The laminated body of the present disclosure may be a laminated body consisting of the second layer and the third layer but not including the first layer, a laminated body including the second layer, the third layer, and other layers but not including the first layer, or a laminated body including the first layer, the second layer, the third layer, and other layers.

[0124] Examples of additional layers include a color layer, a printing layer, and a lightly adhesive layer.

[0125] The color layer, for example, is present between the second layer and the third layer and is a layer that imparts color, pattern, and the like to the entire laminate. Providing a color layer enhances the design of the laminate.

[0126] Examples of the color layer include a layer containing a resin and a colorant. The resin contained in the color layer is not particularly limited, and examples thereof include the same resin as that used for the first layer. The colorant contained in the color layer is not particularly limited, and examples thereof include a pigment and a dye.

[0127] The thickness of the ink layer is not particularly limited and can, for example, be in a range from 1 µm to 50 µm.

[0128] The color layer may be formed by applying a resin composition for forming a color layer to the surface of the second layer on the third layer side, or the color layer may be formed separately and then adhered to the surface of the second layer on the third layer side. In a case where the color layer is adhered to the surface of the second layer, a pressure-sensitive adhesive layer may be further provided between the color layer and the second layer.

[0129] The printing layer is, for example, a layer provided between the second layer and the third layer and formed by a printer. Specifically, the printing layer is formed, for example, by applying a resin composition including a resin, a colorant, a solvent, etc., to the surface of a layer adjacent to the printing layer in the form of a desired pattern, letters, etc., and then subjecting it to a process such as drying and curing, as needed. The provision of a printing layer enhances the design of the laminated body. The printing layer may be provided only on a part of the laminated body toward the surface or on the entire surface.

[0130] Examples of printing processes include inkjet printing, screen printing, gravure printing and flexographic printing.

[0131] The printing layer is formed, for example, by printing on the surface of the second layer on the side of the third layer.

[0132] For example, in a case where the laminated body includes an ink layer, the printing layer may be present between the second layer and the ink layer. The printing layer may be formed by printing on the surface of the second layer on the ink layer side or by printing on the surface of the ink layer on the second layer side.

[0133] In a case where the printing layer is formed by printing on the surface of the second layer, it is preferable that the laser marking composition used for forming the second layer contains at least one of the above-described urethane resin or filler. [Examples]

[0134] The present disclosure will be described below in more detail based on examples, but the present invention is not limited to these examples. [Polymerization Example 1]

[0135] 70.0 parts by mass of ethyl acetate [organic solvent] was added to a reaction vessel of a reaction apparatus equipped with a stirrer, a reflux condenser, a successive dropping device, and a thermometer.

[0136] In a separate vessel, 100.0 parts by mass of a monomer mixture consisting of 65.0 parts by mass of ethyl acrylate [EA; acrylic acid alkyl ester monomer containing an alkyl group having 1 to 4 carbon atoms], 21.0 parts by mass of methyl methacrylate [MMA; methacrylic acid alkyl ester monomer], and 14.0 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; methacrylic acid alkyl ester monomer containing a hydroxy group] were prepared. 20.0 mass % of this prepared monomer mixture was added to the reaction vessel described above and then heated and refluxed at a reflux temperature for 10 minutes.

[0137] Next, under reflux 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 sequentially added dropwise to the reaction vessel over a period of 120 minutes. After the addition was completed, the reaction was allowed to proceed for another 150 minutes to complete the reaction. After the reaction was completed, the solution was diluted with ethyl acetate to a solid concentration of 35.0 mass % to obtain a (meth)acrylic resin solution of Polymerization Example 1.

[0138] The "solid concentration" as used herein means a mass fraction of the (meth)acrylic resin with respect to the (meth)acrylic resin solution.

[0139] Table 1 also describes 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, mass %) of structural units derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms, the total proportion (A-1, 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, mass %) of structural units derived from an alkyl methacrylate, each with respect to 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 formula described above into the Celsius temperature (°C). [Synthesis of Polymerization Example 2 to Polymer 10]

[0140] The (meth)acrylic resin solutions of Polymerization Examples 2 to 10 were obtained in the same manner as in Polymerization Example 1, except that the monomers described in Table 1 were used instead of those in Polymerization Example 1. In Table 1, MA represents methyl acrylate (acrylic acid alkyl ester monomer containing an alkyl group having 1 to 4 carbon atoms), BA represents butyl acrylate (acrylic acid alkyl ester monomer containing an alkyl group having 1 to 4 carbon atoms), 2HEA represents 2-hydroxyethyl acrylate (acrylic acid alkyl ester monomer containing an alkyl group having 1 to 4 carbon atoms and a hydroxy group), nBMA represents n-butyl methacrylate (methacrylic acid alkyl ester monomer), 2EHA represents 2-ethylhexyl acrylate (acrylic acid alkyl ester monomer), and AA represents acrylic acid. [Table 1] (Meth)acrylic resin [bulk parts] (A) (A-1) (B) Tg Mw Polymerization Example No. EA MA BA 2HEA MMA nBMA 2HEMA 2EHA AA [Mass-%] [Mass-%] [Mass-%] (°C) Polymerization Example 1 65,0 21,0 14,0 65,0 65,0 35,0 9,8 120.000 Polymerization Example 2 30,0 69,0 1,0 99,0 30,0 0,0 -37,0 700.000 Polymerization Example 3 23,8 70,2 6,0 94,0 23,8 0,0 -41,1 500.000 Polymerization Example 4 90,0 10,0 90,0 0,0 0,0 -44,3 650.000 Polymerization Example 5 97, 0 3, 0 97, 0 0, 0 0, 0 -51,2 600.000 Polymerization Example 6 52,0 47,0 1,0 52,0 52,0 0,0 -33,7 650.000 Polymerization Example No. EA MA BA 2HEA MMA nBMA 2HEMA 2EHA AA [Mass-%] [Mass-%] [Mass-%] (°C) Polymerization Example 7 5, 0 12,5 81,5 1, 0 17,5 12,5 81,5 72,4 10.000 Polymerization Example 8 13,5 40,0 33,0 13,0 0,5 13,5 0,0 86,0 41,7 10.000 Polymerization Example 9 50,0 49,0 1, 0 99,0 50,0 0,0 -24,9 700.000 Polymerization Example 10 97, 0 3, 0 97, 0 97, 0 0, 0 12,2 110.000

[0089] [Examples 1 to 16 and Comparative Examples 1 to 3]

[0141] The components shown in Table 2 were mixed in the ratios (parts by mass) shown in Table 2 and adjusted to a solid concentration of 20 mass % with ethyl acetate to obtain laser marking compositions of Examples 1 to 16 and Comparative Examples 1 to 3. Table 2 also shows the proportion (A, mass %) of structural units derived from an alkyl acrylic acid ester containing an alkyl group having 1 to 4 carbon atoms, the total proportion (A-1, 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, mass %) of structural units derived from an alkyl methacrylate, each with respect to all structural units of the (meth)acrylic resin.

[0142] Table 2 shows the solids content of the (meth)acrylic resin for polymerization examples 1 to 10. Table 2 shows the solids content of the titanium oxide pigment for the white pigment.

[0143] Details for each component shown in Tables 2 to 4 are as follows: • Color developing pigment 1: Bismuth oxide-based color developing pigment (42-970A, TOMATEC Corporation) • Color developing pigment 2: Iron oxide-based color developing pigment (NX-512 Yellow, pigment manufactured by Dainichiseika Color & Chemicals Co., Ltd., iron oxide: 56% by mass) • White pigment: NBK-967 White (Titanium oxide pigment content: 58.5% by mass, Cellulose acetate butyrate: 7% by mass, Methyl isobutyl ketone, Nikko Bix Co., Ltd)

[0144] Both sides of a 50 µm thick PET film (surface layer) were subjected to corona treatment. The laser marking composition was applied to one side of the PET film so that the film thickness after drying corresponded to the thickness shown in Table 2, and then dried at 70°C for 3 minutes and at 150°C for 3 minutes to form a laser marking layer (color development layer).

[0145] 100 parts by mass of an acrylic resin PE-121 (Nippon Carbide Industries Co., Ltd.) was mixed with 0.53 parts by mass of a crosslinking agent CK-401 (Nippon Carbide Industries Co., Ltd.), mixed with ethyl acetate to achieve an appropriate viscosity, and then coated onto a release-treated PET (75E0010GT, manufactured by Fujimori Kogyo Co., Ltd.) to a thickness of 20 μm and heated at 100°C for 1 minute to form a pressure-sensitive adhesive layer on the release-treated PET. The pressure-sensitive adhesive side of this pressure-sensitive adhesive layer was adhered to the laser marking layer to form a laminated body for laser marking of each example and comparative example.

[0146] The following evaluations were performed on the obtained laminated body for laser marking. [Printability]

[0147] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), the surface layer of the laser marking laminate was irradiated with laser light under conditions of a power (print intensity) of 25%, a pulse cycle of 50 Hz, a line width of 0.07 mm, and 2,000 mm / s to print a 15 mm square area fill pattern. The laser marking laminate was then attached to a glass plate, and a cover test paper specified in JIS K 5600-4-1:1999 was placed on the back of the glass plate to measure the color difference between the laminate itself and the printed area with a colorimeter (product name "Spectrophotometer CM-3600A," manufactured by Konica Minolta, Inc.), and ΔE*ab was calculated. The results are shown in Table 2. When ΔE*ab is 5 or more, there are no problems in practical use. The larger ΔE*ab is, the better the visibility. [Readability of two-dimensional codes]

[0148] The surface layer of the laminate was irradiated with laser light using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation) under conditions of 20%, 30%, and 50% power (print intensity), 50 Hz pulse cycle, 0.07 mm line width, and 2000 mm / s to print 4 mm square and 8 mm square two-dimensional codes. Afterward, a reading test was performed 100 times using a code reader (manufactured by Keyence Corporation, product name SR-H60W) and evaluated according to the following criteria. If the rating was B or higher, there are no problems in practical use. S: The reading success rate for the 8 mm square is 80% or higher. A: The reading success rate for the 8 mm square is 50% or higher. B: The reading success rate for the 4 mm square is 90%. C: The reading success rate for the 4 mm square is 50% or higher. D: The reading success rate for the 4 mm square is less than 50%. [Blistering]

[0149] The surface layer of the laminate was irradiated with laser light using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation) under conditions of 20%, 30%, and 50% power (printing intensity), 50 Hz pulse cycle, 0.07 mm line width, and 2000 mm / s to print 4 mm square and 8 mm square two-dimensional codes. Whether or not bubbles formed between the release agent-treated PET and the pressure-sensitive adhesive layer was visually and tactilely observed, and evaluated according to the following criteria. If the rating is B or higher, there are no problems in practical use.

[0150] It can be said that the fewer bubbles there are, the more gas generation is suppressed during printing. A: No blistering occurs even at a pressure intensity of 50%. B: Bubbles form at a pressure intensity of 50%. C: Bubbles form regardless of the pressure intensity. [Table 2] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Polymerization Example 1 100,00 100,00 Polymerization Example 2 100,00 Polymerization Example 3 100,00 Polymerization Example 4 100,00 100,00 100,00 Polymerization Example 5 100,00 Polymerization Example 6 Polymerization Example 7 Polymerization Example 8 Polymerization Example 9 Polymerization Example 10 (A) 65,00 99,00 94,00 90,00 97,00 90,00 65,00 90,00 (A-1) 65,00 30,00 23,80 0,00 0,00 0,00 65,00 0,00 (B) 35,00 0,00 0,00 0,00 0,00 0,00 35,00 0,00 Color developing pigment 1 1, 60 1, 60 1, 60 1, 60 1, 60 1, 60 1, 60 1, 60 Color developing pigment 2 white pigment 5,00 Film thickness [µm] 10 10 10 10 10 10 20 20 Printability (ΔE*ab) 27,21 14,09 10,29 16,56 22,44 10,82 27,79 19, 96 Readability of 2D codes S A B B B B S B Blistering B A A A A A B A [Table 2] - Continued Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Polymerization Example 1 50,00 Polymerization Example 2 100,00 100,00 Polymerization Example 3 50,00 25,00 Polymerization Example 4 100,00 Polymerization Example 5 100,00 Polymerization Example 6 Polymerization Example 7 50,00 25,00 Polymerization Example 8 Polymerization Example 9 100,00 Polymerization Example 10 100,00 (A) 97,00 99,00 55,75 60,38 99,00 99,00 90,00 97,00 (A-1) 0,00 50,00 18,15 41,58 30,00 30,00 0,00 97,00 (B) 0,00 0,00 40,75 37,88 0,00 0,00 0,00 0,00 Color developing pigment 1 1, 60 1, 60 1,60 1,60 0,50 2,50 1,60 Color developing pigment 2 50,00 white pigment Film thickness [µm] 20 10 35 35 40 30 50 20 Printability (ΔE*ab) 26,79 16,44 21,69 27,85 10,10 14,18 6,62 41,28 Readability of 2D codes B s s s A A B s Blistering A A B B A A B B [Table 2] - Continued See Example 1 See Example 2 See Example 3 Polymerization Example 1 Polymerization Example 2 Polymerization Example 3 Polymerization Example 4 Polymerization Example 5 Polymerization Example 6 100,00 Polymerization Example 7 100,00 Polymerization Example 8 100,00 Polymerization Example 9 Polymerization Example 10 (A) 52,00 17,50 13,50 (A-1) 52,00 12,50 0,00 (B) 0,00 81,50 86,00 Color developing pigment 1 1, 60 1,60 1,60 Color developing pigment 2 white pigment Film thickness [µm] 10 10 10 Printability (ΔE*ab) 2,97 8,93 3,67 Readability of 2D codes A B S Blistering A C C

[0151] From the evaluation results shown in Table 2, it is apparent that the laser marking laminated body having a color developing layer (resin film) obtained from the laser marking composition of Examples achieved a high level of visibility, readability, and gas generation suppression compared with the laser marking laminated body having a color developing layer (resin film) obtained from the laser marking composition of Comparative Examples.

[0152] The disclosure of Japanese Patent Application No. 2022-159099, filed on September 30, 2022, is incorporated herein by reference in its entirety.

[0153] 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 were specifically and individually indicated to be incorporated by reference. [Explanation of reference symbols] 1 layered body 10 first layer (surface layer) 20 second layer (color development layer) 30 third layer (pressure-sensitive adhesive layer) QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 6292429

[0005] JP 7057236

[0005] JP 2022-159099

[0152] Cited non-patent literature

[0000] JIS K 5600-4-1:1999

[0147] < / harzfolie> < / lasermarkierungszusammensetzung>

Claims

[1] A laser marking composition comprising at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium and neodymium, wherein a proportion of structural units derived from an acrylic acid alkyl ester containing an alkyl group having 1 to 4 carbon atoms with respect to all structural units of the (meth)acrylic resin is 55 mass% or more. [2] The laser marking composition according to claim 1, wherein a total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester with respect to all structural units of the (meth)acrylic resin is less than 45 mass%. [3] The laser marking composition according to claim 1, wherein a total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate and structural units derived from 2-hydroxyethyl acrylate with respect to all structural units of the (meth)acrylic resin is 20 mass% or more. [4] The laser marking composition according to claim 1, wherein the metal oxide comprises a bismuth-containing compound. [5] A resin film formed using the laser marking composition according to any one of claims 1 to 4. [6] A laminated body comprising the resin film according to claim 5.

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