Laser marking composition, resin film, and laminate

Abstract

A laser marking composition containing 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, the proportion of the structural units derived from an alkyl acrylate containing an alkyl group having 1-4 carbon atoms in the total structural units of the (meth) acrylic resin is 55% by mass or more.

Description

Technical Field

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

[0002] Variable information such as manufacturing lot numbers and manufacturing dates is required to be printed on various packages such as food and pharmaceuticals, and various components such as electronic components for traceability. As one of the marking methods for this purpose, a laser marking method is sometimes used. In particular, a color-developing type laser marking method in which a resin and a pigment are discolored by laser can be printed without generating odor or dust, and thus has been used in various scenarios in recent years.

[0003] As labels and inks for laser marking, the following compositions are known.

[0004] For example, Patent Document 1 discloses an adhesive containing an adhesive resin (A) and a bismuth-based laser color developer (B) as an adhesive having good contrast after printing and capable of forming an adhesive layer with suppressed coloring.

[0005] In addition, Patent Document 2 discloses a laser marking ink composition that sufficiently has laser printability (visual recognition), anti-blocking property, adhesiveness, and lamination strength. The laser marking ink composition is characterized by containing an adhesive resin, a white pigment, and an organic solvent. The adhesive resin contains a polyurethane resin and a cellulose derivative. The cellulose derivative is a lower acyl-substituted cellulose derivative and / or a lower alkyl-substituted cellulose derivative. The white pigment is titanium oxide having an average particle size of 0.26 μm or less.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent No. 6292429 Gazette

[0009] Patent Document 2: Japanese Patent No. 7057236 Gazette Summary of the Invention

[0010] A resin composition that can be rendered black by laser irradiation develops color by a reduction reaction of an inorganic oxide caused by laser. At this time, carbonization of the resin and generation of gas are caused by the heat generated during reduction. Therefore, carbonization of the resin spreads beyond the target or the film expands, and it is likely to cause poor reading when printing one-dimensional codes and two-dimensional codes.

[0011] For example, the adhesive using a bismuth-based laser color developer disclosed in Patent Document 1 sometimes has a deformed mark due to heat during printing and is sometimes difficult to read depending on the printed content.

[0012] In addition, in the laser marking ink composition disclosed in Patent Document 2, the polyurethane resin is liable to carbonize, so the resin around the inorganic oxide is liable to carbonize, and sometimes it is difficult to read according to the printed content. Furthermore, since the (meth)acrylic copolymer cited as a comparative example in Patent Document 2 is mainly composed of a methacrylic resin, there is sometimes a problem that gas is easily generated during printing and it is liable to expand.

[0013] The present disclosure has been made in view of the above-described conventional circumstances, and an object thereof is to provide a laser marking composition capable of forming a resin film having excellent visual recognition and readability when printed as a one-dimensional code or a two-dimensional code and capable of suppressing the generation of gas during printing, a resin film using the laser marking composition, and a laminate.

[0014] Specific means for achieving the above problems are as follows.

[0015] <1> A laser marking composition containing at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from bismuth, antimony, molybdenum, iron, nickel, chromium, zirconium, and neodymium,

[0016] The proportion of the structural unit derived from an acrylic alkyl ester having 1 to 4 carbon atoms in all the structural units of the above (meth)acrylic resin is 55% by mass or more.

[0017] <2> The laser marking composition according to <1>, wherein the total proportion of the structural unit derived from methacrylic acid and the structural unit derived from a methacrylic acid alkyl ester in all the structural units of the above (meth)acrylic resin is less than 45% by mass.

[0018] <3> The laser marking composition according to <1> or <2>, wherein the total proportion of the structural unit derived from ethyl acrylate, the structural unit derived from methyl acrylate, and the structural unit derived from 2-hydroxyethyl acrylate in all the structural units of the above (meth)acrylic resin is 20% by mass or more.

[0019] <4> The laser marking composition according to any one of <1> to <3>, wherein the above metal oxide contains a bismuth-containing compound.

[0020] <5> A resin film obtained by using the laser marking composition according to any one of <1> to <4>.

[0021] <6> A laminate having the resin film according to <5>.

[0022] According to the present disclosure, there can be provided a laser marking composition for a resin film that can form excellent visual recognition and readability when printed into one-dimensional codes or two-dimensional codes and can suppress the generation of gas during printing, a resin film using the laser marking composition, and a laminate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is an example schematically showing a cross-sectional structure of a laminate according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] 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, unless otherwise specified, the constituent elements (including element steps, etc.) are not essential. The numerical values and their ranges also do not limit the present disclosure.

[0025] In the present disclosure, the term "process" includes not only a process independent of other processes, but also a process that is not clearly distinguishable from other processes as long as the purpose of the process is achieved.

[0026] In the present disclosure, the numerical range represented by "~" includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0027] In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range can be replaced with the upper limit value or the lower limit value of other stepwise described numerical ranges. In addition, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range can be replaced with the value shown in the examples.

[0028] 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, unless otherwise specified, the content rate or content of each component refers to the total content rate or content of the plurality of substances present in the composition.

[0029] In the present disclosure, the particles corresponding to each component may contain a plurality of particles. When there are a plurality of particles corresponding to each component in the composition, unless otherwise specified, the particle size of each component refers to the value of the mixture of the plurality of particles present in the composition.

[0030] In the present disclosure, the term "layer" or "film" includes the case where it is formed over the entire region when observing the region where the layer or film is present and the case where it is formed only in a part of the region.

[0031] In the present disclosure, the term "lamination" means laminating layers, and two or more layers may be combined or two or more layers may be detachable.

[0032] In the present disclosure, "(meth)acrylic acid" refers to at least one of acrylic acid and methacrylic acid, and "(meth)acrylate" refers to at least one of acrylate and methacrylate.

[0033] In the present disclosure, the average thickness of a layer or film is a value obtained by measuring the thicknesses of 5 points of the layer or film to be measured and obtaining their arithmetic mean.

[0034] The thickness of a layer or film can be measured using a micrometer or the like. In the present disclosure, when the thickness of a layer or film can be directly measured, a micrometer is used for measurement. On the other hand, when measuring the thickness of a single layer or the total thickness of multiple layers, it can be measured by observing the cross-section of the measurement object using an electron microscope.

[0035] In the present disclosure, the solid component refers to the components other than the organic solvent in the laser marking composition or the sample solution.

[0036] <Laser Marking Composition>

[0037] The laser marking composition of the present disclosure contains at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium, and the proportion of the structural unit derived from an acrylic alkyl ester containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the above (meth)acrylic resin is 55% by mass or more.

[0038] According to the laser marking composition of the present disclosure, a resin film having excellent visual recognition and readability when printed as a one-dimensional code or a two-dimensional code and capable of suppressing the generation of gas during printing can be formed. The reason is not yet clear, but it is speculated as follows.

[0039] Comparing the structural unit derived from an acrylic alkyl ester and the structural unit derived from a methacrylic alkyl ester that can be contained in the (meth)acrylic resin, they are different depending on whether or not a methyl group is directly bonded to the carbon atom constituting the main chain of the (meth)acrylic resin. The carbon atom directly bonded to the methyl group is a tertiary carbon. At the position where the tertiary carbon in the main chain of the (meth)acrylic resin is present, the (meth)acrylic resin is likely to decompose due to laser irradiation. If the proportion of the structural unit derived from a methacrylic alkyl ester contained in the (meth)acrylic resin is large, gas from the decomposition products is likely to be generated.

[0040] In the present disclosure, since the proportion of the structural unit derived from an acrylic alkyl ester containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is 55% by mass or more, it is considered that the ratio of tertiary carbons in the carbon atoms constituting the main chain of the (meth)acrylic resin can be maintained at a low level, and the generation of gas from the decomposition products is easily suppressed. In addition, as the generation of gas is suppressed, the expansion of the resin film composed of the laser marking composition is easily suppressed.

[0041] In addition, since the number of carbon atoms in the alkyl group contained in the structural unit derived from an alkyl acrylate is 1 to 4, the glass transition temperature of the (meth)acrylic resin is not easily lowered. Therefore, it is easy to suppress the deformation of the resin film caused by the heat generated when reducing the inorganic oxide by laser irradiation.

[0042] It is presumed that as a result, the visual recognition and the readability when printed as a one-dimensional code or a two-dimensional code are improved.

[0043] Hereinafter, each component constituting the laser marking composition of the present disclosure will be described.

[0044] ((Meth)acrylic resin)

[0045] The laser marking composition of the present disclosure contains at least one (meth)acrylic resin, and the proportion of the structural unit derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is 55% by mass or more. The proportion of the structural unit derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is preferably 56% by mass or more, more preferably 60% by mass or more, and further preferably 90% by mass or more. The proportion of the structural unit derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin may be 99% by mass or less. The proportion of the structural unit derived from an alkyl acrylate containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is preferably 55% by mass to 99% by mass.

[0046] When the laser marking composition of the present disclosure contains one (meth)acrylic resin, as long as it is a (meth)acrylic resin that satisfies the above conditions, it may be a homopolymer composed of structural units derived from a single (meth)acrylic monomer, or a copolymer composed of structural units derived from two or more (meth)acrylic monomers.

[0047] In addition, when the laser marking composition of the present disclosure contains two or more (meth)acrylic resins, as long as the proportion of the structural units derived from acrylic acid alkyl esters containing an alkyl group having 1 to 4 carbon atoms in all the structural units contained in two or more (meth)acrylic resins is 55% by mass or more, two or more homopolymers having different structural units, or at least one homopolymer and at least one copolymer, or two or more copolymers having different structural units can be used in combination. In addition, when the laser marking composition of the present disclosure contains two or more (meth)acrylic resins, at least one (meth)acrylic resin in which the proportion of the structural units derived from acrylic acid alkyl esters containing an alkyl group having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is 55% by mass or more and at least one (meth)acrylic resin in which the above proportion is less than 55% can be used in combination.

[0048] Here, the (meth)acrylic monomer refers to at least any one of acrylic acid, derivatives of acrylic acid such as acrylic acid alkyl esters, methacrylic acid, and derivatives of methacrylic acid such as methacrylic acid alkyl esters. The derivatives of acrylic acid and the derivatives of methacrylic acid may have substituents such as a hydroxyl group, an amino group, a carboxyl group, and a glycidyl group.

[0049] In addition, other monomers other than the (meth)acrylic monomer can be used in the (meth)acrylic resin.

[0050] Specific examples of the (meth)acrylic monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-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.

[0051] Specific examples of the (meth)acrylic monomer 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.

[0052] As other monomers, other monomers containing a carboxyl group such as crotonic acid, maleic anhydride, fumaric acid, itaconic acid, pentenedioic acid, and citraconic acid can be cited. As other monomers not containing a carboxyl group, vinyl acetate, vinyl ether, acrylonitrile, styrene, etc. can be cited.

[0053] As the acrylic alkyl ester containing an alkyl group having 1 to 4 carbon atoms, ethyl acrylate, methyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate and other butyl acrylates, and 2-hydroxyethyl acrylate are preferred.

[0054] In one aspect of the present disclosure, the total proportion of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate in all the structural units of the (meth)acrylic resin is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 65% by mass or more. The total proportion of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate in all the structural units of the (meth)acrylic resin may be 99% by mass or less. The total proportion of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate in all the structural units of the (meth)acrylic resin is preferably 20% by mass to 99% by mass.

[0055] Ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate have a high glass transition temperature when made into homopolymers. Therefore, in a part of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate in the (meth)acrylic resin, even if heat is generated by laser irradiation, the main chain of the (meth)acrylic resin is not easily movable. As a result, there is a tendency to perform printing with good accuracy.

[0056] In addition, in other embodiments of the present disclosure, the total proportion of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate in all the structural units of the (meth)acrylic resin may be 1% by mass or less.

[0057] In the present disclosure, the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylates in all the structural units of the (meth)acrylic resin is preferably less than 45% by mass, more preferably 40% by mass or less, still more preferably 35% by mass or less, and particularly preferably 5% by mass or less. The total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylates in all the structural units of the (meth)acrylic resin may be 0% by mass or more. The total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylates in all the structural units of the (meth)acrylic resin is preferably 0% by mass or more and less than 45% by mass.

[0058] If the total proportion of structural units derived from methacrylic acid and structural units derived from alkyl methacrylates in all the structural units of the (meth)acrylic resin is less than 45% by mass, there is a tendency to more easily suppress the generation of gases of decomposition products that may be generated by the decomposition of the (meth)acrylic resin.

[0059] The 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, in all the structural units of the (meth)acrylic resin is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less. The total proportion of structural units derived from monomers containing a carboxyl group in the molecule in all the 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 the molecule in all the structural units of the (meth)acrylic resin is preferably 0.5% to 20% by mass.

[0060] If the total proportion of structural units derived from monomers containing a carboxyl group in the molecule in all the structural units of the (meth)acrylic resin is 20% by mass or less, it is possible to suppress the generation of attenuation of absorbance caused by the reaction of a metal oxide reduced by light irradiation with a carboxyl group, and there is a tendency for visual recognition to be further improved.

[0061] 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.

[0062] 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 still 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 more, the resin film tends not to become brittle. Further, if the weight average molecular weight (Mw) of the (meth)acrylic resin is 1,000,000 or less, the film-forming property is excellent.

[0063] When two or more (meth)acrylic resins are used in combination in the laser marking composition of the present disclosure, the weight average molecular weight (Mw) of the mixture of two or more (meth)acrylic resins is preferably within the above range.

[0064] In the present disclosure, the weight average molecular weight (Mw) of the (meth)acrylic resin is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).

[0065] (1) A solution of the (meth)acrylic resin is coated on a release paper and dried at 100 °C for 1 minute to obtain a film-like (meth)acrylic resin.

[0066] (2) Using the film-like (meth)acrylic resin obtained in the above (1) and tetrahydrofuran, a sample solution with a solid content concentration of 0.2 mass% is obtained.

[0067] (3) Using gel permeation chromatography (GPC), the weight average molecular weight (Mw) of the (meth)acrylic resin is measured in the form of a standard polystyrene conversion value under the following conditions.

[0068] ~Conditions~

[0069] Measurement device: High-speed GPC (Model: HLC-8220GPC, manufactured by Tosoh Corporation)

[0070] Detector: Differential refractive index detector (RI) (built into HLC-8220, manufactured by Tosoh Corporation)

[0071] Column: Four TSK-GEL GMHXL (manufactured by Tosoh Corporation) are connected in series

[0072] Column temperature: 40 °C

[0073] Eluent: Tetrahydrofuran

[0074] Sample concentration: 0.2 mass%

[0075] Injection volume: 100 μL

[0076] Flow rate: 0.6 mL / minute

[0077] In order to suppress the deformation of the printing part caused by heat and gas during printing and be able to print one-dimensional codes and two-dimensional codes with good accuracy, the glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C or higher, more preferably 0°C or higher, and further preferably 10°C or higher. From the viewpoint of good workability of the resin film and not being easily embrittled, the glass transition temperature Tg of the (meth)acrylic resin can be 100°C or lower. The glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C to 100°C.

[0078] The glass transition temperature Tg of the (meth)acrylic resin refers to the value obtained as the inflection point of the DSC curve obtained by measuring 10 mg of the test sample at a heating rate of 10°C / minute in a nitrogen gas stream using a differential scanning calorimetry device (DSC) (for example, manufactured by Seiko Instruments Inc., EXSTAR6000). When two or more inflection points of the DSC curve are observed using the differential scanning calorimetry device (DSC), the temperature at the inflection point with the highest temperature is taken as the glass transition temperature Tg of the (meth)acrylic resin.

[0079] It should be noted that when the structural units constituting the (meth)acrylic resin are identified, the Tg of the (meth)acrylic resin can be the value obtained by converting the absolute temperature (K) calculated by the following formula into Celsius temperature (°C).

[0080]

[0081] In the formula, Tg 1 , Tg 2 , ····· and Tg n are the glass transition temperatures in absolute temperature (K) of the homopolymers of monomer 1, monomer 2, ····· and monomer n, respectively. m 1 , m 2 , ····· and m n are the molar fractions of the respective monomers.

[0082] It should be noted that the "glass transition temperature in absolute temperature (K) of the homopolymer" refers to the glass transition temperature in absolute temperature (K) of the homopolymer prepared by polymerizing the monomer alone. The glass transition temperature of the homopolymer can be measured by the above method using a differential scanning calorimetry device (DSC).

[0083] The "glass transition temperature of the homopolymer in degrees Celsius (°C)" of the representative monomers is as follows. For methyl acrylate, it is 10°C; for ethyl acrylate, it is -22°C; for n-butyl acrylate, it is -54°C; for 2-ethylhexyl acrylate, it is -70°C; for 2-hydroxyethyl acrylate, it is -15°C; for 4-hydroxybutyl acrylate, it is -80°C; for tert-butyl acrylate, it is 43°C; for vinyl acetate, it is 32°C; for acrylic acid, it is 106°C; for methyl methacrylate, it is 105°C; for 2-hydroxyethyl methacrylate, it is 85°C. For example, by using these representative monomers, the above glass transition temperature can be appropriately adjusted.

[0084] For monomers other than the above monomers, the "glass transition temperature when made into a homopolymer" adopts the value recorded in the Polymer Handbook (4th Edition, Wiley-Interscience; the same hereinafter). In the case where it is not recorded in the Polymer Handbook, the value of the glass transition temperature of the homopolymer obtained by the above measurement method is adopted.

[0085] It should be noted that by subtracting 273 from the absolute temperature (K), the absolute temperature (K) can be converted into degrees Celsius (°C), and by adding 273 to the degrees Celsius (°C), the degrees Celsius (°C) can be converted into the absolute temperature (K).

[0086] When two or more kinds of (meth)acrylic resins are used in combination, the glass transition temperature Tg of the (meth)acrylic resin showing the highest glass transition temperature Tg is preferably in the above range.

[0087] The manufacturing method of the (meth)acrylic resin is not particularly limited, and the monomers can be polymerized by methods such as solution polymerization, emulsion polymerization, and suspension polymerization to manufacture. It should be noted that when preparing the laser marking composition after manufacturing the (meth)acrylic resin, from the viewpoint of relatively simple processing procedures and being able to be carried out in a short time, solution polymerization is preferred.

[0088] Solution polymerization generally can use methods such as putting a specified organic solvent, monomer, polymerization initiator, and a chain transfer agent used as needed into a polymerization tank, and heating and reacting with stirring for several hours in a nitrogen stream or at the reflux temperature of the organic solvent. It should be noted that the weight average molecular weight of the (meth)acrylic resin can reach the desired value by adjusting the reaction temperature, reaction time, solvent amount, type and amount of the catalyst.

[0089] Examples of the organic solvents used during the polymerization reaction of the (meth)acrylic resin include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, ethylene glycol ether compounds, alcohol compounds, etc. These organic solvents can be used alone, one kind at a time, or two or more kinds can be used in combination.

[0090] As the organic solvent used during the polymerization reaction, more specifically, for example, the following can be cited: aromatic hydrocarbon-based organic solvents represented by benzene, toluene, ethylbenzene, n-propylbenzene, tert-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic hydrocarbon-based or alicyclic hydrocarbon-based organic solvents represented by n-hexane, n-heptane, n-octane, isooctane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine; ester-based organic solvents represented by ethyl acetate, n-butyl acetate, n-pentyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; ketone-based organic solvents represented by acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; ethylene glycol ether-based organic solvents 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 methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, and tert-butanol.

[0091] In addition, as the polymerization initiator, for example, organic peroxides and azo compounds that can be used in common polymerization methods can be cited.

[0092] (Meth)acrylic resins can be commercially available products. As commercially available (meth)acrylic resins, KP-1876E (trade name: NISSETSU (registered trademark), manufactured by Nippon Carbide Industries Co., Ltd.), H-4002 (manufactured by Negami Kogyo Co., Ltd.), etc. can be cited.

[0093] The content rate of the (meth)acrylic resin in the solid component of the laser marking composition is preferably 15% by mass to 99.5% by mass, more preferably 20% by mass to 99% by mass, and further preferably 40% by mass to 98.5% by mass. If the content rate of the (meth)acrylic resin is 15% by mass to 99.5% by mass, there is a tendency for the heat resistance of the printed portion to increase.

[0094] (Metal oxide)

[0095] The laser marking composition of the present disclosure contains a metal oxide containing at least 1 kind of metal selected from bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium. The metal oxide functions as a color-developing pigment.

[0096] Among these, from the viewpoint of excellent blackness during color development, bismuth-containing compounds are preferred, and bismuth(III) oxide (Bi 2 O 3 ) is more preferred. At this time, in order to improve the laser printability, metal oxides with many oxygen defects are preferred.

[0097] The volume average particle diameter of the metal oxide is not particularly limited, preferably 0.05 μm to 30 μm, more preferably 0.1 μm to 15 μm, and still more preferably 0.3 μm to 1.5 μm. If the volume average particle diameter of the metal oxide is 0.05 μm or more, the metal oxide becomes likely to absorb laser light and generate heat, and thus there is a tendency for the color development property during printing to be further improved. On the other hand, if the volume average particle diameter of the metal oxide is 30 μm or less, there is a tendency for the dispersibility during film formation to be improved. The volume average particle diameter of the metal oxide refers to the value measured by the laser diffraction / light scattering method.

[0098] The specific method of the laser diffraction / light scattering method is as follows. Use a Pasteur pipette to take 5 mL of the aqueous dispersion of the metal oxide into a glass cuvette with a length of 5 mm, a width of 65 mm, and a height of 80 mm, and place it in a laser diffraction / light scattering particle size distribution analyzer [e.g., LA-960A (trade name) manufactured by Horiba, Ltd.]. After adjusting the concentration of the aqueous dispersion of the metal oxide so that the transmittance of the laser (red) is 80% to 90%, computer processing is performed on the measurement results obtained under the condition of a measurement temperature of 25°C ± 1°C, whereby the average particle diameter of the metal oxide particles in the aqueous dispersion is determined. In addition, the value of the average particle diameter uses the volume average value.

[0099] The content of the metal oxide in the solid component of the laser marking composition is preferably 0.2% by mass to 50.0% by mass, more preferably 0.5% by mass to 25.0% by mass, and still more preferably 1.0% by mass to 5.0% by mass. If the content of the metal oxide is 0.2% by mass or more, there is a tendency for proper color development during laser marking and good readability of the laser marking portion. If the content of the metal oxide is 50.0% by mass or more, dust generation during laser marking can be suppressed, and thus there is a tendency for good readability of the laser marking portion.

[0100] (Crosslinking agent)

[0101] In order to improve the strength of the resin film, the laser marking composition of the present disclosure may contain a crosslinking agent. Examples of the crosslinking agent include isocyanate-based crosslinking agents, aluminum chelate-based crosslinking agents, and epoxy-based crosslinking agents. When the laser marking composition contains a crosslinking agent, the (meth)acrylic resin preferably contains structural units derived from a (meth)acrylic monomer having a hydroxyl group or other monomers containing a carboxyl group.

[0102] When the laser marking composition contains a crosslinking agent, the content of the crosslinking agent is preferably 0.1 equivalent to 10 equivalents relative to the total of the hydroxyl groups and carboxyl groups of the (meth)acrylic resin. By making the content of the crosslinking agent 0.1 equivalent or more, the movement of molecules can be suppressed and the printing accuracy can be improved. By making the content of the crosslinking agent 10 equivalents or less, the discoloration of the (meth)acrylic resin can be suppressed. If the content of the crosslinking agent is 0.3 equivalent to 3.0 equivalents, film formation is easy, so it is further preferred.

[0103] (White pigment)

[0104] In order to further improve the visual recognition by increasing the contrast between the black of the printed part and the white of the non-printed part, the laser marking composition of the present disclosure may contain a white pigment.

[0105] As the white pigment, various inorganic pigments can be used. For example, titanium oxide (TiO 2 ), titanium oxide-coated mica, zinc oxide (zinc white), basic lead sulfate, zinc sulfide, and antimony oxide and other white pigments can be cited. In addition, as the white pigment, it can be barium sulfate, barium carbonate, precipitated calcium carbonate, diatomaceous earth, talc, clay, basic magnesium carbonate, and white alumina, etc. Among them, from the viewpoint of excellent whiteness, titanium oxide (TiO 2 ) is preferably used as the white pigment. In addition, from the viewpoint that the reduction reaction efficiency of the metal oxide becomes high by reflecting the transmitted laser and the color rendering property can be improved as a result, titanium oxide-coated mica may also be included.

[0106] 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 further preferably 0.1 μm to 20 μm. The volume average particle diameter of the white pigment refers to the value measured by the laser diffraction / light scattering method.

[0107] When the laser marking composition of the present disclosure contains a white pigment, the content rate of the white pigment in the solid component of the laser marking composition is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and further preferably 1% by mass to 20% by mass. If the content rate of the white pigment is 0.01% by mass or more, there is a tendency that the reduction efficiency of the color-developing pigment can be improved and the visual recognition can be further improved. If the content rate of the white pigment is 50% by mass or less, there is a tendency that the color rendering property of the metal oxide can be prevented from decreasing.

[0108] (Polyurethane resin)

[0109] In order to improve printability when printing on the surface of a resin film, the laser marking composition of the present disclosure may contain a polyurethane resin. By containing a polyurethane resin in the laser marking composition, the fixing of the printed layer formed on the surface of the resin film becomes good.

[0110] The type of polyurethane resin is not particularly limited, and conventionally known polyurethane resins such as polycarbonate-based polyurethane resins, polyester-based polyurethane resins, and polyether-based polyurethane resins can be used. The polyurethane resin can be used alone as one kind, or two or more kinds can be used in combination.

[0111] When the laser marking composition of the present disclosure contains a polyurethane resin, from the viewpoint of improving printability, the content of the polyurethane resin in the solid component of the laser marking composition is preferably 2% by mass to 75% by mass, more preferably 5% by mass to 20% by mass, and still more preferably 10% by mass to 15% by mass. By making the content of the polyurethane resin in the solid component of the laser marking composition 75% by mass or less, laser printability can be maintained. By making the content of the polyurethane resin in the solid component of the laser marking composition 20% by mass or less, lamination adaptability can be maintained.

[0112] As the polyurethane resin, commercially available products can be used.

[0113] Examples of commercially available products of polyurethane resins include, for example, in addition to "NE-8836 (polycarbonate-based)", "NE-8811 (polycarbonate-based)", "NE-8850 (polycarbonate-based)" [all manufactured by Dainichi Seika Kogyo Co., Ltd.], "SUPERFLEX 420 (polycarbonate-based)", "SUPERFLEX 460 (polycarbonate-based)", "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)", "PANDEX T-8190 (polyether-based)" [all manufactured by DIC Covestro Polymer Co., Ltd.], etc.

[0114] (Filler)

[0115] In order to improve printability during printing when printing on the surface of a resin film, the laser marking composition of the present disclosure may contain a filler. By containing a filler in the laser marking composition, the slidability of the surface of the resin film becomes good, and the operability during printing on the surface of the resin film is improved, whereby the printability becomes good.

[0116] As the filler, known fillers such as inorganic particles such as silica particles, resin particles such as acrylic beads and melamine beads can be used. The filler can be used alone as one kind, or two or more kinds can be used in combination.

[0117] The volume average particle diameter of the filler is not particularly limited. From the viewpoint of improving slidability, it is preferably 0.5 μm to 25 μm, more preferably 1 μm to 15 μm, and further 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 above-mentioned metal oxide.

[0118] When the laser marking composition of the present disclosure contains a filler, from the viewpoint of improving slidability, the content rate of the filler in the solid component of the laser marking composition is preferably 0.2 mass% to 30.0 mass%, more preferably 0.5 mass% to 20 mass%, and further preferably 2 mass% to 10 mass%.

[0119] (Other components)

[0120] The laser marking composition of the present disclosure can contain other resins and various additives within a range that does not impair visual recognition, readability when printed as a one-dimensional code or two-dimensional code, and the inhibitory effect of gas generation during printing. Such additives are, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants.

[0121] (Organic solvent)

[0122] In order to improve coating workability, the laser marking composition of the present disclosure can contain an organic solvent. As the organic solvent, as long as it dissolves or disperses various components contained in the laser marking composition, there is no particular limitation. Examples of the organic solvent 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 alone as one kind or in combination of two or more kinds.

[0123] When the laser marking composition of the present disclosure contains an organic solvent, the content rate of the organic solvent contained in the laser marking composition is preferably 40 mass% to 90 mass%.

[0124] <Resin film>

[0125] The resin film of the present disclosure is formed using the laser marking composition of the present disclosure.

[0126] The method for manufacturing a resin film using the laser marking composition of the present disclosure is not particularly limited, and a resin film can be formed by a known method using a single-layer T-die extruder, a multi-layer T-die extruder, a calender, or the like.

[0127] Alternatively, a resin film can be formed by coating one surface of a base film described below with the laser marking composition of the present disclosure containing an organic solvent and drying it. Examples of such coating methods include screen printing, gravure printing, bar coating, knife coating, roll coating, comma coating, doctor blade coating, die coating, spray coating, and the like.

[0128] When the laser marking composition contains a crosslinking agent, the resin film can be cured. Examples of the method for curing the resin film include drying using hot air, heating using a heating device such as an oven or a hot plate.

[0129] The average thickness of the resin film is not particularly limited, and can be, for example, 2 μm to 100 μm.

[0130] <Laminated body>

[0131] The laminated body of the present disclosure has the resin film of the present disclosure. The laminated body of the present disclosure can be a laminated body for a laser marking label. The layer structure of the laminated body is not particularly limited, and a first layer that transmits laser light, a second layer that develops color by laser light, and a third layer having adhesiveness provided as needed can be sequentially laminated. Alternatively, a first layer that transmits laser light and a second layer having adhesiveness that develops color by laser light can be sequentially laminated. When the laminated body has such a structure, it is preferable to use the resin film of the present disclosure as the second layer.

[0132] By having the resin film of the present disclosure, the laminated body of the present disclosure tends to suppress the generation of gas in the second layer during laser marking. Consequently, the generation of odors is suppressed. In addition, the visual recognition and the readability when printed as a one-dimensional code or a two-dimensional code tend to be improved.

[0133] Hereinafter, with reference to Figure 1 A case where the laminated body of the present disclosure is applied to a laser marking label having a three-layer structure will be described. Figure 1 is a diagram schematically showing an example of the cross-sectional structure of a laminated body 1 according to an embodiment of the present disclosure. As Figure 1 shown, the laminated body 1 has a first layer 10, a second layer 20, and a third layer 30, and the first layer 10, the second layer 20, and the third layer 30 are sequentially laminated. The second layer 20 is in contact with the first layer 10.

[0134] Here, the laser marking of the laminate 1 will be described. First, laser light is irradiated from the side of the first layer 10 of the laminate 1. The irradiated laser light passes through the first layer 10 and acts on the second layer 20. Since the second layer 20 is formed of the resin film of the present disclosure, in the portion of the second layer 20 irradiated with the laser, the metal oxide develops color, and the resin is carbonized due to the heat of the laser. The colored and carbonized portions of the second layer 20 become the printed portion of the laser marking label. The printed portion is the area of the second layer 20 that turns black. In this way, a laser marking label of the type in which a resin layer containing a metal oxide is included inside the film and the resin layer is made to develop color by laser irradiation is sometimes particularly referred to as an internally coloring type laser marking label. It should be noted that in the present disclosure, "laser marking" is not limited to the act of recording information such as characters and symbols on the laminate 1, and all acts of causing at least a part of the second layer 20 of the laminate 1 to develop color by laser irradiation are referred to as "laser marking".

[0135] Hereinafter, each layer of the laminate 1 will be described by taking the laminate 1 of one embodiment of the present disclosure as an example.

[0136] [First layer 10]

[0137] The first layer 10 is a layer that transmits laser light. It should be noted that in the present disclosure, the first layer 10 is sometimes referred to as the surface layer.

[0138] As the first layer 10, an optically transparent film is used. "Optically transparent" in the present disclosure means that, for example, 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 of the first layer 10 is sufficiently high, when looking down at the laser-marked laminate 1 from the side of the first layer 10, the second layer 20 as its underlying layer can be clearly seen through the first layer 10. The transmittance of laser light and the transmittance of visible light of the base film can be measured using a known spectrophotometer, for example.

[0139] As the resin used as the material of the base film for the first layer 10, either a thermoplastic resin or a thermosetting resin can be used. More specifically, the resin used as the material of the base film for the first layer 10 is, for example, a (meth)acrylic copolymer, a polyvinyl butyral resin, a vinyl chloride resin, a fluororesin, a polyester resin, a polystyrene resin, or a thermoplastic polyurethane resin (TPU). These resins are excellent in transparency, heat resistance, and workability. These resins can be used alone or in combination of two or more.

[0140] Among the above resins, particularly from the viewpoint of being able to sufficiently transmit laser light and having good workability and heat resistance, the resin used as the material of the base film is preferably a polyester resin. By forming the base film of the first layer 10 from a polyester resin, the versatility of the laminate 1 can be improved, and fine laser marking can be achieved.

[0141] From the viewpoint of suppressing deformation caused by heat during laser marking, the polyester-based resin is preferably an aromatic ester-based resin. From the viewpoint of suppressing deformation caused by heat during laser irradiation, the aromatic ester-based resin is more preferably a transparent resin.

[0142] Examples of the aromatic ester-based resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate, and polyethylene naphthalate (PEN). Among them, from the above viewpoints, the aromatic ester-based resin is more preferably polyethylene terephthalate.

[0143] The thickness of the first layer 10 is not particularly limited, and from the viewpoints of chemical resistance and abrasion resistance, a thicker thickness is more preferable. From the viewpoints of workability and cost, the upper limit of the thickness of the first layer 10 may be appropriately set. For example, from the viewpoint of good workability (such as operability) when laminating the laminate 1 to the adherend, the thickness of the first layer 10 is preferably in the range of 10 μm to 200 μm.

[0144] In addition, the resin used as the material of the base film of the first layer 10 may contain various additives within a range that does not impair print readability and adhesion. Such additives are, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, fillers, and colorants.

[0145] In addition, the first layer 10 may be subjected to corona treatment or provided with an easy-bonding layer on the surface on the side having the second layer 20.

[0146] [Second layer 20]

[0147] The second layer 20 is colored by laser. It should be noted that in the present disclosure, the second layer 20 is sometimes referred to as the color-developing layer 20. The second layer 20 is composed of the resin film of the present disclosure.

[0148] 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 further preferably 15 μm to 50 μm. If the thickness of the second layer 20 is 2 μm or more, the print can be sufficiently recognized. In addition, if the thickness of the second layer 20 is 15 μm or more, the laser penetration resistance and printability are improved. In addition, if the thickness of the second layer 20 is 100 μm or less, the productivity of the second layer 20 is improved.

[0149] [Third layer 30]

[0150] The third layer 30 has adhesiveness. It should be noted that in the present disclosure, the third layer 30 is sometimes referred to as the adhesive layer 30.

[0151] The adhesive used in the third layer 30 only needs to be able to bond to adherends such as resin plates, metal plates, and glass plates and be able to be peeled off from the adherends. Specifically, the adhesive force of the adhesive used in the third layer 30 is preferably 0.1 N / 25 mm to 40 N / 25 mm, more preferably 0.3 N / 25 mm to 30 N / 25 mm. If the adhesive force of the adhesive is 0.1 N / 25 mm or more, the adhesion to the adherend can be obtained. In addition, if the adhesive force of the adhesive is 40 N / 25 mm or less, the peelability of the adhesive is good. It should be noted that the adhesive force of the adhesive refers to the value measured by peeling the laminate with a width of 10 mm from an aluminum plate at a peeling angle of 180°, a peeling speed of 300 mm / minute, and a measurement temperature of 23°C after pasting the laminate on the aluminum plate with a 2 kg load and leaving it at 23°C for 24 hours.

[0152] The third layer 30 is composed of a resin composition. Examples of the resin composition used in the third layer 30 include (meth)acrylic adhesives, silicone adhesives, synthetic rubber adhesives, etc. From the viewpoint of improving the adhesion between the second layer 20 and the third layer 30, (meth)acrylic adhesives are more preferred.

[0153] The thickness of the third layer 30 is not particularly limited, and 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 (such as operability) when laminating the laminate 1 to the adherend is good.

[0154] In addition, the resin composition used in the third layer 30 may contain various additives within the range that does not impair the print readability and adhesion. Such additives are, for example, dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants.

[0155] As the colorant used in the third layer 30, metal oxide-based pigments are preferred. By using metal oxide-based pigments, there is a tendency to improve the covering property of the substrate and reduce the penetrability of the laser. Furthermore, the laser is reflected by the metal oxide-based pigment and the efficiency of the reduction reaction of the metal oxide in the second layer 20 increases, resulting in a tendency to improve the color development property. Examples of the metal oxide-based pigment include metal oxides containing at least one metal selected from titanium, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium, but are not limited to these.

[0156] 〔Laser marking method for laminate 1〕

[0157] Laser marking of the laminate 1 can be performed by irradiating the laser from the first layer 10 side of the laminate 1.

[0158] For the laser used for laser marking, for example, a near-infrared laser with a wavelength of about 1000 nm can be used; YVO 4Laser, YAG laser, and fiber laser. Additionally, UV laser with a wavelength of 300 nm to 400 nm can also be used.

[0159] The laser marking of the laminate 1 is usually performed before the laminate 1 is adhered to the adherend. After the laminate 1 is adhered to the adherend, laser marking can also be performed. However, in this case, it is preferable that the laminate 1 has sufficient penetration resistance so that the laser irradiation does not damage the adherend to which the laminate 1 is adhered.

[0160] 〔Manufacturing method of laminate 1〕

[0161] The laminate 1 can be manufactured by sequentially overlapping the first layer 10, the second layer 20, and the third layer 30. For example, the laminate 1 can be manufactured by a manufacturing method that at least includes the following processes: a second layer forming process of forming the second layer 20 on one surface of the first layer 10; and a third layer forming process of forming the third layer 30 on the surface of the second layer 20 that does not contact the first layer 10 after the second layer forming process.

[0162] The second layer forming process can be a process of coating the laser marking composition used in the second layer 20 on one surface of the base film as the first layer 10 and curing it as needed to form the second layer 20. The forming method of the second layer 20 can be the same as the manufacturing method of the resin film disclosed above in the present disclosure.

[0163] The third layer forming process can be a process of coating the resin composition used in the third layer 30 on the surface of the second layer 20 that does not contact the first layer 10 after the second layer forming process and curing it to form the third layer 30. In other embodiments, the third layer forming process can be a process of coating the resin composition used in the third layer 30 and curing it to form the third layer 30, and then laminating the third layer 30 to the surface of the second layer 20 that does not contact the first layer 10 after the second layer forming process. The resin composition used in the third layer 30 is as described in the item "Third layer 30". In the manufacturing method of the laminate 1, for the coating method of the resin composition used in the third layer 30 and the curing method of the resin composition used in the third layer 30, known coating methods and curing methods can also be used as described above.

[0164] In the manufacturing method of the laminate 1, a first layer forming process of forming the first layer 10 can be further included before the second layer forming process as needed.

[0165] 〔Other embodiments〕

[0166] The laminate of the present disclosure is not limited to the laminate 1 of a laser marking label having a three-layer structure with a first layer, a second layer, and a third layer. The laminate of the present disclosure may be a laminate composed of only a second layer and a third layer without a first layer, or a laminate having a second layer, a third layer, and other layers without a first layer, or a laminate having a first layer, a second layer, a third layer, and other layers.

[0167] Examples of the other layers include a coloring layer, a printing layer, an adhesive layer, etc.

[0168] The coloring layer is, for example, a layer provided between the second layer and the third layer that imparts color, pattern, etc. to the entire laminate. By providing the coloring layer, the designability of the laminate is improved.

[0169] Examples of the coloring layer include a layer containing a resin and a colorant. The resin contained in the coloring layer is not particularly limited, and examples thereof include the same resin as that used in the first layer. The colorant contained in the coloring layer is not particularly limited, and examples thereof include pigments and dyes.

[0170] The thickness of the coloring layer is not particularly limited, and for example, it may be in the range of 1 μm to 50 μm.

[0171] The coloring layer can be formed by coating a resin composition for forming the coloring layer on the surface of the third layer side of the second layer, or can be adhered to the surface of the third layer side of the second layer after separately forming the coloring layer. When adhering the coloring layer to the surface of the second layer, an adhesive layer can be further provided between the coloring layer and the second layer.

[0172] The printing layer is, for example, a layer formed by a printing machine provided between the second layer and the third layer. Specifically, for example, a resin composition containing a resin, a colorant, a solvent, etc. is applied to the surface of the layer adjacent to the printing layer in a desired pattern, text, etc. shape, and after drying, curing, etc. processes as needed, the printing layer is formed. By providing the printing layer, the designability of the laminate is improved. The printing layer can be provided only on a part of the laminate surface direction or on the whole.

[0173] Examples of the printing method include inkjet printing, screen printing, gravure printing, flexographic printing, etc.

[0174] The printing layer is formed, for example, by printing on the surface of the third layer side of the second layer.

[0175] When the laminate has a coloring layer, the printing layer is, for example, provided between the second layer and the coloring layer, and can be formed by printing on the surface of the coloring layer side of the second layer, or can be formed by printing on the surface of the second layer side of the coloring layer.

[0176] When forming a printed layer by printing on the surface of the second layer, it is preferable that the laser marking composition for forming the second layer contains at least one of the above polyurethane resin and filler.

[0177] Examples

[0178] Hereinafter, the present disclosure will be described in more detail based on examples, but the present invention is not limited to these examples.

[0179] 〔Polymerization Example 1〕

[0180] 70.0 parts by mass of ethyl acetate [organic solvent] was put into the reaction vessel of a reaction apparatus equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer.

[0181] In addition, 100.0 parts by mass of a monomer mixture composed of 65.0 parts by mass of ethyl acrylate [EA; an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms], 21.0 parts by mass of methyl methacrylate [MMA; a methyl methacrylate alkyl ester monomer], and 14.0 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; a methyl methacrylate alkyl ester monomer having a hydroxyl group] was prepared in another container. After 20.0 mass% of the prepared monomer mixture was put into the above reaction vessel, it was heated and refluxed at the reflux temperature for 10 minutes.

[0182] Next, at the reflux temperature condition, the remaining 80.0 mass% of the above monomer mixture, 50.0 parts by mass of ethyl acetate, and 0.026 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were successively added dropwise to the above reaction vessel over 120 minutes. After the addition was completed, the reaction was further carried out for 150 minutes to end the reaction. The solution after the reaction was diluted with ethyl acetate so that the solid content concentration was 35.0 mass% to obtain the (meth)acrylic resin solution of Polymerization Example 1.

[0183] The "solid content concentration" mentioned here refers to the mass ratio of the (meth)acrylic resin in the (meth)acrylic resin solution.

[0184] It should be noted that Table 1 comprehensively lists the weight-average molecular weight (Mw), glass transition temperature (Tg) of the (meth)acrylic resin, the proportion (A, mass %) of the structural units derived from acrylic acid alkyl esters containing an alkyl group with 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin, the total proportion (A-1, mass %) of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate, and the total proportion (B, mass %) of the structural units derived from methacrylic acid alkyl esters. The weight-average molecular weight of the (meth)acrylic resin solution is the value measured by the above method. 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 into Celsius temperature (°C).

[0185] [Synthesis of Polymerization Examples 2 to 10]

[0186] In the synthesis of Polymer 1, the monomers described in Table 1 were used, and in addition, (meth)acrylic resin solutions of Polymerization Examples 2 to 10 were obtained in the same manner as in Polymerization Example 1. In Table 1, MA represents methyl acrylate (an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms), BA represents butyl acrylate (an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms), 2HEA represents 2-hydroxyethyl acrylate (an acrylic acid alkyl ester monomer having a hydroxyalkyl group with 1 to 4 carbon atoms), nBMA represents n-butyl methacrylate (a methacrylic acid alkyl ester monomer), 2EHA represents 2-ethylhexyl acrylate (an acrylic acid alkyl ester monomer), and AA represents acrylic acid.

[0187]

[0188] [Examples 1 to 16 and Comparative Examples 1 to 3]

[0189] The components described in Table 2 were blended at the ratios (parts by mass) described in Table 2, and prepared with ethyl acetate at a solid component concentration of 20 mass % to obtain the laser marking compositions of Examples 1 to 16 and Comparative Examples 1 to 3. Table 2 comprehensively lists the proportion (A, mass %) of the structural units derived from acrylic acid alkyl esters containing an alkyl group with 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin, the total proportion (A-1, mass %) of the structural units derived from ethyl acrylate, the structural units derived from methyl acrylate, and the structural units derived from 2-hydroxyethyl acrylate, and the total proportion (B, mass %) of the structural units derived from methacrylic acid alkyl esters.

[0190] It should be noted that in Table 2, for Polymerization Examples 1 to 10, it refers to the content of the solid component of the (meth)acrylic resin. Additionally, in Table 2, for the white pigment, it refers to the content of the solid component of the titanium oxide pigment.

[0191] It should be noted that the details of each component described in Table 2 are as follows.

[0192] · Color-developing pigment 1: Bismuth oxide-based color-developing pigment (42 - 970A, TOMATEC Co., Ltd.)

[0193] · Color-developing pigment 2: Iron oxide-based color-developing pigment (NX - 512Yellow, pigment manufactured by Dainichi Seika Kogyo Co., Ltd., 56% by mass of iron oxide)

[0194] · White pigment: NBK - 967White (58.5% by mass of titanium oxide pigment component, 7% by mass of cellulose acetate butyrate, methyl isobutyl ketone, NIKKO BICS Co., Ltd.)

[0195] Corona treatment was performed on both sides of a PET film (surface layer) with a thickness of 50 μm, and the laser marking composition was coated on one side of the PET film in such a manner that the film thickness after drying was the film thickness described in Table 2, dried at 70 °C for 3 minutes, and dried at 150 °C for 3 minutes to form a laser marking layer (color-developing layer).

[0196] To 100 parts by mass of acrylic resin PE - 121 (manufactured by Nippon Carbide Industries Co., Ltd.), 0.53 parts by mass of crosslinking agent CK - 401 (manufactured by Nippon Carbide Industries Co., Ltd.) was added, mixed with ethyl acetate to an appropriate viscosity, and then coated on 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 an adhesive layer on the release-treated PET. The adhesive surface of this adhesive layer was adhered to the laser marking layer to produce the laser marking laminate for each example and comparative example.

[0197] The following evaluations were performed on the obtained laser marking laminate.

[0198] 〔Printability〕

[0199] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), the surface layer of the laminate for laser marking was irradiated with laser under the conditions of an output (printing intensity) of 25%, a pulse period of 50 Hz, a line width of 0.07 mm, and 2000 mm / second, and a square filling pattern of 15 mm square was printed. Then, the laminate for laser marking was pasted on a glass plate, and on the glass side, a hiding power test paper specified in JIS K 5600-4-1:1999 was pasted on the back, and the color difference between the laminate itself and the printed part was measured with a colorimeter (product name "Spectrophotometer CM-3600A", manufactured by Konica Minolta Inc.), and ΔE ＊ ab was calculated. The results obtained are shown in Table 2. If ΔE ＊ ab is 5 or more, there is no problem in practical use. The larger ΔE ＊ ab is, the more excellent the visual recognition is.

[0200] 〔QR code readability〕

[0201] Using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), the surface layer of the laminate was irradiated with laser under the conditions of an output (printing intensity) of 20%, 30%, 50% and a pulse period of 50 Hz, a line width of 0.07 mm, and 2000 mm / second, and QR codes of 4 mm square and 8 mm square were printed. Then, 100 reading tests were carried out using a barcode reader (product name SR-H60W, manufactured by KEYENCE Corporation), and the evaluation was carried out according to the following criteria. If the evaluation is B or more, there is no problem in practical use.

[0202] S: The reading success rate of the 8 mm square is 80% or more.

[0203] A: The reading success rate of the 8 mm square is 50% or more.

[0204] B: The reading success rate of the 4 mm square is 90%.

[0205] C: The reading success rate of the 4 mm square is 50% or more.

[0206] D: The reading success rate of the 4 mm square is less than 50%.

[0207] 〔Bulge〕

[0208] Using the FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation), the surface layer of the laminate was irradiated with laser under the conditions of output (printing intensity) of 20%, 30%, 50%, pulse period of 50 Hz, line width of 0.07 mm, and 2000 mm / second, and two-dimensional codes with side lengths of 4 mm and 8 mm were printed. At this time, visual inspection and finger touch were used to observe whether bulging (swelling) occurred between the peeled PET and the adhesive layer, and evaluation was carried out according to the following criteria. If the evaluation is B or above, there is no problem in practice.

[0209] It can be said that the less the generation of bulging, the more the generation of gas during printing can be suppressed.

[0210] A: No swelling even when the printing intensity is 50%.

[0211] B: Swelling occurs when the printing intensity is 50%.

[0212] C: Swelling occurs regardless of the printing intensity.

[0213]

[0214] From the evaluation results recorded in Table 2, it can be seen that the laminate for laser marking having the color-developing layer (resin film) obtained from the laser marking composition of the example achieves higher-dimensional visual recognition, readability, and suppression of gas generation compared to the laminate for laser marking having the color-developing layer (resin film) obtained from the laser marking composition of the comparative example.

[0215] The entire disclosure of Japanese Patent Application No. 2022-159099 filed on September 30, 2022 is incorporated herein by reference in its entirety.

[0216] All documents, patent applications, and technical standards described in this specification are incorporated into this specification to the same extent as specifically and individually indicated that they are incorporated by reference.

[0217] Symbol Explanation

[0218] 1 Laminate

[0219] 10 First layer (surface layer)

[0220] 20 Second layer (color-developing layer)

[0221] 30 Third layer (adhesive layer)

Claims

1. A laser marking composition containing at least one (meth)acrylic resin and a metal oxide containing at least one metal selected from bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium. The proportion of the structural unit derived from an alkyl acrylate having 1 to 4 carbon atoms in all the structural units of the (meth)acrylic resin is 55% by mass or more.

2. The laser marking composition according to claim 1. Wherein, The total proportion of the structural unit derived from methacrylic acid and the structural unit derived from an alkyl methacrylate in all the structural units of the (meth)acrylic resin is less than 45% by mass.

3. The laser marking composition according to claim 1. Wherein, The total proportion of the structural unit derived from ethyl acrylate, the structural unit derived from methyl acrylate, and the structural unit derived from 2-hydroxyethyl acrylate in all the structural units of the (meth)acrylic resin is 20% by mass or more.

4. The laser marking composition according to claim 1. Wherein, The metal oxide contains a bismuth-containing compound.

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

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

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