Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/50—Sympathetic, colour changing or similar inks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/267—Marking of plastic artifacts, e.g. with laser
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/65—Additives macromolecular

Definitions

• This disclosure relates to a laser marking composition, a resin film, and a laminate.
• Laser marking is one of the marking methods used for this purpose.
• color-developing laser marking which uses a laser to change the color of resins or pigments, is used in a variety of places in recent years because it can be used to mark without producing odors or dust.
• Patent Document 1 discloses an adhesive that has good contrast after printing and can form an adhesive layer with suppressed coloring, the adhesive comprising an adhesive resin (A) and a bismuth-based laser coloring agent (B).
• Patent Document 2 discloses an ink composition for laser marking that has sufficient laser printability (visibility), blocking resistance, adhesion, and lamination strength, the ink composition comprising a binder resin, a white pigment, and an organic solvent, the binder resin comprising a polyurethane resin and a cellulose derivative, the cellulose derivative being a lower acyl group-substituted cellulose derivative and/or a lower alkyl-substituted cellulose derivative, and the white pigment being titanium oxide having an average particle size of 0.26 ⁇ m or less.
• Patent Document 1 Japanese Patent No. 6292429 Patent Document 2: Japanese Patent No. 7057236
• Resin compositions that can turn black when irradiated with a laser do so by utilizing the reduction reaction of inorganic oxides caused by laser light.
• the heat generated during reduction causes the resin to carbonize and gas to be generated.
• the resin carbonization spreads more than intended, and the laminate swells, which can easily lead to reading problems when one-dimensional or two-dimensional codes are printed.
• the adhesive using a bismuth-based laser coloring agent disclosed in Patent Document 1 may cause the print to deform due to heat during printing, and depending on the print content, it may be difficult to read.
• the urethane resin is easily carbonized, so the resin around the inorganic oxide is easily carbonized, and depending on the printed content, it may be difficult to read.
• the (meth)acrylic copolymer given as a comparative example in Patent Document 2 is mainly composed of methacrylic resin, so there may be problems such as gas generation and swelling during printing.
• the present disclosure has been made in consideration of the above-mentioned conventional circumstances, and has an object to provide a laser marking composition capable of forming a resin film that has excellent visibility and readability when one-dimensional or two-dimensional codes are printed and that suppresses gas generation during printing, as well as a resin film and a laminate that use this laser marking composition.
• An ink 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,
• a laser marking composition wherein the proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in all structural units of the (meth)acrylic resin is 55 mass% or more.
• ⁇ 2> The laser marking composition according to ⁇ 1>, wherein the total proportion of structural units derived from methacrylic acid and structural units derived from a methacrylic acid alkyl ester in all structural units of the (meth)acrylic resin is less than 45 mass%.
• ⁇ 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 in all structural units of the (meth)acrylic resin is 20 mass% or more.
• ⁇ 4> The laser marking composition according to any one of ⁇ 1> to ⁇ 3>, wherein the metal oxide includes a bismuth-containing compound.
• ⁇ 5> A resin film obtained by using the laser marking composition according to any one of ⁇ 1> to ⁇ 4>.
• ⁇ 6> A laminate having the resin film according to ⁇ 5>.
• the present disclosure provides a laser marking composition capable of forming a resin film that has excellent visibility and readability when printing one-dimensional or two-dimensional codes and suppresses gas generation during printing, as well as a resin film and a laminate that use this laser marking composition.
• FIG. 2 is a diagram illustrating an example of a cross-sectional structure of a laminate according to an embodiment of the present disclosure.
• the term "step” includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
• the numerical range indicated using “to” includes the numerical values before and after "to” as the minimum and maximum values, respectively.
• the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages.
• the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
• each component may contain multiple types of corresponding substances.
• the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.
• the particles corresponding to each component may include multiple types of particles.
• the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
• the terms "layer” and “film” include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
• the term “lamination” refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
• “(meth)acrylic” means at least one of acrylic and methacrylic
• “(meth)acrylate” means at least one of acrylate and methacrylate.
• the average thickness of a layer or film is defined as the arithmetic mean value of thicknesses measured at five points on the layer or film of interest. The thickness of the layer or film can be measured using a micrometer or the like. In the present disclosure, when the thickness of the layer or film can be measured directly, it is measured using a micrometer.
• the thickness of one layer or the total thickness of multiple layers is measured, it may be measured by observing the cross section of the measurement target using an electron microscope.
• solids refers to the components excluding the organic solvent in the laser marking composition or sample solution.
• the laser marking composition of the present disclosure contains at least one type of (meth)acrylic resin and a metal oxide containing at least one type of metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium and neodymium, and the proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in all structural units of the (meth)acrylic resin is 55 mass% or more.
• the laser marking composition of the present disclosure makes it possible to form a resin film that has excellent visibility and readability when one-dimensional or two-dimensional codes are printed, and that suppresses gas generation during printing.
• the (meth)acrylic resin contains a large amount of structural units derived from methacrylic acid alkyl esters, gas derived from the decomposition product is likely to be generated.
• the proportion of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms in the total structural units of the (meth)acrylic resin is 55% by mass or more, it is possible to maintain a relatively low ratio of tertiary carbons among the carbon atoms constituting the main chain of the (meth)acrylic resin, and it is believed that the generation of gas derived from decomposition products is easily suppressed.
• the generation of gas is suppressed, the occurrence of blistering of the resin film made of the laser marking composition is easily suppressed.
• the number of carbon atoms in the alkyl group contained in the structural unit derived from the alkyl acrylate ester is 1 to 4, the glass transition temperature of the (meth)acrylic resin is unlikely to be low, and therefore deformation of the resin film due to heat generated by reduction of the inorganic oxide by laser irradiation is easily suppressed. As a result, it is believed that the visibility and readability of printed one-dimensional and two-dimensional codes will improve.
• the laser marking composition of the present disclosure contains at least one (meth)acrylic resin, and the ratio of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin is 55% by mass or more.
• the ratio of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin is preferably 56% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more.
• the ratio of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin may be 99% by mass or less.
• the ratio of structural units derived from an alkyl acrylate ester containing an alkyl group having 1 to 4 carbon atoms to the total structural units of the (meth)acrylic resin is preferably 55% by mass to 99% by mass.
• the laser marking composition of the present disclosure contains one type of (meth)acrylic resin, so long as the (meth)acrylic resin satisfies the above conditions, it may be a homopolymer consisting of structural units derived from a single (meth)acrylic monomer, or it may be a copolymer consisting of structural units derived from two or more types of (meth)acrylic monomers.
• the laser marking composition of the present disclosure contains two or more types of (meth)acrylic resins
• two or more types of homopolymers having different structural units may be used in combination, or at least one type of homopolymer and at least one type of copolymer may be used in combination, or two or more types of copolymers having different structural units may be used in combination, so long as the ratio of structural units derived from acrylic acid alkyl esters having an alkyl group with 1 to 4 carbon atoms to all structural units contained in the two or more types of (meth)acrylic resins is 55% by mass or more.
• the laser marking composition of the present disclosure contains two or more types of (meth)acrylic resins
• at least one type of (meth)acrylic resin in which the ratio of structural units derived from acrylic acid alkyl esters having an alkyl group with 1 to 4 carbon atoms to all structural units of the (meth)acrylic resin is 55% by mass or more and at least one type of (meth)acrylic resin in which the above ratio is less than 55% by mass may be used in combination.
• the (meth)acrylic monomer means at least one of acrylic acid, derivatives of acrylic acid such as acrylic acid alkyl esters, and derivatives of methacrylic acid such as methacrylic acid alkyl esters.
• the derivatives of acrylic acid and the derivatives of methacrylic acid may have a substituent such as a hydroxyl group, an amino group, a carboxyl group, or a glycidyl group.
• the (meth)acrylic resin may contain other monomers in addition to the (meth)acrylic monomer.
• (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, glycidyl (meth)acrylate, and tetrahydrofurfur
• (meth)acrylic monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) mono(meth)acrylate, and pentaerythritol tri(meth)acrylate.
• monomers that contain a carboxy group include crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, and citraconic acid.
• monomers that do not contain a carboxy group include vinyl acetate, vinyl ether, acrylonitrile, and styrene.
• alkyl acrylate esters 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.
• 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 the total structural units of the (meth)acrylic resin is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 65% by mass or more.
• the total proportion of 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 total 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 the total structural units of the (meth)acrylic resin is preferably 20% by mass to 99% by mass.
• Ethyl acrylate, methyl acrylate, and 2-hydroxyethyl acrylate have high glass transition temperatures when made into homopolymers.
• the main chain of the (meth)acrylic resin is less likely to move even if heat is generated by laser irradiation. As a result, there is a tendency for accurate printing to be achieved.
• 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 structural units of the (meth)acrylic resin may be 1 mass% or less.
• the total proportion of the structural units derived from methacrylic acid and the structural units derived from methacrylic acid alkyl esters in the total structural units of the (meth)acrylic resin is preferably less than 45% by mass, more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 5% by mass or less.
• the total proportion of the structural units derived from methacrylic acid and the structural units derived from methacrylic acid alkyl esters in the total structural units of the (meth)acrylic resin may be 0% by mass or more.
• the total proportion of the structural units derived from methacrylic acid and the structural units derived from methacrylic acid alkyl esters in the total structural units of the (meth)acrylic resin is preferably 0% by mass or more and less than 45% by mass.
• the total proportion of structural units derived from methacrylic acid and structural units derived from an alkyl methacrylate ester in all structural units of the (meth)acrylic resin is less than 45 mass%, the generation of gas derived from decomposition products that may be generated by decomposition of the (meth)acrylic resin tends to be more easily suppressed.
• the total proportion of structural units derived from monomers containing a carboxy group in the molecule, such as acrylic acid, methacrylic acid, and other monomers containing a carboxy group, in the total structural units of the (meth)acrylic resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.
• the total proportion of structural units derived from monomers containing a carboxy group in the molecule in the total structural units of the (meth)acrylic resin may be 0.5% by mass or more.
• the total proportion of structural units derived from monomers containing a carboxy group in the molecule in the total structural units of the (meth)acrylic resin is preferably 0.5% by mass to 20% by mass.
• the total proportion of structural units derived from monomers containing a carboxy group in the molecule, among all structural units of the (meth)acrylic resin, is 20 mass% or less, it is possible to suppress attenuation of absorbance caused by a metal oxide reduced by irradiation with laser light reacting with a carboxy group, and visibility tends to be further improved.
• the polymerization mode is not particularly limited and may be random copolymerization, alternating copolymerization, block copolymerization, or graft copolymerization.
• the weight average molecular weight (Mw) of the (meth)acrylic resin is preferably in the range of 5,000 to 1,000,000, more preferably in the range of 10,000 to 800,000, and even more preferably in the range of 100,000 to 750,000. If the weight average molecular weight (Mw) of the (meth)acrylic resin is 5,000 or more, the resin film tends to be less brittle. Also, if the weight average molecular weight (Mw) of the (meth)acrylic resin is 1,000,000 or less, the film-forming property tends to be excellent. When the laser marking composition of the present disclosure uses two or more (meth)acrylic resins in combination, it is preferable that the weight average molecular weight (Mw) of the mixture of two or more (meth)acrylic resins is within the above range.
• the weight average molecular weight (Mw) of the (meth)acrylic resin is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).
• (1) A solution of a (meth)acrylic resin is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the (meth)acrylic resin.
• the weight average molecular weight (Mw) of the (meth)acrylic resin is measured in terms of standard polystyrene using gel permeation chromatography (GPC) under the following conditions.
• GPC gel permeation chromatography
• Measurement device High-speed GPC (model number: HLC-8220 GPC, Tosoh Corporation) Detector: Differential refractometer (RI) (built into HLC-8220, Tosoh Corporation) Column: 4 TSK-GEL GMHXL (Tosoh Corporation) connected in series Column temperature: 40°C Eluent: tetrahydrofuran Sample concentration: 0.2% by mass Injection volume: 100 ⁇ L Flow rate: 0.6 mL/min
• the glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C or higher, more preferably 0°C or higher, and even more preferably 10°C or higher, in order to suppress deformation of the printed portion due to heat or gas during printing and enable one-dimensional or two-dimensional codes to be printed with high accuracy.
• the glass transition temperature Tg of the (meth)acrylic resin may be 100°C or lower, in order to provide a resin film with good workability and less brittleness.
• the glass transition temperature Tg of the (meth)acrylic resin is preferably -20°C to 100°C.
• the glass transition temperature Tg of the (meth)acrylic resin refers to a value determined as an inflection point of the DSC curve obtained by measuring 10 mg of a measurement sample in a nitrogen gas flow at a heating rate of 10° C./min using a differential scanning calorimeter (DSC) (e.g., EXSTAR 6000 manufactured by Seiko Instruments Inc.).
• DSC differential scanning calorimeter
• EXSTAR 6000 manufactured by Seiko Instruments Inc.
• the Tg of the (meth)acrylic resin may be calculated by converting the absolute temperature (K) calculated using the following formula into Celsius temperature (°C).
• Tg 1 , Tg 2 , ..., and Tg n are the glass transition temperatures, expressed in absolute temperature (K), of the homopolymers of monomer 1, monomer 2, ..., and monomer n, respectively, and m 1 , m 2 , ..., and m n are the mole fractions of the respective monomers.
• the "glass transition temperature of a homopolymer expressed in absolute temperature (K)” refers to the glass transition temperature of a homopolymer produced by polymerizing the monomer alone, expressed in absolute temperature (K).
• the glass transition temperature of a homopolymer can be measured by the above-mentioned method using a differential scanning calorimeter (DSC).
• the "glass transition temperatures of homopolymers expressed in Celsius temperature (°C)" of representative monomers are as follows: methyl acrylate is 10°C, ethyl acrylate is -22°C, n-butyl acrylate is -54°C, 2-ethylhexyl acrylate is -70°C, 2-hydroxyethyl acrylate is -15°C, 4-hydroxybutyl acrylate is -80°C, t-butyl acrylate is 43°C, vinyl acetate is 32°C, acrylic acid is 106°C, methyl methacrylate is 105°C, and 2-hydroxyethyl methacrylate is 85°C.
• the glass transition temperature Tg of the (meth)acrylic resin exhibiting the highest glass transition temperature Tg is within the above range.
• the method for producing the (meth)acrylic resin is not particularly limited, and the resin can be produced by polymerizing monomers using methods such as solution polymerization, emulsion polymerization, and suspension polymerization.
• solution polymerization is preferred because the processing steps are relatively simple and can be completed in a short time.
• Solution polymerization can generally be carried out by charging a polymerization vessel with a specified organic solvent, monomers, polymerization initiator, and, if necessary, a chain transfer agent, and then heating and reacting for several hours with stirring in a nitrogen stream or at the reflux temperature of the organic solvent.
• the weight-average molecular weight of the (meth)acrylic resin can be adjusted to the desired value by adjusting the reaction temperature, reaction time, amount of solvent, and type and amount of catalyst.
• Organic solvents used during the polymerization reaction of (meth)acrylic resins include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. These organic solvents may be used alone or in combination of two or more.
• organic solvents used during the polymerization reaction include aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon organic solvents such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine oil; ester organic solvents such as ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; ace
• ketone-based organic solvents such as methyl ketone, methyl i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone
• glycol ether-based organic solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether
• alcohol-based organic solvents such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.
• Polymerization initiators include, for example, organic peroxides and azo compounds that can be used in conventional polymerization methods.
• (meth)acrylic resins may be used.
• Commercially available (meth)acrylic resins include KP-1876E (product name: Nissetsu (registered trademark), manufactured by Nippon Carbide Industries Co., Ltd.) and H-4002 (manufactured by Negami Chemical Industries Co., Ltd.).
• the (meth)acrylic resin content of the solid content 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 even more preferably 40% by mass to 98.5% by mass. If the (meth)acrylic resin content is 15% by mass to 99.5% by mass, the heat resistance of the printed portion tends to be improved.
• the laser marking composition of the present disclosure contains a metal oxide comprising at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium, the metal oxide functioning as a color-developing pigment.
• a metal oxide comprising at least one metal selected from the group consisting of bismuth, antimony, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium, the metal oxide functioning as a color-developing pigment.
• bismuth-containing compounds are preferred because they have excellent black color when colored, and bismuth(III) oxide (Bi 2 O 3 ) is more preferred. In this case, metal oxides with many oxygen defects are preferred in order to improve laser printability.
• the volume average particle diameter of the metal oxide is not particularly limited, and is preferably 0.05 ⁇ m to 30 ⁇ m, more preferably 0.1 ⁇ m to 15 ⁇ m, and even more preferably 0.3 ⁇ m to 1.5 ⁇ m.
• the volume average particle diameter of the metal oxide is 0.05 ⁇ m or more, the metal oxide is more likely to absorb laser light and generate heat, so that the color development during printing tends to be improved.
• the volume average particle diameter of the metal oxide is 30 ⁇ m or less, the dispersibility during film formation tends to be good.
• the volume average particle diameter of the metal oxide refers to a value measured by a laser diffraction/light scattering method.
• a specific method of the laser diffraction/light scattering method is as follows: 5 mL of the aqueous dispersion of the metal oxide is collected using a Pasteur pipette into a glass cell measuring 5 mm in length, 65 mm in width, and 80 mm in height, and this is set in a laser diffraction/light scattering particle size distribution measurement device (for example, LA-960A (product name) manufactured by Horiba, Ltd.).
• LA-960A product name
• 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 results of measurements taken at a measurement temperature of 25°C ⁇ 1°C are then processed by computer to determine the average particle size of the metal oxide particles in the aqueous dispersion.
• the volume average value is used as the average particle size value.
• the metal oxide content of the solids in 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 even more preferably 1.0% by mass to 5.0% by mass. If the metal oxide content is 0.2% by mass or more, appropriate coloring occurs during laser marking, and the readability of the laser-marked area tends to be good. If the metal oxide content is 50.0% by mass or less, dust generation during laser marking is suppressed, and the readability of the laser-marked area tends to be good.
• the laser marking composition of the present disclosure may contain a crosslinking agent to improve the strength of the resin film.
• the crosslinking agent include an isocyanate-based crosslinking agent, an aluminum chelate-based crosslinking agent, and an epoxy-based crosslinking agent.
• the (meth)acrylic resin preferably contains a structural unit derived from a (meth)acrylic monomer having a hydroxyl group or another monomer having a carboxyl group.
• the content of the crosslinking agent is preferably 0.1 to 10 equivalents relative to the total of the hydroxyl and carboxyl groups of the (meth)acrylic resin.
• the content of the crosslinking agent 0.1 equivalent or more By making the content of the crosslinking agent 0.1 equivalent or more, the molecular action can be suppressed and printing accuracy can be improved. By making the content of the crosslinking agent 10 equivalents or less, discoloration of the (meth)acrylic resin can be suppressed. If the content of the crosslinking agent is 0.3 to 3.0 equivalents, it is more preferable because it is easy to form a film.
• the laser marking composition of the present disclosure may contain a white pigment to further improve visibility by increasing the contrast between the black color of the printed area and the white color of the non-printed area.
• a white pigment various inorganic pigments can be used.
• titanium oxide (TiO 2 ) titanium oxide-coated mica, zinc oxide (zinc white), basic lead sulfate, zinc sulfide, antimony oxide, and other white pigments can be mentioned.
• the white pigment may be barium sulfate, barium carbonate, precipitated calcium carbonate, diatomaceous earth, talc, clay, basic magnesium carbonate, alumina white, and the like.
• titanium oxide (TiO 2 ) is preferable as the white pigment because of its excellent whiteness.
• titanium oxide-coated mica may be included because it reflects the transmitted laser light, thereby increasing the efficiency of the reduction reaction of the metal oxide, and as a result, the color development can be improved.
• the volume average particle diameter of the white pigment is not particularly limited, but is preferably 0.01 ⁇ m to 50 ⁇ m, more preferably 0.05 ⁇ m to 30 ⁇ m, and even more preferably 0.1 ⁇ m to 20 ⁇ m.
• the volume average particle diameter of the white pigment refers to a value measured by a laser diffraction/light scattering method.
• the content of the white pigment in the solid content of the laser marking composition is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and even more preferably 1% by mass to 20% by mass. If the white pigment content is 0.01% by mass or more, the reduction efficiency of the color pigment can be improved, and visibility tends to be further improved. If the white pigment content is 50% by mass or less, a decrease in the color development of the metal oxide tends to be prevented.
• the laser marking composition of the present disclosure may contain a urethane resin in order to improve printability when printing on the surface of a resin film.
• a urethane resin in the laser marking composition, the fixing of the printed layer formed on the surface of the resin film is improved.
• the type of urethane resin is not particularly limited, and conventionally known urethane resins such as polycarbonate-based urethane resins, polyester-based urethane resins, polyether-based urethane resins, etc.
• the urethane resins may be used alone or in combination of two or more kinds.
• the content of the urethane resin in the solid content of the laser marking composition is preferably 2% by mass to 75% by mass, more preferably 5% by mass to 20% by mass, and even more preferably 10% by mass to 15% by mass, from the viewpoint of improving printability.
• the content of the urethane resin in the solid content of the laser marking composition is preferably 2% by mass to 75% by mass, more preferably 5% by mass to 20% by mass, and even more preferably 10% by mass to 15% by mass, from the viewpoint of improving printability.
• urethane resin commercially available products can be used.
• examples of commercially available urethane resins include "NE-8836 (polycarbonate-based)", “NE-8811 (polycarbonate-based)”, and “NE-8850 (polycarbonate-based)” (all manufactured by Dainichiseika Color & Chemicals Mfg.
• the laser marking composition of the present disclosure may contain a filler in order to improve printability when printing on the surface of a resin film.
• a filler When the laser marking composition contains a filler, the slipperiness on the surface of the resin film is improved, and the operability when printing on the surface of the resin film is improved, resulting in good printability.
• known fillers such as inorganic particles such as silica particles, resin particles such as acrylic beads, melamine beads, etc. can be used.
• the filler may be used alone or in combination of two or more kinds.
• the volume average particle diameter of the filler is not particularly limited, and from the viewpoint of improving the slipperiness, it is preferably 0.5 ⁇ m to 25 ⁇ m, more preferably 1 ⁇ m to 15 ⁇ m, and even more preferably 2 ⁇ m to 10 ⁇ m.
• 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.
• the content of the filler in the solid content of the laser marking composition is preferably 0.2% by mass to 30.0% by mass, more preferably 0.5% by mass to 20% by mass, and even more preferably 2% by mass to 10% by mass, from the viewpoint of improving slipperiness.
• the laser marking composition of the present disclosure may contain other resins and various additives within the scope of not impairing the visibility, the readability of the one-dimensional code or two-dimensional code when printed, and the effect of suppressing gas generation during printing.
• additives include dispersants, light stabilizers, heat stabilizers, plasticizers, tackifiers, fillers, and colorants.
• the laser marking composition of the present disclosure may contain an organic solvent to improve coating workability.
• the organic solvent is not particularly limited as long as it dissolves or disperses various components contained in the laser marking composition.
• 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, cycloh
• the content of the organic solvent contained in the laser marking composition is preferably 40% by mass to 90% by mass.
• the resin film of the present disclosure is formed using the laser marking composition of the present disclosure.
• the method for producing a resin film using the laser marking composition of the present disclosure is not particularly limited, and the resin film can be formed by a known method using a single layer T-die extruder, a multi-layer T-die extruder, a calendar molding machine, or the like.
• the laser marking composition of the present disclosure containing an organic solvent may be applied to one side of a substrate film described below and then dried to form a resin film. Examples of such application methods include screen printing, gravure printing, bar coating, knife coating, roll coating, comma coating, blade coating, die coating, and spray coating.
• the resin film may be cured by drying with hot air, heating with a heating device such as an oven or a hot plate, or the like.
• the average thickness of the resin film is not particularly limited and may be, for example, 2 ⁇ m to 100 ⁇ m.
• the laminate of the present disclosure has the resin film of the present disclosure.
• the laminate of the present disclosure may be a laminate used for a laser marking label.
• the layer structure of the laminate is not particularly limited, and may be a laminate in which a first layer that transmits laser light, a second layer that develops color by laser light, and a third layer having adhesiveness that is provided as necessary are stacked in this order. Also, a first layer that transmits laser light and a second layer having adhesiveness that develops color by laser light may be stacked in this order. When the laminate has such a structure, it is preferable to use the resin film of the present disclosure as the second layer.
• the laminate of the present disclosure has the resin film of the present disclosure, which tends to suppress the generation of gas in the second layer during laser marking. As a result, the generation of odors is suppressed. In addition, the visibility and readability of one-dimensional and two-dimensional codes when printed also tend to improve.
• FIG. 1 is a schematic diagram showing an example of a cross-sectional structure of a laminate 1 according to an embodiment of the present disclosure.
• the laminate 1 has a first layer 10, a second layer 20, and a third layer 30, which are stacked in this order.
• the second layer 20 is in contact with the first layer 10.
• a laser beam is irradiated from the first layer 10 side of the laminate 1.
• the irradiated laser beam passes through the first layer 10 and acts on the second layer 20.
• the second layer 20 is formed from the resin film of the present disclosure, the metal oxide develops color in the area of the second layer 20 irradiated with the laser beam, and the resin is carbonized by the heat of the laser beam.
• the colored and carbonized area of the second layer 20 becomes the printed area of the laser marking label.
• the printed area is the area of the second layer 20 that has turned black.
• laser marking label that includes a resin layer containing a metal oxide inside the film and causes the resin layer to develop color by laser irradiation may be particularly referred to as an internal coloring type laser marking label.
• laser marking is not limited to the act of writing meaningful information such as letters and symbols on the laminate 1, and the general act of coloring at least a part of the second layer 20 of the laminate 1 by irradiation with laser beam is referred to as "laser marking".
• the first layer 10 is a layer that transmits laser light.
• the first layer 10 may be referred to as a surface layer.
• an optically transparent film is used as the first layer 10.
• “optically transparent” means, for example, that the transmittance of laser light is 50% or more and the transmittance of visible light is 80% or more. If the transmittance of visible light in the first layer 10 is sufficiently high, when the laminate 1 after laser marking is viewed in plan from the first layer 10 side, the second layer 20, which is the lower layer, can be sufficiently seen through the first layer 10.
• the transmittance of laser light and the transmittance of visible light of the substrate film can be measured, for example, using a known spectrophotometer.
• the resin used as the material of the base film as the first layer 10 may be either a thermoplastic resin or a thermosetting resin. More specifically, the resin used as the material of the base 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, or a thermoplastic polyurethane-based resin (TPU). These resins are excellent in transparency, heat resistance, and handling. These resins may be used alone or in combination of two or more types.
• polyester-based resins are particularly suitable for use as materials for the base film, as they are capable of sufficiently transmitting laser light and have good handling and heat resistance.
• the versatility of the laminate 1 can be increased, and fine laser marking can be achieved.
• the polyester resin is preferably an aromatic ester resin from the viewpoint of suppressing deformation due to heat during laser marking. It is more preferable that the aromatic ester resin is a transparent resin from the viewpoint of suppressing deformation due to heat during laser light irradiation.
• aromatic ester resins examples include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexylene dimethylene terephthalate, and polyethylene naphthalate (PEN).
• PET polyethylene terephthalate
• PBT polybutylene terephthalate
• PEN polyethylene naphthalate
• the aromatic ester resin is polyethylene terephthalate.
• the thickness of the first layer 10 is not particularly restricted, but from the viewpoints of chemical resistance and abrasion resistance, a thicker thickness is preferable.
• the upper limit of the thickness of the first layer 10 may be set appropriately from the viewpoints of workability and cost.
• the thickness of the first layer 10 is preferably in the range of 10 ⁇ m to 200 ⁇ m.
• the resin used as the material of the base film as the first layer 10 may contain various additives within the range that does not impair print readability and adhesion.
• additives include dispersants, light stabilizers, heat stabilizers, plasticizers, fillers, and colorants.
• the surface of the first layer 10 on the side having the second layer 20 may be subjected to a corona treatment or provided with an easy-adhesion layer.
• the second layer 20 develops color when exposed to laser light.
• the second layer 20 may be referred to as a color-developing layer 20.
• the second layer 20 is formed of the resin film of the present disclosure.
• the thickness of the second layer 20 is not particularly limited, but is preferably 2 ⁇ m to 100 ⁇ m, more preferably 10 ⁇ m to 70 ⁇ m, and even more preferably 15 ⁇ m to 50 ⁇ m. If the thickness of the second layer 20 is 2 ⁇ m or more, the printing can be sufficiently recognized. Furthermore, if the thickness of the second layer 20 is 15 ⁇ m or more, the penetration resistance to laser light and the printability are improved. Furthermore, if the thickness of the second layer 20 is 100 ⁇ m or less, the productivity of the second layer 20 is improved. [Third layer 30]
• the third layer 30 has adhesiveness. In the present disclosure, the third layer 30 may be referred to as an adhesive layer 30.
• the adhesive used in the third layer 30 should be able to adhere to an adherend such as a resin plate, a metal plate, or a glass plate, and be able to be peeled off from the adherend.
• the adhesive strength of the adhesive used in the third layer 30 is preferably 0.1 N/25 mm to 40 N/25 mm, and more preferably 0.3 N/25 mm to 30/25 mm. If the adhesive strength is 0.1 N/25 mm or more, adhesion to the adherend is obtained. If the adhesive strength is 40 N/25 mm or less, the adhesive has good peelability.
• the adhesive strength is measured by attaching a 10 mm wide laminate to an aluminum plate with a load of 2 kg, leaving it at 23°C for 24 hours, and then peeling the laminate from the aluminum plate at a peel angle of 180°, a peel speed of 300 mm/min, and a measurement temperature of 23°C.
• the third layer 30 is made of a resin composition.
• the resin composition used for the third layer 30 include a (meth)acrylic adhesive, a silicone adhesive, and a synthetic rubber adhesive. From the viewpoint of increasing the adhesion between the second layer 20 and the third layer 30, a (meth)acrylic adhesive is more preferable.
• the thickness of the third layer 30 is not particularly limited, but is preferably in the range of 5 ⁇ m to 100 ⁇ m. If the thickness of the third layer 30 is in the above range, the workability (e.g., handleability) when bonding the laminate 1 to the adherend is improved.
• the resin composition used in the third layer 30 may contain various additives to the extent that the print readability and adhesion are not impaired.
• additives include a dispersant, a light stabilizer, a heat stabilizer, a plasticizer, a tackifier, a filler, and a colorant.
• Metal oxide pigments are preferred as the colorant used in the third layer 30. By using metal oxide pigments, the concealment of the base tends to be improved and the penetration of the laser tends to be reduced. Furthermore, the laser light is reflected by the metal oxide pigment, which increases the efficiency of the reduction reaction of the metal oxide present in the second layer 20, and as a result, the color development tends to be improved.
• metal oxide pigments include, but are not limited to, metal oxides containing at least one metal selected from the group consisting of titanium, molybdenum, copper, iron, nickel, chromium, zirconium, and neodymium.
• Laser marking of the laminate 1 can be performed by irradiating the laminate 1 with laser light from the first layer 10 side.
• the laser used for laser marking may be, for example, a near-infrared laser with a wavelength of about 1000 nm, a YVO4 laser, a YAG laser, or a fiber laser. Also, a UV laser with a wavelength of 300 nm to 400 nm may be used.
• Laser marking of the laminate 1 is usually performed before the laminate 1 is attached to the adherend. It is also possible to perform laser marking after the laminate 1 is attached to the adherend, but in this case, it is preferable that the laminate 1 has sufficient penetration resistance so that the adherend to which the laminate 1 is attached is not damaged by laser irradiation.
• the laminate 1 can be manufactured by forming the first layer 10, the second layer 20, and the third layer 30 in this order.
• the laminate 1 can be manufactured by a manufacturing method including at least a second layer forming step of forming the second layer 20 on one surface of the first layer 10, and a third layer forming step of forming the third layer 30 on the surface of the second layer 20 that is not in contact with the first layer 10 after the second layer forming step.
• the second layer formation process may be a process of applying the laser marking composition used in the second layer 20 to one side of the base film as the first layer 10, and curing it as necessary to form the second layer 20.
• the method of forming the second layer 20 may be the same as the method of manufacturing the resin film of the present disclosure described above.
• 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 that is not in contact with the first layer 10, and curing the resin composition to form the third layer 30.
• 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 bonding the third layer 30 to the surface of the second layer 20 after the second layer forming step that is not in contact with the first layer 10.
• the resin composition used for the third layer 30 is as described in the section "Third layer 30".
• the method for applying the resin composition used for the third layer 30 and the method for curing the resin composition used for the third layer 30 can also be performed by the known application method and curing method as described above.
• the method for manufacturing the laminate 1 may further include a first layer forming step of forming the first layer 10 before the second layer forming step, as necessary.
• the laminate of the present disclosure is not limited to the laminate 1 applied to a laser marking label having a three-layer structure having a first layer, a second layer, and a third layer.
• the laminate of the present disclosure may be a laminate consisting of a second layer and a third layer without a first layer, 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.
• the other layers include a colored layer, a printed layer, and an easy-adhesion layer.
• the colored layer is provided, for example, between the second layer and the third layer, and is a layer that imparts a color, a pattern, etc. to the entire laminate. By providing the colored layer, the design of the laminate is improved.
• the colored layer may be a layer containing a resin and a colorant.
• the resin contained in the colored layer is not particularly limited, and may be the same resin as the resin used in the first layer.
• the colorant contained in the colored layer is not particularly limited, and may be a pigment, a dye, or the like.
• the thickness of the colored layer is not particularly limited, and may be, for example, in the range of 1 ⁇ m to 50 ⁇ m.
• the colored layer may be formed by applying a resin composition for forming a colored layer to the surface of the second layer on the third layer side, or the colored layer may be formed separately and then attached to the surface of the second layer on the third layer side.
• an adhesive layer may be further provided between the colored layer and the second layer.
• the printing layer is, for example, a layer provided between the second layer and the third layer and formed by a printer. Specifically, for example, a resin composition containing a resin, a colorant, a solvent, etc. is applied to the surface of the layer adjacent to the printing layer along the shape of a desired pattern, character, etc., and the printing layer is formed by undergoing a process such as drying and curing as necessary.
• the design of the laminate is improved by providing the printing layer.
• the printing layer may be provided only in a part of the laminate surface direction, or may be provided on the entire laminate surface. Examples of printing methods include inkjet printer printing, screen printing, gravure printing, and flexographic printing.
• the printed layer is formed, for example, by printing on the surface of the second layer facing the third layer.
• the printed layer may be provided, for example, between the second layer and the colored layer, and may be formed by printing on the surface of the second layer facing the colored layer, or may be formed by printing on the surface of the colored layer facing the second layer.
• the laser marking composition used to form the second layer contains at least one of the above-mentioned urethane resin and filler.
• a monomer mixture consisting of 65.0 parts by mass of ethyl acrylate [EA; an acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms], 21.0 parts by mass of methyl methacrylate [MMA; an methacrylic acid alkyl ester monomer], and 14.0 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; an methacrylic acid alkyl ester monomer having a hydroxyl group] was prepared in a separate vessel. 20.0% by mass of this prepared monomer mixture was charged into the reaction vessel, and then heated and refluxed at the reflux temperature for 10 minutes.
• EA ethyl acrylate
• MMA methyl methacrylate
• 2HEMA 2-hydroxyethyl methacrylate
• Table 1 also lists the weight average molecular weight (Mw) and glass transition temperature (Tg) of the (meth)acrylic resin of Polymerization Example 1, as well as the proportion (A, mass%) of structural units derived from acrylic acid alkyl esters 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 methacrylic acid alkyl esters, all of which are contained in the total structural units of the (meth)acrylic resin.
• Mw weight average molecular weight
• Tg glass transition temperature
• the weight average molecular weight of the (meth)acrylic resin solution is a value measured by the above-mentioned method.
• the glass transition temperature Tg of the (meth)acrylic resin is a value obtained by converting the absolute temperature (K) calculated by the above formula into Celsius temperature (°C).
• (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 shown in Table 1 were used.
• 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 1 to 4 carbon atoms)
• nBMA stands for n-butyl methacrylate (a methacrylic acid alkyl ester monomer)
• 2EHA stands for 2-ethylhexyl acrylate (a acrylic acid alkyl ester monomer)
• AA stands for acrylic acid.
• Examples 1 to 16 and Comparative Examples 1 to 3 The components shown in Table 2 were blended in the ratios (parts by mass) shown in Table 2 and adjusted with ethyl acetate to a solids concentration of 20% by mass, to obtain laser marking compositions of Examples 1 to 16 and Comparative Examples 1 to 3.
• Table 2 also shows the proportion (A, %) of structural units derived from acrylic acid alkyl esters containing an alkyl group having 1 to 4 carbon atoms, the total proportion (A-1, %) of structural units derived from ethyl acrylate, structural units derived from methyl acrylate, and structural units derived from 2-hydroxyethyl acrylate, in all structural units of the (meth)acrylic resin, and the total proportion (B, %) of structural units derived from methacrylic acid alkyl esters.
• the solid content of the (meth)acrylic resin is indicated for Polymerization Examples 1 to 10.
• the white pigment is indicated for the solid content of the titanium oxide pigment. The details of each component shown in Table 2 are as follows.
• Color pigment 1 Bismuth oxide color pigment (42-970A, TOMATEC Corporation)
• Color pigment 2 Iron oxide color pigment (NX-512 Yellow, pigment manufactured by Dainichiseika Color & Chemicals Mfg. 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.)
• Both sides of a 50 ⁇ m-thick PET film (surface layer) were subjected to corona treatment, and the laser marking composition was applied to one side of the PET film so that the film thickness after drying would be the film thickness shown in Table 2.
• the composition was then dried at 70° C. for 3 minutes and then at 150° C. for 3 minutes to form a laser marking layer (color-developing layer).
• a laser beam was irradiated onto the surface layer of the laser marking laminate using a FAYb laser marker LP-Z130 (manufactured by Panasonic Corporation) under the conditions of output (printing intensity) 25%, pulse cycle 50 Hz, line width 0.07 mm, and 2000 mm/sec, to print a 15 mm square fill pattern.
• the laser marking laminate was then attached to a glass plate, and a concealment test paper specified in JIS K 5600-4-1:1999 was placed on the back of the glass side to measure the color difference between the laminate itself and the printed part with a colorimeter (trade name "spectrophotometer CM-3600A", manufactured by Konica Minolta, Inc.), and ⁇ E * ab was calculated.
• the results obtained are shown in Table 2. If ⁇ E * ab is 5 or more, there is no practical problem. The larger ⁇ E * ab, the better the visibility.
• the evaluation results shown in Table 2 show that the laser marking laminate having a color-developing layer (resin film) obtained from the laser marking composition of the Example achieves high levels of visibility, readability, and suppression of gas generation, compared to the laser marking laminate having a color-developing layer (resin film) obtained from the laser marking composition of the Comparative Example.
• Laminate 10 First layer (surface layer) 20 Second layer (coloring layer) 30 Third layer (adhesive layer)

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