Laminated body, thermal recording medium, and image forming method

Abstract

The present invention relates to a laminate having a colloidal crystal layer that develops color by light interference, a thermal recording medium, and an image forming method. The laminate of the present invention is formed by sequentially configuring a substrate (3), an undercoat layer (2) formed of a resin, and a colloidal crystal layer (1) that develops color by light interference. The resin forming the undercoat layer (2) has a glass transition point in the range of -35°C to 100°C, and the colloidal crystal layer (1) contains core-shell resin microparticles (4) and achromatic black microparticles (8), and has voids (7). The core-shell resin microparticles (4) contain a shell in the range of 10% to 150% by mass based on the mass of the core, and the shell has a glass transition point in the range of -60°C to 40°C. The thickness of the colloidal crystal layer (1) is set to the range of 0.5μm to 100μm.

Description

[0001] This application claims priority based on Japanese patent application No. 2020-191240, filed on November 17, 2020, and incorporates all disclosed contents into this application. Technical Field

[0002] The present invention relates to a laminate having a colloidal crystal layer that develops color due to interference of light, and a thermosensitive recording medium using the laminate. Background Art

[0003] Colloidal crystals, with regularly arranged particles, are actively researched as a type of photonic crystal that exhibits unique optical properties, such as structural color known as Bragg reflection and light confinement effects utilizing the photonic band gap. While colloidal crystals are relatively easy to manufacture, they are difficult to immobilize while maintaining excellent color development, resulting in a lack of established technology for mass-producing colloidal crystal coatings. Research is also underway to develop materials that effectively utilize colloidal crystals to respond to external stimuli such as heat, but these efforts have encountered challenges such as inconspicuous color changes in the coatings and poor resistance to various coatings.

[0004] Patent document 1 discloses a laminate formed by forming a colloidal crystal layer containing an adhesive component on a substrate formed with a primer layer and fixing it. The laminate including the colloidal crystal layer is heated by irradiation with an infrared laser, and the thermoplastic resin particles in the colloidal crystal are deformed, thereby changing the color. However, since the distribution of the adhesive component in the colloidal crystal layer of the laminate has a large deviation, the adhesion between the particles becomes fragile and the colloidal crystal layer is easily broken. In addition, the adhesion between the primer layer and the colloidal crystal layer is poor, and interface peeling is easily generated. Therefore, for example, when a printer including a thermal head is used for heat treatment, the colloidal crystal layer will be cut in the part contacted by the head, making it difficult to form an image. In addition, cracks are also easily generated on the coating film in the part after heat treatment, and the various coating films have poor resistance.

[0005] Patent Document 2 discloses a colloidal crystal layer in which an elastomer precursor is flowed into voids in a colloidal crystal layer to replace the voids with a resin component.

[0006] Patent Document 3 discloses a colloidal crystal layer in which core-shell resin particles are used in colloidal crystals and voids are completely filled with fluidized shells. The core-shell resin particles include a shell layer having film-forming properties and a core layer for maintaining particle shape.

[0007] The colloidal crystal layers described in Patent Documents 2 and 3 exhibit excellent film durability because their voids are replaced by a resin component. However, due to the small difference in refractive index between the particles and the matrix component, excellent color development is not achieved in thin films. Furthermore, no color change occurs upon heating.

[0008] Patent Document 4 discloses a colloidal crystal layer that utilizes colloidal crystals with an inverse opal structure, with the particle portion composed of a meltable material and the matrix portion composed of a cured gelatin. While this colloidal crystal layer changes color upon heating, the production process is extremely complex. Furthermore, the colloidal crystal layer suffers from poor resistance and durability.

[0009] Furthermore, similar to Patent Documents 2 and 3, the difference in refractive index between the particles and the matrix component is small, so excellent color development cannot be achieved in the thin film. In addition, no color change occurs by heat treatment.

[0010] Patent Document 5 discloses a colloidal crystal layer composed of regularly arranged microcapsules containing hydrocarbon compounds and partially replacing the matrix with a fluoropolymer. Due to the small difference in refractive index between the particles and the matrix component, this colloidal crystal layer fails to exhibit excellent color development in a thin film. Furthermore, heat treatment does not produce color changes. Furthermore, hydrocarbon components dissolved from damaged microcapsules penetrate into the non-heated area, adversely affecting the film's physical properties.

[0011] [Prior art literature]

[0012] [Patent Document]

[0013] Patent Document 1: International Publication No. 2006 / 129506

[0014] Patent Document 2: Japanese Patent Application Laid-Open No. 2006-028202

[0015] Patent Document 3: Japanese Patent Publication No. 2005-516083

[0016] Patent Document 4: Japanese Patent Application Laid-Open No. 2009-210501

[0017] Patent Document 5: Japanese Patent Application Laid-Open No. 2009-293976 Summary of the Invention

[0018] [Problems to be solved by the invention]

[0019] The problem to be solved by the present invention is to provide a laminate, a thermosensitive recording medium formed using the laminate, and an image forming method. The laminate has excellent structural color even when the colloidal crystal layer is a thin film with a thickness of 0.5 μm to 100 μm, and is excellent in storage stability and durability. Furthermore, the color of the colloidal crystal layer is irreversibly faded by heat treatment, and can be suitably used as a thermosensitive recording medium.

[0020] [Technical means to solve the problem]

[0021] The present invention relates to a laminate, which is formed by sequentially arranging a substrate, a primer layer formed of a resin, and a colloidal crystal layer that develops color through interference of light. In the laminate, the resin forming the primer layer has a glass transition point in the range of -35°C to 100°C, the colloidal crystal layer contains core-shell type resin microparticles and achromatic black microparticles, and has voids, the core-shell type resin microparticles contain a shell in the range of 10% to 150% by mass based on the mass of the core, the shell has a glass transition point in the range of -60°C to 40°C, and the thickness of the colloidal crystal layer is in the range of 0.5μm to 100μm.

[0022] Furthermore, the present invention relates to the laminate, wherein the core has a glass transition point of 50° C. or higher.

[0023] Furthermore, the present invention relates to the laminate, wherein the colloidal crystal layer contains the achromatic black fine particles in an amount within a range of 0.3% by mass to 3% by mass based on the mass of the core-shell type resin fine particles.

[0024] Furthermore, the present invention relates to the laminate, wherein the acid value of the resin forming the primer layer is within a range of 5 mgKOH / g to 140 mgKOH / g.

[0025] The present invention also relates to the laminate, wherein the core of the core-shell type resin fine particle contains a structural unit derived from an aromatic ethylenically unsaturated monomer in an amount within a range of 70% by mass to 100% by mass based on the mass of the core.

[0026] In addition, the present invention relates to the laminate, wherein the shell of the core-shell type resin fine particles contains, based on the mass of the shell, a constituent unit derived from an ethylenically unsaturated monomer (s-1) having an octanol / water partition coefficient in the range of 1 to 2.5 in the range of 70 mass % to 99.5 mass %, and contains a constituent unit derived from an ethylenically unsaturated monomer (s-2) having an octanol / water partition coefficient of less than 1 in the range of 0.5 mass % to 15 mass %.

[0027] Furthermore, the present invention relates to the laminate, wherein the core-shell type resin fine particles include a structural unit derived from a reactive surfactant.

[0028] Furthermore, the present invention relates to the laminated body, further comprising a resin layer on the colloidal crystal layer.

[0029] The present invention also relates to a thermosensitive recording material using the laminate.

[0030] The present invention also relates to the thermosensitive recording medium, further comprising an adhesive layer.

[0031] Furthermore, the present invention relates to an image forming method characterized in that the color of the colloidal crystal layer is faded by heating the thermosensitive recording medium.

[0032] Effects of the Invention

[0033] According to the present invention, a laminate, a thermosensitive recording medium formed using the laminate, and an image forming method can be provided. The laminate has excellent structural color even when the colloidal crystal layer is a thin film with a thickness of 0.5 μm to 100 μm, and is excellent in storage stability and durability. Furthermore, the color of the colloidal crystal layer irreversibly fades by heat treatment, and the laminate can be suitably used as a thermosensitive recording medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram schematically showing a laminate according to one embodiment of the present invention.

[0035] Figure 2 This is a diagram schematically showing a state in which the color of the colloidal crystal layer is faded by heating the laminate according to one embodiment of the present invention.

[0036] Explanation of symbols

[0037] 1: Colloidal crystal layer (densely packed structure)

[0038] 2: Base coat

[0039] 3: Base material

[0040] 4: Core-shell resin particles

[0041] 5: Shell

[0042] 6: Nuclear

[0043] 7: Gap

[0044] 8: Colorless black particles

[0045] 9: Colloidal crystal layer after heating (sparsely packed structure)

[0046] 10: Matrix

[0047] 15: Laminated body DETAILED DESCRIPTION

[0048] <Laminated body>

[0049] The laminate of the present invention has a structure comprising a substrate, an undercoat layer, and a colloidal crystal layer laminated in this order. The colloidal crystal layer comprises core-shell resin particles and achromatic black particles and has voids. The resin forming the undercoat layer has a glass transition point within the range of -35°C to 100°C. The core-shell resin particles comprise a shell in a range of 10% to 150% by mass based on the mass of the core, and the shell has a glass transition point within the range of -60°C to 40°C. Furthermore, the thickness of the colloidal crystal layer is set to a range of 0.5 μm to 100 μm.

[0050] Due to this structure, the laminate of the present invention exhibits excellent structural color even in thin films with colloidal crystal layers of 0.5 μm to 100 μm. Furthermore, the laminate exhibits excellent storage stability and various resistance properties (friction resistance, substrate conformability, water resistance, and solvent resistance). Furthermore, heating the laminate using a thermal head or laser significantly changes the color of the colloidal crystal layer.

[0051] Figure 1 : is a schematic cross-sectional view showing an example of the laminate of the present invention. Figure 1 As shown, the laminate 15 of the present invention has a structure comprising a substrate 3, an undercoat layer 2, and a colloidal crystal layer 1 laminated in this order. The colloidal crystal layer 1 includes core-shell resin particles 4, each comprising a core 6 and a shell 5, and achromatic black particles 8. The core-shell resin particles 4 have a densely packed structure with residual voids 7, and the shells 5 are fused and bonded between the core-shell resin particles 4. Due to the large difference in refractive index between the core-shell resin particles 4 and the voids 7, the laminate 15 of the present invention exhibits a bright structural color even in a thin film.

[0052] On the other hand, if a certain amount of thermal energy is applied to the laminate 15 and the laminate is heated, the shells 5 of the core-shell type resin particles 4 flow and fill the gaps. Figure 2 As shown, the heated colloidal crystal layer 9 adopts a sparse packing structure. In this sparse packing structure, since the refractive index difference between the particle-shaped core 6 and the matrix 10 is reduced, the thin film does not show structural color and becomes a translucent layer, and the color of the layer below the heated colloidal crystal layer 9 (sparse packing structure) can be visually recognized.

[0053] Hereinafter, embodiments of the present invention will be described in detail.

[0054] <Base coat>

[0055] The primer layer in the present invention is disposed between the substrate and the colloidal crystal layer and serves to inhibit interfacial delamination between the substrate and the colloidal crystal layer. The primer layer improves adhesion to the colloidal crystal layer, resulting in a laminate with excellent substrate conformability, abrasion resistance, and water resistance. The primer layer is preferably insoluble in water.

[0056] The resin forming the primer layer is not particularly limited and can be appropriately selected depending on the type of substrate or colloidal crystal layer. Preferably, it comprises at least one resin selected from the group consisting of acrylic resins, urethane resins, polyolefin resins, polyester resins, and composite resins formed by combining these resins. Among these, in terms of excellent adhesion to the substrate or colloidal crystal layer, and excellent water resistance, solvent resistance, and transparency of the primer layer, preferably, it comprises at least one resin selected from the group consisting of acrylic resins and urethane resins, more preferably, it comprises an acrylic resin, and even more preferably, it comprises an acrylic resin containing styrene in its constituent units (hereinafter, "styrene acrylic resin").

[0057] The use of an acrylic resin is preferred because it provides excellent adhesion to the substrate or the colloidal crystal layer, excellent substrate conformability of the primer layer, and excellent water resistance, and thus improves the substrate conformability, abrasion resistance, and water resistance of the laminate.

[0058] These resins may be used alone or in combination of two or more.

[0059] From the perspective of suppressing the effects on the colloidal crystal layer, the resin forming the primer layer preferably has a low content of unreacted components or residual solvents, and an aqueous resin can be preferably used. Here, the term "aqueous resin" refers to a resin that can be dispersed or dissolved in an aqueous medium, and the aqueous medium includes water or a dispersion medium or solvent that is miscible with water.

[0060] When the resin forming the primer layer is an aqueous resin, the method for producing the aqueous resin is not particularly limited. From the perspective of obtaining a resin with low viscosity, high solid content, and high molecular weight, an emulsion polymerization method is preferred.

[0061] [Acrylic resin]

[0062] When the resin forming the primer layer is a water-based acrylic resin, the water-based acrylic resin can be obtained by emulsification polymerization of ethylenically unsaturated monomers including (meth)acrylic acid monomers.

[0063] {Ethylenically unsaturated monomer}

[0064] Examples of the ethylenically unsaturated monomer include aromatic ethylenically unsaturated monomers such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate, phenoxydiethylene glycol(meth)acrylate, phenoxytetraethylene glycol(meth)acrylate, phenoxyhexaethylene glycol(meth)acrylate, and phenyl(meth)acrylate; and aromatic ethylenically unsaturated monomers such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth)acrylate, tert-butyl(meth)acrylate, pentyl(meth)acrylate, heptyl(meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, undecyl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, tetradecyl(meth)acrylate, and octyl(meth)acrylate. Ethylenically unsaturated monomers containing a straight-chain alkyl group or a branched alkyl group, such as hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate; ethylenically unsaturated monomers containing an alicyclic alkyl group, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and 1-adamantyl (meth)acrylate; ethylenically unsaturated monomers containing a fluorinated alkyl group, such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate. Ethylenically unsaturated monomers; (anhydride) maleic acid, fumaric acid, itaconic acid, citraconic acid, or alkyl monoesters or alkenyl monoesters thereof, β-(meth)acryloyloxyethyl succinate, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, etc.; ethylenically unsaturated monomers containing a sulfonic group such as sodium 2-acrylamide 2-methylpropanesulfonate, methyl allyl sulfonate, sodium methyl allyl sulfonate, allyl sulfonate, sodium allyl sulfonate, ammonium allyl sulfonate, vinyl sulfonic acid, etc.;(Meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentyloxymethyl-(meth)acrylamide, N,N-bis(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethyl methacrylamide, N,N-bis(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethyl methacrylamide, N,N-bis(propoxymethyl)acrylamide, N-butoxymethyl-N-(propoxymethyl) methacrylamide, N,N-bis(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl) methacrylamide, N,N-bis(pentyloxymethyl)acrylamide, N-methoxymethyl-N-(pentyloxymethyl) methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide Ethylenically unsaturated monomers containing amide groups, such as acrylamide, N,N-diethylacrylamide, and diacetoneacrylamide; ethylenically unsaturated monomers containing hydroxyl groups, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, and allyl alcohol; methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and other polyethylene glycol containing hydroxyl groups. Ethylenically unsaturated monomers containing oxyethylene groups; examples thereof include amino group-containing ethylenically unsaturated monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methylethylaminoethyl (meth)acrylate; epoxy group-containing ethylenically unsaturated monomers such as glycidyl (meth)acrylate and 3,4-epoxycyclohexyl (meth)acrylate; and keto group-containing ethylenically unsaturated monomers such as diacetone (meth)acrylamide and acetoacetoxy (meth)acrylate.Allyl (meth)acrylate, 1-methallyl (meth)acrylate, 2-methallyl (meth)acrylate, 1-butenyl (meth)acrylate, 2-butenyl (meth)acrylate, 3-butenyl (meth)acrylate, 1,3-methyl-3-butenyl (meth)acrylate, 2-chloroallyl (meth)acrylate, 3-chloroallyl (meth)acrylate, o-allylphenyl (meth)acrylate, 2-(allyloxy)ethyl (meth)acrylate, allyl lactoyl (meth)acrylate, citronellyl (meth)acrylate, Geranyl (meth)acrylate, rose (meth)acrylate, cinnamyl (meth)acrylate, diallyl maleate, diallyl itaconate, vinyl (meth)acrylate, vinyl butenoate, vinyl oleate, vinyl linolenate, 2-(2'-vinyloxyethoxy)ethyl (meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, tetraethylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, 1,1,1-trihydroxymethylethane diacrylate, 1,1,1- Ethylenically unsaturated monomers having two or more ethylenically unsaturated groups, such as trihydroxymethylethane triacrylate, 1,1,1-trihydroxymethylpropane triacrylate, divinylbenzene, divinyl adipate, diallyl isophthalate, diallyl phthalate, and diallyl maleate; γ-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltributoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane; Alkoxysilyl group-containing ethylenically unsaturated monomers such as propyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-acryloxypropylmethyldimethoxysilane, 3-methacryloxymethyltrimethoxysilane, 3-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, and vinylmethyldimethoxysilane; and hydroxymethyl group-containing ethylenically unsaturated monomers such as N-hydroxymethyl(meth)acrylamide, N,N-dihydroxymethyl(meth)acrylamide, and alkyl-etherified N-hydroxymethyl(meth)acrylamide.

[0065] These monomers may be used alone or in combination of two or more.

[0066] The ethylenically unsaturated monomer may have a reactive group for the purpose of crosslinking the undercoat layer and the core-shell type resin fine particles forming the colloidal crystal layer.

[0067] As the reactive group, for example, epoxy, carboxyl, hydroxyl, ketone, hydrazide groups can be enumerated, more preferably ketone group.Especially when reactive group is ketone group and the cross-linking agent described later is hydrazide cross-linking agent, ketone-hydrazide cross-linking can be formed.In addition, when water-based acrylic resin is the resin microparticle that can be dispersed in aqueous medium, if the ethylenically unsaturated monomer with the ketone group that hydrophilicity is high is used for copolymerization and forms, then ketone group is imported into the outside of resin microparticle, i.e. near the interface with aqueous medium, thinks that can form crosslinking with hydrazide cross-linking agent efficiently.

[0068] When the aqueous acrylic resin contains ketone groups, the ketone group content is preferably in the range of 0.05 mmol / g to 0.3 mmol / g based on the mass of the aqueous acrylic resin. By incorporating ketone groups within the range of 0.05 mmol / g to 0.3 mmol / g, crosslinking is achieved without hindering the fusion of the aqueous acrylic resin, resulting in a more robust bond between the primer layer and the colloidal crystal layer. Consequently, the resulting laminate exhibits excellent resistance properties (abrasion resistance, water resistance, and solvent resistance).

[0069] {Free Radical Polymerization Initiator}

[0070] As the radical polymerization initiator used in the production of the aqueous acrylic resin, a known oil-soluble polymerization initiator or water-soluble polymerization initiator can be used. These may be used alone or in combination of two or more.

[0071] The oil-soluble polymerization initiator is not particularly limited, and examples thereof include organic peroxides such as benzoyl peroxide, t-butyl peroxybenzoate, t-butyl hydroperoxide, t-butyl peroxy(2-ethylhexanoate), t-butyl peroxy-3,5,5-trimethylhexanoate, and di-t-butyl peroxide; 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 1,1'-azobis-cyclohexane-1-carbonitrile.

[0072] In emulsion polymerization, a water-soluble polymerization initiator is preferably used. Examples of the water-soluble polymerization initiator include conventionally known substances such as ammonium persulfate (APS), potassium persulfate (KPS), hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

[0073] {Surfactant}

[0074] In the manufacture of water-based acrylic resin, surfactant is usually used. By using surfactant, the stability or monodispersity of the resin microparticles can be improved. As surfactant, anionic or nonionic surfactant can be listed, preferably anionic surfactant. These can be used alone or in combination of two or more.

[0075] Examples of surfactants include anionic reactive surfactants, anionic non-reactive surfactants, nonionic reactive surfactants, and nonionic non-reactive surfactants. Here, the term "reactive surfactant" refers to a surfactant that can polymerize with the ethylenically unsaturated monomer. More specifically, it refers to a surfactant having a reactive group that can undergo polymerization with the ethylenically unsaturated bond. Examples of reactive groups include alkenyl groups such as vinyl, allyl, and 1-propenyl, and (meth)acryloyl groups.

[0076] By using a reactive surfactant, the free surfactant component contained in the aqueous acrylic resin is reduced, and the adverse effect on the particle arrangement of the colloidal crystals is suppressed, thereby obtaining a laminate exhibiting brighter structural coloration in the thin film.

[0077] {Other Ingredients}

[0078] In the production of the water-based acrylic resin, a reducing agent, a buffer, a chain transfer agent, and a neutralizing agent may be used as needed.

[0079] [Urethane resin]

[0080] When the resin forming the primer layer is a water-based urethane resin, the water-based urethane resin is not particularly limited. The water-based urethane resin can be obtained, for example, by dispersing a urethane resin obtained by polyaddition polymerization of any polyol and polyisocyanate in a non-aqueous system in water using a surfactant, or by introducing a hydrophilic group such as a carboxyl group into the urethane resin to achieve self-emulsification.

[0081] Waterborne urethane resins can be compounded with various resins by introducing functional groups at the ends through the reaction of diamine or dihydrazide compounds with terminal isocyanate groups, or by chain extension to increase molecular weight. Furthermore, waterborne urethane resins can be grafted onto acrylic or olefinic resin backbones via reactive groups.

[0082] Examples of the polyol constituting the urethane resin include polyether polyol, polyester polyol, polycarbonate polyol, polyolefin polyol, and castor oil polyol.

[0083] Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, poly(ethylene / propylene) glycol, and polytetramethylene glycol.

[0084] Examples of polyester polyols include reaction products of difunctional or trifunctional polyols with dibasic acids. Examples of difunctional polyols include ethylene glycol, propylene glycol, dipropylene glycol, diethylene glycol, triethylene glycol, butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, polyoxyethylene glycol, polyoxypropylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, octanediol, butylethylpentanediol, 2-ethyl-1,3-hexanediol, cyclohexanediol, and bisphenol A. Examples of trifunctional polyols include glycerol, trimethylolpropane, and pentaerythritol. Examples of dibasic acids include terephthalic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, hydrogenated dimer acid, phthalic anhydride, isophthalic acid, and trimellitic acid.

[0085] Examples of the polycarbonate polyol include reaction products of the above-mentioned bifunctional polyol with dialkyl carbonate, alkylene carbonate, and diaryl carbonate.

[0086] Examples of the polyolefin polyol include hydroxyl group-containing polybutadiene, hydroxyl group-containing hydrogenated polybutadiene, hydroxyl group-containing polyisoprene, hydroxyl group-containing hydrogenated polyisoprene, hydroxyl group-containing chlorinated polypropylene, and hydroxyl group-containing chlorinated polyethylene.

[0087] Examples of polyisocyanates constituting the urethane resin include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, lysine diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, and 3,3'-dimethoxy-4,4'-biphenylene diisocyanate. , 3,3'-dichloro-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate and other aromatic polyisocyanates; tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate and other aliphatic polyisocyanates; isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and other alicyclic polyisocyanates.

[0088] When synthesizing a urethane resin, a low molecular weight diol may be used in combination for the purpose of adjusting the urethane bond concentration or introducing various functional groups. The low molecular weight diol is preferably a diol having a molecular weight of 500 or less, and examples thereof include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, dipropylene glycol, glycerol, trimethylolpropane, trimethylolethane, 1,2,6-butanetriol, pentaerythritol, sorbitol, N,N-bis(2-hydroxypropyl)aniline, dimethylol acetic acid, dimethylol propionic acid, dimethylol butyric acid, 2,2-dimethylol butyric acid, 2,2-dimethylol valeric acid, dihydroxysuccinic acid, dihydroxypropionic acid, and dihydroxybenzoic acid.

[0089] Examples of compounds that can be used in the terminal modification or chain extension reaction include diamines such as hydrazine, ethylenediamine, propylenediamine, hexamethylenediamine, nonamethylenediamine, xylylenediamine, isophoronediamine, piperazine and its derivatives, phenylenediamine, toluenediamine, xylylenediamine, and N-(β-aminoethyl)ethanolamine; and dihydrazides such as adipic acid dihydrazide and isophthalic acid dihydrazide.

[0090] Examples of commercially available aqueous urethane resins include the SuperFlex series (SF-170, SF-210, etc.) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Ucoat and Permalyn series (UX-310, UX-3945, etc.) manufactured by Sanyo Chemical Co., Ltd., the Urearno series (W-600, W-321, etc.) manufactured by Arakawa Chemical Co., Ltd., the Adekapon titer series (HUX-420A, HUX-386, etc.) manufactured by Adeka, the UW series (UW-5002, UW-5020, etc.) manufactured by Ube Industries, Ltd., and the Acrit series (WBR2000U, WBR2101, WEM-200U, etc.) manufactured by Daisei Fine Chemicals Co., Ltd.

[0091] [Polyolefin resin]

[0092] When the resin forming the primer layer is a water-based polyolefin resin, an acid-modified polyolefin obtained by modifying a base resin such as ethylene-propylene copolymer, propylene-1-butene copolymer, or ethylene-propylene-1-butene copolymer with maleic acid or the like can be used as the water-based polyolefin resin. The polyolefin resin can also be composited with a different resin by grafting an acrylic resin backbone or the like.

[0093] The aqueous polyolefin resin can be obtained as an aqueous dispersion by dispersing it in water using a surfactant or by introducing a hydrophilic group into the polyolefin resin to make it self-emulsifiable.

[0094] Examples of commercially available water-based polyolefin resins include the Super Clone series and Auroren series (E-480T, AE-301, etc.) manufactured by Nippon Paper Industries, Ltd., the Arrow Base series (SB-1230N, SB-1200, etc.) manufactured by Unitika, and the Aptolok series (BW-5550, etc.) manufactured by Mitsubishi Chemical.

[0095] [Polyester resin]

[0096] When the resin forming the primer layer is a water-based polyester resin, there are no particular limitations on the water-based polyester resin. The water-based polyester resin can be obtained by reacting a difunctional polyol or trifunctional polyol with a dibasic acid. The difunctional polyol or trifunctional polyol and the dibasic acid may be as described above under "Urethane Resin."

[0097] The aqueous polyester resin can be obtained as an aqueous dispersion by dispersing it in water using a surfactant or by introducing a hydrophilic group into the polyester resin to make it self-emulsifiable.

[0098] Examples of commercially available aqueous polyester resins include the Pluscoat series (Z-730, Z-760, etc.) manufactured by Huying Chemical.

[0099] It is important that the resin forming the primer layer of the present invention has a glass transition point (Tg) within the range of -35°C to 100°C. By having a glass transition point within the above range, excessive intrusion of the primer component into the voids of the colloidal crystal layer is suppressed, and a good structural color can be maintained for a long time. In addition, the wettability with the substrate and the surface of the core-shell type resin microparticles becomes good, and the adhesion is excellent. In addition, the fusion between the primer layer and the shell of the core-shell type resin microparticles is promoted, and the strength of the bonding part is excellent. As a result, the obtained laminate is excellent in color development, storage stability, and various resistances (friction resistance, substrate followability).

[0100] The resin is preferably a resin having a glass transition point within a range of -30°C to 70°C, and may have a plurality of glass transition points.

[0101] The glass transition point in this specification can be determined using a differential scanning calorimeter (DSC).

[0102] The resin forming the primer layer preferably has a carboxyl group. The acid value of the resin is preferably in the range of 5mgKOH / g to 140mgKOH / g, more preferably in the range of 5mgKOH / g to 70mgKOH / g. If the acid value is within the range, the adhesion between the primer layer and the substrate is improved. In addition, the adhesion between the colloidal crystal layer and the primer layer is improved. Furthermore, the situation in which the primer layer swells or dissolves due to water and the like and destroys the regular arrangement of the colloidal crystals is also suppressed. As a result, the obtained laminate has excellent color development and resistance (substrate followability, water resistance).

[0103] [Primer composition]

[0104] The method for forming the primer layer is not particularly limited. For example, the primer layer can be formed by applying a primer composition containing an aqueous resin and water to form the primer layer on a substrate and drying the composition as needed.

[0105] The thickness of the primer layer is not particularly limited. From the perspective of primer layer functionality and productivity, it is preferably 0.5 μm to 50 μm, more preferably 2 μm to 20 μm, and even more preferably 2 μm to 10 μm. A primer layer thickness of 0.5 μm or greater improves adhesion between the primer layer and the substrate layer, and between the primer layer and the colloidal crystal layer, resulting in excellent substrate conformability, abrasion resistance, and water resistance in the laminate.

[0106] The thickness of each layer in this specification can be measured by observing a cross section of the laminate using a scanning electron microscope.

[0107] The primer composition may contain various additives such as a hydrophilic solvent, achromatic black particles, a photothermal conversion agent, a crosslinking agent, etc., in order to improve the coating properties, the color development properties of the laminate, the sensitivity of color change, and the film resistance, within a range that does not adversely affect the physical properties of the laminate.

[0108] {Hydrophilic Solvent}

[0109] Examples of the hydrophilic solvent include monohydric alcohol solvents such as ethanol, n-propanol, and isopropanol; glycol solvents such as ethylene glycol, 1,3-propanediol, and propylene glycol; glycol ether solvents such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, and triethylene glycol monoethyl ether; lactam solvents such as N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, and ε-caprolactam; and amide solvents such as formamide and N-methylformamide.

[0110] {Colorless black particles}

[0111] Achromatic black microparticles absorb scattered light within the laminate, making the color more pronounced. Achromatic black microparticles can be those colored with a black dye, carbon black, graphite, or the like. Carbon black is preferred because it minimizes the effect on the visible region's reflectance spectrum and offers excellent durability, such as weather resistance.

[0112] Furthermore, the achromatic black particles absorb laser light such as infrared laser light and promote the heating of the core-shell resin particles in the adjacent colloidal crystal layer. This allows the shell to fluidize efficiently and fill the gaps, resulting in a sensitive color change.

[0113] {Photothermal conversion agent}

[0114] The photothermal conversion agent (except for the achromatic black microparticles) plays the role of promoting the heating of the core-shell resin microparticles in the adjacent colloidal crystal layer when the laminate is irradiated with laser light. As the photothermal conversion agent, for example, cyanine pigments, crotonium pigments, polymethine pigments, azulenium pigments, squarylium pigments, thiopyrylium pigments, naphthoquinone pigments, anthraquinone pigments, phthalocyanine pigments, naphthalocyanine pigments, azo pigments, thioamide pigments, dithiol pigments, and indoaniline pigments can be listed.

[0115] {Crosslinker}

[0116] The crosslinking agent that may be included in the primer composition is not particularly limited. Examples thereof include hydrazide compounds (polyhydrazides) having two or more hydrazide groups that react with active carbonyl groups to form keto-hydrazide crosslinks, polyisocyanate compounds that react with hydroxyl groups or amino groups to form carbamate bonds or urea bonds, and epoxy compounds and carbodiimide compounds that react with carboxyl groups or amino groups. These compounds may be selected as appropriate.

[0117] For example, when the resin contained in the primer composition has a carboxyl group, crosslinking can be achieved using an epoxy crosslinking agent or a polycarbodiimide crosslinking agent. For example, when the resin contained in the primer composition has a hydroxyl group, crosslinking can be achieved using a polyisocyanate crosslinking agent. For example, when the resin contained in the primer composition has a ketone group, crosslinking can be achieved using a hydrazide crosslinking agent.

[0118] As the crosslinking agent, as described above, a hydrazide crosslinking agent is preferably used to form a ketone-hydrazide crosslink. Examples of the hydrazide crosslinking agent include adipic acid dihydrazide and a water-soluble resin modified with a polyfunctional hydrazide group.

[0119] <Colloidal crystal layer>

[0120] The laminate of the present invention comprises a colloidal crystal layer that emits color through light interference. Due to its regularly arranged structure, the colloidal crystal layer exhibits structural color derived from Bragg reflection, fulfilling the color-emitting function. Furthermore, the colloidal crystal layer comprises core-shell resin microparticles and achromatic black microparticles and has voids.

[0121] The regularly arranged structure of the core-shell resin particles facilitates adhesion between the shells of adjacent core-shell resin particles, as well as between the shells of the core-shell resin particles and the layers adjacent to them, resulting in excellent coating durability. The achromatic black particles absorb scattered light in the colloidal crystal layer, enhancing the color. Furthermore, the presence of voids in the colloidal crystal layer increases the refractive index difference between the particles and the voids, resulting in the laminate exhibiting excellent structural color.

[0122] Furthermore, the achromatic black particles absorb laser light, heating the particles and promoting fusion of the core-shell resin particles in the adjacent colloidal crystal layers. This allows the shells to fluidize efficiently and fill the gaps, resulting in a sensitive color change.

[0123] [Core-shell type resin particles]

[0124] The core-shell resin microparticles are polymers whose core and shell are insoluble in water, and comprise a structure of a core (inner layer) and a shell (outer layer) that are incompatible with each other. The core maintains a spherical shape, and the shell has fluidity and functions as a bonding site. The core-shell resin microparticles in this specification may have a multilayer structure inside each of the core and the shell, and may also be inclined to the composition. The composition comprising the core-shell resin microparticles is applied to a substrate, etc., and a medium such as water evaporates, and the particles are advected and regularly arranged, and the shells of the particles are welded to each other to the extent that the gaps are not filled, forming a colloidal crystal layer.

[0125] The shells of the core-shell resin particles also bind the achromatic black particles contained in the colloidal crystal layer, preventing their loss. Consequently, the layered product, comprising the core-shell resin particles, achromatic black particles, and voids, exhibits a vibrant structural color and exhibits excellent film resistance (abrasion resistance, substrate conformability, water resistance, and solvent resistance).

[0126] On the other hand, if a certain level of thermal energy is applied to the laminate, the shells flow and fill the gaps in the heated areas. This causes the structural color of the colloidal crystal layer to fade, significantly changing the color of the laminate. Furthermore, the film formed by the flowing shells in the faded areas is extremely flexible and thus crack-free. As a result, the heated laminate exhibits the same excellent film resistance (friction resistance, substrate conformability, water resistance, and solvent resistance) as the unheated laminate.

[0127] The core-shell resin particles described above importantly contain a shell in a range of 10% to 150% by mass, based on the mass of the core. A shell content of 10% or greater fills the voids during heating, resulting in a laminate exhibiting excellent color change. Furthermore, the adhesion between the core-shell resin particles and between the core-shell resin particles and the primer layer is strengthened, resulting in superior substrate conformability.

[0128] When the shell content is 150% by mass or less, the shells can be prevented from excessively fusing, filling voids and deteriorating color development during drying of the colloidal crystal layer composition and long-term storage of the laminate. This results in an excellent color development and storage stability of the laminate, exhibiting a distinct color change upon heat treatment. The shell content is preferably in the range of 30% to 100% by mass.

[0129] It is important that the shell of the core-shell resin microparticles has a glass transition point within the range of -60°C to 40°C. If the glass transition point is within the range, the situation in which the voids in the colloidal crystal layer are excessively filled due to the fusion of the shells of the core-shell resin microparticles can be suppressed during heat drying. Furthermore, the fusion of the shells is promoted between the core-shell resin microparticles or between the core-shell resin microparticles and the primer layer, or between the core-shell resin microparticles and the resin layer described later, fully demonstrating the strength of the bonded portion. In addition, when heated, the shell can be fluidized with good sensitivity and fill the voids. Thus, the obtained laminate has excellent color development and storage stability, and shows a significant color change by heat treatment. Furthermore, the various film resistances (friction resistance, substrate followability, water resistance, solvent resistance) of the heated portion and the non-heated portion are excellent.

[0130] The core of the core-shell resin fine particles preferably has a glass transition point of 50°C or higher, more preferably within the range of 60°C to 150°C. A glass transition point of 50°C or higher can suppress deformation of the core shape due to external heat or force. This allows the laminate to maintain excellent color development even during long-term storage.

[0131] The shell and the core may have multiple glass transition points.

[0132] The core-shell type resin fine particles in the present invention are not particularly limited, but are preferably polymers of ethylenically unsaturated monomers, more preferably acrylic resins, and even more preferably styrene acrylic resins.

[0133] The method for producing core-shell type resin microparticles is not particularly limited. Examples include methods such as emulsion polymerization, in which ethylenically unsaturated monomers are polymerized in an aqueous medium, or phase inversion emulsification, in which polymerization is performed in a non-aqueous system followed by desolvation and then the phase is inverted to an aqueous phase. Emulsion polymerization is preferably used because it can achieve high molecular weight, low viscosity, and a high solids concentration. In emulsion polymerization, two-stage polymerization, in which the monomer composition is varied in the first and second stages and then added dropwise, or multi-stage polymerization, in which the monomer composition is varied in three or more stages and then added dropwise, can be used.

[0134] The core-shell type resin fine particles can be produced by the two-stage polymerization, specifically, according to the following procedure.

[0135] (1) First, an aqueous medium and a surfactant are placed in a reaction vessel and the temperature is raised. Then, under a nitrogen atmosphere, an emulsion of the first ethylenically unsaturated monomers forming the core is added dropwise while a free radical polymerization initiator is added. After the reaction begins, particles gradually grow according to the amount added dropwise, forming core particles.

[0136] (2) After the first stage of dropwise addition is complete and the heat has subsided, the second stage of the ethylenically unsaturated monomer emulsion, which will form the shell, is added dropwise. Additional initiator may be added at this time. The second stage of ethylenically unsaturated monomer added dropwise is temporarily distributed to the core particles, but as polymerization proceeds, it precipitates as a polymer onto the outer layer of the core particles, forming a shell layer.

[0137] {Ethylenically unsaturated monomer}

[0138] Examples of the ethylenically unsaturated monomers forming the core-shell type resin fine particles include the core-forming ethylenically unsaturated monomer (bc) and the shell-forming ethylenically unsaturated monomer (bs), and the description of the "ethylenically unsaturated monomer" in the "Primer Coat Layer" can be used for both.

[0139] The core of the core-shell resin microparticles preferably contains constituent units derived from aromatic ethylenically unsaturated monomers in a range of 70% to 100% by mass, based on the mass of the core. By including constituent units derived from aromatic ethylenically unsaturated monomers within this range, the refractive index of the core increases, the refractive index difference between the particles and the voids in the colloidal crystal layer increases, and the color development properties of the laminate are further improved. This results in a laminate with a greater contrast between the color changes of the unheated and heated portions, superior color development properties, and a clear color change upon heating. Furthermore, the contrast between the core and shell is clear, allowing for sufficient fusion of the shells, thereby improving the abrasion resistance of the laminate.

[0140] Examples of the aromatic ethylenically unsaturated monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, and phenoxyhexaethylene glycol (meth)acrylate.

[0141] In addition, the shell of the core-shell type resin microparticles preferably contains, based on the mass of the shell, a constituent unit derived from an ethylenically unsaturated monomer (s-1) having an octanol / water partition coefficient (hereinafter, LogKow) in the range of 1 to 2.5 in the range of 70 mass% to 99.5 mass%, and a constituent unit derived from an ethylenically unsaturated monomer (s-2) having a LogKow of less than 1 in the range of 0.5 mass% to 15 mass%.

[0142] The content of the constituent unit by being derived from ethylenic unsaturated monomer (s-1) and ethylenic unsaturated monomer (s-2) is described scope, and the polymkeric substance generated by the dripping component of second section is incompatible with the core that comprises the constituent unit that is derived from aromatic series ethylenic unsaturated monomer, generate polymer at the interface of nucleus particle and water, therefore can form the particle that the contrast of core and shell is more clear and definite.Thus, not only the bonding force between particle by the welding of shell is improved, and the situation of shell excessive hydrophilization is suppressed, and each film tolerance (friction resistance, substrate following property, water resistance) of multilayer body is more excellent.In addition, the dispersion stability when mixing with achromatic black microparticle is also excellent, therefore the further stabilization to the coatability of base material, can obtain not uneven or concavoconvex film, the chromogenicity of multilayer body further improves.

[0143] The octanol / water partition coefficient (LogKow) is represented by the following formula 1 and is used as an indicator of whether a certain compound A is easily partitioned into the aqueous phase or the oil phase (octanol). In the relationship between the aqueous dispersion of resin microparticles and the ethylenically unsaturated monomer added dropwise thereto, the higher the octanol / water partition coefficient of the ethylenically unsaturated monomer, the more easily the ethylenically unsaturated monomer is partitioned into the interior of the particles, and the lower the value, the more easily it is partitioned into the aqueous phase. The octanol / water partition coefficient of each ethylenically unsaturated monomer is a value calculated at 25°C using the YMB method (physical property estimation function) of the Hansen Solubility Parameters software HSPiP.

[0144] Formula 1: Octanol / water partition coefficient = Log (concentration of compound A in the octanol phase / concentration of compound A in the aqueous phase)

[0145] Examples of ethylenically unsaturated monomers (s-1) having an octanol / water partition coefficient in the range of 1 to 2.5 include methyl methacrylate (1.13), ethyl acrylate (1.08), ethyl methacrylate (1.63), propyl acrylate (1.60), propyl methacrylate (2.16), n-butyl acrylate (2.23), tert-butyl acrylate (1.99), trifluoroethyl acrylate (1.41), trifluoroethyl methacrylate (1.96), and ethylene glycol dimethacrylate (2.07).

[0146] When the octanol / water partition coefficient is less than 1, the solubility of the ethylenically unsaturated monomer in water becomes good. Examples of the ethylenically unsaturated monomer (s-2) having an octanol / water partition coefficient of less than 1 include methyl acrylate (0.59), methoxyethyl acrylate (0.24), methoxyethyl methacrylate (0.81), hydroxyethyl acrylate (-0.22), hydroxyethyl methacrylate (0.33), 4-hydroxybutyl acrylate (0.90), acrylic acid (0.14), methacrylic acid (0.67), acrylamide (-0.53), methacrylamide (0), isopropylacrylamide (0.96), diacetoneacrylamide (0.82), 2-acetoacetoxyethyl methacrylate (0.59), and glycidyl methacrylate (0.59).

[0147] The numerical values ​​in parentheses in the monomers (s-1) and (s-2) represent the octanol / water partition coefficients of the monomers.

[0148] Furthermore, the ethylenically unsaturated monomer used in forming the core-shell resin particles may also have a reactive group for the purpose of forming crosslinks within the colloidal crystal layer and between the colloidal crystal layer and the layer in contact with the colloidal crystal layer. By forming crosslinks within the colloidal crystal layer and between the colloidal crystal layer and the layer in contact with the colloidal crystal layer, various film resistances (friction resistance, solvent resistance) of the laminate are improved.

[0149] Crosslinking within the colloidal crystal layer and between the colloidal crystal layer and the layer in contact with the colloidal crystal layer can be introduced by the following methods: a method of causing the reactive groups of core-shell type resin microparticles to react with each other, a method of causing the reactive groups of core-shell type resin microparticles to react with the reactive groups of the primer layer and / or resin layer described later, a method of causing the reactive groups of core-shell type resin microparticles to crosslink with each other via a multifunctional crosslinking agent, and a method of causing the reactive groups of core-shell type resin microparticles to crosslink with the reactive groups of the primer layer and / or resin layer described later.

[0150] As the reactive group, the description of the section "Ethylenically Unsaturated Monomer" in the above-mentioned "Primer Coat Layer" can be cited.

[0151] When the core-shell resin particles contain ketone groups, the ketone group content is preferably in the range of 0.05 mmol / g to 0.3 mmol / g based on the mass of the core-shell resin particles. By maintaining the ketone group content within the range of 0.05 mmol / g to 0.3 mmol / g, crosslinking is achieved without hindering the fusion of the shells, resulting in stronger bonding between particles and between layers, and stronger bonding between the primer layer and the colloidal crystal layer. Consequently, the resulting laminate exhibits excellent film resistance (abrasion resistance, solvent resistance).

[0152] When the core-shell type resin fine particles have reactive groups, the reactive groups are preferably introduced into the shell. Introducing reactive groups into the shell is preferred because thermal fusion and crosslinking based on entanglement of polymer chains produce a synergistic effect.

[0153] {Free Radical Polymerization Initiator}

[0154] As the radical polymerization initiator used in the production of the core-shell type resin fine particles, a known oil-soluble polymerization initiator or water-soluble polymerization initiator can be used, and the description of the "Radical Polymerization Initiator" in the above-mentioned "Undercoat Layer" can be cited.

[0155] {Surfactant}

[0156] In the production of core-shell resin microparticles, a surfactant is usually used. By using a surfactant, the stability or monodispersity of the core-shell resin microparticles can be improved. As the surfactant, anionic or nonionic surfactants can be listed, preferably anionic surfactants. These surfactants can refer to the description of the item "Surfactant" in the "Primer Coat". From the perspective of the influence on particle arrangement caused by the residual surfactant after synthesis or the film resistance, a reactive low-molecular surfactant is preferred. By using a reactive surfactant, the residual surfactant is reduced, and the color development and water resistance of the obtained laminate are excellent. The core-shell resin microparticles in the present invention preferably contain constituent units derived from a reactive surfactant.

[0157] {Other Ingredients}

[0158] In the production of the core-shell type resin fine particles, a reducing agent, a buffer, a chain transfer agent, and a neutralizing agent may be used as needed.

[0159] {Properties of core-shell resin microparticles}

[0160] The average particle size of the core-shell resin microparticles herein is preferably in the range of 180 nm to 330 nm. When the average particle size is 180 nm or greater, the color development of the colloidal crystals in the visible light region becomes more pronounced. When the average particle size is 330 nm or less, the color development of the colloidal crystals in the visible light region is excellent, and scattering by the particles is suppressed, further improving the color development properties.

[0161] The average particle size herein can be measured by a dynamic light scattering method (measurement apparatus: Nanotrac UPA, manufactured by Microtrac BEL), and the peak value of the obtained volume particle size distribution data (histogram) is defined as the average particle size.

[0162] The coefficient of variation (Cv value) of the average particle size of the core-shell type resin fine particles is preferably 30% or less. The coefficient of variation is a numerical value indicating the uniformity of the particle size and can be calculated by the following formula.

[0163] Formula: Coefficient of variation Cv value (%) = standard deviation of particle size / average particle size × 100

[0164] [Where the standard deviation has the same units as the mean particle size]

[0165] By arranging highly monodisperse fine particles with a coefficient of variation of 30% or less, the regularity of the particle arrangement is improved, resulting in a brighter and more distinct structural color.

[0166] [Achromatic black particles]

[0167] The achromatic black particles absorb scattered light within the colloidal crystal layer, making the color more pronounced. Furthermore, they absorb laser light, accelerating the heating of adjacent core-shell resin particles. This promotes the fusion of the core-shell resin particles, rapidly filling the gaps between them and resulting in a more pronounced and sensitive color change.

[0168] As achromatic black microparticles, the description of "Achromatic Black Microparticles" in the "Undercoat Layer" section can be referred to. Carbon black is preferred from the perspective of minimal impact on the reflectance spectrum in the visible region and excellent durability such as weather resistance. Carbon black can be either a dispersed type, dispersed in water using a dispersant, or a self-dispersed type. Self-dispersed carbon black is preferred from the perspective of not being affected by the dispersant on the arrangement of the microparticles.

[0169] The average particle size of the achromatic black microparticles is preferably in the range of 30nm to 300nm, more preferably 30nm to 150nm. In addition, the content of the achromatic black microparticles is preferably in the range of 0.3% by mass to 3% by mass based on the mass of the core-shell type resin microparticles. If the average particle size and the content of the achromatic black microparticles are in the above range, the excess scattered light in the colloidal crystals is appropriately absorbed, and at the same time, the regular arrangement of the core-shell type resin microparticles is not adversely affected. In addition, the excessive loss of achromatic black microparticles from the colloidal crystal layer can be suppressed. As a result, the obtained laminate has excellent color development, the color change during heat treatment is obvious, and various film resistances (water resistance, solvent resistance) are excellent.

[0170] [Gap]

[0171] Regarding the presence or absence of voids in the colloidal crystal layer, when voids with a mode pore size of 10 nm to 200 nm are detected by the nitrogen adsorption method, it is judged to have voids. The Barrett-Joyner-Halenda (BJH) method is used from the adsorption side of the nitrogen adsorption isotherm obtained by the nitrogen adsorption method, and the peak top is set as the mode pore size. The parameters of the BJH method are the Harkins-Jura and volume frequency distribution of the reference t curve. The device named BELSORP-maxII manufactured by Microtrac BEL is used for the measurement. Furthermore, the porosity of the colloidal crystal layer is preferably 10% to 40%. The porosity of the colloidal crystal layer can also be directly measured by mercury intrusion or gas adsorption, and can also be obtained based on the ratio of the true density of each layer.

[0172] [Colloidal crystal layer composition]

[0173] The method for forming the colloidal crystal layer is not particularly limited. For example, it can be formed by applying a colloidal crystal layer composition containing core-shell resin fine particles, achromatic black fine particles, and water to the undercoat layer of a substrate including an undercoat layer. The thickness of the colloidal crystal layer is 0.5 μm to 100 μm, more preferably 3 μm to 20 μm. When the thickness of the colloidal crystal layer falls within this range, a laminate with excellent color development and a clear color change upon heating can be obtained.

[0174] The colloidal crystal layer composition may contain a hydrophilic solvent, a crosslinking agent, etc. for the purpose of improving coating properties and coating film resistance, as long as the composition does not adversely affect the particle arrangement or the physical properties of the laminate.

[0175] {Hydrophilic Solvent}

[0176] The hydrophilic solvent can refer to the description of the "Hydrophilic Solvent" in the "Primer Coat Layer".

[0177] {Crosslinker}

[0178] The cross-linking agent that may be contained in the colloidal crystal layer composition is not particularly limited, and the description of the "cross-linking agent" in the "undercoat layer" above can be cited.

[0179] As the crosslinking agent, a hydrazide crosslinking agent is preferably used in order to form a ketone-hydrazide crosslink. Examples of the hydrazide crosslinking agent include adipic acid dihydrazide and a water-soluble resin modified with a polyfunctional hydrazide group.

[0180] <Resin layer>

[0181] The laminate of the present invention may further include a resin layer on the colloidal crystal layer for the purpose of protecting the colloidal crystal layer and improving various film resistances (friction resistance, water resistance, solvent resistance). The resin layer can be formed by coating a resin composition on the colloidal crystal layer.

[0182] The resin forming the resin layer is not particularly limited. From the perspective of excellent adhesion to the core-shell type resin microparticles, an acrylic resin is preferred, and a styrene acrylic resin is more preferred. In addition, from the perspective of suppressing penetration into the colloidal crystal layer, the resin layer is preferably a layer formed by film-forming water-based resin microparticles.

[0183] The method for producing water-based resin microparticles is not particularly limited, and for example, can be produced by the following emulsion polymerization. First, an aqueous medium and a surfactant are placed in a reaction tank and heated to a predetermined temperature. On the other hand, water, a surfactant, and an ethylenically unsaturated monomer containing a (meth)acrylic acid monomer are placed in a dropping tank and stirred to prepare an emulsion. Thereafter, under a nitrogen atmosphere, the prepared emulsion is added dropwise to the reaction tank while a free radical polymerization initiator is added. After the reaction begins, the polymer particle nuclei are generated, and the particles gradually grow, thereby forming acrylic resin microparticles.

[0184] As the ethylenically unsaturated monomers that can be used in the production of the water-based resin fine particles, the description of the item "Ethylenically Unsaturated Monomers" in the above-mentioned "Primer Coat Layer" can be cited.

[0185] Regarding the radical polymerization initiator, surfactant, and other components that can be used in the production of the water-based resin fine particles, the descriptions of the "Radical Polymerization Initiator", "Surfactant", and "Other Components" in the above-mentioned "Primer Coat Layer" can be cited.

[0186] The water-based resin microparticles preferably have reactive groups for forming crosslinks. As ethylenically unsaturated monomers, ethylenically unsaturated monomers having reactive groups may also be used. The presence of reactive groups in the water-based resin microparticles enables crosslinking within the resin layer and between the resin layer and the colloidal crystal layer. Crosslinking within the resin layer improves the coating strength of the resin layer, and crosslinking between the resin layer and the colloidal crystal layer further strengthens the adhesion between the resin layer and the colloidal crystal layer. Thus, the resulting laminate has excellent solvent resistance.

[0187] Crosslinking inside the resin layer can be introduced by a method in which reactive groups of water-based resin fine particles react with each other or a method in which reactive groups of water-based resin fine particles react via a polyfunctional crosslinking agent.

[0188] Crosslinking of the resin layer and the colloidal crystal layer can be introduced by reacting reactive groups of water-based resin particles and core-shell type resin particles with each other or by reacting reactive groups of water-based resin particles and core-shell type resin particles via a polyfunctional crosslinking agent.

[0189] As the reactive group, the description of the section "Ethylenically Unsaturated Monomer" in the above-mentioned "Primer Coat Layer" can be cited.

[0190] When the water-based resin microparticles contain ketone groups, the ketone group content is preferably in the range of 0.05 mmol / g to 0.3 mmol / g based on the mass of the water-based resin microparticles. By setting the ketone group content in the range of 0.05 mmol / g to 0.3 mmol / g, the fusion of the water-based resin microparticles is not hindered, allowing crosslinking to form. This improves the coating strength of the resin layer and further strengthens the bond between the colloidal crystal layer and the resin layer. Furthermore, since excessive crosslinking is suppressed, the fluidity of the shell of the core-shell type resin microparticles is not adversely affected. Consequently, the resulting laminate exhibits a distinct color change during heat treatment, improving solvent resistance.

[0191] The average particle size of the water-based resin microparticles is preferably in the range of 50 nm to 300 nm, more preferably in the range of 80 nm to 300 nm. The water-based resin microparticles preferably have a glass transition point in the range of -30°C to 30°C. If the average particle size and the glass transition point are in the above range, the water-based resin microparticles are blocked by the surface layer of the colloidal crystal layer, and the resin component is suppressed from penetrating into the voids of the colloidal crystal layer. In addition, due to the excellent film-forming properties, a homogeneous resin layer without uneven coating or cracks can be formed. As a result, the obtained laminate has excellent color development and various film resistances (friction resistance, solvent resistance).

[0192] [Resin composition]

[0193] The method for forming the resin layer is not particularly limited, and can be formed, for example, by applying a resin composition containing aqueous resin particles and water onto the colloidal crystal layer and drying as needed. The dried and film-formed resin layer is preferably a water-insoluble layer.

[0194] The thickness of the resin layer is not particularly limited, but is preferably 3 μm to 50 μm, more preferably 5 μm to 20 μm, from the viewpoint of color development and productivity of the laminate.

[0195] When the thickness of the resin layer is 3 μm or more, the protective function of the laminated body by the resin layer can be fully exerted, and the friction resistance and water resistance of the laminated body can be improved.

[0196] Regarding the resin composition, if it is within a range that does not adversely affect the physical properties of the colloidal crystal layer, it may also contain various additives such as achromatic black particles, photothermal conversion agents, hydrophilic solvents, crosslinking agents, etc. for the purpose of improving the color development of the laminate or increasing the sensitivity of color change, improving the coating properties, or improving the physical properties of the coating brought about by crosslinking.

[0197] {Colorless black particles}

[0198] The achromatic black microparticles absorb scattered light within the laminate, making the laminate's color more pronounced. This is particularly effective when the laminate is used in back-side printing, as a distinct color is achieved. Furthermore, when the laminate is heated using laser light, the achromatic black microparticles in the resin layer absorb infrared light, thereby accelerating the heating of the core-shell resin microparticles in the adjacent colloidal crystal layer, more quickly filling the voids in the shells. Consequently, the heat treatment results in a pronounced color change.

[0199] As the achromatic black fine particles, the description of the item "Achromatic Black Fine Particles" in the above-mentioned "Undercoat Layer" can be cited.

[0200] {Hydrophilic Solvent}

[0201] The hydrophilic solvent can refer to the description of the "Hydrophilic Solvent" in the "Primer Coat Layer".

[0202] {Crosslinker}

[0203] The cross-linking agent is not particularly limited, and the description of the "cross-linking agent" in the "primer layer" can be used.

[0204] {Photothermal conversion agent}

[0205] The photothermal conversion agent (excluding achromatic black fine particles) is not particularly limited, and the description of the "Photothermal Conversion Agent" in the "Undercoat Layer" can be used.

[0206] <Laminated body>

[0207] The laminate of the present invention comprises, in order, a substrate, a primer layer, and a colloidal crystal layer that develops color through light interference, wherein the thickness of the colloidal crystal layer ranges from 0.5 μm to 100 μm. The production method is not particularly limited, but preferably includes the following steps 1 and 2. A drying step may be included during the formation of each layer, if necessary.

[0208] Step 1) A step of applying a primer composition on a substrate and drying it as needed to form a primer layer.

[0209] Step 2) A step of applying a colloidal crystal layer composition containing core-shell type resin fine particles and achromatic black fine particles on the primer layer formed in step 1 and drying the composition as needed to form a colloidal crystal layer having a thickness of 0.5 μm to 100 μm.

[0210] When the laminate has a resin layer, it is preferable to perform the following step 3 after the step 2.

[0211] Step 3) A step of applying a resin composition containing aqueous resin particles and water on the colloidal crystal layer formed in step 2 and drying it as needed to form a resin layer.

[0212] The coating method for the primer composition, colloidal crystal layer composition, and resin composition is not particularly limited. Examples include: plateless printing methods such as inkjet, spray, dip, and spin coating; plate-based printing methods such as gravure coaters, gravure coaters, knife coaters, rod coaters, blade coaters, flexographic coaters, and roll coaters; and stencil printing methods such as screen printing. The primer composition, colloidal crystal layer composition, and resin composition may be printed on the entire surface or as a patterned layer.

[0213] In the case of a drying step, the drying method is not particularly limited, and can be appropriately selected from known methods such as heating drying, hot air drying, infrared drying, microwave drying, and drum drying. One drying method can be used alone, or two or more can be used in combination. From the perspective of reducing damage to the substrate and drying efficiently, hot air drying is preferably used.

[0214] The drying temperature of the primer composition and the resin composition is preferably in the range of 50°C to 100°C, and the drying temperature of the colloidal crystal layer composition is preferably in the range of 25°C to 80°C.

[0215] [Base material]

[0216] The substrate is not particularly limited and can be selected from known substrates. Examples of the substrate include thermoplastic resin substrates such as polyvinyl chloride sheets, polyethylene terephthalate (PET) films, polypropylene (PP) films, polyethylene (PE) films, nylon (Ny) films, polystyrene films, and polyvinyl alcohol films; metal substrates such as aluminum foil; glass substrates; coated paper substrates; and cloth substrates.

[0217] The laminate of the present invention has a primer layer, so even when using a non-polar film substrate such as polyethylene terephthalate film, polypropylene film, polyethylene film, etc., which is difficult to fix due to the peeling of the conventional colloidal crystal layer, it can still exhibit excellent substrate followability, friction resistance, water resistance, solvent resistance, and color development properties.

[0218] The substrate may have a smooth surface or a concave-convex surface, and may be transparent, translucent, or opaque. When the colloidal crystal layer is viewed from the substrate side, the substrate is preferably transparent. In addition, in order to make the color of the colloidal crystal more obvious, the substrate may be a substrate pre-colored in black, or a substrate partially printed with a pigment ink, or may be subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0219] These substrates may be used alone or in the form of a stack of two or more.

[0220] Thermal recording media

[0221] The thermosensitive recording medium of the present invention comprises the laminate of the present invention. The laminate of the present invention is characterized in that heat treatment fluidizes the shells of the colloidal crystal layer, thereby filling the interstices. This causes the color of the colloidal crystal layer to fade, resulting in a significant color change. Therefore, the laminate of the present invention can be used as a thermosensitive recording medium. The image forming method of the present invention comprises a step of heating the thermosensitive recording medium of the present invention to fade the color of the colloidal crystal layer.

[0222] The heating treatment method can be appropriately selected within the range that does not impair the effects of the present invention. For example, the following methods can be listed: using a thermal printer to make the thermal head touch the stack and heat it; irradiating laser light so that the achromatic black particles in the colloidal crystal layer absorb light and heat the adjacent core-shell type resin particles; oven heating, microwave heating, and boiling treatment.

[0223] The image formation that utilizes laser to carry out can carry out image formation when not damaging base material, resin layer, non-image forming portion, so preferably.In addition, with regard to the little aspect of the adverse effect that base material, the resin that forms undercoat layer, core-shell type resin microparticles, the resin that forms resin layer cause, preferably use infrared laser.As infrared laser marking machine (laser marker), can enumerate: CO2 laser marking machine (wavelength 10600nm) or YVO4 laser marking machine (wavelength 1064nm), yttrium aluminum garnet (yttrium aluminum garnet, YAG) laser marking machine (wavelength 1064nm), optical fiber laser marking machine (wavelength 1090nm) etc.

[0224] The heating temperature can be appropriately changed according to the design of the core-shell type resin fine particles. Taking into account storage stability, color change during heating, thermal damage to the substrate, etc., it is preferably in the range of 100°C to 200°C, more preferably in the range of 120°C to 160°C.

[0225] The thermosensitive recording medium of the present invention may also have other layers, such as a hard coat layer and / or an adhesive layer, within the scope of not impairing the effects of the present invention, and may also be in a form further bonded to other substrates via these layers. In addition, these other layers may be arranged on the substrate side or on the colloidal crystal layer side. When the thermosensitive recording medium further has an adhesive layer, it can be used as an adhesive sheet.

[0226] [Adhesive layer]

[0227] The adhesive layer plays a role in adhering the laminate of the present invention having the colloidal crystal layer to any adherend. The thickness of the adhesive layer is usually in the range of 5 μm to 100 μm.

[0228] The adhesive layer can be formed using a known pressure-sensitive adhesive without particular limitation. The pressure-sensitive adhesive can be appropriately selected according to the type of substrate or colloidal crystal layer, and preferably comprises at least one resin selected from the group consisting of acrylic resin and urethane resin.

[0229] The resin forming the adhesion layer is preferably low in the content of unreacted components or residual solvent, and water-based resin can be used suitably. If the unreacted components or residual solvent contained in the resin are low, the influence on base material, colloidal crystal layer, and resin layer can be suppressed. Here, so-called water-based resin represents a resin that can be dispersed or dissolved in an aqueous medium. In addition, aqueous medium represents an aqueous dispersion medium or an aqueous solvent, and also comprises a dispersion medium or a solvent that can be mixed with water except comprising water. Can be for the purpose of adhesion properties, make the adhesion layer include various additives such as a cross-linking agent or a tackifier (tackifier).

[0230] [Example]

[0231] The present invention will be described in more detail below by way of examples. However, the following examples are not intended to limit the scope of the present invention. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. In addition, blank spaces in the tables indicate that no blending was performed.

[0232] [Acid value]

[0233] The acid value was calculated by potentiometric titration using a dried resin with a potassium hydroxide-ethanol solution in accordance with Japanese Industrial Standard (JIS) K2501. The titration was performed using an automatic titrator COM-1600 manufactured by Hiranuma Sangyo Co., Ltd.

[0234] [Glass transition point (Tg)]

[0235] The glass transition point was measured using a DSC (differential scanning calorimeter, manufactured by TA Instruments). Specifically, approximately 2 mg of a dried resin sample was weighed onto an aluminum pan, placed on a DSC measurement stand, and the glass transition point was determined by reading the baseline shift (inflection point) toward the endothermic side of the DSC curve obtained at a temperature increase of 5°C / min.

[0236] [Average particle size]

[0237] A dispersion of core-shell resin particles was diluted 500-fold with water, and approximately 5 mL of the dilution was measured using dynamic light scattering (with a measuring instrument manufactured by Nanotrac UPA and Microtrac BEL). The peak of the obtained volume particle size distribution data (histogram) was defined as the average particle size. The coefficient of variation (Cv), which represents the variation in particle size, was calculated using the following formula.

[0238] Cv value % = particle diameter standard deviation / average particle diameter × 100

[0239] <Production of Aqueous Dispersion of Resin Forming Primer Coat Layer>

[0240] [Production Example 1]

[0241] 7.5 parts of styrene, 10.0 parts of benzyl methacrylate, 25.0 parts of methyl methacrylate, 16.0 parts of 2-ethylhexyl acrylate, 38.0 parts of n-butyl acrylate, 3.0 parts of methacrylic acid, 0.5 part of 3-methacryloxypropyltriethoxysilane, 4.8 parts of a 20% aqueous solution of KH-10, and 40.4 parts of ion-exchanged water were mixed in advance and stirred to prepare an emulsion of ethylenically unsaturated monomers.

[0242] In a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux, 68.9 parts of ion-exchanged water and 0.25 parts of a 20% aqueous solution of Aqualon KH-10 (hereinafter referred to as KH-10) manufactured by Daiichi Industrial Pharmaceutical, a reactive surfactant, and 3% of the emulsion, were added. The internal temperature was raised to 80°C and the atmosphere was fully purged with nitrogen. Then, 2.0 parts of a 5% aqueous solution of potassium persulfate as an initiator were added to initiate emulsion polymerization. While maintaining the internal temperature at 80°C, the remainder of the emulsion and 2.0 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 3 hours, followed by a further 4-hour reaction to obtain an aqueous dispersion of styrene acrylic resin. After the reaction was completed, 2.4 parts of 25% aqueous ammonia were added for neutralization, and the solids content of the aqueous dispersion was adjusted to 45.0% using ion-exchanged water. The resin had an acid value of 19.5 mgKOH / g and a Tg of -8.8°C.

[0243] [Manufacturing Examples 2 to 7]

[0244] A styrene acrylic resin aqueous dispersion was obtained in the same manner as in Preparation Example 1, except that the composition was changed to that shown in Table 1. After the reaction was completed, 25% aqueous ammonia was added to neutralize the dispersion in an equimolar ratio with the carboxyl groups in the resin. The solids content was then adjusted to 45.0% using ion-exchanged water.

[0245] [Table 1]

[0246]

[0247] [Production Example 8]

[0248] A reaction vessel equipped with a stirrer, thermometer, two dropping funnels, and a reflux device was charged with 185.0 parts of ion-exchanged water, 42.9 parts of JONCRYL 67 (BASF styrene acrylic resin with an Mw of 12,500 and an acid value of 213 mgKOH / g) as a polymer dispersant, and 11.1 parts of 25% aqueous ammonia. The temperature was raised while stirring to dissolve the polymer dispersant. After heating to 80°C under nitrogen reflux, a mixture of 14.0 parts of styrene, 15.0 parts of n-butyl methacrylate, 30.0 parts of 2-ethylhexyl acrylate, 10.0 parts of cyclohexyl acrylate, 30.0 parts of n-butyl acrylate, and 1.0 part of glycidyl methacrylate was added dropwise from one of the two dropping funnels over 2 hours. From the other dropping funnel, 3.5 parts of a 20% aqueous ammonium persulfate solution was added dropwise over 2 hours. After the dropwise addition was completed, the mixture was allowed to react for a further 5 hours to obtain an aqueous dispersion of styrene acrylic resin. After the reaction was completed, the solid content was adjusted to 40.0% with ion-exchanged water. The obtained resin had an acid value of 63.9 mgKOH / g and a Tg of -1.3°C.

[0249] [Production Example 9]

[0250] A styrene acrylic resin aqueous dispersion having a solids content of 40.0% was obtained in the same manner as in Preparation Example 8, except that the amount of JONCRYL 67 added was changed to 53.8 parts and the amount of 25% aqueous ammonia was changed to 13.9 parts. The obtained resin had an acid value of 74.6 mgKOH / g and a Tg of 3.4°C.

[0251] [Production Example 10]

[0252] A styrene acrylic resin aqueous dispersion having a solids content of 40.0% was obtained in the same manner as in Preparation Example 8, except that JONCRYL 67 was replaced with JONCRYL 678 (a styrene acrylic resin manufactured by BASF, having an Mw of 8500 and an acid value of 215 mgKOH / g), the amount of ion-exchanged water added to the reaction vessel was changed to 334 parts, JONCRYL 678 was changed to 177.8 parts, and the amount of 25% ammonia water was changed to 46.3 parts. The obtained resin had an acid value of 137.6 mgKOH / g and a Tg of 35.9°C.

[0253] [Production Example 11]

[0254] A styrene acrylic resin aqueous dispersion having a solids content of 40.0% was obtained in the same manner as in Preparation Example 8, except that JONCRYL 67 was replaced with JONCRYL 678 (a styrene acrylic resin manufactured by BASF, having an Mw of 8500 and an acid value of 215 mgKOH / g), the amount of ion-exchanged water added to the reaction vessel was changed to 362 parts, JONCRYL 678 was changed to 203 parts, and the amount of 25% ammonia water was changed to 52.9 parts. The obtained resin had an acid value of 144.1 mgKOH / g and a Tg of 38.4°C.

[0255] [Production Example 12]

[0256] A reaction vessel equipped with a stirrer, thermometer, and reflux was charged with 19.6 parts of PTG-2000SN (polytetramethylene glycol, manufactured by Hodogaya Chemical), 20.3 parts of P-2011 (3-methyl-1,5-pentanediol / adipic acid / terephthalic acid-based polyester polyol, manufactured by Kuraray), 91.6 parts of C-2090 (polycarbonate polyol, manufactured by Kuraray), and 19.7 parts of dimethylolbutyric acid; 48.8 parts of isophorone diisocyanate as a polyisocyanate; and 40.0 parts of methyl ethyl ketone and 10.0 parts of dipropylene glycol dimethyl ether as solvents. The mixture was heated to 78°C under a nitrogen atmosphere while stirring. 0.02 parts of titanium diisopropoxybis(ethylacetoacetate) was added as a catalyst, and the reaction was allowed to proceed for 6 hours to obtain a urethane prepolymer with isocyanate groups at both ends. After adding 13.5 parts of triethylamine as a neutralizing agent, 400 parts of ion-exchanged water and 2.4 parts of ethylenediamine as a chain extender were added. The solvent was removed under reduced pressure while the phase transition to the aqueous phase took place. This accelerated the chain extension reaction of the isocyanate groups in the aqueous medium, producing an aqueous dispersion of a urethane resin with a solids content of 30.0%. The resulting resin had an acid value of 37.4 mgKOH / g and a Tg of 94.0°C.

[0257] [Manufacturing Examples 13 to 15]

[0258] A urethane resin aqueous dispersion having a solid content of 30.0% was obtained in the same manner as in Production Example 9 except that the formulation composition was changed to that shown in Table 2. Table 2 shows the acid value and Tg of the obtained resin.

[0259] [Table 2]

[0260] Table 2

[0261]

[0262] The abbreviations of Table 2 are shown below.

[0263] PTG-2000SN: Polytetramethylene glycol manufactured by Hodogaya Chemical (functional group number 2, hydroxyl value 57.0 mgKOH / g, molecular weight 2,000)

[0264] P-2011: Kuraray 3-methylpentanediol / adipic acid / terephthalic acid polyester polyol (functionality 2, hydroxyl value 55.0 mgKOH / g, molecular weight 2,000)

[0265] C-2090: Polycarbonate polyol manufactured by Kuraray (functional group 2, hydroxyl value 56.0 mgKOH / g, molecular weight 2,000)

[0266] [Production Example 16]

[0267] A reaction vessel equipped with a stirrer, a thermometer, and a reflux system was charged with 100 parts of Auroren 350S (a maleic anhydride-modified polypropylene-polyethylene copolymer manufactured by Nippon Paper Industries, Ltd.), 100 parts of toluene, and 30.0 parts of Noigen TDS-120 (a polyoxyethylene tris-dodecyl ether HLB (hydrophile-lipophile balance) of 14.8 manufactured by Daiichi Kogyo Seiyaku) as a low-molecular-weight surfactant. The mixture was heated to 100°C to dissolve the resin. After complete dissolution, 5.0 parts of dimethylaminoethanol and 600.0 parts of ion-exchanged water were added as neutralizers. The mixture was then desolvated under reduced pressure while transitioning to an aqueous phase to obtain an aqueous dispersion of the olefin resin having a solid content of 30.0%. The resulting aqueous resin had an acid value of 24.0 mgKOH / g and a Tg of -20°C.

[0268] <Preparation of Aqueous Dispersion of Core-Shell Type Resin Microparticles>

[0269] [Production Example 17]

[0270] First, 97.0 parts of styrene, 2.0 parts of acrylic acid, 1.0 part of 3-methacryloyloxypropyltrimethoxysilane, 5.0 parts of a 20% aqueous solution of KH-10, and 39.0 parts of ion-exchanged water were mixed and stirred to prepare an emulsion of the first-stage ethylenically unsaturated monomer. In a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux, 95.0 parts of ion-exchanged water and 1.5% of the first-stage emulsion were added. The internal temperature of the reaction vessel was raised to 70°C and the atmosphere was thoroughly purged with nitrogen. Then, 5.7 parts of a 2.5% aqueous solution of potassium persulfate as an initiator were added to initiate polymerization. While the internal temperature was raised to 80°C and maintained, the remaining emulsion and 4.0 parts of a 2.5% aqueous solution of potassium persulfate were added dropwise over 2 hours to react and synthesize core particles.

[0271] Next, 17.0 parts of methyl methacrylate, 24.1 parts of n-butyl acrylate, 0.9 parts of acrylic acid, 2.1 parts of a 20% aqueous solution of KH-10, and 16.7 parts of ion-exchanged water were mixed and stirred to prepare a second-stage emulsion of ethylenically unsaturated monomers. Twenty minutes after the completion of the first-stage addition, the second-stage emulsion was added dropwise. While maintaining the internal temperature at 80°C, the second-stage emulsion and 2.1 parts of a 2.5% aqueous solution of potassium persulfate were simultaneously added over two hours to react, yielding an aqueous dispersion of core-shell resin microparticles. After the reaction, water was added to adjust the solids content to 45.0%. The resulting microparticles had an average particle size of 250 nm, a Cv value of 24.8%, a core Tg of 100.1°C, and a shell Tg of -6.2°C.

[0272] [Production Examples 18 to 42]

[0273] A water dispersion of core-shell resin microparticles was obtained in the same manner as in Production Example 17, except that the formulation compositions shown in Tables 3 and 4 were changed. The reaction vessel was charged with water in an amount of 67% relative to the total amount of the ethylenically unsaturated monomers. An emulsion of the ethylenically unsaturated monomers was prepared by adding water so that the concentration of the ethylenically unsaturated monomers in the emulsion became 69% and the concentration of the surfactant became 0.69%. The total amount of a 2.5% aqueous solution of potassium persulfate was set so that the amount of potassium persulfate became 0.2% relative to the total amount of the ethylenically unsaturated monomers. The distribution of the 2.5% aqueous solution of potassium persulfate at the start of the reaction / at the time of adding the first stage emulsion dropwise / at the time of adding the second stage emulsion dropwise was set to the same ratio as in Production Example 17.

[0274] In Production Example 25, KH-10 was replaced with a non-reactive surfactant, Hitenol NF-08 (polyoxyethylene distyrylphenyl ether sulfate ammonium salt, manufactured by Daiichi Kogyo Seiyaku).

[0275] In Preparation Examples 36 and 38, the amount of 20% aqueous solution of KH-10 charged to the reaction vessel before the start of the reaction was set to 5.2 parts, and the amount of the first-stage emulsion charged to the reaction vessel was changed to 2.6%.

[0276] In Production Example 39, 0.1 parts of octyl thioglycolate was further added to the second-stage ethylenically unsaturated monomer to prepare an emulsion.

[0277] In Preparation Examples 33, 34, and 35, KH-10 was replaced with AR-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., an anionic reactive surfactant. Furthermore, the amount of the first-stage emulsion charged to the reaction vessel was changed to 4.5%, 1.7%, and 3.7%, respectively.

[0278] Tables 3 and 4 show the average particle size, Cv value, core Tg, and shell Tg of the obtained core-shell type resin fine particles.

[0279]

[0280]

[0281] <Preparation of aqueous dispersion of non-core-shell type resin microparticles>

[0282] [Production Example 43]

[0283] 73.0 parts of styrene, 10.0 parts of methyl methacrylate, 8.0 parts of n-butyl methacrylate, 3.0 parts of 2-ethylhexyl acrylate, 2.0 parts of lauryl methacrylate, 1.0 part of acrylic acid, 1.0 part of acrylamide, 1.0 part of 3-methacryloxypropyltriethoxysilane, 5.0 parts of a 20% aqueous solution of KH-10, and 40.4 parts of water were mixed in advance and stirred to prepare an emulsion of ethylenically unsaturated monomers.

[0284] A reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux was charged with 68.9 parts of water, and 3% of the emulsion was added. The internal temperature was raised to 70°C, and the atmosphere was thoroughly purged with nitrogen. Then, 2.0 parts of a 5% aqueous solution of potassium persulfate was added as an initiator to initiate emulsion polymerization. While the internal temperature was raised to 80°C and maintained, the remainder of the emulsion and 2.0 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 3 hours. The mixture was allowed to react for a further 4 hours to obtain an aqueous dispersion of resin microparticles with a solids content of 45.0%. The obtained resin microparticles had an average particle size of 207 nm, a coefficient of variation (Cv) of 26.2%, and a Tg of 81.7°C.

[0285] <Preparation of an Aqueous Dispersion of Resin Fine Particles to Form the Resin Layer>

[0286] [Production Example 44]

[0287] 15.0 parts of styrene, 30.0 parts of methyl methacrylate, 16.0 parts of 2-ethylhexyl acrylate, 35.0 parts of n-butyl acrylate, 2.0 parts of methacrylic acid, 1.0 part of acrylic acid, 1.0 part of 3-methacryloxypropyltriethoxysilane, 5.0 parts of a 20% aqueous solution of KH-10, and 40.4 parts of ion-exchanged water were mixed in advance and stirred to prepare an emulsion of ethylenically unsaturated monomers.

[0288] A reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux was charged with 68.9 parts of ion-exchanged water, and 3% of the emulsion was added. The internal temperature was raised to 70°C, and the atmosphere was thoroughly purged with nitrogen. Then, 2.0 parts of a 5% aqueous solution of potassium persulfate was added as an initiator to initiate emulsion polymerization. While the internal temperature was raised to 80°C and maintained, the remainder of the emulsion and 2.0 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 3 hours. The mixture was allowed to react for a further 4 hours to obtain an aqueous dispersion of resin microparticles with a solids content of 45.0%. The resulting aqueous resin microparticles had an average particle size of 196 nm and a Tg of -2.4°C.

[0289] [Production Examples 45 to 54]

[0290] Aqueous dispersions of resin microparticles were obtained in the same manner as in Preparation Example 44, except that the formulation composition was changed to that shown in Table 5. In Preparation Examples 45, 48, 49, and 50, the amount of emulsion added to the reaction vessel was changed to 1.5%, 5%, 1.5%, and 1.3%, respectively. In Preparation Examples 51, 52, 53, and 54, the amount of KH-10 was changed to 6.0 parts, 6.3 parts, 7.0 parts, and 6.9 parts, respectively. The average particle size and Tg of the obtained resin microparticles are shown in Table 5.

[0291]

[0292] <Preparation of an aqueous dispersion of resin fine particles forming an adhesive layer>

[0293] [Production Example 55]

[0294] 97.5 parts of 2-ethylhexyl acrylate, 2.0 parts of acrylic acid, 0.5 parts of 3-methacryloyloxypropyltriethoxysilane, 0.03 parts of octyl thioglycolate, 7.0 parts of a 20% aqueous solution of Newcol RA9612 (polyoxyethylene alkyl ether sulfate ammonium salt) manufactured by Nippon Emulsifier Co., Ltd., and 40.4 parts of ion-exchanged water were mixed in advance and stirred to prepare an emulsion of ethylenically unsaturated monomers.

[0295] A reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux was charged with 68.9 parts of ion-exchanged water and 1% of the emulsion was added. The internal temperature was raised to 80°C and the atmosphere was thoroughly purged with nitrogen. Then, 2.0 parts of a 5% aqueous solution of ammonium persulfate was added as an initiator to initiate emulsion polymerization. While maintaining the internal temperature at 80°C, the remaining emulsion and 2.0 parts of a 5% aqueous solution of ammonium persulfate were added dropwise over 3 hours. The mixture was allowed to react for a further 8 hours to obtain an aqueous dispersion of resin microparticles. After the reaction was completed, 1.9 parts of 25% aqueous ammonia was added for neutralization, and the solids content was adjusted to 45.0% using ion-exchanged water. The resulting resin had an acid value of 15.6 mgKOH / g and a Tg of -71.0°C.

[0296] <Preparation of Primer Composition>

[0297] [Production Example 56]

[0298] 2.0 parts of isopropyl alcohol were added to 100 parts of the aqueous dispersion of the resin obtained in Production Example 1, and the mixture was stirred to prepare a primer composition.

[0299] [Production Examples 57 to 74]

[0300] Except having changed into the blending composition shown in Table 6, it carried out similarly to Production Example 56, and prepared the primer composition.

[0301]

[0302] The abbreviations of Table 6 are shown below.

[0303] denacol EX-614B: Made by Nagase ChemteX, sorbitol polyglycidyl ether, epoxy equivalent weight 173 g / eq, non-volatile content 100%

[0304] Carbodilite V-02: Aqueous dispersion of polycarbodiimide manufactured by Nisshinbo Chemical Co., Ltd., with a carbodiimide equivalent weight of 445 and a non-volatile content of 40%.

[0305] CW-1: Orient Chemical Industries, Inc., Bonjet Black CW-1, an aqueous dispersion of surface-modified carbon black, with an average particle size of 62 nm and a solids content of 20.0%.

[0306] <Preparation of colloidal crystal layer composition>

[0307] [Production Example 75]

[0308] To 100 parts of the aqueous dispersion of the core-shell type resin fine particles of Production Example 13, 2.3 parts of BONJET BLACK CW-1 (surface-modified carbon black, average particle size 62 nm, solid content 20.0%) manufactured by Orient Chemical Industries was added and stirred to prepare a composition for a colloidal crystal layer.

[0309] [Production Examples 76 to 105]

[0310] A colloidal crystal layer composition was prepared by the same method as in Production Example 75 except that the blending composition was changed to that shown in Table 7.

[0311]

[0312] [Production Example 106]

[0313] To 100 parts of the aqueous dispersion of the non-core-shell resin microparticles of Preparation Example 43, 45 parts of the aqueous dispersion of the resin microparticles of Preparation Example 44 and 2.3 parts of CW-1 (surface-modified carbon black with an average particle size of 62 nm and a solid content of 20.0%) manufactured by Orient Chemical Industry were added as a binder, and the mixture was stirred to prepare a composition for a colloidal crystal layer.

[0314] <Preparation of resin composition>

[0315] [Production Example 107]

[0316] To 100 parts of the aqueous dispersion of the aqueous resin microparticles obtained in Preparation Example 44, 0.2 parts of isopropyl alcohol and 9.0 parts of CW-1 (surface-modified carbon black, average particle size 62 nm, solid content 20.0%) manufactured by Orient Chemical Industries were added and stirred to prepare a resin composition.

[0317] [Production Examples 108 to 118]

[0318] A resin composition was prepared in the same manner as in Production Example 107 except that the blending composition was changed to that shown in Table 8.

[0319]

[0320] <Production of Laminated Body>

[0321] [Example 1]

[0322] The primer composition of Production Example 56 was applied to the corona-treated surface of a biaxially oriented polypropylene (OPP) film (FOR manufactured by Futamura, thickness 20 μm) using a bar coater to a thickness of 3.0 μm after drying. The film was then oven-dried at 50°C for 3 minutes to form a primer layer. Subsequently, the colloidal crystal layer composition of Production Example 75 was applied to the primer layer using a bar coater to a thickness of 9.0 μm after drying. The film was then dried at 40°C for 5 minutes to obtain a laminate having a structure of OPP / primer layer / colloidal crystal layer.

[0323] [Example 2 to Example 55, Comparative Example 1 to Comparative Example 12]

[0324] A laminate was obtained in the same manner as in Example 1 except that the combinations and thicknesses were changed to those shown in Table 9A and Table 9B.

[0325] In Example 11, Example 19 and Comparative Example 1, after applying the colloidal crystal layer composition, the composition was naturally dried at room temperature for 1 hour to form a colloidal crystal layer.

[0326] In Examples 44 to 55, the resin composition was applied on the colloidal crystal layer using a bar coater and dried in an oven at 50° C. for 5 minutes to form a resin layer.

[0327] In Comparative Example 10, the dispersion of Production Example 17 containing no achromatic black fine particles was used as the composition for a colloidal crystal layer.

[0328] In Comparative Example 12, the colloidal crystal layer composition was directly applied onto the substrate.

[0329]

[0330]

[0331] The abbreviations in Table 9A and Table 9B are shown below.

[0332] OPP: (FOR: biaxially oriented polypropylene film manufactured by Futamura, thickness 20 μm)

[0333] PET (E5101 manufactured by Toyobo Co., Ltd.: polyethylene terephthalate film, thickness 25 μm)

[0334] [Comparative Example 13]

[0335] An aqueous solution of polyvinyl alcohol (Poval 22-88 manufactured by Kuraray; solid content 20.0%) is applied to the colloidal crystal layer of the laminate of Example 1 using a rod coater, and then dried in an oven at 70°C for 3 minutes to replace the voids in the colloidal crystal layer from air to the resin component.

[0336] <Production of Thermal Recording Media>

[0337] [Example 56]

[0338] 100 parts of the aqueous dispersion obtained in Preparation Example 55 and 0.3 parts of denacol EX-313 (glycerol polyglycidyl ether epoxy equivalent 141 g / eq, nonvolatile matter 100%) manufactured by Nagase ChemteX were mixed to obtain a pressure-sensitive adhesive.

[0339] The pressure-sensitive adhesive was applied to the resin layer of the laminate of Example 44 using a bar coater and dried in an oven at 80°C for 5 minutes to form a 20 μm thick adhesive layer. The release side of a release paper was attached to the adhesive layer to obtain a thermosensitive recording medium in the form of an adhesive sheet.

[0340] <Evaluation of Laminated Body>

[0341] The obtained laminates (including the thermosensitive recording medium) were subjected to the following evaluations. The results are shown in Tables 10A to 12.

[0342] [Confirmation of gap]

[0343] The obtained laminate was determined to contain voids if a mode pore size of 10 nm to 200 nm was detected by the nitrogen adsorption method. The BJH method was used on the adsorption side of the nitrogen adsorption isotherm obtained by the nitrogen adsorption method, with the peak top being the mode pore size. The parameters of the BJH method were Harkins-Jura and volume frequency distribution for the reference t-curve. The measurement was performed using the BELSORP-maxII device manufactured by Microtrac BEL.

[0344] Yes: In the colloidal crystal layer, voids with a mode pore diameter of 10 nm to 200 nm were detected.

[0345] None: No voids with a mode pore diameter of 10 nm to 200 nm were detected in the colloidal crystal layer.

[0346] [Color]

[0347] For the laminate, the reflectance spectrum was measured in the wavelength range of 350 nm to 850 nm using an ultraviolet-visible-near-infrared spectrophotometer (V-770D manufactured by JASCO Corporation, integrating sphere unit ISN-923). The reflectance at each wavelength is a relative reflectance measured using a standard white plate with a known reflectance (SRS-99-010 manufactured by Labsphere) as a reference. In Examples 44 and 56, the measurement was performed from the substrate side. In addition, the measurement was performed from the colloidal crystal layer side. For the obtained reflectance spectrum, the maximum value of the reflectance derived from the structural color and the difference (ΔR) between the reflectance and the baseline that is not dependent on the structural color were calculated. The larger the ΔR, the better the color development. Based on the obtained ΔR, the evaluation was performed according to the following benchmarks.

[0348] S: ΔR is 10% or more (very good).

[0349] A: ΔR is 5% or more and less than 10% (good).

[0350] B: ΔR is 2% or more and less than 5% (usable).

[0351] C: ΔR is less than 2%, or the reflectance peak derived from the structural color cannot be discerned (unusable).

[0352] [Storage stability]

[0353] After the laminate was left at room temperature for 6 months, the reflectance spectrum was measured in the same manner as the color development evaluation. The reflectance spectra before and after the time period were compared to calculate the rate of change (reduction rate) of the maximum reflectance. The greater the rate of change, the more the colloidal crystals have faded. Based on the obtained rate of change, the evaluation was performed according to the following criteria.

[0354] S: The change rate of the maximum value of the reflectance is less than 3% (very good).

[0355] A: The rate of change of the maximum value of the reflectance is 3% or more and less than 5% (good).

[0356] B: The change rate of the maximum value of the reflectance is 5% or more and less than 10% (usable).

[0357] C: The change rate of the maximum value of the reflectance is 10% or more (unusable).

[0358] [Color changes when heated]

[0359] The laminate was attached to an A4-sized white paper using adhesive tape, and a thermal printer (PocketJet PJ-673 manufactured by Brother Industries) including a thermal head was used to heat a 2 cm × 2 cm square at a concentration of 5 to form an image.

[0360] Next, the square image was formed using a YVO4 laser marker MD-V9600A (wavelength 1064 nm) manufactured by Keyence Corporation using an infrared laser under the conditions of a laser power of 30% and a scanning speed of 2000 mm / sec.

[0361] In Example 43, heating with a thermal head and infrared laser irradiation were both performed from the colloidal crystal layer side.

[0362] In Examples 44 and 56, heating by a thermal head and infrared laser irradiation were both performed from the substrate side.

[0363] In addition, heating with a thermal head was performed from the colloidal crystal layer side, and infrared laser irradiation was performed from the substrate side.

[0364] After image formation, the laminate was visually observed. Furthermore, the reflectance spectra of the heated portion (image portion) and the unheated portion (non-image portion) were measured in the same manner as described for the color development evaluation. The reflectance spectra of the heated and unheated portions were compared, and the rate of change (reduction) in the maximum reflectance was calculated and evaluated according to the following criteria. A greater rate of change indicates a more pronounced color change due to the heat treatment.

[0365] If the image formation could not be performed due to reasons such as separation of the colloidal crystal layer during image formation, the device was judged as unusable. Furthermore, subsequent evaluations determined the device to be unusable.

[0366] S: The image has a clear outline, and the rate of change in the maximum value of the reflectance is 50% or more (very good).

[0367] A: The image has a clear outline, and the rate of change in the maximum value of the reflectance is 30% or more and less than 50% (good).

[0368] B: The image has a clear outline, and the rate of change in the maximum reflectance is 10% or more and less than 30% (usable).

[0369] C: The outline of the image is unclear, the change rate of the maximum reflectance is less than 10%, or image formation is not possible (unusable).

[0370] [Friction resistance]

[0371] After image formation, the laminate was placed on a smooth glass plate with the heated side facing up. A 2 cm x 2 cm square area was rubbed 40 times with the pads of the fingers, back and forth, in both the heated and unheated areas. The presence of scratches or peeling was observed. Evaluation criteria were as follows.

[0372] S: No scratches or peeling (very good).

[0373] A: The area with scratches or peeling is less than 1% (good).

[0374] B: The area with scratches or peeling is 1% or more and less than 5% (usable).

[0375] C: The area with scratches or peeling is 5% or more (unusable).

[0376] [Substrate followability]

[0377] After image formation, 2 cm x 2 cm square test pieces were cut from the heated and non-heated portions of the laminate. The test pieces were folded 20 times, and the appearance of the heated side was observed. The evaluation criteria were as follows.

[0378] S: No scratches or peeling (very good).

[0379] A: The area with scratches or peeling is less than 1% (good).

[0380] B: The area with scratches or peeling is 1% or more and less than 5% (usable).

[0381] C: The area with scratches or peeling is 5% or more (unusable).

[0382] [Water resistance and solvent resistance]

[0383] After image formation, cut out 2 cm x 2 cm test pieces from the heated and unheated areas of the laminate. Immerse the test pieces in water or ethanol for 1 minute, remove them, and allow them to air dry at room temperature. Observe the appearance of the heated side. Evaluation criteria are as follows.

[0384] S: No scratches or peeling (very good).

[0385] A: The area with scratches or peeling is less than 1% (good).

[0386] B: The area with scratches or peeling is 1% or more and less than 5% (usable).

[0387] C: The area with scratches or peeling is 5% or more (unusable).

[0388]

[0389]

[0390]

[0391]

[0392]

[0393] The laminates and thermosensitive recording media of the present invention exhibit excellent structural color in thin films, excellent long-term storage stability, and a distinct color change before and after heating. Furthermore, they exhibit excellent film resistance (friction resistance, substrate conformability, water resistance, and solvent resistance) in both the heated and unheated portions. In particular, the laminates of Examples 44 to 55, each having a resin layer on a colloidal crystal layer, and the thermosensitive recording media of Example 56 exhibit excellent friction resistance and solvent resistance.

[0394] On the other hand, the laminated bodies of the comparative examples were significantly inferior in any of the aforementioned evaluation items.

[0395] Industrial applicability

[0396] The laminate of the present invention exhibits excellent structural color in thin films, has excellent storage stability, shows a clear color change when heated, and has excellent resistance to various films. Therefore, in addition to imparting design to thermal labels and seals, it can also be expanded to a wide range of applications such as security devices, optical filters, display elements, optical waveguides, optical resonators, and optical switches.

Claims

1. A laminate comprising a substrate, a primer layer formed of a resin, and a colloidal crystal layer that develops color by light interference, wherein: The resin forming the primer layer has a glass transition point within the range of -35°C to 100°C. The colloidal crystal layer contains core-shell type resin particles and achromatic black particles and has voids. The core-shell type resin fine particles contain a shell in an amount ranging from 10% by mass to 150% by mass based on the mass of the core, wherein the shell has a glass transition point within a range of -60°C to 40°C. The thickness of the colloidal crystal layer is in the range of 0.5 μm to 100 μm. 2 . The laminate according to claim 1 , wherein the core has a glass transition point of 50° C. or higher. 3 . The laminate according to claim 1 , wherein the colloidal crystal layer contains the achromatic black fine particles in an amount within a range of 0.3% by mass to 3% by mass based on the mass of the core-shell type resin fine particles. 4 . The laminate according to claim 1 , wherein the acid value of the resin forming the primer layer is in the range of 5 mgKOH / g to 140 mgKOH / g. The laminate according to claim 1 or 2, wherein the core of the core-shell type resin fine particles contains a structural unit derived from an aromatic ethylenically unsaturated monomer in an amount within a range of 70% by mass to 100% by mass based on the mass of the core.

6. The laminate according to claim 1 or 2, wherein the shell of the core-shell type resin fine particles contains, based on the mass of the shell, 70% to 99.5% by mass of constituent units derived from ethylenically unsaturated monomers having an octanol / water partition coefficient in the range of 1 to 2.5, and 0.5% to 15% by mass of constituent units derived from ethylenically unsaturated monomers having an octanol / water partition coefficient of less than 1. 7 . The laminate according to claim 1 , wherein the core-shell type resin fine particles include a structural unit derived from a reactive surfactant. 8 . The laminate according to claim 1 , further comprising a resin layer on the colloidal crystal layer.

9. A thermosensitive recording medium comprising the laminate according to any one of claims 1 to 8. 10 . The thermosensitive recording medium according to claim 9 , further comprising an adhesive layer.

11. An image forming method, characterized in that: The thermosensitive recording material according to claim 9 or 10 is heated to fade the color of the colloidal crystal layer.

Images