Dispersion and structure of infrared reflecting fine particles

Abstract

To provide a dispersion and a structure that feature excellent film-forming properties, optimal for creating an infrared reflective film with sufficient infrared reflection performance.SOLUTION: A dispersion comprises microparticles, a water-soluble resin and a dispersion medium. The number average particle diameter of the microparticles is 451-800 nm, and the CV value of the particle diameter based on a number basis is 15% or less. Relative to 100 pts.mass of the microparticles, the content of the water-soluble resin is 0.001-0.4 pt.mass.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a dispersion of fine particles having infrared reflectivity, and a structure in which the fine particles are arranged to exhibit infrared reflectivity.

Background Art

[0002] Structural coloration refers to a coloration phenomenon caused by a fine structure with a wavelength of light or less. Examples of familiar structural colors include compact discs, soap bubbles, Morpho butterflies, jewel beetles, etc. In these examples, although they are not colored themselves, they appear colored because light is reflected and interfered by their fine structure. In recent years, development has been underway to artificially create a regular structure that exhibits structural color. For example, using a dispersion in which fine particles with a monodisperse particle diameter are dispersed in a medium, pouring this, injecting, coating, flowing, etc. to arrange, align, dry, and fix the fine particles, and various methods have been proposed for manufacturing a structure in which the fine particles are regularly arranged in the planar direction on a substrate. In addition, the phenomenon of light reflection and interference due to such a fine structure occurs not only for visible light but also for infrared rays.

[0003] Colloidal crystals are known as those in which such fine particles are regularly arranged, and it is known that such colloidal crystals exhibit Bragg reflection and structural color. In addition, research and development have been carried out on applying this to color materials and infrared reflection films. As a method for forming a colloidal crystal to exhibit structural color, in Patent Document 1, a method has been proposed for forming a colloidal crystal at low cost only by coating, using core-shell particles composed of a core part and a shell part and utilizing the fluidity of the shell part that fuses by heating. In addition, in Patent Document 2, a method for forming a film that exhibits structural color has been proposed by blending a water-soluble resin having a hydrogel ability such as sodium carboxymethyl cellulose in a dispersion of organic polymer particles at 0.5 to 2.2 parts by mass with respect to 100 parts by mass of the organic polymer particles.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-249527 [Patent Document 2] Japanese Patent Publication No. 2016-187803 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the method proposed in Patent Document 1 had the problem of requiring a long heat treatment time to form colloidal crystals. Furthermore, it did not describe specific examples of using colloidal crystals as an infrared reflective film. Furthermore, the method proposed in Patent Document 2 had the problem of insufficient structural color development and a long drying time required for film formation. In addition, this document does not describe specific examples of using colloidal crystals as infrared reflective films.

[0006] The objective of the present invention is to solve the above-mentioned problems. That is, to provide an optimal dispersion and structure for obtaining an infrared reflective film that has excellent film-forming properties and sufficient infrared reflection performance. [Means for solving the problem]

[0007] As a result of diligent research to solve the aforementioned problems, the inventors of the present invention discovered that a specific amount of a specific water-soluble resin can be blended with fine particles having a specific average particle size, leading to the present invention.

[0008] In other words, the present invention has the following features. [1] A dispersion comprising fine particles, a water-soluble resin, and a dispersion medium, wherein the number average particle diameter of the fine particles is 451 to 800 nm, the CV value of the particle diameter based on the number is 15% or less, and the dispersion contains 0.001 to 0.4 parts by mass of the water-soluble resin per 100 parts by mass of the fine particles. [2] The dispersion according to [1], wherein the contact angle with the polyester film is 2° or more lower than the contact angle of water with the polyester film. [3] The dispersion according to [1] or [2], wherein the solid content concentration is 10% by mass or more. [4] The dispersion according to any one of [1] to [3], wherein the water-soluble resin is an ionic water-soluble resin.

[0009] [5] The dispersion according to any one of [1] to [4], wherein the water-soluble resin is an ionic polyvinyl alcohol-based resin. A structure having infrared reflectivity, comprising a colloidal aggregate containing a water-soluble resin and fine particles contained in any one of the items [6][1] to [5]. [7] The structure according to [6], further comprising an overcoat layer on its surface.

[0010] [8] A dispersion comprising fine particles that exhibit infrared reflectivity when arranged, a water-soluble resin, and a dispersion medium, wherein the dispersion contains 0.001 to 0.4 parts by mass of the water-soluble resin per 100 parts by mass of the fine particles. [9] The dispersion according to [8], wherein the contact angle with the polyester film is 2° or more lower than the contact angle of water with the polyester film.

[10] The dispersion according to [8] or [9], wherein the concentration of solids is 10% by mass or more.

[11] The dispersion according to any one of [8] to

[10] , wherein the water-soluble resin is an ionic water-soluble resin.

[0011]

[12] The dispersion according to any one of [8] to

[11] , wherein the water-soluble resin is an ionic polyvinyl alcohol-based resin. A structure having infrared reflectivity, comprising a colloidal aggregate containing a water-soluble resin and fine particles contained in any one of the items

[13] [8] to

[12] .

[14] The structure according to

[13] , further comprising an overcoat layer on its surface.

[0012] A coating composition using the dispersion according to any one of

[15] [1] to [5] and [8] to

[12] . An ink composition using the dispersion according to any one of

[16] [1] to [5] and [8] to

[12] . A cosmetic using the dispersion according to any one of

[17] [1] to [5] and [8] to

[12] . A decorative film using the dispersion according to any one of

[18] [1] to [5] and [8] to

[12] .

[0013] An optical material using the dispersion according to any one of

[19] [1] to [5] and [8] to

[12] . A coating composition using the structure according to any one of

[20] [6] to [7] and

[13] to

[14] . An ink composition using the structure according to any one of

[21] [6] to [7] and

[13] to

[14] . A cosmetic using the structure according to any one of

[22] [6] to [7] and

[13] to

[14] . A decorative film using the structure according to any one of

[23] [6] to [7] and

[13] to

[14] . An optical material using the structure according to any one of

[24] [6] to [7] and

[13] to

[14] .

Advantages of the Invention

[0014] The dispersion of the present invention is excellent in wettability to the coated substrate and contains few high-viscosity components in the dispersion medium, so it does not inhibit the arrangement of fine particles and has excellent film-forming properties. Since the surface of the film of the structure of the present invention is uniform, the infrared reflection performance is good, and an excellent infrared reflection film can be obtained.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following contents as long as it does not exceed the gist thereof. In addition, when the expression "~" is used in this specification, it shall be used in the sense of including the numerical values or physical values described before and after it. Also, the numerical values or physical values described as upper and lower limits shall be used in the sense of including those values.

[0016] The dispersion of the present invention contains fine particles and a water-soluble resin.

[0017] [Fine particles] The fine particles of the present invention may have a number-average particle diameter of 451 to 800 nm and a CV value of the particle diameter based on the number standard of 15% or less. The fine particles are not particularly limited as long as the number-average particle diameter and the CV value of the particle diameter based on the number standard are within the above ranges, and they may be organic fine particles or inorganic fine particles.

[0018] Among organic fine particles and inorganic fine particles, organic fine particles are preferable because it is easy to precisely control reaction conditions such as composition control and it is easy to obtain fine particles with uniform size and shape.

[0019] <Number-average particle diameter> The average particle diameter (number-average particle diameter) of the fine particles of the present invention based on the number standard is 451 to 800 nm. The number-average particle diameter of the fine particles of the present invention is preferably 460 nm or more, more preferably 470 nm or more, still more preferably 480 nm or more. On the other hand, it is preferably 780 nm or less, more preferably 750 nm or less, still more preferably 700 nm or less. If the number-average particle diameter is within the above range, it is preferable because the infrared reflectivity becomes good. The measuring method of the number-average particle diameter of the present invention is as described in the examples.

[0020] <CV value of the particle diameter based on the number standard> The CV value of the particle diameter of the fine particles of the present invention based on the number standard is 15% or less. The coefficient of variation (CV) of the particle size of the fine particles of the present invention, based on the number of particles, is preferably 10% or less, more preferably 5% or less. There is no particular lower limit to the CV of the particle size based on the number of particles, but it is usually 1% or more. The CV value is also called the "coefficient of variation" or "relative standard deviation," and in this invention, it refers to the relationship between the standard deviation and the number-average particle diameter in the particle diameter distribution based on the number of particles. (Standard deviation / Number mean particle size) × 100 It is calculated using this method. If the CV value of the particle size based on the number of particles falls within the above range, it is preferable because it results in good infrared reflectivity. The method for measuring the CV value of particle size based on the number of particles according to the present invention is as described in the examples.

[0021] <Organic fine particles> The organic microparticles of this invention refer to microparticles made of a general polymer. Common polymers include, for example, polyamides, polyimides, low-density polyethylene, high-density polyethylene, poly(meth)acrylic acid esters, polystyrenes such as polystyrene and its derivatives, polyvinyl chloride, phenolic resins, and polycarbonates.

[0022] Among these, poly(meth)acrylic acid esters and polystyrenes are preferred because the raw materials are readily available and it is easy to produce fine particles with uniform particle size, and polystyrenes are more preferred because they yield polymers with a high refractive index. High refractive index polymers are preferable because they increase the refractive index difference between the inside and outside of the particles, resulting in improved infrared reflectivity. The organic microparticles may be non-crosslinked polymers or crosslinked polymers.

[0023] In order to achieve the effects of the present invention, the organic fine particles of the present invention must have a uniform particle size. To obtain organic fine particles with uniform particle size, one method is to obtain polymers of appropriate size by methods such as bulk polymerization, suspension polymerization, emulsion polymerization, or solution polymerization, then pulverize them into fine powders, and standardize the particle size through operations such as sieving. Alternatively, one method is to directly obtain organic fine particles with uniform particle size by soap-free emulsion polymerization. Among these methods, the soap-free emulsion polymerization method is preferred due to its superior productivity.

[0024] (Poly(meth)acrylic acid esters) The poly(meth)acrylic acid esters of the present invention are polymers mainly composed of (meth)acrylic acid ester units. Here, "main component" means that the content of (meth)acrylic acid ester units relative to the entire polymer is 50% by mass or more, more preferably 60% by mass or more.

[0025] Examples of (meth)acrylic acid esters that serve as raw materials for the (meth)acrylic acid ester units mentioned above include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate.

[0026] The aforementioned poly(meth)acrylic acid esters may be random copolymers or block copolymers, but are generally random copolymers. These poly(meth)acrylic acid esters may be copolymerized with any monomer in addition to the (meth)acrylic acid esters described above. Examples of these arbitrary monomers include styrenes such as styrene and methylstyrene; metal salts such as sodium salt of styrenesulfonic acid; acidic monomers such as acrylic acid and methacrylic acid; and acrylamides such as acrylamide and N-propylacrylamide.

[0027] Among these, metal salts such as sodium salts of styrene sulfonic acid are preferred because they allow for good control of particle size. Furthermore, when introducing a crosslinked structure to poly(meth)acrylic acid esters, known polyfunctional monomers can be copolymerized.

[0028] (Polystyrene) The polystyrenes of the present invention are polymers mainly composed of styrene units. Here, "main component" means that the content of styrene units relative to the entire polymer is 50% by mass or more, and more specifically, 60% by mass or more. Polystyrenes can be either random copolymers or block copolymers, but they are generally random copolymers. Polystyrenes may be copolymerized with any monomer other than styrene.

[0029] Examples of arbitrary monomers include styrenes other than styrene, such as methylstyrene and chlorostyrene; metal salts such as sodium salt of styrene sulfonic acid; acidic monomers such as acrylic acid and methacrylic acid; (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate; and acrylamides such as acrylamide and N-propylacrylamide. Among these, metal salts such as sodium salts of styrene sulfonic acid are preferred because they allow for good control of particle size. Furthermore, when introducing a crosslinked structure to polystyrenes, known polyfunctional monomers can be copolymerized.

[0030] (Composition of polystyrenes) Polystyrenes preferably contain 80.0 to 99.75% by mass of styrene units. A styrene unit content within this range is preferable because it increases the refractive index of the particles and improves infrared reflectivity. A styrene unit content of 90.0% by mass or more is more preferable. Furthermore, 99.4% by mass or less is even more preferable.

[0031] Polystyrenes preferably contain 0.25 to 20.0% by mass of acidic monomer units such as acrylic acid units and methacrylic acid units. A content of acidic monomer units within the above range is preferable because it reduces cullet during polymerization. The content of acidic monomer units is more preferably 0.6% by mass or more. Furthermore, it is more preferably 10.0% by mass or less.

[0032] If the polystyrenes contain any monomer units other than the acidic monomer units and / or polyfunctional monomer units, the content thereof is preferably 3% by mass or less, and more preferably 2% by mass or less. If the aforementioned content is 3% by mass or less, the particle size can be controlled well.

[0033] (Method for manufacturing organic microparticles) The organic fine particles of the present invention are preferably obtained by soap-free emulsion polymerization. Soap-free emulsion polymerization is a known polymerization method, for example, as described below. Deionized water is placed in the reaction vessel, and polymerization aids are added while heating and stirring as needed, ensuring that the polymerization aids are thoroughly dispersed in the deionized water. Next, the polymerization initiator is added while continuing to stir. Then, monomers are added dropwise while continuing to stir to initiate the polymerization reaction. As polymerization progresses, particles are formed.

[0034] The solid content concentration during polymerization, i.e., the concentration of organic fine particles relative to the entire system during polymerization, is preferably 20 to 40% by mass. If the solid content concentration during polymerization is above the lower limit, the productivity of organic fine particles will improve. Furthermore, if it is below the upper limit, there will be no generation of cullet or deposits on the inner walls of the polymerization apparatus during polymerization. When a polymerization initiator is used, the polymerization temperature is generally set to 60-90°C. After the reaction is complete, the organic microparticles are removed as an emulsion.

[0035] Examples of polymerization initiators used in soap-free emulsion polymerization include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate; oil-soluble polymerization initiators such as benzoyl peroxide and lauryl peroxide; and redox polymerization initiators consisting of a combination of an oxidizing agent and a reducing agent. These may be used individually or in combination of two or more types. Among these, water-soluble polymerization initiators are preferred due to their ease of handling.

[0036] <Inorganic fine particles> The inorganic fine particles of the present invention are metal particles or metal oxides. Among these, silica nanoparticles are preferred because they are readily available and have excellent permeability.

[0037] <Water-soluble resin> The dispersion of the present invention contains a water-soluble resin, which gives it excellent affinity with the substrate. As a result, the dispersion of the present invention exhibits excellent film-forming properties. The water-soluble resin of the present invention is a polymer compound that dissolves in water or at least disperses in water. Examples of water-soluble resins include substances that have ionic groups such as sulfonyl groups and carboxyl groups, or water-soluble substituents such as hydroxyl groups, within their molecules, and that dissolve in water.

[0038] Water-soluble resins include nonionic water-soluble resins and ionic water-soluble resins. Examples of nonionic water-soluble resins include water-soluble polyacrylamide, water-soluble acrylic resins, nonionic polyvinyl alcohol-based resins, polyvinylpyrrolidone, polyethylene oxide, polyvinyl acetate; and natural polymer compounds such as starch, gelatin, and casein. Examples of ionic water-soluble resins include water-soluble polyester resins, polyacrylic acid, ionic polyvinyl alcohol-based resins, and carboxymethylcellulose.

[0039] Among these, it is preferable to use a nonionic polyvinyl alcohol-based resin and / or an ionic polyvinyl alcohol-based resin due to the high hydrolysis resistance of the polymer main chain. Furthermore, among water-soluble resins, ionic water-soluble resins are preferred because they offer improved ionic strength.

[0040] (Ionic water-soluble resin) Ionic water-soluble resins are water-soluble resins that have anionic or cationic parts, and are specifically as described above. Among ionic water-soluble resins, ionic polyvinyl alcohol-based resins are preferred because they have excellent solvent resistance.

[0041] (Ionic polyvinyl alcohol-based resin) Ionic polyvinyl alcohol resins are polyvinyl alcohol resins that contain ionic groups such as sulfonyl groups or their salts, carboxyl groups or their salts, or quaternary ammonium salts in their molecular chains.

[0042] Examples of ionic polyvinyl alcohol-based resins include polyvinyl alcohol-based resins containing a sodium salt of a sulfonyl group in the molecular chain, and polyvinyl alcohol-based resins containing a sodium salt of a carboxyl group in the molecular chain. Among these, polyvinyl alcohol-based resins containing a sodium salt of a sulfonyl group are preferred because the salt dissociates easily.

[0043] Examples of commercially available ionic polyvinyl alcohol-based resins include Gosenex (manufactured by Mitsubishi Chemical Corporation, a specially modified polyvinyl alcohol-based resin).

[0044] [Dispersion] The dispersion of the present invention contains the fine particles, the water-soluble resin, and the dispersion medium. Here, "dispersion" means that the fine particles and the water-soluble resin are dispersed in the dispersion medium.

[0045] Any medium can be used as the dispersion medium, but examples include water, water-based media, and organic solvents. A water-based media means that the water content is 50% by mass or more, and even more specifically, 60% by mass or more. Any organic solvent soluble in water can be selected as a component other than water.

[0046] Examples of organic solvents include alcohols such as methanol, ethanol, isopropyl alcohol, and 1-methoxy-2-propanol alcohol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; alkanes such as hexane, cyclohexane, heptane, decane, and hexadecane; halogen solvents such as methyl chloride, methylene chloride, chloroform, and carbon tetrachloride; and ether solvents such as tetrahydroxyfuran, dioxane, ethylene glycol diethyl ether, and ethylene glycol monobutyl ether. These can be used individually or in combination of two or more. Among the above, water-based media such as water or water-based media are preferred as dispersion media because they make it easier to obtain structures with high structural color development.

[0047] The content of fine particles in the dispersion of the present invention is preferably 1% to 70% by mass relative to the total mass of the dispersion. The content of fine particles is more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total mass of the dispersion. On the other hand, it is more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. If the content of fine particles is within the above range, the resulting structure will have good infrared reflectivity.

[0048] The content of the water-soluble resin in the dispersion of the present invention is 0.001 to 0.4 parts by mass per 100 parts by mass of fine particles. The water-soluble resin content is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of fine particles. On the other hand, the water-soluble resin content is preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, and even more preferably 0.1 parts by mass or less, per 100 parts by mass of fine particles. If the water-soluble resin content is within the above range, film-forming properties will be good.

[0049] <Concentration> The concentration of solids in the dispersion of the present invention is preferably 10% by mass or more. The solid content concentration of the dispersion of the present invention is more preferably 20% by mass or more, and even more preferably 25% by mass or more. Furthermore, the upper limit of the solid content concentration of the dispersion of the present invention is preferably 60% by mass or less, and more preferably 50% by mass or less. If the solid content concentration of the dispersion is within the above range, film-forming properties will be good, and the resulting structure will have good infrared reflectivity. Here, the solid content of the dispersion refers to the components other than the dispersion medium in the dispersion, and is usually the sum of fine particles, water-soluble resin, and other components that may be included as needed. The solid content concentration of the dispersion can be measured in the same way as the solid content concentration of the emulsion described in the subsequent examples section, or it can be calculated from the solid content concentration and amount of each component used in the production of the dispersion.

[0050] <Contact angle> In the present invention, it is preferable that the dispersion has a contact angle with the polyester film that is 2° or more lower than the contact angle of water with the polyester film. The contact angle of the dispersion with respect to the polyester film is more preferably 3° or more lower than the contact angle of water with respect to the polyester film, and even more preferably 5° or more lower. Furthermore, the upper limit for the contact angle difference is usually 20°.

[0051] Here, polyester film refers to a film made of polyethylene terephthalate resin that has been subjected to surface treatments such as plasma treatment as needed. Here, "water" refers to deionized water. The method for measuring the contact angle of the present invention is as described in the examples.

[0052] <Other ingredients> The dispersion of the present invention may, as necessary, contain other components such as plasticizers, film-forming aids, and pH adjusters, in addition to fine particles, water-soluble resins, and dispersion media, to the extent that it does not impair the objectives of the present invention. From the viewpoint of the infrared reflectivity of the structure, it is preferable that the content of these other components in the dispersion of the present invention be 5% by mass or less per 100% by mass of the solid content of the dispersion of the present invention.

[0053] [Method for preparing dispersions] The dispersion of the present invention can be prepared by mixing fine particles, a water-soluble resin, a dispersion medium, and other components as needed. For example, it can be prepared by mixing an emulsion containing fine particles, manufactured by the method described above, a water-soluble resin, a dispersion medium, and other components used as needed.

[0054] [Infrared reflective] The fine particles of the present invention have infrared reflectivity. In the present invention, infrared reflectivity means that when fine particles of uniform particle size are arranged regularly, they reflect infrared radiation. Here, infrared radiation refers to electromagnetic waves with wavelengths between 831 and 2500 nm.

[0055] [Structure] The structure of the present invention refers to a colloidal aggregate containing fine particles in the dispersion, which exhibits infrared reflectivity, in which the fine particles are arranged in a regular manner. Here, a colloidal aggregate refers to a colloidal crystal or colloidal amorphous aggregate. By arranging fine particles, the fine particles form a colloidal crystal or colloidal amorphous aggregate, i.e., a colloidal aggregate.

[0056] Examples of the aforementioned structures include a substrate on which fine particles are arranged, and a substrate from which colloidal crystals have been peeled off without impairing the regular arrangement of the fine particles.

[0057] Furthermore, the dispersion of the present invention contains a water-soluble resin. When fine particles are arranged, the water-soluble resin is thought to reduce the surface tension of the dispersion, thereby improving film-forming properties while maintaining high infrared reflectivity. As a result, structures obtained using the dispersion of the present invention have better film-forming properties compared to structures obtained using a dispersion that does not contain a water-soluble resin.

[0058] The aforementioned substrate is not particularly limited, and common materials such as metal, resin, wood, and paper can be used. For surface protection purposes, an overcoat layer may be provided on the surface of the structure as needed. When a film-like material is used as the base material, the resulting structure will be film-like. For the purpose of surface protection, an overcoat layer may be provided on the surface of the film-like structure as needed.

[0059] <Reflectance> The structure of the present invention preferably has a reflectance of 5% or more derived from the arrangement of fine particles in the wavelength range of 831 to 2500 nm. To achieve a reflectance of 5% or more in the structure, for example, the dispersion of the present invention may be used. The reflectance is more preferably 10% or more, and even more preferably 20% or more. A reflectance of 5% or more is preferable because it exhibits excellent infrared reflectivity. There is no particular upper limit to the reflectance derived from the arrangement of microparticles in the structure of the present invention, but it is usually 90% or less. The reflectance derived from the arrangement of fine particles can be measured by the method described in the examples below.

[0060] <Base material> As mentioned above, there are no particular restrictions on the base material used in the aforementioned structure, and it is possible to use common materials such as metal, resin, wood, and paper. For example, thermoplastic resin substrates such as polyvinyl chloride sheets, polyester films such as polyethylene terephthalate (PET), polypropylene films, polyethylene films, nylon films, polystyrene films, and polyvinyl alcohol films, as well as metal substrates such as aluminum foil, glass substrates, and coated paper substrates can also be used. The substrate may have a smooth or uneven surface, and may be transparent, translucent, or opaque. It is also possible to use a substrate that has been pre-colored, such as black. Furthermore, two or more of these substrates may be bonded together. The substrate may be pre-treated with corona or plasma to improve the coating properties of the dispersion of the present invention. A primer layer may also be applied to these substrates.

[0061] <Overcoat layer> The aforementioned overcoat layer is a layer for protecting the surface of the structure, and is not particularly limited as long as it is a material that forms a film on the surface of the structure. In addition to covering the surface of the fine particles, the overcoat layer is preferably filled between the fine particles. Examples of resins that constitute the overcoat layer include acrylic resin, acrylic urethane resin, silicone resin, and epoxy resin. The most common forms of resin are resin solutions diluted with any solvent, or emulsions dispersed in water.

[0062] The thickness of the overcoat layer is not particularly limited, and should be greater than or equal to the thickness that covers the fine particles of the structure. The overcoat layer can be formed on the surface of the structure by applying a thin film of the resin solution or emulsion onto the structure and, if necessary, applying heat treatment or the like.

[0063] [Method for manufacturing the structure] A method for manufacturing the structure of the present invention is, for example, as follows. A dispersion of the present invention, containing fine particles and a water-soluble resin, is applied to a smooth substrate. Then, it is dried at an appropriate temperature. This arranges the fine particles.

[0064] As a method for applying the dispersion of the present invention to a substrate, any printing method that does not use plates, such as inkjet, spray, dipping, or spin coating, or any printing method with plates, such as offset gravure coater, gravure coater, doctor coater, bar coater, blade coater, flexo coater, or roll coater, can be used.

[0065] The coating thickness of the dispersion of the present invention is preferably 1 to 100 μm, more preferably 5 to 50 μm, and even more preferably 10 to 30 μm, depending on the solid content concentration of the dispersion. When the coating thickness is 1 μm or more, the infrared reflectivity of the resulting structure is improved. Furthermore, when the coating thickness is 100 μm or less, the regular arrangement of the resulting structure is improved, and the infrared reflectivity is also improved.

[0066] There are no particular limitations on the drying method after applying the dispersion of the present invention onto a substrate. Conventional known methods such as heat drying, hot air drying, infrared drying, microwave drying, and drum drying can be used. These drying methods may be used individually or in combination. If the drying temperature is too high, the dispersion medium may volatilize rapidly, disrupting the arrangement of the fine particles and negatively affecting color development. On the other hand, if the drying temperature is too low, uneven drying may occur, making it impossible to obtain a uniform colloidal crystal film. From the viewpoint of fine particle arrangement, a drying temperature in the range of 10 to 120°C, and particularly 90 to 110°C, is preferable. The drying time varies depending on the drying temperature, but from the viewpoint of the arrangement of fine particles, it is preferably 0.5 to 30 minutes, more preferably 1 to 10 minutes.

[0067] [Application] The dispersion of the present invention exhibits excellent wettability to the substrate to be coated, and because it contains few high-viscosity components in the dispersion medium, it does not hinder the arrangement of fine particles and exhibits excellent film-forming properties. The structure of the present invention has a uniform film surface, resulting in good infrared reflectivity. Furthermore, binder components and the like can be easily filled between the fine particles. Due to these characteristics, the dispersion of the present invention can be suitably used alone or as a secondary processing material in, for example, paint compositions such as architectural paints, automotive paints, and plastic paints; ink compositions such as inkjet recording inks, gravure printing inks, and stationery inks; cosmetics such as foundations, lipsticks, lip balms, blushes, eyebrow cosmetics, and nail polishes; decorative films such as color sheets and decorative films; and optical materials such as reflective displays, color change sensors, anti-counterfeiting agents, electrodeposited color plates, color filters, and polarizing films. In particular, in the case of architectural paints and automotive paints, the dispersion of the present invention is especially suitable for heat shielding applications because it provides a structure with good infrared reflectivity.

[0068] Furthermore, the structure of the present invention can be suitably used alone or as a secondary processed material in, for example, paint compositions such as architectural paints, automotive paints, and plastic paints; ink compositions such as inkjet recording inks, gravure printing inks, and stationery inks; cosmetics such as foundations, lipsticks, lip balms, blushes, eyebrow cosmetics, and nail polishes; decorative films such as color sheets and decorative films; and optical materials such as reflective displays, color change sensors, anti-counterfeiting agents, electrodeposited color plates, color filters, and polarizing films. In particular, in the case of architectural paints and automotive paints, the structure of the present invention, which has good infrared reflectivity, is especially suitable for heat shielding applications.

[0069] In the various applications described above, the dispersion of the present invention may be used as a direct raw material. Alternatively, a structure in which fine particles are arranged may be used as a raw material, and the fine particles may be dispersed in a matrix material while maintaining their arranged state. [Examples]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention. In the following descriptions, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. Polyvinyl alcohol may also be abbreviated as "PVA." In the following examples and comparative examples, various physical properties were measured by the methods described below.

[0071] [Evaluation Method] (1) Number average particle size of fine particles An emulsion of fine particles was applied to a substrate and dried. Images of the fine particles were then observed using an electron microscope at a magnification of 20,000x or higher. The diameters of at least 400 fine particles in the images were measured, and the number-average particle diameter was calculated by taking an arithmetic mean of these measurements.

[0072] (2) CV value of particle size based on the number of fine particles Using the diameter measurements of at least 400 particles mentioned above, the coefficient of variation (CV) of particle size was calculated using the formula (standard deviation / average particle diameter) × 100.

[0073] (3) Solid content of emulsion The solid content concentration of the emulsion was determined by heating 10 g of emulsion at 190°C for 60 minutes to evaporate the water using an A&D Company, Limited (A&D) MX-50 heating and drying type moisture meter.

[0074] (4) Difference in contact angle The contact angle was determined as follows: Using a KRUSS DSA25 simple contact angle meter, 10 μL droplets of a dispersion were prepared on a plasma-treated polyester film (Toray Films, Lumirror (black), 100 μm thick). The contact angles were measured at two points 60 seconds after droplet placement under conditions of 25°C and 60% RH, and the average value was calculated. Furthermore, the contact angle of deionized water was measured under similar conditions. Next, the difference in contact angles was calculated by subtracting the contact angle of the dispersion from the contact angle of the ion-exchanged water.

[0075] (5) Film forming properties The film-forming properties were determined as follows. Using a wire bar (OSG, OSP-25), the dispersion was applied at 15 mm / second onto a plasma-treated polyester film (Toray Films, Lumirror (black), 100 μm thick). The width of the liquid during application and the width of the coated film (structure) after standing at 25°C for 30 minutes were calculated based on the following formula. Film-forming performance evaluation index = (Width of coated film after standing / Width of liquid during application) The evaluation criteria are as follows: ○(good): When the film-forming performance evaluation index is 0.7 or higher. × (poor): If the film-forming performance index is less than 0.7

[0076] (6)Reflection wavelength A dispersion was applied at 15 mm / second using a wire bar (OSP-25, OSG) onto a plasma-treated polyester film (Lumirror (black), 100 μm thick, manufactured by Toray Industries, Inc.), and dried at 25°C for 10 minutes to form a structure on the film. The reflection spectrum of the obtained structure was measured in the wavelength range of 250 to 2500 nm using an ultraviolet-visible-near-infrared spectrophotometer (V-770, JASCO Corporation) and an absolute reflectance measurement unit (ARSN-917, JASCO Corporation). At this time, both the incident angle and the reflection angle were set to 10°. The mirror in the absolute reflectance measurement unit (ARSN-917, JASCO Corporation) was used as the reference for the measurement. The maximum reflectance value in the obtained reflection spectrum was taken as the reflectance originating from the particle arrangement, and if the wavelength showing that reflectance was between 831 and 2500 nm, it was determined to have infrared reflectivity, and this wavelength was taken as the "reflection wavelength".

[0077] (7) Infrared reflection performance The infrared reflection performance was evaluated as follows, based on the reflectance value derived from the particle arrangement, which was determined by evaluating the reflection wavelength. ○ (good): When the reflectance value derived from the particle arrangement is 5% or more. × (poor): When the reflectance value derived from the particle arrangement is less than 5%.

[0078] [Raw materials, etc.] In the following examples and comparative examples, the raw materials used to produce the aqueous dispersions are as follows. • Styrene (manufactured by Denka Co., Ltd.) • Acrylic acid (manufactured by Mitsubishi Chemical Corporation) • Sodium styrene sulfonate (manufactured by Tosoh Finechem Co., Ltd.) • Sodium bicarbonate (manufactured by Fujifilm Wako Co., Ltd.) • Ammonium persulfate (manufactured by Kanto Chemical Co., Ltd.)

[0079] <Water-soluble resin> • Ionic PVA: Anionic polyvinyl alcohol-based resin (manufactured by Mitsubishi Chemical Corporation, Gosenex CKS50) • Water-soluble polyester: Anionic polyester resin (manufactured by Mitsubishi Chemical Corporation, Nichigo Polyester WR905) • Nonionic PVA: Nonionic polyvinyl alcohol-based resin (manufactured by Mitsubishi Chemical Corporation, Nichigo G Polymer)

[0080] [Preparation of particulate emulsion] <Preparation of emulsion [1]> A monomer mixture was prepared by mixing 880 parts of styrene and 13 parts of acrylic acid. On the other hand, an auxiliary solution was prepared by dissolving 0.42 parts of sodium p-styrene sulfonate and 1.5 parts of sodium bicarbonate in 2056 parts of deionized water. The additive solution was placed in a reaction vessel equipped with a stirring device, a heating and cooling device, a nitrogen introduction device, and a raw material / additive charging device, and the internal temperature was raised to 77°C. Next, a polymerization initiator solution, prepared by dissolving 4.4 parts of ammonium persulfate in 40 parts of deionized water, was added to the reaction vessel. Five minutes later, the monomer mixture was added dropwise over 2.5 hours. After the monomer mixture was added dropwise, stirring was continued at 77°C for 1.5 hours, and then the internal temperature was raised to 90°C. Stirring at 90°C was then maintained for 3 hours. After cooling the internal temperature to 20°C, the polymerization reaction product was filtered through nonwoven gauze (product name "Cross Gauze No. 2", manufactured by Osaki Medical Co., Ltd.) to obtain emulsion A, which consists of fine particles. The pH of emulsion A was adjusted to 7.0 by adding 10% aqueous ammonia. Additionally, deionized water was added as needed to adjust the solid content to 29.0% to obtain emulsion [1]. The obtained fine particles had a number-average particle size of 485 nm and a CV value of 5.6%.

[0081] <Preparation of emulsion [2]> A monomer mixture was prepared by mixing 880 parts of styrene and 13 parts of acrylic acid. On the other hand, an auxiliary solution was prepared by dissolving 0.27 parts of sodium p-styrene sulfonate and 1.5 parts of sodium bicarbonate in 2056 parts of deionized water. The additive solution was placed in a reaction vessel equipped with a stirring device, a heating and cooling device, a nitrogen introduction device, and a raw material / additive charging device, and the internal temperature was raised to 77°C. Next, a polymerization initiator solution, prepared by dissolving 4.4 parts of ammonium persulfate in 40 parts of deionized water, was added to the reaction vessel. Five minutes later, the monomer mixture was added dropwise over 2.5 hours. After the monomer mixture was added dropwise, stirring was continued at 77°C for 1.5 hours, and then the internal temperature was raised to 90°C. Stirring at 90°C was then maintained for 3 hours. After cooling the internal temperature to 20°C, the polymerization reaction product was filtered through nonwoven gauze (product name "Cross Gauze No. 2", manufactured by Osaki Medical Co., Ltd.) to obtain emulsion B, which consists of fine particles. The pH of emulsion B was adjusted to 7.0 by adding 10% aqueous ammonia. Additionally, deionized water was added as needed to adjust the solid content to 29.0% to obtain emulsion [2]. The obtained fine particles had a number-average particle size of 540 nm and a CV of 7.1%.

[0082] <Preparation of emulsion [3]> A monomer mixture was prepared by mixing 880 parts of styrene and 13 parts of acrylic acid. On the other hand, an auxiliary solution was prepared by dissolving 0.18 parts of sodium p-styrene sulfonate and 1.5 parts of sodium bicarbonate in 2056 parts of deionized water. The additive solution was placed in a reaction vessel equipped with a stirring device, a heating and cooling device, a nitrogen introduction device, and a raw material / additive charging device, and the internal temperature was raised to 77°C. Next, a polymerization initiator solution, prepared by dissolving 4.4 parts of ammonium persulfate in 40 parts of deionized water, was added to the reaction vessel. Five minutes later, the monomer mixture was added dropwise over 2.5 hours. After the monomer mixture was added dropwise, stirring was continued at 77°C for 1.5 hours, and then the internal temperature was raised to 90°C. Stirring at 90°C was then maintained for 3 hours. After cooling the internal temperature to 20°C, the polymerization reaction product was filtered through nonwoven gauze (product name "Cross Gauze No. 2", manufactured by Osaki Medical Co., Ltd.) to obtain emulsion C, which consists of fine particles. The pH of emulsion C was adjusted to 7.0 by adding 10% aqueous ammonia. Additionally, deionized water was added as needed to adjust the solid content to 29.0% to obtain emulsion [3]. The obtained fine particles had a number-average particle size of 637 nm and a CV value of 6.3%.

[0083] [Example 1] A dispersion with a solid content of 27% was prepared by mixing 18.6 parts of emulsion [1], 0.013 parts of an aqueous solution containing 4% by mass of ionic PVA as a water-soluble resin, and 1.37 parts of deionized water. The amount of water-soluble resin added was adjusted to 0.01 parts per 100 parts of fine particles. The obtained dispersion was coated onto a plasma-treated polyester film (Toray Films, Lumirror (black), 100 μm thick) using a wire bar (OSG, OSP-25) at a rate of 15 mm / second, and dried at 25°C for 3 minutes to obtain a structure.

[0084] [Example 2] A dispersion with a solid content of 27% was prepared by mixing 18.6 parts of emulsion [1], 0.067 parts of an aqueous solution containing 4% by mass of ionic PVA as a water-soluble resin, and 1.32 parts of deionized water. The amount of water-soluble resin added was adjusted to 0.05 parts per 100 parts of fine particles. The obtained dispersion was coated under the same conditions as in Example 1 to obtain a structure.

[0085] [Example 3] A dispersion with a solid content of 27% was prepared by mixing 18.6 parts of emulsion [1], 0.135 parts of an aqueous solution containing 4% by mass of ionic PVA as a water-soluble resin, and 1.26 parts of deionized water. The amount of water-soluble resin added was adjusted to 0.1 parts per 100 parts of fine particles. The obtained dispersion was coated under the same conditions as in Example 1 to obtain a structure.

[0086] [Example 4] A dispersion with a solid content of 27% was prepared by mixing 18.5 parts of emulsion [1], 0.538 parts of an aqueous solution containing 4% by mass of ionic PVA as a water-soluble resin, and 0.92 parts of deionized water. The amount of water-soluble resin added was adjusted to 0.4 parts per 100 parts of fine particles. The obtained dispersion was coated under the same conditions as in Example 1 to obtain a structure.

[0087] [Example 5] A dispersion and structure were obtained by performing the same procedure as in Example 2, except that 0.067 parts of an aqueous solution containing 4% by mass of water-soluble polyester was added as a water-soluble resin instead of ionic PVA.

[0088] [Example 6] A dispersion and structure were obtained by performing the same procedure as in Example 2, except that 0.067 parts of an aqueous solution containing 4% by mass of nonionic PVA as a water-soluble resin were added instead of ionic PVA.

[0089] [Example 7] A dispersion and structure were obtained by performing the same procedure as in Example 3, except that 0.135 parts of an aqueous solution containing 4% by mass of nonionic PVA as a water-soluble resin were added instead of ionic PVA.

[0090] [Example 8] A dispersion and structure were obtained by performing the same procedure as in Example 1, except that 18.6 parts of emulsion [2] were used instead of emulsion [1].

[0091] [Example 9] A dispersion and structure were obtained by performing the same procedure as in Example 2, except that 18.6 parts of emulsion [2] were used instead of emulsion [1].

[0092] [Example 10] A dispersion and structure were obtained by performing the same procedure as in Example 3, except that 18.6 parts of emulsion [2] were used instead of emulsion [1].

[0093] [Example 11] A dispersion and structure were obtained by performing the same procedure as in Example 5, except that 18.6 parts of emulsion [2] were used instead of emulsion [1].

[0094] [Example 12] A dispersion and structure were obtained by performing the same procedure as in Example 6, except that 18.6 parts of emulsion [2] were used instead of emulsion [1].

[0095] [Example 13] A dispersion and structure were obtained by performing the same procedure as in Example 1, except that 18.6 parts of emulsion [3] were used instead of emulsion [1].

[0096] [Example 14] A dispersion and structure were obtained by performing the same procedure as in Example 2, except that 18.6 parts of emulsion [3] were used instead of emulsion [1].

[0097] [Example 15] A dispersion and structure were obtained by performing the same procedure as in Example 3, except that 18.6 parts of emulsion [3] were used instead of emulsion [1].

[0098] [Example 16] A dispersion and structure were obtained by performing the same procedure as in Example 4, except that 18.5 parts of emulsion [3] were used instead of emulsion [1].

[0099] [Example 17] A dispersion and structure were obtained by performing the same procedure as in Example 5, except that 18.6 parts of emulsion [3] were used instead of emulsion [1].

[0100] [Example 18] A dispersion and structure were obtained by performing the same procedure as in Example 6, except that 18.6 parts of emulsion [3] were used instead of emulsion [1].

[0101] [Comparative Example 1] A dispersion with a solid content of 27% was prepared by mixing 18.6 parts of emulsion [1] with 1.38 parts of deionized water. The obtained dispersion was coated under the same conditions as in Example 1 to obtain a structure.

[0102] [Comparative Example 2] A dispersion with a solid content of 27% was prepared by mixing 18.4 parts of emulsion [1], 1.337 parts of an aqueous solution containing 4% by mass of ionic PVA as a water-soluble resin, and 0.23 parts of deionized water. The amount of water-soluble resin added was adjusted to 1.0 part per 100 parts of fine particles. The obtained dispersion was coated under the same conditions as in Example 1 to obtain a structure.

[0103] Table 1 shows the difference in contact angle, film-forming properties, reflected wavelength, and infrared reflection performance for the dispersions and structures obtained in Examples 1-18 and Comparative Examples 1-2.

[0104] [Table 1]

[0105] As shown in Table 1, Examples 1 to 18 using the dispersion of the present invention were found to have excellent film-forming properties and infrared reflectivity.

[0106] In contrast, Comparative Example 1, which did not use a water-soluble resin, did not exhibit sufficient film-forming properties. Comparative Example 2, in which 1.0 part of water-soluble resin was added per 100 parts of fine particles, showed sufficient film-forming ability, but no clear reflection peak was observed in the resulting structure, indicating insufficient infrared reflection performance.

Claims

1. A dispersion containing fine particles, a water-soluble resin, and a dispersion medium, The number-average particle diameter of the fine particles is 451 to 800 nm, and the CV value of the particle diameter based on the number is 15% or less. A dispersion containing 0.001 to 0.4 parts by mass of the water-soluble resin per 100 parts by mass of the fine particles.

2. The dispersion according to claim 1, wherein the contact angle with the polyester film is 2° or more lower than the contact angle of water with the polyester film.

3. The dispersion according to claim 1 or 2, wherein the concentration of solids is 10% by mass or more.

4. The dispersion according to claim 1 or 2, wherein the water-soluble resin is an ionic water-soluble resin.

5. The dispersion according to claim 1 or 2, wherein the water-soluble resin is an ionic polyvinyl alcohol-based resin.

6. A structure having infrared reflectivity, comprising a colloidal aggregate containing a water-soluble resin and fine particles contained in the dispersion described in claim 1 or 2.

7. Furthermore, the structure according to claim 6, having an overcoat layer on its surface.

8. A paint composition using the dispersion described in claim 1.

9. An ink composition using the dispersion described in claim 1.

10. A cosmetic composition using the dispersion described in claim 1.

11. A decorative film using the dispersion described in claim 1.

12. An optical material using the dispersion described in claim 1.

13. A paint composition using the structure described in claim 6.

14. An ink composition using the structure described in claim 6.

15. A cosmetic product using the structure described in claim 6.

16. A decorative film using the structure described in claim 6.

17. An optical material using the structure described in claim 6.

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