Light-diffusible resin composition and light-diffusing sheet

Abstract

This light-diffusible resin composition is capable of forming a light-diffusing layer that is excellent in light diffusibility and has suppressed unevenness of light diffusion performance, and contains light-diffusible microparticles, a matrix resin, and a solvent. The light-diffusible microparticles are organic microparticles containing a polymer of microparticle-synthesizing polymerizable monomers including a crosslinkable hydrocarbon monomer. The light-diffusible microparticles provide an immersion heat amount of 0.7-100 J / g when immersed in octane at 30°C, and provide an immersion heat amount of 1-100 J / g when immersed in formamide at 30°C. The matrix resin is constituted of at least one type of thermoplastic resin. The surface free energy of each type of thermoplastic resin is at least 20 mN / m and lower than 50 mN / m at 20°C. The solvent is constituted of at least one type of of organic solvent. The surface tension of each type of organic solvent is 20-40 mN / m at 20°C.

Description

Light-diffusing resin composition and light-diffusing sheet

[0001] The present disclosure relates to a light-diffusing resin composition and a light-diffusing sheet formed using the light-diffusing resin composition.

[0002] Light diffusion sheets are used in display devices such as liquid crystal display devices and organic EL display devices to uniformly diffuse light emitted from a light source. Conventionally, light diffusion sheets have been made of a sheet having one or both surfaces roughened, or a sheet having a light diffusion layer containing transparent organic fine particles formed on the surface of a substrate.

[0003] Patent Document 1 discloses a high light-diffusing film that uses a transparent or translucent plastic film, or a plastic film that has been embossed on one or both sides to form fine irregularities and improve the diffusion of transmitted light, and that is characterized by coating one or both sides of the plastic film with a high light-diffusing paint containing highly light-diffusing fine particles to provide a high light-diffusing layer. In the examples of Patent Document 1, a high light-diffusing paint is prepared that contains 50% by weight of a spherical benzoguanamine-melamine-formaldehyde condensate as a high light-diffusing agent, 20% by weight of a polyester resin as a binder, 1% by weight of a dispersant, 14% by weight of MEK (methyl ethyl ketone), and 15% by weight of toluene.

[0004] On the other hand, in a coating agent (paint) made by adding light-diffusing microparticles to a solution in which a matrix resin (binder resin) is dissolved in an organic solvent, it is difficult to improve the dispersibility of the light-diffusing microparticles, and a light-diffusing layer formed using a coating agent in which the dispersibility of the light-diffusing microparticles is insufficient has problems such as insufficient light diffusion properties or uneven light diffusion properties, such as the light diffusion properties varying depending on the measurement location.

[0005] Japanese Patent Application Publication No. 06-059108

[0006] The present disclosure has been made in view of the above problems, and aims to provide a light-diffusing resin composition capable of forming a light-diffusing layer having excellent light diffusibility and reduced unevenness in light diffusing performance. Another aim of the present disclosure is to provide a light-diffusing sheet using the light-diffusing resin composition having excellent light diffusibility and reduced unevenness in light diffusing performance.

[0007] The present disclosure provides the following light-diffusing resin composition: [1] A light-diffusing resin composition comprising light-diffusing microparticles, a matrix resin, and a solvent, wherein the light-diffusing microparticles are organic microparticles containing a polymer of a polymerizable monomer for microparticles, including a crosslinkable hydrocarbon monomer, and the light-diffusing microparticles have a heat of immersion in octane at 30°C of 0.7 J / g or more and 100 J / g or less and a heat of immersion in formamide at 30°C of 1 J / g or more and 100 J / g or less, the matrix resin is at least one thermoplastic resin, and various surface free energies of the thermoplastic resin at 20°C are 20 mN / m or more and less than 50 mN / m, and the solvent is at least one organic solvent, and various surface tensions of the organic solvent at 20°C are 20 mN / m or more and 40 mN / m or less. [2] The light-diffusing resin composition according to [1], wherein the volume-average particle size of the light-diffusing fine particles is 1 to 10 μm, and the particle size distribution of the light-diffusing fine particles (volume-average particle size (Dv) / number-average particle size (Dp)) is 1.0 to 1.4. [3] The light-diffusing resin composition according to [1] or [2], wherein the matrix resin is an amorphous resin. [4] The light-diffusing resin composition according to any one of [1] to [3], wherein the light-diffusing fine particles are hollow particles having a porosity of 60% or more, with a number ratio of particles having only one hollow portion being 90% or more. [5] The light-diffusing resin composition according to any one of [1] to [4], wherein the polymerizable monomer for fine particles contains at least one crosslinkable acrylic monomer selected from the group consisting of 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate.

[0008] The present disclosure also provides the following light diffusion sheet: [6] A light diffusion sheet containing the solid content of the light-diffusing resin composition according to any one of [1] to [5], which has a total light transmittance of 60% or more, a diffuse transmittance of 60% or more, and a standard deviation of the diffuse transmittance of 3% or less.

[0009] According to the present disclosure, it is possible to provide a light-diffusing resin composition capable of forming a light-diffusing layer having excellent light diffusibility and reduced unevenness in light diffusing performance. Furthermore, according to the present disclosure, it is possible to provide a light-diffusing sheet having excellent light diffusibility and reduced unevenness in light diffusing performance.

[0010] FIG. 4 is a diagram illustrating a method for measuring the thickness of a light diffusion sheet.

[0011] In the present disclosure, the term "to" in a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. In the present disclosure, (meth)acrylate refers to each of acrylate and methacrylate, (meth)acrylic refers to each of acrylic and methacrylic, and (meth)acryloyl refers to each of acryloyl and methacryloyl. The light-diffusing resin composition and the light-diffusing sheet of the present disclosure are described in detail below.

[0012] 1. Light-diffusing resin composition The light-diffusing resin composition of the present disclosure comprises light-diffusing microparticles, a matrix resin, and a solvent, wherein the light-diffusing microparticles are organic microparticles containing a polymer of a polymerizable monomer for microparticles including a crosslinkable hydrocarbon monomer, and the light-diffusing microparticles have a heat of immersion in octane at 30°C of 0.7 J / g or more and 100 J / g or less and a heat of immersion in formamide at 30°C of 1 J / g or more and 100 J / g or less, respectively, the matrix resin is at least one thermoplastic resin having a surface free energy of 20 mN / m or more and less than 50 mN / m at 20°C, and the solvent is at least one organic solvent having a surface tension of 20 mN / m or more and 40 mN / m or less at 20°C.

[0013] The light-diffusing resin composition of the present disclosure is used as a coating agent (paint) for forming a light-diffusing layer. By using the light-diffusing resin composition of the present disclosure, a light-diffusing layer having excellent light diffusibility and reduced unevenness in light-diffusing performance can be formed. In this disclosure, "reduced unevenness in light-diffusing performance" means that the standard deviation when the diffuse transmittance is measured at multiple locations is reduced. The light-diffusing microparticles contained in the light-diffusing resin composition of the present disclosure, their production method, matrix resin, solvent, and other materials added as needed will be described in detail below.

[0014] [Light-Diffusing Microparticles] The light-diffusing microparticles used in the present disclosure are organic microparticles containing a polymer of a polymerizable monomer for microparticles, including a crosslinkable hydrocarbon monomer. The heat of immersion of the light-diffusing microparticles in octane at 30°C is 0.7 J / g or more and 100 J / g or less, and the heat of immersion of the light-diffusing microparticles in formamide at 30°C is 1 J / g or more and 100 J / g or less. Note that, in the present disclosure, octane refers to n-octane. Because the light-diffusing microparticles contain a polymer of a polymerizable monomer for microparticles, including a crosslinkable hydrocarbon monomer, dissolution or swelling in the light-diffusing resin composition of the present disclosure is suppressed. While some polymer particles generally dissolve or swell in solvents, the light-diffusing microparticles used in the present disclosure contain a crosslinkable hydrocarbon monomer as a raw material, and therefore the crosslink density of the polymer contained therein is sufficiently high, thereby suppressing dissolution or swelling in solvents. Dissolution or swelling of light-diffusing microparticles in a light-diffusing resin composition may result in a decrease in light diffusion or uneven light diffusion performance in a light-diffusing layer formed using the light-diffusing resin composition. Furthermore, the light-diffusing microparticles have affinity for both polar and non-polar compounds because the heat amounts of immersion in octane at 30°C and formamide at 30°C are within the above ranges. Therefore, the light-diffusing microparticles have high affinity with organic solvents with a surface tension of 20 mN / m or more and 40 mN / m or less, and also high affinity with thermoplastic resins with a surface free energy of 20 mN / m or more and less than 50 mN / m. Therefore, they are less likely to aggregate and have excellent dispersibility in the light-diffusing resin composition of the present disclosure containing these as solvents and matrix resins. As a result, a light-diffusing layer formed using the light-diffusing resin composition of the present disclosure has excellent uniformity in the distribution of light-diffusing microparticles, resulting in excellent light diffusion and less uneven light diffusion performance. If at least one of the heat values ​​of immersion of the light-diffusing fine particles in octane and the heat value of immersion in formamide is outside the above range, the light-diffusing fine particles tend to aggregate in the light-diffusing resin composition, making it difficult to disperse them. Note that the heat value of immersion in octane at 30°C can be used as an index of affinity with non-polar compounds, and the heat value of immersion in formamide at 30°C can be used as an index of affinity with polar compounds.In organic microparticles, the greater the content ratio of carbon atom and hydrogen atom, the greater the heat of immersion in octane tends to be, and the greater the content ratio of oxygen atom, the greater the heat of immersion in formamide tends to be.Therefore, by adjusting the composition of the polymerizable monomer for microparticles used for producing light-diffusing microparticles, the heat of immersion of light-diffusing microparticles in octane and the heat of immersion in formamide can be adjusted within the above range.In addition, the heat of immersion of light-diffusing microparticles in octane and the heat of immersion in formamide are measured by the method described in the examples below.

[0015] The light-diffusing fine particles have an affinity for non-polar compounds because the heat of immersion in octane at 30° C. is 0.7 J / g or more, and because the heat of immersion in octane at 30° C. is 100 J / g or less, the cohesive force between particles is not too strong and they are unlikely to aggregate. From this perspective, the heat of immersion of the light-diffusing fine particles in octane at 30° C. is preferably 0.8 J / g or more and 90 J / g or less, more preferably 0.9 J / g or more and 80 J / g or less, and even more preferably 1 J / g or more and 30 J / g or less.

[0016] The light-diffusing fine particles have an affinity for polar compounds because the heat of immersion in formamide at 30° C. is 1 J / g or more, and because the heat of immersion is 100 J / g or less, the cohesive force between particles is not too strong and they are less likely to aggregate. From this perspective, the heat of immersion of the light-diffusing fine particles in formamide at 30° C. is preferably 2 J / g or more and 95 J / g or less, more preferably 3 J / g or more and 90 J / g or less, and even more preferably 4 J / g or more and 90 J / g or less.

[0017] In addition, among the numerical values ​​described to explain the present disclosure, numerical values ​​that may include decimal places are, unless otherwise specified, values ​​obtained by rounding off the digit that is one place smaller than the smallest digit included in the numerical value. However, with regard to the heat of immersion of the above-mentioned light-diffusing fine particles in octane and formamide, it is sufficient that the value obtained by rounding off the digit to one decimal place falls within the above-mentioned range. For example, when the value obtained by rounding off the digit to one decimal place for the value of the heat of immersion in formamide is 0.9 J / g, it does not fall within the range of 1 J / g to 100 J / g, and when the value obtained by rounding off the digit to one decimal place is 1.0 J / g, it falls within the range of 1 J / g to 100 J / g.

[0018] The light-diffusing microparticles are organic microparticles containing a polymer (resin) of a polymerizable monomer for microparticles, including a crosslinkable hydrocarbon monomer. From the viewpoints of the light diffusion properties, suppression of unevenness in light diffusion performance, and light transmittance of the light-diffusing layer formed, resin microparticles containing, as a main component, a polymer of a polymerizable monomer for microparticles, as described below, are preferably used as the organic microparticles. In this disclosure, a "polymerizable monomer" refers to a monomer having a reactive unsaturated bond. In this disclosure, a polymerizable monomer used as a raw material for light-diffusing microparticles is referred to as a "polymerizable monomer for microparticles." Here, the "reactive unsaturated bond" may be, for example, a reactive unsaturated bond that undergoes an addition reaction in response to a radical, or a reactive unsaturated bond that undergoes an addition reaction in response to active hydrogen, and is not particularly limited. Among these, a radical-reactive unsaturated bond is preferred from the viewpoints of reactivity and the optical properties of the light-diffusing layer formed. Examples of reactive unsaturated bonds include those contained in vinyl groups, (meth)acryloyl groups, allyl groups, butenyl groups, maleimide groups, nadimide groups, propargyl groups, or ethynyl groups, among which ethylenically unsaturated bonds are preferred, more preferably those contained in at least one selected from the group consisting of vinyl groups, (meth)acryloyl groups, and allyl groups, and even more preferably those contained in at least one selected from the group consisting of vinyl groups and (meth)acryloyl groups. Note that the term "(meth)acryloyl group" refers to both acryloyl groups and methacryloyl groups.

[0019] In addition, in the present disclosure, a polymerizable monomer having only one reactive unsaturated bond in one molecule is referred to as a non-crosslinkable monomer, and a polymerizable monomer having multiple reactive unsaturated bonds in one molecule is referred to as a crosslinkable monomer. The crosslinkable monomer can form a crosslinked bond in a polymer by a polymerization reaction. The crosslinkable monomer becomes a crosslinkable monomer unit after the polymerization reaction, and the non-crosslinkable monomer becomes a non-crosslinkable monomer unit after the polymerization reaction. The structure and ratio of each monomer unit constituting a polymer can be determined from the composition of the polymerizable monomers used in the synthesis of the polymer, and from the polymer after the polymerization reaction, １ It can be determined from the integral value obtained by H-NMR measurement.

[0020] In this disclosure, a polymerizable monomer consisting of carbon and hydrogen is referred to as a hydrocarbon monomer, a crosslinkable monomer consisting of carbon and hydrogen is referred to as a crosslinkable hydrocarbon monomer, and a non-crosslinkable monomer consisting of carbon and hydrogen is referred to as a non-crosslinkable hydrocarbon monomer. Furthermore, a polymerizable monomer having a (meth)acryloyl group is referred to as an acrylic monomer, a crosslinkable monomer having a (meth)acryloyl group is referred to as a crosslinkable acrylic monomer, and a non-crosslinkable monomer having a (meth)acryloyl group is referred to as a non-crosslinkable acrylic monomer. While a crosslinkable acrylic monomer may contain at least one (meth)acryloyl group, it is preferable that all reactive unsaturated bonds are contained in (meth)acryloyl groups.

[0021] (Polymerizable Monomer for Fine Particles) As the polymerizable monomer for fine particles, known polymerizable monomers conventionally used in the production of light-diffusing fine particles can be used. The light-diffusing fine particles used in the present disclosure may be formed by polymerizing the polymerizable monomer for fine particles. The polymerizable monomer for fine particles used in the present disclosure includes at least a crosslinkable hydrocarbon monomer. Examples of the crosslinkable hydrocarbon monomer include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; and diene monomers such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, hexadiene, dicyclopentadiene, cyclopentadiene, ethylidenetetracyclododecene, and 2-phenyl-1,3-butadiene.

[0022] The polymerizable monomer for fine particles may further contain a crosslinkable acrylic monomer as a crosslinkable monomer. Examples of the crosslinkable acrylic monomer include allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 3-(meth)acryloyloxy-2-hydroxypropyl (meth)acrylate, 1,3-bis(methacryloyloxy)-2-hydroxypropane, 1,3-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, bisphenol F di(meth)acrylate, bisphenol A di(meth)acrylate, difunctional crosslinkable acrylic monomers such as methyl acrylate, isocyanuric acid di(meth)acrylate, ethoxylated and propoxylated products thereof, difunctional urethane(meth)acrylate, and difunctional polyester(meth)acrylate; trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, Examples of the crosslinkable acrylic monomer include trifunctional or higher crosslinkable acrylic monomers such as tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, glycerol tri(meth)acrylate, diglycerol (meth)acrylate, ethoxylated and propoxylated versions of these, polybasic acid-modified acrylic oligomers, and trifunctional or higher crosslinkable acrylic monomers such as trifunctional or higher polyester (meth)acrylates.

[0023] Further examples of the crosslinkable monomer include crosslinkable allylic monomers such as allyl phthalate, crosslinkable macromers such as polybutadiene, polyisoprene, styrene-butadiene block copolymer (SBS), styrene-isoprene block copolymer (SIS), polyphenylene ether vinyl-modified at both ends, and polyphenylene ether (meth)acrylic-modified at both ends. These crosslinkable monomers can be used alone or in combination of two or more as the polymerizable monomer for fine particles.

[0024] Inclusion of a crosslinkable monomer as the polymerizable monomer for fine particles can increase the crosslink density of the polymer contained in the light-diffusing fine particles, thereby suppressing dissolution or swelling of the light-diffusing fine particles in the light-diffusing resin composition of the present disclosure and further improving the strength of the light-diffusing fine particles. Furthermore, when the light-diffusing fine particles are hollow particles, inclusion of a crosslinkable monomer as the polymerizable monomer for fine particles facilitates the formation of a shell with excellent strength, facilitates the hollow particles to become spherical, and facilitates the formation of hollow portions within the particles that are clearly distinguishable from the shell. From this perspective, the content of the crosslinkable monomer in 100% by weight of the polymerizable monomer for fine particles is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more. In the present disclosure, the polymerizable monomer for fine particles may consist of a crosslinkable monomer, but may also further contain a non-crosslinkable monomer, which will be described later as a polymerizable monomer for fine particles. Therefore, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer for microparticles may be, for example, 99% by mass or less, 98% by mass or less, or 97% by mass or less. The content of each monomer in 100% by mass of the polymerizable monomer for microparticles corresponds to the content of each monomer unit in 100% by mass of all monomer units constituting the polymer of the polymerizable monomer for microparticles.

[0025] In the present disclosure, the polymerizable monomer for fine particles contains at least a crosslinkable hydrocarbon monomer as a crosslinkable monomer. The content of the crosslinkable hydrocarbon monomer in 100% by mass of the polymerizable monomer for fine particles is appropriately adjusted so that the heat values ​​of immersion of the light-diffusing fine particles in octane and in formamide are each within the above-mentioned ranges, and is not particularly limited, but the lower limit is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and the upper limit is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0026] The polymerizable monomer for fine particles preferably contains a combination of a crosslinkable hydrocarbon monomer and a crosslinkable acrylic monomer as a crosslinkable monomer. This allows the heat amounts of immersion of the light-diffusing fine particles in octane and formamide to be easily set within the above ranges, thereby improving the light diffusibility of the formed light diffusion layer and suppressing unevenness in light diffusion performance. The content of the crosslinkable acrylic monomer in 100% by mass of the polymerizable monomer for fine particles is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and even more preferably 50% by mass or more, as a lower limit, and preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, as an upper limit.

[0027] In order to easily control the heat values ​​of immersion of the light-diffusing fine particles in octane and formamide, respectively, within the above-mentioned ranges, the crosslinkable hydrocarbon monomer in the polymerizable monomer for the fine particles is preferably at least one selected from the group consisting of divinylbenzene and 2-phenyl-1,3-butadiene. Furthermore, in order to improve the flexibility of the light-diffusing fine particles, 2-phenyl-1,3-butadiene is particularly preferred. The light-diffusing fine particles become less likely to crack when given flexibility. Therefore, by improving the flexibility of the light-diffusing fine particles, cracking of the light-diffusing fine particles can be suppressed during the production of the light-diffusing resin composition of the present disclosure, thereby improving the operability during the production. In order to easily set the heat values ​​for immersion of the light-diffusing fine particles in octane and formamide within the above ranges, and to improve the strength of the light-diffusing fine particles, the polymerizable monomer for fine particles preferably contains at least a bifunctional crosslinkable acrylic monomer as the crosslinkable acrylic monomer, and more preferably contains a combination of a bifunctional crosslinkable acrylic monomer and a trifunctional or higher crosslinkable acrylic monomer. Among these, the bifunctional crosslinkable acrylic monomer is preferably at least one selected from the group consisting of ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and glycerol di(meth)acrylate. Among them, the trifunctional or higher crosslinkable acrylic monomer is preferably at least one selected from the group consisting of trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and glycerol tri(meth)acrylate.

[0028] When the polymerizable monomer for fine particles contains a combination of a bifunctional crosslinkable acrylic monomer and a trifunctional or higher crosslinkable acrylic monomer, in order to improve the light diffusion properties of the light diffusion layer to be formed, suppress unevenness in light diffusion performance, and improve the strength of the light-diffusing fine particles, the content of the bifunctional crosslinkable acrylic monomer in 100% by mass of the crosslinkable acrylic monomer is preferably 20% by mass or more as a lower limit, more preferably 30% by mass or more, and even more preferably 40% by mass or more as an upper limit, and is preferably 80% by mass or less, more preferably 70% by mass or less.

[0029] In addition, in the polymerizable monomer for fine particles, it is preferable to use a crosslinkable acrylic monomer containing 4 to 6 oxygen atoms per molecule, since this allows the heat amounts of immersion of the light-diffusing fine particles in octane and formamide to be easily controlled within the above-mentioned ranges. Furthermore, among the crosslinkable acrylic monomers, 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate are particularly preferable, since they can improve the flexibility of the light-diffusing fine particles. That is, in the present disclosure, the use of at least one polymerizable monomer for fine particles selected from the group consisting of 2-phenyl-1,3-butadiene, 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate is particularly preferred because it can easily control the heat values ​​of immersion of the light-diffusing fine particles in octane and formamide within the above ranges, and it can also improve the flexibility of the light-diffusing fine particles. From these perspectives, it is preferable that the polymerizable monomer for fine particles contains two or more types selected from the above group, and more preferably three or more types.

[0030] The polymerizable monomer for fine particles may further contain a non-crosslinkable monomer. Among the polymerizable monomers for fine particles, the non-crosslinkable monomer is preferably at least one selected from the group consisting of non-crosslinkable hydrocarbon monomers and non-crosslinkable acrylic monomers. Examples of the non-crosslinkable hydrocarbon monomer include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; and monoolefins such as ethylene, propylene, butylene, vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methano-1,4,4a,9a-tetrahydrofluorene.Examples of non-crosslinkable acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, t-butylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, propoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, hexaoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol polypropylene glycol (meth)acrylate, lauroxypolyethylene glycol (meth)acrylate, stearoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol polypropylene glycol (meth)acrylate, ) acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol propylene glycol mono(meth)acrylate, polyethylene glycol tetramethylene glycol (meth)acrylate, propylene glycol polybutylene glycol mono(meth)acrylate, monoethylene glycol mono(meth)acrylate, phenol EO-modified (meth)acrylate, nonylphenol EO-modified (meth)acrylate, 2-ethylhexyl EO-modified (meth)acrylate, N-(meth)acryloyloxyethyl hexahydrophthalimide, ω-carboxy-polycaprolactone mono(meth)acrylate, monohydroxyethyl phthalate (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and the like.Examples of the non-crosslinkable monomer include vinyl carboxylate ester monomers such as vinyl acetate, halogenated aromatic vinyl monomers such as halogenated styrene, halogenated vinyl monomers such as vinyl chloride, halogenated vinylidene monomers such as vinylidene chloride, vinylpyridine, non-crosslinkable macromers such as polystyrene modified at one end with (meth)acrylic acid, and polymethyl methacrylate modified at one end with (meth)acrylic acid, etc. These non-crosslinkable monomers can be used alone or in combination of two or more as the polymerizable monomer for fine particles.

[0031] The content of the non-crosslinkable monomer in 100% by mass of the polymerizable monomer for fine particles is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and still more preferably 5% by mass or less, from the viewpoint of suppressing dissolution or swelling of the light-diffusing fine particles in the light-diffusing resin composition and suppressing a decrease in the strength of the light-diffusing fine particles. The lower limit of the content of the non-crosslinkable monomer in 100% by mass of the polymerizable monomer for fine particles is not particularly limited, and may be, for example, 1% by mass or more, 2% by mass or more, or 3% by mass or more.

[0032] Since the heat values ​​for immersion of the light-diffusing microparticles in octane and formamide can be easily controlled within the above ranges, the total content of the hydrocarbon monomer and the acrylic monomer in 100% by mass of the polymerizable monomer for microparticles is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and may even be 100% by mass. Furthermore, for the same reasons as above, the mass ratio of the acrylic monomer to the hydrocarbon monomer (acrylic monomer:hydrocarbon monomer) contained in the polymerizable monomer for microparticles is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40. In order for the light-diffusing layer to have light-diffusing properties, it is desirable for the difference in refractive index between the light-diffusing microparticles contained in the light-diffusing layer and the matrix resin to be sufficiently large. From the viewpoint of such a refractive index difference, it is preferable that the mass ratio of the acrylic monomer to the hydrocarbon monomer (acrylic monomer:hydrocarbon monomer) contained in the polymerizable monomer for fine particles is within the above range. When the mass ratio of the acrylic monomer to the hydrocarbon monomer contained in the polymerizable monomer for fine particles is within the above range, the difference between the refractive index of the light-diffusing fine particles and the refractive index of the matrix resin preferably used, which will be described later, becomes sufficiently large.

[0033] In order to easily set the heat of immersion of the light-diffusing microparticles in octane and the heat of immersion in formamide within the above ranges, and to improve the optical properties of the light-diffusing layer formed, the content of the polymer of the polymerizable monomer for the microparticles in the light-diffusing microparticles is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, and may be 100% by mass.

[0034] The light-diffusing fine particles may have polar groups such as amino groups or acidic groups on the particle surface. Examples of methods for introducing polar groups onto the surface of light-diffusing fine particles include a method of reacting a modifier for introducing polar groups, a method of performing surface treatment with a coupling agent having a polar group, and a method of using a polymerizable monomer for fine particles having a polar group.

[0035] The thermal decomposition onset temperature of the light-diffusing fine particles is not particularly limited, but from the viewpoint of heat resistance, it is preferably 345°C or higher, more preferably 350°C or higher. The upper limit of the thermal decomposition onset temperature of the light-diffusing fine particles is not particularly limited, but may be, for example, 400°C or lower. In the present disclosure, the thermal decomposition onset temperature of the light-diffusing fine particles is the temperature at which a 5% weight loss occurs, and can be measured using a TG-DTA device under conditions of a nitrogen atmosphere, a nitrogen flow rate of 230 mL / min, and a temperature rise rate of 10°C / min.

[0036] The shape of the light-diffusing fine particles may be, for example, spherical, ellipsoidal, or amorphous, but is preferably spherical from the viewpoint of the dispersibility and pressure resistance of the light-diffusing fine particles. The shape of the light-diffusing fine particles can be confirmed, for example, by observing the light-diffusing fine particles with a SEM or TEM.

[0037] The volume average particle diameter of the light-diffusing fine particles is not particularly limited, but the lower limit is preferably 1 μm or more, more preferably 2 μm or more, and the upper limit is preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less.When the volume average particle diameter of the light-diffusing fine particles is equal to or greater than the lower limit, the aggregation of the light-diffusing fine particles is suppressed and the dispersibility is improved, so that the light diffusion property of the formed light-diffusing layer is improved, the unevenness of the light-diffusing performance is suppressed, and further, the increase in the film thickness of the light-diffusing layer due to the aggregation of the light-diffusing fine particles is suppressed.When the volume average particle diameter of the fine particles is equal to or less than the upper limit, the light-diffusing layer can be easily thinned.

[0038] The particle size distribution (volume average particle size (Dv) / number average particle size (Dp)) of the light-diffusing microparticles is not particularly limited, but is preferably 1.0 to 1.4, more preferably 1.05 to 1.35, even more preferably 1.10 to 1.30, and even more preferably 1.15 to 1.25. When the particle size distribution is equal to or less than the upper limit, the amount of coarse particles is sufficiently small, making it easy to form a thin light-diffusing layer. Furthermore, when the particle size distribution is equal to or less than the upper limit, the thickness uniformity of the formed light-diffusing layer can be improved. Furthermore, from the viewpoint of ease of production of the light-diffusing microparticles, the particle size distribution may be equal to or greater than the lower limit. The volume average particle size (Dv) and number average particle size (Dp) of the light-diffusing microparticles can be determined, for example, by measuring the particle size of the light-diffusing microparticles using a particle size distribution measuring device according to the Coulter counter method, calculating the volume average and number average, respectively, and using the obtained values ​​as the volume average particle size (Dv) and number average particle size (Dp) of the light-diffusing microparticles. The particle size distribution is the value obtained by dividing the volume average particle size by the number average particle size. The Coulter counter method is a method for measuring particle diameters by an electrical resistance method known as the Coulter principle.

[0039] The light-diffusing fine particles may be solid particles, porous particles, or hollow particles. Hollow particles, in particular, have high light transmittance due to their hollow interior. Therefore, using hollow particles as the light-diffusing fine particles can further improve the light transmittance of the resulting light-diffusing layer. Furthermore, the inclusion of hollow particles as the light-diffusing fine particles can impart various properties to the light-diffusing sheet of the present disclosure, such as weight reduction, heat insulation, and the ability to retain functional components such as antibacterial agents.

[0040] As hollow particles, hollow resin microparticles having a shell (outer shell) containing a polymer of the polymerizable monomer for microparticles and a hollow portion surrounded by the shell are preferably used. In hollow particles, the hollow portion is a hollow space clearly distinguishable from the shell. The shell of the hollow particle may have a porous structure, but in that case, the hollow portion has a size clearly distinguishable from the numerous microscopic spaces uniformly dispersed within the porous structure. Furthermore, from the viewpoint of light transmittance, the hollow portion of the hollow particle is preferably filled with a gas such as air. The hollow particle may have one or more hollow portions, but from the viewpoint of maintaining a good balance between high porosity and mechanical strength, it is preferable that the hollow particle have only one or two hollow portions, and it is even more preferable that the hollow particle have only one hollow portion. Among the hollow particles, the number ratio of particles having only one hollow portion is preferably 90% or more, more preferably 95% or more, and even more preferably more than 95%. The shell of the hollow particle and the partition walls separating adjacent hollow portions when the hollow particle has two or more hollow portions may be porous, but are preferably solid in order to improve the strength of the hollow particle. One example of the shape of the hollow particle is a bag made of a thin film and inflated with gas. The hollow portion of the hollow particle can be confirmed, for example, by observing the cross section of the particle with an SEM or by observing the particle itself with a TEM.

[0041] The porosity of the hollow particles is not particularly limited, but from the viewpoint of light transmittance, it is preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. The upper limit of the porosity of the hollow particles is not particularly limited, but from the viewpoint of suppressing a decrease in the strength of the hollow particles, it is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less.

[0042] The porosity of the hollow particles is the apparent density D １ and true density D ０ The apparent density of the hollow particles D １ The measurement method is as follows: First, a volume of 100 cm ３ About 30 cm３ The volumetric flask is filled with hollow particles, and the mass of the filled hollow particles is accurately weighed. Next, the volumetric flask filled with the hollow particles is accurately filled with isopropanol up to the marked line, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask is accurately weighed, and the apparent density D of the hollow particles is calculated based on the following formula (I): １ (g / cm ３ ) is calculated by the formula (I) Apparent density D １ Apparent density D = [Mass of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature]) １ corresponds to the specific gravity of the entire hollow particle when the hollow portion is considered to be a part of the hollow particle.

[0043] True density D of hollow particles ０ The measurement method is as follows: After crushing the hollow particles in advance, ３ Approximately 10 g of crushed pieces of hollow particles are filled into a measuring flask, and the mass of the crushed pieces is accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol is added to the measuring flask, and the mass of the isopropanol is accurately weighed. The true density D of the hollow particles is calculated based on the following formula (II): ０ (g / cm ３ ) is calculated using the formula (II) ０ = [mass of crushed pieces of hollow particles] / (100 - [mass of isopropanol] / [specific gravity of isopropanol at measurement temperature]) True density D ０ As is clear from the above measurement method, the true density D ０ In calculating the particle diameter, the hollow portion is not considered to be part of the hollow particle.

[0044] The porosity (%) of the hollow particles is calculated by multiplying the apparent density D １ and true density D ０ The porosity (%) is calculated by the following formula (III): １ / True density D ０ ) x 100

[0045] The porosity can also be measured by the method described above for microparticles whose hollowness is unknown. In this disclosure, microparticles with a porosity of less than 20% are considered to be solid particles. Microparticles with a porosity of 20% or more are considered to be hollow particles if they have a hollow portion clearly distinguishable from the shell, and porous particles if the entire interior of the particle is porous.

[0046] The light-diffusing microparticles may contain a small amount of particles with low circularity due to cracks or deformations as impurities. However, from the viewpoint of the light transmittance and light diffusion properties of the formed light diffusion layer, the proportion of particles with a circularity of 0.85 or less is preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably less than 8% by mass of 100% light-diffusing microparticles. Particles with a circularity of 0.85 or less are typically particles that have cracks or deformations such as dents, and may be referred to as "irregularly shaped particles" in the present disclosure. Such irregularly shaped particles have inferior light transmittance and light diffusion properties compared to spherical microparticles. Therefore, reducing the proportion of irregularly shaped particles contained in the light-diffusing microparticles can improve the light transmittance and light diffusion properties of the formed light diffusion layer. Furthermore, irregularly shaped particles have the problem of being more prone to aggregation and having poorer dispersibility than spherical microparticles. Therefore, reducing the proportion of irregularly shaped particles contained in the light-diffusing microparticles can improve the dispersibility of the light-diffusing microparticles, thereby improving the light diffusion properties of the formed light diffusion layer and suppressing uneven light diffusion performance. Furthermore, irregularly shaped particles have the problem of being poorer in pressure resistance than spherical microparticles because they are more susceptible to localized external pressure. When irregularly shaped particles are dispersed in a light-diffusing resin composition, aggregates are likely to form, and the aggregates are more likely to be subjected to external pressure, further reducing the pressure resistance. Therefore, the pressure resistance of the light-diffusing microparticles can be improved by reducing the proportion of irregularly shaped particles contained in the light-diffusing microparticles. From the same viewpoint as above, the proportion of particles with a circularity of 0.85 or less, based on the number, is preferably less than 15%, more preferably less than 10%, and even more preferably less than 8% of 100% of the light-diffusing microparticles.

[0047] Circularity is defined as the diameter of a circle having the same area as the projected image of a particle (equivalent circle area diameter) divided by the diameter of a circle having the same perimeter as the projected image of the particle (equivalent circumferential diameter). When a particle is a perfect sphere, the circularity is 1, and the more complex the particle's surface shape, the smaller the circularity value. The light-diffusing fine particles may have an average circularity of 0.950 to 0.995. In the present disclosure, the circularity is measured using a flow-type particle image analyzer with an image resolution of 0.185 μm / pixel. A preferred example of a flow-type particle image analyzer is the "IF-3200" manufactured by Jasco International Co., Ltd. A measurement sample is prepared by dispersing a mixture of, for example, 0.10 to 0.12 g of light-diffusing fine particles in an aqueous solution of linear alkylbenzenesulfonate (0.3% concentration) in an ultrasonic cleaner for 5 minutes. The average circularity is the average value of the circularity of 1,000 to 3,000 arbitrarily selected particles.

[0048] In the light-diffusing resin composition of the present disclosure, the content of the light-diffusing fine particles is not particularly limited, but the lower limit is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, and even more preferably 150 parts by mass or more, relative to 100 parts by mass of the matrix resin, and the upper limit is preferably 500 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 250 parts by mass or less. When the content of the light-diffusing fine particles is equal to or greater than the lower limit, the light diffusibility of the formed light diffusion layer is improved, and when the content is equal to or less than the upper limit, unevenness in the light diffusing performance and deterioration of light transmittance of the formed light diffusion layer are suppressed.

[0049] [Method of manufacturing light-diffusing microparticles] The light-diffusing microparticles can be manufactured by, for example, a manufacturing method based on suspension polymerization, which will be described later. As one embodiment of the method of manufacturing the light-diffusing microparticles, for example, the method of manufacturing light-diffusing microparticles can include the following steps: preparing a mixed solution containing the polymerizable monomer for microparticles, a polymerization initiator, a dispersion stabilizer and an aqueous medium (mixed solution preparation step); suspending the mixed solution to prepare a suspension in which oil droplets containing the polymerizable monomer for microparticles and the polymerization initiator are dispersed in the aqueous medium (suspension step); and subjecting the suspension to a polymerization reaction to form light-diffusing microparticles containing a polymer of the polymerizable monomer for microparticles (polymerization step).

[0050] Hollow particles can be produced by using a liquid mixture that further contains a hydrophobic solvent. When the liquid mixture contains a hydrophobic solvent, the oil droplets dispersed in the suspension contain a polymerizable monomer for forming fine particles and a hydrophobic solvent, which undergo phase separation, resulting in a distribution structure in which the polymerizable monomer for forming fine particles is concentrated on the surface and the hydrophobic solvent is concentrated in the center. When this suspension is subjected to a polymerization reaction, a polymer of the polymerizable monomer for forming fine particles begins to precipitate on the surface of the oil droplets. As the polymerization reaction progresses, the surface of the oil droplets hardens, forming a shell, resulting in hollow particles with hollow spaces filled with the hydrophobic solvent. When producing hollow particles, it is preferable to further perform a process (solvent removal process) after the polymerization process to remove the hydrophobic solvent that fills the hollow spaces, thereby obtaining hollow particles with gas-filled hollow spaces.

[0051] The above-mentioned method for producing light-diffusing microparticles may further include a step different from the above-mentioned steps. Furthermore, in the above-mentioned method for producing light-diffusing microparticles, as far as technically possible, two or more of the above-mentioned steps and other additional steps may be performed simultaneously as one step, or the order may be reversed. For example, the preparation and suspension of the mixed solution may be performed simultaneously in one step, such as by adding the materials for preparing the mixed solution and suspending them at the same time. Below, each step of the above-mentioned method for producing light-diffusing microparticles will be explained in order.

[0052] (1) Mixed Solution Preparation Step This step is a step of preparing a mixed solution containing a polymerizable monomer for fine particles, a polymerization initiator, a dispersion stabilizer, and an aqueous medium. The mixed solution may further contain other materials within the scope of the present disclosure.

[0053] (Polymerizable Monomer for Microparticles) The polymerizable monomer for microparticles contained in the mixed solution is as described above. The content of the polymerizable monomer for microparticles in the mixed solution is not particularly limited, but when producing hollow particles, it is preferably 15 to 50% by mass, more preferably 20 to 40% by mass, relative to 100% by mass of the total mass of the components in the mixed solution excluding the aqueous medium. On the other hand, when producing solid particles, it is preferably 60 to 90% by mass, more preferably 65 to 85% by mass. When the content of the polymerizable monomer for microparticles in the mixed solution is within the above range, the balance between the particle size and strength of the light-diffusing microparticles is likely to be good. In the present disclosure, the solid content refers to all components excluding the solvent, and liquid polymerizable monomers and the like are considered to be included in the solid content.

[0054] (Polymerization Initiator) In the mixed solution, the polymerization initiator preferably contains an oil-soluble polymerization initiator, from the viewpoint of facilitating control of the particle size of the light-diffusing fine particles. The oil-soluble polymerization initiator is not particularly limited as long as it is an oil-philic initiator having a solubility in water of 0.2 mass% or less, and examples thereof include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxydiethylacetate, t-butylperoxypivalate, and di-t-butylperoxide; and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0055] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the polymerizable monomer for fine particles in the mixed solution. When the content of the polymerization initiator is equal to or greater than the above-mentioned lower limit, the polymerization reaction can proceed sufficiently, while when the content is equal to or less than the above-mentioned upper limit, there is little risk of the polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0056] (Dispersion Stabilizer) The dispersion stabilizer is an agent that disperses oil droplets containing a polymerizable monomer for fine particles in an aqueous medium during the suspension process. Examples of dispersion stabilizers include inorganic dispersion stabilizers, organic or inorganic water-soluble polymer stabilizers, and surfactants. In the present disclosure, it is preferable to use an inorganic dispersion stabilizer as the dispersion stabilizer. This makes it easier to control the particle size of the oil droplets in the suspension and facilitates removal of the dispersion stabilizer during the washing process. Furthermore, when producing hollow particles, the use of an inorganic dispersion stabilizer can prevent the shell from becoming too thin and thus suppress a decrease in the strength of the hollow particles. Examples of inorganic dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and ferric hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used alone or in combination of two or more. Among the inorganic dispersion stabilizers, a poorly water-soluble inorganic dispersion stabilizer can be preferably used. Here, poorly water-soluble means that the solubility in water at 25° C. is preferably less than 1 g / L. Among the poorly water-soluble inorganic dispersion stabilizers, metal hydroxides are preferred, and magnesium hydroxide is more preferred.

[0057] In the present disclosure, it is particularly preferable to use a poorly water-soluble inorganic dispersion stabilizer in a state where it is dispersed in an aqueous medium in the form of colloidal particles, i.e., in a colloidal state. This allows the inorganic dispersion stabilizer to be easily removed by the washing step described below. A colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include barium hydroxide and calcium hydroxide. The water-soluble polyvalent metal salt may be any water-soluble polyvalent metal salt other than the above-mentioned alkaline earth metal hydroxides. Examples include magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred. The method for reacting at least one selected from the group consisting of the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium is not particularly limited. For example, an aqueous solution of at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides may be mixed with an aqueous solution of the water-soluble polyvalent metal salt. Furthermore, colloidal silica may be used as a colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles.

[0058] Examples of organic water-soluble polymer stabilizers include polyvinyl alcohol, polycarboxylic acids (such as polyacrylic acid), celluloses (such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose), polyvinylpyrrolidone, polyacrylimide, polyethylene oxide, and poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymers. Examples of inorganic water-soluble polymer stabilizers include sodium tripolyphosphate. Surfactants are compounds that have both hydrophilic and hydrophobic groups in one molecule, and include known ionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, as well as nonionic surfactants. Water-soluble polymer stabilizers and surfactants typically have a solubility of 1 g / L or more in water at 25°C.

[0059] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the combined mass of the polymerizable monomer for microparticles and the hydrophobic solvent. By having the content of the dispersion stabilizer equal to or greater than the lower limit, oil droplets containing the polymerizable monomer for microparticles can be sufficiently dispersed so as not to coalesce in the suspension. On the other hand, by having the content of the dispersion stabilizer equal to or less than the upper limit, an increase in the viscosity of the suspension during granulation can be prevented, and the problem of the suspension clogging in the granulator can be avoided. Furthermore, the content of the dispersion stabilizer is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the aqueous medium.

[0060] In the present disclosure, from the viewpoint of the optical properties of the light-diffusing microparticles, the smaller the residual amount of dispersion stabilizer, the more preferable, and it is most preferable that no dispersion stabilizer is contained, and it is particularly preferable that no water-soluble polymer stabilizer or surfactant is contained. By using only an inorganic dispersion stabilizer as the dispersion stabilizer, it is possible to obtain light-diffusing microparticles in which both the water-soluble polymer stabilizer and the surfactant are below the detection limit.

[0061] (Aqueous Medium) In the present disclosure, the term "aqueous medium" refers to a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent. When using a mixture of water and a hydrophilic solvent, it is important that the polarity of the entire mixture is not too low in order to form oil droplets containing the polymerizable monomer for microparticles. In this case, for example, the mass ratio of water to hydrophilic solvent (water:hydrophilic solvent) may be 99:1 to 50:50. The hydrophilic solvent in the present disclosure is not particularly limited as long as it is sufficiently miscible with water and does not cause phase separation. Examples of hydrophilic solvents include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO); and the like.

[0062] The content of the aqueous medium is not particularly limited, but from the viewpoint of keeping the particle diameter of the light-diffusing microparticles within a preferred range, the lower limit is preferably 200 parts by mass or more, more preferably 400 parts by mass or more, and even more preferably 600 parts by mass or more, relative to 100 parts by mass of the polymerizable monomer for microparticles contained in the mixed liquid, and the upper limit is preferably 1,000 parts by mass or less, and more preferably 800 parts by mass or less.

[0063] (Hydrophobic Solvent) When producing solid particles as light-diffusing microparticles, the mixed solution does not need to contain a hydrophobic solvent. However, when producing hollow particles as light-diffusing microparticles, it is preferable that the mixed solution further contain a hydrophobic solvent. The hydrophobic solvent can function as a spacer material that forms hollow spaces inside the light-diffusing microparticles, so adding a hydrophobic solvent to the mixed solution makes it possible to produce hollow particles. When the mixed solution contains a hydrophobic solvent, a suspension is obtained in which oil droplets containing a polymerizable monomer for microparticles and a hydrophobic solvent are dispersed in an aqueous medium during the suspension process described below. Phase separation occurs within the oil droplets, and the hydrophobic solvent, which has low polarity, tends to accumulate inside the oil droplets. Because each material is distributed according to its own polarity, the hydrophobic solvent ultimately becomes unevenly distributed inside the oil droplets, and the polymerizable monomer for microparticles becomes unevenly distributed around the periphery of the oil droplets. Then, in the polymerization process described below, an aqueous dispersion is obtained in which hollow particles having a shell containing a polymer of a polymerizable monomer for fine particles and a hollow portion surrounded by the shell, with the hollow portion filled with a hydrophobic solvent, are dispersed in an aqueous medium.

[0064] The hydrophobic solvent is a non-polymerizable, poorly water-soluble organic solvent. The hydrophobic solvent can be appropriately selected from known hydrophobic solvents and is not particularly limited. Examples include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents. Among these, hydrocarbon solvents are preferred, and hydrocarbon solvents having 5 to 8 carbon atoms are more preferred. Examples of hydrocarbon solvents include aliphatic hydrocarbons, including chain hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane, 2-methylpentane, and paraffin solvents, and cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and cycloheptane; and aromatic hydrocarbons such as benzene, toluene, and xylene. These hydrophobic solvents can be used alone or in combination of two or more.

[0065] In the suspension step, since phase separation between the polymerizable monomer for microparticles and the hydrophobic solvent is likely to occur in the oil droplets, it is preferable to select an organic solvent that has a lower solubility in water than the crosslinkable monomer contained in the polymerizable monomer for microparticles. Furthermore, when the polymerizable monomer for microparticles contains a hydrocarbon monomer, the hydrophobic solvent is preferably a hydrocarbon-based solvent, more preferably a chain hydrocarbon-based solvent, even more preferably a chain hydrocarbon-based solvent having 5 to 8 carbon atoms, and even more preferably at least one selected from the group consisting of pentane, hexane, heptane and octane.

[0066] Furthermore, although not particularly limited, the boiling point of the hydrophobic solvent is preferably 130° C. or lower, more preferably 100° C. or lower, from the viewpoint of ease of removal in the solvent removal step described below, and is preferably 50° C. or higher, more preferably 60° C. or higher, from the viewpoint of ease of encapsulation in oil droplets. When the hydrophobic solvent is a mixed solvent containing multiple types of hydrophobic solvents and has multiple boiling points, it is preferable that the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent is not higher than the above-mentioned upper limit, and it is preferable that the boiling point of the solvent with the lowest boiling point among the solvents contained in the mixed solvent is not lower than the above-mentioned lower limit.

[0067] Furthermore, the hydrophobic solvent preferably has a dielectric constant of 2.5 or less at 20°C. Dielectric constant is one indicator of the polarity of a compound. When the dielectric constant of a hydrophobic solvent is sufficiently small, such as 2.5 or less, phase separation proceeds rapidly in oil droplets containing a polymerizable monomer for microparticles and a hydrophobic solvent, and hollow spaces are likely to be formed. Examples of hydrophobic solvents with a dielectric constant of 2.5 or less at 20°C are as follows. The values ​​in parentheses indicate the dielectric constant: pentane (1.8), hexane (1.9), heptane (1.9), octane (1.9), and cyclohexane (2.0). For the dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Chemical Handbook: Basics," 4th Revised Edition, edited by the Chemical Society of Japan, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information. The method for measuring the relative dielectric constant at 20°C includes, for example, a relative dielectric constant test conducted in accordance with JIS C 2101-23 at a measurement temperature of 20°C.

[0068] The porosity of the hollow particles can be adjusted by changing the amount of hydrophobic solvent in the mixed solution. In the suspension process described below, the polymerization reaction proceeds with the oil droplets containing the polymerizable monomer for microparticles and the like encapsulating the hydrophobic solvent. Therefore, the higher the hydrophobic solvent content, the higher the porosity of the resulting hollow particles. In the present disclosure, the content of the hydrophobic solvent in the mixed solution is preferably 100 to 650 parts by weight per 100 parts by weight of the polymerizable monomer for microparticles, as this facilitates control of the particle size of the hollow particles, increases the porosity while maintaining the strength of the hollow particles, and reduces the amount of residual hydrophobic solvent in the hollow particles. The content of the hydrophobic solvent in the mixed solution is more preferably 120 to 500 parts by weight, and even more preferably 140 to 300 parts by weight per 100 parts by weight of the polymerizable monomer for microparticles.

[0069] The mixture may further contain other materials different from the above-mentioned materials, as long as the purpose of the present disclosure is not impaired.

[0070] A mixed solution is obtained by mixing the above-mentioned materials and, if necessary, other materials and stirring appropriately. In this mixed solution, an oil phase containing the above-mentioned polymerizable monomer for fine particles, a polymerization initiator, and a lipophilic material such as a hydrophobic solvent is dispersed in an aqueous phase containing a dispersion stabilizer and an aqueous medium with particle sizes of approximately several millimeters. The dispersion state of these materials in the mixed solution can be observed with the naked eye, depending on the type of material. In the mixed solution preparation step, the mixed solution may be obtained by simply mixing the above-mentioned materials and, if necessary, other materials and stirring appropriately. However, in order to improve the uniformity of the resulting light-diffusing fine particles, it is preferable to prepare a mixed solution by separately preparing an oil phase containing the polymerizable monomer for fine particles and an aqueous phase containing a dispersion stabilizer and an aqueous medium in advance and mixing them. In the present disclosure, a colloidal dispersion in which a poorly water-soluble inorganic dispersion stabilizer is dispersed in the form of colloidal particles in an aqueous medium is preferably used as the aqueous phase. By preparing the oil phase and the water phase separately in advance and then mixing them, uniform light-diffusing fine particles can be produced, and the particle size of the light-diffusing fine particles can be easily controlled.

[0071] (2) Suspension Step The suspension step is a step of preparing a suspension in which oil droplets containing the polymerizable monomer for fine particles and the like are dispersed in an aqueous medium by suspending the mixed liquid described above. The suspension method for forming the oil droplets is not particularly limited, and any known suspension method can be used. Examples of dispersers that can be used in preparing the suspension include horizontal or vertical in-line dispersers such as Milder manufactured by Pacific Machinery Works, Ltd., Cavitron manufactured by Eurotec Co., Ltd., and in-line dispersers manufactured by IKA (e.g., DISPAX-REACTOR (registered trademark) DRS); and emulsifying dispersers such as the Homomixer MARK II series manufactured by Primix Corporation. In the dispersion for preparing the suspension, the rotation speed of the disperser is not particularly limited, but in order to set the volume average particle size of the light-diffusing fine particles within a preferred range, the lower limit is preferably 100 rpm or more, more preferably 200 rpm or more, and even more preferably 300 rpm or more, and the upper limit is preferably 30,000 rpm or less, more preferably 10,000 rpm or less, and even more preferably 5,000 rpm or less. In addition, by reducing the rotation speed of the disperser, it is possible to suppress the generation of irregularly shaped particles.

[0072] In the suspension prepared in the suspending step, oil droplets containing the lipophilic material and having a particle size of approximately 1 to 10 μm are uniformly dispersed in the aqueous medium. Such oil droplets are difficult to observe with the naked eye and can be observed using known observation equipment such as an optical microscope. When the mixed liquid contains a hydrophobic solvent, phase separation between the hydrophobic solvent and lipophilic materials other than the hydrophobic solvent occurs during the suspending step, and the hydrophobic solvent with low polarity collects inside the oil droplets. As a result, the resulting oil droplets have the hydrophobic solvent distributed inside them and the lipophilic materials other than the hydrophobic solvent distributed around their periphery.

[0073] The oil droplets dispersed in the aqueous medium are surrounded by a dispersion stabilizer. The oil droplets contain an oil-soluble polymerization initiator, a polymerizable monomer for forming fine particles, and, if necessary, a hydrophobic solvent. The oil-soluble polymerization initiator generates polymerization initiation radicals inside the oil droplets, so that light-diffusing fine particles of the desired particle size can be produced without excessively growing the oil droplets. In the suspension polymerization method using such an oil-soluble polymerization initiator, there is no opportunity for the polymerization initiator to come into contact with the polymerizable monomer for forming fine particles dispersed in the aqueous medium. Therefore, by using an oil-soluble polymerization initiator, it is possible to suppress the production of by-products such as fine particles having a particle size smaller than the desired light-diffusing fine particles, thereby narrowing the particle size distribution of the light-diffusing fine particles.

[0074] (3) Polymerization Step This step is a step of forming light-diffusing fine particles containing a polymer of a polymerizable monomer for fine particles by subjecting the suspension obtained in the above-mentioned suspension step to a polymerization reaction. This step produces a dispersion in which light-diffusing fine particles are dispersed in an aqueous medium. In the case of producing hollow particles, this step produces a dispersion in which hollow particles having a shell containing a polymer of a polymerizable monomer for fine particles and a hollow portion surrounded by the shell, the hollow portion being filled with a hydrophobic solvent, are dispersed in an aqueous medium.

[0075] The polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, or a continuous method can be used. The polymerization temperature is preferably 40 to 90° C., more preferably 50 to 80° C. The polymerization reaction time is preferably 1 to 48 hours, more preferably 1 to 36 hours.

[0076] (4) Solid-Liquid Separation Step This step is a step of obtaining a solid content containing light-diffusing fine particles by solid-liquid separation of a slurry containing light-diffusing fine particles. The solid-liquid separation step may be performed on the aqueous dispersion of light-diffusing fine particles obtained by the polymerization step described above, or on the aqueous dispersion of light-diffusing fine particles obtained after the solvent removal step described below. The method for solid-liquid separation is not particularly limited, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and static separation. Among these, filtration is preferred because it is easy to operate and has a high efficiency of removing the dispersion stabilizer.

[0077] After the solid-liquid separation step, any step such as a drying step for removing the aqueous medium remaining in the light-diffusing fine particles may be carried out. The drying method in the drying step is not particularly limited, and examples thereof include a method in which the solid content obtained in the solid-liquid separation step is dried using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0078] (5) Solvent Removal Step: This step involves removing the hydrophobic solvent that fills the interior of hollow particles when producing hollow particles as light-diffusing microparticles. For example, after the solid-liquid separation step described above, the hydrophobic solvent that fills the interior of the hollow particles can be removed in air, replacing the hydrophobic solvent with air to obtain hollow particles filled with gas. Here, "in air" strictly refers to an environment in which no liquid is present outside the hollow particles, or an environment in which only a trace amount of liquid is present outside the hollow particles, so as not to affect the removal of the hydrophobic solvent. This can also be described as the state in which the hollow particles are present in a dry powder. In other words, when removing the hydrophobic solvent from hollow particles in air, it is important to remove the hydrophobic solvent in an environment in which the hollow particles are in direct contact with the external gas.

[0079] The method for removing the hydrophobic solvent from the hollow particles in air is not particularly limited, and examples include vacuum drying, heat drying, flash drying, or a combination of these methods. When using heat drying, the heating temperature must be above the boiling point of the hydrophobic solvent and below the maximum temperature at which the light-diffusing fine particles do not collapse. Therefore, depending on the type of polymerizable monomer for the fine particles, the heating temperature may be, for example, 50 to 200°C, 70 to 200°C, or 100 to 200°C. By drying in air, the hydrophobic solvent inside the hollow particles is replaced with the external gas, resulting in hollow particles with a gas-filled hollow space. The drying atmosphere is not particularly limited and can be selected appropriately depending on the application of the hollow particles. Examples of suitable drying atmospheres include air, oxygen, nitrogen, and argon. Alternatively, hollow particles with a temporary vacuum interior can be obtained by first filling the interior of the hollow particles with gas and then drying under reduced pressure.

[0080] Another method for removing the hydrophobic solvent filling the interior of the hollow particles can be to remove the hydrophobic solvent encapsulated in the hollow particles from the slurry without subjecting the aqueous dispersion of hollow particles in a slurry state obtained in the polymerization step to solid-liquid separation. Examples of such methods include a method in which the hydrophobic solvent encapsulated in the hollow particles is evaporated and distilled off from the slurry under a predetermined pressure (high pressure, normal pressure, or reduced pressure) without subjecting the aqueous dispersion of hollow particles in a slurry state obtained in the polymerization step to solid-liquid separation; or a method in which an inert gas such as nitrogen, argon, or helium or water vapor is introduced into the slurry under a predetermined pressure (high pressure, normal pressure, or reduced pressure) to evaporate and distill off the hydrophobic solvent encapsulated in the hollow particles.

[0081] (6) Others As steps other than the above steps (1) to (5), for example, the following steps (6-a) sieving step, (6-b) washing step, and (6-c) particle interior replacement step may be added.

[0082] (6-a) Sieving Step (Foreign Matter Removal Step) The above-mentioned method for producing light-diffusing microparticles may include a sieving step of sieving the light-diffusing microparticles after drying. By performing the sieving step, coarse powder and aggregates can be removed, and foreign matter can be easily removed. The sieving method can be any known method and is not particularly limited. For example, sieving may be performed using a metal mesh such as a stainless steel mesh or a resin mesh such as a nylon mesh. More specifically, the mesh carrying the light-diffusing microparticles is vibrated to obtain the light-diffusing microparticles that have passed through the mesh, thereby obtaining the sieved light-diffusing microparticles. The mesh openings used in the sieving step are appropriately selected depending on the size of the light-diffusing microparticles.

[0083] (6-b) Washing Step The washing step is a step in which an acid or alkali is added to remove the dispersion stabilizer remaining in the light-diffusing fine particles, and washing is performed. When the dispersion stabilizer used is an acid-soluble inorganic dispersion stabilizer, it is preferable to add an acid to the slurry containing the light-diffusing fine particles to perform washing. On the other hand, when the dispersion stabilizer used is an alkali-soluble inorganic dispersion stabilizer, it is preferable to add an alkali to the slurry containing the light-diffusing fine particles to perform washing. Furthermore, when an acid-soluble inorganic dispersion stabilizer is used as the dispersion stabilizer, an acid is added to the slurry containing the light-diffusing fine particles to adjust the pH of the slurry to preferably 6.5 or less, more preferably 6 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, etc., and organic acids such as formic acid and acetic acid can be used, but sulfuric acid is particularly preferred due to its high dispersion stabilizer removal efficiency and its small burden on the production equipment.

[0084] (6-c) Particle Interior Substitution Process The particle interior substitution process is a process in which the gas or liquid inside the hollow particles is replaced with another gas or liquid during hollow particle production. This substitution can change the environment inside the hollow particles, selectively confine molecules inside the hollow particles, or modify the chemical structure inside the hollow particles to suit the application.

[0085] [Matrix Resin] The light-diffusing resin composition of the present disclosure contains at least one thermoplastic resin as a matrix resin, and the surface free energy of the thermoplastic resin at 20°C is 20 mN / m or more and less than 50 mN / m. Here, the thermoplastic resin is a polymer. Thermoplastic resins with surface free energies within this range are soluble in the solvents described below and can be used as matrix resins. The matrix resin contained in the light-diffusing resin composition of the present disclosure may consist of only one thermoplastic resin or a combination of multiple thermoplastic resins. When multiple thermoplastic resins are contained, the above surface free energy values ​​are those of the various thermoplastic resins, i.e., those of the various thermoplastic resins not blended with additives, so-called neat resins. The surface free energy of the various thermoplastic resins may be, for example, the surface free energy of neat resin pellets, films, sheets, or plates. In addition, in the present disclosure, the surface free energy is determined based on the Owens-Wendt (extended Fowkes equation) method by measuring the contact angle between the thermoplastic resin and a polar or nonpolar solvent. From the viewpoint of solvent solubility, the surface free energy at 20° C. of the thermoplastic resin used as the matrix resin in the present invention is preferably 25 mN / m or more and 48 mN / m or less, more preferably 30 mN / m or more and 45 mN / m or less. As the matrix resin, the above-mentioned thermoplastic resins can be used alone or in combination of two or more kinds, but from the viewpoint of light transmittance of the light diffusion layer, it is preferable to use one kind alone.

[0086] The thermoplastic resin used as the matrix resin may be either a crystalline resin or an amorphous resin, but from the viewpoint of improving the light transmittance of the light diffusion layer, it is preferable to use only either an amorphous resin or a crystalline resin, and more preferably to use only an amorphous resin. As the amorphous resin, a thermoplastic resin having an endothermic peak with an endothermic amount of less than 0.5 J / g or no endothermic peak in a DSC curve obtained by differential scanning calorimetry (DSC) in the temperature range of 30 to 300°C is preferably used, and a thermoplastic resin having no endothermic peak is more preferably used. On the other hand, as the crystalline resin, a thermoplastic resin having an endothermic peak with an endothermic amount of 0.5 J / g or more in a DSC curve obtained by DSC in the temperature range of 30 to 300°C is preferably used, and a thermoplastic resin having an endothermic peak with an endothermic amount of 1 J / g or more is more preferably used.

[0087] Examples of amorphous resins having a surface free energy at 20°C within the above range include polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene copolymer (ABS), modified polyphenylene ether (m-PPE), polyethersulfone (PES / PESU), polyetherimide (PEI), polyamideimide (PAI), ethylene propylene diene copolymer (EPDM), amorphous cycloolefin polymer (COP), amorphous polyethylene terephthalate (A-PET), etc. Examples of crystalline resins having a surface free energy at 20°C within the above range include polyethylene (PE), polypropylene (PP), polyoxymethylene (POM), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), crystalline cycloolefin polymer (COP), etc. Furthermore, these amorphous resins and crystalline resins can be suitably used as matrix resins because they have a sufficient difference in refractive index from the light-diffusing fine particles.

[0088] As the matrix resin, from the viewpoint of the difference in refractive index from the light-diffusing microparticles, at least one selected from the group consisting of polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), and polyethylene (PE) is preferred, and among these, polymethyl methacrylate (PMMA) is particularly preferred from the viewpoints of transparency and economy.

[0089] In the light-diffusing resin composition of the present disclosure, the matrix resin is typically a thermoplastic resin pellet, granule, or powder dissolved in a solvent as described below. Commercially available thermoplastic resin pellets may be used as the matrix resin. Examples of commercially available pellets include PPMA pellets such as the ACRYPET series manufactured by Mitsubishi Chemical Corporation, PC pellets such as the Pellet PC series manufactured by Shin-ei Kako Co., Ltd., and PS pellets such as the Pellet PS series manufactured by Shin-ei Kako Co., Ltd. Furthermore, the matrix resin may be a thermoplastic resin in any form, such as a film, sheet, or plate, processed into pellets, granules, or powder. Examples of commercially available thermoplastic resin sheets or plates include PS sheets such as the Santoclear (registered trademark) series manufactured by Mitsubishi Chemical Corporation, and PC plates such as Hishicarbo manufactured by Mitsubishi Chemical Infratec Co., Ltd. Furthermore, examples of pulverized thermoplastic resin products include pulverized PC and pulverized PS manufactured by Shin-ei Kako Co., Ltd.

[0090] In the light-diffusing resin composition of the present disclosure, the total content of the light-diffusing fine particles and the matrix resin is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on 100% by mass of the total solid content of the light-diffusing resin composition, thereby achieving a more excellent effect of improving light diffusion in the light-diffusing layer and suppressing unevenness in light diffusion performance, and further improving the light transmittance of the light-diffusing layer.

[0091] [Solvent] The light-diffusing resin composition of the present disclosure contains at least one organic solvent as a solvent, and the surface tension of the organic solvent at 20°C is 20 mN / m or more and 40 mN / m or less. Any organic solvent with a surface tension within this range can dissolve the matrix resin described above. The solvent contained in the light-diffusing resin composition of the present disclosure may consist of only one organic solvent or a combination of multiple organic solvents. When multiple organic solvents are contained, the above-mentioned surface tension values ​​are those of the various organic solvents. In the present disclosure, the surface tension is determined based on the platinum plate method. It is also possible to refer to the surface tensions of various solvents listed in "Chemical Handbook: Basics," edited by the Chemical Society of Japan, Revised 4th Edition, Maruzen Co., Ltd., published September 30, 1993, pages II-74 to II-86. The surface tension at 20°C of the organic solvent used as the solvent in the present invention is preferably 23 mN / m or more and 37 mN / m or less, more preferably 25 mN / m or more and 30 mN / m or less, from the viewpoint of the dispersibility of the light-diffusing microparticles and the solubility of the matrix resin.

[0092] Furthermore, the solvent used in the light-diffusing resin composition of the present disclosure preferably has a boiling point of 40 to 200°C, more preferably 50 to 150°C, from the viewpoint of handleability, that is, it is unlikely to volatilize when the light-diffusing resin composition is applied and is easy to remove when a light-diffusing layer is formed.

[0093] The organic solvent having a surface tension at 20° C. within the above range can be appropriately selected from known organic solvents and is not particularly limited. Among organic solvents having a surface tension at 20° C. within the above range, examples of organic solvents preferably used in the light-diffusing resin composition of the present disclosure include: chain aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, n-decane, liquid paraffin, and mineral spirits; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, decahydronaphthalene, dicycloheptane, tricyclodecane, hexahydroindene, and cyclooctane; aromatic hydrocarbons such as benzene, toluene, xylene, and indene; nitrogen-containing hydrocarbons such as nitromethane, nitrobenzene, and acetonitrile; and oxygen-containing hydrocarbons such as diethyl ether, tetrahydrofuran, ethyl acetate, butyl acetate, and methyl ethyl ketone. These organic solvents may be used alone or in combination of two or more. The organic solvent to be used is preferably selected from the viewpoints of boiling point, dispersibility of the light-diffusing fine particles, solubility of the matrix resin, low odor, etc., and from these viewpoints, at least one selected from the group consisting of toluene, ethyl acetate, methyl ethyl ketone, n-hexane, and cyclohexane is particularly preferred.

[0094] In the light-diffusing resin composition of the present disclosure, the content of the solvent is not particularly limited, but from the viewpoint of the coatability of the light-diffusing resin composition and the ease of solvent removal when forming a light-diffusing layer, the content is preferably 10 to 1,000 parts by mass, more preferably 50 to 500 parts by mass, and even more preferably 80 to 200 parts by mass, relative to 100 parts by mass of the total amount of the light-diffusing fine particles and the matrix resin.

[0095] [Additives] The light-diffusing resin composition of the present disclosure may further contain various additives conventionally used in light-diffusing sheets, if necessary. Examples of additives include antioxidants, light stabilizers, plasticizers, lubricants, dyes, pigments, fillers, fluorescent agents, antistatic agents, flame retardants, crosslinking agents, surfactants, and dispersants. These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited, and may be adjusted appropriately within a range that does not impair the objectives of the present disclosure. The light-diffusing resin composition of the present disclosure may further contain a resin component different from the light-diffusing fine particles or matrix resin described above. For example, the light-diffusing resin composition may contain, as a dispersant, a thermoplastic resin having a surface free energy at 20°C of less than 20 mN / m or 50 mN / m or more.

[0096] [Method for producing light-diffusing resin composition] The method for producing the light-diffusing resin composition of the present disclosure is not particularly limited, as long as it is a method that can produce the light-diffusing resin composition of the present disclosure described above. For example, the light-diffusing resin composition of the present disclosure can be obtained by mixing the light-diffusing fine particles, matrix resin, solvent, and other materials that are added as needed. The mixing method can be a general method, and is not particularly limited. The following production method can be mentioned as one embodiment of the method for producing the light-diffusing resin composition of the present disclosure. A method for producing a light-diffusing resin composition, comprising the step of adding at least light-diffusing fine particles and a matrix resin to a solvent and mixing them, wherein the light-diffusing fine particles are organic fine particles containing a polymer of a polymerizable monomer for fine particles, including a crosslinkable hydrocarbon monomer, and the light-diffusing fine particles have a heat of immersion in octane at 30°C of 0.7 J / g or more and 100 J / g or less and a heat of immersion in formamide at 30°C of 1 J / g or more and 100 J / g or less, respectively; the matrix resin is at least one thermoplastic resin, and various types of surface free energy of the thermoplastic resin at 20°C are 20 mN / m or more and less than 50 mN / m; and the solvent is at least one organic solvent, and various types of surface tension of the organic solvent at 20°C are 20 mN / m or more and 40 mN / m or less.

[0097] 2. Light Diffusion Sheet The light diffusion sheet of the present disclosure is characterized by containing the solid content of the light diffusing resin composition of the present disclosure. Here, the solid content of the light diffusing resin composition refers to components other than the solvent contained in the light diffusing resin composition. The light diffusing sheet of the present disclosure is preferably a light diffusing sheet having a light diffusing layer containing the solid content of the light diffusing resin composition of the present disclosure, more preferably a light diffusing sheet having a light diffusing layer made of the solid content of the light diffusing resin composition of the present disclosure, and even more preferably a light diffusing sheet made of the solid content of the light diffusing resin composition of the present disclosure. For example, a light diffusing layer made of the solid content of the light diffusing resin composition of the present disclosure can be formed on the substrate by applying the light diffusing resin composition of the present disclosure to a substrate and drying it to remove the solvent. The light diffusing sheet of the present disclosure may have a substrate and a light diffusing layer, or may consist of only a light diffusing layer. The light diffusing sheet of the present disclosure may also have another layer, such as a shape-imparting layer.

[0098] From the viewpoint of optical properties, the light diffusion sheet of the present disclosure preferably has a total light transmittance of 60% or more, a diffuse transmittance of 60% or more, and a standard deviation of the diffuse transmittance of 3% or less. Since such optical properties are easily obtained, the light diffusion sheet of the present disclosure preferably consists solely of a light diffusion layer containing the solid content of the light-diffusing resin composition of the present disclosure. In the present disclosure, the total light transmittance and diffuse transmittance of the light diffusion sheet are both average values ​​of measurements taken at five locations on the sheet, and the standard deviation of the diffuse transmittance is the standard deviation of measurements taken at five locations on the sheet where the diffuse transmittance was measured.

[0099] From the viewpoint of light transmittance, the light diffusion sheet of the present disclosure has a total light transmittance of preferably 60% or more, more preferably 70% or more, and even more preferably 75% or more. Note that, in the present disclosure, the total light transmittance is measured in accordance with JIS K 7375.

[0100] From the viewpoint of light diffusibility, the diffuse transmittance of the light diffusion sheet of the present disclosure is preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. In the present disclosure, the diffuse transmittance is measured in accordance with JIS K 7136. Since the light diffusion sheet of the present disclosure has reduced unevenness in light diffusion performance, the standard deviation of the measured values ​​of the diffuse transmittance at five points on the sheet is preferably 3% or less, more preferably 2.5% or less, and even more preferably 2% or less.

[0101] The thickness of the light diffusion sheet of the present disclosure may be adjusted appropriately depending on the application and is not particularly limited. On the other hand, the light diffusion sheet of the present disclosure has excellent dispersibility of light-diffusing fine particles, so it can be made thin. Therefore, the thickness of the light diffusion sheet of the present disclosure is not particularly limited, but can be, for example, 30 μm or less, or 15 μm or less. On the other hand, from the viewpoint of strength, the lower limit of the thickness of the light diffusion sheet of the present disclosure is preferably 5 μm or more, more preferably 7 μm or more.

[0102] The method for measuring the thickness of the light diffusion sheet of the present disclosure will be described with reference to FIG. 1 . First, a measurement sample is obtained by cutting the light diffusion sheet into a square with sides of 5 cm. Next, a central point (D0) and eight other points (D1 to D8) arranged around this central point are set on the plane of this 5 cm square measurement sample 30. When the nearest points of the other eight points (D1 to D8) are connected with lines, a square with sides of 4 cm is formed, which is concentric with the center point (D0) of the measurement sample and is slightly smaller than the measurement sample. Furthermore, when the center point (D0), one of the four corner points (D1, D2, D3, or D4), and the two points closest to these two points (e.g., D2 and D8) are selected, these nine points are selected so that when the nearest points are connected with lines, four squares with sides of 2 cm are arranged in a grid. Next, the thickness of the measurement sample at each of these nine positions is measured using a micrometer (for example, MDQ-30, manufactured by Mitutoyo Corporation), and the average value is taken as the thickness of the light diffusion sheet.

[0103] [Uses of Light Diffusion Sheet] The use of the light diffusion sheet of the present disclosure is not particularly limited, and it can be used without limitation for uses requiring light diffusion. Specific examples of uses of the light diffusion sheet of the present disclosure include a light diffusion sheet for a backlight unit of a liquid crystal display device, a light extraction sheet for an organic EL element used in an organic EL display device or organic EL lighting, a light scattering sheet for an LED lighting device, and a light capture sheet for a solar cell.

[0104] [Method for manufacturing light diffusion sheet] The method for manufacturing the light diffusion sheet of the present disclosure is not particularly limited, but may include, for example, a method including a step of applying the above-described light-diffusing resin composition of the present disclosure to a substrate and drying the applied composition to form a light diffusion layer.

[0105] The material of the substrate is not particularly limited, and examples thereof include inorganic substrates such as glass, metal, and silicon wafer; and resin substrates such as polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyether ketone, polyimide, and polytetrafluoroethylene. From the viewpoint of ease of peeling, resin substrates are preferably used.

[0106] The thickness of the substrate is not particularly limited, but from the viewpoint of ease of peeling, the upper limit is preferably 100 μm or less, more preferably 50 μm or less, and from the viewpoint of strength, the lower limit is preferably 0.1 μm or more, more preferably 5 μm or more.

[0107] The method for applying the light-diffusing resin composition to the substrate is not particularly limited, and examples thereof include spin coating, roll coating, flow coating, printing, dip coating, film-casting, bar coating, die coating, gravure printing, etc. The region to which the light-diffusing resin composition is applied may be at least a part of the surface of the substrate, and may be either one or both surfaces of the substrate, or may be applied in a pattern to the surface of the substrate.

[0108] The drying method for drying the light-diffusing resin composition is not particularly limited, and known drying methods such as heat drying, reduced pressure drying, and flash drying can be used.

[0109] By drying the light-diffusing resin composition, the solvent is removed, and a light-diffusing layer composed of the solid content of the light-diffusing resin composition is formed. The thickness of the light-diffusing layer may be adjusted appropriately depending on the application and is not particularly limited. However, in the present disclosure, the light-diffusing layer can be thinned due to the excellent dispersibility of the light-diffusing fine particles. Therefore, the thickness of the light-diffusing layer can be, for example, 30 μm or less, or 15 μm or less. On the other hand, the lower limit of the thickness of the light-diffusing layer is preferably 5 μm or more, more preferably 7 μm or more, from the viewpoint of strength.

[0110] After the light diffusion layer is formed on the substrate, the substrate may be peeled off from the light diffusion layer, thereby obtaining a light diffusion sheet consisting of only the light diffusion layer.

[0111] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Note that parts and percentages are by mass unless otherwise specified.

[0112] <Production of Light-Diffusing Fine Particles> [Production Example 1 (Hollow Particles A)] (1) Mixed Solution Preparation Step First, the polymerizable monomer for fine particles shown in Table 1, 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) as an oil-soluble polymerization initiator, and 160 parts of hexane as a hydrophobic solvent were mixed to prepare an oil phase. Meanwhile, in a stirring tank, at room temperature, an aqueous solution of 12.1 parts of sodium hydroxide (alkali metal hydroxide) in 121 parts of ion-exchanged water was gradually added with stirring to an aqueous solution of 17.1 parts of magnesium chloride (a water-soluble polyvalent metal salt) in 494 parts of ion-exchanged water to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (4 parts magnesium hydroxide), which served as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed solution.

[0113] (2) Suspension step The mixture obtained in the mixture preparation step was stirred and suspended for 1 minute using a disperser (manufactured by Primix Corporation, product name: Homomixer) at a rotation speed of 4,000 rpm to prepare a suspension in which oil droplets of the polymerizable monomer for microparticles encapsulating a hydrophobic solvent were dispersed in water.

[0114] (3) Polymerization step: The suspension obtained in the suspension step was stirred for 1 hour and 30 minutes under a nitrogen atmosphere at a temperature of 65°C to carry out a polymerization reaction, thereby obtaining an aqueous dispersion of hollow particles whose hollow spaces were filled with the hydrophobic solvent.

[0115] (4) Washing Step and Solid-Liquid Separation Step The aqueous dispersion of hollow particles obtained above was washed with dilute sulfuric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less. Next, after separating the water by filtration, 200 parts of fresh ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and the mixture was filtered to obtain a solid. The obtained solid was dried in a dryer at 40°C to obtain hollow particles whose hollows were filled with the hydrophobic solvent.

[0116] (5) Solvent Removal Step The hollow particles obtained in the solid-liquid separation step were heat-treated in a vacuum dryer at 200°C in a nitrogen atmosphere for 12 hours to remove the hydrophobic solvent contained in the hollow particles, thereby obtaining hollow particles whose hollow portions were filled with air.

[0117] (6) Sieving Step The hollow particles obtained in the solvent removal step were sieved using a nylon mesh with an opening of 100 μm, and the hollow particles that passed through the mesh and fell to the bottom were collected to remove coarse particles, thereby obtaining hollow particles A.

[0118] [Production Examples 2, 3, and 4 (Hollow Particles B, C, and D)] Hollow particles B of Production Example 2, hollow particles C of Production Example 3, and hollow particles D of Production Example 4 were obtained in the same procedure as in Production Example 1, except that in the above-mentioned "(1) Mixture Preparation Step," the polymerizable monomer for fine particles added to the oil phase was changed according to Table 1.

[0119] [Production Example 5 (Dense Solid Particles A)] Dense solid particles A of Production Example 5 were obtained in the same procedure as Production Example 1, except that in the above "(1) Mixture Preparation Step", the polymerizable monomer for fine particles added to the oil phase was changed according to Table 1 and hexane was not added as a hydrophobic solvent. In Production Example 5, an aqueous dispersion of dense solid particles was obtained in the above "(3) Polymerization Step". In addition, in Production Example 5, the above "(5) Solvent Removal Step" was performed to remove water remaining in the fine particles.

[0120] [Comparative Production Example 1 (Hollow Particles E)] Hollow particles E of Comparative Production Example 1 were obtained in the same procedure as Production Example 1, except that in the above "(1) Mixture Preparation Step", the polymerizable monomer for fine particles added to the oil phase was changed according to Table 1.

[0121] Commercially available products were used as the polymerizable monomers for fine particles shown in Table 1. The manufacturers of the following polymerizable monomers for fine particles are listed below: 1,3-butanediol dimethacrylate: manufactured by Tokyo Chemical Industry Co., Ltd. Glycerol dimethacrylate: manufactured by Tokyo Chemical Industry Co., Ltd. Glycerol trimethacrylate: manufactured by Tokyo Chemical Industry Co., Ltd. 2-phenyl-1,3-butadiene: manufactured by Tokyo Chemical Industry Co., Ltd.

[0122] [Evaluation of Physical Properties of Light-Diffusing Fine Particles] The light-diffusing fine particles (hollow particles or solid particles) obtained in the above Production Examples were evaluated for the following physical properties. The results of the evaluation of the physical properties of the light-diffusing fine particles are shown in Table 1.

[0123] 1. Particle size and particle size distribution The particle size of the light-diffusing microparticles was measured using a particle size distribution analyzer (product name: Multisizer 4e, manufactured by Beckman Coulter, Inc.) using the Coulter counter method, and the number average and volume average were calculated to determine the number average particle size (Dp) and volume average particle size (Dv). The particle size distribution (Dv / Dp) was calculated by dividing the volume average particle size by the number average particle size. The measurement conditions were aperture diameter: 50 μm, dispersion medium: Isoton II (product name), concentration: 10%, and number of particles measured: 100,000. Specifically, 0.2 g of the light-diffusing microparticle sample was placed in a beaker, and a surfactant aqueous solution (product name: Drywell, manufactured by Fujifilm Corporation) was added as a dispersant. 2 ml of dispersion medium was added to the beaker to wet the light-diffusing microparticles, and then 10 ml of dispersion medium was added. The mixture was dispersed in an ultrasonic disperser for 1 minute, and then measured using the particle size distribution analyzer.

[0124] 2. Porosity 2-1. Measurement of apparent density of light-diffusing fine particles First, a volume of 100 cm ３ About 30 cm ３The volumetric flask was filled with light-diffusing microparticles, and the mass of the filled light-diffusing microparticles was accurately weighed. Next, the volumetric flask filled with the light-diffusing microparticles was accurately filled with isopropanol up to the marked line, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D of the light-diffusing microparticles was calculated based on the following formula (I): １ (g / cm ３ The apparent density D was calculated using the formula (I). １ = [Mass of fine particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature])

[0125] 2-2. Measurement of true density of light-diffusing fine particles After crushing the light-diffusing fine particles in advance, a 100 cm ３ Approximately 10 g of crushed pieces of the light-diffusing fine particles were filled into a measuring flask, and the mass of the crushed pieces was accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol was added to the measuring flask, and the mass of the isopropanol was accurately weighed. The true density D of the light-diffusing fine particles was calculated based on the following formula (II): ０ (g / cm ３ ) was calculated. ０ = [Mass of crushed particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at the measurement temperature])

[0126] 2-3. Calculation of porosity Apparent density D of light diffusing fine particles １ and true density D ０ The porosity of the light-diffusing fine particles was calculated based on the following formula (III): １ / True density D ０ ) x 100

[0127] 3. Proportion of Particles with One Hollow Portion Light-diffusing microparticles fixed on carbon tape were rubbed with a cotton swab to intentionally break the light-diffusing microparticles. The interiors of 100 broken light-diffusing microparticles were observed using an SEM to identify the number of hollow portions per particle, and the percentage (%) of particles with only one hollow portion was calculated.

[0128] 4. Measurement of Immersion Calorific Value 4-1. Calorific Value of Immersion in Octane Under a nitrogen atmosphere, light-diffusing microparticles were sampled in a 10 ml glass ampoule, and while maintaining a vacuum inside the glass ampoule with a vacuum pump, the opening of the glass ampoule was burned off and sealed with a burner. The glass ampoule was immersed in octane (n-octane) in an immersion calorimeter (manufactured by SETARAM, model number: C0), and the temperature of the octane was maintained at 30°C (±0.5°C). The glass ampoule inside the immersion calorimeter was broken, and the light-diffusing microparticles were immersed in octane. The change in calorific value generated during this process was measured for 10 hours. The measurement was performed in an air atmosphere, with the temperature inside the immersion calorimeter maintained at 30°C (±0.5°C). The period from the beginning to the end of the obtained calorific peak was arbitrarily selected, and the immersion heat (J / g) was calculated by time integration, and this was taken as the heat of immersion of the light-diffusing fine particles in octane at 30°C.

[0129] 4-2. Calorific value of immersion in formamide The calorific value of immersion of the light-diffusing fine particles in formamide at 30° C. was determined in the same manner as in "4-1. Calorific value of immersion in octane" above, except that formamide was used instead of octane.

[0130]

[0131] As shown in Table 1, by changing the composition of the polymerizable monomer for fine particles, it was possible to produce light-diffusing fine particles with different heat values ​​for immersion in octane at 30°C and for immersion in formamide at 30°C. Furthermore, in Production Examples 1 to 4 and Comparative Production Example 1, hollow particles were produced by adding a hydrophobic solvent to the mixed solution in the mixed solution preparation step. In Production Example 5, dense solid particles were produced by not adding a hydrophobic solvent to the mixed solution in the mixed solution preparation step.

[0132] <Production of Light-Diffusing Resin Composition and Light-Diffusing Sheet> [Example 1] (1) Preparation of Light-Diffusing Resin Composition A mixture was obtained by adding 100 parts of polymethyl methacrylate (PMMA) as a matrix resin and 200 parts of the hollow particles A obtained in Production Example 1 as light-diffusing fine particles to 400 parts of toluene (surface tension at 20°C: 28.4 mN / m, boiling point: 111°C). The mixture was stirred with a stirrer until the matrix resin was dissolved, thereby obtaining the light-diffusing resin composition of Example 1.

[0133] (2) Production of Light Diffusion Sheet The light diffusing resin composition obtained above was applied to one side of a 75 μm thick transparent PET film (trade name "Diafoil (registered trademark) T-600", manufactured by Mitsubishi Chemical Corporation). Thereafter, the film was dried on a hot plate at 80° C. until the solvent in the light diffusing resin composition evaporated, thereby forming a light diffusing layer on the PET film. The PET film was peeled off from the light diffusing layer to obtain a light diffusing sheet consisting of the light diffusing layer.

[0134] [Examples 2 to 10 and Comparative Examples 1 and 2] The light-diffusing resin compositions and light-diffusing sheets of Examples 2 to 10 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that in the above "(1) Preparation of light-diffusing resin composition", the type or amount of light-diffusing fine particles or the type of matrix resin were changed according to Table 2 or Table 3.

[0135] [Comparative Examples 3 to 4] Light-diffusing resin compositions of Comparative Examples 3 to 4 were obtained in the same manner as in Example 1, except that in the above "(1) Preparation of light-diffusing resin composition", the type of matrix resin was changed according to Table 3. In Comparative Examples 3 and 4, the matrix resin was not dissolved in the solvent, and therefore a light-diffusing sheet could not be obtained.

[0136] The following commercially available products (all pellets) were used as the matrix resins shown in Tables 2 and 3. The trade names, manufacturers, and surface free energies at 20°C of the commercially available products used as the matrix resins are shown below. Polymethyl methacrylate (PMMA): trade name "ACRYPET", manufactured by Mitsubishi Chemical Corporation, surface free energy at 20°C: 43 mN / m Polystyrene (PS): trade name "Pellet_Heat-Resistant GP_N (Natural)", manufactured by Shin-ei Kako Co., Ltd., surface free energy at 20°C: 40 mN / m Polycarbonate (PC): trade name "Pellet PC_N (Natural)", manufactured by Shin-ei Kako Co., Ltd., surface free energy at 20°C: 44 mN / m Polyethylene (PE): trade name "Suntech", manufactured by Asahi Kasei Corporation, surface free energy at 20°C: 31 mN / m Polytetrafluoroethylene (PTFE): trade name "Fluon (registered trademark)", manufactured by AGC Inc., surface free energy at 20°C: 18 mN / m Polyimide (PI): trade name "Surprim (registered trademark) TO65", manufactured by Mitsubishi Gas Chemical Company, Inc., surface free energy at 20°C: 50 mN / m

[0137] The surface free energy was measured by the following method. For a measurement sample (pellet), a contact angle meter (Drop Master 700, manufactured by Kyowa Interface Science) was used to measure the contact angle of two solvents (water and diiodomethane) whose surface tension, polarity term (p), and dispersion term (d) were known under the following conditions, and the surface free energy was evaluated by the Owens-Wendt (extended Fowkes equation) method, and the surface free energy of the measurement sample was calculated. <Contact angle measurement conditions> Needle: metal needle 22G (water), Teflon (registered trademark) coated 22G (diiodomethane) Waiting time: 1000 ms Liquid volume: 1.8 μL Liquid contact recognition: water 50 dat, diiodomethane 100 dat Temperature: 20°C

[0138] The surface tension of the solvent was measured in an environment of 20° C. by the platinum plate method using an automatic surface tensiometer ("Dy-300" manufactured by Kyowa Interface Science Co., Ltd.).

[0139] [Evaluation of light diffusion sheet] 1. Measurement of sheet thickness The light diffusion sheet was cut into a square with a side length of 5 cm to prepare a measurement sample. Next, on the plane of this 5 cm square measurement sample 30, one central point (D0) and eight other points (D1 to D8) arranged around this one point were set. At this time, when the other eight points (D1 to D8) were connected with lines to the points closest to each other, a square with a side length of 4 cm was formed, which was concentric with the center point (D0) of the test sheet and was one size smaller than the measurement sample. In addition, the center point (D0), one of the four corner points (D1, D2, D3 or D4), and the two points closest to these two points (for example, D2 and D8) were selected, and when the points closest to each other were connected with lines, four squares with a side length of 2 cm were arranged in a grid pattern. These nine points were selected. Subsequently, the thickness of the measurement sample at each of these nine positions was measured using a micrometer (model number: MDQ-30, manufactured by Mitutoyo Corporation), and the average value was taken as the thickness of the light diffusion sheet.

[0140] 2. Total Light Transmittance The obtained light diffusion sheet was cut out, and the total light transmittance was measured in accordance with JIS K 7375: 2008. The total light transmittance was measured at five points on the light diffusion sheet, and the average value was taken as the total light transmittance of the light diffusion sheet.

[0141] 3. Diffuse transmittance The obtained light diffusion sheet was cut out, and the diffuse transmittance was measured in accordance with JIS K 7136:2000. The diffuse transmittance was measured at five points on the light diffusion sheet, and the average value was taken as the diffuse transmittance of the light diffusion sheet. The standard deviation of the measured values ​​at the five points was taken as the standard deviation of the diffuse transmittance of the light diffusion sheet.

[0142]

[0143]

[0144] [Discussion] The light-diffusing resin compositions obtained in Comparative Examples 1 and 2 contained hollow particles E as light-diffusing microparticles, whose heat of immersion in octane at 30°C was less than 0.7 J / g. Therefore, the resin compositions had insufficient dispersibility of the light-diffusing microparticles. In Comparative Example 1, PMMA, an amorphous resin, was used as the matrix resin. Therefore, the light-diffusing sheet formed using the light-diffusing resin composition of Comparative Example 1 had good light transmittance, but the dispersibility of the light-diffusing microparticles was insufficient, resulting in poor light diffusibility and significant unevenness in light diffusion performance. In Comparative Example 2, polyethylene (PE), a crystalline resin, was used as the matrix resin. Therefore, the light-diffusing sheet formed using the light-diffusing resin composition of Comparative Example 2 contained crystalline portions of polyethylene. Therefore, although the dispersibility of the light-diffusing microparticles was insufficient, the crystalline portions of polyethylene increased the diffuse transmittance. On the other hand, the insufficient dispersibility of the light-diffusing microparticles and the inclusion of crystalline portions of polyethylene resulted in significant unevenness in light diffusion performance, and the inclusion of crystalline portions of polyethylene resulted in low total light transmittance. In Comparative Examples 1 and 2, the light-diffusing fine particles were prone to cracking due to insufficient flexibility, and the cracking of the light-diffusing fine particles is presumed to have also deteriorated the light diffusibility and increased the unevenness of the light diffusion performance. In Comparative Examples 3 and 4, a thermoplastic resin having a surface free energy at 20°C of less than 20 mN / m or 50 mN / m or more was used as the matrix resin, and as described above, the matrix resin was not dissolved in a solvent, and as a result, a light-diffusing sheet could not be produced.

[0145] The light-diffusing resin compositions obtained in Examples 1 to 10 contained, as light-diffusing fine particles, organic fine particles containing a polymer of a polymerizable monomer for fine particles including a crosslinkable hydrocarbon monomer, the light-diffusing fine particles having a heat of immersion in octane at 30°C of 0.7 J / g or more and 100 J / g or less and a heat of immersion in formamide at 30°C of 1 J / g or more and 100 J / g or less, the matrix resin contained a thermoplastic resin having a surface free energy of 20 mN / m or more and less than 50 mN / m, and the solvent contained an organic solvent having a surface tension of 20 mN / m or more and 40 mN / m or less at 20°C, resulting in resin compositions with excellent dispersibility of light-diffusing fine particles. Therefore, in Examples 1 to 10, the light-diffusing sheets formed using the light-diffusing resin compositions had excellent light diffusibility and little unevenness in light diffusing performance. Furthermore, Examples 1 to 3 demonstrated that increasing the content of light-diffusing microparticles can improve the light diffusion properties of the light diffusion sheet, while decreasing the content of light-diffusing microparticles can improve the light transmittance of the light diffusion sheet and suppress unevenness in light diffusion performance. Examples 1 and 4 to 6 demonstrated that a light diffusion sheet with excellent light diffusion properties and suppressed unevenness in light diffusion performance can be obtained when the heat amounts of immersion of light-diffusing microparticles in octane and formamide are within the above ranges. Furthermore, adjusting the monomer composition of the light-diffusing microparticles or the heat amount of immersion in octane or formamide can further improve the light diffusion properties of the light diffusion sheet and further suppress unevenness in light diffusion performance. Examples 1 and 7 demonstrated that whether hollow particles or dense solid particles are used as light-diffusing microparticles, a light diffusion sheet with excellent light diffusion properties and suppressed unevenness in light diffusion performance can be obtained. Furthermore, it was demonstrated that the light transmittance of a light diffusion sheet is improved when hollow particles are used as light-diffusing microparticles compared to dense solid particles. The hollow particles have high light transmittance due to the hollow space. Comparison of Example 1 with Examples 8 to 10 shows that a light diffusion sheet with excellent light diffusibility and reduced unevenness in light diffusion performance can be obtained even when the type of matrix resin is changed.In Example 10, the dispersibility of the light-diffusing microparticles was good, but because the light-diffusing sheet contained crystalline portions of polyethylene (PE), the total light transmittance decreased, the diffuse transmittance increased, and the standard deviation of the diffuse transmittance increased.

[0146] 30 Measurement sample of light diffusion sheet D0, D1, D2, D3, D4, D5, D6, D7 and D8 Measurement points on the measurement sample

Claims

1. A light-diffusing resin composition comprising light-diffusing microparticles, a matrix resin, and a solvent, wherein the light-diffusing microparticles are organic microparticles containing a polymer of a polymerizable monomer for microparticles, including a crosslinkable hydrocarbon monomer, and the light-diffusing microparticles have a heat of immersion in octane at 30°C of 0.7 J / g or more and 100 J / g or less, and a heat of immersion in formamide at 30°C of 1 J / g or more and 100 J / g or less, the matrix resin is at least one thermoplastic resin, and various types of surface free energy of the thermoplastic resin at 20°C are 20 mN / m or more and less than 50 mN / m, and the solvent is at least one organic solvent, and various types of surface tension of the organic solvent at 20°C are 20 mN / m or more and 40 mN / m or less.

2. The light-diffusing resin composition according to claim 1, wherein the volume average particle diameter of the light-diffusing microparticles is 1 to 10 μm, and the particle size distribution (volume average particle diameter (Dv) / number average particle diameter (Dp)) of the light-diffusing microparticles is 1.0 to 1.

4.

3. The light-diffusing resin composition according to claim 1 or 2, wherein the matrix resin is an amorphous resin.

4. A light-diffusing resin composition according to claim 1 or 2, wherein the light-diffusing microparticles are hollow particles having a porosity of 60% or more and a number ratio of particles having only one hollow portion of 90% or more.

5. The light-diffusing resin composition according to claim 1 or 2, wherein the polymerizable monomer for the fine particles comprises at least one crosslinkable acrylic monomer selected from the group consisting of 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate.

6. A light-diffusing sheet containing the solid content of the light-diffusing resin composition according to any one of claims 1 to 5, having a total light transmittance of 60% or more, a diffuse transmittance of 60% or more, and a standard deviation of the diffuse transmittance of 3% or less.

Images