Polymerizable monomer composition for light diffusion film, light diffusion film, and method for producing same

Abstract

Provided is a polymerizable monomer composition for a light diffusion film, which enables the production of a light diffusion film with improved crack resistance while maintaining excellent light diffusibility and light transmissivity, the composition containing fine particles and a polymerizable monomer for a binder. The iodine value of the fine particles is 35 g / 100 g or more and 100 g / 100g or less as measured in accordance with JIS K 0070. The polymerizable monomer for a binder contains a crosslinkable monomer that has a plurality of reactive unsaturated bonds in each molecule.

Description

Polymerizable monomer composition for light diffusion film, light diffusion film and method for producing the same

[0001] The present disclosure relates to a polymerizable monomer composition for a light diffusion film, a light diffusion film made of a cured product of the polymerizable monomer composition, and a method for producing the same.

[0002] Light diffusion films 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 films include films with one or both surfaces roughened, and films in which a light diffusion layer containing transparent organic fine particles is formed on the surface of a substrate. Known coating agents used to form light diffusion layers include hollow particle dispersions in which a reactive monomer and hollow particles are dispersed in an organic solvent (see, for example, Patent Document 1).

[0003] Furthermore, in the case of light diffusion films provided in display devices, if the light diffusion film is thick, a problem occurs in that fine characters displayed on the screen become blurred depending on the angle at which the screen is viewed. Therefore, there is a demand for thinner light diffusion films for display devices in general. A light diffusion film consisting only of a light diffusion layer without a substrate is desirable from the viewpoint of thinning. However, when a film consisting only of a light diffusion layer is obtained by forming a light diffusion layer on the surface of a substrate and then peeling off the substrate, there is a problem in that the light diffusion layer cracks when the substrate is peeled off, making it difficult to obtain a thin light diffusion film without a substrate.

[0004] Meanwhile, coating agents containing organic fine particles are used in a variety of applications in addition to light diffusion films. For example, Patent Document 2 discloses a resin composition containing (A) 1 to 90 wt % of a particulate polymer having an average particle size of 20 to 500 nm and an iodine value of 100 or less, and (B) 10 to 99 wt % of a curable resin, as a curable resin composition having excellent weather resistance. The examples in Patent Document 2 show that excellent weather resistance is exhibited when a particulate polymer having an iodine value of 4 g / 100 g or less is used.

[0005] International Publication No. 2019 / 177013 Japanese Patent Application Laid-Open No. 2001-279101

[0006] The present disclosure has been made in consideration of the problem that a light diffusion layer formed on a substrate surface cracks when the substrate is peeled off after the light diffusion layer is formed, and an object of the present disclosure is to provide a polymerizable monomer composition that can produce a light diffusion film that has improved crack resistance while maintaining good light diffusion and light transmittance. Another object of the present disclosure is to provide a light diffusion film made of a cured product of the polymerizable monomer composition, and a method for producing the same.

[0007] The present disclosure provides the following polymerizable monomer composition for a light diffusion film: [1] A polymerizable monomer composition for a light diffusion film, comprising fine particles and a polymerizable monomer for a binder, wherein the fine particles have an iodine value of 35 g / 100 g or more and 100 g / 100 g or less as measured in accordance with JIS K 0070, and the polymerizable monomer for the binder contains a crosslinkable monomer having multiple reactive unsaturated bonds in one molecule. [2] The polymerizable monomer composition for a light diffusion film according to [1], wherein the content of the crosslinkable monomer is 20 mass% or more in 100 mass% of the total amount of the polymerizable monomer for the binder. [3] The polymerizable monomer composition for a light diffusion film according to [1] or [2], wherein the volume average particle diameter of the fine particles is 1 to 10 μm, and the particle size distribution of the fine particles (volume average particle diameter (Dv) / number average particle diameter (Dp)) is 1.0 to 1.4. [4] The polymerizable monomer composition for a light diffusion film according to any one of [1] to [3], wherein the polymerizable monomer for the binder contains a polyfunctional acrylate as the crosslinkable monomer. [5] The polymerizable monomer composition for a light diffusion film according to any one of [1] to [4], wherein the fine particles are hollow particles having a porosity of 60% or more, and the proportion of particles having only one hollow portion by number is 90% or more.

[0008] The present disclosure also provides the following light diffusion film: [6] A light diffusion film comprising a cured product of the polymerizable monomer composition for a light diffusion film according to any one of [1] to [5].

[0009] The present disclosure also provides the following method for producing a light diffusion film. [7] A method for producing a light diffusion film, comprising: applying the polymerizable monomer composition for a light diffusion film according to any one of [1] to [5] to a substrate; curing the polymerizable monomer composition for a light diffusion film by heating to form a light diffusion film layer made of a cured product of the polymerizable monomer composition for a light diffusion film on at least a portion of the surface of the substrate; and peeling the substrate from the light diffusion film layer to obtain a light diffusion film. [8] A method for producing a light diffusion film, comprising: applying the polymerizable monomer composition for a light diffusion film according to any one of [1] to [5] to a substrate; curing the polymerizable monomer composition for a light diffusion film by exposure to light to form a light diffusion film layer made of a cured product of the polymerizable monomer composition for a light diffusion film on at least a portion of the surface of the substrate; and peeling the substrate from the light diffusion film layer to obtain a light diffusion film.

[0010] According to the present disclosure, it is possible to provide a polymerizable monomer composition that can produce a light diffusion film that has good light diffusion properties and light transmittance and excellent crack resistance. Furthermore, the present disclosure can provide a light diffusion film made of a cured product of the polymerizable monomer composition, and a method for producing the same.

[0011] FIG. 2 is a diagram illustrating a method for measuring the thickness of a light diffusion film.

[0012] 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. Furthermore, among the numerical values ​​described to explain the present disclosure, numerical values ​​that may include decimal places are, unless otherwise specified, numerical values ​​obtained by rounding off the digit that is one place smaller than the lowest digit included in the numerical value. Furthermore, 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.

[0013] In the present disclosure, the term "reactive unsaturated bond" is not particularly limited and may be, for example, a reactive unsaturated bond that undergoes an addition reaction in the presence of a radical, or a reactive unsaturated bond that undergoes an addition reaction in the presence of active hydrogen. Among these, a radical reactive unsaturated bond is preferred from the viewpoint of reactivity and the optical properties of the light diffusion film.

[0014] In the present disclosure, a "polymerizable monomer" refers to a monomer having the above-mentioned reactive unsaturated bond. In the present disclosure, a polymerizable monomer used as a raw material for the binder of a light diffusion film is referred to as a "polymerizable monomer for binder," and a polymerizable monomer used as a raw material for microparticles is referred to as a "polymerizable monomer for microparticles." 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. A crosslinkable monomer can form a crosslinked bond in a polymer by a polymerization reaction. Note that a crosslinkable monomer becomes a crosslinkable monomer unit after a polymerization reaction, and a non-crosslinkable monomer becomes a non-crosslinkable monomer unit after a 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.

[0015] 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. In addition, a (meth)acrylic acid ester-based monomer having a plurality of (meth)acryloyl groups in one molecule may be referred to as a “polyfunctional acrylate,” and a (meth)acrylic acid ester-based monomer having only one (meth)acryloyl group in one molecule may be referred to as a “monofunctional acrylate.” The polymerizable monomer composition, the light diffusion film of the present disclosure, and the method for producing the light diffusion film of the present disclosure will be described in detail below.

[0016] 1. Polymerizable Monomer Composition for Light Diffusion Film The polymerizable monomer composition for light diffusion film of the present disclosure is a polymerizable monomer composition for light diffusion film containing fine particles and a polymerizable monomer for binder, characterized in that the fine particles have an iodine value of 35 g / 100 g or more and 100 g / 100 g or less as measured in accordance with JIS K 0070, and the polymerizable monomer for binder contains a crosslinkable monomer having multiple reactive unsaturated bonds in one molecule. Note that the polymerizable monomer composition for light diffusion film of the present disclosure may also be simply referred to as a "polymerizable monomer composition."

[0017] The polymerizable monomer composition of the present disclosure is used as a curable material for producing a light diffusion film. By using the polymerizable monomer composition of the present disclosure, a light diffusion film having good light diffusion properties and light transmittance while improving crack resistance can be provided. Below, the fine particles contained in the polymerizable monomer composition of the present disclosure and their production method, the polymerizable monomer for the binder, and other materials added as needed will be described in detail.

[0018] [Fine Particles] The fine particles used in the present disclosure have an iodine value of 35 g / 100 g or more and 100 g / 100 g or less, as measured in accordance with JIS K 0070. In the present disclosure, the iodine value measured in accordance with JIS K 0070 may be simply referred to as the iodine value. The iodine value of fine particles can be used as an indicator of the amount of reactive unsaturated bonds present on the outer surface of the fine particles. The fine particles used in the present disclosure have an iodine value of 35 g / 100 g or more and 100 g / 100 g or less, and therefore have an appropriate amount of reactive unsaturated bonds on the outer surface. Such fine particles have good compatibility with the polymerizable monomer for the binder, and therefore exhibit good dispersibility in the polymerizable monomer composition of the present disclosure. Furthermore, the reactive unsaturated bonds present on the outer surfaces of the microparticles react with the reactive unsaturated bonds of the binder polymerizable monomer, and thus, by curing the polymerizable monomer composition of the present disclosure, the outer surfaces of the microparticles can be crosslinked with the polymer of the binder polymerizable monomer. The light diffusion film of the present disclosure obtained by curing such a polymerizable monomer composition of the present disclosure contains a polymer of the binder polymerizable monomer as a binder, and the microparticles are dispersed in the binder. When the polymerizable monomer composition of the present disclosure is cured, the polymerization reaction of the binder polymerizable monomer proceeds, and the crosslinking reaction between the polymer of the binder polymerizable monomer and the microparticles proceeds. Therefore, in the cured product of the polymerizable monomer composition of the present disclosure, crosslinks are formed between the binder and the outer surfaces of the microparticles. As a result, the adhesion at the interface between the microparticles and the binder is improved, and the interface between the microparticles and the binder is less likely to peel. Generally, after forming a cured film containing fine particles on a substrate, when the substrate is separated from the cured film, if the interface between the fine particles and the binder peels off with the bending of the cured film, the cured film is likely to crack.On the other hand, in the cured product of the polymerizable monomer composition of the present disclosure, the interface between the fine particles and the binder is not easily peeled off as described above, so that when the cured film of the polymerizable monomer composition of the present disclosure is formed on a substrate and the substrate is separated from the cured film, even if the cured film is bent, the interface between the fine particles and the binder is not easily peeled off, so the cured film is not likely to crack.Furthermore, in the cured product of the polymerizable monomer composition of the present disclosure, crosslinks are formed between the binder, which is a polymer of the binder polymerizable monomer, and the outer surfaces of the fine particles, thereby forming a three-dimensional crosslinked structure near the surface of the fine particles, which makes the fine particles in the cured product less likely to be crushed and also has the advantage of improving the Young's modulus of the cured product.

[0019] In the present disclosure, the iodine value of the microparticles is 35 g / 100 g or more and 100 g / 100 g or less, thereby achieving good compatibility between the microparticles and the polymerizable monomer for the binder, as described above. This results in excellent dispersibility of the microparticles in the polymerizable monomer for the binder, suppressing aggregation of the microparticles. Therefore, a light diffusion film made of a cured product of the polymerizable monomer composition of the present disclosure is prevented from cracking, deterioration of light diffusion properties, and an increase in film thickness due to aggregation of the microparticles. Furthermore, if the microparticles aggregate in the light diffusion film, the interface between the microparticles and the binder is reduced, resulting in an insufficient amount of crosslinking formed between the microparticles and the binder. As a result, the adhesion between the microparticles and the binder is reduced, making the light diffusion film more susceptible to cracking. Furthermore, if the iodine value of the microparticles is too high, the outer surface of the microparticles will have too many reactive sites, leading to aggregation of the microparticles in the polymerizable monomer for the binder. Furthermore, since the iodine value of the fine particles is 35 g / 100 g or more, a sufficient amount of cross-linking bonds is formed between the fine particles and the binder, thereby improving the adhesion at the interface between the fine particles and the binder, and improving the crack resistance of the light diffusion film of the present disclosure. From this viewpoint, the iodine value of the fine particles is preferably 40 g / 100 g or more as a lower limit, and preferably 80 g / 100 g or less, more preferably 60 g / 100 g or less, and even more preferably 50 g / 100 g or less as an upper limit.

[0020] The reactive unsaturated bond that the above-mentioned microparticle has can be for example the reactive unsaturated bond that is contained in vinyl group, (meth)acryloyl group, allyl group, butenyl group, maleimide group, nadimide group, propargyl group or ethynyl group etc., preferably ethylenic unsaturated bond, more preferably the ethylenic unsaturated bond that is contained in at least one selected from the group consisting of vinyl group, (meth)acryloyl group and allyl group, more preferably the ethylenic unsaturated bond that is contained in at least one selected from the group consisting of vinyl group and (meth)acryloyl group.It should be noted that (meth)acryloyl group represents each of acryloyl group and methacryloyl group.

[0021] In the present disclosure, from the viewpoint of light transmittance and compatibility with the polymerizable monomer for the binder, resin microparticles containing, as a main component, a polymer (resin) of the polymerizable monomer for the microparticles described below are preferably used as the microparticles. In this case, the reactive unsaturated bonds possessed on the outer surface of the microparticles may be unreacted reactive unsaturated bonds possessed by the polymerizable monomer for the microparticles. Alternatively, the reactive unsaturated bonds possessed on the outer surface of the microparticles may be those introduced by surface treatment with a coupling agent or the like. From the viewpoint of light transmittance and compatibility with the polymerizable monomer for the binder, it is preferable that the reactive unsaturated bonds possessed by the polymerizable monomer for the microparticles remain unreacted on the outer surface of the microparticles. In other words, it is preferable that the reactive unsaturated bonds possessed on the outer surface of the microparticles are reactive unsaturated bonds possessed by the monomer units constituting the microparticles. On the other hand, if the microparticles are surface-treated, the mechanical properties of the light diffusion film of the present disclosure can be improved.

[0022] (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 fine particles are formed by polymerizing the polymerizable monomer for fine particles, and the polymer of the polymerizable monomer for fine particles becomes the main component of the fine particles. The polymerizable monomer for fine particles is not particularly limited, but from the viewpoint of excellent reactivity, a monomer having at least one selected from the group consisting of a (meth)acryloyl group, a vinyl group, and an allyl group is preferred, and a monomer having at least one selected from the group consisting of a (meth)acryloyl group and a vinyl group is more preferred.

[0023] In order to set the iodine value of the microparticles within the above range, it is preferable that the polymerizable monomer for microparticles contains at least a crosslinkable monomer. The iodine value of the microparticles can be set within the above range by leaving a portion of the reactive unsaturated bonds of the crosslinkable monomer unreacted on the outer surface of the microparticles. Furthermore, by including a crosslinkable monomer as the polymerizable monomer for microparticles, the crosslinking density of the polymer, which is the main component of the microparticles, can be increased, thereby improving the strength of the microparticles. Furthermore, when the microparticles are hollow particles, including a crosslinkable monomer as the polymerizable monomer for microparticles facilitates the formation of a shell with excellent strength, and also facilitates the hollow particles becoming spherical, with the formation of hollow portions clearly distinguishable from the shell within the particles.

[0024] In the polymerizable monomer for fine particles, the crosslinkable monomer is preferably at least one selected from the group consisting of crosslinkable hydrocarbon monomers and crosslinkable acrylic monomers. Crosslinkable acrylic monomers are preferred from the viewpoint of the optical properties of the light diffusion film and the strength of the fine particles, while crosslinkable hydrocarbon monomers are preferred because they facilitate the introduction of reactive unsaturated bonds into the outer surfaces of the fine particles. Examples of crosslinkable hydrocarbon monomers 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.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.In the polymerizable monomer for microparticles, as the crosslinkable monomer, can also be listed the crosslinkable allylic monomer such as allyl phthalate; crosslinkable macromer such as polybutadiene, polyisoprene, styrene-butadiene block copolymer (SBS), styrene-isoprene block copolymer (SIS), polyphenylene ether whose both ends are vinyl-modified, and polyphenylene ether whose both ends are (meth)acrylic-modified.In addition, as the polymerizable monomer for microparticles, these crosslinkable monomers can be used alone or in combination of two or more kinds.

[0025] In the present disclosure, in order to control the iodine value of the microparticles, improve the compatibility between the microparticles and the polymerizable monomer for the binder, and thereby improve the light diffusion properties and crack resistance of the light diffusion film, it is particularly preferable that the polymerizable monomer for the microparticles contains a combination of a crosslinkable acrylic monomer and a crosslinkable hydrocarbon monomer as the crosslinkable monomer. In order to easily introduce reactive unsaturated bonds into the outer surfaces of the microparticles, the crosslinkable hydrocarbon monomer in the polymerizable monomer for the microparticles 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 microparticles, 2-phenyl-1,3-butadiene is particularly preferred. Furthermore, imparting flexibility to the microparticles makes them less likely to crack. Therefore, by improving the flexibility of the microparticles, cracking of the microparticles during mixing with the polymerizable monomer for the binder can be suppressed, thereby improving the operability during the mixing process. In order to improve the strength of the fine particles and to facilitate good compatibility between the fine particles and the polymerizable monomer for the binder, the polymerizable monomer for the 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 the trifunctional or higher crosslinkable acrylic monomers, 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 is preferred. Furthermore, in the polymerizable monomer for fine particles, the crosslinkable acrylic monomer is preferably a crosslinkable acrylic monomer containing 4 to 6 oxygen atoms per molecule, since this facilitates the introduction of reactive unsaturated bonds onto the outer surfaces of the fine particles.Among the crosslinkable acrylic monomers, 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate are particularly preferred because they facilitate the introduction of reactive unsaturated bonds into the outer surface of the microparticles and also improve the flexibility of the microparticles. That is, in the present disclosure, the use of at least one selected from the group consisting of 2-phenyl-1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate as the polymerizable monomer for microparticles is particularly preferred because it facilitates the introduction of reactive unsaturated bonds into the outer surface of the microparticles, making it possible to easily increase the iodine value of the microparticles and further improve the flexibility of the microparticles. From this perspective, it is preferable that the polymerizable monomer for microparticles contains two or more monomers selected from the above group, and more preferably three or more monomers.

[0026] In the present disclosure, in order to control the iodine value of the microparticles to improve the crack resistance of the light diffusion film and to improve the strength of the microparticles, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer for microparticles is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. In the present disclosure, the polymerizable monomer for microparticles may be composed of a crosslinkable monomer, but may also contain a non-crosslinkable monomer, which will be described later as the polymerizable monomer for microparticles. 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.

[0027] In order to control the iodine value of fine particles, improve the compatibility between fine particles and binder polymerizable monomer, and improve the light diffusion property and crack resistance of light diffusion film, the content of crosslinkable acrylic monomer in 100% by mass of fine particle polymerizable monomer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and more preferably 50% by mass or more, and the upper limit is preferably 90% by mass or less, more preferably 70% by mass or less, and more preferably 60% by mass or less.When the polymerizable monomer for fine particles contains a combination of a bifunctional crosslinkable acrylic monomer and a trifunctional or higher crosslinkable acrylic monomer, from the same viewpoint as above, the content of bifunctional crosslinkable acrylic monomer in 100% by mass of crosslinkable acrylic monomer is preferably 20% by mass or more, more preferably 30% by mass or more, 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.

[0028] The polymerizable monomer for microparticles may further contain a non-crosslinkable monomer. In the polymerizable monomer for microparticles, the non-crosslinkable monomer is preferably at least one selected from the group consisting of non-crosslinkable hydrocarbon monomers and non-crosslinkable acrylic monomers. In the polymerizable monomer for microparticles, 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.In the polymerizable monomer for fine particles, examples of the non-crosslinkable acrylic monomer 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, and phenoxypolyethylene glycol polypropylene glycol. Examples of the acrylate include glycol (meth)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, and N-butoxymethyl (meth)acrylamide.In the polymerizable monomer for microparticles, the non-crosslinkable monomer can further include vinyl carboxylate ester monomer such as vinyl acetate; halogenated aromatic vinyl monomer such as halogenated styrene; halogenated vinyl monomer such as vinyl chloride; halogenated vinylidene monomer such as vinylidene chloride; vinylpyridine; non-crosslinkable macromer such as polystyrene whose one end is (meth)acrylic modified and polymethyl methacrylate whose one end is (meth)acrylic modified.In addition, as the polymerizable monomer for microparticles, these non-crosslinkable monomers can be used alone or in combination of two or more kinds.

[0029] The content of the non-crosslinkable monomer in 100% by mass of the polymerizable monomer for microparticles is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of keeping the iodine value of the microparticles within the above range and preventing a decrease in the strength of the microparticles. The lower limit of the content of the non-crosslinkable monomer in 100% by mass of the polymerizable monomer for microparticles 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.

[0030] From the viewpoint of improving the compatibility between the microparticles and the polymerizable monomer for the binder, the total content of the hydrocarbon monomer and the acrylic monomer in 100% by mass of the polymerizable monomer for the 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, from the viewpoint of improving the compatibility between the microparticles and the polymerizable monomer for the binder, the mass ratio of the acrylic monomer to the hydrocarbon monomer (acrylic monomer:hydrocarbon monomer) contained in the polymerizable monomer for the 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. Furthermore, when the mass ratio is within the above range, the iodine value of the microparticles is likely to be within the above-mentioned preferred range.

[0031] From the viewpoint of compatibility between the fine particles and the polymerizable monomer for the binder, and from the viewpoint of the optical properties of the light diffusion film, the content of the polymer of the polymerizable monomer for the fine particles in the fine particles 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.

[0032] The 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 fine particles include a method of reacting a modifying agent for introducing polar groups, a method of 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.

[0033] The thermal decomposition initiation temperature of the microparticles is not particularly limited, but is preferably 345°C or higher, more preferably 350°C or higher, from the viewpoint of heat resistance. The upper limit of the thermal decomposition initiation temperature of the microparticles is not particularly limited, but may be, for example, 400°C or lower. In the present disclosure, the thermal decomposition initiation temperature of the microparticles 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.

[0034] The shape of the 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 fine particles. The shape of the fine particles can be confirmed, for example, by observing the fine particles with a SEM or TEM.

[0035] The volume average particle diameter of the 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 fine particles is above the lower limit, aggregation of the fine particles is suppressed and dispersibility is improved, thereby improving the light diffusion properties of the light diffusion film, and cracking of the light diffusion film, deterioration of light diffusion properties, and increase in film thickness caused by aggregation of the fine particles are suppressed. When the volume average particle diameter of the fine particles is below the upper limit, reduction in the interface between the fine particles and the binder in the light diffusion film is suppressed, increasing the amount of crosslinking bonds formed between the fine particles and the binder, improving adhesion, and improving the crack resistance of the light diffusion film.

[0036] The particle size distribution (volume average particle size (Dv) / number average particle size (Dp)) of the 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 reduce the thickness of the light diffusion film. Furthermore, when the particle size distribution is equal to or less than the upper limit, the thickness uniformity of the light diffusion film of the present disclosure can be improved. Furthermore, from the viewpoint of ease of production of the 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 microparticles can be determined, for example, by measuring the particle size of the microparticles using a particle size distribution measuring device according to the Coulter counter method, calculating the number average and volume average, respectively, and using the obtained values ​​as the number average particle size (Dp) and volume average particle size (Dv) of the 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.

[0037] The 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 fine particles can further improve the light transmittance of the light diffusion film of the present disclosure. Furthermore, the inclusion of hollow particles as the fine particles can impart various properties to the light diffusion film of the present disclosure, such as weight reduction, heat insulation, and the ability to retain functional components such as antibacterial agents.

[0038] 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 crack resistance of the light diffusion film and the strength of the hollow particles. One example of the shape of the hollow particles is a bag made of a thin film and inflated with gas. The hollow portions of the hollow particles 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.

[0039] 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.

[0040] 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 cm ３ 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.

[0041] 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 D０ 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.

[0042] 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

[0043] The porosity can also be measured by the method described above for microparticles whose hollowness is unknown. In the present 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.

[0044] The microparticles may contain a small amount of low-circularity particles, such as cracked or deformed particles, as impurities. However, from the viewpoint of the light transmittance, light diffusion, and cracking resistance of the light diffusion film, the proportion of particles with a circularity of 0.85 or less per 100% by mass of microparticles is preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably less than 8% by mass. Particles with a circularity of 0.85 or less are typically particles that have deformations such as dents or cracks, and are sometimes referred to as "irregularly shaped particles" in the present disclosure. Compared to spherical microparticles, such irregularly shaped particles have inferior light transmittance and light diffusion properties, and also inferior adhesion to binders. Therefore, reducing the proportion of irregularly shaped particles contained in the microparticles can improve the light transmittance, light diffusion, and cracking resistance of the light diffusion film. Furthermore, irregularly shaped particles have the problem of being more prone to aggregation when dispersed in a polymerizable monomer for a binder, resulting in poor dispersibility, compared to spherical microparticles. Therefore, by reducing the proportion of irregularly shaped particles contained in the microparticles, the dispersibility of the microparticles can be improved, and as a result, the light diffusion properties and crack resistance of the light diffusion film can be improved. Furthermore, irregularly shaped particles have the problem of being less pressure-resistant than spherical microparticles because they are more susceptible to localized external pressure. When irregularly shaped particles are dispersed in a polymerizable monomer for a binder, aggregates are likely to form, and the aggregates are more susceptible to external pressure, further reducing the pressure resistance. Therefore, by reducing the proportion of irregularly shaped particles contained in the microparticles, the pressure resistance of the microparticles can be improved.

[0045] 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 microparticles may have an average circularity of 0.950 to 0.995. In the present disclosure, 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, for example, by dispersing 0.10 to 0.12 g of microparticles 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 circularities of 1,000 to 3,000 randomly selected particles.

[0046] In the polymerizable monomer composition of the present disclosure, the content of the fine particles is not particularly limited, but the ratio of the mass of the fine particles to the mass of the polymerizable monomer for binder (described later) (fine particles / polymerizable monomer for binder) is preferably 0.5 or more, more preferably 1.0 or more, and is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. When the mass ratio of the fine particles is equal to or more than the lower limit, the light diffusion property of the light diffusion film of the present disclosure is improved, and when it is equal to or less than the upper limit, deterioration of light transmittance and deterioration of crack resistance are suppressed.

[0047] [Method for producing microparticles] The microparticles can be produced, for example, by a production method based on suspension polymerization, which will be described later. As one embodiment of the method for producing the microparticles, for example, the method for producing microparticles includes the steps of: 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 microparticles containing a polymer of the polymerizable monomer for microparticles (polymerization step).

[0048] 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.

[0049] The above-mentioned method for producing microparticles may further include a step different from the steps described above. Furthermore, in the above-mentioned method for producing microparticles, as far as technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single 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 microparticles will be explained in order.

[0050] (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.

[0051] (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 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.

[0052] (Polymerization Initiator) In the mixed solution, the polymerization initiator preferably contains an oil-soluble polymerization initiator, since this facilitates control of the particle size of the microparticles. The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator 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).

[0053] 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.

[0054] (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.

[0055] In the present disclosure, it is particularly preferable to use a poorly water-soluble inorganic dispersion stabilizer dispersed in an aqueous medium in the form of colloidal particles, i.e., in the form of a colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles. 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.

[0056] 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.

[0057] 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.

[0058] In the present disclosure, in order to suppress a decrease in the reactivity between the fine particles and the polymerizable monomer for the binder, it is preferable that the residual amount of the dispersion stabilizer is as small as possible, and it is most preferable that the dispersion stabilizer is not contained, and it is particularly preferable that the dispersion stabilizer is not contained. By using only an inorganic dispersion stabilizer as the dispersion stabilizer, it is possible to obtain fine particles in which both the water-soluble polymer stabilizer and the surfactant are below the detection limit.

[0059] (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.

[0060] The content of the aqueous medium is not particularly limited, but from the viewpoint of keeping the particle size of the 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.

[0061] (Hydrophobic Solvent) When producing solid particles as the microparticles, the mixed solution does not need to contain a hydrophobic solvent. However, when producing hollow particles as the microparticles, the mixed solution preferably further contains a hydrophobic solvent. The hydrophobic solvent can function as a spacer material that forms hollow spaces inside the 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] A mixed solution is obtained by mixing the above-mentioned materials and other materials as needed, and stirring appropriately. In this mixed solution, an oil phase containing lipophilic materials such as the polymerizable monomer for microparticles, a polymerization initiator, and a hydrophobic solvent is dispersed in an aqueous phase containing a dispersion stabilizer and an aqueous medium, with particles of a few millimeters in size. 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 process, the above-mentioned materials and other materials as needed can be simply mixed and stirred appropriately to obtain a mixed solution. However, to improve the uniformity of the resulting microparticles, it is preferable to prepare a mixed solution by separately preparing an oil phase containing the polymerizable monomer for microparticles 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 can preferably be used as the aqueous phase. By separately preparing the oil phase and the aqueous phase in this way and then mixing them, uniform microparticles can be produced, and the particle size of the microparticles can be easily controlled.

[0069] (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 dispersion for preparing a suspension, the rotation speed of the disperser is not particularly limited, but in order to keep the volume average particle size of the microparticles 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.

[0070] 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.

[0071] 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 microparticles, and, if necessary, a hydrophobic solvent. The oil-soluble polymerization initiator generates polymerization initiation radicals inside the oil droplets, so that microparticles of the desired particle size can be produced without excessive growth of 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 microparticles 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 microparticles smaller in particle size than the desired microparticles, thereby narrowing the particle size distribution of the microparticles.

[0072] (3) Polymerization Step This step is a step of forming 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 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 the polymer and a hollow portion surrounded by the shell, the hollow portion being filled with a hydrophobic solvent, are dispersed in an aqueous medium.

[0073] 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.

[0074] (4) Solid-liquid separation step This step is a step of obtaining a solid content containing fine particles by solid-liquid separation of a slurry containing fine particles. The solid-liquid separation step may be performed on the aqueous dispersion of fine particles obtained by the above-mentioned polymerization step, or the aqueous dispersion of fine particles obtained after the solvent removal step described below. The method of 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.

[0075] After the solid-liquid separation step, an optional step such as a drying step for removing the aqueous medium remaining in the 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.

[0076] (5) Solvent Removal Step: This step involves removing the hydrophobic solvent that fills the interior of hollow particles when producing hollow particles as microparticles. For example, after the solid-liquid separation step described above, the hydrophobic solvent filling the interior of the hollow particles can be removed in air, replacing the hydrophobic solvent with air and yielding 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, sufficient to not affect the removal of the hydrophobic solvent. This can also be described as the state in which the hollow particles exist 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.

[0077] 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 microparticles do not collapse. Therefore, depending on the type of polymerizable monomer for the microparticles, 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 drying atmospheres include air, oxygen, nitrogen, and argon. Alternatively, hollow particles with a temporary vacuum inside can be obtained by first filling the interior of the hollow particles with gas and then drying under reduced pressure.

[0078] 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.

[0079] (6) Others As steps other than the above steps (1) to (5), for example, the following steps (6-a) surface treatment step, (6-b) sieving step, (6-c) washing step, and (6-d) particle interior substitution step may be added.

[0080] (6-a) Surface Treatment Step The method for producing the above-mentioned microparticles may include a surface treatment step of treating the outer surface of the microparticles with a coupling agent after the above-mentioned polymerization step. The coupling agent has a functional group capable of bonding with an organic substance and a functional group capable of bonding with an inorganic substance in one molecule, and can enhance the affinity between the organic material and the inorganic material. Examples of the coupling agent include silane coupling agents, titanium coupling agents, and aluminum coupling agents, among which silane coupling agents are preferred. Examples of the silane coupling agent include alkoxysilanes having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris(β-methoxyethoxy)silane; alkoxysilanes having a methacryloyl group or an acryloyl group such as γ-acryloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane; and alkoxysilanes having an epoxy group such as γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane. alkoxysilanes having an amino group such as γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)γ-aminopropylmethyldimethoxysilane; alkoxysilanes having a mercapto group such as γ-mercaptopropyltrimethoxysilane; alkoxysilanes having a halogen group such as γ-chloropropyltrimethoxysilane; silanes having a vinyl group and a halogen group such as vinyltrichlorosilane; methyltriacetoxysilane; and the like.Examples of titanium coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate), Examples of suitable coupling agents include bis(dioctyl phosphate)acetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctylphosphate)titanate, isopropyl tri(N-amidoethylaminoethyl)titanate, dicumylphenyloxyacetate titanate, and diisostearoyl ethylene titanate. Examples of suitable aluminum coupling agents include acetoalkoxyaluminum diisopropylate. The coupling agent used in the present disclosure preferably has a functional group in its molecular structure that is capable of crosslinking with the polymerizable monomer for the binder. Examples of suitable functional groups that are capable of crosslinking with the polymerizable monomer for the binder include vinyl groups and (meth)acryloyl groups. The coupling agent may be used as is or dissolved in a solvent.

[0081] (6-b) Sieving step (foreign matter removal step) The method for producing fine particles may include a sieving step of sieving the fine particles after drying. By performing the sieving step, coarse powder and aggregates can be removed, and foreign matter can be easily removed. Any known method can be used as the sieving method, and there is no particular limitation. 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 on which the fine particles are placed is vibrated, and the fine particles that have passed through the mesh are obtained, thereby obtaining the sieved fine particles. The opening size of the mesh used in the sieving step is appropriately selected depending on the size of the fine particles.

[0082] (6-c) Washing Step The washing step is a step in which an acid or alkali is added to wash the particles to remove any dispersion stabilizer remaining in the particles. When the dispersion stabilizer used is an acid-soluble inorganic dispersion stabilizer, it is preferable to add an acid to the slurry containing the 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 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 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 because of its high dispersion stabilizer removal efficiency and its small burden on the production equipment.

[0083] (6-d) 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.

[0084] [Polymerizable Monomer for Binder] In the present disclosure, the polymerizable monomer for binder contains at least a crosslinkable monomer having multiple reactive unsaturated bonds in one molecule. This increases the crosslink density of the cured product of the polymerizable monomer composition of the present disclosure. Furthermore, when the polymerizable monomer composition of the present disclosure is cured, the polymerization reaction of the polymerizable monomer for binder proceeds, and the crosslinking reaction between the polymer of the polymerizable monomer for binder and the fine particles proceeds. This results in the formation of crosslinked bonds between the binder and the outer surface of the fine particles, improving the adhesion at the interface between the fine particles and the binder. Therefore, the light diffusion film of the present disclosure can have sufficient strength and excellent crack resistance. The polymerizable monomer for binder is polymerized to become the binder of the light diffusion film.

[0085] The reactive unsaturated bond possessed by the polymerizable monomer for binder may be, for example, the same as the reactive unsaturated bond possessed by the above-mentioned fine particles. The reactive unsaturated bond possessed by the polymerizable monomer for binder is preferably an ethylenic unsaturated bond, more preferably an ethylenic unsaturated bond contained in at least one selected from the group consisting of a vinyl group, a (meth)acryloyl group, and an allyl group, and even more preferably an ethylenic unsaturated bond contained in at least one selected from the group consisting of a vinyl group and a (meth)acryloyl group.

[0086] The polymerizable monomer for the binder can be any known polymerizable monomer conventionally used in binders for light diffusion films, and is not particularly limited. However, in order to obtain a light diffusion film with excellent optical properties and crack resistance, it is preferable to appropriately select a polymerizable monomer for the binder that has good compatibility with the above-mentioned fine particles. In order to improve the compatibility between the fine particles and the polymerizable monomer for the binder, it is preferable to sufficiently reduce the difference in polarity between the fine particles and the polymerizable monomer for the binder. The polarity of the fine particles and the polarity of the polymerizable monomer for the binder can be adjusted by the composition of the polymerizable monomer for the fine particles and the composition of the polymerizable monomer for the binder, respectively. For example, the smaller the difference between the content of the acrylic monomer in the polymerizable monomer for the fine particles and the content of the acrylic monomer in the polymerizable monomer for the binder, the better the compatibility between the fine particles and the polymerizable monomer for the binder tends to be. Therefore, the content of the acrylic monomer in the polymerizable monomer for the fine particles is set to P Ａ (mass%), and the content ratio of the acrylic monomer in the polymerizable monomer for binder is B Ａ (mass%), P Ａ and B Ａ The difference between the refractive index of the fine particles contained in the light diffusion film and the refractive index of the binder is preferably 80 or less, more preferably 70 or less, even more preferably 60 or less, and particularly preferably 50 or less. On the other hand, in order for the light diffusion film of the present disclosure to have light diffusibility, it is desirable that the difference between the refractive index of the fine particles contained in the light diffusion film and the refractive index of the binder is sufficiently large. From the viewpoint of such a refractive index difference, Ａ and B ＡThe difference between P and P is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. Ａ than the value of B Ａ In addition, when the content of the acrylic monomer in the polymerizable monomer for fine particles is 20% by mass or more, the content of the acrylic monomer in the polymerizable monomer for binder is preferably 70% by mass or more.

[0087] In addition, the smaller the difference between the content of the hydrocarbon monomer in the polymerizable monomer for fine particles and the content of the hydrocarbon monomer in the polymerizable monomer for binder is, the better the compatibility between the fine particles and the polymerizable monomer for binder tends to be. Ｃ (mass%), and the content ratio of the hydrocarbon monomer in the polymerizable monomer for the binder is B Ｃ (mass%), P Ｃ and B Ｃ The difference between is preferably 80 or less, more preferably 70 or less, even more preferably 60 or less, and particularly preferably 50 or less.

[0088] The molecular weight of the polymerizable monomer for the binder is not particularly limited, but from the viewpoint of compatibility with the fine particles and crack resistance of the light diffusion film, it is preferably in the range of 10 to 2000, and more preferably in the range of 50 to 1000.

[0089] From the viewpoint of compatibility with the fine particles, the acid value of the polymerizable monomer for the binder is preferably 500 mg KOH / g or less, more preferably 300 mg KOH / g or less, as an upper limit, and preferably 0.01 mg KOH / g or more, more preferably 0.05 mg KOH / g or more, as a lower limit. When the polymerizable monomer composition of the present disclosure contains multiple types of polymerizable monomers as the polymerizable monomer for the binder, the "acid value of the polymerizable monomer for the binder" refers to the acid value of a mixture of the multiple types of polymerizable monomers. In the present disclosure, the acid value is measured by potentiometric titration in accordance with JIS K 0070.

[0090] In the polymerizable monomer for the binder, the crosslinkable monomer preferably contains a crosslinkable acrylic monomer from the viewpoints of compatibility with the fine particles, the optical properties of the light diffusion film, and the crack resistance of the light diffusion film, and particularly preferably contains a polyfunctional acrylate. Examples of the crosslinkable acrylic monomer in the polymerizable monomer for the binder include the bifunctional crosslinkable acrylic monomers and trifunctional or higher crosslinkable acrylic monomers that can be used as the polymerizable monomer for the fine particles described above. Among these, (meth)acrylic acid ester monomers having multiple (meth)acryloyl groups in one molecule, i.e., polyfunctional acrylates, are particularly preferred. Examples of polyfunctional acrylates that are particularly preferred from the viewpoints of compatibility with the fine particles, the optical properties of the light diffusion film, and the crack resistance of the light diffusion film include bisphenol F EO-modified di(meth)acrylate and bisphenol A. Examples of the di(meth)acrylate include EO-modified di(meth)acrylate, isocyanuric acid EO-modified di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane PO-modified tri(meth)acrylate, trimethylolpropane EO-modified tri(meth)acrylate, isocyanuric acid EO-modified tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, diglycerin EO-modified (meth)acrylate, polybasic acid-modified acrylic oligomer, urethane (meth)acrylate, and polyester (meth)acrylate. As the preferred polyfunctional acrylate, for example, commercially available products such as bifunctional or polyfunctional special acrylates commercially available under the trade name Aronix (registered trademark) manufactured by Toagosei Co., Ltd., bifunctional urethane acrylates, and bifunctional or polyfunctional polyester acrylates can be used.Furthermore, among the above-mentioned preferred polyfunctional acrylates, at least one selected from the group consisting of pentaerythritol tri(meth)acrylate, bifunctional urethane (meth)acrylate, and bifunctional polyester (meth)acrylate is particularly preferred, as it is likely to have good compatibility with fine particles and can further improve the light diffusion properties and crack resistance of the light diffusion film.

[0091] Furthermore, in the polymerizable monomer for binder, the crosslinkable monomer may further include the crosslinkable hydrocarbon monomer and the crosslinkable allylic monomer that can be used as the polymerizable monomer for fine particles described above. These crosslinkable monomers may be used alone or in combination of two or more as the polymerizable monomer for binder.

[0092] In the present disclosure, the content of the crosslinkable monomer is preferably 20% by mass or more relative to 100% by mass of the total amount of polymerizable monomers for the binder. This increases the crosslinking density of the binder and improves the reactivity between the polymerizable monomers for the binder and the fine particles, thereby improving the strength and crack resistance of the light diffusion film. From this perspective, the content of the crosslinkable monomer relative to 100% by mass of the total amount of polymerizable monomers for the binder is more preferably 25% by mass or more. On the other hand, when the polymerizable monomers for the binder contain a combination of a crosslinkable monomer and a non-crosslinkable monomer, the non-crosslinkable monomer functions as a plasticizer, thereby further improving the crack resistance of the light diffusion film of the present disclosure. From the perspective of including a non-crosslinkable monomer in the polymerizable monomers for the binder, the content of the crosslinkable monomer relative to 100% by mass of the total amount of polymerizable monomers for the binder is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 60% by mass or less. The content of each monomer in 100% by mass of the polymerizable monomer for the binder corresponds to the content of each monomer unit in 100% by mass of all monomer units constituting the binder (polymer) of the light diffusion film.

[0093] From the viewpoint of the optical properties and crack resistance of the light diffusion film, the content of the polyfunctional acrylate in 100% by mass of the crosslinkable monomer used as the polymerizable monomer for the binder is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 98% by mass or more, and may be 100% by mass.

[0094] The polymerizable monomer for the binder may further contain a non-crosslinkable monomer. When the polymerizable monomer for the binder contains a combination of a crosslinkable monomer and a non-crosslinkable monomer, the non-crosslinkable monomer functions as a plasticizer, thereby further improving the crack resistance of the light diffusion film of the present disclosure. In the polymerizable monomer for the binder, the non-crosslinkable monomer preferably contains a non-crosslinkable acrylic monomer from the viewpoints of compatibility with the fine particles, the optical properties of the light diffusion film, and the crack resistance of the light diffusion film. Among these, the non-crosslinkable acrylic monomer preferably contains a monofunctional acrylate. In the polymerizable monomer for the binder, examples of the non-crosslinkable acrylic monomer include non-crosslinkable acrylic monomers that can be used as polymerizable monomers for fine particles. Among these, (meth)acrylic acid ester monomers having only one (meth)acryloyl group per molecule, i.e., monofunctional acrylates, are particularly preferred. Particularly preferred monofunctional acrylates from the viewpoints of compatibility with fine particles, the optical properties of the light diffusion film, and the cracking resistance of the light diffusion film include, for example, 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, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Preferred examples of the monofunctional acrylates include commercially available monofunctional specialty acrylates available from Toagosei Co., Ltd. under the trademark Aronix (registered trademark). Furthermore, among the above-mentioned preferred monofunctional acrylates, 2-hydroxy-3-phenoxypropyl (meth)acrylate is particularly preferred because it is likely to have good compatibility with fine particles and can further improve the light diffusion properties and crack resistance of the light diffusion film.

[0095] Furthermore, in the polymerizable monomer for binder, the non-crosslinkable monomer may further include the non-crosslinkable hydrocarbon monomer, vinyl carboxylate monomer, halogenated aromatic vinyl monomer, halogenated vinyl monomer, vinylidene halogenated monomer, and vinylpyridine, which can be used as the polymerizable monomer for fine particles described above. Note that, as the polymerizable monomer for binder, these non-crosslinkable monomers may be used alone or in combination of two or more.

[0096] The polymerizable monomer for the binder does not need to contain a non-crosslinkable monomer, but if it does contain a non-crosslinkable monomer, the content of the non-crosslinkable monomer in 100% by mass of the polymerizable monomer for the binder is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of improving the crack resistance of the light diffusion film, while it is preferably 80% by mass or less, more preferably 75% by mass or less, from the viewpoint of suppressing a decrease in the crack resistance of the light diffusion film.

[0097] From the viewpoint of the optical properties and crack resistance of the light diffusion film, the content of the monofunctional acrylate in 100% by mass of the non-crosslinkable monomer used as the polymerizable monomer for the binder is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 98% by mass or more, and may be 100% by mass.

[0098] In addition, from the viewpoint of the optical properties of the light diffusion film, particularly light transmittance, it is preferable to use a polymerizable monomer that can give an amorphous polymer as the polymerizable monomer for the binder. From this viewpoint, an acrylic monomer is preferably used as the polymerizable monomer for the binder, and the above-mentioned polyfunctional acrylate and monofunctional acrylate are particularly preferably used.

[0099] From the viewpoint of the optical properties of the light diffusion film and the compatibility with the fine particles, the content of the acrylic monomer in 100% by mass of the polymerizable monomer for the binder is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and may be 100% by mass.

[0100] Furthermore, it is preferable to use a polymerizable monomer for the binder that has a glass transition temperature (Tg) when polymerized, i.e., the glass transition temperature (Tg) of the binder for the light diffusion film, of 100 to 350°C. This improves the flexibility of the light diffusion film, thereby improving the crack resistance of the light diffusion film. From the viewpoint of the glass transition temperature, for example, at least one crosslinkable monomer selected from the group consisting of EO-modified isocyanuric acid di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate can be preferably used. From the viewpoint of setting the glass transition temperature of the binder within the above range, the total content of these preferred crosslinkable monomers is preferably 80% by mass or more, and more preferably 90% by mass or more, relative to the total amount (100% by mass) of crosslinkable monomers contained in the polymerizable monomer for the binder. The glass transition temperature (Tg) of the resin can be determined, for example, in accordance with ASTM D3418-82. Specifically, a sample is heated at a rate of 10°C / min using a differential scanning calorimeter (Seiko Instruments Inc.: SSC5200), and the temperature showing the maximum endothermic peak in the DSC curve obtained during this process can be taken as the glass transition temperature.

[0101] In the polymerizable monomer composition of the present disclosure, the content of the polymerizable monomer for the binder is not particularly limited. The lower limit is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, relative to 100% by mass of the polymerizable monomer composition. The upper limit is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the content of the polymerizable monomer for the binder is equal to or greater than the lower limit, the dispersibility of the fine particles is improved, thereby improving the light transmittance of the light diffusion film and suppressing cracking of the light diffusion film, deterioration of light diffusion properties, and increase in film thickness due to aggregation of the fine particles. When the content of the polymerizable monomer for the binder is equal to or less than the upper limit, the fine particles can be sufficiently contained, thereby improving the light diffusion properties of the light diffusion film. Furthermore, in the polymerizable monomer composition of the present disclosure, the total content of the fine particles and the polymerizable monomer for the binder is preferably 90% by mass or more, more preferably 95% by mass or more.

[0102] [Polymerization initiator] A polymerization initiator is usually used when curing the polymerizable monomer composition of the present disclosure. The polymerizable monomer composition of the present disclosure may or may not contain a polymerization initiator. When the polymerizable monomer composition of the present disclosure does not contain a polymerization initiator, a polymerization initiator may be added to the polymerizable monomer composition of the present disclosure when carrying out a polymerization reaction. The polymerization initiator is not particularly limited, but a compound that generates active species upon heating or exposure to light and promotes polymerization of the binder polymerizable monomer is preferably used. Furthermore, an oil-soluble polymerization initiator is preferably used because of its excellent compatibility with the binder polymerizable monomer. Examples of polymerization initiators (thermal initiators) that generate active species upon heating include those similar to the polymerization initiators that can be used in the production of the above-mentioned microparticles. Among these, organic peroxides are preferably used because of their ease of handling. Examples of polymerization initiators (photoinitiators) that generate active species upon exposure to light include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 3-methylacetophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-methyl-1-[4-( Examples of polymerization initiators include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone). These polymerization initiators can be used either alone or in combination of two or more.

[0103] The content of the polymerization initiator is not particularly limited, but the lower limit is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, and even more preferably 0.5 part by mass or more, relative to 100 parts by mass of the polymerizable monomer for the binder, and the upper limit is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. When the content of the polymerization initiator is equal to or more than the lower limit, the polymerization reaction can proceed sufficiently, and when it is equal to or less than the upper limit, there is little risk of the polymerization initiator remaining after completion of the polymerization reaction and there is little risk of an unexpected side reaction proceeding.

[0104] [Additives] The polymerizable monomer composition of the present disclosure may further contain various additives conventionally used in light diffusion films, if necessary. Examples of additives include antioxidants, light stabilizers, plasticizers, lubricants, dyes, pigments, fillers, fluorescent agents, antistatic agents, flame retardants, crosslinking agents, surfactants, etc. 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 appropriately adjusted within a range that does not impair the object of the present disclosure.

[0105] The polymerizable monomer composition of the present disclosure typically has a solvent content of 20% by mass or less, preferably 10% by mass or less, and particularly preferably 0% by mass. The polymerizable monomer composition of the present disclosure has a sufficiently low solvent content or no solvent, which eliminates the need for a process of drying and removing the solvent when producing a light diffusion film, thereby simplifying the manufacturing process of the light diffusion film. Examples of the solvent include non-polymerizable organic solvents and water.

[0106] [Method for Producing Polymerizable Monomer Composition] The method for producing the polymerizable monomer composition of the present disclosure is not particularly limited, as long as it is a method that can produce the polymerizable monomer composition of the present disclosure described above. For example, the polymerizable monomer composition of the present disclosure can be obtained by mixing the above-mentioned fine particles, a polymerizable monomer for binder, and other materials added as needed. The mixing method can be a general method and is not particularly limited. Furthermore, when producing the polymerizable monomer composition of the present disclosure, ultrasonic treatment may be performed after mixing the materials. This can further improve the dispersibility of the fine particles.

[0107] 2. Light Diffusion Film The light diffusion film of the present disclosure is characterized by comprising a cured product of the polymerizable monomer composition of the present disclosure described above. The light diffusion film of the present disclosure is obtained by subjecting the polymerizable monomer composition of the present disclosure to a polymerization reaction and curing. When the polymerizable monomer composition of the present disclosure is cured, the polymerization reaction of the binder polymerizable monomer proceeds, and a crosslinking reaction between the polymer of the binder polymerizable monomer and the reactive unsaturated bonds present on the outer surfaces of the fine particles proceeds. Therefore, the light diffusion film of the present disclosure typically contains a binder, which is a polymer of the binder polymerizable monomer, and fine particles, and the binder and the fine particles are crosslinked.

[0108] The thickness of the light diffusion film of the present disclosure may be adjusted appropriately depending on the application and is not particularly limited. On the other hand, the light diffusion film of the present disclosure can be thinned because it has excellent crack resistance due to the use of the polymerizable monomer composition of the present disclosure. Therefore, the thickness of the light diffusion film 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 film of the present disclosure is preferably 5 μm or more, more preferably 7 μm or more.

[0109] The method for measuring the thickness of the light diffusion film of the present disclosure will be described with reference to FIG. 1 . First, a measurement sample is obtained by cutting the light diffusion film 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 the 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, and when the nearest points are connected with lines, four squares with sides of 2 cm are arranged in a grid. These nine points are selected. Subsequently, 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 film.

[0110] The bending fracture strain (εfB) of the light diffusion film of the present disclosure is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. The larger the bending fracture strain of the light diffusion film, the better the crack resistance of the light diffusion film. On the other hand, the upper limit of the bending fracture strain of the light diffusion film of the present disclosure is not particularly limited, and the bending fracture strain of the light diffusion film of the present disclosure may exceed the measurement limit. In the present disclosure, the bending fracture strain (εfB) is measured in accordance with JIS K 7171.

[0111] From the viewpoint of light transmittance, the total light transmittance of the light diffusion film of the present disclosure is preferably 65% ​​or more, more preferably 70% or more, and even more preferably 75% or more. In the present disclosure, the total light transmittance is measured in accordance with JIS K 7375. The total light transmittance of the light diffusion film of the present disclosure is the average value of measurements taken at five locations on the film.

[0112] From the viewpoint of light diffusibility, the diffuse transmittance of the light diffusion film 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. The diffuse transmittance of the light diffusion film of the present disclosure is the average value of measurements taken at five locations on the film.

[0113] [Uses of Light Diffusion Film] The use of the light diffusion film of the present disclosure is not particularly limited, and it can be used without limitation in any application requiring light diffusion. Specific examples of applications of the light diffusion film of the present disclosure include a light diffusion film for a backlight unit of a liquid crystal display device, a light extraction film for an organic EL element used in an organic EL display device or organic EL lighting, a light scattering film for an LED lighting device, and a light capture film for a solar cell. In particular, from the viewpoint that a thin light diffusion film is particularly required, the light diffusion film of the present invention can be preferably used as a light diffusion film for a display device such as a liquid crystal display device or an organic EL display device. Note that the light diffusion film of the present disclosure may be used in a state where a substrate is attached, depending on the application.

[0114] 3. Manufacturing Method of Light Diffusion Film The manufacturing method of the light diffusion film of the present disclosure includes at least a step of curing the polymerizable monomer composition of the present disclosure described above. The method of curing the polymerizable monomer composition of the present disclosure is appropriately selected depending on the type of polymerization initiator used and is not particularly limited. However, from the viewpoint of reactivity, a method of curing by heating or exposure is preferably used. For example, if the polymerization initiator used is a thermal initiator, the composition can be cured by heating, and if the polymerization initiator used is a photoinitiator, the composition can be cured by exposure. Furthermore, if a polymerization initiator that can initiate a polymerization reaction by either heating or exposure is used, heating alone may be performed, exposure alone may be performed, or a combination of heating and exposure may be performed. Note that, in the present disclosure, "exposure" refers to irradiation with active energy rays such as ultraviolet light, visible light, X-rays, and electron beams, and is preferably ultraviolet light.

[0115] The heating conditions when the polymerizable monomer composition of the present disclosure is cured by heating are not particularly limited, but the heating temperature has a lower limit of preferably 80°C or higher, more preferably 100°C or higher, from the viewpoint of sufficiently progressing the polymerization reaction, and an upper limit of preferably 200°C or lower, more preferably 160°C or lower, from the viewpoint of suppressing yellowing or strength reduction of the light diffusion film. The heating time has a lower limit of preferably 30 minutes or higher, more preferably 60 minutes or higher, from the viewpoint of sufficiently progressing the polymerization reaction, and an upper limit of preferably 200 minutes or lower, more preferably 150 minutes or lower, from the viewpoint of suppressing yellowing or strength reduction of the light diffusion film. The heating means is not particularly limited, and for example, known heating devices such as an oven, an inert oven, or a hot plate can be used.

[0116] The exposure conditions when the polymerizable monomer composition of the present disclosure is cured by exposure are not particularly limited. The exposure dose (irradiation amount) is appropriately adjusted so that the polymerization reaction proceeds sufficiently and the light diffusion film does not yellow or lose strength. The lower limit of the exposure time is preferably 10 minutes or more, more preferably 20 minutes or more, from the viewpoint of proceeding the polymerization reaction sufficiently, and the upper limit is preferably 200 minutes or less, more preferably 150 minutes or less, from the viewpoint of suppressing yellowing or loss of strength of the light diffusion film. The light source of the exposure light is not particularly limited, and examples thereof include a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, and a laser.

[0117] The light diffusion film of the present disclosure has excellent crack resistance and can be easily peeled from the substrate. Therefore, as a method for producing a thin light diffusion film of the present disclosure that does not have a substrate, for example, a production method including: a step of applying the polymerizable monomer composition of the present disclosure to a substrate (coating step); a step of curing the polymerizable monomer composition to form a light diffusion film layer made of a cured product of the polymerizable monomer composition on at least a portion of the surface of the substrate (curing step); and a step of peeling the substrate from the light diffusion film layer to obtain a light diffusion film (peeling step). Among these, in the curing step, a method of curing the polymerizable monomer composition by heating or a method of curing the polymerizable monomer composition by exposure to light is preferred from the viewpoint of reactivity.

[0118] (Coating Step) In the above-described manufacturing method, the coating step is a step of coating a substrate with the polymerizable monomer composition of the present disclosure. Here, the region to which the polymerizable monomer composition is coated may be at least a part of the surface of the substrate, and may be coated on both sides or one side of the substrate, or may be coated in a pattern on the surface of the substrate. The material of the substrate used in the coating step 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. Among these, resin substrates are preferably used from the viewpoint of ease of peeling.

[0119] 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.

[0120] The method for applying the polymerizable monomer composition to the substrate is not particularly limited, and examples thereof include spin coating, roll coating, flow coating, printing, dip coating, casting, bar coating, die coating, and gravure printing.

[0121] (Curing Step) The curing step is a step of forming a light-diffusing film layer composed of a cured product of the polymerizable monomer composition of the present disclosure on at least a portion of the surface of the substrate by curing the polymerizable monomer composition of the present disclosure applied to the substrate. In the curing step, for example, the entire applied polymerizable monomer composition may be cured, or the applied polymerizable monomer composition may be cured in a pattern. From the viewpoint of reactivity, the above-mentioned heating curing method or exposure curing method is preferred as a method for curing the polymerizable monomer composition of the present disclosure. In the curing step, a light-diffusing film layer composed of a cured product of the polymerizable monomer composition of the present disclosure is formed on at least a portion of the surface of the substrate. From the viewpoint of ease of production, the light-diffusing film layer may be formed on one side of the substrate. The thickness of the light-diffusing film layer may be adjusted appropriately depending on the application and is not particularly limited. On the other hand, the light-diffusing film layer can be thinned due to its excellent crack resistance when using the polymerizable monomer composition of the present disclosure. Therefore, the thickness of the light diffusion film layer is not particularly limited, but may 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 diffusion film layer is preferably 5 μm or more, more preferably 7 μm or more, from the viewpoint of strength.

[0122] (Peeling process) The peeling process is a process of peeling the substrate from the light diffusion film layer to obtain a light diffusion film. In the present disclosure, since the light diffusion film layer has excellent crack resistance, the substrate can be peeled off while suppressing cracking of the light diffusion film layer. The method of peeling the substrate from the light diffusion film layer is not particularly limited, but since the light diffusion film layer is not easily cracked in the present disclosure, for example, industrially, a method that is likely to cause bending of the light diffusion film, such as a roll peeling method or a drum peeling method, can be used.

[0123] 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.

[0124] <Production of Microparticles> [Production Example 1 (Hollow Particles A)] (1) Mixed Solution Preparation Step First, the polymerizable monomer for microparticles 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.

[0125] (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.

[0126] (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.

[0127] (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.

[0128] (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.

[0129] (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.

[0130] [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.

[0131] [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.

[0132] [Comparative Production Example 1] 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.

[0133] 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.

[0134] [Evaluation of Physical Properties of Fine Particles] The 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 fine particles are shown in Table 1.

[0135] 1. Particle size and particle size distribution The particle size of the 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 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 mixture to wet the 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.

[0136] 2. Porosity 2-1. Measurement of apparent density of fine particles First, a volume of 100 cm ３ About 30 cm ３ The microparticles were filled into the volumetric flask, and the mass of the filled microparticles was accurately weighed. Next, the volumetric flask filled with the microparticles was accurately filled with isopropanol up to the marked line, taking care not to introduce air bubbles. The mass of the isopropanol added to the volumetric flask was accurately weighed, and the apparent density D of the 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])

[0137] 2-2. Measurement of true density of fine particles After crushing the fine particles in advance, ３ Approximately 10 g of crushed particles of the microparticles was filled into a measuring flask, and the mass of the crushed particles 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 microparticles 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])

[0138] 2-3. Calculation of void ratio Apparent density D of fine particles １ and true density D ０ The porosity of the fine particles was calculated based on the following formula (III): Formula (III) Porosity (%) = 100 - (apparent density D １ / True density D ０ ) x 100

[0139] 3. Percentage of particles with one hollow part Microparticles fixed on carbon tape were rubbed with a cotton swab to intentionally break the particles. The interiors of 100 broken particles were observed using an SEM to identify the number of hollow parts per particle, and the percentage of particles with only one hollow part was calculated.

[0140] 4. Iodine Value Measurement The iodine value of the microparticles was measured in accordance with JIS K 0070:1992. The specific measurement method is as follows: 0.7-2 g of microparticles (sample) and 10 mL of chloroform were added to a 300 mL iodine flask, followed by 25 mL of Wiess's solution as the reaction solution, followed by gentle stirring and sealing. The flask was then left to stand in the dark at 25°C for 30 minutes. Next, 20 mL of 100 g / L potassium iodide solution and 100 mL of purified water were added and stirred. Using a burette, titration was performed with a titrant (0.1 mol / L sodium thiosulfate solution). When the solution turned pale yellow, an indicator (1% starch solution) was added. The titration was continued until the blue color disappeared, marking the end point. A blank test was conducted separately from this main test using a solution without added microparticles, and the iodine value of the microparticles was calculated using the following formula: The iodine value is the amount of halogen bonded to 100 g of a sample when the halogen is reacted with the sample, converted into grams of iodine. Iodine value (g / 100 g) = {(V ０ -V １ ) × f × 1.269} / S, S: sample mass (g), V １ V: Volume of titrant in this test (mL) ０ : Volume of titrant in blank test (mL) f: Factor of titrant

[0141]

[0142] As shown in Table 1, by changing the composition of the polymerizable monomer for fine particles, fine particles with different iodine values ​​could be produced. Furthermore, in Production Examples 1 to 4 and Comparative Production Example 1, hollow particles could be produced by adding a hydrophobic solvent to the mixed solution in the mixed solution preparation step. In Production Example 5, dense solid particles could be produced by not adding a hydrophobic solvent to the mixed solution in the mixed solution preparation step.

[0143] <Production of Polymerizable Monomer Composition and Light Diffusion Film> [Example 1] (1) Preparation of Polymerizable Monomer Composition 200 parts of the hollow particles A obtained in Production Example 1 above were added to 100 parts of pentaerythritol triacrylate (trade name "Aronix (registered trademark) M-306", manufactured by Toagosei Co., Ltd.) as a polymerizable monomer for binder. The resulting mixture was stirred with a stirrer and then subjected to ultrasonic treatment using an ultrasonic disperser, thereby dispersing the hollow particles A in the polymerizable monomer for binder. 1 part of di-t-butyl peroxide (trade name "Perbutyl (registered trademark) D", manufactured by NOF Corporation) as a polymerization initiator was further added to the mixture, thereby obtaining the polymerizable monomer composition of Example 1.

[0144] (2) Coating Step The polymerizable monomer 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) to a predetermined thickness using a bar coater.

[0145] (3) Curing Step The polymerizable monomer composition applied to the PET film was cured by heating at 150°C for 80 minutes using an inert oven, thereby forming a light-diffusing film layer on one side of the PET film.

[0146] (3) Peeling Step The PET film was peeled off from the light diffusion film layer to obtain a light diffusion film made of a cured product of the polymerizable monomer composition.

[0147] [Examples 2 to 7] Polymerizable monomer compositions and light diffusion films of Examples 2 to 7 were obtained in the same manner as in Example 1, except that in the above "(1) Preparation of polymerizable monomer composition", the amount or type of fine particles added was changed according to Table 2.

[0148] [Examples 8 and 9] In the above "(1) Preparation of polymerizable monomer composition", 1 part of 1-hydroxy-cyclohexyl-phenyl-ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.) was used as the polymerization initiator instead of "Perbutyl (registered trademark) D", the above "(3) Curing step" was changed as follows, and further in Example 9, in the above "(1) Preparation of polymerizable monomer composition", the type of polymerizable monomer for binder was changed according to Table 3. Except for these, polymerizable monomer compositions and light diffusion films of Examples 8 and 9 were obtained in the same manner as in Example 1. In Examples 8 and 9, in "(3) curing step", the polymerizable monomer composition applied to the PET film was cured by irradiating it with LED UV for 30 minutes using a metal halide lamp type UV curing device (manufactured by Panasonic Devices SUNX Co., Ltd., product number: ANUP4154), thereby forming a light diffusion film layer on one side of the PET film.

[0149] [Examples 10 to 13 and Comparative Examples 1 and 2] Polymerizable monomer compositions and light diffusion films of Examples 10 to 13 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that in the above "(1) Preparation of polymerizable monomer composition", the polymerizable monomer for binder or fine particles was changed according to Table 3, and in the above "(3) Curing step", the heating temperature was changed to 120°C.

[0150] Commercially available products were used as the polymerizable monomers for binders shown in Tables 2 and 3. The manufacturers of the following polymerizable monomers for binders are shown below. Pentaerythritol triacrylate: trade name "Aronix (registered trademark) M-306", manufactured by Toagosei Co., Ltd. Bifunctional urethane acrylate: trade name "Aronix (registered trademark) M-1100", manufactured by Toagosei Co., Ltd. Bifunctional polyester acrylate: trade name "Aronix (registered trademark) M-6100", manufactured by Toagosei Co., Ltd. 2-Hydroxy-3-phenoxypropyl acrylate: trade name "Aronix (registered trademark) M-5700", manufactured by Toagosei Co., Ltd.

[0151] [Evaluation of light diffusion film] 1. Measurement of film thickness The light diffusion film was cut into a square with a side length of 5 cm to be used as 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 similar to the measurement sample, and was slightly smaller than 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. 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 film.

[0152] 2. Bending fracture strain The bending fracture strain (εfB) of the light diffusion film was measured using a test piece cut into a strip of light diffusion film measuring 80±2 mm in length, 10.0±0.2 mm in width, and 1.0±0.2 mm in thickness. A three-point bending test was carried out in accordance with JIS K 7171:2016 using a Strograph S testing machine (manufactured by Toyo Seiki Co., Ltd.) at a temperature of 25±3°C, a support distance of 16 mm, and a test speed of 2 mm / min.

[0153] 3. Total Light Transmittance The obtained light diffusion film 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 film, and the average value was taken as the total light transmittance of the light diffusion film.

[0154] 4. Diffuse transmittance The obtained light diffusion film 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 film, and the average value was taken as the diffuse transmittance of the light diffusion film.

[0155]

[0156]

[0157] [Discussion] The polymerizable monomer composition obtained in Comparative Example 1 contained fine particles with an iodine value of less than 35 g / 100 g, resulting in insufficient dispersibility of the fine particles and insufficient reactivity between the fine particles and the polymerizable monomer for the binder. Therefore, the light diffusion film made of the cured product of the polymerizable monomer composition obtained in Comparative Example 1 had poor light diffusion properties and crack resistance. Furthermore, in Comparative Example 1, the insufficient flexibility of the fine particles made the fine particles prone to cracking. It is presumed that the cracking of the fine particles also deteriorated the light diffusion properties and further made the light diffusion film prone to cracking along the cross-sections of the cracked fine particles. The polymerizable monomer composition obtained in Comparative Example 2 consisted solely of a non-crosslinkable monomer as the polymerizable monomer for the binder. Therefore, the light diffusion film made of the cured product of the polymerizable monomer composition obtained in Comparative Example 2 had poor crack resistance. In Comparative Example 2, the light diffusion film layer cracked when the substrate was peeled off. The light diffusion film of Comparative Example 2 was evaluated by collecting an uncracked portion of the light diffusion film as a measurement sample.

[0158] The polymerizable monomer compositions obtained in Examples 1 to 13 contained fine particles having an iodine value of 35 g / 100 g or more and 100 g / 100 g or less, and a polymerizable monomer for a binder including a crosslinkable monomer. Therefore, the light diffusion films made of the cured products of the polymerizable monomer compositions obtained in Examples 1 to 13 exhibited good light diffusion and light transmittance, and excellent crack resistance. Furthermore, Examples 1 to 3 demonstrated that increasing the content of fine particles can improve the light diffusion properties of the light diffusion film, while decreasing the content of fine particles can improve the light transmittance and crack resistance of the light diffusion film. In Table 2, the bending fracture strain value of the light diffusion film obtained in Example 3 is listed as "greater than 40," which means that the bending fracture strain exceeded the measurement limit. Examples 1 and 4 to 6 demonstrated that changing the monomer composition or iodine value of the microparticles improves the dispersibility of the microparticles in the polymerizable monomer composition, thereby improving the light diffusion properties of the light diffusion film. Furthermore, using microparticles with an appropriate iodine value improves the crack resistance and light diffusion properties of the light diffusion film. Examples 1 and 7 demonstrated that, regardless of whether hollow particles or solid particles are used as the microparticles, a light diffusion film with good light diffusion properties and light transmittance and excellent crack resistance can be obtained. Furthermore, it was demonstrated that the light transmittance of the light diffusion film is improved when hollow particles are used as the microparticles compared to solid particles. Note that hollow particles have high light transmittance due to their hollow portions. Examples 1 and 8 demonstrated that, regardless of whether heating or exposure is used as the curing method for the polymerizable monomer composition, a light diffusion film with good light diffusion properties and light transmittance and excellent crack resistance can be obtained. Examples 1 and 9 to 10 showed that a light diffusion film having good light diffusion properties and light transmittance and excellent crack resistance can be obtained even when the type of polyfunctional acrylate used as the binder polymerizable monomer is changed. Examples 1 and 11 to 13 showed that the crack resistance of the light diffusion film can be improved by using an appropriate amount of a crosslinkable monomer in combination with a non-crosslinkable monomer as the binder polymerizable monomer.From the above, it has become clear that the balance of the light diffusion properties, light transmittance and crack resistance of the light diffusion film can be adjusted to suit the application by changing the type of microparticles, the monomer composition or iodine value, the content of the microparticles, or the composition of the polymerizable monomer for the binder.

[0159] 30 Measurement sample of light diffusion film D0, D1, D2, D3, D4, D5, D6, D7 and D8 Measurement points on the measurement sample

Claims

1. A polymerizable monomer composition for a light diffusion film, comprising fine particles and a polymerizable monomer for a binder, wherein the fine particles have an iodine value of 35 g / 100 g or more and 100 g / 100 g or less as measured in accordance with JIS K 0070, and the polymerizable monomer for the binder comprises a crosslinkable monomer having a plurality of reactive unsaturated bonds in one molecule.

2. The polymerizable monomer composition for a light diffusion film according to claim 1, wherein the content of the crosslinkable monomer is 20% by mass or more in 100% by mass of the total amount of the polymerizable monomer for the binder.

3. The polymerizable monomer composition for a light diffusion film according to claim 1 or 2, wherein the volume average particle diameter of the microparticles is 1 to 10 μm, and the particle size distribution of the microparticles (volume average particle diameter (Dv) / number average particle diameter (Dp)) is 1.0 to 1.

4.

4. The polymerizable monomer composition for a light diffusion film according to claim 1 or 2, wherein the polymerizable monomer for the binder contains a polyfunctional acrylate as the crosslinkable monomer.

5. A polymerizable monomer composition for a light diffusion film according to claim 1 or 2, wherein the 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.

6. A light diffusion film comprising a cured product of the polymerizable monomer composition for a light diffusion film according to any one of claims 1 to 5.

7. A method for producing a light diffusion film, comprising: applying the polymerizable monomer composition for a light diffusion film according to any one of claims 1 to 5 to a substrate; curing the polymerizable monomer composition for a light diffusion film by heating to form a light diffusion film layer consisting of a cured product of the polymerizable monomer composition for a light diffusion film on at least a part of the surface of the substrate; and peeling the substrate from the light diffusion film layer to obtain a light diffusion film.

8. A method for producing a light diffusion film, comprising: applying the polymerizable monomer composition for a light diffusion film according to any one of claims 1 to 5 to a substrate; curing the polymerizable monomer composition for a light diffusion film by exposure to light to form a light diffusion film layer consisting of a cured product of the polymerizable monomer composition for a light diffusion film on at least a part of the surface of the substrate; and peeling the substrate from the light diffusion film layer to obtain a light diffusion film.

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