Crosslinked polymer particles and optical film

Abstract

The present invention provides crosslinked polymer particles that have excellent heat resistance, exhibit less change in color tone due to heat, and have excellent dispersibility and dispersion stability in a dispersion medium. Crosslinked polymer particles according to the present invention contain an acrylic polymer containing 50-95 mass% of an acrylic monomer component represented by formula (1). Thus, the crosslinked polymer particles have excellent heat resistance, exhibit less change in color tone due to heat, have excellent dispersibility and dispersion stability in a dispersion medium such as a synthetic resin or a solvent, and do not emit odor attributed to a chain-transfer agent since there is no need to use a chain-transfer agent during polymerization.

Description

Crosslinked Polymer Particles and Optical Film

[0001] The present invention relates to crosslinked polymer particles and an optical film.

[0002] Polymer particles produced by suspension polymerization or seed polymerization are widely used in a wide range of fields as anti-blocking agents, matting agents for paints, additives for improving the physical properties of resins, light diffusing agents, etc.

[0003] In order to impart heat resistance to polymer particles and suppress color change due to heat of polymer particles, a thiol-based chain transfer agent such as mercaptan is used during polymerization of polymer particles, or a hindered phenol-based antioxidant is contained in the polymer particles.

[0004] Specifically, Patent Document 1 discloses a (meth)acrylic polymer crosslinked with a bifunctional crosslinkable monomer, wherein the structural unit based on the bifunctional crosslinkable monomer is 5% by mass or more and 35% by mass or less in the crosslinked (meth)acrylic polymer, the following sedimentation start time is 16 seconds or more, the Al content measured by high-frequency inductively coupled plasma (ICP) emission spectrometry is 1 ppm or less, the sulfur atom content measured by high-frequency inductively coupled plasma (ICP) emission spectrometry is 300 ppm or less, and an organic polymer fine particle containing a hindered phenol-based antioxidant or a component derived therefrom is disclosed.

[0005] Patent Document 2 discloses a molded article such as polymer particles containing a (meth)acrylic resin having a terminal double bond ratio of 6.0 mol% or less and a sulfur terminal ratio determined by a predetermined formula of 50 mol% or less.

[0006] Patent Document 3 discloses (meth)acrylic resin particles having a weight average molecular weight of 100,000 or more and 1,000,000 or less and a weight concentration of S atoms of 0.03% by weight or more and 2.50% by weight or less.

[0007] Patent Document 4 discloses polymer particles containing constituent components derived from a monomer component containing a styrene-based monomer and a (meth)acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl group, which satisfy predetermined conditions. <00,00017>

[0008] Japanese Patent Publication No. WO2016 / 195006, Japanese Patent Publication No. 2022-99699; Japanese Patent Publication No. WO2024 / 048303, Japanese Patent Publication No. 2022-79565

[0009] The polymer fine particles described in Patent Documents 1 to 4 all use chain transfer agents during polymerization or contain antioxidants. In particular, thiol-based chain transfer agents have problems such as odor and discoloration due to sulfur elements, as well as corrosion of coating equipment.

[0010] Furthermore, when polymer particles are dispersed in a solvent containing a binder resin and used as a coating solution, additives such as antioxidants contained in the polymer particles bleed out from the polymer particles into the solvent. When additives bleed out from the polymer particles, excessive aggregation of the polymer particles occurs in the coating solution, or a significant change occurs in the dispersibility of the polymer particles, resulting in a large change in the dispersion state. As a result, this leads to problems such as uneven coating of the coating solution or the detachment of polymer particles from the surface of the coating film formed from the coating solution.

[0011] The present invention provides crosslinked polymer particles that can be manufactured without using a chain transfer agent during polymerization, do not contain additives such as antioxidants, have excellent heat resistance, and exhibit reduced color change due to heat. The present invention also provides crosslinked polymer particles that can be uniformly dispersed in synthetic resins such as binder resins and dispersion media such as organic solvents, and that can be stably maintained over time without significantly changing their dispersion state. The present invention also provides an optical film having a coating film containing the crosslinked polymer particles of the present invention, in which the shedding of the crosslinked polymer particles is reduced.

[0012] The crosslinked polymer particles of the present invention include an acrylic polymer containing 50 to 95% by mass of an acrylic monomer component represented by formula (1). However, in formula (1), R represents a hydrogen atom or a methyl group, and Q represents a direct bond or an alkylene group having 1 to 3 carbon atoms.

[0013]

[0014] The optical film of the present invention comprises a film and a coating film formed on the film and containing a synthetic resin and the crosslinked polymer particles dispersed in the synthetic resin.

[0015] The crosslinked polymer particles of the present invention can be manufactured without using a chain transfer agent during polymerization. The crosslinked polymer particles of the present invention have excellent heat resistance and reduced color change due to heat, without containing antioxidants. Since the crosslinked polymer particles of the present invention do not require the use of a chain transfer agent during polymerization, they do not produce odors caused by chain transfer agents.

[0016] Furthermore, the crosslinked polymer particles of the present invention exhibit excellent dispersibility in dispersion media such as synthetic resins and solvents. Moreover, since the crosslinked polymer particles of the present invention do not require the use of chain transfer agents and antioxidants to impart heat resistance to the particles, these additives do not dissolve into the dispersion media, and the dispersibility of the crosslinked polymer particles in the dispersion media does not change significantly, allowing the dispersibility of the crosslinked polymer particles to be maintained substantially constant over time (dispersion stability).Therefore, dispersion media containing crosslinked polymer particles can be easily coated without uneven coating.

[0017] In the numerical ranges described stepwise in this specification, the upper or lower limit of one step in the numerical range can be arbitrarily combined with the upper or lower limit of another step in the numerical range. In the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. In this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0018] [Acrylic Monomers] The crosslinked polymer particles contain an acrylic polymer containing 50 to 95% by mass of an acrylic monomer component represented by formula (1). However, in formula (1), R represents a hydrogen atom or a methyl group, and Q represents a direct bond or an alkylene group having 1 to 3 carbon atoms.

[0019]

[0020] In formula (1), Q is either directly bonded or an alkylene group having 1 to 3 carbon atoms, with an alkylene group having 1 to 3 carbon atoms being preferred. In the present invention, an alkylene group is a divalent atomic group formed by removing (extracting) one hydrogen atom from each of the different carbon atoms bonded to different carbon atoms in an aliphatic saturated hydrocarbon, or a divalent atomic group formed by removing (extracting) two hydrogen atoms from methane, and includes linear and branched atomic groups.

[0021] Aliphatic saturated hydrocarbons refer to saturated hydrocarbons belonging to the category of compounds other than aromatic compounds (aliphatic compounds) that possess aromatic properties. The concept of aliphatic saturated hydrocarbons includes both chain-like aliphatic saturated hydrocarbons, in which carbon atoms are bonded in a single chain, and branched chain-like aliphatic saturated hydrocarbons, which have a branched structure.

[0022] Aromatic compounds have an aromatic ring skeleton (a structure in which carbon atoms are bonded in a ring and which possesses aromatic properties). An aromatic ring skeleton refers to a ring structure that follows Hückel's rule and has (4n+2) π electrons (where n is a natural number). The concept of an aromatic ring skeleton includes monocyclic aromatic rings and condensed rings formed by the combination of monocyclic aromatic rings. Aromatic rings are not particularly limited and include, for example, benzene rings, naphthalene rings, anthracene rings, biphenyls, and phenoxyphenyls.

[0023] Examples of alkylene groups include methylene group [-CH2-], ethylene group [-CH2-CH2-], propylene group [-CH(CH3)-CH2-], and trimethylene group [-CH2-CH2-CH2-], with methylene group being preferred. That is, as the acrylic monomer component represented by formula (1), the acrylic monomer represented by the following formula (2) is preferred.

[0024]

[0025] In formula (1), Q is preferably an alkylene group having 1 to 3 carbon atoms, more preferably Q is an alkylene group having 1 to 3 carbon atoms and R is a hydrogen atom, more preferably Q is an alkylene group having 1 or 2 carbon atoms and R is a hydrogen atom, and more preferably Q is a methylene group and R is a hydrogen atom.

[0026] The crosslinked polymer particles contain a predetermined amount of an acrylic polymer containing the acrylic monomer component shown in formula (1), thereby exhibiting excellent heat resistance without the use of chain transfer agents and antioxidants, and reducing color changes due to heat.

[0027] The crosslinked polymer particles contain an acrylic polymer containing 50 to 95% by mass of an acrylic monomer component represented by formula (1). Therefore, they exhibit excellent affinity with synthetic resins (e.g., binder resins) and dispersion media such as organic solvents, and can impart appropriate interactions between the crosslinked polymer particles. Consequently, they can be uniformly dispersed in dispersion media such as organic solvents and binder resins, and also exhibit excellent dispersion stability in the dispersion media.

[0028] Furthermore, the crosslinked polymer particles exhibit excellent affinity with the dispersion medium and appropriate interaction among themselves, due to the acrylic monomer component represented by formula (1). Therefore, when forming molded articles such as coatings and sheets from a crosslinked polymer particle composition obtained by dispersing crosslinked polymer particles in a dispersion medium, the crosslinked polymer particles remain uniformly dispersed even when the viscosity of the crosslinked polymer particle composition increases during the formation process. Thus, the crosslinked polymer particles are uniformly dispersed in the resulting molded article. In addition, the crosslinked polymer particles are reliably held in place by the binder resin within the molded article, reducing the shedding of crosslinked polymer particles from the surface of the molded article.

[0029] As described above, since crosslinked polymer particles do not require additives to improve thermal stability, such as chain transfer agents and antioxidants, chain transfer agents and antioxidants do not leach into the dispersion medium. Therefore, there is no risk of significant changes in the dispersibility of crosslinked polymer particles in the dispersion medium due to these additives, and the dispersibility of crosslinked polymer particles in the dispersion medium can be maintained without significant changes over time. Furthermore, even during the process of forming a molded article from the crosslinked polymer particle composition, there is no risk of significant changes in the dispersibility of crosslinked polymer particles due to the aforementioned additives to improve thermal stability.

[0030] Even when crosslinked polymer particles aggregate during the process of forming a molded article from a crosslinked polymer particle composition, as described above, the affinity with the dispersion medium is excellent and the interaction between the crosslinked polymer particles is of moderate strength. Therefore, the crosslinked polymer particles do not aggregate excessively, but aggregate to a moderate size, forming aggregated particles of uniform size. Thus, aggregated particles of uniform size are uniformly dispersed in the molded article.

[0031] Furthermore, the crosslinked polymer particles can form aggregated particles of an appropriate size while appropriately incorporating synthetic resins such as binder resins between the crosslinked polymer particles. Therefore, the aggregated particles are reliably held in the synthetic resin within the molded body, and the shedding of aggregated particles from the surface of the molded body is reduced.

[0032] The content of the acrylic monomer component represented by formula (1) in the acrylic polymer contained in the crosslinked polymer particles is 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 65% ​​by mass or more, more preferably 70% by mass or more, more preferably 75% by mass or more, more preferably 80% by mass or more, and more preferably 85% by mass or more. The content of the acrylic monomer component represented by formula (1) in the acrylic polymer contained in the crosslinked polymer particles is 95% by mass or less, more preferably 91% by mass or less, more preferably 90% by mass or less, more preferably 85% by mass or less, and more preferably 80% by mass or less. The content of the acrylic monomer component represented by formula (1) in the acrylic polymer contained in the crosslinked polymer particles is preferably 50 to 91% by mass, more preferably 55 to 91% by mass, more preferably 60 to 91% by mass, more preferably 65 to 91% by mass, more preferably 70 to 91% by mass, more preferably 75 to 91% by mass, more preferably 80 to 91% by mass, and more preferably 85 to 91% by mass. When the content of the acrylic monomer component represented by formula (1) is within the above range, the crosslinked polymer particles exhibit the above effects.

[0033] In the crosslinked polymer particles, the content of the acrylic polymer containing the acrylic monomer component represented by formula (1) is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 99% by mass or more, and more preferably 100% by mass.

[0034] As described above, crosslinked polymer particles have excellent heat resistance without the need to use chain transfer agents or include antioxidants during polymerization. However, chain transfer agents and antioxidants may be included as long as they do not cause elution into the dispersion medium due to bleed-out from the crosslinked polymer particles.

[0035] A chain transfer agent is an additive that receives radicals from the growing polymer chain in a radical polymerization system and generates new radicals. Examples of chain transfer agents include mercaptans such as lauryl mercaptan, 2-mercaptoethyl alcohol, dodecyl mercaptan, and mercaptosuccinic acid; alkyl mercaptopropions such as n-butyl mercaptopropionate and octyl mercaptopropionate; and alkoxyalkyl mercaptopropions such as methoxybutyl mercaptopropionate.

[0036] Antioxidants are additives used to suppress the oxidation of acrylic polymers. Examples of antioxidants include 2,5-di-t-butyl-hydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis-(6-t-butylphenol), 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, and 4,4'-thiobis-(6-t-butylphenol).

[0037] The content of the chain transfer agent in the crosslinked polymer particles is preferably 0.9% by mass or less, more preferably 0.6% by mass or less, more preferably 0.4% by mass or less, more preferably 0.2% by mass or less, and more preferably 0% by mass.

[0038] The antioxidant content in the crosslinked polymer particles is preferably 0.9% by mass or less, more preferably 0.6% by mass or less, more preferably 0.4% by mass or less, more preferably 0.2% by mass or less, and more preferably 0% by mass.

[0039] The acrylic polymer contained in the crosslinked polymer particles may contain monofunctional monomer components other than the acrylic monomer component represented by formula (1). In the acrylic polymer contained in the crosslinked polymer particles, the content of monomer components other than the acrylic monomer component represented by formula (1) is preferably 1% by mass or more, more preferably 2% by mass or more, more preferably 3% by mass or more, preferably 5% by mass or more, more preferably 9% by mass or more, more preferably 10% by mass or more, more preferably 15% by mass or more, and more preferably 20% by mass or more. In the acrylic polymer contained in the crosslinked polymer particles, the content of monomer components other than the acrylic monomer component represented by formula (1) is preferably 50% by mass or less, more preferably 45% by mass or less, more preferably 40% by mass or less, more preferably 35% by mass or less, more preferably 30% by mass or less, and more preferably 25% by mass or less. In the acrylic polymer contained in the crosslinked polymer particles, the content of monomer components other than the acrylic monomer component represented by formula (1) is preferably 1 to 50% by mass, more preferably 2 to 50% by mass, more preferably 2 to 45% by mass, more preferably 3 to 45% by mass, more preferably 3 to 35% by mass, more preferably 3 to 30% by mass, and more preferably 3 to 25% by mass.

[0040] Other monofunctional monomer components besides the acrylic monomer component represented by formula (1) are not particularly limited and include, for example, alkyl (meth)acrylates and styrene monomers. Note that the monomer components other than the acrylic monomer component represented by formula (1) may be used alone or in combination of two or more. (Meth)acrylate means acrylate or methacrylate. A monofunctional monomer is a monomer having only one polymerizable functional group (for example, a vinyl group, epoxy group, isocyanate group, etc.).

[0041] Examples of the alkyl (meth)acrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and isobutyl acrylate; and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate. The (meth)acrylate is preferably an alkyl (meth)acrylate having 1 to 5 carbon atoms in the alkyl group, and more preferably an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl group.

[0042] The styrenic monomer is not particularly limited, and examples thereof include styrene, α-methylstyrene, vinyl toluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. The styrenic monomer may be used alone or in combination of two or more.

[0043] The acrylic polymer contained in the crosslinked polymer particles is crosslinked. The acrylic polymer contained in the crosslinked polymer particles preferably contains a polyfunctional monomer component. The acrylic polymer is preferably crosslinked by the polyfunctional monomer component. When the acrylic polymer contains a polyfunctional monomer component, fluctuations in the interaction between the crosslinked polymer particles due to the absorption of the dispersion medium by the crosslinked polymer particles can be reduced, and the dispersion state of the crosslinked polymer particles in the dispersion medium can be made more uniform and the dispersion stability can be further improved. Furthermore, by the absorption of the dispersion medium by the crosslinked polymer particles, the non-uniformity of the viscosity of the crosslinked polymer particle composition caused by the partial fluctuation of the viscosity of the crosslinked polymer particle composition obtained by dispersing the crosslinked polymer particles in the dispersion medium can be further reduced, and the occurrence of coating unevenness in the crosslinked polymer particle composition can be further reduced.

[0044] The polyfunctional monomer is a monomer having two or more polymerizable functional groups (e.g., vinyl group, epoxy group, isocyanate group, etc.). The polyfunctional monomer preferably has two or more vinyl groups as the functional groups.

[0045] Examples of the polyfunctional monomer include acrylic polyfunctional monomers such as 1,10-decanediol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, decaethylene glycol di(meth)acrylate, pentadecaethylene glycol di(meth)acrylate, pentacontahectaethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,3-butylene di(meth)acrylate, allyl (meth)acrylate, etc., and aromatic divinyl compounds (compounds in which two vinyl groups are directly bonded to an aromatic ring) such as divinylbenzene, divinylnaphthalene or derivatives thereof. Since the affinity for the dispersion medium is improved and the dispersibility and dispersion stability of the crosslinked polymer particles in the dispersion medium can be improved, aromatic divinyl compounds are preferred. The polyfunctional monomer may be used alone or in combination of two or more.

[0046] The aromatic ring may be a monocyclic aromatic ring or a monocyclic aromatic ring may be combined and condensed (condensed aromatic ring). The aromatic ring is not particularly limited and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, biphenyl, phenoxyphenyl, etc., and a benzene ring and a naphthalene ring are preferred. One or more hydrogen atoms of either the aromatic ring or the condensed aromatic ring are extracted and bonded to other atoms by a covalent bond.

[0047] The content of polyfunctional monomer components in the acrylic polymer is preferably 0.5% by mass or more, more preferably 1% by mass or more, and more preferably 2% by mass or more. The content of polyfunctional monomer components in the acrylic polymer is preferably 10% by mass or less, more preferably 8% by mass or less, more preferably 7% by mass or less, and more preferably 6% by mass or less. The content of polyfunctional monomer components in the acrylic polymer is preferably 0.5 to 10% by mass, more preferably 1 to 8% by mass, more preferably 2 to 7% by mass, and more preferably 2 to 6% by mass. When the content of polyfunctional monomer components is 0.5% by mass or more, fluctuations in the interaction between crosslinked polymer particles due to the absorption of the dispersion medium by the crosslinked polymer particles can be reduced, and the uniformity of the dispersion state of the crosslinked polymer particles in the dispersion medium and the dispersion stability can be further improved. Furthermore, by reducing the absorption of the dispersion medium by the crosslinked polymer particles and further reducing the viscosity non-uniformity of the crosslinked polymer particle composition caused by partial fluctuations in the viscosity of the crosslinked polymer particle composition obtained by dispersing the crosslinked polymer particles in the dispersion medium, the occurrence of coating unevenness in the crosslinked polymer particle composition can be further reduced. When the content of the polyfunctional monomer component is 10% by mass or less, the crosslinked polymer particles have even better affinity with the dispersion medium and can be given even more appropriate interactions between the crosslinked polymer particles. Therefore, the uniformity of the dispersion state and dispersion stability of the crosslinked polymer particles in the dispersion medium can be further improved, and the crosslinked polymer particles can be dispersed even more uniformly in the coating film formed from the crosslinked polymer particle composition obtained by dispersing the crosslinked polymer particles in the dispersion medium.

[0048] The monomer content contained in the cross-linked polymer particles refers to the value measured according to the following procedure: A sample of cross-linked polymer particles is weighed to an accurate weight of approximately 0.1 to 0.5 mg. The sample is wrapped in a ferromagnetic metal body with a Curie point of 590°C (product name "Pyrofoil," manufactured by Nippon Analytical Industry Co., Ltd.) to prepare a test specimen.

[0049] The test specimen was prepared so that a ferromagnetic metal body was pressed against the sample. The test specimen was heated using a Curie point pyrolizer (product name "JPS-700" manufactured by Nippon Analytical Industry Co., Ltd.) to decompose the sample. The monomer components generated by the decomposition were measured using a gas chromatograph (product name "GC7820" manufactured by Agilent Technologies, Inc., detector = FID) to determine the peak area of ​​the monomer to be measured. A calibration curve showing the relationship between the amount of monomer and the peak area was prepared in advance for the monomer to be measured. Based on the calibration curve, the amount of monomer contained in the sample was calculated from the measured peak area. (Measurement conditions) Heating = 590°C - 5 sec Oven temperature = 300°C Needle temperature = 300°C Column = Agilent Technologies "DB-5" (0.25 μm × 0.25 mmφ × 30 m) (GC oven heating conditions) Initial temperature = 50°C (held for 0.5 min) First stage heating rate = 10°C / min (up to 200°C, held for 0 min) Second stage heating rate = 20°C / min (up to 320°C) Final temperature = 320°C (held for 0.5 min) Carrier gas = He He flow rate = 1.275 mL / min Inlet pressure = 100 kPa Column inlet pressure = 100 kPa Inlet temperature = 300°C Detector temperature = 300°C Split ratio = 1 / 50

[0050] [Cross-linked polymer particles] In cross-linked polymer particles, the arithmetic mean particle diameter in the particle size distribution based on the number of particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, more preferably 0.3 μm or more, more preferably 0.5 μm or more, and more preferably 1.0 μm or more. In cross-linked polymer particles, the arithmetic mean particle diameter in the particle size distribution based on the number of particles is preferably 15.0 μm or less, more preferably 12.0 μm or less, more preferably 10.0 μm or less, more preferably 7.5 μm or less, more preferably 5.0 μm or less, more preferably 4.0 μm or less, more preferably 3.0 μm or less, and more preferably 2.5 μm or less. In crosslinked polymer particles, the arithmetic mean particle diameter in the particle size distribution based on the number of particles is preferably 0.1 to 15.0 μm, more preferably 0.2 to 12.0 μm, more preferably 0.3 to 10.0 μm, more preferably 0.5 to 7.5 μm, more preferably 1.0 to 7.5 μm, more preferably 1.0 to 5.0 μm, more preferably 1.0 to 4.0 μm, and more preferably 1.0 to 3.0 μm. When the arithmetic mean particle diameter in the particle size distribution based on the number of particles is 0.1 μm or more, it is preferable because when the crosslinked polymer particles are used in optical applications such as light diffusers, they exhibit excellent optical properties such as light diffusion. Furthermore, even after long-term storage of the crosslinked polymer particle composition, uniform dispersion can be achieved by redispersing the crosslinked polymer particles in the crosslinked polymer particle composition. When the arithmetic mean particle diameter in the particle size distribution based on the number of particles is 15.0 μm or less, the thickness of the coating film covering the surface of the crosslinked polymer particles protruding from the coating film surface can be made uniform. Therefore, it is possible to homogenize the coating film and reduce the shedding of crosslinked polymer particles from the coating film surface.

[0051] The coefficient of variation (CV value) of particle size based on the particle size distribution on a number basis of the crosslinked polymer particles is preferably 30% or less, more preferably 20% or less, more preferably 16% or less, more preferably 15% or less, and more preferably 13% or less. When the coefficient of variation of the crosslinked polymer particles is 30% or less, the interactions between the crosslinked polymer particles can be made more uniform overall throughout the crosslinked polymer particles. Therefore, the uniformity of the dispersion and dispersion stability of the crosslinked polymer particles in the dispersion medium can be improved. Furthermore, the crosslinked polymer particles can be dispersed more uniformly in molded articles such as coatings and sheets formed from the crosslinked polymer particle composition, and the shedding from the surface of the molded article can be further reduced.

[0052] The arithmetic mean particle size and coefficient of variation (CV) of particle size in the particle size distribution based on the number of cross-linked polymer particles are measured in the following manner.

[0053] If the arithmetic mean particle diameter in the particle size distribution based on the number of cross-linked polymer particles is 1 μm or larger, it shall be measured in the following manner. The arithmetic mean particle diameter in the particle size distribution based on the number of cross-linked polymer particles shall be measured using a Coulter Multisizer™ 4e (measuring device manufactured by Beckman Coulter, Inc.). The measurement shall be performed using an aperture calibrated in accordance with the Multisizer 4 User's Manual issued by Beckman Coulter, Inc.

[0054] The aperture used for measurement should be appropriately selected depending on the size of the cross-linked polymer particles being measured. Current (aperture current) and Gain should be appropriately set according to the size of the selected aperture.

[0055] For measurement, 0.1 g of cross-linked polymer particles are dispersed in 10 mL of a 0.1% by mass nonionic surfactant aqueous solution using a touch mixer (product name "TOUCHMIXERMT-31" manufactured by Yamato Scientific Co., Ltd.) and an ultrasonic cleaner (product name "ULTRASONICCLEANERVS-150" manufactured by Velvo-Clear Co., Ltd.) to form a dispersion. During measurement, the contents of the beaker are gently stirred to prevent the introduction of air bubbles, and the measurement is terminated when 100,000 cross-linked polymer particles have been measured. The particle diameter of the cross-linked polymer particles is the equivalent diameter of a sphere. That is, the particle diameter of the cross-linked polymer particles is the diameter of a perfect sphere having the same volume as the cross-linked polymer particle. The arithmetic (number) mean particle diameter of the cross-linked polymer particles is the arithmetic mean of the particle size distribution based on the number of 100,000 particles.

[0056] The coefficient of variation (CV) of particle size for cross-linked polymer particles is calculated in the same manner as the arithmetic mean particle size in the particle size distribution based on the number of cross-linked polymer particles. The coefficient of variation (CV) of particle size for cross-linked polymer particles is calculated using the following formula: Coefficient of variation (CV) of particle size for cross-linked polymer particles = 100 × (Standard deviation of particle size in the particle size distribution based on the number of cross-linked polymer particles) / (Arithmetic mean particle size in the particle size distribution based on the number of cross-linked polymer particles)

[0057] If the arithmetic mean particle diameter in the particle size distribution based on the number of cross-linked polymer particles is less than 1 μm, it is measured in the following manner. The arithmetic mean particle diameter in the particle size distribution based on the number of cross-linked polymer particles is measured using a laser diffraction scattering particle size distribution analyzer (Beckman Coulter, Ltd., model number "LS230"). Specifically, 0.1 g of cross-linked polymer particles (equivalent to 0.1 g in the case of a dispersion) and 20 mL of a 2% by mass anionic surfactant solution are placed in a test tube. Then, the mixture is dispersed for 5 minutes using a test tube mixer (AS ONE Corporation, "Test Tube Mixer TRIOHM-1N") and an ultrasonic cleaner (AS ONE Corporation, "ULTRASONICCLEANERVS-150") to prepare a dispersion. The obtained dispersion is measured using a laser diffraction scattering particle size distribution analyzer while irradiating it with ultrasound to measure the number mean particle diameter of the cross-linked polymer particles in the dispersion. The optical model used for measurement was matched to the refractive index of the manufactured crosslinked polymer particles. When one type of monomer was used to manufacture the crosslinked polymer particles, the refractive index of the monomer's homopolymer was used as the refractive index of the crosslinked polymer particles. When multiple types of monomers were used to manufacture the crosslinked polymer particles, the average value obtained by weighting the refractive index of each monomer's homopolymer by the amount of each monomer used was used as the refractive index of the crosslinked polymer particles. <Measurement conditions for laser diffraction scattering particle size distribution analyzer> Medium = Refractive index of water medium = 1.333 Refractive index of solid = Refractive index of crosslinked polymer particles PIDS relative concentration: 40-55%

[0058] The dispersion coefficient of the crosslinked polymer particles is preferably less than 0.20, and more preferably 0.15 or less. When the dispersion coefficient of the crosslinked polymer particles is less than 0.20, the uniformity of the dispersion of the crosslinked polymer particles in the dispersion medium and the dispersion stability can be improved. Furthermore, the crosslinked polymer particles can be dispersed more uniformly in molded articles such as coatings and sheets formed from the crosslinked polymer particle composition, and the shedding from the surface of the molded article can be further reduced.

[0059] The dispersion behavior displacement of the crosslinked polymer particles is preferably less than 0.030, and more preferably 0.020 or less. When the dispersion behavior displacement of the crosslinked polymer particles is less than 0.030, the uniformity of the dispersion of the crosslinked polymer particles in the dispersion medium and the dispersion stability can be improved. Furthermore, the crosslinked polymer particles can be dispersed more uniformly in molded articles such as coatings and sheets formed from the crosslinked polymer particle composition, and the shedding from the surface of the molded article can be further reduced.

[0060] The dispersion coefficient and dispersion behavior displacement of the cross-linked polymer particles are measured in the following manner. [Method for preparing the dispersion] 0.10 g of cross-linked polymer particles and 5.00 g of butyl acetate as a dispersion medium are added to a 10 mL sample tube, and the mixture is stirred for 1 minute using an ultrasonic cleaner (product name "ULTRASONICCLEANERVS-150" manufactured by VelvoClear Co., Ltd.) to disperse the cross-linked polymer particles in the butyl acetate and obtain a dispersion. To this dispersion, 0.50 g of acrylic resin (product name "Acrydic® A-817-Ba" manufactured by DIC Corporation) is added, and the mixture is stirred for about 10 minutes using the ultrasonic cleaner to prepare a dispersion in which the cross-linked polymer particles are dispersed in the butyl acetate and acrylic resin.

[0061] [Measurement Method] The viscosity of the dispersion shall be measured using a viscometer (m-VROC micro-sample viscometer manufactured by Luft Corporation) in the following manner. The viscometer shall be left in the measurement environment for at least 30 minutes before measuring the viscosity.

[0062] Using the viscometer described above, the prepared dispersion was left to stand for 5 hours at room temperature (test room temperature 23°C to 27°C). Then, the dispersion was stirred in an ultrasonic cleaner for 5 minutes (redispersion), and the viscosity (mPa·s) of the dispersion was measured.

[0063] Then, using the measured viscosity (mPa·s) and the measured temperature (K), the viscosity value V (mPa·s / K) per unit temperature (K) is calculated using the following formula. The viscosity value measurement is repeated 10 times, and the average value, maximum value, and minimum value of the viscosity value are calculated. Viscosity value V (mPa·s / K) = Measured value (mPa·s) / Measured temperature (K)

[0064] [Method for Calculating Dispersion Behavior Displacement] Using the maximum, minimum, and average viscosity values ​​from 10 measurements, the viscosity value displacement, i.e., dispersion behavior displacement, is calculated using the following formula: <Formula for Calculating Dispersion Behavior Displacement> Dispersion Behavior Displacement = (VMAX - VMIN) / VAVE VMAX: Maximum viscosity value from 10 measurements (mPa·s / K) VMIN: Minimum viscosity value from 10 measurements (mPa·s / K) VAVE: Average viscosity value from 10 measurements (mPa·s / K)

[0065] [Method for Calculating the Dispersion Coefficient] Prepare a dispersion in the same manner as when measuring dispersion behavior displacement. Using the above viscometer, allow the prepared dispersion to stand for 4, 5, or 6 hours at room temperature (test room temperature 23°C to 27°C). Then, stir the dispersion in an ultrasonic cleaner for 5 minutes (redisperse), and after standing for 4, 5, or 6 hours, measure the viscosity value V (mPa·s / K) of the dispersion in the same manner as when measuring dispersion behavior displacement. Calculate the dispersion coefficient based on the following formula. <Formula for Calculating the Dispersion Coefficient> Dispersion coefficient = |V6hr·AVE - V4hr·AVE| / V5hr·AVE V4hr·AVE: Average value of viscosity values ​​from 10 measurements of the dispersion after standing for 4 hours V5hr·AVE: Average value of viscosity values ​​from 10 measurements of the dispersion after standing for 5 hours V6hr·AVE: Average value of viscosity values ​​from 10 measurements of the dispersion after standing for 6 hours

[0066] The color change rate of the crosslinked polymer particles is preferably 30% or less, and more preferably 29% or less. When the color change rate of the crosslinked polymer particles is 30% or less, the color of the molded article containing the crosslinked polymer particles can be maintained at a generally constant level over a long period of time, and the appearance or performance of the molded article can be maintained well.

[0067] The color change rate of cross-linked polymer particles refers to the value measured according to the following procedure: 3.0 g of cross-linked polymer particles is weighed into a glass petri dish (AS ONE 1-4564-05) and heated in an oven at 80°C for 24 hours. The b* value of the cross-linked polymer particles is measured by chromaticity measurement in the L*a*b* color system in accordance with JIS Z8729.

[0068] Specifically, 2.5 g of cross-linked polymer particles are filled into a measuring container. The b-value of the filled cross-linked polymer particles is measured using a colorimeter. The b-value before heating is defined as b0, and the b-value after heating to 80°C is defined as b. 80 The rate of change was calculated using the following formula. For the measuring container, for example, a powder cell commercially available from Konica Minolta Sensing, Inc. under the product name "CR-A50" can be used. For the color difference meter, for example, a device commercially available from Konica Minolta Sensing, Inc. under the product name "CR-300" can be used. Color change rate (%) = [(b 80 / b0)-1]×100

[0069] The thermal decomposition coefficient of the crosslinked polymer particles is preferably 9% or more, and more preferably 10% or more. When the thermal decomposition coefficient of the crosslinked polymer particles is 10% or more, the heat resistance of the crosslinked polymer particles is improved, and the color change due to heat can be reduced. There is no particular upper limit to the thermal decomposition coefficient of the crosslinked polymer particles, but it is preferably 20% or less. The thermal decomposition coefficient of the crosslinked polymer particles is preferably 9 to 20%, and more preferably 10 to 20%.

[0070] The thermal decomposition coefficient of cross-linked polymer particles refers to the value measured according to the following procedure. Thermogravimetric analysis is performed using a differential thermogravimetric analyzer (TG-DTA; "STA7200" manufactured by Hitachi High-Tech Science Corporation). In this measurement, alumina is used as the reference material, and approximately 15 mg of the obtained cross-linked polymer particles are packed into the bottom of an alumina measuring container so that there are no gaps. The mass loss curve (TG / DTA curve) is obtained when the temperature is raised from 40°C to 800°C at a heating rate of 10°C / min under an air flow rate of 200 mL / min.

[0071] Using the analysis software included with the above-mentioned device, the temperatures at which 3% and 10% mass decreases are read based on the mass loss curve obtained from this measurement, and these temperatures are defined as the 3% and 10% thermal decomposition temperatures (°C). The thermal decomposition coefficient is calculated based on the following formula: Thermal decomposition coefficient (%) = [(10% thermal decomposition temperature / 3% thermal decomposition temperature) - 1] × 100

[0072] In this measurement, in order to sufficiently suppress the influence of moisture content in the dry powder on the measurement results, the mass of the dry powder when heated from 40°C to 125°C at a rate of 10°C / min under an air flow rate of 200 mL / min is used as the reference mass. Based on the above mass loss curve, the temperatures at which the mass decreases by 3% and 10% from the reference mass are read, and these temperatures are defined as the 3% and 10% thermal decomposition temperatures (°C), respectively.

[0073] [Method for Producing Crosslinked Polymer Particles] A method for producing crosslinked polymer particles will be described below. The method for producing crosslinked polymer particles is not particularly limited and can be produced by polymerizing raw material monomers, including an acrylic monomer represented by formula (1), in a general manner in the presence of a polymerization initiator (e.g., peroxide, azo compound, etc.) as needed. The raw material monomers may include monofunctional monomers and / or polyfunctional monomers copolymerizable with the acrylic monomer represented by formula (1) as needed.

[0074] The polymerization method is not particularly limited, and general polymerization methods such as suspension polymerization, seed polymerization, mass polymerization, and solution polymerization can be used, with seed polymerization being preferred. Emulsion polymerization is a polymerization method in which raw material monomers are dispersed in an aqueous medium described later and polymerized in the presence of a polymerization initiator and an emulsifier, and is included in suspension polymerization.

[0075] Seed polymerization is a method in which seed particles consisting of a separately prepared vinyl monomer polymer are added when initiating the polymerization of raw material monomers, including acrylic monomers represented by formula (1).

[0076] In detail, seed polymerization is a method in which crosslinked polymer particles made of vinyl monomer polymers are used as seed particles, and raw material monomers containing acrylic monomers represented by formula (1) are absorbed into the seed particles in an aqueous medium, thereby polymerizing the raw material monomers within the seed particles. In this method, by growing the seed particles, crosslinked polymer particles with a larger particle size than the original seed particles can be obtained. Alternatively, crosslinked polymer particles may be produced by repeating the process of absorbing raw material monomers into seed particles and polymerizing them multiple times.

[0077] The polymerization method used to obtain seed particles by polymerizing vinyl monomers is not particularly limited and can be a general polymerization method. For example, dispersion polymerization, emulsion polymerization, soap-free emulsion polymerization (emulsification polymerization without the use of surfactants as emulsifiers), seed polymerization, and suspension polymerization can be used.

[0078] The reaction solution containing the cross-linked polymer particles obtained by polymerization in the manner described above is supplied to a general-purpose filter, and the cross-linked polymer particles contained in the reaction solution are separated from the aqueous medium. After washing the separated cross-linked polymer particles with water, the water is almost completely removed by drying in a general manner, and the cross-linked polymer particles can be obtained by classification (preferably by air flow classification) as needed.

[0079] [Applications of Crosslinked Polymer Particles] Crosslinked polymer particles can be suitably used for optical films such as anti-glare films and light-diffusing films, and optical components such as light diffusers, and are particularly suitable for use in anti-glare components. Crosslinked polymer particles can also be used as matting agents for paints, anti-blocking agents, and additives for improving the physical properties of resins.

[0080] Crosslinked polymer particles have a higher refractive index compared to crosslinked polymer particles produced by polymerizing other acrylic monomers such as methyl methacrylate and methyl acrylate. For example, when crosslinked polymer particles are used in optical applications, the difference in refractive index with a base resin such as an acrylic polymer makes it possible to produce optical components with high haze values ​​and high resolution. The refractive index of crosslinked polymer particles is preferably between 1.56 and 1.64.

[0081] The refractive index of the cross-linked polymer particles was measured according to the following immersion method. Specifically, first, the cross-linked polymer particles were placed on a glass slide, and several standard refractive solutions, commercially available from companies such as Cargill and Shimadzu Corporation, were prepared with refractive index differences in increments of 0.004, and each solution was added dropwise. After thoroughly mixing the cross-linked polymer particles with the refractive solutions, the contours of the particles were observed from above using an optical microscope while irradiating them from below with light from an Iwasaki Electric high-pressure sodium lamp NX35 (center wavelength 589 nm). If the contours were not visible, it was determined that the refractive index of the refractive solution and the cross-linked polymer particles were equal.

[0082] Observation with an optical microscope is acceptable as long as the magnification allows the outline of the cross-linked polymer particles to be seen. However, for particles with a diameter of 2 to 10 μm, an observation magnification of around 500x is appropriate. The above procedure shows that the closer the refractive index of the cross-linked polymer particles is to that of the refractive solution, the more difficult it becomes to see the outline of the cross-linked polymer particles. Therefore, the refractive index of the refractive solution in which the outline of the cross-linked polymer particles is difficult to discern is judged to be equal to the refractive index of those cross-linked polymer particles.

[0083] Furthermore, if there is no difference in the appearance of the cross-linked polymer particles between two refractive solutions with a refractive index difference of 0.004, the intermediate value between these two refractive solutions is determined to be the refractive index of the cross-linked polymer particles, and the value is rounded to the third decimal place. For example, when testing with refractive solutions with refractive indices of 1.554 and 1.556, if there is no difference in the appearance of the cross-linked polymer particles between the two solutions, the intermediate value of 1.56 (1.555 rounded to the third decimal place) is determined to be the refractive index of the cross-linked polymer particles. Note that the above measurements are performed in a test room at a temperature of 22°C to 24°C.

[0084] [Crosslinked Polymer Particle Composition] A crosslinked polymer particle composition can be prepared by dispersing crosslinked polymer particles in a dispersion medium. By coating this crosslinked polymer particle composition onto a substrate and drying it, a coating film containing crosslinked polymer particles can be prepared on the substrate. Examples of substrates include films and other molded articles. The crosslinked polymer particle composition may also be molded in a general manner to produce molded articles such as sheets.

[0085] The crosslinked polymer particles contain an acrylic polymer containing an acrylic monomer component represented by formula (1), and have excellent dispersibility and dispersion stability in the dispersion medium. Therefore, in the crosslinked polymer particle composition, the crosslinked polymer particles are stably and uniformly dispersed in the dispersion medium, and the crosslinked polymer particle composition can be easily coated onto the substrate without causing uneven coating.

[0086] Furthermore, in coatings and sheets formed by drying the crosslinked polymer particle composition, the crosslinked polymer particles remain uniformly dispersed, resulting in coatings and sheets with homogeneous physical properties. Moreover, since the crosslinked polymer particles are firmly held within the coating and sheet, the shedding of crosslinked polymer particles from the surface of the coating and sheet is reduced. In molded articles obtained by molding the crosslinked polymer particle composition in a general manner, the crosslinked polymer particles also remain uniformly dispersed. Furthermore, since the crosslinked polymer particles are firmly held within the molded article, the shedding of crosslinked polymer particles from the surface of the molded article is reduced.

[0087] Furthermore, even when cross-linked polymer particles aggregate to form aggregated particles during the formation of coatings and sheets or other molded articles, the cross-linked polymer particles do not aggregate excessively, forming aggregated particles of an appropriate and uniform size. As a result, the coatings, sheets, and other molded articles have homogeneous physical properties, and the shedding of aggregated particles from the surface of the molded articles is also reduced.

[0088] The dispersion medium is not particularly limited and can include, for example, synthetic resins such as binder resins and organic solvents.

[0089] The synthetic resin can be appropriately selected depending on the application. Examples of synthetic resins include (meth)acrylic resins; (meth)acrylic-urethane resins; urethane resins; polyvinyl chloride resins; polyvinylidene chloride resins; melamine resins; styrene resins; alkyd resins; phenolic resins; epoxy resins; polyester resins; silicone resins such as alkylpolysiloxane resins; modified silicone resins such as (meth)acrylic-silicone resins, silicone-alkyd resins, silicone-urethane resins, and silicone-polyester resins; and fluorine resins such as polyvinylidene fluoride and fluoroolefin vinyl ether polymers. Note that (meth)acrylic means acrylic or methacrylic.

[0090] The synthetic resin may be a curable resin capable of forming a crosslinked structure through a crosslinking reaction. Curable resins are classified according to the type of curing into UV-curable resins, ionizing radiation-curable resins such as electron beam-curable resins, thermosetting resins, and hot-air curing resins. Curable resins also include those that generate binder components upon curing. The concept of a curable resin also includes compositions containing monomers before curing.

[0091] Examples of thermosetting resins include thermosetting urethane resins containing acrylic polyols and isocyanate prepolymers, phenolic resins, urea melamine resins, epoxy resins, unsaturated polyester resins, and silicone resins.

[0092] Examples of ionizing radiation-curable resins include polyfunctional (meth)acrylate resins such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, and 1,2,4-cyclohexanetri(meth)acrylate; polyfunctional urethane acrylate resins synthesized from diisocyanates, polyhydric alcohols, and (meth)acrylic acid esters having hydroxyl groups; polyether resins having acrylate-based functional groups; polyester resins; epoxy resins; alkyd resins; spiroacetal resins; polybutadiene resins; and polythiol polyene resins.

[0093] Organic solvents may be included to adjust the viscosity of the crosslinked polymer particle composition. Examples of organic solvents include aromatic solvents such as toluene and xylene; alcoholic solvents such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and propylene glycol monomethyl ether; esteric solvents such as ethyl acetate and butyl acetate; ketoneic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; and 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol dimethyl ether. Examples include glycol ethers such as methyl ether and propylene glycol methyl ether; glycol ether esters such as 2-methoxyethyl acetate, 2-ethoxyethyl acetate (cellosolve acetate), 2-butoxyethyl acetate, and propylene glycol methyl ether acetate; chlorinated solvents such as chloroform, dichloromethane, trichloromethane, and methylene chloride; ether solvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and 1,3-dioxolane; and amide solvents such as N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, and dimethylacetamide. Organic solvents may be used individually or in combination of two or more.

[0094] The amount of crosslinked polymer particles in the crosslinked polymer particle composition is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and more preferably 6 parts by mass or more, per 100 parts by mass of synthetic resin. The amount of crosslinked polymer particles in the crosslinked polymer particle composition is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, more preferably 100 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of synthetic resin. The amount of crosslinked polymer particles in the crosslinked polymer particle composition is preferably 2 to 300 parts by mass, more preferably 4 to 200 parts by mass, more preferably 6 to 100 parts by mass, and more preferably 6 to 50 parts by mass, per 100 parts by mass of synthetic resin.

[0095] The substrate material to which the crosslinked polymer particle composition is coated is not particularly limited and includes, for example, synthetic resins such as polyester polymers like polyethylene terephthalate (PET) and polyethylene naphthalate, cellulosic polymers like diacetylcellulose and triacetylcellulose (TAC), polycarbonate polymers, and (meth)acrylic polymers like polymethyl methacrylate, as well as cement, tiles, metals, and glass.

[0096] The method for coating a crosslinked polymer particle composition onto a substrate is not particularly limited and includes, for example, bar coating, blade coating, spin coating, reverse coating, die coating, spray coating, roll coating, gravure coating, microgravure coating, lip coating, air knife coating, and dipping methods.

[0097] The thickness of the coating film formed from the crosslinked polymer particle composition is not particularly limited and is appropriately determined by the particle size of the crosslinked polymer particles, but is preferably 1 to 20 μm, and more preferably 2 to 10 μm. The thickness of the sheet formed from the crosslinked polymer particle composition is not particularly limited and is appropriately determined by the particle size of the crosslinked polymer particles, but is preferably 1 to 20 μm, and more preferably 2 to 10 μm.

[0098] The present invention will be described more specifically below with reference to examples, but the present invention is not limited thereto. Specific numerical values ​​such as blending ratios (content), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to") of the blending ratios (content), physical properties, and parameters described in the "Means for Solving the Problem" and "Modes for Carrying Out the Invention" sections.

[0099] The following compounds were used in the examples and comparative examples: [Acrylic monomer] 1-Naphthylmethylacrylate (NMA) [Formula (3)]

[0100]

[0101] • 1-Naphthylmethyl methacrylate (NMMA) [Formula (4)]

[0102]

[0103] [Monofunctional monomers] ・Methyl methacrylate (MMA) ・Styrene monomer (St)

[0104] [Polyfunctional monomers] ・Ethylene glycol dimethacrylate (EGDMA) ・Divinylbenzene (DVB)

[0105] [Preparation of Seed Particles] In a 5 L reactor equipped with a stirrer and a thermometer, an oil phase was supplied, which consisted of an aqueous phase of 2900 parts by mass of water as an aqueous medium, mixed with 500 parts by mass of ethyl methacrylate and 10.0 parts by mass of n-octyl mercaptan as a molecular weight modifier. The contents were stirred while the inside of the reactor was purged with nitrogen, and the internal temperature of the reactor was raised to 55°C. Furthermore, while maintaining the internal temperature of the reactor at 55°C, an aqueous solution prepared by dissolving 3.0 parts by mass of potassium persulfate in 100 parts by mass of water as a polymerization initiator was supplied to the contents of the reactor, and the polymerization reaction was carried out for 12 hours.

[0106] The reaction solution after polymerization was classified using a 400-mesh (32 μm opening) wire mesh to prepare a slurry containing 15% by mass of seed particles, mainly composed of polyethyl methacrylate, as the solid content. The seed particles in this slurry were perfectly spherical. The arithmetic mean particle size in the particle size distribution based on the number of particles was 0.70 μm. The weight-average molecular weight (Mw) of the polyethyl methacrylate constituting the seed particles was 7500.

[0107] (Examples 1-5 and 7, Comparative Examples 1-7) [Production of Crosslinked Polymer Particles] Raw material monomers were prepared containing predetermined amounts (parts by mass) of acrylic monomer, methyl methacrylate (MMA), styrene monomer (St), ethylene glycol dimethacrylate (EGDMA), and divinylbenzene (DVB) as shown in Table 1. A monomer mixture was prepared by dissolving 0.75 parts by mass of benzoyl peroxide as a polymerization initiator, and predetermined amounts (parts by mass) of pentaerythritol tetrakis[3-[3,5-di(tert-butyl)-4-hydroxyphenyl]propionate] as an antioxidant and n-dodecyl mercaptan as a chain transfer agent, as shown in Table 1, in these raw material monomers.

[0108] A mixture was prepared by adding 2.5 parts by mass of sodium dodecylbenzenesulfonate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "Neogen (registered trademark) S-20D") as a pure component to 125 parts by mass of ion-exchanged water as an aqueous medium, and mixing it with the above monomer mixture.

[0109] The above mixture was supplied to a homomixer (T.K. Homomixer MARK II 2.5 model manufactured by Primix Corporation) and processed at a rotation speed of 5000 rpm for 10 minutes to obtain an emulsion. To this emulsion, a slurry of seed particles was added to a total solid content of 4 g, and the mixture was stirred at 30°C for 3 hours to obtain a dispersion.

[0110] 1.25 parts by mass of polyvinyl alcohol (product name "Gosenol (registered product) GM-14L" manufactured by Nippon Synthetic Chemical Co., Ltd.) as a dispersant, and 250 parts by mass of an aqueous solution containing 0.075 parts by mass of sodium nitrite as a polymerization inhibitor were added to the dispersion. The dispersion was stirred at 75°C for 5 hours, and then at 100°C for 3 hours to carry out the polymerization reaction and obtain a slurry of crosslinked polymer particles.

[0111] [Solid-liquid separation, washing, and drying process] The slurry of cross-linked polymer particles was dewatered using a pressure filter, and additives were washed and removed with hot water. The mixture was then vacuum-dried at 70°C for 24 hours to obtain cross-linked polymer particles.

[0112] [Classification Process] Using an airflow classifier (product name "Turbo Classifier (registered trademark) TC-15" manufactured by Nisshin Engineering Co., Ltd.), coarse particles having a particle size of 2.5 times or more the arithmetic mean particle size of the particle size distribution based on the number of cross-linked polymer particles were removed. Furthermore, small particles having a particle size of less than 0.5 times the arithmetic mean particle size of the particle size distribution based on the number of cross-linked polymer particles were removed until the coefficient of variation of particle size based on the particle size distribution of the cross-linked polymer particles was 15% or less, thereby obtaining the desired cross-linked polymer particles.

[0113] (Example 6) [Production of Crosslinked Polymer Particles] A mixture was prepared by mixing a raw material monomer containing 95 parts by mass of 1-naphthylmethyl acrylate (NMA) and 50 parts by mass of divinylbenzene as a polyfunctional monomer with 0.6 parts by mass of benzoyl peroxide as a polymerization initiator, 300 parts by mass of tricalcium phosphate as a dispersant, 0.01 parts by mass of sodium lauryl sulfate as a surfactant, and 125 parts by mass of ion-exchanged water as an aqueous medium.

[0114] The above mixture was supplied to a homomixer (T.K. Homomixer MARK II 2.5 model manufactured by Primix Corporation) and mixed until the droplet size was approximately 8 μm, obtaining a dispersion in which the monomer raw materials were uniformly dispersed in ion-exchanged water. The dispersion was stirred at 75°C for 5 hours, and then at 100°C for 3 hours to carry out the polymerization reaction and obtain a slurry of crosslinked polymer particles.

[0115] [Solid-liquid separation, washing, and drying process] Hydrochloric acid was added to the cross-linked polymer particle slurry to lower the slurry's pH to 3.0 or less and dissolved the dispersion stabilizer. The cross-linked polymer particle slurry was dewatered using a pressure filter, and additives were washed and removed with hot water. The mixture was then vacuum-dried at 70°C for 24 hours to obtain cross-linked polymer particles.

[0116] [Classification Process] Using an airflow classifier (product name "Turbo Classifier (registered trademark) TC-15" manufactured by Nisshin Engineering Co., Ltd.), the cross-linked polymer particles were subjected to a process to remove coarse particles having a particle diameter of 3.0 times or more the arithmetic mean particle diameter of the particle size distribution based on the number of particles in the cross-linked polymer particles. This process was continued until the coefficient of variation of particle diameter based on the particle size distribution based on the number of particles in the cross-linked polymer particles was less than 30%, thereby obtaining the desired polymer particles.

[0117] For the obtained cross-linked polymer particles, the arithmetic mean particle diameter based on the particle size distribution on a number basis, the coefficient of variation (CV value) of particle diameter, the thermal decomposition coefficient, the color change rate, and the refractive index were measured in the manner described above, and the results are shown in Table 2. In Table 2, "arithmetic mean particle diameter based on the particle size distribution on a number basis," "coefficient of variation (CV value) of particle diameter," "3% thermal decomposition temperature," and "10% thermal decomposition temperature" are denoted as "average particle diameter," "coefficient of variation (CV value)," "3% temperature," and "10% temperature," respectively.

[0118] When the monomer content (mass%) in the obtained cross-linked polymer particles was measured in the manner described above, it was found to be the same as the monomer content (mass%) used to produce the cross-linked polymer particles.

[0119] The dispersion behavior displacement and dispersion coefficient of the crosslinked polymer particles obtained in Examples 1 to 7 and Comparative Examples 5 and 6 were measured in the manner described above, and the results are shown in Table 3.

[0120] The coating properties and particle shedding properties of the crosslinked polymer particles obtained in Examples 1 to 7 and Comparative Examples 5 and 6 were measured according to the following procedure, and the results are shown in Table 3.

[0121] [Coating Properties] (Manufacturing of Optical Film) 0.20 g of crosslinked polymer particles and 1.00 g of butyl acetate as an organic solvent were supplied to a 10 mL sample tube, and the mixture was stirred for 1 minute using an ultrasonic cleaner (product name "ULTRASONICCLEANERVS-150" manufactured by VelvoClear Co., Ltd.) to disperse the crosslinked polymer particles in butyl acetate and obtain a dispersion.

[0122] To the obtained dispersion, 1.50 g of acrylic resin (DIC Corporation product name "Acrydic® A-817-BA") was added as a binder resin, and the mixture was stirred for about 2 minutes using the ultrasonic cleaner described above.

[0123] After allowing the dispersion to stand for 4 hours, 5.50 g of butyl acetate was added to the dispersion as an organic solvent, and the mixture was stirred for 1 minute using the ultrasonic cleaner to obtain a crosslinked polymer particle composition.

[0124] The obtained crosslinked polymer particle composition was coated onto a 100 μm thick polyethylene terephthalate film (product name "FUJIX® OHP Film for Copiers" manufactured by Fujifilm Corporation) using a coater with a 75 μm slit. After coating, the film was placed in a dryer maintained at 70°C for 1 hour to evaporate and remove the organic solvent in the crosslinked polymer particle composition, thereby obtaining an optical film with a coating film formed on the polyethylene terephthalate film. In the coating film, the crosslinked polymer particles were contained in a dispersed state within an acrylic resin.

[0125] (Evaluation of optical properties (low haze variation)) Test specimens were prepared by cutting the optical film into a flat square with sides of 6 cm. The haze of the coating film on the test specimens was measured at the four corners and the center (a total of 5 locations) using a measuring device commercially available from Nippon Denshoku Industries Co., Ltd. under the product name "NDH-4000," in accordance with JIS K7136.

[0126] The maximum, minimum, and arithmetic mean values ​​of the haze (%) measured at five locations were used to calculate the haze difference (%) using the following formula. The haze difference (%) was used as an evaluation of the coating properties.

[0127] Haze difference (%) = 100 × [(Maximum haze value - Minimum haze value) / Arithmetic mean of haze]

[0128] [Particle Shedding Properties] Optical films were prepared in the same manner as when measuring coating properties. Using the JSPS-type friction tester RT-200, commercially available from Daiei Kagaku Seiki, a 20 mm x 20 mm flat friction element with a load of 300 g was slid 10 times across the coating surface, and the results were observed using a digital microscope commercially available from Keyence under the product name "VHX". An arbitrary measurement point on the coating surface, in the shape of a 1 mm square, was observed, and the number of locations where cross-linked polymer particles had fallen off was measured. The number of locations where cross-linked polymer particles had fallen off was used as an evaluation of particle shedding properties.

[0129]

[0130]

[0131]

[0132] (Cross-reference of related applications) This application claims priority under Japanese Patent Application No. 2024-232184, filed on 27 December 2024, and the disclosures of this application are incorporated herein by reference to those applications in their entirety.

[0133] The crosslinked polymer particles of the present invention have excellent heat resistance and reduced color change due to heat. By using the crosslinked polymer particles of the present invention, optical components and other molded articles with excellent heat resistance can be manufactured.

[0134] Since the crosslinked polymer particles of the present invention have excellent dispersibility and dispersion stability in the dispersion medium, molded articles in which the crosslinked polymer particles are uniformly dispersed can be easily manufactured.

Claims

1. Crosslinked polymer particles containing an acrylic polymer that contains 50 to 95% by mass of an acrylic monomer component represented by formula (1). [In formula (1), R represents a hydrogen atom or a methyl group, and Q represents a direct bond or an alkylene group having 1 to 3 carbon atoms.] 2. The crosslinked polymer particles according to claim 1, characterized in that the dispersion coefficient is less than 0.

20.

3. Crosslinked polymer particles according to claim 1 or 2, characterized in that the thermal decomposition coefficient is 10% or more.

4. Crosslinked polymer particles according to claim 1 or 2, characterized in that the color change rate is 30% or less.

5. Crosslinked polymer particles according to claim 1 or 2, characterized in that they are used in optical components.

6. Crosslinked polymer particles according to claim 1 or 2, characterized in that they are used in an anti-glare member.

7. An optical film comprising a film and a coating film formed on the film and containing a synthetic resin and crosslinked polymer particles according to claim 1 or 2 dispersed in the synthetic resin.

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