Particles, method for manufacturing particles, and method for manufacturing optical film

Abstract

The particles of the present disclosure are characterized by containing a (meth) acrylic resin containing a ring structural unit having a ring structure in the main chain thereof, and (meth) acrylic crosslinked particles, the average elastic modulus E1 of the portion where the (meth) acrylic crosslinked particles are not present and the average elastic modulus E2 of the portion where the (meth) acrylic crosslinked particles are present satisfy formula (1). Formula (1): 0.90 < = E2 / E1.

Description

Technical Field

[0001] The present disclosure relates to a particle, a method for manufacturing the particle, and a method for manufacturing an optical film. Background Art

[0002] An optical film containing a (meth)acrylic resin having a ring structure in the main chain is known. In the field of such films, an anti-blocking agent (also simply referred to as fine particles) is usually used as a measure against blocking.

[0003] Patent Document 1 discloses an optical film in which a layer containing a (meth)acrylic resin having a ring structure in the main chain contains an anti-blocking agent in order to suppress blocking. Such an optical film is manufactured by a melt extrusion method using particles containing a (meth)acrylic resin having a ring structure in the main chain and an anti-blocking agent as raw materials.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2010 / 061917 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Although the optical film disclosed in Patent Document 1 contains an anti-blocking agent, it has good transparency. However, in recent years, with the progress of technology, the requirements for the performance that an optical film should have have also been increasing.

[0009] An object of the present disclosure is to provide a particle containing an anti-blocking agent and having good internal haze when formed into a molded body such as a film, and a method for manufacturing the same.

[0010] Solutions to the Problems

[0011] The present disclosure provides a particle, characterized in that the particle contains a (meth)acrylic resin and (meth)acrylic crosslinked particles, the (meth)acrylic resin contains a ring structure unit having a ring structure in the main chain, and the average elastic modulus E1 of a portion where the (meth)acrylic crosslinked particles do not exist and the average elastic modulus E2 of a portion where the (meth)acrylic crosslinked particles exist satisfy the following formula (1).

[0012] Formula (1) 0.90 ≤ E2 / E1

[0013] In another embodiment, the present disclosure provides a particle, characterized in that the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, the (meth)acrylic resin contains a cyclic structural unit having a cyclic structure in the main chain, and when formed into a film by hot pressing at 250 °C for 3 minutes, the internal haze of the film is 0.35% or less in terms of a thickness of 100 μm.

[0014] In yet another embodiment, the present disclosure provides a method for manufacturing a particle, characterized in that the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, the (meth)acrylic resin contains a cyclic structural unit having a cyclic structure in the main chain, and the method for manufacturing the particle includes: a first step of obtaining the (meth)acrylic resin in a flowing state; and a second step of kneading the (meth)acrylic resin in the flowing state obtained in the first step with the (meth)acrylic acid crosslinked particles to obtain a (meth)acrylic resin composition, wherein the (meth)acrylic acid crosslinked particles are first kneaded with the resin constituting the particle in the second step.

[0015] In yet another embodiment, the present disclosure provides a method for manufacturing a particle, characterized in that the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, the (meth)acrylic resin contains a cyclic structural unit having a cyclic structure in the main chain, and the method for manufacturing the particle includes: a synthesis step of synthesizing the (meth)acrylic resin from raw materials; and a devolatilization step of subjecting the (meth)acrylic resin obtained in the synthesis step to devolatilization by feeding it to an extruder equipped with a side feeder and an exhaust port, in which the powder of the (meth)acrylic acid crosslinked particles is fed from the side feeder to the extruder to obtain a (meth)acrylic resin composition containing the (meth)acrylic resin and the (meth)acrylic acid crosslinked particles, and after the devolatilization step, the (meth)acrylic resin composition is extruded from the extruder to obtain particles.

[0016] Advantages of the Invention

[0017] According to the present disclosure, it is possible to provide a particle containing an anti-blocking agent and having good internal haze when formed into a molded article such as a film, and a method for manufacturing the same. Detailed Embodiments

[0018] Hereinafter, embodiments of the present disclosure will be described. However, the present disclosure is not limited to the following embodiments.

[0019] <Definition of Terms>

[0020] In the present disclosure, "(meth)acrylic acid" is a term including both acrylic acid and methacrylic acid. The numerical range described as "X to Y" means "X or more and Y or less".

[0021] <Summary>

[0022] The particles of the first embodiment are characterized in that the particles contain a (meth)acrylic resin (A) and (meth)acrylic crosslinked particles (B), the (meth)acrylic resin (A) contains a ring structure unit having a ring structure in the main chain, and the average elastic modulus E1 of the portion where there are no (meth)acrylic crosslinked particles and the average elastic modulus E2 of the portion where there are (meth)acrylic crosslinked particles satisfy the following formula (1).

[0023] Formula (1) 0.90 ≤ E2 / E1

[0024] The ratio (E2 / E1) can be measured by an atomic force microscope (AFM). The atomic force microscope has a cantilever with a probe attached to the tip. In the measurement of the ratio (E2 / E1), the probe scans the surface of the sample. The probe moves along the surface of the sample, and this movement is detected by the cantilever. The force curve obtained by the force volume measurement can be fitted with the DMT mechanical model, and the elastic modulus can be calculated in the form of Young's modulus.

[0025] In the measurement of the ratio (E2 / E1), for example, the particles are formed into a film-like product as the sample. The particles are hot-pressed at 250°C for 3 minutes to produce a film with a thickness of 40 to 200 μm (for example, 160 μm), and this film can be used as the sample.

[0026] By satisfying formula (1), the internal haze of the molded body obtained from the particles can be made good. The reason is not yet clear, but it is presumed as follows. That is, the particles of the first embodiment are, for example, supplied to the manufacture of an optical film by the melt extrusion method. In the melt extrusion method, the (meth)acrylic resin (A) constituting the particles is melted and formed into a film. When the (meth)acrylic resin (A) flows, the (meth)acrylic crosslinked particles (B) may be deformed by the pressure. If the (meth)acrylic crosslinked particles (B) are deformed, the refraction of light may increase due to the shape of the (meth)acrylic crosslinked particles (B), and the internal haze of the optical film may deteriorate. In contrast, the particles of the first embodiment have a sufficient elastic modulus of the (meth)acrylic crosslinked particles (B) by satisfying formula (1), so that the deterioration of the internal haze caused by the deformation of the (meth)acrylic crosslinked particles (B) can be suppressed.

[0027] The particles preferably satisfy the following formula (2), and more preferably satisfy the following formula (3). In this way, the internal haze of the molded body obtained from the particles can be made better.

[0028] Formula (2) 0.90 ≤ E2 / E1 ≤ 1.10

[0029] Equation (3): 0.95 ≤ E2 / E1 ≤ 1.00

[0030] When a film is formed by hot-pressing the particles at 250°C for 3 minutes, the internal haze of the film, converted to a thickness of 100 μm, is preferably 0.30% or less, more preferably 0.20% or less, and further preferably 0.10% or less. From the viewpoint of ease of particle production, it is preferably 0.01% or more.

[0031] The internal haze of the film converted to a thickness of 100 μm when forming the film can be measured by forming the particles into a film shape. Specifically, the particles are hot-pressed at 250°C for 3 minutes to obtain a film with a thickness of 100 μm, and the internal haze of the film is measured. In the case where it is difficult to obtain a film with a thickness of 100 μm, it can also be calculated by the following method. First, the particles are hot-pressed at 250°C for 3 minutes to produce a plurality of films with a specified thickness. Next, the internal haze of a laminated film formed by laminating n pieces of this film is measured (n represents an integer of 1 or more. Here, even in the case of n = 1, it is also referred to as a laminated film). Then, the value of n is changed, and the internal haze of the laminated film is measured. Since there is a linear relationship between the film thickness and the internal haze, an equation representing the relationship between the film thickness and the internal haze can be obtained by the least squares method based on the obtained measurement results. Based on this equation, the internal haze when the film thickness is 100 μm can be calculated.

[0032] The measurement of the internal haze is carried out in a state where the film is immersed in an appropriate liquid. Usually, the measured haze is the sum of the external haze and the internal haze, but if the measurement is carried out in a state where the film is immersed in an appropriate liquid, since the liquid cancels out the surface roughness of the film, the external haze is substantially 0. Therefore, the measured haze is regarded as the internal haze. As the liquid, for example, tetralin can be cited.

[0033] Similar to the internal haze, the internal b* value of the particles converted to a thickness of 100 μm when forming the film can also be measured.

[0034] In addition, the present disclosure includes particles of a second embodiment. The particles of the second embodiment are characterized in that the particles contain a (meth)acrylic resin (A) and (meth)acrylic crosslinked particles (B), the main chain of the (meth)acrylic resin (A) has a ring structure, and when a film is formed by hot-pressing at 250°C for 3 minutes, the internal haze of the film, converted to a thickness of 100 μm, is 0.35% or less.

[0035] When a film is formed by hot-pressing the particles at 250°C for 3 minutes, the internal haze of the film, converted to a thickness of 100 μm, is preferably 0.30% or less, more preferably 0.20% or less, and further preferably 0.10% or less. From the viewpoint of ease of particle production, it is preferably 0.01% or more.

[0036] Describe the common features of the particles of the first embodiment and the particles of the second embodiment. It should be noted that in the following description, the particles of the first embodiment and the particles of the second embodiment are collectively referred to as the particles of this embodiment.

[0037] <(Meth)acrylic resin (A) containing a ring structure unit having a ring structure in the main chain>

[0038] Typically, the (meth)acrylic resin (A) containing a ring structure unit having a ring structure in the main chain contains a structural unit (a1) derived from a (meth)acrylate and a ring structure unit (a2) having a ring structure in the main chain.

[0039] As the structural unit (a1), for example, structural units derived from monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, etc. can be cited. The structural unit (a1) may contain only one of the above-listed structural units, or may contain two or more of the above-listed structural units. The structural unit (a1) preferably contains a structural unit derived from methyl methacrylate.

[0040] The content of the structural unit (a1) in the (meth)acrylic resin (A) is preferably 50 to 99% by mass, more preferably 60 to 90% by mass, and still more preferably 70 to 80% by mass.

[0041] As the ring structure unit (a2), for example, N-substituted maleimide structural units, maleic anhydride structural units, glutarimide structural units, glutaric anhydride structural units, lactone ring structural units can be cited. The ring structure unit (a2) may contain only one of the above-listed structural units, or may contain two or more of the above-listed structural units. The ring structure unit (a2) preferably contains at least one selected from the group consisting of N-substituted maleimide structural units, glutarimide structural units, and lactone ring structural units, and more preferably contains at least one selected from the group consisting of glutarimide structural units and lactone ring structural units.

[0042] An example of the N-substituted maleimide structural unit and the maleic anhydride structural unit is shown in the following formula (1).

[0043] [Chemical formula 1]

[0044]

[0045] In formula (1), R 1 and R 2 are each independently a hydrogen atom or a methyl group. X1 is an oxygen atom or a nitrogen atom. When X 1 is an oxygen atom, R 3 does not exist. When X 1 is a nitrogen atom, R 3 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a phenyl group optionally having a substituent, or a benzyl group optionally having a substituent.

[0046] When X 1 is a nitrogen atom, formula (1) represents an N-substituted maleimide structural unit. The (meth)acrylic resin (A) having an N-substituted maleimide structural unit as the ring structural unit (a2) is obtained, for example, by copolymerizing an N-substituted maleimide and a (meth)acrylate. Examples of the N-substituted maleimide include N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and N-benzylmaleimide.

[0047] When X 1 is an oxygen atom, formula (1) represents a maleic anhydride structural unit. The (meth)acrylic resin (A) having a maleic anhydride structural unit as the ring structural unit (a2) is obtained, for example, by copolymerizing maleic anhydride and a (meth)acrylate.

[0048] An example of the glutarimide structural unit and the glutaric anhydride structural unit is shown in the following formula (2).

[0049] [Chemical formula 2]

[0050]

[0051] In formula (2), R 4 and R 5 are each independently a hydrogen atom or a methyl group. X 2 is an oxygen atom or a nitrogen atom. When X 2 is an oxygen atom, R 6 does not exist. When X 2 is a nitrogen atom, R 6 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a phenyl group optionally having a substituent, or a benzyl group optionally having a substituent.

[0052] When X 2 is a nitrogen atom, formula (2) represents a glutarimide structural unit. The (meth)acrylic resin (A) having a glutarimide structural unit as the ring structural unit (a2) is obtained, for example, by imidizing polymethyl methacrylate. Examples of the imidizing agent used in the imidization include monomethylamine, ammonia, and cyclohexylamine.

[0053] When X2 When it is an oxygen atom, formula (2) represents a glutaric anhydride structural unit. The (meth)acrylic resin (A) having a glutaric anhydride structure as the ring structural unit (a2) is obtained, for example, by subjecting a copolymer of (meth)acrylate and (meth)acrylic acid to intramolecular dealcoholization cyclocondensation.

[0054] An example of the lactone ring structural unit (X) is shown in the following formula (3).

[0055] [Chemical formula 3]

[0056]

[0057] In formula (3), R 7 , R 8 and R 9 are each independently a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group is an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl. Examples of the aromatic hydrocarbon group include: phenyl, tolyl, benzyl. R 7 is preferably a hydrogen atom, and R 8 and R 9 are preferably methyl groups.

[0058] The (meth)acrylic resin (A) having the lactone ring structural unit (X) as the ring structural unit (a2) is obtained, for example, by subjecting a copolymer of methyl methacrylate and methyl 2-(hydroxymethyl)acrylate to intramolecular dealcoholization cyclocondensation.

[0059] The lactone ring structural unit (X) is defined as a lactone ring structural unit in which two or more atoms forming the ring structure are located on the main chain. The lactone ring structural unit (X) shown in formula (3) is a 6-membered ring, but it can also be, for example, a 4- to 8-membered ring.

[0060] An example of the lactone ring structural unit (Y) is shown in the following formula (4).

[0061] [Chemical formula 4]

[0062]

[0063] In formula (4), R 10 , R 11 , R 12 and R 13Each independently is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group is an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl. Examples of the aromatic hydrocarbon group include: phenyl, tolyl, benzyl. R 10 ~R 13 Preferably all are hydrogen atoms.

[0064] The (meth)acrylic resin (A) having a lactone ring structural unit (Y) as the ring structural unit (a2) is obtained, for example, by polymerizing a monomer represented by the following formula (5).

[0065] [Chemical formula 5]

[0066]

[0067] R in formula (5) 10 、R 11 、R 12 and R 13 have the same meanings as R 10 、R 11 、R 12 and R 13 in formula (4).

[0068] The lactone ring structural unit (Y) is defined as a lactone ring structural unit in which one atom forming the ring is located on the main chain. The lactone ring structural unit (Y) shown in formula (4) is a 5-membered ring, but it can also be, for example, a 4- to 8-membered ring.

[0069] It should be noted that in the present disclosure, when only referred to as a lactone ring structural unit, it includes both the lactone ring structural unit (X) and the lactone ring structural unit (Y).

[0070] The content of the ring structural unit (a2) in the (meth)acrylic resin (A) is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, and still more preferably 20 to 30% by mass.

[0071] (Meth)acrylic resin (A) may also contain other structural units (a3) different from the structural unit (a1) and the cyclic structural unit (a2). As the structural unit (a3), for example, structural units derived from monomers such as styrene, vinyltoluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, N-vinylpyrrolidone, N-vinylcarbazole, vinylpyridine, vinylimidazole, and vinylthiophene can be cited. The structural unit (a3) may contain only one of the above-listed structural units or may contain two or more of the above-listed structural units. Of course, (meth)acrylic resin (A) may not contain the structural unit (a3). When (meth)acrylic resin (A) contains the structural unit (a3), the structural unit (a3) preferably contains a structural unit derived from styrene.

[0072] (Meth)acrylic resin (A) The content of the cyclic structural unit (a3) is not limited as long as it does not significantly impair the properties of the particles, and can be 0 to 10% by mass.

[0073] (Meth)acrylic resin (A) The weight average molecular weight (Mw) is preferably 10,000 to 800,000, more preferably 30,000 to 500,000, and further preferably 50,000 to 300,000.

[0074] (Meth)acrylic resin (A) The number average molecular weight (Mn) is preferably 5,000 to 400,000, more preferably 10,000 to 200,000, and further preferably 20,000 to 120,000.

[0075] (Meth)acrylic resin (A) The glass transition temperature (Tg) measured by the starting point method is preferably 100 to 150 °C, more preferably 110 to 140 °C, and further preferably 115 to 130 °C.

[0076] The particles may contain only one (meth)acrylic resin (A) or may contain two or more (meth)acrylic resins (A). The content of (meth)acrylic resin (A) in the particles is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0077] <Other resins>

[0078] The particles may also contain other resins different from the (meth)acrylic resin (A). Examples of the other resins include: polymethyl methacrylate, polycarbonate, acrylonitrile-styrene resin, methyl methacrylate-styrene resin. The particles may contain only one other resin, or may contain two or more other resins. Of course, the particles may not contain other resins. The content of the other resin in the particles is not limited as long as it does not significantly impair the properties of the particles, and may be 0 to 50% by mass, may be 0 to 30% by mass, may be 0 to 10% by mass, or may be 0 to 5% by mass.

[0079] <(meth)acrylic crosslinked particles (B)>

[0080] (Meth)acrylic crosslinked particles (B) are spherical or substantially spherical particles containing a (meth)acrylic resin having a crosslinked structure ((meth)acrylic crosslinked resin). (Meth)acrylic crosslinked particles (B) function as an anti-blocking agent.

[0081] (Meth)acrylic crosslinked particles (B) are obtained, for example, by suspension polymerization of a monofunctional acrylic monomer such as methyl methacrylate and a polyfunctional acrylic monomer such as trimethylolpropane tri(meth)acrylate, (meth)allyl acrylate, ethylene glycol di(meth)acrylate. (Meth)acrylic crosslinked particles (B) may be particles obtained by copolymerizing a monofunctional acrylic monomer, a polyfunctional acrylic monomer, and a styrene monomer.

[0082] (Meth)acrylic crosslinked particles (B) preferably have a core part containing a (meth)acrylic crosslinked resin and a shell part containing a styrene crosslinked resin. Thereby, the internal haze of the molded body made of the particles can be made better.

[0083] The core part is obtained, for example, by suspension polymerization of a monofunctional acrylic monomer and a polyfunctional acrylic monomer. The shell part is obtained by polymerizing a monofunctional styrene monomer and a polyfunctional styrene monomer in a solution containing the core part. That is, by making the core part contain a polymerization initiator, the polymerization of the monofunctional styrene monomer and the polyfunctional styrene monomer is carried out on the surface of the core part using this polymerization initiator. Thereby, a shell part containing a styrene crosslinked resin is obtained on the surface of the core part.

[0084] It should be noted that examples of the monofunctional styrene monomer include: styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-ethylvinylbenzene, m-ethylvinylbenzene, p-ethylvinylbenzene. Examples of the polyfunctional styrene monomer include: divinylbenzene, divinylnaphthalene.

[0085] The average primary particle diameter of the (meth)acrylic acid crosslinked particles (B) is preferably 0.5 to 2.0 μm, more preferably 1.2 to 2.0 μm. Thereby, the dispersibility of the (meth)acrylic acid crosslinked particles (B) in the particles is improved, and the internal haze of the molded body produced from the particles can be made better.

[0086] In the particles, when the content of the (meth)acrylic resin (A) is set to 100 parts by mass, the content of the (meth)acrylic acid crosslinked particles (B) is preferably 0.01 to 0.20 parts by mass. Thereby, the dispersibility of the (meth)acrylic acid crosslinked particles (B) in the particles is improved, and the internal haze of the molded body produced from the particles can be made better.

[0087] In order to adjust the ratio (E2 / E1), for example, the elastic modulus of the (meth)acrylic acid crosslinked particles (B) can be adjusted. When forming the (meth)acrylic acid crosslinked particles (B), the elastic modulus can be increased by increasing the usage amount of the polyfunctional monomer that functions as a crosslinking agent.

[0088] <Additive>

[0089] The particles may also contain additives such as a UV absorber, an antioxidant, a compatibilizer, a stabilizer, etc. The total content of these additives in the particles is not limited as long as it does not significantly impair the properties of the particles, and can be 0 to 5% by mass.

[0090] Examples of the UV absorber include: triazine-based UV absorbers, triazole-based UV absorbers. Examples of the triazine-based UV absorber include: 2-[4,6-diphenyl-1,3,5-triazin-2-yl]-5-(hexyloxy)phenol, 2,4,6-tris[4-(hexyloxy)-2-hydroxy-3-methylphenyl]-1,3,5-triazine. Examples of the triazole-based UV absorber include: 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol]. The particles may contain only one kind of UV absorber, or may contain two or more kinds of UV absorbers.

[0091] Examples of the antioxidant include: hindered phenol-based antioxidants, hindered amine-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants. Examples of the hindered phenol-based antioxidant include pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Examples of the phosphorus-based antioxidant include tris(2,4-di-tert-butyl-phenyl) phosphite. Examples of the sulfur-based antioxidant include bis[3-(dodecylthio)propionic acid] 2,2-bis[[3-(dodecylthio)-1-propionyloxy]methyl]-1,3-propanediol ester. The particles may contain only one kind of antioxidant, or may contain two or more kinds of antioxidants.

[0092] <Foreign matter>

[0093] In the particles, the number of foreign matters having a major axis of 20 μm or more measured using a particle counter is preferably 20 pieces / g or less, more preferably 10 pieces / g or less, still more preferably 5 pieces / g or less, and particularly preferably 1 piece / g or less. From the viewpoint of ease of manufacturing the particles, more than 0 pieces / g is preferred. The particles of the present embodiment are, for example, supplied to the production of an optical film by a melt extrusion method. In the melt extrusion method, the (meth)acrylic resin (A) constituting the particles is melted, passed through a polymer filter, and then formed into a film shape. When the (meth)acrylic crosslinked particles (B) are contained in the particles, the (meth)acrylic crosslinked particles (B) also pass through the polymer filter. In such a case, in order to prevent clogging caused by the (meth)acrylic crosslinked particles (B), it is sometimes preferred that the filtration accuracy of the polymer filter is slightly coarser. On the other hand, if the filtration accuracy of the polymer filter is made coarser, the removal efficiency of the foreign matters contained in the particles may decrease. In response to this, the particles of the present embodiment can sufficiently reduce the number of foreign matters remaining in the optical film even if the filtration accuracy of the polymer filter is slightly coarsened by sufficiently reducing the number of foreign matters.

[0094] Next, two examples of the method for producing the particles will be described.

[0095] <First method>

[0096] The first-described production method is a conventionally well-known method, for example, the methods described in Production Example 1 and Production Example 2 of Patent Document 1. This is referred to as the first method herein.

[0097] The first method includes: a synthesis step of obtaining a (meth)acrylic resin (A) containing a ring structure unit having a ring structure in the main chain from raw materials; a devolatilization step of subjecting the (meth)acrylic resin (A) obtained in the synthesis step to devolatilization by supplying it to an extruder having an exhaust port; and a first particle obtaining step of extruding the (meth)acrylic resin (A) that has undergone the devolatilization step from the extruder to obtain first particles (P).

[0098] In addition, the first method includes: a masterbatch obtaining step of melt-kneading the first particles (P) and the (meth)acrylic crosslinked particles (B) to obtain a masterbatch; and a second particle obtaining step of melt-kneading the masterbatch and particles (Q) containing no fine particles to obtain second particles (S). Here, the particles (Q) are also preferably the first particles (P). The (meth)acrylic crosslinked particles (B) can be pre-produced by the method described above. Of course, commercially available (meth)acrylic crosslinked particles can also be used.

[0099] Thus, a second particle (S) containing a (meth)acrylic resin (A) having a ring structural unit with a ring structure in the main chain and (meth)acrylic crosslinked particles (B) can be obtained. This second particle (S) can be set as the particle of the present embodiment.

[0100] <Second method>

[0101] The manufacturing method described second is a preferred manufacturing method as a method for manufacturing particles. This is referred to as the second method herein.

[0102] The second method includes: a step of obtaining a (meth)acrylic resin (A) in a flowing state (first step); and a step of kneading the (meth)acrylic resin (A) in the flowing state with (meth)acrylic crosslinked particles (B) to obtain a (meth)acrylic resin composition (second step), wherein the (meth)acrylic crosslinked particles (B) are kneaded with the resin constituting the particles for the first time in the second step. The first step may also be a step of synthesizing to obtain a (meth)acrylic resin (A) in a flowing state. The (meth)acrylic crosslinked particles (B) may be in powder form. The (meth)acrylic resin in a flowing state may refer to a solution containing a (meth)acrylic resin in which the (meth)acrylic resin is dissolved in a solvent, or a molten (meth)acrylic resin. The (meth)acrylic crosslinked particles (B) can be pre-manufactured by the method described previously. Of course, commercially available (meth)acrylic crosslinked particles can also be used.

[0103] From after the first step to the second step, the temperature of the (meth)acrylic resin (A) in the flowing state is preferably maintained at 240 °C or higher and 320 °C or lower, more preferably maintained at 250 °C or higher and 310 °C or lower, and further preferably maintained at 260 °C or higher and 300 °C or lower. Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body manufactured from the particles can be made better.

[0104] The average primary particle diameter of the (meth)acrylic crosslinked particles (B) is preferably 0.5 to 2.0 μm. Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body manufactured from the particles can be made better.

[0105] In the second step, preferably 0.01 to 0.20 parts by mass of the (meth)acrylic crosslinked particles (B) are kneaded with respect to 100 parts by mass of the (meth)acrylic resin (A). Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body manufactured from the particles can be made better.

[0106] Preferably, after the second step, there is provided a step of passing the (meth)acrylic resin composition through a polymer filter (third step). By passing the (meth)acrylic resin composition through the polymer filter, foreign substances and the like contained in the (meth)acrylic resin composition can be effectively removed. In the third step, the temperature of the (meth)acrylic resin composition is preferably maintained at 240°C or higher and 320°C or lower, more preferably maintained at 250°C or higher and 310°C or lower, and further preferably maintained at 260°C or higher and 300°C or lower. Thereby, the (meth)acrylic resin composition can smoothly pass through the polymer filter.

[0107] Finally, particles of the (meth)acrylic resin composition are obtained. These particles can be the particles of the present embodiment.

[0108] As an example of such a manufacturing method, there can be cited a method for manufacturing particles containing a (meth)acrylic resin (A) and (meth)acrylic acid crosslinked particles (B), wherein the (meth)acrylic resin (A) contains a ring structure unit having a ring structure in the main chain. The method for manufacturing the particles includes a synthesis step of synthesizing the (meth)acrylic resin (A) from raw materials, and a devolatilization step of subjecting the (meth)acrylic resin (A) obtained in the synthesis step to devolatilization by feeding it to an extruder equipped with a side feeder and an exhaust port. In the devolatilization step, powder of the (meth)acrylic acid crosslinked particles (B) is fed from the side feeder to the extruder to obtain a (meth)acrylic resin composition containing the (meth)acrylic resin (A) and the (meth)acrylic acid crosslinked particles (B), and after the devolatilization step, the (meth)acrylic resin composition is extruded from the extruder to obtain particles.

[0109] In the synthesis step of synthesizing the (meth)acrylic resin (A) from raw materials, a (meth)acrylic resin (A) in a flowing state is obtained. In the case of synthesizing a (meth)acrylic resin (A) containing a lactone ring structure unit (X), for example, methyl methacrylate as a raw material and methyl 2-(hydroxymethyl)acrylate are subjected to solution polymerization to synthesize a copolymer, and then the copolymer is subjected to intramolecular de-alcoholization cyclization condensation. In this example, a solution containing the (meth)acrylic resin in which the (meth)acrylic resin (A) is dissolved in a solvent is obtained. In the case of synthesizing a (meth)acrylic resin (A) containing a succinimide structure unit, for example, polymethyl methacrylate as a raw material is melted and reacted with gaseous monomethylamine. In this example, a molten (meth)acrylic resin (A) is obtained. In the case of synthesizing a (meth)acrylic resin (A) containing an N-substituted maleimide structure unit, for example, an N-substituted maleimide as a raw material and methyl methacrylate are subjected to solution polymerization. In this example, a solution containing the (meth)acrylic resin in which the (meth)acrylic resin (A) is dissolved in a solvent is obtained.

[0110] In the devolatilization step of subjecting the (meth)acrylic resin (A) obtained in the synthesis step to devolatilization using an extruder equipped with a side feeder and an exhaust port, unnecessary substances are removed from the (meth)acrylic resin (A). When a solution containing the (meth)acrylic resin is obtained in the synthesis step, the solution containing the (meth)acrylic resin is introduced into the extruder to remove the solvent. Further, powder of the (meth)acrylic crosslinked particles (B) is fed from the side feeder to the extruder to obtain a (meth)acrylic resin composition containing the (meth)acrylic resin (A) and the (meth)acrylic crosslinked particles (B). The barrel temperature of the extruder in the devolatilization step is preferably set to a temperature at which the (meth)acrylic resin (A) is maintained at 240°C or higher and 320°C or lower. Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body produced from the particles can be made better. When the molten (meth)acrylic resin (A) is obtained in the synthesis step, the extruder is also used in the same manner to remove unnecessary substances.

[0111] A polymer filter is preferably disposed at the front end of the extruder. Examples of the polymer filter include a disk filter and a candle filter. When the (meth)acrylic resin composition is passed through the polymer filter, foreign substances contained in the (meth)acrylic resin composition can be effectively removed. When the (meth)acrylic resin composition is passed through the polymer filter, it is preferable to maintain the temperature of the (meth)acrylic resin composition at 240°C or higher and 320°C or lower. Thereby, the (meth)acrylic resin composition can smoothly pass through the polymer filter.

[0112] The average primary particle diameter of the (meth)acrylic crosslinked particles (B) is preferably 0.5 to 2.0 μm. Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body produced from the particles can be made better.

[0113] In the devolatilization step, it is preferable to knead 0.01 to 0.20 parts by mass of the (meth)acrylic crosslinked particles (B) with respect to 100 parts by mass of the (meth)acrylic resin (A). Thereby, the dispersibility of the (meth)acrylic crosslinked particles (B) in the particles is improved, and the internal haze of the molded body produced from the particles can be made better.

[0114] Finally, the (meth)acrylic resin composition obtained in the devolatilization step is extruded from the extruder to obtain particles. These particles can be the particles of the present embodiment. The method for obtaining the particles can be a conventionally known method, and can be a strand cut method, a water ring hot cut method, or an underwater cutting method.

[0115] <Comparison between the First Method and the Second Method>

[0116] According to the first method (the method described in Production Examples 1 and 2 of Patent Document 1 as a specific example), first, (meth)acrylic acid crosslinked particles and prefabricated particles are melt-kneaded at a high temperature (for example, 260°C) to produce a masterbatch. Then, the masterbatch and other particles are melt-kneaded at a high temperature (for example, 260°C) to produce particles for the production of a molded body. Therefore, the (meth)acrylic acid crosslinked particles will undergo a thermal history of high temperature twice during the production of the particles for the production of the molded body.

[0117] According to the second method, after obtaining the (meth)acrylic resin (A) in a flowing state, the (meth)acrylic resin (A) in a flowing state and the (meth)acrylic acid crosslinked particles (B) are melt-kneaded at a high temperature (for example, 260°C) to obtain a (meth)acrylic resin composition, and the (meth)acrylic resin composition is granulated to produce particles for the production of a molded body. Therefore, the (meth)acrylic acid crosslinked particles will undergo a thermal history of high temperature once during the production of the particles for the production of the molded body.

[0118] From the above description, it can be seen that according to the second method, the number of times of the thermal history of high temperature of the (meth)acrylic acid crosslinked particles (B) can be reduced. It is considered that this can suppress the deterioration of the (meth)acrylic acid crosslinked particles (B) and make the internal haze of the molded body manufactured from the particles better.

[0119] It should be noted that the "thermal history of high temperature" refers to being exposed to the temperature required for melt-kneading of the resin. For example, it refers to being exposed to a high temperature of 240°C or higher.

[0120] The particles of the present embodiment are particles for the production of a molded body. For example, they are particles for the production of an optical film by the melt extrusion method. Whether the particles are manufactured by the first method or the second method, they can be supplied to a melt extruder for optical film manufacturing to obtain an optical film.

[0121] <Manufacturing Method of Optical Film>

[0122] In the manufacturing method of an optical film by the melt extrusion method, for example, a manufacturing apparatus including a resin hopper and a melt extruder can be used. The resin hopper stores the particles before supplying them to the melt extruder and supplies the particles to the melt extruder via a pipe. The melt extruder can be a single-screw extruder or a twin-screw extruder. The melt extruder sequentially includes a gear pump, a polymer filter, and a die head. The die head is preferably a T-die head and can be, for example, a conventionally known hanger-type die head.

[0123] By supplying particles to a melt extruder, a resin composition in a molten state is obtained. After the resin composition in the molten state is metered by a gear pump, it is discharged in the form of a film through a die.

[0124] The resin composition discharged in the form of a film from the die is cast onto a casting roll, and while being drawn, the resin composition is cooled to form a raw roll film. This raw roll film can be used as an optical film. It should be noted that when casting onto the casting roll, it can also be carried out by sandwiching the resin composition between an elastic roll and the casting roll.

[0125] Next, the raw roll film can be drawn by a drawing machine while being conveyed by rolls. The drawing of the raw roll film can be uniaxial drawing or biaxial drawing. The biaxial drawing can be sequential biaxial drawing in which the longitudinal drawing and the transverse drawing of the film are carried out separately, or simultaneous biaxial drawing in which the longitudinal drawing and the transverse drawing are carried out simultaneously.

[0126] When drawing the film, the drawing temperature of the film is near the glass transition temperature Tg of the resin composition, preferably (Tg - 30)°C to (Tg + 100)°C.

[0127] The drawing speed of the film is preferably 10 to 20000% / minute.

[0128] The drawing ratio of the film is preferably 1.1 to 25 times. The drawing ratio refers to the area ratio of the film before and after drawing. For example, in the case of uniaxial drawing, it refers to its drawing ratio, and in the case of biaxial drawing, it refers to the product of the drawing ratio in the longitudinal direction and the drawing ratio in the transverse direction.

[0129] The optical film obtained as above is wound by a winder to form a film roll.

[0130] The optical film contains resin. Here, when the particles supplied for the manufacture of the optical film are manufactured by a first method equivalent to the conventional method, at least a part of the resin constituting the optical film is derived from a masterbatch. The part derived from the masterbatch has at least one more high-temperature thermal history than the part not derived from the masterbatch, and sometimes deteriorates. This deterioration may deteriorate the optical properties such as the internal haze of the optical film. In contrast, when the particles supplied for the manufacture of the optical film are manufactured by a second method, the particles supplied for the manufacture of the optical film are manufactured without using a masterbatch, so the number of high-temperature thermal histories of the resin constituting the optical film can be reduced. This may be the main reason for improving the internal haze etc. of the optical film obtained from the particles. Therefore, it is preferable to supply the particles manufactured by the second method to the melt extruder for optical film manufacture to obtain an optical film.

[0131] Optical films can be made into, for example, protective films, polarizer protective films, and cover films. For example, a polarizer protective film can be used in the manufacture of a polarizing plate, and the polarizing plate can be used in the manufacture of an image display device. Therefore, the present disclosure also includes a polarizer protective film obtained from the particles of the present embodiment, a polarizing plate including the polarizer protective film, and an image display device including the polarizing plate.

[0132] Examples

[0133] First, a method for evaluating the particles will be described.

[0134] (1) Weight-average molecular weight and number-average molecular weight

[0135] The weight-average molecular weight and number-average molecular weight are determined by gel permeation chromatography (GPC) and converted to polystyrene equivalents. The measuring apparatus and measuring conditions are as described below.

[0136] - System: GPC system HLC-8220 manufactured by TOSOH Corporation.

[0137] - Composition of the measurement side columns.

[0138] Guard column: TSKgel guardcolumn SuperHZ-L manufactured by TOSOH Corporation.

[0139] Separation columns: Two TSKgel SuperHZM-M columns manufactured by TOSOH Corporation connected in series.

[0140] - Composition of the reference side columns.

[0141] Reference column: TSKgel SuperH-RC manufactured by TOSOH Corporation.

[0142] - Developing solvent: Chloroform (manufactured by FUJIFILM Wako Pure Chemical Corporation, special grade).

[0143] - Flow rate of the developing solvent: 0.6 mL / minute.

[0144] - Standard sample: TSK standard polystyrene (manufactured by TOSOH Corporation, PS-Oligomer Kit).

[0145] - Column temperature: 40°C.

[0146] (2) Glass transition temperature

[0147] The glass transition temperature was measured according to the provisions of Japanese Industrial Standard (JIS) K 7121. Using a differential scanning calorimeter (manufactured by Rigaku Corporation; Thermo plus EVO DSC-8230), the DSC curve obtained by heating approximately 10 mg of the sample from room temperature to 200 °C (heating rate: 20 °C / min) in a nitrogen atmosphere was used to determine the glass transition temperature by the starting point method. α-aluminum oxide was used as the reference.

[0148] (3) Internal haze

[0149] The internal haze was measured according to the provisions of Japanese Industrial Standard (JIS) K 7136. The particles were hot-pressed at 250 °C for 3 minutes to produce a film with a thickness of 160 μm (unstretched film). Using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.; NDH-5000), the internal haze was measured in the following order.

[0150] (i) A film with a size of 45 mm × 35 mm and tetralin were placed in a quartz cell with an optical path length of 10 mm, and the haze value was measured.

[0151] (ii) Two films were stacked and the measurement in (i) was performed.

[0152] (iii) Three films were stacked and the measurement in (i) was performed.

[0153] (iv) Based on the measurement results in (i) to (iii), the equation representing the relationship between the film thickness and the internal haze was obtained by the least squares method. According to this equation, the internal haze value of a film with a thickness of 100 μm was calculated.

[0154] (4) Internal b* value

[0155] The internal b* value was measured according to the provisions of Japanese Industrial Standard (JIS) Z 8729. The particles were hot-pressed at 250 °C for 3 minutes to produce a film with a thickness of 160 μm (unstretched film). Using a spectrophotometric color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd.; Colormeter ZE6000), the internal b* value was measured in the following order.

[0156] (i) A film with a size of 45 mm × 35 mm and tetralin were placed in a quartz cell with an optical path length of 10 mm, and the b* value was measured.

[0157] (ii) Two films were stacked and the measurement in (i) was performed.

[0158] (iii) Three films were stacked and the measurement in (i) was performed.

[0159] (iv) Based on the measurement results of (i) to (iii), an equation representing the relationship between the film thickness and the internal b* value is obtained by the least squares method. The internal b* value of a film with a thickness of 100 μm is calculated according to this equation.

[0160] (5) Slip property

[0161] The slip property is measured according to the provisions of Japanese Industrial Standard (JIS) K 7125.

[0162] The pellets are extruded from a T-die using a single-screw extruder at a die temperature of 250 °C to obtain an unstretched film. The unstretched film is stretched two times longitudinally and two times transversely at a specified temperature to produce a stretched film with a thickness of 40 μm. The specified temperature is set to the glass transition temperature Tg + 20 °C of the resin composition constituting the film.

[0163] The film is cut to obtain a lower film with a size of 60 mm × 80 mm and an upper film with a size of 25 mm × 45 mm. An auxiliary plate is assembled on the short side of the upper film.

[0164] Next, the lower film is fixed on a Teflon plate (Teflon is a registered trademark of Chemours Company) with a horizontal surface. The upper film is placed on the lower film. Further, a cylindrical weight (100 g, diameter 25 mm) with a 2-mm-thick cushioning material attached is placed on the upper film. In this state, a spring scale is assembled on the auxiliary plate and stretched horizontally at a speed of 100 mm / min. The maximum load shown by the spring scale from the start of stretching the spring scale until the moment the weight starts to move, that is, the moment the films start to slide against each other, is recorded as the index of "slip property". The higher the slip property of the film surface, the smaller the maximum load.

[0165] (6) Number of foreign substances

[0166] 5 g of the pellets are dissolved in 100 mL of chloroform, and the number of foreign substances with a major axis of 20 μm or more is measured using a particle counter (manufactured by Pamas; model: SVSS-C, sensor specification: HCB-LD-50 / 50). The number of foreign substances is converted to the number per 1 g of the pellets.

[0167] (7) Average primary particle size

[0168] Using a precision particle size distribution measuring device (manufactured by Beckman Coulter, Inc.; Coulter Multisizer III), the particle sizes of 30,000 (meth)acrylic acid crosslinked particles were measured, and the average primary particle size based on the number was determined. When the measurement result is 1.0 μm or more, this value is adopted. When the measurement result is less than 1.0 μm, this value is not adopted, and instead, a laser diffraction / scattering type particle size distribution measuring device (manufactured by HORIBA, Ltd.; LA-920) is used to measure the particle size of the particles, and the average primary particle size based on the number is determined, and this value is adopted. Therefore, the average primary particle size shown in Table 1 is the average primary particle size obtained by the Coulter method when the value is 1.0 μm or more, and the average primary particle size obtained by the laser diffraction / scattering method when the value is less than 1.0 μm. The average primary particle size based on the number refers to the arithmetic mean particle size.

[0169] (8) Ratio of elastic modulus

[0170] The particles were hot-pressed at 250 °C for 3 minutes to produce a film with a thickness of 160 μm (unstretched film). The obtained film was measured at room temperature using an atomic force microscope (AFM) (manufactured by Buruker; Dimension Icon). A cantilever with a spring constant of 40 N / m was used in the calculation of the elastic modulus. In the force curve array mode, observation was carried out under the conditions of a frequency of 5 Hz, a maximum load of 30 nN, and a measurement range of 3 μm × 3 μm. The cross-section of the optical film was measured, and the average elastic modulus E1 of the part without particles and the average elastic modulus E2 of the part with particles were calculated from the obtained elastic modulus mapping image, and the ratio (E2 / E1) was obtained. The elastic modulus was calculated by fitting the force curve obtained by the force curve array measurement using the DMT mechanical model. It should be noted that the average elastic modulus E1 was set as: determining three parts without particles, and taking the average of the elastic moduli measured at each part. The average elastic modulus E2 was set as: determining three parts with particles, and taking the average of the elastic moduli measured at each part.

[0171] <Production of (meth)acrylic acid crosslinked particles (P1)>

[0172] Into a reaction vessel equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 523 parts by mass of deionized water in which 3.6 parts by mass of ammonium polyoxyethylene diphenyl vinyl phenyl ether sulfate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; HITENOL (registered trademark) NF-08) is dissolved was charged. 252 parts by mass of methyl methacrylate, 108 parts by mass of ethylene glycol dimethacrylate, 3.6 parts by mass of lauroyl peroxide, and 1.208 parts by mass of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (manufactured by BASF Japan Ltd.; Irganox (registered trademark) 1010) which were prepared in advance were charged therein, and using a stirrer (manufactured by PRIMIX Corporation; Homomixer MARK II model 2.5), it was stirred at 8500 rpm for 5 minutes. Then, 900 parts by mass of deionized water was added.

[0173] Next, while blowing nitrogen, it was heated until the reaction solution reached 65°C, and the reaction vessel was kept warm at 65°C. Based on the time point when the liquid temperature reached 75°C due to self-heating, after continuously stirring at 75°C for 1.5 hours, the reaction solution was cooled to 50°C or lower, and filtered to collect the polymerization product. Using a hot air dryer (manufactured by Yamato Scientific Co., Ltd.; DN401), the polymerization product was dried at 80°C for 15 hours or more to obtain organic fine particles. The obtained organic fine particles were aggregated by drying. Using a pulverizer (manufactured by Nisshin Engineering Co., Ltd.; Super Jet Mill SJ-500), the organic fine particles were pulverized at a pulverization pressure of 0.3 MPa at room temperature. Thus, non-aggregated (meth)acrylic acid crosslinked particles (P1) were obtained. The refractive index of the (meth)acrylic acid crosslinked particles (P1) was 1.505, and the average primary particle diameter was 2.0 μm.

[0174] <Production of (meth)acrylic acid crosslinked particles (P2)>

[0175] Based on the description of Example 2 in Japanese Patent Publication No. 6348312, (meth)acrylic acid crosslinked particles (P2) having a core-shell structure were obtained. The core part of the (meth)acrylic acid crosslinked particles (P2) was formed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate, and the shell part was formed of a copolymer of styrene and divinylbenzene. The refractive index of the (meth)acrylic acid crosslinked particles (P2) was 1.510, and the average primary particle diameter was 1.2 μm.

[0176] <Production of (meth)acrylic acid crosslinked particles (P3)>

[0177] The (meth)acrylic acid crosslinked particles (P2) were classified using a vortex air classifier (manufactured by Nisshin Engineering Co., Ltd.; Aerofine classifier AC-20) to obtain (meth)acrylic acid crosslinked particles (P3). The refractive index of the (meth)acrylic acid crosslinked particles (P3) was 1.510, and the average primary particle size was 0.8 μm.

[0178] <Production of (meth)acrylic acid crosslinked particles (P4)>

[0179] 523 parts by mass of deionized water in which 3.6 parts by mass of ammonium polyoxyethylene diphenyl vinyl phenyl ether sulfate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; HITENOL (registered trademark) NF-08) was dissolved was charged into a reaction vessel equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe. 252 parts by mass of methyl methacrylate, 108 parts by mass of ethylene glycol dimethacrylate, 3.6 parts by mass of lauroyl peroxide as a polymerization initiator, and 1.208 parts by mass of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (manufactured by BASF Japan Ltd.; Irganox (registered trademark) 1010) were charged therein, and the mixture was stirred at 8000 rpm for 60 minutes using an emulsifying disperser milder (manufactured by Taiheiyo Kiko Co., Ltd.; MDN). Then, 900 parts by mass of deionized water was added.

[0180] Next, while blowing nitrogen, the mixture was heated until the reaction solution reached 65°C, and the reaction vessel was kept at 65°C. Based on the time point when the liquid temperature reached 75°C due to self-heating, after continuously stirring at 75°C for 1.5 hours, the reaction solution was cooled to 50°C or lower, and filtration was performed to collect the polymerization product. The polymerization product was dried at 80°C for 15 hours or more using a hot air dryer (manufactured by Yamato Scientific Co., Ltd.; DN401) to obtain organic fine particles. The obtained organic fine particles were aggregated by drying. The organic fine particles were pulverized at room temperature at a pulverization pressure of 0.3 MPa using a pulverizer (manufactured by Nisshin Engineering Co., Ltd.; Super Jet Mill SJ-500). Thus, non-aggregated (meth)acrylic acid crosslinked particles (P4) were obtained. The refractive index of the (meth)acrylic acid crosslinked particles (P4) was 1.505, and the average primary particle size was 0.5 μm.

[0181] <Production of (meth)acrylic acid crosslinked particles (P5)>

[0182] 710 parts by mass of deionized water and 1.5 parts by mass of sodium lauryl sulfate were put into a reaction vessel equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe and dissolved, and the internal temperature was raised to 70 °C. Then, a mixed solution of 0.93 parts by mass of sodium formaldehyde sulfoxylate, 0.001 parts by mass of ferrous sulfate, 0.003 parts by mass of disodium ethylenediaminetetraacetate, and 20 parts by mass of deionized water was put into the above polymerization vessel at once, and the inside of the reaction vessel was sufficiently replaced with nitrogen.

[0183] The monomer mixture (M-1) (7.10 parts by mass of n-butyl acrylate, 2.86 parts by mass of styrene, 0.02 parts by mass of 1,4-butanediol dimethacrylate, 0.02 parts by mass of allyl methacrylate) and the polymerization initiator solution (I-1) (0.13 parts by mass of tert-butyl hydroperoxide, 10.0 parts by mass of deionized water) were added to the above polymerization vessel at once and polymerized for 60 minutes.

[0184] Then, while dropping the monomer mixture (M-2) (63.90 parts by mass of n-butyl acrylate, 25.20 parts by mass of styrene, 0.9 parts by mass of allyl methacrylate) and the polymerization initiator solution (I-2) (0.246 parts by mass of tert-butyl hydroperoxide, 20.0 parts by mass of deionized water) over 90 minutes respectively, polymerization was carried out. After the dropping was completed, polymerization was continued for 60 minutes.

[0185] Then, while dropping the monomer mixture (M-3) (73.0 parts by mass of styrene, 27.0 parts by mass of acrylonitrile) and the polymerization initiator solution (I-3) (0.27 parts by mass of tert-butyl hydroperoxide, 20.0 parts by mass of deionized water) over 100 minutes respectively, polymerization was carried out. After the dropping was completed, the internal temperature was raised to 80 °C and polymerization was continued for 120 minutes.

[0186] After cooling to an internal temperature of 40 °C, it was passed through a 300-mesh metal screen to obtain an emulsion polymerization liquid of a rubbery polymer. The emulsion polymerization liquid was salted out and solidified with calcium chloride, washed with water, and dried to obtain (meth)acrylic crosslinked particles (P5). The refractive index of the (meth)acrylic crosslinked particles (P5) was 1.520, and the average primary particle size was 0.1 μm.

[0187] <Production of masterbatch (MB-RC1-P1)>

[0188] Based on the description of Example 1 in Japanese Patent Laid-Open No. 2021-172821, a (meth)acrylic resin (RC1) containing a lactone ring structural unit was obtained. The weight-average molecular weight of the (meth)acrylic resin particles (RC1) was 132,000, the number-average molecular weight was 50,000, and the glass transition temperature was 122°C. Next, 100 parts by mass of the (meth)acrylic resin particles (RC1) and 1 part by mass of (meth)acrylic crosslinked particles (P1) were melt-kneaded at 270°C using a twin-screw extruder (manufactured by Ikegai Corporation; PCM37) to obtain a masterbatch (MB-RC1-P1) containing (meth)acrylic crosslinked particles.

[0189] <Preparation of Masterbatch (MB-RC1-S1)>

[0190] 100 parts by mass of the (meth)acrylic resin particles (RC1) and 1 part by mass of silica particles (S1) (manufactured by Nippon Shokubai Co., Ltd.; SEAHOSTAR KE-P30, average primary particle diameter 0.3 μm, refractive index 1.43) were melt-kneaded at 270°C using a twin-screw extruder (manufactured by Ikegai Corporation; PCM37) to obtain a masterbatch (MB-RC1-S1) containing (meth)acrylic crosslinked particles.

[0191] <Preparation of Masterbatch (MB-RC1-P5)>

[0192] 100 parts by mass of the (meth)acrylic resin particles (RC1) and 1 part by mass of (meth)acrylic crosslinked particles (P5) were melt-kneaded at 270°C using a twin-screw extruder (manufactured by Ikegai Corporation; PCM37) to obtain a masterbatch (MB-RC1-P5) containing (meth)acrylic crosslinked particles.

[0193] (Example 1)

[0194] 83.5 parts by mass of methyl methacrylate, 12 parts by mass of methyl 2-(hydroxymethyl)acrylate, 88.7 parts by mass of toluene, and 0.05 part by mass of tris(2,4-di-tert-butylphenyl)phosphite (manufactured by ADEKA Corporation; ADK STAB (registered trademark) 2112) as an antioxidant were charged into a reaction vessel equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe. Nitrogen was introduced and the temperature was raised to 105°C. When reflux started with the temperature rise, 0.435 part by mass of a toluene solution (manufactured by ARKEMA Yoshitomi Corporation; Lupelox (registered trademark) 570T20) in which the concentration of tert-amyl peroxyisononanoate as a polymerization initiator was 20% by mass was added. Next, a solution composed of 4.5 parts by mass of styrene and 0.15 part by mass of n-dodecyl mercaptan was added dropwise over 2 hours. Further, 0.865 part by mass of a toluene solution in which the concentration of tert-amyl peroxyisononanoate was 20% by mass was added dropwise over 4 hours. During the addition thereof, the mixture was refluxed at about 105 to 110°C to carry out solution polymerization. After the addition was completed, aging was further carried out at the same temperature for 2 hours.

[0195] 0.075 part by mass of stearyl phosphate (manufactured by SC Organic Chemistry Co., Ltd.; Phoslex A-18) was added to the obtained polymerization solution, and a cyclization condensation reaction for forming a lactone ring structure was carried out under reflux at about 90 to 110°C for 2 hours. The obtained polymerization solution was passed through a multitubular heat exchanger heated to 240°C to complete the cyclization condensation reaction.

[0196] The obtained polymerization solution was introduced into an exhaust-type twin-screw extruder (L / D = 52) at an input rate of 100 parts by mass / hour in terms of resin amount for devolatilization. The exhaust-type twin-screw extruder has one rear exhaust port, four front exhaust ports (referred to as the first exhaust port, the second exhaust port, the third exhaust port, and the fourth exhaust port from the upstream side), and a side feeder located between the third exhaust port and the fourth exhaust port, and a disk-type polymer filter (filtration accuracy 10 μm) and an extrusion die head are arranged at the front end. The barrel temperature was set to 250°C, the degree of vacuum reduction of the rear exhaust port was set to 798 hPa, the degree of vacuum reduction of the first exhaust port was set to 266 hPa, and the degree of vacuum reduction from the second exhaust port to the fourth exhaust port was set to 27 hPa to carry out devolatilization. Further, (meth)acrylic acid crosslinked particles (P1) were introduced from the side feeder at an input rate of 0.10 part by mass / hour, and ion-exchanged water was introduced from the downstream of each of the second exhaust port, the third exhaust port, and the fourth exhaust port at an input rate of 1.5 parts by mass / hour. Thereby, the (meth)acrylic resin (R1) containing a lactone ring structure unit and the (meth)acrylic acid crosslinked particles (P1) were kneaded.

[0197] After devolatilization, the (meth)acrylic resin composition is extruded from an extrusion die after passing through a polymer filter. The extruded (meth)acrylic resin composition is immersed in cooling water to obtain a strand of the (meth)acrylic resin composition. The above cooling water is filtered through a filter with a pore size of 1 μm (manufactured by Organo Corporation; micropore filter 1EU) and maintained at a temperature within the range of 30 ± 10°C. The cooled strand is introduced into a granulator to obtain particles (1) of the resin composition. The weight-average molecular weight of the (meth)acrylic resin (R1) contained in the particles (1) is 133,000, and the number-average molecular weight is 52,000.

[0198] (Example 2)

[0199] Instead of the (meth)acrylic crosslinked particles (P1), the (meth)acrylic crosslinked particles (P2) are introduced from a side feeder, and otherwise, particles (2) of the resin composition are obtained by the same method as in Example 1.

[0200] (Example 3)

[0201] The (meth)acrylic resin containing a glutarimide structural unit (manufactured by Polyplastics Evonik Corporation; PLEXIMID (registered trademark) TT50) is introduced into a twin-screw extruder (L / D = 30) at an input rate of 100 parts by mass per hour. The twin-screw extruder is equipped with a side feeder and a vent port, and a disk-type polymer filter (filtration accuracy 10 μm) is arranged at the front end. The barrel temperature is set to 270°C. In addition, the (meth)acrylic crosslinked particles (P1) are introduced from the side feeder at an input rate of 0.10 parts by mass per hour. Thus, the (meth)acrylic resin (R2) containing a glutarimide structural unit and the (meth)acrylic crosslinked particles (P1) are kneaded.

[0202] The (meth)acrylic resin composition is extruded from an extrusion die after passing through a polymer filter. The extruded (meth)acrylic resin composition is immersed in cooling water to obtain a strand of the (meth)acrylic resin composition. The above cooling water is filtered through a filter with a pore size of 1 μm (manufactured by Organo Corporation; micropore filter 1EU) and maintained at a temperature within the range of 30 ± 10°C. The cooled strand is introduced into a granulator to obtain particles (3) of the resin composition. The weight-average molecular weight of the (meth)acrylic resin (R2) contained in the particles (3) is 97,000, and the number-average molecular weight is 44,000.

[0203] (Example 4)

[0204] A solution obtained by dissolving 0.66 parts by mass of 2,4,6-tris[4-(hexyloxy)-2-hydroxy-3-methylphenyl]-1,3,5-triazine (manufactured by ADEKA Corporation; ADK STAB (registered trademark) LA-F70) as an ultraviolet absorber in 1.23 parts by mass of toluene was introduced from the downstream of the third exhaust port at an input rate of 1.89 parts by mass per hour, and ion-exchanged water was introduced from the downstream of the second and fourth exhaust ports at an input rate of 1.5 parts by mass per hour. Except for this, particles (4) of the resin composition were obtained by the same method as in Example 1.

[0205] (Example 5)

[0206] (Meth)acrylic acid crosslinked particles (P3) were introduced from the side feeder at an input rate of 0.08 parts by mass per hour instead of (meth)acrylic acid crosslinked particles (P1). Except for this, particles (5) of the resin composition were obtained by the same method as in Example 1.

[0207] (Example 6)

[0208] (Meth)acrylic acid crosslinked particles (P4) were introduced from the side feeder at an input rate of 0.06 parts by mass per hour instead of (meth)acrylic acid crosslinked particles (P1). Except for this, particles (6) of the resin composition were obtained by the same method as in Example 1.

[0209] (Example 7)

[0210] Masterbatch (MB-RC1-P1) was introduced from the side feeder at an input rate of 10 parts by mass per hour instead of (meth)acrylic acid crosslinked particles (P1). Except for this, particles (7) of the resin composition were obtained by the same method as in Example 1.

[0211] (Comparative Example 1)

[0212] Silica particles (S1) were introduced from the side feeder instead of (meth)acrylic acid crosslinked particles (P1). Except for this, particles (1C) of the resin composition were obtained by the same method as in Example 1.

[0213] (Comparative Example 2)

[0214] The anti-blocking agent was not kneaded with the (meth)acrylic resin. Except for this, particles (2C) of the resin composition were obtained by the same method as in Example 1.

[0215] (Comparative Example 3)

[0216] The masterbatch (MB-RC1-S1) was introduced from the side feeder at an input rate of 10 parts by mass per hour to replace the (meth)acrylic acid crosslinked particles (P1). Except for this, the resin composition particles (3C) were obtained by the same method as in Example 1.

[0217] (Comparative Example 4)

[0218] The masterbatch (MB-RC1-P5) was introduced from the side feeder at an input rate of 10 parts by mass per hour to replace the (meth)acrylic acid crosslinked particles (P1). Except for this, the resin composition particles (4C) were obtained by the same method as in Example 1.

[0219] For the particles of each example and each comparative example, the above-mentioned glass transition temperature, internal haze, internal b* value, slipperiness, number of foreign matters, and elastic modulus were measured. The compositions and measurement results of the particles are shown in Table 1. It should be noted that in Table 1, the (meth)acrylic acid crosslinked particles having a core-shell structure are denoted as core-shell type crosslinked particles.

[0220] [Table 1]

[0221]

[0222] As shown in the results of Comparative Example 2, in the case of not containing an anti-blocking agent, the slipperiness deteriorated significantly.

[0223] As shown in the results of Examples 1 to 7, when using (meth)acrylic acid crosslinked particles as the anti-blocking agent and the ratio (E2 / E1) is 0.90 or more, the internal haze shows an excellent value of 0.35% or less. On the other hand, as shown in the results of Comparative Example 1, Comparative Example 3, and Comparative Example 4, when using silica particles as the anti-blocking agent, or even when using (meth)acrylic acid crosslinked particles and the ratio (E2 / E1) is less than 0.90, the internal haze shows a poor value exceeding 0.35%.

[0224] In particular, as shown in the results of Examples 1 to 7 and Comparative Example 4, it is revealed that using only (meth)acrylic acid crosslinked particles as the anti-blocking agent is insufficient, and it is necessary to make the ratio (E2 / E1) large enough.

[0225] As shown in the results of Examples 1 to 6, in the case of adopting the second method, the internal haze shows a more excellent value of 0.30% or less.

[0226] As shown in the results of Example 2 and Example 5, in the case of adopting the second method and using core-shell type (meth)acrylic acid crosslinked particles as the anti-blocking agent, the internal haze shows an even more excellent value of 0.10% or less.

[0227] As shown in the results of Example 3, even when the type of (meth)acrylic resin, which is the main component of the film, is changed, the internal haze shows a good value. As shown in Example 4, even when an ultraviolet absorber is used, the internal haze shows a good value.

[0228] Meanwhile, the difference between the first method and the second method was studied. As shown in the results of Example 1 and Comparative Example 1, it was found that when the second method was adopted, the internal haze could be reduced. In addition, it was found that the internal b* value could be reduced and the number of foreign matters could be decreased. It should be noted that the difference between the first method and the second method lies in the number of times of the high-temperature heat history. Therefore, even when the ratio (E2 / E1) is less than 0.90, if the second method is adopted, it can be expected that the internal haze can be reduced.

[0229] On the other hand, as shown in the results of Comparative Example 1 and Comparative Example 2, when silica particles are used as the anti-blocking agent, even if the second method is adopted, the internal haze cannot be improved.

Claims

1. A particle, characterized in that, the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, and the (meth)acrylic resin contains a ring structure unit having a ring structure in the main chain, the average elastic modulus E1 of the part where the (meth)acrylic acid crosslinked particles do not exist and the average elastic modulus E2 of the part where the (meth)acrylic acid crosslinked particles exist satisfy the following formula (1), Formula (1): 0.90 ≤ E2 / E1.

2. A particle, characterized in that, the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, and the (meth)acrylic resin contains a ring structure unit having a ring structure in the main chain, when formed into a film by hot pressing at 250°C for 3 minutes, the internal haze of the film is 0.35% or less in terms of a thickness of 100 μm.

3. The particle according to claim 1 or 2, characterized in that, when formed into a film by hot pressing at 250°C for 3 minutes, the internal haze of the film is 0.30% or less in terms of a thickness of 100 μm.

4. The particle according to claim 3, characterized in that, when formed into a film by hot pressing at 250°C for 3 minutes, the internal haze of the film is 0.10% or less in terms of a thickness of 100 μm.

5. The particle according to claim 1 or 2, characterized in that, the average primary particle size of the (meth)acrylic acid crosslinked particles is 0.5 to 2.0 μm.

6. The particle according to claim 1 or 2, characterized in that, when the content of the (meth)acrylic resin is set to 100 parts by mass, the content of the (meth)acrylic acid crosslinked particles is 0.01 to 0.20 parts by mass.

7. The particle according to claim 1 or 2, characterized in that, the (meth)acrylic acid crosslinked particles have a core part containing a (meth)acrylic acid crosslinked resin and a shell part containing a styrene crosslinked resin.

8. The particle according to claim 1 or 2, characterized in that, the ring structure unit contains at least one selected from the group consisting of an N-substituted maleimide structure unit, a glutarimide structure unit, and a lactone ring structure unit.

9. The particle according to claim 1 or 2, characterized in that, the number of foreign matters having a major axis of 20 μm or more measured by a particle counter is 20 pieces / g or less.

10. A method for manufacturing a particle, characterized in that, the particle contains a (meth)acrylic resin and (meth)acrylic acid crosslinked particles, and the (meth)acrylic resin contains a ring structure unit having a ring structure in the main chain, the method for manufacturing the particle includes: a first step of obtaining the (meth)acrylic resin in a flowing state; and a second step of kneading the (meth)acrylic resin in the flowing state obtained in the first step with the (meth)acrylic acid crosslinked particles to obtain a (meth)acrylic resin composition, wherein the (meth)acrylic acid crosslinked particles are kneaded with the resin constituting the particle for the first time in the second step.

11. The method for manufacturing a particle according to claim 10, characterized in that, From after the first step to the second step, the temperature of the (meth)acrylic resin in a flowing state is maintained at 240°C or higher and 320°C or lower.

12. The method for producing particles according to claim 10, wherein: it further includes: a third step of passing the (meth)acrylic resin composition through a filter.

13. A method for producing particles, wherein: the particles contain a (meth)acrylic resin and (meth)acrylic crosslinked particles, and the (meth)acrylic resin contains a ring structure unit having a ring structure in the main chain, the method for producing the particles includes: a synthesis step of synthesizing the (meth)acrylic resin from raw materials; and a devolatilization step of subjecting the (meth)acrylic resin obtained in the synthesis step to devolatilization by feeding it to an extruder equipped with a side feeder and an exhaust port, in the devolatilization step, powder of the (meth)acrylic crosslinked particles is fed from the side feeder to the extruder to obtain a (meth)acrylic resin composition containing the (meth)acrylic resin and the (meth)acrylic crosslinked particles, after the devolatilization step, the (meth)acrylic resin composition is extruded from the extruder to obtain particles.

14. The method for producing particles according to claim 10 or 13, wherein: the average primary particle diameter of the (meth)acrylic crosslinked particles is 0.5 to 2.0 μm.

15. The method for producing particles according to claim 10 or 13, wherein: 0.01 to 0.20 parts by mass of the (meth)acrylic crosslinked particles are kneaded with respect to 100 parts by mass of the (meth)acrylic resin.

16. The particles according to claim 10 or 13, wherein: the (meth)acrylic crosslinked particles have a core portion containing a (meth)acrylic crosslinked resin and a shell portion containing a styrene crosslinked resin.

17. The particles according to claim 10 or 13, wherein: the ring structure unit includes at least one selected from the group consisting of an N-substituted maleimide structure unit, a glutarimide structure unit, and a lactone ring structure unit.

18. A method for producing an optical film, wherein: the particles obtained by the method for producing particles according to claim 10 or 13 are fed to a melt extruder for producing an optical film to obtain an optical film.

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