WO2020027082A1

WO2020027082A1 - Optical film, protective film for polarizing plates, optical film roll, and method for producing optical film

Info

Publication number: WO2020027082A1
Application number: PCT/JP2019/029732
Authority: WO
Inventors: 森田　亮
Original assignee: コニカミノルタ株式会社
Priority date: 2018-07-31
Filing date: 2019-07-30
Publication date: 2020-02-06
Also published as: KR102496408B1; JP7452421B2; JPWO2020027082A1; KR20210022722A; CN112513698A; CN112513698B

Abstract

An optical film according to the present invention comprises a (meth)acrylic resin having a glass transition temperature of 110°C or higher and rubber particles. In a cross section of the optical film, the average aspect ratio of the rubber particles is 1.2 to 3.0, at least three among the rubber particles are connected contiguously in the direction of the longer diameters of the rubber particles, the particle-particle distance of the contiguous rubber particles fall within the range of 100 nm or less, and the ratio of the number of the contiguous rubber particles to the total number of the rubber particles contained in the optical film is 15% or more.

Description

Optical film, polarizing plate protective film, roll of optical film, and method for producing optical film

The present invention relates to an optical film, a polarizing plate protective film, a roll of an optical film, and a method for producing an optical film.

偏光 Polarizing plates are used in display devices such as liquid crystal display devices and organic EL display devices. The polarizing plate has a polarizer and a polarizing plate protective film.

Conventionally, a film containing cellulose acylate as a main component has been used as a polarizing plate protective film. However, since a film containing cellulose acylate as a main component has low moisture resistance, when it is used as a polarizing plate, the deterioration of a polarizer due to moisture under high temperature and high humidity may not be sufficiently suppressed. Therefore, it has been studied to use a film mainly composed of a thermoplastic resin having excellent moisture resistance instead of a film mainly composed of cellulose acylate.

Patent Document 1 discloses a maleimide-based copolymer resin film including a maleimide-based copolymer resin and a rubbery polymer having a polymer chain compatible with the same. It is shown that the rubbery polymer has an aspect ratio of 2 or less. The film of the maleimide-based copolymer resin alone is brittle, but the brittleness can be improved by including the rubbery polymer, and the rubbery polymer has a polymer chain compatible with the resin, so that it can be stretched during stretching. It is said that a decrease in the transparency of the film due to the formation of voids at the interface between the resin and the rubbery polymer can be suppressed.

JP 2006-124435 A

By the way, an optical film such as a polarizing plate protective film is usually formed into a long film, wound up in a roll shape, and stored and transported as a roll body. The winding of a long film is usually performed while applying tension. For this reason, the optical film to be wound is easily applied with a stretching force in the longitudinal direction and a contracting force in the width direction due to the winding tension. As a result, a force (stress) that tends to contract in the longitudinal direction and a force (stress) that tends to expand in the width direction are likely to be generated in the optical film of the roll immediately after winding. In addition, a force (stress) that tends to contract in the longitudinal direction easily causes transfer by the winding core due to tightening; a force (stress) that tends to expand in the width direction may cause a chain-shaped failure.

転写 The transfer of the winding core is a planar defect, and is easily formed inside the winding in the longitudinal direction of the film (a portion close to the winding core at the beginning of winding). The chain-like failure is a chain-like defect, and is easily formed over the entire film in the width direction.

In order to reduce the transfer of the winding core and the chain-shaped failure, it is desired that the rubber particles can effectively reduce the stress remaining on the optical film immediately after winding. In order to effectively relieve the stress by the rubber particles, it is desired that the particle size of the rubber particles is large. However, if the particle size of the rubber particles is too large, the haze of the film increases, and the transparency tends to be impaired. Therefore, it is desired to be able to suppress winding defects such as transfer of a winding core and chain-like defects without increasing the haze of the optical film, that is, without significantly increasing the particle size of the rubber particles.

Especially, as display devices become larger and thinner, there is a demand for wider and thinner optical films such as polarizing plate protective films. In such a wide and thin optical film, a winding failure is particularly likely to occur.

The present invention has been made in view of the above circumstances, and is a film containing a (meth) acrylic resin as a main component, in which the brittleness is satisfactorily improved without impairing the transparency and the winding failure is suppressed. It is an object of the present invention to provide an optical film, a polarizing plate protective film, a roll of an optical film, and a method for producing an optical film.

The above problem can be solved by the following configuration.

The optical film of the present invention includes a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher and rubber particles, and the cross section of the optical film has an average aspect ratio of the rubber particles of 1.2 to 1.2. 3.0, wherein the major axes of three or more of the rubber particles are connected in the major axis direction, and the distance between the connected rubber particles is 100 nm or less, and the number of the connected rubber particles is 100 nm or less. Of the rubber particles contained in the optical film is 15% or more.

偏光 The polarizing plate protective film of the present invention includes the optical film of the present invention.

The roll body of the optical film of the present invention comprises a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher, and rubber particles, and the optical film wound in a direction perpendicular to the width direction thereof. In a roll body, in a cross section of the optical film, an average aspect ratio of the rubber particles is 1.2 to 3.0, and three or more rubber particles have major axes connected in the major axis direction. The distance between the rubber particles is 100 nm or less, and the ratio of the number of the continuous rubber particles to the total number of the rubber particles included in the optical film is 15% or more.

The method for producing an optical film of the present invention comprises the step of obtaining a dope containing a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher, rubber particles, and a solvent, and having a solid content of 15% by mass or less. And a step of casting the obtained dope on a support, followed by drying and peeling to obtain a film, and a step of stretching the film by 20% or more.

According to the present invention, it is possible to provide an optical film, a roll of an optical film, and a method for producing an optical film, in which the brittleness is satisfactorily improved without impairing the transparency and the winding failure can be suppressed.

FIG. 1 is a schematic cross-sectional view illustrating a dispersion state of rubber particles in a cross section of an optical film. FIG. 2A is an enlarged view of an area surrounded by a dotted line 2A in FIG. 1, and FIG. 2B is an enlarged view of an area surrounded by a dotted line 2B in FIG.

The present inventors have conducted intensive studies and found that an optical film containing a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher and rubber particles, and in which the rubber particles are dispersed in a specific dispersion structure, is obtained. It was found that the brittleness was satisfactorily improved without impairing the transparency, and that winding failure could be suppressed.

The specific dispersion structure specifically refers to a dispersion structure that satisfies the following 1) and 2) in the cross section of the optical film.
1) The average aspect ratio of the rubber particles is from 1.2 to 3.0. 2) The major axes of three or more rubber particles are continuous in the major axis direction, and the distance between the continuous rubber particles. Is 100 nm or less, and the ratio of the number of continuous rubber particles to the total number of rubber particles contained in the optical film (hereinafter, also referred to as “proximity ratio”) is 15% or more.

That is, when the average aspect ratio of the rubber particles is equal to or more than a certain value (requirement 1), since the rubber particles stretched by stretching are unstable, the rubber particles are restored to a stable original shape (true spherical shape). Easy to produce force. Thereby, the flat rubber particles can absorb and relieve the stress remaining in the optical film immediately after winding by the restoring force.
The effect of suppressing the winding failure due to the restoring force of the rubber particles can be obtained even if the direction of expansion and contraction of the film does not always match the direction of expansion and contraction of rubber (direction of restoring force) for suppressing it. This is considered to be because the rubber particles absorb the force when a certain force acts on the film and convert it into a restoring force (for example, restoring in the thickness direction), thereby exhibiting an effect.

In addition, since the structure in which three or more rubber particles are closely connected in the major axis direction is appropriately included (requirement 2), the stress remaining in the optical film immediately after winding is dispersed well. Can be eased. In particular, in a long and wide film, the stress (stretching force) remaining in the optical film tends to increase, and when the rubber particles are single and uniformly dispersed, the stress locally remaining in the optical film is increased. (Stretching force) may not be fully absorbed; when a plurality of rubber particles are close to each other, the optical film is used similarly to rubber particles having a relatively large particle size regardless of the longitudinal direction and the width direction. Can absorb the residual stress (stretching force).
It is considered that by these actions, the stress (stretching force) remaining on the optical film immediately after winding can be effectively reduced by the rubber particles without increasing the average major axis of the rubber particles.

Further, by appropriately including a structure in which three or more rubber particles are closely connected in the major axis direction (requirement 2), stress is more highly dispersed than a single particle having a large particle diameter. Therefore, the brittleness of the optical film can be improved to a high degree.

要件 The requirement of the above 1) can be adjusted by, for example, the solid content concentration of the dope at the time of film formation by the solution casting method and the stretching conditions (particularly the stretching ratio). In order to increase the average aspect ratio of the rubber particles, for example, it is preferable to lower the solid content of the dope, and it is preferable to increase the stretching ratio.

The requirements of the above 2) include, for example, the glass transition temperature (Tg) of the (meth) acrylic resin, the affinity (ΔSP, etc.) of the (meth) acrylic resin and the rubber particles, the solid concentration of the dope during film formation, It can be adjusted by the composition of the dispersion solvent of the rubber particle dispersion, the stretching ratio, and the like. In order to increase the proximity ratio of the rubber particles, for example, the glass transition temperature (Tg) of the (meth) acrylic resin is preferably set to 110 ° C. or higher, and the affinity (ΔSP) between the (meth) acrylic resin and the rubber particles is preferably increased. And the like), preferably the solid concentration of the dope is preferably low, the poor solvent is preferably added to the dispersion solvent of the rubber particle dispersion, and the stretching ratio is preferably high.

1. Optical Film The optical film of the present invention contains a (meth) acrylic resin and rubber particles.

1-1. (Meth) acrylic resin The glass transition temperature (Tg) of the (meth) acrylic resin is preferably 110 ° C. or higher. When the glass transition temperature (Tg) of the (meth) acrylic resin is 110 ° C. or higher, the rubber particles also move at the same stretching temperature because the glass transition temperature (Tg) is lower than that of the (meth) acrylic resin having a low glass transition temperature (Tg). Can be difficult. Thereby, since the rubber particles are not excessively diffused, the rubber particles can be appropriately brought close to each other. From the above viewpoint, the glass transition temperature (Tg) of the (meth) acrylic resin is preferably from 120 to 160 ° C., and more preferably from 125 to 150 ° C.

The glass transition temperature (Tg) of the (meth) acrylic resin can be measured by using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012.

ガラス The glass transition temperature (Tg) of the (meth) acrylic resin can be adjusted by the type and composition of the monomer. In order to increase the glass transition temperature (Tg) of the (meth) acrylic resin, for example, it is preferable to increase the content ratio of a copolymer monomer having a bulky structure described later.

The (meth) acrylic resin may be a homopolymer of a (meth) acrylic ester or a copolymer of a (meth) acrylic ester and a copolymerizable monomer copolymerizable therewith. . In addition, (meth) acryl means acryl or methacryl. The (meth) acrylate is preferably methyl methacrylate.

That is, the (meth) acrylic resin includes a structural unit derived from methyl methacrylate, and may further include a structural unit derived from a copolymer monomer other than methyl methacrylate (hereinafter, simply referred to as a “copolymer monomer”). preferable.

Examples of copolymerized monomers include:
Methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2- (meth) acrylate Ethylhexyl, octyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, dicyclo (meth) acrylate Acrylate or alkyl group having 1 to 20 carbon atoms in the alkyl group, such as pentanyl, isobornyl (meth) acrylate, adamantyl (meth) acrylate, cyclohexyl (meth) acrylate, and lactone (meth) acrylate Methacrylic esters having a number of 2 to 20;
Aromatic vinyls such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene;
Alicyclic vinyls such as vinylcyclohexane;
Unsaturated nitriles such as (meth) acrylonitrile and (meth) acrylonitrile-styrene copolymer;
Unsaturated carboxylic acids such as (meth) acrylic acid, crotonic acid, (meth) acrylic acid, itaconic acid, itaconic acid monoester, maleic acid and maleic acid monoester;
Olefins such as vinyl acetate, ethylene and propylene;
Vinyl halides such as vinyl chloride, vinylidene chloride and vinylidene fluoride;
(Meth) acrylamides such as (meth) acrylamide, methyl (meth) acrylamide, ethyl (meth) acrylamide, propyl (meth) acrylamide, butyl (meth) acrylamide, tert-butyl (meth) acrylamide, and phenyl (meth) acrylamide;
Unsaturated glycidyls such as glycidyl (meth) acrylate;
Maleimides such as N-phenylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, and No-chlorophenylmaleimide are included. These may be used alone or in combination of two or more.

Among them, a copolymer monomer having a bulky structure is preferable from the viewpoint of appropriately lowering the affinity for rubber particles while increasing the glass transition temperature (Tg) of the optical film.

Examples of copolymerized monomers having a bulky structure include:
(Meth) acrylic acid esters having a cyclo ring such as dicyclopentanyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, and cyclohexyl (meth) acrylate; Vinyls having; and a copolymer monomer selected from the group consisting of maleimides such as N-phenylmaleimide;
Copolymerized monomers such as (meth) acrylate having a branched alkyl group such as t-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are included.
Among them, copolymer monomers having a bulky structure are (meth) acrylates having a cyclo ring, copolymer monomers selected from the group consisting of maleimides, (meth) acrylates having a branched alkyl group, and the like. Is preferable, and a copolymer monomer selected from the group consisting of (meth) acrylates having a cyclo ring and maleimides is more preferable.

The content of the structural unit derived from the copolymerized monomer (preferably, the content of the structural unit derived from the copolymerized monomer having a bulky structure) is reduced to 100% by mass in total of the structural units constituting the (meth) acrylic resin. On the other hand, it is preferably 0 to 50% by mass, more preferably 10 to 40% by mass, and still more preferably 10 to 30% by mass. The type and composition of the monomer of the (meth) acrylic resin can be specified by ¹ H-NMR.

The weight average molecular weight Mw of the (meth) acrylic resin is preferably, for example, 200,000 to 2,000,000. When the weight average molecular weight Mw of the (meth) acrylic resin is in the above range, sufficient mechanical strength (toughness) is imparted to the film, and film formability is not easily impaired. From the above viewpoint, the weight average molecular weight Mw of the (meth) acrylic resin is more preferably from 300,000 to 2,000,000, and still more preferably from 500,000 to 2,000,000. The weight average molecular weight Mw can be measured by gel permeation chromatography (GPC) in terms of polystyrene.

1-2. Rubber Particles The rubber particles may have a function of forming irregularities on the surface of the optical film to impart slipperiness while imparting flexibility and toughness to the optical film.

1-2-1. About Shape of Rubber Particle The average aspect ratio of the rubber particle when observing the cross section of the optical film is preferably from 1.2 to 3.0. When the average aspect ratio of the rubber particles is 1.2 or more, stress (force to shrink) with respect to the stretching tension of the rubber particles is easily applied to the optical film immediately after winding, so that the stress remaining on the optical film is reduced. It is easy to suppress winding failure. When the average aspect ratio of the rubber particles is 3.0 or less, the number of contacts between adjacent rubber particles does not become too small, so that the effect of dispersing the stress remaining in the optical film is hardly impaired, and winding failure is suppressed. be able to. The average aspect ratio of the rubber particles is more preferably from 1.5 to 2.8, and even more preferably from 2.0 to 2.5.

The aspect ratio means the ratio (major axis / minor axis) of the major axis to the minor axis of the rubber particles. The average aspect ratio means an average value of aspect ratios of a plurality of rubber particles.

の長 The long diameter of the rubber particle can be measured as the length in the longitudinal direction (length of the long side) of the rectangle circumscribed by the rubber particle in a TEM image described later. The minor axis of the rubber particle can be measured as a length (length of a short side) of a rectangle circumscribed by the rubber particle in a TEM image described later.

平均 The average major axis of the rubber particles is preferably from 200 to 500 nm. When the average major axis of the rubber particles is 200 nm or more, a stress (force to shrink) with respect to the stretching tension of the rubber particles is likely to be applied to the optical film immediately after winding, so that winding failure is easily suppressed sufficiently. When the average major axis of the rubber particles is 500 nm or less, the number of contacts between adjacent rubber particles does not become too small, so that the effect of dispersing the stress is not easily impaired, and the winding failure is easily suppressed sufficiently. The average major axis of the rubber particles is more preferably from 220 to 400 nm, further preferably from 250 to 350 nm. The average major axis of the rubber particles is an average of the major axes of the rubber particles.

The average aspect ratio and the average major axis of the rubber particles can be calculated by the following method.
1) TEM observation of a cross section of the optical film (of the cross section along the thickness direction of the optical film, a cross section parallel to the in-plane slow axis). The observation region may be a region corresponding to the thickness of the optical film or a region of 5 μm × 5 μm. When a region corresponding to the thickness of the optical film is set as the observation region, the number of measurement points may be one. When an area of 5 μm × 5 μm is set as the observation area, the number of measurement points may be four.
2) Measure the major axis and minor axis of each rubber particle in the obtained TEM image and calculate the aspect ratio. The average value of the aspect ratios obtained from the plurality of rubber particles is referred to as “average aspect ratio”, and the average value of the long diameters obtained from the plurality of rubber particles is referred to as “average long diameter”.

平均 The average aspect ratio and average major axis of the rubber particles can be adjusted by the film forming conditions and the stretching conditions of the optical film. In order to increase the average aspect ratio and the average major axis of the rubber particles, for example, it is preferable to lower the dope concentration at the time of forming the optical film or to increase the draw ratio.

Whether or not the average aspect ratio of the rubber particles is adjusted by stretching can be confirmed by the fact that the ratio of the number of continuous rubber particles is 15% or more (requirement 2)). In other words, when flat rubber particles are used before stretching, in the film forming process, not only are the rubber particles difficult to come close to each other, but even if they are close to each other, a certain amount or more of rubber particles connected in the minor axis direction is included. It is because it is thought that it is done.

1-2-2. About Dispersion Structure of Rubber Particles The optical film includes a dispersion structure in which the major axes of three or more rubber particles are continuous in the major axis direction. Specifically, in the cross section of the optical film, a dispersed structure in which three or more rubber particles are continuous in the major axis direction and the distance between the continuous rubber particles is 100 nm or less is observed.

FIG. 1 is a schematic cross-sectional view for explaining a dispersion state of rubber particles in a cross section of the optical film. FIG. 2A is an enlarged view of an area surrounded by a dotted line 2A in FIG. 1, and FIG. 2B is an enlarged view of an area surrounded by a dotted line 2B in FIG. In FIG. 1, the X direction is, for example, the in-plane slow axis direction of the optical film, and the Y direction is the thickness direction of the optical film. In FIG. 2A, LA indicates a virtual line including the major axis of the rubber particles.

As shown in FIG. 1, in the cross section of the optical film 100, a plurality of rubber particles 120 are dispersed in a matrix 110 mainly composed of a (meth) acrylic resin in a specific dispersion structure.

FIG. 2A shows a state in which four rubber particles are connected at predetermined intervals in the major axis direction. FIG. 2B shows a state in which three rubber particles are connected to each other in the major axis direction while partially overlapping each other. 2A and 2B are examples of the above-mentioned specific dispersion structure.

"The major axes of the rubber particles are connected in the major axis direction" specifically means the angle between the major axes of the adjacent rubber particles (in FIG. 2A, the angle between the virtual lines LA including the major axis). Means that the smaller angle θ is continuous at an angle of 30 ° or less (preferably 10 ° or less). In addition, in the example in which the angle between the long diameters of the adjacent rubber particles is 0 °, not only the mode in which the long diameters of the adjacent rubber particles are aligned on a straight line, but also the long diameters are The aspect in which the parts are connected to each other while overlapping each other is also included.

“The distance between particles is 100 nm or less” means that the minimum distance between adjacent rubber particles is 100 nm or less (see d in FIGS. 2A and 2B). The minimum distance between adjacent rubber particles can be specified by image analysis of a TEM image.

(4) The ratio (proximity ratio) of the number of connected rubber particles (the number of rubber particles constituting the specific dispersion structure) to the total number of rubber particles contained in the optical film is preferably 15% or more. When the proximity ratio is 15% or more, the ratio of a plurality of rubber particles close to each other is large, so that stress is easily dispersed. On the other hand, when the proximity ratio is 70% or less, the haze of the optical film does not easily increase. The proximity ratio is more preferably from 20 to 60%, further preferably from 25 to 50%, and particularly preferably from 30 to 50%.

For example, of a total of 10 rubber particles, there are a structure in which four rubber particles are connected (see, for example, FIG. 2A) and a structure in which three rubber particles are connected (see, for example, FIG. 2B). When the rubber particles are not continuous, the proximity ratio is (4 + 3) / 10 × 100 (%) = 70%.

の長 The major axis direction of the rubber particles is preferably substantially perpendicular to the thickness direction of the optical film. Substantially perpendicular refers to a range of 90 ± 15 °. In addition, from the viewpoint of more easily suppressing the winding failure of the optical film after winding, the major axis direction of the rubber particles is preferably substantially parallel to the in-plane slow axis of the optical film. Substantially parallel means a range of 0 ± 15 °.

1-2-3. About composition and composition of rubber particles Rubber particles are a graft copolymer containing a rubber-like polymer (cross-linked polymer), that is, a core portion made of a rubber-like polymer (cross-linked polymer), and a shell portion covering the core portion. It is preferably a core-shell type rubber particle having the following.

ガラス The rubber-like polymer preferably has a glass transition temperature (Tg) of -10 ° C or lower. When the glass transition temperature (Tg) of the rubbery polymer is −10 ° C. or less, sufficient toughness is easily imparted to the film. The glass transition temperature (Tg) of the rubbery polymer is more preferably -15 ° C or lower, and further preferably -20 ° C or lower. The glass transition temperature (Tg) of the rubbery polymer is measured by the same method as described above.

ガラス The glass transition temperature (Tg) of the rubbery polymer can be adjusted by, for example, the monomer composition. In order to lower the glass transition temperature (Tg) of the rubber-like polymer, as described later, for example, in a monomer mixture constituting the rubber-like polymer, an acrylate / methacrylic acid having an alkyl group having 4 or more carbon atoms in a monomer mixture. It is preferable to increase the mass ratio of methyl (for example, 3 or more, preferably 4 or more and 10 or less).

The rubbery polymer is not particularly limited as long as it has a glass transition temperature in the above range, and examples thereof include, but are not limited to, a butadiene-based crosslinked polymer, a (meth) acrylic crosslinked polymer, and an organosiloxane. -Based crosslinked polymers are included. Among them, from the viewpoint that the difference in the refractive index from the (meth) acrylic resin is small and the transparency of the optical film is not easily impaired, the (meth) acrylic crosslinked polymer is preferable, and the acrylic crosslinked polymer (acrylic rubbery polymer) is preferable. Is more preferred.

That is, the rubber particles are a core-shell having an acrylic graft copolymer containing an acrylic rubbery polymer (a), that is, a core part containing an acrylic rubbery polymer (a), and a shell part covering the core part. Preferably, the particles are of the type. The core-shell type particles are a multi-stage polymer (or multilayer) obtained by polymerizing at least one or more stages of a monomer mixture (b) containing a methacrylic acid ester as a main component in the presence of an acrylic rubber-like polymer (a). Structural polymer). The polymerization can be performed by an emulsion polymerization method.

(Core: Acrylic rubbery polymer (a))
The acrylic rubbery polymer (a) is a crosslinked polymer containing an acrylate ester as a main component. The acrylic rubbery polymer (a) is a monomer mixture (a ′) containing 50 to 100% by mass of an acrylate ester and 50 to 0% by mass of another monomer copolymerizable therewith; It is a crosslinked polymer obtained by polymerizing 0.05 to 10 parts by mass of a polyfunctional monomer having two or more non-conjugated reactive double bonds (based on 100 parts by mass of the monomer mixture (a ')). . The crosslinked polymer may be obtained by mixing all of these monomers and polymerizing them, or may be obtained by polymerizing two or more times by changing the monomer composition.

The acrylate constituting the acrylic rubbery polymer (a) is preferably an alkyl acrylate having 1 to 12 carbon atoms in an alkyl group such as methyl acrylate and butyl acrylate. The acrylate may be one type or two or more types. From the viewpoint of reducing the glass transition temperature of the rubber particles to −10 ° C. or lower, the acrylate preferably contains at least an alkyl acrylate having 4 to 10 carbon atoms.

The content of the acrylate is preferably from 50 to 100% by mass, more preferably from 60 to 99% by mass, and more preferably from 70 to 99% by mass, based on 100% by mass of the monomer mixture (a '). Is more preferable. When the content of the acrylate is 50% by weight or more, it is easy to impart sufficient toughness to the film.

From the viewpoint of easily reducing the glass transition temperature of the acrylic rubbery polymer (a) to −10 ° C. or lower, the mass ratio of the alkyl acrylate / monomer mixture (a ′) having 4 or more carbon atoms in the alkyl group is preferably It is preferably 3 or more, and more preferably 4 or more and 10 or less.

Examples of copolymerizable monomers include methacrylates such as methyl methacrylate; styrenes such as styrene and methylstyrene; and unsaturated nitriles such as acrylonitrile and methacrylonitrile.

Examples of polyfunctional monomers include allyl (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinyl benzene, ethylene glycol di (meth) acrylate, diethylene glycol (meth) Acrylates, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetromethylol methanetetra (meth) acrylate, dipropylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate are included.

The content of the polyfunctional monomer is preferably 0.05 to 10% by mass, more preferably 0.1 to 5% by mass, based on 100% by mass of the total of the monomer mixture (a '). When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the obtained acrylic rubbery polymer (a) is easily increased, so that the hardness and rigidity of the obtained film are not excessively impaired. When the content is 10% by mass or less, the toughness of the film is not easily impaired.

(Shell part: monomer mixture (b))
The monomer mixture (b) is a graft component for the acrylic rubbery polymer (a) and forms a shell part. The monomer mixture (b) preferably contains a methacrylate ester as a main component.

The methacrylate constituting the monomer mixture (b) is preferably an alkyl methacrylate having 1 to 12 carbon atoms in an alkyl group such as methyl methacrylate. The methacrylic acid ester may be one kind or two or more kinds.

The content of the methacrylic acid ester is preferably 50% by mass or more based on 100% by mass of the monomer mixture (b). When the content of the methacrylic acid ester is 50% by mass or more, the hardness and rigidity of the obtained film may be hardly reduced. From the viewpoint of lowering the affinity between the (meth) acrylic resin and the rubber particles (increase ΔSP), the content of the methacrylate ester is 70% by mass or more based on 100% by mass of the monomer mixture (b). Is more preferable, and it is further preferable that it is 80 mass% or more.

The monomer mixture (b) may further contain another monomer as necessary. Examples of other monomers include acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate; benzyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenoxy (meth) acrylate (Meth) acrylic monomers having an alicyclic structure such as ethyl, a heterocyclic structure or an aromatic group (cyclic structure-containing (meth) acrylic monomers) are included.

(Core-shell type rubber particles: acrylic graft copolymer)
Examples of the core-shell type rubber particles include methacrylic acid in the presence of 5 to 90 parts by mass (preferably 5 to 75 parts by mass) of an acrylic rubbery polymer as the (meth) acrylic rubbery polymer (a). It includes a polymer obtained by polymerizing 95 to 25 parts by mass of a monomer mixture (b) containing an acid ester as a main component in at least one stage.

The acrylic graft copolymer may further include a hard polymer inside the acrylic rubbery polymer (a), if necessary. Such an acrylic graft copolymer can be obtained through the following polymerization steps (I) to (III).
(I) a monomer mixture (c1) comprising 40 to 100% by mass of a methacrylic acid ester and 60 to 0% by mass of another monomer copolymerizable therewith, and 0.01 to 10 parts by mass of a polyfunctional monomer (monomer mixture) (II) A step of obtaining a hard polymer by polymerizing (based on a total of 100 parts by mass of (c1)) To obtain a soft polymer by polymerizing the monomer mixture (a1) and 0.1 to 5 parts by mass of the polyfunctional monomer (based on a total of 100 parts by mass of the monomer mixture (a1)) (III) Methacrylate A monomer mixture (b1) consisting of 60 to 100% by mass and 40 to 0% by mass of another monomer copolymerizable therewith; and 0 to 10 parts by mass of a polyfunctional monomer (monomer) Obtaining a hard polymer mixture per 100 parts by weight of (b1)) polymerized

の間に Between the polymerization steps (I) to (III), another polymerization step may be further included.

The acrylic graft copolymer may be further obtained through the polymerization step (IV).
(IV) a monomer mixture (b2) consisting of 40 to 100% by mass of a methacrylate, 0 to 60% by mass of an acrylate, and 0 to 5% by mass of another copolymerizable monomer, and 0 to 10 of a polyfunctional monomer A hard polymer is obtained by polymerizing parts by mass (based on 100 parts by mass of the monomer mixture (b2)).

メタ The same methacrylic acid ester, acrylic acid ester, other copolymerizable monomer, and polyfunctional monomer used in each step can be used.

The soft layer can impart shock absorption to the optical film. Examples of the soft layer include a layer made of an acrylic rubbery polymer (a) containing an acrylate ester as a main component. The hard layer makes it difficult for the toughness of the optical film to be impaired, and can suppress coarsening and agglomeration of the rubber particles during production. Examples of the hard layer include a layer made of a polymer containing a methacrylate ester as a main component.

The graft ratio (mass ratio of the graft component (shell portion) to the acrylic rubbery polymer (a)) of the acrylic graft copolymer is preferably 10 to 250%, and more preferably 40 to 230%. More preferably, it is more preferably 60 to 220%. When the graft ratio is 10% or more, the ratio of the shell portion does not become too small, so that the hardness and rigidity of the film are not easily deteriorated. When the graft ratio of the acrylic graft copolymer is 250% or less, the effect of improving the toughness and brittleness of the film is not easily impaired because the proportion of the acrylic rubbery polymer (a) does not become too small.

The graft ratio of the acrylic graft copolymer is measured by the following method.
1) 2 g of the acrylic graft copolymer was dissolved in 50 ml of methyl ethyl ketone, and centrifuged at 30,000 rpm for 1 hour at a temperature of 12 ° C. using a centrifuge (CP60E, manufactured by Hitachi Koki Co., Ltd.) to obtain an insoluble matter. And soluble components (centrifugation work is set three times in total).
2) The graft ratio is calculated by applying the obtained insoluble weight to the following equation.
Graft ratio (%) = [{(weight of insoluble portion of methyl ethyl ketone) − (weight of acrylic rubbery polymer (a))} / (weight of acrylic rubbery polymer (a))] × 100

In the optical film, in order to bring the rubber particles into close proximity to each other, it is preferable to adjust the combination of the type of the rubber particles (specifically, the monomer composition of the shell portion) and the type of the (meth) acrylic resin.

When the solubility parameter (SolubilityＳParameter; SP value) of the shell part constituting the rubber particles is SP2 and the SP value of the (meth) acrylic resin is SP1, ΔSP = | SP1-SP2 | is 0.3 or more. Is preferably 0.5 or more, and more preferably 0.8 or more. The upper limit of ΔSP may be 5, for example.

As the SP value, a value calculated by inputting the structure of each compound in commercially available simulation software “Material Studios Forcite” (manufactured by Dassault Systèmes) is used.

ΔSP can be adjusted by a combination of the composition of the shell portion of the rubber particles and the composition of the (meth) acrylic resin. In order to make ΔSP equal to or more than a certain value, for example, the content of methyl methacrylate (MMA) in the monomer mixture (b) constituting the shell portion is increased, and the monomer composition constituting the (meth) acrylic resin is It is preferable to increase the content of the comonomer having a bulky structure.

The content of the rubber particles is preferably 5 to 20% by mass based on the (meth) acrylic resin. When the content of the rubber particles is 5% by mass or more, not only can the (meth) acrylic resin film be easily imparted with sufficient flexibility and toughness, but also unevenness can be formed on the surface to impart slipperiness. When the content of the rubber particles is 20% by mass or less, the haze does not increase too much. From the above viewpoint, the content of the rubber particles is more preferably from 5 to 15% by mass, and still more preferably from 5 to 10% by mass, based on the (meth) acrylic resin.

1-3. Organic Fine Particles The optical film of the present invention preferably further contains organic fine particles from the viewpoint of further increasing the slipperiness of the optical film and making the rubber particles more unevenly distributed on the surface layer of the film.

The organic fine particles are preferably particles having a glass transition temperature (Tg) of 80 ° C. or higher. When the glass transition temperature of the organic fine particles is 80 ° C. or higher, it is easy to form irregularities having appropriate hardness on the surface of the optical film, and thus it is easy to enhance the slipperiness. The glass transition temperature of the organic fine particles is more preferably 100 ° C. or higher. The glass transition temperature is measured in the same manner as described above.

ガラス The glass transition temperature (Tg) of the organic fine particles can be adjusted by the monomer composition of the organic fine particles. In order to increase the glass transition temperature (Tg) of the organic fine particles, for example, it is preferable to increase the content of a structural unit derived from a polyfunctional monomer described later.

The resin constituting the organic fine particles may be any resin having a glass transition temperature (Tg) within the above range, and examples thereof include (meth) acrylates, itaconic diesters, maleic diesters, Derived from one or more selected from the group consisting of vinyl esters, olefins, styrenes, (meth) acrylamides, allyl compounds, vinyl ethers, vinyl ketones, unsaturated nitriles, unsaturated carboxylic acids, and polyfunctional monomers. Polymer, a silicone-based resin, a fluorine-based resin, polyphenylene sulfide, and the like.

The (meth) acrylic esters, olefins, styrenes, (meth) acrylamides, unsaturated nitriles, unsaturated carboxylic acids and polyfunctional monomers constituting the polymer are the above-mentioned (meth) acrylic resin and The same ones as the monomers constituting the acrylic rubbery polymer (a) can be used. Examples of itaconic acid diesters include dimethyl itaconate, diethyl itaconate, and dipropyl itaconate. Examples of maleic diesters include dimethyl maleate, diethyl maleate, and dipropyl maleate. Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl chloroacetate, vinyl methoxy acetate, vinyl phenyl acetate, vinyl benzoate, and vinyl salicylate. It is. Examples of allyl compounds include allyl acetate, allyl caproate, allyl laurate, allyl benzoate and the like. Examples of vinyl ethers include methyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, methoxyethyl vinyl ether, dimethylaminoethyl vinyl ether, and the like. Examples of vinyl ketones include methyl vinyl ketone, phenyl vinyl ketone, methoxyethyl vinyl ketone, and the like.

Among them, (meth) acrylates, vinyl esters, styrene, etc., from the viewpoint of high affinity with (meth) acrylic resin, flexibility with respect to stress, and easy adjustment of the glass transition temperature to the above range. , A copolymer containing a structural unit derived from at least one selected from the group consisting of olefins and a structural unit derived from a polyfunctional monomer is preferable, and a structural unit derived from (meth) acrylates is preferred. A copolymer containing a structural unit derived from a polyfunctional monomer is more preferable, and a structural unit derived from a (meth) acrylate, a structural unit derived from styrene, and a copolymer derived from a polyfunctional monomer are more preferable. A copolymer containing a structural unit is more preferred.

When the organic fine particles include a structural unit derived from the polyfunctional monomer, the content of the structural unit derived from the polyfunctional monomer in the organic fine particles is generally higher than the content of the structural unit derived from the polyfunctional monomer in the rubber particles. Many. For example, the content of the structural unit derived from the polyfunctional monomer is, for example, 50 to 500% by mass based on 100% by mass of the total of the structural units derived from the monomers other than the polyfunctional monomer constituting the copolymer. sell.

粒子 Particles (polymer particles) composed of such a polymer can be produced by any method, for example, a method such as emulsion polymerization, suspension polymerization, dispersion polymerization, or seed polymerization. Among them, from the viewpoint of easily obtaining polymer particles having a uniform particle diameter, seed polymerization or emulsion polymerization in an aqueous medium is preferred.

As a method for producing polymer particles, for example,
A one-stage polymerization method in which the monomer mixture is dispersed in an aqueous medium and then polymerized;
A two-stage polymerization method in which the seed particles are obtained by polymerizing the monomer in an aqueous medium, the monomer mixture is absorbed by the seed particles, and then polymerized;
-A multi-stage polymerization method in which a step of producing seed particles in a two-stage polymerization method is repeated. These polymerization methods can be appropriately selected depending on the desired average particle size of the polymer particles. The monomer for producing the seed particles is not particularly limited, and any monomer for polymer particles can be used.

The organic fine particles may be core-shell type particles. Such organic fine particles may be, for example, particles having a low Tg core portion containing a homopolymer or a copolymer of a (meth) acrylate and a high Tg shell portion.

The absolute value Δn of the refractive index difference between the organic fine particles and the (meth) acrylic resin is preferably 0.1 or less, and 0.085 or less, from the viewpoint of highly suppressing the haze increase of the obtained film. Is more preferable, and the value is more preferably 0.065 or less.

The average particle diameter of the organic fine particles is preferably from 0.04 to 2 μm, more preferably from 0.08 to 1 μm. When the average particle diameter of the organic fine particles is 0.04 μm or more, sufficient lubricity is easily imparted to the obtained film. When the average particle diameter of the organic fine particles is 2 μm or less, it is easy to suppress an increase in haze.

平均 The average particle size of the organic fine particles can be measured by the same method as the average particle size of the rubber particles, except for the following points. That is, the average particle diameter of the organic fine particles is specified as the average value of the circle equivalent diameter of 100 organic fine particles obtained by TEM observation of the film cross section. The equivalent circle diameter can be obtained by converting the projected area of a particle obtained by imaging into the diameter of a circle having the same area. The average particle size of the organic fine particles in the dispersion can be measured by a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

The average particle size of the organic fine particles means the average size of the aggregates (average secondary particle size) if the particles are cohesive, and the average of the sizes of one particle if the particles are non-aggregate. Mean value.

含有 The content of the organic fine particles is preferably from 0.03 to 1.5% by mass based on the (meth) acrylic resin. When the content of the organic fine particles is 0.03% by mass or more, sufficient slip properties can be imparted to the optical film. When the content of the organic fine particles is 1.5% by mass or less, an increase in haze is easily suppressed. The content of the fine particles is more preferably from 0.05 to 1.0% by mass, and even more preferably from 0.08 to 0.7% by mass.

1-4. Other Components The optical film of the present invention may further contain other components as long as the effects of the present invention are not impaired. Examples of other components include residual solvents, UV absorbers, antioxidants, and the like.

For example, since the optical film of the present invention is manufactured by a solution casting method as described later, it may contain a residual solvent derived from a solvent of the dope used in the solution casting method.

(4) The residual solvent amount is preferably 700 ppm or less, more preferably 30 to 700 ppm, based on the optical film. The content of the residual solvent can be adjusted by the drying conditions of the dope cast on the support in the optical film manufacturing process described below.

残留 The content of the residual solvent in the optical film can be measured by head space gas chromatography. In the headspace gas chromatography method, a sample is sealed in a container, heated, the gas in the container is quickly injected into the gas chromatograph with the container filled with volatile components, and mass spectrometry is performed to identify the compound. This is to determine volatile components while performing. In the headspace method, it is possible to observe all peaks of volatile components by gas chromatography, and to quantify volatile substances and monomers with high accuracy by using an analysis method that uses electromagnetic interaction. Can also be performed together.

1-5. Physical properties (haze)
The optical film of the present invention preferably has high transparency. The haze of the optical film is preferably 4.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less. The haze can be measured on a sample of 40 mm × 80 nm at 25 ° C. and 60% RH with a haze meter (HGM-2DP, Suga Test Machine) in accordance with JIS K-6714.

(Phase difference Ro and Rt)
From the viewpoint of using the optical film of the present invention as, for example, a retardation film for IPS, the in-plane retardation Ro measured in an environment of a measurement wavelength of 550 nm and 23 ° C. and 55% RH is 0 to 10 nm. Is preferably, and more preferably 0 to 5 nm. The retardation Rt in the thickness direction of the optical film of the invention is preferably from -20 to 20 nm, more preferably from -10 to 10 nm.

Ro and Rt are each defined by the following formula.
Formula (1a): Ro = (nx−ny) × d
Formula (1b): Rt = ((nx + ny) / 2−nz) × d (where,
nx represents the refractive index in the in-plane slow axis direction of the film (the direction in which the refractive index is maximized),
ny represents the refractive index in the direction orthogonal to the in-plane slow axis of the film,
nz represents the refractive index in the thickness direction of the film,
d represents the thickness (nm) of the film. )

内 The in-plane slow axis of the optical film of the present invention refers to an axis at which the refractive index becomes maximum on the film surface. The in-plane slow axis of the optical film can be confirmed by an automatic birefringence meter Axoscan (AxoScan Mueller MatrixPolarimeter: manufactured by Axometrics). The in-plane slow axis usually coincides with the direction in which the stretching ratio is maximized.

Ro and Rt can be measured by the following method.
1) The optical film of the present invention is conditioned for 24 hours in an environment of 23 ° C. and 55% RH. The average refractive index of this film is measured with an Abbe refractometer, and the thickness d is measured with a commercially available micrometer.
2) The retardation Ro and Rt at a measurement wavelength of 550 nm of the film after humidity control were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axometrics). Measure in the environment.

位相 The retardation Ro and Rt of the optical film of the present invention can be adjusted by, for example, the type of the (meth) acrylic resin. In order to reduce the phase differences Ro and Rt of the optical film, the content ratio is preferably such that the structural unit having negative birefringence and the structural unit having positive birefringence can cancel the phase difference.

(Thickness)
The thickness of the optical film of the present invention may be, for example, 5 to 100 μm, preferably 5 to 40 μm.

2. Manufacturing method of optical film The optical film of the present invention is manufactured by a solution casting method (casting method). That is, the optical film of the present invention comprises: 1) a step of obtaining a dope containing at least the above (meth) acrylic resin, rubber particles, and a solvent; and 2) casting the obtained dope on a support. , Drying and peeling to obtain a film, 3) stretching the obtained film, and 4) winding the stretched film into a roll. .

Step 1) A dope is prepared by dissolving or dispersing the (meth) acrylic resin, rubber particles, and, if necessary, organic fine particles in a solvent.

The particle shape of the rubber particles used in the preparation of the dope is not particularly limited, but from the viewpoint of easily developing a good stress relaxation effect by stretching, a rubber particle having a shape close to a true sphere, specifically, having an average aspect ratio of 1 ± 1. It is preferably 0.1.

溶媒 The solvent used for the dope contains at least an organic solvent (good solvent) that can dissolve the (meth) acrylic resin. Examples of good solvents include chlorinated organic solvents such as methylene chloride and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone and tetrahydrofuran. Among them, methylene chloride is preferred.

溶媒 The solvent used for the dope may further contain a poor solvent. Examples of the poor solvent include a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the ratio of the alcohol in the dope is high, the film-like material is apt to gel, and is easily peeled from the metal support. Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol and tert-butanol. Of these, ethanol is preferred because of its stability, the boiling point is relatively low, and the drying property is good.

The solid content concentration of the dope is not particularly limited, but is preferably lower from the viewpoint of making the rubber particles appropriately close to each other in the obtained optical film due to the compression effect of drying. Specifically, the solid content concentration of the dope is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. On the other hand, from the viewpoint of making it easier to obtain a film having a predetermined thickness, the lower limit of the solid content concentration of the dope may be, for example, 9% by mass.

The dope may be prepared by directly adding (meth) acrylic resin, rubber particles, and, if necessary, organic fine particles to the above-mentioned solvent and mixing them; A resin solution in which the system resin is dissolved, a rubber particle dispersion in which rubber particles are dispersed in the above-described solvent, and a fine particle dispersion in which organic fine particles are dispersed in the above-described solvent, if necessary, are prepared in advance, respectively. They may be prepared by mixing them.

溶媒 The solvent contained in the rubber particle dispersion preferably contains a solvent having low affinity for the rubber particles from the viewpoint of making the rubber particles appropriately close to each other in the obtained optical film. Examples of such solvents include the aforementioned poor solvents, for example, straight or branched chain aliphatic alcohols having 1 to 4 carbon atoms. The content of the poor solvent is preferably from 2 to 16% by mass, more preferably from 4 to 16% by mass, based on the whole solvent contained in the rubber particle dispersion.

The method for adding the organic fine particles is not particularly limited, and the organic fine particles may be individually added to the solvent, or may be added to the solvent as an aggregate of the organic fine particles. The aggregate of organic fine particles is composed of an aggregate of a plurality of organic fine particles in which mutual connection (fusion) is suppressed. Therefore, when the aggregate of organic fine particles is dispersed in a (meth) acrylic resin or a solvent, the particles are easily separated into organic fine particles, so that the dispersibility of the organic fine particles can be improved. The aggregate of organic fine particles can be obtained, for example, by spray-drying a slurry containing organic fine particles and inorganic powder.

Step 2) The obtained dope is cast on a support. The dope can be cast by discharging it from a casting die.

Next, the solvent in the dope cast on the support is evaporated and dried. The dried dope is peeled from the support to obtain a film.

The amount of the residual solvent of the dope at the time of peeling from the support (the amount of the residual solvent of the film at the time of peeling) is from 10 to 150 mass in terms of facilitating the reduction of the phase difference of the obtained (meth) acrylic resin film. %, More preferably 20 to 40% by mass. When the amount of the residual solvent at the time of peeling is 10% by mass or more, the (meth) acrylic resin easily flows and becomes non-oriented during drying or stretching, so that the phase difference of the obtained (meth) acrylic resin film is reduced. Easy to reduce. If the amount of the residual solvent at the time of peeling is 150% by mass or less, the force required for peeling the dope is unlikely to be excessively large, so that breakage of the dope is easily suppressed.

The residual solvent amount of the dope at the time of peeling is defined by the following equation. The same applies to the following.
Residual solvent amount (mass%) of dope = (mass before heat treatment of dope−mass after heat treatment of dope) / mass after heat treatment of dope × 100
Note that the heat treatment when measuring the amount of the residual solvent refers to a heat treatment at 140 ° C. for 30 minutes.

(4) The amount of the residual solvent at the time of peeling can be adjusted by the temperature and time for drying the dope on the support, the temperature of the support, and the like.

Step 3) The film obtained by peeling is stretched while being dried.

Stretching may be performed according to the required optical characteristics, and is preferably performed in at least one direction (for example, the width direction (TD direction) of the film-like material), and is performed in two directions perpendicular to each other (for example, Biaxial stretching in the width direction (TD direction) of the article and the transport direction (MD direction) perpendicular thereto may be performed.

The stretching ratio may be set so that the average aspect ratio of the rubber particles falls within the above range, and is preferably, for example, 20 to 200%, more preferably 30 to 100%, and 50 to 70%. Is more preferable. The stretching ratio (%) is defined as (the change in the length of the film before and after stretching in the stretching direction) / (the length of the film before stretching in the stretching direction) × 100 (%). In the case where biaxial stretching is performed, it is preferable that the stretching ratio is set in the TD direction and the MD direction.

The direction of the in-plane slow axis of the optical film (the direction in which the refractive index is maximized in the plane) is usually the direction in which the stretching ratio is maximized.

The stretching temperature (drying temperature) is preferably (Tg−65) ° C. to (Tg + 60) ° C., and is preferably (Tg−50) ° C. to (Tg + 50), where Tg is the glass transition temperature of the (meth) acrylic resin. ) .Degree. C., more preferably (Tg-30) .degree. C. to (Tg + 50) .degree. When the stretching temperature is (Tg-30) ° C. or higher, not only is it easy to make the film-like material suitable for stretching, but also the tension applied to the film-like material at the time of stretching does not become too large, so that the obtained (meth) Excess residual stress may hardly remain in the acrylic resin film. When the stretching temperature is equal to or lower than Tg, it is easy to suppress the generation of bubbles due to the vaporization of the solvent in the film. The stretching temperature can be specifically set at 60 to 220 ° C.

The stretching temperature is as follows: (a) in the case of drying by a non-contact heating type such as a tenter stretching machine, etc .; The temperature can be measured as any one of the temperature of the contact heating section and the surface temperature of the film-like material (the surface to be dried). Above all, when drying is performed by a non-contact heating type such as (a) a tenter stretching machine, an ambient temperature such as a stretching machine temperature or a hot air temperature is preferable.

(4) The amount of residual solvent in the film at the start of stretching is preferably, for example, 5 to 30% by mass. The amount of residual solvent at the start of stretching can be measured in the same manner as described above.

延伸 Stretching of the film in the TD direction (width direction) can be performed by, for example, a method (tenter method) in which both ends of the film are fixed with clips or pins and the interval between the clips or pins is increased in the traveling direction. The stretching of the film in the MD direction can be performed, for example, by a method (roll method) in which a plurality of rolls are provided with a difference in peripheral speed, and a difference in roll peripheral speed is used therebetween.

Step 4) The film obtained after stretching is wound into a roll while being further dried as necessary, to obtain a roll of an optical film.

The drying temperature can be adjusted in the same range as the stretching temperature in the above step 3). The drying temperature is measured by the same method as in the above step 3). (B) When drying with a contact heating type such as a heat roller, the temperature is preferably measured as the temperature of the contact heating section.

Winding is usually performed while applying tension (winding tension) in the MD direction of the film-like material.

ロール In the roll obtained after winding, the major axis direction of the rubber particles is preferably substantially perpendicular to the thickness direction of the optical film. Further, from the viewpoint of more easily suppressing the winding failure of the optical film after winding, the major axis direction of the rubber particles is preferably substantially parallel to the stretching direction (preferably the width direction) of the optical film.

光学 The length of the optical film (the length in the MD direction) of the obtained roll body is preferably from 2000 to 8000 m, more preferably from 5000 to 7000 m. The width (the length in the TD direction) of the optical film is preferably from 1.3 to 3.0 m, more preferably from 2.3 to 2.5 m.

As described above, a force (stress) that tends to contract in the longitudinal direction and a force (stress) that tends to expand in the width direction easily act on the optical film of the roll immediately after winding due to the winding tension. On the other hand, the optical film of the present invention has a structure in which rubber particles having an average aspect ratio of not less than a certain value are appropriately close to each other. Thereby, the optical film of the roll body after winding can effectively reduce the stress without increasing the particle diameter of the rubber particles. Thereby, it is possible to suppress the transfer of the winding core due to the force shrinking in the longitudinal direction and the chain-like failure due to the force shrinking in the width direction. Therefore, the winding shape can be improved without increasing the haze of the optical film.

Especially, as the optical film is longer (longer in the MD direction) and wider (longer in the TD direction), winding failure is more likely to occur. According to the present invention, even in the roll body of such an optical film, the winding failure can be favorably suppressed.

The obtained optical film is preferably used as a polarizing plate protective film or a retardation film in various display devices such as a liquid crystal display and an organic EL display.

3. Polarizing Plate The polarizing plate of the present invention has a polarizer and the optical film of the present invention disposed on at least one surface thereof.

3-1. Polarizer A polarizer is an element that transmits only light having a polarization plane in a certain direction, and is a polyvinyl alcohol-based polarizing film. Polyvinyl alcohol-based polarizing films include those obtained by dyeing a polyvinyl alcohol-based film with iodine and those obtained by dyeing a dichroic dye.

The polyvinyl alcohol-based polarizing film may be a film obtained by uniaxially stretching the polyvinyl alcohol-based film and then dyeing the film with iodine or a dichroic dye (preferably a film further subjected to a durability treatment with a boron compound); A film obtained by dyeing an alcohol-based film with iodine or a dichroic dye and then uniaxially stretching the film (preferably, a film further subjected to a durability treatment with a boron compound) may be used. The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

For example, as disclosed in JP-A-2003-248123, JP-A-2003-342322, etc., ethylene content of 1 to 4 mol%, polymerization degree of 2000 to 4000 and saponification degree of 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is used.

The thickness of the polarizer is preferably from 5 to 30 μm, and more preferably from 5 to 20 μm in order to reduce the thickness of the polarizing plate.

3-2. Other Optical Film When the optical film of the present invention is disposed on only one surface of the polarizer, another optical film may be disposed on the other surface. In addition, an optical film and another optical film can be arrange | positioned via an adhesive layer on a polarizer.

Examples of other optical films include commercially available cellulose ester films (e.g., Konica Minoltack KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6U, KCUEK KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd., Fujitac T40UZ, Fujitack T80UZ, Fujitack T80UZD, Fujitack T60UZD Fujifilm Corporation) and the like.

The thickness of the other optical film is preferably thicker from the viewpoint of suppressing cracks in the polarizing plate, and may be, for example, 5 to 100 μm, and preferably 40 to 80 μm.

3-3. Method for Producing Polarizing Plate The polarizing plate of the present invention can be obtained by bonding a polarizer and the (meth) acrylic resin film of the present invention via an adhesive. The adhesive may be a completely saponified polyvinyl alcohol aqueous solution (water glue) or an active energy ray-curable adhesive. The active energy ray-curable adhesive may be any of a photo-radical polymerization type composition using photo-radical polymerization, a photo-cation polymerization type composition using photo-cation polymerization, or a combination thereof.

4. Liquid crystal display device The liquid crystal display device of the present invention includes a liquid crystal cell, a first polarizer disposed on one surface of the liquid crystal cell, and a second polarizer disposed on the other surface of the liquid crystal cell.

The display mode of the liquid crystal cell is, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybrid aligned Nematic), VA (Vertical Alignment, MVA (Multi-domain Vertical Alignment), PVA). (Patterned Vertical Alignment)), IPS (In-Plane-Switching), and the like. Among them, the VA (MVA, PVA) mode and the IPS mode are preferable.

一方 One or both of the first and second polarizing plates are the polarizing plates of the present invention. The polarizing plate of the present invention is preferably arranged such that the optical film of the present invention is on the liquid crystal cell side.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

1. Optical film material (1) (meth) acrylic resin (meth) acrylic resin A: Methyl methacrylate (MMA) / N-phenylmaleimide (PMI) copolymer (MMA / PMI = 85/15 (mass ratio) , Glass transition temperature (Tg): 125 ° C, weight average molecular weight Mw: 1.5 million)
(Meth) acrylic resin B: Methyl methacrylate (MMA) / dicyclopentanyl methacrylate copolymer (MMA / dicyclopentanyl methacrylate: 70/30 (mass ratio), glass transition temperature (Tg): 115 ° C, weight average molecular weight Mw: 1.7 million)
(Meth) acrylic resin C: Methyl methacrylate (MMA) / adamantyl methacrylate (MADMA) / N-phenylmaleimide (PMI) copolymer (MMA / MADMA / PMI: 50/25/25 (mass ratio), glass Transition temperature (Tg): 135 ° C., weight average molecular weight Mw: 1.9 million)
(Meth) acrylic resin D: methyl methacrylate (MMA) / n-butyl acrylate copolymer (MMA / BA: 90/10 (mass ratio), glass transition temperature (Tg): 109 ° C., weight average molecular weight Mw : 1.2 million)

ガラス The glass transition temperatures (Tg) and weight average molecular weights (Mw) of the (meth) acrylic resins A to D were measured by the following methods.

(Glass transition temperature (Tg))
The glass transition temperature of the (meth) acrylic resin was measured according to JIS K 7121-2012 by using DSC (Differential Scanning Colorimetry).

(Weight average molecular weight (Mw))
The weight average molecular weight (Mw) of the (meth) acrylic resin was measured using gel permeation chromatography (manufactured by Tosoh Corporation, HLC8220GPC) and column (manufactured by Tosoh Corporation, TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL series). . 20 mg ± 0.5 mg of the sample was dissolved in 10 ml of tetrahydrofuran and filtered with a 0.45 mm filter. 100 ml of this solution was injected into a column (at a temperature of 40 ° C.), measured at a detector RI temperature of 40 ° C., and the value converted into styrene was used.

(2) Rubber particles <Preparation of rubber particles C1>
Acrylic modifier Kaneace M210 manufactured by Kaneka Corporation (core: multi-layered acrylic rubber-like polymer (Tg: about -10 ° C.), shell: methacrylic ester-based polymer containing methyl methacrylate as a main component) Coalesced, core-shell type rubber particles, average particle size: 220 nm)

<Preparation of rubber particles C2>
The following components were charged into a glass reactor.
Deionized water: 125 parts by mass Boric acid: 0.47 parts by mass Sodium carbonate: 0.05 parts by mass Polyoxyethylene lauryl ether phosphoric acid: 0.0042 parts by mass

After sufficiently replacing the inside of the polymerization machine with nitrogen gas, the internal temperature was raised to 80 ° C., and 97 parts by mass of methyl methacrylate (MMA), 3 parts by mass of butyl acrylate (BA), and 0.17 parts by mass of allyl methacrylate (ALMA). , And 25% by mass of a monomer mixture (c1) composed of 0.065 parts by mass of tertiary decyl mercaptan (tDM) were added all at once to the polymerization machine. To this were added 0.00645 parts by mass of 5% sodium formaldehyde sulfoxylate, 0.0056 parts by mass of 2-sodium ethylenediaminetetraacetate, and 0.0014 parts by mass of ferrous sulfate. 0.022 parts by mass of -butyl hydroperoxide was added, and the polymerization was further continued for 15 minutes. Thereafter, 0.013 parts by mass of a 2% aqueous sodium hydroxide solution was added.
Next, the remaining 75% by mass of the monomer mixture (c1) was continuously added over 30 minutes. Thirty minutes after the completion of the addition, 0.0069 parts by mass of 69% t-butyl hydroperoxide was added, and the mixture was maintained at the same temperature for 30 minutes to complete the polymerization. The polymerization conversion was 98%.

を The obtained polymer latex was kept at 80 ° C. in a nitrogen stream, and 0.0346 parts by mass of sodium hydroxide and 0.0519 parts by mass of potassium persulfate were added. Thereafter, a mixture comprising 32.5 parts by mass of the monomer mixture (a1) (BA: 82% by mass, MMA: 18% by mass), 0.97 parts by mass of AIMA, and 0.3 parts by mass of polyoxyethylene lauryl ether phosphoric acid was added to 74 parts by mass. Added continuously over minutes. Thereafter, the mixture was held for 45 minutes to complete the polymerization. The average particle size of the obtained rubbery polymer was 260 nm, and the polymerization conversion was 99%.

After keeping the obtained rubbery polymer at 80 ° C. and adding 0.0097 parts by mass of potassium persulfate and 0.05 parts by mass of sodium hydroxide, 50 parts by mass of the monomer mixture (b1) (MMA: 90% by mass, BA : 10% by mass) was continuously added over 150 minutes. After completion of the addition, the mixture was kept for 1 hour.

The obtained graft copolymer containing a rubbery polymer is salted out with magnesium sulfate, coagulated, washed with water and dried to obtain a graft copolymer (rubber particles C2) containing a white powdery rubbery polymer. Obtained. The rubber-like polymer of the obtained rubber particles C2 has a glass transition temperature (Tg) of −30 ° C., an average particle diameter of 380 nm, a graft ratio of about 149%, and a polymerization conversion of 99%. there were.

ΔΔSP of the obtained rubber particles (shell portion) and (meth) acrylic resin was measured by the following method.

(ΔSP)
The ΔSP value of the shell portion of the (meth) acrylic resin and the rubber particles C1 or C2 was calculated. Specifically, in the commercially available simulation software “Material Studios Forcite” (manufactured by Dassault Systèmes), the structural formulas of the (meth) acrylic resin and the resin constituting the shell portion are input, and the SP value is calculated. , By calculating their difference.

(3) Organic fine particles Organic fine particles P1 prepared by the following method were used.

(Preparation of seed particles)
1000 g of deionized water was put into a polymerization vessel equipped with a stirrer and a thermometer, and 50 g of methyl methacrylate and 6 g of t-dodecylmercaptan were charged therein, and the mixture was heated to 70 ° C. while stirring and replacing with nitrogen. The internal temperature was kept at 70 ° C., and 20 g of deionized water in which 1 g of potassium persulfate was dissolved as a polymerization initiator was added, followed by polymerization for 10 hours. The average particle diameter of the seed particles in the obtained emulsion was 0.05 μm.

(Preparation of organic fine particles)
In a polymerization vessel equipped with a stirrer and a thermometer, 800 g of deionized water in which 2.4 g of sodium lauryl sulfate was dissolved was added as a gelling inhibitor, and 66 g of methyl methacrylate, 20 g of styrene, and 64 g of ethylene glycol dimethacrylate were added thereto as a monomer mixture. And 1 g of azobisisobutyronitrile as a polymerization initiator. Then, the mixture was added to T.V. The mixture was stirred with a K homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a dispersion.

６０60 g of the emulsion containing the seed particles was added to the obtained dispersion, and the mixture was stirred at 30 ° C. for 1 hour to allow the seed particles to absorb the monomer mixture. Next, the absorbed monomer mixture is heated at 50 ° C. for 5 hours under a nitrogen stream to polymerize, and then cooled to room temperature (about 25 ° C.) to obtain a slurry of polymer fine particles (organic fine particles 1). Was. The average particle diameter of the obtained organic fine particles P1 was 0.14 μm, and Tg was 280 ° C.

(Preparation of aggregate of organic fine particles)
This emulsion was spray-dried under the following conditions using a spray dryer (model: atomizer take-up system, model: TRS-3WK) manufactured by Sakamoto Giken Co., Ltd. as a spray dryer to obtain an aggregate of organic fine particles. The average particle diameter of the aggregate of the organic fine particles was 30 μm.
Feed rate: 25 ml / min
Atomizer rotation speed: 11000 rpm
Air volume: 2m ³ / min
Slurry inlet temperature of spray dryer: 100 ° C
Outlet temperature of polymer particle aggregate: 50 ° C

平均 The average particle size of the organic fine particles was measured by the following method.

(Average particle size)
The dispersed particle size of the organic fine particles in the obtained dispersion was measured by a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.). The average particle size of the organic fine particles measured using a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.) is almost equal to the average particle size of the organic fine particles measured by TEM observation of the optical film. Matches.

2. Production and evaluation of optical film [Example 1]
(Preparation of rubber particle dispersion)
11.3 parts by mass of the rubber particles C2 and 200 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then under a condition of 1500 rpm using a milder disperser milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.). It was dispersed to obtain a rubber particle dispersion.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressure dissolution tank. Next, the (meth) acrylic resin A was charged into the pressure melting tank with stirring. Next, the rubber particle dispersion liquid prepared as described above was charged, and completely dissolved with stirring. The viscosity of the obtained solution was 16000 mmPa · s, and the water content was 0.50%. This was filtered at a filtration flow rate of 300 L / m ² · h and a filtration pressure of 1.0 × 10 ⁶ Pa using SHP150 manufactured by Loki Techno Co., Ltd. to obtain a dope.
(Dope composition)
(Meth) acrylic resin A: 100 parts by mass Methylene chloride: 220 parts by mass Ethanol: 35 parts by mass Rubber particle dispersion: 200 parts by mass

(Film formation)
Using an endless belt casting device, the dope was uniformly cast on a stainless steel belt support at a temperature of 30 ° C. and a width of 1900 mm. The temperature of the stainless steel belt was controlled at 28 ° C. The conveying speed of the stainless steel belt was 20 m / min.

(4) The solvent was evaporated on the stainless belt support until the amount of the residual solvent in the cast dope became 30% by mass. Subsequently, the film was peeled from the stainless steel belt support at a peeling tension of 128 N / m to obtain a film (the amount of the residual solvent in the film at the time of peeling was 30% by mass). While the peeled film was transported by a number of rollers, the obtained film was stretched by 30% in the width direction with a tenter at (Tg + 15) ° C. (140 ° C. in this example). The amount of residual solvent in the film at the start of stretching was 10% by mass. Thereafter, the film is further dried while being conveyed by a roll, and the end sandwiched between tenter clips is slit and wound with a laser cutter to obtain an optical film having a width of 2.3 m, a length of 7000 m, and a thickness of 40 μm. Was.

[Examples 2 and 3]
An optical film was obtained in the same manner as in Example 1, except that the stretching ratio was changed as shown in Table 1.

[Examples 4 and 5]
An optical film was obtained in the same manner as in Example 2, except that the type of the (meth) acrylic resin was changed as shown in Table 1.

[Example 6]
An optical film was obtained in the same manner as in Example 2, except that the type of the rubber particles was changed as shown in Table 1.

[Example 7]
An optical film was obtained in the same manner as in Example 2 except that the solid content of the dope was changed as shown in Table 1.

[Examples 8 and 13]
An optical film was obtained in the same manner as in Example 2, except that the solvent composition of the rubber particle dispersion was changed as shown in Table 1.

[Example 9]
An optical film was obtained in the same manner as in Example 8, except that the solid content of the dope was changed as shown in Table 1.

[Example 10]
An optical film was obtained in the same manner as in Example 9, except that the length of the optical film was changed as shown in Table 1.

[Example 11]
An optical film was obtained in the same manner as in Example 9 except that the stretching direction was changed as shown in Table 1.

[Example 12]
(Preparation of rubber particle dispersion)
11.3 parts by mass of rubber particles C1, 180 parts by mass of methylene chloride, and 20 parts by mass of ethanol were stirred and mixed with a dissolver for 50 minutes, and then a milder disperser milder disperser (manufactured by Taihei Kiko Co., Ltd.) Was used to perform dispersion under a condition of 1500 rpm to obtain a rubber particle dispersion.

(Preparation of organic fine particle dispersion)
12 parts by mass of the organic fine particles P1 and 388 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed under a condition of 1500 rpm using a milder disperser / milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.). Thus, an organic fine particle dispersion was obtained.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressure dissolution tank. Next, the (meth) acrylic resin 1 was charged into the pressure dissolution tank with stirring. Next, the fine particle dispersion prepared above was charged, heated to 60 ° C., and completely dissolved with stirring. The heating temperature was increased from room temperature at 5 ° C./min, dissolved for 30 minutes, and then decreased at 3 ° C./min. After the obtained solution was filtered, a dope was obtained.

(Dope composition)
(Meth) acrylic resin 1: 100 parts by mass Methylene chloride: 220 parts by mass Ethanol: 16 parts by mass Rubber particle dispersion: 209 parts by mass Organic fine particle dispersion: 18 parts by mass

(Film formation)
An optical film was obtained in the same manner as in Example 2 except that the obtained dope was used.

[Comparative Example 1]
An optical film was obtained in the same manner as in Example 1 except that the type of the (meth) acrylic resin was changed as shown in Table 1.

[Comparative Examples 2, 5]
An optical film was obtained in the same manner as in Comparative Example 1 except that the stretching ratio was changed as shown in Table 1.

[Comparative Example 3]
An optical film was obtained in the same manner as in Comparative Example 1 except that the solid content of the dope was changed as shown in Table 1.

[Comparative Example 4]
An optical film was obtained in the same manner as in Comparative Example 2 except that the type of the (meth) acrylic resin was changed as shown in Table 1.

平均 The average aspect ratio, average major axis, and proximity ratio of rubber particles in the cross sections of the optical films of Examples 1 to 13 and Comparative Examples 1 to 5 were measured by the following methods.

(Average aspect ratio of rubber particles, average major axis)
The average aspect ratio and the average major axis of the rubber particles were calculated according to the following procedure.
1) The cross section of the optical film (the cross section parallel to the width direction among the cross sections along the thickness direction of the optical film) was observed by TEM. The observation area was 5 μm × 5 μm.
2) The major axis and minor axis of each rubber particle in the obtained TEM image were measured, and the aspect ratio was calculated.
3) The above operations 1) and 2) were performed in a total of four places while changing the observation area. Then, the average value of the measured aspect ratio was defined as “average aspect ratio”, and the average value of the measured major axis was defined as “average major axis”.

(Proximity ratio of rubber particles)
The proximity ratio of the rubber particles was measured according to the following procedure.
1) The major axis of each rubber particle was specified in the TEM image (observation area: 5 μm × 5 μm). Then, the smaller one of the angles formed by the long diameters of the adjacent rubber particles was 30 ° or less, and the distance between the particles was 100 nm or less.
2) The ratio of the number of rubber particles specified above to the total number of rubber particles in the observation region was calculated.
3) The above operations 1) and 2) were performed at a total of four places while changing the observation area, and the average value of the calculated ratios was defined as “proximity ratio” (%).

Furthermore, the brittleness (MIT flexibility) and the winding shape (winding failure, chain-like failure) of the optical films of Examples 1 to 13 and Comparative Examples 1 to 5 were evaluated by the following methods, respectively.

(Brittleness: MIT flexibility)
The MIT flexibility of the obtained optical film was measured using a bending resistance tester (MIT, Model BE-201, bending radius of curvature 0.38 mm, manufactured by Tester Sangyo Co., Ltd.).
Specifically, a (meth) acrylic resin film having a width of 15 mm and a length of 150 mm, which was allowed to stand at a temperature of 25 ° C. and a relative humidity of 65% RH for 1 hour or more, was used as a test piece. Under the conditions, the measurement was carried out in accordance with JIS P8115: 2001, and the number of times until breakage was evaluated according to the following evaluation criteria.
＋+: 1000 times or more ◎: 500 times or more and less than 1000 times ：: 300 times or more and less than 500 times Δ: 100 or more and less than 300 times ×: less than 100 times The greater the number of times to break, the better the flexibility. Indicates that it has excellent resistance to repeated bending.
If it was not less than Δ, it was judged to be good.

(Wound shape (winding failure, chain-like failure))
(1) Tightening (core transfer)
After the roll body of the obtained optical film was stored in an atmosphere of 40 ° C. and 80% RH for 10 days, the roll body was unwound and the length (m) of the optical film on which transfer from the core occurred was measured. The transfer from the winding core is a planar defect caused by the deformation (stress of shrinking in the longitudinal direction) of the optical film after winding, and is formed inside the winding in the longitudinal direction.
：: less than 10 m 〇: 10 m or more and less than 50 m Δ: 50 m or more and less than 100 m X: 100 m or more △ or more was judged as good.

(2) Chain-like Failure The roll of the obtained optical film was unwound and the length (m) of the optical film in which the chain-like failure occurred was measured. Note that the chain-like failure is a chain-like defect caused by deformation of the optical film after winding (stress that tends to expand in the width direction), and is formed entirely in the width direction. And it evaluated based on the following.
：: less than 10 m 〇: 10 m or more and less than 200 m Δ: 200 or more and less than 1000 m ×: 1000 m or more △ or more was judged to be good.

Table 1 shows the evaluation results of the optical films of Examples 1 to 13 and Comparative Examples 1 to 5. In Table 1, MC indicates methylene chloride and EtOH indicates ethanol.

As shown in Table 1, when the cross section of the film was observed, the optical films of Examples 1 to 13 in which the average aspect ratio of the rubber particles was 1.3 to 3.0 and the proximity ratio was 15% or more It can be seen that all have high MIT flexibility and good toughness. In addition, in the rolls of the optical films of Examples 1 to 13, it is found that winding failures such as tight winding and chain failure are also suppressed.

In particular, it can be seen that the average aspect ratio and the proximity ratio are further increased by increasing the draw ratio (compared to Examples 1 to 3).

In addition, it can be seen that increasing the glass transition temperature (Tg) of the (meth) acrylic resin further increases the proximity ratio (compared to Examples 1, 4 and 5).

Also, it can be seen that the proximity ratio can be further increased by increasing ΔSP between the (meth) acrylic resin and the rubber particles (compared to Examples 2 and 4 to 6).

わかる It can also be seen that lowering the solids concentration of the dope further increases the proximity ratio. This is considered to be because the rubber particles are likely to be oriented by the compression effect at the time of drying the dope (comparison between Examples 2 and 7 and Examples 8 and 9).

Also, it can be seen that the proximity ratio is further increased by adding a poor solvent (EtOH) to the dispersion solvent of the rubber particles (compared to Examples 2, 8 and 13).

On the other hand, the optical films of Comparative Examples 2 and 4 in which the average aspect ratio of the rubber particles is less than 1.3, Comparative Examples 1 and 3 in which the proximity ratio is less than 15%, and the average aspect ratio of more than 3.0 It can be seen that the optical films of Comparative Example 5 all have low MIT flexibility, and cannot prevent winding failure such as tight winding or chain failure.

The haze of the optical films of Examples 1 to 13 was measured using a haze meter (HGM-2DP, Suga Test Machine) at 25 ° C. and 60% RH in accordance with JIS K-6714. Was also small and good.

This application claims priority based on Japanese Patent Application No. 2018-144438 filed on Jul. 31, 2018. The entire contents described in the specification and drawings of the application are incorporated herein by reference.

According to the present invention, there are provided an optical film, a roll of an optical film, a polarizing plate protective film, and a method for producing an optical film, in which the brittleness is satisfactorily improved without impairing the transparency, and which can suppress winding failure. be able to.

REFERENCE SIGNS LIST 100 optical film 110 matrix 120 rubber particle LA virtual line d distance between particles

Claims

An optical film including a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher and rubber particles,
In the cross section of the optical film,
The rubber particles have an average aspect ratio of 1.2 to 3.0,
The major axes of three or more of the rubber particles are continuous in the major axis direction, and the inter-particle distance of the continuous rubber particles is 100 nm or less,
The ratio of the number of the continuous rubber particles to the total number of the rubber particles included in the optical film is 15% or more.
Optical film.
The major axis direction of the rubber particles is substantially perpendicular to the thickness direction of the optical film,
The optical film according to claim 1.
The optical film has an in-plane slow axis,
The major axis direction of the rubber particles is substantially parallel to the in-plane slow axis,
The optical film according to claim 1.
The rubber particles are core-shell particles having a core portion containing a crosslinked polymer and a shell portion covering the core portion and containing a polymer different from the crosslinked polymer,
The difference ΔSP between the solubility parameter (SP value) of the (meth) acrylic resin and the polymer is 0.8 or more;
The optical film according to any one of claims 1 to 3.
The rubber particles have an average major axis of 200 to 500 nm,
The optical film according to any one of claims 1 to 4.
The (meth) acrylic resin is a (meth) acrylic ester having a structural unit derived from a copolymerized monomer selected from the group consisting of (meth) acrylic esters having a cyclo ring and maleimides, and a branched alkyl group. Including at least one of structural units derived from
The optical film according to any one of claims 1 to 5.
Glass transition temperature further includes organic fine particles having a temperature of 80 ° C. or higher,
The optical film according to any one of claims 1 to 6.
Including the optical film according to any one of claims 1 to 7,
Polarizer protection film.
A roll body of an optical film wound in a direction perpendicular to a width direction thereof, including a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher and rubber particles,
In the cross section of the optical film,
The rubber particles have an average aspect ratio of 1.2 to 3.0,
The major axes of the three or more rubber particles are continuous in the major axis direction, and the distance between the rubber particles is 100 nm or less,
The ratio of the number of the continuous rubber particles to the total number of the rubber particles included in the optical film is 15% or more.
Roll body of optical film.
The major axis direction of the rubber particles is substantially perpendicular to the thickness direction of the optical film,
A roll of the optical film according to claim 9.
The major axis direction of the rubber particles is substantially parallel to the width direction of the optical film,
A roll of the optical film according to claim 9.
The width of the optical film is 2.3 m or more,
The length of the optical film is 5000 m or more,
A roll of the optical film according to any one of claims 9 to 11.
A step of obtaining a dope containing a (meth) acrylic resin having a glass transition temperature of 110 ° C. or higher, rubber particles, and a solvent, and having a solid concentration of 15% by mass or less;
After casting the obtained dope on a support, drying and peeling to obtain a film-like material,
Stretching the film-like material by 20% or more.
The rubber particles are core-shell particles having a core portion containing a crosslinked polymer and a shell portion covering the core portion and containing a polymer different from the crosslinked polymer,
The dope is obtained by mixing the (meth) acrylic resin, a rubber particle dispersion containing the rubber particles and a solvent, and a solvent,
14. The method for producing an optical film according to claim 13, wherein the solvent contained in the rubber particle dispersion contains a poor solvent for the polymer.
The rubber particles are core-shell particles having a core portion containing a crosslinked polymer and a shell portion covering the core portion and containing a polymer different from the crosslinked polymer,
The difference ΔSP between the solubility parameter (SP value) of the (meth) acrylic resin and the polymer is 0.8 or more;
The method for producing an optical film according to claim 13.