JP7452421B2 - Optical film, polarizing plate protective film, optical film roll, and optical film manufacturing method - Google Patents

Description

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

Polarizing plates are used in display devices such as liquid crystal display devices and organic EL display devices. A 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 used as a polarizing plate, it may not be possible to sufficiently suppress deterioration of the polarizer due to moisture under high temperature and high humidity conditions. Therefore, instead of a film containing cellulose acylate as a main component, it is being considered to use a film containing a thermoplastic resin as a main component which has excellent moisture resistance.

Patent Document 1 discloses a maleimide copolymer resin film containing a maleimide copolymer resin and a rubber-like polymer having a polymer chain that is compatible with the maleimide copolymer resin. It has been shown that the aspect ratio of rubbery polymers is 2 or less. Films made of maleimide-based copolymer resin alone are brittle, but by including a rubbery polymer, the brittleness can be improved, and since the rubbery polymer has polymer chains that are compatible with the resin, it is possible to reduce the brittleness during stretching. It is said that the reduction in transparency of the film due to the formation of voids at the interface between the resin and the rubbery polymer can be suppressed.

Japanese Patent Application Publication No. 2006-124435

By the way, optical films such as polarizing plate protective films are usually formed into a long film, then wound up into a roll, and stored and transported as a roll. Winding up of a long film is usually performed while applying tension. Therefore, due to the winding tension, an elongating force is likely to be applied to the optical film being wound up in the longitudinal direction, and a shrinking force is likely to be applied to the optical film in the width direction. As a result, in the optical film of the roll body immediately after being wound up, a force (stress) that tends to shrink is likely to occur in the longitudinal direction, and a force (stress) that tends to expand in the width direction is likely to occur. The force (stress) that tends to shrink in the longitudinal direction tends to cause transfer by the winding core due to tight winding; the force (stress) that tends to stretch in the width direction sometimes causes chain-like failures.

Core transfer is a planar defect that is likely to be formed inside the roll in the longitudinal direction of the film (at a portion close to the core at the initial stage of winding). Chain-like defects are chain-like defects that are likely to be formed throughout the width of the film.

In order to reduce these core transfers and chain-like failures, it is desired that the stress remaining in the optical film immediately after being wound can be effectively alleviated by rubber particles. In order for the rubber particles to effectively relieve stress, it is desirable that the rubber particles have a large particle size. However, if the particle size of the rubber particles is made too large, the haze of the film increases and transparency tends to be impaired. Therefore, it is desired that winding failures such as core transfer and chain failures can be suppressed without increasing the haze of the optical film, that is, without significantly increasing the particle size of the rubber particles.

In particular, as display devices become larger and thinner, optical films such as polarizing plate protective films are required to be wider and thinner. In such wide and thin optical films, curling failures are particularly likely to occur.

The present invention has been made in view of the above circumstances, and is a film mainly composed of (meth)acrylic resin, which has excellent brittleness without impairing transparency and suppresses curling failure. An object of the present invention is to provide an optical film, a polarizing plate protective film, an optical film roll body, 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 in the cross section of the optical film, the average aspect ratio of the rubber particles is 1.2 to 1.2. 3.0, the longer diameters of three or more of the rubber particles are continuous in the long axis direction, and the interparticle distance of the continuous rubber particles is 100 nm or less, and the number of the continuous rubber particles is The ratio of the rubber particles to the total number of the rubber particles contained in the optical film is 15% or more.

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

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

The method for producing an optical film of the present invention includes 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 content concentration of 15% by mass or less. , a step of casting the obtained dope onto a support, drying and peeling to obtain a film-like material, and a step of stretching the film-like material by 20% or more.

According to the present invention, it is possible to provide an optical film, an optical film roll body, and a method for manufacturing an optical film, which can satisfactorily improve brittleness and suppress curling failures without impairing transparency.

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

As a result of intensive studies, the present inventors 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. It was discovered that brittleness was favorably improved and curling failures could be suppressed without impairing transparency.

Specifically, the specific dispersion structure 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 1.2 to 3.0. 2) The major diameters of three or more rubber particles are connected in the major axis direction, and the distance between the consecutive rubber particles is is 100 nm or less, and the ratio of the number of consecutive rubber particles to the total number of rubber particles included in the optical film (hereinafter also referred to as "proximity ratio") is 15% or more.

In other words, if the average aspect ratio of the rubber particles is above a certain level (requirement 1) above), the rubber particles that have been stretched by stretching are unstable, so they tend to return to their stable original shape (perfect spherical shape). Easy to generate force. Thereby, the stress remaining in the optical film immediately after winding can be absorbed by the flat rubber particles and alleviated by the restoring force.
Note that the effect of suppressing the curling failure due to the restoring force of the rubber particles can be obtained even if the stretching direction of the film and the stretching direction (direction of the restoring force) of the rubber for suppressing it do not necessarily match. This is thought to be because when some force is applied to the film, the rubber particles absorb the force and convert it into restoring force (for example, restoring in the thickness direction), thereby exerting the effect.

In addition, by including a moderate amount of structure in which three or more rubber particles are closely connected in the long axis direction (requirement 2) above), stress remaining in the optical film immediately after winding can be dispersed well. It can be relaxed. In particular, with long and wide films, the stress (stretching force) remaining in the optical film tends to increase, and when the rubber particles are single and uniformly dispersed, the stress remaining in the optical film locally increases. (Stretching force) may not be fully absorbed; however, if multiple rubber particles are close to each other, the optical film may can absorb residual stress (stretching force).
It is thought that due to these effects, the stress (stretching force) remaining in the optical film immediately after winding can be effectively alleviated by the rubber particles without increasing the average major axis of the rubber particles.

In addition, by including a moderate amount of structure in which three or more rubber particles are closely connected in the long axis direction (requirement 2) above), stress can be dispersed more highly than a single particle with a large particle size. Therefore, the brittleness of the optical film can also be improved to a high degree.

The above requirement 1) can be adjusted by, for example, the solid content concentration of the dope during film formation by a 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 concentration of the dope and to increase the stretching ratio.

The requirements for 2) above include, for example, the glass transition temperature (Tg) of the (meth)acrylic resin, the affinity between the (meth)acrylic resin and rubber particles (ΔSP, etc.), the solid content 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, etc. In order to increase the proximity ratio of rubber particles, it is preferable to increase the glass transition temperature (Tg) of the (meth)acrylic resin to 110°C or higher, for example, and to increase the affinity (ΔSP) of the (meth)acrylic resin and the rubber particles. etc.) is preferably moderately low, the solid concentration of the dope is preferably low, a 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. If the glass transition temperature (Tg) of the (meth)acrylic resin is 110°C or higher, at the same stretching temperature, the rubber particles will move less because the glass transition temperature (Tg) of the (meth)acrylic resin is lower than that of the (meth)acrylic resin. It can be made difficult. This prevents the rubber particles from spreading too much, allowing them to be brought close to each other appropriately. From the above viewpoint, the glass transition temperature (Tg) of the (meth)acrylic resin is preferably 120 to 160°C, more preferably 125 to 150°C.

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

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, it is preferable to increase the content ratio of a copolymerizable monomer having a bulky structure, which will be described later, for example.

The (meth)acrylic resin may be a homopolymer of (meth)acrylic ester, or a copolymer of (meth)acrylic ester and a copolymerizable monomer copolymerizable with it. . Note that (meth)acrylic means acrylic or methacryl. The (meth)acrylic ester is preferably methyl methacrylate.

That is, the (meth)acrylic resin contains a structural unit derived from methyl methacrylate, and may further contain a structural unit derived from a copolymer monomer other than methyl methacrylate (hereinafter simply referred to as "comonomer"). preferable.

Examples of copolymerizable 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 Acrylic acid esters in which the alkyl group has 1 to 20 carbon atoms, such as pentanyl, isobornyl (meth)acrylate, adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, and lactone (meth)acrylate, or carbon atoms in the alkyl group Methacrylic acid 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, maleic acid monoester;
Vinyl acetate, olefins such as ethylene and propylene;
Vinyl halides such as vinyl chloride, vinylidene chloride, vinylidene fluoride;
(Meth)acrylamides such as (meth)acrylamide, methyl (meth)acrylamide, ethyl (meth)acrylamide, propyl (meth)acrylamide, butyl (meth)acrylamide, tert-butyl (meth)acrylamide, 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 these, copolymerizable monomers having a bulky structure are preferred from the viewpoint of increasing the glass transition temperature (Tg) of the optical film and appropriately lowering the affinity with rubber particles.

Examples of copolymerizable monomers with bulky structures include:
(Meth)acrylic acid esters with a cyclo ring such as dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, and cyclohexyl (meth)acrylate; a copolymerizable monomer selected from the group consisting of vinyls having the compound; and maleimides such as N-phenylmaleimide;
Copolymerizable monomers such as (meth)acrylic acid esters having a branched alkyl group such as t-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are included.
Among them, copolymerization monomers having a bulky structure include copolymerization monomers selected from the group consisting of (meth)acrylic acid esters having a cyclo ring and maleimides, (meth)acrylic acid esters having a branched alkyl group, and the like. A combination of these is preferable, and a copolymerizable monomer selected from the group consisting of (meth)acrylic acid esters and maleimides having a cyclo ring is more preferable.

The content of the structural units derived from the copolymerization monomer (preferably the content of the structural units derived from the copolymerization monomer having a bulky structure) is 100% by mass in total of the structural units constituting the (meth)acrylic resin. It is preferably 0 to 50% by weight, more preferably 10 to 40% by weight, even more preferably 10 to 30% by weight. The type and composition of the monomer of the (meth)acrylic resin can be identified by ¹ H-NMR.

The weight average molecular weight Mw of the (meth)acrylic resin is preferably 200,000 to 2,000,000, for example. When the weight average molecular weight Mw of the (meth)acrylic resin is within 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 even more preferably from 500,000 to 2,000,000. The weight average molecular weight Mw can be measured in terms of polystyrene by gel permeation chromatography (GPC).

1-2. Rubber Particles Rubber particles can have the function of imparting flexibility and toughness to an optical film, as well as forming irregularities on the surface of the optical film to impart slipperiness.

1-2-1. Regarding the shape of the rubber particles: The average aspect ratio of the rubber particles when observing the cross section of the optical film is preferably 1.2 to 3.0. When the average aspect ratio of the rubber particles is 1.2 or more, stress due to the stretching tension of the rubber particles (stretching force) is likely to be applied to the optical film immediately after winding, so the stress remaining in the optical film can be alleviated. It is easy to use, and it is possible to suppress curling failures. When the average aspect ratio of the rubber particles is 3.0 or less, the number of points of contact between adjacent rubber particles does not become too small, so the effect of dispersing stress remaining in the optical film is less likely to be impaired, and curling failures are 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.

Aspect ratio means the ratio of the longer axis to the shorter axis (longer axis/breadth axis) of a rubber particle. Moreover, the average aspect ratio means the average value of the aspect ratios of a plurality of rubber particles.

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

The average length of the rubber particles is preferably 200 to 500 nm. When the average major axis of the rubber particles is 200 nm or more, stress due to the stretching tension of the rubber particles (stretching force) is easily applied to the optical film immediately after being wound, so that it is easy to sufficiently suppress winding failures. When the average major axis of the rubber particles is 500 nm or less, the number of contact points between adjacent rubber particles is not too small, so the effect of dispersing stress is less likely to be impaired, and it is easy to sufficiently suppress curling failures. The average major axis of the rubber particles is more preferably from 220 to 400 nm, even more preferably from 250 to 350 nm. The average length of the rubber particles is the average value of the lengths of the rubber particles.

The average aspect ratio and average major axis of the rubber particles can be calculated by the following method.
1) A cross section of the optical film (a cross section parallel to the in-plane slow axis among the cross sections along the thickness direction of the optical film) is observed with a TEM. The observation area may be an area corresponding to the thickness of the optical film, or may be an area of 5 μm x 5 μm. When the observation area is a region corresponding to the thickness of the optical film, the number of measurement points can be one. When the observation area is a 5 μm×5 μm area, the number of measurement points can 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 defined as the "average aspect ratio", and the average value of the major diameters obtained from the plurality of rubber particles is defined as the "average major axis".

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

Whether the average aspect ratio of the rubber particles has been adjusted by stretching can be confirmed by checking that the ratio of the number of consecutive rubber particles is 15% or more (requirement 2) above). In other words, if flat rubber particles are used before stretching, not only will it be difficult for the rubber particles to come close to each other during the film forming process, but even if they do come close, more than a certain amount of rubber particles that are continuous in the short axis direction will be included. This is because it is thought that

1-2-2. Regarding Dispersed Structure of Rubber Particles The optical film includes a dispersed structure in which the major diameters of three or more rubber particles are closely connected in the major axis direction. Specifically, in the cross section of the optical film, a dispersed structure is observed in which three or more rubber particles are connected in the long axis direction, and the distance between the connected rubber particles is 100 nm or less.

FIG. 1 is a schematic cross-sectional view illustrating the state of dispersion of rubber particles in a cross-section of an optical film. 2A is an enlarged view of the area surrounded by dotted line 2A in FIG. 1, and FIG. 2B is an enlarged view of the area surrounded by dotted line 2B in FIG. 1. 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. Further, in FIG. 2A, LA indicates a virtual line including the long 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 specific dispersion structure in a matrix 110 mainly composed of (meth)acrylic resin.

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 in the long axis direction with some parts overlapping each other. FIGS. 2A and 2B are both examples of the above-mentioned specific distributed structure.

"The long axes of the rubber particles are continuous in the long axis direction" specifically refers to the angle formed between the long axes of adjacent rubber particles (in FIG. 2A, the angle between the imaginary lines LA including the long axes). This means that the smaller angle θ is 30° or less (preferably 10° or less). Note that examples in which the angle between the major axes of adjacent rubber particles is 0° include not only the aspect in which the major axes of adjacent rubber particles are aligned in a straight line, but also the aspect in which the major axes of adjacent rubber particles are aligned in a straight line, as shown in FIG. 2B. It also includes a mode in which the parts are continuous while overlapping each other.

"The interparticle distance 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 determined by analyzing a TEM image.

The ratio (proximity ratio) of the number of consecutive rubber particles (the number of rubber particles constituting a 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 adjacent rubber particles is high, making it easy to disperse stress. On the other hand, when the proximity ratio is 70% or less, the haze of the optical film is unlikely to increase. The proximity ratio is more preferably 20 to 60%, even more preferably 25 to 50%, and particularly preferably 30 to 50%.

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

It is preferable that the long axis direction of the rubber particles is substantially perpendicular to the thickness direction of the optical film. "Substantially perpendicular" refers to a range of 90±15°. Moreover, from the viewpoint of more easily suppressing the winding failure of the optical film after winding, it is preferable that the longer axis direction of the rubber particles is approximately parallel to the in-plane slow axis of the optical film. Substantially parallel refers to a range of 0±15°.

1-2-3. About the composition and structure of rubber particles Rubber particles are made of a graft copolymer containing a rubbery polymer (crosslinked polymer), that is, a core part made of the rubbery polymer (crosslinked polymer) and a shell part that covers it. It is preferable that the rubber particles have a core-shell type.

The glass transition temperature (Tg) of the rubbery polymer is preferably −10° C. or lower. When the glass transition temperature (Tg) of the rubbery polymer is −10° C. or lower, sufficient toughness can be easily imparted to the film. The glass transition temperature (Tg) of the rubbery polymer is more preferably -15°C or lower, and even more preferably -20°C or lower. The glass transition temperature (Tg) of the rubbery polymer is measured in the same manner as described above.

The glass transition temperature (Tg) of the rubbery polymer can be adjusted by, for example, the composition of the constituent monomers. In order to lower the glass transition temperature (Tg) of a rubbery polymer, as will be described later, for example, acrylic ester/methacrylic acid in which the alkyl group has 4 or more carbon atoms in the monomer mixture constituting the rubbery polymer. 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 within the above range, but examples thereof include butadiene crosslinked polymers, (meth)acrylic crosslinked polymers, and organosiloxanes. Contains crosslinked polymers. Among these, (meth)acrylic crosslinked polymers are preferred from the viewpoint of having a small refractive index difference with (meth)acrylic resins and are less likely to impair the transparency of the optical film. combination) is more preferred.

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

(Core part: Regarding acrylic rubber-like polymer (a))
The acrylic rubbery polymer (a) is a crosslinked polymer containing acrylic ester as a main component. The acrylic rubbery polymer (a) consists of a monomer mixture (a') containing 50 to 100% by mass of acrylic acid ester and 50 to 0% by mass of other monomers copolymerizable therewith, and It is a crosslinked polymer obtained by polymerizing 0.05 to 10 parts by mass (based on 100 parts by mass of monomer mixture (a')) of a polyfunctional monomer having two or more nonconjugated reactive double bonds. . The crosslinked polymer may be obtained by mixing all of these monomers and polymerizing them, or by changing the monomer composition and polymerizing them two or more times.

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

The content of the acrylic ester is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, and 70 to 99% by mass based on 100% by mass of the monomer mixture (a'). It is even more preferable. When the content of acrylic ester is 50% by weight or more, sufficient toughness can be easily imparted to the film.

In addition, from the viewpoint of making it easier to lower the glass transition temperature of the acrylic rubbery polymer (a) to -10°C or lower, the mass ratio of the acrylic acid alkyl ester/monomer mixture (a') in which the alkyl group has 4 or more carbon atoms is It is preferably 3 or more, and more preferably 4 or more and 10 or less.

Examples of copolymerizable monomers include methacrylic acid esters 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, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth) Acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate.

The content of the polyfunctional monomer is preferably 0.05 to 10% by mass, more preferably 0.1 to 5% by mass, based on the total 100% by mass of the monomer mixture (a'). When the content of the polyfunctional monomer is 0.05% by mass or more, it is easy to increase the degree of crosslinking of the obtained acrylic rubber-like polymer (a), so that the hardness and rigidity of the obtained film are not excessively impaired. When the amount is 10% by mass or less, the toughness of the film is less likely to be impaired.

(Shell part: Regarding monomer mixture (b))
The monomer mixture (b) is a graft component to the acrylic rubbery polymer (a) and constitutes the shell portion. It is preferable that the monomer mixture (b) contains methacrylic acid ester as a main component.

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

The content of the methacrylic ester is preferably 50% by mass or more based on 100% by mass of the monomer mixture (b). When the content of methacrylic acid ester is 50% by mass or more, the hardness and rigidity of the obtained film can be made difficult to decrease. From the viewpoint of lowering the affinity between the (meth)acrylic resin and the rubber particles (increasing ΔSP), the content of methacrylic acid ester should be 70% by mass or more based on 100% by mass of the monomer mixture (b). is more preferable, and even more preferably 80% by mass or more.

Monomer mixture (b) may further contain other monomers as necessary. Examples of other monomers include acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate; benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, phenoxy (meth)acrylate Includes (meth)acrylic monomers (ring structure-containing (meth)acrylic monomers) having an alicyclic structure such as ethyl, a heterocyclic structure, or an aromatic group.

(Core-shell type rubber particles: Regarding acrylic graft copolymer)
Examples of core-shell type rubber particles include methacrylic rubber particles 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). 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 contain 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) consisting of 40 to 100% by mass of methacrylic acid ester and 60 to 0% by mass of other monomers copolymerizable therewith, and 0.01 to 10 parts by mass of a polyfunctional monomer (monomer mixture A step of polymerizing (relative to a total of 100 parts by mass of (c1)) to obtain a hard polymer. (II) From 60 to 100 mass % of acrylic ester and 0 to 40 mass % of other monomers copolymerizable therewith. A step of obtaining a soft polymer by polymerizing a monomer mixture (a1) and 0.1 to 5 parts by mass of a polyfunctional monomer (based on a total of 100 parts by mass of the monomer mixture (a1)) (III) Methacrylic acid ester A monomer mixture (b1) consisting of 60 to 100% by mass and 40 to 0% by mass of other monomers copolymerizable with this, and 0 to 10 parts by mass of a polyfunctional monomer (total of 100 parts by mass of the monomer mixture (b1)) ) to obtain a hard polymer

Other polymerization steps may be further included between each of the polymerization steps (I) to (III).

The acrylic graft copolymer may be obtained further through the polymerization step (IV).
(IV) Monomer mixture (b2) consisting of 40 to 100% by mass of methacrylic ester, 0 to 60% by mass of acrylic ester, and 0 to 5% by mass of other copolymerizable monomer, and 0 to 10% of polyfunctional monomer Part by mass (based on 100 parts by mass of monomer mixture (b2)) is polymerized to obtain a hard polymer.

The methacrylic ester, acrylic ester, other copolymerizable monomers, and polyfunctional monomers used in each step can be the same as those described above.

The soft layer can impart shock absorption properties to the optical film. Examples of the soft layer include a layer made of an acrylic rubber-like polymer (a) containing an acrylic ester as a main component. The hard layer makes it difficult to impair the toughness of the optical film, and can suppress coarsening and agglomeration of particles during production of rubber particles. Examples of the hard layer include a layer made of a polymer containing methacrylic acid ester as a main component.

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

The grafting rate of the acrylic graft copolymer is measured by the following method.
1) 2 g of acrylic graft copolymer was dissolved in 50 ml of methyl ethyl ketone, and centrifuged for 1 hour at 30,000 rpm and 12°C using a centrifuge (manufactured by Hitachi Koki Co., Ltd., CP60E) to remove the insoluble matter. and the soluble fraction (centrifugation is performed 3 times in total).
2) The weight of the obtained insoluble matter is applied to the following formula to calculate the grafting ratio.
Grafting rate (%) = [{(Weight of methyl ethyl ketone insoluble matter) - (Weight of acrylic rubbery polymer (a))}/(Weight of acrylic rubbery polymer (a))] x 100

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

When the solubility parameter (SP value) of the shell portion constituting the rubber particle is SP2 and the SP value of the (meth)acrylic resin is SP1, ΔSP=|SP1−SP2| is 0.3 or more. It is preferably 0.5 or more, more preferably 0.8 or more. The upper limit value 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 combining the composition of the shell portion of the rubber particle and the composition of the (meth)acrylic resin. In order to make ΔSP above a certain level, for example, increase the content of methyl methacrylate (MMA) in the monomer mixture (b) constituting the shell part, and change the monomer composition constituting the (meth)acrylic resin. It is preferable to increase the content of the copolymerizable monomer 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, it is not only easy to impart sufficient flexibility and toughness to the (meth)acrylic resin film, but also to form irregularities on the surface to impart slipperiness. When the content of rubber particles is 20% by mass or less, haze does not increase too much. From the above viewpoint, the content of the rubber particles is more preferably 5 to 15% by mass, and even more preferably 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 it easier to unevenly distribute rubber particles in the surface layer portion of the film.

The organic fine particles preferably have 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, irregularities with appropriate hardness are likely to be formed on the surface of the optical film, thereby easily improving slipperiness. The glass transition temperature of the organic fine particles is more preferably 100°C or higher. Glass transition temperature is measured in the same manner as described above.

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

The resin constituting the organic fine particles may be one having a glass transition temperature (Tg) within the above range, and examples thereof include (meth)acrylic acid esters, itaconic acid diesters, maleic acid 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 These include polymers containing structural units that have the same structure, silicone resins, fluororesins, polyphenylene sulfide, and the like.

The (meth)acrylic esters, olefins, styrenes, (meth)acrylamides, unsaturated nitriles, unsaturated carboxylic acids, and polyfunctional monomers that constitute the above polymers are the (meth)acrylic resins and The same monomers as those mentioned above for forming the acrylic rubbery polymer (a) can be used. Examples of itaconic acid diesters include dimethyl itaconate, diethyl itaconate, and dipropyl itaconate. Examples of maleic acid 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 phenylacetate, vinyl benzoate, vinyl salicylate. It will be done. 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)acrylic esters, vinyl esters, and styrene are used because they have a high affinity with (meth)acrylic resins, are flexible against stress, and can easily adjust the glass transition temperature within the above range. A copolymer containing a structural unit derived from one or more selected from the group consisting of olefins, polyfunctional monomers, and a structural unit derived from a (meth)acrylic acid ester is preferable. , copolymers containing structural units derived from polyfunctional monomers are more preferable, and copolymers containing structural units derived from (meth)acrylic acid esters, structural units derived from styrenes, and structural units derived from polyfunctional monomers are more preferable. A copolymer containing a structural unit is more preferable.

When the organic fine particles contain structural units derived from polyfunctional monomers, the content of the structural units derived from the polyfunctional monomers in the organic fine particles is usually lower than the content of structural units derived from the polyfunctional monomers in the rubber particles. many. For example, the content of structural units derived from polyfunctional monomers is, for example, 50 to 500% by mass with respect to the total 100% by mass of structural units derived from monomers other than the polyfunctional monomers constituting the copolymer. sell.

Particles made of such a polymer (polymer particles) can be produced by any method such as emulsion polymerization, suspension polymerization, dispersion polymerization, and seed polymerization. Among these, seed polymerization and emulsion polymerization in an aqueous medium are preferred from the viewpoint of easily obtaining polymer particles with uniform particle diameters.

Examples of methods for producing polymer particles include:
・One-stage polymerization method in which a monomer mixture is dispersed in an aqueous medium and then polymerized;
- A two-stage polymerization method in which seed particles are obtained by polymerizing monomers in an aqueous medium, and then the monomer mixture is absorbed into the seed particles and then polymerized;
- A multi-stage polymerization method in which the 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 diameter of the polymer particles. Note that 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 copolymer of (meth)acrylic acid ester 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 increase in haze of the obtained film. is more preferable, and even more preferably 0.065 or less.

The average particle diameter of the organic fine particles is preferably 0.04 to 2 μm, more preferably 0.08 to 1 μm. When the average particle diameter of the organic fine particles is 0.04 μm or more, it is easy to impart sufficient slipperiness to the obtained film. When the average particle diameter of the organic fine particles is 2 μm or less, an increase in haze can be easily suppressed.

The average particle diameter of organic fine particles can be measured in the same manner as the average particle diameter of 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 equivalent circle diameters of 100 organic fine particles obtained by TEM observation of the cross section of the film. The equivalent circle diameter can be determined by converting the projected area of a particle obtained by imaging into the diameter of a circle having the same area. Note that the average particle diameter of the organic fine particles in the dispersion can be measured with a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

The average particle size of organic fine particles means the average size of aggregates (average secondary particle size) in the case of cohesive particles, and the average size of a single particle in the case of non-agglomerated particles. means value.

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

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

The amount of residual solvent 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 onto the support in the optical film manufacturing process described below.

The content of residual solvent in an optical film can be measured by headspace gas chromatography. In the headspace gas chromatography method, a sample is sealed in a container, heated, and while the container is filled with volatile components, the gas in the container is immediately injected into a gas chromatograph and mass spectrometry is performed to identify the compound. The volatile components are quantified while the test is being carried out. In the headspace method, it is possible to observe all peaks of volatile components using a gas chromatograph, and by using an analysis method that utilizes electromagnetic interaction, it is possible to quantify volatile substances and monomers with high precision. You can also do this at the same time.

1-5. Physical properties (haze)
It is preferable that the optical film of the present invention has high transparency. The haze of the optical film is preferably 4.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less. Haze can be measured using a haze meter (HGM-2DP, Suga Test Instruments) using a 40 mm x 80 nm sample at 25° C. and 60% RH according to JISK-6714.

(Phase difference Ro and Rt)
From the viewpoint of using the optical film of the present invention as a retardation film for IPS, for example, the in-plane retardation Ro measured at a measurement wavelength of 550 nm and in an environment of 23° C. and 55% RH is 0 to 10 nm. is preferable, and more preferably 0 to 5 nm. The retardation Rt in the thickness direction of the optical film of the present invention is preferably -20 to 20 nm, more preferably -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 (in the formula,
nx represents the refractive index in the in-plane slow axis direction (direction where the refractive index is maximum) of the film,
ny represents the refractive index in the direction perpendicular 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. )

The in-plane slow axis of the optical film of the present invention refers to the axis where the refractive index is maximum on the film surface. The in-plane slow axis of the optical film can be confirmed using an automatic birefringence meter Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrics). The in-plane slow axis usually coincides with the direction in which the stretching ratio is maximum.

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 using an Abbe refractometer, and the thickness d is measured using a commercially available micrometer.
2) The retardation Ro and Rt of the film after humidity conditioning at a measurement wavelength of 550 nm were measured at 23° C. and 55% RH using an automatic birefringence meter Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrix). Measure under environmental conditions.

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

(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. Method for Producing Optical Film The optical film of the present invention is produced 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-mentioned (meth)acrylic resin, rubber particles, and a solvent, and 2) casting the obtained dope onto a support. , drying and peeling to obtain a film-like material, 3) stretching the obtained film-like material, and 4) winding the stretched film-like material into a roll shape. .

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

The particle shape of the rubber particles used for preparing the dope is not particularly limited, but from the viewpoint of facilitating the development of a good stress relaxation effect by stretching, the shape of the rubber particles should be close to a true sphere, specifically, the average aspect ratio should be 1±1. Preferably it is 0.1.

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; non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Among these, methylene chloride is preferred.

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

Although the solid content concentration of the dope is not particularly limited, it is preferably lower from the viewpoint of making it easier for the rubber particles to be appropriately brought close to each other in the resulting optical film due to the compression effect caused by 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 organic fine particles if necessary to the above-mentioned solvent and mixing; or by adding (meth)acrylic to the above-mentioned solvent. A resin solution in which the system resin is dissolved, a rubber particle dispersion in which rubber particles are dispersed in the above-mentioned solvent, and a fine particle dispersion in which organic fine particles are dispersed in the above-mentioned solvent as necessary are prepared in advance. You may prepare by mixing them.

The solvent contained in the rubber particle dispersion preferably contains a solvent having low affinity with the rubber particles, from the viewpoint of facilitating the proper proximity of the rubber particles in the resulting optical film. Examples of such solvents include the aforementioned poor solvents, such as linear or branched aliphatic alcohols having 1 to 4 carbon atoms. The content of the poor solvent is preferably 2 to 16% by mass, more preferably 4 to 16% by mass, based on the total solvent contained in the rubber particle dispersion.

The method of adding the organic fine particles is not particularly limited, and the organic fine particles may be added to the solvent individually, or may be added to the solvent as an aggregate of organic fine particles. The aggregate of organic fine particles is composed of a plurality of organic fine particles whose mutual connection (fusion) is suppressed. Therefore, it is easy to handle, and when an aggregate of organic fine particles is dispersed in a (meth)acrylic resin or a solvent, it is 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.

Regarding the step 2), the obtained dope is cast onto a support. The dope can be cast by being discharged from a casting die.

Next, the solvent in the dope cast onto the support is evaporated and dried. The dried dope is peeled off from the support to obtain a film-like product.

The amount of residual solvent in the dope when it is peeled off from the support (the amount of residual solvent in the film-like material when it is peeled off) is 10 to 150 mass in terms of facilitating the reduction of the retardation of the obtained (meth)acrylic resin film. %, more preferably 20 to 40% by mass. If the amount of residual solvent at the time of peeling is 10% by mass or more, the (meth)acrylic resin will easily flow during drying or stretching and will be easily unoriented, so that the retardation of the obtained (meth)acrylic resin film will be reduced. Easy to reduce. When the amount of residual solvent at the time of peeling is 150% by mass or less, the force required to peel off the dope is unlikely to become excessively large, making it easy to suppress breakage of the dope.

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

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

Regarding step 3), the film-like material obtained by peeling is stretched while drying.

Stretching may be carried out depending on the required optical properties, and it is preferable to stretch in at least one direction (for example, the width direction (TD direction) of the film-like material), and it is preferable to stretch in two directions perpendicular to each other (for example, in the width direction (TD direction) of the film). Biaxial stretching may be carried out in the width direction (TD direction) of the shaped article and in the transport direction (MD direction) perpendicular thereto.

The stretching ratio may be set so that the average aspect ratio of the rubber particles is within the above range, for example, preferably 20 to 200%, more preferably 30 to 100%, and 50 to 70%. It is more preferable that The stretching ratio (%) is defined as (amount of change in length in the stretching direction of the film before and after stretching)/(length in the stretching direction of the film before stretching)×100 (%). In addition, when performing biaxial stretching, it is preferable to set it as the said stretching magnification about each of TD direction and MD direction.

Note that the in-plane slow axis direction (the direction in which the refractive index is maximized in the plane) of the optical film 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 (Tg-50)°C to (Tg+50), where Tg is the glass transition temperature of the (meth)acrylic resin. )°C, and even more preferably (Tg-30)°C to (Tg+50)°C. When the stretching temperature is (Tg-30)°C or higher, it is easy to make the membrane-like material soft enough for stretching, and the tension applied to the membrane-like material during stretching does not become too large, so that it is possible to obtain (meta) This makes it difficult for excessive residual stress to remain in the acrylic resin film. When the stretching temperature is below Tg, it is easy to suppress the generation of bubbles due to vaporization of the solvent in the film-like material. Specifically, the stretching temperature can be 60 to 220°C.

The stretching temperature is (a) when drying with a non-contact heating type such as a tenter stretching machine, the temperature inside the stretching machine or the ambient temperature such as hot air temperature, and (b) when drying with a contact heating type such as a heated roller. , the temperature of the contact heating section, or (c) the surface temperature of the film-like material (surface to be dried). Among these, when drying is performed using a non-contact heating type such as (a) a tenter stretching machine, the temperature inside the stretching machine or the atmospheric temperature such as hot air temperature is preferable.

The amount of residual solvent in the film-like material 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 by the same method as described above.

Stretching of the film-like material in the TD direction (width direction) can be carried out, for example, by fixing both ends of the film-like material with clips or pins and widening the interval between the clips or pins in the traveling direction (tenter method). Stretching of the film-like material in the MD direction can be carried out, for example, by a method (roll method) in which a plurality of rolls are provided with a difference in peripheral speed and the difference in peripheral speed between the rolls is utilized.

Regarding the step 4), the film-like material obtained after stretching is further dried as necessary and wound up into a roll to obtain a roll of optical film.

The drying temperature can be adjusted within the same range as the stretching temperature in step 3) above. The drying temperature is measured in the same manner as in step 3) above. (b) When drying with a contact heating type such as a heated roller, it is preferable to measure the temperature of the contact heating part.

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

In the roll body obtained after winding, it is preferable that the longer axis direction of the rubber particles is approximately perpendicular to the thickness direction of the optical film. Moreover, from the viewpoint of more easily suppressing the winding failure of the optical film after winding, it is preferable that the longer axis direction of the rubber particles is approximately parallel to the stretching direction (preferably the width direction) of the optical film.

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

As mentioned above, due to the winding tension, a force (stress) tends to act on the optical film of the roll body immediately after being wound to cause it to shrink in the longitudinal direction, and a force (stress) tends to act to stretch it in the width direction. On the other hand, the optical film of the present invention has a structure in which rubber particles having an average aspect ratio of a certain value or more are appropriately close to each other. Thereby, even without increasing the particle size of the rubber particles, the optical film of the rolled body after winding can effectively relieve the stress. Thereby, it is possible to suppress transfer of the winding core due to a force that tends to shrink in the longitudinal direction, and chain-like failure due to a force that tends to stretch in the width direction. Therefore, the winding shape can be improved without increasing the haze of the optical film.

In particular, the longer the optical film is (the longer the length in the MD direction) and the wider the optical film (the longer the length in the TD direction), the more likely the curling failure will occur. The present invention can satisfactorily suppress curling defects even in such roll bodies of optical films.

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

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

3-1. Polarizer A polarizer is an element that passes only light with a plane of polarization in a certain direction, and is a polyvinyl alcohol polarizing film. Polyvinyl alcohol-based polarizing films include those made by dyeing polyvinyl alcohol-based films with iodine and those made by dyeing them with dichroic dyes.

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

For example, the content of ethylene units is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the saponification degree is 99.0 to 99.99 mol%, as described in JP-A No. 2003-248123, JP-A No. 2003-342322, etc. Ethylene-modified polyvinyl alcohol is used.

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

3-2. Other Optical Film When the optical film of the present invention is placed on only one side of the polarizer, another optical film may be placed on the other side. Note that the optical film and other optical films may be placed on the polarizer via an adhesive layer.

Examples of other optical films include commercially available cellulose ester films (e.g., Konica Minolta Tac KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd., Fujitac T40UZ, Fujitac T60UZ, Fujitac T80UZ, Fujitac TD80UL, Fujitac TD60UL, Fujitac TD 40UL, Fujitac R02, Fujitac R06, (manufactured by Fujifilm Co., Ltd.), etc.

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, preferably 40 to 80 μm.

3-3. Method for Manufacturing 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 together 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 a photo-radical polymerizable composition using radical photopolymerization, a photo-cationic polymerizable composition using cationic photopolymerization, 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 polarizing plate placed on one side of the liquid crystal cell, and a second polarizing plate placed on the other side of the liquid crystal cell.

Display modes of liquid crystal cells include, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment), MVA (Multi-domain Vertical Alignment), and PVA. (Patterned Vertical Alignment), IPS (In-Plane-Switching), etc. Among these, VA (MVA, PVA) mode and IPS mode are preferred.

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.

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

1. Optical film materials (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 ℃, 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)

The glass transition temperature (Tg) and weight average molecular weight (Mw) of (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 using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012.

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

(2) Rubber particles <Preparation of rubber particles C1>
Acrylic modifier Kane Ace M210 manufactured by Kaneka Corporation (core part: multilayered acrylic rubber-like polymer (Tg: approx. -10°C), shell part: methacrylic acid ester polymer mainly composed of methyl methacrylate core-shell type rubber particles, average particle diameter: 220 nm)

<Preparation of rubber particles C2>
The following components were charged into a glass reactor.
Ion exchange 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 interior of the polymerization machine with nitrogen gas, the internal temperature was brought 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) were added. , and 0.065 parts by mass of tertiary dodecyl mercaptan (tDM), 25% by mass of a monomer mixture (c1) was added all at once to the polymerization machine. To this, 0.00645 parts by mass of 5% sodium formaldehyde sulfoxylate, 0.0056 parts by mass of sodium ethylenediaminetetraacetate, and 0.0014 parts by mass of ferrous sulfate were added, and after 15 minutes, t -0.022 parts by mass of butyl hydroperoxide was added, and the polymerization was continued for an additional 15 minutes. Thereafter, 0.013 parts by mass of 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 addition was completed, 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 polymerization. The polymerization conversion rate was 98%.

The obtained polymer latex was maintained 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 consisting of 32.5 parts by mass of 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 of monomer mixture (a1). Continuous additions were made over a period of minutes. Thereafter, the mixture was held for 45 minutes to complete the polymerization. The average particle diameter of the obtained rubbery polymer was 260 nm, and the polymerization conversion rate was 99%.

The obtained rubbery polymer was kept at 80° C. and 0.0097 parts by mass of potassium persulfate and 0.05 parts by mass of sodium hydroxide were added, and then 50 parts by mass of monomer mixture (b1) (MMA: 90% by mass, BA :10% by mass) was continuously added over 150 minutes. After the addition was completed, the mixture was held 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 white powdery graft copolymer containing a rubbery polymer (rubber particles C2). Obtained. The glass transition temperature (Tg) of the rubbery polymer of the obtained rubber particles C2 was -30°C, the average particle diameter was 380 nm, the grafting rate was about 149%, and the polymerization conversion rate was 99%. there were.

The ΔSP of the obtained rubber particles (shell part) 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, the structural formulas of the (meth)acrylic resin and the resin constituting the shell were input into the commercially available simulation software "Material Studios Forcite" (manufactured by Dassault Systèmes), and the SP value was calculated. , was obtained by calculating the difference between them.

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

(Preparation of seed particles)
1,000 g of deionized water was placed in a polymerization vessel equipped with a stirrer and a thermometer, and 50 g of methyl methacrylate and 6 g of t-dodecyl mercaptan were charged therein, and the mixture was heated to 70° C. while being stirred and replaced with nitrogen. The internal temperature was maintained 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)
800 g of deionized water in which 2.4 g of sodium lauryl sulfate was dissolved as a gelling inhibitor was placed in a polymerization vessel equipped with a stirrer and a thermometer, and 66 g of methyl methacrylate, 20 g of styrene, and 64 g of ethylene glycol dimethacrylate were added as a monomer mixture. A mixed solution of 1 g of azobisisobutyronitrile as a polymerization initiator was added. Then, the mixture was heated to T. A dispersion liquid was obtained by stirring with a K homo mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.).

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

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

The average particle diameter 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 using a zeta potential/particle size measuring system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.). The average particle diameter of organic fine particles measured using a zeta potential/particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.) is approximately the same as the average particle diameter of organic fine particles measured by TEM observation of an optical film. It matches.

2. Production and evaluation of optical film [Example 1]
(Preparation of rubber particle dispersion)
After stirring and mixing 11.3 parts by mass of rubber particles C2 and 200 parts by mass of methylene chloride with a dissolver for 50 minutes, they were mixed under 1500 rpm using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). The mixture 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 pressurized dissolution tank. Next, (meth)acrylic resin A was charged into a pressurized dissolution tank while being stirred. Next, the rubber particle dispersion prepared above was added and completely dissolved while stirring. The resulting solution had a viscosity of 16,000 mmPa·s and a water content of 0.50%. This was filtered using SHP150 manufactured by Loki Techno Co., Ltd. at a filtration flow rate of 300 L/m ² ·h and a filtration pressure of 1.0×10 ⁶ Pa to obtain a dope.
(Composition of dope)
(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 forming)
Using an endless belt casting device, the dope was uniformly cast onto 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 conveyance speed of the stainless steel belt was 20 m/min.

The solvent was evaporated on a stainless steel belt support until the amount of residual solvent in the cast dope became 30% by mass. Next, it was peeled off from the stainless steel belt support with a peeling tension of 128 N/m to obtain a film-like product (the amount of residual solvent in the film-like product at the time of peeling was 30% by mass). While the peeled film was conveyed by a number of rollers, the obtained film-like material was stretched by 30% in the width direction using a tenter at (Tg+15)°C (140°C in this example). The amount of residual solvent in the film-like material at the start of stretching was 10% by mass. After that, it was further dried while being transported with rolls, and the ends sandwiched between tenter clips were slit with a laser cutter and wound up to obtain an optical film with a widthwise length of 2.3 m, a length of 7000 m, and a film thickness of 40 μm. Ta.

[Example 2, 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 (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 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 concentration of the dope was changed as shown in Table 1.

[Example 8, 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 concentration 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)
After stirring and mixing 11.3 parts by mass of rubber particles C1, 180 parts by mass of methylene chloride, and 20 parts by mass of ethanol using a dissolver for 50 minutes, the mixture was mixed using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). A rubber particle dispersion was obtained by dispersing the rubber particles under 1500 rpm using a rubber particle dispersion.

(Preparation of organic fine particle dispersion)
12 parts by mass of 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 at 1500 rpm using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). , 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 pressurized dissolution tank. Next, (meth)acrylic resin 1 was charged into a pressurized dissolution tank while being stirred. Next, the fine particle dispersion prepared above was added, heated to 60° C., and completely dissolved while stirring. The heating temperature was raised from room temperature at a rate of 5°C/min, and after melting for 30 minutes, the temperature was lowered at a rate of 3°C/min. After filtering the resulting solution, a dope was obtained.

(Composition of dope)
(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 forming)
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 (meth)acrylic resin was changed as shown in Table 1.

[Comparative Examples 2 and 5]
An optical film was obtained in the same manner as 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 concentration of the dope was changed as shown in Table 1.

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

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, average major axis of rubber particles)
The average aspect ratio and average major axis of the rubber particles were calculated using the following procedure.
1) A cross section of the optical film (a cross section parallel to the width direction among the cross sections along the thickness direction of the optical film) was observed using a 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 operations 1) and 2) above were performed at a total of four locations, changing the observation areas. The average value of the measured aspect ratios was defined as the "average aspect ratio", and the average value of the measured major axes was defined as the "average major axis".

(proximity ratio of rubber particles)
The proximity ratio of rubber particles was measured using the following procedure.
1) In the above TEM image (observation area: 5 μm x 5 μm), the major axis of each rubber particle was specified. Then, rubber particles were identified in which the smaller angle between the long diameters of 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 identified above to the total number of rubber particles in the observation area was calculated.
3) The above operations 1) and 2) were performed at a total of four locations while changing the observation area, and the average value of the calculated ratios was taken as the "proximity ratio" (%).

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

(Brittleness: MIT bendability)
The MIT bendability of the obtained optical film was measured using a folding durability tester (manufactured by Tester Sangyo Co., Ltd., MIT, model BE-201, bending radius of curvature 0.38 mm).
Specifically, a (meth)acrylic resin film with a width of 15 mm and a length of 150 mm was used as a test piece, and was left at a temperature of 25°C and a relative humidity of 65% RH for more than 1 hour. Measurements were made under the following conditions in accordance with JIS P8115:2001, and evaluation was made based on the number of times until breakage based on 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 △: 100 or more and less than 300 times ×: less than 100 times The more times it takes to break, the better the flexibility. It represents excellent resistance to repeated bending, and if it is △ or higher, it has practically desirable characteristics.
If it was △ or more, it was judged as good.

(Winding shape (winding tightness failure, chain-like failure))
(1) Tightness of winding (core transfer)
The obtained roll of optical film was stored in an atmosphere of 40° C. and 80% RH for 10 days, and then unwound and the length (m) of the optical film where transfer from the core had occurred was measured. Note that the transfer from the winding core is a surface defect caused by deformation (stress that tends to shrink in the longitudinal direction) of the optical film after winding, and is formed inside the winding in the longitudinal direction.
◎: Less than 10 m ○: 10 m or more and less than 50 m △: 50 m or more and less than 100 m ×: 100 m or more If it was △ or more, it was judged as good.

(2) Chain-like failure The obtained roll of 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 that occurs due to deformation (stress that tends to stretch in the width direction) of the optical film after winding, and is formed throughout the width direction. Then, evaluation was made based on the following.
◎: Less than 10 m ○: 10 m or more and less than 200 m △: 200 or more and less than 1000 m ×: 1000 m or more If it was △ or more, it was judged as 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 represents methylene chloride and EtOH represents ethanol.

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

In particular, it can be seen that by increasing the stretching ratio, the average aspect ratio and proximity ratio become even higher (comparison of Examples 1 to 3).

Furthermore, it can be seen that by increasing the glass transition temperature (Tg) of the (meth)acrylic resin, the proximity ratio becomes even higher (comparison of Examples 1, 4, and 5).

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

Furthermore, it can be seen that by lowering the solid content concentration of the dope, the proximity ratio becomes even higher. This is considered to be because the rubber particles tend to be oriented with respect to each other due to the compression effect during dope drying (comparison between Examples 2 and 7, and comparison between Examples 8 and 9).

Furthermore, it can be seen that the proximity ratio is further increased by including a poor solvent (EtOH) in the dispersion solvent of the rubber particles (comparison of Examples 2, 8, and 13).

In contrast, the optical films of Comparative Examples 2 and 4 in which the average aspect ratio of the rubber particles is less than 1.3, the optical films of 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 suppress winding failures such as tight winding and chain failures.

In addition, when the haze of the optical films of Examples 1 to 13 was measured according to JISK-6714 at 25° C. and 60% RH using a haze meter (HGM-2DP, Suga Test Instruments), all of them were less than 0.3%. It was also small and in good condition.

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

According to the present invention, there is provided an optical film, an optical film roll body, a polarizing plate protective film, and a method for producing an optical film, which can improve brittleness well and suppress curling failure without impairing transparency. be able to.

100 Optical film 110 Matrix 120 Rubber particles LA Virtual line d Interparticle distance

Claims (15)

An optical film comprising 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 average aspect ratio of the rubber particles is 1.2 to 3.0,
Particles of the rubber particles in which the longer diameters of three or more of the rubber particles are connected such that the angle θ, which is the smaller of the angles formed by the longer diameters of the adjacent rubber particles, is 30 ° or less, and the rubber particles are connected in a row. the distance between them 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 long axis direction of the rubber particles is within a range of 90±15° with respect 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 long axis direction of the rubber particles is within a range of 0±15° with respect to the in-plane slow axis.
The optical film according to claim 1 or 2. 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 average major axis of the rubber particles is 200 to 500 nm.
The optical film according to any one of claims 1 to 4. The (meth)acrylic resin has a structural unit derived from a copolymerization monomer selected from the group consisting of (meth)acrylic esters having a cyclo ring and maleimides, and a (meth)acrylic ester having a branched alkyl group. containing at least one of the structural units derived from
The optical film according to any one of claims 1 to 5. further comprising organic fine particles having a glass transition temperature of 80°C or higher;
The optical film according to any one of claims 1 to 6. Comprising the optical film according to any one of claims 1 to 7,
Polarizing plate protective film. A roll body of an optical film containing a (meth)acrylic resin having a glass transition temperature of 110° C. or higher and rubber particles and wound in a direction perpendicular to the width direction thereof,
In the cross section of the optical film,
The average aspect ratio of the rubber particles is 1.2 to 3.0,
The major axes of three or more of the rubber particles are connected such that the smaller angle θ among the angles formed by the major axes of the adjacent rubber particles is 30 ° or less, and the interparticle 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,
A roll of optical film. The long axis direction of the rubber particles is within a range of 90±15° with respect to the thickness direction of the optical film.
The roll body of the optical film according to claim 9. The long axis direction of the rubber particles is within a range of 0±15° with respect to the width direction of the optical film.
The optical film roll body according to claim 9 or 10. The width of the optical film is 2.3 m or more,
The length of the optical film is 5000 m or more,
The optical film roll according to any one of claims 9 to 11. A method for producing an optical film according to claim 1, comprising:
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 content concentration of 15% by mass or lower;
A step of casting the obtained dope onto a support, followed by drying and peeling to obtain a film-like material;
Stretching the film-like material by 20% or more,
Method for manufacturing optical film. 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,
The solvent contained in the rubber particle dispersion includes a poor solvent for the polymer,
The method for producing an optical film according to claim 13. 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 or 14.

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