KR102496408B1 - Optical film, polarizing plate protective film, roll body of optical film, and manufacturing method of optical film - Google Patents

Abstract

The optical film of the present invention contains 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, three or more of the rubber particles are continuous in the major axis direction, and the inter-particle distance of the continuous rubber particles is 100 nm or less and the ratio of the number of continuous rubber particles to the total number of rubber particles contained in the optical film is 15% or more.

Description

Optical film, polarizing plate protective film, roll body of optical film, and manufacturing method of optical film

The present invention relates to an optical film, a polarizing plate protective film, a roll body of an optical film, 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, as a polarizing plate protective film, a film containing cellulose acylate as a main component is used. However, since the film which has cellulose acylate as a main component has low moisture resistance, when it was used as a polarizing plate, it may not be able to fully suppress deterioration by the water|moisture content of a polarizer under high temperature, high humidity. Then, instead of a film containing cellulose acylate as a main component, using a film containing a thermoplastic resin excellent in moisture resistance as a main component has been studied.

Patent Literature 1 discloses a maleimide-based copolymer resin film containing a maleimide-based copolymer resin and a rubber-like polymer having a polymer chain compatible therewith. It is disclosed that the aspect ratio of a rubbery polymer is 2 or less. And, although the film of the maleimide-based copolymer resin alone is brittle, the brittleness can be improved by containing a rubber-like polymer, and the rubber-like polymer has a polymer chain compatible with the resin, so that the resin and rubber are formed during stretching. It is disclosed that the decrease in transparency of the film due to the formation of voids at the interface of the shape polymer can be suppressed.

Japanese Unexamined Patent Publication No. 2006-124435

By the way, after optical films, such as a polarizing plate protective film, are normally formed into a long film shape, they are wound up in roll shape, and are stored and conveyed as a roll body. Winding of a long film is usually performed while applying tension. Therefore, the force to expand in the longitudinal direction is easily applied to the optical film to be wound, and the force to contract in the width direction is easily applied due to the winding tension. As a result, the force (stress) to shrink easily in the longitudinal direction and the force (stress) to expand in the width direction are likely to occur in the optical film of the roll body immediately after winding. And, transfer by winding core due to tight winding by force (stress) to shrink in the longitudinal direction tends to occur; Chain-shaped failures have occurred in some cases due to the force (stress) to extend in the width direction.

The transfer of the winding core is a planar defect, which tends to form inside the winding of the film in the longitudinal direction (a portion close to the winding core at the beginning of winding). A chain-like defect is a chain-like defect that tends to form throughout the width direction of the film.

In order to reduce the transfer of these winding cores and chain failure, it is desired that the stress remaining in the optical film immediately after winding can be effectively relieved by rubber particles. In order to effectively relieve stress by rubber particles, it is desired that the rubber particles have a large particle diameter. However, if the particle size of the rubber particles is too large, the haze of the film increases and the transparency is liable to be impaired. Therefore, it is desired to be able to suppress winding failures such as transfer of winding cores and chain failures without increasing the haze of the optical film, that is, without significantly increasing the particle diameter of the rubber particles.

In particular, widening and thinning of optical films, such as a polarizing plate protective film, are calculated|required with enlargement and thickness reduction of a display device. In such a widened and thinned optical film, winding failure is particularly likely to occur.

The present invention has been made in view of the above circumstances, and is a film containing (meth)acrylic resin as a main component, which does not impair transparency, improves brittleness well, and can suppress winding failure, an optical film and polarizer protection. It aims at providing the manufacturing method of a film, the roll body of an optical film, and an optical film.

The above problem can be solved by the following structure.

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

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

The optical film roll of the present invention contains a (meth)acrylic resin having a glass transition temperature of 110° C. or higher and rubber particles, and is wound in a direction perpendicular to the width direction thereof, wherein the cross section of the optical film is wherein the average aspect ratio of the rubber particles is 1.2 to 3.0, the major diameters of three or more rubber particles are continuous in the major axis direction, and the inter-particle distance between the rubber particles is 100 nm or less; The ratio of the number of continuous rubber particles to the total number of rubber particles contained 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, and using the obtained dope as a support After casting on top, drying and exfoliation to obtain a membranous material, and a process of stretching the membranous material by 20% or more are included.

ADVANTAGE OF THE INVENTION According to this invention, the optical film which does not impair transparency, brittleness is improved favorably, and winding failure can be suppressed, the roll body of an optical film, and the manufacturing method of an optical film can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the dispersion state of rubber particles in the cross section of an optical film.
FIG. 2A is an enlarged view of a region surrounded by dotted line 2A in FIG. 1 , and FIG. 2B is an enlarged view of a region surrounded by dotted line 2B in FIG. 1 .

As a result of intensive studies, the inventors of the present invention have 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, does not impair transparency and is brittle. It was found that this is improved favorably, and also the winding shape failure can be suppressed.

The specific dispersion structure refers to a dispersion structure that satisfies the following 1) and 2) in the cross section of an optical film specifically.

1) Rubber particles having an average aspect ratio of 1.2 to 3.0

2) Three or more rubber particles are continuous in the direction of the major axis, and the distance between the continuous rubber particles is 100 nm or less, and

A ratio of the number of continuous rubber particles to the total number of rubber particles contained in the optical film (hereinafter also referred to as “proximity ratio”) of 15% or more

That is, if the average aspect ratio of the rubber particles is higher than a certain level (requirement of 1 above), since the rubber particles stretched by stretching are unstable, restoring force to return to the stable original shape (spherical shape) is likely to be generated. Thereby, the flat-shaped rubber particle can absorb and alleviate the stress which remains in the optical film immediately after winding-up by the said restoring force.

In addition, the effect of suppressing the winding failure by the restoring force of the rubber particles is obtained even if the stretching direction of the film and the stretching direction of the rubber for suppressing it (the direction of the restoring force) do not necessarily coincide. The reason is considered to be that, when a certain force acts on the film, the rubber particles absorb the force and convert it into a restoring force (for example, restoration in the thickness direction) to exert an effect.

In addition, by appropriately containing a structure in which three or more rubber particles are adjacent to each other in the major axis direction (requirement of 2) above, the stress remaining in the optical film immediately after winding can be well dispersed and relieved. In particular, in a long and wide film, the stress (stretching force) remaining in the optical film tends to increase, and when the rubber particles are single and uniformly dispersed, the stress (stretching force) locally remaining in the optical film tends to increase. may not be able to absorb all; When a plurality of rubber particles are adjacent to each other, the stress (extension force) remaining in the optical film can be absorbed as in the case of rubber particles having a relatively large particle diameter, regardless of the longitudinal direction and the width direction.

It is thought that these actions can effectively alleviate the stress (extension force) remaining in the optical film immediately after winding by the rubber particles without increasing the average major diameter of the rubber particles.

In addition, the brittleness of the optical film is also reduced because three or more rubber particles adjoining in the direction of their major axis and having a continuous structure properly contained (requirement of 2 above) can disperse stress to a higher degree than single particles having a large particle diameter. can be highly improved.

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

The requirements of 2) above are, 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, and the rubber particles It can be adjusted by the composition of the dispersing solvent of the dispersion, the stretching ratio, and the like. In order to increase the proximity ratio of rubber particles, for example, it is preferable to increase the glass transition temperature (Tg) of (meth)acrylic resin to 110 ° C. or higher, and the affinity between (meth)acrylic resin and rubber particles (ΔSP etc.) is preferably moderately low, the solid content concentration of the dope is preferably low, a poor solvent is preferably added to the dispersion solvent of the rubber particle dispersion, and the draw 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 (meth)acrylic resin preferably has a glass transition temperature (Tg) of 110°C or higher. When the glass transition temperature (Tg) of the (meth)acrylic resin is 110°C or higher, at the same stretching temperature, the rubber particles are less likely to move than the (meth)acrylic resin having a lower glass transition temperature (Tg). can do. Because of this, the rubber particles do not diffuse excessively, so that they can be properly brought close to each other. The glass transition temperature (Tg) of the (meth)acrylic resin is preferably from 120 to 160°C, and more preferably from 125 to 150°C from the above viewpoint.

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

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 of a copolymerization monomer having a bulky structure described later, for example.

The (meth)acrylic resin may be a homopolymer of (meth)acrylic acid ester or a copolymer of (meth)acrylic acid ester and a copolymerizable monomer copolymerizable therewith. Moreover, (meth)acryl means an acryl or methacryl. It is preferable that (meth)acrylic acid ester is methyl methacrylate.

That is, the (meth)acrylic resin contains a structural unit derived from methyl methacrylate, and further contains a structural unit derived from a copolymerization monomer other than methyl methacrylate (hereinafter simply referred to as "copolymerization monomer"). It is desirable to do

Examples of copolymerization monomers include:

Methyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid Octyl, phenyl (meth)acrylate, benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, acrylic esters having 1 to 20 carbon atoms in an alkyl group or methacrylic esters having 2 to 20 carbon atoms in an alkyl group, such as adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, and lactone (meth)acrylate;

Aromatic vinyls, such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and (alpha)-methylstyrene;

alicyclic vinyls such as vinylcyclohexane;

unsaturated nitriles such as (meth)acrylonitrile and (meth)acrylonitrile-styrene copolymer;

unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, (meth)acrylic acid, itaconic acid, itaconic acid monoester, maleic acid, and maleic acid monoester;

olefins such as vinyl acetate, ethylene and propylene;

vinyl halides such as vinyl chloride, vinylidene chloride, and vinylidene fluoride;

(meth)acrylamide, methyl (meth)acrylamide, ethyl (meth)acrylamide, propyl (meth)acrylamide, butyl (meth)acrylamide, tert-butyl (meth)acrylamide, phenyl (meth)acrylamide, etc. (meth)acrylamides of;

unsaturated glycidyls such as glycidyl (meth)acrylate;

Maleimides, such as N-phenyl maleimide, N-ethyl maleimide, N-propyl maleimide, N-cyclohexyl maleimide, and N-o-chlorophenyl maleimide, are contained. These may be used independently and may use 2 or more types together.

Especially, the copolymerization monomer which has a bulky structure is preferable from a viewpoint of moderately lowering affinity with a rubber particle, etc., raising the glass transition temperature (Tg) of an optical film.

Examples of copolymerized monomers having a bulky structure include:

(meth)acrylic acid esters having a cyclo ring such as dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, and cyclohexyl (meth)acrylate; vinyls having a cyclo ring such as vinyl cyclohexane; and copolymerization monomers selected from the group consisting of maleimides such as N-phenylmaleimide;

Copolymerization monomers, such as (meth)acrylic acid ester which has a branched alkyl group, such as t-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, are contained.

Among them, the copolymerization monomer having a bulky structure is a copolymerization monomer 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 combinations thereof It is preferable, and it is more preferable that it is a copolymerization monomer selected from the group which consists of (meth)acrylic acid esters and maleimides which have a cyclo ring.

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

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

1-2. rubber particles

The rubber particles may have a function of imparting flexibility and toughness to the optical film and providing slipperiness by forming irregularities on the surface of the optical film.

1-2-1. About the shape of rubber particles

It is preferable that the average aspect ratio of the rubber particle at the time of observing the cross section of an optical film is 1.2-3.0. If the average aspect ratio of the rubber particles is 1.2 or more, since the stress (force to reduce) for the stretching tension of the rubber particles is likely to be applied to the optical film immediately after winding, the stress remaining in the optical film is easy to be relieved, resulting in a winding shape failure. can suppress If the average aspect ratio of rubber particles is 3.0 or less, contact points between adjacent rubber particles are not too small, so the effect of dispersing the stress remaining in the optical film is not easily inhibited, and winding failure can be suppressed. The average aspect ratio of the rubber particles is more preferably from 1.5 to 2.8, and still more preferably from 2.0 to 2.5.

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

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

The average major diameter of the rubber particles is preferably 200 to 500 nm. When the average major diameter of the rubber particles is 200 nm or more, since the stress on the stretching tension of the rubber particles (force to reduce) is easily applied to the optical film immediately after winding, winding failure is easily suppressed sufficiently. When the average major diameter of the rubber particles is 500 nm or less, contact points between adjacent rubber particles are not too small, so the effect of dispersing stress is not easily inhibited, and winding failure is easily suppressed. The average major diameter of the rubber particles is more preferably 220 to 400 nm, and still more preferably 250 to 350 nm. The average major diameter of rubber particles is the average value of the major diameters of rubber particles.

The average aspect ratio and average major diameter of 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 cross sections along the thickness direction of the optical film) is observed by TEM. The observation region may be a region corresponding to the thickness of the optical film, or may be a region of 5 μm × 5 μm. When the area|region corresponding to the thickness of an optical film is made into an observation area, the measurement point can be made into one place. When a region of 5 µm × 5 µm is used as the observation region, four measurement points can be provided.

2) The major axis and minor axis of each rubber particle in the obtained TEM image are measured, and the aspect ratio is calculated, respectively. The average value of the aspect ratios obtained from a plurality of rubber particles is referred to as "average aspect ratio", and the average value of major diameters obtained from a plurality of rubber particles is referred to as "average major axis".

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

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

1-2-2. About the dispersion structure of rubber particles

The optical film contains a dispersed structure in which three or more rubber particles are close to each other in the direction of the major axis and are continuous. Specifically, in the cross section of the optical film, a dispersed structure in which three or more rubber particles are continuous in the major axis direction and the interparticle distance of the continuous rubber particles is 100 nm or less is observed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the dispersion state of rubber particles in the cross section of an optical film. FIG. 2A is an enlarged view of a region surrounded by dotted line 2A in FIG. 1 , and FIG. 2B is an enlarged view of a region 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. In Fig. 2A, LA represents a virtual line including the major axis of the rubber particle.

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

Fig. 2A shows a state in which four rubber particles are continuous at predetermined intervals in the direction of their major axis. Fig. 2B shows a continuous state in which three rubber particles partially overlap each other in the longitudinal direction. 2A and 2B are both examples of the above specific dispersion structure.

"The major diameters of rubber particles are continuous in the major axis direction" means, specifically, the angle formed by the major axes of adjacent rubber particles (in Fig. 2A, the angle formed by virtual lines LA including the major axes) It means that the angle θ of the smaller one is continuous forming 30° or less (preferably 10° or less). In addition, in an example in which the angle formed by the major diameters of neighboring rubber particles is 0°, not only the state in which the major diameters of neighboring rubber particles are arranged on a straight line, but also the long diameters overlapping each other as shown in Fig. 2B. aspects are also included.

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

Further, the ratio (proximity ratio) of the number of continuous rubber particles (the number of rubber particles constituting a specific dispersed structure) to the total number of rubber particles contained in the optical film is preferably 15% or more. If the adjacency ratio is 15% or more, since the ratio of a plurality of adjoining rubber particles is high, stress is easily dispersed. On the other hand, if the proximity ratio is 70% or less, it is difficult for the haze of the optical film to increase. The proximity ratio is more preferably 20 to 60%, still more preferably 25 to 50%, and particularly preferably 30 to 50%.

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

The major axis direction of the rubber particles is preferably substantially perpendicular to the thickness direction of the optical film. Almost perpendicular is the range of 90 ± 15°. Further, from the viewpoint of making it easier to suppress winding failure of the optical film after winding, the major diameter direction of the rubber particles is preferably substantially parallel to the in-plane slow axis of the optical film. Almost parallel refers to a range of 0±15°.

1-2-3. About the composition and structure of rubber particles

The rubber particle is preferably a graft copolymer containing a rubber-like polymer (crosslinked polymer), that is, a core-shell rubber particle having a core portion made of the rubber-like polymer (crosslinked polymer) and a shell portion covering the rubber particle.

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 is easily imparted to the film. The glass transition temperature (Tg) of the rubbery polymer is more preferably -15°C or lower, and still 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 monomers to be constituted. In order to lower the glass transition temperature (Tg) of the rubbery polymer, as described later, for example, in the monomer mixture constituting the rubbery polymer, the mass ratio of acrylic acid ester having 4 or more carbon atoms in the alkyl group/methyl methacrylate It is preferable to increase (eg, 3 or more, preferably 4 or more and 10 or less).

The rubbery polymer may, for example, have a glass transition temperature within the above range, and is not particularly limited. Examples thereof include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. . Among them, (meth)acrylic crosslinked polymers are preferable, and acrylic crosslinked polymers (acrylic rubber-like polymers) are more preferable from the viewpoint that the difference in refractive index with the (meth)acrylic resin is small and the transparency of the optical film is not easily impaired.

That is, the rubber particle is preferably an acrylic graft copolymer containing the acrylic rubber-like polymer (a), that is, a core-shell particle having a core portion containing the acrylic rubber-like polymer (a) and a shell portion covering it. The core-shell particle is a multistage polymer (or multilayered polymer) obtained by polymerizing at least one stage a monomer mixture (b) containing a methacrylic acid ester as a main component in the presence of an acrylic rubber polymer (a). . Polymerization can be carried out by an emulsion polymerization method.

(Core portion: for acrylic rubber-like polymer (a))

The acrylic rubber-like polymer (a) is a crosslinked polymer containing acrylic acid ester as a main component. The acrylic rubber-like polymer (a) is a monomer mixture (a') containing 50 to 100% by mass of an acrylic acid ester and 50 to 0% by mass of another monomer copolymerizable therewith, and two or more non-conjugated reactivity per molecule It is a crosslinked polymer obtained by polymerizing 0.05 to 10 parts by mass of a polyfunctional monomer having a double bond (relative to 100 parts by mass of the monomer mixture (a')). The crosslinked polymer may be obtained by mixing and polymerizing all of these monomers, or may be obtained by changing the monomer composition and polymerizing two or more times.

The acrylic acid ester constituting the acrylic rubber-like polymer (a) is preferably an acrylic acid alkyl ester having 1 to 12 carbon atoms of an alkyl group such as methyl acrylate or butyl acrylate. One type may be sufficient as acrylic acid ester, and two or more types may be sufficient as it. From the viewpoint of setting the glass transition temperature of the rubber particles to -10°C or lower, the acrylic acid ester preferably contains at least an acrylic acid alkyl ester having 4 to 10 carbon atoms.

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

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

For the example of the monomer which can be copolymerized, Methacrylic acid ester, such as methyl methacrylate; Styrene, such as styrene and methyl styrene; Unsaturated nitriles, such as acrylonitrile and methacrylonitrile, are also contained.

Examples of the polyfunctional monomer 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, tetramethylolmethane tetra (meth) acrylate, dipropylene glycol di ( meth)acrylate and polyethylene glycol di(meth)acrylate are included.

It is preferable that it is 0.05-10 mass % with respect to 100 mass % of the total of monomer mixture (a'), and, as for content of a polyfunctional monomer, it is more preferable that it is 0.1-5 mass %. When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the obtained acrylic rubber-like polymer (a) is easily increased, so that the hardness and rigidity of the resulting film are not excessively impaired, and when the content is 10% by mass or less, the film has good toughness. not hindered

(Shell part: for monomer mixture (b))

The monomer mixture (b) is a graft component to the acrylic rubber-like polymer (a) and constitutes the shell portion. The monomer mixture (b) preferably contains methacrylic acid ester as a main component.

It is preferable that the methacrylic acid ester which comprises a monomer mixture (b) is a C1-C12 methacrylic acid alkyl ester of an alkyl group, such as methyl methacrylate. One type may be sufficient as methacrylic acid ester, and two or more types may be sufficient as it.

It is preferable that content of a methacrylic acid ester is 50 mass % or more with respect to 100 mass % of monomer mixtures (b). When content of methacrylic acid ester is 50 mass % or more, it can make it difficult to reduce the hardness and rigidity of the film obtained. From the viewpoint of lowering the affinity between (meth)acrylic resin and rubber particles (increasing ΔSP), the content of methacrylic acid ester is more preferably 70% by mass or more with respect to 100% by mass of monomer mixture (b), It is more preferable that it is 80 mass % or more.

The monomer mixture (b) may further contain other monomers as needed. For the example of another monomer, Acrylic acid ester, such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; (meth)acrylic monomers having an alicyclic structure, heterocyclic structure or aromatic group such as benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and phenoxyethyl (meth)acrylate (meth)acrylic monomers containing a cyclic structure ) are included.

(Core-shell type rubber particles: about acrylic graft copolymer)

Examples of core-shell rubber particles include methacrylic acid ester as a main component in the presence of 5 to 90 parts by mass (preferably 5 to 75 parts by mass) of an acrylic rubber-like polymer as (meth)acrylic rubber-like polymer (a) A polymer obtained by polymerizing 95 to 25 parts by mass of monomer mixture (b) in at least one stage is contained.

The acrylic graft copolymer may further contain a hard polymer inside the acrylic rubber-like polymer (a) as needed. 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 polyfunctional monomers (100 in total of the monomer mixture (c1)) part by mass) to obtain a hard polymer by polymerizing

(II) a monomer mixture (a1) consisting of 60 to 100% by mass of an acrylic acid ester and 0 to 40% by mass of other monomers copolymerizable therewith, and 0.1 to 5 parts by mass of a polyfunctional monomer (100 parts by mass in total of the monomer mixture (a1)) for) to polymerize to obtain a soft polymer

(III) a monomer mixture (b1) consisting of 60 to 100% by mass of methacrylic acid ester and 40 to 0% by mass of other monomers copolymerizable therewith, and 0 to 10 parts by mass of polyfunctional monomers (100 in total of the monomer mixture (b1)) part by mass) to obtain a hard polymer by polymerizing

Between each polymerization process of (I) - (III), another polymerization process may be further included.

The acrylic graft copolymer may be further obtained through the polymerization step of (IV).

(IV) a monomer mixture (b2) consisting of 40 to 100% by mass of methacrylic acid ester, 0 to 60% by mass of acrylic acid ester, and 0 to 5% by mass of another copolymerizable monomer, and 0 to 10 parts by mass of a polyfunctional monomer (monomer with respect to 100 parts by mass of the mixture (b2)) is polymerized to obtain a hard polymer.

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

The soft layer can impart impact absorption to the optical film. Examples of the soft layer include a layer made of an acrylic rubber-like polymer (a) containing acrylic acid 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 the particles during production of the rubber particles. Examples of the hard layer include a layer made of a polymer containing methacrylic acid ester as a main component.

The graft ratio of the acrylic graft copolymer (mass ratio of the graft component (shell portion) to the acrylic rubber-like polymer (a)) is preferably 10 to 250%, more preferably 40 to 230%, and 60 to 220% It is more preferable to be When the graft ratio is 10% or more, the ratio of the shell portion does not decrease too much, so 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 effect of improving the toughness and brittleness of the film is less likely to be impaired because the proportion of the acrylic rubber-like polymer (a) does not decrease too much.

The graft ratio of the acrylic graft copolymer is measured by the following method.

1) 2 g of the acrylic graft copolymer was dissolved in 50 ml of methyl ethyl ketone, centrifuged using a centrifugal separator (CP60E manufactured by Hitachi Koki Co., Ltd.) at a rotation speed of 30000 rpm and a temperature of 12 ° C. for 1 hour to obtain insoluble Separation into powder and soluble content (centrifugation is performed 3 times in total).

2) The graft ratio is calculated by applying the weight of the obtained insoluble matter to the following formula.

Graft rate (%) = [{(weight of methyl ethyl ketone insoluble content) - (weight of acrylic rubber-like polymer (a))}/(weight of acrylic rubber-like polymer (a))] × 100

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

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 preferably 0.3 or more, and is 0.5 or more It is more preferable, and it is still more preferable that it is 0.8 or more. The upper limit of ΔSP may be, for example, 5.

The SP value adopts a value calculated by inputting the structure of each compound in commercially available simulation software "Material Studios Forcite" (manufactured by Dassault Systems Co., Ltd.).

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

It is preferable that content of rubber particle is 5-20 mass % with respect to (meth)acrylic-type resin. When the content of rubber particles is 5% by mass or more, not only it is easy to impart sufficient flexibility and toughness to the (meth)acrylic resin film, but also it is possible to impart slipperiness by forming irregularities on the surface. When the content of the rubber particles is 20% by mass or less, the haze does not rise too much. The content of the rubber particles is more preferably 5 to 15% by mass, and still more preferably 5 to 10% by mass relative to the (meth)acrylic resin from the above viewpoint.

1-3. organic particulates

The optical film of the present invention preferably further contains organic particulates from the viewpoint of further enhancing the slipperiness of the optical film and facilitating the uneven distribution of rubber particles in the surface layer portion of the film.

It is preferable that the organic fine particles are particles having a glass transition temperature (Tg) of 80°C or higher. When the glass transition temperature of the organic particulates is 80°C or higher, it is easy to form irregularities of moderate hardness on the surface of the optical film, so that the slipperiness is easy to be improved. As for the glass transition temperature of organic particulates, it is more preferable that it is 100 degreeC or more. The glass transition temperature is measured in the same manner as described above.

The glass transition temperature (Tg) of the organic particulates can be adjusted by the monomer composition constituting the organic particulates. In order to increase the glass transition temperature (Tg) of organic particulates, it is preferable to increase content of the structural unit derived from the polyfunctional monomer mentioned later, for example.

The resin constituting the organic particulates may have a glass transition temperature (Tg) within the above range, and examples thereof include (meth)acrylic acid esters, itaconic acid diesters, maleic acid diesters, vinyl esters, and olefins. containing structural units derived from at least one selected from the group consisting of styrenes, (meth)acrylamides, allyl compounds, vinyl ethers, vinyl ketones, unsaturated nitriles, unsaturated carboxylic acids, and polyfunctional monomers. polymers, silicone-based resins, fluorine-based resins, polyphenylene sulfide, and the like are included.

The (meth)acrylic acid esters, olefins, styrenes, (meth)acrylamides, unsaturated nitriles, unsaturated carboxylic acids, and polyfunctional monomers constituting the polymer are the (meth)acrylic resin or the acrylic rubber As the monomer constituting the shape polymer (a), the same ones as those listed can be used. Examples of the 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 methoxyacetate, vinylphenyl acetate, vinyl benzoate, and vinyl salicylate. Examples of the allyl compound 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 acid esters, vinyl esters, and styrenes from the viewpoint of having high affinity with (meth)acrylic resins, having flexibility against stress, and being easy to adjust the glass transition temperature within the above range. , a copolymer containing a structural unit derived from at least one selected from the group consisting of olefins and a structural unit derived from polyfunctional monomers is preferable, and a structural unit derived from (meth)acrylic acid esters, A copolymer containing structural units derived from functional monomers is more preferable, and structural units derived from (meth)acrylic acid esters, structural units derived from styrenes, and structural units derived from polyfunctional monomers are used. A containing copolymer is more preferable.

When the organic particulate contains a structural unit derived from a polyfunctional monomer, the content of the structural unit derived from the polyfunctional monomer in the organic particulate is usually the amount of the structural unit derived from the polyfunctional monomer in the rubber particle. more than content. For example, the content of structural units derived from polyfunctional monomers may be, for example, 50 to 500% by mass relative to 100% by mass in total of structural units derived from monomers other than the polyfunctional monomers constituting the copolymer. there is.

Particles (polymer particles) made of such a polymer can be produced by any method, such as emulsion polymerization, suspension polymerization, dispersion polymerization, or seed polymerization. Especially, seed polymerization and emulsion polymerization in an aqueous medium are preferable from a viewpoint that polymer particles with a uniform particle diameter are easy to be obtained.

As a method for producing polymer particles, for example,

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 species particles are obtained by polymerizing monomers in an aqueous medium, and then polymerization is performed after the monomer mixture is absorbed into the species particles;

• A multi-stage polymerization method in which a step of producing seed particles of a two-stage polymerization method is repeated, and the like. These polymerization methods can be appropriately selected according to the desired average particle diameter of the polymer particles. Moreover, the monomer for producing a seed particle is not specifically limited, All monomers for polymer particles can be used.

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

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, more preferably 0.085 or less, and still more preferably 0.065 or less from the viewpoint of highly suppressing the haze increase of the resulting film.

It is preferable that it is 0.04-2 micrometers, and, as for the average particle diameter of organic particulates, it is more preferable that it is 0.08-1 micrometer. When the average particle diameter of the organic particulates is 0.04 μm or more, sufficient slipperiness is easily imparted to the obtained film. When the average particle diameter of the organic particulates is 2 μm or less, it is easy to suppress the increase in haze.

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

The average particle diameter of the organic fine particles means the average size (average secondary particle diameter) of aggregates in the case of agglomerate particles, and means the average value obtained by measuring the size of one particle in the case of non-agglomeration particles.

It is preferable that content of organic particulates is 0.03-1.5 mass % with respect to (meth)acrylic-type resin. Sufficient slipperiness can be provided to an optical film as content of organic particulates is 0.03 mass % or more. When content of organic particulates is 1.5 mass % or less, it is easy to suppress the raise of a haze. The content of the fine particles is more preferably from 0.05 to 1.0% by mass, and still more preferably from 0.08 to 0.7% by mass.

1-4. other ingredients

The optical film of the present invention may further contain other components within a range not impairing the effect of the present invention. Examples of other components include residual solvents, ultraviolet absorbers, antioxidants, and the like.

For example, since the optical film of this invention is manufactured by the solution casting method so that it may mention later, it may contain the residual solvent derived from the solvent of the dope used by the solution casting method.

It is preferable that it is 700 ppm or less with respect to an optical film, and, as for the amount of residual solvent, it is more preferable that it is 30-700 ppm. Content of the residual solvent may be adjusted according to the drying conditions of the dope casted on the support in the manufacturing process of the optical film mentioned later.

Content of the residual solvent in an optical film can be measured by head space gas chromatography. In the head space gas chromatography method, a sample is sealed in a container, heated, and the gas in the container is quickly injected into a gas chromatograph in a state where the container is filled with volatile components, mass spectrometry is performed, and the compound is identified. It is to quantify the volatile components. In the head space method, all peaks of volatile components can be observed with a gas chromatograph, and volatile substances and monomers can be quantified with high accuracy by using an analysis method using electromagnetic interaction. .

1-5. Properties

(Haze)

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

(Phase difference (Ro and Rt))

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

Ro and Rt are each defined by the following formula.

Equation (1a): Ro = (nx - ny) × d

Equation (1b): Rt = ((nx + ny)/2 - nz) × d

(In the expression,

nx represents the refractive index of the film in the in-plane slow axis direction (the direction in which the refractive index becomes maximum),

ny represents the refractive index in the direction orthogonal to the in-plane slow axis of the film,

nz represents the refractive index in the thickness direction of the film,

d represents the thickness (nm) of the film.)

The in-plane slow axis of the optical film of the present invention refers to an axis at which the refractive index is maximized on the film plane. The in-plane slow axis of the optical film can be confirmed by an automatic birefringence meter axo scan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axo Matrix Co., Ltd.). The in-plane slow axis usually coincides with the direction in which the draw ratio is maximized.

Ro and Rt can be measured by the following method.

1) The optical film of the present invention is subjected to humidity control in an environment of 23°C and 55% RH for 24 hours. The average refractive index of this film is measured with 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 control at a measurement wavelength of 550 nm were measured using an automatic birefringence meter Axo Scan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axo Matrix) at 23 ° C. 55% RH measured under the environment of

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

(thickness)

The thickness of the optical film of the present invention is, for example, 5 to 100 μm, preferably 5 to 40 μm.

2. Manufacturing method of optical film

The optical film of the present invention is manufactured by a solution casting method (casting method). That is, the optical film of the present invention is obtained by 1) obtaining a dope containing at least the above-described (meth)acrylic resin, rubber particles, and a solvent, and 2) casting the obtained dope on a support, drying and peeling it to obtain a film-like product. It can be manufactured through a process of obtaining, 3) a process of stretching the obtained membranous material, and 4) a process of winding the stretched membranous material into a roll shape.

1) About the process of

Dope is prepared by dissolving or dispersing the above-described (meth)acrylic resin, rubber particles and, if necessary, organic fine particles in a solvent.

The particle shape of the rubber particles used for preparation of the dope is not particularly limited, but from the viewpoint of well expressing a good stress relaxation action by stretching, those that are close to spherical shapes, specifically those with an average aspect ratio of 1 ± 0.1 are preferred. desirable.

The solvent used for dope contains at least an organic solvent (good solvent) capable of dissolving (meth)acrylic resin. For the example of a good solvent, Chlorine system organic solvents, such as methylene chloride; Non-chlorine-type organic solvents, such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran, are contained. Especially, methylene chloride is preferable.

The solvent used for dope may further contain a poor solvent. Examples of the poor solvent include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of the alcohol in the dope is high, the membranous substance tends to gel and peel easily from the metal support. Methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol are mentioned as a C1-C4 linear or branched aliphatic alcohol. Among these, ethanol is preferable in terms of dope stability, relatively low boiling point, and good drying property.

The solid content concentration of the dope is not particularly limited, but in the optical film obtained by the compression effect by drying, a lower one is preferable from the viewpoint of making it easy to bring the rubber particles into proper proximity. Specifically, the solid content concentration of dope is preferably 25% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less. On the other hand, from the viewpoint of making it easier to obtain a membranous product having a predetermined thickness, the lower limit of the solid content concentration of dope can be, for example, 9% by mass.

Preparation of dope may be prepared by directly adding (meth)acrylic resin, rubber particles, and organic particulates as needed to the solvent described above, and mixing; A resin solution in which a (meth)acrylic resin is dissolved in the above solvent, a rubber particle dispersion in which rubber particles are dispersed in the above solvent, and a fine particle dispersion in which organic particulates are dispersed in the above solvent are prepared in advance, if necessary, 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 obtained optical film. Examples of such a solvent include the aforementioned poor solvent, for example, a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. The content of the poor solvent is preferably from 2 to 16% by mass, more preferably from 4 to 16% by mass, based on the total amount of the solvent contained in the dispersion of rubber particles.

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

2) About the process of

The obtained dope is casted on a support. Casting of dope can be performed by discharging from a casting die.

Then, the solvent in the dope casted on the support is evaporated and dried. The dried dope is peeled off from the support to obtain a membranous substance.

The amount of residual solvent of the dope at the time of peeling from the support (amount of residual solvent of the membranous material at the time of peeling) is preferably 10 to 150% by mass from the viewpoint of making it easy to reduce the phase difference of the obtained (meth)acrylic resin film. , It is more preferable that it is 20-40 mass %. When the amount of residual solvent at the time of peeling is 10% by mass or more, the (meth)acrylic resin easily flows during drying or stretching, and it is easy to make it non-oriented, so that the retardation of the (meth)acrylic resin film obtained is easy to be reduced. When the amount of residual solvent at the time of peeling is 150 mass % or less, since the force required when peeling dope is hard to become large excessively, it is easy to suppress breakage of dope.

The residual solvent amount of dope at the time of peeling is defined by the following formula. The same applies below.

Residual solvent amount of dope (% by mass) = (mass before heat treatment of dope - mass after heat treatment of dope) / mass after heat treatment of dope × 100

In addition, heat treatment at the time of 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 the drying temperature and drying time of dope on a support body, the temperature of a support body, etc.

3) About the process of

The membranous material obtained by peeling is stretched while drying.

Stretching may be carried out according to the required optical properties, and it is preferable to stretch in at least one direction (for example, in the transverse direction (TD direction) of the membranous material), and in two directions orthogonal to each other (for example, , biaxial stretching of the transverse direction (TD direction) of the membranous material and the conveying direction (MD direction) orthogonal thereto).

The draw ratio may be set so that the average aspect ratio of the rubber particles falls within the above range, and is preferably 20 to 200%, more preferably 30 to 100%, and still more preferably 50 to 70%. A stretch ratio (%) is defined as (the amount of change in the length of the film in the stretching direction before and after stretching)/(the length in the stretching direction of the film before stretching) x 100 (%). Moreover, when performing biaxial stretching, it is preferable to set it as the said draw ratio with respect to each of a TD direction and an MD direction.

Moreover, the in-plane slow axis direction (in-plane direction in which a refractive index becomes the largest) of an optical film is a direction in which a draw ratio becomes maximum normally.

The stretching temperature (drying temperature) is preferably (Tg - 65) ℃ to (Tg + 60) ℃, when the glass transition temperature of the (meth) acrylic resin is Tg, (Tg - 50) ℃ to (Tg + 50) °C is more preferable, and it is more preferably (Tg - 30) °C to (Tg + 50) °C. When the stretching temperature is (Tg - 30) ° C. or higher, not only it is easy to make the membranous material soft enough for stretching, but also the tension applied to the membranous material during stretching does not become excessively large, so that excess residual in the obtained (meth)acrylic resin film Stress may not be left well. If the stretching temperature is Tg or less, it is easy to suppress the occurrence of bubbles due to vaporization of the solvent in the membranous article. Extending|stretching temperature can be specifically made into 60-220 degreeC.

The stretching temperature is (a) when drying by a non-contact heating type such as a tenter stretching machine, the temperature inside the stretching machine or an ambient temperature such as a hot air temperature, (b) when drying by a contact heating type such as a hot roller, contact It can be measured as either the temperature of the heating part or (c) the surface temperature of the membranous material (surface to be dried). Among them, (a) in the case of drying in 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 is preferable.

It is preferable that the amount of residual solvent in the membranous material at the time of the start of extending|stretching is 5-30 mass %, for example. The amount of residual solvent at the start of extending|stretching can be measured by the method similar to the above.

Stretching of the membranous material in the TD direction (width direction) can be performed, for example, by a method (tenter method) in which both ends of the membranous material are fixed with clips or pins, and the distance between the clips or pins is widened in the direction of travel. Stretching of the membranous material in the MD direction can be performed by, for example, a method (roll method) in which a difference in circumferential speed is given to a plurality of rolls and a difference in circumferential speed of the rolls is used between them.

4) About the process of

The membranous substance obtained after extending|stretching is wound up in roll shape, further drying as needed, and the roll body of an optical film is obtained.

The drying temperature may be adjusted to the same range as the stretching temperature in the above step 3). The drying temperature is measured in the same way as in step 3). (b) In the case of drying with a contact heating type such as a heat 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 membranous material.

In the roll body obtained after winding, it is preferable that the major axis direction of the rubber particles is substantially perpendicular to the thickness direction of the optical film. Further, from the viewpoint of making it easier to suppress winding failure of the optical film after winding, the major axis direction of the rubber particles is preferably substantially parallel to the stretching direction (preferably the width direction) of the optical film.

It is preferable that it is 2000-8000 m, and, as for the length (length of MD direction) of the optical film in the roll body obtained, it is more preferable that it is 5000-7000 m. It is preferable that it is 1.3-3.0 m, and, as for the width|variety (length of TD direction) of an optical film, it is more preferable that it is 2.3-2.5 m.

As described above, the force (stress) to contract in the longitudinal direction and the force (stress) to expand in the transverse direction tend to act on the optical film of the roll body immediately after winding due to the winding tension. On the other hand, the optical film of the present invention has a structure in which rubber particles having an average aspect ratio of a certain level or more are moderately adjacent. Thereby, the optical film of the roll body after winding can relieve the said stress effectively, even if the particle diameter of a rubber particle is not enlarged. Accordingly, it is possible to suppress transfer of the winding core due to a force intended to contract in the longitudinal direction and chain failure due to a force intended to expand in the width direction. Therefore, the winding shape can be improved without increasing the haze of the optical film.

In particular, as long as the optical film is long (long in the MD direction) and wide (long in the TD direction), winding failure is likely to occur. INDUSTRIAL APPLICABILITY The present invention can favorably suppress winding failure even in such a roll of an optical film.

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

3. Polarizer

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

3-1. polarizer

A polarizer is an element that transmits only light of a polarization plane in a certain direction, and is a polyvinyl alcohol-based polarizing film. Among the polyvinyl alcohol-based polarizing films, there are those obtained by dyeing the polyvinyl alcohol-based film with iodine and those obtained by dyeing the dichroic dye.

The polyvinyl alcohol-type polarizing film may be a film (preferably, a film subjected to a durability treatment with a boron compound further) dyed with iodine or a dichroic dye after uniaxially stretching the polyvinyl alcohol-type film; It may be a film (preferably, a film further subjected to durability treatment with a boron compound) uniaxially stretched after dyeing a polyvinyl alcohol-based film with iodine or a dichroic dye. The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

For example, ethylene-modified polyvinyl having an ethylene unit content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, and a degree of saponification of 99.0 to 99.99 mol% as described in Japanese Unexamined Patent Publication No. 2003-248123 and Japanese Unexamined Patent Publication No. 2003-342322. alcohol is used

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

3-2. other optical films

When the optical film of the present invention is disposed only on one surface of the polarizer, another optical film may be disposed on the other surface. Moreover, an optical film and another optical film may be arrange|positioned through an adhesive bond layer on a polarizer.

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, above, made by Konica Minolta Co., Ltd., Fuji Tak T40UZ, Fuji Tack T60UZ, Fuji Tack T80UZ, Fuji Tack TD80UL, Fuji Tack TD60UL, Fuji Tack TD40UL, Fuji Tak R02, Fuji Tack R06, Fujifilm Co., Ltd.) and the like are included.

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

3-3. Manufacturing method of polarizer

The polarizing plate of the present invention can be obtained by bonding the polarizer and the (meth)acrylic resin film of the present invention together through an adhesive agent. The adhesive may be a fully saponified polyvinyl alcohol aqueous solution (water glue) or an active energy ray-curable adhesive. The active energy ray-curable adhesive may be any of a radical photopolymerization type composition using photoradical polymerization, a photocationic polymerization type composition using photocationic polymerization, or a combination thereof.

4. Liquid crystal display

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

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

One or both of the first and second polarizing plates are the polarizing plates of the present invention. It is preferable that the polarizing plate of this invention is arrange|positioned so that the optical film of this invention may become the liquid crystal cell side.

Example

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited thereto.

1. Materials of optical film

(1) (meth)acrylic resin

(meth)acrylic resin A: methyl methacrylate (MMA) / N-phenylmaleimide (PMI) copolymer (MMA / PMI = 85/15 (mass ratio), glass transition temperature (Tg): 125 ° C., weight average molecular weight (Mw): 1.5 million)

(meth)acrylic resin B: methyl methacrylate (MMA)/dicyclopentanyl methacrylate copolymer (MMA/dicyclopentanyl methacrylate: 70/30 (mass ratio), glass transition temperature (Tg): 115°C, weight average Molecular weight (Mw): 1.7 million)

(meth)acrylic resin C: methyl methacrylate (MMA)/adamantyl methacrylate (MADMA)/N-phenylmaleimide (PMI) copolymer (MMA/MADMA/PMI: 50/25/25 (mass ratio), Glass transition temperature (Tg): 135 ° C, weight average molecular weight (Mw): 1.9 million)

(meth)acrylic resin D: methyl methacrylate (MMA)/n-butyl acrylate copolymer (MMA/BA: 90/10 (mass ratio), glass transition temperature (Tg): 109°C, weight average molecular weight (Mw): 1.2 million)

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 (meth)acrylic resin was measured in accordance with JIS K 7121-2012 using DSC (Differential Scanning Colorimetry: Differential Scanning Calorimetry).

(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 (Series of TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL 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), and the value measured at the detector RI temperature of 40°C and converted to styrene was used.

(2) rubber particles

<Preparation of rubber particle C1>

Acrylic modifier Kane Ace M210 manufactured by Kaneka Co., Ltd. (Core part: multi-layered acrylic rubber polymer (Tg: about -10 ° C), shell part: core-shell type rubber of methacrylic acid ester polymer containing methyl methacrylate as the main component) particles, average particle diameter: 220 nm)

<Preparation of rubber particle C2>

The following components were injected 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 substituting the inside of the polymerization reactor with nitrogen gas, the internal temperature was set to 80°C, 97 parts by mass of methyl methacrylate (MMA), 3 parts by mass of butyl acrylate (BA), and 0.17 part by mass of allyl methacrylate (ALMA). , and 25% by mass of a monomer mixture (c1) consisting of 0.065 parts by mass of tertiary dodecylmercaptan (tDM) was added to the polymerization reactor at once. To this, 0.00645 part by mass of 5% sodium formaldehyde sulfoxylate, 0.0056 part by mass of ethylenediaminetetraacetate-2-sodium, and 0.0014 part by mass of ferrous sulfate were added, and 15 minutes later, 0.022 part by mass of t-butyl hydroperoxide was added, Polymerization was further continued for 15 minutes. Then, 0.013 mass part of 2% sodium hydroxide aqueous solution was added.

Then, the remaining 75% by mass of the above monomer mixture (c1) was continuously added over 30 minutes. 30 minutes after completion of the addition, 0.0069 parts by mass of 69% t-butyl hydroperoxide was added, and the mixture was maintained at the same temperature for 30 minutes to complete 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. Then, a mixture consisting of 32.5 parts by mass (BA: 82 mass%, MMA: 18 mass%) of the monomer mixture (a1), 0.97 parts by mass of AIMA, and 0.3 parts by mass of polyoxyethylene lauryl ether phosphoric acid was continuously added over 74 minutes. did After that, it 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 ratio was 99%.

After maintaining the obtained rubbery polymer at 80°C, adding 0.0097 parts by mass of potassium persulfate and 0.05 part by mass of sodium hydroxide, 50 parts by mass of monomer mixture (b1) (MMA: 90% by mass, BA: 10% by mass) was added to 150 Addition was continued over a period of minutes. After completion of the addition, it was maintained for 1 hour.

The resulting graft copolymer containing the rubbery polymer was salted out with magnesium sulfate, solidified, washed with water and dried to obtain a white powdery graft copolymer containing the rubbery polymer (rubber particle C2). The glass transition temperature (Tg) of the rubber-like polymer of the obtained rubber particle C2 was -30 degreeC, the average particle diameter was 380 nm, the graft ratio was about 149%, and the polymerization conversion ratio was 99%.

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

(ΔSP)

The (meth)acrylic resin and the ΔSP value of the shell portion of rubber particles C1 or C2 were calculated. Specifically, in the commercially available simulation software "Material Studios Forcite" (manufactured by Dassault Systems Co., Ltd.), the structural formulas of the (meth)acrylic resin and the resin constituting the shell are input, respectively, the SP value is calculated, and the difference between them is calculated. It was obtained by calculating.

(3) organic fine particles

Organic particulates P1 prepared by the following method were used.

(Preparation of Species Particles)

1000 g of deionized water was placed in a polymerization reactor equipped with a stirrer and a thermometer, and 50 g of methyl methacrylate and 6 g of t-dodecylmercaptan were injected thereinto, and the mixture was heated to 70°C while purging with nitrogen under stirring. While maintaining the internal temperature at 70°C, 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.

(manufacture of organic fine particles)

800 g of deionized water in which 2.4 g of sodium lauryl sulfate was dissolved as a gelation inhibitor was placed in a polymerization reactor equipped with an agitator and a thermometer, and 66 g of methyl methacrylate, 20 g of styrene, and 64 g of ethylene glycol dimethacrylate were added thereto as a monomer mixture. and a liquid mixture of 1 g of azobisisobutyronitrile as a polymerization initiator. Then, the mixture was stirred with a T.K homomixer (manufactured by Tokushu Kika Kogyo) to obtain a dispersion.

To the obtained dispersion, 60 g of an emulsion containing the above seed particles was added, and the mixture was stirred at 30°C for 1 hour to allow the seed particles to absorb the monomer mixture. Next, the absorbed monomer mixture 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). The average particle diameter of the obtained organic fine particles P1 was 0.14 μm, and the Tg was 280°C.

(Manufacture of Aggregates of Organic Fine Particles)

This emulsion was spray dried under the following conditions with a spray dryer manufactured by Sakamoto Kiken Co., Ltd. (model: atomizer take-up method, model number: TRS-3WK) as a spray dryer to obtain an aggregate of organic particulates. The average particle diameter of the aggregate of organic fine particles was 30 μm.

Feed rate: 25 ml/min

Atomizer RPM: 11000 rpm

Air volume: 2 ㎥/min

Slurry inlet temperature of spray dryer: 100 ℃

Polymer particle aggregate outlet temperature: 50 ℃

The average particle diameter of organic particulates was measured by the following method.

(average particle diameter)

The dispersed particle size of the organic particulates in the resulting dispersion was measured with a zeta potential/particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.). In addition, the average particle diameter of organic particulates measured using a zeta potential/particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.) substantially coincides with the average particle diameter of organic particulates measured by TEM observation of an optical film.

2. Manufacturing and Evaluation of Optical Films

[Example 1]

(Preparation of rubber particle dispersion)

11.3 parts by mass of rubber particles C2 and 200 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed under 1500 rpm conditions using a milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.) to obtain a rubber particle dispersion. .

(Preparation of dope)

Subsequently, dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Next, it injected|threw-in stirring the (meth)acrylic-type resin A to the pressure dissolution tank. Next, the above-prepared rubber particle dispersion was introduced and completely dissolved while stirring. The viscosity of the obtained solution was 16000 mm Pa·s, and the moisture content was 0.50%. This was filtered by 300 L/m<2>*h of filtration flow rates, and the filtration pressure of 1.0x10< ⁶ >Pa using SHP150 by Rocky Techno Co., Ltd., and dope was obtained.

(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

(Unveiling)

Using an endless belt casting apparatus, the dope was uniformly cast on a stainless belt support at a temperature of 30 DEG C and a width of 1900 mm. The temperature of the stainless belt was controlled at 28 degreeC. The conveyance speed of the stainless belt was 20 m/min.

On the stainless steel belt support body, the solvent was evaporated until the amount of residual solvent in the casting (cast) dope became 30% by mass. Next, it was peeled from the stainless belt support body by the peeling tension of 128 N/m, and the membranous material was obtained (the amount of residual solvent of the membranous material at the time of peeling was 30 mass %). While conveying the peeled film with a large number of rollers, the obtained membranous material was stretched 30% in the width direction by a tenter under conditions of (Tg+15)°C (140°C in this example). The amount of residual solvent of the membranous material at the start of stretching was 10% by mass. Thereafter, the film was further dried while conveying with a roll, and an optical film having a length of 2.3 m in the width direction, a length of 7000 m, and a film thickness of 40 µm was obtained by slitting and winding the end sandwiched between tenter clips with a laser cutter.

[Examples 2 and 3]

An optical film was obtained in the same manner as in Example 1 except that the draw ratio was changed as shown in Table 1.

[Example 4, 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 concentration of 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 concentration of 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 particle C1, 180 parts by mass of methylene chloride and 20 parts by mass of ethanol with a dissolver for 50 minutes, a milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.) was used to disperse under 1500 rpm conditions, A rubber particle dispersion was obtained.

(Preparation of Organic Particulate Dispersion)

After stirring and mixing 12 parts by mass of organic particulates P1 and 388 parts by mass of methylene chloride with a dissolver for 50 minutes, they were dispersed under 1500 rpm conditions using a milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.) to obtain an organic particulate dispersion. .

(Preparation of dope)

Subsequently, dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Next, it injected|threw-in stirring the (meth)acrylic-type resin 1 to the pressure dissolution tank. Next, the above-prepared fine particle dispersion was introduced, heated to 60°C, and completely dissolved while stirring. The heating temperature was raised from room temperature at 5°C/min, and after dissolving for 30 minutes, the temperature was decreased at 3°C/min. After filtering the obtained solution, 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

(Unveiling)

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 in Comparative Example 1 except that the draw 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 concentration of dope was changed as shown in Table 1.

[Comparative Example 4]

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

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

(Average aspect ratio of rubber particles, average major diameter)

The average aspect ratio and average major diameter of the rubber particles were calculated in the following procedure.

1) The cross section of the optical film (among the cross sections along the thickness direction of the optical film, the cross section parallel to the width direction) was observed by TEM. The observation area was 5 μm × 5 μm.

2) The major axis and minor axis of each rubber particle in the obtained TEM image were measured, respectively, and the aspect ratio was calculated.

3) Operations of the above 1) and 2) were performed at a total of 4 locations by changing the observation area. Then, the average value of the measured aspect ratios was set as the "average aspect ratio", and the average value of the measured long diameters was set as the "average long axis".

(proximity ratio of rubber particles)

The proximity ratio of rubber particles was measured in the following procedure.

1) In the above TEM image (observation area: 5 µm × 5 µm), the major axis of each rubber particle was specified. Then, it was specified that the angle of the smaller side among the angles formed by the major diameters of neighboring rubber particles was 30° or less, and that the distance between the particles was 100 nm or less.

2) The ratio of the specific number of rubber particles to the total number of rubber particles in the observation area was calculated.

3) The operation of 1) and 2) above was performed at a total of 4 locations by changing the observation area, and the average value of the calculated rates was taken as the “proximity rate” (%).

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

(Brittle: MIT Flexibility)

The MIT flexibility of the obtained optical film was measured using a cutting resistance tester (MIT, BE-201 type manufactured by Tester Sangyo Co., Ltd., bending radius of curvature: 0.38 mm).

Specifically, as a test piece, a (meth)acrylic resin film having a width of 15 mm and a length of 150 mm, which was allowed to stand for 1 hour or more at a temperature of 25 ° C. and a relative humidity of 65% RH, was used, under conditions of a load of 500 g was measured in accordance with JIS P8115: 2001, and evaluated according to the following evaluation criteria according to the number of times until fracture.

◎+ : 1000 times or more

◎: 500 or more and less than 1000

○: 300 or more and less than 500

△: 100 or more and less than 300 times

×: less than 100 times

The greater the number of times until breakage, the better the flexibility, the better the resistance to repeated bending, and if it is Δ or more, it has desirable properties for practical use.

If it was more than △, it was judged as good.

(winding shape (winding defect failure, chain shape failure))

(1) Poor winding (winding core transfer)

After preserving the roll of the obtained optical film in an atmosphere of 40°C and 80% RH for 10 days, it was unwound and the length (m) of the optical film transferred from the core was measured. In addition, the transfer from the winding core is a planar defect caused by deformation of the optical film after winding (stress to be reduced in the longitudinal direction), 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 more than △, it was judged as good.

(2) chain shape failure

The roll of the obtained optical film was unwound, and the length (m) of the optical film in which the chain failure occurred was measured. Chain-like defects are chain-like defects caused by deformation of the optical film after winding (stress to stretch in the width direction), and are formed throughout the width direction. And it evaluated 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 more than △, 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, when the cross section of the film is observed, the average aspect ratio of rubber particles is 1.3 to 3.0 and the optical films of Examples 1 to 13 in which the proximity ratio is 15% or more all have high MIT flexibility and good toughness. It can be seen that it has Further, in the roll bodies of the optical films of Examples 1 to 13, it is understood that winding failures such as winding defects and chain failures are also suppressed.

In particular, it is found that the average aspect ratio and proximity ratio increase further by increasing the draw ratio (compared to Examples 1 to 3).

Further, it is found that the proximity ratio is further increased by increasing the glass transition temperature (Tg) of the (meth)acrylic resin (compared to Examples 1, 4 and 5).

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

Moreover, it turns out that the proximity ratio becomes higher by making solid content concentration of dope low. It is considered that the reason is that the rubber particles are easily oriented to each other due to the compression effect at the time of dope drying (comparison between Examples 2 and 7 and comparison between Examples 8 and 9).

It is also found that the proximity ratio is further increased by incorporating a poor solvent (EtOH) into the dispersion solvent of the rubber particles (compared to Examples 2, 8 and 13).

In contrast, the optical films of Comparative Examples 2 and 4 in which the average aspect ratio of rubber particles is less than 1.3, the optical films in Comparative Examples 1 and 3 in which the proximity ratio is less than 15%, and the optical film in Comparative Example 5 in which the average aspect ratio exceeds 3.0 all have MIT flexibility. It is low, and it turns out that winding failures, such as winding failure and chain failure, cannot be suppressed.

Further, 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 were less than 0.3% and were good. .

This application claims priority based on Japanese Patent Application No. 2018-144438 filed on July 31, 2018. All the content described in the said application specification and drawing is used in this specification.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide an optical film, a roll body of an optical film, a polarizing plate protective film, and a manufacturing method of an optical film that do not impair transparency, have good brittleness, and can suppress winding failure. .

100: optical film
110: Matrix
120: rubber particles
LA: imaginary line
d: distance between particles

Claims (15)

An optical film containing 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,
The major diameters of three or more of the rubber particles are continuous in the major axis direction, and the distance between the continuous rubber particles is 100 nm or less,
The optical film, wherein the ratio of the number of continuous rubber particles to the total number of rubber particles contained in the optical film is 15% or more. According to claim 1,
The major axis direction of the rubber particles is perpendicular to the thickness direction of the optical film. According to claim 1,
The optical film has an in-plane slow axis,
The major axis direction of the rubber particles is parallel to the in-plane slow axis, the optical film. According to claim 1,
The rubber particle is a core-shell type particle 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 optical film, wherein the difference (ΔSP) between the solubility parameter (SP value) of the (meth)acrylic resin and the polymer is 0.8 or more. According to claim 1,
The average major diameter of the rubber particles is 200 ~ 500 nm, the optical film. According to claim 1,
The (meth)acrylic resin has a structural unit derived from a copolymerized monomer selected from the group consisting of (meth)acrylic acid esters and maleimides having a cyclo ring, and a structure derived from (meth)acrylic acid esters having a branched alkyl group An optical film containing at least one of the units. According to claim 1,
An optical film further containing organic particulates having a glass transition temperature of 80°C or higher. A polarizing plate protective film comprising the optical film according to any one of claims 1 to 7. A roll 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 diameters of three or more of the rubber particles are continuous in the major axis direction, and the inter-particle distance between the rubber particles is 100 nm or less,
The optical film roll body wherein the ratio of the number of continuous rubber particles to the total number of rubber particles contained in the optical film is 15% or more. According to claim 9,
The major diameter direction of the rubber particles is perpendicular to the thickness direction of the optical film. According to claim 9,
The major diameter direction of the rubber particles is parallel to the width direction of the optical film. According to any one of claims 9 to 11,
The width of the optical film is 2.3 m or more,
A roll of an optical film having a length of 5000 m or more. A method for producing the optical film according to claim 1,
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 on a support, then drying and peeling to obtain a film-like product;
The manufacturing method of the optical film including the process of extending|stretching the said membranous material by 20% or more. According to claim 13,
The rubber particle is a core-shell type particle 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 method for producing an optical film according to claim 1 , wherein the solvent contained in the rubber particle dispersion contains a poor solvent of the polymer. According to claim 13 or 14,
The rubber particle is a core-shell type particle 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 manufacturing method of the optical film whose difference (ΔSP) of the solubility parameter (SP value) of the said (meth)acrylic-type resin and the said polymer is 0.8 or more.

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