JP7533217B2 - Optical film, polarizing plate, and method for manufacturing optical film - Google Patents

Description

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

As optical films for use in displays such as liquid crystal displays and organic EL displays, (meth)acrylic resin films such as polymethyl methacrylate are used because they have excellent transparency, dimensional stability, and low moisture absorption.

As the display market expands in recent years, there is a demand for larger, thinner and more flexible display devices, and the performance of each component, such as polarizing plates, is improving. In particular, for automotive applications, display devices that emphasize design are required. For this reason, polarizing plates are sometimes manufactured by punching out shapes with rounded corners, complex curved surfaces, or shapes with a hole in the center, rather than the conventional rectangular shape. Displays with such free shapes are also called irregular panels or free-form displays (FFD). It is being considered to use such displays in automobile meters, etc.

Figure 1 is a schematic diagram showing an example of an in-vehicle free-form display. In order to obtain a display device shaped to match the curve of an automobile meter as shown in Figure 1, it is desirable to be able to easily punch out a polarizing plate into irregular shapes such as a circle (improved irregular shape punching properties).

On the other hand, (meth)acrylic resin films are generally brittle (lacking flexibility), and so rubber particles are added to them when used. For example, Patent Document 1 discloses an optical film obtained by stretching a thermoplastic resin composition containing a (meth)acrylic resin and rubber particles.

Patent Document 2 discloses a protective film that includes a core layer that contains polymethyl methacrylate resin and rubber particles, and a skin layer that contains polymethyl methacrylate resin and does not contain rubber particles. Such a protective film is said to have good surface hardness and excellent adhesion to a polarizer.

Patent Document 3 discloses an optical film having a first acrylic resin layer containing a (meth)acrylic resin and a second acrylic resin layer containing a (meth)acrylic resin and a rubber component. Such an optical film is said to be able to improve mechanical strength (fragility) without impairing optical properties. The films in Patent Documents 1 to 3 are all manufactured by the melt casting method.

International Publication No. 2016/158968 JP 2008-40275 A Special Publication No. 2011-508257

However, the film of Patent Document 1 lacked stiffness and was poorly transportable because the rubber particles were uniformly dispersed in the thickness direction of the film. In addition, the film was still brittle (lacking in flexibility), and was therefore insufficient in terms of flexibility and processability into irregular shapes.

In the film of Patent Document 2, the rubber particles are unevenly distributed in the center of the film thickness direction. In other words, the surface layer of the film has few rubber particles and is brittle, so when the film is punched into an irregular shape, if the tip of the blade enters the surface layer of the film, the film is likely to be loaded and cracks (cracking or splitting) are likely to occur. In addition, when the film is bent, the surface layer of the film, where stress tends to concentrate, is brittle and prone to cracking. Thus, the film of Patent Document 2 also does not have sufficient flexibility or processability into irregular shapes.

In the film of Patent Document 3, the rubber particles are unevenly distributed in the surface layer in the film thickness direction. Therefore, it is considered that the film of Patent Document 3 has improved flexibility and processability for irregular shapes compared to the films of Patent Documents 1 and 2. However, since the film of Patent Document 3 is a laminated film in which a second acrylic resin layer containing rubber particles is laminated on a first acrylic resin layer, there is a problem that a difference in stress is likely to occur between the first acrylic resin layer and the second acrylic resin layer during a high-temperature durability test after punching into an irregular shape, and peeling failure is likely to occur between these layers.

The present invention has been made in consideration of the above circumstances, and aims to provide an optical film that has well-improved brittleness, is free from cracks or delamination during punching into irregular shapes or bending, and has excellent transportability, as well as a polarizing plate having the same, and a method for manufacturing the optical film.

The above problem can be solved by the following configuration.

The optical film of the present invention is a single-layer optical film comprising a (meth)acrylic resin and rubber particles having a core portion containing a cross-linked polymer and a shell portion covering the core portion, and the rubber particles are unevenly distributed in the surface layer portion of the optical film in the thickness direction of the optical film.

The optical film of the present invention is an optical film including a (meth)acrylic resin and rubber particles having a core portion including a crosslinked polymer and a shell portion covering the core portion, wherein the density of the rubber particles continuously increases from the inside of the optical film toward a surface portion in a thickness direction of the optical film, and when a region from one surface of the optical film to 20% or less of the thickness of the optical film is defined as region A1, a region from the other surface of the optical film to 20% or less of the thickness of the optical film is defined as region A2, and a region from one or the other surface of the optical film to more than 20% and less than 80% of the thickness of the optical film is defined as region B, the ratio (R A1 /R B ) of the area ratio R A2 per unit area of the rubber particles in region _A1 to the area ratio R _B per unit area of the rubber particles in region B and the ratio (R _A2 /R _B ) of the area ratio R _A2 per unit area of the rubber particles in region _A2 to the area ratio R _B per unit area of the rubber particles in region _B are ) are 1.02 to 1.5, respectively.

The polarizing plate of the present invention comprises a polarizer and an optical film of the present invention arranged on at least one surface of the polarizer.

The method for producing an optical film of the present invention includes the steps of obtaining a dope containing a (meth)acrylic resin, rubber particles, and a solvent, casting the dope onto a support, drying and peeling the dope to obtain a film-like material having a residual solvent content of 25% by mass or more, stretching the film-like material at a temperature equal to or lower than the glass transition temperature (Tg) of the (meth)acrylic resin, and further drying the film-like material after stretching at a temperature equal to or lower than the glass transition temperature (Tg) of the (meth)acrylic resin.

According to the present invention, it is possible to provide an optical film which has excellent brittleness, does not crack or delaminate when punched into irregular shapes or when bent, and has excellent transportability, a polarizing plate having the same, and a method for manufacturing the optical film.

FIG. 1 is a schematic diagram showing an example of an in-vehicle free-form display. FIG. 2 is a schematic cross-sectional view showing an example of the optical film of the present invention. FIG. 3 is a schematic cross-sectional view showing an example of the polarizing plate of the present invention. FIG. 4 is a schematic diagram showing the shape and dimensions of the film that was punched into a profile for testing in the examples.

As a result of extensive research, the inventors have discovered that an optical film that is a single-layer film containing a (meth)acrylic resin and core-shell type rubber particles, in which the rubber particles are concentrated in the surface layer of the film, does not suffer from cracks or delamination during punching into irregular shapes, has improved brittleness, and is excellent in transportability.

The reason for this is not clear, but is presumed to be as follows. That is, by distributing the rubber particles unevenly on the surface layer of the film, the stiffness of the film is less likely to be lost than when the rubber particles are uniformly distributed throughout the film, and therefore transportability is likely to be improved. In addition, since the rubber particles are distributed unevenly on the surface layer of the film, which is the most heavily loaded during the irregular shape punching process or bending process, the brittleness of the surface layer can be significantly improved. As a result, the stress on the surface layer of the film can be dispersed, and it is also possible to suppress the occurrence of cracks on the surface layer of the film during the irregular shape punching process or bending process. Furthermore, in a single-layer film, core-shell type rubber particles are distributed unevenly on the surface layer of the film; that is, the density of the rubber particles (the content of rubber particles per unit area in the cross section of the optical film) is continuously changed in the thickness direction of the film, and thus the stress difference between layers can be reduced, unlike conventional laminated films. As a result, it is possible to suppress delamination during irregular shape punching process, etc.

There are no particular limitations on the method for unevenly distributing rubber particles in a monolayer film. For example, when forming a film using a solution casting method, the uneven distribution can be adjusted by increasing the amount of residual solvent at the time of peeling, lowering the drying temperature of the film after stretching, selecting a (meth)acrylic resin with good solvent volatility or rubber particles with high affinity for the solvent, or by further adding organic or inorganic fine particles.

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 may be a homopolymer of a (meth)acrylic acid ester, or a copolymer of a (meth)acrylic acid ester and a copolymerizable monomer copolymerizable therewith. Here, (meth)acrylic means acrylic or methacrylic. The (meth)acrylic acid ester is preferably methyl methacrylate.

That is, the (meth)acrylic resin contains structural units derived from methyl methacrylate, and preferably further contains structural units derived from a copolymerizable monomer other than methyl methacrylate (hereinafter simply referred to as a "copolymerizable monomer").

Examples of copolymerizable monomers include:
acrylic acid esters having an alkyl group of 1 to 20 carbon atoms or methacrylic acid esters having an alkyl group of 2 to 20 carbon atoms, such as methyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, and six-membered ring lactone (meth)acrylate esters;
Aromatic vinyls such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and α-methylstyrene;
Alicyclic vinyls such as vinylcyclohexane;
Unsaturated nitriles such as (meth)acrylonitrile and (meth)acrylonitrile-styrene copolymers;
Unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, (meth)acrylic acid, itaconic acid, itaconic acid monoesters, maleic acid, and maleic acid monoesters;
Vinyl acetate, olefins such as ethylene and propylene;
Vinyl halides such as vinyl chloride, vinylidene chloride, and vinylidene fluoride;
(meth)acrylamides such as (meth)acrylamide, methyl(meth)acrylamide, ethyl(meth)acrylamide, propyl(meth)acrylamide, butyl(meth)acrylamide, tert-butyl(meth)acrylamide, and phenyl(meth)acrylamide;
Unsaturated glycidyls such as glycidyl (meth)acrylate;
These include maleimides such as N-phenylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-o-chlorophenylmaleimide, etc. These may be used alone or in combination of two or more kinds.

In particular, copolymerization monomers having a bulky structure are preferred from the viewpoint of promoting the evaporation of the solvent in the dope during the formation of the solvent film in the solution casting method described below and facilitating the distribution of rubber particles in the surface layer of the film.

Examples of copolymerizable monomers having a bulky structure include:
a copolymerizable monomer having a cyclo ring selected from the group consisting of (meth)acrylic acid esters having a cyclo ring, such as dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, and six-membered ring lactone (meth)acrylate; alicyclic vinyls such as vinylcyclohexane; and maleimides such as N-phenylmaleimide;
Copolymerizable monomers include (meth)acrylic acid esters having a branched alkyl group, such as t-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate.
Among them, the copolymerizable monomer having a bulky structure is preferably a (meth)acrylic acid ester having a cyclo ring, a copolymerizable monomer having a cyclo ring selected from the group consisting of maleimides, a (meth)acrylic acid ester having a branched alkyl group, or a combination thereof.

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

The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 115 to 160°C. If the Tg of the (meth)acrylic resin is 115°C or higher, the heat resistance of the optical film is likely to be increased, and if it is 160°C or lower, the toughness of the optical film is less likely to be impaired, since there is no need to increase the content of structural units derived from copolymerization monomers having, for example, a cyclo ring or maleimide ring. The Tg of the (meth)acrylic resin is preferably 125 to 160°C, and more preferably 125 to 150°C.

The glass transition temperature (Tg) of the (meth)acrylic resin can be measured in accordance with JIS K 7121-2012 using DSC (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, for example, the content ratio of the copolymerization monomer having the aforementioned cyclo ring may be increased.

The weight average molecular weight Mw of the (meth)acrylic resin is preferably, for example, 200,000 to 2,000,000. When the weight average molecular weight Mw of the (meth)acrylic resin is in the above range, the film is provided with sufficient mechanical strength (toughness) while the film formability is not easily impaired. From the above viewpoint, the weight average molecular weight Mw of the (meth)acrylic resin is more preferably 300,000 to 2,000,000, and even more preferably 500,000 to 1,000,000. The weight average molecular weight Mw can be measured in polystyrene equivalent terms by gel permeation chromatography (GPC).

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

The rubber particles are preferably graft copolymers containing a rubber-like polymer (crosslinked polymer), i.e., core-shell type rubber particles having a core made of a rubber-like polymer (crosslinked polymer) and a shell covering the core.

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, it is easy to impart sufficient toughness to the film. The glass transition temperature (Tg) of the rubbery polymer is more preferably -15°C or lower, and even more preferably -20°C or lower. The glass transition temperature (Tg) of the rubbery polymer is measured by the same method as described above.

The glass transition temperature (Tg) of the rubber-like polymer can be adjusted, for example, by the monomer composition of the polymer. In order to lower the glass transition temperature (Tg) of the rubber-like polymer, it is preferable to increase the mass ratio of the acrylic acid ester having an alkyl group with 4 or more carbon atoms/the total of the copolymerizable monomers in the monomer mixture (a') constituting the acrylic rubber-like polymer (a) of the core portion (for example, 3 or more, preferably 4 to 10).

The rubber-like polymer is not particularly limited as long as it has a glass transition temperature within the above range, but examples include butadiene-based crosslinked polymers, (meth)acrylic crosslinked polymers, and organosiloxane crosslinked polymers. Among them, (meth)acrylic crosslinked polymers are preferred, and acrylic crosslinked polymers (acrylic rubber-like polymers) are more preferred, from the viewpoint of having a small refractive index difference with (meth)acrylic resins and being less likely to impair the transparency of the optical film.

That is, the rubber particles are preferably acrylic graft copolymers containing an acrylic rubber-like polymer (a), i.e., core-shell type particles having a core containing the acrylic rubber-like polymer (a) and a shell covering the core. The core-shell type particles are multi-stage polymers (or multi-layer structure polymers) obtained by polymerizing a monomer mixture (b) mainly composed of methacrylic acid esters in at least one stage in the presence of the acrylic rubber-like polymer (a). The polymerization can be carried out by emulsion polymerization.

(Core: Acrylic Rubber Polymer (a))
The acrylic rubber-like polymer (a) is a crosslinked polymer mainly composed of an acrylic acid ester. The acrylic rubber-like polymer (a) is a crosslinked polymer obtained by polymerizing a monomer mixture (a') containing 50 to 100 mass% of an acrylic acid ester and 50 to 0 mass% of other monomers copolymerizable therewith, and 0.05 to 10 mass parts (based on 100 mass parts of the monomer mixture (a')) of a polyfunctional monomer having two or more non-conjugated reactive double bonds per molecule. The crosslinked polymer may be obtained by mixing and polymerizing all of these monomers, or by polymerizing two or more times with different monomer compositions.

The acrylic ester constituting the acrylic rubber-like polymer (a) is preferably an alkyl acrylate ester having an alkyl group of 1 to 12 carbon atoms, such as methyl acrylate or butyl acrylate. The acrylic ester may be one type or two or more types. From the viewpoint of setting the glass transition temperature of the rubber particles to -15°C or lower, it is preferable that the acrylic ester contains at least an alkyl acrylate ester having 4 to 10 carbon atoms.

The content of the acrylic acid ester is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, and even more preferably 70 to 99% by mass, relative to 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.

In addition, from the viewpoint of easily adjusting the glass transition temperature of the acrylic rubber-like polymer (a) to -10°C or lower, as described above, the mass ratio of the acrylic acid alkyl ester having an alkyl group with 4 or more carbon atoms to the total of the other copolymerizable monomers in the monomer mixture (a') is preferably 3 or more, and more preferably 4 or more and 10 or less.

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

Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl malate, 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.

The content of the polyfunctional monomer is preferably 0.05 to 10% by mass, and more preferably 0.1 to 5% by mass, relative to 100% by mass of the total monomer mixture (a'). If the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the resulting acrylic rubber-like polymer (a) is easily increased, so that the hardness and rigidity of the resulting film are not excessively impaired, and if the content is 10% by mass or less, the toughness of the film is not easily impaired.

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

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

The content of the methacrylic acid ester is preferably 50% by mass or more relative to 100% by mass of the monomer mixture (b). If the content of the methacrylic acid ester is 50% by mass or more, the hardness and rigidity of the resulting film can be prevented from decreasing. In addition, from the viewpoint of increasing the affinity with solvents such as methylene chloride, the content of the methacrylic acid ester is more preferably 70% by mass or more relative to 100% by mass of the monomer mixture (b), and even more preferably 80% by mass or more.

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

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

The acrylic graft copolymer may further contain a hard polymer inside the acrylic rubber-like polymer (a) as necessary. Such an acrylic graft copolymer can be obtained through the following polymerization steps (I) to (III).
(I) A step of polymerizing a monomer mixture (c1) consisting of 40 to 100% by mass of a methacrylic acid ester and 60 to 0% by mass of other monomers copolymerizable therewith, and 0.01 to 10 parts by mass of a polyfunctional monomer (relative to a total of 100 parts by mass of the monomer mixture (c1)) to obtain a rigid polymer. (II) A step of polymerizing 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 (relative to a total of 100 parts by mass of the monomer mixture (a1)) to obtain a flexible polymer. (III) A step of polymerizing a monomer mixture (b1) consisting of 60 to 100% by mass of a methacrylic acid ester and 40 to 0% by mass of other monomers copolymerizable therewith, and 0 to 10 parts by mass of a polyfunctional monomer (relative to a total of 100 parts by mass of the monomer mixture (b1)) to obtain a rigid polymer.

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

The acrylic graft copolymer may be obtained by further passing through a polymerization step (IV).
(IV) A monomer mixture (b2) consisting of 40 to 100% by mass of a methacrylic acid ester, 0 to 60% by mass of an acrylic acid ester, and 0 to 5% by mass of another copolymerizable monomer, and 0 to 10 parts by mass of a polyfunctional monomer (based on 100 parts by mass of the monomer mixture (b2)) are polymerized to obtain a rigid polymer.

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

The soft layer can impart shock absorption to the optical film. Examples of the soft layer include a layer made of an acrylic rubber-like polymer (a) whose main component is an acrylic acid ester. The hard layer can prevent the toughness of the optical film from being damaged, and can suppress the rubber particles from becoming coarse or clumpy during production. Examples of the hard layer include a layer made of a polymer whose main component is a methacrylic acid ester.

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 25 to 200%, more preferably 40 to 200%, and even more preferably 60 to 150%. When the graft ratio is 10% or more, the proportion of the shell portion does not become too small, so the hardness and rigidity of the film are unlikely to be impaired. When the graft ratio of the acrylic graft copolymer is 250% or less, the proportion of the acrylic rubber-like polymer (a) does not become too small, so the toughness and brittleness improvement effect of the film are unlikely to be impaired.

The graft ratio of the acrylic graft copolymer is measured by the following method.
1) 2 g of an acrylic graft copolymer was dissolved in 50 ml of methyl ethyl ketone, and the solution was centrifuged at 30,000 rpm and 12° C. for 1 hour using a centrifuge (Hitachi Koki Co., Ltd., CP60E) to separate the solution into an insoluble fraction and a soluble fraction (the centrifugation process was repeated a total of three times).
2) The weight of the insoluble matter thus obtained is applied to the following formula to calculate the graft ratio.
Graft ratio (%)=[(weight of methyl ethyl ketone insoluble matter)−(weight of acrylic rubber-like polymer (a))/(weight of acrylic rubber-like polymer (a)]×100

The average particle size of the rubber particles (acrylic graft copolymer) is preferably 100 to 400 nm, and more preferably 150 to 300 nm. If the average particle size is 100 nm or more, it is easy to impart sufficient toughness to the film, and if it is 400 nm or less, the transparency of the film is less likely to decrease.

The average particle size of rubber particles (acrylic graft copolymer) is determined as the average of the circle-equivalent diameters of 100 particles obtained by SEM or TEM photography of the film surface and slices. The circle-equivalent diameter can be determined by converting the projected area of the particle obtained by photography into the diameter of a circle with the same area. In this case, the rubber particles (acrylic graft copolymer) observed by SEM observation and/or TEM observation at a magnification of 5000 times are used to calculate the average particle size. The average particle size of rubber particles (acrylic graft copolymer) in the dispersion can be measured using a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

The content of rubber particles is preferably 5 to 40% by mass relative to the (meth)acrylic resin. If the content of rubber particles is 5% by mass or more, not only is it easy to impart sufficient flexibility and toughness to the (meth)acrylic resin film, but it is also possible to form unevenness on the surface and provide slipperiness. If the content is 40% by mass or less, the haze does not increase too much. From the above viewpoint, the content of rubber particles is more preferably 7 to 30% by mass relative to the (meth)acrylic resin, and even more preferably 8 to 25% by mass.

1-3. Fine Particles The optical film of the present invention preferably further contains inorganic or organic fine particles from the viewpoint of further increasing the slipperiness of the optical film and facilitating uneven distribution of the rubber particles in the surface layer portion of the film.

Examples of inorganic materials constituting the inorganic fine particles include silicon dioxide (SiO ₂ ), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Among them, silicon dioxide is preferred in order to reduce the increase in haze of the obtained film.

It is preferable that the organic microparticles are particles having a glass transition temperature (Tg) of 80°C or higher. When the glass transition temperature of the organic microparticles is 80°C or higher, the organic microparticles tend to come out onto the surface of the film-like material during stretching, and thus tend to form unevenness on the surface. This makes it easier to increase the slipperiness of the resulting optical film. It is more preferable that the glass transition temperature of the organic microparticles is 100°C or higher. The glass transition temperature is measured by the same method as described above.

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

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

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

Among these, from the viewpoints of high affinity with (meth)acrylic resins, flexibility against stress, and ease of adjusting the glass transition temperature to the above range, copolymers containing structural units derived from one or more selected from the group consisting of (meth)acrylic acid esters, vinyl esters, styrenes, and olefins, and structural units derived from polyfunctional monomers are preferred, copolymers containing structural units derived from (meth)acrylic acid esters and structural units derived from polyfunctional monomers are more preferred, and copolymers containing structural units derived from (meth)acrylic acid esters, structural units derived from styrenes, and structural units derived from polyfunctional monomers are even more preferred.

When the organic microparticles contain structural units derived from a polyfunctional monomer, the content of the structural units derived from the polyfunctional monomer in the organic microparticles is usually greater than the content of the structural units derived from the polyfunctional monomer in the rubber particles. Specifically, it can be, for example, 50 to 500% by mass relative to 100% by mass of the total of the structural units derived from monomers other than the polyfunctional monomer that constitute the copolymer.

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

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

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

From the viewpoint of highly suppressing an increase in haze in the resulting film, 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 even more preferably 0.065 or less.

The average particle diameter of the organic fine particles is preferably 0.04 to 2 μm, and more preferably 0.08 to 1 μm. When the average particle diameter of the organic fine particles is 0.04 μm or more, it is easy to impart sufficient slipperiness to the resulting film. When the average particle diameter of the organic fine particles is 2 μm or less, it is easy to suppress an increase in haze. The average particle diameter of the organic fine particles can be measured in the same manner as the average particle diameter of the rubber particles.

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

In particular, from the viewpoint of preventing an increase in the haze of the optical film and a loss of toughness of the optical film, it is more preferable that the optical film contains organic fine particles.

The content of the fine particles is preferably 0.3 to 3% by mass relative to the (meth)acrylic resin. If the content of the fine particles is 0.03% by mass or more, not only can sufficient slipperiness be imparted to the optical film, but also gaps (voids) are easily formed between the resins during film formation in the solution casting method. This makes it easier to increase the volatilization rate of the solvent in the dope or film-like material, making it easier to unevenly distribute the rubber particles in the surface layer of the obtained optical film. If the content of the fine particles is 1.0% by mass or less, it is easier to suppress an increase in haze. The content of the fine particles is more preferably 0.5 to 2% by mass, and even more preferably 0.7 to 2% by mass.

1-4. Other Components The optical film of the present invention may further contain other components within the scope of not impairing the effects of the present invention. Examples of other components include residual solvents, ultraviolet absorbers, antioxidants, etc.

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

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

The residual solvent content in optical films can be measured by headspace gas chromatography. In headspace gas chromatography, a sample is sealed in a container and heated, and when the container is filled with volatile components, the gas in the container is quickly injected into a gas chromatograph, and mass analysis is performed to identify the compounds and quantify the volatile components. The headspace method makes it possible to observe all peaks of the volatile components using a gas chromatograph, and by using an analytical method that utilizes electromagnetic interactions, it is also possible to quantify volatile substances, monomers, etc. with high accuracy.

1-5. Layer structure and properties (R _A1 /R _B and R _A2 /R _B )
The optical film of the present invention is preferably a monolayer film composed of one layer (single layer). Specifically, the monolayer film is different from a laminated film obtained through a process such as lamination, co-extrusion, or co-casting of a plurality of films or layers. Whether or not the film is a monolayer film can be confirmed, for example, by observing the cross section of the optical film by TEM, and finding that no boundary line between layers can be confirmed within a thickness range of 1 to 20 μm from the surface of the film.

In the optical film of the present invention, the rubber particles are unevenly distributed in the surface layer portion of the optical film in the thickness direction of the optical film. The rubber particles may be unevenly distributed only in one surface layer portion of the optical film in the thickness direction of the optical film, or may be unevenly distributed in both one surface layer portion and the other surface layer portion of the optical film. In particular, from the viewpoint of easily increasing the flexibility, it is preferable that the rubber particles are unevenly distributed in both one surface layer portion and the other surface layer portion of the optical film.

Figure 2 is a schematic cross-sectional diagram showing an example of an optical film 100 of the present invention.

As shown in FIG. 2 , in the thickness direction of the optical film 100 of the present invention, when a region A1 is a region that is 20% or less of the thickness of the optical film 100 from one side of the optical film 100, a region A2 is a region that is 20% or less of the thickness of the optical film 100 from the other side of the optical film 100, and a region B (the region sandwiched between regions A1 and A2) is a region that is more than 20% but less than 80% of the thickness of the optical film 100 from one or the other side of the optical film 100, it is preferable that the area ratio R _A1 per unit area of the rubber particles in region A1 and the area ratio R _A2 per unit area of the rubber particles in region A2 are higher than the area ratio R _B per unit area of the rubber particles in region B.

The area ratio R _A1 of the rubber particles per unit area in the region A1 is expressed by the following formula.
Area ratio R _A1 (%) = total area of rubber particles in region A1 / area of region A1 × 100
The area ratio R A2 of the rubber particles per unit area in region _A2 and the area ratio R _B of the rubber particles per unit area in region B are defined in the same manner.

Specifically, the ratio (R _A1 /R _B ) of the area ratio R _A1 to the area ratio R _B and the ratio (R _A2 /R _B ) of the area ratio R _A2 to the area ratio R _B are preferably 1.01 or more and less than 2.0. When R _A1 /R _B and R _A2 /R _B are 1.01 or more, respectively, the rubber particles are sufficiently unevenly distributed in the surface layer part of the film. Therefore, sufficient flexibility and toughness can be imparted to the surface layer part of the optical film, which is most stressed during the irregular shape punching process or bending, so that cracks during the irregular shape punching process or bending can be sufficiently suppressed. In addition, when R _A1 /R _B (R _A2 /R _B ) is less than 2.0, the difference in toughness between the surface layer part and the inside of the film is not too large, so that even when the optical film is bent or a heat cycle test is performed in the state of a polarizing plate, a stress difference is unlikely to occur inside the optical film. From these viewpoints, R _A1 /R _B and R _A2 /R _B of the optical film 100 are more preferably from 1.02 to 1.5, and further preferably from 1.25 to 1.45, respectively.

The R _A1 /R _B and R _A2 /R _B of the obtained optical film can be measured by the following method.
1) The optical film is cut with a microtome to obtain a cut surface perpendicular to the surface of the optical film. The cut surface of the obtained optical film is observed by TEM. The observation conditions can be an acceleration voltage (electron energy irradiated to the sample): 30 kV, a working distance (distance between the lens and the sample): 8.6 mm × magnification: 3.00 k. The observation area is an area including the entire thickness direction of the optical film.
2) The brightness gradient of the obtained TEM image is removed using image processing software NiVision (manufactured by National Instruments), and then opening processing is performed to detect the contrast difference between the bulk and the rubber particles, thereby allowing the distribution state of the rubber particles to be identified.
3) In the image after image processing obtained in 2) above, in the thickness direction of the optical film, the area ratio per unit area of rubber particles R _A1 in region A1 that is 20% or less of the film thickness from one side of the optical film, the area ratio per unit area of rubber particles R _A2 in region A2 that is 20% or less of the film thickness from the other side of the optical film, and the area ratio per unit area RB of rubber particles in region _B sandwiched between regions A1 and A2 (a region that is more than 20% but less than 80% of the film thickness from one or the other side of the optical film) are calculated.
4) From the results obtained in 3) above, calculate the ratio ( _RA1 /RB ₎ of the area ratio per unit area of rubber particles in region _A1 , RA1, to the area ratio per unit area of rubber particles in region B, _RB . Similarly, calculate the ratio ( _RA2 / _RB ) of the area ratio per unit area of rubber particles in region _A2 , RA2, to the area ratio per unit area of rubber particles in region B, _RB .

The method of distributing the rubber particles unevenly is not particularly limited, but can be adjusted mainly by the diffusion behavior of the rubber particles in the cast dope or in the film-like material after peeling during film formation by the solution casting method. The diffusion behavior of the rubber particles can be adjusted, for example, by the drying conditions of the dope or film-like material (residual solvent amount at peeling, drying temperature, time, etc.), the type of (meth)acrylic resin, and the affinity between the rubber particles and the solvent. Therefore, in order to distributing a large amount of rubber particles unevenly in the surface layer portion (regions A1 and A2) of the optical film, as described later, it is preferable to increase the amount of residual solvent in the film-like material at peeling and to lower the drying temperature of the film-like material after peeling to Tg or lower. Furthermore, it is more preferable to select a (meth)acrylic resin containing a structural unit derived from a bulky copolymerization monomer that easily volatilizes the solvent, or to select rubber particles that have a high affinity with the solvent, as the (meth)acrylic resin.

In addition, in the cross section of the optical film 100, the density of rubber particles changes continuously in the thickness direction of the film. Specifically, in the optical film 100, the density of rubber particles increases continuously from the inside to the surface portion in the thickness direction of the optical film, that is, in the cross section of the optical film of the present invention, the area ratio of rubber particles per unit area increases continuously from the inside to the surface portion in the thickness direction of the optical film. The term "continuously increasing" may refer to a linear increase, a curved increase, or a multi-step increase.

Therefore, compared to a laminated film in which a (meth)acrylic resin layer that does not contain rubber particles is sandwiched between (meth)acrylic resin layers that do contain rubber particles, the stress difference between the layers can be reduced, and delamination and other problems can be highly suppressed.

(Hayes)
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 even more preferably 1.0% or less. The haze can be measured on a sample of 40 mm x 80 nm at 25°C and 60% RH using a haze meter (HGM-2DP, Suga Test Instruments) in accordance with JIS K-6714.

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

Ro and Rt are defined by the following formulas, respectively.
Formula (2a): Ro=(nx-ny)×d
Formula (2b): Rt=((nx+ny)/2-nz)×d
(Wherein,
nx represents the refractive index in the in-plane slow axis direction of the film (the direction in which the refractive index is maximum);
ny represents the refractive index in a direction perpendicular to the in-plane slow axis of the film,
nz represents the refractive index in the thickness direction of the film,
d represents the thickness of the film (nm).

The in-plane slow axis of the optical film of the present invention refers to the axis in which the refractive index is maximum on the film surface. The in-plane slow axis of the (meth)acrylic resin film can be confirmed by an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axometrics).

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

The phase difference Ro and Rt of the optical film of the present invention can be adjusted, for example, by the type of (meth)acrylic resin. In order to reduce the phase difference Ro and Rt of the optical film, it is preferable to use a (meth)acrylic resin that is less likely to produce phase difference when stretched (for example, a monomer ratio such that the phase difference can be offset between a structural unit derived from a monomer having negative birefringence and a structural unit derived from a monomer having positive birefringence).

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

2. Manufacturing Method of Optical Film The optical film of the present invention may be manufactured by a solution casting method (casting method) or a melt casting method (melt). Among them, the solution casting method (casting method) is preferred from the viewpoint of fewer restrictions on usable materials.

That is, the optical film of the present invention can be manufactured through the steps of 1) obtaining a dope containing at least the above-mentioned (meth)acrylic resin, rubber particles, and a solvent, 2) casting the obtained dope onto a support, drying and peeling it off to obtain a film-like material, 3) stretching the obtained film-like material at a predetermined temperature, and 4) further drying the stretched film-like material at a predetermined temperature.

Regarding step 1), the above-mentioned (meth)acrylic resin and rubber particles are dissolved or dispersed in a solvent to prepare a dope.

The solvent used in the dope includes an organic solvent (good solvent) capable of dissolving at least the (meth)acrylic resin. Examples of good solvents include chlorine-based organic solvents such as methylene chloride; and non-chlorine-based organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Among these, methylene chloride is preferred.

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

The dope may be prepared by directly adding the (meth)acrylic resin and rubber particles to the aforementioned solvent and mixing them; or it may be prepared by previously preparing a resin solution in which the (meth)acrylic resin is dissolved in the aforementioned solvent, and a microparticle dispersion in which rubber particles and, if necessary, organic microparticles are dispersed in the aforementioned solvent, and mixing them.

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

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

The solvent in the dope cast onto the support is then evaporated and the dope is dried. The dried dope is peeled off from the support to obtain a film.

From the viewpoint of easily distributing rubber particles unevenly in the surface layer of the obtained optical film, the amount of residual solvent in the dope when peeled off from the support (amount of residual solvent in the film-like material when peeled off) is preferably 25% by mass or more, more preferably 30 to 37% by mass, and even more preferably 30 to 35% by mass. If the amount of residual solvent when peeled off is 25% by mass or more, the solvent is easily evaporated all at once from the film-like material after peeling, so that the rubber particles are easily distributed unevenly in one surface layer and the other surface layer of the optical film. Furthermore, if the amount of residual solvent when peeled off is 37% by mass or less, excessive stretching of the film-like material due to peeling can be suppressed.

The amount of the remaining solvent in the dope at the time of peeling is defined by the following formula: The same applies hereinafter.
Residual solvent amount of dope (mass %)=(mass of dope before heat treatment−mass of dope after heat treatment)/mass of dope after heat treatment×100
The heat treatment in measuring the amount of residual solvent refers to a 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 the dope on the support, the temperature of the support, etc.

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

Stretching may be performed according to the desired optical properties, and it is preferable to stretch in at least one direction, but stretching in two mutually perpendicular directions (for example, biaxial stretching in the width direction (TD) of the film and the transport direction (MD) perpendicular thereto) may also be performed.

When the optical film is to be used as, for example, a retardation film for IPS, the stretching ratio can be 1.01 to 2 times. The stretching ratio is defined as (size of film in the stretching direction after stretching) / (size of film in the stretching direction before stretching). When performing biaxial stretching, it is preferable to set the above stretching ratios for both the TD and MD directions.

In addition, the in-plane slow axis direction of the optical film (the direction in which the refractive index is maximum in the plane) is usually the direction in which the stretching ratio is maximum.

The stretching temperature (drying temperature), where Tg is the glass transition temperature of the (meth)acrylic resin, is preferably equal to or higher than the boiling point of the main solvent and equal to or lower than Tg (°C), more preferably between (Tg-60)°C and Tg°C, and even more preferably between (Tg-60)°C and (Tg-30)°C. If the stretching temperature is equal to or higher than (Tg-60)°C, the solvent is easily volatilized to an appropriate degree, making it easier to diffuse the solvent into the surface layer of the film-like material, and also making it easier to diffuse the rubber particles (together with the solvent) into the surface layer of the film-like material. If the stretching temperature is equal to or lower than Tg, the solvent does not volatilize too much, making it easier to adjust the amount of residual solvent at the time of peeling to a certain level or higher. Specifically, the stretching temperature can be 38 to 90°C.

The stretching temperature can be measured as either (a) the temperature inside the stretching machine or the hot air temperature, when drying is performed using a non-contact heating method such as a tenter stretching machine, (b) the temperature of the contact heating part, when drying is performed using a contact heating method such as a hot roller, or (c) the surface temperature of the film-like material (surface to be dried). Among these, it is preferable to measure (a) the temperature inside the stretching machine or the hot air temperature, or the like.

It is preferable that the amount of residual solvent in the film-like material at the start of stretching is approximately the same as the amount of residual solvent in the film-like material at the time of peeling, for example, 20 to 30% by mass, and more preferably 25 to 30% by mass.

The film can be stretched in the TD direction (width direction) by, for example, fixing both ends of the film with clips or pins and widening the distance between the clips or pins in the direction of travel (tenter method). The film can be stretched in the MD direction by, for example, applying different peripheral speeds to multiple rolls and utilizing the difference in roll peripheral speeds between them (roll method).

Regarding step 4), the film-like material obtained after the stretching is further dried. Specifically, the film-like material obtained after the stretching is further dried while being transported with a roll or the like, and then wound up, for example, into a roll to obtain an optical film.

The drying temperature is preferably (Tg-60)°C to Tg°C, and more preferably (Tg-60)°C to (Tg-30)°C, similar to the stretching temperature in step 3) above. This makes it difficult for the (meth)acrylic resin to flow in the film-like material after stretching, making it easier to maintain the uneven distribution of the formed rubber particles. The drying temperature may be the same as the stretching temperature in step 3) above, or it may be a temperature lower than that.

As described above, the drying temperature can be measured as either (a) the ambient temperature, such as the temperature inside the oven or the hot air temperature, when drying is performed using a non-contact heating drying device such as a drying oven or a hot air blower, (b) the temperature of the contact heating part, when drying is performed using a contact heating device such as a hot roller, or (c) the surface temperature of the film-like material (surface to be dried). Among these, it is preferable to measure (a) the ambient temperature, such as the temperature inside the stretching machine or the hot air temperature.

The optical film of the present invention obtained has excellent transportability. Therefore, the film has good slip during transport, and the obtained film is less likely to be scratched.

The optical film of the present invention can also be obtained by methods other than those described above, for example by applying a solvent having a high affinity for the rubber particles to the surface of a base film containing a (meth)acrylic resin and rubber particles, and then drying (solvent treatment).

The base film may be manufactured by a solution casting method (casting method) or a melt casting method (melt method). Examples of solvents with high affinity for rubber particles include the same as the good solvents mentioned above, and preferably methylene chloride.

The amount of solvent applied and the time and temperature at which it is left to stand may be such that the rubber particles in the base film can be diffused to the surface layer. The amount of solvent applied may be, for example, in the range of 20% or less of the base film in wet thickness. The standing temperature may be such that the solvent does not volatilize, and may be at least 8°C lower than the boiling point of the solvent. The standing time may be, for example, 10 to 20 minutes.

The drying temperature may be any temperature at which the solvent evaporates, and is preferably, for example, (Tg-60) to Tg°C, and more preferably, (Tg-60) to (Tg-30)°C. For example, 38 to 90°C. The drying temperature may be defined in the same manner as the drying temperature in steps 3) and 4) above.

In this way, a solvent that has a high affinity for the rubber particles is applied to the surface of the base film containing the rubber particles and then dried. This allows the rubber particles in the base film to be concentrated in the surface layer of the film by taking advantage of their affinity with the solvent.

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

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

Figure 3 is a schematic cross-sectional diagram showing an example of a polarizing plate 200 of the present invention.

3, the polarizing plate 200 of the present invention has a polarizer 210, polarizing plate protective films 220A and 220B disposed on both sides of the polarizer 210, and adhesive layers 230A and 230B disposed between the polarizing plate protective films 220A and 220B and the polarizer 210. At least one of the polarizing plate protective films 220A and 220B is the optical film of the present invention.

3-1. Polarizer 210
The polarizer 210 is an element that transmits only light polarized in a certain direction, and is a polyvinyl alcohol polarizing film. There are two types of polyvinyl alcohol polarizing films: one in which the polyvinyl alcohol film is dyed with iodine, and one in which the polyvinyl alcohol film is dyed with a dichroic dye.

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

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

The thickness of the polarizer 210 is preferably 5 to 30 μm, and more preferably 5 to 20 μm in order to make the polarizing plate thinner.

3-2. Polarizing plate protective films 220A and 220B
The polarizing plate protective films 220A and 220B are disposed on both sides of the polarizer 210 via adhesive layers 230A and 230B, respectively. At least one of the polarizing plate protective films 220A and 220B is the optical film of the present invention. When only one of the polarizing plate protective films 220A and 220B is the optical film of the present invention, the other may be another optical film.

Other examples of 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, all manufactured by Konica Minolta, Inc., FUJITAC T40UZ, FUJITAC T60UZ, FUJITAC T80UZ, FUJITAC TD80UL, FUJITAC TD60UL, FUJITAC TD40UL, FUJITAC R02, FUJITAC R06, all manufactured by Fuji Film Corporation.

The thickness of the other optical films is preferably thicker in order to prevent cracks in the polarizing plate, and can be, for example, 5 to 100 μm, preferably 40 to 80 μm.

3-3. Adhesive layers 230A and 230B
The adhesive layers 230A and 230B may be a fully saponified polyvinyl alcohol aqueous solution (water glue) or a cured product of an active energy ray curable adhesive. The active energy ray curable adhesive may be a photoradical polymerization type composition utilizing photoradical polymerization, a photocationic polymerization type composition utilizing photocationic polymerization, or a combination thereof.

3-3. Manufacturing Method of Polarizing Plate The polarizing plate 200 of the present invention can be obtained by bonding the polarizer 210 and the polarizing plate protective films 220A and 220B with an adhesive. The adhesive can be any of the adhesives described above.

The obtained polarizing plate 200 is punched into any shape or size depending on the application. For example, the polarizing plate 200 is punched into any shape, such as a shape with rounded corners, a shape with a complex curved surface, or a shape with a hole in the center. When punching the polarizing plate 200 into an irregular shape, the force of the blade tip tends to concentrate on the polarizing plate protective films 220A and 220B. In addition, when the polarizing plate 200 is bent, stress tends to concentrate on the surface layers of the polarizing plate protective films 220A and 220B.

In contrast, in the polarizing plate 200 of the present invention, at least one of the polarizing plate protective films 220A and 220B is the optical film of the present invention. As described above, the optical film of the present invention has a well-improved brittleness of the surface layer of the film, so that cracks in the optical film when the polarizing plate 200 is punched into an irregular shape and the resulting cracks in the polarizing plate 200 can be suppressed. In addition, as described above, in the optical film of the present invention, the rubber particles change continuously in the thickness direction of the film. Therefore, even in a heat cycle test of the polarizing plate 200 (a test in which low temperature and high temperature are repeatedly held), there is no extreme stress difference between the surface layer and the inside of the optical film, so that delamination of the optical film can also be suppressed.

4. Liquid Crystal Display Device 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 can be, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment, MVA (Multi-domain Vertical Alignment), PVA (Patterned Vertical Alignment)), IPS (In-Plane-Switching), etc. Among them, VA (MVA, PVA) mode and IPS mode are preferred.

One or both of the first and second polarizing plates are polarizing plates of the present invention. It is preferable that the polarizing plate of the present invention is arranged so that the optical film of the present invention is on the liquid crystal cell side.

The present invention will be explained in detail below with reference to examples, but the present invention is not limited to these.

1. Materials for Optical Films (1) (Meth)acrylic Resins (Meth)acrylic Resin A: Polymethylmethacrylate (PMMA) (glass transition temperature (Tg): 100° C., weight average molecular weight Mw: 1,000,000)
(Meth)acrylic resin B: methyl methacrylate (MMA)/adamantyl methacrylate (MADMA) copolymer (MMA/MADMA: 85/15 (mass ratio), glass transition temperature (Tg): 110° C., weight average molecular weight Mw: 1,000,000)
(Meth)acrylic resin C: methyl methacrylate (MMA)/N-phenylmaleimide (PMI) copolymer (MMA/PMI: 85/15 (mass ratio), glass transition temperature (Tg): 120° C., weight average molecular weight Mw: 1,000,000)

The glass transition temperature (Tg) and weight average molecular weight (Mw) of (meth)acrylic resins A to C were measured by the following method.

(Glass Transition Temperature (Tg))
The glass transition temperature of the (meth)acrylic resin was measured using DSC (Differential Scanning Calorimetry) in accordance with JIS K 7121-2012.

(Weight average molecular weight (Mw))
The weight average molecular weight (Mw) of the (meth)acrylic resin was measured using gel permeation chromatography (HLC8220GPC, manufactured by Tosoh Corporation) and a column (TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series, manufactured by Tosoh Corporation). 20 mg ± 0.5 mg of a 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 measurement was performed at a detector RI temperature of 40°C, and the content was converted into styrene equivalent. values were used.

(2) Rubber particles <Preparation of rubber particles C1>
The following compounds were charged into an 8 L polymerization apparatus equipped with a stirrer.
Deionized water: 175 parts by weight Polyoxyethylene lauryl ether phosphate: 0.104 parts by weight Boric acid: 0.4725 parts by weight Sodium carbonate: 0.04725 parts by weight

After the atmosphere inside the polymerization reactor was thoroughly replaced with nitrogen gas, the internal temperature was raised to 80° C., and 26 mass% of a mixture consisting of 27 parts by mass of monomer mixture (c1) (97 mass% methyl methacrylate, 3 mass% butyl acrylate) and 0.135 parts by mass of allyl methacrylate was added all at once to the polymerization reactor, followed by the addition of 0.0645 parts by mass of sodium formaldehyde sulfoxylate, 0.0056 parts by mass of 2-sodium ethylenediaminetetraacetate, 0.0014 parts by mass of ferrous sulfate, and 0.0207 parts by mass of t-butyl hydroperoxide, and 15 minutes later, 0.0345 parts by mass of t-butyl hydroperoxide was added, and the polymerization was continued for a further 15 minutes.
Next, 0.0098 parts by mass of sodium hydroxide in the form of a 2% by mass aqueous solution and 0.0852 parts by mass of polyoxyethylene lauryl ether phosphate were added as they were, and the remaining 74% by mass of the mixture was continuously added over 60 minutes. 30 minutes after the end of the addition, 0.069 parts by mass of t-butyl hydroperoxide was added, and polymerization was continued for another 30 minutes to obtain a polymer. The polymerization conversion rate was 100.0%.

Then, 0.0267 parts by mass of sodium hydroxide was added in the form of a 2% by mass aqueous solution, and 0.08 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, followed by the continuous addition of a mixture consisting of 50 parts by mass of monomer mixture (a1) (butyl acrylate 82% by mass, methyl methacrylate 18% by mass) and 0.75 parts by mass of allyl methacrylate over 150 minutes. After the addition was completed, 0.015 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, and polymerization was continued for 120 minutes to obtain a rubber-like polymer. The polymerization conversion rate was 99.0%, and the average particle size was 225 nm.

Then, 0.023 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, and 15 parts by mass of monomer mixture (b1) (95% by mass of methyl methacrylate, 5% by mass of butyl acrylate) was continuously added over 45 minutes, and polymerization was continued for a further 30 minutes.

Then, 8 parts by mass of monomer mixture (b2) (52% by mass of methyl methacrylate, 48% by mass of butyl acrylate) was added continuously over 25 minutes, and polymerization was continued for another 60 minutes to obtain a graft copolymer latex. The polymerization conversion rate was 100.0%.

The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain a white powdery graft copolymer (rubber particles C1). The graft ratio of rubber particles C1 was 24.2%, the glass transition temperature (Tg) of the rubber-like polymer was -30°C, and the average particle size was 250 nm.

<Preparation of rubber particles C2>
A graft copolymer (rubber particles C2) was obtained in the same manner as rubber particles C1, except that the polymerization time of the monomer mixture (b2) was increased. The graft ratio of rubber particles C2 was 78%, the glass transition temperature (Tg) of the rubber-like polymer was -30°C, and the average particle size was 300 nm.

(3) Microparticles P1: inorganic microparticles (Aerosil (registered trademark) R812, manufactured by Nippon Aerosil Co., Ltd.)
P2: Organic fine particles prepared by the following method

(Preparation of seed particles)
A polymerization vessel equipped with a stirrer and a thermometer was charged with 1000 g of deionized water, to which 50 g of methyl methacrylate and 6 g of t-dodecyl mercaptan were then added, and the mixture was heated to 70°C while being purged with nitrogen and stirred. The internal temperature was kept at 70°C, and 20 g of deionized water in which 1 g of potassium persulfate had been dissolved as a polymerization initiator was added, followed by polymerization for 10 hours. The average particle size of the seed particles in the resulting emulsion was 0.05 μm.

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

60 g of the emulsion containing the seed particles was added to the resulting dispersion, and the mixture was stirred at 30°C for 1 hour to allow the seed particles to absorb the monomer mixture. The absorbed monomer mixture was then heated at 50°C for 5 hours under a nitrogen stream to polymerize, and then cooled to room temperature (approximately 25°C) to obtain a slurry of polymer microparticles (organic microparticles 1). The average particle size of the resulting organic microparticles was 0.14 μm, and the glass transition temperature (Tg) was 280°C.

(Preparation of Aggregates of Organic Fine Particles)
This emulsion was spray-dried under the following conditions using a spray dryer manufactured by Sakamoto Giken Co., Ltd. (type: atomizer take-up type, model number: TRS-3WK) to obtain an aggregate of organic fine particles. The average particle size of the aggregate of organic fine particles was 30 μm.
Supply rate: 25ml/min
Atomizer rotation speed: 11,000 rpm
Air volume: 2 ^m3 /min
Slurry inlet temperature of spray dryer: 100°C
Polymer particle aggregate outlet temperature: 50°C

The average particle size of rubber particles and organic microparticles was measured using the following method.

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

2. Preparation and Evaluation of Optical Films <Preparation of Optical Film 1>
The pellets of (meth)acrylic resin A were dried in a dryer at 80°C for 4 hours, and then fed to a φ65 mm single screw extruder. The resin was heated and melted so that the resin temperature at the extruder outlet was 270°C, and the molten resin was extruded from a T-die. The resin temperature immediately after discharge at the T-die outlet was 270°C. The discharged molten resin was sandwiched between a cast roll adjusted to 70°C and a touch roll adjusted to 70°C, and cooled and solidified to obtain a raw film having a thickness of 140 μm.

The obtained raw film was stretched twice in both the longitudinal and transverse directions at 132°C (Tg+10°C) in a simultaneous biaxial stretching machine (heat treatment zone length/stretching zone length = 1.0), and then heat-treated at 135°C in the heat treatment zone, relaxing the film by 5% in both the longitudinal and transverse directions, and then cooled to below Tg. Both ends of the obtained film were slit continuously, and the film was taken up while being taken up by a take-up roll, to obtain an optical film 1 having a thickness of 40 μm.

<Preparation of Optical Film 2>
(Preparation of Rubber Particle Dispersion)
11.3 parts by mass of rubber particles C1 and 200 parts by mass of methylene chloride were mixed and stirred in a dissolver for 50 minutes, and then dispersed at 1500 rpm using a Milder disperser (manufactured by Pacific Machinery Works, Ltd.) to obtain a rubber particle dispersion.

(Preparation of Dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Next, a (meth)acrylic resin was added to the pressurized dissolution tank while stirring. Next, the prepared fine particle dispersion was added and completely dissolved while stirring. The viscosity of the obtained solution was 16000 mmPa·s and the water content was 0.50%. This was filtered using SHP150 manufactured by ROKI TECHNO CO., LTD. at a filtration flow rate of 300 L/ ^m2 ·h and a filtration pressure of 1.0× ¹⁰⁶ Pa to obtain a dope.
(Dope Composition)
Acrylic resin: 100 parts by weight Methylene chloride: 150 parts by weight Ethanol: 30 parts by weight Rubber dispersion: 200 parts by weight

(Film formation)
Using an endless belt casting apparatus, the dope was uniformly cast onto a stainless steel belt support having a width of 1,800 mm at a temperature of 30° C. The temperature of the stainless steel belt was controlled at 28° C. The conveying speed of the stainless steel belt was 20 m/min.

The solvent was evaporated on the stainless steel belt support until the residual solvent content in the cast dope was 30% by mass. Then, the dope was peeled off from the stainless steel belt support at a peeling tension of 128 N/m to obtain a film-like material. In other words, the residual solvent content of the film-like material at the time of peeling was 30% by mass. While the peeled film was transported by multiple rollers, the obtained film-like material was stretched 1.2 times in the width direction under conditions of 60°C (Tg-60°C) in a tenter. After that, while transporting by rolls, it was further dried at 140°C (Tg+40°C), and the end clamped by the tenter clip was slit by a laser cutter and wound up to obtain an optical film 2 with a film thickness of 40 μm.

<Preparation of Optical Film 3>
Pellets containing (meth)acrylic resin 1, rubber particles C1, and inorganic fine particles P1 in the amounts shown in Table 1 were fed into a double-flight type single-screw extruder (ratio of effective screw length L to screw diameter D L/D = 28), and the molten resin was supplied to one side of the multi-manifold die of the die lip at an extruder outlet temperature of 260°C and a gear pump rotation speed of 6 rpm.

At the same time, pellets containing (meth)acrylic resin 1 but not rubber particles C1 were fed into the double-flight type single-screw extruder, and the molten resin was supplied to the other side of the multi-manifold die of the die lip at an extruder outlet temperature of 260°C.

These molten resins were then extruded (co-cast) from a multi-manifold die at 260°C, cast onto a cooling roll adjusted to 130°C, and then passed through a cooling roll adjusted to a temperature of 50°C and wound up. This resulted in an optical film 3 (laminated film) with a thickness of 40 μm, which had a three-layer structure of a (meth)acrylic resin layer not containing rubber particles C1/a (meth)acrylic resin layer containing rubber particles C1/a (meth)acrylic resin layer not containing rubber particles C1.

<Preparation of Optical Film 4>
A molten resin of pellets containing (meth)acrylic resin 1 but not rubber particles was supplied to one side of a multi-manifold die of a die slip, and a molten resin of pellets containing (meth)acrylic resin 1 and rubber particles C1 was supplied to the other side of the multi-manifold die, thereby obtaining optical film 4 (laminate film) in the same manner as optical film 3, except that a three-layer structure of (meth)acrylic resin layer containing rubber particles C1/(meth)acrylic resin layer not containing rubber particles C1/(meth)acrylic resin layer containing rubber particles C1 was obtained.

<Preparation of Optical Film 5>
Optical film 5 was obtained in the same manner as optical film 2, except that the residual solvent content of the film when peeled off from the stainless steel belt support was 10%, and the drying temperature during roll transport after stretching in the width direction with a tenter was changed to 60°C (Tg-60°C).

<Preparation of Optical Film 6>
Optical film 6 having a thickness of 40 μm was obtained in the same manner as optical film 2, except that the amount of residual solvent in the film-like material at the time of peeling was changed as shown in Table 1, and the drying temperature during roll transport after stretching in the width direction with a tenter was changed to 60° C. (Tg-60)° C.

<Preparation of Optical Film 7>
Optical film 7 having a thickness of 40 μm was obtained in the same manner as optical film 6, except that the amount of residual solvent in the film-like material at the time of peeling was changed as shown in Table 1.

<Preparation of Optical Films 8 and 15>
Optical films 8 and 15 each having a thickness of 40 μm were obtained in the same manner as for optical film 6, except that the type of (meth)acrylic resin was changed as shown in Table 1.

<Preparation of Optical Film 9>
(Preparation of Microparticle Dispersion 1)
11.3 parts by weight of inorganic fine particles P1 (Aerosil (registered trademark) R812, manufactured by Nippon Aerosil Co., Ltd.) and 84 parts by weight of ethanol were mixed and stirred in a dissolver for 50 minutes, and then dispersed with a Manton-Gaulin to obtain an additive solution.
Five parts by mass of the additive solution was slowly added to methylene chloride (100 parts by mass) in a dissolution tank that was being thoroughly stirred. The mixture was then dispersed in an attritor so that the secondary particles had a predetermined particle size. The mixture was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to obtain microparticle dispersion 1.

(Preparation of dope, film formation)
A dope was prepared in the same manner as in the preparation of Optical Film 8, except that the obtained Fine Particle Dispersion 1 was further added so as to have the following composition, to obtain Optical Film 9 having a thickness of 40 μm.
(Dope Composition)
(Meth)acrylic resin B: 100 parts by weight Methylene chloride: 150 parts by weight Ethanol: 30 parts by weight Rubber dispersion: 200 parts by weight Microparticle dispersion 1: 125 parts by weight

<Preparation of Optical Film 10>
(Base film production)
Pellets of (meth)acrylic resin C, rubber particles C1, and inorganic fine particles P1 (Aerosil (registered trademark) R812) were fed into a φ65 mm single screw extruder, heated and melted to a resin temperature of 270 ° C, and the molten resin was extruded from a T-die. The resin temperature immediately after discharge at the T-die outlet was 270 ° C. The discharged molten resin was sandwiched between a cast roll adjusted to 70 ° C and a touch roll adjusted to 70 ° C, and cooled and solidified to obtain a raw film.

The obtained raw film was stretched twice in both the longitudinal and transverse directions at 132°C (Tg+10°C) in a simultaneous biaxial stretching machine (heat treatment zone length/stretching zone length = 1.0), and then heat-treated at 135°C in the heat treatment zone, relaxing the film by 5% in both the longitudinal and transverse directions, and then cooled to below Tg. Both ends of the obtained film were slit continuously, and the film was taken up while being taken up by a take-up roll to obtain a base film with a thickness of 40 μm.

(Solvent Treatment)
Both sides of the obtained base film were coated with methylene chloride using a coating machine [a bar coater manufactured by Daiichi Rika Co., Ltd.] in an atmosphere of 23° C. After the solvent coating, the film was left to stand at room temperature to 30° C. for 10 minutes, and then placed in a drying oven for 10 minutes and dried at 60° C. to obtain an optical film 10.

<Preparation of Optical Films 11 and 12>
(Preparation of Microparticle Dispersion 2)
1 part by weight of organic fine particles P2 and 100 parts by weight of methylene chloride were mixed and stirred in a dissolver for 50 minutes, and then dispersed at 1500 rpm using a Milder disperser (manufactured by Pacific Machinery Works, Ltd.) to obtain fine particle dispersion 2.

Using the microparticle dispersion 2 prepared above, optical films 11 and 12 with a thickness of 40 μm were obtained in the same manner as optical film 9, except that the types of (meth)acrylic resin and rubber particles, and the film composition were changed as shown in Table 1.

<Preparation of Optical Film 13>
Optical film 13 having a thickness of 40 μm was obtained in the same manner as optical film 12, except that the amount of residual solvent in the film-like material at the time of peeling was changed as shown in Table 1.

<Preparation of Optical Film 14>
Optical film 14 having a thickness of 40 μm was obtained in the same manner as optical film 11, except that the amount of residual solvent and the content of fine particles in the film-like material at the time of peeling were changed as shown in Table 1.

The uneven distribution state of the rubber particles (R _A1 /R _B or R _A2 /R _B ), MIT bending property, conveyance property, and irregular shape punching property of the obtained Optical Films 1 to 14 were evaluated by the following methods.

(R _A1 /R _B or R _A2 /R _B )
The R _A /R _B of the obtained optical film was measured by the following method.
1) The optical film was cut with a microtome to obtain a cut surface perpendicular to the surface of the optical film. The cut surface of the obtained optical film was observed with a TEM. The observation conditions were an acceleration voltage of 30 kV, a working distance of 8.6 mm, and a magnification of 3.00 k. The observation area was an area including the entire thickness direction of the optical film.
2) The brightness gradient of the obtained TEM image was removed using image processing software NiVision (manufactured by National Instruments), and then opening processing was performed to detect the contrast difference between the bulk and the rubber particles. This allowed the distribution state of the rubber particles to be identified.
3) In the image after image processing obtained in 2) above, in the thickness direction of the optical film, the area ratio per unit area of rubber particles R _A1 in region A1 that is 20% or less of the film thickness from one side of the optical film, the area ratio per unit area of rubber particles R _A2 in region A2 that is 20% or less of the film thickness from the other side of the optical film, and the area ratio per unit area RB of rubber particles in region _B sandwiched between regions A1 and A2 (a region that is more than 20% but less than 80% of the film thickness from one or the other side of the optical film) were each calculated.
4) From the results obtained in 3) above, the ratio ( _RA1 / _{RB) of} the area ratio per unit area of the rubber particles in region _A1 , RA1, to the area ratio per unit area of the rubber particles in region B, _RB , was calculated. Similarly, the ratio ( _RA2 / _RB ) of the area ratio per unit area of the rubber particles in region A2, _RA2 , to the area ratio per unit area of the rubber particles in region B, RB, was calculated.

(MIT Flexibility)
The obtained optical film was cut into a size of 15 mm wide x 150 mm long to prepare a test piece. The test piece was left to stand for at least 1 hour under conditions of a temperature of 25°C and a relative humidity of 65% RH, and then subjected to an MIT flex test in accordance with JIS P8115:2001 under conditions of a load of 500 g to measure the number of times it was bent until it broke. The MIT flex test was performed using a folding endurance tester (MIT, BE-201 type, bending radius of curvature 0.38 mm, manufactured by Tester Sangyo Co., Ltd.). The test piece was evaluated according to the following evaluation criteria.
⊚: 2000 or more times; ◯: 1500 or more times but less than 2000 times; Δ: 1000 or more times but less than 1500 times; Δx: 500 or more times but less than 1000 times; x: less than 500 times. The more times the sample is subjected to before breaking, the more excellent the flexibility is, and the more excellent the resistance to repeated bending is.
If it was rated as △ or better, it was judged to be good.

(Blocking: Transportability)
The wound optical film was left at room temperature for 3 months, and then the film was unwound and the state of blocking (sticking) between overlapping films was visually observed and evaluated according to the following criteria.
◎: No blocking ○: Almost no blocking △: Slight blocking ×: Significant blocking
If it was rated as △ or better, it was judged to be good.

(Ability to punch irregular shapes)
Fig. 4 is a schematic diagram showing the shape and dimensions of a film that was punched into a profile for testing in the examples. The obtained optical film was cut into the shape for an in-vehicle meter shown in Fig. 4. In Fig. 4, the concave curved portion at the top follows the periphery of a perfect circle with a radius of 60 mm that is assumed to be in contact with the two circles inside the figure.
The film cut into the irregular shape was checked with an optical microscope to see if any breaks had occurred, and the number of cracks and peeling that had occurred was counted. The irregular shape punching property was evaluated based on the number of polarizing plates that had cracks, based on the following evaluation criteria.
⊚: 0 to 1 peel, or 0 to 1 peel. ◯: 2 to 3 peel, or 2 to 3 peels. Δ: 4 to 5 peel, or 4 to 5 peels. ×: 6 or more peels, or many peels. If it was Δ or better, it was judged to be good.

The evaluation results of the obtained optical films 1 to 15 are shown in Table 1.

As shown in Table 1, optical films 6 to 15, which are single-layer films in which rubber particles are unevenly distributed in the surface layer portion of the optical film (R _A1 /R _B or R _A2 /R _B is greater than 1), have good MIT bending properties, conveying properties, and profile punching properties.

In contrast, it is seen that optical film 1, which is a single layer film containing no rubber particles, has low MIT bending property, transportability, and irregular shape punching property. Also, optical films 2 and 5, which are single layer films but in which rubber particles are not unevenly distributed in the surface layer portion of the optical film (R _A1 /R _B or R _A2 /R _B is 1), have somewhat improved MIT bending property but are still insufficient compared to optical film 1 containing no rubber particles, and also have low transportability and irregular shape punching property. Also, optical film 3, which is a laminate film, has low brittleness in the surface layer portion, and optical film 4, which is a laminate film, has a large stress difference between the surface layer portion and the inside, and therefore both have particularly low irregular shape punching property.

The haze of optical films 6 to 15 was measured using a haze meter (HGM-2DP, Suga Test Instruments) at 25°C and 60% RH in accordance with JIS K-6714, and all were found to be small, at 0.5% or less, which was favorable.

This application claims priority from Japanese Patent Application No. 2018-144425, filed on July 31, 2018. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

According to the present invention, it is possible to provide an optical film which has excellent brittleness, does not crack or delaminate when punched into irregular shapes or when bent, and has excellent transportability, a polarizing plate having the same, and a method for manufacturing the optical film.

100 Optical film A1, A2, B Region 200 Polarizing plate 210 Polarizer 220A, 220B Polarizing plate protective film 230A, 230B Adhesive layer

Claims (8)

A single-layer optical film comprising a (meth)acrylic resin and rubber particles having a core portion containing a crosslinked polymer and a shell portion covering the core portion,
The (meth)acrylic resin contains a structural unit derived from methyl methacrylate and a structural unit derived from a copolymerizable monomer other than methyl methacrylate that is copolymerizable therewith,
the copolymerizable monomer includes a copolymerizable monomer selected from the group consisting of maleimides and (meth)acrylic acid esters having a cyclo ring ;
a density of the rubber particles continuously increases from the inside of the optical film to a surface portion in a thickness direction of the optical film,
When a region of 20% or less of the thickness of the optical film from one surface of the optical film is defined as region A1, a region of 20% or less of the thickness of the optical film from the other surface of the optical film is defined as region A2, and a region of more than 20% and less than 80% of the thickness of the optical film from one or the other surface of the optical film is defined as region B,
a ratio (R _A1 /R _B ) of the area ratio R _A1 per unit area of the rubber particles in the region A1 to the area ratio R _B per unit area of the rubber particles in the region B, and a ratio (R A2 /R _B ) of the area ratio R _A2 per unit area of the rubber particles in the region A2 to the area ratio R _B per unit area of the _rubber particles in the region B are each 1.01 or more and less than 2.0.
Optical film. a ratio (R _A1 /R _B ) of the area ratio R _A1 to the area ratio R _B , and a ratio (R _A2 /R _B ) of the area ratio R _A2 to the area ratio R _B , each are 1.02 to 1.5;
The optical film according to claim 1 . The mass ratio of the shell portion to the crosslinked polymer is 25 to 200%.
The optical film according to claim 1 or 2. Further containing inorganic fine particles or organic fine particles having a glass transition temperature (Tg) of 80° C. or higher;
The optical film according to any one of claims 1 to 3. The glass transition temperature (Tg) of the organic fine particles is 80° C. or higher.
The optical film according to claim 4 . An optical film comprising a (meth)acrylic resin and rubber particles having a core portion containing a crosslinked polymer and a shell portion covering the core portion,
The (meth)acrylic resin contains a structural unit derived from methyl methacrylate and a structural unit derived from a copolymerizable monomer other than methyl methacrylate that is copolymerizable therewith,
the copolymerizable monomer includes a copolymerizable monomer selected from the group consisting of maleimides and (meth)acrylic acid esters having a cyclo ring ;
a density of the rubber particles continuously increases from the inside of the optical film to a surface portion in a thickness direction of the optical film,
When a region of 20% or less of the thickness of the optical film from one surface of the optical film is defined as region A1, a region of 20% or less of the thickness of the optical film from the other surface of the optical film is defined as region A2, and a region of more than 20% and less than 80% of the thickness of the optical film from one or the other surface of the optical film is defined as region B,
a ratio (R _A1 /R _B ) of an area ratio per unit area R _A1 of rubber particles in the region A1 to an area ratio per unit area R _B of rubber particles in the region B, and a ratio (R A2 /R _B ) of an area ratio per unit area R _A2 of rubber particles in the region A2 to an area ratio per _unit area R _B of rubber particles in the region B are each 1.02 to 1.5;
Optical film. A polarizer;
and the optical film according to any one of claims 1 to 6, disposed on at least one surface of the polarizer. Obtaining a dope containing a (meth)acrylic resin, rubber particles, and a solvent;
a step of casting the dope on a support, drying and peeling the dope to obtain a film having a residual solvent content of 25% by mass or more;
stretching the film-like material at a temperature equal to or lower than the glass transition temperature (Tg) of the (meth)acrylic resin;
a step of further drying the stretched film at a temperature equal to or lower than the glass transition temperature (Tg) of the (meth)acrylic resin;
A method for producing an optical film, comprising:
The (meth)acrylic resin contains a structural unit derived from methyl methacrylate and a structural unit derived from a copolymerizable monomer other than methyl methacrylate that is copolymerizable therewith,
The copolymerizable monomer includes a copolymerizable monomer selected from the group consisting of maleimides and (meth)acrylic acid esters having a cyclo ring .
A method for producing an optical film.

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