JP7379933B2 - Method for producing dope for optical film and method for producing optical film - Google Patents

Description

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

A polarizing plate used in a display device such as a liquid crystal display device includes a polarizer and protective films disposed on both sides of the polarizer. In recent years, with the diversification of usage environments such as the outdoor use of smartphones, the protective film that makes up the polarizing plate is less likely to cause display unevenness on display devices, even in harsh environments of high temperature and humidity. That is what is required. From this point of view, the use of (meth)acrylic resin films, which have lower hygroscopicity and superior dimensional stability than conventional cellulose ester films, are being considered as protective films.

On the other hand, since methacrylic resin films are brittle, rubber particles may be further added in order to eliminate the brittleness.

For example, a film containing a glutarimide (meth)acrylic resin and a graft copolymer (rubber particles) is known (for example, Patent Document 1). The graft polymer is a core-shell type rubber particle having a core portion containing a crosslinked (meth)acrylic polymer and a shell portion containing a methacrylic polymer graft-bonded to the core portion. The polymer contains structural units derived from vinyl cyanide monomers. As a result, the polarity of the surface of the core-shell type rubber particles can be brought closer to the polarity of the glutarimide (meth)acrylic resin, thereby increasing the compatibility between the rubber particles and the glutarimide (meth)acrylic resin. It is said that it can suppress the aggregation of rubber particles.

Japanese Patent Application Publication No. 2017-137417

Such (meth)acrylic resin films are usually manufactured by a melt casting method (melt method) (see Patent Document 1). On the other hand, it is desired to manufacture by a solution casting method (casting method) because there are few restrictions on the materials used, such as the ability to use high molecular weight resins.

In the solution casting method, a (meth)acrylic resin and rubber particles are dissolved or dispersed in a solvent to prepare a dope, and the resulting dope is cast onto a support and dried. A (meth)acrylic resin film is obtained through a step of peeling off to obtain a film-like material. However, since the compatibility between the rubber particles and the (meth)acrylic resin is low, the rubber particles tend to aggregate. Therefore, there was a problem that not only was it impossible to impart sufficient toughness (flexibility or flexibility) to the resulting film, but also that transparency was likely to be impaired. Additionally, when peeling the film-like material obtained by casting the dope from the support, there was a problem in that aggregates of rubber particles easily fell off from the film-like material, easily contaminating the support (belt). .

The present invention has been made in view of the above circumstances, and provides a dope for optical films that can suppress agglomeration of rubber particles and provide an optical film with sufficient toughness without impairing transparency. The present invention aims to provide a manufacturing method, a dope for an optical film, an optical film, a polarizing plate, and a manufacturing method of an optical film.

The above problem can be solved by the following configuration.

In the method for producing a dope for an optical film of the present invention, rubber particles containing a rubbery polymer having a degree of crosslinking of 0.25 to 4% by mass are dispersed in a first solvent to prepare a rubber particle dispersion. and a step of mixing the rubber particle dispersion, a methacrylic resin, and a second solvent to prepare a dope containing the methacrylic resin, the rubber particles, and a solvent, At least one of the first solvent and the second solvent contains water, and the amount of water in the solvent is 0.5 to 3% by mass.

The dope for optical films of the present invention is a dope for optical films containing a methacrylic resin, rubber particles containing a rubbery polymer having a degree of crosslinking of 0.25 to 4% by mass, and a solvent,
The solvent contains 0.5-3% by weight of water.

The optical film of the present invention is an optical film containing a methacrylic resin and rubber particles containing a rubbery polymer having a degree of crosslinking of 0.25 to 4% by mass, wherein the optical film is heated at 23°C and 55% by weight. The haze measured when the humidity is controlled for 24 hours in an environment is Haze 1, and the haze measured when the humidity is controlled for 24 hours at 23°C and 55% after being stored for 1000 hours in an environment of 60°C and 90%. When the haze is 2, the haze change amount expressed by the following formula (1) is 0.3 or less.
Formula (1): Haze change amount = Haze 2 - Haze 1

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

The method for producing an optical film of the present invention includes a step of preparing a dope, and a step of casting the dope on a support and then peeling it off to obtain a film-like product. process.

According to the present invention, a method for producing a dope for an optical film that can suppress agglomeration of rubber particles and provide an optical film having sufficient toughness without impairing transparency, a dope for an optical film, An optical film, a polarizing plate, and a method for producing an optical film can be provided.

The present inventors speculated as follows about the mechanism by which rubber particles aggregate when producing an optical film by a solution casting method.

In the solution casting method, rubber particles containing a rubbery polymer with a lower degree of crosslinking are used than the rubber particles used in the melt casting method, from the viewpoint of making it easier to disperse the rubber particles in an organic solvent. On the other hand, rubber particles containing rubbery polymers with a low degree of crosslinking (especially acrylic rubbery polymers with a low degree of crosslinking) have a low affinity with methacrylic resins, and the problem is that the rubber particles tend to aggregate. was there.

In contrast, by using core-shell type particles, in which a core part containing a rubbery polymer with a low degree of crosslinking is covered with a shell part containing another polymer that has good compatibility with methacrylic resin, rubber particles The compatibility between the methacrylic resin and the methacrylic resin can be improved to some extent. However, the rubbery polymer with a low degree of crosslinking that constitutes the core part is easily swollen by an organic solvent, and easily pierces through the shell part and is exposed on the surface of the rubber particle. Since the rubbery polymer with a low degree of crosslinking exposed on the surface of the rubber particles has a low affinity with the methacrylic resin, aggregation of the rubber particles could not be sufficiently suppressed.

As a result of intensive studies, the present inventors discovered that the process of dispersing rubber particles in a solvent to prepare a rubber particle dispersion (rubber particle dispersion process), the obtained rubber particle dispersion, and a methacrylic resin. In a dope manufacturing method that includes a step of preparing a dope by mixing with a solvent (dope preparation step), the rubber particles and methacrylic resin are dispersed in a solvent containing water. It has been found that the compatibility of rubber particles can be increased, thereby suppressing aggregation of rubber particles.

Although the reason for this is not clear, it is assumed as follows. That is, by purposefully adding water whose polarity is significantly different from that of the rubbery polymer, swelling of the rubbery polymer with a low degree of crosslinking can be reduced. This can prevent the rubbery polymer with a low degree of crosslinking from breaking through the shell portion and being exposed on the surface of the rubber particles, thereby preventing the compatibility between the rubber particles and the methacrylic resin from being impaired. I can do it.

Although the timing of adding water is not particularly limited, it is preferable to add water to further disperse the rubber particles after the rubber particles are dispersed in the organic solvent in the rubber particle dispersion step. In other words, after loosening the aggregates of rubber particles to some extent in an organic solvent, each swollen rubber particle can be reliably tightened (swelling is suppressed) with water, which allows the rubber particles to be highly dispersed. Cheap. Each configuration of the present invention will be explained below.

1. Method for producing dope The method for producing dope of the present invention includes 1) a step of dispersing rubber particles in a first solvent to prepare a rubber particle dispersion (rubber particle dispersion step); and 2) the obtained rubber The method includes a step of preparing a dope by mixing a particle dispersion, a methacrylic resin, and a second solvent (dope preparation step).

At least one of the first solvent in the rubber particle dispersion step and the second solvent in the dope preparation step contains water. That is, in at least one of the rubber particle dispersion step and the dope preparation step, rubber particles are dispersed in a solvent containing water.

Among these, from the viewpoint of suppressing the aggregation of rubber particles to a higher degree, the first solvent in the rubber particle dispersion step contains water; that is, in the rubber particle dispersion step, the rubber particles are dispersed in the first solvent containing water. It is preferable to let Hereinafter, an example will be explained in which rubber particles are dispersed in a first solvent containing water in the rubber particle dispersion step.

1-1. Rubber Particle Dispersion Step Rubber particles are dispersed in a first solvent to obtain a rubber particle dispersion.

(rubber particles)
The rubber particles can have the function of imparting toughness (flexibility) to the optical film. Rubber particles are particles that include a rubbery polymer. The rubbery polymer is a flexible crosslinked polymer with a glass transition temperature of 20° C. or lower. Examples of such crosslinked polymers include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic crosslinked polymers are preferred from the viewpoint of having a small refractive index difference with (meth)acrylic resins and are less likely to impair the transparency of the optical film. combination) is more preferred.

That is, the rubber particles are preferably particles containing the acrylic rubbery polymer (a).

Regarding the acrylic rubbery polymer (a):
The acrylic rubbery polymer (a) is a crosslinked polymer containing a structural unit derived from an acrylic ester as a main component. Containing as a main component means that the content of structural units derived from acrylic ester is within the range described below. The acrylic rubbery polymer (a) contains a structural unit derived from an acrylic ester, a structural unit derived from another monomer copolymerizable with it, and two or more radically polymerizable groups ( A crosslinked polymer containing a structural unit derived from a polyfunctional monomer having a non-conjugated reactive double bond is preferable.

Acrylic acid esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and acrylic acid. Preferably, it is an acrylic acid alkyl ester having an alkyl group having 1 to 12 carbon atoms, such as n-octyl acid. The number of acrylic esters may be one type or two or more types.

The content of structural units derived from acrylic ester is preferably 40 to 80% by mass, and preferably 50 to 80% by mass, based on the total structural units constituting the acrylic rubbery polymer (a). is more preferable. When the content of acrylic ester is within the above range, sufficient toughness can be easily imparted to the optical film.

The other copolymerizable monomers are monomers copolymerizable with the acrylic ester other than polyfunctional monomers. That is, the copolymerizable monomer does not have two or more radically polymerizable groups. Examples of copolymerizable monomers include methacrylic acid esters such as methyl methacrylate; styrenes such as styrene and methylstyrene; (meth)acrylonitrile; (meth)acrylamides; (meth)acrylic acid . Among these, it is preferable that the other copolymerizable monomers include styrenes. The number of other copolymerizable monomers may be one, or two or more.

The content of structural units derived from other copolymerizable monomers is preferably 5 to 55% by mass, and 10 to 55% by mass, based on the total structural units constituting the acrylic rubbery polymer (a). More preferably, it is 45% by mass.

Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol ( Contains meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate .

The content of the structural unit derived from the polyfunctional monomer is preferably 0.05 to 10% by mass, and 0.1% by mass based on the total structural units constituting the acrylic rubbery polymer (a). More preferably, it is 5% by mass. If the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the obtained acrylic rubber-like polymer (a) is likely to be increased, so that the hardness and rigidity of the obtained film are impaired too much. First, when the content is 10% by mass or less, the toughness of the film is less likely to be impaired.

The monomer composition constituting the acrylic rubbery polymer (a) can be measured, for example, by the peak area ratio detected by pyrolysis GC-MS.

Particles containing an acrylic rubbery polymer (a) are particles made of an acrylic rubbery polymer (a), or a hard layer made of a hard crosslinked polymer (c) having a glass transition temperature of 20° C. or higher. , and a soft layer made of the acrylic rubbery polymer (a) arranged around the particles (these are also referred to as "elastomers"); or the acrylic rubbery polymer (a) The particles may be made of an acrylic graft copolymer obtained by polymerizing a mixture of monomers such as methacrylic acid ester in at least one stage in the presence of. The particles made of the acrylic graft copolymer may be core-shell particles having a core portion containing the acrylic rubbery polymer (a) and a shell portion covering the core portion.

Regarding core-shell type rubber particles containing acrylic rubbery polymer:
(core part)
The core portion contains an acrylic rubber-like polymer (a), and may further contain a hard crosslinked polymer (c) if necessary. That is, the core portion may have a soft layer made of an acrylic rubber-like polymer and a hard layer made of a hard crosslinked polymer (c) disposed inside the soft layer.

The crosslinked polymer (c) may be a crosslinked polymer containing methacrylic acid ester as a main component. That is, the crosslinked polymer (c) has a structural unit derived from a methacrylic acid alkyl ester, a structural unit derived from another monomer copolymerizable with it, and a structural unit derived from a polyfunctional monomer. It is preferable that it is a crosslinked polymer containing.

The methacrylic acid alkyl ester may be the above-mentioned methacrylic acid alkyl ester; other copolymerizable monomers may be the above-mentioned styrenes, acrylic esters, etc.; the polyfunctional monomer is The same monomers as those listed above as the polyfunctional monomers may be mentioned.

The content of the structural unit derived from the methacrylic acid alkyl ester may be 40 to 100% by mass based on the total structural units constituting the crosslinked polymer (c). The content of structural units derived from other copolymerizable monomers may be 60 to 0% by mass based on the total structural units constituting the other crosslinked polymer (c). The content of the structural unit derived from the polyfunctional monomer may be 0.01 to 10% by mass based on the total structural units constituting the other crosslinked polymer.

(shell part)
The shell portion includes a methacrylic polymer (b) (another polymer) containing as a main component a structural unit derived from a methacrylic acid ester, which is graft-bonded to the acrylic rubbery polymer (a). Containing as a main component means that the content of the structural unit derived from methacrylic acid ester is within the range described below.

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

The content of methacrylic acid ester is preferably 50% by mass or more based on the total structural units constituting the methacrylic polymer (b). When the content of methacrylic acid ester is 50% by mass or more, compatibility with a methacrylic resin containing a structural unit derived from methyl methacrylate as a main component is easily obtained. From the above viewpoint, the content of the methacrylic acid ester is more preferably 70% by mass or more based on the total structural units constituting the methacrylic polymer (b).

The methacrylic polymer (b) may further contain a structural unit derived from another monomer copolymerizable with the methacrylic acid ester. Examples of other copolymerizable monomers include acrylic esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, Includes (meth)acrylic monomers (ring-containing (meth)acrylic monomers) having an alicyclic ring, a heterocyclic ring, or an aromatic ring, such as phenoxyethyl (meth)acrylate.

The content of structural units derived from copolymerizable monomers is preferably 50% by mass or less, and 30% by mass or less based on the total structural units constituting the methacrylic polymer (b). is more preferable.

The ratio of the graft component (grafting ratio) in the rubber particles is preferably 10 to 250% by mass, more preferably 15 to 150% by mass. When the grafting rate is above a certain level, the ratio of the graft component, that is, the methacrylic polymer (b) whose main component is a structural unit derived from methacrylic acid ester, is appropriately high, so that the bond between the rubber particles and the methacrylic resin is Easily increases compatibility and makes rubber particles more difficult to aggregate. In addition, the rigidity of the film is less likely to be impaired. When the graft ratio is below a certain level, the proportion of the acrylic rubber-like polymer (a) does not become too small, so that the effect of improving the toughness and brittleness of the film is less likely to be impaired.

Grafting rate is measured by the following method.
1) Dissolve 2 g of core-shell type particles in 50 ml of methyl ethyl ketone and centrifuge for 1 hour at 30,000 rpm and 12°C using a centrifuge (manufactured by Hitachi Koki Co., Ltd., CP60E) to separate insoluble and possible components. Separate into soluble components (centrifugation is performed 3 times in total).
2) The weight of the obtained insoluble matter is applied to the following formula to calculate the grafting rate.
Grafting rate (mass%) = [{(mass of methyl ethyl ketone insoluble matter) - (mass of acrylic rubbery polymer (a))}/(mass of acrylic rubbery polymer (a))] x 100

(degree of crosslinking)
The degree of crosslinking of the rubbery polymer contained in the rubber particles is preferably 0.25 to 4% by mass. When the crosslinking degree of the rubbery polymer is 0.25% by mass or more, the rubbery polymer does not become too flexible, so that the rubbery polymer flows out (exposed) from the gap in the swollen shell part to the particle surface. ) can make it difficult to Therefore, it is easy to suppress a decrease in compatibility between the rubber particles and the methacrylic resin. Further, since the rubber particles do not become too flexible, they are not excessively deformed, and good slipperiness can be imparted to the film. When the degree of crosslinking of the rubbery polymer is 4% by mass or less, rubber particles can be easily dispersed in an organic solvent during film formation by a solution casting method. Furthermore, since the rubbery polymer does not become too hard, the rubber particles are less prone to cracking or chipping. From the above viewpoint, the degree of crosslinking of the rubbery polymer contained in the rubber particles is more preferably 0.3 to 3% by mass.

The degree of crosslinking of a rubbery polymer is determined by the amount of polyfunctional monomers that make up the rubbery polymer relative to the total amount of structural units that make up the rubbery polymer (total amount of monomers that make up the rubbery polymer). It is expressed as a ratio of the total amount of derived structural units (total amount of polyfunctional monomers constituting the rubbery polymer). The degree of crosslinking of the rubbery polymer can be calculated from the monomer charge ratio during the preparation of the rubbery polymer.

(Glass transition temperature (Tg))
The glass transition temperature (Tg) of the rubbery polymer contained in the rubber particles is preferably 0°C or lower, more preferably -10°C or lower. When the glass transition temperature (Tg) of the rubbery polymer is 0° C. or lower, appropriate toughness can be imparted to the film. The glass transition temperature (Tg) of the rubbery polymer is measured in the same manner as described above.

The glass transition temperature (Tg) of the rubbery polymer can be adjusted by the composition of the rubbery polymer. For example, in order to lower the glass transition temperature (Tg) of the acrylic rubbery polymer (a), an acrylic ester with an alkyl group having 4 or more carbon atoms/ It is preferable to increase the mass ratio of other copolymerizable monomers (eg, 3 or more, preferably 4 to 10).

(Average particle size)
The average particle diameter of the rubber particles is preferably 100 to 500 nm. When the average particle diameter of the rubber particles is 100 nm or more, it is easy to impart sufficient toughness or flexibility to the optical film, and when it is 500 nm or less, it is easy to suppress an increase in haze of the optical film. The average particle diameter of the rubber particles is more preferably 200 to 400 nm.

The average particle size (dispersed particle size) of the rubber particles can be measured with a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

The content of the rubber particles is set so that the amount relative to the methacrylic resin contained in the dope falls within the range described below.

The first solvent in the rubber particle dispersion step and the second solvent in the dope preparation step will be explained below. In the present invention, as described above, at least one of the first solvent in the rubber particle dispersion step and the second solvent in the dope preparation step contains water. That is, in at least one of the rubber particle dispersion step and the dope preparation step, rubber particles are dispersed in a solvent containing water. Among these, it is preferable that at least the first solvent in the rubber particle dispersion step contains water.

(first solvent)
The first solvent includes an organic solvent and water.

The organic solvent includes a nonpolar solvent (good solvent) that dissolves at least the methacrylic resin. Examples of non-polar solvents include dichloromethane, hexane, benzene, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran. Among them, dichloromethane is preferred.

Further, it is preferable that the organic solvent further contains a polar solvent (poor solvent) other than water, from the viewpoint of improving releasability from the metal support in the film forming process using the solution casting method. Examples of polar solvents include aprotic solvents such as γ-butyrolactone, acetone, acetonitrile, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and 1,3-dimethyl-2-imidazolidinone (DMI). Protic polar solvents include aliphatic alcohols having 1 to 4 carbon atoms (methanol, ethanol, 1-propanol, 2-propanol, butanol, etc.), acetic acid, ethylenediamine, and other protic polar solvents. Among these, aliphatic alcohols having 1 to 4 carbon atoms are preferred, and methanol and ethanol are more preferred.

The content of the polar solvent in the first solvent is preferably 5 to 30% by mass, more preferably 10 to 20% by mass, based on the total content of the nonpolar solvent and polar solvent in the first solvent. . If the content of the polar solvent exceeds a certain level, the film-like material will not only be easily peeled off from the metal support in the film forming process using the solution casting method, but also will be easy to dissolve water, which will affect the appearance of the resulting optical film. is less likely to be damaged. Moreover, when the content of the polar solvent is below a certain level, the solubility of the (meth)acrylic resin is less likely to be impaired.

The content of water in the first solvent, that is, the amount of water added in the rubber particle dispersion step, is determined so that the content of water in the solvent contained in the obtained dope is within the range described below (0.5 to 3% by mass). ). The amount of water added in the rubber particle dispersion step depends on the mixing ratio of the rubber particle dispersion and the second solvent, but is, for example, 2 to 8% by mass, based on the entire first solvent contained in the rubber particle dispersion. Preferably, it can be 3 to 7.5% by mass. When the amount of water added in the rubber particle dispersion step is above a certain level, the rubbery polymer in the rubber particles is difficult to swell excessively, and the rubbery polymer is difficult to be exposed on the particle surface. This makes it difficult to impair the compatibility between the rubber particles and the methacrylic resin, and makes it easier to suppress aggregation of the rubber particles. On the other hand, if the amount of water added in the rubber particle dispersion process is below a certain level, the affinity between water and other solvents will not be excessively impaired. Poor appearance (roughness and increased haze due to aggregates of rubber particles) and increased haze due to poor compatibility between the solvent and the methacrylic resin can be suppressed.

The timing of adding water is not particularly limited, and may be before dispersing the rubber particles in the organic solvent, at the same time as or after dispersing the rubber particles in the organic solvent. From the viewpoint of easily suppressing agglomeration of rubber particles to a high degree, it is preferable to add water after dispersing the rubber particles to some extent in an organic solvent. That is, the rubber particle dispersion step preferably includes 1) a step of dispersing the rubber particles in an organic solvent, and 2) a step of further adding water to the obtained solution to further disperse the rubber particles. This is because the rubber particles can be highly dispersed by tightening each rubber particle dispersed to some extent in the organic solvent by adding water.

(Dispersion method)
When dispersing the rubber particles in the first solvent, the means for dispersing the rubber particles is not particularly limited, and may include an ultrasonic dispersion machine, a stirrer (for example, a high-speed stirrer such as a dissolver), a dispersion machine (for example, a dispersion machine such as a milder). ). Among these, from the viewpoint of easily dispersing the rubber particles to a high degree by applying high energy, it is preferable to use at least a high-speed stirrer such as a dissolver for dispersion.

1-2. About the dope preparation process The obtained rubber particle dispersion, methacrylic resin, and a solvent (second solvent) are mixed to prepare a dope.

(methacrylic resin)
Methacrylic resin is a polymer containing a structural unit derived from methyl methacrylate as a main component. That is, the methacrylic resin may be a homopolymer containing a structural unit derived from methyl methacrylate, or may be a homopolymer containing a structural unit derived from methyl methacrylate and other units other than methyl methacrylate that can be copolymerized with it. It may also be a copolymer containing a structural unit derived from a polymer.

Other copolymerizable monomers are not particularly limited,
(meth)acrylic acid alkyl esters having an alkyl group other than methyl methacrylate having 1 to 18 carbon atoms, such as ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate;
α,β-unsaturated acids such as (meth)acrylic acid;
Unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid;
Aromatic vinyls such as styrene and α-methylstyrene;
α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile;
Maleimides such as maleimide, N-substituted maleimide (e.g. phenylmaleimide);
Contains maleic anhydride and glutaric anhydride. One type of other copolymerizable monomers may be used, or two or more types may be used in combination.

Among these, other copolymerizable monomers include monomers with relatively low polarity, such as aromatic vinyls such as styrene; ring-containing methacrylic esters such as phenyl methacrylate and adamantyl methacrylate; and phenylmaleimide. More preferred are maleimides. Methacrylic resins that have structural units derived from other monomers that can be copolymerized have a low affinity with the rubbery polymer contained in rubber particles, so adding water can inhibit aggregation. This is because it is easy to get caught.

The content of structural units derived from methyl methacrylate is preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass or more based on the total structural units constituting the methacrylic resin. It is more preferable that As described above, since the methacrylic resin containing many structural units derived from methyl methacrylate has a low affinity with the rubbery polymer contained in the rubber particles, it is easy to obtain the aggregation inhibiting effect by adding water. The type and composition of the monomer of the methacrylic resin can be identified by ¹ H-NMR.

The glass transition temperature (Tg) of the methacrylic resin is preferably 90°C or higher, more preferably 100 to 150°C. An optical film in which the Tg of the methacrylic resin is 90° C. or higher can have good heat resistance.

The glass transition temperature (Tg) of the methacrylic resin can be measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012 or ASTM D 3418-82.

The weight average molecular weight (Mw) of the methacrylic resin is not particularly limited, but is preferably from 300,000 to 3,000,000, more preferably from 1,000,000 to 2,000,000. When the weight average molecular weight of the (meth)acrylic resin is within the above range, sufficient mechanical strength (toughness) can be imparted to the film without impairing film formability.

The weight average molecular weight (Mw) of the methacrylic resin can be measured in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be measured using a column (TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series, manufactured by Tosoh Corporation). The measurement conditions may be the same as in the examples described later.

The content of the methacrylic resin is set so that the amount based on the solid content of the dope falls within the range described below.

(Second solvent)
The second solvent contains at least an organic solvent. As described above, the organic solvent preferably includes a nonpolar solvent (good solvent) and further includes a polar solvent other than water (poor solvent). As the non-polar solvent and the polar solvent, the same ones as mentioned above can be used.

The content of the polar solvent in the second solvent depends on the composition of the first solvent of the rubber particle dispersion, but it must be 18% by mass or less based on the total content of the non-polar solvent and polar solvent in the second solvent. is preferable, and more preferably 8 to 16% by mass.

The second solvent may further contain water as necessary. That is, a dope may be prepared by mixing a rubber particle dispersion, a methacrylic resin, and a second solvent containing water.

At that time, the timing of mixing the rubber particle dispersion and the second solvent containing water is not particularly limited, and may be before the addition of the methacrylic resin, at the same time as or after the addition of the methacrylic resin. There may be. From the viewpoint of easily suppressing agglomeration of rubber particles to a high degree, it is preferable that the rubber particle dispersion liquid and the second solvent containing water be mixed before adding the methacrylic resin. That is, the dope preparation process includes 1) mixing a rubber particle dispersion and a second solvent containing water, and 2) adding a methacrylic resin to the resulting mixture to prepare a dope. It may also include. In addition, when adding the second solvent containing water, water and the organic solvent may be added at the same time or may be added separately.

The content of water in the second solvent, that is, the amount of water added in the dope preparation process, is relative to the entire solvent of the dope obtained (at least the solvent obtained by mixing the first solvent and the second solvent). It is sufficient that the amount is 0.5 to 3% by mass.

(other ingredients)
Other components other than those mentioned above may be further added to the dope as necessary. Examples of other components include matting agents to impart slipperiness to the film. The matting agent may be inorganic fine particles such as silica particles, or organic fine particles having a glass transition temperature of 80° C. or higher.

(Mixing method)
The means for mixing each component is not particularly limited, and may be a stirrer (for example, a dissolver).

Further, when preparing the dope, other dispersions or solutions other than those mentioned above may be further mixed. For example, when obtaining an optical film containing organic fine particles, a second dispersion liquid in which organic fine particles are dispersed may be further mixed.

2. Dope The dope of the present invention is obtained by the above-described dope manufacturing method, and includes a methacrylic resin, rubber particles, and a solvent.

The content of the methacrylic resin is preferably 75% by mass or more, more preferably 80 to 90% by mass, based on the solid content of the dope.

The content of the rubber particles is preferably 10 to 25% by mass, more preferably 15 to 20% by mass, based on the methacrylic resin contained in the dope.

Since the solvent contained in the dope includes the above-mentioned first solvent and second solvent, it also contains a small amount of water derived from them.

Specifically, the content of water in the dope is preferably 0.5 to 3% by mass based on the total solvent contained in the dope. When the water content in the solvent is 0.5% by mass or more, it is difficult to cause the rubber particles to swell excessively, and the rubbery polymer (which has low affinity with methacrylic resin) in the rubber particles forms on the particle surface. can reduce exposure to This makes it difficult to impair the compatibility between the rubber particles and the methacrylic resin, and makes it easier to suppress aggregation of the rubber particles. On the other hand, when the water content in the solvent is 3% by mass or less, the solubility of the methacrylic resin is less likely to be impaired. From the above point of view, the content of water may be in a range of 1 to 3% by mass based on the entire solvent contained in the dope.

In the obtained dope, aggregation of rubber particles is highly suppressed and the rubber particles are well dispersed. Whether the rubber particles are well dispersed can be confirmed, for example, by measuring the dispersed particle size (average particle size) of the rubber particles in the dope.

Specifically, the dispersed particle size (average particle size) of rubber particles in a diluted solution obtained by diluting a dope with an organic solvent having the same composition as the organic solvent constituting the dope until the solid content is 1% by mass is ( It is preferably less than (primary particle diameter + 300 nm), more preferably less than (primary particle diameter + 100 nm), and even more preferably less than (primary particle diameter + 50 nm).

The dispersed particle size (average particle size) of the rubber particles in the dope can be measured with a zeta potential/particle size measuring system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

Note that the primary particle diameter is a value measured by the following method. The optical film obtained by forming a film from the dope is cut, and the cut surface is observed using a TEM. Then, the circle-equivalent diameters of the particle diameters of 100 arbitrary particles are measured, and the average value thereof is defined as the "primary particle diameter."

3. Method for producing an optical film The optical film of the present invention includes 1) the step of preparing the above-mentioned dope, and 2) casting the obtained dope onto a support, followed by drying and peeling to obtain a film-like product. and 3) drying the obtained film-like material while stretching it as necessary.

Regarding the step 1) A dope containing a methacrylic resin, rubber particles, and a solvent is prepared by the above-described dope preparation method.

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

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

The amount of residual solvent in the dope when it is peeled off from the support (the amount of residual solvent in the film-like material when it is peeled off) is preferably, for example, 25% by mass or more, and more preferably 30 to 37% by mass. When the amount of residual solvent at the time of peeling is 37% by mass or less, it is easy to prevent the film-like material from stretching too much due to peeling.

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

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

Regarding step 3): Dry the obtained film-like material. Drying may be performed in one step or in multiple steps. Moreover, drying may be performed while stretching as necessary.

For example, the process of drying a film-like material includes a step of pre-drying the film-like material (pre-drying step), a step of stretching the film-like material (stretching step), and a step of drying the film-like material after stretching (main drying step). drying step).

(Pre-drying process)
The pre-drying temperature (drying temperature before stretching) can be higher than the stretching temperature. Specifically, when the glass transition temperature of the methacrylic resin is Tg, it is preferably (Tg-50) to (Tg+50)°C. If the pre-drying temperature is (Tg - 50) °C or higher, the solvent will easily evaporate to an appropriate degree, making it easier to improve transportability (handling properties), and if it is below (Tg + 50) °C, the solvent will not volatilize too much. , the stretchability in the subsequent stretching step is less likely to be impaired. In the case of drying with a non-contact heating type while conveying with a tenter stretching machine or rollers, the initial drying temperature can be measured as the temperature inside the stretching machine or the ambient temperature such as the hot air temperature.

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

The stretching ratio when producing an optical film is preferably 5 to 100%, more preferably 20 to 100%. In the case of biaxial stretching, the stretching ratio in each direction is preferably within the above range.

The stretching ratio (%) is defined as (stretching direction size of the film after stretching−stretching direction size of the film before stretching)/(stretching direction size of the film before stretching)×100. In addition, when performing biaxial stretching, it is preferable to set it as the said stretching magnification about each of TD direction and MD direction.

As described above, the stretching temperature (drying temperature during stretching) is preferably Tg (°C) or higher, and is (Tg + 10) to (Tg + 50) °C, where Tg is the glass transition temperature of the methacrylic resin. It is more preferable. When the stretching temperature is Tg (°C) or higher, preferably (Tg + 10)°C or higher, the solvent is easily volatilized to an appropriate extent, making it easy to adjust the stretching tension to an appropriate range; does not volatilize too much, so stretchability is less likely to be impaired. The stretching temperature can be, for example, 90°C or higher. As for the stretching temperature, it is preferable to measure the ambient temperature, such as the temperature inside the stretching machine, as described above.

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

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

(Main drying process)
From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry the film-like material obtained after stretching. For example, it is preferable to further dry the film-like material obtained after stretching while conveying it with a roll or the like.

The main drying temperature (drying temperature in the case of unstretched) is preferably (Tg-50) to (Tg-30)°C, where Tg is the glass transition temperature of the methacrylic resin, and (Tg-40) More preferably, the temperature is between (Tg-30)°C. If the post-drying temperature is (Tg-50)°C or higher, the solvent can be sufficiently volatilized and removed from the stretched film, and if it is below (Tg-30)°C, the deformation of the film can be seriously prevented. can be suppressed. As for the main drying temperature, it is preferable to measure the ambient temperature such as the hot air temperature as described above.

4. Optical Film The optical film is obtained by the above-mentioned optical film manufacturing method, and contains the above-mentioned methacrylic resin and rubber particles.

The composition of the optical film is the same as the solid content composition of the dope. As mentioned above, the rubber particles contain a rubbery polymer having a degree of crosslinking of 0.25 to 4% by mass. As described above, the degree of crosslinking of the rubbery polymer can be calculated from the monomer charge ratio during the preparation of the rubbery polymer.

(Haze)
The haze of the optical film is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0.7% or less. The haze of the optical film can be measured using a haze meter (NDH 2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.) after conditioning the film in an environment of 25° C. and 60% RH for 24 hours.

(Haze change amount)
The optical film contains residual moisture derived from the water added during the manufacturing process described above. In this way, even if an optical film containing residual moisture is exposed to high temperature and high humidity for a certain period of time, the haze changes less than an optical film containing no residual moisture.

Specifically, the haze measured when the optical film was conditioned for 24 hours in an environment of 23°C and 55% humidity was 1, and after being stored for 1000 hours in an environment of 90% at 60°C, When the haze measured when humidity is adjusted for 24 hours is defined as haze 2, the amount of change in haze expressed by the following formula (1) is preferably 0.3 or less, and preferably 0.15 or less. is more preferable, and even more preferably 0.1 or less.
Formula (1): Haze change amount = Haze 2 - Haze 1

The haze and amount of change in haze of the optical film can be adjusted by the dispersibility of rubber particles in the dope used. For example, in order to reduce the haze and the amount of change in haze of an optical film, it is preferable to increase the dispersibility of rubber particles in the dope used. As described above, the dispersibility of the rubber particles in the dope can be adjusted by the amount of water added in the rubber particle dispersion step or the dope preparation step, and the timing of water addition. In order to keep the haze of the optical film below a certain level and the amount of change in haze below a certain level, it is preferable that the amount of water added in the method for producing a dope for an optical film be within the above range, and furthermore, the amount of water added is within the above range. It is more preferable to perform this in a rubber particle dispersion step.

(Glass-transition temperature)
The optical film preferably has a glass transition temperature (Tg) of, for example, 90 to 150°C. When the Tg of the optical film is 90° C. or higher, not only can the heat resistance of the optical film be improved, but also the drying temperature can be increased when manufacturing the optical film by the solution casting method, making it easier to improve drying properties. . When the Tg of the optical film is 150° C. or lower, the content of structural units derived from rigid monomers can be reduced, so that the toughness of the optical film is less likely to be impaired. It is more preferable that the optical film has a Tg of 95 to 140°C. The glass transition temperature of an optical film can be measured by the same method as described above.

The glass transition temperature of the optical film is adjusted, for example, by the monomer composition of the methacrylic resin.

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

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

The in-plane slow axis of the optical film can be confirmed using an automatic birefringence meter Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrics).

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

The retardation Ro and Rt of the optical film can be adjusted by, for example, the monomer composition of the methacrylic resin and the stretching conditions.

(Residual solvent amount)
Since the optical film is preferably formed by a solution casting method, it may further contain a residual solvent. The amount of residual solvent is preferably 700 ppm or less, more preferably 30 to 700 ppm, based on the optical film. The content of the residual solvent can be adjusted by the drying conditions of the dope cast on the support in the optical film manufacturing process.

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

(thickness)
The thickness of the optical film is not particularly limited, but is preferably 10 to 60 μm, more preferably 10 to 40 μm.

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

Specifically, the polarizing plate of the present invention includes a polarizer, an optical film of the present invention disposed on one surface thereof, a counter film disposed on the other surface, and a space between the polarizer and the optical film. , and an adhesive layer disposed between the polarizer and the opposing film.

5-1. Polarizer A polarizer is an element that passes only light with a plane of polarization in a certain direction, and is a polyvinyl alcohol-based polarizing film. Polyvinyl alcohol-based polarizing films include those made by dyeing polyvinyl alcohol-based films with iodine and those made by dyeing them with dichroic dyes.

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

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

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

5-2. Optical Film The optical film of the present invention is placed on one surface of the polarizer (preferably on the surface facing the liquid crystal cell). The optical film can function as a polarizing plate protective film (preferably a retardation film).

5-3. Opposing Film The opposing film may be the optical film of the present invention, or may be any other optical film. Examples of other optical films include commercially available cellulose ester films (e.g., Konica Minolta Tac KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd., Fujitac T40UZ, Fujitac T60UZ, Fujitac T80UZ, Fujitac TD80UL, Fujitac TD60UL, Fujitac TD40UL, Fujitac R02, Fujitac R06, (manufactured by Fuji Film Co., Ltd.).

The thickness of the opposing film may be, for example, 5 to 100 μm, preferably 40 to 80 μm.

5-3. Adhesive Layer An adhesive layer may be disposed between the polarizer and the optical film and between the polarizer and the opposing film, respectively.

The adhesive layer may be a layer obtained from a water-based adhesive, or may be a cured layer of an active energy ray-curable adhesive.

Examples of water-based adhesives include water adhesives containing polyvinyl alcohol-based resins (such as completely saponified polyvinyl alcohol aqueous solutions). The active energy ray-curable adhesive may be a radical photopolymerizable composition or a cationic photopolymerizable composition, preferably a photoradical polymerizable composition containing an epoxy compound and a cationic photopolymerization initiator. It can be a cationically polymerizable composition.

The thickness of the adhesive layer is not particularly limited, but may be, for example, about 0.01 to 10 μm, preferably about 0.01 to 5 μm.

5-4. Other Layers The polarizing plate of the present invention may further include layers other than those described above, if necessary. Examples of other layers include an adhesive layer for fixing the polarizing plate to the liquid crystal cell. For example, when the polarizing plate is placed so that the optical film of the present invention is on the liquid crystal cell side, the polarizing plate may further include an adhesive layer placed on the optical film.

The adhesive layer is preferably formed by drying and partially crosslinking an adhesive composition containing a base polymer, a crosslinking agent, and a solvent. Examples of adhesive compositions include acrylic adhesive compositions using (meth)acrylic polymers as a base polymer, silicone adhesive compositions using silicone polymers as a base polymer, and rubber-based adhesive compositions using rubber as a base polymer. Includes adhesive compositions. Among these, acrylic pressure-sensitive adhesive compositions are preferred from the viewpoints of transparency, weather resistance, heat resistance, and processability.

The thickness of the adhesive layer is usually about 3 to 100 μm, preferably 5 to 50 μm.

Note that the surface of the adhesive layer may be protected with a release film (for example, a polyester film, a fluororesin film, etc.) that has been subjected to a release treatment.

5-5. Method for Manufacturing Polarizing Plate The polarizing plate of the present invention can be obtained through a process of bonding a polarizer and the optical film of the present invention together via an adhesive. From the viewpoint of increasing the adhesiveness between the polarizer and the optical film, a surface treatment such as corona treatment may be performed as necessary before the bonding process.

6. Image Display Device The optical film of the present invention can be used as an optical film of an image display device such as a liquid crystal display device or an organic EL display device, preferably as a polarizing plate protective film of a liquid crystal display device.

That is, 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.

Display modes of liquid crystal cells include, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment), MVA (Multi-domain Vertical Alignment), and PVA. (Patterned Vertical Alignment), IPS (In-Plane-Switching), etc. For example, when the liquid crystal display device is used in a smart phone or the like, the IPS mode is preferable.

The first polarizing plate and the second polarizing plate may be arranged such that the absorption axis of the polarizer of the first polarizing plate and the absorption axis of the polarizer of the second polarizing plate are perpendicular to each other (cross Nicols).

At least one of the first polarizing plate and the second polarizing plate is the polarizing plate of the present invention. The polarizing plate of the present invention is preferably arranged such that the optical film of the present invention is on the liquid crystal cell side.

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

1. Dope and optical film materials (1) Methacrylic resin PMMA: Polymethyl methacrylate (weight average molecular weight 1 million, glass transition temperature 105°C)
MMA/PMI: Methyl methacrylate/phenylmaleimide copolymer (85/15 mass ratio) (weight average molecular weight 1 million, glass transition temperature 120°C)

Note that the weight average molecular weight and glass transition temperature (Tg) were measured by the following methods.

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

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

(2) Rubber particles <Preparation of rubber particles A1>
The following compounds were charged into an 8L polymerization apparatus equipped with a stirrer.
Deionized water: 175 parts by mass Polyoxyethylene lauryl ether phosphoric acid: 0.104 parts by mass Boric acid: 0.4725 parts by mass Sodium carbonate: 0.04725 parts by mass

After sufficiently purging the interior of the polymerization machine with nitrogen gas, the internal temperature was raised to 80°C, and 27 parts by mass of the monomer mixture (c') (methyl methacrylate: 96.5 mass%, butyl acrylate: 3 mass%, and methacrylic acid) was added. Allyl: 0.5% by mass) was added to the polymerization machine all at once, and then 0.0645 parts by mass of sodium formaldehyde sulfoxylate, 0.0056 parts by mass of sodium ethylenediaminetetraacetate-2, and 0.5 parts by mass of ferrous sulfate. 0.0014 parts by mass and 0.0207 parts by mass of t-butyl hydroperoxide were added, and 15 minutes later, 0.0345 parts by mass of t-butyl hydroperoxide was added, and the polymerization was continued for an additional 15 minutes.
Next, 0.0098 parts by mass of sodium hydroxide in the form of a 2% by mass aqueous solution, 0.0852 parts by mass of polyoxyethylene lauryl ether phosphoric acid were added as they were, and the remaining 74% by mass of the above mixture was continuously added over 60 minutes. added. Thirty minutes after the completion of the addition, 0.069 parts by mass of t-butyl hydroperoxide was added and polymerization was continued for an additional 30 minutes to obtain a hard crosslinked polymer (c).

Thereafter, 0.0267 parts by mass of sodium hydroxide in the form of a 2% by mass aqueous solution and 0.08 parts by mass of potassium persulfate in the form of a 2% by mass aqueous solution were added, and then 50 parts by mass of the monomer mixture (a') ( Butyl acrylate: 73% by mass, methyl methacrylate: 25.2% by mass, and allyl methacrylate: 1.8% by mass) were continuously added 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 an acrylic rubbery polymer (a).

Thereafter, 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) (methyl methacrylate: 95% by mass, butyl acrylate: 5% by mass) was added over 45 minutes. The polymerization was continued for an additional 30 minutes.

Thereafter, 8 parts by mass of monomer mixture (b2) (methyl methacrylate: 52 mass%, butyl acrylate: 48 mass%) was continuously added over 25 minutes, and the polymerization was continued for an additional 60 minutes. A polymer latex was obtained.

The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain a white powdery graft copolymer (rubber particles A1).

The graft ratio of the obtained rubber particles A1 was 24% by mass, and the average particle diameter was 200 nm. Furthermore, the glass transition temperature (Tg) of the acrylic rubbery polymer (a) contained in the rubber particles A1 is -30°C, and the allyl methacrylate relative to all the structural units constituting the acrylic rubbery polymer (a) is The content of structural units derived from (degree of crosslinking) was 1.8% by mass.

<Preparation of rubber particles A2 to A7>
The graft copolymer (rubber particles ) was obtained.

Table 1 shows the composition and physical properties of rubber particles A1 to A7.

The degree of crosslinking, average particle diameter, and glass transition temperature (Tg) of the rubber particles were measured by the following methods.

(1) Degree of crosslinking The degree of crosslinking is the total mass of the polyfunctional monomers with more than two functionalities used in the preparation of the rubbery polymer, relative to the total mass of the monomers used in the preparation of the rubbery polymer. The ratio (mass%) was defined as the degree of crosslinking.

(2) Average particle size The dispersed particle size of the rubber particles in the obtained dispersion was measured using a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

(3) Glass transition temperature (Tg)
It was measured in the same manner as described above.

2. Preparation of dope <Preparation of dope 101>
(Preparation of rubber particle dispersion 1)
10.5 parts by mass of rubber particles A1, 168 parts by mass of methylene chloride, and 32 parts by mass of ethanol were stirred and mixed with a dissolver for 50 minutes, and then mixed using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). Dispersion was carried out under the condition of 1500 rpm. Next, 7.13 parts by mass of water was added to the obtained solution, and the mixture was stirred and mixed with a dissolver for 30 minutes to obtain rubber particle dispersion 1 (water content in the first solvent: 3.4% by mass). Ta.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. After PMMA was added to this while stirring, the rubber particle dispersion 1 prepared above was further added, and PMMA was completely dissolved while stirring. The obtained solution was filtered using SHP150 manufactured by Loki Techno Co., Ltd. to obtain Dope 101.
Polymethyl methacrylate (PMMA): 100 parts by mass Methylene chloride (second solvent): 393 parts by mass Ethanol (second solvent): 42 parts by mass Rubber particle dispersion 1: 500 parts by mass

<Preparation of dope 102>
(Preparation of rubber particle dispersion 2)
10.5 parts by mass of rubber particles A1, 168 parts by mass of methylene chloride (non-polar solvent: B), 32 parts by mass of ethanol (polar solvent: A), and 7.13 parts by mass of water were mixed into a dissolver. After stirring and mixing for 50 minutes, the mixture was dispersed using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.) at 1500 rpm to obtain a rubber particle dispersion 2.

(Preparation of dope)
Dope 102 was obtained in the same manner as in the preparation of dope 101 except that the obtained rubber particle dispersion 2 was used.

<Preparation of dope 103>
(Preparation of rubber particle dispersion 3)
Rubber particle dispersion 3 was obtained in the same manner as rubber particle dispersion 1 except that water was not added.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. To this was added water in the amount shown in Table 2, and the mixture was stirred with a dissolver for 10 minutes. Next, the rubber particle dispersion 3 prepared above was added to this while stirring, and then PMMA was further added and stirred to dissolve the PMMA. The obtained solution was filtered using SHP150 manufactured by Loki Techno Co., Ltd. to obtain Dope 103.
Polymethyl methacrylate (PMMA): 100 parts by mass Methylene chloride: 393 parts by mass Ethanol: 42 parts by mass Water: 16.7 parts by mass Rubber particle dispersion 3: 500 parts by mass

<Preparation of dope 104>
(Preparation of rubber particle dispersion liquid 4)
Rubber particle dispersion 4 was obtained in the same manner as rubber particle dispersion 1 except that the type of rubber particles was changed to those shown in Table 2.

(Preparation of dope)
Dope 104 was obtained in the same manner as in the preparation of dope 101 except that the obtained rubber particle dispersion 4 was used.

<Preparation of dope 105>
Dope 105 was obtained in the same manner as in the preparation of Dope 101 except that the above-mentioned Rubber Particle Dispersion 3 (no water added) was used.

<Preparation of dope 106>
(Preparation of rubber particle dispersion 5)
10.5 parts by mass of rubber particles A1, 168 parts by mass of methylene chloride, and 32 parts by mass of ethanol were stirred and mixed with a dissolver for 50 minutes, and then mixed using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). Dispersion was carried out under the condition of 1500 rpm. Next, 4.96 parts by mass of water was added to the obtained solution, and the mixture was stirred and mixed with a dissolver for 30 minutes to obtain rubber particle dispersion 5 (water content in the first solvent: 2.4% by mass). Ta.

(Preparation of dope)
A dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. To this was added water in the amount shown in Table 2, and the mixture was stirred with a dissolver for 10 minutes. Next, the rubber particle dispersion 1 prepared above was added to this while stirring, and then PMMA was further added and stirred to dissolve the PMMA. The obtained solution was filtered using SHP150 manufactured by Loki Techno Co., Ltd. to obtain Dope 106.
Polymethyl methacrylate (PMMA): 100 parts by mass Methylene chloride: 393 parts by mass Ethanol: 42 parts by mass Water: 4.96 parts by mass Rubber particle dispersion 5: 500 parts by mass

<Preparation of dopes 107 to 111>
(Preparation of rubber particle dispersions 6 to 10)
Rubber particle dispersions 6 to 10 were obtained in the same manner as rubber particle dispersion 1 except that the degree of crosslinking of the rubber particles was changed as shown in Table 2.

(Preparation of dope)
Dopes 107 to 111 were obtained in the same manner as in the preparation of dope 101 except that the obtained rubber particle dispersion was used.

<Preparation of dopes 112 to 114 and 116>
(Preparation of rubber particle dispersions 11 to 13 and 15)
Rubber particle dispersion 1 except that the amount of water added during the preparation of the rubber particle dispersion was adjusted so that the amount of water relative to the entire nonpolar solvent in the resulting dope was the amount shown in Table 2. Rubber particle dispersions 11 to 13 and 15 were obtained in the same manner.

(Preparation of dope)
Dopes 112 to 114 and 116 were obtained in the same manner as in the preparation of dope 101 except that the obtained rubber particle dispersion was used.

<Preparation of dope 115>
(Preparation of rubber particle dispersion 14)
Rubber particle dispersion 14 was obtained in the same manner as rubber particle dispersion 1, except that the type of nonpolar solvent used in preparing the rubber particle dispersion was changed as shown in Table 2.

(Preparation of dope)
Dope 115 was obtained in the same manner as in the preparation of Dope 101, except that the obtained rubber particle dispersion was used and the type of non-polar solvent used in preparing the dope was changed as shown in Table 2.

<Preparation of dope 117>
Dope 117 was obtained in the same manner as in the preparation of Dope 101, except that polymethyl methacrylate (PMMA) was changed to methyl methacrylate/phenylmaleimide copolymer (MMA/PhMI=85/15 mass ratio).

<Evaluation>
The dispersion state of rubber particles in the obtained dopes 101 to 117 was evaluated by the following method.

(Dispersion state of rubber particles)
The obtained dope was diluted with an organic solvent prepared to have the same composition as the organic solvent in the dope until the solid content was 1% by mass. The dispersed particle size (average particle size) of the rubber particles in the obtained diluted dope was measured using a zeta potential/particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.). Then, the state of dispersion of the rubber particles in the dope was evaluated based on the following criteria.
5: Average particle size in diluted dope is primary particle size + 50 nm or less 4: Average particle size in diluted dope is primary particle size + 50 nm or less + 100 nm or less 3: Average particle size in diluted dope is primary particle size + 100 nm or less + 300 nm or less 2 : Average particle size in diluted dope is primary particle size + more than 300 nm + 500 nm or less 1: Average particle size in diluted dope is more than primary particle size + 500 nm

In addition, the value measured by the following method was used for the primary particle diameter of the rubber particles.
That is, the obtained optical film was cut and the cut surface was observed using a TEM. Then, the equivalent circular diameter of the particle diameter of 100 arbitrary particles was measured, and the average value thereof was defined as the "primary particle diameter".

Table 2 shows the manufacturing conditions and evaluation results for Dopes 101 to 117.

3. Production and evaluation of optical films <Production of optical films 201 to 217>
Using an endless belt casting apparatus, the dopes shown in Table 3 were uniformly cast onto a stainless steel belt support at a temperature of 30° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled at 28°C.

The solvent was evaporated on a stainless steel belt support until the amount of residual solvent in the cast dope became 30% by mass. Next, it was peeled off from the stainless steel belt support with a peeling tension of 128 N/m to obtain a film-like product. The amount of residual solvent in the film-like material at the time of peeling was 30% by mass.

Next, while conveying the peeled film with a number of rollers, the obtained film-like material was heated in a tenter at (Tg+10)°C (Tg: Tg of methacrylic resin) in the width direction (TD direction) for 20 minutes. % stretched. Thereafter, it was further dried at (Tg-30)° C. while being transported by rolls, and the ends sandwiched between tenter clips were slit and wound up to obtain optical films 201 to 217 with a film thickness of 40 μm.

<Evaluation>
The belt stain, MIT flexibility, and haze change (ΔHz) of the obtained optical films 201 to 217 were measured by the following methods.

(1) Belt stain Belt stain when the dope cast onto the stainless steel band support was peeled from the stainless steel band support was evaluated based on the following criteria.
5: None of the evaluators can see any unevenness. 4: Some evaluators may be able to see slight unevenness, but it is at a level where it can be used as a product without any problems. 3: Some evaluators may be able to see slight unevenness. However, the level can be used as a product. 2: Some evaluators may be able to confirm unevenness, and the level cannot be used as a product. 1: Many evaluators can confirm unevenness. If it is 3 or higher, it is judged to be good.

(2) MIT Flexibility The obtained optical film was cut out to a width of 15 mm x length of 150 mm to prepare a test piece. After this test piece was allowed to stand at a temperature of 25°C and a relative humidity of 65% RH for more than 1 hour, it was subjected to an MIT bending test in accordance with JIS P8115:2001 under a load of 500g, and the The number of times was measured. The MIT bending test was conducted using a bending durability tester (manufactured by Tester Sangyo Co., Ltd., MIT, model BE-201, bending radius of curvature 0.38 mm). Then, evaluation was made using the following evaluation criteria.
5: The number of times it takes to break is 60,000 times or more. 4: The number of times it takes to break is 40,000 times or more and less than 60,000 times. 3: The number of times it takes to break is 20,000 times or more and less than 40,000 times. 2: The number of times it takes to break is 20,000 times or more and less than 40,000 times. The number of times is 10,000 or more and less than 20,000 times. 1: The number of times until breakage is less than 10,000 times. The greater the number of times until breakage, the better the flexibility and the better the repeated bending resistance.
If it was 3 or more, it was judged as good.

(3) Haze (initial value, amount of change (ΔHz))
1) Five points in the width direction of the obtained optical film (the center of the film, the ends (at 5% of the total width from both ends), and two points in the middle between the center and the ends) in the longitudinal direction. Sampling was carried out every 100 m, and samples with a size of 5 ^cm2 were prepared.
2) Next, for each of the obtained samples, the haze was measured using a haze meter (NDH 2000: manufactured by Nippon Denshoku Kogyo Co., Ltd.) after 24 hours of humidity control in an environment of 25 ° C. and 60% RH, Their average value was defined as haze 1 (initial value).
3) Next, each obtained sample was left for 1000 hours in an environment of 60° C. and 90% RH. Thereafter, after conditioning the humidity for 24 hours in an environment of 25° C. and 60% RH, the haze of each sample was measured in the same manner as described above, and the average value thereof was defined as Haze 2 (after the durability test).
4) Haze 1 (initial value) obtained in 2) above and Haze 2 (after durability test) obtained in 3) above were applied to the following formula to calculate the amount of change in haze (ΔHz).
Formula (1): Haze change amount (ΔHz) = Haze 2 (after durability test) - Haze 1 (initial value)
5: Haze change amount (ΔHz) is 0.1 or less 4: Haze change amount (ΔHz) is more than 0.1 and 0.15 or less 3: Haze change amount (ΔHz) is more than 0.15 and 0.3 or less 2: Haze If the amount of change (ΔHz) is more than 0.3 and not more than 0.4 1: The amount of change in haze (ΔHz) is more than 0.4 and not more than 3, it was judged as good.

Table 3 shows the evaluation results of optical films 201 to 217.

As shown in Table 3, optical films 201 to 204, 206 to 209, 212 to 215, and 217 (invention) obtained by adding an appropriate amount of water to at least one of the rubber particle dispersion step and the dope preparation step are as follows: It can be seen that there is little belt dirt. This is considered to be because aggregation of rubber particles was suppressed. Furthermore, since these optical films originally contain an appropriate amount of water due to the addition of water during the manufacturing process, it can be seen that the change in haze between before and after the durability test is small.

On the other hand, it can be seen that the optical film 205 (comparative example) in which water was not added in either the rubber particle dispersion step or the dope preparation step caused belt stains. This is thought to be due to the fact that it contains a large amount of aggregates of rubber particles. It can also be seen that since no water is added to the optical film 205 during the manufacturing process, the original water content is low, and the haze changes significantly before and after the durability test.

Furthermore, it can be seen that when the amount of water added is small, the agglomeration of rubber particles cannot be sufficiently suppressed, resulting in large changes in belt staining and haze (optical film 216). On the other hand, if the amount of water added is too large, the resin will not be sufficiently dissolved in the solvent, resulting in poor compatibility, so the initial haze value will tend to increase and the flexibility will be low (Optical Film 214) .

Furthermore, it can be seen that when the degree of crosslinking of the rubber particles is low, the rubber particles tend to aggregate, and thus belt stains are likely to occur (optical film 210). On the other hand, it can be seen that when the degree of crosslinking of the rubber particles is too high, the MIT flexibility of the film is insufficient (optical film 211).

According to the present invention, there is provided a method for producing a dope for an optical film that can suppress aggregation of rubber particles and provide an optical film with sufficient toughness without impairing transparency.

Claims (5)

preparing a rubber particle dispersion containing rubber particles containing a rubbery polymer having a degree of crosslinking of 0.25 to 4% by mass;
A step of mixing the rubber particle dispersion, a methacrylic resin, and a second solvent to prepare a dope containing the methacrylic resin, the rubber particles, and a solvent,
The step of preparing the rubber particle dispersion includes:
Dispersing the rubber particles in an organic solvent;
adding water to the rubber particles dispersed in the organic solvent,
The water content is 0.5 to 3% by mass based on the solvent contained in the dope,
A method for producing dope for optical films. The rubber particles are core-shell particles having a core portion containing the rubbery polymer and a shell portion containing another polymer graft-polymerized to the rubbery polymer.
A method for producing a dope for an optical film according to claim 1. The rubbery polymer is an acrylic rubbery polymer containing a structural unit derived from an acrylic acid alkyl ester as a main component,
The other polymer is a methacrylic polymer containing a structural unit derived from a methacrylic acid alkyl ester as a main component.
A method for producing a dope for an optical film according to claim 2. The methacrylic resin contains 80% by mass or more of structural units derived from methyl methacrylate based on the total structural units constituting the methacrylic resin.
A method for producing a dope for an optical film according to claim 3. A step of preparing a dope by the method for producing a dope for an optical film according to any one of claims 1 to 4;
a step of casting the dope on a support and then peeling it off to obtain a film-like material;
Method for manufacturing optical film.