JP2021033058A - Method for manufacturing optical film dope, optical film dope, optical film, polarizer and method for manufacturing optical film - Google Patents

Abstract

To provide a method for manufacturing an optical film dope, capable of suppressing the aggregation of rubber particles and providing an optical film having sufficient toughness without spoiling transparency.SOLUTION: The method for manufacturing an optical film dope comprises the steps of: dispersing rubber particles including a crosslinked polymer having the degree of crosslinking of 0.25-4 mass% in a first solvent to prepare a rubber particle dispersion; and mixing the rubber particle dispersion, a methacrylic resin and a second solvent to prepare a dope. At least one of the first solvent and the second solvent includes water, and the water content is 0.5-3 mass% relative to the solvent constituting the dope.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a dope for an optical film, a dope for an optical film, 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 polarizing element and protective films arranged on both sides thereof. In recent years, with the diversification of usage environments such as outdoor use of smartphones, the protective film constituting the polarizing plate is less likely to cause display unevenness in the display device even in a harsh environment of high temperature and high humidity. Is required. From such a viewpoint, the use of a (meth) acrylic resin film having lower hygroscopicity and excellent dimensional stability than the conventional cellulose ester film has been studied as the protective film.

On the other hand, since the methacrylic resin film is 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 (meth) acrylic crosslinked polymer and a shell portion containing a methacrylic polymer graft-bonded thereto, and is a methacrylic-based rubber particle constituting the shell 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 close to the polarity of the glutarimide (meth) acrylic resin, so that the compatibility between the rubber particles and the glutarimide (meth) acrylic resin can be enhanced. It is said that it can suppress the aggregation of rubber particles.

JP-A-2017-137417

Such a (meth) acrylic resin film is usually produced by a melt casting method (melt method) (see Patent Document 1). On the other hand, it is desired to be produced by a solution casting method (cast method) from the viewpoint that there are few restrictions on the materials used, such as the ability to use a high molecular weight resin.

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 obtained dope is cast on a support and dried. A (meth) acrylic resin film is obtained through a step of peeling to obtain a film-like substance. However, since the compatibility between the rubber particles and the (meth) acrylic resin is low, the rubber particles tend to aggregate. Therefore, there is a problem that not only sufficient toughness (suppleness or flexibility) cannot be imparted to the obtained film, but also the transparency is easily impaired. Further, when the film-like material obtained by casting the dope is peeled off from the support, there is also a problem that agglomerates of rubber particles easily fall off from the film-like material and easily contaminate the support (belt). ..

The present invention has been made in view of the above circumstances, and is a dope for an optical film capable of suppressing aggregation of rubber particles and imparting an optical film having sufficient toughness without impairing transparency. It is an object of the present invention to provide a manufacturing method, a dope for an optical film, an optical film, a polarizing plate, and a method for manufacturing 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 rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass are dispersed in a first solvent to prepare a rubber particle dispersion. The step of mixing the rubber particle dispersion liquid, the methacrylic resin, and the second solvent to prepare a dope containing the methacrylic resin, the rubber particles, and the solvent. At least one of the first solvent and the second solvent contains water, and the amount of the water in the solvent is 0.5 to 3% by mass.

The dope for an optical film of the present invention is a dope for an optical film containing a methacrylic resin, rubber particles containing a rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass, and a solvent.
The solvent contains 0.5 to 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 rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass. The haze measured when the humidity is adjusted for 24 hours in the environment is the haze 1. The haze measured when the humidity is adjusted for 24 hours in the environment of 23 ° C and 55% after storing for 1000 hours in the environment of 60 ° C and 90%. When the haze is 2, the amount of haze change represented by the following formula (1) is 0.3 or less.
Equation (1): Haze change amount = haze 2-haze 1

The polarizing plate of the present invention has a polarizing element and an optical film of the present invention arranged on at least one surface thereof.

The method for producing an optical film of the present invention is a step of preparing a dope and a step of casting the dope on a support and then peeling to obtain a film-like substance by the method for producing a dope for an optical film of the present invention. Including the process.

According to the present invention, a method for producing a dope for an optical film, which can suppress aggregation of rubber particles and impart an optical film having sufficient toughness without impairing transparency, a dope for an optical film, It is possible to provide an optical film, a polarizing plate, and a method for producing the optical film.

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

In the solution casting method, rubber particles containing a rubber-like polymer having a lower degree of cross-linking than the rubber particles used in the melt casting method are used from the viewpoint of facilitating dispersion of the rubber particles in an organic solvent. On the other hand, rubber particles containing a rubber-like polymer having a low degree of cross-linking (particularly, an acrylic rubber-like polymer having a low degree of cross-linking) have a low affinity with a methacrylic resin, and the rubber particles tend to aggregate. was there.

On the other hand, by using core-shell type particles in which the core portion containing a rubber-like polymer having a low degree of cross-linking is coated with a shell portion containing another polymer having good compatibility with a methacrylic resin, rubber particles are used. The compatibility between the resin and the methacrylic resin can be improved to some extent. However, the rubber-like polymer having a low degree of cross-linking constituting the core portion easily swells due to the organic solvent, easily breaks through the shell portion, and is easily exposed on the surface of the rubber particles. Since the rubber-like polymer with a low degree of cross-linking exposed on the surface of the rubber particles has a low affinity for the methacrylic resin, the aggregation of the rubber particles could not be sufficiently suppressed.

As a result of diligent studies, the present inventors have prepared a rubber particle dispersion liquid by dispersing the rubber particles in a solvent (rubber particle dispersion step), the obtained rubber particle dispersion liquid, and a methacrylic resin. In the method for producing a dope, which includes a step of preparing a dope by mixing with a solvent (dope preparation step), the rubber particles and the methacrylic resin are formed by dispersing the rubber particles in a solvent containing water. It was found that the compatibility of rubber particles can be enhanced, and thereby the aggregation of rubber particles can be suppressed.

The reason for this is not clear, but it is presumed as follows. That is, by intentionally adding water having a polarity significantly different from the polarity of the rubber-like polymer, it is possible to reduce the swelling of the rubber-like polymer having a low degree of cross-linking. As a result, it is possible to prevent the rubber-like polymer having a low degree of cross-linking from penetrating the shell portion and being exposed to the surface of the rubber particles, so that the compatibility between the rubber particles and the methacrylic resin is suppressed. Can be done.

The timing of adding water is not particularly limited, but in the rubber particle dispersion step, it is preferable to disperse the rubber particles in an organic solvent and then add water to further disperse the rubber particles. That is, after the agglomerates of the rubber particles are loosened to some extent in an organic solvent, each of the swelled rubber particles can be reliably tightened (suppressed swelling) with water, so that the rubber particles are highly dispersed. Cheap. Hereinafter, each configuration of the present invention will be described.

1. 1. Doping Production Method The doping production method 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 particle dispersion liquid, the methacrylic resin, and the second solvent are mixed to prepare a dope (doping preparation step).

Then, 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, the rubber particles are dispersed in a solvent containing water.

Above all, 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 it. Hereinafter, in the rubber particle dispersion step, an example of dispersing the rubber particles in a first solvent containing water will be described.

1-1. Rubber particle dispersion step Rubber particles are dispersed in the first solvent to obtain a rubber particle dispersion liquid.

(Rubber particles)
The rubber particles may have a function of imparting toughness (suppleness) to the optical film. The rubber particles are particles containing a rubber-like polymer. The rubber-like polymer is a soft crosslinked polymer having a glass transition temperature of 20 ° C. or lower. Examples of such cross-linked polymers include butadiene-based cross-linked polymers, (meth) acrylic-based cross-linked polymers, and organosiloxane-based cross-linked polymers. Among them, the (meth) acrylic crosslinked polymer is preferable from the viewpoint that the difference in refractive index from the (meth) acrylic resin is small and the transparency of the optical film is not easily impaired, and the acrylic crosslinked polymer (acrylic rubber-like weight) is preferable. Coalescence) is more preferable.

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

About acrylic rubber-like polymer (a):
The acrylic rubber-like polymer (a) is a crosslinked polymer containing a structural unit derived from an acrylic acid ester as a main component. Including as a main component means that the content of structural units derived from acrylic acid ester is in the range described later. The acrylic rubber-like polymer (a) has a structural unit derived from an acrylic acid ester, a structural unit derived from another monomer copolymerizable therewith, and two or more radically polymerizable groups in one molecule ( It is preferably a crosslinked polymer containing a structural unit derived from a polyfunctional monomer having a non-conjugated reactive double bond).

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. An acrylic acid alkyl ester having 1 to 12 carbon atoms of an alkyl group such as n-octyl acid is preferable. The acrylic acid ester may be one kind or two or more kinds.

The content of the structural unit derived from the acrylic acid ester is preferably 40 to 80% by mass, preferably 50 to 80% by mass, based on all the structural units constituting the acrylic rubber-like polymer (a). Is more preferable. When the content of the acrylic acid ester is within the above range, it is easy to impart sufficient toughness to the optical film.

The other copolymerizable monomer is a monomer copolymerizable with the acrylic acid ester other than the polyfunctional monomer. That is, the copolymerizable monomer does not have two or more radically polymerizable groups. Examples of copolymerizable monomers include methacrylic ester such as methyl methacrylate; styrenes such as styrene and methylstyrene; (meth) acrylonitrile; (meth) acrylamide; (meth) acrylic acid. .. Among them, the other copolymerizable monomer preferably contains styrenes. The other copolymerizable monomer may be one kind or two or more kinds.

The content of structural units derived from other copolymerizable monomers is preferably 5 to 55% by mass, preferably 5 to 55% by mass, based on all the structural units constituting the acrylic rubber-like polymer (a). It is more preferably 45% by mass.

Examples of polyfunctional monomers include allyl (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl malate, divinyl adipate, divinylbenzene, ethylene glycol di (meth) acrylate, and diethylene glycol (diethylene glycol). Includes meth) acrylates, triethylene glycol di (meth) acrylates, trimethylrol propanetri (meth) acrylates, tetromethylol methanetetra (meth) acrylates, dipropylene glycol di (meth) acrylates, polyethylene glycol di (meth) acrylates. ..

The content of the structural unit derived from the polyfunctional monomer is preferably 0.05 to 10% by mass, preferably 0.1 to 10% by mass, based on the total structural units constituting the acrylic rubber-like polymer (a). More preferably, it is ~ 5% by mass. When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of cross-linking of the obtained acrylic rubber-like polymer (a) is likely to be increased, so that the hardness and rigidity of the obtained film are excessively impaired. However, when it is 10% by mass or less, the toughness of the film is not easily impaired.

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

The particles containing the acrylic rubber-like polymer (a) are the particles made of the acrylic rubber-like polymer (a) or the hard layer made of the hard crosslinked polymer (c) having a glass transition temperature of 20 ° C. or higher. , Particles having a soft layer made of the acrylic rubber-like polymer (a) arranged around the particles (these are also referred to as “epolymers”); the acrylic rubber-like polymer (a). In the presence of, the particles may be particles made of an acrylic graft copolymer obtained by polymerizing a mixture of monomers such as a methacrylate ester in at least one step or more. The particles made of the acrylic graft copolymer may be core-shell type particles having a core portion containing the acrylic rubber-like polymer (a) and a shell portion covering the core portion.

About core-shell type rubber particles containing acrylic rubber-like 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) arranged inside the soft layer.

The crosslinked polymer (c) can be a crosslinked polymer containing a methacrylic acid ester as a main component. That is, the crosslinked polymer (c) includes a structural unit derived from a methacrylic acid alkyl ester, a structural unit derived from another monomer copolymerizable therewith, and a structural unit derived from a polyfunctional monomer. It is preferably a crosslinked polymer containing.

The alkyl methacrylic acid ester may be the alkyl methacrylic acid ester described above; the other copolymerizable monomer may be the styrenes or acrylic acid ester described above; the polyfunctional monomer may be. Examples thereof include those similar to those mentioned above as the polyfunctional monomer.

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

(Shell part)
The shell portion contains a methacrylic polymer (b) (another polymer) graft-bonded to the acrylic rubber-like polymer (a) and containing a structural unit derived from a methacrylic acid ester as a main component. Including as a main component means that the content of structural units derived from methacrylic acid ester is in the range described later.

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

The content of the methacrylic acid ester is preferably 50% by mass or more with respect to all the structural units constituting the methacrylic acid polymer (b). When the content of the 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 can be easily obtained. From the above viewpoint, the content of the methacrylic acid ester is more preferably 70% by mass or more with respect to all the structural units constituting the methacrylic polymer (b).

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

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

The ratio of the graft component (graft ratio) in the rubber particles is preferably 10 to 250% by mass, and more preferably 15 to 150% by mass. When the graft ratio is above a certain level, the proportion of the graft component, that is, the methacrylic polymer (b) containing the structural unit derived from the methacrylic acid ester as the main component is moderately large, so that the rubber particles and the methacrylic resin are separated from each other. It is easy to improve compatibility and it is more difficult to agglomerate rubber particles. In addition, the rigidity of the film is not easily 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 toughness and brittleness improving effect of the film are not easily impaired.

The graft ratio is measured by the following method.
1) Dissolve 2 g of core-shell type particles in 50 ml of methyl ethyl ketone and centrifuge at a rotation speed of 30,000 rpm and a temperature of 12 ° C. for 1 hour using a centrifuge (manufactured by Hitachi Koki Co., Ltd., CP60E) to make it insoluble. Separate into the dissolved components (centrifugal separation work is set 3 times in total).
2) The graft ratio is calculated by applying the weight of the obtained insoluble matter to the following formula.
Graft ratio (mass%) = [{(mass of methyl ethyl ketone insoluble matter)-(mass of acrylic rubber-like polymer (a))} / (mass of acrylic rubber-like polymer (a))] × 100

(Crosslink degree)
The degree of cross-linking of the rubber-like polymer contained in the rubber particles is preferably 0.25 to 4% by mass. When the degree of cross-linking of the rubber-like polymer is 0.25% by mass or more, the rubber-like polymer does not become too flexible, so that the rubber-like polymer flows out (exposed) from the gaps of the swollen shell portion to the particle surface. ) Can be difficult. Therefore, it is easy to suppress a decrease in compatibility between the rubber particles and the methacrylic resin. In addition, since the rubber particles do not become too flexible, they do not deform excessively and can impart good slipperiness to the film. When the degree of cross-linking of the rubber-like polymer is 4% by mass or less, the rubber particles can be easily dispersed in an organic solvent during film formation by the solution casting method. Further, since the rubber-like polymer does not become too hard, it is possible to prevent the rubber particles from cracking or chipping. From the above viewpoint, the degree of cross-linking of the rubber-like polymer contained in the rubber particles is more preferably 0.3 to 3% by mass.

The degree of cross-linking of the rubber-like polymer is determined by the polyfunctional monomer constituting the rubber-like polymer with respect to the total amount of structural units constituting the rubber-like polymer (total amount of the monomers constituting the rubber-like polymer). It is expressed as a ratio of the total amount of derived structural units (total amount of polyfunctional monomers constituting the rubber-like polymer). The degree of cross-linking of the rubber-like polymer can be calculated from the charging ratio of the monomers at the time of preparation of the rubber-like polymer.

(Glass transition temperature (Tg))
The glass transition temperature (Tg) of the rubber-like 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 rubber-like polymer is 0 ° C. or lower, appropriate toughness can be imparted to the film. The glass transition temperature (Tg) of the rubber-like polymer is measured by the same method as described above.

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

(Average particle size)
The average particle size of the rubber particles is preferably 100 to 500 nm. When the average particle size 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 size 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 by 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 of the methacrylic resin contained in the dope is in the range described later.

Hereinafter, the first solvent in the rubber particle dispersion step and the second solvent in the dope preparation step will be described. 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, the rubber particles are dispersed in a solvent containing water. Above all, 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 contains at least a non-polar solvent (good solvent) that dissolves the methacrylic resin. Examples of non-polar solvents include dichloromethane, hexane, benzene, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran. Of these, dichloromethane is preferable.

Further, the organic solvent preferably further contains a polar solvent (poor solvent) other than water from the viewpoint of improving the peelability from the metal support in the film forming step by the solution casting method. Examples of polar solvents include aprotices such as γ-butyrolactone, acetone, acetonitrile, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), 1,3-dimethyl-2-imidazolidinone (DMI). Sexual polar solvent; includes an aliphatic alcohol having 1 to 4 carbon atoms (methanol, ethanol, 1-propanol, 2-propanol, butanol, etc.), a protonic polar solvent such as acetic acid and ethylenediamine. Of these, aliphatic alcohols having 1 to 4 carbon atoms are preferable, and methanol and ethanol are more preferable.

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 non-polar solvent and the polar solvent in the first solvent. .. When the content of the polar solvent is more than a certain level, not only the film-like substance is easily peeled off from the metal support but also water is easily dissolved in the film forming process by the solution casting method, so that the appearance of the obtained optical film is obtained. Is not easily damaged. Further, when the content of the polar solvent is not more than a certain level, the solubility of the (meth) acrylic resin is not easily impaired.

The content of water in the first solvent, that is, the amount of water added in the rubber particle dispersion step is in the range (0.5 to 3% by mass) described below in terms of the content of water in the solvent contained in the obtained dope. ) May be set. 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 total amount of the first solvent contained in the rubber particle dispersion. It can be preferably 3 to 7.5% by mass. When the amount of water added in the rubber particle dispersion step is a certain amount or more, it is difficult to excessively swell the rubber-like polymer in the rubber particles, and it is possible to make it difficult for the rubber-like polymer to be exposed on the particle surface. As a result, the compatibility between the rubber particles and the methacrylic resin is less likely to be impaired, and the aggregation of the rubber particles can be easily suppressed. On the other hand, if the amount of water added in the rubber particle dispersion step is less than a certain level, the affinity between water and other solvents is not excessively impaired. Poor appearance (roughness and haze increase due to agglomerates of rubber particles) and haze increase 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 the dispersion treatment of the rubber particles in the organic solvent, or at the same time as or after the dispersion treatment of the rubber particles in the organic solvent. From the viewpoint of facilitating the aggregation of the rubber particles to a high degree, it is preferable to add water after the rubber particles are dispersed 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 of the rubber particles dispersed to some extent in the organic solvent by adding water.

(Dispersion method)
The means for dispersing the rubber particles when dispersing the rubber particles in the first solvent is not particularly limited, and is an ultrasonic disperser, a stirrer (for example, a high-speed stirrer such as a dissolver), and a disperser (for example, a disperser such as a milder). ) Can be. Above all, from the viewpoint of making it easy to disperse the rubber particles to a high degree by applying high energy, it is preferable to disperse the rubber particles at least by using a high-speed stirrer such as a dissolver.

1-2. Dope preparation step The obtained rubber particle dispersion is mixed with a methacrylic resin and a solvent (second solvent) to prepare a dope.

(Methacrylic resin)
The 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 a structural unit derived from methyl methacrylate and a simple polymer other than methyl methacrylate copolymerizable therewith. It may be a copolymer containing a structural unit derived from a dimer.

Other copolymerizable monomers are not particularly limited.
Alkyl esters of (meth) acrylate having 1 to 18 carbon atoms of alkyl groups other than methyl methacrylate, such as ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate;
Α, β-unsaturated acids such as (meth) acrylic acid;
Unsaturated group-containing divalent carboxylic acids such as maleic acid, fumaric acid, and 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 (eg, phenylmaleimide);
Maleic anhydride and glutaric anhydride are included. The other copolymerizable monomer may be used alone or in combination of two or more.

Among them, other copolymerizable monomers are monomers having relatively low polarity, such as aromatic vinyls such as styrene; ring-containing methacrylic acid esters such as phenyl methacrylate and adamantyl methacrylate; and phenylmaleimide. More preferably, it is a maleimide. Since the methacrylic resin having a structural unit derived from such another copolymerizable monomer has a low affinity with the rubber-like polymer contained in the rubber particles, the effect of suppressing aggregation by adding water can be obtained. This is because it is easy to get rid of.

The content of the structural unit 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 all the structural units constituting the methacrylic resin. Is more preferable. As described above, the methacrylic resin containing a large amount of structural units derived from methyl methacrylate has a low affinity for the rubber-like polymer contained in the rubber particles, so that the effect of suppressing aggregation by water addition can be easily obtained. The type and composition of the monomer of the methacrylic resin can be specified by ^{1 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 having a Tg of a methacrylic resin of 90 ° C. or higher can have good heat resistance.

The glass transition temperature (Tg) of a methacrylic resin can be measured using DSC (Differential Scanning Colorimetry) according to 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 300,000 to 3,000,000, more preferably 1,000,000 to 2,000,000. When the weight average molecular weight of the (meth) acrylic resin is in the above range, sufficient mechanical strength (toughness) can be imparted to the film without impairing the film-forming property.

The weight average molecular weight (Mw) of the methacrylic resin can be measured by gel permeation chromatography (GPC) in terms of polystyrene. Specifically, the measurement can be performed using a Tosoh HLC8220GPC) and a column (Tosoh TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL series). 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 of the doping with respect to the solid content is in the range described later.

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

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

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

At that time, the mixing timing of the rubber particle dispersion liquid 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 facilitating the agglomeration of rubber particles to a high degree, it is preferable that the rubber particle dispersion liquid and the second solvent containing water are mixed before the addition of the methacrylic resin. That is, the dope preparation steps are 1) a step of mixing the rubber particle dispersion liquid and a second solvent containing water, and 2) a step of adding a methacrylic resin to the obtained mixed liquid to prepare the dope. And may be included. When adding the second solvent containing water, water and the organic solvent may be added at the same time or separately.

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

(Other ingredients)
Other components other than the above may be further added to the dope, if necessary. Examples of other ingredients 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 mixing means of 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 the above may be further mixed. For example, when an optical film containing organic fine particles is obtained, a second dispersion liquid in which organic fine particles are dispersed may be further mixed.

2. Doping The doping of the present invention is obtained by the above-mentioned method for producing a doping, and contains 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 doping.

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 contains the above-mentioned first solvent and second solvent, it contains a small amount of water derived from them.

Specifically, the water content in the dope is preferably 0.5 to 3% by mass with respect to the total solvent contained in the dope. When the content of water in the solvent is 0.5% by mass or more, it is difficult for the rubber particles to swell excessively, and the rubber-like polymer in the rubber particles (having a low affinity with the methacrylic resin) is formed on the particle surface. It can be difficult to expose to. As a result, the compatibility between the rubber particles and the methacrylic resin is less likely to be impaired, and the aggregation of the rubber particles can be easily suppressed. On the other hand, when the content of water in the solvent is 3% by mass or less, the solubility of the methacrylic resin is not easily impaired. From the above viewpoint, the water content may be in the range of 1 to 3% by mass with respect to the total solvent contained in the dope.

In the obtained dope, the aggregation of rubber particles is highly suppressed and the dope is well dispersed. Whether or not 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 the rubber particles in the diluted solution obtained by diluting the dope with an organic solvent having the same composition as the organic solvent constituting the dope until the solid content becomes 1% by mass is (1). It is preferably less than or equal to (primary particle size + 300 nm), more preferably less than or equal to (primary particle size + 100 nm), and more preferably less than or equal to (primary particle size + 50 nm).

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

The primary particle size shall be 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 by TEM. Then, the equivalent circle diameter of 100 arbitrary fine particles is measured, and the average value thereof is defined as the "primary particle diameter".

3. 3. Method for Producing Optical Film The optical film of the present invention is obtained by 1) the step of preparing the above-mentioned dope and 2) casting the obtained dope on a support, and then drying and peeling to obtain a film-like substance. It can be produced through a step and 3) a step of drying the obtained film-like product while stretching it if necessary.

Step 1) Prepare a dope containing a methacrylic resin, rubber particles and a solvent by the above-mentioned method for preparing a dope.

The dope obtained in step 2) is cast on the support. Doping can be cast by discharging from a casting die.

The solvent in the dope cast on the support is then evaporated and dried. The dried dope is stripped from the support to give a film.

The residual solvent amount of the doping at the time of peeling from the support (the residual solvent amount of the film-like substance at the time of peeling) 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 being excessively stretched due to peeling.

The amount of residual solvent in the dope during peeling is defined by the following formula. The same applies to the following.
Residual solvent amount of doping (mass%) = (mass before heat treatment of doping-mass after heat treatment of doping) / mass after heat treatment of doping × 100
The heat treatment for measuring the amount of residual solvent means a 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 doping on the support, the temperature of the support, and the like.

About the step 3) The obtained film-like material is dried. Drying may be carried out in one step or in multiple steps. Further, the drying may be carried out while stretching, if necessary.

For example, the drying step of the 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 stretched film-like material (book). Drying step) and may be included.

(Preliminary 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. When the pre-drying temperature is (Tg-50) ° C. or higher, the solvent is easily volatilized appropriately, so that the transportability (handleability) is easily improved, and when it is (Tg + 50) ° C. or lower, the solvent is not excessively volatilized. , The stretchability in the subsequent stretching step is not easily impaired. The initial drying temperature can be measured as an ambient temperature such as the temperature inside the stretching machine or the hot air temperature when the drying is performed by a non-contact heating type while being conveyed by a tenter stretching machine or a roller.

(Stretching process)
The stretching may be performed according to the required optical characteristics, and is preferably stretched in at least one direction, and stretches in two directions orthogonal to each other (for example, the width direction (TD direction) of the film-like object and orthogonal to it. Biaxial stretching in the transport direction (MD direction)) may be performed.

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

The stretching ratio (%) is defined as (size in the stretching direction of the film after stretching-size in the stretching direction of the film before stretching) / (size in the stretching direction of the film before stretching) × 100. When biaxial stretching is performed, it is preferable to set the stretching ratio in each of the TD direction and the MD direction.

The stretching temperature (drying temperature during stretching) is preferably Tg (° C.) or higher, preferably (Tg + 10) to (Tg + 50) ° C., when the glass transition temperature of the methacrylic resin is Tg, as described above. Is more preferable. When the stretching temperature is Tg (° C.) or higher, preferably (Tg + 10) ° C. or higher, the solvent is easily volatilized, so that the stretching tension can be easily adjusted to an appropriate range. Does not volatilize too much, so the stretchability is not easily impaired. The stretching temperature can be, for example, 90 ° C. or higher. As the stretching temperature, it is preferable to measure the ambient temperature such as the temperature inside the stretching machine in the same manner 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. More preferably.

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

(Main drying process)
From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry the film-like product obtained after stretching. For example, it is preferable that the film-like material obtained after stretching is further dried while being conveyed by 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 is preferably (Tg-40). More preferably, it is ~ (Tg-30) ° C. When the post-drying temperature is (Tg-50) ° C. or higher, it is easy to sufficiently volatilize and remove the solvent from the film-like material after stretching, and when it is (Tg-30) ° C. or lower, the film-like material is highly deformed. Can be suppressed. As the main drying temperature, it is preferable to measure an atmospheric temperature such as a hot air temperature as described above.

4. Optical film The optical film is obtained by the above-mentioned method for producing an optical film, 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 doping. As described above, the rubber particles contain a rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass. As described above, the degree of cross-linking of the rubber-like polymer can be calculated from the charging ratio of the monomers at the time of preparation of the rubber-like 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 adjusting the humidity for 24 hours in an environment of 25 ° C. and 60% RH.

(Haze change amount)
The optical film contains residual water derived from water added in the above-mentioned manufacturing process. As described above, the optical film containing residual water has less change in haze than the optical film containing no residual water even when exposed to high temperature and high humidity for a certain period of time.

Specifically, the haze measured when the optical film is conditioned for 24 hours in a 23 ° C. 55% environment is stored in a haze 1, 60 ° C. 90% environment for 1000 hours, and then in a 23 ° C. 55% environment. When the haze measured when the humidity is adjusted for 24 hours is defined as haze 2, the amount of haze change represented by the following formula (1) is preferably 0.3 or less, and is 0.15 or less. Is more preferable, and 0.1 or less is further preferable.
Equation (1): Haze change amount = haze 2-haze 1

The haze of the optical film and the amount of haze change can be adjusted by the dispersibility of the rubber particles in the dope used. For example, in order to reduce the haze and haze change amount of the optical film, it is preferable to increase the dispersibility of the 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 and the dope preparation step, and the timing of adding the water. 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 is within the above range, and further water is added. Is more preferably performed in the rubber particle dispersion step.

(Glass-transition temperature)
The glass transition temperature (Tg) of the optical film is preferably, for example, 90 to 150 ° C. When the Tg of the optical film is 90 ° C. or higher, not only the heat resistance of the optical film can be improved, but also the drying temperature can be raised during the production of the optical film by the solution casting method, so that the drying property can be easily improved. .. When the Tg of the optical film is 150 ° C. or lower, the content of the structural unit derived from the rigid monomer can be reduced, so that the toughness of the optical film is not easily impaired. The Tg of the optical film is more preferably 95 to 140 ° C. The glass transition temperature of the optical film can be measured by the same method as described above.

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

(Phase difference Ro and Rt)
From the viewpoint of using the optical film as a retardation film for IPS mode, for example, the in-plane retardation Ro measured in an environment with a measurement wavelength of 550 nm and 23 ° C. and 55% RH is preferably 0 to 10 nm. , 0-5 nm, more preferably. The phase difference 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 defined by the following equations, respectively.
Equation (2a): Ro = (nx-ny) × d
Equation (2b): Rt = ((nx + ny) /2-nz) × d
(During the ceremony,
nx represents the refractive index in the in-plane slow-phase axial direction (the direction in which the refractive index is maximized) of the film.
ny represents the refractive index in the direction orthogonal to the in-plane slow phase 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-phase axis of the optical 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 methods.
1) The optical film is humidity-controlled 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 control at a measurement wavelength of 550 nm were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter). Measure in the environment.

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

(Amount of residual solvent)
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 process of manufacturing the optical film.

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 the gas in the container is promptly injected into a gas chromatograph with the container filled with volatile components, and mass spectrometry is performed to identify the compound. The volatile components are quantified while doing so. In the headspace method, it is possible to observe all peaks of volatile components by gas chromatography, and by using an analysis method that utilizes electromagnetic interactions, volatile substances and monomers can be treated with high accuracy. Quantification can also be performed.

(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 has a polarizing element and an optical film of the present invention arranged on at least one surface thereof.

Specifically, the polarizing plate of the present invention is between a polarizing element, an optical film of the present invention arranged on one surface of the polarizing film, an opposing film arranged on the other surface, and between the polarizing element and the optical film. , And an adhesive layer disposed between the polarizer and the opposing film.

5-1. Polarizer A polarizing element is an element that allows only light on a plane of polarization in a certain direction to pass through, and is a polyvinyl alcohol-based polarizing film. The polyvinyl alcohol-based polarizing film includes a polyvinyl alcohol-based film dyed with iodine and a film obtained by dyeing a dichroic dye.

The polyvinyl alcohol-based polarizing film may be a film obtained by uniaxially stretching a polyvinyl alcohol-based film and then dyeing it with iodine or a bicolor dye (preferably a film further subjected to a durability treatment with a boron compound); polyvinyl. An alcohol-based film may be a film that has been dyed with iodine or a bicolor dye and then uniaxially stretched (preferably a film that has been further subjected to a durability treatment with a boron compound). The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

For example, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. has a content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, and a degree of saponification of 99.0 to 99.99 mol%. 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 reduce the thickness of the polarizing plate.

5-2. Optical film The optical film of the present invention is arranged on one surface of the polarizer (preferably 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 other optical film. Examples of other optical films include commercially available cellulose ester films (eg, Konica Minolta Tuck KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC6UY, KC4UY KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd. The above includes Fuji Film Co., Ltd.).

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

5-3. Adhesive layer The adhesive layer can be placed 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 a cured product layer of an active energy ray-curable adhesive.

Examples of the water-based adhesive include a water-based adhesive containing a polyvinyl alcohol-based resin (such as a completely saponified polyvinyl alcohol aqueous solution). The active energy ray-curable adhesive may be a photoradical polymerizable composition or a photocationic polymerizable composition, preferably a light containing an epoxy-based compound and a photocationic polymerization initiator. It can be a cationically polymerizable composition.

The thickness of the adhesive layer is not particularly limited, but may be, for example, 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 have other layers other than the 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 arranged so that the optical film of the present invention is on the liquid crystal cell side, the polarizing plate may further have an adhesive layer arranged on the optical film.

The pressure-sensitive adhesive layer is preferably a pressure-sensitive adhesive composition containing a base polymer, a cross-linking agent and a solvent, which is dried and partially cross-linked. Examples of the pressure-sensitive adhesive composition include an acrylic pressure-sensitive adhesive composition using a (meth) acrylic polymer as a base polymer, a silicone-based pressure-sensitive adhesive composition using a silicone-based polymer as a base polymer, and a rubber-based pressure-sensitive adhesive composition using a rubber as a base polymer. A pressure-sensitive adhesive composition is included. Above all, an acrylic pressure-sensitive adhesive composition is preferable from the viewpoint of transparency, weather resistance, heat resistance, and processability.

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

The surface of the pressure-sensitive adhesive layer can be protected by a release film (for example, a polyester film, a fluororesin film, etc.) that has been subjected to a mold release treatment.

5-5. Method for manufacturing a polarizing plate The polarizing plate of the present invention can be obtained through a step of bonding a polarizing element and an optical film of the present invention via an adhesive. From the viewpoint of enhancing the adhesiveness between the polarizer and the optical film, a step of performing a surface treatment such as a corona treatment may be further performed before the step of bonding.

6. Image Display Device The optical film of the present invention can be used as an optical film for an image display device such as a liquid crystal display device or an organic EL display device, preferably as a polarizing plate protective film for 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 arranged on one surface of the liquid crystal cell, and a second polarizing plate arranged on the other surface of the liquid crystal cell.

The display modes of the liquid crystal cells are, 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. For example, when the liquid crystal display device is used for a smart phone or the like, the IPS mode is preferable.

The first polarizing plate and the second polarizing plate may be arranged so 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 orthogonal to each other (so as to form a cross Nicol).

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 so that the optical film of the present invention is on the liquid crystal cell side.

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

1. 1. Dope and optical film material (1) Methacrylic resin PMMA: Polymethylmethacrylate (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)

The weight average molecular weight and the 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 at a detector RI temperature of 40 ° C., and a styrene-converted value was used.

(Glass-transition temperature)
The glass transition temperature (Tg) of the resin was measured using DSC (Differential Scanning Colorimetry) according to 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 replacing the inside of the polymerization machine with nitrogen gas, the internal temperature was adjusted to 80 ° C., 27 parts by mass of the monomer mixture (c') (methyl methacrylate: 96.5% by mass, butyl acrylate: 3% by mass, and methacrylic acid. Allyl: 0.5% by mass) was added to the polymerization machine in a batch, and then 0.0645 parts by mass of sodium formaldehyde sulfoxylate, 0.0056 parts by mass of -2-sodium ethylenediamine tetraacetate, and 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 another 15 minutes.
Next, 0.0098 parts by mass of sodium hydroxide was added as it was in the form of a 2% by mass aqueous solution, and 0.0852 parts by mass of polyoxyethylene lauryl ether phosphoric acid was added as it was, and the remaining 74% by mass of the mixture was continuously added over 60 minutes. Was added. After 30 minutes from the completion of the addition, 0.069 parts by mass of t-butyl hydroperoxide was added, and the polymerization was continued for another 30 minutes to obtain a hard crosslinked polymer (c).

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, and then 50 parts by mass of the monomer mixture (a') (a') Butyl acrylate: 73% by mass, methyl methacrylate: 25.2% by mass, and allyl methacrylate: 1.8% by mass) were added continuously over 150 minutes. After completion of the addition, 0.015 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, and the polymerization was continued for 120 minutes to obtain an acrylic rubber-like polymer (a).

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 (methyl methacrylate: 95% by mass, butyl acrylate: 5% by mass) of the monomer mixture (b1) was applied over 45 minutes. Was added continuously, and the polymerization was continued for another 30 minutes.

Then, 8 parts by mass (methyl methacrylate: 52% by mass, butyl acrylate: 48% by mass) of the monomer mixture (b2) was continuously added over 25 minutes, and the polymerization was continued for another 60 minutes to carry out the graft copolymerization. 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 size was 200 nm. Further, the glass transition temperature (Tg) of the acrylic rubber-like polymer (a) contained in the rubber particles A1 is −30 ° C., and allyl methacrylate with respect to all the structural units constituting the acrylic rubber-like polymer (a). The content (degree of cross-linking) of the structural unit derived from was 1.8% by mass.

<Preparation of rubber particles A2 to A7>
The graft copolymer (rubber particles) was similar to the rubber particles A1 except that the composition of the monomer mixture (a') was adjusted and the degree of cross-linking in the obtained graft copolymer was changed as shown in Table 1. ) Was obtained.

The composition and physical properties of the rubber particles A1 to A7 are shown in Table 1.

The degree of cross-linking of the rubber particles, the average particle size, and the glass transition temperature (Tg) were measured by the following methods.

(1) Degree of cross-linking The degree of cross-linking is the total mass of the bifunctional or higher polyfunctional monomer used for preparing the rubber-like polymer with respect to the total mass of the monomer used for preparing the rubber-like polymer. The ratio (mass%) was defined as the degree of cross-linking.

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

(3) Glass transition temperature (Tg)
The measurement was performed in the same manner as described above.

2. Doping Preparation <Preparation of Doping 101>
(Preparation of rubber particle dispersion 1)
After stirring and mixing 10.5 parts by mass of rubber particles A1, 168 parts by mass of methylene chloride, and 32 parts by mass of ethanol with a dissolver for 50 minutes, a milder disperser (manufactured by Pacific Machinery & Engineering Co., Ltd.) was used. It was dispersed 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 a rubber particle dispersion 1 (water content in the first solvent: 3.4% by mass). It was.

(Preparation of doping)
Then, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to the pressurized dissolution tank. After adding PMMA to this with 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 Roki 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 in a dissolver. After stirring and mixing for 50 minutes, the mixture was dispersed under a condition of 1500 rpm using a milder disperser (manufactured by Taiheiyo Kiko Co., Ltd.) to obtain a rubber particle dispersion liquid 2.

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

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

(Preparation of doping)
Then, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to the pressurized dissolution tank. To this, the amount of water shown in Table 2 was added, and the mixture was stirred with a dissolver for 10 minutes. Next, the rubber particle dispersion 3 prepared above was added to the mixture with stirring, and then PMMA was further added and stirred to dissolve PMMA. The obtained solution was filtered using SHP150 manufactured by Roki 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 4)
A rubber particle dispersion liquid 4 was obtained in the same manner as the rubber particle dispersion liquid 1 except that the types of rubber particles were changed to those shown in Table 2.

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

<Preparation of dope 105>
A dope 105 was obtained in the same manner as in the preparation of the dope 101 except that the rubber particle dispersion 3 (without water addition) was used.

<Preparation of dope 106>
(Preparation of rubber particle dispersion 5)
After stirring and mixing 10.5 parts by mass of rubber particles A1, 168 parts by mass of methylene chloride, and 32 parts by mass of ethanol with a dissolver for 50 minutes, a milder disperser (manufactured by Pacific Machinery & Engineering Co., Ltd.) was used. It was dispersed 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 a rubber particle dispersion 5 (water content in the first solvent: 2.4% by mass). It was.

(Preparation of doping)
A dope having the following composition was prepared. First, methylene chloride and ethanol were added to the pressurized dissolution tank. To this, the amount of water shown in Table 2 was added, and the mixture was stirred with a dissolver for 10 minutes. Next, the rubber particle dispersion 1 prepared above was added thereto with stirring, and then PMMA was further added and stirred to dissolve PMMA. The obtained solution was filtered using SHP150 manufactured by Roki Techno Co., Ltd. to obtain a 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 dope 107-111>
(Preparation of rubber particle dispersion liquids 6 to 10)
Rubber particle dispersions 6 to 10 were obtained in the same manner as the rubber particle dispersion 1 except that the degree of cross-linking of the rubber particles was changed as shown in Table 2.

(Preparation of doping)
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 Dope 112-114 and 116>
(Preparation of rubber particle dispersions 11 to 13 and 15)
With the 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 with respect to the total non-polar solvent in the obtained dope was the amount shown in Table 2. Similarly, rubber particle dispersions 11 to 13 and 15 were obtained.

(Preparation of doping)
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)
A rubber particle dispersion 14 was obtained in the same manner as the rubber particle dispersion 1 except that the type of non-polar solvent used in the preparation of the rubber particle dispersion was changed as shown in Table 2.

(Preparation of doping)
A dope 115 was obtained in the same manner as in the preparation of the dope 101, except that the obtained rubber particle dispersion was used and the type of non-polar solvent used in the preparation of 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 a methyl methacrylate / phenylmaleimide copolymer (MMA / PhMI = 85/15 mass ratio).

<Evaluation>
The dispersed state of the rubber particles in the obtained dope 101-117 was evaluated by the following method.

(Dispersed 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 became 1% by mass. The dispersed particle size (average particle size) of the rubber particles in the obtained diluted dope was measured by a zeta potential / particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.). Then, the dispersed state of the rubber particles in the doping was evaluated based on the following criteria.
5: Average particle size during dilution dope is primary particle size + 50 nm or less 4: Average particle size during dilution dope is primary particle size + 50 nm or more + 100 nm or less 3: Average particle size during dilution dope is primary particle size + 100 nm or more + 300 nm or less 2 : Average particle size during dilution dope is more than primary particle size + 300 nm + 500 nm or less 1: Average particle size during dilution dope is more than primary particle size + 500 nm

As the primary particle diameter of the rubber particles, the values measured by the following methods were used.
That is, the obtained optical film was cut and the cut surface was observed by TEM. Then, the equivalent circle diameter of 100 arbitrary fine particles was measured, and the average value thereof was taken as the "primary particle diameter".

Table 2 shows the production conditions and evaluation results of the dope 101-117.

3. 3. Fabrication and evaluation of optical films <Preparation of optical films 2001-217>
Using an endless belt casting device, the dope shown in Table 3 was uniformly cast on the stainless belt support at a temperature of 30 ° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled to 28 ° C.

On the stainless belt support, the solvent was evaporated until the amount of residual solvent in the cast dope was 30% by weight. Then, it was peeled from the stainless belt support at a peeling tension of 128 N / m to obtain a film-like material. The amount of residual solvent in the film-like material at the time of peeling was 30% by mass.

Next, while transporting the peeled film with a large number of rollers, the obtained film-like material was subjected to 20 in the width direction (TD direction) under the condition of (Tg + 10) ° C. (Tg: Tg of methacrylic resin) with a tenter. % Stretched. Then, the film was further dried at (Tg-30) ° C. while being conveyed by a roll, and the end portion sandwiched between the tenter clips was slit and wound up to obtain optical films 201 to 217 having a film thickness of 40 μm.

<Evaluation>
The belt stain, MIT flexibility and haze change amount (ΔHz) of the obtained optical films 2001 to 217 were measured by the following methods.

(1) Belt stain The belt stain when the dope spread on the stainless band support was peeled off from the stainless band support was evaluated according to the following criteria.
5: No evaluator can confirm unevenness at all 4: Some evaluators can confirm slight unevenness, but level that can be used as a product without any problem 3: Some evaluators can confirm slight unevenness However, the level that can be used as a product 2: The unevenness may be confirmed depending on the evaluator, and the level that cannot be used as a product 1: The unevenness can be confirmed by many evaluators If it is 3 or more, it is judged to be good.

(2) MIT Flexibility The obtained optical film was cut into a width of 15 mm and a length of 150 mm to prepare a test piece. After allowing this test piece to stand at a temperature of 25 ° C. and a relative humidity of 65% RH for 1 hour or more, a MIT bending test is performed in accordance with JIS P8115: 2001 under the condition of a load of 500 g until the test piece breaks. The number of times was measured. The MIT bending test was performed using a folding resistance tester (manufactured by Tester Sangyo Co., Ltd., MIT, BE-201 type, bending radius of curvature 0.38 mm). Then, it was evaluated according to the following evaluation criteria.
5: Number of times to break is 60,000 or more 4: Number of times to break is 40,000 or more and less than 60,000 3: Number of times to break is 20,000 or more and less than 40,000 2: Until break The number of times is 10,000 or more and less than 20,000 times 1: The number of times until breaking is less than 10,000 times The greater the number of times until breaking, the better the flexibility and the better the resistance to repeated bending.
If it is 3 or more, it is judged to be good.

(3) Haze (initial value, amount of change (ΔHz))
1) Five points in the width direction of the obtained optical film (the central part and the end part of the film (positions of 5% of the total width from both ends), and two points in the middle part between the central part and the end part) in the longitudinal direction. Sampling was performed every 100 m, and a sample having a size of ^{5 cm 2 was prepared.}
2) Next, for each of the obtained samples, after adjusting the humidity for 24 hours in an environment of 25 ° C. and 60% RH, the haze was measured using a haze meter (NDH 2000: manufactured by Nippon Denshoku Kogyo Co., Ltd.). The average value thereof was defined as haze 1 (initial value).
3) Next, each of the obtained samples was left to stand in an environment of 60 ° C. and 90% RH for 1000 hours. Then, after humidity control 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) The amount of change in haze (ΔHz) was calculated by applying the haze 1 (initial value) obtained in 2) above and the haze 2 (after the durability test) obtained in 3) above to the following formula.
Equation (1): Haze change amount (ΔHz) = Haze 2 (after endurance 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 The amount of change (ΔHz) is more than 0.3 and 0.4 or less 1: If the amount of change in haze (ΔHz) is more than 0.4 and 3 or more, it is judged to be good.

The evaluation results of the optical films 2001-217 are shown in Table 3.

As shown in Table 3, the optical films 201-204, 206-209, 212-215 and 217 (the present 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 described. It can be seen that the belt is less dirty. It is considered that this is because the aggregation of the rubber particles was suppressed. It can also be seen that since these optical films originally contain an appropriate amount of water due to the addition of water during the manufacturing process, the change in haze 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 to either the rubber particle dispersion step or the dope preparation step causes belt stains. It is considered that this is because a large amount of agglomerates of rubber particles are contained. Further, it can be seen that since water is not added to the optical film 205 in the manufacturing process, the original water content is small and the haze changes significantly before and after the durability test.

Further, it can be seen that when the amount of water added is small, the aggregation of rubber particles cannot be sufficiently suppressed, so that the belt stains and changes in haze are large (optical film 216). On the other hand, if the amount of water added is too large, the resin is not sufficiently dissolved in the solvent, resulting in poor compatibility. Therefore, it can be seen that the initial haze value tends to increase and the flexibility is low (optical film 214). ..

Further, it can be seen that when the degree of cross-linking of the rubber particles is low, the rubber particles tend to aggregate, so that belt stains are likely to occur (optical film 210). On the other hand, if the degree of cross-linking of the rubber particles is too high, it can be seen that 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, which can suppress agglomeration of rubber particles and can impart an optical film having sufficient toughness without impairing transparency.

Claims (12)

A step of preparing a rubber particle dispersion liquid by dispersing rubber particles containing a rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass in a first solvent.
The step of mixing the rubber particle dispersion liquid, the methacrylic resin, and the second solvent to prepare a dope containing the methacrylic resin, the rubber particles, and the solvent is included.
At least one of the first solvent and the second solvent contains water and contains water.
The content of the water is 0.5 to 3% by mass with respect to the solvent contained in the dope.
A method for producing a dope for an optical film. The first solvent contains water.
The method for producing a doping for an optical film according to claim 1. The step of preparing the rubber particle dispersion is
A step of dispersing the rubber particles in an organic solvent constituting the first solvent, and
Including a step of adding water to the rubber particles dispersed in the organic solvent.
The method for producing a doping for an optical film according to claim 2. The rubber particles are core-shell type particles having a core portion containing the rubber-like polymer and a shell portion containing another polymer graft-polymerized on the rubber-like polymer.
The method for producing a doping for an optical film according to any one of claims 1 to 3. The rubber-like polymer is an acrylic rubber-like 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 an alkyl methacrylate as a main component.
The method for producing a doping for an optical film according to claim 4. The methacrylic resin contains 80% by mass or more of structural units derived from methyl methacrylate with respect to all the structural units constituting the methacrylic resin.
The method for producing a doping for an optical film according to claim 5. A dope for an optical film containing a methacrylic resin, rubber particles containing a rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass, and a solvent.
The solvent contains 0.5 to 3% by weight of water.
Dope for optical films. The rubber particles are core-shell type particles having a core portion containing the rubber-like polymer and a shell portion containing another polymer graft-polymerized on the rubber-like polymer.
The dope for the optical film according to claim 7. An optical film containing a methacrylic resin and rubber particles containing a rubber-like polymer having a degree of cross-linking of 0.25 to 4% by mass.
The haze measured when the optical film was conditioned for 24 hours in a 23 ° C. 55% environment was stored for 1000 hours in a haze 1, 60 ° C. 90% environment, and then adjusted for 24 hours in a 23 ° C. 55% environment. When the haze measured when moistened is haze 2,
The amount of haze change represented by the following equation (1) is 0.3 or less.
Optical film.
Equation (1): Haze change amount = haze 2-haze 1 The rubber particles are core-shell type particles having a core portion containing the rubber-like polymer and a shell portion containing another polymer graft-polymerized on the rubber-like polymer.
The optical film according to claim 9. Polarizer and
The optical film according to claim 9 or 10, which is arranged on at least one of the surfaces thereof.
Polarizer. A step of preparing a doping by the method for producing a doping for an optical film according to any one of claims 1 to 6.
A step of casting the dope on a support and then peeling it off to obtain a film-like substance.
A method for manufacturing an optical film.