JP2023147507A - Method for producing resin film - Google Patents

Abstract

To provide a method for producing a resin film having a low haze and suppressed foaming by a solution casting method using a solidified product of a (meth)acrylic polymer synthesized by emulsion polymerization.SOLUTION: There is provided a method for producing a resin film which comprises: a step of obtaining a latex of a (meth)acrylic polymer by emulsion polymerization; a step of coagulating the (meth)acrylic polymer by adding a coagulant to the latex, followed by separating the (meth)acrylic polymer from the water phase; a step of mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope; and a step of casting the dope on a support surface, followed by evaporating the solvent.SELECTED DRAWING: None

Description

The present invention relates to a method of manufacturing a resin film by a solution casting method.

In recent years, TAC (triacetyl cellulose), which is used in the polarizer protective film of LCD displays, has become larger and has higher definition. Due to its high moisture permeability and water absorption, panels may warp during transportation, resulting in poor image quality. Issues causing the decline are becoming apparent.

Acrylic resin films have excellent optical properties, low moisture permeability, and low water absorption, and are therefore attracting attention as an alternative film to TAC films.

Patent Document 1 discloses that when forming an acrylic resin into a film using a solution casting method, by optimizing conditions such as the amount of residual solvent and temperature in the drying process, whitening of the obtained film and problems that occur in the film can be prevented. Techniques for suppressing air bubbles have been disclosed.

In addition, Patent Document 2 discloses that optical properties and dimensional stability can be improved by using an acrylic polymer obtained by suspension polymerization in the presence of a suspension polymerization dispersant having a specific structure in a solution casting method. It is disclosed that a film with excellent adhesiveness can be obtained.

On the other hand, emulsion polymerization is known as one of the polymerization methods for producing a (meth)acrylic polymer that is the main component of an acrylic resin film.
As a method for separating a polymer from a latex obtained by emulsion polymerization, it is possible to apply a drying method such as heat drying or spray drying to the latex, but the drying method requires a large amount of energy.
As a method that can reduce energy consumption compared to drying methods, a method is known in which a coagulant is added to latex after emulsion polymerization to coagulate the resin component, and then separated from the aqueous phase (for example, Patent Document 3).

Unexamined Japanese Patent Publication No. 2014-177089 Special table 2019-533203 publication Japanese Patent Application Publication No. 2013-124282

When a resin film is produced by a solution casting method using a coagulated product of (meth)acrylic polymer separated from the aqueous phase using a coagulant after emulsion polymerization, the haze of the resulting resin film worsens. It was found that the film may contain fine air bubbles.

In view of the above-mentioned current situation, the present invention provides a method for producing a resin film with low haze and suppressed foaming by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization. The purpose is to provide.

As a result of extensive studies, the present inventor has discovered that when manufacturing a resin film by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization, The inventors have discovered that by using at least ethanol as a solvent for the dope, the resulting resin film has a low haze and foaming can be suppressed, leading to the completion of the present invention.

That is, the present invention comprises a step of obtaining a latex of a (meth)acrylic polymer by emulsion polymerization,
After adding a coagulant to the latex to coagulate the (meth)acrylic polymer, separating the (meth)acrylic polymer from the aqueous phase;
A resin film comprising: mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope, and evaporating the solvent after casting the dope on the surface of a support. Relating to a manufacturing method.
Preferably, the coagulant is an inorganic salt or an acid.
Preferably, the inorganic salt is a calcium salt or a magnesium salt.
Preferably, the content of ethanol in the solvent is 1 to 25% by weight.
Preferably, the solvent further includes methylene chloride.
Preferably, the (meth)acrylic polymer is a polymer having constitutional units of 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable therewith. be.
Preferably, the other copolymerizable monomer unit is a (meth)acrylic acid ester unit (excluding a methyl methacrylate unit) whose ester moiety has 1 to 20 carbon atoms, and/or a substituted or contains an unsubstituted maleimide unit.
Preferably, the (meth)acrylic polymer is a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b), and ) The proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight. .
Preferably, the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more and 99% by weight or less of methyl methacrylate units.
Preferably, the non-crosslinked methacrylic polymer component (b) includes a substituted or unsubstituted maleimide unit, and a methacrylic acid ester unit whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure. Contains at least one of these.
The present invention also relates to a dope containing a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization and a solvent containing ethanol.
Furthermore, the present invention also relates to a method for producing a resin film, which includes a step of evaporating the solvent after casting the dope onto the surface of a support.

According to the present invention, there is provided a method for producing a resin film with low haze and suppressed foaming by a solution casting method using a coagulated product of a (meth)acrylic polymer synthesized by emulsion polymerization. I can do it.
The resin film obtained by the present invention contains fewer fine air bubbles, has an excellent appearance, and can be a highly transparent film. Since such a resin film has few optical defects and high light extraction efficiency, it can be suitably used as an optical film for liquid crystal display members, particularly as a polarizer protective film.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments.
The method for producing a resin film according to the present embodiment includes obtaining a latex of a (meth)acrylic polymer by emulsion polymerization, adding a coagulant to the latex to coagulate the (meth)acrylic polymer, and then A resin film is formed by separating the polymer from the aqueous phase, mixing the polymer with a solvent containing ethanol to form a dope, casting the dope onto a support surface, and then evaporating the solvent. It manufactures.

((meth)acrylic polymer)
First, two types of aspects of the (meth)acrylic polymer in this embodiment will be described. Note that "(meth)acrylic" is a collective expression of acrylic and methacryl, and means acrylic and/or methacryl.

<(Meth)acrylic polymer according to the first embodiment>
The (meth)acrylic polymer according to the first embodiment is a polymer whose constituent units are 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable therewith. It may be a combination. The (meth)acrylic polymer is preferably a polymer that does not have a crosslinked structure.

From the viewpoint of appearance and weather resistance, the (meth)acrylic polymer according to the first embodiment may contain methyl methacrylate units in an amount of 30% by weight or more, but not more than 50% by weight. The content is preferably 60% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more. Further, from the viewpoint of optical properties and heat resistance, the upper limit is preferably 99.9% by weight or less, more preferably 99% by weight or less, even more preferably 97% by weight or less, and 95% by weight. The following is particularly preferable. From the viewpoint of processability and appearance, the (meth)acrylic polymer preferably does not contain a polyfunctional monomer unit having two or more polymerizable functional groups in the molecule.

Other monomer units copolymerizable with the methyl methacrylate unit include, for example, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, and methacrylate. Octyl, stearyl methacrylate, glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxylethyl methacrylate, 2-hydroxylpropyl methacrylate, dicyclopentanyl methacrylate, 2,2,2 methacrylate - trifluoroethyl, 2,2,2-trichloroethyl methacrylate, isobornyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, glycidyl acrylate, (Meth)acrylic acid ester units having 1 to 20 carbon atoms in the ester moiety, such as epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate (excluding methyl methacrylate); (Meth)acrylamide units such as methacrylamide, N-methylolmethacrylamide, acrylamide, N-methylolacrylamide; Carboxylic acids and their salts such as methacrylic acid and acrylic acid; Vinyl cyanide units such as acrylonitrile and methacrylonitrile; styrene, α - Vinyl arene units such as methylstyrene, monochlorostyrene, dichlorostyrene; maleimide units such as N-phenylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide; maleic acid, fumaric acid and their esters; vinyl chloride, bromide Vinyl halides such as vinyl and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; and alkenes such as ethylene, propylene, butylene, butadiene, and isobutylene. These monomers can be used alone or in combination of two or more.

Among these, preferred are (meth)acrylic acid ester units (excluding methyl methacrylate), vinyl arene units, and/or substituted or unsubstituted maleimide units in which the ester moiety has 1 to 20 carbon atoms; Particularly preferred are (meth)acrylic acid ester units having a carbon number of 1 to 20 (excluding methyl methacrylate) and/or substituted or unsubstituted maleimide units.

The (meth)acrylic polymer is used to produce a resin film using a solution casting method. Therefore, as the other copolymerizable monomer unit, it is preferable to include a drying accelerating comonomer that increases the volatilization rate of the solvent as a structural unit.

Examples of drying accelerating comonomer units that have good heat resistance and can increase the volatilization rate of solvents include substituted or unsubstituted maleimide units, and primary or secondary ester moieties having 2 to 8 carbon atoms. A methacrylic acid ester unit that is a class hydrocarbon group or an aromatic hydrocarbon group, a methacrylic acid ester unit that is a saturated hydrocarbon group with 7 to 16 carbon atoms in which the ester moiety has a condensed ring structure, and a methacrylic acid ester unit in which the ester moiety has an ether bond. It is preferable that it is at least one selected from the group consisting of methacrylic acid ester units, which are linear or branched groups, and vinyl arene units. By using these drying-accelerating comonomer units, it is possible to increase the rate of solvent volatilization from the cast membrane in the solution casting method while the (meth)acrylic polymer has excellent heat resistance. Become.

Examples of the maleimide unit include N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, and the like, with N-phenylmaleimide, N-benzylmaleimide, and N-cyclohexylmaleimide being preferred.

Examples of the methacrylic acid ester unit in which the ester moiety is a primary or secondary hydrocarbon group having 2 to 8 carbon atoms, or an aromatic hydrocarbon group include ethyl methacrylate, propyl methacrylate, and n-methacrylate. -butyl, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, phenyl methacrylate, benzyl methacrylate, and the like. Among these, ethyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and benzyl methacrylate are preferred.

Examples of the methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure include dicyclopentanyl methacrylate, isobornyl methacrylate, and the like. The number of carbon atoms in the saturated hydrocarbon group is preferably 8 to 14, more preferably 9 to 12. Further, the fused ring structure is not particularly limited, but is preferably a structure in which two five-membered rings are fused by three consecutive carbon atoms.

Examples of the methacrylic acid ester unit in which the ester moiety is a linear or branched group containing an ether bond include 2-methoxyethyl methacrylate.

Examples of the vinyl arene unit include styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, and the like. Among these, styrene is preferred.

The (meth)acrylic polymer according to the first embodiment may contain 0 to 70% by weight of the other copolymerizable monomer units based on the total amount of structural units of the polymer. However, since optical properties and heat resistance can be adjusted, the (meth)acrylic polymer preferably contains 0.1% by weight or more, and preferably 1% by weight or more of the other copolymerizable monomer units. It is more preferable that the content is 3% by weight or more, and it is particularly preferable that the content is 5% by weight or more. Further, the upper limit is preferably 50% by weight or less, more preferably 40% by weight or less, even more preferably 30% by weight or less, and particularly preferably 20% by weight or less.

The (meth)acrylic polymer according to the first aspect preferably has a ring structure in its main chain because it has excellent heat resistance. Examples of the ring structure include a glutarimide ring structure, a lactone ring structure, a structure derived from maleic anhydride, a substituted or unsubstituted maleimide ring structure, and a glutaric anhydride ring structure. Also included are acrylic resins containing (meth)acrylic acid structural units in their molecules. Specifically, maleimide acrylic resin (acrylic resin in which an unsubstituted or N-substituted maleimide compound is copolymerized as a copolymerization component), glutarimide acrylic resin, lactone ring-containing acrylic resin, hydroxyl group and/or The aromatic ring of a styrene-containing (meth)acrylic polymer obtained by polymerizing an acrylic resin or methacrylic resin containing a carboxyl group, a styrene monomer, and other monomers copolymerizable therewith is partially hydrogenated. Examples include (meth)acrylic polymers containing partially hydrogenated styrene units obtained by adding styrene units, and (meth)acrylic polymers having a cyclic acid anhydride structure such as a glutaric anhydride structure or a structure derived from maleic anhydride. It will be done.

Among these, a glutarimide ring structure and a substituted or unsubstituted maleimide ring structure are particularly preferable because they can effectively improve the heat resistance of the resin film and have an excellent balance with optical properties. These may be used in combination, and can impart optical properties, high thermal stability, and solvent resistance to the (meth)acrylic polymer.

The weight average molecular weight of the (meth)acrylic polymer according to the first embodiment is not particularly limited, but from the viewpoint of making the resulting resin film tough and achieving a balance with good film formability, It is preferably 1,000,000 to 3,500,000, more preferably 800,000 to 3,500,000, even more preferably 800,000 to 3,000,000, and particularly preferably 1,000,000 to 3,000,000. The weight average molecular weight may be from 800,000 to 2,500,000, or from 800,000 to 2,000,000.

In addition, when forming a film by melt extrusion, it is necessary to melt the (meth)acrylic polymer to lower the viscosity, so the molecular weight of the polymer needs to be relatively low. However, in this embodiment, since the film is formed by a solution casting method, the film can be easily formed even if the polymer has a high molecular weight. From this viewpoint, the weight average molecular weight of the (meth)acrylic polymer may be 500,000 or more.
The weight average molecular weight can be calculated by standard polystyrene conversion method using gel permeation chromatography (GPC).

It is preferable that the (meth)acrylic polymer according to the first aspect has excellent heat resistance, and the glass transition temperature can be used as an index indicating the heat resistance. The (meth)acrylic polymer preferably exhibits a glass transition temperature of 110°C or higher, more preferably 114°C or higher, even more preferably 115°C or higher, even more preferably 119°C or higher, particularly preferably 122°C or higher. , 125°C or higher is most preferred.

<(Meth)acrylic polymer according to second embodiment>
The (meth)acrylic polymer according to the second aspect may be a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b). . Below, the (meth)acrylic polymer according to the second embodiment is also referred to as a graft copolymer.

Since the crosslinked (meth)acrylic polymer particles (a) are a rubber component, they can contribute to improving strength. Moreover, excellent heat resistance can be achieved by the non-crosslinked methacrylic polymer component (b). In contrast to a system formed by mixing a core-shell graft copolymer with a methacrylic resin, the crosslinked (meth)acrylic polymer particles (a) correspond to the core rubber component in the core-shell graft copolymer, The non-crosslinked methacrylic polymer component (b) may correspond to the methacrylic resin that is the matrix.

At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). The graft bond can be realized by producing a graft copolymer by emulsion polymerization as described below. Due to this production method, the graft copolymer may also contain a non-crosslinked methacrylic polymer component (b) that is not graft-bonded to the crosslinked (meth)acrylic polymer particles (a).

The graft copolymer according to the second aspect has a structure in which crosslinked (meth)acrylic polymer particles (a) having a small particle size are dispersed in a high molecular weight non-crosslinked methacrylic polymer component (b). Therefore, aggregation of the crosslinked (meth)acrylic polymer particles (a) in the graft copolymer is difficult to proceed. As a result, the graft copolymer according to the second embodiment has good stability whether it is stored in powder form or as a dope dissolved in a solvent. Further, since aggregation of the crosslinked (meth)acrylic polymer particles (a) is suppressed, the graft copolymer according to the second aspect also has the advantage of being easily soluble in a solvent.

(Crosslinked (meth)acrylic polymer particles (a))
The crosslinked (meth)acrylic polymer particles (a) are (meth)acrylic rubber particles. By containing the crosslinked (meth)acrylic polymer particles (a), the graft copolymer according to the second embodiment can achieve high strength when formed into a film, for example.

It is preferable that the crosslinked (meth)acrylic polymer particles (a) have a relatively small particle size, and specifically, it is preferable that the average particle size is 150 nm or less. By using crosslinked (meth)acrylic polymer particles having such a small particle size, a low haze can be achieved when the graft copolymer according to the second embodiment is formed into a film, for example. Further, by reducing the size of the crosslinked (meth)acrylic polymer particles, there is no need to match the refractive index of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b). As a result, it is possible to adopt a monomer composition that lowers the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) without considering the refractive index. High strength can be achieved when

From the viewpoint of low haze, the average particle diameter is more preferably 130 nm or less, even more preferably 120 nm or less, even more preferably 110 nm or less, and particularly preferably 100 nm or less. The lower limit of the average particle diameter is not particularly limited, but from the viewpoint of film strength or ease of particle production, it is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 60 nm or more. The average particle diameter is the volume average particle diameter, and can be measured in the latex state of the crosslinked (meth)acrylic polymer particles (a) using a commercially available measuring device (for example, Microtrac UPA150 manufactured by Nikkiso Co., Ltd.). I can do it. Further, the average particle diameter can be controlled by adjusting the conditions during particle preparation (specifically, the type and amount of emulsifier, stirring conditions during emulsion polymerization, etc.).

The crosslinked (meth)acrylic polymer particles (a) preferably exhibit a glass transition temperature of −10° C. or lower. By using crosslinked (meth)acrylic polymer particles having such a low glass transition temperature, high strength can be achieved when the graft copolymer is formed into a film, for example. The glass transition temperature can be controlled by adjusting the type and ratio of monomers constituting the crosslinked (meth)acrylic polymer particles (a).

The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is more preferably -20°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, particularly preferably -45°C or lower. The lower limit of the glass transition temperature is not particularly limited, but for example, it is preferably -130°C or higher, more preferably -110°C or higher, even more preferably -100°C or higher, even more preferably -80°C or higher, and even more preferably -70°C or higher. is particularly preferred. The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is calculated using the Fox equation using the values described in the Polymer Hand Book (J. Brandrup, Interscience 1989). (For example, n-butyl polyacrylate is -54°C).

The crosslinked (meth)acrylic polymer particles (a) are crosslinked (meth)acrylic polymers obtained by polymerizing a monomer component containing a (meth)acrylic monomer and a polyfunctional monomer. It is a particle formed from. The monomer components other than the polyfunctional monomer contain an acrylic monomer and/or a methacrylic monomer, and preferably contain at least an acrylic monomer.

The acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a) is preferably an acrylic acid alkyl ester in which the alkyl group has 1 to 8 carbon atoms. Specific examples include ethyl acrylate, n-butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. As the acrylic acid alkyl ester, only one type may be used, or two or more types may be used in combination. Among them, n-butyl acrylate is preferred.

As the optional methacrylic monomer that can be contained in the crosslinked (meth)acrylic polymer particles (a), methacrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms are preferred. Specific examples include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, and octyl methacrylate. As the methacrylic acid alkyl ester, only one type may be used, or two or more types may be used in combination. Among these, methacrylic acid alkyl esters in which the alkyl group has 1 to 4 carbon atoms are preferred. Particularly preferred is methyl methacrylate.

In the crosslinked (meth)acrylic polymer particles (a), monomers other than the above-mentioned acrylic acid alkyl ester and methacrylic acid alkyl ester may be used. Examples of such monomers include acrylic acid esters other than the above-mentioned acrylic acid alkyl esters, methacrylic acid esters other than the above-mentioned methacrylic acid alkyl esters, aromatic vinyl monomers, and other copolymerizable vinyl monomers. It will be done. Examples of acrylic esters other than the alkyl acrylic esters include phenyl acrylate, benzyl acrylate, cyclohexyl acrylate, and isobornyl acrylate. Examples of methacrylic esters other than the alkyl methacrylates include phenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate. Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, chlorostyrene, and other styrene derivatives. Examples of the other copolymerizable vinyl monomers include unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile, α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and acetic acid. Vinyl, olefinic monomers such as ethylene and propylene, halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, vinylidene fluoride, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-phenyl Examples include maleimide monomers such as maleimide and No-chlorophenylmaleimide. Any of these may be used alone or in combination of two or more.

From the viewpoint of strength and heat resistance, the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) are selected from among the monomer components excluding polyfunctional monomers, acrylic esters (especially alkyl esters) Acrylic acid alkyl ester whose group has 1 to 8 carbon atoms) preferably contains 70% by weight or more and 100% by weight or less, more preferably 80% by weight or more and 100% by weight or less, and 90% by weight or more and 100% by weight. It is more preferable that the content is below, and it is especially preferable that the content is 95% by weight or more and 100% by weight or less.

The crosslinked (meth)acrylic polymer particles (a) can be formed by polymerizing the monomer components in the presence of a polyfunctional monomer. The polyfunctional monomer is also known as a crosslinking agent or a crosslinkable monomer, and is a compound having two or more unsaturated bonds in one molecule that can be copolymerized with a (meth)acrylic monomer. It is. Specifically, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, alkylene glycol. Examples include diacrylate. These may be used alone or in combination of two or more. Preferably it is allyl methacrylate.

The amount of the polyfunctional monomer used can be set as appropriate from the viewpoint of strength, but specifically, the amount of the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) , monomer components excluding polyfunctional monomers) may be about 0.1 parts by weight or more and 5.0 parts by weight or less based on 100 parts by weight. However, from the viewpoint of the strength of the graft copolymer, the amount of the polyfunctional monomer used is preferably 0.2 to 3.5 parts by weight, more preferably 0.2 to 3.0 parts by weight, and .3 to 2.0 parts by weight is more preferred, and 0.4 to 1.5 parts by weight is particularly preferred.

(Non-crosslinked methacrylic polymer component (b))
The non-crosslinked methacrylic polymer component (b) is mainly composed of polymerized methacrylic monomers and does not have a crosslinked structure (that is, obtained by polymerization without using a polyfunctional monomer). It is a combination. At least a part of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), so that the crosslinked (meth)acrylic polymer particles (a) becomes less likely to aggregate, the graft copolymer according to the second embodiment has good storage stability, and also can achieve low haze when formed into a film.

The non-crosslinked methacrylic polymer component (b) is preferably a high molecular weight polymer, and specifically preferably has a weight average molecular weight of 250,000 or more. Since the non-crosslinked methacrylic polymer component (b) has a high molecular weight, the graft copolymer according to the second embodiment can achieve high heat resistance and can be formed into a film by a solution casting method. becomes. The weight average molecular weight is more preferably 300,000 or more, further preferably 350,000 or more, even more preferably 400,000 or more, particularly preferably 450,000 or more, from the viewpoint of facilitating film formation by solution casting. The upper limit of the weight average molecular weight is not particularly limited, but from the viewpoint of facilitating film formation by solution casting, it is preferably 1,000,000 or less, and more preferably 900,000 or less.

From the viewpoint of heat resistance of the graft copolymer, the non-crosslinked methacrylic polymer component (b) preferably exhibits a glass transition temperature of 115°C or higher, more preferably 118°C or higher, and even more preferably 120°C or higher. The upper limit of the glass transition temperature is not particularly limited, but may be, for example, 160°C or lower, or 150°C or lower. The glass transition temperature can be controlled by adjusting the type and ratio of monomers constituting the non-crosslinked methacrylic polymer component (b). The glass transition temperature of the non-crosslinked methacrylic polymer component (b) was calculated using the Fox formula using the values listed in the Polymer Hand Book (J. Brandrup, Interscience 1989). (for example, polymethyl methacrylate is 105°C).

The non-crosslinked methacrylic polymer component (b) is a polymer mainly composed of methacrylic monomer units. From the viewpoint of heat resistance and film formation of the graft copolymer, the methacrylic monomer unit is preferably a methyl methacrylate unit. In particular, it is preferable that the monomer components constituting the non-crosslinked methacrylic polymer component (b) contain 70% by weight or more and 99% by weight or less of methyl methacrylate units. This improves heat resistance and makes it easier to form a film by solution casting. The content of methyl methacrylate units is more preferably 75 to 98% by weight, even more preferably 80 to 97% by weight, even more preferably 85 to 96% by weight, even more preferably 88 to 95% by weight, and even more preferably 90 to 95% by weight. % by weight is particularly preferred.

The non-crosslinked methacrylic polymer component (b) contains, as a monomer unit other than the methyl methacrylate unit, the drying accelerating comonomer described in relation to the (meth)acrylic polymer according to the first embodiment as a structural unit. is preferred. By including such a monomer unit, the heat resistance of the graft copolymer is not significantly reduced, and when the solvent is evaporated from the cast film when producing a film by the solution casting method, the It becomes possible to increase the volatilization speed. The specific type of the drying-promoting comonomer is the same as that described above regarding the (meth)acrylic polymer according to the first embodiment, so a description thereof will be omitted.

In addition to increasing the volatilization rate of the solvent from the cast membrane in the solution casting method, it is possible to further improve the heat resistance of the graft copolymer, so the non-crosslinked methacrylic polymer component (b) The drying accelerating comonomer unit contains at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure. is preferred.

At this time, as the drying accelerating comonomer unit, at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure Although only the seeds may be used, at least one of a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a condensed ring structure is used. , drying accelerating comonomer units other than these may be used in combination. By using such a combination, it is possible to adjust the heat resistance of the graft copolymer and the volatilization rate of the solvent, thereby increasing both in a well-balanced manner.

The drying accelerating comonomer units other than the substituted or unsubstituted maleimide unit and the methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms having a condensed ring structure are those in which the ester moiety is a carbon atom as described above. A methacrylic acid ester unit that is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having numbers 2 to 8, a methacrylic acid ester unit whose ester moiety is a linear or branched group containing an ether bond. , and at least one selected from the group consisting of vinyl arene units.

Among the monomer components constituting the non-crosslinked methacrylic polymer component (b), the proportion of the drying accelerating comonomer unit is preferably 1% by weight or more and 30% by weight or less, more preferably 2 to 25% by weight. It is preferably 3 to 20% by weight, more preferably 4 to 18% by weight, even more preferably 4 to 15% by weight, even more preferably 4 to 12% by weight, and particularly preferably 5 to 10% by weight. When two or more types of drying accelerating comonomer units are included, the ratio of drying accelerating comonomer units refers to the proportion of the total amount of all included drying accelerating comonomer units to all monomer units. With such a weight ratio, the graft copolymer has excellent heat resistance, and the volatilization rate of the solvent in the solution casting method can be increased. Note that the weight ratio of each of these units can be determined by proton nuclear magnetic resonance spectroscopy.

The non-crosslinked methacrylic polymer component (b) may be a copolymer that does not contain other comonomer units that do not fall under drying accelerating comonomer units, or may contain other comonomer units that do not fall under drying accelerating comonomer units. It may be a copolymer containing Such other comonomers include, for example, glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,2,2-trifluoroethyl Methacrylic acid esters such as methacrylate, 2,2,2-trichloroethyl methacrylate, methacrylamide, N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate , benzyl acrylate, octyl acrylate, glycidyl acrylate, epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, N-methylolacrylamide, and other acrylic esters; methacrylic acid , carboxylic acids such as acrylic acid and their salts; vinyl cyanates such as acrylonitonyl and methacrylonitrile; maleic acid, fumaric acid and their esters, etc.; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl formate , vinyl esters such as vinyl acetate and vinyl propionate; and alkenes such as ethylene, propylene, butylene, butadiene and isobutylene. The proportion of such other comonomer units in the monomer components constituting the non-crosslinked methacrylic polymer component (b) is preferably 10% by weight or less, more preferably 8% by weight or less. The content is preferably 5% by weight or less, and more preferably 5% by weight or less.

In the graft copolymer according to the second aspect, crosslinked (meth)acrylic polymer particles (a) out of the total of crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer component (b) ) is preferably 1% by weight or more and less than 50% by weight, and the proportion occupied by the non-crosslinked methacrylic polymer component (b) is preferably 99% by weight or less and more than 50% by weight. Since the graft copolymer according to the second aspect contains a high proportion of the non-crosslinked methacrylic polymer component (b), the crosslinked (meth)acrylic polymer particles (a) are difficult to aggregate, have high strength and It becomes possible to form a film with low haze, and the storage stability of the graft copolymer or its dope can be improved. The proportion occupied by the crosslinked (meth)acrylic polymer particles (a) is preferably from 3% by weight to 45% by weight, more preferably from 4 to 40% by weight, even more preferably from 5 to 35% by weight, and from 6 to 30% by weight. % by weight is particularly preferred.

Furthermore, from the viewpoint of bending resistance of the resulting film, crosslinked (meth)acrylic polymer particles (out of the total of crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer component (b)) The proportion of a) is preferably 5% by weight or more, more preferably 6% by weight or more, and even more preferably 7% by weight or more. From the viewpoint of moisture permeability and elastic modulus, the upper limit of the ratio is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 15% by weight or less, even more preferably 12% by weight or less, and 10% by weight or less. Particularly preferred is less than % by weight. From the viewpoint of the balance between moisture permeability, elastic modulus, and bending resistance, it is preferably 6% by weight or more, more preferably 7% by weight or more, and preferably 20% by weight or less, more preferably 15% by weight or less, and 12% by weight. % or less is more preferable, and 10% by weight or less is particularly preferable.

(emulsion polymerization)
In this embodiment, the (meth)acrylic polymer can be formed by normal emulsion polymerization using an emulsifier and a polymerization initiator. By carrying out emulsion polymerization, a latex of the above-mentioned (meth)acrylic polymer can be obtained.

In particular, when producing the graft copolymer according to the second embodiment, after forming crosslinked (meth)acrylic polymer particles (a) by emulsion polymerization, a non-crosslinked methacrylic polymer is added to the polymerization system. A non-crosslinked methacrylic polymer component (b) may be formed by adding the monomer component constituting component (b) and then performing emulsion polymerization. Thereby, a graft copolymer in which at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a) can be produced. As a result, a structure can be obtained in which the crosslinked (meth)acrylic polymer particles (a) are sufficiently dispersed in the non-crosslinked methacrylic polymer component (b).

The emulsifier is not particularly limited, but includes, for example, sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate (sodium di(2-ethylhexyl) sulfosuccinate), sodium lauryl sulfate, sodium fatty acid, polyoxyethylene lauryl ether phosphate. Examples include anionic surfactants such as phosphate ester salts such as sodium chloride, nonionic surfactants, and the like. These surfactants may be used alone or in combination of two or more.

Sulfonate salts are preferred as the emulsifier because they can highly suppress foaming marks during film formation and drying and also have excellent polymerization stability. Examples of the sulfonate include dialkyl sulfosuccinate, alkanesulfonate, alpha olefin sulfonate, alkylbenzene sulfonate, naphthalene sulfonate-formaldehyde condensate, alkylnaphthalene sulfonate, N-methyl-N - Examples include acyl taurine salts. Among these, dialkyl sulfosuccinates or alkylbenzene sulfonates are preferred.

The sulfonate is not particularly limited, but may be a lithium salt, a sodium salt, a potassium salt, a calcium salt, a magnesium salt, or the like. In particular, from the viewpoint of effectively suppressing foam marks, it is preferable to contain at least one selected from the group consisting of lithium salts, sodium salts, and potassium salts. When the sulfonate exists as a salt of these monovalent cations, even if the salt remains in the (meth)acrylic polymer, the salt dissolves in the ethanol in the dope solvent, forming a solution. Since it is thought that the salt is finely dispersed in the dope, foaming during film formation and drying can be suppressed.

As the polymerization initiator, known ones can be used, such as persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; tert-butyl hydroperoxide, tert-butyl peroxyisopropyl carbonate. , cumene hydroperoxide, paramenthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di8,5,5-trimethylhexanoyl peroxide, dilauroyl peroxide, benzoyl peroxide, etc. Examples include organic peroxides.
From the viewpoint of improving the thermal stability of the resulting resin film, a polymerization initiator having a 10-hour half-life temperature of 100° C. or lower is preferred. Such a polymerization initiator is not particularly limited, but persulfates are preferred.

The polymerization initiator may be polymerized by cleaving the polymerization initiator only by a thermal decomposition mechanism to generate radicals, or it may be polymerized by cleavage of the polymerization initiator using only a thermal decomposition mechanism, or it may be polymerized by cleavage of the polymerization initiator using only a thermal decomposition mechanism. It may be used as a redox initiator to generate radicals at low temperatures in combination with an oxidizing agent and a reducing agent such as sodium formaldehyde sulfoxylate.

Further, in order to adjust the molecular weight of the (meth)acrylic polymer, a known chain transfer agent may be used during emulsion polymerization. In particular, when producing the graft copolymer according to the second aspect, in order to control the molecular weight of the non-crosslinked methacrylic polymer component (b) in the step of forming the non-crosslinked methacrylic polymer component (b), Chain transfer agents may also be used.

The chain transfer agent is not particularly limited, but includes, for example, primary alkyl mercaptan chain transfer agents such as n-butylmercaptan, n-octylmercaptan, n-hexadecylmercaptan, n-dodecylmercaptan, and n-tetradecylmercaptan; Secondary alkyl mercaptan chain transfer agents such as s-butyl mercaptan and s-dodecyl mercaptan, tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan, 2-ethylhexylthioglycolate, ethylene glycol Thioglycolic acid esters such as dithioglycolate, trimethylolpropane tris (thioglycolate), pentaerythritol tetrakis (thioglycolate), thiophenol, tetraethylthiuram disulfide, pentane phenylethane, acrolein, methacrolein, allyl alcohol, tetrachloride Examples include carbon, ethylene bromide, styrene oligomers such as α-methylstyrene dimer, and terpinolene. These may be used alone or in combination of two or more.

(coagulation)
The (meth)acrylic polymer can be coagulated by adding a coagulant to the latex of the (meth)acrylic polymer obtained by the emulsion polymerization. Thereafter, after carrying out heat treatment as necessary, the solid or powdered (meth)acrylic compound is separated from the aqueous phase and subjected to a known method such as drying. A coagulated product of the polymer can be obtained.

The coagulant is not particularly limited and any known coagulant can be used, but an inorganic salt or an acid is preferable. The coagulant may be in the form of an aqueous solution.

Examples of inorganic salts include alkali metal halides such as sodium chloride, potassium chloride, lithium chloride, sodium bromide, potassium bromide, lithium bromide, potassium iodide, and sodium iodide; alkalis such as potassium sulfate and sodium sulfate; Metal sulfides; ammonium sulfate; ammonium chloride; alkali metal nitrides such as sodium nitrate and potassium nitrate; calcium chloride, ferrous sulfate, magnesium sulfate, zinc sulfate, copper sulfate, barium chloride, ferrous chloride, ferric chloride, Examples include magnesium chloride, ferric sulfate, aluminum sulfate, potassium alum, iron alum, and the like. Examples of the acid include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid and formic acid. As the coagulant, only one type may be used, or two or more types may be used in combination.

As the coagulant, inorganic salts are preferred, especially calcium salts or magnesium salts, and calcium chloride or magnesium chloride are more preferred.

The amount of the coagulant used is not particularly limited, but may be, for example, about 0.1 to 10 parts by weight, 0.5 to 5 parts by weight, based on 100 parts by weight of the total amount of (meth)acrylic polymer contained in the latex. Parts by weight are preferred.

Before adding the coagulant, it is preferable to filter the latex of the (meth)acrylic polymer using a filter, mesh, etc. to remove fine polymer scales in advance. This makes it possible to reduce fish eyes, foreign matter, and the like caused by fine polymerization scales.

After adding the coagulant to the latex, a heat treatment may be performed to heat the latex to promote agglomeration of the polymer particles. The heating temperature during the heat treatment is not particularly limited, but may be, for example, 60 to 130°C, preferably 70 to 120°C, more preferably 70 to 100°C, and even more preferably 70 to 98°C. The heating time is also not particularly limited, but may be, for example, about 1 minute to 1 hour, preferably 3 minutes to 30 minutes. Further, by performing heat treatment under pressure as necessary, resins having a high glass transition temperature can also be solidified.

After the (meth)acrylic polymer is coagulated by adding a coagulant, dehydration is performed. After this dehydration, the resin is washed with, for example, 10 times the amount of water based on the solid weight of the resin, and dehydrated again, thereby reducing the amount of residual contaminants in the system that can be a source of foaming. Although impurities may remain in the system even after this operation, foaming in the resin film can be suppressed by using a specific solvent in the solution casting method as described below. The (meth)acrylic polymer can be obtained by drying the obtained dehydrated resin at, for example, 100°C.

(dope)
A dope can be formed by mixing the solidified product of the (meth)acrylic polymer obtained by separating it from the aqueous phase with a solvent and dissolving or dispersing it in the solvent.

In this embodiment, at least ethanol is used as the solvent. By using the dope containing ethanol, the resin film obtained by the solution casting method has low haze and can suppress the generation of fine bubbles.
On the other hand, if a dope that does not contain ethanol or a dope that contains methanol is used instead of ethanol, the resin film obtained by the solution casting method will have a high haze and contain many fine bubbles.

The reason why low haze and foaming suppression can be achieved by using ethanol as a solvent is not clear. It is thought that this is because they remain in the polymer and dissolve in ethanol, making it difficult for foaming to occur during film formation and drying. On the other hand, when ethanol is not used, the emulsifier and/or salt is difficult to dissolve in the solvent, becomes the core of foaming, and it is thought that a large number of foams may occur during film formation and drying. However, the present invention is not limited by the above description.

Furthermore, by using ethanol as a solvent, it is also possible to improve film forming properties during solution casting, film releasability, handling properties, and the like.

The content ratio of ethanol to the total amount of solvent contained in the dope is determined from the viewpoint of achieving the above-mentioned low haze and foaming suppression while realizing good solubility or dispersibility of the (meth)acrylic polymer in the solvent. It is preferably 1 to 25% by weight, more preferably 3 to 20% by weight, even more preferably 5 to 15% by weight, and particularly preferably 5 to 10% by weight.

As the solvent contained in the dope, in addition to ethanol, it is preferable to use a so-called good solvent in which the (meth)acrylic polymer has high solubility. The types of good solvents are not particularly limited, but include 1,4-dioxane, 2-phenylethanol, acetone, acetonitrile, chloroform, dibasic acid ester, diacetone alcohol, N,N-dimethylformamide, dimethyl sulfoxide, and acetic acid. Methyl, ethyl acetate, γ-butyrolactone, methyl ethyl ketone, methyl isobutyl ketone, methylene chloride, n-butyl acetate, N-methyl-2-pyrrolidone, propylene carbonate, 1,1,2,2-tetrachloroethane, tetrahydrofuran, toluene, etc. Can be mentioned. These good solvents may be used alone or in combination of two or more.

Among good solvents, methyl ethyl ketone, chloroform, and methylene chloride are preferred, and methylene chloride is more preferred, since they have excellent solubility for the (meth)acrylic polymer and have a fast volatilization rate.

The content ratio of the good solvent to the total amount of solvent contained in the dope is determined from the viewpoint of achieving the above-mentioned low haze and foaming suppression while realizing good solubility or dispersibility of the (meth)acrylic polymer in the solvent. , preferably 75 to 99% by weight, more preferably 80 to 97% by weight, even more preferably 85 to 95% by weight, and particularly preferably 90 to 95% by weight.

The dope may or may not contain a solvent other than ethanol and the good solvent. Such other solvents include methanol, isopropanol, butanol, ethylene glycol monoethyl ether, and the like. The content ratio of the other solvent to the total amount of solvent contained in the dope may be, for example, about 0 to 5% by weight. It may be 0 to 3% by weight or 0 to 1% by weight.

The concentration of the (meth)acrylic polymer in the dope is not particularly limited, and the solubility or dispersibility of the (meth)acrylic polymer in the solvent used, the conditions for implementing the solution casting method, etc. are taken into consideration. Although it can be determined appropriately, it is preferably 5 to 50% by weight, more preferably 7 to 45% by weight, even more preferably 10 to 40% by weight, and even more preferably 12 to 35% by weight. , 15-30% by weight is particularly preferred, and 15-20% by weight is most preferred.

An example of the procedure for producing the dope will be described below. First, pellets containing the (meth)acrylic polymer and optionally other components are produced, and then the pellets are mixed with a solvent to produce a dope in which each component is dissolved or dispersed in the solvent. Alternatively, without producing pellets, the (meth)acrylic polymer and other components are mixed in a solvent simultaneously or sequentially to produce a dope in which each component is dissolved or dispersed in the solvent. The step of dissolving or dispersing can be carried out by adjusting the temperature and pressure as appropriate. After the above dissolution or dispersion step, the obtained dope may be filtered or defoamed.

(other ingredients)
The dope may contain only the (meth)acrylic polymer as a resin component, or may contain other resins in addition to the (meth)acrylic polymer.
The other resins are not particularly limited, and include, for example, styrene resins such as acrylonitrile/styrene resin, methyl methacrylate/styrene resin, styrene/maleic anhydride resin, polycarbonate resin, polyvinyl acetal resin, cellulose acylate resin, and polyfluoride resin. Examples include fluororesins such as vinylidene chloride and polyfluorinated alkyl (meth)acrylate resins, silicone resins, polyolefin resins, polyethylene terephthalate resins, and polybutylene terephthalate resins.

The content of the other resin is not particularly limited, but may be, for example, about 0 to 50 parts by weight based on 100 parts by weight of the (meth)acrylic polymer. Further, it may be 0 to 30 parts by weight, 0 to 10 parts by weight, 0 to 5 parts by weight, or 0 to 1 part by weight.

The dope includes a light stabilizer, an ultraviolet absorber, a heat stabilizer, an antioxidant, a matting agent, a light diffusing agent, a coloring agent, a dye, a pigment, an antistatic agent, a heat ray reflective material, a lubricant, a plasticizer, a filler, etc. It may further contain known additives.

The dope may further contain a graft copolymer having a core-shell structure, which does not correspond to the graft copolymer according to the second embodiment. When the graft copolymer having the core-shell structure is blended, mechanical strength such as bending resistance and cracking resistance can be imparted to the resin film.

The graft copolymer having the core-shell structure is referred to as a multistage polymer, a multilayer structure polymer, or a core-shell type polymer. These polymers have a polymer layer (shell layer) obtained by polymerizing a monomer mixture in the presence of crosslinked polymer particles (core layer). Each of the core layer and the shell layer may be composed of one layer, or may be composed of two or more layers. Such a graft copolymer is not particularly limited, and known ones can be used as appropriate. As an example, a monomer mixture containing acrylic ester as a main component and a crosslinking agent are polymerized to form an acrylic ester-based rubbery polymer, and in the presence of the acrylic ester-based rubbery polymer, methacrylic Examples include graft copolymers obtained by polymerizing a monomer mixture containing an acid ester as a main component.

When using the graft copolymer having a core-shell structure, the blending ratio of the (meth)acrylic polymer and the graft copolymer having a core-shell structure is 100% of the (meth)acrylic polymer. For example, the amount may be 1 part by weight to 50 parts by weight, preferably 5 parts by weight to 40 parts by weight, and more preferably 7 parts by weight to 30 parts by weight.

(Solution casting method)
Using the dope obtained as described above, a resin film is formed by a solution casting method. Specifically, a resin film can be produced by casting the dope onto the surface of a support and then evaporating the solvent.

Embodiments of the solution casting method will be described below, but are not limited thereto. The dope is sent to a pressurizing die by a liquid sending pump, and the dope is cast from the slit of the pressurizing die onto the surface (mirror surface) of a support such as an endless belt or drum made of metal or synthetic resin. , forming a cast film.

The formed cast film is heated on the support to evaporate the solvent and form a film. Conditions for evaporating the solvent can be appropriately determined depending on the boiling point of the solvent used.

The resin film thus obtained is peeled off from the surface of the support. Thereafter, the obtained resin film may be subjected to a drying process, a heating process, a stretching process, etc. as appropriate.

(resin film)
The thickness of the resin film produced according to this embodiment is not particularly limited, but is preferably 5 to 200 μm, more preferably 5 to 100 μm. When the thickness of the resin film is 200 μm or less, cooling after molding becomes uniform, so optical properties tend to become uniform and drying speed tends to become faster. Moreover, when the thickness of the resin film is 5 μm or more, the resin film tends to be easy to handle and has an excellent function as a protective film.

The resin film preferably has a haze of 2% or less, more preferably 1.5% or less, more preferably 1% or less, and 0.8% or less when measured at a film thickness of 40 μm. % or less, even more preferably 0.6% or less, and particularly preferably 0.4% or less. When the haze satisfies this range, transparency is high and it can be suitably used for optical members that require light transmittance.

The resin film can be used preferably as a laminated protective film on the surface of another substrate, more preferably as an optical film, and particularly preferably as a polarizer protective film.

When used as a polarizer protective film, it is preferable that the optical isotropy is small. In particular, it is preferable that not only the optical isotropy in the in-plane direction (length direction, width direction) of the resin film but also the optical isotropy in the thickness direction be small.

More specifically, the absolute value of the in-plane retardation is preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. Further, the absolute value of the thickness direction retardation is preferably 50 nm or less, more preferably 20 nm or less, even more preferably 10 nm or less, and particularly preferably 5 nm or less. A resin film having such a retardation can be suitably used as a polarizer protective film included in a polarizing plate of a liquid crystal display device.

Here, the phase difference is an index value calculated based on birefringence, and the in-plane phase difference (Re) and the thickness direction phase difference (Rth) can be calculated by the following formulas. In an ideal molded body that is completely optically isotropic in three-dimensional directions, both the in-plane retardation (Re) and the thickness direction retardation (Rth) are zero.
Re=(nx-ny)×d
Rth=((nx+ny)/2-nz)×d
In the above formula, nx, ny, and nz each represent the in-plane stretching direction (orientation direction of polymer chains) as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the molded body as the Z axis. , represents the refractive index in each axial direction. Further, d represents the thickness of the molded body, and nx-ny represents the orientation birefringence. In addition, although the MD direction of a molded object is made into the X-axis, in the case of a stretched molded object, the stretching direction is taken as the X-axis.

The resin film produced according to the present embodiment preferably has an orientational birefringence of -2.6×10 ⁻⁴ to 2.6×10 ⁻⁴ , preferably −1.7×10 ⁻⁴ to 1.7. ×10 ⁻⁴ is more preferable, −1.0×10 ⁻⁴ to 1.0×10 ⁻⁴ is even more preferable, −0.5×10 ⁻⁴ to 0.5×10 ⁻⁴ It is particularly preferable that it is, and most preferably that it is -0.2×10 ⁻⁴ to 0.2×10 ⁻⁴ . If the orientational birefringence is within the above range, stable optical properties can be obtained without birefringence occurring during molding. It is also very suitable as an optical film used in liquid crystal displays and the like.

The resin film preferably has a photoelastic constant of -6 x 10 ^-12 to 6 x 10 ^-12 Pa ^-1 , more preferably -4 x 10 ^-12 to 4 x 10 ^-12 Pa ^-1 . It is preferably from -2×10 ⁻¹² to 2×10 ⁻¹² Pa ⁻¹ , even more preferably from −1×10 ⁻¹² to 1×10 −12 Pa −1, and even more preferably from −0 to 2×10 ⁻¹² Pa ⁻¹ . Particularly preferably from 5×10 ⁻¹² to 0.5×10 ⁻¹² Pa ⁻¹ and most preferably from −0.2×10 ⁻¹² to 0.2×10 ⁻¹² Pa ⁻¹ .

Here, photoelastic birefringence is birefringence caused by elastic deformation (strain) of the polymer in the molded body when stress is applied to the molded body, and in reality, it is the birefringence caused by the elastic deformation (strain) of the polymer in the molded body. By determining the elastic constant, the degree of photoelastic birefringence of the material can be evaluated. First, stress is applied to a polymer material, and birefringence is measured when elastic strain occurs. The proportionality constant between the obtained birefringence and stress is the photoelastic constant. By comparing these photoelastic constants, it is possible to evaluate the birefringence of the polymer when stress is applied. If the photoelastic constant is within the above range, birefringence will not occur even if stress is applied to the molded product and the molded product is deformed, so that a molded product with low optical isotropy can be obtained. For example, in polarizer protective film applications, even if the panel is deformed during transportation due to the effects of moisture or temperature in the air, stable optical properties are maintained, reducing quality risks such as image quality deterioration. be able to.

(Stretching)
The resin film produced according to this embodiment has high toughness and flexibility, and may be an unstretched film or a stretched film. By stretching, the mechanical strength of the resin film and the accuracy of the film thickness can be improved.

When stretching the resin film, after producing an unstretched film, uniaxial stretching or biaxial stretching may be performed, or stretching may be performed during film forming as the film forming and solvent degassing steps progress. By adding appropriate operations, a stretched film (uniaxially stretched film or biaxially stretched film) can be produced. Furthermore, stretching during film formation and stretching after film formation may be combined as appropriate.

The stretching ratio of the stretched film is not particularly limited, and may be determined depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it depends on the stretching temperature, the stretching ratio is generally preferably selected in the range of 1.1 times to 5 times, more preferably selected in the range of 1.3 times to 4 times, It is more preferable to select it within the range of 1.5 times to 3 times. When the stretching ratio is within the above range, mechanical properties such as elongation rate, tear propagation strength, and resistance to rolling fatigue of the film can be significantly improved.

(Application)
The resin film manufactured according to the present embodiment can have the gloss of the film surface reduced by a known method, if necessary. Such a method includes, for example, a method of adding an inorganic filler or crosslinkable polymer particles. Furthermore, by subjecting the obtained film to embossing, it is possible to form a surface unevenness layer such as a prism shape, pattern, design, or knurling, or to reduce the gloss of the film surface.

The resin film may be laminated with another film using a dry lamination method and/or heat lamination method using an adhesive, adhesive, etc., or a hard coat layer or antireflection layer may be applied to the front or back surface of the film, if necessary. Functional layers such as a layer, an antifouling layer, an antistatic layer, a printed decoration layer, a metallic luster layer, a surface unevenness layer, and a matte layer can be formed and used.

The resin film can be used for various purposes by taking advantage of its properties such as heat resistance, transparency, and flexibility. For example, the interior and exterior of automobiles, the interior and exterior of personal computers, the interior and exterior of mobile phones, the interior and exterior of solar cells, solar battery back sheets; imaging fields such as photographic lenses, viewfinders, filters, prisms, Fresnel lenses, and lens covers for cameras, VTRs, and projectors; Lens field such as pickup lenses for optical discs in CD players, DVD players, MD players, etc., optical recording field for optical discs such as CDs, DVDs, MDs, organic EL films, light guide plates for liquid crystals, diffusion plates, back sheets, reflections. Films for liquid crystal displays such as sheet, polarizer protective film, polarizing film transparent resin sheet, retardation film, light diffusion film, prism sheet, information equipment field such as surface protection film, optical fiber, optical switch, optical connector, etc. Communication field, vehicle field such as automobile headlights, tail lamp lenses, inner lenses, instrument covers, sunroofs, etc., medical equipment field such as eyeglasses, contact lenses, endoscope lenses, medical supplies that require sterilization, road signs, bathrooms. Construction and building materials fields such as equipment, flooring materials, road transmissive plates, lenses for double glazing, lighting windows, carports, lighting lenses, lighting covers, sizing for building materials, microwave cooking containers (tableware), and housings for home appliances. , can be used for toys, sunglasses, stationery, etc. It can also be used as an alternative to molded products using transfer foil sheets.

The resin film can be used by being laminated on a base material such as metal or plastic. Lamination methods for resin films include lamination molding, wet lamination, dry lamination, extrusion lamination, and hot melt lamination, in which adhesive is applied to a metal plate such as a steel plate, the film is placed on the metal plate, and the film is dried and bonded. Examples include.

Methods for laminating films on plastic parts include insert molding or laminate injection press molding, in which the film is placed in a mold and then filled with resin during injection molding, or the film is preformed and then placed in the mold. Examples include in-mold molding in which resin is filled with injection molding.

The resin film laminate can be used as a paint substitute for automobile interior materials and automobile exterior materials, as well as for civil engineering construction materials such as window frames, bathroom equipment, wallpaper, flooring materials, lighting/light control materials, soundproof walls, road signs, etc. Daily goods, housings for furniture and electronic and electrical equipment, housings for OA equipment such as facsimile machines, notebook computers, and copiers, front panels of LCD screens for terminals such as mobile phones, smartphones, and tablets, lighting lenses, and automobile heads. Lights, optical lenses, optical fibers, optical disks, optical components such as light guide plates for liquid crystals, optical elements, parts of electrical or electronic devices, medical supplies that require sterilization, toys or recreational items, fiber-reinforced resin composite materials, etc. can be used.

In particular, the resin film is suitable as an optical film because of its excellent heat resistance and optical properties, and can be used for various optical members. For example, the front panel of the LCD screen of terminals such as mobile phones, smartphones, and tablets, lighting lenses, automobile headlights, optical lenses, optical fibers, optical disks, light guide plates for LCDs, diffusion plates, back sheets, reflective sheets, polarizing films. Transparent resin sheets, retardation films, light diffusion films, prism sheets, surface protection films, optical isotropic films, polarizer protection films, transparent conductive films, etc. around liquid crystal displays, around organic EL devices, in the optical communication field, etc. It can be applied to known optical applications.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. In the following, "parts" and "%" mean "parts by weight" and "% by weight" unless otherwise specified. In addition, the abbreviations indicate the following substances.
BA: Butyl acrylate MMA: Methyl methacrylate BMA: Butyl methacrylate PhMI: Phenylmaleimide 2-EHMA: 2-ethylhexyl methacrylate ALMA: Allyl methacrylate 2-EHTG: 2-ethylhexyl thioglycolate DSS: Sodium dioctyl sulfosuccinate NPS : Sodium persulfate NDS: Sodium pyrosulfite SFS: Sodium sulfoxylate/formaldehyde ED: Ethylenediaminetetraacetic acid/disodium FeSO ₄ : Ferrous sulfate/7hydrate t-BHP: t-Butyl hydroperoxide

(Production Example 1) Production of (meth)acrylic polymer A In an 8L polymerization apparatus equipped with a stirrer, 133 parts of deionized water, 0.004 parts of sodium hydroxide, and 0.0 parts of sodium di(2-ethylhexyl) sulfosuccinate were placed. I prepared the second part. After sufficiently purging the inside of the polymerization machine with nitrogen gas, the internal temperature was raised to 80°C, and 0.03 parts of NPS and 0.001 parts of NDS were added as a 0.5% aqueous solution, and then the crosslinked (meth)acrylics listed in Table 1 were added. 8.5 parts of monomer (a) for polymer particles were continuously added at a rate of 0.523 parts/min. By continuing the polymerization for an additional 30 minutes, crosslinked (meth)acrylic polymer particles (a) were obtained. The volume average particle diameter was 60 nm, and the polymerization conversion rate was 99.5%.
Thereafter, 91.5 parts of the monomer (b) for the non-crosslinked methacrylic polymer component listed in Table 1 was continuously added at a rate of 1.353 parts/min. Further, at the same time as addition of monomer (b) was started, 0.4 part of sodium di(2-ethylhexyl) sulfosuccinate was added continuously as a 5% aqueous solution over the same period of time as monomer (b). After the addition was completed, polymerization was continued for 60 minutes to obtain a graft copolymer latex. The polymerization conversion rate was 100.0%.
Next, 3.0 parts of a coagulant (calcium chloride or magnesium chloride) based on the solid content of the obtained polymerized latex was added in the form of an aqueous solution so that the solid content concentration of the latex solution was 15%. The mixture was stirred at 95° C. for 5 minutes to effect salting out and coagulation. The obtained coagulated liquid was subjected to Nutsche dehydration, reslurried with water 10 times the amount of solid content, further Nutsche dehydration, and dried in a drying oven at 75°C for 12 hours to form a white powdery (meth)acrylic heavy Coalescence A [graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and non-crosslinked methacrylic polymer component (b)] was obtained. The volume average particle diameter was 131 nm, and the weight average molecular weight was 683,496.

(Polymerization conversion rate)
The polymerization conversion rate of the polymer obtained by polymerization was determined by the following method. Approximately 2 g of latex containing a polymer was collected from the polymerization system, accurately weighed, dried in a hot air dryer at 120° C. for 1 hour, and the weight after drying was accurately weighed as the solid content. Next, the ratio of the results of precision weighing before and after drying was determined as the solid content ratio in the sample. Finally, using this solid content ratio, the polymerization conversion rate was calculated using the following formula. In addition, in this calculation formula, the polyfunctional monomer and the chain transfer agent were treated as charged monomers.
Polymerization conversion rate (%) = {(total weight of charged raw materials x solid content ratio - total weight of raw materials other than water and monomers) / weight of charged monomers} x 100

(Production Example 2) Production of (meth)acrylic polymer B In an 8L glass reactor equipped with a paddle stirrer, deionized water: 143 parts, sodium hydroxide: 0.01 part, DSS: 0.15 I prepared a section. Next, the mixture was stirred at 175 rpm and the temperature was raised to 85° C. while purging the inside of the reactor with nitrogen. After reaching 85°C, 0.022 parts of NPS and 0.0005 parts of SFS were added. Thereafter, a monomer mixture consisting of 85 parts of MMA, 5 parts of 2-EHMA, and 10 parts of PhMI was continuously added to the reactor over 80 minutes to carry out a reaction. Further, 15 minutes after the addition of the monomer mixture, 0.55 part of DSS was added dropwise to the reactor, following the addition of the monomer mixture, and was continuously added to the reactor. Note that the stirring speed was increased to 200 rpm at 55 minutes from the start of addition of the monomer mixture, and to 240 rpm at 70 minutes. After the addition of the monomer mixture, a mixed aqueous solution of ED: 0.0055 part, FeSO ₄ : 0.0015 part, SFS: 0.03 part, DSS: 0.3 part, t-BHP: 0.03 part, were sequentially added to the reactor. Thereafter, the reaction was continued for 60 minutes to complete the polymerization and obtain a polymerized latex. The polymerization conversion rate was 99.9%.
Next, 3.0 parts of a coagulant (calcium chloride or magnesium chloride) based on the solid content of the obtained polymerized latex was added in the form of an aqueous solution so that the solid content concentration of the latex solution was 15%. The mixture was stirred at 95° C. for 5 minutes to effect salting out and coagulation. The obtained coagulated liquid was subjected to Nutsche dehydration, reslurred with water 10 times the amount of solid content, further Nutsche dehydration, and dried in a drying oven at 75°C for 12 hours to form a white powdery (meth)acrylic heavy Combined B was obtained. The volume average particle diameter was 196 nm, and the weight average molecular weight was 1,600,000.

(Examples 1 to 4 and Comparative Examples 1 to 5) Production of resin film According to the description in Table 2, using (meth)acrylic polymer A or B obtained in Production Example 1 or 2, resin was A film was produced.
Prepare methylene chloride (MC), a mixed solvent of methylene chloride/methanol (MC/MeOH), or a mixed solvent of methylene chloride/ethanol (MC/EtOH), and add it to this solvent so that the solid content concentration is 20% by weight. After adding (meth)acrylic polymer A or B to the mixture, the mixture was stirred and mixed using a stirrer tip to prepare a dope. The content ratio of alcohol (methanol or ethanol) in the mixed solvent is as shown in Table 2.
This dope was coated on a glass plate with a wet film thickness of 0.25 mm using a bar coater, and allowed to stand at room temperature in a place protected from wind for 8 minutes to produce a half-dried film.
After this half-dried film was peeled off from the glass plate, it was quickly fixed to a metal frame of an appropriate size using heat-resistant tape and clips, and dried at 160° C. for 15 minutes in a hot air dryer. After drying, each resin film was obtained by taking it out from the metal frame.

(Haze measurement of resin film)
The haze of each resin film was measured based on JIS-K7105 using a HZ-V3 haze meter manufactured by Suga Test Instruments Co., Ltd.
On the other hand, the same measurement was performed with both sides of each resin film sandwiched between glycerin and then glass, and the obtained value was taken as the internal haze.

(YI measurement of resin film)
The YI of each resin film was measured using an SC-P spectrophotometer manufactured by Suga Test Instruments Co., Ltd.

(Measurement of number of foam marks on resin film)
The surface of each resin film was observed using a BX51 polarizing microscope manufactured by OLYMPUS Corporation, and the number of foam traces with a diameter of 30 μm or less was counted within a square with a side of 100 μm in the enlarged micrograph. Based on the number, evaluation was performed according to the following criteria.
1: Number of foam traces is 0 to 2 2: Number of foam traces is 3 to 5 3: Number of foam traces is 6 to 10 4: Number of foam traces is 10 to 20 5: Number of foam traces Table 2 shows the measurement results of 20 or more.

From Table 2, in Examples 1 to 3 in which resin films were formed from a dope containing a coagulated product of (meth)acrylic polymer A synthesized by emulsion polymerization and ethanol, comparative examples using a dope that does not contain ethanol It can be seen that the haze is lower and the number of foam marks is reduced compared to samples 1 to 3.
The same applies to Example 4 in which a resin film was formed from a dope containing ethanol and a coagulated product of (meth)acrylic polymer B synthesized by emulsion polymerization, and Comparative Example 4 in which a dope containing no ethanol was used. It can be seen that the haze is lower and the number of foam traces is reduced compared to Samples 5 to 5.

Claims (12)

obtaining a (meth)acrylic polymer latex by emulsion polymerization;
After adding a coagulant to the latex to coagulate the (meth)acrylic polymer, separating the (meth)acrylic polymer from the aqueous phase;
A resin film comprising: mixing the separated (meth)acrylic polymer with a solvent containing ethanol to form a dope, and evaporating the solvent after casting the dope on the surface of a support. manufacturing method. The method for producing a resin film according to claim 1, wherein the coagulant is an inorganic salt or an acid. The method for producing a resin film according to claim 2, wherein the inorganic salt is a calcium salt or a magnesium salt. The method for producing a resin film according to any one of claims 1 to 3, wherein the content of ethanol in the solvent is 1 to 25% by weight. The method for producing a resin film according to any one of claims 1 to 4, wherein the solvent further contains methylene chloride. The (meth)acrylic polymer is a polymer having as constituent units 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable therewith. The method for producing a resin film according to any one of items 1 to 5. The other copolymerizable monomer unit is a (meth)acrylic acid ester unit (excluding methyl methacrylate unit) whose ester moiety has 1 to 20 carbon atoms, and/or substituted or unsubstituted The method for producing a resin film according to claim 6, comprising a maleimide unit of. The (meth)acrylic polymer is a graft copolymer containing crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b),
The proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and 50% by weight. The method for producing a resin film according to any one of claims 1 to 5, which is less than 10%. The method for producing a resin film according to claim 8, wherein the non-crosslinked methacrylic polymer component (b) contains 70% by weight or more and 99% by weight or less of methyl methacrylate units. The non-crosslinked methacrylic polymer component (b) contains at least a substituted or unsubstituted maleimide unit and a methacrylic acid ester unit whose ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and having a condensed ring structure. The method for producing a resin film according to claim 8 or 9, comprising one type. A solidified product of a (meth)acrylic polymer synthesized by emulsion polymerization, and
Dope, including solvent, including ethanol. A method for producing a resin film, comprising a step of evaporating the solvent after casting the dope according to claim 11 onto the surface of a support.