WO2020235687A1

WO2020235687A1 - Dope for manufacturing film, and film

Info

Publication number: WO2020235687A1
Application number: PCT/JP2020/020420
Authority: WO
Inventors: 浩晃杉井; 東田　昇; 大串　眞康
Original assignee: 株式会社クラレ
Priority date: 2019-05-22
Filing date: 2020-05-22
Publication date: 2020-11-26
Also published as: JPWO2020235687A1; JP7428705B2

Abstract

The present invention provides a dope for manufacturing a film, the dope including a (meth)acrylic resin (A), a polyvinyl acetal resin (B), and an organic solvent (C) that contains a chlorinated organic solvent.

Description

Dope and film for film production

The present invention relates to a dope for producing a film containing a (meth) acrylic resin, a polyvinyl acetal resin, and an organic solvent containing a chlorine-based organic solvent, and a film produced from the dope.

(Meta) Acrylic resins are used in various fields because they have properties such as high transparency, high weather resistance, high surface hardness, and excellent workability. However, depending on the application, this acrylic resin may lack mechanical properties, particularly impact resistance and toughness, and improvement thereof is required. In order to improve this, Patent Document 1 proposes an acrylic thermoplastic resin composition containing a methacrylic resin and a polyvinyl acetal resin having a specific structure. Further, Patent Document 2 proposes an optical film obtained by stretching an acrylic thermoplastic resin composition containing a methacrylic resin and a specific polyvinyl acetal resin as a film having low birefringence. ing.
Further, Patent Document 3 proposes a dope for film production by a solution casting method containing a thermoplastic acrylic resin, a graft copolymer, and a solvent.

International Publication No. 2009/130883 International Publication No. 2014/11583 International Publication No. 2018/212227

The melt extrusion methods described in Patent Documents 1 and 2 have a problem that fisheye defects and gel-like defects occur when a film is produced for a long period of time because it is produced at a high temperature. On the other hand, in Patent Document 3, since the graft copolymer which is a rubber particle is contained in the dope for film production, the particles appear on the surface when the film is produced, causing haze, bending, and molding. There was a problem that a problem of whitening occurred when processed.
In the solution casting method as in Patent Document 3, since it is considered that the state of the doping used affects the physical properties and properties of the obtained film, it is suitable for, for example, optical applications by suppressing the haze value of the doping to some extent. It is considered that a film having excellent transparency can be obtained. However, there is a problem that the acrylic graft copolymer aggregates or the belt is contaminated by the emulsifier when the film is formed by the solution casting method of Patent Document 3.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a dope for producing a film suitable for producing a highly transparent film and a film produced from the dope.

The present inventors have focused on polyvinyl acetal resin as a toughness-developing material for acrylic films, and have prepared a dope for producing a film containing a (meth) acrylic resin, a polyvinyl acetal resin, and an organic solvent containing a chlorine-based organic solvent. , I found that the above problem can be solved.

That is, the present invention provides the following [1] to [13].
[1] A dope for producing a film containing a (meth) acrylic resin (A), a polyvinyl acetal resin (B), and an organic solvent (C) containing a chlorine-based organic solvent.
[2] The dope according to the above [1], wherein the content of the organic solvent (C) is 30 to 97% by mass with respect to 100% by mass of the dope.
[3] The mass ratio [S / T] of the chlorine-based organic solvent (S) and the organic solvent (T) other than the chlorine-based organic solvent in the organic solvent (C) is 50/50 to 99/1. , The dope according to the above [1] or [2].
[4] The mass ratio [(A) / (B)] of the (meth) acrylic resin (A) to the polyvinyl acetal resin (B) is 98/2 to 50/50. 3] The dope according to any one of.
[5] The dope according to any one of [1] to [4] above, wherein the content of the methyl methacrylate structural unit in the (meth) acrylic resin (A) is 50% by mass or more.
[6] The polyvinyl acetal resin (B) is a resin obtained by acetalizing a polyvinyl alcohol resin with an aldehyde having 3 or less carbon atoms and optionally an aldehyde having 4 or more carbon atoms, and has a total acetalization degree of 50 to 50 to. The dope according to any one of the above [1] to [5], which is 90 mol%.
[7] A method for producing an acrylic resin film by a solution casting method, which comprises a step of casting the dope according to any one of [1] to [6] above on the surface of a support and then evaporating the solvent. , Film manufacturing method.
[8] An acrylic resin film formed from the dope according to any one of the above [1] to [6] and having a haze value of 2% or less measured in accordance with JIS 7136: 2000.
[9] The acrylic resin film according to the above [8], which has a thickness of 10 to 500 μm.
[10] The acrylic resin film according to the above [8] or [9], which is an optical film.
[11] The acrylic resin film according to the above [10], wherein the optical film is a polarizer protective film.
[12] A polarizing plate in which the acrylic resin film according to the above [11] and a polarizer are laminated.
[13] A display device including the polarizing plate according to the above [12].

According to the present invention, it is possible to provide a dope for producing a film suitable for producing a highly transparent film and a film produced from the dope.

Hereinafter, an example of an embodiment to which the present invention is applied will be described. The numerical value specified in the present specification is a value obtained by the method disclosed in the embodiment or the embodiment. Other embodiments are also included in the scope of the present invention as long as they are consistent with the gist of the present invention. As used herein, the term "(meth) acrylic" means "acrylic or methacrylic". Further, a resin film formed from a dope containing a (meth) acrylic resin may be referred to as an "acrylic resin film".

<Dope>
The dope of the present invention is a dope for producing a film containing a (meth) acrylic resin (A), a polyvinyl acetal resin (B), and an organic solvent (C) containing a chlorine-based organic solvent.
When the polyvinyl acetal resin and the acrylic resin are formed by the solution casting method, the present inventors consider that the obtained film can be used as an optical film or the like, and in order to exhibit a low haze value, the polyvinyl acetal resin is used. It has been found that an appropriate haze range for doping can be defined by optimizing the acetalization rate, the composition ratio of each resin, and the selection of the co-solvent.
The dope is sealed in a cell having a thickness of 1 cm, and the haze value measured in accordance with JIS 7136: 2000 is preferably 98% or less, more preferably 80% or less, and more preferably 70% or less. It is even more preferably 50% or less, even more preferably 20% or less, and particularly preferably 2% or less. When the haze value is 98% or less, for example, whitening of the obtained film can be suppressed, and a highly transparent film can be easily obtained.
The haze value can be measured by the method described in Examples.

[(Meta) acrylic resin (A)]
Examples of the (meth) acrylic resin (A) used in the present invention include those mainly composed of structural units derived from methyl methacrylate (methyl methacrylate structural units). From the viewpoint of heat resistance, the content of the methyl methacrylate structural unit in the (meth) acrylic resin (A) is preferably 50% by mass or more, more preferably 80% by mass or more, and 90% by mass or more. Is more preferable, and 95% by mass or more is particularly preferable, and all structural units may be methyl methacrylate structural units.

The (meth) acrylic resin (A) may contain a structural unit derived from a monomer other than methyl methacrylate. The other monomer is not particularly limited as long as it can be copolymerized with methyl methacrylate, and for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and acrylic. Isobutyl acid, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, phenyl acrylate, Acrylic acid esters such as benzyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-ethoxyethyl acrylate, glycidyl acrylate, allyl acrylate, cyclohexyl acrylate, norbornyl acrylate, isobornyl acrylate; Ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate , 2-ethylhexyl methacrylate, pentadecyl methacrylate, dodecyl methacrylate, phenyl methacrylate, benzyl methacrylate, phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate, 2-ethoxyethyl methacrylate, glycidyl methacrylate, methacrylic acid Methacrylic acid esters other than methyl methacrylate such as allyl, cyclohexyl methacrylate, norbornyl methacrylate, isobornyl methacrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic anhydride, maleic acid, and itaconic acid or their acids. Anhydrous; olefins such as ethylene, propylene, 1-butene, isobutylene and 1-octene; conjugated diene such as butadiene, isoprene and milsen; aromatics such as styrene, α-methylstyrene, p-methylstyrene and m-methylstyrene. Vinyl compounds; acrylamide, methacrylicamide, acrylonitrile, methacrylic nitrile, vinyl acetate, vinylpyridine, vinyl ketone, vinyl chloride, vinylidene chloride, vinylidene fluoride and the like can be mentioned.

The weight average molecular weight (Mw) of the (meth) acrylic resin (A) is preferably 40,000 to 2,000,000, more preferably 50,000 to 1,000,000, and even more preferably 60. It is 000 to 200,000, and even more preferably 70,000 to 150,000. When Mw is 40,000 or more, the toughness of the film can be exhibited, and when it is 2,000,000 or less, good solubility in an organic solvent can be exhibited.

The molecular weight distribution (Mw / Mn) of the (meth) acrylic resin (A) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1.00 to 4.00. It is more preferably 1.01 to 3.50, still more preferably 1.03 to 3.00, and even more preferably 1.70 to 2.50. When the (meth) acrylic resin (A) having a molecular weight distribution (Mw / Mn) within such a range is used, both molding processability and creep characteristics of the film can be achieved at the same time.
The above Mw and Mw / Mn can adjust the polymerization method of the (meth) acrylic resin (A), the type and amount of the polymerization initiator and the chain transfer agent used at the time of production, the polymerization temperature, and have different molecular weights (meth). It can be adjusted by mixing the acrylic resin (A) or the like. In the present specification, Mw and Mn are values obtained by converting chromatograms measured by gel permeation chromatography (GPC) into molecular weights of standard polystyrene. Mw and Mw / Mn in the present invention can be measured by the method described in Examples.
As the (meth) acrylic resin (A), two or more kinds of (meth) acrylic resins (A) having different molecular weights may be used in combination.

The glass transition temperature of the (meth) acrylic resin (A) (hereinafter, may be referred to as Tg) is preferably 100 ° C. or higher, more preferably 105 ° C. or higher, still more preferably 110 ° C. or higher. Yes, and even more preferably 115 ° C. or higher. The upper limit of Tg of the (meth) acrylic resin (A) is usually 150 ° C.
The glass transition temperature in the present invention can be measured by the method described in Examples.

The method for producing the (meth) acrylic resin (A) is not particularly limited, and it can be produced by a massive polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or the like. Of these, any of a massive polymerization method, a solution polymerization method, and a suspension polymerization method is preferable. Of these, the massive polymerization method or the suspension polymerization method is more preferable.

[Polyvinyl acetal resin (B)]
The polyvinyl acetal resin (B) used in the present invention is a vinyl alcohol unit (formula (I)), a vinyl ester unit (formula (II)) and a vinyl acetal unit (two vinyl alcohol units are acetalized with an aldehyde). : A resin having the formula (III)). In the formula below, l is the molar ratio of vinyl alcohol units, m is the molar ratio of vinyl ester units, k / 2 is the molar ratio of vinyl acetal units, and k is the vinyl alcohol acetalized with aldehyde. the molar ratio of the units, ^{R a} is ^{R a} in the aldehyde used for acetalization ^(R a -CHO). R ^b is ^{R b} in the vinyl ester ^{_{(R b COOCH = CH 2)}} . However, l and / or m may be zero. In the polyvinyl acetal resin (B) consisting of only vinyl alcohol units, vinyl ester units and vinyl acetal units, k + l + m = 1. The units are not particularly limited by the arrangement order, and may be arranged randomly, may be arranged in a block shape, or may be arranged in a tapered shape. Further, the connection between the repeating units may be Head-to-Tail or Head-to-Head.

The polyvinyl acetal resin (B) can be obtained by acetalizing a polyvinyl alcohol resin (hereinafter, may be referred to as PVA) with an aldehyde.

The polyvinyl alcohol resin may be a homopolymer composed of only vinyl alcohol units, or a copolymer composed of vinyl alcohol and a monomer copolymerizable therewith (hereinafter, may be referred to as PVA copolymer). May be good. Further, it may be a modified polyvinyl alcohol resin in which a functional group such as a carboxyl group is introduced into the middle, the end, or the side chain of the molecular chain. These polyvinyl alcohol resins can be used alone or in combination of two or more.

The polyvinyl alcohol resin is not particularly limited depending on the production method, and for example, one obtained by saponifying a vinyl ester-based polymer such as polyvinyl acetate can be used. Examples of the vinyl ester monomer for forming the vinyl ester unit include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and the like. Examples include vinyl versatic acid. Among these, vinyl acetate is preferable because a polyvinyl alcohol resin can be obtained with good productivity.

Examples of the monomer copolymerizable with vinyl alcohol constituting the PVA copolymer include α-olefins such as ethylene, propylene, 1-butene, isobutene and 1-hexene; acrylic acid and salts thereof; methyl acrylate and acrylic. Acrylic acid esters such as ethyl acid, n-propyl acrylate, i-propyl acrylate; methacrylic acid and salts thereof; methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate. Esters; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide; methacrylicamide derivatives such as methacrylamide, N-methylmethacrylate, N-ethylmethacrylate; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, Vinyl ethers such as i-propyl vinyl ether and n-butyl vinyl ether; hydroxy group-containing vinyl ethers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether and 1,4-butanediol vinyl ether; allyl acetate, propyl allyl ether and butyl Allyl ethers such as allyl ether and hexyl allyl ether; monomers having an oxyalkylene group such as polyoxyethylene group, polyoxypropylene group and polyoxybutylene group; vinylsilanes such as vinyltrimethoxysilane; isopropenyl acetate, 3-Buten-1-ol, 4-Penten-1-ol, 5-Hexen-1-ol, 7-octen-1-ol, 9-decene-1-ol, 3-methyl-3-buten-1- Hydroxy group-containing α-olefins such as oar or esterified products thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; fumaric acid, maleic acid, itaconic acid, maleic anhydride, Monomer having a carboxyl group derived from phthalic anhydride, trimellitic anhydride, itaconic anhydride, etc .; derived from ethylene sulfonic acid, allylsulfonic acid, metaallylsulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, etc. Monomer having a sulfonic acid group; vinyloxyethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethyla A single amount having a cation group derived from min, N-acrylamide methyltrimethylammonium chloride, N-acrylamide ethyltrimethylammonium chloride, N-acrylamide dimethylamine, allyltrimethylammonium chloride, metaallyltrimethylammonium chloride, dimethylallylamine, allylethylamine, etc. The body is mentioned.

The content of a monomer unit copolymerizable with vinyl alcohol (hereinafter, may be referred to as a comonomer unit) is preferably 20 in 100 mol parts of all the monomer units constituting the PVA copolymer. It is not more than a molar part, and more preferably 10 parts or less. Further, in order to exert the merit of being copolymerized, it is preferable that 0.01 mol part or more is a comonomer unit.

Examples of the polymerization method used in the production of the vinyl ester-based polymer include known methods such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, a bulk polymerization method or a solution polymerization method, which is a method of polymerizing without a solvent or in a solvent such as alcohol, is preferable. As the alcohol used as the solvent in the solution polymerization method, lower alcohols such as methanol, ethanol and propanol are usually used. Examples of the polymerization initiator include α, α'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethyl-valeronitrile), and 2,2'-azobis (2-methylpropionitrile). Examples of the azo compound, benzoyl peroxide, and peroxides such as n-propylperoxycarbonate. The polymerization temperature is not particularly limited, but is usually 0 to 200 ° C.

When saponifying a vinyl ester polymer, an alkaline substance is usually used as a catalyst. Examples of the alkaline substance include potassium hydroxide and sodium hydroxide. The molar ratio of the alkaline substance used in the saponification catalyst is preferably 0.004 to 0.5, more preferably 0.005 to 0.05 with respect to the vinyl ester unit in the vinyl ester polymer. is there. The alkaline substance as a saponification catalyst may be added all at once at the beginning of the saponification reaction, or may be additionally added during the saponification reaction.
Examples of the solvent that can be used during the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, dimethylformamide and the like. Among these solvents, methanol is preferable. The solvent used is preferably one having an adjusted water content. The water content of the solvent is preferably 0.001 to 1% by mass, more preferably 0.003 to 0.9% by mass, and further preferably 0.005 to 0.8% by mass.

From the viewpoint of heat resistance, the saponification degree of the polyvinyl alcohol resin is preferably more than 80 mol%, more preferably 95 mol% or more, and further preferably 98 mol% or more.

After the saponification reaction, the PVA produced is washed. Examples of the cleaning liquid include methanol, acetone, methyl acetate, ethyl acetate, hexane, water and the like. Among these, methanol, methyl acetate, water, or a mixture thereof is preferable.
The amount of the cleaning liquid used is preferably set so as to satisfy the content of the alkali metal or alkaline earth metal described later, and is usually preferably 300 to 10,000 parts by mass with respect to 100 parts by mass of PVA. , 500 to 5,000 parts by mass, more preferably. The cleaning temperature is preferably 5 to 80 ° C, more preferably 20 to 70 ° C. The washing time is preferably 20 minutes to 100 hours, more preferably 1 to 50 hours.

The content of the alkali metal or alkaline earth metal in PVA used in the present invention is preferably 0.00001 to 1 part by mass with respect to 100 parts by mass of PVA. PVA having an alkali metal or alkaline earth metal content of less than 0.00001 parts by mass is industrially difficult to produce. When the content of the alkali metal or alkaline earth metal is 1 part by mass or less, it is possible to suppress the formation of gel at a high temperature and suppress the generation of unnecessary salts and the like.
The content of the alkali metal or alkaline earth metal can be determined by atomic absorption spectroscopy.

The polyvinyl alcohol resin used for producing the polyvinyl acetal resin (B) has a viscosity average degree of polymerization of preferably 200 to 3,000, more preferably 400 to 2,500, still more preferably 600 to 2,000, and further. It is preferably 800 to 1,300. When the viscosity average degree of polymerization of the polyvinyl alcohol resin is 200 or more, the mechanical properties of the obtained polyvinyl acetal resin (B) are improved, and when it is 3,000 or less, good solubility in an organic solvent is obtained. Can be shown. The viscosity average degree of polymerization (P) of the polyvinyl alcohol resin can be measured by the method described in Examples according to JIS K6726: 1994. That is, after the polyvinyl alcohol resin is completely remineralized and purified, the ultimate viscosity [η] (dL / g) is measured in water at 30 ° C., and the value is calculated by the following formula (i).

The polyvinyl acetal resin (B) is an aldehyde having 3 or less carbon atoms and optionally 4 or more carbon atoms from the viewpoint of compatibility with the (meth) acrylic resin (A) and heat resistance. A resin obtained by acetalizing with an aldehyde is preferable.

Examples of the aldehyde having 3 or less carbon atoms used in the production of the polyvinyl acetal resin (B) include formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, and glyoxal. These aldehydes having 3 or less carbon atoms can be used alone or in combination of two or more. Among these aldehydes having 3 or less carbon atoms, those mainly composed of acetaldehyde and formaldehyde are preferable, and acetaldehyde is more preferable, from the viewpoint of ease of production.

Examples of the aldehyde having 4 or more carbon atoms optionally used in the production of the polyvinyl acetal resin (B) include butyl aldehyde, isobutyl aldehyde, n-octyl aldehyde, amyl aldehyde, hexyl aldehyde, heptyl aldehyde, 2-ethylhexyl aldehyde, cyclohexyl aldehyde, and the like. Examples thereof include furfural, glutaaldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde and the like. These aldehydes having 4 or more carbon atoms can be used alone or in combination of two or more. Among these aldehydes having 4 or more carbon atoms, those containing butyraldehyde as a main component are preferable, and butyraldehyde is particularly preferable, from the viewpoint of ease of production.

The reaction between the polyvinyl alcohol resin and the aldehyde, that is, the acetalization reaction can be carried out by a known method. For example, a method in which a polyvinyl alcohol resin is dissolved in water and reacted with aldehyde in the presence of an acid catalyst to precipitate resin particles (water medium method); the polyvinyl alcohol resin is dispersed in an organic solvent and in the presence of an acid catalyst. Examples thereof include a method of reacting with aldehyde and adding the obtained reaction solution to a poor solvent such as water to precipitate resin particles (solvent method). Of these, the water medium method is preferable.

The aldehydes used for acetalization may be charged all at the same time, or one type may be charged separately. By changing the order of adding the aldehyde and the order of adding the acid catalyst, the randomness of the vinyl acetal unit in the polyvinyl acetal resin (B) can be changed.

The acid catalyst used in the acetalization reaction is not particularly limited, and is, for example, organic acids such as acetic acid and p-toluenesulfonic acid; inorganic acids such as nitric acid, sulfuric acid and hydrochloric acid; and shows acidity when made into an aqueous solution such as carbon dioxide gas. Examples thereof include gas, cation exchangers and solid acid catalysts such as metal oxides.

The total acetalization degree of the polyvinyl acetal resin (B) is determined by the mass ratio of non-acetalized vinyl alcohol units (l ₀ ) and the mass ratio of vinyl acetate units (m ₀ ) according to the method described in JIS K 6728: 1977. ) Is determined by titration, and the mass ratio (k ₀ ) of the acetalized vinyl alcohol unit is determined by k ₀ = 1-l _0- m ₀ , and the molar ratio (l) of the non-acetalized vinyl alcohol unit is determined from this. Calculate the molar ratio (m) of vinyl acetate units, calculate the molar ratio (k) of vinyl alcohol units acetalized by the formula of k = 1-lm, and total acetalization degree (mol%) = It may be determined by k / {k + l + m} × 100, or it may be calculated by dissolving a polyvinyl acetal resin in decarburized dimethylsulfoxide and measuring ¹ H-NMR or ¹³ C-NMR.

Further, by using a method of measuring and calculating ¹ H-NMR or ¹³ C-NMR, acetalized vinyl alcohols for the respective aldehydes (1), (2), ..., And (n) are used. The molar ratio of the unit can be calculated. Then, for example, the degree of acetalization (mol%) due to the aldehyde (n) can be obtained by the formula: k (n) / {k (1) + k (2) + ... + k (n) + l + m} × 100. it can. In addition, k (1), k (2), ..., And k (n) are vinyl alcohol units acetalized with aldehydes (1), (2), ..., And (n), respectively. Is the molar ratio of.

The molar proportion of vinyl alcohol units acetalized with butyraldehyde is particularly referred to as the degree of butyraldehyde. The molar ratio of vinyl alcohol units acetalized with acetaldehyde is particularly called the degree of acetaldehyde conversion. Furthermore, the molar proportion of vinyl alcohol units acetalized with formaldehyde is called the degree of formalization.
For example, in a polyvinyl acetal resin obtained by acetalizing a polyvinyl alcohol resin with butylaldehyde, acetaldehyde and formaldehyde, the molar ratio of vinyl alcohol units acetalized with butylaldehyde is k _(BA) , and vinyl acetalized with acetaldehyde. The molar ratio of alcohol units is k _(AA) , the molar ratio of vinyl alcohol units acetalized with formaldehyde is k _(FA) , the molar ratio of non-acetalized vinyl alcohol units is l, and the molar ratio of vinyl acetate units. When m is, the degree of butyralization (mol%) is calculated by the formula: k _(BA) / {k _(BA) + k _(AA) + k _(FA) + l + m} × 100. The degree of acetoacetalization (mol%) is calculated by the formula: k _(AA) / {k _(BA) + k _(AA) + k _(FA) + l + m} × 100. The degree of formalization (mol%) is calculated by the formula: k _(FA) / {k _(BA) + k _(AA) + k _(FA) + l + m} × 100.

When the polyvinyl acetal resin (B) is a resin obtained by acetalizing a polyvinyl alcohol resin with an aldehyde having 3 or less carbon atoms and optionally an aldehyde having 4 or more carbon atoms, the total acetalization degree of the polyvinyl acetal resin (B). Is preferably 50 to 90 mol%, more preferably 60 to 87 mol%, still more preferably 70 to 85 mol%. When the total acetalization degree of the polyvinyl acetal resin (B) is within such a range, the polyvinyl acetal resin (B) can be finely dispersed in the (meth) acrylic resin (A), and the toughness of the film is exhibited. Can be done.

When the polyvinyl acetal resin (B) is a resin obtained by acetalizing a polyvinyl alcohol resin with an aldehyde having 3 or less carbon atoms and optionally an aldehyde having 4 or more carbon atoms, the polyvinyl acetal resin (B) is (meth). From the viewpoint of compatibility with the acrylic resin (A), the molar ratio of the vinyl alcohol unit acetalized with an aldehyde having 3 or less carbon atoms / the vinyl alcohol unit acetalized with an aldehyde having 4 or more carbon atoms is preferably 10. It is / 90 to 100/0, more preferably 20/80 to 100/0, further preferably 40/60 to 100/0, and even more preferably 40/60 to 60/40.

The amount of the vinyl ester unit constituting the polyvinyl acetal resin (B) is preferably less than 20 mol%, more preferably 5 mol% or less. When the amount of the vinyl ester unit is less than 20 mol%, the heat resistance can be improved and the continuous productivity can be enhanced.

Since the degree of polymerization does not change due to acetalization, the degree of polymerization of the polyvinyl alcohol resin and the polyvinyl acetal resin (B) obtained by acetalizing the polyvinyl alcohol resin is the same, and the polyvinyl acetal resin ( The degree of polymerization of B) is preferably 200 to 3,000. When the degree of polymerization of the polyvinyl acetal resin (B) is 200 or more, the toughness of the film can be exhibited, and when it is 3,000 or less, good solubility in an organic solvent can be exhibited. ..

Since the slurry produced by the water medium method, the solvent method, etc. is usually acidic due to the acid catalyst, it is preferable to remove the acid catalyst. As a method for removing the acid catalyst, a method of repeating washing with water until the pH of the slurry is preferably 5 to 9, more preferably 6 to 9, and even more preferably 6 to 8, a neutralizing agent is added to the slurry, and the pH is increased. Is preferably 5 to 9, more preferably 6 to 9, still more preferably 6 to 8, and a method of adding alkylene oxides or the like can be mentioned.

Examples of the neutralizing agent used for removing the acid catalyst include alkali metal compounds such as sodium hydroxide, potassium hydroxide, sodium acetate, sodium carbonate, sodium hydrogencarbonate and potassium carbonate; alkaline earth such as calcium hydroxide. Metal compounds; examples include ammonia and aqueous ammonia. Examples of the alkylene oxides used for removing the acid catalyst include ethylene oxide and propylene oxide; glycidyl ethers such as ethylene glycol diglycidyl ether.

Next, the polyvinyl acetal resin is purified by removing the catalyst residue, the neutralizing agent residue, the salt produced by the neutralization, the unreacted aldehyde, the alkali metal, the alkaline earth metal, the by-products and the like.
The purification method is not particularly limited, and a method such as repeating liquid removal and washing is usually used. The liquid removal and washing are preferably performed twice or more. Examples of the liquid used for purification include water and a mixed liquid of water and alcohol (methanol, ethanol, etc.). Above all, after neutralizing the polyvinyl acetal resin, the pH is preferably 5 to 9, more preferably 6 to 9, and even more preferably 6 to 8 in a mixed solution of water and alcohol (methanol, ethanol, etc.). A method of repeating deliquefaction and washing is preferable in that alkali metals or alkaline earth metals can be efficiently reduced and a polyvinyl acetal resin can be stably produced. The mixing ratio of water / alcohol is preferably 50/50 to 95/5, more preferably 60/40 to 90/10 by mass ratio. If the proportion of water is too small, the elution of the polyvinyl acetal resin into the mixed solution tends to increase. If the proportion of water is too high, the efficiency of removing alkali metals or alkaline earth metals tends to decrease.

The amount of the alkali metal or alkaline earth metal contained in the polyvinyl acetal resin (B) is preferably 100 ppm or less, more preferably 70 ppm or less, and further preferably 50 ppm or less. When it is 100 ppm or less, the generation of gel at a high temperature is suppressed, and the continuous productivity can be enhanced. If the content of the alkali metal or alkaline earth metal is 0.1 ppm or more, it does not require long-term cleaning to obtain it, the manufacturing cost is reduced, and industrial production is facilitated. ..

The water-containing polyvinyl acetal resin (B) from which residues and the like have been removed is dried as necessary, processed into powder, granules or pellets as necessary, and used as a molding material. When processing into powder, granules or pellets, it is preferable to reduce the reaction residue and water content of the aldehyde by degassing under reduced pressure.

The mass ratio [(A) / (B)] of the (meth) acrylic resin (A) and the polyvinyl acetal resin (B) constituting the dope of the present invention is preferably 98/2 to 50/50, and more. It is preferably 95/5 to 60/40, more preferably 92/8 to 65/35, and even more preferably 91/9 to 85/15. When the mass ratio [(A) / (B)] is 98/2 or less, the toughness of the film can be exhibited, and when it is 50/50 or more, it has a high surface hardness (pencil hardness). Can be done.

The total content of the (meth) acrylic resin (A) and the polyvinyl acetal resin (B) constituting the dope of the present invention is preferably 3 to 70% by mass, more preferably 3 to 70% by mass, based on 100% by mass of the dope. It is 3 to 50% by mass, more preferably 4 to 40% by mass. When the total content of the (meth) acrylic resin (A) and the polyvinyl acetal resin (B) is 3% by mass or more, the amount of residual solvent in the film can be suppressed and the deterioration of dimensional stability is avoided. be able to. On the other hand, when it is 70% by mass or less, it exhibits good solubility in an organic solvent and facilitates production of a film having a uniform thickness.

[Organic solvent (C)]
In the solution casting method, in order to suppress fisheye defects and gel-like defects in the film, it is considered that it is one of the effective means to suppress the precipitate and the undissolved residue in the doping. However, since the solvent solubility of the (meth) acrylic resin (A) and the polyvinyl acetal resin (B) is different, the (meth) acrylic resin (A) and / or the polyvinyl acetal resin (B) may be used depending on the type of the organic solvent (C). Precipitation, undissolved residue, etc. may occur due to the fact that B) is not sufficiently dissolved.

It is important that the organic solvent (C) used in the present invention contains a chlorine-based organic solvent from the viewpoint of solubility of the (meth) acrylic resin (A) and the polyvinyl acetal resin (B). Examples of the chlorine-based organic solvent include chloromethane (methane chloride), dichloromethane (methylene chloride), trichloromethane (chloroform), tetrachloromethane (carbon tetrachloride), trichloroethylene, tetrachloroethylene and the like. Of these, methylene chloride is preferable from the viewpoint of ensuring solubility and having a low boiling point. These can be used alone or in combination of two or more.

The organic solvent (C) is an alcohol such as methanol, ethanol, propanol, n-butanol, etc. as another organic solvent that can be used in combination with the chlorine-based organic solvent. Alcohol: ester having 3 to 12 carbon atoms, ketone, ether: carbon number. May contain 1-7 halogenated hydrocarbons :. Esters, ketones and ethers may have a cyclic structure. Compounds having two or more of the functional groups of esters, ketones and ethers (ie, -O-, -CO- and -COO-) can also be used as solvents and other compounds such as alcoholic hydroxyl groups. It may have a functional group. In the case of a solvent having two or more kinds of functional groups, the number of carbon atoms may be within the specified range of the compound having any of the functional groups. It may also be a saturated aliphatic hydrocarbon such as cyclohexanone. These may be used alone or in combination of two or more. Of these, methanol and ethanol are preferable.

When the chlorine-based organic solvent is used in combination with an organic solvent other than the chlorine-based organic solvent, the mass ratio (S / S) of the chlorine-based organic solvent (S) and the organic solvent (T) other than the chlorine-based organic solvent T) is preferably 50/50 to 99/1, more preferably 60/40 to 95/5. It is preferable that the mass ratio (S / T) is within the above range from the viewpoint of more effectively suppressing fisheye defects and gel-like defects.

The content of the organic solvent (C) is preferably 30 to 97% by mass, more preferably 50 to 97% by mass, and further preferably 60 to 96% by mass with respect to 100% by mass of the dope. When the content of the organic solvent (C) is 30% by mass or more, the resin can be satisfactorily dissolved in the organic solvent, and when it is 97% by mass or less, the amount of residual solvent in the film can be suppressed. It is possible to avoid deterioration of dimensional stability.

The dope of the present invention contains, if necessary, a light stabilizer, an ultraviolet absorber, a heat stabilizer, a matting agent, a light diffuser, a colorant, a dye, a pigment, and deterioration prevention, as long as the effect of the present invention is not impaired. It may contain known additives such as agents, release agents, optical modifiers, antistatic agents, heat ray reflectors, lubricants, plasticizers, fillers and the like. The above additives can be used alone or in combination of two or more. On the other hand, it is preferable that rubber particles such as a core-shell type graft copolymer are not contained from the viewpoint of increasing the haze of the doping and the haze of the film.

The dope of the present invention is an acrylic elastomer such as acrylic multilayer structure particles and acrylic rubber; styrene elastomer; styrene resin; carbonate resin; cellulose acylate resin; fluororesin, as long as the effect of the present invention is not impaired. It may contain other resins such as silicone resin; olefin resin; ethylene terephthalate resin; butylene terephthalate resin. The above resins can be used alone or in combination of two or more.

As described above, when a film is produced by the solution casting method, the state (property) of the doping used is considered to affect the physical properties and properties of the obtained film. Therefore, especially in the production of optical films and the like. For example, it is preferable to keep the haze value of the doping low to some extent.
The average particle size measured by the light scattering method of the phase containing the polyvinyl acetal resin in the doping is preferably 1.0 μm or less, more preferably 0.7 μm or less, from the viewpoint of uniform dispersibility and transparency at the time of film. 0.5 μm or less is particularly preferable. On the other hand, the lower limit of the average particle size is preferably 0.05 μm, more preferably 0.10 μm, and even more preferably 0.15 μm.
The average particle size of the phase containing the polyvinyl acetal resin in the doping is analyzed at 25 ° C. using, for example, a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba Seisakusho Co., Ltd., device name “LA-950V2”). can do.
Since the solution casting method is a method of forming a dope film on the support and evaporating the solvent in the dope film to obtain a film, heating on the support depends on the type of solvent and the properties of the dope itself. It may be necessary to lengthen the time or raise the temperature of the support (heating temperature). However, lengthening the heating time or raising the heating temperature may cause deterioration of the resin, leading to fisheye defects and gel-like defects.

The dope of the present invention comprises a (meth) acrylic resin (A), a polyvinyl acetal resin (B), an organic solvent (C) containing a chlorine-based organic solvent, additives to be blended as necessary, and other resins. It can be prepared by uniformly dispersing and mixing a fixed amount of the mixture. The preparation method is not particularly limited, and examples thereof include a method in which a predetermined amount of each of the above components is blended and sufficiently stirred (mixed) with a mixer or the like.

The stirring time depends on the specific method of dispersion mixing, but is preferably, for example, 8 hours or more, more preferably 14 hours or more, and further preferably 20 hours or more. From the viewpoint of production efficiency and the like, the stirring time is usually preferably 48 hours or less, and more preferably 36 hours or less.
The doping may be adjusted at room temperature (1 to 30 ° C.), while cooling or warming, and further, a combination thereof may be used. If it dissolves above the boiling point, heat it under pressure. The pressurization may be performed by a method of press-fitting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. The heating is preferably performed from the outside, and for example, the jacket type is preferable because the temperature can be easily controlled.

The time for dispersion and mixing is preferably 1 minute to 24 hours, more preferably 2 minutes to 5 hours, and even more preferably 3 minutes to 1 hour. The temperature is preferably 5 to 40 ° C., more preferably 10 to 35 ° C. under atmospheric pressure. Under pressure, the temperature is preferably above the boiling point of the solvent used and within the range in which the solvent does not boil, and is preferably set to, for example, 60 ° C. or higher, more preferably 70 to 110 ° C. In addition, the pressure is adjusted at the set temperature so that the solvent does not boil. By dissolving in these temperature ranges, it is possible to prevent the generation of massive undissolved substances called gels and mamaco.

In the dope of the present invention, the (meth) acrylic resin (A) and the polyvinyl acetal resin (B) are dissolved, swollen, or dispersed in the organic solvent (C) containing a chlorine-based organic solvent, respectively, and are visually observed. It is desirable that no residual resin is seen.

<Film manufacturing method>
The method for producing a film of the present invention is a method for producing an acrylic resin film by a solution casting method, which comprises a step of casting the above-mentioned dope on the surface of a support and then evaporating the solvent.

An embodiment of the solution casting method in the present invention will be described below, but the present invention is not limited thereto. First, dope is performed using the above (meth) acrylic resin (A), polyvinyl acetal resin (B), organic solvent (C) containing a chlorine-based organic solvent, additives to be blended as necessary, and other resins. Prepare. The resulting dope may be filtered or defoamed.

The dope is then cast on the surface of the support to form a dope film.
As the casting method, for example, the T-die method, the doctor blade method, the bar coater method, the roll coater method, the lip coater method and the like are used, and industrially, the dope is transferred from the die to a belt-shaped or drum-shaped support. A method of continuously extruding is generally used.
Examples of the support include a glass substrate, a metal substrate, a plastic substrate such as polyimide and polyethylene terephthalate, and the like. A metal substrate having a mirror-finished surface is preferably used as a support for industrially continuous film formation of a substrate having highly excellent surface properties and optical characteristics.

The formed dope film is heated on the support to evaporate the solvent to form an acrylic resin film (cast film). The heating temperature is preferably 0 to 120 ° C, more preferably 5 to 100 ° C. The heating time is preferably 20 seconds to 2 hours, more preferably 30 seconds to 1 hour. The acrylic resin film thus obtained is peeled off from the surface of the support. After that, the obtained acrylic resin film may be appropriately subjected to a drying step, a heating step, a stretching step and the like.

The stretching process is performed to increase the heat resistance and mechanical strength of the film. The stretching method in the stretching step is not particularly limited, and examples thereof include a sequential biaxial stretching method, a simultaneous biaxial stretching method, and a tuber stretching method. The stretching treatment is composed of a preheating step, a stretching step, and a heat fixing step, and a relaxation step may be performed after the heat fixing step.

In the case of the sequential biaxial stretching method, the stretching speed may be the same or different in each stretching direction. The stretching speed is preferably 100 to 5000% / min, and more preferably 100 to 3000% / min. Further, in the case of the simultaneous biaxial stretching method, if the stretching speed is increased, tearing is likely to occur and the productivity is significantly reduced. Therefore, the stretching speed is preferably 50 to 5000% / min, and 100 to 3000% / min. Is more preferable.

The stretching temperature is preferably Tg to (Tg + 30 ° C.), more preferably (Tg + 5 ° C.) to (Tg + 25 ° C.) in both the sequential / simultaneous biaxial stretching method based on the Tg of the acrylic resin film. is there. In such a range, thickness unevenness tends to be suppressed. When the stretching temperature is Tg or more of the acrylic resin film, film breakage can be suppressed, and when the stretching temperature is Tg + 30 ° C. or less of the acrylic resin film, the thermal properties can be improved.

The draw ratio in each axial direction (area ratio of the stretched film with respect to the unstretched film) is preferably 1.01 to 12.25 times, more preferably 1.10 to 9 times. When the draw ratio is within the above range, the mechanical strength of the film can be improved.

<Acrylic resin film>
The acrylic resin film of the present invention includes the above-mentioned unstretched and stretched ones.
The acrylic resin film of the present invention is formed by a solution casting method (solution casting method) using the above-mentioned dope, and the haze value measured in accordance with JIS K7136: 2000 is preferably 2% or less. It is more preferably 1% or less, further preferably 0.7% or less, and even more preferably 0.4% or less. Since the haze value of the acrylic resin film is 2% or less, it is suitable for optical applications.

Further, in the acrylic resin film of the present invention, the polyvinyl acetal resin (B) is dispersed in the acrylic resin (A). The average particle size of the polyvinyl acetal resin (B) in the film is preferably 5 μm or less, more preferably 3 μm or less, still more preferably 1.2 μm or less, still more preferably 0, from the viewpoint of toughness and the like. It is 0.8 μm or less, particularly preferably 0.6 μm or less, and preferably 0.01 μm or more, more preferably 0.05 μm or more, still more preferably 0.07 μm or more. The average particle size of the polyvinyl acetal resin (B) (particles) can be calculated by evaluating the particle size from a transmission electron microscope (TEM) observation image of the particles and obtaining the average value thereof. Can be obtained by the method described in Examples.

The thickness of the acrylic resin film of the present invention is preferably 10 to 500 μm, more preferably 15 to 200 μm, still more preferably 20 to 100 μm, and even more preferably 40 to 80 μm. When the thickness of the acrylic resin film is 10 μm or more, it is possible to suppress film breakage during picking up, and when it is 500 μm or less, secondary processability such as laminateability, handleability, cutability, punching property, etc. Is improved.

The acrylic resin film of the present invention is an optical film such as a polarizer protective film, a viewing angle adjusting film, a retardation film, and a brightness improving film, a liquid crystal protective film, a surface material of a portable information terminal, and a portable information terminal. It is suitable for a display window protective film, a light guide film, a transparent conductive film having silver nanowires or carbon nanotubes coated on its surface, a front film of various displays, and the like, and is particularly suitable for a polarizer protective film and the like.
In addition, the acrylic resin film of the present invention can be used for front films of various displays, diffusion films, glass shatterproof films, liquid crystal ASF films, transparent conductive films, heat shield films, various barrier films and other optical base films. It is suitable.

The acrylic resin film of the present invention may be used alone, as an inner layer of a laminate or a part thereof, or as an outermost layer of a laminate. The other resin used for laminating is preferably a transparent resin such as a methacrylic resin from the viewpoint of film design. From the viewpoint that the film is not easily scratched and the design is long-lasting, the film forming the outermost layer is preferably one having high surface hardness and weather resistance, and is preferably the acrylic resin film of the present invention.

The polarizing plate of the present invention is formed by laminating the acrylic resin film of the present invention and a polarizer. More specifically, the polarizing plate of the present invention comprises a polarizer, a polarizer protective film laminated on at least one surface of the polarizer, and a viewing angle adjustment laminated on the other surface of the polarizer as needed. It has at least one kind of optical film selected from the group consisting of a film, a retardation film, and a brightness improving film. Lamination can be done via an adhesive layer, if desired.

The polarizing plate of the above aspect can be used for a display device. Examples of the display device include a self-luminous display device such as an (organic) electroluminescence display (ELD), a plasma display (PD), and a field emission display (FED: Field Emission Display); a liquid crystal display device (LCD) and the like. .. The LCD has a liquid crystal cell and a polarizing plate arranged on at least one side thereof.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. In addition, the present invention includes all aspects in which items representing technical features such as the above characteristic values, forms, manufacturing methods, and uses are arbitrarily combined. The physical property values in the examples and comparative examples were measured by the following methods.

[Weight average molecular weight (Mw), molecular weight distribution (Mw / Mn)]
A sample solution was prepared by dissolving 4 mg of the resin to be measured in 5 mL of tetrahydrofuran (THF) and filtering with a filter having a pore size of 0.1 μm. As the GPC apparatus, "HLC-8320" manufactured by Tosoh Corporation equipped with a differential refractive index detector (RI detector) was used. As the column, two "TSKgel Super Multipore HZM-M" manufactured by Tosoh Corporation and "Super HZ4000" were connected in series. Tetrahydrofuran (THF) was used as the eluent. The temperature of the column oven was set to 40 ° C., the eluent flow rate was 0.35 mL / min, 20 μL of the sample solution was injected into the apparatus, and the chromatogram was measured. The chromatogram is a chart in which the electric signal value (intensity Y) derived from the difference in refractive index between the sample solution and the reference solution is plotted against the retention time X.
GPC measurement was performed using 10 standard polystyrenes having a molecular weight in the range of 400 to 500000, and a calibration curve showing the relationship between the retention time and the molecular weight was prepared. Based on this calibration curve, Mw and Mw / Mn of the resin to be measured were determined. The chromatogram baseline is the point where the slope of the peak on the high molecular weight side of the GPC chart changes from zero to positive when viewed from the side with the earlier retention time, and the slope of the peak on the low molecular weight side has the earlier retention time. It is a line connecting the points that change from minus to zero when viewed from. If the chromatogram shows multiple peaks, the line connecting the point where the slope of the peak on the highest molecular weight side changes from zero to plus and the point where the slope of the peak on the lowest molecular weight side changes from minus to zero It was the baseline.

〔Glass-transition temperature〕
The glass transition temperature was measured according to JIS K7121: 2012. Using a differential scanning calorimetry device (“DSC-50” manufactured by Shimadzu Corporation), once the sample is heated to 230 ° C. and cooled to 30 ° C or lower, it is again 10 ° C / from 30 ° C to 230 ° C. The DSC curve was measured under the condition that the temperature was raised at the rate of temperature rise of 1 minute. The intermediate point glass transition temperature obtained from the obtained DSC curve was defined as the glass transition temperature.

[Composition of polyvinyl acetal resin (B) (degree of acetalization)]
The composition of the polyvinyl acetal resin (B) was acetalized with an aldehyde having 3 or less carbon atoms in mol% with respect to all repeating units of vinyl alcohol units acetalized with an aldehyde having 4 or more carbon atoms by measuring 13C-NMR. The mol% for all repeating units of vinyl alcohol units, the mol% for all repeating units of non-acetalized vinyl alcohol units, and the mol% for all repeating units of vinyl acetate units were calculated.

[Content of alkali metal or alkaline earth metal]
The polyvinyl acetal resin (B) is carbonized in a platinum crucible and a hot plate, then carbonized in an electric furnace, and the residue is dissolved in acid to obtain an atomic absorption spectrophotometer (manufactured by Hitachi High-Technologies Corporation, model number: Z-2000). Measured using.

[Average particle size]
A 0.1 mm × 0.1 mm sample piece was cut out from the obtained film, an ultrathin section was prepared using an ultramicrotome (Reichert ULTRACUT-S manufactured by RICA), stained with ruthenium tetroxide, and the section was permeated. Observation was performed using a type electron microscope (H-800NA manufactured by Hitachi, Ltd.). The particle size of 50 particles in the observation image was evaluated, and the average particle size was calculated from the average value of these particles.

[Haze (dope, film)]
The dope material is stirred under the conditions of 23 ° C. and atmospheric pressure for 24 hours, and then the dope is sealed in a 1 cm thick cell, and the haze meter (Murakami Color Co., Ltd.) conforms to JIS K7136: 2000. It was measured using HM-150) manufactured by the laboratory.
A 50 mm × 50 mm test piece was cut out from the obtained film and measured using a haze meter (HM-150, manufactured by Murakami Color Research Institute) in accordance with JIS K7136: 2000.

[Production Example 1] Production of (meth) acrylic resin (A) A polymerization initiator (2,2'-azobis (2-methylpropionitrile), hydrogen) is added to 99 parts by mass of methyl methacrylate and 1 part by mass of methyl acrylate. Extraction capacity: 1%, 1 hour half-life temperature: 83 ° C.) 0.1 parts by mass and 0.24 parts by mass of a chain transfer agent (n-octyl mercaptan) were added and dissolved to obtain a raw material solution.
A mixed solution was obtained by mixing 100 parts by mass of ion-exchanged water, 0.03 parts by mass of sodium sulfate and 0.45 parts by mass of a suspension dispersant. 420 parts by mass of the mixed solution and 210 parts by mass of the raw material solution were charged into the pressure-resistant polymerization tank, and the polymerization reaction was started at a temperature of 70 ° C. while stirring in a nitrogen atmosphere. After 3 hours from the start of the polymerization reaction, the temperature was raised to 90 ° C. and stirring was continued for 1 hour to obtain a liquid in which the bead-like copolymer was dispersed. Although some polymer adhered to the wall surface of the polymerization tank or the stirring blade, the polymerization reaction proceeded smoothly without foaming.
The obtained copolymer dispersion was washed with an appropriate amount of ion-exchanged water, the beaded copolymer was taken out by a bucket centrifuge, dried in a hot air dryer at 80 ° C. for 12 hours, and beaded (meth). ) Acrylic resin (A) was obtained.
The obtained (meth) acrylic resin (A) has a content of methyl methacrylate monomer unit of 99% by mass, a content of methyl acrylate monomer unit of 1% by mass, and a weight average molecular weight. (Mw) was 95,000, Mw / Mn was 2.0, and the glass transition temperature was 120 ° C.

[Production Example 2] Production of polyvinyl acetal resin (B) An aqueous solution of a polyvinyl alcohol resin having a viscosity average degree of polymerization of 1000 and a saponification degree of 99 mol% is prepared, and an aldehyde having a butyraldehyde / acetaldehyde = 50/50 mol ratio and an acid catalyst are prepared. The acetalization reaction was carried out by adding hydrochloric acid as the above and stirring. As the reaction proceeded, the resin was precipitated. The slurry was washed according to a known method until pH = 6, then suspended in an alkaline aqueous medium and stirred, and then washed until pH = 7. Then, by drying until the volatile content becomes 1.0%, a polyvinyl acetal resin (B) having a butyl acetal unit of 30 mol%, an acetal acetal unit of 51 mol%, a vinyl alcohol unit of 18 mol%, and a vinyl acetate unit of 1 mol%. ) Was obtained. The alkali metal content was 40 ppm.

[Example 1]
3.15 g of pellets of (meth) acrylic resin (A), 0.35 g of powder of polyvinyl acetal resin (B) and 66.5 g of methylene chloride as organic solvent (C) were put into a screw tube, and a stirrer was further added to room temperature. The mixture was stirred at (23 ° C.) for 24 hours to prepare a dope. The dissolved state of the resin was visually observed every hour, and the time during which the dissolution was confirmed was measured. In addition, haze measurement was performed using the solution after stirring for 24 hours. The dissolution time was 1 hour and the haze value was 0.4%.

The dope obtained in Example 1 was dropped onto a polyimide film substrate to form a dope film with a film applicator. This film was dried in a dryer at 150 ° C. for 60 minutes and then peeled off from the polyimide film to obtain an acrylic resin film. The thickness of this film was 70 μm, and the haze value was 0.2%. Further, as a result of TEM observation, it was a film in which polyvinyl acetal resin particles having an average particle diameter of 0.5 μm were present.

[Example 2]
Except that the organic solvent (C) used was changed to chloroform, and the pellets of (meth) acrylic resin (A), the powder of polyvinyl acetal resin (B) and chloroform were changed to the contents shown in Table 1, respectively. Dope preparation was performed in the same manner as in Example 1. The dissolution time was 4 hours and the haze value was 0.5%.

A film having a thickness of 70 μm was prepared by the same method as in Example 1, and the haze was measured and found to be 0.3%.

[Example 3]
The organic solvent (C) used was changed to a mixed solution of methylene chloride and methanol, and pellets of (meth) acrylic resin (A), powder of polyvinyl acetal resin (B) and mixed solution of methylene chloride and methanol were used, respectively. Dope preparation was carried out in the same manner as in Example 1 except that the content was changed to the content shown in Table 1. The dissolution time was 1 hour and the haze value was 0.5%.

A film having a thickness of 70 μm was prepared by the same method as in Example 1, and the haze was measured and found to be 0.2%.

[Example 4]
Dope production was carried out in the same manner as in Example 1 except that the pellets of the (meth) acrylic resin (A) and the powder of the polyvinyl acetal resin (B) were changed to the contents shown in Table 1, respectively. The dissolution time was 3 hours and the haze value was 1.0%.

A film having a thickness of 70 μm was prepared by the same method as in Example 1, and the haze was measured and found to be 0.6%.

[Comparative Example 1]
Except that the organic solvent used was changed from methylene chloride to toluene, and the contents of the pellet of (meth) acrylic resin (A), the powder of polyvinyl acetal resin (B) and toluene were changed to the contents shown in Table 1, respectively. Dope preparation was performed in the same manner as in Example 1. It did not dissolve in 24 hours and the residual resin was in a state where it could be visually observed.

A film having a thickness of 70 μm was prepared by the same method as in Example 1, and the haze was measured and found to be 34.5%.

[Comparative Example 2]
Except that the organic solvent used was changed from methylene chloride to acetone, and the contents of (meth) acrylic resin (A) pellets, polyvinyl acetal resin (B) powder and acetone were changed to the contents shown in Table 1, respectively. Dope preparation was performed in the same manner as in Example 1. It did not dissolve in 24 hours and the residual resin was in a state where it could be visually observed.

A film having a thickness of 70 μm was prepared by the same method as in Example 1, and the haze was measured and found to be 40.5%.

Claims

A dope for producing a film containing a (meth) acrylic resin (A), a polyvinyl acetal resin (B), and an organic solvent (C) containing a chlorine-based organic solvent.
The dope according to claim 1, wherein the content of the organic solvent (C) is 30 to 97% by mass with respect to 100% by mass of the dope.
The claim that the mass ratio [S / T] of the chlorine-based organic solvent (S) and the organic solvent (T) other than the chlorine-based organic solvent in the organic solvent (C) is 50/50 to 99/1. The dope according to 1 or 2.
Any one of claims 1 to 3 in which the mass ratio [(A) / (B)] of the (meth) acrylic resin (A) to the polyvinyl acetal resin (B) is 98/2 to 50/50. Dope according to section.
The dope according to any one of claims 1 to 4, wherein the content of the methyl methacrylate structural unit in the (meth) acrylic resin (A) is 50% by mass or more.
The polyvinyl acetal resin (B) is a resin obtained by acetalizing a polyvinyl alcohol resin with an aldehyde having 3 or less carbon atoms and optionally an aldehyde having 4 or more carbon atoms, and has a total acetalization degree of 50 to 90 mol%. The dope according to any one of claims 1 to 5.
A method for producing an acrylic resin film by a solution casting method, which comprises a step of casting the dope according to any one of claims 1 to 6 on the surface of a support and then evaporating the solvent. Method.
An acrylic resin film formed from the dope according to any one of claims 1 to 6 and having a haze value of 2% or less measured in accordance with JIS 7136: 2000.
The acrylic resin film according to claim 8, which has a thickness of 10 to 500 μm.
The acrylic resin film according to claim 8 or 9, which is an optical film.
The acrylic resin film according to claim 10, wherein the optical film is a polarizer protective film.
A polarizing plate in which the acrylic resin film according to claim 11 and a polarizer are laminated.
A display device comprising the polarizing plate according to claim 12.