JP7401271B2 - Dope for film production, film and method for producing the same - Google Patents

Description

The present invention relates to a dope used for producing a film by a solution casting method, a film using the dope, and a method for producing the same.

Acrylic resin is an excellent polymer that is used in large quantities in various industrial fields because it has excellent transparency, color tone, appearance, weather resistance, gloss, and processability. In particular, films made from acrylic resin have excellent transparency, appearance, and weather resistance, and are used as interior and exterior materials for automobiles, exterior materials for electrical appliances such as mobile phones and smartphones, and building materials such as architectural flooring materials. It is used for various purposes such as wood. Among these, in recent years, acrylic resins have been applied to optical members such as liquid crystal display devices and organic EL display devices by taking advantage of their excellent optical properties.

However, an essential drawback of acrylic resins is that they have poor impact resistance. In general, a method for improving the impact resistance of acrylic resins is to develop strength by blending graft copolymers with rubber layers (hereinafter also referred to as multilayer structure polymer particles) into acrylic resins. Various proposals have been made.

On the other hand, methods for producing high-quality resin films include the melt extrusion method using a T-die, and the solution flow method in which a dope in which resin is dissolved in a solvent is cast onto the surface of a support, and then the solvent is evaporated to form a film. The elongation method is known. The melt extrusion method using a T-die has the drawback that physical properties tend to differ between the extrusion direction and the direction perpendicular to the extrusion direction in the resulting film, and residual orientation tends to occur. On the other hand, the solution casting method does not apply physical pressure to the film, so polymer orientation does not occur, and the film has the advantage that it is less likely to have directionality in its strength, optical properties, etc. Furthermore, in addition to extremely high film thickness accuracy, the amount of heat given to the resin is low, and there is also the advantage that the amount of heat stabilizers and the like added can be reduced.

Patent Document 1 describes a dope used in a solution casting method that includes a thermoplastic acrylic resin, a rubber-containing graft copolymer, and a solvent.

International Publication No. 2018/212227

As described in Patent Document 1, when producing a film containing a thermoplastic acrylic resin and multilayer structure polymer particles by a solution casting method, first, the thermoplastic acrylic resin and multilayer structure polymer particles are A dope containing However, in this dope, the dispersibility of the multilayer structure polymer particles is not sufficient, and the particles tend to aggregate to form coarse particles in some cases. If coarse particles are included in the dope, problems may occur, such as foreign matter appearing in the manufactured film or the filter becoming clogged when filtering the dope, making it impossible to continue filtration. Ta.

In addition, since multilayer structure polymer particles having a rubber layer are less likely to deform than thermoplastic acrylic resins, multilayer structure polymer particles are less likely to follow the shrinkage of the film when drying a solvent in a solution casting method. Due to this, there is a problem in that the external haze of the film obtained after solvent drying tends to deteriorate. Furthermore, the obtained film was prone to cracking during cutting, and trimmability was sometimes reduced.

In view of the above-mentioned current situation, the present invention provides a dope for film production by a solution casting method, which contains a thermoplastic acrylic resin and multilayer structure polymer particles, which has good particle dispersibility and is difficult to form coarse particles. An object of the present invention is to provide a dope that realizes the production of a film with low external haze and good trimmability.

（式中、Ｒ^９は、水素原子、または、置換もしくは無置換で直鎖状もしくは分岐状の炭素数１～１２のアルキル基を表す。Ｒ^１０は、置換もしくは無置換の炭素数５～２４の芳香族基、または、置換もしくは無置換の炭素数５～２４の脂環式基であり、単素環式構造または複素環式構造を有する。ｌは１～４の整数を示す。ｍは０～１の整数を示す。ｎは０～１０の整数を示す。）
前記硬質シェル層は、メタクリル酸アルキルエステル６０～１００重量％、及び、共重合可能な二重結合を有する他の単量体０～４０重量％からなる単量体成分（ｃ）、並びに、多官能性単量体０～１０重量部（単量体成分（ｃ）１００重量部に対して）から生成される硬質重合体（Ｃ）から構成され、前記多層構造重合体粒子のゲル分率が８５％以上である、ドープに関する。
好ましくは、前記多層構造重合体粒子は、配向複屈折の絶対値が２×１０^－４以下であり、また、光弾性定数の絶対値が３×１０^－１２Ｐａ^－１以下である。
好ましくは、単量体成分（ａ）、単量体成分（ｂ）、及び単量体成分（ｃ）の合計量に対して、単量体成分（ａ）の割合が１５～３５重量％、単量体成分（ｂ）の割合が３０～７０重量％、単量体成分（ｃ）の割合が１５～３５重量％である。
好ましくは、前記単量体成分（ｂ）中の前記一般式（４）で表される単量体の含有割合が、２０重量％以上である。
好ましくは、前記一般式（４）で表される単量体が、（メタ）アクリル酸ベンジル、（メタ）アクリル酸ジシクロペンタニル、及び（メタ）アクリル酸フェノキシエチルからなる群より選択される少なくとも１種である。
好ましくは、前記単量体成分（ａ）における前記一般式（４）で表される単量体及び芳香族基を有するビニル系単量体の合計含有量が０～１５重量％である。
好ましくは、前記単量体成分（ｃ）における前記一般式（４）で表される単量体及び芳香族基を有するビニル系単量体の合計含有量が０～１５重量％である。
好ましくは、前記熱可塑性アクリル系樹脂における前記他の単量体単位が、Ｎ－置換マレイミド単量体単位を含み、より好ましくは、前記熱可塑性アクリル系樹脂中の前記Ｎ－置換マレイミド単量体単位の含有量が１～２５重量％の範囲である。
好ましくは、前記溶剤は、塩化メチレンとエタノールまたはメタノールの混合溶剤である。
第二の本発明は、溶液流延法によるフィルムの製造方法であって、前記ドープを支持体表面に流延した後、溶剤を蒸発させる工程を含む、フィルムの製造方法に関する。
第三の本発明は、前記ドープから形成されてなるフィルムに関する。好ましくは、前記フィルムは、外部ヘイズが１．０％以下である。好ましくは、前記フィルムは、延伸されたフィルムである。 A first aspect of the present invention is a dope for producing a film by a solution casting method, comprising a thermoplastic acrylic resin, multilayer structure polymer particles, and a solvent, wherein the thermoplastic acrylic resin has methyl methacrylate units. 60 to 100% by weight and 0 to 40% by weight of other monomer units having copolymerizable double bonds, and the multilayer structure polymer particles include at least a hard core layer, The hard core layer includes a rubber intermediate layer and a hard shell layer, and the hard core layer contains 60 to 100% by weight of alkyl methacrylate, 0 to 35% by weight of alkyl acrylate, and a copolymerizable double bond. Monomer component (a) consisting of 0 to 40% by weight of a monomer, and 0.1 to 1.0 parts by weight of a polyfunctional monomer (per 100 parts by weight of monomer component (a) ), the rubber intermediate layer comprises 40 to 99% by weight of an acrylic acid alkyl ester, 1 to 60% by weight of a monomer represented by the following general formula (4), and a monomer component (b) consisting of 0 to 40% by weight of another monomer having a copolymerizable double bond, and 0.1 to 1.6 parts by weight of a polyfunctional monomer (monomer component (b) (based on 100 parts by weight of polymer component (b)),

(In the formula, R ⁹ represents a hydrogen atom or a substituted or unsubstituted linear or branched alkyl group having 1 to 12 carbon atoms. R ¹⁰ represents a substituted or unsubstituted linear or branched alkyl group having 5 to 24 carbon atoms. is an aromatic group, or a substituted or unsubstituted alicyclic group having 5 to 24 carbon atoms, and has a monocyclic structure or a heterocyclic structure. l represents an integer of 1 to 4. m is Indicates an integer from 0 to 1. n indicates an integer from 0 to 10.)
The hard shell layer comprises a monomer component (c) consisting of 60 to 100% by weight of alkyl methacrylate and 0 to 40% by weight of another monomer having a copolymerizable double bond, and a polyester. It is composed of a hard polymer (C) produced from 0 to 10 parts by weight of a functional monomer (based on 100 parts by weight of monomer component (c)), and the gel fraction of the multilayer structure polymer particles is It relates to a dope that is 85% or more.
Preferably, the multilayer structure polymer particles have an absolute value of orientational birefringence of 2×10 ⁻⁴ or less, and an absolute value of photoelastic constant of 3×10 ⁻¹² Pa ⁻¹ or less.
Preferably, the proportion of monomer component (a) is 15 to 35% by weight based on the total amount of monomer component (a), monomer component (b), and monomer component (c), The proportion of monomer component (b) is 30 to 70% by weight, and the proportion of monomer component (c) is 15 to 35% by weight.
Preferably, the content of the monomer represented by the general formula (4) in the monomer component (b) is 20% by weight or more.
Preferably, the monomer represented by the general formula (4) is selected from the group consisting of benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and phenoxyethyl (meth)acrylate. At least one type.
Preferably, the total content of the monomer represented by the general formula (4) and the vinyl monomer having an aromatic group in the monomer component (a) is 0 to 15% by weight.
Preferably, the total content of the monomer represented by the general formula (4) and the vinyl monomer having an aromatic group in the monomer component (c) is 0 to 15% by weight.
Preferably, the other monomer unit in the thermoplastic acrylic resin includes an N-substituted maleimide monomer unit, more preferably, the N-substituted maleimide monomer unit in the thermoplastic acrylic resin The unit content is in the range of 1 to 25% by weight.
Preferably, the solvent is a mixed solvent of methylene chloride and ethanol or methanol.
The second invention relates to a method for producing a film by a solution casting method, which includes a step of evaporating the solvent after casting the dope onto the surface of a support.
A third aspect of the present invention relates to a film formed from the dope. Preferably, the film has an external haze of 1.0% or less. Preferably, the film is a stretched film.

According to the present invention, there is provided a dope for producing a film by a solution casting method, which contains a thermoplastic acrylic resin and multilayer structure polymer particles, which has good particle dispersibility, is difficult to form coarse particles, and has no external haze. It is possible to provide a dope that realizes the production of a film with a small amount and good trimmability.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

The dope of this embodiment contains a thermoplastic acrylic resin, multilayer structure polymer particles, and a solvent, and is a dope used for manufacturing a film by a solution casting method. In the dope of this embodiment, the thermoplastic acrylic resin and the multilayer structure polymer particles are dissolved or dispersed in a solvent. Each component will be explained below.

(thermoplastic acrylic resin)
The thermoplastic acrylic resin is a polymer composed of 60 to 100% by weight of methyl methacrylate units and 0 to 40% by weight of other monomer units having copolymerizable double bonds. Preferably, it is a polymer composed of a polymer composed of 70 to 98% by weight of methyl methacrylate units and 2 to 30% by weight of other monomer units having a copolymerizable double bond, More preferably, it is a polymer composed of a polymer composed of 75 to 95% by weight of methyl methacrylate units and 5 to 25% by weight of other monomer units having a copolymerizable double bond. .

As the other monomer having a copolymerizable double bond, for example, a (meth)acrylic ester (excluding methyl methacrylate) whose alkyl group has 1 to 10 carbon atoms is preferable. Specifically, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, octyl methacrylate, glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate. , 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dicyclopentanyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trichloroethyl methacrylate, isobornyl methacrylate, and other methacrylic acids. Esters; Methacrylamides such as methacrylamide and N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, glycidyl acrylate, epoxy acrylate Acrylic acid esters such as cyclohexylmethyl, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate; Acrylamides such as acrylamide and N-methylolacrylamide; α,β-unsaturated carboxylic acids such as methacrylic acid and acrylic acid; Salts thereof; Vinyl cyanates such as acrylonitrile and methacrylonitrile; Vinyl arenes such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; N-phenylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, etc. Substituted maleimides; maleic acid, fumaric acid, and their esters; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; ethylene, propylene, butylene , alkenes such as butadiene, isobutylene; halogenated alkenes; polyfunctionality such as allyl methacrylate, diallyl phthalate, triallyl cyanurate, monoethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, etc. Examples include monomers. These may be used alone or in combination of two or more.

The thermoplastic acrylic resin preferably does not contain a polyfunctional monomer from the viewpoint of film processability and appearance.

The weight average molecular weight of the thermoplastic acrylic resin is not particularly limited, but is preferably from 400,000 to 4,000,000. When the weight average molecular weight is within this range, the viscosity of the dope becomes suitable for solution casting, and furthermore, the obtained film becomes tough and easy to handle when applying the film to various uses. More preferably 800,000 to 3,500,000, still more preferably 1,000,000 to 3,000,000. The weight average molecular weight can be measured using gel permeation chromatography (GPC) under the following conditions.

(Equipment conditions)
Measuring equipment: HLC-8220GPC (Tosoh)
Detector: RI detector (built-in device)
Solvent: Tetrahydrofuran Guard column: TSKguardcolumn SuperHZ-H (4.6 x 35mm) (Tosoh)
Analysis column: TSKgel SuperHZM-H (6.0 x 150mm) (Tosoh)
Measurement temperature: 40℃
Standard material: Standard polystyrene (Tosoh)

The glass transition temperature of the thermoplastic acrylic resin can be appropriately set depending on the conditions of use and application. From the viewpoint of heat resistance during use, the glass transition temperature is preferably 90° C. or higher. In applications other than those requiring excellent heat resistance, the glass transition temperature may be less than 115°C, but in applications requiring excellent heat resistance, the glass transition temperature is preferably 115°C or higher. The glass transition temperature of the thermoplastic acrylic resin is more preferably 118°C or higher, even more preferably 120°C or higher, and particularly preferably 125°C or higher.

Examples of thermoplastic acrylic resins with excellent heat resistance include acrylic resins having a ring structure in the main chain. Examples of the ring structure include a glutarimide ring structure, a lactone ring structure, a maleic anhydride-derived ring structure, a maleimide-derived ring structure (including an N-substituted maleimide-derived ring structure), and a glutaric anhydride ring structure. Also included are acrylic resins containing (meth)acrylic acid structural units in their molecules.

Examples of thermoplastic acrylic resins with excellent heat resistance include maleimide acrylic resins (acrylic resins in which an unsubstituted or N-substituted maleimide compound is copolymerized as a copolymerization component), glutarimide acrylic resins , lactone ring-containing acrylic resin, acrylic resin containing hydroxyl group and/or carboxyl group, methacrylic resin, styrene-containing acrylic resin obtained by polymerizing styrene monomer and other monomers copolymerizable with it. Acrylic polymers containing partially hydrogenated styrene units obtained by partially hydrogenating aromatic rings of polymers, acrylic polymers containing cyclic acid anhydride structures such as glutaric anhydride structures and maleic anhydride-derived structures. Examples include merging. Among these, lactone ring-containing acrylic resins, maleimide acrylic resins, glutarimide acrylic resins, glutaric anhydride structure-containing acrylic resins, and maleic resins are preferred because they improve the heat resistance of films produced from dope. Acrylic resins containing an acid anhydride structure, acrylic polymers composed of 97 to 100% by weight of methyl methacrylate and 3 to 0% by weight of methyl acrylate are preferred, and glutarimide acrylic resins have excellent optical properties. , maleimide acrylic resin is more preferred, and maleimide acrylic resin is even more preferred. Glutarimide acrylic resin and maleimide acrylic resin may be used together. Since both resins have excellent compatibility, they can maintain high transparency, have excellent optical properties, and have high thermal stability and solvent resistance.

Examples of the maleimide acrylic resin include maleimide acrylic resins having a maleimide monomer unit (corresponding to a maleimide-derived ring structure) represented by the following general formula (5).

In general formula (5), R ¹¹ and R ¹² are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms, and R ¹³ is a hydrogen atom, An arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, an alkyl group having 1 to 18 carbon atoms, or at least one type of substitution selected from Group A below. An aryl group having 6 to 14 carbon atoms or an alkyl group having 1 to 12 carbon atoms.
Group A: halogen atom, hydroxyl group, nitro group, alkoxy group having 1 to 12 carbon atoms, alkyl group having 1 to 12 carbon atoms, and arylalkyl group having 7 to 14 carbon atoms.

Specific examples of the maleimide monomer unit represented by general formula (5) include unsubstituted maleimide monomer units; N-methylmaleimide units, N-phenylmaleimide units, N-cyclohexylmaleimide units, N-benzyl Examples include N-substituted maleimide monomer units such as maleimide units. Particularly preferred are N-substituted maleimide monomer units. As the maleimide monomer unit, only one type may be contained, or two or more types may be contained.

When the thermoplastic acrylic resin contains an N-substituted maleimide monomer unit, the content thereof is preferably 1 to 25% by weight of the thermoplastic acrylic resin from the viewpoint of heat resistance and optical properties. , more preferably 3 to 20% by weight, and even more preferably 5 to 15% by weight.

(Multilayer structure polymer particles)
The multilayer structure polymer particles are particles having a multilayer structure consisting of a plurality of polymer layers, and are generally referred to as core-shell type polymers. Sometimes called a multistage polymer. The multilayer structure polymer particles are made by polymerizing an alkyl acrylate ester in the presence of hard polymer particles (hard core layer) formed by polymerizing a monomer component mainly composed of an alkyl methacrylate ester and a polyfunctional monomer. A monomer component containing a large amount of This is the obtained polymer.

In the multilayer structure polymer particles, it is preferable that the rubber intermediate layer has an average particle diameter of 125 to 400 nm. The average particle diameter of the rubber intermediate layer refers to the average particle diameter measured at the stage where the rubber intermediate layer is formed by polymerization in the presence of the hard core layer. When the average particle diameter of the rubber intermediate layer is 125 nm or more, the film produced using the dope can have excellent strength. Moreover, when it is 400 nm or less, the produced film can have excellent transparency, appearance, and optical properties. The average particle diameter of the rubber intermediate layer is preferably 130 to 380 nm, more preferably 150 to 350 nm, even more preferably 180 to 300 nm, particularly preferably 200 to 260 nm. The average particle diameter of the rubber intermediate layer can be calculated by measuring light scattering at a wavelength of 546 nm using a spectrophotometer in the state of the polymer latex formed up to the rubber intermediate layer before polymerizing the hard shell layer. .

The multilayer structure polymer particles have a gel fraction of 85% or more. The gel fraction is the weight ratio of components insoluble in methyl ethyl ketone of the multilayer structure polymer particles to the total amount of the multilayer structure polymer particles. If the gel fraction of the multilayer polymer particles is less than 85%, the multilayer polymer particles will not have sufficient dispersibility in the dope, and many coarse particles will tend to form in the dope. The gel fraction is preferably 85.5% or more, more preferably 87% or more, even more preferably 90% or more, and particularly preferably 92% or more. The upper limit of the gel fraction is not particularly limited and may be 100% or less, but may be 99% or less, or 98% or less.

The gel fraction can be measured by the following procedure. 2 g of multilayer structure polymer particles were dissolved in 50 ml of methyl ethyl ketone, and centrifuged for 3 sets in total for 1 hour at a rotation speed of 30,000 rpm using a centrifuge (CP60E, manufactured by Hitachi Koki Co., Ltd.) to separate insoluble and possible components. Separate the solubles. The weights of the obtained insoluble and soluble components are measured, and the gel fraction is calculated from the following formula.
Gel fraction (%) = {(weight of methyl ethyl ketone insoluble portion)/(weight of methyl ethyl ketone insoluble portion + weight of methyl ethyl ketone soluble portion)}×100

The multilayer structure polymer particles include at least a hard core layer, a rubber intermediate layer, and a hard shell layer. Each layer will be specifically explained below.

(Hard core layer)
The hard core layer is a layer formed in the polymerization step (I), and contains 60 to 100% by weight of alkyl methacrylate, 0 to 35% by weight of alkyl acrylate, and a copolymerizable double bond. Monomer component (a) consisting of 0 to 40% by weight of a monomer, and 0.1 to 1.0 parts by weight of a polyfunctional monomer (per 100 parts by weight of monomer component (a) ) is a polymer particle composed of a hard polymer (A) formed from (A).

Monomer component (a) is 70 to 100% by weight of alkyl methacrylate, 0 to 25% by weight of alkyl acrylate, and 0 to 30% by weight of another monomer having a copolymerizable double bond. It preferably contains 80 to 100% by weight of alkyl methacrylate, 0 to 15% by weight of alkyl acrylate, and 0 to 20% by weight of another monomer having a copolymerizable double bond. More preferably, it contains 90 to 100% by weight of alkyl methacrylate, 0 to 10% by weight of alkyl acrylate, and 0 to 10% by weight of another monomer having a copolymerizable double bond. preferable.

The methacrylic acid alkyl ester is preferably a methacrylic acid alkyl ester in which the alkyl group has 1 to 12 carbon atoms. 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. Specifically, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and t-butyl methacrylate are preferred. Particularly preferred is methyl methacrylate.

The acrylic acid alkyl ester is preferably an acrylic alkyl ester in which the alkyl group has 1 to 12 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.

Examples of the other monomers having a copolymerizable double bond include methacrylic esters other than the methacrylic alkyl esters, acrylic esters other than the acrylic alkyl esters, aromatic vinyl monomers, and other monomers. Examples include copolymerizable vinyl monomers. Examples of methacrylic esters other than the alkyl methacrylates include phenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate. Examples of acrylic esters other than the alkyl acrylic esters include phenyl acrylate, benzyl acrylate, cyclohexyl acrylate, and isobornyl acrylate. 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, olefin monomers such as ethylene and propylene, halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, and vinylidene fluoride, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-o - Maleimide monomers such as chlorophenylmaleimide and the like. Any of these may be used alone or in combination of two or more.

However, due to particle dispersibility in the dope and optical properties of the produced film, in the monomer component (a), a monomer represented by the general formula (4) described below and a vinyl having an aromatic group are used. It is preferable that the amount of the monomer used is small. Specifically, the total content of the monomer represented by the general formula (4) and the vinyl monomer having an aromatic group in the monomer component (a) is 0 to 15% by weight. The amount is preferably 0 to 12% by weight, more preferably 0 to 8% by weight, and particularly preferably 0 to 5% by weight.

In the polymerization step (I), the monomer component (a) is polymerized in the presence of a polyfunctional monomer. As the polyfunctional monomer, those known as crosslinking agents or crosslinking monomers can be used, such as allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, etc. , monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, alkylene glycol diacrylate, and the like. These may be used alone or in combination of two or more. Preferably it is allyl methacrylate.

The amount of polyfunctional monomer used in the polymerization step (I) is 0.1 to 1.0 parts by weight based on 100 parts by weight of monomer component (a). If the amount is less than 0.1 part by weight, a film produced using the dope may not be able to achieve sufficient trimmability. Moreover, when it exceeds 1.0 parts by weight, the external haze value of the film produced becomes large, and the trimmability of the film may not be sufficient. The amount is preferably 0.2 to 0.8 parts by weight, more preferably 0.3 to 0.7 parts by weight, and even more preferably 0.4 to 0.6 parts by weight.

Furthermore, in the polymerization step (I), the mixture of the monomer component (a) and the polyfunctional monomer may be polymerized to form the rigid polymer (A) in the presence of a chain transfer agent. .

The chain transfer agent is not particularly limited, and chain transfer agents known in the art can be used. Specifically, primary alkyl mercaptan chain transfer agents such as n-butyl mercaptan, n-octyl mercaptan, n-hexadecyl mercaptan, n-dodecyl mercaptan, and n-tetradecyl mercaptan, s-butyl mercaptan, s-dodecyl Secondary alkyl mercaptan chain transfer agents such as mercaptan, tertiary alkyl mercaptan chain transfer agents such as t-dodecyl mercaptan and t-tetradecyl mercaptan, 2-ethylhexylthioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris (thioglycolate), thioglycolic acid esters such as pentaerythritol tetrakis (thioglycolate), thiophenol, tetraethylthiuram disulfide, pentane phenylethane, acrolein, methacrolein, allyl alcohol, carbon tetrachloride, ethylene bromide, α- Examples include styrene oligomers such as methylstyrene dimer, terpinolene, and the like. These may be used alone or in combination of two or more.

If the chain transfer agent contains a sulfur component, the thermal stability of the obtained multilayer structure polymer particles will improve, so alkylmercaptan chain transfer agents and thiophenol are preferred, and alkylmercaptan chain transfer agents are more preferred. preferable.

The amount of chain transfer agent used in the polymerization step (I) is preferably 0 to 1.0 parts by weight per 100 parts by weight of monomer component (a). When the amount used exceeds 1.0 parts by weight, the gel fraction becomes a low value, the dispersibility of the multilayer structure polymer particles in the dope is insufficient, and a large number of coarse particles tend to be produced in the dope. The amount is more preferably 0.8 parts by weight or less, further preferably 0.6 parts by weight or less, even more preferably 0.5 parts by weight or less, particularly preferably 0.4 parts by weight or less. Although it is not necessary to use a chain transfer agent in the polymerization step (I), when it is used, the lower limit thereof is preferably 0.1 part by weight or more, and more preferably 0.2 part by weight or more.

(rubber intermediate layer)
The rubber intermediate layer is a layer formed in the polymerization step (II), and contains 40 to 99% by weight of an acrylic acid alkyl ester, 1 to 60% by weight of a monomer represented by general formula (4), and a copolymer. Monomer component (b) consisting of 0 to 40% by weight of other monomers having possible double bonds, and 0.1 to 1.6 parts by weight of a polyfunctional monomer (monomer component ( b) of a soft polymer (B) formed from 100 parts by weight), at least a part of which is grafted to the hard core layer. Specifically, it has a structure in which the soft polymer (B), which is the rubber intermediate layer, covers at least a portion or the entire particulate hard core layer located inside the entire multilayer structured polymer particle. A part of the soft polymer (B) may enter inside the particulate hard core layer. However, all of the soft polymer (B) does not need to be bonded to the hard core layer.

Monomer component (b) contains 50 to 95% by weight of an acrylic acid alkyl ester, 5 to 50% by weight of a monomer represented by general formula (4), and other monomers having a copolymerizable double bond. It preferably contains 0 to 30% by weight of a monomer, 50 to 90% by weight of an acrylic acid alkyl ester, 10 to 50% by weight of a monomer represented by general formula (4), and a copolymerizable double More preferably, it contains 0 to 20% by weight of other monomers having a bond, 50 to 85% by weight of an acrylic acid alkyl ester, 15 to 45% by weight of a monomer represented by general formula (4), and It is further preferred to contain 0 to 10% by weight of other monomers having copolymerizable double bonds. In particular, from the viewpoint of particle dispersibility in the dope, the content of the monomer represented by the general formula (4) in the monomer component (b) is preferably 20% by weight or more, and 25% by weight. It is more preferably at least 30% by weight, and even more preferably at least 30% by weight.

The acrylic alkyl ester contained in the monomer component (b) is preferably an acrylic alkyl ester in which the alkyl group has 1 to 12 carbon atoms. Specifically, the acrylic acid alkyl esters mentioned above for the monomer component (a) can be mentioned. Among them, n-butyl acrylate is preferred. Also preferred are a combination of n-butyl acrylate and ethyl acrylate, and a combination of n-butyl acrylate and 2-ethylhexyl acrylate. The content ratio of n-butyl acrylate in the acrylic acid alkyl ester contained in the monomer component (b) is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and more preferably 80 to 100% by weight. More preferably, it is 100% by weight.

The monomer component (b) contains a monomer represented by the following general formula (4). By using this monomer in the rubber intermediate layer of the multilayer structure polymer particles, it is possible to improve the particle dispersibility in the dope, and further improve the orientational birefringence and photoelastic constant of the multilayer structure polymer particles. can also be reduced.

R ⁹ represents a hydrogen atom or a substituted or unsubstituted linear or branched alkyl group having 1 to 12 carbon atoms. R ¹⁰ is a substituted or unsubstituted aromatic group having 5 to 24 carbon atoms, or a substituted or unsubstituted alicyclic group having 5 to 24 carbon atoms, and has a monocyclic structure or a heterocyclic structure. have Examples of substituents that R ⁹ and R ¹⁰ may have include halogen, hydroxyl group, carboxyl group, alkoxy group, carbonyl group (ketone structure), amino group, amide group, epoxy group, and carbon-carbon group. At least one selected from the group consisting of a double bond, an ester group (a derivative of a carboxyl group), a mercapto group, a sulfonyl group, a sulfone group, and a nitro group. Among these, at least one selected from the group consisting of halogen, hydroxyl group, carboxyl group, alkoxy group, and nitro group is preferred. l represents an integer of 1 to 4, preferably 1 or 2. m is an integer from 0 to 1. n represents an integer of 0 to 10, preferably an integer of 0 to 2, and more preferably 0 or 1.

The monomer represented by formula (4) is preferably a (meth)acrylic monomer in which R ⁹ is a substituted or unsubstituted alkyl group having 1 carbon number. In formula (4), R ¹⁰ is a substituted or unsubstituted aromatic group having 5 to 24 carbon atoms, or a substituted or unsubstituted alicyclic group having 5 to 24 carbon atoms, and is a monocyclic structure. More preferably, it is a (meth)acrylic monomer having the following.

In formula (4), l is an integer of 1 to 2, n is an integer of 0 to 2, and it is more preferable that the monomer is a (meth)acrylic monomer.

Specifically, examples of the monomer having an alicyclic group include dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and the like. Furthermore, examples of the monomer having an aromatic group include benzyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate. Examples of the monomer having a heterocyclic structure include pentamethylpiperidinyl (meth)acrylate, tetramethylpiperidinyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate.

Among the (meth)acrylic monomers represented by formula (4), benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and (meth)acrylic acid are preferred from the viewpoint of orientational birefringence and transparency. Phenoxyethyl is preferred. Among the monomers represented by the formula (4), benzyl (meth)acrylate has optical isotropy, cancels and reduces the orientational birefringence of thermoplastic acrylic resin, and has the advantage of transparency. most preferred. Among these, benzyl methacrylate is preferred when high heat resistance is desired since it has a high glass transition temperature. On the other hand, when seeking strength development, benzyl acrylate is preferable because it has a low glass transition temperature.

In addition, benzyl (meth)acrylate has a relatively large positive photoelastic constant, so if it is added in an amount sufficient to cancel out the negative orientational birefringence caused by methyl methacrylate, the photoelastic constant of the multilayer polymer particles becomes positive. It may become large. However, according to an embodiment in which benzyl (meth)acrylate is blended into a rubber intermediate layer that is in a rubber state at room temperature, the stress is relaxed due to the deformation of the molecular chain, making it difficult to develop photoelasticity, thereby canceling out the orientational birefringence. However, it is also possible to reduce the photoelastic constant.

Other monomers having a copolymerizable double bond contained in monomer component (b) do not correspond to either acrylic acid alkyl ester or the monomer represented by general formula (4). As monomers, the monomers described for monomer component (a) can be used as appropriate.

Also in the polymerization step (II), the monomer component (b) is polymerized in the presence of a polyfunctional monomer. As the polyfunctional monomer, the same compounds as those explained for the polymerization step (I) can be used, but allyl methacrylate is preferred.

The amount of polyfunctional monomer used in the polymerization step (II) is 0.1 to 1.6 parts by weight based on 100 parts by weight of monomer component (b). If the amount is less than 0.1 part by weight, a film produced using the dope may not be able to achieve sufficient trimmability. If the amount exceeds 1.6 parts by weight, the dispersibility of particles in the dope will be poor, and the film produced will have a large external haze value, and furthermore, the trimmability of the film may not be sufficient. The amount is preferably 0.5 to 1.5 parts by weight, more preferably 1.0 to 1.5 parts by weight.
In the polymerization step (II), a chain transfer agent may or may not be used, but it is preferable not to use it.

(hard shell layer)
The hard shell layer is a layer formed by the polymerization step (III) and is composed of 60-100% by weight of alkyl methacrylate and 0-40% by weight of other monomers having copolymerizable double bonds. and a hard polymer (C) formed from 0 to 10 parts by weight of a polyfunctional monomer (based on 100 parts by weight of monomer component (c)). at least a portion of which is grafted to the hard core layer and/or the rubber intermediate layer. Specifically, all of the hard polymer (C) that is the hard shell layer may be graft-bonded to the hard core layer and/or the rubber intermediate layer, or a part of the hard polymer (C) may be grafted to the hard core layer and/or the rubber intermediate layer. layer and/or the rubber intermediate layer, but the remainder may be present as a polymer component (free polymer) that is not grafted to either the hard core layer and/or the rubber intermediate layer. . The non-grafted polymer component also constitutes a part of the multilayer structure polymer particles.

The monomer component (c) preferably contains 70 to 98% by weight of alkyl methacrylate and 2 to 30% by weight of another monomer having a copolymerizable double bond. More preferably, it contains 75 to 96% by weight and 4 to 25% by weight of other monomers having copolymerizable double bonds.

As the methacrylic acid alkyl ester and the other monomer having a copolymerizable double bond, those mentioned above for the monomer component (a) can be used. However, the other monomers having a copolymerizable double bond in the monomer component (c) also include acrylic acid alkyl esters. In the monomer component (c), methyl methacrylate is preferred as the methacrylic acid alkyl ester, and n-butyl acrylate is preferred as the other monomer having a copolymerizable double bond.

Considering the particle dispersibility in the dope and the optical properties of the produced film, the monomer component (c) is composed of a monomer represented by the above-mentioned general formula (4) and a vinyl monomer having an aromatic group. It is preferable that the amount of polymer used is small. Specifically, the total content of the monomer represented by the general formula (4) and the vinyl monomer having an aromatic group in the monomer component (c) is 0 to 15% by weight. The amount is preferably 0 to 12% by weight, more preferably 0 to 8% by weight, and particularly preferably 0 to 5% by weight.

In the polymerization step (III), a polyfunctional monomer may or may not be used, but it is preferable not to use it from the viewpoint of imparting excellent mechanical properties to the film. When using a polyfunctional monomer, the amount used is preferably 10 parts by weight or less, more preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of monomer component (c). 1 part by weight is more preferred. Further, in the polymerization step (III), a chain transfer agent may or may not be used, but it is preferable not to use it. Furthermore, the monomer component (c) may be the same as or different from the monomer component (a).

The hard shell layer may be a layer composed of only one stage, or may have a multi-stage structure composed of two or more stages having the same or different monomer compositions. When the hard shell layer has a multi-stage structure consisting of two or more stages, the content of each monomer in the hard shell layer does not refer to the content of the monomer in each stage of the multi-stage structure. , refers to the monomer content in the entire hard shell layer of two or more stages. When the hard shell layer is composed of two or more stages, it is preferable because the external haze of the produced film may be further reduced and the trimmability of the film may also be improved.

The total amount of the above monomer components (a), (b), and (c) is 80 to 100 parts by weight in 100 parts by weight of the total amount of monomer components constituting the multilayer structure polymer particles. It is preferably 90 to 100 parts by weight, more preferably 95 to 100 parts by weight. Further, the monomer components constituting the multilayer structure polymer particles may be composed only of monomer components (a), (b), and (c). The term "monomer components constituting the multilayer structure polymer particles" refers to monomers other than polyfunctional monomers, that is, monomers having one copolymerizable double bond per molecule. It consists only of the body.

The proportions of monomer components (a), (b), and (c) are not particularly limited, but from the viewpoint of particle dispersibility in the dope, external haze of the film, and trimmability, monomer components (a), With respect to the total amount of monomer component (b) and monomer component (c), the proportion of monomer component (a) is 15 to 35% by weight, and the proportion of monomer component (b) is 30% by weight. ~70% by weight, the proportion of monomer component (c) is preferably 15 to 35% by weight, the proportion of monomer component (a) is preferably 20 to 30% by weight, and the proportion of monomer component (b) is preferably 15 to 35% by weight. More preferably, the proportion is 40 to 60% by weight, and the proportion of monomer component (c) is 20 to 30% by weight.

The multilayer structure polymer particles can be produced by ordinary emulsion polymerization using a known emulsifier. Examples of the emulsifier include anionic interfaces such as phosphate ester salts such as sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sodium lauryl sulfate, sodium fatty acid, and sodium polyoxyethylene lauryl ether phosphate. Active agents, nonionic surfactants, etc. are shown. These surfactants may be used alone or in combination of two or more. From the viewpoint of improving the thermal stability of the film, it is particularly preferable to polymerize using a phosphate ester salt (alkali metal or alkaline earth metal) such as polyoxyethylene lauryl ether sodium phosphate.

The polymerization initiator used in producing the multilayer structure polymer particles is not particularly limited, but from the viewpoint of improving the thermal stability of the film produced using the dope, the 10-hour half-life temperature is 100°C or less. Polymerization initiators are preferred. The polymerization initiator is not particularly limited, but persulfates are preferred. Specific examples include potassium persulfate, sodium persulfate, ammonium persulfate, and the like. Among these, potassium persulfate is particularly preferred.

The polymerization initiator is preferably added at least in polymerization step (I), more preferably added in each polymerization step using a chain transfer agent, and particularly preferably added in all polymerization steps.

The total amount of the polymerization initiator used is not particularly limited, but it is preferably 0.01 to 1.0 parts by weight based on 100 parts by weight of the total amount of monomer components constituting the multilayer structure polymer particles. It is preferably 0.01 to 0.6 parts by weight, more preferably 0.01 to 0.2 parts by weight. The amount of the polymerization initiator used in each polymerization step is 0.01 to 1.85 parts by weight per 100 parts by weight of monomer component (a) in polymerization step (I), and 0.01 to 1.85 parts by weight in polymerization step (II). 0.01 to 0.6 parts by weight per 100 parts by weight of monomer component (b), and 0.01 to 0.90 parts by weight per 100 parts by weight of monomer component (c) in polymerization stage (III). It is preferably 0.01 to 0.2 parts by weight in polymerization stage (I), 0.01 to 0.4 parts by weight in polymerization stage (II), and 0.01 to 0.0 parts by weight in polymerization stage (III). More preferably, it is 2 parts by weight. Moreover, it is preferable that the amount of the polymerization initiator used in the polymerization step (I) is more than 1% by weight and not more than 29% by weight based on the total amount of the polymerization initiator used.

The multilayer structure polymer particle latex obtained by the above-mentioned emulsion polymerization is coagulated by spray drying or by adding a water-soluble electrolyte such as a salt or acid, and after further heat treatment, the resin is removed from the aqueous phase. Solid or powdered multilayer structure polymer particles can be obtained by separating the components and subjecting them to a known method such as drying. Among these, a method in which coagulation is performed using salt is preferred. The salt is not particularly limited, but divalent salts are preferred, and specific examples include calcium salts such as calcium chloride and calcium acetate, and magnesium salts such as magnesium chloride and magnesium sulfate. Among these, magnesium salts such as magnesium chloride and magnesium sulfate are preferred. During coagulation, commonly added additives such as anti-aging agents and ultraviolet absorbers may be added.

Before the coagulation operation, it is preferable to filter the multilayered polymer particle latex using a filter, mesh, etc. to remove fine polymerized scales. This makes it possible to reduce fish eyes and foreign matter caused by fine polymerization scales, and also to reduce coarse particles in the dope.

It is preferable that the multilayer structure polymer particles have small absolute values of orientational birefringence and small absolute values of photoelastic constant when measured individually. According to this embodiment, by using the monomer represented by the general formula (4) in the rubber intermediate layer, the absolute value of the orientational birefringence and the absolute value of the photoelastic constant of the multilayer structure polymer particles can be respectively adjusted. It can be made small. Specifically, the multilayer structure polymer particles preferably have an absolute value of orientational birefringence of 2×10 ⁻⁴ or less, more preferably 1×10 ⁻⁴ or less, and 5×10 ⁻⁵ or less. It is more preferable that Further, the multilayer structure polymer particles preferably have an absolute value of a photoelastic constant of 3×10 ⁻¹² Pa ⁻¹ or less, more preferably 2.5×10 ⁻¹² Pa ⁻¹ or less, More preferably, it is 2×10 ⁻¹² Pa ⁻¹ or less. The orientational birefringence and photoelastic constant of the multilayer structure polymer particles can be measured by the method described in Examples.

The multilayer structure polymer particles have a soft rubber intermediate layer and a hard shell layer covering the soft rubber intermediate layer, so that in the film, the soft rubber intermediate layer (including the hard core layer inside) forms an "island", A discontinuous sea-island structure is formed in which the thermoplastic acrylic resin serving as the matrix resin and the hard shell layer form a "sea". Therefore, it is possible to achieve the excellent effect of improving the mechanical strength of the film and making it difficult to reduce the heat resistance of the film. Further, the multilayer structure polymer particles enable the soft rubber intermediate layer to be uniformly dispersed in the matrix resin.

In this application, "soft" means that the glass transition temperature of the polymer is less than 20°C. From the viewpoint of increasing the impact absorption ability of the soft layer and improving impact resistance such as trimmability, the glass transition temperature of the soft polymer is preferably less than 0°C, more preferably less than -20°C. . In addition, when a layer consists of two or more stages, the glass transition temperature of the entire layer is used as a reference, not the glass transition temperature of each stage.

Moreover, in this application, "hard" means that the glass transition temperature of the polymer is 20° C. or higher. If the glass transition temperature of the polymer forming the core layer or shell layer is less than 20°C, the heat resistance of the film may decrease, or the polymer may become coarse or lumpy when producing multilayer polymer particles. Problems such as increased likelihood of In addition, when a layer consists of two or more stages, the glass transition temperature of the entire layer is used as a reference, not the glass transition temperature of each stage.

In this application, the glass transition temperatures of "soft" and "hard" polymers are determined using the Fox equation using the values listed in the Polymer Hand Book (J. Brandrup, Interscience 1989). The calculated values will be used (for example, polymethyl methacrylate is 105°C and polybutyl acrylate is -54°C).

The blending ratio of the thermoplastic acrylic resin and the multilayer structure polymer particles varies depending on the use of the film, but the blending ratio of the thermoplastic acrylic resin is 30 to 98 parts by weight relative to the total blending amount of both components of 100 parts by weight. The amount of the multilayer structure polymer particles is preferably 70 to 2 parts by weight, the amount of the thermoplastic acrylic resin is 50 to 95 parts by weight, and the amount of the multilayer structure polymer particles is 50 to 5 parts by weight. The blending amount of the thermoplastic acrylic resin is more preferably 60 to 90 parts by weight, the blending amount of the multilayer structure polymer particles is even more preferably 40 to 10 parts by weight, and the blending amount of the thermoplastic acrylic resin is 70 to 90 parts by weight. Particularly preferred is 90 parts by weight, and the blending amount of the multilayer polymer particles is 30 to 10 parts by weight. When the blending amount of the thermoplastic acrylic resin is 30 parts by weight or more, the properties of the thermoplastic acrylic resin can be exhibited, and when the blending amount is 98 parts by weight or less, the thermoplastic acrylic resin can be The mechanical strength of the system resin can be improved.

(solvent)
The solvent contained in the dope is not particularly limited as long as it can dissolve or disperse the thermoplastic acrylic resin and the multilayer structure polymer particles, but the hydrogen bond term δH in the Hansen solubility parameter is 1 or more. It is preferred that the number of solvents (1) is 12 or less. By forming the dope using such a solvent, it is possible to achieve good solubility or dispersibility of the thermoplastic acrylic resin and the multilayer structure polymer particles in the solvent. A solvent in which the hydrogen bond term δH is 3 or more and 10 or less is preferable, and a solvent in which the hydrogen bond term δH is 5 or more and 8 or less is more preferable.

The solubility parameter (SP value) has long been known as an index indicating the solubility of a substance, and the cohesive energy term of the SP value is the type of interaction energy acting between molecules (London dispersion force, dipole-dipole force). Hansen solubility parameters have been proposed, which are divided by the London dispersion force term, the dipole-dipole force term, and the hydrogen bond force term, respectively. In the present application, the hydrogen bond term δH of the Hansen solubility parameter is used as an index indicating the solubility of the thermoplastic acrylic resin and the multilayer structure polymer particles in a solvent. The numerical value of the hydrogen bond term δH has a higher correlation with the solubility of the methacrylic polymer (a) in the solvent than the London dispersion force term or the dipole force term, and the hydrogen bond term δH has a higher correlation with the solubility of the methacrylic polymer (a) in the solvent. It has been found that this can serve as an indicator. Details of the hydrogen bond term δH can be found, for example, in Hideki Yamamoto, “Special Feature: Polymer Compatibilization Design 1. Solubility Evaluation Using Hansen Solubility Parameters (HSP Value),” Adhesion Technology, Vol. 34 No. 3 (2014) Volume 116) pages 1-8.

Examples of the solvent (1) in which the hydrogen bond term δH is 1 or more and 12 or less include 1,4-dioxane (9.0), 2-phenylethanol (11.2), acetone (7.0), and acetonitrile. (6.1), chloroform (5.7), dibasic acid ester (8.4), diacetone alcohol (10.8), N,N-dimethylformamide (11.3), dimethyl sulfoxide (10.2) ), ethyl acetate (7.2), γ-butyrolactone (7.4), methyl ethyl ketone (5.1), methyl isobutyl ketone (4.1), methylene chloride (7.1), n-butyl acetate (6. 3), N-methyl-2-pyrrolidone (7.2), propylene carbonate (4.1), 1,1,2,2-tetrachloroethane (5.3), tetrahydrofuran (8.0), toluene (2) .0) etc. Note that the numbers in parentheses indicate the hydrogen bond term δH. These solvents may be used alone or in combination of two or more.

Among these solvents, methyl ethyl ketone, chloroform, and methylene chloride are preferred, and methylene chloride is more preferred, since they have excellent solubility for the thermoplastic acrylic resin and the multilayer polymer particles and also have a fast volatilization rate.

The solvent contained in the dope may be composed only of the solvent (1) in which the hydrogen bond term δH is 1 or more and 12 or less. However, in consideration of improvements in film formability, film releasability, handling properties, etc. during solution casting, the solvent (1) in which the hydrogen bond term δH is 1 or more and 12 or less, and the solvent (1) in which δH is 14 or more. Those containing the solvent (2) having a molecular weight of 24 or less are preferred.

Examples of the solvent (2) whose δH is 14 or more and 24 or less include methanol (22.3), ethanol (19.4), isopropanol (16.4), butanol (15.8), and ethylene glycol monoethyl. Examples include ether (14.3). These solvents may be used alone or in combination of two or more. Among these, methanol and ethanol, which are solvents with high δH, are preferred because the above-mentioned effects can be obtained by adding a small amount.

When the solvent (2) whose δH is 14 or more and 24 or less is used together, the content of the solvent (1) whose hydrogen bond term δH is 1 or more and 12 or less is 55% by weight based on the entire solvent contained in the dope. % or more and 98 weight% or less, more preferably 60 weight% or more and 97 weight% or less, further preferably 65 weight% or more and 96 weight% or less, and even more preferably 70 weight% or more and 95 weight% or less.

The proportion of the total amount of the thermoplastic acrylic resin and multilayer polymer particles in the dope is not particularly limited, and depends on the solubility or dispersibility of the thermoplastic acrylic resin and multilayer polymer particles in the solvent used, Although it can be determined as appropriate in consideration of the implementation conditions of the solution casting method, it is preferably 5 to 50% by weight, more preferably 6 to 40% by weight, and still more preferably 7 to 35% by weight.

(other ingredients)
The dope may optionally contain a light stabilizer, an ultraviolet absorber, a heat stabilizer, a matting agent, a light diffusing agent, a colorant, a dye, a pigment, an antistatic agent, a heat ray reflective material, a lubricant, a plasticizer, an ultraviolet absorber, Known additives such as stabilizers and fillers, or styrene resins such as acrylonitrile styrene resin and styrene maleic anhydride resin, polycarbonate resin, polyvinyl acetal resin, cellulose acylate resin, polyvinylidene fluoride and poly(alkyl fluoride) It may also contain other resins such as fluororesins such as acrylate resins, silicone resins, polyolefin resins, polyethylene terephthalate resins, and polybutylene terephthalate resins.

The dope is made of inorganic fine particles having birefringence described in Japanese Patent No. 3648201 and Japanese Patent No. 4336586, or birefringence described in Japanese Patent No. 3696649, for the purpose of adjusting the orientational birefringence of the film to be formed. It may contain a low molecular weight compound having a molecular weight of 5,000 or less, preferably 1,000 or less.

(Method for dispersing multilayer structure polymer particles in a solvent)
The dope is a mixture of a thermoplastic acrylic resin and multilayer polymer particles dissolved or dispersed in a solvent. In multilayer structure polymer particles, primary particles having a core-shell structure can be aggregated or welded to a size of several microns to several tens of millimeters. For this reason, when producing the dope, it is preferable to disperse the multilayer structure polymer particles in a solvent uniformly, preferably in a state in which even the primary particles are dispersed.

As a method for dispersing the multilayer structure polymer particles in a solvent, a wide variety of conventionally known methods can be applied. For example, a method in which powder of multilayer structure polymer particles is placed in a solvent and stirred while applying appropriate shear and/or heat to disperse it directly; a method in which multilayer structure polymer particles and thermoplastic acrylic resin are placed in a solvent at the same time; A method in which a dope is directly produced by stirring and dispersing or dissolving while applying appropriate shear and/or heat, or a method in which a thermoplastic acrylic resin and multilayer structure polymer particles are mixed in advance, preferably heated and melted. After applying appropriate shear force and melt-kneading to produce a resin composition in which multilayer structure polymer particles are dispersed in a thermoplastic acrylic resin (for example, a pellet-shaped resin composition), the resin composition is dispersed in a solvent. Examples include, but are not limited to, a method of producing a dope by applying a dope.

When dispersing multilayer polymer particles in a solvent, the action of the solvent (plasticization due to swelling), the action of heat (plasticization), and the action of disintegrating aggregated or welded primary particles by shearing force are applied as appropriate. is preferably applied to the multilayer structure polymer particles. By imparting these effects, the multilayer structure polymer particles are well dispersed in the dope, thereby avoiding negative effects such as the formation of foreign objects, fish eyes, and decreased transparency when producing films from the dope. be able to.

(Solution casting method)
The dope is used to produce a film by solution casting. Specifically, the film can be manufactured by casting the dope onto the surface of the support and then evaporating the solvent. A resin film manufactured by the solution casting method in this manner is also referred to as a cast film.

Embodiments of the solution casting method will be described below, but are not limited thereto. First, pellets containing a thermoplastic acrylic resin, multilayer structure polymer particles, and optionally the other components are prepared, and then the pellets are mixed with a solvent to produce a dope in which each component is dissolved and dispersed in the solvent. . Alternatively, the thermoplastic acrylic resin, the multilayer structure polymer particles, and optionally the other components are mixed in a solvent simultaneously or sequentially to produce a dope in which each component is dissolved and dispersed in the solvent. Alternatively, the thermoplastic acrylic resin and the multilayer structure polymer particles may be individually mixed in a solvent to prepare two or more dope preparation liquids, and the dope may be prepared by mixing these preparation liquids. These dissolution steps can be carried out by adjusting the temperature and pressure as appropriate. Among these methods, a method may be preferable in which pellets containing a thermoplastic acrylic resin, multilayer structure polymer particles, and optionally the other components are prepared and then dissolved and dispersed in a solvent. After the above dissolution step, the obtained dope can be filtered or defoamed.

Next, the dope is sent to a pressure die using a liquid feed pump, and the dope is cast from the slit of the pressure die onto the surface (mirror surface) of a support such as an endless belt or drum made of metal or synthetic resin. Then, a doped film is formed.

The formed doped film is heated on the support to evaporate the solvent and form a film. The film thus obtained is peeled off from the surface of the support. The obtained film may be subjected to a drying process, a heating process, a stretching process, etc. as appropriate.

(film)
The thickness of the film formed by the dope solution casting method described above is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and particularly preferably 200 μm or less. Moreover, it is preferably 10 μm or more, and particularly preferably 20 μm or more. If the thickness of the film is within the above range, it is possible to produce a film with uniform optical properties and good transparency, and it is difficult to deform when performing vacuum forming using the film, and it is difficult to deep draw. It has the advantage of being less likely to break at certain parts. On the other hand, if the thickness of the film exceeds the above range, air bubbles are likely to remain, which may result in appearance defects. Moreover, if the thickness of the film is less than the above range, handling of the film may become difficult.

The film preferably has a total light transmittance of 85% or more, more preferably 88% or more, and even more preferably 90% or more when measured at a film thickness of 40 μm. If the total light transmittance is within the above range, transparency is high and it can be suitably used for optical members, decorative applications, interior applications, and vacuum molding applications that require light transmittance.

The glass transition temperature of the film is preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, even more preferably 115°C or higher, particularly preferably 120°C or higher, and 124°C or higher. C or higher is most preferred. When the glass transition temperature is within the above range, a film with excellent heat resistance can be obtained.

The film preferably has a haze of 3.0% or less, more preferably 2.5% or less, even more preferably 2.0% or less, particularly 1.5% or less when measured at a film thickness of 40 μm. preferable. Further, the film preferably has an internal haze of 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less. Furthermore, the external haze of the film is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.0% or less, and particularly preferably 0.5% or less. When the haze, internal haze, and external haze are within the above ranges, transparency is high and it is suitable for optical members, decorative applications, interior applications, and vacuum molding applications that require light transmittance. Note that haze consists of haze inside the film and haze on the film surface (outside), and these are expressed as internal haze and external haze, respectively.

The film can also be used as an optical film. Especially when used as a polarizer protective film, it is preferable that the optical anisotropy is small. In particular, it is preferable that not only the optical anisotropy in the in-plane direction (length direction, width direction) of the film but also the optical anisotropy in the thickness direction be small. That is, it is preferable that the absolute values of both the in-plane retardation and the thickness direction retardation are small. More specifically, the absolute value of the in-plane retardation is preferably 10 nm or less, more preferably 6 nm or less, even 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 15 nm or less, even more preferably 10 nm or less, and even more preferably 5 nm or less. is most preferable. A 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. On the other hand, if the absolute value of the in-plane retardation of the film exceeds 10 nm or the absolute value of the thickness direction retardation exceeds 50 nm, when used as a polarizer protective film included in a polarizing plate of a liquid crystal display device, In some cases, problems such as a decrease in contrast may occur.

The retardation is an index value calculated based on birefringence, and the in-plane retardation (Re) and the thickness direction retardation (Rth) can be calculated using the following formulas. In an ideal film 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 film as the Z axis. , represents the refractive index in each axial direction. Further, d represents the thickness of the film, and nx-ny represents the orientational birefringence. Note that the MD direction of the film is the X-axis, but in the case of a stretched film, the stretching direction is the X-axis.

The film has an orientation birefringence value of preferably -2.6×10 ⁻⁴ to 2.6×10 ⁻⁴ , more preferably −2.1×10 ⁻⁴ to 2.1×10 ⁻⁴ , More preferably -1.7x10 ^-4 to 1.7x10 ^-4 , still more preferably -1.6x10 ^-4 to 1.6x10 ^-4 , even more preferably -1.5x10 ⁻⁴ to 1.5×10 ⁻⁴ , particularly preferably −1.0×10 ⁻⁴ to 1.0×10 ⁻⁴ , particularly preferably −0.5×10 ⁻⁴ to 0.5×10 ⁻⁴ , most preferably -0.2×10 ⁻⁴ to 0.2×10 ⁻⁴ . If the orientational birefringence is within the above range, stable optical properties can be achieved without birefringence occurring during molding. It is also very suitable as an optical film used in liquid crystal displays and the like.

(Stretching)
Although the film has high toughness and flexibility even as an unstretched film, it may be further stretched, thereby improving the mechanical strength and thickness accuracy of the film.

When stretching the film, an unstretched film is first formed from the dope, and then uniaxial or biaxial stretching is performed, or film formation and solvent degassing steps are performed during film forming. A stretched film (uniaxially stretched film or biaxially stretched film) can be produced by appropriately adding a stretching operation as the film progresses. 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 factors such as the mechanical strength, surface properties, and thickness accuracy 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. If the stretching ratio is within the above range, mechanical properties such as elongation rate, tear propagation strength, and resistance to rubbing fatigue of the film can be significantly improved.

(Application)
The film can have its surface gloss 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.

If necessary, the 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 an antireflection layer may be applied to the front or back surface of the film. Functional layers such as an antifouling layer, an antistatic layer, a printed decoration layer, a metallic luster layer, an uneven surface layer, and a matte layer can be formed and used.

The 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 film can be used by being laminated on a base material such as metal or plastic. Film lamination methods 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. For example,

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 by injection molding.

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

In particular, the 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.

(Manufacturing example 1)
<Production of multilayer structure polymer particles (B1)>
The following substances were charged into an 8L polymerization apparatus equipped with a stirrer.
Deionized water 175 parts Sodium polyoxyethylene lauryl ether phosphate 0.002 parts Sodium carbonate 0.04725 parts 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 potassium persulfate was added. A 2% aqueous solution was added, and then (I) shown in Table 1 was added continuously over 81 minutes. By continuing the polymerization for an additional 60 minutes, a polymer (I) was obtained. The polymerization conversion rate was 99.5%.
Thereafter, 0.08 part of potassium persulfate was added as a 2% aqueous solution, and then (II) shown in Table 1 was added continuously over 150 minutes. After the addition was completed, 0.015 part of pure potassium persulfate was added as a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain a polymer (II). The polymerization conversion rate was 99.7%, and the average particle diameter was 220.0 nm.
Thereafter, 0.023 part of potassium persulfate was added as a 2% aqueous solution, and (III-1) shown in Table 1 was added continuously over 45 minutes, and the polymerization was continued for an additional 30 minutes. Thereafter, (III-2) shown in Table 1 was continuously added over 25 minutes, and polymerization was continued for an additional 60 minutes to obtain a multilayer structure polymer particle latex. The polymerization conversion rate was 101.8%. The obtained latex was salted out with calcium chloride, coagulated, washed with water, and dried to obtain white powdery multilayer structure polymer particles (B1). The gel fraction of the multilayer structure polymer particles (B1) was 92%.

(Manufacturing examples 2 to 13)
<Production of multilayer structure polymer particles (B2) to (B13)>
Multilayer structure polymer particles (B2) to (B13) were produced in the same manner as Production Example 1, except that the types and amounts of the raw materials used were changed as shown in Table 1.

(Average particle diameter of multilayer structure polymer particles up to the rubber intermediate layer)
The average particle diameter was measured in the state of the latex obtained by polymerization up to the polymerization step (II). It was determined by measuring light scattering at a wavelength of 546 nm using a U-5100 ratio beam spectrophotometer manufactured by Hitachi High-Technologies Corporation as a measuring device.

(Polymerization conversion rate)
The polymerization conversion rate of the polymer obtained by polymerization was determined by the following method. Approximately 2 g of a sample (polymer latex) containing the 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 accurate weighing results 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

(gel fraction)
2 g of the obtained multilayer structure polymer particles were dissolved in 50 ml of methyl ethyl ketone, and centrifuged for 3 sets in total at 30,000 rpm for 1 hour using a centrifugal separator (CP60E, manufactured by Hitachi Koki Co., Ltd.) to remove insoluble particles. The components were separated from the soluble components. The weights of the obtained insoluble matter and soluble matter were measured, and the gel fraction and grafting rate were calculated from the following formula.
Gel fraction (%) = {(weight of methyl ethyl ketone insoluble portion)/(weight of methyl ethyl ketone insoluble portion + weight of methyl ethyl ketone soluble portion)}×100

(Manufacturing example 14)
<Manufacture of thermoplastic acrylic resin>
An 8-liter glass reactor equipped with an H-type stirrer was charged with 200 parts of deionized water and 0.5 part of disodium hydrogen phosphate as a suspension aid. Next, while stirring at 300 rpm, 85 parts of methyl methacrylate in which 0.3 part of lauroyl peroxide was dissolved, 10 parts of N-phenylmaleimide, 5 parts of 2-ethylhexyl methacrylate, and thioglycol as a chain transfer agent were added to the reactor. A monomer mixture containing 0.046 parts of 2-ethylhexyl acid (2-EHTG) was added, and the temperature was raised to 60° C. while purging the inside of the reactor with nitrogen to initiate polymerization. 50 minutes after reaching 60°C, 0.15% of ADEKA Pluronic F-68 (manufactured by ADEKA Co., Ltd., polyoxyethylene-polyoxypropylene block copolymer), which is a nonionic water-soluble polymer, was added as a suspension stabilizer. Part was added. Thereafter, the reaction was continued at 60°C for an additional 200 minutes, and then the temperature was raised to 80°C and stirred for 3 hours to complete the polymerization. The resulting polymer was washed four times with deionized water in an amount three times the amount of resin, and dried to obtain bead-shaped suspended polymer particles. The weight average molecular weight of the obtained polymer was confirmed by GPC and was found to be 1.62 million. This is referred to as a thermoplastic acrylic resin (A1).

(Examples 1 to 6 and Comparative Examples 1 to 7)
(Creation of resin dope containing multilayer structure polymer particles)
A mixed solvent consisting of 92% by weight of methylene chloride and 8% by weight of ethanol was placed in a screw tube container, and while stirring, the powder of the multilayer structure polymer particles listed in Table 2 was added little by little, and the mixture was heated using a magnetic stirrer until it became uniform. The obtained dispersion of multilayered polymer particles was further subjected to dispersion treatment for 15 minutes using an ultrasonic bath (Branson Nick 1510J, manufactured by Yamato Scientific Co., Ltd.), and then the dispersion was mixed with the thermoplastic resin shown in Table 2. The acrylic resin was added little by little and stirred until completely dissolved to produce a resin dope with a solid content concentration of 10%.

(Dispersibility evaluation using laser diffraction particle size distribution analyzer)
Measurement was performed using a laser diffraction particle size distribution meter (Mastersizer 3000, manufactured by Malvern). Using a mixed solvent of methylene chloride and ethanol as a dispersion medium, the dope was added dropwise while being circulated, and the measurement was performed so that the laser scattering intensity was 0.5 to 2.0%.
◎ when particles with a particle size of 1 μm or more account for less than 1 volume % of the total particles, ○ when particles with a particle size of 1 μm or more account for 1 volume % or more and less than 10 volume % of the total particles The case where the particles with a particle size of 1 μm or more accounted for 10 volume % or more and less than 15 volume % with respect to the whole particle was rated as Δ, and the case where the particle with a particle size of 1 μm or more occupied 15 volume % or more with respect to the whole particle was graded as ×.

(Preparation of cast film)
The above dope was cast onto a PET film (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and coated in a uniform film with an applicator. The clearance was adjusted so that the thickness after drying was approximately 30 to 50 μm. After coating, it was dried for 5 minutes in a dry atmosphere at 40°C, and then peeled off from the PET film. The obtained film was fixed to a stainless steel frame and dried in a dry atmosphere at 140° C. for 30 minutes to remove residual solvent, thereby obtaining a cast film. The thickness of this cast film is listed in Table 2. The film for evaluation of trimmability was formed in the same manner as above, except that the thickness was set to 70 to 90 μm.

(Total light transmittance and haze value)
The total light transmittance and haze value of the cast film were measured using a haze meter (HZ-V3 manufactured by Suga Test Instruments Co., Ltd.) according to the method described in JIS K7105. On the other hand, the film was placed in a quartz cell filled with pure water, and the value obtained when measuring in water was taken as the internal haze value, and the haze value - internal haze value = external haze value.

(film thickness)
The thickness of the cast film was measured using a Digimatic indicator (manufactured by Mitutoyo Co., Ltd.).

(Trimmability)
The presence or absence of cracks when a cutter blade was inserted in a direction parallel to the TD direction was evaluated on a five-point scale based on the following criteria. An evaluation score of 4 or more can be evaluated as good trimming performance.
1: Even when the film is fixed with a ruler, if you insert a cutter blade into it, cracks and small cracks will appear.
2: If the film is fixed with a ruler, no cracks will occur even if a cutter blade is inserted, but if a cutter blade is inserted without the film being fixed, cracks will occur.
3: When the film is fixed with a ruler, the cut surface is smooth without any cracks or minute cracks even when the cutter blade is inserted, but cracks occur when the cutter blade is inserted without the film being fixed. .
4: No cracking occurs even if a cutter blade is inserted without fixing the film.
5: Even when the cutter blade is inserted into the film without fixing it, no breakage or minute cracks occur, and the cut surface is smooth.

(Preparation of uniaxially stretched film)
A test piece with a width of 20 mm and a length of 100 mm was cut out from the unstretched films obtained in Examples and Comparative Examples, and the free end was uniaxially stretched at 135°C. The stretching ratio was 100% and the stretching speed was 200 mm/min.

(In-plane retardation Re, thickness direction retardation Rth, and orientational birefringence of uniaxially stretched film)
Test pieces were cut out from the center of the stretched films obtained in Examples and Comparative Examples. The in-plane retardation Re of this test piece was measured using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd.) at a wavelength of 590 nm and an incident angle of 0°. At the same time, measurement was performed at an incident angle of 40°, and the thickness direction retardation Rth was also calculated. Further, the value obtained by dividing the in-plane retardation of the above-mentioned uniaxially stretched film by the film thickness is listed in Table 2 as the orientation birefringence.

(Photoelastic constant of unstretched film)
A test piece was cut into a strip of 15 mm x 90 mm in the TD direction from the unstretched films obtained in Examples and Comparative Examples (the long side was cut out in the TD direction). Measurements were performed using an automatic birefringence meter (KOBRA-WR manufactured by Oji Keizoku Co., Ltd.) at a temperature of 23±2° C. and a humidity of 50±5% at a wavelength of 590 nm and an incident angle of 0°. The measurement was carried out by fixing one of the long sides of the film and measuring the birefringence while applying a load of 0.2kgf in increments of 0.2kgf from no load to 2kgf on the other side.From the obtained results, the change in birefringence due to unit stress was calculated. was calculated. The results are listed in Table 2.

(Orientation birefringence and photoelastic constant of multilayer structure polymer particles)
Regarding the orientation birefringence and photoelastic constant of the multilayer structure polymer particles alone, the multilayer structure polymer particles were pressed at 180°C to produce a press-molded sheet with a film thickness of 500 μm, and the orientation birefringence was determined in the same manner as above. and photoelastic constants were measured. Note that the photoelastic constant was measured after uniaxial stretching in the same manner as above. Those that were broken during stretching were considered unstretchable. The results are shown in Table 1.

From Table 2, in Examples 1 to 6, there were few coarse particles with a particle size of 1 μm or more in the dope containing the thermoplastic acrylic resin and multilayer structure polymer particles, and the particle dispersibility was good. It can be seen that the film produced by the solution casting method had a small external haze value, was less prone to cracking during cutting, and had good trimmability.
In Comparative Examples 1 and 2, the gel fraction in the multilayer structure polymer particles was low, and there were extremely many coarse particles with a particle size of 1 μm or more in the dope, resulting in poor particle dispersibility.
In Comparative Example 3, a large amount of polyfunctional monomer was used in the polymerization step (II) for forming the rubber intermediate layer, and the particle dispersibility of the dope was poor. The haze value was large and the trimmability was insufficient.
In Comparative Example 4, no hard core layer was formed, the dope particle dispersibility was poor, and the produced film had a large external haze value.
In Comparative Example 5, the amount of alkyl methacrylate used in the polymerization step (III) for forming the hard shell layer was as low as 57.2% by weight for the entire hard shell layer, and the particle dispersibility of the dope was poor. there were.
In Comparative Example 6, the amount of polyfunctional monomer used in the polymerization step (I) for forming the hard core layer was large, and the external haze value of the produced film was large, and the trimmability was insufficient. Met.
In Comparative Example 7, the monomer represented by the above-mentioned general formula (4) was not used in the polymerization step (II) for forming the rubber intermediate layer, and the particle dispersibility of the dope was poor. . Furthermore, since multilayer structure polymer particles with large birefringence were blended, the produced film also had large birefringence.
Comparative Example 8 did not contain multilayer structure polymer particles, and the trimmability of the film was insufficient.

Claims (14)

A dope for producing a film by a solution casting method, comprising a thermoplastic acrylic resin, multilayer structure polymer particles, and a solvent,
The thermoplastic acrylic resin is a polymer composed of 60 to 100% by weight of methyl methacrylate units and 0 to 40% by weight of other monomer units having copolymerizable double bonds,
The multilayer structure polymer particles include at least a hard core layer, a rubber intermediate layer, and a hard shell layer,
The hard core layer is made of a monomer consisting of 60 to 100% by weight of alkyl methacrylate, 0 to 35% by weight of alkyl acrylate, and 0 to 40% by weight of another monomer having a copolymerizable double bond. From a hard polymer (A) formed from a polymer component (a) and 0.1 to 1.0 parts by weight of a polyfunctional monomer (based on 100 parts by weight of monomer component (a)) configured,
The rubber intermediate layer contains 40 to 99% by weight of an acrylic acid alkyl ester, 1 to 60% by weight of a monomer represented by the following general formula (4), and other monomers having a copolymerizable double bond. Formed from monomer component (b) consisting of 0 to 40% by weight and 0.1 to 1.6 parts by weight of a polyfunctional monomer (based on 100 parts by weight of monomer component (b)) It is composed of a soft polymer (B) that is

(In the formula, R ⁹ represents a hydrogen atom or a substituted or unsubstituted linear or branched alkyl group having 1 to 12 carbon atoms. R ¹⁰ represents a substituted or unsubstituted linear or branched alkyl group having 5 to 24 carbon atoms. is an aromatic group, or a substituted or unsubstituted alicyclic group having 5 to 24 carbon atoms, and has a monocyclic structure or a heterocyclic structure. l represents an integer of 1 to 4. m is Indicates an integer from 0 to 1. n indicates an integer from 0 to 10.)
The hard shell layer comprises a monomer component (c) consisting of 60 to 100% by weight of alkyl methacrylate and 0 to 40% by weight of another monomer having a copolymerizable double bond, and a polyester. Consisting of a hard polymer (C) formed from 0 to 10 parts by weight of a functional monomer (based on 100 parts by weight of monomer component (c)),
The gel fraction of the multilayer structure polymer particles is 85% or more,
A dope, wherein the monomer represented by the general formula (4) is benzyl (meth)acrylate. The dope according to claim 1, wherein the multilayer structure polymer particles have an absolute value of orientational birefringence of 2×10 ⁻⁴ or less. The dope according to claim 1 or 2, wherein the multilayer structure polymer particles have an absolute value of a photoelastic constant of 3×10 ⁻¹² Pa ⁻¹ or less. The proportion of monomer component (a) is 15 to 35% by weight with respect to the total amount of monomer component (a), monomer component (b), and monomer component (c). Dope according to any one of claims 1 to 3, wherein the proportion of component (b) is 30 to 70% by weight and the proportion of monomer component (c) is 15 to 35% by weight. Any one of claims 1 to 4 , wherein the content of benzyl (meth)acrylate, which is a monomer represented by the general formula (4), in the monomer component (b) is 20% by weight or more. The dope according to item 1. The total content of benzyl (meth)acrylate, which is a monomer represented by the general formula (4), and a vinyl monomer having an aromatic group in the monomer component (a) is 0 to 15% by weight. Dope according to any one of claims 1 to 5, which is %. The total content of benzyl (meth)acrylate, which is a monomer represented by the general formula (4), and a vinyl monomer having an aromatic group in the monomer component (c) is 0 to 15% by weight. Dope according to any one of claims 1 to 6, which is %. The dope according to any one of claims 1 to 7, wherein the other monomer unit in the thermoplastic acrylic resin includes an N-substituted maleimide monomer unit. The dope according to claim 8, wherein the content of the N-substituted maleimide monomer unit in the thermoplastic acrylic resin is in the range of 1 to 25% by weight. The dope according to any one of claims 1 to 9, wherein the solvent is a mixed solvent of methylene chloride and ethanol or methanol. A method for producing a film by a solution casting method, the method comprising the step of evaporating the solvent after casting the dope according to any one of claims 1 to 10 on the surface of a support. A film formed from the dope according to any one of claims 1 to 10. The film according to claim 12, wherein the film has an external haze of 1.0% or less. The film according to claim 12 or 13, wherein the film is a stretched film.