JPWO2009150910A1 - Acrylic film manufacturing method and acrylic film manufactured by the manufacturing method - Google Patents

Abstract

A method for producing an acrylic film having excellent flexibility and surface property with high productivity and an acrylic film produced by the method were provided by the following. The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, the acrylic resin (A) has a weight average molecular weight Mw of 80000 to 1000000, and the cellulose ester resin The total substitution degree (T) of the acyl group in (B) is 2.0 or more and 3.0 or less, the substitution degree of the acyl group having 3 or more and 7 or less carbon atoms is 1.2 or more and 3.0 or less, and the weight average molecular weight Mw is A method for producing an acrylic film, comprising producing a resin composition of 75,000 or more and 300,000 or less under the following conditions. 1.10 ° C. ≦ stretching temperature−tension softening point of resin composition ≦ 100 ° C. 2.20% ≦ stretching ratio in at least one of MD direction or TD direction ≦ 100% 3.40% ≦ stretching ratio in MD direction + TD direction Stretch ratio ≦ 200%

Description

  The present invention relates to a method for producing an acrylic film, and more particularly to a method for improving the flexibility and brittleness of an acrylic film used as an optical film containing an acrylic resin.

  An acrylic film typified by a polymethyl methacrylate film (hereinafter abbreviated as PMMA) has been expected as an optical film because it has high transmittance in the visible light region, low intrinsic birefringence, and a small photoelastic coefficient.

  However, acrylic films are prone to cracking, and their inferior handleability has hindered their use.

  As a countermeasure, it has been proposed to mix acrylic rubber or butyl-modified cellulose ester as a toughness improver with an acrylic resin (Patent Document 1).

  Since this method is insufficient in flexibility, a technique has been proposed in which an acrylic resin itself has a new structure and is subjected to a stretching treatment (Patent Document 2).

Also known is a method of imparting flexibility by adding elastic particles to a specific acrylic film and further heat-treating (Patent Document 3).
A technique of mixing a flexible resin having a glass transition temperature of 10 ° C. or lower instead of elastic particles has also been proposed (Patent Document 4).
The method of Patent Document 2 can be applied only to a specific acrylic resin, has a small effect, and lacks versatility.

  In the method of Patent Document 3, there is a problem that the time required for the heat treatment is very long and the surface property of the manufactured acrylic film is inferior.

  Furthermore, the heat resistance is remarkably lowered, and when such an acrylic film is used, for example, in a liquid crystal display device, the film is deformed by continuous use for a long time, and a clear image cannot be displayed. There was a thing.

  The method of Patent Document 4 is effective for a specific acrylic resin having a lactone ring structure, and since it is premised on melt casting, the surface property does not exceed the level of Patent Document 2. It was. Further, as in Patent Document 2, there is a problem that heat resistance is remarkably lowered.

Japanese Patent Laid-Open No. 5-119217 JP 2005-162835 A WO2005 / 105918 JP 2007-100044 A

  The present invention provides a method for producing an acrylic film having excellent flexibility and surface properties with good productivity and an acrylic film produced by the method.

  The above-described problems of the present invention are solved by the following means.

1. The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, the acrylic resin (A) has a weight average molecular weight Mw of 80000 to 1000000, and the cellulose ester resin The total substitution degree (T) of the acyl group in (B) is 2.0 or more and 3.0 or less, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 or more and 3.0 or less, and the weight average molecular weight Mw A method for producing an acrylic film, comprising producing a resin composition having a thickness of 75,000 or more and 300000 or less under the following conditions.
(1) 10 ° C. ≦ stretching temperature−tensile softening point of resin composition ≦ 100 ° C.
(2) 20% ≦ at least one draw ratio in the MD direction or TD direction ≦ 100%
(3) 40% ≦ stretch ratio in MD direction + stretch ratio in TD direction ≦ 200%
2. 2. The method for producing an acrylic film according to 1 above, wherein the acrylic resin (A) is an acrylic resin having a methyl methacrylate unit in a molecule of 50% by mass to 99% by mass.

  3. In the atmosphere of 23 ° C. and 55% RH, ductile fracture does not occur, the tension softening point is 105 to 145 ° C., and the haze value is less than 1.0%. Acrylic film manufactured by the manufacturing method.

  The present invention provides a method for producing an acrylic film having excellent flexibility and surface properties with good productivity and an acrylic film produced by the method.

  That is, the present invention provides a technique for imparting flexibility applicable to general-purpose acrylic resins such as PMMA.

  In the present invention, even if it is an existing resin, not only the selection of an appropriate resin but also the addition of flexibility exceeding the level that has been considered to be insufficient until now depending on the selection of the molecular weight and the selection of the stretching method. Made it clear that

It is the figure which showed typically an example of the dope preparation process of the solution casting film forming method used for this invention, a casting process, and a drying process.

  Hereinafter, the present invention will be described in detail.

[Optical film]
<Acrylic resin (A)>
The acrylic resin used in the present invention includes a methacrylic resin. Although it does not restrict | limit especially as resin, What consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer units copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Unsaturated group-containing divalent carboxylic acids such as saturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, Maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride and the like can be mentioned, and these can be used alone or in combination of two or more monomers.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

  The acrylic resin (A) used in the acrylic film of the present invention has a weight average molecular weight (Mw) particularly from the viewpoint of improving brittleness as an acrylic film and improving transparency when it is compatible with the cellulose ester resin (B). Is 80,000 or more and 1,000,000 or less.

  When the weight average molecular weight (Mw) of the acrylic resin (A) is less than 80000, sufficient brittleness improvement cannot be obtained, and compatibility with the cellulose ester resin (B) deteriorates.

  The weight average molecular weight (Mw) of the acrylic resin (A) is particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000.

  The weight average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin (A) in this invention, It can manufacture by a well-known method. Any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electric Chemical Co., Ltd.), etc. are mentioned. . Two or more acrylic resins can be used in combination.

<Cellulose ester resin (B)>
The cellulose ester resin (B) of the present invention has a total acyl group substitution degree (T) of 2.0 to 3.3 from the viewpoint of transparency, particularly when it is improved in brittleness and is compatible with the acrylic resin (A). 0, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is preferably 2.0 to 3.0. .

  That is, the cellulose ester resin of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, but a propionyl group is particularly preferably used. .

  When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups at the 2, 3, and 6 positions of the cellulose ester molecule is more than 1.0, the acrylic ester When the resin (A) and the acrylic resin (B) are not sufficiently compatible and used as an optical film, haze becomes a problem.

  Moreover, even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, still sufficient compatibility cannot be obtained, Brittleness will decrease.

  For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased.

  Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

  As for the acyl substitution degree of the cellulose ester resin (B) of the present invention, the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but it is preferable that the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms is 1.3 or less.

  The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group.

  In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin (B) has an aromatic acyl group as a substituent, the number of the substituents X substituted on an aromatic ring is 0-3.

  Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0.

  For example, since the benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzoyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the cellulose ester resin (B) as described above, having a structure having at least one kind of an aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used in the cellulose resin of the present invention.

  The substitution degree of the cellulose ester resin (B) according to the present invention is such that the total substitution degree (T) of the acyl group is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 2.0. 3.0.

  Moreover, it is a preferable structure that the sum total of the substitution degree of other than an acyl group having 3 to 7 carbon atoms, that is, an acetyl group and an acyl group having 8 or more carbon atoms is 1.3 or less.

  The cellulose ester resin (B) according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, Those having an acyl group having 3 or 4 carbon atoms as a substituent are preferred.

  Among these, cellulose ester resins that are particularly preferred are cellulose acetate propionate and cellulose propionate.

  The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is in the range of 75,000 to 300,000 and particularly in the range of 100,000 to 240,000 from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness. Are more preferable, and those of 160000 to 240,000 are particularly preferable.

  When the important average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the effect of improving heat resistance and brittleness is not sufficient, and the effect of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  In the acrylic film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70 and in a compatible state, preferably 95: 5 to 50. : 50, more preferably 90: 10-60: 40.

  If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 30:70, the moisture resistance becomes insufficient.

  In the acrylic film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) need to be contained in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

  Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state is determined by the glass transition temperature Tg.

  When both resins are simply mixed, there are two glass transition temperatures for each resin because there is a glass transition temperature for each resin. However, when both resins are compatible, each glass has its own glass transition temperature. The temperature disappears and becomes one glass transition temperature, which becomes the glass transition temperature of the compatible resin.

The glass transition temperature T _g1,2 of the mixture in this compatible state is _approximated by the Gordon-Taylor equation (M. Gordon and JS Taylor, 2 J. of Applied Chem. 493-500 (1952)). It is known that it can be done. :
T _g1,2 = (w ₁ T _g1 + Kw ₂ T _g2 ) / (w ₁ + Kw ₂ )
[Where w ₁ and w ₂ are mass fractions of component 1 (acrylic resin (A)) and 2 (cellulose ester resin (B)); T _g1 and T _g2 are component 1 _{And Tg1,2} is the glass transition temperature of the mixture of components 1 and 2; K is a constant for the free volume of the two resins. ]
The glass transition temperature here is a nitrogen gas stream obtained by using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer Co., Ltd.) for 24 hours in an atmosphere of 23 ° C. and 55% RH. Medium, measured at a heating rate of 20 ° C./min, and defined as the midpoint glass transition temperature (Tmg) determined according to JIS K7121 (1987).

  The acrylic resin (A) and the cellulose ester resin (B) are each preferably an amorphous resin, and either one may be a crystalline polymer or a partially crystalline polymer. In the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably compatible with each other to become an amorphous resin.

  In the present invention, “containing acrylic resin (A) and cellulose ester resin (B) in a compatible state” means mixing each resin (polymer) to result in a compatible state. In this case, a state in which a precursor of acrylic resin such as monomer, dimer, or oligomer is mixed with cellulose ester resin (B) and then polymerized to be mixed resin is not included.

  For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin such as a monomer, dimer or oligomer with the cellulose ester resin (B) and then polymerizing it is complicated by the polymerization reaction. The resin is difficult to control the reaction, and it is difficult to adjust the molecular weight.

  In addition, when a resin is synthesized by such a method, graft polymerization, cross-linking reaction or cyclization reaction often occurs. In many cases, the resin is soluble in a solvent or cannot be melted by heating. Since it is difficult to elute the resin and measure the weight average molecular weight (Mw), it is difficult to control the physical properties and it cannot be used as a resin for stably producing an acrylic film.

  As long as the function as an optical film is not impaired, the acrylic film of this invention may contain resin and additives other than an acrylic resin (A) and a cellulose-ester resin (B).

  When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is contained, even if the added resin is in a compatible state, it may be mixed without being dissolved.

  The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the acrylic film of the present invention is preferably 55% by mass or more of the acrylic film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  When using resins and additives other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the addition amount within a range not impairing the function of the optical film of the present invention.

<Acrylic particles (C)>
The acrylic film of the present invention preferably contains acrylic particles (C).

  The acrylic particles (C) according to the present invention are present in a state of particles (also referred to as an incompatible state) in an acrylic film containing the acrylic resin (A) and the cellulose ester resin (B) in a compatible state. Represents an acrylic component.

  The acrylic particles (C) are obtained, for example, by collecting a predetermined amount of the prepared acrylic film, dissolving in a solvent, stirring, and sufficiently dissolving / dispersing the acrylic particles (C) with a pore size less than the average particle size. It is preferable that the weight of the insoluble matter filtered and collected using a PTFE membrane filter is 90% by mass or more of the acrylic particles (C) added to the acrylic film.

  The acrylic particles (C) used in the present invention are not particularly limited, but are preferably acrylic particles (C) having a layer structure of two or more layers, particularly the following multilayer structure acrylic granular composite. It is preferable.

  The multilayer structure acrylic granular composite is formed by laminating an innermost hard layer polymer, a cross-linked soft layer polymer exhibiting rubber elasticity, and an outermost hard layer polymer from the center to the outer periphery. This refers to a particulate acrylic polymer having a structure.

  That is, the multilayer structure acrylic granular composite is a multilayer structure acrylic granular composite comprising an innermost hard layer, a crosslinked soft layer, and an outermost hard layer from the central portion toward the outer peripheral portion. This three-layer core-shell multilayer acrylic granular composite is preferably used.

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following.

  (A) Monomer composed of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of polyfunctional grafting agent An innermost hard layer polymer obtained by polymerizing a mixture of the body, (b) in the presence of the innermost hard layer polymer, an alkyl acrylate having an alkyl group of 4 to 8 carbon atoms of 75 to 98.5% by mass. A crosslinked soft layer polymer obtained by polymerizing a mixture of monomers comprising 0.01 to 5% by mass of a polyfunctional crosslinking agent and 0.5 to 5% by mass of a multifunctional grafting agent, (c) In the presence of a polymer comprising an inner hard layer and a crosslinked soft layer, a mixture of monomers comprising 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Outermost obtained by polymerizing The layered polymer has a three-layer structure, and the obtained three-layered polymer is the innermost hard layer polymer (a) 5 to 40% by mass, the soft layer polymer (b) 30 to 60% by mass. And the outermost hard layer polymer (c) 20 to 50% by mass, having an insoluble part when fractionated with acetone, and an insoluble granular part having a methyl ethyl ketone swelling degree of 1.5 to 4.0 Complex.

  As disclosed in Japanese Patent Publication No. 60-17406 or Japanese Patent Publication No. 3-39095, not only the composition and particle size of each layer of the multilayer structure acrylic granular composite are defined, but also the multilayer structure acrylic granular composite. By setting the tensile modulus of the body and the degree of swelling of methyl ethyl ketone in the acetone-insoluble part within a specific range, it is possible to realize a further sufficient balance between impact resistance and stress whitening resistance.

  Here, the innermost hard layer polymer (a) constituting the multi-layer structure acrylic granular composite is 80 to 98.9% by mass of methyl methacrylate and 1 to 20% of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. % And a mixture of monomers consisting of 0.01 to 0.3% by mass of a polyfunctional grafting agent is preferred.

  Here, examples of the alkyl acrylate having 1 to 8 carbon atoms in the alkyl group include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like. And n-butyl acrylate are preferably used.

  The proportion of the alkyl acrylate unit in the innermost hard layer polymer (a) is 1 to 20% by mass. When the unit is less than 1% by mass, the thermal decomposability of the polymer is increased, while the unit is 20% by mass. If it exceeds 50%, the glass transition temperature of the innermost hard layer polymer (c) is lowered, and the impact resistance imparting effect of the three-layer structure acrylic granular composite is lowered.

  Examples of the polyfunctional grafting agent include polyfunctional monomers having different polymerizable functional groups, such as allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and allyl methacrylate is preferably used. . The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the ratio used during the innermost hard layer polymerization is 0.01 to 0.3% by mass. .

  The crosslinked soft layer polymer (b) constituting the acrylic granular composite is an alkyl acrylate 75-98.5 having 1 to 8 carbon atoms in the presence of the innermost hard layer polymer (a). What is obtained by polymerizing a monomer mixture consisting of mass%, polyfunctional crosslinking agent 0.01 to 5 mass% and polyfunctional grafting agent 0.5 to 5 mass% is preferred.

  Here, as the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, n-butyl acrylate or 2-ethylhexyl acrylate is preferably used.

  In addition to these polymerizable monomers, it is possible to copolymerize 25% by mass or less of other monofunctional monomers capable of copolymerization.

  Other monofunctional monomers that can be copolymerized include styrene and substituted styrene derivatives. As for the ratio of the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group and styrene, the glass transition temperature of the polymer (b) decreases as the former increases, that is, the ratio can be softened.

  On the other hand, from the viewpoint of the transparency of the resin assembly, the refractive index of the soft layer polymer (b) at room temperature is set to the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard heat. It is more advantageous to make it closer to the plastic acrylic resin, and the ratio between them is selected in consideration of these.

  As the polyfunctional grafting agent, those mentioned in the item of the innermost layer hard polymer (a) can be used.

  The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c), and the proportion used during the innermost hard layer polymerization is impact resistance. 0.5-5 mass% is preferable from a viewpoint of the property provision effect.

  As the polyfunctional crosslinking agent, generally known crosslinking agents such as divinyl compounds, diallyl compounds, diacrylic compounds, and dimethacrylic compounds can be used, and polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used.

  The polyfunctional cross-linking agent used here is used to generate a cross-linked structure at the time of polymerization of the soft layer (b) and develop an effect of imparting impact resistance.

  However, if the above-mentioned polyfunctional grafting agent is used during the polymerization of the soft layer, the polyfunctional crosslinking agent is not an essential component because the crosslinked structure of the soft layer (b) is generated to some extent. Is preferably 0.01 to 5% by mass from the viewpoint of imparting impact resistance.

  In the presence of the innermost hard layer polymer (a) and the soft layer polymer (b), the outermost hard layer polymer (c) constituting the multilayer structure acrylic granular composite is 80 to 99 masses of methyl methacrylate. % And a mixture of monomers consisting of 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferred.

  Here, as the acrylic alkylate, those described above are used, and methyl acrylate and ethyl acrylate are preferably used. The ratio of the alkyl acrylate unit in the outermost hard layer (c) is preferably 1 to 20% by mass.

  Further, for the purpose of improving the compatibility with the acrylic resin (A) during the polymerization of the outermost hard layer (c), it is also possible to use an alkyl mercaptan or the like as a chain transfer agent in order to adjust the molecular weight.

  In particular, it is preferable to provide the outermost hard layer with a gradient such that the molecular weight gradually decreases from the inside toward the outside in order to improve the balance between elongation and impact resistance.

  Specifically, the outermost hard layer is divided into two or more monomer mixtures for forming the outermost hard layer, and the amount of chain transfer agent to be added each time is increased sequentially. It is possible to decrease the molecular weight of the polymer forming the layer from the inside to the outside of the multilayer structure acrylic granular composite.

  The molecular weight formed at this time can also be examined by polymerizing a mixture of monomers used each time under the same conditions and measuring the molecular weight of the resulting polymer.

  The particle diameter of the acrylic particles (C) preferably used in the present invention is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, and more preferably 20 nm or more and 500 nm or less. In particular, the thickness is most preferably from 50 nm to 400 nm.

  In the acrylic granular composite that is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core and the shell is not particularly limited, but when the entire multilayer structure polymer is 100 parts by mass, The core layer is preferably 50 parts by mass or more and 90 parts by mass or less, and more preferably 60 parts by mass or more and 80 parts by mass or less. In addition, the core layer here is an innermost hard layer.

  Further, specific examples of the acrylic particles (c-1) which are graft copolymers suitably used as the acrylic particles (C) preferably used in the present invention include unsaturated carboxylic acids in the presence of a rubbery polymer. Mixtures of monomers consisting of acid ester monomers, unsaturated carboxylic acid monomers, aromatic vinyl monomers, and other vinyl monomers copolymerizable with these if necessary Examples thereof include a graft copolymer obtained by copolymerization.

  The rubbery polymer used for the acrylic particles (c-1) as the graft copolymer is not particularly limited, but diene rubber, acrylic rubber, ethylene rubber, and the like can be used.

  Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned.

  These rubbery polymers can be used alone or in a mixture of two or more.

  Moreover, when adding an acrylic particle (C) to the acrylic film of this invention, the refractive index of the mixture of an acrylic resin (A) and a cellulose-ester resin (B) and the refractive index of an acrylic particle (C) must be near. From the viewpoint of obtaining a film with high transparency.

  Specifically, the refractive index difference between the acrylic particles (C) and the acrylic resin (A) is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

  In order to satisfy such a refractive index condition, a method of adjusting the monomer unit composition ratio of the acrylic resin (A), or the composition of the rubbery polymer or monomer used in the acrylic particles (C) The difference in refractive index can be reduced by a method of adjusting the ratio, and an acrylic film having excellent transparency can be obtained.

  The refractive index difference referred to here is a solution in which the acrylic film of the present invention is sufficiently dissolved under a suitable condition in a solvent in which the acrylic resin (A) is soluble. After separating the solvent-soluble part and the insoluble part and purifying the soluble part (acrylic resin (A)) and insoluble part (acrylic particles (C)), the measured refractive index (23 ° C., measuring wavelength: 550 nm). ) Difference.

  There is no restriction | limiting in particular in the method of mix | blending an acrylic particle (C) with an acrylic resin (A) in this invention, After blending an acrylic resin (A) and another arbitrary component beforehand, normally at 200-350 degreeC, A method of uniformly melt-kneading with a single-screw or twin-screw extruder while adding acrylic particles (C) is preferably used.

  Also, a method in which a solution in which acrylic particles (C) are dispersed in advance is added to and mixed with a solution (dope solution) in which acrylic resin (A) and cellulose ester resin (B) are dissolved, acrylic particles (C) and A method such as in-line addition of a solution obtained by dissolving or mixing other optional additives can be used.

  A commercially available thing can also be used as an acrylic particle concerning this invention. For example, metabrene W-341 (C2) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C3), MS-300X (C4) (manufactured by Soken Chemical Co., Ltd.), Kanesu Chemical Industries Co., Ltd. "Paraloid" manufactured by Kureha Chemical Co., Ltd., "Acryloid" manufactured by Rohm and Haas, "Staffroid" manufactured by Gantz Kasei Kogyo Co., and "Parapet SA manufactured by Kuraray Co., Ltd.".

  In the acrylic film of this invention, it is preferable to contain 0.5-30 mass% acrylic particle (C) with respect to the total mass of resin which comprises this film, and it is the range of 1.0-15 mass%. It is more preferable to contain.

<Other additives>
In the acrylic film of this invention, in order to improve the fluidity | liquidity and softness | flexibility of a composition, it is also possible to use a plasticizer together. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The acrylic film of the present invention preferably uses a polymer plasticizer.

  In particular, polyesters described in paragraphs 0103 to 0116 of JP-A-2007-231157 and the above-described polyester plasticizers can be preferably used.

  In the acrylic film of the present invention, it is also preferable to use a sugar ester plasticizer obtained by esterifying a hydroxyl group of a sugar compound in which at least one type of structure of a selective extruder is bonded from a furanose structure and a pyranose structure.

  Examples of the sugar ester compound used in the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc. What has is preferable. An example is sucrose.

  As a commercial item, monopet SB (Daiichi Kogyo Seiyaku Co., Ltd. product) etc. are mentioned, for example.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the acrylic film of the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

  The acrylic film of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole-based, 2-hydroxybenzophenone-based or salicylic acid phenyl ester-based ones. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine A hybrid system having both structures can be mentioned, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

  Furthermore, various antioxidants can also be added to the acrylic film of the present invention in order to improve thermal decomposability and thermal colorability during molding. It is also possible to add an antistatic agent to impart antistatic performance to the acrylic film.

  For the acrylic film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphates, halogen-containing condensed phosphonates, halogen-containing phosphites, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

  According to the acrylic film of the present invention, improvement in low hygroscopicity, transparency, high heat resistance, and brittleness that cannot be achieved by conventional resin films can be achieved at the same time.

  In the present invention, the brittleness index is determined based on the criterion of whether or not the “acrylic film does not cause ductile fracture”.

  By obtaining an acrylic film with improved brittleness that does not cause ductile fracture, even when creating a polarizing plate for a large-sized liquid crystal display device, it does not break or crack during production and has excellent handling properties. It can be an acrylic film.

  Here, the ductile fracture is a fracture caused by applying a stress larger than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material until the final fracture. The fracture surface is characterized by numerous indentations called dimples.

  In the present invention, whether or not the film is an “acrylic film that does not cause ductile fracture” is evaluated based on the fact that no breakage or the like is observed even when a large stress is applied such that the film is folded in two. .

  If it is an acrylic film that does not cause ductile fracture even when such a large stress is applied, even if it is used as a polarizing plate protective film for an enlarged liquid crystal display device, problems such as breakage during production In addition, even when the acrylic film is used after being peeled off after being pasted once, no breakage occurs, and the acrylic film can be sufficiently reduced in thickness.

  In the present invention, the tension softening point is used as an index of heat resistance.

  In addition to the increasing size of liquid crystal display devices and the increasing brightness of backlight light sources, the use of digital signage and other outdoor applications demands higher brightness. However, if the tension softening point is 105 ° C. to 145 ° C., it can be determined that sufficient heat resistance is exhibited. In particular, it is more preferable to control to 110 ° C to 130 ° C.

  As a specific measuring method of the temperature indicating the tension softening point of the acrylic film, for example, using an Tensilon tester (ORIENTEC, RTC-1225A), the acrylic film is cut out at 120 mm (length) × 10 mm (width). The temperature can be raised at a rate of 30 ° C./min while pulling with a tension of 10 N, and the temperature at the time when the pressure reaches 9 N is measured three times, and the average value can be obtained.

  From the viewpoint of heat resistance, the acrylic film preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  A haze value (turbidity) is used as an index for judging the transparency of the acrylic film in the present invention.

  In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  According to the acrylic film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property. By increasing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and the acrylic particles (C), an increase in haze value can be prevented.

  In addition, since the surface roughness also affects the haze value as surface haze, the particle diameter and addition amount of acrylic particles (C) should be kept within the above range, and the surface roughness of the film contact portion during film formation should be reduced. Is also effective.

  In addition, the hygroscopicity of the acrylic film in the present invention is evaluated by dimensional change with respect to humidity change.

  The following method is used as an evaluation method of dimensional change with respect to humidity change.

  In the casting direction of the produced acrylic film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the mark (cross) before and after treatment was measured with an optical microscope, Obtain the dimensional change rate (%). The dimensional change rate (%) is expressed by the following formula.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
a1: Distance before heat treatment a2: Distance after heat treatment When an acrylic film is used as a protective film for a polarizing plate of a liquid crystal display device, unevenness or a change in retardation value occurs due to a dimensional change due to moisture absorption. This causes problems such as a decrease in contrast and uneven color.

  In particular, the above problem becomes significant when the polarizing plate protective film is used in a liquid crystal display device used outdoors. However, if the dimensional change rate (%) under the above conditions is less than 0.5%, it can be evaluated that the acrylic film exhibits sufficiently low hygroscopicity. Furthermore, it is preferable that it is less than 0.3%.

  In addition, the acrylic film of the present invention preferably has a defect with a diameter of 5 μm or more in the film plane of 1 piece / 10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object.

  When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

  When the number of defects is greater than 1/10 cm square, for example, when the film is tensioned during processing in a later process, the film may break with the defects as a starting point, and productivity may decrease.

  Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

  Moreover, even when it cannot be visually confirmed, when a hard coat layer or the like is formed on the film, the coating agent may not be formed uniformly, resulting in a defect (missing coating).

  Here, the defect is a void in the film (foaming defect) generated due to the rapid evaporation of the solvent in the drying process of the solution casting, a foreign matter in the film forming stock solution, or a foreign matter mixed in the film forming. This refers to the foreign matter (foreign matter defect) in the film.

  The acrylic film of the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more, in the measurement based on JIS-K7127-1999.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  The thickness of the acrylic film of the present invention is preferably 20 μm or more. More preferably, it is 30 μm or more.

  The upper limit of the thickness is not particularly limited, but in the case of forming a film by a solution casting method, the upper limit is about 250 μm from the viewpoint of applicability, foaming, solvent drying, and the like. The thickness of the film can be appropriately selected depending on the application.

  The acrylic film of the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more.

  Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact part (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roll, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the acrylic resin.

  The acrylic film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

  Such physical properties include an acrylic film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and the weight average molecular weight Mw of the acrylic resin (A) is 80000. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.00 to 3.00, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. The weight average molecular weight (Mw) is 75000 or more.

<Film formation of acrylic film>
An example of a method for forming an acrylic film will be described, but the present invention is not limited to this.

  As the method for forming the acrylic film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the standpoint of suppressing optical defects such as die lines and optical defects such as die lines, solution casting by casting is preferred.

(Organic solvent)
The organic solvent useful for forming the dope when the acrylic film of the present invention is produced by the solution casting method is one that simultaneously dissolves the acrylic resin (A), the cellulose ester resin (B), and other additives. It can be used without any limitation.

  For example, as the chlorinated organic solvent, methylene chloride, as the non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the ratio of alcohol in the dope increases, the web gels and peeling from the metal support becomes easy. When the ratio of alcohol is small, acrylic resin (A) and cellulose ester in non-chlorine organic solvent system. There is also a role of promoting dissolution of the resin (B).

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, acrylic resin (A), cellulose ester resin (B), and acrylic particles (C) 3 A dope composition in which at least 15 to 45 mass% of the seed is dissolved is preferable.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

  Hereinafter, the preferable film-forming method of the acrylic film of this invention is demonstrated.

1) Dissolution Step In an organic solvent mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B), the acrylic resin (A), the cellulose ester resin (B), and optionally acrylic particles ( C), a step of dissolving other additives while stirring to form a dope, or the acrylic resin (A) and cellulose ester resin (B) solutions, optionally with acrylic particle (C) solutions and other additive solutions Are mixed to form a dope which is a main solution.

  For dissolving the acrylic resin (A) and the cellulose ester resin (B), a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544 Various dissolution methods such as a method of performing a cooling dissolution method as described in JP-A-9-95557 or JP-A-9-95538, a method of performing at a high pressure as described in JP-A-11-21379, and the like. Although it can be used, a method in which pressure is applied at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

  The total amount of the acrylic resin (A) and the cellulose ester resin (B) in the dope is preferably in the range of 15 to 45% by mass. After the additive is added to the dope during or after dissolution, the dope is dissolved and dispersed, filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  In this method, the aggregate remaining at the time of particle dispersion and the aggregate generated when the main dope is added are aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can only be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

  FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention.

  If necessary, large agglomerates are removed from the acrylic particle charging kettle 41 by the filter 44 and fed to the stock kettle 42. Thereafter, the acrylic particle additive solution is added from the stock kettle 42 to the main dope dissolving kettle 1.

  Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. The return material may contain acrylic particles. In that case, it is preferable to control the addition amount of the acrylic particle addition liquid in accordance with the addition amount of the return material.

  The additive solution containing acrylic particles preferably contains 0.5 to 10% by mass of acrylic particles, more preferably 1 to 10% by mass, and 1 to 5% by mass. Most preferably.

  If it is in the said range, since an addition liquid is low-viscosity, it is easy to handle and it is easy to add to the main dope, it is preferable.

  Recycled material is a finely pulverized acrylic film, which is generated when the acrylic film is formed, and is cut off on both sides of the film, or the original acrylic film that has been speculated out of scratches is used. .

  In addition, an acrylic resin, a cellulose ester resin, and optionally an acrylic particle kneaded into pellets can be preferably used.

2) Casting process An endless metal belt 31 such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting a dope from a pressure die slit to a casting position on a metal support.

  A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

  To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc., but the back side liquid heat transfer method has a drying efficiency. Well preferred. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or to heat by means such as infrared rays.

  From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

  The temperature at the peeling position on the metal support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C.

  In addition, it is preferable that the residual solvent amount at the time of peeling of the web on the metal support at the time of peeling is peeled in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. If the web is peeled off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes are likely to occur due to the peeling tension. The amount of solvent is determined.

  The residual solvent amount of the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

  The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N / m. However, when wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension that can be peeled to 166.6 N / m, and then peel at a minimum tension to 137.2 N / m, and particularly preferably peel at a minimum tension to 100 N / m.

  In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40 ° C, more preferably 10 to 40 ° C, and most preferably 15 to 30 ° C.

5) Drying and stretching step After peeling, using a drying device 35 that alternately feeds the web through a plurality of rolls arranged in the drying device, or a tenter stretching device 34 that clips and transports both ends of the web with clips, Dry the web.

  Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout the drying is generally carried out at 40-250 ° C. It is particularly preferable to dry at 40 to 160 ° C.

  The stretching is preferably performed with a clip tenter, but a pin tenter can also be used.

In the present invention, stretching is preferably performed under the following conditions.
(1) 10 ° C. ≦ stretching temperature−tensile softening point of resin composition ≦ 100 ° C.
(2) 20% ≦ at least one draw ratio in the MD direction or TD direction ≦ 100%
(3) 40% ≦ stretch ratio in MD direction + stretch ratio in TD direction ≦ 200%
Regarding the stretching conditions, if the stretching temperature is too low, the brittleness deteriorates. In this case, an unnecessarily stress is generated at the time of stretching, and the polymer molecules are excessively oriented, and this orientation is not preferable because it is easy to tear in the direction parallel to the stretching.

  An excessively high temperature is not preferable because entanglement of the polymer does not occur. In addition, when the temperature is too high, the polymer may flow or deteriorate.

  If the draw ratio is too low, brittleness will not be improved because the distance of movement of the molecular chain of the polymer is small and entanglement does not occur.

  If the draw ratio is too high, voids may be partially generated, and this void is not preferable because it causes haze increase, cracking, and tearing and deteriorates brittleness.

  Thus, a remarkable effect is obtained only when the film is stretched in a specific temperature range and stretch ratio.

  When using a tenter apparatus for stretching, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

  It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is also preferable to implement biaxial stretching in a casting direction and a width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

  In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  The stretching speed is preferably 10% to 500% / min depending on the web conveyance speed. If the stretching speed is too slow, no stress is applied when the molecular chain of the polymer is moved, so that the molecular chain slides and entanglement hardly occurs, and brittleness has little improvement effect. If the stretching speed is too high, stress is applied too much and the movement of the molecular chain of the polymer cannot catch up, and voids may be partially generated.

In the stretching step, the heat transfer coefficient may be constant or may be changed. The heat transfer coefficient preferably has a heat transfer coefficient in the range of 41.9 to 419 × 103 J / m ² hr. More preferably, in the range of ^{41.9~209.5 × 10 3 J / m 2} hr, and most preferably a range of ^{41.9~126 × 10 3 J / m 2} hr.

  Even under the preferable stretching conditions as described above, this effect cannot be obtained depending on the resin. In particular, PMMA which is a general acrylic is less effective.

  Similarly, the cellulose ester resin hardly improves the brittleness and is less effective. In the case of a cellulose ester resin, since the tension softening point of the resin is relatively high, it is necessary to stretch the resin at a high temperature. However, if the resin is too high, the resin may decompose and the strength may decrease.

  However, as a result of studying the stretching of various resins, the effect of improving the brittleness can be greatly improved by blending a specific resin even in the case of a general acrylic resin such as PMMA, which is less effective in improving the brittleness by stretching. I understood it.

  In particular, a remarkable effect can be obtained by blending cellulose ester resin, which alone has little effect of improving brittleness due to stretching.

  This is because by blending a general acrylic resin with a linear but relatively flexible molecular structure and a cellulose ester resin with a linear and bulky molecular structure, it is possible to create a part where the molecules are entangled. When the film is stretched, the molecular chains become entangled and interact with each other, which is considered to improve brittleness.

  In other words, entanglement of molecules with different structures is considered important for maximizing the interaction and increasing the brittleness improvement effect.

  In addition, the compatibility of the resin to be blended with the acrylic resin is also very important. If the resin is not uniformly compatible, there is almost no effect of improving brittleness.

  About this, the total substitution degree (T) of the acyl group of cellulose-ester resin shall be 2.0 or more and 3.0 or less, and the substitution degree of the acyl group whose carbon number is 3 or more and 7 or less shall be 1.2 or more and 3.0 or less. Can be solved.

  When the molecular weight of the acrylic resin and the cellulose ester resin is small, the entanglement of molecules is insufficient and the effect of improving brittleness is small. Therefore, the weight average molecular weight Mw of the acrylic resin is preferably 80000 or more, and the cellulose ester resin weight average molecular weight Mw is 75000 or more. preferable.

  However, if the molecular weight is too large, the viscosity of the dope increases and film formation becomes difficult. Therefore, the weight average molecular weight Mw of the acrylic resin is preferably 1000000 or less, and the cellulose ester resin weight average molecular weight Mw is preferably 300000 or less.

  When the tenter is stretched, the residual solvent amount of the web is preferably 20 to 100% by mass at the start of the tenter, and drying is performed while the tenter is applied until the residual solvent amount of the web becomes 10% by mass or less. Is more preferable, and more preferably 5% by mass or less.

  In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.

6) Winding step This is the step of winding the acrylic film as an acrylic film by the winder 37 after the residual solvent amount in the web is 2% by mass or less. A film having good properties can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

  As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  The acrylic film of the present invention is preferably a long film. Specifically, the acrylic film has a thickness of about 100 m to 5000 m and is usually provided in a roll shape. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-2m.

  Although there is no restriction | limiting in particular in the film thickness of the acrylic film of this invention, when using for the polarizing plate protective film mentioned later, it is preferable that it is 20-200 micrometers, it is more preferable that it is 25-100 micrometers, and it is 30-80 micrometers. It is particularly preferred.

〔Polarizer〕
When using the acrylic film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the acrylic film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  On the other side, the acrylic film of the present invention may be used, or another polarizing plate protective film may be used.

  For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

[Liquid Crystal Display]
By incorporating the polarizing plate bonded with the acrylic film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate according to the present invention includes a reflective type, a transmissive type, a transflective type LCD or a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), an IPS type (including an FFS type), and the like. It is preferably used in LCDs of various driving methods.

  In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
[Preparation of acrylic resin]
The following acrylic resins A1-A7 and MS1, 2 were prepared by a known method.

A1: Monomer mass ratio (MMA: MA = 98: 2), Mw 70000
A2: monomer mass ratio (MMA: MA = 97: 3), Mw 160000
A3: monomer mass ratio (MMA: MA = 97: 3), Mw350,000
A4: monomer mass ratio (MMA: MA = 97: 3), Mw550,000
A5: monomer mass ratio (MMA: MA = 97: 3), Mw 800000
A6: monomer mass ratio (MMA: MA = 97: 3), Mw 930,000
A7: monomer mass ratio (MMA: MA = 94: 6), Mw1100000
MS1: monomer mass ratio (MMA: ST = 60: 40), Mw100,000
MS2: monomer mass ratio (MMA: ST = 40: 60), Mw100,000
MMA: Methyl methacrylate MA: Methyl acrylate ST: Styrene (Synthesis of A8)
First, a methyl methacrylate / acrylamide copolymer suspension was prepared as follows.

Methyl methacrylate 20 parts by weight Acrylamide 80 parts by weight Potassium persulfate 0.3 part by weight Ion-exchanged water 1500 parts by weight The above is charged into the reactor and the reactor is replaced with nitrogen gas. The reaction was allowed to proceed at 70 ° C. until converted to. The obtained aqueous solution was used as a suspending agent. A solution in which 0.05 part by mass of the above suspending agent is dissolved in 165 parts by mass of ion-exchanged water is supplied to a stainless steel autoclave having a capacity of 5 liters and equipped with a baffle and a foudra-type stirring blade, and the system is filled with nitrogen gas. It stirred at 400 rpm, replacing.

  Next, a mixed substance having the following charge composition was added while stirring the reaction system.

Methacrylic acid 27 parts by weight Methyl methacrylate 73 parts by weight t-dodecyl mercaptan 1.2 parts by weight 2,2′-azobisisobutyronitrile 0.4 part by weight The mixture was heated to 70 ° C. and the internal temperature was 70 ° C. The time at which the polymerization was reached was set as the polymerization start time, and the polymerization was continued for 180 minutes.

  Thereafter, the reaction system was cooled, the polymer was separated, washed and dried in accordance with a normal method to obtain a bead-shaped copolymer. The polymerization rate of this copolymer was 97%, and the weight average molecular weight was 130,000.

  0.2% by mass of an additive (NaOCH3) is blended in this copolymer, and nitrogen is added from the hopper portion to 10 L / L using a twin screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5)). While purging with a minute amount, an intramolecular cyclization reaction was performed at a screw rotation speed of 100 rpm, a raw material supply rate of 5 kg / hour, and a cylinder temperature of 290 ° C. The acrylic resin A8 had a weight average molecular weight (Mw) of 130000 and a Tg of 140 ° C.

  The acrylic resin described in Example 1 of Patent Document 3 (WO2005 / 105918) was prepared by the same method as that described in Patent Document 3, and used as a comparative acrylic film * 1 (sample acrylic film 48). .

  Polymer 1A of Example 1 of Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-100044) was prepared by the same method as that described in Patent Document 4, and used as a comparative acrylic film * 2 (sample acrylic film 50). .

  In addition, the following commercially available acrylic resins were used.

Dianar BR80 (Mitsubishi Rayon Co., Ltd.) Mw95000
Dianar BR83 (Mitsubishi Rayon Co., Ltd.) Mw40000
Dianar BR85 (Mitsubishi Rayon Co., Ltd.) Mw280000
Dianar BR88 (manufactured by Mitsubishi Rayon Co., Ltd.) Mw 480000
80N (Asahi Kasei Chemicals Corporation) Mw100,000
The ratio of the MMA unit in the molecule in the commercially available acrylic resin was 90% by mass or more and 99% by mass or less.

[Production of acrylic film]
<Preparation of acrylic film 1-1>
(Dope solution composition 1)
Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) 70 parts by mass Cellulose ester CE1 30 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass The above composition was sufficiently dissolved while heating to prepare a dope solution.

(Made of acrylic resin film)
The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the amount of residual solvent reached 100%, and peeling was performed from the stainless steel band support with a peeling tension of 162 N / m.

  The peeled acrylic resin web was evaporated at 35 ° C., slit to 1.6 m width, and then stretched to 40% in the width direction (TD direction) while heating to 140 ° C. with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%.

  After stretching with a tenter, relaxation was performed at 130 ° C. for 5 minutes, and then drying was completed while transporting a drying zone at 120 ° C. and 140 ° C. with many rolls, slitting to a width of 1.5 m, and a width of 10 mm at both ends of the film A knurling process having a height of 5 μm was performed, and the film was wound around a core having an inner diameter of 15.24 cm with an initial tension of 220 N / m and a final tension of 110 N / m to obtain an acrylic film 1-1 as an acrylic resin film.

  The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 40%.

  The residual solvent amount of the acrylic film 1 described in Table 1 was 0.1%, the film thickness was 60 μm, and the winding length was 4000 m.

<Preparation of Acrylic Films 1-2 to 1-28, 2-47, 49>
In the production of the acrylic film 1, the acrylic film (A) and the cellulose ester resin (B) were prepared in the same manner except that the types, composition ratios, stretching temperature, and stretching ratio were changed as shown in Table 1. 1-2 to 1-28, 2-47, and 49 were produced. In the table, “amount” represents parts by mass.

  The acyl groups of the cellulose ester resins described in Table 1 are as follows: ac is an acetyl group, pr is a propionyl group, bu is a butyryl group, pen is a pentanoyl group, bz is a benzoyl group, hep is a heptanoyl group, oct is an octanoyl group, ph represents a phthalyl group.

<Preparation of acrylic film 51>
In the production of the acrylic film 1, an acrylic film 51, which is an acrylic resin film, was produced in the same manner except that the dope composition was changed to the following.

(Dope composition liquid 51)
Dianar BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) 70 parts by mass Cellulose ester CE1 30 parts by mass Methylene chloride 140 parts by mass Toluene 200 parts by mass The glass transition temperature of the produced acrylic film 51 is determined by a differential scanning calorimeter (Perkin Elmer). When measured using a DSC-7 model), peaks were observed at two locations of Tg1: 105 ° C and Tg2: 145 ° C, and the acrylic resin (A) and the cellulose ester resin (B) were incompatible. It was found to exist in a state.

"Evaluation methods"
The following evaluation was implemented about the obtained acrylic films 1-51.

(Haze: Transparency evaluation that greatly affects contrast)
A sample conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH was subjected to the same conditions for each of the above-prepared film samples in accordance with JIS K-7136. The color was measured using a color industry.

(Tension softening point: heat resistance evaluation)
A sample conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH was evaluated as follows using a Tensilon tester (produced by ORIENTEC, RTC-1225A) under the same conditions.

  The acrylic film was cut out at 120 mm (length) × 10 mm (width), and the temperature was increased at a rate of 30 ° C./min while pulling with a tension of 10 N. Averaged.

(Ductile fracture: brittleness evaluation)
A sample conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH was cut out at 100 mm (length) × 10 mm (width) under the same conditions, with a radius of curvature of 0 mm and a bending angle of 180 ° at the center in the vertical direction. Then, the film was folded once in a mountain fold and a valley fold so that the films were exactly overlapped, and this evaluation was measured 5 times and evaluated as follows. In addition, breaking of evaluation here represents having broken and isolate | separated into two or more pieces.

○: Cannot be folded 5 times △: Can be folded 1 time out of 5 times ×: Can be folded at least 2 times out of 5 times (Film deformation: heat resistance evaluation for long-term use)
Each acrylic film was left in an atmosphere of 90 ° C. and DRY (relative humidity 5% RH or less) for 1000 hours, and then the degree of film deformation was visually observed and evaluated according to the following criteria.

○: No deformation of the film Δ: Deformation of the film is recognized ×: Remarkable deformation of the film is recognized (Dimensional change with respect to humidity change: evaluation of moisture resistance)
In the casting direction of the produced acrylic film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the mark (cross) before and after treatment was measured with an optical microscope, Evaluation was made according to the following criteria.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
In the formula, a1 represents a distance before heat treatment, and a2 represents a distance after heat treatment.

○: Less than 0.3% Δ: 0.3% or more, less than 0.5% ×: 0.5% or more (slitting property)
The slitting property was evaluated by the number of ruptures during slitting using a 300 mm width film of 1000 m roll, slitting width 50 mm, slitting speed 10 m / min, tension 5 kg, slitting method using an upper blade / lower blade method. There is accumulation of empirical data on the number of breaks when evaluated under conditions and the number of breaks in the actual process,
◯: The number of breaks is 10 or less; almost no breakage occurs in the actual process, and preferable Δ: The number of breaks is 11 to 20; breakage sometimes occurs in the actual process, but somehow practical level ×: the breakage described above Number of times 21 or more: It was found that breakage frequently occurred in an actual process and was not practical, and this was evaluated.

(Film appearance: Manufacturing suitability evaluation)
About the produced acrylic film, the film external appearance was evaluated visually and evaluated according to the following references | standards.

○: Very smooth flatness △: Slightly creased, wrinkled, and steps can be confirmed ×: Clearly creased, creased, and steps can be confirmed

  As is apparent from the table, according to the present invention, it was possible to provide a method for producing an acrylic film having excellent flexibility and surface property with high productivity and an acrylic film produced by the method.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Conduit 10 Ultraviolet absorber charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter

Claims (3)

The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, the acrylic resin (A) has a weight average molecular weight Mw of 80000 to 1000000, and the cellulose ester resin The total substitution degree (T) of the acyl group in (B) is 2.0 or more and 3.0 or less, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 or more and 3.0 or less, and the weight average molecular weight Mw A method for producing an acrylic film, comprising producing a resin composition having a thickness of 75,000 or more and 300000 or less under the following conditions.
(1) 10 ° C. ≦ stretching temperature−tensile softening point of resin composition ≦ 100 ° C.
(2) 20% ≦ at least one draw ratio in the MD direction or TD direction ≦ 100%
(3) 40% ≦ stretch ratio in MD direction + stretch ratio in TD direction ≦ 200%   2. The method for producing an acrylic film according to claim 1, wherein the acrylic resin (A) is an acrylic resin having a methyl methacrylate unit in a molecule of 50% by mass or more and 99% by mass or less.   3. The atmosphere according to claim 1, wherein ductile fracture does not occur under an atmosphere of 23 ° C. and 55% RH, the tension softening point is 105 to 145 ° C., and the haze value is less than 1.0%. Acrylic film manufactured by the manufacturing method.