JP2009052025A - Thermoplastic resin film, optical film, and polarization plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoplastic resin film preferable as an optical film with a simple manufacturing step suitable for polarization element protection usage, and a polarization plate. <P>SOLUTION: The thermoplastic resin film contains an amorphous thermoplastic resin A having negative double refraction property and a glass transition temperature (Tg) of 120°C or higher, and is made to the film simultaneously satisfying the following conditions (i)-(iii): (i) it has a photoelastic efficiency of a positive value and the value of 0.01×10<SP>-12</SP>Pa<SP>-1</SP>-5.0×10<SP>-12</SP>Pa<SP>-1</SP>, (ii) it has dimension variation after the treatment at a temperature of 60°C at a relative humidity of 90% is performed for 300 hours of 0.5% or less, and (iii) it has permeability of the whole light beam of 90% or higher and haze of 1.0% or lower. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is a thermoplastic film, an optical film, and a polarizing film, which are particularly suitable for polarizer protection applications, have a small retardation, a small change in birefringence due to stress, and a small dimensional change in a durability test. Regarding the board.

  A plastic film used for a display device that handles polarized light, such as a liquid crystal display device, is optically transparent and has low birefringence and is required to have optical homogeneity. For this reason, in the case of a polarizer protective film for protecting a polarizer made of highly stretched polyvinyl alcohol or a film substrate for a plastic liquid crystal display device in which the glass substrate is replaced with a resin film, the product of birefringence and thickness The expressed phase difference is required to be small. Further, when the phase difference of the film changes due to external stress or the like, there is a problem that the beauty of the display is impaired and it cannot be used.

  Conventionally, a triacetyl cellulose film has been used as the polarizer protective film. However, the triacetyl cellulose film has insufficient heat resistance and moisture resistance, and when used at high temperature or high humidity, the polarizer and the triacetyl cellulose film may peel off or the triacetyl cellulose may be hydrolyzed to be transparent. The polarizing plate performance is lowered and the degree of polarization of the polarizer is lowered.

  On the other hand, the polarizing plate which uses the polycarbonate (henceforth PC) film which adjusted molecular weight and Tg and was excellent in durability as a polarizer protective film is disclosed (patent document 1). However, since PC has a high photoelastic coefficient, the birefringence of the polarizer protective film changes when an external force is applied to the polarizer protective film due to a dimensional change of the polarizer during actual use. For this reason, when this polarizing plate was incorporated especially in a liquid crystal display, there existed a problem that a color nonuniformity and contrast fall appeared.

  Moreover, the polarizer protective film using the norbornene-type resin with a low photoelastic coefficient is disclosed (patent document 2). However, although norbornene-based resins have a sufficiently small photoelastic coefficient, there is a problem that large birefringence occurs when subjected to processing in which the resin undergoes orientation, such as extrusion molding and stretching. It was.

  In contrast, low-birefringence graft modification in which norbornene-based resin is graft-modified with a graft monomer that gives a polymer having an intrinsic birefringence value opposite to the intrinsic birefringence value of norbornene-based resin. A polarizer protective film using a norbornene resin is disclosed (Patent Document 3). However, such a resin is characterized in that it is difficult to develop a phase difference due to environmental changes, but a manufacturing process for graft modification is required, and the performance of the obtained film (for example, solvent resistance, film strength) Etc.) was reduced.

Furthermore, a polarizer protective film using a resin having a glutarimide structural unit is disclosed (Patent Document 4). Although this resin has a small photoelastic coefficient, the strength when formed into a film is low, and the film has to be stretched. However, since this film has positive intrinsic birefringence, there is a problem that a retardation is developed by stretching.
JP-A-8-62419 JP 2001-272534 A JP 2001-318202 A Japanese Patent Application Laid-Open No. 2006-131689

  An object of the present invention is a thermoplastic resin film, an optical film, and an optical film suitable for use in protecting a polarizer, having a small retardation, a small change in birefringence due to stress, and a small dimensional change in a durability test. It is to provide a polarizing plate.

  The present invention employs the following means in order to solve the above-mentioned problems of obtaining a film suitable for use in protecting a polarizer with a retardation and a small change in birefringence due to stress by a simple manufacturing process.

  [1] A thermoplastic resin film containing a non-crystalline thermoplastic resin A having negative birefringence and a glass transition temperature (Tg) of 120 ° C. or higher, wherein the following conditions (i) to (iii) are satisfied: A thermoplastic film that satisfies the requirements at the same time.

(I) The photoelastic coefficient is a positive value and has a value of 0.01 × 10 ⁻¹² Pa ^{−1 to} 5.0 × 10 ⁻¹² Pa ⁻¹ .

  (Ii) Dimensional changes in the MD direction (film forming direction) and TD direction (direction perpendicular to the film forming direction) after 300 hours of treatment at a temperature of 60 ° C. and a relative humidity of 90% are both 0.5% or less. is there.

  (Iii) The total light transmittance is 90% or more and the haze is 1.0% or less.

  [2] An amorphous thermoplastic resin A having negative birefringence has an unsaturated carboxylic acid alkyl ester unit a represented by the structural formula (a) and an unsaturated carboxylic acid represented by the structural formula (b). The thermoplastic resin film according to the above [1], comprising an acrylic polymer B containing an acid unit b and a cyclized structural unit c represented by the structural formula (c).

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the ^formula, R 4, ^{R 5} represents. In the formula ^X 1, ^{X 2} hydrogen or an organic residue having 1 to 5 carbon atoms, ^{.R 11} representing C = O at or ^{CH-R 11} is Represents hydrogen or an organic residue having 1 to 5 carbon atoms.)
[3] An amorphous thermoplastic resin A having negative birefringence has an unsaturated carboxylic acid alkyl ester unit a represented by the structural formula (a) and an unsaturated carboxylic acid represented by the structural formula (b). [1] containing acrylic polymer B containing acid unit b and cyclized structural unit c represented by structural formula (c), and elastic particles E having a particle diameter of 10 to 1,000 nm. ] Or the thermoplastic resin film according to [2].

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the ^formula, R 4, ^{R 5} represents. In the formula ^X 1, ^{X 2} hydrogen or an organic residue having 1 to 5 carbon atoms, ^{.R 11} representing C = O at or ^{CH-R 11} is Represents hydrogen or an organic residue having 1 to 5 carbon atoms.)
[4] The film according to [2] or [3], wherein the acrylic polymer B contains a glutaric anhydride unit represented by the following structural formula (d).

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
[5] The acrylic polymer B includes an unsaturated carboxylic acid alkyl ester unit and a glutaric anhydride unit, and when the acrylic polymer B is 100 parts by mass, the glutaric anhydride unit is 10 to 15 parts by mass. The thermoplastic resin film according to any one of [2] to [4], wherein the thermoplastic resin film is contained in a part.

  [6] An optical film comprising one or more layers of the thermoplastic resin film according to any one of [1] to [5].

  [7] An optical film in which a hard coat layer is formed on at least one surface of the optical film as described in [6].

  [8] The optical film as described in [6] or [7], which is used as a polarizer protective film.

  [9] A polarizing plate formed using the optical film according to [8].

  According to the present invention, a film having a small retardation, a small change in birefringence due to stress, and a small dimensional change in an endurance test can be provided. For example, a finder such as various covers, cameras, VTRs, projection TVs, It can be used for a filter etc. Furthermore, it can be used very suitably for films for liquid crystal display devices, such as a polarizer protective film, various optical disk substrate protective films, etc.

  A thermoplastic resin film having a negative birefringence and containing an amorphous thermoplastic resin A having a glass transition temperature (Tg) of 120 ° C. or higher, and simultaneously satisfies the following conditions (i) to (iii): When it was made into a film, it was clarified that such problems could be solved all at once.

(I) The photoelastic coefficient is a positive value and has a value of 0.01 × 10 ⁻¹² Pa ^{−1 to} 5.0 × 10 ⁻¹² Pa ⁻¹ .

  (Ii) Dimensional changes in the MD direction (film forming direction) and TD direction (direction perpendicular to the film forming direction) after 300 hours of treatment at a temperature of 60 ° C. and a relative humidity of 90% are both 0.5% or less. is there.

  (Iii) The total light transmittance is 90% or more and the haze is 1.0% or less.

  The structure of the film is not particularly limited as long as it satisfies the properties required for optical applications such as transparency, heat resistance, mechanical properties, etc., but the amorphous thermoplastic resin A having negative birefringence has a structural formula An unsaturated carboxylic acid alkyl ester unit a represented by (a), an unsaturated carboxylic acid unit b represented by structural formula (b), and a cyclized structural unit c represented by structural formula (c). It is preferable to contain acrylic polymer B and elastic particles E having a particle diameter of 10 to 1,000 nm in order to reduce retardation and birefringence change due to stress.

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the ^formula, R 4, ^{R 5} represents. In the formula ^X 1, ^{X 2} hydrogen or an organic residue having 1 to 5 carbon atoms, ^{.R 11} representing C = O at or ^{CH-R 11} is Represents hydrogen or an organic residue having 1 to 5 carbon atoms.)
When acrylic polymer B contains a glutaric anhydride unit represented by the following structural formula (d) (among the structural formula (c), an acrylic polymer having a glutaric anhydride unit represented by structural formula (d) in particular Use of a polymer) is preferable because a film having excellent transparency, heat resistance, and productivity and excellent optical isotropy can be obtained.

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
When the thermoplastic resin film is used as an optical film, it is required to have a small phase difference for optical isotropic applications.

  Here, the optical isotropic application is an application in which optical isotropy is required inside the material, and specific examples include a polarizer protective film, a lens, and an optical waveguide core. In a liquid crystal television, two polarizing plates are used orthogonally or in parallel, but when the polarizer protective film does not exist or is optically isotropic, black is displayed in a state where the two polarizing plates are orthogonal, When two polarizing plates are parallel, white is displayed. On the other hand, when the polarizer protective film is not optically isotropic, for example, dark purple is displayed instead of black when the two polarizing plates are orthogonal to each other, and yellow instead of white is displayed when the two polarizing plates are parallel. . This coloring varies depending on the anisotropy of the polarizer protective film. Ideally, the polarizer protective film does not exist optically, but is indispensable for the purpose of protecting the polarizer from external stress and moisture. In the case of a lens, the lens is intended to refract light at the interface, but it is necessary for light to travel uniformly within the lens. If the inside of the lens is not optically isotropic, there is a problem that the image is distorted. In the case of the optical waveguide core, if it is not optically isotropic, for example, there is a difference in the transmission speed between the horizontal wave signal and the vertical wave signal, which causes noise and interference problems. Other optical isotropic applications include prism sheet substrates, optical disk substrates, flat panel display substrates, and the like.

  As for the resin structure, when an aromatic ring having many π electrons is introduced, the heat resistance is improved more than the introduction of an alicyclic structure, but at the same time, there is a problem that birefringence increases and phase difference is easily developed. For this reason, it is most preferable to contain an alicyclic structure in order to improve heat resistance while maintaining the optical isotropy. Examples of the alicyclic structure include a glutaric anhydride structure, a lactone ring structure, a norbornene structure, and a cyclopentane structure. For optical isotropy and heat resistance, the same effect can be obtained using any structure, but for the introduction of lactone ring structure, norbornene structure, cyclopentane structure, etc., use expensive raw materials having these structures, Alternatively, it is industrially disadvantageous because it is necessary to use an expensive raw material to be a precursor of these structures and to obtain a target structure through several steps of reaction. On the other hand, glutaric anhydride units are industrially very advantageous because they are obtained from a general acrylic raw material by a one-step dehydration and / or dealcoholization reaction.

  When the glass transition temperature (Tg) of the amorphous thermoplastic resin is lower than 120 ° C., a processing step when used for a film for a liquid crystal display device such as a polarizer protective film, various optical disk substrate protective films, Or, due to the widespread use of automobile navigation systems, handy cameras, etc., it cannot withstand use under severe usage environment conditions that require weather resistance and heat resistance such as outdoors or in automobiles. Moreover, it is preferable that a glass transition temperature (Tg) is 200 degrees C or less. When the temperature is higher than 200 ° C., it is necessary to set a corresponding high temperature during film formation, which may be disadvantageous from the viewpoint of film formation.

  In addition, when the retardation (Ret) in the film plane of the thermoplastic resin film exceeds 10 nm, or when the retardation (Rth) in the film thickness direction exceeds 10 nm, the display quality is optically isotropic. It will not be able to withstand use such as lowering.

  Next, although the example of the manufacturing method of the acrylic polymer containing the glutaric anhydride unit represented by Structural formula (d) is demonstrated, this invention is not limited to this.

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
When the acrylic polymer contains an unsaturated carboxylic acid alkyl ester monomer (A), an unsaturated carboxylic acid monomer (B), and other vinyl monomer units, the vinyl polymer that gives the units After the polymer (C) is polymerized to form a copolymer (a), the copolymer (a) is heated in the presence or absence of a suitable catalyst, and a molecule obtained by dealcoholization and / or dehydration. It can be produced by carrying out an internal cyclization reaction. In this case, typically, the carboxyl group of the unsaturated carboxylic acid unit of 2 units is dehydrated by heating the copolymer (a), or the adjacent unsaturated carboxylic acid unit and unsaturated carboxylic acid alkyl ester unit. 1 unit of the glutaric anhydride unit is generated by the elimination of the alcohol.

  There are no particular restrictions on the unsaturated carboxylic acid alkyl ester monomer (A) used in this case, but preferred examples include monomers that lead to structural units represented by the following structural formula (a). .

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
Of these, acrylates and / or methacrylates having an aliphatic or alicyclic hydrocarbon group having 1 to 5 carbon atoms or a hydrocarbon group having a substituent are particularly suitable in terms of excellent thermal stability. is there.

  Preferable specific examples of the unsaturated carboxylic acid alkyl ester monomer (A) include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and n-butyl (meth) acrylate. T-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2- (meth) acrylic acid 2- Hydroxyethyl, 3-hydroxypropyl (meth) acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth) acrylate and 2,3,4,5-tetrahydroxypentyl (meth) acrylate Among them, methyl methacrylate is most preferably used. These can be used alone or in combination of two or more thereof.

  In addition, the unsaturated carboxylic acid monomer (B) used in this case is not particularly limited, and can be copolymerized with another vinyl compound (C). Monomers that lead to structural units can be used.

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)
In particular, acrylic acid and methacrylic acid are preferable from the viewpoint of excellent thermal stability, and methacrylic acid is more preferable. These can be used alone or in combination of two or more thereof.

  Further, in the production of an acrylic polymer having a ring structure used in the present invention, other vinyl monomers (C) such as styrene, acrylamide, methacrylamide, etc. may be used as long as the effects of the present invention are not impaired. Although it does not matter, monomers that do not contain an aromatic ring can be more preferably used in terms of transparency, birefringence, and chemical resistance. These may be used alone or in combination of two or more.

  As for the polymerization method of the acrylic polymer having a ring structure, a polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization or the like by radical polymerization can be basically used. Solution polymerization, bulk polymerization, and suspension polymerization are particularly preferred.

  The polymerization temperature is not particularly limited, but from the viewpoint of color tone, a monomer mixture containing an unsaturated carboxylic acid monomer and an unsaturated carboxylic acid alkyl ester monomer is polymerized at a polymerization temperature of 95 ° C. or less. Is preferred. The lower limit of the polymerization temperature is not particularly limited as long as the polymerization proceeds, but is usually 50 ° C. or higher from the viewpoint of productivity considering the polymerization rate. For the purpose of improving the polymerization yield or polymerization rate, it is possible to raise the polymerization temperature as the polymerization proceeds. The polymerization time is not particularly limited as long as it is a sufficient time to obtain the required degree of polymerization, but is preferably in the range of 60 to 360 minutes from the viewpoint of production efficiency.

  In the present invention, a preferable ratio of the monomer mixture used in the production of the acrylic polymer having a ring structure is 5 parts by weight of the unsaturated carboxylic acid monomer (B) based on 100 parts by mass of the monomer mixture. -35 mass parts, More preferably, it is 7-25 mass parts.

  The unsaturated carboxylic acid alkyl ester monomer (A) is preferably 65 to 95 parts by mass, more preferably 75 to 91 parts by mass. When using the other vinyl monomer (C) copolymerizable with these, the preferable ratio is 0-5 mass parts, and a more preferable ratio is 0-3 mass parts.

  When the unsaturated carboxylic acid monomer amount (B) is less than 5 parts by mass, the amount of glutaric anhydride units represented by the structural formula (d) generated by heating the copolymer (a) is There is a tendency that the effect of improving the heat resistance of the acrylic film of the present invention is reduced. On the other hand, when the amount of the unsaturated carboxylic acid monomer (B) exceeds 35 parts by mass, a large amount of unsaturated carboxylic acid units tend to remain after the cyclization reaction by heating the copolymer (a). , Colorless transparency, residence stability, and dimensional stability after film formation tend to decrease.

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
The acrylic polymer having a ring structure used for the acrylic film of the present invention preferably has a mass average molecular weight of 50,000 to 150,000. The acrylic polymer having a ring structure having such a molecular weight is obtained by controlling the copolymer (a) to a desired molecular weight, that is, a mass average molecular weight of 50,000 to 150,000 in advance during the production of the copolymer (a). This can be achieved. When the mass average molecular weight exceeds 150,000, there is a tendency to color during cyclization in the subsequent step. On the other hand, when the mass average molecular weight is less than 50,000, the mechanical strength of the acrylic film tends to decrease.

  The copolymer (a) used for the production of the acrylic polymer having a ring structure preferably used in the present invention is heated and subjected to intramolecular cyclization reaction by (i) dehydration and / or (b) dealcoholization, and glutaric acid A method for producing a thermoplastic polymer containing an anhydride unit is not particularly limited, but a method for producing a thermoplastic polymer by passing through a heated extruder having a vent, or an apparatus that can be heated and deaerated under an inert gas atmosphere or under reduced pressure. The production method is preferable from the viewpoint of productivity. In particular, when an intramolecular cyclization reaction is carried out by heating in the presence of oxygen, it tends to be colored and the transparency is lowered. Therefore, it is preferable to sufficiently substitute the inside of the system with an inert gas such as nitrogen. Moreover, it is more preferable that the apparatus has a structure capable of introducing an inert gas such as nitrogen into them. For example, as a method for introducing an inert gas such as nitrogen into a twin-screw extruder, a method of connecting a pipe of an inert gas stream of about 10 to 100 liters / minute from the upper part and / or the lower part of the hopper can be mentioned. .

  The temperature during cyclization is not particularly limited as long as (i) dehydration and / or (b) dealcoholization causes an intramolecular cyclization reaction, but is preferably in the range of 180 to 300 ° C, particularly 200 to 200 ° C. A range of 280 ° C is preferred.

  Further, the cyclization time at this time is not particularly limited and can be appropriately set according to the desired copolymer composition, but is usually 1 minute to 60 minutes, preferably 2 minutes to 30 minutes, especially 3 to 20 minutes. The range of is preferable. In particular, the length / diameter ratio (L / D) of the extruder screw is preferably 40 or more in order to secure a heating time for allowing sufficient intramolecular cyclization reaction to proceed using an extruder. When an extruder with a short L / D is used, a large amount of unreacted unsaturated carboxylic acid units remain, so that the reaction proceeds again during the heat molding process, and there is a tendency for bubbles to be seen in the molded product and the color tone during molding retention. Tend to drop significantly.

  Furthermore, in the present invention, when the copolymer (a) is heated by the above method or the like, one or more of acid, alkali and salt compounds may be added as a catalyst for promoting the cyclization reaction to glutaric anhydride. it can. The addition amount is not particularly limited, and is preferably about 0.01 to 1 part by mass with respect to 100 parts by mass of the copolymer (a).

  The acrylic polymer having a ring structure preferably has a glass transition temperature (Tg) of 120 ° C. or more in terms of heat resistance. The method for raising the glass transition temperature is not particularly limited, but it is effective to increase the content of the cyclized structural unit represented by, for example, the structural formula (d) in the acrylic polymer having a ring structure. Is.

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.)
As the acrylic polymer having a ring structure of the present invention, a copolymer comprising a glutaric anhydride unit represented by the structural formula (d) and an unsaturated carboxylic acid alkyl ester unit can be preferably used. The content of the unsaturated carboxylic acid alkyl ester unit and the glutaric anhydride unit is not particularly limited, but in general, the unsaturated carboxylic acid alkyl ester unit has negative birefringence and the glutaric anhydride unit has a positive value. From the viewpoint of expressing birefringence, when the total of unsaturated carboxylic acid alkyl ester units and glutaric anhydride units is 100 parts by mass, preferably 85 to 90 parts by mass of unsaturated carboxylic acid alkyl ester units and glutaric acid. It consists of 10-15 parts by weight of anhydride units, more preferably 86-89 parts by weight of unsaturated carboxylic acid alkyl ester units and 11-14 parts by weight of glutaric anhydride units. When the glutaric anhydride unit is 15 parts by mass or more, the birefringence tends to be positive, and when it is less than 10 parts by mass, the photoelastic coefficient tends to be negative.

In addition, a proton nuclear magnetic resonance ( ¹ H-NMR) measuring instrument is used for quantification of each component unit in the acrylic polymer having a ring structure of the present invention. ^{In the 1} H-NMR method, for example, in the case of a copolymer consisting of a glutaric anhydride unit, methacrylic acid, and methyl methacrylate, the spectral assignment in a dimethyl sulfoxide heavy solvent is 0.5 to 1.5 ppm peak. Is hydrogen of α-methyl group of methacrylic acid, methyl methacrylate and glutaric anhydride ring compound, peak of 1.6 to 2.1 ppm is hydrogen of methylene group of polymer main chain, peak of 3.5 ppm is methyl methacrylate The carboxylic acid ester (—COOCH ₃ ) of hydrogen, the peak at 12.4 ppm can determine the copolymer composition from the carboxylic acid hydrogen of methacrylic acid and the integral ratio of the spectrum. In addition to the above, in the case of a copolymer containing styrene as another copolymer component, hydrogen of an aromatic ring of styrene is seen at 6.5 to 7.5 ppm, and the copolymer is similarly obtained from the spectral ratio. The composition can be determined.

  In addition, the acrylic polymer having a ring structure of the present invention may have other unsaturated carboxylic acid units and / or other copolymerizable copolymer in the acrylic polymer having a ring structure as long as the refractive index is within a predetermined range. A vinyl-type monomer unit can be contained.

  The amount of other unsaturated carboxylic acid units contained in 100 parts by mass of the thermoplastic polymer is preferably 10 parts by mass or less, that is, 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, most preferably Preferably it is 0-1 mass part. When the unsaturated carboxylic acid unit exceeds 10 parts by mass, the colorless transparency and the residence stability tend to decrease.

  Further, the amount of other copolymerizable vinyl monomer units is preferably 5 parts by mass or less, that is, in the range of 0 to 5 parts by mass, more preferably 0 to 5 parts by mass, in 100 parts by mass of the thermoplastic polymer. 3 parts by mass. In particular, when an aromatic vinyl monomer unit such as styrene is contained and the content exceeds the above range, colorless transparency, optical isotropy, and chemical resistance tend to decrease.

  When the acrylic polymer is an acrylic film by the method described later, the retardation is small, the birefringence change due to stress is small, and the film is excellent in durability. Therefore, the acrylic polymer is preferably used as the thermoplastic resin of the present invention. it can. In addition, in the said acrylic film, when toughness is low and workability is insufficient, you may extend | stretch in order to provide toughness. In this case, it is important not to increase the retardation by stretching. For this reason, when the glass transition temperature of the acrylic polymer is Tg (° C.), 1 in at least one direction in the temperature range of Tg to (Tg + 20). It is preferable to perform stretching by 5 times or less. In order to reduce the retardation, the stretching is further preferably performed 1.5 times or less in each of two orthogonal directions.

  In order to impart toughness, the acrylic polymer may contain elastic particles. However, the elastic particles to be used need not deteriorate the optical properties and heat resistance of the film, and the following particles can be preferably used.

  Particles that can be used in the present invention (hereinafter referred to as elastic particles E) preferably have a particle size of 10 to 1,000 nm, and are composed of a layer containing one or more rubbery polymers and a different polymer. A multilayer polymer (E-1) called a so-called core-shell type, which is composed of one or more layers constituted and has a structure in which these layers are adjacent to each other, can be preferably used.

  As the core-shell type multilayer structure polymer (E-1) used in the present invention, the number of layers constituting the core-shell type polymer (E-1) is not particularly limited, and may be two or more, or three or more. Although it may be four layers or more, it is preferably a multilayer structure polymer having at least one rubber layer inside.

  In the multilayer structure polymer (E-1) of the present invention, the type of the rubber layer is not particularly limited as long as it is composed of a polymer component having rubber elasticity. For example, a rubber composed of a polymer obtained by polymerizing an acrylic component, a silicone component, a styrene component, a nitrile component, a conjugated diene component, a urethane component or an ethylene component, a propylene component, an isobutene component, and the like can be given. Preferred rubbers include, for example, acrylic components such as ethyl acrylate units and butyl acrylate units, silicone components such as dimethylsiloxane units and phenylmethylsiloxane units, styrene components such as styrene units and α-methylstyrene units, acrylonitrile units, A rubber composed of a nitrile component such as a methacrylonitrile unit and a conjugated diene component such as a butanediene unit or an isoprene unit. A rubber composed of a combination of two or more of these components is also preferable. For example, (1) acrylic components such as ethyl acrylate units and butyl acrylate units and silicones such as dimethylsiloxane units and phenylmethylsiloxane units. Rubber composed of components, (2) rubber composed of acrylic components such as ethyl acrylate units and butyl acrylate units, and styrene components such as styrene units and α-methylstyrene units, (3) ethyl acrylate units and Rubber composed of acrylic components such as butyl acrylate units and conjugated diene components such as butanediene units and isoprene units, and (4) acrylic components such as ethyl acrylate units and butyl acrylate units, dimethylsiloxane units and phenylmethylsiloxanes Unit etc. Rubber composed of styrene component such as silicone component and styrene units and α- methyl styrene units and the like. In addition to these components, a rubber obtained by crosslinking a copolymer composed of a crosslinking component such as a divinylbenzene unit, an allyl acrylate unit, and a butylene glycol diacrylate unit is also preferable.

  In the above multilayer structure polymer (E-1), the type of layer other than the rubber layer is not particularly limited as long as it is composed of a polymer component having thermoplasticity, but it is more than the rubber layer. A polymer component having a high glass transition temperature is preferred. Polymers having thermoplastic properties include unsaturated carboxylic acid alkyl ester units, unsaturated carboxylic acid units, unsaturated glycidyl group-containing units, unsaturated dicarboxylic acid anhydride units, aliphatic vinyl units, and aromatic vinyls. Examples include polymers containing at least one unit selected from system units, vinyl cyanide units, maleimide units, unsaturated dicarboxylic acid units and other vinyl units. Among them, unsaturated carboxylic acids A polymer containing at least one unit selected from an alkyl ester unit, an unsaturated glycidyl group-containing unit, and an unsaturated dicarboxylic acid anhydride unit is preferable, and further, an unsaturated glycidyl group-containing unit and an unsaturated dicarboxylic acid A polymer containing at least one unit selected from anhydride-based units is more preferable.

  Although it does not specifically limit as a monomer used as the raw material of the said unsaturated carboxylic-acid alkylester type | system | group unit, (meth) acrylic-acid alkylester is used preferably. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, (meth) acrylic N-hexyl acid, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, stearyl (meth) acrylate, octadecyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, ( Chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2,3,4,5,6 (meth) acrylic acid -Pentahydroxyhexyl, 2,3,4,5-tetrahydroxypentyl (meth) acrylate, amino acid acrylate Examples include ethyl, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, phenylaminoethyl methacrylate, and cyclohexylaminoethyl methacrylate, and from the viewpoint that the effect of improving impact resistance is large ( Methyl methacrylate is preferably used. These units can be used alone or in combination of two or more.

  The unsaturated carboxylic acid monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, maleic acid, and further a hydrolyzate of maleic anhydride. Acrylic acid is particularly excellent in terms of thermal stability. Methacrylic acid is preferable, and methacrylic acid is more preferable. These can be used alone or in combination.

  The monomer used as the raw material for the unsaturated glycidyl group-containing unit is not particularly limited, and is glycidyl (meth) acrylate, glycidyl itaconate, diglycidyl itaconate, allyl glycidyl ether, styrene-4-glycidyl ether. And 4-glycidylstyrene, and glycidyl (meth) acrylate is preferably used from the viewpoint that the effect of improving impact resistance is great. These units can be used alone or in combination of two or more.

  Examples of the monomer used as a raw material for the unsaturated dicarboxylic acid anhydride unit include maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, and aconitic anhydride, and the effect of improving impact resistance. From the standpoint of large, maleic anhydride is preferably used. These units can be used alone or in combination of two or more.

  Examples of the monomer that is a raw material for the aliphatic vinyl-based unit include ethylene, propylene, and butadiene. Examples of the monomer that is a raw material for the aromatic vinyl-based unit are styrene, α-methylstyrene, 1 -Vinyl naphthalene, 4-methyl styrene, 4-propyl styrene, 4-cyclohexyl styrene, 4-dodecyl styrene, 2-ethyl-4-benzyl styrene, 4- (phenylbutyl) styrene, halogenated styrene, etc. Acrylonitrile, methacrylonitrile, ethacrylonitrile, etc. are used as the raw material for the vinyl-based unit, and maleimide, N-methylmaleimide, N-ethylmaleimide are used as the monomer for the maleimide-based unit. N-propylmaleimide, N-isopropylmaleimide, Examples of monomers that can be used as raw materials for the unsaturated dicarboxylic acid units include maleic acid and maleic acid such as -cyclohexylmaleimide, N-phenylmaleimide, N- (p-bromophenyl) maleimide, and N- (chlorophenyl) maleimide. Monoethyl ester, itaconic acid, phthalic acid, and the like, which are monomers used as raw materials for the other vinyl units, include acrylamide, methacrylamide, N-methylacrylamide, butoxymethylacrylamide, N-propylmethacrylamide, N- Vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, p-aminostyrene, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, and 2-styrene Examples include ril-oxazoline, and these monomers can be used alone or in combination of two or more.

  In the multilayer structure polymer (E-1) containing the rubber polymer, the type of the outermost layer is not particularly limited, and is an unsaturated carboxylic acid alkyl ester unit, an unsaturated carboxylic acid unit, Unsaturated glycidyl group-containing units, aliphatic vinyl units, aromatic vinyl units, vinyl cyanide units, maleimide units, unsaturated dicarboxylic acid units, unsaturated dicarboxylic anhydride units, and other vinyl units And at least one selected from polymers containing, for example, unsaturated carboxylic acid alkyl ester units, unsaturated carboxylic acid units, unsaturated glycidyl group-containing units, and unsaturated dicarboxylic anhydrides At least one selected from polymers containing units is preferred, and further, unsaturated carboxylic acid alkyl ester units, unsaturated polymers. Polymers containing carbon acid units are more preferable.

  Furthermore, in the present invention, when the outermost layer in the multilayer polymer (E-1) is a polymer containing an unsaturated carboxylic acid alkyl ester unit and an unsaturated carboxylic acid unit, by heating, In the same manner as in the production of the thermoplastic copolymer (A) of the present invention described above, the intramolecular cyclization reaction proceeds to produce a glutaric anhydride unit represented by the general formula (d). Therefore, a multilayer structure polymer (E-1) having a polymer containing an unsaturated carboxylic acid alkyl ester unit and an unsaturated carboxylic acid unit in the outermost layer is blended with the thermoplastic copolymer (A), In the thermoplastic copolymer (A) that becomes a continuous phase (matrix phase) by heating and melt-kneading under such conditions, the glutaric acid represented by the above general formula (d) in the outermost layer is practically used. By dispersing the multilayer structure polymer (E-1) having a polymer containing an anhydride unit, a good dispersion state is possible without agglomeration, and with improved mechanical properties such as impact resistance, It is considered that extremely high transparency can be expressed.

  The monomer used as the raw material for the unsaturated carboxylic acid alkyl ester unit herein is not particularly limited, but (meth) acrylic acid alkyl ester is preferred, and methyl (meth) acrylate is more preferred. Preferably used.

  Further, the monomer used as a raw material for the unsaturated carboxylic acid unit is not particularly limited, but (meth) acrylic acid is preferable, and methacrylic acid is more preferably used.

  As a preferable example of the multilayer structure polymer (E-1) of the present invention, the core layer is butyl acrylate / styrene polymer, the outermost layer is methyl methacrylate / glutaric acid anhydride represented by the above general formula (d). A copolymer consisting of a product unit, or methyl methacrylate / glutaric anhydride unit represented by the above general formula (d) / methacrylic acid polymer, and the core layer is a dimethylsiloxane / butyl acrylate polymer. The outer layer is a methyl methacrylate polymer, the core layer is a butanediene / styrene polymer and the outermost layer is a methyl methacrylate polymer, and the core layer is a butyl acrylate polymer and the outermost layer is a methyl methacrylate polymer ("/" Indicates copolymerization). Furthermore, a preferable example is one in which either one or both of the rubber layer and the outermost layer is a polymer containing a glycidyl methacrylate unit. Among them, the core layer is butyl acrylate / styrene polymer, and the outermost layer is methyl methacrylate / a copolymer of glutaric anhydride units represented by the above general formula (d), or methyl methacrylate / the above general formula. The glutaric anhydride unit represented by (d) / methacrylic acid polymer approximates the refractive index of the amorphous thermoplastic resin (A) that is the continuous phase (matrix phase); and Since it becomes possible to obtain a good dispersion state in the resin composition and the transparency that can satisfy the demand for higher level in recent years appears, it can be preferably used.

  As a method of forming the film, any conventionally known method can be used. Examples thereof include a solution casting method and a melt extrusion method, and any of them can be employed. For example, when trying to obtain a film using the solution casting method, an acrylic polymer having a ring structure is stirred and mixed in a good solvent to form a uniform mixed solution, and cast on a support film or drum to provide self-supporting properties. After pre-drying until it has, it can be obtained by peeling off from the support film or drum and drying. In the melt extrusion method, a film having an arbitrary thickness can be obtained by extruding an acrylic polymer having a ring structure while heating and melting it from an extruder equipped with a T-type die and the like, and taking out the resulting film.

  As thickness of the film of this invention, 1-100 micrometers is preferable from a viewpoint of making the in-plane retardation value of the film obtained, and thickness retardation value low. More preferably, it is 5-50 micrometers.

  The film of the present invention may be unstretched as a final product in terms of simplification of the manufacturing process, cost reduction, etc., but using a known stretching method for improving the strength of the film or reducing the film thickness. Further, at least one axis may be stretched.

  Moreover, the above-mentioned thermoplastic resin film of the present invention can be used for various uses as a final product as it is or after being subjected to various processing. Utilizing particularly excellent transparency, low birefringence, etc., it is suitably used for known optical applications such as optical films, that is, optical isotropic films, polarizer protective films, transparent conductive films, and the like around liquid crystal display devices. be able to. In this case, it is preferable to use an optical film configured to include one or more layers of the thermoplastic resin film.

  Furthermore, the film of the present invention can be subjected to surface treatment on one side or both sides of the film, if necessary. Examples of the surface treatment method include corona treatment, plasma treatment, and ultraviolet irradiation. In particular, when surface processing such as coating is applied to the film surface, or when another film is laminated with an adhesive, surface treatment of the film is performed as a means for improving mutual adhesion. Is preferred.

  In addition, a coating layer such as a hard coat layer can be formed on the surface of the film as necessary. Moreover, the film of this invention may form a transparent conductive layer by sputtering method etc. through or without a coating layer.

  Said film can be used as a polarizer protective film bonded to a polarizer, and can be made into a polarizing plate. Here, as a polarizer, conventionally well-known arbitrary polarizers, such as what made iodine contain in the stretched polyvinyl alcohol, can be used, for example. The polarizer protective film is laminated on one side or both sides of the polarizer. Generally, a polarizer protective film is laminated on both sides of the polarizer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to this Example. Each characteristic value was measured as follows.

1. Film thickness Five points were measured using a micro thickness gauge (manufactured by Anritsu), and an average value was obtained.

2. Glass transition temperature (Tg)
Using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer), the measurement was performed at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere. The sample amount was 5 mg.

The glass transition temperature here was measured at a rate of temperature increase of 20 ° C./min using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer) and determined according to JIS K7121 (1987). The midpoint glass transition temperature (T _mg ).

3. Transparency (total light transmittance, haze value)
Using a direct reading haze meter manufactured by Toyo Seiki Co., Ltd., the total light transmittance (%) and haze value (%) at 23 ° C. were measured three times, and transparency was evaluated with an average value. A halogen lamp (12V50W) was used as the light source, the total light transmittance was measured according to JIS-K7361-1997, and the haze was measured according to JIS-K7136-2000.

4). In-plane retardation Ret and thickness direction retardation Rth
The in-plane retardation is determined by using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Co., Ltd., and in a chromatic dispersion measurement mode, a phase difference for a light beam having a wavelength of 480.4 nm and a phase difference for a light beam having a wavelength of 548.3 nm , The phase difference with respect to the light beam having a wavelength of 628.2 nm, and the phase difference with respect to the light beam with a wavelength of 752.7 nm were measured, and the Cauchy wavelength dispersion formula (R (λ) = a + b / λ2 + c / λ4 + d / λ6) are obtained by substituting the wavelength of 550 nm (λ = 550) into the Cauchy wavelength dispersion formula. The measurement was performed once. The film forming direction was used as a reference, and a positive value was used when the film forming direction was a slow axis, and a negative value was obtained when the direction perpendicular to the film forming direction was a slow axis.

  Thickness direction retardation Rth is determined by using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Co., Ltd., and the refractive index in the orthogonal axis direction within the surface of the amorphous thermoplastic resin film with respect to light having a wavelength of 590 nm. , Nx, ny (where nx ≧ ny), the refractive index nz in the thickness direction of the amorphous thermoplastic resin film with respect to light having a wavelength of 590 nm is measured, and the thickness of the amorphous thermoplastic resin film is defined as d (nm). Was obtained from the following formula. The measurement was performed once.

Thickness direction retardation Rth (nm) = d × {(nx + ny) / 2−nz}
5). Phase difference under load (9.81 MPa) and photoelastic coefficient A sample having a short side of 1 cm and a long side of 7 cm was cut out. Using this sample, TRANSDUCER U3C1-5K manufactured by Shimadzu Corp., the chuck was sandwiched 1 cm above and below, and a tension (F) of 1 kg / mm ² (9.81 MPa) was applied in the long side direction. In this state, Re (nm) was measured using a polarizing microscope 5892 manufactured by Nikon Corporation, and the phase difference was obtained under a load (9.81 MPa). As a light source, sodium D line (589 nm) was used. Further, the photoelastic coefficient was calculated by applying these values to the photoelastic coefficient = Re / (d × F). The measurement was performed once.

6). Confirmation of birefringence Stretched 1.5 times in the film forming direction at a glass transition temperature (Tg) of -10 ° C. In this case, if the slow axis direction is parallel to the stretching direction, the positive birefringence is assumed. If the slow axis direction is perpendicular to the stretching direction, the negative birefringence is assumed.

7). Each component composition The amorphous thermoplastic resin film was dissolved in acetone, and this solution was centrifuged at 9,000 rpm for 30 minutes to separate into an acetone soluble component and an acetone insoluble component. The acetone-soluble component was dried under reduced pressure at 60 ° C. for 5 hours, and each component unit was quantified to identify each component composition of the amorphous thermoplastic resin.

Quantification of each component unit was performed by a proton nuclear magnetic resonance ( ¹ H-NMR) method. ^{In the 1} H-NMR method, for example, in the case of a copolymer consisting of a glutaric anhydride unit, methacrylic acid, and methyl methacrylate, the spectral assignment in a dimethyl sulfoxide heavy solvent is 0.5 to 1.5 ppm peak. Is hydrogen of α-methyl group of methacrylic acid, methyl methacrylate and glutaric anhydride ring compound, peak of 1.6 to 2.1 ppm is hydrogen of methylene group of polymer main chain, peak of 3.5 ppm is methyl methacrylate The carboxylic acid ester (—COOCH ₃ ) of hydrogen, the peak at 12.4 ppm can determine the copolymer composition from the carboxylic acid hydrogen of methacrylic acid and the integral ratio of the spectrum. In addition to the above, in the case of a copolymer containing styrene as another copolymer component, hydrogen of the aromatic ring of styrene is seen at 6.5 to 7.5 ppm, and the copolymer composition is similarly determined from the spectral ratio. Can be determined.

8). Dimensional change Cut the obtained film into squares of 110 mm each in the MD direction (film forming direction) and TD direction (direction perpendicular to the film forming direction) and place it on a graph paper, and draw a 100 mm square with an oil-based magic pen. Filled in and marked the intersection at the midpoint of each side. Among the distances between the intersections, the MD direction distance is the MD dimension, and the TD direction distance is the TD dimension. Compare this value with the value after treatment for 300 hours in a humidified oven with a temperature of 60 ° C and a relative humidity of 90%. X evaluation. The measurement was performed with a universal projector (model V-16A manufactured by NIKON).

9. Average particle diameter of elastic particles The film was made into an ultra-thin section of about 100 to 800 nm in the thickness direction, dyed with ruthenic acid, and then used with a transmission electron microscope (JEM-1200EX manufactured by JEOL Ltd.) at a magnification of 100,000 times. The equivalent circle diameter was determined for 100 particles while changing the location, and the average value was taken as the average particle diameter. For core-shell type and graft copolymer type acrylic elastic particles, the particle size of the rubbery polymer portion was measured.

10. Practical evaluation The film was sampled into a 10 cm square and pasted onto a 1 mm thick glass plate using a hand roller to prepare a sample for evaluation. As the adhesive, SK Dyne (SK-2065) manufactured by Soken Chemical Co., Ltd. was used. Two polarizing plates were placed in crossed Nicols on the light source, and an evaluation sample was placed between the two polarizing plates. Here, a polarizing film G1220DU manufactured by Nitto Denko Corporation was used as the polarizing plate, and the sample for evaluation was installed so that the glass surface was on the light source side. The sample for evaluation sandwiched between the polarizing plates was visually observed from the side opposite to the light source. Furthermore, after the sample for evaluation was treated in a humidified oven at a temperature of 60 ° C. and a relative humidity of 90% for 300 hours, the sample for evaluation sandwiched between the polarizing plates was similarly visually observed and evaluated according to the following criteria.

  ○: About the samples for evaluation before and after the treatment in the humidified oven, both the light leakage in the crossed Nicols is small and the blackness is the same level as when the sample for evaluation is removed.

  X: A portion where light leakage was observed was confirmed for at least one of the samples for evaluation before and after the treatment in the humidifying oven.

Reference Example (1) Amorphous thermoplastic resin (A1)
In a stainless steel autoclave having a capacity of 5 liters and equipped with a baffle and a foudra-type stirring blade, a methyl methacrylate / acrylamide copolymer suspension (adjusted by the following method: 20 parts by weight of methyl methacrylate, 80 parts by weight of acrylamide) , 0.3 parts by weight of potassium persulfate and 1,500 parts by weight of ion-exchanged water were charged into the reactor and maintained at 70 ° C. while replacing the reactor with nitrogen gas. The resulting solution is obtained as an aqueous solution of methyl acrylate and acrylamide copolymer (using the obtained aqueous solution as a suspending agent), and a solution obtained by dissolving 0.05 part by mass in 165 parts by mass of ion-exchanged water is supplied. The mixture was stirred at 400 rpm and the system was replaced with nitrogen gas. Next, the following mixed substances were added while stirring the reaction system, and the temperature was raised to 70 ° C. The time when the internal temperature reached 70 ° C. was set as the start of polymerization, and kept for 180 minutes to complete the polymerization. Thereafter, the reaction system was cooled, the polymer was separated, washed and dried according to the usual method to obtain a bead-shaped copolymer (a-1). The polymerization rate of this copolymer (a-1) was 98%, and the weight average molecular weight was 68,000.

Methacrylic acid: 20 parts by weight Methyl methacrylate: 80 parts by weight t-dodecyl mercaptan: 1.5 parts by weight 2,2′-azobisisobutyronitrile: 0.6 parts by weight The obtained copolymer (a-1 ) Using a twin-screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5)) while purging nitrogen from the hopper at an amount of 10 L / min. / H, an intramolecular cyclization reaction was carried out at a cylinder temperature of 270 ° C. to obtain a pellet-like amorphous thermoplastic resin (A1) Glutar in 100 parts by mass of this amorphous thermoplastic resin (A1) The composition ratio of the acid anhydride unit was 20 parts by mass, and the weight average molecular weight was 100,000.

Reference Example (2) Amorphous Thermoplastic Resin (A2)
An amorphous thermoplastic resin (A2) was obtained in the same manner as in Reference Example 1, except that the substance used was changed to the following.

Methacrylic acid: 27 parts by weight Methyl methacrylate: 73 parts by weight t-dodecyl mercaptan: 1.5 parts by weight 2,2′-azobisisobutyronitrile: 0.4 parts by weight This amorphous thermoplastic resin (A2 ) The composition ratio of glutaric anhydride units in 100 parts by mass was 32 parts by mass, and the weight average molecular weight was 100,000.

Reference Example (3) Amorphous Thermoplastic Resin (A3)
An amorphous thermoplastic resin (A3) was obtained in the same manner as in Reference Example 1 except that the substances used were changed as follows.

Methacrylic acid: 12 parts by weight Methyl methacrylate: 88 parts by weight t-dodecyl mercaptan: 1.5 parts by weight 2,2′-azobisisobutyronitrile: 0.6 parts by weight This amorphous thermoplastic resin (A3 The composition ratio of glutaric anhydride units in 100 parts by mass was 13 parts by mass, and the weight average molecular weight was 100,000.

Reference Example (4) Acrylic Elastic Particle (E1)
The core-shell polymer obtained by the following was used.

  A nitrogen container is charged with 120 parts by mass of deionized water, 0.5 parts by mass of potassium carbonate, 0.5 parts by mass of dioctyl sulfosuccinate, and 0.005 parts by mass of potassium persulfate in a glass container with a condenser (capacity 5 liters). After stirring under, 53 parts by mass of butyl acrylate, 17 parts by mass of styrene, and 1 part by mass of allyl methacrylate (crosslinking agent) were charged. These mixtures were reacted at 70 ° C. for 30 minutes to obtain a core layer polymer. Next, a mixture of 21 parts by weight of methyl methacrylate, 9 parts by weight of methacrylic acid, and 0.005 parts by weight of potassium persulfate was continuously added over 90 minutes, and further maintained for 90 minutes to polymerize the shell layer. The polymer latex was coagulated with sulfuric acid, neutralized with caustic soda, washed, filtered, and dried to obtain acrylic elastic particles (E1) having a two-layer structure. The average particle diameter of the polymer particles measured with an electron microscope was 155 nm.

Example 1
80 parts by mass of the amorphous thermoplastic resin (A1) obtained in Reference Example (1) and acrylic elastic particles (E1) obtained in Reference Example (4) are blended in a composition ratio of 20 parts by mass. Then, using a twin screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5), kneading at a screw rotation speed of 150 rpm and a cylinder temperature of 280 ° C., pelletized amorphous thermoplastic resin (AE1 )

  Next, the amorphous thermoplastic resin (AE1) pellets dried at 100 ° C. for 3 hours are extruded into a sheet form through a T-die (set temperature 250 ° C.) using a 45 mmφ single screw extruder (set temperature 250 ° C.). did. This film was cooled so that one surface was completely adhered to a 130 ° C. cooling roll to obtain an unstretched amorphous thermoplastic resin film. At this time, the speed of the cooling roll was adjusted so that the lip gap of the T die / film thickness = 15. The amorphous thermoplastic resin film thus obtained is excellent in both heat resistance and transparency, and the retardation under a load (9.81 MPa) is in the range of −0.5 to 0.5 nm. It was zero. Moreover, the dimensional change was also small. The characteristics of the film are as follows.

Thickness (μm): 40
Glass transition temperature (Tg) (° C.): 127
Total light transmittance (%): 93
Haze (%): 0.4
Phase difference (nm): -0.8
Thickness direction retardation (nm): 0.4
Photoelastic coefficient (10 ⁻¹² Pa ⁻¹ ): 1.0
Birefringence: phase difference (nm) under negative load (9.81 MPa): 0.2
MD direction dimensional change (%): ○
Dimensional change in TD direction (%): ○
Practical evaluation: ○
Example 2
The amorphous thermoplastic resin (A3) pellets obtained in the above Reference Example (3) were dried at 100 ° C. for 3 hours, and then, using a 45 mmφ single screw extruder (set temperature 250 ° C.), a T die ( Extruded into a sheet through a set temperature of 250 ° C. This film was cooled so that one surface was completely adhered to a 130 ° C. cooling roll to obtain an unstretched amorphous thermoplastic resin film. At this time, the speed of the cooling roll was adjusted so that the lip gap of the T die / film thickness = 15. The amorphous thermoplastic resin film thus obtained was sampled into a 20 cm square, and was simultaneously biaxially stretched 1.3 times in the MD and TD directions at 135 ° C. using a stretcher. The obtained stretched film was excellent in both heat resistance and transparency, and the phase difference under a load (9.81 MPa) was in the range of −0.5 to 0.5 nm and was substantially zero. Moreover, the dimensional change was also small. The characteristics of the film are as follows.

Thickness (μm): 30
Glass transition temperature (Tg) (° C.): 127
Total light transmittance (%): 93
Haze (%): 0.2
Phase difference (nm): -0.7
Thickness direction retardation (nm): 0.4
Photoelastic coefficient (10 ⁻¹² Pa ⁻¹ ): 1.0
Birefringence: phase difference (nm) under negative load (9.81 MPa): 0.1
MD direction dimensional change (%): ○
Dimensional change in TD direction (%): ○
Practical evaluation: ○
Comparative Example 1
Pellet-like amorphous thermoplasticity in the same manner as in Example 1 except that the amorphous thermoplastic resin (A2) obtained in Reference Example (2) above was used as the amorphous thermoplastic resin. Resin (AE2) was obtained.

  Next, an amorphous thermoplastic resin film was obtained in the same manner as in Example 1 except that the amorphous thermoplastic resin (AE2) was used. The amorphous thermoplastic resin film thus obtained was excellent in both heat resistance and transparency, but the phase difference under a load (9.81 MPa) satisfied the range of -0.5 to 0.5 nm. There wasn't. Moreover, the dimensional change was large and light leakage was observed in practical evaluation. The characteristics of the film are as follows.

Thickness (μm): 40
Glass transition temperature (Tg) (° C.): 135
Total light transmittance (%): 93
Haze (%): 0.4
Phase difference (nm): 0.9
Thickness direction retardation (nm): 0.6
Photoelastic coefficient (10 ⁻¹² Pa ⁻¹ ): 1.1
Birefringence: phase difference (nm) under positive load (9.81 MPa): 2.0
MD direction dimensional change (%): ×
Dimensional change in TD direction (%): ×
Practical evaluation: ×
Comparative Example 2
An alicyclic polyolefin resin film was obtained in the same manner as in Example 1 except that an alicyclic polyolefin resin (“ZEONOR” manufactured by Nippon Zeon Co., Ltd.) was used as the thermoplastic resin and the set temperature was 280 ° C. The alicyclic polyolefin resin film thus obtained is excellent in both heat resistance and transparency and has a small dimensional change, but has a positive birefringence and a large phase difference under a load (9.81 MPa). Light leakage was observed in practical evaluation.

Thickness (μm): 40
Glass transition temperature (Tg) (° C.): 163
Total light transmittance (%): 93
Haze (%): 0.3
Phase difference (nm): 0.9
Thickness direction retardation (nm): 0.6
Photoelastic coefficient (10 ⁻¹² Pa ⁻¹ ): 5.0
Birefringence: Phase difference (nm) under positive load (9.81 MPa): 5.9
MD direction dimensional change (%): ○
Dimensional change in TD direction (%): ○
Practical evaluation: ×

  Since the film of the present invention has a negative birefringence and a positive photoelastic coefficient, the birefringence generated at the time of film formation can be canceled by stress, so a film for a liquid crystal display device such as a polarizer protective film, It is extremely useful for an optical disk substrate protective film and the like.

Claims (9)

A thermoplastic resin film having a negative birefringence and containing an amorphous thermoplastic resin A having a glass transition temperature (Tg) of 120 ° C. or higher, and simultaneously satisfies the following conditions (i) to (iii): Thermoplastic resin film.
(I) The photoelastic coefficient is a positive value and has a value of 0.01 × 10 ⁻¹² Pa ^{−1 to} 5.0 × 10 ⁻¹² Pa ⁻¹ .
(Ii) Dimensional changes in the MD direction (film forming direction) and TD direction (direction perpendicular to the film forming direction) after 300 hours of treatment at a temperature of 60 ° C. and a relative humidity of 90% are both 0.5% or less. is there.
(Iii) The total light transmittance is 90% or more and the haze is 1.0% or less. Amorphous thermoplastic resin A having negative birefringence has an unsaturated carboxylic acid alkyl ester unit a represented by the structural formula (a) and an unsaturated carboxylic acid unit b represented by the structural formula (b). The thermoplastic resin film of Claim 1 containing the acrylic polymer B containing the cyclized structural unit c represented by Structural formula (c).

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the ^formula, R 4, ^{R 5} represents. In the formula ^X 1, ^{X 2} hydrogen or an organic residue having 1 to 5 carbon atoms, ^{.R 11} representing C = O at or ^{CH-R 11} is Represents hydrogen or an organic residue having 1 to 5 carbon atoms.) Amorphous thermoplastic resin A having negative birefringence has an unsaturated carboxylic acid alkyl ester unit a represented by the structural formula (a) and an unsaturated carboxylic acid unit b represented by the structural formula (b). And an acrylic polymer B containing a cyclized structural unit c represented by the structural formula (c), and elastic particles E having a particle diameter of 10 to 1,000 nm. The thermoplastic resin film as described.

(In the above formula, R ¹ and R ² represent hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the above formula, R ³ represents hydrogen or an organic residue having 1 to 5 carbon atoms.)

(In the ^formula, R 4, ^{R 5} represents. In the formula ^X 1, ^{X 2} hydrogen or an organic residue having 1 to 5 carbon atoms, ^{.R 11} representing C = O at or ^{CH-R 11} is Represents hydrogen or an organic residue having 1 to 5 carbon atoms.) The film according to claim 2 or 3, wherein the acrylic polymer B contains a glutaric anhydride unit represented by the following structural formula (d).

(In the above formula, R ⁶ and R ⁷ represent hydrogen or an organic residue having 1 to 5 carbon atoms.) The acrylic polymer B contains an unsaturated carboxylic acid alkyl ester unit and a glutaric anhydride unit, and when the acrylic polymer B is 100 parts by mass, it contains 10 to 15 parts by mass of the glutaric anhydride unit. The thermoplastic resin film according to any one of claims 2 to 4. An optical film comprising one or more layers of the thermoplastic resin film according to claim 1. An optical film in which a hard coat layer is formed on at least one surface of the optical film according to claim 6. The optical film according to claim 6 or 7, which is used as a polarizer protective film. A polarizing plate comprising the optical film according to claim 8.