JP2008083285A - Film and polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic film and a polarizing plate showing small retardation suitable for protection of a polarizer and having a simple manufacturing process. <P>SOLUTION: The film simultaneously satisfies the following conditions (i) and (ii). (i) When a direction giving the maximum refractive index in a film plane is denoted as x direction, a direction perpendicular to the x direction in the film plane is denoted as y direction, and the film thickness direction is denoted as z direction, N1 defined by formula (1): N1=¾nx-ny¾ is 0.0001 or less and N2 defined by formula (2): N2=¾(nx+ny)/2-nz¾ is 0.0001 or less. (ii) As for the refractive indices nx', ny', nz' of the film after stretched, N3 defined by formula (3): N3=¾nx'-ny'¾ is 0.0010 or less and N4 defined by formula (4): N4=¾(nx'+ny')/2-nz'¾ is 0.0010 or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film and a polarizing plate which are used as an optical film having a small retardation particularly suitable for protecting a polarizer and having a simple manufacturing process.

  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.

  By the way, polyacrylic acid, polymethyl methacrylate and the like are widely used as optical materials because they have high transparency. However, when used in applications such as a film substrate for a liquid crystal display device or a polarizer protective film, there is a problem that it cannot be passed through a process involving heat treatment because of poor heat resistance. In addition, since birefringence is caused by stress, there is a problem that a display device that handles polarized light cannot be used.

  On the other hand, a technique for improving heat resistance and reducing birefringence change due to stress by generating a glutaric anhydride unit in an acrylic polymer copolymer has been disclosed (Patent Document 1). However, although heat resistance is improved, further reduction of birefringence change due to stress is required for use in large-screen liquid crystal televisions and high-definition liquid crystal monitors.

  Further, a film is disclosed that uses a polymer in which a rubbery polymer is contained in an acrylic polymer in which glutaric anhydride units are generated in order to reduce birefringence (Patent Document 2). However, in this method, the use of the rubber-containing polymer is increased in cost, and a step of kneading the rubber-containing polymer is required, leading to an increase in the cost of the manufacturing apparatus. Moreover, it leads to the malfunction (haze-up, defect) by nonuniformity, such as aggregation of rubber particles.

  Moreover, the method of giving the process by an imidating agent and the process by a ring closure promoter with respect to acrylic resin as a film which does not produce birefringence is disclosed (patent document 4). However, in this method, trimethylamine used as an imidizing agent is a specific malodorous substance defined by the Malodor Control Law. In addition, other amines also need countermeasures against odor, leading to an increase in the cost of manufacturing equipment such as installation of a deodorizing apparatus.

  Furthermore, there is a disclosure (Patent Document 3) in which a lactone ring-containing polymer is used for a polarizer protective film, but it is disclosed that a retardation is imparted by stretching the film, and the film is caused by external stress or the like. Birefringence change cannot be suppressed.

As the polarizer protective film, cellulose triacetate (TAC) is generally used. TAC is excellent in that it has a high light transmittance and good adhesion to a polarizer. However, in reality, improvement is required to further reduce the amount of change in birefringence with respect to stress.
JP 2004-291302 A JP 2004-292812 A Japanese Patent Application Laid-Open No. 2006-131689 JP 2006-96960 A

  In the present invention, in view of the background of the above-described conventional technology, the maximum refractive index in the film plane is 0.0001 or less and the glass transition temperature (Tg) is −1.5 ° C. and stretched 1.5 times while maintaining heat resistance. In-plane maximum refractive index becomes 0.0010 or less, that is, a change in birefringence suitable for polarizer protection is small, and a film suitable for a simple optical process and a polarizer protection film are provided. It is something to be done.

  The present invention employs the following means in order to solve such problems. That is, the film of the present invention is a film containing an amorphous thermoplastic resin and satisfies the following conditions (i) and (ii) at the same time.

  (I) The direction showing the maximum refractive index in the film plane is the x direction, the direction perpendicular to the x direction in the film plane is the y direction, the film thickness direction is the z direction, and the refractive index in each direction is nx in order. When ny and nz are set, the in-plane birefringence N1 represented by the following formula (1) is 0.0001 or less, and the thickness birefringence N2 represented by the following formula (2) is 0.0001 or less. is there.

N1 = | nx−ny | (1)
N2 = | (nx + ny) / 2−nz | (2)
(Ii) A direction showing the maximum refractive index in the film plane when the glass transition temperature of the amorphous thermoplastic resin is Tg and the glass transition temperature (Tg) is stretched 1.5 times at -10 ° C. When the x ′ direction, the direction orthogonal to the x ′ direction in the film plane is the y ′ direction, the film thickness direction is the z ′ direction, and the refractive indexes in the respective directions are nx ′, ny ′, nz ′ in order, The in-plane birefringence N3 represented by the formula (3) is 0.0010 or less, and the thickness birefringence N4 represented by the following formula (4) is 0.0010 or less.

N3 = | nx′−ny ′ | (3)
N4 = | (nx ′ + ny ′) / 2−nz ′ | (4)
Moreover, the polarizing plate of this invention is comprised using the polarizer protective film which consists of this film, It is characterized by the above-mentioned.

  According to the present invention, it is possible to provide a film that is excellent in transparency and hardly generates birefringence, so that it can be used for, for example, various covers, cameras, VTRs, projection TVs, etc., filters, and the like. It can be used very suitably for films for liquid crystal display devices such as polarizer protective films, protective films for various optical disk substrates, and the like.

  As a result of intensive studies to solve the above-mentioned problem of obtaining a film having heat resistance and a low birefringence change suitable for polarizer protection by a simple manufacturing process, an amorphous thermoplastic resin is obtained. When the film satisfies the following conditions (i) and (ii) at the same time, it has been sought to solve such problems all at once.

  (I) The direction showing the maximum refractive index in the film plane is the x direction, the direction perpendicular to the x direction in the film plane is the y direction, the film thickness direction is the z direction, and the refractive index in each direction is nx in order. When ny and nz are set, the in-plane birefringence N1 represented by the following formula (1) is 0.0001 or less, and the thickness birefringence N2 represented by the following formula (2) is 0.0001 or less. is there.

N1 = | nx−ny | (1)
N2 = | (nx + ny) / 2−nz | (2)
(Ii) A direction showing the maximum refractive index in the film plane when the glass transition temperature of the amorphous thermoplastic resin is Tg and the glass transition temperature (Tg) is stretched 1.5 times at -10 ° C. When the x ′ direction, the direction orthogonal to the x ′ direction in the film plane is the y ′ direction, the film thickness direction is the z ′ direction, and the refractive indexes in the respective directions are nx ′, ny ′, nz ′ in order, The in-plane birefringence N3 represented by the formula (3) is 0.0010 or less, and the thickness birefringence N4 represented by the following formula (4) is 0.0010 or less.

N3 = | nx′−ny ′ | (3)
N4 = | (nx ′ + ny ′) / 2−nz ′ | (4)
The film used in the present invention is an amorphous thermoplastic resin, and when the optical anisotropy limit value at 100% orientation calculated by quantum chemical calculation is N0, −0.005 ≦ N0 <0.005, More preferably, a thermoplastic resin satisfying −0.002 ≦ N0 <0.002 is used in order to reduce birefringence.

  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 has the following structural formulas (a) to (c). Is an acrylic polymer containing at least one of the cyclic structural units represented by the formula (1), and when the acrylic polymer is 100 parts by mass, the structural unit is 10 to 25 parts by mass, more preferably 13 to 23 parts. The content by mass is preferable for achieving both improved heat resistance and reduced birefringence.

(In the above formulas, R ¹ and R ² represent the same or different hydrogen atoms, an alkyl group having 1 to 5 carbon atoms, a carboxyl group, or a carboxyalkyl group having 2 to 5 carbon atoms. , X ¹ and X ² represent the same or different CH ₂ or C═O, X ³ represents O or NR ³ , R ³ represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a carboxyl group Represents a group or a carboxyalkyl group having 2 to 5 carbon atoms.)

(In the above formula, R ^{4 represents} a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a carboxyl group, or a carboxyalkyl group having 2 to 5 carbon atoms.)

(In the above formula, R ⁵ represents a substituent containing an alicyclic structure having 6 to 15 carbon atoms.)
In particular, from the viewpoint of low hygroscopicity, R ⁵ is preferably a substituent represented by the following structural formulas (d) and (e).

Among the structural formulas (a) to (c), when an acrylic polymer having a cyclized structure represented by the structural formula (f) is used, the transparency, heat resistance and productivity are excellent, and optical isotropy is achieved. It is preferable because an excellent film can be obtained.
In particular, from the viewpoint of heat resistance, R ¹ and R ² are preferably hydrogen or a methyl group, and particularly preferably a methyl group.

(In said formula, R < ⁶ >, R < ⁷ > represents the same or different hydrogen atom or a C1-C5 alkyl group.).

  From the viewpoint of the strength of the film, the acrylic polymer comprises an unsaturated carboxylic acid alkyl ester unit and a glutaric anhydride unit. When the acrylic polymer having a ring structure is 100 parts by mass, the acrylic polymer is unsaturated. It is desirable that they are 75-90 mass parts of carboxylic acid alkyl ester units and 10-15 mass parts of glutaric anhydride units.

  The film of the present invention satisfies the following conditions (i) and (ii) simultaneously.

  (I) The direction showing the maximum refractive index in the film plane is the x direction, the direction perpendicular to the x direction in the film plane is the y direction, the film thickness direction is the z direction, and the refractive index in each direction is nx in order. When ny and nz are set, the in-plane birefringence N1 represented by the following formula (1) is 0.0001 or less, and the thickness birefringence N2 represented by the following formula (2) is 0.0001 or less. is there.

N1 = | nx−ny | (1)
N2 = | (nx + ny) / 2−nz | (2)
(Ii) A direction showing the maximum refractive index in the film plane when the glass transition temperature of the amorphous thermoplastic resin is Tg and the glass transition temperature (Tg) is stretched 1.5 times at -10 ° C. When the x ′ direction, the direction orthogonal to the x ′ direction in the film plane is the y ′ direction, the film thickness direction is the z ′ direction, and the refractive indexes in the respective directions are nx ′, ny ′, nz ′ in order, The in-plane birefringence N3 represented by the formula (3) is 0.0010 or less, and the thickness birefringence N4 represented by the following formula (4) is 0.0010 or less.

N3 = | nx′−ny ′ | (3)
N4 = | (nx ′ + ny ′) / 2−nz ′ | (4)
In the above, when N1 and N2 exceed the above range, there is a problem that the retardation value which is the product of birefringence and thickness becomes large. For example, when a 50 μm film is used, the retardation value exceeds 5 nm. In this case, when used for protecting a polarizer, there is a problem that correct color display cannot be performed.

  In addition, when N3 and N4 exceed the above ranges, the retardation value increases greatly when stretched for film strength improvement or thinning, and the correct color when used for polarizer protection. It becomes a problem such as being unable to display. In this case, N3 is more preferably 0.0008 or less and N4 is 0.0008 or less, further preferably N3 is 0.0005 or less and N4 is 0.0005 or less.

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

  The acrylic polymer includes an unsaturated carboxylic acid monomer (A) and an unsaturated carboxylic acid alkyl ester monomer (B) that give the glutaric anhydride unit represented by the structural formula (f) by a subsequent heating step. ) And other vinyl-based monomer units, the vinyl-based monomer (C) that gives the units is polymerized to form a copolymer (a), and then the copolymer (a) Can be produced by heating in the presence or absence of a suitable catalyst to cause an intramolecular cyclization reaction by dealcoholization and / or dehydration. 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. The unsaturated carboxylic acid monomer (A) used in this case is not particularly limited, and can be copolymerized with another vinyl compound (C), and the unsaturated carboxylic acid monomer having the structural formula (g). The body can be used.

(In the above formula, R ⁸ represents a hydrogen atom or an alkyl group 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. The unsaturated carboxylic acid monomer (A) represented by the structural formula (g) gives an unsaturated carboxylic acid unit having the structure represented by the structural formula (f) when copolymerized.

  The unsaturated carboxylic acid alkyl ester monomer (B) is not particularly limited, but preferred examples include those represented by the following structural formula (h).

(In the above formula, R ⁹ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R ¹⁰ represents a hydrogen atom or an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms).

  Of these, acrylates and / or methacrylates having an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms or a hydrocarbon group having a substituent are particularly preferred in terms of excellent thermal stability. is there. The unsaturated carboxylic acid alkyl ester monomer represented by the structural formula (h) gives an unsaturated carboxylic acid alkyl ester unit having the structure represented by the structural formula (f) when copolymerized.

  Preferable specific examples of the unsaturated carboxylic acid alkyl ester monomer (B) 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.

  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 preferred 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 (A) based on 100 parts by mass of the monomer mixture. -50 parts by mass, more preferably 9-33 parts by mass, the unsaturated carboxylic acid alkyl ester monomer (B) is preferably 50-95 parts by mass, more preferably 67-91 parts by mass, and can be copolymerized therewith. When using another vinyl-type monomer (C), 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 (A) is less than 5 parts by mass, the amount of glutaric anhydride unit represented by the structural formula (f) 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 unsaturated carboxylic acid monomer (A) exceeds 50 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 and retention stability tend to decrease.

  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 (i) dehydration and / or (b) dealcoholization reaction is carried out by dealcoholization. A method for producing a thermoplastic polymer containing a glutaric anhydride unit is not particularly limited. However, a method for producing a thermoplastic polymer by passing through a heated extruder having a vent, or degassing under an inert gas atmosphere or under reduced pressure. A method of manufacturing in an apparatus that can be used is preferable from the viewpoint of productivity. Among them, when an intramolecular cyclization reaction is carried out by heating in the presence of oxygen, the yellowness tends to decrease, so that 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 silver and bubbles to be seen in the molded product and molding retention. Sometimes the color tone tends 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 increasing the glass transition temperature is not particularly limited, but it is effective to increase the content of the cyclized structural unit represented by the structural formula (f) in the acrylic polymer having a ring structure, for example. Is. It is also effective to orient the obtained film by stretching.

  As the acrylic polymer having a ring structure of the present invention, a copolymer comprising a glutaric anhydride unit represented by the structural formula (f) 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. However, since heat resistance is improved, the total of the unsaturated carboxylic acid alkyl ester unit and the glutaric anhydride unit is 100 masses. Part preferably comprises 50 to 95 parts by weight of unsaturated carboxylic acid alkyl ester units and 5 to 50 parts by weight of glutaric anhydride units, more preferably 55 to 90 parts by weight of unsaturated carboxylic acid alkyl ester units. And 10 to 45 parts by mass of glutaric anhydride units. When the glutaric anhydride unit is less than 5 parts by mass, the heat resistance improving effect tends to be small.

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.

  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 or less.

  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.

  In addition, the film of the present invention can be used for various uses as it is or after being subjected to various processing. In particular, it can be suitably used for known optical applications such as the periphery of liquid crystal display devices such as an optically isotropic film, a polarizer protective film and a transparent conductive film by utilizing excellent transparency and low birefringence.

  Furthermore, the film of the present invention can be subjected to surface treatment on one side or both sides of the film as 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 increasing mutual adhesion. Is preferred.

  In addition, a coating layer such as a hard coat layer can be formed on the surface of the stretched 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.

  The stretched film can be used as a polarizer protective film to be bonded to a polarizer, and can be 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 calculated and measured as follows.

1. Calculation of optical anisotropy limit value at 100% orientation In order to calculate the refractive index using quantum chemical calculation, in the present invention, (1) a unit structure constituting a polymer is input to an electronic computer, and quantum chemistry is performed. Structure optimization calculation to find its stable conformation using calculation, (2) Polarizability calculation to obtain molecular polarizability using quantum chemical calculation for unit structure of stable conformation, and (3) Unit of stable conformation Molecular volume calculation for obtaining the molecular volume of the structure and (4) refractive index calculation for obtaining the refractive index using the molecular polarizability and molecular volume obtained in the above two terms are used.

  In the structural optimization calculation in Step 1, first, the structural formula of the unit structure constituting the polymer is input in a readable form to an electronic computer. For the input, publicly available molecular structure creation software or text editor can be used.

  After that, structural optimization by quantum chemical calculation is performed on the input molecular structural formula to obtain a stable conformation. As a method of quantum chemical calculation, general methods such as Hückel molecular orbital method, semi-empirical molecular orbital method, X-α method, density functional method, and ab initio molecular orbital method can be used.

  The semi-empirical molecular orbital method is preferably used from the viewpoint of balance between calculation speed and accuracy. For example, AM1 method [MJS Dewar et al., Journal of American Chemical Society (J.Am.Chem.Soc .), 1985, 107, p. 3902-3909.] Has sufficient calculation speed and accuracy for the purposes of the present invention. On the other hand, when priority is given to calculation accuracy, the density functional method or the ab initio molecular orbital method is preferably used.

In the polarizability calculation in step 2, the molecular polarizability is obtained using quantum chemical calculation for the stable conformation obtained in step 1. As a method of quantum chemical calculation, it is preferable to use a highly accurate method such as a density functional method or an ab initio molecular orbital method. More preferably, a hybrid method of a density functional method and an ab initio molecular orbital method is used. For example, B3LYP method [AD Becke, Journal of Chemical Physics (J. Chem. Phys.) , 1993, 98, p.5648 / C. Lee, W. Yang, RG Parr, Phys. Rev. B, 1988, 37 , p.785 / B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chemical Phys. Lett , 1989, 157, p.200.] Using time-dependent equations [SP Karna and M. Dupuis, Journal of computational chemistry (J.Comp. Chem.), 1991, 12, p. 487. Density functional method can be obtained molecular polarizability of sufficient accuracy for target, when using the ab initio molecular orbital method or hybrid method, it is necessary to specify the basis functions to expand the one-electron orbitals. In order to obtain sufficient calculation accuracy for the polarizability, a function obtained by adding a function extended to a basis function called a valence double zeta and a polarization function is preferably used. For example, the double valence orbital basis functions by Pople et al. [WJ Hehre, R. Ditchfield, JA Pople, Journal of Chemical Physics (J. Chem. Phys.), 1972, 56, p.2257.], Expanded functions [T. Clark, J. Chandrasekhar, PvR Schleyer ), Journal of Computational Chemistry (J.Comp.Chem.), 1983, 4, p.294.) And polarization functions (PC Hariharan, JA Pople) 6-31 + G (d) and 6-31 + G (d, p) basis functions in combination with Theoret. Chimica Acta 1973, 28, p.213. It is preferably used for the purpose of the invention.

  In the molecular volume calculation in Step 3, the molecular volume is calculated for the stable conformation obtained in Step 1. As a calculation method, a method of calculating based on the electron density obtained by the molecular orbital method, a method of calculating the volume of the molecule considering the molecule as a fusion of spheres having van der Waals radii, and the like are used. Among the methods belonging to the latter, the Connolly surface method (ML Connolly, Science, 1983, 221, p.709.) Is preferably used as a method for simply achieving the object of the present invention. It is done.

  In the refractive index calculation in step 4, the refractive index is calculated according to the Lorentz-Lorenz equation (following equation) using the molecular polarizability α obtained in step 2 and the molecular volume V obtained in step 3.

Here, the number density N is an amount calculated from the molecular volume V as N = 10 ²⁴ / V [1 / cm ³ ].

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

3. Residual solvent The film immediately after film formation was sampled in a 20 cm square, and the film mass w ₂ was weighed. Next, after heat-treating this film for 10 minutes in a hot air oven at a temperature of 200 ° C., the film mass w ₃ was weighed, and the residual solvent in the film was determined from the following formula. The measurement was performed twice and the average value was obtained.

Residual solvent (%) = ((w ₂ −w ₃ ) / w ₃ ) × 100
4). 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 ).

5. 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.

6). In-plane birefringence (N1, N3), thickness birefringence (N2, N4)
Retardation (R (589)) at a wavelength of 589 nm is measured using the following measuring device, the in-plane maximum refractive index direction is the x direction, the in-plane orthogonal direction to x is the y direction, and the film thickness direction is The z direction was defined (stretched films were similarly defined as the nx ′, ny ′, and nz ′ directions) and calculated using the following formula. Measurement was performed at 5 points, and an average value was obtained.

・ Device: Phase difference measuring device KOBRA-21ADH (manufactured by Oji Scientific Instruments)
・ Measurement diameter: φ5mm
-Constant wavelength: 589nm
In-plane birefringence: N1 = | nx−ny |
N3 = | nx′−ny ′ |
Thickness birefringence: N2 = | (nx + ny) / 2−nz |
N4 = | (nx ′ + ny ′) / 2−nz ′ |
7). Photoelastic coefficient Retardation at a wavelength of 589 nm (R (589)) when no load is applied to the test piece and when a load of 4.9 N is applied in the slow axis direction of the test piece, respectively ) And the photoelastic coefficient was calculated according to the following equation. One measurement was performed.

-Retardation measuring device: Polarization microscope 5892 (manufactured by Nikon Corporation)
Photoelastic coefficient [m ² / N] = (phase difference under load [nm] −phase difference under no load [nm]) × width of test piece [mm] × 10 ⁻¹² / load [N]
8). Each component composition The acrylic 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 acrylic 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.

[Example 1]
(1) Preparation of acrylic polymer (A1) First, a methyl methacrylate / acrylamide copolymer suspension was prepared as follows.

  While charging 20 parts by mass of methyl methacrylate, 80 parts by mass of acrylamide, 0.3 part by mass of potassium persulfate, and 1,500 parts by mass of ion-exchanged water into the reactor, replacing the reactor with nitrogen gas, The reaction was allowed to proceed at 70 ° C. until the body was completely converted to a polymer. 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 parts by weight After the addition, the temperature was raised to 70 ° C., The time at which the internal temperature reached 70 ° C. 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 (A1). The polymerization rate of this copolymer was 97%, and the mass average molecular weight was 130,000. Using the above copolymer (A1), 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, An intramolecular cyclization reaction was performed at a screw rotation speed of 100 rpm, a raw material supply rate of 5 kg / h, and a cylinder temperature of 280 ° C. to obtain a pellet-shaped acrylic polymer (a1), and the mass average molecular weight of the acrylic polymer (a1) was 13. The methyl methacrylate unit: methacrylic acid unit: ring structure unit was 83: 5: 12 mol% (78: 4: 17 parts by mass).

  The optical anisotropy limit value at 100% orientation was calculated by the following procedure.

[Structural optimization]
Using molecular modeling software Chem3D manufactured by ChemidgeSoft,
A molecular model in which methyl methacrylate units, methacrylic acid units, and ring structure units are terminated with hydrogen atoms at both ends was prepared. For these models, the structure optimization by the AM1 semi-empirical molecular orbital method incorporated in Chem3D is executed, and when the straight line connecting the hydrogen atoms at both ends is defined as the x-axis of the orthogonal coordinate system, the side chain is perpendicular to the x-axis. A stable conformation with the strongest orientation in the direction was determined. The structure optimization calculation is executed by a personal computer equipped with a Pentium (registered trademark) 4 processor manufactured by Intel and operating Windows (registered trademark) XP as an operating system. The default value of was used. After the structure optimization, the whole molecule was rotated so that the straight line connecting the hydrogen atoms at both ends coincided with the x-axis of the Cartesian coordinate system, and the atomic coordinates were output as a text file in the Cartesian coordinate format.

(Polarizability calculation)
Molecular polarizabilities were calculated using the ab initio molecular orbital calculation software GAMESS (December 2003 version) developed by Iowa State University for the atomic coordinates of the stable conformation obtained in the structure optimization step. HF / 6-31 + G (d, p) was specified as the approximation level of the wave function. In addition, in order to use the time-dependent Hartree-Fock equation as the polarizability calculation algorithm, $ CONTROL RUNTYP = TDHF COORD = UNIQUE NOSYM = 1 $ END is specified as a keyword. The above polarizability calculation was performed on a workstation equipped with an Intel Pentium (registered trademark) 4 processor and operating Linux as an operating system.

  Since the molecular polarizability α by GAMESS is output in atomic units, it was converted into CGS units based on the following formula.

  Here, the suffixes i and j of the α tensor are components of x, y and z in the orthogonal coordinate system.

Note that the methyl methacrylate ^{units, αxx = 87.8457 × 10 -25 [} cm 3], αyy = 85.3778 × 10 -25 [cm 3], αzz = 97.5445 × 10 -25 [cm 3] As for the methacrylic acid unit, αxx = 73.0038 × 10 ⁻²⁵ [cm ³ ], αyy = 71.9635 × 10 ⁻²⁵ [cm ³ ], αzz = 77.5606 × 10 ⁻²⁵ [cm ³ ],
Regarding the ring structural unit, αxx = 1474.4311 × 10 ⁻²⁵ [cm ³ ], αyy = 131.232 × 10 ⁻²⁵ [cm ³ ], and αzz = 12.62.636 × 10 ⁻²⁵ [cm ³ ]. .

(Molecular volume calculation)
For the stable conformation obtained in the structure optimization step, molecular volume was calculated using molecular modeling software MS Modeling 4.0 manufactured by Accelrys. The Connolly surface method was used as the calculation algorithm, and the software default values were used for the parameters required for the calculation. The above molecular volume calculation was performed on a personal computer equipped with an Intel Pentium (registered trademark) 4 processor and operating Windows (registered trademark) XP as an operating system.

Incidentally, methyl methacrylate units, methacrylic acid units, the ring structure units each molecular volume is ^{111.99 × 10 8 [cm 3]} , 93.12 × 10 8 [cm 3], 157.31 × 10 8 [cm 3 ]Met.

  The output molecular volume V was converted to number density N based on the following equation.

N = −4.2879 × 10 ²⁰ + 0.8163 × (10 ²⁴ / V) [1 / cm ³ ]
The number density of each of the methyl methacrylate unit, the methacrylic acid unit, and the ring structure unit is 6.81 × 10 ²¹ [1 / cm ³ ], 8.28 × 10 ²¹ [1 / cm ³ ], 4.71 × 10 ²¹ [1 / cm ³ ].

(Refractive index calculation)
Using the molecular polarizability tensor αCGS_ij obtained in the polarizability calculation step and the number density N obtained in the molecular volume calculation step, the components of the refractive index in the x, y, and z directions were calculated according to the following equations.

  Here, the subscript i is any of x, y and z components in the orthogonal coordinate system.

  Further, the refractive index anisotropy Δn was defined as follows:

  For structural units having flexible side chains such as methyl methacrylate units and methacrylic acid units, not only the conformation in which the side chains are most strongly oriented in the direction perpendicular to the x axis, but also the side chains on the x axis. Since a conformation oriented in a parallel direction is also conceivable, a value ½ of the obtained value is used as a calculated value of Δn. As for the ring structural unit, the value is used as it is because it does not have a side chain whose conformation can be changed flexibly.

  The refractive index anisotropy Δn of each of the obtained methyl methacrylate unit, methacrylic acid unit and ring structure unit is −0.010 (= −0.020 / 2), −0.006 (= −0.012 / 2) +0.078.

(Synthesis of refractive index anisotropy)
When the refractive index anisotropy of the copolymer was determined, the refractive index anisotropy Δnk of the copolymer component k was determined by the above procedure, and calculated by multiplying the molar ratios of the components and adding them.

  Here, pk is the molar ratio of the component k, and is normalized so that the total sum of pk is 1.

  The optical anisotropy limit value at 100% orientation was (−0.010 × 0.83) + (− 0.006 × 0.05) + (+ 0.078 × 0.12) = 0.0008. It was.

(2) Film formation The acrylic polymer (a1) was added to 300 parts by mass of methyl ethyl ketone with respect to 100 parts by mass, and stirred and mixed at room temperature for 4 hours to obtain a transparent solution. This solution is cast on a PET film, 5 minutes at 60 ° C, 5 minutes at 70 ° C, 5 minutes at 90 ° C, 5 minutes at 100 ° C, 5 minutes at 120 ° C, 15 minutes at 130 ° C, and 170 ° C. After drying for 20 minutes, the film was peeled from the PET film to obtain a film (A1). The thickness of the film was 40 μm. The characteristics of the obtained acrylic resin film (A1) are as follows.

Residual solvent: 0.7% by mass
Glass transition temperature (Tg): 123 ° C
Light transmittance: 93%
Haze value: 0.4%
In-plane birefringence (N1): 0.00002
Thickness birefringence (N2): 0.00001
Furthermore, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 113 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00025
Thick birefringence after stretching (N4): 0.00013
Thus, the obtained film (A1) was excellent in optical isotropy.

[Example 2]
A bead-shaped copolymer (A2) was obtained in the same manner as in Example 1 except that the addition amount of t-dodecyl mercaptan as a chain transfer agent was changed to 2.0 parts by mass. Using this copolymer (A2), a pellet-shaped acrylic polymer (a2) was obtained in the same manner as in Example 1. The acrylic polymer (a2) has a mass average molecular weight of 65,000, methyl methacrylate units: methacrylic acid units: ring structural units of 83: 5: 12 mol% (78: 4: 17 parts by mass), and 100% oriented. When calculated in the same manner as in Example 1, the optical anisotropy limit value was 0.0008.

  After this acrylic polymer (a2) was dried at 100 ° C. for 3 hours, the pellets were extruded using a 45 mmφ single screw extruder (set temperature 250 ° C.) and formed into a sheet form via a T-die (set temperature 250 ° C.). Extruded. This film was cooled so that one side was completely adhered to a cooling roll at 130 ° C. to obtain an unstretched acrylic resin film (A2). At this time, the speed of the cooling roll was adjusted so that the lip gap of the T die / film thickness = 15. The thickness of the obtained film was 40 μm.

  The characteristics of the obtained acrylic resin film (A2) are as follows.

Glass transition temperature (Tg): 124 ° C
Light transmittance: 93%
Haze value: 0.5%
In-plane birefringence (N1): 0.00002
Thick birefringence (N2): 0.00002
Further, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 114 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00018
Thickness birefringence after stretching (N4): 0.00011
Thus, the obtained film (A2) was excellent in optical isotropy.

[Comparative Example 1]
Using the bead-shaped copolymer (A1) obtained in the same manner as in Example 1, except that 0.2% by mass of additive (NaOCH ₃ ) was added and the cylinder temperature was 290 ° C. An intramolecular cyclization reaction was performed in the same manner as in Example 1 to obtain a pellet-shaped acrylic polymer (a3). The acrylic polymer (a3) has a mass average molecular weight of 130,000, methyl methacrylate units: methacrylic acid units: ring structural units are 74: 3: 23, 100 mol% (66: 2: 32 parts by mass), and 100% oriented. When calculated in the same manner as in Example 1, the optical anisotropy limit value was 0.0103.

  The obtained acrylic polymer (a3) was filmed in the same manner as in Example 1 to obtain an acrylic resin film (A3). The thickness of the obtained film was 40 μm, and the residual solvent was 0.7% by mass.

  The characteristics of the obtained acrylic resin film (A3) are as follows.

Glass transition temperature (Tg): 128 ° C
Light transmittance: 93%
Haze value: 0.2%
In-plane birefringence (N1): 0.00001
Thick birefringence (N2): 0.00002
Furthermore, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 118 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00168
Thickness birefringence after stretching (N4): 0.00152
Thus, the obtained film (A3) could not maintain optical isotropy.

[Comparative Example 2]
A pellet-shaped acrylic polymer (a4) was obtained in the same manner as in Comparative Example 1 except that (2) was used as the bead-shaped copolymer. The acrylic polymer (a4) has a mass average molecular weight of 65,000, methyl methacrylate unit: methacrylic acid unit: ring structural unit is 74: 3: 23, 100 mol% (66: 2: 32 parts by mass), 100% orientation. When calculated in the same manner as in Example 1, the optical anisotropy limit value at the time was 0.0103.

  Using the pellet-shaped acrylic polymer (a4), an unstretched acrylic resin film (A4) was obtained as a film by the method described in Example 2. The thickness of the obtained film was 40 μm.

  The characteristics of the obtained acrylic resin film are as follows.

Glass transition temperature (Tg): 130 ° C
Light transmittance: 93%
Haze value: 0.3%
In-plane birefringence (N1): 0.00002
Thick birefringence (N2): 0.00002
Furthermore, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 120 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00172
Thickness birefringence after stretching (N4): 0.00169
Thus, the obtained film (A4) could not maintain optical isotropy.

[Comparative Example 3]
Except that the additive (NaOCH ₃ ) was not used, an intramolecular cyclization reaction was performed in the same manner as in Comparative Example 2 to obtain a pellet-shaped acrylic polymer (a5). The acrylic polymer (a5) has a mass average molecular weight of 65,000, methyl methacrylate units: methacrylic acid units: ring structural units of 76: 5: 19, 100 mol% (69: 4: 27 parts by mass), 100%. When calculated in the same manner as in Example 1, the optical anisotropy limit value at the time of orientation was 0.006.

  The characteristics of the obtained acrylic resin film (A5) are as follows.

Glass transition temperature (Tg): 125 ° C
Light transmittance: 93%
Haze value: 0.4%
In-plane birefringence (N1): 0.00002
Thick birefringence (N2): 0.00003
Furthermore, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 119 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00122
Thickness birefringence after stretching (N4): 0.00108
Thus, the obtained film (A6) could not maintain optical isotropy.

[Comparative Example 4]
A film was formed in the same manner as in Example 2 using PMMA (“Delpet (registered trademark) 80N” (manufactured by Asahi Kasei Co., Ltd.)) instead of the pellet-shaped acrylic polymer. ^When confirmed by ¹ H-NMR method, the ring structure could not be confirmed. The optical anisotropy limit value at 100% orientation was −0.010 when calculated in the same manner as in Example 1.

  The characteristics of the obtained PMMA film (A6) are as follows.

Glass transition temperature (Tg): 110 ° C
Light transmittance: 90%
Haze value: 1.0%
In-plane birefringence (N1): 0.00002
Thick birefringence (N2): 0.00003
Furthermore, when a sample having a width of 50 mm and a length of 150 mm was cut out from this film and stretched 1.5 times at 119 ° C., a homogeneous stretch-oriented film was obtained. The characteristics of the obtained acrylic resin film are as follows.

In-plane birefringence after stretching (N3): 0.00250
Thickness birefringence after stretching (N4): 0.00238
Thus, the obtained film (A6) could not maintain optical isotropy.

  Since the film of the present invention is excellent in transparency, it can be used, for example, in various covers, cameras, VTRs, projection TVs and other finders, filters, and the like. Further, since almost no birefringence is generated, it is extremely useful for a film for a liquid crystal display device such as a polarizer protective film, various optical disk substrate protective films and the like.

Claims (7)

A film containing an amorphous thermoplastic resin, which satisfies the following conditions (i) and (ii) simultaneously.
(I) The direction showing the maximum refractive index in the film plane is the x direction, the direction perpendicular to the x direction in the film plane is the y direction, the film thickness direction is the z direction, and the refractive index in each direction is nx in order. When ny and nz are set, the in-plane birefringence N1 represented by the following formula (1) is 0.0001 or less, and the thickness birefringence N2 represented by the following formula (2) is 0.0001 or less. is there.
N1 = | nx−ny | (1)
N2 = | (nx + ny) / 2−nz | (2)
(Ii) A direction showing the maximum refractive index in the film plane when the glass transition temperature of the amorphous thermoplastic resin is Tg and the glass transition temperature (Tg) is stretched 1.5 times at -10 ° C. When the x ′ direction, the direction orthogonal to the x ′ direction in the film plane is the y ′ direction, the film thickness direction is the z ′ direction, and the refractive indexes in the respective directions are nx ′, ny ′, nz ′ in order, The in-plane birefringence N3 represented by the formula (3) is 0.0010 or less, and the thickness birefringence N4 represented by the following formula (4) is 0.0010 or less.
N3 = | nx′−ny ′ | (3)
N4 = | (nx ′ + ny ′) / 2−nz ′ | (4)   As an amorphous thermoplastic resin, a thermoplastic resin satisfying −0.005 ≦ N0 <0.005 is used when the optical anisotropy limit value at 100% orientation calculated by quantum chemical calculation is N0, The film according to claim 1. The amorphous thermoplastic resin is an acrylic polymer containing at least one of the cyclic structural units represented by the following structural formulas (a) to (c), and 100 parts by mass of the acrylic polymer. When it does, the film of Claim 1 or 2 which contains the said structural unit 10-25 mass parts in total.

(In the above formulas, R ¹ and R ² represent the same or different hydrogen atoms, an alkyl group having 1 to 5 carbon atoms, a carboxyl group, or a carboxyalkyl group having 2 to 5 carbon atoms. , X ¹ and X ² represent the same or different CH ₂ or C═O, X ³ represents O or NR ³ , R ³ represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a carboxyl group Represents a group or a carboxyalkyl group having 2 to 5 carbon atoms.)

(In the above formula, R ^{4 represents} a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a carboxyl group, or a carboxyalkyl group having 2 to 5 carbon atoms.)

(In the above formula, R ⁵ represents a substituent containing an alicyclic structure having 6 to 15 carbon atoms.) The film according to claim 3, wherein the acrylic polymer contains a glutaric anhydride unit represented by the following structural formula (f).

(In said formula, R < ⁶ >, R < ⁷ > represents the same or different hydrogen atom or a C1-C5 alkyl group.)   The acrylic polymer comprises an unsaturated carboxylic acid alkyl ester unit and a glutaric anhydride unit. When the acrylic polymer is 100 parts by mass, the unsaturated carboxylic acid alkyl ester unit is 75 to 90 parts by mass and The film of Claim 3 or 4 containing 10-25 mass parts of glutaric anhydride units.   The film in any one of Claims 1-5 used as a polarizer protective film.   The polarizing plate comprised using the film of Claim 6.