JP2010215707A - Biaxially oriented film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented film, containing a thermoplastic acrylic polymer having a ring structure in the main chain, that has characteristics suitable for an optical film such as a high film strength, a low staining property and few appearance defects, etc., while maintaining low birefringence and heat resistance. <P>SOLUTION: This biaxially oriented film includes the thermoplastic acrylic polymer having the ring structure in the main chain, and satisfies the following conditions: (A) an in-plane phase difference value (Re) is &le;5 nm; (B) an absolute value of a thickness-directional phase difference value (Rth) is &le;5 nm; (C) a glass transition temperature (Tg) is &ge;110&deg;C; (D) a content of the thermoplastic acrylic polymer having the ring structure in the main chain is &ge;93 wt.%; and (E) a number of times of folding in an MIT folding endurance test is &ge;500. Preferably, a content of a structural unit derived from an aromatic vinyl monomer in the biaxially oriented film is &le;5 wt.%. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure in the main chain.

  Acrylic resins represented by PMMA (polymethyl methacrylate) are widely used for transparent materials in automobile parts, home appliances, various industrial parts, etc., because they have a good balance of moldability and surface hardness. Furthermore, since it is excellent in optical characteristics such as high light transmittance, low birefringence, and low wavelength dependency, it is also employed in optical related applications such as a light guide plate. However, since the glass transition temperature (Tg) of the acrylic resin is around 100 ° C., it is difficult to use it in a field where heat resistance is required, and a more excellent heat resistant resin is desired. In particular, expectations have been increasing in the field of films for flat displays such as liquid crystal display devices, plasma displays, and organic EL display devices.

  As an acrylic resin having both transparency and heat resistance, a resin containing a thermoplastic acrylic polymer having a ring structure in the main chain has been developed. This resin is brittle due to the introduction of a more rigid ring structure in hard acrylic resin, and in optical film applications, it imparts the necessary film strength during molding and processing, so it can be stretched during molding to reduce brittleness. Are known. Specific examples of the polymer include polymers having a lactone ring structure in the main chain obtained by subjecting a polymer having a hydroxyl group and an ester group in a molecular chain to a lactone cyclocondensation reaction (for example, Patent Documents 1 and 2). And polymers containing a glutarimide ring structure (see, for example, Patent Document 3) are being applied to optical film applications of these stretched films.

  Films containing a thermoplastic acrylic polymer having a ring structure in these main chains were able to impart heat resistance by introducing a ring structure into the main chain of the acrylic polymer. Since the structure has positive birefringence, the excellent optical property of low birefringence, which is a characteristic of acrylic resin, is deteriorated, and when stretched, a biaxially stretched film having low birefringence cannot be obtained. there were. Therefore, in order to reduce birefringence that increases due to orientation during stretching, the introduction of a structure derived from a styrenic monomer has been studied, and a method of polymer blending acrylonitrile-styrene resin (AS resin) or styrene A technique of copolymerizing a monomer based on a monomer has been taken.

JP 2006-171464 A JP 2007-63541 A JP 2006-316153 A

  However, when an AS resin is polymer blended, depending on the ratio of the AS resin, a kneading process or a molding process at a high temperature required for the production of a resin or film containing a thermoplastic acrylic polymer having a ring structure in the main chain The coloring due to the AS resin tends to be strong. In addition, since the time for high temperature becomes longer due to the addition of the kneading process, the amount of polymer gel generated is increased, and further, environmental foreign substances and foreign substances contained in the AS resin are mixed in the kneading process. Therefore, it is necessary to cope with the problem that film defects after molding increase.

  On the other hand, when the styrene monomer was copolymerized, there was no problem of coloring or foreign matter, but since the structural unit derived from the styrene monomer is brittle, high film strength can be obtained even after stretching. Is not easy. Furthermore, when a cyclic structure is introduced into the main chain by a cyclization reaction after polymerization, the introduction of a structural unit derived from a styrenic monomer results in insufficient cyclization. The distribution may spread and the resulting film strength will be reduced.

  In addition, both polymer blending and copolymerization techniques introduce structural units derived from styrenic monomers, so they have excellent characteristics such as high light transmittance, low birefringence, and low wavelength dependence that are inherent to acrylic resins. The optical characteristics will deteriorate.

  The present invention has been made in view of the present situation, and has excellent film strength and optical characteristics while maintaining low birefringence and heat resistance, and is suitable for optical films such as low coloration and few appearance defects. An object of the present invention is to provide a biaxially stretched film including a thermoplastic acrylic polymer having a ring structure in the main chain, which has characteristics.

  In order to achieve the above object, the present inventors have conducted various studies on a biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure in the low birefringence main chain. When the structure is taken, the positive birefringence due to the ring structure of the main chain and the negative birefringence due to the structural unit derived from the (meth) acrylate monomer of the acrylic polymer cancel each other out and stretch Later, a film having a low birefringence was obtained, and furthermore, it was found that the folding resistance of the biaxially stretched film was unexpectedly greatly improved, and the present invention was achieved.

That is, the present invention is a biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure in the main chain, and the following conditions:
(A) In-plane retardation value (Re) is 5 nm or less;
(B) The absolute value of the thickness direction retardation value (Rth) is 5 nm or less;
(C) Glass transition temperature (Tg) is 110 ° C. or higher;
(D) The content ratio of the thermoplastic acrylic polymer having a ring structure in the main chain is 93% by weight or more;
(E) A biaxially stretched film that satisfies the number of folding times of 500 or more in the MIT folding resistance test.

  The content ratio of the structural unit derived from the aromatic vinyl monomer in the biaxially stretched film is preferably 5% by weight or less.

  It is preferable to contain 97% by weight or more of a thermoplastic acrylic polymer having a ring structure in the main chain.

  Furthermore, it is preferable that other thermoplastic resins are included.

  According to the present invention, a thermoplastic acrylic polymer having a ring structure in the main chain, which has excellent film strength and optical properties, particularly high bending resistance, while maintaining heat resistance due to the ring structure of the main chain. A biaxially stretched film can be provided.

  Hereinafter, the present invention will be described in detail. In the present specification, “A to B” means A or more and B or less.

The biaxially stretched film of the present invention contains a thermoplastic acrylic polymer having a ring structure in the main chain and is biaxially stretched.
≪Thermoplastic acrylic polymer having a ring structure in the main chain≫
The thermoplastic acrylic polymer having a ring structure in the main chain contained in the biaxially stretched film of the present invention includes a ring structure and a structure derived from a (meth) acrylate monomer in the main chain. The total content of the structural units derived from the (meth) acrylic acid ester monomer and the content of the ring structure is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight in the copolymer. %, Particularly preferably 95% by weight or more, most preferably 99% by weight or more.
The main chain ring structure usually has positive birefringence, and the structure derived from the (meth) acrylate monomer has weak negative birefringence, so the positive birefringence due to the main chain ring structure. And the negative birefringence due to the structure derived from the (meth) acrylic acid ester monomer cancel each other, and a film having a low birefringence can be obtained even after stretching. Here, positive birefringence means refractive index anisotropy that increases the refractive index in the same direction when the polymer molecular chain, which is a component of the film, is oriented by stretching. Is expressed. On the other hand, negative birefringence means that when a polymer molecular chain, which is a component constituting a film, is molecularly oriented by being stretched, the refractive index in the same direction is reduced, and at the same time, refraction in a direction perpendicular to the film is performed. It means expressing the refractive index anisotropy that increases the rate.

  The thermoplastic acrylic polymer in the present invention is a polymer having a structural unit derived from a (meth) acrylic acid ester monomer, and polymerizes a monomer mixture containing the (meth) acrylic acid ester monomer. As long as the effects of the present invention are not impaired, a known thermoplastic acrylic polymer can be used. The main chain contains a structural unit derived from a (meth) acrylic acid ester monomer and a ring structure. Preferred examples of the (meth) acrylic acid ester monomer include methyl (meth) acrylate and (meth) acrylic. (Meth) such as ethyl acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate Alkyl acrylate; benzyl (meth) acrylate; chloromethyl (meth) acrylate; 2-chloroethyl (meth) acrylate; dicyclopentanyloxyethyl (meth) acrylate; dicyclopentanyl (meth) acrylate 2-hydroxyethyl (meth) acrylate; 3-hydroxypropyl (meth) acrylate; (meth) acrylic acid 2 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydroxypentyl (meth) acrylate, etc., among these structural units derived from these (meth) acrylate monomers 1 type may be included independently and 2 or more types may coexist. Among these, (meth) acrylic acid alkyl ester is preferable, and methyl methacrylate is most preferable in terms of excellent thermal stability and optical characteristics.

  The thermoplastic acrylic polymer may contain a structural unit other than the above-mentioned (meth) acrylate monomer, and a monomer mixture containing a monomer other than the (meth) acrylate monomer. It is obtained by polymerizing. Examples of monomers other than (meth) acrylic acid ester monomers include, for example, acrylonitrile, methyl vinyl ketone, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, methallyl alcohol, allyl alcohol, and 2-hydroxy. Allyl alcohol such as methyl-1-butene, acrylic acid, methacrylic acid, crotonic acid, α-hydroxyethylstyrene, acrylic acid, methacrylic acid, crotonic acid, methyl 2- (hydroxymethyl) acrylate, 2- (hydroxymethyl) 2- (hydroxyalkyl) acrylic acid ester such as ethyl acrylate, 2- (hydroxyalkyl) acrylic acid such as 2- (hydroxyethyl) acrylic acid, N-vinylpyrrolidone, N-vinylcarbazole and the like. Only one monomer may be used And, it may be used in combination of two or more thereof.

  In the thermoplastic acrylic polymer having a ring structure in the main chain, the content of structural units derived from styrene monomers, that is, aromatic vinyl monomers, is preferably less than 5% by weight, more preferably It is less than 3% by weight, more preferably less than 1% by weight, particularly preferably less than 0.1% by weight. When the content of the structural unit derived from the aromatic vinyl monomer is 5% by weight or more, the structure derived from the aromatic vinyl monomer itself is brittle. Since the structure derived from the vinyl group monomer inhibits the cyclization reaction and causes a crosslinking reaction, it is difficult to obtain a high film strength even after stretching. The aromatic vinyl monomer is not particularly limited as long as the effect of the present invention is not impaired as long as it is an aromatic vinyl monomer. For example, styrene, vinyl toluene, α-methyl styrene, α-hydroxymethyl styrene , Α-hydroxyethylstyrene, chlorostyrene and the like.

  As the ring structure of the main chain, N-substituted maleimide such as phenylmaleimide, benzylmaleimide, cyclohexylmaleimide, methylmaleimide or maleic anhydride is copolymerized to form a ring structure derived from N-substituted maleimide or a maleic anhydride-derived ring structure Or a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, a ring structure derived from N-substituted maleimide, or the like may be introduced into the main chain by a cyclization reaction after polymerization. From the viewpoint of heat resistance, those having a ring structure derived from N-substituted maleimide, a lactone ring structure, or a glutarimide structure are preferred. Among them, those having a lactone ring structure in the main chain from the viewpoint of low coloring and excellent optical properties. Is particularly preferred.

  As a method for producing the thermoplastic acrylic polymer having a ring structure in the main chain, a known production method can be applied. For example, a method for producing an acrylic resin containing a lactone ring structure can be produced by the production methods described in JP 2006-96960 A, JP 2006-171464 A, and JP 2007-63541 A. Further, regarding a thermoplastic acrylic polymer copolymerized with N-substituted maleimide and a thermoplastic acrylic polymer containing a glutaric anhydride structure or a glutarimide structure, Japanese Patent Application Laid-Open No. 2007-31537, WO2007 / A manufacturing method described in Japanese Patent No. 26659 or WO 2005/108438 may be used.

  The lactone ring structure of the main chain may be a 4- to 8-membered ring, but a 5- to 6-membered ring is more preferable, and a 6-membered ring is still more preferable in terms of structural stability. Further, when the main chain lactone ring structure is a 6-membered ring, examples include the structure represented by the general formula (1) and Japanese Patent Application Laid-Open No. 2004-168882, but before introducing the lactone ring structure into the main chain. When synthesizing these polymers, it is easy to obtain a polymer with a high polymerization yield, a high content of lactone ring structure, and has good copolymerizability with (meth) acrylic acid esters such as methyl methacrylate. It is preferable that it is a structure represented by General formula (1) at a point.

(In the formula, R1, R2, and R3 each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.)
The content of the ring structure of the thermoplastic acrylic polymer having a ring structure in the main chain is preferably 15% by weight or less, more preferably in the range of 1 to 15% by weight, and further preferably 3 to 15% by weight. %, Particularly preferably in the range of 5 to 12% by weight, most preferably in the range of 5 to 10% by weight. When the content of the ring structure is more than 15% by weight, the positive birefringence becomes high, which is not preferable. By having the ring structure, heat resistance, solvent resistance, and surface hardness are improved.

  The glass transition temperature of the thermoplastic acrylic polymer having a ring structure in the main chain is preferably 110 ° C. or higher. More preferably, it is 115 degreeC or more, More preferably, it is 120 degreeC or more. The upper limit of the glass transition temperature is not particularly limited, but is preferably 200 ° C. or less from the viewpoint of moldability.

The weight average molecular weight of the thermoplastic acrylic polymer having a ring structure in the main chain is preferably 10,000 to 300,000, more preferably 50,000 to 300,000, still more preferably 100,000 to 250, 000, particularly preferably 120,000 to 200,000.

≪Method for producing biaxially stretched film≫
The biaxially stretched film of the present invention is produced by biaxially stretching a raw film.

  The film thickness of the raw film is preferably 1 μm or more and less than 500 μm, more preferably 10 μm or more and less than 350 μm. A film thickness of less than 1 μm is not preferred because of its poor strength, and breakage or the like tends to occur when stretching.

  The method for producing the raw film is not particularly limited, and examples thereof include known film forming methods such as a solution casting method (solution casting method), a melt extrusion method, a calendar method, and a compression molding method. It is also possible to use a uniaxially or biaxially stretched stretched film as the original fabric. Among these, the melt extrusion method is preferable.

  A thermoplastic acrylic polymer having a ring structure in the main chain and other thermoplastic resins and additives are mixed by a conventionally known mixing method to obtain a resin (composition) in advance, and then a raw film is produced. I can do it. As a method for producing this resin (composition), for example, a method of pre-blending with a mixer such as an omni mixer and then extruding and kneading the obtained mixture can be employed. In this case, the kneader used for extrusion kneading is not particularly limited. For example, a conventionally known kneader such as an extruder such as a single screw extruder or a twin screw extruder or a pressure kneader is used. Can do.

  Examples of the melt extrusion method include a T-die method and an inflation method. In this case, the forming temperature of the raw film is preferably 200 to 350 ° C., more preferably 250 to 300 ° C., still more preferably 255 ° C. to 300 ° C, particularly preferably 260 ° C to 300 ° C.

  In the case of extrusion molding by the T-die method, a T-die is attached to the tip of a known single-screw extruder or twin-screw extruder, and a film that has been extruded into a film can be obtained as a take-up roll. At this time, it is possible to adjust the temperature of the take-up roll as appropriate and to perform stretching in the extrusion direction, so that a uniaxial stretching process is possible. Moreover, it is also possible to add processes, such as sequential biaxial stretching and simultaneous biaxial stretching, by adding the process of extending | stretching a film in the direction perpendicular | vertical to an extrusion direction.

  The extruder used for the production of the raw film can be applied to either a single screw extruder or a multi-screw extruder. However, in order to obtain sufficient plasticization and kneading state, L / D (L is The cylinder length of the extruder, D represents the cylinder inner diameter) is preferably 10 or more and 100 or less, more preferably 20 or more and 50 or less, and most preferably 25 or more and 40 or less. If L / D is 10 or less, it is difficult to obtain a sufficient plasticization or kneaded state. If L / D is 100 or more, excessive shearing heat generation is applied to the resin, and the resin may be decomposed.

  The set temperature of the cylinder is preferably 200 ° C. or higher and 300 ° C. or lower, and more preferably 250 ° C. or higher and 300 ° C. or lower. At 200 ° C. or lower, the melt viscosity of the resin becomes high, so that an unnecessarily high power and L / D necessary for plasticization are required, which hinders productivity. If it exceeds 300 ° C, the resin may be decomposed.

  In the production method of the raw film, the shape of the extruder is not particularly specified. However, the extruder has one or more open vent parts, and it is more effective to suck the decomposition gas generated in a reduced pressure state. An increase in minutes can be suppressed. When making an open vent part into a pressure-reduced state, the range of 931-1.3 hPa (700-1 mmHg) is preferable, and the range of 798-13.3 hPa (600-10 mmHg) is more preferable. When the pressure is higher than 931 hPa, residual volatile components in the molten resin, monomer components generated by resin decomposition, and the like are likely to remain. Moreover, when lower than 1.3 hPa, there exists a problem that industrial implementation will become difficult.

  When used for optical applications such as an optical film, it is not particularly limited. However, in order to prevent the appearance after molding from being adversely affected, it is preferable to mold after removing foreign substances in the resin with a polymer filter. When filtered with a polymer filter, the resin deteriorates when the molten resin at high temperature passes through the polymer filter, and when it is continuously molded, the decomposed gas components and colored degradation products flow out, causing defects in the film and sheet. Openings, flow patterns, and flow lines may be observed. Therefore, in order to reduce the melt viscosity of the resin and shorten the residence time in the polymer filter as much as possible, the molding temperature is not particularly limited, but is preferably 255 ° C to 300 ° C, particularly preferably 260 ° C to 300 ° C. It is.

  The polymer filter is not particularly limited, but a polymer filter in which a large number of leaf disk filters are arranged in a housing is preferably used. The filter material in the leaf disk filter may be any of a type in which a metal fiber nonwoven fabric is sintered, a type in which metal powder is sintered, a type in which several metal meshes are laminated, or a hybrid type in which these are combined. The tied type is most preferred.

  Further, the filtration accuracy is not particularly limited, but the upper limit is 15 μm or less, more preferably 10 μm or less, most preferably 5 μm or less, and the lower limit is preferably 1 μm or more. If it is less than 1 μm, the filtration residence time becomes longer, which is not preferable from the viewpoint of thermal degradation and productivity of the resin. On the other hand, if the thickness exceeds 15 μm, foreign matter is likely to be mixed, which is not preferable.

  The filtration area with respect to the resin treatment amount per hour of the polymer filter is not particularly limited, and is appropriately set according to the treatment amount, and is, for example, 0.001 to 0.15 m2 / (kg / h).

  The shape of the center pole is not particularly limited, but it is an internal flow type with multiple resin flow ports and a resin flow path in the center pole. The center pole is in contact with the inner peripheral surface of the leaf disk filter at multiple vertices or faces. An external flow type having a resin flow path on the outer surface of the resin flow path, and the like, and an external flow type with few staying points in the resin flow path are more preferable.

  Although there is no restriction | limiting in particular in the residence time at the time of filtration with the said polymer filter, Preferably it is 20 minutes or less, More preferably, it is 10 minutes or less, Most preferably, it is 5 minutes or less. In addition, the filter inlet pressure and the filter outlet pressure during filtration are, for example, in the range of 3 to 15 MPa and 0.3 to 10 MPa, respectively, and the pressure loss (the pressure difference between the filter inlet pressure and the outlet pressure) is in the range of 1 MPa to 15 MPa. It is preferable to be within. When the pressure loss is 1 MPa or less, the flow path through which the polymer passes through the filter tends to be biased, and the quality tends to deteriorate. Conversely, if the pressure exceeds 15 MPa, the filter is easily damaged.

  The temperature of the thermoplastic acrylic polymer or resin (composition) having a ring structure in the main chain introduced into the filter is appropriately set according to the viscosity, but is in the range of 250 to 300 ° C., preferably 255 to 300. It is the range of ° C, and most preferably is the range of 260 to 300 ° C.

  The process of obtaining a final molded body with less foreign matter and color by filtration with a polymer filter is not particularly limited, but (1) Filtration is performed in a clean environment during polymer production, followed by molding in a clean environment. (2) A process in which a polymer having foreign matters and colored substances is once filtered in a clean environment, and subsequently molded in a clean environment. (3) A polymer having foreign substances and colored matters in a clean environment. A process of performing molding at the same time as the filtration process is raised, and the polymer filter process may be performed a plurality of times for each process. Moreover, it is more preferable to install a gear pump between the extruder and the filter to stabilize the resin pressure in the filter regardless of the single-screw extruder, twin-screw extruder, or multi-screw extruder.

  The biaxially stretched film of the present invention is biaxially stretched. In the case of stretching, it may be biaxially stretched simultaneously or sequentially biaxially stretched. In the case of biaxial stretching, the mechanical strength is improved and the film performance is improved. By mixing other biaxially stretched films, the film of the present invention can suppress an increase in retardation even when stretched, and can maintain optical isotropy.

  Although it does not specifically limit as extending | stretching temperature, It is preferable to carry out in the glass transition temperature vicinity of the biaxially stretched film of a raw film raw material, and specifically, (glass transition temperature-30) degreeC-(glass It is preferable to carry out at (transition temperature +100) degreeC, More preferably, it is (glass transition temperature-20) degreeC-(glass transition temperature +80) degreeC. When it is lower than (glass transition temperature-30) ° C., a sufficient draw ratio cannot be obtained, which is not preferable. When the temperature is higher than (glass transition temperature + 100) ° C., resin flow occurs and stable stretching cannot be performed.

  The court stretch magnification is preferably 1.5 times or more in both biaxial directions. More preferably, it is 1.8 or more in both biaxial directions. If the stretching in either axial direction is less than 1.5 times, a film having both film strength and bending resistance may not be obtained, which is not preferable. Although the upper limit of a draw ratio is not specifically limited, Preferably it is 10 times or less, More preferably, it is 5 times or less. If it is larger than 10 times, a special stretching apparatus may be required.

  The stretching speed (one direction) is preferably in the range of 10 to 20000% / min, more preferably in the range of 100 to 10000% / min. If it is slower than 10% / min, it takes time to obtain a sufficient draw ratio, and the production cost is increased, which is not preferable. If it is faster than 20000% / min, the stretched raw film may be broken, which is not preferable.

In order to stabilize the optical isotropy and mechanical properties of the biaxially stretched film, a heat treatment (annealing) or the like can be performed after the stretching treatment.

≪Biaxially stretched film≫
The biaxially stretched film of the present invention has an in-plane retardation value (Re) of 5 nm or less at a wavelength of 589 nm, and an absolute value of a thickness direction retardation value (Rth) of 5 nm or less. The “phase difference value” is also called a retardation value.

The in-plane retardation value (Re) here is
Re = (nx−ny) × d
The thickness direction retardation value (Rth) is
Rth = [(nx + ny) / 2−nz] × d
Defined. Nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the direction perpendicular to nx in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness (nm). . The slow axis direction is a direction in which the refractive index in the film plane is maximum.

  The glass transition temperature (Tg) of the biaxially stretched film of this invention is 110 degreeC or more. Preferably it is 115 degreeC or more, More preferably, it is 120 degreeC or more. Here, the glass transition temperature is a temperature at which a polymer molecule starts micro-Brownian motion, and there are various measurement methods. In the present invention, a differential scanning calorimeter (DSC) conforms to JIS-K7121. This is defined as the temperature obtained by the starting point method.

  The biaxially stretched film of the present invention has a folding endurance of 500 or more, preferably 550 or more, more preferably 600 or more in a MIT folding endurance test at a load of 200 g measured according to JIS P8115. It is. If the folding resistance test is less than 500 times, the flexibility of the film is not sufficient, and problems such as the film being cut when used as a manufacturing process or an optical member may occur. is there.

  The biaxially stretched film of the present invention contains 93% by weight or more of the thermoplastic acrylic polymer having a ring structure in the main chain, more preferably 95% by weight or more, still more preferably 97% by weight or more, and particularly preferably 99%. Contains more than wt%. When the content of the thermoplastic acrylic polymer having a ring structure in the main chain is less than 93% by weight, the optical properties and heat resistance may be deteriorated, which is not preferable.

  In the biaxially stretched film of the present invention, the content ratio of the structural unit derived from the styrene monomer, that is, the aromatic vinyl monomer, is preferably 5% by weight or less, more preferably 3% by weight or less, and still more preferably. Is 1% by weight or less, particularly preferably 0.1% by weight or less. When the content of the structural unit derived from the aromatic vinyl monomer exceeds 5% by weight, the structure derived from the aromatic vinyl monomer itself is brittle, and high film strength can be obtained even after stretching. difficult. The aromatic vinyl monomer is not particularly limited as long as the effect of the present invention is not impaired as long as it is an aromatic vinyl monomer, and examples thereof include styrene, vinyl toluene, and α-methylstyrene.

  The biaxially stretched film of the present invention is less colored after molding, and the b value in the film is preferably 1.0 or less. More preferably, it is 0.5 or less. By setting the b value in such a range, it can be suitably used for various applications, particularly for engineering applications of optical materials. The thermoplastic acrylic polymer having a ring structure in the main chain is often colored yellow in particular, but as an optical material, it is preferably more colorless, and if the film is colored, the value as an optical material Will be significantly reduced.

  The biaxially stretched film of the present invention preferably has a 5% weight loss temperature in thermogravimetric analysis (TG) of 280 ° C or higher, more preferably 290 ° C or higher, and further preferably 300 ° C or higher. The 5% weight loss temperature in thermogravimetric analysis (TG) is an indicator of thermal stability, and if it is less than 280 ° C., sufficient thermal stability may not be exhibited.

  In the biaxially stretched film of the present invention, the total amount of volatile components having a boiling point equal to or lower than the glass transition temperature is preferably 5000 ppm or less, more preferably 3000 ppm or less. If the total amount of residual volatile components is more than 5000 ppm, coloring, volatilization, or formation defects such as silver streaks may occur due to alteration during formation.

  The film thickness of the biaxially stretched film of the present invention is preferably less than 10 to 100 μm. More preferably, it is 30-50 micrometers.

  The biaxially stretched film of the present invention may contain components other than the thermoplastic acrylic polymer having a ring structure in the main chain. The content ratio of the other thermoplastic resin in the biaxially stretched film of the present invention is preferably less than 7% by weight, more preferably 5% by weight or less, further preferably 3% by weight or less, particularly preferably 1% by weight or less, Most preferably, it is 0.1 weight% or less. It is preferable that the content ratio of the other thermoplastic resin in the biaxially stretched film is smaller because the excellent optical properties inherent in the acrylic resin can be expressed.

  The biaxially stretched film of the present invention may contain a thermoplastic resin other than the thermoplastic acrylic resin having a ring structure in the main chain. These other thermoplastic resins are not particularly limited in type, for example, olefinic polymers such as polyethylene, polypropylene, ethylene-propylene polymer, poly (4-methyl-1-pentene); vinyl chloride, chlorinated vinyl Halogen-containing polymers such as resins; acrylic polymers such as polymethyl methacrylate; styrene resins such as polystyrene, styrene-methyl methacrylate polymer, styrene-acrylonitrile polymer, acrylonitrile-butadiene-styrene block polymer, that is, aromatic Resins containing structural units derived from aromatic vinyl monomers; Polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; Polyamides such as nylon 6, nylon 66, and nylon 610; Polyacetal: Polycar Polyphenylene oxide; Polyphenylene sulfide: Polyether ether ketone; Polysulfone; Polyether sulfone: Polyoxypentylene; Polyamideimide; Rubber polymer such as ABS resin and ASA resin blended with polybutadiene rubber and acrylic rubber; etc. Is mentioned.

  As the other thermoplastic resin, a resin that is thermodynamically compatible with a thermoplastic acrylic polymer having a ring structure in the main chain is preferable in terms of improving transparency and mechanical strength. Examples of thermodynamically compatible resins include a copolymer containing a vinyl cyanide monomer unit and an aromatic vinyl monomer unit, a polyvinyl chloride resin, and methacrylic acid esters of 50% by weight or more. It is good to use the polymer to contain. The thermoplastic acrylic polymer having a ring structure in the main chain and other thermoplastic resins are compatible with each other in terms of thermodynamic compatibility with the glass transition point of the biaxially stretched film obtained by mixing them. This can be confirmed by measuring. Specifically, only one point of the glass transition point measured by a differential scanning calorimeter is observed for a mixture of a thermoplastic thermoplastic acrylic polymer having a ring structure in the main chain and another thermoplastic resin. Therefore, it can be said that they are thermodynamically compatible.

  As the other thermoplastic resin, a resin containing a structural unit derived from a vinyl cyanide monomer and a structural unit derived from an aromatic vinyl monomer, particularly an acrylonitrile-styrene resin (AS resin) is preferable. In this case, compatibility with a wide range of copolymer composition is good, and the phase difference is obtained by combining the positive phase difference of the ring structure of the main chain of the acrylic resin and the negative phase difference of the acrylonitrile-aromatic vinyl polymer. There is an advantage that it becomes possible to control. The content ratio of the resin containing the structural unit derived from the vinyl cyanide monomer and the structural unit derived from the aromatic vinyl monomer in the biaxially stretched film of the present invention is preferably less than 7% by weight, more preferably Is 5% by weight or less, more preferably 3% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.1% by weight or less. When the content is 7% by weight or more, a polymer containing a vinyl cyanide monomer unit and an aromatic vinyl monomer unit easily undergoes thermal yellowing, so that a thermoplastic acrylic having a ring structure in the main chain There is a tendency that coloring is increased in a kneading process or a molding process at a high temperature required for production of a resin or a film containing a polymer. In addition, since the time of high temperature is increased due to the addition of a kneading process, polymer gel is likely to be generated, and furthermore, foreign substances contained in the kneading process and foreign substances contained in the AS resin are mixed in. The problem of increased film defects later may be significant.

  When an acrylonitrile-styrene polymer is used as another thermoplastic resin, an emulsion polymerization method, a suspension polymerization method, a solution polymerization method, a bulk polymerization method, or the like can be used as the production method. From the viewpoint of transparency and optical performance of the film, it is preferably obtained by a solution polymerization method or a bulk polymerization method.

  When other thermoplastic resins contain rubbery polymers, it can be expected to improve the bending resistance of films including raw film, but foreign substances contained in rubbery polymers are mixed in during the kneading process. In addition, since the dispersibility of the rubber-like polymer itself in the thermoplastic acrylic polymer having a ring structure in the main chain during the high-temperature molding process may be reduced and agglomerated, there are many film defects after molding. There is a problem of becoming. Furthermore, when used as a polarizer protective film, it is known that problems in optical characteristics such as a decrease in contrast of a liquid crystal display device described in JP-A-2007-171577 occur. Therefore, it is preferable that the biaxially stretched film does not contain a rubbery polymer, but when the rubbery mass is included, the content of the rubbery polymer in the biaxially stretched film is preferably less than 7%, more preferably 5% or less, more preferably 1% or less, particularly preferably 0.1% or less. As the rubbery polymer, an ABS resin or an ASA resin which is a resin containing a vinyl cyanide monomer unit and an aromatic vinyl monomer unit is preferable. Since ABS resin and ASA resin have a graft part having a composition compatible with a thermoplastic acrylic resin having a ring structure in the main chain, the rubber mass can be uniformly dispersed in the biaxially stretched film. It becomes possible. Further, the average particle diameter of the rubbery polymer is preferably 300 nm or less, and more preferably 150 nm or less, from the viewpoint of improving transparency when formed into a film.

  The biaxially stretched film of the present invention may contain other additives. Other additives include, for example, antioxidants, light stabilizers, weather stabilizers, heat stabilizers and the like: reinforcing materials such as glass fibers and carbon fibers; ultraviolet absorbers; near infrared absorbers; Flame retardants such as dibromopropyl) phosphate, triallyl phosphate, antimony oxide; antistatic agents such as anionic, cationic and nonionic surfactants; colorants such as inorganic pigments, organic pigments, dyes; organic fillers and inorganics Filler: resin modifier; plasticizer; lubricant; The content of other additives in the thermoplastic acrylic polymer molded article is preferably less than 7% by weight, more preferably 2% by weight or less, and further preferably 0.5% by weight or less. It is preferable that the content of other additives in the biaxially stretched film is smaller because the original excellent optical properties of the acrylic resin can be expressed.

  Examples of ultraviolet absorbers include benzophenone compounds, salicinate compounds, benzoate compounds, triazole compounds, and triazine compounds. Examples of the benzophenone compounds include 2,4-dihydroxybenzophenone, 4-n-octyloxy-2-hydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2-hydroxy-4-n-octyl. Examples thereof include oxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 1,4-bis (4-benzoyl-3-hydroxyphenone) -butane and the like. Examples of the silicate compound include pt-butylphenyl silicate. Examples of the benzoate compound include 2,4-di-t-butylphenyl-3 ', 5'-di-t-butyl-4'-hydroxybenzoate. Examples of triazole compounds include 2,2′-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol], 2- (3 , 5-Di-tert-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -p-cresol, 2- (2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol, 2-benzotriazol-2-yl-4,6-di-tert-butylphenol, 2- [5-chloro (2H) -benzotriazole- 2-yl] -4-methyl-6- (tert-butyl) phenol, 2- (2H-benzotriazol-2-yl) -4,6-di-tert-butyl Enol, 2- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol, 2- (2H-benzotriazol-2-yl) -4-methyl-6 -(3,4,5,6-tetrahydrophthalimidylmethyl) phenol, methyl 3- (3- (2H-benzotriazol-2-yl) -5-tert-butyl-4-hydroxyphenyl) propionate / polyethylene glycol 300 reaction products, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-Hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 3- (2H-ben Triazol-2-yl) -5- (1,1-dimethylethyl) -4-hydroxy -C7-9 side chain and straight chain alkyl esters. Further, triazine compounds include 2,4-diphenyl-6- (2-hydroxy-4-methoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-). Ethoxyphenyl) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-propoxyphenyl) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-) Butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2- Hydroxy-4-hexyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-octyloxyphenyl) -1,3,5-tria 2,4-diphenyl-6- (2-hydroxy-4-dodecyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-benzyloxyphenyl)- 1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-butoxyethoxy) -1,3,5-triazine, 2,4-bis “2-hydroxy-4-butoxyphenyl” -6- (2,4-dibutoxyphenyl) -1,3-5-triazine, 2,4-bis (2,4-dimethylphenyl) -6- [2-hydroxy-4- (3-alkyloxy- 2-hydroxypropyloxy) -5-α-cumylphenyl] -s-triazine skeleton (alkyloxy; long-chain alkyloxy groups such as octyloxy, nonyloxy, decyloxy, etc.) A line absorber is mentioned. Commercially available products include, for example, “Tinuvin 1577”, “Tinuvin 460”, “Tinuvin 477” (manufactured by Ciba Specialty Chemicals) as a triazine UV absorber, and “Adeka Stub LA-31” (Asahi Denka) as a triazole UV absorber. Manufactured by Kogyo Co., Ltd.).

  These can be used alone or in combination of two or more. The blending amount of the ultraviolet absorber is not particularly limited, but is preferably 0 to 5.0% by weight, more preferably 0.7 to 3.0% by weight, and further preferably 1.0 to 2.0% by weight in the film. %. On the other hand, if the blending amount of the ultraviolet absorber exceeds 5.0% by weight, foaming or bleed-out may occur during molding.

  The timing for adding the ultraviolet absorber is not particularly limited as long as the physical properties of the film are not impaired. For example, an ultraviolet absorber is added at a predetermined stage during the production of the thermoplastic acrylic polymer having a ring structure in the main chain, or after the polymer is produced, the polymer, the ultraviolet absorber, A method in which components are heated and melted at the same time and kneaded; a polymer and other components are heated and melted; an ultraviolet absorber is added thereto and kneaded; a polymer is heated and melted; And a method of kneading by adding an ultraviolet absorber and other components.

  The biaxially stretched film of the present invention may contain an antioxidant. Although antioxidant is not specifically limited, For example, well-known antioxidants, such as a hindered phenol type, a phosphorus type, or a sulfur type, can be used by 1 type or in combination of 2 or more types. The content of the antioxidant in the biaxially stretched film is preferably 0 to 5%, more preferably 0.01 to 2%, and still more preferably 0.05 to 1%. When the amount of the antioxidant added is excessively large, the antioxidant bleed out or silver streaks may occur during molding.

  Examples of phenolic antioxidants include n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, n-octadecyl-3- (3,5-di-t-butyl). -4-hydroxyphenyl) acetate, n-octadecyl-3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl-3,5-di-t-butyl-4-hydroxyphenylbenzoate, n-dodecyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate, neododecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, dodecyl-β- (3,5-di- t-butyl-4-hydroxyphenyl) propionate, ethyl-α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate Octadecyl-α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl-α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n-octylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (n-octylthio) ethyl-3,5-di-t-butyl-4-hydroxyphenyl acetate, 2 -(N-octadecylthio) ethyl-3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (2-hydroxyethylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol bis- (3,5 -Di-t-butyl-4-hydroxy-phenyl) propionate, 2- (n-octadecylthio) ethyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearamide-N, N -Bis- [ethylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino-N, N-bis- [ethylene-3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate], 2- (2-stearoyloxyethylthio) ethyl-3,5-di-t-butyl-4-hydroxybenzoate, 2- (2-stearoyloxyethylthio) ethyl- 7- (3-Methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,2-propylene glycol bis- [3- (3,5 Di-t-butyl-4-hydroxyphenyl) propionate], ethylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], neopentyl glycol bis- [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], ethylene glycol bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), glycerin-1-n-octadecanoate- 2,3-bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), pentaerythritol tetrakis- [3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) Propionate], 1,1,1-trimethylolethanetris- [3- (3,5-di-tert-butyl-4-hydroxypheny ) Propionate], sorbitol hexa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl-7- (3-methyl-5-tert-butyl-4-hydroxy Phenyl) propionate, 2-stearoyloxyethyl-7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol bis [(3 ', 5'-di-t -Butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis (3,5-di-t-butyl-4-hydroxyhydrocinnamate), 3,9-bis [1,1-dimethyl-2- [β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] ethyl] -2,4,8,10-tetraoxy Spiro [5,5] -undecane, 2,4-di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate ^ and 2-t- And butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate.

  The phenolic antioxidant is preferably used in combination with a thioether antioxidant or a phosphoric acid antioxidant. The amount of the antioxidant added in combination is 0.01% or more of the phenolic antioxidant and the thioether antioxidant relative to the acrylic resin (A), or the phenolic antioxidant and the phosphoric acid oxidation. Each inhibitor is 0.025% or more.

  Examples of the thioether-based antioxidant include pentaerythrityl tetrakis (3-lauryl thiopropionate), dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, and distearyl. -3,3'-thiodipropionate.

  Examples of the phosphoric acid antioxidant include tris (2,4-di-t-butylphenyl) phosphite, 2-[[2,4,8,10-tetrakis (1,1-dimethylethyl) dibenzo [ d, f] [1,3,2] dioxaphosphin-6-yl] oxy] -N, N-bis [2-[[2,4,8,10-tetrakis (1,1 dimethylethyl)] Dibenzo [d, f] [1,3,2] dioxaphosphin-6-yl] oxy] -ethyl] ethanamine, diphenyltridecyl phosphite, triphenyl phosphite, 2,2-methylenebis (4,6 -Di-t-butylphenyl) octyl phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, distearyl pentaerythritol diphosphite Ito, cyclic neopentanetetraylbis (2,6-di -t- butyl-4-methylphenyl) phosphite and the like.

  The biaxially stretched film of the present invention includes an antistatic layer, an adhesive layer, an adhesive layer, an easy-adhesion layer, an antiglare layer (non-glare) layer, a photocatalytic layer and other antifouling layers, and an antireflection layer, depending on the purpose. Various functional coating layers such as hard coat layer, ultraviolet ray shielding layer, heat ray shielding layer, electromagnetic wave shielding layer, light diffusion layer, gas barrier layer, etc. can be laminated and each individual functionality on the raw film The laminated body which laminated | stacked the member with which the coating layer was coated through the adhesive or the adhesive agent may be sufficient. In addition, the stacking order of each layer is not particularly limited, and the stacking method is not particularly limited.

  The biaxially stretched film of the present invention is not particularly limited, but is preferably used for optical applications. Preferably, a polarizer protective film, a retardation film, a viewing angle compensation film, a light diffusion film, a reflection film, an antireflection film, an antiglare film, a brightness enhancement film, a conductive film for a touch panel, used for a polarizing plate for a liquid crystal display device, Examples include protective films for various optical disks (VD, CD, DVD, MD, LD, etc.) substrates, diffusion plates, light guides, retardation plates, prism sheets, and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below. In the following description, for convenience, “part by mass” may be simply referred to as “part”, and “liter” may be simply referred to as “L”.

<Glass transition temperature>
The glass transition temperature (Tg) of each sample was determined in accordance with JIS K7121 regulations. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, DSC-8230), a sample of about 10 mg was heated from a normal temperature to 200 ° C. at a heating rate of 20 ° C./min in a nitrogen gas atmosphere. It calculated by the starting point method from the DSC curve. Α-alumina was used as a reference.

<Average molecular weight and molecular weight distribution>
The weight average molecular weight (Mw) and the weight average molecular weight (Mn) of the polymer were determined by gel permeation chromatography (GPC) under the following conditions. The molecular weight distribution is weight average molecular weight / number average molecular weight, and was calculated from the weight average molecular weight and the number average molecular weight.

System: GPC system HLC-8220 manufactured by Tosoh Corporation
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade), Flow rate: 0.6 ml / min Standard sample: TSK standard polystyrene (Tosoh Corporation, PS-oligomer kit)
Measurement side column configuration: Guard column and two separation columns connected in series Guard column (manufactured by Tosoh Corporation, TSKguardcolumn SuperHZ-L) Separation column (manufactured by Tosoh Corporation, TSKgel SuperHZM-M)
Reference side column configuration:
Reference column (manufactured by Tosoh Corporation, TSKgel SuperH-RC)
<Dynamic TG>
The dynamic TG is measured using a differential type differential thermobalance (Rigaku, Thermo Plus2 TG-8120), and a sample of about 10 mg is heated from room temperature to 500 ° C. at a rate of temperature increase of 10 ° C./min under a nitrogen gas atmosphere. The temperature was increased, and the measurement was performed by controlling the temperature stepwise between 150 ° C. and 500 ° C. with a weight reduction rate value of 0.005 mass% / second or less.

<Ratio of ring structure content>
First, based on the weight loss that occurs when all the hydroxyl groups are dealcoholated as methanol from the polymer composition obtained by polymerization, before the decomposition of the polymer starts from 150 ° C. before the weight reduction starts in dynamic TG measurement. From the weight loss due to the dealcoholization reaction up to 300 ° C, the dealcoholization reaction rate was determined.

That is, in the dynamic TG measurement of the polymer having a lactone ring structure, the weight reduction rate between 150 ° C. and 300 ° C. is measured, and the obtained actual weight reduction rate is defined as (X). On the other hand, from the composition of the polymer, all the hydroxyl groups contained in the polymer composition are involved in the formation of the lactone ring, so that it becomes an alcohol and is dealcoholized. (Y) is the weight loss rate calculated on the assumption that the% dealcoholization reaction has occurred. The theoretical weight reduction rate (Y) is more specifically the molar ratio of raw material monomers having a structure (hydroxyl group) involved in the dealcoholization reaction in the polymer, that is, the raw material unit in the polymer composition. It can be calculated from the content of the monomer. These values (X, Y) are calculated from the dealcoholization formula:
1- (actual weight reduction rate (X) / theoretical weight reduction rate (Y))
Substituting into, the value is obtained and expressed in% to obtain the dealcoholization reaction rate.

  As an example, the proportion of the lactone ring structure in the pellets obtained in Production Example 1 described later is calculated. When the theoretical weight loss rate (Y) of this polymer was determined, the molecular weight of methanol was 32, the molecular weight of methyl 2- (hydroxymethyl) acrylate was 116, and methyl 2- (hydroxymethyl) acrylate. Since the content (weight ratio) in the polymer is 5% by weight in terms of composition, (32/116) × 5≈1.37% by weight. On the other hand, the actual weight loss rate (X) by dynamic TG measurement was 0.02% by weight. When these values are applied to the above-described dealcoholization calculation formula, 1− (0.02 / 1.37) ≈0.985 is obtained, so that the dealcoholization reaction rate is 98.5%.

  And the content rate (weight ratio) in the said copolymerization composition of the raw material monomer which has the structure (hydroxy group) which participates in lactone cyclization as what the predetermined | prescribed lactone cyclization was performed by this dealcoholization reaction rate ) Is multiplied by the dealcoholization reaction rate and converted to the content (weight ratio) of the structure of the lactone ring unit, the content of the lactone ring structure in the copolymer can be calculated. In the case of Production Example 1, 2- (hydroxymethyl) methyl acrylate has a content of 5.0% by weight in the copolymer, a calculated dealcoholization reaction rate of 98.5% by weight, and a molecular weight of 116- ( Since the formula amount of the lactone cyclized structural unit produced when methyl hydroxymethyl) is condensed with methyl methacrylate is 170, the content of the lactone ring in the copolymer is 7.2 (5. 0 × 0.985 × 170/116) wt%.

<Thickness of film>
It measured using the Digimatic micrometer (made by Mitutoyo).

<Refractive index anisotropy>
Regarding the refractive index anisotropy of the film, an in-plane retardation value (Re) and a thickness direction retardation value (Rth) were measured using a KOBRA-WR manufactured by Oji Scientific Instruments at a measurement wavelength of 589 nm. The thickness direction retardation value (Rth) was measured by tilting by 40 ° with the slow axis as the tilt axis.

<Folding strength>
The strength of the film was evaluated by the number of folding times. The number of folding times of the film was 15 mm in width and 90 mm in length using a MIT folding resistance tester (manufactured by Tester Sangyo Co., Ltd., model BE-201) and allowed to stand at 23 ° C. and 50% RH for 1 hour or longer The test film was measured under the condition of a load of 200 g in accordance with JIS P8115.

<Color difference>
The color difference (b value) was measured using a colorimetric color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., ZE 6000). The b value is a hue display based on JIS Z8729 and indicates the value of b *, and was obtained as an average value of 10 points measured by superimposing a film on a standard white plate.

<Impact strength>
The film impact strength was measured according to ASTM D3420 using a film impact tester (manufactured by Tester Sangyo) under the conditions of 23 ° C. and 50% RH.

<Elastic modulus>
The tensile strength of the film was measured based on JIS K7161, and the elastic modulus was determined from the inclination. After stretching, the film sample was allowed to stand for 24 hours or more under a constant temperature and humidity condition of 23 ° C. and 65%, and then measured at a pulling rate of 100 mm / min. However, since the method described in JIS K 7161 does not adapt to the elastic modulus of the film and rubber, in this application, the tensile strength is calculated from the slope of the value of 2 points indicating 10 MPa and 20 MPa. The value obtained is defined as the film elastic modulus.

<Quantification of styrene content>
The content ratio of the structural unit derived from the aromatic vinyl monomer in the biaxially stretched film was calculated from the FT-IR measurement as follows. That is, polystyrene (TSO standard polystyrene F-10, manufactured by Tosoh Corporation) was diluted with 5-butane in the range of 0.1% to 1% using 5-butanone as a standard sample, and between two KBr plates. The peak height in the 703-705 cm ⁻¹ region was determined by FT-IR (manufactured by Thermo Scientific; NEXUS 670) and used as a calibration curve. A biaxially stretched film was dissolved in chloroform and then poured into hexane to insolubilize it, followed by drying under reduced pressure to prepare a sample. This was dissolved at a predetermined concentration using 1-butanone, and the value obtained from the peak height in the 703-705 cm ⁻¹ region was calculated as the amount of styrene. The measurement conditions and the like can be appropriately changed within a range that does not affect the measurement in consideration of the characteristics of the analysis target resin.

(Production Example 1) Production of Resin Pellet (A-1) In a 1000 L reaction kettle equipped with a stirrer, thermometer, cooler and nitrogen introduction tube, 47.5 parts of methyl methacrylate (MMA), 2- (hydroxymethyl) ) 2.5 parts of methyl acrylate (MHMA), 50 parts of toluene, 0.025 part of tris (2,4-di-tert-butylphenyl) phosphite (trade name: ADK STAB 2112) manufactured by ADEKA The temperature was raised to 105 ° C. while refluxing nitrogen, and when refluxed, 0.06 part of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi Co., Ltd., trade name: Luperox 570) was added at the same time as 0.0. While 12 parts of t-amyl peroxyisononanoate was added dropwise over 2 hours, solution polymerization was performed under reflux (about 105 to 110 ° C.), and Aging was carried out over 4 hours.

  0.05 parts of stearyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-18) was added to the above polymer solution, and the lactone cyclization reaction was allowed to proceed for 2 hours under reflux (about 90 to 110 ° C.).

  Next, the polymer solution obtained by the above lactone cyclization reaction was passed through a multitubular heat exchanger heated to 240 ° C., and then the lactone cyclization reaction was completed. .3 to 400 hPa, 1 rear vent, 4 fore vents (referred to as the first, second, third, and fourth vents from the upstream side) Vent having a side feeder between the third vent and the fourth vent It was introduced into a type screw twin screw extruder (φ = 44 mm, L / D = 52.5) at a treatment rate of 20 kg / hour in terms of resin amount, devolatilized, and pelletized. At that time, an antioxidant / deactivator mixed solution prepared separately after the first vent was injected through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump at a charging rate of 0.3 kg / hour. Further, after the second and third ion-exchanged water was injected at a charging rate of 0.33 kg / hour through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump. The antioxidant / deactivator mixed solution was 5 parts Irganox 1010 (manufactured by Ciba Specialty Chemicals), 5 parts Adeka Stub AO-412S (manufactured by Adeka), zinc octylate (manufactured by Nippon Kagaku Sangyo, Nikka Octix Zinc 10) %) 166 parts were diluted with 24 parts of toluene.

  The weight average molecular weight of the resin pellet (A-1) containing the thermoplastic acrylic polymer having a ring structure in the main chain was 140,000, and the glass transition temperature was 115 ° C. Table 1 shows the physical properties of the resin pellet (A-1).

(Production Example 2) Production of Resin Pellet (A-2) As a polymerization initiator, t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., trade name: Luperox 570) was added at the same time as 0.10. A pellet (A-2) was obtained by performing the same operation as in Production Example 1 except that part of t-amylperoxyisononanoate was added dropwise over 2 hours. The physical properties of the obtained resin pellet (A-2) are shown in Table 1.

  The obtained resin pellet (A-2) containing a thermoplastic acrylic polymer having a ring structure in the main chain had a weight average molecular weight of 160,000 and a glass transition temperature of 116 ° C. Table 1 shows the physical properties of the resin pellet (A-2).

Production Example 3 Production of Resin Pellet (A-3) In a 1000 L reactor equipped with a stirrer, a thermometer, a cooler, and a nitrogen introduction tube, 45 parts of MMA, 5 parts of MHMA, 50 parts of toluene, Tris (2,4- Di-tertiary-butylphenyl) phosphite (trade name: ADEKA STAB 2112 manufactured by ADEKA) was charged with 0.025 part, and the temperature was raised to 105 ° C. while refluxing nitrogen. While adding 0.057 parts of peroxyisonononanoate (Arkema Yoshitomi, trade name: Luperox 570), 0.11 part of t-amylperoxyisonononanoate was added dropwise over 2 hours while refluxing. Solution polymerization was performed at (about 105 to 110 ° C.), and further aging was performed for 4 hours.

  0.05 parts of stearyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-18) was added to the above polymer solution, and the lactone cyclization reaction was allowed to proceed for 2 hours under reflux (about 90 to 110 ° C.).

  Next, the polymer solution obtained by the above lactone cyclization reaction was passed through a multitubular heat exchanger heated to 240 ° C., and then the lactone cyclization reaction was completed. .3 to 400 hPa, 1 rear vent, 4 fore vents (referred to as the first, second, third, and fourth vents from the upstream side) Vent having a side feeder between the third vent and the fourth vent It was introduced into a type screw twin screw extruder (φ = 44 mm, L / D = 52.5) at a treatment rate of 20 kg / hour in terms of resin amount, devolatilized, and pelletized. At that time, an antioxidant / deactivator mixed solution prepared separately after the first vent was injected through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump at a charging rate of 0.3 kg / hour. Further, after the second and third ion-exchanged water was injected at a charging rate of 0.33 kg / hour through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump. The antioxidant / deactivator mixed solution was 5 parts Irganox 1010 (manufactured by Ciba Specialty Chemicals), 5 parts Adeka Stub AO-412S (manufactured by Adeka), zinc octylate (manufactured by Nippon Kagaku Sangyo, Nikka Octix Zinc 10) %) 166 parts were diluted with 24 parts of toluene.

  The obtained resin pellet (A-3) containing a thermoplastic acrylic polymer having a ring structure in the main chain had a weight average molecular weight of 165,000 and a glass transition temperature of 122 ° C. Table 1 shows the physical properties of the resin pellet (A-3).

Production Example 4 Production of Resin Pellet (A-4) In a 1000 L reactor equipped with a stirrer, a thermometer, a cooler, and a nitrogen introduction tube, 45 parts of MMA, 5 parts of MHMA, 50 parts of toluene, Tris (2,4- Di-tertiary-butylphenyl) phosphite (trade name: ADEKA STAB 2112 manufactured by ADEKA) was charged with 0.025 part, and the temperature was raised to 105 ° C. while refluxing nitrogen. While adding 0.057 parts of peroxyisonononanoate (Arkema Yoshitomi, trade name: Luperox 570), 0.11 part of t-amylperoxyisonononanoate was added dropwise over 2 hours while refluxing. Solution polymerization was performed at (about 105 to 110 ° C.), and further aging was performed for 4 hours.

  0.05 parts of stearyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-18) was added to the above polymer solution, and the lactone cyclization reaction was allowed to proceed for 2 hours under reflux (about 90 to 110 ° C.).

  Next, the polymer solution obtained by the above lactone cyclization reaction was passed through a multitubular heat exchanger heated to 240 ° C., and then the lactone cyclization reaction was completed, followed by a barrel temperature of 240 ° C., a rotation speed of 120 rpm, and a degree of vacuum of 13 .3 to 400 hPa, 1 rear vent, 4 fore vents (referred to as the first, second, third, and fourth vents from the upstream side) Vent having a side feeder between the third vent and the fourth vent It was introduced into a type screw twin screw extruder (φ = 44 mm, L / D = 52.5) at a treatment rate of 20 kg / hour in terms of resin amount, devolatilized, and pelletized. At that time, an antioxidant / deactivator mixed solution prepared separately after the first vent was injected through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump at a charging rate of 0.3 kg / hour. Further, after the second vent, a separately prepared ultraviolet absorbent solution was injected with a high-pressure pump through a filter having a filtration accuracy of 0.1 μm at a charging rate of 0.4 kg / hour. Further, after the third time, ion exchange water was injected through a filter having a filtration accuracy of 0.1 μm with a high pressure pump at a charging rate of 0.33 kg / hour. The antioxidant / deactivator mixed solution was 5 parts Irganox 1010 (manufactured by Ciba Specialty Chemicals), 5 parts Adeka Stub AO-412S (manufactured by Adeka), zinc octylate (manufactured by Nippon Kagaku Sangyo, Nikka Octix Zinc 10) %) 166 parts were diluted with 24 parts of toluene. The ultraviolet absorbent solution was prepared by diluting 10 parts of Tinuvin 477 (80% active ingredient manufactured by Ciba Specialty Chemicals) with 0.5 part of toluene.

  The obtained resin pellets (A-4) containing a thermoplastic acrylic polymer having a ring structure in the main chain had a weight average molecular weight of 162,000 and a glass transition temperature of 119 ° C. Table 1 shows the physical properties of the resin pellet (A-4).

(Production Example 5) Production of Resin Pellet (A-5) In a 1000 L reaction kettle equipped with a stirrer, thermometer, cooler and nitrogen introduction tube, 40 parts of MMA, 10 parts of MHMA, 50 parts of toluene, Tris (2,4- Di-tertiary-butylphenyl) phosphite (trade name: ADK STAB 2112 manufactured by ADEKA) was charged with 0.25 part, and the temperature was raised to 105 ° C. while refluxing nitrogen. When refluxed, t-amyl was used as an initiator. While adding 0.05 parts of peroxyisononanoate (Arkema Yoshitomi, trade name: Luperox 570), 0.1 part of t-amyl peroxyisononanoate was added dropwise over 2 hours while refluxing. Solution polymerization was performed at (about 105 to 110 ° C.), and further aging was performed for 4 hours.

    0.05 parts of stearyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-18) was added to the above polymer solution, and the lactone cyclization reaction was allowed to proceed for 2 hours under reflux (about 90 to 110 ° C.).

  Next, the polymer solution obtained by the above lactone cyclization reaction was passed through a multitubular heat exchanger heated to 240 ° C., and then the lactone cyclization reaction was completed. .3 to 400 hPa, 1 rear vent, 4 fore vents (referred to as the first, second, third, and fourth vents from the upstream side) Vent having a side feeder between the third vent and the fourth vent It was introduced into a type screw twin screw extruder (φ = 44 mm, L / D = 52.5) at a processing rate of 20 kg / hour in terms of resin amount, devolatilized, and pelletized. At that time, an antioxidant / deactivator mixed solution prepared separately after the first vent was injected through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump at a charging rate of 0.3 kg / hour. Further, after the second and third ion-exchanged water was injected at a charging rate of 0.33 kg / hour through a filter having a filtration accuracy of 0.1 μm with a high-pressure pump. The antioxidant / deactivator mixed solution was 5 parts Irganox 1010 (manufactured by Ciba Specialty Chemicals), 5 parts Adeka Stub AO-412S (manufactured by Adeka), zinc octylate (manufactured by Nippon Kagaku Sangyo, Nikka Octix Zinc 10) %) 166 parts were diluted with 24 parts of toluene.

  The obtained resin pellet (A-5) containing a thermoplastic acrylic polymer having a ring structure in the main chain had a weight average molecular weight of 125,000 and a glass transition temperature of 128 ° C. Table 1 shows the physical properties of the resin pellet (A-5).

Example 1
The resin pellet (A-1) obtained in Production Example 1 was melt-extruded from a coat hanger type T die (width 150 mm) at 265 ° C. using a single screw extruder (φ = 25 mm, L / D = 25). And was discharged onto a cooling roll having a temperature of 100 ° C. to produce an unstretched film having a thickness of 130 μm.

  The obtained unstretched film was cut out to 97 mm × 97 mm, and then sequentially 130 ° C. (temperature higher by 15 ° C. than the glass transition temperature), 800 mm using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X-6S). Biaxial stretching was successively performed at a speed of 1 min / min so as to be 1.8 times in the order of the machine direction and the transverse direction (MD / TD direction). After stretching, the film was quickly taken out from the test apparatus and cooled to obtain a biaxially stretched film (F-1) containing a thermoplastic acrylic polymer having a ring structure in the main chain having a thickness of 40 μm. The glass transition temperature of the stretched film (F-1) is 115 ° C., the weight average molecular weight of the thermoplastic acrylic polymer contained in the stretched film is 140,000, and the polymer content (having a ring structure in the main chain) The content ratio of the thermoplastic acrylic polymer) was 99.5% by weight, and the amount of styrene (the content ratio of the structure derived from the aromatic vinyl monomer) was 0% by weight. Table 2 shows the physical properties of the stretched film (F-1).

(Example 2)
Using the resin pellet (A-2) obtained in Production Example 2, a stretched film is prepared in the same manner as in Example 1 and includes a thermoplastic acrylic polymer having a ring structure in the main chain having a thickness of 40 μm. An axially stretched film (F-2) was obtained. The glass transition temperature of the stretched film (F-2) is 116 ° C., the weight average molecular weight of the thermoplastic acrylic polymer contained in the stretched film is 160,000, the polymer content is 99.5% by weight, and styrene. The amount was 0% by weight. Table 2 shows the physical properties of the stretched film (F-2).

Example 3
Using a mixture of 95 parts by weight of the resin pellet (A-3) obtained in Production Example 3 and 5 parts by weight of a styrene-acrylonitrile copolymer (the ratio of styrene / acrylonitrile is 73% by weight / 27% by weight), Example A stretched film was prepared in the same manner as in Example 1 to obtain a biaxially stretched film (F-3) containing a thermoplastic acrylic polymer having a ring structure in the main chain having a thickness of 40 μm. The stretched film (F-3) has a glass transition temperature of 120 ° C., the weight average molecular weight of the thermoplastic acrylic polymer contained in the stretched film is 165,000, the polymer content is 94.4% by weight, and styrene. The amount was 3.6% by weight. Table 2 shows the physical properties of the stretched film (F-3).

Example 4
Example 95 Using a mixture of 95 parts by weight of the resin pellet (A-4) obtained in Production Example 4 and 5 parts by weight of styrene-acrylonitrile resin pellets (manufactured by Asahi Kasei Chemicals Corporation, trade name: Stylac AS783L) A biaxially stretched film (F-4) containing a thermoplastic acrylic polymer having a ring structure in the main chain having a thickness of 40 μm was obtained. The glass transition temperature of the stretched film (F-4) is 117 ° C., the weight average molecular weight of the thermoplastic acrylic polymer contained in the stretched film is 162,000, the polymer content is 94.1% by weight, and styrene. The amount was 3.5% by weight. Table 2 shows the physical properties of the stretched film (F-4).
(Comparative Example 1)
Using a mixture of 90 parts by weight of the resin pellet (A-5) obtained in Production Example 5 and 10 parts by weight of styrene-acrylonitrile resin pellets (manufactured by Asahi Kasei Chemicals Corporation, trade name: Stylac AS783L), the same as in Example 1 A stretched film was prepared, and a biaxially stretched film (F-5) having a thickness of 40 μm was obtained. The molecular weight of the stretched film (F-5) was 127,000, the polymer content was 89.6 wt%, and the styrene content was 7.2 wt%. Table 2 shows the physical properties of the stretched film (F-5).

(Comparative Example 2)
Using the resin pellet (A-3) obtained in Production Example 3, a stretched film was prepared in the same manner as in Example 1 to obtain a biaxially stretched film (F-6) having a thickness of 40 μm. The stretched film (F-6) had a molecular weight of 165,000, a glass transition temperature of 126 ° C., a polymer content of 99.5% by weight, and a styrene content of 0% by weight. Table 2 shows the physical properties of the stretched film (F-6).

<Creation of anti-glare film>
Acrylic resin beads (made by Nippon Shokubai, particle size 3.5 μm) 4.1 parts, dipentaerythritol hexaacrylate (Kayarad, Nippon Kayaku) 20.3 parts, toluene 24 parts, cyclohexanone 23 parts, Irganocure 184 (Ciba Specialty) (Chemicals) 0.6 parts was mixed, sufficiently stirred using a disper, and further filtered through a 300 mesh mold to obtain a coating solution. This coating solution is applied to (F-1) to (F-6) using an applicator, dried in an oven at 120 ° C. for 1 minute, and then irradiated so that the ultraviolet ray irradiation amount is 250 mJ / cm 2. The coating film was cured to obtain a laminated film having an antiglare layer of 5 to 6 μm. When the obtained laminated film was bent at an angle of 180 °, the laminated film was cracked only when it was laminated on the stretched film (F-5).

  According to the present invention, while maintaining the heat resistance due to the ring structure of the main chain, the film has high strength, has excellent properties for optical film applications such as low coloring, and has a particularly high bending resistance. A biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure can be provided. Moreover, the biaxially stretched film of this invention can be used suitably for the optical member used for various image display apparatuses (a liquid crystal display device, an organic EL display device, PDP, etc.).

Claims (9)

A biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure in the main chain, under the following conditions:
(A) In-plane retardation value (Re) is 5 nm or less;
(B) The absolute value of the thickness direction retardation value (Rth) is 5 nm or less;
(C) Glass transition temperature (Tg) is 110 ° C. or higher;
(D) The content ratio of the thermoplastic acrylic polymer having a ring structure in the main chain is 93% by weight or more;
(E) A biaxially stretched film satisfying that the number of folding times in the MIT folding test is 500 times or more.   The biaxially stretched film according to claim 1, wherein the content ratio of the structural unit derived from the aromatic vinyl monomer in the biaxially stretched film is 5% by weight or less.   The biaxially stretched film according to claim 1 or 2, comprising 97% by weight or more of a thermoplastic acrylic polymer having a ring structure in the main chain.   Furthermore, the biaxially stretched film of Claim 1 or 2 containing another thermoplastic resin. A biaxially stretched film containing a thermoplastic acrylic polymer having a ring structure in the main chain, under the following conditions:
(A) In-plane retardation value (Re) is 5 nm or less;
(B) The absolute value of the thickness direction retardation value (Rth) is 5 nm or less;
(C) Glass transition temperature (Tg) is 110 ° C. or higher;
(D) The content ratio of the thermoplastic acrylic polymer having a ring structure in the main chain is 93% by weight or more;
(E) The folding endurance of the MIT folding endurance test is 500 times or more;
(F) including other thermoplastic resin having a structural unit derived from an aromatic vinyl monomer, and the content ratio of the structural unit derived from the aromatic vinyl monomer in the biaxially stretched film is 5% by weight or less; Satisfied biaxially stretched film.   6. The biaxial stretching according to claim 4 or 5, wherein the other thermoplastic resin is a resin containing a structural unit derived from a vinyl cyanide monomer unit and a structural unit derived from an aromatic vinyl monomer unit. the film. The biaxially stretched film according to any one of claims 1 to 6, wherein the stretch ratio is 1.5 times or more in both biaxial directions.   The biaxially stretched film according to any one of claims 1 to 7, wherein a content ratio of a ring structure of the thermoplastic acrylic polymer having a ring structure in the main chain is 15% by weight or less.   The biaxially stretched film according to any one of claims 1 to 8, wherein a ring structure of the thermoplastic acrylic polymer having a ring structure in the main chain is a lactone ring structure.