JP4449606B2 - Method for producing stretched film - Google Patents

Description

  The present invention relates to a method for producing a stretched film, and more particularly to a method for efficiently producing a stretched film that exhibits negative birefringence and is suitable for an optical compensation film.

  In recent years, thin liquid crystal display elements, electroluminescence elements, and the like that replace CRT-type television monitors have been developed, and film materials with controlled optical anisotropy are required. Transparent resin materials are frequently used as optical compensation films in terms of lightness, productivity, and cost.

  Conventionally, stretch orientation of a film has been performed as a method of developing optical anisotropy of a transparent resin material. According to this stretched orientation, a film made of polymethyl methacrylate (hereinafter referred to as PMMA) or polystyrene (hereinafter referred to as PS) exhibits negative birefringence, and polycarbonate (hereinafter referred to as PC) or the like. A film made of an amorphous cyclic polyolefin (hereinafter referred to as APO) is known to exhibit positive birefringence (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

  Here, positive birefringence refers to a refractive index anisotropy that increases the refractive index in the same direction when the polymer molecular chain, which is a component constituting the film, is oriented by stretching. Refers to expression. On the other hand, negative birefringence means that when a polymer molecular chain, which is a component constituting a film, is stretched to cause molecular orientation, the refractive index in the same direction becomes small, and at the same time, the refractive index in a direction orthogonal It expresses that the refractive index anisotropy is such that becomes large.

  For example, PMMA and PS have a glass transition temperature (hereinafter referred to as Tg) in the vicinity of 100 ° C., and are limited in application due to insufficient heat resistance and brittleness.

  In addition, as a maleimide copolymer, a copolymer composed of phenylmaleimide residues and olefin residues is a thermodynamic material within a specific ratio range in a blend of a copolymer composed of styrene residues and acrylonitrile residues. Are known to show miscibility (see, for example, Patent Document 1).

  However, Patent Document 1 does not have information on a method for producing a stretched film made of the blend and optical properties of the stretched film.

Yasuhiro Koike, “One Point 10 of Polymers, Optical Properties of Polymers”, Kyoritsu Shuppan, May 10, 2000

Koji Minami, “Functional Materials August 2000 Vol.20, No.8” CM Publishing, August 5, 2000, p23-33 US Pat. No. 4,605,700

  Accordingly, the present invention has been made in view of the above-mentioned facts, and its object is to provide a method for efficiently producing a stretched film free from defects such as cracks, particularly an optical compensation film exhibiting negative birefringence. There is to do.

  As a result of intensive studies on the above problems, the present inventors have found that a film comprising a specific copolymer and a specific acrylonitrile-styrene copolymer is pretreated and stretched under specific conditions before stretching. The inventors have found that a stretched film having no defects such as these can be produced, and have completed the present invention.

That is, the present invention comprises an olefin residue unit represented by the following formula (i) and an N-phenyl-substituted maleimide residue unit represented by the following formula (ii), and has a weight average molecular weight of 5 in terms of standard polystyrene. 30 to 95% by weight of the copolymer (a) which is 10 ³ or more and 5 or 10 ⁶ or less, and acrylonitrile residue unit: styrene residue unit = 20: 80 to 35:65 (weight ratio), standard One or more acrylonitrile-styrene copolymers (b) selected from acrylonitrile-styrene copolymers and acrylonitrile-butadiene-styrene copolymers having a weight average molecular weight in terms of polystyrene of 5 × 10 ³ or more and 5 × 10 ⁶ or less. When producing a stretched film made of a resin composition comprising 70 to 5% by weight, each of the film before stretching and the film fixing jig for stretching After stretching and preheating, the film is mounted on the fixing jig and stretched in the range of glass transition temperature-20 ° C to glass transition temperature + 20 ° C of the resin composition. The present invention relates to a film manufacturing method.

（ここで、Ｒ１、Ｒ２、Ｒ３はそれぞれ独立して水素又は炭素数１〜６のアルキル基である。）

(Here, R1, R2, and R3 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms.)

（ここで、Ｒ４、Ｒ５はそれぞれ独立して水素又は炭素数１〜８の直鎖状若しくは分岐状アルキル基であり、Ｒ６、Ｒ７、Ｒ８、Ｒ９、Ｒ１０はそれぞれ独立して水素、ハロゲン系元素、カルボン酸、カルボン酸エステル、水酸基、シアノ基、ニトロ基又は炭素数１〜８の直鎖状若しくは分岐状アルキル基である。）
本発明において用いられる共重合体（ａ）は、標準ポリスチレン換算の重量平均分子量５×１０^３以上５×１０^６以下であり、上記の式（ｉ）で示されるオレフィン残基単位と上記の式（ｉｉ）で表されるＮ−フェニル置換マレイミド残基単位からなる共重合体である。ここで、重量平均分子量は、ゲル・パーミエーション・クロマトグラフィー（以下、ＧＰＣと称する。）による共重合体の溶出曲線を標準ポリスチレン換算値として測定することができる。そして、共重合体（ａ）のポリスチレン換算の重量平均分子量が５×１０^３未満である場合、得られる樹脂組成物を延伸フィルムとして成形加工する際の成形加工が困難となると共に、得られる延伸フィルムは脆いものとなる。一方、重量平均分子量５×１０^６を越える場合、得られる樹脂組成物を延伸フィルムとして成形加工する際の成形加工が困難となる。

(Where R4 and R5 are each independently hydrogen or a linear or branched alkyl group having 1 to 8 carbon atoms, and R6, R7, R8, R9 and R10 are each independently hydrogen or a halogen-based element. A carboxylic acid, a carboxylic acid ester, a hydroxyl group, a cyano group, a nitro group, or a linear or branched alkyl group having 1 to 8 carbon atoms.)
The copolymer (a) used in the present invention has a weight average molecular weight of 5 × 10 ³ or more and 5 × 10 ⁶ or less in terms of standard polystyrene, the olefin residue unit represented by the above formula (i) and the above formula. It is a copolymer consisting of an N-phenyl-substituted maleimide residue unit represented by (ii). Here, the weight average molecular weight can be measured using a gel permeation chromatography (hereinafter referred to as GPC) elution curve of the copolymer as a standard polystyrene equivalent value. And when the polystyrene equivalent weight average molecular weight of the copolymer (a) is less than 5 × 10 ³ , it becomes difficult to mold the resin composition obtained as a stretched film, and the obtained stretch The film becomes brittle. On the other hand, when the weight average molecular weight exceeds 5 × 10 ⁶ , it becomes difficult to mold the resin composition obtained as a stretched film.

  R1, R2, and R3 in the olefin residue unit represented by the formula (i) constituting the copolymer (a) are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, Examples of the alkyl group include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, t-butyl group, n-pentyl group, 2-pentyl group, and n-hexyl. Group, 2-hexyl group and the like. Here, when R 1, R 2 and R 3 are alkyl substituents having more than 6 carbon atoms, there are problems such that the glass transition temperature of the copolymer is remarkably lowered, and the copolymer becomes crystalline and impairs transparency. Specific examples of the olefin residue unit represented by the formula (i) include isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, 2-methyl-1-heptene, 1-isooctene, 2-methyl-1-octene, 2-ethyl-1-pentene, 2-methyl-2-pentene, 2-methyl-2-hexene, ethylene, propylene, 1- Among them, olefins belonging to 1,2-disubstituted olefins are preferable. Particularly, a copolymer (a) having excellent heat resistance, transparency, and mechanical properties can be obtained. Preferably there is. The olefin residue unit may be one or a combination of two or more, and the ratio is not particularly limited.

  R4 and R5 in the N-phenyl-substituted maleimide residue unit represented by the formula (ii) constituting the copolymer (a) are each independently hydrogen or a linear or branched alkyl group having 1 to 8 carbon atoms. Examples of the linear or branched alkyl group having 1 to 8 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group. N-pentyl group, 2-pentyl group, n-hexyl group, 2-hexyl group, n-heptyl group, 2-heptyl group, 3-heptyl group, n-octyl group, 2-octyl group, 3-octyl group Etc. R6, R7, R8, R9, and R10 are each independently hydrogen, halogen-based element, carboxylic acid, carboxylic acid ester, hydroxyl group, cyano group, nitro group, or linear or branched alkyl having 1 to 8 carbon atoms. Examples of the halogen element include fluorine, bromine, chlorine, iodine and the like, and examples of the carboxylic acid ester include methyl carboxylic acid ester and ethyl carboxylic acid ester. Examples of the linear or branched alkyl group of 1 to 8 include, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, t-butyl group, and n-pentyl. Group, 2-pentyl group, n-hexyl group, 2-hexyl group, n-heptyl group, 2-heptyl group, 3-heptyl group, n-octyl group, 2-octyl group, 3 An octyl group. Here, when R4, R5, R6, R7, R8, R9, and R10 are alkyl substituents having more than 8 carbon atoms, the glass transition temperature of the copolymer is remarkably lowered, and the copolymer becomes crystalline and becomes transparent. There are problems such as loss.

  Examples of the compound for deriving the N-phenyl substituted maleimide residue unit represented by the formula (ii) include maleimide compounds in which an unsubstituted phenyl group or a substituted phenyl group is introduced as the N substituent of the maleimide compound. Specifically, N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-n-propylphenyl) maleimide, N- (2-isopropylphenyl) Maleimide, N- (2-n-butylphenyl) maleimide, N- (2-sec-butylphenyl) maleimide, N- (2-tert-butylphenyl) maleimide, N- (2-n-pentylphenyl) maleimide, N- (2-tert-pentylphenyl) maleimide, N- (2,6-dimethylphenyl) Reimide, N- (2,6-diethylphenyl) maleimide, N- (2,6-di-n-propylphenyl) maleimide, N- (2,6-di-isopropylphenyl) maleimide, N- (2-methyl , 6-ethylphenyl) maleimide, N- (2-methyl, 6-isopropylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (2,6-dichlorophenyl) Maleimide, N- (2,6-dibromophenyl) maleimide, N-2-biphenylmaleimide, N-2-diphenylethermaleimide, N- (2-cyanophenyl) maleimide, N- (2-nitrophenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide, N- (2,4-dimethylphenyl) maleimide N-perbromophenylmaleimide, N- (2-methyl, 4-hydroxyphenyl) maleimide, N- (2,6-diethyl, 4-hydroxyphenyl) maleimide and the like can be mentioned, among which N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-n-propylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2-n-butylphenyl) Maleimide, N- (2-sec-butylphenyl) maleimide, N- (2-tert-butylphenyl) maleimide, N- (2-n-pentylphenyl) maleimide, N- (2-tert-pentylphenyl) maleimide, N- (2,6-dimethylphenyl) maleimide, N- (2,6-diethylphenyl) Maleimide, N- (2,6-di-n-propylphenyl) maleimide, N- (2,6-di-isopropylphenyl) maleimide, N- (2-methyl, 6-ethylphenyl) maleimide, N- (2 -Methyl, 6-isopropylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (2,6-dichlorophenyl) maleimide, N- (2,6-dibromophenyl) Maleimide, N-2-biphenylmaleimide, N-2-diphenylethermaleimide, N- (2-cyanophenyl) maleimide, and N- (2-nitrophenyl) maleimide are preferable, and particularly excellent in heat resistance, transparency, and mechanical properties. Since copolymer (a) is obtained, N-phenylmaleimide and N- (2-methylphenyl) male It is preferable that the de. The N-phenyl-substituted maleimide residue unit may be one or a combination of two or more, and the ratio is not particularly limited.

  The copolymer (a) includes a compound that derives an olefin residue unit represented by the above formula (i) and a compound that induces an N-phenyl-substituted maleimide residue unit represented by the formula (ii). It can be obtained by using a legal method. Examples of known polymerization methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. As another method, a copolymer obtained by copolymerizing a compound for deriving the olefin residue unit represented by the above formula (i) and maleic anhydride is further added to, for example, aniline, 2-6 position It can also be obtained by reacting an aniline having a substituent introduced thereon with a dehydration ring-closing imidization reaction.

  The copolymer (a) is a copolymer comprising an olefin residue unit represented by the above formula (i) and an N-phenyl substituted maleimide residue unit represented by the formula (ii), for example, N-phenyl. Maleimide-isobutene copolymer, N-phenylmaleimide-ethylene copolymer, N-phenylmaleimide-2-methyl-1-butene copolymer, N- (2-methylphenyl) maleimide-isobutene copolymer, N- (2-methylphenyl) maleimide-ethylene copolymer, N- (2-methylphenyl) maleimide-2-methyl-1-butene copolymer, N- (2-ethylphenyl) maleimide-isobutene copolymer, N -(2-ethylphenyl) maleimide-ethylene copolymer, N- (2-ethylphenyl) maleimide-2-methyl-1-butene copolymer, etc. Mentioned, in particular heat resistance among them, transparency, because it becomes to have excellent mechanical properties, N- phenylmaleimide - isobutene copolymer, N- (2-methylphenyl) maleimide - isobutene copolymer.

The acrylonitrile-styrene copolymer (b) in the present invention is acrylonitrile residue unit: styrene residue unit = 20: 80 to 35:65 (weight ratio), and has a weight average molecular weight of 5 × 10 ^{3 in} terms of standard polystyrene. The acrylonitrile-styrene copolymer and / or the acrylonitrile-butadiene-styrene copolymer is 5 × 10 ⁶ or less. Here, the weight average molecular weight can be measured by using an elution curve of the copolymer by GPC as a standard polystyrene equivalent value. And when the weight average molecular weight of polystyrene conversion of an acrylonitrile-styrene-type copolymer (b) is less than 5 * 10 < ³ >, while the shaping | molding process at the time of shaping | molding the obtained resin composition as a stretched film becomes difficult. The stretched film obtained is brittle. On the other hand, when the weight average molecular weight exceeds 5 × 10 ⁶ , it becomes difficult to mold the resin composition obtained as a stretched film. In addition, in the acrylonitrile-styrene copolymer (b), when the acrylonitrile residue unit: styrene residue unit = 20: 80 or less, the mechanical properties in the resin composition with the copolymer (a) are reduced, Have problems such as becoming brittle. On the other hand, when it exceeds acrylonitrile residue unit: styrene residue unit = 35: 65, there is a problem that acrylonitrile is easily altered and the hue of the resulting resin composition is deteriorated or hygroscopicity is deteriorated.

  As a method for synthesizing the acrylonitrile-styrene copolymer (b) used in the present invention, a known polymerization method can be used, for example, a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method or the like. It is possible. Moreover, what was obtained as a commercial item may be used.

  The resin composition constituting the stretched film of the present invention comprises 30 to 95% by weight of copolymer (a) and 70 to 5% by weight of acrylonitrile-styrene copolymer (b). Since it becomes a stretched film excellent in balance, it is preferably composed of 40 to 90% by weight of copolymer (a) and 60 to 10% by weight of acrylonitrile-styrene copolymer (b). Here, when a copolymer (a) is less than 30 weight%, the heat resistance of the stretched film obtained falls. On the other hand, when the copolymer (a) exceeds 95% by weight, the obtained stretched film is very brittle and has low mechanical properties.

  In the method for producing a stretched film of the present invention, when the film made of the resin composition is stretched and oriented, each of the unstretched film and the stretching film fixing jig is independently preheated before the film is stretched. Stretched and oriented in the range of -20 ° C to 20 ° C of glass transition temperature of the resin composition after being mounted on a fixing jig, and stably and efficiently stretched without causing problems such as cracks. It becomes the method of manufacturing a film. For example, when the film composed of the resin composition is a well-known general stretching orientation method such as roll stretching, tenter stretching, a small experimental stretching machine, etc. There are many cases where fine cracks are generated from the fixing film fixing jig part and its periphery, and in the worst case, the problem that the stretched film is torn easily occurs and it is difficult to obtain a stretched film stably. A case was seen.

  And as a film shaping | molding method at the time of forming this resin composition into a film, a film can be obtained by shaping | molding methods, such as an extrusion molding method and a solution cast method (it may also be called a solution casting method), for example.

  Hereinafter, the film formation by the extrusion molding method will be described in detail.

  For example, the resin composition described above is applied to an extruder such as a single-screw extruder or a twin-screw extruder equipped with a thin die called a T-shaped die, and is extruded through a gap between the die while being heated and melted. It can be set as the film which has arbitrary thickness by taking up a film. At this time, it is desirable to heat dry the resin composition in a temperature range of 80 to 130 ° C. in advance in order to suppress poor appearance due to gas foaming at the time of film forming. Further, it is desirable to perform extrusion molding by installing a filter for filtering foreign matter according to the desired film thickness and optical purity. Furthermore, in order to efficiently cool the melted film and efficiently produce a film having an excellent appearance, it is desirable to perform extrusion molding by installing a low-temperature metal roll or a steel belt.

As the extrusion molding conditions, it is desirable to perform extrusion molding under conditions where the shear rate is less than 1,000 sec ⁻¹ at a temperature sufficiently higher than Tg at which the resin composition melts and flows due to heating and shear stress.

  In addition, when a film is formed by extrusion, the obtained film is subjected to stretching and orientation processing to obtain an optical compensation film having a stable three-dimensional refractive index relationship when used as an optical compensation film. It is desirable to control the conditions so that the molecular chain orientations in the direction, the width direction, and the thickness direction are as uniform as possible. As such a method, a well-known molding technique can be used. For example, a method of making the resin composition discharged from the die uniform depending on the position, a method of making the film cooling step after discharge uniform, and an apparatus related thereto can be used.

  Hereinafter, film formation by the solution casting method will be described in detail.

  A film can be obtained by dissolving the resin composition in a solvent that is soluble in the resin composition described above to form a solution, casting the solution, and then removing the solvent.

  As the solvent at that time, any solvent may be used as long as the resin composition is soluble, and one or more of them can be mixed and used as necessary, for example, methylene chloride, chloroform , Chlorobenzene, toluene, xylene, methyl ethyl ketone, tetrahydrofuran, acetonitrile, and mixtures thereof. In addition, for the purpose of controlling the solvent volatilization rate at the time of solvent removal after casting, a solvent having a solubility (for example, methylene chloride, chloroform, etc.) and a poor solvent (for example, alcohols such as methanol, ethanol, etc.) may be combined. For example, a combination of methylene chloride and tetrahydrofuran, or a combination of methylene chloride and acetonitrile can be used as the different soluble solvents.

  In the drying of the substrate by the solution casting method, it is important to set the heating conditions so as not to form bubbles or internal voids in the film, and at the time of the subsequent stretching process that is the secondary forming process. It is desirable that the residual solvent concentration be 2 wt% or less. In addition, in order to develop uniform negative birefringence in the film obtained after the stretching process, the film obtained by the primary molding process has no non-uniform orientation and residual distortion, and is optically isotropic. It is desirable that the solution casting method is preferable as such a method.

  And when this invention draws a film obtained by film forming into a stretched film, the stretching film fixing jigs attached to the pre-stretching film and the apparatus used for film stretching orientation are independently provided. Heating in advance enables stable production without causing problems such as film cracks when the film is stretched and oriented. The heating conditions for the film before stretching and orientation of the film and the film-fixing jig for stretching are 110 to 150 ° C. and 0.1 to 5 minutes because a stretched film can be produced particularly stably. Is preferred. Here, when only one or both of the film and the film fixing jig for heating is not heated, the film fixed with the film fixing jig when the film is stretched and oriented in the subsequent film drawing and orientation process. In addition, cracks and tears are likely to occur around the film, making it difficult to produce a stretched film with high production efficiency.

  In the production method of the present invention, the resin composition is obtained by subjecting the film obtained by a molding method such as a melt extrusion method or a solution cast method and the stretching film fixing jig to a stretching orientation process while being heated in advance. By orienting the molecular chain of the copolymer in the product, negative birefringence can be stably expressed, and a stretched film free from defects such as cracks can be obtained. It will be suitable. As a method for orienting molecular chains, any method can be used as long as the molecular chains can be aligned. Examples of stretching include uniaxial stretching such as free-width uniaxial stretching and constant-width uniaxial stretching; Biaxial stretching such as axial stretching and simultaneous biaxial stretching can be used. In this case, the stretching apparatus is a tenter type stretching machine, and the small experimental stretching apparatus is a tensile tester, a uniaxial stretching machine, a sequential biaxial stretching machine, or a simultaneous biaxial stretching machine.

  And when carrying out stretch orientation processing, it becomes possible to produce a stretched film efficiently, and the resulting stretched film exhibits negative birefringence, so that it can also be used as an optical compensation film suitable as a retardation film. Therefore, the stretching process is performed within the range of Tg-20 ° C. to Tg + 20 ° C. of the resin composition described above. Here, Tg refers to the glass transition temperature of the resin composition and can be measured by a differential scanning calorimeter (DSC) or the like.

  Further, the stretching temperature, which is a stretching operation during stretching, the strain rate when stretching the film, the deformation rate, etc. may be appropriately selected as long as the object of the present invention can be achieved. Processing One Point 2 (Making a film) ”(Kiyoichi Matsumoto, edited by the Society of Polymer Science, Kyoritsu Shuppan, published on February 15, 1993), etc. may be referred to.

  In addition, when using the stretched film obtained by the manufacturing method of this invention as an optical compensation film which has negative birefringence, it is possible to grasp | ascertain birefringence characteristics by using phase difference amount. The definition of the retardation amount here is expressed as a value obtained by multiplying the difference between nx, ny, and nz, which are three-dimensional refractive indexes in the x-axis, y-axis, and z-axis directions of the stretched film, by the film thickness (d). be able to. In this case, specific examples of the difference in refractive index include a difference in refractive index within the film plane; nx−ny, a difference in refractive index outside the film plane; nx−nz, and ny−nz. The orientation direction of the stretched film is the x-axis, the in-plane orthogonal direction to the x-axis is the y-axis, the out-of-plane perpendicular direction to the x-axis is the z-axis, and the three-dimensional refractive indexes are nx, ny, nz, respectively. In this case, the in-plane retardation amount; Re or Rexy = (nx−ny) d, the out-of-film retardation amount; Re or Rexz = (nx−nz) d, Re or Reyz = (ny−). nz) It is also effective to express as d, etc.

  As shown in FIG. 1, a stretched film obtained by uniaxial stretching orientation by the production method of the present invention has a stretch direction in the x-axis in the film plane, a direction perpendicular to the x-axis in the in-plane direction, and the x-axis. 2 is the three-dimensional refractive index shown in FIG. 2, where the z-axis is the out-of-plane perpendicular direction, nx is the refractive index in the x-axis direction, ny is the refractive index in the y-axis direction, and nz is the refractive index in the z-axis direction. It becomes the stretched film which shows the negative birefringence which becomes the relationship nz> ny> nx or ny> nz> nx.

  The stretched film obtained by biaxial stretching orientation by the production method of the present invention has the stretching direction as the x-axis and y-axis in the film plane as shown in FIG. 1, and the out-of-plane perpendicular direction orthogonal to this as the z-axis. When the refractive index in the x-axis direction is nx, the refractive index in the y-axis direction is ny, and the refractive index in the z-axis direction is nz, the relationship of the three-dimensional refractive index nz> ny ≧ nx or nz> nx shown in FIG. A stretched film exhibiting negative birefringence satisfying ≧ ny. The relationship between ny and nx at this time can be controlled by the stretching ratio of the x-axis and the y-axis, which is a molding process condition during biaxial stretching.

  The stretched film obtained by the present invention may be blended with additives and plasticizers such as heat stabilizers and UV stabilizers as necessary without departing from the object of the present invention. In general, known materials for resin materials may be used. In addition, the stretched film obtained by the present invention can be used as an optical compensation film exhibiting negative birefringence, and when used as an optical compensation film exhibiting negative birefringence in an LCD or the like, an optical device is produced. From the standpoint of practical heat resistance as an optical device, Tg is preferably 100 ° C. or higher, preferably 120 ° C. or higher.

  In addition, the stretched film obtained by the production method of the present invention may be provided with a hard coat or the like for the purpose of protecting the surface, and a known hard coat agent can be used. Further, the stretched film can be used in a state where the optical properties are further controlled by laminating with the same kind of optical material and / or different kind of optical material in addition to the use alone. Examples of the optical material laminated at this time include, but are not limited to, a polarizing plate made of a combination of polyvinyl alcohol / dye / acetylcellulose, a stretched oriented film made of polycarbonate, and the like.

  The stretched film obtained by the present invention is suitably used as an optical compensation member for a liquid crystal display element. Examples of such films include retardation films for LCDs such as STN type LCDs, TFT-TN type LCDs, OCB type LCDs, VA type LCDs, and IPS type LCDs; 1/2 wavelength plates; 1/4 wavelength plates; Examples include reverse wavelength dispersion film; optical compensation film; color filter; laminated film with polarizing plate; polarizing optical compensation film. Moreover, the use as an application of this invention is not restrict | limited to this, When using a negative birefringence, it can utilize widely.

  The method for producing a stretched film of the present invention makes it possible to produce a stretched film suitable as an optical compensation film that requires negative birefringence without defects such as cracks when stretching the film with high production efficiency. .

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measuring method of each physical property value is shown below.

~ Measurement of light transmittance ~
As an evaluation of transparency, light transmittance was measured in accordance with JIS K 7361-1 (1997 edition).

~ Measurement of haze ~
As an evaluation of transparency, haze was measured according to JIS K 7136 (2000 version).

-Positive / negative judgment of birefringence-
Birefringence by the additive color determination method with a λ / 4 plate using a polarizing microscope described in Introduction to Polarizing Microscope of Polymer Materials (Hiroshi Hiroya, Agne Technology Center Edition, Chapter 5, pp 78-82, (2001)) The positive / negative judgment was performed. In particular, for the determination of a biaxially stretched film, a universal stage was installed and the color addition was determined.

~ Measurement of phase difference ~
Phase difference amount by polarization microscope (Senarmont interferometry) using Senarmont Compensator described in Introduction to Polarizing Microscope of Polymer Materials (Hiroshi Hiroya, Agne Technology Center Edition, Chapter 5, pp94-96, (2001)) Was measured.

~ Measurement of refractive index ~
It was measured according to JIS K 7142 (1996 edition).

~ Measurement of glass transition temperature ~
A differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd., trade name DSC2000) was used and the temperature was 10 ° C./min. It measured at the temperature increase rate of.

-Measurement of weight average molecular weight and number average molecular weight-
The weight average molecular weight (Mw) and the number average molecular weight (Mn) as standard polystyrene conversion values from an elution curve measured using gel permeation chromatography (GPC) (trade name HLC-802A, manufactured by Tosoh Corporation). And the molecular weight distribution (Mw / Mn) which is the ratio was measured.

-Film appearance test by stretch orientation processing-
As the appearance before and after stretching of the film, superiority or inferiority was determined by the presence or absence of cracks, the presence or absence of wrinkles, and the degree of uniformity according to the thickness of the film after stretching.

  Good; no cracks or wrinkles. Uniform stretched film.

  Poor; cracks, wrinkles occurred and / or stretched film is not uniform.

Synthesis Example 1 (Production example of N-phenylmaleimide-isobutene copolymer)
A 1 liter autoclave was charged with 400 ml of toluene as a polymerization solvent, 0.001 mol of perbutyl neodecanoate, 0.42 mol of N-phenylmaleimide and 0.67 mol of isobutene as polymerization initiators, polymerization temperature 60 ° C., polymerization The polymerization reaction is carried out under polymerization conditions for 5 hours, and is represented by N-phenylmaleimide-isobutene copolymer (weight average molecular weight (Mw) = 220,000, weight average molecular weight (Mw) / number average molecular weight (Mn). Molecular weight distribution (Mw / Mn) = 2.6) was obtained.

Example 1
50% by weight of N-phenylmaleimide-isobutene copolymer obtained in Synthesis Example 1 and acrylonitrile-styrene copolymer (manufactured by Daicel Polymer, trade name Sebian N050, weight average molecular weight (Mw) = 130,000, acrylonitrile residue unit: Styrene residue unit (weight ratio) = 24.5: 75.5) A resin composition comprising 50% by weight was prepared, and a methylene chloride solution was prepared so that the concentration of the resin composition was 25% by weight. The methylene solution was cast on a polyethylene terephthalate film (hereinafter abbreviated as PET film), and methylene chloride was volatilized to solidify and peel off to obtain a film. The obtained film after peeling was left for one day and night and then dried at 75 ° C. to 155 ° C. at 20 ° C. intervals for 1 hour to obtain a film having a thickness of about 60 μm.

  The obtained film had a light transmittance of 90.7%, a haze of 0.3%, a refractive index of 1.57, and a glass transition temperature (Tg) of 135 ° C.

  A small piece of 5 cm × 5 cm is cut out from the film, and each of the small piece film and the stretching film fixing jig of the biaxial stretching apparatus (manufactured by Imoto Seisakusho) is heated at a temperature of 145 ° C. for 5 minutes. Is fixed with a film fixing jig, and the temperature is 145 ° C. and the stretching speed is 100 mm / min. A stretched film was obtained by subjecting the film to uniaxial stretching of the free width and stretching of + 100%.

  The obtained stretched film had a thickness of 45.5 μm and exhibited negative birefringence. The in-plane retardation amount Re = (nx−ny) d of the stretched film was −140.5 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Example 2
A film having a size of 21 cm × 29 cm was cut out from the film obtained in Example 1 instead of a small piece film of 5 cm × 5 cm.

As the stretching apparatus, the temperature of the belt conveyor and the stretching film fixing jig attached with the hot air oven that can be heated to 140 ° C. before stretching the film as the film supply apparatus shown in FIG. Using a sequential biaxial stretching machine equipped with a heating device that can be heated to ℃, each of the film and the film fixing jig for stretching of the sequential biaxial stretching machine is heated at a temperature of 140 ℃ for 1 to 3 minutes Then, the film is fixed with a film-fixing jig for stretching, uniaxially stretching only in the film take-off direction, successively under stretching conditions with a stretching temperature of 145 ° C. and a strain rate during stretching of 2.0 sec ^−1. The film was stretched by a biaxial stretching machine to obtain a stretched film.

  The obtained stretched film had a thickness of 40 μm and exhibited negative birefringence. The retardation amount Re = (nx−ny) d in the film plane of the stretched film was −130.5 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Example 3
A stretched film was obtained in the same manner as in Example 1 except that the heating conditions of the small piece film and the stretching film fixing jig were 145 ° C and 110 minutes instead of 5 minutes, respectively.

  The obtained stretched film had a thickness of 46 μm and exhibited negative birefringence. The retardation amount Re = (nx−ny) d in the film plane of the stretched film was −143.0 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Example 4
A stretched film was obtained in the same manner as in Example 1 except that the heating conditions of the small piece film and the stretching film fixing jig were 145 ° C and 5 minutes instead of 150 ° C and 5 minutes.

  The obtained stretched film had a thickness of 44 μm and exhibited negative birefringence. The in-plane retardation amount Re = (nx−ny) d of the stretched film was −138.0 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Example 5
Stretched film by the same method as in Example 2 except that the heating conditions of the film and the jig for fixing the stretching film of the sequential biaxial stretching machine were 110 ° C and 1 minute instead of 1 to 3 minutes. Got.

  The obtained stretched film had a thickness of 40 μm and exhibited negative birefringence. The in-plane retardation amount Re = (nx−ny) d of the stretched film was −132.0 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Example 6
Heating conditions of the film and the jig for fixing the stretching film of the sequential biaxial stretching machine are 140 ° C. for 3 minutes instead of 1-3 minutes, and the stretching conditions are + 50% in the film take-up direction and the film width direction A stretched film was obtained in the same manner as in Example 2 except that the strain rate for stretching was set to 1.0 sec ⁻¹ .

  The obtained stretched film had a thickness of 51 μm and exhibited negative birefringence. The retardation amount Re = (nx−ny) d in the film plane of the stretched film was −8.0 nm. In addition, the stretched film was a stretched film having a good appearance with no unevenness in thickness and without occurrence of cracks or wrinkles in the portion fixed around the stretched film fixing jig and its periphery.

Comparative Example 1
A stretched film was obtained in the same manner as in Example 1 except that each heating of the small piece film and the stretching film fixing jig was not performed in advance.

  The obtained stretched film had a thickness of 42 μm and a retardation Re = (nx−ny) d of −137 nm. However, large cracks are generated at and around the portion of the stretched film that is fixed by the film fixing jig for stretching, and wrinkles are observed, resulting in uneven thickness of the film. It was.

It is a figure which shows the axial direction of the three-dimensional refractive index inside a film. It is a figure which shows the three-dimensional refractive index of the stretched film which shows the negative birefringence by uniaxial stretching. It is a figure which shows the three-dimensional refractive index of the stretched film which shows the negative birefringence by biaxial stretching. It is the schematic of the sequential biaxial stretching machine which attached the heating apparatus which heats the belt conveyor attached with the hot-air oven as a film supply apparatus, and the jig | tool for film fixing for extending | stretching.

Explanation of symbols

A: sequential biaxial stretching apparatus B; stretching film fixing jig C; stretching film fixing jig heating apparatus D; pre-stretching film heating apparatus E; pre-stretching film F; stretched film

Claims (6)

It consists of an olefin residue unit represented by the following formula (i) and an N-phenyl-substituted maleimide residue unit represented by the following formula (ii), and has a weight average molecular weight of 5 × 10 ³ or more and 5 × in terms of standard polystyrene. copolymer is 10 ⁶ or less (a) 30 to 95 wt%, and acrylonitrile residual units: styrene residue unit = 20: 80 to 35: a 65 (weight ratio), weight average molecular weight in terms of standard polystyrene 1 to 1 or more acrylonitrile-styrene copolymer (b) selected from acrylonitrile-styrene copolymer and acrylonitrile-butadiene-styrene copolymer, which is 5 × 10 ³ or more and 5 × 10 ⁶ or less, from 70 to 5% by weight When producing a stretched film made of the resin composition, each of the unstretched film and the stretching film fixing jig was preheated independently in advance. A method for producing a stretched film that the film and performing stretch orientation with a glass transition temperature of -20 ° C. ~ glass transition temperature + 20 ° C. ranging attached to the fixing jig the resin composition.

(Here, R1, R2, and R3 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms.)

(Where R4 and R5 are each independently hydrogen or a linear or branched alkyl group having 1 to 8 carbon atoms, and R6, R7, R8, R9 and R10 are each independently hydrogen or a halogen-based element. A carboxylic acid, a carboxylic acid ester, a hydroxyl group, a cyano group, a nitro group, or a linear or branched alkyl group having 1 to 8 carbon atoms.) The method for producing a stretched film according to claim 1, wherein the copolymer (a) is an N-phenylmaleimide-isobutene copolymer. The stretched film according to claim 1, wherein the film before stretching and the jig for fixing the stretching film are independently heated under conditions of 110 to 150 ° C. and 0.1 to 5 minutes. Manufacturing method. The method for producing a stretched film according to claim 1, wherein the stretch orientation is a uniaxial stretch orientation. The method for producing a stretched film according to claim 1, wherein the stretch orientation is a biaxial stretch orientation. The method for producing a stretched film according to claim 1, wherein the stretched film is an optical compensation film exhibiting negative birefringence.

Images