JP2002331574A - Manufacturing method for optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film excellent in handling properties, accuracy of thickness and optical characteristics. SOLUTION: The film constituted of a resin composition for the film containing an amorphous thermoplastic resin is subjected to longitudinal uniaxial orientation by rolls, and on the occasion, a width reduction index is controlled to be 0.4 or less. The resin composition for the film contains preferably a thermoplastic resin having a substituent or non-substituent imide group in a side chain (A) and a thermoplastic resin having a substituent or non-substituent phenyl group and a nitrile group in the side chain. The film thus obtained shows an excellent performance as the optical film and is useful particularly as a polarizer protecting film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a film which is made of an amorphous thermoplastic resin, has excellent handling properties, thickness accuracy and optical characteristics, and is suitable for optical applications. The present invention also relates to a polarizer protective film using such an optical film.

[0002]

2. Description of the Related Art In recent years, with the miniaturization, thinning, and weight reduction of notebook personal computers, word processors, mobile phones, personal digital assistants, etc., there have been many liquid crystal display devices that make use of the lightweight and compact features of these electronic devices. It is being used. Various films such as polarizing films are used in liquid crystal display devices in order to maintain the display quality. In order to further reduce the weight of liquid crystal display devices for portable information terminals and mobile phones, liquid crystal display devices using a plastic film instead of a glass substrate have been put to practical use.

[0003] Plastic films used in devices that handle polarized light, such as liquid crystal display devices, are required to be optically transparent, have low birefringence, and have optical homogeneity. For this reason, a polarizer protective film for protecting a polarizer made of highly stretched polyvinyl alcohol,
In the case of a film substrate for a plastic liquid crystal display device in which a glass substrate is replaced with a resin film, a small phase difference represented by a product of birefringence and thickness is required. Further, it is required that the phase difference of the film is hard to change due to external stress or the like. Furthermore, it is required that unevenness of these phase differences is small in the plane in the plane direction and the thickness direction.
Furthermore, it is required that an image distortion phenomenon due to a so-called lens effect due to unevenness on the film surface hardly occurs. That is, if the phase difference is large, the phase difference changes due to external stress, etc., the change of the phase difference in the plane is large, or if there is a lens effect due to the unevenness of the film surface, the image quality of the liquid crystal display device remarkably increases. Lower. In other words, color jumping phenomena such as partial lightening of colors and adverse effects such as distorted images occur. As a plastic film used for a liquid crystal display device, an amorphous thermoplastic resin is a suitable material, polycarbonate,
BACKGROUND ART Films made of engineering plastics such as polyarylate, polysulfone, and polyethersulfone, and cellulose-based plastics such as triacetyl cellulose are known. When these plastic films are manufactured, various stresses are generated in the film being formed due to melt flow of the plastic, solvent drying shrinkage, heat shrinkage, and transport stress. Therefore, a retardation tends to remain in the obtained film due to birefringence caused by the molecular orientation induced by these stresses. Therefore, a special treatment for the film such as thermal annealing or the like must be performed as necessary to reduce the remaining phase difference, which causes a problem that the manufacturing process becomes complicated. Further, even when a film in which the remaining retardation is reduced is used, a new retardation is generated due to stress or deformation generated during the subsequent processing of the film. Furthermore, when a plastic film is used as a polarizing protective film, it is known that an undesired retardation is generated in the film due to the shrinkage stress of the polarizer, which adversely affects the polarizing performance of the polarizing film. In order to solve these problems, attempts have been made to obtain a plastic film having a smaller polarization, that is, a resin film in which retardation due to molecular orientation is less likely to be developed. For example, a cycloolefin-based film and an olefin-based film having a maleimide component have been proposed.

[0004] Further, in optical film applications, uniformity of thickness is particularly highly required due to optical homogeneity. For this reason, conventionally, films used for these applications have been produced by a solution casting method having excellent thickness uniformity. However, in recent years, the solution casting method has been pointed out that the solvent is polluted by the environment and low in productivity, and the solution casting method is being switched from the solution casting method to the melt extrusion method, which is another method for producing a film. But,
Until now, films formed by the melt extrusion method have disadvantages such as large thickness unevenness and easy die line, so polarizer protective films and retardation films that require strict thickness uniformity and optical characteristics are required. As a method for producing a film for optical applications, the melt extrusion method has hardly been put to practical use. For a crystalline thermoplastic resin, a film is produced by a melt extrusion method, and subsequently, the film is stretched to increase strength and flexibility, and at the same time, to enhance uniformity of thickness. However, in the case of amorphous thermoplastic resins, although flexibility and strength are improved by stretching, thickness unevenness is rather large, so that they are hardly practically used for high-performance optical films. Thus, it has heretofore been considered difficult to maintain or improve the uniformity of the thickness of the amorphous thermoplastic resin film by stretching. Furthermore, not only a crystalline thermoplastic resin but also an amorphous thermoplastic resin has been considered that a stretched film cannot be used for some optical applications because a large birefringence is generated by stretching and a phase difference is increased. Was.

[0005]

If the uniformity of the thickness of the optical film is inferior, minute unevenness of the thickness causes a so-called lens effect, which causes image distortion in the liquid crystal display device and lowers the image quality. It has been pointed out. Alternatively, if the thickness of the optical film is poor in uniformity, the in-plane variation of the phase difference represented by the product of the birefringence and the thickness caused by the molecular orientation induced by the stress causes the liquid crystal display device to fail. It is pointed out that the image quality deteriorates, for example, a color skip phenomenon such as a partial lightening of the color occurs.

Further, although the photoelastic coefficient and the orientation birefringence of the cycloolefin-based film and the olefin-based film having a maleimide component are relatively small, the viewing angle characteristics are still poor, and a large screen and a wide viewing angle are required. Use for liquid crystal display devices is limited.

On the other hand, a film composed of an olefin-maleimide resin and a styrene-acrylonitrile resin as described in JP-A-2000-80240 can further reduce the photoelastic coefficient, and is induced by stress. Since birefringence due to molecular orientation is relatively small and the phase difference is also relatively small, it is expected as a preferable material.

However, these materials have low mechanical properties and are brittle. For this reason, there is a problem in handleability during film processing. For example, when the film passes through an adhesive roll, when slitting, when manufacturing a film such as when winding or sandwiching between clips of a horizontal stretching machine, or during post-processing of a film such as lamination with other materials. It is said that phenomena such as easy tearing and cracking occur
Have practical problems.

As a method of improving the mechanical properties of the film, there is a method of adding a plasticizer, a flexible polymer, or the like. However, in these methods, the glass transition temperature is generally lowered, and the heat resistance is likely to be impaired. Or, it is not preferable because optical characteristics such as transparency are easily damaged.

On the other hand, Japanese Patent Application Laid-Open No. 9-234786 proposes to stretch a film. But,
If molecules are strongly oriented by stretching, orientation birefringence occurs and the phase difference increases, which is not preferable.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, using a relatively inexpensive roll longitudinal uniaxial stretching machine or the like,

[0012]

(Equation 2)

The present inventors have found that the above problems can be solved by uniaxially stretching a film made of an amorphous thermoplastic resin while controlling the width reduction index a defined in the above, and completed the present invention. That is, according to the method for producing the film, it is possible to improve the mechanical strength such as the elongation rate of the film, the resistance to rubbing fatigue, and the tear propagation strength, and the handling properties during the production and post-processing of the film are significantly improved. Cracks, tears, and other problems are significantly reduced,
The inventors have found that they have excellent thickness accuracy and optical characteristics, and have reached the present invention.

Specifically, according to the present invention, the following film production method and film are provided.

(1) A method for producing a stretched optical film from a resin composition for a film containing an amorphous thermoplastic resin, comprising a step of uniaxially stretching an unstretched film in a machine direction. In the stretching step, a film width W ₀ before the longitudinal uniaxial stretching, a film width W after the longitudinal uniaxial stretching, and a width reduction index a defined by the following formula from the longitudinal uniaxial stretching ratio Φ are 0.4. The method maintained below.

[0016]

(Equation 3)

(2) When the stretching step is 10 mm or more and 1
The method according to the above (1), wherein the stretching is performed in a stretching section of 50 mm or less.

(3) The resin composition for a film is
The above item (1) or (1), wherein (A) contains a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and (B) a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain. The method according to 2).

(4) The thermoplastic resin (A) has a repeating unit represented by the formula (1) and a repeating unit represented by the formula (2). The content is 30 to 80 mol% based on the total repeating units of the thermoplastic resin (A), and the content of the repeating unit of the formula (2) is based on the total repeating units of the thermoplastic resin (A). 70 to 20 mol%, wherein the thermoplastic resin (B) has a repeating unit represented by the formula (3) and a repeating unit represented by the formula (4), and The content of the repeating unit of the formula (3) is 20 to 50% by weight, and the content of the repeating unit of the formula (4) is 50 to 80% by weight based on the total repeating units. )) And the amount of the thermoplastic resin (B), The above item (3), wherein the content of the thermoplastic resin (A) in the resin composition is 50 to 80% by weight, and the content of the thermoplastic resin (B) is 20 to 50% by weight. The described method.

[0020]

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(In the formula (1), R ¹ , R ² and R ³
Each independently represents hydrogen or an alkyl group having 1 to 8 carbon atoms. (In the formula (2), R represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.)

[0022]

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(In the formula (3), R ⁴ and R ⁵ are
Each independently represents hydrogen or an alkyl group having 1 to 8 carbon atoms. ) In (Equation (4), R ⁶ and R ⁷ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, R ⁸
Represents hydrogen, an alkyl group having 1 to 8 carbon atoms, a halogen group, a hydroxyl group, an alkoxy group, or a nitro group. (5) An optical film produced by the method according to any one of the above items (1) to (4).

(6) The film according to the above item (5), wherein the produced optical film is a polarizer protective film.

(7) The method according to the above item (1), wherein the produced optical film is a polarizer protective film.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Film) First, a film according to the present invention will be described.

(Resin Composition) The resin composition for a film used in the production method of the present invention contains an amorphous thermoplastic resin. Preferably, the main component is an amorphous thermoplastic resin. Specifically, the amount of the amorphous thermoplastic resin is preferably 70% by weight or more of the total amount of the resin in the resin composition, more preferably 80% by weight or more, and further preferably 90% by weight or more. % By weight or more. Particularly preferably, 100% by weight of the total amount of the resin in the resin composition is an amorphous thermoplastic resin.

Examples of the amorphous thermoplastic resin include polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cycloolefin resin, cellulose resin, vinyl chloride resin, polysulfone resin, and polyether sulfone. Resin, maleimide / olefin resin, glutarimide resin, and the like. These amorphous thermoplastic resins may be used alone or in combination of two or more. A blend of a resin with negative orientation birefringence selected from methacrylic resin and styrene resin and a resin with positive orientation birefringence selected from polycarbonate, polyphenylene ether resin, imide resin, etc. A preferred example is also a resin composition comprising

Preferred amorphous thermoplastic resins include:
Resin compositions containing (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and (B) a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain. Optical film according to the present invention,
It is preferable that the thermoplastic resin (A) and the thermoplastic resin (B) are produced as a main component, but if necessary, the thermoplastic resin (A) and the thermoplastic resin (B) are used. Alternatively, a third resin may be used.

In the present specification, when the above-mentioned thermoplastic resin (A) is a copolymer resin, this copolymer is also referred to as “thermoplastic copolymer (A)”. In addition, in the present specification, when the thermoplastic resin (B) is a copolymer resin, the copolymer is also referred to as “thermoplastic copolymer (B)”.

The thermoplastic resin (A) preferably used in the present invention is a thermoplastic resin having a substituted or unsubstituted imide group in a side chain. Here, the main chain of the thermoplastic resin (A) may be the main chain of any thermoplastic resin. For example, it may be a main chain composed of only carbon, or a main chain in which atoms other than carbon are inserted between carbons. Alternatively, it may be a main chain composed of atoms other than carbon. Preferably, the main chain is made of only carbon. For example, it may be a hydrocarbon or a substitute thereof. Specifically, for example, the main chain can be a main chain obtained by addition polymerization. Specifically, for example, it is polyolefin or polyvinyl.

The main chain may be a main chain obtained by condensation polymerization. For example, it may be a main chain obtained by an ester bond, an amide bond, or the like.

[0033] Preferably, the main chain is a polyvinyl skeleton obtained by polymerizing a substituted vinyl monomer.

As a method for introducing a substituted or unsubstituted imide group into the thermoplastic resin (A), any conventionally known method can be used. For example, a thermoplastic resin having a substituted or unsubstituted imide group may be obtained by polymerizing a monomer having a substituted or unsubstituted imide group. Also, for example, after polymerizing various monomers to form a main chain,
A substituted or unsubstituted imide group may be introduced into the side chain. For example, a compound having a substituted or unsubstituted imide group may be grafted to a side chain.

When the imide group is substituted with a substituent,
As the substituent, a conventionally known substituent capable of substituting hydrogen of an imide group can be used. Specifically, for example, it is an alkyl group.

Preferably, the thermoplastic resin (A) is a copolymer containing a repeating unit derived from at least one olefin (alkene) and at least one repeating unit having a substituted or unsubstituted maleimide structure. (Binary or higher multi-component copolymer).

Particularly preferably, the thermoplastic resin (A) comprises:
It contains a repeating unit represented by the following formula (1) and a repeating unit represented by the following formula (2).

[0038]

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(In the formula (1), R ¹ , R ² and R ³
Each independently represents hydrogen or an alkyl group having 1 to 8 carbon atoms. The carbon number of the alkyl group is preferably 1 to 4
And more preferably 1 to 2. (In the formula (2), R represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms. The alkyl group preferably has 1 to 4 carbon atoms, More preferably, the content is 1 to 2. Here, the content of the repeating unit of the formula (1) is preferably 30 to 80 mol%, based on the total repeating units of the thermoplastic resin (A). is there. More preferably, 40 to
60 mol%. More preferably, it is 45 to 55 mol%. The content of the repeating unit of the formula (2) is from 20 to 20 based on the total repeating units of the thermoplastic resin (A).
70 mol%. More preferably, 40 to 60 mol%
It is. More preferably, it is 45 to 55 mol%.
In a preferred embodiment, the sum of the repeating unit of the formula (1) and the repeating unit of the formula (2) is 100%. However, a third repeating unit described later may be used if necessary.

When the third repeating unit is used,
The third repeating unit is preferably at least 1 mol%, more preferably at least 2 mol%, even more preferably at least 3 mol%, based on the total repeating units of the thermoplastic copolymer (A). And particularly preferably at least 5 mol%. If the number of the third repeating units is too small, it is difficult to sufficiently obtain the performance of the third repeating unit as the whole composition.

When the third repeating unit is used, the ratio between the repeating unit of the formula (1) and the repeating unit of the formula (2) is the same as that when the third repeating unit does not exist. Is preferred.

(Repeating Unit of Formula (1)) The olefin which provides the repeating unit (olefin unit) of the formula (1) is
It is represented by the following equation (5).

[0043]

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(Here, R ¹ , R ² and R ³ are the same as those of the formula (1).) Preferred examples of such olefins include isobutene, 2-methyl-1-butene, and 2-olefin. Methyl-1-pentene, 2-methyl-1-hexene, 2-methyl-1-heptene, 1-isooctene, 2-methyl-1-octene, 2-ethyl-1-pentene, 2-ethyl-2-butene, 2-methyl-2-pentene, 2-methyl-2-hexene and the like. These olefins may be used alone or in combination of two or more.

(Repeating unit of the formula (2))
(Maleimide unit) can be derived from the corresponding maleimide compound. Such a maleimide compound is represented by the following formula (6).

[0046]

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(Here, R is the same as in formula (2).) Preferred examples of such a maleimide compound include:
Maleimide, and N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ni
-Butylmaleimide, N-s-butylmaleimide, N-
t-butylmaleimide, Nn-pentylmaleimide,
Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, N- N-substituted maleimides such as cyclohexylmaleimide, N-cycloheptylmaleimide and N-cyclooctylmaleimide.

These maleimide compounds may be used alone or in combination of two or more. As the maleimide compound, an N-substituted maleimide (in the formula (6), R is a group other than hydrogen) is particularly preferable. For example, N-
And methylmaleimide.

(Third Repeating Unit) In the thermoplastic copolymer (A) used in the present invention, in addition to the olefin unit and the maleimide unit, another copolymerizable monomer may be used as a third repeating unit. More than one species can be contained. Such copolymerizable monomers include acrylate monomers such as methyl acrylate and butyl acrylate, methacrylate monomers such as methyl methacrylate and cyclohexyl methacrylate, and vinyl acetate. Examples include vinyl ester monomers, vinyl monomers such as vinyl ether monomers such as methyl vinyl ether, and acid anhydrides having an unsaturated double bond such as maleic anhydride. These third repeating units may be a single type of monomer or a combination of two or more types of monomers to form a third type of repeating unit. By including the third repeating unit to such an extent that the optical properties are not significantly impaired, the heat resistance of the thermoplastic copolymer (A) can be improved or the mechanical strength can be increased.

(Method of Polymerizing Thermoplastic Resin) The thermoplastic resin (A) can be produced, for example, by polymerizing the olefin and the maleimide compound by a known polymerization method. This polymerization includes graft polymerization.
Alternatively, the thermoplastic resin (A) is prepared by polymerizing the olefin and maleic anhydride in a conventional manner to produce a precursor polymer, and reacting the precursor polymer with an amine compound to imidize the maleic anhydride site of the precursor polymer. It can also be manufactured by doing. The amine compound used in that case includes an amine corresponding to the imide site in the maleimide unit of the above formula (2). More specifically,
Wherein R-NH ₂ (wherein, R is the same. In equation (2)) amine compounds represented by, for example methylamine, ethylamine, n- propylamine, i- propylamine, n- butylamine, s- butylamine, Preferred examples include alkylamines such as t-butylamine and cyclohexylamine, and ammonia, as well as dimethylurea and diethylurea. Also in this case, a copolymer having the repeating unit of the formula (1) and the repeating unit of the formula (2) is obtained.

The thermoplastic copolymer (A) used in the present invention
May be any of a random copolymer, a block copolymer, a graft copolymer, and an alternating copolymer. It is preferably an alternating copolymer. Thermoplastic copolymer (A)
Is more preferably a maleimide unit represented by the formula (2)
R is a methyl group in, an ethyl group, and contains at least one maleimide unit is an alkyl group selected from isopropyl and cyclohexyl groups, as olefin units, R ¹ is hydrogen in the formula (1), R ² And a copolymer containing at least one olefin unit in which R ³ is a methyl group. Here, when a monomer is referred to as a “unit” in the present specification, it refers to a residue remaining after the monomer is polymerized. Specifically, the “maleimide unit” refers to a residue remaining after one used maleimide molecule is polymerized. Similarly, “olefin unit” refers to a residue remaining after one used olefin monomer is polymerized.

More preferably, the thermoplastic copolymer (A) used in the present invention contains an N-methylmaleimide unit as a maleimide unit and an isobutylene unit as an olefin unit. It is particularly preferable that the thermoplastic copolymer (A) used in the present invention is an alternating copolymer of N-substituted maleimide and isobutene.

In the thermoplastic copolymer (A) used in the present invention, the content of the maleimide unit is from 30 mol% to less than 80 mol%, based on the total repeating units of the thermoplastic copolymer (A). Preferably, there is. If the content of the maleimide unit is too small or too large, the heat resistance and mechanical strength of the resulting film may be impaired. The content ratio of the maleimide unit is more preferably 40 mol% or more and 60 mol% or less. When the third repeating unit is added, the content of the third repeating unit may be 5 mol% or more and 30 mol% or less based on the total repeating units (A) of the thermoplastic copolymer. preferable. More preferably, it is 5 mol% or more and 10 mol% or less. The rest of the repeating units in the thermoplastic copolymer (A) are olefin units. It is particularly preferable that the thermoplastic copolymer (A) contains a maleimide unit and an olefin unit as main components. In one embodiment,
The total of maleimide units and olefin units is at least 50 mol%, preferably at least 70 mol%, in the thermoplastic copolymer (A). More preferably, it is at least 80 mol%, even more preferably at least 90 mol%.

The thermoplastic copolymer (A) preferably has a weight average molecular weight of 1 × 10 ³ or more. More preferably, it is 1 × 10 ⁴ or more.

The thermoplastic copolymer (A) preferably has a weight average molecular weight of 1 × 10 ⁷ or less. More preferably, it is 5 × 10 ⁵ or less.

Further, the thermoplastic copolymer (A) has a glass transition temperature of preferably 80 ° C. or higher, more preferably 1 ° C. or higher.
It is preferable to exhibit heat resistance such that the temperature is at least 00 ° C, more preferably at least 130 ° C.

As another preferred thermoplastic resin A having a substituted or unsubstituted imide group in the side chain, a glutarimide-based thermoplastic resin can be used. The glutarimide-based resin has a glutarimide structural unit and a methyl acrylate or methyl methacrylate structural unit as described in JP-A-2-153904.

A glutarimide resin having a repeating unit represented by the following general formula (20) can be preferably used.

[0059]

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(Wherein R ⁴⁰ is hydrogen or methyl, R ⁵⁰ is hydrogen or an alkyl group having 1 to 8 carbon atoms,
It represents a cycloalkyl group or an aryl group. R is the same as in the above formula (2). A third monomer may be optionally copolymerized in the glutarimide-based resin. Preferred examples of the third monomer include acrylic monomers such as butyl acrylate, styrene monomers such as styrene, substituted styrene and α-methylstyrene, and nitrile monomers such as acrylonitrile and methacrylonitrile. It is possible to use a monomer or a maleimide-based monomer such as maleimide, N-methylmaleimide, or N-phenylmaleimide. Further, these third monomers may be directly copolymerized with a glutarimide-based resin. Further, it may be graft copolymerized with a glutarimide resin.

The preferred content of the imide group is 40 to 80 mol% of the total amount of the repeating unit in the glutarimide resin as the abundance of the repeating unit having the imide group.
It is. Examples of these glutarimide resins are disclosed in, for example, US Pat. No. 4,246,374.

The olefin-maleimide copolymer used in the present invention can be produced by a method known per se as described above. For example, JP-A-5-59193, JP-A-5-195801, JP-A-6-136
No. 058 and JP-A-9-328523. Specifically, for example, an olefin and a maleimide compound are directly copolymerized, one of the polymers is graft-copolymerized with the other, or an amine compound is reacted with the precursor polymer described above to form an imide bond. It can be manufactured by introducing.

(Thermoplastic resin (B)) The thermoplastic resin (B) used in the present invention is a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain. Here, the main chain of the thermoplastic resin (B) may be the main chain of any thermoplastic resin. For example, it may be a main chain composed of only carbon, or a main chain in which atoms other than carbon are inserted between carbons. Alternatively, it may be a main chain composed of atoms other than carbon. Preferably, the main chain is made of only carbon. For example, it may be a hydrocarbon or a substitute thereof. Specifically, for example, the main chain can be a main chain obtained by addition polymerization. Specifically, for example, it is polyolefin or polyvinyl.

The main chain may be a main chain obtained by condensation polymerization. For example, it may be a main chain obtained by an ester bond, an amide bond, or the like.

[0065] Preferably, the main chain is a polyvinyl skeleton obtained by polymerizing a substituted vinyl monomer.

As a method for introducing a substituted or unsubstituted phenyl group into the thermoplastic resin (B), any conventionally known method can be used. For example, a thermoplastic resin having a substituted or unsubstituted phenyl group may be obtained. Further, for example, after forming a main chain by polymerizing various monomers, a substituted or unsubstituted phenyl group may be introduced into a side chain. For example,
A compound having a substituted or unsubstituted phenyl group may be grafted on the side chain.

When the phenyl group is substituted with a substituent, a conventionally known substituent capable of substituting hydrogen of the phenyl group and a substitution position can be used as the substituent.
Specifically, the substituent is, for example, an alkyl group.

As a method for introducing a nitrile group into the thermoplastic resin (B), any conventionally known method can be used.
For example, a thermoplastic resin having a nitrile group may be obtained by polymerizing a monomer having a nitrile group.
Further, for example, after a monomer is polymerized to form a main chain, a nitrile group may be introduced into a side chain. For example, a compound having a nitrile group may be grafted on a side chain.
The thermoplastic resin (B) used in the present invention is preferably a copolymer containing a repeating unit derived from an unsaturated nitrile compound (nitrile unit) and a repeating unit derived from a styrene-based compound (styrene-based unit). It is a union (binary or ternary or higher multi-component copolymer).

It is particularly preferred that the thermoplastic copolymer (B) contains an unsaturated nitrile unit and a styrene unit as main components. The total of the unsaturated nitrile units and the styrene units is preferably at least 70% by weight of the thermoplastic resin (B). More preferably 80% by weight or more,
It is more preferably 90% by weight, particularly preferably 9% by weight.
5% by weight or more. Of course, it may be 100% by weight.

(Nitrile Compound) Preferred examples of the unsaturated nitrile compound constituting the above-mentioned preferred copolymer (B) include α-substituted unsaturated nitriles such as acrylonitrile and methacrylonitrile, and α-substituted unsaturated nitriles such as fumaronitrile. , A nitrile compound having a β-disubstituted olefinically unsaturated bond.

(Styrene Compound) Examples of the styrene compound constituting the preferable copolymer (B) include unsubstituted or substituted styrene compounds such as styrene, vinyltoluene, methoxystyrene and chlorostyrene;
Α-substituted styrene compounds such as -methylstyrene can be used.

In a preferred embodiment, the thermoplastic resin (B) has a repeating unit represented by the formula (3) and a repeating unit represented by the formula (4).

[0073]

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(In the formula (3), R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms. The alkyl group preferably has 1 to 4 carbon atoms. preferably, 1 to 2.) in (equation (4), R ⁶ and R ⁷ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, R ⁸
Represents hydrogen, an alkyl group having 1 to 8 carbon atoms, a halogen group, a hydroxyl group, an alkoxy group, or a nitro group. The number of carbon atoms in the alkyl group is preferably from 1 to 4, more preferably from 1 to 2. The carbon number of the alkoxy group is preferably 1 to 20, more preferably 1 to 8, and further preferably 1 to 4. ) Based on the total repeating units in the thermoplastic resin (B),
The repeating unit of the general formula (3) is preferably 10 to 7
0% by weight, more preferably 20 to 60% by weight, even more preferably 20 to 50% by weight. More preferably, it is 20 to 40% by weight. Still more preferably, it is 20 to 30% by weight. Very preferably 2
0 to 29% by weight. Most preferably, it is 20 to 28% by weight.

Based on the total repeating units in the thermoplastic resin (B), the repeating unit of the formula (4) is preferably
The content is 30 to 70% by weight, more preferably 40 to 80% by weight, and still more preferably 50 to 80% by weight. Particularly preferably, it is 60 to 80% by weight. Most preferably, it is 70 to 80% by weight.

In one preferred embodiment, the sum of the repeating unit of the formula (3) and the repeating unit of the formula (4) is 100
%. However, a third repeating unit described later may be used if necessary.

(Third Repeating Unit) The thermoplastic copolymer (B) contains, in addition to the nitrile unit and the styrene unit,
As the third component, another copolymerizable monomer may be contained. Such a third component preferably contains an acrylic monomer such as butyl acrylate and an olefin monomer such as ethylene and propylene, and copolymerizes one or more of these monomers. By doing so, the flexibility of the obtained film can be improved. Further, as the third component, N-substituted maleimide can be used, and by using this N-substituted maleimide, particularly phenylmaleimide as a copolymer component, the heat resistance of the copolymer can be improved.

When the third repeating unit is used, it is preferably at most 30% by weight, more preferably at most 20% by weight, based on the weight of the thermoplastic copolymer (B). Yes, more preferably 15% by weight or less, particularly preferably 10% by weight or less.
When there are too many third repeating units, the above formula (3)
It is difficult to sufficiently obtain the performance of the repeating unit represented by the formula (1) and the repeating unit represented by the formula (4).

When the third repeating unit is used,
The third repeating unit is preferably at least 1% by weight, more preferably at least 2% by weight, further preferably at least 3% by weight, based on the weight of the thermoplastic copolymer (B), Particularly preferably, it is at least 5% by weight. If the number of the third repeating units is too small, it is difficult to sufficiently obtain the performance of the third repeating unit as the whole composition.

Even when the third repeating unit is used, the ratio between the repeating unit of the formula (3) and the repeating unit of the formula (4) is the same as that when the third repeating unit does not exist. It is preferable to set the ratio.

(Polymerization Method of Thermoplastic Resin (B)) The thermoplastic copolymer (B) is obtained by directly copolymerizing these monomers, and is obtained by polymerizing a styrene compound and an unsaturated nitrile compound. One of the polymers may be graft-copolymerized with the other. A preferred copolymer can be obtained by graft-polymerizing a styrene-based compound and an unsaturated nitrile-based compound onto an acrylic polymer having rubber elasticity.

A particularly preferred thermoplastic copolymer is a copolymer containing acrylonitrile as an unsaturated nitrile component and styrene as a styrene component. These copolymers are known as AS resins and AAS resins.

In the thermoplastic copolymer (B) used in the present invention, the content of the unsaturated nitrile-based repeating unit in the thermoplastic resin is preferably 20 to 60% by weight, and the content of the styrene-based repeating unit is preferably , 40 to 80% by weight. As for the ratio of the unsaturated nitrile unit to the styrene unit, the former is preferably 20 to 50% by weight, and the latter is preferably 50 to 80% by weight, more preferably,
The former is 20 to 40% by weight, and the latter is 60 to 80% by weight. In particular, the former is 20 to 30% by weight and the latter is 7% by weight.
When it is 0 to 80% by weight, more preferable results are obtained. If the content of the styrene-based compound or the nitrile-based compound is too large or too small, the phase difference due to the orientation of the molecules in the film tends to be large, and the compatibility with the thermoplastic resin (A) becomes poor. When used as a material, it is difficult to obtain a film having excellent transparency.

The thermoplastic copolymer (B) preferably has a weight average molecular weight of 1 × 10 ³ or more. More preferably, it is 1 × 10 ⁴ or more.

The thermoplastic copolymer (B) preferably has a weight average molecular weight of 1 × 10 ⁷ or less. More preferably, it is 5 × 10 ⁵ or less.

(Ratio of thermoplastic resin (A) to (B)) The ratio of the thermoplastic resin (A) to the thermoplastic resin (B) used to obtain the optical film of the present invention is as follows. (A) 10 to 90% by weight of thermoplastic resin (B)
It is preferable to mix them in a ratio of 10 to 90% by weight. It is more preferable to mix the thermoplastic resin (B) at a ratio of 15 to 60% by weight with respect to the thermoplastic resin (A) at 40 to 85% by weight. More preferably, the thermoplastic resin (B) is blended in a proportion of 20 to 50% by weight with respect to the thermoplastic resin (A) in a proportion of 50 to 80% by weight.
Thermoplastic resin (B) 25 to 35% by weight to 75% by weight
The proportion by weight is particularly preferred.

If the thermoplastic resin (B) is out of the preferred range, when it is formed into a stretched film, the phase difference in the plane direction or the thickness direction may be large. On the other hand, if the blending ratio of the thermoplastic resin (B) is too large, the transparency of the obtained film tends to decrease.

By blending the two resins (A) and (B) in the above ratio, an optical film having an extremely small retardation in both the plane direction and the thickness direction of the film can be obtained.

In a preferred embodiment, the sum of the thermoplastic resin (A) and the thermoplastic resin (B) is 100% by weight.

A particularly preferable mixing ratio is thermoplastic resin (A)
And the type of thermoplastic resin (B). Generally, the ratio (I / P) of the number of moles I of imide groups contained in the thermoplastic resins (A) and (B) to the number of moles P of phenyl groups contained in the thermoplastic resins (B) and (A) used ratio)
Is preferably 0.7 or more, more preferably 0.9 or more, and still more preferably 1.0 or more. Also,
It is preferably at most 2.9, more preferably at most 2.6, even more preferably at most 2.4. In one embodiment, the I / P ratio is preferably from 1.3 to 2.0, and more preferably the I / P ratio is from 1.5 to 1.9.

Thermoplastic resin (A) in which an alternating polymer of N-methylmaleimide and isobutene is selected as thermoplastic resin (A) and a copolymer of acrylonitrile and styrene is selected as thermoplastic resin (B): The weight ratio of the thermoplastic resin (B) is preferably 50:50 to 80:20,
65:35 to 75:25 is more preferred. The amount of the acrylonitrile component in the thermoplastic resin (B) is preferably 20 to 30% by weight, more preferably 25 to 29% by weight. The amount of the styrene-based component in the thermoplastic resin (B) is preferably from 80 to 70% by weight, more preferably from 75 to 71% by weight.

By appropriately selecting the preferred composition as described above, an optical film having substantially no birefringence can be obtained. For example, in a preferred embodiment, the retardation in the planar direction of the film can be controlled to 10 nm or less, and in a more preferred embodiment, it is 6 nm.
The following can be controlled. Further, for example, the retardation in the film thickness direction can be controlled to 50 nm or less,
In a more preferred embodiment, it can be controlled to 20 nm or less. In a particularly preferred embodiment, it can be controlled to 10 nm or less. The retardation in the plane direction of the film is 10 nm or less and the retardation in the thickness direction of the film is 5
When it is 0 nm or less, it can be generally evaluated that there is substantially no birefringence.

If the above-mentioned preferred composition is appropriately selected, an optical film having a high light transmittance and a low haze can be obtained simultaneously with the birefringence performance.
Specifically, for example, in a preferred embodiment, a film having a light transmittance of 85% or more can be easily obtained, and in a more preferred embodiment, a film having a light transmittance of 88% or more can be obtained.
In a preferred embodiment, the haze can be controlled to 2% or less, and in a more preferred embodiment, the haze can be controlled to 1% or less. In a particularly preferred embodiment, it can be controlled below 0.5%. Light transmittance of 85% or more and haze of 2
% Can be used as a high-performance film for various optical applications.

(Production of Composition) As a method for obtaining the resin composition used in the present invention, the thermoplastic resin (A) and the thermoplastic resin (B) are mixed so that they can be put into a film forming machine. As far as possible, any known method can be adopted.

For example, there are a method of obtaining a resin composition by simply mixing the thermoplastic resin (A) and the thermoplastic resin (B), and a method of obtaining a resin composition by hot-melting and kneading both resins.

These resin compositions may contain, if necessary, known additives such as plasticizers, heat stabilizers, processability improvers, ultraviolet absorbers and fillers, and other resins.
In this specification, such resins other than the thermoplastic resin (A) and the thermoplastic resin (B) are referred to as “third resin”.
Resin ".

In order to improve the mechanical properties of the film, a plasticizer or a polymer having flexibility may be added to the resin composition. However, when these materials are used, there is a possibility that the glass transition temperature is lowered and heat resistance is impaired, or that the transparency is impaired. For this reason, when using these plasticizers or flexible polymers, the amount of addition should be an amount which does not hinder the performance of the film. Preferably, it is 20% by weight or less in the resin composition. More preferably, it is 10% by weight or less, and still more preferably 5% by weight or less.

When the imide content of the thermoplastic resin (A) is high, specifically, for example, when the imide content of the thermoplastic resin (A) is 40 mol% or more, the resulting film Is hard and brittle, so adding a small amount of a plasticizer is effective because it can prevent stress whitening and tearing of the film. As such a plasticizer, a conventionally known plasticizer can be used. For example, aliphatic dibasic acid-based plasticizers such as di-n-decyl adipate and phosphate ester-based plasticizers such as tributyl phosphate can be exemplified.

The third resin is a resin other than the thermoplastic resins (A) and (B). The third resin may be a thermoplastic resin or a thermosetting resin. Preferably, it is a thermoplastic resin. In addition, the third resin may be a single resin or a blend of a plurality of types of resins. The amount used when the third resin is used is 30% by weight of the total amount of the resins used in the resin composition, that is, the total amount of the thermoplastic resins (A) and (B) and the third resin. Is preferably not more than 20% by weight, more preferably not more than 20% by weight, still more preferably not more than 10% by weight. Further, it is preferably at least 1% by weight of the total amount of the resin used,
It is more preferably at least 2% by weight, and even more preferably at least 3% by weight.

When the amount of the third resin is too large, the performance of the thermoplastic resins (A) and (B) is not sufficiently exhibited. In addition, when a resin having low compatibility with the thermoplastic resins (A) and (B) is used, the optical performance of the obtained film tends to decrease. When the amount of the third resin is too small, it is difficult to obtain the effect of adding the third resin.

Even when the third resin is used, the blending ratio of the thermoplastic resin (A) and the thermoplastic resin (B) is the same as the case where the third resin is not used. Preferably it is a ratio.

(Filler) If necessary, the film of the present invention may contain a filler for the purpose of improving the slipperiness of the film or for other purposes. As the filler, any conventionally known filler used for a film can be used. The filler may be inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include silicon oxide, titanium dioxide, aluminum oxide, and metal oxide fine particles such as zirconium oxide, calcined calcium silicate, hydrated calcium silicate,
Examples include silicate particulates such as aluminum silicate and magnesium silicate, as well as calcium carbonate, talc, clay, calcined kaolin, and calcium phosphate. Examples of organic fine particles include silicon-based resin,
Resin fine particles such as a fluorine resin, an acrylic resin, and a crosslinked styrene resin can be given.

The filler is added in a range that does not significantly impair the optical properties of the film. Preferably, it is 10% by weight or less in the resin composition.

(Ultraviolet absorber) The film of the present invention comprises
If necessary, an ultraviolet absorber can be contained.
When the film contains an ultraviolet absorber, the weather resistance of the film is improved. Further, the durability of a liquid crystal display device using the film can be improved, which is practically preferable. Any conventionally known ultraviolet absorber can be used for the film of the present invention. Specific examples of the ultraviolet absorber include 2- (2H-benzotriazol-2-yl) -p
A benzotriazole-based ultraviolet absorber such as -cresol and 2-benzotriazol-2-yl-4,6-di-t-butylphenol; 2- (4,6-diphenyl-
Examples include triazine-based ultraviolet absorbers such as 1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol, and benzophenone-based ultraviolet absorbers such as octabenzone.

Further, if necessary, a light stabilizer other than the ultraviolet absorber can be added to the film of the present invention. Specifically, for example, a benzoate light stabilizer such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate or bis (2,2-di-t-butylphenyl-3,5-hydroxybenzoate)
Light stabilizers such as hindered amine light stabilizers such as (2,6,6-tetramethyl-4-piperidyl) sebacate can be used.

(Production of Film) As a method of forming a film, any conventionally known method can be used. For example, there are a solution casting method and a melt extrusion method. Either of them can be adopted, but the melt extrusion method without using a solvent is preferable from the viewpoint of global environment, working environment, and production cost.

In the present specification, a film formed by the above-mentioned melt extrusion method is referred to as a melt-extruded film to distinguish it from a film formed by another method such as a solution casting method.

In a preferred embodiment, the thermoplastic resin to be used is preliminarily dried before film formation. Preliminary drying is performed, for example, using a hot-air drier or the like in the form of pellets of the raw material. Predrying is very useful because it can prevent foaming of the extruded resin.

The thermoplastic resin is supplied to an extruder. The thermoplastic resin heated and melted in the extruder is supplied to a T-die through a gear pump and a filter. The use of a gear pump is very useful because it improves the uniformity of resin extrusion and reduces thickness unevenness. The use of a filter is useful for removing foreign matters in the resin and obtaining a film excellent in appearance without defects.

In a further preferred embodiment, a sheet-like molten resin extruded from a T-die is sandwiched between two cooling drums and cooled to form an optical film.
It is particularly preferable that one of the two cooling drums is a rigid metal drum having a smooth surface and the other is a flexible drum having a metal elastic outer cylinder having a smooth surface and being elastically deformable. . By sandwiching a sheet-like molten resin extruded from a T-die between a rigid drum and a flexible drum and cooling to form a film, fine irregularities and die lines on the surface are corrected, and the surface becomes smooth. This is particularly useful because a film having a thickness unevenness of 5 μm or less can be obtained.

The cooling drum is sometimes called a “touch roll” or a “cooling roll”, and the term “cooling drum” in this specification includes these rolls.

When a sheet-like molten resin extruded from a T-die is cooled and formed into a film while being sandwiched between a rigid drum and a flexible drum, even if one of the drums is elastically deformable, Since the surface is also metal, when forming a thin film, the drum surfaces come into contact with each other and the drum outer surface is easily damaged.
Alternatively, the drum itself is easily damaged. Therefore, the thickness of the film to be formed is preferably at least 10 μm, more preferably at least 50 μm, further preferably at least 80 μm, particularly preferably at least 100 μm.

When a film is formed by cooling a sheet-like molten resin extruded from a T-die while sandwiching it between a rigid drum and a flexible drum, if the film is thick, the cooling of the film tends to be uneven. , Optical characteristics are likely to be non-uniform. Therefore, the thickness of the film is preferably 200 μm or less, more preferably 170 μm or less.

In the case of producing a thinner film, as an embodiment, a relatively thick raw material film is obtained by such sandwich molding, and then uniaxially or biaxially stretched to obtain a film having a predetermined thickness. It is preferred to produce As an example of the embodiment, after a raw material film having a thickness of 150 μm is produced by such sandwiching molding, an optical film having a thickness of 40 μm can be produced by biaxial stretching in the vertical and horizontal directions.

(Stretching) The stretched film according to the present invention is obtained by molding an amorphous thermoplastic resin into a raw material film in an unstretched state, and further performing uniaxial stretching. In the present specification, for convenience of explanation, a film before the resin composition is stretched after the resin composition is formed into a film shape is referred to as a “raw film” or an unstretched film.

By stretching, the mechanical properties are improved. In the case of a conventional film, it was difficult to avoid occurrence of a phase difference when a stretching treatment was performed. However, a film formed using the particularly preferred resin composition used in the present invention has an advantage that a retardation is not substantially generated even when a stretching treatment is performed.

The stretching of the film may be performed continuously immediately after forming the raw material film. Here, there is a case where the state of the “raw material film” exists only momentarily. When the film exists only momentarily, the momentary state from when the film is formed to when it is stretched is referred to as a raw material film. In addition, the raw material film may be in the form of a film enough to be stretched thereafter, and need not be in a perfect film state, and of course, does not have the performance as a completed film. Is also good.

If necessary, after forming the raw material film, the film may be temporarily stored or moved, and then the film may be stretched.

As a method for stretching the raw material film, any conventionally known stretching method can be adopted. In particular,
For example, there are transverse stretching using a tenter, longitudinal stretching using a roll, and sequential biaxial stretching in which these are sequentially combined. Also, a simultaneous biaxial stretching method in which the film is stretched in the machine and transverse directions at the same time can be adopted. A method of performing transverse stretching with a tenter after performing roll longitudinal stretching may be employed.

In the present invention, longitudinal stretching using a roll is preferred. Particularly preferred is longitudinal uniaxial stretching using a roll.

The film of the present invention can be used as a final product in the state of a uniaxially stretched film. Further, if necessary, the film may be further combined with a stretching step to obtain a biaxially stretched film. However, according to the present invention, even in the case of a uniaxially stretched film, almost the same performance as a biaxially stretched film can be obtained. This is particularly advantageous because sufficient film performance can be obtained.

(Width reduction index) The width reduction index a in the present invention is:

[0123]

(Equation 4)

Is defined. In the present invention, a preferable value of the width reduction index at the time of uniaxial stretching of the film is 0.4 or less. Preferably, it is 0.3 or less. More preferably, it is 0.2 or less. More preferably, it is 0.15 or less. Especially preferably, it is 0.1 or less.

If the width reduction index is too high, the mechanical strength tends to decrease in the direction perpendicular to the stretching direction of the film. For this reason, it is difficult to obtain sufficient handleability.
That is, when the film passes through the adhesive roll, when peeling or slitting, when manufacturing a film such as when winding or sandwiching the clip of the horizontal stretching machine, or during post-processing such as lamination with other materials Problems such as easy tearing of the film and tearing are likely to occur.

In the case of a crystalline thermoplastic resin, the necking phenomenon can be used in stretching, and in that case, the thickness accuracy is improved by stretching. On the other hand, in the case of the amorphous thermoplastic resin used in the present invention, since it is difficult to use the necking phenomenon during stretching, the width reduction index is controlled in the above range in order to maintain or improve the thickness accuracy. Is particularly important.

As a method of controlling the width reduction index, any method can be adopted as long as the preferable width reduction index is obtained.

Specifically, for example, there is a method of shortening the stretching section, that is, a method of shortening a distance between common tangents (a distance between stretching rolls) between a roll rotating at a low speed and a roll rotating at a high speed. Here, the stretching section refers to a distance between two points at which a force for stretching the film is applied to the film.

More specifically, for example, the stretching section (for example, the distance between rolls) is preferably 150 mm or less, more preferably 100 mm or less, further preferably 70 mm or less, particularly preferably 50 m or less.
m or less. If the stretching section is too long, it becomes difficult to control the width reduction index. The stretching section is preferably 10
mm or more, more preferably 20 mm or more. If the stretching section is too short, the film is likely to be stretched unevenly. In a preferred embodiment, the distance between the rolls is between 20 mm and 70 mm.

As a method of controlling the width reduction index,
A method using a cross guider for pulling a film in a running direction and a direction perpendicular to the running direction may be used.

In a roll-shaped film obtained by tenter transverse stretching, neck-in does not substantially occur. However, only transverse stretching tends to cause insufficient mechanical strength in the running direction of the film, and cracks and tears are very likely to occur in the production of the film. Also, cracks and tears are very likely to occur during post-processing, for example, when laminating with another film.

The stretching temperature and the stretching ratio of the film can be appropriately adjusted using the mechanical strength of the obtained film as an index. When the glass transition temperature of the film determined by the DSC method is Tg, the stretching temperature is preferably in the range of Tg−30 ° C. to Tg + 30 ° C.
More preferably, it is Tg-20 ° C to Tg + 20 ° C.
More preferably, it is in the range of Tg or more and Tg + 20 ° C. or less. If the stretching temperature is too high, the resulting film tends to be insufficiently improved in elongation, tear propagation strength, and resistance to rubbing fatigue, and the film tends to stick to rolls. Conversely, if the stretching temperature is too low, the haze of the stretched film tends to increase, and in extreme cases, the film tends to tear or break easily.

The stretch ratio of the film is defined by the ratio of the linear velocity of the roll rotating at a low speed to the linear velocity of the roll rotating at a high speed. That is, (drawing ratio) = (linear speed of high-speed roll) / (linear speed of low-speed roll). The preferred stretching ratio depends on the stretching temperature, but is selected in the range of 1.1 to 3 times. More preferably, it is 1.3 times to 2.5 times. More preferably, 1.
It is 5 times to 2.3 times.

By adjusting the thermoplastic resin (A) and the thermoplastic resin (B) to the above-mentioned preferable mixing range and selecting appropriate stretching conditions, substantially no birefringence is produced. It is possible to easily obtain a film having a small thickness non-uniformity without substantially reducing the light transmittance or increasing the haze. Preferably, 1.3 times or more,
More preferably, by stretching 1.5 times or more, the mechanical properties such as elongation, tear propagation strength, and resistance to rubbing fatigue of the film are significantly improved, and the thickness unevenness is 5 μm.
Or less, the birefringence is substantially zero, and the light transmittance is 85.
% Or more and a haze of 1% or less can be obtained.

The thickness of the stretched film according to the present invention is preferably from 10 μm to 200 μm, more preferably from 20 μm to 150 μm, and further preferably from 3 μm to 150 μm.
It is from 0 μm to 100 μm. In order to form a thicker film, a film exceeding 200 μm is required as an unstretched film. In such a case, the cooling of the film becomes non-uniform and the optical homogeneity is undesirably reduced. When a thinner film is formed, the draw ratio becomes excessively large, and there is an adverse effect such as deterioration of haze.
The glass transition temperature of the film of the present invention is preferably 80 ° C. or higher, more preferably 100 ° C. or higher. More preferably, it is 130 ° C. or higher. Although there is no particular upper limit of the glass transition temperature, an excessively high glass transition temperature makes the drawing process difficult,
Or there is a possibility that the cost of the stretching processing equipment will be high,
250 ° C. or lower is preferable, and 200 ° C. or lower is more preferable.

The light transmittance of the optical film of the present invention is:
It is preferably at least 85%, more preferably at least 88%. Further, the haze of the film is preferably 2% or less,
More preferably, it is 1% or less. More preferably,
0.5% or less.

The optical film of the present invention can be used as it is as a final product for various uses. Alternatively, it can be used for various applications by performing various processes. Utilizing particularly excellent optical homogeneity, transparency, low birefringence, etc., it is suitably used for known optical applications such as around an LCD device such as an optically isotropic film, a polarizer protective film or a transparent conductive film. be able to.

The optical film of the present invention can be subjected to a surface treatment on one or both sides of the film if necessary. Examples of the surface treatment method include corona treatment, plasma treatment, ultraviolet irradiation, and alkali treatment. In particular, when the surface of the film is subjected to surface processing such as coating, or when another film is laminated with an adhesive, the film should be subjected to a surface treatment as a means for increasing mutual adhesion. Is preferred. Corona treatment is a particularly preferred method. The preferred degree of surface treatment is 50 dyn / cm or more. The upper limit is not particularly defined, but is preferably 80 dyn / cm or less from the viewpoint of equipment for surface treatment.

Further, a coating layer such as a hard coat layer can be formed on the surface of the optical film of the present invention, if necessary. The optical film of the present invention can form a transparent conductive layer of indium tin oxide or the like by a sputtering method or the like with or without a coating layer. Also, it can be used as an electrode substrate of a touch panel.

(Application of Film) The optical film of the present invention can be used as it is as a final product for various applications. Alternatively, it can be used for various applications by performing various processes. Utilizing particularly excellent optical homogeneity, transparency, low birefringence, etc., it is suitably used for known optical applications such as an optically isotropic film, a polarizer protective film, a transparent conductive film, and the like around a liquid crystal display device. Can do things.

(Polarizer Protective Film) The optical film of the present invention can be used by being bonded to a polarizer. That is, it can be used as a polarizer protective film. Here, any conventionally known polarizer can be used as the polarizer. Specifically, for example, a polarizer can be obtained by adding iodine to stretched polyvinyl alcohol. A polarizing plate can be obtained by laminating the film of the present invention on such a polarizer as a polarizer protective film. The polarizer protective film is laminated on one or both sides of the polarizer. Generally, a polarizer protective film is laminated on both sides of the polarizer.

[0142]

EXAMPLES (Method of Measuring Physical Properties) Examples of the present invention will be described below. Before explaining the specific contents of the embodiment,
The measuring method of each physical property value shown as each experimental result is shown below.

<Thickness measuring method> A stylus type continuous film thickness gauge (Film Thickness Tester KG) manufactured by Anritsu Corporation
601B and an electronic micrometer K3001A). The thickness of the film cut into a width of 30 mm and a length of 200 mm or more was continuously measured in the width and length directions of the film except for 50 mm from both ends in the width direction of the film. The thickness unevenness was defined as a difference between the maximum value and the minimum value of the thickness.

<Haze> JIS K7105-1981
Was measured by the method described in 6.4.

<Light Transmittance> JIS K7105-19
The measurement was performed using light of 550 nm according to the method described in 5.5 of No. 81.

<Phase Difference in the Plane Direction> The phase difference was measured at a measurement wavelength of 514.5 nm using a microscopic polarization spectrophotometer (Oak Seisakusho: TFM-120AFT).

<Phase Difference in Thickness Direction> Using a microscopic polarization spectrophotometer (Oak Seisakusho: TFM-120AFT),
Measuring the angle dependence of the phase difference at a measurement wavelength of 4.5 nm,
nx, ny, nz are obtained. Separately, the thickness of the film was measured, and the retardation in the thickness direction was calculated using the following equation. [Phase difference in thickness direction] = | (nx + ny) / 2−nz |
× d <Unevenness of phase difference> Unevenness of phase difference was measured at five or more locations 1 cm apart, and the difference between the maximum value and the minimum value was determined.

<Mass Fatigue Resistance> MIT manufactured by Toyo Seiki Seisaku-sho, Ltd.
Folding Endurance Tester (FOLDING ENDURANCE)
TESTER) type D was measured according to JIS C5016. The measurement was performed with a width of 15 mm and a length of 2
Using a sample having a shape of 00 mm and an average thickness of 50 ± 5 μm, the sample was bent at 135 ° (R = 0.38). The resulting MD value indicates a numerical value when bent in the MD direction.

<Tear Propagation Strength> The tear propagation strength was measured according to JIS K7128 (trouser method) using an autograph manufactured by Shimadzu Corporation. Note that the measurement was performed using a film having an average thickness of 50 ± 5 μm and a tensile speed of 200 mm / min. Further, the resulting MD value indicates a numerical value when the film is torn in the MD direction.

<Glass transition temperature> Measured according to JIS K7121.

Hereinafter, the present invention will be described specifically with reference to Examples.

(Production Example 1) 65 parts by weight of an alternating copolymer composed of isobutene and N-methylmaleimide (N-methylmaleimide content: 50 mol%, glass transition temperature: 157 ° C.), and acrylonitrile content: 27% by weight 35 parts by weight of an acrylonitrile / styrene copolymer are dissolved in a methylene chloride solution so as to have a solid concentration of 15% by weight,
The film was continuously cast on a support and dried, and after the film was peeled from the support, it was further dried to obtain a long film.

(Example 1) The film of Production Example 1 was subsequently set at 142 ° C. and a distance between stretching rolls of 25 mm using a roll longitudinal uniaxial stretching machine, while controlling the width reduction index to be 0.15. And stretched 2.2 times. The thickness unevenness of the obtained film is 2 μm, the haze is 0.3%, the light transmittance is 91.6%, the phase difference in the plane direction of the film is 5 nm,
The phase difference unevenness in the plane direction of the film is 1 nm or less, the phase difference in the thickness direction is 6 nm, and the phase difference unevenness in the thickness direction is 1 n.
m or less. Also, the anti-rubbing fatigue was 54 times in the MD direction,
The TD direction was 204 times, and the tear propagation strength was 1.
The glass transition temperature was 12 N / mm, the TD direction was 2.00 N / mm, and the glass transition temperature was 138 ° C. This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. Further, the film was passed through an adhesive roll at a line speed of 3 m / min under a tension of 0.1 kg / cm. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in thickness accuracy, optical properties, and handling properties.

Comparative Example 1 The film of Production Example 1 was evaluated for its performance without stretching. The thickness unevenness of the film is 5 μm, the haze is 0.3%, and the light transmittance is 9
The phase difference in the plane direction of the film was 1.4 nm, the phase difference in the plane direction of the film was 1 nm or less, the phase difference in the thickness direction was 4 nm, and the phase difference in the thickness direction was 1 nm or less. The resistance to massage fatigue was 4 times in the MD direction, 5 times in the TD direction, and the tear propagation strength was 0.79 N / m in the MD direction.
m, TD direction is 0.73 N / mm, glass transition temperature is 1
38 ° C. When the film of Production Example 1 was slit with a cutter, the film frequently cracked when slitting.

As described above, the obtained film was excellent in optical properties, but was extremely poor in handleability.

(Production Example 2) The same resin as in Production Example 1 was previously pelletized by an extruder, dried at 100 ° C. for 5 hours, and then dried by using a 40 mm single screw extruder and a 400 mm width T die. Extruded at ℃ to obtain a film.

(Example 2) The film of Production Example 2 was subsequently set at 142 ° C. and a distance between stretching rolls of 40 mm using a roll longitudinal uniaxial stretching machine while controlling the width reduction index to be 0.25. And stretched 2.0 times.

The thickness unevenness of the obtained film is 2 μm, the haze is 0.3%, the light transmittance is 91.8%, the phase difference in the plane direction of the film is 5 nm, and the unevenness of the phase difference in the plane direction of the film is 1 nm or less. The phase difference in the thickness direction was 7 nm, and the unevenness in the thickness direction was 1 nm or less. The resistance to massage fatigue was 63 times in the MD direction, 177 times in the TD direction, the tear propagation strength was 1.29 N / mm in the MD direction, 1.87 N / mm in the TD direction, and the glass transition temperature was 138 ° C. . This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. In addition, the film is 0.1 kg / cm
Under a tension of 3 m / min at a line speed of 3 m / min. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in thickness accuracy, optical characteristics, and handling properties.

(Example 3) A stretched film was produced in the same manner as in Example 2 except that the distance between the stretching rolls was set to 60 mm and the film was stretched 2.3 times while controlling the width reduction index to be 0.30. I got

The thickness unevenness of the obtained film is 3 μm, the haze is 0.3%, the light transmittance is 91.5%, the phase difference in the plane direction of the film is 5 nm, and the unevenness of the phase difference in the plane direction of the film is 1 nm or less. The phase difference in the thickness direction was 8 nm, and the unevenness in the thickness direction was 1 nm or less. The resistance to massage fatigue was 57 times in the MD direction, 180 times in the TD direction, the tear propagation strength was 1.31 N / mm in the MD direction, 2.13 N / mm in the TD direction, and the glass transition temperature was 138 ° C. . This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. In addition, the film is 0.1 kg / cm
Under a tension of 3 m / min at a line speed of 3 m / min. As a result, no crack occurred in the film.

As described above, the obtained film was a film excellent in thickness accuracy, optical characteristics, and handleability.

Comparative Example 2 The film of Production Example 2 was evaluated without performing stretching. The thickness unevenness of the film is 5 μm, the haze is 0.3%, and the light transmittance is 9
1.7%, the phase difference in the plane direction of the film was 5 nm, the phase difference in the plane direction of the film was 1 nm or less, the phase difference in the thickness direction was 4 nm, and the phase difference in the thickness direction was 1 nm or less. The resistance to massage fatigue was 5 times in the MD direction, 7 times in the TD direction, and the tear propagation strength was 0.77 N / m in the MD direction.
m, TD direction is 0.75 N / mm, glass transition temperature is 1
38 ° C. When the film of Production Example 2 was slit with a cutter, the film frequently cracked when slitting.

As described above, the obtained film was excellent in optical properties, but was extremely poor in handleability.

(Comparative Example 3) After the film of Production Example 2 was produced, the film was successively set to 142 ° C and the distance between the stretching rolls to 200 mm using a roll longitudinal uniaxial stretching machine, and the width reduction index was set to 0.
The film was stretched 1.9 times while controlling to 50.

The thickness unevenness of the obtained film was 12 μm,
The haze is 0.5%, the light transmittance is 91.6%, the phase difference in the plane direction of the film is 5 nm, the unevenness of the phase difference in the plane direction of the film is 1 nm or less, the phase difference in the thickness direction is 7 nm,
The unevenness of the retardation in the thickness direction was 1 nm or less. Also,
The massaging fatigue resistance was 30 times in the MD direction, 171 times in the TD direction, the tear propagation strength was 0.75 N / mm in the MD direction, 1.84 N / mm in the TD direction, and the glass transition temperature was 138 ° C. This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. In addition, the film is 0.1 kg / cm
Under a tension of 3 m / min at a line speed of 3 m / min. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in optical properties and handleability, but was extremely poor in thickness accuracy.

(Production Example 3) In Production Example 2, an alternating copolymer (N-methylmaleimide) comprising isobutene and N-methylmaleimide was prepared.
Methylmaleimide content 50 mol%, glass transition temperature 15
7 ° C.) and an acrylonitrile content of 26 parts by weight.
Acrylonitrile / styrene copolymer (weight%)
A film was obtained in the same manner except that the amount was 0 parts by weight (I / P ratio = 2.46).

Example 4 The film of Production Example 2 was subsequently set at 142 ° C. and a distance between stretching rolls of 15 mm using a roll longitudinal uniaxial stretching machine while controlling the width reduction index to 0.08. Stretched 2.1 times.

The thickness unevenness of the obtained film was 2 μm, the haze was 0.3%, the light transmittance was 91.3%, the phase difference in the plane direction of the film was 5 nm, and the unevenness in the phase difference in the plane direction of the film was 1 nm. The thickness direction retardation was 7 nm, and the thickness direction unevenness was 1 nm. The resistance to massage fatigue was 64 times in the MD direction, 191 times in the TD direction, and the tear propagation strength was 1.27 N / mm in the MD direction and 1.83 in the TD direction.
N / mm, glass transition temperature was 138 ° C. This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. Also, the film was placed under a tension of 0.1 kg / cm,
It passed through the adhesive roll at a line speed of 3 m / min. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in thickness accuracy, optical characteristics, and handleability.

(Example 5) Distance between stretching rolls 100 mm
And a stretched film was obtained in the same manner as in Example 4, except that the film was stretched 1.9 times while controlling the width reduction index to be 0.35.

The thickness unevenness of the obtained film was 3 μm, the haze was 0.3%, the light transmittance was 91.2%, the phase difference in the plane direction of the film was 6 nm, and the unevenness in the phase difference in the plane direction of the film was 1 nm. The thickness direction retardation was 8 nm, and the thickness direction unevenness was 1 nm. The resistance to massage fatigue was 53 times in the MD direction, 185 times in the TD direction, and the tear propagation strength was 1.23 N / mm in the MD direction and 1.84 in the TD direction.
N / mm, glass transition temperature was 138 ° C. This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. Also, the film was placed under a tension of 0.1 kg / cm,
It passed through the adhesive roll at a line speed of 3 m / min. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in thickness accuracy, optical characteristics, and handling properties.

(Comparative Example 4) The performance of the film of Production Example 3 was evaluated without stretching. The thickness unevenness of the film is 5 μm, the haze is 0.4%, and the light transmittance is 9
The phase difference in the plane direction of the film was 0.9%, the phase difference in the plane direction of the film was 1 nm, the phase difference in the thickness direction was 5 nm, and the phase difference in the thickness direction was 1 nm. The resistance to massaging was 5 times in the MD direction and 6 in the TD direction.
Times, the tear propagation strength is 0.75 N / mm in the MD direction, T
0.77 N / mm in D direction, glass transition temperature 138 ° C
Met. When the film of Production Example 3 was slit with a cutter, the film frequently cracked when slitting.

As described above, the obtained film was excellent in optical properties, but was extremely poor in handleability.

(Production Example 4) A film was produced in the same manner as in Production Example 2 except that only an alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content: 50 mol%, glass transition temperature: 157 ° C) was used. I got

(Comparative Example 5) Using the film of Production Example 4, the stretching temperature was 160 ° C, and the distance between the stretching rolls was 40 mm.
And a stretched film was obtained in the same manner as in Example 2 except that stretching was performed while controlling the width reduction index to be 0.50.

The thickness unevenness of the obtained film was 10 μm,
The haze is 0.5%, the light transmittance is 90.8%, the phase difference in the plane direction of the film is 11 nm, the unevenness of the phase s difference in the plane direction of the film is 8 nm, and the phase difference in the thickness direction is 538 n.
m, unevenness of retardation in the thickness direction was 35 nm. The anti-rubbing fatigue was 32 times in the MD direction and 183 in the TD direction.
Times, the tear propagation strength is 0.78 N / mm in MD direction, T
2.18 N / mm in D direction, glass transition temperature is 157 ° C
Met. This film was slit using a leather cutter at a line speed of 3 m / min. As a result, no crack occurred in the film. 0.1 kg of film
/ Cm under a tension of 3 m / min at a line speed. As a result, no crack occurred in the film.

As described above, the obtained film was excellent in handling properties, but was extremely poor in thickness accuracy and optical characteristics.

Tables 1 and 2 below show the examples and comparative examples.

[0183]

[Table 1]

[0184]

[Table 2]

[0185]

According to the present invention, an optical film having excellent handling properties, thickness accuracy and optical characteristics is provided by stretching a film made of an amorphous thermoplastic resin in the longitudinal and uniaxial directions while controlling the width reduction index. Is done.

Specifically, according to the present invention, a film made of an amorphous thermoplastic resin is uniaxially stretched while controlling the width reduction index using a relatively inexpensive roll longitudinal uniaxial stretching machine or the like. Thereby, the mechanical strength such as the elongation of the film, the kneading fatigue resistance, and the tear propagation strength can be improved. In addition, handling properties during the production and post-processing of the film are greatly improved, and the occurrence of problems such as cracking and tearing of the film is greatly reduced. Further, the thickness accuracy can be greatly improved. Furthermore, a film is obtained in which birefringence hardly occurs and a retardation does not substantially occur.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08J 5/18 CER C08J 5/18 CER C08L 101/02 C08L 101/02 G02B 5/30 G02B 5/30 F term (reference) ) 2H049 BA02 BB22 BC03 BC09 BC22 4F071 AA14X AA22X AA34X AA36X AH19 BB06 BC01 4F210 AE10 AG01 AH73 QA03 QC02 QG01 QG18 4J002 BB101 BB141 BB171 BC062 BC082 BG09A02PB02A00A02A

Claims (7)

[Claims] 1. A method for producing an optically stretched film from a film resin composition containing an amorphous thermoplastic resin, comprising a step of uniaxially stretching an unstretched film in a machine direction.
Here, in the stretching step, the width reduction index a defined by the following equation is _{0 based on} the film width W ₀ before the longitudinal uniaxial stretching, the film width W after the longitudinal uniaxial stretching, and the longitudinal uniaxial stretching ratio Φ. .
The method, which is maintained at 4 or less. (Equation 1) 2. The method according to claim 1, wherein the stretching step is performed in a range of 10 mm to 150 m.
The method according to claim 1, wherein the stretching is performed in a stretching section of m or less. 3. The resin composition for a film according to claim 1, wherein (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain,
The method according to claim 1 or 2, further comprising (B) a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain. 4. The thermoplastic resin (A) has a repeating unit represented by the formula (1) and a repeating unit represented by the formula (2), and contains a repeating unit represented by the formula (1). And the content of the repeating unit of the formula (2) is 70 to 80 mol% based on the total repeating units of the thermoplastic resin (A). And the thermoplastic resin (B) has a repeating unit represented by the formula (3) and a repeating unit represented by the formula (4),
When the content of the repeating unit of the formula (3) is 20 to 50% by weight and the content of the repeating unit of the formula (4) is 50 to 80% by weight based on the total repeating units of the thermoplastic resin (B). The content of the thermoplastic resin (A) in the resin composition is 50 to 80% by weight based on the total of the amount of the thermoplastic resin (A) and the amount of the thermoplastic resin (B). And
The method according to claim 3, wherein the content of the thermoplastic resin (B) is 20 to 50% by weight. Embedded image (In the formula (1), R ¹ , R ² and R ³ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms.) (In the formula (2), R represents hydrogen and 1 carbon atom. And represents an alkyl group having from 18 to 18 or a cycloalkyl group having from 3 to 12 carbon atoms.) (In the formula (3), R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms.) (In the formula (4), R ⁶ and R ⁷ each independently represent R ⁸ represents hydrogen or an alkyl group having 1 to 8 carbon atoms;
Represents hydrogen, an alkyl group having 1 to 8 carbon atoms, a halogen group, a hydroxyl group, an alkoxy group, or a nitro group. ) 5. An optical film produced by the method according to claim 1. Description: 6. The film according to claim 5, wherein the produced optical film is a polarizer protective film. 7. The method according to claim 1, wherein the produced optical film is a polarizer protective film.