JP2002328232A - Film, protective film for polarizer and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical film in which a phase difference is hardly caused but the development of the phase difference and its wavelength dependence can be controlled by changing the composition ratio. SOLUTION: The film has <=3 nm phase difference for the light at 515 nm wavelength and <=5 nm phase difference in the thickness direction for the light at 515 nm wavelength. The value (A) defined by A=Re(442)-Re(780), wherein Re(442) is the phase difference for the light at 442 nm wavelength and Re(780) is the phase difference for the light at 780 nm wavelength, ranges from -3 nm to 3 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a transparent optical film. In particular, the present invention relates to films having excellent optical properties and being useful in various optical applications. Specifically, the present invention relates to a film having substantially no retardation. A film having substantially no retardation is useful for a polarizer protective film and the like.

[0002]

[Prior Art] In recent years, electronic devices have become smaller and smaller.
As typified by a notebook computer, a word processor, a mobile phone, and a portable information terminal, a liquid crystal display device utilizing the features of light weight and compactness has been widely used. In these liquid crystal display devices, various films (for example, polarizing films, etc.) are used to maintain the display quality. For applications such as portable information terminals and mobile phones, plastic liquid crystal display devices using a resin film instead of a glass substrate have been put to practical use in order to further reduce the weight of the liquid crystal display device.

[0003] A resin film used in a device that handles polarized light, such as a liquid crystal display device, is required not only to be optically transparent but also to have optical homogeneity. In the case of a film substrate for a plastic liquid crystal display device, not only is the phase difference represented by the product of birefringence and thickness required to be small, but also the phase difference of the film is unlikely to change even when an external stress is applied. Is required.

[0004] In the case of a resin film, it is known that the polarization and orientation of the molecules of the resin in the film are related to the phase difference. In order to obtain a film with a small retardation, it is necessary to use a resin having a molecular structure with a small polarization. Further, it is necessary to adjust the conditions for forming the film so that the molecular orientation is suppressed as much as possible.

[0005] Generally, engineering plastic resins such as polycarbonate, polyarylate, polysulfone, and polyethersulfone, and celluloses such as triacetyl cellulose are known as resins for films. When a film is formed using these resins, stress caused by back pressure for melting and flowing the resin, shrinkage when drying the solvent, heat shrinkage, or tension for transporting the film, etc. As a result, various stresses are applied to the film being formed. Because of the stress, molecules in the film are oriented, so that a retardation very easily remains in the film.

In order to solve these problems, attempts have been made to obtain a film using a resin having a small polarization.
For example, an attempt has been made to produce a film from an olefin resin represented by a cycloolefin resin.

[0007]

A film made of an engineering plastic resin such as the polycarbonate described above has a phase difference. Therefore, it is necessary to reduce the residual phase difference by providing a special process such as heating and annealing the film.

[0008] Even when a film having a reduced retardation is produced in this way, molecular orientation is often caused when the film is subsequently handled, and the retardation often occurs again. For example, when bonding a film to a polarizing plate, the polarizing plate often deforms. When the polarizing plate is deformed, stress is generated. This stress causes a molecular orientation and a phase difference. For this reason, when handling the above-mentioned film, sufficient care had to be taken. Further, even if sufficient attention is paid, there is a drawback that the probability of obtaining a final product having a small phase difference, that is, the yield rate is low.

In particular, when the above-mentioned film is used as a polarizer protective film, it is known that an undesired phase difference is generated in the film due to stress when the polarizer tries to shrink. Such a retardation adversely affects the polarization performance of the polarizing film.

[0010]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive research. As a result, the present inventors have found that the above problem can be solved by using a polymer composition having a specific structure and composition. Then, they have found that a retardation is unlikely to occur, and that the retardation and the wavelength dependence of the obtained film can be controlled by adjusting the composition ratio, thereby completing the present invention.

That is, the film of the present invention is a film comprising two or more kinds of thermoplastic resins, wherein at least one kind of thermoplastic resin is a thermoplastic resin having a positive birefringence, and at least one kind of thermoplastic resin is used. Consists of a thermoplastic resin having negative birefringence.

The film of the present invention has a retardation value of 3 nm or less with respect to light having a wavelength of 515 nm and a wavelength of 515 nm.
Has a phase difference of 5 nm or less in the thickness direction with respect to light, and the A value defined by the following equation is -3 nm to 3 nm.

A = Re (442) −Re (780) Formula Re (442): Retardation value for light having a wavelength of 442 nm Re (780): Retardation value for light having a wavelength of 780 nm The film of the present invention is preferably It contains (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain, and (B) a thermoplastic resin having at least a substituted or unsubstituted phenyl group and a nitrile group in a side chain. In this specification, a thermoplastic resin having a substituted or unsubstituted imide group in a side chain is referred to as “thermoplastic resin A”. A thermoplastic resin having at least a substituted or unsubstituted phenyl group and a nitrile group in a side chain is referred to as “thermoplastic resin B”.

In one embodiment, in the optical film, the thermoplastic resin (A) has a repeating unit represented by the formula (1) and a repeating unit represented by the formula (2), wherein The content of the repeating unit of the formula (1) is from 30 to 80 based on the total repeating units of the thermoplastic resin (A).
Mol%, and the content of the repeating unit of the formula (2) is from 70 to 70 based on the total repeating units of the thermoplastic resin (A).
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 total amount in the thermoplastic resin (B) is Based on the repeating unit, the content of the repeating unit of the formula (3) is 20 to 50% by weight, the content of the repeating unit of the formula (4) is 50 to 80% by weight, and the thermoplastic resin (A ) And the amount of the thermoplastic resin (B), the content of the thermoplastic resin (A) is 50 to 80% by weight, and the content of the thermoplastic resin (B) is 20 ~
50% by weight.

[0015]

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.)

[0016]

Embedded image (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.)

[0017]

Embedded image (In the formula (3), R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms.)

[0018]

Embedded image (In the formula (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. In one embodiment, the transparent film is stretched in at least one direction.

In another aspect, the present invention provides a polarizer protective film using the above stretched film.

In still another aspect, the present invention provides a polarizing plate having a polarizer and the above-mentioned polarizer protective film for protecting at least one surface of the polarizer.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The film of the present invention comprises (A) a thermoplastic resin A having a substituted or unsubstituted imide group in a side chain, and (B) at least a substituted or unsubstituted phenyl group and a nitrile group in a side chain. A thermoplastic resin B having
Made from a resin composition containing

The film of the present invention comprises the above thermoplastic resin A
And it is preferable to be manufactured only from thermoplastic resin B. However, the thermoplastic resin A and the thermoplastic resin B
Alternatively, a third resin may be used as necessary.

In the present specification, when the thermoplastic resin A is a copolymer resin, this copolymer is
Also referred to as “thermoplastic copolymer A”. Further, in the present specification, when the thermoplastic resin B is a copolymer, the copolymer is also referred to as “thermoplastic copolymer B”.

(Thermoplastic resin A) The thermoplastic resin A 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,
The main chain may be composed of only carbon, or may be 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.

Further, 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.

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.
Further, for example, after forming a main chain by polymerizing various monomers, a substituted or unsubstituted imide group may be introduced into a 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 at least one repeating unit derived from an olefin (alkene) and at least one repeating unit having a substituted or unsubstituted maleimide structure. Or higher multi-component copolymer).

The olefin / maleimide copolymer is
It can be synthesized by a known method. For example, Japanese Patent Application Laid-Open No. 5-591
No. 93, JP-A-5-195801, JP-A-6-195801
As described in JP-A-1336058 and JP-A-9-328523, a method of directly copolymerizing two kinds of monomers, a method in which a polymer obtained by polymerizing one monomer is It can be obtained by various methods such as a method of graft copolymerizing a monomer and a method of introducing an imide bond into a precursor polymer described below by a polymer reaction.

Particularly preferably, the thermoplastic resin A comprises a repeating unit derived from at least one type of olefin (alkene) represented by the following formula (1) and at least one type of repeating unit represented by the following formula (2). It contains a repeating unit having a substituted or unsubstituted maleimide structure.

[0032]

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.
The number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 2, and particularly preferably 1. )

[0033]

Embedded image (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. Preferably, it is 1-2, particularly preferably 1
It is. The carbon number of the cycloalkyl group is preferably from 3 to
9, and more preferably 4-7. Here, the content of the repeating unit of the formula (1) is preferably based on the total repeating units of the thermoplastic resin A,
20 to 70 mol%. More preferably, 40-60
Mol%, more preferably 45 to 55 mol%.

The content of the repeating unit of the formula (2) is preferably 30 to 80 mol% based on the total repeating units of the thermoplastic resin A. More preferably, 40 to 6
0 mol%, more preferably 45 to 55 mol%
It is. If the content of the repeating unit of the formula (2) is too small or too large, the heat resistance and mechanical strength of the obtained film are likely to be reduced.

It is particularly preferable that the thermoplastic resin A contains a repeating unit of the formula (1) and a repeating unit of the formula (2) as main components. In one embodiment, the sum of the repeating unit of the formula (1) and the repeating unit of the formula (2) is 50 mol% or more in the thermoplastic resin A, and is preferably 70% or more.
Mol% or more. More preferably, it is at least 80 mol%, even more preferably at least 90 mol%. In a preferred embodiment, the repeating unit of the formula (1) and 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 amount of the third repeating unit is preferably 30 mol% or less, more preferably 20 mol% or less, based on the total repeating units of the thermoplastic copolymer A. Yes, more preferably 1
It is at most 5 mol%, particularly preferably at most 10 mol%. When the number of the third repeating units is too large, 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 (2).

When the third repeating unit is used,
The third repeating unit is preferably at least 1 mol%, based on the total repeating units of the thermoplastic copolymer A,
It is more preferably at least 2 mol%, further preferably at least 3 mol%, 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.

In the case where 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 in the absence of the third repeating unit. Is preferred.

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

[0040]

Embedded image (Here, R ¹ , R ² and R ³ are the same as in the formula (1).) Examples of preferred olefin-based monomers include isobutene and 2-
Methyl-1-butene, 2-methyl-1-pentene, 2-
Methyl-1-hexene, 2-methyl-1-heptene, 2
-Methyl-1-heptene, 1-isooctene, 2-methyl-1-octene, 2-ethyl-1-pentene, 2-ethyl-2-butene, 2-methyl-2-pentene, and 2-methyl-2- Hexene and the like. Isobutene is most preferred. 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):

[0042]

Embedded image (Here, R is the same as in formula (2).) Preferred examples of such a maleimide compound include:
Maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-
Propylmaleimide, Nn-butylmaleimide, N-
s-butylmaleimide, Nt-butylmaleimide, N
-N-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, N -Cyclopentylmaleimide, N
N- such as cyclohexylmaleimide, N-cycloheptylmaleimide, and N-cyclooctylmaleimide
It is a substituted maleimide. N-methylmaleimide is most preferred.

These maleimide compounds may be used alone or in combination of two or more. As the maleimide compound, N-substituted maleimide is preferable. That is, a compound in which R is a group other than hydrogen in the formula (6) is particularly preferable. An example is N-methylmaleimide. In an N-substituted maleimide,
Examples of preferred N substituents are methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n- Octyl, lauryl, stearyl, cyclopropyl, cyclobutyl, cyclohexyl and the like.

(Third Repeating Unit) The thermoplastic copolymer A used in the present invention may comprise, as a third repeating unit, at least one other copolymerizable monomer in addition to the olefin unit and the maleimide unit. Can be contained. For example,
It can contain a vinyl monomer. Such copolymerizable monomers include acrylic monomers such as methyl acrylate and butyl acrylate, methacrylic monomers such as methyl methacrylate and cyclohexyl methacrylate, and vinyl acetate. Vinyl monomers such as vinyl ester monomers and vinyl ether monomers such as methyl vinyl ether; acid anhydrides having an unsaturated double bond such as maleic anhydride; styrene, α-methylstyrene, and p-methoxy Substituted or unsubstituted styrene monomers such as styrene are included. These third repeating units may be one kind of monomer, or two or more kinds of monomers may be combined to form a third repeating unit. By including the third repeating unit to such an extent that the optical properties of the film are not impaired, the heat resistance of the thermoplastic copolymer A can be improved or the mechanical strength can be increased.

(Method of Polymerizing Thermoplastic Resin A) The thermoplastic resin A can be produced, for example, by polymerizing the above olefin and a maleimide compound by a known polymerization method. This polymerization includes graft polymerization. Alternatively, the thermoplastic resin A is prepared by polymerizing the olefin with maleic acid or maleic anhydride according to a conventional method to produce a precursor polymer, and reacting this with an amine compound to convert the maleic anhydride moiety of the precursor polymer into an imide. It can also be manufactured by converting The precursor polymer may include the third repeating unit as necessary. Alternatively, the precursor polymer may include an unsubstituted or substituted maleimide. 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, the formula R-NH ₂
(However, R is the same as in the formula (2)). For example, methylamine, ethylamine, n-propylamine, i-propylamine, n-
Butylamine, s-butylamine, t-butylamine,
In addition to alkylamines such as cyclohexylamine and ammonia, and ammonia, dimethylurea, diethylurea and the like can be preferably used. Also in this case, a thermoplastic resin having the repeating unit of the above formula (1) and the repeating unit of the formula (2) can be 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 thermoplastic copolymer containing at least one olefin unit in which R ³ is a methyl group. These production methods are described in, for example, JP-A-5-59193, JP-A-5-195801, and JP-A-6-136558.
And JP-A-9-328523.

Here, in the present specification, the term "unit" for a monomer means 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"
The residue remaining after one olefin monomer used is polymerized.

More preferably, the thermoplastic copolymer A
Contains an N-methylmaleimide unit as a maleimide unit and an isobutylene unit as an olefin unit. The thermoplastic copolymer A is particularly preferably an alternating copolymer of N-substituted maleimide and isobutene.

The thermoplastic resin 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 resin A preferably has a weight average molecular weight of 5 × 10 ⁶ or less. More preferably,
5 × 10 ⁵ or less.

The glass transition temperature of the thermoplastic resin A is 80
C. or higher is preferred from the viewpoint of heat resistance. It is more preferably at least 100 ° C, and even more preferably at least 130 ° C.

The preferable content of the imide group is determined by using the above-mentioned thermoplastic resin A, which is 40 to 80 mol% of the total amount of the repeating units in the thermoplastic resin A, as the abundance of the imide group-containing repeating unit. The resulting film is
It has the property of relatively poor flexibility and easy tearing.
Above all, a film made of an isobutylene / substituted maleimide copolymer is particularly poor in flexibility and easily tears. However, by blending thermoplastic resin A (for example, acrylonitrile-styrene copolymer) with thermoplastic resin A, the mechanical properties of the film can be improved.

(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. Preferably, the backbone is
It 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 by polymerizing a monomer having a substituted or unsubstituted phenyl group. 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 to a 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. Also, for example, after polymerizing various monomers to form a main chain,
A nitrile group may be introduced into the 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 preferably contains 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 polymer (binary or ternary or higher multi-component copolymer). Therefore, an acrylonitrile-styrene copolymer can be preferably used.

(Nitrile Compound) As the unsaturated nitrile compound, any compound having a cyano group and a reactive double bond can be used. Preferred examples differ depending on the thermoplastic resins A and B used.

Preferred examples of the unsaturated nitrile compound constituting the above-mentioned preferred thermoplastic copolymer B include, for example, α-substituted unsaturated nitriles such as acrylonitrile and methacrylonitrile, and α, such as fumaronitrile. It is a nitrile compound having a β-disubstituted olefinically unsaturated bond.

(Styrene Compound) As the styrene compound, any compound having a phenyl group and a reactive double bond can be used. Preferred examples differ depending on the thermoplastic resins A and B used.

Examples of the styrene compound constituting the preferable thermoplastic copolymer B include, for example, an unsubstituted or substituted styrene compound such as styrene, vinyltoluene, methoxystyrene or chlorostyrene;
An α-substituted styrene compound such as methylstyrene can be used.

In a particularly preferred embodiment, the thermoplastic resin B contains an unsaturated nitrile unit represented by the following formula (3) and a styrene-based unit represented by the following formula (4).

[0064]

Embedded image (In the formula (3), R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms. The carbon number of the alkyl group is preferably 1 to 4, more preferably 1-2.)

[0065]

Embedded image (In the formula (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, a hydroxyl group, an alkoxy group or a nitro group. The carbon number of the alkyl group is preferably 1 to 4, more preferably,
1 to 3. More preferably, it is 1-2. The carbon number of the alkoxy group is preferably 1 to 20, more preferably 1 to 8, and still more preferably 1 to 8.
4. ).

Preferred examples of the unsaturated nitrile compound constituting the above-mentioned preferred thermoplastic copolymer B are an α-substituted unsaturated nitrile and a nitrile compound having an α, β-disubstituted olefinically unsaturated bond. Examples of the α-substituted unsaturated nitrile include acrylonitrile and methacrylonitrile. Examples of the nitrile compound having an α, β-disubstituted olefinically unsaturated bond include fumaronitrile. More preferably, the unsaturated nitrile compound is acrylonitrile.

Preferred examples of the styrene compound constituting the above thermoplastic copolymer B include an unsubstituted or substituted styrene compound and an α-substituted styrene compound. Examples of unsubstituted or substituted styrenic compounds include styrene, vinyltoluene, methoxystyrene and chlorostyrene. Examples of the α-substituted styrene-based compound include α-methylstyrene. In a more preferred embodiment, the styrenic compound is styrene.

Based on the total repeating units in the thermoplastic resin B, the repeating units of the formula (7)
To 70% by weight, more preferably 20 to 60% by weight.
And more preferably 20 to 50% by weight. Particularly preferably, the content is 20 to 40% by weight. Most preferably, it is 20 to 30% by weight.

Based on the total repeating units in the thermoplastic resin B, the repeating unit of the formula (8) is preferably 30
To 70% by weight, more preferably 40 to 80% by weight.
And 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.

When the repeating unit of the formula (7) is 20 to 30% by weight and the repeating unit of the formula (8) is 70 to 80% by weight, very preferable results are obtained.

If the amount of the styrene-based or nitrile-based repeating unit is too large, the compatibility with the thermoplastic resin A becomes poor, the transparency of the obtained film tends to decrease, and the haze tends to increase.

It is particularly preferable that the thermoplastic copolymer B contains an unsaturated nitrile unit and a styrene-based 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 copolymer B. It is more preferably at least 80% by weight, further preferably at least 90% by weight, particularly preferably at least 95% by weight. Of course, it may be 100% by weight.

It is particularly preferable that the thermoplastic copolymer B contains an unsaturated nitrile unit and a styrene-based unit as main components. In one preferred embodiment, the sum of the repeating unit of the formula (7) and the repeating unit of the formula (8) is 100%. The total of the unsaturated nitrile units and the styrene units is preferably at least 70% by weight of the thermoplastic copolymer B. It is more preferably at least 80% by weight, further preferably at least 90% by weight, particularly preferably at least 95% by weight. However, if necessary, a third
May be used.

(Third Repeating Unit) In addition to the above-mentioned nitrile unit and styrene-based unit, thermoplastic copolymer B
May contain other copolymerizable monomers as necessary. Such a third repeating unit preferably includes an acrylic monomer such as butyl acrylate and an olefin monomer such as ethylene and propylene. By copolymerizing one or two or more of these monomers, the flexibility of the obtained film can be improved. Also, as the third repeating unit, N-substituted maleimide can be used. By using an N-substituted maleimide, particularly phenylmaleimide, as a copolymer component, the heat resistance of the resin can be improved.

When the third repeating unit is used, the amount of the third repeating unit is preferably 30% by weight or less, more preferably 20% by weight or less, based on the weight of the thermoplastic copolymer B. It is more preferably at most 15% by weight, particularly preferably at most 10% by weight. Third
When there are too many repeating units, it is difficult to sufficiently obtain the performance of the repeating unit represented by the above formula (7) and the repeating unit represented by the formula (8).

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, still more preferably at least 3% by weight, particularly preferably at least 3% by weight, based on the weight of the thermoplastic copolymer B. Is 5% by weight or more. 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 (7) and the repeating unit of the formula (8) is the same as that when the third repeating unit does not exist. Is preferred.

(Method of Polymerizing Thermoplastic Resin B) The thermoplastic resin B can be obtained by directly copolymerizing the above-mentioned monomers. One of the polymer of the styrene compound and the polymer of the unsaturated nitrile compound may be graft-copolymerized with the other. Further, a preferable resin can be obtained by graft-polymerizing a styrene compound and an unsaturated nitrile compound to an acrylic polymer having rubber elasticity.

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

The thermoplastic resin 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 resin B preferably has a weight average molecular weight of 5 × 10 ⁶ or less. More preferably,
5 × 10 ⁵ or less.

The content of the unsaturated nitrile repeating unit in the thermoplastic resin is preferably from 20 to 60% by weight.
More preferably, it is 20 to 50% by weight. Further, the content of the styrene-based repeating unit is preferably from 40 to 80% by weight, and more preferably from 50 to 80% by weight. In particular,
When the content of the unsaturated nitrile type repeating unit is 20 to 30% by weight and the content of the styrene type repeating unit is 70 to 80% by weight, more preferable results are obtained. When there are too many styrene-based repeating units or nitrile-based repeating units, the phase difference due to the orientation of the molecules in the film tends to increase. In addition, the wavelength dependency tends to increase. Further, the compatibility with the above-mentioned thermoplastic resin A tends to decrease, and the haze of the obtained film tends to increase.
Therefore, when there are too many styrene-based repeating units or nitrile-based repeating units, it is difficult to obtain a practical transparent film.

(Preparation 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 as long as the mixture can be put into a film forming machine. Any known method can be adopted.

For example, thermoplastic resin A and thermoplastic resin B
And a method of obtaining a resin composition by simply mixing the above and a method of obtaining a resin composition by hot-melt kneading thermoplastic resins A and B.

(Ratio between Thermoplastic Resins A and B) The ratio between the thermoplastic resins A and B used in the film of the present invention is selected according to the phase difference required for the target film. This is because the ratio of the thermoplastic resin A to the thermoplastic resin B greatly changes the ease of occurrence of the retardation, and the retardation of the finally obtained film greatly varies.

(Production of Film) A method for producing a film will be described below.

By appropriately selecting the mixing ratio of the thermoplastic resin A and the thermoplastic resin B, it is possible to obtain a film having substantially no retardation even when the molecules are oriented by the stress applied to the film. That is, it is possible to obtain a film having substantially no retardation even when stretched. In other words, a stretched film having substantially no retardation can be obtained. A preferable compounding ratio exhibiting such characteristics depends on the types of the thermoplastic resin A and the thermoplastic resin B. Generally, the ratio (I / P ratio) 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 is 0.7 or more. Preferably, it is 0.9 or more, 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.

The mixing ratio of the thermoplastic resin A and the thermoplastic resin B is generally preferably such that the content of the thermoplastic resin A is 50 to 80% by weight of the total amount of the resin in the film. The content is more preferably 55 to 75% by weight, and still more preferably 55 to 70% by weight. The content of the thermoplastic resin B is preferably 20 to 50% by weight, more preferably 25 to 45% by weight, even more preferably 30 to 50% by weight of the total amount of the resin in the film.
~ 45% by weight. .

When the amount of the thermoplastic resin A or B is too large, the phase difference tends to increase when the film is formed into a stretched film.

When the thermoplastic resin A is a copolymer mainly composed of isobutylene and N-methylmaleimide and the thermoplastic resin B is a copolymer mainly composed of acrylonitrile and styrene, the content of acrylonitrile is The content is preferably 20 to 50% by weight, more preferably 25 to 40% by weight. More preferably, it is 26 to 29% by weight. Further, the content of styrene is preferably set to 50 to 80% by weight,
More preferably, the content is 60 to 75% by weight. 71-7
More preferably, it is 4% by weight.

In particular, when the content of acrylonitrile is 26 to
29% by weight, and the styrene content is 71 to 74%.
By setting the amount by weight, the thermoplastic resin B exhibits good compatibility with the thermoplastic resin A in a composition range of 0 to 80% by weight.
In the above-mentioned composition, good compatibility between the thermoplastic resin A and the thermoplastic resin B is shown in a wide range. Then, a stretched film having an extremely small retardation in both the plane direction and the thickness direction of the film can be obtained. The weight ratio of thermoplastic resin A: thermoplastic resin B is 50:50 to 80:20.
Is preferred. 55:45 to 75:25 is more preferred,
55:45 to 70:30 is more preferred.

By appropriately selecting such a preferable composition, a stretched film having substantially no birefringence can be obtained. Further, a film having a high total light transmittance and a small haze can be obtained. Thermoplastic resin A
This is because if the composition ratio of the resin and the thermoplastic resin B is appropriately adjusted, the phase difference due to the orientation of the molecules in the obtained film can be reduced.

That is, by having the composition described above,
The phase difference in the plane direction of the film can be reduced.
Specifically, for example, preferably, the retardation in the planar direction of the film is 3 nm or less for light having a wavelength of 515 nm,
More preferably, it is 2 nm or less. The phase difference in the thickness direction with respect to light having a wavelength of 515 nm is 5 nm or less, and more preferably 4 nm or less. Further, the phase difference value Re (442) in the planar direction with respect to the light having a wavelength of
The phase difference value Re (78 in the plane direction for light of 80 nm
0) can be controlled to -3 to 3 nm,
More preferably, it can be controlled to -2 nm to 2 nm. In addition, a transparent film having a light transmittance of 85% or more, more preferably 88% or more, further preferably 90% or more, and a haze of 2% or less, preferably 1% or less can be obtained. In a particularly preferred embodiment, the haze can be controlled to 0.5% or less.

Light transmittance is 85% or more and haze is 2
% Can be used as a high-performance film for various optical applications.

(Production of Resin Composition) The resin composition used in the present invention may contain, if necessary, a known additive such as a plasticizer, a heat stabilizer, a processability improver, an ultraviolet absorber, or a filler; A resin other than the thermoplastic resins A and B may be contained. In this specification, such
Resins other than thermoplastic resin A and thermoplastic resin B,
Also referred to as “third resin”.

In a preferred embodiment, the sum of thermoplastic resin A and thermoplastic resin B is 100% by weight. However, the third resin may be used if necessary.

In order to improve the mechanical properties of the unstretched film, a plasticizer or a polymer having flexibility may be added to the resin composition for preparing the film. 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 10% by weight or less in the resin composition. More preferably, it is 5% by weight or less, and still more preferably 3% by weight or less.

When the imide content of the thermoplastic resin A is high, specifically, for example, when the content of the maleimide unit of the thermoplastic resin A is 40 mol% or more,
Since the resulting film tends to be hard and brittle, it is effective to add a small amount of a plasticizer since stress whitening and tearing of the film can be prevented. As such a plasticizer, a conventionally known plasticizer can be used. For example,
Examples thereof include aliphatic dibasic acid-based plasticizers such as di-n-decyl adipate and phosphate ester-based plasticizers such as tributyl phosphate.

The third resin is the thermoplastic resin A
And resins other than 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 or less 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 20% by weight or less, more preferably 10% by weight or less. Further, it is preferably at least 1% by weight of the total amount of the resin used, more preferably at least 2% by weight, further preferably at least 3% by weight.

When the amount of the third resin is too large, it is difficult for the thermoplastic resins A and B to exhibit their performance sufficiently. Also,
If a large amount of resin having low compatibility with the thermoplastic resins A and B is used, the optical performance of the obtained film is likely to deteriorate. 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 mixing ratio of the thermoplastic resin A and the thermoplastic resin B is
As in the case where the third resin is not used, the ratio is preferably the above-described ratio.

(Production of Film) As a method for forming the above resin composition into a film form, any conventionally known method can be used. For example, a solution casting method, a melt molding method and the like can be mentioned. Any of them can be adopted. Examples of the melt molding method include a melt extrusion method and an inflation method.

In a preferred embodiment, the resin composition to be used is pre-dried before forming the film.
Predrying is very useful because defects such as foaming of the film can be prevented.

When the film is formed, the film may be formed using a resin composition obtained by simply mixing the thermoplastic resin A and the thermoplastic resin B. The thermoplastic resin A and the thermoplastic resin B may be previously melt-kneaded to obtain a material in the form of a pellet or the like, and then formed into a film shape using the material in the form of a pellet or the like.

(Melt Forming Method) Since the film of the present invention has a feature that a retardation due to molecular orientation during processing is hardly produced, a method of forming a film by a melt forming method is also a preferable method.

In the case of forming a film by a melt forming method, any known method can be employed. For example, a melt extrusion method such as a T-die method or an inflation method can be employed. In addition, a calendering method, a hot pressing method, an injection molding method, or the like may be employed. A melt molding method using a T-die is preferred because a wide film having good thickness accuracy can be easily obtained.

(Solution casting method) The solution casting method is also a preferable method in that a film having extremely uniform thickness accuracy can be obtained. According to the solution casting method, a film free from defects such as die lines can be obtained. Further, a film having a small variation in film thickness can be easily obtained. For example, a film having a thickness variation of 5% or less can be easily obtained. Further, an optically isotropic film having a small retardation can be easily obtained. Note that casting is also referred to as casting in this specification.

Solvents that can be used in the solvent casting method include
It can be selected from known solvents. Halogenated hydrocarbon solvents such as methylene chloride and trichloroethane are preferred solvents because they readily dissolve the thermoplastic resin A and the thermoplastic resin B and have low boiling points. In addition, a highly polar non-halogen solvent such as dimethylformamide and dimethylacetamide can also be used. Further, aromatic solvents such as toluene, xylene and anisole, cyclic ether solvents such as dioxane, dioxolan, tetrahydrofuran and pyran, and ketone solvents such as methyl ethyl ketone can be used. These solvents may be used alone. Also, a plurality of types may be mixed and used.

When a film is formed by the solution casting method, the thermoplastic resin A and the thermoplastic resin B are dissolved in the solvent. The thermoplastic resin A and the thermoplastic resin B used in the above-mentioned film of the present invention easily give a substantially uniform solution by being blended in the above-mentioned solvent with the above-mentioned appropriate composition. Before dissolving, the thermoplastic resins A and B may be previously melt-kneaded and formed into a shape such as a pellet, and then dissolved in a solvent.

The resin concentration in the solution is preferably from 1% by weight to 90% by weight, more preferably from 5% by weight to 7% by weight.
0% by weight, more preferably 10% by weight to 50% by weight.
% By weight.

Next, the obtained solution is cast on a support. As the casting method, any conventionally known method can be used. As a preferable support used at the time of casting, an endless belt made of stainless steel may be used. Alternatively, a film such as a polyimide film or a polyethylene terephthalate film can be used.

Next, the obtained intermediate product is dried to obtain a film. In one embodiment, the intermediate product obtained by casting may be dried on a support until the residual solvent amount is 1% or less. In yet another embodiment, once the solvent has been dried until the intermediate product is self-supporting, it can be released from the support. If necessary, after the film obtained by drying to have self-supporting property is peeled off from the support, it can be further dried.

As a drying method, any conventionally known drying method can be used. Specifically, for example, a float method, a tenter or a roll conveying method can be used.

(Mass Fatigue Resistance) According to the present invention, a film having good mass fatigue resistance can be obtained. The resistance to massage fatigue is JIS
It can be measured according to C5016. For example, Toyo Seiki Seisakusho Co., Ltd., MIT rub-resistant fatigue tester (FO
LDING ENDURANCE TESTER) type D or the like can be used as the measuring device. The resistance to rubbing fatigue of the film is preferably 30 times or more. More preferably, it is 50 times or more, and further preferably, 100 times or more. Especially preferably, it is 150 times or more.

In the present specification, if the above-mentioned rubbing fatigue resistance is obtained in at least one direction in the plane of the film, the film is said to have the rubbing fatigue resistance. It is preferable to have the above-mentioned good anti-rubbing fatigue resistance (that is, 30 times or more, 50 times or more, 100 times or more, or 150 times or more) in two directions orthogonal to each other in the film plane.

In the present specification, unless otherwise specified, the term "rubbing fatigue resistance" refers to the resistance to rubbing fatigue of a film having a thickness of 50 μm. Alternatively, in the case of a film having a thickness other than 50 μm, the term refers to the kneading fatigue resistance converted to a film having a thickness of 50 μm. That is, in the case of a film other than 50μ, the composition and stretched state of the film are exactly the same, and only the thickness is changed to 50μ. The value of the resistance to rubbing fatigue. For example, if the thickness is 30
If there is a film of μ, except that the thickness was changed to 50μ, a film having the same composition and stretched state of the material was produced, and the result of evaluation with the 50μ film was evaluated for the 30μ film. It is the value of resistance to massage fatigue.

(Tear Propagation Strength) According to the present invention, a film having good tear propagation strength can be obtained. The tear propagation strength can be measured according to JIS K7128 (trouser method). As the measuring device, for example, an autograph manufactured by Shimadzu Corporation can be used. The tear propagation strength of the film is preferably at least 150 gf / mm. More preferably, 1
It is 80 gf / mm or more. More preferably, 200
gf / mm or more.

In the present specification, if the above-mentioned tear propagation strength is obtained in at least one direction in the plane of the film, the film is said to have the tear propagation strength. In two directions perpendicular to each other in the plane of the film, the preferred tear propagation strength (ie, 150
gf / mm or more, 180 gf / mm or more, or 20
0 gf / mm or more).

(Stretched) The unstretched film obtained from thermoplastic resin A and thermoplastic resin B usually has low mechanical strength in many cases. In particular, the resistance to rubbing fatigue, which indicates the durability against repeated bending, is often about 10 times or less. Further, the tear propagation strength is often about 100 to 120 gf / mm. For this reason, unstretched wide films are somewhat disadvantageous in terms of industrial handling. However, the present inventors have found that stretching the films significantly improves their mechanical strength, as described above. In the case of such a composition, even after the film is stretched to improve the tear propagation strength and the kneading fatigue resistance, the retardation does not increase. For this reason, stretching a film having the thermoplastic resin A and the thermoplastic resin B is one of the particularly preferred embodiments of the present invention.

Stretching the film improves the resistance to kneading fatigue against bending in the stretching direction. Further, when the film is stretched, the tear propagation strength in a direction orthogonal to the stretching direction is improved. Therefore, when a film having an improved tear propagation strength in the film width direction is required in a roll-shaped film, it is generally preferable to perform longitudinal stretching. In order to improve the tear propagation strength in the machine direction (longitudinal direction) of the film, it is preferable to perform transverse stretching. To improve in both directions,
Preferably, biaxial stretching is performed. Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. Simultaneous biaxial stretching is particularly preferred because it can improve these mechanical properties uniformly in the plane of the film. By adjusting the stretching in both directions at the time of biaxial stretching to offset the retardation caused by each stretching, the in-plane retardation can be further reduced.

As the stretching method, any conventionally known stretching method can be adopted. A hot stretching method is preferred.
It may be uniaxial stretching or biaxial stretching. Films using thermoplastic resins A and B are less likely to exhibit retardation during stretching than conventional polycarbonates. Therefore, in general, the stretching ratio is made larger than in the case where the conventional polycarbonate is stretched. Therefore, longitudinal uniaxial stretching, in which a large stretching ratio can be easily realized, is preferred. Further, when optical uniaxiality of the obtained retardation film is important, free end longitudinal uniaxial stretching is a particularly preferred stretching method.

It is also possible to control the three-dimensional refractive index of the film by performing a special biaxial stretching as disclosed in Japanese Patent Application Laid-Open No. 5-157911. When a retardation is imparted, a film using the thermoplastic resins A and B does not easily exhibit a retardation due to orientation, and thus has an advantage that the in-plane retardation variation of the obtained film can be reduced.

As the stretching temperature and the stretching ratio, optimal values can be adopted using the tear propagation strength of the obtained film as an index. Generally, the stretching ratio is 1.1 to 3 times.
Preferably it is twice. More preferably 1.3 times or more
2.5 times. More preferably, 1.5 times to 2.3 times.
It is twice.

When the thermoplastic resin A and the thermoplastic resin B are in the above-mentioned preferable composition ranges, by selecting appropriate stretching conditions, the film can be formed without substantially lowering the light transmittance and the haze. It is possible to stretch. In particular, 1.3 times or more, more preferably 1.times.
By stretching by 5 times or more, the tear propagation strength and the resistance to rubbing fatigue of the film are greatly improved, and the film having a high light transmittance (for example, 85% or more) and a small haze (for example, 1% or less) can be obtained. Obtainable.

The stretching temperature is preferably set at DS
The glass transition temperature of the film obtained by the method C is selected from the range of (Tg−30) ° C. to (Tg + 30) ° C. as Tg. A particularly preferred stretching temperature is (Tg-2
0) ° C to (Tg + 20) ° C. Stretching in an appropriate temperature range can reduce or prevent film whitening during stretching. Further, the retardation variation of the obtained retardation film can be reduced. If the stretching temperature is too high, the resulting film tends to have insufficient improvement in tear propagation strength and resistance to rubbing fatigue. Further, the stretching ratio may be too large, and industrial implementation may be difficult. Conversely, when the film is stretched at an excessively low temperature, the haze of the stretched film tends to increase. In extreme cases, process problems such as tearing of the film are likely to occur.

As the stretching method, a transverse stretching using a tenter, a longitudinal stretching using a hot roll, a free-end uniaxial stretching, a sequential combination of these, a sequential biaxial stretching, and a simultaneous stretching in the longitudinal and transverse directions are performed. A known stretching method such as simultaneous biaxial stretching can be used.

The characteristics of the film of the present invention will be described below.

(Thickness of Film) The thickness of the film of the present invention is preferably from 20 μm to 300 μm, more preferably from 30 μm to 200 μm. More preferably, it is 50 μm to 100 μm.

(Light Transmittance and Haze) The light transmittance of the film is preferably 85% or more, more preferably
It is at least 88%, more preferably at least 90%. The haze of the film is preferably 2% or less, more preferably 1% or less.

(Birefringence) Whether the birefringence is positive or negative can be evaluated by a change in the refractive index in the stretching direction which is developed by stretching the film under a certain condition. When the refractive index of the film in the stretching direction is nx, the birefringence is positive when nx after stretching is larger than nx before stretching, and when nx after stretching is smaller than nx before stretching. Is defined as having negative birefringence.

The sign of the birefringence is determined by the film forming method,
It is determined by the resin composition without depending on the thickness.

(Retardation) The retardation of the film of the present invention is 3 nm or less with respect to light having a wavelength of 515 nm. More preferably, it is 2 nm or less. Further wavelength 780 nm
The absolute value of the difference between the phase difference value for the light having a wavelength of 442 nm and the phase difference value for the light having a wavelength of 442 nm is 3 nm or less. It is more preferably at most 2.5 nm, even more preferably at most 2 nm.

As described above, by setting the thermoplastic resins A and B to the above specific composition, an optically transparent film having a high light transmittance and a small haze can be obtained. The obtained film is characterized in that a retardation due to molecular orientation due to stress or the like acting on the film is unlikely to be developed, and the retardation is small over a visible light region.

(Surface Treatment Method) The above-mentioned thermoplastic resin A
The film having (B) and (B) may be subjected to a surface treatment as necessary. The surface treatment can be performed at any timing after the film is formed. If it is an unstretched film, a surface treatment is performed after the film is formed. In the case of a uniaxially stretched film, the surface treatment may be performed before stretching or after stretching. In the case of a simultaneously biaxially stretched film, the surface treatment may be performed before stretching or after stretching. In the case of a sequentially biaxially stretched film, the surface treatment may be before the first stretch, after the first stretch and before the second stretch, or after the second stretch. It may be. In the case of a stretched film, it is generally preferable to perform a surface treatment after stretching.

As the surface treatment method, any conventionally known method can be used. For example, electrical treatment such as corona discharge treatment or spark treatment, plasma treatment under low pressure or normal pressure, ultraviolet irradiation treatment in the presence or absence of ozone, acid treatment with chromic acid, flame treatment, and silane-based A primer treatment such as a primer treatment or a titanium-based primer treatment is exemplified.

(Use) The film of the present invention may be used as it is as a final product for various uses. Alternatively, various types of processing may be further performed to use for various purposes. Specifically, for example, for an optically isotropic film or a polarizing protective film, it can be suitably used for optical uses such as around a liquid crystal display device.

The above-mentioned film having substantially no retardation is suitably used as an optically isotropic film or a polarizing protective film.

The preferred use of the transparent film of the present invention is as follows:
An optically isotropic film, another preferred application is a retardation film. The optically isotropic film is further applied to various uses. One such preferred use is as an electrode substrate for a plastic liquid crystal display or a resistive touch panel. Another preferred application is a polarizer protective film.

When the transparent film of the present invention is used as a polarizer protective film, for example, a polarizer can be obtained by adding iodine or a dye to a stretched polyvinyl alcohol film. A polarizing plate can be obtained by bonding the film of the present invention to a polarizer using an appropriate adhesive.

The polarizer protective film is laminated on one side or both sides of the polarizer. Generally, a polarizer protective film is laminated on both sides of the polarizer.

Although it depends on the kind of the adhesive, the film of the present invention having been subjected to the surface treatment has an adhesive strength with polyvinyl alcohol of preferably at least 50 kg / cm ² , more preferably at least 100 kg / cm ² , especially Preferably 20
It can be set to 0 kg / cm ² or more. In particular, since the film of the present invention has an appropriate water vapor transmission rate,
A polyvinyl alcohol-based water-based adhesive can also be suitably used.

[0142]

EXAMPLES Examples and comparative examples will be described below.
First, methods for measuring physical properties shown in Examples and Comparative Examples are described below.

<Glass transition temperature> JIS K7121
Compliant with Seiko Electronics' differential scanning calorimeter (DSC)
It measured using. That is, 10 mg of a sample was set in a DSC device, and the temperature of the sample was raised from room temperature at 10 ° C./min, and the glass transition temperature was measured.

<Light Transmittance> JIS K7105-1
The measurement was performed using light of 550 nm according to the method described in 5.5 of 981.

<Haze> JIS K7105-198
The measurement was performed according to the method described in 6.4 of 1).

<Phase Difference> Using a microscopic polarization spectrophotometer (Oak Seisakusho: TFM-120AFT),
Each phase difference at a measurement wavelength of 515 nm and 780 nm was measured by the Senarmont method. Here, unless otherwise noted, a phase difference value for light of 515 nm is described as a phase difference value. The phase difference value Re (442) measured at a wavelength of 442 nm and the phase difference value R measured at a wavelength of 780 nm
The difference Re (442) -Re (780) from e (780) is defined as the A value.

<Phase Difference in Thickness Direction> Using a microscopic polarization spectrophotometer (Oak Manufacturing Co., Ltd .: TFM-120AFT),
The angle dependence of the phase difference at a measurement wavelength of 15 nm was measured, and nx, ny, and nz were determined. Further, the thickness of the film was separately measured, and the retardation in the thickness direction was calculated from the measured value using the following equation.

Phase difference in thickness direction = | (nx + ny) / 2
−nz | × d

<Judgment of Positive / Negative Birefringence> nx and ny were obtained using the method described in the above <Phase Difference in Thickness Direction>, and the positive or negative judgment was made by obtaining the difference.

<Tear Propagation Strength> The tear propagation strength was measured according to JIS K7128 (trouser method) using an autograph manufactured by Shimadzu Corporation. 200m tensile speed for measurement
m / min. For measurement, the average thickness was 50 ± 5 μm.
Was used.

<Mass Fatigue Resistance> MI manufactured by Toyo Seiki Seisaku-sho, Ltd.
T rubbing fatigue tester (FOLDINGENDURANCE)
TESTER) type D was measured according to JIS C5016. For the measurement, a width of 15 mm and a length of 2
A sample having a shape of 00 mm and an average thickness of 50 ± 5 μm was used.

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

REFERENCE EXAMPLE 1 An alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content: 50 mol%, glass transition temperature: 157 ° C.) was dissolved in methylene chloride to give a solid content of 15% by weight. A solution was obtained. This solution was cast on a biaxially stretched polyethylene terephthalate film spread on a glass plate. The obtained sample was left at room temperature for 60 minutes. Thereafter, the sample was peeled off from the polyethylene terephthalate film, four sides of the sample were fixed, dried at 100 ° C. for 10 minutes, and further dried at 140 ° C. for 10 minutes. A 30 cm × 10 cm sample film was cut from the obtained film. Stretching test equipment (Toyo Seiki Seisakusho, X4HD-HT)
The sample film was stretched uniaxially at the free end at a stretching speed of 10 cm / min, a stretching magnification of 1.5 and a stretching temperature of 160 ° C. This stretched film was found to have positive birefringence.

Reference Example 2 A thermoplastic copolymer composed of styrene and acrylonitrile having acrylonitrile and styrene contents of 27% by weight and 73% by weight, respectively, was dissolved in methylene chloride to obtain a solution having a solid content of 15% by weight. Obtained. This solution was cast on a biaxially stretched polyethylene terephthalate film spread on a glass plate. The obtained sample was left at room temperature for 60 minutes. Thereafter, the sample was peeled off from the polyethylene terephthalate film, four sides of the sample were fixed, dried at 60 ° C. for 10 minutes, and further dried at 80 ° C. for 10 minutes. A 30 cm × 10 cm sample film was cut from the obtained film. Stretching test equipment (Toyo Seiki Seisakusho, X4HD-
HT), a stretching speed of 10 cm / min and a stretching ratio of 1.5
The sample film was stretched uniaxially at the free end at a stretching temperature of 110 ° C. This stretched film was found to have negative birefringence.

Example 1 80 parts by weight (56% by weight) of an alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content: 50 mol%, glass transition temperature: 157 ° C.) and acrylonitrile and styrene 63 parts by weight (44% by weight) of a thermoplastic copolymer composed of styrene and acrylonitrile having a content of 27% by weight and 73% by weight, respectively, were dissolved in methylene chloride to obtain a solution having a solid content of 15% by weight. . This solution was cast on a biaxially stretched polyethylene terephthalate film spread on a glass plate. The obtained sample was treated at room temperature for 6 hours.
Left for 0 minutes. Thereafter, the sample was peeled off from the polyethylene terephthalate film, four sides of the sample were fixed, dried at 100 ° C. for 10 minutes, and further dried at 140 ° C. for 10 minutes. 30cm × 10c from the obtained film
m of the sample film was cut out. Using a stretching test device (Toyo Seiki Seisakusho, X4HD-HT), a stretching speed of 10
The sample film was stretched uniaxially at the free end at a cm / min, a stretching ratio of 1.5, and a stretching temperature of 150 ° C. The retardation of the obtained uniaxially stretched film was 3 nm, the retardation in the thickness direction was 4 nm, and the A value was 2 nm. The light transmittance was 92%. Haze was 0.4%. The stretch strength of the stretched film having a thickness of 45 μm in the direction perpendicular to the stretching direction was 192 gf / mm. The kneading fatigue in the stretching direction (kneading fatigue with the stretching direction being the longitudinal direction of the sample) was 218 times.

Example 2 A uniaxially stretched film was obtained in the same manner as in Example 1. Next, the film was stretched in a direction perpendicular to the stretching direction to obtain a sequentially biaxially stretched film having a film thickness of 50 μm. The tear propagation strength of the film in the direction perpendicular to the second stretching direction was 151 gf / mm, and the resistance to rubbing fatigue was 121 times. The phase difference was 3 nm, the phase difference in the thickness direction was 4 nm, and the A value was 1 nm.

Example 3 The same resin as in Example 1 was pelletized in advance with an extruder, dried at 100 ° C. for 5 hours, and then extruded with a 40 mm single screw extruder and a 400 mm width T screw.
Extruded at 270 ° C. using a die to obtain a film. Subsequently, it is 1.6 times at 140 ° C. with a roll longitudinal uniaxial stretching machine,
The film was stretched 1.6 times at 160 ° C. using a tenter transverse stretching machine to obtain a stretched film having a thickness of 53 μm. The retardation value of the obtained stretched film was 1 nm, the retardation in the thickness direction was 1 nm, and the A value was -1 nm. The light transmittance was 92%. Haze was 0.4%. The film tear propagation strength in the running direction (MD) of the stretched film is 182 gf / mm, and the film tear propagation strength in the direction perpendicular to the running direction (TD) is 214 g.
f / mm. MD fatigue resistance 135 times, T
The rubbing fatigue resistance in the D direction was 185 times.

Example 4 80 parts by weight (72% by weight) of an alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content: 50 mol%, glass transition temperature: 157 ° C.) and acrylonitrile and styrene 31 parts by weight (28% by weight) of a thermoplastic copolymer composed of styrene and acrylonitrile having contents of 24% by weight and 76% by weight, respectively, were dissolved in methylene chloride to obtain a solution having a solid content of 15% by weight. . This solution was cast on a biaxially stretched polyethylene terephthalate film spread on a glass plate. The obtained sample was left at room temperature for 60 minutes. Thereafter, the sample was peeled off from the polyethylene terephthalate film, four sides of the sample were fixed, dried at 100 ° C. for 10 minutes, and further dried at 140 ° C. for 1 minute.
After drying for 0 minutes, an unstretched film having a thickness of about 100 μm was obtained. The retardation value of this unstretched film is 8 nm,
The phase difference in the thickness direction was 14 nm, and the A value was 4 nm. The light transmittance was 92%. Haze was 0.3%.

Comparative Example 1 Polycarbonate resin (C-1400, Teijin Chemicals Limited, glass transition temperature 149)
° C) was used. The bisphenol component of this polycarbonate resin was bisphenol A. This polycarbonate resin was dissolved in methylene chloride to obtain a solution having a concentration of 15% by weight. This solution was cast on a biaxially stretched polyethylene terephthalate film spread on a glass plate. After leaving this sample at room temperature for 60 minutes, the sample was peeled off from the polyethylene terephthalate film, and the four sides of the sample were fixed, dried at 100 ° C. for 10 minutes, and further dried at 120 ° C. for 10 minutes to obtain a thickness of about 10 minutes. An unstretched film of 80 μm was obtained. The retardation value of this unstretched film is 21
nm, and the phase difference in the thickness direction was 70 nm. The light transmittance was 90%. Haze was 0.3%.

[0160]

According to the present invention, a transparent film having a low retardation can be obtained by using a polymer having a specific structure and composition. The film of the present invention has an advantage that a retardation due to the orientation of molecules hardly occurs. According to the present invention, the retardation can be adjusted to a desired value by appropriately adjusting the composition ratio of the resin used for the film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 35/02 C08L 35/02 // (C08F 210/00 C08F 212: 10 212: 10) C08L 25:12 (C08L 35/02 25:12)

Claims (7)

[Claims] 1. A film comprising two or more kinds of thermoplastic resins, wherein at least one kind of thermoplastic resin is a thermoplastic resin having positive birefringence, and at least one kind of thermoplastic resin is negative. A film comprising a birefringent thermoplastic resin. 2. The film according to claim 1, wherein a retardation value for light having a wavelength of 515 nm is 3 nm or less,
The phase difference in the thickness direction with respect to light having a wavelength of 515 nm is 5 nm.
A film according to the following, wherein the A value defined by the following formula is -3 nm to 3 nm. A = Re (442) -Re (780) Formula Re (442): Phase difference value for light having a wavelength of 442 nm Re (780): Phase difference value for light having a wavelength of 780 nm 3. The film according to claim 1, wherein (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain, and (B) a substituted or unsubstituted phenyl group and a nitrile group in a side chain. A film comprising a resin composition containing a thermoplastic resin having the following. 4. The film according to claim 3, wherein the thermoplastic resin (A) has a repeating unit represented by the formula (1) and a repeating unit represented by the formula (2), Here, the content of the repeating unit of the formula (1) is 30 to 80 mol% based on the total repeating units of the thermoplastic resin (A).
Wherein the content of the repeating unit of the formula (2) is 70 to 20 mol% based on the total repeating units of the thermoplastic resin (A), and the thermoplastic resin (B) is represented by the formula (3) Having a repeating unit represented by the formula (4) and a repeating unit represented by the formula (4),
Based on the total repeating units in the thermoplastic resin (B), 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 8%.
0% by weight, based on the sum of the amount of the thermoplastic resin (A) and the amount of the thermoplastic resin (B), the content of the thermoplastic resin (A) is 50 to 80% by weight, A film having a thermoplastic resin (B) content of 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, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 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 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. The film according to claim 1, wherein the film is a stretched film stretched in at least one direction. 6. A polarizer protective film using the film according to claim 1. 7. A polarizing plate comprising the polarizer protective film provided on at least one surface of a polarizing film.