JP2013011725A - Bi-layered film and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bi-layered film having a layer B formed of resin b whose inherent birefringence value is negative and a layer A which is formed over at least one face of the layer B and is formed of resin a whose inherent birefringence value is positive, in which the layer A and the layer B are highly adhesive to each other, and to provide a manufacturing method permitting manufacture of the bi-layered film as a phase difference film having a desired extent of retardation.SOLUTION: A bi-layered film has, over at least one face of a layer formed of resin b whose inherent birefringence value is negative (layer B), a layer formed of resin a whose inherent birefringence value is positive (layer A). The resin b contains a styrene-based polymer, the resin a contains an unsaturated nitrile-styrene copolymer, and the unsaturated nitrile-styrene copolymer content in the resin a is not less than 4 weight% but not more than 20 weight%.

Description

  The present invention relates to a multilayer film and a method for producing the same, and more particularly to an optical multilayer film and a method for producing the same.

  For example, a retardation film used for optical compensation of a liquid crystal display device is required to be capable of reducing a change in color tone of the display device depending on an observation angle, and various techniques have been developed conventionally. For example, Patent Document 1 proposes a retardation film in which a film made of a resin having a positive intrinsic birefringence value and a film made of a resin having a negative intrinsic birefringence value are bonded together. However, a resin having a negative intrinsic birefringence value usually has low strength and is brittle. Therefore, it has been pointed out that when a layer made of a resin having a negative intrinsic birefringence value is stretched and subjected to a retardation film stretching treatment, it is easily broken and the manufacturing efficiency is poor.

  In order to prevent damage to a layer made of a resin having a negative intrinsic birefringence value, in Patent Document 2, a resin having a negative intrinsic birefringence value and a resin having a positive intrinsic birefringence value are coextruded or co-cast. A production method has been proposed in which a laminated film is obtained and stretched to obtain a retardation film. According to this manufacturing method, a layer made of a resin having a negative intrinsic birefringence value can be protected by a layer made of a resin having a positive intrinsic birefringence value. Can be prevented.

JP 2008-216998 A JP 2009-192844 A

  The retardation film obtained by the production method described in Patent Document 2 sometimes has insufficient adhesion between layers. In other words, the adhesive strength between the layer made of a resin having a negative intrinsic birefringence value and the layer made of a resin having a positive intrinsic birefringence value is insufficient, so that the two layers are relatively easily separated. There was a problem.

  The present invention was devised in view of the above-described problem, and has a B layer made of a resin b having a negative intrinsic birefringence value, and a positive intrinsic birefringence value formed on at least one surface of the B layer. Provided is a multilayer film comprising an A layer made of resin a and having excellent adhesion between the A layer and the B layer, and a production method capable of producing the multilayer film as a retardation film having a desired retardation. The purpose is to do.

As a result of intensive studies to solve the above problems, the present inventor has found that the resin b contains a styrene-based polymer, the resin a contains a polycarbonate and an unsaturated nitrile-styrene copolymer, and the unsaturated nitrile- It has been found that a multilayer film having a styrene copolymer content in a specific range is excellent in adhesive strength. Furthermore, it has been found that a retardation film having a desired retardation can be obtained by stretching this multilayer film, and the present invention has been completed based on these findings.
That is, the gist of the present invention is the following [1] to [7].

[1] A multilayer film comprising a layer (A layer) made of resin a having a positive intrinsic birefringence value on at least one surface of a layer made of resin b (B layer) having a negative intrinsic birefringence value. And
Resin b contains a styrenic polymer,
Resin a comprises a polycarbonate and an unsaturated nitrile-styrene copolymer,
A multilayer film, wherein the content of the unsaturated nitrile-styrene copolymer in the resin a is 4% by weight or more and 20% by weight or less.
[2] The multilayer film according to [1], wherein the styrenic polymer is a copolymer containing a monomer unit derived from maleic anhydride.
[3] When the uniaxial stretching direction is the X-axis, the direction orthogonal to the uniaxial stretching direction in the film plane is the Y-axis, and the film thickness direction is the Z-axis, it is incident perpendicular to the film surface and the electric vector When the phase of the linearly polarized light having the vibration plane in the XZ plane incident perpendicularly to the film plane and the plane of polarization of the electric vector in the YZ plane is uniaxially stretched in the X-axis direction at the temperature T1, the temperature is delayed. The multilayer film according to [1] or [2], which advances when uniaxially stretched in the X-axis direction at a temperature T2 different from T1.

[4] A method for producing a multilayer film according to any one of [1] to [3],
A resin b containing a styrenic polymer and having a negative intrinsic birefringence value;
A resin a containing a polycarbonate and an unsaturated nitrile-styrene copolymer, the content of the unsaturated nitrile-styrene copolymer being not less than 4 wt% and not more than 20 wt%, having a positive intrinsic birefringence value;
The manufacturing method of a multilayer film including co-extrusion.

[5] A retardation film obtained by stretching the multilayer film according to any one of [1] to [3].
[6] The retardation film according to [5], wherein retardation Re at an incident angle of 0 ° and retardation R40 at an incident angle of 40 ° satisfy a relationship of 0.92 ≦ R40 / Re ≦ 1.08.

[7] A method for producing a retardation film according to [6],
Resin b having a negative intrinsic birefringence value and resin a having a positive intrinsic birefringence value are coextruded, the uniaxial stretching direction is the X axis, and the direction perpendicular to the uniaxial stretching direction in the film plane is the Y axis. When the thickness direction of the film is the Z axis, the plane of incidence is linearly polarized with the plane of vibration of the electric vector on the XZ plane, and the plane of plane of incidence of the electric vector with the plane of electric vector is the YZ plane. A co-extrusion step of obtaining a pre-stretched film that is delayed when the phase with respect to the linearly polarized light is uniaxially stretched in the X-axis direction at a temperature T1 and advanced when uniaxially stretched in the X-axis direction at a temperature T2 different from the temperature T1;
A first stretching step for subjecting the pre-stretched film to a uniaxial stretching treatment in one direction at a temperature T1 or T2.
A second stretching step in which a uniaxial stretching treatment is performed at a temperature T2 or T1 different from the above in a direction orthogonal to the direction in which the uniaxial stretching treatment is performed in the first stretching step;
Resin b contains a styrenic polymer,
Resin a comprises a polycarbonate and an unsaturated nitrile-styrene copolymer,
A method for producing a retardation film, wherein the content of the unsaturated nitrile-styrene copolymer in the resin a is 4% by weight or more and 20% by weight or less.

According to the multilayer film of the present invention, the adhesive strength of a layer made of a resin having a positive intrinsic birefringence value and a layer made of a resin having a negative intrinsic birefringence value is high. Peeling can be suppressed.
According to the method for producing a multilayer film of the present invention, the multilayer film of the present invention can be produced as a retardation film having a desired retardation.

When it is assumed that the glass transition temperature Tg _A of the resin a forming the A layer is high and the glass transition temperature Tg _B of the resin b forming the B layer is low, the A layer and the B layer of the film before stretching are each stretched. The figure which shows an example of the temperature dependence of the retardation of each of A layer and B layer, and the temperature dependence of retardation Δ of the film before stretching when a film before stretching (here, A layer + B layer) is stretched It is.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples, but the present invention is not limited to the following embodiments and examples, and the gist of the present invention and its equivalent scope are described below. You may implement arbitrarily changing in the range which does not deviate.

[1. (Multilayer film)
The multilayer film of the present invention includes a B layer made of a resin b having a negative intrinsic birefringence value, and an A layer made of a resin a having a positive intrinsic birefringence value formed on at least one surface of the B layer. .
Here, a positive intrinsic birefringence value means that the refractive index in the stretching direction is larger than the refractive index in the direction orthogonal to the stretching direction. Further, the negative intrinsic birefringence value means that the refractive index in the stretching direction is smaller than the refractive index in the direction orthogonal to the stretching direction. The intrinsic birefringence value can also be calculated from the dielectric constant distribution.

[1-1. B layer]
The B layer is made of a resin b having a negative intrinsic birefringence value. The resin b having a negative intrinsic birefringence value includes at least a styrene polymer. In addition, a styrenic polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The styrenic polymer is a polymer containing a repeating unit derived from a styrenic monomer (hereinafter referred to as “styrenic monomer unit” as appropriate). The aforementioned styrene monomer refers to styrene and styrene derivatives. Examples of the styrene derivative include α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, and the like. . In addition, a styrenic monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the styrenic polymer may contain one type of styrenic monomer unit alone, or may contain two or more types of styrenic monomer units in combination at any ratio. .

  The styrene polymer may be a homopolymer or copolymer containing only a styrene monomer, or may be a copolymer of a styrene monomer and another monomer. Good. Examples of monomers that can be copolymerized with styrene monomers include, for example, ethylene, propylene, butadiene, isoprene, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, N-phenylmaleimide, methyl acrylate, methyl methacrylate, Examples include ethyl acrylate, ethyl methacrylate, maleic anhydride, acrylic acid, methacrylic acid, and vinyl acetate. In addition, these monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In particular, when the styrenic polymer is a copolymer, the styrenic polymer is a copolymer containing a repeating unit derived from maleic anhydride (hereinafter referred to as “maleic anhydride unit” as appropriate). It is preferable. When the copolymer contains maleic anhydride units, the heat resistance of the styrenic polymer can be improved. The amount of maleic anhydride units is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, particularly preferably 15 parts by weight or more, preferably 30 parts by weight or less, based on 100 parts by weight of the styrenic polymer. More preferably, it is 28 parts by weight or less, and particularly preferably 26 parts by weight or less.

  In addition, the resin b having a negative intrinsic birefringence value may contain components other than the styrene polymer as long as the effects of the present invention are not significantly impaired. For example, the resin b having a negative intrinsic birefringence value may contain another polymer in addition to the styrene polymer. From the viewpoint of making the intrinsic birefringence value of the resin constituting the B layer negative, the other polymer is preferably a polymer having a negative intrinsic birefringence value. Specific examples thereof include a polyacrylonitrile polymer, a polymethyl methacrylate polymer, a cellulose ester polymer, or a multi-component copolymer thereof. In addition, other polymer constituent components may be contained as a repeating unit in a part of the styrene polymer. However, from the viewpoint of remarkably exhibiting the advantages of the present invention, the amount of the other polymer in the B layer is preferably small. The specific amount of the other polymer is, for example, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and still more preferably 3 parts by weight or less with respect to 100 parts by weight of the styrene polymer. Among these, it is particularly preferable that no other polymer is contained.

  In addition, the resin b having a negative intrinsic birefringence value may contain, for example, a compounding agent. Examples of compounding agents include: lubricants; layered crystal compounds; inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near infrared absorbers; plasticizers; dyes And coloring agents such as pigments and pigments; antistatic agents; and the like. Among these, a lubricant and an ultraviolet absorber are preferable because they can improve flexibility and weather resistance. In addition, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Further, the amount of the compounding agent can be appropriately determined within a range that does not significantly impair the effects of the present invention. For example, the total light transmittance in terms of 1 mm thickness of the multilayer film of the present invention can be maintained at 80% or more. It is good.

  Examples of the lubricant include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, strontium sulfate; polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, cellulose acetate pro Organic particles such as pionate can be mentioned. Among these, organic particles are preferable as the lubricant.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, acrylonitrile ultraviolet absorbers, triazine compounds, nickel complex compounds. And inorganic powders. Specific examples of suitable UV absorbers include 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) ) Phenol, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, and the like. Particularly preferred are 2,2′-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol).

The glass transition temperature Tg _B of the resin b having a negative intrinsic birefringence value is usually 80 ° C. or higher, preferably 90 ° C. or higher, more preferably 100 ° C. or higher, still more preferably 110 ° C. or higher, and particularly preferably 120 ° C. or higher. . With such a high glass transition temperature Tg _B, it is possible to reduce orientation relaxation of the resin b having a negative intrinsic birefringence value. Although not particularly limited to the upper limit of the glass transition temperature Tg _B, usually it is 200 ° C. or less.

The breaking elongation of the resin b having a negative intrinsic birefringence value at the glass transition temperature Tg _A of the resin a having a positive intrinsic birefringence value is preferably 50% or more, and more preferably 80% or more. The upper limit of the breaking elongation of the resin b having a negative intrinsic birefringence value is not particularly limited, but is usually 200% or less. When the elongation at break is within this range, the multilayer film of the present invention can be stably produced by stretching. The elongation at break is determined using a test piece type 1B test piece described in JIS K7127 at a pulling speed of 100 mm / min.

The absolute value | Tg _A −Tg _B | of the difference between the glass transition temperature Tg _A of the resin a having a positive intrinsic birefringence value and the glass transition temperature Tg _B of the resin b having a negative intrinsic birefringence value is preferably 5 It is larger than ° C., more preferably 8 ° C. or higher, preferably 40 ° C. or lower, more preferably 20 ° C. or lower. If the absolute value | Tg _A −Tg _B | of the difference between the glass transition temperatures is too small, the temperature dependence of retardation development tends to be small. On the other hand, if the absolute value | Tg _A −Tg _B | of the difference between the glass transition temperatures is too large, it is difficult to stretch a resin having a high glass transition temperature, and the planarity of the multilayer film may be easily lowered. is there. The glass transition temperature Tg _A is preferably higher than the glass transition temperature Tg _B. Therefore, it is usually preferable that the resin having a positive intrinsic birefringence value and the resin b having a negative intrinsic birefringence value satisfy the relationship of Tg _A > Tg _B + 5 ° C.

  In the multilayer film of the present invention, the B layer is laminated with the A layer, so that even if the strength of the resin b is low, the B layer formed by the resin b is not damaged.

  When the multilayer film of the present invention is used as a retardation film, the polymer molecules contained in the resin b having a negative intrinsic birefringence value in the B layer are usually oriented by, for example, stretching treatment. When the molecules of the polymer are oriented, refractive index anisotropy occurs, and retardation is developed in the B layer. In the multilayer film of the present invention, the retardation of the B layer expressed in this way and the retardation expressed in the A layer are synthesized to produce the desired retardation of the multilayer film of the present invention as a whole. It is like that. Therefore, the thickness of the B layer may be set to an appropriate value according to the specific retardation to be expressed in the multilayer film of the present invention.

  The multilayer film of the present invention may be provided with two or more B layers, but from the viewpoint of simplifying the control of retardation and reducing the thickness of the multilayer film of the present invention, it is provided with only one layer. Is preferred.

[1-2. A layer]
The A layer is made of a resin a having a positive intrinsic birefringence value. The resin a having a positive intrinsic birefringence value includes at least a polycarbonate and an unsaturated nitrile-styrene copolymer.

  Polycarbonate is a polymer excellent in retardation development, low temperature stretchability, and adhesion to other layers. Any polycarbonate can be used as long as it is a polymer having a repeating unit due to a carbonate bond (—O—C (═O) —O—). Moreover, what consists of one type of repeating unit may be used for a polycarbonate, and what combined two or more types of repeating units in arbitrary ratios may be used.

Examples of the polycarbonate include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ′, o′-tetramethylbisphenol A polycarbonate, and the like.
As the polycarbonate, one type may be used alone, or two or more types may be used in combination at any ratio.

  The unsaturated nitrile-styrene copolymer is a polymer containing a repeating unit derived from an unsaturated nitrile compound (hereinafter referred to as “unsaturated nitrile monomer unit” as appropriate) and a styrene monomer unit. When the A layer contains the unsaturated nitrile-styrene copolymer, both high adhesiveness with the B layer and optical characteristics suitable as a retardation film can be achieved.

  Examples of the unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and the like, and acrylonitrile is preferable. As the styrenic monomer, any of those described above can be used, and styrene is preferred. The ratio of the unsaturated nitrile monomer unit to the styrene monomer unit is preferably 5:95 to 50:50, more preferably 10:90 to 40:60, by weight.

  The unsaturated nitrile-styrene copolymer may contain monomer units other than the unsaturated nitrile monomer unit and the styrene monomer unit as long as the effects of the present invention are not significantly impaired. Examples of such a polymer include acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-chlorinated polyethylene-styrene copolymer (ACS), acrylonitrile-EPDM-styrene copolymer (AES), and acrylonitrile-styrene- An acrylate copolymer (ASA) etc. are mentioned.

  The content of the unsaturated nitrile-styrene copolymer in the resin a having a positive intrinsic birefringence value is 4% by weight to 20% by weight, preferably 6% by weight to 15% by weight. When the content of the unsaturated nitrile-styrene copolymer is within this range, both high adhesiveness between the A layer and the B layer and high transparency suitable as an optical film can be achieved.

  The resin a having a positive intrinsic birefringence value may contain components other than polycarbonate and acrylic polymer as long as the effects of the present invention are not significantly impaired. For example, the resin a having a positive intrinsic birefringence value may contain a polymer other than polycarbonate and an unsaturated nitrile-styrene copolymer, a compounding agent, and the like.

  Examples of polymers other than polycarbonate and unsaturated nitrile-styrene copolymer that may be contained in the resin a having a positive intrinsic birefringence value include olefin polymers such as polyethylene and polypropylene; polyethylene terephthalate, polybutylene terephthalate Polyarylene sulfide such as polyphenylene sulfide; Polyvinyl alcohol; Cellulose ester; Polyether sulfone; Polysulfone; Polyallyl sulfone; Polyvinyl chloride; Norbornene polymer; Moreover, the structural component of these polymers may be contained as a repeating unit in a part of polycarbonate or unsaturated nitrile-styrene copolymer. Furthermore, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. However, from the viewpoint of remarkably exhibiting the advantages of the present invention, it is preferable that the amount of the polymer other than the polycarbonate and the unsaturated nitrile-styrene copolymer in the resin a is small. Parts by weight or less, preferably 5 parts by weight or less, more preferably 3 parts by weight or less. Among these, it is particularly preferable that no polymer other than polycarbonate and unsaturated nitrile-styrene copolymer is contained.

  Examples of the compounding agent that may include the resin a having a positive intrinsic birefringence value include the same examples as the compounding agent that may include the resin b having a negative intrinsic birefringence value. In addition, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the compounding agent can be appropriately determined within a range that does not significantly impair the effects of the present invention. For example, the total light transmittance in terms of 1 mm thickness of the multilayer film may be maintained within 80% or more. .

The glass transition temperature Tg _A of the resin a having a positive intrinsic birefringence value is usually 80 ° C. or higher, preferably 90 ° C. or higher, more preferably 100 ° C. or higher, still more preferably 110 ° C. or higher, and particularly preferably 120 ° C. or higher. . With such a high glass transition temperature Tg _{A, the} relaxation of the orientation of the resin a having a positive intrinsic birefringence value can be reduced. When the resin a having a positive intrinsic birefringence value has a glass transition temperature of 2 or more, the glass transition temperature Tg _A represents the highest glass transition temperature. Particular upper limit to the glass transition temperature Tg _A is not, but usually is 200 ° C. or less.

The breaking elongation of the resin a having a positive intrinsic birefringence value at the glass transition temperature Tg _B of the resin b having a negative intrinsic birefringence value is preferably 50% or more, and more preferably 80% or more. . When the elongation at break is within this range, a retardation film can be stably produced by stretching.

  Usually, the A layer is provided exposed on the main surface of the multilayer film of the present invention. That is, the A layer is usually the outermost layer of the multilayer film of the present invention. Even if the A layer is exposed as described above, the strength of the A layer is usually strong, so that it is difficult to break during handling and the handling property is not deteriorated.

  In the multilayer film of the present invention, the A layer may be provided on at least one surface of the B layer, but from the viewpoint of further suppressing breakage of the B layer, the A layer is provided on both sides of the B layer. It is preferable. In addition, the multilayer film of the present invention may have three or more A layers, but from the viewpoint of simplifying the control of retardation and reducing the thickness of the multilayer film of the present invention, only two layers are provided. Is preferred.

  When the multilayer film of the present invention is used as a retardation film, the molecules of the polymer contained in the resin a having a positive intrinsic birefringence value in the layer A are usually oriented by, for example, stretching. When the molecules of the polymer are oriented, refractive index anisotropy occurs, and retardation is developed in the A layer. In the multilayer film of the present invention, the retardation of the A layer expressed in this way and the retardation expressed in the B layer are synthesized to produce the desired retardation of the multilayer film of the present invention as a whole. . Therefore, the film thickness of the A layer may be set to an appropriate value according to the specific retardation to be expressed in the multilayer film of the present invention.

[1-3. Other layers]
The multilayer film of the present invention may be provided with other layers in addition to the A layer and the B layer as long as the effects of the present invention are not significantly impaired.
For example, the multilayer film of the present invention has, on its surface, a mat layer that improves the slipperiness of the film, a hard coat layer that prevents scratches on the film surface, and an antireflection layer that suppresses reflection of light on the film surface. Further, an antifouling layer or the like for preventing the adhesion of dirt may be provided.

[1-4. (Physical properties of multilayer film)
The multilayer film of the present invention preferably has a total light transmittance of 85% or more from the viewpoint of stably exhibiting the function as an optical member. The light transmittance can be measured using a spectrophotometer (manufactured by JASCO Corporation, ultraviolet-visible near-infrared spectrophotometer “V-570”) in accordance with JIS K0115.

  The haze of the multilayer film of the present invention is preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less. By setting the haze to a low value, the sharpness of the display image of the display device incorporating the multilayer film of the present invention can be enhanced. Here, the haze is an average value obtained by measuring five points using a “turbidimeter NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K7361-1997.

  In the multilayer film of the present invention, ΔYI is preferably 5 or less, and more preferably 3 or less. When this ΔYI is in the above range, there is no coloring and the visibility is good. ΔYI is measured using a “spectral color difference meter SE2000” manufactured by Nippon Denshoku Industries Co., Ltd. according to ASTM E313. The same measurement is performed five times, and the arithmetic average value is obtained.

When the multilayer film of the present invention is a retardation film, the multilayer film of the present invention preferably has a desired retardation depending on the use as the retardation film. For example, when used as a retardation film for a liquid crystal display device, the multilayer film of the present invention has a retardation Re at an incident angle of 0 ° and a retardation R ₄₀ at an incident angle of 40 ° of 0.92 ≦ R ₄₀ /. It is preferable to satisfy the relationship of Re ≦ 1.08. Among these, R ₄₀ / Re is preferably 0.95 or more, and preferably 1.05 or less. When Re and R ₄₀ have such a relationship, when the multilayer film of the present invention is applied to a display device such as a liquid crystal display device, the angle dependency of the display color tone of the device is particularly preferably reduced. Can do.

Here, the incident angle of 0 ° is the normal direction of the main surface of the multilayer film, and the incident angle of 40 ° is an angle inclined by 40 ° from the normal direction of the main surface of the multilayer film. In measuring R _40, the direction in which the observation angle is tilted is not particularly limited, and the value of R ₄₀ when tilted in any one direction may satisfy the requirement.
The measurement wavelength of retardation Re and R ₄₀ may be any wavelength within the visible light region, but is preferably 590 nm.

The retardations Re and R ₄₀ at the incident angles of 0 ° and 40 ° can be measured by a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments. When Re and R ₄₀ satisfy the above relationship, the refractive indices nx and ny in the principal axis direction and the refractive index nz in the thickness direction in the plane of the multilayer film usually satisfy nx>nz> ny. Here, the refractive indexes nx, nz, and ny are weighted averages n _ave of the refractive indexes in the respective directions of each layer included in the multilayer film of the present invention, and the refractive index of the i-layer resin is ni, and the i-layer film. The thickness is determined by the following equation, where Li is:
n _ave = Σ (ni × Li) / ΣLi

  When the multilayer film of the present invention is a retardation film, the retardation Re at an incident angle of 0 ° of the multilayer film of the present invention is preferably 50 nm or more, more preferably 100 nm or more, It is preferably 400 nm or less, and more preferably 350 nm or less.

  The outer surface of the multilayer film of the present invention is in the MD direction (machine direction; the film flow direction in the production line, and usually coincides with the long direction of the long film, also referred to as the vertical direction). It is preferably flat without substantially having irregularly extending linear concave portions or linear convex portions (so-called die lines). Here, “the surface is substantially free of irregularly formed linear recesses and linear protrusions and is flat” means that the depth is less than 50 nm even if linear recesses and linear protrusions are formed. Or it is a linear recessed part with a width larger than 500 nm, and a linear convex part with a height less than 50 nm or a width larger than 500 nm. More preferably, it is a linear concave part having a depth of less than 30 nm or a width of more than 700 nm, and a linear convex part having a height of less than 30 nm or a width of more than 700 nm. By adopting such a configuration, it is possible to prevent the occurrence of light interference and light leakage based on the light refraction at the linear concave portions or the linear convex portions, and the optical performance can be improved. In addition, irregularly occurring means that it is formed with an unintended size, shape, or the like at an unintended position.

The depth of the linear concave portion described above, the height of the linear convex portion, and the width thereof can be obtained by the following method. Light is applied to the multilayer film, the transmitted light is projected on the screen, and the lighted or dark stripes of light appearing on the screen (this part has the depth of the linear recess and the height of the linear protrusion) Cut out at 30 mm square. The surface of the cut film piece is observed using a three-dimensional surface structure analysis microscope (field region 5 mm × 7 mm), converted into a three-dimensional image, and a cross-sectional profile is obtained from the three-dimensional image. The cross-sectional profile is obtained at 1 mm intervals in the visual field region.
In this cross-sectional profile, an average line is drawn, the length from the average line to the bottom of the linear concave portion is the depth of the linear concave portion, and the length from the average line to the top of the linear convex portion is the height of the linear convex portion. It becomes. The distance between the intersection of the average line and the profile is the width. The maximum values are obtained from the measured values of the linear concave portion depth and the linear convex portion height, respectively, and the width of the linear concave portion or the linear convex portion showing the maximum value is obtained. The maximum value of the linear recess depth and the height of the linear convex portion obtained from the above, the width of the linear concave portion and the width of the linear convex portion showing the maximum value, the depth of the linear concave portion of the film Let the height of the linear protrusions and their widths.

  The multilayer film of the present invention is subjected to heat treatment at 60 ° C., 90% RH, 100 hours, in the MD direction and TD direction (traverse direction; a direction parallel to the film surface and perpendicular to the MD direction, usually in the width direction). May be contracted in the horizontal direction), but the contraction rate is preferably 0.5% or less, more preferably 0.3% or less. With such a small shrinkage rate, it is possible to prevent the multilayer film of the present invention from being deformed by the shrinkage stress and being peeled off from the display device even in a high temperature and high humidity environment.

  The multilayer film of the present invention may have a dimension in the TD direction of, for example, 1000 mm to 2000 mm. Moreover, although the multilayer film of this invention does not have a restriction | limiting in the dimension of the MD direction, it is preferable that it is a long film. Here, the “long” film means a film having a length of at least 5 times the width of the film, preferably a length of 10 times or more, specifically a roll. It has a length enough to be wound up into a shape and stored or transported.

  The specific thickness of the multilayer film of the present invention may be set according to the film strength required according to the application and the size of the retardation to be expressed, but is preferably 10 μm or more, more preferably 30 μm or more. Moreover, 200 micrometers or less are preferable and 150 micrometers or less are more preferable.

[2. (Method for producing multilayer film)
[2-1. (Co-extrusion method)
The production method of the multilayer film of the present invention is not limited. For example, a coextrusion method such as coextrusion T-die method, coextrusion inflation method, coextrusion lamination method, etc .; film lamination molding method such as dry lamination; A coating molding method such as coating a resin solution on the surface of the resin film; Among these, the co-extrusion method is preferable from the viewpoint of manufacturing efficiency and preventing a volatile component such as a solvent from remaining in the film.

  When employing the coextrusion method, the multilayer film is obtained, for example, by coextruding a resin a having a positive intrinsic birefringence value and a resin b having a negative intrinsic birefringence value. Examples of the co-extrusion method include a co-extrusion T-die method, a co-extrusion inflation method, and a co-extrusion lamination method. Among them, the co-extrusion T-die method is preferable. Further, the coextrusion T-die method includes a feed block method and a multi-manifold method, but the multi-manifold method is particularly preferable in that variation in thickness can be reduced.

  When the co-extrusion T-die method is adopted, the melting temperature of the resin in the extruder having the T-die is preferably 80 ° C. higher than the glass transition temperature of the resin a and the resin b, and a temperature higher by 100 ° C. It is more preferable to set it above, and it is preferable that the temperature be 180 ° C. or higher, and more preferable that the temperature be 150 ° C. or higher. If the melting temperature in the extruder is excessively low, the fluidity of the resin may be insufficient. Conversely, if the melting temperature is excessively high, the resin may be deteriorated.

In the coextrusion method, the film-like molten resin extruded from the opening of the die is usually brought into close contact with a cooling roll (also referred to as a cooling drum). The method for bringing the molten resin into close contact with the cooling roll is not particularly limited, and examples thereof include an air knife method, a vacuum box method, and an electrostatic contact method.
The number of cooling rolls is not particularly limited, but is usually 2 or more. In addition, examples of the arrangement method of the cooling roll include, but are not particularly limited to, a linear type, a Z type, and an L type. Further, the way of passing the molten resin extruded from the opening of the die through the cooling roll is not particularly limited.

  The degree of adhesion of the extruded film-like resin to the cooling roll varies depending on the temperature of the cooling roll. When the temperature of the cooling roll is raised, the adhesion is improved. However, if the temperature is raised too much, the film-like resin may not be peeled off from the cooling roll, and there is a possibility that a problem of winding around the drum may occur. Therefore, the temperature of the cooling roll is preferably (Tg + 30) ° C. or less, more preferably (Tg-5) ° C. to (Tg−), where Tg is the glass transition temperature of the resin of the layer that is extruded from the die and contacts the drum. 45) Set to a range of ° C. By doing so, problems such as slipping and scratches can be prevented.

  Moreover, it is preferable to reduce content of the residual solvent in a multilayer film. Means for that purpose include (1) reducing residual solvent contained in resin a and resin b as raw materials; (2) pre-drying resin a and resin b before forming a multilayer film; Is mentioned. The preliminary drying is performed by a hot air dryer or the like, for example, by converting the resin a and the resin b into a pellet form. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, it is possible to reduce the residual solvent in the multilayer film, and to prevent foaming of the extruded film-like resin.

[2-2. Method for producing retardation film]
When producing a retardation film in which Re and R ₄₀ satisfy the relationship of 0.92 ≦ R ₄₀ /Re≦1.08 as the multilayer film of the present invention, resin b and resin a are usually coextruded. A co-extrusion step for obtaining a predetermined pre-stretching film, a first stretching step for subjecting the pre-stretching film to a uniaxial stretching treatment in a single direction at a predetermined temperature, and a direction for performing a uniaxial stretching treatment in the first stretching step; A retardation film is produced by a production method having a second stretching step in which a uniaxial stretching process is performed at a predetermined temperature different from the first stretching step in a direction orthogonal to the first stretching step. Hereinafter, this manufacturing method will be described in detail.

-Coextrusion process In a coextrusion process, resin b and resin a are coextruded and a predetermined film before extending | stretching is manufactured. Since the retardation film is produced by subjecting the pre-stretching film to a stretching treatment, the pre-stretching film comprises a B layer composed of the resin b and an A layer composed of the resin a formed on both surfaces of the B layer. Prepare. Therefore, the film before stretching corresponds to the multilayer film of the present invention.

  The film before stretching exhibits retardation according to the temperatures T1 and T2 and the stretching direction in each of the A layer and the B layer by stretching at different angles of temperatures T1 and T2 and different angles substantially orthogonal to each other. In this way, the retardation produced in the A layer and the retardation produced in the B layer are synthesized, and the desired retardation is exhibited as a whole retardation film. In addition, “substantially orthogonal” means that they intersect at an angle of usually 85 ° or more, preferably 89 ° or more, and usually 95 ° or less, preferably 91 ° or less.

  The size of the retardation developed in the A layer and the B layer by stretching depends on the thickness of the film before stretching, the stretching temperature, the stretching ratio, and the like. Therefore, it is preferable that the configuration of the pre-stretched film is appropriately determined according to the retardation to be expressed.

Although the specific composition of the film before stretching can be variously set, among them, the film before stretching is oriented in the film plane with respect to the X-axis and the uniaxial stretching direction in the direction of stretching in a certain direction (that is, uniaxial stretching direction). Linearly polarized light (hereinafter referred to as “XZ-polarized light” as appropriate) is incident perpendicularly to the film surface and the vibration plane of the electric vector is in the XZ plane when the orthogonal direction is the Y-axis and the film thickness direction is the Z-axis. The phase with respect to linearly polarized light (hereinafter referred to as “YZ polarized light” where appropriate) that is perpendicularly incident on the film surface and whose electric vector vibration surface is on the YZ plane is
Delayed when uniaxially stretched in the X-axis direction at temperature T1,
When the uniaxial stretching is performed in the X-axis direction at a temperature T2 different from the temperature T1,
(Hereinafter referred to as “requirement P” as appropriate).

  The requirement P may be satisfied when at least one of the various directions in the plane of the unstretched film is taken as the X axis. Usually, since the film before stretching is an isotropic raw film, the above-mentioned requirement P is satisfied when one direction in the plane is the X axis, and any other direction is the X axis. The requirement P can be satisfied.

  In a film in which a slow axis appears in the X axis by uniaxial stretching, the phase of XZ polarized light is usually delayed from that of YZ polarized light. Conversely, in a film in which a fast axis appears on the X-axis by uniaxial stretching, the phase of XZ polarized light is usually advanced relative to that of YZ polarized light. The pre-stretch film according to the present invention is a multilayer film utilizing these properties, and is a film in which the appearance of the slow axis or the fast axis depends on the stretching temperature. The temperature dependence of the expression of such retardation can be adjusted, for example, by adjusting the relationship between the photoelastic coefficient of the resin a and the resin b and the film thickness ratio of each layer.

The in-plane retardation of a certain layer is the difference between the refractive index nx in the X-axis direction that is the stretching direction and the refractive index ny in the Y-axis direction that is perpendicular to the stretching direction (= | nx−ny |). It is a value obtained by multiplying the film thickness d. The retardation of the multilayer film comprising the A layer and the B layer is synthesized from the retardation of the A layer and the retardation of the B layer. Therefore, for example, in order to reverse the sign of retardation developed in the entire film by stretching at a high temperature T _H and a low temperature T _L , (i) the glass transition temperature of the stretching at a low temperature T _L the absolute value of the retardation high resin is expressed is smaller than the absolute value of the retardation expressing low resin glass transition temperature, a draw in (ii) a higher temperature T _H, low glass transition temperature resin is expressed It is preferable to adjust the film thicknesses of the A layer and the B layer so that the absolute value of retardation is smaller than the absolute value of retardation at which a resin having a high glass transition temperature is developed.

Thus, as the resin constituting the A layer and the B layer, the refractive index in the X-axis direction and the refractive index in the Y-axis direction are respectively applied to the A layer and the B layer by stretching in one direction (that is, uniaxial stretching). The combination of the resin a and the resin b that can cause a difference is selected, and the above requirement P is satisfied by adjusting the total thickness of the A layer and the total thickness of the B layer in consideration of the stretching conditions. A film before stretching can be obtained.
The temperature T1 is one of T _{H and} T _L , and the temperature T2 is either T _H or T _L that is different from T1.

The expression of retardation when a pre-stretch film satisfying the above requirement P is stretched will be specifically described with reference to the drawings. FIG. 2 shows that when the glass transition temperature Tg _A of the resin a forming the A layer is high and the glass transition temperature Tg _B of the resin b forming the B layer is low, the A layer and the B layer of the film before stretching. The temperature dependence of the retardation of each of the A layer and the B layer when the film is stretched, and the temperature dependence of the retardation Δ of the film before stretching when the film before stretching (here, A layer + B layer) is stretched. An example is shown. The pre-stretch film as shown in FIG. 2, since the larger the negative retardation expressed in B layer compared with the retardation of the positive expressed in A layer in stretching at a temperature T _b, minus the A layer + B layer Retardation Δ is developed. On the other hand, since a stretching at the temperature T _a is smaller for negative retardation expressed in B layer compared with the retardation of the positive expressed in A layer, it will express a positive retardation Δ in A layer + B layer . Therefore, by combining the drawing of such different temperatures T _a and T _b, by combining the retardation caused by stretching at each temperature can be produced a retardation film having a desired retardation.

  When the example of the structure of the film before extending | stretching is given, when resin b is resin containing a styrene-maleic anhydride copolymer, for example, with the sum total of the film thickness of A layer, and the sum total of the film thickness of B layer The ratio (total thickness of layer A / total thickness of layer B) is usually 1/15 or more, preferably 1/10 or more, and usually 1/4 or less. Even if the A layer becomes too thick or the B layer becomes too thick, the temperature dependency of the expression of retardation tends to decrease.

  The total thickness of the film before stretching is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, preferably 500 μm or less, more preferably 400 μm or less, and particularly preferably 300 μm or less. If the pre-stretch film is thinner than the lower limit of the range, sufficient retardation tends to be difficult and mechanical strength tends to be weakened. If the film is thicker than the upper limit of the range, the flexibility is deteriorated and handling may be hindered. There is sex.

  When the number of A layers included in the pre-stretch film is 2, the ratio of the thickness of one A layer to the other A layer (thickness of the thicker A layer / thickness of the thinner A layer) Is preferably 1.5 / 1 or more from the viewpoint of ensuring light leakage of the polarizing plate when combined with the polarizing plate in a liquid crystal display device. Further, from the viewpoint of maintaining the accuracy of the film thickness of the thinner A layer, the ratio of the film thickness between one A layer and the other A layer is preferably 10/1 or less.

  In the pre-stretch film, the variation in the film thicknesses of the A layer and the B layer is preferably 1 μm or less over the entire surface. Thereby, also in the A layer and the B layer of the retardation film, the variation in the film thickness is 1 μm or less over the entire surface, and the variation in the color tone of the display device including the retardation film can be reduced. In addition, the color tone change after long-term use of the retardation film can be made uniform.

  In order to make the variation in the film thicknesses of the A layer and the B layer 1 μm or less as described above, for example, (1) a polymer filter having an opening of 20 μm or less is provided in the extruder; (2) the gear pump is 5 rpm or more (3) Arrange the surrounding means around the die; (4) Set the air gap to 200 mm or less; (5) Perform edge pinning when casting the film on a chill roll; and (6) Extrusion As the machine, a twin screw extruder or a double-flight type single screw extruder may be used. Further, for example, the thickness of the A layer and the B layer can be reduced by measuring the film thickness of the A layer and the B layer during the manufacturing process and performing feedback control based on the film thickness as in the embodiment described later. can do.

The film thickness variations of the A layer and the B layer are measured at regular intervals in the MD direction and TD direction of the film, and the measured film thickness T is measured based on the arithmetic average value T _ave of the measured values. The maximum value is T _max , and the minimum value is T _min . Note that the variation in film thickness (μm) is the larger of T _ave −T _min and T _max −T _ave .

The above-mentioned pre-stretch film is preferably produced by a coextrusion method. The coextrusion method is as described above.
Moreover, although an isotropic raw film is usually used as the pre-stretch film, a film once stretched may be used as a pre-stretch film, which may be further stretched.

-1st extending | stretching process In a 1st extending | stretching process, the uniaxial stretching process is performed to one direction at the temperature of either the temperature T1 or T2. When the film is stretched at the temperature T1, the phase of the XZ polarized light with respect to the YZ polarized light is delayed in the pre-stretched film that satisfies the requirement P. On the other hand, when the uniaxial stretching is performed at the temperature T2, the phase of the XZ polarized light with respect to the YZ polarized light advances.

When the relationship between the glass transition temperatures is Tg _A > Tg _B , the temperature T1 is preferably higher than Tg _B, more preferably higher than Tg _B + 5 ° C., and preferably lower than Tg _A + 40 ° C. More preferably, it is lower than Tg _A + 20 ° C. By making the temperature T1 higher than the lower limit of the above range, the desired retardation can be stably expressed in the B layer, and by making the temperature T1 lower than the upper limit, the desired retardation can be stably expressed in the A layer. it can.
Furthermore, when the relationship between the glass transition temperatures is Tg _A > Tg _B , the temperature T2 is preferably higher than Tg _B −20 ° C., more preferably higher than Tg _B −10 ° C., and Tg _B + 5 ° C. Preferably, it is lower than Tg _B. By making the temperature T2 higher than the lower limit of the above range, it is possible to prevent the pre-stretched film from being broken or clouded during stretching, and by making the temperature T2 lower than the upper limit, the desired retardation is stably expressed in the resin B. be able to.
In this case the glass transition temperature relation is Tg _A> Tg _B, it is preferably carried out at a temperature T1 in the first stretching step.

When the relationship of glass transition temperature is Tg _B > Tg _A , the temperature T1 is preferably higher than Tg _A, more preferably higher than Tg _A + 5 ° C., and preferably lower than Tg _B + 40 ° C. More preferably, it is lower than Tg _B + 20 ° C. By making the temperature T1 higher than the lower limit of the above range, the desired retardation can be stably expressed in the A layer, and by making the temperature T1 lower than the upper limit, the desired retardation can be stably expressed in the B layer. it can.
Furthermore, when the relationship between the glass transition temperatures is Tg _B > Tg _A , the temperature T2 is preferably higher than Tg _A −20 ° C., more preferably higher than Tg _A −10 ° C., and Tg _A + 5 ° C. Preferably, it is lower than Tg _A. By making the temperature T2 higher than the lower limit of the above range, it is possible to prevent the pre-stretching film from being broken or clouded during stretching, and by making the temperature T2 lower than the upper limit, the desired retardation is stably expressed in the resin A. be able to.
In this case the glass transition temperature relation is Tg _B> Tg _A, is preferably performed at a temperature T2 in the first stretching step.

  The uniaxial stretching process can be performed by a conventionally known method. For example, a method of uniaxially stretching in the MD direction using a difference in peripheral speed between rolls, a method of uniaxially stretching in the TD direction using a tenter, and the like can be mentioned. Examples of the uniaxial stretching method in the MD direction include an IR heating method between rolls, a float method, and the like. Of these, the float method is preferred because a retardation film having high optical uniformity can be obtained. On the other hand, as a method of uniaxially stretching in the TD direction, a tenter method can be mentioned.

  In the uniaxial stretching treatment, in order to reduce stretching unevenness and thickness unevenness, a temperature difference may be created in the TD direction in the stretching zone. In order to create a temperature difference in the TD direction in the stretching zone, for example, a known method such as adjusting the opening degree of the hot air nozzle in the TD direction or controlling the heating by arranging the IR heaters in the TD direction may be used. it can.

-2nd extending process A 2nd extending process is performed after performing a 1st extending process. In the second stretching step, the film stretched in one direction in the first stretching step is uniaxially stretched in a direction orthogonal to the direction in which the uniaxial stretching process was performed in the first stretching step.
In the second stretching step, uniaxial stretching is performed at a temperature T2 or T1 different from that in the first stretching step. In the second stretching step, when the relationship of glass transition temperature is Tg _A > Tg _B , it is preferable to perform uniaxial stretching at temperature T2, and when Tg _B > Tg _A , uniaxial stretching is performed at temperature T1. preferable.

  The difference between the temperature T1 and the temperature T2 is usually 5 ° C. or higher, preferably 10 ° C. or higher. By increasing the difference between the temperature T1 and the temperature T2 as described above, a desired retardation can be stably expressed in the retardation film. In addition, although there is no restriction | limiting in the upper limit of the difference of temperature T1 and temperature T2, it is 100 degrees C or less from a viewpoint of industrial productivity.

  For the uniaxial stretching treatment in the second stretching step, a method similar to the method that can be adopted in the uniaxial stretching treatment in the first stretching step can be applied. However, the uniaxial stretching process in the second stretching process is preferably performed at a smaller stretching ratio than the uniaxial stretching process in the first stretching process. Specifically, the first draw ratio is preferably 2 to 4 times, and the second draw ratio is preferably 1.1 to 2 times.

  The combinations of the stretching directions in the first stretching process and the second stretching process are, for example, stretching in the MD direction in the first stretching process and stretching in the TD direction in the second stretching process, or stretching in the TD direction in the first stretching process. What is necessary is just to extend | stretch to MD direction at a 2nd extending | stretching process, or to extend | stretch to the diagonal direction substantially orthogonal to it by extending | stretching to an oblique direction at a 1st extending | stretching process. Especially, it is preferable to extend | stretch in a TD direction at a 1st extending | stretching process, and to extend | stretch to MD direction at a 2nd extending | stretching process. This is because the variation in the direction of the optical axis can be reduced over the entire width of the obtained retardation film by performing stretching in the MD direction in the second stretching step having a small stretching ratio.

  As described above, by performing the first stretching step and the second stretching step on the pre-stretching film, the stretching temperature, stretching direction and stretching are performed on the A layer and the B layer in each of the first stretching step and the second stretching step. Retardation according to the magnification and the like occurs. For this reason, in the retardation film obtained through the first stretching step and the second stretching step, the retardation expressed in the A layer and the B layer in each of the first stretching step and the second stretching step is synthesized. The desired retardation will occur.

  Also, by co-stretching the pre-stretched film comprising the A layer and the B layer, the manufacturing process is shortened compared to the case of manufacturing the retardation film by laminating the separately stretched A layer and B layer. Cost can be reduced. In addition, the B layer made of the resin b having a negative intrinsic birefringence value is difficult to be stretched by itself and may cause stretching unevenness or breakage. However, it is possible to stably co-stretch by laminating with the A layer. And the thickness unevenness of the B layer can be reduced.

-Other process In the manufacturing method of the retardation film mentioned above, you may make it perform other processes other than a coextrusion process, a 1st extending process, and a 2nd extending process.
For example, you may provide the process (preheating process) of heating a film before extending | stretching previously before extending | stretching the film before extending | stretching. Examples of the means for heating the pre-stretched film include an oven-type heating device, a radiation heating device, or immersion in a liquid. Of these, an oven-type heating device is preferable. The heating temperature in the preheating step is usually a stretching temperature of −40 ° C. or higher, preferably a stretching temperature of −30 ° C. or higher, and is usually a stretching temperature of + 20 ° C. or lower, preferably a stretching temperature of + 15 ° C. or lower. The stretching temperature means the set temperature of the heating device.

  For example, the stretched film may be fixed after one or both of the first stretching step and the second stretching step. The temperature in the fixing treatment is usually room temperature or higher, preferably stretching temperature −40 ° C. or higher, and usually stretching temperature + 30 ° C. or lower, preferably stretching temperature + 20 ° C. or lower.

  Furthermore, for example, a step of providing, for example, a mat layer, a hard coat layer, an antireflection layer, an antifouling layer, or the like on the surface of the obtained retardation film may be performed.

[3. Liquid crystal display device)
According to the multilayer film of the present invention, a retardation film having a precisely controlled retardation can be realized, so that a high degree of birefringence compensation is possible. For this reason, for example, the multilayer film of the present invention can be used alone or in combination with other members to provide a liquid crystal display device, an organic electroluminescence display device, a plasma display device, an FED (field emission) display device, an SED (surface electric field). ) It may be applied to a display device such as a display device.

  A liquid crystal display device generally includes a pair of polarizers (light incident side polarizing plate and light emitting side polarizing plate) whose absorption axes are substantially orthogonal to each other, and a liquid crystal cell provided between the pair of polarizers. . When the multilayer film of the present invention is provided as a retardation film in a liquid crystal display device, for example, the multilayer film of the present invention may be provided between the pair of polarizers. Under the present circumstances, the multilayer film of this invention may be provided in the light-incidence side rather than a liquid crystal cell, and may be provided in the light-projection side rather than a liquid crystal cell.

  Usually, the pair of polarizers, the multilayer film of the present invention, and the liquid crystal cell are combined to form a single member called a liquid crystal panel, and the liquid crystal panel is irradiated with light from a light source to be directed to the light output side of the liquid crystal panel. An image is displayed on an existing display surface. In this case, the multilayer film of the present invention exhibits an excellent polarizing plate compensation function because the retardation is precisely controlled, and can reduce light leakage when the display surface of the liquid crystal display device is viewed obliquely. Is possible. In addition, since the multilayer film of the present invention usually has an excellent optical function in addition to the polarizing plate compensation function, it is possible to further improve the visibility of the liquid crystal display device.

  Liquid crystal cell driving methods include, for example, in-plane switching (IPS) method, vertical alignment (VA) method, multi-domain vertical alignment (MVA) method, continuous spin wheel alignment (CPA) method, hybrid alignment nematic (HAN) Examples thereof include a twisted nematic (TN) method, a super twisted nematic (STN) method, and an optically compensated bend (OCB) method. Of these, the in-plane switching method and the vertical alignment method are preferable, and the in-plane switching method is particularly preferable. Although the in-plane switching type liquid crystal cell has a wide viewing angle, the viewing angle can be further expanded by applying the multilayer film of the present invention as a retardation film.

The multilayer film of the present invention may be bonded to a liquid crystal cell or a polarizing plate. For example, the multilayer film may be bonded to both sides of the polarizing plate, or may be bonded only to one side. A known adhesive can be used for bonding.
Moreover, the multilayer film of this invention may be used individually by 1 sheet, and may be used in combination of 2 or more sheets.
Furthermore, when providing the multilayer film of this invention in a display apparatus, you may use it in combination with another retardation film. For example, when the multilayer film of the present invention is provided as a retardation film in a liquid crystal display device having a vertical alignment type liquid crystal cell, the viewing angle characteristics are improved between a pair of polarizers in addition to the multilayer film of the present invention. Another retardation film may be provided.

[4. Others]
The multilayer film of the present invention may be used as a quarter wavelength plate, for example. In this case, by setting the in-plane retardation of the multilayer film of the present invention to 120 nm to 160 nm, the multilayer film of the present invention can be a quarter wavelength plate, and this quarter wavelength plate can be combined with a linear polarizer. Thus, a circularly polarizing plate can be obtained. At this time, the angle formed by the slow axis of the quarter-wave plate and the absorption axis of the linear polarizer is preferably 45 ° ± 2 °.

  Moreover, you may use the multilayer film of this invention as a protective film in a polarizing plate. The polarizing plate usually includes a polarizer and protective films bonded to both sides thereof. In this case, instead of the protective film, the multilayer film of the present invention may be bonded to a polarizer, and the multilayer film may be used as a protective film. In this case, since the protective film is omitted, the liquid crystal display device can be reduced in thickness, weight, and cost.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily changed without departing from the gist of the present invention and its equivalent scope. Can be implemented. In the following description, parts and% indicating amounts are based on weight unless otherwise specified.

〔Evaluation method〕
(1) Measurement of glass transition temperature (Tg) Based on JIS K7121, it measured by differential scanning calorimetry (DSC) at the temperature increase rate of 10 degree-C / min, and measured the midpoint glass transition temperature.

(2) Retardation measurement parallel Nicol rotation method (Oji Scientific Instruments Co., KOBRA-WR) with respect to light having a wavelength of 590 nm, retardation _{R 40} in retardation Re, the angle of incidence 40 ° at an incident angle of 0 ° , And the angle of the slow axis with respect to the longitudinal direction of the film.

(3) Measurement of haze Haze was measured according to JIS K7136.

(4) Measurement of interlayer adhesive strength According to JIS K6854-1, the peel adhesive strength between the A layer and the B layer was measured at a gripping moving speed of 50 mm / min, and used as an index of interlayer adhesive strength.

(5) Measurement of bending resistance Based on JIS K5600-5-1, the bending resistance of the multilayer film was measured. It represents that it is excellent in bending resistance, so that a value is small.

[Example 1]
Pellets of polycarbonate resin (Asahi Kasei Corporation, Wonderlite PC-115, glass transition temperature 145 ° C.) 100.0 parts by weight, acrylonitrile-styrene copolymer resin (Asahi Kasei Co., Ltd., Stylac AS767) pellets 11.1 parts by weight Was melt-kneaded with a twin-screw extruder to obtain pellets of mixed resin 1 having glass transition temperatures of 110 ° C. and 141 ° C. This mixed resin 1 corresponds to a resin a having a positive intrinsic birefringence value.

Next, a film forming apparatus for co-extrusion molding of two types and two layers was prepared, and the pellets of the mixed resin 1 were put into one uniaxial extruder equipped with a double flight type screw and melted.
Styrene / maleic anhydride copolymer resin (manufactured by Nova Chemicals, Dylark D332, glass transition point 135 ° C.) was put into another uniaxial extruder equipped with a double flight screw and melted.

  The molten 260 ° C. styrene melted at 260 ° C. was passed through a polymer filter in the form of a leaf disk having a mesh size of 10 μm to one manifold of a multi-manifold die (die slip surface roughness Ra: 0.1 μm). Maleic anhydride copolymer resin was supplied to the other manifold through a leaf disk-shaped polymer filter with an opening of 10 μm.

  The mixed resin 1 and the styrene / maleic anhydride copolymer resin were simultaneously extruded from the multi-manifold die at 260 ° C. to form a film. The formed film-like molten resin was cast on a cooling roll adjusted to a surface temperature of 130 ° C., and then passed between two cooling rolls adjusted to a surface temperature of 50 ° C. : 30 μm thick) and a layer (B layer: 180 μm thick) made of a styrene / maleic anhydride copolymer resin, and a laminate 1 having a width of 1350 mm and a thickness of 210 μm was obtained. This laminated body 1 corresponds to the multilayer film of the present invention. When the haze of this laminate 1 was measured, it was 0.2%.

  The obtained laminate 1 was stretched 1.5 times in one direction at 145 ° C. Linearly polarized light ΨX that is incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector is on the XZ plane. The phase with respect to was delayed 185 nm from that before stretching.

  Separately, the obtained laminate 1 was stretched 1.5 times in one direction at 130 ° C. Linearly polarized light ΨX that is incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector is on the XZ plane, and linearly polarized light ΨY that is incident on the film surface at an incident angle of 0 ° and the vibration surface of the electric vector is on the YZ plane The phase with respect to was advanced by 161 nm from before stretching.

Separately, the obtained laminate 1 was supplied to a tenter stretching machine and stretched in the transverse direction at a stretching temperature of 155 ° C. and a stretching ratio of 3.0. Subsequently, the stretched film is supplied to a longitudinal stretching machine, and stretched in the longitudinal direction (a direction perpendicular to the longitudinal direction stretched at 155 ° C.) at a stretching temperature of 130 ° C. and a stretching ratio of 1.2, to obtain a retardation film. 1 was obtained.
The obtained retardation plate 1 had a R ₄₀ / Re of 1.01, and satisfied a relationship of 0.92 ≦ R ₄₀ /Re≦1.08. Table 1 shows the evaluation results of interlayer adhesive strength and flex resistance between the A layer / B layer.

[Comparative Example 1]
Example 1 except that an acrylonitrile-styrene copolymer resin was not used and only a polycarbonate resin (Asahi Kasei Co., Ltd., Wonderlight PC-115, glass transition temperature 145 ° C.) was used as the resin a having a positive intrinsic birefringence value. In the same manner, a layer made of a polycarbonate resin (A layer: thickness 25 μm) and a layer made of a styrene / maleic anhydride copolymer resin (B layer: thickness 180 μm), having a width of 1350 mm and a thickness. A 205 μm laminate 2 was obtained. When the haze of the laminate 2 was measured, it was 0.2%.

  When this laminate 2 was stretched 1.5 times in one direction at 145 ° C. or 130 ° C. in the same manner as in Example 1, it was incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector was XZ Table 1 shows the phase change of the linearly polarized light ΨX on the surface with respect to the linearly polarized light ΨY that is incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector is on the YZ plane.

Separately, the laminate 2 was sequentially biaxially stretched in the same manner as in Example 1 to obtain a retardation film 2. The obtained retardation plate 2 had R ₄₀ / Re of 1.03 and satisfied the relationship of 0.92 ≦ R ₄₀ /Re≦1.08. Table 1 shows the evaluation results of interlayer adhesive strength and flex resistance between the A layer / B layer.

[Comparative Example 2]
100.0 parts by weight of pellets of polycarbonate resin (Asahi Kasei Corporation, Wonderlite PC-115, glass transition temperature 145 ° C.), acrylonitrile-styrene copolymer resin (Asahi Kasei Corporation, Stylac AS767, glass transition temperature? ° C.) 42.9 parts by weight of the pellets were melt-kneaded with a twin screw extruder to obtain pellets of the mixed resin 2 having a glass transition temperature of 112 ° C. and 140 ° C. This mixed resin 2 corresponds to a resin a having a positive intrinsic birefringence value.

  A layer (A layer: thickness 35 μm) composed of the mixed resin 2 and a styrene / maleic anhydride copolymer resin in the same manner as in Example 1 except that the mixed resin 2 obtained instead of the mixed resin 1 was used. A layered product 3 having a width of 1350 mm and a thickness of 215 μm was obtained. When the haze of this laminate 3 was measured, it was 5.2%.

  When this laminate 3 was stretched 1.5 times in one direction at 145 ° C. or 130 ° C. in the same manner as in Example 1, it was incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector was XZ Table 1 shows the phase change of the linearly polarized light ΨX on the surface with respect to the linearly polarized light ΨY that is incident on the film surface at an incident angle of 0 ° and the vibration plane of the electric vector is on the YZ plane.

Separately, the laminate 3 was sequentially biaxially stretched in the same manner as in Example 1 to obtain a retardation film 3. The obtained retardation plate 2 had an R ₄₀ / Re of 1.02, and satisfied a relationship of 0.92 ≦ R ₄₀ /Re≦1.08. Table 1 shows the evaluation results of interlayer adhesive strength and flex resistance between the A layer / B layer.

  As is clear from the above Examples and Comparative Examples, it can be seen that the multilayer film of the present invention has small haze and excellent transparency. Further, by stretching the multilayer film, retardation Re at an incident angle of 0 ° and retardation R40 at an incident angle of 40 ° satisfy a relationship of 0.92 ≦ R40 / Re ≦ 1.08. A film can be obtained easily. And it turns out that this retardation film is excellent in interlayer adhesive force and bending resistance. On the other hand, when a resin that does not contain an unsaturated nitrile-styrene copolymer is used as a resin having a positive intrinsic birefringence value, interlayer adhesion and flex resistance are insufficient. Further, if the content of the unsaturated nitrile-styrene copolymer was excessive, the haze was high and the transparency was poor.

Claims (7)

A multilayer film comprising a layer (A layer) made of resin a having a positive intrinsic birefringence value on at least one surface of a layer made of resin b having a negative intrinsic birefringence value (B layer),
Resin b contains a styrenic polymer,
Resin a comprises a polycarbonate and an unsaturated nitrile-styrene copolymer,
A multilayer film, wherein the content of the unsaturated nitrile-styrene copolymer in the resin a is 4% by weight or more and 20% by weight or less.   The multilayer film according to claim 1, wherein the styrenic polymer is a copolymer containing monomer units derived from maleic anhydride.   When the uniaxial stretching direction is the X-axis, the direction perpendicular to the uniaxial stretching direction in the film plane is the Y-axis, and the film thickness direction is the Z-axis, the plane of incidence is perpendicular to the film plane and the vibration plane of the electric vector Is delayed when the phase of the linearly polarized light in the XZ plane perpendicular to the film plane and the plane of vibration of the electric vector in the YZ plane is uniaxially stretched in the X-axis direction at the temperature T1. The multilayer film according to claim 1 or 2, which proceeds when uniaxially stretched in the X-axis direction at different temperatures T2. It is a manufacturing method of the multilayer film in any one of Claims 1-3,
A resin b containing a styrenic polymer and having a negative intrinsic birefringence value;
A resin a containing a polycarbonate and an unsaturated nitrile-styrene copolymer, the content of the unsaturated nitrile-styrene copolymer being not less than 4 wt% and not more than 20 wt%, having a positive intrinsic birefringence value;
The manufacturing method of a multilayer film including co-extrusion.   A retardation film obtained by stretching the multilayer film according to claim 1.   The retardation film according to claim 5, wherein the retardation Re at an incident angle of 0 ° and the retardation R40 at an incident angle of 40 ° satisfy a relationship of 0.92 ≦ R40 / Re ≦ 1.08. It is a manufacturing method of the phase contrast film according to claim 6,
Resin b having a negative intrinsic birefringence value and resin a having a positive intrinsic birefringence value are coextruded, the uniaxial stretching direction is the X axis, and the direction perpendicular to the uniaxial stretching direction in the film plane is the Y axis. When the thickness direction of the film is the Z axis, the plane of incidence is linearly polarized with the plane of vibration of the electric vector on the XZ plane, and the plane of plane of incidence of the electric vector with the plane of electric vector is the YZ plane. A co-extrusion step of obtaining a pre-stretched film that is delayed when the phase with respect to the linearly polarized light is uniaxially stretched in the X-axis direction at a temperature T1 and advanced when uniaxially stretched in the X-axis direction at a temperature T2 different from the temperature T1;
A first stretching step for subjecting the pre-stretched film to a uniaxial stretching treatment in one direction at a temperature T1 or T2.
A second stretching step in which a uniaxial stretching treatment is performed at a temperature T2 or T1 different from the above in a direction orthogonal to the direction in which the uniaxial stretching treatment is performed in the first stretching step;
Resin b contains a styrenic polymer,
Resin a comprises a polycarbonate and an unsaturated nitrile-styrene copolymer,
A method for producing a retardation film, wherein the content of the unsaturated nitrile-styrene copolymer in the resin a is 4% by weight or more and 20% by weight or less.

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