WO2016002665A1

WO2016002665A1 - Optical film and method for manufacturing same

Info

Publication number: WO2016002665A1
Application number: PCT/JP2015/068546
Authority: WO
Inventors: 拓波多野; 智一木平
Original assignee: 日本ゼオン株式会社
Priority date: 2014-06-30
Filing date: 2015-06-26
Publication date: 2016-01-07
Also published as: JPWO2016002665A1; TW201605624A

Abstract

　An optical film provided with a layer (A) comprising a resin (a) including polycarbonate, the thickness of the layer (A) being 10 µm or less, and the amount of phenolic hydroxyl groups included in the polycarbonate being 0.005 mol or less per 1 mol of main-chain carbonate units of the polycarbonate.

Description

Optical film and manufacturing method thereof

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

Polycarbonate resins containing polycarbonate are widely used as raw materials for optical disks and films because of their high transparency and toughness (Patent Documents 1 and 2). Moreover, when a film is manufactured with a polycarbonate resin, the film can easily exhibit birefringence by stretching, and thus can be used as a retardation film.

JP2013-231815A JP-A-11-269260

When a film is produced using a polycarbonate resin, a melt extrusion method may be used. However, when the melt extrusion method is used, optical defects such as fish eyes tend to occur more than when another method such as an injection molding method is used. Here, the fish eye refers to foreign matters that can be generated inside the film. Such an optical defect may occur not only in a single-layer film having only a layer made of polycarbonate resin, but also in a multilayer film having another layer in addition to a layer made of polycarbonate resin. Such optical defects are particularly likely to occur when the thickness of the layer made of polycarbonate resin is as thin as 10 μm or less.

The present invention was devised in view of the above problems, and includes a layer (A) having a thickness of 10 μm or less made of a resin (a) containing polycarbonate, and suppresses the occurrence of optical defects in the layer (A). It is an object of the present invention to provide an optical film that can be produced, and a method for producing the optical film.

As a result of intensive studies to solve the above-mentioned problems, the present inventor used the resin (a) containing a polycarbonate having an amount of phenolic hydroxyl group of 0.005 mol or less with respect to 1 mol of the main chain carbonate unit of the polycarbonate. The inventors have found that generation of optical defects in the layer (A) made of the resin (a) can be suppressed, and completed the present invention.
That is, the present invention is as follows.

[1] A layer (A) comprising a resin (a) containing polycarbonate,
The thickness of the layer (A) is 10 μm or less,
The optical film whose quantity of the phenolic hydroxyl group contained in the said polycarbonate is 0.005 mol or less with respect to 1 mol of main chain carbonate units of the said polycarbonate.
[2] The optical film according to [1], wherein the layer (A) has birefringence, and the variation of the slow axis of the layer (A) is within ± 1 °.
[3] The optical film according to [1] or [2], comprising a layer (B) comprising a resin (b) containing a polymer having at least one of a styrene unit and a methyl methacrylate unit.
[4] The method for producing an optical film according to any one of [1] to [3],
Melting the resin (a) at a temperature of the glass transition temperature Tg (a) + 80 ° C. of the resin (a);
A step of extruding the molten resin (a) from a die into a film,
The manufacturing method of the optical film whose residence time after the said resin (a) fuse | melts until it discharges from the said die | dye is 5 hours or less.

According to the present invention, an optical film comprising a layer (A) made of a resin (a) containing polycarbonate and having a thickness of 10 μm or less and capable of suppressing the occurrence of optical defects in the layer (A); and the optical film Can be provided.

FIG. 1 shows the temperature dependence of retardation Δ when the pre-stretched film is stretched, and the temperature dependence of retardation Δ when the layers (A) and (B) of the pre-stretched film are stretched. It is a figure which shows an example.

Hereinafter, the present invention will be described in detail with reference to examples and embodiments. However, the present invention is not limited to the following examples and embodiments, and can be implemented with any modifications without departing from the scope of the claims and the equivalents thereof.

In the following description, the intrinsic birefringence being positive means that the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular thereto unless otherwise noted. Further, negative intrinsic birefringence means that the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction unless otherwise specified. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, retardation is a value represented by “(nx−ny) × d” unless otherwise specified. Further, the plane orientation coefficient is a value represented by “(nx + ny) / 2−nz” unless otherwise specified. The birefringence is a value represented by “nx−ny” unless otherwise specified. Further, the Nz coefficient is a value represented by “(nx−nz) / (nx−ny)” unless otherwise specified. Here, nx represents a refractive index in a direction (in-plane direction) perpendicular to the thickness direction and giving the maximum refractive index. ny represents the refractive index in the in-plane direction and perpendicular to the nx direction. nz represents the refractive index in the thickness direction. d represents the thickness. Unless otherwise noted, the measurement wavelength of these refractive indices nx, ny and nz is 532 nm.

Also, the slow axis of the film or layer represents the in-plane slow axis unless otherwise specified.

The “polarizing plate” includes not only a rigid member but also a flexible member such as a resin film.

Further, unless the direction of the component is “parallel”, “vertical” or “orthogonal”, unless otherwise specified, it is within a range not impairing the effect of the present invention, for example, usually ± 5 °, preferably ± 2 °, Preferably, an error within a range of ± 1 ° may be included.

Also, the MD direction (machine direction) is the film flow direction in the production line, and usually coincides with the longitudinal direction and the longitudinal direction of the long film. Further, the TD direction (traverse direction) is a direction parallel to the film surface and perpendicular to the MD direction, and usually coincides with the width direction and the lateral direction of a long film. Further, the “long” means one having a length of 5 times or more with respect to the width, preferably 10 times or more, and specifically wound in a roll shape. It has a length that can be stored or transported.

[1. Overview]
The optical film of the present invention includes a layer (A) made of a resin (a) containing polycarbonate. Moreover, the optical film of this invention may be equipped with layers other than a layer (A). For example, when performing viewing angle compensation of a polarizing plate using the optical film of the present invention, the optical film of the present invention includes a layer (B) made of a resin (b) different from the resin (a). Is preferred.

[2. Layer (A)]
The resin (a) forming the layer (A) contains polycarbonate. Polycarbonate is a polymer having a carbonate unit, and is excellent in retardation development, low temperature stretchability, and adhesion to other layers. Here, the carbonate unit is a structural unit containing a carbonate bond (—O—C (═O) —O—), and examples thereof include a structural unit of the following formula (I).

In the formula (I), R ⁰ represents a divalent hydrocarbon group.
In the formula (I), R ¹ to R ⁸ each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, or an aryl group. The alkyl group, cycloalkyl group, and aryl group may be substituted or unsubstituted. Further, the alkyl group usually has 1 to 10 carbon atoms, the cycloalkyl group usually has 1 to 10 carbon atoms, and the aryl group usually has 1 to 10 carbon atoms.

Among the polycarbonate units represented by the formula (I), carbonate units represented by the following formula (II) and carbonate units represented by the following formula (III) are preferable.

In the formula (II), R ¹ to R ⁸ are the same as those in the formula (I).
In the formula (II), R ⁹ represents a hydrogen atom, an alkyl group or an aryl group. Here, the number of carbon atoms of the alkyl group is usually 1 to 9, and the number of carbon atoms of the aryl group is usually 1 to 9.
In the formula (II), Z is a residue capable of forming a saturated or unsaturated hydrocarbon ring having 4 to 11 carbon atoms together with the carbon atom to which it is bonded. Among these, the hydrocarbon ring is preferably a saturated hydrocarbon ring having 6 carbon atoms.

In the formula (III), R ¹ to R ⁸ are the same as those in the formula (I).

Among the carbonate units, preferred examples include the following.

As the polycarbonate, one containing one type of carbonate unit may be used, or one containing two or more types of carbonate units combined at an arbitrary ratio may be used.

Further, the polycarbonate may contain an arbitrary structural unit in addition to the carbonate unit. However, in the polycarbonate, the proportion of the carbonate unit is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more from the viewpoint of effectively exhibiting the advantages of the polycarbonate.

Examples of suitable polycarbonates include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ′, o′-tetramethylbisphenol A polycarbonate, and the like.
Moreover, a polycarbonate may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

However, in the resin (a), the amount of the phenolic hydroxyl group contained in the polycarbonate is usually 0.005 mol or less, preferably 0.003 mol or less, more preferably 0.002 mol or less with respect to 1 mol of the main chain carbonate unit of the polycarbonate. Ideally 0 mol. Here, the phenolic hydroxyl group represents a hydroxyl group directly bonded to the benzene ring. The main chain carbonate unit represents a carbonate unit contained in the main chain of the polycarbonate. By using a polycarbonate having a small amount of phenolic hydroxyl group as described above, even if the thickness of the layer (A) is as thin as 10 μm or less, the occurrence of optical defects in the layer (A) can be suppressed.

The reason why the occurrence of optical defects can be suppressed by using the resin (a) containing a polycarbonate having a small amount of phenolic hydroxyl group as described above is not necessarily clear, but according to the study of the present inventor, as follows: Inferred. However, the present invention is not limited by the following inference.
When the resin (a) is formed into a film by a melt extrusion method, the resin (a) is in a molten state. In this molten state, the resin (a) is at a high temperature not lower than the glass transition temperature. In particular, the melt extrusion method generally takes a longer time for the resin (a) to remain in a molten state at a high temperature than other methods such as an injection molding method. Therefore, if the polycarbonate contained in the resin (a) has many phenolic hydroxyl groups, the phenolic hydroxyl groups may react to increase the molecular weight, thereby causing the polycarbonate to gel. When gelation occurs, the physical properties of the resin (a) change, and the generated gel becomes a fish eye, which may contribute to optical defects.
On the other hand, in the melt extrusion method using a polycarbonate having a small amount of phenolic hydroxyl groups, gelation is unlikely to occur, and it is assumed that optical defects caused by this gelation can be prevented.

The amount of the phenolic hydroxyl group contained in the polycarbonate relative to 1 mol of the main chain carbonate unit of the polycarbonate can be measured by ¹ H-NMR.

There is no limitation on the method of keeping the amount of the phenolic hydroxyl group in the polycarbonate within the above range, and examples thereof include a method of protecting the phenolic hydroxyl group with an appropriate protecting group after the production of the polycarbonate.

Further, the resin (a) may contain an optional component other than polycarbonate as long as the effects of the present invention are not significantly impaired. For example, the resin (a) may contain a polymer other than polycarbonate, a compounding agent, and the like.

Examples of polymers other than polycarbonate that can be contained in the resin (a) include acrylic polymers such as polymethyl methacrylate; olefin polymers such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene sulfide and the like. Polyarylene sulfide; Polyvinyl alcohol; Cellulose ester; Polyether sulfone; Polysulfone; Polyallyl sulfone; Polyvinyl chloride; Norbornene polymer; Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

However, it is preferable that the amount of the polymer other than polycarbonate is small in the resin (a) from the viewpoint of effectively utilizing the advantages of the polycarbonate. Specifically, the amount of the polymer other than polycarbonate is 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 polycarbonate. Among these, it is particularly preferable that no polymer other than polycarbonate is contained.

Examples of compounding agents that can be contained in the resin (a) include lubricants; layered crystal compounds; inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers; Agents, plasticizers, coloring agents such as dyes and pigments, antistatic agents, and the like. Among these, a lubricant and an ultraviolet absorber are preferable because they can improve the flexibility and weather resistance of the optical film. A compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

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 amount of the compounding agent can be appropriately determined as long as the effects of the present invention are not significantly impaired. For example, the amount of the compounding agent may be within a range where the total light transmittance in terms of 1 mm thickness of the optical film can be maintained at 80% or more.

The glass transition temperature Tg (a) of the resin (a) is usually 147 ° C. or higher, preferably 150 ° C. or higher. By increasing the glass transition temperature Tg (a) in this way, the molecular chain contained in the resin (a) can be largely oriented by stretching, and the thickness of the optical film can be reduced. Moreover, the orientational relaxation of the resin (a) can be reduced. Moreover, the upper limit of the glass transition temperature Tg (a) of the resin (a) is usually 200 ° C. or lower.

When the optical film of the present invention includes the layer (B), the elongation at break of the resin (a) at the glass transition temperature Tg (b) of the resin (b) is preferably 50% or more, and 80% or more. More preferably. Although there is no restriction | limiting in particular in the upper limit of the breaking elongation of resin (a), Usually, it is 200% or less. When the breaking elongation is within this range, the optical film can be stably stretched.
Here, the elongation at break can be determined by using a test piece of test piece type 1B described in JIS K 7127 at a pulling speed of 100 mm / min.

The optical film of the present invention can suppress the occurrence of optical defects in the layer (A). Therefore, the number of optical defects in the layer (A) is small. Specifically, the number of optical defects in the layer (A) per unit area is usually 0.1 / m ² or less, preferably 0.06 / m ² or less, more preferably 0.03 / m 2. ² or less, ideally zero.

In the present invention, the thickness of the layer (A) is 10 μm or less. When the thickness of the layer (A) is so thin, conventionally, optical defects such as fish eyes were easily generated in the layer (A). However, in the optical film of the present invention, such optical defects are not generated. Can be suppressed. Further, the lower limit of the thickness of the layer (A) is usually 0.2 μm or more, preferably 0.5 μm or more, more preferably 1.0 μm or more.

Also, the layer (A) can have birefringence. When the layer (A) has birefringence, the birefringence value is preferably 0.002 or more, more preferably 0.004 or more. By setting the birefringence of the layer (A) within the above range, variations in the slow axis of the layer (A) can be reduced. Moreover, the upper limit of the birefringence of a layer (A) is 0.020 or less normally from a viewpoint on industrial production.

Further, when the layer (A) has birefringence, it is preferable that the variation in the slow axis of the layer (A) is small. Specifically, the variation of the slow axis of the layer (A) is preferably within ± 1 °, more preferably within ± 0.5 °, particularly preferably within ± 0.3 °, ideally Zero. By setting the variation of the slow axis in the above range, when the optical film of the present invention is applied to a liquid crystal display device, it is possible to realize a good display without color unevenness and color loss.

Furthermore, the Nz coefficient of the layer (A) is preferably 10 or less, more preferably 5 or less. By setting the Nz coefficient of the layer (A) within the above range, it is easy to reduce the variation of the slow axis of the layer (A). The lower limit value of the Nz coefficient of the layer (A) can be 1 or more, but is usually 1.5 or more from the viewpoint of industrial production.

The plane orientation coefficient of the layer (A) is preferably larger than 0.025, more preferably 0.026 or more, preferably 0.035 or less, more preferably 0.030 or less. By making the plane orientation coefficient of the layer (A) at least the lower limit of the above range, the thickness of the optical film is reduced when the optical film satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08. be able to. Moreover, it is possible to manufacture an optical film stably by making it below an upper limit.

The optical film of the present invention may have only one layer (A) or two or more layers. For example, the optical film of the present invention may be a multilayer film having the first layer (A), the layer (B), and the second layer (A) in this order.

Furthermore, the layer (A) is preferably on the outermost surface of the optical film of the present invention. When an optical defect can be caused by a depression or protrusion on the surface of the layer (A), if a layer covering the surface of the layer (A) is provided, the depression or protrusion is a layer covering the surface of the layer (A). It may be buried to prevent the appearance of optical defects. However, when the layer (A) is on the outermost surface, the depressions or protrusions are not filled with another layer, so conventionally it has been particularly difficult to prevent the occurrence of optical defects. On the other hand, in the optical film of the present invention, since the generation of the depressions and protrusions can be suppressed, the generation of optical defects can be effectively suppressed even when the layer (A) is on the outermost surface.

[3. Layer (B)]
The resin (b) is preferably a thermoplastic resin. Examples of the polymer contained in the resin (b) include a styrene or a homopolymer of a styrene derivative, and a polystyrene polymer including a copolymer of styrene or a styrene derivative and an arbitrary monomer; a polyacrylonitrile polymer. A polymethyl methacrylate polymer; or a multi-component copolymer thereof. Moreover, as an arbitrary monomer copolymerized to styrene or a styrene derivative, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene are mentioned as a preferable thing, for example. Moreover, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, a polymer having at least one of a styrene unit and a methyl methacrylate unit is preferable. Here, the styrene unit is a structural unit having a structure formed by polymerizing styrene. The methyl methacrylate unit is a structural unit having a structure formed by polymerizing methyl methacrylate. Among them, a polystyrene polymer is particularly preferable from the viewpoint of high retardation development.

Among them, from the viewpoint of high heat resistance, a copolymer of styrene or a styrene derivative and maleic anhydride is more preferable, and a styrene-maleic anhydride copolymer is particularly preferable. In this case, the amount of the structural unit having a structure formed by polymerizing maleic anhydride is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, particularly preferably 100 parts by weight of the polystyrene polymer. Is 15 parts by weight or more, preferably 30 parts by weight or less, more preferably 28 parts by weight or less, and particularly preferably 26 parts by weight or less.

The resin (b) may contain an optional component other than the polymer as long as the effects of the present invention are not significantly impaired. For example, the resin (b) may contain a compounding agent or the like.

Examples of the compounding agent that can be contained in the resin (b) include those in the same range as those described as the compounding agent that the resin (a) can contain. Moreover, these 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 as long as the effects of the present invention are not significantly impaired. For example, the amount of the compounding agent may be within a range where the total light transmittance in terms of 1 mm thickness of the optical film can be maintained at 80% or more.

The glass transition temperature Tg (b) of the resin (b) 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. Since the glass transition temperature Tg (b) is thus high, the relaxation of the orientation of the resin (b) can be reduced. Moreover, although there is no restriction | limiting in particular in the upper limit of the glass transition temperature Tg (b) of resin (b), Usually, it is 200 degrees C or less.

When the optical film satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08, the glass transition temperature Tg (b) of the resin (b) is equal to the glass transition temperature Tg (a) of the resin (a). Even if the difference Tg (a) −Tg (b) from the glass transition temperature Tg (b) of the resin (b) is set to satisfy the relationship of “Tg (a) −Tg (b)> 20 ° C.” Good. More specifically, Tg (a) -Tg (b) may be preferably greater than 20 ° C, more preferably greater than 22 ° C. Thereby, when it is desired to develop retardation in the optical film of the present invention by stretching, the temperature dependency of the development of retardation can be increased during stretching. Further, the molecular chains contained in the layer (A) and the layer (B) can be largely oriented by stretching. Therefore, the thickness of the optical film after stretching can be reduced. Further, the upper limit of the temperature difference Tg (a) −Tg (b) is preferably 50 ° C. or less, more preferably 40 ° C. or less, and particularly preferably 30 ° C. or less. Thereby, it is easy to improve the flatness of the optical film.

The breaking elongation of the resin (b) at the glass transition temperature Tg (a) of the resin (a) is preferably 50% or more, and more preferably 80% or more. Although there is no restriction | limiting in particular in the upper limit of the breaking elongation of resin (b), Usually, it is 200% or less. If the elongation at break is within this range, the optical film can be stably stretched.

The thickness of the layer (B) is usually 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more, and usually 100 μm or less, preferably 60 μm or less, more preferably 40 μm or less. By setting the thickness of the layer (B) to be equal to or greater than the lower limit of the above range, the strength of the entire film can be increased and handling can be facilitated. Moreover, by making it below an upper limit, the whole film can be made thin, and the display in which a film is used can be made thin.

The layer (B) can have birefringence. When the layer (B) has birefringence, the birefringence value is preferably 0.004 or more, more preferably 0.005 or more, preferably 0.010 or less, more preferably 0.008 or less. is there. When the birefringence of the layer (B) is not less than the lower limit of the above range, the thickness of the optical film is reduced when the optical film satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08. Is possible. Moreover, it is possible to manufacture an optical film stably by making it below an upper limit.

The Nz coefficient of the layer (B) is preferably −0.30 or more, more preferably −0.25 or more. By setting the Nz coefficient of the layer (B) in the above range, when the optical film satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08, it is possible to reduce the thickness of the optical film. . The upper limit may be 0 or less, but is usually −0.10 or less from the viewpoint of industrial production.

The plane orientation coefficient of the layer (B) is preferably −0.002 or less, more preferably −0.003 or less. By setting the plane orientation coefficient of the layer (B) within the above range, when the optical film satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08, it is possible to reduce the thickness of the optical film. is there. Further, the lower limit is usually −0.008 or more from the viewpoint of industrial production.

The optical film of the present invention may have only one layer (B) or two or more layers.

[4. Any layer]
The optical film of the present invention may further include an arbitrary layer in addition to the layer (A) and the layer (B). Examples of the optional layer include a mat layer capable of improving the slipperiness of the film, a hard coat layer such as an impact-resistant polymethacrylate resin layer, an antireflection layer, and an antifouling layer.

[5. Physical properties of optical film]
The optical film of the present invention can have desired optical properties depending on the application. For example, the optical film may be an optically isotropic film having substantially no retardation. Further, for example, the optical film may be a film having optical anisotropy having a retardation of a desired size.

In particular, when the optical film of the present invention is used as a viewing angle compensation film in an image display device, the optical film preferably satisfies 0.92 ≦ R ₄₀ /Re≦1.08. Here, Re represents retardation at an incident angle of 0 ° of the optical film. R ₄₀ represents retardation at an incident angle of 40 ° of the optical film. By satisfying the relationship of 0.92 ≦ R ₄₀ /Re≦1.08, the optical film of the present invention can realize good viewing angle compensation performance, so that the change in color tone of the display device due to the observation angle can be reduced. (See JP 2013-137394 A).

The total light transmittance of the optical film of the present invention is preferably 85% or more. 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 optical 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 clarity of the display image of the display device including the optical film can be improved. Here, the haze can be measured at five locations using “turbidity meter NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7361-1997, and the average value obtained therefrom can be adopted.

In the optical 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. The lower limit is ideally zero. ΔYI can be measured using “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.

The optical film of the present invention preferably has a JIS pencil hardness of H or higher. This JIS pencil hardness can be adjusted by the type of resin and the thickness of the resin layer. Here, in accordance with JIS K5600-5-4, the JIS pencil hardness is determined by tilting a pencil of various hardnesses by 45 °, applying a load of 500 g weight from above, scratching the film surface, and starting scratching. That's it.

The optical film of the present invention may shrink in the longitudinal direction and the transverse direction by heat treatment at a temperature of 60 ° C., a humidity of 90% RH, and 100 hours. However, the shrinkage rate is preferably 0.5% or less, more preferably 0.3% or less. By reducing the shrinkage rate in this way, it is possible to prevent a phenomenon in which the optical film is deformed by the shrinkage stress and peeled off from the display device when the optical film is used in a high temperature and high humidity environment.

The dimension in the width direction of the optical film of the present invention is preferably 500 mm or more, more preferably 1000 mm or more, and preferably 2000 mm or less.

[6. Manufacturing method of optical film]
The optical film of the present invention can be produced by a melt extrusion method. The melt extrusion method is an excellent production method from the viewpoints of production efficiency and that a volatile component such as a solvent does not remain in the film.

Further, when an optical film having two or more layers is produced, for example, a coextrusion method can be used in the melt extrusion method. Examples of the coextrusion method include a coextrusion T-die method, a coextrusion inflation method, and a coextrusion lamination method. Of these, the coextrusion T-die method is preferable. The coextrusion T-die method includes a feed block method and a multi-manifold method, and the multi-manifold method is particularly preferable in that variation in thickness can be reduced.

In the melt extrusion method, generally, a process of melting a resin as a raw material and a process of extruding the melted resin from a die into a film are performed. Therefore, the method for producing an optical film of the present invention includes a step of heating and melting the resin (a), and a step of extruding the molten resin (a) from a die into a film. Furthermore, when manufacturing an optical film provided with a layer (B), the manufacturing method of an optical film includes the process of heating and fuse | melting resin (b), And the molten resin (a) is made into a film form from a die | dye. In the extrusion molding step, the resin (b) is also extruded from the die into a film at the same time as the resin (a).

In the step of melting the resin (a), the melting temperature of the resin (a) is preferably Tg (a) + 80 ° C. or higher, more preferably Tg (a) + 100 ° C. or higher, preferably Tg (a) + 180 ° C. Hereinafter, it is more preferably Tg (a) + 150 ° C. or less. By setting the melting temperature of the resin (a) to be equal to or higher than the lower limit of the above range, the fluidity of the resin (a) can be sufficiently enhanced. Moreover, deterioration of resin (a) can be prevented by setting it as an upper limit or less. Further, even at such a high temperature, since the amount of the phenolic hydroxyl group contained in the polycarbonate contained in the resin (a) is small, the resin (a) is hardly gelled.

In the method for producing an optical film, the residence time from when the resin (a) is melted until it is discharged from the die is preferably 5 hours or less, more preferably 3 hours or less, and particularly preferably 2 hours or less. By shortening the residence time of the resin (a) as described above, the gelation of the resin (a) can be made more difficult to occur, so that the generation of optical defects in the layer (A) can be more effectively suppressed.

In the melt extrusion method, a film-like molten resin extruded from an opening of a die is usually brought into close contact with a cooling roll (including a cooling drum). Examples of the method for bringing the resin into close contact with the cooling roll 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 resin extruded from the opening of the die through the cooling roll is not particularly limited.

Normally, the degree of adhesion of the extruded film-like resin to the cooling roll varies depending on the temperature of the cooling roll. Increasing the temperature of the cooling roll tends to improve adhesion. Moreover, by not making the temperature of a cooling roll too high, peeling from the cooling roll of film-form resin can be made easy, and the winding of resin to a cooling roll can be prevented. From this point of view, the temperature of the cooling roll is preferably (Tg ′ + 30 ° C.) or less, more preferably (Tg ′ −−), where Tg ′ is the glass transition temperature of the resin extruded from the die and contacting the drum. 5 ° C.) to (Tg′−45 ° C.). Thereby, malfunctions, such as a slip and a crack, can be prevented.

In the melt extrusion method, in order to reduce the content of the residual solvent in the obtained optical film, (1) the residual solvent contained in the resin as a raw material is reduced; (2) before the film is formed The resin may be pre-dried. The preliminary drying is performed using, for example, a hot air dryer or the like in the form of pellets or the like. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, the residual solvent in the obtained optical film can be reduced, and foaming of the extruded film-like resin can be prevented.

The optical film of the present invention is obtained by the melt extrusion method. Usually, the optical film obtained in this way does not develop a large retardation. Therefore, for example, in order to express a desired retardation, the obtained optical film may be stretched. Therefore, in the following, an example of producing an optical film having the layer (A) and the layer (B) and satisfying 0.92 ≦ R ₄₀ /Re≦1.08 will be described. The extending | stretching process in a manufacturing method is demonstrated. In the following description, an optical film before being subjected to stretching treatment may be appropriately referred to as “film before stretching” and an optical film that has been subjected to stretching treatment as “stretched film”.

The film before stretching in the example shown here is a film including a layer (A) made of the resin (a) and a layer (B) made of the resin (b). This pre-stretched film satisfies the following requirement P in order to obtain a film satisfying 0.92 ≦ R ₄₀ /Re≦1.08 as a stretched film.

Requirement P: 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 phase of the XZ polarized light with respect to the YZ polarized light is
Delayed when uniaxially stretched in the X-axis direction at temperature T1,
The process proceeds when uniaxial stretching is performed in the X-axis direction at a temperature T2 different from the temperature T1.
Here, “XZ polarized light” refers to linearly polarized light that is incident perpendicularly to the film surface and has an electric vector vibration plane in the XZ plane. “YZ polarized light” refers to linearly polarized light that is incident perpendicularly to the film surface and the vibration plane of the electric vector is on the YZ plane.

The above requirement P is satisfied when at least one of the various directions in the plane of the film before stretching is taken as the X axis. Usually, the pre-stretch film is an isotropic (that is, has no anisotropy) raw film, so if one of the in-plane directions is taken as the X-axis, any other direction can be satisfied. The requirement P can also be satisfied when is the X axis.

In a film in which an in-plane slow axis appears on the X axis by uniaxial stretching, the phase of XZ polarized light is usually delayed from that of YZ polarized light. On the other hand, in a film in which a fast axis appears on the X axis by uniaxial stretching, the phase of XZ polarized light usually proceeds with respect to that of YZ polarized light. The pre-stretch film satisfying the above requirement P is a film using these properties, and the slow axis or fast axis appears depending on the stretch temperature. The temperature dependence of the expression of such retardation can be adjusted, for example, by adjusting the relationship such as the photoelastic coefficient of the resin contained in the pre-stretched film and the thickness ratio of each layer.

Here, taking the retardation Δ based on the stretching direction as an example, the conditions to be satisfied by the film before stretching will be described. The retardation Δ with respect to the stretching direction 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 the direction orthogonal to the stretching direction in the plane (= nX−nY ) And the thickness d. In this case, the retardation Δ that can be expressed in the entire pre-stretched film when the pre-stretched film is stretched is synthesized from the retardation Δ that is expressed in each resin layer included in the pre-stretched film. Therefore, for example, in order to reverse the sign of retardation Δ expressed when the pre-stretched film is stretched between stretching at a high temperature T1 and stretching at a low temperature T2, the following conditions (i) and ( It is preferable to adjust the thickness of the resin layer contained in the pre-stretch film so as to satisfy ii).
(I) By stretching at a low temperature T _L, the absolute value of retardation Δ expressed by a resin having a high glass transition temperature becomes smaller than the absolute value of retardation Δ expressed by a resin having a low glass transition temperature.
(Ii) By stretching at a high temperature T _H, the absolute value of retardation Δ expressed by a resin having a low glass transition temperature is smaller than the absolute value of retardation Δ expressed by a resin having a high glass transition temperature.

Temperature T1 of the requirements P is a temperature either temperature _{T H} or _{T L,} the temperature T2 is the other of the temperature of different temperatures _{T H} or _{T L} is the temperature T1. The temperature satisfying the requirement P is preferably (Tg ₁ −10 ° C.) to (Tg _h + 10 ° C.) because the birefringence can be easily adjusted. That is, the temperatures T1 and T2 are preferably included in the temperature range of (Tg ₁ −10 ° C.) to (Tg _h + 10 ° C.). Here, the temperature Tg _l, in the resin contained in the film before stretching, most glass transition temperature means a glass transition temperature of the resin having low. The temperature Tg _h and, among the resin contained in the film before stretching, most glass transition temperature means a glass transition temperature of the high resin.

The expression of retardation Δ when a pre-stretch film satisfying the requirement P is stretched will be specifically described with reference to the drawings. FIG. 1 shows the temperature dependence of retardation Δ when the pre-stretched film is stretched, and the temperature dependence of retardation Δ when the layers (A) and (B) of the pre-stretched film are stretched. It is a figure which shows an example. In the example shown in FIG. 1, the glass transition temperature of the resin (a) is high, and the glass transition temperature of the resin (b) is low.

In the film before stretching as shown in FIG. 1, in the stretching at a low temperature Tb, the negative retardation Δ expressed in the layer (B) is larger than the positive retardation Δ expressed in the layer (A). Overall, a negative retardation Δ is developed. On the other hand, in the stretching at a high temperature Ta, the negative retardation Δ expressed in the layer (B) is smaller than the positive retardation Δ expressed in the layer (A), so that the positive retardation Δ is expressed as a whole. To do. Therefore, by combining such stretching at different temperatures Ta and Tb, a retardation Δ generated by stretching at each temperature is synthesized, and a stretched film having a desired retardation Δ and thus exhibiting desired optical properties. Can be realized stably.

As described above, the resin contained in the pre-stretch film is a resin that can cause a difference between the refractive index in the X-axis direction and the refractive index in the Y-axis direction in each layer by stretching in one direction (that is, uniaxial stretching). By selecting a combination and further adjusting the total thickness of each layer in consideration of the stretching conditions, a pre-stretched film satisfying the above requirement P can be obtained. At this time, if a resin having a large degree of orientation developed by stretching is used, a large retardation Δ can be expressed even if the layer thickness is reduced.

The specific thickness of the layer constituting the pre-stretched film can be set according to the optical properties of the stretched film to be manufactured so as to satisfy the requirement P described above. At this time, the ratio TA / TB of the total thickness TA of the layer (A) and the total thickness TB of the layer (B) is preferably 1/20 or more, more preferably 1/15 or more, preferably 1/4 or less, more preferably 1/5 or less. Thereby, the temperature dependence of retardation expression can be increased.

After the pre-stretching film as described above is manufactured, a stretching process for stretching the pre-stretching film is performed. When the pre-stretching film is stretched in this stretching step, each layer included in the pre-stretching film is also stretched, and the stretched layers exhibit predetermined optical characteristics.
In the stretching process, the film before stretching is subjected to a uniaxial stretching process in one direction at one of the temperatures T1 and T2, and a direction orthogonal to the direction in which the uniaxial stretching process is performed in the first stretching process, And a second stretching step in which a uniaxial stretching process is performed at the other temperature of T1 and T2.

In the first stretching step, the film before stretching is uniaxially stretched in one direction at one of the temperatures T1 and 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. Among these, in the first stretching step, it is preferable to perform a uniaxial stretching process at a temperature T1.

The temperature T1 is preferably higher than Tg (b), more preferably higher than Tg (b) + 5 ° C, preferably lower than Tg (a) + 40 ° C, and lower than Tg (a) + 20 ° C. Is more preferable. By making the temperature T1 higher than the lower limit of the above range, the optical characteristics of the layer (B) can be stably kept within a desired range. Moreover, by making temperature T1 lower than the upper limit of the said range, the optical characteristic of a layer (A) can be stably stored in a desired range.

The stretching ratio in the first stretching step is preferably 2 times or more, more preferably 3 times or more, preferably 4 times or less, more preferably 3.5 times or less. By setting the draw ratio in the first drawing step to be equal to or higher than the lower limit value of the above range, the molecules contained in the layer can be largely oriented, so that desired optical characteristics can be expressed with a thin thickness. Moreover, extending | stretching can be stably performed by setting it as below an upper limit.

The uniaxial stretching process can be performed by a 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 method of uniaxially stretching in the MD direction include an IR heating method between rolls, a float method, and the like. Of these, the float method is preferable because a stretched 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 of the film in the stretching zone. In order to give a temperature difference in the TD direction in the stretching zone, for example, a method of 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 can be used.

After performing a 1st extending process, a 2nd extending process is performed. In the second stretching step, the film subjected to the uniaxial stretching process in one direction in the first stretching process is subjected to a uniaxial stretching process in a direction orthogonal to the direction in which the uniaxial stretching process is performed in the first stretching process.
The uniaxial stretching process in the second stretching step is performed at a temperature different from the stretching temperature in the first stretching step among the temperatures T1 and T2. In the second stretching step, it is preferable to perform a uniaxial stretching process at a temperature T2.

The temperature T2 is usually a temperature lower than the temperature T1. The specific temperature T2 is preferably higher than Tg (b) −20 ° C., more preferably higher than Tg (b) −10 ° C., preferably lower than Tg (b) + 5 ° C., and Tg (b b) is preferably lower. By making temperature T2 higher than the lower limit of the above range, it is possible to prevent the film from being broken or clouded during stretching. Moreover, by making temperature T2 lower than the upper limit of the said range, a desired optical characteristic can be stably expressed in a layer (B).

The difference between the temperature T1 and the temperature T2 is usually 10 ° C. or higher, preferably 20 ° C. or higher. By increasing the difference between the temperature T1 and the temperature T2 as described above, desired optical characteristics can be stably expressed in the stretched film. Moreover, although there is no restriction | limiting in the upper limit of the difference of temperature T1 and temperature T2, 100 degrees C or less is preferable from a viewpoint of industrial productivity.

The stretching ratio in the second stretching step is preferably smaller than the stretching ratio in the first stretching step. In the successive stretching step, the state of molecular orientation in the stretched film obtained tends to be more strongly influenced in the second stretching step than in the first stretching step. Therefore, adjustment of the optical characteristic of a stretched film is easy, so that the draw ratio of a 2nd extending process is small. The stretching ratio in the specific second stretching step is preferably 1.1 times or more, preferably 2 times or less, more preferably 1.5 times or less, and particularly preferably 1.3 times or less.

Further, from the viewpoint of obtaining a high plane orientation coefficient, it is preferable that the stretching ratio is high in both the first stretching step and the second stretching step. Specifically, the product of the draw ratio in the first draw step and the draw ratio in the second draw step is preferably 3.6 or more, more preferably 3.8 or more, and even more preferably 4.0 or more. is there. The upper limit of the product of the draw ratio in the first draw step and the draw ratio in the second draw step is preferably 6.0 or less from the viewpoint of facilitating adjustment of optical properties in the draw step.

The same method as that which can be adopted in the uniaxial stretching process in the first stretching process can be applied to the uniaxial stretching process in the second stretching process.

The combination of the stretching directions in the first stretching process and the second stretching process is arbitrary. For example, the film may be stretched in the MD direction in the first stretching process and stretched in the TD direction in the second stretching process. Further, for example, the film may be stretched in the TD direction in the first stretching process and stretched in the MD direction in the second stretching process. Further, for example, the film may be stretched in an oblique direction in the first stretching process, and may be stretched in an oblique direction orthogonal to the second stretching process. Here, the oblique direction represents a direction that is neither parallel nor perpendicular to the width direction of the film. 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. By performing the stretching in the second stretching step with a small stretching ratio in the MD direction, variations in the optical axis such as the slow axis can be reduced over the entire width of the stretched film obtained.

Since the molecules contained in the layer (A) and the layer (B) are oriented by the stretching step described above, desired optical characteristics are exhibited. Thereby, in this example, an optical film satisfying 0.92 ≦ R ₄₀ /Re≦1.08 is obtained.

Moreover, in the manufacturing method of the optical film of this invention, you may include arbitrary processes other than having mentioned above.
For example, the method for producing an optical film of the present invention may include a step of heat-treating the film at a predetermined temperature after the first stretching step or after the second stretching step. The temperature of the heat treatment is preferably Tg (b) -30 ° C. or more, more preferably Tg (b) -20 ° C. or more, preferably Tg (b) or less, more preferably Tg (b) −5 ° C. or less. is there. By performing such heat treatment, the state of the molecular chain oriented by stretching can be fixed. Therefore, since the relaxation of orientation can be suppressed, it is possible to suppress changes over time in the optical characteristics of each layer.

For example, the method for producing an optical film of the present invention may include a step (preheating step) of preheating the pre-stretching film before the stretching step. Examples of the heating means 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 this step is preferably a stretching temperature of −40 ° C. or more, more preferably a stretching temperature of −30 ° C. or more, preferably a stretching temperature of + 20 ° C. or less, more preferably a stretching temperature of + 15 ° C. or less. Here, the stretching temperature means a set temperature of the heating device.

For example, the method for producing an optical film of the present invention may further include a step of further providing an arbitrary layer on the surface of the film obtained as described above.

[7. Application of optical film]
The use of the optical film of the present invention is arbitrary. The optical film of the present invention can be used for, for example, a viewing angle compensation film, a polarizing plate protective film, and the like.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Example 1]
[1. Production and evaluation of stretched film)
A polycarbonate resin (“Iupilon S3000” manufactured by Mitsubishi Engineering Plastics, glass transition temperature 149 ° C.) was prepared as the resin (a). The amount of the phenolic hydroxyl group of the polycarbonate contained in this polycarbonate resin is 0.0016 mol with respect to 1 mol of the main chain carbonate unit of the polycarbonate.
Further, a styrene / maleic anhydride copolymer resin ("Dialark D332" manufactured by Nova Chemicals, glass transition temperature 128 ° C) was prepared as the resin (b).

A film forming apparatus for coextrusion molding of two types and two layers (layer (A) / layer (B)) was prepared. This film forming apparatus is provided with a single screw extruder for each of the layer (A) and the layer (B).

The resin (a) was supplied to a single screw extruder for the layer (A) of the film forming apparatus and melted at 270 ° C. The molten resin (a) was supplied to the manifold for the layer (A) of the multi-manifold die through 20 4.4 inch leaf disk filters having a filtration accuracy of 5 μm.

Also, the resin (b) was supplied to a uniaxial stretching machine for the layer (B) of the film forming apparatus and melted at 260 ° C. The molten resin (b) was supplied to the manifold for the layer (B) of the multi-manifold die through 50 12 inch leaf disk filters having a filtration accuracy of 5 μm.

The resin (a) and the resin (b) were simultaneously extruded from the multi-manifold die and formed into a film shape. At this time, the extrusion rate of the resin (a) was 20 kg / hour, and the extrusion rate of the resin (b) was 200 kg / hour. This obtained the elongate multilayer film provided with the layer (A) which consists of resin (a) with a thickness of 20 micrometers, and the layer (B) which consists of resin (b) with a thickness of 200 micrometers.

The above multilayer film was stretched in the width direction at a stretching temperature of 160 ° C. and a stretching ratio of 3.0 times using a transverse stretching machine to obtain an intermediate film. Thereafter, this intermediate film was stretched in the longitudinal direction using a longitudinal stretching machine at a stretching temperature of 125 ° C. and a stretching ratio of 1.3 times to obtain a stretched film. The layer (A) of the obtained stretched film had a thickness of 7 μm, and the layer (B) had a thickness of 67 μm.

The surface of the stretched film thus obtained was washed with pure water. Thereafter, the stretched film was sandwiched between two polarizing plates to produce a sample sheet having a polarizing plate / stretched film / polarizing plate in this order. At this time, the polarizing plates were arranged in crossed Nicols so that the polarization transmission axes of the polarizing plates were perpendicular to each other.

The sample sheet was illuminated with a backlight, and the side opposite to the backlight of the data sheet was observed to count the number of bright spots. Since the bright spots are caused by optical defects, a stretched film having a smaller number of bright spots is used as a high-quality optical film with fewer optical defects.

[2. (Measurement of the longest residence time of polycarbonate resin)
A coloring resin was prepared by adding 1% by weight of a pigment (“Kayaset Red ECG” manufactured by Nippon Kayaku Co., Ltd.) to the polycarbonate resin prepared as the resin (a). This colored resin was filled from the single screw extruder for the layer (A) of the film forming apparatus to the multi-manifold die. Thereafter, the polycarbonate resin containing no dye was put into a single screw extruder for the layer (A) and extruded at an extrusion speed of 20 kg / hour. The time from the start of extrusion until the dye concentration of the resin discharged from the multi-manifold die became 1 ppm or less was measured, and this was defined as the longest residence time.

[Example 2]
The kind of polycarbonate resin used as the resin (a) was changed to “Taflon A1900” (glass transition temperature 149 ° C.) manufactured by Idemitsu Kosan Co., Ltd. The amount of the phenolic hydroxyl group of the polycarbonate contained in the polycarbonate resin used in Example 2 is 0.0029 mol with respect to 1 mol of the main chain carbonate unit of the polycarbonate.
Except for the above, the production and evaluation of a stretched film and the measurement of the longest residence time of the polycarbonate resin were performed in the same manner as in Example 1.

[Comparative Example 1]
The kind of polycarbonate resin used as resin (a) was changed. The glass transition temperature of the polycarbonate resin used in Comparative Example 1 is 144 ° C. Moreover, the amount of the phenolic hydroxyl group of the polycarbonate contained in the polycarbonate resin used in Comparative Example 1 is 0.0065 mol with respect to 1 mol of the main chain carbonate unit of the polycarbonate.
Except for the above, the production and evaluation of a stretched film and the measurement of the longest residence time of the polycarbonate resin were performed in the same manner as in Example 1.

[Comparative Example 2]
The kind of polycarbonate resin used as resin (a) was changed. The glass transition temperature of the polycarbonate resin used in Comparative Example 2 is 147 ° C. The amount of the phenolic hydroxyl group of the polycarbonate contained in the polycarbonate resin used in Comparative Example 2 is 0.011 mol with respect to 1 mol of the main chain carbonate unit of the polycarbonate.
Except for the above, the production and evaluation of a stretched film and the measurement of the longest residence time of the polycarbonate resin were performed in the same manner as in Example 1.

[result]
The results of Examples and Comparative Examples are shown in the following table. In the following table, the OH amount indicates the amount of the phenolic hydroxyl group of the polycarbonate contained in the polycarbonate resin with respect to 1 mol of the main chain carbonate unit of the polycarbonate.

[Consideration]
As can be seen from Table 1, since the number of bright spots is smaller in the example than in the comparative example, it can be seen that the occurrence of optical defects is suppressed. Therefore, from the results of these examples, it was confirmed that the present invention can suppress the occurrence of optical defects in the layer (A) even when the thickness of the layer (A) made of polycarbonate resin is as thin as 10 μm or less.

Claims

A layer (A) comprising a resin (a) containing polycarbonate;
The thickness of the layer (A) is 10 μm or less,
The optical film whose quantity of the phenolic hydroxyl group contained in the said polycarbonate is 0.005 mol or less with respect to 1 mol of main chain carbonate units of the said polycarbonate.
The optical film according to claim 1, wherein the layer (A) has birefringence, and the variation of the slow axis of the layer (A) is within ± 1 °.
The optical film of Claim 1 or 2 provided with the layer (B) which consists of resin (b) containing the polymer which has at least one of a styrene unit and a methylmethacrylate unit.
A method for producing an optical film according to any one of claims 1 to 3,
Melting the resin (a) at a temperature of the glass transition temperature Tg (a) + 80 ° C. of the resin (a);
A step of extruding the molten resin (a) from a die into a film,
The manufacturing method of the optical film whose residence time after the said resin (a) fuse | melts until it discharges from the said die | dye is 5 hours or less.