JP2010078905A - Optical film and liquid crystal display - Google Patents

Abstract

An optical film capable of producing a high-quality liquid crystal display screen with little change in phase difference depending on the viewing angle and improving the productivity thereof, and a liquid crystal display device using the optical film are provided.
The present invention is an optical film comprising a resin composition P containing a resin A having a positive intrinsic birefringence value and a resin B having a negative intrinsic birefringence value. Resin B is a polystyrene resin having a syndiotactic structure. Optical film, in-plane retardation _{R 450} at an incident angle of 0 ° in the optical wavelength 450 nm, incident angle of 0 ° in the light plane retardation _{R 550} and wavelength 650 nm, at an incident angle of 0 ° in the optical wavelength 550nm The in-plane retardation R ₆₅₀ is R ₄₅₀ <R ₅₅₀ <R ₆₅₀ , and the retardation Rth in the thickness direction in the entire wavelength range of 400 to 700 nm is a negative value.
[Selection] Figure 1

Description

  The present invention relates to an optical film and a liquid crystal display device, and in particular, an optical film capable of producing a high-quality liquid crystal display screen with little change in phase difference depending on a viewing angle and improving productivity, and a liquid crystal display device including the same. About.

  Liquid crystal display devices have features such as thinness, light weight, and low power consumption, and are widely used in televisions, personal computers, and the like. The liquid crystal display device includes a liquid crystal panel including a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate in this order, and a light source that emits light from the light incident side of the light incident side polarizing plate. Yes. At this time, the transmission axis of the light incident side polarizing plate and the transmission axis of the light output side polarizing plate are arranged to be orthogonal to each other. In such a liquid crystal display device, an image is displayed on the screen by changing the orientation of the liquid crystal molecules by applying a voltage to the liquid crystal cell and adjusting the amount of transmitted light.

  In the liquid crystal display device in which the two polarizing plates described above are arranged so that their transmission axes are perpendicular to the vertical direction and the horizontal direction, sufficient contrast is obtained when the screen is viewed from the vertical and horizontal directions. However, when the screen is viewed from a direction deviating from the top, bottom, left, and right, that is, from an oblique direction, the transmission axis of the light incident side polarizing plate and the transmission axis of the light output side polarizer are apparently not orthogonal. Polarization is not completely blocked and light leakage occurs, resulting in a decrease in contrast. For this reason, in order to prevent such a decrease in contrast, an attempt has been made to perform optical compensation by arranging a retardation film between two polarizing plates. As such a retardation film, the in-plane refractive index of the retardation film is nx, ny (nx ≧ ny, where nx and ny are orthogonal to each other), and the refractive index in the thickness direction of the retardation film is In the case of nz, a so-called positive letterer that satisfies the relationship of nz> nx ≧ ny, that is, the relationship that the retardation Rth in the thickness direction is negative is used.

  Examples of such a film having a negative Rth include a film obtained by biaxially stretching a pre-stretch film made of a resin having a negative intrinsic birefringence value such as a styrene resin. However, the styrene resin is considered to be an effective material for expressing desired optical properties because it has high transparency and a negative intrinsic birefringence value, but a film using this is very brittle. In many cases, breakage and wrinkles are generated during continuous conveyance during stretching for expressing desired optical properties, and the workability (stretchability) is inferior, and the durability of the stretched film after processing is low. .

  Therefore, Patent Document 1 discloses a layer made of a styrene resin in a laminated film in which a thermoplastic resin layer is laminated on both sides of a layer made of a styrene resin for the purpose of improving stretch processability, durability, and optical properties. It is disclosed that a retardation film is produced by simultaneously biaxially stretching after prescribing to a predetermined amount or less. According to such a method, stretching processability, durability, and optical properties can be improved. However, since the optical film shown in Patent Document 1 is a laminated film, the productivity of the film is not sufficient as compared with a single layer film, and further improvement is required.

  By the way, in Patent Document 2, for the purpose of improving the image quality of a liquid crystal display device, in creating a so-called reverse wavelength dispersion type film in which the retardation value increases as the wavelength becomes longer, polyphenylene oxide and polystyrene are used. A retardation film having a wavelength band in which a retardation value (in-plane retardation Re) is positive and a wavelength band in which a retardation value is negative at a wavelength of 400 to 700 nm. It is disclosed to use a laminated film obtained by laminating a plate and a retardation film made of, for example, polycarbonate that has a positive or negative retardation value at a wavelength of 400 to 700 nm. However, as shown in Patent Document 2, since it is necessary to laminate a plurality of films, the productivity of the films is not sufficient, and further improvements are required.

  Further, as a film other than an optical film, Patent Document 3 discloses a film obtained by uniaxially stretching a film made of a resin composition containing a polystyrene resin having a syndiotactic structure and a polyphenylene ether resin (polyphenylene oxide). . However, as used as a retardation film for a liquid crystal display device or the like, the wavelength dependency and retardation in the thickness direction of the film are not considered, and are not necessarily suitable for optical applications.

JP 2005-274725 A JP 2001-42121 A JP 2004-256539 A

  An object of the present invention is to provide an optical film capable of producing a high-quality liquid crystal display screen with little change in phase difference depending on the viewing angle and improving the productivity thereof, and a liquid crystal display device using the optical film. It is.

As a result of intensive studies to solve the above problems, the inventor is an optical film comprising a resin composition P containing a resin A having a positive intrinsic birefringence value and a resin B having a negative intrinsic birefringence value. The resin B having a negative intrinsic birefringence value is a polystyrene resin having a syndiotactic structure, and has a retardation R ₄₅₀ at an incident angle of 0 ° in light having a wavelength of 450 nm and an incident angle of 0 ° in light having a wavelength of 550 nm. Retardation R ₅₅₀ and retardation R ₆₅₀ at an incident angle of 0 ° for light having a wavelength of 650 nm are R ₄₅₀ <R ₅₅₀ <R ₆₅₀ and retardation in the thickness direction Rth in the entire wavelength range of 400 to 700 nm. Is a negative value, it is possible to produce a high-quality liquid crystal display screen with little change in phase difference depending on the viewing angle, and to produce Based on this finding, the present invention has been completed.

That is, according to the present invention, the following optical film and liquid crystal display device are provided.
(1) An optical film comprising a resin composition P containing a resin A having a positive intrinsic birefringence value and a resin B having a negative intrinsic birefringence value, wherein the resin B having a negative intrinsic birefringence value is An optical film which is a polystyrene resin having an tactic structure and satisfies the following relationships (1) and (2).
(I) In-plane retardation R _{450 at} an incident angle of 0 ° in light having a wavelength of ₄₅₀ nm, In-plane retardation R _{550 at} an incident angle of 0 ° in light having a wavelength of ₅₅₀ nm, and an incident angle of 0 ° in light having a wavelength of 650 nm The in-plane retardation R ₆₅₀ is R ₄₅₀ <R ₅₅₀ <R ₆₅₀ .
(Ii) The thickness direction retardation Rth in the entire wavelength range of 400 to 700 nm is a negative value.
(2) The optical film, wherein the resin A having a positive intrinsic birefringence value is polyphenylene oxide.
(3) In the resin composition P, the weight ratio of the resin A and the resin B is resin A / resin B = 1/9 to 3/7.
(4) The optical film obtained by stretching a film before stretching composed of the resin composition P one or more times.
(5) A liquid crystal display device having a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate in this order, and a light source that emits light from the light incident side of the light incident side polarizing plate. A liquid crystal display device comprising the optical film disposed between the light incident side polarizing plate and the liquid crystal cell and / or between the liquid crystal cell and the light emitting side polarizing plate.

  According to the optical film of the present invention, it is possible to produce a high-quality liquid crystal display screen with little change in phase difference depending on the viewing angle and to improve the productivity. Further, there is an effect that a liquid crystal display device with good display characteristics can be provided.

  The optical film of the present invention is an optical film comprising a resin composition P containing a resin A having a positive intrinsic birefringence value and a resin B having a negative intrinsic birefringence value. It is a polystyrene resin having an tactic structure.

  Examples of the resin A having a positive intrinsic birefringence value include olefin resins such as polyethylene and polypropylene; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfide resins such as polyphenylene sulfide; polyvinyl alcohol resins, polycarbonate resins, and polyarylate resins. , Cellulose ester resins, polyethersulfone resins, polysulfone resins, polyallyl sulfone resins, polyvinyl chloride resins, norbornene resins, rod-like liquid crystal polymers, polyarylene ether resins such as polyphenylene ether resins, and the like. You may use these individually by 1 type or in combination of 2 or more types. In the present invention, among these, polycarbonate resin, norbornene resin, and polyphenylene ether resin are preferable, and polyphenylene ether resin is particularly preferable, from the viewpoint of retardation development. Furthermore, as the polyphenylene ether resin, known resins having a polyphenylene ether skeleton in the main chain can be used, and in particular, poly (2,6-dimethyl-) having high compatibility with a polystyrene resin having a syndiotactic structure. 1,4-phenylene oxide) is preferably used.

  As the resin B having a negative intrinsic birefringence value, a polystyrene resin having a syndiotactic structure is used from the viewpoint of improving mechanical strength and suppressing heat shrinkability. A polystyrene resin having a syndiotactic structure is a crystalline polystyrene in which benzene rings are arranged alternately and regularly. Compared with conventional polystyrene (atactic type), it has lower specific gravity, hydrolysis resistance, heat resistance, Has chemical resistance. The polystyrene resin having a syndiotactic structure of the present invention is not particularly limited as long as it has syndiotactic stereoregularity, and a styrene or substituted styrene homopolymer or copolymer can be used. Examples of the substituted styrene include alkyl styrene such as methyl styrene and 2,4-dimethyl styrene; halogenated styrene such as chlorostyrene; halogen-substituted alkyl styrene such as chloromethyl styrene; alkoxy styrene such as methoxy styrene. A styrene homopolymer having no substituent is preferable.

The optical film of the present invention satisfies the following requirement (i) and requirement (ii).
<Requirement (i)>
A retardation R ₄₅₀ at an incident angle of 0 ° in light of a wavelength of 450 nm, a retardation R ₅₅₀ at an incident angle of 0 ° in light of a wavelength of 550 nm, and a retardation R ₆₅₀ at an incident angle of 0 ° in light of a wavelength of 650 nm, The relationship of R ₄₅₀ <R ₅₅₀ <R ₆₅₀ is satisfied.
<Requirement (ii)>
The retardation Rth in the thickness direction in the entire wavelength range of 400 to 700 nm is a negative value.

  Satisfying the requirement (i) has an advantage that the optical compensation effect in the entire visible range can be made uniform. Further, satisfying the requirement (ii) has an advantage that light leakage between a pair of polarizing plates can be suppressed and contrast can be improved even when observed from an oblique direction.

Regarding requirement (i), it is preferable that R ₄₅₀ / R ₅₅₀ ≦ 0.95. Further, it is preferable that R ₆₅₀ / R ₅₅₀ ≧ 1.05. In requirement (i), the incident angle of 0 ° is the normal direction of the film. The retardation at an incident angle of 0 ° can be measured by a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

  In requirement (ii), the retardation Rth in the thickness direction may be a negative value in the entire range of 400 to 700 nm, but is preferably −30 nm or less, more preferably −50 nm or less.

In the present invention, it is preferable that the resin A and the resin B constituting the resin composition P have a wavelength dispersion of the resin A larger than that of the resin B. That is, the ratio of the in-plane retardation R ₄₅₀ (A) at a wavelength of 450 nm to the in-plane retardation R ₆₅₀ (A) at a wavelength of 0650 nm (R ₄₅₀ (A)). / R ₆₅₀ (A)), and the wavelength dispersion characteristic of the film consisting only of the resin B is represented by an in-plane retardation R ₄₅₀ (B) at a wavelength of ₄₅₀ nm and an in-plane retardation R ₆₅₀ (B) at a wavelength of 650 nm. (R ₄₅₀ (A) / R ₆₅₀ (A)) / (R ₄₅₀ (B) / R ₆₅₀ (B))> 1 when expressed as a ratio of (R ₄₅₀ (B) / R ₆₅₀ (B)) It is preferable that R ₄₅₀ (A) / R ₆₅₀ (A)) / (R ₄₅₀ (B) / R ₆₅₀ (B))> 1.02.

  In the present invention, in the resin composition P, the mixing ratio (weight ratio) of the resin A and the resin B may be appropriately selected according to the wavelength dispersion characteristics of the resin to be mixed, but resin A / resin B = 1/9. It is preferably ˜3 / 7, and more preferably resin A / resin B = 2/8 to 2.7 / 7.5.

  The resin composition P has a deflection temperature Ts under load of preferably 80 ° C. or higher, more preferably 90 ° C. or higher, and particularly preferably 100 ° C. or higher. By setting the deflection temperature under load within the above range, orientation relaxation can be reduced, and the optical film of the present invention can be easily obtained by a production method by stretching described later. Further, the breaking elongation of the resin composition P at the temperature Ts is preferably 50% or more, and particularly preferably 80% or more. If the resin composition has a breaking elongation in this range, a retardation film can be stably produced by stretching. The elongation at break can be determined by using a test piece type 1B described in JISK7127 at a pulling speed of 100 mm / min.

A compounding agent can be added to the resin composition P as needed.
The compounding agent to be added is not particularly limited. For example, lubricants; layered crystal compounds; inorganic fine particles; antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near infrared absorbers, and other stabilizers. Plasticizers: coloring agents such as dyes and pigments; antistatic agents; and the like. The amount of the compounding agent can be appropriately determined within a range not impairing the object of the present invention. As a compounding agent, it is preferable to add a lubricant or an ultraviolet absorber in terms of improving flexibility and weather resistance. The addition amount of a compounding agent can be made into the range which can maintain 85% or more of the total light transmittance of the optical film obtained, for example.

  As lubricant, 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 propionate Organic particles such as In the present invention, organic particles are preferred as the lubricant.

  UV absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone UV absorbers, benzotriazole UV absorbers, acrylonitrile UV absorbers, triazine compounds, nickel complex compounds, inorganic Examples include powder. Suitable ultraviolet 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 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, and particularly preferred is 2,2′-methylenebis (4- (1, 1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol.

  The optical film of the present invention preferably has a total light transmittance of 85% or more from the viewpoint of being suitable for an optical film. The total light transmittance is a value measured using a spectrophotometer (manufactured by JASCO Corporation, ultraviolet-visible near-infrared spectrophotometer “V570”) 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 sharpness of the display image of the display device incorporating the optical 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 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 visibility is improved. ΔYI is determined as an arithmetic average value by performing the same measurement five times using “Spectral Color Difference Meter SE2000” manufactured by Nippon Denshoku Industries Co., Ltd. according to ASTM E313.

  The optical film of the present invention preferably has a JIS pencil hardness of H or higher. The adjustment of the JIS pencil hardness can be performed by changing the type of resin, changing the layer thickness of the resin, or the like. JIS pencil hardness is the hardness of a pencil that begins to scratch, scratching the surface of the film by tilting a pencil of various hardness by 45 °, applying a load of 500 g weight from the top, in accordance with JIS K5600-5-4. .

  The optical film of the present invention is preferably a long film from the viewpoint of production efficiency. A long film is a film having a length direction that is long (for example, a length of 10 times or more) with respect to the dimension in the width direction. Such a film is continuous in the length direction in a production line. It is obtained by performing the manufacturing process. In particular, when the optical film of the present invention is produced by a process of preparing a pre-stretch film described below as a long film and further stretching the film, some or all of these processes are simply and efficiently inline. Can be done automatically.

  The optical film of the present invention preferably has a heat shrinkage rate of 0.5% or less, and more preferably 0.3% or less. The thermal shrinkage rate can be expressed as a shrinkage rate when left in an atmosphere of 120 ° C. for 30 minutes without applying tension to the optical film. In addition, when an optical film is a stretched film, the shrinkage rate along the stretch direction is measured.

  The optical film of the present invention can be obtained by a stretched film obtained by stretching a film before stretching. Here, the pre-stretch film is made of the resin composition P. The pre-stretch film is usually an isotropic raw film, but the film once stretched may be used as a pre-stretch film, which may be further subjected to a stretch treatment in the present invention. it can.

  FIG. 1 is a diagram showing the relationship between the wavelength and the absolute value of each phase difference of the resin A and the resin B constituting the resin composition P in the visible region (400 to 700 nm), and the line LA represents the wavelength of the resin A. The dispersion characteristic is shown, and the line LB shows the wavelength dispersion characteristic of the resin B. As shown in FIG. 1, the wavelength dispersion of the resin A having a positive intrinsic birefringence value is larger than that of the resin B having a negative intrinsic birefringence value. As shown in FIG. 1, the resin composition P used in the present invention is slightly affected by the orientation of the resin B on the lower wavelength side than the orientation of the resin A, and the orientation of the resin B toward the longer wavelength side. The blending and the like have been adjusted so that the effects of the above appear more greatly. The film before stretching is obtained using the resin composition P adjusted as described above.

  The total thickness of the film before stretching is preferably 10 to 800 μm, more preferably 50 to 600 μm. By setting it as 10 micrometers or more, sufficient phase difference and mechanical strength can be obtained, and a softness | flexibility and handling property can be made favorable by setting it as 800 micrometers or less.

  As methods for preparing the film before stretching, coextrusion molding methods such as coextrusion T-die method, coextrusion inflation method, coextrusion lamination method, etc .; co-casting method in which the materials of each resin layer are cast and laminated one after another; dry lamination And a known method such as a film lamination molding method such as coating; and a coating molding method such as coating a resin solution on the surface of the resin film. For example, a co-extrusion method can be used from the viewpoint of production efficiency and not leaving volatile components such as a solvent in the film.

  The optical film of the present invention can be obtained by subjecting the pre-stretching film having the above-described structure to stretching treatment one or more times. That is, when the pre-stretching film having the above structure is stretched, the influence of the resin B appears more than that of the resin A in the entire range of 400 to 700 nm. Therefore, the refractive index nz in the thickness direction of the film is the in-plane refractive index. It becomes larger than nx, ny, and the retardation Rth in the thickness direction is a negative value. Moreover, since it adjusted so that the influence of resin B might become large as it goes to a long wavelength side, the optical film of reverse wavelength dispersion can be obtained. Examples of the stretching treatment include a method of uniaxially stretching in the longitudinal direction using the difference in peripheral speed between rolls (longitudinal uniaxial stretching), and a method of uniaxially stretching in the transverse direction using a tenter (lateral uniaxial stretching). A method in which longitudinal uniaxial stretching and lateral uniaxial stretching are sequentially performed (sequential biaxial stretching) or the like can be employed.

The liquid crystal display device of the present invention includes the optical film of the present invention.
The liquid crystal display device of the present invention includes a liquid crystal panel in which a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate are arranged in this order, and a light source that irradiates the liquid crystal panel.
By arranging the optical film of the present invention as a retardation film between the liquid crystal cell and the light incident side polarizing plate and / or between the liquid crystal cell and the light emitting side polarizing plate, the visibility of the liquid crystal display device is greatly increased. It can be improved. Liquid crystal cell driving methods include in-plane switching (IPS) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, continuous spin wheel alignment (CPA) mode, hybrid alignment nematic (HAN) mode, Examples thereof include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, an optically compensated bend (OCB) mode, and the like.

  In the liquid crystal display device of the present invention, the optical film of the present invention may be bonded to a liquid crystal cell or a polarizing plate as a retardation film. The optical film of the present invention may be bonded to each of the two polarizing plates. Two or more optical films of the present invention may be used. A known adhesive can be used for bonding. A polarizing plate shall consist of a polarizer and the protective film bonded together on both surfaces. Instead of the protective film, the optical film of the present invention can be directly bonded to a polarizer and used as a layer having both functions of a retardation plate and a protective film. By adopting such a configuration, the protective film can be omitted, and the liquid crystal display device can be reduced in thickness, weight, and cost.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these. In the examples and comparative examples, the physical properties were measured as follows.

(R ₄₅₀ , R ₅₅₀ , R ₆₅₀ )
R ₄₅₀ , R ₅₅₀ , and R ₆₅₀ (unit: nm) were determined by the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments. The phase differences observed from incident angles of 0 ° (in the normal direction of the film) at wavelengths of 450 nm, 550 nm, and 650 nm were R ₄₅₀ , R _550, and R ₆₅₀ , respectively.

(Heat shrinkage)
The optical film was left in an atmosphere of 120 ° C. for 30 minutes in a state where no tension was applied, and the shrinkage rate along the stretching direction was determined as the heat shrinkage rate.

(Haze)
Based on JIS K7361-1997, haze was measured at five locations using “Durbidity Meter NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd., and the average value was obtained.

(Production Example 1)
17.8 g (71 mmol) of copper sulfate pentahydrate (CuSO ₄ .5H ₂ O), 200 ml of toluene and 24 ml (250 mmol) of trimethylaluminum were placed in a glass container having an internal volume of 500 ml purged with argon. Reacted for hours. Thereafter, from the solution obtained by removing the solid portion, toluene was further distilled off under reduced pressure at room temperature to obtain 6.7 g of a contact product. The molecular weight of this product was 610 as measured by the freezing point lowering method.
Next, 5 molmol of the contact product as an aluminum atom, 5 mmol of triisobutylaluminum, 0.025 mmol of pentamethylcyclopentadienyl titanium trimethoxide, and 1 mmol of purified styrene were added to the reaction vessel at 90 ° C. The polymerization reaction was performed for 5 hours. Thereafter, the product was decomposed with a methanol solution of sodium hydroxide, the catalyst component was decomposed, washed repeatedly with methanol, and dried to obtain 308 g of a polymer (polystyrene).
Subsequently, this polymer was measured by gel permeation chromatography at 135 ° C. using 1,2,4-trichlorobenzene as a solvent. As a result, the weight average molecular weight of this polymer was 350,000. Further, it was confirmed by melting point and 13C-NMR measurement that the obtained polymer was a polystyrene resin having a syndiotactic structure.

<Example 1>
75 parts by weight of the polystyrene resin having a syndiotactic structure obtained in Production Example 1 and poly (2,6-dimethyl-1,4-phenylene oxide) (Aldrich catalog No. 18242-7, weight average molecular weight 244) 000) 25 parts by weight was dissolved in chloroform so that the solid content concentration was 20% by weight to prepare a dope solution. This dope solution was cast on a release-treated polyethylene terephthalate film, and dried at room temperature for 5 minutes and then at 50 ° C. for 2 hours. Next, the dried film was peeled from the polyethylene terephthalate film to obtain a film before stretching having a thickness of 161 μm. Next, the pre-stretched film was uniaxially stretched 3.0 times at 120 ° C. and then heat-treated at 200 ° C. for 15 seconds to obtain a stretched optical film having a thickness of 82 μm. Table 1 shows the physical properties of the obtained stretched optical film. As shown in Table 1, the stretched optical film satisfied the requirements of R ₄₅₀ <R ₅₅₀ <R ₆₅₀ and had a negative Rth value in the entire range of 400 to 700 nm.

<Comparative Example 1>
Using only the polystyrene resin having a syndiotactic structure obtained in Production Example 1, it was dissolved in chloroform so that the solid content concentration was 20% by weight to prepare a dope solution. This dope solution was cast on a release-treated polyethylene terephthalate film and dried at room temperature for 5 minutes and then at 50 ° C. for 2 hours. Next, the dried film was peeled off from the polyethylene terephthalate film to obtain a 96-μm-thick film before stretching. Next, the pre-stretched film was longitudinally uniaxially stretched 3.0 times at 90 ° C. and then heat-treated at 200 ° C. for 15 seconds to obtain a stretched optical film having a thickness of 35 μm. Table 1 shows the physical properties of the obtained stretched optical film. As shown in Table 1, this stretched optical film was excellent in terms of thermal shrinkage, but did not satisfy the requirement of R ₄₅₀ <R ₅₅₀ <R ₆₅₀ and was inferior in terms of haze.

<Comparative example 2>
A dope solution in which a commercially available polystyrene resin (HF77 manufactured by Polystyrene Japan Co., Ltd.) was dissolved in chloroform so as to have a solid content concentration of 20% by weight was prepared. This dope solution was cast on a release-treated polyethylene terephthalate film and dried at room temperature for 5 minutes and then at 50 ° C. for 2 hours. Subsequently, the dried film was peeled from the polyethylene terephthalate film to obtain a film before stretching having a thickness of 101 μm. Next, this unstretched film was uniaxially stretched 2.0 times at 90 ° C. to obtain a stretched optical film having a thickness of 54 μm. Table 1 shows the physical properties of the obtained stretched optical film. As shown in Table 1, this stretched optical film was excellent in terms of haze, but did not satisfy the requirement of R ₄₅₀ <R ₅₅₀ <R ₆₅₀ . Moreover, it was inferior also in the point of heat shrinkage rate.

<Comparative Example 3>
A dope solution was prepared by dissolving a styrene-maleic anhydride copolymer resin (manufactured by Nova Chemicals, Dylark D332) in chloroform so that the solid content concentration was 20% by weight. The dope solution was cast on a release-treated polyethylene terephthalate film, dried at room temperature for 5 minutes and then at 50 ° C. for 2 hours, and then peeled off from the polyethylene terephthalate film to obtain a 97 μm-thick film before stretching. This unstretched film was stretched 2.0 times at 130 ° C. to obtain a film having a thickness of 49 μm. Table 1 shows the physical properties of the obtained stretched optical film. As shown in Table 1, this stretched optical film was excellent in terms of heat shrinkage and haze, but did not satisfy the requirement of R ₄₅₀ <R ₅₅₀ <R ₆₅₀ .

It is a figure which shows the relationship between a wavelength and the absolute value of each phase difference of resin A and resin B which comprise the resin composition P, line LA shows the wavelength dispersion characteristic of resin A, and line LB shows the wavelength dispersion of resin B The characteristics are shown.

Explanation of symbols

Curve showing the wavelength dispersion characteristics of LA resin A
Curve showing wavelength dispersion characteristics of LB resin B

Claims (5)

An optical film comprising a resin composition P containing a resin A having a positive intrinsic birefringence value and a resin B having a negative intrinsic birefringence value,
The resin B having a negative intrinsic birefringence value is a polystyrene resin having a syndiotactic structure and satisfies the following relationships (i) and (ii).
(I) In-plane retardation R _{450 at} an incident angle of 0 ° in light having a wavelength of ₄₅₀ nm, In-plane retardation R _{550 at} an incident angle of 0 ° in light having a wavelength of ₅₅₀ nm, and an incident angle of 0 ° in light having a wavelength of 650 nm The in-plane retardation R ₆₅₀ is R ₄₅₀ <R ₅₅₀ <R ₆₅₀ .
(Ii) The thickness direction retardation Rth in the entire wavelength range of 400 to 700 nm is a negative value. The optical film according to claim 1,
The resin A having a positive intrinsic birefringence value is an optical film that is a polyphenylene ether resin. The optical film according to claim 2,
The resin composition P is an optical film in which a weight ratio of the resin A and the resin B is resin A / resin B = 1/9 to 3/7. In the optical film in any one of Claims 1-3,
An optical film obtained by subjecting a pre-stretching film comprising the resin composition P to stretching treatment one or more times. A liquid crystal display device having a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate in this order, and a light source that emits light from the light incident side of the light incident side polarizing plate,
The optical film according to claim 1, wherein the optical film is disposed between the light incident side polarizing plate and the liquid crystal cell and / or between the liquid crystal cell and the light emitting side polarizing plate. A liquid crystal display device provided.

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