JP2002148437A - Optical compensation film, method for manufacturing the same, and polarizing plate and liquid crystal display device which use the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical compensation film and a method for manufacturing the film which uniformly has the required characteristics in its plane and to provide a polarizer and a liquid crystal display device which use the above film. SOLUTION: When a thermoplastic resin film is subjected to successive biaxial stretching or lateral stretching, the lateral stretching process is carried out in multiple steps so that the obtained optical compensation film has 0 to 500 nm retardation in the plane (Re=(nx-ny)d), 0 to 500 nm retardation in the thickness direction (Rth=(nx-nz)d) with Re/Rth<1, wherein d is the thickness of the film, nx, ny are the principal refractive indices in the film plane (nx>ny) and nz is the principal refractive index in the thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film used for improving a viewing angle and a contrast of a liquid crystal display device, a method for producing the same, and a polarizing plate using the film.
The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art A high-contrast liquid crystal display device utilizing birefringence such as an STN type is used for various screen displays such as a personal computer and a word processor. In such a liquid crystal display device, there is a problem that incident light that has been linearly polarized through a polarizing plate becomes elliptically polarized light due to birefringence by a liquid crystal cell, and the display is colored yellow or blue when viewed through the polarizing plate. is there. Therefore, in order to return the elliptically polarized light after passing through the liquid crystal cell to linearly polarized light and to prevent coloration, as a means for compensating for the phase difference due to birefringence of the liquid crystal cell, a retardation plate (optically formed of a stretched film) between the liquid crystal cell and the polarizing plate is used. Compensation film) has been proposed.

However, optical compensation in the FTN system
Using a normal stretched film as the film,
If you change the viewpoint slightly, the color display will appear again.
The viewing angle that can be seen as a black display is narrow and good
Viewing angle is narrow, so you can see with good contrast
Poor sex. As a result, viewing angle improvements and
As an optical compensation film used to improve contrast,
The thickness of the film is d, and the main refractive index in the plane of the film is n_x,
n_y, The main refractive index in the thickness direction is n_zAnd n_x> N _yMade
In this case, the in-plane retardation value (Re = (n_x−
n_y) D) is from 0 to 500 nm, and the retardation in the thickness direction is
Option value (Rth = (n_x-N_z) D) is 0-500 nm, R
Films with e / Rth <1 are required.

[0004] However, an optical compensation film satisfying the above characteristics could not be obtained by a conventional method using only longitudinal uniaxial stretching or horizontal uniaxial stretching alone. In addition, although the above properties can be partially obtained by sequential biaxial stretching used in the production of general-purpose packaging films and the like, there is a problem that the uniformity in the film plane is lacking.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention provides an optical compensation film having the above properties uniformly in a film plane, a method for producing the same, a polarizing plate using the film, and a liquid crystal. It is an object to provide a display device.

[0006]

In order to achieve the above object, the method for producing an optical compensation film of the present invention comprises a multi-stage transverse stretching step when a thermoplastic resin film is successively stretched biaxially or transversely. It is characterized by the following. The horizontal stretching machine used in the horizontal stretching step preferably has a rail opening angle of 5 degrees or less.

[0007] The optical compensation film of the present invention produced by the above method, the thickness of the film d, the main refractive indices n _x in the film plane, n _y, the main refractive index in the thickness direction n _z, and when the n _x> n _y, retardation values in a film plane _{(Re = (n x -n y} ) d) is 0~500n
m, the thickness direction retardation value (Rth = (n _x -
_nz ) d) is 0 to 500 nm, and Re / Rth <1.

[0008] The optical compensation film of the present invention produced by the above method, the thickness of the film d, the main refractive indices n _x in the film plane, n _y, the main refractive index in the thickness direction n _z, and when the n _x> n _y, retardation values in a film plane _{(Re = (n x -n y} ) d) 10 to 100
nm, the thickness direction of the retardation value (Rth = (n _x -
_nz ) d) is 100 to 300 nm, and Re / Rth is 1 to 4.

In the optical compensation film of the present invention, the Re distribution in the width direction is ± 10% at 80% or more of the sheet width.
It is characterized by being within the range.

The thermoplastic resin film is preferably a norbornene resin film.

Further, the polarizing plate of the present invention is characterized in that it is a polarizing plate comprising a laminate of the optical compensation film and the polarizing plate.

Further, the liquid crystal display of the present invention is characterized in that the optical compensation film is disposed on at least one side of a liquid crystal cell.

Further, the liquid crystal display device of the present invention is characterized in that the polarizing plate is arranged on at least one side of a liquid crystal cell.

According to the method of the present invention, the rail opening angle of the transverse stretching machine (tenter) is reduced, and the bowing phenomenon that occurs during transverse stretching is suppressed. When used in a display device, an optical compensation film having a wide viewing angle that can be viewed as a black-and-white display and a wide viewing angle that can be viewed with good contrast can be manufactured with excellent visibility.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The thermoplastic resin film used in the present invention includes polyester resins such as polycarbonate resin, polyarylate and polyethylene terephthalate, polyimide resins, polysulfone resins, polyethersulfone resins, and polystyrene. Resins, polyolefin resins such as polyethylene and polypropylene, polyvinyl alcohol resins, cellulose acetate resins, polyvinyl chloride resins, polynorbornene resins, polymethyl methacrylate resins, and liquid crystal polymers. The film may be manufactured by any of a casting method, a calendar method, and an extrusion method. Among them, polycarbonate resin, polystyrene resin,
Polynorbornene resins are preferred. Polynorbornene-based resins are particularly preferred because they have a relatively small photoelastic coefficient, are flexible, and are unlikely to crack or split against bending stress or shear stress. The weight average molecular weight of the thermoplastic resin is
There is no particular limitation, and appropriate ones can be used.

The thickness of the thermoplastic resin film used for the stretching treatment is not particularly limited, and can be appropriately determined according to the intended use of the produced stretched film. Generally, from the point of obtaining a homogeneous stretched film by a stable stretching process, 3 mm or less, preferably 1 μm to 1 mm,
Particularly preferably, a film having a thickness of 5 to 500 μm is used.

In the present invention, when a film is produced only by sequential biaxial stretching or transverse stretching, the transverse stretching step is performed in two or more stages. By increasing the number of stages, the opening angle of the tenter can be reduced, so that the bowing phenomenon that occurs at the time of lateral stretching can be suppressed, and variation in the optical axis angle distribution can be reduced. When a film is produced by sequential biaxial stretching, stretching between rolls, rolling stretching, or the like is used for stretching in the longitudinal direction, and a tenter is used for stretching in the transverse direction. When a film is produced only by transverse stretching, a tenter is used. Examples of the multi-stage method include a method of stretching using one tenter and further stretching, a method of stretching with a tenter and further stretching with another tenter. In each stretching step, the respective stretching conditions may be the same or different. Specific stretching methods include, for example, (1) a method of longitudinal stretching after transverse stretching and further transverse stretching, (2) a method of further transverse stretching after transverse stretching and longitudinal stretching, and (3) longitudinal stretching. Later stretched laterally,
Further, a method of laterally stretching, (4) a method of further laterally stretching after laterally stretching, and the like can be given.

When a tenter is used in the stretching step, the rail opening angle is preferably within 5 degrees, more preferably within 3 degrees. By setting the rail opening angle to 5 degrees or less, the bowing phenomenon that occurs at the time of lateral stretching is suppressed, so that the variation in the optical axis angle distribution can be reduced.

The stretching temperature of the thermoplastic resin film varies depending on the type of the resin used, but is usually from 80 to 250.
° C, preferably 120 to 200 ° C, particularly preferably 14 ° C.
0-180 ° C.

When a film is produced by sequential biaxial stretching, the stretching ratio is 1 to 5 times in the machine direction, preferably 1 to 5 times.
It is 3 times, particularly preferably 1 to 2 times. Further, the width is 1 to 5 times, preferably 1 to 3 times, particularly preferably 1 to 5 times.
It is twice. The stretching ratio when a film is prepared only by transverse stretching is 1 to 5 times, preferably 1 to 3 times.
Fold, particularly preferably 1-2 fold. The ratio of the stretching ratio in the machine direction to the stretching ratio in the transverse direction is calculated as follows: longitudinal stretching ratio / lateral stretching ratio =
It is 0.2-5.0, preferably 0.3-3.0.

After stretching, an appropriate relaxation step may be provided. In the relaxation step, the stretched thermoplastic resin film is held at a predetermined temperature for a predetermined time to shrink the stretched film. In this case, the relaxation rate is preferably within 20%, and the holding temperature is determined by the glass transition point (T
g) The temperature is in the range of −30 ° C. to Tg + 30 ° C., and the holding time is 1 second to 60 seconds.

According to the production method of the present invention, the thickness of the film
D, the main refractive index in the film plane is n _x, N_yIn the thickness direction
The main refractive index is n_zAnd n_x> N_yIn the plane,
A retardation value (Re) of 0 to 500 nm, in the thickness direction
Has a retardation value (Rth) of 0 to 500 nm, Re
/ Rth <1 to produce an optical compensation film.
Wear.

The optical compensation film produced by the production method of the present invention has an in-plane retardation value.
(Re) is 10 to 100 nm, the retardation value (Rth) in the thickness direction is 100 to 300 nm, and Rth / Re is 1 to 4.

Furthermore, in the optical compensation film produced by the production method of the present invention, the Re distribution in the width direction is within a range of ± 10% at 80% or more of the sheet width, and the dispersion of Re is small and uniform in the plane. It has excellent properties.
That is, when measuring the width direction Re of the film produced by the stretching treatment, the ratio of the difference between the film center Re and the width direction Re within ± 10% of the film center Re is 80% or more. Occupy. The thickness of the film is
It can be appropriately determined by a phase difference or the like according to the purpose of use, but is generally 1 mm or less, preferably 1 to 50 mm.
0 μm, particularly preferably 5 to 300 μm.

The optical compensation film of the present invention may be used alone or as a superposed body. Although the number of superimpositions is arbitrary, two to five superimpositions are generally used in terms of light transmittance and the like. The combination of stretched films to be superimposed is also optional,
With the same orientation angle or different orientation angles,
It is possible to appropriately combine materials of the same material, materials of different materials, materials of the same phase difference, materials of different phase differences, and the like.

Next, the polarizing plate used in the present invention will be described.

The basic structure of the polarizing plate used in the present invention is as follows.
On one or both sides of a polarizer made of a dichroic substance-containing polyvinyl alcohol-based polarizing film or the like, a transparent protective film serving as a protective layer was bonded via an appropriate adhesive layer, for example, an adhesive layer made of a vinyl alcohol-based polymer or the like. Consist of things.

As the polarizer (polarizing film), for example, a film made of a suitable vinyl alcohol-based polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol, or a dichroic film made of iodine or a dichroic dye is used. Appropriate treatments such as dyeing treatment, stretching treatment, and cross-linking treatment with a substance are performed in an appropriate order and manner, and an appropriate material that transmits linearly polarized light when natural light is incident thereon can be used. In particular, those having excellent light transmittance and degree of polarization are preferable. The thickness of the polarizing film is generally from 5 to 80 μm, but is not limited thereto.

As a protective film material to be a transparent protective layer provided on one side or both sides of a polarizer (polarizing film), an appropriate transparent film can be used. Above all, a film made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include an acetate resin such as triacetyl cellulose, a polyester resin, a polyethersulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, and an acrylic resin. However, the present invention is not limited to this.

A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. The thickness of the transparent protective film is arbitrary, but is generally 500 μm or less, preferably 5 to 300 μm, and particularly preferably 5 to 1 μm for the purpose of reducing the thickness of the polarizing plate.
It is 50 μm. When transparent protective films are provided on both sides of the polarizing film, the transparent protective films may be made of different polymers on the front and back.

The transparent protective film used for the protective layer is
As long as the object of the present invention is not impaired, a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion or anti-glare, or the like may be performed. The hard coat treatment is performed for the purpose of preventing scratches on the polarizing plate surface and the like.
It can be formed by a method of adding a cured film made of a suitable ultraviolet-curable resin such as a urethane-based, acrylic-based, or epoxy-based resin having excellent hardness and slipperiness to the surface of the transparent protective film.

On the other hand, the anti-reflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, anti-sticking is performed to prevent adhesion between adjacent layers, and anti-glare treatment is performed to prevent external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate. For example, the transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a roughening method by a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Fine particles may be used, or organic fine particles composed of crosslinked or uncrosslinked polymer particles or the like may also be used.
The amount of the transparent fine particles used is 2 per 100 parts by mass of the transparent resin.
It is generally from 70 to 70 parts by weight, especially from 5 to 50 parts by weight.

The anti-glare layer containing the transparent fine particles can be provided as the transparent protective film itself or as a coating layer on the surface of the transparent protective film. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle. The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer, and the like can be provided as an optical layer made of a sheet or the like provided with these layers, separately from the transparent protective film.

The bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive composed of a vinyl alcohol polymer, boric acid or boric acid may be used. It can be carried out via an adhesive or the like comprising at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as sand, glutaraldehyde, melamine, and oxalic acid. This makes it difficult for the film to be peeled off due to the influence of humidity or heat, and can have excellent light transmittance and degree of polarization. Such an adhesive layer is formed as a coating and drying layer of an aqueous solution, and at the time of preparing the aqueous solution, other additives and a catalyst such as an acid can be blended as necessary.

The polarizing plate can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited, and may be, for example, a reflection plate, a semi-transmission reflection plate, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 波長 wavelength plate), the optical compensation film of the present invention, and brightness. One or more suitable optical layers that may be used for forming a liquid crystal display device or the like, such as an enhancement film, can be used. In particular, a polarizing plate including a polarizer and a protective layer, and a reflecting plate Alternatively, a reflective polarizing plate or a transflective polarizing plate in which a semi-transmissive reflecting plate is laminated, an elliptically polarizing plate or a circularly polarized light in which a retardation plate is further laminated on the above-described polarizing plate comprising a polarizer and a protective layer. Plate, a polarizing plate comprising the above-described polarizer and a protective layer, a polarizing plate further laminated with the optical compensation film of the present invention, or a polarizing plate comprising the above-described polarizer and a protective layer, further comprising a brightness enhancement film. Polarized polarizing plates are preferred There.

The above-mentioned reflection plate is provided on a polarizing plate to form a reflection-type polarizing plate. The reflection-type polarizing plate is usually provided on the back side of a liquid crystal cell.
There is an advantage that a liquid crystal display device of a type that reflects and reflects incident light from the LCD can be formed, and a built-in light source such as a backlight can be omitted, so that the liquid crystal display device can be easily made thin.

The reflection type polarizing plate can be formed by an appropriate method such as a method in which a reflection layer made of metal or the like is provided on one side of the polarizing plate via the transparent protective film or the like as necessary. Specific examples thereof include a transparent protective film that has been matted as necessary, and a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one surface.

Further, a reflection type polarizing plate having a reflection layer reflecting the fine unevenness structure on the transparent protective film having a fine unevenness surface containing fine particles may also be used. The reflection layer having the fine surface irregularity structure has an advantage that the incident light can be diffused by irregular reflection to prevent directivity and glare, and that unevenness in brightness can be suppressed. The formation of the reflective layer of the fine uneven structure reflecting the fine uneven structure on the surface of the transparent protective film is performed by, for example, making the metal transparent by an appropriate method such as an evaporation method such as a vacuum evaporation method, an ion plating method, or a sputtering method, or a plating method. It can be carried out by a method of directly attaching to the surface of the protective film.

In addition, the reflecting plate may be used as a reflecting sheet in which a reflecting layer is provided on an appropriate film conforming to the transparent protective film, instead of directly attaching the reflective plate to the transparent protective film. it can. Since the reflection layer of the reflection plate is usually made of a metal, the use form in which the reflection surface is covered with a film, a polarizing plate, or the like is used to prevent a decrease in the reflectance due to oxidation, and furthermore, a point that a long term of the initial reflectance is maintained. It is preferable from the viewpoint of avoiding separately providing a protective layer.

The transflective polarizing plate can be obtained by forming a transflective reflective layer such as a half mirror that reflects and transmits light on the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, a liquid crystal display device of a type that displays an image using a built-in light source such as a backlight built in the back site of a transflective polarizing plate can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere and is useful for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. It is.

The brightness enhancement film reflects linearly polarized light having a predetermined polarization axis or circularly polarized light having a predetermined direction when natural light is incident thereon, and exhibits a property of transmitting other light. The polarizing plate laminated with the polarizing plate comprising the protective layer, while transmitting light of a predetermined polarization state by making light from a light source such as a backlight incident, light other than the predetermined polarization state is reflected without transmitting. You. The light reflected on the surface of the brightness enhancement film is further inverted via a reflection layer or the like provided on the rear side thereof and re-incident on the brightness enhancement plate, and a part or all of the light is transmitted as light of a predetermined polarization state to achieve brightness. The luminance can be improved by increasing the amount of light transmitted through the enhancement film and by increasing the amount of light that can be used for liquid crystal image display by supplying polarized light that is hardly absorbed by the polarizer.

As the above-mentioned brightness enhancing film, for example, a multilayer thin film of a dielectric thin film or a multilayer laminate of thin films having different refractive index anisotropies transmits linearly polarized light having a predetermined polarization axis and reflects other light. Such as a cholesteric liquid crystal layer, particularly an alignment film of a cholesteric liquid crystal polymer or a film in which the alignment liquid crystal layer is supported on a film substrate, reflecting either left-handed or right-handed circularly polarized light, An appropriate material such as a material exhibiting a characteristic of transmitting light can be used.

Therefore, in a brightness enhancement film of a type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is directly incident on the polarizing plate with the polarization axis aligned.
It is possible to transmit light efficiently while suppressing absorption loss by the polarizing plate. On the other hand, a brightness enhancement film that transmits circularly polarized light, such as a cholesteric liquid crystal layer, can be directly incident on a polarizer.However, from the viewpoint of suppressing absorption loss, the transmitted circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on the polarizing plate. By using a quarter-wave plate as the retardation plate, circularly polarized light can be converted to linearly polarized light.

A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a quarter-wave plate with respect to monochromatic light such as light having a wavelength of 550 nm. Retardation layer exhibiting retardation characteristics of, for example, 1/2
It can be obtained by a method in which a retardation layer functioning as a wavelength plate is superimposed. Therefore, the retardation plate provided between the polarizing plate and the brightness enhancement film may be composed of one or more layers.

Note that the cholesteric liquid crystal layer is also
By combining two or more layers having different reflection wavelengths to form an arrangement structure in which two or more layers are superimposed, it is possible to obtain a material that reflects circularly polarized light in a wide wavelength range such as a visible light region, and a wide wavelength based on that. A range of transmitted circularly polarized light can be obtained.

Next, a polarizing plate in which an optical compensation film is further laminated on the above-described polarizing plate will be described.

The polarizing plate of the present invention is obtained by laminating one or more optical compensation films of the present invention on the above polarizing plate, and may be formed by laminating two or three or more layers with the polarizing plate. Accordingly, a reflective elliptically polarizing plate or a semi-transmissive elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate or transflective polarizing plate with the optical compensation film of the present invention may be used. There is no particular limitation on the lamination method, and an appropriate bonding means such as an adhesive layer can be used. The polarizing plate in which two or three or more optical layers are laminated can also be formed by a method of sequentially laminating them in a manufacturing process of a liquid crystal display device or the like. Since the body-type polarizing plate is excellent in quality stability, assembling workability, and the like, there is an advantage that manufacturing efficiency of a liquid crystal display device or the like can be improved.

Next, a liquid crystal display device in which the optical compensatory film of the present invention or the polarizing plate obtained by further laminating the optical compensatory film of the present invention on the above-described polarizing plate will be described on at least one side of a liquid crystal cell.

The liquid crystal display device of the present invention has an appropriate structure according to the prior art, such as a transmission type or reflection type in which a polarizing plate is disposed on one or both sides of a liquid crystal cell, or a transmission / reflection type. Can be formed. Therefore, the liquid crystal cell forming the liquid crystal display device is optional, and for example, an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twisted nematic type or a super twisted nematic type, or the like is suitable. A liquid crystal cell of any type may be used.

When polarizing plates and optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, in forming the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, and a backlight can be arranged at appropriate positions.

An adhesive layer may be provided for bonding the optical compensation film or the polarizing plate of the present invention to a liquid crystal cell. The adhesive layer can be appropriately formed using a conventionally known adhesive such as an acrylic adhesive. Above all, from the viewpoints of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of liquid crystal cell warpage, and, in view of formability of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. It is preferable that the pressure-sensitive adhesive layer is low and has excellent heat resistance. In addition, an adhesive layer or the like that contains fine particles and exhibits light diffusivity can also be used.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until the adhesive layer is put to practical use for the purpose of preventing contamination and the like. The separator is formed by, for example, providing a release coat with an appropriate release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide on a suitable thin leaf according to the above transparent protective film or the like. be able to.

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer which form the above-mentioned polarizing plate and optical member are made of, for example, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds and cyanoacrylate compounds. A compound having an ultraviolet absorbing ability by an appropriate method such as a method of treating with a compound or a nickel complex salt-based compound or the like may be used. Next, the present invention will be described specifically with reference to examples.

[0055]

Example 1 A 100 μm thick polynorbornene-based resin film (trade name “ARTON FILM” manufactured by JSR Corporation) was stretched at a stretching temperature of 180 ° using a tenter (rail opening angle 1.2 °). After the film was horizontally uniaxially stretched at 1.25 ° C. and a stretching ratio of 1.25, the rail opening angle was further set to 1.3 °, and the film was horizontally uniaxially stretched at a stretching temperature of 180 ° C. and a stretching ratio of 1.25. 64μm thick, 450mm wide
Was produced.

Example 2 An apparatus for stretching a 100 μm-thick polynorbornene-based resin film (manufactured by JSR Corporation under the trade name “Arton Film”) at a peripheral speed difference between two pairs of pinch rolls was used. Then, the film is longitudinally and uniaxially stretched at a stretching temperature of 180 ° C. and a stretching ratio of 1.10 times, and then horizontally uniaxially stretched at a stretching temperature of 180 ° C. and a stretching ratio of 1.25 times using a tenter (rail opening angle of 1.2 °). Then, the rail opening angle was set to 1.3 degrees, the stretching temperature was 180 ° C., and the stretching ratio was 1.
Stretched uniaxially at 25 times and the thickness at the center of the film was 62μ.
m, an optical compensation film having a width of 510 mm was produced.

Comparative Example 1 A 100 μm-thick polynorbornene-based resin film (trade name “Arton Film” manufactured by JSR Corporation) was stretched at 180 ° C. under a tenter (rail opening angle of 7 °) at a stretching temperature of 180 ° C. The film is stretched horizontally uniaxially at 1.50 times, and the thickness at the center of the film is 63 μm and the width is 450 mm.
Was produced.

Comparative Example 2 An apparatus for stretching a 100 μm-thick polynorbornene-based resin film (trade name “Arton Film”, manufactured by JSR Corporation) was used between two pairs of pinch rolls at a peripheral speed difference between the rolls. After stretching longitudinally uniaxially at a stretching temperature of 180 ° C. and a stretching ratio of 1.10, the film was horizontally uniaxially stretched at a stretching temperature of 180 ° C. and a stretching ratio of 1.50 by using a tenter (rail opening angle: 7 °). The thickness at the center of the film is 6
An optical compensation film having a thickness of 1 μm and a width of 510 mm was produced.

(Evaluation of Characteristics of Optical Compensation Film)
The thickness of the optical compensation film of the example and the comparative example is d, the film
The in-plane principal refractive index is n_x, N_y, The main refractive index in the thickness direction is n_z
Where Re = (n) at the center of the film _x-N_y) D, Rt
h = (n_x-N_z) D, Re / Rth are automatically measured by Oji Keiki
It was measured with a birefringence meter (KOBRA21ADH). So
Table 1 shows the results.

[Table 1] Re Rth Re / Rth Axial angle in axial direction (nm) (nm) Variation (deg) Example 1 82.6 144.8 0.57 4 Example 2 52.8 137.8 0.38 5 Comparative Example 1 89.8 158.9 0.57 7 Comparative Example 2 58.7 157.8 0.37 9 As is clear from the above results, the optical compensation film of the present invention has less variation in the axial angle in the width direction and is excellent in in-plane uniformity as compared with the optical compensation film of the comparative example.

Example 3 An elliptically polarizing plate comprising a laminate of the optical compensation film produced in Example 1 and a polyvinyl alcohol-based polarizing plate was bonded to both sides of an STN type liquid crystal cell to form a display device. . As a result, coloring was not recognized in a wide range, and the contrast ratio was good.

[0062]

As described above, according to the present invention, when a thermoplastic resin film is produced only by sequential biaxial stretching or transverse stretching only, the transverse stretching process is performed in multiple stages, whereby the rail opening angle of the transverse stretching machine is increased. Can be reduced,
It is possible to suppress the bowing phenomenon that occurs during the transverse stretching. Therefore, it is possible to provide an optical compensation film which satisfies the required performance of the film, reduces the variation of the optical axis angle distribution, and has excellent in-plane uniformity.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 45:00 B29K 45:00 101: 12 101: 12 B29L 7:00 B29L 7:00 11:00 11:00 (72) Inventor Shinichi Sasaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Akihiro Nishida 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F term (reference) 2H049 BA02 BA06 BA25 BB03 BB48 BC03 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FC08 FD07 FD15 LA11 LA16 4F210 AA12 AG01 AH73 QA02 QA03 QC02 QC06 QD04 QG01 QG18

Claims (10)

[Claims] 1. A method for producing an optical compensation film, comprising, when a thermoplastic resin film is successively biaxially or laterally stretched, multiplying a transverse stretching step. 2. The production method according to claim 1, wherein the rail opening angle of the horizontal stretching machine used in the horizontal stretching step is within 5 degrees. Wherein the thickness of the film d, the main refractive index in the film plane n _x, n _y, the main refractive index in the thickness direction n _z and,
in case of the n _x> n _y, in-plane retardation value (R
_{e = (n x -n y)} d) is 0 to 500 nm, the thickness direction retardation value _{(Rth = (n x -n z} ) d) 0 to 50
An optical compensation film produced by the method according to claim 1, wherein 0 nm and Re / Rth <1. 4. An in-plane retardation value (Re) of 1
0 to 100 nm, the retardation value in the thickness direction (Rt
The optical compensation film according to claim 3, wherein h) is 100 to 300 nm and Rth / Re is 1 to 4. 5. The optical compensation film according to claim 3, wherein the in-plane retardation distribution in the width direction is within ± 10% at 80% or more of the sheet width. 6. The optical compensation film according to claim 3, wherein the thermoplastic resin film is a norbornene-based resin film. 7. A polarizing plate comprising a laminate of an optical compensation film produced by the method of claim 1 and a polarizing plate. 8. A polarizing plate comprising a laminate of the optical compensation film according to claim 3 and a polarizing plate. 9. A liquid crystal display device wherein the optical compensation film according to claim 3 is arranged on at least one side of a liquid crystal cell. 10. The polarizing plate according to claim 7 or 8,
A liquid crystal display device arranged on at least one side of a liquid crystal cell.