JP2006301522A - Method for manufacturing retardation film, and retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film, with which the retardation film having sufficiently large in-plane retardation R<SB>e</SB>and retardation R<SB>th</SB>in the thickness direction and improving contrast and a viewing angle of a liquid crystal display device is manufactured, and the retardation film obtained with such a manufacturing method. <P>SOLUTION: The method for manufacturing the retardation film, which is composed of an addition copolymer of a norbornene based monomer and an olefin based monomer, has a film forming step to form a thick film with 150-350 μm thickness with extrusion molding, and a stretching step to biaxially stretch the thick film to a direction vertical to the extrusion direction, and to the extrusion direction, and in the stretching step, the biaxial stretching is conducted in such a way that at least a stretching ratio in the direction vertical to the extrusion direction is 2.5-5, and film thickness after the biaxial stretching is 90 μm or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention can produce a retardation film that has a sufficiently large in-plane retardation R _e and thickness direction retardation R _{th, and} can reduce the contrast and narrow the viewing angle of the liquid crystal display device. The present invention relates to a method for producing a retardation film, and a retardation film obtained by such a production method.

In recent years, liquid crystal display devices have become widespread as display devices for personal computers, and TN mode liquid crystal display devices are used as one of such liquid crystal display devices. However, the TN mode liquid crystal display device has a problem that the viewing angle is narrow and the response speed is slow. Therefore, in recent years, a VA mode liquid crystal display device using a birefringence mode instead of an optical rotation mode as in the TN mode liquid crystal display device has been proposed.

As such a VA mode liquid crystal display device, for example, in Patent Document 1, there is provided a domain regulating means comprising a projection having an inclined surface on the inner surface of a substrate constituting a liquid crystal cell, and the orientation direction of liquid crystal molecules is changed by this domain regulating means. An MVA (Multi-domain Vertical Alignment) mode liquid crystal display device has been disclosed in which the viewing angle dependency varies greatly depending on the expected angle by dividing the light into two or more directions and making the amount of light passing through the liquid crystal cell uniform. Has been.

However, even when the MVA mode liquid crystal display device is used, when the liquid crystal display surface is viewed from an angle of 45 ° with respect to the normal line of the liquid crystal display surface, the contrast is lowered and the viewing angle is narrow. Could not be resolved.

As a method for improving such viewing angle dependency, a method using a biaxial retardation film made of a synthetic resin having high transparency and high heat resistance such as polycarbonate and polysulfone has been proposed. In recent years, in addition to these properties, it has been studied to use a cyclic olefin-based resin film excellent in photoelastic coefficient, wavelength dispersibility, water vapor transmission rate and the like as a retardation film.

However, the cyclic olefin resin, expression of retardation is smaller than the polycarbonate and polysulfone, the retardation R _th retardation R _e and the thickness direction in a plane per unit thickness was difficult both to increase . Therefore, in order to obtain an optical compensation required, for example, it was necessary or a laminate of two sheets of retardation films made of a cyclic olefin based resin having a half value of the required retardation R _th. However, when two retardation films are used in an overlapping manner, foreign matter is mixed when the retardation films are overlapped with each other, or misalignment occurs when the retardation films are overlapped with each other. There was a point.

On the other hand, Patent Document 2 discloses a method for improving retardation by adding an aromatic compound having two aromatic rings. However, when the additive is used in this way, if the additive is not sufficiently dispersed and compatible, the resulting retardation film may be less transparent or cause optical defects. Occurred.

Examples of the cyclic olefin resin used for the retardation film include a ring-opening polymer of a norbornene monomer and an addition copolymer of a norbornene monomer and an olefin monomer, and a ring-opening polymer of a norbornene monomer. As shown in the following formula, an unsaturated double bond remains in the polymer obtained after the ring-opening polymerization, and even if hydrogenation is performed, the remaining double bond is completely hydrogenated. There was a problem that the heat resistance stability and light resistance stability of the obtained retardation film deteriorated. For this reason, use of an addition copolymer of a norbornene monomer and an olefin monomer having no residual double bond has been studied. However, the addition copolymer of norbornene-based monomer and olefin-based monomer has a problem that the film-forming property and the expression of retardation are low as compared with the ring-opening polymer of norbornene-based monomer.
Therefore, even when an addition copolymer of a norbornene monomer and an olefin monomer is used, the retardation R _e in the plane of the retardation film and the retardation R _{th in the} thickness direction can be sufficiently increased. There has been a demand for a method for producing a phase difference film.

Japanese Patent Laid-Open No. 11-242225 Japanese Patent Laid-Open No. 2002-14230

The present invention can produce a retardation film that has a sufficiently large in-plane retardation R _e and thickness direction retardation R _{th, and} can reduce the contrast and narrow the viewing angle of the liquid crystal display device. An object of the present invention is to provide a method for producing a retardation film, and a retardation film obtained by such a production method.

The present invention is a method for producing a retardation film comprising an addition copolymer of a norbornene monomer and an olefin monomer, and a film forming step of forming a thick film having a thickness of 150 to 350 μm by an extrusion method, A stretching step of biaxially stretching the thick film in a direction orthogonal to the extrusion direction and in the extrusion direction, and in the stretching step, at least a stretching ratio in a direction orthogonal to the extrusion direction is 2.5 to 5 times, and This is a method for producing a retardation film in which biaxial stretching is performed so that the thickness after biaxial stretching is 90 μm or less.
The present invention is described in detail below.

In the method for producing a retardation film of the present invention, first, a film forming step of forming a thick film having a thickness of 150 to 350 μm is performed by an extrusion method.
By using the extrusion method, a thick film having a thickness in the above range can be easily produced. When the thickness of the thick film is less than 150 μm, the development of retardation, which is a problem when an addition copolymer of a norbornene monomer and an olefin monomer (hereinafter also referred to as a norbornene addition copolymer) is used. The problem cannot be improved, and it becomes difficult to obtain a desired retardation. When the thickness exceeds 350 μm, problems such as cracking of the ear during winding occur.

In the method for producing a retardation film of the present invention, next, a stretching process is performed in which a thick film having a thickness of 150 to 350 μm and comprising a norbornene-based addition copolymer is biaxially stretched in a direction perpendicular to the extrusion direction and in the extrusion direction. Thus, a retardation film is produced.
By biaxially stretching the thick film, the norbornene-based addition copolymer molecule can be oriented in a predetermined direction to obtain a retardation film.

In the stretching step, the lower limit of the stretching ratio in the direction orthogonal to the extrusion direction is 2.5 times, and the upper limit is 5 times. If it is less than 2.5 times, the directions of the alignment axes are not evenly aligned, and if it exceeds 5 times, unevenness in the tension distribution in the width direction occurs, and unevenness in retardation increases. A preferable upper limit is 4.0 times.

In the stretching step, biaxial stretching is performed so that the thickness after biaxial stretching of a thick film having a thickness of 150 to 350 μm is 90 μm or less.
By stretching the thick film until the thickness after biaxial stretching is 90 μm or less, it is possible to increase both the in-plane retardation R _e and the retardation R _{th in the} thickness direction of the obtained retardation film.
When the thickness after biaxial stretching exceeds 90 μm, the orientation of the norbornene-based addition copolymer molecule becomes insufficient, and both the in-plane retardation R _e and the thickness direction retardation R _th of the resulting retardation film are increased. It becomes difficult.
A preferred lower limit is 170 μm and a preferred upper limit is 250 μm.

Examples of the method of biaxially stretching the thick film in the direction orthogonal to the extrusion direction and in the extrusion direction include, for example, (1) a temperature in the vicinity of the glass transition temperature Tg of the norbornene-based addition copolymer. And a method of stretching in the extrusion direction (length direction) after stretching in a direction (width direction) orthogonal to the extrusion direction, (2) a long thick film made of norbornene-based addition copolymer glass A stretching method in which the film is heated to a temperature near the transition temperature Tg and simultaneously stretched in the direction perpendicular to the extrusion direction (width direction) and in the extrusion direction (length direction), and (3) a glass of norbornene-based addition copolymer Examples of the stretching method include heating to a temperature in the vicinity of the transition temperature Tg, applying a pressing force in the thickness direction to form a thin film, and stretching in the direction perpendicular to the extrusion direction (width direction) and the extrusion direction (length direction) at the same time. Among these, thermal relaxation amount in the stretching step is small, since it is possible to increase the retardation R _th in the thickness direction, it is preferable to use a method shown in the above (1). Hereinafter, the method shown in the above (1) will be described.

In the method shown in (1), first, the thick film is heated to a temperature in the vicinity of the glass transition temperature Tg of the norbornene-based addition copolymer, and both ends in the width direction of the thick film are arbitrarily gripped by a tenter clip or the like. Grasping by means. Next, the thick film is stretched in the direction perpendicular to the extrusion direction by gradually displacing the gripping means such as a tenter clip in a direction away from each other, and then the orientation of the norbornene-based addition copolymer molecule is fixed. For this purpose, it is cooled to a temperature lower than the glass transition temperature Tg of the norbornene-based addition copolymer.

By stretching the thick film in the direction perpendicular to the extrusion direction in this way, norbornene-based addition copolymer molecules are arranged in the stretch direction, the refractive index in the stretch direction is increased, and the thickness is perpendicular to the extrusion direction of the thick film. A slow axis is formed in the direction of
In addition, after extending | stretching the said thick film in the direction orthogonal to an extrusion direction, before cooling, you may perform a thermal relaxation process for the purpose of aligning the orientation of a norbornene-type addition copolymer molecule.

The heating temperature when the thick film is stretched in the direction orthogonal to the extrusion direction is appropriately adjusted depending on the compensation retardation amount to be imparted to the obtained retardation film, but the preferred lower limit is glass of norbornene-based addition copolymer. The transition temperature (Tg) is −10 ° C., and the preferable upper limit is Tg + 20 ° C. of the norbornene-based addition copolymer. If it is less than Tg-10 ° C., the thick film may be broken during stretching or retardation unevenness may be increased. When Tg + 20 ° C is exceeded, it may be difficult to obtain a desired retardation. A more preferred lower limit is Tg-5 ° C, and a more preferred upper limit is Tg + 10 ° C. In addition, the glass transition temperature Tg of the said norbornene-type addition copolymer says what was measured with the differential scanning calorimeter.

A preferred lower limit of the retardation R _e in the plane of the thick film after providing stretched in a direction perpendicular to the extrusion direction is 80 nm, the upper limit is preferably 450nm. When the thickness is less than 80 nm, even if the thick film is stretched in the length direction, the retardation R _{th in the} thickness direction may be difficult to be expressed. When the thickness exceeds 450 nm, the norbornene-based addition copolymer molecule is excessively distorted. when obtained by stretching a thick film in the length direction in the process, it may be difficult to control the retardation R _th in the thickness direction. A more preferable lower limit is 100 nm, and a more preferable upper limit is 400 nm.

Next, the thick film stretched in the direction orthogonal to the extrusion direction is stretched in the extrusion direction (length direction), and a stretching force is applied in the direction orthogonal to the slow axis generated in the direction orthogonal to the extrusion direction. Biaxiality can be imparted to a thick film.

As a method of stretching the thick film in the extrusion direction, a roll-to-roll neck-in stretching method, a proximity roll stretching method, etc. can be used, but the retardation is easily controlled and defects such as scratches and wrinkles occur in the thick film. It is preferable to use a roll-to-roll neck-in stretching method because it has the advantage of being difficult to perform.
Note that the above-mentioned neck-in-stretching method between rolls is a method in which a film being transported is sandwiched between a pair of nip rolls positioned across a stretching zone that is sufficiently longer than the film width, and the peripheral speed of the nip roll on the upstream side. This is a method of obtaining a desired draw ratio by increasing the peripheral speed of the nip roll on the downstream side. At this time, both ends in the width direction of the thick film are free ends that are not restrained, and exhibit a neck-in phenomenon in the width direction along with the stretching in the length direction.

The preferable lower limit of the draw ratio when the thick film is stretched in the extrusion direction is 1.05 times, and the preferable upper limit is 2 times. If it is less than 1.05 times, the amount of deformation in the extrusion direction of the thick film is too small, and sufficient retardation _Rth may not be obtained. If it exceeds 2 times, the direction of the slow axis is thick film. As a result, the direction accuracy of the slow axis decreases, and when used in a liquid crystal display device, display quality such as a decrease in contrast may be caused. A more preferred lower limit is 1.1 times and a more preferred upper limit is 1.7 times.

The temperature of the thick film when the thick film is stretched in the extrusion direction is appropriately adjusted depending on the amount of compensation retardation to be imparted to the retardation film, but the preferred lower limit is the glass transition temperature (Tg of the norbornene-based addition copolymer). ) −10 ° C., and the preferable upper limit is Tg + 20 ° C. of norbornene-based addition copolymer. If it is less than Tg-10 ° C., the thick film may be broken during stretching or retardation unevenness may be increased. When Tg + 20 ° C is exceeded, it may be difficult to obtain a desired retardation. A more preferred lower limit is Tg-5 ° C, and a more preferred upper limit is Tg + 10 ° C.

Next, a retardation film can be obtained by cooling the thick film stretched in the direction perpendicular to the extrusion direction and in the extrusion direction to a temperature lower than the glass transition temperature Tg of the norbornene-based addition copolymer.
By performing such a cooling step, it is possible to prevent the retardations R _e and R _th from being lowered due to thermal relaxation.

The retardation film produced by the method for producing a retardation film of the present invention comprises an addition copolymer of a norbornene monomer and an olefin monomer.
Since the addition copolymer of the norbornene monomer and the olefin monomer does not have a residual double bond, the resulting retardation film has heat resistance stability and light resistance stability due to the presence of the residual double bond. There is no problem.

Specific examples of the addition copolymer of the norbornene monomer and the olefin monomer include those described in JP-A-1-240517, and specific examples of commercially available products include, for example, commercial products. Name "Apel" series (made by Mitsui Chemicals), brand name "Topas" series (made by Chikona), etc. are mentioned.

Examples of the addition copolymer of the norbornene monomer and the olefin monomer include a copolymer of a norbornene monomer and an α-olefin, and a copolymer of a norbornene monomer and a cyclic olefin monomer.

The norbornene-based monomer is not particularly limited as long as it has a norbornene ring. For example, bicyclic compounds such as norbornene and norbornadiene; Tetracycles; pentacycles such as cyclopentadiene trimers; heptacycles such as tetracyclopentadiene; alkyls such as methyl, ethyl, propyl and butyl, alkenyls such as vinyl, alkylidenes such as ethylidene, phenyl and tolyl , Substituents such as aryl such as naphthyl; furthermore, these ester groups, ether groups, cyano groups, halogen atoms, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, hydroxyl groups-free, silyl groups, epoxy groups, Contains elements other than carbon and hydrogen, such as acrylic and methacrylic groups Group, so-called polar group-containing substituents, etc. are easily available, excellent in reactivity, and excellent in the heat resistance of the resulting retardation film. Monomers are preferable, and tricyclic, tetracyclic and pentacyclic norbornene monomers are more preferable. In addition, a norbornene-type monomer may be used independently and may use 2 or more types together.

Examples of the α-olefin include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1 -Octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and the like. Among these, ethylene is preferable because of its high copolymerizability, and other α-olefins are combined with norbornene monomers. Even in the case of copolymerization, the copolymerizability can be enhanced by adding ethylene.
As the α-olefin, an α-olefin having 2 to 20 carbon atoms is preferable, and an α-olefin having 2 to 10 carbon atoms is more preferable.

Examples of the cyclic olefin monomer include cyclooctadiene, cyclooctene, cyclohexene, cyclododecene, cyclododecatriene, and the like.

The preferable lower limit of the number average molecular weight of the addition copolymer of the norbornene monomer and the olefin monomer is 5000, and the preferable upper limit is 150,000. When it is less than 5,000, the mechanical strength of the obtained retardation film may be lowered, and when it exceeds 150,000, the melt viscosity is increased and the moldability may be lowered. A more preferable lower limit is 10,000, and a more preferable upper limit is 100,000. In addition, the said number average molecular weight means the standard polystyrene conversion value measured by the gel permeation chromatography method.

The addition copolymer of the norbornene-based monomer and the olefin-based monomer includes, for example, the presence of a catalyst system composed of a vanadium compound and an organoaluminum compound such as a halogen-containing organoaluminum compound in a solvent or without a solvent. The polymerization can be usually carried out by copolymerization at a polymerization temperature of −50 to 100 ° C. and a polymerization pressure of 0 to 5 MPa.

In the method for producing a retardation film of the present invention, the deterioration of the norbornene-based addition copolymer during molding can be prevented and the heat resistance, ultraviolet resistance, and smoothness of the retardation film can be reduced within the range that does not impair the function of the obtained retardation film. In order to improve the properties such as phenol-based, phosphorus-based antioxidants; lactone-based thermal degradation inhibitors; benzophenone-based, benzotriazole-based, acrylonitrile-based ultraviolet absorbers; aliphatic alcohol ester-based, Various additives such as partial ester-based and partial ether-based lubricants of polyhydric alcohols; amine-based antistatic agents and the like may be added. In addition, the said additive may be used independently and may use 2 or more types together.

By carrying out the method for producing a retardation film of the present invention, for example, a retardation film in which in-plane retardation R _e and retardation R _{th in the} thickness direction satisfy the following formulas (1) to (3) can be obtained. Such a retardation film is also one aspect of the present invention.

式中、ｄは位相差フィルムの平均厚みを表す。

In the formula, d represents the average thickness of the retardation film.

In the present invention, the in-plane retardation R _e and the thickness direction retardation R _th are defined by the following formulas (4) and (5).

式中、ｎ_ｘ はフィルム面内の遅相軸方向の屈折率、ｎ_ｙ はフィルム面内の進相軸方向の屈折率、ｎ_ｚ はフィルムの厚み方向の屈折率、ｄは位相差フィルムの平均厚み（ｎｍ）を表す。

Wherein, n _x is a refractive index in a slow axis direction in the film plane, n _y is the fast axis direction of the refractive index in the film plane, n _z is a refractive index in the thickness direction of the film, d is the phase difference film Represents the average thickness (nm).

The retardation film of the present invention, as shown in the equation (1), the lower limit of the retardation _{R e} in-plane 10 nm, the upper limit is 200 nm. This is because the birefringence generated when linearly polarized light passes through the liquid crystal cell cannot be sufficiently compensated if the above range is not satisfied.

The retardation film of the present invention, as shown in the equation (2), the lower limit of the retardation _{R th} in the thickness direction is 50 nm, the upper limit is 400 nm. If it is out of the above range, birefringence generated when linearly polarized light passes through the liquid crystal cell cannot be sufficiently compensated.

R _e and R _th in the retardation film of the present invention satisfy the relationship represented by the above formula (3). If it is out of the range of the above formula (3), birefringence generated when linearly polarized light passes cannot be sufficiently compensated.

The retardation film of the present invention may be used alone, or may be laminated and integrated with a polarizing plate to be used as a composite polarizing plate. Further, an adhesive is used instead of the protective film on the liquid crystal cell side of the polarizing plate. It may be used as a polarizing plate by laminating and integrating, but since it can improve the thinning and manufacturing efficiency of the liquid crystal display device, instead of the protective film on the liquid crystal cell side of the polarizing plate, an adhesive is used. It is preferable to use it as a polarizing plate laminated and integrated.

When the retardation film of the present invention is used alone, a polarizing plate is disposed on each of the pair of substrate outer surfaces constituting the liquid crystal cell, and at least one of the substrates of the liquid crystal cell, preferably The retardation film is interposed between the substrate on the liquid crystal display surface side and the polarizing plate facing the substrate, and on the polarizing plate disposed on the substrate side opposite to the liquid crystal display surface in the liquid crystal cell. A liquid crystal display device can be obtained by disposing a known illumination system of a backlight type or a sidelight type and incorporating a drive circuit.

The liquid crystal cell is not particularly limited as long as it is a conventionally used liquid crystal cell, but OCB mode, VA mode, and TN mode are preferable. In the VA mode, the liquid crystal molecules stand in a state in which the length direction thereof is perpendicular to the substrate of the liquid crystal cell when the voltage is off. At this time, the refractive index in the thickness direction of the liquid crystal cell in the light passing through the liquid crystal cell increases, and refractive index anisotropy appears, and light leaks depending on the viewing angle.
The retardation film of the present invention has a small refractive index nz in the thickness direction and effectively relaxes the refractive index in the thickness direction of the increased liquid crystal cell, depending on the front contrast and the expected angle of the liquid crystal display device to be obtained. Since the change in contrast, so-called viewing angle dependency, can be greatly improved, this is particularly suitable when the VA mode is used.

According to the present invention, an in-plane retardation R _e and a thickness direction retardation R _th are sufficiently large, and a retardation film capable of producing a retardation film capable of improving the contrast and viewing angle of a liquid crystal display device. The manufacturing method of a film and the phase difference film obtained by such a manufacturing method can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
Using thermoplastic saturated norbornene resin (Topas # 6013, manufactured by Ticona), which is an addition polymer of norbornene monomer and ethylene, this thermoplastic saturated norbornene resin is supplied to a single screw extruder, melted, kneaded, and single screw extruded Melt extrusion was performed from a T die attached to the tip of the machine to obtain a long thermoplastic saturated norbornene resin film having a width of 500 mm and an average thickness of 170 μm.
In addition, it was 136.0 degreeC when the glass transition temperature Tg of the thermoplastic saturated norbornene-type resin was measured with the differential scanning calorimeter.

Next, the obtained long-sized thermoplastic saturated norbornene resin film is continuously unwound, and the thermoplastic saturated norbornene resin film is preheated to 136 ° C. and then heated to the temperature shown in Table 1, and this heating is performed. While maintaining the temperature (stretching temperature in the width direction), the film was stretched in the direction (width direction) perpendicular to the extrusion direction at the stretching ratio shown in Table 1, and then the thermoplastic saturated norbornene resin film was cooled to 90 ° C. After forming a slow axis in the width direction on the thermoplastic saturated norbornene resin film, the thermoplastic saturated norbornene resin film stretched in the width direction was obtained by continuously winding in a roll.

Next, the thermoplastic saturated norbornene-based resin film stretched in the width direction of the roll is continuously preheated at 135 ° C. while being continuously unwound at a constant unwinding speed of 5 m / min. The film was stretched in the length direction at the indicated draw ratio. Next, the film was cooled at 90 ° C. to fix the orientation, and then rolled up again to obtain a retardation film.

(Example 2)
Using the same resin as in Example 1, this thermoplastic saturated norbornene resin was supplied to a single-screw extruder in the same manner as in Example 1, and a long thermoplastic saturated norbornene resin film having a width of 500 mm and an average thickness of 270 μm was used. Got.

Next, the obtained long thermoplastic saturated norbornene resin film was continuously unwound, and the thermoplastic saturated norbornene resin film was preheated to 139 ° C. and then subjected to the temperatures and stretch ratios shown in Table 1. It extended | stretched to the direction (width direction) orthogonal to an extrusion direction similarly to Example 1, and wound up continuously in roll shape.

Next, the thermoplastic saturated norbornene-based resin film stretched in the width direction of the roll is continuously preheated at 136 ° C. while continuously unwinding at a constant unwinding speed of 5 m / min, and then at Table 2 at 136 ° C. The film was stretched in the length direction at the indicated draw ratio. Subsequently, the film was passed through a 90 ° C. cooling zone to fix the orientation, and then rolled up again to obtain a retardation film.

(Comparative Example 1)
A long thermoplastic saturated norbornene resin film was obtained in the same manner as in Example 1 except that the same resin as in Example 1 was used and the average thickness was 140 μm.

Next, the obtained long thermoplastic saturated norbornene resin film was continuously unwound, and the thermoplastic saturated norbornene resin film was preheated to 139 ° C. and then subjected to the temperatures and stretch ratios shown in Table 1. It extended | stretched to the direction (width direction) orthogonal to an extrusion direction similarly to Example 1, and wound up continuously in roll shape.

Next, the thermoplastic saturated norbornene-based resin film stretched in the width direction of the roll is continuously preheated at 136 ° C. while continuously unwinding at a constant unwinding speed of 5 m / min, and then at Table 2 at 136 ° C. The film was stretched in the length direction at the indicated draw ratio. Next, the film was cooled at 90 ° C. to fix the orientation, and then rolled up again to obtain a retardation film.

(Evaluation)
The thermoplastic saturated norbornene resin films and retardation films stretched in the width direction obtained in Examples 1 and 2 and Comparative Example 1 were evaluated by the following methods. The evaluation results of the thermoplastic saturated norbornene resin film stretched in the width direction are shown in Table 1, and the evaluation results of the retardation film are shown in Table 2 and Table 3.

(1) Evaluation of thermoplastic saturated norbornene-based resin film stretched in the width direction (1-1) Front retardation value In-plane retardation R _e excluding both 150 mm portions in the width direction is measured using an automatic birefringence measuring device (KOBRA- 21ADH, measured at 10mm intervals in the width direction using a Oji Scientific instruments), and calculates an average value of the obtained R _e, and the front retardation value.

(1-2) Average thickness 1/1000 mm Using a digital thickness meter, the thickness was measured at 10 mm intervals in the width direction, and the average value of the obtained thicknesses was calculated as the average thickness.

(2) Evaluation of retardation film (2-1) Retardation R _e , R _th value measurement In-plane retardation R _e of retardation film and retardation R _{th in} thickness direction are measured by an automatic birefringence measuring device (manufactured by Oji Scientific Instruments). The product name was measured using “KOBRA-21ADH”).

(2-2) Average thickness 1/1000 mm Using a digital thickness gauge, measurements were made at 10 mm intervals in the width direction, and the average value of the obtained thicknesses was calculated as the average thickness.

(2-3) Strip the polarizing plate and retardation film disposed on both sides of the liquid crystal cell of a liquid crystal display device (VL-1530SW, manufactured by Fujitsu Limited) using a liquid crystal cell with front contrast ratio and viewing angle VA mode. The retardation films and polarizing plates (HLC2-5618, manufactured by Sanlitz) obtained in Examples and Comparative Examples were laminated and integrated with each other on the outer surface of the substrate of the liquid crystal cell via an acrylic adhesive. A liquid crystal display device was obtained. The slow axis of the retardation film and the absorption axis of the polarizing plate were adjusted so as to be in the same direction as the slow axis of the retardation film and the absorption axis of the polarizing plate before peeling.

A signal is input to the obtained liquid crystal display device using an input device (Pattern Generator 408, manufactured by Reader Electronics Co., Ltd.), and black luminance and white luminance at any nine positions on the display surface of the liquid crystal display device are measured with a luminance meter (LS- 110, manufactured by Minolta Co., Ltd.), the front contrast ratio was calculated, and the maximum value and the minimum value of the front contrast ratio were measured.

In addition, the contrast ratio is measured while changing the measurement angle from the normal direction to the horizontal direction left and right at each of the measurement point where the front contrast ratio is maximum and the minimum measurement point, and the contrast ratio is less than 10. The angle was defined as the left / right limit tilt position, the angle formed by the left and right limit tilt positions was measured, and the angle was defined as the viewing angle. Note that the contrast ratio could not be measured in a state where the liquid crystal display device was tilted by 80 ° or more to the left and right in the horizontal direction from the normal direction of the display surface.

According to the present invention, an in-plane retardation R _e and a thickness direction retardation R _th are sufficiently large, and a retardation film capable of producing a retardation film capable of improving the contrast and viewing angle of a liquid crystal display device. The manufacturing method of a film and the phase difference film obtained by such a manufacturing method can be provided.

Claims (3)

A method for producing a retardation film comprising an addition copolymer of a norbornene monomer and an olefin monomer,
A film forming step of forming a thick film having a thickness of 150 to 350 μm by an extrusion method;
A stretching step of biaxially stretching the thick film in a direction orthogonal to the extrusion direction and in the extrusion direction;
In the stretching step, biaxial stretching is performed so that at least the stretching ratio in the direction orthogonal to the extrusion direction is 2.5 to 5 times, and the thickness after biaxial stretching is 90 μm or less. A method for producing a phase difference film. The method for producing a retardation film according to claim 1, wherein the addition copolymer of the norbornene monomer and the olefin monomer is a random copolymer of the norbornene monomer and ethylene. A retardation film produced by the method for producing a retardation film according to claim 1 or 2,
A retardation film retardation R _th retardation R _e and the thickness direction of the in-plane and satisfies the following formulas (1) to (3).

In the formula, d represents the average thickness of the retardation film.