JP2006018212A - Method for manufacturing retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film which has a satisfactorily large retardation Re and Rth, is capable of improving viewing field angle dependence and contrast of a liquid crystal display, can be used as a protective film of a polarizer in common and is superior in sticking efficiency with a polarizing plate. <P>SOLUTION: In the method for manufacturing the retardation film, the width of longitudinally stretched film after stretching a laterally stretched film, made by stretching a cyclic olefin base resin film in the width direction, in the length direction (longitudinal direction) is controlled so as to be 85 to 99% of (laterally stretched film width/√n), when the longitudinally stretching magnification is set to be (n) times. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a retardation film used for improving the contrast and viewing angle of a liquid crystal display device.

  In recent years, liquid crystal display devices have become widespread as display devices for personal computers, and one of them is a TN (Twisted Nematic) mode liquid crystal display device. However, the TN mode liquid crystal display device has a problem that the viewing angle is narrow and the response speed is slow. Therefore, a VA (Vertical Alignment) mode liquid crystal display device using a birefringence mode instead of an optical rotation mode such as a TN mode liquid crystal display device has been proposed. As this VA mode liquid crystal display device, a domain regulating means comprising a projection having an inclined surface is provided on the inner surface of the substrate constituting the liquid crystal cell, and the orientation direction of the liquid crystal molecules is divided into two or more directions by this domain regulating means, There has been proposed an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device in which the viewing angle dependency is greatly different depending on the expected angle by making the amount of light passing through the liquid crystal cell uniform (for example, a patent) Reference 1).

However, even the MVA mode liquid crystal display device has a problem that the contrast is lowered when the liquid crystal display surface is viewed at an angle of 45 ° with respect to the normal line of the liquid crystal display surface. In order to improve the dependency, a biaxial retardation film is used.
As a material for such a retardation film, synthetic resin films having high transparency and high heat resistance such as polycarbonate and polysulfone have been used. In addition to the above characteristics, photoelastic coefficient, wavelength dispersion It is conceivable to use a cyclic olefin resin film having excellent properties such as properties and water vapor permeability as a retardation film.

  As a liquid crystal display device using the retardation film, for example, Patent Document 2 discloses a liquid crystal display device using a biaxial retardation film made of the above synthetic resin film having a specific photoelastic coefficient and retardation value. Is disclosed.

  In order to assemble a liquid crystal display device, a polarizing plate to be bonded to such a biaxial retardation film is usually wound in a roll shape with an absorption axis formed in the length direction thereof. When laminating the polarizing plate and the retardation film, it is necessary to superimpose the polarizing axis with the absorption axis of the polarizing plate and the slow axis in the plane of the retardation film orthogonal to each other, but the conventional biaxial retardation film In general, the film was stretched in the longitudinal direction and then in the transverse direction of the tenter, and since the in-plane slow axis was in the length direction, the retardation film was usually cut into single sheets and bonded to the polarizing plate. .

JP 2000-131893 A JP-A-11-95208

In such a case, by setting the slow axis direction of the biaxial retardation film as the width direction, continuous bonding of the polarizing plate and the retardation film can be realized, but the slow axis direction of the retardation film covers the entire surface. If not expressed accurately, the polarizing plate absorption axis and retardation film slow axis will not be orthogonal, and problems such as insufficient viewing angle compensation and reduced contrast will occur when combined with a liquid crystal cell. There was a thing.
In view of the above problems, the object of the present invention is to have a sufficiently large retardation Re in the film plane and retardation Rth in the film thickness direction, and can improve the viewing angle dependency and contrast of the liquid crystal display device. And it is providing the manufacturing method of the phase difference film which can be used also as a protective film of a polarizer, and was excellent in the bonding efficiency with a polarizing plate.
The maximum refractive index direction of the refractive index n _x, the direction of the refractive index n _y orthogonal to the maximum refractive index _direction, when the refractive index in the thickness direction is n _z, the retardation Re and the retardation Rth is the following It is expressed by an expression.
_{Re (nm) = | n x} -n y | × Thickness (nm)
Rth (nm) = | (n _x + n _y ) / 2−n _z | × thickness (nm)

  The method for producing a retardation film according to the present invention is such that a longitudinally stretched film width after stretching a transversely stretched film obtained by stretching a cyclic olefin-based resin film in its width direction in the length direction (longitudinal direction) is longitudinal. When the draw ratio is n times, it is controlled to be 85 to 99% of (laterally stretched film width / √n).

  Moreover, the manufacturing method of the retardation film by this invention is the longitudinal stretch film thickness after extending | stretching the horizontal stretch film formed by extending | stretching the cyclic olefin resin film in the width direction in the length direction (longitudinal direction). When the longitudinal draw ratio is n times, it is controlled to be 101 to 110% of (laterally stretched film thickness / √n).

  The cyclic olefin resin used in the retardation film of the present invention is not particularly limited, but a norbornene resin is preferable, and a saturated norbornene resin is particularly preferable. For example, hydrogen of a ring-opening (co) polymer of a norbornene monomer Additives, addition copolymers of norbornene monomers and olefin monomers, addition (co) polymers of norbornene monomers, or derivatives thereof may be used, and these may be used alone or in combination.

  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, Elements other than carbon and hydrogen, such as acrylic and methacrylic groups A tricyclic or higher polycyclic norbornene because it is easily available, has excellent reactivity, and has excellent heat resistance of the obtained retardation film. Type monomers are preferred, and tricyclic, tetracyclic or pentacyclic norbornene monomers are more preferred. In addition, a norbornene-type monomer may be used independently or 2 or more types may be used together.

  Further, as the hydrogenated product of the ring-opening (co) polymer of the norbornene monomer, the remaining double bond is hydrogenated after ring-opening polymerization of the norbornene monomer by a known method. These are widely used, and may be a hydrogenated product of a norbornene-based monomer homopolymer or a hydrogenated product of a copolymer of different norbornene-based monomers.

Furthermore, examples of the addition copolymer of the norbornene monomer and the olefin monomer include a copolymer of a norbornene monomer and an α-olefin, a copolymer of a norbornene monomer and a cyclic olefin monomer, and the like. As said alpha olefin, a C2-C20 alpha olefin is preferable, A C2-C10 alpha olefin is more preferable, for example, 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, etc. Since the copolymerizability is high, ethylene is preferable. Even when other α-olefin is copolymerized with the norbornene-based monomer, the presence of ethylene improves the copolymerizability.
Examples of the cyclic olefin monomer include cyclooctadiene, cyclooctene, cyclohexene, cyclododecene, cyclododecatriene, and the like.

  In addition, the method for obtaining the ring-opening (co) polymer of the norbornene-based monomer includes, for example, converting the norbornene-based monomer to a metal halide such as ruthenium, rhodium, palladium, osmium, iridium, platinum, nitrate or acetylacetone compound and a reducing agent. Or a catalyst system comprising a metal halide such as titanium, tungsten or molybdenum or a catalyst system comprising an acetylacetone compound and an organoaluminum compound. It can be obtained by ring-opening (co) polymerization at a polymerization temperature of 0 ° C. and a polymerization pressure of 0 to 5 MPa.

  The method for obtaining the addition copolymer of the norbornene monomer and the olefin monomer includes, for example, a monomer component in a solvent or without a solvent, and a vanadium compound and an organoaluminum compound (preferably a halogen-containing organoaluminum compound). In the presence of a catalyst system, it can be usually obtained by copolymerization at a polymerization temperature of −50 ° C. to 100 ° C. and a polymerization pressure of 0 to 5 MPa.

  Specific examples of the norbornene-based resin include those described in JP-A-1-240517. Specific examples of commercially available norbornene-based resins include those manufactured by JSR Corporation. The product name “Arton” series, the product name “Zeonoa” series manufactured by Nippon Zeon Co., Ltd., the product name “Apel” series manufactured by Mitsui Chemicals, and the like can be mentioned.

  As the number average molecular weight of the cyclic olefin-based resin of the present invention, the mechanical strength of the obtained retardation film may be lowered when it is small, while the moldability of the film may be hindered when it is large. 50000 is preferable, and 8000-30000 is more preferable. In addition, the number average molecular weight of cyclic olefin resin means what was measured by the gel permeation chromatography method.

  In addition, the cyclic olefin-based resin has the heat resistance, ultraviolet resistance, smoothness, etc. of the retardation film in order to prevent deterioration of the cyclic olefin-based resin during molding within the range that does not hinder the function of the retardation film. In order to improve, antioxidants such as phenols and phosphoruss; thermal degradation inhibitors such as lactones; UV absorbers such as benzophenones, benzotriazoles and acrylonitriles; esters of aliphatic alcohols, polyhydric alcohols Various additives such as a partial ester type or partial ether type lubricant; an amine type antistatic agent or the like may be added. In addition, an additive may be used independently or 2 or more types may be used together.

  As a method for forming the cyclic olefin resin film of the present invention, a conventionally used method is used. Specifically, the cyclic olefin resin is supplied to an extruder and melted and kneaded. In addition to the so-called melt-extrusion method, a cyclic olefin resin is dissolved in an organic solvent. Examples thereof include a method of casting a solution on a drum or band and then evaporating the organic solvent to form a long cyclic olefin-based resin film, a so-called solution casting method.

When the thickness of the cyclic olefin-based resin film is thin, it is difficult to obtain a desired retardation. On the other hand, when the thickness is thick, it is disadvantageous for thinning of the liquid crystal display device, so 50-200 μm is preferable, and 80-150 μm is more preferable. .
If the thickness of the cyclic olefin resin film exceeds 80 μm, it may be difficult to sufficiently evaporate and remove the organic solvent by the solution casting method. It is preferable to produce a resin-based resin film.

In the method for producing a retardation film of the present invention, first, the above-mentioned cyclic olefin resin film is stretched in the width direction (lateral direction) to produce a laterally stretched film.
Specifically, while continuously unwinding a long cyclic olefin resin film, in the temperature region near the glass transition temperature (Tg) of the cyclic olefin resin, both ends in the width direction of the film are tentered. The film is gripped by an arbitrary gripping means such as a clip, and the film is moved in the width direction by gradually displacing the gripping means in a direction away from each other while moving in the transport direction at substantially the same speed as the transport speed of the film. Then, the film is cooled to a temperature lower than Tg in order to fix the orientation of the cyclic olefin-based resin molecule.

  The temperature of the cyclic olefin resin film when the above-mentioned cyclic olefin resin film is stretched in the transverse direction is appropriately adjusted according to the amount of compensation retardation to be imparted to the retardation film. On the other hand, since it may be difficult to obtain a desired retardation when it is high, the range of Tg to Tg + 20 ° C. of the cyclic olefin resin film is preferable, and Tg of the cyclic olefin resin film + 2 ° C. to 2 ° C. A range of Tg + 10 ° C. is more preferable. The Tg is measured by a differential scanning calorimeter.

Further, when the stretching ratio in stretching the cyclic olefin-based resin film in the transverse direction is low, the orientation axis direction may not be evenly aligned. Is uneven, and retardation unevenness may be large. Therefore, 1.2 to 3.0 times is preferable, and 1.5 to 2.5 times is more preferable.
In addition, before extending | stretching a cyclic olefin resin film in the width direction and before cooling, you may perform a thermal relaxation process in order to arrange the orientation of a cyclic olefin resin molecule.

  In this way, by stretching the cyclic olefin resin film in the transverse direction, the cyclic olefin resin molecules are arranged in the stretching direction, the refractive index in the stretching direction is increased, and a slow axis is formed in the transverse direction. A transversely stretched film can be obtained.

  When the retardation Re in the plane of the laterally stretched film is low, even if the laterally stretched film is stretched in the length direction (a direction orthogonal to the width direction, so-called longitudinal direction), the retardation Rth in the thickness direction is hardly expressed. On the other hand, if it is high, the result is the same as when the cyclic olefin-based resin molecule is excessively distorted, and it becomes difficult to control the retardation Rth in the thickness direction expressed by stretching the transversely stretched film in the longitudinal direction. Therefore, 50 to 300 nm is preferable, and 80 to 250 nm is more preferable.

  If the thickness of the film after the transverse stretching is large, a liquid crystal display device constituted by using the obtained retardation film becomes thick, and if it is thin, there is a risk of breakage or the like when stretching in the longitudinal direction. 120 μm is preferable, and 35 to 80 μm is more preferable.

  In the method for producing a retardation film of the present invention, next, the transversely stretched film is stretched in the length direction (longitudinal direction) to thereby exert a stretching force in a direction perpendicular to the slow axis generated in the transverse direction. In addition, a retardation film is obtained.

  As a method of stretching this transversely stretched film in the length direction (longitudinal direction), an inter-roll neck-in stretching method, a proximity roll stretching method, etc. can be applied, but the phase difference can be easily controlled and the cyclic olefin-based resin film is scratched. It is desirable to adopt a roll-to-roll neck-in stretching method that has the advantage that defects such as cracks and wrinkles are unlikely to occur. The inter-roll neck-in stretching method is a method in which a film being transported is sandwiched between a pair of nip rolls or S-shaped wrap rolls located across a stretching zone that is sufficiently longer than the film width, and the peripheral speed of the upstream roll In contrast, this is a method of obtaining a desired draw ratio by increasing the peripheral speed of the downstream roll. At this time, both end portions in the width direction of the laterally stretched film are free ends that are not restrained, and exhibit a neck-in phenomenon in the width direction along with stretching in the longitudinal direction.

In the method for producing a retardation film of the present invention, the longitudinally stretched film width after stretching in the longitudinal direction is 85 to 99% of (laterally stretched film width / √n) when the longitudinal stretch ratio is n times. Control to be
In general, it is known that the width after the neck-in of an amorphous substance in longitudinal stretching with the width direction as a free end is 1 / √n times when the longitudinal stretching ratio is n times. However, it has been found that when a transversely stretched film is stretched longitudinally, the phenomenon of excessive neck-in occurs due to the release of stress accumulated in the width direction. This excessive neck-in shrinkage results in a variation in the orientation direction during cooling and solidification because stress is applied in a direction different from the stretching direction. The present inventor can control this phenomenon by the neck-in temperature at the time of longitudinal stretching. By performing longitudinal stretching at a furnace temperature of Tg to Tg + 3 ° C., the width after neck-in is reduced to 1 / √n. The present invention was completed by finding out that it can be suppressed to 85 to 99% of the above.

  On the other hand, if the draw ratio in stretching the transversely stretched film in the longitudinal direction is low, the amount of deformation in the longitudinal direction of the transversely stretched film may be too small to obtain a sufficient retardation Rth. It becomes difficult to hold the slow axis in the direction, and finally the direction of the slow axis is changed to the vertical direction. As a result, the direction accuracy of the slow axis is lowered, and continuous sticking to the polarizing plate roll is performed. When used in a liquid crystal display device, display quality such as contrast may be deteriorated, so 1.01 to 1.40 times is preferable, and 1.05 to 1.30 times is more preferable. .

Moreover, in the manufacturing method of the retardation film of this invention, when the thickness of the longitudinally stretched film after extending | stretching to the vertical direction makes the longitudinal draw ratio n times, it is 101 of (laterally stretched film thickness / √n). Control to be ~ 110%.
As described above, it is generally known that the thickness of an amorphous substance after neck-in becomes 1 / √n times when the longitudinal draw ratio is n times.
However, when the transversely stretched film is stretched longitudinally, the phenomenon of excessive neck-in occurs due to the release of the stress accumulated in the width direction, and this excessive neck-in shrinkage causes stress in a direction different from the stretching direction. As a result, the orientation direction during cooling and solidification varied. The present inventor can control this phenomenon by the neck-in temperature at the time of longitudinal stretching. By performing longitudinal stretching at a furnace temperature of Tg to Tg + 3 ° C., the thickness after neck-in can be reduced to 1 / √n. It was found that it can be suppressed to 101 to 110% of the above.

  The draw ratio at the time of extending | stretching a horizontal stretched film to the vertical direction is the same as the above, 1.01-1.40 times are preferable and 1.05-1.30 times are more preferable.

In the method for producing a retardation film of the present invention, when the glass transition temperature of the cyclic olefin resin is Tg (° C.), the transverse stretching temperature is T _ST (° C.), and the longitudinal stretching temperature is T _SM (° C.). Tg ≦ _TSM ≦ _TST is preferably satisfied. By setting the longitudinal stretching temperature within this range, the Rth value can be effectively expressed with a slight deformation in the longitudinal direction without disturbing the orientation direction aligned in the lateral direction.

  In the manner described above, the retardation film obtained by stretching the transversely stretched film in the longitudinal direction is a temperature lower than the glass transition temperature Tg of the cyclic olefin resin in order to prevent retardation Re and Rth from being lowered due to thermal relaxation. It should be cooled immediately.

  The retardation film obtained in the method for producing a retardation film of the present invention is suitably used as a component of a liquid crystal display device. Even if the retardation film is used alone, the retardation film is laminated and integrated with a polarizing plate. Even if it is used as a composite polarizing plate, the polarizing plate may be used by being laminated and integrated on the polarizing plate through an adhesive instead of the protective film on the liquid crystal cell side. Among them, since the thickness of the liquid crystal display device can be improved and the production efficiency can be improved, the retardation film is preferably laminated and integrated through a water-based adhesive instead of the protective film on the liquid crystal cell side, and used as a polarizing plate. Is preferred.

  In any case, the retardation film needs to be adjusted so that the slow axis of the retardation film and the absorption axis of the polarizing plate or polarizer adjacent to the retardation film are orthogonal to each other. .

  The liquid crystal cell is not particularly limited as long as it is a conventionally used liquid crystal cell, but an OCB mode, a VA mode, or the like is 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 has a small refractive index in the thickness direction and effectively relaxes the refractive index in the thickness direction of the increased liquid crystal cell, so that the front contrast of the resulting liquid crystal display device and the change in contrast depending on the expected angle Since the so-called viewing angle dependency can be greatly improved, the retardation film is particularly suitable for the VA mode.

  According to the method for producing a retardation film of the present invention, it has sufficiently large retardations Re and Rth, can improve the viewing angle dependency and contrast of a liquid crystal display device, and can protect a polarizer. In addition, a retardation film excellent in bonding efficiency with a polarizing plate can be obtained.

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

(Production of transversely stretched films 1 and 2)
A thermoplastic saturated norbornene resin (trade name “Zeonor # 1600”, number-average molecular weight: 20000) manufactured by Nippon Zeon Co., Ltd. is used as the cyclic olefin resin, and this resin is supplied to a single screw extruder and melted and kneaded. Melting extrusion was performed at a resin temperature of 230 ° C. from a T die attached to the tip of the extruder to obtain a long thermoplastic saturated norbornene resin film having a width of 500 mm and an average thickness of 100 μm. In addition, it was 161.0 degreeC when the glass transition temperature Tg of this thermoplastic saturated norbornene-type resin was measured with the differential scanning calorimeter (The Seiko Denshi Kogyo make, brand name "DSC220C").

Next, the obtained long thermoplastic saturated norbornene-based resin film is continuously unwound, and both end portions in the width direction of the film are sequentially held by tenter clips, and then supplied into the preheating zone and preheated to 155 ° C. did. Thereafter, the preheated film is continuously supplied into the stretching zone and passed through the stretching zone set to the temperature shown in Table 1 while being heated, and the tenter clip is moved at the same speed as the resin film transport speed. Thus, the film was moved in the film conveying direction and displaced in the transverse direction away from each other, and stretched in the direction (lateral direction) perpendicular to the extrusion direction at a transverse stretching ratio of 2 times. After the stretching of the resin film in the transverse direction is completed, heat relaxation is performed in a 160 ° C. atmosphere while being held by a tenter clip, and the orientation direction is aligned in the film width direction, and then the orientation is performed in a 120 ° C. atmosphere as it is. The transversely stretched film in which the slow axis was formed in the transverse direction was continuously wound up in a roll shape.
Moreover, in order to remove the influence of a clip holding | grip part, the 250 mm part of the both ends of the width direction in a laterally stretched film was removed, and the full width was 500 mm.

The in-plane retardation Re in the obtained laterally stretched film was measured at an interval of 10 mm in the lateral direction using an automatic birefringence measuring apparatus (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments) and averaged. Calculated.
In addition, the thickness was measured at a pitch of 10 mm with a contact-type continuous thickness meter (manufactured by Seiko EM) over the entire width. The results were as shown in Table 1.

(Examples 1 and 2 and Comparative Examples 1 and 2)
The transversely stretched film obtained above is continuously unwound from the upstream nip roll at a constant unwinding speed of 6.6 m / min, and is wound on the downstream nip roll faster than the peripheral speed of the upstream nip roll. While winding at a speed, the space between the unwinding shaft and the winding shaft is divided into three zones, a preheating zone, a stretching zone, and a cooling zone, sequentially from the unwinding shaft side. Were passed sequentially and sequentially. The temperature in the preheating zone, stretching zone, and cooling zone was adjusted so that the temperature of the transversely stretched film was 155 ° C, 162-165 ° C, and 110 ° C in order, and the longitudinal stretching ratios shown in Table 2 were obtained. Thus, a stretched retardation film was obtained.
The obtained retardation film has a longitudinal stretching ratio (n), a width ratio (%) represented by a longitudinally stretched film width / (laterally stretched film width / √n), a longitudinally stretched film thickness / (a laterally stretched film thickness / The thickness ratio (%) represented by √n), the in-plane retardation Re, the thickness direction retardation Rth, and the slow axis direction (axis accuracy) were measured. The results were as shown in Table 2.

  The retardations Re and Rth were measured in the same manner as in the case of the transversely stretched film, and the slow axis direction was measured with the width direction being 0 degree.

Claims (3)

  When the longitudinally stretched film width after stretching the transversely stretched film obtained by stretching the cyclic olefin-based resin film in the width direction thereof in the length direction (longitudinal direction) is n times the longitudinal stretch ratio, A method for producing a retardation film, wherein the width is controlled to be 85 to 99% of the transversely stretched film width / √n).   When the longitudinally stretched film thickness after stretching the transversely stretched film formed by stretching the cyclic olefin-based resin film in the width direction thereof in the length direction (longitudinal direction) is n times the longitudinal stretch ratio, A method for producing a retardation film, wherein the thickness is controlled to be 101 to 110% of a transversely stretched film thickness / √n). When the glass transition temperature of the cyclic olefin resin is Tg (° C.), the transverse stretching temperature is T _ST (° C.), and the longitudinal stretching temperature is T _SM (° C.), Tg ≦ T _SM ≦ T _ST is satisfied. The method for producing a retardation film according to claim 1 or 2.