JP2005309339A - Optical compensating film and manufacturing method for polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensating film which is unwound to a part near to a core in a no-curling state and stuck to a polarizing plate in a smooth state, and suitably used as the optical compensating film of a vertical alignment type liquid crystal cell. <P>SOLUTION: The optical compensating film is obtained by stretching long-length film composed of saturated cyclic olefin polymer resin at least in one direction and has effective width ≥650mm. When the longitudinal direction of the film is defined as (x), the width direction thereof is defined as (y), the thickness direction thereof is defined as (z), and refractive indexes in the respective directions are specified as (nx), (ny) and (nz), the optical compensating film satisfies relation ny≥nx>nz, and is wound around the core whose outside diameter is ≥125mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical compensation film used for improving the contrast and viewing angle of a liquid crystal display device and a method for producing a polarizing plate using the optical compensation film.

In order to prevent changes in display color, contrast, etc. depending on the viewing angle when viewing the display device due to the birefringence due to the liquid crystal, a retardation plate is arranged for the liquid crystal cell to compensate the optical characteristics based on the birefringence and to improve the viewing angle characteristics. Improvement techniques have been proposed.
Particularly in the optical compensation of a vertical alignment type liquid crystal cell called VA type, the refractive index in the thickness direction is small, that is, the refractive index in the direction showing the maximum refractive index in the film plane is nx (or ny), Use a retardation film showing a relationship of nx ≧ ny> nz (or ny ≧ nx> nz) when the refractive index in the direction perpendicular to the direction is defined as ny (or nx) and the refractive index in the thickness direction is defined as nz. (See Patent Document 1).
However, such a retardation film must be bonded so that a direction of a large refractive index called a slow axis out of nx and ny is orthogonal to an absorption axis of a polarizing plate adjacent to the retardation film, The retardation film is generally thin, and if the film has a slight curl during bonding, the bonding angle will shift, or the retardation film will be bonded in a state where stress is applied. Sometimes the phase difference change becomes large, and as a result, the liquid crystal display may not exhibit a predetermined performance.
In particular, the tendency was strong on the core side of the retardation film, and the longer the elapsed time after winding, the more the curl along the outer periphery of the core tended to appear significantly.

Japanese Patent No. 3383359

  In view of the above-described situation, the present invention allows the optical compensation film to be unwound to a portion near the core without curling, and can be bonded to a polarizing plate in a smooth state, and is suitable as an optical compensation film for a vertically aligned liquid crystal cell. It is an object of the present invention to provide an optical compensation film used and a method for producing a polarizing plate using the optical compensation film.

  This problem can be solved by setting the outer diameter of the winding core during production of the optical compensation film to 125 mm or more.

  The invention according to claim 1 is an optical compensation film having an effective width of 650 mm or more obtained by stretching a long film made of a saturated cyclic olefin polymer-based resin in at least one direction, wherein the longitudinal direction of the film is x, When the width direction is y, the thickness direction is z, and the refractive index in each direction is defined as nx, ny, nz, the relationship of ny ≧ nx> nz is satisfied, and the coil is wound around a core having an outer diameter of 125 mm or more. It is an optical compensation film.

  In the invention according to claim 2, the longitudinal direction of the polarizing film having the absorption axis in the longitudinal direction is rewound, and the longitudinal direction thereof is matched with the adhesive or the adhesive. It is a manufacturing method of a polarizing plate characterized by pasting together.

As the resin of the optical compensation film used in the present invention, a saturated cyclic olefin resin is used because of its excellent low wavelength dispersibility and low photoelastic coefficient.
The saturated cyclic olefin-based resin is not particularly limited. For example, a hydrogenated product of a ring-opening (co) polymer of norbornene monomers, an addition polymer of a norbornene monomer and an olefin monomer, or between norbornene monomers Examples include addition (co) polymers, and these saturated cyclic olefin resins may be used alone or in combination of two or more.

  The norbornene-based monomer is not particularly limited as long as it is a monomer having a norbornene ring. For example, bicyclic compounds such as norbornene and norbornadiene; tricyclic compounds such as dicyclopentadiene and dihydroxypentadiene; tetracyclododecene and the like Tetracycles; pentacycles such as cyclopentadiene trimers; heptacycles such as tetracyclopentadiene; alkyl substitutions such as methyl, ethyl, propyl and butyl, alkenyl substitutions such as vinyl, and alkylidenes such as ethylidene Substituents, aryl substituents such as phenyl, tolyl, naphthyl; and ester groups, ether groups, cyano groups, halogen atoms, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, non-hydroxyl groups, silyl groups , Epoxy group, acrylic group, methacryl group and other carbon Containing elements other than hydrogen, substitution products having a so-called polar group. Among these norbornene monomers, tricyclic or higher polycyclic norbornene monomers are preferred because they are easily available, have excellent reactivity, and the resulting optical compensation film has excellent heat resistance. More preferred are tetracyclic and pentacyclic norbornene monomers. 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 (co) polymerization of the norbornene monomer by a known method. What is currently used is widely used, and may be a hydrogenated product of a homopolymer of norbornene-based monomers 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. 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 α-olefin include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, and 1-hexene. , 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like, and ethylene is preferable because of high copolymerizability. Further, when other α-olefin is copolymerized with a norbornene-based monomer, the copolymerization property of the α-olefin can be enhanced by the presence of ethylene.

  The ring-opening (co) polymer of the norbornene monomer comprises, for example, a norbornene monomer comprising a metal halide such as ruthenium, rhodium, palladium, osmium, iridium, platinum, nitrate or acetylacetone compound, and a reducing agent. Using a catalyst system or a catalyst system composed of a metal halide such as titanium, tungsten, molybdenum, or an acetylacetone compound and an organoaluminum compound, in a solvent or without a solvent, usually at -50 ° C to 100 ° C. It can be obtained by ring-opening (co) polymerization at a temperature of 0 to 4.9 MPa.

  The addition copolymer of the norbornene monomer and the olefin compound includes, for example, a catalyst composed of a vanadium compound and an organoaluminum compound, preferably a halogen-containing organoaluminum compound, with a monomer component in a solvent or without a solvent. In general, it can be obtained by copolymerization at a temperature of −50 ° C. to 100 ° C. and a pressure of 0 to 4.9 MPa.

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

  If the number average molecular weight of the saturated cyclic olefin-based resin is too small, the mechanical strength of the optical compensation film obtained may decrease, and if it is too large, the solution viscosity and melt viscosity will increase, making film formation difficult. 5000 to 50000 is preferable, and 8000 to 30000 is more preferable. In addition, the number average molecular weight of saturated cyclic olefin resin is the number average molecular weight of polystyrene conversion measured by GPC (gel permeation chromatograph).

  In addition, the saturated cyclic olefin resin does not deteriorate the saturated cyclic olefin resin during molding, and the heat resistance, ultraviolet resistance, smoothness, etc. of the optical compensation film are within the range that does not impair the function of the optical compensation 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 partial ester-based and polyhydric alcohol partial ether-based lubricants; amine-based antistatic agents and the like may be added. In addition, an additive may be used independently or 2 or more types may be used together.

Next, although the manufacturing method of the said optical compensation film is demonstrated, a manufacturing method consists of the process of film forming of a film, extending | stretching, and winding up.
The production of the saturated cyclic olefin-based resin film is performed by a method conventionally used as a method for producing a film. As a specific method, a saturated cyclic olefin-based resin film is produced by supplying a saturated cyclic olefin-based resin to an extruder, melting and kneading, and extruding it from a mold attached to the tip of the extruder into a film shape. A so-called melt-extrusion method, a solution obtained by dissolving a saturated cyclic olefin resin in an organic solvent is cast on a drum or band, and then the organic solvent is evaporated to form a long saturated cyclic olefin resin film. Examples include so-called solution casting method for forming a film.

  Although the thickness of the said saturated cyclic olefin resin film is not specifically limited, 50-200 micrometers is preferable and 80-150 micrometers is more preferable. When the thickness is less than 50 μm, it is difficult to develop a retardation value, and when the thickness exceeds 200 μm, the total thickness of the liquid crystal panel is preferably increased when it is applied to the polarizing film and used in the liquid crystal panel. Absent.

  When the thickness of the saturated cyclic olefin resin film is 80 μm or more, it is difficult to sufficiently evaporate and remove the organic solvent by the solution casting method. It is preferable to produce a resin-based resin film.

  By stretching the saturated cyclic olefin resin film, the saturated cyclic olefin resin molecules are oriented in at least one direction to obtain a biaxial optical compensation film. As the stretching method, a transverse stretching method in which a tenter clip or the like is used to pull in the width direction of the roll, a sequential biaxial stretching method in which longitudinal stretching is performed in a separate process (see JP 2002-148438 A), these two directions A simultaneous biaxial stretching method in which stretching is performed simultaneously is known. In the present invention, any stretching method may be used.

  When an optical compensation film is used for a VA mode liquid crystal cell, it is necessary to make its slow axis orthogonal to the absorption axis of the adjacent polarizing plate. However, the polarizing plate of a polarizing plate that has been generally used has an absorption axis that coincides with the longitudinal direction. On the other hand, the slow axis of the optical compensation film obtained as described above also coincides with the longitudinal direction of the optical compensation film. As a result, it was impossible to continuously orthogonally cross the long original fabrics. The slow axis of the optical compensation film used in the present invention is perpendicular to the longitudinal direction.

Hereinafter, a method of reducing the refractive index in the thickness direction of the saturated cyclic olefin-based resin film by the sequential biaxial stretching method while the slow axis thereof is orthogonal to the longitudinal direction will be described in detail.
First, the film formed by melt extrusion is transversely stretched in the width direction (TD direction). The transverse stretching is generally performed by a tenter stretching method in which the film is widened in the TD direction at a temperature around Tg of the resin while holding both ends of the film with a tenter clip.
The stretching temperature is appropriately set depending on the retardation value required together with the stretching ratio. In order to obtain a high phase difference at a low magnification, stretching is performed at a temperature close to Tg, and in order to obtain a high phase difference at a high magnification, it is desirable to perform stretching at a temperature of Tg + 5 to 30 ° C., preferably Tg + 5 to 15 ° C.
The front birefringence | nx−ny | after widening stretching is preferably 0.0010 to 0.0060, more preferably 0.0015 to 0.0040. That is, the in-plane retardation (Re) is preferably 50 to 300 nm, more preferably 75 to 200 nm in terms of a thickness of 50 μm.
If the birefringence after this widening is too low, the retardation (Rth) in the thickness direction will be difficult to develop in the next step (at the time of stretching in the longitudinal direction). This is because it becomes difficult.
A phase difference plate intermediate product having a slow axis in the TD direction is obtained by the widening stretching.

  Next, longitudinal stretching is performed in a direction (MD direction) perpendicular to the direction of the slow axis generated in the previous step. Examples of the longitudinal stretching method include an inter-roll neck-in stretching method and a proximity roll stretching method, but the former inter-roll neck-in stretching method is preferable in that scratches, wrinkles and the like are less likely to enter the film.

The neck-in stretching method between rolls is the neck-in deformation at the free end in a heating furnace around Tg, while the traveling long film is clamped by two pairs of nip rolls with different speed ratios installed at a predetermined interval. It is the method of extending | stretching.
By making the stretching amount at this time 1/3 or less of the stretching amount in the previous step (lateral stretching step), an optical compensation film can be obtained efficiently without changing the direction of the slow axis.
When the amount of stretching in the subsequent process (longitudinal stretching) exceeds 1/3 of the amount of stretching in the preceding process (lateral stretching), the direction of the slow axis is changed, and the MD direction (flow direction) is obtained.
When the slow axis is in the MD direction, it becomes unsuitable for the main usage of the biaxial optical compensation film that uses the polarizing plate absorption axis and the slow axis of the optical compensation film orthogonal to each other.
The optical compensation film having the slow axis obtained in the above direction in the TD direction is finally bonded to a protective film and wound up through steps such as slits at the end and corona treatment as necessary. The protective film is preferably a polyester-based resin, and the pressure-sensitive adhesive portion is appropriately selected and used depending on the application, such as EVA or acrylic, but a film without a pressure-sensitive adhesive is continuously inserted between the optical compensation films. You can wind it up.

After being stretched by the above process, the optical compensation film is wound around a core having an outer diameter of 125 mm or more. The material of the winding core is smooth, and general materials such as polyvinyl chloride, ABS, and PS can be used without any particular limitation as long as they have a strength that does not cause cracks, cracks, deflection, etc. during product winding or transportation.
In general, a film wound in a roll shape is fixed in a shape along the winding core due to tightening over time, and the smaller the winding diameter, the greater the generation of stress when returning to the original state.
In addition, the winding tension can be made high with the effect of the outer diameter of the core in addition to the effect of curling the outer diameter of the core by winding with the minimum tension that does not generate a winding nest, telescope and the like.

The optical compensation film thus obtained is suitably used as an assembly material for a liquid crystal display device in combination with a polarizing plate.
The polarizing plate is not particularly limited as long as it is conventionally used in a liquid crystal display device, and includes one obtained by coating both surfaces of a polarizer with a protective film. The above-mentioned optical compensation film may be substituted for the cell-side surface) instead of the protective film, and in this way, the liquid crystal display device can be made thinner and the manufacturing efficiency can be improved.
Bonding with a polarizing plate is a method in which a polarizing plate roll and a retardation plate roll are wound in parallel and bonded between nip rolls (FIG. 1a), and a retardation plate is attached to a polarizing plate that runs on a smooth surface. Although there is a method of combining (FIG. 1b), etc., either bonding method may be used.
The optical compensation film unwound from the optical compensation film roll according to the present invention is less likely to curl and can be uniformly bonded without causing any deviation or unexpected stress during polarizing plate bonding.

  Since the optical compensation film of the present invention has the above-mentioned contents, the optical compensation film unwound from the roll has a small amount of curling, and is uniform without any occurrence of misalignment or unexpected stress during polarizing plate bonding. It becomes possible to paste.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
1) Preparation of raw fabric As a thermoplastic saturated norbornene-based resin, a commercially available norbornene-based resin (Zeonor # 1600, manufactured by Nippon Zeon Co., Ltd.) is used in a melt extrusion molding machine in which a T-die is disposed in a single-screw melt extruder. Extrusion was performed at a melting temperature of 0 ° C. to obtain a film having a width of 800 mm and an average thickness of 100 μm.
2) Measurement of Tg When Tg of the film obtained above was measured using DSC220C (manufactured by Seiko Denshi Kogyo Co., Ltd.), Tg was 161.0 ° C.
3) Stretching (lateral stretching) / measurement In a transverse stretching apparatus using a general tenter clip, a magnification of 200% in a zone configuration with a preheating temperature of 150 ° C., a stretching temperature of 163 ° C., a thermal relaxation temperature of 163 ° C., and a cooling temperature of 120 ° C. And an optical compensation film having a slow axis with a front phase difference Re (= (ny−nx) × d) = 210 nm in the TD direction was produced. (See Figure 2)
4) Longitudinal Stretching / Measurement Using the inter-roll longitudinal uniaxial stretching apparatus, the film produced in 3) above was subjected to 115% uniaxial stretching in a zone configuration with a preheating temperature of 100 ° C, a stretching temperature of 161 ° C, and a cooling temperature of 100 ° C. Thus, a biaxial optical compensation film having Re = 80 nm and Rth = 150 nm was prepared. 5) Winding 4) A polyethylene protective film having a total thickness of 60 μm (made by Sekisui Chemical Co., Ltd.) # 6221F), and then slit to 700 mm width with a shear blade type slitter. As shown in Table 1, each of the examples is divided into a PVC core having an outer diameter of 150 mm as an example and a PVC core having an outer diameter of 75 mm as a comparative example. 500 m and 1000 m were wound up to obtain four types of roll films. Thereafter, it was left in a room adjusted to 40 ° C. for 500 hours.
6) Evaluation of curls The above four types of films are left in a room where the temperature and humidity are controlled at 23 ° C. × 55% RH for 24 hours, and then unwound to leave 20 m in the core portion, from there in the longitudinal direction. A sample with a total width of 500 mm was cut out and left in the same room on a horizontal desk for 10 minutes in the direction of increasing curl, and the height of the portion with the largest curl was measured. The results are shown in Table 1.
7) Measurement of retardation (Re) The above four kinds of films were bonded to a polarizing plate (HLC2-5618, manufactured by Sanlitz) by a roll method using a laminator. The bonded product was cut into a size of 100 mm × 100 mm, bonded to 2 mm thick alkali glass using a laminator, and then treated for 20 minutes at 50 ° C. and 4.9 MPa using an autoclave. After being left for 30 minutes after the treatment, Re at the center is measured using a phase difference meter (KOBRA-WR, manufactured by Oji Scientific), treated in an oven at 100 ° C. for 24 hours, and then allowed to cool for 30 minutes. The Re of the part was measured. The results are shown in Table 1.

The schematic diagram of the method of sticking an optical compensation film on a polarizing plate. Schematic diagram of transverse stretching.

Claims (2)

  An optical compensation film having an effective width of 650 mm or more obtained by stretching a long film made of a saturated cyclic olefin polymer resin in at least one direction, wherein the longitudinal direction of the film is x, the width direction is y, and the thick direction Is an optical compensation film that satisfies the relationship of ny ≧ nx> nz and is wound around a core having an outer diameter of 125 mm or more, where z is a refractive index in each direction and nx, ny, nz . The polarizing film having an absorption axis in the longitudinal direction is continuously bonded via an adhesive or an adhesive while the optical compensation film is rewound while the longitudinal direction is matched. A method for producing a polarizing plate.

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