JP2007334140A - Optical retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical retardation film which can be easily and inexpensively produced, is excellent in low photoelastic coefficient and low wavelength dispersibility, and can maintain high optical retardation even if it is heated. <P>SOLUTION: The optical retardation film is obtained by drawing a raw roll film composed of a cyclic olefin resin and characterized in that the difference between the glass transition temperature measured by thermomechanical analysis, of the raw roll film and the heat shrinkage temperature measured by thermomechanical analysis, of the optical retardation film is not higher than 20°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a retardation film that can be produced easily and inexpensively, has a low photoelastic coefficient and low wavelength dispersibility, and can retain a high retardation even when heated.

2. Description of the Related Art In recent years, liquid crystal display devices (Liquid Crystal Display: LCD) have been widely used in display devices such as computers as well as cathode ray tube CRT (Cathode Ray Tube). In such a liquid crystal display device, a retardation film is usually bonded to a glass cell in which an electrode encapsulating liquid crystal molecules is incorporated via a transparent adhesive, and a polarizing plate is further bonded thereon via an adhesive. It has a combined structure.

Retardation films used in such liquid crystal display devices are generally polycarbonate resins, cellulose resins, vinyl chloride resins, acrylonitrile resins, styrene resins, polyolefin resins, polysulfone resins, thermoplastic saturated norbornene. It is produced by forming a thermoplastic resin such as a resin based on a casting (solution cast) film forming method, a calender film forming method, a melt extrusion film forming method, etc., and stretching it in the vertical direction, the horizontal direction, or both. Has been. Among these, thermoplastic saturated norbornene resins are considered as retardation films because they have excellent characteristics such as heat resistance, low specific gravity, low birefringence, low photoelastic coefficient, and low wavelength dispersion. Yes.
However, the thermoplastic saturated norbornene-based resin has a low expression of retardation after being subjected to a stretching treatment for imparting a function as a retardation film, and the retardation compensation range of the obtained retardation film is limited. was there. Examples of a method for obtaining a required retardation value using such a resin include a method of increasing a retardation film and a method of increasing a stretching ratio and a stretching temperature in a stretching step. Conceivable.
However, the method of increasing the thickness of the retardation film has a problem in that the application is limited due to restrictions when the retardation film is mounted. In addition, the method of increasing the draw ratio has a problem that the effect of the reduction of the film thickness is reduced when the retardation development property is low, and the method of decreasing the stretching temperature obtains the required retardation value. Even if it was possible, there was a problem that the phase difference value decreased when the heat resistance test was performed.

On the other hand, as a method for increasing the retardation of the retardation film, for example, Patent Document 1 discloses a method of blending a retardation adjusting agent having a specific structure as an additive of the film.
However, in this method, there is a problem of complication of the process and an increase in cost because it requires a separate step of blending the retardation adjusting agent, and only a stretching process is performed after the resin composition is formed into a film. A retardation film showing a sufficiently high retardation by a simple method has been desired.
In addition, the fact that such a retardation film having high retardation can be obtained by a simple method provides a wide retardation film in the field of large-sized liquid crystal televisions, for which demand is expected to increase further. It is especially desirable because it is necessary.
Japanese Patent Application Laid-Open No. 2004-051562

In view of the above situation, the present invention provides a retardation film that can be easily and inexpensively manufactured, has a low photoelastic coefficient and low wavelength dispersibility, and can retain a high retardation even when heated. The purpose is to provide.

The present invention is a retardation film obtained by stretching a raw film made of a cyclic olefin-based resin, the glass transition temperature measured by thermomechanical analysis of the raw film, and the thermomechanical analysis of the retardation film The retardation film is characterized in that the difference from the measured heat shrinkage temperature is within 20 ° C. The present invention is described in detail below.

In the present invention, the difference between the glass transition temperature (hereinafter referred to as Tg) measured by thermomechanical analysis of the raw film (hereinafter referred to as TMA) and the heat shrinkage temperature measured by thermomechanical analysis of the retardation film is determined. 20 ° C. or less.
As a method for preventing a decrease in retardation value due to heating, which has been a problem in the past, there is a method using a resin having a high Tg as a material for a raw film. However, if only a resin having a high Tg is used, a decrease in retardation value during heating could not be reliably prevented. Therefore, as a result of intensive studies, the present inventors reduced the difference between the Tg measured by TMA of the raw film and the heat shrinkage temperature measured by TMA of the obtained retardation film, and further increased the upper limit of the difference. When the temperature is set to 20 ° C., it has been found that the change in retardation value due to heating can be greatly reduced, and the present invention has been completed.
When the difference between the Tg measured by TMA of the raw film and the heat shrinkage temperature measured by TMA of the retardation film exceeds 20 ° C., the heat resistance is lowered, or the retardation value is greatly lowered by heating. To do. A preferred upper limit is 18 ° C.

In the present invention, the reason why it is possible to prevent a decrease in phase difference due to heating is considered as follows. That is, in the retardation film, the phase difference is caused by the orientation of the molecular chain. Such molecular chain orientation is the orientation of the main chain derived from the orientation of the molecule itself and the orientation of the end of the molecule. And can be broadly divided. Here, since the orientation of the molecular end portion has a high degree of freedom of movement, it is considered that the orientation is easily relaxed by heating.
Therefore, even in the case of retardation films having the same retardation value, when the orientation of the end of the molecule is large, the apparent Tg is locally lowered, and when the TMA is measured, the heat shrinkage temperature is lowered to the low temperature side. It is thought to shift. In the present invention, by increasing the heat shrinkage temperature of the obtained retardation film and reducing the difference from the Tg of the original film, it becomes possible to reduce the portion where the orientation is easily relaxed, It is possible to prevent a decrease in phase difference due to.

Since the retardation film of the present invention has the above-described characteristics, it has an advantage that the retardation value does not decrease even when a heat durability test generally performed in actual products is performed. For example, even when a durability test is performed at 80 ° C., which is a temperature required for a general liquid crystal display such as a liquid crystal television, the retardation value does not decrease, and the heat durability is excellent.

In this invention, the preferable minimum of Tg measured by TMA of the said raw film is 120 degreeC. When the temperature is lower than 120 ° C., a decrease in phase difference due to heating in a heat resistance test assuming a severe use environment may not be sufficiently prevented.
Moreover, the preferable minimum of the heat shrinkage temperature measured by TMA of the retardation film of this invention is 115 degreeC. When the temperature is lower than 115 ° C., a decrease in retardation due to heating may not be sufficiently prevented.

In the present invention, the Tg and the heat shrinkage temperature are measured by TMA. As a method for measuring Tg by TMA, specifically, for example, a raw film is cut out with a predetermined width, set in a thermomechanical analyzer, and then heated at a predetermined heating rate to deform the film. The method of measuring is mentioned. FIG. 1 is a graph showing the relationship between the temperature and the thermal expansion coefficient when the Tg of the raw film is measured by the method described above. As shown in FIG. 1, when the raw film before stretching is measured, the coefficient of thermal expansion rapidly increases after linear expansion by linear expansion. In this specification, a tangent line is drawn on the curve before and after the ascent, and the intersection of the tangent lines is defined as Tg.

Even when the heat shrinkage temperature is measured by TMA, it can be measured by performing the same operation as described above. FIG. 2 is a graph showing the relationship between the temperature and the thermal expansion coefficient when the heating shrinkage temperature of the retardation film is measured. As shown in FIG. 2, when the retardation film after stretching is measured, it expands linearly by linear expansion in the low temperature range, but there is a temperature at which expansion turns into contraction due to relaxation of stretching. In this specification, this maximum value is defined as the heat shrinkage temperature.
When measuring the above heat shrinkage temperature, the thermal expansion coefficient is the stretching direction, that is, if the material has positive birefringence, the thermal expansion coefficient in the direction that becomes the slow axis direction when the phase difference is measured. taking measurement.

The cyclic olefin resin is not particularly limited. For example, a ring-opening (co) polymer of a cyclic olefin monomer (hereinafter, also simply referred to as a ring-opening (co) polymer), a cyclic olefin monomer, and an olefin monomer. Addition (co) polymers (hereinafter also simply referred to as addition (co) polymers), addition (co) polymers of cyclic olefin monomers and their derivatives, etc., may be used alone, Two or more kinds may be used in combination.
The addition (co) polymer tends to have lower retardation as compared with a ring-opening (co) polymer. That is, when a film made of an addition (co) polymer of the same shape and a film made of a ring-opening (co) polymer are stretched under the same stretching conditions (stretching temperature; Tg), the addition (co) polymer When the film made of is stretched, the retardation value is lowered.
Therefore, since the present invention is an effective means for stretching a film made of a resin having a low retardation, the addition (co) polymer comprising the cyclic olefin monomer and the olefin monomer is used. In this case, the effects of the present invention can be further exerted, and it is more preferable to use an addition (co) polymer composed of the cyclic olefin monomer and the acyclic olefin monomer. Hereinafter, a case where a norbornene monomer is used as the cyclic olefin monomer will be described.

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; tricyclic compounds such as dicyclopentadiene and dihydroxydicyclopentadiene; tetracyclododecene and the like A pentacycle such as cyclopentadiene trimer; a heptacycle such as tetracyclopentadiene; an alkyl such as methyl, ethyl, propyl and butyl; an alkenyl such as vinyl; an alkylidene such as ethylidene; a phenyl; Substituents such as aryl such as tolyl and naphthyl; furthermore, these ester groups, ether groups, cyano groups, halogen atoms, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, no hydroxyl groups, silyl groups, epoxy groups Other than carbon, hydrogen such as acrylic group, methacrylic group, etc. Containing group, substitution products having a so-called polar group. In addition, the said norbornene-type monomer may be used independently and may use 2 or more types together.

The ring-opening (co) polymer of the norbornene monomer includes, for example, a norbornene monomer comprising a metal halide such as ruthenium, rhodium, palladium, osmium, iridium, platinum, a nitrate or an 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 polymerization temperature and a polymerization pressure of 0 to 5 MPa.

Examples of the addition (co) polymer comprising a norbornene monomer and an olefin monomer include, for example, an addition (co) polymer comprising a norbornene monomer and an α-olefin, a norbornene monomer and a cyclic olefin monomer. Addition (co) polymers consisting of:
As the norbornene-based monomer, norbornene is particularly preferable from the viewpoint of the balance between mechanical properties and thermophysical properties represented by Tg and copolymerization.

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. Specifically, for example, ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, Examples include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and the like, and ethylene is preferable because of high copolymerizability.
Examples of the cyclic olefin monomer include cyclooctadiene, cyclooctene, cyclohexene, cyclododecene, cyclododecatriene and the like.

Examples of the polymerization catalyst used when synthesizing the addition (co) polymer of the norbornene monomer and the olefin monomer include a Ziegler-Natta type catalyst and a metallocene catalyst, and specifically include a vanadium compound and titanium. And a catalyst system comprising a compound comprising zirconium and an organoaluminum compound (preferably a halogen-containing organoaluminum compound).

Of the cyclic olefin-based resins described above, an unsaturated bond inevitably remains in a (co) polymer with ring opening, and even an addition (co) polymer has an unsaturated bond depending on the type of monomer. May remain. In such a case, it is preferable to hydrogenate these unsaturated bonds from the viewpoint of emphasizing durability such as oxidative degradation due to thermal history and discoloration due to ultraviolet rays. As a method of hydrogenating the ring-opening (co) polymer of the norbornene-based monomer, after the ring-opening (co) polymerization of the norbornene-based monomer by a known method, the remaining double bond is a known method. Hydrogenation may be performed at

Specific examples of the cyclic olefin-based resin include those described in JP-A-1-240517, for example, and examples of commercially available ring-opening (co) polymers include those manufactured by JSR Corporation. Product name "Arton" series, product name "Zeonor" series made by Nippon Zeon Co., Ltd. can be mentioned. Moreover, as a commercial item of an addition (co) polymer, the brand name "Topas" series made from Ticona, the brand name "Apel" series made from Mitsui Chemicals, etc. are mentioned.

The preferable lower limit of the number average molecular weight of the cyclic olefin-based resin is 5000, and the preferable upper limit is 80,000. When it is less than 5,000, the mechanical strength of the retardation film may be lowered, and when it exceeds 150,000, the melt viscosity is increased and the moldability of the original film may be lowered. A more preferable lower limit is 10,000, and a more preferable upper limit is 50,000. In addition, the said number average molecular weight means the standard polystyrene conversion value measured by the gel permeation chromatography method.

The retardation film of the present invention is for preventing deterioration of the cyclic olefin-based resin during molding and improving the heat resistance, ultraviolet resistance, smoothness, etc. of the retardation film within a range that does not hinder the function of the retardation film. Antioxidants such as phenols and phosphoruss; Thermal degradation inhibitors such as lactones; UV absorbers such as benzophenones, benzotriazoles, and acrylonitriles; Aliphatic alcohol esters and polyhydric alcohol partial esters Various additives such as a partial ether type lubricant, an amine type antistatic agent and the like may be added. In addition, the said additive may be used independently and may use 2 or more types together.

The retardation film of the present invention can be produced by producing a raw film by forming a cyclic olefin-based resin as described above, and then performing a stretching treatment.

The method for producing the raw film by forming the cyclic olefin resin into a film is not particularly limited, and a conventionally known film forming method can be used. For example, a melt extrusion film forming method, a calender film forming method, a solution Cast (casting) film forming methods and the like are mentioned, and among them, the melt extrusion film forming method is preferable because of excellent productivity and environmental symbiosis.

The stretching method is not particularly limited, and examples thereof include stretching methods such as longitudinal uniaxial stretching, lateral uniaxial stretching, simultaneous biaxial stretching, and sequential biaxial stretching. Moreover, a continuous system or a batch system may be used.

In general, the temperature in the stretching treatment is such that the lower the temperature, the higher the retardation compensation performance of the retardation film obtained.However, depending on the conditions, whitening of the film, which is fatal as an optical film due to the occurrence of craze, etc. There is a possibility that breakage may occur or a phase difference may greatly decrease when a heat durability test is performed.
In order to avoid such a phenomenon, it is necessary to appropriately adjust the stretching conditions. As a means for that, it is possible to continuously change the stretching temperature, the stretching ratio, and the stretching speed. Were intricately intertwined and difficult to compare centrally.
However, in the present invention, it is possible to avoid these problems by adjusting the difference between the Tg of the raw film and the heat shrinkage temperature of the retardation film.

According to the present invention, the difference between the Tg measured by TMA of the raw film and the heat shrinkage temperature measured by TMA of the obtained retardation film is 20 ° C. or less, so that at the end of the molecular chain In addition, it is possible to reduce a portion where the orientation is easily relaxed locally, and it is possible to provide a retardation film that exhibits a high retardation value even during heating. Thereby, even if the product using the retardation film of the present invention is subjected to a heat durability test, the retardation value does not decrease and has high reliability. In addition, the retardation film of the present invention can be produced easily and inexpensively, and can be excellent in low photoelastic coefficient and low wavelength dispersibility.

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
(Preparation of raw film)
A copolymer of norbornene and ethylene (manufactured by Ticona, Topas 6013) was melt-extruded using a single screw extruder (GM Engineering, GM50) to produce a 150 μm thick raw film.

(Measurement of glass transition temperature)
About the obtained raw film, it cuts out to width 3mm x length 20mm, produces a sample, and sets to 10 mm between chuck | zippers in a thermomechanical analyzer (the Seiko Instruments company make, TMA), The temperature is 30 to 250 degreeC. The temperature was increased at a rate of 5 ° C./min until the temperature dependence of the deformation amount in the TD direction was measured. Then, a tangent line is drawn on the curve before and after the expansion coefficient rapidly increases, and the intersection of the tangent lines is defined as Tg.
As a result of the measurement, the glass transition temperature was 135.2 ° C.

(Production of retardation film)
A retardation film was produced by fixing the length direction of the obtained raw film under an atmosphere of 140 ° C. and performing tenter stretching of 2.2 times in the width direction.

(Example 2)
In Example 1 (production of retardation film), a retardation film was produced in the same manner as in Example 1 except that tenter stretching was performed in an atmosphere at 141 ° C.

(Comparative Example 1)
In Example 1 (production of retardation film), a retardation film was produced in the same manner as in Example 1 except that the length direction was fixed and tenter stretching was performed 2.5 times in the width direction.

(Comparative Example 2)
In Example 1 (production of retardation film), the same as in Example 1 except that the length direction was fixed and the tenter stretching was performed 3.0 times in the width direction in an atmosphere of 145 ° C. A retardation film was prepared.

(Evaluation)
(1) Measurement of Heat Shrinkage Temperature The retardation films obtained in Examples and Comparative Examples were cut into a width of 3 mm and a length of 20 mm to prepare a sample, which was applied to a thermomechanical analyzer (manufactured by Seiko Instruments Inc., TMA). The distance between chucks was set to 10 mm, the temperature was raised from 30 ° C. to 250 ° C. at 5 ° C./min, and the temperature dependency of the deformation amount of the length was measured. And the temperature which shows the maximum point which changes from expansion | swelling to shrinkage | contraction was calculated | required, and it was set as the heating shrinkage temperature.

(2) Measurement of retardation value The in-plane retardation value Re of the retardation film was measured with light having a wavelength of 550 nm using an automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-21ADH). The thickness direction retardation Rth was also measured. Re and Rth can be calculated by the following equations.
Re (nm) = | nx−ny | × d
Rth (nm) = | (nx + ny) / 2−nz | × d
Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d (nm) is the average of the film It is thickness.

(3) Change in retardation value due to heating The retardation film was cut into 4 cm square, and after measuring the in-plane retardation value, the film was put into an 80 ° C. oven for 1000 hours, and then the in-plane retardation value was measured again. Then, assuming that the in-plane retardation value before being put into the oven is Rb and the in-plane retardation value after being put into the oven is Ra, the retardation holding ratio Rr (%) was obtained by the following equation.
Rr (%) = Ra / Rb × 100

As shown in Table 1, when Example 1 and Comparative Example 1 are compared, the in-plane retardation value is almost the same, but in Example 1, compared with Comparative Example 1, Tg and heating shrinkage temperature It can be seen that the difference between the two is small, and the retardation retention before and after heating is high. Moreover, even if Example 2 and Comparative Example 2 are compared, it turns out that the same tendency is shown.

According to the present invention, there is provided a retardation film that can be produced easily and inexpensively, has a low photoelastic coefficient and low wavelength dispersibility, and can retain a high retardation even when heated. Can do.

It is a graph which shows the relationship between the temperature and heating expansion coefficient when Tg of a raw film is measured by TMA. It is a graph which shows the relationship between the temperature at the time of measuring the heat shrinkage temperature of a phase difference film by TMA, and a heating expansion coefficient.

Claims (5)

A retardation film formed by stretching a raw film made of a cyclic olefin-based resin, the glass transition temperature measured by thermomechanical analysis of the raw film, and heating measured by thermomechanical analysis of the retardation film A retardation film having a difference from a shrinkage temperature of 20 ° C. or less. The retardation film according to claim 1, wherein a glass transition temperature measured by thermomechanical analysis of the raw film is 120 ° C. or higher. The retardation film according to claim 1, wherein the heat shrinkage temperature measured by thermomechanical analysis is 115 ° C. or higher. 4. The retardation film according to claim 1, wherein the cyclic olefin resin is an addition (co) polymer comprising a cyclic olefin monomer and an acyclic olefin monomer. The retardation film according to claim 4, wherein the cyclic olefin-based resin is a copolymer composed of norbornene and ethylene.

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