JPH0466002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester film for liquid crystal panel substrates. Glass plates have traditionally been used as substrates for liquid crystal panels. Although a glass plate is a base material with excellent performance, it is brittle against impact, and it is difficult to make it thin from the viewpoint of mechanical strength. Therefore, it is being considered to use plastic film as a base material for liquid crystal panels instead of glass plates. Liquid crystal panels based on plastic film are expected to exhibit properties that cannot be achieved with glass, such as flexibility, lightness, processability, impact resistance, and thinness. Various types of plastic films have been proposed for use as substrates for LCD panels, but terephthalate or 2,6-naphthalate polyesters are promising in terms of heat resistance, moisture resistance, chemical resistance, mechanical strength, etc. It is. Plastic films for LCD panel substrates are
It must be something that does not narrow the appropriate viewing angle as a panel and does not reduce readability as a liquid crystal display device. To this end, it is necessary that no interference fringes occur when the film is sandwiched between two polarizing plates, no matter which direction it is viewed from. Conventionally, in order to satisfy this condition, the retardation value (R
value) was required to be 80 mμ or less (see Japanese Patent Application Laid-Open No. 118220/1983). However, according to the inventor's study, terephthalate or 2,6
-For liquid crystal panels based on naphthalate polyester film, the R value of the film is 80 mμ.
It has been found that in the following cases, even if there are no interference fringes when viewed from directly above, there is coloration due to interference fringes when viewed from a different direction. As a result of considering this point, the present inventor surprisingly found that if a highly oriented film, that is, a film with a large R value, is incorporated into a panel so that the polarization axis of the polarizing plate and the main axis of the film coincide, For example, the present invention was completed based on the discovery that coloring due to interference fringes does not occur when viewed from any direction. That is, the gist of the present invention is that the polyester is made of terephthalate or 2,6-naphthalate type polyester, has a birefringence of 30 x 10 ^-3 to 110 x 10 ^-3 , and has a haze of 5% or less at a thickness of 100 μ. A polyester film for a liquid crystal panel substrate, characterized in that: To explain the present invention in detail, the terephthalate or 2,6-naphthalate polyester used in the present invention refers to terephthalic acid or 2,6-naphthalate polyester.
- Naphthalene dicarboxylic acid is the main acid component,
A polyester whose main glycol component is ethylene glycol. terephthalic acid and 2,
A part of 6-naphthalene dicarboxylic acid may be substituted with a polyfunctional carboxylic acid such as isophthalic acid, phthalic acid, adipic acid, sebacic acid, succinic acid, p-hydroxybenzoic acid, and ω-hydroxycaproic acid. . Similarly, some of ethylene glycol is trimethylene glycol, hexamethylene glycol, cyclohexanedimethanol (1,
4) may be substituted with a polyhydric alcohol such as polyethylene glycol. Usually the terephthalic acid or 2,6-naphthalene dicarboxylic acid component and the ethylene glycol component are each 80 mol%.
As mentioned above, preferably polyester having a content of 90 mol% or more is used. Most commonly used are polyesters made from terephthalic acid or 2,6-naphthalene dicarboxylic acid components and ethylene glycol. In addition to components that are inevitably mixed in the ester manufacturing process, such as transesterification catalysts and polymerization catalysts, the polyester used in the present invention contains various components that are commonly used in the production of polyester films, such as stabilizers, ultraviolet absorbers, and lubricants. It may contain additives. However, since the film according to the present invention is required to have transparency and surface smoothness, it is preferable that the polyester be substantially free of particles or contain only extremely fine particles. Such polyesters are produced by adding a phosphorus compound such as ethyleneamide phosphate in the polycondensation process of transesterification products, and adding calcium or fine particles containing calcium and lithium and phosphorus used as a transesterification catalyst. It can be manufactured by precipitation. Furthermore, a polyester that provides a film with excellent transparency and surface smoothness can also be produced by adding a small amount of ultrafine particles such as silica or kaolin to a polyester that does not contain particles. The polyester film according to the present invention can be produced by a normal film manufacturing method using the above-mentioned polyester.
That is, it can be produced by extruding molten polyester into a sheet form from an extruder, bringing it into contact with a cooling roll to rapidly solidify it, then stretching it, and then heat-setting it. When bringing the molten polyester sheet into contact with a cooling roll, it is preferable to apply the so-called electrostatic cooling method so that a film with good thickness accuracy can be produced at high speed (Japanese Patent Publication No. 37
-Refer to Publication No. 6142). The electrostatic application cooling method is difficult to apply to polyester, which has a high specific resistance when melted, so polyester with a specific resistance when melted of 5×
It is preferable to use one having a resistance of 10 ⁸ Ω-cm or less. Stretching and heat setting are carried out so that the resulting film has a birefringence index of 30×10 ⁻³ to 110×10 ⁻³ and a haze of 5% or less at a thickness of 100 μm.
These conditions include, for example, stretching an unstretched film in the longitudinal direction until a film with a degree of plane orientation of 30 × 10 ^-3 or more and little thickness unevenness is obtained, then gripping it with tenter clips and heating it without transverse stretching. This is achieved by fixing. If the degree of plane orientation is less than 30×10 ^-3 , non-uniform shrinkage occurs in the film during heat setting, resulting in increased thickness unevenness, or spherulites are likely to form, causing the film to become white. Note that if the longitudinal stretching ratio becomes too large, it will be easy to avoid in the stretching direction, so care must be taken. In order to avoid this, it is also possible to adopt a method in which the film is stretched in the vertical direction and then slightly stretched in the horizontal direction. Another method is to stretch in the longitudinal direction at a low magnification before the yield point is reached on the stress-strain curve, then stretch in the transverse direction with a tenter, and then heat set, so that the refractive index in the transverse direction changes from the refractive index in the longitudinal direction. It is also possible to use a larger film. Further, it is preferable that the film thus obtained has a thickness unevenness of 8% or less, particularly 5% or less. A film with large thickness unevenness is disadvantageous because a good portion of the film must be selected for use. The thickness of the film is suitably 10-500μ, preferably 50-200μ. If the film is too thin, the so-called "stiffness" will be weakened, and if it is too thick, it will not meet the demand for thinner LCD panels. Further, the film according to the present invention has a haze of 5%.
The birefringence must be between 30×10 ⁻³ and 110×10 ⁻³ . A film with a haze greater than 5% has poor transparency, and when used as a liquid crystal panel, it is difficult to read displayed characters, figures, symbols, etc. Furthermore, if the birefringence is smaller than 30×10 ⁻³ , interference fringes occur when used as a liquid crystal panel, reducing readability. However, if the birefringence is greater than 110×10 ⁻³ , the film becomes easy to avoid, causing problems when slitting it into a product during manufacturing or into a liquid crystal panel plate, which is undesirable. It is desirable that the film according to the present invention further has good heat resistance. In other words, when manufacturing liquid crystal panels, the film is often subjected to heating conditions for purposes such as forming a conductive film on the film, so the film must not lose transparency or change dimensions due to heating. is desirable. From a practical standpoint, it is desirable that the shrinkage rate be 5% or less when held in an atmosphere at 150° C. for 30 minutes, and that the haze at a thickness of 100 μm be 5% or less.
According to studies by the present inventors, this condition can be achieved by heat-treating a film with a plane orientation of 30×10 ^-3 or more so as to have an average refractive index of 1.595 or more during the film manufacturing process. As detailed above, the film for liquid crystal panel substrate according to the present invention has a haze of 5% or less and a birefringence of 30×10 ^-3 to 110×10 ^-3 at a thickness of 100 μ. A liquid crystal panel manufactured using this method does not produce interference fringes depending on the viewing direction, and has excellent readability. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In this specification, thickness unevenness, thermal shrinkage rate, average refractive index, degree of plane orientation, birefringence, film haze, and interference fringes are measured by the following methods. (a) Thickness irregularities Measurements were made for 2 m along the main axis direction of the film using a continuous film thickness measuring device manufactured by Stable Denki Co., Ltd. (using an electronic micrometer), and the thickness was calculated using the following formula. Thickness unevenness = Maximum film thickness - Minimum film thickness / Average film thickness x 100 (%) (b) Heat shrinkage rate Cut out test pieces of 300 mm x 15 mm along the main axis direction of the film and the direction perpendicular to this. This was suspended by holding one end in a hot air circulating oven maintained at 150°C, and heat treated for 30 minutes. The longitudinal dimension of the test piece before and after the heat treatment was measured, and the heat shrinkage rate was calculated using the following formula. Heat shrinkage rate = (Length before heat treatment - Length after heat treatment) / Length before heat treatment x 100 (%) (c) Average refractive index, birefringence and degree of plane orientation To measure the refractive index of the film, The measurements were carried out using an Atsube refractometer manufactured by Atago Co., Ltd. and a sodium lamp as the light source. The maximum refractive index nγ in the film plane, the refractive index nβ in the direction perpendicular to it, and the refractive index nα in the thickness direction were determined, and the average refractive index, birefringence, and degree of plane orientation were calculated according to the following equations. Average refractive index = nγ + nβ + nα / 3 Birefringence = nγ - nβ Plane orientation = nγ + nβ / 2 - nα (d) Film haze According to ASTM-D-1003, Nippon Denshoku Kogyo Co., Ltd. integrating sphere type digital turbidity (haze) degree) Total NDH−
Obtained using 20D. The thickness of the film is d (μ), the measured value of film haze is H ₁ (%), and the measured value of haze measured by applying liquid paraffin to the film surface to eliminate the contribution of the film surface is H ₂ (%). Then,
The film haze H (%) with a thickness of 100μ is defined by the following formula. H=H ₂ ×100/d+H ₁ −H ₂ Film haze is expressed as the sum of film surface haze (H ₁ −H ₂ ) and film internal haze (H ₂ ), and (H ₂ ×100/d) is the internal haze of the film converted to a thickness of 100 μm. (E) Interference fringes First, two polarizing plates are stacked so that their polarizing axes are perpendicular to each other, and a film is sandwiched between the polarizing plates so that the polarizing axis of the polarizing plate and the principal axis of the film coincide. When held up to sunlight and viewed from all angles in this condition, those that did not show any color due to interference were considered good, and those that appeared depending on the angle were judged to be poor. Example 1 100 parts of dimethyl terephthalate (parts by weight, hereinafter referred to as
Unless otherwise specified, parts are by weight. ), 60 parts of ethylene glycol, and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor and heated to raise the temperature, and methanol was distilled off, and the temperature was raised to 230° C. over about 4 hours to complete the transesterification reaction. Next, 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added to this reaction product, and polymerization was carried out according to a conventional method to obtain a polyester chip having a specific resistance of 3.0×10 ^-7 Ω/cm. After vacuum drying this chip at 160℃ for 10 hours, it was dried at 290℃.
The film was melted, extruded through a T-die, and rapidly cooled by an electrostatic cooling method to obtain an unstretched film of 350 μm. This unstretched film was stretched 3.5 times in the machine direction at 87°C.
This film is fed into a tenter with the rails of the horizontal stretching machine straightened to prevent stretching.
Heat setting was performed at 220° C. for 10 seconds to obtain a uniaxially stretched film with a thickness of 100 μm. The physical properties of the obtained film are
Shown in the table. Comparative Example 1 The longitudinal stretching ratio of an unstretched film with a thickness of 150μ was 1.5.
The thickness was 100μ in the same manner as in Example 1 except that it was doubled.
A uniaxially stretched film was obtained. The physical properties of this film are shown in Table 1. Example 2 In Example 1, an unstretched film with a thickness of 450μ was stretched 1.5 times in the machine direction at 87°C, then 3.3 times in the transverse direction at 100°C, and then heat-set at 220°C for 10 seconds. A biaxially stretched film with a thickness of 100μ was obtained.
The physical properties of this film are shown in Table 1. Example 3 A biaxially stretched film was obtained in the same manner as in Example 2, except that heat setting was performed at 160° C. for 10 seconds. The physical properties of this film are shown in Table 1. Comparative Example 2 In Example 1, a 1400μ unstretched film was
The film was stretched 3.6 times in the machine direction at 87°C, then 3.7 times in the machine direction at 100°C, and then heat set at 220°C for 10 seconds to obtain a biaxially stretched film with a thickness of 105 μm. The physical properties of this film are shown in Table 1. 【table】

Claims (1)

[Claims] 1. Made of terephthalate or 2,6-naphthalate polyester, and has a birefringence of 30×10 ^-3 ~
A polyester film for a liquid crystal panel substrate having a size of 110×10 ^-3 and a haze of 5% or less at a thickness of 100 μ. 2. The polyester film according to claim 1, which has an average refractive index of 1.595 or more. 3. Claims 1 or 2 characterized in that the haze at a thickness of 100μ when held at 150°C for 30 minutes is 5% or less, and the shrinkage rate is 5% or less. polyester film. 4. Any one of claims 1 to 3, characterized in that it is a uniaxially or biaxially stretched polyester film with a degree of plane orientation of 30×10 ^-3 or higher, heat-set at 180°C to 245°C. Polyester film described in Crab.