JP2017062498A - Polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, with a good yield, a polyester film that is provided on the outside of a polarizing plate on a visible side of a liquid crystal display to prevent a display image from being darkened depending on the angle even when the display image is seen through an optical member having a polarization effect, has a small difference in characteristic from a functional layer laminated on the polarizing plate, has excellent processability, and is suitable for a polarizing plate.SOLUTION: There is provided a polarizing plate having a polyester film with a change in orientation angle in a film of 6 degree/500 mm or more and a haze of the film of 5.0% or less, laminated on one surface (visible side) of a polarizing film with an adhesive therebetween.SELECTED DRAWING: None

Description

  The present invention is provided outside the polarizing plate on the viewing side of the liquid crystal display, so that even when the liquid crystal display is viewed through a polarizing optical member, the visibility of the display image caused by the direction of the polarization axis is reduced. The present invention relates to a polyester film that can reduce the occurrence of light interference colors and is suitable for a polarizing plate.

  In recent years, polarizing plates used for liquid crystal displays widely used as display devices for televisions, personal computers, digital cameras, mobile phones and the like are generally protective films / polarizing films / protective films or protective films / polarizing films. / Most of them consist of a retardation film.

  In a liquid crystal display, the display light emitted from the polarizing plate on the viewing side is linearly polarized light. For example, when a display image is viewed through an optical member having a polarizing action such as sunglasses, the polarization axis of the display light and the absorption of the optical member When the angle of the axis is not appropriate, the display image becomes dark or invisible.

  In order to solve the above problem, there is known a method of modulating linearly polarized light into circularly polarized light by providing a λ / 4 retardation film further outside the polarizing plate on the viewing side (Patent Documents 1 to 3). It is not preferable from the viewpoint of cost to use a retardation film.

  Moreover, although the method of providing a retardation plate with a large retardation outside the polarizing plate on the viewing side is known (Patent Documents 4 and 5), it is not preferable because the polarizing plate becomes thick.

  Furthermore, although the method of using the polyester film by which the inclination with respect to the main orientation axis | shaft and a film longitudinal direction was designated as 30-60 degrees is known for a polarizing plate protective film (patent document 6), it is unpreferable at the following points. That is, when the main orientation axis exceeds 90 degrees, when the angle of catch is the angle of the main orientation axis with respect to the film longitudinal direction, the range of angles that the main orientation axis and the film longitudinal direction can take is 0 to 90 degrees. It becomes. In a normal biaxially stretched film, a distortion called a bowing phenomenon occurs in which the orientation direction of the polymer chain changes in the width direction, so the angle between the main orientation axis and the film longitudinal direction gradually increases in the width direction of the produced film. A changing phenomenon is seen. At this time, since the center position in the width direction of the film is not distorted, it is always 0 degree or 90 degrees, and the angle changes with this value as a base point. Therefore, in a normal biaxially stretched film, there is always a place that is 0 to 30 degrees or 90 to 60 degrees near the center in the product width direction, but if this place occupies the entire film width, The number of places where the product can be used for the purpose is reduced, and the yield is greatly deteriorated.

  On the other hand, a method for producing a film by performing so-called oblique stretching so that the central portion of the film does not become 0 degree or 90 degrees is known (Patent Document 7). Moreover, since it becomes huge and control becomes complicated, there exists a problem which manufacturing cost will increase.

JP 2000-137116 A JP 2002-22944 A JP 2008-83307 A JP-A-6-258634 JP 2004-170875 A JP 2011-232660 A JP 2012-103651 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that the angle is provided even if the display image is viewed through an optical member having a polarizing action by being provided outside the polarizing plate on the viewing side of the liquid crystal display. Accordingly, it is an object to provide a polyester film for a polarizing plate that does not darken a display image and that has a small difference in characteristics from the functional layer laminated on the polarizing plate and is excellent in workability with a high yield.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a specific polyester film for polarizing plate, and have completed the present invention.

That is, the gist of the present invention is that a polyester film having a change in orientation angle in the film of 6 degrees / 500 mm or more and a haze of the film of 5.0% or less is formed on one surface of the polarizing film via an adhesive. It exists in the polarizing plate bonded together (viewing side) .

  According to the present invention, a polyester film having excellent optical properties can be provided at a low cost as a polarizing plate film, and the industrial value of the present invention is high.

  The polyester film referred to in the present invention is a film obtained by stretching a sheet melt-extruded from an extrusion die according to a so-called extrusion method.

  The polyester constituting the film of the present invention refers to a polymer containing an ester group obtained by polycondensation from dicarboxylic acid and diol or from hydroxycarboxylic acid. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and diols include ethylene glycol and 1,4-butane. Examples include diol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and examples of hydroxycarboxylic acid include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. be able to. Typical examples of such polymers include polyethylene terephthalate and polyethylene-2, 6 naphthalate.

  In order to facilitate handling, the polyester film in the present invention may contain particles under conditions that do not impair transparency. Examples of particles used in the present invention include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, and crosslinked polymers. Examples thereof include organic particles such as particles and calcium oxalate. Examples of the method of adding particles include a method of adding particles in a polyester as a raw material, a method of adding directly to an extruder, and the like. Well, you may use two methods together.

  The particle diameter of the particles used is usually 0.05 to 5.0 μm, preferably 0.1 to 4.0 μm. When the average particle size is larger than 5.0 μm, the haze of the film increases, and the transparency of the film may decrease. If the average particle size is less than 0.1 μm, the surface roughness may be too small, making it difficult to handle the film. The particle content is usually 0.001 to 30.0% by weight, preferably 0.01 to 10.0% by weight, based on the polyester. If the particle content is large, the haze increases and the transparency of the film may be lowered. If the particle content is small, the film may be difficult to handle.

  The method of adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder. It is performed by the method of blending.

  The polyester film in the present invention needs to have a variation of the orientation angle in the film of 6 degrees / 500 mm or more. When the variation in the orientation angle is less than 6 degrees / 500 mm, the number of places where the product can be used for this application is reduced, and the yield is greatly deteriorated.

  In the polarizing plate using the polyester film of the present invention, the in-plane retardation of the polyester film is preferably 2000 nm or less, and more preferably 1500 nm or less, in order to prevent the occurrence of light interference color. When the in-plane retardation of the film is larger than 2000 nm, the interference color of light becomes strong, and the original color of the image cannot be obtained on the liquid crystal display.

  In the polarizing plate using the polyester film of the present invention, in order to prevent a decrease in transparency, the haze of the film in the polyester film needs to be 5.0% or less, preferably 2.0% or less, particularly preferably. 1.0% or less. When the haze of the film is larger than 5.0%, the transparency of the polarizing plate is lowered and the visibility is lowered.

  The thermal shrinkage in the film width direction when the polyester film of the present invention is heat-treated at 120 ° C. for 5 minutes is preferably 0.4% or less, more preferably 0.2% or less, and most preferably 0.00. 0% or less. When the thermal shrinkage rate exceeds 0.4%, the dimensional change becomes too large in the negative direction in the plane direction at high temperatures. For example, when bonded to the polarizing plate, the gas barrier layer and electrode laminated on the polarizing plate A difference in thermal contraction rate from a layer or the like occurs, and the workability deteriorates due to defects in the functional layer during high-temperature processing.

  The thickness of the polyester film of the present invention is preferably 4 to 50 μm, more preferably 4 to 38 μm. Especially preferably, it is 4-25 micrometers. If the thickness of the film is less than 4 μm, it may be difficult to form the film and the film may be difficult to handle. When the film thickness is thicker than 50 μm, the polarizing plate becomes thick when used for mobile use.

  In the present invention, other additives may be added as necessary. Examples of such additives include an ultraviolet absorber, a stabilizer, a lubricant, a crosslinking agent, an antiblocking agent, an antioxidant, a dye, and a pigment.

  In the present invention, a polyester chip dried by a known method is supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to be melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition point to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is preferably stretched in the biaxial direction to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 1.3 to 6 times at 80 to 130 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 90 to 160 ° C. in the lateral direction. And stretched 1.3 to 6 times. Heat treatment is preferably performed at 150 to 240 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 3 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the outlet of the heat treatment is preferable.

  As the polarizing plate, it is preferable to provide a coating layer on at least one surface in order to make it adhere to the polarizing plate protective film or to improve the adhesion to the hard coat.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As a coating method of the coating agent, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these can be used.

  In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  In addition, as needed, you may coat by the method called the off-line coating which coats after manufacture of a film. The coating material may be either water-based and / or solvent-based in the case of off-line coating.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. Various physical properties and characteristics are measured or defined as follows. In the examples, “%” means “% by weight”.

(1) Measurement of variation in orientation angle in main orientation axis and film In the width direction of the polyester film, from the center position toward both ends, the sample is cut out from the position at every 500 mm and from both ends. The orientation of the polyester film was observed using a polarization microscope manufactured by Carl Zeiss, respectively, and the number of directions of the main orientation axis in the polyester film plane was determined with respect to the MD of the polyester film. For measurement, when the main orientation axis exceeded 90 degrees, the complementary angle was defined as the angle of the main orientation axis with respect to the MD direction. Further, when calculating the change in the orientation angle including the positions at the extreme ends, if the distance between the sample positions is less than 500 mm, the change in the orientation angle every 500 mm is calculated by proportional calculation. Subsequently, a 3 m length was cut out in the longitudinal direction of the film, and a sample was cut out from a total of 7 positions every 500 mm (including both ends) in the longitudinal direction from the center in the film width direction, and the orientation angle was determined. Thus, the variation of the orientation angle for every 500 mm in the width direction and the longitudinal direction was obtained, and the maximum variation value was set as the variation of the orientation angle of the film.

(2) Measurement of in-plane retardation Using a cell gap inspection apparatus RETS-1100A manufactured by Otsuka Electronics Co., Ltd., the in-plane retardation at the center of the film width direction was measured. The in-plane retardation of the film was measured at 23 ° C. using an optical interference method with an aperture diameter of 5 mm.

(3) Measurement of heat shrinkage rate A sample was cut out on a strip of 15 mm width × 150 mm length in the width direction at both ends of the film, heat treated in a no tension state for 5 minutes at 120 ° C., and the length of the sample before and after that was measured. Thus, the heat shrinkage rate (%) was calculated by the following formula.
Heat shrinkage rate (%) = [(ab) / a] × 100
In the above formula, a is the sample length before heat treatment, and b is the sample length after heat treatment.

(4) Measurement of haze Film haze was measured with an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7136.

(5) Visibility (light transmission reduction rate) evaluation Locations corresponding to positions of 10, 20, 30, 40, 50% with respect to the film width in the film width direction from the end of the obtained polyester film (50% A4 size samples are cut out from the center of the width direction, and the 10% position is the position of the end in the width direction, so that the MD of the polyester film is parallel to the orientation axis of the polarizing film. The polarizing plate 1 for evaluation is superposed on the polyester film side so that the orientation axis is orthogonal to the MD of the polyester film, and the polarizing plate 1 side is the incident light side. Thus, the total light transmittance T was measured. In addition, the Nippon Denshoku Industries Co., Ltd. integrating sphere type turbidimeter NDH-20D was used for the measuring apparatus. Separately from this, the total light transmittance measured only by the polarizing plate 1 was T0, and the light transmission reduction rate was calculated by the following equation.
Light transmission reduction rate (%) = [(T0−T) / T0] × 100

(6) Application applicability evaluation Applicability was evaluated in accordance with the ratio of the light transmission reduction rate obtained in the same manner as in the previous item (5) to 80% or less with respect to the total film width. In addition, the value of the light transmission reduction rate in the full width direction was assumed to be symmetrical with respect to the center position (50% position) of the film, and the ratio to the full film width was obtained.
A: 65% or more of a film having a light transmission reduction rate of 80% or less is obtained with respect to the entire width, and a film that can be used in this application can be collected with good yield. B: A light transmission reduction rate is obtained. A film that is 80% or less is obtained in an amount of 50 to 65% with respect to the full width, and the yield of the film that can be used in this application is within an allowable range. C: A film that has a light transmission reduction rate of 80% or less is full width. The yield of the film that can be used for this application is out of the allowable range.

The manufacturing method of the polyester raw material used in the following examples and comparative examples is as follows.
(Method for producing polyester a)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and a polyester (a) was obtained by converting into chips according to a conventional method. The solution viscosity IV of the obtained polyester chip was 0.66.

(Method for producing polyester b)
When manufacturing the said polyester a, 3000 ppm of amorphous silica with an average particle diameter of 2.7 micrometers was added, and the polyester b was created.

(Method for producing polyester c)
When manufacturing the said polyester a, 6000 ppm of amorphous silica with an average particle diameter of 3.2 micrometers was added, and the polyester c was created.

Example 1:
The raw materials obtained by mixing the polyesters a and b in proportions of 68% and 32%, respectively, are used as the raw material for the A layer, the polyester a is used as the raw material for the B layer, and the raw materials for the A layer and the B layer are separately provided. To obtain an amorphous sheet of two types and three layers (A / B / A). Next, the sheet was coextruded on a cooled casting drum and solidified by cooling to obtain a non-oriented sheet. Next, the film is stretched 3.5 times in the longitudinal direction at 90 ° C., further subjected to a preheating process in the tenter, stretched 4.1 times in the lateral direction at 130 ° C., and heat-treated at 230 ° C. for 10 seconds, and then in the width direction. Then, a relaxation treatment of 4.3% was performed to obtain a polyester film having a thickness of 38 μm. The evaluation results are shown in Table 2 below.

Examples 2-5 and Comparative Examples 1-3:
A polyester film was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were changed. The evaluation results are shown in Table 2. In Comparative Example 3, when mounted as a polarizing plate, the haze was high and the luminance as a display was low.

Example 6:
In Example 2, a polyester film was obtained in the same manner as in Example 2 except that the layer thickness of the polyester film was 55 μm. The evaluation results are shown in Table 2.
In Example 6, when mounted as a polarizing plate, the thickness was thick, so that it was inferior in design for mobile use.

Example 7:
In Example 2, a polyester film was obtained in the same manner as in Example 2 except that the layer thickness of the polyester film was 3 μm. The evaluation results are shown in Table 2.
In Example 7, wrinkles occurred when the polyester film was bonded to the polarizing film, and the quality as a polarizing plate was poor.

Example 8:
A polyester film was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were changed. The evaluation results are shown in Table 2. In Example 8, curling occurred when the polyester film was bonded to the polarizing film, and the quality as a polarizing plate was poor.

  The film of the present invention can be suitably used, for example, as a film provided outside the polarizing plate on the viewing side of a liquid crystal display.

Claims (3)

A polyester film having a variation in orientation angle in the film of 6 degrees / 500 mm or more and a haze of the film of 5.0% or less was bonded to one surface (viewing side) of the polarizing film via an adhesive. Polarizing plate . The polarizing plate according to claim 1, wherein the thickness of the polyester film is 4 to 50 μm. The polarizing plate according to claim 1 or 2, wherein the heat shrinkage rate in the film width direction of the polyester film heat-treated at 120 ° C for 5 minutes is 0.4% or less.