JP2012008229A - Polyester film for polarization plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a polarization plate in which the darkening of display images occurs depending on angles or the generation of light interference color does not occur even if the display images are observed through an optical member with polarization effect by providing the film on the outside of the polarization plate at the visible side of a liquid crystal display.SOLUTION: A polyester film for a polarization plate has a inclination angle of 30 to 60 degrees with respect to the film longitudinal direction of a main orientation axis, an in-plain retardation of the film of 2000 nm or less and a oligomer deposition amount on the surface of the film of 8 mg/mor less.

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 for polarizing plates that can reduce the occurrence of light interference colors.

  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.

JP 2000-137116 A JP 2002-22944 A JP 2008-83307 A JP-A-6-258634 JP 2004-170875 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 of the present invention to provide a polyester film for polarizing plates in which a display image is not darkened and a light interference color is not generated.

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

That is, the inclination of the main orientation axis with respect to the film longitudinal direction is 30 to 60 degrees, the in-plane retardation of the film is 2000 nm or less, and the surface oligomer precipitation amount of the film is 8 mg / m ² or less. It exists in the polyester film for polarizing plates.

  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.

  In the polarizing plate using the polyester film of the present invention, in order to prevent a decrease in luminance, the angle of the main orientation axis in the polyester film with respect to the film longitudinal direction (hereinafter sometimes abbreviated as MD) is 30 to 60 degrees. Is preferably 35 to 55 degrees, and more preferably 40 to 50 degrees. When the angle of the main alignment axis with respect to MD is larger than 60 degrees, the decrease in luminance becomes large. Even when the angle of the main alignment axis with respect to MD is smaller than 30 degrees, the luminance is greatly lowered, and the luminance becomes insufficient as a polarizing plate.

  In the polarizing plate using the polyester film of the present invention, in order to prevent the occurrence of light interference color, the in-plane retardation of the film in the polyester film needs to be 2000 nm or less, preferably 1500 nm or less. 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.

It is necessary that the amount of oligomer deposited from the surface of the polyester film of the present invention is 8 mg / m ² or less. When the amount of precipitation exceeds 8 mg / m ² , processing suitability in the polarizing plate manufacturing process is reduced, and various problems occur when used as a polarizing plate.

  The thickness of the polyester film of the present invention is preferably 4 to 50 μm, more preferably 4 to 38 μm. 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 stabilizers, lubricants, crosslinking agents, antiblocking agents, antioxidants, dyes, pigments, and the like.

  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 0.1 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 heat treatment outlet 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.
If necessary, the film may be coated by a method called offline coating which is coated after the production of the 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 main orientation axis Using a polarizing microscope manufactured by Carl Zeiss, the orientation of the polyester film is observed, and how many times the direction of the main orientation axis in the polyester film plane is inclined with respect to the MD of the polyester film. Asked. 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.

(2) Measurement of in-plane retardation The in-plane retardation of the film was measured using a cell gap inspection apparatus RETS-1100A manufactured by Otsuka Electronics Co., Ltd. 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 surface oligomer amount A sample sample was cut into a 4 cm square, placed in an Erlenmeyer flask containing 20 cm 3 of chloroform, and immersed at 30 ° C. for 20 minutes. Thereafter, the sample sample was removed, the ultraviolet absorption spectrum of the treatment solution was measured, and the absorbance at a wavelength of 246 nm was measured. The amount of oligomer extracted from the sample sample was determined from the relationship between the absorbance and the amount of oligomer. A calibration curve for absorbance and oligomer amount is prepared in advance.

(3) Visibility inspection Using polyvinyl alcohol (PVA) film (manufactured by Kuraray Co., Ltd., degree of polymerization 2400), after stretching 3 times in the first bath (iodine, KI aqueous solution-30 ° C.), the second bath ( The total draw ratio was stretched up to 6 times in boric acid and KI aqueous solution (55 ° C.) to obtain a polarizer. Thereafter, using a PVA adhesive, a TAC film having a thickness of 40 μm was bonded to both surfaces, and a polyester film was bonded onto the one side TAC film via an adhesive to prepare a polarizing plate. The polarizing plate was mounted on a liquid crystal panel so that the polyester film was on the outside of the viewing side, and the visibility was confirmed.
◎: Brightness reduction is good with no light interference color ○: Brightness reduction or light interference color is a little but no problem △: Brightness reduction or light interference color is present but acceptable X: Decreased brightness or strong light interference color, cannot be used as a polarizing plate

(4) Comprehensive judgment ◎: Decreased brightness No light interference color, good processing suitability and no problem as polarizing plate ○: Either light interference color or processing suitability is slightly inferior, but can be used as a polarizing plate Δ: Either the optical interference color or the processing suitability is inferior, but it is an acceptable level as a polarizing plate. Δ: Either the optical interference color or the processing suitability is inferior, but is barely an acceptable level as a polarizing plate. Either color or processing suitability is inferior and cannot be used as a polarizing plate.

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)
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. Two hours later, the reaction was completed, and a chip was obtained according to a conventional method to obtain polyester B. The solution viscosity IV of the obtained polyester chip was 0.45.

(Method for producing polyester c)
The intrinsic viscosity of polyester a was increased by a solid phase polycondensation method. After treating in a preliminary crystallization tank under a nitrogen atmosphere at 170 ° C. for 0.5 hour, the moisture content becomes 0.005% at a temperature of 200 ° C. using a tower dryer in which an inert gas flows. Until dried. Thereafter, it was sent to a solid phase polymerization tank and subjected to solid phase polymerization at 240 ° C. for 4 hours to obtain polyester c having an intrinsic viscosity of 0.77.
(Method for producing polyester d)
When manufacturing the said polyester a, 1000 ppm of amorphous silica with an average particle diameter of 2 micrometers was added, and the polyester d was created.

Example 1:
The raw materials obtained by mixing the polyesters c and d in proportions of 85% and 15% 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 respectively separate melt extruders. To obtain an amorphous sheet of two types and three layers (A / B / A). Subsequently, the sheet was coextruded on a cooled casting drum and solidified by cooling to obtain a non-oriented sheet. Next, the film was stretched 3.4 times in the longitudinal direction at 90 ° C., further subjected to a preheating process in the tenter, stretched 4.5 times in the lateral direction at 90 ° C., and subjected to heat treatment at 230 ° C. for 10 seconds, A polyester film having a thickness of 38 μm was obtained from the end position of the roll wound up by. The evaluation results are shown in Table 1 below.

Example 2:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 4.0 times. The evaluation results are shown in Table 1.

Example 3:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the film was obtained from the position of the main orientation axis of 58 degrees of the roll wound up by the film forming machine. The evaluation results are shown in Table 1.

Example 4:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the film was obtained from the position of the main orientation axis 52 degrees of the roll wound up by the film forming machine. The evaluation results are shown in Table 1.

Example 5:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 3.6 times. The evaluation results are shown in Table 1.

Example 6:
In Example 1, a polyester film was obtained in the same manner as in Example 1, except that the film was obtained from the position of the main orientation axis 48 degrees of the roll wound up by the film forming machine. The evaluation results are shown in Table 1.

Example 7:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the thickness of the film was 25 μm. The evaluation results are shown in Table 1.

Comparative Example 1:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the film was obtained from the position of the main orientation axis of 70 degrees of the roll wound by the film forming machine. The evaluation results are shown in Table 1.

Comparative Example 2:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the thickness of the film was 48 μm. The evaluation results are shown in Table 1.

Comparative Example 3:
A polyester film was obtained in the same manner as in Example 1 except that the raw material obtained by mixing polyester b and d in proportions of 85% and 15%, respectively, was used as the raw material for the A layer. The evaluation results are shown in Table 1.

  The obtained results are summarized in Table 1 below.

  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 (1)

A polarizing plate characterized in that the inclination of the main orientation axis with respect to the film longitudinal direction is 30 to 60 degrees, the in-plane retardation of the film is 2000 nm or less, and the surface oligomer precipitation amount of the film is 8 mg / m ² or less. Polyester film.