JP2015200786A - Polyester film for protection of polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for protection of a polarizing plate, which can decrease degradation of a liquid crystal by UV rays when disposed outside a polarizing plate on a viewing side of a liquid crystal display using a white light-emitting diode as a backlight light source, without darkening a displayed image or generation of interferential colors of light when the displayed image is viewed through an optical member having a polarizing effect.SOLUTION: The polyester film for protection of a polarizing plate is a laminate film comprising at least three layers and containing polyethylene terephthalate and a resin composition having a refractive index higher by 0.02 or more than that of polyethylene terephthalate. The content of the resin composition in the film is 10 to 80 wt.%. The film has a birefringence Δn of 0.060 or more within the film plane; contains a UV absorbent in a layer other than the outermost layers of the film; and exhibits a transmittance of 20.0% or less for rays at a wavelength of 380 nm and a transmittance of 80.0% or more for rays at a wavelength of 550 nm.

Description

  The present invention is provided outside the polarizing plate on the viewing side of a liquid crystal display using a white light emitting diode as a backlight light source, so that the liquid crystal display can be viewed in the direction of the polarization axis even when viewed through a polarizing optical member. The present invention relates to a polarizing plate-protecting polyester film that can reduce the visibility of the display image and the occurrence of light interference colors, and can suppress deterioration of liquid crystal due to ultraviolet rays.

  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 / Consists 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 and 2). ) Use of a retardation film is not preferable from the viewpoint of cost. 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 3 and 4), it is not preferable because the polarizing plate becomes thick.

  Furthermore, since normal polyester does not have UV absorbing ability, there is a problem that the liquid crystal deteriorates when used as a polarizing plate protective film. In the case of using a polyester film as a polarizing plate protective film in a liquid crystal display, there is a known method of blending a polyester film with an ultraviolet absorber in order to prevent deterioration of the liquid crystal due to ultraviolet rays, but the outermost layer of the polyester film absorbs ultraviolet rays. When an agent is blended, the ultraviolet absorber may bleed out from the polyester film, which is not preferable.

  In order to solve the above-described problems, studies have been conducted to add an ultraviolet absorber to the inner layer of a laminated polyester film composed of at least three layers (Patent Document 5). However, Patent Document 5 does not consider a method for suppressing the light interference color.

JP 2000-137116 A JP 2002-22944 A JP-A-6-258634 JP 2004-170875 A JP 2010-243630 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that it is provided outside the polarizing plate on the viewing side of a liquid crystal display using a white light-emitting diode as a backlight light source, and through a polarizing optical member. To provide a polyester film for protecting a polarizing plate that can reduce deterioration of liquid crystal due to ultraviolet rays without darkening a display image or generating a light interference color depending on an angle even when viewing a display image. is there.

  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 polarizing plate protecting polyester film, and have completed the present invention.

  That is, the gist of the present invention is a laminated film comprising at least three layers containing a resin composition having a refractive index higher than that of polyethylene terephthalate by 0.02 or more and polyethylene terephthalate, and the content of the resin composition in the film Is 10 to 80% by weight, the in-plane birefringence Δn is 0.060 or more, contains an ultraviolet absorber in any layer other than the outermost layer of the film, and has a light transmittance at a wavelength of 380 nm. It exists in the polyester film for polarizing plate protection characterized by the light transmittance in 20.0% or less and wavelength 550nm being 80.0% or more.

  According to the present invention, an inexpensive polyester film having excellent optical properties can be provided as a polarizing plate protective 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.

  Examples of the polyethylene terephthalate constituting the film include terephthalic acid as the dicarboxylic acid, and ethylene glycol as the diol.

  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. Two methods may be used in combination.

  The particle size 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 be lowered. If the average particle size is smaller than 0.1 μm, the surface roughness becomes too small, and the film may be difficult to handle. 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 polyester film of the present invention, the in-plane birefringence Δn is 0.060 or more, preferably 0.100 or more, more preferably 0.120 or more, and particularly preferably 0.150 or more. When Δn of the stretched film is smaller than 0.060, the interference color of light becomes strong and the original color of the image cannot be obtained in the liquid crystal display.

  The polyester film of the present invention contains 10 to 80% by weight of a resin composition having a refractive index higher than that of polyethylene terephthalate by 0.02 or more. Examples of the resin composition having a refractive index higher by 0.02 or more than polyethylene terephthalate include polyethylene-2,6-naphthalate, polymethacrylic acid resin, polystyrene, fluororesin (PTFE), vinylidene fluoride, and silicon resin. From the standpoint of compatibility with polyethylene terephthalate, polyethylene-2,6-naphthalate is preferred.

  In the present invention, the polyester film needs to contain an ultraviolet absorber in any layer other than the outermost layer of the laminated polyester film. The ultraviolet absorber is blended in order to prevent the deterioration of the liquid crystal of the liquid crystal display due to ultraviolet rays. Examples of the ultraviolet absorber contained in the polyester film include an organic ultraviolet absorber and an inorganic ultraviolet absorber.

  Examples of organic ultraviolet absorbers include salicylic acid-based compounds such as phenyl salicylate, pt-butylphenyl salicylate, p-octylphenyl salicylate, and benzophenone-based compounds such as 2-hydroxy-4-benzyloxy. Benzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2 -2'-dihydroxy-4,4'-dimethoxybenzophenone and the like, benzotriazole-based, for example, 2- (2'-hydroxy-5'-t-octylphenyl) -benzotriazole, 2- (2'-hydroxy-5 '-T-octylphenyl) -benzotriazo 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3′5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy) -3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3'5'-di-t-butylphenyl) 5-chlorobenzotriazole, and other natural products Examples include biological systems such as oryzanol, shea butter and baicalin, such as keratinocytes, melanin and urocanic acid. These organic ultraviolet absorbers can be used alone or in combination of two or more. These organic ultraviolet absorbers can be used in combination with a hindered amine compound as an ultraviolet stabilizer.

  Inorganic UV absorbers include titanium oxide, zinc oxide, indium oxide, tin oxide, talc, kaolin, calcium carbonate, titanium oxide-based composite oxide, zinc oxide-based composite oxide, ITO (tin-doped indium oxide), ATO (Antimony-doped tin oxide) and the like. Examples of the titanium oxide-based composite oxide include zinc oxide doped with silica and alumina. These inorganic ultraviolet absorbers can be used alone or in combination of two or more. Moreover, you may use together an organic type ultraviolet absorber and an inorganic type ultraviolet absorber. In order to make the light transmittance at 550 nm 80.0% or more, it is preferable to use an organic ultraviolet absorber.

  Examples of the method of blending the UV absorber into the polyester film include a method of directly adding the UV absorber to the extruder, a method of adding a polyester resin kneaded in advance to the extruder, and the like. Either one of the methods may be employed, or two methods may be used in combination.

  In the polyester film of the present invention, the light transmittance at a wavelength of 380 nm is 20.0% or less, preferably 10.0% or less. When the light transmittance at a wavelength of 380 nm is greater than 20.0%, the deterioration of the liquid crystal is promoted, which is not preferable.

  In the polyester film of the present invention, the light transmittance at a wavelength of 550 nm is 80.0% or more. When the light transmittance at a wavelength of 550 nm is smaller than 80.0%, the light transmittance as a polarizing plate is lowered, which is not preferable.

  The content of the resin composition is preferably 10 to 50% by weight, more preferably 10 to 20% by weight. When the content of the resin composition is small, the interference color of light becomes strong when the polyester film of the present invention is used for a liquid crystal display, and the original color of the image cannot be obtained on the liquid crystal display. On the other hand, if the content is large, a good color can be obtained in a liquid crystal display, but this is not preferable because of increased cost.

  It is preferable that the thickness of the polyester film of this invention is 4-100 micrometers, More preferably, it is 23-75 micrometers, More preferably, it is 38-50 micrometers. When the thickness of the film is less than 4 μm, it is difficult to form the film and it is difficult to handle the film. When the thickness of the film is greater than 100 μm, the polarizing plate becomes thick for mobile use, which may not be preferable.

  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, two or three or more polyester melt extruders can be used to form a laminated film having at least three layers by a so-called coextrusion method. As the structure of the layer, an A / B / A structure using the A raw material and the B raw material, an A / B / C structure using the C raw material, or other three or more layers can be used.

  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. In that case, first, the unoriented sheet is stretched in the longitudinal direction. The stretching temperature is usually 80 to 150 ° C., preferably 90 to 130 ° C., and the stretching ratio is usually 1.1 to 6.0 times, preferably 1.5 to 2.0 times. After forming a longitudinal uniaxially stretched film, it is stretched in the transverse direction. The stretching temperature is usually from 80 to 160 ° C., and the stretching ratio is usually from 2.0 to 6.0 times, preferably from 5.3 to 6.0 times. Subsequently, heat treatment is performed at 150 to 240 ° C. for 1 to 600 seconds to obtain a biaxially oriented film. 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 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, you may coat by the method called offline coating which coats after manufacture of a film as needed. 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 refractive index The refractive index of each resin was measured using a precision refractometer KPR-2000 manufactured by Shimadzu Corporation.

(2) Definition of in-plane birefringence index Δn The birefringence index Δn is defined by the following equation.
Birefringence index Δn = (nx−ny) (1)
(In the above formula (1), nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the in-plane direction of the film, and ny is the slow axis direction x in the in-plane direction of the film. Represents the refractive index in the orthogonal direction y)

(3) Measurement of nx and ny Using an Abbe refractometer manufactured by Atago Co., Ltd., the refractive index nx in the slow axis direction x where the refractive index in the film in-plane direction is maximized, and orthogonal to the slow axis direction x The refractive index ny in the direction y was measured, and the birefringence Δn was calculated from the above equation (1). In addition, the measurement was performed at 23 degreeC using the sodium D line | wire.

(4) Measurement of light transmittance Using a spectrophotometer (Shimadzu Corporation UV-3100PC type), the light transmittance is measured continuously at a low scanning speed, a sampling pitch of 2 nm, and a wavelength range of 300 to 700 nm. And light transmittance at a wavelength of 550 nm was detected.

(5) Evaluation method of bleed-out of ultraviolet absorber The obtained polyester film and a polyester film not containing the ultraviolet absorber (Mitsubishi Resin Co., Ltd. T100, thickness 50 μm) are 150 ° C. for 30 minutes in a gear oven (GHSP-222 manufactured by Espec Corp.) After heating, it was observed at 300 times with a microscope (VH-Z250R manufactured by Keyence Corporation). The polyester film obtained by the following criteria was evaluated.
○: There is no difference from a polyester film not containing an ultraviolet absorber. ×: The amount of precipitates is larger than that of a polyester film not containing an ultraviolet absorber.
Moreover, since the big difference between the polyester film which does not contain an ultraviolet absorber with a large magnitude | size and the obtained polyester film is the presence or absence of an ultraviolet absorber, it is thought that the observed difference originates in an ultraviolet absorber.

(6) Inspection of visibility 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. Then, using a PVA-based adhesive, a TAC film having a thickness of 40 μm is bonded to both surfaces, and the angle between the polyester film and the absorption axis of the polarizing plate is 45 ° via an adhesive on one side TAC film. In this manner, a polarizing plate was prepared. The polarizing plate was mounted on a liquid crystal panel using a phosphor-type white light emitting diode as a backlight light source so that the polyester film was on the outside of the viewing side, and the visibility was confirmed.
A: There is no light interference color and it is good. ○: There is a little light interference color but no problem. X: The light interference color is strong and cannot be used as a polarizing plate.

(7) Productivity and handleability ◎: Good film productivity and good handleability during processing ○: No problem in both film productivity and processability ×: Film productivity and processing Either or both of the handling times are poor and not suitable for production or processing

(8) Comprehensive judgment Visibility, productivity, handleability, light transmittance at wavelengths of 380 nm and 550 nm, and bleed out are comprehensively evaluated, and the best film as a polarizing plate film is excellent. Goods were marked with ◯, acceptable ones with △, and inadequate with x. △ More than pass.

The raw materials used in the following examples and comparative examples were prepared 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 chip was obtained according to a conventional method to obtain polyester A. The obtained polyethylene terephthalate had a refractive index of 1.58.

(Method for producing polyester B)
When the polyester A was produced, 6000 ppm of amorphous silica having an average particle size of 3.2 μm was added to prepare polyester B.

(Polyester C manufacturing method)
Polyester C which is polyethylene-2,6-naphthalate was obtained by changing the dicarboxylic acid raw material in the production method of polyester A. The obtained polyethylene-2,6-naphthalate had a refractive index of 1.64.

(Polyester D manufacturing method)
When the polyester (A) is produced, 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] is added as a UV absorber so as to have a concentration of 10%. Thus, polyester (D) was prepared.

(Polyester E production method)
Polyester (E) was prepared by mixing the polyester (A) with fine particles of zinc oxide as an ultraviolet absorber so as to have a concentration of 10%.

Example 1:
The raw materials obtained by mixing the polyesters (A), (C), and (D) at a ratio of 80%, 10%, and 10%, respectively, are used as raw materials for the B layer, and polyesters (A), (B), and (C) The raw materials mixed at a ratio of 85%, 5%, and 10% are used as the raw material for the A layer, and the raw materials for the A layer and the B layer are melt-extruded by separate melt extruders (A / B / A) 2 An amorphous sheet having a three-layered seed layer was obtained. 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 2.5 times in the longitudinal direction at 90 ° C., and further subjected to a preheating process in the tenter, 5.3 times in the transverse direction at 120 ° C., and heat-treated at 180 ° C. for 10 seconds. The polyester film with a thickness of 50 μm (A layer: 5 μm, B layer: 40 μm) was obtained. The evaluation results are shown in Table 1.

Example 2:
In Example 1, the film was stretched 1.5 times in the machine direction at 90 ° C., and further subjected to a preheating step in the tenter and then stretched 5.2 times in the transverse direction at 120 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 3:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 70%, 20%, and 10%, respectively. A polyester film was obtained in the same manner as in Example 1 except that a raw material obtained by mixing (C) at a ratio of 75%, 5%, and 20% was used as the raw material for the A layer. The evaluation results are shown in Table 1.

Example 4:
In Example 3, the film was stretched 1.8 times in the longitudinal direction at 90 ° C., and further subjected to a preheating step in the tenter and then stretched 5.3 times in the lateral direction at 120 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 5:
In Example 4, polyesters (A), (C), and (D) were mixed in proportions of 65%, 20%, and 15%, respectively, and the same procedure as in Example 4 was used except that the raw materials for layer B were used. A polyester film was obtained. The evaluation results are shown in Table 1.

Example 6:
In Example 4, polyesters (A), (C), and (D) were mixed in the proportions of 75%, 20%, and 5%, respectively, except that a raw material for the B layer was used as in the case of Example 4. A polyester film was obtained. The evaluation results are shown in Table 1.

Example 7:
In Example 4, the film was stretched 1.5 times in the longitudinal direction at 90 ° C., and further subjected to a preheating step in the tenter and then stretched 5.2 times in the transverse direction at 120 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 8:
In Example 1, polyesters (A), (C), and (D) were mixed in proportions of 40%, 50%, and 10%, respectively, as raw materials for the B layer, and polyesters (A), (B), (C) was mixed at a ratio of 45%, 5%, and 50%, respectively, as a raw material for the A layer, and stretched 2.8 times in the longitudinal direction at 120 ° C., and further through a preheating step in the tenter A polyester film was obtained in the same manner as in Example 1 except that the film was stretched 5.3 times in the transverse direction at 120 ° C. and heat-treated at 150 ° C. for 10 seconds to obtain a film. The evaluation results are shown in Table 1.

Example 9:
In Example 8, the film was stretched 2.0 times in the longitudinal direction at 120 ° C., then further subjected to a preheating step in the tenter and then stretched 5.4 times in the transverse direction at 120 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 10:
In Example 9, polyesters (A), (C), and (D) were mixed in proportions of 35%, 50%, and 15%, respectively, except that the raw materials for the B layer were used as in the case of Example 9. A polyester film was obtained. The evaluation results are shown in Table 1.

Example 11:
In Example 9, polyesters (A), (C), and (D) were mixed in the proportions of 45%, 50%, and 5%, respectively, except that a raw material for the B layer was used as in the case of Example 9. A polyester film was obtained. The evaluation results are shown in Table 1.

Example 12:
In Example 9, the film was stretched 1.5 times in the machine direction at 120 ° C., and further subjected to a preheating step in the tenter and then stretched 5.2 times in the transverse direction at 120 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 13:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 10%, 80%, and 10%, respectively. The raw materials mixed with 15%, 5%, and 80% of (C) are used as the raw material for the A layer, and are stretched 2.8 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter. A polyester film was obtained in the same manner as in Example 1 except that a film was obtained by performing 5.2 times stretching in the transverse direction at 130 ° C. and heat treatment at 150 ° C. for 10 seconds. The evaluation results are shown in Table 1.

Example 14:
In Example 13, the film was stretched 2.0 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter and then stretched 5.4 times in the lateral direction at 130 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 15:
In Example 13, the film was stretched 1.5 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter and 5.3 times in the transverse direction at 130 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Example 16:
In Example 13, the film was stretched 1.5 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter and then 6.0 times in the transverse direction at 130 ° C. to obtain a film. A polyester film was obtained in the same manner. The evaluation results are shown in Table 1.

Comparative Example 1:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 85%, 5%, and 10%, respectively. The raw materials mixed with 90%, 5%, and 5% of (C) were used as the raw material for the A layer, and were stretched 1.1 times in the longitudinal direction at 90 ° C., and further subjected to a preheating step in the tenter. A polyester film was obtained in the same manner as in Example 1 except that a film was obtained by stretching 5.0 times in the transverse direction at 120 ° C. The evaluation results are shown in Table 1.

Comparative Example 2:
In Example 1, the raw materials obtained by mixing polyesters (C) and (D) at a ratio of 90% and 10%, respectively, were used as the raw material for the B layer, and polyesters (A), (B), and (C) were each 5%. The raw material mixed at a ratio of 5% and 90% is used as the raw material for the A layer, stretched 2.5 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter and 5 in the lateral direction at 130 ° C. A polyester film was obtained in the same manner as in Example 1 except that the film was obtained by stretching twice and heat-treating at 150 ° C. for 10 seconds. The evaluation results are shown in Table 1.

Comparative Example 3:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 70%, 20%, and 10%, respectively. (C) was mixed at a rate of 75%, 5%, and 20%, respectively, and used as the raw material for layer A. After stretching 3.0 times in the longitudinal direction at 90 ° C., a preheating step was further performed in the tenter. A polyester film was obtained in the same manner as in Example 1 except that the film was obtained by stretching the film in the transverse direction by 5.2 times at 120 ° C. The evaluation results are shown in Table 1.

Comparative Example 4:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 10%, 80%, and 10%, respectively. The raw materials mixed with 15%, 5%, and 80% of (C) are used as the raw material for the A layer, and are stretched 3.0 times in the longitudinal direction at 130 ° C., and further subjected to a preheating step in the tenter. A polyester film was obtained in the same manner as in Example 1 except that the film was stretched 4.5 times in the transverse direction at 130 ° C. and heat-treated at 150 ° C. for 10 seconds to obtain a film. The evaluation results are shown in Table 1.

Comparative Example 5:
In Example 1, the raw materials obtained by mixing the polyesters (A) and (C) at a ratio of 80% and 20%, respectively, were used as the raw materials for the B layer, and the polyesters (A), (B), and (C) were 75% each. The raw material mixed at a ratio of 5% and 20% was used as the raw material for the A layer, and after stretching 1.8 times in the longitudinal direction at 90 ° C, it was further subjected to a preheating step in a tenter and 5 in the lateral direction at 120 ° C. A polyester film was obtained in the same manner as in Example 1 except that a film was obtained by stretching 3 times. The evaluation results are shown in Table 1.

Comparative Example 6:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 77%, 20%, and 3%, respectively. (C) was mixed at a ratio of 75%, 5%, and 20%, respectively, and used as the raw material for the A layer. After stretching 1.8 times in the longitudinal direction at 90 ° C., a preheating step was further performed in the tenter. A polyester film was obtained in the same manner as in Example 1 except that the film was obtained by stretching 5.3 times in the transverse direction at 120 ° C. The evaluation results are shown in Table 1.

Comparative Example 7:
In Example 1, polyesters (A), (C), and (E) were mixed at a ratio of 75%, 20%, and 5%, respectively. (C) was mixed at a ratio of 75%, 5%, and 20%, respectively, and used as the raw material for the A layer. After stretching 1.8 times in the longitudinal direction at 90 ° C., a preheating step was further performed in the tenter. A polyester film was obtained in the same manner as in Example 1 except that the film was obtained by stretching 5.3 times in the transverse direction at 120 ° C. The evaluation results are shown in Table 1.

Comparative Example 8:
In Example 1, polyesters (A), (C), and (D) were mixed at a ratio of 70%, 20%, and 10%, respectively. (C) and (D) were mixed at a ratio of 65%, 5%, 20%, and 10%, respectively, and used as the raw material for the A layer. After stretching 1.8 times in the longitudinal direction at 90 ° C., Further, a polyester film was obtained in the same manner as in Example 1 except that a film was obtained by stretching 5.3 times in the transverse direction at 120 ° C. through a preheating step in a tenter. The evaluation results are shown in Table 1.

Comparative Example 9:
In Example 1, polyesters (A), (C), (C) were mixed at a ratio of 80% and 20%, respectively, and the raw materials for the B layer were used as polyesters (A), (B), (C), (D). Were mixed at a ratio of 55%, 5%, 20%, and 20%, respectively, as a raw material for the A layer, and stretched 1.8 times in the longitudinal direction at 90 ° C., and then a preheating step was performed in the tenter. Then, a polyester film was obtained in the same manner as in Example 1 except that a film was obtained by stretching the film transversely at 120 ° C. by 5.3 times. 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 polarizing plate protective film.

Claims (1)

A laminated film comprising at least three layers containing a resin composition having a refractive index of 0.02 or more higher than that of polyethylene terephthalate and polyethylene terephthalate, and the content of the resin composition in the film is 10 to 80% by weight. The birefringence Δn in the film plane is 0.060 or more, and an ultraviolet absorber is contained in any layer other than the outermost layer of the film, the light transmittance at a wavelength of 380 nm is 20.0% or less, and the wavelength is 550 nm. The polyester film for protecting a polarizing plate is characterized by having a light transmittance of 80.0% or more.