JP2002040249A - Polyester film for lamination with polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for lamination with a polarizing film, minimizing light transmission and optical interference color which cause overlooking of mixed foreign matters and defects in inspection of polarizing plates and excellent in easiness of inspection. SOLUTION: In the stretched polyester film with >=5 deg. maximum orientation angle, the polyester film for lamination with the polarizing film is characterized by making variance of retardation (Re) expressed by an equation (1) be 200 nm or less. Re=Δn.d... equation (1) (Provided that in the equation (1) Δn is birefringence in the film plane directions at wavelength λ=590 nm and d is film thickness (nm)).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyester film for bonding a polarizing film,
More specifically, the present invention relates to a polarizing plate, a retardation polarizing plate or a polyester film suitable for use as a release film or the like, which is suitable for use as a release film or the like capable of easily finding foreign substances and defects by visual inspection of the retardation plate. It is about.

[0002]

2. Description of the Related Art In recent years, a conventional CRT (Cathode
Liquid crystal display (Liquid Crysta), which has the advantages of thinner, lighter, lower power consumption, and higher image quality than Ray Tube
(1) The importance of Display is growing rapidly. In particular, a large screen TFT (Thin Film Transistor)
or STN (Super Twisted N)
In the case of the (ematic) method, the rejection rate is high, and improvement in cost is urgently required. Polarizers, retardation polarizers, or retardation plates are indispensable components for imparting light and darkness to the transmitted light of the LCD and changing the hue, and maintaining stable quality is also an important issue for these components. ing.

A polarizing plate usually comprises a polarizing film 1, a surface protective film 2, an adhesive layer and a release film 4, as shown in FIG. The polarizing film 1 is made of a polarizing element such as iodine or a dichroic dye, and is adsorbed and oriented on a hydrophilic film such as a polyvinyl alcohol-based film. Or coated with an acrylic resin. As the surface protective film 2, a transparent plastic film having a low moisture permeability and a small deformation such as elongation, such as a polyester film, is used.
The surface protective film 2 and the polarizing film 1 are adhered with an adhesive (not shown).
Are strongly adhered to the polarizing film 1, but can be easily separated from the polarizing film 1 even over time. The pressure-sensitive adhesive layer 3 is made of a pressure-sensitive pressure-sensitive adhesive for adhering the polarizing film 1 to a liquid crystal cell (not shown), and the release film 4 is made of a polyester film or the like.

In manufacturing such a polarizing plate, optical characteristics such as light transmittance, degree of polarization and haze of the polarizing film 1 as a raw material are inspected and used in advance.
Mechanical stress on the polarizing film during the manufacturing process on the polarizing plate,
There is a possibility that a defect may occur due to foreign matter mixing or adhesion. For this reason, in the inspection of contaminants and defects in the final product, as shown in FIG. 2, the crossed Nicols method (two polarizing plates, the stretching axes are perpendicular to each other, and the length and width directions of the release film are perpendicular to each other, as shown in FIG. 2). (A method of observing the transmitted light in a state of being sandwiched along the stretching axis of the plate) by human visual inspection. In a visual inspection of an actual polarizing plate, a polarizing plate is attached to a normal analyzer 7 so that the polarizing direction is perpendicular to the polarizing direction of the polarizing plate 5 and the film 6 as a release film. If they are overlapped at a position, a defect point such as a foreign substance mixture or a defect in the polarizing plate appears in principle as a bright spot, so that the defect can be visually inspected. However, since the conventional polarizing plate uses a biaxially oriented polyester film as a polyester film for bonding a polarizing film used as a release film, light leakage easily occurs due to its optical anisotropy, Accurate visual inspection becomes difficult, and there is a problem that a foreign substance as a bright spot or a defect is overlooked.

[0005]

At present, as a release film for a polarizing plate, a polyester film for laminating a polarizing film (hereinafter simply referred to as a "polyester film") having excellent transparency, strength, heat resistance and flatness. Polyester film "). However, in the polyester film, when the main axis of alignment is deviated from the orthogonal coordinates formed by the two polarizing plates in the visual inspection of the polarizing plate by the crossed Nicols method, when the polarizing plate is observed as shown in FIG. It is known that light interference colors occur. In particular, in the entire width of the film,
The shift in the orientation angle of the film (the smaller one of the orthogonal coordinate axes formed in the film longitudinal direction and the width direction and the angle formed between the main alignment axes) increases due to the bowing as the shift from the center to the end increases, and light transmission and Light interference becomes rich.

When the light interference color occurs, the polarizing plate itself appears brightly colored iridescent, so that it is difficult to find foreign matter or defects appearing as bright spots. The bowing here is a tenter method which has been widely used in the polyester film forming process (both ends of the film are gripped with clips running on rails, guided to a hot air oven, etc., and stretched in the width direction and heat-treated. How to do)
As a result of the stress difference generated in the longitudinal direction of the film during the heat treatment, a straight line drawn by magic (registered trademark) in the width direction of the film before the tenter comes out in the shape of being pulled back in a bow shape in the longitudinal direction of the film after the heat treatment. A phenomenon.

At present, a polyester film is indispensable as a release film in terms of product management in a polarizing plate manufacturing process. Therefore, light interference color is a very important problem to be solved in order to obtain a good release film for a polarizing plate with good productivity. It is understood that the cause depends on the retardation of the polyester film, and the relationship between the light interference color and the retardation is apparent from the conventional Michel-Levy interference color chart.

When linearly polarized light is incident on a birefringent material such as a stretched polyester film, generally only two polarized waves having vibration directions orthogonal to each other and having different velocities pass through. The phase difference between the two polarized waves due to the different speeds is called retardation. The light interference color is determined by its retardation,
In general, the larger the variation of the retardation, the more the plurality of interference colors are observed in the visual inspection by the cross Nicol method. This variation in retardation is caused by positional dependence of film physical properties such as variations in the molecular structure and thickness in the longitudinal and width directions of the film which occur during the film forming process. It is also known that the larger the retardation of the polyester film is, the less the wavelength dependence of visible light is, and the whitener the film is.

Under these circumstances, as a result of intensive studies,
An object of the present invention is to provide a polyester film for bonding a polarizing film which is excellent in easy testability and minimizes light transmission and light interference color, which are causes of overlooking foreign matter contamination and defects during polarizing plate inspection. It is in.

[0010]

In order to solve the above-mentioned problems, the present invention relates to a stretched polyester film having a maximum orientation angle of 5 ° or more and a retardation (Re) represented by the following formula (1). A polyester film for laminating a polarizing film, characterized in that the variation is 200 nm or less.

Re = Δn · d (1) (where, Δn is the birefringence in the in-plane direction of the film at a wavelength λ = 590 nm, and d is the thickness (nm) of the film) Is.)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester film of the present invention has a maximum orientation angle measured by a birefringence meter of 5 ° or more and a retardation (R) in the longitudinal direction and width direction of the film.
e) is a polyester film having a variation of 200 nm or less.

Here, the maximum orientation angle is the maximum value of the orientation angle in a sample obtained by taking several samples in the width direction of the film. Usually, a polarizing plate to which the polyester film is adhered as a release film can minimize the light interference color in the visual inspection by the cross Nicol method by setting the variation of the retardation (Re) within the above range. it can. The variation in the retardation is a change in the physical property value retardation represented by the following formula (1).

Re = Δn · d Expression (1) (where, in Expression (1), Δn is birefringence in the in-plane direction of the film at a wavelength λ = 590 nm, and d is the thickness (nm) of the film) Further, from the viewpoint of suppressing the light interference color, it is more preferable that the variation of the retardation is 100 nm or less.

Further, the polyester film of the present invention comprises:
The thickness unevenness in the longitudinal direction of the film is preferably 8% or less. When the thickness unevenness of the polyester film is set to 8% or less, a plurality of light interference colors do not appear, so that the polyester film can be used as a polarizing film bonding polyester film excellent in visual inspection. When the thickness unevenness is 10% or more, a film having an unstable structure can be obtained because it is not a stretch film forming technique having stable physical properties in terms of quality. Therefore, in the visual inspection by the crossed Nicols method, a plurality of light interference colors are generated, which is unsuitable as a polyester film for polarizing film bonding. Here, the unstable structure includes poor planarity, deviation of the main alignment axis, and non-uniformity of the physical properties of the film. A more preferable range of the thickness unevenness is 6% or less.

Further, the standard deviation of the thickness variation in the longitudinal direction of the polyester film of the present invention is preferably 0.09 or less. According to the present invention, when the standard deviation is 0.09 or less, a plurality of light interference colors do not appear,
It can be used as a polyester film for bonding polarizing films excellent in visual inspection. From this viewpoint, more preferably, the standard deviation is 0.08 or less.

Further, the average retardation (Re (ave)) of the polyester film of the present invention is 335 n
It is preferably at least m and at most 745 nm. When the average value of the retardation at several measurement points of the polyester film is 335 nm or more and 745 nm or less, the light transmittance is low even when the maximum orientation angle is 18 ° or less, so that it is difficult to confirm the light interference color, and visual inspection is performed. It can be used as a polyester film for bonding a polarizing film which is excellent in quality. From this perspective, the average retardation is 420
More preferably, it is not less than nm and not more than 660 nm.

The polyester film of the present invention has an average retardation (Re (ave)) of 1000 n.
A preferred range is from m to 1250 nm. The average value of the retardation of several measurement points of the polyester film is 1000 nm or more and 1250 n.
When it is less than m, the light transmittance is low even when the maximum orientation angle is 9 ° or less, so that it is difficult to confirm the light interference color, and it can be used as a polyester film for polarizing film bonding excellent in visual inspection. From this viewpoint, the average retardation is more preferably 1075 nm or more and 1175 nm or less.

The range of these average retardations is
It seems to be evident from the periodic dependence of the retardation of the light transmission under crossed Nicols. This is supported by the fact that the relational expression is expressed by the following expression (2).

T = {(sin2θ) (sinπRe / λ)} ² (2) (where T is the light transmittance, θ is the orientation angle of the birefringent body, Re
Is the retardation, and λ is the wavelength of the light beam used).
Therefore, the following conditions (a) and (b) are given as conditions for lowering the light transmittance. (A) When the orientation angle θ is reduced to 5 degrees or less, or even 3 degrees or less (b) When Re / λ is 0 or a natural number 1, 2, 3,... These contents are existing facts. Also, it is disclosed in Japanese Patent Application Laid-Open No. 7-101026.

However, unlike the conventional fact, the present invention experimentally shows the allowable condition of the maximum value of the orientation angle to maintain the easy inspection property in the range of the retardation. The light source used for visual inspection is
The reason is that the periodicity is slightly shifted because of the wavelength distribution and not the monochromatic light (wavelength λ) represented by the above equation (2). As a proof, the midpoint of the average retardation of claim 4 is 540 nm, whereas that of claim 5 is 1125 nm, which is not necessarily an integral multiple, indicating novelty.

When the polyester film of the present invention is used as a polyester film for laminating a polarizing film, it is preferable to subject the polyester film to a release treatment from the viewpoint of peelability. The release treatment is not particularly limited, but a silicone coating treatment is preferred. Among them, a treatment for forming a cured silicone resin coating film is preferably used. This cured silicone resin coating
A coating liquid containing a curable silicone resin can be applied to at least one side of the film, and dried and cured to form the film.

The thickness of the polyester film of the present invention is
10μ from the viewpoint of ease of use as a release film
It is preferably at least m and at most 60 μm, more preferably at least 20 μm and at most 50 μm.

The polyester film of the present invention can be produced by the film forming method described below. The polyester used for the polyester film in the present invention is a polyester containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main components. Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-
Naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid,
4,4'-diphenylsulfonedicarboxylic acid and the like can be mentioned. In addition, examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dodecandionic acid, and the like. Among them, terephthalic acid and isophthalic acid are preferred. One of these acid components may be used alone, or two or more thereof may be used in combination. Further, an oxyacid such as hydroxybenzoic acid may be partially copolymerized. Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3
-Cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4-hydroxyethoxyphenyl) propane, and the like. Among them, ethylene glycol is preferably used. These diol components may be used alone or in combination of two or more.

The polyester used in the polyester film of the present invention is preferably polyethylene terephthalate, a copolymer of ethylene terephthalate and ethylene isophthalate, polybutylene terephthalate and its copolymer, polybutylene naphthalate and its copolymer, Furthermore, polyhexamethylene terephthalate and its copolymer, polyhexamethylene naphthalate and its copolymer, and the like can be mentioned. In particular, polyethylene terephthalate is preferably used from the viewpoint of balance between heat resistance, transparency, and mechanical strength.

The polyester in the present invention can be produced by a conventionally known method. For example, a method in which an acid component is directly esterified with a diol component, and then the product of this reaction is heated under reduced pressure to remove the excess diol component and polycondensate to produce a dialkyl acid. There is a method of using an ester, performing a transesterification reaction between the ester and a diol component, and then performing polycondensation in the same manner as described above. In this case, if necessary, conventionally known alkali metals, alkaline earth metals, manganese, cobalt, zinc, antimony, germanium and titanium compounds can be used as the reaction catalyst.

The polyester of the present invention may further contain, if necessary, a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, an organic lubricant such as a pigment, a fatty acid ester, a wax, or a siloxane. An antifoaming agent or the like can be blended.

Further, if desired, lubricity can be imparted to the polyester film of the present invention. To impart lubricity, conventionally known techniques for polyester films, for example, polyester, clay, mica, titanium oxide, calcium carbonate, silica, kaolin,
Addition of inorganic or organic fine particles made of acrylic, polystyrene, polydivinylbenzene, etc., method using particles formed by deactivating catalyst during polyester polymerization, interface on or after polyester film formation There is a method of coating a polymer containing an activator, a release agent, or fine particles.

In the present invention, if the dispersion of the retardation of the polyester film is set to 200 nm or less, a film composed of a single layer or a film laminated from a plurality of layers can be used.

The polyester is supplied to an extruder and melt-extruded into a sheet using a T-type die or the like. Thereafter, the unstretched film cooled and solidified on the casting drum is stretched at a temperature equal to or higher than the glass transition point of the polyester. The stretching method may be any method, a method of uniaxially stretching in the longitudinal direction, a method of uniaxially stretching in the width direction, a method of stretching in the width direction after stretching in the longitudinal direction, and a method of stretching in the width direction. A method of stretching in the direction, or a method of stretching in the longitudinal direction and the width direction simultaneously,
Further, the stretching in the longitudinal direction and the stretching in the width direction may be performed plural times in combination. The stretching ratio in the longitudinal direction depends on the type of resin,
It is usually 2 to 15 times, though different depending on the use. In particular, in the case of a polyethylene film for bonding a polarizing film of polyethylene terephthalate, the ratio is about 1 to 5 times. Further, the stretching ratio in the width direction varies depending on the type of resin, application, and the like, but is usually 2 to 10 times. In particular, in the case of a polyethylene film for bonding a polarizing film of polyethylene terephthalate, the ratio is about 2 to 5 times.

Next, the stretched film is heat-treated. The heat treatment temperature is generally higher than the stretching temperature and lower than the crystal melting point, but if it is too high, the bowing tends to increase, so if it is polyethylene terephthalate, it should be in the range of 130 ° C to 230 ° C. preferable.

When the stretching in the width direction and the heat treatment are performed in a continuous hot air oven, various methods for reducing bowing can be employed.

As a method for reducing bowing of the film, a method of once cooling the glass to a glass transition temperature or lower after the stretching in the width direction and then performing a heat treatment, a method of providing a nip roll after the stretching in the width direction, and dividing the heat treatment chamber into a plurality of zones. A method in which the temperature is increased stepwise, a method in which a temperature distribution is provided in the width direction, and the temperature is guided to the heat treatment zone.
For example, there is a method of stretching about 1 time.

At this time, by adjusting the stretching temperature, the stretching ratio, the heat treatment temperature and the combination of the methods variously, it is possible to adjust so as to satisfy the variation of the retardation. For example, stretching in the longitudinal direction at high temperature and low magnification tends to cause variations in retardation and thickness unevenness. Therefore, when the stretching temperature in the longitudinal direction is 115 ° C. or higher, it is preferable to stretch 3.2 times or more.
When the temperature is lower than or equal to ° C., it is preferable that the film is stretched 2.3 times or more. Further, the stretching ratio in the width direction at that time is 3.5 from the viewpoint of easily correcting variations in retardation and thickness unevenness.
It is preferable that it be twice or more.

The average retardation can be adjusted by changing the stretching temperature and magnification in the longitudinal and width directions, but from the viewpoint that the light transmittance can be reduced even when the maximum orientation angle is large. Biaxially stretched films are preferred. From this viewpoint, the stretching ratio in the longitudinal direction is preferably 2.8 times or more, and the stretching ratio in the lateral direction is preferably 3.2 times or more. The breaking strength, breaking elongation, and elastic modulus of the polyester film of the present invention are preferably set to 130 MPa or more, 200% or less, and 2 GPa or more in both the film longitudinal direction and the width direction, for ease of release treatment and dimensional stability. Preferred from the point. Furthermore, the polyester film of the present invention has a heat shrinkage of 3% or less in both the longitudinal direction and the width direction when held at 150 ° C. for 10 minutes in terms of ease of use as a polyester film for laminating a polarizing film. Is preferred.

[Method of measuring properties] In the present invention, the properties of the film were measured by the following methods.

(1) Thickness unevenness Using a film thick nest tester KG601A and an electronic micrometer K306 (manufactured by Iritsu Corporation), a film sampled from the center in the width direction of the film to the width of the film, 50 mm in the longitudinal direction, and 25 cm in length. Was continuously measured for thickness. Film transport speed is 50
mm / min. The thickness unevenness is obtained by dividing the difference between the maximum value T (max) and the minimum value T (min) of the thickness at a measurement length of 17 cm by the average value T (ave) from the viewpoint that the maximum dimension of a normal polarizing plate is 50 × 130 cm. Multiplied by 100.

(2) Standard Deviation of Thickness Fluctuation The thickness measurement point was determined as a sample point by statistical processing.

(3) Variation in Retardation (Re) Samples were taken from the longitudinal direction of a film of A4 size cut out from the film width direction and some from the width direction.
Cut out to a size of 3.5 cm in width, and each of the retardations is automatically birefringent (KOBRA-21AD manufactured by Shin-Oji).
H), and the difference between the maximum value Re (max) and the minimum value Re (min) was taken as the dispersion of the retardation.

The average value was defined as the average retardation.

(4) Orientation Angle Samples were taken from the longitudinal direction of the A4 size film cut out from the film width direction, and some from the width direction.
It was cut out to a width of 3.5 cm, and each orientation angle was measured using an automatic birefringence meter (KOBRA-21ADH manufactured by Shin-Oji).

(5) Mechanical Strength Characteristics The sample was cut out from the center of the film in the width direction at a size of 1.5 × 15 cm in each of the longitudinal direction and the width direction.
The elastic modulus, breaking strength, and breaking elongation can be measured by using a tensile tester (Tensilon UTM-III manufactured by Toyo Sokki Co., Ltd.) by gripping at a test length of 10 cm, pulling at a speed of 20 cm / min, and recording a stress-strain curve. I asked.

(6) Thermal dimensional change rate The sample was cut out from the center in the width direction of the film at 1 × 16 cm in each of the longitudinal direction and the width direction, and was marked with a felt-tip pen at a position 3 cm from the end. . The thermal dimensional change rate was determined by comparing the longitudinal and width directions of the film before and after heat treatment at 150 ° C. for 10 minutes in a gear oven (GHPS-222 manufactured by TABAI) with a universal projector (77-7 Nikon). E0
It was determined by measuring the length in 4).

(7) Polarizing Plate Inspection In the cross Nicol method shown in FIG. 2, a visual inspection was performed using a Fujicolor light box 100V8W (KK Shinko Co., Ltd.) for the light source. At this time, the dimension width 28 × on the observation surface side
The direction of the polarization axis of the 34 cm long polarizing plate was made to coincide with the longitudinal direction of the film of the A4 cut sample. The visual inspection evaluation criteria were determined as follows. ：: Inspection possible without light interference. C: Inspection is possible although there is light interference. X: Inspection is impossible with light interference.

[0045]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a casting drum at 25 ° C., and then heated and stretched by a roll heated to 85 ° C. and a radiating heater. The film is stretched 2.8 times in the machine direction, then stretched 3.53 times in the width direction at 110 ° C. in the tenter, and further heat-treated at 200 ° C. in the subsequent heat treatment zone of the tenter, to thereby obtain a 38.2 μm-thick polyester film. I got The breaking strength, breaking elongation and elastic modulus of the obtained film were 189 MPa and 26 in the longitudinal and width directions, respectively.
0 MPa, 200%, 105%, 3.9 GPa, 5.5
GPa.

Example 2 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a 25 ° C. casting drum, and then heated and stretched a plurality of times by a roll heated to 110 ° C. and a radiation heater. Stretched 4.8 times in the longitudinal direction,
Subsequently, it is stretched 4.1 times in the width direction at 110 ° C. with a tenter,
The polyester film was further heat-treated at 200 ° C. in a heat treatment zone subsequent to the tenter to obtain a 14.8 μm-thick polyester film.

Example 3 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a casting drum at 25 ° C., and then stretched a plurality of times by a roll heated to 118 ° C. and a radiation heater to obtain a longitudinal direction. The film is stretched 2.3 times in the width direction, and then stretched 3.7 times in the width direction at 90 ° C. with a tenter.
The film is stretched 1.56 times in the longitudinal direction by a roll heated to 5 ° C., introduced into a second tenter, and subjected to 205 ° C. in a heat treatment zone.
To give a polyester film.

Example 4 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a 25 ° C. casting drum, and then heated to 95 ° C. by a roll to stretch the film 2.5 times in the longitudinal direction. And
Subsequently, it is stretched 3.7 times in the width direction at 100 ° C. with a tenter,
Further, a polyester film having a thickness of 39 μm was obtained by performing a heat treatment at 220 ° C. in a heat treatment zone subsequent to the tenter.

Example 5 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a 25 ° C. casting drum, and then stretched 3.0 times in the longitudinal direction by a roll heated to 100 ° C. The film was stretched 3.55 times at 85 ° C. in the width direction with a tenter, and further heat-treated at 180 ° C. in a heat treatment zone of the tenter to obtain a polyester film.

Example 6 Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a 25 ° C. casting drum, and then stretched 1.05 times in the longitudinal direction by a roll heated to 85 ° C. The film was stretched 3.53 times in the width direction at 100 ° C. with a tenter, and further heat-treated at 130 ° C. in a heat treatment zone subsequent to the tenter to obtain a 58.9 μm-thick polyester film.

Table 1 shows the results of various evaluations of the characteristics of Examples 1 to 6.

[Comparative Example 1] Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a casting drum at 25 ° C, and then stretched 2.5 times in the longitudinal direction by a roll heated at 85 ° C, followed by stretching. The film was stretched 3.53 times at 110 ° C. in the width direction with a tenter, and further heat-treated at 230 ° C. in a heat treatment zone subsequent to the tenter to obtain a 37.5 μm-thick polyester film.

[Comparative Example 2] Polyethylene terephthalate was melted, extruded from a die, cooled and solidified by a casting drum at 25 ° C, and then stretched 2.3 times in the longitudinal direction by a roll heated at 85 ° C. The film was stretched 3.53 times at 110 ° C. in the width direction with a tenter, and further heat-treated at 230 ° C. in a heat treatment zone of the tenter to obtain a 47.9 μm-thick polyester film.

Table 1 shows the results of various evaluations of the characteristics of Comparative Examples 1 and 2.

[0056]

According to the present invention, in a polarizing plate visual inspection, a polyester film useful for laminating a polarizing film which is excellent in easy inspection property and minimizes light interference color which is a hindrance to foreign matter contamination and defects. Can be obtained.

[0057]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the configuration of a polarizing plate.

FIG. 2 is a view for explaining a visual inspection method by the crossed Nicols method.

[Explanation of symbols]

 1: Polarizing film 2: Surface protective film 3: Adhesive layer 4: Release film 5: Polarizer 6: Film 7: Analyzer 8: White light source 9: Eye of inspector

Continued on the front page F term (reference) 2H049 BA02 BA42 BB23 BB43 BB54 BC03 BC21 2H091 FA08X FA08Z FC30 GA01 GA16 KA02 LA12 LA20

Claims (7)

[Claims] 1. A polyester for laminating a polarizing film, wherein in a stretched polyester film having a maximum orientation angle of 5 ° or more, the dispersion of retardation (Re) represented by the following formula (1) is set to 200 nm or less. the film. Re = Δn · d Expression (1) (where, in Expression (1), Δn is a wavelength λ = 590)
The birefringence in the film plane direction in nm, and d is the thickness (nm) of the film. ) 2. The polyester film for laminating a polarizing film according to claim 1, wherein the thickness unevenness in the longitudinal direction of the film is 8% or less. 3. The polyester film for laminating a polarizing film according to claim 2, wherein the standard deviation of the thickness fluctuation in the longitudinal direction of the film is 0.09 or less. 4. An average retardation (Re (av)
4. The polyester film for laminating a polarizing film according to claim 1, wherein e)) is from 335 nm to 745 nm. 5. An average retardation (Re (av)
The polyester film for laminating a polarizing film according to any one of claims 1 to 3, wherein e)) is from 1000 nm to 1250 nm. 6. The polyester film for bonding a polarizing film according to claim 4, wherein the polyester film is used after being subjected to a release treatment on the surface. 7. The polyester film for laminating a polarizing film according to claim 1, wherein the polyester film is a polyethylene terephthalate film.