WO2015046120A1 - Polyester film, production method for polyester film, polarizing plate, and image display device - Google Patents

Abstract

Provided is a production method for a polyester film that comprises: a step in which a tenter-type stretching device comprising a clip that travels along a pair of endless rails that are arranged on both sides of a film conveyance path is used to hold an unstretched polyester film by means of the clip while laterally stretching said polyester film to a thickness of 150 µm or less; and a step in which the polyester film is released from the clip after lateral stretching. The temperature of the clip when the clip grips the unstretched polyester film and the temperature of the clip when releasing the polyester film from the clip after lateral stretching are controlled so as to be 80 °C or less. The production method for a polyester film makes it possible to improve film separation defects at the time of clip release and uneven stretching in the vicinity of the clip when laterally stretching an unstretched polyester film using a tenter. Also provided are a polarizing plate and an image display device.

Description

Polyester film and method for producing polyester film, polarizing plate and image display device

The present invention relates to a polyester film and a method for producing the same, a polarizing plate, and an image display device. In particular, the present invention relates to a production method of a polyester film preferably used as a liquid crystal display substrate, preferably a uniaxially oriented polyester film, a polyester film produced by the production method of the polyester film, a polarizing plate including the polyester film, and an image display device.

Image display devices such as liquid crystal display (LCD), plasma display (PDP), electroluminescence display (OELD or IELD), field emission display (FED), touch panel, and electronic paper have a polarizing plate on the display screen side of the image display panel. Is arranged. For example, a liquid crystal display device has low power consumption, and its application is expanding year by year as a space-saving image display device. Conventionally, a liquid crystal display device has a major drawback that the viewing angle dependency of a display image is large. However, a wide viewing angle liquid crystal mode such as a VA mode and an IPS mode has been put into practical use. The demand for liquid crystal display devices is rapidly expanding even in the market where such images are required.

A polarizing plate used in a liquid crystal display device is generally composed of a polarizer made of a polyvinyl alcohol film or the like on which iodine or dye is adsorbed and oriented, and a transparent protective film (polarizing plate protective film) on both sides of the polarizer. It has a configuration. For convenience, the protective film on the surface (the side opposite to the display side) to be bonded to the liquid crystal cell is called an inner film, and the opposite side (display side) is called an outer film. Polyester, polycarbonate resin, and the like have advantages such as low cost, high mechanical strength, low moisture permeability, and the like, and are expected to be used as outer films.
In recent years, a uniaxially oriented polyester film is increasingly used as a base material for liquid crystal displays (such as a protective film for a polarizing plate) in place of a conventional biaxially oriented polyester resin film. For example, as a polarizing plate protective film with improved rainbow unevenness, rainbow unevenness can be visually recognized by using a uniaxially or biaxially oriented polyester film with Re = 3000 to 30000 nm and Re / Rth ≧ 0.2 as a polarizer protective film. An example is known in which rainbow unevenness is eliminated by making it inconspicuous to the extent that it cannot be performed (see Patent Document 1). Patent Document 1 also describes that the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced in a complete uniaxial (uniaxial symmetry) film.
The uniaxially or biaxially oriented polyester resin film having the optical properties as described above is produced by laterally uniaxially stretching at least an unstretched film while holding it with a clip using a tenter type stretching device.

On the other hand, when a film is stretched laterally using a tenter type stretching apparatus, a method for improving a failure in the vicinity of the clip is known when the film is gripped and released by a tenter clip.
For example, in Patent Document 2, when manufacturing a biaxially stretched polylactic acid film in which a large amount of plasticizer is added, a clip for gripping the film with a tenter clip when transversely stretching the polylactic acid film after longitudinal stretching It describes a method for improving the curl of the film ear by solving the poor gripping of the film by the clip by setting the temperature to 70 ° C. or lower. However, in Patent Document 2, the clip temperature when the film is released from the clip has not been studied.
In Patent Document 3, when a uniaxially oriented polyester film is produced by laterally uniaxially stretching an unstretched PET film, it is easy to tear along the orientation direction of the film because it is stretched only in the direction perpendicular to the film transport direction. Paying attention to that, when the film is released from the clip, the tenter rail width when releasing the film from the clip is expanded in the range of 0.1 to 10% of the minimum rail width after the heat setting zone. A method for suppressing breakage is described.

JP 2012-256014 A International Publication WO2008 / 035762 Patent No. 5021453

However, in the method for producing a uniaxially oriented polyester resin film described in Patent Documents 1 to 3, the inventors have studied and the film is still caught by the clip at the clip detachment portion of the tenter, and the ear portion of the film is torn off. In addition, it was found that holes in the film near the clip or unevenness of stretching occurred, and in particular, it was likely to occur in a thin film of 150 μm or less after stretching.
In particular, when a non-stretched polyester film is stretched laterally, it has been found that the separation failure at the time of separation of the clip cannot be eliminated simply by widening the tenter rail width as described in Patent Document 3.
The problem to be solved by the present invention is to provide a method for producing a polyester film that can improve poor film detachment at the time of opening a clip and uneven stretching in the vicinity of the clip when a non-stretched polyester film is stretched by a tenter. .

As a result of the study of the above problems by the present inventors, it has been found that the cause is that the temperature of the clip (usually 90 to 100 ° C. in a tenter) is higher than the film properties. Unstretched film and laterally uniaxially stretched film have low Tg (in the case of unstretched PET film mainly composed of polyethylene terephthalate, around 70 ° C, and in the case of biaxially stretched PET film, Tg is about 90-100 ° C) At the time of detachment, it adheres to a high-temperature clip (90-100 ° C) and cannot be detached, and the ear (referred to as the end of the film) is torn off (especially unstretched PET film has a dramatic Tg compared to other resins) The Tg is low and the clip is hot, so the film temperature near the clip suddenly and excessively rises due to heat transfer from the clip before stretching. It was found that the film in the vicinity of the clip became too soft and excessively stretched to form a hole, or stretching unevenness occurred in the vicinity of the clip.
On the other hand, by controlling the clip temperature to 80 ° C or lower when gripping and releasing the tenter, when the unstretched polyester film is stretched laterally by the tenter, the film disconnection failure when the clip is opened and stretching unevenness near the clip are improved. We found out that we could do it and found out that we could solve the above problems.
That is, the said subject is solved by this invention of the following structures.

[1] A thickness of 150 μm or less while gripping an unstretched polyester film with the above-described clip using a tenter-type stretching device having a clip that runs along a pair of endless rails installed on both sides of the film conveyance path. A step of transverse stretching until
Including the step of releasing the polyester film after transverse stretching described above from the clip described above,
Polyester that controls the temperature of the clip when the above-mentioned unstretched polyester film is gripped by the above-mentioned clip and the temperature of the clip when the above-mentioned polyester film after transverse stretching is released from the above-mentioned clip to 80 ° C. or less A method for producing a film.
[2] In the method for producing a polyester film according to [1], the film surface temperature of the above-mentioned unstretched polyester film at the time of starting the above-mentioned transverse stretching is determined by using the above-mentioned clip with the above-mentioned unstretched polyester film. It is preferable that the temperature is higher than the clip temperature when gripping.
[3] In the method for producing a polyester film according to [1] or [2], the distance between a pair of rails when the polyester film after the transverse stretching is released from the clip is set as the transverse stretching zone. It is preferable to increase the distance within a range of 0.1 to 5% with respect to the shortest distance between the pair of rails thereafter.
[4] The method for producing a polyester film according to any one of [1] to [3], wherein the polyester film after the transverse stretching is released before the polyester film after the transverse stretching is released from the clip. It is preferable to include a heat setting step of heating the film to the maximum temperature in the tenter.
[5] The method for producing a polyester film according to [4] includes a step of cooling the heat-fixed polyester film before releasing the heat-fixed polyester film from the clip. preferable.
[6] In the method for producing a polyester film according to any one of [1] to [5], a refractive index in a longitudinal direction of the unstretched polyester film is 1.590 or less, and
The crystallinity of the unstretched polyester film is preferably 5% or less.
[7] The method for producing a polyester film according to any one of [1] to [6], wherein the tenter described above includes a return rail to which cold air of 40 ° C. or lower is supplied at a flow rate of 50 m ³ / min or higher. Including
It is preferable to run the aforementioned clip that does not hold the film along the aforementioned return rail.
[8] In the method for producing a polyester film according to any one of [1] to [7], the clip is preferably covered with a cover that blocks wind.
[9] In the method for producing a polyester film according to any one of [1] to [8], the unstretched polyester film preferably includes a polyethylene terephthalate resin as a main component.
[10] A polyester film produced by the method for producing a polyester film according to any one of [1] to [9].
[11] The polyester film according to [10] includes a clip gripping part in which the polyester film is gripped by the clip.
It is preferable that the thickness unevenness in the longitudinal direction at a position 200 mm or more away from the clip gripping portion in the width direction is 10% or less.
[12] In the polyester film according to [10] or [11], it is preferable that the thickness unevenness in the longitudinal direction at a position away from the end of the polyester film by 50 mm or more in the width direction is 10% or less.
[13] The polyester film according to any one of [10] to [12] has a film thickness of 20 to 150 μm,
Retardation Re in the in-plane direction of the film is 3000 to 30000 nm,
The retardation Rth in the thickness direction is 3000 to 30000 nm,
Re / Rth is preferably 0.5 to 2.5.
[14] The polyester film according to any one of [10] to [13] is preferably uniaxially oriented.
[15] The polyester film according to [14] has a refractive index in the longitudinal direction of the polyester film of 1.590 or less, and
It is preferable that the degree of crystallinity of the polyester film exceeds 5%.
[16] A polarizing plate comprising a polarizer and the polyester film according to any one of [10] to [15].
[17] An image display device comprising the polyester film according to any one of [10] to [15] or the polarizing plate according to [16].

According to the present invention, it is possible to provide a method for producing a polyester film that can improve the film detachment failure when the clip is opened and the stretching unevenness in the vicinity of the clip when the unstretched polyester film is horizontally stretched by a tenter.

FIG. 1 is a schematic view of an outer return type tenter type stretching device which is an example of a tenter type stretching device used in the method for producing a polyester film of the present invention. FIG. 2 is a schematic view of an inner return type tenter type stretching apparatus which is another example of the tenter type stretching apparatus used in the method for producing a polyester film of the present invention. FIG. 3 is a schematic view showing an example of a cover of a clip used in the method for producing a polyester film of the present invention.

Hereinafter, the polyester film of the present invention and the production method thereof will be described in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Production method of polyester film]
The method for producing a polyester film of the present invention (hereinafter also referred to as the production method of the present invention) uses a tenter type stretching apparatus having clips that run along a pair of endless rails installed on both sides of a film conveyance path. And holding the unstretched polyester film with a clip, and then stretching the film to a thickness of 150 μm or less, and releasing the polyester film after transverse stretching from the clip. Both the temperature of the clip when performing and the temperature of the clip when releasing the polyester film after transverse stretching from the clip are controlled to 80 ° C. or less.
With such a configuration, when the unstretched polyester film is laterally stretched by a tenter, it is possible to improve film separation failure when the clip is opened and stretching unevenness in the vicinity of the clip.
Hereinafter, the preferable aspect of the manufacturing method of this invention is demonstrated.

<Preparation of unstretched polyester film>
(1) Polyester resin:
The unstretched polyester film preferably contains a polyester resin as a main component and a polyethylene terephthalate resin as a main component. A main component means the component which occupies 50 mass% or more of a film. As the polyester resin, those having the composition of [0042] of WO2012 / 157762 are preferably used.
As the polyester, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexanedimethylene terephthalate (PCT), etc. can be used, but PET and PEN are more preferable because of cost and heat resistance. More preferably, it is PET (PEN tends to have a small Re / Rth).
Polyester is most preferably polyethylene terephthalate, but polyethylene naphthalate can also be preferably used. For example, those described in JP-A-2008-39803 can be preferably used.

Polyethylene terephthalate is a polyester having a structural unit derived from terephthalic acid as a dicarboxylic acid component and a structural unit derived from ethylene glycol as a diol component, and 80 mol% or more of all repeating units are preferably ethylene terephthalate. The structural unit derived from other copolymerization components may be included. Other copolymer components include isophthalic acid, p-β-oxyethoxybenzoic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid , Dicarboxylic acid components such as sebacic acid, 5-sodium sulfoisophthalic acid, 1,4-dicarboxycyclohexane, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, bisphenol A ethylene oxide adduct, polyethylene glycol And diol components such as polypropylene glycol and polytetramethylene glycol. These dicarboxylic acid components and diol components can be used in combination of two or more if necessary. In addition, an oxycarboxylic acid such as p-oxybenzoic acid can be used in combination with the carboxylic acid component or diol component. As another copolymer component, a dicarboxylic acid component and / or a diol component containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be used. Polyethylene terephthalate can be produced by a direct polymerization method in which terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid and / or other diol are directly reacted, dimethyl ester of terephthalic acid and ethylene glycol, and necessary Depending on the above, any production method such as a so-called transesterification method in which a dimethyl ester of another dicarboxylic acid and / or another diol is transesterified can be applied.

(1-1) Intrinsic viscosity The intrinsic viscosity IV of the polyester resin is preferably 0.5 or more and 0.9 or less, more preferably 0.52 or more and 0.8 or less, and further preferably 0.54 or more and 0.7 or less. . In order to obtain such an IV, solid phase polymerization may be used in combination with the melt polymerization described later when the polyester resin is synthesized.

(1-2) Acetaldehyde content The acetaldehyde content of the polyester resin is preferably 50 ppm or less. More preferably, it is 40 ppm or less, Most preferably, it is 30 ppm or less. Acetaldehyde easily causes a condensation reaction between acetaldehydes, and water is generated as a side reaction product, which may cause hydrolysis of the polyester. The lower limit of the acetaldehyde content is practically about 1 ppm. In order to keep the acetaldehyde content in the above range, keep the oxygen concentration in each step such as melt polymerization and solid phase polymerization at the time of resin production, keep the oxygen concentration at the time of resin storage and drying, at the time of film production Methods such as lowering the heat history applied to the resin by an extruder, melt piping, die, etc., or preventing local strong shearing by the screw configuration of the extruder during melting, etc. can be employed.

(1-3) Catalyst For the polymerization of the polyester resin, Sb, Ge, Ti, Al-based catalysts are used, preferably Sb, Ti, Al-based catalysts, and more preferably Al-based catalysts.
That is, it is preferable that the polyester resin used as the raw material resin is polymerized using an aluminum catalyst.
By using an Al-based catalyst, it becomes easier for Re to be expressed than when other catalysts (for example, Sb, Ti) are used, and PET can be thinned. That is, it means that the Al-based catalyst is more easily oriented. This is presumed to be due to the following reasons.
Since the Al-based catalyst has a lower reactivity (polymerization activity) than Sb and Ti, the reaction is mild, and a by-product (diethylene glycol unit: DEG) is hardly generated.
As a result, the regularity of PET increases, and it is easy to align and to express Re.
(1-3-1) Al-based catalyst As the Al-based catalyst, those described in WO0013 / 040161 [0013] to [0148] (US2012 / 0183761 [0021] to [0123]) are used. The contents described in these publications are incorporated in the present specification.
The method for polymerizing the polyester resin using the Al-based catalyst is not particularly limited, but specifically, [0091] to [0094] of WO2012 / 008488 ([0144] to [0094] of US2013 / 0112271). 0153]) can be used to polymerize according to these publications, and the contents described in these publications are incorporated herein.
Such Al-based catalysts include, for example, [0052] to [0054], [0099] to [0104] of JP2012-122051 ([0045] to [0047], [0091] of WO2012 / 029725. To [0096]) can be prepared according to these publications, and the contents described in these publications are incorporated herein. The amount of the Al-based catalyst is preferably 3 to 80 ppm, more preferably 5 to 60 ppm, and still more preferably 5 to 40 ppm as the amount of Al element with respect to the mass of the polyester resin.

(1-3-2) Sb-based catalyst:
As the Sb-based catalyst, those described in [0050], [0052] to [0054] of JP 2012-41519 A can be used.
The method for polymerizing the polyester resin using the Sb-based catalyst is not particularly limited, but specifically, the polymerization can be performed according to [0086] to [0087] of WO2012 / 157762.

It is also preferable to add a known additive to the unstretched polyester film used for the polyester film of the present invention. Examples thereof include ultraviolet absorbers, particles, lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light resistance agents, impact resistance improvers, lubricants, dyes, pigments and the like. However, since the polyester film generally requires transparency, it is preferable to keep the additive amount to a minimum.

(1-4-1)
The unstretched polyester film used for the polyester film of the present invention can contain an ultraviolet absorber in order to prevent the liquid crystal of the liquid crystal display from being deteriorated by ultraviolet rays. The ultraviolet absorber is not particularly limited as long as it is a compound having ultraviolet absorbing ability and can withstand the heat applied in the production process of the polyester film.
As the ultraviolet absorber, there are an organic ultraviolet absorber and an inorganic ultraviolet absorber. From the viewpoint of transparency, an organic ultraviolet absorber is preferable. Those described in [0057] of WO2012 / 157762 and cyclic iminoester-based ultraviolet absorbers described later can be used.

The cyclic imino ester-based ultraviolet absorber is not limited to the following, and examples thereof include 2-methyl-3,1-benzoxazin-4-one and 2-butyl-3,1-benzoxazine-4. -One, 2-phenyl-3,1-benzoxazin-4-one, 2- (1- or 2-naphthyl) -3,1-benzoxazin-4-one, 2- (4-biphenyl) -3, 1-benzoxazin-4-one, 2-p-nitrophenyl-3,1-benzoxazin-4-one, 2-m-nitrophenyl-3,1-benzoxazin-4-one, 2-p-benzoyl Phenyl-3,1-benzoxazin-4-one, 2-p-methoxyphenyl-3,1-benzoxazin-4-one, 2-o-methoxyphenyl-3,1-benzoxazin-4-one 2-cyclohexyl-3,1-benzoxazin-4-one, 2-p- (or m-) phthalimidophenyl-3,1-benzoxazin-4-one, N-phenyl-4- (3,1-benzo Oxazin-4-one-2-yl) phthalimide, N-benzoyl-4- (3,1-benzoxazin-4-one-2-yl) aniline, N-benzoyl-N-methyl-4- (3,1 -Benzoxazin-4-one-2-yl) aniline, 2- (p- (N-methylcarbonyl) phenyl) -3,1-benzoxazin-4-one, 2,2'-bis (3,1- Benzoxazin-4-one), 2,2′-ethylenebis (3,1-benzoxazin-4-one), 2,2′-tetramethylenebis (3,1-benzoxazin-4-one), 2 , 2'-Deca Tylene bis (3,1-benzoxazin-4-one, 2,2 '-(1,4-phenylene) bis (4H-3,1-benzoxazin-4-one) [Note that 2,2'-p- Phenylenebis (3,1-benzoxazin-4-one)], 2,2'-m-phenylenebis (3,1-benzoxazin-4-one), 2,2 '-(4,4' -Diphenylene) bis (3,1-benzoxazin-4-one), 2,2 '-(2,6- or 1,5-naphthylene) bis (3,1-benzoxazin-4-one), 2, 2 '-(2-methyl-p-phenylene) bis (3,1-benzoxazin-4-one), 2,2'-(2-nitro-p-phenylene) bis (3,1-benzoxazine-4 -One), 2,2 '-(2-chloro-p-phenylene) bis ( 3,1-benzoxazin-4-one), 2,2 ′-(1,4-cyclohexylene) bis (3,1-benzoxazin-4-one), 1,3,5-tri (3,1 -Benzoxazin-4-one-2-yl) benzene, 1,3,5-tri (3,1-benzoxazin-4-one-2-yl) naphthalene, 2,4,6-tri (3,1 -Benzoxazin-4-one-2-yl) naphthalene, 2,8-dimethyl-4H, 6H-benzo (1,2-d; 5,4-d ') bis (1,3) -oxazine-4, 6-dione, 2,7-dimethyl-4H, 9H-benzo (1,2-d; 4,5-d ′) bis (1,3) -oxazine-4,9-dione, 2,8-diphenyl- 4H, 8H-benzo (1,2-d; 5,4-d ′) bis (1,3) -oxazine-4,6-di 2,7-diphenyl-4H, 9H-benzo (1,2-d; 4,5-d ′) bis (1,3) -oxazine-4,6-dione, 6,6′-bis (2 -Methyl-4H, 3,1-benzoxazin-4-one), 6,6′-bis (2-ethyl-4H, 3,1-benzoxazin-4-one), 6,6′-bis (2 -Phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-methylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-methylenebis (2 -Phenyl-4H, 3,1-benzoxazin-4-one), 6,6′-ethylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-ethylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6 ′ Butylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-butylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6′- Oxybis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-oxybis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6′- Sulfonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-sulfonylbis (2-phenyl-4H, 3,1-benzoxazin-4-one), 6,6 '-Carbonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6'-carbonylbis (2-phenyl-4H, 3,1-benzoxazin-4-one), 7 , 7'-methylenebis ( 2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-methylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one), 7,7′-bis ( 2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-ethylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-oxybis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′-sulfonylbis (2-methyl-4H, 3,1-benzoxazin-4-one), 7,7′- Carbonyl bis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,7′-bis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,7 ′ -Bis (2-phenyl-4H, 3,1-benzoxazine- -One, 6,7'-methylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,7'-methylenebis (2-phenyl-4H, 3,1-benzoxazine-4-one) ON).

Among the above compounds, when considering the color tone, a benzoxazinone-based compound which is difficult to be yellowed is preferably used. As an example thereof, a compound represented by the following general formula (1) is more preferably used. It is done.

In the general formula (1), R represents a divalent aromatic hydrocarbon group, and X ¹ and X ² are each independently selected from hydrogen or the following functional group group, but are not necessarily limited thereto. Absent.

Functional group: alkyl group, aryl group, heteroaryl group, halogen, alkoxyl group, aryloxy group, hydroxyl group, carboxyl group, ester group, nitro group.

Among the compounds represented by the general formula (1), 2,2 ′-(1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] is particularly preferable in the present invention.

The amount of the ultraviolet absorber contained in the polyester film of the present invention is usually 10.0% by mass or less, preferably 0.3 to 3.0% by mass. When an ultraviolet absorber in an amount exceeding 10.0% by mass is contained, the ultraviolet absorber may bleed out on the surface, which may cause deterioration of surface functionality such as adhesion deterioration.

Further, in the case of the polyester film of the present invention having a multilayer structure, it is preferably at least a three-layer structure, and the ultraviolet absorber is preferably blended in the intermediate layer. By blending an ultraviolet absorber in the intermediate layer, this compound can be prevented from bleeding out to the film surface, and as a result, characteristics such as film adhesion can be maintained.

The masterbatch method described in [0050] to [0051] of WO2011 / 162198 can be used for these formulations.

(1-4-2) Other Additives Other additives may be used for the unstretched polyester film used in the polyester film of the present invention, for example, those described in [0058] of WO2012 / 157762. The contents described in these publications are incorporated herein by reference.

(2) Melt kneading:
The unstretched polyester film is preferably formed into a film by melt-extruding a polyester resin.
It is preferable to dry the polyester resin or the master batch of the polyester resin and additive produced by the above-described master batch method to a moisture content of 200 ppm or less, and then introduce the melt into a single or twin screw extruder and melt it. At this time, in order to suppress degradation of the polyester, it is also preferable to melt in nitrogen or vacuum. The detailed conditions can be implemented in accordance with these publications with the aid of Patent Nos. 4992661 [0051] to [0052] (US 2013/0100378 publication [0085] to [0086]) and are described in these publications. The contents are incorporated herein. Furthermore, it is also preferable to use a gear pump in order to increase the delivery accuracy of the molten resin (melt). It is also preferable to use a 3 μm to 20 μm filter for removing foreign substances.

(3) Extrusion, coextrusion:
Although it is preferable to extrude the melt containing the polyester resin melt-kneaded from the die, it may be extruded as a single layer or as a multilayer. When extruding in multiple layers, for example, a layer containing an ultraviolet grade agent (UV agent) and a layer not containing it may be laminated. In addition to suppressing deterioration, it is preferable to suppress bleeding out of the UV agent.
The bleed-out UV agent is undesirably easily transferred to a pass roll in the film-forming process, increasing the coefficient of friction between the film and the roll, and causing scratches.
When the polyester film is produced by being extruded in multiple layers, the preferred inner layer thickness (ratio to the total layer) of the resulting polyester film is preferably 50% or more and 95% or less, more preferably 60% or more and 90% or less, Preferably they are 70% or more and 85% or less. Such lamination can be performed by using a feed block die or a multi-manifold die.

(4) Cast:
According to [0059] of JP-A-2009-269301, it is preferable to extrude the melt extruded from the die onto a casting drum and cool and solidify to obtain an unstretched polyester film (raw fabric).
In the production method of the present invention, the refractive index in the longitudinal direction of the unstretched polyester film is preferably 1.590 or less, more preferably 1.585 or less, and further preferably 1.580 or less.
In the production method of the present invention, the crystallinity of the unstretched polyester film is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. In addition, the crystallinity degree of the unstretched polyester film here means the crystallinity degree of the center part of a film width direction.
When adjusting the degree of crystallinity, the temperature of the end of the casting drum may be lowered, or air may be blown onto the cast drum.
The crystallinity can be calculated from the film density. That is, the density X (g / ^cm 3) of the film density at a crystallinity of ^{0% Y = 1.335g / cm 3} , using density Z = 1.501g / cm ³ at 100% crystalline below The crystallinity (%) can be derived from the calculation formula.
Crystallinity = {Z × (XY)} / {X × (ZY)} × 100
The density can be measured according to JIS K7112.

(5) Formation of polymer layer (adhesive layer):
On the melt-extruded unstretched polyester film, a polymer layer (preferably an easy-adhesion layer) may be formed by coating before or after stretching described later.
Examples of the polymer layer generally include a functional layer that the polarizing plate may have, and among them, it is preferable to form an easy adhesion layer as the polymer layer. The easy-adhesion layer can be applied by the method described in [0062] to [0070] of WO2012 / 157762.

<Horizontal stretching>
The production method of the present invention uses a tenter-type stretching apparatus having a clip that runs along a pair of endless rails installed on both sides of a film conveyance path, and grips an unstretched polyester film with a clip to 150 μm or less. Including the step of transversely stretching until the thickness becomes, and the temperature of the clip when the unstretched polyester film is gripped by the clip is controlled to 80 ° C. or less.

(1) Tenter type stretching device:
There is no particular limitation on the tenter type stretching device having a clip that travels along a pair of endless rails installed on both sides of the film conveyance path, but the outer return type tenter type stretching device shown in FIG. 2, an inner return type tenter type stretching apparatus.
In the example of the outer return type tenter type stretching apparatus shown in FIG. 1, reference numeral 41 denotes the traveling direction of the film. 42 is a tenter oven, and 43 is a clip cooling tank for cooling the return rail. Reference numeral 44 denotes a clip wheel that supports a clip with a tenter. As shown in FIG. 1, in the outer return, a return clip cooling tank can be installed outside the oven, but the wheel with a tenter cannot be made to follow the film width because of the structure.
In the example of the inner return type tenter type stretching apparatus shown in FIG. 2, 45 indicates the traveling direction of the film. 46 is a tenter oven, and 47 is a clip cooling tank for cooling the return clip. Reference numeral 48 denotes a clip wheel that supports a clip with a tenter. As shown in FIG. 2, in the inner return type, it is possible to follow the distance between the wheels in accordance with the fluctuation of the film width. However, it is necessary to install a return rail cooling tank in the heated tenter oven.
These clips travel along a pair of endless rails installed on both sides of the film transport path, and after gripping the film, pass through the preheating zone, stretching zone, heat setting zone, and cooling zone along the rails. It is preferable to cool the clip itself by running a clip that does not hold the film along the return rail after the film is opened. It is preferable that the film whose both ends are gripped at the tenter inlet is heated in advance by hot air or the like in the preheating zone. In the stretching zone, the clip interval at both ends is widened and stretched in the width direction. Thereafter, it is preferable that the heat setting treatment is performed at a temperature higher than the stretching temperature in a stretched width or a width narrower than the stretched width. When the stretching temperature and the heat setting temperature are greatly different, a neutral zone is often provided so that hot air does not interfere with each other. After completion of crystallization of the film in the heat setting zone, the film is preferably cooled with cold air in the cooling zone. Thereafter, the film is removed from the clip, and the process proceeds to the winder.

(2) Clip temperature during gripping:
In the production method of the present invention, the temperature of the clip when the unstretched polyester film is held by the clip is controlled to 80 ° C. or less.
The clip temperature when gripping an unstretched polyester film with a clip is preferably 80 ° C. or lower, more preferably 75 ° C. or lower, still more preferably 70 ° C. or lower, and most preferably 65 ° C. or lower. When the clip temperature when gripping an unstretched polyester film with a clip is 80 ° C. or less, it is possible to improve stretching failure such as uneven thickness in the film transport direction around the clip and perforation of the film.
The lower the clip temperature when gripping the unstretched polyester film with the clip, the better. However, it is difficult to control to 30 ° C. or lower.

There is no particular limitation on the method for controlling the temperature of the clip when holding the unstretched polyester film with the clip and the temperature of the clip when releasing the polyester film after transverse stretching from the clip to the above temperature or less. The tenter preferably includes a return rail to which cold air of 40 ° C. or lower is supplied at an air volume of 50 m ³ / min or more, and the clip that does not hold the film is run along the return rail. The cold air temperature supplied to the return rail is preferably 40 ° C. or lower, more preferably 35 ° C. or lower, still more preferably 30 ° C. or lower, and most preferably 25 ° C. or lower. The amount of air supplied to the return rail is 50 m ³ / min or more, not only the temperature of the clip when gripping the unstretched polyester film, but also the temperature of the clip when opening the polyester film after transverse stretching. From the viewpoint of controlling to below the range of the present invention, it is preferably 100 m ³ / min or more, more preferably 150 m ³ / min or more, and further preferably 200 m ³ / min or more.
In the tenter type stretching machine, when the endless chain with clip circulates the front and rear wheels, the so-called return side that travels in the direction opposite to the flow direction not gripping the film is not stored in the tenter oven. There is a stored method. The former is called the outer return type and the latter is called the inner return type. As shown in FIG. 1, in the outer return type, the return rail is opened to the atmosphere. In this case, when the clip is on the return rail, the clip is cooled by passing through a tank in which cold air is circulated. In addition, in order to cool the clip to the target temperature, the length of the tank and the cold air temperature are determined.
However, Edge Positioning Control (EPC) that automatically changes the clip width of the lateral stretcher film introduction portion in accordance with the width variation of the longitudinally stretched film is often used in production apparatuses. This EPC is a system that detects a film edge and moves the wheel on the tenter entry side in the width direction in accordance with the fluctuation.
As shown in FIG. 2, in this case, the wheel is housed in a tenter oven and a return rail is also placed in the oven in order to ensure a movable range in the width direction. This inner return type is widely used in production equipment. When the clip is cooled by this inner return type, a heat insulating room for isolating the return rail portion is prepared in the tenter oven. Further, cold air is supplied to the room from the outside to cool the clip on the return rail. The cold air supplied to the heat insulation chamber is preferably discharged because it may interfere with the uniformity of the stretching temperature and the heat setting temperature when discharged into the tenter oven. The volume ratio of the cool air to be discharged is preferably 0.9 or more with respect to the supplied amount of the cool air. It is because it becomes easy to prevent generation | occurrence | production of the temperature spot of the extending | stretching chamber and heat setting chamber by a cold wind from a heat insulation chamber. Further, the volume ratio of the discharged cool air is preferably 1.1 or less with respect to the supplied cool air flow rate. This is because hot air in the tenter oven is less likely to flow into the heat insulation chamber, and quick cooling of the clip is easily achieved.

In the method for producing a polyester film of the present invention, when the clip is covered with a cover that blocks wind, the temperature of the clip when the unstretched polyester film is gripped by the clip and when the polyester film after transverse stretching is released from the clip It is easy to control the temperature of any of the clips below 80 ° C, and the film surface temperature of the unstretched polyester film at the start of transverse stretching is set higher than the clip temperature when the unstretched polyester film is gripped by the clips. It is preferable from the viewpoint that it can be easily made.
FIG. 3 shows a configuration of an example of a cover that blocks preferable wind. Hereinafter, the cover of the clip shown in FIG. 3 will be described.
As shown in FIG. 3, a metal plate-like cover is provided so as to cover the clip 2 so that the hot air from the nozzle is not directly applied to the clip upper part 2a and the clip lower part 2b by preheating, stretching, heat setting, heat relaxation process, etc. 3 surround clip 2. In order to hold the film 1, it is necessary to provide a clearance 4 between the film 1 and the cover 3, and the clearance 4 between the film 1 and the cover 3 is preferably 60 mm or less, more preferably 40 mm or less, and further 20 mm or less. preferable.

(3) Film surface temperature at the start of transverse stretching:
In the production method of the present invention, it is preferable that the film surface temperature of the unstretched polyester film at the start of transverse stretching is higher than the clip temperature when the unstretched polyester film is held by the clip. When the stretching start film surface temperature is higher than the clip temperature, it is possible to easily improve stretching defects such as thickness unevenness and film perforation in the film transport direction around the clip.
The film surface temperature of the unstretched polyester film at the start of transverse stretching is preferably 5 ° C. or higher, preferably 10 ° C. or higher than the clip temperature when gripping the unstretched polyester film with a clip. More preferably, the temperature is most preferably 15 ° C. or higher.

(4) Transverse stretching conditions:
In the method for producing a polyester film of the present invention, the extruded film is stretched transversely. Transverse stretching is performed in a direction perpendicular to the film transport direction while transporting an unstretched polyester film along the film transport path.
By stretching, retardation Re in the in-plane direction of the film can be greatly expressed. In particular, in order to achieve a polyester film satisfying the ranges of Re, Rth, and Re / Rth described later, at least lateral stretching is performed. When the longitudinal stretching is performed thereafter, the stretching ratio of the lateral stretching may be increased among the longitudinal and lateral stretching ratios, and the stretching may be performed unbalanced.

The stretching temperature in the stretching step is preferably 70 ° C. or higher and 170 ° C. or lower, more preferably 80 ° C. or higher and 160 ° C. or lower, and still more preferably 90 ° C. or higher and 150 ° C. or lower. The stretching temperature here refers to an average temperature from the start to the end of stretching.

That is, it can be achieved by holding both ends of the film with clips and widening between the clips while heating. The transverse draw ratio is preferably 2 to 5.5 times, more preferably 2.5 to 5 times, and particularly preferably 3 to 4.5 times.

<Heat setting>
The production method of the present invention preferably includes a heat setting step of heating the polyester film after transverse stretching to the maximum temperature in the tenter before releasing the polyester film after transverse stretching from the clip.
In order to promote crystallization after stretching, it is preferable to perform a heat treatment called “heat setting”. This can be performed at a temperature exceeding the stretching temperature to promote crystallization and increase the strength of the film.
In heat setting, volume shrinks due to crystallization.
As a heat fixing method, several slits for sending hot air to the extending portion are provided in parallel to the width direction. This can be achieved by making the temperature of the gas blown out from the slit higher than the stretched portion. Further, a heat source (IR heater, halogen heater, etc.) may be installed near the drawing (part) exit to raise the temperature.

The preferred temperature for heat setting is preferably from 100 ° C. to 250 ° C., more preferably from 150 ° C. to 245 ° C.

At this time, it is preferable to relax (shrink the film) simultaneously with the heat treatment, and it is preferable to perform at least one of TD (transverse direction) and MD (vertical direction).
Such relaxation can be achieved, for example, by using a pantograph-like chuck for the tenter, reducing the interval between the pantographs, and driving the click on the electromagnet to reduce the speed.
Longitudinal relaxation is preferably performed at 120 ° C. or higher and 230 or lower, more preferably 130 ° C. or higher and 220 ° C. or lower, and further preferably 140 ° C. or higher and 210 ° C. or lower from the viewpoint of suppression of scratches. Longitudinal relaxation also has the effect of increasing Re / Rth in widthwise stretching. This is because loosening the longitudinal direction during transverse stretching facilitates lateral orientation and easily increases Re. The amount of relaxation is preferably 1% or more and 10% or less from the viewpoint of suppressing generation of scratches on the polyester film, more preferably 2% or more and 8% or less, and even more preferably 3% or more and 7%. % Or less. If it is more than the lower limit value of this preferable range, the above-mentioned effect is difficult to occur and scratches are hardly generated. On the other hand, if it is less than or equal to the upper limit of this preferred range, it will be difficult for slack to occur, it will be difficult to come into contact with a stretching machine, and scratches will not easily occur.

The lateral relaxation temperature is preferably in the range of the above-mentioned heat setting temperature, and may be the same as that of heat setting, or may be high or low.
The lateral relaxation amount is preferably in the same range as the longitudinal relaxation amount. Lateral relaxation can be achieved by reducing the width of the widened click.

By the above stretching and heat setting, Re, Rth and Re / Rth of the polyester film of the present invention can be easily achieved. That is, it is easy to form the polyester film of the present invention that exhibits the effect of reducing rainbow unevenness by performing stretching and heat setting by these methods.

<Cooling>
It is preferable that the manufacturing method of this invention includes the process of cooling the polyester film after heat setting, before releasing the polyester film after heat setting from a clip. From the viewpoint of easily reducing the temperature of the clip when the polyester film after stretching, preferably the heat-set polyester film is cooled before being released from the clip, when the polyester film after transverse stretching is released from the clip, preferable.
The cooling temperature of the polyester film after heat setting is preferably 80 ° C. or less, more preferably 70 ° C. or less, and particularly preferably 60 ° C. or less.
Specific examples of the method for cooling the polyester film after heat setting include a method in which cold air is applied to the polyester film.

<Release film from clip>
The manufacturing method of this invention includes the process of releasing the polyester film after lateral stretching from a clip, and controls the temperature of a clip at 80 degrees C or less when releasing the polyester film after lateral stretching from a clip.
When the polyester film after transverse stretching is released from the clip, the clip temperature is preferably 80 ° C. or lower, more preferably 75 ° C. or lower, still more preferably 70 ° C. or lower, and most preferably 65 ° C. or lower. If the temperature of the clip when releasing the polyester film after transverse stretching from the clip is 80 ° C or less, it is possible to improve the disconnection failure such as the breakage of the film ear when the clip is released from the clip. Further, it is possible to improve stretching defects such as thickness unevenness in the film transport direction around the clip and perforation of the film.
The lower the clip temperature, the better. However, it is difficult to control it to 30 ° C. or lower.

In the production method of the present invention, the distance between the pair of rails when the polyester film after transverse stretching is released from the clip is 0.1 to 5% of the distance between the shortest pair of rails after the transverse stretching zone. It is preferable to widen the range. When the distance between the pair of rails when the polyester film after transverse stretching is released from the clip is wider than the distance between the shortest pair of rails after the transverse stretching zone is 0.1% or more from the clip It is possible to easily improve poor clip detachment such as breakage of the film ear when the film is opened. The range in which the distance between the pair of rails when the polyester film after transverse stretching is released from the clip is wider than the distance between the shortest pair of rails after the transverse stretching zone is 5% or less, and the film is difficult to break. .
The distance between the pair of rails when the polyester film after transverse stretching is released from the clip may be increased within a range of 0.2% to 4% with respect to the shortest distance between the pair of rails after the transverse stretching zone. More preferably, it is more preferably in the range of 0.3% to 3.5%, and most preferably in the range of 0.3% to 3%.

The thickness of the polyester film after completion of film formation (after the transverse stretching and releasing step from the clip) is preferably 20 to 150 μm, more preferably 30 to 130 μm, and further preferably 35 to 110 μm or less. The reason why this range is preferable is the same as the reason why the thickness of the polyester film of the present invention is preferably within this range.

<Recovery and winding of film>
After the transverse stretching and the step of releasing from the clip, the film is trimmed and thickened as necessary and wound up for collection.

The trimming at both ends may or may not be performed. Since the polyester film manufactured by the manufacturing method of the present invention has little edge breakage at the end of the film and stretching unevenness in the vicinity of the clip gripping portion, trimming may not be performed.
Thickening processing (knurling) is preferably performed at both ends.
The winding is preferably performed at a diameter of not less than 1000 m and not more than 10000 m on a core having a diameter of not less than 70 mm and not more than 600 mm. Winding tension per cross-sectional area of the film is preferably 3 ~ 30kgf / cm ^2, more preferably 5 ~ 25kgf / cm ^2, more preferably from 7 ~ 20kgf / cm ^2. The thickness of the wound film is the same as [0049] of Japanese Patent No. 4926661. It is also preferable to bond a masking film before winding.

[Polyester film]
The polyester film of the present invention is produced by the method for producing a polyester film of the present invention.

<Characteristics of polyester film>
The polyester film of the present invention preferably includes a clip gripping part in which the polyester film is gripped by a clip, and the thickness unevenness in the longitudinal direction at a position away from the clip gripping part by 200 mm or more in the width direction is preferably 10% or less. 8% or less is more preferable, 6% or less is more preferable, and 5% or less is most preferable. When it is 10% or less, it can be used as an optical film.

In the polyester film of the present invention, the thickness unevenness in the longitudinal direction at a position 50 mm or more away from the end of the polyester film in the width direction is preferably 10% or less, more preferably 8% or less, and further 6% or less. Preferably, 5% or less is most preferable.

-Phase difference-
In the polyester film of the present invention, the in-plane retardation Re is preferably 3000 to 30000 nm, more preferably 3500 to 25000 nm, and still more preferably 4000 to 20000 nm or less. When Re is less than 3000 nm, color unevenness on the screen is less likely to occur when a panel is used, which is preferable. In principle, it is difficult to produce a film exceeding 30000 nm. Even if Re of the polyester film exceeds 30000 nm, the effect of reducing rainbow unevenness is only saturated, and the effect of the present invention can be obtained.
Rainbow spot appears when observing light incident obliquely from a backlight source on a polarizing plate having a large birefringence, specifically, a polymer film having Re of 500 nm or more and less than 3000 nm as a protective film. This is conspicuous in a liquid crystal display device including a bright line spectrum and having a light source such as a cold cathode tube as a backlight.
Here, when a white light source having a continuous emission spectrum is used as a backlight light source, it is preferable that the Re of the polyester film of the present invention is in the above range because rainbow unevenness is hardly visible.

The polyester film of the present invention has a thickness direction retardation Rth of preferably 3000 to 30000 nm, more preferably 3500 to 25000 nm, and further preferably 4000 to 20000 nm. In principle, it is difficult to make a film with Rth below 3000 nm. When it is 30000 nm or less, color unevenness on the screen hardly occurs when a panel is used, which is preferable.

In the polyester film of the present invention, the ratio (Re / Rth) between the in-plane retardation Re and the thickness direction retardation Rth is preferably 0.5 to 2.5, more preferably 0.6 to 2.2. More preferably, it is 0.7 to 2.0. When Re / Rth is 0.5 or more, color unevenness hardly occurs on the screen when the polyester film of the present invention is incorporated as a polarizing plate protective film in a liquid crystal panel, which is preferable. In principle, it is difficult to make a film exceeding 2.5. Moreover, even if Re / Rth exceeds 1.2, the effect of reducing the viewing angle dependency of rainbow spot is only saturated, and if Re / Rth is 1.2 or less, there is little decrease in mechanical properties, and there is no scratch. It is difficult to generate and is preferable.

Rainbow spot unevenness can also be reduced by setting the Nz value representing the relationship between Re and Rth to an appropriate value, and the absolute value of the Nz value is 2.0 or less due to the effect of reducing rainbow-like unevenness and manufacturing suitability. It is preferably 0.5 to 2.0, more preferably 0.5 to 1.5.
Since iridescent unevenness is caused by incident light, it is usually observed during white display.
The in-plane retardation value Re of the polyester film of the present invention is represented by the following formula (4).

Re = (nx−ny) × y ₁ (4)
Here, nx is the refractive index in the in-plane slow axis direction of the polyester film, ny is the refractive index in the in-plane fast axis direction (direction perpendicular to the in-plane slow axis direction) of the polyester film, and y ₁ is the thickness of the polyester film.

The retardation Rth in the thickness direction of the polyester film of the present invention is represented by the following formula (5).

Rth = {(nx + ny) / 2−nz} × y ₁ (5)
Here, nz is the refractive index in the thickness direction of the polyester film.

Note that the Nz value of the polyester film is represented by the following formula (6).

Nz = (nx−nz) / (nx−ny) (6)

In this specification, Re, Rth, and Nz at a wavelength λnm can be measured as follows.
Using two polarizing plates, the orientation axis direction of the polyester film was determined, and a 4 cm × 2 cm rectangle was cut out so that the orientation axis directions were perpendicular to each other, and used as a measurement sample. For this sample, the biaxial refractive index (Nx, Ny) perpendicular to each other and the refractive index (Nz) in the thickness direction were determined by an Abbe refractometer (Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). The absolute value of the refractive index difference (| Nx−Ny |) was defined as the refractive index anisotropy (ΔNxy). The thickness y ₁ (nm) of the polyester film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Measured Nx, Ny, Nz, Re from the value of _{y 1,} Rth, Nz was calculated.

The above Re and Rth can be adjusted by the type of polyester resin used in the film, the amount of the polyester resin and the additive, the addition of the retardation enhancer, the film thickness, the stretching direction and the stretching ratio of the film, and the like. .
Although there is no restriction | limiting in particular in the method of controlling the polyester film of this invention to the range of said Re and Rth, For example, it can achieve by the drawing method.

-Film thickness-
The thickness of the polyester film of the present invention is 150 μm or less, preferably 20 to 150 μm, more preferably 30 to 130 μm, still more preferably 35 to 110 μm. If the thickness is less than 20 μm, uneven color occurs on the screen when the panel is formed. If it exceeds 150 μm, the cost is high and the profitability is not suitable.

The polyester film of the present invention is preferably uniaxially oriented. Specifically, the polyester film of the present invention preferably has a longitudinal refractive index of 1.590 or less and a crystallinity of more than 5%.
The preferable range of the refractive index in the longitudinal direction of the polyester film of the present invention is the same as the preferable range of the refractive index in the longitudinal direction of the unstretched polyester film.
The degree of crystallinity of the polyester film of the present invention is preferably 20% or more, and more preferably 30% or more.

<Layer structure of polyester film, surface treatment>
The polyester film of the present invention contains a polyester resin.
The polyester film of the present invention may be a single layer film having a polyester resin as a main component or a multilayer film having at least one layer having a polyester resin as a main component. Moreover, the surface treatment may be performed on both surfaces or one surface of these single layer films or multilayer films, and this surface treatment is performed by corona treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation, or the like. Modification may be sufficient, and thin film formation by application | coating, vapor deposition, etc. of a polymer, a metal, etc. may be sufficient. The mass ratio of the polyester resin in the entire film is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more.

[Polarizer]
The polyester film of the present invention can be used as a polarizing plate protective film.
The polarizing plate of the present invention includes a polarizer having polarizing performance and the polyester film of the present invention. The polarizing plate of the present invention may further contain a polarizing plate protective film such as a cellulose acylate film in addition to the polyester film of the present invention.

The shape of the polarizing plate was not only a polarizing plate in the form of a film piece cut to a size that can be incorporated into a liquid crystal display device as it is, but also produced in a long shape by continuous production and rolled up into a roll shape. A polarizing plate of an embodiment (for example, an embodiment having a roll length of 2500 m or more or 3900 m or more) is also included. In order to use for a large-screen liquid crystal display device, the width of the polarizing plate is preferably 1470 mm or more.

As described in [0025] of WO2011 / 162198, a polarizer comprising PVA and the polyester film of the present invention can be bonded to prepare a polarizing plate. Under the present circumstances, it is preferable to make the said easily bonding layer contact PVA. Furthermore, it is also preferable to combine with a protective film having retardation as described in [0024] of WO2011 / 162198.

[Image display device]
The polyester film of this invention can be used for an image display apparatus, and the polarizing plate containing the polyester film of this invention can be used as a polarizing plate of an image display apparatus.
The image display device of the present invention includes the polyester film of the present invention or the polarizing plate of the present invention.
Examples of the image display device include a liquid crystal display (LCD), a plasma display (PDP), an electroluminescence display (OELD or IELD), a field emission display (FED), a touch panel, and electronic paper. These image display devices preferably include the polarizing plate of the present invention on the display screen side of the image display panel.

As a method of bonding the polarizing plate to an image display device such as a liquid crystal display device, a known method can be used. In addition, a roll-to-panel manufacturing method can be used, which is preferable for improving productivity and yield. The roll-to-panel manufacturing method is described in JP2011-48381, JP2009-175653, JP4628488, JP4729647, WO2012 / 014602, WO2012 / 014571, and the like. It is not limited.

In the image display device, it is preferable to use a light source having an emission spectrum having a continuous emission spectrum as the light source.
This is because it becomes easy to eliminate rainbow unevenness as described in [0019] to [0020] of WO2011 / 162198.
As a light source used in the image display device, the one described in [0013] of WO2011 / 162198 is used. On the other hand, the light sources described in [0014] to [0015] of WO 2011/162198 are not continuous light sources and are not preferable.
When the image display device is an LCD, the configuration described in [0011] to [0012] of WO2011 / 162198 can be used as the liquid crystal display device (LCD).
The liquid crystal display device using the polyester film of the present invention and / or the polarizing plate of the present invention is preferably one using a white light source having a continuous emission spectrum, whereby a discontinuous (bright line) light source is used. Rainbow unevenness can be reduced more effectively. This is due to the reason similar to this reason, with the reason described in [0015] to [0027] of Patent No. 4888853 ([0029] to [0041] of US2012 / 0229732). The contents described in these publications are incorporated herein.
The liquid crystal display device preferably includes the polarizing plate of the present invention and a liquid crystal display element. Here, the liquid crystal display element is typically a liquid crystal panel having a liquid crystal cell in which liquid crystal is sealed between upper and lower substrates and displaying an image by changing the alignment state of the liquid crystal by applying a voltage. The polarizing plate of the present invention can be applied to various known displays such as a display panel, a CRT display, and an organic EL display. Thus, when the polarizing plate which has a polyester film of this invention with high retardation is applied to a liquid crystal display element, the curvature of a liquid crystal display element can be prevented.

Here, the rainbow-like color spots are caused by the retardation of the polyester film having a high retardation and the emission spectrum of the backlight light source. Conventionally, a fluorescent tube such as a cold cathode tube or a hot cathode tube is used as a backlight source of a liquid crystal display device. The spectral distribution of a fluorescent lamp such as a cold cathode tube or a hot cathode tube shows an emission spectrum having a plurality of peaks, and these discontinuous emission spectra are combined to obtain a white light source. When light passes through a film having a high retardation, the transmitted light intensity varies depending on the wavelength. For this reason, when the backlight light source has a discontinuous emission spectrum, only a specific wavelength is strongly transmitted, and a rainbow-like color spot is generated.

When the image display device is a liquid crystal display device, it is preferable to include a backlight light source and a liquid crystal cell disposed between two polarizing plates as constituent members. Moreover, you may have suitably other structures other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film etc. suitably.

The configuration of the backlight may be an edge light method using a light guide plate, a reflection plate, or the like, or a direct type, but in the present invention, white is used as the backlight light source of the liquid crystal display device. It is preferable to use a light emitting diode (white LED) from the viewpoint of improving rainbow unevenness. In the present invention, the white LED is an element that emits white by combining a phosphor with a phosphor system, that is, a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor. Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. In particular, white light-emitting diodes, which are composed of light-emitting elements that combine blue light-emitting diodes using compound semiconductors with yttrium, aluminum, and garnet-based yellow phosphors, have a continuous and broad emission spectrum and are also efficient in light emission. Since it is excellent, it is suitable as a backlight light source of the image display device of the present invention. Here, the continuous emission spectrum means that there is no wavelength at which the light intensity becomes zero at least in the visible light region. Further, since the white LED with low power consumption can be widely used according to the present invention, an effect of energy saving can be achieved.
The mechanism by which the occurrence of rainbow-like color spots is suppressed by the above embodiment is described in International Publication No. WO2011 / 162198, and the contents of this publication are incorporated in the present invention.

When the image display device of the present invention is a liquid crystal display device, the arrangement of the polarizing plate of the present invention is not particularly limited. The polarizing plate of the present invention is preferably used as a polarizing plate for the viewing side in a liquid crystal display device.
The arrangement of the polyester film of the present invention having a high retardation in the in-plane direction is not particularly limited, but is arranged on the polarizing plate arranged on the incident light side (light source side), the liquid crystal cell, and the outgoing light side (viewing side). In the case of a liquid crystal display device provided with a polarizing plate, the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side, or the polarizer on the outgoing light side of the polarizing plate arranged on the outgoing light side The protective film is preferably the polyester film of the present invention having a high in-plane retardation. A particularly preferred embodiment is an embodiment in which the polarizer protective film on the exit light side of the polarizing plate arranged on the exit light side is the polyester film of the present invention having a high retardation in the in-plane direction. When a polyester film having a high retardation in the in-plane direction is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed. Since the polyester film of the present invention having a high retardation in the in-plane direction is preferably used in a place where no polarizing property is required, it is preferably used as a protective film for the polarizing plate at such a specific position.

The liquid crystal cell of the liquid crystal display device preferably has a liquid crystal layer and two glass substrates provided on both sides of the liquid crystal layer. The thickness of the glass substrate is preferably 0.5 mm or less, more preferably 0.4 mm or less, and particularly preferably 0.3 mm or less.
The liquid crystal cell of the liquid crystal display device is preferably IPS mode, VA mode, or FFS mode.

Hereinafter, the features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Example 1]
<Synthesis of raw material polyester>
(Raw material polyester 1)
As shown below, by directly reacting terephthalic acid and ethylene glycol to distill off water, esterify, and then use a direct esterification method in which polycondensation is performed under reduced pressure, raw polyester 1 ( Sb catalyst system PET) was obtained.

(1) Esterification reaction In a first esterification reactor, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol are mixed over 90 minutes to form a slurry, and continuously at a flow rate of 3800 kg / h. It supplied to the 1st esterification reaction tank. Further, an ethylene glycol solution of antimony trioxide was continuously supplied, and the reaction was carried out at a reaction vessel temperature of 250 ° C. with stirring and an average residence time of about 4.3 hours. At this time, antimony trioxide was continuously added so that the amount of Sb added was 150 ppm in terms of element.

The reaction product was transferred to a second esterification reaction vessel, and reacted with stirring at a temperature in the reaction vessel of 250 ° C. and an average residence time of 1.2 hours. To the second esterification reaction tank, an ethylene glycol solution of magnesium acetate and an ethylene glycol solution of trimethyl phosphate are continuously supplied so that the added amount of Mg and the added amount of P are 65 ppm and 35 ppm in terms of element, respectively. did.

(2) the polycondensation reaction above-obtained esterification reaction product supplied to the first polycondensation reaction vessel continuously stirring, the reaction temperature 270 ° C., the reaction vessel pressure 20 torr (2.67 × 10 ^{- 3} MPa) and polycondensation with an average residence time of about 1.8 hours.

Further, it was transferred to the second double condensation reaction tank, and while stirring in this reaction tank, the reaction tank temperature was 276 ° C., the reaction tank pressure was 5 torr (6.67 × 10 ⁻⁴ MPa), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions.

Subsequently, it was further transferred to the third triple condensation reaction tank, in which the temperature in the reaction tank was 278 ° C., the pressure in the reaction tank was 1.5 torr (2.0 × 10 ⁻⁴ MPa), and the residence time was 1.5 hours. The reaction product (polyethylene terephthalate (PET)) was obtained by reaction (polycondensation) under the following conditions.

Next, the obtained reaction product was discharged into cold water in a strand shape and immediately cut to prepare polyester pellets (cross section: major axis: about 4 mm, minor axis: about 2 mm, length: about 3 mm).

The obtained polymer had IV = 0.63. This polymer was designated as raw material polyester 1 (hereinafter abbreviated as PET1).

(Raw material polyester 2)
10 parts by weight of the dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazin-4-one)), 90 parts by weight of PET1 (IV = 0.63) Were mixed and pelletized using a kneading extruder in the same manner as the production of PET 1 to obtain a raw material polyester 2 containing an ultraviolet absorber (hereinafter abbreviated as PET 2).

<Manufacture of polyester film>
-Film forming process-
The raw material polyester 1 (PET1) was dried to a moisture content of 20 ppm or less and then charged into the hopper 1 of a single-screw kneading extruder 1 having a diameter of 50 mm. The raw material polyester 1 was melted at 300 ° C. and extruded from a die through a gear pump and a filter (pore diameter: 20 μm) under the following extrusion conditions.
The molten resin was extruded from the die under the conditions that the pressure fluctuation was 1% and the temperature distribution of the molten resin was 2%. Specifically, the back pressure was increased by 1% with respect to the average pressure in the barrel of the extruder, and the piping temperature of the extruder was heated at a temperature 2% higher than the average temperature in the barrel of the extruder.
The molten resin extruded from the die was extruded onto a cooling cast drum set at a temperature of 25 ° C., and was brought into close contact with the cooling cast drum using an electrostatic application method. It peeled using the peeling roll arrange | positioned facing the cooling cast drum, and the unstretched polyester film 1 was obtained.

The obtained unstretched polyester film 1 had an intrinsic viscosity IV = 0.62, a refractive index in the longitudinal direction of 1.573, and a crystallinity of 0.2%.

In IV, the unstretched polyester film 1 was dissolved in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent, and from the solution viscosity at 25 ° C. in the mixed solvent. Asked.
The refractive index of the unstretched polyester film was measured by the following method.
Using two polarizing plates, the orientation axis direction of the unstretched polyester film was determined, and a 4 cm × 2 cm rectangle was cut out so that the orientation axis directions were perpendicular to each other, and used as a measurement sample. With respect to this sample, the biaxial refractive index (Nx, Ny) perpendicular to each other and the refractive index (Nz) in the thickness direction were determined by an Abbe refractometer (NAGO-4T manufactured by Atago Co., Ltd., measurement wavelength 589 nm).
The crystallinity of the unstretched polyester film was measured by the following method.
The crystallinity can be calculated from the density of the film. That is, the density X (g / ^cm 3) of the film density at a crystallinity of ^{0% Y = 1.335g / cm 3} , using density Z = 1.501g / cm ³ at 100% crystalline below The crystallinity (%) can be derived from the calculation formula.
Crystallinity = {Z × (XY)} / {X × (ZY)} × 100
The density was measured according to JIS K7112.

-Transverse stretching process-
The unstretched polyester film 1 was guided to a tenter (lateral stretching machine), and was stretched laterally by the following method and conditions while gripping a position 15 mm away from both ends of the film in the width direction with a clip.

(Preheating part)
The preheating temperature was set to 90 ° C., and the hot air blown from the hot air nozzle was heated to a temperature at which stretching was possible.

(Extension part)
The preheated unstretched polyester film 1 was transversely stretched in the TD direction using a tenter in the width direction under the following conditions.
This tenter is an inner return type similar to that of WO2008 / 035762. The clips on the endless rails on both sides pass through the return rail chamber after releasing the film, and then grip the film again. A clip on the return rail side that does not hold the film is run in a return rail chamber where cold air of 22 ° C. is supplied at 250 m ³ / min, and returns at the same amount (250 m ³ / min) as the supply amount on each side at the same time. The rail chamber was evacuated. The clip has a structure shown in FIG. 3 so that the hot air blown from the hot air nozzle does not hit, and a cover that blocks air with a clearance of 15 mm between the film and the cover is provided. Even if there is a cover that blocks the wind, even if the return rail chamber itself is sufficiently cooled, a cover is provided on the clip that runs on the return rail so that the clip is not directly exposed to cold air. Fully, the clip is cooled. As described above, the temperature of the clip when gripping the film was 56 ° C. as described in Table 1 below. Here, the temperature of the clip when gripping the film was measured by the following method.
The temperature of the clip when gripping the film was measured by emergency stopping the running clip and directly sandwiching the thermocouple between the clips just before the grip within 30 seconds after stopping.
Further, the film film surface temperature at the start of stretching was controlled as described in Table 1 as the film surface temperature at the start of stretching or the stretched film temperature. This was done by adjusting the output by installing a panel heater at a point where the horizontal stretching zone was sufficiently divided in the conveying direction. The film surface temperature at the start of stretching was measured directly on the surface of the film using a thermocouple. As a result, the difference between the film surface temperature at the start of stretching and the clip temperature during gripping was controlled to be 32 ° C.
-Transverse stretching temperature (average temperature during transverse stretching): 90 ° C
・ Horizontal stretch ratio: 4.3 times

(Heat fixing part)
Next, a heat setting treatment was performed while controlling the film surface temperature of the polyester film within the following range.
<Condition>
・ Heat setting temperature: 180 ℃
・ Heat setting time: 15 seconds

(Heat relaxation part)
The polyester film after heat setting was heated to the following temperature to relax the film.
-Thermal relaxation temperature: 170 ° C
-Thermal relaxation rate: TD direction (film width direction) 2%

(Cooling section)
Next, the polyester film after heat relaxation was cooled at a cooling temperature of 50 ° C. The cooling temperature means the film surface temperature of the film. Actually, cooling was performed by applying cold air of 50 ° C. to the polyester film.

(Open film)
The distance between the pair of rails when the clip opens the film was increased by 1.5% with respect to the shortest distance between the pair of rails in the process downstream of the transverse stretching process in the tenter.
Further, by cooling in the return rail chamber described above, the temperature of the clip when the film was opened was controlled to 59 ° C. as described in Table 1 below. Here, the temperature of the clip when the film was opened was measured by the following method.
The temperature of the clip when the film was opened was measured by emergency stopping the running clip and directly inserting the thermocouple into the clip immediately after opening within 30 seconds after stopping.

(Recovery of film)
After opening the film, both ends of the polyester film were trimmed by 165 mm. In addition, the part (clip holding part) where the clip was holding the film remained in the polyester film after trimming. The distance from the film edge after trimming to the clip gripping part was 150 mm. From the collected film, the clip gripping portion can be visually identified as a portion having an uneven trace of the film generated when gripping the clip.
Then, after extruding (knurling) with a width of 10 mm at both ends, it was wound up 3000 m with a tension of 18 kg / m.
As described above, the polyester film of Example 1 having a thickness of 65 μm was manufactured.

[Example 2]
In Example 1, the heating temperature in the heat setting part was changed, and the film surface temperature of the polyester film, that is, the heat setting temperature was changed to 225 ° C. Thereby, the temperature of the clip when gripping the film was 64 ° C., the clip temperature when opening the film was 65 ° C., and the difference between the film surface temperature at the start of stretching and the clip temperature during gripping was 24 ° C.
Otherwise, the polyester film of Example 2 was produced in the same manner as Example 1.

[Examples 3 and 4]
In Example 1, the temperature and air volume of the cool air applied to the clip in the return rail chamber were changed as shown in Table 1 below, and the clip cover was removed. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Otherwise, the polyester films of Examples 3 and 4 were produced in the same manner as in Example 1.

[Example 5]
In Example 1, the film surface temperature at the start of stretching and the temperature and air volume of the cool air applied to the clip in the return rail chamber were changed as shown in Table 1 below, and the clip cover was removed. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Others were carried out similarly to Example 1, and manufactured the polyester film of Example 5.

[Examples 6 and 7]
In Example 1, the distance between the pair of rails when the clip opens the film with respect to the shortest part of the distance between the pair of rails in each step downstream of the transverse stretching step in the tenter is shown in Table 1 below. Changed as described in.
Otherwise, the polyester films of Examples 6 and 7 were produced in the same manner as in Example 1.

[Example 8]
In Example 1, the temperature and air volume of the cool air applied to the clip in the return rail chamber were changed as shown in Table 1 below. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Others were carried out similarly to Example 1, and manufactured the polyester film of Example 8.

[Examples 9 and 10]
In Example 1, the thickness of the unstretched polyester film was adjusted so that the film thickness after lateral stretching was as shown in Table 1 below without changing the lateral stretching ratio.
Otherwise, the polyester films of Examples 9 and 10 were produced in the same manner as in Example 1.

[Example 11]
-Film forming process-
After drying 90 parts by mass of the raw material polyester 1 (PET1) and 10 parts by mass of the raw material polyester 2 (PET2) containing an ultraviolet absorber to a moisture content of 20 ppm or less, the hopper 1 of the uniaxial kneading extruder 1 having a diameter of 50 mm is used. And melted at 300 ° C. with the extruder 1. Extrusion was performed from a die through a gear pump and a filter (pore diameter: 20 μm) under the following extrusion conditions.
The molten resin was extruded from the die under the conditions that the pressure fluctuation was 1% and the temperature distribution of the molten resin was 2%. Specifically, the back pressure was increased by 1% with respect to the average pressure in the barrel of the extruder, and the piping temperature of the extruder was heated at a temperature 2% higher than the average temperature in the barrel of the extruder.
The molten resin extruded from the die was extruded onto a cooling cast drum set at a temperature of 25 ° C., and was brought into close contact with the cooling cast drum using an electrostatic application method. It peeled off using the peeling roll arrange | positioned facing the cooling cast drum, and the unstretched polyester film 2 was obtained.
The obtained unstretched polyester film 2 had an intrinsic viscosity IV = 0.61, a refractive index in the longitudinal direction of 1.574, and a crystallinity of 0.1%.

The obtained unstretched polyester film 2 was horizontally stretched under the same conditions as in Example 1 to produce a polyester film of Example 11 having a thickness of 65 μm.

[Example 12]
-Film forming process-
After drying 90 parts by mass of the raw material polyester 1 (PET1) and 10 parts by mass of the raw material polyester 2 (PET2) containing an ultraviolet absorber to a moisture content of 20 ppm or less, the hopper 1 of the uniaxial kneading extruder 1 having a diameter of 50 mm is used. And melted to 300 ° C. with the extruder 1 (intermediate layer II layer). Moreover, after drying PET1 to a water content of 20 ppm or less, it was put into a hopper 2 of a single screw kneading extruder 2 having a diameter of 30 mm and melted at 300 ° C. by the extruder 2 (outer layer I layer, outer layer III layer). After these two types of polymers are respectively passed through a gear pump and a filter (pore diameter 20 μm), the polymer extruded from the extruder 1 in the two-type three-layer confluence block is transferred to the intermediate layer (II layer) from the extruder 2. The extruded polymer was laminated so as to be outer layers (I layer and III layer), and extruded from a die into a sheet.
The molten resin was extruded from the die under the conditions that the pressure fluctuation was 1% and the temperature distribution of the molten resin was 2%. Specifically, the back pressure was increased by 1% with respect to the average pressure in the barrel of the extruder, and the piping temperature of the extruder was heated at a temperature 2% higher than the average temperature in the barrel of the extruder.
The molten resin extruded from the die was extruded onto a cooling cast drum set at a temperature of 25 ° C., and was brought into close contact with the cooling cast drum using an electrostatic application method. It peeled off using the peeling roll arrange | positioned facing the cooling cast drum, and the unstretched polyester film 3 was obtained. At this time, the discharge amount of each extruder was adjusted so that the ratio of the thicknesses of the I layer, the II layer, and the III layer was 10:80:10.
The obtained unstretched polyester film 3 had an intrinsic viscosity IV = 0.61, a refractive index in the longitudinal direction of 1.574, and a crystallinity of 0.2%. In addition, the intrinsic viscosity, the refractive index in the longitudinal direction, and the crystallinity of the unstretched polyester film 3 that is a three-layer laminate can also be measured by the same method as in Example 1.

The obtained unstretched polyester film 3 was horizontally stretched under the same conditions as in Example 1 to produce a polyester film of Example 12 having a thickness of 65 μm.

[Comparative Example 1]
In Example 1, the film surface temperature at the start of stretching was changed as shown in Table 1 below, and the temperature of the clip in the return rail chamber was changed as shown in Table 1 below without applying cold air to the clip in the return rail chamber. Changed to, and removed the clip cover. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Further, the distance between the pair of rails when the clip opens the film is not extended with respect to the shortest part of the distance between the pair of rails in each process downstream of the transverse stretching process in the tenter.
Others were carried out similarly to Example 1, and manufactured the polyester film of the comparative example 1. FIG.

[Comparative Example 2]
In Example 1, the film surface temperature at the start of stretching was changed as shown in Table 1 below, and cold air was not applied to the clip in the return rail chamber, and the temperature of the clip in the return rail chamber was as shown in Table 1 below. Changed to, and removed the clip cover. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Others were carried out similarly to Example 1, and manufactured the polyester film of the comparative example 2. FIG.

[Comparative Example 3]
In Example 1, the film surface temperature at the start of stretching and the temperature and air volume of the cool air applied to the clip in the return rail chamber were changed as shown in Table 1 below, and the clip cover was removed. Thereby, the temperature of the clip at the time of gripping the film, the clip temperature at the time of opening the film, and the difference between the film surface temperature at the start of stretching and the clip temperature at the time of grip were as shown in Table 1 below.
Others were carried out similarly to Example 1, and manufactured the polyester film of the comparative example 3. FIG.

[Evaluation]
(Re, Rth, Re / Rth)
Re and Rth were measured by the method described in JP-A-2012-256057, [0054] to [0055] for each example and comparative example film, and the values of Re, Rth, and Re / Rth were determined. It described in Table 1.

(MD thickness unevenness)
About the polyester film of each Example and the comparative example, the thickness in the inner side in the 200 mm film width direction from the position (clip holding part) currently hold | gripped with the clip was measured 10m. In addition, the position of 200 mm from the clip holding part which measured film thickness is equivalent to the position of 50 mm from the edge part of the polyester film of each Example and a comparative example.
MD direction thickness nonuniformity was calculated | required according to the following formula | equation.
(MD thickness unevenness) = {(maximum thickness) − (minimum thickness)} / (average thickness) × 100%
The results evaluated according to the following criteria are shown in Table 1 below.
It is practically necessary that the MD thickness unevenness at the 200 mm position from the clip is 10% or less, the MD thickness unevenness at the 200 mm position from the clip is preferably 8% or less, and the MD thickness thickness at the 200 mm position from the clip. The unevenness is more preferably 5% or less.

(Ear break)
The film of each Example and Comparative Example was formed into a film of 1000 m or more, and the number of breaks of the film ear (position within 165 mm from the end of the film) at the clip opening part was measured.
The term “break” refers to a scratch having a length of 50 mm or more and penetrating in the film thickness direction.
The results evaluated according to the following criteria are shown in Table 1 below.
A: No ear breakage of 1000 m or more.
B: Ear breaks 1 to 5 times at 1000 m.
C: There are 6 to 10 ear breaks at 1000 m.
D: Ear breaks 11 times or more at 1000 m.

From Table 1 above, it was found that when the method for producing a polyester film of the present invention was used, there was little thickness unevenness in the film transport direction in the vicinity of the clip, and the film ears were not easily broken when released from the clip. That is, it has been found that the method for producing a polyester film of the present invention can improve poor film detachment when the clip is opened and stretching unevenness in the vicinity of the clip when the unstretched polyester film is horizontally stretched with a tenter.
On the other hand, from Comparative Examples 1 and 2, when the temperature of the clip when gripping an unstretched polyester film with the clip and the temperature of the clip when releasing the film after transverse stretching from the clip are both above the scope of the present invention It was found that the thickness unevenness in the film transport direction in the vicinity of the clip increased, and the film ears were easily broken when released from the clip.
From Comparative Example 3, it was found that when the temperature of the clip when the film after transverse stretching was released from the clip exceeded the range of the present invention, breakage of the ear portion of the film at the time of release from the clip was likely to occur. .
It should be noted that the refractive index in the longitudinal direction of the polyester film produced by the method for producing a polyester film of the present invention is 1.590 or less, and the crystallinity exceeds 5%. It confirmed by the method similar to 3.
Moreover, it confirmed that the polyester film manufactured with the manufacturing method of the polyester film of this invention was uniaxially oriented with the following method.
That is, the refractive index in the longitudinal direction, the width direction, and the thickness direction is measured with an Abbe refractometer, the refractive index in the longitudinal direction is 1.590 or less, the refractive index in the width direction is sufficiently large, and the thickness By confirming that the refractive index in the direction was sufficiently smaller than that, it was confirmed that the polyester film was uniaxially oriented.

[Examples 101 to 112, Comparative Examples 101 to 103]
(Production of polarizing plate and liquid crystal display and evaluation of rainbow unevenness)
Using the polyester films of the examples and comparative examples, polarizing plates of the examples and comparative examples and liquid crystal display devices of the examples and comparative examples were produced and evaluated.

According to [0225] of JP2011-59488A, a polarizer containing PVA was prepared.

The following cellulose acylate film was immersed in an alkaline aqueous solution and saponified according to [0275] of Japanese Patent No. 4438270 ([0393] of US2007 / 0178252, the contents described in these publications are incorporated in the present specification). .

Preparation of a cellulose acylate film in the same manner as [0199] to [0202] of Japanese Patent No. 4713143 ([0412] to [0416] of US2008 / 0158483, the contents described in these publications are incorporated herein) did.

The above polarizer is sandwiched between the polyester film of each example and comparative example and the saponified cellulose acylate, and an aqueous PVA solution (fully saponified PVA5) is placed between the polarizer / polyester and between the cellulose acylate / polarizer. % Aqueous solution) was applied, these were pressure-bonded with a nip roll and bonded together, and then dried at 70 ° C. for 10 minutes to obtain a polarizing plate.
The obtained polarizing plate was made into the polarizing plate of each Example and a comparative example.

The obtained two pairs of polarizing plates have the polyester film outside with respect to the liquid crystal cell, the absorption axis of the polarizer is orthogonally arranged, and a continuous light source (white LED) or a discontinuous light source (cold cathode tube) as a backlight. It was incorporated in a liquid crystal display device, and the light transmittance was adjusted to 50%.
The obtained liquid crystal display device was used as the image display device of each example and comparative example.

Using a continuous light source (white LED) and a discontinuous light source (cold cathode tube) from one side, light was incident, and the number of rainbows generated visually through polarized sunglasses from the opposite side was counted to evaluate rainbow unevenness.
In the image display device of each example, rainbow unevenness did not occur at normal humidity of 25 degrees and relative humidity of 50%.
Note that the rainbow unevenness was observed both from the normal direction of the polarizing plate and from the oblique direction (45 ° from the normal line).

DESCRIPTION OF SYMBOLS 1 Film 2 Clip 2a Clip upper part 2b Clip lower part 3 Cover 4 Clearance 41 Film moving direction 42 Tenter oven 43 Clip cooling tank 44 Clip wheel 45 Film moving direction 46 Tenter oven 47 Clip cooling tank 48 Clip wheel

Claims (17)

1. Using a tenter type stretching device having a clip that runs along a pair of endless rails installed on both sides of the film conveyance path, the unstretched polyester film is held by the clip until the thickness becomes 150 μm or less. Stretching step;
   Opening the polyester film after the transverse stretching from the clip,
   A method for producing a polyester film, wherein the temperature of the clip when the unstretched polyester film is held by the clip and the temperature of the clip when the polyester film after transverse stretching is released from the clip are both controlled to 80 ° C. or less. .
2. 2. The polyester film according to claim 1, wherein a film surface temperature of the unstretched polyester film at the start of the transverse stretching is higher than a clip temperature when the unstretched polyester film is held by the clip. Production method.
3. The distance between the pair of rails when releasing the laterally stretched polyester film from the clip is increased in a range of 0.1 to 5% with respect to the shortest distance between the pair of rails after the lateral stretching zone. The manufacturing method of the polyester film of Claim 1 or 2.
4. The heat setting step of heating the polyester film after the transverse stretching to the maximum temperature in the tenter before releasing the polyester film after the transverse stretching from the clip. A method for producing a polyester film.
5. The method for producing a polyester film according to claim 4, comprising a step of cooling the heat-fixed polyester film before releasing the heat-fixed polyester film from the clip.
6. The refractive index in the longitudinal direction of the unstretched polyester film is 1.590 or less, and
   The method for producing a polyester film according to any one of claims 1 to 5, wherein the crystallinity of the unstretched polyester film is 5% or less.
7. The tenter includes a return rail to which cold air of 40 ° C. or less is supplied at an air volume of 50 m ³ / min or more,
   The method for producing a polyester film according to any one of claims 1 to 6, wherein the clip that does not hold the film is run along the return rail.
8. The method for producing a polyester film according to any one of claims 1 to 7, wherein the clip is covered with a cover that blocks wind.
9. The method for producing a polyester film according to any one of claims 1 to 8, wherein the unstretched polyester film comprises a polyethylene terephthalate resin as a main component.
10. A polyester film produced by the method for producing a polyester film according to any one of claims 1 to 9.
11. The polyester film includes a clip gripping part gripped by the clip,
    The polyester film according to claim 10, wherein the thickness unevenness in the longitudinal direction at a position away from the clip gripping part by 200 mm or more in the width direction is 10% or less.
12. The polyester film according to claim 10 or 11, wherein the thickness unevenness in the longitudinal direction at a position away from the end of the polyester film by 50 mm or more in the width direction is 10% or less.
13. The film thickness is 20 to 150 μm,
    Retardation Re in the in-plane direction of the film is 3000 to 30000 nm,
    The retardation Rth in the thickness direction is 3000 to 30000 nm,
    The polyester film according to any one of claims 10 to 12, wherein Re / Rth is 0.5 to 2.5.
14. The polyester film according to any one of claims 10 to 13, which is uniaxially oriented.
15. The refractive index in the longitudinal direction of the polyester film is 1.590 or less, and
    The polyester film according to claim 14, wherein the crystallinity of the polyester film exceeds 5%.
16. A polarizing plate comprising a polarizer and the polyester film according to any one of claims 10 to 15.
17. An image display device comprising the polyester film according to any one of claims 10 to 15 or the polarizing plate according to claim 16.

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