JP2015225129A - Polyester film and method for manufacturing the same, polarizer, image display device, hard coat film and touch panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film less in scratches, less in cracks and fractures when conveyed and capable of suppressing the occurrence of rainbow unevenness when incorporated into a liquid crystal display device.SOLUTION: The polyester film has a thickness of 10-150 μm, Re and Rth of 3000-30000 nm, Re/Rth of more than 0.8 and 2.5 or less and 0.6% or less of a heat shrinkage rate in a direction orthogonal to an orientation direction. When a polyester film obtained by unwinding the outermost layer of the polyester film wound in a roll to be cut into a square having a side of 500 mm is placed on a flat surface, the float of the polyester film is 1.8 mm or less. The method for manufacturing the polyester film is provided. Provided are the polarizer, image display device, hard coat film and touch panel using the polyester film.

Description

  The present invention relates to a polyester film that is suitably used as a liquid crystal film substrate or a touch panel member. More specifically, it is particularly suitable for use as an optical film application, particularly as a base material for liquid crystal displays, which eliminates film breakage in polarizing plate processing and coating processes, and preferably a uniaxially oriented polyester film and a method for producing the same, and this polyester The present invention relates to a polarizing plate, an image display device, a hard coat film and a touch panel using the film.

  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. Has been placed. 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.
Among them, in recent years, a uniaxially oriented polyester film is increasingly used as a base material for a liquid crystal display (such as a protective film for a polarizing plate) instead of the conventional biaxially oriented polyester film. For example, as a polarizing plate protective film with improved rainbow unevenness, rainbow unevenness is 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 film having the optical properties as described above is produced by uniaxially stretching at least an unstretched film while holding it with a clip using a tenter-type stretching device.

JP 2012-256014 A

When a film having a strong orientation in a uniaxial direction is used for a polarizer protective film, the rainbow unevenness is difficult to visually recognize, while the mechanical strength in the direction orthogonal to the orientation direction is remarkably lowered, and during the conveyance after stretching. There was a problem that it was easily broken when heat contracted. Actually, the uniaxially oriented polyester film mainly subjected to transverse stretching described in Patent Document 1 has low longitudinal breaking strength because the film is oriented only in the transverse direction, and the film breaks or breaks during transportation. Often.
Furthermore, as a result of studies by the present inventors, it has been found that a film having a strong orientation in a uniaxial direction has poor flatness and is easily scratched. When the polyester film is used for optical applications, it is preferable that the scratches are less likely to cause image failure.

  The problem to be solved by the present invention is to provide a polyester film and a method for producing the polyester film that have few scratches, few cracks and breaks during conveyance, and can suppress the occurrence of rainbow unevenness when incorporated in a liquid crystal display device. It is.

As a result of intensive studies by the inventor in order to solve the above problems, the film is thin and has a large Re / Rth ratio. As a result, it has been found that a polyester film with high practicality capable of suppressing generation of rainbow unevenness when incorporated in a liquid crystal display device with few scratches and cracks or breakage during transportation can be obtained.
The present invention, which is a specific means for achieving the above object, is as follows.

式Ｂ１、Ｂ２およびＢ３中、
ｘは延伸機の入口の幅を表し、単位はｍｍであり；
ｘ'は延伸中の各位置でのポリエステルフィルムの幅を表し、単位はｍｍであり；
ｘ_maxは延伸中のポリエステルフィルムの最大幅を表し、単位はｍｍであり；
ｙは延伸機の入口での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ'は延伸中の各位置での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ_minは延伸中の各レール上におけるクリップ間の距離の最小値を表し、単位はｍｍである。
［４］ フィルムを把持しながら一対のレール間を走行する複数のクリップを有する延伸機を用いて、各レール上において前述のクリップ間の距離を縮めることによるフィルム搬送方向への収縮と、前述のクリップが走行する一対のレール間の距離を広げることによるフィルム搬送方向に直交する方向への延伸とを同時に行う工程を含み、
前述のフィルム搬送方向への収縮率とフィルム搬送方向に直交する方向への延伸倍率が下記式Ｂ１の関係を延伸中常に満たし、かつ下記式Ｂ２および式Ｂ３を満たすポリエステルフィルムの製造方法であって、
前述のポリエステルフィルムの厚みが１０〜１５０μｍであり、
前述のポリエステルフィルムの配向方向と直交する方向の熱収縮率が０．６％以下であるポリエステルフィルムの製造方法；

式Ｂ１、Ｂ２およびＢ３中、
ｘは延伸機の入口の幅を表し、単位はｍｍであり；
ｘ'は延伸中の各位置でのポリエステルフィルムの幅を表し、単位はｍｍであり；
ｘ_maxは延伸中のポリエステルフィルムの最大幅を表し、単位はｍｍであり；
ｙは延伸機の入口での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ'は延伸中の各位置での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ_minは延伸中の各レール上におけるクリップ間の距離の最小値を表し、単位はｍｍである。
［５］ ［３］または［４］に記載のポリエステルフィルムの製造方法は、フィルム搬送方向への収縮と前述のフィルム搬送方向に直交する方向への延伸とを同時に延伸平均温度Ｔ１で行った後、熱固定温度Ｔ２≧Ｔ１＋３０℃にて加熱する熱固定工程を含むことが好ましい；
ただし、Ｔ１およびＴ２の単位は℃である。
［６］ ［５］に記載のポリエステルフィルムの製造方法は、熱固定を、フィルム搬送方向への収縮を行いながら行うことが好ましい。
［７］ ［５］または［６］に記載のポリエステルフィルムの製造方法は、熱固定温度Ｔ２がＴ１＋５０℃を超えることが好ましい。
［８］ 偏光子と、［１］または［２］に記載のポリエステルフィルムとを含む偏光板。
［９］ ［１］または［２］に記載のポリエステルフィルム、または、［８］に記載の偏光板を備えることを特徴とする画像表示装置。
［１０］ ［１］または［２］に記載のポリエステルフィルムを含むハードコートフィルム。
［１１］ ［１］または［２］に記載のポリエステルフィルム、［８］に記載の偏光板、または［１０］に記載のハードコートフィルムを備えるタッチパネル。 [1] The thickness is 10 to 150 μm,
In-plane direction retardation Re and thickness direction retardation Rth are 3000 to 30000 nm,
Re / Rth exceeds 0.8 and is 2.5 or less,
It is a polyester film having a heat shrinkage rate of 0.6% or less in the direction orthogonal to the orientation direction,
A polyester film in which the polyester film floats up to 1.8 mm or less when the polyester film wound up in a roll shape is unrolled and placed on a flat surface.
[2] The polyester film according to [1] preferably has a thermal shrinkage unevenness of 0.4% or less in a direction orthogonal to the orientation direction represented by the following formula A.
Formula A:
(Unevenness of thermal shrinkage in the direction orthogonal to the orientation direction) = (Difference between the maximum value and the minimum value of the thermal shrinkage rate in the direction perpendicular to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) / (Average value of thermal shrinkage in the direction orthogonal to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) × 100%
[3] Using a stretching machine having a plurality of clips that run between a pair of rails while gripping the film, shrinking in the film transport direction by reducing the distance between the clips on each rail, Including simultaneously performing stretching in a direction perpendicular to the film transport direction by widening the distance between the pair of rails on which the clip travels,
A method for producing a polyester film in which the shrinkage ratio in the film transport direction and the stretch ratio in the direction perpendicular to the film transport direction always satisfy the following formula B1 during stretching and satisfy the following formulas B2 and B3;

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm.
[4] Using a stretching machine having a plurality of clips running between a pair of rails while gripping the film, shrinking in the film transport direction by reducing the distance between the clips on each rail, Including simultaneously performing stretching in a direction perpendicular to the film transport direction by widening the distance between the pair of rails on which the clip travels,
A method for producing a polyester film in which the shrinkage ratio in the film transport direction and the stretch ratio in the direction perpendicular to the film transport direction always satisfy the relationship of the following formula B1 during stretching and satisfy the following formulas B2 and B3: ,
The polyester film has a thickness of 10 to 150 μm,
A method for producing a polyester film, wherein the thermal shrinkage in the direction perpendicular to the orientation direction of the polyester film is 0.6% or less;

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm.
[5] In the method for producing a polyester film according to [3] or [4], the shrinkage in the film transport direction and the stretching in the direction perpendicular to the film transport direction are simultaneously performed at the stretch average temperature T1. It preferably includes a heat setting step of heating at a heat setting temperature T2 ≧ T1 + 30 ° C .;
However, the unit of T1 and T2 is ° C.
[6] In the method for producing a polyester film according to [5], it is preferable to perform heat setting while shrinking in the film transport direction.
[7] In the method for producing a polyester film according to [5] or [6], it is preferable that the heat setting temperature T2 exceeds T1 + 50 ° C.
[8] A polarizing plate comprising a polarizer and the polyester film according to [1] or [2].
[9] An image display device comprising the polyester film according to [1] or [2] or the polarizing plate according to [8].
[10] A hard coat film comprising the polyester film according to [1] or [2].
[11] A touch panel comprising the polyester film according to [1] or [2], the polarizing plate according to [8], or the hard coat film according to [10].

According to the present invention, it is possible to provide a polyester film that has few scratches, has few cracks and breaks during conveyance, and can suppress the occurrence of rainbow unevenness when incorporated in a liquid crystal display device.
According to this invention, the manufacturing method of this polyester film can be provided. According to the present invention, a polarizing plate, an image display device, a hard coat film and a touch panel using this polyester film can be provided.

Hereinafter, the polyester film and the production method thereof, the polarizing plate, the image display device, the hard coat film and the touch panel of the present invention 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.
Moreover, although mentioned later in detail, a polyester film is normally obtained by conveying using a roll etc. and extending | stretching. At this time, the film conveyance direction is also referred to as MD (Machine Direction) direction. Moreover, the conveyance direction of a film is also called the longitudinal direction of a film. The film transport direction is also called the longitudinal direction, stretching in the film transport direction is called longitudinal stretching, and contraction in the film transport direction is also called longitudinal shrinkage.
The film width direction is a direction orthogonal to the longitudinal direction. In the film manufactured while transporting the film, the film width direction is also referred to as a direction orthogonal to the film transport direction, that is, a TD (Transverse Direction) direction. The direction orthogonal to the film transport direction is also referred to as the transverse direction, and stretching in the direction orthogonal to the film transport direction is also referred to as lateral stretching.

[Polyester film]
The polyester film of the present invention has a thickness of 10 to 150 μm, an in-plane direction retardation Re and a thickness direction retardation Rth of 3000 to 30000 nm, and Re / Rth of more than 0.8 and 2.5 or less. Yes, it is a polyester film having a heat shrinkage rate of 0.6% or less in the direction orthogonal to the orientation direction, and the polyester film cut out in a 500 mm square by unwinding the outermost layer of the polyester film wound up in a roll shape is flat. The polyester film float when placed on top is 1.8 mm or less.
With such a configuration, the polyester film of the present invention has few scratches, few cracks and breaks during conveyance, and can suppress the occurrence of rainbow unevenness when incorporated in a liquid crystal display device.
Hereinafter, the preferable aspect of the polyester film of this invention is demonstrated.

<Characteristics of polyester film>
(Film thickness)
The thickness of the polyester film of the present invention is 10 to 150 μm, preferably 20 to 150 μm, more preferably 30 to 130 μm, and still more preferably 35 to 110 μm or less. If it is 10 μm or less, the mechanical strength is low and it is easy to be broken during conveyance, and the practicality is low. If it is 150 micrometers or more, the thickness of a polarizing plate will become thick and it is unpreferable as a liquid crystal television and a touchscreen use by which thinness is calculated | required.

(Phase difference)
In-plane retardation Re and thickness-direction retardation Rth are 3000 to 30000 nm, and the Re / Rth ratio is more than 0.8 and 2.5 or less, so that it is oblique when used as a polarizer protective film. When observed from the direction, rainbow unevenness is not visible and good visibility can be obtained.
The polyester film of the present invention has an in-plane retardation Re of 3000 to 30000 nm, preferably 3500 to 25000 nm, and more preferably 4000 to 20000 nm. When Re is less than 3000 nm, rainbow unevenness hardly occurs on the screen when the 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 unevenness appears when large birefringence, specifically, light incident obliquely from a backlight light source on a polarizing plate having a polymer film having a Re of 500 nm or more and less than 3000 nm as a protective film is observed from the viewing side. 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 difficult to be visually recognized.

  The polyester film of the present invention has a thickness direction retardation Rth of 3000 to 30000 nm or less, preferably 3500 to 25000 nm, and more 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, rainbow unevenness hardly occurs on the screen when the panel is formed, 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 more than 0.8 and less than 2.5, more than 0.8 and less than 2.2. Is preferable, more than 0.8 and 2.0 or less is particularly preferable, and 0.9 to 2.0 is more particularly preferable. When Re / Rth exceeds 0.8, when the polyester film of the present invention is incorporated in a liquid crystal panel as a polarizing plate protective film, rainbow unevenness hardly occurs on the screen, which is preferable. In principle, it is difficult to make a film exceeding 2.5. Even if Re / Rth exceeds 2.5, the effect of reducing the viewing angle dependence of rainbow unevenness is only saturated.

Rainbow 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 because of the effect of reducing the 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.

  In addition, Nz value of a polyester film is represented by 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 (| Nx−Ny |) of the biaxial refractive index difference 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 should be adjusted according to the type of polyester resin used in the film, the amount of the polyester resin and additives described above, the addition of a retardation developer, the film thickness, the film stretching direction and the stretching ratio, etc. Can do.
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 extending | stretching method.

(MD thermal shrinkage in the direction orthogonal to the orientation direction)
The polyester film of the present invention has a heat shrinkage rate of 0.6% or less in a direction orthogonal to the orientation direction. When the thermal shrinkage rate in the direction orthogonal to the orientation direction is 0.6% or less, cracks and breaks during transportation due to thermal shrinkage that occurs during transportation are reduced, and preferably tearing in the TD direction due to thermal shrinkage that occurs during polarizing plate processing Can be suppressed. The heat shrinkage rate in the direction perpendicular to the orientation direction of the polyester film of the present invention is preferably the heat shrinkage rate in the direction perpendicular to the orientation direction after heating at 150 ° C. for 30 minutes.
In the present invention, the heat shrinkage rate (150 ° C., 30 minutes) in the longitudinal direction of the film after heating at 150 ° C. for 30 minutes is defined as follows.
Two reference lines are put in advance in a sample piece M of a polyester film cut in 30 mm in the TD direction and 120 mm in the MD direction so as to have an interval of 100 mm in the MD direction in advance. After the sample piece M is left in a heating oven at 150 ° C. for 30 minutes under no tension, the sample piece M is cooled to room temperature, and the interval between the two reference lines is measured. The interval after processing measured at this time is A [mm]. The numerical value [%] calculated by using the formula “100 × (100−A) / 100” from the interval 100 mm before the treatment and the interval Amm after the treatment is used as the MD thermal contraction rate (S ).
Hereinafter, the heat shrinkage rate (150 ° C., 30 minutes) is also simply referred to as the heat shrinkage rate.
The heat shrinkage rate in the direction orthogonal to the orientation direction of the polyester film of the present invention is an average value of the heat shrinkage rates in the direction perpendicular to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction.

  In the present invention, the film width direction is referred to as TD or TD direction, and the direction orthogonal to the film width direction is referred to as MD or MD direction. In addition, the heat shrinkage in the MD direction is also referred to as MD heat shrinkage, and the ratio is referred to as MD heat shrinkage rate. Therefore, the thermal contraction rate in the direction orthogonal to the film width direction is also expressed as MD thermal contraction rate.

(Unevenness of MD heat shrinkage in the width direction)
In the polyester film of the present invention, the MD thermal shrinkage unevenness in the width direction represented by the following formula A is 0.4% or less, and the difference in the amount of heat shrinkage in the width direction is reduced to suppress the tearing in the orientation direction. From the viewpoint of being possible, it is preferable.
Formula A:
(Unevenness of thermal shrinkage in the direction orthogonal to the orientation direction) = (Difference between the maximum value and the minimum value of the thermal shrinkage rate in the direction perpendicular to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) / (Average value of thermal shrinkage in the direction orthogonal to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) × 100%
The MD thermal contraction rate unevenness in the width direction is more preferably 0.3% or less, and most preferably 0.2% or less.

(Film flatness)
The polyester film of the present invention has a polyester film float of 1.8 mm or less when the polyester film wound up in a roll shape is unwound and placed on a flat surface. Hereinafter, the polyester film lift (maximum value of float) when the outermost layer of the polyester film wound up in a roll is unwound and the polyester film cut out in a square of 500 mm is placed on a flat surface. Also called sex. By making the flatness of the polyester film of the present invention 1.8 mm or less, the stress concentration applied to the film at the time of contact with the transport roll can be dispersed and tearing can be suppressed.
The polyester film of the present invention preferably has a flatness of 0 to 1.0 mm, and more preferably a flatness of 0 to 0.5 mm.
When determining the flatness, the time taken to measure the float of the polyester film is 30 minutes after unwinding the outermost layer of the polyester film wound up in a roll and placing the polyester film cut into a square of 500 mm on a flat surface. Is preferably less than 10 minutes, more preferably less than 10 minutes, and particularly preferably less than 5 minutes.
Moreover, it is preferable that the temperature when calculating | requiring planarity is 0-30 degreeC, It is more preferable that it is 10-28 degreeC, It is especially preferable that it is 15-25 degreeC.
Moreover, it is preferable that relative humidity when calculating | requiring planarity is 30 to 80%, It is more preferable that it is 40 to 70%, It is especially preferable that it is 50 to 60%.

(Film width)
The film width W is preferably 0.8 to 6.0 m, more preferably 1 to 5 m, particularly preferably 1 to 4 m, and particularly preferably 1 to 3 m.

(Film length)
The polyester film of the present invention preferably has a film length of 100 m or longer. Further, it is preferably wound in a roll form.
The film length is preferably 100 m or more, more preferably 300 m or more, and even more preferably 500 m or more.

(Refractive index, crystallinity)
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 5% or more, more preferably 20% or more, and still more preferably 30% or more.

<Polyester film material, layer structure, 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. In addition, the single layer film or the multilayer film may be subjected to surface treatment on both sides or one side, and this surface treatment includes corona treatment, plasma treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation. The surface may be modified by, for example, thin film formation by coating or vapor deposition of polymer or metal. 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.

(1-1) Polyester resin As the above-mentioned polyester resin, one having the composition of [0042] of WO2012 / 157762 is 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 in terms of cost and heat resistance, 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. It is also possible to use an oxycarboxylic acid such as p-oxybenzoic acid 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.

(1-2) Physical properties of polyester resin (1-2-1) 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. Is 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.

(1-2-2) Acetaldehyde content The polyester resin preferably has an acetaldehyde content of 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 above-mentioned Al-based catalyst, those described in [0013] to [0148] of WO2011 / 040161 ([0021] to [0123] of US2012 / 0183761) The contents described in these publications are incorporated in the present specification.
Although there is no restriction | limiting in particular as a method of superposing | polymerizing a polyester resin using the above-mentioned Al type catalyst, Specifically, [0091]-[0094] of WO2012 / 008488 ([0144] of US2013 / 0112271) To [0153]) can be polymerized 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 aforementioned Sb-based catalyst, those described in JP-A-2012-41519, [0050] and [0052] to [0054] can be used.
Although there is no restriction | limiting in particular as a method of superposing | polymerizing a polyester resin using the above-mentioned Sb type catalyst, Specifically, it can superpose | polymerize according to [0086]-[0087] of WO2012 / 157762.

(1-4) Additive:
It is also preferable to add a known additive to 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) Ultraviolet (UV) absorber:
The polyester film of the present invention can contain an ultraviolet absorber in order to prevent the liquid crystal or the like 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.

  Examples of the cyclic imino ester-based ultraviolet absorber include, but are not limited to, 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazine-4, for example. -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, -Cyclohexyl-3,1-benzoxazin-4-one, 2-p- (or m-) phthalimidophenyl-3,1-benzoxazin-4-one, N-phenyl-4- (3,1-benzoxazine -4-On-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-benzo Oxazin-4-one), 2,2′-ethylenebis (3,1-benzoxazin-4-one), 2,2′-tetramethylenebis (3,1-benzoxazin-4-one), 2, 2'-Decame Renbis (3,1-benzoxazin-4-one, 2,2 '-(1,4-phenylene) bis (4H-3,1-benzoxazin-4-one) [In addition, 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-on-2-yl) benzene, 1,3,5-tri (3,1-benzoxazin-4-on-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-dio 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′- Tylene bis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,6′-butylene bis (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-4 ON, 6,7′-methylenebis (2-methyl-4H, 3,1-benzoxazin-4-one), 6,7′-methylenebis (2-phenyl-4H, 3,1-benzoxazin-4-one) ) And the like.

  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 to be 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.

In addition, in the case of the polyester film of the present invention having a multilayer structure, the film having at least a three-layer structure is preferable, 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.
For these formulations, the master batch method described in [0050] to [0051] of WO2011 / 162198 can be used.

(1-4-2) Other additives In the polyester film of the present invention, other additives may be used. For example, those described in [0058] of WO2012 / 157762 can be used, and these The contents described in the publication are incorporated herein.

[Production method of polyester film]
There is no restriction | limiting in particular as a manufacturing method of the polyester film of this invention, The polyester film of this invention can be manufactured by a well-known method.
The polyester film of the present invention can be produced with high productivity by the first aspect and the second aspect of the following method for producing a polyester film of the present invention.

式Ｂ１、Ｂ２およびＢ３中、
ｘは延伸機の入口の幅を表し、単位はｍｍであり；
ｘ'は延伸中の各位置でのポリエステルフィルムの幅を表し、単位はｍｍであり；
ｘ_maxは延伸中のポリエステルフィルムの最大幅を表し、単位はｍｍであり；
ｙは延伸機の入口での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ'は延伸中の各位置での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ_minは延伸中の各レール上におけるクリップ間の距離の最小値を表し、単位はｍｍである。
以下、本発明のポリエステルフィルムの製造方法の好ましい態様について、説明する。 The first aspect of the polyester film manufacturing method of the present invention is to reduce the distance between the clips on each rail using a stretching machine having a plurality of clips that run between a pair of rails while gripping the film. Including the step of simultaneously contracting in the film transport direction and extending in the direction perpendicular to the film transport direction by widening the distance between the pair of rails on which the clip travels,
The shrinkage rate in the film transport direction and the stretching ratio in the direction orthogonal to the film transport direction always satisfy the relationship of the following formula B1 during stretching and satisfy the following formulas B2 and B3.
The second aspect of the method for producing a polyester film of the present invention is to reduce the distance between the clips on each rail using a stretching machine having a plurality of clips that run between a pair of rails while gripping the film. Including the step of simultaneously contracting in the film transport direction and extending in the direction perpendicular to the film transport direction by widening the distance between the pair of rails on which the clip travels,
A method for producing a polyester film in which the shrinkage ratio in the film transport direction and the stretch ratio in the direction perpendicular to the film transport direction always satisfy the relationship of the following formula B1 during stretching and satisfy the following formulas B2 and B3: ,
The polyester film has a thickness of 10 to 150 μm,
The heat shrinkage rate in the direction orthogonal to the orientation direction of the polyester film is 0.6% or less.

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm.
Hereinafter, the preferable aspect of the manufacturing method of the polyester film of this invention is demonstrated.

<Melting and 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. Detailed conditions can be carried out according to these publications with the aid of Patent Nos. 4926661 [0051] to [0052] (US2013 / 0100378 [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.

<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.

<Cast>
According to [0059] of JP-A-2009-269301, it is preferable to extrude the melt extruded from a die onto a casting drum and solidify by cooling to obtain an unstretched polyester film (raw fabric).
In the method for producing a polyester film 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 still more preferably 1.580 or less.
In the method for producing a polyester film 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 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.

<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 include functional layers that the polarizing plate may generally 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.

式Ｂ１、Ｂ２およびＢ３中、
ｘは延伸機の入口の幅を表し、単位はｍｍであり；
ｘ'は延伸中の各位置でのポリエステルフィルムの幅を表し、単位はｍｍであり；
ｘ_maxは延伸中のポリエステルフィルムの最大幅を表し、単位はｍｍであり；
ｙは延伸機の入口での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ'は延伸中の各位置での各レール上におけるクリップ間の距離を表し、単位はｍｍであり；
ｙ_minは延伸中の各レール上におけるクリップ間の距離の最小値を表し、単位はｍｍである。
本明細書中では、フィルムを把持しながら一対のレール間を走行する複数のクリップを有する延伸機を用いて、各レール上において前述のクリップ間の距離を縮めることによるフィルム搬送方向への収縮と、前述のクリップが走行する一対のレール間の距離を広げることによるフィルム搬送方向に直交する方向への延伸とを同時に行う工程のことを「横延伸および縦収縮」とも言う。
具体的には、本発明のポリエステルフィルムの製造方法は、フィルム搬送路の両側に設置された一対のレールに沿って走行するクリップを有するテンター式延伸装置を用いて、未延伸のポリエステルフィルムを前述のクリップで把持しながら横延伸または横延伸及び縦収縮または縦収縮させる工程を含むことが好ましい。 <Horizontal stretching>
The polyester film manufacturing method of the present invention uses a stretching machine having a plurality of clips that run between a pair of rails while gripping the film, and reduces the distance between the aforementioned clips on each rail. Including the step of simultaneously shrinking the film and stretching in the direction perpendicular to the film conveying direction by increasing the distance between the pair of rails on which the clip travels, and the shrinkage rate in the film conveying direction and the film The draw ratio in the direction orthogonal to the transport direction always satisfies the relationship of the following formula B1 during stretching, and satisfies the following formulas B2 and B3.

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm.
In this specification, using a stretching machine having a plurality of clips that run between a pair of rails while gripping a film, shrinking in the film transport direction by reducing the distance between the clips on each rail. The process of simultaneously stretching in the direction orthogonal to the film conveying direction by increasing the distance between the pair of rails on which the above-mentioned clip travels is also referred to as “lateral stretching and longitudinal shrinkage”.
Specifically, in the method for producing a polyester film of the present invention, an unstretched polyester film is previously described using a tenter-type stretching device having clips that run along a pair of rails installed on both sides of a film transport path. It is preferable to include a step of transverse stretching or transverse stretching and longitudinal shrinkage or longitudinal shrinkage while being held by a clip.

  There is no restriction | limiting in particular as a tenter type extending | stretching apparatus which has a clip which drive | works along a pair of rail installed in the both sides of a film conveyance path. A pair of endless rails is usually used as the pair of rails. In addition, a clip is synonymous with a holding member.

In the method for producing a polyester film of the present invention, a film after extrusion is subjected to transverse stretching or transverse stretching and longitudinal shrinkage or longitudinal shrinkage. Transverse stretching is performed in a direction perpendicular to the film transport direction while transporting an unstretched polyester film along the film transport path. Longitudinal shrinkage is performed in the film transport direction.
By stretching, the retardation Re in the in-plane direction 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 transverse stretching or transverse stretching and longitudinal shrinkage or longitudinal shrinkage are performed. When the transverse or longitudinal stretching is performed thereafter, the stretching ratio of the transverse stretching may be increased among the longitudinal and lateral stretching ratios so as to be unbalanced.

が

以上の場合、最終的な延伸中の各レール上におけるクリップ間の距離の最小値ｙｍｉｎが式Ｂ２を満たす範囲にすると、フィルムがたるまずにｙｍｉｎまで収縮することでたるみキズの発生を抑制するとともに、平面性が良好となり、搬送中（好ましくは後工程でも）の破断を抑制できる。
次に、式Ｂ１の右側の不等式について説明すると、

が

以下とすることで、延伸機内でフィルムがたるまずに、キズの発生を抑制できる。 First, the inequality on the left side of Formula B1 will be described.

But

In the above case, when the minimum value ymin of the distance between the clips on each rail during the final stretching is in a range satisfying the formula B2, the film shrinks to ymin without sagging, thereby suppressing the occurrence of sagging scratches. Further, the flatness is improved, and breakage during conveyance (preferably also in a post-process) can be suppressed.
Next, the inequality on the right side of the formula B1 will be described.

But

By setting it as the following, the generation | occurrence | production of a damage | wound can be suppressed, without a film dripping within a drawing machine.

式Ｂ２は、横延伸および縦収縮における、縦収縮の倍率を表す。式Ｂ２の範囲、すなわち縦収縮の倍率は、０．４〜０．９倍であり、０．５〜０．８倍であることが好ましく、０．５〜０．７倍であることがより好ましい。 The manufacturing method of the polyester film of this invention satisfy | fills following formula B2.

Formula B2 represents the ratio of longitudinal shrinkage in transverse stretching and longitudinal shrinkage. The range of Formula B2, that is, the magnification of longitudinal contraction is 0.4 to 0.9 times, preferably 0.5 to 0.8 times, more preferably 0.5 to 0.7 times. preferable.

式Ｂ３は、横延伸および縦収縮における、横延伸の倍率を表す。即ちクリップでフィルムの両端を把持し、加熱しながらクリップ間を拡幅することで式Ｂ３を達成できる。式Ｂ３の範囲、すなわち横延伸倍率は、３〜６．５倍であり、３．５〜６倍であることがより好ましく、４〜５．５倍であることが特に好ましい。 The manufacturing method of the polyester film of this invention satisfy | fills following formula B3.

Formula B3 represents the ratio of transverse stretching in transverse stretching and longitudinal shrinkage. That is, Formula B3 can be achieved by gripping both ends of the film with a clip and widening between the clips while heating. The range of Formula B3, that is, the transverse draw ratio is 3 to 6.5 times, more preferably 3.5 to 6 times, and particularly preferably 4 to 5.5 times.

  The stretching temperature (stretching average temperature T1) in the transverse 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 further 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.

  As temperature control means for heating or cooling the polyester film in preheating, stretching, heat setting, heat relaxation, and cooling in the transverse stretching process, hot or cold air is blown on the polyester film, or the polyester film is temperature controlled. The surface of the possible metal plate can be contacted or the vicinity of the metal plate can be passed.

<Heat fixing, thermal relaxation>
In the method for producing a polyester film of the present invention, the shrinkage in the film transport direction and the stretching in the direction perpendicular to the film transport direction are simultaneously performed at the stretching average temperature T1, and then the heat setting temperature T2 ≧ T1 + 30 ° C. It is preferable to include a heat setting step of heating. However, the unit of T1 and T2 is ° C.
The method for producing a polyester film of the present invention comprises the step of releasing the above-mentioned stretched polyester film to the maximum temperature in the tenter before releasing the above-mentioned transverse stretch or transverse stretch and longitudinal shrinkage or longitudinal shrinkage polyester film from the above clip. It is preferable to include a heat setting step for heating and a heat relaxation step for narrowing the distance between the pair of rails while heating the polyester film after the heat setting step.
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. Furthermore, in the manufacturing method of the polyester film of this invention, it is preferable to radiate-heat the edge part of the width direction of a polyester film with a heater so that it may mention later.
In the polyester film manufacturing method of the present invention, one or a plurality of wind shielding plates are attached to a desired position on the end side of the hot air blowing nozzle for heating the film, the cooling of the film end is moderated, and the above clip To the film surface temperature at the central part in the film width direction when the polyester film after transverse stretching described above is opened, the film surface temperature at the end of the film that is 200 mm away from the clip in the film width direction is 1 to 20 It is also preferable to increase the temperature easily.
Further, a heat source (IR heater, halogen heater, etc.) may be installed near the drawing (part) exit to raise the temperature.

The heat setting temperature T2 ≧ T1 + 30 ° C. is preferable, the heat setting temperature T2 is more preferably more than T1 + 50 ° C., and the heat setting temperature T2 is particularly preferably T1 + 60 ° C. or more.
A preferable temperature for heat setting is 100 ° C. or more and 250 ° C. or less, and more preferably 150 ° C. or more and 245 ° C. or less.

You may perform vertical contraction at the time of heat setting.
It is preferable to shrink (also referred to as relaxation, shrink the film) simultaneously with the heat treatment, and it is preferable to carry out at least one of TD (transverse direction) and MD (vertical direction). It is preferable that the manufacturing method of the polyester film of this invention performs heat setting, performing the shrinkage | contraction to a film conveyance 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.
The 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 suppressing 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.
By performing vertical contraction during heat setting, the Re, Rth, and Re / Rth ratios can be optimized, and the occurrence of rainbow unevenness can be suppressed.

The lateral relaxation temperature is preferably in the above-mentioned range of the heat setting temperature, and may be the same as that of heat setting, or may be the same as that of heat setting.
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 stretching and heat setting by these methods.

Furthermore, in the polyester film production method of the present invention, the end of the polyester film in the width direction is radiated by a heater in at least one of the above-described heat fixing zone and the above-described thermal relaxation zone in the tenter. It is preferable to heat. When such radiant heating is performed, the MD thermal shrinkage rate in the TD direction of the produced polyester film tends to decrease, and the distribution of the MD thermal shrinkage rate tends to become small, satisfying the above-described formulas (1) to (4). Easy to manufacture film.
When the end portion of the film in the TD direction is radiantly heated in the heat relaxation portion, the radiant heating in the heat fixing portion may be omitted, or may be performed in both the heat fixing portion and the heat relaxation portion.

The heating of the end portion in the TD direction of the polyester film is performed using a heater capable of radiation heating, and it is preferable to selectively heat at least one end portion of the polyester film in the TD direction. From the viewpoint of suppressing local MD heat shrinkage, it is preferable to heat both ends of the polyester film in the TD direction. Note that “selectively heating” means that the entire film including the end of the polyester film is not heated but the end of the film is locally heated.
As a heater capable of radiation heating, for example, an infrared heater can be mentioned, and it is particularly preferable to use a ceramic heater (ceramic heater).
Only one heater capable of radiant heating may be used, or two or more heaters may be used.

The heating of the end portion in the TD direction of the polyester film is preferably performed by setting the shortest distance between the polyester film surface and the heater to 10 mm or more and 300 mm or less.
If the shortest distance between the polyester film surface and the heater is 10 mm or more, temperature unevenness hardly occurs at the heater pitch, and if it is 300 mm or less, the radiant heat is sufficiently transmitted to the film.
The shortest distance between the heater surface and the film surface is preferably 50 mm or more and 250 mm or less, and more preferably 80 mm or more and 200 mm or less.

In addition to the distance between the film surface and the heater surface, it is preferable to heat the film by adjusting the surface temperature of the heater as required.
It is preferable that at least one surface temperature of the ceramic heater is 300 ° C. or higher and 700 ° C. or lower. When the surface temperature is 300 ° C. or higher, radiant heat is easily transmitted to the film, and when the surface temperature is 700 ° C. or lower, overheating of the film can be suppressed.
The surface temperature of the ceramic heater is more preferably 400 ° C. or higher and 650 ° C. or lower, and further preferably 450 ° C. or higher and 650 ° C. or lower.

  The ceramic heater is preferably covered with a grid-like metal cover. Since the heater is covered with the grid-like metal cover, it is possible to prevent the torn film from colliding with the heater and damaging the heater. The metal constituting the cover is not particularly limited, and examples thereof include stainless steel such as SUS304.

  In addition, when radiant heating is performed, it is preferable to narrow the temperature variation in the film TD direction to a range of 0.7 ° C. or more and 3.0 ° C. or less, and thereby the variation in crystallinity in the film width direction is 0.5% or more. It can be reduced to a range of ˜3.0%. If it does in this way, the slack difference in the width direction will reduce, generation | occurrence | production of a damage | wound will be suppressed, and hydrolysis resistance can be improved more.

  The length distribution in the MD direction of the polyester film tends to depend on the mode of cooling in the vicinity of the exit of the stretching apparatus that performs transverse stretching. In general, the length of the film in the MD direction tends to be longer at a rapidly cooled portion and shorter at a gradually cooled portion. This is thought to be due to the following reason. Although the film shrinks by cooling (a phenomenon opposite to thermal expansion), the film does not shrink sufficiently when cooled rapidly, and as a result, the film length in the MD direction is considered to be long. On the contrary, it is considered that the film length in the MD direction is shortened because the film contracts sufficiently when cooled slowly.

  The temperature of the gripping member of the stretching apparatus is about 100 ° C. to 150 ° C., which is relatively high compared to the cooling temperature of the stretching apparatus (generally, about room temperature to about 100 ° C.). For this reason, in the cooling unit of the stretching device, the temperature of the film end is increased due to the high temperature of the gripping member, and the film end is gradually cooled compared to the cooling state in the center of the film. Tend to be. Thereby, the film length in the MD direction tends to be shorter at the film end than at the center of the film.

In the conventional polyester film, since the film length distribution (arc) in the MD direction is generated, the central portion of the film has a smaller MD heat shrinkage than the end portion of the film and has a large film length in the MD direction. There is a tendency.
In that case, the center of the film is longer in the original MD direction before unheated, and more difficult to shrink during heating and transport, so it becomes longer and loosens, causing scratches and wrinkles. Easy to break.

<Recovery of film, slit, winding>
After the transverse stretching and the step of releasing from the clip, the film is trimmed, slit, and thickened as necessary, and wound for recovery.
In the method for producing a polyester film of the present invention, the film width after opening from the clip is preferably 0.8 to 6 m from the viewpoint of efficiently securing the film product width and preventing the apparatus size from becoming excessive, and 1 to 5 m. Is more preferable, and it is especially preferable that it is 1-4 m. An optical film requiring accuracy is usually formed with a thickness of less than 3 m, but in the present invention, it is preferable to form a film with the above-mentioned width.
In addition, the film formed into a wide film may be slit to preferably 2 or more, 6 or less, more preferably 2 or more and 5 or less, and still more preferably 3 or more and 4 or less, and then wound.
In addition, when trimming the edge part of a film by arbitrary width, or when slitting in arbitrary numbers after film forming, the film width after trimming or slit corresponds to the film width of the polyester film of this invention.

Moreover, after slitting, it is preferable to process the thickness at both ends (providing knurling).
The winding is preferably performed at a diameter of not less than 1000 m and not more than 10,000 m on a winding core having a diameter of 70 mm or more and 600 mm or less. 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.

[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 made of PVA and the polyester film of the present invention can be bonded together 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 for 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 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 source described in [0014] to [0015] of WO2011 / 162198 is not a continuous light source and is not preferable.
When the image display device is an LCD, a 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 same reason as described above, 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 iridescent 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.

In addition, the image display device according to the present invention preferably includes a light source unit having at least blue, green, and red emission peaks as a backlight light source, and a liquid crystal cell having polarizing plates on both sides.
The emission spectrum of the light source unit has at least blue, green and red emission peaks, the full width at half maximum of the green and red emission peaks is 20 nm or more, and at least one minimum value L1 is present between wavelengths 460 nm to 520 nm. Having at least one maximum value L2 between wavelengths 520 nm and 560 nm, having at least one minimum value L3 between wavelengths 560 nm and 620 nm, and the values of L1 and L3 being less than 35% of L2 Preferably there is.
The full width at half maximum of the green and red emission peaks is preferably 20 nm or more and 60 nm or less. Of the green emission peak and red emission peak of the light source unit, the half width W of the smaller half width is 50 nm or less. It is preferable that it is 20 nm or more and 40 nm or less. It is preferable that the full width at half maximum is small because the color reproducibility of the liquid crystal display device can be improved. Moreover, it is preferable for the full width at half maximum to be 20 nm or more because rainbow unevenness can be prevented from occurring by using the first protective film having Re of 5000 nm or more.
The values of L1 and L3 are more preferably less than 20% of L2, and most preferably less than 10%. It is preferable that the values of L1 and L3 are smaller than the value of L2, because light emission of blue, green, and red is separated and the color reproducibility of the liquid crystal display device can be improved.
The light source unit may include a blue light emitting diode, a green light emitting diode, and a red light emitting diode, but from the viewpoint of cost reduction, the blue light emitting diode or the ultraviolet light emitting diode and the blue light emitting diode or the ultraviolet light emitting diode are used. It is preferable to have at least a phosphor capable of emitting light when excited by light. When using a blue light emitting diode, it is preferable to have a phosphor that emits green light and a phosphor that emits red light. When an ultraviolet light emitting diode is used, a phosphor that emits blue light, It is preferable to have a phosphor that emits green light and a phosphor that emits red light.
The aforementioned phosphor may be enclosed in a blue light emitting diode or an ultraviolet light emitting diode, but in order to prevent deterioration of the phosphor due to heat, the phosphor is enclosed in a glass tube, Or it is preferable to arrange | position so that light emission of a ultraviolet-ray light-emitting diode may hit, or to arrange | position the film containing a fluorescent substance inside a light source unit.
The phosphor preferably includes quantum dots, at least one of which is a nanometer-sized semiconductor particle. The quantum dot phosphor is preferable because it can reduce the full width at half maximum of the emission peak and can improve the color reproducibility of the liquid crystal display device.

  In general, since a light source including quantum dots has high luminous efficiency, heat generation from the backlight unit can be suppressed as compared with a backlight unit using a white LED or a cold cathode fluorescent lamp (CCFL). Therefore, after the liquid crystal display device is stored in a high-temperature and high-humidity environment, an increase in temperature when it is turned on can be suppressed, and warpage of the liquid crystal cell and display unevenness can be further reduced.

  The emission spectrum of the light source unit can be measured using a spectroradiometer “SR-3” manufactured by Topcon Techno House Co., Ltd.

  An emission spectrum of a general cold cathode fluorescent lamp (CCFL) will be described. Blue, green, and red have sharp emission peaks, so blue, green, and red light emission are separated, and the color reproducibility of liquid crystal display devices using CCFLs is generally higher than that of liquid crystal displays using white LEDs. Also excellent. On the other hand, since the full width at half maximum of the green and red light emission peaks is as small as about 2 nm or less, when a film having high Re is used as the first protective film, rainbow unevenness is visually recognized.

  The emission spectrum of a general white LED will be described. A white LED is usually manufactured by enclosing an organic phosphor that emits yellow or green and red light inside a blue light emitting diode. In this case, the full width at half maximum of the green and red emission peaks is 20 nm or more. Therefore, in general, in a liquid crystal display device using a white LED, when a film having a high Re is used as the first protective film, rainbow unevenness occurs. It is suppressed. On the other hand, since there is no minimum value between wavelengths 460 nm and 520 nm and between wavelengths 560 nm and 620 nm, or the minimum value is larger than the maximum value L2 between wavelengths 520 nm and 560 nm, blue, green, and Separation of red light emission is insufficient and color reproducibility is poor.

  An emission spectrum of a light source using the quantum dot phosphor will be described. A light source using a quantum dot phosphor generally has a full width at half maximum of green and red emission peaks of 20 nm or more, has at least one minimum value L1 between wavelengths of 460 nm and 520 nm, and has a wavelength of 520 nm to 520 nm. Since it has at least one maximum value L2 between 560 nm, at least one minimum value L3 between wavelengths 560 nm and 620 nm, and the values of L1 and L3 are less than 35% of L2, It can be suitably used as a light source unit of an image display device.

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.

[Hard coat film]
The polyester film of the present invention can be used for a hard coat film. The hard coat film has a hard coat layer and the polyester film of the present invention as a transparent film.
The hard coat layer may be formed by either a wet coating method or a dry coating method (vacuum film formation), but is preferably formed by a wet coating method having excellent productivity.
As the hard coat layer, for example, JP 2013-45045 A, JP 2013-43352 A, JP 2012-232459 A, JP 2012-128157 A, JP 2011-131409 A, JP JP2011-131404A, JP2011-126162A, JP2011-75705A, JP2009-286981, JP2009-263567, JP2009-75248, JP2007-. No. 164206, JP-A No. 2006-96811, JP-A No. 2004-75970, JP-A No. 2002-156505, JP-A No. 2001-272503, WO12 / 018087, WO12 / 098967, WO12 / 0886659, WO11 / Described in 105594 The can be used.

The polyester film of the present invention can be used for a sensor film for a touch panel. In the sensor film for a touch panel, a hard coat layer and a transparent conductive layer are laminated on a polyester film.
As a general method for forming the transparent conductive layer, there are a PVD method such as a sputtering method, a vacuum deposition method, and an ion plating method, a CVD method, a coating method, a printing method, and the like. The material for forming the transparent conductive layer is not particularly limited, and examples thereof include indium-tin composite oxide (ITO), tin oxide, copper, silver, aluminum, nickel, chromium, and the like. May be formed in an overlapping manner. In addition, the transparent conductive layer may be provided with an undercoat layer for improving transparency and optical characteristics before forming the transparent conductive layer. In order to further improve the adhesion, a metal layer made of a single metal element or an alloy of two or more metal elements may be provided between the undercoat layer and the polyester film. It is desirable to use a metal selected from the group consisting of silicon, titanium, tin and zinc for the metal layer.

The polyester film of the present invention can be used for a glass scattering prevention film. In the glass scattering prevention film, a hard coat layer and an adhesive layer are laminated on a polyester film.
The pressure-sensitive adhesive layer may be formed by either a wet coating method or a dry coating method. To form the pressure-sensitive adhesive layer, an acrylic pressure-sensitive adhesive composition such as a solvent-based acrylic polymer, a solvent-based acrylic syrup, a solvent-free acrylic syrup, or a solvent-free urethane acrylate can be used.

[Touch panel]
The polyester film of the present invention can be used in a touch panel. Moreover, at least any one of the above-mentioned hard coat film, the above-mentioned sensor film for touch panels, and the above-mentioned glass scattering prevention film can be used in a touch panel.
There is no restriction | limiting in particular in the touchscreen of this invention, According to the objective, it can select suitably, For example, a surface capacitive touch panel, a projection capacitive touch panel, a resistive touch panel etc. are mentioned. The touch panel includes a so-called touch sensor and a touch pad. The layer structure of the touch panel sensor electrode part in the touch panel is a bonding method in which two transparent electrodes are bonded, a method in which transparent electrodes are provided on both surfaces of a single substrate, a single-sided jumper or a through-hole method, or a single-area layer method. But you can. In addition, the projected capacitive touch panel is preferably AC driven rather than DC driven, and more preferably is a drive system that requires less time to apply voltage to the electrodes.

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.
Unless otherwise specified, “part” is based on mass.

[Example 1]
<Synthesis of raw material polyester>
(Raw material polyester 1)
As shown below, terephthalic acid and ethylene glycol are directly reacted to distill off water, esterify, and then, using 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 reaction tank, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol are mixed for 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 temperature in the reaction vessel 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.

  This 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, the mixture 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 this reaction tank, the reaction tank temperature was 278 ° C., the reaction tank pressure 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 form 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 (hereinafter abbreviated as PET1). This polymer was designated as raw material polyester 1.

<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 conditions of pressure fluctuation of 1% and molten resin temperature distribution of 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%.

IV is an unstretched polyester film 1 dissolved in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent, and the solution viscosity at 25 ° C. in this mixed solvent. I asked for it.
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. 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 (NAR-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.).
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 1.335 g / cm ³ in crystallinity 0%, using density 1.501g / cm ³ at 100% crystalline crystal from the following formula The degree of conversion (%) can be derived.
Crystallinity = {Z × (XY)} / {X × (ZY)} × 100
The density was measured according to JIS K7112.

-Transverse stretching process-
The unstretched polyester film 1 is guided to a tenter stretching machine having a plurality of clips that run between a pair of rails while gripping the film, and the following methods and conditions are performed while gripping the ends of the unstretched polyester film 1 with the clips. Was stretched transversely.

(Preheating part)
The preheating temperature was 75 ° C., and heating was performed to a temperature at which stretching was possible.

：０．６２
・延伸中の各レール上におけるクリップ間の距離の最小値ｙ_min：６７．５ｍｍ
・縦延伸倍率（：縦収縮倍率；ｙ_min／ｙ）：０．４５倍
・ｘ’＝ｘ_max／２（＝２３４０ｍｍ）のときのｙ’：８９ｍｍ
・ｘ’＝ｘ_max／２（＝２３４０ｍｍ）のときのｙ’／ｙ：０．６倍

(Extension part)
The preheated unstretched polyester film 1 has the following conditions in the width direction, the width x ′ of the polyester film at each position during stretching, and the distance y ′ between the clips on each rail at each position during stretching: The relationship of Formula B1 was set to always hold during stretching, and transverse stretching and longitudinal shrinkage were simultaneously performed using a tenter.
<Condition>
・ Width of the entrance of the drawing machine x: 900 mm
-Distance y between clips on each rail at the entrance of the stretching machine: 150 mm
-Transverse stretching and longitudinal shrinkage temperature (average stretching temperature T1 during transverse stretching and longitudinal shrinkage): 75 ° C
-Maximum width of the polyester film being stretched x _max : 4680 mm
And transverse stretching ratio (x _max /x):5.2 maximum width of the polyester film in the fold-stretched x _max / 2 in x when ': 2340mm
・ When x ′ = x _max / 2 (= 2340 mm)

: 0.62
・ Minimum value y _min of the distance between clips on each rail during stretching: 67.5 mm
-Longitudinal draw ratio (: Longitudinal shrinkage ratio: y _min / y): 0.45 times-y 'when x' = x _max / 2 (= 2340 mm): 89 mm
Y ′ / y when x ′ = x _max / 2 (= 2340 mm): 0.6 times

(Heat fixing part)
Next, hot fixing from the vertical direction was applied to the film from the hot air blowing nozzle to the film, and heat setting was performed while controlling the film surface temperature of the polyester film within the following range.
<Condition>
-Shrinkage distance between clips (= distance between clips on each rail at the heat fixing zone outlet / distance between clips on each rail at the heat fixing zone inlet): 1.0 times (no contraction)
Maximum film surface temperature (heat setting temperature T2): 167 ° C
・ Heat setting time: 15 seconds

  Furthermore, in Example 1, both ends in the film width direction (TD direction), specifically, a total of 40% of 20% in the width direction from both ends with respect to the entire width of the film, were cast drums in the film forming process. Radiation heating was performed from the contacted cast surface side with a ceramic infrared heater (heater surface temperature: 650 ° C.). At this time, the distance between the heater and the polyester film was 170 mm.

(Cooling section)
Next, without heat relaxation, the film surface temperature (A) at the center of the film in the TD direction of the polyester film after heat setting is 80 ° C., and is 200 mm away from the clip in the film width direction. It cooled at the cooling temperature from which the film surface temperature (B) of an edge part will be 88 degreeC. The film surface temperature at the center and the end of the film can be adjusted by attaching one or more wind shields at desired positions on the end side of the blowing nozzle that cools the film, and gradually cooling the end of the film. Controlled.
Cooling temperature means the film film surface temperature in a cooling part, and 95 degreeC cold wind is applied from the up-and-down direction, and combined with the radiation heating to the edge part in the said heat fixation and heat relaxation, said (B)-(A ) Temperature difference could be imparted. The values of (B)-(A) are shown in Table 1 below.
Also in the other Examples and Comparative Examples, the cooling temperature was set to the same value as the film film surface temperature when the clip opened the film.

(Open film)
The cooled film was released from the tenter clip. The film surface temperature (A) at the center in the TD direction of the film when the clip releases the film is 80 ° C., the film surface temperature at the end of the film in the TD direction (B) at a position 200 mm away from the clip in the film width direction. Was 88 ° C.
The film surface temperature (A) at the center in the TD direction of the film when the clip opened the film was measured with a radiation thermometer (manufactured by Hayashi Denko, model number: RT61-2, used at an emissivity of 0.95).
When the clip releases the film, the film surface temperature (B) at the end in the TD direction of the film at a position 200 mm away from the clip in the film width direction is a radiation thermometer (manufactured by Hayashi Denko, model number: RT61-2, Used at an emissivity of 0.95).

(Recovery of film)
After cooling and releasing the film from the clip, both ends of the polyester film were trimmed by 20 cm. The film width after trimming was 3 m. Then, after extruding (knurling) with a width of 10 mm at both ends, a film having a length of 10,000 m was wound up in a roll form with a tension of 18 kg / m.
As described above, the polyester film of Example 1 having a thickness of 10 μm wound in a roll form was produced.

を満たす条件にテンターの設定をし、比較例６では延伸中常に

を満たす条件にテンターの設定をした。
実施例１１、１２、１４、１６、２２、２４および比較例８における熱固定時の最高到達膜面温度Ｔ２は、セラミック製の赤外線ヒーターの表面温度を変更することにより制御した。
実施例２〜２４、比較例１〜８のポリエステルフィルムの膜厚は、実施例１と同じ未延伸ポリエステルフィルム１を用いてポリエステルフィルムの製造条件を下記表１に記載のように変更するだけで下記表２に記載の範囲に制御できた。 [Examples 2 to 24, Comparative Examples 1 to 8]
In Example 1, the polyester film of Examples 2-24 and Comparative Examples 1-8 was manufactured like Example 1 except having changed the manufacturing conditions of the polyester film as described in Table 1 below.
In addition, each manufacturing condition of the transverse stretching process and the distance contraction ratio between clips at the time of heat fixing were controlled by changing the setting of the tenter. In Comparative Example 5, always during stretching.

The tenter was set to satisfy the conditions, and in Comparative Example 6, it was always during stretching.

The tenter was set to satisfy the conditions.
In Examples 11, 12, 14, 16, 22, 24 and Comparative Example 8, the maximum film surface temperature T2 at the time of heat setting was controlled by changing the surface temperature of the ceramic infrared heater.
The film thicknesses of the polyester films of Examples 2 to 24 and Comparative Examples 1 to 8 are simply changed by using the same unstretched polyester film 1 as in Example 1 and changing the production conditions of the polyester film as shown in Table 1 below. It was possible to control within the range described in Table 2 below.

[Example 25]
(Raw material polyester 2)
10 parts by mass of dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazin-4-one)), 90 parts by mass of PET1 (IV = 0.63) Were mixed and pelletized in the same manner as in the preparation of PET 1 using a kneading extruder to obtain a raw material polyester 2 containing an ultraviolet absorber (hereinafter abbreviated as PET 2).

-Film forming process-
After 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 are dried to a water 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 conditions of pressure fluctuation of 1% and molten resin temperature distribution of 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 longitudinal refractive index 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 15 to produce a polyester film of Example 25 having a thickness of 65 μm.

[Film properties]
<Measurement of film thickness>
The thicknesses of the obtained polyester films of each Example and Comparative Example were determined as follows.
Using a contact-type film thickness meter (manufactured by Anritsu Co., Ltd.) for the polyester film of each example and comparative example, 50 points were sampled at equal intervals over 0.5 m in the longitudinally stretched direction (longitudinal direction). After sampling 50 points at equal intervals (50 equal parts in the width direction) over the entire width of the film in the film width direction (direction perpendicular to the longitudinal direction), the thicknesses of these 100 points were measured. The average thickness of these 100 points was determined and used as the thickness of the polyester film. The results are shown in Table 2 below.

<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 2.

<MD heat shrinkage rate in width direction and MD heat shrinkage rate unevenness in width direction>
The film F obtained as described above is cut, and both ends of the film F in the TD direction at positions that are half the film length in the MD direction (L = 26 m) (from the film end to the width of 10 to 40 mm) 30 mm portion) and three types of sample pieces M at the center portion in the TD direction (a 30 mm portion having the center line in the film width direction as the center of the sample piece). The three kinds of sample pieces M were 30 mm in the TD direction and 120 mm in the MD direction.
Two reference lines were inserted into the three kinds of sample pieces M so as to have an interval of 100 mm in the MD direction, and left in a heating oven at 150 ° C. for 30 minutes under no tension. After this standing, the three kinds of sample pieces M were cooled to room temperature, the distance between the two reference lines was measured, and this value was defined as A (unit: mm). The numerical value calculated from the measured A and the formula of “100 × (100−A) / 100” was defined as the MD heat shrinkage rate.

The MD thermal contraction rate obtained by measuring the sample piece M located at the end in the TD direction on the film F was S _S1 with a larger value and S _S2 with a smaller value. Further, the MD thermal shrinkage rate obtained by measuring a test piece M located in central TD direction in the film F was S _CT.
S _S1 is the heat shrinkage in the direction perpendicular to the film width direction of the polyester film having the larger heat shrinkage rate (150 ° C., 30 minutes) in the direction perpendicular to the film width direction among the ends in the film width direction. S _S2 represents the rate [%], and S _S2 is orthogonal to the film width direction of the polyester film on the side where the thermal shrinkage rate (150 ° C., 30 minutes) in the direction orthogonal to the film width direction is small. The heat shrinkage rate [%] in the direction of _SCT represents the thermal shrinkage rate (150 ° C., 30 minutes) [%] in the direction perpendicular to the film width direction of the polyester film at the film center in the film width direction.

(MD heat shrinkage in the width direction)
The average value of the three points of MD heat shrinkage S _S1 , S _S2 and _{SCT was taken} as the MD heat shrinkage in the width direction. The results are shown in Table 2 below.

(MD heat shrinkage rate unevenness in the width direction)
The difference between the maximum value and the minimum value of the resultant of the three-point MD thermal shrinkage rate S _S1, S _S2 and S _CT at above the average value of the MD thermal shrinkage rate of 3 points S _S1, S _S2 and S _CT The percentage expressed as a percentage was determined as the thermal shrinkage rate unevenness (variation rate) in the MD direction. The results are shown in Table 2 below.

<Flatness>
After stretching, within 15 minutes after the roll wound up by the winding device was rolled up, a film of the most surface layer portion (outer winding portion, winding diameter: 600 mm) of the roll was cut into a 500 mm square.
The cut film was placed on a flat surface, and the height of the highest part from the flat surface was measured under the conditions of a temperature of 25 ° C. and a relative humidity of 60%.
The results are shown in Table 2 below.

[Film evaluation]
<Scratch evaluation>
Scratches on the surface of the produced polyester film were evaluated by a visual test and an optical microscope manufactured by Olympus. Visual inspection was carried out with respect to the length direction of 500 mm and the entire width, and the length of the found scratch was measured with an optical microscope. Further, the average value per 1 m ² was calculated for the number of scratches.
The evaluation criteria are as follows.
A: Scratches with a length of 1 mm or more are less than 10 pieces / m ² .
B: Scratches having a length of 1 mm or more are 10 pieces / m ² or more and less than 20 pieces / m ² .
C: Scratches with a length of 1 mm or more are 20 pieces / m ² or more.
The results are shown in Table 2 below.

[Evaluation of process suitability]
<Transportability>
The results evaluated according to the following criteria are shown in Table 1 below.
A: The winding length is 1000 m or more, and it can be conveyed without partial cracking / breaking during conveyance after stretching.
B: Partial cracking or breakage in less than three locations during conveyance after drawing within a winding length of 1000 m.
C: Three or more partial cracks or breaks occurred during conveyance after stretching within a winding length of 1000 m.
D: Cracking / breaking occurs within a winding length of 100 m.
The results are shown in Table 2 below.

[Production of polarizing plate and liquid crystal display device and evaluation of rainbow unevenness of liquid crystal display device]
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. 4731143 ([0412] to [0416] of US2008 / 0158483, the contents described in these publications are incorporated in the present specification) 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.

<Evaluation of rainbow unevenness>
Using a continuous light source (white LED) and a discontinuous light source (cold cathode tube) from one side, light was incident and rainbow unevenness was evaluated by counting the number of rainbows generated visually through polarized sunglasses from the opposite side.
Note that the rainbow unevenness was evaluated from both the normal direction of the polarizing plate and the oblique direction (45 ° from the normal line).
A: Rainbow unevenness is not visible at all B: Rainbow unevenness is not visible C: Rainbow unevenness is hardly visible D: Rainbow unevenness is visible The results are shown in Table 2 below.

From the above Tables 1 and 2, it was found that the polyester film of the present invention has few scratches, few cracks and breaks during transportation, and can suppress the occurrence of rainbow unevenness when incorporated in a liquid crystal display device.
On the other hand, from Comparative Example 1, the polyester film produced under the production conditions in which the draw ratio in the direction orthogonal to the transport direction is lower than the lower limit value of the present invention, Re is lower than the lower limit value of the present invention, was incorporated in the liquid crystal display device. It was found that rainbow unevenness sometimes occurred.
From Comparative Example 2, it was found that when the film was produced under production conditions in which the draw ratio in the direction perpendicular to the conveyance direction exceeded the upper limit of the present invention, breakage occurred during the drawing and the film could not be produced.
From Comparative Example 3, the polyester film produced under the production conditions in which the shrinkage in the conveying direction exceeds the upper limit value of the present invention, the Re / Rth is less than the lower limit value of the present invention. It was found to occur.
From the comparative example 4, the polyester film when the shrinkage in the transport direction is less than the lower limit value of the present invention and the polyester film floats on the flat surface exceeds the upper limit value of the present invention has many scratches. It was found that there were many cracks and breaks during transportation.
From Comparative Example 5, the polyester film produced under the production conditions that do not satisfy the inequality on the left side of the formula B1 and the polyester film floating above the upper limit of the present invention when placed on a plane has cracks and breaks during transportation. I found many.
From Comparative Example 6, the polyester film produced under the production conditions that do not satisfy the inequality on the right side of the formula B1 and the polyester film floating above the upper limit of the present invention when placed on a flat surface has many scratches, and it is It was found that there were many cracks and breaks.
From Comparative Example 7, it was found that the polyester film having a thickness below the lower limit of the present invention was broken by the tension during conveyance.
From the comparative example 8, it turned out that the polyester film in which the thermal contraction rate in the direction orthogonal to the orientation direction exceeds the upper limit of the present invention has many cracks and breaks during transportation.

In addition, the refractive index of the longitudinal direction of the polyester film of each Example manufactured with the manufacturing method of the polyester film of this invention is 1.590 or less in all, and it is unstretched that crystallinity exceeds 5% in all. It confirmed by the method similar to the polyester films 1 and 2.
Moreover, it confirmed with the following method that the polyester film of each Example manufactured with the manufacturing method of the polyester film of this invention was uniaxially oriented.
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 films of each Example were uniaxially oriented.

Claims (11)

The thickness is 10 to 150 μm,
In-plane direction retardation Re and thickness direction retardation Rth are 3000 to 30000 nm,
Re / Rth exceeds 0.8 and is 2.5 or less,
It is a polyester film having a heat shrinkage rate of 0.6% or less in the direction orthogonal to the orientation direction,
A polyester film in which the polyester film floats up to 1.8 mm or less when the polyester film wound up in a roll shape is unrolled and placed on a flat surface. The polyester film according to claim 1, wherein the heat shrinkage ratio unevenness in a direction orthogonal to the orientation direction represented by the following formula A is 0.4% or less.
Formula A:
(Unevenness of thermal shrinkage in the direction orthogonal to the orientation direction) = (Difference between the maximum value and the minimum value of the thermal shrinkage rate in the direction perpendicular to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) / (Average value of thermal shrinkage in the direction orthogonal to the orientation direction after heating at 150 ° C. for 30 minutes at three points in the orientation direction) × 100% Using a stretching machine having a plurality of clips that travel between a pair of rails while gripping the film, a pair of the clips that travel in the film transport direction by reducing the distance between the clips on each rail, Including a step of simultaneously stretching in a direction perpendicular to the film conveying direction by widening the distance between the rails,
A method for producing a polyester film in which the shrinkage ratio in the film transport direction and the stretch ratio in the direction perpendicular to the film transport direction always satisfy the following formula B1 during stretching and satisfy the following formulas B2 and B3;

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm. Using a stretching machine having a plurality of clips that travel between a pair of rails while gripping the film, a pair of the clips that travel in the film transport direction by reducing the distance between the clips on each rail, Including a step of simultaneously stretching in a direction perpendicular to the film conveying direction by widening the distance between the rails,
The shrinkage rate in the film transport direction and the stretching ratio in the direction orthogonal to the film transport direction always satisfy the relationship of the following formula B1 during stretching, and satisfy the following formulas B2 and B3:
The polyester film has a thickness of 10 to 150 μm,
A method for producing a polyester film, wherein the thermal shrinkage in the direction perpendicular to the orientation direction of the polyester film is 0.6% or less;

In formulas B1, B2 and B3,
x represents the width of the inlet of the stretching machine, the unit is mm;
x ′ represents the width of the polyester film at each position during stretching, the unit is mm;
x _max represents the maximum width of the polyester film during stretching, the unit is mm;
y represents the distance between clips on each rail at the entrance of the stretcher, the unit is mm;
y ′ represents the distance between clips on each rail at each position during stretching, the unit being mm;
y _min represents the minimum value of the distance between clips on each rail during stretching, and the unit is mm. The method includes a heat setting step in which the shrinkage in the film transport direction and the stretching in the direction orthogonal to the film transport direction are simultaneously performed at a stretching average temperature T1 and then heated at a heat setting temperature T2 ≧ T1 + 30 ° C. Or the manufacturing method of the polyester film of 4;
However, the unit of T1 and T2 is ° C.   The method for producing a polyester film according to claim 5, wherein the heat setting is performed while shrinking in the film conveyance direction.   The method for producing a polyester film according to claim 5 or 6, wherein the heat setting temperature T2 exceeds T1 + 50 ° C.   A polarizing plate comprising a polarizer and the polyester film according to claim 1.   An image display device comprising the polyester film according to claim 1 or 2, or the polarizing plate according to claim 8.   A hard coat film comprising the polyester film according to claim 1.   A touch panel comprising the polyester film according to claim 1, the polarizing plate according to claim 8, or the hard coat film according to claim 10.