WO2015146883A1

WO2015146883A1 - Polyester resin film, method for producing polyester resin film, polarizing plate, image display device, hard coat film, sensor film for touch panels, glass scattering prevention film and touch panel

Info

Publication number: WO2015146883A1
Application number: PCT/JP2015/058674
Authority: WO
Inventors: 真一中居; 直良山田
Original assignee: 富士フイルム株式会社
Priority date: 2014-03-26
Filing date: 2015-03-23
Publication date: 2015-10-01
Also published as: CN106104332A; JP2015184664A; JP6297379B2; CN106104332B

Abstract

A polyester resin film satisfying formulae (1)-(4), which is capable of improving iridescent unevenness when viewed from the front and iridescent unevenness when viewed from an oblique direction at the same time; a method for producing a polyester resin film; a polarizing plate; an image display device; a hard coat film; a sensor film for touch panels; a glass scattering prevention film; and a touch panel. 15 μm ≤ Th ≤ 60 μm formula (1) 0 < nx - ny ≤ 0.020 formula (2) 0.120 ≤ (nx + ny)/2 - nz < 0.160 formula (3) 0 < n∆ ≤ 0.014 formula (4)

Description

Polyester resin film, method for producing polyester resin film, polarizing plate, image display device, hard coat film, sensor film for touch panel, glass scattering prevention film, and touch panel

The present invention relates to a polyester resin film, a method for producing a polyester resin film, a polarizing plate, an image display device, a hard coat film, a sensor film for a touch panel, a glass scattering prevention film, and a touch panel.

Image display devices such as liquid crystal display (LCD), plasma display (PDP), electroluminescence display (OELD or IELD), field emission display (FED), touch panel, and electronic paper have a polarizing plate on the display screen side of the image display panel. Is arranged. For example, a liquid crystal display device has low power consumption, and its application is expanding year by year as a space-saving image display device. Conventionally, a liquid crystal display device has a major disadvantage that the viewing angle dependence of a display image is large, but a wide viewing angle liquid crystal mode such as a VA (Virtual Alignment) mode and an IPS (In-Place-Switching) mode is put into practical use As a result, the demand for liquid crystal display devices is rapidly expanding even in markets where high-quality images such as televisions 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 resin films and the like have advantages such as low cost, high mechanical strength, and low moisture permeability, and therefore are expected to be used as outer films.

In addition to being used as a base material for liquid crystal display devices such as a protective film for polarizing plates, polyester resin films are increasingly used as touch panel members such as transparent conductive films, scattering prevention films, and hard coat films. .

When using a polyester resin film for such a substrate or member, for example, as in Patent Document 1 and Patent Document 2, by reducing in-plane birefringence, the rainbow unevenness on the front when displaying on the display is reduced. It is known that it can be suppressed.

International Publication No. 2011/043131 Pamphlet JP 2010-107892 A

However, with the methods described in Patent Document 1 and Patent Document 2, rainbow unevenness when the display is viewed from the front can be suppressed to some extent by reducing in-plane birefringence, but when the display is viewed from an oblique direction. There is a problem that rainbow unevenness cannot be suppressed.

Problems to be solved by the present invention are a polyester resin film that can simultaneously improve rainbow unevenness when viewed from the front and rainbow unevenness when viewed from the oblique direction, a method for producing a polyester resin film, a polarizing plate, and an image. A display device, a hard coat film, a sensor film for a touch panel, a glass scattering prevention film, and a touch panel are provided.

As a result of intensive studies to solve the above problems, the present inventors have controlled the film thickness, the birefringence in the film in-plane direction, the birefringence in the film thickness direction, and the birefringence unevenness in the film plane. As a result, it was found that rainbow unevenness when the display is viewed from an oblique direction can be eliminated, and the present invention has been completed.
The present invention, which is a specific means for achieving the above object, is as follows.

[1] A polyester resin film satisfying the following formulas (1) to (4);
15 μm ≦ Th ≦ 60 μm (1)
0 <nx−ny ≦ 0.020 (2)
0.120 ≦ (nx + ny) / 2−nz <0.160 Formula (3)
0 <nΔ ≦ 0.014 (4)
In the formulas (1) to (4), Th represents the thickness of the polyester resin film, the unit of the thickness of the polyester resin film is μm; nx represents the refractive index in the slow axis direction in the polyester resin film plane, ny represents the refractive index in the fast axis direction in the plane of the polyester resin film, nz represents the refractive index in the thickness direction of the polyester resin film, and nΔ represents (nx−ny) in an arbitrary area 1 m ² of the polyester resin film. It represents the difference between the maximum and minimum values.
[2] The polyester resin film according to [1] preferably satisfies the following formula (5);
130 ° C. ≦ Tpre ≦ 200 ° C. Formula (5)
In formula (5), Tpre represents the pre-peak temperature measured by differential scanning calorimetry of the polyester resin film, and the unit is ° C.
[3] The polyester resin film according to [1] or [2] preferably has a polyester resin film density of 1.370 to 1.390 g / cm ³ .
[4] The polyester resin film according to any one of [1] to [3] has a thermal shrinkage ratio of 3.5 and TD in the polyester resin film after standing at 150 ° C. for 30 minutes. % Or less is preferable.
[5] The polyester resin film according to any one of [1] to [4] has a thermal shrinkage of 0.3% in the MD direction and the TD direction of the polyester resin film after standing at 80 ° C. for 24 hours. The following is preferable.
[6] In the polyester resin film according to any one of [1] to [5], the width of the polyester resin film is preferably 0.6 to 6 m.
[7] The polyester resin film according to any one of [1] to [6] is preferably biaxially oriented.
[8] A step of melt-extruding a polyester raw resin into a sheet and cooling on a casting drum to form a polyester resin film;
A longitudinal stretching step of longitudinally stretching the molded polyester resin film in the longitudinal direction;
A transverse stretching step of transversely stretching the polyester resin film after the longitudinal stretching in the width direction perpendicular to the longitudinal direction,
A method for producing a polyester resin film satisfying the following formulas (1 ′) and (6) to (11);
15 μm ≦ Th ′ ≦ 60 μm Formula (1 ′)
2.8 ≦ DMD ≦ 3.6 Formula (6)
DMD−1.0 ≦ DTD ≦ DMD + 0.5 (7)
130 ° C. ≦ TSET ≦ 200 ° C. Formula (8)
80 ° C. ≦ TTDs ≦ 120 ° C. Formula (9)
120 ° C. ≦ TTDe ≦ 180 ° C. Formula (10)
20 ° C. ≦ TTDe−TTDs ≦ 80 ° C. Formula (11)
In the formulas (1 ′) and (6) to (11), Th ′ represents the thickness of the polyester resin film after the transverse stretching step, and the unit of the thickness of the polyester resin film after the transverse stretching step is μm; Represents the draw ratio in the machine direction, DTD represents the draw ratio in the transverse direction, TSET represents the maximum surface temperature at the time of heat setting, TTDs represents the film surface temperature at the start of transverse stretching, and TTDe is the end of transverse stretching Represents the film surface temperature of the hour; units of TSET, TTDs, and TTDe are in ° C.
[9] In the method for producing a polyester resin film according to [8], it is preferable that the birefringence of the polyester resin film after longitudinal stretching and before lateral stretching satisfies the following formulas (12) and (13);
0.030 <nx (MD) −ny (MD) ≦ 0.090 (12)
0.030 ≦ (nx (MD) + ny (MD)) / 2−nz (MD) <0.090 (13)
In formula (12) and formula (13), nx (MD) represents the refractive index in the slow axis direction in the plane of the polyester resin film after longitudinal stretching, and ny (MD) represents the polyester resin film after longitudinal stretching. The refractive index in the in-plane fast axis direction is represented, and nz (MD) represents the refractive index in the thickness direction of the polyester resin film after longitudinal stretching.
[10] The method for producing a polyester resin film according to [8] or [9] includes a heat fixing part for heating and crystallizing a heat-fixed portion of the polyester resin film after longitudinal stretching and transverse stretching, and heat fixing. Heating the formed polyester resin film, and including a step of transporting a thermal relaxation portion that relaxes the tension of the polyester resin film and removes residual distortion of the film,
In the thermal relaxation portion, it is preferable that the longitudinal relaxation rate is 1 to 10% and the lateral relaxation rate is 3 to 23%.
[11] The method for producing a polyester resin film according to any one of [8] to [10] is a method of heating and crystallizing the heat-fixed polyester resin film after longitudinal and transverse stretching. The fixing unit includes a step of heating the heat-fixed polyester resin film, transporting a heat relaxation unit that relaxes the tension of the polyester resin film and removes residual distortion of the film,
It is preferable that an intermediate cooling part is included between the laterally stretched part and the heat fixing part.
[12] The method for producing a polyester resin film according to [11] preferably satisfies the following formula (14) in the intermediate cooling section;
30 ° C. ≦ TMC ≦ (TTDe−10) ° C. Formula (14)
In the formula (14), TMC represents the minimum film surface temperature, TTDe represents the film surface temperature at the end of the transverse stretching, and both units are ° C.
[13] A polarizing plate comprising a polarizer and the polyester resin film according to any one of [1] to [7].
[14] An image display device comprising the polyester resin film according to any one of [1] to [7] or the polarizing plate according to claim 13.
[15] The image display device according to [14] includes a light source unit having at least blue, green, and red light emission peaks, and a liquid crystal cell having polarizing plates on both sides, the green light emission peak of the light source unit, and red Of the emission peaks, the half width W having the smaller half width is preferably 50 nm or less.
[16] In the image display device according to [15], the light source unit includes at least a blue light emitting diode or an ultraviolet light emitting diode and a phosphor capable of emitting light by being excited by light from the blue light emitting diode or the ultraviolet light emitting diode. It is preferable.
[17] In the image display device according to [16], it is preferable that at least one of the phosphors is a quantum dot.
[18] A hard coat film comprising the polyester resin film according to any one of [1] to [7].
[19] A touch panel sensor film comprising the polyester resin film according to any one of [1] to [7].
[20] A glass scattering prevention film comprising the polyester resin film according to any one of [1] to [7].
[21] The polyester resin film according to any one of [1] to [7], the polarizing plate according to [13], the hard coat film according to [18], and the touch panel sensor according to [19]. A touch panel provided with at least any one of a film and the glass scattering prevention film as described in [20].

According to the present invention, a polyester resin film capable of simultaneously improving rainbow unevenness when viewed from the front and rainbow unevenness when viewed from an oblique direction, a method for producing a polyester resin film, a polarizing plate, an image display device, and hardware A coat film, a sensor film for a touch panel, a glass scattering prevention film, and a touch panel can be provided.

It is a top view which shows an example of a biaxial stretching machine from the upper surface.

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

[Polyester resin film]
The polyester resin film of the present invention (hereinafter also simply referred to as “film”) satisfies the following formulas (1) to (4).
15 μm ≦ Th ≦ 60 μm (1)
0 <nx−ny ≦ 0.020 (2)
0.120 ≦ (nx + ny) / 2−nz <0.160 Formula (3)
0 <nΔ ≦ 0.014 (4)
In the formulas (1) to (4), Th represents the thickness of the polyester resin film, the unit of the thickness of the polyester resin film is μm; nx represents the refractive index in the slow axis direction in the polyester resin film plane, ny represents the refractive index in the fast axis direction in the plane of the polyester resin film, nz represents the refractive index in the thickness direction of the polyester resin film, and nΔ represents (nx−ny) in an arbitrary area 1 m ² of the polyester resin film. It represents the difference between the maximum and minimum values.

With such a configuration, the polyester resin film of the present invention can simultaneously improve rainbow unevenness when viewed from the front and rainbow unevenness when viewed from an oblique direction.
The rainbow unevenness when viewed from the front can be improved by reducing the in-plane birefringence, but the rainbow unevenness when viewed from an oblique direction cannot be improved.
In the present invention, the maximum thickness and the minimum of the birefringence in the film plane, the birefringence in the thickness direction of the film, and the birefringence in the plane within an arbitrary area 1 m ² of the film are set in a specific range. By making unevenness as a difference from the value (hereinafter also referred to as in-plane birefringence distribution) a specific range, rainbow unevenness when viewed from the front and rainbow unevenness when viewed from an oblique direction are simultaneously improved. be able to.
Hereinafter, the preferable aspect of the polyester resin film of this invention is demonstrated.

<Thickness of polyester resin film>
The thickness of the polyester resin film of the present invention satisfies the following formula (1), preferably satisfies the following formula (1-2), and more preferably satisfies the following formula (1-3).
15 μm ≦ Th ≦ 60 μm (1)
20 μm ≦ Th ≦ 55 μm Formula (1-2)
23 μm ≦ Th ≦ 50 μm Formula (1-3)
Th represents the thickness (μm) of the polyester resin film.
When the thickness of the polyester resin film is 15 μm or more, wrinkles or the like are unlikely to occur at the time of bonding to a liquid crystal display device or a touch panel, which is unlikely to cause a rainbow unevenness display failure. If the thickness of the polyester resin film is 60 μm or less, rainbow unevenness becomes difficult to see.
As for the thickness Th of the polyester resin film, for example, using a contact-type film thickness meter, 50 points are sampled at equal intervals over 0.5 m in the longitudinally stretched direction (longitudinal direction), and further, the film width direction (perpendicular to the longitudinal direction). ) Was sampled at regular intervals (50 equal parts in the width direction) over the entire width of the film, and 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.

<Birefringence of polyester resin film>
The in-plane birefringence of the polyester resin film of the present invention satisfies the following formula (2), preferably satisfies the following formula (2-2), and more preferably satisfies the following formula (2-3).
0 <nx−ny ≦ 0.020 (2)
0.001 ≦ nx−ny ≦ 0.015 Formula (2-2)
0.002 ≦ nx−ny ≦ 0.012 Formula (2-3)
nx represents the refractive index in the slow axis direction in the polyester resin film surface, and ny represents the refractive index in the fast axis direction in the polyester resin film surface.
When the in-plane birefringence of the polyester resin film of the present invention is larger than 0, the in-plane birefringence distribution (nΔ) does not become too large, and rainbow unevenness becomes difficult to see. If the in-plane birefringence of the polyester resin film of the present invention is 0.020 or less, rainbow unevenness is difficult to see.

The birefringence in the thickness direction of the polyester resin film of the present invention satisfies the following formula (3) from the viewpoint of rainbow unevenness, preferably satisfies the following formula (3-2), and satisfies the following formula (3-3): It is more preferable.
0.120 ≦ (nx + ny) / 2−nz <0.160 Formula (3)
0.130 ≦ (nx + ny) / 2−nz <0.159 Expression (3-2)
0.140 ≦ (nx + ny) / 2−nz <0.158 Formula (3-3)
nx represents the refractive index in the slow axis direction in the polyester resin film surface, ny represents the refractive index in the fast axis direction in the polyester resin film surface, and nz represents the refractive index in the polyester resin film thickness direction.
If the birefringence in the thickness direction of the polyester resin film of the present invention is less than 0.120, the vertical and horizontal orientations become too small, causing problems in film strength, and the film cannot be formed. If the birefringence in the thickness direction of the polyester resin film of the present invention is less than 0.160, rainbow unevenness is difficult to see.

nx, ny, and nz can be measured as follows.
Using two polarizing plates, the orientation axis direction of the polyester resin 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, and equations (2) to (4) were determined.

The unevenness (in-plane birefringence distribution) as a difference between the maximum value and the minimum value of (nx−ny) in an arbitrary area 1 m ² of the polyester resin film of the present invention satisfies the following formula (4), and It is preferable to satisfy the formula (4-2), and it is more preferable to satisfy the following formula (4-3).
0 <nΔ ≦ 0.014 (4)
0.001 <nΔ ≦ 0.010 Formula (4-2)
0.002 <nΔ ≦ 0.008 Formula (4-3)
When the in-plane birefringence distribution nΔ is larger than 0, it is not necessary to stretch the polyester resin film at a high magnification, and the in-plane birefringence and the birefringence in the thickness direction are expressed by the above formulas (2) and (3). It becomes easy to control the polyester resin film so as to be within the range. If the in-plane birefringence distribution nΔ is 0.014 or less, rainbow unevenness is difficult to see.
nΔ can be measured as follows.
For a polyester resin film 1 m ^2, uniformly sampled film width direction, the flow direction for each 100 mm. For example, in the case of a film having a film width of 2 m and a film length of 0.5 m, a total of 100 film pieces are cut out, 20 points in the width direction and 5 points in the flow direction. About the magnitude | size of a film piece, it cuts out to the same size as the method described by the above-mentioned refractive index measurement (Abbe refractometer). With respect to all the cut film pieces, the refractive index is measured by the same method as the refractive index measurement described above, and the value of nx−ny is derived. The difference between the maximum value and the minimum value of the nx−ny values of all the film pieces is defined as nΔ.

In-plane birefringence, birefringence in the thickness direction, and in-plane birefringence distribution are the types of polyester resin used in the film, the amount of the polyester resin and additives, the addition of a retardation developer, and the film thickness. The film can be adjusted by the stretching direction and stretching ratio of the film.
There is no particular limitation on the method for controlling the in-plane birefringence, the birefringence in the thickness direction, and the in-plane birefringence distribution within a predetermined range for the polyester resin film of the present invention. Can be achieved. Details will be described later.

<Characteristics of polyester resin film>
(DSC pre-peak temperature)
In the polyester resin film of the present invention, the pre-peak temperature measured by differential scanning calorimetry (DSC) preferably satisfies the following formula (5), more preferably satisfies the following formula (5-2), and the following formula ( It is more preferable to satisfy 5-3).
130 ° C. ≦ Tpre ≦ 200 ° C. Formula (5)
140 ° C. ≦ Tpre ≦ 190 ° C. Formula (5-2)
150 ° C. ≦ Tpre ≦ 180 ° C. Formula (5-3)
Tpre represents a pre-peak temperature measured by differential scanning calorimetry of a polyester resin film, and its unit is ° C.
By setting the pre-peak temperature to 130 ° C. or higher, rainbow unevenness can be suppressed, and further, the problem of strength and heat resistance of the polyester resin film can be solved due to insufficient crystallization. The polyester resin film can be controlled so that the in-plane birefringence distribution falls within the ranges of the above formulas (3) and (4), and the rainbow unevenness becomes difficult to see.
Here, DSC is an abbreviation for differential scanning calorimetry, and the “pre-peak temperature” of DSC is the temperature of the peak that appears first when the polyester resin film is subjected to DSC measurement.
The DSC pre-peak temperature generally corresponds to the highest film surface temperature (heat setting temperature) of the polyester resin film at the time of heat setting during the transverse stretching step performed by uniaxial stretching of the polyester resin film.
The DSC pre-peak temperature is a value obtained by a conventional method in differential scanning calorimetry (DSC).

(density)
The density of the polyester resin film of the present invention is preferably 1.370 to 1.390 g / cm ³ , more preferably 1.372 to 1.388 g / cm ³ , and 1.374 to 1.386 g. More preferably, it is / m ³ .
With a density 1.370g / cm ³ or more, it is possible to eliminate the film strength and heat resistance issues, With 1.390g / cm ³ or less, rainbow unevenness is hardly visible.
The density can be measured according to JIS K7112.

(Heat shrinkage in MD and TD directions)
In the present invention, the thermal shrinkage in the MD direction and TD direction of the polyester resin film after standing at 150 ° C. for 30 minutes is preferably 3.5% or less, more preferably 3% or less. More preferably, it is 5% or less.
By setting the thermal shrinkage rate to 3.5% or less, the shrinkage of the polyester resin film is suppressed when used in a liquid crystal display device or a touch panel, and display failure is less likely to occur.

In the present invention, the heat shrinkage rate in the MD direction of the film after standing 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 resin 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 leaving the sample piece M 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 processing and the interval Amm after the processing is used as the MD thermal contraction rate (S ).

In the present invention, the thermal shrinkage rate in the TD direction of the film after standing 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 resin film cut in 30 mm in the MD direction and 120 mm in the TD direction so as to have an interval of 100 mm in the TD direction. After leaving the sample piece M 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 processing and the interval Amm after the processing is used as the TD thermal contraction rate (S ).

Moreover, although the manufacturing method of a polyester resin film is explained in full detail behind, a polyester resin 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. The MD direction of the film is also referred to as the longitudinal direction of the film. The film width direction is a direction orthogonal to the longitudinal direction. The film width direction is also called a TD (Transverse Direction) direction in a film manufactured while transporting the film.
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.

In the present invention, the thermal shrinkage in the MD direction and TD direction of the polyester resin film after standing at 80 ° C. for 24 hours is preferably 0.3% or less, more preferably 0.2% or less, More preferably, it is 0.15% or less.
By setting the thermal shrinkage rate to 0.3% or less, the shrinkage of the polyester resin film is suppressed when used for a liquid crystal display device or a touch panel, and display failure is less likely to occur.

In the present invention, the thermal shrinkage rate in the MD direction of the film after standing at 80 ° C. for 24 hours is defined as follows.
Two reference lines are put in advance in a sample piece M of a polyester resin 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 leaving the sample piece M in a heating oven at 80 ° C. under no tension for 24 hours, 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 processing and the interval Amm after the processing is used as the MD thermal contraction rate (S ).

The thermal shrinkage rate in the TD direction of the film after standing at 80 ° C. for 24 hours is defined as follows.
Two reference lines are put in advance in a sample piece M of a polyester resin film cut in 30 mm in the MD direction and 120 mm in the TD direction so as to have an interval of 100 mm in the TD direction. After leaving the sample piece M in a heating oven at 80 ° C. under no tension for 24 hours, 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 processing and the interval Amm after the processing is used as the TD thermal contraction rate (S ).

(Film width)
The width of the polyester resin film of the present invention is preferably 0.6 to 6 m, more preferably 0.8 to 5.6 m, and further preferably 1.0 to 3.0 m.

(Orientation angle unevenness in the width direction)
The polyester resin film of the present invention has a non-uniformity (hereinafter also referred to as width-direction orientation angle unevenness) of 15 ° or less as a difference between the maximum value and the minimum value of the orientation angle in the film width direction. It is preferable from the viewpoint that the shrinkage rate unevenness does not become excessively large and the film is difficult to break in the subsequent process.
The orientation angle unevenness in the width direction is more preferably 12 ° or less, further preferably 10 ° or less, and most preferably 8 ° or less.

(Refractive index, crystallinity)
The polyester resin film of the present invention is preferably biaxially oriented. Specifically, the polyester resin film of the present invention preferably has a refractive index in the longitudinal direction of 1.590 or less and a crystallinity exceeding 5%.
The degree of crystallinity of the polyester resin film of the present invention is preferably 5% or more, more preferably 20% or more, and further preferably 30% or more.

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

(1-1) Polyester Resin As the above polyester resin, one having a 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 because of cost and heat resistance. More preferably, it is PET (PEN has a slight Re / Rth, that is, in-plane retardation / thickness direction retardation tends to be small).
Polyester is most preferably polyethylene terephthalate, but polyethylene naphthalate can also be preferably used. For example, those described in JP-A-2008-39803 can be preferably used.

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

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

(1-3) Catalyst For the polymerization of the polyester resin, Sb, Ge, Ti, Al-based catalysts are used, preferably Sb, Ti, Al-based catalysts, and more preferably Al-based catalysts.
That is, it is preferable that the polyester resin used as the raw material resin is polymerized using an aluminum catalyst.
By using an Al-based catalyst, Re (in-plane retardation) is more easily 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 be oriented and to develop in-plane birefringence.

(1-3-1) Al-based catalyst As the Al-based catalyst, those described in [0013] to [0148] of WO2011 / 040161 ([0021] to [0123] of US2012 / 0183761) are used. The contents described in these publications are incorporated herein by reference.
The method for polymerizing the polyester resin using the Al-based catalyst is not particularly limited, but specifically, [0091] to [0094] of WO2012 / 008488 ([0144] to US2013 / 0112271) [0153]) can be used to polymerize according to these publications, the contents of which are incorporated herein.
Such Al-based catalysts include, for example, [0052] to [0054], [0099] to [0104] of JP2012-122051 ([0045] to [0047], [0091] of WO2012 / 029725. To [0096]) can be prepared according to these publications, and the contents described in these publications are incorporated herein. The amount of the Al-based catalyst is preferably 3 to 80 ppm, more preferably 5 to 60 ppm, and still more preferably 5 to 40 ppm as the amount of Al element with respect to the mass of the polyester resin.

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

(1-4) Additive:
It is also preferable to add a known additive to the polyester resin 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 resin film generally requires transparency, it is preferable to keep the additive amount to a minimum.

(1-4-1) Ultraviolet (UV) absorber:
The polyester resin film of the present invention may 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 resin film.
As the ultraviolet absorber, there are an organic ultraviolet absorber and an inorganic ultraviolet absorber. From the viewpoint of transparency, an organic ultraviolet absorber is preferable. Those described in [0057] of WO2012 / 157762 and cyclic iminoester-based ultraviolet absorbers described later can be used.

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

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

General formula (1)

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 resin 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.

Moreover, in the case of the polyester resin film of the present invention having a multilayer structure, those having at least a three-layer structure are preferred, and the ultraviolet absorber is preferably blended in the intermediate layer. By blending an ultraviolet absorber in the intermediate layer, this compound can be prevented from bleeding out to the film surface, and as a result, characteristics such as film adhesion can be maintained.
The masterbatch method described in [0050] to [0051] of WO2011 / 162198 can be used for these formulations.

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

[Production method of polyester resin film]
The method for producing a polyester resin film of the present invention includes a step of melt-extruding a polyester raw material resin into a sheet shape, cooling on a casting drum to form a polyester resin film, and longitudinally stretching the formed polyester resin film in the longitudinal direction. A longitudinal stretching step and a transverse stretching step of transversely stretching the longitudinally stretched polyester resin film in the width direction perpendicular to the longitudinal direction, and satisfying the following formulas (1 ′) and (6) to (11).
15 μm ≦ Th ′ ≦ 60 μm Formula (1 ′)
2.8 ≦ DMD ≦ 3.6 Formula (6)
DMD−1.0 ≦ DTD ≦ DMD + 0.5 (7)
130 ° C. ≦ TSET ≦ 200 ° C. Formula (8)
80 ° C. ≦ TTDs ≦ 120 ° C. Formula (9)
120 ° C. ≦ TTDe ≦ 180 ° C. Formula (10)
20 ° C. ≦ TTDe−TTDs ≦ 80 ° C. Formula (11)
In the formulas (1 ′) and (6) to (11), Th ′ represents the thickness of the polyester resin film after the transverse stretching step, and the unit of the thickness of the polyester resin film after the transverse stretching step is μm; Represents the draw ratio in the machine direction, DTD represents the draw ratio in the transverse direction, TSET represents the maximum surface temperature at the time of heat setting, TTDs represents the film surface temperature at the start of transverse stretching, and TTDe is the end of transverse stretching Represents the film surface temperature of the hour; units of TSET, TTDs, and TTDe are in ° C.
The method for producing a polyester resin film of the present invention includes a preheating portion for preheating the polyester resin film after longitudinal stretching to a temperature at which the polyester resin film can be stretched, and stretching the preheated polyester resin film in the width direction perpendicular to the longitudinal direction. The heat-fixed part that heats and crystallizes the stretched part, the longitudinally stretched and the laterally stretched polyester resin film, and heat-sets, heats the polyester resin film that is heat-fixed, and relaxes the tension of the polyester resin film It is preferable to convey the polyester resin film in this order to a heat relaxation part for removing residual distortion of the film and a cooling part for cooling the polyester resin film after heat relaxation.

In the method for producing a polyester resin film of the present invention, the draw ratio in the machine direction and the transverse direction are within a specific range, and the highest reached film surface temperature at the time of heat setting, the film surface temperature at the start of transverse stretching, and the end of transverse stretching. By setting the film surface temperature at a specific range, it is possible to simultaneously improve rainbow unevenness when viewed from the front and rainbow unevenness when viewed from an oblique direction.

There is no restriction | limiting in particular as a manufacturing method of the polyester resin film of this invention, The polyester resin film of this invention can be manufactured by a well-known method.
Hereinafter, the preferable aspect of the manufacturing method of the polyester resin film of this invention is demonstrated.

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

<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 resin film is produced by being extruded in multiple layers, the thickness of the inner layer (ratio to the total layer) of the obtained polyester resin film is preferably 50% to 95%, more preferably 60% to 90%. More preferably, it is 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 the die onto a casting drum and cool and solidify to obtain an unstretched polyester resin film (raw fabric).
In the production method of the present invention, the refractive index in the longitudinal direction of the unstretched polyester resin film is preferably 1.590 or less, more preferably 1.585 or less, and further preferably 1.580 or less.
In the production method of the present invention, the crystallinity of the unstretched polyester resin 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 resin 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 resin film, a polymer layer (preferably an easy-adhesion layer) may be formed by coating before or after stretching described later.
Examples of the polymer layer generally include a functional layer that the polarizing plate may have, and among them, it is preferable to form an easy adhesion layer as the polymer layer. The easy-adhesion layer can be applied by the method described in [0062] to [0070] of WO2012 / 157762.

<Longitudinal stretching>
The production method of the present invention includes a longitudinal stretching step of longitudinally stretching the molded polyester resin film in the longitudinal direction.
The longitudinal stretching of the film is performed, for example, by applying tension between two or more pairs of nip rolls arranged in the film conveyance direction while passing the film through a pair of nip rolls sandwiching the film and conveying the film in the longitudinal direction of the film. be able to. Specifically, for example, when a pair of nip rolls A is installed on the upstream side in the film conveyance direction and a pair of nip rolls B is installed on the downstream side, when the film is conveyed, the rotational speed of the nip roll B on the downstream side is By making it faster than the rotational speed of the nip roll A on the upstream side, the film is stretched in the transport direction (MD direction). Two or more pairs of nip rolls may be installed independently on the upstream side and the downstream side, respectively. Moreover, you may perform the longitudinal stretch of a polyester resin film using the longitudinal stretch apparatus provided with the said nip roll.

In the longitudinal stretching step, the stretching ratio in the longitudinal direction of the polyester resin film satisfies the following formula (6), preferably satisfies the following formula (6-2), and more preferably satisfies the following formula (6-3). .
2.8 ≦ DMD ≦ 3.6 Formula (6)
2.9 ≦ DMD ≦ 3.5 Formula (6-2)
3.0 ≦ DMD ≦ 3.4 Formula (6-3)
In the formula, DMD represents the stretching ratio in the longitudinal direction.
When the stretching ratio in the longitudinal direction is 2.8 times or more, the problem of strength due to insufficient orientation hardly occurs. When it is 3.6 times or less, it becomes easy to control the birefringence in the thickness direction in the above formula (3) and the in-plane birefringence distribution in the above formula (4) to a specific range, and rainbow unevenness can be seen. It becomes difficult.

The area stretch ratio represented by the product of the longitudinal and lateral stretch ratios is preferably 6 to 18 times, more preferably 8 to 16 times, more preferably 9 to 15 times the area of the polyester resin film before stretching. More preferably, it is double.
The temperature during the longitudinal stretching of the polyester resin film (hereinafter also referred to as “longitudinal stretching temperature”) is preferably Tg−20 ° C. or more and Tg + 50 ° C. or less when the glass transition temperature of the polyester resin film is Tg. It is preferably Tg-10 ° C. or higher and Tg + 40 ° C. or lower, more preferably Tg ° C. or higher and Tg + 30 ° C. or lower.

In addition, as a means for heating the polyester resin film, when stretching using a roll such as a nip roll, the polyester resin film in contact with the roll is heated by providing a pipe that can flow a heater or a hot solvent inside the roll. can do. Moreover, even when not using a roll, a polyester resin film can be heated by spraying a warm air on a polyester resin film, making it contact with heat sources, such as a heater, or letting the vicinity of a heat source pass.

In the manufacturing method of the polyester resin film of this invention, the horizontal stretch process mentioned later is included separately from a vertical stretch process. Therefore, in the method for producing a polyester resin film of the present invention, the polyester resin film is at least 2 in the longitudinal direction (conveying direction, MD) of the polyester resin film and the direction (TD direction) orthogonal to the longitudinal direction of the polyester resin film. It will stretch to the axis. The stretching in the MD direction and the TD direction may be performed at least once each.
In addition, "the direction (TD) orthogonal to the longitudinal direction (conveyance direction, MD) of a polyester resin film" intends the direction perpendicular | vertical (90 degrees) with the longitudinal direction (conveyance direction, MD) of a polyester resin film. However, a direction in which the angle with respect to the longitudinal direction (that is, the conveyance direction) can be regarded as 90 ° due to mechanical errors or the like (for example, a direction of 90 ° ± 5 ° with respect to the MD direction) is included.

The biaxial stretching method may be any of a sequential biaxial stretching method in which longitudinal stretching and lateral stretching are separated and a simultaneous biaxial stretching method in which longitudinal stretching and lateral stretching are simultaneously performed. The longitudinal stretching and the lateral stretching may be independently performed twice or more, and the order of the longitudinal stretching and the lateral stretching is not limited. For example, stretching modes such as longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, transverse stretching → longitudinal stretching can be mentioned. Of these, longitudinal stretching → transverse stretching is preferred.

The birefringence of the film after longitudinal stretching and before lateral stretching preferably satisfies the following formula (12), more preferably satisfies the following formula (12-2), and satisfies the following formula (12-3). Further preferred.
0.030 <nx (MD) −ny (MD) ≦ 0.090 (12)
0.040 ≦ nx (MD) −ny (MD) ≦ 0.080 Expression (12-2)
0.045 ≦ nx (MD) −ny (MD) ≦ 0.075 Formula (12-3)
In the formula, nx (MD) represents the refractive index in the slow axis direction in the plane of the polyester resin film after longitudinal stretching, and ny (MD) represents the fast axis direction in the plane of the polyester resin film after longitudinal stretching. Refractive index.
When Expression (12) exceeds 0.030 and is equal to or less than 0.090, control within the predetermined range in Expressions (2) to (4) can be performed, and rainbow unevenness becomes difficult to see.
The birefringence of the film after longitudinal stretching and before lateral stretching preferably satisfies the following formula (13) in addition to satisfying the above formula (12), and preferably satisfies the following formula (13-2): It is more preferable that the following formula (13-3) is satisfied.
0.030 ≦ (nx (MD) + ny (MD)) / 2−nz (MD) <0.090 (13)
0.035 ≦ (nx (MD) + ny (MD)) / 2−nz (MD) ≦ 0.080 (13-2)
0.040 ≦ (nx (MD) + ny (MD)) / 2−nz (MD) ≦ 0.075 (13-3)
In the formula, nx (MD) represents the refractive index in the slow axis direction in the plane of the polyester resin film after longitudinal stretching, and ny (MD) represents the fast axis direction in the plane of the polyester resin film after longitudinal stretching. The refractive index is represented, and nz (MD) represents the refractive index in the thickness direction of the polyester resin film after longitudinal stretching.
If the expression (13) is 0.030 or more and less than 0.090, it becomes possible to control within the predetermined range in the above expressions (2) to (4), and the rainbow unevenness becomes difficult to see.
nx (MD), ny (MD), and nz (MD) can be measured by the same method as the above nx, ny, and nz.

<Horizontal stretching>
In the present invention, the polyester resin film after longitudinal stretching is stretched in the width direction perpendicular to the longitudinal direction.

The transverse stretching step in the present invention is a step of transversely stretching the polyester resin film after longitudinal stretching in the width direction orthogonal to the longitudinal direction.
(A) a preheating portion for preheating the polyester resin film after longitudinal stretching to a temperature at which it can be stretched;
(B) a stretched part that stretches the preheated polyester resin film in a transverse direction by applying tension to the width direction perpendicular to the longitudinal direction;
(C) a heat fixing part for heating and crystallizing the heat-fixed polyester resin film after the longitudinal stretching and the transverse stretching;
(D) a heat relaxation portion that heats the heat-fixed polyester resin film, relaxes the tension of the polyester resin film, and removes residual strain of the film; and
(E) It is preferable to convey a polyester resin film in this order to the cooling part which cools the polyester resin film after heat relaxation.
In the transverse stretching step of the present invention, the specific means is not limited as long as the polyester resin film is transversely stretched in the above configuration, but a lateral stretching apparatus or biaxial capable of processing each step constituting the above configuration. It is preferable to use a stretching machine.

-Axis stretching machine-
As shown in FIG. 1, the biaxial stretching machine 100 includes a pair of

annular rails

60a and 60b, and gripping members 2a to 2l attached to the respective annular rails and movable along the rails. The

annular rails

60a and 60b are arranged symmetrically with respect to the polyester resin film 200, and can be stretched in the film width direction by holding the polyester resin film 200 with the gripping members 2a to 2l and moving along the rails. It is like that.
FIG. 1 is a top view showing an example of a biaxial stretching machine from the top.

The biaxial stretching machine 100 includes a preheating unit 10 that preheats the polyester resin film 200 and a stretching unit that stretches the polyester resin film 200 in the arrow TD direction, which is a direction orthogonal to the arrow MD direction, and applies tension to the polyester resin film. 20, a heat fixing portion 30 for heating the tensioned polyester resin film while applying tension, and a heat relaxation portion 40 for relaxing the tension of the heat-fixed polyester resin film by heating. The cooling part 50 which cools the polyester resin film which passed through the heat relaxation part is comprised.

Grip members

2a, 2b, 2e, 2f, 2i, and 2j that are movable along the annular rail 60a are attached to the annular rail 60a, and the annular rail 60b is movable along the annular rail 60b. Gripping

members

2c, 2d, 2g, 2h, 2k, and 2l are attached. The

grip members

2a, 2b, 2e, 2f, 2i, and 2j grip one end of the polyester resin film 200 in the TD direction, and the

grip members

2c, 2d, 2g, 2h, 2k, and 2l are polyester resins. The other end of the film 200 in the TD direction is gripped. The gripping members 2a to 2l are generally called chucks, clips, and the like.
The gripping

members

2a, 2b, 2e, 2f, 2i, and 2j move counterclockwise along the annular rail 60a, and the gripping

members

2c, 2d, 2g, 2h, 2k, and 2l move along the annular rail 60b. Move clockwise.

The gripping members 2a to 2d grip the end portion of the polyester resin film 200 in the preheating portion 10 and move along the

annular rail

60a or 60b while being gripped, and the extending portion 20 and the gripping members 2e to 2h are located. It proceeds through the thermal relaxation section 40 to the cooling section 50 where the gripping members 2i to 2l are located. Thereafter, the gripping

members

2a and 2b and the gripping

members

2c and 2d are separated from the end of the polyester resin film 200 at the end of the cooling unit 50 on the downstream side in the MD direction in the transport direction, and then the annular rail 60a or It moves along 60b and returns to the preheating part 10. At this time, the polyester resin film 200 moves in the direction of the arrow MD, and sequentially preheats in the preheating unit 10, stretches in the stretching unit 20, heat fixing in the heat fixing unit 30, heat relaxation in the heat relaxation unit 40, Cooling in the cooling unit 50 is performed and transverse stretching is performed. The moving speed of the gripping members 2a to 2l in each region such as the preheating portion becomes the conveying speed of the polyester resin film 200.

The gripping members 2a to 2l can change the moving speed independently of each other.
The biaxial stretching machine 100 enables transverse stretching in which the polyester resin film 200 is stretched in the TD direction in the stretching unit 20, but the polyester resin film can be changed by changing the moving speed of the gripping members 2a to 2l. 200 can also be stretched in the MD direction. That is, simultaneous biaxial stretching can be performed using the biaxial stretching machine 100.

The gripping member for gripping the end portion in the TD direction of the polyester resin film 200 is only 2a to 2l in FIG. 1, but in order to support the polyester resin film 200, the biaxial stretching machine 100 is not limited to 2a to 2l. A gripping member (not shown) is attached. Hereinafter, the gripping members 2a to 21 may be collectively referred to as “grip member 2”.

(A. Preheating part)
In the preheating part, the polyester resin film after longitudinal stretching in the longitudinal stretching step is preheated to a temperature at which stretching is possible.
As shown in FIG. 1, the polyester resin film 200 is preheated in the preheating unit 10. In the preheating unit 10, the polyester resin film 200 is heated in advance before being stretched so that the polyester resin film 200 can be easily stretched laterally.

The film surface temperature at the end point of the preheating part (hereinafter also referred to as “preheating temperature”) is preferably Tg−10 ° C. to Tg + 60 ° C., where Tg is the glass transition temperature of the polyester resin film 200, and Tg ° C. It is more preferable that Tg + 50 ° C.
The end point of the preheating portion refers to the time when the preheating of the polyester resin film 200 is finished, that is, the position where the polyester resin film 200 is separated from the region of the preheating portion 10.

(B. Stretched part)
In the stretching portion, the polyester resin film preheated in the preheating portion is stretched in the transverse direction with tension in the width direction (TD direction) perpendicular to the longitudinal direction (MD direction).
As shown in FIG. 1, in the stretched portion 20, the preheated polyester resin film 200 is laterally stretched at least in the TD direction orthogonal to the longitudinal direction of the polyester resin film 200 to give tension to the polyester resin film 200.
Stretching (lateral stretching) in the direction (TD) perpendicular to the longitudinal direction (conveying direction, MD) of the polyester resin film 200 is an angle perpendicular to the longitudinal direction (conveying direction, MD) of the polyester resin film 200 (90 °). Although it is intended to be stretched in the direction, the direction may be in the range of mechanical error. The range of the mechanical error is a direction at an angle (90 ° ± 5 °) that can be regarded as perpendicular to the longitudinal direction (conveying direction, MD) of the polyester.

In the stretched portion 20, the stretch ratio (stretch ratio in the transverse direction) of the polyester resin film 200 satisfies the following formula (7), preferably satisfies the following formula (7-2), It is more preferable to satisfy.
DMD−1.0 ≦ DTD ≦ DMD + 0.5 (7)
DMD−0.8 ≦ DTD ≦ DMD + 0.3 (7-2)
DMD−0.6 ≦ DTD ≦ DMD + 0.2 Formula (7-3)
In the formula, DMD represents the stretching ratio in the longitudinal direction, and DTD represents the stretching ratio in the transverse direction.
When the transverse draw ratio is (DMD-1.0) times or more or (DMD + 0.5) times or less, the in-plane birefringence in the above formula (2) is controlled within a predetermined range. Becomes easier and the rainbow unevenness becomes difficult to see.

In the stretched portion 20, the area stretch ratio (product of each stretch ratio) of the polyester resin film 200 is preferably 6 to 18 times, more preferably 8 to 16 times the area of the polyester resin film 200 before stretching. Preferably, it is 9 to 15 times.

The film surface temperature at the start of transverse stretching of the polyester resin film 200 satisfies the following formula (9), preferably satisfies the following formula (9-2), and more preferably satisfies the following formula (9-3).
80 ° C. ≦ TTDs ≦ 120 ° C. Formula (9)
85 ° C. ≦ TTDs ≦ 115 ° C. Formula (9-2)
90 ° C. ≦ TTDs ≦ 110 ° C. Formula (9-3)
In the formula, TTDs represents the film surface temperature at the start of transverse stretching (unit: ° C.).
When the film surface temperature at the start of the transverse stretching is 80 ° C. or higher or 120 ° C. or lower, the in-plane birefringence distribution in the above formula (4) can be easily controlled within a predetermined range, and rainbow unevenness Becomes difficult to see.

The film surface temperature at the end of the transverse stretching of the polyester resin film 200 satisfies the following formula (10), preferably satisfies the following formula (10-2), and more preferably satisfies the following formula (10-3). preferable.
120 ° C. ≦ TTDe ≦ 180 ° C. Formula (10)
125 ° C. ≦ TTDe ≦ 170 ° C. Formula (10-2)
130 ° C. ≦ TTDe ≦ 160 ° C. Formula (10-3)
In the formula, TTDe represents the film surface temperature at the end of transverse stretching (unit: ° C.).
When the film surface temperature at the end of the transverse stretching is 120 ° C. or higher or 180 ° C. or lower, the in-plane birefringence distribution in the formula (4) can be easily controlled within a predetermined range, and rainbow unevenness is caused. It becomes difficult to see.

Further, the difference (TTDe−TTDs) between the film surface temperature at the end of the lateral stretching of the polyester resin film 200 and the film surface temperature at the start of the lateral stretching of the polyester resin film 200 satisfies the following formula (11), 11-2) is preferably satisfied, and it is more preferable that the following formula (11-3) is satisfied.
20 ° C. ≦ TTDe−TTDs ≦ 80 ° C. Formula (11)
25 ° C. ≦ TTDe−TTDs ≦ 70 ° C. Formula (11-2)
30 ° C. ≦ TTDe−TTDs ≦ 60 ° C. Formula (11-3)
In the formula, TTDs represents the film surface temperature at the start of transverse stretching (unit: ° C), and TTDe represents the film surface temperature at the end of transverse stretching (unit: ° C).
If the difference is 20 ° C. or more or 80 ° C. or less, it is easy to control the in-plane birefringence distribution in the formula (4) to a predetermined range, and rainbow unevenness is difficult to see.

As described above, the movement speeds of the gripping members 2a to 2l can be changed independently. Therefore, for example, by increasing the moving speed of the gripping member 2 on the downstream side in the MD direction of the stretching section 20 such as the stretching section 20 and the heat fixing section 30 rather than the moving speed of the gripping member 2 in the preheating section 10, the polyester resin film It is also possible to perform longitudinal stretching in which 200 is stretched in the transport direction (MD direction).
The longitudinal stretching of the polyester resin film 200 in the lateral stretching step may be performed only by the stretching unit 20, or may be performed by the heat fixing unit 30, the thermal relaxation unit 40, or the cooling unit 50 described later. You may longitudinally stretch in several places.

(C. Heat fixing part)
In the heat setting section, the polyester resin film that has already been subjected to longitudinal stretching and lateral stretching is heated and crystallized to be heat-set.
The heat setting means that the polyester resin film 200 is heated in the stretched portion 20 while being tensioned to crystallize the polyester.

In the heat fixing part 30 shown in FIG. 1, the maximum reached film surface temperature of the surface of the polyester resin film 200 with respect to the tensioned polyester resin film 200 (in this specification, “TSET”, “heat fixing temperature”) Also satisfies the following formula (8), preferably satisfies the following formula (8-2), and more preferably satisfies the following formula (8-3).
130 ° C. ≦ TSET ≦ 200 ° C. Formula (8)
140 ° C. ≦ TSET ≦ 190 ° C. Formula (8-2)
150 ° C. ≦ TSET ≦ 180 ° C. Formula (8-3)
In the formula, TSET represents the maximum film surface temperature at the time of heat setting (unit: ° C).
When the heat setting temperature (TSET) is 130 ° C. or higher, crystallization is sufficient and problems with film strength and heat resistance hardly occur. Moreover, it becomes easy to control the birefringence distribution in the above formula (4) within a favorable range, and rainbow unevenness becomes difficult to see. When the heat setting temperature (TSET) is 200 ° C. or less, it becomes easy to control the birefringence in the thickness direction in the above formula (3) and the in-plane birefringence distribution in the above formula (4) to a predetermined range. Rainbow rainbow becomes difficult to see.
The maximum film surface temperature (heat setting temperature) is a value measured by bringing a thermocouple into contact with the surface of the polyester resin film 200.

Furthermore, when TSET is controlled to 130 ° C. to 200 ° C., it is preferable that the variation in the maximum film surface temperature in the film width direction is 0.5 ° C. or higher and 10.0 ° C. or lower. In the film width direction, the variation in the maximum film surface temperature of the film is 0.5 ° C. or more, which is advantageous in terms of wrinkles during conveyance in the subsequent process, and the variation is 10.0 ° C. or less. By suppressing, variation in crystallinity in the width direction is suppressed. Thereby, the difference in slackness in the film width direction is reduced, the generation of scratches on the film surface during the production process is prevented, and the hydrolysis resistance is enhanced.
Among the above, the variation in the maximum reached film surface temperature is more preferably 0.5 ° C. or more and 7.0 ° C. or less, further preferably 0.5 ° C. or more and 5.0 ° C. or less, for the same reason as described above. It is particularly preferably from 5 ° C to 4.0 ° C.

Further, the heating of the film during heat setting may be performed only from one side of the film or from both sides. For example, when cooled on a casting drum after melt extrusion in the film forming process, the molded polyester resin film is cooled differently on one side and the opposite side, so the film is likely to curl easily It has become. For this reason, it is preferable to perform the heating in the heat setting on the surface brought into contact with the casting drum in the film forming step. Curling can be eliminated by making the heating surface in heat setting a surface in contact with the casting drum, that is, a cooling surface.
At this time, in the heating, the surface temperature immediately after heating on the heating surface in heat setting is higher in the range of 0.5 ° C. or more and 5.0 ° C. or less than the surface temperature of the non-heating surface opposite to the heating surface. It is preferable to be carried out as follows. When the temperature of the heating surface during heat setting is higher than that of the opposite surface and the temperature difference between the front and back surfaces is 0.5 to 5.0 ° C., the curl of the film is more effectively eliminated. From the viewpoint of curling elimination effect, the temperature difference between the heated surface and the non-heated surface on the opposite side is more preferably in the range of 0.7 to 3.0 ° C, and 0.8 ° C or higher and 2.0 ° C. The following is more preferable.

Moreover, in this invention, the TD direction edge part of a polyester resin film is selectively radiatively heated with a heater in at least one of the heat fixing part 30 and the heat relaxation part 40. Unless such radiant heating is performed, the MD thermal shrinkage rate in the TD direction of the produced polyester resin film is not lowered, and the distribution of the MD thermal shrinkage rate and the amount of change in the MD thermal shrinkage rate are not reduced.
When the end portion of the film in the TD direction is radiantly heated in the heat relaxation unit 40, the radiant heating in the heat fixing unit 30 may be omitted, or may be performed in both the heat fixing unit 30 and the heat relaxation unit 40. .
Here, “the end portion in the TD direction of the polyester resin film” refers to the edge of both ends in the TD direction of the polyester resin film and the region from the edge to 10% of the total length (that is, the width) of the polyester resin film in the TD direction. Say.

The heating of the end portion in the TD direction of the polyester resin film is performed using a heater capable of radiation heating, and at least one end portion in the TD direction of the polyester resin film is selectively heated. From the viewpoint of suppressing local MD heat shrinkage, it is preferable to heat both ends of the polyester resin film in the TD direction. Note that “selectively heating” means that the entire film including the end of the polyester resin film is not heated but the film end 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).

The heating of the end portion in the TD direction of the polyester resin film is preferably performed by adjusting the surface temperature of the heater and the distance (linear distance) between the polyester resin film surface and the heater.
When the surface temperature of the heater is 300 ° C. to 800 ° C., the distance between the polyester resin film surface and the heater is preferably 20 mm to 250 mm, the heater surface temperature is 400 ° C. to 700 ° C., and between the film and the heater The distance is more preferably 50 mm to 200 mm.

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 up to 3.0%. If it does in this way, the local increase / decrease in MD thermal contraction rate can be suppressed, generation | occurrence | production of a stripe burr can be suppressed, and hydrolysis resistance can be improved more.

When heating in the heat setting part, it is preferable that the residence time in the heat setting part is 5 seconds or more and 50 seconds or less. The residence time is the time during which the state in which the film is heated in the heat fixing part is continued. When the residence time is 5 seconds or longer, the change in crystallinity with respect to the heating time is small, and therefore, it is advantageous in that unevenness of crystallinity in the width direction is relatively less likely to occur. This is advantageous in terms of productivity because it is not necessary to extremely reduce the line speed.
Among these, the residence time is preferably 8 seconds or longer and 40 seconds or shorter, and more preferably 10 seconds or longer and 30 seconds or shorter, for the same reason as described above.

In the present invention, the polyester resin film end is radiantly heated in at least one of the heat fixing part and the heat relaxation part. Alternatively, selective radiant heating may be performed.
Radiant heating to the end of the polyester resin film in the TD direction reduces the temperature variation in the TD direction of the film, and hence the variation in crystallinity, and makes it easy to suppress local increase and decrease in the MD thermal shrinkage rate.

(D. Thermal relaxation part)
In the heat relaxation portion, the heat-fixed polyester resin film is heated to relieve the tension of the polyester resin film and remove the residual distortion of the film.
As described above, in the method for producing a polyester resin film of the present invention, at least one of the heat fixing portion and the heat relaxation portion, the end portion in the TD direction of the polyester resin film is selectively radiantly heated by the heater. The selective radiant heating of the end portion in the TD direction of the polyester resin film at the heat relaxation portion may be performed in the same manner as the selective radiant heating of the end portion in the TD direction of the polyester resin film at the heat fixing portion. The numerical range and preferred embodiments are also the same.

By the way, heat relaxation is to heat the polyester resin film that has been heat-fixed to relieve the tension of the polyester resin film, and it is preferable to heat the polyester resin film at the heat relaxation portion as follows. .
In the thermal relaxation part 40 shown in FIG. 1, the maximum ultimate film surface temperature of the surface of the polyester resin film 200 is 5 ° C. or more lower than the maximum ultimate film surface temperature (TSET) of the polyester resin film 200 in the heat fixing part 30. Thus, the aspect which heats the polyester resin film 200 is preferable.
Hereinafter, the highest reached film surface temperature of the surface of the polyester resin film 200 during _{thermal relaxation} is also referred to as “thermal relaxation temperature (T _{thermal relaxation} )”.

In the thermal relaxation section 40, the thermal relaxation temperature (T _{thermal relaxation} ) is heated at a temperature lower by 5 ° C. or more (T _{thermal relaxation} ≦ TSET−5 ° C.) than the heat fixing temperature (TSET) to release the tension (the stretching tension is _reduced ). By reducing the size, the dimensional stability of the polyester resin film can be further improved.
When the T _{heat relaxation} is “TSET-5 ° C.” or less, the hydrolysis resistance of the polyester resin film is excellent. Further, TSET is preferably 100 ° C. or higher in that the dimensional stability is improved.
Further, T _{thermal relaxation} is preferably in a temperature range of 100 ° C. or higher and 15 ° C. or lower than TSET (100 ° C. ≦ T _{thermal relaxation} ≦ TSET−15 ° C.), 110 ° C. or higher, and TSET Is more preferably a temperature range lower than 25 ° C. (110 ° C. ≦ T _{thermal relaxation} ≦ TSET−25 ° C.), 120 ° C. or higher and 30 ° C. lower than TSET (120 ° C. ≦ T _{thermal relaxation} ≦ TSET-30 ° C. is particularly preferable.
The T _{heat relaxation} is a value measured by bringing a thermocouple into contact with the surface of the polyester resin film 200.

The longitudinal relaxation rate ΔS in the thermal relaxation portion is preferably 1 to 10%, more preferably 2 to 9%, and further preferably 3 to 8%.
By setting the longitudinal relaxation rate to 1% or more, the thermal shrinkage rate in the vertical direction of the film is reduced, and when it is used as a liquid crystal display or a touch panel, the shrinkage of the film is suppressed and the display failure is reduced. By setting the relaxation rate to 10% or less, the relaxation unevenness is reduced and the display failure is reduced.
The lateral relaxation rate ΔL in the thermal relaxation portion is preferably 3 to 23%, more preferably 5 to 21%, and even more preferably 7 to 19%.
By making the lateral relaxation rate 3% or more, the thermal shrinkage rate in the lateral direction of the film is reduced, and when it is used as a liquid crystal display or touch panel, the shrinkage of the film is suppressed and the display failure is reduced. By setting the relaxation rate to 23% or less, relaxation unevenness is reduced and display failure is reduced.

The relaxation rate ΔS in the vertical direction can be obtained by the following equation, and the relaxation rate ΔL in the horizontal direction can be obtained by the following equation.

In the formula, L1 represents the maximum width (length in the TD direction) of the polyester resin film 200, and L2 represents the width of the polyester resin film at the end of the cooling part where the polyester resin film is separated from the cooling part. S1 represents the conveyance speed in the preheating part 10 of the polyester resin film 200, and S2 represents the conveyance speed of the polyester resin film in the edge part of a cooling part.

L1 is the maximum length of the polyester resin film in the TD direction after the polyester resin film is widened in the TD direction at the stretched portion.
L2 is the width of the polyester resin film when the gripping members (the gripping members 2j and 2l in FIG. 1), which are located in the cooling section and grip the polyester resin film, release the polyester resin film.
S1 corresponds to the moving speed of a gripping member (2a to 2d in FIG. 1) that grips the polyester resin film and moves the edge of the annular rail.
S2 corresponds to the conveyance speed when the polyester resin film 200 exceeds the straight line connecting the P point and the Q point.

(E. Cooling part)
In a cooling part, the polyester resin film after heat-relaxing in a heat relaxation part is cooled.
As shown in FIG. 1, in the cooling part 50, the polyester resin film 200 which passed through the heat relaxation part 40 is cooled. By cooling the polyester resin film 200 heated by the heat fixing part 30 or the heat relaxation part 40, the shape of the polyester resin film 200 is fixed.

The temperature (hereinafter also referred to as “cooling temperature”) of the polyester at the cooling part outlet of the polyester resin film 200 in the cooling part 50 is lower than the glass transition temperature Tg + 50 ° C. of the polyester resin film 200. preferable. Specifically, the temperature is preferably 25 ° C to 110 ° C, more preferably 25 ° C to 95 ° C, and further preferably 25 ° C to 80 ° C. When the cooling temperature is in the above range, it is possible to prevent the film from shrinking unevenly after releasing the clip.
Here, the cooling unit outlet refers to an end of the cooling unit 50 when the polyester resin film 200 is separated from the cooling unit 50, and the holding member 2 that holds the polyester resin film 200 (in FIG. 1, the holding member 2j and the holding member 2j). 2l) refers to the position when the polyester resin film 200 is released.

Further, in the cooling unit 50, the average cooling rate when the temperature of the surface (film surface) of the polyester resin film is cooled from 150 ° C. to 70 ° C. is preferably in the range of 2 ° C./second to 100 ° C./second. .
Here, an average cooling rate is calculated | required by actually measuring the film | membrane temperature of the film in a cooling zone with a radiation thermometer. That is, the cooling time (Z ÷ S) seconds from 150 to 70 ° C. is obtained from the distance Zm between the point where the film temperature becomes 150 ° C. and the point where the film temperature becomes 70 ° C. and the film conveyance speed Sm / second. From this, the average cooling rate is obtained by further calculating (150−70) ÷ (Z ÷ S).

By setting the average cooling rate to 2 ° C./second or more, insufficient cooling of the polyester resin film in the stretching apparatus is suppressed, and the tackiness of the polyester resin film is lowered. Therefore, in the process after the polyester resin film is separated from the outlet of the cooling section, it is difficult to cause a failure such as the polyester resin film sticking to the roll for film conveyance. Further, by setting the average cooling rate to 100 ° C./second or less, rapid cooling of the polyester resin film is prevented, unevenness of residual stress is hardly generated in the film surface, unevenness of the heat shrinkage rate is suppressed, and streaking is less likely to occur. .
The average cooling rate is more preferably 4 ° C./second to 80 ° C./second, and further preferably 5 ° C./second to 50 ° C./second.

As a temperature control means for heating or cooling the polyester resin film 200 in preheating, stretching, heat setting, heat relaxation, and cooling in the transverse stretching step, hot or cold air is blown on the polyester resin film 200, or polyester resin is used. For example, the film 200 may be brought into contact with the surface of a metal plate whose temperature can be controlled, or the film 200 is passed through the vicinity of the metal plate.

The method for producing a polyester resin of the present invention may include an intermediate cooling part between the laterally stretched part and the heat fixing part.
In the intermediate cooling unit, cooling is performed by the same method as that of the cooling unit.

The minimum film surface temperature of the film in the intermediate cooling section preferably satisfies the following formula (14), more preferably satisfies the following formula (14-2), and further preferably satisfies the following formula (14-3). .
30 ° C. ≦ TMC ≦ (TTDe−10) ° C. Formula (14)
40 ° C. ≦ TMC ≦ (TTDe-30) ° C. Formula (14-2)
50 ° C. ≦ TMC ≦ (TTDe-50) ° C. Formula (14-3)
In the formula, TMC represents the minimum film surface temperature (unit: ° C.), and TTDe represents the film surface temperature at the end of transverse stretching (unit: ° C.).
By setting the minimum film surface temperature (TMC) to 30 ° C. or higher, the zone length of the intermediate cooling section can be extremely shortened, and the apparatus cost can be reduced. By setting TMC to (TTDe−10) ° C. or lower, the in-plane birefringence distribution in the above formula (4) can be controlled within a predetermined range, and rainbow unevenness becomes difficult to see.

<Release film from clip>
In the production method of the present invention, the laterally stretched polyester resin film is released from the clip.

<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 production method of the present invention, the thickness of the polyester resin film after the transverse stretching step preferably satisfies the following formula (1 ′), preferably satisfies the following formula (1′-2), and the following formula (1′-3): It is more preferable to satisfy.
15 μm ≦ Th ′ ≦ 60 μm Formula (1 ′)
20 μm ≦ Th ′ ≦ 55 μm Formula (1′-2)
23 μm ≦ Th ′ ≦ 50 μm Formula (1′-3)
In formula (1 ′), Th ′ represents the thickness of the polyester resin film after the transverse stretching step, and the unit of the thickness of the polyester resin film after the transverse stretching step is μm.
In the production method of the present invention, the film width after being released 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 is preferably 1 to 5 m. Is more preferably 1 to 4 m. An optical film that requires accuracy is usually formed with a thickness of less than 3 m.
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 the film with an arbitrary width or slitting into an arbitrary number after film formation, the film width after trimming or slit corresponds to the film width of the polyester resin film of the present invention, and 0 It is preferable to satisfy 6 to 6 m.

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 10000 m on a core having a diameter of not less than 70 mm and not more than 600 mm. Winding tension per cross-sectional area of the ^{film, 3 ~ 30kgf / cm 2 (} 1kgf = 9.80665N) , 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.

[Hard coat film]
The polyester resin 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 resin 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, JP2013-45045A, JP2013-43352A, JP2012-232424A, JP2012-128157A, JP2011-131409A, JP JP2011-131404A, JP2011-126162A, JP2011-75705A, JP2009-286981, JP2009-263567, JP2009-75248, JP2007-. No. 164206, JP-A-2006-96811, JP-A-2004-75970, JP-A-2002-156505, JP-A-2001-272503, WO12 / 018087, WO12 / 098967, WO12 / 0886659, WO11 / 866659 Described in 105594 The can be used.

[Sensor film for touch panel]
The polyester resin 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 resin 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 (Chemical Vapor Deposition) method, a coating method, and a printing method. 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 resin film. It is desirable to use a metal selected from the group consisting of silicon, titanium, tin and zinc for the metal layer.

[Glass scattering prevention film]
The polyester resin film of this 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 resin 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 resin film of the present invention can be used in a touch panel. In addition, at least one of the hard coat film of the present invention, the sensor film for touch panel of the present invention, and the glass scattering prevention film of the present invention can be used in the 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 (Alternating Current) drive than DC (Direct Current) drive, and more preferably a drive method in which the voltage application time to the electrodes is short.

[Polarizer]
The polyester resin 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 resin film of the present invention. The polarizing plate of the present invention may further include a polarizing plate protective film such as a cellulose acylate film in addition to the polyester resin film of the present invention.

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

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

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

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

In the image display device, it is preferable to use a light source having an emission spectrum having a continuous emission spectrum as the light source.
This is because it becomes easy to eliminate rainbow unevenness as described in [0019] to [0020] of WO2011 / 162198.
As a light source used in the image display device, the one described in [0013] of WO2011 / 162198 is used. On the other hand, the light sources described in [0014] to [0015] of WO 2011/162198 are not continuous light sources and are not preferable.
When the image display device is an LCD, the configuration described in [0011] to [0012] of WO2011 / 162198 can be used as the liquid crystal display device (LCD).
The liquid crystal display device using the polyester resin film of the present invention and / or the polarizing plate of the present invention preferably uses a white light source having a continuous emission spectrum, thereby using a discontinuous (bright line) light source. Rainbow unevenness can be reduced more effectively than in the case. This is due to the reason similar to this reason, with the reason described in [0015] to [0027] of Patent No. 4888853 ([0029] to [0041] of US2012 / 0229732). The contents described in these publications are incorporated herein.

The liquid crystal display device preferably includes the polarizing plate of the present invention and a liquid crystal display element. Here, the liquid crystal display element is typically a liquid crystal panel having a liquid crystal cell in which liquid crystal is sealed between upper and lower substrates and displaying an image by changing the alignment state of the liquid crystal by applying a voltage. The polarizing plate of the present invention can be applied to various known displays such as a display panel, a CRT (Cathode Ray Tube) display, and an organic EL display. Thus, when the polarizing plate which has the polyester resin film of this invention with high retardation is applied to a liquid crystal display element, the curvature of a liquid crystal display element can be prevented.

Here, the rainbow-like color spots are caused by the retardation of the polyester resin 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: Light Emitting Diode) 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 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 and the blue light emitting diode or ultraviolet light is emitted. It is preferable that the light emitting diode is disposed so as to emit light, or a film containing a phosphor is disposed inside the 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 Technohouse Co., Ltd.

The 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 the wavelengths 460 nm and 520 nm and between the wavelengths 560 nm and 620 nm, or the minimum value is larger than the maximum value L2 between the 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 a 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 Since it has at least one maximum value L2 between 560 nm, at least one minimum value L3 between wavelengths 560 nm to 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.

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 resin film of the present invention having a high retardation in the in-plane direction is not particularly limited, but is arranged on the incident light side (light source side), the polarizing plate, 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 polarized light on the outgoing light side of the polarizing plate arranged on the outgoing light side The child protective film is preferably the polyester resin film of the present invention having 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 disposed on the exit light side is the polyester resin film of the present invention having a high retardation in the in-plane direction. When a polyester resin 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 resin film of the present invention having high retardation in the in-plane direction is preferably used in a place where polarization characteristics are not required, it is preferably used as a protective film for a 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 in the IPS mode, VA mode, or FFS (Fringe Field Switching) mode.

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

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

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

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

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

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

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

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

The obtained unstretched polyester resin film 1 had an intrinsic viscosity (also referred to as IV) IV = 0.62, a longitudinal refractive index of 1.573, and a crystallinity of 0.2%.

IV is an unstretched polyester resin film 1 dissolved in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent and a solution at 25 ° C. in the mixed solvent. It was determined from the viscosity.
The refractive index of the unstretched polyester resin film was measured by the following method.
Using two polarizing plates, the orientation axis direction of the unstretched polyester resin film was determined, and a 4 cm × 2 cm rectangle was cut out so that the orientation axis directions were orthogonal to each other, and used as a measurement sample. For this sample, the biaxial refractive index (nx, ny) orthogonal to each other and the refractive index (nz) in the thickness direction were determined by an Abbe refractometer (NAGO-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.).
The crystallinity of the unstretched polyester resin 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.

-Longitudinal drawing process-
The unstretched polyester resin film 1 was passed between two pairs of nip rolls having different peripheral speeds and stretched in the longitudinal direction (conveying direction) under the following conditions. In addition, each refractive index (nx (MD), ny (MD), nz (MD)) and each birefringence of the polyester resin film 1 after longitudinal stretching are the measuring methods of the refractive index and birefringence of the polyester resin film mentioned later. It measured by the same method.
<Condition>
-Preheating temperature: 80 ° C
-Longitudinal stretching temperature: 90 ° C
-Longitudinal stretch ratio: 3.2 times

-Transverse stretching process-
The vertically stretched polyester resin film 1 was guided to a tenter (transverse stretching machine), and was stretched laterally by the following method and conditions while gripping the ends of the film with clips.

(Preheating part)
The preheating temperature was 90 ° C., and the mixture was heated to a temperature at which stretching was possible.

(Extension part)
The preheated unstretched polyester resin film 1 was stretched in the width direction using a tenter under the following conditions.
<Condition>
-Transverse stretching temperature (average temperature during transverse stretching): 90 ° C
・ Horizontal draw ratio: 3.0 times ・ Film surface temperature at the start of transverse draw: 95 ° C.
-Film surface temperature at the end of transverse stretching: 150 ° C
The film surface temperature was measured with a radiation thermometer (manufactured by Hayashi Denko, model number: RT61-2, used at an emissivity of 0.95).

(Intermediate cooling section)
The stretched polyester resin film was cooled in an intermediate cooling section so that cool air from the up and down direction was applied to the film from the blowing nozzle to the film, and the minimum film surface temperature TMC of the polyester resin film was 85 ° C.
The film surface temperature of the film in the intermediate cooling part was measured with a radiation thermometer (manufactured by Hayashi Denko, model number: RT61-2, used at an emissivity of 0.95). The 10-point film surface temperature was measured uniformly in the MD direction in the intermediate cooling section, and the minimum temperature was defined as the minimum film surface temperature TMC.

(Heat fixing part)
Next, hot fixing treatment was performed while hot air from the up and down direction was applied to the film from the hot air blowing nozzle to the film and the film surface temperature of the polyester resin film was controlled within the following range.
<Condition>
・ Maximum film surface temperature (heat setting temperature): 170 ℃
Heat setting time: 15 seconds The heat setting temperature here is the DSC pre-peak temperature [° C.].

(Heat relaxation part)
The heat-fixed polyester resin film was subjected to hot air from above and below the film through a hot air blowing nozzle and heated to the following temperature to relax the film.
-Thermal relaxation temperature: Maximum film surface temperature of the heat fixing part -10 ° C (in the case of Example 1, 160 ° C)
-Thermal relaxation rate: TD direction (film width direction) 15%
MD direction (film flow direction) 5.5%

(Cooling section)
Next, the polyester resin film after heat relaxation was cooled at a cooling temperature at which the film surface temperature of the film was 40 ° C.
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.
The film surface temperature was measured with 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 resin film were trimmed by 20 cm. The film width after trimming was 2.1 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 resin film of Example 1 having a thickness of 35 μm wound in a roll form was produced.

[Examples 2 to 14, 16 and Comparative Examples 1 to 4, 6 to 9]
In Example 1, as described in the following table, the longitudinal draw ratio, the transverse draw ratio, the film surface temperature at the start of the transverse draw, the film surface temperature at the end of the transverse draw, the minimum film surface temperature of the intermediate cooling section, and heat setting A polyester resin film was produced in the same manner as in Example 1 except that the maximum film surface temperature, the longitudinal relaxation rate, the lateral relaxation rate, and the film width were changed.

[Example 15, Comparative Example 5]
In Example 1, a polyester resin film was produced in the same manner as in Example 1 except that the cooling in the intermediate cooling part was not performed.

[Evaluation]
<Measurement of refractive index and birefringence>
(Measurement of nx, ny, nz, and birefringence)
Measurements of nx, ny, nz, and birefringence were performed on the films of the examples and comparative examples. Using two polarizing plates, the orientation axis direction of the 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) orthogonal to each other and the refractive index (nz) in the thickness direction were determined by an Abbe refractometer (NAGO-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.). From the values, the values of nx-ny and (nx + ny) / 2-nz were calculated and listed in the table below.

(Measurement of nΔ)
nΔ is a film having a film width of 2 m and a film length of 0.5 m for each 100 mm of the film 1 m ² of each Example and Comparative Example. A piece of film was cut out. About the magnitude | size of the film piece, it cut out to the same size as the method described by the above-mentioned refractive index measurement (Abbe refractometer). For all of the cut film pieces, the refractive index is measured by the same method as the above-described refractive index measurement, the nx−ny value is derived, and the difference between the maximum value and the minimum value of the nx−ny values of all the film pieces. Was determined as nΔ.

(Measurement of MD heat shrinkage ratio after standing at 150 ° C. for 30 minutes)
The width direction center part of the polyester resin film of each Example and a comparative example and 3 points | pieces of both ends were cut, and three types of sample pieces M of the size of TD direction 30mm and MD direction 120mm were produced.
Two reference lines were inserted into the three types of sample pieces M so as to have an interval of 100 mm in the MD direction, and the samples were 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 the average of these three values was 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.

(Measurement of TD heat shrinkage ratio after standing at 150 ° C. for 30 minutes)
The width direction center part of the polyester resin film of each Example and a comparative example and 3 points | pieces of both ends were cut | judged, and three types of sample pieces M of the size of MD direction 30mm and TD direction 120mm were produced.
Two reference lines were inserted into the three types of sample pieces M so as to have an interval of 100 mm in the TD direction, and the samples were 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 the average of these three values was 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.

(Measurement of MD thermal shrinkage after standing at 80 ° C. for 24 hours)
The measurement was performed in the same manner as the measurement of the MD heat shrinkage ratio after standing at 150 ° C. for 30 minutes, except that it was allowed to stand in a heating oven at 80 ° C. for 24 hours under no tension.

(Measurement of TD thermal shrinkage after standing at 80 ° C. for 24 hours)
The measurement was carried out in the same manner as the measurement of the TD heat shrinkage ratio after standing at 150 ° C. for 30 minutes except that it was left standing in a heating oven at 80 ° C. for 24 hours under no tension.

<Measurement of film thickness>
The thickness of the obtained polyester resin film of each Example and Comparative Example was obtained as follows.
For the polyester resin film of each example and comparative example, using a contact-type film thickness meter (manufactured by Anritsu), 50 points were sampled at equal intervals over 0.5 m in the longitudinally stretched direction (longitudinal direction), Furthermore, 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 resin film. The results are shown in the table below.

<Measurement of density>
According to JIS K7112, measurement was performed using ASG-320K manufactured by Kanto Major Co., Ltd. and AUX320 manufactured by Shimadzu Corporation.

<Evaluation of rainbow unevenness>
(Production of polarizing plate and liquid crystal display and evaluation of rainbow unevenness)
Using the polyester resin films of the examples and comparative examples, polarizing plates of the examples and comparative examples and liquid crystal display devices of the examples and comparative examples were produced and evaluated.

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

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

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

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

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

Using a continuous light source (white LED) and a discontinuous light source (cold cathode tube) from one side, light was incident, and rainbow unevenness generated visually through polarized sunglasses from the opposite side was evaluated according to the following criteria.
Note that the rainbow unevenness was observed both from the normal direction of the polarizing plate and from the oblique direction (45 ° from the normal line).
A: Rainbow unevenness is not visible at all B: Rainbow unevenness is not visible C: Rainbow unevenness is almost invisible D: Rainbow unevenness is visible

From the above table, the polyester resin films of Examples manufactured so as to fall within the range of the above formulas (6) to (11) satisfy all the above formulas (1) to (4) and are viewed from the front. It can be seen that the rainbow unevenness and the rainbow unevenness when viewed from an oblique direction are simultaneously improved.
On the other hand, since the polyester resin film of Comparative Example 1 or 2 manufactured without satisfying the formula (1 ′) does not satisfy the formula (1), the rainbow unevenness when viewed from the front, and when viewed from the oblique direction. Rainbow unevenness has not been improved at the same time.
Further, the polyester resin films of Comparative Examples 3 to 9 produced without satisfying at least one of the above formulas (6) to (11) do not satisfy at least one of the formulas (2) to (4). The rainbow unevenness when viewed from the front and the rainbow unevenness when viewed from the diagonal are not simultaneously improved.
In addition, since the polyester resin film of the comparative example 7 did not satisfy | fill said Formula (5), intensity | strength and heat resistance were also bad.

2a to 2l Holding member 10 Preheating part 20 Stretching part 30 Heat fixing part 40 Thermal relaxation part 50 Cooling part 60 Annular rail 100 Biaxial stretching machine 200 Polyester resin film

Claims

A polyester resin film satisfying the following formulas (1) to (4);
15 μm ≦ Th ≦ 60 μm (1)
0 <nx−ny ≦ 0.020 (2)
0.120 ≦ (nx + ny) / 2−nz <0.160 Formula (3)
0 <nΔ ≦ 0.014 (4)
In the formulas (1) to (4), Th represents the thickness of the polyester resin film, the unit of the thickness of the polyester resin film is μm; nx represents the refractive index in the slow axis direction in the polyester resin film plane, ny represents the refractive index in the fast axis direction in the plane of the polyester resin film, nz represents the refractive index in the thickness direction of the polyester resin film, and nΔ represents (nx−ny) in an arbitrary area 1 m 2 of the polyester resin film. It represents the difference between the maximum and minimum values.
The polyester resin film according to claim 1, which satisfies the following formula (5):
130 ° C. ≦ Tpre ≦ 200 ° C. Formula (5)
In formula (5), Tpre represents the pre-peak temperature measured by differential scanning calorimetry of the polyester resin film, and the unit is ° C.
The polyester resin film according to claim 1 or 2, wherein the density of the polyester resin film is 1.370 to 1.390 g / cm 3 .
The polyester resin film according to any one of claims 1 to 3, wherein the thermal shrinkage in the MD direction and the TD direction of the polyester resin film after standing at 150 ° C for 30 minutes is 3.5% or less.
The polyester resin film according to any one of claims 1 to 4, wherein the thermal shrinkage in the MD direction and the TD direction of the polyester resin film after standing at 80 ° C for 24 hours is 0.3% or less.
The polyester resin film according to any one of claims 1 to 5, wherein the width of the polyester resin film is 0.6 to 6 m.
The polyester resin film according to any one of claims 1 to 6, which is biaxially oriented.
A step of melt-extruding a polyester raw resin into a sheet and cooling it on a casting drum to form a polyester resin film;
A longitudinal stretching step of longitudinally stretching the molded polyester resin film in the longitudinal direction;
A lateral stretching step of laterally stretching the polyester resin film after the longitudinal stretching in a width direction orthogonal to the longitudinal direction,
A method for producing a polyester resin film satisfying the following formulas (1 ′) and (6) to (11);
15 μm ≦ Th ′ ≦ 60 μm Formula (1 ′)
2.8 ≦ DMD ≦ 3.6 Formula (6)
DMD−1.0 ≦ DTD ≦ DMD + 0.5 (7)
130 ° C. ≦ TSET ≦ 200 ° C. Formula (8)
80 ° C. ≦ TTDs ≦ 120 ° C. Formula (9)
120 ° C. ≦ TTDe ≦ 180 ° C. Formula (10)
20 ° C. ≦ TTDe−TTDs ≦ 80 ° C. Formula (11)
In the formulas (1 ′) and (6) to (11), Th ′ represents the thickness of the polyester resin film after the transverse stretching step, and the unit of the thickness of the polyester resin film after the transverse stretching step is μm; Represents the draw ratio in the machine direction, DTD represents the draw ratio in the transverse direction, TSET represents the maximum surface temperature at the time of heat setting, TTDs represents the film surface temperature at the start of transverse stretching, and TTDe is the end of transverse stretching Represents the film surface temperature of the hour; units of TSET, TTDs, and TTDe are in ° C.
The method for producing a polyester resin film according to claim 8, wherein the birefringence of the polyester resin film after the longitudinal stretching and before the lateral stretching satisfies the following formulas (12) and (13):
0.030 <nx (MD) −ny (MD) ≦ 0.090 (12)
0.030 ≦ (nx (MD) + ny (MD)) / 2−nz (MD) <0.090 (13)
In Formula (12) and Formula (13), nx (MD) represents the refractive index in the slow axis direction in the plane of the polyester resin film after longitudinal stretching, and ny (MD) is the polyester resin film after longitudinal stretching. Represents the refractive index in the fast axis direction, and nz (MD) represents the refractive index in the thickness direction of the polyester resin film after longitudinal stretching.
The polyester resin film that has been subjected to the longitudinal stretching and the transverse stretching is heated and crystallized to heat-fix the heat-fixing part, the heat-fixed polyester resin film is heated, and the tension of the polyester resin film is relieved. Including a step of transporting a thermal relaxation part for removing residual distortion of the film,
10. The method for producing a polyester resin film according to claim 8, wherein a relaxation rate in the vertical direction is 1 to 10% and a relaxation rate in the horizontal direction is 3 to 23% in the heat relaxation part.
The polyester resin film that has been subjected to the longitudinal stretching and the transverse stretching is heated and crystallized to heat-fix the heat-fixing part, the heat-fixed polyester resin film is heated, and the tension of the polyester resin film is relieved. Including a step of transporting a thermal relaxation part for removing residual distortion of the film,
The method for producing a polyester resin film according to any one of claims 8 to 10, further comprising an intermediate cooling portion between the laterally stretched portion and the heat fixing portion.
In the said intermediate | middle cooling part, the manufacturing method of the polyester resin film of Claim 11 which satisfy | fills following formula (14);
30 ° C. ≦ TMC ≦ (TTDe−10) ° C. Formula (14)
In the formula (14), TMC represents the minimum film surface temperature, TTDe represents the film surface temperature at the end of the transverse stretching, and both units are ° C.
A polarizing plate comprising a polarizer and the polyester resin film according to any one of claims 1 to 7.
An image display device comprising the polyester resin film according to any one of claims 1 to 7 or the polarizing plate according to claim 13.
The image display device includes a light source unit having at least blue, green, and red emission peaks, and a liquid crystal cell having polarizing plates on both sides, and half of the green emission peak and the red emission peak of the light source unit. The image display device according to claim 14, wherein the half value width W of the smaller value range is 50 nm or less.
The image display device according to claim 15, wherein the light source unit includes at least a blue light emitting diode or an ultraviolet light emitting diode and a phosphor capable of emitting light by being excited by light from the blue light emitting diode or the ultraviolet light emitting diode.
The image display device according to claim 16, wherein at least one of the phosphors is a quantum dot.
A hard coat film comprising the polyester resin film according to any one of claims 1 to 7.
A touch panel sensor film comprising the polyester resin film according to any one of claims 1 to 7.
A glass scattering prevention film comprising the polyester resin film according to any one of claims 1 to 7.
The polyester resin film according to any one of claims 1 to 7, the polarizing plate according to claim 13, the hard coat film according to claim 18, the sensor film for touch panel according to claim 19, and the claim A touch panel provided with at least one of the glass scattering prevention films of 20.