KR20160140224A - Polyester film for a substrate of a touch panel and preparation method thereof - Google Patents

Abstract

The present invention relates to a polyester film for a touch panel substrate and a method for preparing the same. The substrate film according to the present invention is a single-axis or double-axis drawn polyester film that has a three-layer coextrusion structure made up of a first outermost layer, a central layer, and a second outermost layer, drawn 2.5-fold to six-fold in a first direction, and drawn two-fold or less in a second direction perpendicular to the first direction. Each of the first outermost layer and the second outermost layer is a polyester layer containing polyester resin obtained by the polymerization of 100 mol % of 1,4-cyclohexanedimethanol (CHDM) as a diol component and (i) 75 to 100 mol % of at least one selected from terephthalic acid, dimethyl terephthalic acid, isophthalic acid, dimethyl isophthalic acid, and cyclohexane dicarboxylic acid and (ii) 0 to 25 mol % of at least one selected from terephthalic acid, dimethyl terephthalic acid, isophthalic acid, and cyclohexane dicarboxylic acid that is different from the component (i) as dicarboxylic acid components. Accordingly, the substrate film according to the present invention results in no rainbow stains and exhibits minimized oligomer elution characteristics along with a high heat resistance. Therefore, it can be effectively used as a substrate film for touch panel electrode films including an ITO layer, a silver nano wire layer, a metallic mesh layer, and so on.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a polyester film for a touch panel substrate,

Embodiments relate to a polyester film for a touch panel substrate and a method of manufacturing the same.

The electrode film for a touch panel has a structure in which an ITO layer, a silver nanowire layer, a metal mesh layer, or the like is laminated on a base film.

Various materials such as polycarbonate (PC), acrylic, cyclic olefin copolymer (COC), and polyethylene terephthalate (PET) have been applied as the base film according to applications and characteristics.

Among them, a biaxially stretched PET film excellent in mechanical properties and electrical characteristics was mainly used as a base film. An ITO layer was deposited on one side of a biaxially stretched PET film and annealed in an oven at 150 to 160 ° C to crystallize ITO There is a problem that the oligomer inside the PET film is eluted to the surface to increase the haze and cause appearance of defects such as white dots. Further, when a biaxially stretched PET film is applied to a display as a base film for a touch panel, there is a problem that rainbow stains (mura) are observed.

In order to prevent elution of the oligomer, a method of applying a hard coating layer to the surface of the substrate film or coating a high refractive index resin layer to eliminate rainbow stains has been carried out (Japanese Patent Laid-Open No. 2007-253511 ), Which complicates the process and increases the manufacturing cost.

Japanese Patent Laid-Open No. 2007-253511

Therefore, it is an object of the present invention to provide a polyester film for a touch panel substrate that does not exhibit rainbow stains and minimizes elution of oligomers at a high temperature.

The embodiments are also intended to provide a method for producing the polyester film for a touch panel substrate.

According to one embodiment,

Layer structure having a three-layer coextruded structure of a first outermost layer / a middle layer / a second outermost layer and being stretched 2.5 to 6 times in a first direction and stretched 2 times or less in a second direction perpendicular to the first direction As a uniaxial or biaxially stretched polyester film,

Each of the first outermost layer and the second outermost layer

100 mol% of 1,4-cyclohexanedimethanol (CHDM) as a diol component,

(I) at least one selected from the group consisting of terephthalic acid (TPA), dimethyl terephthalic acid (DMT), isophthalic acid (IPA), dimethyl isophthalic acid (DMI) and cyclohexanedicarboxylic acid At least one selected from terephthalic acid (TPA), dimethyl terephthalic acid (DMT), isophthalic acid (IPA) and cyclohexanedicarboxylic acid (CHDA), which is different from said component (i) And a polyester resin comprising a polyester resin obtained by polymerization reaction in an amount of 0.1 to 5 mol%

A polyester film for a touch panel substrate is provided.

According to one embodiment,

(a) providing a polyester resin constituting a first outermost layer, a middle layer and a second outermost layer, respectively; (b) co-extruding the resins to produce an unoriented sheet; And (c) stretching the unstretched sheet by 2.5 to 6 times in a first direction and stretching by 2 times or less in a second direction perpendicular to the first direction. A method for producing a film is provided.

The base film according to the embodiment exhibits high heat resistance and minimal oligomer elution characteristics without showing rainbow stains and is useful as a base film of an electrode film for a touch panel including an ITO layer, a silver nanowire layer, a metal mesh layer and the like Can be used. The base film according to the embodiment can also be applied as a shutter electrode substrate of a 3D display.

1 shows a laminated structure of an electrode film (base film + ITO layer) and a protective film formed in a process for manufacturing an electrode film for a touch panel (ITO film), and a laminated structure of a three- Fig.
Fig. 2 (a) is a photograph of a case where a rainbow visibility is confirmed (a film of Example 1), Fig. 2 (c) And a case where the rainbow visor is strong (film of Comparative Example 3).
Fig. 3A schematically shows the orientation / phase difference measurement system of Test Example 3, and Fig. 3B is a graph showing the widthwise orientation angle measured with respect to the films of Example 1 and Comparative Example 3. Fig.

In the description of the embodiments, in the case where each film, film, panel or layer is described as being formed "on" or "under" of each film, film, panel, , "On" and "under" all include being formed "directly" or "indirectly" through "another element". In addition, the upper and lower standards for each component are described with reference to the drawings. The size of each component in the drawings may be exaggerated for the sake of explanation and does not mean the size actually applied.

1 shows a laminated structure of an electrode film (base film + ITO layer) and a protective film formed in a process for manufacturing an electrode film for a touch panel (ITO film), and a laminated structure of a three- 22 is a first outermost layer (skins layer), and 22 'is a second outermost layer). As shown in FIG.

The base film according to an embodiment has a three-layer coextruded structure of a first outermost layer / a middle layer / a second outermost layer and is stretched 2.5 to 6 times in a first direction, and is perpendicular to the first direction A uniaxially or biaxially stretched polyester film stretched not more than 2 times in two directions,

Wherein each of the first outermost layer and the second outermost layer contains 100 mol% of 1,4-cyclohexanedimethanol (CHDM) as a diol component and at least one of terephthalic acid (TPA), dimethyl terephthalic acid 75 to 100 mol% of at least one member selected from the group consisting of isophthalic acid (IPA), dimethyl isophthalic acid (DMI) and cyclohexanedicarboxylic acid (CHDA), and (ii) terephthalic acid And 0 to 25 mol% of at least one member selected from the group consisting of terephthalic acid (TPA), dimethyl terephthalic acid (DMT), isophthalic acid (IPA) and cyclohexanedicarboxylic acid (CHDA). The polyester layers constituting the first outermost layer and the second outermost layer may be the same or different.

More specifically, each of the first outermost layer and the second outermost layer contains 100 mol% of 1,4-cyclohexanedimethanol (CHDM) as a diol component and 100 mol% of terephthalic acid (TPA) as a dicarboxylic acid component, 85 to 95 mol% of at least one member selected from the group consisting of dimethyl terephthalic acid (DMT), isophthalic acid (IPA), dimethyl isophthalic acid (DMI) and cyclohexanedicarboxylic acid (CHDA), and (ii) A polyester resin obtained by polymerization reaction of at least one selected from terephthalic acid (TPA), dimethyl terephthalic acid (DMT), isophthalic acid (IPA) and cyclohexanedicarboxylic acid (CHDA) in an amount of 5 to 15 mol% Layer.

The polyester resin may be poly (1,4-cyclohexanedimethylene terephthalate) (PCT) or poly (1,4-cyclohexanedimethylene terephthalate / isophthalate) (PCTA, i.e. PCT + IPA).

The center layer may be composed of a polyester resin which is the same as or different from the polyester resin constituting the outermost layer.

The center layer is a polyester obtained by polymerizing 80 mol% or more, preferably 90 to 100 mol% of ethylene glycol as a diol component and 80 mol% or more, and preferably 90 to 100 mol% of terephthalic acid as a dicarboxylic acid component And a polyester layer containing a resin. At this time, usable diol components other than ethylene glycol and dicarboxylic acid components usable in addition to terephthalic acid may be those conventionally used in the art.

Specific examples of diol components usable in addition to ethylene glycol include 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3-butanediol, Pentanediol, 2,2-dimethyl-1,3-propanediol (i.e. neopentyl glycol), 2-butyl-2-ethyl-1,3-propanediol, 2,2- Pentanediol, 1, 5-pentanediol, 1, 4-diethyl-1,5-pentanediol, 3-methyl- Methanol, and mixtures thereof.

The center layer may be composed of polyethylene terephthalate (PET).

Referring to FIG. 1, the base film 20 according to the embodiment has a structure in which a first outermost layer 22, a center layer 21, and a second outermost layer 22 'are sequentially stacked.

The first outermost layer, the middle layer, and the second outermost layer are simultaneously extruded by a co-extrusion process, uniaxially or biaxially stretched, stretched in one direction, not elongated in the other direction, do.

The base film according to the embodiment having the three-layer coextruded structure of the first outermost layer / central portion layer / second outermost layer has no color distortion such as rainbow stains due to the in-plane retardation maximized by the uniaxial or biaxial stretching described above. In addition, the base film according to an embodiment may also include poly (1,4-cyclohexanedimethylene terephthalate) (PCT) or poly (1,4-cyclohexanedimethylene terephthalate) obtained from 100 mol% (PCTA, i.e., PCT + IPA) as the outermost layers on both sides, and has high oligomer blocking properties and high heat resistance.

The base film according to an embodiment may have a thickness of 10 to 200 mu m, preferably 40 to 120 mu m. At this time, the first outermost layer, the middle layer and the second outermost layer may have a thickness ratio of 1: 0.5 to 100: 1. More specifically, the first outermost layer, the middle layer and the second outermost layer may have a thickness ratio of 1: 0.5 to 50: 1. More specifically, the first outermost layer, the middle layer and the second outermost layer may have a thickness ratio of 1: 1 to 20: 1.

Further, although the base film according to this embodiment has been described as a three-layer structure, it is not limited thereto. For example, the base film according to the present embodiment may further include an additional layer (inner layer) in addition to the first outermost layer, the center layer and the second outermost layer.

The base film according to this embodiment may have an in-plane retardation of 3,000 nm or more. More specifically, the base film according to this embodiment may have an in-plane retardation of 5,000 nm or more. More specifically, the base film according to this embodiment may have an in-plane retardation of 10,000 nm or more.

The in-plane retardation is a measure indicating the optical isotropy or anisotropy of a film, and can be calculated, for example, by the following equation 1:

[Equation 1]

Re = (nx-ny) xd

In the above equation, nx is the in-plane refractive index in the X-axis direction, ny is the refractive index in the Y-axis direction, and d is the thickness of the film.

Here, the X-axis is the direction in which the in-plane refractive index of the film becomes the maximum, and the Y-axis is the direction perpendicular to the X-axis.

The base film may be a film which is stretched in one direction and stretched in the other direction or stretched slightly. For example, the base film may be a film stretched 2.5 to 6 times in the first direction and 2 times or less in the second direction perpendicular to the first direction. More specifically, the base film may be a film stretched 3 to 5 times in the first direction and 1.3 times or less in the second direction perpendicular to the first direction. More specifically, the base film may be a film stretched 4 to 5 times in the first direction and 1.2 times or less in the second direction perpendicular to the first direction. More specifically, the base film may be a film stretched 4 to 4.5 times in the first direction only.

When the base film according to the present embodiment is heat-treated at a temperature of 150 캜 for 30 minutes, the heat shrinkage may be less than 3%. More specifically, when the base film according to the present embodiment is heat-treated at a temperature of 150 캜 for 30 minutes, the heat shrinkage may be less than 2%.

Further, when the base film according to the present embodiment is heat-treated at a temperature of 150 캜 for 3 hours, the haze change may be less than 1%. More specifically, when the base film according to the present embodiment is heat-treated at a temperature of 150 캜 for 3 hours, the haze change may be less than 0.5%. More specifically, when the base film according to the present embodiment is heat-treated at a temperature of 150 캜 for 3 hours, the haze change may be less than 0.2%.

The base film of the three-layer structure according to the embodiment can be produced by the following process.

(a) providing a polyester resin constituting a first outermost layer, a middle layer and a second outermost layer, respectively; (b) co-extruding the resins to produce an unoriented sheet; And (c) stretching the unstretched sheet by 2.5 to 6 times in the first direction and by 2 times or less in the second direction perpendicular to the first direction.

More specifically, first, each polyester resin can be produced by an esterification reaction of the corresponding diol component and the corresponding dicarboxylic acid component and a solid phase polymerization process.

These polyester resins are co-extruded (melt extruded) and cooled to produce an unstretched sheet having a laminated structure.

Thereafter, the non-stretched sheet is stretched in either one or both of the longitudinal direction (machine direction) and the width direction (tenter direction) and is heat-set so that the polyester base film can be produced.

The melt extrusion is preferably performed at a temperature of Tm + 20 to Tm + 40 占 폚. If the temperature of the extruder is less than Tm + 20 ° C in the melt extrusion process, the melt will not be smoothly melted and the viscosity of the extrudate will increase and the productivity will deteriorate. On the contrary, if the temperature exceeds Tm + 40 ° C, the molecular weight of the resin decreases due to depolymerization due to thermal decomposition, A problem may arise. The cooling is preferably carried out at a temperature of 30 ° C or lower, more preferably 15 to 30 ° C.

The unstretched sheet is uniaxially or biaxially stretched, and may be stretched in one direction, and stretched in another direction or stretched slightly. The unstretched sheet may be stretched 2.5 to 6 times in a first direction, for example, in a width direction, and may be stretched in a second direction perpendicular to the first direction, for example, 2 times or less in a longitudinal direction. More specifically, the unstretched sheet may be stretched in the first direction, for example, 3 to 5 times in the width direction, and in the second direction perpendicular to the first direction, for example, 1.3 times or less in the length direction. More specifically, the unstretched sheet is stretched in the first direction, for example, 4 to 5 times or 4 to 4.5 times in the width direction, and in the second direction perpendicular to the first direction, for example, 1.2 times Or less.

The stretching temperature is preferably in the range of Tg + 5 to Tg + 80 DEG C, and the lower the Tg, the better the stretchability, but the breakage may occur. In particular, in order to improve the brittleness, a stretching temperature range of Tg + 10 to Tg + 50 ° C is preferable.

After initiating the heat setting, the film relaxes in the longitudinal direction and / or the width direction, and the stretched sheet can be heat set at a temperature of 200 to 260 캜, preferably 210 to 230 캜.

The thus-produced three-layer base film exhibits high heat resistance and minimal oligomer elution characteristics without showing rainbow stains, and thus can be used as a base film of an electrode film for a touch panel including an ITO layer, a silver nanowire layer, a metal mesh layer and the like Can be usefully used. The base film according to the embodiment can also be applied as a shutter electrode substrate of a 3D display.

In addition, the features, structures, effects and the like described in the embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects and the like illustrated in the embodiments can be combined and modified by other persons skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are illustrative of the present invention, but the present invention is not limited to the following examples.

Manufacturing example

(1) Production of first polyester resin

After raising the temperature of the esterification reaction tube to 200 ° C, 100 mol% of 1,4-cyclohexane dimethanol (CHDM), 90 mol% of terephthalic acid (TPA) and 10 mol% of isophthalic acid (IPA) 0.017 part by weight of manganese acetate was added as a catalyst based on the weight part, and the mixture was stirred. Then, the mixture was subjected to pressure esterification at a gauge pressure of 0.34 MPa and at 240 ° C, and then the esterification reaction tube was returned to normal pressure. Then, 0.014 part by weight of phosphoric acid was added. Thereafter, the temperature was raised to 260 DEG C over 15 minutes, and 0.012 part by weight of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was carried out with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tube and subjected to a polycondensation reaction under reduced pressure at 280 占 폚.

After completion of the polycondensation reaction, the mixture was filtered through a nylon filter having a cut-off size of 95% at a size of 5 탆, extruded from the nozzle into a strand shape, and cooled and solidified using cooling water previously subjected to filtration treatment (pore size: And cut into pellets to obtain a first polyester resin chip.

(2) Production of second polyester resin

Except that 100 mol% of ethylene glycol was used as the diol component and 100 mol% of terephthalic acid was used as the dicarboxylic acid component, the same procedure as in the production of the first polyester resin was carried out to obtain the desired second polyester resin chip .

Example 1

The resin chips were melt-kneaded in an extruder at about 280 DEG C so that the first polyester resin produced in the above-mentioned production example constituted the outermost layers on both sides, and the second polyester resin produced in the above- Extruded, and then cooled in a casting roll at about 20 DEG C to prepare an unoriented sheet. The thus-obtained unstretched sheet was preheated at 85 DEG C and then stretched 4.3 times in the width direction at 110 DEG C to maximize anisotropy. Thereafter, the uniaxially stretched sheet was heat set at 220 캜 for about 4 minutes to obtain a three-layer polyester film (first outermost layer: middle layer: thickness ratio of the second outermost layer = 5: 90: 5) .

Examples 2 to 8

A three-layer polyester film of various thicknesses was produced in the same manner as in Example 1, except that the thicknesses of the outermost layer and the middle layer and / or the stretching ratios in the longitudinal direction and the transverse direction were changed as shown in Table 1 Respectively.

Comparative Example 1

A single-layer polyester film having a thickness of 50 탆 was prepared in the same manner as in Example 1, except that a polyester film having a single-layer structure was produced using only the second polyester resin prepared in the above Production Example.

Comparative Examples 2 to 6

A single-layer polyester film having a thickness of 50 or 100 탆 was produced in the same manner as in Comparative Example 1, except that the thickness of the single-layer polyester film and the stretch ratio in the longitudinal direction and the transverse direction were changed as shown in Table 1 .

Test Example 1: Heat shrinkage

The films obtained in the above Examples and Comparative Examples were subjected to heat treatment in an oven at 150 ° C for 30 minutes and the heat shrinkage in the longitudinal direction (MD, machine direction) and the width direction (TD, tenter direction) was measured according to the following formula . The measurement results are shown in Table 1 below.

Heat shrinkage (%) = (initial length - length after heat treatment) / initial length x 100

Test Example 2: Elimination of oligomers (presence of white spot, change in haze and decrease in total transmittance)

A protective film was adhered to one surface of the film obtained in the above Examples and Comparative Examples, and then ITO was deposited to a thickness of 20 nm on the other surface.

 Then, after heat treatment in an oven at 150 캜 for 3 hours, the presence or absence of a white spot was visually observed, and haze change (△ Haze,%) and decrease in total transmittance were measured.

In the case of the presence of a white dot, the cross section of the sample was visually observed and then the abnormal part was marked and the surface of the marking part was observed by SEM. In the case of the haze change, the haze was measured before and after the heat treatment using the haze meter. Further, whether the total transmittance was decreased or not was confirmed by measuring the total transmittance before and after the heat treatment. The measurement results are shown in Table 1 below.

Test Example 3: In-plane retardation and orientation angle

The refractive index (nx, ny) and the refractive index (nz) in the thickness direction perpendicular to the films obtained in the Examples and Comparative Examples were measured using Abbe's refractometer (NAR-4T manufactured by Atago KK, measurement wavelength: 589 nm) , And the absolute value (| nx-ny |) of the refractive index difference of the biaxial axis was defined as anisotropy (? Nxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Pahrung Paste), and the unit was converted to nm. Plane retardation Re was determined from the product (? Nxy x d) of the anisotropy (? Nxy) of the refractive index and the thickness d (nm) of the film. Further, the orientation angle of the film was determined using a measurement system as shown in Fig. 3A. The measurement results are shown in Table 1, and the widthwise orientation angles measured for the films of Example 1 and Comparative Example 3 are shown in a graph in FIG. 3B. The orientation angle was expressed by the Max orientation angle measured with respect to the film 1000 mm width.

Test Example 4: Rainbow Poetry

ITO was deposited to a thickness of 20 nm on one side of the film obtained in the above Examples and Comparative Examples to prepare an ITO electrode film. The thus-prepared electrode film was mounted on a TV display as shown in Fig. 2A (in a state in which it coincided with the polarization axis), and whether a rainbow was observed was visually observed. The results of the measurement are shown in Table 1 below, and a photograph of the case where there is no visible rainbow (film of Example 1) is shown in FIG. 2b and a photograph of the case where the rainbow visibility is strong (film of Comparative Example 3) is shown in FIG. 2c.

division Layer configuration (thickness, 탆) Stretching cost Heat shrinkage (%) Phase difference
(Re)
(nx-ny)
Xd Orientation angle After heat treatment
Whether oligomer elution Rainbow
Whether to be a poet The first outermost layer Center floor The second outermost layer MD TD MD TD one hundred points
The presence or absence Hz
(%) TT
Lowering Example 1 5 90 5 One 4.3 2.7 0.3 11200 2.5 radish 0.09 radish radish Example 2 10 80 10 One 4.2 2.5 0.5 10900 1.8 radish 0.06 radish radish Example 3 5 35 5 One 4.15 1.2 0.7 10500 2.3 radish 0.11 radish radish Example 4 10 30 10 One 3.8 1.8 0.2 3800 6.2 radish 0.06 radish Amblyopia Example 5 5 90 5 1.2 4.3 2.3 0.5 5400 2.9 radish 0.09 radish radish Example 6 10 80 10 1.2 4.5 3.1 0.8 11800 1.8 radish 0.03 radish radish Example 7 5 35 5 1.2 4 2.1 0.4 5100 2.1 radish 0.09 radish radish Example 8 10 30 10 1.2 3.8 1.4 0.1 4400 6.4 radish 0.03 radish Amblyopia Comparative Example 1 0 50 0 One 4.3 3.1 0.6 5560 2.0 U 3.7 U radish Comparative Example 2 0 50 0 1.2 4.3 2.8 0.7 5310 2.8 U 4.1 U radish Comparative Example 3 0 50 0 2.7 4.1 1.2 0.3 450 27 U 3.9 U Jiangxi Inn Comparative Example 4 0 100 0 One 4.2 3.1 0.9 10320 2.8 U 4.5 U radish Comparative Example 5 0 100 0 1.2 4.15 2.8 0.5 10100 3.0 U 3.9 U radish Comparative Example 6 0 100 0 2.4 4.1 1.5 0.1 1300 21 U 4.2 U Jiangxi Inn

As shown in Table 1, the three-layer polyester films of Examples 1 to 8 exhibited little haze change without generating white spots by minimizing elution of oligomers even when treated at high temperatures, and showed almost no rainbow stains .

10: Protective film
20: base film
30: ITO layer
21: center floor
22: 1st outermost layer
22 ': second outermost layer

Claims (11)

Layer structure having a three-layer coextruded structure of a first outermost layer / a middle layer / a second outermost layer and being stretched 2.5 to 6 times in a first direction and stretched 2 times or less in a second direction perpendicular to the first direction As a uniaxial or biaxially stretched polyester film,
Each of the first outermost layer and the second outermost layer
100 mol% of 1,4-cyclohexanedimethanol (CHDM) as a diol component,
(I) from 75 to 100 mol% of at least one selected from among terephthalic acid, dimethylterephthalic acid, isophthalic acid, dimethylisophthalic acid and cyclohexanedicarboxylic acid, and (ii) A polyester resin comprising a polyester resin obtained by a polymerization reaction of at least one selected from terephthalic acid, dimethyl terephthalic acid, isophthalic acid and cyclohexane dicarboxylic acid in an amount of 0 to 25 mol%
Polyester film for touch panel substrate.
The method according to claim 1,
The polyester resin constituting the first outermost layer and the second outermost layer is obtained by polymerizing 85 to 95 mol% of at least one selected from terephthalic acid, dimethylterephthalic acid, isophthalic acid, dimethylisophthalic acid and cyclohexanedicarboxylic acid And a polyester film for a touch panel substrate.
The method according to claim 1,
Wherein the polyester resin constituting the first outermost layer and the second outermost layer comprises 5 to 15 mol% of at least one selected from terephthalic acid, dimethyl terephthalic acid, isophthalic acid and cyclohexanedicarboxylic acid, which is different from the component (i) Wherein the polyester film is obtained by a polymerization reaction.
The method according to claim 1,
Wherein the center-
A polyester film for a touch panel substrate, comprising a polyester layer comprising a polyester resin obtained by polymerizing 80 mol% or more of ethylene glycol as a diol component and 80 mol% or more of terephthalic acid as a dicarboxylic acid component.
The method according to claim 1 or 4,
Wherein each of the first outermost layer and the second outermost layer is composed of poly (1,4-cyclohexanedimethylene terephthalate) or poly (1,4-cyclohexanedimethylene terephthalate / isophthalate) A polyester film for a touch panel substrate, comprising polyethylene terephthalate.
The method according to claim 1,
Wherein the first outermost layer, the middle layer and the second outermost layer have a thickness ratio of 1: 0.5 to 100: 1, Polyester film for touch panel substrate.
The method according to claim 1,
Wherein the base film has an in-plane retardation of 3,000 nm or more, Polyester film for touch panel substrate.
The method according to claim 1,
Wherein the heat shrinkage is less than 3% when the base film is heat-treated at a temperature of 150 캜 for 30 minutes.
The method according to claim 1,
Wherein the haze change is less than 1% when the base film is heat-treated at a temperature of 150 캜 for 3 hours.
(a) providing a polyester resin constituting a first outermost layer, a middle layer and a second outermost layer, respectively;
(b) co-extruding the resins to produce an unoriented sheet; And
(c) stretching the unstretched sheet by 2.5 to 6 times in the first direction and by 2 times or less in the second direction perpendicular to the first direction,
A method for producing a polyester film for a touch panel substrate.
11. The method of claim 10,
Wherein the unstretched sheet is stretched by 4 to 5 times in the first direction and stretched by 1.2 times or less in the second direction in the step (c).

Images