JP2000094513A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which is excellent in heat shrinkage properties, flexibility, and others and applicable to shrinkage packaging and shrinkable labels. SOLUTION: In a biaxially oriented polyester film having trimethylene terephthalate units of at least 80 mole % of the total repeating units, when the film is treated at 150 deg.C for 30 min, the heat shrinkage ratio in the machine direction(MD) and/or the transverse direction(TD) is at least 7%, and the strength at break in the machine direction(MID) and the transverse direction(TD) is at least 10 kg/mm2, and the thickness mottle is 12% or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film, and more particularly, to a biaxially stretched film comprising polytrimethylene terephthalate as a main component and having excellent properties such as shrinkage and flexibility, particularly for coating and bundling. The present invention relates to a film suitable for shrink packaging or a label.

[0002]

2. Description of the Related Art Polyolefin films represented by polyethylene (PE), polyester films represented by polyvinyl chloride, polystyrene, rubber hydrochloride and polyethylene terephthalate (PET) are generally used as shrinkable packaging films. . Polyolefin films are excellent in flexibility and sealing properties, but are inferior in strength, printability and barrier properties, and are being dealt with by forming composite films with other materials. Polyvinyl chloride tends to be avoided due to pollution problems during incineration, and polystyrene films have insufficient mechanical strength.

[0003] On the other hand, polyester films are excellent in strength, barrier properties and non-adsorption properties, but are inferior in flexibility, heat shrinkage and pinhole resistance and are very difficult to handle as shrinkable packaging films. Has become. Since this polyester film is used for packaging, improvements have been made by lowering the film strength or lowering the crystallinity of the polymer.

However, the above-mentioned changes in strength and crystallinity cannot achieve both flexibility, gas barrier properties, and non-adsorption properties. Further, in order to achieve the above object, a polyester film comprising polytrimethylene terephthalate (PTT) has been proposed (JP-A-8-10).
No. 4763, JP-A-8-325391), which is more suitable for packaging films than conventional polyethylene terephthalate (PET) films. However, the shrinkage and barrier properties of shrink-wrapping films are still unsatisfactory. Was enough.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide excellent properties such as shrinkage, barrier properties, and flexibility which comprise polytrimethylene terephthalate (PTT) as a main component. Another object of the present invention is to provide a biaxially stretched film, particularly a shrinkable biaxially oriented film suitable for coating, bundling, labeling and the like.

[0006]

The present inventors have conducted intensive studies and as a result, have found that polytrimethylene terephthalate (PT)
By optimizing the heat shrinkage, breaking strength, thickness unevenness, density and the like of the polyester film composed of T), the polyester film is made of a polyethylene terephthalate-based film or a polytrimethylene terephthalate (PTT) -based polyester film. Finding that a film for packaging materials with excellent gas barrier properties and flexibility can be obtained,
The present invention has been reached.

That is, the present invention relates to a biaxially oriented film comprising a polyester in which trimethylene terephthalate units are at least 80 mol% of all repeating units.
The heat shrinkage in at least one of the longitudinal (MD) and transverse (TD) directions after treatment at 50 ° C. for 30 minutes is 7% or more, and the breaking strength of the film is in the longitudinal (MD) and transverse (TD) directions. ) Both are 10 kg / mm ² or more, and the thickness unevenness of the film is 12% or less.

(Polytrimethylene terephthalate) The polytrimethylene terephthalate used in the present invention is a polyester containing terephthalic acid as a main acid component and 1,3-propanediol as a main glycol component.
As the polytrimethylene terephthalate, a homopolymer having trimethylene terephthalate as a total repeating unit or a copolymer having trimethylene terephthalate at least 80 mol%, preferably 90 mol%, of all the repeating units is preferably used. If the repeating unit of trimethylene terephthalate is less than 80 mol%, the crystallinity will be lost, and properties inherent to polytrimethylene terephthalate, such as mechanical strength and gas barrier properties, will deteriorate.

In the case of a copolymer, a compound having two ester-forming functional groups in a molecule can be used as a copolymerization component constituting a copolymer other than trimethylene terephthalate as a main component. Oxalic acid, adipic acid, phthalic acid, sebacic acid, malonic acid, succinic acid, glutaric acid, dodecanedicarboxylic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-
Diphenylsulfonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, phenylindanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalin Dicarboxylic acids such as dicarboxylic acids and diphenyl ether dicarboxylic acids;
Oxycarboxylic acids such as oxybenzoic acid and p-oxyethoxybenzoic acid; or ethylene oxide adducts of ethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, bisphenolsulfone, bisphenol Dihydric alcohols such as ethylene oxide adduct of A, diethylene glycol, polyethylene oxide glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be preferably used.

These compounds can be used alone or in combination of two or more. Of these, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and p
-Oxybenzoic acid and the glycol component are ethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, and ethylene oxide adducts of bisphenolsulfone.

The polytrimethylene terephthalate may be one in which a terminal hydroxyl group and / or a carboxyl group is partially or entirely blocked by a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. A very small amount of a trifunctional or higher functional ester-forming compound such as glycerin or pentaerythritol may be copolymerized within a range where a substantially linear polymer can be obtained.

Further, the polytrimethylene terephthalate film of the present invention may be composed of a mixture of an organic polymer in addition to the main component polytrimethylene terephthalate. Such organic polymers include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polyethylene-4,4'-tetramethylenediphenyldicarboxylate, polyethylene-2,6-naphthalenedicarboxylate, and polyethylene-2,7-naphthalenedicarboxylate. Rate, polytrimethylene-2,6-naphthalenedicarboxylate, polybutylene-2,6-naphthalenedicarboxylate,
Polycyclohexane dimethylene terephthalate, poly neopentylene-2,6-naphthalenedicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate and the like can be mentioned. Among them, polyethylene isophthalate, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, polytrimethylene-2,6-naphthalenedicarboxylate, polybutylene-2,6-naphthalenedicarboxylate, poly ( Bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate is preferred.

In the polytrimethylene terephthalate film of the present invention, not only one kind but also two or more kinds of these organic polymers may be used in an amount of 20% by mole, preferably up to 10% by mole of the polytrimethylene terephthalate. And can be used to form a mixture mixed therewith. If the mixing amount of the mixture exceeds the above range, the crystallinity is lowered, and characteristics inherent to polytrimethylene terephthalate, such as mechanical strength and barrier properties, are undesirably deteriorated. The production of such a mixture can be carried out by a generally known method for producing a polyester composition.

The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low-polymerized polyester by the reaction of dicarboxylic acid and glycol, or a conventionally known transesterification catalyst for converting a lower alkyl ester of dicarboxylic acid and glycol. For example, after reacting with one or more compounds containing sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt, polymerization is carried out in the presence of a polymerization catalyst. Antimony trioxide, an antimony compound such as antimony pentoxide, a germanium compound represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or a partial hydrolyzate thereof, titanyl ammonium oxalate, Titanium compounds such as potassium titanyl oxalate and titanium trisacetylacetonate are exemplified.

The polyester may be formed into chips after melt polymerization and solid-phase polymerized under reduced pressure under heating or in an inert gas stream such as nitrogen.

(Additives) The polyester film of the present invention may contain additives such as a lubricant, a stabilizer, a flame retardant and the like. Includes a small percentage of inert fine particles such as inorganic particles, organic particles, and cross-linked polymer particles to impart slipperiness to the film for the purpose of improving runnability and handling during film production, processing, and use. It is preferred.

The inorganic particles are not particularly limited, but include calcium carbonate, porous silica, spherical silica, kaolin,
Talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, lithium fluoride and the like can be mentioned. Porous silica is particularly preferred.

The organic salt particles include calcium oxalate, terephthalate such as calcium, barium, zinc, manganese and magnesium.

Examples of the crosslinked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, homopolymers or copolymers of vinyl monomers of acrylic acid or methacrylic acid, and polytetrafluoroethylene, silicone, and the like. Organic fine particles such as resin, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin are also used. Among these, silicone resin particles are preferred.

The average particle size of these lubricants is 0.01
It is preferable that it is not less than μm and not more than 5 μm. The average particle diameter is more preferably 0.05 μm or more and 4 μm or less, and particularly preferably 0.1 μm or more and 3 μm or less. 0.
If it is less than 01 μm, the effect of improving the slipperiness is not obtained, and if it exceeds 5 μm, film breakage increases in the production process, and the dropout of particles increases, which is not preferable. 0.001% by weight
It is preferably at least 1.5% by weight. The addition amount is more preferably 0.003% by weight or more and 1.2% by weight or less, and particularly preferably 0.004% by weight or more and 1.0% by weight or less. If the amount is less than 0.001% by weight, the improvement of the slipperiness is insufficient, and if it exceeds 1.5% by weight, the haze value increases, which is not preferable as a packaging material.

The inert fine particles to be added to the film may be a single component selected from those exemplified above, or a multi-component containing two or more components.

[0022] The polyester film of the present invention may contain a nucleating agent, an antioxidant, a coloring inhibitor, a pigment,
Dyes, ultraviolet absorbers, heat stabilizers, release agents, lubricating agents, flame retardants, antistatic agents, polysiloxanes and the like can be added.

The timing of adding the inert fine particles and other additives is not particularly limited as long as it is a stage before polytrimethylene terephthalate is formed. For example, it may be added at the polymerization stage. It may be added.

(Heat Shrinkage) The polyester film of the present invention was stretched in the machine direction (M
D) The heat shrinkage in at least one direction in the transverse direction (TD) needs to be 7% or more. This heat shrinkage rate is 7%
If it is less than 3, shrinkage is insufficient, and the function as a shrinkable packaging material or shrinkable label cannot be exhibited. The direction of the contraction, that is, whether the contraction should be performed in only one direction or whether the contraction should be uniform in the longitudinal direction (MD) and the transverse direction (TD) cannot be unconditionally described. It can be appropriately selected depending on the shape of the packaging object and the purpose of use.

(Breaking Strength) The polyester film of the present invention has a breaking strength of the machine direction (MD) and the transverse direction (T
D) Both must be 10 kg / mm ² or more, and
More preferably, it is ² kg / mm ² or more. When a material having a breaking strength of less than 10 kg / mm ² is used for packaging, the bag may be broken due to insufficient strength.

(Thickness unevenness) The polyester film of the present invention requires that the thickness unevenness of the film be 12% or less, preferably 10% or less, particularly preferably 8% or less.
If the thickness unevenness exceeds 12%, when the film is thermally shrunk, shrinkage unevenness occurs, and wrinkles and partial whitening occur, resulting in poor finish.

The Young's modulus of the polyester film (Young's modulus) A longitudinal direction (MD), is preferably transversely (TD) both a 110 kg / mm ² or more 600 kg / mm ^2. A more preferred range is 150 kg / mm ² or more and 550 kg / mm ² or less, and particularly preferably 180 kg / mm ² or more and 500 kg / mm ² or less. When the Young's modulus is less than 110 kg / mm ² , the elasticity of the film is insufficient, so that the film easily expands. 600k
If it exceeds g / mm ² , flexibility decreases.

The polyester film (thickness direction of the refractive index nz) the present invention is preferably a refractive index n _Z in the thickness direction of the film is 1.570 or less. If the refractive index n _Z exceeds 1.570, the unevenness of the thickness of the film becomes worse, and the flatness of the film becomes worse. The preferred range of the refractive index n _Z is from 1.420 to 1.570, and when it is less than 1.420, the frequency of breakage during stretching increases.

(Density) The density of the polyester film of the present invention is preferably at least 1.315 g / cm ³ . More preferably, it is 1.320 g / cm ³ or more and 1.3.
65 g / cm ³ or less, particularly preferably 1.325 g / c
m ³ or more and 1.362 g / cm ³ or less. Density 1.3
If it is less than 15 g / cm ³ , the mechanical strength and gas barrier properties of the film deteriorate.

(Surface Roughness Ra) The surface roughness Ra of the polyester film of the present invention is preferably 2 nm or more and 100 nm or less. More preferably, 3 nm or more and 85 n
m, particularly preferably from 5 nm to 70 nm. When the surface roughness Ra is less than 2 nm, blocking tends to occur when the films overlap each other, and the handling property is deteriorated. On the other hand, if it exceeds 100 nm, it is necessary to increase the amount of the lubricant to roughen the film surface, and the transparency of the film is lost.

(Haze Value) The haze value of the polyester film of the present invention is preferably 12% or less. It is more preferably at most 10%, particularly preferably at most 8%. If the haze value exceeds 12%, the transparency of the packaging film is insufficient, and the appearance of the contents is poor.

The film thickness of the polyester film of the present invention is preferably 5 μm or more and 125 μm or less for use in packaging. The intrinsic viscosity (IV) obtained by dissolving the film in orthochlorophenol and using an Ostwald viscometer is 0.45 dl / g or more and 0.9 or more.
0 dl / g or less is preferable, and the plane orientation coefficient ns (=
_{{(N MD + n TD)} / 2} -n z n MD: longitudinal direction of the refractive index,
(n _TD : refractive index in the lateral direction, _nz : refractive index in the thickness direction) is preferably 0.030 or more and 0.110 or less.

(Specific production conditions) The polyester film of the present invention is a biaxially stretched film containing polytrimethylene terephthalate as a main component. The biaxially stretched film is melted at a temperature higher than its melting point, extruded from a die slit onto a cooled cooling drum and solidified and cooled and solidified to obtain an unstretched film of polytrimethylene terephthalate. The unstretched film can be manufactured by biaxially stretching it in the longitudinal and transverse directions and then heat-setting.

The film is stretched by a known roll-type longitudinal stretching machine, infrared heating longitudinal stretching machine, tenter clip type transverse stretching machine, a multi-stage stretching machine for performing these stretching in a plurality of stages, a tubular stretching machine, and an oven-type vertical stretching machine. The stretching can be performed using a stretching machine, a simultaneous biaxial tenter stretching machine, or the like, but is not particularly limited.

Next, the method for producing the polyester film of the present invention will be described in detail, but is not necessarily limited thereto. As described above, the unstretched film of polytrimethylene terephthalate obtained by a known method is
1.5 to 6 with an infrared heating type vertical stretching machine in the longitudinal direction at ~ 90 ° C
Stretch twice. Although a roll heating type vertical stretching machine may be used,
An infrared heating type is preferred because defects such as scratches are likely to occur on the film surface.

After the longitudinal stretching, it is further subjected to 40-90 in a stenter.
At 1.5 to 6 times in the transverse direction at 60 ° C,
Preferably from 60 to 170 ° C, particularly preferably from 60 to 16 ° C.
By performing a heat treatment at 0 ° C. for 1 to 100 seconds, a desired polyester film can be obtained.

When the heat treatment temperature exceeds 180 ° C., the heat shrinkage decreases. If you want to reduce the horizontal heat shrinkage,
At the time of heat treatment, 1 to 10% relaxation can be given in the width direction. Further, multi-stage stretching in which the above-described stretching in the longitudinal direction and / or the transverse direction is divided into a plurality of stages may be used. Of course, the polyester film of the present invention may be laminated with another film by a co-extrusion method or an extrusion lamination method during the film-forming process, or may be laminated with an adhesive after the film is formed.

[0038]

The present invention will be further described with reference to the following examples.
The present invention is not limited only to the following examples unless the gist is changed. The measurement methods and definitions of various physical property values and characteristics in the present invention are as follows.

(1) Calculation of Component Amounts of Trimethylene Terephthalate (Mole Ratio of Main Component and Copolymer Component) A film sample was measured using a solvent (CDCl ₃ : CF ₃ COO).
(D = 1: 1), and ¹ H-NMR measurement is carried out, and it is calculated by the integration ratio of each obtained signal.

(2) Heat Shrinkage Rate A film whose exact length has been measured beforehand is placed in a thermostatic chamber set at 150 ° C. without tension, kept for 30 minutes, taken out, returned to room temperature, and then cooled. Read the dimensional change. From the length L ₀ before the heat treatment and the length L after the heat treatment, the heat shrinkage is calculated by the following equation. Heat shrinkage = (L ₀ −L) × 100 / L ₀ (%)

(3) Young's modulus A sample was cut into a width of 10 mm and a length of 150 mm.
Set to 00 mm, pulling speed 10 mm / min, chart speed 5
It is pulled with an Instron type universal tensile tester at 00 mm / min. The measurement is performed in both the MD and TD directions, and the Young's modulus is calculated from the tangent to the rising portion of the obtained load-elongation curve.

(4) Breaking strength and elongation A sample was cut into a width of 10 mm and a length of 150 mm.
The tension is set to 100 mm and the tensile speed is 100 mm / min. The chart speed is 100 mm / min. MD and TD were measured in both directions, and the elongation at break was read from the obtained load-elongation curve, and the elongation relative to the original length was expressed in%. Also, the strength at break is divided by the original cross-sectional area to obtain the break strength (kg / mm ² ).

(5) Refractive index (n _Z ) in the thickness direction An Abbe refractometer (manufactured by Atago Co., Ltd.) was used.
Using a-D line, the refractive index in the film thickness direction is measured at 25 ° C. Measured on the front and back surfaces of the film sample, and the average value and the refractive index n _Z. (6) Density This is a value measured by a flotation method at 25 ° C. in a density gradient tube using an aqueous solution of calcium nitrate.

(7) Haze value According to the method of JIS K-6714, the total haze value per film is measured with a commercially available haze meter. Assuming that the number of measurements n = 3, the average value is used as the measurement value.

(8) Surface Roughness (Center Line Surface Roughness Ra) Both sides of the film are measured with a surface roughness meter (Surfcom 111A, Tokyo Seimitsu Co., Ltd.), and the average value is calculated to be the surface roughness.

(9) Unevenness of thickness An electronic micrometer (K-312A) manufactured by Anritsu Corporation
The thickness of the film was measured at a stylus pressure of 30 g and a running speed of 25 mm / sec over a length of 2 m in each of the longitudinal direction and the lateral direction of the film to obtain a continuous thickness chart. Read the maximum thickness and minimum thickness from this chart.

Further, for the same sample, the width (c
m), length (cm), weight (g), density (g / cm ³ )
And the thickness (μm) is calculated by the following equation 1, and is defined as the average thickness.

The ratio of the difference between the above-mentioned maximum thickness and minimum thickness to the average thickness was calculated by the following equation 2 to obtain thickness unevenness.

[0049]

Equation 1 Average thickness (μm) = {weight / (width × length × density)} × 10000 (formula 1)

[0050]

## EQU2 ## Thickness unevenness (%) = {(maximum thickness−minimum thickness) / average thickness} × 100 (formula 2)

(10) Flexibility The sample was cut into a size of 350 mm × 350 mm, and the feel of the sample being rolled with both hands and strongly rubbed was evaluated on a three-point scale. ◎: Soft as polyethylene and very flexible ○: Harder than polyethylene but softer and slightly more flexible than polyethylene terephthalate ×: Hard as polyethylene terephthalate and less flexible Polyethylene film is Tamapoli Co., Ltd. Low-density polyethylene film (V-1) was used.

(11) Evaluation of Film State After Heat Shrinkage The state of the film after heat shrinkage was evaluated according to the following criteria. ◎: Wrinkles, distortions, shrinkage spots and partial whitening were completely absent in the film. ○: Wrinkles, distortions, shrinkage spots and partial whitening were slightly observed in the film, but there was no practical problem. There are distortion, shrinkage spots, partial whitening, and there is real harm.

Example 1 Dimethyl terephthalate 100
A transesterification reaction was performed by using 60 parts by weight of 1,3-propanediol and 0.08 part by weight of tetrabutyl titanate. Next, an average particle size of 2 μm is used as a lubricant.
Was added so as to be 0.05% by weight per polymer, and a polycondensation reaction was carried out under a high vacuum to obtain polytrimethylene terephthalate having an intrinsic viscosity of 0.65 dl / g.

After melt-extruding this polytrimethylene terephthalate from a die slit, it was tightly cooled and solidified on a casting drum to prepare an unstretched film. While heating this unstretched film with an infrared heater, 60
After stretching 3.3 times in the longitudinal direction (machine axis direction) at 60 ° C, successively biaxially stretching in the tenter in the transverse direction (width direction) 3.6 times at 60 ° C, heat-treating at 135 ° C, Was 15 μm. Table 1 shows the properties of the obtained biaxially oriented film.

[Examples 2 to 7] As shown in Tables 1 and 2, a film was formed under the conditions shown in Tables 1 and 2 according to Example 1 except that the polymer components and the stretching conditions were changed. Thus, a biaxially oriented film having a thickness of 15 μm was obtained. The properties are shown in Tables 1 and 2.

Comparative Examples 1 and 2 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 0.038 parts by weight of manganese acetate and 0.04 part of antimony trioxide
A transesterification reaction was performed using 1 part by weight. Then, 0.097 parts of trimethyl phosphate and porous silica having an average particle size of 2 μm are added so that the content becomes 0.05% by weight, and a polycondensation reaction is performed under a high vacuum to obtain an intrinsic viscosity of 0.64 dl / g. Was obtained. Thereafter, a film was formed under the conditions shown in Table 2 in the same manner as in Example 1 to obtain a biaxially oriented film having a thickness of 15 μm. Table 2 shows the properties of the obtained biaxially oriented film. The flexibility and shrinkage were poor.

Comparative Examples 3 and 4 The molar ratio of PTT was 80%
A biaxially oriented film having a thickness of 15 μm was obtained according to Example 2, except for the following. Table 2 shows the properties of the obtained biaxially oriented film. The strength and contraction were poor.

Comparative Example 5 A biaxially oriented film having a thickness of 15 μm was obtained in the same manner as in Example 2 except that the heat shrinkage was reduced. Table 2 shows the properties of the obtained biaxially oriented film. The contracted state was poor.

Comparative Example 6 A biaxially oriented film having a thickness of 15 μm was obtained in the same manner as in Example 2 except that the stretching ratio was lowered. Table 2 shows the properties of the obtained biaxially oriented film. The strength and contraction were poor.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

According to the present invention, a biaxially oriented polyester comprising polytrimethylene terephthalate (PTT) as a main component and having excellent properties such as heat shrinkability and flexibility, and particularly suitable for shrink wrapping and shrink labels. Film can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 67:02 F term (Reference) 4F071 AA45 AF15Y AF20Y AF30Y AF31Y AF54Y AH04 BB08 BC01 BC11 BC12 BC16 4F210 AA24 AB07 AB17 AE01 AG01 QA02 QC06 QG01 QG18 QW06

Claims (4)

[Claims] 1. A biaxially oriented film made of a polyester having trimethylene terephthalate units in an amount of 80 mol% or more of all repeating units.
The heat shrinkage in at least one of the machine direction (MD) and transverse direction (TD) after treatment for 7 minutes is 7% or more, and the breaking strength of the film in both machine direction (MD) and transverse direction (TD) is 10 kg / mm ² or more, and the thickness unevenness of the film is 12
% Or less. 2. The film has a Young's modulus in the machine direction (MD),
110 kg / mm ² or more and 600 k in both transverse directions (TD)
Polyester film according to claim 1, characterized in that g / mm ² or less. 3. A refractive index (n) in a thickness (Z) direction of a film.
The polyester film according to claim 1, wherein _Z ) is 1.570 or less, and the density is 1.315 g / cm ³ or more and 1.365 g / cm ³ or less. 4. The polyester film according to claim 1, wherein a haze value of the film is 12% or less, and a surface roughness (Ra) is 2 nm or more and 100 nm or less.