JPH11130879A - Modified polyethylene-2,6-naphthalate film - Google Patents

Abstract

(57) [Problem] To provide a biaxially oriented film which has excellent delamination resistance and mechanical strength, and also has excellent anti-curl properties. SOLUTION: 2,6-Naphthalenedicarboxylic acid is a main acid component, ethylene glycol is a main glycol component, and bis (4- (2-hydroxyethoxy)) is used.
(Phenyl) sulfone as a copolymer component, the content of the diethylene glycol component in the copolymer polyester is 3 mol% or less (based on the total amount of all glycol components), and the density of the film is 1. A modified polyethylene-2,6-naphthalate film having a surface roughness of at least 352 g / cm ³ , a surface roughness of the film of at most 2.0 nm, and a sum of longitudinal and transverse Young's modulus of at least 1000 kg / mm ^2; .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a modified polyethylene
More specifically, the present invention relates to a modified polyethylene-2,6-naphthalate film having excellent delamination resistance and mechanical strength.

[0002]

2. Description of the Related Art Polyesters represented by polyethylene terephthalate are widely used today in applications such as fibers, films and molded products because of their excellent physical and chemical properties. Among them, polyethylene-2,6-naphthalate is a polyester having a naphthalene ring in place of the benzene ring of polyethylene terephthalate (PET), is more rigid than the molecular chain of PET, and has a glass transition temperature. It has high mechanical properties, heat resistance, dimensional stability, chemical resistance, low adsorption, gas barrier properties due to its high melting point, and is electrically stable over a wide temperature range. In response to recent demands for high quality, etc., PET has been used for various purposes instead of PET.

[0003] Polyethylene-2,6-naphthalate film is a film having excellent characteristics as described above.
Since the planarity of the polymer molecule is high, it has disadvantages such as low tear strength and poor delamination resistance. For this reason, there are problems such as breakage during film formation and user processes, whitening of the bent part during bending, and delamination during film drilling. It is rare.

[0004]

DISCLOSURE OF THE INVENTION In view of the above circumstances, the present inventors have made intensive studies to develop a polymer and a film thereof suitable for solving the above problems, and as a result, have found that polyethylene-2,6-naphthalate having a specific composition has been obtained. The present inventors have found that a biaxially oriented film made of a copolymer has excellent properties and can solve the above-mentioned problems, and have reached the present invention.

An object of the present invention is to provide a modified polyethylene-2,6-
Biaxially oriented film made of naphthalate and having excellent delamination resistance and mechanical strength, and also having excellent anti-curl properties, for example, motor transformer insulation having both delamination resistance and mechanical strength An object of the present invention is to provide a biaxially oriented film suitable for electrical applications such as wire coating, capacitors, adhesive tapes, etc., gold / silver thread, stamping foils, labels, FPCs (flexible printed circuit boards), and membrane switches.

[0006]

According to the present invention, the object of the present invention is attained by the following constitutions. 2,6
-A copolyester having naphthalenedicarboxylic acid as a main acid component, ethylene glycol as a main glycol component, and bis (4- (2-hydroxyethoxy) phenyl) sulfone as a copolymer component; Is not more than 3 mol% (based on the total amount of all glycol components), and the density of the film is 1.352 g / cm.
³ or more, the surface roughness of the film is 2.0 nm or less, and the sum of the vertical and horizontal Young's moduli is 1000 kg /
mm- ² or more modified polyethylene-2,6-naphthalate film. Hereinafter, the present invention will be described in detail.

[Polyester Copolymer] In the present invention, the copolymerized polyethylene-2,6-naphthalate must have a bis (4- (2-hydroxyethoxy) phenyl) sulfone component copolymerized as a copolymer component. . This bis (4- (2-hydroxyethoxy) phenyl) sulfone component is represented by the following formula:

[0008]

Embedded image

When bis (4-hydroxyphenyl) sulfone having no ethylene glycol residue at both terminals is used as a copolymerization component, the hydroxyl group of bis (4-hydroxyphenyl) sulfone is a phenolic hydroxyl group.
-Poor polymerization reactivity with naphthalenedicarboxylic acid component. Even if it can be polymerized, it becomes a polymer in which 2,6-naphthalenedicarboxylic acid and bis (4-hydroxyphenyl) sulfone are polymerized without passing through an ethylene glycol component, and thus a polymer having a lost symmetry. in this case,
The resulting polymer has poor symmetry and poor mechanical strength as compared with polyethylene-2,6-naphthalate.

In the present invention, the copolymerized polyethylene-2,6-
Naphthalate is a copolymerized polyester containing 2,6-naphthalenedicarboxylic acid as a main acid component and ethylene glycol and bis (4- (2-hydroxyethoxy) phenyl) sulfone as a main glycol component.

Bis (4- (2-hydroxyethoxy) phenyl)
The copolymerization ratio of the sulfone component is from 0.2 to 10 mol%, preferably from 1 to 7 mol%, based on the dicarboxylic acid component.
If the copolymerization ratio of the bis (4- (2-hydroxyethoxy) phenyl) sulfone component is less than 0.2 mol%, the effect of suppressing the plane orientation of the film is insufficient, so that delamination cannot be improved. On the other hand, when it is more than 10 mol%, the delamination can be improved, but the mechanical strength of the film becomes insufficient.

In the present invention, the copolymer polyethylene-
In 2,6-naphthalate, the copolymerization amount of the diethylene glycol component must be 3 mol% or less (based on the total glycol component).

This diethylene glycol component is not added in the form of diethylene glycol or its ester-forming derivative as a copolymer component during the production of the copolymer, but is a copolymer produced as a by-product during the production reaction. is there.

When the copolymerization amount of the diethylene glycol component is 3
If it exceeds mol%, the effect of improving the delamination resistance of the film is large, but the crystallinity of the polymer is impaired, so that the mechanical strength is greatly reduced.
The copolymerization amount of the diethylene glycol component is preferably 2.
It is at most 5 mol%, more preferably at most 2 mol%. In order to suppress the by-product of diethylene glycol during the production reaction, the ratio of the molar amount of ethylene glycol to be added to the molar amount of dicarboxylic acid is preferably 2.0 to 3.0. The shorter the time required for the transesterification reaction, the better.

This copolymerized polyester can be copolymerized with a small proportion of another copolymerization component in addition to the bis (4- (2-hydroxyethoxy) phenyl) sulfone component. The amount is 3
Mol% or less, more preferably 1 mol% or less.
It is preferably at most 0.1 mol%, more preferably at most 0.1 mol%. The other copolymer component may be brought in the form of, for example, a blend of reclaim (recovery) chips of the copolyester.

The other copolymer component may be a compound having two ester-forming functional groups, for example, oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, isophthalic acid, 5-sodium sulfo acid. Isophthalic acid, terephthalic acid, 2-potassium sulfoterephthalic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, diphenyletherdicarboxylic acid, and lower thereof Alkyl esters; oxycarboxylic acids such as p-oxyethoxybenzoic acid and lower alkyl esters thereof; propylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane Diol, 1,6-hexa Diol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, p-xylylene glycol, ethylene oxide adduct of bisphenol A, triethylene glycol, polyethylene oxide glycol, polytetra Methylene oxide glycol, neopentyl glycol and the like can be mentioned.

The copolymerized polyethylene-2,6-naphthalate is partially or entirely blocked with a hydroxyl group and / or a carboxyl group at the terminal by a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. It may be modified or modified with a very small amount of an ester-forming compound having three or more functions such as glycerin and pentaerythritol within a range where a substantially linear polymer can be obtained. .

[Additives] The modified polyethylene-2 of the present invention,
6-naphthalate film has additives, such as a stabilizer,
Dyes, lubricants, ultraviolet absorbers, flame retardants, and the like can be added as desired.

In order to impart a favorable slip property to the film, it is preferable to contain a small amount of inert particles. Such inert particles include, for example, spherical silica, porous silica, calcium carbonate, silica alumina, alumina, titanium dioxide, kaolin clay, barium sulfate, inorganic particles such as zeolite, or crosslinked silicon resin particles,
Organic particles such as cross-linked polystyrene particles can be mentioned. The inorganic particles are preferably synthetic products rather than natural products for reasons such as uniform particle size, and inorganic particles of any crystal form, hardness, specific gravity, and color can be used.

The inert fine particles have an average particle size of 0.05.
Μ5.0 μm, preferably 0.1-5.0 μm.
More preferably, it is 3.0 μm. Further, the content of the inert fine particles is preferably from 0.001 to 1.0% by weight, and more preferably from 0.03 to 0.5% by weight.

The inert 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 than three components.

The timing of adding the inert particles is not particularly limited as long as it is a stage before the formation of the copolymerized polyethylene-2,6-naphthalate. For example, the inert particles may be added at the polymerization stage. May be added.

[Young's Modulus] The modified polyethylene of the present invention
It is necessary that the sum of the vertical and horizontal Young's modulus of the 2,6-naphthalate film is 1000 kg / mm ² or more. If the Young's modulus is lower than this, the delamination resistance becomes good, but the excellent high strength inherent in polyethylene-2,6-naphthalate is lost, which is not preferable. In order to obtain a film having good delamination resistance, the sum of Young's modulus is desirably 1600 kg / mm ² or less.

[Density] Modified polyethylene-2,6 of the present invention
The naphthalate film has a density of 1.352 g / cm ³ or more; If the density is lower than this, orientation crystallization does not sufficiently proceed by heat setting after stretching, and a film having poor mechanical strength and anti-curl property is obtained. On the other hand, the density is desirably 1.362 g / cm ³ or less in order to keep the film surface flat.

[Surface roughness] Modified polyethylene of the present invention
The 2,6-naphthalate film has a background roughness of 2.0 nm or less. If this value is larger than 2.0 nm, the incident light is irregularly reflected, and the transparency is impaired. Further, when an easy-adhesion layer, a barrier layer, or a magnetic layer is applied or vapor-deposited, the flatness of the film is impaired, resulting in poor electromagnetic conversion characteristics.

When the polymer extruded from the die is cooled by a casting drum, the most effective way to flatten the background of the film is not to crystallize the surface of the unstretched film. Examples of the method include a method in which the temperature of the casting drum is maintained at 40 to 80 ° C., and the film on the casting drum is cooled rapidly by applying cold water thereto. is not.

[Coarse protrusion] Modified polyethylene of the present invention
The 2,6-naphthalate film has a number of coarse protrusions having a height of 1.2 μm or more being 2/100 cm ² or less. If the value is larger than this value, when a photographic film is formed, there is a portion that does not pass light and is not developed. Further, it is not preferable because it causes dropout in magnetic applications.

In the case where the coarse projections are unmelted polyethylene-2,6-naphthalate, it can be dealt with by setting the temperature at the time of extrusion to 300 ° C. or higher. In the case of dust originally contained in the raw material chips, it can be dealt with by reducing the filter aperture. The aperture is set individually for each application.

[ANSI curl value] The modified polyethylene-2,6-naphthalate film of the present invention preferably further has a property of hardly curling, that is, an anti-curling property. It is preferable that the property be 50 [m-1] or less in ANSI curl value. This 80 ° C. is an approximate value of the maximum temperature to which the photographic film is usually exposed in daily life. If the ANSI curl value is larger than 50 [m-1], it becomes difficult to handle in the photographic processing step, which is not preferable.

Conventionally, evaluation of curling of a photographic film is as follows.
It depends on the extent to which the curl is eliminated through the usual photo film development or drying process. However, if the base film for a photo film has the above ANSI curl value, the curl of the curl is hard to occur. It is excellent in properties, that is, excellent in anti-curling property, and also excellent in curl recovery property in which curled curl generated once is easily eliminated.

The anti-curling property is determined by, for example, heat treating a roll film at a temperature of (Tg-40) ° C. to Tg (where Tg is the glass transition point of copolymerized polyethylene-2,6-naphthalenedicarboxylate). Can be provided. The time of this heat treatment depends on production efficiency.
0.1 to 1500 hours are preferred. Heat treatment temperature is (Tg
If the temperature is lower than −40) ° C., a very long time is required for the heat treatment, and the production efficiency is deteriorated. On the other hand, when the heat treatment temperature exceeds Tg, the anti-curling property becomes inferior (the curl tends to be formed).

[Endothermic peak] Modified polyethylene of the present invention
The 2,6-naphthalate film has a film thickness of 120 to 1 when the film is thermally analyzed by a differential scanning calorimeter (DSC).
It is preferred that an endothermic peak (abnormal specific heat) is observed at 60 ° C, particularly within the range of 130 to 150 ° C. This endothermic peak is different from the peak indicating the heat of crystal fusion. Further, the endothermic energy indicating the size of the endothermic peak is 0.3 mJ / mg or more, and furthermore, 0.5 mJ / mg.
/ Mg or more.

When the endothermic peak temperature and the endothermic energy are within the above ranges, the curl recovery property of the film becomes more excellent.

[Plane orientation coefficient] The modified polyethylene of the present invention
The 2,6-naphthalate film preferably has a surface orientation coefficient of 0.255 or less. Exceeding this value is not preferable because of poor delamination resistance. The plane orientation coefficient is 0.20 to maintain mechanical strength.
0 or more is preferable.

[Film Production Method] The film of the present invention is obtained by subjecting an unstretched film extruded by an I-die or a T-die to biaxial stretching, heat fixing, and then annealing (heat treatment). Can be produced more advantageously.

The stretching method may be a known method, but the stretching temperature is usually 80 to 150 ° C., and the stretching ratio is preferably 1.5 to 5.0 times, more preferably 2.5 to 4.0 times in the machine direction.
0 times, preferably 2.5 to 5.0 times, more preferably 2.8 to 4.0 times in the horizontal direction. The biaxially stretched film obtained by stretching is 170 to 255 ° C., preferably 1 to 255 ° C.
Heat set at 80-250 ° C for 1-100 seconds.

The stretching can be performed by a generally used method, for example, a method using a roll or a method using a stenter. The film may be stretched simultaneously in the machine direction and the transverse direction, or may be stretched sequentially in the machine direction and the transverse direction. Is also good. However, as the proportion of the bis (4- (2-hydroxyethoxy) phenyl) sulfone component, which is a copolymer component, increases, the non-crystallinity increases. Therefore, the heat setting temperature must be lowered with respect to the increase in the copolymerization ratio. Is preferred for preventing a decrease in the Young's modulus of the film and maintaining the flatness of the film.

When performing an annealing treatment (heat treatment), 10
10 minutes to 100 hours at a temperature of 0 to 115 ° C, and even 1
It is preferable to carry out the reaction for a period of time to 30 hours.

[0039]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The nuclear properties were measured by the following method.

(1) Content of Diethylene Glycol (DEG) The sample polymer is decomposed using hydrazine hydrate and quantified by gas chromatography.

(2) 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 as a solvent.

(3) Background Roughness Using a J scanner of an atomic force microscope Nano Scope III AFM manufactured by Digital Instruments, it is measured and calculated under the following conditions and expressed as Ra (root mean square roughness). Probe: single crystal silicon sensor Scanning mode: tapping mode Inspection range: 0.3 μm × 0.3 μm (however, the background without protrusions such as lubricants) Number of pixels: 256 × 256 data points Scanning speed: 2.0 Hz Measurement environment: Room temperature, in air

(4) Young's Modulus The film is cut into a sample having a width of 10 mm and a length of 15 cm, and the distance between the chucks is set to 100 mm. The Young's modulus is calculated from the tangent line at the top of the obtained load-elongation curve.

(5) Endothermic peak temperature TK (° C.) 10 mg of the film was subjected to a thermal analysis system (differential scanning calorimeter) SSC5200, DSC22 manufactured by Seiko Electronic Industry Co., Ltd.
The film is heated at a rate of 20 ° C./min in a nitrogen stream, and the endothermic behavior of the film is analyzed by first and second derivatives to determine the temperature at which the film exhibits a peak. Temperature.

(6) Glass transition temperature Tg (° C.) 10 mg of a film is melted at 320 ° C. for 5 minutes and then rapidly cooled to prepare an amorphous sample. Similarly to (5), it was set in a thermal analysis system (differential scanning calorimeter) SSC5200 and DSC220 manufactured by Seiko Electronic Industry Co., Ltd., and heated at a heating rate of 20 ° C./min in a nitrogen gas stream. It is represented by the midpoint of the region where continuity appears.

(7) Endothermic energy ΔHK (° C.) In the same manner as in the above (5), 10 mg of the film was subjected to a thermal analysis system (differential scanning calorimeter) SSC manufactured by Seiko Electronic Industry Co., Ltd.
5200, set to DSC 220, and set in a nitrogen stream for 20 minutes.
The film is heated at a heating rate of ° C./min, and is determined from the area on the endothermic side on the DSC chart corresponding to the endothermic energy of the film.
This area is shifted from the baseline to the endothermic side by increasing the temperature, and is the area on the endothermic side from the endothermic peak after returning to the baseline position after continuing the temperature increase and going through the endothermic peak. To the area (A). In (indium) was measured under the same DSC measurement conditions, and this area (B) was determined to be 28.5 mJ / mg.
Is obtained from the following equation.

[0047]

(A / B) × 28.5 = △ HK (mJ / mg)

(8) Plane orientation coefficient (NS) The refractive index is measured using an Atsube refractometer and a sodium D line (589 nm) as a light source, and is determined by the following equation. NS = (nMD + nTD) / 2-nZ Here, nMD represents the refractive index in the machine axis direction of the biaxially oriented film, nTD represents the refractive index in the direction (width direction) orthogonal to the machine axis direction, and nZ is the film's refractive index. Indicates the refractive index in the thickness direction.

(9) Coarse protrusions The film was observed at a magnification of 10 times below the crossed Nicols, a mark was made on the shining portion as a fish eye, and the height of the portion was measured by a two-beam method. The number of protrusions having the above height was measured for 100 cm ² , and the number was regarded as the number of coarse protrusions.

(10) Crease Delamination Whitening Ratio A film was cut out into a size of 80 mm × 80 mm, folded into two by a hand, sandwiched between a pair of flat metal plates, and then pressed at a predetermined pressure P1 (kg / cm) by a press. ² G)
Press for 20 seconds. After pressing, return the folded film to the original state by hand, and apply pressure P2 (kg / cm ² ) for 20 minutes.
Press for seconds. Then, remove the sample, measure the length (mm) of the whitened portion that appears on the fold, and total the length.

Using each new film sample, press pressure P1 = 4.2, 6.3, 8.4, 10.5
kg / cm ² ) and press pressure P2 = 1.26 (k
g / cm ² ) and open the fold and repeat the measurement.

Length of whitened portion at each press pressure (mm)
The ratio of the average value of the total to the total length (80 mm) of the fold is defined as the fold delamination whitening ratio, and this value is used as an index indicating the likelihood of delamination (delamination) of the film.

[0053]

## EQU2 ## (Crease Delamination Whitening Ratio (%)) = ((total length of whitened portion (mm)) / (80 mm × 4)) × 100

(11) Anti-curl property (ANSI curl value) A sample film having a size of 120 mm × 35 mm was prepared by
Wound around a 7 mm diameter core, temporarily fixed so as not to unwind, heated at 80 ° C for 2 hours, released from the core,
Immerse in distilled water at 40 ° C. for 15 minutes. Next, a load of 33 g is applied, and the sample is suspended vertically and heat-treated at 55 ° C. for 3 minutes. Sample with curls remaining
The measurement is carried out according to the test method A of SI PH 1.29-1971, and the curl value is calculated by changing inches to metric system.

(12) Intrinsic viscosity Measured at 35 ° C. in a phenol / tetrachloroethane (weight ratio 6 * 4) mixed solvent.

Example 1 100 parts by weight of dimethyl naphthalene-2,6-dicarboxylate, 60 parts by weight of ethylene glycol and bis (4- (2-hydroxyethoxy) phenyl) sulfone (hereinafter abbreviated as BPS-EO) 4. Using 2 parts by weight (3 mol% based on the total dicarboxylic acid component) of 0.03 parts by weight of manganese acetate tetrahydrate as a transesterification catalyst, and using silica particles having an average particle diameter of 0.3 μm as a lubricant as a lubricant.
After adding 005% by weight and subjecting to a transesterification reaction according to a conventional method, 0.023 parts by weight of trimethyl phosphate was added to substantially terminate the transesterification reaction.

Then, 0.024 parts by weight of antimony trioxide was added, and a polymerization reaction was carried out by a conventional method at a high temperature and a high vacuum to obtain an intrinsic viscosity of 0.61 dl / g and a DEG copolymerization amount of 1.1 mol%. Of polyethylene-2,6-naphthalate copolymer was obtained.

The pellets of the polyethylene-2,6-naphthalate copolymer were dried at 170 ° C. for 6 hours, fed to an extruder hopper, melted at a melting temperature of 310 ° C., and passed through a 1 mm slit die at a surface temperature of 60 ° C. To obtain an unstretched film. The unstretched film thus obtained is preheated at 120 ° C., and is further heated at 900 ° C. from 15 mm above between low-speed and high-speed rolls.
The film was heated by an R heater and stretched 3.0 times in the machine direction, and then supplied to a stenter.
It was stretched twice. The obtained biaxially oriented film was heat-set at a temperature of 240 ° C. for 5 seconds, and 0.5 ° in the width direction at a temperature of 190 ° C.
% To give a biaxially oriented film having a thickness of 75 μm.
Following the heat treatment, the biaxially oriented film was released from gripping in the lateral direction, contacted with a cooling roll in a longitudinally tensioned state, rapidly cooled, and wound around a roll.

The obtained biaxially oriented film is 500 mm wide.
Into a sample roll having a length of 500 m, and the temperature is raised from room temperature to 110 ° C. over a period of 24 to 72 hours.
After holding at 0 ° C. for 24 hours, annealing treatment (heat treatment) was performed under annealing conditions in which the temperature was lowered to room temperature over 24 to 72 hours to obtain a biaxially oriented film having a thickness of 75 μm. As shown in Table 1, the characteristics of the obtained film were good.

Example 2 The copolymerization amount of BPS-EO was 1
A biaxially oriented film was obtained in the same manner as in Example 1 except that the content was changed to mol%. As shown in Table 1, the characteristics of the obtained film were good.

Example 3 A biaxially oriented film was obtained in the same manner as in Example 2 except that the stretching ratio was changed to 3.6 times vertically and 3.9 times horizontally. As shown in Table 1, the characteristics of the obtained film were good.

Example 4 The copolymerization amount of BPS-EO was 7
A biaxially oriented film was obtained in the same manner as in Example 1 except that the content was changed to mol%. As shown in Table 1, the characteristics of the obtained film were good.

Comparative Example 1 A biaxially oriented film was obtained in the same manner as in Example 1 except that BPS-EO was not copolymerized. Table 1 shows the properties of the obtained film. The resulting film had poor delamination resistance.

Comparative Example 2 Diethylene glycol (DE
G) was performed in the same manner as in Example 1 except for adding 2.5 parts of a biaxially oriented film. Table 1 shows the properties of the obtained film. The obtained film had good delamination resistance, but had insufficient Young's modulus.

Comparative Example 3 A biaxially oriented film was obtained in the same manner as in Example 1 except that 3 mol% of dimethyl terephthalate was copolymerized instead of BPS-EO. Table 1 shows the properties of the obtained film. The resulting film had insufficient Young's modulus.

[Comparative Example 4] BPS-EO was not copolymerized.
In addition, a biaxially oriented film was obtained in the same manner as in Example 1 except that the heat treatment was not performed at 110 ° C. for 24 hours. Table 1 shows the properties of the obtained film. The resulting film had poor delamination resistance and poor curl resistance.

Comparative Example 5 The temperature of the rotary cooling drum for extruding an unstretched film was 90 ° C., and the heat setting temperature was 265.
A biaxially oriented film was obtained in the same manner as in Example 1 except that the temperature was changed to ° C. Table 1 shows the properties of the obtained film. The obtained film had a rough background and an insufficient Young's modulus.

[0068]

[Table 1]

[0069]

According to the present invention, a biaxially oriented film having excellent delamination resistance and mechanical strength, and also having excellent anti-curl properties, such as delamination resistance and mechanical strength. Combined electrical applications such as motor transformer insulation, electric wire coating, capacitors, adhesive tape, gold and silver thread, stamping foil, labels, FPC
(Flexible printed circuit board), a biaxially oriented film suitable for a membrane switch and the like can be provided.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:02 (72) Inventor Shinichi Kawai 3-37-19 Koyama, Sagamihara-shi, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (72 ) Inventor Kenji Suzuki 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture, Sagamihara Research Center, Teijin Limited

Claims (6)

[Claims] 1. A composition comprising 2,6-naphthalenedicarboxylic acid as a main acid component, ethylene glycol as a main glycol component, and bis (4- (2-hydroxyethoxy)
(Phenyl) sulfone as a copolymer component, the content of the diethylene glycol component in the copolymer polyester is 3 mol% or less (based on the total amount of all glycol components), and the density of the film is 1. 352 g / cm ³ or more, the surface roughness of the film is 2.0 nm or less, and the sum of longitudinal and horizontal Young's modulus is 1000 kg / mm ² or more. 6-naphthalate film. 2. Bis (4- (2-hydroxyethoxy)
2. The copolymerized polyethylene-2,6-naphthalate film according to claim 1, wherein the copolymerization amount of phenyl) sulfone is 0.1 to 10 mol% based on all dicarboxylic acid components. 3. The modified polyethylene-2,6-naphthalate film according to claim 1, wherein the glass transition temperature measured by a differential scanning calorimeter is less than 125 ° C. 4. Measurement of a film by a differential scanning calorimeter in a temperature range of 120.degree.
The modified polyethylene-2,6-naphthalate film according to claim 1, which shows an endothermic peak of at least / mg. 5. The modified polyethylene-2,6-naphthalate film according to claim 1, wherein the film has a plane orientation coefficient of 0.256 or less. 6. The modified polyethylene-2,6-naphthalate film according to claim 1, wherein the number of coarse projections having a height of 1.1 μm or more on the film surface is 5/100 cm ² or less.