JPH1036494A - Thermoplastic polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic polyester film excellent in transparency, strength and heat resistance. SOLUTION: This film comprises a polyester mainly comprising ethylene napthalate repeating units and ethylene terephthalate repeating units and containing a magnesium compd., a cobalt compd. and a phosphorus compd. in amounts which satisfy all of the following relations (1) to (3): (1) 80.0<=Mg<=300.0, (2) 2.0<=Co<=40.0 and (3) 2.0<=(Mg+Co)/P<=5.0 wherein Mg, Co and P represent the amounts (ppm) of the magnesium compd., cobalt compd., and phosphorus compd. in terms of magnesium atom, cobalt atom and phosphorus atom, respectively, based on the polyester. This film is at least monoaxially oriented and has a light transmittance of at least 80%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic polyester film having excellent transparency, strength and heat resistance.

[0002]

2. Description of the Related Art Conventionally, a film made of a thermoplastic polyester represented by polyethylene terephthalate (hereinafter abbreviated as PET) has excellent mechanical properties, heat resistance, weather resistance, and the like.
Since it has electrical insulation properties, it is widely used in a wide range of fields such as packaging, photography, electrical use, and magnetic tape.

[0003] Usually, a thermoplastic polyester film is
It is obtained by melt-extruding PET and stretching it in at least one direction. However, in recent years, there have been many applications where the heat resistance of PET films is not satisfactory, and there is a tendency that attention is paid to materials having better heat resistance than PET films such as polyethylene naphthalate (hereinafter abbreviated as PEN) films.

[0004] It is known that PEN has a higher Tg (glass transition point) and better heat resistance than PET. However, PEN has a higher Tm (melting point) than PET, and thus has poor heat moldability, and has a rigid structure having a naphthalene ring in the molecular chain, so that it is difficult to obtain stable film-forming properties. . Also, PEN is more expensive than PET, so it is difficult to simply use it as a substitute for PET.

In order to improve the heat resistance of PET films, it is conceivable to blend PET with PEN and melt extrude the PET film to obtain a film.
And PEN are poorly compatible, and simply melt-blended into a whitened blend and cannot be used for film applications. In addition, it has been confirmed that melt blending at high temperatures for a long period of time makes it transparent, but it is difficult to melt blend for a long time during film formation practically, and other physical properties may deteriorate due to thermal degradation etc. Is also a concern.
The technology relating to such a blend is disclosed in JP-B-49-229.
No. 57 is disclosed.

[0006]

Therefore, PEN and PE
In order to obtain a film having excellent physical properties with T, it is necessary to improve the compatibility of these resins and to provide a film from a uniform polyester having a small amount of pyrolysis products. It depends.

The present invention solves the problems (especially compatibility and whitening) present in a film having a PEN component and a PET component, and is excellent in compatibility, transparency, strength, heat resistance and film forming stability. The purpose is to obtain a thermoplastic polyester film.

[0008]

In order to achieve the above object, the thermoplastic polyester film of the present invention mainly comprises ethylene naphthalate units and ethylene terephthalate units as repeating units, and the following formulas (1) to (3) are obtained. It is made of a polyester containing a satisfactory amount of a magnesium compound, a cobalt compound and a phosphorus compound at the same time, is at least uniaxially stretched, and has a light transmittance of 80% or more.

(1) 80.0 ≦ Mg ≦ 300.0 (2) 2.0 ≦ Co ≦ 40.0 (3) 2.0 ≦ (Mg + Co) /P≦5.0 {wherein Mg, Co, P is the amount of magnesium compound, cobalt compound and phosphorus compound as magnesium atom, cobalt atom and phosphorus atom with respect to polyester (ppm)
Indicates｝

Here, the ethylene naphthalate unit is

Embedded image Say.

The ethylene terephthalate unit is

Embedded image Say.

The phrase "mainly ethylene naphthalate units and ethylene terephthalate units as repeating units" means "98 to 2 mol% of ethylene naphthalate units and 2 to 98 mol% of ethylene terephthalate units." And ".

The thermoplastic polyester film having the above structure has sufficient strength, and excellent transparency and heat resistance.

In this case, the polyester is a naphthalate-based polyester (A) having 98-80 mol% of ethylene naphthalate units and 99-1 wt% of a terephthalate-based polyester (B) having 98-80 mol% of ethylene terephthalate units. ) A resin obtained by melt-mixing 1 to 99% by weight.

The thermoplastic polyester film having the above constitution has particularly excellent compatibility and film forming stability.

In this case, the magnesium atom contained in the naphthalate-based polyester (A) is 180 pp.
m to 400 ppm, 10 to 40 ppm of cobalt atoms and 40 to 90 ppm of phosphorus atoms.

The thermoplastic polyester film having the above-mentioned structure does not cause coloring of the film and deterioration of mechanical properties due to heat deterioration.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the thermoplastic polyester film of the present invention will be described in detail.

In the present invention, "a polyester mainly composed of ethylene naphthalate units and ethylene terephthalate units as repeating units" is defined as "a proportion of 98 to 2 mol% of ethylene naphthalate units and 2 to 98 mol% of ethylene terephthalate units". Means a `` polyester constituting a repeating unit '', does not particularly specify the production method, even a copolymer having an ethylene naphthalate unit and an ethylene terephthalate unit,
A melt blend of two or more copolymers having different molar ratios of these structural units may be used. Typically, a naphthalate-based polyester (A) having 98-80 mol% of ethylene naphthalate units (abbreviated as naphthalate-based polyester (A)) and a terephthalate-based polyester having 98-80 mol% of ethylene terephthalate units (B) (which is abbreviated as terephthalate-based polyester (B)) and a resin obtained by melt-blending. In order to maintain the crystallinity of the obtained film, the content of ethylene naphthalate unit is 98 to 90 mol%. It is preferable to use a certain naphthalate-based polyester and a terephthalate-based polyester having 98 to 90 mol% of ethylene terephthalate units.

When a copolymerized polyester having an ethylene naphthalate unit of more than 98 mol% or a copolymerized polyester having an ethylene terephthalate unit of more than 98 mol% is used, whitening can be achieved by simple melt-mixing, and transparent and uniform. It takes a long time to obtain a proper mixture, which deteriorates the resin and consequently lowers the physical properties of the molded product, and increases the amount of oligomer. In such a case, the light transmittance is far out of the range specified in the present invention.

Further, a copolymerized polyester containing less than 80 mol% of ethylene naphthalate units and more than 20 mol% of ethylene terephthalate units or a copolymerized polyester containing less than 80 mol% of ethylene terephthalate units and more than 20 mol% of ethylene naphthalate units In the case of using as a main component, melt blending will result in
Although a homogeneous mixture can be obtained, fusion or blocking occurs during drying or solid-phase polymerization prior to melt blending, and the light transmittance may fall outside the range specified in the present invention.

The naphthalate-based polyester (A)
And a copolymer component forming an ethylene naphthalate unit or a unit other than the ethylene terephthalate unit in the terephthalate-based polyester (B), and the acid component is terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hexahydroterephthalic acid. Acid, hexahydroisophthalic acid, succinic acid, P-oxybenzoic acid, 4,
4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis (4-carboxyphenyl)
Examples thereof include ethane, adipic acid, sebacic acid, dimer acid, 5-sodium sulfoisophthalic acid and ester-forming derivatives thereof, and the like. Preferred dicarboxylic acids do not lower heat resistance, that is, do not lower Tg than PET. Acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, dimer acid, 5-sodium sulfoisophthalic acid It is recommended to use etc.

The glycol component as a copolymer component in the naphthalate-based polyester (A) and the terephthalate-based polyester (B) includes ethylene glycol, propylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, 4-cyclohexanedimethanol, neopentyl glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, an ethylene oxide adduct of bisphenol A, an ethylene oxide adduct of bisphenol S, and the like can be given. Propylene glycol, tetramethylene glycol, neope, so as not to lower Tg below PET. Chill glycol, diethylene glycol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, and ethylene oxide adduct of bisphenol S.

The intrinsic viscosities of the naphthalate-based polyester (A) and the terephthalate-based polyester (B) are generally IV = 0.4 to 1.5, preferably 0.4 to 1.5, respectively.
It is about 1.2.

When the naphthalate-based polyester (A) and the terephthalate-based polyester (B) are mixed to form a polyester mainly composed of ethylene naphthalate units and ethylene terephthalate units, the mixing ratio (weight ratio) is , 99: 1 to 1:
It can be set in the range of 99.

The polyester used in the present invention, which mainly comprises ethylene naphthalate units and ethylene terephthalate units as repeating units, in particular, naphthalate polyester (A) and terephthalate polyester (B) are obtained by polycondensation from dicarboxylic acid and glycol, respectively. In this case, it is desirable that the amounts of magnesium, cobalt, and phosphorus in the obtained polymer be in the range of the above formulas (1) to (3) by controlling the polymerization catalyst.

The phosphorus compound is intended to increase the rate of transesterification by the catalyst within the above range and to shorten the melt mixing time required for compatibilization (clearing). Therefore,
Stabilization of the catalyst by the phosphorus compound means loss of catalytic activity.

As the phosphorus compound used in the present invention to obtain a polyester mainly composed of ethylene naphthalate units and ethylene terephthalate units as repeating units, particularly a naphthalate polyester (A) and a terephthalate polyester (B), phosphoric acid is used. Trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, triphenyl phosphate, etc. Examples of hypophosphorous compounds include dimethyl phosphite, diethyl phosphite, dipropyl phosphite, dibutyl phosphite, diphenyl phosphite and the like.

Next, a method of polymerizing a polyester having a repeating unit mainly composed of an ethylene naphthalate unit and an ethylene terephthalate unit, particularly a naphthalate-based polyester (A) and a terephthalate-based polyester (B) used in the present invention will be described.

The polymerization method basically follows a known polymerization method for polyethylene terephthalate. And now,
2,6-Naphthalenedicarboxylic acid is supplied as raw material in the form of dimethyl ester as its ester-forming derivative. Therefore, polymerization by a transesterification method is desirable.

As the catalyst used for the polymerization,
Mg, Co, Sb, Ge, Ti, Sn, Zn, Mn, C
oxides such as a, hydroxides, lower aliphatic carboxylate, and the like.

As a desirable catalyst system, since a dimethyl ester of 2,6-naphthalenedicarboxylic acid is used as one of the raw acid components, a catalyst for transesterification is essential.

As a preferred combination of catalysts, a transesterification catalyst may be a compound of Mg, Co, Mn, Ca or Zn, and a polycondensation catalyst may be a compound of Sb or Ge.

The amount of the catalyst is not limited, but is 10 ^-5 to 10 ^-2 gram atom, preferably 5 × 10 ^{-5 to} 5 × 10 ^-3 gram atom per 1 mol of the total acid component. Is usually the case.

If the added amount of magnesium is less than 80.0 ppm, there is a problem that the polymer is melted and extruded and the adhesion is inferior when electrostatically applied to the cooling roll. On the other hand, when the amount of magnesium exceeds 300.0 ppm, there is a disadvantage that hydrolysis resistance, which is one of the physical properties of the polymer, deteriorates.

When the amount of cobalt is less than 2.0 ppm,
There is a problem that the yellow tint of the film becomes strong, that is, the color b value becomes large. If it exceeds 40.0 ppm, there is also a problem that the film becomes blackish.

If (Mg + Co) / P is less than 2.0, the compatibility is poor, and if it exceeds 5.0, the film becomes more yellow.

In any case, the amounts of magnesium, cobalt and phosphorus are used so as to fall within the range of the above formula.

Furthermore, a lubricant composed of inorganic or organic particles may be contained, and if the above requirements are satisfied, particles precipitated in the polyester production step, so-called internal particles, may be contained.

The film of the present invention is mainly composed of a polyester having an ethylene naphthalate unit and an ethylene terephthalate unit as repeating units, in particular, a naphthalate polyester (A) and a terephthalate polyester (B).
Are melt-mixed, extruded from a T-die, cooled, and then stretched in at least one direction by 1.1 times or more, preferably 2.5 times or more. More preferably, it can be obtained as a biaxially stretched film by a sequential or simultaneous biaxial stretching method, and has excellent mechanical properties and other physical properties,
It can be used for various applications.

In the above-described method, the melt-extruded film is usually cooled by bringing it into close contact with a cooling roll by an electrostatic adhesion method. There is no limitation on the conditions for applying static electricity, and any condition may be selected. For example, as the structure of the electrostatic application device, the electrode structure, the presence or absence of the counter electrode, the positional relationship between the electrode and the counter electrode, the extrusion port, the cooling roll, and the like, and the set voltage and current value can be arbitrarily selected as the electrostatic application conditions Good.

[0042]

EXAMPLES Hereinafter, the thermoplastic polyester film of the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist.

The evaluation method in this specification is as follows.

Compatibility After melt-blending at 280 ° C. for 10 minutes using a Labo Plastomill manufactured by Toyo Seiki Co., Ltd., the blend was quenched with liquid nitrogen and the compatibility was visually determined. The criteria are as follows.

Transparent ○ Slightly turbid △ Strong turbidity × Only ○ was accepted according to the above criteria.

Transparency Integrating sphere formula T. The light transmittance (%) was determined using an R meter (manufactured by Nippon Seimitsu Kagaku).

Polymer Melting Resistance Two electrode plates were placed in polyester melted at 275 ° C., and a current value (I) when a voltage of 120 V was applied was measured. Ask by

Ρ (Ω.cm) = A / D × V / IA A = electrode area (cm), D = distance between electrodes (cm) V = voltage (V) Thermal characteristics Differential thermal analysis measuring instrument manufactured by Shimadzu Corporation The secondary transition point (Tg) was measured using (DSC).

Determination of Metal Atom The atomic weight (ppm) was determined by a fluorescent X-ray method.

Example 1 Using a stainless steel autoclave, 98 mol% of dimethylnaphthalate and 2 mol% of dimethyl terephthalate were used as dibasic acid components, and ethylene glycol was used as a glycol component at 2.2 times the acid content. %, Antimony trioxide was used as a catalyst in an amount of 0.04 mol% based on the acid content, magnesium acetate tetrahydrate and cobalt acetate tetrahydrate were adjusted to 200 ppm of magnesium atoms and 30 ppm of cobalt atoms per polyester unit unit. At the same time, and the temperature was increased to 230 ° C. with stirring to carry out a transesterification reaction. The end of the transesterification reaction was when the predetermined methanol was distilled off. After the transesterification reaction, 20 ppm of sodium acetate trihydrate as sodium atom,
74 ppm of trimethyl phosphate was added as a phosphorus atom, and the temperature was raised to 280 ° C. under reduced pressure to carry out a polycondensation reaction.

After the completion of the polycondensation reaction, the intrinsic viscosity of the copolymer was 0.46. This copolymer was used as a naphthalate-based polyester (a).

In a similar apparatus, dimethyl terephthalate was added to 9
8 mol%, dimethyl naphthalate 2 mol%, and ethylene glycol as a glycol component in an amount of 2.0 to the acid component.
Double mole% was charged, antimony trioxide was used as a catalyst in an amount of 0.04 mol% based on the acid component, and magnesium acetate tetrahydrate and cobalt acetate tetrahydrate became 200 ppm as magnesium atoms and 30 ppm as cobalt atoms per polyester unit. The temperature was increased to 230 ° C. with stirring to carry out a transesterification reaction. After completion of the transesterification reaction, it was determined that predetermined methanol was distilled off.

After completion of the transesterification, 20 ppm of sodium acetate trihydrate as sodium atom and 74 ppm of trimethyl phosphate as phosphorus atom were added, and the temperature was raised to 270 ° C. under reduced pressure to carry out a polycondensation reaction.

After the completion of the polycondensation reaction, the intrinsic viscosity of the copolymer was 0.58. This copolymer was designated as terephthalate-based polyester (b).

The copolymers (a) and (b) were mixed at a weight ratio of (a) :( b) = 1: 1 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. 3.5 times the film lengthwise at 100 ° C, then 130 ° C
Stretched in the horizontal direction at 220 ° C.
A biaxially stretched film of μm was obtained. Table 1 shows the physical property values of the obtained film.

Example 2 According to the polymerization method of Example 1,
98 mol% of dimethylnaphthalate as a dibasic acid component,
2 mol% of dimethyl terephthalate, 2.2 times mol% of ethylene glycol as glycol component to acid component
The preparation was carried out in the same manner as in Example 1, except that antimony trioxide was used as a catalyst in an amount of 0.04 mol% based on the acid component, magnesium atoms were adjusted to 300 ppm, and cobalt atoms were adjusted to 30 ppm (per polyester unit). An exchange reaction was performed.

Next, the polycondensation reaction was carried out by adjusting the amount of sodium atoms to 20 ppm and the amount of phosphorus atoms to 50 ppm to obtain a naphthalate-based polyester (c).

Similarly, 98 mol% of dimethyl terephthalate, 2 mol% of dimethyl naphthalate, and 2.2 times mol% of ethylene glycol were added to the acid component, and antimony trioxide was used as a catalyst at 0.04 mol% to the acid component. 80p magnesium atoms per polyester unit
Example 1 so that pm and cobalt atoms become 30 ppm.
The transesterification reaction was performed in the same manner as described above. Then, a polycondensation reaction was carried out in the same manner as in Example 1 so that the sodium atom became 20 ppm and the phosphorus atom became 50 ppm, to obtain a terephthalate-based polyester (d).

The copolymers (c) and (d) were mixed at a weight ratio of (c) :( d) = 1: 1 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. The film is stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and is heat-set at 220 ° C. to have a thickness of 20 μm.
Was obtained. Table 1 shows the physical property values of the obtained film.

Example 3 A polymerization reaction was carried out in the same manner as in Example 2 to obtain a naphthalate-based polyester (c).

Similarly, 98 mol% of dimethyl terephthalate, 2 mol% of dimethyl naphthalate and 2.2 times by mol of ethylene glycol were charged as the dibasic acid component, and antimony trioxide was added as a catalyst to the acid component. 0.04 mol%, zinc acetate dihydrate is added to the acid component in an amount of 0.
04 mol%, cobalt acetate was charged so that the cobalt atom was 20 ppm per polyester unit,
Otherwise, transesterification was carried out in the same manner as in Example 2. Next, 20 ppm of sodium atoms and 5 ppm of phosphorus atoms
A polycondensation reaction was performed by adjusting the concentration to 0 ppm to obtain a terephthalate-based polyester (e).

The copolymers (c) and (e) were mixed at a weight ratio of (c) :( e) = 1: 1 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. . The film is stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and is heat-set at 220 ° C. to have a thickness of 20 μm.
Was obtained. Table 1 shows the physical property values of the obtained film.

Example 4 A polymerization reaction was carried out in the same manner as in Example 2 to obtain a naphthalate-based polyester (c) and a terephthalate-based polyester (d).

The copolymers (c) and (d) were mixed at a weight ratio of (c) :( d) = 3: 7 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. . The film is stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and is heat-set at 220 ° C. to have a thickness of 20 μm.
Was obtained. Table 1 shows the physical property values of the obtained film.

Comparative Example 1 According to the polymerization method of Example 1,
98 mol% of dimethylnaphthalate as a dibasic acid component,
2 mol% of dimethyl terephthalate, 2.2 times mol% of ethylene glycol as glycol component to acid component
The transesterification was carried out in the same manner as in Example 1 except that antimony trioxide was charged as a catalyst and adjusted to be 0.04 mol% with respect to the acid component, magnesium atoms were 150 ppm, and cobalt atoms were 30 ppm (per polyester unit). The reaction was performed.

Next, the polycondensation reaction was carried out by adjusting the amount of sodium atoms to 20 ppm and the amount of phosphorus atoms to 100 ppm to obtain a naphthalate-based polyester (f).

Similarly, 98 mol% of dimethyl terephthalate and 2 mol% of dimethyl naphthalate as the dibasic acid component, and 2.2 times mol% of ethylene glycol as the glycol component with respect to the acid component were added. A transesterification reaction was carried out in the same manner as in Example 1, except that the components were adjusted to be 0.04 mol%, magnesium atoms were 150 ppm, and cobalt atoms were 30 ppm (per polyester unit). Next, 20 ppm of sodium atom and 100 p of phosphorus atom
pm and a polycondensation reaction was performed to obtain a terephthalate-based polyester (g).

The copolymers (f) and (g) were mixed in a weight ratio of (f) :( g) = 1: 1 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. . The film is stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and is heat-set at 220 ° C. to have a thickness of 20 μm.
Was obtained. Table 1 shows the physical property values of the obtained film.

(Comparative Example 2) A naphthalate-based polyester (c) was obtained by a reaction according to the same polymerization method as in Example 2.

Further, by the same polymerization method as in Example 3,
The reaction was performed to obtain a terephthalate-based polyester (e).

The copolymers (c) and (e) were mixed at a weight ratio of (c) :( e) = 1: 9 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. . The film is stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and is heat-set at 220 ° C. to have a thickness of 20 μm.
Was obtained. Table 1 shows the physical property values of the obtained film.

Comparative Example 3 According to the polymerization method of Example 1,
98 mol% of dimethylnaphthalate as a dibasic acid component,
2 mol% of dimethyl terephthalate, 2.2 times mol% of ethylene glycol as glycol component to acid component
The same procedure as in Example 1 was carried out except that antimony trioxide was used as a catalyst and adjusted to be 0.04 mol% with respect to the acid component, magnesium atoms were 80 ppm, and cobalt atoms were 30 ppm (per polyester unit).
A transesterification reaction was performed.

Next, the polycondensation reaction was carried out by adjusting the amount of sodium atoms to 20 ppm and the amount of phosphorus atoms to 50 ppm to obtain a naphthalate-based polyester (h).

Similarly, 98 mol% of dimethyl terephthalate, 2 mol% of dimethyl naphthalate as the dibasic acid component, and 2.2 times mol% of ethylene glycol as the glycol component were added to the acid component. A transesterification reaction was carried out in the same manner as in Example 1 except that 0.04 mol% of the components, magnesium atoms were adjusted to 80 ppm, and cobalt atoms were adjusted to 30 ppm (per polyester unit).

Next, a polycondensation reaction was carried out by adjusting the amount of sodium atoms to 20 ppm and the amount of phosphorus atoms to 50 ppm to obtain a terephthalate-based polyester (j).

The copolymers (h) and (j) were mixed at a weight ratio of (h) :( j) = 1: 1 and melt-extruded at 280 ° C. to obtain an unstretched film having a thickness of 250 μm. The film was stretched 3.5 times in the longitudinal direction at 100 ° C. and then in the transverse direction at 130 ° C., and heat-set at 220 ° C. to obtain a biaxially stretched film having a thickness of 20 μm. Table 1 shows the physical property values of the obtained film.

[0077]

[Table 1]

[0078]

The thermoplastic polyester film according to the first aspect of the present invention is excellent in transparency, strength and heat resistance.

The thermoplastic polyester film according to the second aspect of the present invention is excellent in compatibility and film forming stability.

The thermoplastic polyester film according to the third aspect of the present invention is free from coloring and mechanical properties of the film due to heat deterioration.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C08L 67/02 KKC C08L 67/02 KKC // B29K 67:00 B29L 7:00

Claims (3)

[Claims] 1. A polyester comprising an ethylene naphthalate unit and an ethylene terephthalate unit as a repeating unit and containing a magnesium compound, a cobalt compound, and a phosphorus compound in an amount that simultaneously satisfies the following formulas (1) to (3). A thermoplastic polyester film which is uniaxially stretched and has a light transmittance of 80% or more. (1) 80.0 ≦ Mg ≦ 300.0 (2) 2.0 ≦ Co ≦ 40.0 (3) 2.0 ≦ (Mg + Co) /P≦5.0 {where Mg, Co and P are magnesium Amount of compound, cobalt compound and phosphorus compound as magnesium atom, cobalt atom and phosphorus atom with respect to polyester (ppm)
Is shown. ｝ 2. A polyester comprising 99 to 1% by weight of a naphthalate-based polyester (A) having 98 to 80 mol% of ethylene naphthalate units and a terephthalate-based polyester (B) 1 having 98 to 80 mol% of ethylene terephthalate units. 2. The thermoplastic polyester film according to claim 1, wherein the resin is obtained by melt-mixing the resin in an amount of about 99% by weight. 3. The naphthalate-based polyester (A) contains 180 ppm to 400 pp of magnesium atoms.
m, 10-40 ppm of cobalt atoms and 4 of phosphorus atoms
3. The thermoplastic polyester film according to claim 2, wherein the content is 0 to 90 ppm.