JPH08245811A - Polyester film - Google Patents

Abstract

PURPOSE: To improve resistance to thermal deterioration by forming a mixture of a polyester incapable of functioning as a liquid crystal and a polyarylate capable of functioning as a liquid crystal into a sheet, stretching the sheet, and conducting heat setting. CONSTITUTION: A polyester incapable of functioning as a liquid crystal and having an intrinsic viscosity of 0.8 or higher is blended with 0.1-40wt.% polyarylate capable of functioning as a liquid crystal and having a melt viscosity of 100-1,000 P, a diameter of 5μm or smaller, and an aspect ratio of 10 or higher. The blend is extruded into a sheet and cooled to obtain an amorphous cast film. The film is heated to 80-150 deg.C, stretched in the machine direction 2-7 times, and cooled to 20-50 deg.C. This film is stretched at 80-150 deg.C in the transverse direction 2-6 times and then subjected to heat setting at 150-250 deg.C. Thus, the objective film is obtained which has an oligomer content of 0.4wt.% or lower and a terminal carboxyl content of 15eq/ton or lower, and in which the 180 deg.C-heating time required for the film to have a machine-direction elongation at break which is a half of the initial value thereof is 50hr or longer.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a polyester film,
More specifically, the present invention relates to a polyester film which has a low oligomer content and is excellent in heat deterioration resistance, and is particularly suitable for electrical insulation and the like.

[0002]

2. Description of the Related Art Polyester films are widely used in industrial applications because of their excellent mechanical properties, thermal properties, and electrical properties, and the demand for them is also increasing. In particular, among the polyesters, polyethylene terephthalate and polyethylene naphthalate have excellent mechanical properties and thermal properties, and since polyethylene terephthalate is inexpensive, it is used in a wide range of fields. One of the fields of application of these films is for electrical insulation applications.
It is required that the film contains a small amount of oligomers and is excellent in heat deterioration resistance.

Polyethylene terephthalate or a polyethylene terephthalate film usually contains 1.3 to 1.7% by weight of an oligomer having an ethylene terephthalate cyclic trimer as a main component. When a polyethylene terephthalate film containing such an oligomer is used for electrical insulation of a sealed motor for a refrigerator, for example, the oligomer is extracted from the polyethylene terephthalate film by the refrigerator oil or the refrigerant in the motor,
The ethylene terephthalate cyclic trimer contained therein deposits in various places of the refrigerator, causing troubles. Therefore,
There is a demand for an insulating material having a low content of oligomers. The heat deterioration resistance is generally related to the polymerization degree of polyester, and the heat deterioration resistance can be improved by increasing the polymerization degree. Further, with respect to heat deterioration resistance, hydrolysis resistance may be particularly required. And this hydrolysis resistance becomes more excellent as the amount of carboxyl end groups of the polyester is smaller.

Conventionally, in order to reduce the amount of oligomer contained in the film, a method of extracting the oligomer with xylene, dimethylformamide, benzyl alcohol, etc. has been proposed (Japanese Patent Publication No. 43-23348 and Japanese Patent Publication No. 44-44). 2120, JP-A-51-115433.
Issue). When the polyester film is extracted with such a high boiling point organic solvent, most of the oligomers present on the surface of the film and inside the film are removed. However, since extraction with an organic solvent causes the film to swell,
Even if the organic solvent is removed after the extraction, there are problems that the flatness of the film is significantly deteriorated and the surface morphology of the film is changed. In addition, long-time extraction has the drawbacks that the mechanical properties and heat deterioration resistance are significantly reduced, and the manufacturing cost is increased.

Further, as a means for reducing the content of oligomers and at the same time the content of carboxyl terminal groups, there is a method of subjecting the raw material polyester chips to solid phase polymerization. However, the chips obtained by solid-state polymerization have a high degree of polymerization and thus a high melt viscosity at the same time, and when melt extruding while filtering to obtain a film,
The temperature of the filter must be set high in order to generate heat due to shearing in the extruder and to raise the filtering pressure in the filter, resulting in an increase in the content of oligomers and a thermal decomposition of the polymer resulting in a large degree of polymerization. There is a disadvantage that the amount of carboxyl end groups is decreased and the amount of carboxyl terminal groups is also increased.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have arrived at the present invention as a result of extensive studies in order to solve such conventional drawbacks. That is, it is an object of the present invention to provide a high-performance polyester film having a low content of oligomers and excellent heat deterioration resistance.

[0007]

The polyester film of the present invention for this purpose has an oligomer content of 0.4.
% Or less and the carboxyl end group amount is 15 equivalents /
is less than or equal to ton.

The polyester applicable to the present invention is a polymer having an ester group in the main chain, which is obtained by polycondensation from a diol and a carboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, diphenic acid and phthalic acid. , Naphthalenedicarboxylic acid, adipic acid, sebacic acid, dimer acid, eicoic acid, dodecanedioic acid, etc. It is something.
Specific examples thereof include polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalate. Of course, these polyesters may be homopolymers or copolymers, and examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, Examples of the dicarboxylic acid component include isophthalic acid and 2,6-naphthalenedicarboxylic acid. In the case of the present invention,
Especially polyethylene terephthalate, polyethylene-2,
6-naphthalate is preferable from the viewpoint of mechanical strength, heat resistance, chemical resistance, durability, versatility and the like. In the case of the present invention,
Particularly, polyethylene terephthalate and polyethylene naphthalate having an intrinsic viscosity of 0.8 or more, preferably 1.0 or more are preferable. The solid phase polymerization method is most preferably used as a means for obtaining such a polyester having a high intrinsic viscosity.

In the polyester film of the present invention, it is preferable that the polyester is a non-liquid crystalline polyester, and the non-liquid crystalline polyester is combined with a liquid crystalline polyarylate (hereinafter sometimes abbreviated as PA). .

The liquid crystalline polyarylate (P
A) is melt moldability having a mesogen group in the main chain,
And it means polyester which has liquid crystal forming property. Particularly preferred are the following units. First, as the structural unit derived from the diol,
For example, the one shown in the following chemical formula 1 may be mentioned. In the following chemical formula 1, X and Y each independently represent hydrogen, halogen, or an alkyl group having 4 or less carbon atoms.

[0011]

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Further, examples of the structural unit derived from dicarboxylic acid include those represented by the following chemical formula 2. In Chemical formula 2, X represents hydrogen, halogen, or an alkyl group having 4 or less carbon atoms.

[0013]

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Further, examples of the structural unit derived from hydroxycarboxylic acid include those represented by the following chemical formula 3. In Chemical Formula 3, X represents hydrogen, halogen, or an alkyl group having 4 or less carbon atoms.

[0015]

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In order to adjust the melt viscosity and melting point of the PA of the present invention, it is also effective to introduce the structural units shown in the following chemical formulas 4 and 5, for example. That is, Chemical formula 4 (where X is O, CH ₂ , CH ₂ , C (CH ₃ ) ₂ , SO
Represents ₂ . ), A structural unit that can rotate relatively freely between aromatic rings, or
n is an integer of 2 to 10) and examples thereof include an aliphatic diol and a structural unit derived from an aliphatic dicarboxylic acid.

[0017]

[Chemical 4]

[0018]

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Further, particularly preferable PAs include those having the structural formulas shown in the following chemical formulas 6-8. That is

[0020]

[Chemical 6]

[0021]

[Chemical 7]

[0022]

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In the above Chemical Formulas 6 to 8, Σni = 10
0. Of course, each ni is preferably 4 or more. Further, a part of these polymers may be substituted with various substituents such as halogen.

In the case of the present invention, p-hydroxybenzoic acid (PHB) / ethylene terephthalate copolymer, PHB
/ 6-Bidroxy-2-naphthoic acid copolymer, PHB /
Most preferred are 4,4'-dihydroxybiphenyl / terephthalic acid / isophthalic acid copolymer, PHB / ethylene terephthalate / 4,4'-dihydroxybiphenyl / terephthalic acid copolymer.

The melt viscosity of the PA of the present invention is 100.
A range of up to 1000 poises is preferred. The melt viscosity ratio of the non-liquid crystalline polyester of the present invention to PA (non-liquid crystalline polyester / PA) is 5 or more, preferably 10 or more,
More preferably, it is 20 or more. Further, the melting point of the non-liquid crystalline polyester is preferably equal to or higher than that of PA.

The composite form of the polyester film of the present invention is not particularly limited, but PA is finely dispersed in the non-liquid crystalline polyester, and various forms such as skin-core type, sea-island type, multi-layer type and fiber type are available. However, in the case of the present invention, it is particularly preferable that PA is finely dispersed in a fibrous state, and the diameter of the PA fiber is 5 μm or less, preferably 3 μm or less, more preferably 1 μm or less. It is good because it is excellent in prevention of deterioration of heat and thermal decomposition. The aspect ratio of the fibers at this time is 10 or more, preferably 20 or more. The amount of PA added is 0.1 to 40% by weight, preferably 0.3 to 20% by weight, and more preferably 0.5 to 10% by weight. This is because if the addition amount is less than 0.1% by weight, it is not possible to obtain a film having low oligomers and excellent heat deterioration resistance, which are the effects of the present invention. On the contrary, if the addition amount exceeds 40% by weight, the polyester film of the present invention is This is because not only the physical properties are unbalanced in the longitudinal direction and the width direction, but also an appropriate breaking elongation cannot be obtained and the heat deterioration resistance is deteriorated.

In the polyester film of the present invention, only non-liquid crystalline polyester and PA may be used, but in addition, compatibilizer, plasticizer, weathering agent, antioxidant, heat stabilizer, lubricant, antistatic agent. A whitening agent, a coloring agent, a conductive agent, etc. may be added.

The polyester film of the present invention may be a single film, but other polymer layers such as polyester,
You may laminate polyolefin, polyamide, polyvinylidene chloride, an acrylic polymer, etc.

The polyester film of the present invention may be an unstretched or unoriented film, but a known uniaxially or biaxially oriented, heat treated oriented film is preferred in terms of high elasticity, toughness, heat resistance and the like.

The oligomer content of the polyester film of the present invention is preferably less than 0.4% by weight when it is used for motor insulation or the like. Further, it is preferable that the amount of the carboxyl terminal group is 15 equivalents / ton or less, preferably 10 equivalents / ton or less from the viewpoint of heat deterioration resistance including hydrolysis resistance. In addition, the polyester film of the present invention is often used under high temperature, and the time required for the longitudinal elongation at break of the film when heat-treated in an atmosphere of 180 ° C. to be reduced to half that before the heat treatment. The (half-life time of elongation at break) is 50 hours or longer, preferably 70 hours or longer, more preferably 100 hours or longer,
It is preferable in terms of heat deterioration resistance. Furthermore, it is preferable that the intrinsic viscosity representing the degree of polymerization of the film is 0.8 or more, preferably 1.0 or more from the viewpoint of heat deterioration resistance.

A polyester film satisfying the above characteristics is prepared by mixing PA with a non-liquid crystalline polyester produced by a solid phase polymerization method and having a low content of oligomers and a small amount of carboxyl terminal groups and a high degree of polymerization. It is achieved by molding. If there is no PA, when melt-extruding while filtering to obtain a film, shear heat is generated in the extruder due to its high melt viscosity, and filtration pressure is increased in the filter. The filter temperature must be set high, resulting in an increase in the content of oligomers, thermal decomposition of the polymer, a significant decrease in the degree of polymerization, and an increase in the amount of carboxyl end groups. However, in the presence of PA, even if the degree of polymerization is high,
Smooth extruding is possible without causing shear heat generation and filter pressure increase, and it is possible to produce a film with low oligomer, high polymerization degree and small amount of carboxy terminal groups and excellent in heat deterioration resistance. Become.

Next, a method for producing the polyester film of the present invention will be described, but the invention is not limited to such an example. An example in which polyethylene terephthalate is used as the non-liquid crystalline polyester is shown, but the production conditions differ depending on the polymer. According to a conventional method, bis-β-hydroxyethyl terephthalate (BH) is esterified from terephthalic acid and ethylene glycol, or dimethyl terephthalate and ethylene glycol are transesterified.
T) is obtained. Next, while transferring this BHT to the polymerization tank,
The polymerization reaction proceeds by heating to 280 to 290 ° C under vacuum. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is solid-phase polymerized in a chip form under reduced pressure. When solid-phase polymerization is performed, 180
After pre-crystallization at a temperature below ℃, 190-250 ℃
Then, solid phase polymerization is performed under reduced pressure of about 1 mmHg to increase the intrinsic viscosity.

Next, the polyester chips are mixed with PA chips, vacuum-dried at 180 ° C. for 3 hours or more, supplied to an extruder heated to 280 ° C., filtered through a filter, and then subjected to T-die. To extrude into a sheet. The non-liquid crystalline polyester and PA may be mixed as they are as chips, but in order to improve the dispersibility, a non-liquid crystalline polyester master chip containing high concentration of PA is once prepared using a biaxial kneader or the like. It is also preferable to dilute the chip with a non-liquid crystalline polyester chip before use. The sheet melt-extruded from the T-die is adhered and solidified on a drum cooled to a surface temperature of 25 ° C. by electrostatic force to obtain a substantially amorphous cast film. The cast film is heated by a heating roll group at 80 to 150 ° C., stretched in the longitudinal direction by 2 to 7 times in one stage or in multiple stages, and 20 to 50 ° C.
It cools with the cooling roll group. Then, while guiding it to a tenter and grasping both ends of the film with clips,
It is heated in a hot air atmosphere heated to ˜150 ° C. and stretched 2 to 6 times in the transverse direction. Then, the film is 150-2
Heat set at a temperature of 50 ° C. The heat setting may be performed under tension, and in order to further improve the thermal dimensional stability,
Relaxation in the width direction is also preferably performed.

[Measurement Method of Physical Properties and Evaluation Method of Effect] (1) Content of Oligomer 100 mg of the polymer was dissolved in 1 ml of orthochlorophenol and subjected to liquid chromatography (model 8500, VARIAN).
(Manufactured by K.K.) and is shown as a ratio (% by weight) to the polymer.

(2) Carboxyl terminal amount It is determined by dissolving the polymer in orthocresol / chloroform and potentiometric titration with alkali. Unit is equivalent / t
Expressed as on.

(3) Intrinsic viscosity 25 ° C at a concentration of 0.1 g / ml in orthochlorophenol
It is the value measured in. The unit is dl / g.

(4) Melt viscosity A value at a shear rate of 1000 sec ^-1 is measured using a melt indexer. The unit is expressed in poise.

(5) Elongation at break, Young's modulus Tensilon type tensile test (manufactured by Orientec Co.) width 10
mm, and the length between chucks is set to 100 mm, and a tensile test is performed at a tensile speed of 200 mm / min in an atmosphere of 23 ° C. and 65% RH to obtain the value. The unit is the elongation at break, and the Young's modulus is kg / mm ² .

(6) Half-life time of elongation at break The film before heat treatment is cut out in the longitudinal direction and the elongation at break is measured by a Tensilon type tensile test to obtain the initial elongation at break. The film is heat-treated in a heating oven in an atmosphere of 180 ° C., and the time required for the breaking elongation in the longitudinal direction to decrease to 1/2 of the initial breaking elongation is determined.

(7) Fiber Diameter and Aspect Ratio of Liquid Crystalline Polyarylate (PA) The film was dissolved using orthochlorophenol,
Unmelted PA is separated by centrifugation and observed by using a scanning microscope to obtain the value.

[0041]

EXAMPLES Examples and comparative examples will be shown below in order to clarify the effects of the present invention. Examples 1 to 4 0.08 parts of calcium acetate in a mixture of 100 parts of dimethyl terephthalate and 60 parts of ethylene glycol,
Antimony trioxide (0.03 part) was added, and the temperature was elevated by a conventional method to carry out a transesterification reaction. Next, after adding 0.16 parts of lithium acetate and 0.24 parts of trimethyl phosphate to the transesterification reaction product, the product was transferred to a polymerization reaction tank. Then, the reaction system was gradually depressurized while heating and heating, and polymerization was carried out by a conventional method at 285 ° C. under a reduced pressure of 1 mmHg to obtain polyethylene terephthalate (PET) having an intrinsic viscosity of 0.52. The PET is made into chips, and a rotary vacuum polymerization device is used to reduce the pressure to 0.5 mmHg at 225 ° C.
As shown in Table 1, solid phase polymerization was performed at different times with
The intrinsic viscosity was changed from 0.87 to 1.43. As a liquid crystalline polyarylate (PA), a copolymer of p-hydroxybenzoic acid (80 mol%) and ethylene terephthalate (20 mol%) (liquid crystal starting temperature 240 ° C., melting point 2
60 ° C., melt viscosity 500 poise) was used. The PET9
The dried and dehydrated mixture of 5% by weight and 5% by weight of PA was supplied to a known 150 mm extruder, melted at 285 ° C., then extruded from a T-die, and placed on a cooling drum kept at 25 ° C. While applying static electricity, it was rapidly cooled and solidified. The cast film was stretched 3.0 times at 95 ° C. by a longitudinal roll type stretching machine. Then, it was introduced into a tenter, and stretched 3.5 times in the width direction, and then 5% in the width direction at 235 ° C.
Heat setting was performed while relaxing to obtain a biaxially oriented film having a thickness of 150 μm. The properties of the film are listed in Tables 1-2. It can be seen that the film thus obtained is a low oligomer and is excellent in heat deterioration resistance.

Comparative Examples 1 to 5 Intrinsic viscosities of 0.5 obtained in the same manner as in Examples 1 to 4
The intrinsic viscosity of PET of 2 was changed to 0.6 by changing the solid-state polymerization time.
Changed from 4 to 1.43. Biaxially oriented films were obtained in exactly the same manner as in Examples 1 to 4 except that the PA added in Examples 1 to 4 was not added. From the results shown in Tables 1 and 2, it can be seen that, if PA is not used, only a film having a large increase in oligomers during melt extrusion, an increase in carboxyl terminal groups, a decrease in intrinsic viscosity, and a decrease in heat deterioration resistance can be obtained.

Examples 5 to 10 Comparative Examples 6 and 7 The PET polymer having an intrinsic viscosity of 1.43 used in Example 4 and the PA used in Examples 1 to 4 were added in an amount of 0.
A biaxially oriented film was obtained in the same manner as in Examples 1 to 4 while changing the content to 05 to 45.0% by weight. From the results shown in Tables 3 and 4, it is understood that the effect is not so great when the amount of PA added is less than 0.1% by weight. On the contrary, when the amount of PA added is more than 40% by weight, not only the anisotropy of the film is remarkable, but also the elongation at break is remarkably reduced to make the film brittle and the heat deterioration resistance is deteriorated.

Comparative Example 8 The biaxially oriented film obtained in Comparative Example 5 was heated at 140 ° C. for 24 hours.
Oligomers were extracted with xylene for a period of time. Tables 3-4
As shown in (1), although the amount of the oligomer contained in the obtained film is reduced, the amount of the carboxyl terminal group is increased, the heat deterioration resistance is lowered, and the mechanical properties are greatly lowered.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

In the film of the present invention, in order to obtain a film having high viscosity, that is, a high molecular weight, the following effects are brought about by forming a composite with a liquid crystalline polyarylate. (1) Even in the case of polyester having a high intrinsic viscosity, that is, a melt viscosity, a significant decrease in melt viscosity is observed by mixing a specific liquid crystal polyarylate with the polyester.
For this reason, it is possible to increase the number of oligomers during extrusion, reduce the molecular weight, and decrease the heat deterioration resistance due to the increase in the amount of carboxyl end groups.

(2) The film thus obtained exhibits excellent effects in various applications such as magnetic recording media, OA / FA, agriculture, and graphics, but is particularly useful for electrical insulation. The effect of is remarkable.

Claims (6)

[Claims] 1. A polyester film having an oligomer content of 0.4% by weight or less and a carboxyl terminal group content of 15 equivalents / ton or less. 2. The time required for the longitudinal elongation at break of the film when heat-treated in an atmosphere of 180 ° C. to decrease to half that before the heat treatment (half-time of elongation at break) is 50 hours or more. The polyester film according to claim 1, which is present. 3. The intrinsic viscosity is 0.8 or more.
Or the polyester film according to 2. 4. The polyester film according to claim 1, wherein the polyester film is a uniaxially or biaxially oriented film. 5. The polyester is a composite of a non-liquid crystalline polyester and a liquid crystalline polyarylate.
5. The polyester film according to any one of 4 to 4. 6. The polyester film according to claim 5, wherein the liquid crystalline polyarylate is contained in an amount of 0.1 to 40% by weight.