JPS6189826A - Copolyester film - Google Patents

Abstract

PURPOSE:To enable to obtain film, which is easily made into shape under un- oriented state and successively easily oriented and has thermosetting effect, by a method wherein copolyester film, which is obtained by the ester-exchange reaction of two kinds of polymers and has the specified melting point, is oriented. CONSTITUTION:The title film is obtained by biaxially orienting copolyester, which consists of terephthalic acid, isophthalic acid, dihydric phenol compound and glycol compound having carbon atoms of less than 5 and has a melting point, which is not more than 250 deg.C and not less than 230 deg.C. Said copolyester is obtained by ester-exchanging polyarylate consisting of terephthalic acid, isophthalic acid and dihydric phenol compound and linear polyester consisting of terephthalic acid and glycol compound having carbon atoms of less than 5. The copolyester obtained as mentioned above can be easily made into film shape under un-oriented state, oriented and set only in the case that said copolyester has a melting point, which is not more than 250 deg.C and not less than 230 deg.C. In addition, the electrically insulating properties of the obtained oriented film are also excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a copolyester film having excellent electrical properties. More specifically, it is a copolyester film that can be easily formed into an unstretched film, has good stretchability, and can maintain its electrical insulation properties up to high temperatures.

(Prior Art) Among polyester films, polyethylene terephthalate films have good electrical and mechanical properties and are therefore used in various electrical applications including capacitors. However, even though polyethylene terephthalate has electrical properties, it is not sufficient to maintain its electrical insulation properties up to a high temperature range, and rapidly deteriorates when the glass transition temperature of polyethylene terephthalate is exceeded.

Conventionally, the electrical properties and temperature characteristics of polymer films have been increased (if changed, this is often achieved by changing the polymer material that makes up the film). For example, materials with heat resistance superior to polyethylene terephthalate Examples include polyethylene terephthalate, polycarbonate, polysulfone, etc., and the heat resistance rank of the material increases in this order, but the unstretched forming temperature also increases.

Stretching the resulting unstretched film becomes extremely difficult and almost impossible. Furthermore, materials other than polyethylene terephthalate have poor crystallinity, and even if they can be stretched slightly, the heat cent effect after stretching is slight and the dimensional stability is poor.

Furthermore, the electrical insulation temperature characteristics of stretched films made of these materials are almost the same as those of unstretched films.

Those similar to the present invention include Japanese Patent Publication No. 47-24249, Japanese Patent Application Laid-Open No. 51-31774, and Japanese Patent Application Laid-open No. 57-1.
There is a publication No. 21619. Japanese Patent Publication No. 47-24249 discloses that 0.1 to 20 w of polyarylate is added to polyester in order to improve the light resistance of polyethylene terephthalate.
It is added at a ratio of t% of stone, but as is clear from the text, there is a description of preventing polyethylene terephthalate and polyarylate from depolymerizing and lowering the melting point of polyethylene terephthalate. JP-A-51-31774, which does not intend to create copolymerization holes due to transesterification, relates to a method for producing a polyester matte film, and is not intended to create copolymerization holes due to transesterification.
-t % of a polyarylate added thereto is stretched at a specific temperature range, and both are clearly methods for producing films consisting of a simple mixture of two types of polymers. Japanese Patent Publication No. 57-121
Publication No. 619 describes a polyester fiber and a method for producing the same, and it is claimed that polyethylene terephthalate and polyarylate form a heterogeneous phase, and the purpose thereof is to improve the elastic modulus.

As mentioned above, the purpose of these three inventions is completely different from the present invention, and the polymer used is a simple blend of polyester and polyarylate, and the two do not form a copolymer. This is a basic condition and is a completely different substance from the copolymer used in the present invention.

(Problems to be Solved by the Invention) We have arrived at the present invention as a result of our earnest efforts to obtain a film that is easy to stretch, has a heat sink effect, and has good electrical insulation properties even at high temperatures, following the unstretched film formation. That is, the present invention is obtained by biaxially stretching a co-polyester comprising terephthalic acid, isophthalic acid, a divalent phenolic compound, and a glycol compound having 4 or less carbon atoms and having a melting point of 250°C or lower and 230°C or higher. According to the present invention, which is a copolymerized polyester film, it is easy to form an unstretched film at a relatively low temperature, the stretching process is stable, and there is a 7-layer effect, and the electrical insulation property is excellent even at high temperatures. You can get the film.

Furthermore, what should be emphasized in the present invention is that the electrically insulating temperature characteristics of the unstretched film made of the above-mentioned monopolyester are significantly improved by stretching. That is, as shown in FIG. 1, by stretching, the inflection point of the temperature characteristics of electrical resistivity is significantly shifted to high temperatures. This type of polymer is unlike any other polymer that we know of, and it is unclear what kind of structural changes occur during stretching and the theory behind this improvement in electrical insulation properties, but in any case, the above-mentioned The present invention was achieved by discovering that the temperature characteristics of electrical insulation can be significantly improved by stretching the copolymerized polyester.

(Means for solving problems) Terephthalic acid and isophthalic acid used in the present invention.

A copolymerized polyester consisting of a divalent phenolic compound and a glycol compound having 4 or less carbon atoms and having a melting point of 250°C or lower and 230°C or higher is a copolymerized polyester consisting of a polyarylate consisting of terephthalic acid, isophthalic acid and a divalent phenolic compound, terephthalic acid and carbon It is obtained by a transesterification method with a linear polyester consisting of a glycol compound of 4 or less.

During this transesterification, a catalyst such as sodium acetate is added to the resin mixture in an amount of 0.03 to 0.1 wt%.
Heat to 290°C and mix. The method for obtaining a copolymerized polyester is not limited to the method starting from two types of polymers as described above, but the above method can be implemented relatively easily.

In addition, 21 cities of phenolic (2.2-
(4,4°-dihydroxydiphenyl)propane is typical, but 4,4'-dihydroxydiphenylmethane, 1.1-(4,4'-dihydroxydiphenyl)
Examples include ethane, 1,1-(4,4'-dihydroxydiphenyl)butane, 4,4°-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, and the like. Examples of glycol compounds having 4 or less carbon atoms include ethylene glycol, propylene glycol, and tetramethylene glycol.

The biaxial stretching method may be either a sequential biaxial stretching method or a simultaneous biaxial stretching method. 1 7 g or more of the normal copolyester
lii at a stretching temperature of 5140°C or less? Stretched in two horizontal directions to an extent of 2.5 times or more and 4 times or less, respectively, and Tm or less
@ Heat treated at a temperature of about -40°C or higher.

(effect) In the present invention, terephthalic acid and isophthalic acid.

The melting point of the copolyester consisting of a divalent phenolic compound and a glycol compound having 4 or less carbon atoms is 250.
If the temperature exceeds .degree. C., the electrical insulation properties cannot be improved sufficiently by stretching. That is, the bending point in the temperature characteristic of electrical resistivity shown in FIG. 1 is not much different after stretching than that before stretching. On the other hand, if the melting point of the copolyester is lower than 230°C, the copolymer composition will be too large and the stretchability will be poor. As described above, the copolymerized polyester used in the present invention has a melting point of 250°C.
Below, only when the temperature is 230° C. or higher, unstretched film formation, stretching, and seven strokes can be carried out satisfactorily, and the obtained stretched film also has excellent electrical insulation properties.

In addition, the effect of improving electrical insulation properties can be achieved by uniaxial stretching, but biaxial stretching is better in order to improve the mechanical performance of the film and the accuracy of film thickness.
At 20°C/win, t is a fixed value and not a thermodynamic equilibrium value.

Examples 1 to 3 A copolymerized polyarylate was produced by an interfacial polymerization method from a methylene chloride solution of a mixed acid chloride having a molar ratio of terephthalic acid dichloride/isophthalic acid dichloride of 1:1 and an alkaline aqueous solution of bisphenol A. and polyethylene terephthalate were mixed with the composition shown in Table 1.

0.0ht% of sodium acid was added, and the mixture was mixed and stirred at 280° C. using a twin-screw extruder to produce transesterified chips. The melting point of each chip was determined by DSC.
Measurement was performed at a temperature increase rate of 0° C./win.

Next, the chips were extruded from a T-die at 280°C to create an unstretched film, and then Comparative Examples 1, 2. Example 1 is 9
Simultaneous biaxial stretching was carried out at 0°C, 105°C for Example 2, 1) 0°C for Example 3, and 1) 5°C for Comparative Example 3 at a stretching ratio MD3 x TD 3.3 times. Comparative Example 3 could not be stretched and was cut. Heat setting was performed at 220°C.

The interbody resistivity of the unstretched film and the stretched film was measured at different temperatures. The measurement method was in accordance with JIS C-2318. As a representative example of these data, the results of Example 2 are shown in Figure 1.The bending point of the unstretched film and the bending point of the stretched film are significantly different, and the bending point temperature can be significantly shifted to the higher temperature side by stretching. Recognize. The tendency of the bending point of the volume resistivity to move toward the high temperature side is the same in Example 1, and it is completely the same in Example 3 as well.

Comparative Example 1 is polyethylene terephthalate itself, and Comparative Example 2 is outside the upper limit of the claimed scope of the present invention and lacks a degree of copolymerization modification.

In both cases, the bending points of the unstretched film and the stretched film are almost the same. Comparative Example 3 falls outside the lower limit of the claimed scope of the present invention and has a high degree of copolymerization modification, making it extremely difficult to stretch the unstretched film.

Table 1 also shows the results of measuring the tensile strength and heat shrinkage rate of the coaxially stretched film obtained.

Table 1 (Effects) As described above, the ? Polyester is easily and economically relatively inexpensive, unstretched films can be formed smoothly at low temperatures, has good stretchability and does not break, has crystallinity and has a heat setting effect, and has low electroporation properties. Excellent films can be efficiently obtained even at high temperatures.

[Brief explanation of drawings]

FIG. 1 shows Example 2. In the temperature characteristics of body resistivity, the vertical axis shows the resistivity and the horizontal axis shows the temperature. Unstretched Filno, -Stretched Fil J1 By stretching, the bending point of the volume resistivity shifts to a high temperature. Patent applicant Unitika Co., Ltd. 19.1 Temρ. C

Claims (1)

[Claims] (1) Copolymer polyester obtained by biaxially stretching a copolymer polyester consisting of terephthalic acid, isophthalic acid, a divalent phenolic compound, and a glycol compound having 4 or less carbon atoms and having a melting point of 250°C or lower and 230°C or higher. film.