JPH0378725B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a novel electrically insulating material made of polyester. More specifically, the present invention relates to an electrically insulating material made of polyester having ultra-low moisture absorption and improved moisture absorption dimensional stability. [Prior art] Polyester, represented by polyethylene terephthalate, has traditionally been used as a material for electrical insulation purposes, such as films, sheets,
It is widely used in the form of tubes or fiber cloth (woven, knitted, etc.). Even for these uses,
In order to respond to the recent advances in device performance, there is an increasing demand for electrically insulating materials with superior material quality. One of the directions for the development of materials suitable for this purpose is the development of new materials, and the other is the modification and improvement of materials already used in this application field, such as polyester. . However, in the former direction, even if high performance is obtained in some physical properties, other properties are often inferior. [Problem to be solved by the invention] The present invention is a modification from the latter standpoint, and has recently been improved to the point where even polyesters, which are originally considered to have low hygroscopicity, can no longer ignore the slight hygroscopic behavior. The object of the present invention is to provide an ultra-low hygroscopic polyester electrical insulating material that can meet the performance requirements for electrical insulating materials. [Means for Solving the Problems] According to the research of the present inventors, in a substantially linear polyester in which 90 mol% or more of polymer repeating units are terephthalate units (i.e., polyethylene terephthalate-based polyester), Polyesters that have an intrinsic viscosity and whose terminal hydroxyl groups and terminal carboxyl groups are end-blocked and modified to below a certain level exhibit ultra-low hygroscopicity that has not been previously available with this type of polymer. It has been discovered that an electrical insulating material using this material exhibits excellent moisture absorption dimensional stability and electrical insulation properties that have not been previously available. The present invention is based on this new finding, and provides an electrical material made of polyester, which has an intrinsic viscosity (o
- a substantially linear polyester with a polyester of 0.4 or more (measured at 35°C in chlorophenol), in which the sum of terminal hydroxyl groups and carboxyl groups in the polyester is 90% or less of the total terminal group amount, and other hydrophilic groups It is characterized by the fact that it does not contain. The polyester electrical insulating material of the present invention is composed of a film or fiber cloth (woven or knitted fabric, non-woven fabric) of substantially linear polyester having ethylene terephthalate units as repeating units, that is, polyethylene terephthalate-based polyester. A portion (for example, 10 mol % or less) of the acid component and/or glycol component of polyethylene terephthalate may be replaced with an acid component other than terephthalic acid or a glycol component other than ethylene glycol. Examples of such third components include isophthalic acid, 1,5,2,6,2,7-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,
4'-diphenoxyenedicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, p-β-hydroxyethoxybenzoic acid, adipic acid, azelaic acid,
Sebacic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, ε-oxycaproic acid, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentylene glycol, 1,1-
Examples include cyclohexanedimethanol, 1,4-cyclohexanedimethanol, etc., and functional derivatives thereof. These may be used alone or in combination of two or more. The polyester may also contain one or more polyfunctional compounds such as pentaerythritol, trimethylolpropane, trimellitic acid, trimesic acid and functional derivatives thereof and/or o-benzoylbenzoic acid, to the extent that the polyester is substantially linear. It may also be one in which a small amount of one or more monofunctional compounds such as methoxypolyethylene glycol and functional derivatives thereof are copolymerized. The polyester may contain additives such as stabilizers (for example, stabilizers against heat, ultraviolet rays, and oxygen), lubricants, pigments, fillers, mold release agents, antistatic agents, and other additives. It is preferable to use additives with high stability. In the present invention, the above-mentioned polyester is polymerized, and the activation is performed at any stage until the end of producing a support base film or sheet-like material, or a fiber/woven or knitted fabric by melt-casting or filament-forming and stretching by a conventional method. At least a portion of the terminal hydroxyl group and terminal carboxyl group, which are terminal groups, are converted to other terminal groups so that the total amount of these terminal groups is 90% or less of the total amount of terminal groups, preferably 60% or less.
% or less, more preferably 40% or less, most preferably 20% or less. As a result, surprisingly, the hygroscopicity of the polyester can be extremely reduced, and as a result, the deterioration in insulation properties and dimensional changes due to moisture absorption of the electrically insulating material can be significantly reduced. The means for converting this terminal group is not limited, but a suitable method is, for example, when the degree of polymerization has increased to a certain degree before the polymerization is completed, diphenyl carbonate, tetraphenyl There is a method in which an appropriate amount of an end-blocking agent such as orthocarbonate, diphenyl terephthalate, diphenyl oxalate, or cyclohexenyl acetate is added and reacted with the active end group. In addition, the terminal hydroxyl group is reacted with an acid anhydride in advance to convert it into a carboxyl group, and then treated with diazomethane in the form of a molded product or an intermediate (for example, a polymer powder) to reduce the active terminal group. However, since this method slows down the reaction, caution is required in practical use. Furthermore, in the present invention, it is important that the polyester does not contain any other hydrophilic groups. Such hydrophilic groups include hydrophilic groups introduced by copolymerizing polyoxyethylene glycol and 5-sulfoisophthalic acid components, and hydrophilic groups introduced as a result of the end-capping process (for example, urethane, amide groups, etc.). (such groups), but it is not preferable to introduce these groups. The polyester constituting the electrically insulating material of the present invention was heated at 35°C (concentration) in orthochlorophenol.
Intrinsic viscosity measured under the conditions of 1.2g/100c.c.) is 0.4
It is necessary that it is above. Polyester having an intrinsic viscosity below this range is difficult to mold into films, fibers, etc., and is not practical. In the present invention, forming a film or the like into a molded product can be carried out by a conventionally known method. For example, when producing a film, a polymer is melt-extruded using an extruder or the like, rapidly cooled on a casting drum, and this substantially unstretched film is stretched in at least one axial direction in one or more stages, as necessary. Depending on the situation, apply tension heat treatment or heat relaxation treatment. Recent electrical insulating materials are increasingly required to have greater Young's modulus and dimensional stability, but it is now possible to meet the Young's modulus requirements through multi-stage high-magnification stretching after examining various stretching methods. . Even in the present invention, conventionally known manufacturing means for obtaining a high Young's modulus film can be applied. In the case of a film-like molded product according to the present invention, the thickness can be selected as necessary, but it is usually 1 to 500 μm.
m, preferably 3 to 350 μm, particularly preferably 10
~300μm. Further, the fineness of the single fiber in the case of forming a fibrous material is usually about 0.1 to 10 deniers, preferably about 1 to 7 deniers. Furthermore, instead of woven or knitted fabrics, it is also possible to use a nonwoven fabric by a conventionally known method. [Effects of the Invention] The polyester electrical insulating material of the present invention as described above exhibits very little insulation deterioration or dimensional change due to moisture absorption (water absorption), and can be widely used in various electrical insulation applications. [Example] Next, the present invention will be further explained with reference to Examples.
The present invention is not limited thereby.
In the examples, "parts" simply represent parts by weight,
Intrinsic viscosity is 1.2 at 35℃ in orthochlorophenol.
It was measured as a solution with a concentration of g/100 c.c. Also,
For the measurement of carboxyl groups, the method of A. Conix (Makromol, Chem, 26 226 (1958)) was adopted. The hydroxyl groups were converted into carboxyl groups by reacting the polymer with succinic anhydride in α-methylnaphthalene, and measured by the method described above, and the difference from the original carboxyl group value was determined as the hydroxyl group. In addition, to measure dimensional changes due to water absorption, dry the sample (sample length, approximately 20 cm) in a dryer at 150°C for 16 hours.
Measure the length of the taken sample in the longitudinal direction (machine direction), leave it in water at 25°C for 24 hours, take it out and measure the length again, and calculate the difference in length as the length of the dried sample. Divide by and express as a percentage,
It was expressed as water absorption expansion coefficient. On the other hand, the water absorption rate was calculated based on the weight increase at that time. Examples 1 to 3, Comparative Examples 1 to 2 In the examples described below, the active end groups of polyethylene terephthalate were blocked with diphenyl carbonate, and its high performance as an electrically insulating material was demonstrated. Of course, the present invention is not limited to this method. 194 parts of dimethyl terephthalate, 130 parts of ethylene glycol, 0.095 parts of manganese acetate tetrahydrate, and 0.080 parts of antimony trioxide were placed in a reactor equipped with a rectification column, and gradually heated and stirred under a nitrogen atmosphere. As a result of the transesterification reaction, methanol produced was taken out of the system via a rectification column, and when the collected amount reached a transesterification rate of 98.5%, the temperature inside the system was 235°C. The rectification column was removed, a distillation condenser was installed, and 0.0395 parts of phosphoric acid as a stabilizer and 0.03% by weight of kaolin as a lubricant were added to the system. System temperature to 280℃
After the reaction was continued for 30 minutes, the pressure inside the system was gradually reduced to a high vacuum of 0.5 mmHg or less over about 40 minutes. The reaction was continued for another 90 minutes. The intrinsic viscosity obtained from the sample at this time was 0.67. At this point, return the system to normal pressure with nitrogen,
7.5 parts of diphenyl carbonate (3.5 mol % based on the acid component) was added, stirred for 5 minutes, and again brought to a high vacuum of 0.5 mmHg or less while being careful to prevent foaming, stirred for 15 minutes, and the polymer was taken out. The intrinsic viscosity of this polymer was 0.61. This polymer was chipped and dried in a hot air dryer at 150°C for 7 hours. This polymer was immediately extruded into an extruder type film forming machine at a T-die temperature of 280° C., and taken from the inside onto a water-cooled casting drum. Next, this semi-stretched film was sequentially biaxially stretched. The stretching ratio is 3.8 at 80℃ in the longitudinal direction.
It was multiplied by 3.5 times at 110°C in the width direction. This at 200℃
It was heat treated for a fixed length. The resulting film had a thickness of 25 μm and good transparency, and an intrinsic viscosity of 0.54. The active end groups of this film were measured and found to be 21 equivalents/ton of hydroxyl groups and 15 equivalents/ton of carboxyl groups. Similarly, various end-blocking samples were prepared, and changes in dielectric breakdown voltage and dimensional changes due to water absorption were measured in comparison with ordinary polyester films not treated with diphenyl carbonate. The results are shown in Table 1 below.

[Table] *Polyimide film is shown for reference.

Claims (1)

[Claims] 1. In an electrical material made of polyester, the polyester is a substantially linear polyester having an intrinsic viscosity (measured in o-chlorophenol at 35°C) of 0.4 or more, in which the polymer repeating units are substantially ethylene terephthalate units, and An electrically insulating material characterized in that the total amount of terminal hydroxyl groups and carboxyl groups in the polyester is 90% or less of the total amount of terminal groups and does not contain other hydrophilic groups.