JPH0668711A - Manufacture of heat-resistant insulating sheet - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for producing a meta-aromatic polyamide sheet for heat-resistant insulation, which is excellent in thermal deterioration prevention property, low in cost, and improved in electric insulation property. [Structure] In a method for producing a heat-resistant insulating sheet, which comprises using meta-aromatic polyamide fibers and fibrids as raw materials and adding an oxidation deterioration inhibitor to a raw material slurry to prevent oxidation deterioration added to the raw material slurry The particle size of the agent is 1 to 10 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heat resistant insulation sheet. More specifically, the present invention relates to a method for producing a polyamide sheet for heat-resistant insulation, which has a significantly improved deterioration-preventing property, or has an improved deterioration-preventing property and a low manufacturing cost.

[0002]

2. Description of the Related Art As an insulating material for a transformer or a high-voltage cable, a polyamide sheet made from fibers of meta-aromatic polyamide and fibrils is widely known.
For example, "Nomex" manufactured by DuPont, USA and the like are commercially available. This polyamide sheet has excellent heat resistance and electric insulation. However, when this polyamide sheet is used as a heat resistant insulation sheet, the quality of the sheet tends to deteriorate due to contact with a metal in a high temperature environment.

In order to prevent this deterioration, conventionally, oxidation preventive agents such as oxides, hydroxides, nitrates, carbonates of manganese, bismuth, zinc, aluminum, magnesium and the like are added to the sheet or coated on the sheet. It is generally done.

[0004]

However, the above-mentioned oxidative deterioration inhibitor is generally expensive, and the production cost is inevitably increased by adding or coating an amount for exhibiting the intended deterioration preventing effect. Has been done.

Therefore, an object of the present invention is to improve the deterioration prevention property as compared with the conventional heat-resistant insulating polyamide sheet while the addition amount of the oxidation deterioration preventing agent is the same as the conventional amount, or the deterioration prevention property is improved. An object of the present invention is to provide a method for manufacturing a polyamide sheet for heat-resistant insulation, which is improved and has a low manufacturing cost.

[0006]

In view of the present situation, the inventors of the present invention have earnestly studied to improve the deterioration preventive property of the heat-resistant insulating polyamide sheet. As a result, in order to improve the deterioration prevention property of the polyamide sheet, the particle size of the oxidative deterioration inhibitor added to the sheet is made smaller than that conventionally used, and chlorine ion and oxidative deterioration prevention which induce the deterioration of the sheet are prevented. It was concluded that the contact area with the agent should be increased, and the deterioration preventive property of the conventional polyamide sheet was obtained by adding an oxidative deterioration inhibitor having a particle size of 1 to 10 μm to the raw material slurry for papermaking. The present invention has been completed by finding that it is possible to manufacture a product significantly exceeding the above.

That is, the present invention provides a method for producing a heat-resistant insulating sheet, which comprises using meta-aromatic polyamide fibers and fibrids as raw materials and adding an oxidative deterioration inhibitor to the raw material slurry to produce a paper. It is characterized in that the particle size of the added antioxidant is 1 to 10 μm.

The cause of deterioration of the heat-resistant insulating sheet in a high temperature environment is considered to be chlorine ions mixed in the aromatic polyamide in the process of producing the aromatic polyamide as a raw material. Pure aromatic polyamide is, for example, 300
It is generally stable even when exposed to a high temperature environment up to ℃, but when a small amount of chlorine ions are mixed, it is exposed to a high temperature environment under the conditions of contact with air containing steam and metal. However, aromatic polyamide is oxidatively deteriorated. The above-mentioned state is an environment that can be easily assumed in a semi-closed electrical system which is often seen as a usage environment of the heat-resistant insulating sheet. Since it is technically very difficult to eradicate chlorine ions mixed in during the production process of the aromatic polyamide that is the raw material of the heat-resistant insulating sheet, an oxidation deterioration inhibitor that prevents the deterioration reaction of the heat-resistant insulating sheet is used. It is considered that the addition in the manufacturing process of is essential for maintaining its quality.

The inventors of the present invention have found that the deterioration preventing effect of the oxidative deterioration preventive agent is such that the chlorine ions and the oxidative deterioration preventing agent, which are generated directly in the environment and cause the deterioration, are present on the surface of the oxidative deterioration preventing agent. Focusing on the manifestation by reaction, increasing the surface area per weight of the antioxidant, that is, the area of the antioxidant capable of reacting with chlorine ions, by reducing the particle size of the antioxidant used. I found that I can do it. As a result, the amount of oxidative deterioration inhibitor added is the same as the conventional product, but the deterioration prevention property can be significantly improved compared to the conventional polyamide sheet for heat-resistant insulation, or the amount of oxidative deterioration inhibitor added is higher than that of the conventional product. Even if the manufacturing cost is reduced by using a small amount, the deterioration prevention property can be improved as compared with the conventional product.

As the oxidative deterioration inhibitor used in the present invention, oxides, hydroxides, nitrates of manganese, bismuth, zinc, aluminum, magnesium, nickel and the like,
What was conventionally used as an antioxidant of the polyamide sheet for heat resistant insulation, such as carbonate, can be used similarly. However, the particle size of these oxidative deterioration inhibitors which have been conventionally added to the raw material slurry is about 11 to 20 μm, but in the present invention, the particle size is made smaller than this and oxidation of the particle size of 1 to 10 μm is performed. A deterioration inhibitor is added to the raw material slurry. When the particle size is smaller than 1 μm, the yield of the antioxidant is reduced at the time of sheet making, and the amount of the antioxidant used for containing a predetermined amount of the antioxidant in the sheet is increased, which is preferable. Absent. On the other hand, if the particle size is larger than 10 μm, the surface area per weight of the antioxidant is not sufficient, and it is difficult to achieve the desired effect of preventing deterioration.

The addition ratio of the antioxidant to the aromatic polyamide fiber and fibrite is generally about 1 to 10% based on the total weight of the polyamide raw material. However, particularly in the present invention, even if the addition rate of the antioxidant is lower than that of the conventional heat-resistant insulating polyamide sheet, the thermal deterioration-preventing property maintains the conventional level and the degree of identification or higher. It is possible.

[0012]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following examples,% means% by weight. In the examples, the weight loss on heating,
The dielectric breakdown strength and tensile strength were evaluated by the following methods.

1) Heat loss: The decrease in the total weight of the sheet before and after the thermal deterioration promoting treatment was expressed as a percentage based on the weight of the sheet before the treatment. That is,

2) Dielectric breakdown voltage: JIS-C-2111
Was measured according to. 3) Tensile strength: Measured according to JIS-P-8113.

Example 1 A raw material slurry used for manufacturing a polyamide sheet for heat resistant insulation was prepared in the following manner. First, using poly (metaphenylene isophthalamide) fibrids (manufactured by Unitika Ltd.), disaggregation is performed using a disintegrator,
A fibrid slurry having a concentration of 1.0% was prepared. Next, using poly (metaphenylene isophthalamide) short fibers (manufactured by Unitika Ltd.), a stirrer was used to obtain a concentration of 1.0.
% Fiber slurry was made.

A raw material slurry obtained by mixing and stirring the above fiber slurry and fibrid slurry at a compounding ratio of 40% fiber and 60% fibrid was added to bismuth trioxide (Bi ₂ O ₃ : purity 99.7%). , Average particle size 4.2 μm,
Sumitomo Metal Mining Co., Ltd.) was added in an amount of 1.0% based on the total weight of the polyamide raw material. Using this slurry, length 25 cm
Basis weight 40.0 g /
A polyamide sheet having m ² and a density of 0.33 g / cm ³ was handmade. After that, temperature 280 ℃, linear pressure 400kg
Thermal calendering was performed under the condition of / cm, and the dielectric breakdown voltage and the tensile strength of the obtained sheet were measured.

Further, the heat deterioration accelerating treatment test of the obtained sheet was conducted in the following manner. Test 1: The sheet was hung in a constant temperature bath at 280 ° C., and after 4 weeks, the sheet was taken out and the heat loss, dielectric breakdown voltage and tensile strength of the sheet were measured. Test 2: The sheet was cut into a size of 5 cm × 10 cm. 15 cm of rectangular copper wire with a thickness of 1.5 mm x 8 mm
The sheet was cut to a length of, and the cut sheet was wound around this rectangular copper wire as an axis. Then, an aluminum foil (thickness 0.02 mm) cut into a size of 5 cm × 8 cm was wound around a copper wire wound around this sheet as an axis. Put the sample prepared as above into a constant temperature bath at 280 ° C and
After a week, it was taken out, a voltage was applied to the copper wire and the aluminum foil, and the dielectric breakdown voltage was measured.

Example 2 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Example 1 was added in an amount of 3.0% with respect to the total weight of the polyamide raw material. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Example 3 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Example 1 was added in an amount of 8.0% based on the total weight of the polyamide raw material, and heat-calendered. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 1 The bismuth trioxide used in Example 1 was changed to bismuth trioxide having a large particle size (Bi ₂ O ₃ : purity 98.9%, average particle size 11.9 μm, rare metal company). A polyamide sheet was prepared in the same manner as in Example 1 except that 1.0% was added to the total weight of the polyamide raw material, and the heat treatment was performed. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 2 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Comparative Example 1 was added in an amount of 3.0% with respect to the total weight of the polyamide raw material, and the sheet was heat calendered. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 3 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Comparative Example 1 was added in an amount of 8.0% based on the total weight of the polyamide raw material, and the sheet was heat calendered. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 4 The bismuth trioxide used in Example 1 was replaced with bismuth trioxide having a large particle size (Bi ₂ O ₃ : purity 99.0%, average particle size 22.9 μm, rare metal company). A polyamide sheet was prepared in the same manner as in Example 1 except that 1.0% was added to the total weight of the polyamide raw material, and the heat treatment was performed. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 5 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Comparative Example 4 was added in an amount of 3.0% based on the total weight of the polyamide raw material, and the sheet was heat calendered. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 6 A polyamide sheet was prepared in the same manner as in Example 1 except that the bismuth trioxide used in Comparative Example 4 was added in an amount of 8.0% based on the total weight of the polyamide raw material, and the sheet was heat calendered. went. About the obtained sheet, Example 1
A heat deterioration accelerating treatment test was conducted in the same manner as described above.

Comparative Example 7 After preparing a raw material slurry by the method as in Example 1, a polyamide sheet was handmade by the method as in Example 1 without adding bismuth trioxide for comparison. The sheet thus obtained was subjected to a heat calendar treatment and then subjected to a heat deterioration accelerating treatment test in the same manner as described in Example 1.

Table 1 shows the measurement results of the sheet physical properties in the above Examples and Comparative Examples.

[0028]

As is apparent from Table 1, the heat-resistant insulating polyamide sheet of the present invention obtained in Example 1 was used in Comparative Example 1.
In comparison with Nos. 4 and 4, the thermal deterioration prevention property is excellent. Similarly,
The heat-resistant insulating polyamide sheet of the present invention obtained in Example 2 is compared with Comparative Examples 2 and 5, and the heat-resistant insulating polyamide sheet of the present invention obtained in Example 3 is Comparative Example 3 and Comparative Compared to Example 6, all of them have excellent thermal deterioration prevention properties.

Further, the heat-resistant insulating polyamide sheet of the present invention obtained in Example 1 is compared with Comparative Example 2, and the heat-resistant insulating polyamide sheet of the present invention obtained in Example 2 is shown in Comparative Example 3. In comparison, all of them have the same or superior deterioration preventive property despite the small addition rate of the antioxidant.

[0031]

According to the above-described method of the present invention, the particle size of the oxidative deterioration inhibitor, which has been conventionally used internally in the production of a polyamide sheet for heat-resistant insulation, is 1 to 10 μm, which is smaller than that of the conventional one. By setting the above, it is possible to obtain a heat-resistant insulating polyamide sheet having excellent heat deterioration preventing properties.

Further, the heat-resistant insulating polyamide sheet obtained by the method of the present invention is more resistant to thermal deterioration than conventional polyamide sheets in which the addition ratio of the oxidation deterioration inhibitor is high within the range of 3 times or less compared to this polyamide sheet. It is possible to improve the sex. Therefore, it is possible to manufacture a heat-resistant insulating polyamide sheet which is lower in manufacturing cost than the conventional polyamide sheet and has improved electric insulation.

Claims (1)

[Claims] 1. A method for producing a heat-resistant insulating sheet, which comprises using a meta-aromatic polyamide fiber and fibrid as a raw material and adding an oxidative deterioration inhibitor to the raw material slurry to produce paper, and then adding the oxidation to the raw material slurry. A method for producing a heat-resistant insulating sheet, characterized in that the particle size of the deterioration inhibitor is 1 to 10 μm.