JPH0757579A - Manufacture of heat-resistant insulating sheet - Google Patents

Abstract

PURPOSE:To manufacture a meta-aromatic polyamide sheet for heat-resistant insulation having a sharply improved deterioration prevention property in the high-temperature environment. CONSTITUTION:When the raw material slurry containing fibers and fibrils of meta-aromatic polyamide is formed into a sheet, the grain size of an oxidation/deterioration inhibitor to be added into it is set to the range of 3mum or below, a low-molecular weight cationic agent and an anionic organic polymer are added into the raw material slurry containing the oxidation/deterioration inhibitor, and its zeta-potential is controlled within a range from 0 to +20mV.

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 prevention property or an improved deterioration prevention property and is inexpensive.

[0002]

2. Description of the Related Art A meta-aromatic polyamide sheet is widely known as an insulating material for a transformer or a high-voltage cable. For example, "Nomex" manufactured by DuPont, USA is commercially available. This polyamide sheet has excellent heat resistance,
Has electrical insulation. However, when this polyamide sheet is used as a heat resistant insulation sheet, its paper quality 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 metal compounds are generally expensive, and therefore, the production cost can be increased by adding or coating in an amount sufficient to exert the intended deterioration preventing effect. It has the disadvantage of increasing.

Therefore, an object of the present invention is to improve the deterioration prevention property as compared with the conventional polyamide sheet for heat-insulating insulation while the addition amount of the oxidative deterioration inhibitor is the same as or smaller than that of the conventional one, or deteriorated. It is an object of the present invention to provide a method for producing a polyamide sheet for heat resistant insulation, which has improved preventive properties and is inexpensive.

[0006]

In view of the present situation, the inventors of the present invention have conducted earnest research on improvement of deterioration preventive property of a polyamide sheet, and as a result, the particle size of the antioxidant additive to be added to the sheet has been conventionally used. It was found that the contact area of the oxidative deterioration inhibitor against chlorine ions, which induces the deterioration of the sheet, should be increased by making the size smaller than that of the existing one. Since the yield of the oxidative deterioration inhibitor tends to be low,
In order to increase the yield of the antioxidant, a low molecular weight cationizing agent and an anionic organic polymer should be added so that the zeta potential of the raw material slurry should be 0 to +20 mV. By adding an oxidative deterioration inhibitor of 3 μm or less to the raw material slurry and adding a predetermined amount of a low molecular weight cationizing agent and an anionic organic polymer to make paper, the deterioration preventive properties of conventional polyamide sheets are greatly exceeded. They have found that they can manufacture products and have completed the present invention.

That is, in the method for producing a heat-resistant insulating sheet according to the present invention, when a raw material slurry containing meta-aromatic polyamide fibers and fibrids as main raw materials and further containing an antioxidant is used to make a paper, The particle size of the antioxidant is controlled to 3 μm or less, and the zeta potential of the raw material slurry obtained by adding the low molecular weight cationizing agent and the anionic organic polymer to the raw material slurry is controlled to 0 to +20 mV. It is a feature.

[0008]

It is said that the cause of the deterioration of the heat resistant insulating sheet in a high temperature environment is chlorine ions mixed in the aromatic polyamide during the production process of the aromatic polyamide as a raw material. Pure aromatic polyamide is generally stable even when exposed to a high temperature environment up to 300 ° C., but when trace amounts of chlorine ions are mixed, air containing water vapor and contact conditions with metals. When exposed to a high temperature environment, the aromatic polyamide is oxidized and deteriorates. 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 which is the raw material of the heat resistant insulation sheet, an oxidative deterioration inhibitor for preventing the deterioration reaction of the heat resistant insulation sheet is used as a heat resistant material. It is considered that the addition in the manufacturing process of the insulating sheet is indispensable 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 under the above-mentioned conditions and are a direct cause of deterioration, are present on the surface of the oxidative deterioration preventing agent. Focusing on the manifestation by reaction, increasing the surface area per unit 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. 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,
It is possible to select from carbonates and the like that have been conventionally used as antioxidants for oxidative deterioration of polyamide sheets for heat resistant insulation. However, the particle size of these antioxidants conventionally added to the raw material slurry was about 11 to 20 μm, but in the present invention, the particle size is made smaller than this and the particle size is controlled to 3 μm or less. The oxidative deterioration inhibitor is added to the raw material slurry. When the particle size is larger than 3 μm, the coating surface area per unit weight of the antioxidant is not sufficient, and it is difficult to achieve the desired effect of preventing deterioration.

On the other hand, the oxidative deterioration inhibitor having a particle size of less than 3 μm lowers the yield of the oxidative deterioration inhibitor during sheet making, and therefore the oxidative deterioration inhibitor necessary for containing a predetermined amount of the oxidative deterioration inhibitor in the sheet. The amount of deterioration inhibitor used increases. In the present invention, a low molecular weight cationizing agent and an anionic organic polymer are added to the raw material slurry, and the zeta potential thereof is controlled to 0 to +20 mV, whereby the reduction in the yield of the antioxidant can be prevented. . It is considered that this is because the fibrids, the fibers, the anionic polymer, and the heat deterioration inhibitor are electrically attached by the low molecular weight cationizing agent.

The zeta potential is also called an electrokinetic potential and is a potential that effectively acts on the electrokinetic phenomenon in the potential difference at the interface between a solid and a liquid. When a relative motion occurs between a liquid and a solid, the fixed layer moves together with the solid.Therefore, it is the potential difference between the fixed layer and the liquid that controls the electrokinetic phenomenon at this time, which is called the zeta potential. . The zeta potential of the raw material slurry (before adding the low molecular weight cationizing agent and the anionic organic polymer) used in the present invention is generally -10.
mV or less.

If the zeta potential of the raw material slurry containing the oxidative deterioration inhibitor is lower than 0 mV, the oxidative deterioration inhibitor cannot be attached to the polyamide fibers or / and fibrids,
This is not preferable because the yield of the antioxidant is reduced during sheet making, and the amount of the antioxidant required to contain a predetermined amount of the antioxidant in the sheet is increased, resulting in an increase in manufacturing cost. Further, if the zeta potential of the raw material slurry containing the antioxidant is higher than +20 mV, the drainage during the papermaking is too fast, and the sheet formation is too fast when it is converted into a sheet by a papermaking machine, so that a uniform texture can be obtained. It becomes difficult, and the dielectric breakdown voltage of the sheet is lowered, which is not preferable.

As the low molecular weight cationizing agent used in the present invention, polyethyleneimine having a molecular weight of 300,000 or less,
Polyethyleneimine-epichlorohydrin condensate, aminopolyamide epichlorohydrin resin, polyvinyl pyridine, styrene-dimethylaminoethyl methacrylate copolymer, cationic polyurethane resin, urea formaldehyde resin, melamine formaldehyde resin, dimethylamine epichlorohydrin resin and derivatives thereof,
Cationized starch or the like, which may be used alone, or 2
You may use together more than one kind.

The anionic organic polymer used in the present invention is an anionic polyacrylamide, an acrylic resin, a styrene resin or the like and has a molecular weight of 2
It is preferably, 000,000 or less and has a molecular weight of 300,000 or more and 10
It is more preferably 100,000 or less. If the molecular weight is too small, the yield of the oxidative deterioration inhibitor decreases at the time of sheet making, and the amount of the oxidative deterioration inhibitor necessary for containing a predetermined amount of the oxidative deterioration inhibitor in the sheet increases. On the other hand, if the molecular weight is too large, the raw material slurry agglomerates to deteriorate the formation of the sheet, which lowers the dielectric breakdown voltage of the sheet, which is not preferable. This anionic organic polymer may be used alone or in combination of two or more kinds.

Generally, the low molecular weight cationizing agent and the anionic organic polymer are mixed in a weight ratio of 1: 1 to 10: 1. The amount of this mixture used depends on its composition,
The amount used is sufficient to control the zeta potential of the raw material slurry to 0 to +20 mV, for example, 0.001 to 0.1 g with respect to 1 g of the raw material (weight of solid content).

The addition ratio of the oxidative deterioration inhibitor used in the present invention to the polyamide raw material is generally about 1 to 10% with respect to the total weight of the polyamide raw material. Even if the addition ratio of the antioxidant is lower than that of the polyamide paper for use, the deterioration preventing property in a high temperature environment can be maintained at the same level as or higher than the conventional level.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In Examples and Comparative Examples, “%” and “part” are
Represents "wt%" and "parts by weight", respectively.

Example 1 A solution of 100 parts of m-phenylenediamine in 1000 parts of N-methylpyrrolidone was cooled to 0 ° C., 200 parts of isophthalic acid chloride was added thereto, and the mixture was reacted for 1 hour. It was After completion of the reaction, 74 parts of calcium hydroxide was added thereto to neutralize the hydrochloric acid generated by the polymerization to obtain a transparent and viscous liquid A. Liquid A is poly (m
17% by weight of (phenylene isophthalamide). 25 g of the liquid A was introduced into 300 g of glycerin in a homomixer which was stirred at a high speed, filtered and washed with water to produce fibrids. On the other hand, the liquid A is extruded into the glycerin through the spinneret, coagulated in the glycerin, and then wet-heat stretched in hot water to produce a fiber having a fineness of 1.5 decitex, which is cut to a length of 5 mm to form a short fiber. did.

On the other hand, polycarboxylic acid salt (Aron T-4
0, bismuth trioxide (average particle size 2.7 μm, manufactured by Sumitomo Metal Mining Co., Ltd.) in 80 parts of a 1% aqueous solution of
The slurry added with 1 part was treated with a sand grinder for 60 minutes under normal conditions to prepare a crushed product (A) of bismuth trioxide having an average particle size of 0.2 μm.

5000 parts of 1% slurry of aramid fibrids and 50% of 1% slurry of aramid short fibers.
00 parts were disintegrated using a disintegrator and then mixed and stirred to prepare a raw material slurry, in which 100 parts of a 0.1% aqueous solution of polyacrylamide (trademark: Polystron 191, manufactured by Arakawa Chemical Industries), polyamide 200 parts of a 0.1% aqueous solution of epihydrochlorin (trademark: WS-570, manufactured by Japan PMC) and 30 parts of a 10% slurry of the fine powder of bismuth trioxide (A) were added, and a basis weight was measured with a handmade paper machine. A 40 g / m ² polyamide sheet was prepared.

On this sheet, a temperature of 280 ° C. and a linear pressure of 400
A heat calendering treatment was performed under the condition of kg / cm to produce a polyamide sheet for heat resistant insulation.

Example 2 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, 100 parts of a 0.1% aqueous solution of polyacrylamide, 400 parts of a 0.1% aqueous solution of polyamide epihydrochlorin, and 30 parts of a 10% slurry of bismuth trioxide (A) were added to the raw material slurry.

Example 3 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, the bismuth trioxide added to the raw material slurry was not subjected to the sand grinder treatment, and the average particle size was 2.7 μm.
m bismuth trioxide was used.

Comparative Example 1 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, polyacrylamide and polyamide epihydrochlorin were not added.

Comparative Example 2 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, the amount of a 0.1% aqueous solution of polyacrylamide was 200 parts, and the amount of a 0.1% aqueous solution of polyamide epihydrochlorin was 100 parts.

Comparative Example 3 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, 0.1 of polyamide epihydrochlorin
% Aqueous solution to 600 parts.

Comparative Example 4 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, polyacrylamide was not added.

Comparative Example 5 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, the amount of pulverized bismuth trioxide added to the raw material slurry was 20 parts, and polyamide epihydrochlorin was not added.

Comparative Example 6 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, the bismuth trioxide added to the raw material slurry was not subjected to the sand grinder treatment and had an average particle size of 4.2 μm (manufactured by Sumitomo Metal Mining Co., Ltd.).

Comparative Example 7 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, the bismuth trioxide added to the raw material slurry was not subjected to sand grinder treatment and had an average particle size of 4.2 μm, and 10 parts of this was used, and polyamide epihydrochlorin added to the raw material slurry was used. The amount of 0.1% aqueous solution of was set to 300 parts.

Comparative Example 8 A heat-resistant insulating polyamide sheet was prepared in the same manner as in Example 1. However, bismuth trioxide, polyacrylamide, and polyamide epihydrochlorin were not added.

The particle size of bismuth trioxide used in Test Examples 1 to 3 and Comparative Examples 1 to 8 and the mixed slurry of the cationic organic polymer or / and the anionic organic polymer, the raw material slurry, and the oxidation deterioration inhibitor were used. The zeta potential and the deterioration evaluation of the sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 8 under a high temperature environment were performed as follows.

The average particle size of bismuth trioxide was measured using a Shimadzu laser diffraction particle size distribution analyzer SALD-1000 (manufactured by Shimadzu Corporation), and the cumulative volume% of particle size was 5%.
The particle size at 0% was taken as the average particle size.

The zeta potential is measured by ZETASIZER.
II (manufactured by MALVERN) was used.

The deterioration evaluation was performed by the following method. That is, a rectangular copper wire with a thickness of 1.5 mm x 8 mm and a length of 150 mm is 50
A mm × 100 mm polyamide sheet for heat resistant insulation was wound, and a 50 mm × 80 mm aluminum foil (thickness 0.02 mm) was further wound thereon. This sample is 28
It was put in a constant temperature bath at 0 ° C., taken out after 4 weeks, a voltage was applied to the copper wire and the aluminum foil, and the dielectric breakdown voltage was measured according to JIS-C-2111. The higher the dielectric breakdown voltage, the better the deterioration prevention property in a high temperature environment.

The manufacturing cost is evaluated in four levels,
Very excellent ones were classified as 1, excellent ones as 2, ordinary ones as 3, and bad ones as 4. Table 1 shows the above evaluation results.

[0039]

[Table 1]

[Note of Table 1] Raw material slurry: 100 parts (solid content) Cationic chemical: Polyamide epihydrochlorin Anionic chemical: Polyacrylamide Zeta potential: Zeta potential of mixed slurry of chemicals, raw material slurry and oxidative deterioration inhibitor Breakdown voltage (Before treatment): Breakdown voltage before exposing sample to high temperature environment Breakdown voltage (After treatment): Breakdown voltage after exposing sample to high temperature environment

As is clear from Table 1, the heat-resistant insulating polyamide sheets obtained in Examples 1 to 3 were excellent in deterioration preventing property in a high temperature environment and were well balanced with the manufacturing cost.

[0042]

EFFECTS OF THE INVENTION The method for producing a polyamide sheet for heat-resistant insulation of the present invention is not only low in production cost, but also the obtained product has good deterioration-preventing property in a high temperature environment, so that it has excellent heat resistance for a long time. And electrical insulation. That is, according to the method of the present invention, it is possible to provide a polyamide sheet for heat-resistant insulation, which has high-quality heat-resistant insulation and is inexpensive.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01B 3/30 Q 9059-5G

Claims (1)

[Claims] 1. When making paper using a raw material slurry containing meta-aromatic polyamide fibers and fibrids as main raw materials and further containing an antioxidant, the particle size of the antioxidant is 3 μm or less. And a low molecular cationizing agent and an anionic organic polymer are added to the raw material slurry to control the zeta potential of the resulting raw material slurry to 0 to +20 mV.