JPS6313288B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention generally relates to an oil-immersed insulating board used in electromagnetic induction devices such as transformers and reactors, and specifically relates to a method for producing a laminated insulating board with excellent heat resistance and suitable for sail use. be. In recent years, transformers have been required to be smaller, lighter, and flame retardant, and for this reason, heat-resistant insulating materials have been required. Since aromatic polyamide has high heat resistance and excellent electrical properties, it has been recognized as the most suitable material for these uses, and sheets made of the above polymers have begun to be used. All of the above-mentioned sheets are made by mixing short fibers made of aromatic polyamide and pulp-like particles made of aromatic polyamide having a shape similar to wood pulp, and made using a normal paper machine, and have a density of about It is limited to a low value of 0.3 g/cm ³ and a thickness of 0.5 mm or less, and in order to use it as a structural insulation material for transformers, it is necessary to laminate them into a board shape. Lamination methods include a method using an adhesive and a method of heat-sealing sheets at high temperature and high pressure. The former is a method in which sheets are coated with a heat-resistant adhesive, laminated, and heated and pressed, and it has been proposed that the adhesive be coated or impregnated with a solvent that dissolves aromatic polyamide. It requires environmental measures due to the toxicity of the solvent used, and has disadvantages in that a board with a uniform internal structure cannot be obtained and its strength and toxicity are unsatisfactory. In addition, the thermal properties of laminated boards are controlled by the adhesive used, and no matter how heat-resistant the adhesive is, it is inferior to aromatic polymers, and it thermally decomposes at high temperatures, producing gas and causing insulating oil. It has the disadvantage that corona discharge tends to occur as a result in the impregnated system. As an example of the latter lamination method using heat fusion, for example, sheets made of aromatic polyamide are laminated at a temperature of 280°C, which is around the softening point of aromatic polyamide.
It is necessary to carry out thermocompression bonding at high temperatures and pressures such as ~300°C and 70~200 kg/cm ² , which has the disadvantage of increasing density and significantly impairing oil immersion. As a lamination method that does not use other adhesives, wet paper making is performed by wet paper making from an aqueous slurry in which pulp-like particles made of an aromatic polymer are mixed with short fibers made of the polymer and/or short inorganic fibers. The present invention has already developed a so-called integrated molding method in the papermaking process, in which an arbitrary number of sheets of wet paper with a moisture content of 50 to 95% are laminated and then dehydrated and dried under heat and pressure. There is a ``Method for manufacturing an oil-immersed insulating board'' proposed by one of the researchers in Japanese Patent Publication No. 1983-46163. The present invention overcomes the drawbacks caused by the adhesive, and furthermore has superior insulating oil impregnation properties that are more versatile than the above-mentioned integral forming method, and does not generate pyrolysis gas, etc., which can cause corona discharge. It is based on the lamination method to obtain a laminated insulating board, and was published in 1983.
A wet paper obtained by paper-making two or more insulating boards obtained according to Publication No. 46163 from pulp-like particles made of an aromatic polymer or a mixed aqueous slurry of pulp-like particles made of an aromatic polymer and short fibers. This paper proposes a method of laminating paper. That is, the present invention forms a wet paper by wet papermaking from an aqueous slurry in which pulp-like particles made of an aromatic polymer and short fibers made of the polymer and/or short inorganic fibers are mixed. When laminating two or more insulating boards that have been laminated with an arbitrary number of sheets of wet paper with a wet moisture content adjusted to 50 to 95% and then dehydrated and dried under heat and pressure, moisture is removed between the layers of the boards. An aromatic polymer wet paper having a freeness of 30% or more, the wet paper has a freeness of 80 to 300ml (Canadian
After interposing one or more pulp-like particles of standard freeness or short fibers of the pulp-like particles and an aromatic polymer with a thickness of 100 to 500 μm, the softening point of the polymer is 80 ~160
This is a method for manufacturing a laminated insulating board, which is characterized by heat-pressure bonding at a temperature as low as 30°C and a pressure of 30 kg/cm <sup>2</sup> or more. The aromatic polymer wet paper referred to here is important in bonding the above-mentioned insulating board. That is, without using epoxy, silicone, or boron fluorine adhesives that have been conventionally used as adhesives for insulating boards, the water content of the wet paper is used to hydrate the board during hot pressing. It is characterized by adhesion. Therefore, the critical value of the moisture content of the wet paper has a close relationship with the adhesive strength of the resulting laminated insulating board, and if the moisture content is lower than 20%, even if the heat pressure is increased, sufficient hydration will not occur. As a result, the adhesive strength is not satisfied. In our experiments,
From the correlation with heat pressure and time, it was confirmed that a preferred water content of 30% or more is practical, although there are no uniform limiting factors. The heating temperature should be lower than the softening point of the aromatic polymer. Generally, the temperature is 50°C or more lower than the softening point of the polymer, preferably 80°C to 160°C lower. If the temperature is lower than 160°C, the adhesive strength will not be sufficient, and if the temperature is closer to or above the softening point, blistering will occur on the insulating boards to be laminated, which is disadvantageous. The preferred pressure is 30Kg/cm <sup>2</sup> or more; if it is less than 30Kg/cm <sup>2</sup> , the adhesive force will be insufficient and workability will be reduced, while if it is 300Kg/cm <sup>2</sup> or more, the density will increase and oil impregnation will occur. cause inconvenience. These heating pressures should be selected appropriately within the above range, but generally 75°C at 160°C.
Applicable to heating pressure for 30 minutes at Kg/ <sup>cm2</sup> . One of the typical manufacturing methods for such aromatic polymer wet paper was proposed earlier by one of the present inventors under the title of ``Method for manufacturing thin paper for electrical insulation'' (Japanese Patent Publication No. 57-46164).
Publication No.). This wet paper is usually produced in the papermaking process by using pulp-like particles of 80 ml to 300 ml (Canadian Standard Freeness) of aromatic polymers or pulp-like particles and aromatic polymers with freeness within a range suitable for paper-making. It is made of a combination of short fibers,
The blending ratio of pulp particles and short fibers is 10:0 to 2:
8, preferably in the range of 10:0 to 4:6. Mixing 8 or more of the short fibers is not preferred because it lowers the strength of the wet paper and impairs lamination efficiency. Usually, one or two or more layers of 500 μm or less may be used, and it is preferable to use 2 to 3 layers of about 200 μm. Next, the insulating board laminated with the above-mentioned aromatic polymer wet paper is made of aromatic polymer pulp particles and the polymer and/or inorganic short fibers, and a typical manufacturing method thereof is as described above. Pulp-like particles made of an aromatic polymer and short fibers made of the polymer and/or inorganic short fibers shown in "Method for manufacturing oil-immersed insulation board" (Japanese Patent Publication No. 57-46163) Wet paper is formed from the mixed aqueous slurry by wet papermaking, the moisture content of the wet paper is adjusted to 50 to 95%, and any number of sheets of wet paper are stacked on top of each other, and then dehydrated and dried under heat and pressure. It is created by integrating. If the moisture content of the wet paper is less than 50%, when the wet paper is laminated and dried, the adhesion between the paper layers will be weak and the board will not form as a single piece. Moreover, if the moisture content is more than 95%, the wet paper paper will easily crumble, making lamination difficult and causing cracks during pressurization and heating. Pulp-like particles of aromatic polymers, short fibers of the polymer, and short inorganic fibers used in insulating boards and wet paper are as follows. That is, aromatic polymers are aromatic polyamides and aromatic polyimides, and pulp-like particles are fiber-like, thin-film-like, or It refers to particles with a ribbon-like structure, and is obtained by introducing a solution of an aromatic polymer into a precipitant to precipitate fine particles. Typical manufacturing methods for these are as shown in Japanese Patent Publication No. 37-5732. The short fibers to be mixed with the above-mentioned pulp-like particles include short fibers made of an aromatic polymer and short fibers made of an inorganic substance. As the inorganic short fibers, glass, ceramic, alumina, rock wool fibers, asbestos, etc. are preferable. That is, from the attributes of the oil-immersed insulating board referred to in the present invention, these short fibers naturally have insulating properties, and therefore, even if they are the same short fibers, conductive fibers such as carbon fibers are excluded. Should. Further, in the case of short fibers made of an aromatic polymer, the polymer may have the same structure as the pulp-like particles, or may have a different structure. The short fibers may be only fibers made of an aromatic polymer, or they may be mixed with inorganic fibers. Alternatively, the inorganic fiber may be used alone. In this way, the present invention can be realized by bonding any aromatic polymer insulating board through any aromatic polymer wet paper, and the resulting laminated insulating board can be bonded using any known adhesive. It has great utility value because it satisfies the impregnating properties and corona properties without using any agents, and the preferred embodiment can of course easily provide a laminated insulating board having a desired thickness. In particular, when used in a transformer, an insulating board is intermittently and discontinuously bonded under heat and pressure as a path for impregnated oil, and is suitable as a so-called washer spacer. Examples will be shown below, but the present invention can be embodied in various ways by those skilled in the art based on the scope of the claims, and is not limited thereto. Example 1 (1) Manufacture of board 10 parts of polymetaphenylene isophthalamide with a logarithmic viscosity of 1.5 in sulfuric acid was dissolved in 90 parts of N-N-dimethylacetamide containing 5 parts of lithium chloride, and this solution was stirred at high speed. Pulp-like particles were obtained by introducing the mixture into a glycerin aqueous solution in a homomixer. The freeness of the pulp-like particles was 80 ml Canadian Standard Freeness. On the other hand, 2-denier fibers obtained by wet-spinning polymetaphenylene isophthalamide and post-stretching them by 2.5 times in boiling water were cut into 6 mm lengths to obtain short fibers. 60 parts of the above pulp-like particles and short fibers
40 parts were dispersed in water to form a slurry, formed into a wet paper using a cylinder paper machine, transferred to felt, and vacuumed to bring the moisture content of the wet paper to 90%. The weight of solid content in the same wet paper was 80 g/m ² . By continuously wrapping the wet paper obtained in this way around a cylinder, 30 sheets were laminated and removed from the cylinder, and heated to 140°C by sandwiching them between iron plates with a wire mesh to facilitate dehydration. Dry at 40Kg/ ^cm2 for 40 minutes,
I got a 2.85mm board. (2) Production of wet paper Polymetaphenylene isophthalamide, which has a logarithmic viscosity of 1.6 in sulfuric acid, was dissolved in dimethylacetamide (DMAC) containing 5 parts of lithium chloride, and the polymer concentration was varied from 15 to 8%. A polymer solution was obtained. A precipitant solution consisting of 40% DMAC, 25% calcium chloride, and 35% water was prepared and brought into contact with each other in a homomixer at a ratio of 30 parts of the precipitant solution to 1 part of the polymer solution while stirring at high speed to form a pulp. The particles were obtained, washed thoroughly with water, dispersed in pure water to prepare an aqueous slurry with a concentration of 0.21%, and paper-made to obtain a wet paper of 26 g/m ² . (3) Lamination The wet paper obtained in step (2) was sandwiched between the two insulating boards obtained in step (1), and the two sheets were heated at 120°C for 30 minutes and bonded together under the conditions that the moisture content of the wet paper was 70%. The characteristics of the product were as follows.

[Table] Example 2 According to Example 1, lamination condition: 160℃, 60 minutes, 75Kg/
The properties of the wet paper bonded with the following moisture content at cm ² were as follows.

[Table] Example 3 According to Example 1, lamination conditions 220℃, 40 minutes in 60 minutes
Kg/cm ² and wet paper moisture at 90%, 3.3Kg
The adhesive strength was obtained. This is quite practical. Comparative Example 1 According to Example 1, lamination conditions were 250°C, 10Kg/cm ² ,
Wet paper paper with a moisture content of 90% and bonded for 3 minutes and 5 minutes had satisfactory bonding strength, but blistered on the insulating board and sank into the board, making it impractical.

Claims (1)

[Claims] 1. A wet paper is formed by wet papermaking from an aqueous slurry in which pulp-like particles made of an aromatic polymer and short fibers made of the polymer and/or short inorganic fibers are mixed, and the water content of the wet paper is reduced. When laminating two or more insulating boards that have been laminated with an arbitrary number of sheets of wet paper with a moisture content adjusted to 50 to 95% and then dehydrated and dried under heat and pressure, the moisture content between the layers of the boards must be 30% or more. An aromatic polymer wet paper with a freeness of 80
~300ml (Canadian Standard Freeness) of pulp-like particles or pulp-like particles and short fibers of aromatic polymer, with a thickness of ~100ml
After intervening one or more particles having a diameter of 500 μm, the polymer is heated at a temperature 80 to 160°C lower than the softening point of the polymer, at a temperature of 30 kg/
A method for producing a laminated insulating board, characterized by bonding under heat and pressure at a pressure of cm ² or more.