JPH0379313B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a heat-resistant inorganic composite having excellent heat resistance and nonflammability. The heat-resistant inorganic composite obtained by the present invention has excellent heat resistance and heat resistance, as well as excellent electrical insulation properties, and can be suitably used for applications such as arc extinguishing materials that are directly exposed to arcs, etc., and insulating spacers used in electric furnaces, etc. I can do it. By the way, a method for manufacturing a composite obtained by pressurizing and heating molding using a main agent consisting of inorganic fibers and/or inorganic powder and a binder consisting of orthoboric acid, boric anhydride, and zinc oxide is described, for example, by Tokko Sho. This method is known from, for example, Japanese Patent No. 54-7359. Accordingly, the present inventors investigated the conventionally known method for manufacturing such a composite, and as a result, the following findings were found. That is, in particular, boric acid and zinc oxide used as binders were heated at 350°C during pressure and heat molding and afterwards.
By heating to 2ZnO.3B ₂ O _{3.3H 2} O, a hydrated zinc borate salt is formed. Furthermore, heating at 350 to 450°C changes this to βZnO·B ₂ O ₃ . The formation of these crystals provides excellent water resistance and heat resistance. However, conventional composites inevitably suffer from the defect of having pores. The reasons for this are as follows. That is, during hot-pressure molding, moisture associated with thermal changes in H ₃ BO ₃ remains in the composite, and heating up to 200° C. causes this moisture to scatter, causing pores. Furthermore, when 2ZnO ₃ .3H ₂ O is thermally transformed into βZnO .B ₂ O ₃ , bound water is dehydrated, leaving pores in the composite.
This phenomenon is an inevitable defect of the binder, and it has been almost impossible to reduce the number of pores in the composite using conventional manufacturing methods. It goes without saying that a composite with many pores has a high water absorption rate and is inferior in strength and electrical insulation. The present invention is a method for producing a heat-resistant inorganic composite that reduces pores in the composite, which are defects of conventional products, and obtains an inorganic composite that has excellent properties such as heat resistance, heat resistance, strength, electrical insulation, and water absorption. The purpose is to provide In the present invention, by impregnating and coating a composite obtained by a conventionally known manufacturing method with a water-soluble inorganic adhesive having excellent water resistance and heat resistance, heat resistance and heat resistance do not deteriorate compared to conventional methods, and water absorption The present invention aims to obtain a heat-resistant inorganic composite that is superior in strength and electrical insulation properties to conventional materials. First, the conventionally known composite used in the present invention will be briefly explained. First, as the inorganic fibers that are the main ingredient, asbestos fibers and glass fibers are mainly used, but ceramic fibers such as potassium titanate fibers and silica fibers can also be used. Further, as the inorganic powder, layered materials such as mica powder and taruri powder are suitable, and high melting point alumina and magnesia can also be used. As the base material, any material can be used as long as it has excellent heat resistance and electrical insulation. As a binder, a material mainly composed of orthoboric acid and zinc oxide mixed with boric anhydride is generally used. In the present invention, as an example of the composition, a composition having a ratio of 46.58% by weight of orthoboric acid, 10.50% by weight of boric anhydride, and 42.92% by weight of zinc oxide was used. These base materials and binders are combined and molded under heat and pressure to obtain a composite.The composite used in the present invention consists of 100 parts by weight of the base material (46.16 parts by weight of mica powder and 53.85 parts by weight of aluminum oxide). 53.85 parts by weight of the binder having the above composition was used. The mixed powder consisting of the base agent and the binder was filled into a mold at room temperature (in the present invention, a mold with a height of 50 mm, a width of 125 mm, and a length of 125 mm was used) (in the present invention, 250 g was filled). ), this mold is inserted between heating plates heated to 160 to 200℃, and heated to 20 to 20℃ with a pressure of 50 to 100Kg/ ^cm2 .
Heat and pressure mold for 30 minutes. Next, the mold was cooled by cooling the hot platen, and when the temperature of the mold fell below 100°C, the pressure was released to obtain a composite with a thickness of 5 mm, width of 125 mm, and length of 125 mm. . This composite was further placed in an electric furnace or the like, and the temperature was gradually increased from room temperature to approximately 450 to 500°C, and heat treatment was performed by holding the temperature for 3 hours to obtain a conventional composite. In the present invention, this conventional composite is further impregnated and coated with a water-soluble inorganic adhesive having excellent water resistance and heat resistance, thereby reducing the pores of the composite.
It is possible to obtain an inorganic composite that has excellent heat resistance and heat resistance as before, has a low water absorption rate, and has better strength and electrical insulation than before. The present invention will be further explained based on representative examples. Example 1 Monobasic aluminum phosphate Al(H ₂ PO ₄ ) ₃ and monobasic magnesium phosphate as water-soluble inorganic adhesives
A 25-50% _aqueous solution of Mg( _H2PO4 ) ₂ is suitable.
This solution is placed in a suitable container and the conventional composite is immersed therein. The immersion time may be arbitrarily determined depending on the thickness, shape, etc. of the composite, and may be any time that allows the solution to sufficiently enter the pores formed in the composite. In this example, immersion was carried out for 3 to 5 hours. After that, the composite was taken out, the phosphate solution adhering to the surface was wiped off, and the mixture was left at room temperature for 1 to 2 hours, then gradually heated to 500℃ and kept for 3 hours to form the desired heat-resistant inorganic composite. Obtained. It goes without saying that vacuum impregnation is more effective as a method for impregnating with the phosphate solution. If the effect of the impregnated coating is not significant, a desired inorganic composite can be obtained by repeating these operations. By the way, these phosphoric acid solutions react with aluminum oxide, zinc oxide, etc. that form the complex, exhibiting strong binding properties, and also flow into the pores of the complex and have the effect of densifying the complex. have To further explain the changes in these phosphate solutions, primary aluminum phosphate Al(H ₂ PO ₄ ) ₃ is
It becomes amorphous when heated to 200~300℃, and 300~
At 400℃, it becomes H ₂ AlP ₃ O ₁₀ and H ₂ AlP ₃ O ₁₀・2H ₂ O.
Furthermore, it becomes Al(PO ₃ ) ₃ at 400 to 500°C, and has excellent water resistance and heat resistance. Furthermore, monobasic magnesium phosphate Mg(H ₂ PO ₄ ) ₂ becomes amorphous at around 200°C, becomes MgH ₂ P ₂ O ₇ at 200 to 400°C, and becomes Mg(PO ₃ ) ₂ above 400°C. Are known. In this example, as described above, a more complex reaction occurs with the materials in the composite, resulting in excellent water resistance and heat resistance, and is effective in improving strength, electrical insulation, etc. as well as densification. The results of measuring the properties of the heat-resistant inorganic composite of this example produced in this manner are shown in the table together with those of other examples. Here, the water absorption rate is the width of the original thickness.
A test piece having a shape of 50 mm and a length of 50 mm was used, and the weight (W ₀ ) was measured after drying at 150° C. for 4 hours, and then immersed in pure water for 24 hours, the surface was wiped, and the weight was measured. The water absorption rate was calculated using the following formula. Water absorption rate (%) = W ₁ −W ₀ /W ₀ ×100 It was determined that the smaller the water absorption rate, the fewer pores there were. The bending strength is based on JISC2210 (asbestos cement board for electrical insulation), and the original thickness is 20 mm in width and length.

[Table] The sample was cut to 125 mm, and the distance between the supporting points was 100 mm.
The bending strength under normal conditions was measured in mm. Arc resistance is
Arc resistance under normal conditions was measured according to JISK6911 (General Test Methods for Thermosetting Plastics), Section 5.15. Insulation resistance was measured in accordance with JISK6911 Section 5.12.3 under normal conditions and after 100 hours at 25°C and 90%RH. Dielectric breakdown voltage is 2mm thick
The sample was polished and the translaminar breakdown voltage under normal conditions was measured. Example 2 Ethyl silicate Si(OC ₂ H ₅ ) ₄ , which is a metal alkoxide, was used as a water-soluble inorganic adhesive. Add 75 parts by weight of ethanol (95%) to 100 parts by weight of ethyl silicate and mix, then 90 parts by weight of water.
A mixture of 1.2 parts by weight of hydrochloric acid (35%) and further 75 parts by weight of ethanol (95%) was added to the above mixture to obtain the water-soluble inorganic adhesive of this example. A conventional composite was immersed in this solution and heated at 40-60°C for 5 hours. Thereafter, the surface of the composite was wiped off and heated at 60-80°C for 5-8 hours. Next, the mixture was gradually heated to 500°C and maintained for 3 hours to obtain the heat-resistant inorganic composite of this example. In general, the process from metal alkoxide to inorganic amorphous is, for example, in the case of ethyl silicate, it is hydrolyzed as nSi(OC ₂ H ₅ ) ₄ +4nH ₂ O→nSi(OH) ₄ +4nC ₂ H ₅ OH, and as the hydrolysis progresses, The viscosity of the liquid increases and it becomes a gel. It is known that when the gel is then gradually heated, it changes to an amorphous oxide, and in the process, decomposition of the OR group, decarbonization, and dehydration condensation occur, resulting in densification. In addition to ethyl silicate, commonly used metal alkoxides include titanium isopropoxide Ti(OisoC ₃ H ₇ ) ₄ and the like. The properties of the heat-resistant inorganic composite obtained in Example 2 are shown in the table above. All test methods were the same as in Example 1. Example 3 A conventional composite was immersed in a colloidal silica solution containing 20 to 40% by weight of silicic acid for 24 hours, then the surface was wiped off and heated at 60 to 80°C for 5 to 8 hours. then 500
The heat-resistant inorganic composite of this example was obtained by gradually heating the mixture to .degree. C. and maintaining it for 3 hours. The surface of the colloidal silica particles has a siloxane structure of -Si-O-Si and is covered with silanol groups. When such colloidal silica is heated, most of the bound water is lost at about 200°C. Colloidal silica has a weak adhesive force due to Van der Waals force, but it works effectively when reducing the pores of a composite as in the present invention. Additionally, colloidal silica has excellent water resistance and high electrical insulation properties. The properties of the heat-resistant inorganic composite obtained in this example are also shown in the table. All test methods were the same as in Example 1. Example 4 An inorganic adhesive mainly composed of silica or alumina (commercially available under trade names such as Aron Ceramic and Sumiceram) was diluted appropriately with water, and a conventional composite was placed in it for 24 hours. After soaking for an hour, the surface was wiped off and heated at 60 to 80°C for 5 to 8 hours. Next, the mixture was gradually heated to 500°C and maintained for 3 hours to obtain the heat-resistant inorganic composite of this example. The characteristics are shown in the table. All test methods were the same as in Example 1. Comparative Example The properties of a conventional composite obtained using the materials and manufacturing methods described above are shown in the table. All test methods were the same as in Example 1. As described above, in the present invention, a composite obtained by heating and press-molding a main agent consisting of inorganic fibers and/or inorganic powder and a binder consisting of boric acid and zinc oxide is heated to about 450 to 500 ° C. By further impregnating and coating the treated conventional composite with a water-soluble inorganic adhesive, the adhesive flows into and fills the pores of the composite, making the composite denser and deteriorating its heat resistance and heat resistance. It has low water absorption and can improve strength and electrical insulation. The heat-resistant inorganic composite obtained according to the present invention can be suitably used as an arc-extinguishing material that is directly exposed to arcs, or as an insulating spacer for electric furnaces and the like.

Claims (1)

[Scope of Claims] 1. A composite obtained by heating and press-molding a main material consisting of inorganic fibers and/or inorganic powder and a binder consisting of orthoboric acid, boric anhydride, and zinc oxide. 1. A method for producing a heat-resistant inorganic composite, characterized in that the composite is impregnated and coated with a water-soluble inorganic adhesive after being heat-treated at a temperature of about 450 to 500°C. 2. The method for producing a heat-resistant inorganic composite according to claim 1, wherein a phosphate solution such as an aluminum monophosphate aqueous solution or a magnesium monophosphate aqueous solution is used as the water-soluble inorganic adhesive. 3. The method for producing a heat-resistant inorganic composite according to claim 1, characterized in that an aqueous solution of metal alkoxide is used as the water-soluble inorganic adhesive. 4 Claim 1 characterized in that a colloidal silica solution is used as the water-soluble inorganic adhesive
A method for producing a heat-resistant inorganic adhesive as described in Section 1. 5. The heat-resistant inorganic composite according to claim 1, wherein a water-soluble inorganic adhesive containing silica or alumina as a main component is used.