JPS623179B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cast insulator made by adding alumina powder to an epoxy resin composition comprising an epoxy resin and an acid anhydride curing agent. It is known that when an acid anhydride curing agent is used as a curing agent for an epoxy resin, a cured product having better electrical properties can be obtained than when an amine compound is used as the curing agent. In addition, epoxy resin compositions can improve their electrical, mechanical, or physical properties by containing fillers, so various fillers are used depending on the application, but among them, alumina powder is It has excellent thermal conductivity, high filling properties, and chemical resistance, and is especially known in the field of electrical equipment as a filler that shows excellent durability in equipment that uses sulfur hexafluoride as an arc-extinguishing medium or an insulating medium. It is being Currently, the current carrying capacity of electrical equipment tends to increase, and as equipment becomes more complex, insulators also tend to become larger and more complex in shape. Many commercially available alumina powders are contaminated with many impurities during the alumina powder manufacturing process, and an alumina powder-filled epoxy resin composition consisting of this alumina powder, epoxy resin, and acid anhydride curing agent is , has a significantly high reaction rate and an extremely short pot life, making it difficult to manufacture cast products with complex shapes or large sizes. Also,
It is assumed that the reaction between an epoxy resin and an acid anhydride is such that the acid anhydride generates a carboxy anion in the presence of a trace amount of water in the system or the presence of a hydroxyl group in the epoxy resin, and the esterification reaction proceeds. It is also known that the production of this carboxy anion is promoted under basic conditions. The first alumina is a powder in which high-purity α-alumina with an alumina content of 99.5% or more is ground in an alumina porcelain mill to reduce the particle size to 44 μm or less, in order to reduce the impurities mentioned above. However, trace amounts of alkali metals such as sodium appear on the surface of alumina particles during the granulation process such as crushing, and salts that dissolve in water and exhibit basicity are adsorbed on the surface of fine alumina particles during the particle size classification process. Such phenomena cannot be avoided. The alumina powder-filled epoxy resin composition comprising the first alumina, epoxy resin, and acid anhydride curing agent reacts quickly and has a short pot life. This not only makes manufacturing difficult for cast products with complex shapes or large sizes, but also tends to cause sink marks and voids in the cured product.Furthermore, when molded products have embedded objects, etc. During curing, internal stress is locally concentrated and cracks are likely to occur, resulting in a decrease in productivity and the electrical and mechanical properties of the cured product. From the above, in order to extend and stabilize the pot life of a cast insulator made by adding alumina powder as a filler to an epoxy resin composition consisting of an epoxy resin and an acid anhydride curing agent. It is necessary to remove or render harmless alkali metals such as sodium present on the surface of the alumina powder and salts that dissolve in water and exhibit basicity. The second alumina is used to eliminate the problems seen when using the first alumina.
This is powdered alumina obtained by washing alumina with an inorganic acid aqueous solution to remove impurities present on the surface of the alumina particles, and then dehydrating and drying the alumina. This second
An alumina powder-filled epoxy resin composition consisting of alumina, an epoxy resin, and an acid anhydride curing agent reacted extremely slowly and had a significantly long pot life. Therefore, a long time is required for complete curing, which reduces productivity. Furthermore, since the specific gravity of alumina powder and resin components is significantly different,
If the reaction is slow, significant sedimentation of the alumina particles occurs, leading to a significant distribution of the alumina powder content in the cured product. Such a phenomenon results in non-uniformity of the dielectric constant within the cured material, resulting in an imbalance in local potential sharing within the same cured insulator, which may lead to problems with electrical equipment using such an insulator. This causes electrical problems such as a decrease in AC withstand voltage characteristics. Furthermore, since the filling rate within the cured product is naturally non-uniform, the mechanical properties also deteriorate. Including the above-mentioned phenomenon, the cured product has the drawback that stable properties are difficult to obtain. The present invention has been made in view of the above, and is made by mixing a first alumina and a second alumina with different reactivities in an arbitrary ratio, and the obtained alumina powder is suitable as a filler for an epoxy resin composition. The present invention provides a cast insulator that exhibits excellent properties. The present invention is characterized by: a powdered first alumina whose particle size is 44 μm or less obtained by pulverizing high-purity α-alumina with an alumina content of 99.5% or more in an alumina porcelain mill; Alumina is washed with an aqueous inorganic acid solution, and then dehydrated and dried to form a second acid-washed powdered alumina, with the first alumina being 5 to 70 wt% and the second alumina being 95 to 30 wt%.
%, and is added as mixed alumina powder in an amount of 40 to 60 vol% into an epoxy resin composition consisting of an epoxy resin and an acid anhydride curing agent. In the present invention, most acids are suitable as the inorganic acid used for cleaning the first alumina, but preferably alkali metals present on the surface of the alumina particles or salts that dissolve in water and exhibit basicity are suitable. Preferred examples include hydrochloric acid, nitric acid, and sulfuric acid, which can be dissolved in water to form a neutral to acidic salt. In addition, the mixing amount of the alumina powder is preferably in the range of 5 to 70 wt% for the first alumina and 95 to 30 wt% for the second alumina, but it is preferable that the first alumina is less than 5 wt% and the second alumina is less than 5 wt%.
If the content exceeds 95 wt%, the alumina powder-filled epoxy resin composition as a whole will exhibit the characteristics of a secondary alumina, and the pot life of the alumina powder-filled epoxy resin composition will become longer and various problems such as sedimentation will occur. In addition, the first alumina exceeds 70wt% and the second alumina exceeds 30wt%.
If it is less than %, the overall properties of alumina will be exhibited as a whole, and the reaction of the alumina powder-filled epoxy resin composition will be rapid, making it difficult to manufacture complex-shaped or large-sized cast products. come. Further, the amount of alumina powder added to the epoxy resin composition according to the present invention is preferably 40 to 60 vol%, and 60 vol%.
If the above amount is added, the viscosity of the mixture of epoxy resin and filler becomes too high, which causes the mixing pot to wear out and the metal components of the pot to mix in, resulting in deterioration of the electrical properties as an insulator. The pot life of the alumina powder of the present invention can be adjusted by adjusting the content of both alumina powders within the above range depending on the shape and capacity of the cast product. One of its characteristics is that it can be used as a suitable filler without causing any problems. Furthermore, the alumina powder-filled epoxy resin composition according to the present invention may optionally contain fillers other than alumina powder, flexibility imparting agents, curing accelerators, colorants, modifiers, deterioration inhibitors, internal mold release agents, or It is also possible to add diluents and the like. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. However, parts in these examples mean parts by weight. The pot life was determined by measuring the viscosity after adding the curing agent to the epoxy resin, and was defined as the time required for the viscosity to reach 2×10 ⁴ cp (centipoise). Further, the complete curing time was defined as the heating time required for the heat distortion temperature to reach the upper limit. Comparative example 1 Epoxy resin CH-200 (manufactured by Ciba Geigy)
100 parts, 40 parts of HT-903 (manufactured by Ciba Geigy) as a hardening agent and 400 parts of the first alumina at 130°C.
The mixture was stirred under reduced pressure to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130°C was 21 minutes, and the complete curing time at the same temperature was 16 hours. Comparative Example 2 100 parts of epoxy resin CT-200, 40 parts of HT-903 as a hardening agent, and 400 parts of second alumina were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130°C was 132 minutes, and the complete curing time at the same temperature was 20 hours. Example 1 For 100 parts of CT-200 as an epoxy resin,
40 parts of HT-903 as a hardening agent, 10 parts of the first alumina, and 390 parts of the second alumina were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130℃ is 100
The complete curing time at the same temperature was 20 hours. Example 2 100 parts of CT-200 as an epoxy resin, 40 parts of HT-903 as a hardening agent, and the first alumina
160 parts of the second alumina and 240 parts of the second alumina were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130°C was 88 minutes, and the complete curing time at the same temperature was 18 hours. Example 3 100 parts of CT-200 as an epoxy resin, 40 parts of HT-903 as a hardening agent, and alumina powder (A)
200 parts of alumina powder (B) were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130°C was 72 minutes, and the complete curing time at the same temperature was 18 hours. Example 4 For 100 parts of CT-200 as an epoxy resin,
40 parts of HT-903 as a hardening agent, 240 parts of the first alumina, and 160 parts of the second alumina were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130℃ is 63
The complete curing time at the same temperature was 18 hours. Example 5 For 100 parts of CT-200 as an epoxy resin,
40 parts of HT-903 as a hardening agent, 320 parts of the first alumina, and 80 parts of the second alumina were stirred under reduced pressure at 130°C to obtain an alumina powder-filled epoxy resin composition. The pot life of this composition at 130°C was 32 minutes, and the complete curing time at the same temperature was 16 hours. The graph shows the viscosity characteristics over time of the alumina powder-filled epoxy resin compositions of the above Comparative Examples and Examples. In addition, the properties after curing of the alumina powder-filled epoxy resin composition using the mixed alumina powder of the first alumina and the second alumina were compared to the compositions of Comparative Example 1, Comparative Example 2, Example 2, and Example 4. The results are shown in the table below.

[Table] As is clear from the above examples, the alumina powder-filled epoxy resin composition using alumina powder according to the present invention has a significantly improved pot life and has excellent effects on various properties after curing. show.

[Brief explanation of the drawing]

The figure is a characteristic diagram showing the viscosity characteristics over time of the alumina powder-filled epoxy resin compositions of Comparative Examples and Examples based on the present invention.

Claims (1)

[Scope of Claims] 1. A first alumina in powder form obtained by pulverizing high-purity α-alumina with an alumina content of 99.5% or more in an alumina porcelain mill to have a powder particle size of 44 μm or less; An epoxy resin composition consisting of an epoxy resin and an acid anhydride curing agent, using as a filler a mixture of a first alumina and a dehydrated and dried powdery second alumina washed with an inorganic acid aqueous solution in an arbitrary ratio. A cast insulator characterized by the addition of. 2 40 to 60 vol% of mixed alumina powder, which is a mixture of 5 to 70 wt% of the first alumina powder and 95 to 30 wt% of the second alumina, is added to the epoxy resin composition.
The cast insulator according to claim 1, characterized in that the material is added.