JPS624053B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an epoxy resin composition using alumina powder as a filler and a polybasic carboxylic acid anhydride as a hardening agent. The present invention relates to an epoxy resin composition characterized in that it is produced by a method in which sulfuric acid is added during pulverization to form a fine powder, and then residual sulfuric acid is removed by heating and drying. It is generally known that when a polybasic carboxylic acid anhydride is used as a curing agent for epoxy resin, a cured product with better electrical properties can be obtained than when an amine compound is used as the curing agent. There is. On the other hand, the electrical, mechanical, or physical properties of epoxy resin compositions can be modified by containing fillers, so various fillers are used depending on the application, but among them, alumina The powder is used as a filler with excellent thermal conductivity, adhesive properties, and chemical resistance. In particular, it is a filler that shows particularly excellent performance in electrical equipment that uses sulfur hexafluoride (SF ₆ ) as an arc-extinguishing medium or an insulating medium. However, many commercially available alumina powder-filled epoxy resin compositions using alumina powder are unfilled with epoxy resin and polybasic carboxylic acid anhydride due to impurities mixed in during the alumina powder manufacturing process. The reaction rate is significantly higher than that of the composition, and the pot life is extremely short, making it difficult to manufacture cast or molded articles with complex shapes or large sizes. For this reason, depending on the type of alumina powder, the type of epoxy resin or polybasic carboxylic acid anhydride must be selected with emphasis on pot life rather than on the properties of the composition after curing. When determining an epoxy resin composition, the degree of freedom in selecting the epoxy resin and polybasic carboxylic acid anhydride is significantly reduced, and an alumina powder-filled epoxy resin composition with a stable pot life can be obtained. It had some serious flaws. By the way, alumina powder, which is industrially manufactured at low cost, is generally supplied by heating aluminum hydroxide obtained by the Bayer process to turn it into α-alumina, and then going through a granulation process. The contamination of alkali metals such as sodium is unavoidable, and although the soda content has been reduced through chemical treatment, it is not possible to completely eliminate trace amounts of alkali metals that appear on the surface of alumina particles during the granulation process such as crushing. It was difficult. In addition, when producing alumina powder using the dry pulverization method, coarsely pulverized alumina is usually used as the raw material.
Fine pulverization is performed using a ball mill or the like, but in this case, if steel balls are used, iron will be mixed into the alumina powder, which is unfavorable in terms of electrical properties, and a step of iron removal is required. Therefore, in order to eliminate the need for this iron removal process, alumina balls are used instead of steel balls, but in order to increase the grinding efficiency, a small amount (usually 2 ~
3 c.c.) of water is added. However, even in this case, a small amount of alkali metal appears on the surface of the alumina particles during pulverization, so if left as is, the reaction of the epoxy resin composition would be significantly accelerated and the pot life would be shortened. On the other hand, when a sulfate is added to an epoxy resin composition using a polybasic carboxylic acid anhydride as a curing agent, the gelation reaction is delayed and the pot life is increased without changing the properties of the cured product. It is known that it is possible to extend the
31679). Therefore, the present inventors added sulfuric acid as a grinding aid during the pulverization of the coarsely pulverized raw material of alumina powder to increase the pulverization efficiency and to react with trace amounts of alkali metals appearing on the surface of the alumina particles during the pulverization. This resulted in the formation of sulfate. Then, the alumina powder treated with this sulfuric acid is
When heated at a temperature of 290°C or higher to remove unreacted sulfuric acid and then filled into an epoxy resin composition containing a polybasic carboxylic acid anhydride as a curing agent, the gelation reaction is delayed and the pot life is shortened. As an example of the manufacturing process of the alumina powder according to the present invention, it was discovered that the present invention found that the alumina powder becomes long and does not change the properties after hardening.
15ml of 1N sulfuric acid was added to the mixture, and the mixture was pulverized for 16 hours using an alumina ball vibrating mill.
It is obtained by drying in an electric oven at ℃ for 8 hours. In the present invention, the epoxy resin composition is preferably filled with the alumina powder in an amount of 65 to 85 wt%. This is because if it is less than 65 wt%, sufficient strength cannot be obtained after curing, and if it is more than 85 wt%, the epoxy resin composition becomes highly viscous, making it difficult to remove voids. Further, the epoxy resin used in the present invention preferably has two or more oxirane rings in the molecule and has an epoxy equivalent in the range of 130 to 450 g/eq. For those with an epoxy equivalent of 450g/eq or more
A cured product with a high HDT (heat distortion temperature) cannot be obtained,
In addition, if it is less than 130 g/eq, a high HDT can be obtained, but the cured product has the disadvantage of being brittle. Specifically, for example, epoxy equivalents of cycloaliphatic epoxy, bisphenol type epoxy, novolacic epoxy, cyanuric acid epoxy, hydantoin type epoxy, glycidyl ester type epoxy, etc. that are liquid or solid at room temperature are 130 to
450g/eq of resin is mentioned. Further, in the present invention, a polybasic carboxylic acid anhydride is used as a curing agent, and a dibasic one is particularly preferred. This is because when an amine compound is used as a curing agent, the epoxy resin composition cures in a relatively short time, but the pot life is short and storage stability is poor. If it is monobasic, it will not crosslink, and if it is tribasic or higher, it will have a high melting point and high reactivity with epoxy resin, so it can be applied to large-sized casting epoxy resin compositions that are usually used without solvent. This is because it is difficult to use in terms of time. Specific examples of the dibasic carboxylic anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, etc. is used. Further, depending on the case, it is also possible to use additives such as a flexibility imparting agent, a curing accelerator, or a pigment. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples in the case of treatment with sulfuric acid. 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). The complete curing time was defined as the heating time required for the heat distortion temperature to reach the upper limit of the sample composition. Comparative example 1 (a) Bisphenol A type epoxy resin (epoxy equivalent: 400 g/eq) ...100 parts (b) Methyltetrahydrophthalic anhydride ...40 parts (c) Alumina powder (no sulfuric acid added) ...420 parts The above (a) to (c) were blended at 130°C to obtain an epoxy resin composition. The pot life of this composition at 130°C was 25 minutes, and the complete curing time at the same temperature was 18 hours. Example 1 (a) Bisphenol A type epoxy resin (epoxy equivalent: 400 g/eq)...100 parts (b) Methyltetrahydrophthalic anhydride...40 parts (c) Alumina powder of the present invention (sulfuric acid treatment)
...420 parts The above (a) to (c) were blended at 130°C to obtain an epoxy resin composition. The pot life of this composition at 130°C was 70 minutes, and the complete curing time at the same temperature was 18 hours. Comparative Example 2 (a) Cycloaliphatic epoxy resin (epoxy equivalent
140g/eq...50 parts(b) Bisphenol A type epoxy resin (epoxy equivalent 400g/eq)...50 parts(c) Methyltetrahydrophthalic anhydride...72 parts(d) Alumina powder (no sulfuric acid added) ...680 parts The above (a) to (d) were blended at 130°C to obtain an epoxy resin composition. The pot life of this composition at 130°C was 20 minutes, and the complete curing time at the same temperature was 16 hours. Example 2 (a) Cycloaliphatic epoxy resin (epoxy equivalent
140g/eq) ...50 parts (b) Bisphenol A type epoxy resin (epoxy equivalent 400g/eq) ...50 parts (c) Methyltetrahydrophthalic anhydride ...72 parts (d) Alumina powder of the present invention ( sulfuric acid treatment)
...680 parts The above (a) to (d) were blended at 130°C to obtain an epoxy resin composition. The pot life of this composition at 130°C was 60 minutes, and the complete curing time at the same temperature was 16 hours. Note that the viscosity characteristics over time at 130° C. of the epoxy resin compositions of Comparative Example 1 and Example 1 are shown in the figure. Furthermore, Table 1 shows that the addition of sulfuric acid had almost no effect on the electrical or mechanical properties of the epoxy resin composition after curing, for the compositions of Comparative Example 1 and Example 1. In this case, the curing conditions were 130°C for 24 hours, and the characteristics were measured using JISK6911 "Testing method for thermosetting plastics" and JISK6717 "Methacrylic resin molding material."
I followed.

【table】

[Table] As described above, according to the present invention, it is possible to extend the pot life of an epoxy resin composition without substantially changing the curing time and without changing the properties after curing. This improves work efficiency.

[Brief explanation of the drawing]

The figure is a characteristic diagram showing the viscosity characteristics over time of an epoxy resin composition.

Claims (1)

[Scope of Claims] 1. An epoxy resin composition comprising an epoxy resin having two or more oxirane rings in the molecule, a polybasic carboxylic acid anhydride as a curing agent, and alumina powder as a filler, An epoxy resin composition characterized in that the alumina powder is obtained by adding sulfuric acid to raw alumina granules, pulverizing them, pulverizing them, and then removing residual sulfuric acid by heating and drying. 2. The epoxy resin composition according to claim 1, wherein the composition is filled with 65 to 85 wt% of alumina powder. 3 As an epoxy resin, it has two or more oxirane rings in the molecule and has an epoxy equivalent of 130 to 450 g/eq.
3. The epoxy resin composition according to claim 1 or 2, characterized in that an epoxy resin falling within the following range is used. 4. The epoxy resin composition according to claim 1, 2, or 3, characterized in that a dibasic carboxylic acid anhydride is used as a curing agent.