JPH09124837A - Cast resin composition for electrical insulation and prefabricated joint obtained using the same - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To further improve electrical characteristics and mechanical characteristics without lowering workability. A cast resin composition for electrical insulation containing a thermosetting resin and spherical fused silica powder, wherein the spherical fused silica powder has a particle size of 50 μm or less in total.
A material having an average particle diameter of 9% by weight or more and an average particle diameter of 35 μm or less is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast resin composition for electrical insulation used for molding an insulator for high voltage, and in particular,
It is useful for miniaturizing the insulation part of electric equipment and the connection part of power cable under the super high voltage.

[0002]

2. Description of the Related Art In a resin composition used for an insulating member of an electric device or a power cable connecting portion, for example, a casting of a prefabricated joint or a sleeve, in order to improve electric characteristics and mechanical characteristics, Inorganic filler is compounded.
Various fillers are used as the filler, and a typical filler is silica powder.

Conventionally, crushed crystalline silica powder obtained by grinding or crushing has been used as this silica powder. However, in this crushed crystalline silica powder, electric stress is concentrated because of its crushed shape, and because of its crystallinity, its dielectric breakdown strength is lower than that of an amorphous structure, and the polarization effect is further increased. Also has a large dielectric loss because it is stronger than that of an amorphous structure.

Under the circumstances, it has been proposed to use the spherical fused silica powder obtained by melting the crushed crystalline silica powder and quenching the fused granules as a filler for the resin composition ( (JP-A-2-117936). The resin composition using the spherical fused silica powder as a filler is superior to the resin composition using the crushed crystalline silica powder as a filler in electrical characteristics such as tan δ, dielectric constant, and dielectric breakdown strength. There is.

In this spherical fused silica powder, crushed crystalline silica powder obtained by crushing with a ball mill or the like is transferred to a thermal spraying device with oxygen gas or the like, and the silica powder is sprayed into a furnace by a burner in the thermal spraying device. Is obtained by water cooling in a water bath. The obtained particle size is approximately equal to that of the crushed crystalline silica powder, and the particle size distribution is 1
Within the range of up to 100 μm.

However, if a resin having a too small particle diameter is used, the viscosity of the resin composition becomes remarkably high under the usual compounding amount (50 to 70% by weight), and casting becomes difficult. Further, if a resin having a too large particle size is used, remarkable sedimentation of the resin product during curing is unavoidable, and the characteristics are unavoidably deteriorated due to the uneven distribution of the filler. Therefore, in the above-mentioned JP-A No. 2-117936, it is proposed to use spherical fused silica powder having an average particle size of 10 to 50 μm.

[0007]

In recent years, the trend toward miniaturization and ultra-high voltage of high-voltage equipment has become more and more intense, and under such circumstances, the electric stress acting on the insulator becomes significantly stronger. Therefore, first, further improvement in withstand voltage strength of the insulating material (resin composition) is required. Further, the dielectric loss (εtan δ · V ² ) also increases with an increase in the ultra high voltage, and there is concern that the generated heat may cause thermal damage to the insulator. Especially, if ε tan δ rises as the temperature rises, it is difficult to deny thermal runaway destruction.

[0008] Conventionally, in using spherical fused silica powder instead of crushed crystalline silica powder, the above-mentioned JP-A-2-
In Japanese Patent No. 117936, the average particle size is limited (10 to 50 μm) as described above in order to secure an appropriate viscosity for ensuring casting workability and prevent the filler from settling during resin curing.
However, in reality, the limitation of the average particle size is not sufficient to cope with the downsizing and ultra-high voltage of high voltage equipment.

The present invention has been made in view of the above circumstances, and uses an electrically insulating casting resin composition having excellent electrical properties and mechanical properties without impairing the casting workability and the use thereof. The purpose is to provide prefabricated joints obtained by the above.

[0010]

In order to achieve the above object, an electrical insulating casting resin composition of the present invention is an electrical insulating casting resin composition containing a thermosetting resin and spherical fused silica powder. And the spherical fused silica powder satisfies the requirements (A) and (B) shown below. (A) 99% by weight or more of the total particles having a particle diameter of 50 μm or less. (B) The average particle size is 35 μm or less.

The present inventors have studied to further improve the electrical characteristics of a resin composition using spherical fused silica powder as a main filler in order to cope with the above-mentioned ultra-high electrical stress. As a result, in the range of particle diameters of 1 to 100 μm, those having a particle diameter of 50 μm or more have higher electrical characteristics (withstand voltage value, ε, tan) than those having a particle diameter of 50 μm or less.
We found that it was inferior to δ). For example, the amount of silica powder is about 60% by weight of the total resin composition, and the average particle size is about 2
In the case of the resin composition using 0 μm silica powder, the withstand voltage values of the particles having a particle size of 50 μm or more of 1% by weight and the particles of 50 μm or more of about 10% by weight were measured and compared. The former was about 50% higher.

The cause of this is not always clear, but it is presumed that the smaller the particle size of the silica powder, the more complicated the interface between the resin and the filler, which is considered to be the route of electric breakdown, becomes. On the other hand, in the latter case where the content of 50 μm or more is approximately 10% by weight, the sedimentation phenomenon of the filler was confirmed.

Further, the inventors of the present invention have continuously and continuously conducted a series of studies. As a result, even if the maximum particle size is substantially suppressed to 50 μm or less, that is, the particle size distribution is 1 to 5
It has been found that even if the range is limited to 0 μm, if the content of fine particles in the vicinity of 1 μm is large, the electrical properties and mechanical properties are slightly deteriorated.

The cause of this is that the ultrafine particles have a large specific surface area, the interface between the ultrafine spherical fused silica powder and the resin liquid develops remarkably, and the spherical fused silica powder as a whole becomes difficult to wet with the resin liquid. It is estimated that this is the result.

From the above, particles having a particle size of 50 μm or less are 99% by weight or more (A) of the whole and substantially particles having a particle size of 50 μm or less, and the average particle size is 35.
When spherical fused silica powder having a particle diameter of less than μm (B) is used,
It has been found that a workability is not deteriorated due to an increase in viscosity, and a casting resin composition for electrical insulation, which is excellent in both electrical properties and mechanical properties, can be obtained. That is, by setting the average particle diameter of the spherical fused silica powder to 35 μm or less,
It is possible to sufficiently prevent the sedimentation and segregation of the silica powder during the curing of the product and to achieve the uniform dispersion of the silica powder. Also,
When the average particle diameter of the spherical fused silica powder is 5 μm or more, the viscosity of the resin composition at the time of casting can be set to a sufficiently low viscosity, and a voidless product can be cast with good workability. When the average particle diameter of the spherical fused silica powder is around 5 μm or less, wet sieving is performed, and the specific surface area is adjusted to 3.0 m ² / g or less to obtain electrical characteristics and mechanical properties. It is possible to secure good workability and effectively exert the effect of the filler, in addition to improving the physical properties.

The spherical fused silica powder is obtained by melting crushed crystalline silica powder and water cooling. If the particle size is large, the core of the crushed crystalline silica powder is not melted and the core is crystalline. It remains as it is, the whole does not become non-crystalline, and the ratio of edges remaining becomes large. Therefore, since 99 wt% or more uses spherical fused silica powder having a particle size of 50 μm or less and excludes the use of particles having a large particle size, the inside is completely melted and rapidly cooled to be non-crystallized. ,
In addition, the use of spherical fused silica powder, which has almost no edges and is almost spherical, improves the withstand voltage strength by eliminating the concentration of electrical stress at the edges, the low dielectric constant of amorphous silica, and the effective electrical characteristics due to the low dielectric loss tangent. Expected to improve.

In addition to the above requirements (A) and (B) of the spherical fused silica powder, a specific surface area of 10.0 m ²
When it is set to be equal to or less than / g, the wettability of the entire spherical fused silica powder to be mixed with the resin liquid is improved, the uniform dispersion of the entire spherical fused silica powder is promoted, and the compounding amount of the spherical fused silica powder is set to be large. Therefore, the effect as a filler can be further exerted. Furthermore, when the spherical fused silica powder is subjected to wet sieving or the like to remove ultrafine particles and the specific surface area is set to 3.0 m ² / g or less, in addition to the above effects, it is produced from a resin composition. The withstand voltage strength and mechanical strength of molded products are 10-20%
Can be improved.

Further, by setting the average particle size of the spherical fused silica powder, which is the requirement (B), to 3 to 20 μm, the uniform dispersibility of the spherical silica powder is further improved, and particularly, the average particle size is By setting 3 to 9.5 μm,
It is possible to dramatically improve the withstand voltage strength and the mechanical strength of a molded product produced from the resin composition.

Various epoxy resins are generally used as the thermosetting resin in such a cast resin composition for electrical insulation.

[0020]

Next, embodiments of the present invention will be described in detail.

The cast resin composition for electrical insulation of the present invention is obtained by using a thermosetting resin and a spherical fused silica powder satisfying specific requirements.

As the thermosetting resin, epoxy resin, polyester resin, phenol resin, etc. are used.
Generally, an epoxy resin is used because it has excellent electrical characteristics and mechanical characteristics and also has good moldability. As the epoxy resin, a bisphenol A type epoxy resin, a crystalline epoxy resin, a novolac type epoxy resin, a cycloaliphatic epoxy resin or the like which is liquid or solid at room temperature (about 25 ° C.) is suitable. These epoxy equivalents are
Usually, it is 170 to 500. These epoxy resins are
They may be used alone or in combination of two or more.

When an epoxy resin is used as the thermosetting resin, an acid anhydride is usually used as a curing agent. As the acid anhydride, phthalic anhydride,
Examples thereof include maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride and the like. These may be used alone or in combination of two or more. For example, it is preferable to use phthalic anhydride and tetrahydrophthalic anhydride together in terms of excellent heat resistance and improved mechanical strength.

The mixing ratio of the epoxy resin and the acid anhydride is such that the acid anhydride is 0.6 to 1 equivalent to 1 equivalent of the epoxy resin.
It is preferable to set it as 1.0 equivalent. That is, when the compounding ratio of the acid anhydride exceeds 1.0 equivalent, the electrical characteristics tend to deteriorate, and conversely, when it is less than 0.6 equivalent, the heat resistance may decrease. The equivalent of the acid anhydride (acid anhydride equivalent) is 1 when the number of acid anhydride groups in the acid anhydride is 1 with respect to 1 of the epoxy group in the epoxy resin.
Equivalent. And the said compounding ratio is 0.6-1.0 equivalent, the number of the acid anhydride groups in an acid anhydride is 0.6-1.0 with respect to one epoxy group in an epoxy resin. It means that there is.

The spherical fused silica powder used together with the thermosetting resin can be manufactured by the same method as that for manufacturing spherical silicate, spherical alumina and the like. For example,
Grinding or crushing, for example, crushed crystalline silica powder of high SiO ₂ purity (particle size distribution 1 to 100 μm) obtained by crushing with a ball mill is transferred to a thermal spraying device with oxygen gas and sprayed with a burner of the thermal spraying device. , These spray particles are cooled in a water tank.
It can be obtained by collecting.

The spherical fused silica powder used in the present invention must satisfy the requirements (A) and (B) shown below. (A) 99% by weight or more of the total particles having a particle diameter of 50 μm or less. (B) The average particle size is 35 μm or less.

That is, the upper limit of the particle size distribution is 5
By setting the average particle size to 0 μm (A) and setting the average particle size to a fine particle size of 35 μm or less (B), it is possible to further improve the electrical characteristics. In particular, the average particle size of (B) is 3
The average particle size is preferably 3 to 9.5 μm. In addition to the above particle size distribution, the spherical fused silica particles preferably have a specific surface area of 10.0 m ² / g or less, more preferably 3.0 m ² / g or less. By setting such a particle size distribution, and further by setting the above specific surface area, the resulting resin composition has a low viscosity, and thus excellent electrical properties and mechanical properties can be obtained without impairing workability. .

The treatment of the spherical fused silica particles having a particle diameter of 50 μm or less in an amount of 99% by weight or more, that is, the treatment of the spherical fused silica particles having a particle diameter of 50 μm or more in an amount of less than 1% by weight is performed, for example, by using 270 mesh It can be carried out by sieving, and in this case, it is preferable to use wet sieving in which the particles captured on the mesh are washed out with water in a timely manner.
Further, the treatment for setting the specific surface area to 10.0 m ² / g or less or the treatment for setting the specific surface area to 3.0 m ² / g or less wets fine particles having a particle size of about 1 μm in the above particle size distribution. It can be removed by sieving.

The average particle diameter of the spherical fused silica powder in the present invention can be measured, for example, as follows. That is, first, the sieves with different meshes are arranged in multiple stages, and the finer the mesh, the lower side (the higher the number of stages of the multistage sieve, the more accurate the average particle size can be measured), and the sample is optimized. The particle size-weight distribution curve is determined by passing the sample through the upper sieve toward the lowermost sieve and measuring the weight of the sample remaining on each sieve. The weight w of the sample having the particle size r is w = (4r ³ ρn), where n is the number of particles having the particle size r and ρ is the specific gravity of the particles.
Calculated as / 3. Then, the particle size-number distribution (r-n distribution) is obtained from the particle size-weight distribution (r-w distribution), and the average particle size can be calculated from this distribution curve. Actually, a particle size distribution measuring instrument (for example, C
It is determined by the 50% cumulative value of the particle size distribution obtained by Laser Granulometer model 715 manufactured by ILAS.

The specific surface area of the spherical fused silica particles in the present invention can be calculated from the above particle size-number distribution (rn distribution). That is, the specific surface area λ of a particle having a particle size r is λ = r
ρ / 3, and the specific surface area ξ of the spherical fused silica powder is ξ
= ∫λndn / ∫ndr = ρ∫rndn / 3∫ndr. Actually, it can be determined from the surface area (at the time of desorption of nitrogen gas) and the weight of the measurement sample obtained by a surface area measuring device (for example, Flowsorb II2300 manufactured by Micromeritics) to which this theory is applied.

The compounding amount of the above spherical fused silica powder is set so as to obtain an appropriate viscosity on casting (for example, the minimum melt viscosity is 5 to 25 poise measured by a B-type viscometer at 130 ° C.). Usually, it is set to 50 to 70% by weight based on the whole composition. In the viscosity measured by the B-type viscometer,
If the viscosity is out of the above-mentioned viscosity range and the viscosity is too high, the mixing property and the fluidity are deteriorated. On the contrary, if the viscosity is too low, the filler is precipitated.
When the blending amount of the spherical fused silica powder is less than 50% by weight, the melt viscosity of the resin composition is remarkably lowered and the filler is precipitated. In addition, the mechanical strength also decreases. Conversely, 7
If it exceeds 0% by weight, the viscosity tends to be too high, and adverse effects such as deterioration of the mixing property and the fluidity tend to appear.

Further, in the present invention, the spherical fused silica powder is mainly blended as a filler, but other fillers may be supplementarily appropriately blended. Other fillers include alumina, glass fiber, carbon fiber, calcium carbonate, talc, kaolin, metal powder and the like. When these other fillers are blended, the blending ratio is preferably set to be within 10% by weight of the entire filler.

In addition to the above-mentioned thermosetting resin, spherical fused silica powder and other fillers, the casting resin composition for electrical insulation of the present invention may further contain a curing accelerator, a diluent and a plasticizer, if necessary. , Other additives such as a pigment, a release agent, and a flame retardant can be appropriately mixed.

The cast resin composition for electrical insulation of the present invention is prepared by mixing the above-mentioned raw materials in a predetermined ratio and stirring and mixing under vacuum heating while eliminating bubbles.
The stirring temperature is usually set to 100 to 140 ° C. Then, the thus-prepared cast resin composition for electrical insulation is injected into a predetermined molding die, heated and cured under predetermined conditions, and molded into a desired product.

The resin composition for electrical insulation of the present invention is particularly preferably used as a molding material for a high-voltage insulator such as a prefabricated joint or a sleeve used as a power cable connecting portion. Then, the obtained insulator has excellent electrical characteristics and mechanical characteristics.

As described above, the casting resin composition for electrical insulation of the present invention is preferably prepared, for example, to have a minimum melt viscosity of 5 to 25 poise by a B type viscometer at 130 ° C.

Next, examples will be described together with comparative examples.

[0038]

Example 1 70 parts by weight of bisphenol A type epoxy resin (epoxy equivalent 450-500) (hereinafter abbreviated as "part"), crystalline epoxy resin (epoxy equivalent 150-20).
0) 30 parts by weight, 40 parts of acid anhydrides (phthalic anhydride and tetrahydrophthalic anhydride), and 0.3 part of a curing accelerator have an average particle size of 5 μm and a particle size of 50 μm or more.
200 parts of less than wt% spherical fused silica powder were compounded.
This resin composition was heated at a temperature of about 120 ° C under reduced pressure (3-5
A cast resin composition for electrical insulation was obtained by stirring and mixing with Torr). Then, the cast resin composition for electrical insulation was used to mold and cure by a casting method to produce a molded product having a predetermined shape. The spherical fused silica powder had a specific surface area of 6.4 m ² / g, and the viscosity was slightly high at the final stage of stirring and at the time of casting, but there was no problem in casting.

[0039]

[Example 2] Compared to Example 1, fine particles having a particle size of about 1 µm were removed by a wet sieving method to reduce the specific surface area of the spherical fused silica powder to 3.0 m ² / g, and the average particle size to be 6 µm. did. And the compounding amount was set to 200 parts. Otherwise in the same manner as in Example 1 to obtain a cast resin composition for electrical insulation,
This cast resin composition for electrical insulation was used to mold and cure by a casting method to produce a molded product having a predetermined shape.

[0040]

Example 3 A spherical fused silica powder having an average particle size of 9
200 parts of particles having a particle size of 50 μm or more and less than 1% by weight were compounded. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 3.6 m ² / g.

[0041]

[Example 4] Compared to Example 3, fine particles having a particle size of about 1 µm were removed by a wet sieving method to reduce the specific surface area of the spherical fused silica powder to 2.1 m ² / g, and the average particle diameter was set to 11 µm. did. And the compounding amount was set to 200 parts. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape.

[0042]

Example 5 A spherical fused silica powder having an average particle size of 1
200 parts of less than 1% by weight of 5 μm and particle size of 50 μm or more were blended. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 1.9 m ² / g.

[0043]

[Example 6] In contrast to Example 5, fine particles having a particle size of around 1 µm were removed by a wet sieving method to reduce the specific surface area of the spherical fused silica powder to 1.3 m ² / g, and the average particle diameter was changed to 18 µm. did. And the compounding amount was set to 200 parts. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape.

[0044]

Example 7 A spherical fused silica powder having an average particle size of 3
200 parts of particles having a particle size of 0 μm and a particle size of 50 μm or more and less than 1% by weight were mixed. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 0.9 m ² / g.

[0045]

Example 8 A spherical fused silica powder having an average particle size of 3
160 parts of particles having a particle size of 50 μm or more and less than 1% by weight were compounded. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 12.5 m ² / g.

[0046]

Example 9 A spherical fused silica powder having an average particle size of 4
160 parts of particles having a particle size of 50 μm or more and less than 1% by weight were compounded. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 10.0 m ² / g.

[0047]

[Comparative Example] A spherical fused silica powder having an average particle size of 40
The content ratio of particles having a particle size of 50 μm or more in μm is 10% by weight.
200 parts were blended. Otherwise in the same manner as in Example 1, an electrically insulating casting resin composition was obtained, and this electrically insulating casting resin composition was molded and cured by a casting method to produce a molded product having a predetermined shape. The specific surface area of the spherical fused silica powder was 0.6 m ² / g.

Using the molded products (samples) of these Examples and Comparative Examples, the dielectric breakdown strength, dielectric loss tangent, dielectric constant and bending strength were measured according to the following test methods. In all tests, the number of samples was 10
The average value of the individual was calculated. Table 1 below shows these results together.
~ Shown in Table 2.

[Dielectric Breakdown Strength] A sample having a thickness of 1 mm and having electrodes integrally provided on both surfaces was prepared, and the sample was immersed in insulating oil to increase the initial voltage to 50 kV and to increase the voltage by 10 kV.
Then, each step-up voltage was applied to hold the voltage for 1 minute to obtain the voltage value (effective value) when the sample was broken.

[Dielectric Loss Tangent and Dielectric Constant] A sample having a thickness of 1 mm and a diameter of 60 mm, in which a main electrode and a guard electrode around it were formed on one surface and a counter electrode was formed on the other surface by a conductive coating, was prepared. Then, this sample is placed in a constant temperature bath for 100
Measured frequency: 50Hz by the transformer bridge method at ℃
The capacitance and the conductance were measured respectively, and the dielectric loss tangent and the dielectric constant were calculated from these results.

[Bending strength] Width 10 mm x length 100 mm
× A sample having a thickness of 4 mm was prepared, and a load was applied to the center by a pressure wedge while supporting both ends at intervals of 64 mm, and the maximum load at the time of bending fracture was determined.

[0052]

[Table 1]

[0053]

[Table 2]

From Tables 1 and 2 above, the products of the examples have considerably excellent results in terms of dielectric breakdown strength, dielectric loss tangent, and bending strength, as compared with the products of the comparative examples. The ratio of the spherical fused silica powder is less than 1% by weight of the total spherical fused silica powder, and the particle size is substantially 50 μm.
The effect of eliminating the mixing of the spherical fused silica powder was confirmed.

Further, in comparison with Example 1, in Example 2 in which the powder having a particle diameter of about 1 μm is wet-sieved to reduce the specific surface area of the spherical fused silica powder, the dielectric breakdown strength and bending are smaller than those in Example 1. An improvement in strength was observed. Further, in comparison with Example 3, Example 4 in which the specific surface area of the spherical fused silica powder is reduced by wet sieving the powder having a particle size of about 1 μm is improved in dielectric breakdown strength and bending strength as compared with Example 3. Was recognized. From these facts, in the present invention, it was confirmed that by further increasing the specific surface area of the spherical fused silica powder to 3.0 m ² / g or less, the effect of further improving the electrical and mechanical properties can be obtained. .

Further, in the spherical fused silica powder having an average particle size of 15 μm, comparing Example 5 and Example 6, it is found that Example 6 in which wet sieving has a smaller specific surface area has a higher dielectric breakdown strength and bending strength. It was confirmed that the effect of improving the characteristics was high.

[0057]

As described above, the casting resin composition for electrical insulation of the present invention contains a specific spherical fused silica powder. This spherical fused silica powder has a particle size of 50μ
Particle size of 50
Particles having a size of not more than μm satisfying the requirements of 99% by weight or more (A) of the whole and an average particle size of not more than 35 μm (B) are used. Therefore, excellent electrical characteristics and mechanical characteristics are improved without lowering workability. In this way, the properties of the spherical fused silica powder based on the non-crystalline and non-edge physical properties are effectively exhibited, and the inclusion of fine particles in the vicinity of 1 μm is eliminated to improve the wettability of the entire spherical fused silica powder with the resin liquid. It further improves the uniform dispersion of spherical fused silica powder.

Furthermore, when the specific surface area of the spherical fused silica powder is set to 3.0 m ² / g or less, the wettability of the entire spherical fused silica powder to be mixed with the resin liquid is improved, and the entire spherical fused silica powder is Since the uniform dispersion can be promoted and the compounding amount of the spherical fused silica powder can be set to be large, the effect as the filler can be further exerted.

Further, by setting the average particle diameter of the spherical fused silica powder, which is the requirement (B), to 3 to 20 μm, the uniform dispersibility of the spherical silica powder can be further improved, and particularly, the average particle diameter By setting the thickness to 3 to 9.5 μm, the above effect is particularly remarkable. Therefore, in particular, it has excellent dielectric breakdown strength and dielectric loss tangent, and is extremely useful for ultrahigh voltage and downsizing of high voltage equipment.

Therefore, the cast resin composition for electrical insulation of the present invention is optimal as a molding material for a high-voltage insulator such as a prefabricated joint or a sleeve used as a power cable connecting portion. The resulting insulation has excellent electrical and mechanical properties.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Tan, 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (7)

[Claims] 1. A cast resin composition for electrical insulation containing a thermosetting resin and spherical fused silica powder, wherein the spherical fused silica powder satisfies the requirements (A) and (B) shown below. What is claimed is: 1. A cast resin composition for electrical insulation, comprising: (A) 99% by weight or more of the total particles having a particle diameter of 50 μm or less. (B) The average particle size is 35 μm or less. 2. The specific surface area of the spherical fused silica powder is 10.
The cast resin composition for electrical insulation according to claim 1, which has a content of 0 m ² / g or less. 3. The average particle diameter of the spherical fused silica powder is 3 to 2.
The cast resin composition for electrical insulation according to claim 1, which has a thickness of 0 μm. 4. The average particle diameter of the spherical fused silica powder is 3 to.
The cast resin composition for electrical insulation according to claim 1, which has a thickness of 9.5 μm. 5. The specific surface area of the spherical fused silica powder is 3.0.
electrical insulating casting resin composition according to any one of m ² / g according to claim 1 to 4 less. 6. The cast resin composition for electrical insulation according to claim 1, wherein the thermosetting resin is an epoxy resin. 7. A prefabricated joint formed by molding the cast resin composition for electrical insulation according to claim 1. Description: