Electrical insulating material and high voltage equipment

Abstract

 An electrical insulating material excellent in crack resistance properties without deteriorating the properties of an insulating resin in a solid insulation system, and a high voltage equipment using the same are provided.
An electrical insulating material comprising: an epoxy resin; a curing agent; and an elastomer particle (3) and an inorganic particle (2) as an additive material, wherein at least a part of the elastomer particle (3) is radiation cross-linked. A high voltage equipment such as a transformer, a circuit breaker, a motor, and an inverter, in which this electrical insulating material is applied at a site requiring an electrical insulation of an electrical equipment.

Description

[Technical Field]

[0001] The present invention relates to an electrical insulating material and a high voltage equipment in which the insulating material is applied at a site requiring an electrical insulation.

[Summary of Invention]

[0002] A gaseous insulation with an insulating gas, a vacuum insulation, or an oil insulation, in which an insulating oil is encapsulated, has been a conventional mainstream of an insulation system which is applied to a transmission and distribution equipment including a transformer and a circuit breaker, or to a high voltage equipment such as a motor and an inverter. However, due to the stream of recent downsizing and weight saving of equipment, the application of a solid insulation system, in which a solid insulation material having a good insulation strength is adopted, is advanced.

[0003] In the solid insulation system, a thermosetting resin such as an epoxy resin is in heavy usage due to its excellent insulation properties, heat resisting properties, mechanical characteristics, and chemical stability. However, since generally the thermosetting resin is large in a thermal expansion coefficient as compared with metals, its surface in contact with a dissimilar material becomes very high in a thermal stress due to a differential thermal expansion.

[0004] Consequently, a crack may be caused in the resin to remarkably lower a strength or insulation properties. Against this problem, in order to reduce the thermal expansion coefficient of the resin, and also in light of a cost reduction and enhancing a mechanical strength, an inorganic particle having a very small thermal expansion coefficient, such as silica or alumina, is added to the resin in a large amount.

[0005] On the other hand, an excessive addition of the inorganic particle considerably increases the viscosity of the resin to reduce a workability. Further, it may cause a void in the resin hardened material. The void in the resin hardened material is in danger of causing a decrease in insulation properties due to a concentration of an electric field, or a decrease in a mechanical strength. Accordingly, the technology of highly filling an inorganic particle, the technology of making the low viscosity of the resin, or the technology of making the high strength, whereby crack resistance properties are provided to the resin itself to inhibit a crack in the resin, has been eagerly considered.

[0006] As one of methods of enhancing the crack resistance properties of a solid insulation resin, a method of imparting a flexible additive to the resin has been known from a long time ago. Patent Document 1 discloses a method wherein an ultrafine particle thermoplastic resin, epoxy resin, a curing agent, an inorganic filler, and a hardening accelerator are mixed with each other whereby a resin excellent in adhesive property and toughness is provided. Further, Patent Document 2 discloses a method in which to a thermosetting resin comprising an epoxy resin and a curing agent, an inorganic particle having different µm sizes and a rubber particle comprising a core-shell structure are added whereby an electrical insulating material excellent in mechanical properties is provided.

[0007] However, Patent Document 1 mentioned above does not refer to a method of manufacturing the ultrafine particle thermoplastic resin. In order to derive an ultrafine particle of a thermoplastic resin, a thermoplastic resin is commonly and preliminarily cross-linked to be formed and shaped to a finite size. However, for example, when a chemical crosslinking is used, an impurity such as sulfur is apt to be incorporated due to the use of a vulcanizing agent as a cross-linking agent. When an insulating material including such an impurity is arranged in close vicinity to a conducting body, the progression of a migration, which is caused due to a moisture absorption or the like, may be accelerated to remarkably lower insulation performance.

[0008] Additionally, Patent Document 2 selects a core-shell type of rubber particles as elastomer particles. In order to enhance the dispersibility of elastomer particles in the resin, the core-shell type comprises a structure having a core layer having the elastomer particles within the rubber particle, and a further shell layer which is compatible with the resin and provided at the outer side, whereby the dispersibility of the elastomer particles in the resin is enhanced and the crack resistance properties of the resin can be stably enhanced. However, when the core-shell type of elastomer particles are used, according to our experiments it has been confirmed that the effects can not be derived without an addition in a large amount. When the elastomer particles were not added in a large amount, as a result the flexibility of the resin is enhanced, while the other resin properties are decreased, in particular, the increase in dielectric constant, the increase in tanδ, or the decrease in mechanical properties such as thermal resistance or breaking strength comes into question.

[Prior Art]

[Patent Documents]

[0009] 

[Patent Document 1]

JP-A-2006-22188.

[Patent Document 2]

JP-A-2002-15621.

[Problems to be Solved by the Invention]

[0010] An object of the present invention is to provide an electrical insulating material excellent in crack resistance properties without deteriorating the properties of an insulating resin in a solid insulation system, and a high voltage equipment using the same.

[Means for Solving the Problem]

[0011] That is, the present invention provides an electrical insulating material comprising:

an epoxy resin;

a curing agent; and

an elastomer particle and an inorganic particle as an additive material, wherein at least a part of said elastomer particle is radiation cross-linked.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

[Advantages of the Invention]

[0012] The present invention can obtain an electrical insulating material excellent in crack resistance properties without deteriorating its properties (a thermal resistance and insulation properties), and a high voltage equipment to which the electrical insulating material is applied.

[Brief Description of the Drawings]

[0013] 

[Fig.1] Figure 1 is a sectional view of an electrical insulating material showing an embodiment of the present invention.

[Fig.2]Figure 2 is a sectional view for illustrating another embodiment of the present invention.

[Embodiments for Carrying Out the Invention]

[0014] The epoxy resin in the present invention is a compound including two or more epoxy groups comprising two carbon atoms and one oxygen atom within its molecule, while the epoxy group can be subjected to a ring-opening reaction with an appropriate curing agent, and as the epoxy resin, any one can be applied, provided that it can be formed into a hardened resin material. For example, as its preferred examples, a bisphenol A type epoxy resin which can be derived by the condensation of epichlorohydrin with a polyhydric phenol or polyhydric alcohol such as bisphenols; a bisphenol A type epoxy resin which can be derived by the condensation of epichlorohydrin with a polyhydric phenol or polyhydric alcohol such as bisphenols; a brominated bisphenol A type epoxy resin; a hydrogenated bisphenol A type epoxy resin; a bisphenol F type epoxy resin; a bisphenol S type epoxy resin; a bisphenol AF type epoxy resin; a biphenyl type epoxy resin; a naphthalene type epoxy resin; a fluorene type epoxy resin; a novolac type epoxy resin; a phenolnovolac type epoxy resin; an ortho-cresol novolac type epoxy resin; a tris(hydroxyphenyl)methane type epoxy resin; a glycidyl ether type of epoxy resin such as tetraphenylolethane type epoxy resins, and a glycidyl ester type of epoxy resin which can be derived by the condensation of epichlorohydrin with carboxylic acid; a heterocyclic epoxy resin such as a hydantoin type epoxy resin which can be derived by the reaction of triglycidyl isocyanate or epichlorohydrin with hydantoins. Besides, these can be applied independently or as a mixture of two or more.

[0015] In the present invention wherein the above materials are used, an elastomer particle derived by a radiation cross-linking is excellent in a thermal resistance due to its high crosslink density, and further a difference in crosslink density between the elastomer particles is small due to a homogeneous progress in cross-linking so that crack resistance properties can be stably enhanced. Furthermore, since the radiation cross-linking is progressed merely by irradiating radiation rays (electron beams), it is not necessary to add an extra cross linking agent, and thus for example, impurities such as sulfur in a vulcanizing agent used as a cross linking agent are difficult to incorporate. As a result, a migration, whose progress is accelerated with an impurity element, can be inhibited. Accordingly, when according to the present invention the radiation cross-linked elastomer particle is used, the crack resistance properties of the resin is undoubtedly enhanced, the resin has excellent insulation properties including the inhibition of migration, and further the decrease of a thermal resistance can be inhibited. Incidentally, the presence or absence of the radiation cross-linked elastomer particle can be evaluated through a chemical analysis such as a solid NMR.

[0016] Further, in the present invention, the average particle size of elastomer particles is preferably 500 nm or less, and more preferably 100 nm or less, and the elastomer particle is preferably uniformly dispersed in an electrical insulating material.

[0017] Table 1 shows a relationship among a spheric particle radius, an interparticle distance, and a relative specific surface area in a disperse system having a volume concentration of 2%.

[0018] [Table 1]

Table 1

Particle radius [nm]	Interparticle distance [nm]	Particle specific surface area
40000	160000	1
4000	1600	100
4	16	10000

[0019] According to Table 1, as the particle radius becomes small, the interparticle distance is decreased, and the relative specific surface area is increased. As a result, an interaction range between the elastomer particles and the resin is enlarged, and thus even an addition of the elastomer particles in a small amount remarkably enhances the properties of the resin. Accordingly, the use of finer elastomer particles increases the advantageous effect, while a decrease in resin properties themselves and an increase in cost can be minimized.

[0020] Furthermore, in the present invention, an amount of the elastomer particle added is preferably 50 parts by weight or less relative to 100 parts by weight of the epoxy resin, and more preferably 30 parts by weight or less.

[0021]  When the elastomer particle is added in an amount of more than 30 parts by weight relative to 100 parts by weight of the epoxy resin, the viscosity of the whole of the resin is increased, and thus the workability is decreased. Additionally, since voids are easily caused in the resin before curing, defects may be caused in a hardened material to lower mechanical properties and electrical properties. Besides, an excessive addition may deteriorate resin properties themselves. Accordingly, the amount of the elastomer particle added is more preferably 30 parts by weight or less relative to 100 parts by weight of the epoxy resin.

[0022] In addition, in the present invention, a part (or the whole) of the elastomer particle preferably comprises any one of acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, epichlorohydrin rubber, chloroprene rubber, styrene rubber, silicone rubber, fluoro rubber or butyl rubber, or a modified material thereof, or a combination thereof, and a surface or inside thereof is modified with any one of a carboxyl group, acid anhydrides, amines or imidazoles, or a combination thereof.

[0023] The rubbers mentioned above are ones which are industrially produced, and are inexpensively available. In addition, in order to enhance a compatibility between the elastomer particle and the resin, the elastomer particle can be modified with any one of a carboxyl group, acid anhydrides, amines and imidazoles, a combination thereof, whereby the elastomer particle can be uniformly and easily dispersed in the resin. Further, the elastomer particle can be preliminarily dispersed in the epoxy resin and a curing agent, whereby the compatibility between the elastomer particle and the resin can be enhanced. On the other hand, we have confirmed through our experiment that when inorganic particle is added to the epoxy resin and a curing agent, followed by the mixture of the elastomer particle, or even when epoxy resin including the inorganic particle and the curing agent are mixed, followed by the addition of the elastomer particle, an enhancement effect of crack resistance properties can be obtained.

[0024] In addition, in the present invention, a part of the elastomer particle preferably comprises the elastomer particle mentioned above, and an elastomer particle except the above part of the elastomer particle preferably comprises a core-shell type of an elastomer particle.

[0025] Radiation cross-linked elastomer particle according to the present invention preferably has an average particle size of 100 nm or less, while in a system wherein the elastomer particle is mixed with a core-shell type of elastomer particle, the average particle size of the core-shell type of elastomer particle is preferably in the range of approximately from 100 nm to several hundreds nm for the purpose of suppressing a remarkable increase in material cost, such an elastomer particle being commercially available. As a result, the amount of a core-shell type of elastomer particle added in a conventional resin can be decreased, and a decrease in resin properties such as insulation properties, and a thermal resistance can be inhibited to a minimum, while crack resistance properties can be more stably obtained.

[0026] Furthermore, in the present invention, a part or the whole of the inorganic particle is preferably any one of silica (SiO₂), alumina (Al₂O₃), alumina hydrate, titanium oxide (TiO₂), aluminum nitride (AlN) or boron nitride (BN), or a combination thereof, and preferably has an average particle size of 500µm or less.

[0027] The addition of the inorganic particle can decrease the thermal expansion of the resin to inhibit the occurrence of resin peeling or resin crack at a site wherein the resin is in contact with a dissimilar material. For example, as silica of inorganic materials corresponding to this, a natural silica (a crushed silica), a molten silica, and a crystal silica can be enumerated, while as alumina, for example, a low-soda alumina, and an easily sinterable alumina can be enumerated. Aluminum nitride and boron nitride are high cost, but excellent in thermal conductivity performance, and thus are preferred for the purpose of enhancing the thermal conductivity of a hardened material. It is preferred that these inorganic particle has an average particle size of 500 µm or less, and a wide particle size distribution in the range of from 0.1 µm to 100 µm. Thereby, even when inorganic particles are highly filled, making a low viscosity is feasible.

[0028] In addition, in the present invention, a surface of the inorganic particle is preferably modified with any one selected from the group consisting of a group comprising a hydrocarbon, such as an alkyl group, an acrylic group, a methacrylic group, a hydroxyl group, acid anhydrides, imidazoles, amines, a carboxyl group, and an alkoxyl group, or a combination thereof.

[0029] Thereby, a compatibility between the inorganic particle and the epoxy resin is increased, which can contribute to making a low viscosity.

[0030] In addition, in the present invention, an amount of the inorganic particle added is preferably from 300 to 600 parts by weight relative to 100 parts by weight of the epoxy resin.

[0031] When the amount of the inorganic particle is more than 300 parts by weight, the thermal expansion coefficient of the resin is remarkably large, so that the peeling or resin crack at a joint area is easily caused. Further, when more than 600 parts by weight, the resin viscosity is remarkably increased, whereby the workability is lowered, while defects are caused in the hardened material, so that mechanical properties and electrical properties are lowered.

[0032] In addition in the present invention, at least a part of the curing agent preferably comprises acid anhydrides. Other curing agents for the epoxy resin can include amines, imidasoles, phenol resins, hydrazides in addition to acid anhydrides, while an epoxy resin using an acid anhydride curing agent has a long usable time, and further electrical, chemical and mechanical properties can be provided in a balanced manner. The acid anhydride curing agent, can include, for example, dodecenylsuccinic anhydride, poly(adipic anhydride), poly(azelaic anhydride), poly(sebacic anhydride), poly(ethyloctadecanedioic anhydride), poly(phenylhexadecanedioic anhydride), methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl himic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic dianhydride, benzophenone tetracarboxylic acid, ethylene glycol bistrimellitate, glycerol tristrimellitate, chlorendic anhydride, tetrabromophthalic anhydride, nadic anhydride, methyl nadic anhydride, and polyazelaic polyanhydride.

[0033] In addition, together with the curing agent for the epoxy compound, a hardening accelerator for epoxy compounds which promotes or controls the curing reaction of the epoxy compound can be used at the same time. In particular, when an anhydride system curing agent is added, the curing reaction is slow as compared to the one of other curing agent such as an amine system curing agent, and thus the hardening accelerator for epoxy compounds can be often applied. The hardening accelerator for epoxy compounds can include a tertiary amine and a salt thereof, a quaternary ammonium compound, imidazole, alkali metal alkoxide, and the like.

[0034] Further, in the present invention, a silane coupling agent, a titanate coupling agent, or other surface modifying agent for the inorganic particle and elastomer particle can be further added.

[0035] The silane coupling agent enhances wetting properties between the resin and the inorganic particle, while strengthens an adhesion between the resin and the inorganic particle. The tinanate coupling agent makes a low viscosity and enhances the mechanical properties of the hardened material. Additionally, a device for mixing is not limited, provided that the device can mix a liquid to be treated, strongly providing to the liquid a shearing force and/or a load for stretching. For example, a rotary and revolutionary type of mixer, a homogenizer, a dissolver type of mixer, a homomixer, a ball mill, or a triple roll mill can be used.

[0036] In addition, a viscosity of the electrical insulating material manufactured according to the present invention is preferably 150 Pa · s or less at 80°C, and more preferably 20 Pa · s or less.

[0037] According to the present invention, the electrical insulating material is chiefly inpoured into a vessel such as a die, within which a site requiring an electrical insulation is disposed, to be cast into a predetermined shape. Therefore, when the resin viscosity is more than 150 Pa · s, voids are caused without the resin being inpoured in every detail to lower mechanical and/or electrical properties. Further, for the purpose of the decrease of resin viscosity, the resin, a die, a working bench, and the like are previously and preliminarily heated to approximately 80°C. On this occasion, when the resin viscosity is 20 Pa · s or less, the resin can be inpoured into a vessel such as a die, and resultantly the mechanical and/or electrical properties of the hardened material can be stably obtained.

[0038] The present invention further provides a high voltage equipment, in which said electrical insulating material according to claim 1 is applied at a site requiring an electrical insulation of an electrical equipment.
In addition, in the present invention, the electrical insulating material mentioned above can be applied to the high voltage equipment such as a transformer, a circuit breaker, a motor, or an inverter.

[0039] Hereinafter, Examples of the electrical insulating material according to the present invention, and Comparative Examples to validate the advantageous effects will be explained.

[0040]  Table 2 shows the compounding composition of epoxy resins, inorganic particles, and elastomer particles in each of Examples 1 to 3, and Comparative Examples 1 to 3. Figure 2 shows a sectional view wherein an electrical insulating material according to the present invention is applied to a transformer. Further, Tables 3 and 4 show the results of the properties evaluation of resins in Examples and Comparative Examples.

[0041] 

[Table 2] Table 2

	Epoxy resin	Elastomer particles	Core-shell rubber particles	Inorganic particles
Example 1	100	10	-	415
Example 2	100	10	-	300
Example 3	100	8	-	600
Comp. Ex. 1	100	-	-	415
Comp. Ex. 2	100	-	-	300
Comp. Ex. 3	100	-	8	600

(Example 1)

[0042] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 10 parts by weight of a radiation cross-linked acrylonitrile-butadiene rubber particles (having an average particle size of 50 to 100 nm) modified with carboxylic acid, 415 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

(Example 2)

[0043] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 10 parts by weight of a radiation cross-linked acrylonitrile-butadiene rubber particles (having an average particle size of 50 to 100 nm) modified with carboxylic acid, 300 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

(Example 3)

[0044] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 8 parts by weight of a radiation cross-linked acrylonitrile-butadiene rubber particles (having an average particle size of 50 to 100 nm) modified with carboxylic acid, 600 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

(Example 4)

[0045] An electrical insulating material according to the present invention was applied to a transformer. As shown in Fig. 2, a primary winding, a secondary winding, an interlayer isolation material, an iron core, and constituent elements thereof were molded with the electrical insulating material. In the same structure, temperature change in operation, or temperature change in transit locally causes thermal stress in the electrical insulating material, the occurrence of crack and resins breaking are inhibited due to having crack resistance properties. Furthermore, due to high thermal resistance, the resin properties at a high temperature are also excellent, and in addition to crack resistance properties, the decrease of other mechanical properties is inhibited. In addition, when impurity ions exists within the resin, in case where ion migration is caused due to moisture absorption, the progress of the migration is accelerated, which may resultantly lead to insulation breakdown. However, in the present invention, insulation properties are enhanced since impurities are lowered as compared to conventional ones. Besides, since an electrical insulating material according to the present invention is low in viscosity, even in the vicinity of a winding wire or an interlayer insulator, it can be filled with no space therebetween. As a result, insulation properties and mechanical strength become high. Accordingly, it can be applied even to a small transformer being large in thermal and electrical stress.

(Comparative Example 1)

[0046] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 415 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

(Comparative Example 2)

[0047] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 300 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

(Comparative Example 3)

[0048] To 100 parts by weight of epoxy resins (bisphenol A type and bisphenol F type), 8 parts by weight of a core-shell type of fine rubber particle (having an average particle size of 100 to 500 nm) wherein its core layer comprises butadiene rubber, 600 parts by weight of crushed silica as inorganic particles were added. Additionally an anhydride curing agent, a silane coupling agent, a titanate coupling agent, and an imidazole compound as a hardening accelerator were suitably added thereto, followed by kneading the same with the addition of a sufficient shearing force in a state of heating at 80°C. After defoaming the prepared mixed liquid, the same was cured under a heating condition of 100°C/5 hours plus 170°C/7 hours to prepare a hardened material.

[0049] Next, with respect to an electrical material according to each of Examples 1 to 3 and Comparative Examples 1 to 3, each of fracture toughness, coefficient of linear expansion, and deformation temperature was determined in the following manner.

(Measuring method of fracture toughness)

[0050] According to ASTM D5045-91, an initial crack was caused in a three-point bending test piece using a razor, and compressive load was applied thereto, so that the crack was progressed to lead to tension fracture. Then, a fracture toughness value (K_IC) was calculated from loading. The examination was carried out in room temperature, while the crosshead speed was set to be 0.5 mm/minute.

(Measuring method of coefficient of linear expansion)

[0051] The coefficient of linear expansion of the hardened material was determined using a thermomechanical analysis apparatus (TMA). The rate of temperature rise was set to be 5°C/minute. In addition, in order to remove the distortion of a hardened material, the hardened material was preheated to 160°C, and thereafter slowly cooled, followed by determination.

(Measuring method of deformation temperature)

[0052] The deformation temperature of a hardened material was determined using TMA in a similar manner. The rate of temperature rise was set to be 5°C/min. Further, in order to remove the distortion of the hardened material, the hardened material was preheated to 160°C, and thereafter slowly cooled, followed by determination.

[0053] Comparative results of fracture toughness according to Example 1 and Comparative Example 1 are shown in Table 3, while comparative results of fracture toughness, coefficient of linear expansion, and deformation temperature according to Example 2 and Comparative Example 2 are shown in Table 4. Besides, comparative results of fracture toughness according to Example 3 and Comparative Example 3 are shown in Table 5. Incidentally, the values in each Table were put into shape by being normalized based on the value of each Comparative Example. With reference to these results, the specific advantageous effects of the present invention will be explained hereinafter.

[0054] [Table 3]

Table 3

	Fracture toughness
Comp. Exam. 1	1.00
Example 1	1.14

[0055] [Table 4]

Table 4

	Fracture toughness	Coefficient of linear expansion	Deformation temperature
Comp. Exam. 1	1.00	1.00	1.00
Example 1	1.56	0.97	0.96

[0056] [Table 5]

Table 5

	Fracture toughness
Comp. Exam. 3	1.00
Example 3	1.26

[0057] First of all, from Tables 3 and 4, the enhancement of fracture toughness, that is, the enhancement of crack resistance properties, and the deterioration and depression effects of the resin properties due to the mixture of elastomer particles according to the present invention can be explained. That is, according to the comparison between Example 1 of the present invention and Comparative Example 1, or the comparison between Example 2 of the present invention and Comparative Example 2, fracture toughness was drastically enhanced. This is an effect derived from the fact that elastomer particles dispersed in epoxy resin inhibit the progress of crack. Furthermore, from Table 4, it is found that even when elastomer particles were added, the decrease of the deformation temperature of the resin was inhibited to 4% or less. This is due to an effect derived from the fact that since the elastomer particles are radiation cross-linked, the resin has thermal resistance. In a similar manner, from Table 4, it is found that even when elastomer particles were added, the decrease of the coefficient of linear expansion of the resin was inhibited to 3% or less. This is due to an effect derived from the fact that since the additive amount of the elastomer particles is small, the deterioration of resin properties is inhibited to a minimum. From the above descriptions, it is understood that elastomer particles according to the present invention were used, resin properties such as thermal resistance and coefficient of linear expansion are maintained, while crack resistance properties can be enhanced.

[0058] Table 5 can explain the advantageous effect that fracture toughness is enhanced by mixing finer elastomer particles and the resin, that is, crack resistance properties are enhanced. Example 3 according to the present invention enhanced fracture toughness, that is, enhanced crack resistance properties as compared to Comparative Example 3 wherein coarser elastomer particles were used. This is an advantageous effect derived from the fact that an interacting region between the particles and the resin has been spread out by the use of the finer elastomer particles, and the enhancement effect of fracture toughness has been increased as compared with a case wherein coarser elastomer particles were used.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the sprit of the invention and the scope of the appended claims.
The above embodiments of the invention as well as the appended claims and figures show multiple characterizing features of the invention in specific combinations. The skilled person will easily be able to consider further combinations or sub-combinations of these features in order to adapt the invention as defined in the claims to his specific needs.

[Description of Reference Numerals]

[0059] 

1

electrical insulating material

2

inorganic particle

3

elastomer particle

4

primary winding

5

secondary winding

6

iron core

7

interlayer insulator

Claims

1. An electrical insulating material comprising:

an epoxy resin;

a curing agent; and

an elastomer particle (3) and an inorganic particle (3) as an additive material,

wherein at least a part of said elastomer particle (3) is radiation cross-linked.

2. The electrical insulating material according to claim 1, wherein the average particle size of said elastomer particle (3) is 500 nm or less, and said elastomer particle (3) is uniformly dispersed in said electrical insulating material.

3. The electrical insulating material according to claim 1 or 2, wherein an amount of said elastomer particle (3) added is 50 parts by weight or less relative to 100 parts by weight of said epoxy resin.

4. The electrical insulating material according to one of the preceding claims, wherein at least a part of said elastomer particle (3) comprises any one of acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, epichlorohydrin rubber, chloroprene rubber, styrene rubber, silicone rubber, fluoro rubber or butyl rubber, or a modified material thereof, or a combination thereof, and a surface or inside thereof is modified with at least one of a carboxyl group, acid anhydrides, amines or imidazoles.

5. The electrical insulating material according to one of the preceding claims, wherein at least a part of said inorganic particle (2) is at least one of silica (SiO₂), alumina (Al₂O₃), alumina hydrate, titanium oxide (TiO₂), aluminum nitride (AlN) or boron nitride (BN), and an average particle size thereof is 500 µm or less.

6. The electrical insulating material according to one of the preceding claims, wherein a surface of said inorganic particle (2) is modified with at least one selected from the group consisting of a group comprising a hydrocarbon, an acrylic group, a methacryl group, a hydroxyl group, an acid anhydride, a carboxyl group and an alkoxyl group.

7. The electrical insulating material according to one of the preceding claims, wherein an amount of said inorganic particle (2) added is from 300 to 600 parts by weight relative to 100 parts by weight of said epoxy resin.

8. The electrical insulating material according to one of the preceding claims, wherein at least a part of said curing agent comprises acid anhydride.

9. The electrical insulating material according to one of the preceding claims, wherein a silane coupling agent, a titanate coupling agent, or other surface modifying agent is further added.

10. The electrical insulating material according to one of the preceding claims, wherein a viscosity of said electrical insulating material is 150 Pa · s or less at 80°C.

11. A high voltage equipment, in which said electrical insulating material according to one of the preceding claims is applied at a site requiring an electrical insulation of an electrical equipment.

12. The high voltage equipment according to claim 11, wherein said high voltage equipment is any one of a transformer, a circuit breaker, a motor, or an inverter.

Drawing