KR840001365B1 - Corona-resistant resin composition - Google Patents

Abstract

Electrical insulating system was made of corona-resistant resin and film. Thus, a coating compn. of 5-40wt.% additive selected from organo aluminate compd., organo silicate compd.,<0.1μ diameter silicone powder and<0.1μ diameter alumina powder, and synthetic resin film(vinyl resin-free) was coated on electrical conductor to make corona-resistant electrical insulation system.

Description

Corona-resistance insulation method

1 is a schematic diagram of a needle corona test apparatus for evaluating corona resistance of a resin composition prepared according to the present invention and a conventional resin composition.

The present invention relates to a method of providing an electrical insulation system using corona-resistant resins and films.

Resin compositions are generally known to be relatively low molecular weight materials which are converted to high molecular weight solids with useful properties by heating or by addition of a curing agent. Such materials are known as thermosetting materials, and other polymerizable (ie, plastic) materials are also known to be thermoplastic. Such thermoplastics are generally treated in high molecular weight states. Thermoplastics exhibit high solubility in solvents, while cured thermosetting resins are insoluble. Most thermoplastics are softened by heating and have fluidity, while thermosetting resins may be softened by heating but have no fluidity. The cured thermosetting resin and the thermoplastic film are both used as dielectrics. Thus, the term polymerizable material used in the specification and claims means both thermosetting resins and thermoplastic films.

However, the dielectric used as the insulator of the electric conductor may have a problem due to the corona discharge generated when the voltage higher than the corona starting voltage is applied to the conductor and the dielectric. This type of problem may arise, for example, when the motor is running.

Problems with corona discharge are likely to occur, particularly when the insulator is a solid organic polymer. Thus, the need for improved dielectrics resistant to corona discharge-induced degradation has greatly increased. In fact, in some cases mica-based insulation systems have been used as a solution to this problem, and mica provides resistance to corona discharge. However, due to a defect in mica's inherent physical properties, this solution was only theoretical.

Solid, corona-resistive dielectric materials are particularly needed in high voltage devices with open spaces where corona discharges can occur, the space being at least about 1 mil thick, located between the conductor and the dielectric, or This is especially necessary if there are voids in the dielectric itself. If such gaps or spaces exist in the dielectric, the service life of the dielectric is very short.

Mckeown described resins containing small amounts of organometallic compounds such as silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, iron, ruthenium or nickel as having improved corona resistance (US Patent No. 3,577,346).

It is stated here that the corona lifetime is 400 times that of the polymer without the use of organometallic additives.

However, no mention is made of the use of organosilicates or organoaluminates.

In addition, in U.S. Patent No. 3,228,883, Digiulio et al. Are single or copolymers which can be co-cured with ethylene alpha-urepin copolymers, ethylene alpha-olefin copolymers, and zinc, iron, aluminum or silicon oxides. It is described as a composition having anti-corona properties consisting of a mixture of non-absorbing inorganic fillers. The patent does not, however, state that the use of ultrafine particle size alumina or silica particles is necessary to significantly improve corona resistance.

In US Pat. No. 3,645,899, Linson described a molded epoxy resin composition containing alumina and silica with good inner and corrosion resistance, but this resin composition has no specific resistance to corona destruction.

Epoxy resins containing significant amounts of reactive organosiloxane derivatives have been described by Markovitz in US Pat. Nos. 3,469,139 and 3,519,670. However, these materials are only theoretical because of their high reactivity, which reduces the storage-period, which is one of the most important properties. In particular, amine silicones in US Pat. No. 3,469,139 are derived from bifunctional and trifunctional silicon having silicon atoms having two Si—O bonds and two Si—C bonds or two Si—C bonds and one Si—O bond. Polysiloxane produced. This is another distinction from the present invention using silicate and aluminate exhibiting tetrafunctional bonds with oxygen atoms as described below.

Epoxy resins containing up to 5% by weight of metal acetyl acetonate are described in US Pat. No. 3,812,214, but such resins do not have corona resistance.

Polymerizable resins containing silica and talc as fillers are described in U.S. Patent No. 3,742,084 to Olyphamt et al. (Patent date: June 26, 1973). However, when silica is used, it is not stated that it is important to use microparticle sized silica to obtain improved corona resistance.

In addition, US Pat. No. 4,102,851 (Luck, July 25, 1978) to Luck et al. Describes ultrafine silicon-containing resins. However, silica was added only as a thixotropic agent and no mention of corona resistance was made.

Polyethylene resins containing various fillers, including alumina and silica, are described in US Pat. No. 2,888,424 to Precopio et al. (Patent Date: May 26, 1959). However, here too, there is no mention of corona resistance, but only mechanical properties have been improved by adding fillers such as corona discharge liquid products such as carbon black.

U.S. Patent No. 3,697,467 to Haughney (patent date: October 10, 1972) also discloses ultrafine silicon-containing rubber. However, as in the patent of Luck et al., The patent mentioned nothing about corona resistance.

Accordingly, the need for corona-resistant materials that can be easily assembled for use as electrical insulators continues to emerge, and there is also a need for additives that can convert dielectrics susceptible to damage by corona discharge into corona-resistant materials.

It is therefore a primary object of the present invention to provide corona resistance resins that are useful in a variety of electrical insulation forms that can meet the urgent needs for long periods of time.

The present invention provides a corona-resistant resin composition containing from about 5 to 40% by weight of an organosilicate or organoaluminate compound or particles of alumina or silica as polymerizable materials and additives. The additives are characterized in that they typically contain aluminum or silicon, preferably aluminum and silicon combined only with oxygen atoms. Conventional resins or epoxy resins can be used in the present invention, in the case of epoxy resins can be used together with organic compounds that act as reactive curing agents. The polymerizable material also includes a thermoplastic film. The composition containing the organoaluminate or organosilicate compound is a uniform liquid composition, whereas the silica or alumina particle-containing composition is formed of particles that are almost uniformly distributed throughout the resin. The size of the silica and alumina particles is preferably less than about 0.1 micron.

Similarly, the method described above is used in a method of obtaining a corona resistive insulator for an electrical conductor.

According to the present invention, corona-resistant resins can be used to coat conductors or wires or to impregnate laminated electrical insulators, thereby obtaining excellent electrical insulation systems.

(kapton)과 같은 폴리아미드 필름 및 폴리이미드 필름이 포함된다. 이러한 필름은 고분자량 상태로 사용되며 경화제가 필요없다.Resins useful in the practice of the present invention include, for example, epoxy resins, polyester resins and ester-imide resins. The epoxy resin formed according to the present invention requires a curing agent as in the usual case of such a resin. Thermoplastic films useful in the present invention include Kapton

polyamide films and polyimide films such as kapton. These films are used in high molecular weight states and do not require a curing agent.

Representative epoxy resins that can be used are resins based on bisphenol-A diglycidyl ether, epoxy knoblac resins, cycloaliphatic epoxy resins, diglycidyl ester resins, glycidyl ethers of polyphenols, and the like. Such resins preferably have an epoxy equivalent of 130 to 1500. Such resins are well known in the art and described in various patents, including 2,324,483, 2,444,333, 2,494,295, 2,500,600 and 2,511,913.

Catalytic curing agents or curing agents for epoxy type resins include aluminum acetyl acetonates, aluminum di-butoxide acetoacetic acid mixed with phenolic accelerators and corresponding dihydroxy naphthalene compounds, including tesolcinol, catechol or hydroquinone. Ester chelates or tetra octylene glycol titanate. Compositions of this type are described in US Pat. Nos. 3,776,978 and 3,812,214. Organic aluminate catalysts may also be provided as reactive organoaluminum compounds in the present invention, but are used in much larger amounts than previously used to produce corona-resistant products.

Also useful in the practice of the present invention as a curing agent for epoxy resins are polyester-polyacid resins, particularly those having acid values of 200 to 500. Preferred of these are those having an acid value of 300 to 400.

Useful ester-imide resins, which are useful in carrying out the present invention, include resins used to coat magnetic radiation. Examples of compositions that can be used are described in US Pat. Nos. 3,426,098 and 3,697,471.

Organosilicates and organoaluminate compounds that can be used in accordance with the purpose of the present invention include compounds that are reactive with epoxy groups of the epoxy resin. These silicates and aluminate compounds are also characterized by containing only monovalent bonds of silicon-oxygen or aluminum-oxygen. These compounds are reacted to produce a transparent hard resin containing Si-O or Al-O bonds according to the following structural formula throughout the body of resin.

Representative compounds useful for this purpose are the reaction products of ethyl silicates (or all alkylsilicates) with ethanol amines or other alkanol amines, whereby amino functional organic silicate compounds are produced. Organic aluminate compounds that may be used include aluminum acetylacetonate, aluminum di-butoxide acetoacetic acid ester chelate, aluminum di-iso-propoxide acetoacetic acid ester chelate, aluminum iso-propoxide stearate acetoacetic acid Ester chelates, aluminum tri-iso-propoxide or aluminum tri (secondary-butoxide) and the like.

In the above-mentioned inventors' patent No. 3,496,139, polysiloxane was used in the preparation of a curing agent for epoxy resins. In the present invention, however, organosilicates are used. Polysiloxanes are not organosilicates in which the silicon atoms exhibit only Si—O bonds. In other words, the organosilicate of the present invention is prepared from 4-functional silicone. Epoxy resins cured with organosilicates are more suitable as corona-resistant compositions because they are more strongly crosslinked than epoxy resins cured with polysiloxanes.

Organosilicates or organoaluminates may be used alone or in combination with other known typical curing agents as the curing agent for epoxy resins. For example, when aluminum acetyl acetonate is used as an additive / curing agent, a phenolic accelerator such as catechol is required to properly cure the epoxy resin.

Preferred epoxy resins for the present invention include resins cured by organosilicate, which is a reaction product of ethyl silicate and ethanol amine, and organoaluminates, which are aluminum acetylacetonate or aluminum di-butoxide acetoacetic acid ester chelate. Included resins are cured and promoted by phenolic compounds such as catechol. Preferred polyester-imide resins include resins modified with aluminum acetylacetonate.

According to one aspect of the invention the corona-resistant composition consists of conventional epoxy or ester imide resins or other resins dispersed in alumina or silica particles having a particle size of less than about 0.1 micron.

The epoxy composition here requires in particular a curing agent to fix the resin. The curing system may be any of the catalytic curing agents conventionally used to cure conventional polyamines, polyacids, acid anhydrides or epoxy resins, or phenolic compounds such as resorcinol or catechol can be used as reactive organic aluminum. And catalytic curing agents such as organotitanium, or organozirconium compounds (double tetraoctyleneglycol titanate is representative of which are described in US Pat. Nos. 3,776,978 and 3,812,214).

:실리카) 또는 알론(Alon

:알루미나)과 데구사(Degussa)에 의해 제조·시판되고 있는 상품명 에어로실(Aerosil

:실리카) 또는 알루미늄 옥사이드 C(Aluminum Oxide C

)가 있다. 사용될 수 있는 대표적인 침강 실리카에는 필라델피아 쿼르쯔 컴패니(Philadelphia Quartz Co.)에서 제조·시판하고 있는 상품명 큐소(Quso

) 또는 피피지 인더스트리(PPG Industries)에 의해 판매되고 있는 상품명 로-벨(Lo-Vel

)이 있다.Alumina or silica preferably has a particle size of about 0.005 to about 0.05 microns, which can be obtained by gas phase hydrolysis or precipitation of the corresponding chloride or other halide. Such oxides, when distributed in the polymeric material, form chain-like particle networks. Oxide particles useful in the present invention and formed in the gas phase are also known as fuming oxides. Representative examples of commercially available fuming oxides include the trade name Cabosil manufactured and marketed by Cabot Corporation.

Silica or Alon

: Alumina and trade name Aerosil manufactured and marketed by Degussa

: Silica) or Aluminum Oxide C

There is). Representative precipitated silicas that may be used include the trade name Quso, manufactured and marketed by Philadelphia Quartz Co.

) Or trade name Lo-Vel sold by PPG Industries

There is).

In the resin composition of the present invention, about 5% by weight to about 40% by weight of organosilicate, organoaluminate, microparticulate silica, or microparticulate alumina is used, and preferably 5% by weight to about 30% by weight.

Preferred organoaluminate and organosilicate compounds are those that are water soluble and contain only Si—O or Al—O monovalent bonds to silicon or aluminum, as described above. By using these compounds, organoaluminate or organosilicate compounds can be dissolved to produce a transparent resin that is homogenized with the resin.

As can be seen from the following table, it is very important to use the ultrafine particles in the use of alumina and silica additives. Table 1 shows that the polyimide film breaks only after an average of 9 hours under the experimental conditions described herein and the voltage stress state described in the table. Obviously, using 20% dispersion of alumina with an average particle size of about 0.020 microns results in an average lifetime of 2776 hours or more. The use of 40% pulverized alumina with a particle size of 1 micron or more gives better results than without the use of additives, but much worse than with the use of ultrafine alumina.

TABLE I

"+" In the table means that the sample has not yet been destroyed when measuring the experimental results.

Similar results are obtained using polyamide films composed of microparticle alumina.

These are summarized in Table II below.

TABLE II

The particles are distributed in the film material according to conventional manufacturing methods prior to conversion to the high molecular weight state.

Similar results are obtained by using resins other than the films described above. These results are summarized in the following Tables IV-A and III-B. Except for the epoxy resin “A” without the addition of the additives listed in the table, Table III-A shows the corona test results obtained using the ultrafine alumina. Clearly, the results obtained when the additive consists of particles having a size of at least 1 micron are shown in Table III-B.

Table III-A

Table III-B

All additives in this table have a particle size greater than 1 micron.

From the above tables, it can be seen that unexpected increase in corona-resistance properties can be obtained by using microparticles of alumina and silica in the resin as well.

In another aspect, the present invention relates to a laminated electrical component containing organosilicate or organoaluminate as the binder composition. Conveniently, compositions containing organosilicates or organoaluminates can be dissolved in a solvent such as methylene chloride, benzene or methyl ethyl ketone and are impregnating agents of laminated materials such as polyester mats, ceravig, mica, glass webs, and the like. Used as

In another aspect of the present invention, the ultrafine silica or ultrafine alumina particles dispersed in the resin are used for the treatment of the laminate material wherein the resin acts as a binder. Laminate may be prepared by coating the ultrafine silica or the ultrafine alumina dispersion in a resin or a solvent between layers during lamination. Laminates have very increased resistance to corona-induced degradation and improved insulation after curing under heating and pressing under normal conditions.

In another aspect, the invention provides a conductor coated with an epoxy resin, an ester-imide resin or other resin containing a resin, i.e. organoaluminate, organosilicate, microparticulate silica or microparticulate alumina, as described above, or It's about wires. Coating by conventional methods provides a product that exhibits very increased resistance to corona-induced degradation.

In providing an insulated conductor that is resistant to corona-induced degradation using the resin composition of the present invention, the conductor may be covered with an insulating paper such as mica tape impregnated with the resin composition of the present invention.

The following examples describe in more detail the preparation of the representative compositions according to the invention and their use. The standard test conditions and apparatus described below are used in all examples described below.

The corona test device in FIG. 1 consists of a needle electrode, a planar electrode, and a dielectric sample positioned therebetween. In this test, a 2500 volt A.C voltage is applied between the needle electrode and the planar electrode at a frequency of 3000 Hz.

Sample sizes used for corona life measurements are standardized to a thickness of 30 mils (7.6 × 10 ⁻² cm). The distance between the tip of the needle electrode and the dielectric surface is 15 mils (3.8 × 10 ⁻² cm). Corona life is measured in air and / or hydrogen atmospheres. Test results for which the mean and range of data are found are based on 4 to 6 composition samples.

Example 1

(a) Test-Polyethylene Terephthalate on Conventional Thermoplastic Compositions:

Polyethylene terephthalate resin films were stacked 30 mil thick and tested in the needle electrode corona test apparatus shown and described in FIG. Samples break within 17 to 26 hours with an average break time of 21 hours.

(b) Test-Aromatic Polyimide for Conventional Resin Compositions

)은 평균 41시간후에 파괴된다.Aromatic polyimide film (Kapton under the above-mentioned conditions)

) Is destroyed after an average of 41 hours.

(c) Test-crosslinked epoxy resins for conventional resin compositions

Bisphenol A-diglycidyl ether epoxy resins having 875 to 1025 epoxide equivalents are crosslinked with a polyester-polyacid resin of acid values 340 to 360. When tested according to the method, the 30 mil film breaks after 22 hours.

Example 2

(a) Preparation of Epoxy-Reactive Organosilicates

Ethanolamine (732 g) is added to 624 mg of ethyl silicate 40 (polysilicate having an average of 5 silicon atoms per molecule). Heating the originally immiscible mixture results in a clear and homogeneous solution. After 4 hours of heating to 65 to 185 ° C., 471.2 g of liquid, mostly ethanol, are distilled from the reaction mixture. The mixture is heated at 99 to 143 ° C. for 65 minutes under 2 to 3 mm Hg pressure to remove unreacted ethanolamine (151 g is collected). Residue liquid amino-functional silicates are used as curing agents for epoxy resin compositions.

(b) Preparation and Testing of Epoxy Resin Cured by Epoxy-Reactive Silicate

A mixture is prepared from an alicyclic epoxy resin having an epoxide equivalent of 80 parts by weight of epoxy resin CY 183,147 to 161 and 20 parts by weight of the amino-functional silicate prepared in (a) above. The mixture is cured to yield a clear yellow solid. A 30 mil thick solid film is tested in the needle-shaped electrode test apparatus of Example 1 (a). Samples were destroyed after 437 to 770 hours with an average break time of 611 hours.

(c) Test on conventional epoxy-resin cured with N-aminoethyl piperazine

The average breakdown time of the epoxy resin cured with N-aminoethyl piperazine ranges from 17 hours to 3 to 23 hours.

Example 3

(a) Test on ordinary epoxide resin

The resin is obtained from a mixture of bisphenol-A epoxy resins, resorcinol and tetraoctylene glycol titanate as described in US Pat. No. 3,776,978, which is incorporated herein by reference. The 30-mil-thick resin produced was broken after an average of 25 hours in the needle electrode test, and the breaking time ranges from 18 to 32 hours.

(b) Preparation and Testing of Epoxide Resin and Ultrafine Silica Fillers

M-5, Cabot Corporation) 10.0중량부로부터 제조된다. 실리카를 침적시키지 않고 경화시킨 수지, 즉 경화된 수지는 전체에 균질하게 분산된 극미립자 실리카를 함유한다. 샘플을 바늘형 전극 장치에서 시험하면 3,900시간 이상이 지난후에도 파괴되지 않는다.The composition comprises fumed silica (Cabosil) having a particle size of about 90 parts by weight of the resin prepared in (a)

M-5, Cabot Corporation) 10.0 parts by weight. The resin cured without depositing the silica, i.e. the cured resin, contains microparticulate silica homogeneously dispersed throughout. When the sample is tested in the needle electrode device, it is not destroyed after more than 3900 hours.

(c) Preparation and Testing of Epoxide Resin and Microparticulate Silica Fillers:

G 32, Philadelphia Quartz Co.) 10.0중량부 로부터 수득된 조성물을 경화시켜 수지체를 통해 미세하게 분산된 실리카를 함유하는 생성물을 수득한다. 이 생성물은 바늘형 코로나 시험 장치에서 3,900시간 이후에도 파괴되지 않는다.90.0 parts by weight of the resin obtained in (a) and fine precipitated silica having a particle size of 0.014 microns (Quso

G 32, Philadelphia Quartz Co.) 10.0 parts by weight of the composition obtained by curing to obtain a product containing finely dispersed silica through the resin body. This product is not destroyed after 3900 hours in the needle corona test apparatus.

Example 4

(a) Tests on conventional resins cured with organoaluminates:

Epoxy resins containing metal acetyl acetonate as an epoxy resin catalytic curing agent with phenolic accelerators are described in US Pat. No. 3,812,214. Metal acetyl acetonate is limited to up to 5.0% by weight of the epoxy resin. However, the patent does not mention corona resistance. This material sample is destroyed within 40 hours in the needle test because of its low metal acetylacetonate content.

(b) Preparation and Testing of Epoxide Resin Containing Organoaluminates:

Aluminum acetylacetonate (25.0 parts by weight) and catechol (5.0 parts by weight) were dissolved in 100 parts by weight of a liquid bisphenol-A epoxy resin containing an epoxy equivalent of 180 to 188 to prepare a transparent homogeneous solution. The admixture is cured to produce a transparent solid in which the dissolved Al-O compound is uniformly dispersed. Here, Al content is 1.60 weight%. Testing of samples in the air by a needle corona test destroys the samples between an average of 930 hours and between 542 and 1360 hours. When tested in hydrogen atmospheres, the average lifetime is increased to 2457 hours.

(c) Preparation and Testing of Epoxy Resin Containing Organoaluminates:

100.0 parts by weight of the liquid bisphenol-A epoxy resin, 29.0 parts by weight of aluminum acetylacetonate and 5.0 parts by weight of catechol are cured to prepare a transparent resin. 1.80% of aluminum required in the resin in the form of Al-O compound is contained in the cured resin. In the needle electrode corona test, the average break time is 2072 hours, and the break time ranges from 1500 to 3015 hours.

(d) Preparation and Testing of Epoxy Resin Containing Organoaluminates:

25.0 g of aluminum acetylacetonate and 5.0 g of catechol are dissolved in 75.0 g of a liquid bisphenol-A diglycidyl ether resin having an epoxide equivalent of 180 to 188 to obtain a transparent resin solution. The solution is cured to obtain a transparent resin containing 1.98% Al in the form of a dissolved Al-O compound. None of the samples failed after 1850 hours in the needle corona test.

(e) Preparation and Testing of Epoxy Resin Containing Organoaluminates:

Catechol (0.5 parts by weight) and 40.0 parts by weight of aluminum di-butoxide acetoacetic acid ester chelate 3,4-epoxy-cyclohexylmethyl-3,4-epoxycyclo hexanecarboxylate epoxy having an epoxide equivalent of 131 to 143 It is dissolved in 99.5 parts by weight of epoxy resin 4221 resin. The resin is cured to yield a clear solid containing Al 2.55 in the form of a dissolved Al—O compound. In the needle electrode corona test, the breakdown time averaged 1600 hours and the breakdown time ranged from 1152 to 2045 hours.

Example 5

(a) Test on conventional epoxy resins

Samples are prepared according to the method of Example 3 (a). The breaking time is 18 to 32 hours, and the average breaking time is 25 hours.

(b) Preparation and Testing of Epoxy Resin Containing Ultrafine Alumina

, Cabot Corporation 불꽃 반응에서 염화 알루미늄을 가수분해시켜 수득하며 입자 크기는 0.03마이크론이다) 6.0g과 혼합하고 혼합물을 알루미나 입자를 침강시키지 않은채 경화시킨다. 바늘형 전극 코로나 시험에서 파괴시간은 169 내지 423시간이며, 평균 275시간이다.Epoxy resin (94.0 g) obtained according to the method of Example 3 (a) was fumed alumina (Alon

Obtained by hydrolysis of aluminum chloride in a Cabot Corporation flame reaction, with a particle size of 0.03 microns) and 6.0 g and the mixture is cured without sedimenting the alumina particles. Break time in the needle electrode corona test is 169 to 423 hours, with an average of 275 hours.

(c) Preparation and Testing of Epoxy Resin Containing Fuming Alumina

A sample is prepared from 90.0 parts by weight of the resin of Example 3 (a) and 10.0 parts by weight of fumed alumina. The alumina particles do not settle during curing. Samples are recovered unbroken after more than 5000 hours in the needle corona tester.

Example 6

(a) Preparation and Testing of Laminates-Epoxy-Immersed Polyester

A 30 mil thick laminate made from 19 layers of polyester mat and the epoxy polyester polyacid resin described in Example 1 (c) is used for the needle electrode corona test. The breakdown time is 11 to 16 hours, with an average of 14 hours.

(b) Preparation and Testing of Laminates- Epoxy Resin Containing Organoaluminates

The experiment of Example 6 (a) was carried out using a polyester mat treated first with a 20% solution of aluminum acetylacetonate in benzene, dried and treated with an epoxy-polyester polyacid resin as in (a). Repeat it. The break time of the sample is 154 to 458 hours, with an average of 278 hours.

(c) Preparation and Testing of Laminates-Epoxy-impregnated Ceramic Paper

Laminates produced by compression-curing three layers of ceramic paper (nominal thickness 15 mils) impregnated with epoxy resins described in US Pat. No. 3,812,214 have an average breakdown time of 168 hours in a corona test apparatus. This happens even though the paper consists mainly of alumina fibers.

(d) Preparation and Testing of Laminates-Ceramic Paper Impregnated with Epoxy-Organoaluminate Modified Resin

A 30 mil thick laminate was prepared from three layers of ceramic paper impregnated with the epoxy-aluminum acetylacetonate resin of Example 4 (d). None of the cured samples failed after 1700 hours.

(e) Preparation and Testing of Laminates-Ceramic Paper Impregnated with Epoxy-Combustible Alumina Compositions

Laminates of ceramic paper impregnated with a mixture of 90.0 parts by weight of epoxy-resorcinol-tetraoctylene glycol titanate and 10.0 parts by weight of fumed alumina according to Example 3 (a) were subjected to at least 3800 hours in the needle electrode corona test. It is not destroyed afterwards.

Example 7

(a) Preparation and Testing of Conventional Enameled Wire

Ester-imide enamels, such as those described in US Pat. Nos. 3,426,098 and 3,697,471, are cast on a metal plate to 7 mils thick. The needle-shaped electrode is placed on the sample so that the spacing between the needle and the enamel surface is 15 mils. Samples are taken at 2400 volts, 3000 Hz and 105 ° C. Destroy after 13 hours on average.

(b) Preparation and Testing of Organoaluminate-Modified Enamels

The ester-imide enamel modified by dissolving 20% of aluminum acetylacetonate (1.66% Al on anhydrous basis) on an enamel solid coated on a metal plate with a thickness of 7 mils was averaged after 118 hours under the same conditions as in (a) above. Destroyed.

(c) Preparation and Testing of Ultrafine Silica-Modified Enamelled Wire

The ester-imide resin modified with microparticulate silica shows an equivalent or greater improvement in corona resistance as in (a) above. The same result is obtained when ultra-fine alumina is added to the resin.

Example 8

(a) Preparation and testing of conductors covered with conventional resin

The conductor is insulated by covering a total of 13 layers around the conductor with a mica tape (resin of Example 3 (a)) containing a large amount of resin. Insulation broke after 1870 hours of testing at 190 volts / mill.

(b) Preparation and testing of conductors covered with fumed alumina between layers

Conductors covered in the same manner as in (a) above were tested under a stress of 190 to 200 volts / mill, except that 5.0% by weight of a fuming alumina dispersion in methylene chloride was applied between the layers of tape.

None of the samples failed after 5064 hours of testing.

(c) Preparation and Testing of Conductors Covered with Layers of Fine Silica

Conductors covered in the same manner as in (a) above were tested using a needle corona device at 190 to 191 volts / mill, except that 5.0% by weight dispersion of fine precipitated silica in methylene chloride was applied between the tape layers. None of the samples failed after 5064 hours of testing.

As a result of the examples and test as described above, the improvements and advantages provided by the present invention are apparent.

According to the present invention, new and improved corona-resistant insulators are prepared to contain from about 5% to about 40% of organoaluminate or organosilicate compounds, or from about 5% to about 40% of ultrafine alumina or silica. It is a substance composed of a conventional resin composition or an epoxy resin composition prepared to form an almost homogeneous dendritic dispersion.

Although the invention has been described in detail herein in accordance with its preferred embodiments, various modifications and changes can be made by the expert. Accordingly, all modifications and changes are intended to be included herein without departing from the spirit and scope of the invention.

Claims (1)

Contains about 5% to about 40% by weight of an additive selected from the group consisting of organoaluminate compounds, organosilicate compounds, silicon particles having a particle size of less than about 0.1 micron and alumina particles having a particle size of less than about 0.1 micron, vinyl At least part of the electrical conductor is covered with a polymerizable material selected from a resin and a thermoplastic film containing almost no resin, wherein the electrical conductor is corona-resistive insulated.

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