Switch and arc extinguishing material for use therein

Abstract: A switch comprising a switch case, contacts adapted to be opened and closed, an arc extinguishing chamber disposed in the vicinity of the contacts, and an arc extinguishing material capable of reducing the amount of metal particles and free carbons to be scattered from components disposed within the switch by an arc generated when the contacts are opened or closed or capable of insulating the metal particles and the free carbons to convert into an insulator, thereby inhibiting a decrease in arc resistance expected to occur upon the generation and extinction of the arc and a decrease in insulation resistance expected to occur within and around the arc extinguishing chamber and at inner wall surfaces of the switch case upon and after the extinction of the arc. The switch according to the present invention is applicable to a switch expected to generate an arc upon interruption of electric current flowing therethrough such as a circuit breaker, current-limiting device or electromagnetic contactor and is capable of immediately extinguishing the arc and inhibiting the decrease in insulation resistance within and around the arc extinguishing chamber and at inner wall surfaces of the switch case.

Description: The present invention relates to an arc extinguishing material according to the preamble of claim 1, and more particularly to an arc extinguishing material capable of immediately extinguishing the arc and inhibiting a decrease in insulation resistance within and around an arc extinguishing chamber of the switch and at inner wall surfaces of the switch box. The invention further relates to a switch including such an arc extinguishing material. Such a switch could be a circuit breaker, current-limiting device or electromagnetic contactor, which is expected to generate an arc when the current passed therethrough is interrupted. In a switch kept applied with an overcurrent or rated current, when the contact of a moving contact element is opened from the contact of a fixed contact element, an arc is generated between the two contacts. To extinguish this arc, there is used an arc extinguishing device 8 as shown in Fig. 1 having insulator-(1) 1 and insulator-(2) 2 provided around a region where arc 9 is expected to generate between the moving contact 4 (not shown) of moving contact element 3 fixed movably by axis 7 and the fixed contact 5 of fixed contact element 6. The term "contact portion" on "contact section" as used herein means a portion where the contact point 4 or 5 is located and which includes the contact point and its peripheral portion in the contact element. The insulator (1) 1 and insulator (2) 2 of the arc extinguishing device 8 generate a thermal decomposition gas owing to the arc 9, and the thermal decomposition gas cools and extinguishes the arc 9. Examples of such arc extinguishing devices include one employing an insulator comprising polymethylpentene, polybutylene or polymethyl methacrylate and 5 to 35 wt% of glass fiber included therein, one employing an insulator comprising an acrylic acid ester copolymer, aliphatic hydrocarbon resin, polyvinyl alcohol, polybutadiene, polyvinyl acetate, polyvinyl acetal, isoprene resin, ethylene-propylene rubber, ethylene-vinyl acetate copolymer or polyamide resin, and 5 to 30 wt% of glass fiber included therein, and one employing an insulator comprising a melamine resin containing at least two of ε-caprolactam, aluminum hydroxide and an epoxy resin. To realize a switch having the arc extinguishing device 8 miniaturized and exhibiting an improved current limiting or interrupting property, the provision of the insulator (1) covering a contact portion from which an arc will be generated or the insulator (2) disposed on opposite sides of the aforesaid plane or around the contact portion is effective. In this case, the arc extinguishing property of the insulators (1) and (2) is required to be enhanced. Where the moving contact element or fixed contact element is reduced in cross-sectional area as compared to the conventional one for the purpose of miniaturizing the arc extinguishing device 8, the electrical resistance thereof is increased and, hence, the temperatures of the contact portion and the periphery thereof at the time when current is being applied to the switch are raised to higher temperatures than in the conventional switch. For this reason, the insulators (1) and (2) are required to have a higher heat resistance than the conventional ones. As described above, where the width W of the insulator (2) is reduced as compared to that of the conventional one in order to miniaturize the arc extinguishing device 8, the distance between the insulator (2) and the plane including the locus of the opening or closing movement of the contact element is shortened, resulting in increase of the pressure of thermal decomposition gas to be generated from the insulator (2) by arc. Therefore, the insulators (1) and (2) are required to have a higher pressure withstand strength than the conventional ones. Further, if the distance between the aforesaid plane and the insulator (2) is shortened, the insulator (2) will be much more consumed by arc. Hence, the insulator (2) is required to have improved consumption-by-arc resistance, specifically to such a degree that a hole is not formed therein. It has been conventionally considered that the insulation failure of a switch occurring upon the generation of an arc is caused by a decrease in the electric resistance due to carbons resulting from the decomposition of an organic substance and adhering to wall surfaces of an arc extinguishing device of the switch or to the contact section of the switch. There have been proposed methods for preventing such a decrease in the electric resistance, including a method employing an organic substance that is rich in hydrogen atom as disclosed in, for example, Japanese Unexamined Patent Publication No. 310534/1988, and a method using crystal water dissociated from alumina hydrate as disclosed in Japanese Unexamined Patent Publication No. 144811/1990. Such methods, however, pose a problem of an insufficient effect in preventing the decrease in electric resistance and a problem of cracking of an organic material occurring due to rapid expansion of the crystal water. The present inventors made detailed analysis on the deposit adhering to wall surfaces and contact section within the arc extinguishing chamber of a switch. As a result, there was found the fact that a metal layer was formed from metals that were scattered from electrodes, contacts and other metal components in the vicinity thereof upon an open-close operation of the electrodes of the switch, and such a metal layer greatly influenced the decrease in electric resistance. Accordingly, the conventional method of inhibiting only the deposition of carbon was found to be incapable of satisfactory preventing the decrease in electric resistance. During generation of an arc in a switch, metal particles are scattered from the contact elements, contacts and other metal components existing adjacent the contacts in an arc extinguishing chamber and are deposited onto wall surfaces within and around the arc extinguishing chamber. When the arc extinguishing device is scaled down, however, the density of the scattered metal particles adhering to the wall surfaces within the arc extinguishing chamber is increased, so that the insulation resistance of such wall surfaces is considerably lowered. Further, if the distance between the insulator (2) 2 and the aforesaid plane is shortened, the pressure of thermal decomposition gas to be generated from the insulator (2) 2 by an arc is increased to scatter the metal particles farther than in the conventional switch, so that the insulation resistance of wall surfaces existing outside the arc extinguishing chamber is also considerably lowered. Such scattered metal particles may reach and adhere to the inner wall of the switch box. As described above, with the miniaturization of the arc extinguising device 8, the metal scattered and deposited on wall surfaces within and around the arc extinguishing chamber causes the insulation resistance of the wall surfaces to be considerably decreased. Accordingly, it is required to insulate the metal particles to be scattered from metal components existing within the arc extinguishing chamber at the time of arc generation to prevent the decrease in the insulation resistance of the wall surfaces attributable to a metal layer formed of such deposited metal particles. According to the document DE-A-1105028 there is disclosed an arc extinguishing material according to the preamble claim 1. This document discloses, in particular, a composition comprising a thermosetting resin and further heat resistant compounds which behave passively even under the influence of an arc. Another kind of material disclosed in this reference relates to a composition which generate a gas capable of avoiding the deposition of metal or of carbon particles. This composition may include different inorganic substances which, when degraded, serve for resource of generating water steam. As a material for the preparation of isolating inserts in a switch, inorganic non-carbonaceous compounds can be used. The object of the present invention is to provide an improved arc extinguishing material, capable of immediately extinguishing the arc. There is also to be provided a switch including such a arc extinguishing material capable of immediately extinguishing the arc and inhibiting a decrease in insulation resistance within and around an arc extinguishing chamber of the switch and at inner wall surfaces of a switch box. The object of the invention is achieved by the combination of the features defined in claim 1. Preferable embodiments of the arc extinguishing material according to the invention and a switch including said material, are set forth in claims 2 to 12. In the following the invention is further illustrated by examples with reference to the accompanying drawings. Fig. 1 is a perspective view of a conventional arc extinguishing device for illustrating an arc generation state; Fig. 2-1 is a partially cutaway perspective view showing an embodiment of an arc extinguishing chamber in which a gas generating source material is disposed in a switch to which an insulating method according to the present invention is applied and used; Fig. 2-2 is a side view showing the closed state of the contacts in the arc extinguishing chamber shown in Fig. 2-1; Fig. 2-3 is a side view showing the opened state of the contacts in the arc extinguishing chamber shown in Fig. 2-1; Fig. 2-4 is a plan view of the arc extinguishing chamber shown in Fig. 2-1; Fig. 2-5 is a partially cutaway explanatory view showing an experimental device used in Examples 2-1 to 2-27 and Comparative Examples 2-1 and 2-2; Fig. 2-6 is a side view showing the closed condition of one embodiment of a switch which includes an arc extinguishing device using one example of a gas generating source material comprising an organic binder and a gas generating source compound according to the present invention; Fig. 2-7 is a side view showing the opened state of the arc extinguishing device shown in Fig. 2-6; Fig. 2-8 is a schematic explanatory view showing one example of a switch of three-phase configuration using the arc extinguishing device shown in Fig. 2-6; Fig. 2-9 is a sectional view of the switch taken along line A-A of Fig. 2-8 showing the closed state of the arc extinguishing device; Fig. 2-10 is a sectional view of the switch taken along line A-A of Fig. 2-8 showing the closed state of the arc extinguishing device; Fig. 2-11 is a graphic representation showing an infrared absorption spectrum of the deposit in the arc extinguishing device of Example 2-29; Fig. 2-12 is a graphic representation showing an infrared absorption spectrum of the deposit in the arc extinguishing device of Example 2-42; Fig. 2-13 is a graphic representation showing an infrared absorption spectrum of the deposit in the arc extinguishing device of Comparative Example 2-3; A gas generating source material namely the arc extinguishing material, of the present invention contains a gas generating source compound which is capable of generating an insulation imparting gas combinable with metal particles scattered from the electrodes, contacts and other metal components of a switch by an arc generated when the contacts are operated to be opened or closed. According to the present invention, when an arc is generated upon an opening or closing operation of the respective contacts of electrodes of a switch, the gas generating source compound is caused to generate an insulation imparting gas which is combinable with metal particles that are scattered from the electrodes, contacts and other metal components in the vicinity thereof by the arc. Therefore the scattered metal particles are insulated. The switch of the present invention includes such gas generating source material provided in the vicinity of the electrodes, contacts and neighboring other metal components, and therefore makes it possible to insulate scattered metal particles or the like. The gas generating source material, namely the arc extinguishing material, of the present invention comprises the aforementioned gas generating source compound or a combination of the gas generating source compound and a binder. The gas generating source compound generates gases such as H 2 O, O 2 , atomic oxygen, oxygen ion and oxygen plasma when subjected to heat caused by arc. These gases convert the metallic substances into a metal oxide or metal hydroxide so as to reduce the amount of an electroconductive substance. The present invention uses a compound such as a hydroxide, hydrate or oxide which is easy to generate H 2 O, O 2 , atomic oxygen, oxygen ion and oxygen plasma when subjected to arc and, hence, a reaction for insulating the aforementioned scattered metal particles is easy to occur. Thus, it is possible to advantageouly reduce the amount of an electroconductive substance. In the present invention, the term "metallic substances", "metals" or "metal particles" as used herein is meant to include, for example, a sublimated metal vapor, molten metal droplet, metal particulate, metal ion (metal plasma), which are possible to be scattered from the electrodes, contacts and other metal components of a switch located in the vicinity thereof by an arc which generate upon an opening or closing operation of the contacts. In the present invention, the process of insulating the aforementioned metal particles scattered from the metal components of a switch with use of the insulation imparting gas scattered from the gas generating source compound is assumed to proceed in the following manner. First, an arc is generated between the contacts of the electrodes in an arc extinguishing chamber of a switch when the contacts are operated to be opened or closed. The arc usually generates heat of about 4000° to about 6000°C, which in turn heats up the electrodes, contacts and other metal components located in the vicinity thereof to cause them to scatter metal particles therefrom. Subsequently, the gas generating source compound provided in the vicinity of the electrodes, contacts and other metal components is heated by the arc as well as by the scattered metal particles to scatteredly generate the insulation imparting gas. In the present invention, the insulation imparting gas is meant by a gas which is generated from the aforementioned gas generating source compound and possesses a characteristic of combining with the metal particles so as to insulate the same. In the present invention, the expression "the insulation imparting gas combinable with the scattered metal particles" or a like expression is meant to include the case where the insulation imparting gas reacts with the scattered metals, the case where the insulation imparting gas adheres to the surface of each metal particle, and the case where the insulation imparting gas intervenes between metal particles. The insulation imparting gas for insulating the metal particles is roughly divided into the type which is reactive with the metals and the type which is, per se, electrically insulative. Where there is generated the gas which is reactive with the metals, the gas reacts with the metals, and the reaction product together with the unreacted gas generating source compound is scattered and deposited around the electrodes and contacts as an insulator. On the other hand, where there is generated the gas which is, per se, electrically insulative, such gas adheres onto the scattered metal particles to form an insulative layer on the surface of each particle, or particulates of the gas intervene between metal particles to insulate these metal particles, and the metal particles thus imparted with insulation property are deposited around the electrodes and contacts to form an insulative layer. Thus, in either case the scattered metal particles, which have conventionally being greatly influencing a decrease in electric resistance, are insulated thereby inhibiting the decrease in electric resistance, hence the occurrence of insulation failure due to arc. It should be noted that when the metal particles being forcibly scattered from the electrodes, contacts and other metal components by arc are insulated, the insulation imparting gas generated by arc is prevented from approaching the contacts by an expanding high pressure metal vapor, whereby an insulative layer containing metal particles is not formed on the contacts and, hence, the electroconductivity of the contacts is not affected. As described above, gas generating source compounds for use in the present invention include those compounds which are each adapted to generate a gas that is reactive mainly with metals and those compounds which are each adapted to generate a gas that is, per se, electrically insulative. Preferable compounds of the former type include, for instance, a metal peroxide, a metal hydroxide, a metal hydrate, a metal alkoxide hydrolysate, a metal carbonate, a metal sulfate, a metal sulfide, a metal fluoride and a fluorine-containing silicate. These compounds offer a great insulation imparting effect. Representative examples of the metal peroxides are calcium peroxide (CaO 2 ), barium peroxide (BaO 2 ) and magnesium peroxide (MgO 2 ). Representative examples of the metal hydroxides are zinc hydroxide (Zn(OH) 2 ), aluminum hydroxide (Al(OH) 3 ), calcium hydroxide (Ca(OH) 2 ), barium hydroxide (Ba(OH) 2 ) and magnesium hydroxide (Mg(OH) 2 ). Aluminum hydroxide and magnesium hydroxide are preferred in view of the quantity of the gas generated by thermal decomposition. Of these, magnesium hydroxide is more preferable in view of its effect in insulating metal particles. Representative examples of the metal hydrates are barium octohydrate (Ba(OH) 2 ·8H 2 O), magnesium phosphate· octohydrate (Mg(PO 4 ) 2 · 8H 2 O), alumina hydrate (Al 2 O 3 · 3H 2 O), zinc borate (2ZnO· 3B 2 O 3 · 3.5H 2 O) and ammonium borate ((NH 4 ) 2 O· 5B 2 O 3 · 8H 2 O). Among these, alumina hydrate is preferred in view of its metal insulating effect. Representative examples of the metal alkoxide hydrolysates are silicon ethoxide hydrolysate (Si(OC 2 H 5 ) 4-x (OH) x , where x is an integer of 1 to 3), silicon methoxide hydrolysate (Si(OCH 3 ) 4-x (OH) x , where x is the same as above), barium ethoxide hydrolysate (Ba(OC 2 H 5 )(OH)), aluminum ethoxide hydrolysate (Al(OC 2 H 5 ) 3-y (OH) y , where y is 1 or 2), aluminum butoxide hydrolysate (Al(OC 4 H 9 ) 3-y (OH) y , where y is the same as above), zirconium methoxide hydrolysate (Zr(OCH 3 ) 4-x (OH) x , where x is the same as above) and titanium methoxide hydrolysate (Ti(OCH 3 ) 4-x (OH) x , where x is the same as above). Among these, silicon ethoxide is preferred in view of its metal insulating effect. Representative examples of the metal carbonates are calcium carbonate (CaCO 3 ), barium carbonate (BaCO 3 ), magnesium carbonate (MgCO 3 ) and dolomite (CaMg(CO 3 ) 2 ). Among these, calcium carbonate and magnesium carbonate are preferred in view of their metal insulating effect. Representative examples of the metal sulfates are aluminum sulfate (Al 2 (SO 4 ) 3 ), calcium sulfate· dihydrate (CaSO 4 · 2H 2 O) and magnesium sulfate (MgSO 4 ·7H 2 O). Representative examples of the metal sulfides are barium sulfide (BaS) and magnesium sulfide (MgS). Of these, barium sulfide is preferred in view of its metal insulating effect. Representative examples of the metal fluorides are zinc fluoride (ZnF 2 ), iron fluoride (FeF 2 ), barium fluoride (BaF 2 ) and magnesium fluoride (MgF 2 ). Among these, zinc fluoride and magnesium fluoride are preferred in view of their metal insulating effect. Representative examples of the fluorine-containing silicates are fluorophlogopite (KMg 3 (Si 3 Al)O 10 F 2 ), fluorine-containing tetrasilicate mica (KMg 2.5 Si 4 O 10 F 2 ) and litium taeniolite (KLiMg 2 Si 4 O 10 F 2 ). Among these, fluorine-containing phlogopite is preferred in view of its metal insulating effect. The foregoing gas generating compounds which are each adapted to generate a gas that is reactive mainly with metals can be used either alone or as mixtures thereof. Among these, particularly preferable are magnesium hydroxide, calcium carbonate and magnesium carbonate because these compounds each generate a gas exhibiting a great insulating effect and are less expensive. Preferable gas generating compounds of the type which mainly generate an electrically insulative gas include, for instance, a metal oxide, a compound oxide and a silicate hydrate. These compounds exhibits a great insulation imparting effect. Representative examples of the metal oxides are aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), magnesium oxide (MgO), silicon dioxide (SiO 2 ), antimony pentoxide (Sb 2 O 5 ), ammonium octamolybdate ((NH 4 ) 4 Mo 8 O 26 ). Representative examples of the compound oxides are zircon (ZrO 2 · SiO 2 ), cordierite (2MgO· 2Al 2 O 3 · 5SiO 2 ), mullite (3Al 2 O 3 ·2SiO 2 ) and wollastonite (CaO·SiO 2 ). Representative examples of the silicate hydrates are muscovite (KAl 2 (Si 3 Al)O 10 (OH) 2 ), kaoline (Al 2 (Si 2 O 5 )(OH) 4 ), talc (Mg 3 (Si 4 O 10 )(OH) 2 ) and ASTON (5MgO· 3SiO 2 · 3H 2 O). Among these, ASTON is preferred in view of its metal insulating effect and mechanical strength. These compounds of the type which generates a gas that is, per se, electrically insulative can be used either- alone or as mixtures thereof. Hydroxides, hydrates, oxides and the like have a good effect of converting the metallic substances into insulative substances. In particular, magnesium hydroxide is very easy to generate H 2 O, O 2 , atomic oxygen, oxygen ion and oxygen plasma by dehydration reaction owing to arc and is easy to cause a reaction to insulate metals and, hence, magnesium hydroxide is advantageous in reducing the amount of electroconductive substances. In the present invention, the binder contributes to improvements in moldability and mechanical strength of the gas generating source material. Such binders include inorganic binders and organic binders. The inorganic binders include, for instance, an alkali metal silicate-based binder, a phosphate-based binder, and the like. The organic binders include, for instance, a thermoplastic resin, a thermoplastic elastomer, a thermosetting resin, a rubber, an organic wax, a polymer blend, and the like. Examples of the thermoplastic resin are, for instance, polyolefins such as high density polyethylene, low density polyethylene, polypropylene and polymethyl pentene, of which are preferable the high density polyethylene, polypropylene and polymethyl pentene in view of their mechanical strength; olefin copolymers such as ethylene-vinyl alcohol copolymer and ethylene-vinyl acetate copolymer, of which is preferable the ethylene-vinyl alcohol copolymer in view of its mechanical strength; general purpose plastics such as polystyrene and polyvinyl chloride; and polyamides such as nylon 6, nylon 12 and nylon 66, of which are preferable nylon 6 and nylon 12 because they provide for easy filling. Examples of the thermoplastic elastomer are, for instance, a polyolefin thermoplastic elastomer, polyurethane thermoplastic elastomer and polyamide thermoplastic elastomer, of which are preferable the polyolefin thermoplastic elastomer and polyamide thermoplastic elastomer because they provide for easy filling and a high mechanical strength. Examples of the thermosetting resin are, for instance, a bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, biphenyl epoxy resin, unsaturated polyester, melamine resin and urea resin, of which are preferable the bisphenol F-type epoxy resin, biphenyl epoxy resin and melamine resin because they provide for easy filling and great metal insulating effect. Examples of the rubber are, for instance, an ethylene-propylene rubber, isoprene rubber and Neoprene rubber, of which are preferable the ethylene-propylene rubber because it provides for easy filling. Examples of the organic wax are, for instance, a paraffin wax and microcrystalline wax, of which is preferable the paraffin wax because it is inexpensive and provides for easy filling. Examples of the polymer blend are, for instance, blends of two or more polymers selected from the foregoing resins, elastomers and rubbers, specifically a blend of a polyamide and a polyolefin, that of a polyamide and a thermoplastic elastomer, that of a polyamide and a rubber, and that of a polyamide and a thermosetting resin, of which are preferable the blend of a polyamide and a polyolefin because they provide for easy filling and a high mechanical strength. Examples of the aforementioned reinforcing filler are, for instance, a glass fiber material, glass beads and ceramic fiber material. The glass fiber is preferred from the viewpoint of its reinforcing effect and low price. The gas generating source material of the present invention can be in any form without particular limitations, for example, in the form of powder, molded product or a supported material in which the gas generating source compound is supported by a carrier. Where the gas generating source compound is in the form of powder, the average particle diameter thereof is not particularly limited. However, if there are taken into consideration the moldability, adhesion to the carrier, mixability in a medium to be described later, and cost, preferable particle diameter of the powder is usually about 0.3 to about 30 µm in the case of the metal peroxide, metal oxide or compound oxide, usually about 0.6 to about 40 µm in the case of the metal hydroxide, metal hydrate, metal alkoxide hydrolysate or silicate hydrate, usually about 3 to about 20 µm in the case of the metal carbonate, usually about 6 to about 40 µm in the case of the metal sulfate, usually about 0.6 to about 40 µm in the case of the metal sulfide, or usually about 0.3 to about 20 µm in the case of the metal fluoride or fluorine-containing silicate. If the gas generating source compound in the form of powder is provided in the vicinity of the electrodes, contacts and neighboring other metal components, the amount of the powder is preferably to such an extent as to generate a sufficient amount of the insulation imparting gas to insulate the scattered metal particles, though such amount cannot be unconditionally determined because it depends on the kind of the gas generating compound, the dimensions of an arc extinguishing chamber in a switch, or a like factor. Where the arc extinguishing chamber is of the dimensions: about 20 mm long x about 50 mm wide x about 20 mm high x about 2 mm thick, the amount of the powder to be used is preferably about 0.4 g or greater. Where the gas generating source compound is in the form of a molded product for use as the gas generating source material, the gas generating source compound in the form of, for example, powder may be molded by, for example, press molding. Although the size of such a molded product differs depending on, for example, the kind of the gas generating compound and the size of the arc extinguishing chamber in a switch and hence cannot be unconditionally determined, the size of the molded product is preferably to such an extent as to generate a sufficient amount of the insulation imparting gas to insulate the scattered metal particles. To obtain such a molded product of the gas generating source material from the gas generating source compound using the organic binder, it is possible that 25 to 300 parts, preferably 40 to 100 parts of the binder and 100 parts of the gas generating source compound are homogeneously mixed using a roll kneader or extrusion kneader, and then the resulting mixture is molded using an injection molding machine or press molding machine. If the proportion of the binder is less than 25 parts, the kneadability and moldability of the mixture tend to degrade, whereas if it exceeds 300 parts, the metal insulating effect of the molded product tends to become poor. The molded product should have such a strength as to withstand a rise in pressure due to generation of an arc. Where the molded product is provided in the vicinity of the electrodes, contacts and neighboring other metal components, the surface area of the molded product is preferably about 50 mm 2 or larger, more preferably about 100 mm 2 or larger. Where the arc extinguishing chamber itself is formed of the molded product, the inner surface area of such a chamber is preferably about 50 mm 2 or larger, more preferably about 100 mm 2 or larger. Further, where the gas generating source material is in the form of a supported material in which the gas generating source compound is supported by a carrier, there can be preferably used as the carrier a metal material having a high melting point, porous material having a high melting point and a laminated material. Examples of such a metal material having a high melting point include tungsten, titanium alloy and stainless steel. Examples of such a porous material having a high melting point include a sintered metal, porous ceramic material, stainless steel mesh, ceramic paper, ceramic mat, ceramic blanket and electrocast metal product. The laminated material may be either inorganic or organic, and examples of such a laminated material are FRPs such as a laminated material of glass fiber in combination with a polyester resin, melamine resin or epoxy resin, and a glass-mica laminated material. The gas generating source compound can be supported by the carrier through such a coating method as roll coating, spray coating, flow coating or brush coating with use of, for example, a medium. Where the porous material having a high melting point is used as the carrier, the pores of the porous material may be filled with the gas generating source compound. If the pores of the porous material are filled with the gas generating source compound, an advantage will result such that the gas generating source compound can hardly be released from the porous material by anchoring effect. If the porous material is coated with the gas generating source compound, it is preferable to coat the entire surface of the porous material with the gas generating source compound. The aforementioned medium may be any one which allows the gas generating source compound to be dispersed therein. Examples of preferable media are fat and oil, including oils such as silicone oil and greases such as silicone grease. Although it is impossible to unconditionally determine the size of the supported material in which the gas generating source compound is supported by the carrier because the size thereof differs depending on, for example, the kind of the gas generating source compound to be used and the size of the arc extinguishing chamber in a switch as in the aforementioned molded product, the size of such gas generating source material is usually such as to generate a sufficient amount of the insulation imparting gas to insulate the scattered metal particles. If such a supported material is provided, for example, in the vicinity of the electrodes, contacts and other metal components, the surface area of the supported material is preferably about 50 mm 2 or larger, more preferably about 100 mm 2 or larger. Alternatively, if the arc extinguishing chamber itself is formed of the supported material, the gas generating source compound is supported by the carrier in the arc extinguishing chamber partially or entirely. The surface area in which the gas generating source compound is supported by the carrier is preferably about 50 mm 2 or larger, more preferably about 100 mm 2 or larger. Further, alternatively, it is possible to form a side plate of the arc extinguishing chamber from the gas generating source material. It is noted that the gas generating source material may, as required, be incorporated with a binder such as methyl cellulose or polyvinyl alcohol for an improvement in moldability and mechanical strength, or a coloring agent such as glass frit seal or ceramic color, within such a proportion range as not to affect the purpose of the present invention in addition to the aforementioned binder. The insulating method and switch employing the same according to the present invention are greatly characterized in that the gas generating source material is provided in the vicinity of the electrodes, contacts and neighboring other metal components in a switch. The location represented by "in the vicinity of the electrodes, contacts and neighboring other metal components" is herein meant by that location which enables the insulation imparting gas generated from the gas generating material to effectively insulate the scattered metal particles generated from such metal components. Although the location where the gas generating source material is to be provided differs depending on the kind of the gas generating source compound to be used in the gas generating source material, the contact gap distance in the arc extinguishing chamber of the switch in which an arc will generate and a like factor and hence cannot be unconditionally determined, the location is at least such as to permit the gas generating source compound to generate the insulation imparting gas by an arc. Preferably, such location is usually within the radius range from the contacts of about 5 to about 50 mm, more preferably about 5 to about 30 mm. Specifically, the gas generating source material is preferably provided as shown in, for example, Fig. 2-1. Fig. 2-1 is a partially cutaway schematic perspective view showing one embodiment of an arc extinguishing chamber including the gas generating source material provided therein, which chamber is used in a switch employing the insulating method of the present invention. Fig. 2-2 is a side view of the arc extinguishing chamber shown in Fig. 2-1, in which the contacts are in closed state. Fig. 2-3 is a side view of the arc extinguishing chamber shown in Fig. 2-1, in which the contacts are in opened state. Fig. 2-4 is a plan view of the arc extinguishing chamber shown in Fig. 2-1. It is to be noted that Fig. 2-1 also illustrates an arc generated between the contacts. In these figures, there are illustrated a molded product 101 of the gas generating source material, an arc extinguishing side plate 102, a moving contact element 103, a moving contact 104, a fixed contact 105, a fixed contact element 106, a pivoting center 107, and an arc 108 generated between the contacts. The molded product 101 is secured to the tip of the moving contact element 103 by, for example, a screw within the space defined by the arc extinguishing side plate 102 of the arc extinguishing chamber provided in the switch. Likewise, to the tip of the fixed contact element 106 is secured the molded product 101 on top of which is provided the fixed contact 105. When the moving contact element 103 in opened state is downwardly moved to provide a contact between the moving contact 104 and the fixed contact 105 as shown in Fig. 2-2 and is then upwardly moved to separate the moving contact 104 from the the fixed contact 105 as shown in Fig.2-3, the arc 108 is generated between the moving contact 104 and the fixed contact 105 as shown in Fig. 2-1. This arc 108 heats up the moving contact 104, fixed contact 105 and other metal components in the vicinity thereof to cause metal particles to be scattered therefrom. At the same time therewith, the molded product 101 is also heated up by the arc 108 thereby generating an insulation imparting gas. The insulation imparting gas generated from the molded product 101 serves to insulate the scattered metal particles. In the present invention, the gas generating source material may be provided as overlying the moving contact 104 and as underlying the fixed contact 105, as described above. Further, the inner surface of the arc extinguishing plate 102 shown in, for example, Fig. 2-1 may be coated with, for example, a dispersion of the gas generating source material in a medium to usually about 2 to about 150 µm thickness by roll coating, flow coating, spray coating or a like coating process, thereby using the arc extinguishing side plate comprising the supported material. Alternatively, the arc extinguishing side plate 102 itself may comprise a molded product formed from the gas generating source material. By thus insulating the scattered metal particles, it is possible to satisfactorily prevent a decrease in electric resistance upon an opening or closing operation of the contacts of the electrodes, thereby eliminating the cause of insulation failure. Although the thickness of the deposited layer resulting from the insulation of the scattered metal particle is not particularly limited, preferably such thickness is usually limited to the range of about 3 to about 20 µm so as to prevent the deposited layer from being peeled off or removed away. Further, particularly where the metal hydroxide is used as the gas generating source compound, the insulation imparting gas generated from the metal hydroxide reacts with the scattered metal particles to insulate them and, hence, the resulting deposited layer preferably has a thickness of about 5 to about 15 µm when the arc resistant property of the deposited layer is taken into account. The switch according to the present invention includes the arc extinguishing chamber and the gas generating source material provided in the vicinity of the electrodes, contacts and neighboring other metal components in the arc extinguishing chamber. In such a switch the scattered metal particles produced by an arc generated between the contacts upon an opening or closing operation of the contacts are insulated by the insulation imparting gas thereby preventing the decrease in the electric resistance of the switch, hence the occurrence of insulation failure within the switch. The present invention is applicable to any kind of switch which generates an arc in the arc extinguishing chamber thereof when the contacts of the electrodes thereof are operated to be opened or closed, for example, an electromagnetic contactor, circuit breaker and current limiting device. The electrodes of such a switch are usually formed of, for example, Ag-WC alloy or Ag-CdO alloy. The insulation method of the present invention is adapted to insulate metal particles to be scattered from the electrodes, contacts and other metal components of a switch in the vicinity thereof by the generation of arc by means of an insulation imparting gas generated from the gas generating compound, thereby preventing a decrease in the electric resistance of the switch, hence the occurrence of insulation failure thereof. The gas generating source material according to the present invention contains a gas generating source compound for generating an insulation imparting gas which is capable of combining with the metal particles scattered from the electrodes, contacts and neighboring other metal components of a switch. Hence, the gas generating source material can be advantageously used in any switch which generates an arc. The switch according to the present invention is remarkably improved to prevent a decrease in the electrical resistance thereof and hence can be advantageously applied to any kind of switch which generates an arc such as an electromagnetic contactor, circuit breaker or current limiting device. The present invention will be more fully described by way of specific examples thereof. The present invention will not be limited to such examples. EXAMPLE 2-1 Barium peroxide powder (first grade chemical, average particle diameter of 6 µm) for use as a gas generating source compound was press-molded into a molded article having a diameter of 30 mm and a thickness of 6 mm. The following experiment was conducted on the molded product using an experimental device shown in Fig. 2-5 for measuring the electric resistance of a scattered deposit produced by arc and for identifying the scattered deposit. The experimental device shown comprised a cylindrical sealed container 109 and a pair of opposing electrodes 111, 111. Molded article 110 of the gas generating source material was placed just below the opposing electrodes 111, 111 and then exposed to an arc generated between the electrodes 111, 111 to give a scattered deposit, which adhered to a deposition plate 112 provided on the inside surface of a circular panel of the sealed container 109. The opposing electrodes 111, 111 each comprised 60 % of Ag and 40 % of WC and were spaced from each other by 18 mm. The electric resistance (MΩ ) of the scattered deposit was immediately measured in accordance with the measuring method for molded case circuit breakers (for practical use) described in JIS C 8370 using an insulation resistance tester (500 V portable megger described in JIS C 1301). Further, the scattered deposit was identified by measuring a peak intensity X-ray diffraction pattern of the scattered deposit in powdered condition with use of X-ray diffractometer XD-3A of SHIMADZU CORPORATION. The results were as shown in Table 2-1. If the electric resistance thus measured was 100 MΩ or higher, the insulation imparting gas generated from the gas generating source compound is considered to have exhibited the effect of inhibiting the electric resistance from lowering. Further, in the column of Table 2-1 for the results of identification of the scattered deposit there are shown principal ones of the substances in which diffraction peaks are found, with the peak intensities of the principal substances being compared using a sign of inequality. EXAMPLE 2-2 In the same manner as in Example 2-1 except that aluminum oxide powder (average particle diameter of 0.3 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-3 In the same manner as in Example 2-1 except that magnesium oxide powder (average particle diameter of 20 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-4 In the same manner as in Example 2-1 except that zircon powder (average particle diameter of 16 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-5 In the same manner as in Example 2-1 except that cordierite powder (average particle diameter of 7.5 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-6 In the same manner as in Example 2-1 except that mullite powder (average particle diameter of 4 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-7 In the same manner as in Example 2-1 except that wollastonite needle-like crystal (FPW-350, a product of Kinsei Matec Kabushiki Kaisha, average particle diameter of 20 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-8 In the same manner as in Example 2-1 except that aluminum hydroxide powder (average particle diameter of 0.8 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-9 In the same manner as in Example 2-1 except that magnesium hydroxide powder (average particle diameter of 0.6 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-10 In the same manner as in Example 2-1 except that muscovite powder (325-mesh through) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-11 In the same manner as in Example 2-1 except that talc powder (product of Nippon Talc Kabushiki Kaisha, average particle diameter of 0.6 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-12 In the same manner as in Example 2-1 except that calcium carbonate powder (average particle diameter of 0.3 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-13 In the same manner as in Example 2-1 except that magnesium carbonate powder (average particle diameter of 0.4 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2 -14 In the same manner as in Example 2-1 except that dolomite powder (average particle diameter of 2.4 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-15 In the same manner as in Example 2-1 except that magnesium sulfate powder (average particle diameter of 8 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-16 In the same manner as in Example 2-1 except that aluminum sulfate powder (average particle diameter of 6 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-17 In the same manner as in Example 2-1 except that calcium sulfate powder (pulverized calcium sulfate dihydrate, average particle diameter of 8 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-18 In the same manner as in Example 2-1 except that barium sulfide powder (first grade chemical, average particle diameter of 1 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-19 In the same manner as in Example 2-1 except that zinc fluoride powder (zinc fluoride tetrahydrate, first grade chemical, average particle diameter of 2 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-20 In the same manner as in Example 2-1 except that magnesium fluoride powder (first grade chemical, average particle diameter of 2 µm) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-21 In the same manner as in Example 2-1 except that fluorophlogopite powder treated with fluorine (synthetic phlogopite PDM-KG325 of Topy Kogyo Kabushiki Kaisha, 325-mesh through) was used as the gas generating source compound, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-22 Magnesium hydroxide powder of the same type as used in Example 2-9 for use as the gas generating source compound was contained in the proportion of 70 % in a silicone grease to form a paste, which was in turn filled into pores of a 3 mm-thick sintered metal body (copper-cadmium oxide alloy) of a size of 30 mm x 30 mm with a filling rate of 60 mg/3 cm x 3cm, to prepare a supported material. In the same manner as in Example 2-1 except that the thus prepared carrier product was used instead of the molded article, the carrier product was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-23 Magnesium hydroxide of the same type as used in Example 2-9 for use as the gas generating source compound was contained in the proportion of 50 % in ethyl alcohol to form a slurry, which was in turn applied with brush onto a one-side surface of a 5 mm-thick aluminum oxide plate of a size of 30 mm x 30 mm in such an amount as to afford a 50 µm-thick coating when dried, to prepare a supported material. In the same manner as in Example 2-1 except that the thus prepared carrier product was used instead of the molded article, the carrier product was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-24 A carrier product was prepared in the same manner as in Example 2-23 except that silicon ethoxide hydrolysate (Si(OC 2 H 5 ) 2 (OH) 2 , with ethanol contained) was used as the gas generating source compound and that a slurry containing the silicon ethoxide was applied onto an aluminum oxide plate of the same type as above by roll coating in such an amount as to afford a 20 µm-thick coating when dried. In the same manner as in Example 2-1 except that the thus prepared carrier product was used instead of the molded article, the supported material was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-25 Magnesium hydroxide of the same type as used in Example 2-9 for use as the gas generating source compound was filled into pores of a 5 mm-thick porous ceramic body mainly containing zircon-cordierite porcelain of a size of 3 mm x 3 mm with a filling rate of 120 mg/3 cm x 3cm, to prepare a supported material. In the same manner as in Example 2-1 except that the thus prepared supported material was used instead of the molded article, the carrier product was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-26 A polyester material was prepared as containing, as the gas generating source compound, 30 % of magnesium hydroxide powder of the same type as used in Example 2-9, and a glass fabric-polyester laminated body was molded as containing the polyester material with a filling rate of 30 g/30 cm x 30 cm and was processed as having a size of 30 mm x 30 mm and a thickness of 1 mm, to prepare a supported material. In the same manner as in Example 2-1 except that the thus prepared supported material was used instead of the molded article, the supported material was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. EXAMPLE 2-27 A supported material was prepared in the same manner as in Example 2-26 except for the use of a glass fabric-polyester laminated body (GLASSMER of Nikko Kasei Kabushiki Kaisha) filled with a polyester material containing 30 % of alumina hydrate powder instead of the magnesium hydroxide powder. In the same manner as in Example 2-1 except that the thus prepared supported material was used instead of the molded article, the supported material was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. COMPARATIVE EXAMPLE 2-1 In the same manner as in Example 2-1 except that instead of the barium peroxide powder was used a composition comprising, as an organic material that was free of any aromatic ring having many carbon atoms but was rich in hydrogen atom, a blend of an acrylic ester copolymer and an aliphatic hydrocarbon resin (polyethylene) (acrylic ester copolymer : polyethylene = 70 : 30 in weight ratio), and 30 % of a glass fiber material filled therein, a molded article was prepared and then exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. COMPARATIVE EXAMPLE 2-2 In the same manner as in Example 2-9 except that the molded product was disposed within the experimental device shown in Fig. 2-5 at a location adjacent the deposition plate 12 spaced by 150 mm from the opposing electrodes 111, not at a location adjacent (just below) the opposing electrodes 111, the molded article was exposed to an arc, followed by measuring the electric resistance of the resulting scattered deposit and identifying the scattered deposit. The results were as shown in Table 2-1. Gas generating source material Electric registance (MΩ ) Result of identification of scattered deposit Example 2-1 Barium peroxide >500 BaO>Ag, W 2-2 Aluminum oxide > 1000 Al 2 O 3 > Ag, W 2-3 Magnesium oxide > 2000 MgO>Ag, W 2-4 Zircon > 500 ZrO 2 ·SiO 2 , Ag 2-5 Cordierite > 500 MgO·Al 2 O 3 , Ag 2-6 Mullite >1000 3Al 2 O 3a . 2SiO 2 , Ag 2-7 Wollastonite >2000 α-CaO·SiO 2 , Ag, W 2-8 Aluminum hydroxide >5000 γ-Al 2 O 3 >Ag, W 2-9 Magnesium hydroxide ∞ MgO, Ag 2 O>Ag, W 2-10 Muscovite >500 KAℓ Si 2 O 6 , Ag, W 2-11 Talc >2000 MgO.SiO 4 , Ag, W 2-12 Calcium carbonate ∞ Ca(OH) 2 >Ag, W 2-13 Magnesium carbonate ∞ Mg(OH) 2 >Ag, W 2-14 Dolomite >5000 MgO, CaO>Ag, W 2-15 Magnesium sulfate >200 MgO< Ag 2-16 Aluminum sulfate >200 γ-Al 2 O 3 < Ag 2-17 Calcium sulfate > 100 CaO< Ag 2-18 Barium sulfide >1000 BaS, AgS, Ag, W 2-19 Zinc fluoride >2000 ZnO, AgF, Ag, W 2-20 Magnesium fluoride >2000 MgO, AgF, Ag, W 2-21 Phlogopite treated with fluorine >1000 Fluorophlogopite, AgF, Ag, W 2-22 Magnesium hydroxide (+ silicone grease) ∞ MgO, Ag 2 O>Ag, W 2-23 Magnesium hydroxide (+ ethyl alcohol) ∞ MgO, Ag 2 O>Ag, W 2-24 Silicon ethoxide hydrolysate (+ ethyl alcohol) >300 SiO 2 >Ag, W 2-25 Magnesium hydroxide (+ porous ceramic) >2000 MgO, Ag 2 O>Ag 2-26 Magnesium hydroxide (+ glass fabric-polyester lamination) >1000 MgO, Ag 2 O>Ag, W 2-27 Alumina hydrate (+ glass fabric-polyester lamination) >100 γ-Al 2 O 3 <Ag, W 2-1 - < 50 Ag, W 2-2 Magnesium hydroxide < 20 MgO « Ag, WC As can be understood from the results shown in Table 2-1, in any of Examples 2-1 to 2-27 the electric resistance measured was higher than 100 MΩ and was satisfactorily inhibited from lowering. Since the electric resistance was as high as infinity in Examples 2-9, 2-12 and 2-13 in particular, the materials used in these Examples, i.e., magnesium hydroxide, calcium carbonate and magnesium carbonate were found to generate an insulation imparting gas exhibiting a particularly great insulation imparting effect. Further, since each of the gas generating source compounds used in Examples 2-1 to 2-7 deposited together with the conductor metal, Ag or W, of the electrodes onto the deposition plate with little chemical change of itself and the peak intensity of X-ray diffraction pattern of Ag or W was lower than those of the identified oxides, these oxides (insulators) are considered to have intervened between scattered metal particles to insulate these metal particles. The gas generating source compounds used in Examples 2-8 to 2-11 and 2-24 were dehydrated into oxides. In the case of magnesium hydroxide in particular, Ag 2 O was confirmed to be produced. Since the peak intensity of X-ray diffraction pattern of each of the oxides was higher than that of Ag or W, these oxides are considered to have intervened between scattered metal particles to insulate these metal particles as in Examples 2-1 to 2-7. In Examples 2-22, 2-23, 2-25 and 2-26 also, Ag 2 O was confirmed to be produced with the aid of magnesium hydroxide, an insulator of high electric resistance was found to be formed. The gas generating source compounds used in Examples 2-12 to 2-14 were changed into oxides by decarboxylation or into hydroxides by reaction with moisture in the ambient air. Since the peak intensity of X-ray diffraction pattern of each of the oxides or hydroxides was higher than that of Ag or W, these oxides or hydroxides are considered to have intervened between scattered metal particles to insulate these metal particles. The gas generating source compounds used in Examples 2-15 to 2-17 were changed into oxides by desulfurization. Although a metal sulfide was supposed to be produced, definite identification of such a metal sulfide could not be achieved by X-ray diffraction. Since the peak intensity of X-ray diffraction pattern of Ag or W was higher than that of each of the oxides, the electric resistance of the resulting scattered deposit was relatively low, compared to other Examples. The gas generating source compound used in Example 2-18 is assumed to have decomposed at a highly elevated temperature, and AgS resulting from the reaction of the compound with Ag was identified though in a trace amount. In this Example too, the sulfide is considered to have intervened between scattered metal particles to insulate these metal particles. The gas generating source compounds used in Examples 2-19 to 2-21 are considered to have decomposed into oxides and have fluorinated Ag or W to turn it into an insulator. In Example 2-27 crystal water was dissociated from the gas generating source compound and adhered to the deposition plate together with Ag or W. Since the peak intensity of X-ray diffraction pattern of Ag or W was higher than that of the oxide, the electric resistance of the resulting scattered deposit was relatively low, compared to other Examples. On the other hand, Comparative Example 2-1 carried out a conventional method not using the gas generating source material, and the resulting scattered deposit contained Ag or W kept uninsulated and hence had a low electric resistance. In Comparative Example 2-2 magnesium hydroxide exhibiting an excellent insulation imparting effect was disposed adjacent the deposition plate significantly spaced apart from the electrodes. Unlike Example 2-9, since Ag 2 O was not produced with a small amount of MgO produced, it is not considered that the decrease in the electric resistance of the resulting scattered deposit was effectively inhibited. As can be understood from these results, as in Examples 2-1 to 2-27 the gas generating source compound for generating a highly effective insulation imparting gas is required to be disposed in such a position in the vicinity of the electrodes, contacts and other metal components located adjacent thereto as to enable the compound to generate the gas at a highly elevated temperature when exposed to an arc developed and to enable the scattered metal deposit to be insulated successfully. Next, reference is made to examples of gas generating source material comprising an organic binder and a gas generating source compound, insulating method and switch using the same according to the present invention, and also to comparative examples thereof. Fig. 2-6 illustrates in side elevation an arc extinguishing device provided in one example of a switch in closed state. There are included gas generating source material 113, moving contact element 114, moving contact 115, fixed contact 116, fixed contact element 117, and pivoting center 118 of the moving contact element. Fig. 2-7 illustrates in side elevation the arc extinguishing device of the switch shown in Fig. 2-6 in opened state and wherein same reference numerals denote same parts as above. Fig. 2-8 illustrates a switch (circuit breaker) of three-phase configuration to which the arc extinguishing device shown in Fig. 2-6 is applied. The switch includes the same parts 113 and 114 as above, power side terminals 119 including left terminal 119a, central terminal 119b and right terminal 119c, load side terminals 120 including left terminal 120a, central terminal 120b and right terminal 120c, power side terminal holes 121 including left terminal hole 121a, central terminal hole 121b and right terminal hole 121c, load side terminal holes 122 including left terminal hole 122a, central terminal hole 122b and right terminal hole 122c, handle (lever portion) 123, handle (slide portion) 124, and connecting bar 125. Fig. 2-9 is a sectional view of the switch including the arc extinguishing device in closed state taken along lines A-A of Fig. 2-8, and Fig. 2-10 is also a sectional view of the switch including the arc extinguishing device in opened state taken along lines A-A of Fig. 2-8. In Figs. 2-9 and 2-10 numerals 13 to 18, 23 and 24 denote the same parts as above. EXAMPLE 2-28 Forty parts by weight of a high density polyethylene and 60 parts by weight of magnesium hydroxide were homogeneously mixed using a kneading extruder, and the mixture was formed into a molded article having dimensions of 2 cm (length) x 2 cm (width) x 0.2 cm (thickness) using an injection molding machine to afford the gas generating source material of the present invention, followed by subjecting the material to the following test. The test was carried out in the following manner according to the measurement method for circuit breaker provided in JIS C8370. An overcurrent of three-phase 460 V/25 kA was applied to the switch in closed state shown in Fig. 2-8 and the moving contact element was opened to generate an arc current, followed by measuring the insulation resistances between load side terminals with use of an insulation resistance tester provided in JIS C1302. The results of the test were as shown in Table 2-2 where the abbreviations represent as follows: HDPE: high density polyethylene PP: polypropylene PS: polystyrene PVC: polyvinyl chloride EVOH: ethylene-vinyl alcohol copolymer EVA: ethylene-vinyl acetate copolymer PA12: nylon 12 PA6: nylon 6 TPE: thermoplastic olefin elastomer EPR: ethylene-propylene rubber GF: glass fiber EP: bisphenol A-type epoxy resin. EXAMPLES 2-29 to 2-41 In the same manner as in Example 2-28 except that each gas generating source material comprised the ingredients shown in Table 2-2 at the compounding ratio also shown in Table 2-2, gas generating source materials according to the present invention were obtained, followed by conducting the same test as in Example 2-28. The results were as shown in Table 2-2. EXAMPLES 2-42 to 2-52 In the same manner as in Example 2-28 except that each gas generating source material comprised the ingredients shown in Table 2-3, gas generating source materials according to the present invention were obtained, followed by conducting the same test as in Example 2-28. The results were as shown in Table 2-3. COMPARATIVE EXAMPLE 2-3 In the same manner as in Example 2-28 except that the gas generating source material was not used, the test was conducted. The results were as shown in Table 2-3. COMPARATIVE EXAMPLE 2-4 In the same manner as in Example 2-28 except that the gas generating source material comprised polypropylene only, the test was conducted. The results were as shown in Table 2-3. As can be readily understood from Tables 2-2 and 2-3, the use of the gas generating source material of the present invention ensured a high insulation resistance and hence inhibited the decrease in electric resistance. In particular, the gas generating source material containing 50 % or greater of Mg(OH) 2 as in Examples 2-28 to 2-31 and 2-33 to 2-44 ensured a particularly large insulation resistance. As can be understood from these results, a high filling rate of Mg(OH) 2 resulted in a high insulation imparting effect. (From the infrared absorption spectra of Figs. 2-11 and 2-12, it was confirmed that silver oxide was produced, namely silver used as the electrode material was oxidized.) In Example 2-32, though the proportion of Mg(OH) 2 was 30 % which was less than those in Examples 2-28 to 2-31 and 2-33 to 2-44, the gas generating source material provided an insulation resistance larger than those in Comparative Examples 2-3 and 2-4 and, hence, an insulation imparting effect was developed. Also, in Examples 2-45 to 2-52 the gas generating source material provided an insulation resistance larger than those in Comparative Examples 2-3 and 2-4 and, was thus confirmed to exhibit an insulation imparting effect. It should be noted that silver oxide was not produced in Comparative Example 2-3. Fig. 2-11 is a graphic representation of the infrared absorption spectrum of a deposit adhering to a wall surface of the arc extinguishing device after the test in Example 2-29. Fig. 2-12 is a graphic representation of the infrared absorption spectrum of a deposit adhering to a wall surface of the arc extinguishing device after the test in Example 2-42. Fig. 2-13 is a graphic representation of the infrared absorption spectrum of a deposit adhering to a wall surface of the arc extinguishing device after the test in Comparative Example 2-3. Silver oxide was confirmed to be produced in in Examples 2-29 and 2-42 from these figures and, hence, it can be understood that oxidation reaction of the electrode material, or silver occurred thereby inhibiting the decrease in insulation resistance. In contrast, such an oxide was not found to be produced in Comparative Example 2-3 and, hence, a large decrease in insulation resistance resulted.

Claims: An arc extinguishing material for use in a switch comprising a gas generating source compound capable of generating an insulation imparting gas combinable with particles of metals which are scattered from contact elements (103, 106), contacts (104, 105) and other metal components located adjacent thereto of the switch by an arc generated when the contacts of the contact elements are operated to be opened or closed, said insulation imparting gas being reactive with said metals or being per se electrically insulative, characterised in that said gas generating source compound is a nember selected from the group consisting of a metal peroxide, a metal hydrate excepting alumina hydrate and ammonium pentaborate, a metal alkoxide hydrolysate, a metal carbonate excepting marble, a metal sulfate excepting ammonium alum, a metal sulfide, a metal fluoride, a fluorine-containing silicate, a metal oxide, a compound oxide and a silicate hydrate. The arc extinguishing material of claim 1, which contains a thermosetting resin. The arc extinguishing material of claim 1 or 2, which is in the form of a powder, a molded article or a supported material in which said gas generating source compound is supported on a carrier selected from the group consisting of a metal material having a high melting point, a porous material having a high melting point and a laminated material. The arc extinguishing material of claim 1 or 2, wherein said thermosetting resin is a member selected from the group consisting of bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, biphenyl epoxy resin, unsaturated polyester, melamine resin and urea resin. The arc extinguishing material of claim 1 or 2, wherein said gas generating source compound is a member selected from the group consisting of calcium peroxide, barium peroxide, magnesium peroxide, silicon ethoxide hydrolysate, silicon methoxide hydrolysate, barium ethoxide hydrolysate, aluminium ethoxide hydrolysate, aluminium butoxide hydrolysate, zirconium methoxide hydrolysate, titanium methoxide hydrolysate, aluminium sulfate, calcium sulfate dihydrate, magnesium sulfate, barium sulfate, magnesium sulfide, zinc fluoride, iron fluoxide, barium fluoride, magnesium fluoride, fluorophlogopite, fluorine-containing tetrasilicate mica, lithium, taeniolite, muscovite, kaoline, talc, and aston. The arc extinguishing material of claim 1 or 2, wherein said gas generating source compound is a member selected from the group consisting of barium octohydrate, magnesium phosphate octohydrate, zinc borate, barium carbonate, magnesium carbonate, and dolomite. The arc extinguishing material of claim 1 or 2, wherein said gas generating source compound is a member selected from the group consisting of aluminium oxide, zirconium oxide, magnesium oxide, silicon dioxide, antimony pentoxide, ammonium octamolybdate, zircon, cordierite, mullite and wollastonite. The arc extinguishing material of claim 1, which contains a thermoplastic resin. The arc extinguishing material of claim 8, wherein said thermoplastic resin is a polyamide or a polyamide polymer blend. The arc extinguishing material according to one of claims 1 or 9, which is in the form of a powder, a molded article or a supported material in which said gas generating source compound is supported on a carrier selected from the group consisting of a metal material having a high melting point, a porous material having a high melting point and a laminated material. The arc extinguishing material of claim 1, which contains a reinforcing filler, and a thermoplastic or thermosetting resin. A switch comprising a fixed contact element (106) having a fixed contact (105) joined to the upper surface thereof, a moving contact element (103) having a moving contact (104) joined to the under surface thereof so as to provide electrical contact with the fixed contact, and an arc extinguishing device (102) including the arc extinguishing material of one of claims 1 to 11 provided in the vicinity of the contact elements (103, 106), contacts (104, 105) and other metal components located adjacent thereto.

Inventors: ADACHI HIROSHI, BABA FUMIAKI, FUKUYA KAZUNORI, HIROI OSAMU, KATO KAZUHARU, KATSUBE SHUNICHI, MITSUHASHI TAKAO, MURAKAMI TADAKI, NISHINA KENICHI, NISHIYAMA ITSUO, TAKAHASI MITUGU, YAMAGATA SHINJI, YAMAGUCHI SHOJI, ADACHI, HIROSHI, BABA, FUMIAKI, FUKUYA, KAZUNORI, HIROI, OSAMU, KATO, KAZUHARU, KATSUBE, SHUNICHI, MITSUHASHI, TAKAO, MURAKAMI, TADAKI, NISHINA, KENICHI, NISHIYAMA, ITSUO, TAKAHASI, MITUGU, YAMAGATA, SHINJI, YAMAGUCHI, SHOJI, ADACHI, HIROSHI, C/O MITSUBISHI DENKI K. K., BABA, FUMIAKI, C/O MITSUBISHI DENKI K. K., FUKUYA, KAZUNORI, C/O MITSUBISHI DENKI K. K., HIROI, OSAMU, C/O MITSUBISHI DENKI K. K., KATO, KAZUHARU, C/O MITSUBISHI DENKI K. K., KATSUBE, SHUNICHI, C/O MITSUBISHI DENKI K. K., MITSUHASHI, TAKAO, C/O MITSUBISHI DENKI K. K., MURAKAMI, TADAKI, C/O MITSUBISHI DENKI K. K., NISHINA, KENICHI, C/O MITSUBISHI DENKI K. K., NISHIYAMA, ITSUO, C/O MITSUBISHI DENKI K. K., TAKAHASI, MITUGU, C/O MITSUBISHI DENKI K. K., YAMAGATA, SHINJI, C/O MITSUBISHI DENKI K. K., YAMAGUCHI, SHOJI, C/O MITSUBISHI DENKI K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1995
Main classification: H01H33
IPC codes: H01H9