JPS6123239B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be applied to grease for electrical contacts, and more specifically, to base metal electrical contacts, such as copper sliding contacts. , relates to a grease for electrical contacts that allows the use of base metal contacts. Since base metals have low corrosion resistance and are easily oxidized at high temperatures, it is necessary to keep the electrical contact resistance extremely low for some types of electrical contacts. Although expensive metals such as high melting point metals are used, it would be highly desirable from the standpoint of resource and energy conservation if these could be replaced with base metals. On the other hand, conventionally, lubricating greases have been used as lubricants for the sliding surfaces of electrical contacts, and in particular, gel-like greases made by adding fatty acid lithium soap as a thickener to base oil, and greases made by combining these with volatile solvents, Spray-applied greases are preferred because they do not disturb base metals such as copper, can be applied at relatively high temperatures, and do not create inorganics or semiconductors in the electric arc that would impair electrical contact. It is thought that if base metal contacts are given high corrosion resistance and high temperature resistance, they can be replaced with contacts made of noble metals or high melting point metals. However, when grease using such fatty acid lithium soap as a thickener is left in a high-temperature environment of 90 to 120 degrees Celsius for a long time, it becomes agglomerated and becomes hard like varnish.
They do not get crushed even when contact pressure is applied, which impedes electrical contact and also prevents them from acting as a lubricant, and also has the problem of causing noise in low current contacts. Furthermore, it is difficult to apply a uniform thickness because of the stickiness of gel-like grease, and because spray coating grease foams during application. Therefore, excess grease is carbonized by the electric arc, which causes early dielectric breakdown of switches, etc., and insufficient application causes the problem that abrasion and corrosion of the contacts cannot be sufficiently prevented. Therefore, even if conventional lubricating grease is simply applied to a base metal node, it is difficult to replace it with a contact point made of a noble metal or a high melting point metal. While conducting various studies on grease for electrical contacts, the present inventors discovered that when a specific fatty acid lithium soap is used as a thickener and a specific surfactant is blended with this, problems and drawbacks of conventional lubricating grease can be solved. The present inventors have discovered that it is possible to obtain a lubricating grease that eliminates the above problems and allows the use of base metal contacts even in fields that require contacts made of noble metals or high-melting point metals, and have completed the present invention. That is, the present invention uses a lithium soap of a fatty acid having 14 to 24 carbon atoms as a thickener, and converts a long-chain hydrocarbon group having the same number of carbon atoms as that of the fatty acid and having an unsaturated bond into a hydrophobic group. Grease for electrical contacts is prepared by blending a surfactant with an HLB of 4 to 12 and adding a volatile solvent to the surfactant. In the present invention, by blending the surfactant, it is possible to prevent the grease from clumping due to being left at high temperatures.
The adsorption and film-forming action on the contact surface is improved, and an adsorption film can be formed on the contact surface that is difficult to dissolve in water, impermeable to water and oil, and has a lower electrical resistivity than oil.
It exhibits excellent dispersion and antifoaming properties, allowing for uniform application. Furthermore, by matching the number of carbon atoms in the hydrophobic group of the surfactant and the number of carbon atoms in the fatty acid of the fatty acid lithium soap, the adsorption film formed on the contact surface exhibits excellent wear resistance. As a result, the grease for electrical contacts of the present invention forms a wear-resistant adsorption film with low electrical contact resistance that shields external corrosive factors such as water (moisture) and oxygen on base metal contact surfaces such as copper contacts. Base metal contacts can now be used for current contacts below 0.1 mA, which previously could only be satisfied with noble metal contacts. In addition, the grease for electrical contacts of the present invention can be applied uniformly to a desired thickness, and even if a portion of the formed oil film is scraped off, oil oozes out from the surrounding area and has the property of repairing the oil film. It can solve various problems caused by uneven application of grease, and exhibits excellent rust prevention and wear resistance even on base metal contacts that are prone to corrosion due to external corrosion factors, improving the reliability and durability of switches. Furthermore, the grease for electrical contacts of the present invention does not solidify even when left at a high temperature of 120°C for more than 200 hours, and even when applied to the surface of plastic molding, it does not allow oil to seep in and remains stable at the interface for a long time. Because it forms a strong oil film, it can be used as a lubricating grease not only for base metal contacts but also for plastic sliding parts of switches and control equipment that are used at high temperatures of around 120°C, as well as various other metal and plastic sliding parts. Thus, the electrical contact grease of the present invention is essentially a spray-appliable grease comprising a mixture of a base oil, the fatty acid lithium soap thickener, and the surfactant, plus a volatile solvent. The base oil used is not particularly limited,
Any commonly used oil may be used, but mineral oil-based oils such as α-olefin synthetic oil, liquid paraffin, etc. may be used in view of long-term storage stability. Further, examples of the lithium soap of a fatty acid having 14 to 24 carbon atoms used as a thickener include lithium stearate soap (lithium stearate or lithium hydroxystearate).
This is blended in the base oil and thickener mixture in an amount of 10 to 30% (weight %, same hereinafter). As a surfactant with an HLB of 4 to 12, which has the same number of carbon atoms as the fatty acid of the thickener and contains a long-chain hydrocarbon group having an unsaturated bond as a hydrophobic group, for example, carbon Sorbitan esters of unsaturated fatty acids having 14 to 24 carbon atoms (e.g. sorbitan monooleate, etc.) Phosphatidylcholine, phosphatidylethanolamine, phosphatidyl having at least one unsaturated fatty acid residue having 14 to 24 carbon atoms Examples include those containing polyhydric alcohols or derivatives thereof as hydrophilic groups, such as glycerophospholipids such as inositol and phosphatidylserine. These may be used alone or in combination of two or more, but in either case, they are selected so that the number of carbon atoms in the main hydrophobic group matches the number of carbon atoms in the fatty acid lithium soap that is the thickener. For example, soybean lecithin purified with acetone can be used as the surfactant, but this is a mixture of glycerophospholipids and its main hydrophobic group has 18 carbon atoms, and in this case, it can be used as a thickener. uses lithium stearate soap. These are blended in an amount of 0.1 to 50% based on the total amount of the base oil and thickener mixture. The volatile solvent may be commonly used trichlorotrifluoroethane or chlorofluorocarbons. The volatile solvent evaporates and is removed from the grease after application, and its amount is not particularly limited and can be selected as appropriate from a range that provides the grease with a viscosity suitable for spray application.
From the viewpoint of work hygiene, it is preferably about 10 times or less the weight of the compound. The electrical contact grease of the present invention can be prepared by mixing the desired ingredients in a conventional manner and, if desired, sealed in a pressurized spray can for spray application. Further, if desired, other additives such as antioxidants can be added to the electrical contact grease of the present invention. The electrical contact grease of the present invention can be applied to base metal electrical contacts, plastic sliding parts of switches and control equipment, other metals, plastic sliding parts, etc. in a uniform thickness and with good workability according to a conventional method. . Next, the present invention will be further explained in detail with reference to Examples and Comparative Examples. Example 1 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.6 Purified soybean lecithin 0.1 Trichlorotrifluoroethane 83.3 According to this recipe, a grease for electrical contacts for spray application was obtained by a conventional method. Example 2 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.5 Refined soybean lecithin 0.7 Trichlorotrifluoroethane 82.8 According to this recipe, a grease for electrical contacts for spray application was obtained by a conventional method. Example 3 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.6 Sorbitan monooleate 0.1 Trichlorotrifluoroethane 83.3 Grease for electrical contacts for spray application was obtained by a conventional method according to this recipe. Comparative Example 1 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.7 Trichlorotrifluoroethane 83.3 According to this recipe, a grease for spray application was obtained by a conventional method. Comparative Example 2 Ingredients Weight % Lithium stearate soap 20.0 α-olefin synthetic oil 80.0 According to this recipe, a gel-like grease was obtained by a conventional method. Comparative Example 3 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.6 Dipalmitoylphosphatidylethanolamine 0.1 Trichlorotrifluoroethane 83.3 According to this recipe, a grease for spray application was obtained by a conventional method. Comparative Example 4 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.6 Sorbitan stearate 0.1 Trichlorotrifluoroethane 83.3 Grease for spray application was obtained by a conventional method according to this recipe. Comparative Example 5 Ingredients Weight % Lithium stearate soap 3.0 α-olefin synthetic oil 13.6 Sodium oleoyl sarcosine 0.1 Trichlorotrifluoroethane 83.3 Grease for spray application was obtained by a conventional method according to this recipe. The following tests were conducted to examine the performance of the obtained grease. (1) Performance as a base metal contact grease (a) Durability under current conduction Using similar copper contact switches coated with each grease, the switch was repeatedly opened and closed at 20A, and the durability under current conduction was evaluated according to the following criteria. ○: No abnormality after 400,000 repeated opening and closing operations. △: No abnormality after 100,000 repeated opening/closing operations. ×: Does not exhibit durability after repeated opening/closing operations of 50,000 times or less. (b) High temperature stability Apply each grease to a clean copper plate and heat at 120℃.
The properties were evaluated. 〇: Neither the copper plate nor the grease changes even after being held at 120℃ for 200 hours. ×: After 24 hours at 80°C, the properties of the grease and the contact metal changed. (c) Corrosion resistance Apply each grease to a clean copper plate, 70℃, 95℃
The copper plate was kept under %RH for 72 hours and the corrosion state of the copper plate was observed. ○: The copper plate was unchanged from the one before the start of the test. ×: The copper plate was corroded brown. (2) Resin resistance Apply each grease to a standard molded product of ABS or polycarbonate, perform a stress crack test,
The reduction in critical stress was measured compared to a standard molded product without grease. 〇: No decrease in critical stress. ×: Decrease the critical stress. (3) Application performance Each grease was applied onto a copper plate using a spray gun, and its uniform application and adsorption properties were examined. ○: Can be applied uniformly without foaming, and the coating film does not change even after washing with running water for 3 hours. Δ: Can be applied uniformly, but the coating film is likely to peel off with running water. ×: Cannot be applied uniformly and the coating film is unstable. The results are shown in Table 1.

[Table] As is clear from the results, the grease for electrical contacts of the present invention does not have the problems of agglomeration and uneven application unlike conventional lubricating greases because it contains specific thickeners and surfactants. By applying the present invention to base metal contacts, base metal contacts can be used even in electrical contacts that conventionally require noble metals, high melting point metals, and the like.

Claims (1)

[Claims] 1. A lithium soap of a fatty acid having 14 to 24 carbon atoms is used as a thickener, and a long-chain hydrocarbon group having the same number of carbon atoms as the fatty acid and having an unsaturated bond is hydrophobic. Grease for electrical contacts characterized by containing a surfactant with HLB4 to 12 as a base and a volatile solvent. 2. The first surfactant contains a polyhydric alcohol or a derivative thereof as a hydrophilic group.
Grease for electrical contacts. 3. The grease for electrical contacts according to item 2 above, wherein the surfactant is a glycerophospholipid. 4. The electrical contact grease of item 3 above, which uses soybean lecithin as the glycerophospholipid. 5. The electrical contact grease of item 2 above, wherein the surfactant is a sorbitan ester. 6. The electrical contact grease of item 1 above, wherein the volatile solvent is trichlorotrifluoroethane. 7. The electrical contact grease of item 1 above, wherein the volatile solvent is a chlorofluorocarbon.