LUBRICATING OIL COMPOSITIONS

Abstract: A lubricating oil composition having excellent defoamability, which includes as an essential component a perfluoro ether in an amount by weight of 1-1000 ppm based on the total weight of the composition.

Description: This invention relates to lubricating oil compositions and more particularly to lubricating oil compositions which have low tendency to foaming, i.e. excellent defoamability (defoaming ability), and are utilizable as engine oils, gear oils, hydraulic oils, automatic transmission oils and bearing oils. Generally, lubricating oils are circulated through portions of an engine to be lubricated (lubricating portions) during operation of such portions and, as a result, the amount of oil uses is reduced. Therefore, the oils which have passed through the lubricating portions are then returned to a sump. Since the oils have air entrapped therein at the lubricating portions, the oils so returned ordinarily foam or bubble. If the foam in the oils is difficult to break down, it will gradually increase during the use of the oils and the oils will finally overflow the sump. Accordingly, defoamability is required in lubricating oils. Antifoaming agents, such as silicone oils and polyacrylates, have heretofore been added to base oils for the sake of improving the resulting lubricating oils in defoamability. Although silicone oils are known to be good antifoaming agents, they have comparatively high solubility in light-fraction oils and they will impart remarkably low defoamability when used in light-fraction oils. Further, the silicone oils will deteriorate when used for a long period of time, when used under severe operating conditions or when used with certain chemical materials, thereby causing the silicone oils to lose their defoamability. Polyacrylates possess inferior defoamability imparting effect. On the other hand, although perfluoro ethers are known for use as base oils for synthetic lubricating oils, in for example FR-A-2 099 935, where they are used because of their resistance to heat and oxidation at high temperatures and contain aryl group terminated perfluoroethers as stabilizers, they have never been used, as such, as minor components in lubricating oils since they are hardly soluble in other mineral oils and synthetic oils. It is also known from DD-A-213 944 that perfluoroalkanes and other organic compounds containing perfluoroalkyl(ene) groups, including ether compounds, but which compounds are not perfluoro compounds may be used as foaming inhibitors for mineral oil-based lubricating oils. It is an object of the present invention to provide a lubricating oil composition having excellent defoamability or defoaming ability which hardly drops even if the composition is used for a long period of time or under severe operating conditions. According to the present invention, there is provided a lubricating oil composition exhibiting antifoaming properties comprising as the base oil a mineral oil-based lubricating oil and/or a synthetic oil-based lubricating oil, and as an essential component a perfluoro ether in an amount by weight of 1 to 1000 ppm based on the total weight of the composition. The present inventors have made intensive studies in attempts to achieve the object mentioned above and, as the result of their studies, they found that a lubricating oil composition including a perfluoroalkyl ether has excellent defoamability. The present invention will be further explained in detail. All kinds of mineral oil and synthetic oil-based oils ordinarily used for lubricating oils are utilizable as base oils used in the lubricating oil compositions of the present invention. Examples of mineral oil-based lubricating oils for use herein are those produced by subjection of fractions obtained by atmospheric distillation or reduced pressure distillation of mineral oils, to any suitable refining treatment such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, hydrodewaxing, sulfuric acid treatment , clay treatment and hydrorefining or to any suitable combination of such refining treatments. Furthermore, examples of synthetic oil-based lubricating oils to which the perfluoroethers can be added include alpha-olefin oligomers such as normal paraffins, isoparaffins, polybutene, polyisobutylene and 1-decene oligomers; alkylbenzenes such as a monoalkylbenzenes, dialkylbenzenes and polyalkylbenzenes; alkylnaphthalenes such as monoalkylnaphthalenes, dialkylnaphthalenes and polyalkylnaphthalenes; diesters such as di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate and ditridecyl glutarate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate and pentaerythritol pelargonate; polyglycols such as polyethylene glycol, polyethylene glycol monoether, polypropylene glycol and polypropylene glycol monoether; polyphenyl ethers; tricresyl phosphate; and silicone oils. In the present invention, these oils may be used singly or jointly. The base oils mentioned above should have a viscosity at 40°C of preferably 2 to 1000 x 10 ⁻⁶m²/S. Perfluoro ethers having various chemical structures can be used as an essential component in the lubricating oil composition of the present invention. The perfluoro ethers may be any compound represented by the general formule R₁-0[R₃-0] n R₂ and may be used singly or in mixtures thereof. In this general formula, R₁ and R₂ may be identical with, or different from, each other and each represent a straight-chain or branched-chain perfluoroalkyl group having 1 to 4 carbon atoms, R₃ represents a straight-chain or branched-chain perfluoroalkylene group having 1 to 4 carbon atoms, and n is an integer of 2 or more, preferably 10 to 300. Each of R₁ and R₂ is thus selected from a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluoroisobutyl group, a perfluro-sec.butyl group and a perfluoro-tert.butyl group. Further, R₃ may be selected from a perfluoromethylene group, a perfluoroethylene group, a perfluorotrimethylene group, a perfluoropropylene group, a perfluorotetramethylene group, a perfluorobutylene group, a perfluoro-1,3-dimethylethylene group, a perfluoro 1-methyltrimethylene group, and a perfluoro 2-methyltrimethylene group. The perfluoro ether used in the present invention may contain different perfluoroalkylene groups in the molecule. In this case, the different perfluoroalkylene groups present may form a random copolymer or a block copolymer. The viscosity of the perfluoro ether used in the present invention is not particularly limited, but it is preferably in the range of 1 to 1000 x 10⁻⁵m²/s at 20°C, more preferably 20 - 2-200 x 15⁻⁵m²/s at 20°C. Further, the average molecular weight of the perfluoro ether is not particularly limited, but it is usually in the range of 500 to 50,000, preferably 1,800 to 10,000. It is important that the lubricating oil composition of the present invention include the perfluoro ether in an amount by weight of 1-1000 ppm, preferably 3-100 ppm, based on the total weight of the composition. In a case where the content of the perfluoro ether in such a lubricating oil composition is less than 1 ppm by weight, the perfluoro ether will undesirably not exert a satisfactory defoaming effect, while in a case where the content of the perfluoro ether exceeds 1000 ppm by weight in such a lubricating oil composition, the perfluoro ether may undesirably separate out from the composition. The lubricating oil compositions of the present invention may further include, as required, known additives for the purpose of further improving their properties or performance. Such additives include, for example, antioxidants, detergent-dispersants, viscosity index improvers, pour point depressants, lubricity improvers, wear resistance agents, extreme pressure agents, corrosion inhibitors, metal-deactivators, antifoaming agents apart from the perfluoro ethers mentioned above, emulsifiers, demulsifiers, bactericides and colorants. These various additives are described in detail, for example, in "Junkatsuyu Gakkaishi (Japanese Journal of Lubricating Oil Society), Vol.15, No.6", and "Sekiyuseihin Tenkazai (Additives For Petroleum Protucts" written by Toshio Sakurai and published by Saiwai Bookstore. These additives may suitably be selected depending on the purpose for which the resulting lubricating oil is used. The lubricating oil compositions of the present invention have a particular advantage in that the perfluoro ethers which are essential components of the compositions will be less deteriorated by interaction with other additives to be used therewith than the heretofore known antifoaming agents, thereby enabling a wider-range of other additives to be present. The total amount of these various additives used is ordinarily up to 50 % by weight, preferably up to 30 % by weight, based on the total weight of the composition. The lubricating oils of the present invention may be for use as engine oils such as for a four-cycle gasoline engine, a land diesel engine, a marine diesel engine and a gas engine; as turbine oil such as for an industrial turbine, a marine turbine, or a gas turbine; as gear oil such as for an automobile gear box, an industrial gear box or an automatic transmission unit; as hydraulic oil; as compressor oil; as vacuum pump oils; as refrigerator oils; as metal working oils such as for cutting, grinding, rolling, pressing, drawing, throttling-ironing and forging; as slide guiding surface oils or as bearing oils. The lubricating oil compositions of the present invention contain a certain small amount of the perfluoro ether which impart excellent behaviour to the oil composition as follows: (1) The present lubricating compositions comprising a light-fraction oil as base oil exhibit no foaming; (2) They exhibit less reduction in defoamability due to the degradation thereof, thereby reducing the oil change frequency and achieving cost reduction; and (3) They can include therein additives which have heretofore been incapable of use in lubricating oils containing silicone oils because of their degrading action on the latter. This invention will be better understood by means of the following Examples and Comparative Examples. Example 1 and Comparative Example 1 A perfluoro ether (trade name, Fomblin Y25: viscosity 2.5 x 10⁻⁴m²/s at 20°C: molecular weight: 3000: produced by Asahi Glass Co., Ltd) was added in an amount by weight of 30 ppm based on the total oil, to an industrial bearing oil used as the base oil (mineral oil-based base oil whose viscosity was 2.2 x 10⁻⁴m²/s at 40°C) to obtain a lubricating oil composition (Example 1), while a silicone oil (viscosity: 3 x 10⁻³m²/s at 25°C), was added, instead of the perfluoro ether, in an amount by weight of 30 ppm based on the total oil, to the same industrial bearing oil as in Example 1 to obtain a lubricating oil composition (Comparative Example 1). The thus obtained lubricating oil compositions were subjected to the following oxidizing test and then to the following foaming test, respectively. The test conditions are indicated below, and the results of the foaming test are indicated in Table 1. (Oxidizing Test) The oil compositions were each subjected to oxidition at 150°C for 120 hours in accordance with JIS K 2514 3.1. (Foaming Test) A foaming test was carried out on each of the oxidized oil compositions at 24°C in accordance with JIS K 2518. Example 2 and Comparative Example 2 A perfluoro ether (trade name, Fomblin Y45: viscosity, 2.5 x 10⁻⁴m²/S at 20°C: molecular weight, 3000: produced by Asahi Glass Co.,Ltd.) was added in an amount by weight of 30 ppm based on the total oil, to an automobile transmission oil as the base oil (mineral oil-based base oil whose viscosity is 1.4 x 10⁻⁵m²/S at 100°C) to obtain a lubricating oil composition (Example 2), while a polyacrylate instead of the perfluoro ether was added in an amount by weight of 200 ppm based on the total oil, to the same automobile transmission oil as in Example 2 to obtain a lubricating oil composition (Comparative Example 2). The thus obtained lubricating oil compositions were subjected to the following oxidizing test and then to the same foaming test as in Example 1, respectively. The oxidizing test conditions are indicated hereunder, and the results of the foaming test are indicated in Table 2. (Oxidizing Test) The oil compositions were each subjected to oxidation at 150°C for 100 hours in accordance with JIS K 2514 3.1.

Claims: A lubricating oil composition exhibiting antifoaming properties comprising as the base oil a mineral oil-based lubricating oil and/or a synthetic oil-based lubricating oil, and as an essential component a perfluoro ether in an amount by weight of 1 to 1000 ppm based on the total weight of the composition. A lubricating oil composition according to Claim 1, wherein, as perfluoro ether component, there is present at least one compound represented by the general formula R₁ - O (R₃ - O ) n R₂ wherein R₁ and R₂ may be identical with, or different from, each other and each represents a straight-chain perfluoroalkyl group having 1 to 4 carbon atoms or a branched-chain perfluoroalkyl group having 1 to 4 carbon atoms, R₃ is at least one group selected from straight-chain perfluoroalkylene groups having 1 to 4 carbon atoms, and branched-chain perfluoroalkylene groups having 1 to 4 carbon atoms, and n is an integer of 2 or more, preferably 10 to 300. A lubricating oil composition according to Claim 2, wherein the perfluoro ether contains different perfluoroalkylene groups as group R₃ in each molecule to form a random copolymer of a block copolymer. A lubricating oil composition according to any preceding claim, wherein the perfluoro ether has a viscosity of 1 to 1000 x 10⁻⁵m²/S at 20°C, preferably 2 - 200 x 10⁻⁵m²/S. A lubricating oil composition according to any preceding claim, wherein the perfluoro ether has an average molecular weight of 500 to 50,000, preferably 1,800 to 10,000. A lubricating oil composition according to any preceding claim, wherein the perfluoro ether is present in an amount by weight of 3 to 100 ppm based on the total weight of the composition. A lubricating oil composition according to any preceding claim comprising a mineral oil-based lubricating oil which is selected from lubricating oils produced by subjection fractions obtained by atmospheric distillation or reduced pressure distillation of mineral oils to a refining treatment which is solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, hydrodewaxing, sulfuric acid treatment, clay treatment, hydrorefining, or a combination thereof. A lubricating oil composition according to any one of Claims 1 to 6, comprising a synthetic oil-based lubricating oil which is selected from alpha-olefin oligomers, alkylbenzenes, alkylnaphthalenes, diesters, polyol esters, polyglycols, polyphenyl ethers, tricresyl phosphate and silicone oils. A lubricating oil composition according to any preceding claim, wherein the mineral oil-based lubricating oil and/or a synthetic oil-based lubricating oil has a viscosity of 2 to 1000 x 10⁻⁶m²/S at 40°C.

Inventors: IKEMOTO, YUJI, SHIRAHAMA, SHINICHI
Applicants: NIPPON OIL CO. LTD.
Application year: 1990
Main classification: C10M147
IPC codes: C10M147, C10M171, C10N40, C10N30