Synergistic combination of metallic and ashless rust inhibitors to yield improved rust protection and demulsibility in dispersant-containing lubricants

[0002] This application claims the benefit of U.S. Provisional Application(s) No(s).: APPLICATION NO(S).: 60/296,916 filed Jun. 8, 2001 and 60/285,109 filed Apr. 20, 2001.

[0003] The present invention relates to industrial lubricants. More specifically the invention relates to lubricants for industrial machinery that provides improved rust protection, deposit control and demulsibility.

[0004] The art of lubricating oil formulation has become more complex with ever more stringent standards dictated by the increasing complexity of industrial equipment technology. For example, industrial oils and circulating oils such as compressor, gear, and hydraulic oils typically are required to be capable of separating from water in order that any water contamination arising during use does not adversely impact equipment operation and durability. In addition to industrial lubricants having demulsification properties, these oils are also required to be thermally and oxidatively stable in order to minimize deposit formation caused by degradation products. To further enhance deposit control performance industrial lubricants typically employ dispersants to keep deposit-forming precursors suspended in the bulk oil and away from working surfaces. Dispersants, however, tend to be effective in emulsifying water in the oil phase. Thus, additives that may enhance one property may adversely effect another property.

[0005] Another required property of industrial oils is rust inhibition.

[0006] An object of the present invention therefore is to provide an industrial lubricant that provides rust protection, deposit control and is capable of demulsifying water.

[0007] It has now been found that a specific balance of a metallic and ashless rust inhibitor and a dispersant provides improved anti-rust and demulsibility performance. Accordingly, in one embodiment, a lubricant composition is provided comprising:

[0008] (a) a lubricating oil basestock;

[0009] (b) an effective amount of a rust inhibitor additive combination consisting essentially of a metal containing rust inhibitor and an ashless rust inhibitor; and

[0010] (c) an ashless polyolefin dispersant wherein the weight ratio of dispersant to rust inhibitor additive combination is less than 1.14.

[0011] Other embodiments of the invention will become apparent from the detailed description which follows.

[0012] The lubricating oil basestock comprising a major portion of the composition of the present invention has a viscosity in the ISO 10-1500 viscosity grade range and preferably ISO 32 to 680 viscosity grade range. Individual oils meeting this viscosity requirement can be used or a mixture of oils of different viscosities can be combined. Preferably the basestock will be selected from any of the natural mineral oils of API Group II basestocks.

[0013] The lubricant composition also includes an effective amount of a rust inhibitor additive combination consisting essentially of a metal containing rust inhibitor and an ashless rust inhibitor. In the combination the metal containing rust inhibitor preferably is selected from Group 2ametal sulfonates. Indeed, the preferred metal sulfonates are calcium and barium alkylaryl sulfonates. Examples of such sulfonates include calcium dinonyl naphthalene sulfonate, barium dinonyl naphthalene sulfonate, and neutral calcium sulfonate.

[0014] The metal sulfonate typically is used in an amount in the range of about 0.20 to about 0.50 wt % based on the lubricating composition and preferably in the range of 0.20 to 0.30 wt %.

[0015] Combined with the metal sulfonate rust inhibitor is an ashless rust inhibitor. The ashless rust inhibitor preferably is an alkenyl succinimide, especially alkenyl succinimides having alkenyl groups of from about 15 to about 30 carbon atoms.

[0016] The ashless rust inhibitor typically is used in an amount in the range of from about 0.05 to about 0.30 wt % based on the lubricating composition.

[0017] The composition of the present invention includes an ashless polyolefin dispersant. Preferred polyolefin dispersants include homo- and copolymers of ethylene, propylene, butylene, isobutylene, pentene and the like. These polymer dispersants will have weight average molecular weights in the range of about 800 to about 5000 and preferably from about 2000 to about 2500. Preferably the dispersant is borated. Indeed, an especially preferred borated ashless dispersant is a borated polyisobutylene having a weight average molecular weight in the range of about 2000 to about 2500.

[0018] Unexpectedly it has been found that the weight ratio of dispersant to rust inhibitor combination should be less than 1.14 and preferably in the range of 0.55 to 1.14.

[0019] Other conventional additives which can be used in the lubricants of this invention include oxidation inhibitors, antifoam agents, viscosity index improvers, pour point depressants, and the like. These include hindered phenols, alkylated diphenyl amines, benzotriaozole derivatives, silicone oils and the like.

[0020] In general these other additives can be used in total amounts ranging from about 1.5 to 5 wt %.

[0021] A series of industrial lubricants were formulated and evaluated for rust performance and emulsion properties. The compositions and the test results are given in the Table. Referring to blends 1 to 15, it can be seen that using only a metal containing rust inhibitor with or without an ashless dispersant, unacceptable antirust performance was obtained.

[0022] Blends 16 to 18 demonstrate a need for higher levels of metal rust inhibitor to yield acceptable demulsification at higher levels of ashless dispersant.

[0023] Blends 20 through 24 showed unacceptable antirust performance of the metallic rust inhibitor at various treat levels while using a more demulsifiable lower molecular weight Mannich dispersant.

[0024] Blends 25 through 29 demonstrate some level of the metallic rust inhibitor is necessary to impart acceptable demulsibility. In the presence of ashless dispersant, a wide range of treat rates of the ashless rust inhibitor alone give poor demulsibility.

[0025] Blends 30 through 36 indicate a specific balance of combined rust inhibitor and dispersant is required to optimize antirust and demulsibility performance. The ratio of dispersant to rust inhibitor should not exceed 1.14. Results indicate a 0.8 ratio is optimal (Blend 36).