United States Patent Office Patented Jan
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3,711,407 United States Patent Office Patented Jan. 16, 1973 2 in the finished grease or during the neutralization step in 3,711,407 the Soap-making stage of grease manufacture. INCORPORATENG LITHIUM SALCYLATE OR THE The aliphatic alcohol whose ester is used in this inven LKE ENTO A GREASE tion will preferably be one whose boiling point is not so Richard J. Plumstead, Mississauga, Ontario, Canada, as high as to prevent its being driven off during the reaction, signor to Esso Research and Engineering Company, 5 Linden, N.Y. unless it is desired to have all or a portion of the alcohol No Drawing. Filed Nov. 18, 1970, Ser. No. 90,878 remain in the composition. Reaction temperatures can Int, C. C10m 5/14 range from about 150 F. to about 550 F., more usually U.S. C. 252-4 6 Claims from about 180° F. to about 380 F. In the case of greases, residual alcohol in the grease may be objection 10 able in that it may exert excessive softening characteris ABSTRACT OF THE DISCLOSURE tics. On the other hand, some softening action may actu An alkali metal salt and particularly a lithium salt ally be desirable where it is necessary to have a high of Salicylic acid or related hydroxy benzoic acid is in thickener content and cost is a secondary consideration. corporated into a lubricating oil or grease as an antioxi Generally the esters will be of C1 to about Caliphatic 15 alcohols, but preferably they will be about C to Cs dant by Saponifying an aliphatic alcohol ester of the hy aliphatic alcohols, including methanol, ethanol, propanol, droxy benzoic acid and then removing the water and isopropanol, secondary butanol, 2-methylbutanol, 2,2-di alcohol formed in the reaction. Improvements over prior methyl propanol, etc. Particularly preferred are the esters art methods include better particle size distribution and of C to Caliphatic alcohols. lower cost. 20 The hydroxy benzoates of this invention will be incor porated in the lubricant in an amount ranging from about BACKGROUND OF THE INVENTION 0.01 to about 10 wt. percent, or more usually from about This invention concerns an improved method for in 0.1 to about 5 wt. percent based on the total weight of corporating an alkali metal salt of a hydroxybenzoic acid the composition. Such as salicylic acid into a lubricant composition to im 25 The additives of the invention can be used in any of part antioxidant properties thereto. It is taught in U.S. the conventionally employed mineral lubricating oils as Pat. 2,951,808 to employ alkali metal salts of hydroxy well as in greases prepared using any of such base oils. benzoic acids as antioxidants for grease compositions. The Lubricating greases generally comprise a major propor hydroxy benzoic acids, the metal salts of which are of tion of a lubricating oil base into which has been incorpo 30 rated from about 2 to 30 weight percent, based on the concern in the present invention, have the general for total weight of the composition, of a salt, soap, or a mula: mixed-salt or soap-salt complex thickener, or a polymeric goon thickener such as polyethylene, or inorganic thickeners such as graphite, colloidal asbestos, carbon black, clays, 35 etc. Such salt and soap thickeners are generally metal R OE salts of monocarboxylic acids, such as fatty acids, al though sulfonic acids are also frequently used. The soap salt and mixed-salt thickeners are generally complex thick wherein R is hydrogen or short chain alkyl of insufficient eners which are prepared by the co-neutralization of a high length to render the salt soluble in oil, e.g. methyl. 40 molecular weight fatty acid, and/or an intermediate The hydroxy group can be in the ortho, meta, or para molecular weight fatty acid, and a low molecular weight position relative to the carboxyl group, although the fatty acid, with metal bases, generally alkali metal or ortho position is preferred, e.g. as in salicylic acid. The alkaline earth metal bases. sodium and lithium salts of salicylic acid are particu The high molecular weight fatty acids or aliphatic larly useful. 45 monocarboxylic acids useful for forming the soaps, soap Since the salts discussed above are insoluble in mineral salt complexes and mixed-salt complexes, include nat oil, it is necessary to use some method of dispersing such urally occurring or synthetic, substituted and unsubsti salts into lubricants in the form of small particles. The tuted, saturated and unsaturated, mixed or unmixed fatty prior art methods that have been used for incorporating acids having about 12 to 30, more usually 16 to 22, carbon such salts into greases include (a) co-neutralizing sali 50 atoms per molecule. Examples of such acids include cylic acid with the soap-making fatty acid during grease stearic, hydroxy stearic, such as 12-hydroxy stearic, di manufacture, (b) adding an aqueous solution of the salic hydroxy stearic, polyhydroxy stearic, and other saturated ylate salt to the grease and subsequently dehydrating hydroxy fatty acids, arachidic, oleic, ricinoleic, hydro the mixture, and (c) adding to a finished grease a pre genated fish oil acids, and tallow acids. viously formed salicylate salt that has been ground to a 55 Intermediate molecular weight fatty acids include ali fine powder of the desired particle size. Experience has phatic, saturated or unsaturated, unsubstituted, monocar shown that only the last-named method gives particles boxylic acids that contain 7 to 12 carbon atoms per mole small enough so as not to interfere with lubrication. How cule, e.g., capric, caprylic and lauric acids. ever, the required micro-grinding of the salt renders this Suitable low molecular weight acids include saturated method undesirably expensive. 60 and unsaturated, substituted and unsubstituted aliphatic DESCRIPTION OF THE INVENTION monocarboxylic acids having about 2 to 6 carbon atoms. In accordance with the present invention, it has now These acids include fatty acids such as acetic, propionic, been found that lithium salicylate and related alkali metal and similar acids, including their hydroxy derivatives such salts of hydroxybenzoic acids can be formed as extremely as lactic acid. small particles evenly dispersed throughout a lubricating 65 The metal component of the soaps, salts or soap-salt oil or grease by saponifying an aliphatic alcohol ester of complex thickeners can be any soap-forming metal such the hydroxy benzoic acid and then removing the water as aluminum, but generally is an alkali metal such as and alcohol that are formed in the reaction. The reaction lithium, potassium, or sodium; or an alkaline earth metal can be conducted in a mineral oil composition that con such as calcium, strontium, barium, or magnesium. tains a dispersant. When the salicylate salt is to be incor 70 The nature of this invention and the manner in which porated into a grease, the reaction can be conducted either it can be practiced will be better understood when refer- . 3,711,407 3 4. ence is made to the following examples, which include a Test Method 3005.3. The results obtained are shown in preferred embodiment. Table I which follows. ABLE. I.-EFECT OF INCORPORATION METEOD ON EXAMPLE 1. PARTICLE SIZE One preferred method for incorporating dilithium Particleber of size particles distribution, per cc. num of salicylate into a grease by the process of this invention is grease, microis as follows. Method of salicylate salt Over Ower. Over Over About one-third of the oil required in the finished Grease formation 300 50 90 30 grease is charged to a hot-oil-heated kettle. About 10 O A.-------- Co-neutralization in situ 3,800 8,660 ---------------- wt. percent of 12-hydroxy stearic acid based on the with fatty acid. B-------- Aqueous Solution de- 66 2,230 8,600 ------- finished composition is then charged to the kettle. This hydrated in grease. mixture is heated to about 180° F. to dissolve the acid C-------- Ball millpowdered salt.----- l, 580 5,800 ---------------- D-------- Jet millpowdered Salt------- O O 357. 1,250 in the oil. At this point, about 1.5% by wt. of lithium hy E-------- In situ fron methyl O O O droxide monohydrate dissolved in water is added. This salicylate while prepairs results in a thickening of the mixture due to the forma 5 ing grease. tion of the lithium soap. The contents are stirred for about 2 hour. After this time 3.3% of methyl salicylate It is to be noted from the data in Table I that the par is added and, after this is stirred in, another 1.7% of ticle size was undesirably large in those cases where the lithium hydroxide dissolved in water is added. The con 20 salt was formed by co-neutralizing salicylic acid in situ tents are then heated to about 300 F. during which time with the fatty acid during grease manufacture, where the the mixture is dehydrated and the methyl salicylate re salt was dispersed by adding a water solution of the salt acts with the lithium hydroxide to form dilithium salicy to the grease and then dehydrating, and where the salt late. After the addition of the methyl salicylate it may be was added to the finished grease as a powder that had desirable to add the second portion of lithium hydroxide 25 been ground in a ball mill. Jet milling involves impinging in stages so that very little free water is in the mixer at particles against a metal wall at high impact speeds, and any one time. Without this precaution the dilithium gives a finer product than when the powder is ball milled.