Abstract:
The present invention comprises a process for improving the corrosion inhibiting properties of lecithin by heating a lecithin oil composition for a period of time sufficient to produce darkening of the lecithin. An optional step further improves the corrosion inhibiting properties of the composition by combining zinc oxide with the lecithin oil prior to heating.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 07/652,112, filed Feb. 6, 1991. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to corrosion inhibitors and in particular to lecithin and associated phosphatide compounds which can be used to inhibit the corrosion of metal surfaces. 
     BACKGROUND OF THE INVENTION 
     While the term &#34;lecithin&#34; classically refers to phosphatidylcholine, in commercial parlance &#34;lecithin&#34; is understood to include the mixture of phosphatidylcholine and other phosphatides such as phosphatidylethanolamine and phosphatidylinositol with minor constituents including sterol and carbohydrate. These and other examples can be found in the Food Chemicals Codex. The most abundant source of lecithin is an oil containing concentrate which is recovered in the degumming of vegetable oils and is comprised of lecithin and associated phosphatides. This concentrate usually comprises about 60 to 65% mixed phosphatides (lecithin along with naturally occurring minor constituents) and 35 to 40% oil from the degumming process. 
     It has been known that lecithin functions as an anti-oxidant in polyunsaturated fatty oils, in mineral oils and even in gasoline. It is also known that lecithin counteracts the corrosion of metals exposed to moisture and to solvent/moisture systems. However, the level of protection previously afforded by lecithin compositions has proven to be insufficient for commercial utilization. 
     SUMMARY OF THE INVENTION 
     Briefly described, the present invention provides a heat treated lecithin compound with significantly improved anti-corrosive characteristics. Changes in the character of lecithin (when used hereafter &#34;lecithin&#34; shall refer to the mixed phosphatides) occur when lecithin is heated to temperatures in excess of 70° centigrade for a period of time, the higher the temperature, the shorter the time. Substantial darkening of lecithin indicates that these changes have occurred. 
     Our work shows that the corrosion protection properties of lecithin increase dramatically after this substantial heat darkening. We find this for soybean lecithin and even more so for corn lecithin similarly treated. We find further that the corrosion protection properties can be enhanced by adding a minor amount of zinc oxide to lecithin before the heat treatment. 
     Lecithin from other sources can, of course, be used as commercially available, for example, peanut lecithin, safflower lecithin, or rapeseed lecithin. Vegetable seed oils generally contain appreciable amounts of lecithin. 
     It is therefore an object of the present invention to provide method and product by the preparation of a corrosion inhibiting lecithin composition which may include zinc oxide. 
     Also an object of this invention is to provide anti-corrosive agents which comprise significantly heat darkened lecithin compositions to which thinning or thickening agents have been added. 
     A further object of this invention is to provide an effective method of corrosion protection for surfaces of materials subject to corrosion. 
     Another object of the present invention is to provide corrosion protection to metal surfaces, whereby the protective coating could subsequently be easily removed with a suitable solvent. 
     Other objects, features and advantages of the present invention will become apparent upon reading and understanding this specification. 
    
    
     DETAILED DESCRIPTION 
     The method of the present invention comprises the step of heating lecithin, preferably substantially in excess of about 70° centigrade, and most preferably to temperatures between 130° and 160° centigrade, to produce substantial darkening in the color of the lecithin. Experimental results show that an embodiment of the present invented method utilizing heat darkened corn lecithin provides better protection from corrosion than a heat darkened soybean lecithin embodiment of the present invented method which has a similar phosphatide content. 
     In alternate embodiments of the present invention heat darkened lecithin is applied full strength to a metal surface, or may contain an added oil or other thickening or thinning agent. The added agent will vary from a thickening agent, such as a grease, or even a finely powdered solid to a fluidizing agent, such as mineral oil or fatty oil, depending on the conditions of use. An alternate method also includes the step of mixing a small amount of zinc oxide (generally 1 to 10% by weight) with the lecithin before heating. 
     The following examples are illustrative of the present invention, and while they cover specific embodiments of the present invention, it will be readily apparent to one skilled in the art that these are given by way of explanation, not as limitation, and that numerous changes in the details may be made without departing from the spirit and scope of the invention as hereinafter claimed. 
     EXAMPLE 1 
     Comparative exposure tests were conducted by placing 3 inch by 3 inch test panels of automotive steel (R-36 Q-Panels) in a humidity-condensation tester in an inclined position, for periods of 40 to 60 days. A control panel, coated only with unmodified mineral oil (URSA P-150, made by Texaco) developed increased corrosion areas over 50% of the exposed surface area after 14 days, over 70% of the exposed surface area after 21 days, and 80% of the exposed surface area after 42 days. 
     EXAMPLE 2 
     A second control test demonstrates the protective benefits of lecithin, without heat darkening. In this test lecithin was added to the same mineral oil to form a 5% to 20% (by weight) lecithin solution. This composition was applied to test panels which were then placed in the humidity-condensation tester. After 42 days corrosion occurred over 10% to 40% of the surface area of the test panels as illustrated below. 
     
         ______________________________________Concentration of          % Surface AreasALCOLEC S in   Corroded AfterMineral Oil    42 Days of Exposure______________________________________ 5%            40%10%            20%20%            10%______________________________________ 
    
     EXAMPLE 3 
     Lecithin (ALCOLEC S soybean lecithin, as sold by American Lecithin Company, Danbury, Conn.) was heated for two hours to produce darkening, at a temperature of 160° centigrade. This heat darkened lecithin was then mixed with a mineral oil (URSA P-150) to form a 20% lecithin solution. A test panel coated with this solution was placed in a humidity-condensation tester in an inclined position for 42 days, after which only 5% of the surface area of the panel was corroded. 
     EXAMPLE 4 
     A blend of a major amount of corn lecithin, and a minor amount of soybean lecithin, heat darkened at 160° centigrade, for one hour was mixed with the same mineral oil to form a 20% lecithin solution. A test panel coated with this solution was placed in a humidity-condensation tester for 42 days, after which less than 1% of the surface area of the panel was corroded. 
     EXAMPLE 5 
     Corn lecithin heat darkened at 130° centigrade for one hour was mixed with the same mineral oil to form a 20% LECITHIN solution. A test panel coated with this solution was placed in a humidity-condensation tester for 42 days, after which 2% of the surface area of the panel was corroded. 
     EXAMPLE 6 
     Soybean lecithin was mixed with 2.5 % zinc-oxide and heat darkened at 140° centigrade for one and one-half hours, and this composition added to the same mineral oil to form a 20% lecithin concentration and coated on a test panel. The panel was placed in a humidity-condensation tester for 42 days, after which no corrosion was detectable on the surface of the panel. 
     EXAMPLE 7 
     Soybean lecithin was mixed with 2.5% zinc-oxide and heat darkened at 140° centigrade for one and one-half hours, and 10% of this composition was mixed with the same mineral oil. A test panel coated with this composition was placed in a humidity-condensation tester for 42 days, after which 5% of the surface area of the panel was corroded. 
     EXAMPLE 8 
     Soybean lecithin was mixed containing 2.5% added zinc-oxide and heat darkened at 140° centigrade for one and one-half hours, with the same mineral oil at 5% concentration. A test panel coated with this composition was placed in a humidity-condensation tester for 42 days, after which 6% of the surface area of the panel was corroded. 
     EXAMPLE 9 
     To corn lecithin was added 2.5% zinc-oxide and the mixture heat darkened at 140° centigrade for one hour, then 20% was added to a protective oil. A test panel coated with this composition was placed in a humidity-condensation tester for 42 days, after which no corrosion was detectable on the surface of the panel. 
     EXAMPLE 10 
     To corn lecithin was added 2.5% zinc-oxide and the mixture heat darkened at 140° centigrade for one hour, then 10% was added to a protective oil. A test panel coated with this solution was placed in a humidity-condensation tester for 42 days, after which less than 1% of the surface area of the panel was corroded. 
     EXAMPLE 11 
     To corn lecithin was added 2.5% zinc-oxide and the mixture heat darkened at 140° centigrade for one hour, then 5% was added to a protective oil. A test panel coated with this solution was placed in a humidity-condensation tester for 42 days, after which 3% of the surface area of the panel was corroded. 
     EXAMPLE 12 
     To corn lecithin was added 2.5% zinc-oxide and the mixture heat darkened at 140° centigrade for one hour, then 2% was added to a protective oil. A test panel coated with this solution was placed in a humidity-condensation tester for 42 days, after which 5% of the surface area of the panel was corroded. 
     It will be apparent, upon practicing the foregoing Examples 3-12, that the lecithin has been substantially heat darkened to a point where it is no longer possible to make a Gardner color reading; that is, the lecithin has been darkened to a color which exceeds the maximum Gardner Standard of 18 Gardner. The Gardner color Standards and their use are considered well known in the industry. With respect to the most preferred embodiments of the present invention, the term substantial darkening refers to this darkening of the lecithin to a color which exceeds 18 Gardner. 
     Whereas the present invention has been described in detail with specific reference to particular embodiments thereof, it will be understood that variations and modifications may be effected within the spirit and scope of the present invention as hereinbefore described and as defined in the appended claims.