Oil composition and method for treating phosphated metal surfaces

Superior corrosion resistance is provided by an improved oil composition an aqueous emulsified phosphating oil, an effective amount of polyvinylpyrrolidone and metallic zinc powder dispersed therein, which is applied, preferably by immersion or spraying, to a phosphated metal surface.

BACKGROUND OF THE INVENTION 
The present invention pertains to the treatment of metal surfaces in order 
to improve the corrosion resistance thereof. More specifically, the 
invention provides a novel and improved emulsified oil composition, 
usually referred to as a "phosphating oil", and method of treating 
phosphated metal surfaces therewith. 
In the field of metal surface treatment, it is of considerable importance 
to provide metal surfaces with the maximum degree of resistance against 
corrosion. Otherwise, corrosion can readily attack either ferrous or 
non-ferrous metals, which are routinely exposed to corrosive agents and 
environments. For example, corrosion can result from the presence of water 
and oxygen causing the formation of rust on ferrous metal surfaces, or 
from oxidation or formation of metallic residues on non-ferrous metal 
surfaces. 
One known way to inhibit corrosion has been to subject metallic surfaces to 
a "phosphating" treatment. For purposes of the present invention, the 
terms "phosphating" or "phosphated" refer to treatment by which a metal 
surface is rendered relatively inactive to attack by corrosive agents by 
formation or deposition thereupon of adherent crystalline deposits of 
phosphate salts. Typically, a phosphating treatment involves immersion of 
the metal surface in a hot aqueous solution containing phosphoric acid 
and/or phosphate salts, as well as one or more other organic salts, such 
as zinc nitrate, calcium nitrate, copper sulphate, etc. As a consequence, 
the solution acts chemically on the metallic surface, so that the desired 
crystalline phosphate deposit forms and adheres thereupon. This provides 
an initial passivation of the metal surface against attack by corrosive 
agents or environments and is a technique which is well known and used 
commercially in the art. 
It is also known that the degree of corrosion resistance provided by 
phosphated metal surfaces can be enhanced by application of an oil 
composition which adheres to the phosphated surface and further prevents 
penetration of water, oxygen or other corrosive agents. Typically such an 
oil composition, commonly referred to as a "phosphating oil", comprises an 
aqueous emulsion of an oil composition, which may contain stabilizers, 
emulsifying agents and extenders and other additives. 
However, even phosphated metal surfaces to which a phosphating oil has been 
applied provide insufficient corrosion resistance for certain environments 
and applications. In accordance with the present invention, a novel and 
improved phosphating oil composition has been developed which can provide 
in excess of a 100% increase in the degree of corrosion resistance of the 
phosphated metallic surface to which it is applied. Thus, the present 
invention constitutes a substantial and beneficial improvement over prior 
art techniques, compositions and methods. 
Accordingly, the primary object of this invention is to provide an improved 
phosphating oil composition which yields substantially improved and 
superior corrosion resistance in comparison with conventional phosphating 
oil compositions. 
It is a further object of the invention to provide a novel bath and method 
for treating phosphated metal surfaces, so as to impart superior corrosion 
resistance properties thereto. 
It is yet a further object of the invention to provide additives for 
conventional phosphating oil compositions which improve the corrosion 
resistance properties thereof in applications over phosphated metal 
surfaces. 
SUMMARY OF THE INVENTION 
The invention provides a novel and improved aqueous emulsion or nonaqueous 
solution of oil used for treatment of phosphated metal or metallic 
surfaces to improve corrosion resistance. This improved aqueous emulsion 
or nonaqueous solution of oil comprises an aqueous emulsified or 
nonaqueous solution of oil containing an effective amount of 
polyvinylpyrrolidone and dispersed metallic zinc powder. 
Also, in accordance with the invention, a novel method for providing 
superior corrosion resistance properties to a phosphated metal surface is 
provided comprising application, preferably by immersion or spraying, of 
the improved aqueous emulsion or nonaqueous solution of oil of the 
invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the invention, it has been discovered that the corrosion 
resistance provided by a conventional phosphating oil can be substantially 
improved by addition of an effective amount of polyvinylpyrrolidone and 
dispersed metallic zinc powder in a conventional phosphating oil. 
For purposes of the invention, polyvinylpyrrolidone polymers of any 
available molecular weight are effective and can be utilized. Preferably, 
however, polyvinylpyrrolidone polymers having an average molecular weight 
of between 10,000 to 360,000 are utilized. Amounts of polyvinylpyrrolidone 
ranging from about 1 to 60 grams per liter have been found to be 
particularly effective in accordance with the present invention. 
Likewise, in accordance with the invention it has been found that fine 
particulate zinc metal, generally referred to as "zinc dust", can be 
beneficially used in combination with polyvinylpyrrolidone and will 
contribute to a substantial improvement in the degree of corrosion 
resistance available from phosphating oil compositions containing the 
same. While not being limited by any theory, it is nevertheless believed 
that the zinc dust contributes to the improvement in corrosion resistance 
of the improved phosphating oil composition of the invention, because it 
is able to accumulate or be deposited in micro-pores formed in the 
crystalline matrix of the phosphate coating on the phosphated metal 
surface. It has been found that, preferably, an amount of zinc dust 
ranging from 1 to 100 grams per liter is effective for purposes of the 
invention. Preferably, zinc dust ranging from about 0.5 to 25 microns in 
size is utilized, although larger or smaller sizes are also operable. 
Effective amounts of polyvinylpyrrolidone and zinc dust may be added to any 
conventional phosphating oil composition, such as Rustarest.RTM.53253, 
sold by R. O. Hull and Company of Cleveland, Ohio. It is fully within the 
purview of this invention that any conventional phosphating oil 
composition may be utilized, without limitation. Such phosphating oils 
primarily comprise an aqueous emulsion or nonaqueous solution of oil 
containing a substantial amount of either mineral oil, vegetable oil, 
animal oil, synthetic oil or any combination thereof, together with 
optional emulsifiers, stabilizers, extenders, other corrosion resistant 
additives or the like. 
In accordance with the invention, the improved aqueous emulsion or 
nonaqueous solution of phosphating oil comprises a substantial portion of 
a conventional phosphating oil, preferably of the aqueous emulsified-type, 
and an effective amount of polyvinylpyrrolidone and zinc powder. 
Preferably, the conventional phosphating oil is provided in a range of 
between about 1 to 40% by volume. The preferred effective amounts of 
polyvinylpyrrolidone range from about 1 to 60 grams per liter and zinc 
powder range between about 1 to 100 grams per liter. 
The improved phosphating composition of the invention is applied to a 
phosphated metal surface utilizing any conventional application technique. 
However, immersion or spraying are preferred. It is also preferable to 
maintain the temperature of the improved composition of the invention 
between about 75.degree.-160.degree. F. during application. Above this 
temperature range, difficulties may be encountered with maintaining the 
emulsification of the oil composition.

EXAMPLE 
A 1 liter solution of the improved aqueous emulsified oil composition was 
prepared by diluting 20% by volume of a conventional phosphating oil, 
Restarest.RTM.53253 supplied by R. O. Hull and Company, Inc., Cleveland, 
Ohio, with water. To this solution was added 20 grams of 
polyvinylpyrrolidone, having an average molecular weight of about 40,000, 
and 20 grams of zinc dust. The composition was mixed thoroughly, so as to 
uniformly disperse the zinc powder and maintain its dispersion in the 
phosphating oil composition. 
A steel fastener, having previously been phosphated by application of Irco 
Bond.RTM.51800 Phosphating Concentrate, also supplied by R. O. Hull and 
Company, Inc., was immersed in the improved composition of the invention 
for a period of 30 seconds, while the composition was maintained at a 
temperature of 140.degree. F. Following immersion of the steel fastener, 
it was allowed to drain and dry, and thereafter was subjected to the 
standard 72 hour neutral salt spray test, ASTM B-117. 
For purposes of comparison, an identical phosphated steel fastener was 
similarly treated with the same phosphated oil (Rustarest.RTM.53253), but 
without the polyvinylpyrrolidone and zinc dust additives of the invention. 
Likewise, following drying, this fastener was subjected to the same salt 
spray test and was found to endure 90 hours before failure. By comparison, 
the phosphatized steel fastener treated with the improved composition of 
the invention indured 180 hours of exposure before failure in the salt 
spray test. This represents a 100% improvement in corrosion resistance in 
accordance with the invention. 
The above Example is given solely for purposes of illustration, it being 
understood that such composition and method of application and improvement 
of corrosion resistance on a phosphatized metal substrate may be altered, 
varied or modified without departing from the spirit or scope of the 
invention as defined by the appended claims.