US3338754A - Process and composition for phosphatizing metals - Google Patents

Description

UnitedStates Patent 3,338,754 PROCESS AND COMPOSITION FOR PHOSPHATIZING METALS William J. Vullo, Tonawanda, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed Nov. 13, 1962, Ser. No. 237,353

4 Claims. (Cl. 1486.15)

This invention relates to an improved process for phosphatizing metals and more particularly relates to improvements in a substantially non-aqueous process for applying phosphate coatings to metal surfaces.

In the art of metal finishing, it has been the practice for a number of years to apply phosphate coatings to metal surfaces to prevent the oxidation of the metal and to condition the metal surfaces for applying paint finishes. While many methods are available for applying such phosphate coatings, perhaps the most widely used at the present time is the so called aqueous phosphatizing system. In this system, an aqueous acidic solution of a metal phosphate, such as zinc phosphate is utilized. The aqueous solution is heated and the metal surface to be coated, after cleaning, is immersed in the hot aqueous phosphatizing solution for a period of time sufiicient to give the desired phosphate coating and is then removed from the solution. Although the phosphate coating produced by this method is generally satisfactory, the method is disadvantageous in that a large number of rather expensive operating steps are required.

In view of this, a non-aqueous phosphatizing system has recently been developed. In this system, a solution of phosphoric acid dissolved in organic solvents is utilized. Because of their absence of flash'point and low boiling points, the preferred organic solvents for use in such systems are the chlorinated hydrocarbons such as trichloroethylene. In addition to the phosphoric acid and trichloroethylene, such non-aqueous systems generally also contain a solubilizing agent for the phosphoric acid, such as a lower alkyl alcohol and may also contain other components such as inhibitors or the like which are effective in controlling the thickness of the phosphate coating placed on the metal surface, or in stabilizing the solution against decomposition.

While such a system does overcome the principal disadvantages encountered in the use of an aqueous phosphatizing system, e.g., the numerous expensive and time consuming steps, some difliculties have been encountered in using these systems. One of the principal difficulties encountered has been at the time of start-up of the system. At such time, it has been found that the first metal pieces which are put through the phosphatizing solution do not have a satisfactory phosphate coating formed on them. The phosphate coating on these pieces is generally uneven, sticky or tacky and badly blistered. Generally, after the system has been in operation for several minutes, e.g., perhaps a half hour or even longer, this ditficulty ceases and the parts coming out of the phosphatizing solution all have a smooth, substantially uniform, acceptable phos phate coating. Although one obvious solution to this problem is merely to accept this as a difliculty of the process and discard the initial pieces run through the phosphatizing solution, this is not satisfactory in that it is both time consuming and wasteful of the parts being coated.

In an effort to overcome this ditficulty, considerable work has been done in order to determine the cause for the unsatisfactory coatings which are placed on the parts 3,338,754 Patented Aug. 29, 1967 initially run through the non-aqueous phosphatizing solution, It is known, that in an aqueous phosphatizing solution similar ditliculties have been encountered at the time of start-up. These difficulties, however, have been traced to the fact that the phosphatizing solution is not, initially,

saturated with iron, or similar metal which is to be phosphatized. As a result, during the time the initial parts are run through the phosphatizing solution, metal is being dissolved from the surface of the part until such time as the phosphatizing solution becomes saturated with metal. In the case of a non-aqueous phosphatizing solution, however, this is not the case in that because of the low solubility of iron phosphate in the non-aqueous solvents employed, the solution rapidly becomes saturated. Accordingly, up to the present time it has not been known what causes these difiiculties during start-up with a non-aqueous phosphatizing solution.

It is, therefore, an object of the present invention to provide a means whereby the problems encountered during the start-up of the operation of a non-aqueous phos' phatizing solution may be overcome.

Another object of the present invention is to provide a means whereby the quality of the phosphate coating placed on the first metal pieces passed through a nonaqueous phosphatizing solution after start-up is improved.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

It has now been found that the difiiculties which have heretofore been encountered in the operation of a nonaqueous phosphatizing solution, in terms of poorer phosphate coating obtained on the parts initially passed through the phosphatizing solution at the time of start up of the operation of the solution, are caused by the presence of small amounts of water in the system. Although, as the name implies, these systems are substantially non-aqueous, small amounts of Water are still present in the system. This water comes, primarily, from the phosphoric acid generally added to the phosphatizing solution in the form of the commercial grade of percent phosphoric acid. The present invention, therefore, resides in the finding that in order to improve the phosphate coatings placed on the first parts passed through a non-aqueous phosphatizing solution, the small amounts of water normally present in the substantially non-aqueous system must be removed.

It will be appreciated by those skilled in the art that the small amounts of water normally present in the substantially non-aqueous phosphatizing solution may be removed in any of a number of Ways. Perhaps the simplest, from the standpoint of a commercial operation, is to use a more concentrated phosphoric acid, than the general commercial 85 percent phosphoric acid. For example, it has been found that the coating ditficulties encountered when using a phosphatizing solution made up of 85 percent phosphoric acid are substantially completely eliminated when phosphoric acid having a concentration of about 96-100 percent by weight is used in place of the 85 percent phosphoric acid. It will be appreciated, however, that although the use of such more highly concentrated phosphoric acid does overcome the coating difficulties heretofore encountered Without adding any additional steps to the phosphatizing process, the cost of this more highly concentrated acid is greater than that of the more commonly available 85 percent phosphoric acid. Additionally, when using a more concentrated phosphoric acid, such as 98 percent phosphoric acid, difficulties may be encountered in handling this more concentrated acid.

.Another method by which water may be removed from the substantially anhydrous phosphatizing solutions takes advantage of the fact that water forms azeotropes with most chlorinated hydrocarbons. Thus, the phosphatizing solution may be dehydrated by refluxing it in an apparatus which condenses the vapors, separates water out as the upper phase of the condensate, and returns the lower phase to the boiling solution.

Another method by which the water may be removed from the substantially non-aqueous phosphatizing solution is storing the entire phosphatizing solution, prior to use, in the presence of any of the well known drying agents, such as magnesium sulfate. The details of the method in which this drying of the phosphatizing solution is accomplished are believed to be obvious to those skilled in the art, the actual techniques being those used for drying organic liquids.

Still another method by which water may be removed with substantially non-aqueous phosphatizing solutions, is admixing a small amount of powdered metal with the solution prior to passing the pieces to be phosphatized therethrough. The slurry resulting from the addition of the metal powder is then heated and after being held at an elevated temperature for a sufiicient period of time, the suspended solids are removed from the slurry. Although it is not known for certain why the addition of a finely divided metal powder to the solution is efiective, it is believed that the metal reacts with the phosphoric acid in the solution to form anhydrous iron phosphate and that the anhydrous iron phosphate takes up the small amounts of water which are present in the solution. Thereafter, the water, bound to the metal salts, is removed from the solution as the suspended solids are removed. Any finely divided metal powder may be added to the phosphatizing solution in order to remove the water in this manner, the only requirement being that the metal reacts with phosphoric acid without detrimentally effecting the phosphatizing characteristics of the solution. Exemplary of the metals which may be added are finely divided iron, zinc, magnesium, alloys containing two or more of these, and the like. Of these, the finely divided iron is preferred. Generally, the finely divided metal powder is added to the solution in an amount within the range of about 0.01 to about 0.1 percent by weight of the solution. The exact amount of finely divided metal powder which is necessary to remove the water can be determined in each instance, so that the amounts given above are merely exemplary of the amounts which may be added. During and/or after the addition of metal powder, the solution is heated to a temperature generally within the range of about 55 degrees centigrade to the boiling point of the solution for a period sufficient to effect removal of substantially all of the water. Here again, the temperature and time at which the solution is heated may vary depending on the specific conditions encountered. The removal of the finely divided metal powder from the solution may be accomplished in any desired manner, as for example by filtration, centrifuging or the like.

It will be appreciated that the removal of the small amounts of water from the substantially non-aqueous phosphatizing solution may be accomplished in ways other than the tour which have been set forth specifically hereinabove. The four methods which have been given are to be taken merely as being exemplary of those which may be used for the removal of this water and are not a limitation on the manner in which this removal may be accomplished. It is to be kept in mind that the essence of the present invention is the finding that the small amounts of water normally present in the substantially non-aqueous phosphatizing solution are detrimental to the phosphate coating which is produced, particularly the coating which is produced on the first pieces which are passed through the phosphatizing solution.

Considering now the phosphatizing solutions to which the method of the present invention is applicable, these solutions are comprised of a chlorinated hydrocarbon solvent, orthophosphoric acid, and a solubilizing agent for the phosphoric acid. Additionally, the phosphatizing composition may contain materials which are effective in inhibiting or controlling the amount of the phosphate coating produced, so as to obtain a hard, thin, substantially uniform phosphate coating, and materials which are effective in stabilizing the solution against oxidative and thermal degradation.

More specifically, any chlorinated hydrocarbon normally used as a degreasing solvent may be employed in the present phosphatizing compositions. Examples of such chlorinated hydrocarbons include trichloroethylene, perchloroethylene, trichloroethanes, tetrachloroethanes, methylene chloride, ethylene dichloride, ethylidene chloride, dichlorotetrafluoroethanes, trichlorotrifluoroethanes, trichlorodifluoroethanes, tetrachlorodifluoroethanes, fluorotrichloroethanes, fluorotetrachloroethanes, methyl trichloroethylene, l,2dichloropropane, 1,2-dichloropropene, l,l,2-trichloropropane, ethyltrichloroethylene, and mixtures thereof. As will be noted they are usually of 1 to 4 carbon atoms and 1 to 6 halogen atoms. The amount of the chlorinated hydrocarbon used will generally be within the range of about 65 to about 99 percent by Weight of the total composition. The chlorinated hydrocarbon used may be unstabilized or, if desired, may contain one or more of the various known stabilizers which are eifective in preventing or inhibiting the decomposition of the chlorinated hydrocarbon.

The orthophosphoric acid used in the phosphatizing composition is generally the commercially available percent phosphoric acid. Inasmuch as substantially all of the water introduced into the phosphatizing solution with the phosphoric acid is ultimately removed prior to the use of the solution, more dilute phosphoric acid solutions may be employed as desired. Additionally, where the removal of the water from the phosphatizing solution is to be accomplished by using a more concentrated phosphoric acid, phosphoric acids having a concentration within the range of 96-100 percent by weight are employed. Generally, the amount of phosphoric acid used will be Within the range of about 0.05 to about 6 percent by weight of the total composition.

Any one of numerous solubilizing agents for the phosphoric acid may be included in the composition. Exemplary of such solubilizing agent-s are the acid alkyl phosphates, and the various aliphatic monohydroxy alcohols and alicyclic monohydroxy alcohols. Typical examples of suitable alcohols include the alcohols which contain between one and about eighteen carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary butanyl alcohol, tertiary amyl alcohol, octyl alcohol, decyl alcohol, lauryl alcohol, stearyl alcohol, cyclohexyl alcohol and mixtures thereof. Other solvents capable of dissolving phosphoric acid in trichloroethylene may be used in place of or in addition to the above solvents. Such solvents include halogenated alcohols such as 2-chloroethanol, alkyl acetates such as ethyl acetate, amyl acetate and the like, amides such as N,N-dimethyl formamide and dimethyl acetamide, dioxane, monoethers of polyalkylene oxide glycols such as the Cellosolves and carbitols, ketones such as acetone and methyl ethyl ketone, and dialkyl sulfoxides such as dimethyl sulfoxides. Generally, the solubilizing agent will be present in the composition in amounts within the range of about 1 to about 35 percent by weight of the total composition.

In addition to the above substituents, the phosphatizing compositions may also contain various materials which act as inhibitors or phosphate coating control agents. Exemplary of such materials are nitrated organic compounds such as nitrobenzene; glacial acetic acid; and the alkyl thioureas, such as N,N'-diethylthiourea. Generally,

these materials will be present in the composition in amounts within the range of about 0.001 to about 6 percent by weight of the total composition. Greater or lesser amounts of these materials may be used, however, depending upon the specific materials involved.

Additionally, stabilizers for the composition may also be included, such as octyl phenol, diisobutylene, diethylthiourea, tert-butylpyrocatechol and the like. Such stabilizers will generally be present in an amount within the range of about 0.0001 to about 15 percent by weight of the total composition, although greater or lesser amounts may be used.

Substantially non-aqueous phosphatizing compositions with which the method of the present invention may be utilized are described in US. Patent 2,789,070 as well as numerous co-pending applications including S.N. 16,125, now abandoned, S.N. 16,126, now US. Patent 3,100,- 728, and SN. 16,127, now abandoned, filed Mar. 21, 1960, and SN. 165,288, now abandoned, S.N. 165,289, now abandoned, and SN. 165,303, filed Jan. 10, 1962, now US. Patent 3,220,890. The compositions described in these applications and the patent are merely exemplary of those which may be used with the present method and are not to be taken as limiting the phosphatizing compositions.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, the initial phosphatizing solution was prepared by dissolving the phosphoric acid in the solubilizing agent, e.g., normal butyl alcohol, and then adding to this the trichloroethylene.

Example 1 A phosphatizing solution was prepared containing the following components in the following proportions:

Component: Percent by weight Trichloroethylene 92.7 Normal butyl alcohol 6.1 85% phosphoric acid 1.2

Example 2 A phosphatizing solution was prepared containing the following components in the following proportions: Component: Percent by weight Trichloroethylene (containing 0.01% octylphenol) 92.1 Normal butyl alcohol 5.7 85% phosphoric acid 1.2

To this solution was added 100 milligrams of iron powder and the resulting slurry was heated to a temperature of about 70 degrees centigrade for a period of twenty minutes. Thereafter, the slurry was filtered through glass wool to remove the suspended solid material. A degreased steelpanel of the type used in Example 1, was then dipped into 800 milliliters of the clarified filtrate obtained. The panel was maintained in the solution for a period of five minutes while the solution was maintained at a temperature of about 65 degrees centigrade. Upon removing the panel from the solution, the phosphate coating obtained was found to be tacky with some blistering. The weight of the phosphate coating was determined to be 1,025 milligrams per square foot.

Example 3 A phosphatizing solution was prepared containing the following components in the following proportions.

Component: Percent by weight Trichloroethylene (containing 0.01% octyl phenol) 92.6 Normal butyl alcohol 5.8 85% phosphoric acid 1.2 Nitrobenzene 0.4

Example 4 A phosphatizing solution was prepared as in the preceding example. To 800 milliliters of this solution was added 300 milligrams of iron powder. The resulting slurry was then heated for a period of 50 minutes at a temperature of 65 centigrade and then filtered through glass wool. A degreased steel panel of the type used in Example 1 was dipped into the clear filtrate obtained for a period of five minutes while the filtrate was maintained at a temperature of about 65 centigrade. Upon removing the panel from the solution, it was found to have a thin, dry uniform, blue-gray phosphate coating. The weight of this phosphate coating was determined to be 44 milligrams per square foot.

Example 5 A phosphatizing solution was prepared containing the following components in the following proportions:

Component: Percent by weight Trichloroethylene (containing 0.01 octyl phenol) 93.0 Normal butyl alcohol 5.8 85 phosphoric acid 1.2

- Upon removing the panel from the solution, it was found to be coated with a thin, blue-gray phosphate coating, the weight of which coating was determined to be 2-9 milligrams per square foot. This coating, however, was not completely uniform, being partially covered with loose deposits of white powder.

Example 6 Four milliliters (4.8 grams) of nitrobenzene was added to the salt dried solution of Example 5. A steel test panel of the same type as used in the previous examples was then dipped into the solution for a period of three minutes while the solution was maintained at a temperature of about 65 degrees centigrade. Upon removing the panel from the solution, it was found to have a uniform, thin, blue-gray, powder-free phosphate coating. The weight of phosphate coating was determined to be 33 milligrams per square foot.

Example 7 A phosphatizing solution was made up using the same components and proportions as in Example 1. 800 mil- 7 liliters of this solution was refluxed beneath a water separator until no more water was separated from the solution. A steel test panel of the same type used in the previous examples was dipped into the solution for a period of five minutes while the solution was maintained at a temperature of 65 degrees centigrade. Upon removing the material from the solution, it was covered with a thin, dry, smooth, gray phosphate coating, which was partially covered with a loose white powder. The weight of this phosphate coating was determined to be 76 milligrams per square foot.

Example 8 The procedure of Example 7 was repeated with the exception that 0.21 gram of 1.3-diethylthiourea was added to the phosphatizing solution before distillation. When distillation of the solution was complete, a steel test panel of the same type used in the previous examples was dipped into this solution for a period of five minutes while the solution was maintained at a tempearture of 65 degrees centigrade. Upon removing the panel from the solution, it was found to have a thin, smooth, uniform, dry, gray coating free of loose deposits. The weight of this coating was determined to be 61 milligrams per square foot.

Example 9 A degreased steel test panel of the type employed in the previous example was dipped into 800 ml. of th phosphatizing solution of Example 1. The panel was maintained in the solution for a period of three minutes while the solution was maintained at 85 i1 Centigrade. After removal from the solution, the phosphate coating produced on the panel was found to be sticky and badly blistered. The weight of the phosphate coating was determined to be 2040 milligrams per square foot.

Example 10 A phosphatizing solution of the following composition was prepared from n-butyl alcohol, unstabilized trichloroethylene, and 98 percent phosphoric acid.

Component: Percent by weight Trichloroethylene 92.92 Normal butyl alcohol 6.04 98% phosphoric acid 1.04

A clean steel panel of the type employed in the previous example was dipped into about 800 ml. of the above phosphatizing solution. The panel was maintained in the solution for a period of three minutes at 86 centigrade. The phosphate coating thereby produced was not blistered and weighed 425 miligrams per square foot.

The results obtained in the above examples are summarized as follows:

SUMMARY Ex. Treatment Results 1 None Thick, blistered. sticky coating.

Fe powder Coating thinner. less blister-ed and less sticky than i. 13 Nitrobenzene Thick, blistered, strcaky coating. 4 Fe powder plus nitro- Thin, smooth, uniform coating.

benzene. 5 Salt drying Thin coating but powdery. ti Salt drying plus nitro- Thin, uniform coatingno powder.

benzene. 7 Distillation t Thin coating but powdery. B Distillation plus dieth- Thin, uniform coating-no powder.

ylthiourea. i 9 None Thick, blistered. sticky coating. 10..." 98% H PO4 Coating thinner than 9 and nonblistered.

From the above summary, it is seen that when the phosphatizing solution is subjected to the various treatments of the present invention to remove the small amounts of water from the solution, the coating produced on the first panel treated with the solution is improved over that produced when using a phosphatizing solution from which the water has not been removed. It is further shown that the addition of an inhibiting compound, such as nitrobenzene or diethylthiourea, without the removal of the small amounts of water from the solution, does not give the improved coating results obtained when the water is removed. It is further shown that the best results are obtained when the small amounts of water are removed and, a coating inhibiting compound is also added to the solution. This is clearly shown by the results obtained in Examples 4, 6 and 8. From the above results it is seen that the removal of water from the phosphatizing solution, in accordance with the practice of the present invention, does result in an improvement in the coating obtained on the first pieces passed through the phosphatizing solution.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention, as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A process for phosphatizing metal surfaces wherein the surface to be phosphatized is contacted with a solution comprising a chlorinated hydrocarbon, orthophosphoric acid, a solubilizing agent for the phosphoric acid and small amounts of water, the improvement which comprises removing substantially all of the water from the Solution by contacting the solution with a finely divided metal powder and separating the suspended solids from the resulting slurry prior to bringing the solution into contact with the metal surface to be phosphatized, thereby obtaining an improved phosphate coating on the first metal surfaces contacted with the solution.

2. The process as claimed in claim 1 wherein the chlorinated hydrocarbon in the phosphatizing solution is trichloroethylene.

3. The process as claimed in claim 2 wherein the phosphatizing solution also contains a material which is capable of controlling the amount of phosphate coating which is placed on the metal surface.

4. A phosphatizing composition comprising a chlorinated hydrocarbon, orthophosphoric acid, a solubilizing agent for the phosphoric acid and a minor amount of a finely divided metal powder.

References Cited UNITED STATES PATENTS 2,789,070 4/1957 Copelin 148-6.l5 2,986,482 5/1961 Sharp 148-6.l5 3,051,595 8/1962 Fullhart et al. 1486.l5 3,100,728 8/1963 Vullo et al. l4 86.15 3,197,345 7/1965 Vullo et a1. 148--6.15 3,220,890 11/1965 Vullo et al. 148-6.l5

OTHER REFERENCES Azeotropic Data. Washington, D.C., American Chemical Society, 1952, p. 6.

ALFRED L. LEAVITT, Primary Examiner.

MURRAY KATZ, JOSEPH B. SPENCER, Examiners.

J. R. BAT'IEN, Assistant Examiner.

Claims (2)

1. A PROCESS FOR PHOSPHATIZING METAL SURFACES WHEREIN THE SURFACE TO BE PHOSPHATIZED IS CONTACTED WITH A SOLUTION COMPRISING A CHLORINATED HYDROCARBON, ORTHOPHOSPHORIC ACID, A SOLUBILIZING AGENT FOR THE PHOSPHORIC ACID AND SMALL AMOUNTS OF WATER, THE IMPROVEMENT WHICH COMPRISES REMOVING SUBSTANTIALLY ALL OF THE WATER FROM THE SOLUTION BY CONTACTING THE SOLUTION WITH A FINELY DIVIDED METAL POWDER AND SEPARATING THE SUSPENDED SOLIDS FROM THE RESULTING SLURRY PRIOR TO BRINGING THE SOLUTION INTO CONTACT WITH THE METAL SURFACE TO BE PHOSPHATIZED, THEREBY OBTAINING AN IMPROVED PHOSPHATE COATING ON THE FIRST METAL SURFACES CONTACTED WITH THE SOLUTION.

4. A PHOSPHATIZING COMPOSITION COMPRISING A CHLORINATED HYDROCARBON, ORTHOPHOSPHORIC ACID, A SOLUBILIZING AGENT FOR THE PHOSPHORIC ACID AND MINOR AMOUNT OF A FINELY DIVIDED METAL POWDER.