METHOD AND COMPOSITION FOR PRODUCING A BLACK MATTE FINISH ON FERROUS METALS
United States Patent 3644152
A method is provided for producing a black matte finish on ferrous metal objects, wherein the ferrous metal object is contacted with a sulfuric acid solution of a trivalent antimony salt and a complexing agent and thereafter a phosphate coating is deposited on the object. The treating solution may also contain a minor amount of hydrochloric acid or a salt of hydrochloric acid. The finish produced on the ferrous metal is of a uniform black stable shade.
US Patent References:
Rustproofing coating
Scanlan - November 1922 - 1436729
Process for coating metal surfaces
Morris - February 1942 - 2271706
Method for producing black coatings on metal surfaces
Jones et al. - March 1968 - 3372064
Rustproofing coating
Scanlan - November 1922 - 1436729
Process for coating metal surfaces
Morris - February 1942 - 2271706
Method for producing black coatings on metal surfaces
Jones et al. - March 1968 - 3372064
Inventors:
Schlossberg, Louis (Farmington, MI)
Sokalski, Stanley M. (Southfield, MI)
Sokalski, Stanley M. (Southfield, MI)
Application Number:
04/868218
Publication Date:
02/22/1972
Filing Date:
10/21/1969
View Patent Images:
Export Citation:
Assignee:
Detrex Chemical Industries, Inc. (Detroit, MI)
Primary Class:
Other Classes:
428/469, 148/254, 428/697
International Classes:
C23C22/78; C23F7/10
Field of Search:
148/6.17,6.14,6.15R,31.5
Other References:
hopkins, The Scientific American Cyclopedia of Formulas 1925 Scientific American Pub. Co. pp. 444, 448..
Primary Examiner:
Kendall, Ralph S.
Claims:
We claim
1. The method of forming a black matte finish on a ferrous metal object which comprises contacting said object with an aqueous solution comprised of: about 9-235 grams per liter of sulphuric acid; an amount of a water soluble trivalent antimony salt up to the limit of solubility of said salt in said solution and an effective amount of complexing agent selected from a group consisting of tartaric acid, gluconic acid, citric acid, glycolic acid, phytic acid, kojic acid, sorbitol, and ethylenediaminetetraacetic acid, said effective amount being an amount sufficient to prevent oxidation of said trivalent antimony salt in said solution to the pentavalent state; said object being contacted with said solution from about 0.5 to about 5 minutes at a temperature of about 60° F. to about 100° F., and thereafter depositing a phosphate conversion coating on said object.
2. The method according to claim 1, wherein said trivalent antimony salt is antimony trichloride.
3. The method according to claim 1, wherein said complexing agent is tartaric acid.
4. The method according to claim 1 wherein said solution further contains a member selected from the group consisting of hydrochloric acid or a salt of hydrochloric acid.
5. The method according to claim 1 wherein said solution contains up to 10 grams per liter of hydrochloric acid.
6. The method according to claim 1 wherein said aqueous solution is comprised of from about 9 to 235 grams per liter of sulfuric acid, 0.5 to 15 grams per liter of antimony trichloride, 0.5 to 20 grams per liter of tartaric acid, and 0 to 10 grams per liter of hydrochloric acid, and said object is contacted for 0.5 to 5 minutes at room temperature to 100° F. with said solution.
7. The aqueous solution for employment in the method according to claim 1 comprised of about 9 to about 235 grams per liter of sulfuric acid, 0.5 to 15 grams per liter of a trivalent antimony salt, 0 to 10 grams per liter of hydrochloric acid and an effective amount of a complexing agent.
8. The ferrous metal object having a black matte finish applied according to the process of claim 1.
1. The method of forming a black matte finish on a ferrous metal object which comprises contacting said object with an aqueous solution comprised of: about 9-235 grams per liter of sulphuric acid; an amount of a water soluble trivalent antimony salt up to the limit of solubility of said salt in said solution and an effective amount of complexing agent selected from a group consisting of tartaric acid, gluconic acid, citric acid, glycolic acid, phytic acid, kojic acid, sorbitol, and ethylenediaminetetraacetic acid, said effective amount being an amount sufficient to prevent oxidation of said trivalent antimony salt in said solution to the pentavalent state; said object being contacted with said solution from about 0.5 to about 5 minutes at a temperature of about 60° F. to about 100° F., and thereafter depositing a phosphate conversion coating on said object.
2. The method according to claim 1, wherein said trivalent antimony salt is antimony trichloride.
3. The method according to claim 1, wherein said complexing agent is tartaric acid.
4. The method according to claim 1 wherein said solution further contains a member selected from the group consisting of hydrochloric acid or a salt of hydrochloric acid.
5. The method according to claim 1 wherein said solution contains up to 10 grams per liter of hydrochloric acid.
6. The method according to claim 1 wherein said aqueous solution is comprised of from about 9 to 235 grams per liter of sulfuric acid, 0.5 to 15 grams per liter of antimony trichloride, 0.5 to 20 grams per liter of tartaric acid, and 0 to 10 grams per liter of hydrochloric acid, and said object is contacted for 0.5 to 5 minutes at room temperature to 100° F. with said solution.
7. The aqueous solution for employment in the method according to claim 1 comprised of about 9 to about 235 grams per liter of sulfuric acid, 0.5 to 15 grams per liter of a trivalent antimony salt, 0 to 10 grams per liter of hydrochloric acid and an effective amount of a complexing agent.
8. The ferrous metal object having a black matte finish applied according to the process of claim 1.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for treating ferrous metals. More particularly this invention is concerned with a method for producing a black matte finish on ferrous metals.
2. Description of the Prior Art
Black matte finishes are required on certain ferrous metal products. Depending on the particular method employed to form the black matte finish, the finish can be decorative, protective, or used as a bonding layer for additional treatments such as phosphate coating treatments. Various methods have been suggested in the prior art to form a black matte finish on ferrous metals. None of the methods suggested to date have proven to be completely satisfactory. Certain of the methods employed have produced somewhat uneven results, and the shade of black was not sufficiently deep.
The most commonly employed method suggested in the prior art utilizes the compounds of arsenic, antimony, tin or nickel to obtain the desired finish. However, the disclosed processes generally required special reaction conditions which limited their use in the large scale treatments of ferrous metals, or substantially increased the cost of the treatment. One method consisted of treating the metal with a hydrocarbon solution, for example a kerosene solution of the antimony salts (Arent U.S. Pat. No. 1,770,828). It can be seen that this method was not satisfactory because of the substantial fire hazard and the problem of removing the solvent from the treated metal. Other methods suggested in the prior art consisted of treating the metals with alkaline solutions containing reactants such as an antimony compound (Scanlan U.S. Pat. No. 1,436,729).
Certain of the methods suggested in the prior art were conducted in an acid media. However, the particular acids which could be employed were rather limited. It was indicated in the prior art (Morris U.S. Pat. No. 2,271,706, Jones U.S. Pat. No. 3,372,064) that hydrochloric acid solution of trivalent antimony salts could be employed. These references specifically taught against using acids such as sulfuric or nitric acid. It was recognized in the prior art that the trivalent antimony salts are readily oxidized to the pentavalent state by the sulfuric acid, and accordingly sulfuric acid was excluded from the treatment baths. The processes using the relatively concentrated hydrochloric acid solutions were not completely satisfactory. Because of the relatively high concentrations of acid required, there was considerable amounts of hydrochloric acid fumes in the area adjacent the treating equipment. In addition, the concentrated hydrochloric acid solutions were highly corrosive causing considerable damage to the processing and ventilation equipment.
A further difficulty in employing the prior art process for applying black matte finishes was that ferrous metals are often pretreated by pickling them in sulfuric acid. Once any residual sulfuric acid was left on the pickled ferrous metals, it would cause oxidation of the treating baths.
It is the object of the invention to provide a method of obtaining black matte finishes on ferrous metals which are a deep and uniform shade.
It is a further object of this invention to provide a method wherein the metal may be treated under acid conditions.
It is still a further object of the invention to provide an improved process for the production of black matte finish on ferrous metals which can be conducted in a continuous manner with a minimal amount of controls in the presence of sulphuric acid and which will produce uniform results.
Other objects and advantages of the present invention will become further apparent from a reading of the specifications, examples and subjoined claims.
SUMMARY OF THE INVENTION
The object of this invention has been achieved by providing a method wherein a black matte finish is formed on ferrous metals by treating the metals with an aqueous sulfuric acid solution containing a trivalent antimony salt and a complexing agent and thereafter depositing a phosphate coating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Aqueous solution which consists of only sulfuric acid and a trivalent antimony salt such as antimony trichloride are unsuitable for forming black matte finishes on ferrous metals in that the sulfuric acid in the solution oxidizes the trivalent antimony to the pentavalent state. It was for the above reasons that the prior art specifically taught against the use of sulfuric acid. However, it has been found that sulfuric acid solutions of trivalent antimony compounds can be used effectively and excellent results obtained on ferrous metals if, in addition to the sulfuric acid and the trivalent salt, a complexing agent is added to the treating bath. The exact effect of the complexing agent on the treating solution is not known. Ferrous metals treated with the sulfuric acid solution containing a complexing agent and a trivalent antimony salt and thereafter treated with a phosphate coating have a deep level, stable, matte finish.
The compositions used in the present invention advantageously contain from about 9 grams per liter to about 235 grams per liter of sulfuric acid (calculated at 100 percent concentration). Amounts less than 9 grams per liter can be employed but the reaction time is considerably increased so that it becomes impractical to use amounts substantially less than 9 grams per liter. It is also possible to use a higher concentration of sulfuric acid, however the higher concentrations are somewhat impractical for most commercial installations.
The trivalent salts employed in the present invention may be any of the water soluble salts of trivalent antimony with the preferred trivalent antimony compound being antimony trichloride.
Since the antimony ion is the effective reactant of the treating composition with regard to the formation of the black coating on the ferrous metal, it is of advantage to have a maximum amount of the trivalent antimony salt in the treating solution. Accordingly, the upper limit of the amount of the trivalent antimony salt in the treating composition is governed by the solubility of the salt in the treating composition. There is no lower limit with regard to the amount of the trivalent antimony salt which can be added to the composition. However, for practical purposes there must be a minimal amount of the trivalent antimony salt in the composition in order to obtain the desired effect in a reasonable length of time. Using antimony salt, the amount of the antimony trichloride which is preferably employed is between 0.5 gram per liter to about 15 grams per liter.
Various types of well known complexing agents can be employed in the present invention. Compounds which deserve particular attention in this regard are, for example, tartaric acid, gluconic acid, citric acid, glycolic acid, phytic acid, kojic acid, sorbitol and ethylenediamine-tetraacetic acid, with tartaric acid being the preferred complexing agent for employment in the present invention. The amount of the complexing agent that is added to the composition of this invention, is dependent on the particular complexing agent which is employed and the relative amount of sulfuric acid and the trivalent antimony salt in the composition. The amount of a particular complexing agent which must be added in order to be effective in preventing the oxidation of the trivalent antimony to the pentavalent state in a given composition can readily be determined on a small scale by preparing compositions containing various amounts of the complexing agent and the required amount of sulfuric acid and the trivalent antimony, and increasing the amount of the complexing agent in each composition until a stable composition is obtained.
Using tartaric acid as an example, an amount at least 0.5 gram per liter is required in order to have a stable solution. However, amounts in excess of this are generally employed with the amount up to 20 grams per liter being practical. Amounts above 20 grams per liter are generally not employed in that the excess amounts do not have any beneficial effect on the stability of the solution.
When the surfaces of the ferrous metals which are to be treated are somewhat contaminated, as for example by having a light oxide film coating or a film of a lubricant thereon, it is considerably advantageous to include in the treating composition a small amount of either hydrochloric acid or a salt of hydrochloric acid. The amount of hydrochloric acid that is employed can be relatively small, with at most 10 grams per liter of hydrochloric acid calculated on 100 percent concentration being required. Generally however, amounts between 1 and 10 grams per liter are quite sufficient to remove any contamination from the surface of the metals to be treated. Various types of hydrochloric acid salts can be used. These would include the acid salts and even the neutral salts such as sodium chloride. The amount of the salt that is added is calculated so that the chloride ion concentration would be equivalent to that when 1-10 grams of hydrochloric acid calculated at 100 percent concentration is used.
In accordance with the method of this invention, the ferrous metal object on which the black matte coating is to be formed is thoroughly cleaned. The metal object is contacted with the sulfuric acid solution of the trivalent antimony salt and the complexing agent. The object may be immersed in a bath of the composition or the composition may be sprayed onto the subject. The object should be in contact with the treating solution for between 0.5 and 5 minutes with the treating solution at a temperature from 60° to 100° F. Higher treating temperatures and longer treating times can be employed to increase the thickness of the black matte coating on the treated object. Depending upon the surface involved, a small quantity of HCl may be added to the pretreat solution in quantities up to about 10 g./. Following treatment with the sulfuric acid solution, the metal object is rinsed with water. The object, as a result of this treatment has a black coating on the surface thereof.
The treated object is thereafter subjected to a phosphate coating treatment. The composition of the phosphate coating bath is not critical. Any of the well-known phosphate compositions may be employed. In addition to the zinc and phosphate ions, it is of advantage to include nickel ions.
Especially good results are obtained with the process of the present invention when phosphate solutions such as those disclosed in Schlossberg et al. U.S. Pat. No. 3,269,877 are employed. These phosphate compositions impart an additional blackening effect, in addition to substantially improving the physical properties of the black matte finish.
The following examples are given by way of illustration of additional compositions included within the scope of the present invention and are not intended to limit in any way the scope of the subjoined claims. All percentages are percent by weight unless otherwise indicated.
EXAMPLE 1
A cleaned and pickled 4X4 inch cold rolled steel test panel was immersed for 1 minute at 80° F. in an aqueous solution containing 88 grams per liter of sulfuric acid, (calculated at 100 percent concentration), 2 grams per liter of antimony trichloride, and 2 grams per liter of tartaric acid. The test panel was rinsed in cold water. The test panel at this stage had a black coating deposited on its surface. A phosphate coating was deposited on the surface by immersing the test panel in an aqueous solution containing 0.9 percent phosphate ion (H 3 PO 4 ), 0.28 percent nitrate ion (HNO 3 ), 0.351 percent zinc ion (ZnO) and 0.012 percent cobalt ion (Co(NO 3 ) 2 ). The sample was immersed for 15 minutes at a temperature between 190°-200° F. The panel was rinsed with hot water and dried.
The test panel after this treatment had a uniform black matte finish.
EXAMPLE 2
Example 1 was repeated with the exception that the test panel was not pickled and which had a slight but visual oxide coating. The treated test panel had an uneven black matte finish.
EXAMPLE 3
Example 1 was repeated with the exception that a test panel of cold rolled steel having a slight but visual oxide coating was employed and 10 grams per liter of hydrochloric acid (calculated at 100 percent concentration) was added to the treating composition. The treated sample after the phosphate treatment had a uniform black matte finish equivalent to the finish on the test panel prepared in Example 1.
EXAMPLE 4
Test panels of cleaned and pickled cold rolled steel were immersed in an aqueous treating composition comprised of 100 grams per liter of sulfuric acid (calculated at 100 percent concentration), 10 grams per liter of antimony trichloride (anhydrous) and 10 grams per liter of tartaric acid, for the times and temperatures noted below, and thereafter a phosphate coating was applied as described in Example 1.
Time Degrees Sample Minutes Fahrenheit Results ____________________________________________________________ ______________ 1 0.5 60 Thin black matte finish 2 0.5 80 Thin but even black matte finish, heavier than sample 1 3 0.5 100 Full black matte finish 4 1.0 60 Sample obtained about equivalent to sample 2 5 1.0 80 Sample having a finish equivalent to sample 3 6 1.0 100 Heavy Black matte finish 7 5.0 100 Thick black matte finish ____________________________________________________________ ______________
EXAMPLE 5
Example 1 was repeated with the exception that 12 grams per liter of gluconic acid was employed in place of the tartaric acid. The results obtained were equivalent to the results obtained in Example 1
EXAMPLE 6
Example 1 was repeated with the exception that 12 grams per liter of citric acid was employed in place of the tartaric acid. The black matte finishes obtained on the samples in this example were equivalent to those in Example 1.
EXAMPLE 7
Example 1 was repeated with the exception that the tartaric acid was replaced with 1 gram per liter of glycolic acid. The results obtained in this example were equivalent to the results obtained in Example 1.
EXAMPLE 8
Example 1 was repeated with the exception that the tartaric acid was replaced with 8 grams per liter of phytic acid. The coating obtained in this example was equivalent to the coating obtained in Example 1.
EXAMPLE 9
Example 1 was repeated with the exception that the tartaric acid was replaced with 6 grams per liter of kojic acid. The coating obtained in this example was the same as the coating obtained in Example 1.
EXAMPLE 10
Example 1 was repeated with the exception that the tartaric acid was replaced with 9 grams per liter of sorbitol. The samples treated in accordance with this example were equivalent to the samples obtained in Example 1.
EXAMPLE 11
Example 1 was repeated with the exception that the tartaric acid was replaced with 5 grams per liter of ethylenediaminetetraacetic acid. Samples treated in accordance with this example were equivalent to the samples obtained in Example 1.
EXAMPLE 12
Measured test panels of cold rolled steel were treated at room temperature (70° F.) for one minute with the aqueous composition comprised of 88 grams per liter of sulfuric acid (calculated at 100 percent), 2 grams per liter of antimony trichloride (anhydrous) and 2 grams per liter of tartaric acid (anhydrous) and 10 grams per liter of hydrochloric acid (calculated at 100 percent) and thereafter a phosphate coating was applied as in Example 1.
The treated samples had a uniform black matte finish. It was found that when the above solution was employed as the finishing agent for obtaining the black matte finish, that it could satisfactorily treat 140 sq. feet of the steel panels per gallon of treating solution before serious depletion of the solution occurs.
EXAMPLE 13
Example 1 was repeated with the exception that the phosphate coating solution employed in Example 1 was replaced with a phosphate solution comprised of 0.9 percent phosphate ion (H 3 Po 4 ), 0.284 percent nitrate ion (HNO 3 ) and 0.351 percent zinc ion (ZnO). The test panel had a deep black matte finish which was slightly lighter in color than the sample prepared in Example 1 but it would be of desirable and commercially acceptable quality.
1. Field of the Invention
This invention relates to a process for treating ferrous metals. More particularly this invention is concerned with a method for producing a black matte finish on ferrous metals.
2. Description of the Prior Art
Black matte finishes are required on certain ferrous metal products. Depending on the particular method employed to form the black matte finish, the finish can be decorative, protective, or used as a bonding layer for additional treatments such as phosphate coating treatments. Various methods have been suggested in the prior art to form a black matte finish on ferrous metals. None of the methods suggested to date have proven to be completely satisfactory. Certain of the methods employed have produced somewhat uneven results, and the shade of black was not sufficiently deep.
The most commonly employed method suggested in the prior art utilizes the compounds of arsenic, antimony, tin or nickel to obtain the desired finish. However, the disclosed processes generally required special reaction conditions which limited their use in the large scale treatments of ferrous metals, or substantially increased the cost of the treatment. One method consisted of treating the metal with a hydrocarbon solution, for example a kerosene solution of the antimony salts (Arent U.S. Pat. No. 1,770,828). It can be seen that this method was not satisfactory because of the substantial fire hazard and the problem of removing the solvent from the treated metal. Other methods suggested in the prior art consisted of treating the metals with alkaline solutions containing reactants such as an antimony compound (Scanlan U.S. Pat. No. 1,436,729).
Certain of the methods suggested in the prior art were conducted in an acid media. However, the particular acids which could be employed were rather limited. It was indicated in the prior art (Morris U.S. Pat. No. 2,271,706, Jones U.S. Pat. No. 3,372,064) that hydrochloric acid solution of trivalent antimony salts could be employed. These references specifically taught against using acids such as sulfuric or nitric acid. It was recognized in the prior art that the trivalent antimony salts are readily oxidized to the pentavalent state by the sulfuric acid, and accordingly sulfuric acid was excluded from the treatment baths. The processes using the relatively concentrated hydrochloric acid solutions were not completely satisfactory. Because of the relatively high concentrations of acid required, there was considerable amounts of hydrochloric acid fumes in the area adjacent the treating equipment. In addition, the concentrated hydrochloric acid solutions were highly corrosive causing considerable damage to the processing and ventilation equipment.
A further difficulty in employing the prior art process for applying black matte finishes was that ferrous metals are often pretreated by pickling them in sulfuric acid. Once any residual sulfuric acid was left on the pickled ferrous metals, it would cause oxidation of the treating baths.
It is the object of the invention to provide a method of obtaining black matte finishes on ferrous metals which are a deep and uniform shade.
It is a further object of this invention to provide a method wherein the metal may be treated under acid conditions.
It is still a further object of the invention to provide an improved process for the production of black matte finish on ferrous metals which can be conducted in a continuous manner with a minimal amount of controls in the presence of sulphuric acid and which will produce uniform results.
Other objects and advantages of the present invention will become further apparent from a reading of the specifications, examples and subjoined claims.
SUMMARY OF THE INVENTION
The object of this invention has been achieved by providing a method wherein a black matte finish is formed on ferrous metals by treating the metals with an aqueous sulfuric acid solution containing a trivalent antimony salt and a complexing agent and thereafter depositing a phosphate coating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Aqueous solution which consists of only sulfuric acid and a trivalent antimony salt such as antimony trichloride are unsuitable for forming black matte finishes on ferrous metals in that the sulfuric acid in the solution oxidizes the trivalent antimony to the pentavalent state. It was for the above reasons that the prior art specifically taught against the use of sulfuric acid. However, it has been found that sulfuric acid solutions of trivalent antimony compounds can be used effectively and excellent results obtained on ferrous metals if, in addition to the sulfuric acid and the trivalent salt, a complexing agent is added to the treating bath. The exact effect of the complexing agent on the treating solution is not known. Ferrous metals treated with the sulfuric acid solution containing a complexing agent and a trivalent antimony salt and thereafter treated with a phosphate coating have a deep level, stable, matte finish.
The compositions used in the present invention advantageously contain from about 9 grams per liter to about 235 grams per liter of sulfuric acid (calculated at 100 percent concentration). Amounts less than 9 grams per liter can be employed but the reaction time is considerably increased so that it becomes impractical to use amounts substantially less than 9 grams per liter. It is also possible to use a higher concentration of sulfuric acid, however the higher concentrations are somewhat impractical for most commercial installations.
The trivalent salts employed in the present invention may be any of the water soluble salts of trivalent antimony with the preferred trivalent antimony compound being antimony trichloride.
Since the antimony ion is the effective reactant of the treating composition with regard to the formation of the black coating on the ferrous metal, it is of advantage to have a maximum amount of the trivalent antimony salt in the treating solution. Accordingly, the upper limit of the amount of the trivalent antimony salt in the treating composition is governed by the solubility of the salt in the treating composition. There is no lower limit with regard to the amount of the trivalent antimony salt which can be added to the composition. However, for practical purposes there must be a minimal amount of the trivalent antimony salt in the composition in order to obtain the desired effect in a reasonable length of time. Using antimony salt, the amount of the antimony trichloride which is preferably employed is between 0.5 gram per liter to about 15 grams per liter.
Various types of well known complexing agents can be employed in the present invention. Compounds which deserve particular attention in this regard are, for example, tartaric acid, gluconic acid, citric acid, glycolic acid, phytic acid, kojic acid, sorbitol and ethylenediamine-tetraacetic acid, with tartaric acid being the preferred complexing agent for employment in the present invention. The amount of the complexing agent that is added to the composition of this invention, is dependent on the particular complexing agent which is employed and the relative amount of sulfuric acid and the trivalent antimony salt in the composition. The amount of a particular complexing agent which must be added in order to be effective in preventing the oxidation of the trivalent antimony to the pentavalent state in a given composition can readily be determined on a small scale by preparing compositions containing various amounts of the complexing agent and the required amount of sulfuric acid and the trivalent antimony, and increasing the amount of the complexing agent in each composition until a stable composition is obtained.
Using tartaric acid as an example, an amount at least 0.5 gram per liter is required in order to have a stable solution. However, amounts in excess of this are generally employed with the amount up to 20 grams per liter being practical. Amounts above 20 grams per liter are generally not employed in that the excess amounts do not have any beneficial effect on the stability of the solution.
When the surfaces of the ferrous metals which are to be treated are somewhat contaminated, as for example by having a light oxide film coating or a film of a lubricant thereon, it is considerably advantageous to include in the treating composition a small amount of either hydrochloric acid or a salt of hydrochloric acid. The amount of hydrochloric acid that is employed can be relatively small, with at most 10 grams per liter of hydrochloric acid calculated on 100 percent concentration being required. Generally however, amounts between 1 and 10 grams per liter are quite sufficient to remove any contamination from the surface of the metals to be treated. Various types of hydrochloric acid salts can be used. These would include the acid salts and even the neutral salts such as sodium chloride. The amount of the salt that is added is calculated so that the chloride ion concentration would be equivalent to that when 1-10 grams of hydrochloric acid calculated at 100 percent concentration is used.
In accordance with the method of this invention, the ferrous metal object on which the black matte coating is to be formed is thoroughly cleaned. The metal object is contacted with the sulfuric acid solution of the trivalent antimony salt and the complexing agent. The object may be immersed in a bath of the composition or the composition may be sprayed onto the subject. The object should be in contact with the treating solution for between 0.5 and 5 minutes with the treating solution at a temperature from 60° to 100° F. Higher treating temperatures and longer treating times can be employed to increase the thickness of the black matte coating on the treated object. Depending upon the surface involved, a small quantity of HCl may be added to the pretreat solution in quantities up to about 10 g./. Following treatment with the sulfuric acid solution, the metal object is rinsed with water. The object, as a result of this treatment has a black coating on the surface thereof.
The treated object is thereafter subjected to a phosphate coating treatment. The composition of the phosphate coating bath is not critical. Any of the well-known phosphate compositions may be employed. In addition to the zinc and phosphate ions, it is of advantage to include nickel ions.
Especially good results are obtained with the process of the present invention when phosphate solutions such as those disclosed in Schlossberg et al. U.S. Pat. No. 3,269,877 are employed. These phosphate compositions impart an additional blackening effect, in addition to substantially improving the physical properties of the black matte finish.
The following examples are given by way of illustration of additional compositions included within the scope of the present invention and are not intended to limit in any way the scope of the subjoined claims. All percentages are percent by weight unless otherwise indicated.
EXAMPLE 1
A cleaned and pickled 4X4 inch cold rolled steel test panel was immersed for 1 minute at 80° F. in an aqueous solution containing 88 grams per liter of sulfuric acid, (calculated at 100 percent concentration), 2 grams per liter of antimony trichloride, and 2 grams per liter of tartaric acid. The test panel was rinsed in cold water. The test panel at this stage had a black coating deposited on its surface. A phosphate coating was deposited on the surface by immersing the test panel in an aqueous solution containing 0.9 percent phosphate ion (H 3 PO 4 ), 0.28 percent nitrate ion (HNO 3 ), 0.351 percent zinc ion (ZnO) and 0.012 percent cobalt ion (Co(NO 3 ) 2 ). The sample was immersed for 15 minutes at a temperature between 190°-200° F. The panel was rinsed with hot water and dried.
The test panel after this treatment had a uniform black matte finish.
EXAMPLE 2
Example 1 was repeated with the exception that the test panel was not pickled and which had a slight but visual oxide coating. The treated test panel had an uneven black matte finish.
EXAMPLE 3
Example 1 was repeated with the exception that a test panel of cold rolled steel having a slight but visual oxide coating was employed and 10 grams per liter of hydrochloric acid (calculated at 100 percent concentration) was added to the treating composition. The treated sample after the phosphate treatment had a uniform black matte finish equivalent to the finish on the test panel prepared in Example 1.
EXAMPLE 4
Test panels of cleaned and pickled cold rolled steel were immersed in an aqueous treating composition comprised of 100 grams per liter of sulfuric acid (calculated at 100 percent concentration), 10 grams per liter of antimony trichloride (anhydrous) and 10 grams per liter of tartaric acid, for the times and temperatures noted below, and thereafter a phosphate coating was applied as described in Example 1.
Time Degrees Sample Minutes Fahrenheit Results ____________________________________________________________ ______________ 1 0.5 60 Thin black matte finish 2 0.5 80 Thin but even black matte finish, heavier than sample 1 3 0.5 100 Full black matte finish 4 1.0 60 Sample obtained about equivalent to sample 2 5 1.0 80 Sample having a finish equivalent to sample 3 6 1.0 100 Heavy Black matte finish 7 5.0 100 Thick black matte finish ____________________________________________________________ ______________
EXAMPLE 5
Example 1 was repeated with the exception that 12 grams per liter of gluconic acid was employed in place of the tartaric acid. The results obtained were equivalent to the results obtained in Example 1
EXAMPLE 6
Example 1 was repeated with the exception that 12 grams per liter of citric acid was employed in place of the tartaric acid. The black matte finishes obtained on the samples in this example were equivalent to those in Example 1.
EXAMPLE 7
Example 1 was repeated with the exception that the tartaric acid was replaced with 1 gram per liter of glycolic acid. The results obtained in this example were equivalent to the results obtained in Example 1.
EXAMPLE 8
Example 1 was repeated with the exception that the tartaric acid was replaced with 8 grams per liter of phytic acid. The coating obtained in this example was equivalent to the coating obtained in Example 1.
EXAMPLE 9
Example 1 was repeated with the exception that the tartaric acid was replaced with 6 grams per liter of kojic acid. The coating obtained in this example was the same as the coating obtained in Example 1.
EXAMPLE 10
Example 1 was repeated with the exception that the tartaric acid was replaced with 9 grams per liter of sorbitol. The samples treated in accordance with this example were equivalent to the samples obtained in Example 1.
EXAMPLE 11
Example 1 was repeated with the exception that the tartaric acid was replaced with 5 grams per liter of ethylenediaminetetraacetic acid. Samples treated in accordance with this example were equivalent to the samples obtained in Example 1.
EXAMPLE 12
Measured test panels of cold rolled steel were treated at room temperature (70° F.) for one minute with the aqueous composition comprised of 88 grams per liter of sulfuric acid (calculated at 100 percent), 2 grams per liter of antimony trichloride (anhydrous) and 2 grams per liter of tartaric acid (anhydrous) and 10 grams per liter of hydrochloric acid (calculated at 100 percent) and thereafter a phosphate coating was applied as in Example 1.
The treated samples had a uniform black matte finish. It was found that when the above solution was employed as the finishing agent for obtaining the black matte finish, that it could satisfactorily treat 140 sq. feet of the steel panels per gallon of treating solution before serious depletion of the solution occurs.
EXAMPLE 13
Example 1 was repeated with the exception that the phosphate coating solution employed in Example 1 was replaced with a phosphate solution comprised of 0.9 percent phosphate ion (H 3 Po 4 ), 0.284 percent nitrate ion (HNO 3 ) and 0.351 percent zinc ion (ZnO). The test panel had a deep black matte finish which was slightly lighter in color than the sample prepared in Example 1 but it would be of desirable and commercially acceptable quality.