US3615912A

US3615912A - Metal-treating process

Info

Publication number: US3615912A
Application number: US11901A
Authority: US
Inventors: Friedrich Dittel; Peter Jorns; Walter Stenger
Original assignee: Hooker Chemical Corp
Current assignee: Henkel Corp
Priority date: 1969-08-19
Filing date: 1970-02-16
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: ES377516A1; FR2058366A1; DE1942156A1; DE1942156B2; BE742133A

Abstract

A process for forming a phosphate coating on metal surfaces wherein an alkali metal and/or ammonium orthophosphate solution, having a pH within the range of about 3.0 to 5.5 is sprayed on the metal surface at a pump pressure of from about 10 to 75 atmospheres. The process carried out in this manner is effective in both cleaning and coating the metal surfaces to which it is applied. In addition to the alkali metal and/or ammonium orthophosphate, the phosphating solution may also contain a benzoate, an hydroxyl amine, a molybdate, and a surface-active agent.

Description

United States Patent [72] lnventors Friedrich Dittel Mainz-Kostheim;

Peter Jorns, Frankfurt am Main; Walter Stenger, Frankfurt am Main, all of Germany [21] Appl. No. 11,901

[22] Filed Feb. 16, 1970 [45] Patented Oct. 26, 1971 [73] Assignee Hooker Chemical Corporation Niagara Falls, N.Y.

[32] Priority Aug. 19, 1969 [3 3] Germany [54] METAL-TREATING PROCESS Primary Examiner-Ralph S. Kendall Attorneys-Stanley l-l. Lieberstein and William J. Schramm ABSTRACT: A process for forming a phosphate coating on metal surfaces wherein an alkali metal and/or ammonium orthophosphate solution, having a pH within the range of about 3.0 to 5.5 is sprayed on the metal surface at a pump pressure of from about 10 to 75 atmospheres. The process carried out in this manner is effective in both cleaning and coating the metal surfaces to which it is applied. In addition to the alkali metal and/or ammonium orthophosphate, the phosphating solution may also contain a benzoate, an hydroxyl amine, a molybdate, and a surface-active agent.

METAL-TREATING PROCESS This invention relates to a method for the chemical surface treatment of metal, and more particularly it relates to a process for treating ferrous metal surfaces to degrease and clean the surfaces and fonn thereon a thin, adherent phosphate coating.

It is well known in the art that aqueous acidic solutions based on alkali and/or ammonium orthophosphates and having a pH value in the range of about 3 to 6, may be used for simultaneously degreasing, cleaning and forming protective phosphate layers on iron or steel surfaces. Generally, the phosphating solutions have been applied from stationary immersion or spraying equipment and produce good rust-proofing and/or paint-base coatings.

it has further been known to apply treating solutions of the above type from nonstationary systems, i.e., by means of steam injection or in combination with steam suction. In this manner of operation, the solution is heated to about 140 C. and conveyed to a jet orifice under about 5-9 atmospheres excess pressure (gauge pressure). The stream of very hot watersteam, which contains the solution components, is then sprayed onto the object which is to be treated. Although the coatings produced in this manner are comparable to those obtained in stationary systems, frequently considerable variations in the quality of the coating obtained will result. Moreover, in order to maintain the desired concentration of chemicals in the steam, special metering arrangements are required, which necessitate constant control. Additionally, in many plants there is no central supply of steam available so that an oil or gas-fed steam generator must be installed, which generator requires considerable waiting time before it reaches operating condition and also requires constant maintenance. Further drawbacks which are encountered in this method involve the fact that the process must be carried out at very high temperatures, so that the steam emerging from the jets creates difficult working conditions for operating personnel and, frequently, prevents any visual observation of the surfaces being treated. This latter aspect, in itself, may contribute considerably to the difiiculties which are involved in maintaining uniform quality of the coatings produced.

It is, therefore, an object of the present invention to provide a method for the pressure application of phosphate coatings, which method operates at appreciably lower temperatures than present methods using steam.

A further object of the present invention is to provide an improved pressure application process for phosphate coatings, which process requires appreciably less maintenance in operation while producing consistently acceptable coating results.

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

Pursuant to the above objects, the present invention includes a method for the treatment of metal surfaces which comprises spraying an aqueous acidic solution, containing alkali and/or ammonium orthophosphates and having a pH value of from about 3.0 to 5.5, and effecting the spraying of this solution onto the metal surface to be treated at a pump pressure of from about to 75 atmospheres (gauge). The coatings produced by this method are found to provide an excellent base for the application of paints and similar protective films and although the method is particularly adapted for the treatment of ferrous metal surfaces, such as iron and steel, it may also be used on surfaces of zinc, aluminum, and their al loys.

More specifically, in the method of the present invention the aqueous acidic phosphating solutions used have a pH within the range of about 3 to 5.5 and are based on alkali and/or ammonium orthophosphates. Preferably, these phosphates are present in the solution in amounts within the range of about 2 to 10 grams per liter, calculated as NaH,P0,. it is to be appreciated that the compositions for use in the present invention may contain one or more of the alkali, i.e., sodium, potassium, lithium, cessium, or rhubidium,

orthophosphates or ammonium orthophosphates. Accordingly, for convenience hereinafter, reference will be made to the use of alkali orthophosphates, as including both the above-indicated alkali orthophosphates and the ammonium orthophosphates. Additionally, although the use of the monoalkali orthophosphates, such as monosodium orthophosphate are preferred, the diand tri-alkali orthophosphates may also be used. Particularly with the use of these latter materials, phosphoric acid may be added to the solution to adjust the pH of the solution to within the desired range of 3 to 5.5 and preferably within the range of about 3.5 to 4.

The treating solutions for use in the present method utilize the orthophosphates and it is preferred that any appreciable amounts of condensed alkali and/or ammonium phosphates in the solution be avoided. In this regard, it has been found that quantities of condensed alkali and/or ammonium phosphates even as small as 3 percent by weight of the orthophosphates have a deliterious effect on the coatings which are formed. It is for this reason that the coating solutions of the present invention should be substantially free of any condensed alkali and/or ammonium phosphates.

The phosphating solutions used in the method of the present invention desirably also contain a benzoate. The benzoate content of these coating solutions is desirably within the range of about 0.05 to 0.5 grams per liter, calculated as sodium benzoate, and preferably within the range of about 0.1 to 0.4 grams per liter. The benzoate may be incorporated in the solution in the form of a benzoic acid, or as one of the soluble salts thereof, such as sodium benzoate.

in many instances, it is further desirable to effect the acceleration of the coating action of the solution by addition thereto of hydroxyl amine or its salts. Preferably, the hydroxyl amine is added as the salt, such as hydroxyl amine acid sulfate, hydroxyl amine sulfate, hydroxyl amine hydrochloride, or the like, with the hydroxyl amine sulfate being preferred. Preferably, the hydroxyl amine content of the treating bath is from about 0.04 to 0.3 grams per liter, calculated as NH,OH. Additionally, the efficiency of the phosphating solution may be further improved by the addition of a molybdate to the bath. Various soluble molybdate materials, particularly the alkali molybdates may be used. The molybdate content of the bath is preferably from about 0.0l to 0.l grams per liter, calculated as Na,MoO..

It has further been found that the cleaning and degreasing efficiency of the phosphating solutions may further be improved by incorporating a suitable surface-active agent in the solution. Although various surface-active agents have been found to be suitable, in many instances the nonionic surfaceactive agents, and particularly the derivatives of the polyoxyalkylenes are preferred. In some instances, however, various anionic surface-active agents may also be used. Desirably, the surface-active agents are present in the solution in amounts within the range of about 0.05 to l gram per liter.

in formulating the treating solutions for use in the method of the present invention, these solutions are desirably prepared from a concentrate material, which concentrate may contain up to percent by weight of the monoalkali and/or monoammonium orthophosphate. Preferably, however, the concentrate composition will contain from about 60 to 97 percent by weight of the monoalkali and/or monoammonium orthophosphate, from about 3 to 12 percent by weight of benzoate, calculated as sodium benzoate, up to about 7 percent by weight of hydroxyl amines or its salts, calculated as Na oH, up to about 3 percent by weight of a molbdate, calculated as Na,MoO,, and up to about l2 percent by weight of the surface-active agent. This concentrate composition is then dissolved in water to form the phosphating solutions for use in the present method. Desirably, the concentrate composition is dissolved in water in amounts of from about 3 to 10 grams per liter, with amounts within the range of from about 4 to 6 grams per liter being preferred.

In applying the phosphating solutions, in accordance with the present method, the solution is sprayed onto the metal surface to be treated under a pump pressure of from about to 75 atmospheres excess pressure. To obtain these high pressures, various pump systems may be used, as for example, double-acting piston pumps with compressed-air drives; piston pumps with electromotor drives; multistage rotary pumps; or gear pumps. With whatever type of pump is used, the treating solution is drawn by the pump from a suitable storage tank, the temperature of the treating solution typically being within the range of about 50 to 80 C., although higher and lower temperatures may be used in some instances. After the solution has been compressed to the required high pressure, i.e., about 10 to 75 atmospheres, it is led through one or more tubes or lances which are provided, at their exit points, with appropriate spray jets. Although various types of jets may be used, in many instances it has been found to be preferred to utilize flat jets, i.e. fishtail jets, having a capacity of from about 4 to 6 liters per minute.

In applying the coating solution, the spraying tubes or lances are preferably used in such a manner that the jet is passed in a crosswise motion at a distance of about l0 centimeters from the surface which is to be treated. Normally, the treatment should start at the top or upper end of the surface to be treated so as to minimize the quantities of runoff solution which come into contact with already treated surfaces. Where the solutions used contain surface-active agents, it has been found that frequently the surfaces will become grease-free and fully wetted after only about l0 to seconds treatment. Moreover, through the appropriate atomization of the treating solution into very fine droplets, which are sprayed at these high velocities, the solutions react very rapidly with the surface being treated and will, in very short time, form thin coherent iron oxide-iron phosphate layers. Generally, it has been found that when using only one spraying lance, depending upon the size, form and surface condition of the objects being treated, about 1 to 5 square meters of surface may be treated per minute.

In addition to pumping the actual treating solution, in carrying out the method of the present invention, a preconcentrate containing up to as much as I00 grams per liter of the concentrate compositions described above, may also be used. In this method, these preconcentrate compositions will be admixed with water, in a mixing line, using appropriate valve systems, to bring them to the desired treating concentration. In this manner, the need for bulky and cumbersome equipment and storage tanks for the treating solution is avoided.

Once the application of the treating solutions, using the present method, has been completed, it is generally desirable to rinse the treated surfaces with water. This rinsing may be effected using either the same spraying lances, which have been appropriately switched over to water, or alternatively, by means of a separate rinsing system. Where the treated objects are to be given a subsequent paint or similar coating, they are desirably rinsed with deionized water so as to provide satisfactory paint stability. Generally, and particularly where the treating solutions contain benzoate,'an after treatment with a corrosion inhibiting material, such as a solution containing chromic acid, is not necessary. If desired, however, rinsing with chromic acid solutions or similar inhibiting materials may be utilized.

It has been found that where the treating solutions applied in the method of the present invention contain a benzoate, there is substantially no susceptability of the treated surfaces to rusting or other corrosion attack when they are allowed to dry in air, either with or without a subsequent water rinse. Accordingly, when such solutions are used, neither oven drying or drying with compressed air is necessary. In contrast, however, where the treating solutions used contain appreciable amounts of condensed phosphates, even with the benzoates present, it is found that the treated surfaces have increased corrosion susceptability so that appreciable corrosion of the surfaces takes place when they are permitted to dry in air.

The method of the present invention has been found to be extremely efficient, requiring low installation and chemical cost and involving a simple method of operation and a rapid startup and is, therefore, suitable for a wide variety of uses. This method has been found to be particularly applicable in those installations where objects with large surfaces, such as for example, agricultural machinery, buses, trucks of bulky constructional components and the like are being produced. Additionally, the method is particularly applicable to operations wherein the number of objects treated per day is relatively small as for example in the manufacture of special bodies, as well as in short runs or in repair and maintenance shops.

Although the method of the present invention is particularly suited for the surface treatment of ferrous metal, e.g. iron and steel, the method is also suitable for treating the surfaces of the zinc, aluminum, and their alloys. In the treatment of ferrous metal, the iron oxide-iron phosphate layer which is formed is generally from a blue to reddish shiny color, having a coating weight typically within the range of about 0.3 to 0.8 grams per square meter. This coating has been found to provide an excellent base for paint and similar organic coatings. Additionally, it is to be appreciated that although by use of the method of the present invention, degreasing and cleaning of the metal surfaces is also effected, in those instances where the surfaces are covered with strongly adhering impurities, it may be necessary to subject them to appropriate precleaning treatments before the utilization of the present method.

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, unless otherwise indicated, parts and percents are by weight and temperatures are in degrees Centigrade. It is to be appreciated, however, that these are merely exemplary of the present invention and are not to be taken as a limitation thereof.

EXAMPLE I An aqueous treating solution was formulated containing the following components in the amounts indicated:

Phosphoric acid was added to the solution to adjust the pH to 3.5 and the solution was heated to C. The solution was then compressed to about 30 atmospheres excess pressure by means of a compressed air-driven high-pressure pump and was then sprayed onto grease-coated steel sheets for one minute. The temperature of the solution as it emerged from the spraying jets was about 60 C., and the distance between the jet and the sheet being treated was about 10 centimeters.

Thereafter, the treated sheets were rinsed by spraying with water for 30 seconds at 20 C.; sprayed for 30 seconds with a 55 C. solution containing 0.16 grams per liter CrO, and 0.03 grams per liter Cr(IlI) ions; rinsed by spraying with deionized water and then dried for l0 minutes in a forced air circulating oven at I10 C. The thus'treated sheets were coated with a deep-blue, uniform iron oxide-iron phosphate layer.

The thus-treated surfaces were then spray painted with a polyacrylate base paint, the thickness of the applied paint film being about 26 pm. The painted sheets were then subjected to the standard salt-spray test in accordance with the procedure ASTM Bl 17-64. After 168 hours in the test, there was found to be a corrosion creepage of only 3 millimeters from the scratch line.

EXAMPLE 2 By way of comparison, a treating solution was formulated containing the following components in the amounts indicated:

ComponenLs Grams per Liter NaH,PO,(water-free) 2.8 Na,H,P,O,(water-free) L6 Phosphoric acid (P,O, content 725) 0,3 Nonionic surface active agent (as in Exam le I) 0.3

The pH of this solution was 4. Identical steel sheets, as used in example 1 were then treated with the solution in a conventional stationary four-zone spraying installation, the treating solution being sprayed for 2 minutes at 60 C. under a pressure of 1.5 atmospheres. This spray treatment with the treating solution was then repeated following which the sheets were rinsed with water, chromic-acid-containing solutions, deionized water, and dried, in the same manner as set forth in example 1. The iron oxide-iron phosphate coatings produced on the sheets were light blue in color.

The treated steel sheets were then painted, as in example I, and subjected to the same salt-spray test. In this instance, however, a corrosion creepage of three millimeters from the scratch line was produced after only 92 hours in the test.

EXAMPLE 3 In an automobile production plant, car bodies were treated using the high-pressure application method of the present invention to form a paint-base coating. In these experiments, a high-pressure spraying device was used in conjunction with a double-acting piston pump driven by compressed air at about 3 atmospheres over pressure. The phosphatizing solutions used were drawn into the pump from a storage tank, compressed to about 30 atmospheres excess pressure and were then sprayed onto the surfaces to be treated using two spraying lances. Each of the lances was provided with fishtail jets having an equivalent diameter of about 0.9 millimeters and an angle of the opening of the fishtailjets of about 65.

Two different solutions, designated A and B, were used for the experiments, which solutions contained the following components in the amounts indicated:

Both of these solutions were adjusted with phosphoric acid to a pH of about 4 and were then heated to about 80 C. by means of immersion heaters. The treating solutions were sprayed onto the objects with a jet having a spray capacity of about 4 liters per minute. The temperature of the sprayed solution was about 60 C. and the distance between the jets and metal surfaces was about to 20 centimeters. The spraying was started on the upper portion of the body and progressed slowly downwardly with a double crosswise motion. About one to two square meters of surface area were treated per minute. After about 10 minutes, the cleaning and protective layer formation was completed over the entire body. Thereafter, the bodies were sprayed with water and the residual water film was allowed to dry in air, about 3 to 5 minutes being required to effect complete drying. On those bodies which had been sprayed with solution A, it was found that a very heavy rust layer appeared within about 30 seconds after drying. In contrast, on the bodies on which solution B had been used, there was no evidence of rust or other corrosion after the drying in air.

The above experiments were again repeated with the exception that following the water rinsing, the bodies were after rinsed with a solution, at 50 C., made up with deionized water and containing 0.16 grams per liter CrO and 0.03 grams per liter Cr(lll) ions. In this instance, it was found that the bodies which had been treated with solution A, as well as those treated with solution B were dried in air without any sign of COlTOSlOn.

EXAMPLE 4 Grease-coated steel sheets were treated for one minute with the solutions A and B, as described in example 3 above, using a pump pressure of about 30 atmospheres and a solution temperature of 60 C. The treated sheets were then rinsed with water, after-rinsed with deionized water and dried. A polyacrylate base paint was then applied by spraying to form a paint thickness of about 25 t. These sheets were then subjected to the standard salt-spray test, according to ASTM B l l764. The sheets treated with solution A SHOWED A corrosion creepage of 3 millimeters after 96 hours in test while the sheets treated with solution 8 showed a corrosion creepage of 3 millimeters after I20 hours in tests.

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 thercwithin are possible and it is 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. In the process, wherein a phosphate coating is formed on a metal surface by the spray application of an aqueous acidic phosphatizing solution, the improvement which comprises formulating the phosphating solution with alkali and/or ammonium orthophosphates, maintaining the solution pH within the range of about 3.0 to 5.5 and spraying the solution onto the metal surface at a pump pressure of from about l0 to 75 atmospheres excess pressure.

2. The method as claimed in claim I wherein the phosphatizing solution used also contains from about 0.05 to 0.5 grams per liter benzoate, calculated as sodium benzoate.

3. The method as claimed in claim 2 wherein the solution contains from about 0.1 to 0.4 grams per liter benzoate.

4. The method as claimed in claim 2 wherein the phosphatizing solution also contains an accelerator selected from hydroxyl amine and hydroxyl amine salts, in an amount of from about 0.04 to 0.3 grams per liter, calculated as NH,OH.

5. The method as claimed in claim 4 wherein the phosphatizing solution also contains from about 0.01 to 0.l gram per liter molybdate, calculated as Na,MoO,.

6. The method as claimed in claim 5 wherein the phosphatizing solution also contains from about 0.05 to l gram per liter of a surface-active agent.

7. A concentrate composition, suitable for the preparation of an aqueous acidic phosphating solution for use in the method of claim 1, which concentrate composition comprises from about 60 to 97 percent by weight ofa monoalkali and/or monoammonium orthophosphate, from about 3 to l2 percent by weight benzoate, calculated as sodium benzoate, an accelerator selected from hydroxyamine and hydroxylamine salts, in an amount up to about 7 percent by weight, calculated as N H OH, up to about 3 percent by weight molyhdate, calculated as Na Moo and up to about 12 percent by weight of a surface-active agent.

i i i

Claims

2. The method as claimed in claim 1 wherein the phosphatizing solution used also contains from about 0.05 to 0.5 grams per liter benzoate, calculated as sodium benzoate.
3. The method as claimed in claim 2 wherein the solution contains from about 0.1 to 0.4 grams per liter benzoate.
4. The method as claimed in claim 2 wherein the phosphatizing solution also contains an accelerator selected from hydroxyl amine and hydroxyl amine salts, in an amount of from about 0.04 to 0.3 grams per liter, calculated as NH2OH.
5. The method as claimed in claim 4 wherein the phosphatizing solution also contains from about 0.01 to 0.1 gram per liter molybdate, calculated as Na2MoO4.
6. The method as claimed in claim 5 wherein the phosphatizing solution also contains from about 0.05 to 1 gram per liter of a surface-active agent.
7. A concentrate composition, suitable for the preparation of an aqueous acidic phosphating solution for use in the method of claim 1, which concentrate composition comprises from about 60 to 97 percent by weight of a monoalkali and/or monoammonium orthophosphate, from about 3 to 12 percent by weight benzoate, calculated as sodium benzoate, an accelerator selected from hydroxyamine and hydroxylamine salts, in an amount up to about 7 percent by weight, calculated as NH2OH, up to about 3 percent by weight molybdate, calculated as Na2MoO4 and up to about 12 percent by weight of a surface-active agent.