US2837449A - Composition of matter for and process of producing phosphate layers on iron surfaces - Google Patents

Description

United States Patent COMPOSITION OF MATTER FOR AND PROCESS OF PRODUCING PHOSPHATE LAYERS 0N IRON SURFACES Bruno Blaser, Dusseldorf-Urdenbach, Germany, assignor to Henkel & Cie. G. m. b. H., Dusseldorf-Holthausen, Germany, a corporation of Germany No Drawing. Application August 11, 1953 Serial No. 373,691

Claims priority, application Germany August 14, 1952 7 Claims. (Cl. 1486.15)

This invention relates to a composition of matter adapted to provide articles made of iron and parts thereof with a protective or rust proofing layer, and more particularly to a composition of matter adapted to provide iron articles with a phosphate layer, and to a process of producing such phosphate layer on iron surfaces.

The practice is well known to provide iron articles and parts thereof with a phospate layer for rust proofing said articles by treating said articles and parts with solutions of phosphoric acid. The adhesiveness of paints and lacquers to iron surfaces is considerably improved by such phosphate layers. Solutions suitable for the production of such layers are prepared with free phosphoric acid as well as with acid alkali phosphates.

When packing and shipping such free phosphoric acid or working therewith, there are only available containers which, on damage or breakage, allow the phosphoric acid to run out and, thus, to cause considerable damage. Dry alkali salts of phosphoric acid yielding aqueous solutions of acid reaction do not possess said disadvantage; however, the adhesiveness of lacquer and paint coatings to the iron surfaces is not satisfactory when using such salt solutions because the salts remain in the dry state on the treated iron surface after drying subsequent to the treatment.

It is, of course, possible to rinse the treated parts or articles before drying. This rinsing step, however, involves an additional operation and may cause subsequent rusting of the rinsed surface. Such subsequent rusting is avoided if a small amount of the bath liquid is permitted to remain on the surface of the article during drying after the workpiece has been removed from the bath.

It is one object of this invention to provide a new composition of matter adapted to provide iron articles and parts thereof with a phosphate layer which does not have the drawbacks and disadvantages of heretofore used phosphatizing, parkerizing, and the like compositions.

Another object is to provide a rust proofing composition capable of depositing a phosphate layer on iron or other metal surfaces which can be prepared and shipped as a dry powder and used in the rust proofing plant merely by the addition of water thereto.

Another object of this invention is to providea simple and effective process of producing phosphate layers on iron surfaces by means of such new compositions of matter.

Various other objects and advantages of this invention will become apparent as this description proceeds.

in principle, the present invention involves the use of aqueous solutions prepared from addition products of phosphoric acid and amides of low molecular carboxylic acids in the surface treatment of iron or other metal articles and parts thereof. The use of such' compositions of matter and solutions thereof avoids and 2,837,449 Patented June 3, 1958 ice 2 eliminates the drawbacks and disadvantages of known processes, compositions and solutions.

Addition products of amides of low molecular carboxylic acids and phosphoric acid suitable for the purpose of this invention are produced in a simple manner by mixing phosphoric acid of high concentration and the corresponding carboxylic acid amide with each other. The proportion of phosphoric acid and carboxylic acid amide in said mixture is between about 1 mol to about 2 mols of amide to 1 mol of phosphoric acid. Preferably about equimolecular amounts of both components are used. Addition products obtained with an excess of phosphoric acid become stickier and more hygroscopic with increasing excess of phosphoric acid. Therefore it is advisable to use an excess of carboxylic acid amide. This does not impair the usefulness of the resulting addition products in the production of phosphate layers on iron surfaces. The addition product or adduct is immediately formed on mixing the components. Sometimes it is expedient to moderately heat the mixture to temperatures up to about 60 C. According to a preferred mode of operation, the addition product is formed at temperatures between 10 C. and 40 C. while stirring the mixture. The resulting; addition products are water soluble, solid, crystalline, pulverulent substances. The linkage between phosphoric acid and carboxylic acid amide, however, is not a salt-like linkage because the pH- value of aqueous solutions of said addition products is not higher, or only slightly higher, than the pH-value of equimolecular solutions of phosphoric acid whereas if the compounds, for example of phosphoric acid and urea, were in fact salts (i. e. compounds wherein the acid hydrogen atom of phosphoric acid were neutralized) the pH-value would be considerably higher than the pH- value of an equimolecular solution of phosphoric acid.

Low molecular carboxylic acids, the amides of which, according to this reaction, form addition products with phosphoric acid are monoand di-basic carboxylic acids having 1 to 3 carbon atoms in their molecule. Especially suitable amides of this. type are the amides of carbonic acid, formic acid, acetic acid, propionic acid, or malonic acid. The most important addition product for all practical purposes is the addition product of phosphoric acid and urea.

It is advisable to subject the iron or other metal articles or parts thereof before treatment to a deg-teasing treatment. Such degreasingrnay be effected by means of acid, neutral or alkaline baths which may contain water soluble or water insoluble emulsified solvents. The degreased articles or parts thereof are treated according to the present-invention with solutions of said carboxylic acid amide-phosphoric acid addition products in about the same manner as with other known phosphatizing solutions. tions has proved to yield excellent results.

The concentrationof the solution used for said treatment may be within'the range between 0.125% and 10.0% of phosphoruspentoxide. This concentration corresponds to a concentrationof between 0.25% and 20.0% of phosphorus pentoxide, calculated for the ureaphosphoric acid addition product. The treatment is preferably carried outwithin a range of concentration of between about 0.5% and about 2.5% of phosphorus pentoxide.

about 2.0 and about 1.0. The temperature of treatment is between about room temperature, i. e. about 20 C., and boiling temperature, and preferably between about 60 C. and about C. The duration of treatment varies considerably. Primarily it is dependent upon the thickness of thedesired phosphate layer, i. e., the

Working under the following special condi- Thereby the pH-value of the solutions is between about 3.0 and'about 0.5 and preferably between depth to which the surface is to be phosphatized and changed. Duration of treatment is also "dependent at least to a certain extent upon:- the thickness of the work pieces to be treated; for iron" sheets and plates or thinwalled articles and parts thereof are more readily heated to the required temperature of treatment than articles and parts of greater wall thickness. In general, the duration of treatment will be between about one-quarter of a minute and about minutes and preferably between about half a minute and about 3 minutes.

It is abvisable to add water soluble organic solvents as well as acid resistant capillary active substances to the bath in order to improve wetting of the iron articles and parts with said liquid. Especially suitable solvents for this purpose are water soluble lower aliphatic alcohols or ketones. Capillary active substances which may be successfully used as additional wetting agents in the process according to this invention are organic compounds having in their molecule a group which renders the compound water soluble, as well as a water insoluble group. The water solubilizing group may be of acid, basic, or non-ionic character. The water insoluble group is a non-aromatic, i. e. an aliphatic or cycloaliphatic hydrocarbon residue with at least 8 and not more than carbon atoms, and preferably with 12 to 18 carbon atoms in its molecule. As a group which renders the compound water soluble there is preferably used a group which exhibits its solubilizing property also in acid solution such as, for instance, a sulfonic acid or a sulfuric acid mono ester group. Capillary active compounds of this type are, for instance, fatty alcohol sulfonates, parafiin or alkyl phenyl sulfonates and the like. In the last mentioned compounds the aromatic residue represents the connecting link between the alkyl residue and the water solubilizing group.

Capillary active compounds with basic groups which render such compounds water soluble are especially quaternary ammonium compounds, such as, for instance, alkyl pyridium salts with 8 to 14 carbon atoms in the alkyl residue, or alkyl trimethyl ammonium salts in which the alkyl residue is a higher molecular residue, i. e. contains the above mentioned number of carbon atoms. Especially noteworthy compounds of the group of capillary active compounds with non-ionic, water solubilizing groups are capillary active compounds with polyglycol ether chains. They may be derived from fatty acids, fatty acid amides, fatty alcohols, alkyl phenols, alkyl sulfonam-ides, or alkyl phenyl sulfonamides. The use of such additions is recommended especially when iron articles or parts are to be treatedv which are relatively clean or are only slightly soiled so that contamination of the surface may be removed by the phosphatizing bath itself.

The addition products of phosphoric acid suitable for carrying out the process according to this invention can be readily handled and worked with since they are solid, pulverulent products. They can be mixed with wetting agents or emulsifiers for simultaneous use therewith and may be marketed in such mixture as solid, pulverulent products which are free of the disadvantages of rust proofing preparations using liquid phosphoric acid. When used to produce phosphate layers on iron or other metals, for instance, urea phosphate dried on said treated ironsurface does not impair the adhesiveness of subsequent paint or lacquer coating applied to such treated surface, as is the case when using alkali phosphates. Therefore the liquid fromthe treatment bath remaining on the treated surface need not be rinsed off after treatment, thus eliminatingone operation in the working up of the treated articles .or parts.

The phosphoric acid amide addition products for use according to my invention may be prepared in various ways by the simple mixture of the phosphoric acid and an amide of a low molecular carboxylic acid. Some examples of methods of preparation which may be used are as follows:

Example 1 addition product or adduct, which may be added to water to provide a rust proofing bath.

Example 2 100 grams of phosphoric acid (76%) are mixed with 63 grams of phosphorus pentoxide and kept from one to two days at room temperature. 100 grams of urea dissolved in a small amount of methanol are added to' the solution. After the heat of reaction has been dissipated, the urea addition product crystallizes in fine crystals. Crystallization may be improved by cooling rapidly to a lower temperature. After filtration a finely crystallized urea addition product of great purity is recovered. The methanol which still contains a small amount of said addition product may serve as a solvent for the next batch.

Example 3 142 grams of phosphorus pentoxide are carefully added to 54 grams of water. The mixture is then heated on a steam bath for several hours. The cool hydrolysate is then mixed with 120 grams acetamide whereby the temperature of the reaction mixture increases. A clear solution results which, on cooling, solidifies to a crystalline addition product or adduct suitable for the production of treatment baths for the formation of protective layers on iron or other metal articles.

Example 4 142 grams of phosphorus pentoxide are carefully added to 54 grams of water. The mixture is heated on a steam bath for several hours. The cooled hydrolysate is then mixed with a solution of 90 grams of formamicle dissolved in cc. of methanol. After the heat of reaction has been dissipated, a colorless addition product crystallizes which is filtered ofi. The mother liquor may be used as solvent for the next batch.

The following examples serve to illustratethe application of the products of my invention to the treatment of metal articles without, however, limiting the same thereto.

Example 5 Several cold rolled iron sheets of the size 50 mm. by 150 mm. and 30 mm. by 15% mm. and the thickness of 0.6 mm. were dcgrcased by means of an alkaline bath, thoroughly rinsed with water, and then placed for 3 minutes into a phosphoric acid solution heated to C. and containing 0.72% of phosphorus pentoxiclc. One of the two solutions used in this comparative test was prepared from monobasic sodium phosphate and had a pH of 4.5; the other solution was made from a phosphoric acid-urea addition product or adduct and had a pH of 1.6-1.8. The treated sheets were removed from the bath and immediately thereafter dried in a drying oven at C. The dried sheets, after cooling, were immersed in a black nitrocellulose lacquer. Untreated sheets as controls were lacquered in the same way. The nitrocellulose lacquer used was diluted with solvents in order to adjust its viscosity to a time of efrlux of 35 to 36 seconds in a Ford beaker. Such a lacquer layer is very sensitive to cracking and peeling in the subsequent shaping and working of the treated workpieces. After said lacquering, the sheets remained first in the workrom for 48 hours and were then exposed for weathering to the open air for 4 days.

The lacquer layer on the various test sheets was tested for its bending and impact resistance.

In the bending.

test the 30 mm. by 150 mm. sheets were bent about 180 around a 7 mm. mandrel. The untreated sheets and the sheets treated with monobasic sodium phosphate showed in the bending test considerable breaking and peeling of the lacquer layer. Sheets treated with the solution of a phosphoric acid-urea addition product did not exhibit any noticeable peeling of the lacquer layer.

Impact tests were carried out on the 50 mm. by 150 mm. test sheets with the device described in the journal, Farben, Lacke, Anstrichstofie (Pigments, Lacquers and Paints) year 1949, page 10. The impact resistance of the lacquer was observed, however, not electrically but visually. The drop weight, weighing 2 kg., was allowed to drop upon the 50 mm. by 150 mm. sheet to be tested from a height of 40, 50, 60, 70, 80, and 90 cm. In these tests the lacquer layer of the untreated sheets cracked off at all heights of dropping. No cracking oiT of the lacquer was observed with sheets treated with monobasic sodium phosphate at drops of 40 cm. and 50 cm. while at drops of between 60 cm. and 90 cm. the lacquer cracked off. The sheets treated with a solution of the phosphoric acid-urea addition product or adduct did not show any cracking of the lacquer at any of the heights from which the weight was dropped.

Example 6 A pulverulent product for carrying out the process according to this invention may consist of 6% of urea phosphate adduct and 3% of an alkyl phenyl sulfonate with 10 to carbon atoms in its alkyl residue. The alkyl phenyl sulfonate may be substituted in said powder by the same amount of a fatty alcohol sulfonate having 12 to 14 carbon atoms in its alkyl residue or by the same amount of an addition product of about 8 mols of ethylene oxide to such a fatty alcohol. The same amount of an alkyl pyridium chloride obtained by condensing a mixture of alkyl chlorides having 8 to 14 carbon atoms in their alkyl residue and pyridine may also be used in place of said alkyl phenyl sulfonate. Any of these products or mixtures thereof may be added to water to provide a treatment bath for coating or rust proofing iron or other metal articles.

The treatment of iron articles in the above described phosphatizing bath may be carried out under the same conditions as described in Example 5, or under the usual conditions of phosphatizing or rust proofing iron or steel articles.

In place of the addition product of phosphoric acid and urea used in the above examples, and which are the most important from a practical standpoint, there may be employed other addition products of phosphoric acid and other acid amides such as, for instead, formamide,

acetamide, oxamide, malonamide, and other amides of monoand di-basic carboxylic acids having 1 to 3 carbon atoms in their molecule.

Various changes and modifications in the composition of the phosphoric acid addition products, the con-' centration of the phosphatizing bath, the temperature and duration of treatment, and the like, may be made by those skilled in the art in accordance with the principles set forth herein within the spirit of my invention and the scope of the following claims.

I claim:

1. In a process of producing phosphate layers on iron surfaces, the step comprising immersing iron articles in an aqueous phosphatizing solution consisting essentially of the addition product of phosphoric acid and an amide of a low molecular carboxylic acid containing from 1 to 3 carbon atoms to cause formation of a phosphate layer on the surface of said iron article.

2. In a process of producing phosphate layers on iron surfaces according to claim 1, wherein the amide of a low molecular carboxylic acid is urea.

3. In a process of producing phosphate layers on iron surfaces according to claim 1, wherein the pH of the aqueous phosphatizing solution, during treatment, is between 05 and 3.0.

4. In a process of producing phosphate layers on iron surfaces according to claim 3, wherein the pH of the aqueous phosphatizing solution, during treatment, is between 1.0 and 2.0.

5. In a process of producing phosphate layers on iron surfaces according to claim 1, wherein the temperature of the aqueous phosphatizing solution, during treatment, is between about 20 C. and about boiling temperature.

6. In a process of producing phosphate layers on iron surfaces according to claim 5, wherein the temperature of the aqueous phosphatizing solution, during treatment, is between about C. and C.

7. In a process of producing phosphate layers on iron surfaces according to claim 1, wherein the aqueous phosphatizing solution contains between about 0.125% and about 10.0% of phosphorus pentoxide.

References Cited in the file of this patent UNITED STATES PATENTS 1,428,087 Gravell Sept. 5, 1922 1,440,056 Clarkson et al Dec. 26, 1922 1,936,533 Albrecht Nov. 21, 1933 1,951,518 Meisner et a1. Mar. 20, 1934 2,318,606 Goebel May 11, 1943 2,476,345 Zavarella July 19, 1949 2,481,977 Cinamon Sept. 13, 1949 2,715,059 Miller Aug. 9, 1955

Claims (1)

1. IN A PROCESS OF PRODUCING PHOSPHATE LAYERS ON IRON SURFACES, THE STEP COMPRISING IMMERSING IRON ARTICLES IN AN AQUEOUS PHOSPHATIZING SOLUTION CONSISTING ESSENTIALLY OF THE ADDITION PRODUCT OF PHOSPHORIC ACID AND AN AMIDE OF A LOW MOLECULAR CARBOXYLIC ACID CONTAINING FROM 1 TO 3 CARBON ATOMS TO CAUSE FORMATION OF A PHOSPHATE LAYER ON THE SURFACE OF SAID IRON ARTICLE.