DE1279429B - Process for the production of corrosion-resistant protective coatings from electrochemically generated hydrated chromium oxide on metal surfaces - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C23f

German EL: 4g 41 - 15/00

Number: 1279429

File number: P 12 79 429.5-45 (T 29751)

Filing date: November 9, 1965

Open date: October 3, 1968

The invention relates to a method for producing protective coatings from electrochemically generated, hydrated chromium oxide on metal surfaces with improved corrosion resistance and excellent adhesion for paints, which is characterized in that the metal surface after the electrochemical production of the protective coating and before drying, initially with Washed water and then treated with an aqueous solution which is at least one water-soluble or a water-dispersible, cation-active wetting agent from the group of the aliphatic primary amine acetates, quaternary ammonium salts and their derivatives, pyridinium and methylpyridinium salts and their derivatives, polyoxyethylene alkylamines and polycondensation products of formaldehyde and dicyandiamides in an amount contains from about Γ to 50 g / l, and is then washed again with water.

The electrochemically generated, hydrated protective coatings treated according to the invention Chromium oxide on metal surfaces has excellent corrosion resistance under very humid conditions Conditions. Their adhesiveness to paints is especially in the case of the immediate Painting after degreasing or separating off lubricants improved in all respects.

U.S. Patent 3,136,663 describes a method of improving corrosion resistance of metals that have a protective layer. This improvement is due to the fact that an additional organic coating through the reaction of one in a second process step applied cationic compound is formed with an anionic polymeric compound, which is contained in the first protective layer.

US Pat. No. 3,107,221 discloses the use of cationic wetting agents as corrosion inhibitors known in acidic solutions that come into contact with metals.

Process for the electrochemical production of protective coatings from hydrated chromium oxide Metal surfaces are known. In this process, the metal to be coated is used as the cathode in an electrolyte subjected to electrolysis, the other than hexavalent chromium ions in the form of Chromic acid, chromates or bichromates contains a wide variety of additives, such as boric acid, phosphoric acid, Sulfuric acid, disulfonic acids derived from phenol or pyrocatechol or their salts, Nitric acid, acetic acid and their salts and halogen compounds.

Process for the production of corrosion-resistant anti-pollution pulls from electrochemically generated,
hydrated chromium oxide on metal surfaces

Applicant:

Toyo Kohan Co., Ltd., Tokyo

Representative:

Dr. E. Jung and Dr. V. Vossius, patent attorneys,

8000 Munich 23, Siegesstr. 26th

Named as inventor:
Yoiclii Kitamura, Yokohama;
Tsuneo Inui, Kadamatsu-shi (Japan)

Claimed priority:

Japan November 12, 1964 (63 648)

Of these additives, the strongly acidic anions, such as the sulfate ions, nitrate ions or Chlorate ions, a role in the electrolytic reduction of hexavalent chromium ions, and they are adsorbed by the hydrated chromium oxide coating on the metal surface. The adsorbed Anions in the chromium oxide coating are water-soluble; they are removed from the coating under extremely damp conditions Dissolved conditions, and they accelerate the corrosion of the electrolytically chromated metal. For this reason, the adsorbed anions must either be carefully separated off or safely retained will.

Furthermore, the absorption capacity of the protective coating made of hydrated chromium oxide has opposite oil also has an unfavorable effect on the adhesion to paints, especially when directly Painting after degreasing or separating lubricants from the protective coating because that adsorbed oil from the protective coating is very difficult to remove by conventional degreasing methods and this causes poor adhesiveness. Accordingly, the absorption capacity should the protective coating against oil are reduced within such limits that the original adhesion to paints is not impaired.

To hold back the strongly acidic anions from the protective coating of hydrated chromium oxide are adsorbed, and to improve the adsorption

809 619-574

tion properties of the protective coating is according to the invention the treatment of the electrochemically chromated metal surfaces in an aqueous solution particularly effective, the at least one water-soluble or water-dispersible cation-active Contains wetting agents from the aforementioned group.

The following cation-active wetting agents are used in the process according to the invention:

1. aliphatic primary amine acetates of the general formula

'"^. - ,, RNH ₃ COOCH ₃

in which R represents an aliphatic hydrocarbon radical having 8 to 18 carbon atoms; Examples of such compounds are undecylamine acetate, heptadecylamine acetate and octadecylamine acetate;

2. Quaternary ammonium salts of the general Formula [RRR'R "N] ®X ^

in which R is an alkyl group with 1 to 5 carbon atoms, R 'is a saturated or unsaturated aliphatic hydrocarbon radical with 1 to 22 carbon atoms, the benzyl group or an alkanol group with 1 to 5 carbon atoms, R "is an aliphatic hydrocarbon radical with 8 to 22 carbon atoms and X is a halogen atom or a hydroxyl group. There are also derivatives of these compounds in question, the at least one ester bond, an ether bond or an amide bond contained in the molecule and which are cationic wetting agents.

Examples of this class of compounds are: Trimethyloctadecylammonium chloride
[CH ₃ (CH ₂ ) i ₇ N (CH ₃ ) ₃ ] Cl
Trimethylcetylammonium bromide

. [CH ₃ (CH ₂ ) is N (CH ₃ ) ₃ ] Br
Dimethyl acetyl benzyl ammonium chloride

CH ₃

CH ₃ (CH ₂ ) ₁₅ -N-CH ₂ - ^ 3

CH,

Cl

Dimethylheptadecyi-2-hydroxyethylammonium chloride

CH ₃
CH ₃ (CH ₂ ) ₁₆ - N - CH ₂ CH ₂ OH

CH,

Cl

3. Pyridinium salts of the formula

in which R is an aliphatic hydrocarbon radical having 12 to 18 carbon atoms and X. Is halogen atom. There are also the derivatives of these compounds in question, which at least contain an ester bond, an ether bond or an amide bond in the molecule and which are cationic wetting agents.

Examples of this class of compounds are:
Cetyl pyridinium bromide

Br

CH ₃ (CH ₂ ) _I5 -n /

Octadecyloxymethyl pyridinium chloride

CH ₃ (CH ₂ J ₁₇ OCH ₂ -

Cl

Lauramidomethyl pyridinium chloride
CH ₃ (CH ₂ J ₁₀ CONHCH ₂ - N <

Cl

4. Methylpyridinium salts of the general formula 'CH ₃

in which R is an aliphatic hydrocarbon radical having 12 to 18 carbon atoms and X is a Halogen atom and its derivatives, with at least one ester bond, an ether bond or an amide bond in the molecule and which are cation-active wetting agents.

Examples of this class of compounds are:
Lauryl picolinium bromide

CH ₃ (CH ₂ ) _n N <

Br

Stearaniidomethyl picolinium chloride
CH ₃ (CH ₂ ) ₁₆ CONHCH ₂ -ti /

Cetyloxymethyl picolinium chloride

CH ₃ (CH ₂ ) I ₅ OCH ₂ -

Cl

Diethylbenzyllauramidoäthylammoniumchlorid 5. Polyoxyäthylenalkylamines of the general

60 _ ■.

C ₂ H ₅

Cl

C ₂ H ₅

Trimethyllauroyföxymethylarnmoniurnchlorid
[CH ₃ (CH ₂ ) ₁₀ COOCH ₂ N (CH ₃ ) 3] C1

formula

^ CH ₂ CH ₂ OLH
RN

NcH ₂ CH ₁ O) JH
or
RNH (CH ₂ CH ₂ O) _n H

in which R is an aliphatic hydrocarbon radical with 8 to 22 carbon atoms and «and m have a value of 8 to 18 and the cation-active wetting agents are.

Examples of these connection classes are:
Tetradecaoxyethylene pentadecylamine

CH ₃ (CH ₂ ) LiNH (CH ₃ - CH ₂ O) i.jH
Dioctaoxyethylene heptadecylamine

IO

CH ₃ (CHJ ₁₆ N

4CH ₂ -CH ₂ O) ₈ H.

^ CH ₂ - CH ₂ O) ₈ H

6. Polycondensation products of formaldehyde and dicyandiamides which are cationic wetting agents, e.g. B. a polycondensation product of dicyandiamide [NH ₂ - (NH =) CNH — CN] and formaldehyde, a polycondensation product of dicyandiamidine and formaldehyde, a polycondensation product of guanidine and formaldehyde or a polycondensation product of diguanide and formaldehyde.

These cation-active wetting agents can be used alone or in admixture.

The method of the present invention is effective in retaining adsorbed anions in protective coatings from electrochemically generated hydrated chromium oxide on metal surfaces and for Prevents roasting in extremely humid conditions.

The method according to the invention is also suitable for increasing the adhesion of paints Electrolytically chromated metal surfaces, which is particularly evident from the improved adhesive strength shows paintwork on mechanically deformed metal objects.

In the process according to the invention, the aforementioned cationic wetting agents can be used in the hydrated Moist chromium oxide film easily adsorbs adsorbed anions and forms a barrier against oil adsorption form.

The conditions for carrying out the method according to the invention are as follows:

1. Concentration of the cationic wetting agent in the

aqueous treatment

liquid 1 to 50 g / l

2. Treatment temperature ... 30 to 70 ^{° C}

3. Treatment time or

Dive time 1 to 60 seconds

55

The optimal and preferred concentration of the cationic wetting agent is between 1 and 50 g / l.

In general, an increase in the concentration of the cationic surfactant has an increase the amount adsorbed in the chromium oxide film. However, if the concentration of the cationic active Wetting agent exceeds the value of 50 g / l, the hydrated chromium oxide film becomes bluish yellow, and there is no further improvement.

If the concentration of the cationic surfactant is less than 1 g / l, the method requires a longer treatment time, which is unfavorable from an economic point of view.

An increase in the treatment temperature results in an improvement, but at higher temperatures the evaporation loss of water is increased and the cation-active wetting agent decomposes. The inventive process should preferably be carried out at a temperature below about 70 ⁰ C.

A decrease in temperature results in a decrease in the penetration of the cationic wetting agent into the chromium oxide film. At a temperature below about 30 ^° C., the method according to the invention requires an impractically long treatment time.

Therefore, the method according to the invention is in practice preferably in the range of about 30 to 70 ⁰ C.

An increase in the immersion time has an increase in the adsorbed amount of the cationic surfactant in the chromium oxide film. When using a treatment solution with 1 to 50 g / l of cationic active Wetting agent and at a temperature of 30 to 70 ° C, an immersion time of 1 to 60 seconds is sufficient to improve the corrosion resistance and adhesion of paints to the chromium oxide film.

If the time of treatment with the aqueous solution of the cationic surfactant is less than 1 second, a higher concentration and higher working temperature is required, which is for commercial purposes is also impractical. If you have the protective coating from electrochemically generated hydrated chromium oxide dries, is the inventive treatment with the aqueous solution of the cationic wetting agent is less effective because the dried chromium oxide film looks like a hard barrier behaves against the action of the surface-active wetting agent. That's why the Treatment immediately after the electrochemical production of the protective coating, if this is still damp.

Electrochemically chromated sheets made of iron and steel, which have been treated according to the method according to the invention, pass a two-month weathering test in winter and a 15-day weathering test in summer as well as a 48-hour salt spray test without any signs of rust formation. These sheets still exist humidity chamber tests in an atmosphere of 90% relative humidity at 4O ⁰ C for one week without any signs of discoloration of the protective coating.

Conventional treatments of metals have not resulted in such high corrosion resistance.

After applying an approximately 10 micron thick coating of a modified alkyd resin varnish or a modified epoxy lacquer on treated by the method according to the invention Electrochemically chromated sheet steel can be painted sheet with a stretching ratio of 2.2 deep drawing. If you put an adhesive strip firmly on the painted side of the received thermoformed Pressing on the hollow vessel and then quickly pulling it off, the adhesive tape does not take any paint with it. At the Painting the mechanically deformed sheet after degreasing provides a superior bond strength of the paint in the electrochemically chromated sheet metal treated according to the invention.

Other characteristics of the adhesive strength of paints are described in the examples.

Electrochemically chromated metals treated by the process according to the invention show good heat resistance up to 300 ^° C. Their weldability is just as good as that of the base metals.

As electrochemically chromated metals treated by the process according to the invention those metals on which electrochemically hydrated protective chromium oxide coatings are usually suitable are suitable Can be applied, such as iron, steel, aluminum, chromium, nickel, zinc, tin, cadmium, magnesium, copper, titanium and theirs For corresponding alloys, see as well as metals that are plated with the aforementioned metals.

The examples explain the process according to the invention.

example 1

20th

40

A 0.25 mm thick cold-rolled black ^{plate was cathodically cleaned for 20 seconds at 70 °} C. and a current density of A / dm ² in a 7% sodium hydroxide solution, then rinsed with water, pickled for 10 seconds at room temperature in 7% sulfuric acid and again rinsed with water. The black plate was then hung in an electrolyte bath and connected to a direct current source. The black plate was used as the cathode and a lead-antimony alloy as the anode. The electrolyte bath had the composition given below. The black plate was then rinsed with water and treated according to the invention with a solution of the composition given below and then immediately rinsed again with water and dried.

A) The electrolyte and the conditions of electrolysis:

Chromic acid 50 g / l

Sulfuric acid 0.2 g / l

Hydrofluoric acid ... 0.3 g / l

Temperature 50 ^c C

Current density 20 A / dm ²

Time 10 seconds

B) Treatment conditions according to the invention:

Trimethyloctadecylammonium

chloride 50 g / l

Temperature 6O ⁰ C

Dive time 30 seconds

The protective coating produced was blue and transparent, and the treated black plate showed a few rust spots after it had been subjected to a salt spray test with a 5% sodium chloride solution at 35 ° C for 48 hours % exposed for a week at 40 ^° C., there were no rust spots and no discoloration.

Example 2

A 0.5 mm thick cold-rolled steel sheet was subjected to the same pretreatment and the same electrolytic Subjected to chromating as described in Example 1 and then immediately washed with water and then immediately into the treatment solution according to the invention among those specified below Submerged conditions and then washed again with water and dried.

Polycondensation product from formaldehyde and dicyandiamide 10 g / l

Temperature 50 ⁰ C

Dive time 2 seconds

The protective coating obtained was bluish yellow and transparent.

About 30 mg / dm ^{2 of} mineral lubricating oil was applied to the treated chromated steel sheet and left to stand for 24 hours. The steel sheet was then steam degreased with trichlorethylene for 2 minutes and then painted to a thickness of about 20 microns with a melamine-modified alkyd stoving varnish. The lacquer coating was cross-hatched and the sheet was immersed in boiling water for 8 hours. After the lacquer coating of the lacquered sheet is crosshatched and the sheet has been immersed in boiling water for 8 hours, the stoving varnish cannot be peeled off with the adhesive tape.

If you put a steel ball with a diameter of 12.7 mm and a weight of 500 g from a A height of 20 cm on the sheet steel coated with the stoving lacquer and the point of impact checked with the adhesive tape, no loss of adhesion of the stoving varnish can be determined.

Example 3

The same type of cold-rolled black plate is used in the pretreatment described in Example 1 and then immediately using a lead-antimony anode among those mentioned below Conditions treated with the chromating solution of the composition given below, then immediately rinsed again with water * and immediately afterwards with the inventive Treated solution under the specified conditions and rinsed again with water and dried.

A) The electrolyte and the conditions of the electro-lytic Chromating:

Chromic acid 60 g / l

Phenol-2,4-disulfonic acid 0.6 g / l

Temperature 50 C

Current density 20 A / dm ²

Time 20 seconds

B) Treatment conditions of the method according to the invention:

Octadecylamine acetate lg / 1

Temperature 55 C

Dive time 60 seconds

The coating produced was bluish yellow and transparent, and the treated black panel showed practically no rust stains after being subjected to the same salt spray test as in Example 1 for 48 hours became. If you coat the treated black plate with an approximately 20 micron thick coat of a melamine-modified Alkyd enamel coats and the same salt spray test as in Example 1 150 hours no blisters appear on the paintwork.

Example 4

The same kind of cold-rolled black plate was subjected to the same pretreatment as in Example 1 subjected and then immediately in an electrolyte bath of the following composition and under introduced under the following conditions and connected to a direct current source. That Black plate was used as the cathode and a lead-antimony alloy as the anode. Thereafter the black plate was rinsed immediately with water and immediately afterwards with the inventive Solution under the following conditions. treated and then again immediately Rinsed with water and then dried.

A) The electrolyte and the conditions of electrolytic chromating:

Sodium dichromate 500 g / l

Chromium sulfate 10 g / l

Ammonium sulfate 20 g / l

Temperature 5O ⁰ C

Current density 25 A / dm ²

Time 8 seconds

B) Treatment conditions of the method according to the invention:

Cetylpyridinium chloride 5 g / l

Temperature 30 ° C

Dive time 20 seconds

The coating produced was bluish purple in color and had a corrosion resistance similar to that in example 1.

20th

30th

Example 5

35

45

The same kind of cold rolled black plate was subjected to the same pretreatment and the same electrolytic chromating, as described in Example 1, subjected, then immediately rinsed with water and then immediately in the solution of the following for the treatment according to the invention Dipped composition, rinsed again with water and dried.

Dimethyloleylbenzylammonium

chloride 10 g / l

Dioctaoxyethylene stearylamine ... 10 g / l

Temperature 70 ° C

Dive time 5 seconds

A transparent, yellowish and bluish-purple-colored coating is obtained. If you can treated black panel with an approximately 10 micron thick coat of white melamine modified Alkyd enamel coated and deep-drawn to a cup with a draw ratio of 2.2: 1 it was found that there was no loss of adhesion on the deep-drawn part of the cup Stoving varnish occurred. When the cup is in a 3% boiling solution of sodium chloride for 1 hour was immersed, no loss of adhesion of the stoving varnish could be determined either.

Example 6

A 0.5 mm thick sheet of aluminum was / _(l sodium bicarbonate cleaned for 10 seconds at room temperature in a 2 °, rinsed with water and then immediately passivated electrolytically in the manner described in Example 1. Thereafter, the aluminum plate was immediately rinsed with water and then immersed in a solution of the composition given below for the treatment according to the invention, then immediately rinsed with water and dried.

Polycondensation product from formaldehyde and dicyandiamide 5 g / l

Temperature 55 ⁰ C

Dive time 20 seconds

The protective coating produced was colorless and transparent. When the aluminum sheet treated according to the invention was subjected to a porosity test with a copper sulfate solution for 2 hours no porosity can be determined.

Example 7

A steel sheet hot-dip galvanized in a zinc bath containing 0.15% aluminum was used as the cathode and using a lead-antimony alloy as an anode under the following conditions suspended in an electrolyte bath and connected to a direct current source. After electrolysis the steel sheet was rinsed immediately with water and immediately afterwards according to the invention with a Solution of the composition given below treated, then immediately again with water rinsed and dried.

A) The electrolyte and the conditions of electrolytic chromating:

Sodium dichromate 100 g / l

Sulfuric acid 2 g / l

Temperature 50 ⁰ C

Current density 5 A / dm ²

Time - 1 second

B) The treatment conditions of the method according to the invention:

Trimethyloctadecylammonium

chloride 30 g / l

Temperature 50C

Dive time 10 seconds

The protective coating produced was colorless and transparent, and when the obtained hot-dip galvanized Sheet steel with the electrochemically generated protective coating of hydrated chromium oxide with a About 20 microns thick coat of melamine-modified alkyd stoving enamel and the The cross-cut test and the impact test showed no loss of adhesion of the stoving varnish to be established.

Claims (9)

Patent claims: 1. Method of making corrosion-resistant Protective coatings of electrochemically generated, hydrated chromium oxide on metal surfaces, characterized in that the metal surface nr.ch the electrochemical Production of the protective coating and first washed with water before drying and then treated with an aqueous solution which is at least a water-soluble or in Water-dispersible, cation-active wetting agent from the group of aliphatic primary amine acetates, quaternary ammonium salts and their derivatives, pyridinium and methylpyridinium salts 809 619/574 and their derivatives, polyoxyethylene alkylamines and polycondensation products of formaldehyde and dicyandiamides in an amount of about 1 to 50 g / l, and then again is washed with water. 2. The method according to claim 1, characterized in that the treatment with the aqueous solution of the cation-active compound at 30 to 70 ⁰ C is carried out. 3. The method according to claim 1 and 2, characterized in that the treatment with the aqueous solution of the cation active compound for 1 to 60 seconds. 4. The method according to claim 1 to 3, characterized in that a compound of the general formula RNH ₃ COOCH _{3 as the aliphatic primary amine acetate} is used in which R is an aliphatic hydrocarbon radical having 8 to 18 carbon atoms represents. 5. The method according to claim 1 to 3, characterized in that the quaternary ammonium salt a compound of the general formula [RRR'R "N] ®X® is used in which R is an alkyl group with 1 to 5 carbon atoms, R 'a saturated one or unsaturated aliphatic hydrocarbon radical having 1 to 22 carbon atoms, a Benzyl group or an alkanol group with 1 to 5 carbon atoms, R "an aliphatic group Hydrocarbon radical having 8 to 22 carbon atoms and X is a halogen atom or a hydroxyl group means, or that derivatives of this compound are used which have at least one ester, ether or amide bond in the molecule contain. 6. The method according to claim 1 to 3, characterized in that a compound is used as the pyridinium salt the general formula 45 is used in which R is an aliphatic hydrocarbon radical having 12 to 18 carbon atoms and X denotes a halogen atom, or that a derivative of this compound is used which contains at least one ester, ether or amide bond in the molecule. 7. The method according to claim 1 to 3, characterized in that a methylpyridinium salt the general formula is used in which R is an aliphatic hydrocarbon radical having 12 to 18 carbon atoms and X represents a halogen atom, or that uses a derivative of this compound which contains at least one ester, ether or amide bond in the molecule. 8. The method according to claim 1 to 3, characterized in that a polyoxyethylene alkylamine the general formula / (CH ₂ CH ₂ O) _n H. RN (CH ₂ CH ₂ OLH RNH (CH ₂ CH ₂ O) _n H is used in which R is an aliphatic hydrocarbon radical having 8 to 22 carbon atoms and η and m are integers with a value of 8 to 18. 9. The method according to claim 1 to 3, characterized in that the dicyandiamide is dicyandiamide, Dicyandiamidine, guanidine or diguanide is used. Considered publications:
U.S. Patent No. 3,136,663. M * «19/57« tH% BuAdMdTtKkCWi BtTlin