US3853593A

US3853593A - Process for improving the protective properties of chromium-oxide based compound coatings, by means of stabilization of the chromium ion

Info

Publication number: US3853593A
Application number: US00270291A
Authority: US
Inventors: G Baudo; G Bombara
Original assignee: Centro Sperimentale Metallurgico SpA
Current assignee: Centro Sperimentale Metallurgico SpA
Priority date: 1971-07-31
Filing date: 1972-07-10
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10
Also published as: JPS553439B1; FR2148023A1; BE786634A; GB1394244A; DE2236301B2; DE2236301A1; FR2148023B1

Abstract

BY INDUCTIVE EFFECT; - IMMERSING THE COATED MATERIAL INTO THE SAID SOLUTION AT A TEMPERATURE RANGING FROM 30* TO 90*C, for a time ranging from 1'''' to 15'', while keeping the solution under constant stirring; - RINSING IN WATER AND DRYING THE SURFACE OF THE COATING.

Wherein: R is a monovalent radical derived from an aromatic type ring, either condensed or not, either containing hetero atoms or not; R'' is a monovalent radical, able to impoverish the electronic density of the enolic group

Process for improving the protecting properties of chromium oxide based coatings, including sequentially the following operations: - PREPARING AN AQUEOUS SOLUTION, WITH CONCENTRATIONS RANGING FROM 0.1 TO 10 G/LITER OF A BETA-DIKETONE WITH THE FOLLOWING GENERAL FORMULA

Description

ijllifitm @TEKQS PHTQTTT 11 5 1 Baudo et a1. Dee. 1Q, 197i 1 PROCESS FOR IMPROVING THE chromium oxide based coatings, including sequentially PROTECTIVE PROPERTIES OF the following operations: CHROMIUM-OXIIDE BASED COMPOUND COATINGS BY MEANS OF preparlng an aqueous solution, w1th concentratlons ranging from 0.1 to 10 g/liter of a. beta-diketone with STABILIZATION OF THE CHROMIUM ION the following general formula [75] Inventors: Giuseppe Baudo, Vicenza; Giuseppe Bombara, Rome, both of Italy [73] Assignee: Centre Sperimentale Metallurgico R S.p.A., Rome, Italy 0=0 c-o1r [22] Filed: July 10, 11972 21 Appl. No.: 270,291

[] Foreign Application Priority Data J1 31,1971 I l 5204271 u y ta y Wherein: 52 us. c1 117/62, 117/71 117/127 R is a mmovalem radical derived from an aromatic 1 30, l ring, either Condensed Or not, either 51 1m, (:1 B44d 1M4 containing hetero amms ml; [58] Field oi search ll7/6 2 71 M 127 130 R R is a monovalent radical, able to impoverish the 117/621. 204/ 1 6 electronic density of the enolic group [56] References Cited OH UNITED STATES PATENTS 11 3,484,343 12/1969 Kitamura et a1. 204/35 R 3,567,599 3/1971 3,615,888 10/1971 3,761,303 9/1973 by inductive effect;

- immersing the coated material into the said solution at a temperature ranging from 30 to C,

Primary Examiner wmiam Martin for a time ranging from 1" to 15, while keeping the Assistant Examiner-Janyce A. Bell Solution under constant Surfing;

Attorney, Agent, or FirmYoung & Thompson rinsing in water and drying the surface of the coating.

[57] ABSTRACT Process for improving the protecting properties of 7 Claims, 1 Drawing Figure PATENIE' an: 1 01974 POTENTIAL The present invention covers a process and a composition for improving the protective properties of chromium oxide based compound coatings by means of stabilization of the chromium ion. More particularly the invention coversthe improvement of the protective properties of thin chromium oxide based coatings, by means of a superficial stabilization processing of the chromium ion, based on the chelating action exerted upon the same ion, by the beta-diketones.

It is known, for example, that the products called Tin-Free Steels, Chromium-Type resulted as the most suitable for the substitution of tin in the tin plate used for food containers. In the herein mentioned products, tin is substituted with a thin compound coating of chromium-chromium oxide (of the order of a few tenths of a micron). The chromium oxide has the twofold function of sealing the microporosities presented by the chromium layer which is thin on account of economy and stability, and of supplying a very good anchorage basis for the application of protective varnishes or paints.

The object of thepresent invention is precisely improving the sealing action of chromium oxide upon the microporosities of the coating, increasing, in the same time, the adhesion of the varnish to the substratum. In the process, which is the object of the present invention, this purpose is fulfilled by means of stabilization of the chromium ion. This stabilization is obtained, on the basis of the present invention, by blocking the chromium ions into chelated complexes insoluble in water, obtained by reaction of the chromium ion with the beta-diketones corresponding to the general formula:

The complexing action of the beta-diketones determines a decrease of the porosity of the coating which becomes more compact and therefore develops a more efficacious protective action.

As it is known, beta-diketones in aqueous solution originate an equilibrium wherein the following tautomeric forms participate (which forms are distinguishable for the migration of a hydrogen atom from a carbon atom to the adjacent carbon atom):

Since the enolic form II presents an acidic character,

- and since unshared electronic doublets are present on the oxygen atom of the ketonic group in a beta position in respect to the enolic group, the formation of a 6- terms ring, wherein the enolic and ketonic oxygen atoms are bound to the chromium ion, respectively, with a covalent and a donor bond, is possible:

It is advisable now, to emphasize that the nature of the radical R and R plays a fundamental role in connection with the present invention. The substituting radical R, according to the process which is the object of the present invention, is chosen actually, so as to stabilize, as much as possible, the ring structure (1). This is possible every time R is a group containing double conjugated bonds with extension, therefore of the double bond alternation up to the ketonic group. In this case, in fact, resonance structures can be inferred, such as, for example, the following ones in the case where R is a phenyl group:

which stabilizes the chelate structure.

The radical R may be chosen among the monovalent radicals derived from aromatic type rings, either condensed or not, either containing hetero atoms or not.

In the process, which is the object of the present invention, the choice of the radical R is effected among the electrons acceptor functional groups, the inductive effect of which implies an impoverishment of the electronic density of the enolic group. In this way, the detachment of the proton H bound to it, is favoured, and, therefore, the acidity of the enolic group itself is enhanced. In order to realize the importance of what has been previously said, it is sufficient to remember that, in this way, the number of beta-ketoenolate ions present in the solution is increased, with a consequent increase of the formation kinetic of the ring (1), and besides, chosing properly the radical R, the production of beta-keto-enolate ions in sufficient amounts, for the purposes of the present invention, is secured even with slightly acidic or neutral pH. If the R group were not an acidifying group, the production of enolate ions would still be possible with alkaline pH, but in these conditions, the chromium oxide would begin to become soluble and thence the treatment would be less efficacious.

The experience has indicated, as particularly fit for the purpose to be attained, the groups obtained from the methyl radical by partial or total substitution of the hydrogen atoms with halogen atoms.

Inc

where R is a monovalent radical, such as the phenyl group C H the thenyl group C H S, the naphthyl group C H the pyrryl group C H N and the p. fluoro phenyl group C H. ,F. R is a monovalent radical able to impoverish the electronic density of the enolic group by inductive effect, such as the trichloro-methyl group CCl or trifluoro-methyl group CF heating the solution prepared as hereinbefore described at a temperature ranging from 30 to 90C;

immerging the chromium plated material into the hot solution for a time ranging from 1 sec. to minutes, while keeping the solution under stirring;

rinsing with PM) and drying the surface of the coating.

Furthermore, it should be remembered, that in the case where the water solubility of the chosen betadiketone is low, the present invention provides the addition of a nonionic surface active agent in a concentration up to 1% by weight to the processing solution. This surface active agent facilitates the formation of a dispersion.

Now, it should be emphasized that the present invention process is not limited to the case of the coatings based on chromium-chromium oxide. In fact it can be also applied in all these cases wherein a film of chromium oxide is used to seal the porosity of any metallic coating.

In order to make clearer the principle of the use and of the operation of the present invention, some illustrative, but not limitative embodiment examples are supplied with reference to the drawing, which is a plot which shows in the curves a and b the trend of the cur rent density of the anodic dissolution of the substratum,

respectively before and after the treatment, as a function of the potential.

In the drawing the porosity of the coating is measured by means of an electro-chemical technique, consisting of the determination of the potentiodynamic anodic curve of the said material in an aggressive medium. The maximum density of the current of the anodic dissolution of the substratum is directly proportional to the degree of the porosity of the coating. M is the maximum of the current density of the material before the treatment, M is that of the material after the treatment.

EXAMPLE 1 The material to be treated is a carbon steel (black sheet-steel) electrolytically coated with a film with the following composition:

Metallic chromium Chromium in the oxide 227 mg/dm 0.596 mg/dm This material is immerged into an aqueous solution of Z-thenoyltrifiuoro acetone (H T T A), with the following characteristics:

60C 20 g/ liter temperature H T T A concentration EXAMPLE 2 The material to be treated is a carbon steel (black sheet-steel) electrolytically coated with a film with the following composition:

Metallic chromium Chromium in the oxide 3.10 mg/dm 0.11s mg/dm This material is immerged into an aqueous solution of 2-thenoyl-trifluoro-acetone (H T T A) with the following characteristics:

Temperature C H T T A concentration 50 g/liter Nonionic surface active agent concentration 2 g/liter After a 30 seconds immersion in the said solution, under stirring, the material is rinsed.

The untreated material presents a maximum of current density M equal to 0.21 mA/cm after the treatment the maximum M is 0.12 mA/cm EXAMPLE 3 The material to be treated is a carbon steel (black steel-sheet) electrolytically coated with a film with the following composition:

Metallic chromium Chromium in the oxide 2.14 mg/dm 0.254 mg/dm This material is irrunerged in an aqueous solution of 2-furoyltrifiuoro acetone with the following characteristics:

Temperature 80C 2-furoyl-trifluoro acetone concentration g/liter Nonionic surface active agent concentration 2.5 g/liter.

After a seconds immersion into the solution, under stirring, the material is rinsed and dried.

The untreated material present a maximum of current density lVl equal to 0.21 mA/cm while after the treatment the maximum M is 0.13 mA/cm The present invention has been described with particular reference to the specific embodiments thereof, but it is intended that modifications and variations may be introduced therein, without infringing the protection limits of the invention.

What is claimed is:

1. A process for improving the protecting properties of chromium oxide based coatings, comprising immersing a metal substrate having thereon a chromium oxide based coating, in an aqueous solution of 0.1 to 10 grams per liter of a beta-diketone of the formula in which R is a monovalent aromatic ring-containing radical and R is a monovalent radical able to impoverish the electronic density of the enolic group by inductive effect, at a temperature from 30 to 90C., for 1 second to minutes, with constant stirring, then 0 rinsing the coated substrate in water and drying the surface of the coating.

2. A process as claimed in claim 1, in which R is a member selected from the group consisting of phenyl, thenyl, furyl, naphthyl, pyrryl and fluoro-phenyl.

3. A process as claimed in claim 1, in which R is a member selected from the group consisting of trifluoromethyl and trichloro-methyl.

4. A process as claimed in claim l, in which said solution contains up to 1% by weight of a nonionic surface active agent.

5. A process as claimed in claim 1, in which said substrate is steel.

6. A process as claimed in claim l, in which the ring of R contains at least one hetero atom.

7. A coated substrate produced by the process of

Claims

1. A PROCESS FOR IMPROVING THE PROTECTING PROPERTIES OF CHROMIUM OXIDE BASED COATINGS, COMPRISING IMMERSING A METAL SUBSTRATE HAVING THEREON A CHROMIUM OXIDE BASED COATING, IN AN AQUEOUS SOLUTION OF 0.1 TO 10 GRAMS PER LITER OF A BETA-DIKETONE OF THE FORMULA

3. A process as claimed in claim 1, in which R'' is a member selected from the group consisting of trifluoro-methyl and trichloro-methyl.

4. A process as claimed in claim 1, in which said solution contains up to 1% by weight of a nonionic surface active agent.

5. A process as claimed in claim 1, in which said substrate is steel.

6. A process as claimed in claim 1, in which the ring of R contains at least one hetero atom.

7. A coated substrate produced by the process of claim 1.