FR2812640A1 - PROCESS FOR THE PREPARATION OF AN ORGANIC COMPLEX OF CHROMIUM III, ITS USE AS A CORROSION INHIBITOR AND ANTICORROSION COATING - Google Patents

Abstract

The invention relates to a process for the preparation of a water-insoluble organic chromium III complex. The complex is produced by reaction between a CrIII compound formed in situ and at least one aromatic compound carrying a carboxylic acid function or its salt. The reaction takes place in an aqueous medium, in the absence of concentrated mineral acid and at a temperature between approximately 15 and 90 ° C. The insoluble complex obtained is used as a corrosion inhibitor agent, in particular in anticorrosion coatings such as paints.

Description

The present invention relates to a process for the preparation of a complex

  organic chromium and its use as a corrosion inhibitor,

  especially in metal coatings.

  For the protection of metals against corrosion, chemical or electrochemical treatment processes are frequently used, and / or the metal surfaces are covered with a protective coating in the form of coatings, varnishes or paints. Paints are mixtures of organic or mineral binders and solvents in which fillers and mineral or organic pigments are suspended. In addition to their covering and / or coloring power, some of these mineral pigments are used as anti-corrosion agents. This is for example lead orthoplombate said minium, zinc salts such as zinc phosphates, zinc borates, barium, zinc chromates, strontium, barium. Chromates are among most effective against corrosion of metals, but have

  high toxicity, because chromium is present in the hexavalent form.

  An object of the present invention is therefore to find new chromium derivatives in another degree of oxidation (valence III chromium being the most stable),

effective against corrosion.

  Organic chromium III complexes are already described in various patents. They

  are used either for tanning leathers and protecting fibers against micro-

  organisms (FR-B-1.115.088; US-A-2.273.040; US-A-2.356.161 and US-A-2.549. 220), either in paints mixed with high proportions of hexavalent chromium

  (US-A-4,161,409 and US-A-4,341,564) after insertion into a polymer.

  Such chromium complexes have the major drawback of being soluble in water and therefore cannot be used as an anticorrosive pigment in paints, since they are rapidly leached from the coating. In addition, their manufacturing processes are of particular implementation, that is to say either in the presence in the reaction medium of concentrated sulfuric acid, or gaseous hydrochloric acid and at boiling for several hours, or in an anhydrous medium in the absence of free water, or in

  solvents such as carbon tetrachloride.

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  Consequently, one of the aims of the present invention is to provide chromium III compounds which are practically insoluble in water and in the usual solvents,

  particularly those used in anticorrosion coatings such as paints.

  Another object of the present invention is to provide a process for the preparation of these organic chromium III complexes of simple implementation, and if possible in

using water as a solvent.

  These objects are achieved by the present invention which provides a process for the preparation of an organic chromium Im complex by reaction between at least one CrIII compound, formed in situ, and at least one organic compound carrying a carboxylic acid function or its salt. , characterized in that the reaction takes place in an aqueous medium and at a temperature between about 15 and about 90 C, in that the compound

  organic has at least one aromatic ring, preferably benzene.

  The chromium III complex obtained by the process according to the present invention is practically insoluble in water and the usual solvents used in coatings

  anticorrosion, and is practically free of chlorine.

  According to the present invention, the addition of additional mineral acid in strong

  concentration is not essential for the complexation reaction.

  Advantageously, said aromatic nucleus carries both at least one carboxylic acid group directly or via an alkyl radical and one or more groups among the hydroxy, thiol, methoxy, amine, amide or sulfonic groups, these groups being able to be attached directly to the aromatic nucleus or via

an alkyl chain.

  Preferably, the organic compound carrying a carboxylic acid function is chosen from hydroxybenzoic, aminobenzoic, thiobenzoic, dihydroxyphenylacetic, picolinic, salicylic, anthranilic, thiosalicylic, 2,6-benzoic, amino naphthalene dicarboxylic or trihydroxy-2,4 acids, 6-benzoic, 3,4-dimethoxysalicylic, 4amino salicylic, 3-methyl salicylic, 5-sulfo salicylic,

  1-hydroxy 2-naphthoic or 3-hydroxy 2-naphthoic.

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  Advantageously, the molar ratio between the organic compound carrying a carboxylic acid function and the chromium is between approximately 1: 3 and approximately 1: 1. The CrIII compound is formed in situ by reduction of one or more hexavalent chromium compounds by at least one organic reducing agent. The practically complete reduction of chromium VI to chromium III preferably takes place in the presence of the complexing agent. The organic reducing agent can be chosen from: a) an alcoholic solution composed of an alcohol or a mixture of primary or secondary alcohol (s) comprising one or more alcohol functions, b) an aqueous solution of hydrazine , c) an aqueous solution of hexamethylenetetramine or

  d) a mixture of at least two of the reducing agents a), b) or c).

  Advantageously, the alcoholic solution is chosen from: ethanol, methanol, propanol, isopropanol, 1,2-propanediol, a secondary butanol or a

mixture of these alcohols.

  The hexavalent chromium compound can be in the form of a bichromate or a chromate of potassium, sodium, ammonium or calcium, chromic acid, chromic anhydride, chromyl chloride or fluoride, potassium chloro chromate, pyridinium chloro chromate or pyridinium dichromate in

  presence or absence of weakly concentrated mineral acid (for example IN).

  The reaction temperature can be higher than room temperature (15-25 C), but never exceeds 90 C, preferably 70 C. At the end of the reaction, it is possible, depending on the case, to either directly filter the precipitate obtained and drying it, either evaporating part of the reaction solvent to recover the organic chromium III complex in the form of a paste, or evaporating the reaction solvent completely to recover said complex in the form of a powder.

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  The chromium III complex prepared by the process according to the invention has the characteristic of being practically insoluble in water, and the usual solvents in the field of paints. Preferably, it contains between 5 and 40% by weight of

  chromium, in the form of trivalent chromium.

  Said organic chromium III complex exhibits excellent metal corrosion inhibiting properties. It can therefore be used as an inhibitor of corrosion, in anticorrosion coatings such as coatings, varnishes or paints. Preferably, it is present in a proportion of at least about 1% by weight. It can be used alone or mixed with corrosion inhibitors and / or with inhibiting organic or mineral pigments such as phosphates of zinc, calcium, barium or strontium, meta or tetra borates of zinc, calcium, strontium or magnesium or calcium silicates. The term “corrosion inhibitor” is intended to mean compounds which are rather soluble in the application solvents and which act quickly, and the term “anticorrosion pigment” means compounds which are rather insoluble in

  application solvent (suspension) and act in the longer term.

  The organic complex according to the invention, whether or not mixed with other corrosion inhibitors or other anticorrosion mineral pigments, can be combined with organic binders, either thermosetting or thermoplastic, or with binders.

  hardening by oxidation or chemical reaction.

  The following examples illustrate, without limiting them, on the one hand, the process for preparing the organic chromium complex according to the invention (examples 1 to 6), or according to other processes (examples 7 to 10), on the other hand the use of complexes

  above in the formulation of paints (examples 1 1 to 13).

  Preparation of the organic chromium III complex:

  In the examples below, the quantities are expressed in grams.

  - The complexing agent (s) are dissolved in the organic reducing agent (s) with the optional addition of water. The amount of water is defined by the solubility of the complexing agent in the water-reducing mixture (s). The mixture can be heated to promote the dissolution of the complexing agent (at a temperature not exceeding

90 C, preferably 70 C).

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  - The compound (s) based on chromium VI as it (s) has (have) been defined (s)

  previously is (are) dissolved in water.

  - The solution based on chromium VI is added with stirring and slowly, to the solution containing the complexing agent (s) and reducing agent (s). The two solutions can also be poured simultaneously into a stirred reactor. At the end of the addition, the mixture is left under stirring for a few hours, preferably at reflux when an alcohol is used as a reducing agent. Then, part of the organic solvent can be distilled when an alcohol is used as a reducing agent; the distilled volume can be compensated with water to promote agitation. Depending on the consistency of the complex formed, the product can be collected in solid form by filtration or

  centrifugation before being dried in the oven.

  Example 1: (molar ratio 1: 1) Solution N 1 chromic acid VI 369 water 795 Solution N 2 salicylic acid 510 isopropyl alcohol 1650 water 881 The solution N 2 is heated to about 40 C to allow the dissolution of salicylic acid. The solution N 1 is introduced slowly with stirring into the solution N 2 so that the temperature does not exceed 70 C. After the end of the introduction the mixture is left under stirring for 1 hour at approximately 70 C. The mixture is then heated to 90 ° C. in order to distill part of the organic solvents. 1,200 g of solvent are collected and compensated with 1,200 g of water to facilitate agitation. The complex obtained is filtered and then dried at 80-100 C. The product, which contains a chromium VI concentration of less than about 0.1% by weight of the complex, can after grinding be

  used as a corrosion inhibiting agent (see examples 1 1 to 13 below).

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Example 2:

  Solution N 1 salicylic acid 852 isopropyl alcohol 1476 water 800 Solution N 2 sodium bichromate 877 water 800 Solution 1 is prepared at approximately 40 ° C. until the salicylic acid is dissolved. Solution 2 is introduced slowly with stirring into solution 1 so that the temperature does not exceed 70 C. When all of solution 2 is introduced, stirring is maintained for 1 hour at around 70 C. The mixture is then heated up to 90 C to distill part of the organic solvents. During distillation it may be necessary to add water to the reactor to facilitate agitation. At this stage, the organic chromium complex takes on a dark green pasty appearance. This paste is collected and dehydrated at a temperature of 80 to 100 C. The

  dried and ground product will be used as a corrosion inhibitor.

  In this example, the sodium dichromate can be replaced by potassium dichromate or any other dichromate and isopropyl alcohol by another.

  alcohol, primary or preferably secondary, or a mixture of these alcohols.

Example 3

  Solution N 1 anthranilic acid 137 isopropyl alcohol 670 water 400 Solution N 2 chromic acid VI 100 water 212

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  Solution 1 is prepared at 50 ° C. to allow the anthranilic acid to dissolve. Solution 2 is prepared cold. With stirring, solution 2 is added to solution 1. At the end of the addition, the mixture is left stirring at approximately 70 ° C. for 1 hour. Then, the mixture is heated to 90 ° C. to distill part of the solvents. During the distillation, water is added to compensate for the distillation of the alcohol. The complex is then collected by filtration and then dried at 90 C. This complex essentially contains chromium III (the chromium VI concentration is

  less than 0.1% by weight of the complex).

  Example 4: According to a procedure identical to that of Example 1, the following solutions are prepared and then brought into contact: Solution N 1 chromic acid 100 water 212 Solution N 2 3-hydroxy-2-naphthoic acid 188 isopropyl alcohol 670 water 400 The product, after filtration and drying, is dark green in color and contains

less than 0.1% Crv '.

Example 5:

  According to a procedure identical to that of Example 1, the following solutions are prepared and then brought into contact:

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  Solution N 1 chromic acid 100 water 212 Solution N 2 acid 3 methyl salicylic 197 isopropyl alcohol 670 water 400 The product, after filtration and drying, is brown in color and contains less

0.1% Crvi.

  Example 6: According to a procedure identical to that of Example 1, but for this example with an organic compound: chromium stoichiometry of 1: 2, the following solutions are prepared, then brought into contact: Solution N 1 chromic acid 370 water 800 N 2 solution salicylic acid 255 isopropyl alcohol 1700 water 800 The product, after filtration and drying, contains less than 0.1% CrvI and is

practically insoluble in water.

  Other processes for the preparation of chromium III complex and compound

organic with aromatic nucleus.

  Examples 7 to 10 describe methods different from that of the present invention, in particular as regards stoichiometry. These complexes are

  prepared directly from chromium III.

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  Example 7: (comparative) in the presence of a base, and at a stoichiometry of 2: 1 Solution N 1 salicylic acid 27.6 NaOH 8 water 500 Solution N 2 CrOHCI2 (11.7% Cr) 45.5 water 200 NaOH 0.25 N solution - Preparation of solution 1: 8 g of NaOH are introduced into 500 ml of water

  and the mixture is heated to 65 C. The salicylic acid is added with stirring.

  - Preparation of solution 2: The CrOHCI2 is placed in 200 ml of water, and the pH is adjusted to 3.9 with the 0.25 N NaOH solution, then it is heated to 60 C. Solution 1 is added to solution 2 in 2 hours. The reaction mixture is then left for 1 h 30 min with stirring at 65 ° C., then the solid product obtained is filtered, washed and dried at 100 ° C.

  The pigment, green in color, is not very soluble in water and the usual solvents.

  Example 8: (comparative) Solution N 1 salicylic acid 138 NaOH 40 water 2000 Solution N 2 basic chromium sulfate (18.5% Cr) 140.5 water 1500 Preparation of solution 1: 40 g of NaOH are introduced into 2000 ml of water and

  heated to 60 C. The salicylic acid is added with stirring.

  - Preparation of solution 2: The basic chromium sulfate is dissolved in 1500 g of water at 60 C.

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  Solution 1 is added over 2 hours to solution 2, the reaction mixture is kept for 2 hours at 60 ° C., then filtered, washed and the product obtained is dried at 100 ° C.

  The pigment, green in color, is not very soluble in water and the usual solvents.

  Example 9: (comparative) chromium alum 37.5 salicylic acid 30 NaOH 11.5 water 1000 The chromium alum is dissolved in 900 g of water, salicylic acid is added, then NaOH is slowly stirred. The mixture is brought to reflux for 20 min. The precipitate obtained is washed with boiling water and alcohol and then dried at 70 C. The pigment, gray-yellow in color, is not very soluble in water and the usual solvents. Example 10: (comparative) stoichiometry 1: 1 Solution N 1 salicylic acid 276 water 1500 NaOH 160 Solution N 2 CrOHCI2 (11.7% Cr) 867 water 500 - Preparation of solution 1: the 160 g of NaOH are dissolved in 1500 ml

  of water, then salicylic acid is added with stirring.

  - Preparation of solution 2: CrOHCI2 are dissolved in 500 ml of water.

  Solution 2 is added to solution 1 over 2 hours, then the reaction mixture is left stirring for 1 hour. The product obtained is filtered, washed and dried at

1000 C.

  This complex can be defined as a chromous mono-hydroxy salicylate. It is gray-blue in color and is sparingly soluble in water and common solvents. Incorporation of organic complex (s) of chromium III in the formulation of paints: Example 11: "Coil-coating" primer (continuous prepainting) based on polyurethane The following components (% by weight) are mixed using a disperser then ground to a North fineness of 8 using a ball mill: 1- Alkynol 1665 (polyester binder) 32.7 2 Desmodur BL1265 (blocked isocyanate) 27.8 3- Anti-corrosion pigment 12.5 4TiO2 3.9 - Talc 3.9 - Solvesso 150 (solvent) 14 7 - PMA (methoxypropanol acetate) 4.7 8 - Anti-sedimentation agent 0.5 total 100 Primers are applied with a threaded bar on a plate Galfan type galvanized steel (ZincAlu) having received a Bonderit 4590 surface treatment. The primers are baked 35 s at 350 C to reach a PMT (Peak Metal Temperature) of 224 C. The dry thickness is S micrometers. The primers are covered with a commercial polyester finish with a dry thickness of 20 micrometers. The plates are shaped and branded according to the ECCA T8 standard, then exposed 750 h

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  in salt spray according to standard ASTM B 17. The results are evaluated according to the following rating: from 5 = good to 0 = bad and presented in table 1 below:

Table 1

  Anti-corrosion pigments Slice Claw a- Strontium chromate 5 5

(L203E)

  b- Zn phosphate (PZ20) 1 1 c- Ca silicate (Wollastonite) 1 complex example nl 4 4 e- complex example n 2 3 4 f- complex example n 3 4 4 g- complex example n 6 3 4 h- complex example n 7 3 3 icomplex example n 8 3 3 j- complex example n 9 2 2 k- complex example n 10 4 4 1- mixture b (80%) + d (20%) 4 4 m-mixture c (80% ) + d (20%) 4 4 The organic complexes of Crm d, e, f, g, h have a level of performance very close to the strontium chromate which is the reference for this application. There is also a markedly increased effectiveness of Zinc phosphate and Wollastonite in the resistance to corrosion when they are combined with the complexes according to the invention,

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  even when the latter are only present in proportions of only 20%

in the mixture.

  Example 12: Air drying paint of glycerophthalic type: The following primers of composition are prepared 1-Alftalat AL544 (linseed oil) 43.9 2-Varsol 40 (solvent) 19.5 3-Wetting 0.3 4 -Anti-corrosion pigment 11.3 -Talc 4.5 6-Ca carbonate 2.8 7-Mica 5.5 8-Red iron oxide 11.0 9-Drying agent 0.6 -MEKO (solvent) 0.6 total 100 The paints are applied to shot-blasted steel to a thickness of 40 micrometers, dry film and dried for 8 days at 20 ° C. then exposed for 500 hours to salt spray according to standard ASTM B1 17. The results are evaluated according to the following rating: Table 2 Full anticorrosion pigments plate Claw Zn aphosphate (PZ20) 3 3 b- complex example nl (20%) + PZ20 5 5 (80%) c- complex example n 7 4 4

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  Example 13: Painting on aluminum and light alloy The following composition formulas are prepared

Table 3

A B C

  Epoxy resin (index 29.8 29.8 29.8 epoxy = 600) Rutile titanium 2.9 2.9 2.9 Wollastonite 4.7 4.7 4.7 Strontium chromate 11 0 0 Complex e.g. n 1 il 0 Zinc phosphate 0 0 11 Micronized talc 10.7 10.7 10.7 Dispersing agent 0.5 0.5 0.5 MEK (solvent) 14.6 14.6 14.6 _ MIBK (solvent) 8.4 8.4 8.4 PMA (solvent) 10.2 10.2 10.2 Hardener: 7.2 7.2 7.2 Total 100 100 100 The formulas are applied on aluminum plates 99.98% and

  aluminum type TU2024 and covered with an aliphatic polyurethane finish.

  The thickness of the primary is close to 30prm, the friition of 40rm. The panels are exposed to the humid chamber test after one hour of exposure to a 37% HCl vapor according to MIL-P-23377G and to salt spray according to ASTM B-117 to

evidence of filiform corrosion.

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  The results observed show that the performance level of formula B is equivalent to formula A and is much higher than formula C whether it is on

Aluminum 99.98 or TU2024.

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Claims (15)

CLAIMS I1- Process for the preparation of an organic chromium III complex by reaction between at least one CrIII compound and at least one organic compound carrying a carboxylic acid function or its salt, characterized in that the reaction takes place in an aqueous medium , in the absence of concentrated mineral acid, and at a temperature between about 15 and about 90 C, in that the organic compound has at least one aromatic carboxylic nucleus and in that the CrIII compound is formed in situ by reduction of one or more hexavalent chromium compounds by at least one organic reducing agent, the CrIII complex obtained being practically insoluble in water and practically free from chlorine.   2- A method according to claim 1 characterized in that said aromatic nucleus carries both at least one carboxylic acid group or its salt directly or via an alkyl radical and one or more groups among: hydroxy, thiol, methoxy, amine, amide, or sulfonic these groups can be attached directly to the nucleus   aromatic or via an alkyl chain.   3- Method according to one of claims 1 or 2 characterized in that the compound   organic carrying a carboxylic acid function is chosen from hydroxybenzoic, aminobenzoic, thiobenzoic, dihydroxyphenylacetic, picolinic, salicylic, anthranilic, thiosalicylic, dihydroxy-2,6-benzoic, amino naphthalene dicarboxylic, trihydroxy-2,4,6-benzoic acid, 3 , 4-dimethoxysalicylic, 4-amino salicylic, 3-methyl salicylic, 5-sulfo salicylic, 1-hydroxy 2- naphthoic or 3-hydroxy 2-naphthoic.   4- Method according to one of claims 1 to 3 characterized in that the ratio   molar between the organic compound carrying a carboxylic acid function and the   composed of CrIII is between about 1: 3 and about 1: 1.   - Method according to any one of the preceding claims, characterized in   what the hexavalent chromium compound is in the form of a dichromate or chromate of potassium, sodium, ammonium or calcium, chromic acid or chromic anhydride, chromyl chloride or fluoride , of chloro chromate of   potassium, pyridinium chloro chromate or pyridinium dichromate. 17 2812640   6- Method according to any one of the preceding claims, characterized in   that the reaction takes place at a temperature between about 15 C and about 70 C.   7- Method according to any one of the preceding claims, characterized in   what the organic reducing agent is chosen from: a) an alcoholic solution composed of an alcohol or a mixture of primary or secondary alcohol (s) comprising one or more alcohol functions, b) an aqueous solution of hydrazine, c) an aqueous solution of hexamethylenetetramine or,   d) a mixture of at least two of the reducing agents a), b) or c).   8- Process according to claim 7, characterized in that the alcoholic solution a) is chosen from: ethanol, methanol, propanol, isopropanol,   1,2-propanediol, a secondary butanol, or a mixture of these alcohols.   9- A method according to claim 7 or 8 characterized in that after the end of the   complexation reaction part of the reaction solvent is evaporated by distillation.   10- Method according to any one of the preceding claims, characterized   in that at the end of the reaction, part of the reaction solvent is evaporated and the   organic chromium III complex is recovered in the form of a paste.   11- Method according to any one of claims 1 to 9, characterized in that   that at the end of the reaction, the reaction solvent is completely evaporated and the complex   organic chromium III is recovered in the form of a powder after drying.   12- Method according to any one of claims 1 to 9, characterized in that   that at the end of the reaction, the complex is collected in solid form by filtration or centrifugation, then dried.   13- Organic chromium III complex prepared by the processes according to   previous claims, practically insoluble in water, containing between 5 and % by weight of trivalent chromium.   14- Use of complex, practically insoluble in water, of chromium III and   of organic compound with aromatic nucleus, as corrosion inhibiting agent. 18 2812640   - Anticorrosive coating in which the corrosion inhibiting agent is a complex, practically insoluble in water, of chromium III and of organic compound with aromatic nucleus.   16. Anti-corrosion coating according to claim 15, in which the inhibiting agent is mixed with mineral or organic pigments.   17- Anti-corrosion coating according to one of claims 15 or 16 in which   the inhibiting agent is combined with a thermosetting or thermoplastic binder,   18- Anti-corrosion coating according to one of claims 15 or 16 in which   the inhibiting agent is associated with a binder hardening by oxidation, or by reaction chemical.