CA1039157A - Phosphate film layering on metallic surfaces - Google Patents

Abstract

The invention relates to a process for the film-forming phosphating of a metal surface, by applying to said surface, in a single operation, an aqueous solution containing phosphoric acid or a derivative of such an acid, acid chromic or a salt of such an acid and a reducing agent, followed by heating in order to accelerate the crosslinking of the film formed. According to the invention, the aqueous solution contains primary phosphates of iron, zinc or manganese formed in phosphoric acid, borosphoric acid or an ester of phosphoric acid. The reducing agent contains hydroxyl, aldehyde, ketone or amine groups; this reducing agent is oxidized by chromic acid or its gels introduced into the solution so that the hexavalent chromium is partially reduced to trivalent chromium. Finally said aqueous solution is dried at a temperature between 50.degree.C and 250.degree.C. The method according to the invention reducing the number of treatment phases, provides savings on the installation, saving time, and increasing the yield.

Description

1 ~ 3 ~
The subject of the present invention is a method of filmog ~ ne phosphating of a metal surface, mainly for subsequent application of painting on the surface thus treated.
Among all the anticorrosive protection methods, one of the most important is the process consisting of a phospha-tation generally followed by a chromium plating treatment allowing to ensure good anticorrosive resistance and the adhesion of paints applied later.
Multiple procedures, protected by numerous patents have been designed, which ensure the formation of phosphate deposits metallic, usually zinc, iron, and manganese, crystal or amorphous structures; the speed of formation of phosphate layers (including cold ones), depends on the use accelerators and other auxiliary products, such as by wetting, dispersing, passivating examples.
However, all these phosphating procedures require a triple treatment, namely:
1 a phosphating bath,

2 washing to remove acid products, not combined,

3 and a bath based on chromic acid to passivate phosphate layers, in order to increase their anticorrosion resistance rosive.
It is therefore obvious that such a treatment of phosphata-1 tion requires complex and expensive installations and a time of '~ prolonged treatment.
The present invention relates to a method providing I an important simplification compared to known methods.
This simplification resides in the fact that the processing takes place kills in one impregnation.

, More pr ~ precisely, the present invention relates to ~ 3 ~

a film-forming phosphating process for a metal surface, by application on said surface, in a single operation, an aqueous solution containing phosphoric acid or a derived from such an acid, chromic acid or a salt thereof acid and a reducing agent, followed by heating to to accelerate the crosslinking of the film formed, characterized in that:
- the aqueous solution used contains phosphates primary iron, zinc or mangan ~ formed in phospho- acid rique, borophosphoric acid or an ester of phosphoric acid;
- the reducing agent used contains groups 'hydroxyl, aldehyde, ketone or amine;
-: age ~ nt.reducer is oxidized ~ by chromic acid or its salts introduced into the solution so that the hexavalent chromium is partially reduced to trivalent chromium;
and - the metal surface once coated with the formed film the aqueous solution is dried at a temperature comprised I between 50C and 250C;
.I The process according to the invention combines phosphating, washing, and chromic passivation in one operation, which makes it possible to reduce the various phases of the treatment, this not only ensuring a great saving on the installations.
and a saving of time, but this also increases the: - ' ~ yield of p ~. production. The method according to the invention , ~ is carried out cold which represents a significant saving energetic. . .
¦ Compared to the anticorrosive protection obtained ¦ by classical phosphating whose resistance is - very limited, due to rapid reoxidation, the process according to the invention provides very superior anticorrosive protection, due to the film-forming and hydrophobic qualities of the coating, as well 3 ~ u'à its microcrystalline nature, avoiding subsequent application I ~ _ 2 _ anti-rust oils. Paints applied to surfaces thus treated, have better adhesion qualities, in comparison ~ those obtained by traditional phosphating.
~ es applications of the method according to the invention extend not only to the phosphating of ferrous metals, but also the protection of galvanized and cadmine surfaces, as well than zinc, ~ aluminum and their alloys. We obtain also the elimination of oxides on the surface of iron and steel, which thus acquire anticorrosive protection, due to the phosphate film.
The novelty of this process, which simplifies operations treatment while giving superior anticorrosive properties resides in the reactivity of the compounds used for the formation of a film obtained by crosslinking, which contains all of the compounds and the residual acidity, thereby passivating the porosities of the phosphate film.
The various phases implemented in this process, are the following:
1. Incorporation of primary zinc phosphates or manganare or iron has a phosphoric acid solution, 2. Phosphorylation of carbohydrates (polysaccha-wrinkles), cellulose and their derivatives, starches, starches, poly-alcohols, proteins alone or in combination with carbohydrates cited, primary, secondary or tertiary, aliphatic alcohols, or aromatic, heterocyclic QUs, ald ~ hydes, ketones, esters, primary, secondary and tertiary amines and more generally substances containing hydroxyl groups, or free amines, 1 ~ 3 ~ r ~
either aliphatic, aromatic or heterocyclic, by acid concentrated phosphoric acid, or borophosphoric acid, or acidic ! alquyl-vinyl- or polyvinylphosp ~ oriques until solubilisa-1 tion in water;
j 3. Partial oxidation, diri ~ ée of the resulting compo-sition by chromic acid or its salts and formation . aldehyde, ketone or carboxylic groups, this pro-. citing both a partial reduction of hexavalent chromium by trivalent chromium and the formation of a soluble chromium phosphate.

4. Application of the green transparent solution obtained . naked, usually in dilute solution, on surfaces of iron, zinc or aluminum (for the latter two the reaction of alinC ~ 1 is optional) ~ causing the attack on the metal and the deposition of metallic phosphates, together with the formation of a pel-lLcule transparent of good adhesion ~ of a large re ~ resistance corro ~ ion and completely insoluble in water, said forma-t ~ on film being accelerated at temp ~ erasures high ~ es.
According to another variant of the process, the phase is eliminated phosphorylation, proceeding to the direct solubili ~ ation of products mentioned in paragraph 2e, above, such as for example al-primary, secondary and tertiary cool aliphati ~ ueg, aromatiqv.es or h ~ t ~ rocycligues, ald ~ hydes, ketones, esters, primary ~ secondary ~ and tertiary amines and more generally ~ ubstance ~ containing hydroxyl groups ~ or free amines, either allphatic, aromatic or heterocyclic by phos- acid.
phoric, by phosphorous anhydride, by borophosphoric acid that ~ by phosphonic acid or by acid esters of steel phosphoric, without producing any chemical reaction.
ha presence of chromium-hexavalent and chromium ions trivalent, con ~ era more ~ d ~ p2ssivantes properties, a better-water resistance, especially when there is phosphory--3-:
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. ~ .... ~. . . -. . .... .. -; . . ..,. ... . ,. . ... . , -1 ~ 3 .
lization and oxidation, according to the reactions mentioned in the a ~ 2nd and 3rd above. ~ ar ~ ticulation and insolubilization can also be favored by tannic acid, acry-. lique, methacrylic, polyacrylic, or their derivatives, thus ~ ue .1 by polycarboxylic or hydrocarboxylic acids.
.j To this basic composition can be added possibly-,., .1 also other products such as:
¦ accelerators, such as fluorides, nitrates, nitrites, oxalic acid, boric acid, fluosilica-tes, p ~ crique acid, ethylendiaminotetracetic acid, between other;
hardened, such as ammonium salts and aliphatic, aromatic or heterocyclic amines, particularly ~ ement guaniaine, phenylbiguanidines, diethylenetriamine, . morpholine ~ melamines and its derivatives, ur ~ e, phenylurea and polyurea, benzydine, quaternary bases, dicyandia-minc ~ succinimide, aniline, toluidlne ~ xylidine, i phthalimine, polivinylamine, acrylamide, resins and amino complexes, promoting crosslinking and the formation of a-. 20 complex oides, polyesters of phosphoric and chromic acid, iron chromate, capable of reacting with acid groups and aldehydes formed in reaction phases 2 and 3 mentioned above . above, this facilitating obtaining a macromolecular structure re more closed and resistant film forming ~ corro ~ ion;
: plasticizers, such as polyvi ~ yliqueset polyallyliques alcohols ~ allyl starch ~ le ~ g} ycols et polygiycol ~ le ~
¦l .. derivative ~ polyoxy ~ thylen ~ s;
corrosion inhibitors, such as, for example, borateæ, primary, secondary or tertiary amines, ames oxyethylenated, nitrophenols;
~, substances with amino, hydroxylated, car-boxyles and the like3, chemically active, capable of reacting with ~ 3 ~
. I.
I resins contained in the paintings which are applied later rement on the treated surface;
resins in solution, emulsion or aqueous dispersion, such as acrylic or methacrylic urea-formaldehyde resins, ~; etc., ensuring better adhesion of organic coatings (paints, etc.) applied afterwards due to their penetration tration in the phosphatic film, the great advantage of this process dice being to avoid washing and to allow to maintain the subs-tances solubilized in the phosphating layer, before their Insolubilization during the drying period;
wetting agents, defoamers, dryers trants and other auxiliary products, in small quantities.
r ~ application of this versatile product is done ~ for example ~ -ple ~ by immersion or pro ~ cold ection, treatment times ~ t ~ nt diff ~ rents depending on the ~ compositlons used, or else elect ~ rolytically on the metal surface ~ the solution has ~ issant .
as an electrolyte and the surface of the metal as a cathode. ~ es ca-electrolytically deposit forming a coating which ~ ouit of quality ~ s superior to those of traditional rev8te-~ electrolytic ~ elements, because there is simultaneously to the coating form-mation of a phosphate layer.
~ es parts treated by immersion or pro ~ ection are ~ strikes at the oven at a temperature which varies between 50O to 250C, approximately, to accelerate crosslinking components. This treatment can be combined simultaneously a ~ ec drying of the paints, thus ensuring the crosslinking of the phosphatic film.
If the phosphochromating liquid is applied hot on the metal surface, the reaction is faster. ~ a The concentration of solution used varies according to the desired result.
The higher the concentration of the solution, the more protection 3 anticorrosive is great.
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~ 3 ~ ~ ~ 7 ~ 'example described below of a case of execution of the pro-ceded has only an informative character and not l_mitatif:
ExEI ~ pLæ
, - Preferably added hot to phos acid-commercial phoric (85%) of zinc oxide in powder for ~ or-sea soluble primary zinc phosphate. To this solut ~ on we ~ adds reducing substances, as described above j cédemment, like ethylenglycol which one mixes cold. We ¦ then proceeds to the oxidation of the hydroxyl groups, etc. By chromic acid or its salts ~. This reaction takes place ~ cold and can be accelerated by raising the temperature. ~ e product re-is colored green, which proves that there is a reduction in hexavalent chromium in trivalent chromium. ~ possibly we can add also film-forming substances, such as methylolurea, capable of reacting with the resin ~ contained in dan ~
..
~ the painting ~ which is applied later.

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Claims (7)

The embodiments of the invention about which an exclusive right of property or privilege is claimed are defined as follows: 1. Method of film-forming phosphating of a surface metallic, by application on said surface, in a single operation, of an aqueous solution containing phospho- acid or a derivative of such an acid, chromic acid or a salt of such an acid and a reducing agent, followed by heating in view of accelerating the crosslinking of the film formed, characterized in what:
- said aqueous solution contains primary phosphates of iron, zinc or manganese forms in phosphoric acid, acid borophosphoric or an ester of phosphoric acid;
- said reducing agent contains hydroxyl groups, aldehyde, ketone or amine;
- said reducing agent is oxidized by chromic acid or its salts introduced into the solution so that the hexavalent chromium is partially reduced to trivalent chromium; and - the metal surface once coated with the film formed by said aqueous solution is dried at a temperature between 50 ° C and 250 ° C. 2. Method according to claim 1, characterized in that that said reducing agent is directly dissolved in the acid phosphoric, borophosphoric acid or an ester of the acid phosphoric. 3. Method according to claim 1, characterized in that that said reducing agent is combined with phosphoric acid, borophosphoric acid or an ester of phosphoric acid by a phosphorylization reaction. 4. Method according to claim 1, 2 or 3, characterized in that said reducing agent is selected from the group consisting by carbohydrates, primary and secondary alcohols, tertiary, aliphatic, aromatic or heterocyclic, the polyalcohols, aldehydes, ketones, esters, amines primary, secondary and tertiary, aliphatic, aromatic or heterocyclic. 5. Method according to claim 1, 2 or 3, character-dried in that the aqueous treatment solution also contains one or more accelerator, hardener, plasticizer additives, corrosion inhibitors, wetting agents, anti-foaming products, sequestering. 6. Method according to claim 1, 2 or 3, characterized in that the aqueous treatment solution additionally contains a crosslinking and insolubilizing agent chosen among tannic acid, acrylic acid, methacrylic acid, polyacrylic acids and their derivatives, as well as among the polycarboxylic acids. 7. Method according to claim 1, 2 or 3, characterized in that the aqueous treatment solution additionally contains acrylic, methacrylic or urea-formaldehyde resins in solution, aqueous emulsion or dispersion.