LT4579B - Process for preparing non-chromate conversion films onto zinc surface - Google Patents

Abstract

The production method of non-chromatic conversion film on zinc surfaces may be used in various branches of industry for protecting products and components thereof against corrosion and improving the appearance thereof (decorativeness). Using this method conversion, films on zinc surfaces are produced of a solution containing condensed phosphates, oxidisers and 0.5-10 g/dm<3> of at least one of these compounds containing borate, molybdate and/or complex fluoride ions, and the components are covered in a 15-120 s acid solution - pH = 1.0-2.0.

Description

The present invention relates to a process for the preparation of conversion films, in particular non-chromatic conversion films, on zinc surfaces in acidic solutions of condensed phosphates and can be used in various industrial applications for protecting products or their parts from corrosion and improving their appearance.

Zinc coatings, especially galvanic, are widely used for corrosion protection of steel products. Zinc coatings are usually further treated, usually with acidic solutions of chromium compounds. The surface of the zinc so treated produces a colored or colorless chromium-plated (chromium-containing) film which improves the corrosion resistance of the zinc coatings and helps the articles maintain their decorative appearance under operating conditions.

Chromium compounds are highly toxic, so it is important to develop novel conversion films on zinc surface using non-toxic or less toxic compounds.

To

There is a known process for preparing non-chromatic conversion films on zinc surface (U.S. Patent No. 4,3381,140, C 23F7 / 00, 1982), wherein zinc coated parts are immersed in a solution containing (g / dm ³ ): Hf and / or Zr ions -4-100 , F ions -4-100, Plant tannins 25-500, Phosphate ions -25-75, followed by extraction, washing and drying. Solution pH = 2-4.5, temperature -20-70 ° C, treatment time -2-60s. As a result of this treatment, the surface of the zinc becomes a yellowish conversion film.

The disadvantage of this method is that the resulting non-chromatic conversion films have relatively low corrosion resistance.

There is a known process for preparing non-chromatic conversion films on zinc surface (U.S. Patent No. 4,359,347, C23F 9/00, 1982), wherein zinc coated parts are immersed in a solution containing (g / dm ³ ): Fe ions -0.05 - 0.1, Co ions - 0.05 - 0.1, oxidizing agents (H2O2, ammonium or alkali metal peroxides) -3-7, sulfate ions -0.55, halogen - (Cl, F or Br) ions - 0.1 -2.5, surfactants - 0.05 -0.1, after it is pulled out, washed and dried. PH of solution = 1.5 -2.0, temperature 5 - 65 ° C, treatment time 10 - 60 s.

The aforementioned metal ions are the main 'constituents' of decorative colorless films. To obtain a yellowish film, an additional 1 to 4 g / dm ^{3 of} Ce ions is still required.

The disadvantage of this method is that the resulting non-chromatic conversion films have relatively low corrosion resistance.

There is a known process for preparing non-chromatic conversion films on zinc surface (International Patent WO 93/10278, C 23C22 / 40, 1993), wherein zinc coated parts are immersed in a solution containing (g / dm ³ ): sodium molybdate -4.8 -9.6 (converted to Mo), phosphoric acid - 4.7 (converted to P), then extracted, washed and dried. Solution pH = 2 -4.6, temperature 60 ° C, treatment time 2 min. Corrosion resistant yellow decorative conversion films are obtained.

The disadvantage of this method is that the processing time is too long (2 min), which prevents it from being used in typical automatic mode galvanic lines where the duration of such operation is 15-60 s and the high temperature of the solution (60 ° C), which increases the cost of energy.

There is a known process for preparing non-chromatic conversion films on zinc surface (U.S. Patent No. 5294265, C 23C22 / 02, 1994), wherein a hot zinc-coated surface is treated with a solution containing (g / dm ³ ): organic phosphate (phosphoric acid epoxyester) or organic of phosphonate (phosphonic acid epoxyester) -10-50 and F or Cl ions -0.8-1.2.

Solution pH = 2.7-3.5, temperature -20-60 ° C, treatment time -0.5-180s. The treatment can be done by immersing the product in solution or by spraying or applying the solution on the zinc surface

After such treatment, the zinc surface is washed and dried. In order to improve the protective properties of the resulting conversion films, the treated surface may be further washed with an aqueous solution of alkali metal nitrate.

The disadvantage of this method is that the non-chromatic conversion films obtained on the surface of zinc coatings have relatively low corrosion resistance.

There is a known process for preparing non-chromatic films on zinc surfaces (U.S. Patent No. 5344,505, C23C 22/07, 1994), wherein a hot zinc-coated surface is treated with a solution (by spraying or spraying on a zinc surface) containing (%) : phosphoric acid-2, boric acid -0.2 and molybdenum acid -0.2, then heat to high temperature - 230 ° C.

The disadvantage of this method is that the non-chromatic conversion coatings obtained on the surface of the zinc coatings have a relatively low corrosion resistance and a high energy consumption is achieved at 230 ° C.

The closest technical solution is, in essence, a process for the preparation of converting pyrophosphate films on a zinc surface (French Patent No. 2,492,413, C 237/12, C23C 1/02 1982), wherein zinc coated parts are immersed in a solution containing 5Ί0 ′ ² 1Ί0 ¹ M pyrophosphate. ions and oxidizer-nitrate ions (concentration ratios NO ₃ : P2O ⁴ = 0.4 -1.2), followed by extraction, washing and drying. PH of the solution = 4.2 -5.3, temperature 60-65 ° C, treatment time 24 hours. The solution may also contain zinc and / or calcium ions. 20-150 µm thick corrosion resistant conversion films based on zinc pyrophosphate are obtained.

The disadvantages of this method are the relatively high solution temperature of -6065 ° C and the extremely long treatment time of 24 hours. For these reasons, the power consumption is greatly increased and the technique itself is practically impossible to use on typical automatic mode galvanic lines where the duration of such an operation is 15-60 s.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for preparing non-chromatic conversion films on zinc surface which allows the formation of decorative, corrosion resistant films in solution without toxic chromium compounds.

Another object of the present invention is to improve the technology of the method, i.e., to obtain films at relatively low temperature (room) and short time (15-60s), which would reduce power consumption and use the method in typical automatic mode galvanic lines and standard equipment.

The essence of the invention is that the zinc coated parts are immersed in a solution containing condensed phosphates, oxidizing agents and 0.5-10 g / dm ^{3 of} at least one of the compounds containing borate, molybdate and / or complex fluoride ions and coating the parts in 15-120s acid solution - pH = 1.0 - 2.0.

The proposed method is more technological, since sufficiently high corrosion resistance decorative nochromatic conversion films are obtained at room temperature without the use of chromium compounds and additional operations.

This technique helps to int'ensify the process of obtaining conversion films, since high quality films are formed in a relatively short time of -15-60 s. In addition, the proposed method can be used on typical automatic mode power lines and standard equipment.

The parts are treated in a solution containing (g / dm ³ ): temperature of 3-25 condensed phosphate, 2-10 oxidizer and 0.5 -10 solution of at least one of the compounds containing borate, molybdate and / or complex fluoride ions, pH 1.0 - 2.0 15-35 ° C.

The solution is prepared in salted water by dissolving the amounts of the substances specified in the recipe. Adjust the acidity of the solution, if necessary, with caustic soda or mineral acid (orthophosphoric, nitric or boron).

Mixtures of condensed phosphate pyrophosphates, eg, polyphosphates, eg, NaiPaOg, Na ₄ P ₄ 0i ₂ .

ion source can Ν3 ₄ Ρ ₂ θ7, NaH ₃ P ₂ O7,, Na ₅ P ₃ Oio, Na ₆ P ₄ 0i3 and so on

NagPgOig and so on. and be soluble in Na ₂ H ₂ P ₂ O ₇ and metaphosphates of these compounds

Oxidising agents may be used compounds having an oxidizer in an acidic medium, as follows: peroxides such as., H ₂ O _2, K ₂ O _2, Na ₂ O ₂ and the like., Permanganates, for example., KMnO _4, namn ₄ etc. , nitric acid and nitrates such as NH ₄ NO ₃ , KNO ₃ , NaNO ₃ and so on. and mixtures of these compounds.

Borate ion source can be. boric acid H3BO3 and its soluble salts, eg Zn ₃ (BO ₃ ) 2, 2A1 ₂ O ₃ * B ₂ O3 «5H ₂ O, metaborates such as NaBO ₂ * 4H ₂ O, 2KBO ₂ * 2.5H ₂ O and the like., tetraborates eg., Na ₂ B ₄ O7 "10H ₂ O, K ₂ B ₄ O7 * 4H ₂ O and so on.In mixtures of these compounds.

The source of molybdate ions may be soluble salts of molybdenic acid, such as Na ₂ Mo0 ₄ · 2Η ₂ Ο, K ₂ Mo0 ₄ , Al ₂ (Mo0 ₄ ) 3, ZnMo0 ₄ , (NH ₄ ) ₆ Μο ₇ 0 ₂₄ · Η ₂ 0 and so on. and mixtures of these compounds.

The source of complex fluoride ions may be soluble boron fluorides, e.g. NH ₄ BF ₄ , NaBF 8, KBF 6, etc., silicon fluorides e.g. , (NH ₄ ) ₂ SiF ₅ , Na ₂ SiF ₆ , K ₂ SiF ₆ , ZnSiF ₆ * ₆ H ₂ O, etc., titanium fluorides such as (NH ₄ ) ₂ TiF 6, Na ₂ TiF ₆ , K ₂ TiF ₆ and so on., aluminum fluoride, for example., Na3AlF ₆ K ₃ A1f ₆ and so on., as well as mixtures of these compounds.

The zinc-coated parts are washed with cold water, immersed in a solution prepared according to the proposed method at pH = 1.0 -2.0 and a temperature of 15-35 ° C, maintained in solution for 5-120s with compressed air or mechanically moving workpieces, then extracted, washed water and dries.

The quality of the conversion films is evaluated after 24 hours. after their receipt by appearance (ornamentation) and corrosion resistance.

Evaluates the appearance (ornamentation) of the films visually with the naked eye in daylight in three parameters: colorless, colorless with blue tint, colorless with rainbow tint, rainbow;

color uniformity even, uneven, spotty;

gloss glossy., semi glossy, matte.

The film is evaluated for corrosion resistance by the number of hours before the onset of zinc corrosion in the humidity chamber according to GOST 9.308 -85.

To evaluate the effectiveness of the proposed method, 8 samples were prepared, of which 1 and 2 are control, 3 to 8 prepared according to the proposed method with different concentrations of solution components and different technological regimes. In all cases, steel plates (10cm x 5cm) coated with a glossy, not thinner than 7 μπι zinc coating in weakly acidic galvanizing electrolyte were used for the conversion process.

EXAMPLES example (control)

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Na ₄ P ₂ O ₇ (converted to P ₂ O ₇ ⁴ ) HNO3 (converted to NO3)

6th

The acidity of the solution was adjusted by adding H ₃ PO ₄ .

The solution is stirred under compressed air, pH = 1.5, temperature 20 ° C, immersion time 24 hours.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example (control)

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Well ₄ P ₂ O ₇ (converted to P ₂ O ₇ ⁴ ') -15

HNO ₃ (converted to N0 ₃ ') -6.

The acidity of the solution was adjusted by adding H ₃ PO ₄

The solution is stirred under compressed air, pH = 1.5, temperature 20 ° C, immersion time 90s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Well ₄ P ₂ O ₇ (converted to P ₂ O ₇ ⁴ ) -15

HNO3 (converted to NO3 ”) -6

Well ₂ Mo0 ₄ * 2H ₂ 0 (converted to Mo0 ₄ ² ~) -5.

The acidity of the solution was adjusted by adding H3PO ₄ .

The solution is stirred under compressed air, pH = 1.5, temperature 20 ° C, immersion time 90s.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Na ₆ PsOi ₈ (converted to PgOis ⁶ ) -3

H ₂ O ₂ (converted to 100% product) -2

Al ₂ (Mo0 ₄ ) 3 (converted to Mo0 ₄ ^2- ) -0.5

NaNC> 3 (converted to NO3) -4.

The acidity of the solution was adjusted by the addition of H3PO4.

The solution is stirred under compressed air, pH = 1.0, temperature 35 ° C, immersion time 120s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Well ₆ P ₄ 0i3 (converted to P ₄ 0i3 ⁶ ) -20

Well ₆ P ₆ O ₁₈ (converted to P ₆ O ₁₈ ^6- ) -5

NaNO ₃ (converted to NO ₃ ) -6

KMnO ₄ (converted to MnO ₄ ⁷ ') -0.5

Na ₂ TiF6 (converted to TiFg ² ') -10.

The acidity of the solution was adjusted by adding H3PO ₄ .

The plates are moved mechanically in solution, pH = 2.0, temperature 15 ° C, immersion time 90s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

NaH ₃ P ₂ O7 (converted to F ₂ 07 ^{, _} ) -4

Na _s P ₆ O ₁₈ (converted to ΡβΟιβ ⁶ ”) -6

HNO ₃ (converted to N0 ₃ ) - -4

Na ₂ O ₂ - 6

Well ₂ B ₄ O -! «10H ₂ O (converted to B ₄ O ₃ ² ~) -2.5

NaBO ₂ «4H ₂ O (converted to B0 ₂ ~) -2.5.

The acidity of the solution was adjusted by the addition of H3PO4.

Stir the solution with compressed air, pH = 1.4, 30 ° C, immersion time 15 s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

Well ₆ P ₆ 0ia (converted to P ₆ 0i ₈ ⁶ ') -8

Well ₃ P ₃ O ₉ (converted to P ₃ O ₈ ³ ) -4

HNO ₃ (converted to N0 ₃ ) -3

NaNO ₃ (converted to N0 ₃ ~) -2

Well ₃ AlF ₆ (converted to A1F ₆ ³ ) -4

H ₃ BO ₃ (converted to BO ₃ ³ ') - -2.

The acidity of the solution was adjusted by the addition of H3PO4.

The plates are moved mechanically in solution, pH = 1.6, temperature 25 ° C, immersion time 30 s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

example

Wash the zinc-coated plates with cold water and immerse in a solution containing (g / dm ³ ):

; 4a2H ₂ PO7 (converted to P2O7 ⁴ ') -2

NagPfiOia (converted to P ₆ 0i _a ⁶ ~) -10

H ₂ O ₂ (converted to 100% product) -2

KMnO ₄ (converted to MnO ₄ ~) -1

NaNO ₃ (converted to N0 ₃ ^- ) -5

K ₂ SiF ₆ (converted to SiFg ² ) -1.

The acidity of the solution was adjusted by the addition of H3PO4.

The solution is stirred under compressed air, pH = 1.5, 20 ° C, immersion time 60 s.

After treatment with the solution, the plates are removed, washed with cold water and dried.

Comparative data on film quality are given in the table

As can be seen from the data in the table, the non-chromatic conversion films obtained according to the proposed method (Examples 3-8) have better protective and some decorative (luster) properties as compared to the prototype. In addition, decorative non-chromatic conversion films with good corrosion resistance (72 to 156 hours in a humidity chamber) are obtained in room temperature solutions as early as 15 -60s, and their quality does not deteriorate with longer processing times up to 120s. Not only does this reduce energy costs, it can also be used on typical galvanic lines, which extends its power consumption.

TABLE

Examples co colorless with bluish in shade smooth shiny LO 20th 09 compressed air 144 b- colorless to bluish in shade smooth shiny T " 25th 30th movable details 156 co colorless to bluish smooth shiny 'T 30th m depressed weather 144 u> colorless with a rainbow tint smooth shiny 2.0 m 06 movable details 120 't rainbow smooth shiny o 35 120 compressed air 96 co colorless smooth shiny LO 20th 06 depressed weather 72 'ω c o L. c o Her CM colorless with a rainbow tint smooth half shiny LO 20th 06 compressed air 48 £ ) c O u C O She, v yellowish smooth matte in 20th 24 or compressed air 09 Films quality indicators 1.Appearance (ornamentation): color colors smoothness shine II.Technological characteristics: pH of the solution temperature, ° C processing time, s mixing II.Film corrosion resistance (hours before onset of Zn corrosion)

Claims (4)

DEFINITION OF INVENTION 1. A method of preparing non-chromatic conversion films on a zinc surface, wherein the zinc coated parts are immersed in a solution containing condensed phosphates, an oxidizing agent comprising the addition of 0.5 to 10 g / dm ^{2 of} at least one of the compounds containing borate, molybdate and / or complex of fluoride ions and details in 15-120 s acid solution - PH = 1.0-2.0 2.Conversion films method of preparation according to 1 point, divergent in that borate ion source can be boron acid H3BO3 and its soluble salts such as Zn ₃ (BO3) ₂ , 2Α1 ₂ Ο ₃ · 32Ο ₃ · 5Η2Ο, metaborates such as NaBO ₂ * 4H ₂ O, 2Κ3Ο ₂ · 5Η ₂ Ο, tetraborates such as Na ₂ B.:O7*10K ₂ C), K ₂ B; O7 * 4K ₂ O, and mixtures of these compounds. Third conversion process for the preparation of films according to claim 1, characterized in 'that the molybdate ion source can be acid molybdenum salts, such as Na ₂ Mo0; "2H ₂ 0, Κ _2' · ίο0 ₄ Aljd '-' oOJj, ZnMoOø, (NK ₄ ) _ζ Μθ7θ ₂ 4 · Η ₂ 0, and mixtures of these compounds. ⁴ Fourth conversion process for the preparation of films according to claim 1 characterized in that the complex fluoride ion source may be soluble boron fluorides such as NH; 3E \, Na3F ;, K3F ;, silicon fluorides such as ₍₂ NHJ Ziphion Na ₂ Ziphion , K; SiFi, ZnSiF, * oH ₂ 0, titanium fluorides such as (NKJ ₂ TiF ₀ -, Na ₂ TiFi, K ₂ TiF _s , aluminum fluorides such as Na ₃ AlFs, K ₃ .AIF 5, and their compounds). mixtures.