JPH0387374A - Method of creating phosphate coat on metal and application of this method - Google Patents

Abstract

In a process for phosphating iron and steel surfaces according to the low-zinc technology, a nitrite-free aqueous acidic phosphating solution of 30 to 65 DEG C is used which contains 0.4 to 1.7 g/l of Zn 7 to 25 g/l of P2O5 2 to 30 g/l of NO3 and in which the weight ratio of free P2O5 to total P2O5 is adjusted to a value in the range from 0.04 to 0.20. H2O2 or alkali metal perborate is added to the phosphating solution in an amount such that - in the incorporated state - its maximum peroxide concentration is 17 mg/l, preferably 8 mg/l (calculated as H2O2), or its maximum Fe(II) concentration is 60 mg/l, preferably 30 mg/l (calculated as Fe). It is particularly advantageous to control the addition of H2O2 and/or alkali metal perborate according to the electrochemical potential determined with a redox electrode. The phosphating solution may additionally contain Mn, Ni, Co, Mg and/or Ca or fluoroborate, fluorosilicate and/or fluoride. The process can be used in particular for the preparation of metal surfaces for coating. <IMAGE>

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to the surface treatment of iron and steel by a low zinc method using a phosphating solution containing zinc, phosphates and nitrates, but not nitrites. The present invention relates to a method for preparing phosphate coatings on metals by phosphoric acid treatment and the use of this method in the pretreatment of iron and steel surfaces for painting.

[Conventional technology]

Zinc phosphate processing methods are used on a large scale in the metalworking industry. The phosphate layer created by this method on the metal surface reduces slippage, facilitates chip-free cold working, helps prevent corrosion, and serves as an adhesion basis for coatings.

As a pre-treatment before painting, phosphoric acid treatment with a low zinc method offers particular benefits. The bath solution used in this case contains only a zinc concentration of about 0.4 to 1.7 g/l and forms a phosphate layer on the steel containing a high proportion of phosphate stone. gives better coating adhesion and higher resistance to sub-coating migration of corrosive stresses than the hopeite obtained in high zinc content phosphating baths.

Nitrite, chlorate and organic nitro compounds have been found to be particularly useful as accelerators in low zinc phosphate treatment baths. These give high quality and uniform coated phosphate layers in a short time. It is also known to use peroxides as accelerators in low zinc phosphate treatment baths. Although peroxides are preferred over the aforementioned accelerators for reasons of workplace hygiene and environmental protection, their accelerating action is not sufficient under the processing conditions conventionally used. Another disadvantage of peroxy compounds is that even after long processing times relatively thin phosphate layers are obtained with only moderate corrosion resistance.

(Problem to be Solved by the Invention) The problem of the present invention is to treat iron and steel as necessary with a low zinc phosphating solution that does not contain nitrites. The object of the present invention is to provide a method for the treatment with zinc phosphate that does not have the known drawbacks, especially those mentioned above.

[Means to solve the problem]

The problem is solved according to the invention in the manner mentioned at the outset.
0.4-1.7g//2 of Zn, 7-25g of p2o
Contacting the surface at 30 to 65°C with a phosphoric acid treatment solution containing 2 to 30 g/l and N03 and adjusting the weight ratio of free P2O5 to total P2O5 to 0.04 to 0.20, and action. The maximum peroxide concentration of the phosphoric acid treatment solution is 17 mg/Q (calculated as H20□) and the maximum Fe(II) concentration of the same solution is 60 mg.
/ 1 (calculated as Fe) by adding 1120 □ or an alkali perborate to the phosphating solution.

The method of the invention is for surface treatment of iron and steel. Iron and steel as well as low alloy steel, galvanized steel, zinc alloy coated steel, i.e. for example ZnAj2, ZnFe and Zn
Ni coated steel, aluminized steel, aluminum and its alloys can be treated.

The phosphoric acid treatment is carried out at a temperature range of 30-65°C.

Below 30° C., the phosphating rate is not sufficient for modern mass production (while at temperatures above 65° C., disadvantages arise, such as significant encrustation on the surfaces of the equipment).

Z in the phosphoric acid treatment solution is a common practice in the so-called low zinc method.
The weight ratio of n: P2O5 is preferably (0,075 to
0°15):1.

The peroxide or Fe(II) content of the phosphating solution is determined in a conventional manner, for example by potassium permanganate titration. According to a preferred embodiment of the present invention, H20□ and/or
Alternatively, the surface is contacted with a phosphating solution in which the addition of alkaline perborate is adjusted according to the electrochemical potential determined by the redox electrode. For example, a platinum electrode and a suitable reference electrode, such as a calomel electrode or a silver-silver chloride electrode, can be used to continuously monitor the phosphating solution, providing a constant Fe(If) ion concentration and a constant Addition of peroxide can be carried out such that the hydrogen peroxide concentration remains within the above range.

The selection of the type and amount of cations and anions in the phosphating solution used in the process of the invention is such that the ratio of free A11P z Os to total P2O5 is between 0.04 and 0.20. Typically high bath temperatures and/or
Or in the case of high zinc concentrations, this ratio should be selected in the high range of said range, and in the case of low bath temperatures and/or low zinc concentrations, this ratio should be selected in the low range.

According to a preferred embodiment of the invention, the maximum peroxide concentration of the phosphating solution is 8 mg/i and the maximum Fe (
If) 11□0□ in an amount such that the concentration is 30 mg/l
and/or contacting the surface with a phosphating solution containing an alkaline perborate.

According to another preferred embodiment of the invention, manganese in an amount of 3 g/l or less, nickel and/or cobalt in an amount of 3 g/l or less, magnesium in an amount of 3 g/l! The surface is contacted with a phosphating solution further containing calcium in an amount of: The combined use of manganese and/or magnesium and/or calcium results in phosphate coatings containing these cations in addition to zinc and optionally iron (n). Such mixed phosphates are characterized by high alkali resistance and are particularly suitable as adhesive bases for paints. It is preferred to add nickel and/or cobalt to increase the aggressiveness of the phosphating solution to tears and to improve the phosphating of the zinc surface if the zinc surface is also treated. The addition of small amounts of copper, if necessary, increases the accelerating effect of the phosphating solution. Alkali and/or ammonium are primarily used to adjust the desired acid ratio.

According to another preferred embodiment of the invention, the fluoroborate salt is
g/IBF) and/or silicofluoride in an amount of 3 g/l Calculated as C3=Fb) and/or in an amount of 1.5 g/F! (Calculated as F) The surface is brought into contact with a phosphoric acid treatment solution containing the following amounts: Fluoroboric acid, silicofluoride and/or fluoride anions generally increase the rate of phosphoric acid treatment and are particularly advantageous when further treatment of aluminum-containing zinc surfaces is intended. The presence of free fluoride (F-) is essential for crystalline phosphoric acid treatment of aluminum and its alloys.

Chlorides and sulfates are used to adjust the electroneutrality of the phosphating solution and, in special cases, to improve its aggressiveness. The optionally used polyhydroxycarboxylic acids, such as tartaric acid and/or citric acid, can influence the thickness and weight per unit surface of the resulting phosphate coating.

When the phosphating solution further contains manganese and/or nickel and/or cobalt and/or magnesium, Mn:Zn, (Ni and/or Co): Z
The weight ratio of Mg:Zn and/or Ca:Zn should be at most 2:1, respectively.

According to another advantageous embodiment of the invention, the free P2O5 of the phosphating solution of the working bath is adjusted by adding manganese carbonate, zinc carbonate and/or zinc oxide to the surface. bring into contact. At that time, it is preferable to add each of these components as an aqueous dispersion.

The method of the present invention can be carried out by a spray method, a dipping method, a spray dipping method, or a flow coating method.

According to another preferred embodiment of the invention, the surface is contacted with a phosphating solution in which water is removed and compensated for by subsequent wash water. Water can be removed from the phosphating bath, for example, by evaporation, reverse osmosis and/or electrodialysis. Particularly when H2O2 is used as peroxide component, these steps make it possible to carry out the process of the invention in such a way that no phosphate-contaminated wastewater is produced from the washing step after phosphoric acid treatment. The washing steps, preferably configured as a washing bath cascade, are carried out with the last washing bath being salt-free or low-salt water, which flows in the opposite direction of the workpiece from washing step to washing step to absorb the phosphoric acid. supplied to the processing bath. The water thus supplied is used in the phosphating bath to compensate for the water removed from the phosphating solution as described above. Water removed from the phosphating solution, for example by reverse osmosis or aerothermic dialysis, can be recycled to the washing process.

According to another preferred embodiment of the invention, replenishment of free P2O
The ratio of 5 and total P2O5 is (-0.50 to +0.20)
The surface is contacted with a phosphating solution supplemented by the addition of phosphate salt: 1:1. In the above definition for the ratio of free P2O5 and total P20, a negative value means that no free 11Pzos is present, but rather that some of the phosphate is in the diphosphate stage. A value of -0.19 means that 19% of the total P2O5 is present as diphosphate.

According to another definition, the phosphate component in supplementation is on the one hand 5
0% diphosphate and 50% monophosphate (P2O3
the other is limited by 80% primary phosphate and 20% free phosphate (calculated as P2O5)
within the range limited by.

Since the liquid replenishment concentrate is not stable within the above-mentioned ranges of P2O5 and total P2O5, replenishment in the present invention is usually carried out in at least two concentrates.

The method of the present invention, particularly the method of the preferred embodiment in which the coating phosphating solution is replenished, provides a uniform and complete phosphate coating and is effective for coating iron and steel as well as their associated surfaces, i.e. galvanized. , zinc alloy plated or aluminium plated steel and aluminum can be provided with a satisfactory coating for a long time.

The method of the invention is particularly advantageous for the pretreatment of surfaces for painting, especially by immersion electrodeposition. In that case, it is particularly useful as a pretreatment for electrophoretic immersion electrodeposition.

[Example] The present invention will be exemplified and explained in detail using the following example.

The solution for phosphoric acid treatment prepared for the spray treatment of Fushi Akeito is as follows: Zn 0.8g/l Free F'1lPzOz=1
．． 04 g/QNi 1.0g/N Total P
2O5-13g#! Mn 1. Og/jl!
Free acid -0.9 points Na 2.6g/lf
Total acid = 23 points t'zos 13.0 g/I NO:l 2.1 g/e, and the concentration of H,O□ was increased from 10 to 10 by adding 11.0□.
If H20□ does not exist, the concentration of iron (n) is changed from 10 to 90 m by processing the steel plate.
It was varied in the range of g/l Fe(II).

A steel plate degreased with an organic solvent was sprayed with the bath at 58°C. FIG. 1 shows the phosphate coating weight obtained by spraying for 3 minutes. FIG. 2 shows the minimum phosphoric acid treatment time found in this experiment, ie, the treatment time required to deposit a uniform phosphate coating on the cut. Both figures represent the advantageous results obtained by the method of the invention.

Degreased steel sheets of Senran Ikki steel (80%) and electrogalvanized steel (20%) were phosphoricated with a phosphating solution having the following composition in a phosphating apparatus of capacity Ffi 5 e.

Zn 0.8g/l M weak acid = 0.9 points Ni LOg/l total acid = 23 points Mn 1.0g/l Na 2.6g/lf1 has 13.0 g/IN(h 2.1g, # .

The temperature of this solution was 55-60°C. The treatment was carried out by spraying for 3 minutes. The treatment capacity at a treatment rate of 0.1 n/h was 3 nf/l. The composition of the bath was maintained throughout the process by the addition of zinc carbonate and a replenishment solution of appropriate composition. 19 g of the following replenishment concentrate was required per surface.

P2O5 23.4% Na 1.89% Gate n 1.74% Ni 1.34% Zn 3.39% F, (III) 0.01%NOi
3.09%it AIi p zo
5 and total P2O5, an additional 1.8 g/
Basic zinc carbonate (53.5% Zn) was added. This replenishment results in a ratio of free P, O, and total P2O5 to (-0).

18): corresponds to 1.

According to the measured electrochemical potential, hydrogen peroxide
The maximum constant Fe(II) ion concentration and H20 concentration in the bath is 10 mg/j! The amount was used. The resulting phosphate coating is uniform and complete throughout, with a coating weight of 2 on steel.
．． 0±0.2g/%, 2.5±0 in electrogalvanized cavities
．． It was 2g/bo.

Example 3 A degreased steel plate made of AJ 2-shaft St and A1 G3 grade steel (60%), electrogalvanized steel (30%) and aluminum (10%) was treated with phosphoric acid having the following composition using a phosphoric acid treatment device with a capacity of 5N. Treated with an acid treatment solution.

Zn 0.8g/l free acid =1. INi
1. Og/lfi total acid = 23Mn
1. Og/l Na 3.2 g/'P2O513,0g/'NOz 2.1 g/QFO,5g/l Under the above conditions and the steady concentrations of Fe(U), H, and O□, the maximum When maintained at 6 mg/lfi, uniform and complete coatings were obtained on the three materials at the following coating weights:

I: 2.1 ± 0.2 g/Bo electrodeposited zinc: 2.6 ± 0.2 g/Bo AfMgSi: 2.9 ± 0.3 g/rdAfM
g,: 3.1 ±0.3g/rd

[Brief explanation of drawings]

Figure 1 shows the phosphate coating weight obtained with a 3 minute spray and Figure 2 shows the minimum phosphating time.

Claims (9)

[Claims] 1. In a method of phosphating the surface of iron and steel by a low zinc method using a phosphating solution containing zinc, phosphates and nitrates but not nitrites to form a phosphate film on the metal. , Zn 0.4-1.7g/l, P
_2O_5 7-25g/l and NO_3 2-30g
/l of free P_2O_5 relative to total P_2O_5
The surface is brought into contact with an acidic aqueous phosphoric acid solution having a weight ratio of 0.04 to 0.20 at 30 to 65°C, and the maximum peroxide concentration of the phosphoric acid solution in the working state is 17 mg/l ( A method characterized in that H_2O_2 or an alkali perborate is added to the phosphating solution in an amount such that the maximum Fe(II) concentration of the solution is 60 mg/l (calculated as Fe). 2. 2. Process according to claim 1, characterized in that the surface is brought into contact with a phosphating solution in which the addition of H_2O_2 and/or alkali perborate is adjusted according to the electrochemical potential determined by a redox electrode. 3. Maximum peroxide concentration of phosphating solution is 8mg
The surface is brought into contact with a phosphating solution to which an amount of H_2O_2 and/or alkali perborate is added such that the maximum Fe(II) concentration of the solution is 30 mg/l and the maximum Fe(II) concentration of the solution is 30 mg/l. The method according to claim 1 or 2. 4. Manganese in an amount of 3 g/l or less, nickel and/or cobalt in an amount of 3 g/l or less, magnesium 3 g/l
4. The surface according to claim 1, 2 or 3, characterized in that the surface is contacted with a phosphating solution further containing calcium in an amount of: Method. 5. Fluoroborates in amounts up to 3 g/l (calculated as BF_4) and/or silicofluorides in amounts up to 3 g/l (S_i
Calculated as F_b) the following amounts and/or fluoride: 1.
5. A method according to claim 1, characterized in that the surface is brought into contact with a phosphating solution containing not more than 5 g/l (calculated as F). 6. Free P_2O_5 of the phosphating solution of the working bath
6. A method according to claim 1, characterized in that the surface is brought into contact with a phosphating solution, wherein the surface is adjusted by the addition of manganese carbonate, zinc carbonate and/or zinc oxide. 7. 7. The surface is brought into contact with a phosphating solution such that water is removed and compensated for by wash water of a subsequent wash step. the method of. 8. The proportion of free P_2O_5 during replenishment is (-0.50
~+0.20): 1 to 10% of the phosphoric acid treatment solution supplemented by the addition of 1 phosphate salt.
The method according to any one of the above. 9. Claim 1 for the preliminary treatment of iron and steel surfaces, especially for coating by electrophoretic immersion electrodeposition, preferably by electrophoretic immersion electrodeposition.
A use using the method according to any one of items 1 to 8.