JP2992619B2 - Method of making phosphate coating on metal and uses 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

The present invention relates to a surface treatment of iron and steel by a low zinc method using a phosphating solution containing zinc, phosphate and nitrate and not containing nitrite. Phosphoric acid to form a phosphate coating on metal and the use of this method for pretreatment of iron and steel surfaces for painting.

[Conventional technology]

Zinc phosphate treatment is used extensively in the metalworking industry. The phosphate layer created on the surface of the metal to be treated in this way reduces slippage, facilitates chip-free cold working, helps to prevent corrosion, and serves as an adhesion basis for the coating.

Phosphating with the low zinc method as a pretreatment before painting offers special benefits. The bath solution used contains zinc at a concentration of only about 0.4 to 1.7 g /, forming a phosphate layer on steel with a high proportion of phosphite, which is highly zinc-rich. It produces better coating adhesion and higher resistance to undercoat migration of corrosive stress than hopite obtained with a content phosphating bath.

Nitrite, chlorate and organic nitro compounds have been found to be particularly useful as accelerators in low zinc phosphating baths. These give a high quality, uniform coating phosphate layer in a short time. It is also known to use peroxides as accelerators in low zinc phosphating baths. Peroxides are preferred over the abovementioned accelerators for reasons of workplace hygiene and environmental protection, but their promoting effect is not satisfactory under the conventionally used processing conditions. Another disadvantage of peroxy compounds is that relatively long phosphate treatments result in relatively thin phosphate layers with slightly moderate corrosion resistance.

[Problems to be solved by the invention]

The object of the present invention is to provide a zinc-plated steel, if necessary, with iron and steel by a low zinc phosphating solution containing no nitrite.
It is an object of the present invention to provide a method for zinc phosphate treatment with zinc alloy coated steel, aluminized steel and aluminum, which is free from the above-mentioned disadvantages.

[Means for solving the problem]

This object is achieved according to the invention in the method mentioned at the outset, 0.4～1.7G the Zn /, the P ₂ O ₅ the 7～25G / and NO ₃ 2
3030 g / content, and the weight ratio of free P ₂ O ₅ to total P ₂ O ₅ is 0.
30 ~ 65 ° C in phosphating solution adjusted to 04 ~ 0.20
The maximum peroxide concentration of the phosphating solution is 17 mg / (calculated as H ₂ O ₂ ) and the maximum Fe (II) concentration of the solution is 60 mg / (calculated as Fe) The problem is solved by adding H ₂ O ₂ or alkali perborate to the phosphating solution. The working state means the state of the phosphating solution when in contact with the surface to be treated.

The method of the present invention is for surface treatment of iron and steel. Low alloy steels, galvanized steels, zinc alloy coated steels, ie steels coated with, for example, ZnAl, ZnFe and ZnNi, aluminized steel, aluminum and its alloys can be treated with iron and steel.

The phosphating is performed in a temperature range of 30 to 65 ° C. 30 ℃
At lower temperatures, the phosphating rate is not sufficient for modern mass production, while temperatures above 65 ° C. have the disadvantage that, for example, there is significant jacketing on the surface of the equipment.

As a usual way of the so-called low zinc method,
Zn: weight ratio of P ₂ O ₅ is preferably (0.075 to 0.15): 1.

The peroxide or Fe (II) content of the phosphating solution is determined in the usual way, for example by potassium permanganate titration. According to a preferred embodiment of the present invention, the addition of H ₂ O ₂ and / or alkali perborate is brought into contact with the phosphating solution, the surface of which is adjusted according to the electrochemical potential determined by the redox electrode. For example, a phosphating solution can be continuously monitored using a platinum electrode and a suitable reference electrode, such as a calomel electrode or a silver-silver chloride electrode, with a constant Fe (II) ion concentration and a constant The peroxide can be added so that the hydrogen peroxide concentration stays within the above range.

The selection of the type and amount of cations and anions in the phosphating solution used in the method of the present invention is made such that the ratio of free P ₂ O ₅ to total P ₂ O ₅ is between 0.04 and 0.20. Generally, for high bath temperatures and / or high zinc concentrations, this ratio should select a high region of the range,
For low bath temperatures and / or low zinc concentrations, this ratio should select a low region.

According to a preferred embodiment of the present invention, the amount of H ₂ O ₂ and / or the alkali peroxide is such that the maximum peroxide concentration of the phosphating solution is 8 mg / and the maximum Fe (II) concentration of the solution is 30 mg /. The surface is contacted with a phosphating solution to which an acid salt has been added.

According to another preferred embodiment of the present invention, manganese in an amount of 3 g / or less, nickel and / or cobalt in an amount of 3 g / or less, magnesium in an amount of 3 g / or less and / or calcium in an amount of 3 g / or less. The surface is brought into contact with the contained phosphating solution. The combined use of manganese and / or magnesium and / or calcium results in a phosphate coating containing these cations in addition to zinc and optionally iron (II). Such a mixed phosphate is characterized by high alkali resistance, and is particularly suitable as an adhesive base for paint. Nickel and / or nickel are used to increase the aggressiveness of the phosphating solution on the steel and to improve the phosphating of the zinc surface if the zinc surface is also treated together.
Alternatively, it is preferable to add cobalt. Addition of a small amount of copper as needed increases the promoting action of the phosphating solution. Alkali and / or ammonium are used primarily to adjust the desired acid ratio.

According to another preferred embodiment of the present invention, the fluoroborate is
The 3 g / the amount and / or silicofluoride follows (calculated as S _i F ₆₎ 3g / (calculated as BF ₄₎ following quantities and / or fluoride containing an amount of less (calculated as F) 1.5 g / The surface is contacted with a phosphating solution. Fluoroboric acid,
The anions of silicofluoride and / or fluoride generally increase the rate of phosphating and are particularly advantageous when the treatment of an aluminum-containing zinc surface is intended. The presence of free fluoride (F ⁻ ) is essential for the crystalline phosphating of aluminum and its alloys.

Chloride and sulphate are used for adjusting the electrical neutrality of the phosphating solution and, in special cases, for increasing the aggressiveness. Polyhydroxycarboxylic acids, such as tartaric acid and / or citric acid, optionally used together, can affect the thickness of the resulting phosphate coating and the weight per unit surface.

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

According to another advantageous embodiment of the invention, the phosphating solution wherein the free P ₂ O ₅ of the phosphating solution in the working bath is adjusted by the addition of manganese carbonate, zinc carbonate and / or zinc oxide. Bring the surface into contact. At this time, it is preferable to add 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 brought into contact with a phosphating solution whose water has been removed and which has been made up by the subsequent washing water. Water can be removed from the phosphating bath, for example, by evaporation, reverse osmosis and / or electrodialysis. In particular, when H ₂ O ₂ is used as a peroxide component, it is possible to carry out the method of the present invention so that these steps do not generate wastewater contaminated with phosphate from the washing step after the phosphoric acid treatment. The washing step, which is preferably configured as a washing bath cascade, is carried out with the last washing bath being salt-free or salt-free water, which flows in the opposite direction to the workpiece going from the washing step to the washing step and the phosphoric acid It is supplied to the processing bath. The water thus supplied makes up the water removed from the phosphating solution in the phosphating bath as described above. Water removed from the phosphating solution, for example, by reverse osmosis or electrodialysis, can be recycled to the washing step.

According to another preferred embodiment of the present invention, the free P ₂ O ₅
The ratio of the total P ₂ O ₅ is (- 0.50 + 0.20): contacting supplemented with phosphating solutions on the surface by the addition of phosphate is 1. In the above provisions regarding the ratio of free P ₂ O ₅ to total P ₂ O ₅ , a negative value indicates that no free P ₂ O ₅ is present, but rather that some of the phosphate is in the second phosphate stage. Means −
Value of 0.19 means that 19% of the total P ₂ O ₅ is present as the diphosphate.

According to another definition, the phosphate component during replenishment is one of
Limited by 50% of secondary phosphate and 50% of primary phosphate (calculated as P ₂ O ₅ ), the other with 80% of primary phosphate
It is within a limited range by 20% of the free phosphate (calculated as P ₂ O _5).

The liquid replenishing concentrates are all P ₂ O ₅ and the free P ₂ O ₅ is not stable in the range of the refill in the present invention is carried out usually divided into at least two concentrate.

The process of the present invention, particularly the preferred embodiment in which the coating phosphating solution is replenished, provides a uniform and complete phosphate coating and not only iron and steel but also the surfaces associated therewith, ie galvanized. It is possible to provide a satisfactory coating on steel and aluminum with zinc alloy plating or aluminum plating for a long time.

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

〔Example〕

The present invention is illustrated and described in detail by the following examples.

Example 1 Phosphoric acid solution prepared for spray treatment was as follows: Zn 0.8 g / free P ₂ O ₂ = 1.04 g / Ni 1.0 g / total P ₂ O ₅ = 13 g / Mn 1.0 g / free acid = 0.9 point Na lye 2.6 g / total acid = 23 points P ₂ O ₅ 13.0 g / NO ₃ 2.1 g /, H ₂ O ₂ concentration was changed in the range of 10 to 70 mg / by addition of H ₂ O ₂ , When H ₂ O ₂ was not present, the concentration of iron (II) was changed in the range of 10 to 90 mg / Fe (II) by treating the steel sheet.

A steel sheet degreased with an organic solvent was sprayed at 58 ° C. using the bath. FIG. 1 shows the phosphate coating weight obtained by spraying for 3 minutes. FIG. 2 shows the minimum phosphating time determined in this experiment, ie the processing time required to deposit a uniformly coated phosphate coating on the steel sheet. Both figures show the advantageous results obtained with the method of the invention.

Example 2 A degreased steel plate of steel (80%) and electrogalvanized steel (20%) was subjected to a phosphoric acid treatment with a phosphoric acid solution having the following composition in a phosphoric acid treatment apparatus having a capacity of 5:

Zn 0.8 g / free acid = 0.9 point Ni 1.0 g / total acid = 23 point Mn 1.0 g / Na 2.6 g / P ₂ O ₅ 13.0 g / NO ₃ 2.1 g / The temperature of this solution was 55-60 ° C. . The treatment was performed by spraying for 3 minutes. Processing capacity in processing percentage of 0.1 m ² / h was 3m ² / a. The bath composition was maintained throughout the process by the addition of zinc carbonate and a replenisher solution of the appropriate composition. Following replenisher concentrates surface 1 m ² per 19g for replenishing a certain point is required.

_{P 2 O 5 23.4% Na 1.89} % Mn 1.74% Ni 1.34% Zn 3.39% F e (III) 0.01% NO 3 3.09% free P ₂ O ₅ and further to adjust the percentage of total P ₂ O ₅ 1.8 g / m
m ² of basic zinc carbonate (53.5% Zn) was added. This supplementation corresponds to a ratio of free P ₂ O ₅ to total P ₂ O ₅ of (−0.18): 1.

The amount of hydrogen peroxide used was such that the steady Fe (II) ion concentration and the H ₂ O concentration in the bath were at most 10 mg / according to the measured electrochemical potential. The resulting phosphate coating is uniform and complete throughout, with a coating weight of 2.0 ± 0.2 g /
m ² and 2.5 ± 0.2 g / m ² for electrogalvanized steel.

Example 3 AlMgSi and AlMg Grade ₃ steel (60%), electrogalvanized steel (30%), and aluminum (10%) degreased steel plate with a capacity of 5
Was treated with a phosphating solution having the following composition.

Zn 0.8 g / free acid = 1.1 Ni 1.0 g / total acid = 23 Mn 1.0g / Na 3.2g / P 2 O 5 13.0g / NO 3 2.1g / F 0.5g / above conditions and Fe (II) and H _When each steady-state concentration of ₂ O ₂ was maintained up to 6 mg /, uniform and complete coatings were obtained on the three materials at the following coating weights.

Steel: 2.1 ± 0.2g / m ² electrodeposited ^{zinc: 2.6 ± 0.2g / m 2 AlMgSi} : 2.9 ± 0.3g / m 2 AlMg 3: 3.1 ± 0.3g / m 2

[Brief description of the drawings]

FIG. 1 shows the phosphate coating weight obtained by spraying for 3 minutes, and FIG. 2 shows the minimum phosphating time.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Deirk Mayer 6100 Darmstadt Gruberstrasse 16 (72) Inventor Gerhard Muller 6450 Hanau am Main Hoppenstrasse 29 (Germany) 72) Inventor Berner Rausch, Germany 6370 Oberursel 6, Urse Marstrasse 43 (56) References JP-A-59-110785 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00-22/86

Claims (8)

(57) [Claims] An iron and steel surface is phosphoric acid-treated by a low zinc method using a phosphating solution containing zinc, phosphate and nitrate and not containing nitrite, thereby forming phosphate on metal. In the method of forming a coating, 0.4 to 1.7 g of Zn and 7 of P ₂ O ₅
The 25 g / and NO ₃ 2 to 30 g / contain, the surface weight ratio of free P ₂ O ₅ in a phosphate treatment acidic aqueous solution was adjusted to 0.04 to 0.20 to the total P ₂ O ₅ at 30 to 65 ° C. maximum peroxide concentration of the phosphating solution in it and act state contacting is 17 mg / (calculated as H ₂ 0 ₂₎ and the maximum Fe in the same solution
(II) An amount of H ₂ O ₂ having a concentration of 60 mg / (calculated as Fe)
Alternatively, a method comprising adding an alkali perborate to the phosphating solution. Wherein H ₂ 0 ₂ and / or alkali claims the addition of perborate, characterized in that contacting the surface with phosphating solution which is adjusted according to the electrochemical potential which is determined by the redox electrode Item 7. The method according to Item 1. 3. An H ₂ O ₂ and / or alkali perborate is added in such an amount that the maximum peroxide concentration of the phosphating solution is 8 mg / and the maximum Fe (II) concentration of the solution is 30 mg /. The method according to claim 1, wherein the surface is brought into contact with a solution for phosphoric acid treatment. 4. An amount of manganese of 3 g / or less, nickel and / or cobalt of 3 g / or less, and magnesium of 3 g / or less.
The method according to any one of claims 1, 2 or 3, wherein the surface is contacted with a phosphating solution further containing the following amount and / or calcium in an amount of 3g / or less. . 5. An amount of 3 g / (calculated as BF ₄ ) of fluoroborate and / or an amount of 3 g / (calculated as SiF ₆ ) of silicofluoride and / or 1.5 g / (F
The method according to any one of claims 1 to 4, wherein the surface is brought into contact with a phosphating solution containing the following amount. 6. The free P ₂ O ₅ of the phosphating solution of the working bath.
The method according to any one of claims 1 to 5, wherein the surface is contacted with a phosphating solution adjusted by the addition of manganese carbonate, zinc carbonate and / or zinc oxide. 7. The method according to claim 1, wherein the surface is brought into contact with a phosphating solution adapted to remove water and to make up for it by the washing water of a subsequent washing step.
The method according to any one of claims 1 to 6. 8. The phosphating solution replenished by the addition of a phosphate having a ratio of free P ₂ O ₅ to total P ₂ O _{5 at} the time of replenishment of (−0.50 to +0.20): 1. The method according to claim 1, wherein the surface is contacted.