JPS6041148B2 - Phosphate film conversion treatment method for metal surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for chemical conversion treatment of a metal surface with a phosphate film, and more particularly, to a treatment method which is particularly useful when carried out using a metal surface cleaning treatment apparatus having a multi-stage water washing process. .

In the present invention, the term "metal surface" refers to surfaces of iron, zinc, and alloys thereof. Generally, metal surfaces are degreased and washed with water before forming a phosphate film.

The degreased metal surface is washed with water to remove residual degreasing liquid and oil, and then subjected to film formation. Furthermore, in order to form a phosphate film having sufficient performance as a paint base on a metal surface, the degreased and water-washed metal surface is sometimes preconditioned prior to film formation. for example,
A neutral or slightly alkaline aqueous solution containing a phosphate and a titanium compound is brought into contact with the metal surface to activate the metal surface and increase its reactivity with the phosphate film chemical conversion treatment solution, thereby forming a uniform and fine chemical conversion film. A method of forming such a material has been used (see Japanese Patent Publication No. 39-7125). however,
This method causes the following problems. ■
Degreased metal surfaces are highly reactive, so depending on the design of the metal surface cleaning treatment equipment and the water washing conditions after degreasing,
There is a problem that rust occurs before the phosphate film is formed.

■ If the temperature of the degreased metal surface is high or the transfer time between each process is long, the metal surface dries with water before entering the film formation process, causing yellow rust and spot rust, resulting in uneven and rough chemical formation. A film will be formed. ■ If chemical conversion treatment using a continuous metal surface cleaning treatment equipment is forced to stop midway through, the treated material that has remained between the degreasing and film formation processes will rust over the entire surface and cannot be used for film formation.

Recently, multi-stage washing equipment and exhaust equipment have been installed in the processing chamber to save washing water and reduce the amount of wastewater to be treated, and by discharging the air in the processing chamber, the excess water is evaporated and removed, and the excess water is used as wastewater. Closed system metal surface cleaning treatment equipment (
For example, Tokusei No. 48-69728) has become widely adopted for the phosphate film chemical conversion treatment.
When such equipment is used, the above-mentioned rust formation is especially a problem. On the other hand, under such circumstances, a method has been proposed for preventing rust on the metal surface by treating the degreased metal surface with an alkaline solution prior to film formation (see JP-A-52-6343). ).

However, this also does not have a sufficient rust prevention effect, and when using the above-mentioned multi-stage water washing equipment or closed system metal surface cleaning equipment, it is difficult to avoid rusting on the metal surface, and excessive alkaline solution is added to the film conversion treatment tank. If the amount is too specific, the bath balance will be disrupted and this will cause poor chemical formation. The present invention solves these problems, and its first purpose is to prevent the degreased metal surface from rusting in the water washing process, thereby forcing the chemical conversion treatment using a continuous metal surface cleaning treatment device to stop midway through. To provide a method for chemically converting a phosphate film onto a metal surface, which enables the use of a multi-stage water washing device or a closed system metal surface cleaning treatment device, without causing rust on the degreased metal surface even when the metal surface is degreased. Second, it promotes the film formation properties of metal surfaces, does not have any negative effect on the film formation process, and makes it possible to form a uniform and dense phosphate film that is particularly suitable for use as a base for haze painting. An object of the present invention is to provide a method for chemically treating a metal surface with a phosphate film.

As a result of intensive research to achieve the above object, the present inventors found that in the series of steps in the phosphate film chemical conversion treatment, the water washing process that is carried out between the degreasing process and the film formation process is simply water-based. By using an aqueous solution containing 0.01 to 0.5 (wt%) of an oxidizing substance (the same applies hereinafter) instead of using a They discovered this and completed the present invention.

The gist of the present invention is a step of degreasing a metal surface, a step of cleaning the degreased metal surface with an aqueous solution containing 0.01 to 0.5% of an oxidizing substance, a step of chemically forming a phosphate film on the metal surface, and a method for chemical conversion treatment of a phosphate film on a metal surface, comprising the steps of washing the chemically converted metal surface with water.

The step of degreasing the metal surface in the method of the present invention may be appropriately carried out by conventional methods such as solvent degreasing, emulsion degreasing, alkaline degreasing, or a combination thereof, with alkaline degreasing being particularly common.

In the case of alkaline degreasing, use ordinary commercially available degreasers (for example, Nippon Paint Co., Ltd.'s product name "Ridrin #7 Egg-41" as a weak alkaline degreaser, and "Ridrin #100" manufactured by Nippon Paint Co., Ltd. as a medium alkaline degreaser). -1 grade, and a strong alkaline degreasing agent manufactured by the same company under the trade name "Ridrine #5-41 grade", using an aqueous solution containing usually 1 to 2%, and at a temperature of 40 to 6
It may be carried out at 0° C. for 0.5 to 5 minutes.

The degreasing bath contains 0.002% or more, preferably 0.01% or more of oxidizing substances to be used in the next step (specifically described below, but among them, for example, sodium nitrite and sodium pershelate). It is desirable to include it. The cleaning step performed after the degreasing step in the method of the present invention not only removes oils, solvents, alkaline substances, etc. remaining on the degreased metal surface, but also removes oil, solvents, alkaline substances, etc., which is the intended purpose of the present invention. It is characterized by the use of an aqueous solution (hereinafter referred to as a cleaning solution) that can impart a rusting effect and contains an oxidizing substance.

The above-mentioned acidic substances include those that are used as accelerators for phosphate film formation, such as nitrate (
(e.g., sodium nitrite), hydrogen peroxide, persylates (e.g., sodium perselate), aromatic nitro compounds (e.g., sodium metanitrobenzene sulfonate), aromatic nitroso compounds (e.g., nitrosobenzene), hydroxylamine sulfate, Examples include sodium chlorate and ammonium persulfate, and at least one selected from these groups is used.

Particularly suitable are sodium nitrite, hydrogen peroxide, and sodium pershelate. In the above cleaning liquid, the content of the oxidizing substance is preferably selected in the range of 0.01 to 0.5%. If this content is less than 0.01%, it is difficult to impart a sufficient rust prevention effect to the degreased metal surface, and
%, no further rust prevention effect can be obtained. In addition,
In addition to the above-mentioned oxidizing substances, for example,
A neutral or slightly alkaline aqueous solution containing a phosphate and a titanium compound (titanium sulfate, titanium oxide, etc.) disclosed in No. 5, that is, an M oxidizing substance and a surface activator that may contain a surface activator. Due to the mutual effect of these, the film formation properties are further improved, and a uniform and dense phosphate film is formed, which is particularly suitable as a base for electrodeposition coating.

The content of the surface activator is usually determined as the titanium concentration is lop
pm or more, preferably in a range such that the titanium concentration in the final cleaning solution after degreasing is 10 to 100 ppm. If the titanium concentration exceeds 100 ppm, the metal surface will be excessively activated, resulting in poor chemical formation. Furthermore, various surfactants, organic acids, inorganic acids, alkaline substances, etc. may be added to the extent that they do not adversely affect the film formation in the next step. It is desirable that the cleaning liquid configured as described above is usually set at a pH value of 4 to 9. If the pH is lower than 4, it is difficult to impart a sufficient antirust effect to the degreased metal surface, and if it is higher than 9, the film formation property in the next step is inhibited. The washing step may be carried out in one stage or in multiple stages, such as two or more stages, as in the conventional water washing step, and the conditions are usually a temperature of room temperature to 800° and a time of 0.5 to 5 minutes. It's fine.

In the conventional method, if the water washing temperature is 40 qC or higher, the degreased and washed metal surface dries with water and causes rust, but in the case of the present invention, rust does not occur even if the metal surface is similarly dried with water. There is no adverse effect on the film formation properties in the next step, and there is no need to specially control the cleaning temperature. The coating chemical conversion step in the method of the present invention is performed using a common iron phosphate coating chemical conversion treatment agent (
For example, Nippon Paint Co., Ltd.'s product name "Durijin #21 Funa-1, etc.", zinc phosphate film chemical conversion treatment agent (for example, Nippon Paint's product name "Granodiso #1 Carp-21, etc."), calcium-modified zinc phosphate film chemical conversion treatment agent ( For example, products manufactured by the same company under the trade name "Granodin #21N" may be used, and the test may be carried out under normal conditions according to the respective specifications.

In addition, when performing calcium-modified zinc phosphate film conversion, sodium pershelate may be used as the oxidizing substance in the previous cleaning step, and an alkaline substance may be added thereto. This is because calcium-modified zinc phosphate film conversion is
It is easily affected by metal surfaces and tends to rust slightly and cause poor chemical formation, but if a cleaning solution containing sodium peroxide and an alkaline substance is applied, the cleaned metal surface will not form a film. This is because not only rusting before the process is prevented, but also the chemical formation properties of the calcium-modified zinc phosphate film are greatly improved. Such alkaline substances may be those commonly used in phosphate film formation, such as sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium metasilicate, sodium orthosilicate, sodium orthophosphate, and sodium pyrophosphate. , sodium tripolyphosphate, sodium tetraphosphate and sodium hexaphosphate. The method of the present invention is carried out by carrying out the above-mentioned three steps, that is, the degreasing step, one or more stages of cleaning step, and film formation step, continuously or discontinuously in that order by a conventional method (spray method, immersion method, etc.). and then the usual 1 or 2 steps.
By performing the water washing step and the drying step in stages or more, the final film chemical conversion treatment product is obtained. According to this final product, no rust was observed during or after the series of treatment steps, and the formation of a uniform, dense, and high quality chemical conversion coating was observed in the end. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Example 1 In this example, a rolled steel sheet is subjected to a zinc phosphate coating chemical conversion treatment in a spray-type multi-stage water-washing pilot plant.

'1} Treatment process (conditions): Degreasing (50-600C, 2
minutes) → 1st wash (35-40oo, 1 minute) → 2nd wash (
35-4000, 1 minute) → 3rd cleaning (30-3500,
1 minute) → Film formation (50-55oo, 2 minutes) → First water washing (35-4000, 1 minute) → Second water washing (35-4000
, 1 minute) → Third washing (30-35 qo, 1 minute) → Drying.
1. Degreasing liquid: An aqueous solution containing 1.5% of a weak alkaline degreasing agent (product name: "Ridrin #7-4" manufactured by Nippon Paint Co., Ltd.) was used.

2 Cleaning liquid: Use an aqueous solution containing 0.03% sodium nitrite.

The cleaning liquid is supplied to the third-stage cleaning tank, and overflows from the first-stage cleaning tank. 3. Film chemical conversion treatment solution: Its composition is as follows.

Composition P043-...1.50%, Na+...0.43%
N03-...0.60%, N02-...0.013
~0.016%Zn20...0.16%, pH3.0
4. Rinsing liquid: Tap water is supplied to the third-stage washing tank, and overflows from the first-stage washing tank.

■ Result: The zinc phosphate film formed is good.

No rust was observed at any stage of the cleaning process, and even when the continuous operation was interrupted midway through, no rust was observed on the treated material. Example
2 In this example, the same treatment equipment and cold-rolled steel sheet as in Example 1 were used to carry out chemical conversion treatment for calcium-modified zinc phosphate film.

'1} Treatment process (conditions): Film formation conditions 75-8
The procedure of Example 1 was followed except that the temperature was 0°C for 2 minutes.

1. Degreasing liquid: An aqueous solution containing 1% of a strong alkaline degreasing agent (product name: "Ridrin #5-4" manufactured by Nippon Paint Co., Ltd.) was used.

2. Cleaning solution: Use an aqueous solution containing 0.03% sodium palate.

3. Film chemical conversion treatment solution: Its composition is as follows.

Composition PO43-...0.49%, Na+...0.60%
N03-.・．． 3.60%, N02-...0.
005~0.01%Ca2...0.59%, pH2.9
Zn20...0.17%, 4 Washing liquid: Use tap water.

■ Result: A calcium-modified zinc phosphate film of good quality was formed.

Example 3 In this example, a single-sided galvanized steel sheet was subjected to a zinc phosphate coating chemical conversion treatment using a spray-type closed system metal surface cleaning treatment apparatus.

○} Treatment process (conditions): Degreasing (60qo, 2 minutes) → 1st cleaning (48~5〆0, 0.8 minutes) → 2nd cleaning (43~
470, 0.5 minutes) → 3rd cleaning (38-420, 0.5
minutes) → Film formation (50-55o0, 2 minutes) → First water washing (
35-40qo, 0.5 minutes) → 2nd water washing (35-40qo
o, 0.5 minutes) → 3rd water washing (30-35oo, 0.5 minutes) → 4th water washing (room temperature, 0.5 minutes) → drying.

1. Degreasing liquid: An aqueous solution containing 1.5% of a medium alkaline degreasing agent (product name: "Ridrin #100S-1" manufactured by Nippon Bait Co., Ltd.) was used.

2 Cleaning liquid: Content of sodium nitrite in the third stage cleaning tank is 0.02% and content of surface activator containing sodium phosphate and titanium compound (trade name "Fixogen #5" manufactured by Nippon Paint Co., Ltd.) is 0. Manage at .1%.

Supply amount of third stage cleaning liquid is 500 so/hr.

3. Film chemical conversion treatment solution: Its composition is as follows.

Composition P043-...1.10%, Na+...0.45%
N03-. ...0.70%, N02- ...0.
01~0.015%Zn20...0.05%, PH3
．． 44 Washing liquid: Add tap water to the 4th stage washing tank with 700 ml/
hr, and excess water is evaporated in the film formation process.

■Results: A uniform, dense film was formed on both the iron and galvanized surfaces, which was suitable as a base for coating.

Although the liquid temperature reached 4,000 or higher in the cleaning process after the degreasing process and the surface of the treated product was water-dried, no rust was observed. Comparative Example 1 When the zinc phosphate coating treatment of Example 1 was carried out under the same conditions except that the sodium nitrite aqueous solution in the cleaning step after degreasing was replaced with tap water, an uneven and rough chemical conversion coating was formed. Ta.

That is, dotted rust was observed on the metal surface after the second and third water washings after degreasing, and when the continuous treatment was interrupted midway, the treated material that remained in the water washing process after degreasing developed rust on the entire surface. Comparative Example 2 The zinc phosphate film chemical conversion treatment of Example 1 was carried out under the same conditions except that the sodium nitrite aqueous solution in the cleaning step after degreasing was replaced with the first washing water after film formation.
A uniform zinc phosphate film was not obtained.

That is, it is considered that an iron phosphate-based film was partially formed by the diluted film conversion treatment solution, and subsequent film formation was not performed sufficiently. Further, spot rust was observed on the metal surface after the second and third water washings after degreasing. Comparative Example 3 In the zinc phosphate film chemical conversion treatment of Example 1, the sodium nitrite aqueous solution in the cleaning step after degreasing and the first wash water after film formation were neutralized to pH 7 to 8 with sodium hydroxide to remove the precipitate. When the test was carried out under the same conditions except that the removed solution was used, a non-uniform and rough chemical conversion film was formed as in Comparative Example 1.

Claims (1)

[Scope of Claims] 1 A step of degreasing a metal surface, a step of cleaning the degreased metal surface with an aqueous solution containing 0.01 to 0.5% by weight of an oxidizing substance, and a step of adding phosphorus to the metal surface cleaned with the aqueous solution. A method for chemically converting a phosphate film on a metal surface, comprising the steps of chemically converting a salt film and washing the chemically formed metal surface with water. 2. The method according to item 1 above, wherein the oxidizing substance is at least one selected from the group of nitrites, hydrogen peroxide, perborates, aromatic nitro compounds, aromatic nitroso compounds, and hydroxylamine sulfate. 3. At least one selected from the group of sodium nitrite, hydrogen peroxide, and sodium perborate in a concentration of 0.01 to 0.
The method according to item 2 above, wherein the amount is 5% by weight. 4. The method according to any one of items 1 to 3 above, wherein each water washing step is carried out in a metal surface cleaning treatment apparatus equipped with a means for reducing the amount of water supplied by performing two or more stages of water washing. 5. A method for reducing or eliminating the discharge of excess water as wastewater by evaporating excess water by installing exhaust equipment in the spray treatment chamber and discharging the air in the treatment chamber, and for each washing process to be carried out in two or more stages. The method according to any one of the above items 1 to 3, which is carried out in a metal surface cleaning treatment apparatus equipped with a means for reducing the amount of water supplied as multi-stage water washing. 6. The method according to any one of items 1 to 5 above, wherein the phosphate film is an iron phosphate film. 7 Item 1 above where the phosphate film is a zinc phosphate film
The method according to any of paragraph 5. 8. The method according to any one of items 1 to 5 above, wherein the phosphate film is a calcium-modified zinc phosphate film. 9 Step of degreasing the metal surface, degreasing the degreased metal surface with 0.01 to 0.5% by weight of an oxidizing substance and 10 to 10% of a titanium compound.
100 ppm (titanium concentration equivalent), a step of chemically forming a phosphate film on the metal surface cleaned with the aqueous solution, and a step of washing the chemically formed metal surface with water. Phosphate film conversion treatment method for metal surfaces. 10 Oxidizing substances include nitrite, hydrogen peroxide, perborate,
10. The method according to item 9, wherein the compound is at least one selected from the group consisting of aromatic nitro compounds, aromatic nitroso compounds, and hydroxylamine sulfate. 11 At least one selected from the group of sodium nitrite, hydrogen peroxide, and sodium perborate at 0.01 to 0
．． 11. The method of item 10 above, wherein the amount is 5% by weight. 12. The method according to any one of the above items 9 to 11, wherein each water washing step is carried out in a metal surface cleaning treatment apparatus equipped with means for reducing the amount of water supplied by performing two or more multi-stage washing steps. 13. A method for reducing or eliminating the discharge of excess water as wastewater by evaporating excess water by installing exhaust equipment in the spray treatment chamber and discharging the air in the treatment chamber, and for each washing process to be carried out in two or more stages. 12. The method according to any one of items 9 to 11 above, which is carried out in a metal surface cleaning treatment apparatus comprising means for reducing the amount of water supplied as multi-stage water washing. 14 Item 9 above, wherein the phosphate film is an iron phosphate film
The method according to any of paragraph 13. 15. The method according to any one of items 9 to 13 above, wherein the phosphate film is a zinc phosphate film. 16. The method according to any one of items 9 to 13 above, wherein the phosphate film is a calcium-modified zinc phosphate film. 17. The method according to item 16, wherein the aqueous solution containing an oxidizing substance contains sodium perborate and an alkaline substance.