JPS6029476A - Phosphation of galvanized steel sheet - Google Patents

Abstract

PURPOSE:To form a phosphate film having excellent properties on the surface of a galvanized steel sheet with good workability by repeating alternately a stage in which a phosphating liquid is brought into contact with said surface for short time of several seconds and a stage in which said liquid is not brought into contact therewith. CONSTITUTION:A stage consisting of bringing a phosphating liquid into contact with the surface of a galvanized steel sheet for several seconds and of prohibiting forcibly said contact for several seconds in succession to said contact is repeated at least twice to treat said steel sheet, by which the amt. of the sludge to be generated is decreased and the phosphate film having excellent properties is formed with good workability as a pretreatment for a painting surface. In the above-described method, the contact time is preferably 1-3sec, more preferably 1-2sec, particularly 1sec and the time when no contact is made is 1-3sec and 1-2sec are particularly preferable. The above-mentioned method is effective for the galvanized steel sheet having good resistance to corrosion. Said method has the effect of suppressing the elution and accumulation of Al in the galvanized layer contg. >=3wt% Al and permitting easy control of the bath.

Description

[Detailed description of the invention] Ki-ni F! A is a phosphate chemical conversion treatment method for galvanized steel sheets, more specifically, a method that forms a phosphate film that has excellent properties as a pretreatment for a painting base, and that can be formed with good workability. Regarding possible chemical conversion treatment methods.

In the phosphate chemical conversion treatment of metal surfaces, sludge is generally generated during the treatment, and if this accumulates in the treatment bath, it will no longer be possible to provide a good chemical conversion film, so the sludge is normally discharged from the system at all times. Taking this point into consideration, various attempts have been made to reduce the amount of sludge generated. For example, as a method focusing on the formulation of processing liquid,
No. 6-17047, No. 52-43737, No. 54-2
The inventions disclosed in No. 4972 and No. 57-7232 are cited. These products are characterized by the addition of starch, its acid decomposition products, and the reaction products of amino alcohol and phosphoric acid as essential components, but improvements are still needed to reduce the amount of sludge generated. There's room. On the other hand, as for the treatment method itself, immersion treatment or pressure 0.
A method has been proposed that uses a soft spray treatment at a rate of 3 kg/cd or less to thicken the diffusion layer at the interface between the metal surface and the treatment solution, making it easier to incorporate eluted zinc into the film, and at the same time avoiding excessive etching. (Metal Surface Technology ■01゜23, No. 10 (1982)). However, even with this method, there is still room for improvement in reducing the amount of sludge generated.

With regard to galvanized steel sheets, which are the objects to be treated, with the recent trend toward higher quality, there is a tendency for hot-dip galvanized steel sheets with good corrosion resistance to be frequently used, especially hot-dip galvanized steel sheets with an aluminum content of about 4 to 5% by weight. has appeared. When a steel plate containing aluminum in such a plating layer is subjected to chemical conversion treatment,
Aluminum is eluted into the chemical conversion bath, and this amount is approximately 700 pp.
If it accumulates even at a low concentration of m, the processing solution will age, so it is necessary to strictly control the removal and replenishment of the processing solution or to renew it within a short period of time.
Economically, this is a problem that should be improved.

The present invention was devised to solve the above-mentioned problems, by improving the phosphate treatment method itself, and by actively applying the treatment liquid to the metal surface within a short period of several seconds. By repeating the contacting step and the non-contacting step alternately, it is possible to further reduce the amount of sludge generated, and when processing aluminum-containing hot-dip galvanized steel sheets, the elution of aluminum into the conversion bath can be reduced. The present invention was completed based on the discovery that accumulation can be suppressed and bath management can be facilitated.

The gist of the present invention is to provide a method for forming a phosphoric acid conversion film on the surface of a galvanized steel sheet by at least a step of contacting the surface with a treatment liquid for several seconds and then not forcibly contacting the surface for several seconds. The method is characterized in that the process is repeated twice.

As the phosphate treatment solution used to carry out the method of the present invention, any conventional phosphate treatment solution may be used, and examples of the standard composition include the following.

Zinc ion 700-1800ppm Nickel ion 500-2000ppm Nitrate ion
400-1200ppm Phosphate ion 7000-12000ppm Silicon hexafluoride ion 300-11000pp Total acidity 10-2
5 points Free acidity 05 to 2.0 points Acid ratio 8 to 20 Phosphate treatment of galvanized steel sheets using such a treatment solution is carried out in the usual manner, except for adopting the specific treatment mode described above. It's okay to be. That is, the treatment method may be either a spray method or a dipping method.

The contact time between the metal surface and the phosphating solution may practically be 1 to 3 seconds, preferably 1 to 2 seconds, especially 1 second. If the contact time is too long, results similar to conventional continuous processing will only be obtained, and the amount of sludge generated will not be reduced.

The non-contact time is practically 1 to 3 seconds, preferably 1 to 3 seconds.
2 seconds is enough. If the non-contact time is too long, the total treatment time is set at a maximum of 12 seconds in recent high-speed practical processing lines, so the contact time will inevitably become short and the desired amount of chemical conversion coating will not be obtained. Note that this non-contact includes not forcibly bringing the treatment liquid into contact with the metal surface, and it goes without saying that there is no direct contact with the metal surface;
This includes being in contact with the spray and also being in contact with the adhesion treatment liquid taken out from the treatment bath. The process consisting of contact and non-contact can be repeated at least twice, and typically can be repeated an appropriate number of times until a chemical conversion film of 1 g/n'' or more is formed. Since it is not practical if the total treatment time exceeds 12 seconds, the contact time, non-contact time and number of repetitions may be adjusted as appropriate so that a predetermined amount of chemical conversion film is formed within the above time.

Other conditions in the chemical conversion treatment of the present invention (e.g. treatment temperature)
Regarding this, conditions normally employed in the prior art may be employed. It's a moat, various treatments before and after chemical treatment (
Examples, degreasing, surface conditioning, post-water treatment, drying) may also be carried out in the same manner as in the prior art.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Examples 1 to 10 and Comparative Example 1 A hot-dip galvanized steel sheet with a thickness of 0.35 mm was treated with a 0.3 weight polyhydric solution of a commercially available titanium phosphate surface conditioner ("Fixodine 5" manufactured by Nippon Paint Co., Ltd.) for 25 minutes. After spraying at 65°C for 2 seconds and squeezing with a roll, it is subjected to spray chemical conversion treatment at 65°C according to the steps shown in Table 1 using a zinc phosphate film conversion solution having the following composition.

Standard blend of zinc phosphate coating chemical solution Zinc ion 1000 ppm Nickel ion 1400 ppm Nitrate ion 1400 ppm Phosphate ion 7500 ppm Silicon hexafluoride ion 11000 ppm Total acidity 15.
0 points Free acidity 19 points Acid ratio 8° 1st table zone ×: Table 2 shows the amount of chemical conversion film formed by chemical conversion treatment over the time period when the metal surface is not in contact with the treatment liquid and the amount of sludge generated. .

(1) Measurement of sludge generation amount The above steel plate 5 m' was heated at a temperature of 65° in the chemical conversion bath of 11.
C. Spray pressure I Icg/cr! After the treatment is completed, the bath is filtered through a filter of known weight, the filter residue is washed with pure water, and then it is dried at 100° C. for 3 hours and the weight of the residue (0) is measured.

(2) Calculation of K value The concept of evaluating the balance of zinc balance is generally adopted as an evaluation of sludge generation. The amount of sludge generated can be estimated from the ratio (K) of the amount of zinc eluted from the material (etching amount) and the amount of zinc incorporated into the film (amount of lead in the film) Czn.

Since the main component of the film is Zn3 (PO4)2 .4H20, the amount of Czn medium film is X O, '428. Therefore, the larger the value of znEzn, the less the amount of sludge generated.

Table 2 shows the calculation results of the K value.

Next, the chemical conversion treated board was treated with a 01% aqueous solution of a commercially available chromic acid post-treatment agent (Deoxyrye 41J, manufactured by Nippon Paint Co., Ltd.).
Rinse at 5℃ for 2 seconds, wash with water, dry, and then apply a commercially available epoxy primer (“Superlac DI F” manufactured by Nippon Pei 21 Co., Ltd.).
The plate temperature reached when baking with ``POl Primer'') was 19.
0°C1 film thickness 5 g/m'), and then painted with a commercially available oil-free polyester paint for top coating (Nippon Paint Co., Ltd. "Super Rank DIFFSQ 23 Blue") (achieved board temperature at baking 200°C1 film thickness 15 , ji'
/ m').

The obtained painted board is subjected to a bending adhesion test and a coin scratch test. The results are shown in Table 2.

(3) Bending adhesion test Two plates of the same thickness as the test plate are sandwiched together, the test plate is bent 180 degrees at 20°C, and an adhesive tape is applied to the bent portion and peeled off. Visually observe and evaluate the condition of the coating film attached to the adhesive tape.

5 points: No peeling of the paint film 4 points: Peeling of the paint film within 5% 3 points: Peeling of the paint film within 20% 2 points: Peeling of the paint film within 50% 1 point: Peeling of the paint film 51-100% ( 4) Coin scratch test: Scratch the surface of the painted board with a coin with sufficient force, observe and evaluate the occurrence of scratches.

○: Metal surface exposed within 1 mm △: Metal surface exposed within 5 u ×: Metal surface exposed along the scratched surface Table 2 Examples 11 to 20 and Comparative Example 2 Aluminum with a thickness of 0.35 mm Surface treatment and painting were carried out in the same manner as in the previous Examples and Comparative Examples, except that a hot-dip galvanized steel sheet containing 5% by weight was subjected to chemical conversion treatment according to the steps shown in Table 3.

Table 4 shows the measurement results of the amount of chemical conversion film, bending adhesion, and coin scratch resistance.

(5) Measurement of the amount of aluminum accumulated in the bath ■The above steel plate 5 m' was treated in the chemical conversion treatment bath at a temperature of 65°C and a spray pressure of 11 cg/crd, and the aluminum ions accumulated in the bath were measured by atomic absorption spectrophotometry. Analyze using the side. The measurement results are shown in Table 4.

Table 3 Table 4

Claims (1)

[Scope of Claims] A method for forming a silica conversion film on the surface of a 1° galvanized steel sheet by phosphate treatment, which comprises bringing a treatment liquid into contact with the surface for several seconds and then not forcibly contacting the surface for several seconds. A method characterized in that the process is repeated at least twice. 2. The method according to item 1 above, wherein the contact time is 1 to 3 seconds and the non-contact time is 1 to 3 seconds. 3. The method according to item 2 above, wherein the contact time is 1 to 2 seconds and the non-contact time is 1 to 2 seconds. 4Contact time is 1 second, non-contact time is 1~
The method of item 3 above, wherein the time is 2 seconds. 5. The method of item 1 above, wherein the galvanized steel sheet is a hot-dip galvanized strip. 6. The method according to item 5 above, wherein the galvanized layer of the steel sheet contains 3% by weight or more of aluminum. 7. The method according to any one of items 1 to 6 above, in which the treatment liquid is brought into contact with the surface of the L steel plate in a spray manner. 8. The method according to any one of items 1 to 7 above, wherein the total processing time is 12 seconds or less.