JPH01277A - Electrodeposition pretreatment phosphate treatment method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for applying pretreatment for electrodeposition coating to a workpiece made of steel or partially galvanized steel, which is degreased and washed with water. The present invention relates to a method in which a treated object is first activated with a weakly alkaline aqueous solution containing titanium phosphate and then immersed in an acidic and aqueous phosphating solution containing zinc phosphate. The present invention relates to a method for preparing a base for cationic electrodeposition coating.

BACKGROUND OF THE INVENTION It is known to immerse steel in an acidic, aqueous phosphating solution containing zinc/Fe(1)/nitrate/phosphate before painting.

(Problems to be Solved by the Invention) When the known method was applied to electrodeposition coating, an essential drawback was found. That is, variations in the thickness of the phosphate film formed by a known method lead to variations in the thickness of the coating film deposited by electrodeposition, some of which result in surface undulations, cracks, and dents. In addition, it often happens that the corrosion resistance does not meet the requirements.

It is an object of the present invention to provide a method for the phosphate treatment of steel or articles made partly of galvanized steel, which provides a uniform phosphate coating and which is particularly suitable as a base treatment for electrocoating. It is in.

(Means for Solving the Problems) The above object is, in the method described at the beginning, in which the workpiece is treated with 1.8 to 5 g/I2 of Zn 061 to 7 g/ρ Fe(1) 8 to 25 g/ρ p2o.

By contacting with a phosphate treatment solution containing from 2 to 30 g/(l of NO3 and having a free acid to total concentration ratio of 0.04 to 0.07) at a temperature of 40 to 60°C. achieved.

The steels treated by the method according to the present invention include cold-rolled steel sheets, non-alloy steels, high-strength cold-rolled steel sheets, phosphorus-added cold-rolled steel sheets, microalloy steels, duplex steels, and galvanized steels. The layers are Zn, Zn+Fe, and Zn+ by hot-dip plating.
A1. It includes a layer made of Zn+AI+Si, etc., and a layer made of Zn, Zn+Ni, and Zn+Fe formed by electroplating.

The types and shapes of objects to be treated to which the method according to the present invention is applied are wide-ranging, such as flat materials 1, deep drawn parts, welded structures, seam welded structures, and adhesive bonded structures. In order to efficiently treat the inner surface of a hollow body, it is necessary to properly degas and drain the liquid properly. A typical object to be processed that has a complex shape and is made of various materials is an automobile body.

The object to be treated is first degreased using an alkaline degreaser or the like in a conventional manner, and then washed with water. Thereafter, treatment is performed with a weakly alkaline aqueous solution containing a finely dispersed titanium phosphate activator.

Phosphating is carried out at a temperature of 40 to 60°C. If the temperature is lower, phosphate film formation will be slower and the phosphate layer coating will not form in a reasonable amount of time. Above 60° C., energy losses increase rapidly and the risk of formation of interfering substances such as dry deposits or crusts increases.

Since the method according to the present invention belongs to the method carried out on the rFe side, it has the advantage of generating relatively little sludge. The initial Fe(1) concentration of the bath may be less than 0.1 g/ρ. Etching with a phosphate treatment solution causes dissolution of the steel, so Fe(m) is removed after several passes.
The concentration of 1 falls within the range required by the present invention. Zn, Fe ([1, P2es and N
Maintaining o3 is important to form a suitable phosphate film for subsequent electrodeposition coating. That is, if the zinc content is less than 1.8 g/ρ, the phosphate film formed on the steel will be incomplete, while if the zinc content exceeds 5 g/g, the phosphate film formed on the steel will be incomplete. If it becomes too thick, the coating performance after painting will deteriorate. If the Fe(1) content exceeds 7 g/(l), the quality of the phosphate film as a base for electrodeposition coating will clearly deteriorate. If the P2O5 content is less than 8 g/42, the PO4 content will decrease. Due to insufficient amount, proper phosphate treatment cannot be performed.Pies
Even if the content exceeds 25 g/R, no further technical advantages can be obtained. If the content of N 2 O) is less than 5 g/ρ, the effect of promoting phosphate film formation will not be as desired. If the NOi content exceeds 30 g/N, the increase in film formation rate is still impractical.

The ratio of free acid to total acid is of great significance in the present invention.

That is, if this ratio is less than 0.04, sludge formation increases and useful components of the phosphate treatment solution are lost.

When this ratio exceeds 0.07, the rate of phosphate formation decreases rapidly. The concentration of bath components is controlled and N a ,
Cations such as K, NH4, or Ca.

By further adding anions such as S 04, the conversion rate can be optimized.

A preferred embodiment for obtaining optimal results in electrocoating after the formation of a phosphate film is a phosphoric acid solution containing up to 3 g/(l) of zinc and preferably 0.5 to 5 g/Q of Fe(1). 0, which is a method of bringing the object to be treated into contact with a salt treatment solution.
For example, Ca, Co.

The resulting phosphate coating can be modified by further adding divalent cations selected from the group consisting of Cu, Mg, Mn, and Ni to the phosphate treatment solution. 3g
/(l or less Mn and/or 3g/(l or less Mg
It is preferable to contact the object to be treated with a phosphate treatment solution further containing C, preferably 0.3 g/ρ or less.
O and preferably 0.15 g/Q or less Ni can be added. If Co is present in an amount greater than 0.3 g/l or Ni greater than 0.15 g/j2, the phosphate film formed on the steel will be sushi-like. Another preferred embodiment is to contact the treated material with a phosphate treatment solution containing no more than 3 g/Q, preferably at least 0.3 g/R of hydroxylamine. If it contains at least 0.3 g/ρ of hydroxylamine, the Ni content can be increased to 0.5 g/ρ. Hydroxylamine promotes phosphate film formation. In order to improve the etching properties of the phosphate treatment solution, increase the rate of phosphate film formation, and optimize the film formation on galvanized surfaces containing aluminum, it is necessary to BFa below /Q,
It is preferable that the object to be treated is brought into contact with a phosphate treatment solution containing at least one F of 1.5 g/l or less.

Tartaric acid and/or citric acid, preferably up to 3 g/l, can be added to reduce the weight of the phosphate film per unit surface area and to further promote film formation.

0.5 g/g or less of m-nitrobenzenesulfonate,
It is also desirable to use a phosphate treatment solution containing preferably 0.05 to 0.35 g/72 Om-nitrobenzenesulfonate, which strongly promotes phosphate film formation and reduces the thickness of the phosphate film. Significantly lower. In order to prevent the phosphating solution from migrating from the iron side to the nitrite side due to the autocatalytic action of nitrite, it is preferred to add a nitrite-decomposing substance to the bath, such as urea or amidosulfonic acid.

In order to prevent the Fe(II) concentration from increasing above the desired value, some of the excess Fe(II) mixed into the phosphating solution is oxidized to Fe(II) by an etching action.
1), and it is desirable to precipitate it as a sparingly soluble iron(III) phosphate sludge. In a preferred embodiment of the invention, the phosphating solution is contacted with an oxygen-containing gas or a chlorate and/or peroxide compound is added to remove Fe.
(If) is oxidized to Fe(1).

The free acid content in the phosphating solution can be lowered by the addition of alkali hydroxides, alkali carbonates, and the like. The use of zinc oxide, calcium carbonate and/or manganese carbonate is preferred as it further introduces film-forming cations into the phosphating solution.

Furthermore, as a variation of the method of the invention, a spray treatment with the phosphate solution may be carried out after/or prior to the immersion in the phosphate solution. can. Immersion times are usually in the range from 2 to 5 minutes, and preceding and/or subsequent spraying times are from a few seconds to 0.5 minutes.

According to a preferred embodiment of the present invention, the method of the present invention is carried out to form a phosphate coating of 1 to 5 g/m2. As a result, optimum corrosion resistance can be obtained in combination with a coating film having high bending strength.

The film formed by the method of the present invention is effective as a base film for anionic electrodeposition coating and cationic electrodeposition coating.

Particularly desirable results are obtained when the method of the invention is carried out as a base treatment for cationic electrodeposition coatings with coating thicknesses in the range of about 15 to 40 .mu.m. A coating film formed by electrodeposition can be used as a base coating film on which several or a single layer of coating film is formed.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) A steel plate consisting of a steel plate for an automobile body and a plated steel plate was degreased with an alkaline degreaser, washed with water, and activated. The solution used for activation was a suspension of about 50 mg/12 titanium phosphate in an aqueous solution containing 1 g/12 disodium phosphate and 0.25 g/12 sodium pyrophosphate. After the activation treatment, they were immersed in phosphate treatment solutions 1 to 6 shown in Table 1 at 55°C to undergo phosphate conversion treatment.

The minimum phosphate conversion treatment time is at least 2-3 for steel.
minutes, and was found to be less than 1 minute for galvanized steel. The minimum phosphate conversion treatment time is the treatment time in the phosphate treatment solution necessary to form a visually uniform phosphate coating.

The weight of the coating is 3.6 to 4.3 g/m2 for steel.
and 2.2 to 3.0 g/m2 for galvanized steel.
Met.

For free acid (completely defeated), treat solution 10r12 with dimethyl yellow (phenolphthalein) as an indicator, O, I
0, IN NaO required to neutralize with N NaOH
It is expressed as the amount of H (mff). The ratio of free N acid to total loss is (0,
054 to 0.063):1.

(The following is a blank space) 1st Expression 123456 19HIIJJJf (Effects of the Invention) After the phosphate chemical treatment, washing with water, passivation treatment with a chromium-containing treatment solution, and washing with deionized water were performed. Subsequently, when electrodeposition coating was performed, a uniform coating film was obtained. This coating showed very strong adhesion to the metal substrate and excellent corrosion resistance, with or without further coating. It also contains chlorate and/or nitrite vi salts as accelerators, effectively F e (I
The quality was equivalent to or better than that obtained by the known low zinc phosphate treatment method using a bath not containing I).

Claims (1)

[Claims] 1. When pre-treating a workpiece made of steel or partially galvanized steel for electrodeposition coating, the workpiece, which has been degreased and washed with water, is treated with titanium phosphate. 1.8 to 5 g/l of the treated material is activated in a slightly alkaline aqueous solution containing zinc phosphate and then immersed in an acidic and aqueous phosphate treatment solution containing zinc phosphate. Zn 0.1 to 7 g/l Fe(II) 8 to 25 g/l P_2O_5 5 to 30 g/l NO_3, and the ratio of free acid to total acid is adjusted to 0.04 to 0.07. A phosphate treatment method comprising contacting with a phosphate treatment solution at a temperature of 40 to 60°C. Process according to claim 1, characterized in that the workpiece is brought into contact with a phosphating solution containing not more than 2.3 g/l of zinc and preferably 0.5 to 5 g/l of Fe(II). . Claim 1, characterized in that the object to be treated is brought into contact with a phosphate treatment solution further containing 3.3 g/l or less of Mn.
Or the method described in 2. Claim 1, characterized in that the object to be treated is brought into contact with a phosphate treatment solution further containing 4.3 g/l or less of Mg.
The method described in any one of 3 to 3. 5. Co less than 0.3g/l and/or 0.15g
5. The method according to any one of claims 1 to 4, characterized in that the object to be treated is brought into contact with a phosphate treatment solution that further contains less than /l of Ni. 6.3 g/l or less, preferably at least 0.3 g/l
6. A method according to claim 1, characterized in that the workpiece is brought into contact with a phosphate treatment solution containing hydroxylamine. 7. Claims 1 to 6, characterized in that the object to be treated is brought into contact with a phosphate treatment solution containing not more than 0.5 g/l of Ni when it contains at least 0.3 g/l of hydroxylamine. The method described in any one of the above. 8. SiF_6 below 3g/l, BF_ below 3g/l
8. The method according to any one of claims 1 to 7, characterized in that the object to be treated is brought into contact with a phosphate treatment solution containing at least one of F.4 and 1.5 g/l or less of F. . 9. Process according to claim 1, characterized in that the workpiece is brought into contact with a phosphate treatment solution containing not more than 9.3 g/l of tartaric acid and/or citric acid. 10, 0.5 g/l or less, preferably 0.05 to 0
．． 10. A process according to claim 1, characterized in that the workpiece is brought into contact with a phosphate treatment solution containing 35 g/l of m-nitrobenzenesulfonate. 11. The method according to any one of claims 1 to 10, characterized in that the object to be treated is brought into contact with a phosphate treatment solution containing a nitrite-decomposing substance such as urea or amidosulfonic acid. 12. Excess divalent iron mixed into the phosphating solution is treated with at least one of an oxygen-containing gas, chlorate, and a peroxide compound.
Claims 1 to 11 characterized in that the object to be treated is brought into contact with a phosphating solution in which the concentration of divalent iron is adjusted by precipitating Fe(II) as iron(III) phosphate by seeds. The method described in any one of the above. 13. Any one of claims 1 to 12, characterized in that the object to be treated is brought into contact with a phosphate treatment solution in which the free acid content is adjusted by adding zinc oxide, calcium carbonate and/or manganese carbonate. The method described in section. 14. Any one of claims 1 to 13, characterized in that the object to be treated is brought into contact with the phosphate treatment solution by a spray method before and/or after immersing the object in the phosphate treatment solution. The method described in section. 15. According to any one of claims 1 to 14, characterized in that the object to be treated is brought into contact with a phosphate treatment solution to form a phosphate film having a weight of 1 to 5 g/m^2. the method of. 16. The method according to any one of claims 1 to 15, wherein the electrodeposition coating is a cationic electrodeposition coating.