JPS61582A - Pretreatment of steel sheet before coating - Google Patents

Abstract

PURPOSE:To improve the covering power of a zinc phosphate film formed on a steel sheet by chemical conversion treatment by applying ultrasonic vibration to a soln. for chemical conversion treatment. CONSTITUTION:When the body 3 of an automobile is pretreated before coating to form a zinc phosphate film by chemical conversion treatment, a chemical conversion treatment tank 1 is filled with a zinc phosphate soln. 2 for chemical conversion treatment, and a zinc phosphate film is formed on the surface of the body 3 by chemical conversion treatment while transferring the body 3 in the soln. 2 with a hanger 4. At this time, an ultrasonic oscillator 5 is placed on the bottom of the tank 1 to apply ultrasonic oscillation at <=4.5X10<3>W/m<2> output to the soln. 2 from an oscillator 6. The covering power of the resulting film on a joint in the iron plate of the body 3 and a narrow part is improved, and a uniform film is easily formed on the whole body 3.

Description

Detailed Description of the Invention (Technical Field) This invention relates to a method for pre-painting a steel plate, and more particularly, to improving rust prevention after painting a steel plate on an automobile body, especially in narrow spaces and seams. The present invention relates to a method for pre-painting a steel plate.

(Prior Art) Conventionally, rust prevention of automobile bodies has been done by applying chemical conversion coatings made of zinc phosphate-based inorganic materials, electrodeposition coatings, and top coatings to prevent steel plates from rusting. Unlike the outer body parts, it is difficult to apply a top coat by spraying on the joints and hemming parts of steel plates in the automatic body, so chemical conversion coatings and electrodeposited coatings are the only way to prevent rust compared to other flat areas. It maintains its strength. For this reason, electrodeposition paints are required to have good throwing power and be able to coat joints and narrow spaces well.Through various improvements to date, paints that meet these requirements have been developed and are now in use. It is being said.

However, in such a conventional painting method using paint, pre-painting treatment is carried out on, for example, an automobile body. After degreasing and surface conditioning, the body is transferred to a chemical conversion treatment tank using a hanger for transporting the body. Because the process involved simple immersion in an acid-zinc-based chemical conversion treatment solution, followed by washing and drying, a considerable amount of electrodeposited paint was applied to the seams and narrow areas after painting. Nevertheless, there is a problem in that, especially when vehicles drive in areas where salt is sprinkled on roads during the winter, rust develops from the inner surface of the seals, the lower parts of the doors, and the like. Therefore, the inventors have repeatedly investigated the causes of rust formation from inside as described above, and have discovered that the main cause of rust formation is that the chemical conversion film is not sufficiently covered in the eyes and narrow spaces. Ta. On the other hand, the role that chemical conversion coatings play in rust prevention is well known, and it is thought that they should play a large role even in narrow spaces. However, no literature has been found that actually discusses the throwing power of chemical conversion coatings in narrow spaces.

(Object of the Invention) This invention was made by focusing on the above-mentioned problems in pre-painting treatment, and involves forming a chemical conversion film on a steel plate while applying ultrasonic vibration to the chemical conversion treatment liquid in the chemical conversion treatment process. The aim is to solve the above-mentioned problems by improving the coverage of the chemical conversion coating to joints and narrow spaces.

(Structure of the Invention) The method of pre-painting a steel sheet by immersing it in a zinc phosphate-based chemical conversion treatment solution includes the following steps:
, □5゜0. YO, □□□, the feature is that chemical conversion treatment is performed on the steel plate while 1.

Generally, zinc phosphate-based chemical conversion reactions are carried out from steel sheets to iron (Fe).
) is eluted, and hydrogen ions decrease accordingly, and zinc phosphate (Zn8 (
PO,), -4H20,zn,ye(po,), -4H
, O) are precipitated on the steel sheet.

When chemically treating steel plates, for example, car bodies, it is necessary to maintain a liquid concentration that is sufficient to replenish precipitated ions due to a certain amount of liquid flow, movement of the body, and tank capacity in the outer panel of the body. However, in narrow spaces on the inner surface, not only the amount of liquid in contact is small, but also the flow of the liquid is small, so the concentration of liquid is not sufficient to deposit a chemical conversion film. I have no choice but to become a state. A countermeasure to this problem is to increase the flow of the liquid to replenish the decreased ion concentration at the interface, but as long as conventional stirring methods are relied on, especially in narrow spaces, it is not necessary to use any special stirring method. Separately, sufficient liquid flow must be provided to the inner surface.

It's difficult.

However, in the method of the present invention, a vibrator is placed at an appropriate position in the chemical conversion solution, and the chemical conversion treatment is performed without propagating ultrasonic vibrations to the chemical conversion solution, so the amount of ion movement to the narrow part is small. increases, and the diffusion of ions near the interface becomes smoother, replenishing the decrease in ion concentration is achieved, and the same chemical conversion treatment as that of the outer panel is performed on the narrow part.

When actually performing chemical conversion treatment, if the output per unit area of the vibrator is set to less than 4.5 x 108W, and the chemical conversion treatment is performed while applying ultrasonic vibration, the crystal shape of the chemical conversion coating may become coarse. , the composition will not change,
It is preferable to set the output to 4.5×10 8 W/ν or less since the chemical conversion film can be applied to the entire surface with good throwing power.

(Embodiment of the Invention) Fig. 1 is a diagram showing an embodiment of the present invention, in which a chemical conversion treatment liquid 2 is put into a chemical conversion treatment tank 1, and an automobile body 8 is immersed in the liquid using a body conveyance hanger. Indicates the state to be processed. An ultrasonic vibrator 5 is installed at the bottom of the chemical conversion treatment tank 1, and an oscillator 6 is provided to oscillate ultrasonic vibrations from the vibrator 5 to the chemical conversion treatment liquid 2. By propagating the ultrasonic vibrations to the liquid while the body 8 is in contact with the chemical conversion treatment liquid 2, the chemical conversion treatment can be performed satisfactorily throughout the body up to the narrow portion. In the illustrated example, the ultrasonic transducer 6 is installed at the bottom of the tank 1, but it is needless to say that the present invention is not limited to this.

Next, the present invention will be further explained in detail based on specific examples.

Example 1 Bt manufactured by Nippon Parriki Rising Co., Ltd. was added as a chemical conversion treatment liquid to a chemical conversion tank equipped with a circulation device that filled approximately 201 kg of chemical conversion treatment liquid.
8004, i.e., main agent 5 og/l.

It was filled with a solution of AD4818 (fluoride) 59/1XA01st (accelerator) 0.8 l/l and soda carbonate w, q 59/l dissolved in water, and the temperature was raised to 50°C. On the other hand, the company's FC
4857 as a degreaser, Part A (alkali builder)
169/1, C agent (surfactant) was added at a ratio of 12 parts, and PL4081 was added as a surface conditioner at a ratio of 109/l to prepare a bath.
After degreasing and surface conditioning two cold rolled steel plates of 0 mm x 1 gm thickness, as shown in Fig. 2, polyester films 7 of 11511 x 150111 x 800 μm thick are used as spacers to separate the left and right sides of the steel plates. placed on both ends, 2
A sample was prepared by fixing two steel plates 8 facing each other. This sample was immersed so that its upper end was approximately 2 cm below the liquid surface. A ferrite vibrator was also placed at the bottom of the tank to generate ultrasonic waves. The strength of ultrasonic vibration is changed by adjusting the output per unit area of the vibrator, and 4
．． 5 x 10' and 6. Ultrasonic vibration was applied with an output of OX 108 □2.

As a result, when no ultrasonic waves were applied, the height at which the chemical conversion film adhered from the bottom edge of the steel plate was 85 to 49 gm, but it was 4.5 gm.
When the chemical conversion treatment was performed under ultrasonic vibration with an output of X108, 6.0XIO8W/-, a chemical conversion film was attached to almost the entire inner surface. If no ultrasound is applied to Fig. 8, Fig. 4 shows 6. The state of adhesion of a chemical conversion film on the inner surface of a steel plate is shown when ultrasonic vibration with an output of OX 108W/- is applied.

In the drawing, 9 shows the steel plate base, 10 shows the spacer trace, and 11 shows the chemical conversion coating, and the effect of applying ultrasonic vibration is clearer from these drawings.

Furthermore, when a chemical conversion film prepared by applying ultrasonic vibration with an output of 4,5 x 10' W/ν was observed using an electron microscope (
D Crystal (7) Structure wotJ s Figure d, 6. OX1
FIG. 6 shows a similar crystal structure produced by applying ultrasonic vibration at an output of 08w//l2f). From this 4,5
At X 108 W/, 1, a crystal similar to the conventional one was obtained, but at an output of 6.0 X 108%2, the crystal became somewhat coarse and ψ.

(Effects of the Invention) As explained above, according to the present invention, during the chemical conversion treatment of the steel plate before painting, a vibrator connected to an oscillator is placed at an appropriate position in the chemical treatment tank, and the treated steel plate is exposed to the chemical conversion liquid. By applying ultrasonic vibration during immersion, the chemical conversion coating can be applied to areas where the coverage of the chemical coating was not always sufficient, such as the narrow spaces on the car body and the inner surface of the hem. It is possible to improve the adhesion of the electrodeposited coating on the inner surface of the hemming part and the hemming part, which in turn has the effect of significantly improving its corrosion resistance.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is an explanatory diagram of the chemical conversion treatment of an automobile body by the method of the present invention, and Fig. 2 is a perspective view of a sample for examining the throwing power of the chemical conversion film in the narrow part. FIG. 8 and FIG. 4 show the case where ultrasonic vibration is not applied in the chemical conversion treatment in Example and 6. OX108
Figures 5 and 6 are explanatory diagrams showing the state of adhesion of the inner surface film of the sample when ultrasonic vibration is applied by the output of w/L2.
08V-16, o x 108"/@" +7) is an electron micrograph (magnification: X8500) showing the crystal structure of a chemical conversion film when ultrasonic vibration is applied by output. 1... Chemical conversion treatment tank 2... Chemical conversion treatment liquid 3...
Automobile body 4... Hanger for transporting automobile body 5... Ultrasonic vibrator 6... Oscillator 7... Polyester film spacer 8... Steel plate 9... Steel plate base 10... Spacer trace 11... Chemical conversion film. Patent applicant Nissan Motor Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. When pre-painting a steel plate by immersing it in a zinc phosphate-based chemical conversion solution, the chemical conversion treatment of the steel plate is carried out while applying ultrasonic vibrations using a vibrator placed in the solution. A method for pre-painting a steel plate.