JPS5976880A - Production of steel sheet painted on one side - Google Patents

Abstract

PURPOSE:To prevent the deterioration in chemical convertibility of a non-painted surface of a steel sheet painted on one side by providing a stage for applying a specific amt. of Ba salt on the non-painted surface and a stage for drying the same before a stoving stage. CONSTITUTION:A cold rolled steel sheet from a pay-off reel 2 is introduced through a defatting and washing stage 4, a surface preparation and washing stage 6 into an application stage 8 of Ba salt before a painting stage 12 for one surface. Ba salt, for example, Ba borate is applied at 0.01-1g/m<2> in terms of Ba on the non-coated surface of the cold rolled steel sheet. The Ba Salt applied thereon is dried in a drying stage 10, whereafter the steel sheet is subjected to painting on one side in the stage 12. The painting is then stoved in the stage 14. After the above-mentioned operation is repeated twice, oil is applied on the non- painted surface in an oiling stage 16, then the sheet is taken up on a tension reel 18.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a single-sided coated steel sheet, and particularly to a manufacturing method that can prevent deterioration in chemical conversion treatment properties of the non-coated surface.

Due to its high corrosion resistance, di/critique-coated steel sheets, which are single-sided coated steel sheets, are widely used as outer panels of automobiles, such as floor/fender materials, door materials, etc., which are subject to severe corrosion.

Single-sided coated steel sheets are press-formed and
After assembly, chemical conversion treatment using zinc phosphate, etc. is performed. However, it is said that the chemical conversion properties of the unpainted cold-rolled surface, which should be the same as that of cold-rolled steel sheets, are inferior to that of ordinary cold-rolled steel sheets.

This is due to the following reasons. In other words, the viscosity f in organic solvent
7! :w! The 4-section zinc-rich paint is applied using a roll coder or the like and baked with oat, but at this time the interior of the orb becomes a vaporized organic solvent atmosphere. On the other hand, the unpainted surface of the cold-rolled steel sheet is activated by degreasing and brushing before painting. Therefore, the organic matter inside the opening is attached and baked onto the board surface, creating a strong inert film. In addition, trace amounts of carbon and sulfur in the combustion gas used as the heat source of the oven tend to adhere to the board surface, and these deposits are firmly attached and cannot be removed by degreasing before chemical conversion treatment. These deposits deteriorate chemical conversion treatment properties.

As a countermeasure against these problems, inert coatings on the surface and substances that interfere with chemical conversion treatment have conventionally been removed by means of a plastic/gut or the like. However, this method has the disadvantage that it is difficult to uniformly activate the board surface - and that jitter marks are likely to occur.

An object of the present invention is to provide a method for producing a G-surface coated steel sheet that solves the problems of the prior art described above and can prevent deterioration of the chemical conversion treatment properties of the non-coated surface.

The gist of the present invention is as follows.

That is, the degreasing and water washing process of the cold rolled steel plate, the base treatment and water washing process of the degreasing and water washed steel plate, the pupil surface painting process of the base treatment and water washed steel plate, the baking process of the single side coated steel plate, and the In the manufacturing method of a single-sided coated steel plate, the baking process includes the step of applying oil to the steel plate, and in the baking of the single-sided coated steel plate, the unpainted surface of the single-sided coated steel plate is coated with barium equivalent to 0. OIf/rr? The following is a method for manufacturing a single-sided coated steel sheet, which is characterized by comprising a step of applying a barium salt of less than 11/♂ and a step of drying the applied barium salt.

Attached is salt TL that does not inhibit chemical conversion treatment before unpainted cold rolling.
- This is based on the knowledge that by coating, it is possible to prevent the attachment and seizure of organic substances, etc., and also to absorb inorganic elements attached by combustion gas during seizure, making them harmless.

Various salts of alkali metals and alkaline earth metals can be considered as salts to be applied to non-painted surfaces, but in basic experiments, these salts were applied, baked with combustion gas in an organic atmosphere, and then coated with anti-corrosion oil. After degreasing and chemical conversion treatment, it was found that only barium salt had the desired effect. Baliuno, salt and 1. Barium phosphate and parium phosphate are especially excellent. The amount of coating is barium equivalent, and is 11.111f'≠ 1 so, and 1 is a cost increase button (degreasing - [about 1
Since the degradation of the degreasing liquid in c is considered to be significant, the barium equivalent amount was limited to a range of 0.01F/a or more and less than 1f/+TI''.

The barium salt may be applied by any known method such as a roll coater edge method or a spray 6 method.

EXAMPLE Cold-rolled rolled board was processed according to the steps shown in the attached drawings. That is, the payoff reel 2 goes through a degreasing/washing step 4, a base treatment/washing step 6, and is then sprayed with the types and shellfish coating reagents shown in Table 1 in the barium salt coating step 8, which is a feature of the present invention. It was sprayed onto the surface and dried with hot air in drying step 10. For comparison, calcium salt and magnesium salt were also applied in addition to barium salt, and the amount of adhesion was expressed as the converted amount of Ba, Ca, and Mf, respectively.

Next, for baking by roll coating, step 14 was repeated twice, and the non-coated surface was coated with gold oil in step 16, and then wound up on a tape/reel 18. For reference, a conventional example in which salt is not applied to the non-painted surface before the baking process is also included.

Test specimens were cut from these single-sided coated steel plates, spray degreased with an alkaline degreasing solution, and then chemically treated with a zinc phosphate solution. shows the results.

The degreasing property was evaluated by the water wettability of the board surface after degreasing by spraying for 2 minutes with an alkaline degreaser at a concentration of 2.

All samples tested had a water wettability of 95 cm or more, indicated by a circle, and had good degreasing properties.

In addition, chemical conversion treatment properties include a total acidity of 17 v/t and a free acidity of 0.7.
After spraying the Voight/Gate solution for 2 minutes, it was observed with a scanning electron microscope and evaluated based on the crystal size, which was expressed as follows.

O: Less than 15μ Δ: 15-30μ
3 to 10), and the free acid is the N required to change the color of the bromophenol blue indicator (color change pH 3 to 4.6).
/10 Refers to the number of ml of NaOH consumed.

Regarding chemical conversion treatment properties, as shown in Table 1, all of the examples of the present invention coated with barium salt have crystal sizes of less than 15 μm, whereas the comparative examples coated with other than barium salt and the conventional example without coating were all excellent. It was found that chemical conversion treatment properties were poor at 15 μm or higher.

As is clear from the above examples, the present invention prevents the deterioration of the chemical conversion properties of the non-painted surface by applying a limited amount of barium salt to the non-painted surface before the baking process of single-sided coated steel sheets. became possible.

[Brief explanation of drawings]

The accompanying drawings are process diagrams of embodiments of the present invention. 4... Degreasing/washing process 6... Base treatment/washing process 8... Bar IJ r horn/salt application process 10... Drying 1 culm 12... Painting process 14... Baking is a process 16...Anointing] - Agent Cheng Takeo Nakaro

Claims (1)

[Claims] (1) Degreasing and washing of the cold-rolled steel plate, a base treatment and washing process of the four degreasing and water-washed steel plates, a surface painting process of the base treatment O water-washed steel plate, and a baking process of the single-sided coated steel plate;
In the method for manufacturing a single-sided coated steel plate, the baking process includes the step of applying oil to the steel plate, and the baking of the single-sided coated steel plate is performed by adding 0 barium equivalent amount to the non-painted surface of the single-sided coated steel plate before the process.
．． 01f/n? As described above, a method for manufacturing a single-sided coated steel sheet is characterized by comprising a step of applying barium salt of less than 1 f/- and a step of drying the applied barium salt.