JPH02173274A - Method for phosphating galvanized steel sheet - Google Patents

Abstract

PURPOSE:To form a phosphate film excellent in adhesion to the base steel sheet or to the coating film when the steel sheet is coated by rubbing the surface of a galvanized steel sheet immediately after the sheet is dipped in a phosphating soln. at the time of dipping the sheet in the soln. to form a phosphate film. CONSTITUTION:A phosphate film is formed on the surface of the steel sheet plated with Zn or a Zn alloy by electrogalvanizing, hot-dip galvanizing, etc. In this case, the galvanized steel sheet is passed over a rubber or steel roller rotating at a speed higher or lower than that of the steel sheet traveling in a phosphating soln. immediately after the sheet is dipped in the soln. or less than four seconds after the sheet is dipped in the soln. As a result, the surface of the sheet is rubbed with the roller by the difference between the traveling speed of the sheet and the rotating speed of the surface of the sheet, hence the extremely chemically active surface is exposed, a phosphate film having extremely fine and uniform crystal structure is formed, and a phosphate film excellent in adhesion to the base galvanized steel sheet or to the coating when the sheet is coated is easily and stably formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for phosphate treatment of galvanized steel sheets.

(Prior Art) A galvanized steel sheet is obtained by electrolytic galvanizing or hot-dip galvanizing a steel sheet. Zinc here refers to Zn or Zn-based alloy.

Such galvanized steel sheets are widely used as base sheets for colored galvanized iron sheets, pre-painted steel sheets, etc. due to their high corrosion resistance. In this case, the galvanized steel sheet is generally subjected to phosphate treatment as a base treatment for painting, and after the treatment, it is painted and used. Note that the phosphate treatment forms a so-called phosphate film on the surface of the galvanized layer.

In the above-mentioned applications, the material after painting needs to have a high degree of processability in order to undergo processing, and therefore the phosphate film also has a high adhesion between the film and the paint (hereinafter referred to as paint). It is also required that the film itself has fine and uniform crystals.

By the way, the usual phosphate treatment method is to immerse a galvanized steel sheet in a phosphate treatment solution for a predetermined period of time, or to spray a phosphate treatment solution onto a galvanized steel sheet. The surface of the plating layer has a relatively thick oxide film, and in the case of hot-dip galvanized steel sheets, A1 is often concentrated in the surface layer. Therefore, in the above-mentioned conventional glue/acid treatment method, the crystals of the phosphate film often become coarse and non-uniform.

Therefore, in applications that require a high degree of workability as described above, in order to remove the oxide film and the AI4 layer, the galvanized layer is removed by polishing and grinding means such as Scotchbrite before being immersed in the phosphate treatment solution. A method of grinding the surface layer is being used.

(Problems to be Solved by the Invention) However, the method described above (grinding the surface layer of a galvanized layer) requires large-scale equipment, basically requires a large space, and is uneconomical. In addition, in applications that require a high degree of processability, there are problems in that the adhesion of the phosphate film to paint, the degree of crystal fineness and uniformity are insufficient. The problem is that
In particular, when a galvanized steel sheet obtained by hot-dip galvanizing is used, the degree of the galvanized steel sheet is the head weight.

The present invention was made in response to these circumstances, and its purpose is to solve the above-mentioned problems of the conventional ones, to have better paint adhesion than the conventional ones, and to provide a coating with fine particles. Uniform crystal &l! The object of the present invention is to provide a method for phosphate treatment of a galvanized steel sheet, which can simply form a phosphate film on the surface of a galvanized layer without requiring large-scale equipment.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for phosphate treatment of galvanized steel sheets having the following configuration.

That is, the method according to the first claim is a method for phosphating a galvanized steel sheet in which a galvanized steel sheet is immersed in a phosphate treatment solution to form a phosphate film on the surface of the galvanized layer. This is a method for phosphating a galvanized steel sheet, which is characterized by applying friction and/or polishing to the surface of the galvanized steel sheet in a phosphating solution during the initial stage of formation.

The method according to claim 2 is a method for phosphating a galvanized steel sheet according to claim 1, wherein the friction and/or abrasive application is performed immediately after immersion of the galvanized steel sheet in a phosphating solution. It is.

The method according to claim 3 is characterized in that the abrasion and/or abrasive application is performed within 4 seconds after immersing the galvanized steel sheet in the phosphating solution. This is a phosphate treatment method.

(Function) The present invention is a continuous phosphate treatment line in which a long galvanized steel plate is run by rollers in a liquid tank in which a phosphate treatment liquid is stored, immersed in it, and then brought out of the liquid tank. This is based on the following knowledge discovered during actual operation of phosphate treatment of galvanized steel sheets.

That is, during the above operation, among the liquid tank self-propelled rollers placed in the liquid, the liquid tank self-propelled roller located closest to the inlet side of the steel plate into the liquid tank (the steel plate is moved to that roller immediately after being immersed) Although the train stopped operating due to an abnormality, it continued to operate for a while. After the line was stopped, it was noticed that the outside n<gloss of the phosphate-treated steel plate differed depending on the part of the steel plate, so observation was performed using a scanning electron microscope. As a result, the portion of the steel plate that passed through the roller after the abnormality of the roller stoppage was found to have a phosphate film containing finer and more uniform crystalline Mi than the portion of the steel plate that passed before the abnormality occurred. It turned out that it was.

When the steel plate is run after the rollers have stopped as described above, the surface of the galvanized layer is slightly subjected to friction as it passes through the rollers. This friction has an extremely small mechanical effect on the surface layer compared to the conventional surface grinding method.Therefore, the cause of the crystal refinement and uniformity effect is mechanical. It cannot be explained by just that.

Therefore, in order to investigate the cause of this, we conducted various studies such as reproduction tests and basic experiments, and found the following. That is, in the case of oxide film removal treatment by polishing or pickling in the atmosphere, even if the oxide film is removed, it is immediately oxidized by oxygen in the atmosphere and an oxide film is formed again, so that the phosphoric acid Salt treatment results in the formation of a phosphate film on the oxide film.

On the other hand, when the surface of a galvanized steel sheet is rubbed or polished in a phosphate treatment solution, when the oxide film is removed and a new surface appears, the phosphate treatment solution is present around the new surface. Moreover, since the amount of dissolved oxygen in the liquid is extremely small compared to that in the atmosphere, the phosphate film forming reaction takes priority over the oxidation reaction on the newly formed surface. Since such a new surface is chemically extremely active, the phosphate film forming reaction proceeds quickly and stably, so that the crystals of the film formed are fine and uniform. or,
Since the phosphate film is directly formed on the new surface, the adhesion between the film and the galvanized layer is excellent.

Further, the surface layer portion of the galvanized layer and/or the phosphate film is subjected to distortion due to the above-mentioned friction or polishing (hereinafter referred to as friction or the like). When a metal is subjected to strain, chemically active sites such as slip planes and kinks due to dislocations increase in number. Microscopically, a film nucleus is first generated at the active site, and a film grows from this nucleus to form a film. Therefore, if there are a large number of active points, the crystals of the formed film will be fine and uniform.

However, when the active points are generated in the atmosphere, an oxide film is formed on them, so the activity quickly deteriorates, but when the active points are generated in the phosphate treatment solution, the activity deteriorates. The activity is maintained at least until the phosphate film forming reaction occurs at the active site. Therefore, when rubbed in a phosphate treatment solution, the crystals of the film formed will be fine and uniform.

As explained above, when the surface of a galvanized steel sheet is rubbed in a phosphate treatment solution, a phosphate film is directly formed on the new surface, and chemical Since a large number of active sites remain active, the crystals of the formed film are fine and uniform.

Furthermore, the effect of friction in the phosphate treatment solution as described above is noticeable when such friction is applied at the early stage of phosphate film formation, and when it is applied only at the middle to late stages. It was found that the effect of crystal refinement becomes smaller or almost no effect is observed. In addition, at the initial stage of phosphate film formation, the phosphate film is not formed at all, or even if it is formed, the thickness of the phosphate film is very thin, so the oxide film is easily removed. , and the thickness of the phosphate film that is scraped off as the oxide film is removed.
becomes smaller, thus ultimately ensuring a phosphate film of a predetermined thickness. However, in the middle to late stages of phosphate film formation, the thickness of the phosphate film becomes large, making it difficult to remove the oxide film, and the amount of phosphate film that is scraped off as the oxide film is removed. (thickness) increases,
Therefore, it was confirmed that a phosphate film of a predetermined thickness could not be secured in the end.

Therefore, in the method for phosphate treatment of galvanized steel sheets according to the present invention, as described above, the surface of the galvanized steel sheet is subjected to friction, etc. (friction and/or polishing) in the phosphate treatment solution in the initial stage of phosphate film formation. ). Therefore, it becomes possible to form a phosphate film on the surface of the galvanized layer, which has better paint adhesion than before and has a fine and uniform crystal structure.

A phosphate film having such a fine and uniform crystal structure has excellent paint adhesion and processability. Therefore, if a galvanized steel sheet is treated with phosphate by the method according to the present invention as described above, a sheet material having highly excellent paint adhesion and workability can be obtained.

Friction and the like at the initial stage of forming the phosphate film may be extremely slight. Because it is in the initial stage, the thickness of the phosphate film on the oxide film is extremely thin, or there is no phosphate film on the oxide film, and the oxide film is originally extremely thin, so there is slight friction. This is because the oxide film is removed even if the surface layer is subjected to such a process, and since it is only necessary to apply strain to the surface layer, it is sufficient to apply a slight strain. Such slight friction and the like can be achieved mechanically with extremely small force. Therefore, such provision of Pa1 etc. can be easily performed without requiring large-scale equipment.

When a galvanized steel sheet is immersed in a phosphate treatment solution, the phosphate film formation reaction begins at the same time or immediately after immersion, so depending on the temperature and concentration of the phosphate treatment solution, the film formation reaction may proceed quickly and may take some time after immersion. After this time has elapsed, the formation of a phosphate film is in the middle to late stages. Therefore, in order to reliably apply friction, etc. at the initial stage of phosphate film formation, it is desirable to apply the friction, etc. immediately after immersing the galvanized steel sheet in the phosphate treatment solution. .

Said T'I! It is desirable that the rubbing etc. be performed within 4 seconds after the galvanized steel sheet is immersed in the phosphate treatment solution. If you do this, you will get fine and uniform crystals & uIQ at the 11th time! This is because a phosphate film having the following properties can be obtained. The reason why it is within 4 seconds is that if it is within 4 seconds, a film with high-level properties as mentioned above can be obtained, but if friction is applied after 4 seconds, the fineness and uniformity of the film crystals may deteriorate. This is because the degree gradually decreases. Incidentally, even after 4 seconds have elapsed, a sufficiently fine crystal skin I11 can be obtained if friction etc. are applied at a relatively early stage.

[The method of applying 1af etc. is, for example, in the case of a continuous phosphate treatment line, a rubber or steel roller is moved faster than the galvanized steel plate, or slower (by rotating it by itself, It is possible to adopt a method of friction between the roller and the galvanized steel sheet, or a method of pressing a fixed object made of resin or the like against the surface of the galvanized steel sheet to bring both Fi!+=. !The rubbing means is not limited, but it is necessary to select a method that can apply friction etc. uniformly to the surface of the galvanized steel sheet and does not cause scratches on the surface.The location of the friction means may be located at a position where friction or the like can be applied to the surface of the galvanized steel sheet in the phosphate treatment solution at the initial stage of phosphate film formation.

(Example) Zero spangle material of hot-dip Zn-plated steel plate (thickness: 0.6
+wm, Zn coating: 90g/90gt) was subjected to phosphate treatment using a continuous phosphate treatment line. A running roller is placed outside the liquid tank in this line.
In the liquid in the liquid tank, a running roller is arranged on the steel plate outlet side of tank a, and a roller for applying friction is arranged on the temporary entrance side of tank m. The friction imparting roller is made of neoprene rubber and rotates in the running direction of the steel plate at a speed slower than the running speed of the steel plate.

When the above-mentioned line is operated, the hot-dip Zn-coated steel sheet travels, enters the phosphating solution in the bath, and is immersed. When 1.5 seconds have elapsed since the steel plate was immersed, the steel plate passes between the friction rollers while being subjected to friction. The contact pressure of the roller against the steel plate is 1.83Kg/c+s"
(temporary unit area of 114). After passing through the phosphate treatment solution, it travels for a while, and then comes out of the solution tank, completing the phosphate treatment. After the treatment, it is washed with water and dried. Ru.

After drying, an epoxy primer was applied and baked, and then a polyester paint was applied thereon and baked. At this time, the total coating film thickness was 15 μ-.

The plate thus produced (hereinafter referred to as the plate of Example 1) was subjected to measurement of adhesion of the phosphate film, observation of crystals in the film, and coating film adhesion test. In addition, skin 1
For crystal observation, the plate surface was observed using a scanning electron microscope. The amount of film deposited was measured during the crystal observation. In the adhesion test, a strip-shaped specimen is taken from the manufactured temporary, the specimen is bent 180' closely, an adhesive tape is pasted around the bent part, and after removal, the presence or absence of peeling of the coating film is determined. observed.

On the other hand, for comparison, a molten Zn-plated temporary coat was run at the same speed as above using a line with running rollers instead of the above-mentioned friction imparting rollers, treated with phosphate, and then coated and baked. I did it. Note that this manufacturing condition is the same as the manufacturing condition of the plate of Example 1 except that no friction is applied during the phosphate treatment. Observations and tests similar to those described above were also performed on the plate manufactured in this way (hereinafter referred to as "temporary product of Comparative Example 1").

As a result of test drilling and measurement of the amount of phosphate film deposited, the amount of adhesion was 0.70 g/■2 for the temporary plate of Example 1, and 0 for the board made of Comparative Example 1.
．． It was 68g/l112, which was equivalent to both Jin and Jin.

As a result of the paint film adhesion test, the paint film of the temporary board of Comparative Example 1 peeled off at the bent portion, but no peeling of the paint film was observed in the board of Example 1. Therefore, the plate produced in Example 1 has excellent coating film adhesion.

FIG. 1 shows an example of the observation results (i.e., crystal structure) of the film crystals for the plate produced in Example 1. Figure 2 shows comparative example 1.
Observation results of film crystals (i.e. crystal structure) for preliminary preparation of
As shown in these figures, regarding the crystal mta of the phosphate coating, the plate produced in Comparative Example 1 had coarse crystals, whereas the plate produced in Example 1 had an average crystal mta. The particle size was 1/25 of that of the plate of Comparative Example 1, and was extremely fine. It was also confirmed by a bending test that the fabricated fabric of Example I having a phosphate film made of such fine crystals could be satisfactorily used in applications requiring a high degree of workability.

(Effects of the Invention) According to the method for phosphate treatment of galvanized steel sheets according to the present invention, a phosphate film having better paint adhesion than before and having a fine and uniform crystal structure can be formed without a large-scale process. It can be easily formed on the surface of a galvanized layer without requiring any equipment. Therefore, it is possible to obtain a sheet material obtained by treating a galvanized steel sheet with a phosphate, or a sheet material further subjected to a coating treatment, which has a high degree of workability.

In addition to the above, there is also the effect that the adhesion between the phosphate film and the galvanized layer becomes excellent.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an example of the crystal structure of the coating for the plate produced in Example 1, and FIG. 2 is a diagram illustrating an example of the crystal structure of the coating for the prefabricated plate of Comparative Example 1. Patent applicant Kobe Steel Co., Ltd. Representative Patent attorney Akira Toneri

Claims (3)

[Claims] (1) In a method for phosphating a galvanized steel sheet in which a galvanized steel sheet is immersed in a phosphating solution to form a phosphate film on the surface of the galvanized layer, phosphate treatment is performed at the initial stage of film formation. A method for phosphate treatment of a galvanized steel sheet, characterized by applying friction and/or polishing to the surface of the galvanized steel sheet in a liquid. (2) The method for phosphating a galvanized steel sheet according to claim 1, wherein the friction and/or abrasive application is performed immediately after immersing the galvanized steel sheet in the phosphating solution. (3) The method for phosphating a galvanized steel sheet according to claim 1, wherein the friction and/or polishing is performed within 4 seconds after immersing the galvanized steel sheet in the phosphate treatment solution.