JPS6335782A - Production of surface-treated steel sheet having excellent appearance and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain the title surface-treated steel sheet having excellent appearance and corrosion resistance by depositing a chromate coated film on an electro-galvanized steel sheet with an aq. soln. consisting essentially of Cr<6+>, and successively heating and cathodically electrolyzing the sheet under specified conditions. CONSTITUTION:A coated film of a chromate at about 15-250mg/m<2> per one face, expressed in terms of Cr, is deposited on a zinc or zinc alloy-plated steel sheet or an aluminum or aluminum alloy-plated steel sheet with use of an aq. soln. consisting essentially of Cr<6+> by a coating system or a reaction system. The sheet as such or the sheet washed with water is heated at 50-250 deg.C to form a chromate film having >=0.2 ratio of Cr<6+>/(Cr<6+>+Cr<3+>). The sheet is then cathodically electrolyzed at the electricity quantity of 0.1-25 coulomb/dm<2> in an aq. soln. at about 2-13 pH and about 30-60 deg.C contg. about 0.1-100g/l electrically conductive salt (alkali metal salt of Cl<-> ion). The chromate coated film thus formed is not yellowed, and has excellent appearance, corrosion resistance, and adhesion.

Description

[Detailed Description of the Invention] (Industrial Application Field) The non-invention is the use of chromate treatment on the surface of zinc and zinc alloy plated steel sheets, aluminum and aluminum alloy plated steel sheets! The present invention relates to a method for producing a surface-treated steel sheet that is superior in pleasure performance, corrosion resistance, and painting performance in addition to coating.

(Prior Art) There are various methods for chromate treatment of zinc or zinc alloy plating or aluminum or aluminum alloy plated steel sheets, such as a coating type treatment method, a reaction type treatment method, and an electrolytic treatment method.

According to many patent publications to date, the coating type includes, for example, C
Chromate treatment methods using ry3-Sin, aqueous treatment solutions, Cr03-water-soluble resin aqueous solutions, and the like are known.

In addition, the reactive type has a process that has been known for a long time.
Cr 03-804 bath, Cry, -8O, 27P
O,”-F-based baths, and furthermore, Tl + Zr
There is a chromate treatment method in which the surface of a galvanized steel plate or the like is subjected to a reaction (etching) in a treatment bath to which metal ions such as + Zn are added.

These methods yield a romate film with good corrosion resistance and coating performance, but they also have the disadvantage that the outside + inkstone surface turns yellow and good visibility cannot be obtained, as well as the disadvantages mentioned in the first section. Ta. In the coating type chromate treatment method,
Since a large amount of Cr6 + is eluted in the subsequent degreasing process from the chromate film mainly composed of Cr6+,
There is a problem of deterioration of corrosion resistance.

On the other hand, in the reactive chromate treatment method, since a chromate film containing Cr3+ as a main component is formed, cracks occur in the film during processing, resulting in deterioration of corrosion resistance after processing.

In addition, as a 'decomposition chromate treatment,
417 (method of cathodic electrolytic treatment using Cr03-HzSO4 treatment solution), JP-A-60-110896 (CrO2-
All of these methods involve forming a chromate film on the surface of a galvanized steel sheet by cathodic electrolytic treatment. In general, these cathode electrolytic coatings have good adhesive properties and coating properties, but do not necessarily have sufficient corrosion resistance.

(Problems to be solved by the invention) Therefore, non-invention means that all of the above-mentioned problems have been solved.
A chromate coating with excellent appearance performance that does not cause yellowing even when the coating sensitivity increases.Furthermore, a chromate coating that prevents the elution of Cr in the chromate coating during the degreasing process of the coating type chromate treatment and prevents deterioration of corrosion resistance. It produces a chromate film that does not deteriorate the corrosion resistance after processing like the reactive chromate treatment method, and it also forms a highly corrosion-resistant chromate film that can replace the romate film when the corrosion resistance is insufficient like the electrolytic chromate treatment method. The purpose is to provide a manufacturing method that will allow

(Means for solving the problem) As a result of various studies on chromate treatment methods for zinc and zinc alloy plated steel sheets, aluminum and aluminum alloy plated steel sheets, etc., we found that Cr6+ was applied to zinc and lead alloy plated steel sheets, aluminum or aluminum alloy plated steel sheets, etc. A chromate film is completely deposited by coating or reaction treatment using a water bath solution containing Cr6 as a main component, and then heat-treated for 7 times in a temperature range of 50 to 250°C either as it is or after washing with water.
+A! :r6"+cr3+) ratio is 0.2 or more, and then cathodic electrolytic treatment is carried out in an aqueous solution containing a conductive salt with an amount of electricity of 01 to 25 couron/dm'. It has been found that the object of the invention is to produce a surface-treated steel sheet with excellent appearance and corrosion resistance.

That is, the treatment method of the present invention involves forming a chromate treatment on the surface of a zinc or zinc alloy plated steel sheet, aluminum or aluminum alloy plated steel sheet, in which the chromate film contains 20% or more of Cr6+, and then yellowing the film to improve its appearance. Cr deteriorates the performance completely and is easily eluted during the degreasing process.
By cathodic electrolytic treatment in a water bath containing f-conductive salt, it is removed from the surface layer of the coating, and at the same time, it is reduced to Cr3+ remaining on the surface layer of the chromate coating, and as an end result, it is formed. The chromate film 11j is made entirely of white Cr, which has excellent appearance performance and does not cause yellowing on the surface layer, and also prevents the Cr existing inside the chromate film 11j from being eluted during the degreasing process, and prevents it from being processed. A chromate film with excellent corrosion resistance is formed inside the film without removing the entire chromate film of the Cr"+ living body, which is susceptible to cracks.

(effect) The present invention will be explained in detail below.

In the present invention, the surfaces of zinc or zinc alloy plated steel sheets, aluminum and aluminum alloy plated steel sheets are subjected to an activation treatment immediately after drying or an alkaline bath, and then subjected to a chromate treatment using an aqueous solution containing Cr'+ ions as the main component. Chromate treatment is performed using a coating method or a reaction treatment method using a bath.

In the present invention, the chromate treatment bath is not particularly specified, but for example, the following baths are used.

■ Water bath liquid containing Cr'+ ions, silica and/or silicon salts, and Cr"+ ions ■ Cr'+ ions, PO4 io/and/or fluorine compounds, silica and/or silicates, and An aqueous solution containing all Cr ions ■ Chromate of the above ■ or ■ ■ or ■ Zn + A in the chromate bath
g, Ni, Co, My, Ti, Zr
After a chromate film is attached to the surface of the steel plate by immersing a steel plate plated with zinc or zinc alloy in an aqueous solution containing one or more types of cationic gold, etc., or by spraying the chromate bath. The above-mentioned surface treatment can be carried out by a coating amount control method using a roll coater, which wipes away excess chromate bath by roll squeezing or high-pressure gas, or by a method in which a predetermined amount is deposited using a chromate treatment or electrostatic atomization method. A predetermined amount of chromate film is deposited on the surface of the steel plate. In this way, the chromate-coated surface-treated steel sheet is subjected to heat treatment at a temperature of 50 to 250 °C, either as it is or after washing with water.
A chromate film 2 is formed in which the ratio of Cr6+/(Cr6++Cr+3) is 0.2 or more.

In the present invention, the heating temperature for forming the chromate film and the amount of Cr total 20 in the chromate film are as follows.
% or more is necessary.

By cathodic electrolytic treatment in an aqueous solution containing a conductive salt after forming a chromate film, the chromate film is extremely easily dissolved in an aqueous solution containing a conductive salt, which will be described in detail later, when the heating temperature is lower than 50'C. However, most of the formed chromate film is dissolved, which is not preferable.

If the heating temperature exceeds 250° C., the chromate film's difficult-to-solubility effect is saturated, and a dehydration reaction occurs in the chromate film, making the chromate film susceptible to embrittlement and deterioration of the material of the plated original plate.

Therefore, the heating temperature is 50 to 250°C, preferably 80 to 250°C.
The temperature is 150°C. In this case, the heating time is 1 to 3
0 seconds, preferably 3 to 10 seconds.

This heat treatment is performed particularly to reduce dissolution of the chromate film in the subsequent cathodic electrolytic treatment step, and the heating temperature is more important than the heating time. Furthermore, the formed chromate film cr”/(cr
It is important that the ratio of "+cr" is 02 or more.

That is, Cr/(Cr+.r)(D ratio is 02
If it is less than 100%, the effect of improving the appearance performance by the cathodic electrolytic treatment that follows cannot be sufficiently obtained, and since most of the chromate film after the cathodic treatment is formed of Cr3+, no damage to the film such as cracks will occur during processing. , corrosion resistance deteriorates after processing.

Therefore, the chromate film that provides the effects of the present invention is C
The ratio of r6+nr6''+cr3+) is 02-1, preferably 04-08.

This means that the performance of the film formed by cathodic electrolytic treatment is
If the ratio of Cr6+ (r6+ + Cr3+) is 04 or more, the corrosion resistance after processing will be improved, and Cr"+ will be added in advance to the chromate film formed after heat treatment.
By containing more than 0.2 in the ratio of 3R + Cr, the dissolution properties of the coating in a water bath solution containing conductive salts are ensured, making it suitable for treatment baths during cathodic electrolysis. It plays a long-lasting effect that can completely prevent contamination and extend its lifespan.

Therefore, Cr3+τ is present in the chromate film such as θ') above.
For example, the method of producing a chromate film with a chromate film is to mix Cr6+ and Cr3+ ions in advance in a chromate treatment bath so that the ratio of Cr'+ and Cr3+ ions corresponds to the target ratio of Cr'+ and Cr3+ ions in the film, and then perform the chromate treatment and treatment. A method of providing by heat treatment, etc. is adopted.

Next, in the method of the present invention, after the heat treatment, cathodic electrolysis treatment is performed in an aqueous solution containing a conductive salt. The solution used in this treatment is not particularly limited, but the following treatment bath may be used. For example (4
-ion, 1)04''-ion, PO, ion, NO3
- Aqueous solution containing one or more of alkali metal, alkaline earth metal salts and ammonium salts of ions, or Cl- ions, SO4 ions, No, - ions of N
An aqueous solution containing one or more of i, Co, and Mn salts is used.

Although the concentration and pHi' of these aqueous solutions are not particularly specified, the treatment bath degree is 0.1 to 1oooy.
/, 1. , (preferably 1 to 30 l/l) and pIr
is preferably 2 to 13, (preferably 1 to L], 5).

In other words, if the solution concentration is less than 0.1 t/l, the conductivity of the solution will be poor and the voltage during cathode electrolysis will tend to increase, and if the concentration exceeds 1ooy/l, the amount of solution carried out will decrease. Depending on the type of solution mentioned above, there is a tendency for a part of the underlying plating layer to dissolve from the end face or from defects such as pinholes in the chromate coating.

In addition, regarding the pH of the treatment bath, in order to prevent or reduce dissolution of the plating layer from the end face or defective parts of the chromate coating, the pH of the treatment bath is set to 4 to 13 for zinc or zinc alloy plated steel sheets. FJ I) For aluminum or aluminum alloy plated steel sheets, it is recommended to use the pH in the range of 2 to 115, and the preferred range for both is 4 to 11.
．． 5 is mentioned.

Next, the place f! The temperature V of JAi is not particularly specified, but it is 80゛C1 from room temperature, preferably 30
Used at processing temperatures of ~60°C.

A higher temperature is preferable in order to ensure conductivity τ, and as described above, a lower temperature is preferable in terms of preventing dissolution of the plating layer or reducing generation of mist in the processing bath.

Therefore, in the present invention, the bath temperature is 10 to 80°C, preferably 30 to 60''C.

Therefore, the heat-treated surface-treated coated steel sheet is used after being cooled down to a range that does not cause a change in the temperature of the treatment bath used after the heat treatment.

Furthermore, in order to obtain the steel plate targeted by the present invention, the amount of electricity must be 0.
．． 1-25 coulombs/am”, preferably 0.5
~10 coulombs/d m” cathodic electrolytic treatment is required.

If the amount of electrolytic electricity is less than 0.1 coron/dm', Cr'+ ions are partially eluted from the surface layer of the heat-treated chromate film and reduced to Cr"+ ions.

In addition, when the amount of electrolytic electricity exceeds 25 coulombs/dni'', the elution prevention of Cr'+ ions and the reduction suppression effect of Cr''+ ions are saturated, and the carbon content in the chromate film is saturated.
Since r'+ is reduced and the entire film is formed of a film mainly composed of Cr""'z, there is a drawback that the corrosion resistance deteriorates after processing.

Therefore, the amount of electrolytic electricity used for cathode retroanalysis is 0.1 to 2
5 coulombs/am', preferably 0.5 to 10 coulombs/am'.

Next, from the viewpoint of appearance performance, corrosion resistance, etc., the amount of chromate coating of the present invention is 15 to 2 per side in terms of metal Cr amount.
50 m97m2, (preferably 25-150111L)
? /m') is better.

The steel plate treated as described above is washed with water, dried or heat treated (50 to 25 o'C) to be made into a product.

In addition, zinc or zinc alloy plated steel sheets to which the present invention is applied,
The present invention can be applied to the following steel plates manufactured by electroplating, hot-dip plating, vacuum evaporation, etc. as aluminum or aluminum alloy plated steel plates.

For example, ■ Lead and zinc alloy plated steel sheet refers to plated steel sheet containing Zn and M with a coefficient of 0.5 or less to Zn, and plated steel sheet containing a small amount of St) or unavoidable impurities such as Pb and Cd. 4 sheets of steel, containing Ag gold (3-6%) in Zn,
In addition to this, Si, M, @, Mitsushmetal] species or more or 2
Alloy-plated steel sheet containing 2% or less of Zn or Ni
, an alloy plated steel sheet containing one or more of Co (5 to 25), and 8102 + Cr (7)
) Alloy-plated steel sheet containing 10% or less of one or more types, alloy-plated steel sheet containing Zn and Fe (8-90%) ■ Aluminum and aluminum alloy-plated steel sheet are aluminum made of Ag and inevitable impurities. Plated steel plate, Ag (1 to 1
Examples include an aluminum alloy plated steel sheet containing 81 (5%) and unavoidable impurities, and an alloy plated steel sheet containing (1 to 15% 81 and 3 or less My) in AA.

(Example) Examples and comparative examples of the present invention are shown below.

All steel plate strips: For zinc and galvanized steel sheets, aluminum and aluminum alloy plated steel sheets, which are manufactured using pre-treatment applied in the manufacturing process of normal surface treated steel sheets,
A chromate coating treatment was immediately applied online according to the method of the invention shown in Table 1.

After the treatment of the present invention, the sample was washed with water, squeezed with a roll, and then dried in a heated atmosphere of 70° C. for 3 seconds for performance evaluation.

Regarding the performance comparison of the treated material of the present invention and the comparative material, we compared the product of the present invention with a product in which only conventional paint-type or reactive chromate treatment and heat treatment were performed on surface-treated steel sheets having the same plating layer. The performance of each treatment method was evaluated relatively.

The evaluation test method and evaluation criteria were as follows.

■Appearance performance The appearance after chromate treatment was inspected, and the appearance performance was evaluated based on the following evaluation criteria.

◎... Uniform appearance with white metallic luster ○... Appearance with white metallic luster, but slight unevenness in appearance △... Uniform appearance with yellow coloring ×... Non-uniform appearance with yellow coloring Appearance with unevenness ■ Corrosion resistance performance Salt water spray 4 test (S
, S, T), the state of rust after a specific time (white rust, F
Red discoloration of the e-containing alloy plating layer, black spots due to partial dissolution of the plating layer, etc.) were observed, and the corrosion resistance of the flat plate and after processing was evaluated using the following evaluation criteria. Regarding processing,
For a sample with a thickness of 0.8 mm, 150 fins x 50 m
From the blank size of 70rtas x 70wm
A square cylinder with a depth of 30 mm was drawn.

(a) Corrosion resistance evaluation criteria for flat plates ◎... Rust of 1 inch or less ○... # More than 1% to 3% or less △... ! More than 3% to 10φ or less ×... I More than 10% to (b) Corrosion resistance evaluation criteria after processing ■... Rust 1% or less ○... I More than 1% to 5 inches or less △... 15 % ~ 10% or less
r shell/a), the same sample was spray degreased for 5 minutes at 60°C using a commercially available alkaline degreaser and washed with hot water (60"C
) After degreasing, the amount of residual chromium deposited is measured by fluorescent X-ray method (a, nrq/m"), and the ratio of the amount of chromium remaining without being dissolved by degreasing to the initial amount of chromium is determined as the amount of chromium fixed. percentage.

(0ri---Chromium fixation rate 0.95≦a, /a.

○・・・0.85≦a2/al<0
= 5△・= 0.70≦a2/a, (0
,85×...a2/a, (
0-70■ Corrosion resistance after processing A rectangular cylinder drawn material produced by the same processing method as in (1) above was degreased under the alkaline degreasing conditions in (1) above, and then evaluated using the salt spray test method and evaluation criteria in (3) above. We performed one song.

■Painting performance After painting with 25μ of melamine alkyd-based paint,
Scratches reaching the plating surface were made, and a 240-hour evaluation test was conducted using the salt spray test method described in (1) above. After the evaluation test, wash with water and remove cellophane tape.
The coating performance was evaluated by observing the blistering width of the coating film using the following evaluation criteria.

(Q...The average width of blisters from the scratch area is 2 degrees or less, and the paint film peels off from the flat surface other than the scratch area at 3 points or less (
Peeling diameter: 1 mm or less) ○... Average blistering width from the scratch area is more than 2 mm to 4 mm or less, and the paint film peels off from the flat surface other than the scratch area from 4 mm to 4 mm.
7 points (Peeling 111 with a diameter of 1W or less) △... Average width of blisters from the scratch area is more than 4 to 7 mm or less. Several points of peeling of the paint film with a diameter of 1 to 3 inches occurred from the flat area other than the scratch area ×・・The average blistering width from the scratch area is more than 7 mm, or several large scale peelings with a diameter of 3111II+ or more occur on flat areas other than the scratch area (effects of the invention) Zinc or zinc alloy plating obtained by the method of the present invention As mentioned above, steel sheets, aluminum or aluminum alloy plated steel sheets have Cr
It has excellent properties such as almost no elution of '+ and no deterioration in corrosion resistance due to γd release of Cr'+.

In addition, as an advantage of the performance improvement effect of the chromate film, the surface layer of the chromate film is cr3 +
Since it is formed of a coating mainly composed of K, it is possible to improve the adhesion and corrosion resistance after painting.

In other words, when a corrosive aqueous solution enters from a defective part of the paint film or passes through the paint film in a corrosive environment, the dissolution of Cr from the surface of the chromate film is extremely reduced, which prevents the formation of blisters from under the paint film, that is, the coating Since film blisters and the like are less likely to occur, the adhesion of the paint film and the tendency to eat after painting are significantly improved.

Claims (1)

[Claims] A chromate film is applied to zinc or zinc alloy plated steel sheet, aluminum or aluminum alloy plated steel sheet by coating method or reaction treatment method using an aqueous solution containing Cr^6^+ as the main component, and it is coated as it is or after washing with water at 50 to 250℃. Cr^6^+(Cr^
A chromate film with a ratio of 6^+Cr^3^+) of 0.2 or more is formed, and then cathodic electrolysis treatment is performed in an aqueous solution containing conductive salt or the like with an amount of electricity of 0.1 to 25 coulombs/cm^2. A method for producing a surface-treated steel sheet with excellent appearance performance and corrosion resistance.