JPH0672316B2 - Metal chromating method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface treatment method for a metal, and more particularly to a chromate treatment method capable of forming a film excellent in corrosion resistance of a metal and coating adhesion.

The metals referred to here are iron, zinc, tin, aluminum, chromium, nickel, copper and alloys thereof, or those obtained by subjecting these to various platings, and especially polished steel sheets or various plated steel sheets (alloys). When applied to coated steel sheets), it can provide excellent corrosion resistance and paint adhesion in a very short time.

[Conventional technology]

At present, so-called TEIN FREE STEEL, which has a chromate film on the outermost layer of steel sheet, is widely available on the market, and generally has a beautiful surface tone and has excellent properties as a base steel sheet for painting. Widely used in.

On the other hand, galvanized steel sheets, Zn-Ni-based, Zn-Fe-based, Zn-Ni-
Various alloy-plated steel sheets, including Co-based, Zn-Mn-based, and Zn-Co-based, are manufactured and used in large quantities in home appliances, steel sheets for automobiles, building materials, and the like. In particular, household appliances and building materials are often chromated before use.

Many of the chromate treatments for these Zn-based plated steel sheets are already known, and various chromate treatment methods have been developed and made proper.

For example, chromic acid is the main component, and sulfuric acid (Japanese Patent Publication No. 39-74
No. 61), phosphoric acid (Japanese Patent Publication No. 30-3514, Japanese Patent Publication No. 35-89)
No. 17, Japanese Patent Publication No. 36-9559, Japanese Patent Publication No. 36-9560), boric acid (US Patent No. 2733199, No. 2780592),
Cathodic electrolytic treatment of a steel sheet has been carried out using a bath containing various anions such as halogen (Cl ⁻ , F ⁻ ) (Japanese Patent Publication No. 39-14363).

[Problems to be solved by the invention]

However, in general, thein-free steel still has a feeling of rust resistance, and its adhesion to low temperature baking type paint (for example, melamine type paint) is insufficient.

Further, in the manufacturing process, a series of pretreatments such as degreasing and pickling are performed, and then a predetermined surface treatment is applied, so many processes are required and the equipment cost increases, and the manufacturing cost is considerably higher than that of the brush. It has the drawback of becoming expensive

On the other hand, it is no exaggeration to say that chromate treatment for galvanized steel sheets (including alloy-plated steel sheets) that has both corrosion resistance and paint adhesion at the same time is extremely rare.
Many of them have excellent corrosion resistance and poor paint adhesion.
On the other hand, those with excellent paint adhesion have poor corrosion resistance.

[Means for solving problems]

It is an object of the present invention to provide a chromate treatment method having a film excellent in metal corrosion resistance and paint adhesion, which solves the above-mentioned drawbacks of the prior art.

That is, the present invention, Cu, Z as a cation in the chromic acid bath
n, Ni, Cd, Pb, Mn, Fe, Co of ions, one or more kinds and _{^{F -, Cl -, SO 4}} -, containing PO ₄ ^--- ions are one or more of And SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ ,
Fe ₃ O ₄ , MgO, ZnO ₂ , Al ₂ O ₃ , TiO ₂ , SnO ₂ colloids (sols) may be contained in one or more kinds, and chromic anhydride, cations, anions and colloids By electrolytically treating the metal as a cathode in a treatment liquid adjusted to have a specific ratio, a film is formed on the metal in a very short time, and corrosion resistance and paint adhesion are significantly improved, It significantly enhances the product value.

First, regarding the corrosion resistance and the coating property, the above-mentioned conventionally known Japanese Patent Publication No. 39-7461, Japanese Patent Publication No. 30-3514, and Japanese Patent Publication No. 35-8917.
No. 36-5959, 36-9560, 39-39
According to the No. 14363 chromate treatment method, if a coating having good corrosion resistance is formed by prolonging the treatment time or the like, the coating property is deteriorated, and if the coating property is improved, the corrosion resistance is conversely deteriorated. On the other hand, the chromate film according to the method of the present invention can simultaneously satisfy the excellent corrosion resistance and the excellent coatability as described above.

This excellent property cannot be obtained when the chromic anhydride bath contains only the above cation, or when it contains only the above anion, or when it contains only the colloid. It is due to the effect.

It has been found that the following relationship must be established among the chromic anhydride, the cation, the anion, and the colloid in this case.

Concentration of chromic anhydride or chromate or dichromate converted to chromic anhydride: 0.05 mol / l ~
5 mol / l and And, And, It was confirmed that when a metal is electrolytically treated with a cathode in a treatment bath satisfying the above conditions at the same time, the resulting coating has a markedly improved corrosion resistance and coating adhesion.

1, 2 and 3 are the above (1), (2) and (3).
4 and 5, the above (1), (2),
The effect of corrosion resistance and paint adhesion of the steel sheet by the treatment of the present invention when the concentration of chromic anhydride was changed by fixing (3) was examined.

That is, the curve (a) in FIG. 1 is 50 g / l of chromic anhydride.
And 0.44 to 44 g / l of cobalt carbonate And further contain chlorine ions in the range of 0.018 to 1.8 g / l. And also add various colloidal silica SiO _2. This shows the change in corrosion resistance when the value is changed.

Curve (b) shows 50 g / l of chromic anhydride and 0.4 of cobalt carbonate.
4 to 44 g / l contained, And also contain chlorine ions of 0-0.018g / l And various colloidal silica (SiO ₂ ) is added, This shows the change in corrosion resistance when the value is changed.

Further, in the curve (c), 50 g / l of chromic anhydride is made to contain 0.44 to 44 g / l of cobalt carbonate, And further contains chlorine ions of 1.8 g / l or more. To more than 0.1, and various colloidal silica added This shows the change in corrosion resistance when the value is changed.

Next, the curves (a), (b), and (c) in FIG. 2 are obtained by adding 50 g / l of chromic anhydride to 0 to 0.44 g / l of cobalt carbonate. And as in Figure 1. Value of 0.001 to 0.1, 0 to 0.001 and over 0.1 respectively,
For each value This shows the change in corrosion resistance when the value is changed.

Next, the curves (a), (b) and (c) in Fig. 3 show that 50g / l of chromic anhydride contains more than 44g / l of cobalt carbonate. And as in Figure 1. And above 0.1 respectively, for each value This shows the change in corrosion resistance when the value is changed.

Then, as is clear from FIG. 1, FIG. 2, and FIG.
For corrosion resistance It shows excellent characteristics for the first time at a specific ratio, that is, the characteristics are that in a chromic anhydride bath, only Co ⁺⁺ ions or only chlorine ions or colloidal silica (Si
Much better than adding O ₂ ) alone, which is an anion (chlorine ion) and a cation (Co ⁺⁺ ion).
This is due to the synergistic effect of colloidal silica (SiO ₂ ).

Next, in FIG. Similar to FIGS. 1, 2, and 3, the changes in the paint adhesion when variously changed are shown.

Curves (a) 'and (b)' in FIGS. 4, 5, and 6
(C) 'is shown in FIGS. 1, 2, 3 (a), (b),
The conditions are the same as in (c).

As is clear from FIG. 4, FIG. 5 and FIG. so And Shows excellent properties.

Next, change the number of moles of chromic anhydride dissolved in FIGS. Shows the corrosion resistance and paint adhesion when Co ⁺⁺ ions, chlorine ions, and colloidal silica are added so that

As is clear from FIGS. 7 and 8, the concentration of chromic anhydride is suitably 0.05 mol / l to 5 mol / l.

Incidentally, FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, and FIG.
The figure shows Co ⁺⁺ ions as metal ions and Cl as anions.
^- ions, but shows the case where the additional inclusion of colloidal (sol) as colloidal silica (SiO _2), including colloidal silica, in the case of the additional inclusion of other colloids, best corrosion resistance, paint adhesion obtained To be What is Table 1 and Table 2 were examined with 0.001 to 0.001.

That, SiO ₂ Tables 1 and 2 are respectively a chromic anhydride _{50g / l, Cr 2 O 3} , Fe 2 O 3, Fe 3 O 4, MgO, ZnO 2, Al
₂ O ₃ , TiO ₂ , SnO ₂ colloid (sol) To contain The following shows the film characteristics when the electrogalvanized steel sheet is subjected to cathodic electrolytic treatment in a treatment bath in which the Co ⁺⁺ ion concentration is changed so that

The electrolysis conditions are: current density 20 A / dm ² , electrolysis time 1 second, bath temperature 45.
℃.

Table 1 shows the relationship between Co ⁺⁺ ion concentration and corrosion resistance. The corrosion resistance shown in Table 1 is the salt rust test according to JIS-Z-2371 standard (saline concentration 5%, bath temperature 35 ° C, spray pressure 20Psi), and the rusting condition after 240 hours can be visually evaluated. ○ 、
Evaluation is made in four grades of Δ and ×, and ◎ is the best.

The paints shown in Table 2 are melamine-based (baking temperature 120 ° C) and acrylic-based (baking temperature 180 ° C) baking paints, and the paint adhesion evaluation method is drawn by JIS-5400.
Each test of impact and 2T bending was performed, and judged by the comprehensive evaluation of these. The evaluation is performed by four-level judgment of ⊚, ○, Δ, and ×, and ⊚ is the best.

Table 2 shows the relationship between Co ⁺⁺ ion concentration and paint adhesion. Incidentally, F in place of the chloride ion ^- ion or SO ₄ ^- ions, even when the additional inclusion of PO ₄ ^--- ions were obtained exactly the same results.

Also, instead of Co ⁺⁺ ions, Cu ⁺⁺ , Zn ⁺⁺ , Ni ⁺⁺ , Cd ⁺⁺ ,
When Pb ⁺⁺ , Mn ⁺⁺ , and Fe ⁺⁺ ions were contained, quite similar results were obtained.

As is clear from FIGS. 1 to 8 and Tables 1 and 2, the chromic anhydride concentration satisfying both corrosion resistance and paint adhesion is 0.05 mol / l to 5 mol / l, It turns out that

It was carried out by incorporating bromine ion, iodine ion, etc. as anions, but there was no effect at all.

At this time, chromic anhydride and chromic anhydride, chromate, can be contained by dichromate, in which case chromate, dichromate is converted to chromic anhydride 0.05%.
It may be contained at up to 5 mol / l.

The cation may be added in the form of carbonate, oxide, hydroxide or organic metal. Further, the anion may be added in the form of a metal salt or an organic substance other than the inorganic acid.

However, in any case, the cation dissociated by addition,
It should be noted that the anion must be contained so as to satisfy the above ratio.

Here, the addition of the colloid (sol) further improves the performance of the chromate film for the following reason.

That is, as in the present invention, when a heavy metal ion and a colloid coexist, the heavy metal ion is adsorbed on the colloid,
The colloid becomes ionized. Therefore, when electrolyzed, the colloid easily co-deposits in the chromate film, and a chromate film in which a colloid completely different from the conventionally known film exists in the film is formed. By forming a film having a structure in which a colloid and a chromate coexist in this way, further excellent performance can be obtained.

The electrolytic treatment conditions in the treatment method of the present invention include a bath temperature of 20 to
80 ° C. is effective, the current density is 0.5 to 120 A / dm ² , the quantity of electricity is 1 C / dm ² or more, and the treatment time is 0.1 seconds or more. As the amount of electricity increases, the corrosion resistance further improves, but the paint adhesion does not change.

An ordinary plating original plate is used after being cold-rolled and then annealed and temper-rolled, but since the oxide film on the surface thereof deteriorates the adhesion of the plating, it is usually degreased, pickled and plated. . However, according to the treatment method of the present invention, it can be directly applied to the ordinary plating original plate without pretreatment of degreasing and pickling.

That is, in the known chromate treatment, if the pretreatment is not sufficiently performed even if a lomo plate is used, a film is not uniformly formed and the adhesion is poor, but in the treatment of the present invention, the corrosion resistance , A film with excellent paint adhesion is produced.

When the plating original plate is subjected to the treatment of the present invention without performing the pretreatment, the cathodic electrolytic treatment is suddenly performed. First dip in the same treatment bath, followed by cathodic electrolysis.
There are methods such as first anodic electrolysis treatment in the same treatment bath and then cathodic electrolysis treatment, but in either case, extremely excellent performance is obtained.

Further, as described above, it has many excellent points such as high-speed processing, pre-processing can be omitted, and the processing apparatus can be extremely compact.

The steel sheet to be treated is cold rolled steel sheet, Zn plated steel sheet or
The chromate film can be easily formed on any material such as Zn-Ni-based, Zn-Ni-Co-based, Zn-Fe-based alloy plated steel sheet or Sn plated steel sheet.

Hereinafter, examples of the present invention will be shown together with comparative examples.

Example 1 A cold rolled steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 50g / l CoCO ₃ 5g / l HCl 0.2g / l Colloidal silica (SiO ₂ ) 1g / l Electrolysis conditions Current density 20 A / dm ² Electrolysis time 1 second Bath temperature 45 ° C. <Example 2> The cold rolled steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 60g / l ZnCO ₃ 5g / l NiCO ₃ 5g / l HF 0.4g / l Colloidal silica (SiO ₂ ) 1.5g / l Electrolysis conditions Current density 40 A / dm ² Electrolysis time 0.5 sec Bath temperature 45 ° C. <Example 3> The cold rolled steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 80g / l NiCO ₃ 10g / l HCl 0.2g / l Al ₂ O ₃ sol 0.7g / l Electrolysis conditions Current density 60 A / dm ² Electrolysis time 0.2 sec Bath temperature 45 ° C. <Example 4> A Zn-plated steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 40g / l CoCO ₃ 5g / l H ₂ SO ₄ 0.5g / l MgO sol 0.5g / l TiO ₂ sol 0.5g / l Electrolysis conditions Current density 80 A / dm ² Electrolysis time 0.2 sec Bath temperature 50 ° C. <Example 5> A Zn-Ni alloy plated steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 100g / l CuCO ₃ 10g / l H ₃ PO ₄ 1.0g / l Cr ₂ O ₃ sol 1.5g / l Electrolysis conditions Current density 100 A / dm ² Electrolysis time 0.1 sec Bath temperature 55 ° C. <Example 6> A Zn-Ni-Co alloy plated steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 50g / l PbCO ₃ 5g / l HCl 0.2g / l ZnO ₂ sol 1.0g / l Electrolysis conditions Current density 40 A / dm ² Electrolysis time 0.4 sec Bath temperature 45 ° C. <Example 7> A Zn-Fe alloy plated steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 50g / l FeCO ₃ 5g / l HCl 0.2g / l Fe ₂ O ₃ sol 1g / l Electrolysis conditions Current density 20 A / dm ² Electrolysis time 1 second Bath temperature 50 ° C. <Comparative example 1> A cold rolled steel sheet was subjected to cathodic electrolysis treatment under the following conditions.

CrO ₃ 50 g / l H ₂ SO ₄ 0.2 g / l Electrolysis conditions Current density 40 A / dm ² Electrolysis time 2 seconds Bath temperature 60 ° C. <Comparative example 2> Commercially available untainted steel of tin-free steel <Comparative example 3> The Zn-plated steel sheet was subjected to cathodic electrolytic treatment under the following conditions.

CrO ₃ 50 g / l H ₂ SO ₄ 0.3 g / l Electrolysis conditions Current density 60 A / dm ² Electrolysis time 2 seconds Bath temperature 55 ° C. <Comparative example 4> A Zn-Ni alloy plated steel sheet was subjected to cathodic electrolysis treatment under the following conditions. .

CrO ₃ 50g / l H ₂ SO ₄ 0.25g / l Electrolysis conditions Current density 50A / dm ² Electrolysis time 2 seconds Bath temperature 60 ° C Table 3 shows the corrosion resistance by salt spray test of each Example and Comparative Example. The paint adhesion is shown in the table.

As is clear from Table 3, when the present invention was carried out on a cold-rolled steel sheet, the corrosion resistance did not change at all in SST48h, and a slight amount (0.01% or less) of red rust was generated in 72h.
When treated with a known chromate bath <Comparative Example 1> or commercially available TFS <Comparative Example 2>, considerable red rust occurred (10% or more) after 6 hours of SST, and 50% or more occurred at 24 hours.

Further, when the present invention was carried out on an electrogalvanized steel sheet, the corrosion resistance was about 0.5% of white rust at SST144h, while when treated with a known chromate bath <Comparative Example 3>, SS
After T72h, white rust had already occurred in 2-3%.

Further, when the present invention is carried out on various alloy-plated steel sheets, corrosion resistance is SST1000h and no rust occurs, whereas when treated with a known chromate bath <Comparative Example 4>, SST400
About 50% of white rust had already occurred at the time point h.

On the other hand, paint adhesion is SPC, electric Zn in the case of implementing the present invention.
It shows excellent paint adhesion irrespective of the material such as plating and various alloy plating, and regardless of the paint, but when the well-known chromate treatment is performed, in the case of high temperature baking type paint, well It shows good paint adhesion, but in the case of low temperature baking type paint, the coating film peels off almost the entire surface.

〔The invention's effect〕

Conventionally, there is no known chromate treatment that sufficiently satisfies both corrosion resistance and paint adhesion. On the other hand, when treated with a bath in which chromic anhydride, a special anion, cation and colloid (sol) are mixed in the ratio of the present invention,
Due to the synergistic effect and the co-deposition of the above four factors, an excellent film is obtained in which extremely excellent corrosion resistance and paint adhesion are obtained at the same time, and by applying the present invention, its economic effect is extremely great. .

[Brief description of drawings]

Figures 1 to 3 are charts investigating the effects of cations, anions and colloids in a chromic anhydride bath on corrosion resistance, and Figures 4 to 6 are coatings of cations, anions and colloids in a chromic anhydride bath. A chart for investigating the influence on the adhesion, and FIGS. 7 to 8 are charts for investigating the influence of chromic anhydride on the corrosion resistance and paint adhesion in a bath in which cations, anions and colloids coexist.

Claims (1)

[Claims] 1. Chromic anhydride or chromate or dichromate converted to chromic anhydride in an amount of 0.05 mol / l to
To 5 mol / l including bath, Cu, Ni, Zn, Fe , Cd, Pb, Mn, ions of Co for the additional inclusion of one or more further Cl ^-, F ^-, SO ₄
^- , PO ₄ ^{--- Contains} one or more ions, and further contains SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZnO ₂ , Al ₂ O ₃ , TiO _2.
2 , one or more kinds of SnO ₂ colloids (sols) are contained, and And, And, The method for chromate treatment of metal, wherein the metal is used as a cathode in the bath.