JPH01202439A - Chromate-treated steel plate - Google Patents

Abstract

PURPOSE:To obtain chemically treated steel plate having chromate film structure, wherein all of the corrosion resistance, adhesion of paint, resistance to fingerprint and color non- uniformity are improved, by a method wherein zinc- or zinc alloy-plated steel plate, onto which specified chromium compound film has been produced, is treated with P- and Si- containing second layer forming processing solution so as to form a second layer. CONSTITUTION:A chromium compound film, which contains 10mg or more of chromium atom per unit square meter of steel plate and in which the hexavalent chromium-total chromium ratio is 0.1 or less, is produced by electrolytically separating chromium from chromium ion-containing water solution onto zinc- or zinc alloy-plated steel plate and rinsing the plate thoroughly. After that, the resultant plate is processed with P- and Si-containing second layer forming processing solution in order to form a second layer, which contains 3mg or more of P+Si per unit square meter of steel plate and in which the P-Si ratio lies within the range of 0.1-10. Further, the essential ingredient of the second layer is organic resin. Furthermore, the content of either P or Si or both P and Si in the second layer becomes effective under the condition that unit square meter of steel plate contains 3mg or more of the total sum of organic resin, Si and P and the organic resin to the sum of Si and P ratio is 0.05 or more. In addition, the content of chromium, which is 20% or less of the total sum of Si, P and organic resin, in the second layer is allowed for the improvement of corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface-treated steel sheet in which a chromate film is formed on a zinc-plated or zinc-based alloy-plated steel sheet.

(Prior Art) If zinc or zinc-based alloy coated steel sheets are used as is, white rust, which is a corrosion product of zinc, will occur during use, impairing the appearance. In order to prevent this, a method is used in which a chromate film containing chromium oxide or hydroxide as a main component is formed on the surface of the plating layer. Known methods for forming a chromate film include electrolytic deposition from an aqueous solution containing chromium ions (electrolytic chromate) and coating and drying an aqueous solution containing chromic anhydride (coated chromate). In general, electrolytic chromate films are mainly composed of trivalent Cr and have low corrosion resistance, whereas coated chromate films are mainly composed of hexavalent Cr and exhibit high corrosion resistance. It is known to incorporate SL, P, or resin into the chromate film in order to obtain higher corrosion resistance and paint adhesion.

For example, as one containing Si,
There are Japanese Patent Publication No. 61-1508, Japanese Patent Publication No. 60-13079, Japanese Patent Publication No. 61-54880, etc. Furthermore, there is Japanese Patent Publication No. 53-41621 which has P added thereto, and Japanese Patent Publication No. 60-18751 which has both Si and P added thereto.

On the other hand, in recent years, steel sheets used for home appliances, office equipment, etc. are zinc or zinc-based alloy coated steel sheets, either unpainted or coated. In other words, the properties required for the steel plate are:
These include corrosion resistance and appearance without painting (two-color unevenness), resistance to fingerprints during product manufacture and use, and adhesion of paint when painted.

For a long time, chromate films formed by chromic acid treatment simply provided corrosion resistance, but as the various properties mentioned above became required, Si, P, and metal ions were added to the treatment solution. , In order to further improve fingerprint resistance,
JP-A-61-207579, JP-A-59-140050
Organic resins have started to be added, as shown in, for example.

(Problem to be solved by the invention) However, none of the above-mentioned conventional technologies can completely satisfy all required performances, but only by balancing some performances. .

In particular, when used unpainted, coated chromate based on hexavalent chromium is poor, while electrolytic chromate based on trivalent chromium is better.

However, as mentioned above, electrolytic chromate has low corrosion resistance,
Coated chromate exhibits higher corrosion resistance, making it difficult to achieve both performance.

In view of the above points, the present invention aims to improve the corrosion resistance of chromate coatings on galvanized and zinc-based alloy coated steel sheets.

The object of the present invention is to provide a chemical conversion treated steel sheet having a chromate film structure that improves paint adhesion, fingerprint resistance, and two-color unevenness.

(Means for Solving the Problems) The above object can be advantageously achieved by forming a film having the structure shown below on a zinc or zinc-based alloy plated steel sheet. That is, chromium is electrolytically deposited on a zinc or zinc-based alloy coated steel sheet from an aqueous solution containing chromium ions, and thoroughly washed with water to obtain a concentration of 10 mg/rd or more as chromium atoms.
After generating a chromium compound film in the range of hexavalent chromium/total chromium≦0.1, it is treated with a second layer forming treatment solution containing P and SL to achieve P+Si≧3 mg/rn', P
This is a chromate-treated steel sheet characterized by forming a second layer in the range of /5L=0.1''IO.

In addition, the second layer contains an organic resin (water-soluble or water-dispersible).
organic resin + Si + P≧3mg/n? , organic resin/(SL+
It is also effective to include the range of P)≧0.05.

In order to further improve corrosion resistance, Si is included in the second layer.

There is no problem in containing Cr in an amount of 20% or less based on the total amount of P and organic resin.

(Function) In developing the present invention, one of the inventors conducted a detailed study on how the above-mentioned performances are affected by the constituent components of the film. As a result, although Cr is effective for corrosion resistance, it tends to cause color unevenness, which impairs the appearance. It is also disadvantageous in terms of paint adhesion and fingerprint resistance. Although Si is particularly effective in improving paint-substance adhesion, it is disadvantageous in terms of paint-substance adhesion and fingerprint resistance. It has also been found that P is advantageous in corrosion resistance and fingerprint resistance, but disadvantageous in paint-substance adhesion, and that organic resins exhibit properties between those of Si and P for both. Paint-adhesion refers to the adhesion between the paint and the surface of the steel plate immediately after it has been applied.
The evaluation was made based on the number of -f holes that were peeled off when 100 (10' x 10) incisions were made with an adhesive tape. (Goban tape method) Secondary paint adhesion refers to the paint adhesion after a painted steel plate is aged in a certain environment, and in the present invention, after being kept in a 100% humidity tank for one week, This was evaluated using the goban tape method.

If we carefully consider the details of the various performances, we can see that corrosion resistance, two-color unevenness, etc. are the performance of the entire chromate film, while paint adhesion and fingerprint resistance are the performance of the outermost layer of the film. Conceivable. In other words, the outermost layer should have a structure that is advantageous for paint adhesion and fingerprint resistance, and the inner layer should have a structure that has excellent corrosion resistance for paint adhesion.

It should be possible to satisfy both fingerprint resistance and corrosion resistance.

If corrosion resistance is important, the inner layer may be made of chromate mainly composed of hexavalent chromium, but in this case the appearance will be poor. Therefore, the inventors deposited an electrolytic chromate layer mainly composed of trivalent chromium in the inner layer and thoroughly washed it with water to remove as much of the hexavalent Cr as possible. By producing the second M), the paint has sufficient corrosion resistance and appearance as a whole.
This product succeeded in improving all of the secondary adhesion, secondary paint adhesion, and fingerprint resistance.

The -th layer is a layer for ensuring corrosion resistance, so it is made of electrodeposited Cr.
The amount of is required to be 10 mg/M or more. Any aqueous solution containing chromic anhydride and anions such as SO2''-, C1-, Po, and 3- can be used as the electrodeposition bath, but when analyzed by xPS, the deposited film is mostly composed of trivalent Cr. Formed from oxides or hydroxides.

Since hexavalent Cr contained in the electrodeposition bath is attached to the outermost layer, it is preferable from the viewpoint of appearance to thoroughly wash it with water so that hexavalent Cr/total Cr≦0.1.

The second layer is paint-secondary adhesion, paint secondary adhesion.

Although this layer is for maintaining fingerprint resistance, it also needs to have a function that supplements the corrosion resistance of the second layer. That is, the second layer is P
When composed of and Si, it is necessary that P+Si≧3111g/♂, and if it is less than that, the corrosion resistance will be insufficient. If P/Si is less than 0.1, the secondary paint adhesion and fingerprint resistance will be poor, and if it exceeds 10, the secondary paint adhesion will be poor. When the second layer contains an organic resin, in order to ensure corrosion resistance, organic resin + Si + P≧3mg/rr? If it is less than that, corrosion resistance will be insufficient. The organic resin has the role of supplementing the secondary paint adhesion and fingerprint resistance of Si, and the secondary paint adhesion of P. In other words, the performance required for the second layer (paint -
Next adhesion.

Regarding secondary paint adhesion and fingerprint resistance), Si
It has intermediate properties between and P, and alleviates the weaknesses of each.

Therefore, when emphasis is placed on paint-substance adhesion, organic resin and S
i. If secondary paint adhesion and anti-fingerprint properties are important, it is best to use a combination of organic resin and P. Organic resins are useful for improving the corrosion resistance of the film as a whole. By using a ternary system of organic resin, Si, and P, it is possible to balance all required performances. The required amount of organic resin must be organic resin/(Si+P)≧0.05 and 0.0
If it is less than 5, no effect of the organic resin on improving corrosion resistance will be recognized. When containing Si, the ratio of organic resin/Si must be 0.05 or more and 10 or less. If it is less than 0.05, there will be no effect on corrosion resistance, and if it is more than 10, the adhesion between paint and paint, which is an advantage of corrosion, will decrease. When containing P, organic resin/P
must be greater than or equal to O,OS and less than or equal to 20.

If it is less than 0.05, there is no effect on corrosion resistance, and if it is more than 20, the fingerprint resistance, which is an advantage of P, decreases.

Regardless of the presence or absence of organic resin in the second layer, inclusion of a small amount of Cr is effective for improving corrosion resistance. However, it lowers all of the paint-substance adhesion, the post-paint adhesion, and the fingerprint resistance. Therefore cr/(P+Si) or Cr/
(Amount of organic resin P+Si) must be 0.2 or less, and if it exceeds 0.2, the above-mentioned properties necessary for the second layer will deteriorate significantly in any case. In applications where the requirement for corrosion resistance is relatively small, it is more preferably 0.1 or less.

A known method for depositing an electrodeposited chromate layer is to dissolve chromic anhydride to form hexavalent Cr ions, and to perform electrolytic deposition from an aqueous solution containing sulfate ions, fluorine ions, carbonate ions, etc. as anions.

For example, JP-A-61-73893, JP-A-60-1282
68 etc. An example of adding cationic colloidal silica as an additive to an electrolytic solution (Special Publication No. 6l-548)
80) Examples of adding metal ions and chlorine ions
2-31393). In the present invention, since it is not intended to satisfy all required performance with only the electrolytic chromate layer, Cr oxide or hydroxide is
Any aqueous solution and electrolytic conditions may be used as long as it is mg/rn' or more. In order to wash and remove attached hexavalent Cr, methods such as water spraying and immersion in water are possible, and it becomes even more efficient if the water temperature is set to 40° C. or higher.

The second layer is applied by dipping and roll coating immediately after the first layer is formed.

All application methods such as spray application can be applied.

Si can be obtained by dissolving or dispersing silica powder, colloidal silica, a silane coupling agent, and various silicates in water, and P can be obtained by dissolving or dispersing silica powder, colloidal silica, silane coupling agents, and various silicates in water, and P is phosphoric acid or polyphosphoric acid.

A second layer forming treatment solution can be easily created by adding phosphate to water.

Any organic resin that is water-soluble or water-dispersible can be used. - For boat fishing, increase affinity with water by bonding hydroxyl and carboxyl groups to the molecular chain.
Often water-soluble or water-dispersible. Patent Publication No. 61-287 using polyvinyl alcohol as a patent example
51, Special Publication Showa 6 using carboxylated polyethylene
0-33192, JP 60-149726, JP 62-50479 using carboxylated polyolefin
, Japanese Patent Publication No. 50-6417 using maleic anhydride or maleic acid copolymer. It can be assumed that all of these become chemically stable and hard films after heating and drying, making it difficult for fingerprints to adhere to them.

The chemical conversion treatment of the present invention can be applied to all steel sheets whose outermost layer is plated with zinc or zinc-based alloy. Galvanizing includes all electrolytic galvanizing, hot-dip galvanizing, and vacuum-deposited galvanizing. Zinc-based alloy plating refers to all alloy plating containing zinc and one or more other metals, such as zinc-nickel, zinc-iron, and zinc-aluminum, as well as metal oxide plating such as silicon, titanium, aluminum, and chromium. It includes all the particles dispersed in the layer. Even in the case of having a plurality of plating layers, it can be applied as long as the uppermost layer is a plating layer containing the above-mentioned zinc. It can also be similarly applied to composite steel plates that are plated on one side or have a resin between them.

[Example 1] Electrogalvanized steel sheet (zinc coating amount 20g/rr?)
in an aqueous solution of chromic anhydride 50 g/Q and sulfuric acid 0.3 g/Q (1) Current density 5 A/dI11
” 0.06 seconds (2) Current density 5
A/dm20.12 seconds (3) Current density 5 A
/dm20.24 seconds (4) Current density 2.7A/
dm20.44 seconds (5) Current density 1.2A/d
m21.00 seconds (6) Current density 0.7A/dm
5-20 mg/m after electrolytic treatment under the conditions of 21.71 seconds
For (1) to (3), Cr was electrolytically deposited in 60°C hot water for 5 minutes (4) for 3 minutes (5) for 1.5 minutes (6) for 10 seconds After washing with water, colloidal silica 1 note Table 1 shows the results of evaluating the corrosion resistance of materials that were immersed in an aqueous solution, pulled up, and then dried (130°C, 2 minutes).

From Table 1, it can be seen that in order to ensure corrosion resistance, the amount of Cr deposited in electrolytic chromate should be 10 mg/rrr or more, and in order to ensure good appearance, Cr' /total Cr should be 0.1 or less.

[Example 2] Electrolytic galvanized steel sheet (20 mg/g of electrolytic Cr was deposited using the same method as in Example 1 (3) on an electrolytic galvanized steel sheet (zinc coating amount: 20 g/n ( )), and spray washing was performed with warm water at 60°C for 5 minutes. After that, (7) Colloidal silica 1.8g#L
Phosphoric acid 1.2g/Q(8) Colloidal silica
3.6g/Q Phosphoric acid 1.2g/Q(9)
Colloidal silica 1.8g/Q Phosphoric acid 2.4g/fl(10) :IO Ida) Ii ShiIJ
Force 3.6g/Q) J lua 2.4gI
Q(11) Colloidal silica 25 gIQ
Phosphoric acid 1, 2gIQ (12) Colloidal silica 18 r,IQ Phosphoric acid 1, 2
g/Q (13) Colloidal silica 18 gIQ
Phosphoric acid 12 gIQ (14) Colloidal silica 1.8gIQ Phosphoric acid 12 g/l
2 (15) Colloidal silica 1, 8g/Q
Table 2 shows the results of evaluating the performance of materials that were immersed in an aqueous solution containing 15 g IQ of phosphoric acid, pulled up, and then dried (130°C, 2 minutes). From this result, P+Si
must be 3 mg7 m or more. P/
It can be seen that Si is preferably 0.1 or more and 10 or less.

[Example 3] Electrolytic galvanized steel sheet (zinc coating amount 20 g/r&) was subjected to electrolytic chromate treatment in the same manner as in (3) of Example 1 (16) Colloidal silica 1, 8 g/ρ, Acrylamide resin 0 .2g/Ω (17) Rin @1.2g
/Q, Acrylamide resin 0.2g IQ (18) Colloidal silica 3.6g IQ, Acrylamide resin 0.2g #1 (19) Colloidal silica 1.8g #l,
Phosphoric acid 1.2g/Q Acrylamide resin 0.2gIQ (20) Colloidal silica 3.6gIQ, Ri
Acid 2.4g/Q acrylamide resin 0.2g
IQ (21) Colloidal silica 9 g/11. Li
Acid 7.5g/Ω Acrylamide resin 0. I
g/Q (22) Colloidal silica 9 gIQ, Li
Acid 6 g IQ acrylamide resin 0.1 g
IQ (23) Colloidal Silica 9 gIQ, Li
Acid 6 g IQ acrylamide resin 0.2 g
Immerse in an aqueous solution containing IQ, pull up, and dry (130℃, 2 minutes)
Table 3 shows the results of evaluating the performance of the materials.

From these results, it can be seen that organic resin+Si+P is required to be 3 g/rrf or more, and organic resin/(Si+P) is preferably 0.05 or more.

, [Example 4] Electrolytic galvanized steel sheet (zinc coating amount 20 g/m) was subjected to electrolytic chromate treatment in the same manner as in Example 1 (3) (24) Colloidal silica 36 g IQ, Acrylamide resin 0.08 g /Q(25) Colloidal silica 36
gIQ, acrylamide resin 0.2 gIQ (26
) Colloidal silica 36 gIQ, acrylamide resin 40 gIQ (27) Colloidal silica 36 gIQ
, acrylamide resin 50 gIQ (28) phosphoric acid 24 gIQ, acrylamide resin 0.0
8g/Q (29) phosphoric acid 24g/ρ, acrylamide resin 0.2g/Ω (30) phosphoric acid
24 gIQ, acrylamide resin 40 gIQ (3
1) Immerse in an aqueous solution containing 24 gIQ of phosphoric acid and 50 gIQ of acrylamide resin, pull up and dry (
Table 4 shows the results of the performance evaluation of the materials heated at 130° C. for 2 minutes.

From this result, both organic resin/Si and organic resin/P are 0.
．． It can be seen that it must be in the range of 05-10.

[Example 5] After electrolytic chromate treatment was applied to an electrogalvanized steel sheet (zinc coating amount 20 g/m) in the same manner as in Examples 1 and (3), colloidal silica 18 gIQ,
Acid 12 gIQ Chromic anhydride 2.5
g/u (33) Colloidal Silica 18 gIQ, Li
Acid 12 gIQ Chromic anhydride 3.3
gIQ (34) Colloidal Silica 18 gIQ, Li
Acid 1.2 gIQ Chromic anhydride 5
gIQ (35) Colloidal Silica 18 gIQ, Li
Acid 12 g IQ acrylamide resin 1 g
/Q, chromic anhydride 3.3gIQ (36) colloidal silica 18g/fl, phosphoric acid 12g/Q acrylamide resin 1g/Q,
Chromic anhydride 4.2gIQ (37): to idarushiri force 18g#! , phosphoric acid 12
Table 5 shows the results of performance evaluation of the material that was immersed in an aqueous solution containing 1 g IQ of g#1 acrylamide resin and 6.3 g/Q of chromic acid anhydride, pulled up and dried (130° C., 2 minutes).

From this result, when the second layer does not contain an organic resin, the second layer is Cr/(P + Si), and when it contains an organic resin, the second layer is Cr/(P + Si).
It can be seen that (organic resin + P + Si) must all be 0.2 or less.

9gj1 Table 2 Table 3 Table 5 [Effects of the invention] The present invention separates the first layer and the second layer to share their functions, and collectively improves corrosion resistance, paint adhesion, and fingerprint resistance. We provide superior chromate treated steel sheets for all types of products.

Claims (1)

[Claims] 1. Chromium is electrolytically deposited on a zinc or zinc-based alloy coated steel sheet from an aqueous solution containing chromium ions, and thoroughly washed with water to give a concentration of 10 mg/m^2 or more as chromium atoms, hexavalent chromium/total After generating a chromium compound film in the range of chromium≦0.1, it is treated with a second layer forming treatment solution containing P and Si to form a chromium compound film with P+Si≧3mg/m^2P/Si=0.1-1
A chromate-treated steel sheet characterized by forming a second layer in a range of 0. 2. Chromium is electrolytically deposited on a zinc or zinc-based alloy coated steel sheet from an aqueous solution containing chromium ions, and thoroughly washed with water to obtain a chromium concentration of 10 mg/m^2 or more as chromium atoms, hexavalent chromium/total chromium ≦0.1. After forming a chromium compound film within the range, the organic Resin + Si + P
≧3mg/m^2, organic resin/(Si+P)≧0.05
Furthermore, when containing Si, organic resin/Si=0.05 to 10 When containing P, organic resin/P=0.05 to 20. A chromate-treated steel sheet. 3. Cr/(P
Chromate-treated steel sheet according to claim 1, characterized in that the content is in the range of +Si)≦0.2. 4. The chromate-treated steel sheet according to claim 2, wherein the second layer contains a Cr compound as Cr atoms in the range of Cr/(organic resin+P+Si)≦0.2.