JPS6250480A - Production of zn alloy plated steel sheet having excellent corrosion resistance, paintability, solvent resistance, alkali resistance and fingerprint resistance - Google Patents

Abstract

PURPOSE:To improve corrosion resistance, paintability, solvent resistance, alkali resistance and fingerprint resistance by coating an aq. soln. of a specific compsn. contg. a carboxylated polyolefin resin on a Zn alloy having a chromate film and drying the coating. CONSTITUTION:The chromate film of 5-200mg/m<2> Cr deposition is formed on the surface of the Zn or Zn alloy plated steel sheet. An aq. soln. of the compsn. contg. 5-50pts.wt. liquid epoxy resin and 5-60pts.wt. colloidal silica in solid content in 100pts.wt. in solid content of water soluble or water dispersible resin of carboxylated polyolefin contg. 3-20mol% -CH2H is coated thereon. The coating is dried at >=60 deg.C sheet temp. to form the film and is so treated that the deposition thereof is 0.3-3g/m<2>. The Zn or Zn alloy plated steel sheet having the excellent corrosion resistance, paintability, solvent resistance, alkali resistance and fingerprint resistance and having the weldability as well is thus obtd.

Description

[Detailed Description of the Invention] <Industry> Second Field of Application The present invention has excellent corrosion resistance, paintability, solvent resistance, alkali resistance, and fingerprint resistance, and is used in home appliances, building materials, etc.
This invention relates to an n- or Zn-based alloy plated steel sheet.

<Prior art and its problems> Zn or Zn-based alloy coated steel sheets used in home appliances and building materials products are used unpainted or painted, but they have gone through various stages before then, and during that time, It is left unpainted for quite some time. Therefore, there are problems such as rust occurring during this time, and various substances adsorbing or adhering to the surface of the plated steel sheet, resulting in poor adhesion of paint.

Therefore, chromate treatment is generally applied to Zn or Zn-based alloy plated steel sheets as a primary rust preventive measure until they are used by consumers. However, the corrosion resistance of this chromate treatment is generally about 24 to 48 hours in a salt spray test, and
As a special chromate, even a coated chromate with silica sol added can only provide corrosion resistance of 100 to 200 hours in a salt spray test, which is insufficient for a product used in a severe corrosive environment for a long period of time.

When used in such a severe corrosive environment, phosphate treatment should be applied instead of chromate treatment.
- There is a method of applying a thick coating to prevent corrosion, but if such a thick coating is applied, the coating may peel or crack during processing such as pressing, and the corrosion resistance may be localized in that area. This results in a decrease in

In addition, with painted plates, welding such as spot welding is impossible, and the paint film must be removed from the welded areas in advance. Furthermore, there is also the problem that the thicker the coating film, the higher the cost of the coating material, and efforts have been made to develop Zn-based plated plates that have excellent corrosion resistance without the use of coating materials.

Furthermore, when products are manufactured by customers through various processes using conventional Zn-based plated steel sheets, fingerprints and other stains adhere to the surface of the plated steel sheets due to handling by workers, which significantly reduces the product value. Therefore, it is desired to develop a Zn-based plated steel sheet that is less susceptible to fingerprints and other stains during handling.

Furthermore, degreasing treatment is always performed in the process of producing hk final products. The degreasing treatment is generally carried out by organic solvent degreasing or alkaline degreasing. Hence, solvent resistance.

There is a high demand for Zn-based plated steel sheets with excellent alkali resistance.

For this purpose, as conventional technology, a) Japanese Patent Application Laid-open No. 5
7-185987, mouth) Japanese Patent Application Publication No. 58-100685, c) 41F opening/closing 58-153785゜2) Japanese Patent Application Publication No. 1977-100685
-177476, e) JP-A-59-189975, f) JP-A-59-140050゜1.) JP-A-60-50179, etc.

b) Polyacrylic acid and CrO3 on the chromate film
Simply applying a mixture of 41 to 100% gives insufficient corrosion resistance, with a salt spray test of about 150 hours.

(1), (3), (2), and (e) are similar to the present invention in that carboxylated polyethylene resin is used, but these treatments do not allow dry explosion in the final process to reach a board temperature of 130°C or higher. requires heating, making online processing in a plating line impossible. When processing, it must be carried out on a painting line, which has the disadvantage of increasing processing costs.

f) and g) are possible at a final drying temperature of 100°C or less;
Although these methods are excellent in that they have good corrosion resistance, both have poor corrosion resistance, and the film dissolves or swells during the organic solvent degreasing process, resulting in a decrease in corrosion resistance or adhesion between plates. It has some limitations and drawbacks.

<Object of the Invention> The object of the present invention is to improve the shortcomings of conventional Zn-based plated steel sheets, to provide a steel sheet with excellent corrosion resistance, paintability, solvent resistance, alkali resistance, and finger wring resistance, as well as weldability. It is an object of the present invention to provide an improved Zn or Zn-based alloy plated steel sheet having the following properties.

<Structure of the Invention> As mentioned above, some conventional technologies have properties such as excellent corrosion resistance and low drying temperature, but those that perform low temperature drying have excellent corrosion resistance, solvent resistance, alkali resistance, and There is no established technology that has properties such as finger wringability and weldability.

The inventors of the present invention have made extensive studies to comprehensively provide the above-mentioned performance, and in particular have proceeded with the development of a processing agent that can provide performance at a drying temperature of 100° C. or lower.

As seen in the prior art, corrosion resistance can be improved by forming a water-based resin film on a Zn or Zn-based alloy plated steel sheet after chromate treatment. With reference to these conventional technologies, the present inventors have conducted intensive research into resin systems that can be dried at low temperatures, have excellent solvent resistance, and alkalinity.As a result, the inventors have found that by mixing liquid epoxy resins with carboxylated polyolefin resins, low-temperature drying is possible. It has been found that drying is possible and a film with excellent solvent resistance and alkali resistance is formed. Furthermore, the present inventors have discovered that corrosion resistance and fingerprint resistance can be improved by adding colloidal silica to a carboxylated polyolefin resin-epoxy resin mixed system.

That is, in the present invention, a chromate film having a chromium adhesion amount of 5 to 200 mg/m' is formed on the surface of a Zn or Zn-based alloy plated steel sheet, and 3 carboxyl groups are added on the chromate film.
Contains 5 to 50 parts by weight of liquid epoxy resin and colloidal silica in a solid content of 5 to 60 parts by weight per 100 parts by weight of solid content of carboxylated polyolefin water-soluble or water-dispersible resin containing ~20 mol%. Corrosion resistance, paintability, characterized by applying an aqueous solution of the composition, drying to a board temperature of 60°C or higher to form a film, and treating it so that the amount of adhesion is 0.3 to 3g1rr1'. The present invention provides a method for producing a Zn-based alloy plated steel sheet having excellent solvent resistance, alkali resistance, and fingerprint resistance.

The present invention will be explained in more detail below.

The present invention aims to improve the corrosion resistance of Zn or Zn-based alloy plated steel sheets,
The present invention relates to a surface treatment method that dramatically improves paintability, solvent resistance, alkalinity, fingerprint resistance, and weldability.

The Zn- or Zn-based alloy-plated steel sheets that are the object of the present invention include electrolytic Zn-plated steel sheets, electrolytic Zn-Ni alloy-plated steel sheets, electrolytic Zn-Fe alloy-plated steel sheets, and Zn-Fe alloy-plated steel sheets.
o-Mo alloy plated steel plate, hot dip Zn plated steel plate, hot dip 5
Examples include, but are not limited to, Zn-plated steel sheets.

In addition, chromate treatment can be carried out by the usual treatment methods, such as immersion chromate treatment in an aqueous solution containing chromic anhydride, chromate, dichromate, etc. as the main ingredient, electrolytic chromate treatment, and mixing of colloidal silica, etc. with these solutions. This is a coating-type chromate treatment in which a liquid is applied to form a film mainly composed of hydrated chromium oxide on the plating layer.

The appropriate amount of chromium adhesion is about 5 to 200 mg/m'; if it is less than 51 g/m', sufficient corrosion resistance cannot be obtained, and if it exceeds 200 IIg/m', chromium adhesion may occur.
Compared to this, the effect of improving corrosion resistance is small, the treatment solution ages rapidly, and the surface appearance also deteriorates.

The top coat applied to the chromate-treated surface is made by adding 5 to 50 parts by weight of a liquid epoxy resin to 100 parts by weight of a solid content of a carboxylated polyolefin water-soluble or water-dispersible resin containing 3 to 20 mol% of carboxyl groups. An aqueous solution containing colloidal silica in a solid content range of 5 to 60% is applied and dried to a plate temperature of 60° C. or higher to form a film. The amount of adhesion is 0.3-3 g
/m'.

If the carboxylation rate of the carboxylated polyolefin resin is lower than 3 mol %, the polyolefin resin cannot be emulsion polymerized, and the liquid epoxy resin cannot be emulsified, and film adhesion deteriorates. If more than 20 mol % of carboxy groups are introduced, the water solubility will increase, the water permeability of the film after drying will increase, and the corrosion resistance will decrease.

Next, the reason why 5 to 50 parts by weight of liquid epoxy resin is added and mixed will be described. If the amount is less than 5 parts by weight, the film will not dry at a drying temperature of 100° C. or lower, and stickiness will remain on the surface. In addition, corrosion resistance and solvent resistance deteriorate due to insufficient crosslinking of the film. If it exceeds 50 parts by weight, the drying properties of the film will be poor, and corrosion resistance and solvent resistance will be poor when drying at low temperatures.If the drying temperature is increased and sufficient crosslinking is performed, the film hardness will increase and cracks may occur in the film during processing. corrosion resistance is significantly reduced.

Next, the reason why colloidal silica is added and mixed in the range of 5 to 60 parts by weight will be described.If the amount is less than 5 parts by weight, the fingerprint resistance will be insufficient and the corrosion resistance will also deteriorate. If it exceeds 60 parts by weight, weldability will deteriorate significantly.

As a carboxylated polyolefin resin.

Examples include water-dispersible or water-soluble carboxylated polyethylene, carboxylated polypropylene, carboxylated polybutylene, and the like.

As liquid epoxy resins, the product names (Shell Chemical ■) are Epicote 812, Epicote 815, and Epicote 81.
9. Epicoat 827, 2-pint 828. Epicote 832, Epicote 834, Epicote 871, Epicote 872, etc. can be used, and products equivalent to these can be used.

Examples of colloidal silica include Snowtex-0, Snowtex-N, and Snowtex- manufactured by Nissan Chemical ■.
20, Snowtex-30, etc. can be used.

The reason why the coating amount is specified as 0.3 to 3 g/n1' is that if it is less than 0.3 g/m', the unevenness of the Zn crystal cannot be completely filled and the effect of improving corrosion resistance and fingerprint resistance is small. m
If it exceeds l, the corrosion resistance is greatly improved, but weldability deteriorates and it is not economical.

<Examples> Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

(Examples 1 to 24) Using the following test materials, chromate treatment and resin film treatment were performed as follows. (1) Test materials (type of plated sheet) A: Electrolytic Zn-plated steel sheet Zn adhesion is 20 g/m' Plate thickness 0, 8 mm B: Electrolytic Zn-Ni plated steel plate Coating amount 20 g
/m' Plate thickness 0.8mm Ni content 12%C: Hot-dip Zn-plated steel plate Zn adhesion% 60g/m2 Plate thickness 0.8
mm (2) Chromate treatment: CrO320gIn, Na2AuF
A chromate treatment solution containing 64 g of In was sprayed, squeezed with a flat rubber roll, and dried with hot air.

The amount of chromium deposited is 5-200II1g depending on the spray treatment time.
/m' as shown in Table 1.

(3) Resin film treatment The resin film was treated using the treatment liquid composition, coating amount (dry weight), and drying temperature shown in Table-1.

(Comparative Example 1) A coating type chromate treatment liquid was applied to sample material A with a Cr adhesion ψ of 60
mg/m' and dried.

Chromate treatment liquid composition is CrO320g/Ai, 510
It was 240g/statement.

(Comparative Example 2, 3.4) Sample material A was subjected to the same chromate treatment as described in Example (2), and the acrylic composite silicate and epoxy used in JP-A-60-50179-2 were treated. An organic composite silicate treatment solution prepared by mixing composite silicate (organic resin: silicone = 60:40) at a ratio of 70:30 was mixed at 600.1000.1500 rag/m' (
After drying, the coating was applied and dried at 120°C.

(Comparative Example 5, 6.7) Sample material B was treated in the same manner as in Comparative Examples 2 and 3.4.

(Comparative Example 8) Sample material A was treated with C by the chromate treatment described in Example (2).
The solid content of a carboxylated polyethylene resin dispersion containing 12 mol% of carboxyl groups with a r41 density of 40 mg/m' and 2 parts of a water-soluble melamine resin as a solid content of 15 An aqueous solution containing 20 parts by weight of colloidal silica as a solid content was applied and dried. The board temperature at the time of drying was 90°C, and the amount of film deposited was 2y,/rrT'.

The performance test method and evaluation method are as follows.

(1) 1 Corrosion resistance Expressed as white rust generation time according to salt spray test (JIS Z-2371).

(2) Paintable acrylic paint (Sparac F47 manufactured by Nippon Paint Co., Ltd.
) For coating thickness 30, dry at 50℃ for 20 minutes ■ Paint! 2. Adhesion After cutting 100 squares of 1 mm square to reach the steel plate base with a cutter knife, extrusion was performed for 7 times using an Erichsen tester, the convex portions were peeled off with tape, and the number of remaining coating films was evaluated.

@ After painting, a cross-cut was made in the corrosion-resistant paint film until it reached the base steel plate using a cutter knife, and a water spray test was conducted, and the degree of paint film blistering at the cross-cut portion was evaluated. Test time is 500 hours
It was r.

■ Paint film bulge width 1.5 mm or less O Paint film bulge width 1.8 to 2.5 m layer Δ Paint film bulge width 2.6 to 3.5 ■ × Paint film bulge width 3.6 m or more (3) Solvent resistant A rubbing test was performed using absorbent cotton impregnated with acetone.

No change in O × Dissolution (4) Alkali resistance A 3% NaOH solution was heated to 60° C., immersed in this solution for 3 minutes, washed with water and dried, and the remaining amount was calculated from the amount of coating before and after treatment.

The coating amount was measured by C count using an X-ray microanalyzer.

(5) Wet the #fingerprint rubber stopper with an artificial juice solution (liquid containing NaCJl, lactic acid, urea, and lanolin), strongly stamp it on the plating surface, and evaluate the degree of remaining adhesion of the stamp mark of the artificial juice solution according to the following ranks. did.

■ No stamp marks left at all Very slight traces of the O stamp remain. Δ　Slight stamp marks remain × Stamp marks remain clearly (6) Weldability Continuous spot welding conditions Welding current 9500A Pressure force: 250K.

Electrode　Cr-CuCF type　6■φ Welding time 8Hz The number of consecutive hits was measured under the above conditions.

Number of continuous welding points = Number of welding times until normal nugget formation is no longer possible with one pair of electrodes and the steel plate and electrode are welded - IT Example processing conditions table - 2 Comparative example processing conditions book Carboxylated polyethylene resin desversion Solid content: 100 parts by weight Water-soluble melamine resin Solid content: 15 Jushuto colloidal silica Solid content: 20 parts by weight Table-3 Performance test results of Examples Table-4 Performance test results of comparative examples <Effects of the invention> Zn or Zn according to the present invention Compared to conventional Zn or Zn alloy-plated steel sheets, Zn-based alloy-plated steel sheets can be dried at low temperatures to provide treated films with excellent corrosion resistance, #solvent resistance, and alkali resistance, and eliminate the need for major equipment modifications on the Metsuki line. It can be easily manufactured.

In conventional organic coatings, a drying temperature of at least 100° C. or higher (attaining plate temperature) is required to obtain solvent resistance and alkali resistance, but in the present invention, a drying temperature of 60° C. or higher is sufficient. "Line production" 2L Lowering the temperature from 0°C to 60°C is a huge advantage in terms of drying equipment and energy costs.

Even with similar organic treatments, corrosion resistance, solvent resistance, and alkali resistance are significantly improved compared to conventional treatments, and the fields of use by users have expanded. Conventional products had to be used in limited fields and had to be handled carefully because they could not be degreased.

The present invention is resistant to stains caused by fingerprints etc. during handling.
Moreover, even if oil is applied by pressing or the like, degreasing treatment can be performed in the end. The degreasing treatment can also be carried out using organic solvents, alkali degreasing, or the like.

Moreover, Spon) Welding i! I! The number of consecutive hits is also the same as that of conventional Zn.
Performance equivalent to or better than plated steel sheets can be obtained.

As described above, the uninvented product is easier to manufacture than conventional products, and has significantly superior corrosion resistance, paintability, and solvent resistance.
Zn or Zn with alkali resistance and fingerprint resistance
can provide alloy-plated steel sheets.

Claims (1)

[Claims] A chromate film with a chromium adhesion amount of 5 to 200 mg/m^2 is formed on the surface of a Zn or Zn-based alloy plated steel sheet, and a water-soluble or carboxylated polyolefin containing 3 to 20 mol% of carboxyl groups is applied thereon. 5 to 50 parts by weight of liquid epoxy resin and 5 to 50 parts by weight of colloidal silica to 100 parts by weight of solid content of water-dispersible resin.
An aqueous liquid having a composition in the range of 60 parts by weight is applied, and the plate temperature is 6.
Corrosion resistance, paintability, solvent resistance, alkali resistance and A method for manufacturing a Zn-based alloy plated steel sheet with excellent fingerprint resistance.