JPH11216801A - Precoated metallic sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve weatherability, processability, and corrosion resistance in a processed part, and to prevent environmental pollution at the time of disposal by forming, on a surface-treated metallic sheet, an undercoat layer of a resin coating containing a rust preventive pigment, an intercoat layer of a high-molecular resin coating having specifie molecular weight, and a topcoat layer of a resin coating so that each coating has a specific thickness. SOLUTION: A resin coating containing a rust prevention pigment is applied on the surface of a surface-treated metallic sheet 1 to form an undercoat layer 2 having 2-15 μm thickness, and a high-molecular resin coating having number- average molecular weight of 5,000 or higher is applied thereon to form an intercoat layer 3 having 10-30 μm thickness, and a resin coating is coated thereon to form a topcoat layer 4 having a thickness of 7-30 μm. A backcoat layer 5 is applied on the back side of the metallic sheet 1 for corrosion prevention. The metallic sheet 1 is subjected to the surface treatment by chromate treatment or the like before applying coating. The undercoat layer 2 is formed of an epoxy resin coating or the like, the intercoat layer 3 is formed of a high- molecular polyester resin coating, and topcoat layer 4 is formed of an acrylic resin coating, where each coating is applied by a roller to be baked and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated metal sheet having particularly excellent corrosion resistance in a processed portion.

[0002]

2. Description of the Related Art Conventionally, there are various types of precoated metal plates.
(I) acrylic resin-based paint, polyester resin-based paint,
A weather-resistant exterior pre-coated metal plate coated with a silicone resin-based paint, a fluororesin-based paint, etc., (ii) a pre-processed metal plate coated with a high-molecular-weight polyester resin-based paint, and (iii) vinyl chloride. It is a weather-resistant and workable pre-coated metal plate coated with a resin paint.

[0003]

However, the precoated metal sheet for exterior (i) is durable even when exposed to outdoor conditions such as light, heat, wind, and rain, and is suitable for exterior use. Although it is suitable, it has a drawback that the workability, particularly the corrosion resistance of the processed part when bent, is low. The preformed metal sheet for high working of the above (ii) is excellent in workability and has good corrosion resistance in a bent portion, but has a disadvantage that it is not suitable for exterior use because of poor weather resistance. The above (ii)
Although the vinyl chloride precoated metal sheet of i) is excellent in both weather resistance and workability, harmful gases such as dioxin and chlorine-based gas are generated at the time of incineration of waste, and there is a problem of environmental pollution. That is, in the existing pre-coated metal plate, one coat or two
There is a limit in satisfying many conditions necessary for the resin film of the coat, and none of them satisfy all the conditions of weather resistance, workability, corrosion resistance of processed parts, and environmental properties to some extent.

[0004] Therefore, the present invention is to make up the properties that cannot be exhibited by one or two coats, by overcoating, intermediate coating, and undercoating by making three coats, the properties that are lacking in one or two coats. Accordingly, an object of the present invention is to provide a precoated metal sheet which is excellent in weather resistance, workability, corrosion resistance in a processed portion, and can also prevent the occurrence of environmental pollution during incineration of waste.

[0005]

According to the precoated metal sheet of the present invention, an undercoat layer having a thickness of 2 to 15 .mu.m is formed by applying a resin coating containing a rust-preventive pigment on the surface of the surface-treated metal sheet. The surface of this undercoat layer has a number average molecular weight of 5
000 or more polymer resin paint is applied and the film thickness is 10-3
A 0 μm intermediate coating layer is formed, and on the surface of this intermediate coating layer,
The resin coating is applied to form an overcoat layer having a thickness of 7 to 30 μm.

The overcoat layer is formed of a polymer resin paint having a number average molecular weight of 5,000 or more in which 1 to 20 parts by weight of an organic resin particle such as an acrylic resin or a fluororesin is mixed with 100 parts by weight of a resin solid content. Alternatively, the overcoat layer is formed of a shrink coat mainly composed of a polyester resin mixed with a low nucleated methylated melamine resin, a sulfonic acid and an amine.

[0007]

Since the undercoat layer is formed of a resin coating containing a rust preventive pigment, it contributes to the improvement of corrosion resistance. If the thickness of the undercoat layer is less than 2 μm, the required rust-preventing force cannot be maintained, and if it exceeds 15 μm, it causes a reduction in processing performance and also causes a problem in coating workability.

[0008] Since the intermediate coating layer is formed of a polymer resin coating having a number average molecular weight of 5,000 or more, it can contribute to improvement of workability. If the thickness of the intermediate coating layer is less than 10 μm, required processing performance cannot be maintained, and corrosion resistance cannot be obtained. If it exceeds 30 μm, there is a problem in coating workability.

Since the overcoat layer is formed, the low weather resistance of the intermediate coat layer can be compensated for. If the thickness of the overcoat layer is less than 7 μm, the required corrosion resistance cannot be obtained, and
If it exceeds m, workability will be reduced, and a problem will also occur in coating workability.

The overcoat layer contains an organic resin particle such as an acrylic resin or a fluororesin, so that weather resistance is improved, and since it is formed of a polymer resin paint, workability is also improved. Corrosion resistance is further improved. When the overcoat layer is formed with a thin coating film, a design effect is obtained, and since the thin coating film is mainly composed of a polyester resin mixed with a low nucleated methylated melamine resin, a sulfonic acid, and an amine, Particularly resistant to ultraviolet rays, the weather resistance is further enhanced.

[0011]

FIG. 1 is a sectional view of a precoated metal plate according to an embodiment of the present invention. 1 is a metal plate, 2 is an undercoat layer coated on the surface of the metal plate 1, 3 is an intermediate coating layer coated on the surface of the undercoat layer 2, 4 is an overcoat layer coated on the surface of the intermediate coating layer 3, 5 Is a back coat layer coated on the back surface of the metal plate 1 for anticorrosion.

The metal plate 1 is a steel plate, various types of plated steel plates such as galvanized, stainless steel plates, aluminum plates and the like. The metal plate 1 is subjected to a surface treatment by a chemical conversion treatment such as a chromate treatment or a phosphate treatment before painting.

The undercoat layer 2 is coated with a roll of an epoxy resin paint or a polyester resin paint containing a rust-preventive pigment such as strontium chromate or zinc chromate on the surface of the metal plate 1 which has been subjected to a surface treatment. 23
Bake and dry at 0 ° C. The rust preventive pigment is blended in an amount of 10 to 50 parts by weight based on 100 parts by weight of the resin solid content of the epoxy resin paint or the polyester resin paint. If the thickness of the undercoat layer 2 is less than 2 μm, the required rust-preventive force cannot be obtained, and
If it exceeds μm, the workability decreases, so that 2 to 15 μm is preferable.

The intermediate coating layer 3 has a number average molecular weight of 5,000 to 5,
A high-molecular-weight polyester resin paint having excellent workability of 0000 is roll-coated on the undercoat layer 2 and has a sheet temperature of 220 to 2.
Bake and dry at 40 ° C. The thickness of the intermediate coating layer 3 is 10 μm.
If it is less than m, required processing performance cannot be maintained, and corrosion resistance cannot be obtained. If it exceeds 30 μm, there is a problem in coating workability.

The top coat layer 4 is formed by applying an acrylic resin paint having excellent weather resistance on the intermediate coat layer 3 by roll coating, and baking and drying at a baking plate temperature of 200 to 220 ° C. In addition to the acrylic resin-based coating, a polyester resin-based coating or a fluororesin-based coating also having excellent weather resistance can be used.
If the film thickness of the overcoat layer 4 is less than 7 μm, the required corrosion resistance cannot be obtained, and if it exceeds 30 μm, the workability is reduced and the coating workability is problematic.

As the coating material for the overcoat layer 4, a high-molecular-weight polyester resin coating material having a number average molecular weight of 5,000 to 50,000 and excellent in processability is selected from polyester resin-based coating materials, and polyacrylonitrile or polyacrylonitrile is added to the high-molecular polyester resin coating material. An acrylic resin such as methyl methacrylate: a fluororesin such as polytetrafluoroethylene and polyvinylidene fluoride: a melamine resin: a urethane resin: a coating compounded with organic resin particles having an average particle size of 2 to 70 μm such as a polyester resin is used. In this case, the compounding ratio of the organic resin particles is such that the resin solid content of the high molecular polyester resin paint is 100%.
The organic resin particles are used in an amount of 1 to 20 parts by weight based on parts by weight. When the overcoat layer 4 is formed of a coating material in which organic resin particles are mixed with such a high-molecular polyester resin coating material, the weather resistance is improved and the processability is further improved.

As the above-mentioned paint obtained by blending organic resin particles with a polymer polyester resin paint, the following paints can be selected. The paint has a hydroxyl value of 5 to 110.
The reaction mixture of sulfonic acid and amine is used in an amount of 0.1 to 3 based on 100 parts by weight of the total of 65 to 95 parts by weight of the polyester resin of the above and 5 to 35 parts by weight of the low nucleated methylated melamine resin. It is a coating material containing 1 to 15 parts by weight of silica fine particles having an average particle diameter of 10 μm or less and 1 to 20 parts by weight of the above-mentioned organic resin particles in order to further lower the gloss and stabilize the gloss. When a paint of this composition is applied and baked on the intermediate coating layer 3, the amine evaporates from the surface layer of the uncured coating film, and free sulfonic acid generated in the surface layer exerts a catalytic action to cure the surface layer. However, a phenomenon occurs in which the amine remains in the coating film and the sulfonic acid does not exhibit a catalytic action and is uncured (so-called upper drying phenomenon), so that a concave and convex pattern is formed.

[0018]

EXAMPLE 1 The surface of a hot-dip galvanized steel sheet was subjected to a chromate treatment, and an undercoat paint comprising 46 parts by weight of an anticorrosive pigment, strontium chromate, was added to 100 parts by weight of an epoxy resin, and the surface was baked. Undercoat layer 2 was formed.
On this undercoat layer 2, a high-molecular polyester resin paint having a number average molecular weight of 15,000 is applied and baked to form a film having a thickness of 20 μm.
The intermediate coating layer 3 having a thickness of 15 μm was formed by coating and baking a polyester resin paint having a number average molecular weight of 1300 on the surface of the intermediate coating layer 3.

Example 2 High molecular weight polyester resin coating material 1 having a number average molecular weight of 5000
Example 1 was repeated except that a top coat containing 3 parts by weight of organic resin particles per 100 parts by weight was coated and baked on the surface of the intermediate coat 3 to form a 20 µm thick top coat 4.
Is exactly the same as

EXAMPLE 3 A paint 100 comprising 80 parts by weight of a polyester resin having a hydroxyl value of 30 and 20 parts by weight of a low nucleated methylated melamine resin.
1 part by weight of a reaction mixture of a sulfonic acid and an amine with respect to 1 part by weight of a sulfonic acid and 3 parts by weight of organic resin particles were blended with the top coating composition, and the surface of the intermediate coating layer 3 was baked to a film thickness of 20 μm. Except that the overcoat layer 4 was formed, it was completely the same as Example 1.

COMPARATIVE EXAMPLE 1 The surface of a hot-dip galvanized steel sheet was subjected to chromate treatment, and an undercoat paint containing 46 parts by weight of a rust-preventive pigment, strontium chromate, was added to 100 parts by weight of the epoxy resin and baked. The point of forming the undercoat layer is the same as in each of the above embodiments, except that a polyester resin paint having a number average molecular weight of 1300 (film thickness: 15 μm) is baked on the undercoat layer to form two coats. This point is different from the above embodiments.

COMPARATIVE EXAMPLE 2 The surface of a hot-dip galvanized steel sheet was subjected to chromate treatment, and an undercoat paint containing 46 parts by weight of a rust-preventive pigment, strontium chromate, was added to 100 parts by weight of the epoxy resin, and the surface was baked. The point of forming the undercoat layer is the same as in each of the above embodiments, except that a high-molecular polyester resin paint (film thickness: 15 μm) having a number average molecular weight of 15,000 is baked on the undercoat layer to form two coats. The point in which it is formed is different from the above-described embodiments.

Comparative Example 3 A surface of a hot-dip galvanized steel sheet was subjected to chromate treatment, and a paint in which 20 parts by weight of a rust-preventive pigment, strontium chromate, was added to 100 parts by weight of an epoxy-phenol resin was applied and baked. Only the vinyl chloride resin paint (film thickness 200 μm) was applied and baked.

The weather resistance test, the workability test, and the corrosion resistance test of the processed portion of each of the examples and comparative examples prepared as described above were carried out in the following manner.

(1) Weathering test The weathering test was carried out using a sunshine weatherometer at 1000.
Time tested. (2) Workability test The workability test was a bending test based on JIS Z2208. (3) Corrosion resistance test of processed part The corrosion resistance test of the processed part is based on JIS K540 of the bent part.
A 0 salt spray (1000 hours) test was performed.

FIG. 2 shows the results of the weather resistance test, the workability test, and the corrosion resistance test of the processed part. However, in the charts, in the weather resistance test, the x mark indicates that the discoloration is greater than the color difference ΔE = 5 and the gloss retention is less than 50%, and the ○ mark indicates that the discoloration is the color difference Δ
E = 3 to 5, the gloss retention is 50% or more and less than 70%, and the mark ◎ indicates that the discoloration is color difference ΔE = 3 or less and the gloss retention is 70% or more. In the workability test, the mark x is 7T or more at a crackless T number of 20 ° C, the mark ○ is 3 to 6T at a crackless T number of 20 ° C, and the mark ０〜 is 0 to 0 at a crackless T number of 20 ° C. 2T is shown. In the corrosion resistance test of the processed part, the cross indicates that the corroded area of the processed part is 30%.
As described above, ○ indicates that the corroded area of the processed portion is 15 to 30%, and ◎ indicates that the corroded area of the processed portion is 15% or less.

As a result of the above test, it was confirmed that all of Examples 1 to 3 were excellent in all of the weather resistance, workability, and corrosion resistance of the processed part in substantially the same manner as the vinyl chloride resin coated steel sheet of Comparative Example 3. In addition, there is no harmful gas generated at the time of disposal and incineration as in the case of a vinyl chloride resin steel sheet, and it is excellent in environmental friendliness.

[0028]

According to the precoated metal sheet of the present invention, it is possible to obtain a useful effect that it is excellent in weather resistance, workability, and corrosion resistance in a processed portion, and does not cause environmental pollution during incineration of waste.

[Brief description of the drawings]

FIG. 1 is a sectional view of a precoated metal plate.

FIG. 2 is a table showing the results of a weather resistance test, a workability test, and a processed part corrosion resistance test of Examples and Comparative Examples.

[Explanation of symbols]

 1 Metal plate 2 Undercoat layer 3 Intermediate layer 4 Overcoat layer

Claims (3)

[Claims] 1. A resin coating containing a rust-preventive pigment is applied to the surface of a metal plate subjected to a surface treatment to a thickness of 2 to 15 μm.
An undercoat layer is formed, and a high-molecular resin paint having a number average molecular weight of 5,000 or more is applied on the surface of the undercoat layer to form an intermediate coat layer having a thickness of 10 to 30 μm. A precoated metal sheet, wherein a paint is applied to form an overcoat layer having a thickness of 7 to 30 μm. 2. An overcoating layer comprising organic resin particles such as acrylic resin and fluororesin per 100 parts by weight of resin solid content.
2. The pre-coated metal sheet according to claim 1, wherein the pre-coated metal sheet is formed of a polymer resin paint having a number average molecular weight of 5,000 or more blended in an amount of 20 to 20 parts by weight. 3. The pre-coated metal sheet according to claim 1, wherein the overcoat layer is formed of a shrink coating mainly composed of a polyester resin mixed with a low nucleated methylated melamine resin, a sulfonic acid and an amine. .