JPH0412842A - Durable coated metal plate - Google Patents

Abstract

PURPOSE:To obtain a metal plate extremely excellent in weatherability, corrosion resistance, scratch resistance, molding processability and chemical resistance by a method wherein coating pretreatment is applied to the surface of a metal plate and a primer containing anticorrosion pigment is applied to the treated metal plate as undercoat paint and, after drying, fluoroplastic type organo-paint is applied thereon as topcoat paint to be dried. CONSTITUTION:Coating pretreatment of a phosphate or chromate type is applied to the surface of a metal plate. As the resin of a primer for undercoat paint, either one of an epoxy resin and a modified polyester resin is used. The surface of the anticorrosion pigment such as strontium chromate or potassium zinc chromate kneaded with the primer is treated with silica or alumina or alumina and silica to be coated therewith. As fluoroplastic type organo-paint for topcoat paint, sol paint obtained by stably dispersing fluoroplastic fine particles having high affinity in matrix fluoroplastic is used. The fluoroplastic type organosol paint is applied, baked and dried after the undercoat primer is applied, baked and dried.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a metal plate obtained by subjecting the surface of a metal plate to pre-painting treatment, applying and drying an undercoat primer, and applying and drying a fluororesin-based organosol paint as a topcoat. The invention relates to durable coated metal plates.

[Conventional technology]

By mixing inorganic hard fillers such as glass flakes, glass fibers, silica particles, and silicon carbide into the organic coating film, the apparent hardness of the coating film is improved and the coating film has wear resistance and scratch resistance. It is known to give.

The strength of the paint film can be strengthened by mixing filler into the organic paint film up to the critical volume pigment concentration (CPVC value), but if filler is mixed in beyond the CPvC value, the strength of the paint film decreases rapidly. However, the bow elongation and tensile strength of the coating film decrease.

That is, the ability of the coating film to follow the processing deformation of the coated steel sheet is reduced, causing cracks in the processed portion, and the corrosion resistance of the processed portion is reduced.

In addition, the hardness of the coating film is increased by mixing an inorganic filler into the organic polymer resin matrix, and as a result of the increased hardness of the coating surface, the paper adhesion and abrasion properties of the coating surface are greatly improved. However, when forming painted metal sheets with a multi-stage roll forming machine, the forming rolls wear out quickly, requiring a lot of time to replace forming rolls and maintaining the rolls, and also requires a lot of cost for repairs. .

Furthermore, by applying a paint containing an inorganic filler to one side of a double-sided coated metal plate, it can be applied to the surface of a general paint film applied to the other side, during transportation of the painted coil or during construction on site. Scratches are likely to occur on the abrasive surface, which has the disadvantage of being aesthetically pleasing and also becoming a starting point for rust to form on the abrasive surface.

[Problem to be solved by the invention]

The present invention has been made in view of the above points, and it is an object of the present invention to improve the hardness of the coating film without impairing the long-term weather resistance, which is a characteristic originally possessed by the fluororesin-based organosol paint coating film. It can prevent scratches that occur on the coating surface during roll molding and reduce wear and tear on the forming roll, and also prevents scratches on the coating surface due to melting, freezing, fresh water, etc. caused by snowfall, etc. over a long period of time. To provide a durable coated metal plate which can prevent the occurrence of scratches and thereby prevent shortening of the life of the coated metal plate due to wear starting from the surface where the flaws occur.

[Means to solve the problem]

The present invention involves applying a phosphoric acid-based or chromic acid-based pre-painting treatment to the surface of a metal plate, applying and drying a primer containing a surface-treated anti-corrosion pigment as an undercoat, and using a fluororesin organo paint as a topcoat. The present invention relates to a durable coated metal plate characterized by coating and drying a fluororesin-based organosol paint in which fluororesin-based fine particles are stably dispersed.

The present invention will be explained in detail below.

As the base material, a galvanized metal plate, a zinc-aluminum alloy plated metal plate, an aluminum plated metal plate, a stainless steel plate, an aluminum plate, etc. are provided. The zinc-aluminum alloy plating composition includes one containing 5% aluminum and another containing 55% aluminum.

For the surface treatment of a substrate containing 5% aluminum, both zinc phosphate treatment and chromic acid treatment are performed, and for a substrate containing 55% aluminum, it is appropriate to perform a chromic acid treatment. In the treatment process, a film is formed on the substrate by a process similar to the known pre-painting treatment of galvanized plates. Furthermore, a film can be formed on the substrate of other metal plates by a known treatment process.

As the primer resin as the undercoat paint, either an epoxy resin or a modified polyester resin can be used. When using an epoxy resin, epichlorohydrin hisphenol type is suitable, and it is desirable to select a resin with a molecular weight in the range of 7,000 to 10,000.

When using modified polyester resin, epochino-modified polyester resin is preferred, and the degree of epochinolation is 5% to 50.
It can be modified arbitrarily within the range of %.

The degree of modification may be determined by considering the adhesion with the base material and the interlayer adhesion with the top coat, and the molecular weight, which is a flexibility factor, may be determined arbitrarily within the range of s, ooo to 2o, ooo. You can choose.

Treating the surface of anti-rust pigments such as strontium chromate, potassium zinc chromate, etc., which are used by mixing with the primer, with Norica, alumina, or alumina and 7 LiCa, and coating the pigment surface with these, is due to humidity, temperature, moisture, pH
The purpose is to control the solubility of the rust preventive pigment due to factors such as the above, and to control the elution rate of chromium ions.As a result, it is possible to maintain the rust preventive function of the painted metal plate over a long period of time, and then the binder resin It is possible to prevent the anticorrosion effect from being reduced due to reaction with reactive groups contained therein, such as acidic groups, and to ensure long-term storage stability as a paint.

Furthermore, especially when the binder resin contains acidic groups, the anticorrosion pigment is generally basic, so it is difficult to knead a large amount of the basic pigment because it reacts with the acid and forms a salt. However, by weakening the basic properties through surface treatment, it becomes possible to incorporate a high concentration of basic antirust pigments.

The concentration of the rust preventive pigment added to the binder is practically effective in the range of 10 to 50% by weight, but the optimum rotation is 30% by weight.
Any value between ~45% by weight can be selected depending on the purpose. When selecting an epochino resin as a primer, it is desirable to apply the coating so that the dry film thickness is 3 to 15 μm, and to set the baking plate temperature to 180 to 220° C. and the baking time to about 20 to 40 seconds.

When selecting a modified polyester resin as a primer, apply it to a dry coating thickness of 5 to 25 μm.
It is desirable to set the baking plate temperature to 180 to 260°C and the baking time to about 20 to 50 seconds.

The effectiveness of the epoxy resin type primer can be better exhibited by applying it in a relatively thin film, and the modified polyester resin type primer can be applied in a relatively thick film.

The fluororesin organo paint used as a soil coating should be a sol paint obtained by stably dispersing fluororesin fine particles that have a high affinity for the matrix fluororesin, and the coating film thickness should be set in the range of 20 to 50 μm. is desirable.

As the fluororesin organosol paint, for example, a mixture of polyhynylidene fluoride resin and polymethyl methacrylate resin in a weight ratio of 80:20 to 40:60 can be used.

Furthermore, in the top coat, the apparent hardness of the paint film increases,
In order to prevent scratches during molding by molding machines, to prevent scratches to the surface of the back coating film, and to prevent scratches on the construction roof surface due to snow melting, freezing, etc., fluororesin-based fine particles, such as trifluorochloride edileno, are used. Among resins, tetrafluoroethylene resins, tetrafluoroethylene-hexafluoropropylene copolymer resins, tetrafluoroethylene-ethylene copolymer resins, perfluoroalcoquino resins, trifluorochloride ethylene copolymer resins, etc. , to stably disperse arbitrarily selected resin fine particles.

When selecting resin microparticles, we give due consideration to characteristics such as weather resistance, heat resistance, chemical resistance, dispersion stability, light transmittance, light shielding properties, and surface appearance design. It is desirable to determine the degree of polymerization, bulk specific gravity, etc., and then mix the materials.

It is preferable that the particle shape is as round as possible. The particle size of the fluororesin-based fine particles may be arbitrarily selected within the range of 1 to 70 μm depending on the set film thickness. - For boat fishing, it is better to choose a diameter slightly larger than the dry coating thickness. The amount of fine particles mixed in can range from 1 to 40%! ! It can be selected within a range, but in practice it is preferably selected within a range of 10 to 30%.

The reason why fluororesin-based fine particles were selected as the dispersible fine particles is that they can be stably dispersed in the paint because their specific gravity is similar to that of the matrix resin.

Due to the similar surface tension (SP) with the matrix resin, a dense film is formed at the particle interface and the matrix interface when melted by heating.

Therefore, it is useful for preventing the intrusion of gas from the film and the penetration of various electrolytes.

In addition, due to the similarity in chemical structure and physical properties with the matrix resin, the addition of granular resin can newly increase the mechanical strength of the film without impairing the properties of the coating film originally possessed by the matrix resin. It can be strengthened and its practical functionality can be greatly improved.

Fluororesin-based organosol paint with the above functions,
After baking and drying the undercoat primer, the dry film thickness is 20
Copper plates coated with fluororesin organosol paint with a total coating thickness of 23 to 75 μm obtained by baking and drying the paint to ~50 μm have excellent weather resistance, corrosion resistance, scratch resistance, moldability, and chemical resistance. Very good in terms of properties.

[Example] Example 1 As a zinc-aluminum alloy plated plate, the composition of the plating layer is AQ
= 55% by weight, Zn = 43.4% by weight, S+ = 1.6% by weight, plating deposition amount on both sides 150g/la'', thickness 0.
A 5A+m metal plate was used, and the surface was treated with a reactive chromate surface treatment agent, and then heated and dried at 70°C to perform a chromate-based chemical conversion treatment on the metal plate surface. Surface treatment of 45% strontium chromate anti-corrosion pigment Epokin resin undercoat primer (FG
64) to a dry coating thickness of 5 to 7 μm,
A coating layer was formed by heating and drying under conditions of a baking plate temperature of 190° C. and a baking time of 30 seconds.

On the other hand, fluoropolymer fine particles, which had been pre-wetted with a ketone solvent and treated with a small amount of acrylic dispersant, were added to a fluoropolymer organo paint (Fluoropon R) manufactured by Dainippon Ink and Chemicals at a rate of 30% per 100 parts of the organo paint. After mixing, the paint was stirred and mixed in a stirring tank for about 30 minutes with a propeller stirrer rotating at 800 to 1000 rpm while keeping the stirring temperature below 40°C.The resulting paint was further filtered through a 100 mesh wire mesh to obtain the top coat paint. get.

Finally, a titanium-based chelating agent is added and mixed as an agent for adjusting the thixotropic index of the paint obtained as described above to obtain a top coat. The thus prepared fluororesin organo paint containing fluororesin fine particles (YF-84M
R) was applied as a top coat onto the zinc-aluminum alloy plating metal plate that had already been coated with the primer so that the dry film thickness was 23 μm or more, and was heated and dried under conditions such that the board temperature was 250°C and the baking time was 60 seconds. A coating layer was formed. In this way, a zinc-aluminum alloy plating metal plate coated with fluororesin organo paint was obtained.

Example 2 Epoxy resin undercoat primer (F
Instead of G64), a modified polyester resin is blended with a surface-treated anti-corrosion pigment and a primer manufactured by Dainippon Ink and Chemicals (
A coated zinc/aluminum alloy plated plate was obtained by coating in the same manner as in Example 1, except that CA-8) was used as the undercoat.

Comparative Example I A fluororesin organo paint manufactured by Dainippon Ink Chemical Industry Co., Ltd., Fluorobot YF-41 paint, which does not contain fluororesin particles, was used instead of YF-84MH as the top coat, and the coating procedure was the same as in Example I. An aluminum alloy plated plate was obtained.

Comparative Example 2 The coating procedure was carried out in the same manner as in Comparative Example 1, except that the modified polyester resin primer (CA-8) manufactured by Dainippon Ink and Chemicals was used as the undercoat paint, using the top coat paint, Fluoropon YF-41. Coated zinc and aluminum alloy plated plates were obtained in the same manner as in the examples.

Example 3 JIS-standard Z-27 galvanized plate with a thickness of 0.5
A zinc-plated metal plate was subjected to a zinc phosphate chemical conversion treatment as a pre-painting treatment, and then was further subjected to a tooling treatment using chromic acid.

This galvanized metal plate was coated with No25P manufactured by Dainippon Ink Chemical Industry Co., Ltd., which is a standard Evokin-based primer for Nohin Meggi metal plates. Got the board.

Comparative Example 3 JIS-standard Z-27 galvanized plate with a thickness of 0.5
After applying pre-painting treatment in the same manner as in Comparative Example 3 using a metal plate with a diameter of Obtained.

Example 4 Using a zinc/5% aluminum plating plate with a thickness of 0.5 mm,
The surface of this alloy plated plate was treated with a zinc phosphate treatment agent as a pre-painting treatment, and was further subjected to a tooling treatment with chromic acid.

This zinc/aluminum plated plate was coated with an undercoat and a top coat in the same manner as in Example 1 to obtain a coated zinc/aluminum alloy plated metal plate.

Example 5 Using the same procedure as in Example 4, a surface-treated zinc/aluminum plating plate was used, an undercoat was applied, and the same CA-8 undercoat primer manufactured by Dainippon Ink and Chemicals as in Example 2 was applied, and the topcoat was applied. A coated zinc/aluminum alloy plated metal plate was obtained in the same manner as in Example 1.

The physical properties of the coating film of the obtained coated metal plate are shown in Table 1.

Margins below [Effects of the Invention] According to the present invention, it is possible to obtain a durable coated metal plate that is extremely excellent in various properties such as weather resistance, corrosion resistance, scratch resistance, moldability, and chemical resistance. can.

Claims (1)

[Scope of Claims] 1. Pre-painting treatment is applied to the surface of the metal plate, a primer containing a surface-treated anti-corrosion pigment is applied as an undercoat and dried, and a fluororesin based organo paint is applied as a topcoat. A durable coated metal plate characterized by being coated and dried with a fluororesin organo paint made by stably dispersing fine particles. 2. The durable coated metal plate according to claim 1, wherein the binder of the undercoat is an epoxy resin or a modified polyester resin. 3. Claim 1, wherein the rust-preventive pigment is a rust-preventive pigment obtained by surface-treating strontium chromate or potassium zinc chromate with silica or alumina, or silica and alumina.
Or the durable coated metal plate according to claim 2. 4. The durable coated metal plate according to claim 1, 2 or 3, wherein the content of the anti-rust pigment is 10 to 50% by weight. 5. The content of fluororesin fine particles in the top coat is
The durable coated metal plate according to claim 1, claim 2, claim 3, or claim 4, wherein the content is 1 to 40% by weight. 6. Acrylic-based as a flow property modifier in top coat paint,
The durable coated metal sheet according to claim 1, claim 2, claim 3, claim 4, or claim 5, which contains a silicon-based, aluminum-based, or zirconium-based additive.