JP2003327915A - Coating material for metal plate for non-conversion coating, non-conversion coated metal plate and method for producing the coated metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating material for a metal plate for non-conversion coating, a non-conversion coated metal plate produced by using the coating material, and a method for producing the coated metal. <P>SOLUTION: The coating material for the metal plate for non-conversion coating and applicable without using a conversion treatment contains a main resin and a curing agent composed of an aromatic isocyanate compound and/or an alicyclic isocyanate compound as essential components. The non-conversion coated metal plate has a coating film formed by applying and baking the coating material for non-conversion coating to one or both surfaces of a metal plate. This invention further provides a method for producing the coated metal plate. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal plate used for home appliances, building materials and the like, and more particularly to a coated metal plate which requires no chemical conversion treatment.

[0002]

2. Description of the Related Art Painted metal sheets have been widely used in the field of outdoor building materials and the field of home appliances by taking advantage of various designs, heat resistance, pollution resistance, and antibacterial characteristics. Generally, when applying a coating on a metal plate for such an application, a chemical conversion treatment called a chromate treatment (for example, JP-A-11-86353) or a phosphate treatment (for example, JP-A-7-85511) is performed. It was applied, and the paint was applied on it.

The main purpose of chemical conversion treatment is to improve paint adhesion and corrosion resistance. If chemical conversion treatment is not applied, the coating will peel off after a long period of use, which causes problems not only in appearance but also in corrosion resistance. Therefore, chemical conversion treatment has been essential for coated metal sheets.

The coated metal plate can be roughly classified into two types. The first is to treat a topcoat with colored pigments or dyes,
This topcoat is the design. The other is to apply a clear coating to make use of the design of the underlying metal plate.

Since the chromate treatment mainly used as the chemical conversion treatment of the coated metal plate is colored (brown), when the clear coating containing no coloring pigment is applied, the color of the chromate treatment is transparent and the underlying metal plate is slightly colored. There was a problem that it looked yellowish. Further, in both clear coating and colored coating, the chromate treatment contains hexavalent chromium although it is slight, so it has been desired not to use it if possible.

Although the phosphate treatment is applied less frequently than the chromate treatment, the clear coating has a problem in appearance that the underlying metal plate is dull like the chromate treatment. Further, in both the clear coating and the colored coating, the phosphate coating has crystallinity, so that there is a problem that cracking occurs in severe bending.

As a method for solving the problems of these coated metal plates, a colorless silane coupling treatment can be used as a pretreatment in place of the chromate treatment or the phosphate treatment, but the silane coupling treatment is expensive. Therefore, it is not always the optimal method.

[0008]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned problems. Specifically, the coated metal sheet is eliminated by eliminating chemical conversion treatment such as chromate treatment or phosphate treatment during the production of the coated metal sheet. It is to provide a coated metal plate which has an improved appearance and is excellent in environmental compatibility.

[0009]

Means for Solving the Problems As a result of intensive studies on the means for solving the above problems, the inventors of the present invention essentially include one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a curing agent. Even if the paint does not undergo chemical conversion treatment such as chromate treatment or phosphate treatment,
The inventors have found that they adhere well to a metal plate, and have completed the present invention.

According to the present invention, since it is not necessary to carry out a chemical conversion treatment such as a chromate treatment, it is environmentally friendly, and since there is no yellowish color in the chromate treatment, the appearance of the clear coated metal plate can be improved. Further, when it is used outdoors or the like, it has excellent adhesion to a metal plate, and therefore has excellent peeling resistance and corrosion resistance, and long-term durability is improved.

The gist of the present invention is as follows. (1) A non-chemical conversion-treated coating for a metal plate, which essentially contains one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a main resin and a curing agent. (2) A coating film obtained by applying and baking a main resin and a coating essentially containing one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a curing agent without applying chemical conversion treatment, or on one side or Non-chemical conversion coated metal plate characterized by having on both sides. (3) A non-chemical-treated coated metal sheet having at least one coating film on at least one coated surface of the non-chemical-treated coated metal sheet according to (2). (4) The metal plate is a stainless steel plate, a plated steel plate or an aluminum alloy plate (2)
The non-chemical conversion coated metal plate according to (3). (5) Coating / baking of a coating material essentially containing one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a curing agent as a curing agent on one or both surfaces of a metal plate without chemical conversion treatment. A method for producing a non-chemical conversion treated metal sheet, which comprises forming a coating film. (6) In the above (1) to (5), the compounding ratio [NCO / X] of the isocyanate group of the isocyanate compound and the functional group X that reacts with the isocyanate group of the main resin is 0.5 to 2.0 in molar ratio. The coating composition for non-chemical conversion coated metal sheet, the non-chemical conversion coated metal sheet and the method for producing the same.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The coating material used in the present invention essentially comprises one or both of an aromatic isocyanate compound and an alicyclic isocyanate as a curing agent. Isocyanate compounds are originally used as a curing agent for the resin components that make up the paint, but when the adhesiveness with the metal plate was examined in detail focusing on the structure of the isocyanate compound, it was found that It was found that the alicyclic isocyanate has durability that can withstand long-term outdoor use. Isocyanate groups are also used in adhesives, and originally have a structure with excellent adhesion to metals, but those having a cyclic structure like this are particularly durable for long-term adhesion to metal plates. It was found to be excellent. It is considered that this is because the bulky cyclic structure prevents the invasion of water and prevents the bond between the metal plate and the isocyanate from being broken, and suppresses the corrosion reaction on the surface of the metal plate. .

The aromatic isocyanate is not particularly limited, but tolylene diisocyanate (hereinafter referred to as TD)
I) and its derivatives, 4,4′-diphenylmethane diisocyanate (hereinafter abbreviated as MDI) and its derivatives, xylylene diisocyanate (XDI) and its derivatives, and the like. Especially excellent performance is TDI and its derivatives.

The alicyclic isocyanate is also not particularly limited, but isophorone diisocyanate (hereinafter referred to as I
PDI) and its derivatives, hydrogenated TDI and its derivatives, hydrogenated MDI and its derivatives, hydrogenated XDI and its derivatives, and the like. Particularly excellent performance is I
PDI and its derivatives.

Considering the stability as a one-pack type coating in consideration of the use of coated steel sheet, it is preferable that the isocyanate group of the present invention has a blocked isocyanate group. Known blocking agents can be used, and examples thereof include blocked polyisocyanate compounds blocked with compounds such as ε-caprolactam, phenol, cresol, oxime and alcohol.

The paint of the present invention can be applied with a usual paint composition. The details will be described below.

The main resin constituting the paint of the present invention is not particularly limited, but acrylic resin, urethane resin, epoxy resin, polyester resin, silicone polyester resin, vinyl chloride resin, fluorine resin, butyral resin,
Examples thereof include polycarbonate resin and phenol resin. Mixtures or copolymers of these can also be used.

The main resin constituting the paint of the present invention is required to have an isocyanate compound having a functional group whose isocyanate group can act as a crosslinking agent. Examples of functional groups that can act as such functional groups include a hydroxyl group, a carboxyl group, an amino group, and the like.

If desired, a rust preventive pigment may be added to the coating composition of the present invention. When the coating of the present invention is a base coating, it is possible to further improve the corrosion resistance by adding a rust preventive pigment. As the rust preventive pigment, a known rust preventive pigment can be applied, for example, zinc phosphate, iron phosphate,
Phosphoric acid anticorrosion pigments such as aluminum phosphate and zinc phosphite, molybdate anticorrosion pigments such as calcium molybdate, aluminum molybdate, barium molybdate, vanadium anticorrosion pigments such as vanadium oxide, calcium Silicate-based pigments such as silicates, chromate-based rust preventive pigments such as strontium chromate, zinc chromate, calcium chromate, potassium chromate, barium chromate, water-dispersed silica, fumed silica,
And the like, and ferroalloys such as ferrosilicon can be used. These may be used alone or in combination of two or more.

As the curing agent for the coating composition of the present invention, the curing agent of the present invention may be used alone, but an isocyanate resin or amino resin having no cyclic structure, which is outside the scope of the present invention, is used in a weight ratio to the curing agent of the present invention. You may mix and use it to 20%. Examples of the isocyanate resin other than the present invention include hexamethylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate. Examples of the amino resin include resins obtained by reacting urea, benzoguanamine, melamine and the like with formaldehyde, and resins obtained by alkylating these with alcohols such as methanol and butanol. Specific examples include methylated urea resin, n-butylated benzoguanamine resin, methylated melamine resin, and n-butylated melamine resin. Furthermore, a silane coupling agent, a titanium coupling agent, or the like can be used as an auxiliary component in the coating material of the present invention.

As the compounding ratio of the curing agent of the present invention, a known compounding ratio of isocyanate curing agent can be applied. The compounding ratio [NCO / X] of the isocyanate group of the isocyanate compound of the present invention to the functional group X that reacts with the isocyanate group of the main resin is preferably in the range of 0.5 to 2.0 in terms of molar ratio. For example, taking a polyester resin system widely used for precoated steel sheet as an example, the compounding ratio [NCO / OH] of the isocyanate group of the isocyanate compound of the present invention and the polyol group of the polyester compound is used.
Is preferably in the range of 0.5 to 2.0 in terms of molar ratio. If it is less than 0.5, the curing of the resin and the adhesion to the metal plate are insufficient, and if it exceeds 2.0, a side reaction between the excess isocyanate groups occurs to harden the coating film, resulting in poor processability. Become.

The coating composition of the present invention may contain a curing catalyst for promoting curing. Examples of the curing catalyst include organic tin compounds such as dibutylene dilaurate, dodecylbenzene sulfonic acid, and di-n-butyltin dilaurylate;
Examples thereof include primary amines, and these may be used alone, or two or more kinds may be appropriately mixed and used.

If desired, known additives may be used in the coating composition of the present invention. For example, coloring pigments, dyes, extender pigments, surface smoothing agents, ultraviolet absorbers, hindered amine light stabilizers, viscosity modifiers, curing catalysts, pigment dispersants, pigment settling inhibitors, color separation inhibitors, plasticizers, waxes, A silane coupling agent, silica sol or the like can be used.

The paint of the present invention can also be used as a clear paint. The clear painted metal plate makes use of the design of the base metal plate, and it is used in the field of outdoor building materials and the field of home appliances such as large refrigerators.
Furthermore, it is used around kitchens and the like, and the resins, pigments, and additives for the above various paints can be applied as they are. However, the color pigments and dyes are limited to the range in which the transparency is not impaired. Since the currently used clear-coated metal sheet is subjected to chromate treatment as a chemical conversion treatment, there is a problem that a slight yellow tint occurs. However, since the coating material of the present invention adheres well to the metal plate without chromate treatment, it is possible to manufacture a coating material having an excellent appearance.

As the pretreatment for coating the metal plate before applying the coating composition of the present invention, water washing, hot water washing, pickling, alkaline degreasing,
There are solvent degreasing, grinding, polishing, etc., and these may be performed alone or in combination as necessary. The conditions for the pretreatment for coating may be appropriately selected. Conventionally, pretreatment for painting (washing,
(Washing, pickling, alkaline degreasing, solvent degreasing, grinding, polishing, etc.)
The coating was performed in the steps of → chemical conversion treatment (chromate treatment, etc.) → coating. However, according to the present invention, the chemical conversion treatment is not necessary, so the process is pre-coating → coating.

The form of the paint of the present invention is not particularly limited, and examples thereof include organic solvent-based paints, water-based paints, colloidal dispersion-based paints, powder paints, electrodeposition paints, etc. Paint directly on the metal plate without the chemical conversion treatment used. The coating film thickness is not particularly limited, but is preferably 0.2 μm or more and less than 40 μm. If it is less than 0.2 μm, the adhesion effect is insufficient, and if it exceeds 40 μm, the workability is lowered and cracking of the coating film occurs in severe working, resulting in lower corrosion resistance.

As the coating method, for example, brush, roll coater, curtain flow coater, roller curtain coater, electrostatic coating, spray coating, blade coater,
There are die coaters, dip coating, etc. After that, it is dried and cured by heating with hot air, induction heating, near infrared, far infrared, or the like. The baking temperature of the paint is preferably 150 ° C. or higher and lower than 320 ° C. If the baking temperature is lower than 150 ° C., the solvent in the paint is not sufficiently volatilized, and there is a possibility that a good coating film may not be formed due to insufficient curing of the paint, which is not preferable. On the other hand, when the baking temperature of the paint is 320 ° C. or higher, the resin component in the paint is thermally deteriorated, which causes problems in appearance and workability, which is not preferable.

The metal plates used in the present invention are stainless steel plates, plated steel plates and aluminum alloy plates.

Examples of the stainless steel sheet include ferritic stainless steel sheet, martensitic stainless steel sheet, austenitic stainless steel sheet and the like.

As the plated steel sheet, a galvanized steel sheet, a zinc-iron alloy plated steel sheet, a zinc-nickel alloy plated steel sheet,
Zinc-chromium alloy plated steel plate, zinc-aluminum alloy plated steel plate, aluminized steel plate, zinc-aluminum-magnesium alloy plated steel plate, zinc-aluminum-magnesium-silicon alloy plated steel plate, aluminum-silicon alloy plated steel plate,
Examples thereof include galvanized stainless steel sheet and aluminum plated stainless steel sheet.

As an aluminum alloy plate, JIS H
Pure Al system (1000 system) specified by 4000, A
1-Cu system (2000 series), Al-Mn system (3000
System), Al-Si system (4000 system), Al-Mg system (5000 system), Al-Mg-Si system (6000 system), Al-Zn system (7000 system) and the like.

A top coat may be further applied on the coated surface of the non-chemical conversion treated metal plate coated with the paint of the present invention. The topcoat is not particularly limited, and a known topcoat currently used can be used as it is. As the top coating, polyester resin coating, acrylic resin coating, silicone polyester resin coating, PET resin coating, urethane resin coating,
Examples thereof include polyvinyl chloride resin-based coating and fluorine resin-based coating. Known additives may be used for the top coating, if necessary. For example, coloring pigments, dyes, extender pigments, surface smoothing agents, ultraviolet absorbers, hindered amine light stabilizers, viscosity modifiers, curing catalysts, pigment dispersants, pigment settling inhibitors, color separation inhibitors, plasticizers, waxes, A silane coupling agent, silica sol or the like can be used.

[0034]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

As the coating material for study, a polyester coating material was prepared. Among the curing agents of the present invention, toluene diisocyanate was used as the aromatic isocyanate compound and isophorone diisocyanate was used as the alicyclic isocyanate compound. Hexamethylene diisocyanate, which is widely used among isocyanate-based curing agents, was used as a comparative curing agent. These details are shown below.

Curing agent A: Toluene diisocyanate prepolymer oxime block (trade name "Desmodule BL1100", Sumitomo Bayer Urethane Co., Ltd.)
Made).

Curing agent B: an oxime block of isocyanurate of isophorone diisocyanate (trade name "Desmodule BL4265", manufactured by Sumitomo Bayer Urethane Co., Ltd.).

Curing agent C: oxime block of isocyanurate of hexamethylene diisocyanate (trade name "Desmodule BL3175", manufactured by Sumitomo Bayer Urethane Co., Ltd.).

These hardeners were prepared individually and as a mixture. As the mixed curing agent, a mixture of A: B = 1: 1 by weight and A: C =
Two levels of mix were made at a weight ratio of 1: 0.2.

Both of the curing agents are O of the main resin polyester.
The ratio of the H group to the NCO group of the isocyanate compound is [NC
A mixture of O] / [OH] = 1.2 was used as a standard. [NCO] / [OH] = 0.4 in the case where the curing agent is A,
A combination of 0.6, 1.8 and 2.2 was also produced. Further, as a curing catalyst, dibutyltin dilaurate was mixed in a solid content ratio of resin of 250 ppm.

As the coating material of the present invention, polyester is used as the main resin, the above-mentioned curing agent and curing catalyst are added, and 25% by mass of Sr—Cr type rust preventive pigment is added as a rust preventive pigment to the nonvolatile content. After that, titanium oxide and silica powder were added as extender pigments, and the dispersion treatment was performed for about 30 minutes using a sand mill containing glass beads having a diameter of 1 mm. Cyclohexane was further added to obtain a nonvolatile content of 60
Various paints were adjusted so as to be mass%. As a general rule, various paints were adjusted so that only the curing agent was different. Also,
We also made clear paints without rust preventive pigments.

As the metal plate, a hot dip galvanized steel plate (plate thickness 0.6 mm, coating amount Z08), stainless steel plate (plate thickness 0.6 mm, SUS430), aluminum alloy plate (plate thickness: 0.6 mm, JIS H 4000) Symbol A
3005P (Al-Mn system)) was used.

After subjecting these metal plate samples to alkali degreasing treatment, the coating composition of the present invention and the comparative coating composition shown in Table 1 were coated by adjusting the bar coater so that the dry film thickness was 5 μm, and then heated in a hot air heating furnace. Then, it was heated and cured under the conditions of a baking temperature (PMT) of 210 ° C. Further, as a top coating film, a polymer polyester resin coating (trade name "NSC200H
Q ", blue, manufactured by Nippon Paint Co., Ltd., with a dry film thickness of 15
After coating with a bar coater to a thickness of μm, PMT2
It was heat-cured under the condition of 30 ° C. to obtain a test material. However,
In the case of clear coating that makes the most of the design of the underlying metal plate, no top coating was applied.

The water resistance adhesion and the adhesion after the outdoor exposure test of the prepared test material were evaluated under the following conditions. 1) Water-resistant adhesion The coated metal plate produced by the above method was immersed in boiling water for 30 minutes. After that, a grid pattern was attached in accordance with the grid pattern test method described in JIS K5400, and further subjected to Erichsen processing of 6 mm. Adhesive tape (product name "Cellotape", manufactured by Nichiban Co., Ltd.) was attached to the processed part, and it was quickly pulled in an angle of 45 ° to be peeled off, and the number of crosses was peeled off within 100 crosses. Counted. Evaluation was made on a scale of 5 according to the degree of peeling, and 4 or more were regarded as passing. 2) Adhesion test after outdoor exposure test An outdoor exposure test was performed at a point about 100 m from the sea in Futtsu City, Chiba Prefecture. The test piece was cut into a size of 150 mm × 60 mm, the cut end surface was left as it was, and the seal coating was not performed. The outdoor exposure test is conducted for one year, and then JIS K
After making a grid according to the grid test method described in 5400, affix an adhesive tape (trade name "Cellotape", manufactured by Nichiban Co., Ltd.) and swiftly
It was peeled by pulling in the direction of 5 °, and the number of peeled cross-cuts was counted out of 100 cross-cuts. 5 depending on the degree of peeling
The grade was evaluated and 4 or more were passed.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

As shown in Tables 3 to 5, for a non-chemical conversion coated metal sheet which essentially contains one or both of the main resin of the present invention and an aromatic isocyanate compound and an alicyclic isocyanate compound as a curing agent. The non-chemical conversion coated metal plate produced by directly applying and baking the paint has good adhesion after the water resistance test and the outdoor exposure test, even without pretreatment such as chromate treatment. It was

[0051]

EFFECTS OF THE INVENTION According to the present invention, since chromate treatment, which is a chemical conversion treatment of a coated metal plate, is unnecessary, the yellowishness due to chromate is eliminated and the appearance is improved. Further, hexavalent Cr may be used. Since it is not present, it is possible to provide a paint, a coated metal plate and a method for producing the same which are excellent from the environmental aspect. Therefore, it can be said that the industrial value of the present invention is extremely high.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Kanai             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F term (reference) 4D075 AE03 AE24 BB26Z CA03                       CA13 DA06 DB04 DB07 DC03                       DC18 EA07 EA27 EB19 EB22                       EB32 EB33 EB35 EB38 EB43                       EB56                 4J038 CD021 CD091 CE071 CG001                       DA061 DB001 DD001 DE001                       DG001 DG272 DG282 GA03                       GA06 GA09 KA03 NA27 PA19                       PB05 PB09 PC02

Claims (5)

[Claims] 1. A non-chemical conversion coating metal plate coating material which essentially contains one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a main resin and a curing agent. 2. A coating film obtained by applying and baking a main resin and a coating material essentially containing one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a curing agent without applying a chemical conversion treatment. A non-chemical conversion coated metal plate having one or both sides. 3. A non-chemical-treated coated metal sheet according to claim 2, further comprising at least one coating film on at least one coated surface of the non-chemical-treated coated metal sheet. 4. The non-chemical conversion treatment coated metal plate according to claim 2, wherein the metal plate is a stainless steel plate, a plated steel plate or an aluminum alloy plate. 5. A coating material which essentially contains one or both of an aromatic isocyanate compound and an alicyclic isocyanate compound as a main resin and a curing agent is applied to one or both surfaces of a metal plate without chemical conversion treatment.・ Baked,
A method for producing a non-chemical-treated coated metal sheet, which comprises using a coating film.