JPH0472592B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) In a method for manufacturing coated metal plates in which a thermosetting paint and a radiation-curing paint are applied as the undercoat and topcoat, respectively, radiation-curable monomers or oligomers are blended into the undercoat to form the undercoat film. The present invention relates to a method for improving interlayer adhesion between a topcoat film and a topcoat film. (Prior art) Painted metal plates have traditionally been manufactured using thermosetting paints, but in recent years electron beam curing paints have been used from the viewpoint of improving quality, being pollution-free, saving resources, and saving energy. A manufacturing method using this method has been put into practical use. For example, when an electron beam-curable paint is subjected to a high degree of cross-linking reaction using an electron beam, the paint film becomes extremely dense, resulting in significant improvements in film hardness, stain resistance, solvent resistance, etc. We can produce painted metal sheets of a quality that cannot be obtained elsewhere. However, during curing of electron beam curable paints, the curing reaction proceeds rapidly at room temperature, resulting in significant shrinkage of the paint film, resulting in large residual stress in the paint film.
For this reason, coated metal plates obtained by applying electron beam curing paints directly to metal plates are inferior to those coated with thermosetting paints in terms of film adhesion and workability. A method to improve the deterioration in film adhesion and workability of painted metal plates caused by the use of electron beam curing paints is to apply heat curing, which has excellent adhesion to the metal plate, before applying electron beam curing C paint to the metal plate. A known method is to coat the mold with an epoxy paint to absorb the shrinkage of the paint film during curing of the electron beam curable paint. However, in the case of this method, cracks occur during processing due to the high film hardness of the epoxy paint, and the interlayer adhesion of the epoxy paint to the electron beam curing paint film is not sufficient. It was hot. (Problems to be Solved by the Invention) The present invention proposes that if an epoxy paint is applied as an undercoat as described above, the adhesion of the paint film will be improved compared to when it is applied directly to the metal plate, but the undercoat still remains unprocessed. In view of the problems caused by the occurrence of cracks and interlayer adhesion, the object of the present invention is to provide a method for producing a coated metal plate that is free from such problems. (Means for Solving the Problems) The method of the present invention involves applying a thermosetting undercoat before applying the radiation-curable paint, as in the conventional method, but the undercoat is made of polyester resin, which has excellent workability. A radiation-curable monomer or oligomer having a functional group that reacts with the polyester resin is added thereto to prevent cracks from occurring even when processed.
When the top coat film of the radiation-curable paint is cured with radiation, the top coat film is reacted to improve interlayer adhesion between the undercoat film and the top coat film. That is, the present invention comprises (A) a polyester resin having active hydrogen in its molecule, (B) a curing agent that reacts with the active hydrogen of (A), and (C) a functional group that reacts with the active hydrogen of (A). The main components are radiation-curable monomers or oligomers that have ethylenically unsaturated double bonds, and the mixture of (A), (B), and (C) is (A) = 100 parts by weight, (B) = 10 ~50 parts by weight, (C) = 5 to 50 parts by weight of a thermosetting undercoat is applied to a metal plate and cured by heat, and then a radiation-curable topcoat is applied and cured by radiation to form a coated metal. It manufactures boards. The present invention will be explained in detail below. First, the undercoat paint is made by blending a curing agent that reacts with the active hydrogen into a polyester-type resin that has active hydrogen in its molecules, and during hot rolling hardening, the polyester molecules are crosslinked by the curing agent to impart hardness to the coating film. This is a compounding method that is generally used for conventional polyester resin paints. Conventional polyester resins have functional groups that easily release hydrogen, such as hydroxyl groups, mercapto groups, amino groups, and carboxyl groups. Further, as the curing agent, a resin having an amino group such as a melamine resin, a guanamine resin, or a urea resin, or a resin having a functional group such as an isocyanate group or an epoxy group is used. In the case of the present invention, special resins and curing agents are not required, so conventional resins and curing agents are sufficient. It is preferable that this polyester resin has a main chain of polyethylene terephthalate because it has excellent processability. However, in the present invention, a radiation-curable monomer or oligomer having both a functional group that reacts with the active hydrogen of the polyester resin and an ethylenically unsaturated double bond is blended into the polyester resin paint, and the undercoat is coated via these. and the top coat are chemically bonded to each other. In other words, when such thermosetting and radiation-curing monomers or oligomers are blended, the functional groups react with the polyester resin when the undercoat is thermally cured, and the ethylenically unsaturated double bonds cause the topcoat to harden. During radiation curing, it reacts with the radiation-curable paint of the top coat, so the undercoat and top coat are chemically bonded and become one body, resulting in strong interlayer adhesion between the two coats. The other functional group that reacts with the active hydrogen of the monomer or oligomer polyester is an amino group, an isocyanate group,
These include epoxy groups and hydroxyl groups. In the present invention, the above-mentioned three components are used as the main components of the undercoat paint, and the composition is 10 to 50 parts by weight of the curing agent, based on 100 parts by weight of the polyester resin.
The amount of monomer or oligomer should be 5 to 50 parts by weight. The reason for setting the amount of curing agent to be 10 to 50 parts by weight is that if it is less than 10 parts by weight, the coating film hardness will be insufficient, and if it exceeds 50 parts by weight, the coating film hardness will become too large. This is because the ability to relax the residual stress that occurs when a certain radiation-curable paint film is cured is reduced, and sufficient paint film adhesion cannot be obtained.
In addition, the amount of monomer or oligomer added is 5 to 50.
The reason for using parts by weight is that if the amount exceeds 50 parts by weight, these monomers and oligomers will increase the hardness of the coating film, resulting in an excessively high coating hardness, similar to the case with the curing agent described above. Yes, 5 again
When the amount is less than 1 part by weight, the number of ethylene double bonds on the surface of the coating film decreases, and even if radiation is irradiated to cure the topcoat film, radical reactions with the topcoat film will be less likely to occur, resulting in sufficient interlayer adhesion. This is because it cannot be obtained. In order to impart corrosion resistance to the undercoat paint, anti-rust pigments (zinc chromate, strontium chromate, calcium chromate, lead zincide, basic lead sulfate, calcium leadate, lead cyanamide, zinc phosphate, zinc powder, etc.) are used. ) may be added. The paint film of this undercoat is the same as in the conventional production of coated metal sheets (for example, the dry film thickness is 4 to 8 μm).
m) is fine. Next is the top coat.This top coat is a conventional radiation-curable paint, which is mainly composed of oligomers with ethylenically unsaturated double bonds that can be radically polymerized by radiation, and is blended with monomers and other additives as appropriate. Paint is fine. For example, oligomers include unsaturated polyester resins, polyester (meth)acrylates, epoxy (meth)acrylates, polyurethane (meth)acrylates, polyamide (meth)acrylates, and polyol (meth)acrylates;
Alternatively, as a monomer, ethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, other (meth)
Acrylic esters, diallyl phthalate, methylene bisacrylamide, triacrylisocyanate, styrene, (meth)acrylonitrile,
Monomers such as vinyl acetate. For the purpose of adjusting the viscosity, a solvent that does not react with ordinary radiation may be appropriately added to these and evaporated before curing with radiation. The coating film thickness of the top coat is not particularly limited and may be determined depending on the application. The amount of radiation irradiation during curing is, for example, when the radiation-curing monomer or oligomer blended in the undercoat and the topcoat are both electron beam curable, and the dry film thickness is 15 to 25 μm. 5～
It will harden if irradiated with 15 Mrad. When the top coating is cured by ultraviolet rays, a clear or colored clear coating is used and a photopolymerization initiator is added. As a photopolymerization initiator, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, benzophenone/tertiary amine, benzyl methyl ketal,
There are 2,2-diethoxyacetophenone, α-hydroxyisobutylophenone, 1,1-dichloroacetophenone, 2-chlorothioxanthone, etc., but if you add 0.1 to 5% by weight of these, 200n
It can be cured with ultraviolet light of m to 350 nm.
In addition, when painting with colored clear paint, the paint film should be thin. When producing a coated metal plate according to the present invention, a pretreatment is performed before applying the undercoat. This pretreatment may be carried out by conventional mechanical polishing, phosphate treatment, chromate treatment, pickling, etc. depending on the type and surface condition of the metal plate. Further, the metal plate may be a cold-rolled steel plate, various galvanized steel plates, a steel plate such as a stainless steel plate, or a non-ferrous metal plate typified by aluminum. Next, the present invention will be explained with reference to examples. (Example) After applying zinc phosphate treatment to a hot-dip galvanized steel sheet with a zinc coating amount of 60 g/m ² , a bar coater was used to apply an undercoat of the composition shown in Table 1 to a dry film thickness of 5 μm. After that, it was baked and cured at 210±10℃ (maximum board temperature). Next, a top coat consisting of 60 parts by weight of polyfunctional polyester acrylate (manufactured by Toagosei Kagaku Kogyo), 20 parts by weight of monofunctional oligoester acrylate (same), 10 parts by weight of trimethylolpropane acrylate, and 10 parts by weight of xylene was applied to a dry film thickness. After coating to a thickness of 20μm and evaporating the diluent xylene, it was applied under the conditions of an acceleration voltage of 160KeV and an electron current of 15mA.
It was cured by irradiation with a 10 Mrad electron beam. Next, a goblin was made in the painted steel plate obtained here, the part was extruded using an 8 mm Erichsen tester, and Sellotape was applied and peeled off. Table 1 shows the results along with the composition of the undercoat.

[Table] As shown in Table 1, the coated steel sheets manufactured according to the present invention have superior interlayer adhesion than those coated with an epoxy resin paint as an undercoat. (Effects) As described above, since the present invention uses a polyester resin paint as the undercoat, cracks do not occur in the undercoat film even during processing, and the undercoat contains a radiation curing component. Therefore, the undercoat film and topcoat film are chemically bonded when the topcoat paint is cured by radiation, and interlayer adhesion is improved.

Claims (1)

[Claims] 1 (A) a polyester resin having active hydrogen in its molecule, (B) a curing agent that reacts with the active hydrogen of (A), and (C) a functional group that reacts with the active hydrogen of (A) and an ethylenic inorganic resin. The three main components are radiation-curable monomers or oligomers that also have saturated double bonds, and the mixture of (A), (B), and (C) is (A) = 100 parts by weight, (B) = 10 parts by weight.
~50 parts by weight, (C) = 5 to 50 parts by weight of a thermosetting undercoat is applied to a metal plate and cured by heat, and then a radiation-curable topcoat is applied and cured by radiation. A method for producing a coated metal plate using a radiation-cured paint.