JPS62125879A - Production of painted metallic sheet by paint curable by radiation - Google Patents

Abstract

PURPOSE:To improve the adhesiveness of a primer paint to the coated film of a finish paint curable by radiation by using a polyester resin paint for the primer paint to obviate cracking in the primer coated film and compounding a component curable by radiation with the primer paint. CONSTITUTION:The thermosetting primer paint which consists essentially of the three components; A) the polyester resin having active hydrogen in the molecule, B) curing agent (e.g., melamine resin) to react with the active hydrogen of A), and C) the monomer or oligomer curable by radiation having the functional group and ethylenic unsatd. double bonds to react with the active hydrogen of A) in combination and in which the compounding of A), B), and C) are A)=100pts.wt., B)=10-50pts.wt., C)=5-50pts.wt. is coated on a metallic sheet and is thermally cured. The finish paint curable by radiation is then coated thereon and is cured by the radiation. As a result, cracking of the primer coated film is obviated and the inter-layer adhesiveness between the primer coated film and the finish paint coated film is improved.

Description

Detailed Description of the Invention (Industrial Application Field) In a method for producing a coated metal plate in which a thermosetting paint and a radiation curing paint are applied as an undercoat and a topcoat, respectively, a radiation curing monomer or oligomer is added to the undercoat. It relates to a method for improving interlayer adhesion between an undercoat film and a topcoat film.

(Prior art) Painted metal plates have traditionally been manufactured using thermosetting paints, but in recent years, quality has improved, pollution-free, resource-saving, and
From the viewpoint of energy saving, etc., a method using electron beam curing paint has been put into practical use. For example, when an electron beam-curable paint is subjected to a high degree of cross-linking reaction with an electron beam, the paint film becomes extremely dense, which significantly improves the hardness, stain resistance, solvent resistance, etc. of the thermosetting paint. It is possible to produce coated metal plates with a quality that cannot be obtained by painting.

However, during curing of electron beam curable paints, the curing reaction proceeds rapidly at room temperature, resulting in severe shrinkage of the paint film and large residual stress in the paint film.

For this reason, coated metal plates obtained by directly applying electron beam curable paints to metal plates were inferior to those coated with thermosetting paints in terms of coating film adhesion and workability.

A method to improve the deterioration in film adhesion and workability of coated metal plates due to the use of electron beam curable paints is to apply heat curing, which has excellent adhesion to the metal plate, before applying electron beam curable paints 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 coating hardness of the epoxy paint, and the adhesion of the epoxy paint to the eyebrows of the electron beam curable paint is not sufficient. Met.

(Problems to be Solved by the Invention) The present invention provides the above-mentioned problem (7). Although the adhesion of the paint film is improved by applying an undercoat of epoxy paint to the metal plate compared to the case where the paint is applied directly to the metal plate, the undercoat film still remains. In view of the problems of cracks occurring during processing and glabella adhesion, the present invention provides a method for manufacturing a coated metal plate that does not have such problems.

(Means for solving the problem α) In the method of the present invention, a thermosetting undercoat is applied before applying the radiation-curable paint, as in the conventional method, but polyester I, which has excellent processability, 05 resin is used to prevent cracks from occurring during processing, and a radiation-curable monomer or oligomer having a functional group that reacts with the polyester resin is blended therein to form a radiation-curable paint. When the top coat film is cured with radiation, it reacts with the top coat film to improve the adhesion between the eyebrows between the undercoat film and the top coat film.

That is, the present invention provides (A) a polyester-based Af resin having active hydrogen in the molecule, (B) a curing agent that reacts with the active hydrogen of (A), and (C) a functional that reacts with the active hydrogen of (A). The main components are radiation-curable monomers or oligomers having both groups and ethylenically unsaturated double bonds, and the mixture of (A), (B), and (C) is (A) = 10
0 parts by weight, (B) = 10 to 50 parts by weight, (C) = 5 to 50 parts by weight
After applying 50 parts by weight of a thermosetting undercoat to a metal plate and curing it with heat, a radiation-curable topcoat is applied and cured by radiation to produce a coated metal plate.

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 with a polyester resin that has active hydrogen in its molecules.
During hot rolling and curing, polyester molecules are crosslinked with a curing agent to impart hardness to the coating film. This is a compounding method commonly used for conventional polyester resin paints. Conventional polyester resins have functional groups that easily release hydrogen, such as hydroxyl groups, mercapto groups, amine 7 groups, and carboxyl groups. Also, as a hardening agent, amide resin such as melamine resin, guanamine resin, urea resin, etc.
A resin having a group or a resin having a functional group such as an incyanate 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 should be noted that this polyester-based fN is preferably one whose main chain is polyethylene terephthalate-based 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. When curing with radiation, it reacts with the radiation-curable paint of the top coat, so the base coat and top coat chemically bond and become one body.
The adhesion of both coatings to the glabella will be strong.

The other functional group that reacts with the active hydrogen of the heptamer or oligomer polyester is an ami-7 group, an incyanate group, an epoxy group, a hydroxyl group, etc. as in the curing agent.

In the present invention, the above-mentioned three components are used as the main components of the undercoat, and the blend is made of polyester resin 100%
The amount of curing agent is 10 to 50 parts by weight, and the monomer or oligomer is 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 of a certain radiation-curable paint film to relax the residual stress caused by soil removal during hardening is reduced, and sufficient paint film adhesion cannot be obtained. In addition, the amount of monomer or oligomer added is 5 to 5.
The reason for setting it to 0 parts by weight is that if it exceeds 50 parts by weight + J, these moars and oligomers will increase the hardness of the coating film, and the hardness of the coating film will become too large. If the amount is less than 5 parts by weight, the number of ethylene double bonds on the coating film surface will decrease, and even if radiation is irradiated to cure the topcoat film, radical reactions with the topcoat film will not occur. This is because it becomes difficult for this to occur, and sufficient interlayer adhesion cannot be obtained.

In addition, anti-rust pigments (
Zinc chromate, sulfur chromate)+17tinium, calcium chromate, lead zincide, basic lead sulfate, calcium leadate, lead cyanamide, zinc phosphate, zinc powder, etc.) may be added.

The coating film of this undercoat may be the same as in the case of conventional production of coated metal plates (for example, the dry coating thickness is 4 to 8 μm).

Next is the topcoat (r) paint.This topcoat is a conventional radiation-curable paint, that is, it is mainly composed of oligomers having ethylenically unsaturated double bonds that can be radically polymerized by radiation, and monomers and other additives are added as appropriate. A blended paint is fine. For example, oligomers include unsaturated polyesters, such as polyester (meth)acrylate, epoxy (meth)acrylate, polyurethane (meth)acrylate, polyamide (meth)acrylate, and polyol (meth)acrylate, or monomers such as ethylene Glycol (meth)acrylate, triethylene glycol di(〆ri)acrylate, tetraethylene glycol di(meth)acrylate,
Trimethylolpropane tri(7)acrylate, other (meth)acrylic acid esters, noaryl 7thale F
, methylenebisacrylamide, triacrylisocyanate, styrene, (meth)acrylonyl, vinyl acetate, and other monomers. 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-curable monomer or oligomer blended in the undercoat and the topcoat are both electron beam-curable, and the dry coating thickness is 15 to 25 μm. It is cured by irradiation with 5 to 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, Teha, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin butyl ether tertiary amine, benzyl methyl ketal ethoxyacetate, α-hydroxyisobutyrophenone, 1,1-nochloroacetate , 2-chlorothioxanthone, etc., and if they are added in an amount of 0.1 to 5% by weight, they can be cured with ultraviolet rays of 20 Onta to 350 nm. When painting with colored clear paint, make the paint film thinner.

When producing a coated metal plate according to the present invention, the 111 treatment is performed on the undercoat coating station f. 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 any of cold-rolled steel plates, various plated steel plates, steel plates such as stainless steel plates, and non-ferrous metal plates such as 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 6 0 9 /+a2, an undercoat of the composition shown in Table 1 was applied with a bar toner to a dry film thickness of 5 μm. It was painted and then baked and cured at 210±10°C (maximum board temperature).

Next, a top coat consisting of 60 parts by weight of polyfunctional polyester acrylate (manufactured by Toagosei Chemical Industry Co., Ltd.), 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 the dried film. After coating to a thickness of 20 μm and evaporating the diluent xylene, an accelerating voltage of 160 KeV,
It was cured by irradiation with a 10 Mrad electron beam under the conditions of electron flow 15 images.

Next, the painted steel plate obtained here was made with goban marks, and the part was extruded using an 8I engineering Riksen testing machine, and Sellotape was applied and peeled off. Table 1 shows the results along with the composition of the undercoat.

As shown in Table 1, the coated steel sheets manufactured according to the present invention have better interlayer adhesion than those coated with an epoxy-based paint (oil paint) as an undercoat.

(Effects) As described above, since the present invention uses a polyester-based (fatty) paint as the undercoat, cracks will not occur in the undercoat film even when processed, and the undercoat does not contain radiation-curable components. As a result, the undercoat film and topcoat film are chemically bonded when the topcoat film is cured by radiation, and the layer opening adhesion is improved.

Claims (1)

[Claims] (A) polyester resin having active hydrogen in the molecule,
(B) A curing agent that reacts with the active hydrogen of (A) and (
C) The three main components of (A) are radiation-curable monomers or oligomers that have both a functional group that reacts with active hydrogen and an ethylenically unsaturated double bond, (A) and (B).
), the composition of (C) is (A) = 100 parts by weight, (B) = 1
0 to 50 parts by weight, (C) = 5 to 50 parts by weight of a thermosetting undercoat paint 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 manufacturing coated metal plates using a characteristic radiation-curable paint.