JPH069675B2 - Radiation-curable resin coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to coating a metal plate with a radiation-curable resin by pre-treating the metal plate with a polyacrylic acid aqueous solution when the metal plate is coated with the radiation-curable resin. The present invention relates to a method for coating a radiation-curable resin that significantly improves coating film adhesion to a film.

(Prior art) Conventionally, it was common to manufacture coated steel sheets and laminated steel sheets using thermosetting resin paints and adhesives, but in recent years, quality improvement, resource saving, energy saving, high productivity From the viewpoint of the above, electron beam curable resins have been used. For example, when electron beam curable resin coating material is highly cross-linked by electron beam, the coating film becomes very dense, and therefore the coating film hardness, stain resistance, solvent resistance, etc. are significantly improved. It is possible to manufacture coated products of a quality that cannot be obtained by the above coating.

However, since the curing reaction of the electron beam curable resin coating rapidly proceeds at room temperature during curing, the coating film remarkably shrinks, and a large residual stress is generated in the coating film. For this reason, when the electron beam curable resin coating is directly applied to the metal plate, mechanical abrasion, phosphate treatment, chromate treatment, pickling, etc. that improve the coating adhesion to the thermosetting resin coating are performed. Even when the pretreatment for coating was applied, the adhesion of the coating film was inferior to that when the coating material of thermosetting resin was applied.

As a method of improving the decrease in coating film adhesion of the electron beam curable resin in paints and adhesives, a thermosetting type resin that has excellent adhesion to the metal plate before applying the electron beam curable resin to the metal plate is used. A method is known in which an epoxy resin paint is undercoated to absorb the shrinkage of the coating film when the electron beam curable resin is cured. However, this method requires a facility such as an oven to cure the epoxy resin coating material, and thus there are still problems in terms of resource saving and energy saving.

(Problems to be Solved by the Invention) Since the present invention still has various problems in the conventional coating method as described above, a radiation-curable resin that can obtain sufficient coating adhesion by a simple pretreatment is used. A coating method is provided.

(Means for Solving the Problems) As a result of various studies on the coating method for improving the coating adhesion of the radiation-curable resin, the present inventors have used a polyacrylic acid aqueous solution as a pretreatment, and have used the radiation-curable resin. It has been found that, when the resin is cured, it is sufficient to irradiate with radiation having an intensity which penetrates the coating film of the radiation-curable resin and reaches the pretreated polyacrylic acid film. The present invention has been made based on such findings, and the metal plate has a molecular weight of 3,000 to 5
50,000 is treated with an aqueous solution of polyacrylic acid to form a dry coating amount of 10 to 100 mg / m ² , and then a radiation-curable resin liquid is applied to the polyacrylic acid coating to obtain a radiation of a sufficient intensity. It is characterized by irradiating and curing.

In the present invention, the mechanism by which the coating property of the radiation-curable resin is improved by treating the metal plate with the aqueous polyacrylic acid solution has not been theoretically sufficiently clarified, but it is considered as follows. That is, since polyacrylic acid has a polar group (—COOH) and an ethylenic double bond, the polar group of the polyacrylic acid film is oriented on the surface of the metal plate and firmly adheres to the metal plate. On the other hand, when the ethylenic double bond is irradiated with radiation having a strength reaching the polyacrylic acid film when curing the radiation-curable resin, radicals are generated by the radiation, so radical polymerization with the radiation-curable resin occurs.
Chemically bond. Therefore, it is considered that the radiation curable resin adheres to the metal plate via the polyacrylic acid film.

As the polyacrylic acid aqueous solution used for the treatment of the metal plate in the present invention, it is preferable to use a solution in which polyacrylic acid having a molecular weight of 3,000 to 50,000 is dissolved. This is because when the molecular weight is lower than 3,000, the cohesive force between the molecules is weak, so the film strength is weak and the film peels off from the film. On the other hand, the molecular weight exceeds 50,000. If so, it becomes difficult to dissolve, it becomes difficult to always maintain a stable aqueous solution, the coating operation becomes unstable, and it becomes impossible to form a uniform film.

There is no particular limitation on the method of treating the metal plate with the aqueous polyacrylic acid solution, and for example, a conventionally known method such as a spray method, an immersion roll drawing method, an immersion air knife drawing method, a roll coating method, a brush coating method, or a curtain flow coating method is used. Just process it.

However, when treated, the polyacrylic acid film was 10
It is necessary to set it to ˜100 mg / m ² . If the coating amount is less than 10 mg / m ² , the number of ethylenic double bonds on the coating surface will decrease, and the amount of radicals generated will be insufficient even when the radiation is irradiated until it reaches the coating when curing the radiation curable resin. Therefore, radical polymerization with the radiation-curable resin coating film is less likely to occur, and sufficient interlayer adhesion cannot be obtained.
When the amount exceeds 100 mg / m ² , the radical generation amount increases remarkably, the crosslinking reaction of polyacrylic acid progresses, and the coating itself becomes hard and brittle. As a result, the internal stress due to curing cannot be withstood, and the radiation curable resin The coating film adhesion, especially the adhesion during processing, rather decreases. Further, the drying after application may be carried out by evaporating the water content, and in the case of forced drying, the plate temperature may be heated to 40 to 120 ° C.

In the present invention, after the polyacrylic acid film is formed as described above, the radiation-curable resin liquid is applied, and the radiation of the intensity reaching the polyacrylic acid film is applied to cure. The resin of the resin liquid may be any resin having an ethylenically unsaturated double bond capable of radical polymerization by radiation, for example, unsaturated polyester resin, polyester (meth) acrylate, epoxy (meth) acrylate, polyurethane (meth) acrylate. Oligomers such as polyamide (meth) acrylate and polyol (meth) acrylate, or ethylene glycol (meth) acrylate, triethylene glycol (meth) acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Other (meth) acrylic acid esters, diallyl phthalate,
Monomers such as methylene bis acrylamide, triacryl isocyanate, styrene, (meth) acrylonitrile and vinyl acetate. The radiation curable resin liquid may be mixed with a reactive diluent having the same reaction mechanism, or may be mixed with a pigment or various additives.

The coating film thickness of the radiation curable resin is not particularly limited and may be determined according to the application. The radiation dose for curing is, for example, when the resin of the radiation curable resin liquid is an electron beam curable type and is coated with a dry coating film thickness of 10 to 50 μm, an acceleration voltage of about 100 KeV and a dose of 5 to 15 Mrad. Irradiation with an electron beam allows curing and radical polymerization with the polyacrylic acid film.

When the resin is cured by ultraviolet rays, the resin liquid is made clear or colored and a photopolymerization initiator is added. As the photopolymerization initiator, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, benzophenone / tertiary amine, benzyl methyl ketal, 2,2-
There are diethoxyacetophenone, α-hydroxyisobutyrophenone, 1,1-dichloroacetophenone, 2-chlorothioxanthone, etc., but if these are added in an amount of 0.1 to 5% by weight, they can be cured by ultraviolet rays of 200 nm to 350 nm. . When the colored clear resin liquid is applied, the coating film should be thin.

When the radiation-curable resin is coated according to the present invention, if necessary, pre-coating treatment such as mechanical polishing, phosphate treatment, chromate treatment, pickling, etc., which is generally performed before, is applied before polyacrylic acid aqueous solution coating. May be.

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 represented by aluminum.

Next, the present invention will be described with reference to the implementation order.

(Example) Hot-dip galvanized steel sheet with a zinc adhesion amount of 60 g / m ² (sheet thickness 0.5 m
m) is treated with an aqueous solution in which polyacrylic acid having a molecular weight as shown in Table 1 is dissolved, and then dried to obtain a dry film amount of 5 to 1
A 20 mg / m ² film was formed. After that, resin solutions of various radiation-curable resins as shown in Table 1 are applied on this film, and 10M under the conditions of an acceleration voltage of 160 KeV and an electron flow of 15 mA.
The coating film was irradiated with a rad electron beam and cured to form a resin coating film having a dry coating film thickness of 20 μm.

Next, the coated steel sheet obtained here was subjected to the following coating film adhesion test.

(1) Goggle test 100 pieces of 1 mm x 1 mm goggles were cut into pieces on the surface of the coated steel sheet with a cutter knife, and a cellophane tape was attached to the goggles to remove the pieces, and evaluation was performed according to the following criteria.

○ Those with 80 or more goggles without peeling off coating △ Those with less than 80 goggles without peeling coating with 50 or more × Those with less than 50 goggles without peeling coating (2) Gobin's eye Erichsen test After cutting the Gobang's eyes on the coated steel plate in the same manner as the Gobang's eye test, the Gobang's eyes are 6 mm with an Erichsen tester.
It was extruded, a cellophane tape was attached, and it was peeled off, and evaluated according to the same criteria as above.

Table 1 shows the results of this coating film adhesion test together with the types of polyacrylic acid aqueous solution and radiation curable resin.

As shown in Table 1, polyacrylic acid having a molecular weight of 3,000 to 50,000 may be treated with an aqueous solution while being dissolved to form a film having a dry film amount of 10 to 100 mg / m ² before applying the radiation curable resin liquid. For example, the coating adhesion of the radiation-curable resin is improved as compared with the case where the conventional chemical conversion treatment is applied.

(Effect) As described above, in the coating method of the present invention, a metal plate is treated with an aqueous solution of polyacrylic acid to form a polyacrylic acid film having excellent adhesion on both the metal plate and the radiation curable resin. Since it improves the coating film adhesion of the curable resin, the equipment can be simple and resource and energy can be saved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koji Mori Inventor, Ichikawa Research Institute, Ichikawa Research Institute, Ichikawa City, Ichikawa City, Chiba Prefecture (72) Inventor, Masuhiko Maekita 7 Takamachi, Ichikawa City, Chiba Prefecture No. 1 Nisshin Steel Co., Ltd. Ichikawa Research Center

Claims (1)

[Claims] 1. A metal plate having a molecular weight of 3,000 to 50,000.
Treated with an aqueous solution of polyacrylic acid of 0, and the dry film amount is 1
A method for coating a radiation-curable resin, which comprises coating a radiation-curable resin liquid after forming a coating film of 0 to 100 mg / m ² and irradiating it with a radiation having a strength reaching a polyacrylic acid coating to cure the resin. .