JPH0149185B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming an active energy ray-curable coating film that exhibits excellent adhesion to coating materials, and particularly has excellent corrosion resistance and post-processability on metal materials. In recent years, it has been discovered that curing methods that use active energy rays such as ultraviolet rays and electron beams as a means of curing coating films can cure coating films in a shorter time and at lower temperatures than conventional heat curing methods and natural drying methods. It is rapidly gaining popularity because it can provide a hardened coating film that cannot be obtained with conventional paints. Active energy ray-curable paints are so-called radically polymerizable compounds that are made by appropriately combining prepolymers, monomers, and oligomers that have polymerizable unsaturated groups, but in general, rapid contraction of the paint film occurs during polymerization and curing, causing the formation of There is a tendency for the adhesion of the paint film to decrease because distortion remains in the paint film. This tendency is particularly noticeable in the case of metal materials where paint absorption into the material or graft reaction cannot be expected. On the other hand, in order to improve the adhesion of paint films to metal materials, a method has been proposed that first provides a primer layer with excellent adhesion on the metal material, and then provides a top coat layer on the painted surface. Widely used. However, when current baking-type solvent primers are used as they are as primers for active energy ray-curable paints, their performance in adhesion, corrosion resistance, etc. is inadequate due to differences in their constituent components and curing methods. It was necessary to develop a primer suitable for hardening paints. In view of the above-mentioned circumstances, the present inventors have arrived at the present invention as a result of various studies on methods of forming a cured coating film with excellent properties using a specific primer composition. In the present invention, an active energy ray-curable resin (C) is added to a mixture of an epoxy resin (A) containing an ether bond in the main chain molecule and an aminoplast resin (B) such as a urea resin or a melamine resin on a base material. A primer resin composition obtained by adding is applied, heat-treated to form a primer layer, an active energy ray-curable top coat is applied thereon, and then active energy rays are irradiated to form a cured coating film. This is the way to do it. The epoxy resin containing an ether bond in the main chain molecule used in the present invention includes bisphenol A diglycidyl ether type epoxy resin, bisphenol A dimetaglycidyl ether type epoxy resin, glycerin glycidyl ether type epoxy resin, or glycerin metaglycidyl ether type epoxy resin. Examples include epoxy resin. In addition, the aminoplast resin used in the present invention must have crosslinking ability with the above-mentioned epoxy resin, and melamine resins such as methylated melamine, butylated melamine, and isobutylated melamine, which are commonly used as crosslinking agents, and benzoguanamine ,
Examples include guanamine resins such as acetoguanamine, urea resins such as urea, thiourea, and N,N'-dimethylurea. Furthermore, as the active energy ray-curable resin added to the mixture of the above two components, epoxy polyacrylate obtained by reacting a bisphenol A-based epoxy resin with acrylic acid, and epoxy polyacrylate obtained by reacting a novolac-based epoxy resin with acrylic acid are used. Epoxy polyacrylate obtained by reacting an alicyclic epoxy resin with acrylic acid, epoxy polyacrylate obtained by reacting an alicyclic epoxy resin with acrylic acid, phthalate diglycidyl ester and acrylic Epoxy polyacrylate obtained by reacting bisphenol A-based epoxy resin with polycarboxylic acid and acrylic acid, epoxy resin, polycarboxylic acid, acrylic acid, and monoepoxide are reacted. Examples include epoxy polyacrylates obtained by The blending ratio (A) + (B) / (C) of the active energy ray-curable resin (C) added to the mixture of the epoxy resin (A) and aminoplast resin (B) used in the present invention is the weight ratio. It is desirable that the ratio is from 100/5 to 100/200; outside this range, the resulting coating film will have insufficient adhesion, corrosion resistance, processability, etc., and will be impractical. Also, the ratio of epoxy resin (A) to aminoplast resin (B)
It is desirable that (A)/(B) is in a weight ratio of 100/5 to 100/50; outside this range, the adhesion, corrosion resistance, processability, etc. of the resulting coating film will be insufficient, making it impractical. Poor. Since the primer obtained using the resin composition for primers of the present invention contains a thermosetting component and an active energy ray curing component, it can be cured by both heat and active energy rays, so it is compatible with the base material. It is possible to improve the adhesion between the active energy ray-cured top coat and form a coating film with excellent coating film properties such as corrosion resistance and processability. The active energy rays referred to in the present invention include electron beams,
When curing the primer of the present invention with ultraviolet rays, gamma rays, etc., commonly used photoinitiators and photosensitizers are used. In the following production examples and examples, parts represent parts by weight, and % represents weight %. Production Example 1 23 parts of ethylene glycol, 26 parts of itaconic acid, 28 parts of phthalic anhydride, and 0.5 part of hydroquinone monomethyl ether were reacted in a nitrogen atmosphere at 185°C for 5 hours while water was distilled off to produce an unsaturated polyester with a molecular weight of about 1300. Obtained. 70 parts of this unsaturated polyester, 15 parts of styrene, and 15 parts of methyl methacrylate were mixed to obtain a resin composition for top coating (). Production Example 2 In a reaction vessel, 230 parts of Epikote #834 (epoxy resin manufactured by Ciel Chemical Co., Ltd.), 76 parts of acrylic acid, 200 parts of butyl acrylate, 5 parts of dimethylaminoethyl methacrylate, and hydroquinone monomethyl ether were added.
0.5 part was added and reacted at 90° C. for 7 hours to obtain a resin composition for top coat () mainly consisting of an acrylic acid-modified epoxy resin. Example 1 66 parts of Supervetsukamine J-820 (butylated melamine resin, manufactured by Dainippon Ink Co., Ltd.) was added to 320 parts of a 50% diacetone alcohol solution of Epicoat #828 (epoxy resin manufactured by Ciel Chemical Co., Ltd.), and then Epicoat was added to this mixture. 40 parts of bisphenol A type epoxy polyacrylate to which acrylic acid had been added was added to #1001 (epoxy resin manufactured by Ciel Chemical Co., Ltd.). To this mixture, 42 parts of strontium chromate (manufactured by Kikuchi Color Industries), 44 parts of special clay, and 44 parts of titanium oxide R-550 (manufactured by Ishihara Sangyo Co., Ltd.) were added, diluted with an appropriate amount of thinner, and glass beads were added to reduce the particle size. 10μ
A primer paint was obtained by dispersing with a high-speed disperser as shown below. The above primer paint was applied onto a Bonderite #3300 treated board to a thickness of 5 μm, and dried in a high speed hot air drying oven at 240°C for 30 seconds to obtain a primer coated board. A top coat obtained by kneading 50 parts of titanium oxide with 100 parts of the resin composition for top coat () was applied onto this primer-coated board to a thickness of 20μ, and applied at an accelerating voltage of 300 KV and a dose rate of 10 Mrad/sec. A coated plate was obtained by irradiating it with an electron beam of 5 Mrad, and the coating performance of the coated plate is shown in Table 1. Comparative Example 1 A primer paint was prepared in the same manner as in Example 1, except that the bisphenol A type epoxy polyacrylate obtained by adding acrylic acid to Epicoat #1001 of the primer paint used in Example 1 was not added. A painted board was obtained. As shown in Table 1, the coating film of the coated board was extremely poor in adhesion and impact resistance compared to the coated board.

[Table] (1) Shows the number of coatings remaining on the board after making 100 goblets with a width of 2 mm, covering them with cellophane tape, and peeling them off all at once. (2) A test plate with a thickness of 1 mm was held between scissors and cellophane tape was attached to the part bent 180 degrees, and when it was peeled off, the coating was removed along with it.
Items with no abnormalities are marked with a circle. (3) After immersion in boiling water for 2 hours, those with no abnormalities on the painted surface were marked with ○, and those with abnormalities were marked with ×. Example 2 66 parts of Supervecamine G-821 (isobutylated melamine resin manufactured by Dainippon Ink Co., Ltd.) was added to 320 parts of a 50% diacetone alcohol solution of Epikote #1004 (epoxy resin manufactured by Ciel Chemical Co., Ltd.), and further added to this mixture. 40 parts of bisphenol A type epoxy polyacrylate to which acrylic acid had been added was added to Epicote #1001. To this mixture were added 42 parts of strontium chromate, 44 parts of special clay, and 44 parts of titanium oxide R-550 to obtain a primer paint in the same manner as in Example 1. Apply the primer paint to the thickness of the hot-dip galvanized plate.
Paint to a thickness of 5μ, dry at 240℃ x 30 seconds,
A primer-coated plate was obtained, and a top coat obtained by kneading 100 parts of titanium oxide with 100 parts of the resin composition for top coat was applied to the plate to a thickness of 15μ, and exposed to electron beams under the same conditions as in Example 1. When irradiated with 5 Mrad, the coating film was completely cured and showed good adhesion. Comparative Example 2 A primer paint was prepared in the same manner as in Example 2, except that bisphenol A type epoxy polyacrylate, which is made by adding acrylic acid to Epicoat #1001, was not added to the primer paint used in Example 2, and painted in the same manner as in Example 2. Although a plate was obtained, the adhesion was poor, and delamination occurred between the undercoat layer and the topcoat layer.

Claims (1)

[Claims] 1 A primer resin mainly consisting of a mixture of an epoxy resin (A) containing an ether bond in the main chain molecule on the base material and an aminoplast resin (B), to which an active energy ray-curable resin (C) is added. A coating film characterized in that a composition is applied, heat treated to form a primer layer, an active energy ray-curable top coat is applied thereon, and then active energy rays are irradiated to form a cured coating film. How to form.