JPS5939195B2 - Paint curing method for pre-coated metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for curing a precoated metal coating.

The application of electron beam curable paint to pre-coated metal has already been introduced in the literature, and design for its application to industrial production lines is also underway.

However, since electron beam curable paints use a large amount of vinyl monomer (which becomes a coating film after electron beam curing) as a diluent, the high workability required for pre-coated metal is difficult.
It is difficult to form a coating film with good physical properties, and if the amount of vinyl monomer is reduced in order to improve these properties, the suitability for coating becomes unsatisfactory. In addition, for pre-coated metal, an electron beam-curable paint is applied, heated and dried, and then an electron beam-cured paint is applied on top of the coating, which is cured by electron beam irradiation. After heat-dried, the electron beam-cured paint is cured by electron beam irradiation. Although it is known that the process involves many steps, there is a lot of energy loss, and the adhesion between the top coat and the base coat is insufficient. The present inventors have arrived at the present invention as a result of intensive research into a coating curing method that eliminates the above-mentioned drawbacks, is economically advantageous, and provides excellent performance as a precoated metal.

That is, in the present invention, a water-soluble or water-dispersible electron beam-curable paint having a polymerizable unsaturated bond is used as an undercoat paint for pre-coated metal, and after applying the undercoat paint, the object to be coated is coated for 7 days.
After heating to 0 to 200°C to remove most or all of the water in the undercoat film, an electron beam curing type top coat is applied before the surface temperature of the object to be coated returns to room temperature, and then electron beam curing is applied. The present invention relates to a method for curing a precoated metal coating, which is characterized in that the undercoat film and the top coat film are simultaneously cured by irradiation with a beam. The water-soluble or water-dispersible electron beam curable paint for undercoating used in the present invention will hereinafter be referred to as a water-based electron beam curable paint.

The resin used in the water-based electron beam curable paint in the present invention is a water-soluble or water-dispersible resin having a polymerizable unsaturated bond that is cured by electron beam irradiation and is known in the related technical field. Any of these may be used, and typical examples include neutralizing epoxy resins, acrylic resins, polyester resins, etc. that have polymerizable unsaturated bonds with a base,
Water-solubilized or water-dispersed resins or mixtures of these with vinyl monomers, and mixtures of vinyl monomers with vinyl acetate monovinyl chloride copolymer emulsion resins, vinyl acetate ethylene copolymer emulsion resins, acrylic emulsion resins, etc. Or a mixture of these resins.

When making a paint, there is no problem in adding pigments, dyes, fillers, additives, which are commonly used in water-based paints, and inert organic solvents to improve paintability. Examples of the vinyl monomer include ethylene glycol dimethacrylate, diallyl phthalate, methylene bisacrylamide,
One or more types of triallylisocyanurate, trimethylolpropane triacrylate, acrylic esters, methacrylic esters, styrene, acrylonitrile, methacrylonitrile, vinyl acetate, methyl succinate, vinyl esters, and acrylamides. Vinyl monomers are used.

Examples of the inert organic solvent include methyl alcohol,
Monoalcohols such as ethyl alcohol, n-propyl alcohol, n-butyl alcohol, Sec-butyl alcohol, isobutyl alcohol; polyols such as ethylene glycol, propylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, 1-methoxy-2-propanol, 1-ethoxy-
Ether alcohols such as 2-propanol; 1J4-
Ethers such as dioxane; acetone, methyl ethyl ketone, methyl-n-propyl ketone, diethyl ketone,
Methyl isobutyl ketone, methyl-n-butyl ketone,
Ketones such as ethyl-n-butyl ketone; Acetates such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, 2-methoxyethyl acetate; n-pentane, n-hexane, One or more inert organic solvents such as hydrocarbons such as n-heptane, n-octane, benzene, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane are used. The vinyl monomer is preferably contained in an amount of 40% or less by weight based on the water-based electron beam curable coating material.

If it exceeds 40%, the high workability and physical properties required for precoated metal will deteriorate as described above.

Further, the amount of the inert organic solvent is preferably 20% or less by weight based on the water-based electron beam curable paint.

If it exceeds 20%, the working environment may deteriorate due to evaporation of the solvent during heating to remove water.

The resin used in the electron beam curable top coating of the present invention is a resin having a polymerizable unsaturated bond that is cured by electron beam irradiation and is known in the related technical field (including water-soluble resins). Any of them may be used, for example, unsaturated polyester resins, acrylic resins, urethane resins, epoxy resins, butadiene resins, alkyd resins, or mixtures of these and the vinyl monomers, vinyl chloride resins, There are mixtures of vinyl acetate resins, butyral resins, ethylene monovinyl acetate resins, amide resins, and the above vinyl monomers.

In making a paint, there is no problem in adding pigments, dyes, fillers, additives, and solvents (water or the above-mentioned inert organic solvents) that are commonly used in electron beam curable paints. When an inert organic solvent is used, the amount of inert organic solvent contained in the top coating is desirably 40% or less by weight, preferably 20% or less.

If the amount of solvent exceeds 40%, a large amount of solvent remains in the coating film, which reduces the hardness and solvent resistance of the coating film, which is not desirable in terms of coating performance. In the present invention, after applying the water-based electron beam curable paint for the base coat as described above, heating is performed to remove most or all of the water contained in the base coat film, and the residual heat is utilized. This also evaporates the solvent in the electron beam curable top coat.

Therefore, in order to apply the top coat, the surface temperature of the metal plate must be raised (heated) before it returns to normal temperature.
The previous surface temperature is T. (room temperature) and the surface temperature immediately after heating (heating) is T1, the hardness of the formed coating film, solvent resistance,
Considering the finishing condition, etc., it is desirable that the surface temperature T of the metal plate is between T1 and T1-TO? It means applying top coat paint within the range of +TO.

If the top coat is applied when the surface temperature T of the metal plate is lower than ++ island, the solvent in the top coat (inert organic solvent and/or
or water) may not evaporate sufficiently, and a large amount of solvent may remain in the coating film, resulting in a decrease in coating film performance, especially hardness, and solvent resistance after curing, or due to insufficient evaporation of the solvent. It takes a long time and may not be applicable to industrial production lines.

Since the undercoat paint of the present invention is a water-based electron beam curable paint, it is extremely easy to adjust the viscosity, and unlike 100% solids type paints, it is easy to apply thin coats, so it can be used as a baking paint for ordinary pre-coated metal. Compared to other methods, heating can be done at a lower temperature and in a shorter time.

That is, the heating of the undercoat film in the present invention is carried out in order to remove most or all of the moisture contained in the undercoat film, and the heating temperature is 70°C to 200°C, preferably 100°C to 200°C.
180°C, heating time is 10 to 180 seconds, preferably 20
~80 seconds is sufficient. In addition, the undercoat paint has a good physical paint flow, and since it is heated, the stress strain during curing of the paint film by electron beams is reduced, resulting in improved adhesion to the material. be.

Furthermore, in the present invention, a water-based electron beam curable undercoat paint is applied, and the water in the paint and, if necessary, the organic solvent is heated in a short period of time to evaporate, and the residual heat is used to remove the organic solvent in the top coat paint. Since the water is evaporated and then cured by irradiation with electron beams, the adhesion between the top coat and the base coat and the finish are good, and it is also advantageous in saving energy and shortening the process.

As the method for applying the undercoat and topcoat in the present invention, commonly used coating methods can be applied, such as roll coating, spray coating, curtain coating, etc.

The coating film in the present invention is cured by irradiation with an electron beam, and examples of the electron accelerator include Kotscroft type, Kotscroft-Walton type, Van de Graaf type, resonant transformer type, insulated core transformer type, There are electron accelerators such as Dynamitron type and high frequency type, and the 100 to 2000 Ke (especially preferably 100 to 500 Ke) emitted from them is available.
The undercoat film and topcoat film are simultaneously cured by irradiating the paint film with an electron beam having an acceleration energy of (KeV).

In general, curing of electron beam curable paints tends to be inhibited or inhibited by oxygen, so in the present invention, it is also desirable to irradiate electron beams in an inert gas.

A detailed explanation will be given below with reference to production examples and examples. Parts used in the present invention indicate parts by weight. Manufacturing example
1. Epicoat Resin 1004, hydroquinone, and butyl acetate were placed in a reaction vessel No. 52, and the temperature was raised to 120° C. with stirring using a mantle heater to dissolve the Epicoat resin.

Next, a mixture of acrylic acid and triethylamine was added to the stirring reaction vessel, and the mixture was further heated at 120° C. for about 5 hours. After measuring the resin acid value and confirming that it was 10 or less, succinic anhydride was added and stirring was continued at 120° C. for about 3 hours to obtain a varnish with a resin acid value of 104.

The nonvolatile content of this varnish was approximately 75%. When the pressure was further reduced to 95% nonvolatile content, the varnish 79
0 parts to 210 parts of 2-hydroxypropyl acrylate
The mixture was mixed and a varnish was obtained. Varnish CA) 100 copies, 2
- 50 parts and 70% of hydroxypropyl acrylate
After thoroughly mixing 12 parts of dimethylaminoethanol,
Varnish (B) was obtained by adding 200 parts of purified water. Varnish (B) is an aqueous varnish. Next, 362 parts of varnish (B), 50 parts of rutile titanium oxide, and 15 parts of strontium chromate were dispersed in a paint conditioner to obtain an undercoat (1).

Production Example 487 parts of methyl methacrylate, 454 parts of ethyl acrylate, and 126 parts of acrylic acid were subjected to solution polymerization in xylene by a conventional method.

Furthermore, 102 parts of glycidyl methacrylate and 2 parts of triethylamine were blended and reacted in a conventional manner to obtain an unsaturated acrylic resin. The acid value of this resin was 53. The pressure of this acrylic resin varnish was reduced to obtain a varnish with a nonvolatile content of 90%. 170 parts of 2-hydroxyethyl methacrylate was added to 830 parts of this varnish and mixed and dissolved. 100 parts of 28% ammonia water was added to 1000 parts of this varnish to neutralize it, and 1000 parts of purified water was added and mixed to obtain an aqueous varnish (C). This water-based varnish (C) 10
00 parts, 300 parts of rutile titanium oxide, 10 parts of iron oxide pigment
0 parts were blended and dispersed in a ball mill to obtain an undercoat paint 9. Production example Vinyl acetate monovinyl chloride copolymer emulsion (46% non-volatile content) 1
000 parts, 300 parts of titanium oxide and 100 parts of barium sulfate were blended and dispersed to obtain a paint.

50 parts of triethylene glycol diacrylate was added to 1,000 parts of this paint to obtain an electron beam-curable water-based undercoating paint (self). Production example Acrylic resin water-based emulsion paint (white) (manufactured by Kansai Paint Co., Ltd., trade name Vinidelux, non-volatile content 50%) 10
00 parts, 30 parts of pentaerythritol dimethacrylate was blended to obtain an undercoat (4).

Production example Asuka Primer 1 (red rust) (manufactured by Kansai Paint Co., Ltd., product name, acrylic resin emulsion, non-volatile content 50%) 1
000 parts of polyethylene glycol dimethacrylate 2
An undercoat (7) was obtained by blending 0 parts.

Production Example (f) was added to xylene and reacted in a conventional manner to obtain an acrylic resin varnish.

The whole was then cooled to 50°C. Add methacrylic acid (d) to the contents and bring the temperature to 138°C over about 1.5 hours.
gradually increased to

This temperature was maintained for about 1 hour, and xylene was removed to obtain an acrylic resin. 500 parts of this acrylic resin, 250 parts of isobutyl acrylate, and 250 parts of 2-hydroxyethyl acrylate were added and dissolved to obtain Varnish Co., Ltd. Production Example 1.0 mol of isophthalic acid, 1.0 mol of adipic acid, and 3 mol of neopentyl glycol were heated in a conventional manner to give an acid value of 6.
of polyester was obtained.

Hexamethylene diisocyanate 2 is added to this polyester.
2 moles of 2-hydroxyethyl acrylate were added and reacted to obtain an unsaturated urethane resin. This resin 70
0 parts to 150 parts of hydroxypropyl methacrylate, 2
- Mix and dissolve in 150 parts of ethylhexyl acrylate to obtain a varnish. Production example Acrylic resin (Paraloid B-72: BOOm&Has
Acrylic resin varnish (proprietary) was obtained by dissolving 400 parts of (manufactured by S Company) in 300 parts of butyl acetate and 300 parts of hydroxypropyl methacrylate.

Production example Varnish 2500 parts, Varnish 6000 parts, Varnish 1
500 parts of hydroxyethyl methacrylate and 5000 parts of titanium oxide were added and blended and dispersed by a conventional method to obtain a white enamel top coat 1.

Example 1 Primer paint 1 was applied to a surface-treated galvanized iron plate with a thickness of 0.6 mm using a roll coater so that the film thickness was approximately 5 μm, and then immediately placed in a hot air oven to bring the material temperature (T1) to 130°C. It was heated for 40 seconds so that

Then, when the material temperature (T) was 80°C, topcoat 1 was applied to a film thickness of 25μ using a curtain flow coater, and after 20 seconds, an electron beam was applied to the film at 5 Mrad in an inert atmosphere.
Irradiated. TO was at 20°C. The resulting coating film had a good finish and good processability (bending properties, impact resistance) and adhesion. Example 2 A 0.3 mL surface-treated galvanized steel plate was coated with an undercoat using a rotary coater to a film thickness of approximately 5 μm, and then immediately placed in a hot air oven at an ambient temperature of 200° C. and heated for 40 seconds.

The material temperature (T1) was 200°C. Thereafter, when the material temperature (1) was 100'C, a top coat I was applied to the film using a curtain flow coater to a film thickness of 20 μm, and then an electron beam was irradiated at 5 Mrad to cure the film. What about T.O.?
It was warm at ℃. The resulting coating film had a good finish and good workability. Example 3 A 0.6 mTfL surface-treated galvanized iron plate was coated with an undercoat to a thickness of 5 μm using a roll coater, and then immediately placed in a hot air oven at an ambient temperature of 70° C. and heated for 180 seconds.

The material temperature (T1) was 70°C. Then the material temperature (
When T) is 50℃, apply top coat 1 to 2 using a roll coater.
It was coated to a thickness of 5μ, and then irradiated with an electron beam of 9 Mrad to cure the coating film. TO was at 20°C. The resulting coating film had a good finish and good workability.
Example 40.6 A surface-treated galvanized steel plate was coated with an undercoat to a thickness of 5 μm using a roll coater, and then immediately placed in a hot air oven at an ambient temperature of 150° C. and heated for 60 seconds.

The material temperature (T1) was 150°C. After that, when the material temperature (1) is 80℃, apply top coat 1 with a curtain flow coater to a thickness of 25μ, and then apply an electron beam to 5M.
The coating film was cured by rad irradiation. TO was at 20°C. The resulting coating film had a good finish and good workability. Example 5 A 0.6 mm surface-treated galvanized iron plate was coated with an undercoat using a curtain flow coater to a film thickness of 7 μm, and placed in a hot air oven at an ambient temperature of 200° C. and heated for 40 seconds.

The material temperature (T1) was 200°C. Thereafter, when the material temperature (1) was 80° C., a top coat of 25 μm was applied using a curtain flow coater, and an electron beam of 5 Mrad was irradiated to cure the coating film. TO was at 20°C. The resulting coating film had a good finish and good workability. In addition, in order to compare with these Examples, the top coat 1 in Examples 1 to 5 above was tested when the material surface temperature (T) was room temperature (20C).
), and then painted under the same conditions and methods as in each example, and cured. Compared to the above examples, the finished coating was inferior, and the workability and adhesion were poor. etc. were not sufficient.

Table 1 shows the test results of the coating films obtained in the above examples and comparative examples.
It was as follows.

Claims (1)

[Claims] 1 70 to 20 minutes after applying a water-soluble or water-dispersible electron beam-curable undercoat having a polymerizable unsaturated bond to the metal.
After heating to 0°C to remove most or all of the moisture in the undercoat film, an electron beam curing type top coat is applied before the surface temperature of the object to be coated returns to room temperature. A method for curing a precoated metal coating, characterized by curing the undercoat film and the topcoat film simultaneously by irradiating with.