JPH06210241A - Coating of metal plate - Google Patents

Abstract

PURPOSE:To provide a coating method having coating workability capable of curing the film on a large metal plate having large heat capacity within a short time. CONSTITUTION:Active energy curable powdery coating containing a resin with an m.p. of 60-130 deg.C having a polymerizable double bond is applied to the surface of a metal panel and, subsequently, the formed coating film is melted under heating and irradiated with active energy beam to be cured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a metal plate, and more particularly to a coating work capable of curing a coating film on a large metal plate having a large heat capacity in a short time. The present invention relates to a coating method with good properties.

[0002]

2. Description of the Related Art Thermosetting powder coatings do not use organic solvents like organic solvent coatings, so there is no danger of poisoning or fire, so the working environment is good and the coating film is simple. Since it can be made extremely thick, it has come to be widely used especially for coating metal plates. However, the thermosetting powder coating usually requires a baking temperature of 160 to 250 ° C. to cure the coating film, and the baking time is as long as 10 to 30 minutes. Therefore, with a large heat capacity, for example, a metal plate with a plate thickness of several tens of millimeters,
When applying this powder coating, it takes time to raise the temperature of the metal plate to the baking temperature, and since the temperature must be maintained during the baking, the coating film is cured in a short time. Not only is it impossible to do so, but there is also the problem that a huge amount of heat energy is required. on the other hand,
An active energy ray-curable liquid coating composition containing a reactive diluent having a polymerizable double bond and / or an organic solvent can be cured in a short time by irradiating with an active energy ray, and thus a metal plate. It is widely used for various coated objects including. However, when a metal plate coated with such a liquid coating material is usually processed by welding at a high temperature such as welding and fusing as is done, when a coating film is present in such a processed portion, It causes inconveniences such as defective processing, burning of the coating film at that location, and spread of fire.

On the other hand, conventionally, when a metal plate having a coating-free portion such as the above-mentioned processed portion is coated, (a) the coating-free portion is masked in advance, then the entire surface is coated, and the coating film is cured. , A method of removing the masking layer, and (b) a method of coating on the entire surface, curing the coating film, and then dissolving or swelling the coating film on the unnecessary coating portion with a treatment liquid such as an organic solvent to remove it. It was However, the method (a) has a drawback that the masking process is complicated, and particularly when it is applied to a large-sized metal plate, the process takes a long time. However, it has a drawback that it not only causes the environmental pollution but also takes a long time to remove the coating film. When coating a metal plate that does not require coating with an active energy ray-curable liquid paint, it takes a lot of processing time for masking and coating stripping, and the coating workability is poor. There has been a problem that the merit of being able to cure the coating film in a short time of the curable liquid coating composition cannot be fully exerted.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, makes the best use of the characteristics of the powder coating material and the active energy ray curable coating material, and is short even for a metal plate having a large heat capacity. Provides a coating method for metal plates that allows the coating film to be cured in a short time, and that even when applied to a metal plate that does not require coating, it is easy to remove the coating from the coating-free part and has good workability. The purpose is to do.

[0005]

Means for Solving the Problems As a result of studies aimed at reducing the cost of heat energy while simultaneously curing a coating film of powder coating material in a short time, the present inventors have found that The coating film of a powder coating material, which uses a resin having a double bond that polymerizes by energy rays as a binder, has the same mechanism as a conventional active energy ray-curing liquid coating material when irradiated with active energy rays in a molten state by heating. A cured coating film is formed with active energy rays in a short time, and as a result, unlike conventional thermosetting powder coating materials, the high temperature baking temperature and long baking time are not required, and the powder coating material is simply melted. Since we only need to maintain the temperature of, we have found that it can be applied to a metal plate with a large heat capacity without requiring a large amount of heat energy.

Therefore, according to the present invention, an active energy ray-curable powder coating material containing a resin having a polymerizable double bond and having a melting point of 60 to 130 ° C. is applied to the surface of a metal plate, and then the coating film is melted by heating. Then, irradiate with active energy rays,
The present invention provides a method for coating a metal plate, which comprises curing the coating film. Furthermore, the present inventors have studied a method of applying a liquid coating material to the entire surface of a metal plate and removing the coating film on the unpainted portion before curing the coating film. Therefore, it was found that the coating film peeling work was complicated and the processing time was long. In the course of this research, the present inventors have found that the coating film formed by coating powder coating forms a film with dry powder. We have found that it is as easy as suctioning dust with a machine, can be removed by suction in a short time, and has good coating workability. Therefore, the present invention further has a melting point of 60 to 130 ° C on the surface of the metal plate.
Then, apply an active energy ray-curable powder coating material using a resin having a polymerizable double bond as a binder, remove the coating film formed on the unnecessary coating part by suction, and then apply it. Provided is a method for coating a metal plate, which comprises melting the film by heating and then irradiating it with an active energy ray to cure the coating film.

The present invention will be described in detail below. The active energy ray-curable powder coating material used in the present invention is a radically polymerized by irradiation with an active energy ray to be polymerized to bind a resin having a polymerizable double bond which forms a cured coating film. Except for being used as an agent, it is composed of a composition almost similar to the conventionally known powder coating material. That is, the powder coating material used in the present invention contains a resin having a polymerizable double bond as an essential component, and if necessary, various coloring pigments, extender pigments, photoconductive materials and surface conditioners, anti-sagging agents, antistatic agents. It is composed of various additives such as. When using ultraviolet rays as the active energy rays, it is necessary to further add a photopolymerization initiator.

The resin has a melting point of 60 to 130 ° C., preferably
It is a resin that is solid at room temperature at 70 to 120 ° C and has a polymerizable double bond. When the melting point is lower than the above range, the powder coating tends to be blocked, so that the storage stability deteriorates. On the other hand, when the melting point is higher than the above range, when the powder coating is melted, the powder coating is melted. All of them are not preferable because they require enormous heat energy and the object of the present invention cannot be achieved. The resin of the present invention is provided with a polymerizable double bond by radically polymerizing the resin by irradiating the molten coating with active energy rays, and further polymerizing the resin to improve physical and chemical strength. This is to improve. Therefore, a polymerizable double bond is added to the resin on average in one molecule.
It is suitable to have 1.2 to 10, preferably 1.5 to 5. In addition, it is desirable not to add a resin curing agent to the coating material of the present invention. This is because it is not preferable that curing starts after the coating film is melted and before it is irradiated with energy rays. Therefore, the coating material of the present invention is one in which the molecules of each resin are directly bonded by the polymerizable double bond and cured.

The resin that can be used in the present invention is not particularly limited as long as it satisfies the above conditions, and conventionally known acrylic resin-based, epoxy resin-based, unsaturated polyester resin-based, and fluororesin-based resins. Various resins such as are applicable. Generally, it is preferable that the molecular weight of the resin is about 100 to 100,000. Specifically, the acrylic resin has a molecular weight of 1500 to 50000, especially 5000 to 30000, and the epoxy resin has a molecular weight of 1000 to 30000, especially 1200 to 1000.
0 to 100,000 for unsaturated polyester resin
Especially, those of 3000 to 20000 are preferable. These resins are typically monomers or oligomers having a functional group having reactivity with a polymer or oligomer (A) having a functional group such as a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group, and an amino group, and the functional group. Alternatively, it can be produced by reacting the polymer (B) by a conventional method, but at that time, use of a monomer, oligomer or polymer having a polymerizable double bond in at least one of (A) and (B). Thus, a resin having a polymerizable double bond is obtained.

As the combination of the functional groups (A) and (B), for example, a combination of a hydroxyl group and a carboxyl group, an isocyanate group, a glycidyl group, etc .; a combination of an isocyanate group and an amino group; a carboxyl group and an amino group. Base,
A typical example is a combination with a glycidyl group or the like; a combination with a glycidyl group and an amino group or the like. The reaction ratio of the above-mentioned (A) and (B) is suitable such that the equivalent ratio of both functional groups is 1/1, but unreacted free functional groups adversely affect the properties of the cured coating film. When it does not reach, it may be mixed and reacted in such a ratio that one of the functional groups remains. The resin used in the present invention is 30-
It is suitable to add 100% by weight, preferably 40 to 80% by weight. This is because when the resin content is less than 30% by weight, various physical and chemical strengths of the formed cured coating film tend to decrease.

Examples of the pigments include titanium oxide, zinc oxide, zinc sulfide, carbon black, red iron oxide, lithopone, phthalocyanine blue, ultramarine blue, and other coloring pigments, calcium carbonate, calcium sulfate, barium sulfate, talc, and other extender pigments. Various pigments that have been conventionally used in powder coating materials such as metallic pigments and rust preventive pigments can be used without particular limitation. The pigment is 70% by weight in the paint.
It is possible to add up to about 50% by weight.
The following are appropriate: Representative examples of the photoconductive material include transparent spherical glass beads having an average particle diameter of about 5 to 60 μm, transparent amorphous glass powder, transparent hollow glass powder and the like. When UV rays are used as active energy rays, the photoconductive material is blended to propagate the UV rays to the deep part of the coating film. Therefore, use a powder coating that does not contain an opaque component such as a coloring pigment. When it is applied or when a thin film is applied, it is not always necessary to mix it. However, when a powder coating containing an opaque component is used, or when the coating thickness is 200 μm or more, it is appropriate to add 10 to 60% by weight of the photoconductive material in the coating.

The above-mentioned photopolymerization initiator is necessary when the active energy ray is ultraviolet rays, but is used when necessary when it is an electron beam. Examples of the photopolymerization initiator used in the present invention include benzoin compounds such as benzoin and benzoin methyl ether; anthraquinone compounds such as anthraquinone and methylanthraquinone; benzyl; phenylketone compounds such as acetophenone and benzophenone; diphenyldisulfide and tetramethyl. Sulfide compounds such as thiuram sulfide; various photopolymerization initiators that have been conventionally used in UV-curable coating materials such as aromatic onium salt compounds can be used without particular limitation. However, when using a powder coating containing an opaque component or thickening the film, trimethylbenzoyldiphenylphosphine oxide having excellent curability, dimethoxybenzoyldiphenylphosphine oxide, dichlorobenzoyldiphenylphosphine oxide,
Acylphosphine oxide compounds such as dimethylpropioyldiphenylphosphine oxide are particularly suitable. In addition, in order to appropriately cure the coating film, it is appropriate to add 0.1 to 5 parts by weight of the photopolymerization initiator to 100 parts by weight of the binder.

The surface conditioner used in the present invention includes
There are cellulose derivatives, polymers of long-chain acrylic acid alkyl esters, fluorinated polymers, waxes, etc., anti-sagging agents include silica powder, bentonite, metallic soap, etc., and antistatic agents include guanidine derivatives, sulfones. Examples include acids, quaternary ammonium salts, polyethylene glycol-based nonionic activators, phosphorus-containing anionic activators, tin oxide surface-treated titanium oxide, mica, and carbon. The powder coating material used in the present invention can be produced by a conventionally-used method. For example, a mixture of the above-mentioned respective components is melt-kneaded with an extruder, a heat roll, a kneader or the like at a temperature about 5 to 50 ° C. higher than the melting point of the binder to be used, and after cooling, finely pulverized to obtain an average particle diameter. About 20-150μ
It is manufactured by making the powder of m 2, but it is not limited to these methods, and it goes without saying that other conventionally known manufacturing methods can be adopted.

Next, the method for coating the metal plate of the present invention will be described. A wide range of metal plates such as cold rolled steel plates, various plated steel plates, aluminum plates, and stainless steel plates selected according to the purpose of use are subjected to blasting, degreasing, surface treatment, primer coating, etc. as necessary. ,
The powder coating is applied to the metal plate by means such as electrostatic spray coating and air spray coating. The coating amount can be arbitrarily selected according to the purpose of use of the metal plate, but it is usually suitable to set the cured film thickness to about 50 to 500 μm. Next, the powder coating material applied to the unpainted portion in the portion where the coating film such as the welded portion or the melted portion causes the inconvenience is removed by suction. There is no particular limitation on the means for sucking and removing, but the tip of the pipe-shaped object is brought into contact with the metal plate while sucking the pipe-shaped object having a flat opening with a narrower diameter than the width of the unpainted part at the tip from the rear. Alternatively, a method of moving the powder coating material to the entire unpainted portion from a distance of several mm and suction removing the powder coating material of the coating film formed thereon is suitable. The powder paint removed by suction can be recovered and reused.

After the coating film is formed in this manner, or after the coating film on the unpainted portion is further removed, the coating film remaining on the surface of the metal plate is heated and melted. The heating temperature is usually about 10 to 50 ° C. higher than the melting point of the resin which is the binder of the powder coating composition. That is, it is suitable to melt at a temperature of about 80 to 150 ° C. It should be noted that this temperature is several tens of degrees Celsius (10 to 100 ° C) lower than the baking temperature of the conventional thermosetting powder coating. As a heating means, a high frequency heating means, a far infrared heating means, etc. can be adopted as a typical means. In this way, after the coating film is melted to the same extent as when the conventional active energy ray-curable liquid coating material is applied, the active energy ray is irradiated to cure the coating film. Ultraviolet rays and electron beams can be preferably used as the active energy rays. Typical examples of the ultraviolet ray irradiation source include a mercury lamp, a xenon lamp, a metal halide lamp, a carbon arc, and the like, and an irradiation amount of about 200 to 2000 mj / cm ² is suitable. Typical electron beam sources include Cockcroft type, Van de Graaff type, resonance transformer type, dynamitron type, high frequency type, etc., and the appropriate dose is 0.5 to 20 megarads. is there. Other γ rays, X as active energy rays
Radiation such as rays and α rays can also be used.

[0016]

According to the method of the present invention, the following effects not found in the prior art can be obtained. (I) Since the active energy ray-curable powder coating material is used, it is not necessary to bake it at a high temperature unlike the conventional thermosetting powder coating material. Therefore, even for a metal plate having a large heat capacity. It can be applied, does not require a large amount of heat energy to cure the coating film, can save energy, and can be cured in a short time. (Ii) Applying an active energy ray-curable powder coating material, the formed coating film is once melted by heating at a temperature considerably lower than the baking temperature, and then irradiated with an active energy ray,
Since the coating film is cured, the coating film is easily cured by irradiation with active energy rays as in the conventional active energy ray-curable liquid coating material. (Iii) When coating a metal plate including an unpainted part, since powder paint is used, it is possible to easily remove the powder paint in the unpainted part by suction after the entire surface is coated. It is possible to omit complicated steps, and the painting workability is good.

[0017]

EXAMPLES The present invention will now be described in more detail by way of examples. In the examples, "parts" and "%" are based on weight. <Preparation of Acrylic Resin A> Xylene was added to a four-necked flask.
Charge 200 parts and 260 parts of methyl isobutyl ketone, raise the temperature to 110 ° C in a nitrogen atmosphere, and then, with stirring, 180 parts of methyl methacrylate, 217.5 parts of ethyl acrylate, 53.2 parts of 2-hydroxyethyl methacrylate, acrylic. acid
A solution prepared by dissolving 13.7 parts of tertiary butyl peroxy 2-ethylhexanoate in 4.6 parts of the mixture was added dropwise over 2.5 hours. After 30 minutes, in 30 parts of methyl isobutyl ketone, tertiary butyl peroxy 2 was added.
-Add 30 parts of a mixture containing 2.0 parts of ethyl hexanoate.
The mixture was added dropwise over minutes and aged for 2 hours.

Next, after cooling to 90 ° C., 2.5 parts of dibutyltin dilaurate and 49.8 parts of 3-isopropenyl-α, α-dimethylbenzidine isocyanate were added and reacted for 1 hour, and then the solvent was removed under reduced pressure. The weight average molecular weight of the obtained copolymer was 10500 and the hydroxyl value was 25.2 mg.
KOH / g (solid content), melting point was 95 ° C., and the number of polymerizable double bonds was about 4.7 per weight average molecular weight (hereinafter, this copolymer is referred to as acrylic resin A). <Preparation of Epoxy Resin B> Bisphenol A epoxy resin [trade name "Epicoat 1004" manufactured by Yuka Shell Epoxy Co., melting point 98 ° C, epoxy equivalent 87 in a four-necked flask]
5 to 975] 900 parts, methacrylic acid 86 parts, hydroquinone
0.2 part and imidazole (1.5 parts) were charged, and the mixture was heated to 150 ° C. in a nitrogen atmosphere and reacted until the acid value became 5. The number average molecular weight of the obtained epoxy acrylate resin is 1550,
The melting point was 118 ° C., and the number of polymerizable double bonds was about 1.8 per number average molecular weight. (Hereinafter, this epoxy acrylate resin is referred to as epoxy resin B) <Preparation of powder coatings A to F> After mixing the formulations shown in Table 1 with a Henschel mixer, melt kneading with a Busco kneader heated to 125 ° C, Then, it was cooled and coarsely pulverized to obtain a pellet-shaped kneaded material. The kneaded product was pulverized with a pin mill to obtain powder coatings A to F having an average particle size of about 40 μm.

Example 1 Powder coating material A was electrostatically applied to a surface of a shot-blasted steel plate (size 100 × 200 mm, thickness 10 mm) surface-treated with an iron phosphate-based surface treatment agent so that the film thickness would be about 150 μm. Spray painted. Next, the coating film on the unpainted portion of the 20 mm wide peripheral edge of the coated steel plate was removed by suction with a suction device having a 15 mm wide flat opening at the tip. Then, the coated steel sheet is put into an electric furnace, heated to a material temperature of 130 ° C., melted for 3 minutes, immediately put into an ultraviolet irradiation device, and irradiated with ultraviolet rays,
The coating was cured. The ultraviolet irradiation conditions were as follows. Lamp: metal halide lamp irradiation amount is set parallel reflection plate: about 800 mj / cm ² irradiation time distance between 20 seconds ramp and the steel sheet: 100 mm per resulting cured coatings were tested hardness and solvent resistance, The results are shown in the lower part of Table 1.

Examples 2-3 and Comparative Examples 1-2 Powder coating, coating and coating were carried out in the same manner as in Example 1 except that melting conditions in an electric furnace and UV irradiation conditions were changed as shown in Table 1. The film was cured. A similar test was conducted on the obtained cured coating film, and the results are shown in the lower part of Table 1. Comparative Example 3 The coating was applied and the coating film was cured in the same manner as in Example 1 except that the powder coating and the melting conditions in the electric furnace were changed as shown in Table 1 and the ultraviolet irradiation was not performed. A similar test was conducted on the obtained cured coating film, and the results are shown in the lower part of Table 1. The method of Comparative Example 3 is the same as the conventional method except that the coating film on the unnecessary coating portion is removed by suction.

[0021]

[Table 1] Table 1 ─────────────────────────────────── Actual Example Ratio Comparative Example 1 2 3 1 2 3 ─────────────────────────────────── Powder coating / Powder coating blend ABCDEF (Unit: Part)) ─────────────────────────────────── Acrylic resin A 60 Epoxy resin B 60 60 Epicoat 1004 60 56 56 Dicyandiamide 2.1 2 2 Transparent glass powder Note 1) 25 25 25 25 Titanium oxide Note 2) 10 10 10 12 20 Quartz sand powder Note 3) 30 30 Fine powder silica Note 4) 1 1 Carbon black 0.04 Trimethylphosphine 1.2 1.2 Oxide Dichlorobenzoyl 1.2 Diphenylphosphine oxide Flow regulator Note 5) 0.2 0.2 0.2 0.2 0.3 0.3 ─────────────────────────────── ── ─ Melting condition 130 × 3 140 × 5 140 × 5 140 × 5 140 × 8 180 × 25 [Material temperature (℃) × Melting time (min)] UV irradiation condition 800 × 20 600 × 30 800 × 30 600 × 30 600 × 30 − (Irradiation amount (mj / cm ² ) × Irradiation time (sec)) Test hardness Note 6) 7H 3H 3H 2B 2B 2H Test solvent resistance Note 7) 200 <200 <200 <3 5 200 <(times) ───────────────────────────────────

Note 1) Average particle size 15 μm Note 2) Examples 1 and 2 and Comparative Example 1 are anatase type titanium oxide, Comparative Examples 2 and 3 are rutile type titanium oxide Note 3) Average particle size 5 μm Note 4) Average particle Diameter 0.1 μm Note 5) “PF-S” (product name of Kyoeisha Yushi Co., Ltd.) Note 6) Pencil hardness based on JIS K 5400 Note 7) Rubbing the coated surface with gauze soaked with xylene, the material surface is exposed Measure the number of times to do. As is clear from Table 1, Examples 1 to 1 according to the method of the present invention
No. 3 was cured for a short time and had excellent coating film performance. On the other hand, the coating performance was poor in Comparative Examples 1 and 2 in which powder coatings containing a resin having no polymerizable double bond as a binder were used. Further, in Comparative Example 3 using the conventional powder coating and using the conventional curing method, although the heating temperature was higher and the heating time was longer than in Examples 1 to 3, the coating film hardness was slightly increased. It was inferior.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B05D 7/24 A 8720-4D // C09D 5/00 PNW 6904-4J 5/03 PMZ 6904-4J (72) Inventor Osamu Terao 1-2-2-10 Taishibashi, Asahi-ku, Osaka City (72) Inventor Atsushi Takamatsu 9-6-1 Karigaoka, Hirakata-shi D13-223 (72) Terumi Hibi Marunouchi, Chiyoda-ku, Tokyo 2-5-1 Sanryo Heavy Industries Co., Ltd. Ship & Marine Business Division (72) Inventor Akio Shibata 5-717-1 Fukahoricho, Nagasaki-shi, Nagasaki Sanryo Heavy Industry Co., Ltd. Nagasaki Research Institute

Claims (2)

[Claims] 1. A metal plate surface is coated with an active energy ray-curable powder coating material having a melting point of 60 to 130 ° C. and containing a resin having a polymerizable double bond, and then the coating film is melted by heating, A method for coating a metal plate, which comprises irradiating an active energy ray to cure the coating film. 2. A metal plate surface is coated with an active energy ray-curable powder coating material having a melting point of 60 to 130 ° C. and containing a resin having a polymerizable double bond, and the formed coating film is applied to an unnecessary coating portion. A method for coating a metal plate, which comprises removing the formed coating film by suction, melting the coating film by heating, and then irradiating an active energy ray to cure the coating film.