JP3368055B2 - Thermosetting powder coating method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thermosetting powder coating film. 2. Description of the Related Art Conventionally, when a usual thermosetting powder coating is applied to a surface to be coated having an edge, it is difficult for the powder coating to adhere to the edge due to electrostatic repulsion of the powder coating. In addition, the coating thickness at the edge portion is reduced due to the fact and the surface tension of the heated melt. For this reason, there was a defect that the corrosion resistance of the edge portion was inferior. In order to improve the corrosion resistance of the edge portion, various methods have been tried, such as adding a large amount of a pigment to a thermosetting powder coating or compounding gelled fine particles. The fact is that it is incompatible with the formation of a coating film, and a product satisfying these has not yet been obtained. SUMMARY OF THE INVENTION The present invention has been made as a result of intensive studies to solve the above-mentioned problems, and as a result, a surface to be coated is coated with a thermosetting powder coating, and then the powder is coated. A coating method in which another thermosetting powder coating is applied from above without heating and melting the body coating, followed by simultaneously heating and curing these thermosetting powder coatings, and The present inventors have found that a thermosetting powder coating prepared to have a specific flow property can form a cured coating film having excellent smoothness and excellent anticorrosion properties on edge portions, and have completed the present invention. That is, according to the present invention, as a first step, about 0.8 g of a thermosetting powder coating is formed on a surface to be coated into a column having a diameter of 13 mm and a height of about 4 mm by a pressure of 30 kg / mm ^2. The spread length when heated and flowed at 150 ° C. for 10 minutes has an average diameter of 13 to 25 mm, and the thermosetting resin 1
A thermosetting powder coating material containing 1 to 19.9 parts by weight of a filler with respect to 00 parts by weight (hereinafter referred to as “powder coating material A”) is applied, and then two steps. As an eye, the thermosetting powder coating has a spread length of 20 to 40 mm in average diameter and a difference in the spread length of 2 mm or more larger than that of the first stage measured by the same method as described above. (Hereinafter, this is abbreviated as “powder coating B”.) The present invention relates to a method for forming a thermosetting powder coating film, characterized in that these coating films are simultaneously baked and cured. The powder coating A used in the method of the present invention is obtained by pressing about 0.8 g of the powder coating into a column having a diameter of 13 mm and a height of about 4 mm at a pressure of 30 kg / mm ² at 150 ° C.-10 The length of the spread when heated for a minute is 13 ~
It is 25mm. In the pressure molding, for example, the powder coating is
It can be carried out using a tablet molding machine (manufactured by Shimadzu Corporation) in a Br desk press (diameter: 13 mm) (manufactured by Hitachi, Ltd.). In addition, the one molded by pressure has a size of 15
Bright steel plate of cm × 10cm × 0.08cm thickness (JIS
G-3141, SPCC, SB) and then heated. [0007] The spread of the powder coating material A has an average diameter of 13 to
An important requirement is to be in the range of 25 mm. If the length of the spread exceeds 25 mm in average diameter, it is difficult to sufficiently cover the edge portion, so that the corrosion resistance of the coating film is inferior. As the powder coating A, for example, an epoxy resin powder coating, a polyester resin powder coating, an acrylic resin powder coating, a mixture thereof or a hybrid coating can be used. As the epoxy resin-based powder coating, for example, an epoxy resin of bisphenol-epichlorohydrin type, novolak type, alicyclic type or the like is used as a base resin, and aromatic amine, acid anhydride, dicyandiamide or a derivative thereof, dihydrazide, Those containing a phenol resin or the like as a curing agent are preferred. As the polyester resin powder coating, for example, saturated polybasic acids such as terephthalic acid, isophthalic acid and trimellitic acid and ethylene glycol, glycerin,
The base resin is a hydroxyl group- and / or carboxyl group-containing oil-free polyester made from a polyhydric alcohol such as neopentyl glycol or trimethylolpropane, and a block polyisocyanate, an amino resin, triglycidyl isocyanurate or the like is contained as a curing agent. Are preferred. As the acrylic resin-based powder coating, for example, a hydroxyl group-containing acrylic resin containing hydroxyethyl (meth) acrylate as a copolymer component is used as a base resin and a block polyisocyanate, an amino resin as a curing agent, or glycidyl ( A glycidyl group-containing acrylic resin containing (meth) acrylate as a copolymer component is preferably used as a base resin and a polybasic acid such as dodecane diacid as a curing agent. The powder coating material A preferably contains a filler in an amount of 1 to 19.9 parts by weight based on 100 parts by weight of the curable resin (including the hardener component) of the powder coating material. If the content of the filler is less than 1 part by weight, the anticorrosion property against the edge portion is not sufficient, while if it exceeds 19.9 parts by weight, the finish is undesirably deteriorated. As the filler, silica, alumina,
It is a fine powder such as titania and zirconia, and has an average particle diameter of 5 to 50 mμ (0.005 to 0.05 μm
), Preferably 5 to 23 mμ (0.005 to 0.02
3 μm) in an amount of 90% by weight or more. When the average particle size of these powders is smaller than 5 mμ, the viscosity and thixotropic properties are too high, and the workability of the coating material is significantly reduced. On the other hand, when the average particle size is larger than 50 mμ, the thixotropic properties are reduced and the coating of the edge portion is reduced. Any of these is not preferred because the properties are insufficient. The length of the spread of the powder coating A can be adjusted, for example, by the molecular weight of the base resin, Tg (glass transition temperature) and the proportion of the filler. The powder coating material B used in the method of the present invention has a spread length after heating of a molded article under pressure measured by the same method as described above and has an average diameter of 20 to 40 mm, preferably 24 to 4 mm.
The range is 0 mm. The average length of the spread is 20mm
If it is below, the finished appearance due to yuzu silk etc. will be inferior,
When the average diameter exceeds 40 mm, there is a disadvantage that a coating film defect due to sagging or the like occurs. As the powder coating material B, one obtained by molding under pressure and having a difference in spread length after heating of 2 mm or more in average diameter is used. If this difference is less than 2 mm in average diameter, the finished appearance due to yuzu skin etc. will be poor. As the powder coating B, the same epoxy resin powder coating, polyester resin powder coating, acrylic resin powder coating, and mixtures or hybrids thereof as described above can be used. The length of the spread of the powder coating material B can be adjusted, for example, by the molecular weight and Tg of the base resin. The average particle size of the powder coatings A and B is about 10 to 150.
μm is preferred. In the method of the present invention, it is preferable to use acrylic resin-based powder coatings as the powder coatings A and B, respectively, from the viewpoint of finishing properties. To the powder coatings A and B, coating additives such as a coloring pigment, an anti-cissing agent, and an ultraviolet absorber can be added as necessary. The method of the present invention can be carried out by electrostatically applying a powder coating A on a surface to be coated, electrostatically applying a powder coating B, and then baking and hardening. The surface to be coated is not particularly limited as long as it can be coated with an electrostatic powder. For example, aluminum, iron,
Metals such as zinc and those obtained by applying an undercoating film such as an electrodeposition coating film, an intermediate coating film and a colored base coating film (solid color, metallic color, etc.) to this can be used. Also,
The surface to be coated having the edge portion includes, for example, an aluminum wheel for an automobile. It can be finished, for example, with a metallic base (aqueous or solvent type) paint as an undercoat, and powder paints A and B as an overcoat clear. The coating thickness of the powder coatings A and B is preferably 30 to 150 μm after baking and curing. In addition, baking varies depending on the type of a curing agent, but is usually 140 ° C. to 26 ° C.
10 seconds to 60 minutes at 0 ° C. seems sufficient. Hereinafter, the present invention will be described in detail with reference to examples. Production Examples of Powder Coatings E, P, A The components listed in Table 1 were mixed with a Henschel mixer (manufactured by Mitsui Miike Co., Ltd.), and the mixture was kneaded with a Busconi Kneader PR46 (manufactured by Buss Co., Switzerland) at a discharge rate of 30-70 kg / H Temperature 80-12
Kneading is performed at 0 ° C. and a screw rotation speed of 100 rpm.
The kneaded material is taken out into a flat plate having a thickness of 3 to 6 mm and rapidly cooled. Thereafter, the mixture is roughly pulverized to a size of 2 to 3 mm and then finely pulverized using an atomizer (manufactured by Fuji Sangyo Co., Ltd.). Then, sieve using a 150 mesh standard sieve. The coarse particles are removed to obtain powder coatings E, P and A. The components in Table 1 are as follows. Base resin Epoxy resin: EPON 1004 (Bisphenol A-epichlorohydrin type epoxy resin, manufactured by Yuka Shell Epoxy Co., Ltd., average molecular weight: about 1400) Polyester resin: Finedec M8010 (hydroxyl-containing polyester resin manufactured by Dainippon Ink) Acrylic resin: Aroma TEC PD6300 (Mitsui Toatsu Co., Ltd., glycidyl group-containing acrylic resin) Curing agent Epoxy curing agent: Epicure 108FF (Yuika Shell Epoxy, amine type) Polyester curing agent: IPD1-B1530 (Daicel Huls Co., Ltd.) Isophorone diisocyanate blocked with ε-caprolactam) Acrylic curing agent: Dodecane diacid Filler: Aerosil # 380 (Nippon Aerosil Co., Ltd.)
Additive a: Acronal 4F (manufactured by BASF) Additive b: Paintad M (manufactured by Dow Corning) Additives a: Acronal 4F (manufactured by Dow Corning) Is about 0.8
g into a column with a diameter of 13mm and a height of about 4mm
/ mm ² is a numerical value obtained by measuring the average diameter when the product molded under pressure was heated at 150 ° C. for 10 minutes. [Table 1] EXAMPLES AND COMPARATIVE EXAMPLES The powder coating for the first step coating shown in Table 2 was electrostatically coated on panel A so that the cured film thickness became 30 to 40 μm. Hardened film thickness of powder coating for stage coating is 30
After electrostatic coating to a thickness of ４０40 μm, the coating was formed by heating at 170 ° C. for 30 minutes with a hot air drier. The finish of the formed coating film was evaluated. Next, using Panel B, a coating film was formed in the same manner as described above. The formed coating film was evaluated for edge corrosion resistance. Panel A: Cold-rolled steel plate SPCC (width 100 mm x length 3
(00 mm x 0.8 mm thick) degreased with toluene. This panel was used for finishing. Panel B: The panel A using a drill (φ10 mm blade)
5 holes were made at 5 mm intervals in the center of the sample, a hole having an edge (burr, projection) on the back surface was formed, and this back surface was used as a surface to be coated. Table 2 shows the results. [Table 2] The coating properties in Table 2 were evaluated according to the following criteria. The coating film applied to the finished panel A was visually observed to examine its smoothness. ◎ Excellent smoothness. ○ There are slight irregularities. △ There are considerable irregularities × Irregularities are severe. The coating applied to the edge anti-corrosion panel B is subjected to a salt spray test (JIS Z-
2371) for 72H. The occurrence of rust on the edge portion (burrs, protrusions) around the hole was examined. ◎ No rust occurred. ○ Slight rusting. △ Significant rust occurred. X: Rust is remarkable. The method of the present invention has the following effects because it is the method described above. (1) The corrosion resistance of the coating film on the edge portion is good. (2) Good finish appearance with no paint defects such as sagging and yuzu silk. (3) Conventionally, in a method in which two types of powder coatings are applied and baked and cured simultaneously, the surface tension of the coating is reduced by making the coating forming the upper coating film smaller than the coating forming the lower coating film. Improvements have been made to the finished appearance. However, in this method, the corrosion resistance against the edge portion is not sufficient, and the finished appearance is not sufficient just by adjusting the surface tension of the two types of paints. A combination of different paint systems is used so that the powder paint is applied to the varnish, and there is a drawback that the process is complicated. The method of the present invention is characterized in that, for example, a coating film having excellent anticorrosion properties and finish properties can be formed only by using powder coatings of the same system and by adding a filler to one of them.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-115584 (JP, A) JP-A-62-269780 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/06 B05D 7/24 301 C09D 5/03

Claims (1)

(57) [Claim 1] As a first step, about 0.8 g of a thermosetting powder coating is applied to a surface to be coated in a cylindrical shape having a diameter of 13 mm and a height of about 4 mm in a weight of 30 kg. / mm ² Press molded at 150 ℃ -1
The average length of the spread when heated for 0 minutes is 1
A thermosetting powder coating material having a thickness of 3 to 25 mm and containing 1 to 19.9 parts by weight of a filler with respect to 100 parts by weight of the thermosetting resin is applied. The spread length of the pressure-molded product measured by the same method is coated with a thermosetting powder coating material having an average diameter of 20 to 40 mm and a difference in the spread length of 2 mm or more larger than the first stage, A thermosetting powder coating film forming method, wherein these coating films are simultaneously baked and cured.