JP2003181371A - Coating method of metal material having surface defect and coated product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method capable of forming a coating with a smooth surface without using a paste or carrying out polishing a metal surface in the case of coating a metal material such as a die cast magnesium alloy having surface defects with a powder coating and provide a coated product. <P>SOLUTION: The coating method involves applying a powder coating to a metal material having surface defects and baking and hardening the pint and the powder coating to be used here has a minimum melt viscosity in a range of 1.0 to 2.0 Pa s. The baking and hardening conditions may be, for example, at 140-200°C for 1-30 minutes. <P>COPYRIGHT: (C)2003,JPO

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 thermosetting powder coating on a metal material having a surface defect such as a magnesium alloy material, and a home electric appliance, an office automation equipment / mobile equipment obtained by this coating method. Etc. regarding coated objects.

[0002]

2. Description of the Related Art Die casts of magnesium alloys and aluminum alloys are often used as materials for housings and parts of home electric appliances, office automation equipment and the like. This die cast is painted for the purpose of improving corrosion resistance and aesthetics, but the die cast surface has defects such as wrinkles and burrows that occur when pouring molten metal into a mold. There are still many. When powder coating is applied to such a die-cast and baked, the air trapped in the defect causes the coating to foam, resulting in the loss of smoothness of the coating. Has been needed.

As the above-mentioned pretreatment method, conventionally, a putty paint has been applied as a thick film, and this has been polished to smooth the surface. Recently, omitting the polishing process after coating by defining the particle size of the powder coating,
JP-A-2000-273390, JP-A-11-19
No. 7596 and Japanese Patent Laid-Open No. 2001-38290. However, it was not possible to obtain a sufficiently smooth coating film only by defining the particle size.

[0004]

The present invention can provide a coating film having a smooth surface on a metal material having a surface defect such as die-cast magnesium alloy without using putty or polishing. An object of the present invention is to provide a coating method using powder coating material and a coated article.

[0005]

A method for coating a metal material according to the present invention is a coating method in which a powder coating material is applied to a metal material having a surface defect and baking and curing are performed. The minimum melting viscosity of body paint is 1.0 to
The range is 2.0 Pa · s. Here, the bake hardening conditions may be a temperature of 140 to 200 ° C. and a time of 1 to 30 minutes. Further, the metal material having the surface defects may be any of magnesium alloy, aluminum alloy and zinc alloy.

In the coating method of the present invention, the coating film may be completed by a single coating, but if necessary, further top coating or lamination may be performed.

The coated article of the present invention is obtained by coating the powder coating by the previous coating method, and may be, for example, a home electric appliance, OA equipment / mobile equipment, or automobile part.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

The coating method of the present invention is a coating method in which a powder coating material is applied to a metal material having a surface defect and baking-hardening is performed, and the melting minimum viscosity of the powder coating material under the baking-hardening condition is It is in the range of 1.0 to 2.0 Pa · s.

As the metal material having the above surface defects,
Examples include magnesium alloys, aluminum alloys, zinc alloys, and the like. These are often used as die casts, for example, in the form of housings for electric products and metal products. Examples of the die cast include magnesium die cast, thixomolded magnesium alloy, and aluminum die cast.

In the method for coating a metal material according to the present invention, first,
Powder coating is applied to the metal material having the surface defects.
The application means is not particularly limited, and specifically, a spray coating method, an electrostatic powder coating method, a fluidized dipping method and the like well known to those skilled in the art can be mentioned. However, from the viewpoint of coating efficiency, it is preferable to use the electrostatic powder coating method using a powder coating gun. Further, as the powder coating gun, it is preferable to use a corona charging type coating gun or a friction charging type coating gun.

The coating film formed on the metal material having surface defects by the above coating has a film thickness after baking of 20 to 40 μm.
Is preferably coated. The film thickness is 20
If it is less than μm, the surface defect portion may not be completely filled, and if it exceeds 40 μm, it is useless.

The powder coating material used in the method for coating a metal material according to the present invention has a minimum melt viscosity in the range of 1.0 to 2.0 Pa · s under the bake-hardening condition described later. If the minimum melt viscosity is less than 1.0 Pa · s, the viscosity is insufficient, so
The molten paint sinks to the bottom of the surface defect hole and cannot cover the surface of the defect, resulting in a concave surface. If it exceeds 2.0 Pa · s, the fluidity will be insufficient,
Since the coating film is formed only along the defect shape of the metal surface, the concave surface remains as a result. The preferred upper limit is 1.5 Pa
-S, the lower limit is 1.8 Pa-s. The minimum melt viscosity can be determined by continuously measuring the change in viscosity under bake-curing conditions using a viscosity measuring instrument such as Urizo Solikit Meter MR300.

The bake-hardening conditions are such that the surface temperature of the metal material is maintained at 140 to 200 ° C. for 1 to 30 minutes. The preferred lower limit is 150 ° C and the upper limit is 1.
It is 70 ° C. If the surface temperature is lower than 140 ° C., it is difficult to lower the melting minimum viscosity to the above-specified range, and if it exceeds 200 ° C., air escapes from the defective portion of the metal surface, and the smoothness of the coating film is reduced. May be damaged. The preferable lower limit of the surface temperature holding time is 4 minutes, and the upper limit thereof is 20 minutes. If this holding time is less than 1 minute, it is difficult to lower the above-mentioned minimum melt viscosity to the above-specified range, and since normally the melting of powder coating material is completed in 30 minutes, the temperature is further increased. Holding it wastes energy.

The powder coating used in the coating method of the present invention is
It is not particularly limited as long as it satisfies the requirement of the minimum melt viscosity under the bake-curing condition. The above powder coating material can be selected by measuring the minimum melting viscosity under the bake-curing condition of a conventionally known general powder coating material. Further, in designing powder coatings, the melting point can be improved by considering the Tg of the resin, selecting each component, especially the type of curing agent and thickener, and changing the blending amount thereof in accordance with the bake curing conditions. It is possible to control the minimum viscosity.

As a powder coating suitable for the coating method of the present invention, an epoxy group-containing resin and a carboxylic acid group- or carboxylic acid anhydride-containing curing agent (hereinafter referred to as "(anhydrous) carboxylic acid group-containing curing agent"). The thing which has as a main component can be mentioned.

Examples of the epoxy group-containing resin include compounds having two or more epoxy groups in one molecule, and specifically, a reaction product of a novolac type phenol resin and epichlorohydrin, a bisphenol resin. (A-type, B-type, F-type, etc.) and epichlorohydrin reaction products, novolac-type phenol resin and bisphenol resin (A-type, B-type, F-type, etc.) and epichlorohydrin reaction product, novolac-type phenol resin Reaction products with bisphenol resins (A type, B type, F type, etc.), reaction products with cresol compounds such as cresol novolac and epichlorohydrin, ethylene glycol, propylene glycol, 1,4-butanediol, polyethylene glycol, polypropylene Glycol, Neopentyl glycol, Gu By the reaction of glycidyl ether, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid, hexahydrophthalic acid, trimellitic acid and other carboxylic acid compounds obtained by the reaction of alcohol compounds such as cerol with epichlorohydrin, and epichlorohydrin The obtained glycidyl ester, a reaction product of hydroxycarboxylic acid such as p-oxybenzoic acid and β-oxynaphthoic acid with epichlorohydrin, triglycidyl isocyanurate and its derivative are used.

Further, an epoxy group-containing acrylic resin can also be used. For example, 2-hydroxyethyl (meth) acrylate, which contains an epoxy group-containing monomer such as glycidyl acrylate, glycidyl methacrylate, and 2-methylglycidyl methacrylate as an essential component, 2-
Hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, an adduct of 2-hydroxyethyl (meth) acrylate and polycaprolactone, a hydroxyl group-containing monomer such as polyalkylene glycol mono (meth) acrylate, and ( Methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, styrene,
Examples thereof include those obtained by polymerizing radically polymerizable monomers such as vinyltoluene and p-chlorostyrene according to a conventional method.

The epoxy group-containing resin may be used in combination of two or more kinds. The epoxy equivalent of the epoxy group-containing resin is not particularly limited, but is 200 to 300.
It is preferably 0, and more preferably 300 to 2800.
If the epoxy equivalent is less than 200, the storage stability may decrease, and if it is more than 3000, the curability may decrease. On the other hand, the number average molecular weight of the epoxy group-containing resin is not particularly limited, but 2
It is preferably from 00 to 10000, more preferably from 500 to 5000. When the number average molecular weight is less than 200, the resulting coating film performance may be deteriorated or the minimum melt viscosity may be less than 1 Pa · s.
If it is larger than 00, the smoothness of the obtained coating film may be deteriorated or the minimum melt viscosity may be larger than 2 Pa · s. Further, the softening point of the epoxy group-containing resin is not particularly limited, but is usually 20 to 100 ° C.,
Further, it is preferably 50 to 100 ° C. If the softening point is lower than 20 ° C, the blocking resistance may be lowered, while if it is higher than 100 ° C, the smoothness of the obtained coating film may be lowered.

Examples of the (anhydrous) carboxylic acid group-containing curing agent include compounds and resins having two or more (anhydrous) carboxylic acid groups in one molecule. Specific examples thereof include polyvalent (anhydrous) carboxylic acid compounds, (anhydrous) carboxylic acid group-containing acrylic resins, and (anhydrous) carboxylic acid-containing polyester resins. These can be used in combination of plural kinds.

Examples of the polyvalent (anhydrous) carboxylic acid compound include aromatic polyvalent (anhydrous) carboxylic acids such as trimellitic acid and phthalic acid, and heterocyclic polyvalent (anhydrous) carboxylic acids such as imidazoline dicarboxylic acid. Examples thereof include acids, decanedicarboxylic acid, sebacic acid, and other aliphatic polycarboxylic acids. Further, as the (anhydrous) carboxylic acid group-containing acrylic resin, an acrylic resin having two or more (anhydrous) carboxylic acid groups in one molecule, for example, an (anhydrous) carboxylic acid group-containing monomer such as acrylic acid or methacrylic acid As an essential monomer, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-
Addition product of hydroxyethyl (meth) acrylate and polycaprolactone, hydroxyl group-containing monomer such as polyalkylene glycol mono (meth) acrylate, and methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid Examples thereof include those obtained by polymerizing radical-polymerizable monomers such as n-butyl, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, styrene, vinyltoluene, and p-chlorostyrene according to a conventional method. .

Further, as the above-mentioned (anhydrous) carboxylic acid group-containing polyester resin, two or more (anhydrous) resins in one molecule
Examples thereof include those obtained by polycondensation using an acid component having a carboxylic acid group and containing a polycarboxylic acid as a main component and an alcohol component containing a polyhydric alcohol as a main component. Examples of the acid component include terephthalic acid, isophthalic acid, phthalic acid and anhydrides thereof, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid, and anhydrides thereof, succinic acid, Saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and their anhydrides, lactones such as γ-butyrolactone and ε-caprolactone, p-oxyethoxybenzoic acid Examples thereof include aromatic oxymonocarboxylic acids such as acids and hydroxycarboxylic acids corresponding thereto. You may use these 2 or more types together.

As the alcohol component, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4 -Butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,4-hexanediol, 1,5-hexanediol, 2,5- Hexanediol, 1,4-cyclohexanediol,
1,4-cyclohexanedimethanol, alkylene oxide adduct of bisphenol-A, bisphenol-
S alkylene oxide adduct, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,2
Examples thereof include aliphatic glycols having a side chain such as dodecanediol and 1,2-octadecanediol, and trivalent or higher polyhydric alcohols such as trimethylolpropane, glycerin and pentaerythritol. These may be two or more.

The number average molecular weight of the (anhydrous) carboxylic acid group-containing curing agent is not particularly limited, but it is 100 to 1
It is preferably 0000, and more preferably 200 to 5000. The number average molecular weight is 100
If it is smaller, the resulting coating film performance may be deteriorated, while if it is larger than 10,000, the smoothness of the obtained coating film may be deteriorated.

T of the above-mentioned (anhydrous) carboxylic acid group-containing curing agent
From the viewpoint of blocking resistance and the smoothness of the resulting coating film, g is preferably 20 to 100 ° C., and more preferably 50 to 100 ° C. The Tg in the present invention is the differential scanning calorimeter (DS
C), but when the (anhydrous) carboxylic acid group-containing curing agent is an (anhydrous) carboxylic acid group-containing acrylic resin, it should be determined from the monomer ratio having a known Tg constituting the copolymer. You can also

The molar ratio of the total amount of epoxy groups contained in the epoxy group-containing resin to the total amount of acid groups contained in the (anhydrous) carboxylic acid-containing curing agent can be appropriately set in relation to the minimum melt viscosity, , 1/1 to 1 / 0.5, preferably 1 / 0.8 to 1 / 0.6. The epoxy group is 1
When it is less than / 1, the melting minimum viscosity of the obtained coating composition may be less than 1.0 Pa · s. Further, when the number of the epoxy groups is more than 1 / 0.5, the obtained coating composition may have a minimum melt viscosity of more than 2.0 Pa · s.

In addition to the above components, the powder coating used in the present invention may further contain a surface conditioner, a matting agent, and
Additives such as a thickener, a coloring pigment, a rust preventive pigment, an extender pigment, a curing catalyst, a plasticizer, and a pigment dispersant may be contained.

Examples of the surface modifier include silicones such as dimethyl silicone and methylphenyl silicone, acrylic oligomers and the like. As a delustering agent, various waxes, various extender pigments described below,
As thickeners, colloidal silica, bentonite, etc.,
As the coloring pigment, titanium dioxide, red iron oxide, iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacone-based pigment, azo-based pigment, rust-preventive pigment such as aluminum tripolyphosphate, and body pigment such as alumina, talc, clay. , Calcium carbonate,
Examples thereof include barium sulfate and silica.

Further, an imidazole type curing catalyst, imidazoline or the like can be used as a curing catalyst, and epoxidized soybean oil or the like can be used as a plasticizer. The content of each of the various additives is preferably 10 parts by mass or less in 100 parts by mass of the powder coating material except for the pigment. When it exceeds 10 parts by mass, the smoothness of the obtained coating film may be deteriorated. Further, regarding the pigment, the total content thereof is preferably 50 parts by mass or less in 100 parts by mass of the powder coating material. If it exceeds 50 parts by mass, the smoothness of the coating film may decrease.

The method for producing the powder coating material used in the present invention is not particularly limited, and any known production method in the powder coating field may be used. As an example, after dry-mixing the above raw materials with a Henschel mixer or the like, melt-kneading with a Busco kneader or the like at a temperature at which the epoxy group-containing resin and the (anhydrous) carboxylic acid group-containing curing agent do not react, cool and then pulverize and classify. There is a way.

The volume average particle diameter of the powder coating material of the present invention is not particularly limited, but from the viewpoint of coating workability and smoothness of the resulting coating film, it is preferably 5 to 50 μm, and 15 to 40 μm. Is more preferable.

Next, in the coating method of the present invention, baking is performed under the above-mentioned baking and hardening conditions. In the coating method of the present invention, the coating film may be completed by a single coating, but if necessary, top coating or lamination may be further performed. The above-mentioned topcoat preferably has a design property such as metallic or texture. There is no particular limitation on the type of top coating used at this time,
In addition to the powder coating material, other general organic solvent type coating material, water-dispersible or water-soluble water-based coating material can be used. When lamination is performed instead of coating, a transparent film or colored film made of polyethylene or the like can be used.

The coated article of the present invention is obtained by coating the powder coating material by the above coating method. Specific examples include home appliances such as televisions and videos, mobile phones, PHSs, notebook computers, PDAs, digital cameras, projectors, MDs, CDs, which use at least part of the metal material having the above-mentioned surface defects. OA equipment such as DVD and mobile equipment, and automobile parts such as tire wheels, engine covers and steering wheels can be mentioned.

[0034]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. In the formulation of each example, “parts” means “parts by mass”.

Synthesis of powder coating Synthesis Example 1 Epotote NT111 (epoxy resin having an epoxy equivalent of 475, manufactured by Tohto Kasei Co., Ltd.) 33 parts, Epotote NT112
(Epoxy resin with epoxy equivalent of 650, manufactured by Tohto Kasei Co., Ltd.)
33 parts, 2.5 parts surface modifier, 1 part matting agent, 20 parts titanium dioxide as white pigment, 10 parts alumina and silica as extender pigment, and 4.1 parts acid anhydride compound of imidazoline as hardening agent Mix the raw materials with a super mixer (made by Nippon Spindle Manufacturing Co., Ltd.) for about 3 minutes,
The mixture was melt-kneaded with a cokneader (manufactured by Buss Co., Ltd.) under the condition of about 100 ° C.

The obtained melt-kneaded product was cooled to room temperature, coarsely pulverized and then pulverized by an atomizer (manufactured by Fujisha Paudal Co., Ltd.), and then classified by a 150-mesh sieve to obtain a volume average particle diameter of 40.
A powder coating 1 of μm was obtained. Microtrac HRA X-100 (manufactured by Nikkiso Co., Ltd.) was used for measuring the volume average particle diameter.

Synthetic Example 2 In the formulation of Synthetic Example 1, imidazole 0.
A powder coating material 2 was obtained by the same formulation and method as in Synthesis Example 1 except that 05 parts were added.

Synthesis Example 3 A powder coating material 3 was prepared by the same formulation and method as in Synthesis Example 2 except that 66 parts of the epoxy resin was changed to Epotote NT112 in the formulation of Synthesis Example 2.

Synthesis Example 4 Preparation was carried out by the same formulation and method as in Synthesis Example 3, except that the addition of the curing catalyst was stopped during the formulation of Synthesis Example 3 and 0.5 part of colloidal silica as a thickener was added instead. Powder coating 4 was obtained.

Synthesis Example 5 Instead of the epoxy resin of Synthesis Example 4, Epotote NT11
4 (epoxy resin having an epoxy equivalent of 950, manufactured by Tohto Kasei Co., Ltd.) was used, and the addition of the curing catalyst was stopped.
A powder coating material 5 was obtained by the same formulation and method.

Synthesis Example 6 Instead of the epoxy resin of Synthesis Example 5, Epotote NT11
Powder coating material 6 was obtained by the same formulation and method as in Synthesis Example 5, except that 3 (epoxy resin having an epoxy equivalent of 750, manufactured by Tohto Kasei Co., Ltd.) was used.

Synthesis Example 7 A powder coating material 7 was prepared by the same formulation and method as in Synthesis Example 4, except that the thickener was not added during the formulation of Synthesis Example 4.

Example 1 Coating on Magnesium Alloy Test piece (die-cast magnesium alloy, 50
(mm x 200 mm x 2 mm) with a tip diameter of 5
With a pencil hardness tester equipped with a μm sapphire needle,
A scratch having a width of 150 μm and a depth of 60 μm was made with a load of 19.6 N.

The powder coating material 1 was electrostatically coated on the scratched test piece so that the coating thickness after baking would be 35 μm, and the temperature was increased from room temperature of 20 ° C. to about 10 minutes in a baking oven. The test piece temperature was raised to 160 ° C., and this temperature was maintained for 5 minutes to bake the coating film. During this period, powder coating 1
Change with time of viscosity in Solikit meter MR3
When measured with 00 (viscosity meter, UBM), the minimum melt viscosity was 1.6 Pa · s.

The coating film after bake-curing was completely smooth by visual observation, and when the dents on the coating film surface were measured with Form Talysurf S3C (surface roughness measuring instrument, manufactured by Taylor Hobson Co.), even the deepest one was found. Only 5 μm
Met.

A commercially available solvent type paint (Superlac 100, manufactured by Nippon Paint Co., Ltd.) was electrostatically coated on this coating film and baked to form a 50 μm thick top coat film. The obtained coating film was very smooth by visual observation, and the result by the surface roughness measuring device was 0 μm (the measurement level was not reached).

Examples 2 to 10 and Comparative Examples 1 to 6 In the same manner as in Example 1, the type of powder coating material was changed,
Regarding baking, various samples were prepared by changing the surface temperature of the test piece in the furnace and the holding time of the surface temperature, and the surface roughness of the coating film was measured. These details are shown in Table 1.

[0048]

[Table 1]

In Table 1, "evaluation" is based on visual observation, and was performed according to the following criteria. ∘: No defects were found on the surface of the coating film and it was smooth. ○ ……… Slightly lacking in smoothness, but withstands sufficient use. △ ……… If you look closely, you can see the irregularities on the coating surface. ×: There are obvious irregularities scattered around.

[0050]

Since the coating method of the present invention regulates the minimum melting viscosity of the powder coating material under bake-curing conditions, the coating film formed on the metal material having surface defects is smooth and beautiful without dents. It is possible to obtain an excellent coating film. Therefore, it is not necessary to pre-treat the surface defects with putty, re-polish the surface after forming the powder coating film, and then perform coating again. Further coating or laminating on the coating film formed by the coating method of the present invention makes it possible to develop into products requiring weather resistance, designability and the like. Therefore, in addition to magnesium alloys that often have surface defects, home appliances such as televisions, videos, MDs, CDs, DVDs, PHSs and notebooks, which are partially or entirely formed of metal materials such as aluminum alloys and zinc alloys. It is suitable for manufacturing OA equipment / mobile equipment such as personal computers, PDAs, digital cameras, and projectors, or automobile parts such as tire wheels, engine covers, and steering wheels, because it has a smooth and beautiful coating film surface.

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Claims (6)

[Claims] 1. A coating method in which a powder coating material is applied to a metal material having a surface defect and baking-hardening is performed, wherein the melting minimum viscosity of the powder coating material under the baking-hardening condition is 1.
A coating method for a metal material, which is in the range of 0 to 2.0 Pa · s. 2. The bake-hardening condition is a temperature of 140 to 200.
The method for coating a metal material according to claim 1, wherein the temperature is 1 ° C for 30 minutes. 3. The method for coating a metal material according to claim 1, wherein the metal material having the surface defect is one of a magnesium alloy, an aluminum alloy and a zinc alloy. 4. The method for coating a metal material according to claim 1, further comprising topcoating or laminating. 5. A coated article coated with a powder coating material by the coating method according to any one of claims 1 to 4. 6. The coated article according to claim 4, wherein the coated article is any one of a home electric appliance, OA equipment / mobile equipment, and automobile parts.