JP2001026738A - Powder coating composition for aluminum wheel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating composition having excellent appearance, weather-resistance substrate adhesivity, filiform corrosion resistance and rust- proofness by including two specific kinds of epoxy-containing acrylic resins and a curing agent having a functional group reactive with epoxy group. SOLUTION: The objective coating composition contains, as essential components, (A) an epoxy-containing acrylic resin having a glass transition temperature of 40-100 deg.C, (B) an epoxy-containing acrylic resin having a glass transition temperature of -80 to 0 deg.C and (C) a curing agent having a functional group reactive with epoxy group (e.g. dodecanedicarboxylic acid). The components A and B are each produced by the solution radical polymerization of preferably an alkyl (meth)acrylate and an acrylic monomer having epoxy group [e.g. glycidyl (meth)acrylate]. The weight ratio of A to B (A/B) is preferably 80/20 to 99.5/0.5 in terms of solid component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a new and useful powder coating composition for aluminum wheels. More specifically, the present invention provides two types of epoxy group-containing acrylic resins (A) and (B) having a specific glass transition temperature,
A curing agent (C) having a functional group capable of reacting with the epoxy group of the acrylic resin is contained as an essential film-forming component. The present invention relates to an extremely practical powder coating composition for aluminum wheels that gives an excellent coating film.

[0002]

2. Description of the Related Art In recent years, regulations on organic solvents have become stricter due to problems such as air pollution, and environmentally friendly paints have been receiving attention. Among them, powder coatings have been spotlighted as solvent-free coatings from the viewpoint of environmental protection. In particular, acrylic powder coatings have excellent coating properties such as weather resistance and stain resistance, and are used for building materials and automotive parts, Attention is focused on the use of top clear coats for automobiles.

[0003] By the way, automobile wheels are generally made of steel, but in recent years, aluminum alloys have attracted attention for their excellent lightness, corrosion resistance, and design, and the mounting rate of aluminum wheels is mainly for luxury cars. To 30% or more.

[0004] In addition, compared to steel wheels, the production method has a relatively high degree of freedom in molding, such as casting, and it is a material that is easy to machine such as cutting and polishing. Has been pursued. As a result, the painting process becomes complicated, and sophistication of the painting quality and enhancement of the functionality of the paint film are important issues.

[0005] There are two types of aluminum wheel coating: a glossy specification that finishes with a transparent clear paint, and a color specification that finishes with a metallic or various paint colors. Used and considered.

[0006] The recent problems of aluminum wheel coating include high rust prevention function, high appearance function, high weather resistance function, and no pollution, among which high rust prevention function is particularly important. ing. This is because, in terms of design, in order to obtain a sense of quality, complicated three-dimensional structures have been increased in design, so that the number of sharp edges intentionally created by cutting has increased, and various types have been used to cover and protect this. In particular, the occurrence of thread-like corrosion called thread rust from that part due to salt damage in a cold region or the like has become a general problem, and improvement is demanded.

At present, a paint system such as acrylic baking, which is used for painting aluminum wheels, is most effective for preventing the generation of thread rust, especially in the case of clear finish.
In addition, as a commonly used method, a colorless chromate conversion treatment is performed. However, because of its harmfulness, regulations on adoption in new lines are becoming very strict in many fields.

As a paint for preventing yarn rust, Japanese Patent Application Laid-Open
JP-A-123475 and JP-A-3-162468 are disclosed. However, the former is an undercoat of a paint using a thermoplastic resin and a top coat of a paint made of a thermosetting acrylic resin, and is inferior in solvent resistance.
It is necessary to apply two different paints, and the workability is poor. Further, in the latter, yarn rust is prevented by using a paint that crosslinks a specific copolymerized polyester resin with a polyisocyanate compound, but it is necessary to dissolve the obtained polyester in a solvent having a high boiling point when preparing the paint. Therefore, there is a drawback that it becomes a solvent-containing paint and is not suitable for recent environmental measures.

As described above, when the conventional solvent-based acrylic baking paint and solvent-based polyester baking paint are applied, foaming and the like caused by the curing system are suppressed as much as possible.
In order to maintain the physical properties of the coating film, it is necessary to use a solvent having a very high boiling point or a resin having a low glass transition temperature. Therefore, the general phenomenon is that the release of the solvent after coating is delayed, the viscosity of the coating after coating is insufficiently increased, the coating with a sharp edge coating is insufficient, and thread rust occurs. There is still no solvent composition which is a solvent-type thermosetting type and which completely satisfies the thread rust resistance.

[0010] Furthermore, as one effective means, it has been practiced to incorporate a powder coating material into a coating system.
However, in order to obtain high smoothness, it is necessary to lower the glass transition temperature of the resin and to lower the molecular weight. In this case, the powdered resin is easily aggregated and solidified, and the storage stability ( Practical problems such as poor blocking resistance). In particular, the fact that the thread rust resistance is inferior to that of the coating film obtained from the conventional baking paint as described above,
Such rust prevention cannot be used and applied to applications that are highly required, for example, coatings for automotive aluminum wheels.

[0011]

Thus, as long as the conventional technology is followed, the appearance and weather resistance,
An extremely practical paint composition for aluminum wheels that gives a coating film excellent in substrate adhesion and the like, and in particular, can provide a coating film excellent in rust resistance such as thread rust resistance. Providing was extremely difficult.

Accordingly, an object of the present invention is to provide a coating film which is excellent in appearance, weather resistance, substrate adhesion and the like. It is an object of the present invention to provide an extremely practical powder coating composition for aluminum wheels, which can form a coating film having excellent rust prevention properties such as rust resistance.

[0013]

SUMMARY OF THE INVENTION The present inventor has sought to solve the various drawbacks and problems of the prior art as described above. As a result of intensive studies, aiming at the aim, the epoxy group-containing acrylic resin (A) having a glass transition temperature of 40 to 100 ° C. and a glass transition temperature of −
An essential coating film comprising two types of epoxy group-containing acrylic resins (B) in the range of 80 to 0 ° C. and a curing agent having a functional group capable of reacting with an epoxy group in these acrylic resins. When the powder coating composition as a forming component is used for an aluminum wheel, it is particularly excellent in rust resistance, that is, thread rust resistance, and further, it is excellent in appearance, weather resistance, substrate adhesion, and the like,

The solid content ratio of the acrylic resin (A) / the acrylic resin (B) is from 80/20 to 99.5.
/0.5, preferably 90/10 to 99/1,

The glass transition temperature of the acrylic resin (A) is in the range of 50 to 80 ° C., and its epoxy equivalent is 200 to 1600 g / eq.
The range of 00 g / eq is 10 as the number average molecular weight.
The range of 00 to 50,000 is preferable, and the glass transition temperature of the acrylic resin (B) is-
The range of 50 to −20 ° C. is 200 to 3000 g / eq as the epoxy equivalent, particularly 400 to 1500.
The range of g / eq is 1000 as the number average molecular weight.
The range of ~ 50,000 is preferred,

As the curing agent (C), it has been found that aliphatic polycarboxylic acids and / or anhydrides thereof are preferred, and the present invention has been completed.

That is, the present invention provides: The epoxy group-containing acrylic resin (A) having a glass transition temperature within a range of 40 to 100 ° C, the epoxy group-containing acrylic resin (B) having a glass transition temperature within a range of -80 to 0 ° C, and an epoxy group A powder coating composition for an aluminum wheel, comprising a curing agent (C) having a functional group to be obtained as an essential film-forming component;

2. Acrylic resin containing epoxy group (A)
And the solid content weight ratio of the epoxy group-containing acrylic resin (B) [(A) / (B)] is 80/20 to 99.5 / 0.5.
The powder coating composition according to the above 1, which is within a range,

3. Acrylic resin containing epoxy group (A)
The powder according to the above 1 or 2, wherein the epoxy equivalent of the epoxy resin is within the range of 200 to 1600 g / eq, and the epoxy equivalent of the epoxy group-containing acrylic resin (B) is within the range of 200 to 3000 g / eq. Paint composition,

4. Acrylic resin containing epoxy group (A)
Is in the range of 50 to 80 ° C. and the epoxy equivalent is in the range of 400 to 1000 g / eq, and the glass transition temperature of the epoxy group-containing acrylic resin (B) is −50 to −20 ° C. The powder coating composition according to 1 or 2, wherein the powder coating composition has an epoxy equivalent within a range of 400 to 1500 g / eq.

5. Acrylic resin containing epoxy group (A)
The powder coating composition according to the above 3 or 4, wherein the solid content weight ratio [(A) / (B)] of the epoxy resin and the epoxy group-containing acrylic resin (B) is within a range of 90/10 to 99/1.

6. Acrylic resin containing epoxy group (A)
Is in the range of 1,000 to 50,000, and the number average molecular weight of the epoxy group-containing acrylic resin (B) is in the range of 1,000 to 50,000,
The powder coating composition according to any one of the above 1 to 5, and

7. A curing agent (C) having a functional group capable of reacting with an epoxy group comprises an aliphatic polycarboxylic acid and / or
Or an anhydride thereof, the powder coating composition according to any one of the above 1 to 6,

The powder coating composition for an aluminum wheel of the present invention is remarkably resistant to thread rust as compared with conventional acrylic powder coatings, acrylic baking coatings, and polyester baking coatings. Excellent substrate adhesion.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The above-mentioned epoxy group-containing acrylic resins (A) and (B), which are essential components of the powder coating composition for aluminum wheels of the present invention, include, for example, An acrylic copolymer having an epoxy group is exemplified.

The copolymers (A) and (B) are
For example, a solution radical polymerization method in which an acrylic monomer having an alkyl (meth) acrylate and an epoxy group and, if necessary, another vinyl monomer is copolymerized, various known acrylic copolymers may be used. The polymer can be prepared by various methods such as a method of introducing an epoxy group by modifying the polymer by a known and common method,
The solution radical polymerization method is particularly recommended because it is the simplest.

[0027] Of the alkyl (meth) acrylates used in the polymerization method of the epoxy group-containing acrylic resins (A) and (B), only typical ones are exemplified. ) Methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate,
Sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate,
And stearyl (meth) acrylate. These can be used alone or in combination of two or more, if necessary.

Similarly, if only typical examples of the epoxy group-containing acrylic monomer are given as examples, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, (meth) allyl glycidyl Examples thereof include ether, (meth) allylmethyl glycidyl ether, and 3,4-epoxycyclohexylmethyl (meth) acrylate. Of these, glycidyl (meth) acrylate is preferably used. Of course, these may be used alone or in combination of two or more, if necessary.

The epoxy group-containing acrylic resins (A) and (B) are optionally used in the above polymerization method.
Other vinyl monomers include, for example, (meth)
(Meth) acrylic acid hydroxyesters such as 2-hydroxyethyl acrylate, 2-hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate; various types such as styrene, α-methylstyrene and vinyltoluene Styrene-based monomers; various polyvalent carboxyl group-containing monomers such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid, and having 1 to 18 carbon atoms (C _{1 to} C _18). Mono- or diesters with a monoalkyl alcohol: N-dimethylaminoethyl (meth) acrylamide, N-diethylaminoethyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, N-diethylaminopropyl (meth) acrylamide Various amino group-containing amide unsaturated monomers such as ; Dimethylaminoethyl (meth)
Various dialkylaminoalkyl (meth) acrylates such as acrylate; tert-butylaminoethyl (meth) acrylate, tert-bitylaminopropyl (meth) acrylate, aziridinylethyl (meth) acrylate, pyrrolidinylethyl ( Various amino group-containing monomers such as meth) acrylate and piperidinylethyl (meth) acrylate; γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth)
Acryloyloxypropyltriethoxysilane, γ-
Various kinds of hydrolyzable silyl group-containing substances such as (meth) acryloyloxypropylmethyldimethoxysilane; vinyl acetate, vinyl propionate, vinyl citrate, vinyl isoenate, vinyl caproate, vinyl caprate, vinyl laurate, Various aliphatic vinyl carboxylate such as C11-C11 branched aliphatic vinyl carboxylate, vinyl stearate; vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, vinyl para-tert-butylbenzoate And various vinyl esters of a carboxylic acid having a cyclic structure.

The epoxy group-containing acrylic resin (A) used in the present invention has a glass transition temperature of 40 to 100.
° C, and particularly preferably within a range of 50 to 80 ° C. The glass transition temperature of the epoxy group-containing acrylic resin (B) is in the range of −80 to 0 ° C., and particularly preferably in the range of −50 to −20 ° C.

When the epoxy group-containing acrylic resin (A) has a glass transition temperature of less than 40 ° C., the storage stability (blocking resistance) of the obtained powder coating composition is lowered, and exceeds 100 ° C. Each of them is not preferable because the smoothness and the rust resistance are reduced. Further, the glass transition temperature of the epoxy group-containing acrylic resin (B) is -80.
When the temperature is lower than 0 ° C., the storage stability (blocking resistance) of the powder coating composition is lowered, and the rust resistance exceeding 0 ° C. is lowered, which is not preferable.

The proportions of the epoxy group-containing acrylic resin (A) and the epoxy group-containing acrylic resin (B) are as follows: the storage stability (blocking resistance) of the powder coating composition, the smoothness of the coating film, and the impact resistance. In consideration of the adhesion of the base material, the rust resistance, and the like, the solid content weight ratio [(A) / (B)] is 80/20.
９９99.5 / 0.5 is appropriate, and 90/1
The range of 0 to 99/1 is particularly preferred.

The epoxy equivalent of the epoxy group-containing acrylic resin (A) includes, for example, a decrease in substrate adhesion, generation of rust, a decrease in curability, and various physical properties of the coating film, particularly, impact resistance and water resistance. From the viewpoint of prevention of reduction, 200 to 1600 g / eq
Is appropriate, and among them, 400 to 1000 g /
Especially within the range of eq is preferable. In addition, the epoxy equivalent of the epoxy group-containing acrylic resin (B) is appropriately in the range of 200 to 3000 g / eq from the viewpoint of preventing a decrease in substrate adhesion, coating film appearance, impact resistance, water resistance, and the like. ,
Above all, a range of 400 to 1500 g / eq is particularly preferable.

The epoxy equivalent referred to here means the number of grams of resin (g / e) required to obtain 1 mole of epoxy group.
q).

The epoxy group-containing acrylic resins (A) and (B) have a number average molecular weight of 1000 from the viewpoints of blocking resistance and prevention of deterioration of coating film smoothness.
The range of ５０50,000 is appropriate, and especially 2,000
The range of -30,000 is particularly preferred.

The curing agent (C) used in the present invention includes polycarboxylic acids and their anhydrides, polyhydric phenols and the like. Among these, it is preferable to use aliphatic polycarboxylic acids and their anhydrides from the viewpoint of coating film properties. Preferred aliphatic polycarboxylic acids include dodecanedicarboxylic acid and the like. And
The amount of the curing agent (C) used is within the range of 0.8 to 1.2 times equivalent, particularly the amount of the functional group substantially corresponding to the total epoxy group amount of the epoxy group-containing acrylic resins (A) and (B). It is preferred that

The powder coating composition for an aluminum wheel according to the present invention and the powder using the essential components such as the epoxy group-containing acrylic resins (A) and (B) and the curing agent (C) as described above. In preparing a powder coating obtained from the body coating composition, various known and commonly used methods can be used and applied. If only a particularly representative method is exemplified among them, first, as described above,
It is said that each essential component is mixed, and further, if necessary, various additive components such as a pigment or a surface conditioner are mixed, and then they are melt-kneaded and then pulverized. And a so-called mechanical pulverization method. Epoxy group-containing acrylic resin (A),
When mixing of (B) is difficult, (A), (B)
May be used after being melt-mixed, or may be used after previously mixed in a solution state and then solidified.

The powder coating composition comprising the powder coating composition for an aluminum wheel of the present invention may be used within a range that does not deviate from the object of the present invention or within a range that does not impair the effects of the present invention. In addition, various known additives such as organic or inorganic pigments, flow regulators, light stabilizers, ultraviolet absorbers, antioxidants and the like can be added, and when printing, A catalyst can be added for the purpose of accelerating the curing (reaction) of the catalyst.

The powder coating composition for an aluminum wheel of the present invention thus obtained and the powder coating obtained from the powder coating composition are coated on a substrate to be coated by various known and common methods. After that, by baking, the intended cured coating film is formed on the substrate to be coated.

The baking temperature and time of the substrate to be coated are as follows:
Although it can be appropriately selected according to the type and purpose of the substrate to be coated, for example, in a temperature range of 120 to 250 ° C., the baking time is in a range of 5 to 30 minutes.

[0041]

EXAMPLES Next, the present invention will be described more specifically with reference examples, examples and comparative examples. However, the present invention is by no means limited to only these illustrative examples. Absent. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation of Acrylic Resin Containing Epoxy Group (A)] In a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet, 426 parts of xylene were charged, and placed under a nitrogen atmosphere at 135 ° C. The temperature was raised to. There, 25 parts of styrene, 47 parts of methyl methacrylate, 8 parts of butyl acrylate, 20 parts of glycidyl methacrylate and tert-
A mixture of 6 parts of butyl peroxyoctoate (hereinafter, abbreviated as TBPO) was added dropwise over 6 hours, and after completion of the addition, the mixture was kept at the same temperature for 10 hours to carry out a polymerization reaction. Excluding the solvent under a reduced pressure of 20 mmHg, the number average molecular weight is 2700 and the glass transition temperature is 5
A solid acrylic resin having an epoxy equivalent of 710 g / eq at 5 ° C. was obtained. Hereinafter, this is abbreviated as acrylic resin (A-1). The characteristic value of the obtained acrylic resin (A-1)
It is shown in the table.

Reference Example 2 (same as above) As monomers, 58 parts of methyl methacrylate, 10 parts of n-butyl methacrylate and 3 parts of glycidyl methacrylate were used.
The number average molecular weight was 430 in the same manner as in Reference Example 1 except that 2 parts were used and 3 parts of TBPO were used together.
0, glass transition temperature 64 ° C, epoxy equivalent 450g / e
q solid acrylic resin was obtained. Hereinafter, this is abbreviated as acrylic resin (A-2). The obtained acrylic resin (A
Table 1 shows the characteristic values of -2).

Reference Example 3 (same as above) As a monomer, 40 parts of styrene, methyl methacrylate 2
4 parts, 11 parts of 2-ethylhexyl acrylate and 25 parts of glycidyl methacrylate.
Except having changed to using 5 parts, it carried out similarly to the reference example 1, and carried out the number average molecular weight 2600, the glass transition temperature 45 degreeC,
A solid acrylic resin having an epoxy equivalent of 570 g / eq was obtained. Hereinafter, this is abbreviated as acrylic resin (A-3).
Table 1 shows the characteristic values of the obtained acrylic resin (A-3).

Reference Example 4 [Preparation of Epoxy Group-Containing Acrylic Resin (B)] In a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet, 410 parts of xylene were charged, and placed under a nitrogen atmosphere at 135 ° C. The temperature was raised to. Here, in the same manner as in Reference Example 1 except that 27 parts of 2-ethylhexyl acrylate, 38 parts of 2-ethylhexyl methacrylate, 35 parts of glycidyl methacrylate, and 0.5 part of TBPO were used, the number average molecular weight was 5200, An acrylic resin having a glass transition temperature of −20 ° C. and an epoxy equivalent of 420 g / eq was obtained. Hereinafter, this is abbreviated as acrylic resin (B-1). Table 2 shows the characteristic values of the obtained acrylic resin (B-1).

Reference Example 5 (same as above) The same procedures as in Reference Example 4 were carried out except that 20 parts of styrene, 70 parts of 2-ethylhexyl acrylate and 10 parts of glycidyl methacrylate were used as monomers.
An acrylic resin having a number average molecular weight of 7,800, a glass transition temperature of −31 ° C., and an epoxy equivalent of 1,530 g / eq was obtained. Hereinafter, this is abbreviated as acrylic resin (B-2). Table 2 shows the characteristic values of the obtained acrylic resin (B-2).

[0047]

[Table 1] Table 1

[0048]

[Table 2] Table 2

The glass transition temperatures, epoxy equivalents, and number average molecular weights in Tables 1 and 2 were measured by the following methods.

(1) Glass transition temperature (° C.) DSC method (differential scanning calorimetry, heating rate 10 ° C./mi)
n).

(2) Epoxy equivalent (g / eq) Measured by a hydrochloric acid-pyridine method. 25 ml of a hydrochloric acid-pyridine solution was added to the resin, and the resin was dissolved by heating at 130 ° C. for 1 hour.
Titration was performed with a potassium hydroxide alcohol solution. The epoxy equivalent was calculated from the amount of the consumed 0.1 N potassium hydroxide alcohol solution. (2) Number average molecular weight Measured by gel permeation chromatography (GPC). The sample was a tetrahydrofuran solution in which 0.4 part of a resin was dissolved in 100 parts of tetrahydrofuran, and this was LC-08 (A-54) manufactured by JASCO Corporation.
32) It was measured by GPC and calculated in terms of polystyrene.

Examples 1 to 4 and Comparative Examples 1 to 3 (Preparation of Powder Coatings) The components shown in Tables 3 and 4 were separately mixed in the proportions shown in Table 3 and thus obtained. Each formulation is called "APV.
Kneader MP-2015 type] [Tubaco Yokohama Sales Co., Ltd.
Using a twin-screw kneader), after melt-kneading,
The powder coatings [P-1] to [P-4] obtained by using the powder coating composition for an aluminum wheel of the present invention by pulverizing and classifying with a 200 mesh wire mesh.
And powder coatings [p-1] to [p-3] for comparison and control were prepared.

[0053]

[Table 3] Table 3

[0054]

[Table 4] Table 4

<< Footnotes to Tables 3 and 4 >> 1) "DDA": dodecanedicarboxylic acid 2) "Acronal 4F": Surface conditioner manufactured by BASF, Germany

(Coating film performance test) Next, the obtained powder coating materials [P-1] to [P-4] and [p-1] to [p-3]
Was used to prepare various coating films according to the following coating film forming method.

The base material used as an object to be coated is an aluminum alloy plate "A5052P" [Japan Test Panel Co., Ltd.]
Manufactured).

Powder coatings [P-1] to [P-4], [p-
1] to [p-3] were applied to the above-mentioned substrate to be coated by electrostatic powder coating so that the film thickness after baking would be 80 μm, and then under conditions of 160 ° C./20 minutes. Baking was performed.

Each of the cured coating films thus obtained was evaluated for various properties. The results are summarized in Tables 5 and 6.

[0060]

[Table 5] Table 5

[0061]

[Table 6] Table 6

The evaluation of the coating film performance test in Examples and Comparative Examples in Tables 5 and 6 was performed by the following method.

(4) Coating Smoothness The coating film surface was visually evaluated according to the following criteria. ○: Very smooth and smooth. Δ: A large round is recognized. ×: Fine dust skin is observed.

(5) Yarn rust resistance A cross cut was made on the coating film with a cutter knife so as to reach the base material, and the temperature was 35 ± 5 ° C. with a salt spray tester.
After spraying 5% saline for 24 hours under the conditions of
Leave in a constant temperature / humidity bath at a temperature of 40 ± 1 ° C and a relative humidity of 85 ± 2% for 240 hours. This cycle is repeated as one cycle until 3 cycles, and the number of thread rusts and the maximum length of one side rust width of cross cut Was measured and evaluated according to the following criteria. ○: The length of thread rust is less than 2 mm △: The length of thread rust is 2 mm or more and less than 5 mm ×: The length of thread rust is 5 mm or more

(6) Water resistance The coated plate was immersed in warm water of 60 ° C. for 3 days, and after 30 minutes from the lifting, a 1 mm cross cut was cut into the coating film with a cutter to form an adhesive. A peel test with a tape was performed. As a criterion for the evaluation judgment, the remaining number of cross cuts was indicated by X / 100. The higher the value, the better the adhesion. Further, the presence or absence of blisters in the coating film after withdrawing from the warm water was visually determined.

[0066]

The composition for powder coating according to the present invention, when used for coating aluminum wheels, has, among other things, a coating film appearance and
It provides a cured coating film having excellent properties such as thread rust resistance and water adhesion, and is extremely practical as a powder coating composition for aluminum wheels.

Claims (7)

[Claims] 1. An epoxy group-containing acrylic resin (A) having a glass transition temperature of 40 to 100 ° C., and an epoxy group-containing acrylic resin (B) having a glass transition temperature of -80 to 0 ° C. A powder coating composition for an aluminum wheel, comprising a curing agent (C) having a functional group capable of reacting with an epoxy group as an essential film-forming component. 2. The epoxy resin-containing acrylic resin (A) and the epoxy-containing acrylic resin (B) have a solid content weight ratio ((A) / (B)) of 80/20 to 99.5 / 0.5.
The powder coating composition according to claim 1, which is within a range. 3. The epoxy equivalent of the epoxy group-containing acrylic resin (A) is in the range of 200 to 1600 g / eq, and the epoxy equivalent of the epoxy group-containing acrylic resin (B) is 200 to 3000 g / eq. The powder coating composition according to claim 1, which is within the range. 4. The epoxy group-containing acrylic resin (A) has a glass transition temperature of 50 to 80 ° C. and an epoxy equivalent of 400 to 1000 g / eq.
The powder according to claim 1, wherein the epoxy group-containing acrylic resin (B) has a glass transition temperature of -50 to -20C and an epoxy equivalent of 400 to 1500 g / eq. Paint composition. 5. The solid content weight ratio [(A) / (B)] of the epoxy group-containing acrylic resin (A) and the epoxy group-containing acrylic resin (B) is in the range of 90/10 to 99/1. The powder coating composition according to claim 3 or 4. 6. The epoxy group-containing acrylic resin (A) has a number average molecular weight of 1,000 to 50,000, and the epoxy group-containing acrylic resin (B) has a number average molecular weight of 1,000 to 50,000. The powder coating composition according to any one of claims 1 to 5, which is: 7. The method according to claim 1, wherein the curing agent (C) having a functional group capable of reacting with an epoxy group is an aliphatic polycarboxylic acid and / or an anhydride thereof. Powder coating composition.