JPH0689295B2 - Coating composition for aluminum wheels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a coating composition which is particularly advantageous to be applied to the coating of a disc type wheel made of an aluminum alloy casting (hereinafter abbreviated as “aluminum wheel”) which is a tire mounting member for automobiles. Regarding things.

Conventionally, automobile wheels were mainly made of steel,
In recent years, aluminum alloy castings, which are excellent in weight reduction, corrosion resistance, and design, are being replaced. The aluminum wheel is coated with, for example, a transparent or colored organic solvent thermosetting acrylic resin-based coating material once or twice or more for the purpose of enhancing the cosmetic properties and weather resistance. .

However, the aluminum wheel has many sharp cuts to improve the design, etc. When the above-mentioned conventional acrylic resin paint is applied to such a material, the aesthetic appearance of the flat part is improved. However, in the sharp and sharp parts (hereinafter sometimes abbreviated as "edge parts"), the paint flows during baking and it is difficult to form a paint film. Therefore, thread-like rust occurs and progresses from the edge parts. Then, there is a serious defect that the cosmetic property is remarkably lost.
As a method of solving these defects, it is effective to polish the edge portion to eliminate it at an acute angle, but it takes too many man-hours, so that it is difficult to incorporate it into the production line, and polishing itself is not preferable in terms of design. Sometimes. Further, there is a restriction that it is difficult to mix a pigment that impairs the transparency of a coating film into an aluminum wheel coating material so as not to impair the feeling of aluminum.

Therefore, the present inventors have solved the above defects, the coating material applied to the edge portion does not flow during baking, the coating film formability of the edge portion is good, and the transparency, weather resistance, and smoothness are good. ,
An intensive study was conducted for the purpose of developing a coating composition for an aluminum wheel which forms a coating film excellent in adhesion and physical properties. As a result, the above object can be achieved by blending a specific amount of a specific ultrafine powder in a thermosetting resin, and adjusting the organic solvent composition in the coating material to a specific component and ratio, thereby completing the present invention. did.

That is, the present invention is a coating composition containing (A) 5 to 35 parts by weight of (B) silica and / or alumina, which is a transparent fine powder having a particle size of 5 to 50 mμ, per 100 parts by weight of a thermosetting resin. And (C) the composition of the organic solvent in the coating composition is 10 to 70% by weight of a polar organic solvent having a boiling point of 130 ° C. or less and a boiling point of 105.
Consisting of 90 to 30% by weight of non-polar organic solvent at ℃ to 250 ℃,
And, (D) a coating composition for an aluminum wheel, characterized in that the solid content at the time of coating is adjusted to 20 to 50% by weight.

The feature of the present invention is that the component (A) as a coating film forming basic component is blended with a specific amount of the components (B) and (C), and the fixed component content specified in the component (D) is prepared. Where it is.

That is, the component (A) is the main component constituting the coating film, and the component (B) is for imparting thixotropic properties to the coating material. In particular, the component (B) is already known as an extender pigment for imparting thixotropic properties, but its amount is usually less than 5 parts by weight per 100 parts by weight of the base resin. This is because the spray coating workability is remarkably deteriorated, and defects such as insufficient smoothness of the coating film occur. However,
In the present invention, the component (B) is blended in a large amount of 5 to 35 parts by weight as described above, which has hardly been used so far.
In addition, by satisfying the requirements of (C) and (D) above, a coating material having extremely unique fluidity was obtained.

That is, a coating obtained by imparting the requirements of (C) and (D) to a system consisting of the component (A) and the component (B) becomes a pudding when left standing and almost no fluidity is observed. However, if it is stirred, the viscosity is lowered and the fluidity is easily recovered, and spray coating is possible. Then, due to the high shear (shearing force) at the time of coating, the viscosity of the coating is reduced and a coated surface having excellent smoothness can be obtained. In addition, the applied paint becomes a pudding again when left to stand and loses fluidity, and the paint is sufficiently applied even to the edge part, and even if it is baked at high temperature as it is, the applied paint is almost heat flowable. However, since the coating material applied to the edge portion is hardened almost as it is, as a result, the edge covering property is improved, and the occurrence of thread rust from the portion is hardly recognized.

Further, the coating composition of the present invention does not impede the unique metallic feeling of aluminum because the formed coating film is colorless and transparent, and is excellent in smoothness, weather resistance, adhesion, physical performance and the like. ing.

The coating composition of the present invention will be described in more detail.

Component (A): Thermosetting resin A main component of a coating film formed by the coating composition of the present invention, which is composed of a base resin and a curing agent. Any of these can be used as already known ones for paints, for example, acrylic resin, polyester resin, urethane resin, silicone resin, fluororesin, etc. as the base resin, and methylol and / or alkoxylated melamine resin as the curing agent. , Blocked isocyanate compounds and the like. Among these, acrylic resin / melamine resin system, which has excellent weather resistance, is particularly preferable,
Specifically, the acrylic resin has a number average molecular weight of 5,000.
-80,000, hydroxyl value is 20-150, acid value is 0-50, and glass transition temperature is -50- + 110 ° C.

Component (B): Finely powdered silica and / or alumina This is for imparting thixotropic properties to the coating composition of the present invention and has a particle size of 5 to 50 mμ (0.005 to 0.05).
μ), preferably 5 to 23 mμ (0.007 to 0.02μ)
A fine powder containing 90% by weight or more. Here, silica is referred to as finely divided silicic acid or white carbon, and alumina is also referred to as aluminum oxide, both of which are known as extender pigments to be added to paints. If the particle size is less than 5 mμ, the viscosity and thixotropic properties are too high, and the paint structure and coating workability are significantly reduced, while if it is greater than 50 mμ, the thixotropic properties decrease and the edge coverage is insufficient. Therefore, both are not preferable.

The amount of these fine powders to be blended is 5 to 35 parts by weight, preferably 15 to 25 parts by weight, based on 100 parts by weight (solid content) of the component (A) thermosetting resin. If the amount is too small, the coverage of the edge portion is not sufficient, and if it is more than 35 parts by weight, the coating workability is deteriorated.

Component (C): Organic solvent component An organic solvent that constitutes the coating composition of the present invention, and is composed of a polar organic solvent and a nonpolar organic solvent. The former has a boiling point of 13
0 ℃ or less, preferably 100 ~ 120 ℃, the latter has a boiling point of 105 ℃ ~
It is included in the range of 250 ℃, preferably 110 ~ 210 ℃, these composition ratio, the former is 10 ~ 70%, preferably 15 ~ 50%, based on the total weight ratio of both. The latter is
90 to 30%, preferably 85 to 50%.

In the present invention, the polar solvent imparts fluidity to the coating material and contributes to improvement of coating workability and coating surface smoothness, while the nonpolar solvent imparts thixotropic property to the coating material,
Prevents fluidization of the coating film during baking and improves edge coverage.

First, a polar solvent is a relatively conductive and chemically active solvent that dissolves many types of resins well, and specifically, an organic solvent having a dielectric constant of 4.0ε · 20 ° C or higher is preferable. Hydroxyl group in the molecule, carbonyl group, a solvent having a polar group such as an ester bond, the boiling point is 130 ℃ or less, the thixotropy of the coating material applied to the surface to be coated is lowered when it is higher than 130 ℃, It is not preferable that heat flow is facilitated and the edge coverage is lowered. Examples of the polar solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diethyl ketone, ester solvents such as ethyl acetate and isobutyl acetate, and alcohol solvents such as n-butanol and isobutanol. It is particularly preferable to use methyl isobutyl ketone, diethyl ketone, isobutyl acetate, n-butanol, isobutanol and the like.

Next, the non-polar solvent is chemically inert, specifically, the dielectric constant is preferably less than 4.0 ε · 20 ℃, a solvent having no polar group as described above, and its Boiling point
It is in the range of 105 ℃ to 250 ℃, and if it is lower than 105 ℃, the smoothness of the coated surface and the edge coverage will decrease.
If the temperature is higher than 0 ° C., the coating film tends to flow and the edge coverage is deteriorated. Examples of such non-polar organic solvents include aromatic hydrocarbons such as toluene and xylene: Mineral spirits: Swazol # 1000, Swazol # 1500, Swazol # 1900 (all are trade names of Shell Chemical Co., Ltd.) Examples thereof include petroleum naphtha. Of these, xylene, toluene and the above aromatic petroleum naphtha are particularly preferable.

Further, the composition ratio of the polar solvent and the non-polar solvent constituting the solvent component in the coating composition of the present invention is as described above, the fluidity of the coating is significantly reduced when the former is less than 10 wt%, The coating workability and the finished appearance are not sufficient, and if the content is more than 70% by weight, the coated coating material tends to flow and the edge coverage is deteriorated.

Further, regarding the non-polar solvent, in order to further improve the smoothness of the coating film and the workability of manufacturing the coating material, the boiling point is 105
A boiling point of 150 or more with a non-polar solvent selected from less than 150 ℃,
It is particularly preferable to use a mixed non-polar solvent composed of a non-polar solvent selected from 250 ° C. based on the total weight of the both, the former being 30 to 70% and the latter being 70 to 30%. .

(D): The solid content at coating is 20 to 50% by weight.

The coating method of the coating composition of the present invention is not particularly limited,
From the viewpoint of excellent coating workability and coating efficiency, spray coating methods such as air spelling, airless spraying and electrostatic coating are particularly suitable, and when coating by these methods, the solid composition of the coating composition of the present invention is used. Minute content rate 20 to 50
It is important to adjust the weight ratio to 25% to 40% by weight. When the solid content is less than 20% by weight, the thixotropy of the coating composition is insufficient and the coverage of the edge portion is reduced, while when it is more than 50% by weight, the smoothness of the coating film is reduced. Not preferable.

The coating composition of the present invention contains the above-mentioned components (A), (B) and (C) as essential components, and further, above-mentioned (D).
Although it is necessary to meet the requirements of the components, an epoxy resin and various coating additives can be further compounded, if necessary.

Further, the coating of the coating composition of the present invention on an aluminum wheel is preferably carried out by the above-mentioned spraying method. Prior to this painting, the aluminum wheel may be subjected to normal surface treatment, if necessary,
It is also possible to apply an undercoat paint in advance. Further, it is preferable that the coating composition of the present invention is coated on these surfaces so as to have a film thickness of 10 to 50 μm based on the cured coating film on the flat portion, and heated at 130 to 170 ° C. to cure.

The coating composition of the present invention can be applied to an aluminum wheel directly or after applying another undercoat or intermediate coat in advance, and it is also possible to apply another top coat to the coated surface.

Examples and comparative examples of the present invention will be described. In addition,
Parts and percentages are as a rule by weight.

I. Examples and Comparative Examples A coating composition for an aluminum wheel was manufactured by mixing and dispersing the components and the compounding amounts shown in Table 1.

II. Performance test results After cutting, Bonderite BT3753 (Nippon Parker Co., Ltd.)
Aluminum wheel and NT cutter spare blade L-300 (manufactured by Nippon Transfer Paper Co., Ltd., blade angle 20 °) surface-treated with the above coating composition by spray coating so that the cured film thickness of the flat part is 30μ. Then, it was heated at 150 ° C. for 30 minutes to be cured.

A performance test was conducted on the formed cured coating film, and the results are shown in Table 3.

Claims (1)

[Claims] 1. A thermosetting resin (A) per 100 parts by weight of
(B) A paint comprising 5 to 35 parts by weight of transparent fine powder silica having a particle size of 5 to 50 m and / or alumina, and (C) the organic solvent composition in the paint has a boiling point of 130.
10 ~ 70wt% of polar organic solvent below ℃ and boiling point is 105 ℃ ~ 250
90 to 30% by weight of a non-polar organic solvent at ℃, and
(D) A coating composition for an aluminum wheel, which is prepared by adjusting the solid content content during coating to 20 to 50% by weight.