JP2790402B2 - Primer composition for aluminum castings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primer composition for an aluminum casting, which is used as an undercoat, that is, as a primer, for coating an aluminum casting such as an aluminum wheel. The present invention relates to a primer composition for an aluminum casting, which can secure good adhesion (adhesion) even when the primer composition is used.

[0002]

2. Description of the Related Art In recent years, automobiles have become lighter or more diverse.
With the upscaling, etc., the wheels are made of aluminum alloy because they are not only lightweight, but also rich in design, high quality, and relatively excellent in corrosion resistance. Wheel, that is, an aluminum wheel is increasingly used. In addition, in the case of such aluminum wheels, a simple surface finish by an oxide film treatment or the like has been generally used, but recently, in order to further enhance the design and decorativeness, a color coat using a colored paint or the like is used. Increasingly, paint finishes including clear coats with transparent paints are applied.

[0003] Incidentally, the aluminum wheel may be formed as a two-piece type or a three-piece type provided with a rim by forging, but at least a disk portion as a main body thereof is formed by casting. Then, the aluminum wheel formed by casting is subjected to a shot blasting process for removing sand and cleaning the surface after heat treatment for age hardening. Therefore, since the surface of the aluminum wheel is formed on a rough surface having relatively rough irregularities, when applying a coating finish as described above, simply applying a normal coating with a color coat or the like will remove the irregularities on the surface. They cannot be sufficiently covered, and the desired appearance cannot be obtained. In other words, since the formed coating film loses its smoothness due to the unevenness of the surface of the aluminum wheel, it has a particularly good gloss.
It lacks the feeling or glossiness, the feeling of flesh, the feeling of sharpness, and the like.

[0004] Therefore, conventionally, in the case of the aluminum wheel which is an aluminum cast product, a sufficiently thick undercoat is applied in advance to the finish coating with a normal color coat and a clear coat, so that the casting surface is thereby formed. To cover the unevenness of the surface and to ensure the smoothness of the finished coating film. The undercoating is generally performed by coating with a powder coating because the coating of a thick film is easy, and the powder coating includes a powder made of an acrylic or epoxy thermosetting resin. Body clear paint is used. That is, specifically, the finish of the aluminum wheel coating is performed by subjecting the shot-blasted aluminum wheel to a chemical conversion coating treatment as a coating base treatment, and then applying a powder clear coating to a film thickness of about 100 to 150 μm. Bake, then paint a color coat and bake, then paint a clear coat and bake 3 coats 3
Made by Bake.

[0005]

As described above, the coating of an aluminum wheel, which is an aluminum casting, is performed by first applying a thick film undercoat using a powder clear paint as a primer, and then finishing with a color coat and a clear coat. It is done by applying paint. Thereby, since the smoothness of the finished coating film can be secured by covering the unevenness of the casting surface, it is possible to form a coating film having an excellent appearance such as a glossy feeling, An excellent aluminum wheel can be formed.

[0006] However, with regard to an aluminum wheel coated and finished using this powder clear paint as a primer, the adhesion (adhesion) of the coating film under severe conditions is particularly high.
Is not enough, for example, when a salt water spray test is performed after putting a cross cut on the coating film, the coating film floats from the cross cut portion as a starting point, and eventually the entire coating film interfacially peels off from the substrate surface. There was a tendency. The same applies to the results of the water adhesion test or the moisture adhesion test. This is due to the fact that the inherent adhesion is significantly reduced due to the increase in internal strain and the concentration of stress at the substrate interface due to the large cohesive force of the coating film formed by the powder clear coating and, in particular, the thick film, which results in increased internal strain and concentration of stress at the substrate interface. Conceivable. Further, it is considered that the powder coating has a relatively high viscosity at the time of melting and has poor wettability with the surface of the base material.

[0007] As described above, the primer made of the powder clear paint has insufficient adhesion, especially when used in an RV vehicle or the like, considering that it is exposed to severe environmental conditions. Therefore, the rust prevention and chipping resistance were not sufficiently satisfactory. For this reason, this type of primer, which is used as an undercoat of aluminum castings and is applied in a thick film to sufficiently cover the irregularities on the surface of the aluminum substrate, is likely to cause a decrease in adhesion due to such a thick film. Regardless, there has been a demand for a composition that can sufficiently ensure the quality of the coating film.

Accordingly, the present invention provides a primer composition for an aluminum casting, which can secure sufficient adhesion even when applied to a thick film, and is excellent in rust prevention and chipping resistance. The purpose is to provide

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has been based on a thermosetting solvent-type composition containing a hydroxyl group-containing resin, that is, a polyol resin as a main component. Various trial and error and examination were repeated for the crosslinking agent (curing agent) component. As a result, by using a certain kind of benzoguanamine resin as a cross-linking agent and using epoxy resin in combination with an adhesion improver, excellent adhesion is ensured regardless of thickening as a primer for aluminum castings. We found what we could do and confirmed it.

That is, the primer composition for an aluminum casting according to claim 1 comprises a polyol resin as a main component, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group as a crosslinking agent for the polyol resin, and an adhesion improver. An epoxy resin as an essential component, a strong acid catalyst for promoting a crosslinking reaction, and an organic solvent.

Here, the polyol resin as the main agent is
It is a hydroxyl group-containing resin having a large number of hydroxyl groups in a molecule, which is generally used as a main component of a thermosetting coating composition, and specifically, a polyester polyol resin, an acrylic polyol resin and the like can be used. Also,
Its OH value (hydroxyl value) is preferably about 100 to 200 (mgKOH / g), which is typical for this type of resin.

A crosslinking agent (curing agent) for crosslinking and curing the polyol resin is a benzoguanamine resin (benzoguanamine formaldehyde resin), the methylol group of which is alkyl etherified with methyl, ethyl, butyl or the like. A benzoguanamine resin having an alkoxymethyl group and having a carboxyl group by modification with a carboxyl group-containing compound is used. Specifically, as such a benzoguanamine resin having an alkoxymethyl group and a carboxyl group,
For example, commercially available "Symel 1125-80" (manufactured by Mitsui Cyanamid Co., Ltd.) or the like can be used. The benzoguanamine resin also functions as a curing agent (crosslinking agent) for the epoxy resin. The blending ratio of the benzoguanamine resin can be appropriately determined according to the curing conditions and the like.
A ratio of 40 to 60 parts by weight with respect to parts by weight is preferred.

The epoxy resin is added as an adhesion improver for further improving the adhesion to the surface of the aluminum base. As the epoxy resin, any one such as bisphenol A type or F type can be used, and its compounding ratio is 10 to 20 parts by weight based on 100 parts by weight of the polyol resin. Parts are generally preferred.

Further, as a strongly acidic catalyst for accelerating the crosslinking reaction between the polyol resin and the benzoguanamine resin, sulfonic acids such as paratoluenesulfonic acid and dodecylbenzenesulfonic acid, which are well-known as this type of catalyst, are used. It can be suitably used. Moreover, the addition ratio is about 0.5 to 1.5 PHR with respect to the whole resin component.

In addition to these components, since the primer composition for aluminum castings is formed as a solvent type (solution type) paint, an organic solvent for dissolving or dispersing these components is an essential component. I do. As the organic solvent, an appropriate one can be used according to the kind of the main agent and the like, and an appropriate amount can be used for adjusting the viscosity to a desired value.

The primer composition for aluminum castings may further contain a pigment. As the pigment, any one or more of various coloring pigments, extender pigments, rust-preventive pigments, metal pigments and the like can be appropriately used. To suppress sagging at the time of coating, or to moderately reduce the cohesive force of the formed coating film to further suppress interfacial peeling. Therefore, the pigment can be blended in a relatively large amount, and the pigment concentration (PWC) is 5% based on the total material components of the composition.
It can be blended at a ratio of up to 0%, preferably at a ratio of 25 to 50%. However, this primer composition can also be formed as a clear coating without a pigment.

The primer composition for an aluminum casting, which comprises these polyol resins, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group, an epoxy resin, a strongly acidic catalyst, and an organic solvent as essential components, It can be advantageously applied as a primer of an aluminum casting such as an aluminum wheel, that is, as an undercoat applied to the surface of an aluminum base material before a finish coating such as a color coat or a clear coat is applied. The primer composition is applied with a thickness capable of sufficiently covering the unevenness of the surface of the aluminum base and flattening it, that is, a thickness of generally about 100 to 150 μm. In addition, baking of the applied primer composition can be performed alone, but it is preferable to perform baking and curing of a color coat or a clear coat which is overcoated on the coating film. Thereby, productivity can be improved and resources can be saved. Specifically, for example, after the primer composition is applied to the surface of an aluminum casting, a color coat is applied on the coating to a thickness of about 15 to 20 μm by wet-on-wet and baked. , 30 ~ clear coat on the surface
The coating can be performed by three coats and two bake steps of applying and baking to a film thickness of about 35 μm. The application of the primer composition can be performed by ordinary application means such as general air spray application.

[0018]

The primer composition for an aluminum casting contains an epoxy resin as an adhesion improver and, in particular, a benzoguanamine having an alkoxymethyl group and a carboxyl group as an amino resin used as a crosslinking agent for a polyol resin. Since resin is used, sufficient adhesion (adhesion) can be obtained even when applied to a thick film, as can be seen from the test results described below. Can also be obtained.

The reason why such excellent adhesion is obtained is not only that the adhesion is improved by the epoxy resin, but also that the carboxyl group introduced into the benzoguanamine resin is bonded to the base aluminum, As a result, it is considered that a strong adhesive force is generated between the cured coating film of the primer composition containing the same and the surface of the aluminum substrate. Further, the coating film of the primer composition also has excellent water adhesion resistance and moisture adhesion resistance. This is because, as described above, the carboxyl group provides strong adhesion and the benzoguanamine skeleton of the benzoguanamine resin. Is considered to be because of having a resistance to moisture.
Furthermore, since the benzoguanamine skeleton also has flexibility (flexibility), it contributes to improvement of chipping resistance, and since the coating film can be made thicker, it obtains excellent chipping resistance. Can be.

Since the primer composition is of a solvent type, the baking temperature can be lowered as compared with the powder clear coating, and furthermore, the color coat can be overcoated wet-on-wet, so that It can improve productivity (production efficiency) and contribute to resource saving. The primer composition is used as a single solution, and can be applied by mass-production by ordinary application means such as air spray application. Further, masking coating, which is generally impossible with powder coating, is also possible.

[0021]

The present invention will be described below in more detail with reference to examples and comparative examples.

FIG. 1 is a table showing the composition of the primer compositions for aluminum castings of Examples 1 to 8 of the present invention. FIG. 2 is a table showing the composition of the pigment dispersion paste in which the pigment in FIG. 1 is dispersed. Furthermore,
FIG. 3 is a table showing the types of crosslinking agents used in the primer compositions for aluminum castings of Examples 1 to 8 of the present invention and the results of evaluation tests of the coating film performance. FIG. 4 is a table showing the types of cross-linking agents used in the primer compositions for aluminum castings of Comparative Examples 1 to 5 and the results of evaluation tests of their coating film performance. FIG. 5 shows the results of an evaluation test of the coating film performance of an example product (aluminum wheel) using the primer composition of Example 1 as an undercoat and a conventional product using a powder clear coating as an undercoat. FIG.

[Preparation of Composition] Aluminum castings of Examples 1 to 8 of the present invention were prepared using the composition shown in FIG. 1 and the composition shown in FIG. 2 as a pigment dispersion paste. A primer composition was prepared.

As shown in FIG. 1, the primer compositions for aluminum castings of these examples contain a polyol resin, a cross-linking agent, an epoxy resin, a strong acid catalyst, and a pigment, and are prepared as a solvent type paint. Have been. In addition, the following were specifically used as these compounding materials.

The polyol resin as the main component includes OH
Polyester polyol resin with a value of about 140 (mgKOH / mg) (“Desmophen 670” Sumitomo Bayer Urethane Co., Ltd.)
Manufactured).

As a crosslinking agent for the polyol resin, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group (“Cymel 1125-80” manufactured by Mitsui Cyanamid Co., Ltd.) was used. This benzoguanamine resin has an alkoxymethyl group in which a methylol group is alkyl-etherified with methyl and ethyl and has a carboxyl group by modification with a carboxyl group-containing compound (carboxyl group-containing methyl / ethyl mixed alkylated benzoguanamine resin). is there. The benzoguanamine resin also functions as a curing agent for the epoxy resin.

A bisphenol A type epoxy resin ("Epicoat 1001" manufactured by Yuka Shell Epoxy Co., Ltd.) was used as the epoxy resin as an adhesion improver.

As a strongly acidic catalyst for accelerating the crosslinking reaction between these polyol resins and benzoguanamine resins, paratoluenesulfonic acid (Cat.
3B "manufactured by Mitsui Toatsu Co., Ltd.).

The pigment was used by dispersing it in a dispersion paste having the composition (parts by weight) shown in FIG. Here, the pigment-dispersed paste is a paste-like mixture containing the polyester polyol resin described above, and titanium oxide (“JR-701” manufactured by Teikoku Kako Co., Ltd.) 541.
5 parts by weight / carbon ("R-400" manufactured by Cabot)
2.4 parts by weight / calcium carbonate (“Homocal-D” manufactured by Shiraishi Kogyo Co., Ltd.) 221.3 parts by weight / rust preventive pigment (“K White # 105” manufactured by Teikoku Chemical Co., Ltd.) 424.8 parts by weight 495.9 parts by weight of the above polyester polyol resin and 21.8 parts by weight of a dispersant ("BYK104S" manufactured by BYK Chemie) are added to a pigment component consisting of (1190 parts by weight) and a 4 liter pebble ball mill for 24 hours. After dispersing, four kinds of organic solvents having different boiling points, n
-Butyl alcohol (manufactured by Chisso Corporation) 29.0 parts by weight / toluene (manufactured by Mitsubishi Petroleum Corporation) 42.0 parts by weight / xylene (manufactured by Idemitsu Oil Co., Ltd.) 174.2 parts by weight / high boiling point solvent (“Swazol 1000” manufactured by Maruzen Oil Co., Ltd.) 9
It was obtained by blending 4.4 parts by weight. The pigment concentration (PWC) of this pigment dispersion paste was 70%,
Its solid content concentration (NV) is 83%.

Using these materials and changing the composition thereof,
The solvent-based primer compositions for aluminum castings of Examples 1 to 8 were respectively prepared.

Specifically, in Example 1, 70 parts by weight of a polyol resin, 30 parts by weight of a cross-linking agent, and 7 parts by weight of an epoxy resin were blended, and a strongly acidic catalyst was added to these resin components. At 0 PHR, 117 parts by weight of a pigment dispersion paste was further added so that the PWC became 35%. Here, the compounding amounts of the resin components all indicate solid parts by weight.

Example 2 is different from Example 1 in that the amount of the epoxy resin was increased to 10 parts by weight.

In Example 3, the amount of the polyol resin was reduced to 67.5 parts by weight, and the amount of the crosslinking agent was increased to 32.5 parts by weight. .

In Example 4, the composition of the polyol resin was further reduced to 65 parts by weight, the composition of the crosslinking agent was further increased to 35 parts by weight, and the composition of the epoxy resin was further reduced. And at most 13 parts by weight.

Example 5 is different from Example 2 in that the compounding ratio of the strongly acidic catalyst is reduced to 0.5 PHR. In Example 6, on the contrary, the compounding ratio of the strong acidic catalyst is increased. And 1.5 PHR.

Example 7 is different from Example 2 in that the blending ratio of the pigment is reduced to 25% in PWC. In Example 8, conversely, the blending ratio of the pigment is increased and the PWC is increased.
And 50%.

In contrast to these examples, the primer compositions for aluminum castings of Comparative Examples 1 to 5 each contained a polyol resin, a crosslinking agent, an epoxy resin, a strongly acidic catalyst, and a dispersion paste. The benzoguanamine resin having an alkoxymethyl group and a carboxyl group (carboxyl group-containing methyl / ethyl mixed alkylated benzoguanamine resin) having an alkoxymethyl group and a carboxyl group used in Examples is used as a crosslinking agent. It was prepared using an amino resin. The mixing ratio of each material component is the same as in Example 2.

Specifically, in Comparative Example 1, a methylated melamine resin ("Cymel 325" manufactured by Mitsui Cyanamid Co., Ltd.) was blended as a crosslinking agent. Comparative Example 2
Is a butylated melamine resin (“Uban 20SE ・ 60”)
Comparative Example 3 was a butylated melamine resin (“Super Beckamine L-117” manufactured by Dainippon Ink and Chemicals, Inc.). Comparative Example 4 was a methyl / ethyl mixed alkylated benzoguanamine resin. (“Cymel 1123” manufactured by Mitsui Cyanamid Co., Ltd.) and Comparative Example 5 were mixed with a butylated glycoluril resin (“Cymel 1170” manufactured by Mitsui Cyanamid Co., Ltd.) as a crosslinking agent.

[Evaluation Test] Next, the primer compositions for aluminum castings of Examples and Comparative Examples prepared by changing the blending of each component and the type of amino resin as a crosslinking agent as described above were used. Evaluation tests were performed on the initial adhesion, water adhesion, and moisture resistance of the film. The details of these evaluation tests are as follows.

<Initial Adhesion> An evaluation test of the initial adhesion was performed as follows.

In the test, 150 × 70 × 8 mm
The aluminum casting AC4C-T6 was subjected to an alkali degreasing cleaning and a chromate (chemical conversion coating) treatment to prepare a test piece. And each primer composition of an Example and a comparative example is 100-150 as an undercoat on this test piece.
After coating each to a thickness of μm and drying naturally for 1 minute,
Color coat wet on wet 15 ~ 20μm
, And baked at 140 ° C. for 20 minutes to cure the color coat and the primer composition together. Then, a clear coat was applied to a thickness of 30 to 35 μm and baked at 140 ° C. for 20 minutes (3). Coat 2 bake).

Then, the thus-prepared painted test pieces were subjected to a Goban-like adhesion test. That is, 11 parallel lines were vertically and horizontally inserted into the painted test piece at an interval of 2 mm until the metal surface was reached.
Gobang-shaped cuts were made so that 0 cells could be formed. Then, the painted test piece having the cut-like cut was cut off with a cellophane tape, and the number of meshes of the coating film remaining on the test piece was measured to evaluate the adhesion.

<Water Adhesion Resistance> With respect to the evaluation test for water adhesion, each primer composition of Examples and Comparative Examples was used as an undercoat, and a color coat and a clear coat were overcoated similarly to the above initial adhesion test. A painted test piece was prepared and then the test piece was
After being immersed in warm water of 0 ° C. for 10 days, a Goban-like adhesion test was performed and evaluated in the same manner as described above.

<Moisture Adhesion Resistance> With respect to the evaluation test for moisture adhesion, the primer compositions of Examples and Comparative Examples were used as an undercoat, and a color coat and a clear coat were overcoated similarly to the above initial adhesion test. A coated test piece was prepared, and then the test piece was allowed to stand in an atmosphere of a temperature of 50 ° C. and a humidity of 98% for 500 hours.

The results of these evaluation tests performed on the primer compositions for aluminum castings of the examples and comparative examples are shown in FIGS. 3 and 4 together with the type of amino resin used as a crosslinking agent. The coating film thickness in FIGS. 3 and 4 indicates the total film thickness including the color coat and the clear coat.

<Preparation of Painted Aluminum Wheel and Its Evaluation Test> Separately from this, the primer composition for an aluminum casting of Example 1 was actually applied to an aluminum wheel of an automobile, and painted as an example product. Aluminum wheels were made. Then, the coated aluminum wheel of this example product, together with the conventional coated aluminum wheel using powder clear paint as a primer, has its initial adhesion, water resistance (adhesion and appearance), moisture adhesion, and salt spray resistance. An evaluation test was conducted on the properties and the two were compared. The details of each of these evaluation tests are as follows.

<Initial Adhesion, Water Resistance (Adhesion and Appearance), and Moisture Adhesion Resistance> In each test, a coated aluminum wheel of an example was manufactured as follows.

That is, an aluminum wheel which had been subjected to alkali degreasing cleaning and conversion coating treatment was prepared in advance, and a primer of Example 1 which was a solution type paint as an undercoat under the same coating conditions as in the preparation of the above-mentioned coated test piece was prepared. The composition was applied, then a color coat was applied and baked, and a clear coat was applied and baked (3 coats 2 bake).

The coated aluminum wheel of the conventional product subjected to the comparative evaluation with the product of the present example is an aluminum wheel which has been subjected to alkali degreasing cleaning and a chemical conversion coating process, and having an epoxy powder clear coating having a film thickness of about 120 μm. Thick 16
Bake at 0 ° C for 20 minutes, then apply color coat to about 20μ
m, and baked at 140 ° C. for 20 minutes. Further, a clear coat is applied to a thickness of about 30 μm and baked at 140 ° C. for 20 minutes (3 coats, 3 bake, total film thickness of about 170 μm).
μm).

The initial adhesion, water adhesion, and moisture adhesion evaluation tests were performed in the same manner as described above. The appearance after the water resistance test was evaluated together with the water resistance test. That is, 10 warm water at 40 ° C.
The surface of the coating film after immersion for days was visually observed and evaluated.

<Salt Water Spray Resistance> With respect to the salt water spray resistance, a coated aluminum wheel of an example product was prepared in the same manner as described above by applying the primer composition of Example 1 as an undercoat, Put a cross cut on the coating film of each painted aluminum wheel of the conventional product,
After exposing them to salt spray at 40 ° C. for 500 hours,
The rust width of the cross cut portion and the state of the coating film were observed and evaluated.

FIG. 5 shows the results of these evaluation tests.

[Test Results] As shown in FIGS. 3 and 4, a polyester polyol resin, a cross-linking agent, an epoxy resin, a strongly acidic catalyst, and an organic solvent were contained. In each of the examples using a benzoguanamine resin having a group, excellent initial adhesion, water resistance, and moisture resistance are exhibited despite the formation of a thick film.

On the other hand, in each of the comparative examples using an amino resin other than the benzoguanamine resin having a carboxyl group as the crosslinking agent, the initial adhesion is good, but the water adhesion and the moisture adhesion are low. That is, both after immersion in water and after standing under high humidity, the adhesion of the coating film was reduced, and complete peeling or partial peeling occurred.

As described above, the results show that a benzoguanamine resin having an alkoxymethyl group and a carboxyl group was blended as a crosslinking agent by blending a polyol resin, a crosslinking agent, an epoxy resin, a strongly acidic catalyst, and an organic solvent. It can be seen that by using the composition, good adhesion can be obtained even in the case of thick coating, and that this good adhesion can be maintained even after immersion in water or standing under high humidity. This is presumably because the carboxyl group of the benzoguanamine resin binds to the base aluminum, resulting in strong adhesion between the coating film and the aluminum base. Further, it is considered that the fact that the benzoguanamine skeleton has resistance to moisture also contributes to the improvement of the water adhesion resistance and the moisture adhesion resistance of the coating film.

Also, when this primer composition was actually applied to an aluminum wheel, as shown in FIG. 5, better results were obtained in terms of adhesion and rust prevention as compared with a conventional product in which a powder coating was used as an undercoat. Has been obtained. In other words, in the conventional product in which the powder clear coating is used as an undercoat, the coating film has good initial adhesion, but has low water adhesion, and there is no abnormality in appearance even after immersion in water. It has decreased and partial peeling has occurred. In addition, the film has low moisture adhesion, and after being left under high humidity, the adhesion is significantly reduced, and the entire surface is peeled off. Furthermore, in the salt spray resistance test, the coating film floats around the cross cut portion, and the entire surface is peeled off. On the other hand, the products of the examples had good initial adhesion, water resistance (adhesion and appearance), and moisture adhesion, and the rust width was only 0.5 mm in the salt spray resistance test. Yes, showing good rust prevention. Thus, from this result,
According to the coated aluminum wheel using the primer composition of this example, it can be seen that even when applied to an aluminum wheel and exposed to severe conditions, good adhesion can be maintained and its quality can be maintained.

Although specific examples of the primer composition for aluminum castings and specific examples in which the primer composition is actually applied to an aluminum wheel have been described, the present invention is not limited to these examples. It is not limited, and specific types and blending ratios of a polyol resin, a benzoguanamine resin having an alkoxylmethyl group and a carboxyl group, an epoxy resin, a strongly acidic catalyst, an organic solvent, and other components can be variously changed. In addition, this primer composition can be advantageously applied not only to aluminum wheels of automobiles but also to aluminum castings that require other design properties.

[0058]

As described above, the primer composition for an aluminum casting according to claim 1 is characterized in that a polyol resin as a main component, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group as a cross-linking agent, and an adhesive property are improved. An essential component is an epoxy resin as an agent, a strongly acidic catalyst for promoting a crosslinking reaction, and an organic solvent.

Therefore, in this primer composition, an epoxy resin is blended as an adhesion improver, and in particular, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group is used as a crosslinking agent for a polyol resin. In addition, even when applied to a thick film, sufficient adhesion can be obtained. In addition, moisture adhesion and water adhesion can be improved, and high adhesion can be maintained even under severe conditions. And thereby, the coating film can obtain excellent rust prevention and durability. Further, the benzoguanamine skeleton contributes to the improvement of flexibility, and the adhesion is improved, so that a thick film can be formed. Therefore, excellent chipping resistance can be obtained. That is, according to the primer composition for an aluminum casting, sufficient adhesion can be ensured even when applied to a thick film, and excellent rust prevention and chipping resistance can be obtained. it can.

[Brief description of the drawings]

FIG. 1 is a table showing the composition of a primer composition for an aluminum casting according to an example of the present invention.

FIG. 2 is a table showing the composition of a pigment dispersion paste in which the pigment in FIG. 1 is dispersed.

FIG. 3 is a table showing the types of cross-linking agents used in the primer composition for aluminum castings of the examples of the present invention and the results of evaluation tests of the coating film performance.

FIG. 4 is a table showing the types of cross-linking agents used in a primer composition for aluminum castings of a comparative example and the results of evaluation tests of the coating film performance.

FIG. 5 shows the results of evaluation tests of an example product (aluminum wheel) using the primer composition for an aluminum cast product of Example 1 as an undercoat and a conventional product using a powder clear paint as an undercoat. FIG.

Claims (1)

(57) [Claims] 1. A polyol resin as a main component, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group as a crosslinking agent for the polyol resin, an epoxy resin as an adhesion improver, and a strong acid for accelerating a crosslinking reaction. A primer composition for an aluminum casting, comprising a neutral catalyst and an organic solvent as essential components.