JP2003190878A - Method for coating aluminum material and aluminum alloy material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method by which the appearance finish equal to that of a coating film formed by the conventional ≥2 bake coating is attained in a ≥3 coat coating film though the number of baking processes is reduced and the coating film keeps impact resistance, weather resistance, corrosion resistance, and the like. <P>SOLUTION: In the coating method for depositing the coating film composed of a primer layer, a color layer and a clear layer on a workpiece composed of an aluminum material or an aluminum alloy material, a coating process performed in each layer of the coating film and one baking process are provided and a preliminary heating process for drying at 20-120°C for 1-30 min is performed after each coating process and before the baking process. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coating method used when an object to be coated is made of an aluminum material or an aluminum alloy material. More specifically,
Particularly, it is preferably used in the field of automobile coating and has a finish appearance and coating performance which are not inferior to those obtained by the conventional coating method of 2 to 3 bake (baking), and cost reduction and environmental load reduction. The present invention relates to a new one-bake coating method in which the number of bakings is reduced.

[0002]

2. Description of the Related Art Aluminum materials and aluminum alloy materials, which are provided with the luster of the material itself, are also lightweight, and thus are in high demand in various fields. For example, conventionally, wheels made of iron have been mainly used, but aluminum wheels made of an aluminum alloy material have been demanded because automobiles are required to have higher fuel efficiency due to the sophistication of automobiles or the problem of global warming. Has become widely used.

In general, aluminum materials and aluminum alloy materials have the above-described excellent characteristics, but have insufficient corrosion resistance, and thus are prone to thread rusting and dull oxide film formation. It has properties to consider. Therefore, a product made of an aluminum material or an aluminum alloy material is usually painted.
In recent years, in the field of paints, particularly in the field of automobile painting, the object to be coated is to improve the impact resistance and to reduce the carbon dioxide emission while demanding that the article to be coated can have a better design. To achieve this, it is required to review the painting method.

For example, when painting an aluminum wheel for a vehicle (hereinafter also referred to as an aluminum wheel),
Conventionally, after degreasing and surface treatment with chromate etc., primer, baking, color, clear, baking, or primer, color, baking, clear, baking 3
The coating film is formed through a coating step of coating 2 bake (hereinafter also referred to as 3C2B). In addition, in order to enhance the smoothness of the casting surface, or to improve elasticity and make it more scratch-resistant and to create a feeling of fleshness, an intermediate coating is added to the primer, baking, intermediate coating, baking, color ,clear,
4C3B called baking, or primer, intermediate coating,
The 4C2B coating process of baking, color, clear, and baking is performed.

The reason why 2B (twice baking) or more is required in the coating process for forming a coating film of 3C or more is that after forming a coating film having a predetermined thickness or more, for example, about 15 μm or more, the drying degree This is because the solvent of the coating film of the lower layer cannot be completely removed and foaming occurs in the coating film (hereinafter, this phenomenon is also referred to as “armpit”), resulting in poor aesthetics and poor coating film performance.

Generally, in coating aluminum wheels, a layer thickness of about 10 to 30 μm is required for the primer, and a layer thickness of about 15 to 30 μm is required for both the color and the clear. Therefore, the coating including the two bakings as described above is required. The process is adopted. Further, when a thick coating film is formed by adding an intermediate coat having a layer thickness of usually about 30 to 60 μm, baking may be performed 3B (three times of baking) after the intermediate coat.

However, since baking is generally performed at a high temperature of around 150 ° C., a larger amount of heat is required, resulting in an increase in coating cost and an increase in the amount of carbon dioxide generated in the coating process. In addition, baking requires temperature increase / decrease, and the time required per cycle is generally long, 1 to 1.5 hours.
It reduces the throughput of the entire painting process. Further, since the coating material is heated by baking, the coating material forming the coating film is rather deteriorated, and the adhesiveness between the coating film layers may be deteriorated due to deterioration after heating.

[0008]

An object of the present invention is to solve the above-mentioned conventional problems in a coating method for forming a coating film on an aluminum material or an aluminum alloy material. Specifically, for coatings of 3 coats or more,
A coating method that reduces the number of baking steps and achieves an appearance finish equivalent to that of a conventional coating film of two or more baking, and yet retains impact resistance, weather resistance and corrosion resistance. For the purpose of provision. As a result of repeated studies and studies on coating methods for aluminum materials and aluminum alloy materials, it was found that the objectives can be achieved by the following coating methods for aluminum materials and aluminum alloy materials.

[0009]

[Means for Solving the Problems] That is, according to the present invention, there are provided the following two coating methods for aluminum materials and aluminum alloy materials. The first coating method is a coating film having a primer layer, a color layer and a clear layer,
A coating method for forming a workpiece made of an aluminum material or an aluminum alloy material, comprising: a coating step performed for each layer of a coating film; and a baking step performed once.
A method of coating an aluminum material and an aluminum alloy material, characterized in that a preheating step of drying at 1 to 30 ° C. for 1 to 30 minutes is performed before the baking step and after each coating step is completed.

In the first coating method, it is preferable that the coating material forming the primer layer contains an anti-arming agent. The primer layer can be formed of a plurality of chromium-free films and made thicker. Further, it is preferable that the coating material forming the primer layer or the color layer contains a sagging preventing agent.

Further, in the first coating method, the primer layer preferably contains 15% by mass or more of the epoxy resin, and the color layer preferably contains 10% by mass or more of the polyester resin. Such a first coating method can be suitably used for forming a thick coating film having a thickness of 80 μm or more.

The second coating method is a coating film having at least a primer layer, an intermediate coating layer, a color layer, and a clear layer,
A coating method for forming a workpiece made of an aluminum material or an aluminum alloy material, wherein an anti-arming agent is added to at least the paint forming the intermediate coating layer or the color layer, and sagging occurs in at least the paint forming the intermediate coating layer. A coating process in which an inhibitor is added and performed for each layer of the coating film, a preheating process of drying at 20 to 120 ° C. for 1 to 30 minutes after each coating process, and a one-time process after the completion of all coating processes. A coating method for an aluminum material and an aluminum alloy material, the method including: a single baking step. Such a second coating method can be suitably used for forming a thick coating film having a thickness of 100 μm or more.

In the first and second coating methods of the aluminum material and the aluminum alloy material according to the present invention, an example of a workpiece which is preferably a target is a vehicle wheel.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, with respect to a coating method of an aluminum material and an aluminum alloy material of the present invention,
The embodiment will be specifically described. The coating method of the aluminum material and the aluminum alloy material of the present invention is a coating method of forming a coating film composed of a plurality of layers on a workpiece. The number of layers of the coating film is not limited, but when the object to be coated is an aluminum wheel, it is usually about 3 to 5 layers. In addition, in the present invention, the layer, for example, constitutes a coating film, different composition and role such as primer, color, clear,
Refers to each membrane. Even if the primer is composed of a plurality of continuously stacked films of two or more through the steps of coating, drying, and coating, this is called one layer.

The term “armpit” as used in the present invention refers to a phenomenon in which the solvent of the coating film of the lower layer cannot be completely exhausted during repeated coating and foams in the coating film, resulting in poor appearance. The “armpit formation preventing agent” refers to a substance that prevents this phenomenon, and the components of the armpit formation preventing agent are not particularly limited. Usually, the armpit prevention agent is
It is used by adding it to the paint or preliminarily containing it.

The term “sauce” as used in the present invention means that during coating,
This is a phenomenon in which the thickness of the surface layer becomes uneven due to gravity, etc., causing poor gloss. This is a phenomenon that tends to occur particularly when a thick film is formed. "Sagging prevention agent" refers to a substance that prevents this phenomenon. The components of the sagging prevention agent are not limited, but it is preferable to use those capable of controlling the viscosity of the coating material by mixing them. Usually, the sag-preventing agent is used by adding it to the coating material or preliminarily containing it.

The coating method of the aluminum material and the aluminum alloy material of the present invention includes the first coating method and the second coating method.
It is composed of two coating methods of the above-mentioned coating method. The term "coating method" means both the first coating method and the second coating method. First, the first coating method will be described. The first coating method of the present invention is a coating method for forming a three-layer coating film including a primer layer, a color layer, and a clear layer. It is a coating method that is excellent in impact resistance, produces a feeling of longevity, and has a desirable appearance even without an intermediate coating layer.

The first coating method is characterized in that baking is performed in a single baking step after the completion of all the coating steps, and that a preheating step is performed before the baking step and after each coating step. There is. Preheating process is the temperature of the atmosphere 2
It is a step of drying at 0 to 120 ° C. for 1 to 30 minutes.
The temperature of the atmosphere is preferably 40 to 90 ° C, more preferably about 60 ° C.

By passing through the preheating step, even if it is a thick layer of 20 μm or more, it is easy to dry the solvent contained in the paint, and it is difficult for the foamed traces to remain on the surface of the coating film, that is, it is difficult to cause cracking. Therefore, it is unlikely that the finished appearance and coating film performance are deteriorated.

Since preheating is performed at a lower temperature than baking, less heat is required for the entire coating process. Therefore, it is possible to reduce the coating cost and the amount of carbon dioxide generated in the coating process. Further, preheating requires a shorter time per cycle than baking.
Therefore, the throughput of the entire coating process can be improved.
Furthermore, since preheating is performed at a low temperature, the paint forming the coating film is not hardened and altered like baking, that is, it is more difficult to deteriorate and the adhesion between coating film layers can be further improved. It will be possible. Therefore, weather resistance and corrosion resistance can be maintained for a long time.

In the first coating method, it is preferable that the coating material forming the primer layer contains an anti-arming agent. The paint containing the underarm prevention agent is 20
Even with a thick layer having a thickness of μm or more, foam marks are unlikely to remain on the surface of the coating film, and further, deterioration of the finished appearance and coating film performance is unlikely to occur.

The primer layer is preferably a chromium-free film. That is, it is preferably obtained by applying a chrome-free paint. Chromium is harmful and causes environmental damage, and if used, its treatment requires high cost.

Further, the primer layer can be made thicker by forming a plurality of films. For example, 20 μm × 2 = 40 μ
It is possible to obtain m primer layers. This is because if the primer layer is made thick, it is possible to easily absorb an impact from the outside, to give a feeling of being full, and to obtain a preferable appearance finish.

Further, it is preferable that the coating material forming the primer layer or the color layer contains a sagging preventing agent. It is even more preferable if it is contained in both layers. Conventionally, for example, when a thick layer having a thickness of 20 μm or more, for example, is applied in a state where the object to be coated is not horizontal, the paint flows due to gravity, the layer thickness is not uniform, and the coating film has poor gloss. However, if a coating containing an anti-sagging agent is used and a preheating step as described above is performed, these problems can be solved, and furthermore, the finish appearance and the coating performance are deteriorated. hard.

In the first coating method, the primer layer preferably contains the epoxy resin in an amount of 15% by mass or more. The epoxy resin may be contained in the coating material forming the primer layer in an amount of 15% by mass or more before coating. This is because, by containing a large amount of epoxy resin, the adhesion of the primer layer to the base material is improved and the rust prevention performance is improved.

The color layer is made of polyester resin 10
It is preferable that the content is at least mass%. The color layer-forming paint may be applied using a paint containing 10% by mass or more of a polyester resin. It is desirable to use a soft polyester resin. This is because by containing a large amount of a soft polyester resin, elongation and flexibility are imparted to the color layer, internal stress in the color layer is reduced, impact absorption performance is improved, and peeling becomes difficult.

According to the first coating method of the present invention,
It is less likely to cause armpits and sagging is suppressed. For example, a thick coating film having a total thickness of 80 μm or more, such as a primer layer of 40 μm or more, a color layer of 20 μm or more, and a clear layer of 20 μm or more. It can be preferably used for forming.

Next, other preferable conditions in the first coating method will be described. The primer layer preferably contains a pigment. In particular, it is preferable to contain the coloring pigment in an amount of 12% by mass or more. This is because, in addition to coloring, the primer layer is made hydrophobic, oxygen hardly permeates, and corrosion resistance is improved. Further, it is preferable that the extender pigment is contained in an amount of 15% by mass or more. This is because the scale effect can disperse the internal stress and improve the shock absorbing performance.

Next, the second coating method will be described. The second coating method of the present invention is a coating method of forming at least four or more coating films including a primer layer, an intermediate coating layer, a color layer, and a clear layer. It is a coating method that has an intermediate coating layer, is excellent in impact resistance, and has a desirable appearance with a feeling of longevity.

In the second coating method, as in the first coating method, baking is performed in a single baking step after the completion of all the coating steps, and before the baking step and after each coating step. The feature is that each of them performs a preheating step. The conditions of the preheating step conform to the first coating method.

Also, the effects obtained are similar to those of the first coating method. That is, even in the case of a thick layer, the finish appearance and the coating film performance are less likely to deteriorate, and the coating cost is reduced, and
It is possible to reduce the amount of carbon dioxide generated in the painting process and improve the throughput of the entire painting process. Furthermore, the weather resistance and corrosion resistance can be a coating film that is retained for a long period of time.

In the second coating method, it is essential that an anti-arming agent is added to the coating material forming the intermediate coating layer and the color layer, and the coating material forming the intermediate coating layer is sagged. It differs from the first coating method in that it is essential to add an anti-generation agent. In particular, a thick intermediate coating layer can easily absorb impact from the outside, can give a feeling of flesh, and can obtain a desirable appearance finish, but at the same time, it is easy to cause armpits and easily cause sagging. , It is important to suppress these.

In the coating material to which the anti-arming agent is added, even if it is a thick layer having a thickness of 40 μm or more, for example, it is difficult for foam marks to remain on the surface of the coating film, and furthermore, the finish appearance and the coating film performance are less likely to deteriorate. In addition, the coating material to which the sagging prevention agent is added is a thick layer of, for example, 40 μm or more. For example, even when the coating object is not leveled, the coating material flows due to gravity and the layer thickness is It does not become uniform and the coating does not suffer from gloss failure.

According to the second coating method of the present invention,
It is less likely to cause armpits and sagging is suppressed. For example, the primer layer has a thickness of 15 μm or more, the intermediate coating layer has a thickness of 40 μm or more, the color layer has a thickness of 15 μm or more, and the clear layer has a thickness of 30 μm or more. Can be suitably used for forming a thick coating film having a thickness of 100 μm or more.

The above-mentioned first and second coating methods for the aluminum material and aluminum alloy material according to the present invention can form a good coating film on various objects to be coated, but in particular, a gloss defect is caused. Since it is hard to generate and has a good appearance finish, it has excellent corrosion resistance even though it is chrome-free, and it has excellent impact resistance, a beautiful appearance finish is required, it is hard to corrode in contact with muddy water, and it hits stones, gravel, etc. It is suitable for painting aluminum wheels that are required to be resistant to scratches.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. (Example 1) FIG. 1 is a cross-sectional view showing an embodiment of a coating film according to the first coating method of the present invention, showing a three-layer coating film. An extremely thin pretreatment layer 2 is formed on the base material 1 by pretreatment, and a coating film 10 including a primer layer 3, a color layer 4 and a clear layer 5 is formed thereon. As the base material 1,
Aluminum wheels were used.

First, the base material 1 was subjected to a degreasing treatment, and then subjected to a chromium-free pretreatment to form a pretreatment layer 2. Next, after washing with water and drying, N made by Kansai Paint
o. 550 primer paint (epoxy resin 15.5 mass%
Was used to perform coating, preheating (60 ° C. for 10 minutes), coating, and preheating (60 ° C. for 15 minutes) to form a 45 μm-thick primer layer 3 in which two films overlap.

Next, Kansai Paint's Magiclon AL-
2000 paint (containing 10.2% by mass of polyester resin)
Was used to form a color layer 4 having a thickness of 15 μm. Then, it preheated at 60 degreeC for 15 minutes.

Next, Kansai Paint's Magiclon KP-
Coating was performed using 130 paints to form a clear layer 5 having a thickness of 20 μm. Then, it preheated at 60 degreeC for 10 minutes.

Then, the dried coating film 10 was baked. The baking conditions were 150 ° C. and 30 minutes. still,
All coatings were performed with the spoke surface of the aluminum wheel (base material 1) facing up.

Various tests were conducted on the obtained coating film 10. Table 1 shows the test items, test methods, criteria, and test results. The test results were generally good or equivalent to Comparative Example 1 described later.

(Embodiment 2) FIG. 2 is a cross-sectional view showing an embodiment of a coating film according to the second coating method of the present invention, showing a four-layer coating film. An extremely thin pretreatment layer 2 is formed on the base material 1 by pretreatment, and a coating film 20 composed of a primer layer 3, an intermediate coating layer 6, a color layer 4, and a clear layer 5 is formed thereon. The base material 1 is an aluminum wheel.

First, the base material 1 was subjected to a degreasing treatment, and then subjected to a chromium-free pretreatment to form a pretreatment layer 2. Next, after washing with water and drying, coating and preheating (6
Performing 10 minutes at 0 ° C.) to form a 20 μm thick primer layer
Was formed.

Next, Nippon Paint Olga O-100
0 Intermediate coating layer 40 having a thickness of 40 μm is coated by using a paint with an anti-arming agent and an anti-sagging agent added.
Was formed. Then, it preheated at 60 degreeC for 15 minutes.

Next, Nippon Paint Super Rack S
Coating was performed using PM-26 paint to which an anti-arming agent was added to form a color layer 4 having a thickness of 15 μm. Then, it preheated at 60 degreeC for 15 minutes.

Next, Nippon Paint Super Rack O
Painting was performed using -70 paint to form a clear layer 5 having a thickness of 30 μm. Then, it preheated at 60 degreeC for 10 minutes.

Then, the coating film 20 was baked. The baking conditions were 150 ° C. and 30 minutes. In addition, all coating was performed with the spoke surface of the aluminum wheel (base material 1) facing up.

When the obtained coating film 20 was observed, no cracking, no glossiness was observed, and a good coating film was formed.

(Comparative Example 1) As shown in FIG. 2, a constitution similar to that of Example 2 was used, which consisted of a primer layer 3, an intermediate coating layer 6, a color layer 4 and a clear layer 5 on a pretreatment layer 2. The coating film 20 of No. 1 was formed by a conventional method. The base material 1 is an aluminum wheel.

First, the base material 1 was subjected to a degreasing treatment, and then subjected to a chromium-free pretreatment to form a pretreatment layer 2. Next, it was washed with water and dried, and then coated with Asahi Solvent Capron 800 primer coating and baked (at 150 ° C. for 30 minutes) to form a primer layer 3 having a thickness of 20 μm.

Next, Nippon Paint Olga O-100
Paint using 0 paint and bake (150 ° C for 30 minutes)
Then, an intermediate coating layer 6 having a thickness of 20 μm was formed.

Next, Super Rack S made by Nippon Paint
The PM-26 paint was used for coating to form a color layer 4 having a thickness of 15 μm.

After setting (standing at room temperature for 10 minutes), coating was performed using Superlac O-70 paint made by Nippon Paint to form a clear layer 5 having a thickness of 20 μm.

After setting, baking was performed. The baking conditions are 150 ° C. and 30 minutes. In addition, all coating was performed with the spoke surface of the aluminum wheel (base material 1) facing up.

Various tests were performed on the obtained coating film. Table 1 shows the test items, test methods, criteria, and test results.

[0056]

[Table 1]

[0057]

As described above, according to the coating method of the aluminum material and the aluminum alloy material of the present invention, even if the number of baking steps is reduced, the coating film is equivalent to or more than the conventional coating film of two or more baking. The appearance finish, weather resistance and corrosion resistance of can be maintained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a coating film according to a coating method of an aluminum material and an aluminum alloy material of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the coating film according to the coating method of the aluminum material and the aluminum alloy material of the present invention.

[Explanation of symbols]

1 ... Substrate, 2 ... Pretreatment layer, 3 ... Primer layer, 4 ... Color layer, 5 ... Clear layer, 6 ... Intermediate coating layer, 10, 20 ... Coating film.

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Claims (10)

[Claims] 1. A coating method for forming a coating film having a primer layer, a color layer, and a clear layer on a workpiece made of an aluminum material or an aluminum alloy material, the coating step being performed for each layer of the coating film. And a single baking step, and a preheating step of drying at 20 to 120 ° C. for 1 to 30 minutes is performed before the baking step and after each coating step is completed. Aluminum material and aluminum alloy material coating method. 2. The method for coating an aluminum material and an aluminum alloy material according to claim 1, wherein the coating material forming the primer layer contains an anti-arming agent. 3. The method for coating an aluminum material and an aluminum alloy material according to claim 1, wherein the primer layer is composed of a plurality of chromium-free films. 4. The sagging preventing agent is contained in the coating material forming the primer layer or the color layer.
A method for coating the aluminum material and the aluminum alloy material according to any one of 1. 5. The epoxy resin is used as the primer layer.
The coating method of the aluminum material and the aluminum alloy material according to any one of claims 1 to 4, which contains at least mass%. 6. The polyester resin is used for the color layer.
The coating method of the aluminum material and the aluminum alloy material according to any one of claims 1 to 5, which contains 0 mass% or more. 7. The method for coating an aluminum material and an aluminum alloy material according to claim 1, wherein the coating film has a thickness of 80 μm or more. 8. A coating method for forming a coating film having at least a primer layer, an intermediate coating layer, a color layer and a clear layer on a workpiece made of an aluminum material or an aluminum alloy material, which comprises at least the intermediate coating layer or An anti-arming agent is added to the paint that forms the color layer, and a sagging prevention agent is added to at least the paint that forms the intermediate coating layer, and the coating process is performed for each layer of the coating film, and each coating process ends. 1 to 30 at 20 to 120 ° C
A method for coating an aluminum material and an aluminum alloy material, which comprises a preheating step of drying for a minute and a baking step after the completion of all coating steps. 9. The method for coating an aluminum material and an aluminum alloy material according to claim 1, wherein the coating film has a thickness of 100 μm or more. 10. The method for coating an aluminum material and an aluminum alloy material according to claim 1, wherein the workpiece is a vehicle wheel.