JP6846741B2 - Insulation coating method for aluminum die-cast products - Google Patents

Description

The present invention relates to an insulating coating method for aluminum die-cast products, and more particularly to an insulating coating method using powder baking coating and an insulating coating material.

Painting the surface of metal products has been practiced for a long time, but recently, powder baking coating has been widely used. This is because according to this coating method, not only a strong coating film can be obtained, but also a plurality of advantages such as environmental friendliness can be expected because it is not necessary to use an organic solvent.
Since aluminum die-cast products are relatively lightweight and easy to form complicated shapes, they are widely used for wheels of automobiles, mechanical parts, hardware such as gates, building materials, etc., and among them, Patent Document 1 As described, some of them are subjected to the above-mentioned powder baking coating in order to improve strength and toughness.

Japanese Unexamined Patent Publication No. 2001-301402

Recently, there has been increasing interest in electric vehicles due to concerns about the depletion of petroleum resources and global warming, and further technological development is underway to promote their widespread use, including battery-related products. It has been.
Therefore, aluminum has been conventionally used to fix multiple batteries, but all of them are rolled materials, and if they can be replaced with die-cast products that can handle complicated shapes, the degree of freedom in the structure of the entire battery system is as high as possible. Will also increase, and it is thought that it can greatly contribute to technological development.

However, battery-related members are required to have high insulation on their surfaces.
On the other hand, since a large number of burrows are originally formed in the die-cast product, it is difficult to form a coating film without pinholes. Although powder baking is applied after painting, it is still difficult to prevent the occurrence of pinholes with high accuracy. Therefore, in the past, for the purpose of insulation, the film thickness was relatively increased to about 250 to 400 μm to utilize the film thickness effect, and we have not heard of an example of successful insulation coating with a thin film thickness of 190 μm or less. ..

The present invention makes it possible to impart insulation to the surface of an aluminum die-cast product, which is applied to applications in which high surface insulation is required for a thin film as described above in order to solve the above problems. It relates to an insulating coating method and an insulating coating using a new and useful powder baking coating.

The present invention has been made to solve the above problems, and the invention of claim 1 is to apply a first powder coating material on an aluminum die-cast product to be coated by an electrostatic method to obtain a high frequency. After heating and melting by baking and drying by the induction heating method and cooling to form the powder coating film on the lower side, a second powder paint is applied on it by the electrostatic method and baking and drying by the high frequency induction heating method. This is an insulating coating method for aluminum die-cast products that imparts insulating properties by forming a powder coating film on the upper side after heating and melting , and the baking temperature of the second powder coating material is set to the standard baking temperature. Then, the baking temperature of the first powder coating material is set to a temperature 20 ° C. higher than the baking temperature of the second powder coating material, and the first powder coating material and the second powder coating material are of the same type. This is an insulating coating method, characterized in that the first powder coating material is applied thicker than the second powder coating material.

The invention of claim 2 is the method for insulating coating an aluminum die-cast product according to claim 1 , wherein the first powder coating material is applied to a thickness of 70 to 120 μm and the second powder coating material is applied to a thickness of 30 to 70 μm, respectively. It is an insulating coating method characterized by the fact that it is used.

According to the insulating coating method using the powder baking coating of the present invention, the insulating coating can be applied to the surface of an aluminum die-cast product having burrows with a thin film thickness.

It is an overall block diagram of the powder baking coating apparatus which carries out the insulation coating method which concerns on embodiment of this invention. It is explanatory drawing of the object to be coated which is insulatingly coated by the apparatus of FIG.

The insulating coating method according to the embodiment of the present invention will be described below.
<Object to be coated>
The object to be coated, which is the subject of the present invention, is an aluminum die-cast product.
Aluminum die-cast products are die-cast products after degassing and slagging a molten aluminum alloy having a chemical composition for die casting. Inside, a shrinkage nest and a entanglement nest are formed. Although they have different causes of formation, they are all hollow and are collectively called burrows.

<Painting pretreatment>
After removing the aluminum die-cast product from the mold, surface treatment is applied, and pinhole countermeasures are taken as much as possible at this stage.
First, since the mold release agent is attached to the aluminum die-cast product, it is degreased.
Next, since burrs and irregularities appear on the aluminum die-cast product, large burrs are removed by cutting, and smaller burrs are removed and smoothed by shot blasting.
Then, after the above-mentioned treatment, the ionizer is placed in an operating atmosphere as a countermeasure against static electricity adhesion so that dust and dirt do not adhere.

<Insulation coating method>
The pretreated aluminum die-cast product is subjected to powder baking coating.
The powder coating material contains a resin that is the main component of the coating film, and includes epoxy resin, polyester resin, epoxy polyester resin, etc., which are used properly according to the intended use, but in the case of the present invention. Is an application that requires electrical insulation, so the one containing epoxy resin, which is currently the mainstream in that application, is used.
As will be described later, in the present invention, since the coating is applied twice, it is possible to change the size of the powder between the first and second coatings, and to change the type if the paints are compatible with each other. ..

The powder coating method includes an electrostatic method in which the powder coating is charged, the surface of the object to be coated is coated with the powder coating by the force of the static electricity, and then baked and dried, and a flow tank containing the powder coating. There is a flow-immersion method in which a preheated object is immersed in the material to dissolve and adhere the powder coating material to the surface of the object to be coated. In the case of the present invention, the electrostatic method is assumed to be used.

In electrostatic powder coating, coating of powder coating and subsequent baking and drying are integrated, and it is necessary to charge the surface of the object to be coated. Therefore, the 1-coat, 1-bake (1C1B) method is standard. However, in the case of the present invention, a 2-coat 2-bake (2C2B) method is adopted.
As measures against pinholes at this stage, it has been conventionally proposed to dry-bake the object to be coated in advance or to pre-coat it using a solvent or powder primer, but in the present invention, these are used. No measures will be taken.

However, it is an indispensable condition to use the high frequency induction heating method for baking and drying.
In the high-frequency induction heating method, the object to be coated is heated using high frequency, and the powder coating material adhering to the object to be coated is melted from the side in contact with the object to be coated to form a network-like structure by a chemical reaction. It has become.

With one coat and one bake, a coating film with good adhesion is formed on the surface of the aluminum die-cast product. However, when the gas remaining in the burrow on the surface of the aluminum die-cast product to be coated is heated, it expands and breaks through the coating layer, so after baking and drying (1 bake), a pinhole is formed on the burrow. The surface of the aluminum die-casting is exposed and the surrounding area is swollen. In this state, there is no insulation and no surface smoothness.
However, in the present invention, the second coat of two coats is carried out, and by effectively using the induction heating in the second bake stage, the powder coating material of the second coat coated is melted, there is no pinhole, and there is no pinhole. We have succeeded in forming a coating film with good surface smoothness. It is unknown whether the pinhole generated at the first bake was filled or left inside as a cavity, but no trace of the pinhole remains on the coated surface after the second bake.

The preferred conditions for carrying out the above two coats and two bake are as follows.
It is preferable that the baking temperature of the powder coating material of the first coating is set to a temperature slightly higher than the standard baking temperature, and the baking temperature of the powder coating material of the second coating is set to about the standard baking temperature.
Therefore, if the types of powder coating materials are the same, it is recommended that the baking temperature of the powder coating material of the first coating be higher than the baking temperature of the powder coating material of the second coating by about 20 to 50 ° C.
Further, it is preferable to increase the coating film thickness of the powder coating material of the first coat and reduce the coating film thickness of the powder coating material of the second coating.
Specifically, it is preferable that the coating film thickness of the powder coating material is 70 to 120 μm in the first coating and the coating film thickness of the powder coating material is 30 to 70 μm in the second coating.
By performing the first bake at a high temperature, the effect of exhausting gas is expected, and by making the first coat thicker, the effect of suppressing gas generation at the second bake stage is expected. Therefore, a better effect can be expected when both the temperature and the film thickness are adjusted.
Even if the first bake is performed at a high temperature, it is premised that it is within the permissible range of baking and drying by the high frequency induction heating method.

<Powder baking coating equipment>
An example of the powder baking coating apparatus 1 for carrying out the above-mentioned insulating coating method is shown below.
FIG. 1 is an overall configuration diagram of the powder baking coating apparatus 1.
An example of the aluminum die-cast product 3 as the object to be processed by this device forms a part of the insulating cartridge for the battery shown in FIG. 2, and has a rectangular plate shape and a large number of mounting holes 5 formed therein. There is.
A plurality of bolt holes 7 are provided on both ends in the longitudinal direction of the aluminum die-cast product 3, and it is necessary to mask these portions.

Reference numeral 9 indicates a masking jig. The masking jig 9 includes a receiving portion 11 formed by bending a copper cutting plate into a U shape, and a support shaft 13 made of a copper pipe is connected to the outside of the receiving portion 11. An insulating holding portion 15 formed by bending a Teflon (registered trademark) plate into a U shape is integrally attached to the holding side of the receiving portion 11 to form a U shape as a whole. .. A plurality of communication holes 17 are provided in the integrated receiving portion 11 and the holding portion 15.
Reference numeral 19 indicates a masking jig different from the above. The masking jig 19 is not provided with the support shaft 13, and other configurations are the same as those of the masking jig 9.
The masking jigs 9 and 19 are slid from both ends of the aluminum die-cast product 3 in the longitudinal direction to sandwich the aluminum die-cast product 3. In that state, since the communication hole 17 communicates with the bolt hole 7 of the aluminum die-cast product 3, the bolt 20 is passed through the communication hole 7 and tightened to connect the aluminum die-cast product 3.
In FIG. 2, the bolt hole 7 and the communication hole 17 are shown with solid lines so that the hole edges can be easily seen.

The aluminum die-cast product 3 is subjected to powder baking coating with the masking jigs 9 and 19 attached.
In the powder baking coating apparatus 1, the transport line 21 of the annular track is provided with two coating portions 23, two heating portions 25, and two air blow-off portions 27, and the first coating is provided. The bake part (painting part 23 to heating part 25 to air blowing part 27) to the second coat baking part (painting part 23 to heating part 25 to air blowing part 27) are arranged in this order, and when passing through them. Each treatment is applied to.
Therefore, when the aluminum die-cast product 3 goes around the transport line 21, the two coats and two bake are completed.

In the transport line 21, the support shaft 13 of the masking jig 9 is attached to a transport hanger (not shown), and the plate surface of the aluminum die-cast product 3 is transported in a vertical direction.
In the coating portion 23, the coating gun 24 faces downward, and the aluminum die-cast product 3 passes below the coating gun 24. Since the aluminum die-cast product 3 rotates around the axis there, the powder paint is evenly sprayed and applied to both plate surfaces and the surfaces of both plate portions. The inside of the club room is maintained at a negative pressure by using a vacuum, and an ionizer is also used to prevent the powder coating material from adhering to the coating apparatus.
The heating unit 25 is sandwiched between the flat work coils 26 and 26 from above and below, and the aluminum die-cast product 3 is induced and heated by supplying a high-frequency power source to the work coils 26.
In the air blow-off portion 27, air is blown to remove excess powder paint on the masking jigs 9 and 19 for cleaning.
After the bake, there is an interval on the transport line 21 up to the next processing unit, where it is allowed to cool. That is, it works as a cooling unit 29.

Under the following implementation conditions, a powder coating material containing an epoxy resin as a main component was used, and the aluminum die-cast product 3 was insulatingly coated using the above apparatus 1.
It should be noted that the heating unit has a high heating rate and can raise the temperature to 240 ° C. in about 150 seconds. When applied to the high-frequency induction heating method, the powder coating material used has an optimum baking temperature of 220 ° C., and the standard baking temperature is within plus or minus 20 ° C.
(Implementation condition 1)
The first coat bake portion was heated to 260 ° C. and then cooled without painting to aim for an air-baking effect.
In the second coat bake portion, the coating was applied to 120 to 150 μm, heated to 220 ° C., cleaned, cooled, and the treatment was completed. In addition, in order to improve the fluidity of the powder coating material, a powder coating material finer than other implementation conditions was used.

(Implementation condition 2)
In the first coat bake portion, the coating was applied to 50 to 80 μm, heated to 230 ° C., cleaned, cooled, and the treatment was completed.
In the second coat bake portion, the coating was applied to 80 to 100 μm, heated to 230 ° C., cleaned, cooled, and the treatment was completed.
(Implementation condition 3)
In the first coat bake portion, the coating was applied to 50 to 80 μm, heated to 240 ° C., cleaned, cooled, and the treatment was completed.
In the second coat bake portion, the coating was applied to 60 to 100 μm, heated to 220 ° C., cleaned, cooled, and the treatment was completed.

(Implementation condition 4)
In the first coat bake portion, the coating was applied to 50 to 80 μm, heated to 210 ° C., cleaned, cooled, and the treatment was completed.
In the second coat bake portion, the coating was applied to 60 to 100 μm, heated to 240 ° C., cleaned, cooled, and the treatment was completed.
(Implementation condition 5)
In the first coat bake portion, the coating was applied to 40 to 50 μm, heated to 210 ° C., cleaned, cooled, and the treatment was completed.
In the second coat bake portion, the coating was applied to 100 to 120 μm, heated to 240 ° C., cleaned, cooled, and the treatment was completed.

(Implementation condition 6)
In the first coat bake portion, the coating was applied to 70 to 120 μm, heated to 240 ° C., cleaned, cooled, and the treatment was completed.
In the second coat bake portion, the coating was applied to 30 to 70 μm, heated to 220 ° C., cleaned, cooled, and the treatment was completed.

Among these conditions, under (implementation condition 1), a large number of pinholes were observed in the coating film, and no insulating effect could be expected.
In (Implementation condition 2) to (Implementation condition 5), almost no pinholes were observed, and an insulating effect could be expected.
Under (Implementation condition 6), pinholes could not be confirmed, surface smoothness comparable to that when the rolled material was processed was obtained, and a remarkable insulating effect could be expected.

1 ... Powder baking coating equipment 3 ... Aluminum die-cast product 5 ... Mounting hole 7 ... Bolt hole 9 ... Masking jig 11 ... Receiving part 13 ... Support shaft 15 ... Holding part 17 ... Communication hole 19 ... Another masking jig 20 ... Bolt 21 ... Transport line 23 ... Painting part 24 ... Painting gun 25 ... Heating part 26 ... Work coil 27 ... Air blow-off part

Claims (2)

The first powder paint was applied to the aluminum die-cast product to be coated by an electrostatic method, and then heated and melted by baking and drying by a high-frequency induction heating method, and then cooled to form a powder coating film on the lower side. Later, a second powder paint is applied onto it by an electrostatic method, and by baking and drying by a high-frequency induction heating method, it is heated and melted and then cooled to form an upper powder coating, thereby imparting insulation. It is an insulation coating method for aluminum die-cast products.
The baking temperature of the second powder coating material is set to the standard baking temperature, and the baking temperature of the first powder coating material is set to a temperature 20 ° C. higher than the baking temperature of the second powder coating material.
The first powder coating material and the second powder coating material are of the same type.
An insulating coating method comprising applying the first powder coating material thicker than the second powder coating material. In the method for insulating and coating an aluminum die-cast product according to claim 1.
An insulating coating method characterized in that the first powder coating material is applied to a thickness of 70 to 120 μm and the second powder coating material is applied to a thickness of 30 to 70 μm.

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