JPH10317192A - Electrodeposition coating method for vehicle steel plate, vehicle structure and bag structure - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To improve the turnability with electrodeposition without changing the coating equipment, coating equipment or coating method. A sill outer panel (41) and a sill inner panel (42) are joined in a middle shape and applied to a vehicle side sill structure (4) provided with reinforcing panels (43, 44) inside a bag structure portion. After forming an electric resistance film having a surface resistivity of 1 × 10 ⁹ Ω / Square or more at room temperature on at least one of the panel surfaces located inside the bag structure, electrodeposition coating is performed. The electric resistance film is formed at a position where no electrodeposition film is required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeposition coating of a vehicle and a vehicle component, and more particularly, to a steel plate for a vehicle, an electrodeposition coating of a vehicle structure, and a bag structure in which the electrodeposition of a bag structure is improved. About the method.

[0002]

2. Description of the Related Art Electrodeposition coating, intermediate coating, and top coating are effective as rust preventive treatments for automobile bodies and parts made of steel sheet materials. Since it is made by the atomization type coating method, the inside of the bag structure is not painted. That is, it is mainly a rust prevention measure for the outer plate portion.

[0003] On the other hand, in the electrodeposition coating, a vehicle body or a part is immersed in an electrodeposition paint, and an electric current is applied between the electrodeposition paint and an object to be coated. The object to be coated is a cathode.) An electrodeposited film is deposited on the surface of the object to be coated by electrophoresis and finally baked in a drying oven. Since such electrodeposition coating is performed by a dipping coating method, an electrodeposition coating film is also formed inside the bag structure, which is an important treatment as a measure for preventing rust in the bag structure.

As a measure against rust in the bag structure, it is known to use a rust-proof steel plate or to apply a rust-proof wax. It is remarkably excellent, and has advantages in both performance and cost such that no separate process is required.

[0005]

By the way, it is generally known that the bag structure portion has a lower spread of the electrodeposition paint than the outer plate portion. However, there is a problem in terms of cost that the film thickness of the outer plate portion is inevitably increased (excessive film thickness).

[0006] As an improvement of this type of electrodeposition coverage, a method of controlling the temperature of an electrodeposition paint (Japanese Patent Application Laid-Open No. 3-164, Hei 3-164).
630), applying a pulsed voltage (Japanese Patent Application Laid-Open No. 3-265240), and controlling the film thickness variation while rotating the vehicle body around an axis in the vehicle length direction (Japanese Patent Application Laid-Open No. 2-75). 933, JP-A-62-29
Japanese Patent Application Laid-Open No. 3,994 / 99) discloses a method in which the body is taken out of the tank in the middle of the electrodeposition coating process, and the electric resistance of the outer plate portion is increased by blowing air to improve the spreadability to the bag structure portion. No. 6,86,554) is known, but there is a problem that the coating equipment and the coating equipment are complicated and the equipment cost is high.

[0007] On the other hand, the improvement of the electrocoating property can be achieved by the structure of the electrodeposition paint or the object to be coated. No. 63-133,897), when designing the vehicle body, a bag-shaped panel is provided with a hole for electrodeposition and a gap between the panels is widened.

However, in the method of improving the electrodeposition paint,
There are problems that the cost of the paint increases and the painting method becomes complicated. In addition, in the case of measures against the structure of the object to be coated, there is a limit to the provision of holes for turning due to the strength or structure of the car body, and there may be cases where it is not possible to secure a sufficient gap between panels. Did not become.

In particular, in the side sill portion of the vehicle body, a reinforcing panel is often provided inside the bag structure portion for the purpose of improving strength, thereby further complicating the internal structure, and further increasing the electrodeposition turning property. It becomes difficult to secure.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and has been made in consideration of such problems of the prior art. It is an object of the present invention to provide an electrodeposition coating method for a structure for use and a bag structure.

[0011]

In order to achieve the above object, a steel sheet for a vehicle according to the present invention has an electric resistance film having a surface resistivity at room temperature of 1 × 10 ⁹ Ω / Square or more. .

Further, the vehicle structure according to the second aspect is characterized in that an electric resistance film having a surface resistivity of 1 × 10 ⁹ Ω / Square or more at room temperature is formed on a part of the inner surface of the bag structure. I do.

According to a third aspect of the present invention, there is provided a side sill structure for a vehicle, wherein a sill outer panel and a sill inner panel are joined in a middle shape, and a reinforcing panel is provided inside the bag structure. At least one of the panel surfaces of the sill outer panel, the sill inner panel and the reinforcing panel located inside the bag structure has a surface resistivity of 1 × 10 ⁹ Ω / Squa at room temperature.
It is characterized in that an electric resistance film of re or more is formed.

According to a fourth aspect of the present invention, there is provided a method for electrodeposition coating a bag structure, comprising forming an electric resistance film for suppressing the electrocoating on a part of a surface located inside the bag structure, and then applying the electrodeposition coating. Is performed.

According to a fifth aspect of the present invention, in the method for electrodepositing a bag structure, the electric resistance coating is formed on a portion that does not require an electrodeposition coating.

In the present invention, attention is paid to the electrical properties of the steel sheet constituting the bag structure, that is, by forming an electric resistance film for suppressing electrodeposition deposition on a part of the inner surface of the bag structure,
The electrodeposition area is reduced, thereby promoting the electrodeposition around a portion where the electric resistance film is not formed, and securing a required film thickness.

In the present invention, the formation site of the electric resistance film is not particularly limited, and the electric resistance film can be formed on any one or a plurality of panels constituting the bag structure portion, and may be partially formed on the entire surface of the panel. It is also possible to form.

In the present invention, where the electric resistance film is to be formed may be set so that the required film thickness can be secured in the region where the electrodeposition coating film needs to be formed. For example, in the side sill structure of a car, rainwater and mud are most likely to accumulate at the lower part of the sill outer panel and the lower part of the sill inner panel,
Therefore, since the corrosive environment is considered to be the most severe, an electric resistance film is formed on some or all of the other portions so that an electrodeposition coating film of 10 μm or more required in a portion where the corrosive environment is severe is formed. I do.

In the present invention, the step of forming the electric resistance film is not particularly limited as long as it is before the electrodeposition coating, and it may be formed not only on the surface of the steel sheet but also on a pressed product after forging. Further, the electric resistance film may be formed after the structure is formed by welding or fastening.

The electric resistance film of the present invention has a surface resistivity of 1 × 10 ⁹ Ω / Square or more at room temperature, preferably 1 × 10 ⁹ Ω / Square.
It is 10 ¹⁰ Ω / Square or more. If it is less than this, the electrodeposition coating film is deposited, and the required surrounding area cannot be sufficiently ensured.

In the present invention, although the electrodeposition coating film is not formed on the portion where the electric resistance film is formed, there is a concern that corrosion may occur. This can be dealt with by improving the self-corrosion performance of the coating itself, plating the steel plate and increasing the plating type and plating weight, etc. to increase the self-corrosion performance or increasing the thickness of the steel plate. In this case, there is no restriction on which means to select, and individual measures can be taken in consideration of economic efficiency and the like.

[0022]

The principle of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing an electrodeposition coating model,
An electrodeposition tank 1 is filled with an electrodeposition paint, and an electrode plate 2 connected to an anode is immersed therein. The work 4 is a closed box having a rectangular shape with a uniform cross section as shown in the figure, and has an electrodeposition turning hole 3 on one side thereof. When the object to be coated 4 is immersed in the electrodeposition paint 5 and a voltage is applied by connecting a cathode, a current flows through each of the outer surface 4a and the inner surface 4b of the box 4, and the electrodeposition coating film is formed by electrophoresis. Precipitates. Hereinafter, the outer surface of the box 4 is referred to as an outer plate portion 4a, and the inner surface of the box 4 is referred to as an inner plate portion 4b.

At this time, the coulomb amount of the current flowing through the object 4 is represented by Q (c), and the outer plate portion 4a and the inner plate portion 4 of the object 4 are coated.
The total surface area of b is S (m ² ), the thickness of the electrodeposited film to be formed is M (μm), the specific gravity of the electrodeposited film is ρ, and the Coulomb efficiency of the electrodeposition paint 5 is C (mg / c). Then

Q / S = kMρ / C (k is a constant) (1) In the equation (1), the specific gravity ρ of the electrodeposition coating film and the Coulomb efficiency C of the electrodeposition coating material are constant depending on the type of the electrodeposition coating material. The thickness M will be proportional to Q / S.

[0024]

## EQU2 ## M is proportional to Q / S (2) Next, the effect of the electrodeposition area when the box 4 shown in FIG. 1 is electrodeposited is considered. FIG. 2 is a circuit diagram showing the electric action at the time of the electrodeposition coating. The resistance inherent in the electrodeposition coating or the electrodeposition equipment is R ′, and the outer plate portion 4a of the box 4 is shown.
Aout, the current flowing through the inner plate portion 4b is Ain, and the power supply voltage 6 is V, the voltage V ′ applied to the outer plate portion 4a and the inner plate portion 4b is equal,

V ′ = V− (Aout + Ain) R ′ (3) Further, the relationship between the voltage V 'applied to the inner plate portion 4b and the current Ain flowing through the inner plate portion 4b is such that the resistance generated in the surrounding hole 3 through which the current passes is r, and the resistance of the inner plate portion 4b is Rin.
Then

Ain = V '/ (r + Rin) (4)

Incidentally, since the resistance Rin of the inner plate portion 4b is inversely proportional to the energized area, if the area of the inner plate portion 4b is Sin,

Rin = Kin / Sin (Kin is a constant) (5). From the expressions (4) and (5),

## EQU6 ## Ain = V '/ (r + Kin / Sin) (6) is obtained. By multiplying both sides by the unit time Δt,

Ain · Δt = ｛V ′ / (r + Kin / Sin)｝ Δt (7) On the other hand, the coulomb amount ΔQ per unit time Δt is given by ΔQ = A · Δ
Since t, the above equation (7) becomes

ΔQin = ｛V ′ / (r + Kin / Sin)｝ Δt (8) When the equation (8) is substituted into the above equation (2),

ΔMin is proportional to {V ′ / (r · Sin + Kin)} Δt (9) From (9), it can be understood that reducing the area Sin of the inner plate portion 4b is effective for increasing the film thickness.

Since Kin is a constant in the equation (9), to increase the thickness M of the inner plate 4b, the voltage V 'applied to the inner plate 4b must be increased or the resistance of the hole 3 must be increased. The product of r and the area Sin of the inner plate portion 4b may be reduced, but when the voltage V ′ applied to the inner plate portion 4b is increased, the film thickness of the outer plate portion 4a also increases as described above. On the other hand, reducing the resistance r of the hole 3 means increasing the hole diameter, which is also not preferable in terms of structure as described above.

[0027]

According to the present invention, it is possible to improve the electrodeposition turning property of the bag structure without changing the coating equipment, coating equipment or coating method. In addition, by appropriately selecting the formation range of the electric resistance film, it is possible to realize the controllability of the electrodeposition coverage.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a side view showing the appearance of the automobile V. The present invention is preferably applied to a bag structure of a vehicle body. In the following embodiments, the present invention will be described by taking a side sill 4 provided on a side portion of a floor as an example of a bag structure portion.

Preparation of Side Sill Model First, as a side sill model, the structure shown in FIG. 4 which is a cross-sectional view taken along the line IV-IV of FIG. 3 and FIG. The side sill 4 of this model has a total length of 800 mm, a total height of 150 mm, and a total width of 200 mm, and is located on the outermost side of the vehicle.
1 and a sill inner panel 42 located on the innermost side of the vehicle were joined in a so-called middle manner, and a reinforcement sill outer panel 43 was sandwiched therebetween to join. These panels 41, 42, 43 were joined by spot welding. Before this joining, the brace sill outer panel 44 was previously joined to the reinforce sill outer panel 43 by spot welding. Each of the panels 41 to 44 used a cold-rolled steel plate.

The turning hole 3 has a hole of 20 mmφ on the vertical wall surface of the sill inner panel 42 and the sill outer panel 4.
A hole having a diameter of 15 mm was formed on the upper surface of Sample No. 1.

Example 1 Before producing the side sill model 4 described above, an acrylic melamine resin-based clear paint (manufactured by Kansai Paint Co., Ltd.) was applied to each of the surfaces B, C, D, E and F shown in FIG. Then, this was dried in a baking oven at 140 ° C. for 20 minutes to obtain a coating film having a thickness of 3 to 5 μm (high electric resistance coating film of the present invention). The spot welds were masked. The surface resistivity of each coating film was measured using a surface resistivity meter (Model 150, manufactured by Trek Corp.) and found to be 1 × ^{10 10} Ω / Square.

This was assembled into a side sill model as described above, immersed in an electrodeposition tank containing 10 m ³ of electrodeposition paint, applied with a voltage of 300 V for 3 minutes, and painted in a baking oven for 170 minutes. Dry at 20 ° C. for 20 minutes.

The side sill model thus electrodeposited is disassembled, and the film thickness measurement points A, B, G, and H shown in FIG.
The thickness of the electrodeposited coating film at each point was measured using an electromagnetic film thickness meter. The result is shown in FIG. However, since the electrodeposition coating film is not formed at each of the measurement point B in Example 1 and the measurement point G in Example 3, the film thickness of the electrodeposition is not measured.

Incidentally, as a film thickness measuring point, 4 shown in FIG.
The points were selected in order to verify the equilibrium of the film thickness with the outer plate portion for the measurement points A and H, which are the outer plate portions.
On the other hand, the measurement points B and G, which are the inner plate portions, are sites where rainwater and muddy soil easily accumulate and the corrosive environment is the severest in the market.

Example 2 The application site of the acrylic melamine resin paint was C, D, E,
Electrodeposition coating was performed under the same conditions as in Example 1 except that F was used, and the film thickness of the electrodeposition coating film formed by disassembly in the same procedure was measured. The result is shown in FIG.

Example 3 The application sites of the acrylic melamine resin paint were C, D, E,
Electrodeposition coating was performed under the same conditions as in Example 1 except that F and G were used, and the film thickness of the electrodeposition coating film formed by disassembly in the same procedure was measured. The result is shown in FIG.

COMPARATIVE EXAMPLE 1 A side sill model was assembled without applying an acrylic melamine resin paint, electrodeposition coating was performed under the same conditions as in Example 1, and the electrodeposition coating formed by dismantling in the same procedure. The thickness of the film was measured. The result is shown in FIG.

Comparative Example 2 In place of the acrylic melamine resin paint in Example 1, a polyester resin paint containing carbon black (manufactured by Shinto Paint Co., Ltd.) was applied and dried, and the surface resistivity was 5 × 10 ⁸ Ω /. Electrodeposition coating was performed under the same conditions as in Example 1 except that a square coating was formed, and the film thickness of the electrodeposition coating film formed by disassembly in the same procedure was measured. The result is shown in FIG.

From the above results, in Comparative Example 1 in which the high electric resistance film of the present invention was not formed and Comparative Example 2 in which the film having a low surface resistivity was formed, the electrodeposition film thickness of the outer plate portions A and H was smaller. While the thickness was 20 to 21 μm, the electrodeposited film thickness of the inner plate portion was as thin as 4 to 7 μm. Further, in the coating paint used in Comparative Example 2, it was observed that the electrodeposition coating film was partially deposited on the coating film after the electrodeposition coating, and the effect of suppressing the rotation was not sufficiently exhibited.

On the other hand, in Examples 1 to 3 in which the high electric resistance film of the present invention was formed, the electrodeposition film thickness of the outer plate portions A and H was 20 to 21 μm, whereas the inner plate portion was The electrodeposition film thickness was 10 to 14 μm, which was sufficient for rust prevention. In particular, in the case of Example 2, a film thickness of 10 μm was obtained even though the electrodeposition coating sites were increased on the B and G planes, and the rust prevention effect was sufficiently expected in the market.

The embodiments described above are described for the purpose of facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element and each numerical value disclosed in the above embodiment are:
It is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

For example, in the above, the present invention has been described with reference to the embodiment applied to the side sill. However, the present invention is not limited to the side sill, and the same applies to the side member, the cross member, and other bag structures. Can be applied to

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an electrodeposition model for explaining a coating principle of the present invention.

FIG. 2 is an electric circuit diagram showing the electric action of the electrodeposition model shown in FIG. 1 as a model.

FIG. 3 is a vehicle side view for explaining a side sill used in the embodiment of the present invention.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a perspective view showing a main part of a side sill model used in the embodiment of the present invention.

FIG. 6 is a diagram showing the results of an example of the present invention.

[Explanation of symbols]

 4: Side sill (bag structure)

Claims (5)

[Claims] 1. A surface resistivity at room temperature of 1 × 10 ⁹ Ω /
A steel plate for vehicles, having a square or more electric resistance coating. 2. The surface resistivity at room temperature is 1 × 10 ⁹ Ω /
A vehicle structure, wherein an electric resistance film of Square or more is formed on a part of the inner surface of the bag structure. 3. A side sill structure for a vehicle, wherein a sill outer panel and a sill inner panel are joined in a bridge shape, and a reinforcing panel is provided inside a bag structure portion thereof. At least one of the panel surfaces located inside the bag structure has a surface resistivity of 1 × 10 at room temperature.
^A side sill structure for a vehicle, wherein an electric resistance film of ⁹ Ω / Square or more is formed. 4. An electrodeposition coating method for a bag structure, comprising: forming an electric resistance film for suppressing the rotation of electrodeposition on a part of a surface located inside the bag structure; and applying an electrodeposition coating. . 5. The electrodeposition coating method for a bag structure according to claim 4, wherein said electric resistance coating is formed at a portion where no electrodeposition coating is required.