JPS59160568A - Film thickness equalizing method of immersion painting - Google Patents

Abstract

PURPOSE:To perform uniform painting of an object to be painted having an uneven surface or a curved surface shape by drawing up the object to be painted at a constant speed and also by keeping the painting surface and the painting liquid surface at a prescribed angle. CONSTITUTION:A device for holding and drawing up an object to be processed 1 is a multi-joint robot 8, and a drawing-up operation along the shape of the painting surface is given so that an angle made by the painting surface of the object to be processed 1 and the liquid surface of a painting liquid is kept at a prescribed angle at all times by its arm 9. Also, the object to be painted is drawn up at a constant speed from the painting liquid. According to such a constitution, an immersion painting having a high quality in its finish, hardening of the film and durability is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a treatment method for making a coating film uniform by a dipping treatment method applied to surface hardening treatment using a coating liquid.

(Prior Art) The substitution of plastics for iron, aluminum, wood, etc. is progressing in various fields due to the increasing quality of products, improved durability, and quantification.

The use of plastic in automobile parts is also progressing, but substitution with plastic has been slow due to its tendency to get scratched or dirty easily. The reason for the easy dirtiness is the adhesion of dust due to the generation of static electricity and the ease with which the surface gets scratched.

In order to improve this drawback of plastic, plastic surface hardening treatment technology has been developed. This curing treatment includes coating treatment, lamination/gamma treatment, vacuum evaporation method, etc., and among these, coating treatment is often used. Spray methods, flow coating methods, dipping methods, etc. are used as coating treatment methods, and the most commonly applied method is the dipping method. However, with the immersion method, the shape of the object to be treated is limited due to the problem of dripping of the treatment liquid, making it difficult to apply to parts with complex shapes. Furthermore, when applied to exterior plastic parts of automobiles, in addition to the problem of sagging, it is necessary to increase the durability of the coating film (deterioration after weathering tests) and increase the hardness in order to improve the ease with which the plastic scratches. be. Therefore, it is required that the thickness of the coating film be made uniform, and the thickness range must satisfy the range of 3 to 10 μm, although it varies depending on the materials used and the required quality level. If the film thickness is too thick, the durability of the treated film (
Cracks after weathering tests may occur, and if the film thickness is too thin, hardness cannot be ensured, causing trouble. Therefore, currently, this coating film has a viscosity of coating liquid,
Set an appropriate pulling speed according to characteristics such as density,
Film thickness is controlled. However, this method is difficult to apply only to parts with a simple shape such as a flat plate, and it is not possible to sufficiently control the film thickness to parts having a relatively complicated shape with a curved surface and an uneven shape.

(Purpose) The present invention was made in order to improve the above-mentioned drawbacks of the surface hardening treatment of 7' rustic by the dipping method. The present invention provides a method for uniformizing the film thickness of dip coating, which is applicable not only to shapes but also to curved or uneven surfaces.

(Structure) The feature of the method according to the present invention is that the speed at which the object to be painted is lifted out of the coating liquid is kept constant, and the angle between the surface of the object to be painted and the surface of the coating liquid is maintained at a predetermined angle. This involves pulling up the object to be coated from inside.

(Function) Since the present invention is configured and implemented as described above, the paint applied to the plastic surface can always be applied in a uniform amount by pulling the object to be painted out of the coating solution at a constant speed, and Since the angle between the painted surface of the object and the coating liquid level is maintained at a predetermined angle, the sagging of the paint becomes constant in each part, and uneven film thickness in each part of the object to be painted is eliminated. As a result, the object to be coated is not limited to a flat plate shape, but can also be applied to a member having a curved surface or the like.

(Example) An embodiment of the present invention will be explained below with reference to the drawings.

Regarding the coating thickness distribution in the dip coating method, in general, even if the coating is pulled up at a constant speed (from the inside of the treatment liquid tank), the thickness of the attached coating will gradually float from the top to the bottom, and eventually increase. Once the film thickness reaches a certain level, the film thickness will hardly change in the areas below that level. If the range in which the coating film thickness becomes a constant value is defined as a steady state, then the coating thickness of the object to be treated can be determined by considering the film thickness in this steady state.

This means that when the liquid is lifted from the liquid tank at a constant speed v (m/5ee), the paint density ρ (f/'cd') and the paint viscosity μ (
Poise), paint surface tension σ(dyne/,,), then
In the theoretical coating thickness, the term σ ρ2 is a dimensionless term called the Ca number (capillary number),
This solution holds true when the Ca number is 10 or less, and 1 when the Ca number is 10 or more.
It is said that when the temperature becomes direct, the influence of the Ca number disappears. For hardening treatment by dipping method, ρ=0.85~(1
, 93(f/1ri), μ=0.03~l), [)4
(Poise), σ = 32 to 35 (dyne/,), the appropriate practical pulling speed is v = 0.25 to 0.5 (η), and the Ca number at this time is 10'-10 Nashi (1)
) is within the applicable range of formula. Therefore, the pulling speed V can be selected within this range depending on the characteristics of the paint (values of .mu., .sigma., and .rho.), and the theoretical coating thickness can be kept constant.

As shown in FIG. 1, a specific device for this purpose includes a processing tank 2 having a sufficient size to allow the workpiece 1 having a concave shape and a curved surface to be immersed in the processing tank 2. A metering pump 6 for overflowing the coating liquid is installed at the top of the pipe 2 (near the liquid level), and a main pump 5 and a filter 6 are installed at the bottom of the pipe 4.
are arranged in series so that the coating solution can be supplied and circulated. A heat exchanger 7 surrounds the treatment tank 2 and keeps the temperature of the coating liquid constant so as to maintain its properties at all times.

The device to hold and pull up the workpiece 1 is an articulated robot 8, which uses an arm 9 to paint the workpiece 1 so that the angle between the painted surface of the workpiece 1 and the coating liquid level is always a predetermined angle. Gives a lifting action that follows the shape of the surface. The predetermined angle here is most preferably 90 degrees, but if the object to be treated has a drip shape, the angle that allows the liquid to flow down (in the shape of the enlarged view of section A in Figure 1, θ1 is 45 degrees). When the painted surface has a certain angle θ with respect to the vertical line as shown in FIG. 2, the lifting speed is changed to V/ring θ with respect to the specified speed V.

Also, the surface treatment using this method is as shown in Figure 6.
Using the jig 10, it is possible to handle a plurality of objects 1 to be processed. In this way, if a plurality of objects 1 to be processed can be processed with uniform film thickness at once, it will greatly contribute to improving productivity.

(Effects) As described above, by applying the dip coating film thickness uniformization method of the present invention, it is possible to immerse plastic parts with uneven or curved surfaces, which is difficult to do with conventional immersion methods. surface hardening treatment technology can be established. As a result, it becomes possible to incorporate into the production line a surface hardening treatment that provides a uniform film thickness for plastic parts having an uneven or curved surface.

Therefore, the film thickness of mass-produced products can be made uniform, and high-quality products can be supplied even for exterior parts that require durable quality.

Furthermore, the method of the present invention is not limited to surface hardening treatment of plastics, but can also be applied to the field of general dip coating methods.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of dip coating of a workpiece having a concave shape and a curved shape, Fig. 2 is an explanatory diagram of a lifting angle of a curved part, and Fig. 3 is an explanatory diagram showing a case where there are multiple workpieces. It is. 1...To be processed/? I 2... Processing tank 5... Metering pump 4... Piping 5... Main pump 6... Filter 7... Heat exchanger 8... Articulated robot 9... Arm
10... Jig patent applicant Toyota Motor Corporation agent Patent attorney Yumi Sae and 1 talented person 1
Figure 2

Claims (1)

[Claims] (1) Keep the speed at which the object to be painted is lifted out of the coating liquid constant, and 1. A method for uniformizing the film thickness of dip coating, which is characterized by lifting the object to be coated from the coating solution while keeping the angle between the surface of the object to be coated and the surface of the coating liquid at a constant angle.