JPH0154104B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dip coating method and apparatus for applying a coating film of a substantially constant thickness to an article (hereinafter sometimes simply referred to as article) having a relatively flat surface. Spray painting has traditionally been a common method for painting articles, but since it uses a large amount of diluting solvent, it has drawbacks such as polluting the atmosphere and causing a large amount of paint to be lost. On the other hand, dip coating, so-called dip coating, has been known for some time, but although this method does not have the above-mentioned drawbacks, it does have the disadvantage that the deposited paint flows down, resulting in a difference in film thickness between the upper and lower parts of the product. The inventors of the present invention have conducted intensive studies on ways to automate the dip coating method in a relatively simple manner to save labor and improve the uniformity of the quality of coated articles. The pulling speed of the object to be coated is determined by considering various changes and uniformity of the film thickness of the product.
In other words, it was discovered that a certain relational expression holds true for the relationship between the vertical lifting position and time, and dip coating is carried out so as to satisfy this relational expression.Moreover, with a device that embodies this, it is possible to easily reduce the thickness of the coating film to approximately the same value. The present invention was completed by being able to obtain a consistent dip coating film. That is, the present inventors conducted an experiment in which a plastic flat plate article as shown in FIG. 1 was dip coated. This article has, for example, holes 10 for attaching the article and has no large irregularities on its surface.
After dipping this material into a paint tank, it was pulled up at a constant speed to dry and harden, and the thickness of the paint film was measured.
It was found that the film thickness varied depending on the position of the pulled flat plate (the farther from the paint liquid surface, the thinner it was), and that the higher the pulling speed, the greater the non-uniformity of the film thickness (see Figure 2). Other factors that change the film thickness include the type of paint, viscosity, specific gravity, and environmental temperature, which all combine to change in a complex way. It has been found that the following relationship holds between , vertical pulling position Y, and thickness T of the coating film. T=a・Y・√+b (however, a and b are constants)
...(1) From equation (1), Y√=T-b/a, so T-b/a
= √ ₁ , equation (1) becomes Y ² V = k ₁ . ...(3) Since V=dY/dt, equation (3) becomes Y ² dY/dt=k ₁ and ∫Y ² dY=∫k ¹ dt. Solving this gives 1/3Y ³ = k ₁ t
+k ₂ (k ₂ is a constant) therefore

[Formula] becomes.

[Formula] If we put k ₂ /k ₁ = n

[Formula] is obtained. In other words, the relationship between the vertical pulling position and time for obtaining a constant film thickness has been obtained, and once m and n are determined, the vertical pulling position can be derived from the above equation if the time is known. In this case, m,
n is a constant determined experimentally depending on the type of paint, viscosity, specific gravity, working temperature, etc. The above formula can also be applied from the beginning of pulling, or after pulling at a constant speed to a certain distance from the beginning of pulling. As shown in FIG. 3, in order to maintain a constant film thickness, as the vertical position of the film is pulled farther from the liquid surface, the time becomes longer, that is, the pulling speed becomes slower. Here, the article to which the method of the present invention can be applied is an article that has a relatively flat surface, and does not necessarily have to be a flat plate, but an article that has large irregularities on the surface, such as an article that has holes, etc. It is not preferable to have a surface that causes large changes. Next, an apparatus capable of carrying out the dip coating method of the present invention for obtaining a uniform film thickness, that is, a dip coating apparatus will be described with reference to the drawings. FIG. 4 is a diagram showing an example of a dipping paint tank lifting device, in which a flat product 1 is attached to a chain conveyor 3 by a hanger 2. A paint tank 4 is filled with paint, and the paint tank is raised and lowered by the actions of a pantograph jack 6 and a hydraulic cylinder 7, thereby performing immersion. A viscosity detector 8 is installed inside the tank, and a tank vertical position detector 9 is installed on the side of the tank.
is installed. The mechanism for raising and lowering the paint tank using hydraulic pressure can be done in any way, but for example, in the case of raising, oil is sent from the oil tank to a hydraulic cylinder by a pump using a set hydraulic pressure via a relief valve and a check valve. Therefore, in the case of lowering, oil in the hydraulic cylinder returns to the oil tank via a throttle valve and a solenoid valve, both of which are activated by the tank vertical position detector. Particularly in the case of descending, since the pulling speed must be varied in order to keep the film thickness constant, a speed control electric circuit is provided to adjust the speed. This electrical circuit is shown in block diagram form in FIG. When the film thickness is set in the microcomputer 11 and a start signal is then input, a set position signal R is output. On the other hand, the tank vertical position detector 9 outputs a tank vertical position signal (detected position signal). When the difference E between the set position signal R and the detected position signal D is input into the microcomputer 13, it is calculated and a throttle valve operation signal is generated, which activates the throttle valve control device 14 to correct the tank lowering speed. As a result, the process of lowering the tank is adjusted according to a program that has been calculated and set in advance based on data such as film thickness. 6 is a plan view schematically showing an embodiment of the dip coating method and apparatus including the dip tank shown in FIG. 4. FIG. Products 1 are set at equal intervals on a product transfer chain 3 driven by a constant speed rotation stop motor 21, and the chain 3 transfers the products 1. A constant speed rotation stop motor rotates for a certain period of time and then stops, so the constant speed,
Transfers the product a certain distance and then stops. A cleaning tank 24, an undercoat paint tank 25, and a finishing paint tank 26 are located directly below the place where the stop is to be made.
Set it up. Further, a timer is used to set the transfer stop time to be longer than the time required for the dipping operation. If the product to be dip coated stops on the dip coating paint tank, it will be dip coated by the above method,
As explained above, once the coating is finished, the product is pulled up from the paint tank so that the thickness of the coating film is constant. The product thus pulled up passes through the drying tunnel ovens 27, 27' while suspended from the chain 3.
The coating film is cured by heating. The moving speed of the chain, the stopping time, the moving distance, the length of the drying tunnel furnace, the heating temperature, etc. are adjusted depending on the type of paint used, viscosity, specific gravity, etc. The dip coating method and apparatus of the present invention have significantly improved the dip coating of articles for which uniform coating was conventionally difficult.As a result, it has helped improve coating productivity and quality, and its industrial value is extremely large. . Next, the present invention will be explained with reference to Examples. Example Paint used Trigger 510 (manufactured by Toshiba Silicone Corporation) Product material dimensions Polycarbonate flat plate 400×
500mm Painting environment 25℃ 40%RH Drying and curing conditions 120℃ 1 hour Measuring device Coating film thickness Beta Technostar (manufactured by Densoku Kogyo Co., Ltd.) Viscosity B-type viscometer Viscosity 7cps Specific gravity 0.95

When dip coating was carried out using the above paint in the above coating environment and the coating thickness T was 5 μm, the relationship between the vertical lifting position Y and the time t was as shown in FIG. Therefore, from Figure 3, time t ₁ = 6.7 ... position Y ₁ = 200 t ₂ = 20 ... Y ₂ = 400 Substituting this into equation (4), 200 = m (6.7 + n) ^1/3 400 = m (20 + n ) ^1/3 gives m=161.5 n=-4.8. Substituting this into equation (4)

[Formula] and Become. On the other hand, from the pulling speed V=dY/dt

[Formula] becomes. Experimental example 1 Method of the present invention Pull up at a constant speed of 30 mm/sec from the liquid level to 200 mm,
After that, it was pulled up at the pulling speed according to equation (5). time,
Table 1 shows the relationship between the distance from the liquid surface and the pulling speed at that time.

[Table] In other words, Pulling speed 30 to 8.8 mm/sec (range from liquid level to 400 mm) Paint film thickness 4 to 5 μ Difference in paint film thickness 1.0 μ Required time 20 seconds Experimental example 2 Conventional method (1) ( High-speed pulling method) Pulling speed 30 mm/sec constant Paint film thickness 4 to 6 μ (range from liquid level to 400 mm) Difference in paint film thickness 2 μ Required time 13.3 seconds Example 3 Conventional method (2) (Low speed pulling Method) Pulling speed: 10 mm/sec constant Paint film thickness: 4 to 5.1 μ (range from liquid level to 400 mm) Difference in paint film thickness: 1.1 μ Required time: 40 seconds Compared to the conventional constant high speed pulling method, the method of the present invention has the following advantages:
Although it takes 50% more time, the difference in film thickness is halved.Also, compared to the constant low speed pulling method, the difference in film thickness is almost the same, but the time required is halved, which helps improve productivity. .

[Brief explanation of drawings]

FIG. 1 is a front view A and a plan view B showing an example of a flat plate article used in the present invention. FIG. 2 is a graph showing the relationship between film thickness and vertical position for each pulling speed, and FIG. 3 is a graph showing the relationship between vertical position and time for a constant film thickness (5μ).
FIG. 4 is a diagram showing an example of a paint tank lifting device in the immersion apparatus of the present invention, and FIG. 5 is a block diagram of an electric circuit for controlling the lowering speed of the paint tank. FIG. 6 is a plan view schematically showing an example of the entire dip coating method and apparatus of the present invention. 1... Flat plate article, 2... Hanger, 3... Chain conveyor, 4... Paint tank, 5... Paint,
6... Pantograph jack, 7... Hydraulic cylinder, 8... Viscosity detector, 9... Tank vertical position detector, 10... Hole, 11, 13... Computer, 14... Throttle valve control device, D ...Detected position signal, R...Setting position signal, E...R-D, 21
. . . Constant speed rotation stop motor, 24 . . . Cleaning tank, 25 . . . Undercoat paint tank, 26 .

Claims (1)

[Scope of Claims] 1. When dip-coating an article with a relatively flat surface, the relative vertical position Y of lifting the article from the paint liquid surface after immersion is expressed as Y=m ³ √+ (where m , n are constants determined experimentally depending on the type of paint, viscosity, specific gravity, and working temperature), thereby making the thickness of the coating film on the article almost constant. dip coating method for articles with relatively flat surfaces. 2. A chain conveyor for transporting articles that has a hanger for hanging articles, a paint tank in which the articles hung from the hanger are immersed, a lifting device for the paint tank, a vertical position detector installed on the side of the paint tank, and a detection device for the detector. an immersion coating apparatus comprising a signal-operated lifting rate control electrical circuit, the apparatus comprising a signal-operated lifting rate control electric circuit for determining, based on the signal from the detector, the vertical lifting position Y of the article relative to the paint surface after immersion with respect to time t; = m ³ √+ (where m and n are constants determined experimentally depending on the type of paint, viscosity, specific gravity, and working temperature). Apparatus for dip-coating articles having a relatively flat surface that allows for a substantially constant thickness.