JPS6033550B2 - Electrostatic painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic coating method, and more specifically, during electrostatic coating, it increases the efficiency of paint adhesion to articles, prevents scattering and adhesion of spray dust, and improves the efficiency of coating inside a coating booth. This invention relates to improvements for saving condensation and exhaust air volume.

'In electrostatic painting, charged paint particles are atomized by a paint gun by electrostatic means and/or mechanical means, and the paint particles are atomized by the action of an electrostatic field formed between the paint gun and the object to be painted. is applied onto the article to be coated.

Therefore, although the electrostatic coating method has considerably higher adhesion efficiency than the ordinary spray coating method, there are still many problems that need to be improved in actual coating operations. First, in electrostatic painting, because the paint particles adhere to each other due to electrostatic attraction, the more windless the area around the object to be coated, the better.
Although the adhesion efficiency of paint is improved, on the other hand, there are two conflicting problems: problems due to scattering and adhesion of spray dust are likely to occur.

In other words, in electrostatic painting, which aims for high adhesion efficiency, there is a risk of damage not only between the coating gun and the object to be coated, but also between the coating gun and equipment in the booth, products that have been previously coated, or objects that are scheduled to be coated next. Similarly, due to the formation of an electrostatic field, there is a problem in that floating charged coating particles adhere to these articles, causing so-called fogging and contamination.

Furthermore, charged paint particles remain suspended in a windless painting atmosphere for a relatively long period of time, and as a result, liquid paints generate so-called dry mist, which is formed by drying the paint. It has the disadvantage that it adheres to the paint film of articles and pre-painted products, making the paint film dull and rough. As a secondary painting booth, a static pressure chamber for supplying controlled air through a filter is installed in the upper part of the painting room, and a paint mist collection castle is installed in the lower part of the painting room through a lattice-like floor. Painting booths that provide controlled airflow and ventilation are widely used, but even when such painting booths are used for electrostatic painting, it is difficult to resolve the two conflicting problems mentioned above. As a compromise, the ventilation air speed is set to about 0.3 m/sec, but the paint adhesion efficiency is relatively low at 50 to 60%, and there is also a problem in terms of scattering and adhesion of spray dust.

Further, in an automobile painting booth, a second filter is arranged around the first filter to supply a low-speed airflow to the painting space through the first filter and to allow a higher-speed airflow to pass through the first filter. However, a coating method is known in which a high-speed shielding airflow is supplied around the coating space through this second filter (Jitsugu 54-174).
Publication No. 669).

When such a coating method is adopted for electrostatic coating, it is expected that the above-mentioned problems will be effectively solved, but in such a case, a new problem arises in that it is difficult to obtain a stable airflow velocity distribution. . That is, in this coating method, the wind speed passing through the second filter surface is extremely higher than the wind speed passing through the first filter surface, so that the clogging of the second filter is caused by the clogging of the first filter surface. The clogging becomes more significant compared to No. 3. Therefore, the pressure loss in the second filter increases cumulatively, and as a result, the balance between the air flows passing through the first filter and the second filter is lost in a short period of time.
3. According to the present invention, the efficiency of paint adhesion to the article to be painted is increased, the scattering and adhesion of spray dust is prevented,
Furthermore, an electrostatic coating method is provided that can save on the amount of air supplied and exhausted within the coating booth. Further, according to the present invention, there is provided an electrostatic coating method that can maintain a constant balance over a long period of time between the four flows of low-velocity air into the painting space and the shielding air flow around the space. . That is, according to the present invention, high-speed shielding air is vertically integrated around the coating bag space including the article to be coated, and
A low-velocity downward ventilation airflow is supplied into the painting space that is shielded from the surroundings by the shielding airflow, and the electrostatic painting gun is arranged so that its discharge port is located inside the shielding airflow. In a method of electrostatically coating an article to be coated,
A static pressure chamber for air supply is arranged above the painting space through a filter, and a portion with a large zero air permeation cross section is provided in the filter in a positional relationship that substantially surrounds the painting space. An electrostatic installation method is provided, characterized in that a high-speed shielding air flow is supplied from this portion to the periphery of a painting space.

The invention will be explained in detail below with reference to the accompanying drawings. A first example showing an example of a painting booth used in the method of the present invention
2, this painting booth includes a painting room 1, a static pressure chamber 2 for supplying controlled air located above the painting room 1, and a paint mist (spray dust) located below the painting room 1.
It consists of Ore Shujo 3.

The painting room 1 and the static pressure room 2 are separated by a filter 4.
On the other hand, the painting room 1 and the paint mist collection area 3 are separated by a grid-like floor 5. In the specific example shown in Figures 1 and 2,
Air from a suitable air supply source 6 is passed through a duct 7 to
Once supplied into the pressure chamber 8 located above the static pressure chamber 2,
It is distributed and supplied to the static pressure chamber 2 through a plurality of distribution holes 10 provided in the boundary wall 9 between the dynamic pressure chamber 8 and the static pressure chamber 2 .

Pressurized air is trapped inside the static pressure chamber 2, and the air in the static pressure chamber passes through the filter 4 and flows downward into the painting chamber 1.

In the painting room 1, an article 11 to be painted, such as an automobile body, is conveyed to a stereotaxic layer by a conveyor (not shown), and the charged paint is atomized by electrostatic painting guns 12, 12 in an atmosphere of downward controlled air flow. Then, electrostatic adhesion is performed, and painting work is performed. The air containing the paint mist that has not been applied to the article 11 to be painted flows out into the paint mist repair castle 3 through the grid-like floor 5, and comes into contact with the water film flowing down on the overflow plate 13 to remove the paint. Mist's collection will be removed. The gas from which the paint mist has been removed passes through the exhaust duct 14 and is either discharged into the atmosphere or sent to a secondary exhaust treatment facility. According to the present invention, high-speed shielding air 16 is supplied vertically so as to completely surround the coating space 15 including the article 11 to be coated, and this shielding air flow 16 is used to cover the surrounding area, i.e. A low-velocity downward ventilation air flow 18 is supplied into the painting space 15 that is shielded from the non-painting area 17, and the paint discharge port 19 of the electrostatic painting gun 12 is connected to the shielding air flow 1.
Arrange it so that it is located inside of 6.

In the present invention, as shown in FIGS. 1 and 2, for example, the filter 4 is arranged in a positional relationship that completely surrounds the painting space 15 in the painting room 1.
A portion 20 having a large air permeation cross-sectional area is formed.

This portion 20 with a large air permeation cross-sectional area is formed by the filter sheet standing up on the side of the static pressure chamber.
The lower end closures 22 of the opposed risers 21, 21 of this filter serve as outlets for the high-speed shielding air flow 16, while the upper ends of the risers 21, 21 are closed.

On the other hand, the other filter portions 23 corresponding to the painting space 15 and the non-painting area 17 are supported in a substantially horizontal state. In this case, the air pressure applied to the surface of the filter sheet is static pressure, and therefore the amount of air passing through the filter is approximately constant per air permeation cross-sectional area.

Thus, in the specific example shown in FIG.
3, the amount of air per horizontal cross-sectional area is large, and therefore the flow velocity of the downward regulating air flow is also large, as shown by the dotted line flow velocity distribution curve in FIG. In addition, in the present invention, as mentioned above, the amount of air passing through the filter is approximately constant per air permeation cross-sectional area in all parts, so the clogging rate of the filter is constant as a whole, and therefore the high-speed shielding air This makes it possible to maintain a constant balance between the flow 16 and the slow ventilation air flow 18 over a long period of time.

It also has the advantage that the filters through which these air flows can be replaced at the same time. Further, according to the present invention, when forming a high-speed shielding airflow and a low-speed ventilation airflow, there is no need to place a shielding object such as an extra duct below the filter, thereby eliminating stagnation in the airflow. In addition, in order to form these air flows, it is only necessary to increase the area of the filter at the necessary locations, so the layer installation is extremely easy and simple.

In the specific example shown in FIGS. 1 and 2, the risers 21, 21 of the filter are provided with dampers 24, 24 for the purpose of adjusting their permeation cross-section and thereby the flow velocity of the shielding air flow 16. It is provided so as to be slidable, and wind direction adjusting plates 25, 25 for adjusting the wind direction are provided on the lower end entrance portion 22 via a hinge (not shown) so as to be able to adjust the angle.

In the present invention, the coating space 15 for electrostatic coating is protected by the shielding air flow 16 at a high speed, particularly at a flow rate of 1 to 3 skins/sec, to the surrounding area, for example, the pre-painted product 1.
1a (Fig. 2), the product to be painted next 11b (Fig. 2), or various equipment for painting (not shown),
A ventilation air flow 18 at a low velocity, particularly at a flow rate of 0.1 to 0.2/sec, is supplied downward into this blocked coating space 15 to perform electrostatic coating within this space 15. preferable. That is, in the present invention, even when the ventilation wind speed in the painting space 15 is reduced to a significantly low level such as 0.1 to 0.2 kite/sec, the high speed The effect of the shielding airflow prevents the spray dust from scattering outside the painting space and from adhering to various equipment, previously painted items, or items to be painted next. .

Moreover, the flow velocity of ventilation air is set at 0.1 to 0.2 m/sec.
By suppressing c to a low level, the coating efficiency of electrostatic coating is 50 to 60% in a conventional uniform draft type coating room.
While the coating efficiency is at the level of 80-90
% level. Furthermore, the problem of dry mist re-adhering to the object to be coated, which occurs when an electrostatic coating gun is used in windless conditions, can be almost completely resolved by supplying ventilation air within the above range. Furthermore, it has become possible to supply high-speed shielding airflow only around the painting space and suppress the ventilation wind speed in other areas, including the painting space, to an extremely low level, reducing the air supply and exhaust air volume. can be reduced by at least approximately 45% compared to the conventional uniform draft type coating, significantly reducing equipment and operating energy costs for air supply air conditioning equipment, and reducing equipment space. It became. In the present invention, making the flow velocity of the shielding air flow smaller than 1 skin/sec is unsatisfactory in terms of preventing spray dust scattering, while making it larger than 3 skin/sec causes wake generation. This creates an undesirable reverse or upward flow within the coating space.

On the other hand, if the wind speed of the low-speed ventilation airflow is lower than 0.1 skin/sec, problems such as re-deposition of dry mist are likely to occur; This is still disadvantageous for the purpose of the present invention since the coating efficiency is reduced. Furthermore, if the discharge port of the electrostatic coating gun is not located inside the shielding airflow, the coating pattern tends to be significantly disturbed and the coating efficiency tends to decrease.

The electrostatic coating principle and apparatus used in the present invention are known per se, and any known electrostatic coating apparatus can be used in the method of the present invention.

In particular, the present invention is an electrostatic coating method in which liquid paint is supplied in a thin film along the inner peripheral surface of a high-speed rotating body to which a high voltage is applied, and the paint is atomized from the circumferential edge of the high-speed rotating body. It is particularly useful when performing automatic painting while moving the rotating body with a moving device. That is, by combining this electrostatic coating method and the ventilation method of the present invention, it becomes possible to achieve remarkable coating efficiency and to form a uniform coating film without defects.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a coating booth used in the present invention, and FIG. 2 is a top view of the coating booth of FIG. 1. 1 is a painting room, 2 is a static pressure room, 3 is a spray dust collection room,
4 is a filter, 5 is a grid-like floor, 7 is an air supply duct, 11 is an article to be coated, 12 is an electrostatic coating gun, 15 is a painting space, 16 is a high-speed shielding air, 18 is a low-speed ventilation Each indicates air. Hishiryo zuta 2

Claims (1)

[Scope of Claims] 1. High-speed shielding air is supplied vertically around the coating space including the article to be coated, and the shielding air flow is used to supply downward air into the coating space shielded from the surroundings. A method for electrostatically coating an object to be coated by supplying a low-velocity airflow for ventilation and arranging an electrostatic coating gun such that its discharge port is located inside the shielding airflow, A static pressure air for air supply is arranged above the painting space through a filter, and a portion with a large air permeation cross section is formed in the filter in a positional relationship that substantially surrounds the periphery of the painting space. An electrostatic painting method characterized by supplying a high-speed shielding air flow from a portion to the periphery of a painting space. 2. The method of claim 1, wherein the shielding air has a flow velocity of 1 to 3 m/sec and the ventilation air has a flow velocity of 0.1 to 0.2 m/sec. 3. The electrostatic coating gun is equipped with a discharge port consisting of a rotating body to which a high voltage is applied, and supplies a thin film of liquid paint along the inner peripheral surface of the rotating body, so that The method according to claim 1, wherein electrostatic painting is carried out by atomizing the paint from the circumferential edge.