JPS63119879A - Electrostatic painting method for plastic parts - Google Patents

Abstract

PURPOSE:To stably assure high painting efficiency in wet on wet painting of plastic parts by electrostatic painting by forming a thin film of water contg. carbon dioxide on the surface of the material to be coated between continuous painting stages. CONSTITUTION:A thin film of the water contg. carbon dioxide is formed on the surface of the material to be coated between the painting stages at the time of wet on wet painting of the plastic parts by electrostatic painting. The air contg. the carbon dioxide contains preferably 0.1-30vol% carbon dioxide. As a result, the electric resistance is lowered, destaticization is facilitated and the accumulation capacity thereof is decreased, by which the continuous high- voltage electrostatic painting is permitted and the high painting efficiency is stably assured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrostatic coating method. More specifically, the present invention relates to a method that allows continuous electrostatic coating when overcoating plastic parts.

[Conventional technology]

Conventionally, air spray painting methods have been generally employed for painting plastic parts and the like. This was adopted from the viewpoint of safety. However, in recent years, the cost of paint has increased due to the rise in the price of oil, and therefore, increasing the efficiency of coating methods has attracted attention, and as a result, the application of electrostatic coating technology has been studied and realized. The electrostatic coating method has many advantages, such as increasing coating efficiency and forming a high-quality coating film with a small amount of paint.

When carrying out the electrostatic coating method, especially when carrying out multiple coatings of plastic parts using this method, there is static electricity that accumulates on the surface of the object to be coated during electrostatic coating. This causes problems such as a decrease in coating efficiency, and in some cases, the accumulated electricity may generate sparks, creating a risk of ignition. Recently, during electrostatic painting, it has become clear that
Application of alcohol is beginning to be used industrially as a means to lower capacitance. When an alcohol as a static neutralizing agent is applied to the surface of the object to be coated, the specific resistance of the surface can usually be lowered to 4×10 hΩ or less.

[Problem that the invention seeks to solve]

However, the technique of using alcohol as a static eliminator during electrostatic painting does not only affect the quality of the paint finish, but also tends to cause sagging and flaking, and if non-volatile impurities are mixed in, they will leave a residue. Okasare causes Gutsu 9. Furthermore, since this technique atomizes the alcohol and sprays it onto the painted surface, there is a high risk of ignition due to electrostatic sparks.

In addition, the odor of alcohols produced during use degrades the environment, and those dissolved in water require wastewater treatment. Instead of spraying alcohol, static electricity may be removed by ion blowing, but this is not the most suitable technique.

[Means for solving problems]

According to the present invention, when plastic parts are repeatedly coated by electrostatic coating, a thin film of water containing carbon dioxide gas is formed on the surface of the object to be coated during successive coating processes. This problem can be solved by an electrostatic coating method, which is characterized by the provision of a process.

In the practice of the present invention, the formation of a thin film of water containing carbon dioxide is preferably carried out in an atmosphere of air maintained at a humidity higher than 75% and a temperature higher than that of the object to be coated. This can be done by spraying onto the object. Here, the blowing of air includes both fast and slow air flow speeds. Furthermore, air mixed with carbon dioxide gas can be sprayed onto the surface of the object to be coated using various methods. Some useful techniques include using a premix of carbon dioxide and air, dissolving carbon dioxide in air using pressurized operations,
This includes mixing carbon dioxide and air just before spraying. In any case, it is preferable that the amount of carbon dioxide gas mixed into the air is 0.1 to 30% by volume.

In a preferred embodiment of the present invention, the present invention provides a zone -a in which carbon dioxide gas is mixed with an air zone having high humidity (75% or more) and a temperature higher than that of the object to be coated while the object to be coated is being transported by a trolley or the like. A setting zone is provided to condense water on the surface of the object to be coated to form a thin film, which adsorbs and dissolves carbon dioxide gas, reducing electrical sensitivity and reducing the storage capacity of static electricity due to surface leakage. This enables continuous high-voltage electrostatic painting and ensures painting efficiency.

In this case, the surface resistance of condensed water containing carbon dioxide is 109Ω
[The following is better. Generally, the specific resistance is 1QI2Ω
If the surface is larger than 109Ω, a charging phenomenon will appear, and if it is smaller than 109Ω, no charging phenomenon will occur.

[For production]

Regarding static electricity charging, evaluation is different from general electrical resistance. That is, a material having a surface resistance of 109 Ωl is electrically a resistor, but electrostatically works as a conductor. Therefore, the solvent shown in the following table is 4X106Ω1
It has the following surface resistance and is used as a static remover.

*Measured at 54% relative humidity and 27"C temperature.

The above-mentioned types of solvents are highly dangerous as they become flammable gases and burn with a minimum ignition energy of 2 x 10-' Joules. For example, at 200μF and voltage 1500V,
2.3 x 10-' joules, and has sufficient ignition ability for explosive gas mixtures. In contrast, with the thin film of carbon dioxide-absorbed water of the present invention, there is no problem because the static electricity that would lead to an explosion is not charged. When carbon dioxide gas is absorbed into water, it becomes carbonate ions, which is thought to lower the electrical resistance of water.

〔Example〕

A preferred example of the method of the present invention will be explained with reference to the attached FIG. 1.

The objects to be coated 1a, lb and IC are each painted on a painting trolley'l.
a, 2b, and 2C, and are continuously conveyed within the coating room 5 by the conveyor 3.

First, at stage ■, electrostatic paint spray gun 4
The paint is sprayed onto the object 1a by a. After completion of this electrostatic coating process, the object to be coated is sent to stage (also called static elimination zone or setting zone).

At this stage, high temperature, high humidity air mixed with carbon dioxide gas is blown onto the object 1b from the air nozzle 8.

Thereafter, the object to be coated is transported to stage (2), where it is further coated with a higher voltage by the electrostatic spray gun 4C. Air whose temperature and humidity have been adjusted is sent to the painting room (or spraying room) 5 from an air supply room 6 via an air supply fan (not shown). The air in the painting chamber 5 is further exhausted to the outside through an exhaust chamber 7 via an exhaust fan (not shown).

〔Effect of the invention〕

According to the present invention, a thin carbon dioxide-containing film is scraped onto the surface of the coating film already formed on the object while it is being transported from one painting process to the next. form,
By doing so, it is possible to lower electrical resistance, facilitate static elimination, make effective use of the power of static electricity, and stably ensure high coating efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a preferred embodiment of the present invention, in which la, lb and IC are objects to be coated, 2a, 2
b and 2C are painting carts, 3 is a conveyor, 4a and 4
C is an electrostatic paint spray gun, 5 is a coating chamber, 6 is an air supply chamber, 7 is an exhaust chamber, and 8 is an air nozzle.

Claims (1)

[Scope of Claims] 1. When repeatedly coating plastic parts by electrostatic coating, a step is provided between successive coating steps to form a thin film of water containing carbon dioxide gas on the surface of the object to be coated. Electrostatic painting method. 2. A patent for forming a thin film of water containing carbon dioxide gas by blowing air containing carbon dioxide gas onto the object to be coated in an air atmosphere maintained at a humidity higher than 75% and a temperature higher than that of the object to be coated. The electrostatic coating method according to claim 1. 3. The electrostatic coating method according to claim 2, wherein the air containing carbon dioxide gas is a mixture of carbon dioxide gas and air in advance. 4. The electrostatic coating method according to claim 2, wherein the air containing carbon dioxide gas is obtained by dissolving gas by pressurizing operation. 5. The electrostatic coating method according to claim 2, wherein the air containing carbon dioxide gas is a mixture of carbon dioxide gas and air immediately before spraying. 6. The electrostatic coating method according to any one of claims 2 to 5, wherein the carbon dioxide-containing air contains 0.1 to 30% by volume of carbon dioxide.