JPS63194771A - Method for coating resin - Google Patents

Abstract

PURPOSE:To form a uniform coating film with high coating efficiency, by heating a powdery resin, electrifying the obtained resin droplets, and electrostatically coating the liq. droplets on the surface of a material to be coated. CONSTITUTION:The powdery resin 1 in a hopper 2 is supplied to a resin heater 8 from a powder feeder 3 by a supply gas 14 through a resin transport line 7. The supplied resin 1 is heated to a temp. higher than the m.p., and the liq. resin droplets 12 are obtained. The resin 12 is supplied to an injection nozzle 6 from a resin transport line 7, positively or negatively charged by a charging electrode 5, and electrostatically coated on the grounded 10 material 9 to form a coating film 11. As a result, a uniform coating film can be easily formed, and the coating efficiency of the raw material resin is improved. In addition, even a large-sized and intricate material to be coated incapable of being coated by the conventional method can be coated.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a resin coating method, and more specifically, to forming anticorrosive coatings on flues, chimneys, electrostatic precipitators, chemical plants, etc., ships, marine structures, This invention relates to a resin coating method that can be applied to forming corrosion-resistant, wear-resistant, and low-adhesion coatings on piping, machine tool sliding parts, non-lubricated bearings, electronic parts, irons, frying pans, etc.

[Conventional technology]

Resins that melt when heated include olefin resins such as polyethylene and polypropylene, thermoplastic resins such as polyamide resins, polyimides, amide resins, and fluorine resins, and epoxy resins that have been crushed in a semi-cured state. It is being

Conventionally, the following methods have been applied as coating methods using these resins.

(1) Fluidized immersion method This is a method in which a heated object is immersed in a tank in which resin powder flows (fluidized tank), and when the powder adheres to the heated object,
The powder absorbs the heat of the object and melts, forming a resin coating.

This method uses polyethylene, polyamide, epoxy resin,
This method is applied to resins that melt at relatively low temperatures, such as vinylidene fluoride resin, but depending on the size of the fluidized bath or the size of the equipment for dipping the object, it may be difficult to coat the object easily. Since there is a size limit, there are no examples of it being applied to large products.

(2) Electrostatic dynamic dipping method Resin powder is charged with static electricity while flowing in a fluidized bath to form a layer of resin powder on the grounded surface of the object to be coated, and then fired in an electric furnace. This is a method of forming a film.

Like the fluidized dipping method, this method is not only difficult to apply to large-sized products, but also has a relatively low melting temperature when fired, such as polyethylene, polyamide, and epoxy resin.
With resins that have a low latent heat of fusion, it is possible to form a film in a short period of time with a small amount of heat, but if the melting temperature is high and the latent heat of fusion is large, such as a fluororesin, a very large amount of heat is required. However, due to the high melt viscosity of the melt, it is difficult to form a continuous pinhole-free coating in a furnace at a temperature close to the melting temperature. Also, the melt viscosity is 1
When heated at a high temperature of 0.4 to 105 poise, the resin at the very surface layer first melts due to the heat of the heating furnace and forms a film, so it can be heated at room temperature (or the object to be coated may be preheated). The gas (air) present between the adhered powder particles is difficult to dissipate, and the coating film must contain air bubbles, making it impossible to obtain a good coating film without pinholes.

Therefore, in order to form a good film, even at the expense of reducing the film formation speed due to a decrease in melt viscosity, the material to which fluororesin powder is attached is fired for a long time at a temperature slightly higher than the melting temperature. This is the current situation. For example, fluorine-based resins are baked over several hours.

(3) Electrostatic spraying method This method is a method of forming a coating film in almost the same steps as the electrostatic dynamic dipping method, and is also called electrostatic powder coating method.

Resin powder is dispersed and pressure-fed with air, and when the powder is sprayed onto the object to be coated, the powder is charged with static electricity and adheres to the grounded surface of the object. This is a method of burning powder onto a coated object. Compared to the electrostatic dynamic immersion method, this method can apply powder even to large objects by moving the electrostatic coating gun, but since baking is performed in a furnace, the equipment required for baking is The cost and time are no different from the electrostatic immersion method.

(4) Post-baking method for spraying dispersion solution When spraying resin powder suspended in an organic solvent or water onto the object to be coated using an air spray or airless spray gun, after removing the solvent (dehydration), This is a method of firing. However, in order to prevent the powder from falling off after solvent removal (dehydration), the industrially used diversion solution contains a small amount of resin used in suitable paints, such as epoxy resin, alkyd resin, and acrylic resin. There are many things that have been done. therefore,
When baking fluororesin dispersion, first
After removing the solvent, the mixed resin other than the fluororesin is slowly thermally decomposed and released, and then the fluororesin is melted to form a film made only of the fluororesin.
Staged firing is used.

This method includes the steps described above until the resin powder is attached to the object to be coated.
Although it is easier to perform than other methods, it takes a long time to fire and requires two stages of firing, making it very difficult to control the firing temperature and the timing of moving to the next firing process. If the resin is not completely decomposed, there are drawbacks such as not only air bubbles remaining in the coating film but also very poor adhesion.

(5) Thermal spraying method Similar to thermal spraying of metals and ceramics, this method is similar to thermal spraying of metals and ceramics. In this method, the melted and softened material is blown into the surface of the object to be coated by collision, thereby instantaneously forming a coating film that undergoes the melting process.

In this method, since the resin is sprayed at a high flow rate, the resin attached to the object to be coated is heated too much, the melt viscosity decreases, wind pressure causes ripples, and it is not only difficult to obtain a uniform thick film, but also thermal decomposition occurs. Low-temperature resins have drawbacks such as thermal decomposition of the coating film if the moving speed of the thermal spray gun becomes slow. In addition, it is difficult to form a film on only the sprayed surface in a state close to a right angle, making it difficult to apply to objects with complex shapes.

[Problem that the invention seeks to solve]

As mentioned above, using resin that melts when heated,
The method of forming the coating film has corrosion resistance, wear resistance,
It takes a lot of heat and time to form a fired film that achieves good performance such as low friction resistance and low adhesion, and it also requires a lot of equipment, making it difficult to make large products economically. The situation is such that it cannot be applied.

[Purpose of the invention]

The present invention aims to eliminate the above-mentioned drawbacks and provide a coating method that can instantaneously and inexpensively form a coating film of a resin that melts when heated on all products ranging from small mass-produced products to large individual products. It is.

[Means for solving problems]

The present invention is a method of forming a thermally fused uniform coating film using a resin that melts when heated, which includes: (1) heating and melting powdered resin to form droplet-shaped resin; (2) charging the droplet-shaped resin; (2) Electrostatically depositing a charged resin droplet on the surface of a material to be coated to form a coating film.

[Effect]

The method of the present invention is not a method in which solid powder resin is attached to the material to be coated and then fired, but the powder resin is melted before reaching the material to be coated, and the droplets are electrostatically charged. This is a method of coating by spraying electrostatically onto the material to be coated.The resin droplets condense together on the surface to be coated, forming a liquid film of resin, and then simply cooling the resin to below its melting temperature. A coating film is formed through the melting process.

Hereinafter, one embodiment of the coating method according to the present invention will be explained as follows.
This will be explained using figures.

The powdered resin 1 (e.g. evaporated tetrafluoroethylene perfluoroalkyl ether copolymer) held in the hopper 2 is transferred from the resin transport line 7 by a supply gas 14 (particularly air, nitrogen, etc.) from the powder supply device 5. The resin is supplied to a resin heating device 8. The average particle diameter of the powdered resin 1 supplied at this time is about 10 to 100 microns, preferably about 50 microns.

The powdered resin 1 supplied to the resin heating device 8 is heated to a temperature higher than its melting point (550° C. to 500° C.), and becomes a droplet-like resin 12. The droplet-shaped resin 12 is supplied from the resin transport line 7 to the injection nozzle 6, and the charging electrode 5 (4 is a charging device,
The coating film 11 is formed by being electrostatically attached to the material 9 to be coated which is grounded 10 while being charged with a positive or negative electrostatic charge by a conductive wire 15. At this time, in order to facilitate electrostatic adhesion, the voltage of the charging electrode 5 is set at 80°C.
kV or less is desirable, and the flow rate of the droplet-shaped resin 12 is 10
%/FjeO or less, especially about 2rrL/8θC, is confirmed by experimental results.

By depositing the droplet-shaped resin over the entire surface of the material to be coated in the above steps, a resin film can be created on the surface of the material to be coated.

〔Effect of the invention〕

According to the method of the present invention, the melted resin droplets can be sprayed with static electricity without increasing the flow rate of the pressurized gas, unlike conventional thermal spraying methods, making it easy to obtain a uniform coating film. Therefore, the coating efficiency of the raw resin can be greatly improved. Furthermore, the present invention enables coating of large and complex objects, which was not possible with conventional methods.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an embodiment of the coating method according to the invention.

Claims (1)

[Claims] A method for coating a surface of a material to be coated with a molten resin includes (1) heating and melting a powdered resin to form resin droplets, (2) charging the resin droplets, (3)
) A resin coating method comprising the step of electrostatically depositing charged resin droplets on the surface of a material to be coated to form a coating film.