Finishing method of polyolefin foamed plastics
DATE：2022/4/27 8:45:49 / READ： / SOURCE：This station
Finishing method of polyolefin foamed plastics
The finishing methods include brush coating, roller coating, spraying, dip coating, etc. The characteristics and applicability of these finishing methods are shown in table 11-3.1. Electrostatic spraying
Electrostatic spraying is to use a rotating cup with sharp edge, high-speed rotation and high-voltage negative charge to atomize the paint reaching the edge of the rotating cup into negatively charged paint particles by using mechanical centrifugal force or compressed air. Under the action of electric field force, the paint particles quickly fly to the positively charged parts to form a paint film. Film coating production line www.handern.com com
Electrostatic spraying equipment mainly includes high voltage generator, electrostatic spray gun, paint conveying barrel, spraying room and drying system.
(1) High voltage generator high voltage generator requires high power. When there is load, the pressure drop cannot be too large. If 10kV ball gap discharge method is used for test, the discharge distance shall be at least 1cm. In practical use, the voltage of 80 ~ 100kV is usually used, because the high voltage also has high requirements for the insulation performance of the equipment. In addition, after the voltage is determined, the distance between the spray gun and the painted surface of the part shall be selected based on this. If the voltage is 80kV, the distance between two poles is 25 ~ 30cm; If the voltage is 100kV, the distance is 30 ~ 40cm. During specific setting, appropriate adjustment shall be made according to the surface shape of the workpiece and the position of the spray gun.
(2) Electrostatic spray gun electrostatic spray gun has two types: rotary cup type and cyclone type. They are metal cups with sharp edges. Their respective characteristics are shown in the table. Film coating production line www.handern.com com
(3) There are two types of transportation: gas type and pump wave type. The former is applicable to paints without weight limited molding materials, while the latter is applicable to all kinds of paints.
(4) the static spraying room of the spraying room is across the middle of the conveyor belt, and there shall be good air facilities to avoid fire.
(5) The dry system is composed of heat or far-infrared radiation elements, and the heat source is matched with a conveyor belt. The heating source and the spraying room shall have a stroke of at least 5min to allow sufficient time for the coating of the workpiece to level and obtain slow initial drying, and then heat and dry. Thus, a dense, bright and beautiful paint film can be obtained. This system shall also have exhaust facilities of appropriate size, and there shall also be an air curtain at the outlet of the drying channel to prevent the outward emission of gas and heat. Electrostatic spraying coating shall be easy to be charged, with good atomization in electrostatic field, low viscosity, high solid content and finer particle size than ordinary coating. Film coating production line www.handern.com com
If two spray guns are used for spraying at the same time, pay attention to the distance control between the spray guns. According to experience, if two spray guns are on the same horizontal line, the spacing should be at least 1m; If the two spray guns are not on the same horizontal line, the distance between the guns should be larger.
The rotating speed of the spray gun is related to its form and the properties of the coating. Generally speaking, the coating particle size is fine, the viscosity is small, and it is easy to disperse. If the cyclone spray gun is used, the rotating speed is only 800-1000t / min; If the rotating speed of the spray gun is up to 3000r / min, the fine particles can be evenly atomized, but if the rotating speed of the spray gun is up to 3000r / min, the paint film can be smooth. The diameter of the spray gun is directly related to the atomization area. The diameter of the spray gun is large and the diameter of the paint mist is large, but the central hole also increases. The adhesion performance of electrostatic spraying coating is related to the shape of parts. In the edge or tip part of the workpiece, if the power is large, the adsorption capacity of the coating is strong and the adsorption capacity is also large. Therefore, the method of rotating parts can be used to solve this problem. The rotation speed is determined according to the shape and size of the workpiece, generally 3 ~ 4 / min.
2. Manual spraying
The manual spraying equipment is mainly composed of air compressor, oil-water separator, spray gun, etc. The working environment of manual spraying should be 20 ℃ and 50% ~ 60% relative humidity. If the humidity is too low, an appropriate amount of cosolvent or diluent can be added to the coating to slow down the excessive etching of the solvent on the parts. If the humidity is too high, it is not suitable for operation.
The pressure of air for manual spraying is 0.196 ~ 0.294mpa. Film coating production line www.handern.com com
3. Automatic spraying
Automatic spraying is based on manual spraying and equipped with mechanical transmission and automatic control device. When the parts to be sprayed are automatically sent to the spraying room, the spray gun placed above will start spraying under the command of the sending device. When the parts leave the spraying room, the spraying can be stopped automatically. There is an exhaust device above the spraying room, which can be closed. Automatic spraying reduces labor intensity and improves working conditions. Film coating production line www.handern.com com
4. Airless spraying
Airless spraying uses high-pressure liquid (paint) for spraying, and its principle is similar to that of spray. The main equipment includes high-pressure pump, pressure storage filter, long handle spray gun, paint heater and other accessories. The high-pressure pump consists of three parts: the upper part is a low-pressure air cylinder, the middle part is a compressed air distribution chamber, and the lower part is a high-pressure paint cylinder. The pump pressure conversion ratio can be 1:40, that is, the compressed air pressure is
At 0.49mpa, the coating pressure increases to 19.6Mpa, and the pressure storage filter plays two roles: stabilizing pressure and filtering.
The long handle spray gun is connected with a retractable plastic hose and is equipped with a concave coating in Fig. 11-3 to adjust the spray nozzle rotating in various angles, which expands the distance between the spray gun and the parts in the schematic diagram of the decoration device. High pressure resistant plastic hose is a rubber roller with steel wire mesh 1 for the outside; 2. Finished products; Reinforced PVC pipe. 3 - semi finished products; 4-anilox roller; The temperature of the paint heater can be adjusted automatically to adapt to the low 5-1 scraper; 6. Operation under the environment of paint bath temperature. The device has the advantages of few components, small volume, light weight, convenient carrying and flexible operation.
5. Roller coating
There are two types of roller coating: concave type and reverse type, which are suitable for the surface coating of continuous flat sheet materials (such as foam artificial leather).
The concave anilox roller can vary between 60 ~ 120 mesh, so as to control the amount of finishing. The linear speed of the two rollers should be consistent.
Author：admin