Painting process of plastic door of the hottest re

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Painting process of plastic door body of refrigerator

painting process of plastic door body of refrigerator

December 15, 2018

1 preface although plastic parts are colored before molding, their decorative effect is affected by the color of the resin itself, which has certain limitations, and they often need to be painted. Plastic spraying refers to a process of coating the plastic surface with appropriate paint and compressed air through manual or automatic spraying machine. Spraying plastic parts can increase the variety of products, cover up the defects such as silver wire, small collapse pit, inconspicuous seam, color spot, stain and mottle on the surface of plastic parts, improve its surface hardness, prevent the aging of plastic parts and prolong the service life of Chinese paint. Bcd-160w/hc refrigerator is a new product launched by Chengdu Kelong refrigerator Co., Ltd. its door panel and drawer door panel have complex structure due to the unique shape of double arc surface. If the traditional metal door panel is adopted, the processing technology is difficult to meet the requirements, and the plastic injection molding technology can solve this problem well. The refrigerator door body is made of ABS material and processed by painting. It has high requirements in terms of appearance, decoration and performance. The qualification rate of the new product in the initial stage of investment is only 85%. After continuous exploration and research, the painting processing technology is improved and the air cleanliness of the painting environment is tested to meet the requirements of the painting environment. At present, the qualification rate reaches more than 95%

2 according to the time of the stopwatch, the door body painting appearance and coating technical requirements of the refrigerator (see Table 1). It can be seen from table 1 that the refrigerator has high requirements in appearance decoration and chemical properties

painting appearance and coating technology of refrigerator door

3 the process flow focuses on the defects of the door → alcohol degreasing → electrostatic dust removal → spraying acrylic one-component primer (or two-component polyurethane paint) → leveling (5 ~ 10) min → drying (60 ℃) × 30min) → light grinding of spraying defects → electrostatic dust removal → spraying two-component pearlescent polyurethane varnish → curing (70 ~ 75) ℃ × 60min → standing for (24 ~ 48) H → inspection → packaging of qualified parts

(1) grinding treatment: grind with 800 # ~ 1600 # sandpaper to eliminate the defects on the surface of the workpiece

(2) degreasing: residual release agents (such as wax, silicone, stearic acid, etc.) on the surface of plastic products are easy to cause shrinkage of paint film and poor adhesion, so degreasing must be carried out before painting. Plastic products sensitive to solvents, such as ABS, hips, etc., use low-grade alcohols (such as methanol, ethanol, isopropanol, etc.), or aliphatic solvents with fast volatilization speed (such as ethane, 180# gasoline, etc.); Plastic products that are very sensitive to solvents shall be wiped with toluene, etc

(3) electrostatic dust removal: after injection molding, the surface of plastic products has electrostatic effect, which is positively charged, and the surface is easy to adsorb dust. Use a nozzle with negative ions to aim at the plastic parts for spraying and sweeping, then the positive charge will be neutralized, and the electrostatic adsorbed dust will lose its adsorption force, and will be blown into the dust collection device by compressed air

(4) spray acrylic one-component primer (or two-component polyurethane paint): acrylic paint is a paint with various acrylic resins as the main film-forming material, and its advantages are: the paint film dries quickly; Good adhesion; The paint film has good gloss, light and color retention, excellent outdoor durability and no yellowing; It has excellent chemical resistance, water resistance, high temperature resistance, UV resistance, etc. Attention during spraying: due to the low solid content of acrylic resin, if the viscosity is too large, it is easy to produce wiredrawing and orange peel during spraying

(5) polyurethane two-component paint is selected as the glazing paint of the door body. It uses aliphatic isocyanate 3. The measured hardness value is different from the indicated value of the standard hardness block as the curing agent, which has good chemical resistance and mechanical properties, as well as excellent light and color retention. The polymer contains a considerable amount of urethane bond -nh-coo-, with high urethane bond content and better chemical resistance. Polyurethane is mainly formed by the reaction of polyisocyanate and polyol, which is a gradual polymerization or addition polymerization reaction

in addition to the urethane bond, the resin also contains ester bond, ether bond, urea bond, etc., so it is easy to form hydrogen bond between molecules and has good wear resistance and adhesion. Hydroxyl containing resins can be polyester, polyether, epoxy resin, hydroxyl containing acrylic resin, etc., and different resins are selected according to different purposes. Generally, acrylic acid and polyester systems are used in industrial paints with high durability requirements, because acrylic resin and polyester resin have excellent outdoor durability and are not easy to yellowing. Since the service life of refrigerators is more than 10a, hydroxyl acrylic resin is generally selected to ensure the color of paint film. In the two-component paint, the film hardness increases with the increase of curing dose, which is the result of more cross-linking points; With the passage of time, the hardness also increases, because the reaction between -nco group and -oh group is a slow process, and -nco group can also react with moisture in the air to increase the hardness

(6) curing conditions: because what kind of material AB is used for the refrigerator door, it can be used in the horizontal tensile testing machine s material, which is easy to deform under high temperature. It has been proved by long-term practice that at (70 ~ 75) ℃ × Under the condition of 60min curing, the hardness increases significantly after placing for 48h, and the door body will not be deformed

4 effect of the amount of curing agent on the hardness of paint film by gradually increasing the amount of curing agent, the hardness of paint film at different times is tested. The experimental results are shown in Table 2

the influence of the change of the ratio of paint to curing agent and time on the hardness

from the above results, it can be seen that with the increase of curing dose, the hardness of paint film increases, which is due to the increase of cross-linking points. With the increase of time, the hardness also increases, indicating that the reaction between -nco and -oh is a slow process, which is related to the reaction activity of the resin and the curing agent itself. It can also be seen from table 2 that the hardness of 1 # paint does not increase much after 48h, indicating that the curing is complete, while the fixture on the 2 # paint and 3 # paint testing machine should be able to immediately align into a line, and the hardness is also increasing, because -nco group not only reacts with -oh in the resin, but also absorbs moisture in the air and reacts with it, the cross-linking point continues to increase, and the hardness continues to increase, but the curing time increases correspondingly with the increase of curing dose

5 common defects and solutions of refrigerator door spray products after long-term exploration and practice, the common defects and solutions of door spray products are summarized. See Table 3 for details

common defects and solutions of door spraying products

after a period of exploration, the company's refrigerator door spraying has been greatly improved in appearance and performance, with a qualification rate of more than 95%, meeting the technical requirements

6 conclusion (1) polyurethane paint has excellent chemical resistance and good mechanical properties, which can meet the technical requirements of refrigerator door spraying

(2) in the two-component paint, the film hardness increases with the increase of curing dose, and this reaction is a slow process

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