Defects in injection molded products - colour differences
August 01, 2022
The color difference is also called discoloration, and the gloss is poor.
The mechanism of chromatic aberration:
Chromatic aberration is a common defect in injection molding . There are many factors affecting chromatic aberration, including raw material resin, color masterbatch, color masterbatch and raw material mixing, injection molding process, and injection molding machine.
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material
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Material is contaminated;
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High moisture and volatile content;
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Decomposition of colorants and additives;
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The color or color master is not enough or unevenly dispersed;
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Raw materials and color masterbatch have different color in different batches;
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Mold
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Poor mold exhaust, material burning;
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The mold gate is too small;
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The size of the main channel and the runner are too small;
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There is a dead angle in the mold structure;
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Molding
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The screw speed is too high and the pre-plastic back pressure is too large;
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The barrel and nozzle temperature are not uniform;
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The injection pressure is too high, the time is too long, and the injection speed is too fast to discolor the product;
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If the mold temperature is too low, the solidified layer is accumulated or pushed and pulled to produce fog marks, resulting in chromatic aberration;
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Injection molding machine
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Dust pollution on the equipment, causing the material to change color;
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Equipment heating system failure;
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There are obstacles in the barrel to promote material degradation;
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The foreign matter in the barrel or the screw groove causes the material to change after grinding;
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solution
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material
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Control raw materials, strengthen the inspection of different batches of raw materials and color masterbatch, and eliminate the influence of raw materials and color masterbatch;
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Volatile lubricants and mold release agents are used in an appropriate amount;
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Mold
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Through the maintenance of the corresponding part of the mold, to solve the problem of chromatic aberration caused by the mold casting system, the exhaust groove, etc.;
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Molding
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Master the influence of the temperature of the cylinder and the amount of the color masterbatch on the color change of the product, and determine the change law through the color test process;
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Avoid the chromatic aberration caused by local overheating and decomposition of the material, and strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part close to the nozzle;
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The injection speed is too high, reducing the injection speed: multi-stage injection: fast-slow;
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Reduce injection pressure and screw pre-plastic back pressure to prevent shear overheating;
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Injection molding machine
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Select an injection molding machine with the right specifications to solve the problem of material dead angle in the injection molding machine;
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During the production, the heating part should be inspected frequently, and the damaged or out-of-control components of the heating part should be replaced and repaired in time to reduce the probability of chromatic aberration;
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Ensure the cleaning of injection molding workshops, injection machines and molds;
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Adjust the appropriate screw plasticizing speed.
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