Introduction: In modern industry and daily-use products, more and more plastics are used instead of glass, especially in packaging, and the development is particularly rapid. However, it is required to have good transparency to ensure that the surface quality of these plastics used to replace glass is good, so as to meet the requirements of use. The following share the influencing factors that affect the transparency of injection molded products, and the content is for the reference of purchasing friends:
Transparency of injection molded products
Regarding transparent injection molding products, PC is the ideal choice, but due to its high raw material price and difficult injection molding process, PMMA is still the main choice (for products with general requirements), while PET can only be obtained due to stretching Good mechanical properties, so it is mostly used in packaging containers.
The reasons for the poor transparency of injection molded products can be divided into two categories. One type is caused by the tiny convexities on the surface of the molded part (because the surface finish of the product (the entire area in contact with the mold) is determined by the finish of the mold surface. If the finish of the mold is not good, the small concave and convex surface will Make the finish of the product worse, so in the product of transparent material, the light transmittance will decrease, and the transparency will decrease); the other type is caused by the decrease of light transmittance.
Caused by tiny bumps on the surface
Due to this reason, the transparency is not good, and it can be eliminated as long as the surface of the part is smooth. Transparency can be improved if the mold cavity is polished, the temperature of the melt or mold is increased, and the mold release agent is used correctly. In order to obtain a mold with high smoothness, the surface of the mold product is plated with hard chromium (or a hard mold material such as diamond abrasive powder is used for grinding), but it is difficult to repair the mold after it is damaged.
Changes in the plastic itself
If the plastic or additives decompose in the barrel, it will change the original transparency of the plastic. Reduce the temperature of the melt, shorten the residence time of the melt in the barrel, and eliminate the defect of poor transparency without thermal decomposition. Since materials with poor fluidity come into contact with the surface of the mold product, they solidify immediately, and cannot adhere well to the surface of the mold product. In addition, the material with insufficient pre-drying and the volatile components in the material evaporate and condense in contact with the mold and exist between the product and the mold, making the product poorly smooth.
Different crystallinity of plastic caused
High-density polyethylene, polypropylene, nylon, etc. are all crystalline copolymers, and the crystallinity will change due to different cooling rates. To improve the transparency, it is enough to limit the generation of spherulites, so the mold temperature should be as low as possible. However, the transparency of thick-walled parts decreases due to the slow cooling rate. It is difficult to improve the transparency without adopting a uniform wall thickness product design.
Because the mold temperature is high, the smoothness becomes better, so a large amount of warm water is used in the mold to keep the mold temperature at a certain value, so that the heat of the product can be transferred immediately, so that the cycle can be shortened and the product with low residual stress can be obtained.
Degradation of plastics
Description: Injection molded parts or parts of injection molded parts have changed color. The color usually darkens where it degrades.
Injection molding machine:
A. Excessive heating of the plastic in the injection cylinder reduces the temperature of the melt
B. The temperature controller is not working properly. Check whether the temperature controller is in the correct area to control the injection cylinder; re-calibrate the temperature controller and check whether there is sticky contact, etc.
C. An incorrect type of thermocouple is used. Check whether the type of thermocouple used is consistent with the one provided on the temperature controller, such as FECOM. Check if all thermocouples are operating correctly
D. The retention time of the plastic in the injection cylinder is too long. Check the injection weight. If it is less than 25% of the injection pressure of the injection molding machine, transfer the mold to a smaller injection molding machine; if not, transfer to a smaller injection molding machine. The use will reduce the temperature of the injection cylinder to the lowest value, which will produce injection molded parts that meet the quality requirements.
E. The plastic stays in the injection cylinder when production is stopped. When production is stopped, the injection cylinder should be cleaned and the screw is in the most forward position.
F. The plastic is “stranded F” somewhere in the injection cylinder and degrades. Check the injection cylinder and remove any residual defects on the clamping surface.
G. The injection volume of the mold is too small, move the mold to an injection molding machine with a smaller capacity
A. The moisture content in the plastic is too high, use the correct drying sequence
B. If the quality of the recycled material is different or contains impurities, separate and strictly check the impurities in the recycled material