Mr. Liu of Anhui is a manufacturer of PC products. Recently, his products failed to meet purchaser’s requirements, for the reason that his products appeared to be yellow. After careful investigation, Taili Plastic Machinery found the main reason by adjusting the production temperature and conducting the non-mold injection experiment, which helped to solve a big problem!
Injection molded PC (polycarbonate) products have good temperature resistance and impact resistance, which are widely used in the manufacture of household appliances and lighting appliances. However, due to its poor fluidity and easy hydrolysis, it is a kind of raw material which is extremely difficult to process.
Recently, Mr. Liu of Anhui complains to Taili Plastic Machinery that their products have been rejected by the purchaser. Due to the change of injection molding technicians after the Spring Festival, the manufacturing and processing technology of his products has been adjusted, resulting in yellowing and black spots of the products. He asked for us to take an inspection and provide a solution.
Mr. Liu's products are transparent PC products, which must be transparent and have no marks on the surface. There are no obvious yellow lines or black spots on the last batch of goods delivered by Mr. Liu. However, when looking against the light, there’s yellow lines on the products, which is the exact reason why his products are rejected by the purchaser. For PC materials, yellowing phenomena are very easy to appear. But for pure PC, due to its good heat resistance and high temperature resistance, the temperature is generally set at 240-300 degrees. Even if it stays for a long time, it is not easy to decompose. So why is yellowing a very common phenomenon in normal production (especially for transparent products)?

The reason is that due to the cost control, PC modified materials or recycled materials are mostly used in the production process. These fillers are mottled in composition and easy to decompose and discolor at high temperature.
For this problem, we can solve it from the following two aspects:
1. Adjust Production Temperature
It’s necessary to consider the melting temperature, especially the temperature of the first two sections of the barrel. The yellowing problem can be solved by properly reducing the temperature for different modified materials.
2. Non-Mold Injection Experiment
When the machine starts to work, if the material in the raw material barrel is PC material, conduct the non-mold Injection for 2-3 times to observe whether there is yellowing phenomenon. If yes, it is generally necessary to check whether the nozzle, three small pieces (screw head, thrust ring, check ring), barrel and screw have corrosion.
After a series of careful inspection, we found that that the screw cylinder hadn’t been cleaned before the Spring Festival, which caused the serious corrosion in the screw. This is exactly the reason that made the product yellowing. After we change the screw, the products are refined.
Taili Plastic Machinery always keeps in mind that what a good injection molding machine factory should do is to help improving the capacity and boosting the profits, rather than offer the similar products the customers need. This is also what Taili Plastic Machinery keeps doing.
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