June 3, 2020

What problems make PC injection molded parts becoming brittle and white mist

In the past, the problem of brittleness of injection molded PC materials was rarely seen. That was because the PC materials brands used at that time were relatively small. Usually, only two types of PC7025A and 1250Y made in Japan were used. Nowadays, there are more and more manufacturers producing PC materials, and there are naturally many brands and brands. The injection molding technology of PC materials of various brands is not the same, and the strictness of the process requirements are also different. Therefore, the use of the injection molding process of PC7025A and 1250Y to produce PC materials of other brands will inevitably cause problems. It can be seen that PC injection molded parts can sometimes not withstand the brittleness of impact.

After careful research, it was found that due to the different heat resistance and physical properties of various PC materials, the melt temperature, even the baking temperature and baking time will have a significant impact on the impact resistance of injection molded parts.

Usually when producing PC7025A and 1250Y materials, the melt temperature is generally adjustable to 290 ~ 310 ℃, and when producing certain brands of PC materials, and then use this temperature for injection molding, injection molded parts will become very brittle. Therefore, to treat this PC material, the injection temperature should not exceed 290 ℃, and some may be lower to solve the brittleness problem. Therefore, as long as the fluidity of the melt is sufficient to fill, it is better to produce at a lower temperature to prevent the injection molded parts from becoming brittle and causing unstable strength.

The second is the effect of baking temperature. PC7025A and 1250Y can usually be baked to 110 ~ 120 ℃, the time can exceed 4h. However, some grades of PC material can not exceed 100 ℃, otherwise injection molded parts will become very brittle, and will also appear white mist, affecting the appearance and transparency.

The least likely to cause people’s attention but the most prone to problems is the baking time. Generally, when injection molding PC7025A and 1250Y materials, the 50kg hopper is filled, as long as it is baked until no moisture is generated, it will not cause any problems for six or seven hours of slow production. However, some PC materials are baked in the hopper for more than 4 hours. The injection molded parts will not only produce obvious white mist, but also become very brittle. The longer the time, the more brittle, the more white mist, the plastic parts become brittle. At this time, if one bucket of material is enough to produce 6h, then only half of the bucket of material can be added. If there is moisture in the injection molded part, as long as a little more and a little more feeding, the problem will not happen again. Sometimes, there will be white mist from time to time. This should be because some raw materials are stuck in the hopper for long-term baking, and then from time to time a few pieces of material flow out into the barrel and are shot into the mold.

This is an important reason why PC injection molded parts become brittle and have white mist during production. Therefore, to produce PC injection parts of various brands, we must pay attention to the characteristics and requirements of the injection molding process of raw materials of various brands. Of course, due to the different performance of various brands, the strength and impact resistance will also be different, and some brands are indeed very poor in impact resistance.

Therefore, in the actual injection molding production, if the PC injection molded parts suddenly have problems of brittleness and insufficient transparency, priority can be given to the melt temperature, the baking temperature and the baking time, which can speed up the process of solving the problem.

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