The comprehensive performance of PC materials is excellent, and PC plastic products are also common in daily life. However, because PC materials are prone to internal stress during the injection molding process, especially transparent parts such as sunglasses, windshields, and eye masks, it can cause deformation, astigmatism, poor transparency, and even cracking of PC plastic products, limiting their application range. How can the internal stress problem of PC plastic products be solved? The editor will analyze the reasons together and provide several solutions. Let's take a look together!

1、 The Causes of Internal Stress in PC Plastic Products

1. The internal stress of PC products is mainly caused by orientation stress and temperature stress, and sometimes also affected by improper demolding;

2. The thickness of the product also affects the internal stress, and the orientation stress decreases with the increase of the product thickness;

3. Temperature stress plastic has a large temperature difference between the melt temperature and the mold temperature during injection molding, which causes the melt near the mold wall to cool quickly, resulting in uneven stress distribution within the product volume.

4. The shape and size of the product also have a significant impact on internal stress. The larger the ratio of surface area to volume of the product, the faster the surface cooling, and the greater the orientation stress and temperature stress;

5. From the above analysis, it can be seen that due to the structural characteristics of plastics and the limitations of injection molding process conditions, it is impossible to completely avoid internal stress. Only by minimizing internal stress or distributing it evenly within the product can internal stress be minimized as much as possible.

2、 Solution to internal stress generation in PC plastic products

1. The injection temperature has a significant impact on the internal stress of PC plastic products. Therefore, it is necessary to appropriately increase the barrel temperature to ensure good material plasticization, uniform composition, and reduce shrinkage rate and internal stress;

2. To increase the mold temperature, it is necessary to use a lower injection pressure as much as possible, and the holding time should not be too long;

3. The impact of injection rate on the internal stress of injection molded parts is much smaller than factors such as temperature and pressure. Variable speed injection can be used, that is, rapid mold filling. When the mold cavity is filled, low speed injection can be used. On the one hand, the filling process is fast, reducing weld marks, and on the other hand, low speed pressure maintaining can reduce molecular orientation. Reasonably design the gate position, and it is best to use slot or fan shaped gates for flat products; The ejection device should be designed to eject over a large area;

4. The demolding slope should be large;

5. After demolding, heat treatment can be used to eliminate internal stress. The temperature of heat treatment is about 120 ℃, and the time is about 2 hours;

6. Raise the temperature of the barrel and nozzle, increase the temperature of the mold, to reduce the impact of cold materials;

7. Slow down the injection rate and increase the injection pressure to avoid melt fracture or interference from gas inside the mold;

8. Adjust the injection time and pressure holding time to avoid overfilling; Reasonable mold gate design can reduce or avoid the formation of cold material spots in advance. The traditional and effective method is to set up a cold material trap at the end of the flow channel, so that the front material can sink into the trap without entering the mold cavity. In addition to setting up a cold material trap, some molds also need to consider the rationality of the gate form, size, and position; Strengthen mold exhaust;

9. Remove pollutants from the material, enhance the drying effect of the material, reduce or replace lubricants, and minimize the use of release agents.