Because the fluidity of glass fiber is much worse than that of plastic, and the flow of plastic in the mold is from the middle of the interlayer to the front, and the two sides are turned outward, so the best fluidity must run to the front. , and those with poor fluidity will stay on the surface of the mold.
At the same time, glass fiber has the effect of promoting crystallization, while PP and PA are both crystalline materials. The faster the crystallization is cooled, the harder the glass fiber is to be bound and covered by the resin, so it is easy to expose the glass fiber.
At present, the usual solutions mainly include the following:
1. Materials:
1. Considering the compatibility of glass fiber and matrix, surface treatment of glass fiber, such as adding some coupling agents and grafts;
2. Add lubricant. The lubricant mainly considers the dispersion of glass fiber and some lubricants themselves have external lubrication effect, and it is easy to run to the surface of the product during molding to form a smooth layer.
3. There are other fillers that also have improved effects, which will not be listed here.
2. The injection molding process:
1. Increase material temperature and mold temperature;
2. High pressure and high speed;
3. Adopt rapid hot and cold forming technology (RHCM).
Because if the molten plastic solidifies too quickly when it touches the mold wall, the glass fibers cannot be fully coated, resulting in surface floatation. For RHCM molding, due to the high mold temperature, the glass fibers at the interface of the cavity can be completely covered by the plastic melt, and because this part is in a molten state, the orientation of the glass fibers tends to be consistent, ensuring the uniformity of shrinkage, thereby ensuring the molding quality.
3. Mould
The appearance surface of the product is deliberately made into a matte surface or an etched surface to reduce the visual response of glass fiber exposure.
