How can injection molding improve the transparency of PP products?
1. The matrix resin itself
The brightness of the matrix resin itself has a great influence on the brightness of PP products. In order to improve the brightness of PP injection molding processing, a small amount of polyacrylate resin with excellent compatibility can be added.
2. Injection molding processing into nucleating agent
It can significantly improve the crystallization rate, improve the crystallization rate and crystallization insignificance ratio.
(1) Inorganic nucleating agent Inorganic nucleating agent is mainly ultrafine talc and SiO2, but also contains calcium carbonate, mica powder, inorganic pigments and fillers, etc., the cost is cheap, the origin is rich, but it has an inevitable impact on the gloss and brightness of the finished product.
(2) Organic nucleating agent Organic nucleating agent is a low relative molecular quality organic matter with nucleation benefits, represented by sorbitol and its derivatives, which has good compatibility with the matrix resin and can significantly improve the clarity and surface gloss of the finished product.
(3) The dosage of nucleating agent is concerned, after the dosage of nucleating agent exceeds 0.3%, the brightness improvement effect is not obvious, and even will fall; However, when the dosage is less than 0.2%, the number of nucleation is not enough, and the brightness growth is not enough. It can be seen that the amount of nucleating agent is very good, between 0.2-0.3%. Therefore, the appropriate nucleating agent content can better improve the clarity of PP.
3. Injection molding temperature
If the temperature is too high, the low molecular weight substances in the nucleating agent will be dissected and volatilized, which reduces the active ingredients in the nucleating agent, reduces the improvement effect of brightness, and the higher temperature will destroy some crystal nuclei of PP Huaxia, reduce the middle of heterogeneous nucleation, so that the modification effect is low; If the temperature is too low, the evacuation of the nucleating agent is not good, and the brightness effect is poor. Therefore, selecting a suitable molding temperature is particularly difficult to improve clarity.
4. Flexibilizer
Because the toughening agent and PP are not miscible, the refractive index is also different, and it will be refracted at the interface with each other, thus affecting the light transmittance of the article. With the increase of toughening content, the area of the interface between each other is also more violent, and the light transmittance of the finished product is worse.
5. Process parameters
Process parameters are more ambitious processing temperature, cooling temperature, injection pressure and other process parameters also greatly sponsor the clarity of PP.
Processing temperature: Under the premise of satisfying processing, the lower the processing temperature, the smaller the crystallization size, and the better the clarity; Cooling temperature: The lower the cooling temperature, the lower the crystallinity and better the clarity.
Injection pressure, injection time, and holding time affect the orientation of the molecule. The orientation will affect the crystallization of the molecule, so without affecting the function and appearance of the finished product, shortening the injection and holding time and low drop pressure can inevitably improve its clarity.
6. Injection molding processing technology
Compared with the finished products obtained by the injection, drawing and blowing process, it is found that the injection and blowing process is very beneficial to increase the clarity.
7. Mold
The higher the finish of the mold, the better the clarity of the finished product.
