PP is a typical crystalline polymer. To improve the tra […]
PP is a typical crystalline polymer. To improve the transparency of plastic bottles, you can consider the following 7 aspects:
1. The matrix resin itself
The transparency of the matrix resin itself has a great influence on the transparency of PP products. In order to improve the transparency of PP, a small amount of polyacrylate resin with good compatibility with good transparency can be added.
2. Nucleating agent
Nucleating agent: can significantly increase the crystallization rate, increase the crystallization rate and crystal fineness ratio.
(1) Inorganic nucleating agent Inorganic nucleating agent is mainly composed of ultrafine talc powder and SiO2, and also includes calcium carbonate, mica powder, inorganic pigments and fillers, etc. The price is low, the source is rich, but it has certain gloss and transparency for the product influences.
(2) Organic nucleating agent Organic nucleating agent is a low-molecular-weight organic substance with nucleation effect, represented by sorbitol and its derivatives. It has good compatibility with matrix resin and can significantly improve the transparency of the product. And surface gloss.
(3) Dosage of nucleating agent As far as sorbitol is concerned, when the amount of nucleating agent exceeds 0.3%, the transparency improvement effect is not obvious, and it may even decrease; but when the amount is less than 0.2%, the number of nucleating agents is insufficient and the transparency increases not enough. It can be seen that the amount of nucleating agent is preferably between 0.2-0.3%. Therefore, proper nucleating agent content can better improve the transparency of PP.
3. Extrusion temperature
If the temperature is too high, the low molecular weight substances in the nucleating agent will decompose and volatilize, reducing the effective ingredients in the nucleating agent, reducing the improvement effect of transparency, and higher temperature will destroy the original crystal nucleus in PP, reducing The heterogeneous nucleation center reduces the modification effect; while the temperature is too low, the dispersibility of the nucleating agent is not good, and the transparency effect is poor. Therefore, choosing an appropriate extrusion temperature is particularly important for improving transparency.
Tougheners Because tougheners and PP are not miscible, and the refractive index is also different, they will refract at the mutual interface, thereby affecting the light transmission of the article. As the toughening content increases, the area of the interface is stronger, and the light transmittance of the product is worse.
5. Process parameters
Process parameters such as ideal processing temperature, cooling temperature, injection pressure and other process parameters also greatly help the transparency of PP.
Processing temperature: Under the processing conditions, the lower the processing temperature, the smaller the crystal size and the better the transparency;
Cooling temperature: The lower the cooling temperature, the lower the crystallinity and the better the transparency.
Injection pressure, injection time and holding time will affect the molecular orientation. Orientation can affect the crystallization of molecules, so shortening the injection and holding time and reducing the pressure without affecting the performance and appearance of the product can improve its transparency to a certain extent.
6. Molding process
The molding process compares the products obtained by the injection, drawing and blowing processes, and finds that the injection and blowing processes are the most beneficial for increasing transparency.
The higher the mold finish, the better the transparency of the product.