Help improve PP product transparency
the crystallization of PP are typical type of polymer, to improve its transparency, can from the following seven aspects to consider:
, matrix resin resin itself
The transparency of matrix resin itself, has a great impact on the transparency of PP products. In order to improve the transparency of PP, a small amount of polyacrylate resin with good compatibility and excellent transparency can be added.
2, nucleating agent
nucleating agent, can significantly improve the crystallization rate, increase the rate of crystallization and crystallization slight than.
(1) Inorganic nucleating agent Inorganic nucleating agent is based on ultrafine talc powder and SiO2, but also includes calcium carbonate, mica powder, inorganic pigments and fillers, etc., low price, rich sources, but has a certain impact on the luster and transparency of products.
(2) organic nucleating agent organic nucleating agent is a nucleation effect of low molecular weight organic matter, represented by sorbitol and its derivatives, It has good compatibility with the matrix resin, and can significantly improve the transparency and surface gloss of the product.
(3) The amount of nucleating agent for sorbitol, after the amount of nucleating agent more than 0.3%, the transparency improvement effect is not obvious, and even decreased; However, when the dosage is lower than 0.2%, the amount of nucleation is insufficient, and the transparency is not enough. It can be seen that the dosage of nucleating agent is best between 0.2-0.3%. Therefore, appropriate nucleating agent content can better improve the transparency of PP.
three, extrusion temperature
The temperature is too high, the substance of low molecular weight in the nucleating agent will decompose and volatilize, reduce the active ingredient in the nucleating agent, reduce the improvement effect of transparency, and the higher temperature, It will destroy the original crystal nucleus of PP, reduce the heterogeneous nucleation center, resulting in reduced modification effect; And the temperature is too low, the dispersity of nucleating agent is not good, the transparency effect is poor. Therefore, it is particularly important to choose a suitable extrusion temperature to improve the transparency.
4, toughening agent
Toughening agent Because the toughening agent and PP are not miscible, refractive index is different, will refract on the mutual interface, thus affecting the light transmission of the article. With the increase of the toughening content, the area of the mutual interface is also stronger, and the light transmission of the product is worse.
5, process parameter
process parameters ideal processing temperature, cooling temperature, Injection pressure and other process parameters are also of great help to the transparency of PP.
processing temperature: under the condition of satisfy processing, lower processing temperature, crystal size is smaller, transparency is better;
cooling temperature, cooling temperature is lower, will reduce crystallinity, transparency, also will be better.
injection pressure, injection time, and the holding time affects the orientation of molecules. And the orientation will affect the crystallization of the molecules, so in the condition of not affecting the performance and appearance of the product, shorten the injection and pressure holding time and reduce the pressure, can improve its transparency to a certain extent.
6, molding processing technology
forming process comparison note, pull, blowing process of the proceeds of the products, It is found that injection and blowing technology is the most beneficial to increase transparency.
the higher the mould finish, The transparency of the product will be better.