The molecules of the polymer interact with the molecules so that they can aggregate together, generally rarely linear, mostly curly-like aggregates. For aggregates, the size of the size will determine its transparency. Its aggregate size than the light wavelength, the polymer itself is opaque; the other hand, it was transparent, you can let the light through. Therefore, to improve the transparency of PP, the main starting point is to reduce the size of its polymer grain size. Therefore, the method of improving PP transparency can be considered from the following aspects:

1. The matrix of the resin

Under the condition of satisfying mechanical properties, try to select low molecular weight PP, homogeneous PP with small bulk polymerization, and PP with good optical properties. Figure 1 and Figure 2, we can see that the transparency of the resin itself, the production of different transparency products, have constraints, so the choice of different matrix resin should be based on the ability to improve the transparency of PP to choose. 

2. Selection of nucleating agents

(Nucleating agent: can significantly improve the crystallization rate, improve the crystallization rate and crystal fine ratio)

(1) inorganic nucleating agent

Inorganic nucleating agent with ultrafine talc and SiO2, including calcium carbonate, mica powder, inorganic pigments and fillers, low prices, rich sources, but the products have a certain impact on gloss and transparency.

(2) organic nucleating agent

Organic nucleating agent is a low molecular weight organic matter with nucleation. It is represented by sorbitol and its derivatives, and its compatibility with matrix resin is good, which can improve the transparency and surface gloss of the product remarkably.

Figure 3 and Figure 4, respectively, PP + CaCO3 film and PP + sorbitol film, it can be seen that the former transparency is much worse than the latter.

(3) the amount of nucleating agent

In the case of sorbitol, when the amount of nucleating agent exceeds 0.3%, the effect of improving the transparency is not obvious or even decreased. However, when the amount is less than 0.2%, the number of nucleation is insufficient and the transparency is not enough. It can be seen that the amount of nucleating agent is preferably between 0.2 and 0.3%. Therefore, the appropriate nucleating agent content can better improve the transparency of PP. Reply to "PP" or "nucleating agent" to see more related articles

3. Extrusion temperature

The temperature is too high, the low molecular weight of the nucleating agent in the material will produce decomposition and evaporation, reducing the nucleating agent in the active ingredient, reducing the transparency of the improvement effect, and the higher temperature, will destroy the original PP nuclei, Heterogeneous nucleation center, resulting in reduced effect of modification; and the temperature is too low, the dispersion of the nucleating agent is not good, the transparency effect is poor. Therefore, the choice of a suitable extrusion temperature to improve the transparency is particularly important.

4. Effect of toughening agent and its addition

As the toughening agent and PP and can not be miscible, refractive index is also different, will occur in the interface of the refraction, thus affecting the light transmission. With the increase in toughening content, the interface area is also stronger, the light transmission of the product is worse.

5. Effect of process parameters

The ideal processing temperature, cooling temperature, injection pressure and other process parameters on the transparency of PP is also a great help.

Processing temperature: to meet the processing conditions, the lower the processing temperature, the smaller the size of the crystal, the transparency is better

Cooling temperature: the lower the cooling temperature, will reduce the crystallinity, transparency will be better.

Injection pressure, injection time and holding time will affect the orientation of the molecule. And the orientation will affect the crystallization of molecules, so without affecting the performance and appearance of the conditions, shorten the injection and holding time and reduce the pressure, can be a certain extent to improve its transparency.

6. Molding process

Comparison of note, pull, blowing process products, found to note, blowing process to increase the transparency of the most useful.

7. The impact of mold: mold the higher the finish, the transparency of the product will be better.