Bulk Factory Price Rigid PP Plastic Roll for Cups Packing

Among the general plastics, PP has the best heat resistance, its hot deformation temperature is 80-100 ℃, and it can be boiled in boiling water. PP has good stress cracking resistance and high bending fatigue life, commonly known as “hundred fold glue”. The comprehensive properties of PP are better than that of PE. PP products are light in weight, good in toughness and good in chemical resistance. Disadvantages of PP: low dimensional accuracy, insufficient rigidity, poor weather resistance, it has post shrinkage phenomenon, easy aging, brittle, easy deformation after demoulding. In daily life, the commonly used fresh-keeping box is made of PP material.

Molding characteristics:
1. Crystalline material, hygroscopicity is small, easy to melt fracture, long-term contact with hot metal is easy to decompose.
2. Good fluidity, but large shrinkage range and shrinkage value, easy to occur shrinkage cavity, dent, deformation
3. The cooling speed is fast, the pouring system and cooling system should slow heat dissipation, and pay attention to control the molding temperature. When the material temperature is low temperature and high pressure, it is easy to orientation. When the mold temperature is lower than 50 ℃, the plastic parts are not smooth, and it is easy to produce poor fusion and flow marks. When the temperature is above 90 ℃, it is easy to produce warping deformation.
4. In order to prevent stress concentration. Process characteristics PP has good fluidity and good formability at melting temperature. PP has two characteristics in processing: one is that the viscosity of PP melt decreases significantly with the increase of shear rate (less affected by temperature); the other is that the molecular orientation degree is high and presents a large shrinkage rate. The processing temperature of PP is about 200-300 ℃, and it has good thermal stability (decomposition temperature is 310 ℃), but at high temperature (270-300 ℃), it may degrade if it stays in the barrel for a long time.

Because the viscosity of PP decreases obviously with the increase of shear rate, the increase of injection pressure and injection speed will improve the fluidity, shrinkage deformation and depression of PP. The mold temperature should be controlled in the range of 30-50 ℃. PP melt can pass through a very narrow mold gap to form a sharp edge. PP in the melting process, to absorb a lot of melting heat (the specific heat is larger), the product is hot after the mold. The shrinkage and crystallinity of PP are lower than that of PE.