Polypropylene English name: Polypropylene, referred to as: PP, commonly known as: pleated plastic.
Polypropylene is representative of poly-α-olefins, obtained by the polymerization of propylene and a thermoplastic resin which is a propylene monomer CH2 = CH-CH3. Depending on the initiator and the polymerization process, the polypropylene can be divided into isotactic polypropylene and atactic polypropylene and syndiotactic polypropylene three configurations. Isotactic polypropylene is easy to form the crystalline state, up to 95% crystallinity, molecular weight between 8-15 million and give him good thermal and solvent resistance; atactic polypropylene at room temperature is a non-crystalline, microstrip sticky white wax, low molecular weight, in 3000-10000, irregular structure lacks cohesion, is seldom used.
1 crystalline material, moisture absorption, prone to melt fracture, prolonged contact with hot metal decomposition.
2 good mobility, but the scope and shrinkage shrink large, prone to shrinkage, dents, deformation.
3. Cooling speed, gating system and cooling system should be slow to heat, and pay attention to controlling the molding temperature. Easy orientation when feeding high temperature and low mold temperature is below 50 degrees, the plastic is not smooth, easy to produce bad welding, flow marks, 90 degrees prone to warpage.
4 plastic wall thickness shall be uniform to avoid the lack of plastic, sharp corners to prevent stress concentration
Drying: Drying is not necessary if stored properly handled.
Melting temperature: 220 ~ 275 ℃, careful not to exceed 275 ℃.
Mold temperature: 40 ~ 80 ℃, recommended 50 ℃. Degree of crystallinity determined by the mold temperature.
Injection pressure: can be as large 1800bar.
Injection speed: Generally, high speed injection molding can make the internal pressure is reduced to a minimum. If the product surface defects, then you should use low-speed injection molding high temperature.
Runners and Gates: For cold runner, runner typical diameter range is 4 ~ 7mm. Recommend the use of whole body circular sprue and runner. All types of gates can be used. The gate diameter is typically 1 ~ 1.5mm, but can also be used as small as 0.7mm gate. For the edge of the gate, the minimum depth should be half the gate thickness; smallest gate width should be at least twice the thickness. PP materials can use the hot runner system.
PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Since the type of PP homopolymer temperature above 0 ℃ very brittle, so many commercial PP material is added 1-4% ethylene random copolymers of ethylene content or a higher ratio of block-type copolymer. PP copolymer-based material has a lower heat distortion temperature (100 ℃), low transparency, low gloss, low rigidity, but have a stronger impact strength. PP intensity with increasing ethylene content increases. The Vicat softening temperature of PP is 150 ℃. Due to the high degree of crystallinity, surface stiffness and scratch resistance of this material is very good. PP environmental stress cracking problem does not exist. Generally, the use of glass fiber, metal additives or thermoplastic rubber modified PP. PP turnover MFR range of 1 to 40. PP material impact properties of low MFR better but extended lower intensity. For the same MFR, copolymer-type homopolymer intensity ratio is higher. As the crystal, PP contraction rate is very high, typically 1.8 to 2.5%. Direction and uniformity of shrinkage than PE-HD material is much better. 30% of the glass additive can shrink rate to 0.7%. Homo-and copolymer PP materials have excellent resistance to moisture absorption, anti-acid corrosion and solvent resistance. However, it aromatic hydrocarbons (such as benzene) solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents no resistance. PP did not like PE is still at a high temperature oxidation resistance.
Polypropylene (PP) is a common plastic lighter, excellent electrical properties, can be used as heat-resistant insulating material of high frequency applications. PP is a crystalline polymer by melt condensation of a large volume change ratio, a high degree of molecular orientation and showed greater shrinkage (1.0% -1.5%). PP in the molten state, to reduce its viscosity by heating a minor role. Therefore, in the molding process should be to increase the shear rate and the main injection pressure, in order to improve the quality of molded articles.