Definition and description of PP plastic

PP plastic, chemical name: polypropylene English name: Polypropylene (referred to as PP) Features: low density, strength and stiffness, hardness and heat resistance are better than low-pressure polyethylene, can be used at about 100 degrees. It has good electrical properties and high frequency Insulation is not affected by humidity, but it becomes brittle, non-wearing, and easy to age at low temperatures. It is suitable for making general mechanical parts, corrosion-resistant parts and insulating parts. Molding characteristics: 1. Crystal material, low moisture absorption, easy to melt fracture, long-term contact with hot metal and easy to decompose. 2. Good fluidity, but the shrinkage range and shrinkage value are large, and shrinkage, dents, and deformation are easy to occur. 3. The cooling speed is fast, the pouring system and the cooling system should slowly dissipate heat, and pay attention to controlling the molding temperature. The material temperature is easy to orient at low temperature and high pressure. When the mold temperature is lower than 50 degrees, the plastic part is not smooth, which is easy to produce poor welding, flow marks, Warping and deformation are prone to occur above 90 degrees. 4. The plastic wall thickness must be uniform to avoid lack of glue and sharp corners to prevent stress concentration. PP characteristicsNon-toxic, tasteless, low density, strength, stiffness, hardness and heat resistance are better than low-pressure polyethyleneIt can be used at about 100 degrees. It has good electrical properties and high-frequency insulation. It is not affected by humidity, but it becomes brittle, non-wearing, and easy to age at low temperatures. Suitable for making general mechanical parts, corrosion-resistantParts and insulating parts. Common acid and alkali organic solvents have almost no effect on it and can be used for food utensils.PP polypropylene Typical application range:Automotive industry (mainly using PP containing metal additives: mudguards, ventilation ducts, fans, etc.), appliances (dishwasher door liners, dryer ventilation ducts, washing machine frames and covers, refrigerator door liners, etc.), Japan Consumer goods (lawn and garden equipment such as lawnmowers and sprinklers, etc.). Injection molding process conditions: Drying treatment: If stored properly, no drying treatment is required. Melting temperature: 220~275C, be careful not to exceed 275C. Mold temperature: 40~80C, 50C is recommended. The degree of crystallization is mainly determined by the mold temperature. Injection pressure: up to 1800bar. Injection speed: Generally, the use of high-speed injection can reduce the internal pressure to a minimum. If there are defects on the surface of the product, low-speed injection at a higher temperature should be used. Runners and gates: For cold runners, the typical runner diameter range is 4~7mm. It is recommended to use a circular injection port and runner. All types of gates can be used. The typical gate diameter ranges from 1 to 1.5mm, but gates as small as 0.7mm can also be used. For edge gates, the minimum gate depth should be half the wall thickness; the minimum gate width should be at least twice the wall thickness. PPThe material can use the hot runner system. PP production method1 Slurry method. Polymerization in a diluent (such as hexane) is the earliest industrialized method and the largest production method so far. 2 Liquid phase bulk method. Polymerize in liquid propylene at 70°C and 3MPa. 3 Gas phase method. Polymerize under gaseous conditions of propylene. The latter two methods do not use diluent, the process is short, and the energy consumption is low. The liquid phase bulk method has now shown the advantage of coming from behind. Chemical and physical properties: PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Since homopolymer PP is very brittle when the temperature is higher than 0C, many commercial PP materials are random copolymers with 1 to 4% ethylene or clamp copolymers with higher ethylene content. Copolymer PP material has lower thermal distortion temperature (100C), low transparency, low gloss, low rigidity, but has stronger impact strength. The strength of PP increases with the increase of ethylene content. The Vicat softening temperature of PP is 150C. Due to the high crystallinity, the surface rigidity and scratch resistance of this material are very good. PP does not have the problem of environmental stress cracking. Usually, the PP is modified by adding glass fiber, metal additives or thermoplastic rubber. The flow rate MFR of PP ranges from 1 to 40. PP materials with low MFR have better impact resistance but lower elongation strength. For materials with the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, generally 1.8~2.5%. And the direction uniformity of shrinkage is much better than that of PE-HD and other materials. Adding 30% of glass additives can reduce the shrinkage to 0.7%. Both homopolymer and copolymer PP materials have excellent moisture absorption, acid and alkali corrosion resistance, and solubility resistance. However, it has no resistance to aromatic hydrocarbons (such as benzene) solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents, etc. PP does not have oxidation resistance at high temperatures like PE. PP glass fiber reinforced:Using a higher grade of plastic can definitely increase the rigidity of the plastic parts, but this will increase the cost, so the material cost is never increased in terms of materials, and the method of low-cost plastics and reinforcement is used to solve the problem. Adding glass fiber is a common and mature method. Adding glass fiber can also improve the creep properties of the material.
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