PP plastic definition and description
Publisher：Manager Release time：2017-03-23
PP plastic, chemical name: Polypropylene English name: Polypropylene (referred to as PP) Features: low density, strength stiffness, hardness and heat resistance are better than low-pressure polyethylene, can be used in about 100 degrees. Has good electrical properties and high frequency Insulation is not affected by humidity, but at low temperature brittle, not wear, easy to aging. Suitable for the production of general mechanical parts, corrosion-resistant parts and insulation parts.
Molding characteristics: 1. Crystalline material, hygroscopicity is small, prone to melt rupture, long-term contact with the hot metal easily decomposed. 2. Good fluidity, but the contraction range and shrinkage value, prone to shrinkage. Dents, deformation. 3. Cooling speed, pouring system and cooling system should be slow to heat, and pay attention to control the molding temperature. Temperature is low temperature and high pressure easy to orientation, mold temperature below 50 degrees, the plastic parts are not smooth, easy to produce bad welding, 90 degrees or more prone to warping deformation 4. Plastic wall thickness to be uniform, to avoid lack of plastic, sharp corners, to prevent stress concentration.
PP characteristics
Non-toxic, tasteless, low density, strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene
, Can be used in about 100 degrees. Has good electrical properties and high frequency insulation from humidity, but low temperature brittle, not wear, easy aging. Suitable for the production of general mechanical parts, corrosion resistance
Parts and insulation parts. Common acid, alkali organic solvents have little effect on it and can be used for utensils.
PP Polypropylene Typical Applications:
(The main use of metal additives containing PP: fender, ventilation ducts, fans, etc.), equipment (dishwasher door liner, dryer ventilation pipe, washing machine frame and cover, refrigerator door gasket, etc.), With consumer goods (lawn and gardening equipment such as lawn mowers and sprinklers). Injection molding process conditions: Drying: If stored properly do not need to dry. Melting temperature: 220 ~ 275C, be careful not to exceed 275C. Mold temperature: 40 ~ 80C, it is recommended to use 50C. The degree of crystallization is mainly determined by the mold temperature. Injection pressure: up to 1800 bar. Injection speed: Typically, the use of high-speed injection can reduce the internal pressure to a minimum. If there is a defect on the surface of the product, low-speed injection at higher temperatures should be used. Runners and gates: For cold runners, the typical flow path diameter range is 4 to 7 mm. It is recommended to use a circular inlet and a flow path. All types of gates can be used. Typical gate diameters range from 1 to 1.5 mm, but gate sizes as small as 0.7 mm 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. PP
Material can use hot runner system.
PP production methods
1 slurry method. In the diluent (such as hexane) polymerization, is the earliest industrialization, is also the largest production method so far. 2 liquid phase bulk method. And polymerized in liquid propylene at 70 ° C and 3 MPa. 3 gas phase method. Polymerization of propylene in gaseous conditions. The latter two methods do not use thinner, short process, low energy consumption. Liquid-phase ontology 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 the homopolymer PP temperature is higher than 0C is very brittle, so many commercial PP material is added 1 ~ 4% ethylene random copolymer or higher ratio of ethylene content of the claw-type copolymer. Copolymer PP material has a low thermal distortion temperature (100C), low transparency, low gloss, low rigidity, but has a stronger impact strength. The strength of PP increases with increasing ethylene content. PP Vicat softening temperature of 150C. Due to the high degree of crystallinity, the surface stiffness and scratch resistance of this material is very good. PP does not exist environmental stress cracking problem. In general, PP is modified by the addition of glass fibers, metal additives or thermoplastic rubbers. PP flow rate MFR range of 1 to 40. Low MFR PP material has better impact resistance but lower ductility. For the same MFR material, the copolymer type has a higher strength than the homopolymer type. As a result of crystallization, PP shrinkage is quite high, generally 1.8 to 2.5%. And the direction of the uniformity of shrinkage than PE-HD and other materials much better. Adding 30% of the glass additive reduced the shrinkage to 0.7%. Both homopolymer and copolymer PP materials have excellent resistance to moisture absorption, acid and alkali corrosion resistance, anti-solubility. However, it has no resistance to aromatics (such as benzene) solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents and the like. PP is not like PE as at high temperatures still have antioxidant properties.
PP glass fiber reinforced:
With a high grade of plastic can certainly improve the rigidity of plastic parts, but this will increase the cost, so the material never to improve the cost of materials, low-cost plastic and then strengthen the method to solve the problem. Plus fiberglass is a commonly used, mature method. Glass fiber can also improve the creep properties of the material.
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