PP for non-polar crystalline plastics, water absorption is very low, about 0.03% to 0.04%, injection molding generally do not need to dry (if necessary, can be dried at 80 ~ 100 ℃ 1 ~ 2h can be). PP melting point of 165 ~ 170 ℃, decomposition temperature of 350 ℃, the maximum crystallization rate temperature of 120 ~ 130 ℃, a wide range of molding temperature (205 ~ 315 ℃). Injection molding PP suitable MFR range of 2 ~ 15 g / 10min, melt fluidity is better, barrel temperature control at 210 ~ 280 ℃, the nozzle temperature is lower than the maximum barrel temperature of 10 ~ 30 ℃. When the products are thin-walled, complex shape, the barrel temperature can be increased to 280-300 ℃: when the products are thick wall or high MFR resin, the barrel temperature can be reduced to 200-230 ℃. PP melt viscosity is more dependent on the shear rate than on the temperature, so it is more effective to increase the melt fluidity by increasing the injection pressure or the injection rate than by increasing the barrel temperature during injection molding (the injection pressure is usually 70 to 120 MPa). In addition, the increase in injection pressure is also conducive to improving the tensile strength and elongation at break of the product, the impact strength of the product has no adverse effect on the impact strength of the product, in particular, greatly reducing the shrinkage rate, but too high an injection pressure is prone to cause overflow of the product, and increase the internal stress of the product. Mold temperature when injecting PP is 40 to 90 ℃. Increase the mold temperature, the crystallinity of PP to increase the rigidity and hardness of the products, the surface finish is better, but prone to overflow, dents, shrinkage and other defects; while the mold temperature is too low, the crystallinity decreases. Product toughness increases, shrinkage decreases, but the product surface finish is poor, larger area, thicker wall products are also prone to warping. In the PP molding cycle, the choice of holding time is more important. In general, the holding time is long, the shrinkage of the product is low, but due to the condensation sealing pressure increases, the product will produce internal stress, so the holding time can not be too long. Unlike other plastics, PP products demolded at higher temperatures do not produce deformation or deformation is very small, the actual tendency to use a lower mold temperature, therefore, the PP molding cycle is shorter Physical and chemical properties 1 at low temperatures with poor impact resistance 2 difficult to be painted or by adhesives stick 3 with glass fiber reinforcement of molding surfaces are not smooth Polypropylene provides most of the characteristics of thermoplastic plastics can not be achieved with a balance between the price point. Polypropylene offers a balance of properties and price that most thermoplastics cannot. Polypropylene is easy to mold and has good chemical and mechanical resistance. Glass-reinforced polypropylene improves dimensional stability, warpage resistance, stiffness and strength. The heat deflection temperature of 40% glass-reinforced polypropylene can be increased to 149°C at 264 psi. The coefficient of thermal expansion of polypropylene with 40% glass-reinforcement is reduced to one-half its original value. When a chemical coupling agent is added, glass-reinforced polypropylene meaningfully improves its tensile and flexural strengths beyond those of normal glass-reinforced polypropylene. Polypropylene reinforced with 30% chemically coupled glass fiber improves tensile strength by 180% over un-reinforced polypropylene and by 50% over normal glass fiber reinforced polypropylene. Overall, chemically coupled polypropylene improves strength characteristics without changing modulus, heat resistance, electrical properties, or hardness. Talc-filled PP improves the stiffness, hardness, and heat resistance of the material. PP has a low Tg, and after demolding, post-shrinkage occurs, which increases with the thickness of the product. About 6h after demolding to complete 90%, and 10% to be completed in ten days. Specific measures to reduce shrinkage are: shorten the injection time, extend the holding time, improve the material temperature and mold temperature. Molding, increase the injection pressure, extend the injection and holding pressure time and reduce mold temperature, etc., can reduce the shrinkage after. The use of *** poly PP or modified PP, is conducive to reducing shrinkage. For products with high dimensional stability requirements, heat treatment should be carried out, the heat treatment temperature is 80 ~ 100 ℃, time is 1 ~ 2h. It is worth noting that the PP products are more serious after shrinkage. Therefore, the products should be aging treatment.PP products at low temperatures show brittleness, sensitive to notch. PP Polypropylene chemical and physical properties PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Because homopolymer-type PP is very brittle at temperatures above 0C, many commercial PP materials are irregular ****polymers with 1 to 4% ethylene or clamp-type ****polymers with higher ratios of ethylene content. The *** polymer type of PP material has a lower heat distortion temperature (100C), low transparency, low gloss, and low rigidity, but has greater impact strength.The strength of PP increases as the ethylene content increases. PP has a Vicat softening temperature of 150 C. Due to its high degree of crystallinity, this material has good surface stiffness and scratch resistance properties. PP does not suffer from environmental stress cracking. Typically, PP is modified by adding glass fibers, metal additives, or thermoplastic rubber.The flow rate MFR of PP ranges from 1 to 40.PP materials with low MFR have better impact characteristics but lower ductile strength. For the same MFR, the *** polymer type is stronger than the homopolymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.8 to 2.5%. And the directional uniformity of shrinkage is much better than materials such as PE-HD. Adding 30% glass additive can reduce the shrinkage to 0.7%. Both homopolymer-type and *** polymer-type PP materials have excellent resistance to moisture absorption, acid and alkali corrosion, and solubility. However, it is not resistant to aromatic hydrocarbon (e.g., benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. Injection molding process Drying treatment: Drying treatment is not required if stored properly. 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: can be as big as 1800bar. Injection speed: usually, using high speed injection can minimize the internal pressure. If defects appear on the surface of the product, then lower injection speeds at higher temperatures should be used. Runners and Gates:For cold runners, typical runner diameters range from 4 to 7mm.It is recommended to use injection ports and runners that are round through and through. All types of sprues can be used. Typical gate diameters range from 1 to 1.5 mm, but gates as small as 0.7 mm can 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. hot runner systems can be used exclusively for PP materials. Special Composites Typical Injection
Molding Conditions
General Injection Molding Conditions English
English SI Metric
Metric Temperature Rear zone Back zone °F193 - 216°C Center zone Middle zone 390 - 430°F199 - 221°C Front zone Front zone 400 - 440°F204 - 227°C Melt Melt temperature 375 - 450°F191 - 232°C Mold Mold temperature 90 - 150°F32 - 66°CPressures Injection Injection pressures 10000 - 15000psi69 - 66°C 10000 - 15000psi69 - 103MPa Hold Hold Pressure5000 - 10000psi34 - 69MPa Back Back Pressure50 - 100psi0.34 - 0.69MPaSpeeds Speed Fill Fill Speed1 - 2in/sec25 - 51mm/sec Screw Screw Speed60 - 90rpm60 - 90rpm 90rpm60 - 90rpmDrying Conditions Time & Temperature
Time & Temperature2 Hrs @ 175°F2 Hrs @ 79°C Dew Point Dew Pointn/a°Fn/a°C Moisture Content
Moisture Contentn/a%n/a% Permanent Antistatic Composite Material. a% Permanent Antistatic Composites Typical Injection
Molding Conditions
General Injection Molding Conditions English
English SI Metric
Metric Temperature Rear zone Rear zone 330 - 360° F166 - 182° C Center zone 330 - 360° F166 - 182° C Center zone 330 - 360° C F166 - 182°C Center zone Middle zone 340 - 370°F171 - 188°C Front zone Front zone 350 - 380°F177 - 193°C Melt Melt temperature 340 - 400°F171 - 204°C Mold Mold temperature 90 - 150°F32 - 66°CPressures Injection Injection Pressure7000 - 11000psi48 - 76MPa Hold Hold Pressure4000 - 9000psi28 - 62MPa Back Back Pressure50 - 100psi0.34 - 0.69MPaSpeeds Speed Fill Fill Speed0.5 - 1in/sec13 - 25mm/sec Screw Screw Speed60 - 90rpm60 - 90mm/sec Speed60 - 90rpm60 - 90rpmDrying Conditions Time & Temperature
Time & Temperature2 Hrs @ 175°F2 Hrs @ 79°C Dew Point Dew Pointn/a°Fn/a°C Moisture Content
Moisture Content 0.10%0.10%EMI Masking Composite Typical Injection
Molding Conditions
General Injection Molding Conditions English
English SI Metric
Metric Temperature Temperature Rear zone Rear Zone 390 - 420°F199 - 216°C Center zone Middle zone 380 - 400°F193 - 204°C Front zone Front zone 370 - 390°F188 - 199°C Melt Melt temperature 380 - 430°F193 - 221°C Mold Mould temperature 100 - 125°F38 - 52°C CPressures Injection Injection 10,000 - 15,000psi69 - 103MPa Hold Hold Pressure 5,000 - 10,000psi34 - 69MPa Back Back Pressure 50 - 100psi0.34 - 0.69MPaSpeeds Speeds Fill Fill Speed0.5 - 1in/sec13 - 25mm/sec Screw 25mm/sec Screw Screw Speed30 - 60rpm30 - 60rpmDrying Drying Conditions Time & Temperature
Time & Temperature2 Hrs @ 175°F2 Hrs @ 79°C Dew Point Dew Pointn/a°Fn/a°C Moisture Content
Moisture Content0.10%0.10% Long Fiber Composites Typical Injection
Molding Conditions
General Injection Molding Conditions English
English SI Metric
Metric Temperature Temperature Rear zone Rear zone 420 - 450°F216 - 232°C Center zone Middle zone 410 - 440°F210 - 227°C Front zone Front zone 400 - 430°F204 - 221°C Melt Temperature 410 - 480°F210 - 249°C Mold Mold Temperature100 - 170°F38 - 77°CPressures Injection Injection 10,000 - 15,000psi69 - 103MPa Hold Hold Pressure 5,000 - 10,000psi34 - 69MPa Back Back Pressure 25 - 50psi0.17 - 0.34MPaSpeeds Speed Fill Fill Speed0.5 - 1in/sec13 - 25mm/sec Screw Screw RPM30 - 70rpm30 - 70rpmDrying Drying Conditions Time & Temperature
Time & Temperature4 Hrs @ 180°F4 Hrs @ 82°C Dew Point Dew Point-20°F-29°C Moisture Content
Time & Temperature4 Hrs @ 180°F4 Hrs @ 82°C Dew Point F-29°C Moisture Content
Moisture Content 0.02%0.02% Applications Automotive (mainly using PP with metal additives: fenders, vents, fans, etc.), Appliances (dishwasher door gaskets, dryer vents, washer frames and lids, refrigerator door gaskets, etc.), Consumer Goods (lawn and garden equipment such as lawn mowers and sprinklers, etc.). sprinklers, etc.).