Polypropylene/PP injection molding material , is a thermoplastic addition polymer made by combining several propylene monomers. It features a wide range of applications that include packaging of consumer products, plastic components for such industries as the automotive industry.Relatively speaking, the surface of the PP plastic is very slippery, so in some low-friction applications, it can be used to replace some plastics like polyacetal (POM), or used as a contact point for furniture. One of the weaknesses of this property might be that it is not easy to adhere PP to the surface of other materials (it does not bond ideally with certain types of glues, so sometimes it needs to be welded when it is required to form a joint). PP is slippery at the molecular level, but it has a relatively high friction coefficient. As a result, POM, nylon or PTFE will sometimes be used instead of it. When compared with other common plastics, PP also has a relatively lower density, meaning weight reductions for producers and sellers of injection molded PP products.The features described above and below demonstrate that the PP material can be used in a great number of applications: safe plates of a dishwasher, food trays and cups, etc., as well as opaque to-go containers and an extensive range of toys.
Plastic Injection Molding Speed
Generally speaking, for PP injection molding process , a fast speed is usually adopted to keep the internal stresses at the lowest possible level; in case of surface defects, it is preferred to use a slower molding speed at higher temperature conditions. It is strongly recommended to employ machines that are able to provide profiled speed.
Runners and Gates
With regard to the cold runner molds, the commonly used diameters is between 4 to 7mm. We recommend the application of full round sprues and runners. It is OK to employ all types of gates. Typically, the diameters of a pin gate is set between 1 to 1.5mm, but it is also possible to use diameters of as low as 0.7 mm. When it comes to edge gating, the depth of the gate should be kept no lower than half of the wall thickness, but it should be at least twice as wide as the thickness. On the other hand, the hot runner molds are able to be directly used for thePP injection molding .
PP is easy to access and not expensive.
PP possesses a high flexural strength by virtue of its semi-crystalline property.
PP is characterized by a relatively slippery surface.
PP is rather resistant to moisture absorption.
PP is chemically resistant to an extensive range of bases and acids.
PP is very resistant to fatigue.
PP possesses great resistance to impact.
PP can act as a great electrical insulator.
PP has a high thermal expansion coefficient which limits its high temperature applications.
PP is sensitive to UV.
PP is not strongly resistant to chlorinated solvents and aromatics.
It is not easy to paint on PP, due to its poor bonding properties.
PP is highly flammable.
In spite of its weaknesses, PP is still a great injection molding material. It features a diversity of unique qualities that cannot be found in any other materials, making it an ideal choice for a diversity of application projects.
When producing PP injection molding, propylene polymerization is performed by involving stereospecific catalysts. Usually, it is isotactic PP that is produced (the methyl groups is lying on one side of the carbon chain). Due to the ordered molecular structure, this linear plastic is semi-crystalline, which is stiffer and has a higher melting temperature than PE. The PP homopolymer will become fragile when the temperature is higher than 0 degrees Celsius (32 degrees Fahrenheit). For this reason, many grades of PP available in the market are random copolymers with 1 – 4% ethylene or block copolymers with a higher ethylene proportion. Copolymers possess a lower heat distortion temperature (approx. 100 degrees Celsius / 212 degrees Fahrenheit), less clarity, surface gloss and rigidity, but a greater resistance to impact. When the ratio of ethylene increases, this material will become tougher and tougher. Its Vicat softening temperature is about 150 degrees Celsius (302 degrees Fahrenheit). For these materials, the surface hardness and resistance to scratch are higher thanks to the higher levels of crystallinity.
The PP plastic is not prone to stress cracking. It is usually adjusted by adding glass fibers, mineral fillers or thermoplastic rubbers. The melt flow rate of the PP material ranges between 1 and 40; materials with a lower melt flow rate feature a better resistance to impact but a lower tensile strength. When compared with homopolymer of the same melt flow rate, the copolymer appears to be tougher. Its viscosity leads to more shear, while being more temperature sensitive than PE.
By virtue of its crystallinity, the shrinkage rate of PP is quite high (0.018 – 0.025 mm/mm or 1.8 – 2.5%), but its shrinkage is more uniform than that PE-HD (the variance in flow and cross-flow shrinkage is usually lower than 0.2%). Increase of glass by 30% is helpful with reducing the shrinkage rate to about 0.7%.
Both the homopolymer and copolymer PP injection molding materials are strongly resistant to moisture, as well as chemicals like acids, alkalis and solvents. But, it does not offer excellent resistance to aromatic hydrocarbons, like benzene, as well as chlorinated hydrocarbons, like carbon tetrachloride. And, under high temperature conditions, its resistance to oxidation is not as strong as that of the PE plastic.
At Advanced Plastiform, Inc. we design and manufacture custom plastics for industries and businesses across the Southeast and Mid-Atlantic. In order to ensure that we are producing highly-durable plastics that can fulfill the needs of our customers, we work with numerous thermoplastic materials to provide the best result. Due to its versatility and multitude of uses, we are a leading polypropylene plastic manufacturer.
Polypropylene is a thermoplastic polymer that is one of the most widely used plastics worldwide, second only to polyethylene. It was created in 1951 by petroleum chemists and was quickly used in large-scale commercial production.
Because it has a unique chemical makeup, it offers the following qualities:
In addition to its versatility, it’s also one of the lowest cost plastics, making it a popular option for mass producing plastics across the automotive, furniture, and material handling industries.
Polypropylene thermoforming is a lower-cost, efficient way to manufacture large plastic goods and components. We heat the polypropylene until it is malleable, then fit it around a custom tool and finish the product using one of three methods:
Vacuum forming is the simplest method of polypropylene thermoforming. Once the plastic is heated and fitted around the custom tool, a high-powered vacuum removes air and draws the plastic more tightly against the tool. This method is best for plastic components that don’t require sharp edges, defined corners, or intricate details, such as car dashboards and shipping trays.
Often used as a less expensive alternative to polypropylene injection molding, pressure forming plastics allows us to achieve higher levels of detail and sharp edges than with vacuum forming. Once the polypropylene is fitted around the tool, the plastic is blasted at high pressure with air, pushing it against the tool and creating the sought after design and detail. Because it’s low electrical conductivity, polypropylene pressure forming is used for manufacturing scientific instruments and medical equipment.
Twin sheet forming is a complex method of polypropylene plastic manufacturing, requiring high levels of precision and care. It involves heating two plastic sheets at the same time, then fitting them together and fusing them. Because the plastic must be matched with pressed points where the fusion occurs, there’s no room for error or the integrity of the product is weakened. Twin sheet forming is ideal for manufacturing double-walled and hollow products, like air ducts, chutes used in material handling, and bed liners.
Polypropylene injection molding is a method of manufacturing in which polypropylene is melted to its liquid state, then injected into a double-sided mold. Injection molding is ideal for small components and parts or plastic pieces that require intricate detailing and varying thickness throughout the item. While the up-front cost is more expensive and has a longer lead time than thermoforming, for high volume orders or orders that will be fulfilled regularly, the per-unit cost is actually very cost efficient.
It’s not much of an exaggeration to say polypropylene is used for everything. It’s easy to customize, has a high melting point, high flexibility, and is water resistant so it’s most commonly used for:
To learn more, please visit our frequently asked questions about polypropylene.
We are proud to be a leader in polypropylene plastics manufacturing, capable of providing custom plastics to customers across numerous industries. Our clients know we offer the durable, long-lasting products they need while providing competitive pricing and fast lead times. We work with businesses in North Carolina, South Carolina, Pennsylvania, Maryland, Tennessee, Georgia, and Virginia.