For a double-shot plastic injection moulding to work, the substrate and over-mould plastic material has to be chemically compatible in order  for them to form a solid bond.

Multi-shot moulding is a process that moulds two or more more materials onto each other, in a single injection moulding cycle.

That is because 3K and more material or colour injection processes entail more detailed studies on the bonding of materials, geometry parts, and many other considerations.

Due to PP’s beneficial physical, chemical, and mechanical properties, there are countless applications for which this material is used. PP is a food-grade thermoplastic, making it safe for food containers, cups, and children’s toys. Also, due to it being lightweight and strong, it can act as a replacement for metal parts in the automotive industry. Its chemical resistance also makes it ideal for use in medical products, and it’s even durable enough to be used in autoclaves. Beyond these examples, this plastic is also used in construction, household appliances, power tools, and much more.

PP can also be combined with other materials, such as rubber, to create a stronger copolymer. However, polypropylene is not without its downsides. This polymer is susceptible to UV degradation, has poor resistance to chlorinated solvents, and has limits regarding very high-temperature applications, accompanied by high flammability.

Next, the mould opens and the moving half or the core side of the mould is rotated 180 degrees and closed for the second half of the injection moulding cycle.

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Plastic injection molding offers a wide variety of resins providing all sorts of unique characteristics. But polypropylene is one of the most popular material choices for businesses looking to create tough and flexible parts. The customizability, easy processing traits, and affordability of this plastic allow it to be used in many diverse applications. If you’re wondering whether you should consider this material for your next project, we’re here to help by providing the benefits, types, and applications of polypropylene in plastic injection molding.

Due to its positive traits and affordability, there’s much to gain when using polypropylene in plastic injection molding. Knowing its characteristics opens up so many possibilities when it comes to planning your next project. At Midstate Mold, we have experienced molding numerous different thermoplastics, and we can perform production on your parts and closely inspect them for quality. If you’re looking to partner with a manufacturer experienced with polypropylene and so much more, contact us today.

Since double-shot injection moulding is the most common multi-shot injection type, we will discuss this topic in further details below.

First, the substrate is injected into its respective mould cavity, while the second shot over mould is injected into its own cavity over the substrate from the first half of the injection moulding cycle.

There are two main types of PP: homopolymers and copolymers. However, copolymers can be broken down into two separate categories: random copolymers and block copolymers. Here are some of the differences between these market-available PP types:

It is important to note that such method is ideal for surfaces with maximum friction, i.e. first shot hard plastics with a second shot soft rubber designed to enhance grip non-slip surfaces for industrial hand-held devices and infant products.

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Polypropylene (PP) is so prevalent in plastic injection molding because it is amongst the least expensive thermoplastics available, yet it boasts so many beneficial characteristics. Some of the biggest advantages of using polypropylene in plastic injection molding include:

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Unsurprisingly, the most common type of multi-shot moulding is the double-shot injection moulding, or what is commonly known as 2K injection moulding.

Alternatively, in cases where the substrate and over-mould plastic material are not chemically compatible, the substrate geometry has to incorporate mechanical bonding features such as through holes or other similar features.