Co-injection molding involves injecting different polymers into the same mold to change physical properties or reduce costs. There are two types: machine-based and mold-based. It allows for creating double-layered effects and combining materials for different properties. It also reduces cooling time and allows for recycling materials, benefiting both manufacturers and consumers.
Coinjection is an injection molding process where different polymers are injected into the same mold to produce a specific effect. In many cases, the desired effects include changing the physical properties of the polymers or reducing manufacturing costs. This process is also known as sandwich molding. There are two types of co-injection processes: machine-based and mold-based. Each type offers specific benefits and applications.
Machine co-injection requires the use of two or more processing units. This is considered a cold runner process. The molten plastic from each processing unit is forced through a manifold where it is combined and then exits through a single nozzle. By working the plastic in this way, the result is a core product covered with a polymer skin.
Mold co-injection is a hot runner process in which the two molten plastics are kept separate until the last stage. The streams merge as they reach the mould, forming a part with a double layered effect. This type of molding is commonly found in household products such as toothbrush handles which have a clear outer surface surrounding a colored core. While this application is suitable for creating certain aesthetic effects, it is useful in other ways as well. Combining a core product with a polymer overlay allows manufacturers to create a wide variety of different properties for products.
The reduced cooling time required in the co-injection process makes this method a practical technique for low temperature core products. By using an inexpensive recycled base material coated with a more expensive polymer skin, the manufacturer can save on production costs. In a similar arrangement, a strong base material, such as glass, can be used to add strength and stiffness to a more flexible polymer. In some cases, co-injection molding is combined with a foam core to create products with sound absorbing properties.
In addition to the obvious benefits for the manufacturing side of the process, co-injection also offers benefits from a consumer and environmental perspective. This process makes it possible to recycle plastic parts and post-industrial materials. These materials are ground up and used to form inexpensive cores for injection molded parts. By using recycled materials, it reduces costs for consumers and eliminates waste products in landfills. The added strength of fundamental choices can also translate into more durable and long-lasting products.
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