Current Status of the PMIP (Part Molding Insert Process)
Published Time:
2024-06-11
Secondary injection molding can create products with a soft, supple surface, and it can also enhance product functionality and added value. In the past 10 years, secondary injection molding technology has fundamentally changed consumer product aesthetics, design concepts, and functional requirements. Secondary injection molding technology is known for creating "soft-touch surfaces," but it also has many other functions, such as ergonomic design, two-tone appearance, branding, and improved properties. Using this technology, product functions such as noise reduction, shock absorption, waterproofing, and impact resistance can be added, as well as added value. In Phone Cases / Phone Covers applications are relatively widespread.
Secondary injection molding, like co-injection molding, double injection molding, and insert molding, belongs to multi-material injection molding technology. The basic idea of multi-material injection molding is to combine two or more materials with different properties to increase product value. Generally, the first injected material is called the base material or substrate; the second injected material is called the cover material.
In various secondary injection molding technologies, during the secondary injection molding process, the cover material is injected above, below, around, or inside the base material, combining to form a complete part. This process can be completed through multiple injections or insert molding. Commonly used cover materials are elastic materials.
Generally, to strengthen adhesion, the melting temperature of the cover material resin should be the same as that of the base material. If the melting temperature of the cover material is too low, it will not be able to melt the surface of the base material. The bonding between the two will not be strong enough. However, if the melting temperature is too high, the base material will soften and deform. In severe cases, the cover material will penetrate the base material, resulting in processing failure. Therefore, selecting matching materials can ensure good bonding. Generally speaking, matching materials should have similar chemical properties or contain matching composite components.
When the base material and the cover material are not matched, usually only mechanical interlocking can be formed, rather than chemical bonding.
Multi-material injection molding also needs to pay attention to some issues, the most common ones include:
1. Insufficient chemical or mechanical bonding strength between polymers; incomplete filling of single or multiple component materials;
2. Flashing of single or multiple material components.
3. The injection molding machine must maintain consistent injection molding.
In addition, the ratio of the injection volume of the injection molding machine barrel to the size of the injection molded part is also an important factor affecting the injection molding quality. This ratio is crucial for all injection molding operations, and it is particularly important in secondary injection molding.
A check valve can separate the cover material like a sluice gate. When both secondary injection molding materials are metal, the check valve operation is easier. If it is a metal substrate and a more elastic plastic, the check valve operation is more difficult.
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