What is Secondary Injection Molding?

Secondary injection molding: It is a special plastic molding process, also known as bagging or encapsulation. It is similar to the two-color molding process, but has significant differences from the two-color molding process. It is a process of molding a certain plastic raw material in a plastic mold, taking out the formed parts, and then injecting the same or another plastic material into the secondary mold for molding. A more complex process involves multiple molding processes to achieve the desired shape and craftsmanship of plastic products, known as secondary injection molding.
Description: Insert molding,two-time molding, over molding 
Definition: A special plastic molding process
Catalogue
1. Development status
2. Precautions

Development status
Secondary injection molding can make the surface of the product full of softness, and can also increase the functionality and added value of the product. In the past 10 years, secondary injection molding technology has completely changed the aesthetic standards, design concepts, and functional requirements of consumer goods. Secondary injection molding technology is known for creating "soft surfaces", but it also has many other functions such as ergonomic design, dual color appearance, brand identity, and feature improvements. By utilizing this technology, the product's features can be increased, such as noise reduction, shock absorption, waterproofing, collision avoidance, and added value. It is widely used in mobile phone protective cases/cases.
Secondary injection molding, like co injection molding, double injection molding, and sandwich injection molding, all belong to multi material injection molding technology. The basic idea of multi material injection molding is to combine two or more materials with different characteristics to increase product value. Generally speaking, the first type of injection material is called a substrate or substrate material; The second type of injection material is called a covering material.
In the process of secondary injection molding, various secondary injection molding techniques combine the covering material injected into the substrate above, below, around, or inside to form a complete component. This process can be completed through multiple injection molding or embedded injection molding. The commonly used covering material is elastic material.

Matters needing attention
Generally speaking, to enhance adhesion, the melting temperature of the covering material resin should be the same as that of the substrate. If the melting temperature of the covering material is too low, the surface of the substrate cannot be melted. The adhesion between the two is not strong enough. But if the melting temperature is too high, the substrate will soften and deform. In severe cases, the covering material may penetrate the substrate, leading to component processing failure. Therefore, selecting matching materials is essential to ensure good adhesion. Generally speaking, matching materials should have similar chemical properties or contain matching composite components. 
When the substrate and covering material do not match, mechanical interlocking can usually only be formed. Instead of chemical bonding.
There are still some issues to pay attention to in multi material injection molding, the most common of which include:
1. Insufficient chemical or mechanical bonding strength between polymers, incomplete filling of single or multiple component materials;
2. Single or multiple material components exhibit flash evaporation due to burrs.
3. The injection molding machine must maintain consistency in 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 quality of injection molding. This ratio is crucial for all injection molding operations, especially in secondary injection molding.
The check device can separate the covering material like a water gate. When the secondary injection molding material is all metal, the operation of the check device is easier. If the metal substrate and more elastic plastic are used, the operation of the check device is more difficult.