Vertical two-color injection molding machines are essential for the overmolding of soft rubber onto hard plastic components. This process often employs secondary molding techniques and specialized two-color molds. Secondary molds, specifically designed for applying soft rubber to rigid plastic, typically utilize materials such as artificial rubber, TPU, TPR, and TPE for the soft part, while ABS and PC are common choices for the hard part.
Differences Between Secondary Molding and Two-Color Molds
A. Two-Color Molds:
This method involves a two-stage injection process on the same machine, resulting in a single ejection of the final product.
B. Overmolding Molds (Secondary Molding):
In contrast, this process allows for the use of different machines for each injection stage. After the hard plastic component is formed, it can be placed into a second mold for the injection of the soft rubber. This approach usually involves two separate sets of molds and does not necessitate a specialized two-color injection molding machine.
Key Design Aspects of Secondary Molding Molds
When designing molds for secondary molding, ensuring the precise alignment of the hard plastic component is crucial to achieving effective encapsulation. Additionally, features like undercuts on the rubber part can help prevent deformation during the process. While two-color molds permit some deformation of the rubber, they are generally more expensive and demand higher technical expertise.
It’s important to consider the potential for plastic flow during the secondary injection process, as it can lead to the deformation of the rubber component. Typically, in about 99% of cases, the hard plastic is injected first, followed by the soft rubber. Given the susceptibility of soft rubber to deformation, attention must be paid to the “adhesion” between the materials and the roughness of the mold surface. Vertical two-color injection molding machines are particularly suited for processing TPU, and a smoother mold surface can enhance the adhesion, resulting in a stronger bond between the components.
By understanding the nuances of these processes and materials, manufacturers can effectively utilize vertical two-color injection molding machines for high-quality overmolded products.
