The opportunity in multi-shot molding
Multi-shot injection molding and over-molding have growth potential due to their capability to simplify and streamline the production process of complex composite components. Multi-step production process with manual operations like priming, application of adhesive and assembly of complex parts with multiple material combinations, like polycarbonate and silicone or polypropylene, and soft touch polyurethane instead can be manufactured in one automated process.
To date, only a few material combinations, or even specific grades of material can be combined in a multi-shot injection molding or over-molding processes. Dissimilar materials do not adhere, and those that work have a very small process window of operation and are not very strong. Material combinations, for instance between polycarbonate and silicone, may work, but they may not be medical grade or amenable to sonic welding.
Openair® plasma technology gives new possibilities
Openair® plasma technology opens up a wide range of possibilities and enables established processes like injection molding, compression molding, foaming and over-molding to be used on a wide variety of metallic or polymer based components, including liquid silicone rubber (LSR), polybutylene terephthalate (PBT) and thermoplastic polyurethane (TPU). Not only is adhesion considerably enhanced, but also the range of possible injection temperatures is extended.
 |
A two-shot injection molded cellular phone housing made by utilizing Openair® plasma.
The base is a thermoplastic and the grip is thermoplastic polyurethane (TPU). |
The details of the exact material are critical, as illustrated by the following table. It compares the adhesion of various different thermoplastics to injection molded liquid silicone rubber (LSR/LIM) after a two component molding process. The base polymer is Silopren 2040 (standard grade) from GE Bayer Silicones.
| MATERIAL |
NORMAL PROCESS |
PLASMA PRETREATMENT |
| PBT (GE) |
- |
+ |
| PPS (Philips) |
- |
+ |
| PA 12 50GF ( Ems ) |
+
+ |
+
+ |
| PA 6T 50 GF ( Ems ) |
- |
+
+ |
| PC (Bayer) |
- - |
+
+
+ |
| PPS (Philips) |
- - |
+
+ |
| PPS (Bayer) |
- - |
+
+
+ |
| PPE+PA (GE) |
+ + |
+
+ |
| PA |
+ |
+
+ |
| PPS (Ticona) |
- |
+
+ |
Data courtesy Christoph Lange, Krauss Maffei.
The benefits of Openair® plasma technology
The benefits of using Openair® plasma technology in multi-shot injection molding are far reaching and include:
- Adhesion of a wide variety of material combinations in two-shot injection molding or over-molding of metal and polymer surfaces is enabled that otherwise would not be possible.
- Increases adhesion of existing material combinations.
- In-mold application with short cycle times, special rotating mold technology makes possible no increase in cycle time.
- Repeatable process with widely adjustable controls, leading to a larger operation window.
- Selective and complex areas can be treated.
- Environment-friendly, uses air and electricity.
- Scalable to size and complexity of product.
Partnering for success
Multi-shot molding is a rapidly developing field and there are many complexities. As we have experience working with progressive manufacturers from around the world we can assist you in making the best technical choices. By providing a development partnership for your next generation engineering components and products, PlasmatreatTM can be your effective partner in helping you develop the best and most competitive production process. |
