Overmoulding
Over moulding or ‘insert moulding’ consists of placing a preformed part (or section of a part) into an injection mould and injecting a material around it. If the insert and the TPE are compatible a melt bond occurs between the two materials. The strength of this bond is affected by several factors, including interface temperature, cleanliness of the insert and the melt temperature of the TPE.
Engineering plastics, to which Dryflex and Mediprene have documented good adhesion include; PP, PE, PA6, PA66, PC, ABS, PC/ABS, ASA and SAN. Non-compatible materials can also be overmoulded, either by using an adhesive to create the bond or designing a mechanical lock into the part.
2K (Two shot moulding)
Two-shot injection moulding involves first injecting one material into a mould to form the initial part or section of a part. Once formed, a second material is injected into the mould to form the remainder of the part. Dryflex and Mediprene can be either the first or second material injected.
Dryflex and Mediprene TPEs can be combined with compatible polymers through several types of multi-shot injection moulding processes. By combining multiple materials, an even wider variety of applications is possible.
Setting Parameters
The following recommendations are intended to improve the adhesion between Dryflex and the engineering plastic.
1. High mix temperature
2. High injection rate
3. The mould temperature of the TPE part should be in the range of 20°C to 60°C
4. Avoid excessively high holding pressures
5. Avoid shrink marks
6. Highest possible injection pressure
7. Pre-drying of hygroscopic (moisture absorbing) materials
8. Homogeneous preheating of the engineering plastic (approx. 100°C is ideal)
9. Dry, clean and smooth surface of the engineering plastic. The surface should not be structured
10. Sufficient thickness (at least 1.5 mm) of the TPE part
11. Venting of the mould
12. Location and design of the gate
The setting parameters 1 - 6 are easiest to implement, since they involve only the machine settings, while parameters 7 - 9 are pre-treatment stages. These can be simplified if production of the engineering plastic part and the application of Dryflex or Mediprene take place in a continuos process in an over moulding machine. Parameters 10 - 12 concern the mould and should be considered at the mould design stage.
We are happy to advice our customers on mould design and processing techniques, please contact us with any questions you may have. Alternatively, a more detailed explanation of the setting parameters is available by downloading our Processing Guide for Adhesion.
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