2-component injection molding with integrated plasma pretreatment: The solution for PP-TPU composites

Join TPU to PP. Strongly bonded hard-soft combinations with Openair-Plasma®

Molded parts made from thermoplastics and thermoplastic elastomers (hard-soft combinations) are increasingly used in automotive engineering, medical engineering and consumer goods. These compounds satisfy growing quality standards for the look, feel and function of a component. The plastics processing industry is increasingly turning to multi-component injection molding as a manufacturing technology for hard-soft combinations.

Openair-Plasma® technology is already used successfully in 2-component injection molding to produce strongly bonded compounds. With the aim of extending the spectrum of materials and rationalizing the process, Plasmatreat has developed the InMould-Plasma® process in conjunction with the Plastics Technology Institute at the Paderborn University. This process can be used to join previously incompatible materials such as PP (polypropylene) and TPU (thermoplastic polyurethane) to create diverse plastic combinations.

InMould-Plasma rationalizes the 2-component process

The InMould-Plasma® process activates the plasma inside the injection mold, thereby reducing the entire manufacturing cycle to a single process step. Additional steps such as the separate plasma treatment of the semi-finished part, a downstream bonding process or the insertion of the second component (seal) are no longer needed.

Integrated, reliable process with rotary disc technology for lids with seal

For 2-component parts, plasma activation is integrated into the demonstration model illustrated using tried and tested rotary disc technology. The mold for the InMould-Plasma process is designed with three stations: 1. Production of pre-molded part (lid) 2. Plasma activation 3. Overmolding of elastomer component.

Cased lid with seal – part of the demonstration model

The plasma treatment itself takes place in an activation channel on the mold. A combination of a powerful plasma jet and a suction ensures that the plasma is conducted along the entire length of the channel. The plasma reacts with the surface of the substrate as it passes over, activating it in seconds before the overmolding of the elastomer component.

Cycle time-neutral production & full process control

The InMould-Plasma® treatment process takes only a few seconds. As a result, it is normally cycle time-neutral since it is completed in less time than required to cool the two components (thermoplastic substrate and elastomer component).

The entire plasma cycle is monitored by a plasma control unit (PCU) to ensure full process control. The PCU records the plasma power and adjusts it as required.

*The specific duration depends on the material combination and component geometry.

The compact design of the plasma nozzle allows for easy, space-saving integration into the injection mold.

Benefits as the InMould-Plasma® process

+ New material combinations
Significantly enhances the adhesive strength of material combinations that were previously difficult or impossible to join. Extends the material spectrum to include PP+TPU, PBT+TPU and TPE-S or PC+TPE-S without the need for adhesion promoters, thereby improving the compression set of the elastomer, for example.

+ Enhanced retention
Soft components such as sealing gaskets remain in position to ensure reliable assembly with minimum risk of failure.

+ Fully integrated and controlled process for quality assurance
Pressure and temperature sensors monitor the injection molding process and control plasma activation. InMould-Plasma® provides the basis for a high-quality technical process which can be monitored and controlled entirely by process parameters.

+ Allows for different mold concepts
Rotary discs, sliding tables, cube or stack turning technology – diverse tool concepts can be used with InMould-Plasma® systems. Since the process does not require any clamping force, it can also be used outside the area between the machine’s clamping plates.

+ Increased design flexibility
Soft components can be applied where they are needed or should ideally be located, for example on rotationally symmetrical components. This removes any restrictions due to geometric constraints or anchoring points for soft components.

+ Reduced production costs
The production of multi-component parts on an injection molding machine inline without the need for additional assembly processes, extensive opportunities for process and quality control, advantageous use of standard plastics – the InMould-Plasma technology offers diverse solutions for cost effective production.

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