Mr. Tesch, as part of your new collaborative project, you are looking at various influencing factors and ways of improving properties with regard to the development and improvements of various plastic compounds. You yourself have been dealing primarily with the thermal conductivity factor. What role does ceramic as a material play in this context?
Tesch: A very important one. Ceramic has a few other excellent properties as a filler, but the main focus of the applications is thermal conductivity in combination with electrical insulation. In this respect, we also looked very intensively at the topic of plastic-ceramic composite materials as part of our project.
How would you describe the importance of ceramic as a heat conductor in a compound with plastic, especially in comparison to the use of other materials?
Tesch: Ceramic is an excellent heat conductor and as such can be used for a variety of materials in corresponding applications. From our perspective, we consider it primarily a functional filler from which other functional components can be created – especially in connection with its insulating properties. In this two-fold function, ceramic serves as a typical housing material, for example in engineering plastics such as polyamide or other housing materials such as PC/ABS. But in high-performance plastics, too, ceramic can add value within a component as a functional filler. In addition, there are ceramics that offer highly direction-dependent behavior in heat conduction. In comparison to mineral fillers, which generally enable direction-independent heat conduction at significantly lower heat conduction, targeted heat spots (hot spots) can be eliminated much more efficiently in applications with these ceramics.
In comparison to mineral fillers, which generally enable direction-independent heat conduction at significantly lower heat conduction, targeted heat spots (hot spots) can be eliminated much more efficiently in applications with these ceramics.
Besides heat dissipation, does it have other properties, possibly in combination with the capacity for insulation?
Tesch: Yes, but these strengths of ceramic are mainly used in connection with the properties I first mentioned. Ceramic has a relatively low Mohs hardness compared to other fillers – in hexagonal boron nitride, for example, it is merely two. This in turn ensures advantages when processing the materials, especially when it comes to wear behavior.
The low density of ceramic as a filler can offer further advantages in terms of composition, also in comparison to other materials – mineral materials, for example. This ensures advantages in lightweight applications and plays an increasingly important role today, when many applications are concerned with realising every possible way of reducing the weight of a component. Ultimately, it’s the requirements in their specific combinations that make them comparable to other fillers – in the heating sector, these are for example aluminosilicates, -oxides or -nitrides or zinc sulfites – with which ceramic competes as a filler.
And what are the disadvantages when using ceramic in compounds with plastics?
Tesch: First and foremost, it’s price. Ceramic is relatively expensive compared to most competing fillers. But you must always consider the price in relation to the respective requirements. If thermal conductivity plays a central role, if electrical insulation is needed and possibly another essential requirement such as low hardness or density, then the performance achieved with the use of ceramic fillers can actually result in cost advantages when compared to other material groups.
Besides the price factor as a possible disadvantage, you always have to keep an eye on the different types of ceramics. These can make applications comparatively more complex than with other materials. Depending on the type of filler, for instance, there is a so-called “anisometric” effect. As an example, with ceramic platelets we have to take into account the directional dependence of heat conduction both in the direction of the flow and across it.
A third possible disadvantage of ceramic as a filler can be the low impact resistance, where this or the low stretch values of the material are required. These aspects are also pronounced to a lesser and greater extent in all other fillers and are influenced not only by the filler type but also by the filler content in the compound.
We believe that there is still plenty of potential, especially in places where you can bring about advantages with regard to mechanical properties by adapting the fillers.
Speaking of price, are there also ways of significantly reducing the price when using ceramic in plastics?
Tesch: Yes, there are options here, but not with regard to the prices of the base materials – these are relatively stable. However, costs can for example be saved in component manufacturing by minimising the filler content of ceramic in the thermally conductive compound and supplementing it with a less expensive aluminosilicate. By doing this, we have been able to reduce the share of ceramic – which used to be fifty percent – to thirty, without negatively affecting the required thermal conductivity. Of course, the important thing is that the relevant requirements can be met in full.
What potential does the use of ceramic in plastics offer for the future? Are there still opportunities here, or have the limits of application already been somewhat defined?
Tesch: We believe that there is still plenty of potential, especially in places where you can bring about advantages with regard to mechanical properties by adapting the fillers. Thermal conductivity is just one side of the coin; it’s important that we can combine it with the required mechanical properties – depending on the specific requirements. We need to resolve these conflicting goals, such as generating composite materials with a high level of resilience.
A second point is the hot spots. Here, “hot spots” refer to heat sources in the housing, where high temperatures occur in great concentration in some places. Here there are attempts at avoiding such hot spots by modifying the materials that are used. The goal is to get an optimal distribution of temperature.
Thirdly, we are looking for other ways to further optimise adhesion in a compound, both organic and inorganic. Only when the process has good adhesion in the polymer can the advantages in terms of thermal conductivity and mechanical properties be fully exploited. Here, too, we believe there’s room for development. We also want to achieve greater control over the flow properties of the compounds. The viscosity changes due to high filler additions – here, too, we can influence the development of new combinations.
And from the perspective of application? What potential do you see here?
Tesch: The need for cooling solutions and thermally conductive plastics is definitely increasing – for example, when it comes to dissipating heat from LED diodes and extending the life of lighting fixtures. Heat is often perceived as a disruptive factor, not least because the corresponding components are designed to be smaller and smaller. There’s an increasing need for solutions in the field of heat dissipation, especially in the medical industry, and in particular when it comes to the handling and lightweight design of transportable devices.
Heat dissipation is also an important factor in e-mobility, for example with regard to efficiency. When it comes to cooling, convection is the decisive factor. Plastic can be used very successfully when there is no air circulating around a housing, whereas its use with forced heating, such as through flowing air or water cooling, is less successful. In this case, the thermal conductivity values of material systems that can be achieved in combination with electrical insulation are not sufficient.
Michael Tesch has been working for the Plastics Institute in Lüdenscheid since 1994. A trained toolmaker and qualified plastics engineer, he assumed management of the Institute’s laboratory in 1999 and in 2006 created the Materials Technology/New Materials division, which he has been managing since then. He has also been a member of the Institute’s management team since 2012.
Numerous material development projects have to date been successfully implemented under his leadership. In addition to topics such as flame retardancy, recycling of carbon fibres, acoustics, bioplastics and the use of natural fibres, the Institute has recently intensively examined the use of thermally conductive plastics in market-relevant applications – most recently as part of a collaborative project involving more than twenty industrial companies from different industries and industry segments.
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