PTFE High-performance Polymers
The Great Freedom of Fluoropolymers

ChemicaI resistance, working temperatures up to 250°C and exceptional slip properties: An injection moldable fully fluorinated polymer combines these properties with a high degree of design freedom. This PTFE high-performance polymer and its customized compounds therefore open a new dimension in potential applications and cost effective system solutions.

Claudia Stern
Martin Maier

Seals and engineering design elements from polytetrafluoroethylene (PTFE) and PTFE compounds have to meet extremely harsh demands in the field [1]. The composition of the novel Moldflon material, a development of ElringKlinger Kunststofftechnik GmbH, largely corresponds to conventional modified PTFE but, unlike modified PTFE, can be melt-processed. This extends the range of options available to plastics processors who are now developing new application possibilities while being able to shorten the process chain as well.

In the case of conventional PTFE at least three steps – compression molding, sintering and machining – are required to produce an assembly component. The thermoplastic processing of the new material makes it possible to even realize complex component geometries, which were previously not achievable by machining, in a single step. Particularly due to the fact that the shapes are tailor-made and that waste, which is inevitably generated when machining PTFE, is largely avoided, Moldflon now allows economical system solutions [2-4].

The key markets for this high-performance plastic material are the automotive and electronics industries, the semiconductors and life science sectors, aerospace and other industrial applications (cover photo). The savings potential for large-volume manufacturing and the production of complex components is considerable. The parts can be made using any typical thermoplastic molding process like injection molding or extrusion. In addition, when using extrusion, all kinds of fusible compounds with tailor-made properties can be made from PTFE. Since Moldflon was launched on the market in 2006 several compounds have been developed in order to meet the constantly rising demands which the user industries make on the concept design of seals and the properties profiles of the materials.

In Competition with Other High-Performance Plastics
Through targeted copolymerization of tetrafluoroethylene and perfluorovinylpropylether Moldflon can be produced as a thermoplastic material with the associated good PTFE properties. In the environment of the fully fluorinated PTFE and thermoplastic products the material ranges somewhere between modified PTFE and perfluoroalkoxy polymer (PFA) (Figure 1). With a melting point between 324 and 315 °C it is in the direct neighborhood of modified PTFE. Accordingly, Moldflon exhibits a well-balanced spectrum of properties. It is highly temperature-resistant, almost universally chemical-resistant, anti-adhesive, non-flammable, electrically insulating and possesses good non-stick/low-friction characteristics, high creep resistance and very good abrasion properties.

As a material that is suitable for thermoplastic processing, Moldflon competes with high-performance plastics such as PEEK, PPS and HT polyamides (Table 1), as well as with ceramics and metals. The material in particular excels with respect to its high permanent service temperature. Among the thermoplastic materials that have been used for many years only PEEK achieves similar thermal resistance. The service temperatures of the traditional high-performance plastics PPS, PSU and PA are clearly lower. Another advantage which Moldflon offers in comparison to the aforementioned plastics is that it retains its mechanical properties almost up to the melting point. Therefore, the PTFE derivative is the material of choice where other thermoplastics fail due to their low permanent service temperatures.

Longer Use of Components Subjected to Tribological Loads
For many applications, in addition to good temperature and chemical resistance, conformability plays an important role as well. In comparison to all plastics listed in Table 1 Moldflon exhibits very good conformability under monaxial stress, which is evident in the low modulus in tension (modulus of elasticity) and high ultimate elongation. Many materials such as PEEK, PPS and PSU exhibit considerable embrittlement above a permanent service temperature of 200 °C and are therefore not usable for applications with a deformation of >5%. This quality leap is due to the special molecular structure of Moldflon [2], which allows easier compensation for design- and production technology-based tolerances.

The excellent non-stick/low-friction properties parallel with high wear resistance. With a friction coefficient of 0.1 to 0.3 Moldflon is better than the other plastics. As a direct consequence this results in clearly longer service life of components subjected to triobological loads. In addition, fillers enable the tribological properties to be adapted to the respective requirements.

Wear-Resistant Compounds
Since they are suitable for thermoplastic processing Moldflon compounds excel in terms of their filler homogeneity. A comparison of two morphological structures (Figure 2) provides proof of this. While in the case of the PTFE-PEEK compound inert filler particles are partially embedded in the matrix, Moldflon in a melt blends with PEEK to create a uniform material and subsequently forms a homogenous morphological structure. This is the reason why compounds based on the co-polymer also exhibit lower wear than PTFE-based compounds.

In addition, Moldflon-PEEK compounds have excellent mechanical characteristics. There elongation at break, for instance, is five times higher than that of the PTFE-PEEK compounds (Figure 3).
Due to their poor setting or embedding in the PEEK matrix the PTFE particles act like foreign particles and adversely affect the mechanical properties. Therefore, ultimate breaking stress of PTFE-filled PEEK is reduced by approx. 20 % while the Moldflon-PEEK compound can fully exploit the high ultimate breaking stress of PEEK. This provides a high-performance material which combines the best properties of both base polymers and eliminates undesirable ones. Hence the application limits which have existed so far for fluoropolymers and PEEK can now be extended.

Extended Fields of Application
The first example used to illustrate this extension is friction bearings and guide bushings for the chemical, food and automotive industries and general mechanical engineering (Figure 4). Not least due to the very good tribological properties, chemical resistance and low creep tendency Moldflon and its compounds are suitable candidates in bearing technology such as in supports for rotating shafts and guides for alternating pistons and rods [5]. The advantages of Moldflon as a material for supporting and guiding parts are mainly based on its

• Low friction coefficient
• High peripheral speeds of up to 5 m/s in no-lube operation
• Outstanding wear properties
• High p Ÿ v values in no-lube operation (above 2.5 N/mm² x m/s)
• High static pressure resistance (up to 80 N/mm²),
• Low moisture absorption (no corrosion) and
• Approval qualifications (BAM, FDA, 3A etc.) which correspond to conventional PTFE

For the product launch, ElringKlinger offers a standard range of friction bearings made from various Moldflon compounds which essentially differ from commercially available products in terms of maximum peripheral speed, maximum static surface compression and maximum p Ÿ v value. In addition, the friction bearings are characterized by their good wear and damping properties plus insensitivity to edge loading. Therefore, they can be used for the desired application without any concerns. Particularly in the food industry Moldflon can be used as an FDA-conformant and physiologically harmless material.

Conclusion
Moldflon allows users to extend the range of previously used fluorothermoplastics and high-performance plastics. Because this material is suitable for thermoplastic processing it is possible to produce compounds featuring tailor-made properties for specific requirements. There are virtually no design limits when it comes to giving even complex component geometries a precise shape through injection molding.

Literature
[1] www.elringklinger-kunststoff.de
[2] Widmann, K.; Schlipf, M.: Nur ein Schritt statt drei. Kunststoffe 99 (2009) 12, S. 66-69
[3] Schlipf, M.: Viele Herausforderungen – eine Lösung. cav (2007) 3, S. 32-33
[4] Stern, C.; Maier, M.; Schlipf, M.; Sich, D.; Frick, A.: Mit neuartigen PTFE-Fertigungsverfahren zu innovativen Dichtungslösungen. 16. ISC, Stuttgart 2010
[5] Wagner, D.: Tribologisch wertvoll. KEM (2010) 6, S. 40-41

The Authors
Dr. Claudia Stern, born in 1975, is the product manager for Moldflon at ElringKlinger Kunststofftechnik GmbH, Bietigheim-Bissingen, Germany.
Martin Maier, born in 1967, is the sales consultant for Moldflon at ElringKlinger Kunststofftechnik GmbH, Bietigheim-Bissingen, Germany.

(0) Injection-molded tangential full cone nozzle made from Moldflon for cleaning small tanks and storage containers (photos: ElringKlinger)

Figure 1. The graph illustrates the positioning of Moldflon within the fully fluorinated fluoropolymers

Figure 2. The comparison between the morphological structures of compounds from PTFE+PEEK (left) and Moldflon+PEEK (right) with the same percentage-wise composition reveals the higher homogeneity in the second case

Figure 3. When comparing the mechanical characteristics, the compound from Moldflon+PEEK also ranks in front of PTFE+PEEK

Figure 4. The commercially available friction bearings made from various Moldflon compounds have tailor-made properties

Table 1. Comparison between the material characteristics of various plastics. The co-polymer Moldflon has advantages with respect to several crucial parameters