ASTM D 1418 Designation: FFKM

ASTM D 2000, SAE J200 Type / Class: JK, HK

STANDARD COLOR: Black

TRADE NAMES:
• Aegis® (International Seal - FNGP)
• Chemraz® (Greene, Tweed & Company)
• Kalrez® (DuPont Dow Elastomers)

RELATIVE COST: Very High

GENERAL TEMPERATURE RANGE: -25° to +575° F

Most commercial perfluoroelastomers are terpolymers of tetrafluoroethylene (TFE), perfluoromethylvinyl ether (PMVE), and a cure site monomer (CSM). The fully-fluorinated monomers contained in perfluoroelastomers are the reason they exhibit superior chemical resistance (see Figure 43). As with fluorocarbon elastomers, the bonds between carbon and fluorine atoms are extremely strong, making the chemical structure virtually unbreakable. Also, polymers with high levels of fluorine (as opposed to hydrogen) have proven to be more stable and less chemically reactive. Perfluoroelastomers also enjoy immunity from chemical attack due to saturation along the polymer’s backbone. There are no double bonds to be attacked by degradants such as oxygen, ozone, UV light, or harsh chemicals.

Perfluoroelastomers can trace their lineage back to the late 1960s, when chemists at DuPont pioneered what came to be known as Kalrez®. In so doing, they combined the chemical resistance of Teflon® and the elasticity of Viton® into a fully-fluorinated polymer that could be cross-linked. Differences in perfluoroelastomer performance are often due to the manner in which the material is cross-linked. In the early days, perfluoroelastomer compounds made use of bisphenol cross-links (like those still seen in current copolymer fluoroelastomers). Bisphenol curing works fine for fluoroelastomers, but it became clear that these bisphenol cross-links were causing perfluoroelastomers to undergo a high degree of compression set. As a result, in the mid-80s DuPont developed compound 4079. This new perfluoroelastomer formulation utilized high temperature triazine cross-links. Compression set was reduced, and, as an added bonus, thermal properties were enhanced, allowing the material to stay resilient even in temperatures approaching 600° F, 316° C (see Table 11).

Because of the presence of aggressive chemicals and the need to exclude microcontaminants, seals used in the manufacturing of integrated circuits (ICs) must withstand harsh fluids while resisting extraction. Perfluoroelastomers like Kalrez (which is resistant to over 1,600 solvents, chemicals, and plasmas) have found wide use within the semiconductor industry. Kalrez seals are also common in the oil exploration and refining industries, as well as in chemical processing and transportation seals. Be aware that Kalrez’s vulnerability to compression set generally increases as temperatures go up. Despite its overall chemical resistance, Kalrez can swell when in contact with uranium hexafluoride, fully halogenated Freon®, and some fluorinated solvents. Kalrez should not be exposed to molten or gaseous alkali metals.

As instrumental as they were to the development and acceptance of perfluoroelastomer compounds, the DuPont personnel were not the only ones on the case. At about the same time that DuPont was finding new success with triazine cross-links, another company was experimenting with peroxide cure systems. Greene, Tweed & Company started producing Chemraz® parts based on an imported peroxide cross-linked perfluoroelastomer.

Chief among Chemraz’s virtues is its outstanding overall chemical compatibility. Chemraz compounds are resistant to almost every chemical compound, including fuels, ketones, esters, alkalines, alcohols, aldehydes, and both organic and inorganic acids. Chemraz also has very good resistance to compression set, and it offers outstanding steam resistance. Chemraz has an upper temperature limit of about 450° F (232° C). As with Kalrez, Chemraz has found a place in the demanding semiconductor industry. Greene, Tweed prepares Chemraz compounds in a state-of-the-art clean room to ensure purity from the very beginning.

Not to be outdone, International Seal Company (now known as International Seal - FNGP) launched a perfluoroelastomer program in 1996. They developed their compound – known as Aegis® – with an eye toward providing a cost-competitive (yet still high performance) alternative to Kalrez and Chemraz. The 1998 merger of International Seal with Freudenberg-NOK provided significant improvements in both the technology and the processing of perfluoroelastomers. Some of IS-FNGP’s perfluoroelastomer compounds are cross-linked using peroxide; some are not.

In 1999, IS-FNGP (International Seal - FNGP) introduced five new Aegis compounds specifically tailored to the semiconductor industry, and each of these “SC” perfluoroelastomers is environment-specific. For example, SC1001 is a low compression set compound intended primarily for wet chemical applications. SC1011 is used mainly in dry process, vacuum, and plasma environments. SC1090 is the cleanest grade and is useful for both wet chemical and plasma projects. SC1070 is a high temperature formulation (viable up to 572° F, 300° C) intended for low-pressure chemical vapor deposition and furnace applications. With high temperature resistance comparable to SC1070, SC1071 is suited for aggressive plasma environments. New Aegis compounds are also being developed in response to industry needs. As a matter of fact, IS-FNGP offers a wide range of seal materials (produced in a class 100/1000 clean room) specifically designed to provide both the high purity and the extraordinary chemical resistance demanded by the semiconductor industry.

Aegis seals are also commonly used in chemical and petroleum processing, analytical instruments, automotive systems (fuel and oil), and spray painting systems. The main advantages of Aegis compounds over Kalrez and Chemraz: less compression set and higher strength at a lower cost.

FFKM PERFORMS WELL IN:
• Most chemical & petrochemical situations

FFKM DOES NOT PERFORM WELL IN:
• Uranium hexafluoride
• Fully halogenated Freon®
• Some fluorinated solvents

“The fully-fluorinated monomers contained in FFKM are the reason it exhibits superior chemical resistance.”

Figure 43

Table 11