What Is FKM?
FKM is a rubber with excellent heat resistance, oil resistance, flame resistance, weather resistance, and chemical resistance. These physical properties are outstanding when compared to other synthetic rubbers.
FKM stands for Fluoro (fluorine), Kautschuk (German for rubber), and M Group (abbreviation for rubber classification: M is for rubber with a saturated main chain of polymethylene type).
FKM is an expensive rubber, partly because it is extremely difficult to polymerize. However, it is often used in harsh environments due to its high durability across various aspects.
Applications of FKM
FKM exhibits excellent properties in special environments. The following are some of the applications in which fluorine rubber can be used to take advantage of its characteristics:
1. Automotive Field
In the automotive field, it is used as a fuel hose due to its ability to handle gasoline evaporation. It is also used as oil seals and gaskets for sealing equipment inside automobiles due to its heat resistance and oil resistance.
2. Semiconductor Manufacturing Equipment
FKM is used because of its resistance to various chemicals.
3. Aerospace
FKM is used because of the use of highly corrosive fuels and the need for oil, heat, and weather resistance.
4. Food and Medical Fields
Fluoroelastomers are used for endoscope components, etc., taking advantage of their high acid resistance.
Characteristics of FKM
FKM is characterized by its outstanding heat resistance, oil resistance, flame resistance, weather resistance, and chemical resistance. FKM atoms easily bond with all elements. However, the C-F bond with carbon atoms in particular has high bonding energy and is electrically stable, which is also the source of FKM’s high durability.
On the other hand, the elasticity and workability of the rubber are inferior to those of other synthetic rubbers.
Types of FKM
There are several types of FKM. The main types are vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), and tetrafluoroethylene-perfluoromethyl vinyl ether rubber (FFKM).
Among these, vinylidene fluoride-based fluoroelastomer (FKM) is the most widely distributed in the market since it offers a good balance of the aforementioned various properties, processability, and price. Therefore, the term “fluoro rubber” generally refers to vinylidene fluoride rubber (FKM).
FKM can be further classified into the following three types:
1. Binary FKM
Binary FKM is a copolymer of vinylidene fluoride (VDF) and propylene hexafluoride (HFP). Binary FKM accounts for about 80% of the FKM on the market.
Since HFP contains a larger proportion of fluorine in its molecules, the larger the proportion of HFP in the polymer, the larger the proportion of fluorine in the polymer.
As the percentage of fluorine increases, heat resistance and oil resistance increase, while cold resistance decreases.
Most of the binary FKM currently traded are designed to have a fluorine concentration of 66%, which is considered to be a good balance of physical properties.
2. Ternary FKM
In addition to the above two monomers, this copolymer is copolymerized with tetrafluoroethylene (TFE). It is superior to binary FKM in most properties such as mechanical strength, chemical properties, and chemical resistance, but is more expensive.
3. Low-Temperature Type FKM
Also called cold-resistant FKM, this material is made from perfluoromethyl vinyl ether (PMVE) instead of HFP, which is used in ternary fluoroelastomers. It has high cold resistance and excellent sealing properties at low temperatures and is used in various sealing materials for automobiles.