Thermoplastic polyurethanes (TPU) are block copolymers with domains of varying length resulting in a polymer with both hard and soft domains with varying degrees of crystallization. The crystalline domains form a form of “pseudo-crosslinks” that will be broken when the polymer is heated and hence allow the use of the polymer in injection molding etc. TPU’s are widely used for properties such as:
- High abrasion resistance
- High performance at low temperature
- High shear strength
- Oil and grease resistance
TPU’s are generally produced in two forms, namely the polyester based and the poly-ether based TPU. Polyester-based TPU is generally used where mechanical requirements are high and a strong abrasion resistance is required, whereas the poly-ether types are often used due to their flexibility.
In all cases, adhesion of TPU to various materials is not easy. Due to the chemical stability of the TPU block copolymers, they generally show only weak to moderate adhesion to other materials. Common trade-names for TPU’s are Elastollan (BASF), Desmopan (Covestro), Estane (Lubrizol), Irogran (Huntsman).
TPU Adhesion using RadiSurf Molecular Adhesion
The RadiSurf technology consists of applying a nanometer-thin molecular adhesion layer on the substrate where you wish to bind the TPU. The adhesion layer is stable for prolonged storage (months) and even high temperatures (up to 100°C). The TPU may be applied on a substrate coated with the molecular adhesives layer using traditional techniques such as injection molding, compression molding or even welding techniques may be possible depending on your substrate geometry.
TPU Adhesion to Steel, Aluminum, other metals or carbon materials
The RadiSurf adhesion layers are applicable for various materials and you can obtain a strong adhesion of TPU on a broad number of materials. The major requirements for the surfaces are that they are either electrically conducting or contain a surface oxide layer. Some of the materials we can apply our coating onto are:
- Stainless steel (various alloys)
- Aluminum (various alloys)
- Carbon materials (raw fibers, glassy carbon etc.)
- Glass / Silicon surfaces
Adhesion of polyether and polyester based TPU’s
While the properties and the chemistry of the different types of TPU are very different, our adhesive layers are suitable for both types of TPU’s. However, the final strength will in large part be defined by the choice of TPU material. We have shown that we can obtain strengths with a partial cohesive fracture of both polyether and polyester based TPU systems. In all cases, however, our solution is not tested with any possible grade of TPU produced and you will always need to test our adhesion solution with your choice of material. Furthermore, process parameters play a crucial role in adhesion and an optimization of these parameters is always needed.
RadiBond™ TPU Performance data
|Pull-out tensile strength (Elastollane 1185A)|
|Stainless steel (SS316):|
|RadiBond™ TPU*||2.5 MPa|
|Stainless steel (SS304):|
|RadiBond™ TPU†||15 MPa|
|Commercial primer:||8 MPa|
|*Cohesive fracture, Clear TPU residues on steel rods †Partly cohesive fracture, TPU film on lap-shear specimens|