Adhesion of LSR (Liquid Silicone Rubber) on metal, carbon and glass surfaces

Liquid Silicone Rubber primer solution for metal, using molecular adhesives

LSR is chemically and thermally a very stable compound and hence used for a large number of applications, ranging from electrical and thermal insulations, sealings, molds for medical devices, hoses and much more in a broad range of industries. However, adhesion of LSR remains a huge challenge in general. There are silicone primers and silicone adhesives, however, many of them are not suitable for metals. Yet, for an optimal production of devices, a direct adhesion of silicone on metals may be desirable and that is what molecular adhesives can deliver.

Molecular adhesives are a special kind of stable ultra-thin (~50 nanometers) primers made on glass, metal or carbon elements. When the silicone is cured in contact with the primer, a true covalent adhesion is finally obtained from the silicone through the molecular adhesive and down to the metal part. Essentially you chemically bind the silicone directly to the element you need. The requirements of the process are that you actually handle the silicone curing and are able to do this in an over-molding process.

 

Silicone adhesion on metal parts - with cohesive strength

Examples of the RadiSurf molecular adhesive primer tested on two Pt cured medical grade LSR types. In all cases, the fracture in tensile testing is cohesive and primarily a measure of the strength of the LSR and any internal stresses.

Liquid Silicone Rubber to metal bonding for sealings or food- and medico applications

Achieving bonding between metals and LSR are often not easy, especially if you are limited in the choice of LSR and metal parts due to the requirements of the final part or regulations for medical or food applications. However, utilizing RadiSurfs molecular adhesives allow for a chemically clean, safe and direct bonding between almost any kind of metal, glass or carbon surface and the LSR part. The RadiSurf molecular adhesive is chemically clean compared to primers which often contain additives. In addition, our adhesive layer also creates a chemically strong bond to the element it is bonded to and therefore does not release any material. The result is a solution that will be safe in any kind of situation.

 

Liquid Silicone Rubber bonding on glass

With our molecular adhesives, we are able to bond to not only metal and carbon surfaces but also glass and other silicium based surfaces.

 

Adhesion for Pt cured Liquid Silicone Rubber for medical devices

Pt cured LSR are widely used in the medical industry, as platinum-based curing systems are generally considered the safest and biocompatible. However, the requirements of for a safe LSR system also limits the bonding possibilities and these LSR bonds are generally very weak when bonded to most substrates. However, by using RadiSurfs molecular adhesives we are able to make a perfectly strong cohesion and hence make the LSR the weakest part.

 

Adhesion of peroxide cured Liquid Silicone Rubber

Peroxide cured LSR require a different approach for the molecular adhesives however, the systems will in most cases work equally well and result in perfect cohesion between the cured LSR and the substrate.

 

Molecular adhesives as primers for traditional LSR adhesives

Traditional LSR adhesives most often rely on the same curing systems as the LSR compounds do. As a result, they often suffer from the same problems with weak adhesion to some substrates. Hence, you may be able to find an adhesive that works well for the LSR in question, but will not bond strongly to the hard element (metal, glass, carbon). In such situations, RadiSurfs molecular adhesives will work as an efficient primer, ensuring perfect adhesion to the substrate.

RadiSurf
RadiSurf ApS
Arresoevej 5B
DK-8240 Risskov
Denmark
Phone: +45 91 91 91 10
Email: info@radisurf.com
VAT/CVR: DK-37039403