Natural rubber comes from a milky emulsion in the sap of several varieties of plants, called latex. Given the growing world market shortage of natural rubber supply, the demand for sythetic rubber is increasing. Synthetic rubbers offer a very wide range of properties, some far exceeding those of natural rubber. Sythetic rubbers are produced through the polymerisation of a variety of monomers to produce polymers. Synthetic rubber is an elastic hydrocarbon polymer, also called an elastomer and is a thermoset material. Thermoplastics are materials with the property becoming hard and rigid when cured and are moldable when heated. Rubber softens or fuses when heated and hardens and becomes semi-rigid again when cooled without undergoing any appreciable chemical change. Different chemical properties in the various synthetic rubbers, and varying thicknesses, affect the rubber's coefficient-of-expansion COE, which is a critical issue which must be addressed in bonding for long term deployment.

Synthetic rubbers include:

EPM and EPDM (ethylene propylene rubber)
Aflas
Nitrile
Polyisoprene and butyl
Polybutadiene (Styrene Butadiene Rubber or SBR) or Nitrile called buna N rubber)
Chloroprene, also called neoprene
Silicone RTV (Room Temperature Vulanized)
FKM Viton®, Tecnoflon®
Santoprene® (PP and EPDM)
Flouorosilicone Rubber
Polyurethane Rubber
Epichlorohydrine Rubber (ECO)
Polysulfide Rubber
Cholorsulfonated Polyethylene (CSM), (Hypalon®)

The field of thermoplastic elastomers (TPE) has grown rapidly in the last twenty years. There are three general classes of TPE.

Thermoplastic vulcanizates,the fastest growing class of TPE's perform like thermoset rubbers. Silicone rubber is vulcanized using peroxide or sulfur and, sometimes, platinum to cure it. Silicone rubbers, such as caulking compounds, are composed of one or two part liquids, cured with moisture or platinum or metal.

Block copolymers, comprise the second class, where one region is rubber and the other has a rigid nature, and includes styrene block copolymers (SBCs or styrene-butadiene-styrene or SBS), copolyester TPEs (COPEs), thermoplastic urethanes (TPUs) copolyamide TPEs (COPAs) and melt-processible rubber (MPRs).

The third class are rubber/plastic blends including thermoplastic olefins (TPOs) where EP rubber and polypropylene are blended and the polyvinyl chloride / nitrile rubber blends (PVC/NBRs). A key process for the manufacture of TPE parts is injection molding. TPE's are used in a huge variety of industries to mold parts, among them are automotive, medical equipment, appliance construction, architectural seals, highway markers, agricultural and construction equipment assembly, electronic component manufacturers (feet, soft touch buttons and panels, plugs, connectors, insulation, wire jacketing, cladding), Hose and tubing manufacturers, tool grips, strain relief, containers, plumbing and faucet seals, sporting goods, toy manufacturers, etc.

Successful long term bonding of rubbers to themselves -- and to other substrates -- requires careful preparation and matching of the adhesive being used with the differing coefficient-of-expansion (COE) and chemistries of the substrates involved. This COE differential is not usually an issue in bonding rubber to rubber but may be an issue when bonding rubber to rigid substrates, such as metal, glass, ceramic or other substrates -- depending on the rubber. BONDiT^TM products are among the few available that can be used to bond rubber to substrates with differing COE's and chemistries for harsh environments and long term deployment without debonding.

Our first recommended product for the vulcanized rubbers is the BONDiT^TM B-45. BONDiT^TM A-43 will bond to cured RTV silicone as a primer. BONDiT^TM B-45 will then bond to the A-43.

Our recommendation would change if Aflas or silicone rubber or RTV silicone is one of the substrates, in which case we recommend priming that substrate with an adhesion promoter, such as BONDiT^TM A-43, prior to using B-45. If bonding EPDM or neoprene to silicone, we recommend priming the silicone with A-43, coating C-31 on top of that, and then vulcanizing the EPDM rubber to silicon rubber.

Among the other substrates to which rubber can be bonded using BONDiT^TM products are: UHMW, Delrin, flouropolymers, polyethylene, polyolefin, polypropylene, polyurethane, silicone, thermoplastics, thermoset, urethane, other rubbers, ceramics, glass, fiberglass, wood, metals, stone, aggregate and concrete.

Your application may call for other BONDiT^TM adhesives or primers, depending on the resistance to chemicals, moisture or impact, or elongation required. To see our tables comparing properties of the various BONDiT^TM products click here. Call or email us for advice on COE ratings and matching BONDiT^TM products for your specific substrates and application at (707) 284-8808 or reltek@reltekllc.com.