WACKER® PRIMER G 790 TOLUENE FREE 

Primer for silicone rubber
WACKER® PRIMER G 790 is a solution of reactive siloxanes and silanes in an organic solvent. WACKER® PRIMER G 790
TOLUENE FREE is free of toluene and free of other aromatic solvents. The primer composition can be applied to the
substrate as such or diluted. During evaporation of the solvent and on exposure to atmospheric humidity at ambient
temperature a rigid primer film is formed which firmly adheres to the substrate. Application of a silicone rubber onto the
primed substrate and subsequent vulcanization will then result in a tight bond between the silicone rubber and the
substrate.

 Properties
• bonding agent preferably used with addition-curing silicone rubbers
• suitable for various coating techniques like dipping, brushing or spraying
• free of toluene and other aromatic solvents

Specific features
• Adhesion promoting primer
• Solvent-based

Technical data
General Characteristics

Applications
• Arresters
• Cable Accessories
• Insulators

Application details
Bonding agent preferably used with addition-curing silicone rubbers like WACKER® ELASTOSIL® RTV-2 and LSR as well as WACKER® POWERSIL® RTV-2 and LSR. WACKER® PRIMER G 790 TOLUENE FREE is especially suited for bonding addition-curing silicone rubbers to metallic and non-metallic substrates.

Processing
Surfaces to be primed have to be dry and free from grease, oil, wax, dust, rust or other contaminants. The surface should
be cleaned, e.g. with a non-polar solvent such as mineral spirits (boiling range between 80 °C and 140 °C), followed by a
polar solvent, such as acetone. Very smooth surfaces may be roughened by grinding. In case of metals the substrate
should be given several hours time to regenerate its oxygen layer before applying the primer. Loose particles must be
removed.

The primer may be applied directly or in diluted form with a variety of application methods (e.g. coating, dipping, brushing
or spraying). The resulting primer layer should be as thin as possible. Usually the best results can be achieved with a primer
layer between 1 an 10 μm thickness, corresponding to a coating weight of 5 to 50 g/m². If the primer needs to be diluted,
organic solvents like white spirits or ISOPAR® E can be used in a ratio of up to 1:10.
If a visual control of the applicated primer layer is desired, it is possible to add a red color concentrate to the primer. Please
get in touch with your technical or sales contact at WACKER for further information.

Evaporation of the solvent should be done at ambient temperature. The formation of a consistent primer film which firmly
adheres to the substrate requires a certain atmospheric humidity. Higher or lower humidity will reduce or prolong the
necessary reaction time. As a guiding value an evaporation or drying time of 1 – 2 h at ambient temperature and 40 %
relative humidity should be applied to allow for a formation of a consistent primer film. In some cases the adhesion can be
improved by heating the primered substrate at 100 – 150 °C for up to one hour after evaporation of the solvent at room
temperature. Tests should be performed if special conditions are needed.

The silicone rubber should be applied to the primed surface soon after the drying or heating process, if possible. It is
recommended that this is done not later than approximately 5 hours after priming the substrate. Otherwise a drop in
adhesive strength may occur. Prior to the application of the silicone rubber, the primed surface has to be kept free of
contaminations.

Important:
Initial adhesion directly after vulcanization of the rubber will in many cases be high already. In some cases, however, initial
adhesion will be sufficient for handling the composite while maximum adhesive strength will only be achieved after about 4
days. ELASTOSIL® AUX PRIMERS are sensitive towards humidity. In contact with moisture the liquid primer becomes
turbid and the adhesive strength of the primer is impaired. The ELASTOSIL® AUX PRIMERS should therefore be stored in a
sealed container after usage.
For detailed information, refer to brochures on www.wacker.com.

Packaging and storage
Storage
The ‘Best use before end’ date of each batch is shown on the product label. Storage beyond the date specified on the
label does not necessarily mean that the product is no longer usable. In this case however, the properties required for the
intended use must be checked for quality assurance reasons.

Safety notes
Due to its high content of organic solvent WACKER® PRIMER G 790 TOLUENE FREE is subject to the same safety
regulations as these, i.e., it is a flammable liquid. Appropriate precautions are an absolute must. Comprehensive
instructions are given in the corresponding Material Safety Data Sheets. They are available on request from WACKER
subsidiaries or may be printed via WACKER web site http://www.wacker.com.