SILRES® 64558 VP is designed for the formulation of silicone pressure-sensitive adhesives (PSA) and for the manufacture of composite tapes. For both applications the product needs to be processed in the presence of a condensation curing catalyst and at elevated temperature.
1. Manufacture of Mica Tapes:
Fully cured SILRES® 64558 VP is a flexible touch-dry solid body. Since it additionally provides excellent electrical insulation properties, outstanding heat resistance, water repellency and long term stability against weathering, moisture and UV light, this silicone resin formulation is often used as a binder for flexible mica tapes.
For this particular application purpose WACKER's patent specification DE 10 2005 030 discloses a simple "in-situ process" sequence which avoids the time-consuming preparation of silicone PSA formulations typically used in the past:
1. SILRES® 64558 VP is diluted by additional solvent to form a silicone resin formulation with a solids content of about 10 - 20 wt.%.
2. Before processing the curing catalyst is added. Suitable catalysts are GENIOSIL® GF 91 or WACKER® Catalyst K83, which are applied in a quantity of typically 2 - 5 wt.% (based on the solids content of the silicone resin formulation). The catalyzed formulation is then immediately transferred to the impregnation reservoir of the process equipment.
3. For the impregnation of the glass cloth the fabric web is run through the impregnation reservoir.
4. Following to this, binder-free dry mica paper web is laminated to the wet glass cloth layer by a roller set.
5. After the SILRES® 64558 VP formulation has been soaked by the mica paper, the moist bilayer assembly is dried at moderate temperature (90 to 130 °C) in a circulating air oven to remove all solvents.
6. Finally, the laminate web is fully cured under heat (150 °C or higher), rolled up in layers on a hollow roll and cut into smaller sections to give mica tape rolls of desired width.
Typical curing conditions are listed in adjacent table above. Please note: manufacturing composite tapes is a complex process that needs a thorough control of various process parameters, such as temperature, catalyst quantity, nature of catalyst, solvent composition, machine specific conditions, etc. Therefore, the following indications are intended as a guide only, and we recommend running preliminary tests to optimize the particular process conditions.
2. Manufacture of Silicone Pressure Sensitive Adhesive (PSA) Formulations:
Under heat and in the presence of catalysts that accelerate the condensation reaction if silanol groups, SILRES® 64558 VP can be converted into silicone PSA formulations. Suitable catalysts are basic compounds, such as alkali metal hydroxides, alkali metal alcoholates, tetraalkylammonium hydroxides or tetraalkylguanidinium salts, which are added in a quantity of 100 - 1000 ppm (based on the solids content of the reaction mixture).
The catalyzed blend is reacted for 1 - 3 hours at 100 - 120 °C to convert SILRES® 64558 VP into the silicone PSA compound. Silicone PSA formation is indicated by a steep increase of viscosity. The reaction is complete when viscosity remains constant for at least 15 minutes. Finally, the solids contents can be adjusted to the particular needs by either distilling off or adding solvent.
For an optimum balance of surface tack, adhesive strength and cohesive strength, the silicone PSA compound can be modified by adding some WACKER® A 232 (up to 25 wt.%, based on the solids content of the formulation) either before or after the conversion process.
Please note: reaction time and reaction temperature depend on the catalyst type and its amount used. We therefore recommend running preliminary tests to optimize the particular process conditions.
