Wacker is attending the K 2010, with a powder additive that significantly improves the impact strength of epoxy resins without compromising their mechanical strength or heat resistance. The dispersible product, sold under the name Genioperl P52, is efficient even in small amounts. Epoxy adhesives containing Genioperl P52 can withstand heavy stresses caused by shock and vibration.

The impact modifier, which is dispersible in the uncured epoxy reaction resin, consists of spherical particles of equal size. These are composed of a soft-elastic, crosslinked silicone core and a hard shell made of an organic polymer. In the powder additive, the core-shell particles are present as agglomerates with a particle size in the double-digit micron range. The agglomerates disintegrate completely when mixed into the liquid epoxy reaction resin.

The core-shell particles distribute themselves evenly throughout the resin matrix. The polymer shell has a special structure that allows the particles to bond to the reaction resin and yield a stable, fine dispersion. It is the stability of this fine dispersion in the liquid resin and the structure of the dispersed particles which make the additive highly efficient. In contrast to conventional impact modifiers, it takes only relatively small quantities of Genioperl P52 to significantly reduce the brittleness of the cured resin. Since the amounts used are small, the epoxy resin retains its characteristic properties, especially its high rigidity and high softening point.

The particulate nature of Genioperl P52 dictates the structure of the fine disperse phase. The advantage to processors is that they can thus reproducibly adjust the end properties of the modified epoxy resin. In particular, the level of toughening is not dependent on the process conditions that prevail while the resin is curing. The special structure of the additive simplifies processing, too: the viscosity of the uncured resin mixture increases only slightly during mixing.

The toughening effect of the additive stems from the fact that the elastic silicone cores deform differently than does the resin matrix when exposed to shock. As a result of the different deformations, the energy introduced during a shock is dissipated over a larger volume than it is in a non-modified resin. In addition, the energy is absorbed in the vicinity of the particle-resin phase boundary. As a result, shock- or vibration-induced cracks in the resin matrix do not propagate uncontrollably. Since the silicone domains remain soft-elastic down to around minus 110 degrees Celsius, the toughening effect is retained even at very low temperatures.