Loudspeaker prodn. for increasing acoustic pressure or giving determined resonant response - comprises bonding metallised piezoceramic disc to metal carrier plate with non-conductive adhesive contg. filler with specified viscosity

摘要

Prodn. comprises adhesively bonding a metallised piezo ceramic disc to a larger metal carrier plate. The adhesive is a non-conductive material contg. a filler with a dynamic viscosity of 800-100000 mPa/s. USE/ADVANTAGE - The system is used for mounting in a housing to increase acoustic pressure or give a determined resonant response. The unit can be fitted and mounted by ultrasonic welding without damage. In an example, an adhesive of 0.02g bicomponent Permabond E32 (RTM) epoxy resin with a viscosity of about 80000 mPa/s is applied by screen printing centrally to a metal carrier plate with a dia. of 46mm. A piezoceramic with a dia. of 25mm and a thickness of 0.1mm is laid on it. The bonding is applied by a die with a dia. of 24mm and at a pressure of 6 bar to spread the adhesive between the two. Surplus adhesive is spread outwards to form a beading round the edge of the piezoceramic without affecting the visible insulating edge of the ceramic. In the combined hardening stage, thermal and UV energy are used so that in the thermal stage at 80 deg.C, the adhesive is hardened in the gap between the two sections, and in the UV stage at 300-400 nm wavelength, the beading is hardened and the surface is hardened at a wavelength of less than 300 nm. The finished unit has high mechanical stability for operation up to very high acoustic pressure levels and can be subjected to ultrasonic welding within a thermoplastic housing at a light pressure without exceeding a temp. of about 80 deg.C. The ultrasound for bonding is by friction at the mating surfaces of the housing sections by a sonotrode at 20 kHz at right angles to the bonding surfaces.