Esschem

Gary R Shaw

Susan C Sheariss

George F Cowperthwaite

The disclosed method for making hollow shells (e.g. housing for in-ear hearing aids) employs a radiation-curable polymer comprising (a) a major amount of urethane methacrylate monomer (molecular weight 360-950) having a viscosity less than about 15,000 cps at 25.degree. C., (b) a viscosity-adjusting minor amount of unreacted hydroxyalkyl-methacrylate monomer, (c) a photoinitiating amount of a photoinitiator of the formula Ar.sup.1 --CO--C(OR).sub.2 --R', where Ar.sup.1 is aryl (e.g. phenyl), R is C.sub.1 -C.sub.4 -alkyl (e.g. methyl), and R' is hydrogen or alkyl or, preferably, aryl, and, optionally, (d) a coloring agent, e.g. a pigment concentrate. Viscosity control is of major importance; so the curable composition is generally solvent-free and free of viscosity-modifying solids (other than coloring agents). Acrylates (as distinct from methacrylates) are also omitted. The fully-formulated, curable composition is easily pourable and has a viscosity of less than about 2,000 cps. The hollow shells are made by:

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Norristown, PA, United States of America

Gary R Shaw