(255bj) Organically Modified Clays As Rheology Modifiers and Dispersing Agents for Epoxy Packing of White LED

We develop a new class of polyetheramine-modified organoclays that enable the homogenous dispersion of inorganic phosphorescent phosphor powder, yttrium aluminum garnet Y₃Al₅O₁₂ (YAG), in epoxy, which can then be used for packing of light-emitting diode (LED) devices. The organoclays are prepared from the ionic exchange reaction of sodium montmorillonite (Na⁺-MMT) with poly(oxypropylene) (POP) diamines of sufficiently high molecular weight, which are found to be effective for homogenizing YAG in the two-component epoxy system involving an anhydride curing agent and an aliphatic epoxy resin. By adding the POP-diamine-based organoclays, the viscosity of the anhydride/epoxy resins is greatly enhanced and the resin shows a non-Newtonian shear-thinning behavior. Because of the high viscosity that retards the molecular motion, the micrometer-scaled YAG particles can remain dispersed in the resins for a fairly long time without precipitation during the curing process. We investigate the rheological properties of the organoclays as the thickening agent and applied the organoclays to fabricate YAG particle-dispersed epoxy for packing of blue light LED that mixes the yellow light of the well-dispersed YAG particles to form uniform white illumination.