The influence of nanoparticles on the properties of UV coatings

Over the past few years the variety of the nanoparticle offer has increased exponentially. In UV-curable coatings, nanoparticles are widely used to control two properties: aluminium-oxide and silica particles for scratch resistance, and zinc- or iron-oxide particles as inorganic UV absorbers.
The improvement in scratch resistance achieved by using nanoparticles varies from 0 to 100% of the relative gloss level of the UV-curable resin without nanoparticles. The degree of improvement depends on the resin, on the compatibility and concentration of the nanoparticle, and on the testing method used.
Iron- or zinc-oxide nanoparticles compete as UV absorbers with the photoinitiator for UV light, which could potentially lead to cure retardation. The selection of a very small particle size to give a transparent coating is not a solution, since the effectiveness of the UV absorber would be reduced in parallel. However, the relevant literature provides numerous recommendations on suitable photoinitiator selection.
To incorporate nanoparticles successfully into the coating and make the most of their advantages, the particles must be thoroughly dispersed. For transparent, low-viscosity formulations, surface modification of the nanoparticles is essential to ensure chemical and physical compatibility with the resins.

Tunja Jung, Technical Manager New Ventures, Ciba Inc.