Control of Refractive Index of Pressure-Sensitive Adhesives for the Optimization of Multilayered Media

We describe the method of controlling the refractive index of pressure sensitive adhesives (PSAs) from 1.461 to 1.531 by changing the ratio of component monomers. The difference in refractive index between recording and PSA layers determines the penetration depth for recording and reading light due to multiple reflections at layer interfaces. We fabricated multilayered media that contained one, five and ten recording layers and measured their transmittances. The readout signal intensities of ten-layered media, which were fabricated using PSA films of various refractive indices, were measured. We found that a smaller refractive-index difference between recording and transparent layers led to a larger transmittance of the medium and that a refractive index difference smaller than 0.01 provided a signal sufficient for distinguishing each layer. We also calculated reflection intensity distribution for the optimization of the structure of multilayered media.