The study of light guide plate fabricated by inkjet printing technique

Abstract

When molding thin light guide plates, high injection speed and high molding pressure are required to fill the mold completely, but it is easy to have parts with defects like high residual stress and high warpage. Inkjet printing is a drop-on-demand (DOD) and direct writing process, there is no need to fabricate stampers for the DOD processes thus it saves lots of time on the development of light guide plates. With those benefits, back light unit suppliers around the world have envisioned the DOD process as a great potential for fabricating thin light guide plates. The aim of this study is to develop a complete light guide plate fabrication process using inkjet printing technology. That includes ink selection, substrate surface treatment, microlens array design, printing process parameters determination, and printing qualities investigation. A Dimatix DMP-2800 inkjet printing machine is used for printing the microlens and a polyacrylamide-based ink is selected. To make the PMMA substrate more hydrophobic, it is coated with a thin Teflon layer before the printing process. For this specific combination of machine, ink and substrate, when the distance between inkjet nozzle and substrate is 0.7mm and the driving voltage is 12V the printed microlens has the best quality. Referring to the microlens size of light guide plates made by industry, the microlens with 38μm in diameter and 26μm in height are selected for this study. A 3″ light guide plate, designed with TracePro software, is successfully fabricated using the proposed ink-jet printing scheme. The optical measurement result indicated that the light guide plate has an averaged luminance of 1012.58 nits and a luminance uniformity of 83.85%. Thus work demonstrates the feasibility and effectiveness of utilizing inkjet printing technique to prepare light guide plates with low cost.