For 4- to 15-inch displays from cell phones to monitors, a new Loctite Primer and Liquid Optically Clear Adhesive (LOCA) combination from Henkel Corporation cures in less than 90 minutes in shadowed areas where light cannot penetrate during UV cure processes. Formulated for direct bonding, Loctite 7389 Primer and Loctite 3196PR LOCA provide a solution for the cure through depth limitation of side curing, the work-in-process and potential damage to the LCD of heat curing, and the long cure time required for moisture cure. To fully leverage existing equipment, a simple, low-cost workstation positioned before lamination precisely and rapidly dispenses the primer and requires no modification or adjustment of the laminating process.
LOCAs that are not cured properly in shadowed areas can cause bubbles, delamination, MURA and/or adhesive migration into the backlight unit of the LCD. Application of the primer that ensures full cure in shadowed areas is a simple, non-invasive process that takes place off-line, directly before parts are fed into the laminating equipment.
The Loctite 200 D-Series Dispensing Robot applies solvent-based Loctite 7389 Primer to the cover glass and/or LCD using a foam transfer pad, and allows the solvent to evaporate in less than 10 seconds. The panel is then loaded into the laminating equipment, the adhesive is applied, and light cure occurs. At this point, the primer assumes responsibility for adhesive in shadowed areas, typically curing in less than 90 minutes and guaranteeing that there is no uncured adhesive that remains in the assembly.
The automated Loctite 200 D-Series robotic workstation includes an adhesive reservoir, dispense controller, and a volumetric dispense pump for accurately supplying primer to the foam transfer pad. This system is easily integrated with Loctite® robots or third-party automation systems. Studies have shown that the workstation ensures high process capability and provides application accuracy from 50 to 150 microns, values that approach those of CCD alignment.
Loctite 3196PR LOCA is a low durometer, low modulus, low shrinkage acrylic adhesive that delivers high tensile and adhesion strength on polarizer films, PMMA, glass and ITO-coated glass. This ultra-soft LOCA reduces the potential for MURA while filling gaps from 200 to 300 microns. Typical cure time in shadowed areas is 50 minutes for gaps of 100 microns and 90 minutes for gaps of 250 microns.
For more information on Loctite 7389 Primer and Loctite 3196PR LOCA, or to download a copy of the Loctite LOCA brochure, go to www.henkelna.com/loca.