When the gap between the LCD module and the front panel is filled with hardened UV curable resin, the resulting internal stress can be calculated using the following formula: Internal stress = Elasticity modulus X shrinkage during curing. If the elasticity modulus is high, warping will result in alignment errors. Substantial shrinkage during curing can result in curving. Therefore, when designing the resin, Sony strived to keep the elasticity modulus low while also minimizing shrinkage during curing to avoid optical deterioration risks associated with such problems.
The development of slimmer LCD panels has also reduced the size of the air gap. With a 4-5µm air gap, variation of just 100nm-200nm can cause alignment errors. Sony avoided this problem by reducing the elasticity modulus of the silicon gel to 5.0 X 103
Pa. This was achieved in a number of ways, including developing a resin material with a specific molecular design and meticulously adjusting its composition. Shrinkage during curing was reduced to 1.8%, compared with 6-7% for conventional acrylic UV-curable adhesives. In this way, Sony succeeded in perfecting an optical elasticity resin that does not interfere with LCD performance.
Figure 3: Comparison of optical distortion and effects on LCDs resulting from differences in shrinkage during hardening and elasticity modulus.