The properties and benefits of optical elastic resin (SVR)

Basic SVR requirements

Dexerials manufactures optical elastic resin (SVR) that bonds the top plate and LCD module in smartphone displays by filling the air gap between the substrates.. This resin improves visibility and impact resistance of liquid crystal display (LCD) screens. The below explains the requirements for SVRs to ensure functionality.

The first requirement is that they must remain colorless and transparent even after UV curing and under any usage conditions. SVRs are used to improve screen visibility, so it would be problematic if the resin deteriorated and changed color due to sunlight or other factors. In addition, since SVRs function as an adhesive to bond the top plate and LCD, it is important that the adhesive does not peel off after bonding. The SVR lamination process also requires that the liquid SVR has adequate fluidity to fill the air gaps between the substrates. Furthermore, the resin must prevent optical non-uniformity caused by shrinkage that occurs after UV curing process and be flexible enough to absorb the generated force. Dexerials’ SVRs have met all the above-mentioned requirements.

Measures to prevent optical non-uniformity of LCD caused by UV-curing process

Display optical defects can occur if SVR flexibility is not sufficiently retained. The photo on the left below shows the results of a test that intentionally produced cell phone LCD screens with optical non-uniformity due to the shrinkage of resin. The photo shows that the peripheral areas have turned square and white. This unevenness is caused by the resin shrinking as it cures, pulling the bonded LCD toward the center of the screen and deforming part of the flat material. If the resin itself has a low shrinkage rate and is flexible enough, it will not generate enough stress to change the orientation of the LCD or induce any irregularities.

Flexible SVRs that match the top plate’s shape and prevent delamination

SVRs have been increasingly used in automotive displays. These SVRs also require flexibility in some cases. While most recent smartphone displays use glass for the top plate, most in-vehicle displays use plastic top plates to prevent glass from shattering in the event of a collision. However, plastic is susceptible to significant curvature under the influence of humidity and temperature, so it is necessary for SVRs to have a resin designed to withstand such factors. An effective approach is to improve the flexibility of the resin so that even if the bonded top plate curves and changes shape, the resin will stretch with it and prevent delamination.

The material composition determines the traits of the SVR

SVR formulations are based on UV-curable acrylic resins to achieve abovementioned properties. By selecting and controlling the appropriate amount of the right material, parameters such as viscosity, hardness, curing speed, shrinkage rate, refractive index, and elastic modulus can be customized to meet the specifications required by the customer. As an example, below is a table with specifications for two types of Dexerials SVRs for small and medium-sized flat panel displays, which are used in mobile and automotive displays. Dexerials also offers other SVRs for thin and high-contrast displays in large-size TVs and signage applications. SVR product line-up  is designed to meet the various needs of many customers.