Norland UV Sealant 91 ("UVS 91") is a screenable paste adhesive specifically designed to seal the perimeter of liquid crystal displays. It provides the ultimate solution for manufacturing displays because it is a single component, solventless, sealant that cures quickly at room temperature by exposure to UV light. UVS 91 is cured by ultraviolet light with maximum absorption within the range of 320-380 nanometers and peak sensitivity around 365nm. The recommended energy required for full cure is 4.5 Joules/cm2 in these wavelengths. The cure is not inhibited by oxygen, hence any areas in contact with air will cure to a non-tacky state when exposed to ultraviolet light.
The overall benefit to the user is simplification of the operation which saves time while still providing a high quality product.
|Elongation at Failure||58%|
|Modulus of Elasticity (psi)||45,000|
|Tensile Strength (psi)||2,900|
|Hardness - Shore D||55|
|Water Absorption (24 hrs @ 50° C)||0.14%|
|Shear Strength - Glass to Glass (psi)||850|
Figure 1 shows the viscosity vs shear rate as measured on a plate and cone viscometer. UVS 91 is formulated to allow easy screening in thin layers. The viscosity is designed to flow under shear and to be relatively high on standing.
One of the major advantages of UVS 91 is its non-reactivity with liquid crystal chemistry. Figure 2 below shows the typical compatibility of this material with liquid crystals. UVS 91 shows no contamination when used to make cells with an undoped ester liquid crystal even under accelerated heat aging at 100° C.
The adhesive should be screened onto clean glass or metaloxide surfaces. No primers are required. A 350 to 400 mesh polyester screen is recommended to provide the very thin coatings necessary for LCD's. Adjust the screen tension and application pressure to get the coating thickness desired.
When the top plate is laminated to the bottom, even pressure must be applied to bring the spacing in all areas down to the required distance. Controlled size spacers are often added to the adhesive or sprayed onto the surface to provide the exact distance for each application.
The display is then placed on a conveyor which travels under a high intensity UV light source. Curing occurs in 5 to 10 seconds using a 1000 watt or 1500 watt medium pressure mercury lamp @ 4 to 6 inches. Conveyor speed would be approximately 12 ft/min to accomplish this. For small production or test work, curing can be accomplished in 5 minutes with a 100 watt mercury spot lamp at a distance of 12 inches. Longer exposure to UV light will in no way harm the adhesive.
Clean up of equipment can be accomplished with acetone or trichloroethylene. Care should be taken in handling this sealant. Prolonged skin contact should be avoided and affected areas should be washed well with soap and water. Avoid prolonged vapor inhalation and use in a well ventilated area.
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