UV display adhesives are commonly referred to as LOCA, otherwise known as liquid optically-clear adhesives. This specific type of adhesives is primarily used for the electronic industry, including products such as smartphones, touchpads, LCD screens and much more. Due to its rapid drying process, high transmittance and low shrinkage, LOCA has become an increasingly useful product among small businesses and larger corporations.
Several pieces of technology such as laptops, televisions, monitors and cell phones contain an air gap between the module and the cover glass. The touch interface will become universal within the next several years, leading manufacturers to enhance customer satisfaction through the strategies listed below.
- Improvements in the Viewing Experience –Through both LOCA and A/R glass, the contrast ratio can increase by 400% in the sunlight.
- Better Display Toughness – The falling ball impact resistance can increase by up to 3x depending on the gap size.
- Longer Battery Life – The battery life can be significantly extended by minimizing the light loss caused by reflection. This allows the user to have a better viewing experience without the need to maximize backlight power.
- Extended Display Product Life & Thinner Designs – LOCA increases the durability of a display to heat and moisture. Additionally, UV display adhesives allow for thinner designed electronics because they absorb the impact of a given load. Absorbance of impact is directly correlated with the adhesives modulus. The lower the modulus the more force is absorbed by the adhesive.
Applications Where LOCA is Utilized
Touch Panel Sensor
LOCA can be used to laminate two layers of ITO coated glass in a touch panel sensor, however, a majority of the time the two ITO layers can be placed on a single layer of glass. Some of the requirements include a low viscosity and durometer, high adhesion to glass, greater than 99% transmission, less than 1% haze, low shrinkage, yellowness (b*)<1, thermal shock and long term resistance to UV light.
Cover Lens Bonding
In order to sufficiently optimize the viewing experience, the air gap between the cover lens and touch panel sensor must be filled. Similar to a touch panel sensor assembly, this is a tight fitting application and contains the same key performance requirements.
Direct bonding allows the highest amount contrast and get the image close to the user. The LCD module is typically protected from degradation caused by expansion, contraction and impact due to the high bondline gaps. A high viscosity dam is typically required by higher gaps because they increase the edge definition. Key performance requirements include low viscosity, very low durometer, high adhesion to plastic and glass, greater than 99% transmission, less than 1% haze, yellowness (b*)<1, low shrinkage, long term resistance to UV light and thermal shock, and resistance to MURA.
General Requirements for LOCA
Some of the typical requirements for LOCAs are fast curing, optically clear, particle free, similar refractive index to glass, low shrinkage, low modulus, low hardness and high elongation.
There cannot be performance degradation after high temperature high humidity testing (65C/90%RH or 85C/85%RH), high temperature aging (85C or 95C), low temperature aging, UV aging, thermal cycling or thermal shock.
Why Low Modulus is Important for LOCA
A low modulus is one of the most critical elements when it comes to UV display adhesives. All UV acrylates reduce in size, whether minimally or otherwise, during cure. When you have a lower modulus, you will notice a greater reduction of MURA (fuzziness around the edge or center of a LCD screen). Mura can be caused by the stresses between the adhesive and substrate during shrinkage. The lower the modulus the less stress between the adhesive and the substrate. It’s important to note modulus become more important as screen size increases.
Choose Resin Designs for UV Display Adhesives
Resin Designs offers custom UV display adhesives for the aerospace, automotive, electronics, industrial and communications industries. Our Vivid Cure 70501 is a fast curing, water white, urethane acrylate that is specifically designed for LCD displays. This product offers a high amount of bond strength, excellent moisture and yellowing resistance. Additionally, the glass transition temperature of the Vivid Cure 70501 is low (-35 degrees C) which is quite unique considering a majority of LOCAs turn to into “rock” at lower temperatures. In fact, since other adhesives have higher glass transition temperatures, they do not have the same modulus properties at lower temperatures.