Here at Microtips Technology we put a lot of focus on Projective Capacitive (PCAP) touch panels. This is because we see a huge trend in the industry for these products. They have far exceeded the popularity of resistive touch technology due to their highly responsive nature, wide range of applications and convenience of use. We've previously talked about how touch panels help increase the usability, intuitiveness and user friendly experience with your product, the wide range of applications, sizes and features (multi-touch, gestures, swipe, pinch-zoom), cover glass support, and so on. In this article we want to focus on one aspect of your product design: viewability. A typical PCAP stack-up can include various combinations of multiple layers of glass and film. Typical layer thickness is generally touch lens (glass or film) of 0.3~3.0mm, optically clear adhesive (OCA) of 0.05mm, and ITO glass of 0.55/0.7/1.1mm.
It's easy to see that PCAP touch panels can add quite a few extra layers of material between the user's eyes and your display, which can highly affect viewability. Specialty double sided tape materials are a common and cost effective method to adhere these layers together. However this creates small air gaps between the layers which causes a reduction in image clarity due to added ambient light reflections, Newton Ring phenomena, and reduced transmissivity leading to a loss of brightness, contrast and color saturation. This is where Optical Bonding technology really shines! Using optically clear adhesive (OCA) materials instead of tape can make a huge improvement by eliminating these air gaps. From an optical perspective it essentially creates a single layer, which by design also further improves durability among many other benefits. There are two primary methods for applying OCA material. Die-cut OCA sheets are more common as they are simple, clean, bubble free by a lamination/vacuum process, and are the easier, faster & more cost effective option. The Liquid OCA method further improves the optical benefits and adds many other inherent ones. However, the costs of liquid OCA are higher due to concerns such as longer laminating process, added UV/thermal curing, run-off and yield rate issues. Typical benefits & characteristics include 10% increase in brightness, reduced reflected ambient light, greatly improved sunlight readability, improved contrast, higher durability, better resistance to temperature/condensation/fogging, application on uneven surfaces, re-workability, no size restrictions, better adhesion, thinner and lighter designs.
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