Overview
Optical bonding, including LOCA and non-liquid OCA tape, are used in a wide range of electronic equipment, especially those with touch panels. The adhesive bonds the touch panel to the main liquid crystal display, and also bonds any protective cover, such as the lens, to the touch panel. After application, the adhesive is cured onto the device through ultraviolet light (UV), heat, moisture, or a combination, depending on the manufacturer and specifications. Major applications include capacitive touch panels, 3D televisions (3D TV), and glass retarders.
Optical bonding improves optical performance of displays. It eliminates the air gap between the cover glass and LCD, and usually includes an anti-reflective (A/R) coating (as well as anti-smudge and anti-glare treatments on the cover glass). Optical bonding improves the contrast ratio by reducing the amount of reflected light, thus improving viewability. This is especially important in outdoor applications, where direct sunlight can decrease viewability. [1]
Fresnel reflections from the glass as well as the adhesive can degrade LCD viewability. Reflection is caused by an impedance mismatch between air and the glass. The reflection makes the white brighter, but dilutes black and other colors, which decreases contrast. LOCA suppliers aim to match the refractive index of glass and clear plastic PMMA (refractive index approximately 1.5) used in displays to minimize loss. LOCA suppliers such as Momentive Materials and Henkel report an increased contrast of 400% in sunlight through the use of LOCA with anti-reflective glass, vastly improving the viewing experience. [2]
Besides the optical advantages, bonding a sheet of glass to the LCD also improves display durability. It can resist scratches, condensation, and has an improved operating temperature range. As touchpad devices become ubiquitous in consumer markets, this increased ruggedness becomes even more important. Also, reducing light loss due to reflection extends battery life, as the device can use less backlight.
Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation.
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color or monochrome. LCDs are available to display arbitrary images or fixed images with low information content, which can be displayed or hidden: preset words, digits, and seven-segment displays are all examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.
Poly(methyl methacrylate) (PMMA) is the synthetic polymer derived from methyl methacrylate. It is used as an engineering plastic, and it is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Hesalite, Plexiglas, Acrylite, Lucite, and Perspex, among several others. This plastic is often used in sheet form as a lightweight or shatter-resistant alternative to glass. It can also be used as a casting resin, in inks and coatings, and for many other purposes.
Liquid crystal on silicon is a miniaturized reflective active-matrix liquid-crystal display or "microdisplay" using a liquid crystal layer on top of a silicon backplane. It is also referred to as a spatial light modulator. LCoS was initially developed for projection televisions but is now used for wavelength selective switching, structured illumination, near-eye displays and optical pulse shaping. By way of comparison, some LCD projectors use transmissive LCD, allowing light to pass through the liquid crystal.
A touchscreen or touch screen is the assembly of both an input and output ('display') device. The touch panel is normally layered on the top of an electronic visual display of an electronic device.
In photography, a viewfinder is a small window the photographer looks through to see what a photo will look like before they capture it.
Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication.
Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers are often one- or two-part polymers, and may contain fillers to improve properties or reduce cost.
Loctite is an American brand of adhesives, sealants, surface treatments, and other industrial chemicals that include acrylic, anaerobic, cyanoacrylate, epoxy, hot melt, silicone, urethane, and UV/light curing technologies. Loctite products are sold globally and are used in a variety of industrial and hobbyist applications.
An electrochromic device (ECD) controls optical properties such as optical transmission, absorption, reflectance and/or emittance in a continual but reversible manner on application of voltage (electrochromism). This property enables an ECD to be used for applications like smart glass, electrochromic mirrors, and electrochromic display devices.
Anisotropic conductive film (ACF) is an adhesive interconnect system that is commonly used in liquid crystal display manufacturing to make the electrical and mechanical connections from the driver electronics to the glass substrates of the LCD. The material is also available in a paste form referred to as anisotropic conductive paste (ACP), and both are grouped together as anisotropic conductive adhesives (ACAs). ACAs have more recently been used to perform the flex-to-board or flex-to-flex connections used in handheld electronic devices such as mobile phones, MP3 players, or in the assembly of CMOS camera modules.
A defective pixel is a pixel on a liquid crystal display (LCD) that is not functioning properly. The ISO standard ISO 13406-2 distinguishes between three different types of defective pixels, while hardware companies tend to have further distinguishing types.
An electronic visual display, informally a screen, is a display device for presentation of images, text, or video transmitted electronically, without producing a permanent record. Electronic visual displays include television sets, computer monitors, and digital signage. By the above definition, an overhead projector could reasonably be considered an electronic visual display since it is a display device for the presentation of an images, plain text, or video transmitted electronically without producing a permanent record. They are also ubiquitous in mobile computing applications like tablet computers, smartphones, and information appliances.
Optical bonding refers to a protective glass that is glued in front of a display to enhance its readability where installed in high humidity outdoor environments. When a normal display is used in an outdoor environment, there are some factors that affect its readability. The most common one is “fog”, or condensation, which forms on the inner surface of display's vandal shield. Another factor is the reflection of sunlight, which causes a mirror-image on the display. Both phenomena can be solved by using optical bonding.
IPS is a screen technology for liquid-crystal displays (LCDs). In IPS, a layer of liquid crystals is sandwiched between two glass surfaces. The liquid crystal molecules are aligned parallel to those surfaces in predetermined directions (in-plane). The molecules are reoriented by an applied electric field, whilst remaining essentially parallel to the surfaces to produce an image. It was designed to solve the strong viewing angle dependence and low-quality color reproduction of the twisted nematic field effect (TN) matrix LCDs prevalent in the late 1980s.
Zytronic is a manufacturer and developer of touch technology products based in Blaydon upon Tyne, United Kingdom.
One Glass Solution (OGS) is a touchscreen technology which reduces the thickness of a display by removing one of the layers of glass from the traditional capacitive touchscreen stack. The basic idea is to replace the touch module glass with a thin layer of insulating material. In general, there are two ways to achieve this.
Adhesive bonding is a joining technique used in the manufacture and repair of a wide range of products. Along with welding and soldering, adhesive bonding is one of the basic joining processes. In this technique, components are bonded together using adhesives. The broad range of types of adhesives available allows numerous materials to be bonded together in products as diverse as vehicles, mobile phones, personal care products, buildings, computers and medical devices.
