Types Of Optical Films
Optical films are everywhere in our lives, from precision and optical equipment, display equipment to optical film applications in daily life; for example, glasses, digital cameras, various household appliances, or anti-counterfeiting technology on banknotes can all be called extensions of optical film technology applications. Without optical film technology as a development foundation, modern optoelectronics, communications or laser technology will not be able to make progress, which also shows the importance of research and development of optical film technology.
According to their use, characteristics and applications, optical films can be divided into: reflective film, anti-reflection film/anti-reflection film, filter, polarizer/polarizing film, compensation film/phase difference plate, alignment film, diffusion film/film, brightness enhancement film/prism film/condenser, shading film/black and white film, etc. Related derivatives include optical grade protective film, window film, etc.
1. Reflective film
Reflective films can generally be divided into two categories, one is metal reflective film and the other is all-dielectric reflective film. In addition, there is a metal-dielectric reflective film that combines the two, which functions to increase the reflectivity of the optical surface.
The avantages of metal reflective film are simple preparation process and wide working wavelength range; the disadvantages are large light loss and high reflectivity. In order to further improve the reflectivity of the metal reflective film, several dielectric layers of a certain thickness can be plated on the outside of the film to form a metal-dielectric reflective film. It should be pointed out that the metal-dielectric reflective film increases the reflectivity of a certain wavelength (or a certain wavelength range), but destroys the neutral reflection characteristics of the metal film.
The all-dielectric reflective film is based on multi-beam interference. In contrast to the anti-reflection film, coating a thin film with a refractive index higher than the base material on the optical surface can increase the reflectivity of the optical surface. The simplest multi-layer reflection is formed by alternating evaporation of two materials with high and low refractive indices, and the optical thickness of each film is one-quarter of a certain wavelength. Under this condition, the reflected light vectors on each interface participating in the superposition have the same vibration direction. The synthetic amplitude increases with the increase of the number of film layers.
Aluminum foil reflective film Dike aluminum foil insulation coil, also known as barrier film, insulation film, insulation foil, heat-extraction film, reflective film, etc. It is made of aluminum foil veneer + polyethylene film + fiber woven fabric + metal coating laminated by hot melt adhesive. The aluminum foil coil has the functions of heat insulation, waterproof and moisture-proof. The sunlight absorption rate (solar radiation absorption coefficient) of aluminum foil insulation coil is extremely low (0.07), with excellent heat insulation performance, which can reflect more than 93% of radiant heat and is widely used in building roof and exterior wall insulation.
The corresponding is an anti-reflection film, the main function of which is to improve the diffraction of light, so that people can watch text and graphics for a long time. This requires an anti-reflection film with a smooth surface and less reflection.
2. Anti-reflection film/anti-reflection film
Anti-reflection film is also called anti-reflection film. Its main function is to reduce or eliminate the reflected light from the surfaces of lenses, prisms, plane mirrors, etc., thereby increasing the light transmittance of these components and reducing or eliminating the stray light of the system.
Anti-reflection film is based on the wave nature and interference phenomenon of light. If two light waves with the same amplitude and wavelength are superimposed, the amplitude of the light wave is enhanced; if the two light waves have the same origin and the path difference, if these two light waves are superimposed, they will cancel each other out. Anti-reflection film uses this principle to coat the surface of the lens with anti-reflection film (AR-coating), so that the reflected light generated by the front and back surfaces of the film layer interferes with each other, thereby canceling out the reflected light and achieving the effect of anti-reflection. The simplest anti-reflection film is a single-layer film. In general, it is difficult to achieve the ideal anti-reflection effect using a single-layer anti-reflection film. In order to achieve zero reflection at a single wavelength or to achieve a good anti-reflection effect in a wider spectral range, double-layer, triple-layer or even more layers of anti-reflection film are often used.
The practical application of anti-reflection film is very extensive, the most common of which is lenses and solar cells - by preparing anti-reflection film to increase the power wattage of photovoltaic modules. At present, the anti-reflection film material used in crystalline silicon photovoltaic cells is silicon nitride, which uses plasma enhanced chemical vapor deposition technology to ionize ammonia and silane and deposit them on the surface of silicon wafers. It has a high refractive index and can achieve a good anti-reflection effect. Early photovoltaic cells used silicon dioxide and titanium dioxide films as anti-reflection layers.
3. Filters
The filter is made of plastic or glass with special dyes added. The red filter can only let red light pass through, and so on. The refractive index of the glass is similar to that of air, so it is transparent. However, after being dyed, the molecular structure changes, the refractive index also changes, and the passage of certain colors of light changes. For example, a beam of white light passes through a blue filter, and a beam of blue light is emitted, while green and red light are very rare, and most of them are absorbed by the filter.
The color filter is an important component of the TFT-LCD backlight module.
4. Polarizer
The full name of polarizing film should be polarizing film. The imaging of liquid crystal display must rely on polarized light. The main function of polarizing film is to polarize natural light without polarization, and transform it into polarized light. Combined with the twisting characteristics of liquid crystal molecules, it can control whether the light passes through, thereby improving the transmittance and viewing angle range, and forming anti-glare and other functions.
Polarizing film can be widely used in modern liquid crystal display products: LCD TVs, laptops, mobile phones, PDAs, electronic dictionaries, MP3s, instruments, projectors, etc., and can also be used in fashionable polarized glasses. Among them, the application of LCD is the main force driving the development of the polarizing film industry.
5. Compensation film/phase difference plate
The compensation principle of compensation film is to correct the phase difference produced by liquid crystal at various viewing angles in various display modes (TN/STN/TFT (VA/IPS/OCB)). In short, it is to compensate the birefringence of liquid crystal molecules symmetrically. If we want to distinguish them based on their functional purpose, they can be roughly divided into phase difference film that simply changes the phase, color difference compensation film and viewing angle expansion film. Compensation film can reduce the amount of light leakage in the dark state of liquid crystal display, and can greatly improve the contrast and color of the image within a certain viewing angle and overcome some grayscale inversion problems.
6. Alignment film
The alignment film is a thin film with straight stripes, and its function is to guide the alignment direction of liquid crystal molecules (Figure 1.1). On the glass substrate that has been evaporated with a transparent conductive film (ITO), use PI coating liquid and a roller to print parallel grooves on the ITO film. At that time, the liquid crystal can follow the direction of the grooves. Lying horizontally in the groove achieves the purpose of arranging the liquid crystals in the same direction. This film with one direction is called an alignment film.
The coating methods involved in the alignment film include non-roll wet coating, including the traditional directional brushing method and the current UV light alignment method, electron slurry alignment and ion beam alignment.
7. Diffusion film
The diffusion film is a key component in the TFT-LCD backlight module, which can provide a uniform surface light source for the liquid crystal display. Generally, the traditional diffusion film mainly adds chemical particles to the diffusion film substrate as scattering particles, and the existing diffusion plate has its particles dispersed between the resin layers. Therefore, when the light passes through the diffusion layer, it will continuously pass through two media with different refractive indices, so the light will undergo many refractions, reflections and scattering phenomena, thus creating an optical diffusion effect.
8. Brightness enhancement film/prism sheet/focusing sheet
Brightness enhancing film, also called Prism Sheet, often abbreviated as BEF, is a key component in the TFT-LCD backlight module. It mainly uses the principle of refraction and reflection of light to correct the direction of the light and concentrate the light on the front. , and can recycle and utilize unused light outside the viewing angle, while improving the overall brightness and uniformity to achieve a brightening effect, also known as a light condensing film. Composite optical film mainly integrates the functions of the original condensing sheet and the diffusion function. This will reduce the use of one diffusion sheet, which will help downstream manufacturers simplify backlight design, save processes, and reduce costs. At the same time, the brightness efficiency can also be improved. . For optical film manufacturers, although the composite brightness-enhancing film will replace the traditional condensing film (brightness-enhancing film), the unit price and profit are better.
9. Shading film/black and white glue
Black and white shading glue | shading film is mainly used on the backlight source, which plays a role of fixing and shading (shielding the side light and the light from the lamp position). It is also called shading film, black and white film, or black and white glue for short (it can be said to be a double-sided tape). Compared with the backlight source used by TFT-LCD, the shading requirements are higher, so most black and white glue is used on the backlight source of TFT-LCD. In addition to black and white glue, there is also black-black glue (double-sided black), the main function is still fixing and shading; black-silver glue (single-sided black, single-sided silver), in addition to shading, the silver side has a reflective effect. Relatively black and white glue is the mainstream product in the LCD market. In contrast to the viscosity of the black side and the white side, the white side needs to be larger, because the white side is connected to the rubber frame, while the black side is connected to the glass. Compared with the glass, the adhesion of the rubber frame to the glue is worse, so the white side needs to have a greater viscosity to ensure the stability of the entire module.
Wet coating machine recommendation:
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