The concept, working principle, market application of Reflective film

  Reflective film is a part of the constituent material of the LCD backlight module. It is located at the bottom of the backlight module and under the light guide plate. The function of the reflective film is to reflect the light leaking through the light guide plate back to the panel side. Thereby achieving the effect of reducing light loss and increasing brightness.

The types of reflective films are mainly divided into white reflective films and silver-plated mirror reflective films. The white reflective film can be further divided into a white polyester reflective film and a white polypropylene reflective film according to the material, wherein the white polyester reflective film accounts for more than 99.8%.

1)The white reflective film is further divided into a reflective film coated with a high reflectivity coating and an uncoated reflective film.

2)The white reflective film can be used for backlight modules of all sizes, and the silver-plated specular reflection film is mainly used for small and medium-sized backlight modules such as mobile phones and notebook computers.

3)The reflectivity of the reflective film is generally required to be above 96%, and after coating the high reflectivity coating or after mirror plating, the reflectance will increase to over 97%, and the highest will reach 100%.

4)The reflective film was originally introduced by Toray, Japan, as a low-density white polyester film, which was first used in flat panel display.

Structure of the reflective film

The white reflective film can be classified into a single layer structure, a two layer structure, and a three layer structure according to the interlayer structure.

The single-layer structure reflective film, that is, the cross-section of the whole film is uniform, the single-layer structure has a high density of reflective film, and a large amount of inorganic additives are added therein to form an opaque effect, thereby functioning as a surface reflection, single-layer reflection. The film reflectance is generally low or too thick.

The cross-section of the reflective film of the three-layer structure can be divided into a core layer and two upper and lower surface layers. The density of the reflective film of the three-layer structure is generally low, and the core layer is made a fuss by adding a small density olefin material or adding a foaming material. By reducing the density, the density can be below 0.8 g/cm3 or even lower.

The surface layer is generally made of pure polyester or appropriately filled with a part of inorganic particles to improve surface gloss and improve reflectance. The reflectivity of the three-layered inversion reflective film is generally high.

The double-layered reflective film is similar to the three-layer structure, with one surface layer missing.

How the reflective film works

When light is projected onto the surface of the reflective film, since the opacity of the reflective film is more than 99%, most of the light is reflected by the surface.

The silver-plated specular reflection film has a one-to-one correspondence between incident light and reflected light, and specular reflection occurs. The higher the gloss of the surface of the reflective film, the higher the reflectance.

The fine concavo-convex structure on the surface of the white reflective film causes the light to be reflected in multiple directions, that is, diffuse reflection, which is the main reflection mode of the white reflective film.

For white reflective films, in addition to surface scattering, a portion of the light is refracted into the film medium. The interior of the film is reflected, refracted, and re-reflected due to the presence of a large amount of filler and/or microbubbles. In particular, the refractive index of the medium in the microbubble is 1.0, and the light will be reflected on the inner surface of the microbubble and at a larger angle.

All of these complex internal structures are a good way to prevent light from passing through the film medium and change the path of the light back into the film.

Therefore, the white film not only requires high opacity, but the surface gloss at 60° angle is required to be less than 40%.

If a white coating is applied to the back of the film, or a mirror coating is applied, the reflectivity is also increased.

 Reflective film production raw materials and process technology

The production of a white polyester film by different technical means and the coating (or plating) thereon as a base film further improve the reflectance, which is a direction that is constantly being developed and improved now and in the future.

The production equipment of white polyester reflective film is a biaxially stretched polyester film production line, including storage and conveying unit, crystal drying machine, extruder and melting pipe and die, casting machine, longitudinal drawing machine, horizontal drawing machine, Traction station, thickness gauge and winding station, slitting machine and packaging.

Therefore, the white polyester reflective film manufacturing process is generally divided into drying, extrusion casting, biaxial stretching, traction winding and slitting packaging processes.