Surprise! Big Research Progress and Trend of Optical Diffusion Film

In recent years, electronic equipment such as communication lighting has been developed rapidly. For example, liquid crystal displays, notebooks and mobile phones have become indispensable electronic products in our daily life. Therefore, the demand for diffusion films used in these electronic products is greatly increased. At present, the domestic demand for optical diffusion film is conservatively estimated to be more than 1000 million m2, but most of them rely on imports from the United States, Japan and South Korea. For example, 3M company, Bright View Technologies company and Luminit company in the United States; Kimoto KIMOTO company, Huihe KEIWA company and Chi Seiji Tsujiden company in Japan; SKC company, Shihan Seahan company, Xinhe Shinwha company in Korea, etc.

The United States, South Korea, Japan and China have accumulated some research achievements in the research and development of light diffusion films. Luminit of the United States has developed a LSD light diffusion film, as shown in figure 1-7. It has the advantages of beam shaping, high transmittance, uniform light and so on. Luminit’s patented technology can precisely control the shape of the light spot by designing micro-nano structures on the surface of the diffused film to control the energy distribution of light, making it a series of round or oval shapes. The LSD light diffusion film can pass through light with a wavelength in the range of 200 nm-1500 nm, and the transmittance can reach 85% Mel 92%. LSD film has low reflectivity and can reduce the loss caused by natural light and other light reflection. LSD light diffusion film can make the point light source soft and uniform, and solve the problem of uneven distribution of point light sources such as LED and cold cathode fluorescent lamp (CCFL).

Bright View Technologies company of the United States can regulate the light diffusion film, referred to as BVT light diffusion film [54]. As shown in figure 1-8, this light diffusion film can not only eliminate dazzling glare, but also obtain uniform and soft light, and the lighting efficiency can reach 88%-96% BVT light diffusion film can form illumination forms such as ellipses, bat wings, asymmetry and circles.

A kind of light diffusion film with stretching wrinkle structure has been prepared by Takuya Ohzono research group in Japan. As shown in figure 1-9, the optical diffusion film achieves the effect of optical diffusion by adjusting the wrinkle structure of the film. When the uniaxial tensile force is applied to the light diffusion film, the film material will have the effect of wrinkling structure and optical diffusion. The effect of fold structure and optical diffusion depends on the external force applied. The greater the uniaxial force is, the stronger the effect of optical diffusion is. The relationship between stretching state and diffusion state can be explained by the relevant principle of geometrical optics.

Dr. Hu Jingang of Southeast University first explored the way of hydrothermal synthesis of large-size photodiffusion hybrid microspheres and synthesized ZnO@polysiloxane core-shell hybrid microspheres [30]. As shown in figure 1-10. The particle sizes of these microspheres are mainly distributed in the range of 5-8 μ m. The light diffusion films prepared by ZnO@polysiloxane core-shell hybrid microspheres have good transmittance and haze, and the light intensity distribution in the diffusion region is uniform. However, the preparation process of diffusion microspheres is complex, and the thickness of diffusion film prepared by the coating process is difficult to control.

The S.M.Mahpeykar research group of the University of Alberta in Canada has developed a stretchable and tunable transmission diffraction grating. PS nanospheres were arranged on the surface of PDMS by self-assembly, as shown in figure 1-11. With the help of the photon control ability of PS nano-microspheres and the characteristics of PDMS elastomers, the tunable diffraction efficiency, angle, order number, energy distribution and spectral range are realized, and the maximum diffraction efficiency is 80%. The optical diffusion film shows high efficiency and wide-band light diffusion ability, and does not depend on the polarization characteristics and incident angle of the incident light. Because of the high light energy efficiency and tunable diffraction efficiency of the optical diffusion film, it can be used for wideband photon control in solar cells and photodetectors.

HJ Kim, DW Kim and SW Kim in Korea have prepared photodiffusion films using porous silica and silicone particles as photodiffusives and PC as substrates, respectively, using extrusion molding, as shown in figure 1-13. The photodiffuser and PC were well mixed by hot pressing extrusion process, and the cross-linked structure was formed, which improved the mechanical properties of the photodiffusion film.Korean researchers S Ahn and GH Kim improved the traditional electrospray coating to spread a uniform hemispherical PMMA droplet layer on PET substrate, as shown in figure 1-12. The results show that the diffusion layer of this process is more uniform than that of the traditional method. And this improved electric injection method can obtain better diffusion effect than the light diffusion film prepared by the traditional electric injection method.

HJ Kim, DW Kim and SW Kim in Korea have prepared photodiffusion films using porous silica and silicone particles as light diffusion agent and PC as substrates, respectively, using extrusion molding, as shown in figure 1-13. The light diffusion agent and PC were well mixed by hot pressing extrusion process, and the cross-linked structure was formed, which improved the mechanical properties of the light diffusion film.

Taiwanese researchers H.P. Kuo, M.Y. Chuang and C. C. Lin studied the effect of the particle size of the selected optical diffuser on the properties of the LCD diffusion film and the relationship between the film thickness and the diffusion particle size, as shown in figure 1-14. The results show that the diffusion film has higher transmittance and haze and better optical properties when the ratio of film thickness to particle size is between 2 and 3.

Japanese researcher Hideaki Honma has developed a light diffusion film that can be selectively diffused, as shown in figure 1-15. When the light is irradiated from one side of the high refractive index material, it has the effect of optical diffusion, and the diffusion film is semi-transparent; when the light is irradiated from one side of the low refractive index material, the effect of optical diffusion is relatively weak, and the diffusion film is transparent. This kind of diffusion film has the potential to be used in special display devices.

In this paper, a UV curing imprint technology based on PDMS soft mold is proposed to prepare doped microstructure light diffusion films. A roll-to-plane UV curing nanoimprint system is used [59-60]. This method can replicate the surface microstructure of photodiffusion film without complex process or expensive equipment. The close contact between the polyethylene terephthalate (PET) substrate and the soft mold can ensure the high fidelity and uniform uniformity of the surface microstructure. By adjusting the pressure on the imprint roller, the thickness of the imprint residue of the microstructure can be controlled to be less than 10 μ m, and can be adjusted in the range of 50 μ m. When the incident light irradiates on the surface of the light diffusion film, the diffusion characteristics can be divided into two kinds: the diffraction formed by the undulating microstructure of the surface and the scattering of diffusion particles in the structure. The light is made uniform and soft by the scattering of scattered particles, and a new type of light diffusion film is controlled by the diffraction of microstructure. Satisfy the diffusion film. Towards the needs of lightweight and multi-functional development.