Coating technology for PET optical films is the key technology for optical films. According to the role of the coating, it can be divided into three categories, namely, protective coating, decorative coating and functional coating. By applying different coatings on PET polyester films, different functional films can be produced. For example, the surface of PET polyester film is coated with anti-scratch and anti-static coatings to make screen protection film for cell phone or computer screen surface protection; PET polyester film is coated with coatings containing optical particles or glass beads to make optical diffusion film, which can be used for LCD panel backlight module to effectively eliminate light and dark interlacing or dot phenomenon, enhance the brightness of light, and make the light emitted from the light guide plate It can be used for LCD panel backlight module, which can effectively eliminate light and dark streaks or dots, enhance light brightness, and soften the light emitted from the light guide to provide a uniform surface light source for LCD panel. There are mainly silicone coatings, polyurethane coatings and acrylate coatings or their modified derivatives.
I. Silicone coatings.
Silicone materials are generally composed of silicone oxygen links as the basic structural unit, and the side chains can be connected with various other organic groups through silicon atoms, so the structure contains both “organic groups” and “inorganic structure”. This special composition and molecular structure makes it combine the characteristics of organic materials with the functions of inorganic materials. Silicone coatings have good light transmission and are often used as a material for transparent wear-resistant coatings. This kind of coating has sufficient flexibility, and has good bonding performance with the base material; there is no double bond in the main chain, so it is not easy to be decomposed by ultraviolet light and ozone, even if it is exposed to outdoor or high ozone concentration for a long time, it will not occur cracking and viscous creep, and the physical and electrical properties are basically unchanged; resin type silicone coating material will not yellow even under strong ultraviolet light, and its color The color can be kept unchanged for many years. If suitable UV absorbers and light stabilizers are added to the coating formulations, the anti-aging properties of the coatings can be further enhanced.
The organic/inorganic composite transparent wear-resistant coating was prepared on the surface of the substrate by adjusting the pH value of the two mixed solutions and using the co-condensation reaction between the hydroxyl groups of methacryloxypropyltrimethoxysilane (KH570) as the main film-forming substance and introducing ethyl orthosilicate (TEOS) hydrolysis product silica sol as inorganic reinforcement. The coating has excellent fogging, abrasion resistance, transparency, adhesion and rupture resistance; the surface is homogeneous and flat, the pencil hardness can reach 3H~4H, and the contact angle with water is about 10°.
A hard coating containing fluoro-siloxane graft polymer and UV-curable resin is applied to the transparent film substrate, and the weight ratio of fluoro-siloxane graft polymer to UV-curable resin is preferably 0.05:100~5.00:100, and the hard coating is treated with alkali saponification. The hardness of the pencil is tested to 2H~8H. The coating can be used as a base coat for anti-reflective films when a high refractive index silicone is selected.
Add nitric acid to the combination of sodium acetate, tetraethoxysilane, methyltriethoxysilane, isopropanol and ethanol, and carry out catalytic reaction for 2h to get silica sol, which can be used as wear-resistant and anti-scratch coating.
Second, polyurethane type coating.
Polyurethane coating molecule contains a considerable number of polyurethane bonds, but also contains urea bonds, ether bonds, ester bonds, urethane bonds, its cured coating film has good wear resistance, corrosion resistance, chemical resistance, temperature resistance and elasticity and other advantages, is a coating material with excellent performance and wide application.
A coating can be made by dissolving and soaking elastic powder with xylene, then adding butyl ester, diacetone alcohol, cyclohexanone, matting powder, hand elastic paste and anti-settling agent, then adding elastic resin and leveling agent, and after coating, and conducting performance test. The results show that the coating has good adhesion, fine and smooth handfeel, strong scratch resistance and excellent corrosion resistance. Diffusion film or brightening film can be prepared by adding different particles to the coating.
By dehydrating polyether diol at high temperature and adding TDI and catalyst, a polyurethane prepolymer can be obtained; then adding dimethyl silicone oil, epoxy resin, chain extender, crosslinker, plasticizer, defoamer and filler in turn, a polyurethane coating modified with silicone and epoxy resin can be obtained. The coating film of this coating has high mechanical strength, good adhesion, low water absorption, good thermal stability and acid and alkali resistance.
The UV-curable acrylate polyurethane was prepared by introducing acrylate groups into the side chains of polyurethane using hydroxyethyl acrylate (HEA) and dihydroxyacrylate as raw materials. The coating film has better heat resistance, solvent resistance, pendulum hardness and mechanical properties than the polyurethane coating film without acrylate monomer.
Diffusion films can be prepared by applying a resin coating to a substrate such as PET film. The coating uses a polyurethane resin to which one or more organic or inorganic particles with a single particle size distribution are added as diffusion particles with a particle size of 1 to 50 μm, and modified polysiloxane (polysiloxane) or polycarboxylic acid (polycarboxylic acid) is used to improve the dispersion effect.
Third, acrylic coatings.
Acrylic coatings for optical films generally use ultraviolet curing (UV curing coating). Compared with the traditional natural drying or heat curing coating, UV curing coating has the advantages of high crosslink density, fast curing speed, energy saving, excellent coating film performance, wide range of substrates, etc., and has become an important curing process for optical film production. In addition to high crosslinking density, acrylic resins also have good wetting and dispersing properties for inorganic nano-metal oxides and organic polymer particles.