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Diamond carbon film coating: PET bottle's high Yin 'underwear'
compared with other plastic packaging materials, PET is the best material for soft drink packaging. This is because PET has high melting temperature, strength and transparency, excellent gas barrier performance, flavor barrier performance, low cost, easy molding and recyclability, etc.
However, PET bottles cannot meet the special requirements of some beverages, such as hot beverages and some soft drinks. PET is used for packaging beverages such as beer and fruit juice. Its barrier to oxygen, carbon dioxide, water vapor and flavor cannot meet the packaging requirements, which affects the quality of these products. Oxygen in the air is released into plastic bottles or carbon dioxide in carbonated beverages in bottles, which will accelerate the deterioration of beverages. Although other polymers (Such as PEN) It can solve the barrier problem, but the cost is too high and it is difficult to recycle. Improving the barrier performance of PET to oxygen and carbon dioxide has attracted extensive attention. At present, some technologies are to combine PET with some materials with barrier performance to improve its performance.
coating treatment of PET bottles
in order to ensure the quality of soft drinks, it is necessary to prevent gas from penetrating on the wall of plastic bottles, this requires the selection of packaging materials with low gas permeability, which are generally called high barrier packaging materials. There are four main ways to improve the gas barrier performance of PET bottles: processing by multi-layer coextrusion technology to make it have multi-layer composite structure; Surface coating treatment; Add some gas trapping agents; Blend with other materials with barrier properties. Among them, multi-layer coextrusion technology has been successfully applied at present. However, the improvement of barrier performance is small, and it is difficult to recycle and has high cost. Surface coating is a new technology used to improve the gas barrier performance of PET bottles. A very thin gas barrier film can be obtained, which can effectively prevent gas molecules from passing through the PET bottle wall and can be solved at the same time, the problem of recycling.
Some coating materials currently used have been tested in practice, among which diamond carbon film (DLC) And silicon oxide materials are very popular materials in industry. Silicon oxide coating is used to improve the gas barrier performance of PET film earlier than diamond carbon film. In the early 1980s S, silicon oxide coatings were obtained by physical vapor deposition and chemical vapor deposition. However, silicon oxide films are brittle, and relatively complicated treatment is required to obtain lasting mechanical strength on PET surface. In recent years, Diamond carbon film (Amorphous hydrocarbons) Some products coated on the surface of PET have appeared in the market, and the gas barrier performance of PET bottles has been greatly improved.
Diamond carbon film coating process
Diamond carbon film coating generally adopts plasma chemical vapor deposition technology (PCVD) Under vacuum conditions, a very thin DLC coating is obtained on the inner surface of PET bottles by plasma and bulk vapor deposition technology. The preparation process of the coating is as follows: firstly, the bottle is placed in a vacuum chamber for vacuumizing treatment, and then C2H2 gas is injected to generate isosurion and daughter of hydrocarbons under the action of frequency conversion and high voltage, finally, ions and free radicals are deposited on the inner surface of PET bottles to obtain DLC coating.
characteristics of diamond carbon film coating
DLC film contains a large amount of hydrogen, so it has very good adhesion and crack resistance, at the same time, the PET bottle has the following advantages: High gas barrier performance, blocking oxygen and carbon dioxide, ensuring the quality of the beverage; The flavor barrier performance prevents the migration and adsorption process between the bottle and the package, so that the soft drink maintains the original flavor; UV barrier performance, with the function of absorbing ultraviolet rays, to avoid the influence of ultraviolet rays on soft drinks; Chemically inert, does not react with other substances, and has Chemical stability; It is beneficial for recycling while maintaining the existing advantages of PET bottles.
DLC coating greatly improves the barrier property of PET bottles, but the barrier property of PET bottles is closely related to the change of temperature. When the temperature rises, the barrier properties of coated and uncoated PET bottles will decrease, which indicates that although the coating is a thermal stable material, the thermal movement of molecules will still affect the gas barrier properties of PET bottles.
The Development of DLC-coated PET bottles
DLC-coated PET bottles will start from the market demand and focus on the development and perfection of technology in the future. The application prospect is very promising and the market potential is very large. It is estimated to occupy 10% of PET's market share and is widely used in soft drink packaging, including tea, fruit juice, carbonated drinks, etc. At present, the packaging of tea drinks in Japan has appeared in the market, and 50 million have entered the market in 2005. With the gradual expansion of the soft drink market, DLC coated PET bottles will be further promoted and applied.