Surface coating improves PET bottle barrier

Polyester (PET) is one of the main raw materials in the field of beverage packaging. It has many advantages such as good transparency, stable chemical properties, relatively good barrier properties, light weight, low cost and recyclability, but as a beer bottle, PET Gas barrier is still not high enough. Therefore, improving the gas barrier properties of PET bottles is a major research direction for beer plastic packaging. Among them, the surface coating method is one of the earliest and the most studied technologies, and has become an important means to improve the gas barrier properties of polyester bottles.

The surface coating method uses a variety of high-barrier coatings and various coating techniques to form a very thin barrier layer on the inner and outer surfaces of PET bottles to block the ingress and egress of gases and achieve beer preservation and prolong shelf life.

Plasma coating technology

One of the most promising development points in various coating methods is plasma coating technology. The plasma surface treatment technology emerged in the 1960s and is a dry treatment process. It has the advantages of easy operation, cleanness, high efficiency, safety and no pollution, and can meet the requirements of environmental protection. The depth of the plasma surface treatment is nano-scale, and the physical properties of the material interface are not significantly affected while the physical properties of the material interface are significantly improved.

Diamond Type Carbon Coating (DLC)

Nissei ASB Japan cooperated with Japan Kirin Brewery, Mitsubishi Corporation and Youtec to develop a diamond carbon treatment process (DLC). The process uses high-frequency current vacuum discharge to make ionized carbon and hydrogen phase on the inner surface of the bottle to form a diamond-like carbon structure fine coating with a thickness of 20-40 nm. The material is more than 20 times more oxygen barrier than regular PET bottles, 7 times more resistant to CO2, 8 times more resistant to water, and also has improved UV resistance. The coating is not only highly transparent, the coating is soft, not easily cracked, and resistant to acids and bases. These companies are cooperating to develop industrial production equipment and plan to first promote it to the Chinese market.

Amorphous carbon coating

Amorphous carbon treatment technology (Actis) is a barrier treatment technology developed by the French company Sidel. This technology is similar to DLC technology. Plasma acetylene condenses into a layer of highly hydrogenated amorphous carbon uniform solid film on the inner wall of the bottle, with a thickness of 20-150 nm. Compared with ordinary PET bottles, PET bottles treated with Actis have a 30-fold increase in the oxygen barrier effect, a 7-fold increase in barrier properties to CO2, and a 6-fold increase in acetaldehyde penetration resistance. After the bottled beer was stored for 6 months, the carbon dioxide loss rate was only 6%, which is lower than the current 10% carbonation loss rate of the beer industry standard. The safety of the coating to food has been approved by the European Community Agency and approved by the US FDA for food packaging.

The PET bottle processed by this process has a strong advantage in recycling. Due to the small amount of coating material and the structure similar to the polymer, the fibers made from recycled Actis bottles have no effect on the physical properties and color. Mixing with other uncoated raw materials does not affect the conversion process or the final The characteristics of the package.

Sidel's first commercial device, Actis20, can process 10,000 0.6l PET bottles per hour. The equipment has been sold to the United States, Japan, Australia, Portugal and other countries.

Barrier silicone coating

Coca-Cola has cooperated with Essen University in Germany, Krones GmbH and Leybold Systems in Germany to develop the silicone-enhanced PET technology. The technology uses SiOx for physical vapor deposition under high vacuum plasma conditions, with the treatment layer on the outside of the bottle. Bottles treated with this process are said to increase barrier properties by 2 to 4 times, extend the shelf life of at least 6 months, and do not affect the odor of beer. According to Krones, the process cost of the process is more economical than using a PEN or multilayer bottle. In cooperation with Leybold, the company has installed a production line at a Coca-Cola bottling plant in Germany.

Switzerland's TetraPak Packaging has developed a technique for plasma coating the SiOx coating on the inner wall of PET bottles, which can form a glass-like barrier coating with a thickness of 0.1 to 0.2 μm on the inner wall of the bottle. Filling beer or juice with this kind of bottle, the shelf life can be extended to 4 to 12 months. The system can handle 18,000 PET bottles of 0.2 to 2.0 l per hour, and has been applied at the Spendrups Brewing Company in Sweden.

Other coating technologies

Swiss Instant Surface Technology has developed a plasma coating technology at atmospheric pressure to deposit a barrier layer on the inner wall of a PET bottle. It is said that this technology does not require expensive equipment and simplifies the coating process, and the oxygen barrier of the coated PET bottle is 10 times higher than that of the conventional bottle.

Italian company Sipa has developed an epoxy-amine topcoat PET bottle. This process uses the epoxy-amine barrier coating from PPG of the United States to form a bright, scratch-resistant barrier. TetraPak also introduced a new barrier coating technology that uses a two-layer bottle to achieve the desired barrier effect by adjusting the thickness of the barrier layer. The barrier layer uses Dow Chemical's thermoplastic epoxy resin, which has both high transparency and excellent gas barrier properties.

DuPont Polyester Co., Ltd. has developed a new two-stage coating technology that can increase the barrier to O2 and CO2 by 30 times. The primer can be separated by water and the material can be easily recycled. Another coating technology developed by DuPont, known as 'transparent aluminum', can increase barrier properties by 30 to 40 times, and the technology is close to commercialization.

However, the barrier properties provided by the surface coating technology may be affected by the specific surface area of ​​the bottle, and the internal coating may have problems with the safety of the food. In addition, the partial coating has poor flexibility, and the SiOx coating is relatively brittle and easily peels off. . Other methods also have more or less problems. Therefore, there is still a long way to go to develop new processes and improve the barrier properties of PET bottles.

News Source: China Garment Network