Using Surface Coating Method to Effectively Improve PET Bottle Barrier Property

Polyester (PET) is one of the main raw materials in the field of beverage packaging, and has many advantages such as good transparency, stable chemical properties, relatively good barrier properties, light weight, 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 to 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. Plasma surface treatment technology emerged in the 1960s as a dry treatment process. It has the advantages of simple operation, cleanness, high efficiency, safety, and no pollution, and can meet the requirements of environmental protection. The depth of plasma surface treatment is nano-scale. The physical properties of the material interface are significantly improved while the material body is not affected.

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 the ionic hydrocarbon 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 has 8 times higher oxygen barrier properties and 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

Non-conservative carbon treatment technology (Actis) is a barrier treatment technology developed by the French company Sidel. This technology is similar to DLC technology in that plasma acetylene condenses into a layer of highly hydrogenated amorphous carbon homogenous solid wax on the inner wall of the bottle, with a thickness of 20-150 nm. The oxygen barrier effect of PET bottles treated with Actis was 30 times higher than that of ordinary PET bottles, and the barrier to C02 was increased by more than 7 times, and the penetration resistance of acetaldehyde was increased by 6 times. After 6 months storage of this bottled beer, the loss of carbon dioxide from the North Sea is 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 silicon-enhanced PET technology to improve barrier properties. 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 known to increase barrier properties by 2 to 4 times, extend shelf life by 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.
Swiss TetraPak Packaging has developed a technology for plasma coating SiOx coating on the inner wall of PET bottles. This process can form a PET bottle with a thickness of 0.1-0.2 l on the inner wall of the bottle, and it has been applied at 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 overcoat technology developed by DuPont, called “transparent aluminum”, can increase barrier properties by 30-40 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 polyester bottles.