The plastic coating structure is not a new invention, but the materials and technical methods to meet the specific needs of the packaging are also constantly innovating. So far, all coatings are passive, they can effectively protect the product from the internal and external environment, unless physically damaged, the physical damage from the pressure of carbon dioxide, or due to the pressure of gas emissions caused by the decline Short-term contraction. Here are a few new barrier coating techniques:
The PVDC technology for PVDC coating in polyester bottles was put into commercial use very early and is now widely used. However, in some parts of the world, especially in Europe, there are many disputes over its economy and environment. The development of this technology has slowed down.
Bairocade's most widely used barrier coating technology for commercial use over the past five years is Baieroeade, which is a "heat-cured epoxy amine spray" developed by PPG Industries. This coating technology was first commercially used by Amcor, Australia, for the outer coating of polyester beer bottles. Graham Packaging USA also uses PPG's Bairocade oxygen barrier coating technology. In the version of Granam, a sulphur ammonia agent was added to the wall structure of the polyester bottle to enhance its ability to block ammonia.
Plasma Enhanced Chemical Vapor Deposition (PECVD) Chemical Vapor Deposition is currently the most commonly used technique for carbon dioxide glass barrier coating. In the past, the glass was sublimated under a very high vacuum and then applied to the packaging. This method was very uneconomical. PECVD was used for glass coating of films and bottles in the early 1990s and is currently the fastest growing technology.
The PECVD technology can make the coating layer microscopically thin, and the silica coating layer formed on the plastic bottle is only about 40-60 nm. Under low vacuum. Silicon-containing materials (such as H-MDSO hexamethyldisilane) form plasma regions in microwaves or audio frequencies. In this plasma region, silicon-containing oxidation products can adhere to the surface of the plastic to form a coating layer. The silica composite layer may be continuous or intermittent, and its role is to block the entry of oxygen, carbon dioxide, moisture, or flavor substances. However, the silicon barrier layer may present some defects, such as the adhesion is not strong, the coating surface is uneven and more brittle. Therefore, when used in a carbonated beverage bottle, the coating layer may be damaged due to a change in the shape of the bottle body after pressure or pressure loss.
Plasma coating is mainly divided into three categories: carbon inner coating, silicon inner coating and silicon outer coating.
The carbon inner layer is coated with two carbon inner layer coating methods. One is called Actis, which coats the amorphous carbon in the inner layer of the already formed polyester bottle. Uses microwave energy to form acetylene plasma regions. The coating thickness is about 200nm, with high transparency but slightly amber. As it is on the inside of the bottle, the coating blocks the leakage of gas and flavor from the plastic. The company that owns the technology received FDA's no-objection approval. The coating layer can be in direct contact with beverages. Moreover, PET bottles using this technology have been put into the production of “Pepsi-Cola” carbonated beverages, which can extend the storage time of their products' carbon dioxide. The other method is called PNS. It uses an audio source plus internal and external electrodes to ionize the gas, and finally forms a 20-40nm thick coating. This coating has excellent gas and moisture barrier properties.
Sitra, layer coating Sweden's TetraPak company developed a coating technology called Glaskin. This technique utilizes the reaction of HMDSO with ammonia to form a di-aminated silicon coating on the inner layer of the bottle. The oxygen and carbon dioxide barriers of the treated bottles are twice that of the original polyester bottles. This coating has the same advantages as the coating formed by the Actis method, but its drawback is that the pressure changes cause the bottle to stretch or shrink, which may cause damage to the coating.
Silicone coating This “best PET” system was developed by Krones and its customer, Coca-Cola, which uses an energy-enhanced evaporation process to generate ions and deposit them on the outside of the bottle. Because the coating is relatively sensitive to overuse. Therefore, a second coating was applied on its surface to enhance its mutual cooperation function. With this technology, the carbon dioxide retention rate has increased five-fold.
Combustion Chemistry Gas Deposition (CCVD) The relatively new thin layer coating method is the CCVD technology, which was developed by Micro Coating Technology. This technology develops submicroscopic thin-film electronic and analog devices and makes them suitable for the coating of plastic bottles and films. Unlike other coating technologies, it can be performed at atmospheric pressure, eliminating the need for expensive vacuum chambers.
The time it takes for the package to pass through the combustion zone is so short that it does not measure its temperature increase. No vacuum environment is required, and the process can be performed continuously, which can solve the problems encountered in cost and conventional ion discharge type coating. Compared with other coating technologies, the ccvD technology has a thinner coating layer when achieving the same barrier effect. Also, compared to the conventional plasma deposition method, no pretreatment of the plastic is required and the achieved adhesion effect is better.
