With the improvement of living standards, people have put forward higher requirements for food safety and its durability, freshness preservation and shelf life. Therefore, barrier packaging materials have emerged as a result and have been rapidly developed. There are many ways in which people in the food packaging industry explain the barrier. Some are based on physical protection, some focus on the movement of liquids between packages, and also involve gases such as water vapor.
For plastics as a packaging material, the first task is to control oxygen, because oxygen is an important factor that causes the deterioration of food quality in the environment. Since polyester was used as a carbonated beverage packaging material, another control project focused on carbon dioxide. At present, the use of packaging for food and beverage flavor blocking is more and more important, of course, there are barriers of fat and hydrocarbons.
The type and number of barriers mainly depend on:
Products and their environment—chemical composition, temperature, time, climate, predicted shelf life of sales, corruption vectors, and infectious activity;
• Leakage and physical damage to the structure of the package—one is the material itself, and the other is due to mechanical damage to the package such as extrusion, needling, or tearing;
· Adverse reactions affecting food ingredients.
Barrier packaging generally involves reducing or hindering substances from passing through the packaging material. Polyvinylidene chloride (PVDC) and polyvinyl alcohol (EVOH) are excellent barrier materials. The bent structure of polyethylene naphthalene (PEN), nylon MXD6, and other similar micro-composites can prevent the passage of substances.
Multilayer composite
Multilayered composites have been the standard technology for enhancing oxygen barriers for more than 30 years. Packaging materials such as aluminum foil laminates have successfully built a strong barrier. When the all-plastic structure prevails in the field of packaging materials, aluminum foil has not yet been applied, so people began to study plastic barriers and similar materials such as coating methods, metal plating methods, and the like.
Multi-layer composites are still an effective method of forming barriers: EVOH and polypropylene multi-layer composites that began in the 1970s have become mainstream materials for ketchup bottles, recyclable drums, and hot-fill cans. In the 1990s, the demand for and research on the transparency of the packaging of ketchup and other condiments led to the creation of mixed injection of polyester and EVOH. Today, packaging products made from these two basic polymers account for most of the market for barrier plastic bottles. Polypropylene has good water vapor barrier properties and is more economical, while polyester has excellent transparency and physical strength.
Barrier packaging materials depend on the needs of the product being packaged, such as carbonated beverages, beer, and juice drinks, and the requirements for effective barriers are different. Carbonated drink producers are concerned not with oxygen but with carbon dioxide. In contrast, beer fillers are concerned with both oxygen and carbon dioxide and water vapor, flavor leakage, visibility, and thermal protection. Fruit juice drink producers are primarily concerned with oxygen because the product is sensitive to oxygen and is now starting to pay attention to flavor leaks. In the past, the focus of debate has mainly focused on the use of hot or cold filling to protect the product's microbiological stability; now, the focus has shifted to how to provide targeted consumers with better flavor and color products under sterile packaging.
Coating technology
The coating plastic structure is not a new invention, but the materials and technical methods to meet the specific needs of the packaging are continuously innovating. So far, all coatings are passive, they can effectively protect products from the internal and external environment, unless they are physically damaged, this physical damage can come from the pressure of carbon dioxide, or due to pressure on the gas distribution Caused a short-term contraction. Here are a few new barrier coating techniques:
PVDC: The technology of PVDC coating in polyester bottles was put into commercial use very early and is still 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: The most widely used barrier coating technology for commercial use in the past five years is the Bairocade, which is a "heat-cured epoxy amine spray" coating 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 Graham's version, oxygen scavenger was added to the wall structure of the PET bottle to enhance its ability to block oxygen.
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.
Carbon Inner Layer Coating Currently, there are two types of 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. Not long ago, the company that owns the technology received unanimous approval from the FDA. 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.
Another method, called PNS, was developed by the Japanese company Kirin. 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 barriers. Sex.
The silicone coating company Tetra Pak in Sweden developed a coating technology called Glaskin, which uses a reaction of HMD-SO with oxygen to form a silica coating on the inner layer of the bottle. It is reported that 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 The “best PET†system was developed by Krones and its customer, Coca-Cola, which uses energy-enhanced evaporation processes to generate ions and coat them on the outside of the bottle. Since the coating is relatively sensitive to overuse, a second coating is 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) Currently, the relatively new thin layer coating method is the CCVD technology, which was developed by Micro Coating Technologies. 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 technological process of this technology is as follows.
In this process, the precursors of the materials to be coated are ionized in the company's special ionization device, Nanomisertm, and the oxygen is converted into sub-microscopic mists, which form a coating material after combustion. The heat of combustion provides oxygen atomization, both reactions and the energy required for the coating material to steam coat the packaging material. The coating can be completed while passing through the combustion zone.
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. In addition, when used for the coating of organic matter, the thermal energy of burning can be polymerized by itself, and the thermosetting plastic does not need to be subjected to the heat treatment process after coating, thereby saving expensive heat treatment channels and related costs. At the same time, the technology can also be applied in multi-layer structures if needed.
According to the company, 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. The successful application of this technology means that the company's organic coating is completely flexible and can withstand physical damage during filling and distribution.
As with other silicon and carbon deposition technologies, CCVD has also been continuously improving and developing. The “family†of coating technology will continue to grow and grow, and will be further applied to food and beverage packaging for the benefit of mankind.