High barrier plastic packaging material

In recent years, China's plastic packaging material industry has developed rapidly. In 2002, the output reached 3.85 million tons. It is expected that the output will reach about 4.2 million tons in 2003, and the average annual growth rate will be maintained at about 10%. New products will emerge in an endless stream. In the future, the requirements for plastic packaging materials in the market are diversification, high functionality, and high barrier properties.

At present, high barrier properties have become one of the important development directions of plastic packaging materials, especially in food and pharmaceutical packaging, and more emphasis is placed on high barrier properties.

Application and Progress of High Barrier Plastic Packaging Materials

At present, barrier materials that are industrialized or have industrialized production prospects include PVDC, EVOH, PEN, nitrile-based resins, and polyamides.

â—†PVDC

PVDC (polyvinylidene chloride) is characterized by low permeability, barrier properties, and chemical resistance. China's PVDC is accompanied by the introduction of ham sausage processing technology and has been developed. In 2002, domestic PVDC production was approximately 20,000 tons. It has been widely used in food, cigarette, beverage preservation and odor separation, and chemical, pharmaceutical, electronic and military industries. Moisture-proof packaging. China Zhejiang Juhua Company and Dalian Plastics Research Institute have done a lot of work on their synthesis and processing and achieved breakthroughs.

Single-layer PVDC film is made by biaxial stretch blow molding, has shrinkage, barrier property, water resistance, does not decompose under microwave heating conditions, and is widely used in household cling film; PVDC and polyethylene (PE), polypropylene ( PP), Polystyrene (HIPS) and Other synthetic resin multilayer extrusion for vacuum dairy products, jams and other packaging, its good tensile properties, suitable for larger volume packaging; PVDC and PE, polyvinyl chloride (PVC The composite sheet is suitable for packaging of moisture-absorbing and volatile chemicals. At present, many domestic research institutes and manufacturers focus on PVDC and other resin composite laminated film technology and composite film high temperature technology.

Because PVDC is currently the only high-barrier and transparent material that can be contacted with foods by the US FDA, coating PVDC latex on many plastic packaging materials has become one of the commonly used methods in the international food packaging industry. PVDC is used on various substrates such as PE, PP, PVC, polyamide (PA), polyethylene terephthalate (PET), etc. The biaxially oriented polypropylene film is taken as an example to show the oxygen permeability after coating. 1000 times lower, the water permeability is reduced by 3 times; the coating can be single or multi-layered, and a single layer coating of 2.5 μm can provide a good barrier effect.

â—†EVOH

The barrier properties of EVOH depend on the content of ethylene. In general, when the ethylene content increases, the gas barrier properties decrease, but it is easy to process. EVOH is distinguished by its excellent barrier properties to gas and excellent processability, as well as excellent transparency, gloss, mechanical strength, flexibility, abrasion resistance, cold resistance and surface strength. At present, major foreign manufacturers are Eval Corporation of the United States, Japan Kuraray Corporation, Synthetic Chemical Industry Corporation, Belgium SOLVAY Corporation and so on.

In the packaging field, EVOH is made into a composite film intermediate barrier for all hard and soft packaging; in the food industry for aseptic packaging, hot pots and retort pouches, packaged dairy products, meats, juice cans and Condiment; For non-food products, used for packaging solvents, chemicals, air-conditioning components, petrol barrel lining, electronic components. In terms of food packaging, EVOH's plastic containers can completely replace glass and metal containers. Seafoods from several domestic seafood companies use five-layer co-extrusion PE/EVOH/PA/RVOH/PE vacuum packaging. While accelerating the study of EVOH composite membranes, EVOH stretching orientation has also been studied abroad. The barrier properties of new EVOH membranes to gases are three times that of existing high-performance non-stretched EVOH membranes. In addition, EVOH can also be used as a barrier material on other synthetic resin packaging materials to enhance barrier properties.

â—† PEN

The structure of PEN (polyethylene naphthalate) is similar to that of PET. The difference is that the naphthalene ring is used to replace the benzene ring, but it is superior to PET in almost all aspects: Its barrier property is about PET 5 times, heat resistance, Chemical resistance is better.

With breakthroughs in its raw material synthesis technology of 2,6-naphthalenedicarboxylic acid, well-known chemical companies such as ICI, Shell, Amoco, and Eastman have been producing and accelerating their application research. Currently used in food, beverages, pharmaceuticals, cosmetics, etc., such as small-sized carbonated beverage bottles, fruit juice, mineral water, milk, beer bottles, baby food (potable sterilization) packaging, requiring high barrier, radiation resistance and chemical resistance Drug-based pharmaceutical packaging requires high strength, impact resistance, chemical resistance, and high barrier industrial packaging. In terms of beer and beverage packaging, it is more than made up for the defects of PET and glass, and has become a hot topic in recent years.

Some countries in Western Europe have begun to use PEN beer bottles in the market, which has the same preservation effect as glass bottles and is resistant to impact and easy to recycle. In recent years, China has also conducted certain researches. For example, the product technology development center of Yizheng Chemical Fiber Co., Ltd. performs PEN synthesis and process optimization. Guilin Electric Science and Technology also tries to synthesize PEN. At present, the development of raw materials is restricted by the immaturity of raw material synthesis technology. Many domestic scientific research institutions conduct research, but no breakthrough has been made. Domestic companies plan to introduce foreign raw material production technology to further synthesize PEN.

Although PEN synthesis technology has been considerably improved and perfected abroad in recent years, the application cost is still high, so alloying has become one of the effective ways to expand the application range of PEN. On the one hand, under the premise that the PEN performance is not changed, the production cost is reduced. On the other hand, under the condition that the price increase is not much, the barrier properties and other properties of the alloy are greatly improved. At present, the research of PEN alloying has become a hot topic in the packaging industry. Due to the similar structure of PET and PEN, rich source and low price, and extensive application in the packaging industry, PEN/PET alloys are the most studied. The key to the PEN/PET blend molding is the compatibility of the two, and its measure index is the transesterification rate, so choosing the right transesterification rate is the key. PEN/PET alloys can be modified on existing stretch blow molding machines for PET to produce containers; PEN-rich copolymers are copolymerized with PET to form a variety of block copolymers that can be stretched, blow molded, and Processing on the injection equipment makes PEN in a more advantageous position in the packaging field. At present, the use of PEN/PET copolymers and blends can make heat-resistant bottles, high barrier bottles, UV absorption bottles, thermoforming containers, and the like.

â—† Nitrile-based resin

Nitrile-based resin is a polymer, which is a copolymer of about 70% acrylonitrile and methyl methacrylate or styrene and impact modified monomer butadiene. It has good gas barrier properties, chemical resistance, and preservation properties. Processed into blow molded containers and thermoplastic containers for condiments, processed meat, etc. Non-food components include extruded containers for packaging of household products, automotive and industrial products, etc. Injection-blow molded containers for packaging Correction fluid, nail polish, and thermoformed packaging. At present, foreign nitrile-based resins have been applied industrially, and a few research institutes in China have conducted research and development, but they have not yet achieved industrialization.

â—†Polyamide

Polyamide (PA) has been continuously developed as an important barrier material for multilayer composite films. The combination of PA and polyolefin can meet the requirements of many foods that need to block gas, aroma, and moisture retention.

In recent years, PA6 nano-barrier composites have been successfully developed both at home and abroad, and their barrier properties and stretching have been significantly improved. For example, Nano PA6 successfully developed by the Yueyang Petrochemical Research Institute in China has better oxygen barrier than ordinary PA6. And heat resistance; CAS Institute of Chemistry and Japan Unichema Co., Ltd. also conducted nanometer PA6 research; the PA6/n-MMT composite developed jointly by Eastman and Nanolor Co., USA not only has higher gas barrier properties, but also Consistent with PET processing characteristics, good compatibility, can also be processed on PET processing machinery or with the PET for a total of mixed gold.

MXD6 is a new polyamide material developed in recent years. It is a semi-crystalline polymer made from the condensation of m-xylylenediamine and adipic acid. Its gas barrier and thermal properties are significantly better than those of PA6, and it has good transparency. The oxygen permeability is 10 times smaller than PA6. Tests by foreign research institutes have shown that using special polyamide MXD6 as a barrier layer is better than EVOH. At present, DuPont and other foreign companies have produced MXD6. The blends with PET meet the FDA requirements for food contact. The low-temperature barrier properties are inferior to those of PVDC. When the temperature rises, the barrier property is better than that of PVDC, and its odor barrier property and mechanics The performance is very good.

At present, MXD6 is mainly used for high-barrier films and high-strength barrier materials. The most important feature is that the barrier properties do not decrease with the increase of humidity, but the price is relatively expensive, and the use of MXD6 is limited in some fields. The main raw materials among the dimethylbenzene diamine domestic Shanghai Petrochemical Research Institute, Wenzhou Qingming Chemical Plant, and other production, domestic and some also engaged in polyamide synthesis and modification research institutions on MXD6

Synthesis and application for research.

in conclusion

China's development and production of plastic packaging materials, especially high-barrier packaging materials, is still in its infancy. Among the above-mentioned typical high barrier materials, only domestic PVDC and polyamide can be produced in China, and development in other areas is still in a blank state. On the one hand, many plastic packaging materials in China, especially foods and pharmaceuticals, require high barrier materials to fail to meet international market competition; on the other hand, domestic high-barrier packaging requirements for foods and pharmaceuticals are increasingly demanding. China's current research and development of high barrier packaging materials can not meet the rapid growth of the domestic market demand, and vigorous development of high barrier packaging materials, social and economic benefits are very obvious.

China's development and production of plastic packaging materials, especially high-barrier packaging materials, is still in its infancy. Among the above-mentioned typical high barrier materials, only domestic PVDC and polyamide can be produced in China, and development in other areas is still in a blank state. On the one hand, many plastic packaging materials in China, especially foods and pharmaceuticals, require high barrier materials to fail to meet international market competition; on the other hand, domestic high-barrier packaging requirements for foods and pharmaceuticals are increasingly demanding. China's current research and development of high barrier packaging materials can not meet the rapid growth of the domestic market demand, and vigorous development of high barrier packaging materials, social and economic benefits are very obvious.