1、 Performance and application of PVDC: The international plastic industry is used to use the physical quantity of permeability to indicate the difference in performance and the materials with oxygen permeability below 10 are called high barrier materials. 10~100 are called medium barrier materials. More than 100 is called ordinary barrier material. At present, the three recognized high barrier materials in the world are PVDC, EVOH and PAN. The three materials are all copolymers. The oxygen barrier of EVOH is better than that of PVDC and that of PVDC is better than that of PAN; For water vapor barrier, EVOH is better than PVDC, and PVDC is better than PAN.
However, under high humidity conditions, EVOH molecular structure contains – OH group, which is very easy to absorb moisture, and its barrier performance will be significantly reduced. At the same time, the barrier performance of PAN material is also significantly decreased with the increase of environmental humidity. PVDC is the best comprehensive barrier performance of plastic packaging materials in the world.
Polyvinylidene chloride resin (PVDC) is a copolymer with vinylidene chloride monomer as the main component. It is an ideal packaging material with high barrier, strong toughness, excellent thermal shrinkage and chemical stability and excellent printing and heat-sealing properties. It is widely used in food, medicine, military and other fields.
Actively developing PVDC products with high technology content is of great significance to balance chlorine resources in chlor-alkali industry and greatly improve enterprise efficiency and competitiveness. PVDC has excellent barrier property as a packaging material. Using PVDC to package food can greatly extend the shelf life, and at the same time, it has excellent protective effect on the color, smell and taste of food. PVDC composite packaging has lower unit resource consumption than ordinary PE film, paper, wood, aluminum foil and other packaging materials. The volume of packaging waste has been greatly reduced and the total cost has been reduced, so as to achieve the purpose of packaging reduction.
PVDC is widely used in western countries, involving food, chemicals, cosmetics, pharmaceuticals, hardware and mechanical products, and is known as “green” packaging materials. The application of PVDC is related to the national living standard. At present, the annual consumption of PVDC is about 50000 tons in the Americas & 45000 tons in Europe, and a total of about 40000 tons in Asia and Australia. The average annual growth rate of PVDC market consumption in Europe, America and Japan is 10%. In the Americas, more than 15000 tons of PVDC resin are used for vacuum packaging of large pieces of fresh meat each year, and the consumption of PVDC coating on paper accounts for 40% of the total consumption of PVDC. In Japan and South Korea, a large number of PVDC packaging materials are used in food, medicine, chemical products and electronic products packaging materials. The annual consumption of PVDC resin is more than 10000 tons only for plastic film.
2、 Specific application of PVDC composite membrane in China: China has started the practical application of PVDC resin since the early 1980s. First, the birth of ham sausage introduced PVDC film into China. Then Chinese companies broke the blockade of the United States and Japan on this technology and introduced the processing technology and equipment of PVDC film. With the continuous growth of China’s national economy and the improvement of people’s material and cultural life, the level of demand for packaging is also increasing. More and more functional packaging is widely used in all aspects of the national economy and people’s livelihood. PVDC is a leader in achieving high barrier packaging structure cost efficiency and reliable moisture, oxygen and odor barrier.
Since everyone has more knowledge of PVDC casing film, here we will focus on the technical methods and properties of PVDC composite film. The composite film makes up for the shortcomings of each material, gives full play to its excellent performance, and has characteristics that a single material does not have. Common composite methods of PVDC:
Coating, dry, solvent-free, hot-melt, co-extrusion, etc. At present, the domestic production of PVDC composite film mainly adopts coating method, dry method, solvent-free and co-extrusion method:
1) PVDC coating film PVDC latex coating is applied on the surface of the substrate (OPP, PA, PE, PET, etc.) to form a composite film to improve the gas barrier performance of the substrate. Performance characteristics: Good barrier; The thickness of PVDC layer is generally 2~3um, with low cost; Can not withstand high temperature cooking.
2) PVDC laminated composite membrane It is composed of multiple single-layer films, and each layer is bonded with adhesive. It can be divided into: Dry (solvent) lamination and solvent-free lamination.
Performance characteristics:
A. With high barrier property and flexible structure, it can be compounded with BOPA, CPP, CPE, BOPP, BOPET, PVC and other films (for example, BOPP, PET, PA can be used as the outermost printing layer, PE, CPP and other good thermal sealing effects can be used as the thermal sealing layer, PA’s good puncture resistance can be used as the puncture resistance layer, and PVDC can be used as the barrier layer to block oxygen and water).
B. Good temperature resistance. It can be made into high temperature and low temperature resistant structural composite film with temperature resistance of – 20 ℃~121 ℃; Good mechanical and heat-sealing properties, suitable for a variety of packaging machinery, color printing, limited by single film, meanwhile the thickness of each layer can not be very thin and the number of composite layers should not be too many (generally not more than 5 layers).
3) PVDC multilayer co-extruded composite film A variety of plastics are extruded by multiple extruders at one time through a die head to form a film with orderly arrangement, obvious interlayer issuance, tight binding and consistent interlayer thickness. According to different forming methods, it can be divided into co-extrusion blown film and co-extrusion cast film. PVDC material is generally used as the intermediate barrier layer of composite film. Performance characteristics: high barrier, good hygiene, adhesive resin is used for bonding, avoiding the problem of solvent residue in dry composite (solvent-based), and can be cooked at less than 100 degrees; The film can be processed by secondary thermal forming by using flow branch production; There are many layers that can be made, and now it has reached 13 layers. The interlayer thickness can be made very thin, which can save the amount of resin with high price and obtain a more economical cost performance.
3、 Advantages of PVDC composite membrane: The development and application of PVDC composite membrane is a great production change in the field of PVDC reference. Compare the current circulation of high-temperature cooking resistant composite membrane on the market:
A. Comparison between PVDC and aluminum foil composite film: Aluminum foil composite film is not suitable for microwave heating and can not adapt to modern fast-paced life; The aluminum foil is opaque and cannot satisfy people’s desire to see the contents; The fold of aluminum foil bag is easy to break and leak. At present, most meat food packaging is vacuum packaging. After vacuuming the aluminum foil bag, the fold of the aluminum foil bag is easy to crack and break after vacuuming, resulting in reduced barrier. However, the aluminum foil composite film has better shading performance.
B. Comparison between PVDC and nylon composite membrane: Both nylon composite film and PVDC composite film overcome the above shortcomings of aluminum foil and are widely used in the packaging of meat products. Compared with PVDC composite membrane, nylon composite membrane has lower price, better transparency and strong puncture resistance; However, the barrier property of nylon composite film is poor. After sterilization at high temperature, the shelf life of meat packaged with nylon cooking bags is only 2-3 weeks at normal temperature; Under the condition of higher temperature in summer, the shelf life is shorter; Meat packaged with it is generally refrigerated at low temperature and rarely stored at normal temperature.
The most prominent example of the application of PVDC in liquid food is the use of PVDC as a milk film. The good oxygen resistance of PVDC can extend the shelf life to a greater extent. The excellent gas resistance of PVDC can effectively prevent dehydration, maintain quality and quantity, and its excellent flavor resistance can maximize the original flavor of milk. In addition, the use of PVDC composite film can also replace the glass can packaging of some fruits, which can effectively reduce the cost share of packaging in the whole food production.
To summarize the excellent barrier performance of PVDC, we can roughly summarize the application fields of PVDC: A. Milk powder, tea, biscuits and other foods that need to prevent moisture absorption; B. Food, chilled meat and other meat products that do not need high temperature sterilization; C. Cigarettes, cosmetics and other products that need to prevent the loss of flavor; D. Meat products, boiled vegetables, and convenience foods that need high and low humidity sterilization for pharmaceutical powder and blister packaging; E. Vacuum and inflatable packaging of raw meat and chilled meat; F. Food, high-protein, high-fat grain and oil crops, such as: Rice, peanut kernel, almond etc. G. Precision instruments: All kinds of precision instruments that need moisture-proof and rust-proof need to be sealed for a long time for military equipment, weapons and ammunition; H. Vacuum and inflatable packaging for pasteurized meat products, boiled vegetables, raw meat for convenience food segmentation, and chilled meat for composite processing with other paper and plastic materials.
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