· High barrier to oxygen, water vapor and other special gases, the barrier properties change little with the change of humidity;
· High shrinkage due to qualitative change;
Chemical stability, no chemical reaction with acids, alkalis, salts, etc. Resistant to grease and solvents, non-toxic and harmless to human body;
· Temperature resistance up to -20 °C ~ 140 °C;
Printability is good.
The so-called barrier property (airtightness) refers to the performance of a plastic film to permeate oxygen, water vapor, and other gases including gases of various tastes. Such as oxygen permeability refers to 25.4um (1mil) thick plastic film at 23°C, an atmospheric pressure (atm) relative humidity RH50%, 1M2 area in 24 hours through the volume of gas (water vapor weight), the unit of writing For cm3/m2·24h·23°C·atm·RH50%, the international plastics community is accustomed to using the physical property of transmittance to indicate the difference in performance. The material with an oxygen transmission rate of 10 or less is called a high barrier material; 10～ 100 is called medium barrier material; 100 or more is called ordinary barrier material. PVDC oxygen barrier rate of 8 to 9, water vapor transmission rate of 3 to 5, in favor of high barrier material, and because PVDC molecules do not contain hydrophilic groups, do not absorb water, barrier properties are not Hu Hu and changes and obvious The change is therefore called as an all-weather high barrier material. (See table for barrier properties of each material)
Second, the various types of PVDC composite membrane and its characteristics Composite declaration: two or more materials (different or the same) through the stick to the whole method into a layer, so that it becomes a new material, this process is called composite. The composite film has the disadvantages of each material, exerts its excellent performance, and has characteristics that a single material does not have.
Common compounding methods for plastic materials: coating method, dry method, solvent-free, hot melt, co-extrusion, etc.
At present, the production of domestic PVDC composite membranes mainly uses coating methods, dry methods, solvent-free and coextrusion methods:
1) PVDC coating film is coated on the substrate surface (OPP, PA, PE, PET, etc.) to form a composite film with PVDC latex to improve the gas barrier properties of the substrate.
Performance characteristics:
·Good barrier property;
· PVDC layer thickness is generally 2 ~ 3um, lower cost;
· Can not withstand high temperature cooking.
2) The PVDC laminated composite film is composed of a plurality of single-layer films, and each layer is bonded with an adhesive. According to the different adhesives used, they can be divided into: dry (solvent) laminated composites and solventless laminated composites. Due to the thermal shrinkage characteristics of PVDC, there is no precedent for the dry-process composite processing of PVDC composite film in actual production, and further research is needed.
Performance characteristics:
· High barrier property;
· Flexible structure, can be combined with BOPA, CPP, CPE, BOPP, BOPET, PVC and other films;
· Good temperature resistance, can be made of high temperature resistant and low temperature structural composite film, temperature or up to -20 °C ~ 121 °C;
Mechanical, good heat sealing, applicable to a variety of packaging machinery;
· Color printing can be performed;
· Limited by a single membrane, the thickness of each layer can not be made very thin, and the number of composite layers should not be too much (generally no more than 5 layers).
3) PVDC multi-layer co-extruded composite film A variety of plastics are extruded at once by multiple extruders through a single die to form an ordered, well-proportioned film that is promulgated between layers, tightly bonded, and thin across the layers. Different forming methods can be divided into coextrusion blown film and coextrusion cast film. PVDC material is generally used as the intermediate barrier layer of composite film.
Performance characteristics:
· High barrier property;
· Good hygienic property, using adhesive full resin for bonding, avoiding the problem of solvent residue in dry compound (solvent type);
· Can be cooked below 100 degrees;
· Adopting flow branch production, the film can be subjected to secondary thermoforming processing;
· A lot can be done, currently reaching 13th floor;
· The thickness between the layers can be made very thin, which can save the cost of high resin consumption and get the performance cost ratio.
·It is not easy to change the structure between layers.
III. Application of PVDC Composite Film 1. Application Field of PVDC Composite Film
┌ Milk powder, tea, biscuits, etc. that need to prevent moisture absorption, foods, foods, cooling meats, etc.
PVDC Coating Film│
├Cigarettes, cosmetics, and other products that need to prevent the loss of taste └ Pharmaceutical powders, blister packs
There is an urgent need for high- and low-humidity sterilized meat products, boiled vegetables, convenience foods, vacuums for raw meats, cooling meats, air-packed foods, high-protein, high-fat grain and oil crops such as rice, peanuts, almonds, etc. ├Milk powder, tea and other foods that need to prevent moisture absorption │All kinds of microwave foods │ ┌All kinds of chemical resins, additives that need to prevent oxidation, prevent moisture absorption ├ Chemicals ├ Pharmaceutical powder, granules │ └ Pesticide powders, granules
PVDC Laminated Composite Membrane ├ Precision Instruments ┌ A variety of precision instruments that require moisture and rust prevention │ It is imperative to permanently store military equipment, weapons, and ammunition as a substrate film to be combined with other paper and plastic materials.
No need for pasteurized meat products, boiled vegetables, instant foods, vacuum and air-packing for separating raw meat and cooling meat, and vacuum hot-forming automatic packaging machines for the production of meat products, soy products, food products, and liquid filling machines. Liquid milk, seasonings, liquid flavors, fats, etc. ├ ├ High-protein, high-fat, grain and oil crops such as rice, peanuts, almonds, etc. └ Milk powder, tea, and other foods that need to prevent moisture absorption │ Various anti-oxidants Anti-absorption chemical resins, additives, chemicals, pharmaceutical powders, granules
PVDC multi-layer co-extruded composite membrane │ └Pesticide powder, granules │ ┌A variety of precision instruments that require moisture, rust-proof precision instruments │
│ Requires long-term storage of military equipment and weak weapons as base film and other paper and plastic materials for composite processing
2. The application of PVDC composite membrane in China:
The production, processing and application of high barrier packaging materials were developed on the basis of research in China in the 7th and 8th, but until 1991, with the introduction of ham sausage processing technology, PVDC casing films appeared in the form of single membranes received a large number of Application, created China's PVDC high barrier material applications. In the following ten years, PVDC entered a period of rapid development in China. Up till now, China's PVDC material has produced 10,000 tons per year, ranking the world's third largest producer of PVDC after the United States and Japan. However, at present, the structure of PVDC products in China is relatively simple, and the output of composite film production is relatively small. In the earlier period, China could only produce and process PVDC coating film. Due to the characteristics of the product itself, the base application field was affected. In recent years, China has introduced and developed PVDC coextruded composite film and laminated composite production technology to make the production of PVDC composite film in China. The application has taken a new step.
IV. Market Prospect of PVDC Composite Films The development of high-barrier packaging materials in recent years is a worldwide trend, and PVDC plays an irreplaceable role in the packaging field. In the decades since its inception, the world's plastics industry has also developed a variety of high barrier materials, but due to a variety of reasons, it has failed to industrial production. In 1992, the production of high-barrier plastics worldwide was 126,000 tons, of which PVDC resin 10.8 million tons, so far, PVDC material production accounts for more than 90% of the world's total production of high plastic materials. From the perspective of the development of China's PVDC materials and China's special national conditions, the production and application of PVDC materials in China will surely achieve remarkable results.
1. PVDC performance in nylon, aluminum foil, EVOH and other materials.
2. The application of PVDC in various fields.
(1) Food Packaging (2) Pharmaceutical Packaging (3) Chemical Packaging (4) Precision Instruments, Meters, Precision Measuring Tools, etc. (5) Military Product Packaging
Polymer Oxygen Nitrogen Carbon dioxide Water vapor PVDC 0.4 to 1.0 0.1 to 0.8 0.3 to 0.7 0.4 to 1.0 Nylon 6, Nylon 66 25 to 43 to 59 93 to 155 Polypropylene (PP) 300 60 1200 3.6 to 10.2 Polyester (PET) 74 ~138 12~24 35~50 27.4~46.7 Polyvinyl chloride (PVC) 77~310 - 140~400 13.2~71.3 LDPE 500~700 200~400 2000~4000 15.2~23.4 Polystyrene (PS)