Nowadays, with the continuous development of science and technology, people have higher and higher requirements for the quality of life, and the demand for material life is increasing, which leads to the tension of resources and energy. At the same time, environmental issues are becoming increasingly important, in the packaging industry, plastic flexible packaging materials have achieved rapid development, but also withstood severe challenges. In addition to the requirements for plastic flexible packaging materials to meet the increasing requirements of packaging quality and efficiency of different products, it is further required that it must save resources, save energy, easy to recycle after use or easy to be degraded by the environment as the starting point for technology development, so plastic flexible packaging materials are developing in the direction of high performance, multi-function, environmental protection and expand application fields.
Nowadays, high-performance and multi-functional plastic flexible packaging materials are becoming hot packaging materials. And some products have been put into industrial production. Such materials include plastic flexible packaging materials such as high barrier, selective permeability, heat resistance, resealing and easy to open. Among them, the development of high barrier, selective permeability and heat resistant packaging materials is more rapid.
1. High barrier plastic packaging materials
High barrier plastic packaging materials are developed with the rapid development of the food industry, and high barrier packaging materials have been rapidly developed and widely used in the packaging industry, especially in the food packaging industry. It has played a role in food quality preservation, freshness preservation, flavor preservation and shelf life extension, and a variety of food preservation technologies, such as vacuum packaging, gas displacement packaging, sealed deoxidizer packaging, food dry packaging, sterile filling packaging, cooking packaging, liquid hot filling packaging and so on. Many of the plastic packaging materials used in these packaging technologies require a variety of properties, but the important point is that they must have good barrier properties. The following is a variety of common flexible packaging forms of barrier materials to make some introductions.
The more common high barrier film materials are as follows:
(1) PVDC materials (polyvinylidene chloride)
Polyvinylidene chloride (PVDC) resin, often used as a composite material or monomer material and co-extruded film, is the most used high barrier packaging material. Among them, the use of PVDC coated films is particularly large. PVDC coated film is the use of polypropylene (OPP), polyethylene terephthalate (PET) as the base material. Due to the high softening temperature of pure PVDC, close to its decomposition temperature, and poor compatibility with general plasticizers, heating molding is difficult and difficult to apply directly. The actual PVDC films are mostly the copolymers of vinylidene chloride (VDC) and vinyl chloride (VC), and the films with particularly good barrier properties made of copolymerization with methacrylate (MA).
(2) Nylon packaging materials
Nylon packaging materials before - straight use "nylon 6". But the air tightness of "nylon 6" is not ideal. One kind of nylon (MXD6) made from the condensation of m-dimethylamine and adipic acid is 10 times more airtight than "nylon 6", and has good transparency and puncture resistance. It is mainly used for high barrier packaging film for food flexible packaging with high barrier requirements. It is also approved by the FDA for food hygiene. Its biggest feature as a film is that the barrier property does not decrease with the rise of humidity. In Europe, due to outstanding environmental protection issues, as an alternative to PVDC films, the use of MXD6 nylon is very large.
In addition, MXD6 nylon and EVOH composite film with bi-directional extensibility, as a kind of high barrier nylon film. The composite methods include multilayer composite, and the method of blending MXD6 nylon and EVOH is also used.
(3) EVOH materials
EVOH - is the most widely used high barrier material.
The film types of this material in addition to non-tensile type, there are bidirectional tensile type, aluminum evaporation type, adhesive coating type and so on. The bidirectional stretch type also has heat-resistant products for aseptic packaging. EVOH resin and polyolefin, nylon and other resins co-extruded film is mainly used for livestock product packaging.
(4) inorganic oxide coated film
PVDC, which is widely used as a high barrier packaging material, has a tendency to be replaced by other packaging materials due to the environmental pollution caused by the HCl generated in the combustion of its waste. For example, the so-called coated film produced after the coating of SiOX (silicon oxide) on the film of other substrates has been paid attention to, in addition to the silicon oxide coating, there are also alumina evaporation films. Its airtight performance is the same as that of the silicon oxide coating obtained by the same method.
In recent years, the technology of multilayer composite, blending, copolymerization and evaporation has developed rapidly. High barrier packaging materials such as ethylene glycol copolymer (EVOH), polyvinylidene chloride (PVDC), polyamide (PA), polyethylene terephthalate (PET) multi-layer composite materials and silicon oxide evaporation films have been further developed, especially the following products are more eye-catching: MXD6 polyamide packaging materials; Polyethylene naphthalene dicarboxylate (PEN); Silicon oxide evaporation film, etc.
2. New plastic wrap
Due to the specialization of agricultural production, more and more remote transportation, long-distance transportation of fresh fruits and vegetables, and people's requirements for improving the quality of life, the demand for fresh fruit and vegetable preservation and shelf life extension of fresh film is growing. A common feature of fresh fruits and vegetables is that they continue to breathe after picking, and respiration is accompanied by metabolism, water evaporation and ethylene production, which further ripen fruits and vegetables until they die. At the same time, this environment also makes it easy for bacteria to breed and multiply rapidly, causing fruits and vegetables to rot quickly. In order to extend the storage and shelf life of fruits and vegetables, the research and development of new multi-functional preservation films have been strengthened at home and abroad.
Fresh food packaging attaches great importance to the permeability of gas, and choose different plastic materials. With the development of the food industry and the progress of material science, as a food packaging material not only requires high gas resistance, but further requires the development of the function of selective permeability, that is, according to the requirements of the packaging contents, only allow the needed (or not needed) gas molecules to pass through, to establish a suitable gas regulation environment. This kind of selection of permeable packaging materials has entered the practical stage in foreign countries, mainly the addition of dissolved gas material film, the addition of porous zeolite or silicon oxide powder film, the use of gamma ray irradiation to change the properties of the film and the use of diffusion coefficient on water content, the introduction of films containing hydroxyl groups and amide groups. In addition, some antibacterial agents and preservatives can be added to the film to inhibit the growth and reproduction of bacteria and mold.
In recent years, the preservation technology that has attracted much attention is through micropores or improving the film formula structure, improving the air conditioning environment (atmosphere) in the bag, and using the combination of deaerator and selective permeation film. In particular, the following products will receive greater attention:
(1) Functional plastic wrap
A Japanese company launched a strong sealing bag, it is made of a kind of plastic called "Chikren", with excellent oxygen insulation, use it to package new rice, the preservation effect is particularly good, can maintain the color of rice for a long time, fragrance, taste unchanged, and the carbon dioxide produced in the bag also has the effect of insect prevention and mildew prevention.
