Plastic flexible packaging material
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With the continuous development of science and technology, people's requirements for quality of life are getting higher and higher. High-performance, versatile plastic flexible packaging materials are becoming a hot-spot packaging material.
First, high barrier plastic packaging materials
High-barrier plastic packaging materials have been developed with the rapid development of the food industry, which plays a role in food quality, preservation, flavor retention and shelf life. There are many techniques for preserving food, such as vacuum packaging, gas replacement packaging, encapsulation of deoxidizer packaging, food dry packaging, aseptic filling packaging, retort packaging liquid hot filling packaging, and the like. Many of these packaging technologies use plastic packaging materials. Although they are required to have a variety of properties, it is important to have good barrier properties. The following is a description of the barrier materials used in various common flexible packaging forms.
The more common high barrier film materials are as follows:
1. PVDC type material (polyvinylidene chloride)
Polyvinylidene chloride (PVDC) resin, often used as a composite or monomer material and coextruded film, is the most widely used high barrier packaging material, of which PVDC coated film is used in a particularly large amount. The PVDC coated film is made of polypropylene (OPP), polyethylene terephthalate (PET) or the like as a substrate. Since pure PVDC has a high softening temperature and is close to its decomposition temperature and poor in compatibility with general plasticizers, it is difficult to heat-form and is difficult to apply directly. The PVDC film actually used is mostly a copolymer of vinylidene chloride (VDC) and vinyl chloride (VC), and a film having a particularly good barrier property by copolymerization with methyl acrylate (MA).
2. Nylon packaging materials
Nylon packaging materials have previously used "nylon 6". However, the airtightness of "nylon 6" is not satisfactory. There is a kind of nylon (MKD6) which is obtained by polycondensation of m-dimethylamine and adipic acid. The gas tightness is 10 times higher than that of "nylon 6". At the same time, it has good transparency and puncture resistance. It is mainly used. It is a high barrier packaging film for food packaging with high barrier properties. Its food hygiene is also licensed by the FDA. Its greatest feature as a film is that the barrier properties do not decrease with increasing humidity. In Europe, due to the outstanding environmental protection issues, the use of MXD6 nylon is very large as an alternative to PVDC film. A new biaxially stretchable film made of MXD6 nylon and EV0H as a high barrier nylon film. The composite method has a multilayered composite, and a method of blending MXD6 nylon and EVOH is also used.
3. EVOH materials
EVOH has always been the most widely used high barrier material. In addition to the non-stretch type, the film type of this material includes a biaxial stretching type, an aluminum vapor deposition type, a binder coating type, and the like. The biaxially stretched type also has a heat-resistant type for aseptic packaging products. The film obtained by co-extruding EBOH resin with other resins such as polyolefin and nylon is mainly used for packaging of animal products.
4. Inorganic oxide plating film
PVDC, which is widely used as a high-barrier packaging material, has a tendency to be replaced by other packaging materials because of the environmental pollution caused by the HCI generated by the waste during combustion treatment. For example, a so-called plated film obtained by plating SIOx (silicon oxide) on a film of another substrate has been paid attention to, in addition to a silicon oxide film, an alumina deposited film. Its airtight performance is the same as that of the silicon oxide coating obtained by the same method.
In recent years, multi-layer composite, blending, copolymerization, and evaporation techniques have developed extremely rapidly. High-barrier packaging materials such as ethylene vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), polyamine (PA), polyethylene terephthalate (PET) multilayer composites and silicon oxides The vapor-deposited film and the like have been further developed, among which the following products are more attractive: MXD6; polyamide packaging materials; polyethylene naphthalate (PEN); silicon oxide vapor-deposited film.
Second, the new plastic wrap
Due to the specialization of agricultural production, the increasing number of long-distance transportation, the long-distance transportation of fresh fruits and vegetables, and the improvement of people's quality of life, the demand for fresh-keeping films that can prolong the shelf life and shelf life of fresh fruits and vegetables The bigger it is.
With the development of the food industry and the advancement of materials science, as food packaging materials, not only high gas barrier properties are required, but also the development of selective permeability functions is required. Such selective permeability packaging materials have entered the practical stage abroad. There are mainly films in which a dissolved gas substance is added, a film in which a powder such as porous zeolite or silica is added, and the properties of the film are changed by irradiation with gamma rays, and the dependence on the water content by the diffusion coefficient is introduced, and the hydroxyl group-containing group and the amide group are introduced. Film of the group, etc.
In recent years, the preservation technology that has attracted much attention has been through micropores or improved film formulation structures, improved air conditioning environment (ambience) in packaging bags, and a combination of oxygen scavengers and selectively permeable membranes. Among them, the following products will receive more attention.
1. Functional wrap film
Japan introduced a strong hermetic bag, which is made of a plastic called “Chiklun”. It has excellent oxidation resistance and is used to package new rice. It has a good preservation effect and can maintain rice for a long time. The color, fragrance and taste are unchanged, and the carbon dioxide generated in the bag also has the functions of preventing insects and mildew.
In addition, a fruit fresh-keeping package is also introduced, which is placed on a corrugated paper liner of a corrugated box, with a layer of polyethylene film, and then coated with a waterproof wax coating containing a trace amount of fruit disinfectant to prevent the fruit from evaporating. Suppresses breathing for fresh-keeping purposes. Packing the fruit in this box keeps the fruit fresh for a month.
American companies have introduced new types of fruit and vegetable fresh-keeping plastic bags, which can extend the shelf life of fruits and vegetables and reduce the loss of fruits and vegetables due to excessive ripening. The bag is made of natural activated clay and polyethylene. It is like a very fine filter screen. The gas and moisture generated by the fruits and vegetables during the ripening process can pass through the bag. The bag is not easy to breed fungi, so that the fruits and vegetables can be made. The preservation of the freshness is more than doubled.
American companies have developed plastic storage bags that can last up to three years. The fresh-keeping bag is attached with a plastic film on the inside of the ordinary plastic bag. The film contains an oxygen absorbing agent, which can absorb the oxygen that enters during the food packaging process, which causes the microorganisms that cause the food to rot to survive due to lack of oxygen. .
2. Silicon window air conditioning bag
The silicone window air conditioning bag is filled with a suitable area of silicone rubber film on the plastic film bag. The silicone rubber film selectively penetrates oxygen, carbon dioxide and nitrogen. This silicon window air conditioning bag has achieved good results in fruit storage. It can be used to determine the appropriate silicon window area under certain storage conditions. After a certain period of time, the concentration of oxygen and carbon dioxide in the package can be automatically adjusted to the required level. Generally, the large account of 1000kg apple is stored, and the silicon window area is 0.6m2, which can maintain oxygen and carbon dioxide at an appropriate level. Excessive carbon dioxide generated by respiration can be discharged through the silicon window. When the oxygen in the bag is insufficient, it can be penetrated by the silicon window. The key to silicon window air-conditioning technology is to select a silicon window film to determine the area of the silicon window and the suitable storage and storage temperature.
Third, sterile and antibacterial plastic packaging materials
Aseptic packaging can maximize the original nutrients and flavor of the food at room temperature under sterile conditions without the addition of preservatives. Extend shelf life for easy transportation and storage. Aseptic packaging is mainly used in food, high seasoning, medicine and cosmetics. The flexible packaging materials used are paper, plastic, aluminum-plastic composite film, multi-layer co-extruded aseptic packaging sheets containing high barrier plastics.
Antibacterial plastic packaging materials give certain antibacterial properties to plastic packaging materials. Now, a new type of masterbatch containing silver ions as inorganic antibacterial agents has been developed. Silver ions have significant antibacterial effect, and their antibacterial effect lasts for a long time. It will not be high due to gasification and migration, and will not pollute the environment. A film prepared by adding a silver ion-containing masterbatch (content of 1% to 3%) or a container having such a film laminated on the surface, which has been tested and found to contain 1% silver ion mother without a nutrient source. The film can completely kill the fungi that cause food poisoning within 1-2 days, and is widely used in deli meat, aquatic products and liquid food packaging.
Fourth, high heat resistant plastic packaging materials
Heat-resistant plastic flexible packaging materials used to be resistant to retort sterilization. They meet the packaging requirements for retort sterilization. At 12O°C, 10-20min, retort sterilization or heating, there is no obvious change in appearance shape and quality. Packaged foods are stored. During the process, no damage to the container, leakage of contents, secondary contamination of the microorganisms, and deterioration of the contents by light and heat occur. Basically, the aluminum foil having a light-shielding property is used as an intermediate layer, the high-barrier plastics PA and PET are outer layers, and the retort pouch made of a multi-layer composite cooking film having heat-sealing PE and PP as an inner layer is used most. Some new multilayer composite materials such as EVOH, PVDC, MXD6, and silicon oxide vapor-deposited films containing high barrier materials are also increasingly used.
With the increasing popularity of microwave ovens and microwave ovens, there is an increasing demand for packaging containers suitable for use in induction cookers and microwave ovens. In the electromagnetic oven, the requirements of the microwave oven for packaging materials are not significantly deformed, damaged at high temperature, and the content (additive) is not volatile, especially the heating characteristics of the microwave oven, and the metal material is not allowed in the packaging material, thus limiting The use of aluminum foil as the intermediate layer, PE, PP as the inner layer of the retort pouch. Therefore, a packaging container made of a multilayer composite material filled with PP and inorganic materials and a crystalline polyester (CPET) sheet is now widely used. New heat-resistant packaging materials resistant to higher temperatures, such as polysulfone film, polyetherimide, poly-4-methylpentene (TPX)/paperboard, etc., have also been developed, and they are all resistant to temperatures above 180 °C. It can meet the requirements of electromagnetic cookers and microwave ovens for packaging materials.
Five, special functional materials
Functional packaging materials: Other flexible packaging materials with special functions include moisture absorption, deodorization, deodorization, antistatic, rust prevention, UV blocking, release or adsorption of volatile gases, and convenience (easy to open, easy to seal) and Food and other materials. For example, a film prepared by adding a compound such as iron or ascorbic acid or activated carbon or zeolite to PE, PP or PVC, which has been developed in recent years, has an effect of removing malodor such as ammonia gas, mercaptan, hydrogen sulfide or dimethylamine. The agricultural and sideline products, aquatic products, and fresh foods with special odors are not scented, and are also suitable for garbage bags.
Sixth, nano composite packaging materials
Nanotechnology is a high-tech science and technology that has emerged in recent years. The most researched nanocomposite packaging material is polymer-based nanocomposites (PNMC). Commonly used polymers are PA, PP, PVC, PET, and the like. The plasticity, wear resistance, hardness and strength of nanocomposite plastic packaging materials have been significantly improved and enhanced. Compared with ordinary composite PA packaging materials, the PA6 nanocomposite packaging materials developed in Japan have improved tensile strength and tensile modulus by 110 MPa and 2.1 GPa, respectively, and the heat distortion temperature is increased to 150%, and the thermal expansion coefficient and water absorption rate are greatly reduced.
At present, the development trend of newly developed plastic packaging films at home and abroad is toward high performance, non-toxic and harmless, green, environmentally friendly, inexpensive, and convenient to use. Among them, soft packaging materials have been developed from non-food packaging fields such as industrial packaging, pharmaceutical packaging, building materials packaging, and cosmetic packaging, and their use range and dosage will be larger and larger.