1. Types of Substrates for Composite Flexible Packaging Flexible composite packaging is easy to sell and use. Composite films, such as paper/plastic composite films, plastic/plastic composite films, and aluminum/plastic composite films, are produced by compounding various substrates (mainly paper, plastic film, aluminum foil). Among these substrates is a plastic film.
Different substrates have different roles in the composite film, according to which the substrate can be divided into: (1) base film. Mainly to give the basic packaging of the composite film required performance, such as a certain degree of mechanical strength, barrier properties, transparency, etc.; (2) functional film, to give special features to the composite film, such as high barrier properties, gas selective penetration, etc. (3) Heat-seal the adhesive film so that the composite film can be heat-sealed and bonded. Usually, the composite film is divided and called by the base film, and a polypropylene composite film, a polyester composite film, a nylon composite film and the like are added.
Almost all plastic films can be used as packaging materials, but as a composite film substrate, mainly a large number of varieties, such as polyethylene (PE), polypropylene (PP), polyester (PET), nylon ( PA-6, PA-66), etc., as well as functional (barrier properties, etc.) excellent varieties, such as polyvinylidene chloride copolymer (PVDC). Ethylene and ethylene acid copolymers (EVOH), ionomers, and the like. These substrates (plastic films) can be divided into calendered film, blown film, cast film (CPE, CPP), biaxially stretched film (BOPP, BOPET, BOPA), coextruded composite film, etc. according to the forming process; The barrier properties are classified into special high barrier properties (such as PVDC, EVOH), excellent barrier properties (such as BOPA, BOPET, acrylonitrile copolymers), and barrier properties (such as CPE, CPP, and BOPP).
2. Properties and Applications of Composite Flexible Packaging Substrates Which kinds of substrates are used to form a composite film for composite flexible packaging depends on the nature, state, and packaging requirements of the packaged product. From what we now know, there are many types of goods or products that can be packaged in composite flexible packaging, such as dry foods such as beverages, fruit juices and jams, oils, biscuits, and dried vegetables, and powdered products such as tea and milk powder. Medicines and supplies, meat products, hardware, etc., their properties and packaging requirements vary, some require preservation, some require preservation of fragrance, some require transparency, and some require higher intensity, and so on. Therefore, the basic physical properties of the substrate must be fully understood.
For the physical properties of the substrate, please refer to the "Handbook of Packaging Materials and Containers" published by Guangdong Science and Technology Press. For the composition and packaging applications of the composite film, the composition and packaging applications of the BOPP composite film, BOPET composite film and BOPA composite film are provided in detail in the “Packaging Materials and Containers Manual†book 258-261.
In addition to the packaging requirements, the processability and economics of the substrate (packaging costs) must also be considered. The following is an example.
Dry food packaging for instant noodles, biscuits, etc., audio cassettes, video tapes, cigarettes and other box packaging, candy and other small packaging, because the packaged goods require moisture, anti-pollution, a tightening effect, etc., and hope that the packaging costs are low, the selection of low prices The biaxially oriented polypropylene film (BOPP) is a suitable composite film for the base film. In addition to the lower price of BOPP, the more important is the low water vapor transmission rate.
Tea, coffee, milk powder, etc., require both moisture protection and sufficient preservation of fragrance. Therefore, a composite film with a good barrier property and a high retention of BOPET as a base material is more appropriate if higher barrier properties are required. For UV resistance, a layer of aluminum foil or vacuum-evaporated aluminum film is also required.
Meat products, such as sausages and ham, require fresh-keeping, anti-corrosion, and certain moisture retention. Nylon film is a flexible film for base film. Because nylon film is better for oxygen barrier, it has more water. Air permeability.
Liquids such as beverages, fruit juices, oils, shampoos, etc. require packaging that is resistant to extrusion. Therefore, good strength substrates such as BOPET, BOPA, etc. should be used. In addition, the packaging of beverages, juices, and other foods requires preservation. , anti-corrosion, etc., so we must also consider the barrier properties of the substrate, BOPET, BOPA can meet the requirements.
For packaging of foods or articles that require steaming, the strength of the base film, such as BOPET, BOPA, and heat-sealable, heat-sealable, heat-sealable adhesive film, such as cast polypropylene film (CPP), should be selected. ), cast polyethylene film (CPE). Of course, the use of composite films made of them can be used to cook and package products can be resistant to cooking, but also depends on the choice of adhesive (now a lot of polyurethane adhesives) and quality, as well as the level of production technology.
3. Development of New Substrate for Composite Flexible Packaging The development of new substrates includes two aspects: the development of new thin films of new plastic varieties and the modification of composite flexible packaging substrates.
Thin films of new plastics are expected to be used in composite flexible packaging substrates, including polycarbonate (PC), poly(2,6-naphthalene dicarbonate) (PEN), poly 4-methyl-1-pentene (TPX) and so on. PC film has been manufactured in China by casting method; the thickness can be 20μm. TPX film is resistant to boiling water and non-toxic. Its main characteristic is that it has a large difference in the rate of nitrogen and oxygen permeation. It is especially suitable for packaging meat and vegetables. It has high heat resistance and can be used in cooking bags.
The new substrate developed by the modification has a polyester film modified by isophthalic acid, and the barrier property of the film is improved compared to the unmodified one; there are new film varieties developed through blending or additive technology, such as high transparency. Polyester film and polypropylene film, extinction and white polypropylene film, etc. (Guangzhou Chemical Industry, 1998, 26(1): 61)
In addition, the use of new post-processing technology to develop new substrates has achieved new results in recent years. For example, vacuum evaporation of silica on BOPET film improves barrier properties, or addition of a small amount of titanium during vacuum evaporation of aluminum can improve evaporation. Aluminum film appearance and packaging effect.
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