Application of plastics in the hottest packaging i

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Application of plastics in the packaging industry

first, the position of plastic packaging materials in the national economy. Plastic is a material with the largest application and the widest application range among the three major synthetic polymer materials: plastic, rubber and synthetic fiber. Its application range has penetrated into all fields of the national economy. Now the annual output of plastics in the world has exceeded 1. 600 million tons. However, there are still great differences in the consumption of plastic products in various fields. At present, the most widely used field of plastic products is the packaging and packaging industry, of which packaging plastic products rank first, accounting for the total amount of plastic products? 0%, which is nearly 10% higher than the total amount of plastic building materials, and has obvious advantages over other applications. In terms of packaging materials, plastic packaging materials have far exceeded traditional packaging materials such as glass, metal and wood, ranking second only to paper products. In terms of development speed, plastic packaging materials have surpassed other packaging materials and ranked first. It goes without saying that plastic packaging materials play a very important role in the whole national economy. However, compared with other traditional packaging materials, plastic is still a rising star applied in a short time after all, and its many potential advantages have yet to be developed and utilized. As a new type of material, its many shortcomings and limitations in performance also need to be well understood in order to avoid in use. Therefore, we need to objectively introduce and evaluate plastic packaging materials while engaging in plastic research, production and application, so as to promote the further development of plastic packaging materials. 2、 The main variety of plastic packaging materials. Most of the packaging materials used for various commodities are usually disposable. When the commodities are circulated from the production unit to the hands of consumers or the commodities are opened for use, the packaging materials will complete its mission and be recycled or disposed of as waste materials. Therefore, for packaging materials, first, their performance is required to be good, which should be able to meet the needs of protection and publicity of goods, and second, their cost should be as low as possible. The so-called general-purpose plastics in today's plastics, such as polyethylene and polypropylene, have the common characteristics of excellent performance, large production volume and low price, and are the preferred materials for plastic packaging materials; The second is the general engineering plastics with larger production scale, better performance, but higher price, such as thermoplastic polyester. As for expensive special engineering plastics, although they have unique advantages in some properties, they are generally not used as packaging materials for economic reasons. 1 general purpose plastics thermoplastics in general purpose plastics have the advantages of balanced performance, convenient molding and processing, convenient recycling of materials and waste materials, and low product prices. They are widely used in plastic packaging materials. The main varieties are polyethylene and ethylene copolymer. This kind of plastic includes high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene, vinyl acetate copolymer, etc. Polyethylene plastic is a typical polyolefin compound, non-toxic, odorless, tasteless, reliable health performance, acid, alkali, salt and a variety of chemical substances, stable performance; It has balanced physical and mechanical properties, outstanding moisture and moisture resistance, and special molding and processing properties. It can be easily made into plates, films, containers, flat wires and other plastic products for packaging, and the price is low. Therefore, it is widely used in packaging. As a packaging material, its main disadvantage is poor oxygen resistance. Among several kinds of polyethylene, high-density polyethylene has the best mechanical strength among polyethylene, and its barrier ability to water vapor is the best among various plastics. However, among several kinds of polyethylene, it has the worst softness and transparency. When products with good softness and transparency are needed, low-density polyethylene should be selected. The mechanical strength of linear low-density polyethylene is between high-density polyethylene and low-density polyethylene, Its biggest advantage is high puncture strength, high tear propagation strength, and outstanding stress cracking resistance; In addition, its heat sealing performance is also better than that of high-density polyethylene and ordinary low-density polyethylene. Therefore, it is a good substrate for film, and one of its main disadvantages is that its molding processing performance is slightly inferior. Ethylene vinyl acetate copolymer is also an ethylene polymer widely used in packaging. Its price is slightly higher than that of polyethylene, but it is still a relatively cheap variety in plastics. With the increase of the content of vinyl acetate, its cold resistance, softness, heat sealing and transparency are improved. However, when the content of vinyl acetate exceeds 10%, it may show sour taste and is not suitable for direct contact with food. 2. Polypropylene and propylene copolymer. Polypropylene, like polyethylene, is a typical polyolefin polymer, so it has many similar properties, such as good chemical stability, non-toxic, odorless, tasteless, reliable sanitary performance, etc. compared with polyethylene, polypropylene has the main advantage of good heat resistance, and the use temperature can reach 120 degrees. Therefore, the composite bag with propylene as the heat sealing layer is used for cooking and sterilization. In addition, the strength of polypropylene is significantly higher than that of polyethylene. One of the biggest defects of polypropylene performance is poor low temperature resistance. Polypropylene homopolymer has a large brittleness on the surface at 0 ℃. The copolymer of propylene and a small amount of ethylene can significantly improve the cold resistance of polypropylene, but the heat resistance also decreases correspondingly. As a packaging material, it is very similar to polyethylene. Polypropylene has good moisture resistance and moisture resistance, but it has poor barrier to non-polar gases such as oxygen, carbon dioxide and nitrogen. When goods need to be stored in oxygen barrier, they need to be packed with the so-called barrier packaging material, or the composite of polypropylene (polyethylene) and barrier packaging material is used as the packaging material. 3. PVC is also a general-purpose plastic with good comprehensive performance and low price, and it has many additives. Through the adjustment of the formula, the performance of the product can be greatly changed. For example, rigid PVC products can be made with little or no plasticizer. UPVC products have good rigidity and good water and moisture resistance as well as the permeability of oxygen, carbon dioxide and nitrogen. Its oil resistance and transparency are also significantly better than polyolefin plastics. However, it is difficult to recycle and incinerate the waste after packaging. It is easy to decompose in the process of recycling and processing. During incineration, substances such as hydrogen chloride harmful to the environment will be produced, and energy will be consumed. Therefore, the application of PVC in packaging is limited, and with the continuous improvement of people's awareness of environmental protection, its application in packaging is gradually replaced by other plastics. 2 engineering plastics in the field of packaging, the engineering plastics used more are thermoplastic polyester and polyamide. These two kinds of plastics have many similarities. At first, they were studied and developed as raw materials of synthetic fibers. Later, they entered the plastic field because of their high strength and easy molding, and became one of the main varieties of engineering plastics, and then gradually used as packaging substrates. The main characteristics of thermoplastic polyester and polyamide in performance are oil resistance, high and low temperature resistance, good performance in blocking oxygen, carbon dioxide and nitrogen, non-toxic and sanitary performance, so they are common substrates for barrier films. The composite films made of them can be used for cooking packaging, vacuum packaging, deoxygenation packaging, etc. As a composite film substrate, in addition to the above characteristics, the main feature of nylon is its outstanding puncture resistance, which is very beneficial for packaging bone food, but it is relatively easy to be affected by moisture in the air, and its oxygen resistance decreases in a humid environment. It is particularly worth mentioning yesterday that recently, with the improvement of thermoplastic ester production technology and the expansion of production scale, its price has decreased significantly. At the same time, due to the enhancement of people's awareness of environmental protection, waste is easy to be recycled by physical or chemical methods. Thermoplastic polyester products have doubled their value, and have achieved rapid development in hollow containers and film products. In addition to thermoplastic polyester and polyamide, polycarbonate is also used as working plastics in packaging. Polycarbonate is mainly characterized by high temperature resistance, high transparency and high strength, which is especially suitable for recyclable (repeated filling) hollow containers. At present, the practical products are mainly milk bottles and 25L purified water buckets. Due to the high price, other applications are rare. 3 other common packaging plastics worth mentioning include polyvinylidene chloride (PVDC), ethylene vinyl alcohol copolymer (EVOH), high acrylonitrile resin (Pan) and polyvinyl alcohol (PVA). These plastics are famous for their high barrier to non-polar gases such as oxygen, carbon dioxide and nitrogen. In addition, they have outstanding oil resistance. In addition to the above characteristics, polyvinylidene chloride also has high moisture and moisture resistance, which is an ideal packaging material for food commodities. In addition, polyvinylidene chloride solution or lotion can be used to form an extremely thin protective layer on the film (or the surface of hollow containers), which can play an obvious effect of oxygen and moisture resistance. For this reason, although PVDC has some disadvantages, such as high price, difficult molding and processing, and hazardous substances such as hydrogen chloride will be produced during waste incineration, PVDC is still widely used in packaging at present. Ethylene vinyl alcohol copolymer is one of the best barrier plastics, and it is also the best type of high barrier plastics. In addition, waste incineration will not produce toxic substances harmful to the environment. Therefore, it is generally considered to be an excellent plastic packaging material with great development prospects. However, due to its high price, its application is greatly limited. At present, it is only used for high-grade composite bottles, multilayer composite films and barrier layers of composite sheets. However, it cannot be used to test the tensile properties of rubber. High acrylonitrile resin and polyvinyl alcohol are limited in promotion and application due to difficult molding and processing. High acrylonitrile resin can be used to make biaxial tensile bottles with good barrier properties, while polyvinyl alcohol is mainly used to make thin film plastic packaging materials. PVA biaxially stretched film is mainly used as the substrate of high barrier composite film; Non stretched polyvinyl alcohol film is mainly used for single film bag making, which is used as a high-grade packaging bag for clothing. It can provide high transparency, high gloss and bright and firm printing patterns. In addition, it also has excellent antistatic property, without the common problem of dust absorption of ordinary plastic film bags due to static electricity, making the packaged goods have excellent display effect. 3、 Main forms of plastic packaging materials 1. Plastic film plastic film usually refers to the thickness of 0. Flat and soft plastic products below 25mm plastic film is the most widely used variety of plastic packaging materials. In addition to the plastic film used in ordinary plastic packaging bags, there are many special varieties, such as liquid packaging film, shrink film, wrapping film, refrigerator fresh-keeping film, fruit and vegetable fresh-keeping film, surface protective film, kink film, etc. plastic film is mainly used to prepare all kinds of packaging bags. In addition, there are some common packaging forms, such as winding packaging, kink packaging, surface protection and so on. 2. Plastic containers are another kind of widely used plastic packaging materials that can be compared with plastic film. Plastic containers, hollow containers, turnover boxes, cups, plates, etc. (1) hollow containers, its main

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