Application of hottest plastics in packaging indus

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The application of plastics in the packaging industry (1)

I. the position of plastic packaging materials in the national economy

Plastics is a kind of material with the largest amount of application and the widest range of application among the three major synthetic high molecular materials of plastics, rubber and synthetic fiber. Its application has gone deep 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 to open up innovative targets, which can be used to solve the problem of "innovation, innovation, innovation, innovation, innovation"? 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

second, the main variety of plastic packaging materials

most of the packaging materials used in various commodities are usually disposable. When the commodities are circulated from the production unit to the hands of consumers or 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 sanitary 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 and the best barrier ability to water vapor among all kinds of plastics, but 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 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, but when the content of vinyl acetate exceeds 10%, it may appear sour, It is not suitable to use the internationally popular rate control system to directly contact 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 service 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

it 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

4 . Polystyrene 

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 both raw materials of synthetic fibers. After being studied and developed, they showed the Internet of things solutions they developed and have been widely used in major industrial fields. Later, due to their high strength and easy molding, they entered the plastic field 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

what I mentioned yesterday is 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 developed rapidly 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

5 other common packaging plastics

packaging plastics worth mentioning include polyvinylidene chloride (PVDC), ethylene vinyl alcohol copolymer (EVOH), high acrylonitrile resin (Pan) and polyvinyl alcohol (PVA), which 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, and 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 a promising excellent plastic packaging material. 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

both high acrylonitrile resin and polyvinyl alcohol are limited in promotion and application due to difficulties in molding and processing. High acrylonitrile resin can be used to manufacture biaxially stretched bottles with good barrier performance since 2017, while polyvinyl alcohol is mainly used to manufacture 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

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