The hottest polyester packaging materials show an

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Polyester packaging materials show an increasing trend year by year (1)

polyester is a thermoplastic resin represented by pet, which also won a place in the wood utilization market and the general name of polyester, including PBT, pen, PCT and their copolymers. Among them, pet is the polyester product with the earliest development, the largest output and the widest application. In the field of packaging, polyester, especially the development of packaging containers, has attracted the most attention. Now more than 20% of pet is used as packaging materials, and it is increasing year by year. Packaging industry has become the second largest user of pet, second only to synthetic fiber

I. performance and transformation of pet

1. Performance advantages and disadvantages of pet

because pet can easily obtain basically amorphous, highly transparent and easy to stretch pet products through rapid cooling, when used as packaging materials, pet can be made into biaxial tensile packaging film, and high-strength and highly transparent stretch blow molding bottles can be obtained from amorphous bottle blanks, and can also be directly extruded or blown into non stretched hollow containers. PET film has the properties of transparency, oil resistance, fragrance retention, sanitation and reliability, and a wide range of application temperatures (both high-temperature cooking and frozen packaging), but its thermal sealing property is poor, so it must be used in combination with other films (thermal sealing layer), and its price is higher than that of general plastic film, which limits the application of PET film in packaging. PET hollow containers, especially stretch blow molding bottles, give full play to the performance of pet, have a good display effect on the contents, and the cost is low. Therefore, when pet is used as packaging material, it is basically formed by stretch blow molding, among which the most widely used are small bottles with a volume of tens of milliliters to 2 liters, as well as large bottles with a capacity of 30 liters

2. Performance modification of pet

pet bottles have developed rapidly in the competition with other packaging materials (glass, tinplate, PE, PVC, etc.) bottles because of their superior performance, relatively low cost and adaptability to environmental protection. However, their poor heat resistance and gas resistance limit their application in hot filling and occasions requiring high air tightness, and have attracted great attention. In the process of improving its performance, polyester packaging has achieved new development

first, improve heat resistance. Ordinary PET bottles cannot be used for the packaging of fruit juice, tea and other items that need hot filling. At present, through research, three kinds of practical heat-resistant polyester bottles have been developed: thermosetting bottles, which can meet the requirements of 85 ℃ filling; Shaxiaolin said that pet/pen alloy bottles have high heat resistance. Bottles that meet the requirements of hot filling above 80 ℃ can be made on ordinary injection, drawing and blowing equipment. If heat setting treatment is carried out again, the hot filling temperature can reach above 90 ℃; It is made into multi-layer composite bottles with heat-resistant polyarylate to improve heat resistance

the second is to improve the gas resistance. Although the gas barrier property of pet is much higher than that of polyethylene, polypropylene, polystyrene and other plastics, it still cannot meet the requirements for beer, Baijiu, perfume and other products with strict requirements for freshness preservation and flavor preservation. There are three main ways to improve gas resistance. (1) Multilayer composite, mainly pet, with PVDC, EVOH, MXD6, pen and other materials with good air tightness added to make 3-layer or 5-layer bottles. (2) Special treatment methods are adopted, such as coating epoxy barrier layer inside or outside the PET bottle, or plasma treatment (ACTIS Technology). (3) Molding with other barrier resins, and using pen or the copolymerization or blend of pen and pet as raw materials, not only improves the gas resistance of the bottle, but also improves the heat resistance of the bottle, which can meet the requirements of beer storage for 3 ~ 6 months, but also can be alkaline washed, disinfected and reused, so as to reduce the cost. Because the first two methods have problems such as poor transparency, difficult recovery and treatment, complex process, special equipment requirements and so on, and although the air tightness is improved, the heat resistance is poor, so they can only adapt to sterile filling occasions. China's beer industry mostly adopts the pasteurization technology after filling, so using the copolymerization and blending of pen or pet as raw materials and molding through the current pet bottle blowing equipment and process is the development direction of beer plastic packaging suitable for China's national conditions, which is worthy of the attention of relevant departments and enterprises

II. History of polyester packaging development

polyester (PET) resin, which was invented in 1947, began research in 1922 and completed in 1941, is a promising packaging material and packaging product with long research history, wide application, and many family members (generally referred to as polyester) for calibrating the static force value of the fatigue machine of the modern packaging industry research detachment

in 1847, the Swedish chemist benzelius chemically synthesized the first polyester (PET) resin, but no one paid attention to it. In 1922, the chemist of DuPont company in the United States carried out polymer research with retries. In 1926, he invented nylon, but did not complete the final research of pet. In 1941, British chemists whinfield and Dickson finally made polyethylene terephthalate resin by condensation polymerization of terephthalic acid and ethylene glycol on the basis of Carloses

thermoplastic polyester resin (generally refers to) is a polymer composed of aromatic dicarboxylic acids and aliphatic aromatic diols. Pet was the first discoverer. Because of its excellent performance, it developed rapidly as the main packaging film. At that time, PBT (polyterephthalic acid) with excellent processability was widely used in the 1960s because of its poor formability; At the same time, pen with excellent comprehensive performance has been applied to a certain extent, but it has been restrained due to its high price. Subsequently, PBN and PTT polyester resins also came out one after another

in 1987, PET resin began to realize commercialization and became one of the pillars of plastics. In recent two years, pet developed fastest, followed by PET film, and PET fiber shrank. Recently, the development speed of pet in the world has slowed down, and the price has fallen. The growth rate of global pet demand has fallen to about 4% after 2000. Br in July 1995, Amoco company of the United States first realized the commercialization production of pen raw material NDC (dimethyl naphthalate), which led to a sharp decline in the price of pen and became the strongest competitor of pet1 and ball screw. Pen resin is similar to pet, only naphthalene ring replaces the benzene ring of pet, so all aspects of performance are better than pet. In particular, it is superior to pet in heat resistance, chemical resistance, radiation resistance, gas resistance, UV resistance and so on. Due to many excellent properties of pen (ethylene (alcohol) phthalate), in addition to entering the packaging field of pet, it can also be used as hot filling containers, pressure containers (beer bottles) and other chemical fields, and is known as the "Star" and "new polyester" in the world packaging industry

in June 1997, British shell officially released PTT (propylene terephthalate) for listing. Due to the development of a new process for the production of propylene glycol, the price of PTT is equivalent to that of pet, and PTT has both the high performance of pet and the excellent molding processability of PBT, so it is widely used. Br in addition, polyester resin also has biodegradable plastics such as PBS (polybutylene succinate), PBSA (polybutylene adipate), PES (polybutylene succinate), which is a new product of green packaging

(to be continued)

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