What is the polyester bottle made of?
Polyester is the general name of thermoplastic saturated polyester represented by PET, including PBT, PEN, PCT and their * * * polymers. Among them, PET is the earliest developed, largest output and most widely used polyester product. In the field of packaging, the development of polyester, especially the development of packaging containers, is the most concerned. At present, more than 20% of PET has been used as packaging material, and the trend is increasing year by year. Packaging has become the second largest user of PET, second only to synthetic fibers.
Are polyester bottles plastic?
1, the backbone of the polyester family for packaging
(1)PET (polyethylene terephthalate)
Because PET can easily obtain amorphous, highly transparent and easy-to-stretch PET products through rapid cooling, when PET is used as packaging material, it can be made into bi-directional stretch packaging film, high-strength and highly transparent stretch blow-molded bottles from amorphous bottle blanks, or directly extruded or blow-molded into non-stretch hollow containers. PET film is transparent, oil-resistant, fragrant, hygienic and reliable, and is suitable for a wide range of temperatures (both high-temperature cooking and frozen packaging). However, the heat sealing performance is poor, so it must be used with other films (heat sealing layer), and the price is higher than that of ordinary plastic films, which limits the application of PET films in packaging. PET hollow containers, especially stretch blow-molded bottles, give full play to the properties of PET, have a good display effect on the contents and have a low cost. Therefore, when PET is used as packaging material, it is basically stretch blow molding, and the most widely used one is the small bottle below 2L.
With its superior performance, low cost and environmental adaptability, PET bottles have developed rapidly in the competition with other packaging materials (glass, tinplate, PE, PVC, etc.). ), but its poor heat resistance and gas barrier limit its application in occasions with high requirements for hot filling and air tightness, which people attach great importance to. In the process of improving its performance, polyester packaging has made new development. The first is to improve heat resistance. Ordinary PET bottles cannot be used to package things that need hot filling, such as juice, tea and so on. At present, three kinds of practical heat-resistant polyester bottles have been developed through research: heat-set bottles, which can meet the requirements of filling at 85℃; PET/PEN alloy bottles have high heat resistance, and can meet the requirements of hot filling above 80℃ on common injection, stretching and blow molding equipment. If it is heat setting, the hot filling temperature can reach above 90℃. And heat-resistant polyaryl compounds. To improve heat resistance.
The second is to improve the gas barrier. Although the gas barrier performance of PET is much higher than that of polyethylene, polypropylene, polystyrene and other plastics, it still can't meet the requirements for beer, liquor, perfume and other products that need strict preservation and taste preservation. There are three main ways to improve the gas barrier.
(1) Multi-layer composite, with PET as the main material, and other materials with good air tightness such as PVDC, EVOH, MXD6, PEN, etc. to make 3-layer or 5-layer bottles;
(2) adopting special treatment methods, such as coating epoxy resin barrier layer inside or outside the PET bottle, or carrying out plasma treatment (ACTIS technology);
(3) molding with other barrier resins, using PEN or PEN and PET * * * poly or * * * as raw materials, which not only improves the gas barrier performance of the bottle, but also improves the heat resistance of the bottle, and can meet the requirement of beer preservation for 3-6 months; It can also be disinfected by alkali washing and reused to reduce the cost. Because the first two methods have some problems, such as poor transparency, difficult recycling, complex technology and special equipment requirements, and although the air tightness has been improved, the heat resistance is poor, so they can only adapt to aseptic filling occasions. China's beer industry mostly adopts pasteurization technology after filling, so it is the development direction of beer plastic packaging suitable for China's national conditions to use PEN or the mixture of PEN and PET as raw materials and shape it through the existing PET bottle blowing machine equipment and technology, which deserves the attention of relevant departments and enterprises.
At present, the production capacity of non-fiber PET (polyethylene terephthalate) in China is 649,000 t/a, so developing the application of PET in other fields has become a hot spot in the industry at present. At present, there are three restrictive factors in the application of PET: ① poor melt strength; ② The crystallization speed is slow; ③ The dimensional stability is poor, which can not meet the needs of rapid injection molding in industry.
High viscosity polyethylene terephthalate (HVPET) is a crystalline polymer, which has the characteristics of high viscosity, excellent heat resistance, light resistance, acid resistance, low temperature resistance, oil resistance and impact resistance. The product has the characteristics of good crystallinity, good orientation, light weight, high strength and good air tightness. Its product surface is smooth, transparent, non-toxic and hygienic, and can be directly used for food packaging.
When packaging soup, spaghetti sauce, applesauce, jam, jelly and other foods, glass bottles are no longer used, but polyethylene terephthalate (PET) materials are used to make packaging cans. These cans are safe to use and will not be broken. For convenience of use, molded handles are also provided on the sides of these plastic cans. At an international packaging exhibition, several companies, including Rebecca Company of Schmalbach, showed several transparent PET bottles, which were much better than opaque HDPE bottles.
(2) polyethylene naphthalate
In 1998, polyethylene naphthalate (PEN) is a new type of "polyester" packaging material. This is because the molecular structure of PEN is similar to that of PET, but naphthalene ring is used instead of benzene ring, so the barrier performance of PEN is better than that of PET, especially gas barrier, ultraviolet resistance and good heat resistance (the thermal deformation temperature of common amorphous PEN reaches 100℃, while that of PET is only 70℃). Due to the industrial production of PEN, it will enter the packaging field in a large number in the near future, which will inevitably lead to another packaging revolution after PET. Aoki Company of Japan and Shell Company jointly developed the pen container for baby food. The resin used was Hipertuf90000 produced by Shell Company, and the production equipment was Aoki Company's 100LL220 injection stretch blow molding machine. PEN bottles can withstand the disinfection conditions required by low-acid foods (1 16℃ for 63min), and the shelf life is more than 16 months, almost the same as that of glass bottles. According to the dosage of PEN/PET of 10/90, the price per kilogram is only $2.00 (while the price of PEN is 1 1 USD), which shows that it has obvious price advantage.
The rapid development of new pen-making materials benefits from the industrialized production of ——NDC, a pen-making raw material, which will be attributed to Amoco of the United States and Mitsubishi of Japan, as well as the companies that develop and produce pens. In addition, due to the advantages of PEN, it also has broad prospects in the packaging of beverages, beer and cosmetics.
(3)PBS (polybutylene succinate)
At present, more and more attention is paid to biodegradable and economical polymer materials in the world. The synthesis of aliphatic polyester has become one of the research hotspots at home and abroad because of its biodegradability and economy. Its synthesis methods include biological fermentation and chemical synthesis. The former is mainly used to synthesize hydroxy fatty acid esters (PHA), and the polymer synthesized by the former is expensive. The latter is mainly used to synthesize linear polyester, which can be used for molecular design of products with low cost by ring opening and condensation. Because of their low melting point, aliphatic polyesters cannot be used as plastics alone, except poly (oxalate) and poly (butylene succinate). Poly (oxalate) is difficult to achieve high relative molecular weight, with poor stability and difficult practical application, while poly (butylene succinate) is favored because of its good thermal stability and high relative molecular weight.
Poly (butylene succinate) is a linear polyester, which was successfully synthesized by Polymer Research Institute of Tsinghua University Department of Chemical Engineering. The synthesis process includes esterification and post-polycondensation. Post-polycondensation can be carried out in vacuum, or at high vacuum and high temperature in an extruder in the presence of a chain extender. The resin synthesized by this method can be directly extruded into products, and the production efficiency can be further improved. At present, the research has done the following work: by controlling the appropriate reaction conditions, synthesize or find new catalysts to make the products have higher relative molecular weight; Catalytic polymerization and its biodegradation mechanism were studied. A variety of chain extenders were synthesized, and the chain extenders that quickly reacted with the terminal hydroxyl groups of prepolymerized polyester were discussed, so that the reaction could be completed in the extruder. Different monomers were polymerized with succinic acid and butanediol ester, and the molecular design of linear polyester was carried out to adjust its mechanical properties and biodegradability to meet the application requirements in different fields. The relationship between the structure and properties of linear polyester and its microbial degradability under different conditions was studied. At present, only a small batch of polybutylene succinate products are produced in Japan, and the relative molecular weight of products developed in Tsinghua University has reached the level of Japanese products. At present, the mechanism and application development research are being carried out, and pilot and expanded production are planned.
2. The main packaging fields of polyester application
(1) beverage packaging
In beverage packaging, the most successful application of polyester bottles is carbonated soft drinks (CSD), such as cola and sprite. CSD bottles have accounted for 1/3 of the total number of PET bottles. PET bottles are beautiful in appearance, flexible in design, high in strength, good in sealing performance to carbon dioxide, sanitary and reliable, and are ideal packaging containers for CSD, which are widely used in CSD industry. According to the statistics of China Beverage Industry Association 1998, PET bottles account for 57.4% of CSD packaging in China, followed by cans and glass bottles, accounting for 3 1% and 7% respectively.
(2) Edible oil packaging
PET bottle has good oil resistance, transparency, non-toxic, tasteless, not easy to break, good barrier to oxygen and good shielding to ultraviolet rays, and can protect edible oil from oxidation and deterioration for a long time. It has been successfully applied abroad, and the domestic demand in this field has been rising in recent years.
(3) Packaging of seasoning commodities
Liquid condiments such as soy sauce are a huge potential market for polyester bottles. The advantages of PET bottle in this field are its good fragrance retention, light weight and not easy to break. As early as 1995, Japan's application in this field has exceeded 30,000 t, accounting for 13% of the total consumption of PET bottles. In China, this kind of goods are still mainly packed in glass bottles, and the application of polyester bottles is still in its infancy.
(4) Beer packaging
China is a big country in beer production. In 2000, the beer output exceeded 210.4 million tons, ranking second in the world. With the rapid growth of beverage industry, the development prospect of polyester packaging bottle industry is very bright. PET bottles have the characteristics of light weight, low price, high use safety, good environmental protection and energy saving, and the production energy consumption can be reduced by about 50%. With the rapid growth of soft drink market, the annual consumption of PET bottles has increased to 65,438+08% in the past five years, ranking first in plastic food packaging. In particular, hot-filled PET bottles for filling beverages have become the fastest growing varieties of PET bottles, with an annual growth rate of over 50%. With the appearance of PET polyester beer bottles, it provides a broad development space. At present, some breweries in the United States, Britain, Japan and other countries have adopted polyester bottle packaging. If China's beer output exceeds 20 million t in 2000, it will consume about 25-30 billion beer bottles (including recycling), and even if it is partially replaced, its market prospect is immeasurable.
(5) Packaging of pesticide, medicine and daily chemical products
Polyester bottles can be used for some pesticide packaging, and low-cost PET pesticide bottles made of polyester have been put into production in China. PET bottles are safe and hygienic, and have good moisture-proof, oxygen-proof and display functions, so they are used in the field of medical packaging. Cosmetics, detergents and other daily chemical products are also a huge market for polyester bottles. PBT and PEN bottles have good chemical resistance, fragrance retention, high transparency, ultraviolet shielding and flexibility in styling design, which are the expected characteristics of cosmetics and other daily chemical products. Therefore, polyester bottles are widely used in the packaging of daily chemical products, especially the new PEN resin bottles with gas barrier and ultraviolet shielding will occupy a place in the packaging of perfumes and cosmetics.