Overview of extrusion composite flexible packaging technology
I. overview of extrusion composite
extrusion composite, also known as salivation composite, is one of the main production methods of composite flexible packaging. It melts thermoplastic plastics such as polyethylene and polypropylene in the extrusion compounding machine, and flows uniformly in a film form from the flat head. The construction awards are for separate land supply projects, which are continuously coated on the substrate, pressed by the press roller and cooled by the cooling roller, Make two or more composite films.
extrusion compounding has the advantages of fast production speed, simple production process, clean production environment, high production efficiency, simple operation, low cost, no solvent residue, no diaminotoluene (carcinogen) residue, etc. it is an economic and environmental protection composite film production method, which plays an important role in plastic flexible packaging
extrusion composite and dry composite have their own advantages and disadvantages:
1 Dry compounding is suitable for many varieties and a small amount of compounding. It is best to choose G-type impact device for film production, and extrusion compounding is most suitable for large-scale continuous production;
２. The production cost of dry compounding is high, and the production cost of extrusion compounding is relatively low;
３. Production speed, dry compounding is affected by the solvent volatilization rate in the adhesive. Generally, the maximum speed is only about 100m/min, extrusion compounding can generally reach 150m/min, and some extrusion compounding machines can reach 300m/min.
４. Under normal process conditions of dry compounding, the peel strength (plastic/plastic compounding) is generally 1 ~ 3 5N/15mm, suitable for most product requirements. The peel strength (plastic/plastic composite) of extrusion composite under general process conditions is 0 ７～１. 5N/15mm, suitable for general packaging materials. Products with high peel strength requirements must be added with thermal bonding resin. When compounded with thermal bonding resin, the peel strength can reach 10N/15mm or even higher;
５. Dry compounding adopts adhesive, and the coating amount is large, so it is easy to leave unreacted monomer (diaminotoluene) and solvent. It is difficult to control the process to fully meet the health requirements; Extrusion compounding basically does not use or only uses water-based primer (coating amount is small), there is no solvent and diaminotoluene residue, and the sanitary performance is good;
６. The dry composite film has good hardness and stiffness, and the extruded composite film is soft;
７. The thickness uniformity of dry-type composite film depends on the quality of the selected substrate and cannot be adjusted. The thickness uniformity and average thickness of the film must be adjusted for extrusion composite;
８. Dry compound production is easy to operate, and the labor intensity of workers is low; Extrusion compound production operation is not difficult, but the labor intensity of workers is slightly higher;
９. When compounding different products, the dry compounding process technology changes little, the extrusion compounding process needs to be adjusted frequently, and the requirements for process engineers are higher;
１０. Dry compounding has environmental pollution, safe operation and labor hygiene problems caused by solvent volatilization; Extrusion compounding has the problems of high ambient temperature and sometimes smoke.
II. The history and current situation of extrusion compounding at home and abroad
extrusion compounding has been emerging for 40 years since the 1960s, especially since the 1980s. Extrusion compounding has been in a high-speed development stage in Europe, America, Japan and South Korea. At present, extrusion compounding accounts for about 50% of flexible packaging in the United States and Europe, and 70% in Japan and South Korea. Extrusion composite products cover almost all packaging fields: food, daily chemical products, beverages, drugs, protective films, card protection films, and even aerospace products. All our products that adopt dry composite adopt extrusion composite in foreign countries. Dental paste tubes, paper plastic aluminum composite products, aerospace products that cannot be produced by dry composite also adopt extrusion composite, because foreign countries are in extrusion composite resin, process With in-depth research and continuous innovation in all aspects of equipment, extrusion compounding is moving forward to a higher level and has become the mainstream of the development of flexible packaging.
compared with advanced countries, the development level of extrusion compounding in China is far behind. At present, extrusion compounding products in China account for about 25% of flexible packaging, and most of them are low-grade instant noodles packaging. The development history of extrusion compounding in China can be said to be twists and turns, which has experienced the process of development, pause and redevelopment.
China began to develop extrusion compounding in the 1980s. In that year, a group of state-owned enterprises represented by Dalian color printing factory, Shijiazhuang color printing general factory, Qingdao No.8 plastic factory, Shanghai People's printing factory, Shenzhen best, Jiangmen plastic No.2 factory, Foshan Oriental introduced composite soft bags from Japan and other countries. In the third quarter, they were subject to environmental protection supervision and installation production lines. The main type of compounding was extrusion compounding machine, and the products were mainly two-layer instant noodles, The structure is BOPP/LDPE, the product grade is low, and the peel strength is not high. Only a few enterprises produce three-layer composite packaging film for biscuits, tea, milk powder and other packaging through continuous process and technology improvement. At the same time, some domestic machinery industries represented by Xuzhou light industry machinery factory have also begun to study and manufacture extrusion laminating machines, but the product grade is low, which fails to meet the requirements of soft packaging extrusion lamination. By the early 1990s, China's flexible packaging entered a large development period, and enterprises with various systems have mushroomed. Generally, small and medium-sized enterprises choose domestic equipment (the price of tens of millions of imported extruders is unbearable). The grade of domestic extruders is too poor, and the products produced cannot meet the needs of customers. During this period, domestic dry laminating machines, dry reusable adhesives Through the unremitting efforts of relevant enterprises, the products have reached a high level, which has promoted the rapid development of dry compounding, and the dry compounding products have also been recognized by customers. During this period, dry compounding products covered almost all packaging fields, and even instant noodles packaging also used dry compounding. By 1996 and 1997, most color printing products were dry compounding, including some products that used to use extrusion three-layer compounding. At this time, extrusion compounding can be said to have entered a dead end, and there is no hope
in 1998, with the rise of a new generation of domestic extrusion compounding machines represented by the exc series extrusion compounding machines of Jiangmen Huilong plastic machinery factory and the reform of extrusion compounding technology, extrusion compounding again attracted the attention of the industry and ushered in the spring of vigorous development. In addition to the traditional two-layer compounding, extrusion compounding is constantly expanding to the original dry household chemical products, food and other fields, Entering a new round of high-speed development period, more and more color printing and packaging enterprises began to use extrusion composite process to produce flexible packaging products. The tortuous development process of extrusion compounding in China is mainly determined by our national conditions: ① financial problems: China's flexible packaging enterprises, except for a few large packaging groups, are generally relatively small in scale and limited in capital. Domestic extrusion compounding machines are insufficient in performance and can only be imported, and the price of tens of millions of yuan of imported machines is unbearable, so they can only give up extrusion compounding, Switch to purchasing dry compound machine; ② Lack of performance of extrusion composite products: China's packaging has long emphasized stiffness and strength, and extrusion composite has obvious disadvantages in this regard - in the 1990s, the peel strength of extrusion composite was generally 0 6N/15mm, only pure LD with good vibration damping performance is used as the internal heat sealing layer. The heat sealing strength and tensile strength are low, and the film is relatively soft. In recent years, with the innovation of extrusion compounding process, the peel strength has been improved, and the heat sealing material has also been changed. The heat sealing strength has been greatly improved, and the tensile strength has also been improved. In addition to stiffness, other aspects have basically reached the level of dry compounding. ③ Although dry compounding has serious defects of solvent and diaminotoluene residues, which are stipulated in China's national standards, its indicators are far from the requirements of foreign countries, and only some large enterprises can detect and control solvent residues, most small and medium-sized enterprises do not detect at all, as for diaminotoluene, China's flexible packaging enterprises basically do not detect and control. In fact, these harmful and toxic substances do great harm to human body, especially the packaging of food, a large part of which is children's food. Children's long-term consumption of food packaged with toxic and harmful substances is very harmful to their health. At present, people in the industry have begun to pay attention to these problems. Extrusion compounding has been paid more and more attention because it has no solvent residue, no diaminotoluene residue and good hygienic performance; ④ Extrusion composite materials: China's petrochemical enterprises have insufficient production technology and cannot produce special extrusion composite resins. Thermal bonding resins such as EAA, EEA and EMA cannot be manufactured, and PP resin for extrusion composite has not been put into industrial production. Even the commonly used LDPE resin has only 1c7a1 models in China, and its performance is not very stable. There is a large gap between batches. In recent years, relevant petrochemical enterprises and scientific research institutions are also strengthening research. The trial production of PP for extrusion composite has been successful, and the thermal bonding resin produced by grafting method is also in trial production. Therefore, the problem of resin shortage can be solved in the short term (at present, it is mainly imported, and there are many types of imported materials). (to be continued)
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