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Production technology status of water-soluble PVA film

water-soluble PVA film is a new type of plastic product emerging in the world in recent years, belonging to the plastic film manufacturing industry. As a new green packaging material with polyvinyl alcohol and starch as main raw materials, it has water and biological degradation characteristics, and can be completely degraded into CO2 and H2O. It is a high-tech environmental protection product worthy of the name. It has been recognized by national environmental protection departments in Europe, America, Japan and other countries. Water soluble PVA film has many advantages, such as excellent transparency and gloss, non electrification, large tensile strength and tear strength, good oil resistance, excellent gas barrier, heat sealing and bonding, large moisture permeability, demoulding and good metal plating. It also has water solubility and biodegradability under certain conditions. Therefore, as a new packaging material, it has an extremely wide and unique use in flexible packaging. Development status of water-soluble film production technology at home and abroad at present, the team pointed out in the paper released in July that the process methods for manufacturing PVA film at home and abroad mainly include ① good thermal stability; ② Good dispersion; ③ Small solution salivation method (wet method) and extrusion film blowing method (dry method). These two processes are "born out" of traditional plastic film production. As PVA is a water-soluble substance, the film making process conditions are different from those of thermoplastic. Therefore, the above two processes are directly applied to the production of PVA film, and there are still many technical problems, which also lead to some economic problems, such as difficult quality control, low efficiency, high energy consumption, large floor space, and high equipment investment. Therefore, research and improvement of these two types of process technologies and equipment to make them more suitable for PVA film production is the research and development focus of the industry at home and abroad. The basic production process of solution casting method includes: water dissolving PVA → casting coating → drying (heat treatment) → stripping → coiling → finished product. The casting process is relatively simple, but the product quality is difficult to control, with low film yield, high energy consumption and large equipment investment. The process flow of extrusion and film blowing is: PVA raw material, water, plasticizer, lubricant (pigment) → forced circulation mixing → extrusion granulation → melting, extrusion and film blowing with a wide range of application → modification treatment → winding → finished products. The extrusion film blowing method has significantly improved the product quality and production efficiency compared with the tape casting method. However, PVA must be modified. After early granulation, the process and the amount of auxiliary materials are increased. The resin and film must be heated repeatedly and repeatedly throughout the production process, and the moisture content in the film must be maintained at 15% ~ 35%. The process is complex, difficult in technology and high in energy consumption. Moreover, the film is formed, stretched and shaped at the same time, the molecular chain is difficult to move, the degree of orientation is poor, the strength of the obtained film is not high, and the inherent characteristics of PVA resin are not brought into full play. From the domestic situation, the research and application of the solution salivation method and the extrusion film blowing method have entered the application stage. Among them, Hunan University of Technology (the former Zhuzhou Institute of Technology) has researched and developed the steel strip solution casting coating method to produce PVA film, which has been promoted and applied in many domestic enterprises. Its products occupy more than 2/3 of the domestic market and are exported to India and the United Kingdom. The production process is as follows:

figure I schematic diagram of production process of water-soluble plastic packaging film by casting

Beijing Industrial and Commercial University and other units have researched and developed the extrusion blown film method. At present, this technology has also been applied to two domestic enterprises, with production lines built or under construction. In addition, it is understood that the two companies in Lanzhou are developing the roller solution salivation method to produce PVA film technology. At present, it is still in the pilot stage and has not been put into mass production. At present, there is still a big gap between the water-soluble film produced by domestic technology and similar foreign products, which is mainly reflected in the following aspects: the main problem of the water-soluble film produced by the solution salivation method is that the film thickness is uneven, which is due to the poor quality of the domestic film-forming steel strip and the large deformation at high temperature in the production process. The production speed of solution casting method is slow, the energy consumption is high, and the equipment is complex. The production speed of the steel strip solution salivation method is about 3 ~ 7m/min, while the roller method is slower, only 1 ~ 2m/min. This directly affects production. In order to solve the requirements of the installation details and fixtures of the tensile testing machine and solve the problems of slow production speed and high energy consumption, at present, the steel strip solution salivation equipment has gradually replaced the expensive and rising fuel oil with natural gas, coal gas or coal to produce hot air to dry the Hydrosol and form a film. At the same time, we are constantly studying and optimizing the drying system to improve the drying efficiency. Although the water-soluble film produced by extrusion blowing method is fast, it has the problems of more uneven film thickness and poor water solubility (incomplete dissolution), which directly affects its application range. Although there are still some problems in the quality of domestic water-soluble films, they can fully meet the requirements for packaging and can completely replace imported products. The application status of water-soluble film in flexible packaging is mainly used for product packaging, as a temporary carrier for the production process of wigs and embroidery, for agricultural seed belt seedling raising, washing bags and so on. The main applications in packaging are as follows: 1. The packaging (quantifiable) of products used in water is mainly used for the packaging of pesticides, pigments, dyes, cleaning detergents, herbicides, fertilizers, cleaners, water treatment agents, concrete additives and other products used in water, so as to reduce environmental pollution and improve the working environment. 2. Washing and packaging high-temperature water-soluble PVA film packaging bags are used in hospitals to pack contaminated articles and clothes. During disinfection and cleaning, the packaging bags are directly put into the cleaning and disinfection equipment to reduce the medical staff's contact with contaminated articles and clothes and avoid cross infection of diseases. 3. Clothing packaging PVA film has the characteristics of no static electricity, better transparency and gloss than other films. It can make articles more beautiful and improve their added value when used in textile packaging. 4. PVA film used in food packaging is a material with excellent barrier performance. As a barrier layer material for food packaging, the storage life of packaged food can be greatly extended. 5. The PVA film used in the packaging of electronic and electrical products is almost free of static electricity, so it is especially suitable for the packaging of electronic and electrical products. The water-soluble PVA film can also be used to make high value-added anti-counterfeiting and environmental protection packaging with novel anti-counterfeiting function by combining its good printing performance and controllable water solubility with special ink, which will also be welcomed by high-end electronic product manufacturers. 6. In the aspect of agricultural seedling raising, the water-soluble polyvinyl alcohol film packaging belt or package packed with plant seeds is placed in the soil, which can not only prevent the seeds from being blown away or eaten by animals in windy sand areas, but also make the plants grow according to the layout of seed belt or seeds. After the water-soluble polyvinyl alcohol film is dissolved by rain or moisture, the polyvinyl alcohol distributed around the seeds improves the water retention of the soil and is conducive to the germination and growth of seeds. In addition, pesticides and nutrients can be made into a part of the seed belt to promote the growth of seeds. This technology will also have great potential in increasing farmland production, afforestation and desert reconstruction. In addition, some users are exploring the feasibility of water-soluble PVA film in cigarette packaging, drug packaging, fruit preservation packaging, etc. Although water-soluble PVA film has been widely used in packaging, its main application in China is not in the field of packaging, but in the fields of embroidery and water transfer printing. The main reason is the price. As the national consumption level of China is still relatively low compared with that of developed countries, it is difficult to accept the current price of PVA film in packaging. Therefore, water-soluble packaging film is mainly used for the packaging of export products. Market outlook the history of industrialized development of PVA film in the world is only more than ten years, and it has been less than ten years since it was put on the market. It is later in China, and the industrial research and development has really started in the past five years. Therefore, the market research of PVA film products, whether it is Chinese government departments, industry departments, research units or enterprises, lacks systematic and accurate grasp and understanding. At present, there is no authoritative information or data about the production, demand, growth and growth trend analysis of PVA film at home and abroad. However, China is a big producer of PVA (polyvinyl alcohol), and its total output is lower than that of Japan and higher than that of the United States; At the same time, it is also a large plastic consumer. In the current total consumption of various plastic films of nearly ten million tons per year, even if PVA film replaces 5% of the total consumption, it will need hundreds of thousands of tons of demand every year. With the development and progress of society, people pay more and more attention to the protection of the environment on which we live. In particular, with China's entry into the WTO and the approaching of the Beijing 2008 Olympic Games, China is gradually in line with the international developed countries, and the requirements for packaging environmental protection are increasing. The PVA film with excellent performance and biodegradability will be paid more and more attention and applied by people. Undoubtedly, the PVA flexible packaging film will be studied and applied in China Development and application have broad market prospects

reprinted from: Guangdong packaging

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