In the new century, the world economic restructuring continues to deepen and the transformation of sustainable development strategies is the overall background of the world's industrial transformation, and it is also the background of the environmental changes in the plastic flexible packaging industry. With the impact of the environmental protection wave, consumers are increasingly demanding the packaging of goods. Green packaging is a requirement for the development of international environmental protection. It also represents the development trend of packaging industry in various countries, and is one of the important contents of improving product market competitiveness and avoiding new trade barriers. Corresponding to this, the greenization of plastic flexible packaging has also become an important development trend. First, what is green packaging? In general, moderate packaging that can be reused, reused, or degraded, and that does not pose a hazard to the human body or the environment throughout the product's lifecycle is called green packaging. The most important meaning of green packaging is to protect the environment, but it also has the significance of resource regeneration. Specifically, it should have the following meanings: 1 Implement packaging reduction. The green packaging should be the least amount of appropriate packaging under the conditions of protection, convenience, and sales. To save resources and energy while minimizing the amount of packaging waste. 2 It should be easy to reuse or easy to recycle. Through repeated use, or through the recovery of waste, production of recycled products, incineration and heat energy, and composting to improve the soil and other measures to achieve the purpose of recycling. 3 Waste can degrade and decay. In order not to form permanent waste, non-recyclable packaging waste should be able to decompose, and then achieve the purpose of improving the soil. 4 Materials should be non-toxic and harmless to humans and organisms. The packaging material should not contain toxic elements, halogens, heavy metals, or the content should be controlled below the relevant standards. 5 During the entire life cycle of the packaged product, no pollution should be caused to the environment. That is to say, the packaging products shall not cause harm to the human body and the environment from the collection of raw materials, material processing, manufacturing of products, use of products, recycling of wastes, and the whole process of the final disposal. According to the above requirements of the green packaging, the plastic flexible packaging industry is undergoing a profound transformation in terms of green, whether it is processing equipment and processes or material selection. Second, the green process of plastic flexible packaging processing process 1. Greening process of gravure printing The gravure ink contains a large amount of volatile organic solvents, accounting for almost 50% of the gravure ink. Among them, xylene, toluene, ethyl acetate, butanone and other low-boiling, highly volatile solvents contain aromatic hydrocarbons that are toxic and flammable, and are the main factors of environmental pollution. In addition, the gravure printing speed is extremely high, and it is necessary to use fast-drying inks with extremely strong volatility. External drying (gravure printing with a drying process) is also required by electricity or infrared heating to meet the printing requirements, resulting in large gravure exhaust emissions. Gravure printing is particularly prominent in the environmental issues of all printing processes. Many authorities in the printing industry believe that gravure printing will lose its competitiveness in the market and will eventually be replaced by other printing technologies unless practical measures are taken to solve the gravure problem of gravure printing and improve the environmental performance of gravure printing. (1) Reduce the impact of organic solvents on the environment Due to the large amount of solvents used in the gravure printing process, it is an important cause of solvent contamination in the gravure plastic flexible packaging industry. With the enhancement of people's environmental awareness, the environmental issue of solvent in the gravure printing process has gained wide attention. In recent years, we have seen the environmental protection awareness of the flexible packaging industry and related departments strengthened and reflected in the improvement of production processes and related product emissions. Emission of solvent-laden exhaust gas from the exhaust system of the gravure printing machine and the composite machine caused environmental pollution. At the same time, the volatilization of the solvent during use also caused indoor pollution and safety problems. Therefore, the entire printing unit can be fully enclosed. Reduce the spread of solvents in the workshop. Ultrasonic gravure roll cleaning system is used to reduce the amount of solvent used. By setting up the printing plate pre-cleaning device of the printing plate, the printing plate roller is automatically cleaned on the machine at the end of the printing, which can effectively prevent the ink from drying on the printing plate. This type of cleaning device can complete most of the cleaning of the printing plate rollers, significantly reducing the amount of manual cleaning work and also improving the operating environment. In the gravure discharge system, the solvent is treated by means such as solvent recovery treatment to reduce the discharge of solvent into the air; some printing plants have begun to use a single solvent ink in order to make the solvent more convenient for recycling. At the same time, the explosive lower limit control system with volatile solvent concentration is adopted, and through part of the hot gas circulation, the energy consumption for drying is maximally saved. In order to reduce the total amount of solvents, the development of high-concentration, low-viscosity inks suitable for shallow printing is an important research direction. Even solvent-free solid inks are likely to be on the market. Relevant persons of Siegwerk Ink Company believe that the HotTech ink technology they are developing has great application potential. This patented HotTech ink technology is a solvent-free, solid gravure ink that dissolves immediately before being transferred to a printing plate roll and is expected to be on the market within a few years. (2) Development and application of benzene-free solvent inks and water-based inks to achieve solvent-free benzene and water-based gravure ink printing Currently used gravure printing inks are generally made of chlorinated polymers. In the ink production process, the chlorinated polymer needs to be dissolved using a strong solvent (such as toluene and other aromatic solvents), and the viscosity of the ink needs to be adjusted during the printing process using toluene. Chlorinated polymer ink systems are now considered unsuitable for environmental protection. This is because the chlorofluorocarbons that are volatilized during production can damage the ozone layer. The use of aromatic solvents (toluene) can cause injury to the health and safety of workers during ink production and printing. In addition, the solvent residue in the packaging ink is another important issue to pay attention to. Since toluene is a slow-drying solvent, it easily remains in the dried ink film layer, corrupting the food in the package and causing harmful odors. The production of plastic gravure inks is under the control of fire laws, labor safety laws, and health laws and regulations. Therefore, it is an inevitable trend to actively develop and apply green gravure inks and water-based inks that meet environmental protection requirements. Although water-based gravure inks have attracted much attention as an alternative to toluene-based inks, the inks in packaging film printing are still water-based and have not yet reached a truly practical stage. On the whole, the important reason why water-based gravure inks have not been popularized further is that the printing performance and quality are still not up to the standard for solvent-based gravure inks. This is mainly due to the higher surface tension of water, which makes it difficult for the ink to wet. If the printing speed and the printing quality of the gravure solvent ink are to be obtained, not only the aqueous ink itself requires advanced technology, but also the gravure printing apparatus and the printing plate roller need to be improved. For example, changing a corrugated or engraved drum with a groove depth of approximately 38-42 micrometers to a laser-made plate roll with a groove depth of approximately 24-28 micrometers also requires more effective and powerful drying equipment and printing that must be manufactured using corrosion-resistant materials. Roller, ink pump and scraper components. These improvements require considerable investment. (4) Development and application of gravure alcohol-soluble composite plastic ink Since water-based gravure inks are not yet fully capable of replacing toluene inks, the ink industry has been working hard to develop alcohol-soluble inks that can be accepted by the environment. Alcohol-soluble ink can effectively solve the health problems caused by toluene ink and solvent residue affect the quality of packaged food and other issues. In Europe and the United States, this development has become a trend. In Asia, such as Singapore, South Korea and other countries, toluene ink is being eliminated, will be replaced by alcohol-soluble gravure ink. Alcohol-soluble inks are now widely used in the domestic gravure printing industry. It can be predicted that in the near future, alcohol-soluble inks will occupy a major share of the high-grade food and pharmaceutical flexible packaging ink market in China. The gravure alcohol-soluble composite plastic ink has the characteristics of low odor, benzene-free, and the use of such environmentally-friendly inks will certainly increase the competitiveness of gravure printing in the field of packaging printing. $Page break $ 2. The greening of the composite processing process. (1) Development and Application of High Solids, Low Viscosity Composite Adhesives Domestic adhesive production companies have matured and their technological development capabilities have been greatly enhanced. Representative companies such as Zhejiang New Oriental, Beijing Chemical Research Institute and Beijing Gaomeng have emerged. These enterprises have strong research and development capabilities and their products are increasing. Solid, low viscosity and functional development. The use of high solids and low viscosity adhesives has become an important development direction for dry composite adhesives. Previous two-component polyurethane adhesives, whose main agent had a solids content of 35% or 50%, have now been increased to 75% or 80%. 75% solids two-component polyurethane adhesives account for 60% of the market, and the market for 50% solids two-component polyurethane adhesives is shrinking to less than 30% of the market. Due to the characteristics of high solids and low viscosity, it is possible to use high solids content for high-speed composite machining. Using a high solids binder at the same coating weight can effectively reduce the amount of solvent used and has the following advantages: 1 Reduce solvent consumption. (2) Development and application of water-soluble adhesives The advantage of water-soluble binders is that water replaces organic solvents, there is no potential risk of combustion explosion, there is no pollution to the environment and the operator is poisonous, and the cost is low. However, this adhesive has poor coating properties and poor wettability to the composite substrate (because the surface tension of water is 72 mN/m, and the surface tension of the substrate is mostly only about 38 mN/m). Adhesion is not high. In addition, the heat capacity of water is large, and it takes more energy to dry the ink. This not only limits the production speed, but also increases the production cost. At the same time, water vapor also causes certain corrosion to the equipment. These factors, to a certain extent, limit the widespread use of aqueous adhesives. (3) Development of solventless composite process Solvent-free adhesives are basically also composed of two-component polyurethane adhesives, whose main agent and curing agent have higher viscosity at room temperature but still have fluidity and are semi-solid substances. When compounding is required, the main agent and the curing agent are mixed in proportion, placed in an adhesive tray having a heat-retaining function, heated to a viscosity to a suitable degree, and then passed through a heat-insulating net pattern. Roller is applied to the substrate. After coating, it is not necessary to heat and dry directly to compound with another substrate. The solvent-free composite process does not have the problem of exhaust emissions. It does not require large and complex heated blasts and exhaust air exhaust devices. The equipment is simple and energy consumption is reduced. The solvent-free compounding process is simple, the equipment covers an area that is small, it is appropriate to reduce costs, save resources, and protect the environment. Therefore, it will be the main direction for the development of composite processes in the future. In recent years, with the strengthening of product quality and environmental protection awareness in China, solvent-free compounding has become more and more popular among people in the composite film packaging industry in China. Many domestic solventless laminators have begun to operate. At present, most middle and low-grade plastic flexible packaging materials can be produced with solvent-free adhesives, but due to factors such as the quality of composites, they cannot completely replace the dry composite process. Although the development of adhesives is ultimately going to be solventless, because solventless adhesives require dedicated solventless laminators, the investment in equipment is large, and it takes a long time for large-scale deployment. therefore
(3) Water-based gravure film packaging material
2 Reduce drying load Increase production efficiency and reduce energy consumption.
3 Reduce the residual solvent.
However, increasing the solids content (working concentration) also brings some problems:
1 The uniform coating of the adhesive is difficult due to the sharp change in viscosity of the solvent when it evaporates.
2 Because the activation period is short, it is easy to cause blockage, and it is difficult to ensure a uniform coating amount. And also easily lead to poor appearance.
3 Since the binder has a small molecular weight (low viscosity), the cohesive force is small, and processing problems such as tunneling are easily caused. At present, some adhesive manufacturers in China have produced high-solids, low-viscosity products with high initial tack by adjusting the molecular weight and molecular structure.