Environmental Pollution Problems Faced by the Printing Industry (II)

2, water-based ink. It has been used in flexo, gravure and screen printing but it has not been used in offset printing inks. Water-based flexographic printing inks have been widely used in newspaper printing. Water-based gravure inks have also begun to replace solvent-based inks. However, this trend has slowed down and will continue to be introduced into more stringent laws.
3, vegetable oil base ink (mainly soy oil ink). Successful in offset printing inks.
In solving the VOC problem, the current Western countries will focus on the development of a new curing device control system and a new ink drying method. Here's a look at the new ink drying method.
The VOC law requires printers and ink manufacturers to strictly control emissions of volatile organic solvents (VOCs). Therefore, regardless of the drying system or the development of a new ink drying method, the following points must be considered:
1. Reduce VOC emissions;
2. Because the drying system consumes a lot of energy, improving the energy use efficiency becomes the second objective that the drying system should achieve.
3. As the printing speed of printers is getting faster and faster, the drying system must keep up with this trend to ensure printing efficiency;
4. In order to reduce the volatilization of VOC, for the printing machine with high solvent content and large amount of ink, online recycling of solvent products should be considered during the printing process;
5. On the premise that all the above points are satisfied, the last point is to consider ensuring the printing quality.
How should the drying system be improved? It can be improved in the following ways:
1. Improve the drying system. The first is to improve the air nozzle system, reduce the speed of air in the drying device, reduce air consumption, and reduce energy consumption. However, to maintain the efficiency of drying, reducing the speed of air in the drying device is not simply a matter of lowering the fan speed, but rather improving the nozzle system while maintaining the drying efficiency. For already installed equipment, carefully adjust it to the best working condition. If adjusted properly, it can save energy by 30%-50% (max.) and increase printing speed by 40% (max.), which is also very important for the equipment being used.
2, improve the drying device control system. Many new drying devices now directly measure the temperature of the surface of the substrate, unlike the previous drying device, which measures the temperature of the air in the oven. This responds to temperature changes on the surface of the substrate in time and adjusts the speed and heat in time. Which in turn saves energy;
3, should consider the use of hot air circulation. It is relatively easy to solve this problem. Install a heat exchanger at the hot air outlet to preheat the drawn cold air so that energy can be saved.
4. Introduce inert gas in the drying device. Because some solvents have a low flash point and are prone to production accidents, this can ensure the safety of highly volatile solvents that are flammable and explosive in the air, improve the efficiency of solvent recovery devices, and at the same time reduce the flow of air, thus reducing the use of To heat the heat of the air, it greatly saves energy.
5. Because of the use of new reflectors and UV lamps, the efficiency of the UV curing system has also been greatly improved.
What should we do with the newly developed ink drying method? The purpose of the new ink drying method should be consistent with the purpose of the drying system. The newly developed ink drying methods are roughly the following:
1, reaction curing type. This kind of ink is different from the previous two-component reactive curable inks. When the ink comes into contact with paper, it is dried and solidified due to a reaction between a component of the ink and a certain component of the paper. This result was used in HP inkjet printers. Used in the application. This reaction occurs on the coating layer on the surface of the ink and paper, allowing the ink to dry quickly. This method allows the ink to cure quickly without VOC environmental problems, but must use inks and papers that react with each other to print.
2, pressure curing. The microcapsules (components containing more than two components) are pressed with pressure to cause a chemical reaction. This is a technique used in carbonless copy paper. This technique is used on inks. It is the process of making ink into microcapsules. During the printing process, the ink microcapsules are ruptured and the two components in the microcapsules react. And quickly solidified. This drying process is free of VOCs and requires no drying device.
3, temperature and curing. This kind of ink shows a solid state at normal temperature. When printing, the temperature is raised to make the ink change from a solid state to a liquid state. When the ink is transferred to the surface of the substrate, the ink film rapidly changes from a liquid state to a solid state, and the drying proceeds quickly. The solvent evaporates without the need for a drying device, but it requires heating of the printed components and can be implemented first in silk screen printing.
4, water-based UV curing technology. This technique will overcome many of the shortcomings of current cure technology, the most important being the treatment of water before curing.
5, hot combustion curing. The heat-curing device turns organic vapor into carbon dioxide and water at a high temperature of 600-1000°C. Its advantages are: a wide range of applications, almost completely eliminating volatile substances - up to 99.5%, effective for a variety of solvents. It is also possible to install a heat recovery circulation device. The disadvantages are: the investment and daily operation costs are very high and the energy consumption is high; at the same time carbon dioxide and nitric oxide are produced.
6, catalytic combustion curing. The temperature of catalytic combustion and drying is lower than the temperature of hot combustion drying, around 350-600°C. The typical drying temperature of rotary offset press is 350-420°C, which can reduce the volatilization of VOC by 95%. However, the catalyst is usually toxic. The life of the catalyst is limited and needs to be updated regularly. The advantages are: less investment in the specific heat combustion drying device, less energy consumption, effective for a variety of solvents, and low content of nitric oxide residue.
Catalytic combustion methods will be more commonly used, especially for small printers using solvent-based inks, because solvent recovery is less important for small printers.
7, vacuum curing. Can help solvent volatilization, no heat, faster curing speed, can install solvent recovery device, but technically difficult to achieve.
8, freeze curing. The ink is quickly cured by blowing cold air, and the solidified ink film remains solid at room temperature. This curing method does not have VOC problems, but it is technically difficult to achieve.
The last two curing methods are curing methods that are under development. There are still many difficulties in printing.
The concept of ink formulation development will change, that is, the cost of converting from the first consideration of ink cost to ink must be subject to the economic benefits of the full printing process.
At the same time, the compound drying device will continue to be developed. Some new ink drying methods will be used in special requirements areas. The most important ones are trademarks and packaging printing, especially anti-counterfeiting and printing with confidentiality requirements.
The Chinese government has already taken environmental protection as a basic national policy. To achieve coordinated development of economic construction and environmental protection, and sustainable development of the national economy, we must achieve the goals of the 2008 Green Olympics. It can be foreseen that in the future, environmental protection laws for all walks of life will become stricter and more complete. The printing industry should take precautions to face this challenge. Now we should have a sober understanding of the environmental pollution problems in China's printing industry, have a good planning investigation and systematic research, and do some work for China to establish laws or regulations in this area; and for our country's printing companies to adapt to this The progress of the times, the improvement of craftsmanship do some work.