How to avoid the impact of flying ink on printing
The greater harm that flying ink brings to the printing process:
1. Pollution to the environment
Ink is scattered into the air, on machinery and equipment, on the wall, etc. The light ones will affect the cleanliness and beauty of the environment, and the heavy ones will even cause explosions and cause safety accidents.
2. Negative impact on product quality
If the ink is scattered on the printed product, it will cause a certain degree of dirt on the surface of the printed product, which will affect the clarity of the printed product, and will cause the printed product to be scrapped in severe cases.
3. Long-term damage to human health
Due to the widespread use of organic pigments, organic solvents and additives in current inks, many of the raw materials contain heavy metal components. These harmful substances will be adsorbed on the surface of the worker's skin through flying ink and be sucked into the respiratory tract, which will inevitably cause adverse effects on the health of the operator.
It can be seen that the discharge of harmful gases, the use of harmful liquids and solids and the discharge of waste in the printing industry all pose a serious threat to human health and human living environment. Environmental issues are not only related to the future of human civilization, but also to the survival and development of enterprises.
When formulating the development plan for the printing industry, we must simultaneously consider the issue of environmental protection and formulate practical and effective measures.
To limit pollution abroad, some countries have enacted a series of regulations such as the “Labor Hygiene Law†and “Organic Solvent Discharge Lawâ€. These laws and regulations determine the research and development direction of printing production process and ink.
Foreign countries such as Germany, promulgated the "Chemical Products Law" as early as 1982, which contains three provisions: the protection of workers in the workshop; the protection of general health; the protection of the environment. Under the pressure of environmental protection laws, foreign research departments and some manufacturers are forced to research and develop solvent-free inks, or screen printing inks with low solvent content.
European and American countries passed volatile organic solvent (VOC) laws related to environmental protection around the 1990s. VOC laws require printing houses and ink manufacturers to meet the following requirements:
There should be no smell of organic solvents outside the workshop.
The concentration of volatile substances in the workshop must be lower than:
50 mg / m3 of volatile organic solvent;
Carbon monoxide 100 mg / m3;
Nitric oxide 100 mg / m3.
Sooner or later, this strict environmental protection law will become the benchmark for environmental protection in countries around the world.
This requirement is currently difficult for most domestic manufacturers (including printing plants and printing consumables manufacturers) to meet, because there are many components related to VOC and other environmental pollution problems in various printing processes and traditional consumables, but through hard work The problems that can be solved are the following:
The problem of volatile substances in most cleaning supplies and dampening fluids during cold-set rotation and sheet-fed offset printing. At present, gasoline has been abandoned as a cleaning product abroad, and a special ink cleaning agent (W / O emulsion type) has been replaced. This ink cleaning agent should be promoted vigorously; at the same time, a new high-speed rotary offset printing machine should be developed for offset printing. Alcohol fountain solution.
It is necessary to strictly check the components contained in the ink. Pigments containing harmful heavy metals can not be used to produce inks to ensure that the workers ’brothers are not harmed by heavy metals; at the same time, the quality of the ink must be further improved to reduce the generation of flying ink.
The thermosetting rotary offset printing process is the main producer of VOC, because its solvent distillation range is 230-340 ℃; the drying of the ink is forcibly dried at a high temperature of 300 ℃ in the drying device. According to the carbon content, each kilogram in the ink Carbon releases 0.3 kg of VOC material; it should be recovered through a recycling device.
The rotogravure printing process uses a lot of volatile low-boiling solvents, so it will cause serious VOC problems. If a solvent recovery device is installed on the rotogravure printing machine, the purpose of reducing VOC volatilization can be achieved; in the gravure printing process, flexible In the printing process and screen printing process, try to use water-based ink (water-based ink) as possible, which may reduce VOC problems, and should reduce the alcohol content of water-based ink as much as possible (usually containing 15% alcohol ).
In the production and development of inks, in order to comply with the requirements of the VOC law, Western countries have made great improvements in ink formulations and drying systems. The inks that are currently used more often have the following varieties:
Radiation curing ink. In fact, UV-curable inks have been developed as early as the 1940s, but they have not been greatly developed until the last 20 years. Since the ink contains no solvent, there is no VOC problem, and the printing process is environmentally friendly.
After the 1990s, with the implementation of VOC laws in Western countries, it should be said that people have a better understanding of UV curing inks. However, UV-curable inks cost more and the use process is more complicated than conventional inks.
Water-based ink. It has long been used in flexographic, gravure, and screen printing, but it has not been used in offset inks. Water-based flexographic inks have been widely used in newspaper printing, and water-based gravure inks have also begun to replace solvent-based inks, but this trend is currently showing signs of slowing down and will continue until stricter laws are introduced.
Vegetable oil-based ink (mainly soybean oil ink). Was successful in offset printing ink.
In solving the VOC problem, the western countries are currently focusing on the development of a new type of curing device control system and a new ink drying method. Let's take a look at the new ink drying method.
The VOC law requires printing and ink manufacturers to strictly control the emission of organic solvent volatilization (VOC). Therefore, no matter the drying system or the development of new ink drying methods, the following points must be considered:
Reduce VOC emissions; because the drying system consumes a lot of energy, improving energy efficiency becomes the second goal the drying system should achieve. As the printing speed of the printing press becomes faster and faster, the drying system should keep up with this trend to ensure the printing efficiency. Online recycling of solvent products; on the premise that all of the above points are met, the last point is to ensure the printing quality. [next]
Improve drying system to reduce ink pollution
So how should the drying system be improved? Can be improved according to the following aspects:
1. Improve the drying system
The first is to improve the air nozzle system, reduce the speed of air in the drying device, reduce the amount of air, and reduce energy consumption. But to maintain the efficiency of drying, reducing the speed of the air in the drying device is not simply to reduce the fan speed, but to improve the nozzle system while maintaining the drying efficiency. For the equipment that has been installed, carefully adjust it to make it in the best working state. If adjusted, it can save energy by 30% -50% (at most) and increase printing speed by 40% (at most). This is also very important for the equipment being used.
2. Improve the control system of the drying device
Many new drying devices now directly measure the temperature of the substrate surface, unlike the previous drying device that measures the temperature of the air in the oven, so that it can respond to the temperature change of the substrate surface in time and adjust the wind speed and heat in time. This saves energy; the recycling of hot air should be considered.
It is easier to solve this problem. Install a heat exchanger at the outlet of the hot air to preheat the cold air drawn in, which can achieve the purpose of energy saving;
3. Introduce inert gas into the drying device
Because some solvents have a relatively low flash point and are prone to production accidents, this can ensure the safety of highly volatile and flammable solvents in the air, improve the efficiency of the solvent recovery device, and reduce the air flow rate, which reduces the use of The heat used to heat the air greatly saves energy.
Because of the use of new reflectors and UV lamps, the efficiency of the UV curing system has also been greatly improved.
So what should the newly developed ink drying method do? 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 ink is different from the previous two-component reaction-curable ink. When the ink is in contact with the paper, it is dried and cured due to the reaction of a component in the ink with a component in the paper. This achievement was once used in HP inkjet printers. Get applied. This reaction exists on the coating layer on the surface of the ink and paper, which makes the ink dry quickly. This method allows the ink to cure quickly without VOC environmental issues. However, it is necessary to use ink and paper that can react with each other for printing.
The Jinding single-component polyurethane waterproof coating first developed by the Beijing Institute of Building Materials Science in China is an environmentally friendly product with a high technological content, also known as moisture-curing polyurethane waterproof coating. It passes through the humidity in the air It is cured by gas reaction and has excellent mechanical properties and low temperature properties. No harmful substances are precipitated during construction and use, which is safe and environmentally friendly. It has strong adaptability to the moisture content of the substrate and has good adhesion to the substrate. It can be constructed on a humid substrate and a relatively high relative humidity. The Beijing Institute of Building Materials Science has a waterproof coating production line with an annual output of 5,000 tons. It is equipped with advanced quality testing instruments and equipment, and strictly controls the production process and quality testing, thus ensuring the excellent and stable product quality. Over the years, Jinding single-component polyurethane waterproof coating has been widely used in many domestic key projects. With excellent product quality and good service, it has won praise and trust from users.
2. Pressure curing
The microcapsules (components containing more than two components) are pressurized with pressure to cause chemical reactions. This is the technology used in carbonless copy paper. This technology is used in ink to make the ink into microcapsule particles. During the printing process, the ink microcapsules are pressed to break them, and the two components in the microcapsule particles react And quickly cured. There is no VOC problem in this drying process, and no drying device is needed.
3. Temperature regulation and curing
This ink is solid at normal temperature, and the temperature is increased during printing, so that the ink changes from solid to liquid; when the ink is transferred to the surface of the substrate, the ink film quickly changes from liquid to solid due to the temperature drop, drying quickly, without The solvent evaporates without the need for a drying device, but it requires heating of the printed components, which can be achieved first in screen printing.
4. Water-based UV curing technology
This technology will overcome many shortcomings of current curing technology, the most important thing is to treat the water before curing.
5. Thermal combustion curing
The thermal curing device converts 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-can be as high as 99.5%, effective for a variety of solvents. A heat recovery circulation device can also be installed. The disadvantages are: the cost of investment and daily operation is very high, and the energy consumption is high; at the same time, carbon dioxide and nitric oxide are produced.
6. Catalytic combustion and solidification
The temperature of catalytic combustion drying is lower than that of thermal combustion drying, about 350-600 ℃, and the typical drying temperature of rotary offset press is 350-420 ℃, which can reduce the volatilization of VOC by 95%. But the catalyst is usually toxic. The life of the catalyst is limited and needs to be updated regularly. The advantages are: less investment, less energy consumption, less energy consumption, more solvents, and lower content of nitric oxide residue.
Catalytic combustion methods will be more commonly used, especially for small presses that use solvent-based inks, because for small presses, solvent recovery is not very important.
7. Vacuum curing
It can help the solvent volatilize without heat, the curing speed is relatively fast, and a solvent recovery device can be installed, but it is technically difficult to achieve.
8. Freeze solidification
The method of blowing cold air to cure the ink quickly, the cured ink film remains solid at room temperature, this curing method will not have VOC problems, but it is also technically difficult to achieve.
The last two curing methods are the curing methods under development. There are still many difficulties in real use in printing.
The concept of ink formulation development will change, that is, from the first consideration of the cost of ink to the cost of ink must be subject to the economic benefits of the entire printing process.
At the same time, composite drying devices will be continuously developed, and some new ink drying methods will be used in special demand fields, the most important of which are trademarks and packaging printing, especially anti-counterfeiting and confidentiality printing.
The Chinese government has long regarded environmental protection as a basic national policy. To achieve the coordinated development of economic construction and environmental protection, as well as the sustainable development of the national economy, we must achieve the goal of the 2008 Green Olympics. It is foreseeable that the environmental protection laws for all walks of life will become stricter and more sound in the future. The printing industry should plan ahead and face this challenge. Now we should have a clear understanding of the environmental pollution problems in China's printing industry. There is a good planning investigation and systematic research to do some work for China to establish laws or regulations in this field; The progress of the times and the improvement of technology do some work.
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