For the book printing industry, shutting down production is not the way, the best way is for enterprises to establish a correct awareness, find the source of pollution, do a good job of prevention, and fundamentally minimize the problem of pollution.
In the past two years, under the haze environment, the printing industry has been pushed to the cusp of environmental protection, and the printing industry of books and periodicals is no exception. Despite the grievances of the high-pressure policy issued by the government department, the book printers complained, but after complaining, the printers began to rationally analyze the problem and actively develop countermeasures.
In the common sense, volatile organic compounds refer to volatile organic compounds with a melting point below room temperature and a boiling point range between 50 and 260 degrees Celsius; the definition in the environmental sense refers to volatile non-methane total hydrocarbons (alkanes, olefins, Alkynes, aromatic hydrocarbons), oxygen-containing organic compounds (aldehydes, ketones, alcohols, ethers, etc.), halogenated hydrocarbons, nitrogen-containing compounds, sulfur-containing compounds, etc. Volatile organic compounds are extremely harmful. Once they are discharged into the air in large quantities, they will also cause huge environmental harm.
VOCs are the general term for volatile organic compounds. Some of the compounds in VOCs have acute and long-term toxicity to the human body; on the other hand, most VOCs compounds have photochemical reactivity, especially the rapid increase of industrial VOCs emissions in recent years, causing urban haze One of the main reasons for photochemical smog. Current domestic studies on VOCs emission inventories show that: VOCs emissions mainly come from the use of solvents, flow sources, stationary combustion sources, etc., of which the use of solvents contributes significantly to VOCs emissions, mainly including printing, furniture manufacturing, paint use, Footwear industry, etc.
1. Sources of VOCs in book printing enterprises
Multi-party data shows that the current VOCs emissions in the book and printing industry mainly come from processes such as printing, bookbinding, laminating, glazing and bronzing. The data shown in Figure 1 shows the impact of various raw materials on VOCs.
Figure 1 Sources and proportion of VOCs in book printing companies (data from the Academy of Environmental Sciences)
(1) Printing process
The emission of VOCs in the printing process of books and periodicals mainly comes from the use of inks, fountain solutions, cleaning agents, and thinners. According to the survey of Beijing printing companies, there are still a small number of companies that use solvent-based inks. It is composed of filler, auxiliary agent and connecting material solvent. The solvent often contains ethanol, propanol, isopropanol, butanol, toluene, xylene, methyl ethyl ketone, ethyl acetate, butyl acetate and other VOCs. Studies have shown that solvent-based inks generally contain about 50% of organic volatile substances. When heated and dried during the printing process, the VOCs mixed in the pigment will be released. During the printing process, the larger the inked area and the thicker the ink layer, the more VOCs will be released.
At present, most of the fountain solution used in lithographic offset presses in book and printing companies is ionic fountain solution. Ethanol, isopropyl alcohol and ethylene glycol are the main additives in this type of fountain solution. Ethanol (alcohol) can improve the spreading performance of the fountain solution on the printing plate, can reduce the amount of fountain solution, and can also reduce the excessive emulsification of the ink and the expansion of the paper after water absorption. In addition, it can prevent the paper from brushing and other phenomena , Is very helpful to improve the printing process and improve the printing quality, so it is widely used in printing enterprises. However, ethanol is highly volatile and almost 100% escapes into the atmosphere, causing VOCs.
(2) Binding technology
The parts for glue binding are on the spine and sides. The EVA hot-melt adhesive is composed of basic resin, tackifier, viscosity regulator and antioxidant. The basic resin of hot melt adhesive is made by copolymerization of ethylene and vinyl acetate under high temperature and high pressure. The hot-melt adhesives used are also different. The temperature of hot-melt adhesives is generally 120 ℃ ～ 200 ℃. During the heating process, the volatile organic compounds in the hot melt adhesive will evaporate into the air to generate VOCs.
(3) Laminating process
Lamination is a product processing technology in which a plastic film is coated with an adhesive and paper prints are heated and pressed to bond them together to form a paper-plastic integration. The adhesives used in domestic lamination mainly include polyurethanes, rubbers and thermoplastic polymer resins. During the lamination process, the adhesives will release VOCs when heated.
(4) Polishing process
The basic composition of glazing paint is mainly composed of three parts: main agent, auxiliary agent and solvent. The main agent is divided into natural resin and synthetic resin; auxiliary agents include curing agents, surfactants, plasticizers, etc .; commonly used solvents are aromatic hydrocarbons, esters and alcohols. During the glazing process, a small amount of VOCs will be released when the solvent is heated.
(5) Hot stamping (anodized aluminum stamping) process
The foil used in the bronzing process is generally composed of several layers of different materials, followed by an adhesive layer, an aluminum film layer, a protective layer, an isolation layer, and a base film layer. The adhesive layer contains organic solvents. During the hot stamping process, the adhesive layer is heated to release VOCs.
2. VOCs governance measures
Attention should be paid to the reduction of VOCs from the source control, the transformation of the production process, the end treatment, and the design of the plant. Only by finding the source of pollution and doing a good job of prevention can the problem of pollution be fundamentally minimized. At the same time, it is also closely related to the selection of materials in the printing process and the ability of enterprise management execution and control.
(1) Source control
1. Replacement of raw and auxiliary materials
(1) Use new environmentally friendly inks.
Promoting and using non-polluting, environmentally friendly inks is the fundamental measure for reducing VOCs in the printing industry. At present, the more common new environmentally friendly inks are mainly water-based inks, vegetable oil inks, UV-curable inks, water-based UV inks, etc. Among them, water-based inks are the most widely used, and the binders of water-based inks are mainly divided into water-dispersed and water-diluted types. The water-dispersed binder is obtained by polymerizing emulsified monomers in water. It is a two-phase system in which the oil phase is dispersed in the water phase in the form of particles. Although it cannot be dissolved by water, it can be diluted by water. It can be considered as an oil-in-water emulsion type. There are many types of resins that can be used in water-reducible inks, such as maleic acid resin, shellac, maleic resin modified shellac, urethane, water-soluble acrylic resin and water-based amino resin. Water-based inks hardly emit VOCs to the atmosphere.
(2) The amount of alcohol added in the fountain solution should be ≤5%.
At present, the alcohol-free fountain solution that has appeared on the market basically meets the requirements for the use of sheet-fed printing presses and high-speed rotary printing presses, and the technology is relatively mature. Measure the VOC content of the fountain solution and its conductivity value daily, and draw the relevant data into a chart to formulate the most acceptable range of conductivity value for the fountain solution.
(3) Do not use kerosene or gasoline as a cleaning agent.
Volatile organic compounds are present in most cleaning supplies during cold-set rotation and sheet-fed offset printing. Now many printing companies at home and abroad have abandoned gasoline as a cleaning agent, and replaced it with a special ink cleaning agent (W / O emulsion type). This ink cleaning agent should be promoted vigorously.
(4) Solvent-based varnish should not be used, and water-based varnish should be used.
The new water-based varnish has a very low solvent content and can be widely used. It can reduce the emissions of organic volatiles by about 20%, and can also reduce the concentration of organic volatiles in the factory air to protect the health of the operators.
(5) Solvent-based adhesives for book binding should not be used. The harmful substances of adhesives should meet the requirements of HJ / T220.
2. Improved process
Books and periodicals printing enterprises can reduce the emission of VOCs during production operations by improving technological measures.
(1) Install the central ink supply system.
In the printing workshop, in order to reduce the loss of ink and reduce the amount of ink stored in different printing machines, a central ink supply system can be set up to centrally process the ink. The central ink supply system can not only reduce the emission of volatile organic compounds, but also reduce the potential waste caused by manual ink filling. According to statistics, the centralized ink supply system can reduce the emission of organic volatiles by about 15% to 30%.
(2) Adopt automatic cleaning blanket device.
The introduction of an automatic cleaning blanket device on the printing press can not only reduce the time to stop cleaning the cylinder, but also avoid the waste generated during the cleaning process and reduce the emission of organic volatiles. Of emissions.
(3) Improve the drying system.
In the drying system of printing equipment, the air nozzle system can be improved to reduce the flow speed of hot air and reduce energy consumption. At the same time, in order to maintain the drying efficiency and reduce the wind speed, the fan speed cannot be simply reduced, but the nozzle system should be improved on the premise of maintaining the drying efficiency. At present, many new drying devices on the market can directly measure the surface temperature of printed matter instead of measuring the temperature of the air in the oven, which can respond to the temperature change of the surface of the substrate in time, save energy and reduce the emission of VOCs.
(4) Adopt fountain solution filtering and recycling system.
The fountain solution filtration and recovery system can remove impurities such as ink and paper powder in fountain solution, keep the water quality clean, and maintain an ideal water-ink balance. The clean water quality reduces many troubles in printing, and avoids the blockage of pipes caused by ink adhesion, which reduces the maintenance cost of the printing press. At the same time, it does not need frequent water changes to clean the cooling water tank, which improves production efficiency and reduces The cost of chemical solutions such as printing solution, alcohol, etc.?
(2) End treatment
1. Production plant closed
The printing enterprise should close the production workshop to reduce the unorganized emission of exhaust gas. Confined measures mean that volatile organic compounds are directly discharged into the treatment facility through a closed pipeline, and are not discharged into the atmosphere unorganized; or unorganized discharge in the confined space area but discharged into the treatment facility through the exhaust facility, unorganized discharge area, personnel, materials Both the inlet and the outlet are under negative pressure operation and are equipped with a pressure monitor.
2. Centralized processing of VOCs
VOCs generated from production activities (cleaning, ink adjustment, etc.) and equipment (printing machines, laminators, laminating machines, etc.) containing raw and auxiliary materials containing volatile organic compounds should be introduced into volatile organic compounds for treatment through local or overall gas collection systems Equipment or discharge pipeline, discharge up to standard.
At present, there are two main stages of VOCs treatment technology: recycling and destruction. There are four main types of recycling technology: adsorption, absorption, condensation and membrane technology. There are six types of destruction technologies: catalytic combustion, thermal combustion, biological treatment, plasma, photocatalysis and photooxidation. Recycling technology and destruction technology are used in combination to produce a variety of comprehensive treatment plans.
(3) Strengthen production management
The improvement of production management in the printing industry also has an important impact on the VOCs emissions of enterprises. Enterprises should establish an environmental management committee, appoint an executive to take charge of environmental protection, and have specific responsible persons to formulate and implement emission reduction plans. Educate and involve employees at all levels in decisions and improvement measures under the emission reduction plan. Regularly review and review emission reduction plans and measures to facilitate continuous improvement.
Ink, cleaning agents, fountain solution, adhesives, organic solvents and other raw and auxiliary materials containing volatile organic compounds should be kept closed during storage and transportation, and should be opened as needed during use, and should be closed in time after use to reduce Volatile.
The waste adsorbent should be handed over to the unit holding the hazardous waste business license for disposal or comprehensive utilization; waste ink, waste cleaning agent, waste solvent, cotton yarn, rags, etc. with ink or solvent should be placed in a sealed airtight In the container, process regularly, and record the processing volume and destination.
Arrange the operation of the printing press to reduce color conversion, thereby reducing the number of times the ink needs to be converted.
Use solvents only when cleaning ink and oil stains. Before using solvents to clean the printing equipment, wipe off excess ink. Use an automatically switched solvent dispenser. Only take a sufficient amount of solvent to complete the cleaning work. Use a plunger can or a squeeze bottle to moisten the cloth without dampening it, thereby controlling the amount of solvent used.
Try to extend the use time of the wipes of the printing press; the old wipes can be used for the first wipe, and the clean wipes should be used for the second wipe. Wring out the dirty rags and collect the squeezed solvent for reuse, such as cleaning equipment to deal with dirty mechanical parts.
Environmental protection is a basic national policy of China. At the Fifth Plenary Session of the Eighteenth Central Committee, the five major development concepts of the "Thirteenth Five-Year Plan" period were proposed: innovation, coordination, greenness, openness, and sharing. Several provinces and cities across the country have successively issued VOCs emission charging schemes for printing companies and started to implement them. It is imperative for printing companies to control VOCs emissions. The key to VOC governance is to "govern", and the focus is on "reason". Only by fundamentally finding the root cause of the problem can the problem be completely solved, and the process cannot be solved only by seeking results without seeking process. Therefore, for the book printing industry, shutting down production is not the way, the best way is for enterprises to establish a correct awareness, find the source of pollution, do a good job of prevention, and fundamentally minimize the problem of pollution, so as to completely achieve Green printing, clean production. 
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