Green offset printing: traditional offset printing also comes to fight VOCs
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There are frequent measures to limit VOCs (Volatile Organic Compounds) emissions, and the environmental protection situation in the printing industry is becoming increasingly severe. Although compared with the petroleum and petrochemical industries, even compared with the gravure printing process, the traditional offset printing production has very few VOCs emissions, but with the refinement and comprehensiveness of the greening work in the printing industry, as well as the printing Considering the health of workers, some industry professionals have already paid attention to the reduction of VOCs in the traditional offset printing field and began to actively fight VOCs.
Below, the author will start from the identification of VOCs in the offset printing process and the currently feasible VOCs emission reduction measures, and summarize some of the experiences of our company in the reduction of traditional offset VOCs for many years. The VOCs emission reduction effects described in this paper are mostly According to the actual use of our company, the calculation is for the reference of the industry.
Offset process VOCs source identification
In order to do a good job in reducing VOCs, the first issue is to find out the source of VOCs. Let us discuss the source of VOCs in the offset printing process.
1. Chemicals used in prepress plating
The traditional use of color separation film to make the PS plate requires two steps of development and water washing, and it is also necessary to apply a protective glue on the printing plate. These processes produce a large amount of chemicals and waste solutions that are harmful to the human body and the environment, and also generate a large amount of VOCs.
2. Ink
The printing ink is composed of a pigment, a binder, a solvent, and an auxiliary agent. Alcohol solvents such as isopropyl alcohol (IPA) are used in offset inks. During use, most of these solvents will volatilize into the air, posing a hazard to the working environment and the ecological environment.
3. Run solution
The dampening solution ensures that the blank portion of the printing plate forms a hydrophilic layer, and the main components of the dampening solution are usually isopropanol and phosphoric acid. Isopropanol can reduce the surface tension of water and avoid the emulsification of ink and dampening solution, but it is also a photochemical oxidant. It will form ozone when exposed to sunlight, irritating human eyes and respiratory system, endangering human health and affecting plant growth. . The higher the isopropanol content in the dampening solution, the more VOCs are emitted.
4. Car wash water
The components of the printing press must be cleaned frequently. Common cleaning solvents include n-heptane, gasoline, kerosene, glycol ethers, alcohols, toluene, ethane and specially formulated mixtures. When the printer wipes the parts of the printing machine with a rag to pick up the car wash water, the cleaning solvent in the car wash water will volatilize into the air and escape to the atmosphere with the ventilation system of the plant. This is the VOCs discharge caused by the car wash water. It is worth mentioning that although the conventionally used solvents such as n-heptane, gasoline and kerosene have an ideal cleaning effect, they have a certain corrosive effect on the printing machine ink roller and blanket.
5. Adhesive
The adhesive in a broad sense also includes a film adhesive, but the adhesive mentioned herein mainly refers to the material used in the post-printing process of the book, excluding the film adhesive.
6. Film adhesive
The film is a processing technique in which a plastic film is coated with a bonding material, and is heated and pressed to bond with a paper printed matter to form a paper-plastic composite. At present, many film printing processes in the book printing industry and the packaging printing industry use solvent-based coating glue. Since the solvent-based coating rubber needs to be blended with chemical diluents such as benzene and alcohol, toxic VOCs are volatilized during production and use or after disposal, which causes great harm to human health and the environment.
7. Varnish
The glazing belongs to the finishing process of the printed surface, which can increase the gloss of the surface of the printed product, so that it has the effects of moisture proof, heat prevention and light fastness. Solvent-based varnish is generally used in the industry. The solvent-based varnish is mainly made of toluene, and the VOCs formed by the VOCs may cause damage to the respiratory system and the blood circulation system.
Currently feasible VOCs emission reduction measures
Defining the source of VOCs for the offset process, let's explore the corresponding reduction measures. Printing companies control VOCs generally have three methods: one is the use of environmentally friendly materials for source control; the second is the use of various air purification equipment for process control; the third is printed product testing and product control. The author believes that to judge whether an environmental protection measure has application value, the principle is to take into account technical feasibility and economic rationality. Below, the author will propose feasible emission reduction measures from the sources of material emission reduction and technology emission reduction in view of the sources of VOCs mentioned in the above-mentioned offset printing process, combined with the information contacted and learned in the current work.
VOCs for chemicals used in prepress plates
Material reduction
Introduce a new type of treatment-free/rinsing-free CTP plate for trial evaluation. Compared with ordinary CTP plates, the process-free/rinsing-free CTP plate eliminates the development and rinsing process and produces almost no chemical waste and VOCs. However, the printing durability of the plate is still lower than that of the ordinary plate, and it needs constant attention, and is introduced after the technology is mature.
Environmental performance: Reduce the waste of plate-making waste liquid and related VOCs, eliminating the cost of purchasing developer and developing equipment.
Technical emission reduction
The use of CTP platemaking instead of film platemaking can greatly reduce emissions of toxic and hazardous chemical waste liquids and VOCs. According to statistics, in the PS plate making process, every 2m2 of PS plate will produce 1L of waste developer solution, fixer solution and 1L of waste water, while CTP platemaking will greatly reduce the discharge of waste liquid by eliminating the development and fixing process. Only 0.2 L of waste liquid was produced per 2 m2 of CTP.
Environmental performance: CTP can improve prepress production efficiency, reduce chemical use and reduce VOC emissions by 80%; reduce energy consumption, save prepress and print preparation time, and save manpower.
All the chemical waste liquid generated by the CTP platesetter is sealed and packaged and sent to a qualified supplier for recycling to reduce environmental hazards and VOCs emissions during transportation.
Environmental performance: Properly dispose of waste and reduce the environmental hazards of chemical waste. Properly packaged to reduce the generation of VOCs in the waste stream.
Use the plate retainer to reuse the plate. Use the plate retainer to clean the used plates, then apply a protective film to store them and use them when needed.
Environmental performance: no need to re-plate during reprinting and printing, reduce the amount of media used, reduce the consumption of plate-making chemicals and related VOCs emissions.