How much organic solvent emissions are caused by the solvent ink film gravure printing process? Here is a case study: a film gravure printing machine with a printing speed of 300 meters/minute, an effective operation time of 20 hours a day, and a film width of 1 meter, the daily output is 360,000 square meters. Calculated based on the average ink consumption of the gravure printing process of 7g/m2 (note: it is wet ink, not dry ink), it requires about 2.52 tons of ink consumption. During the gravure printing process, solvent needs to be used to adjust the viscosity of the ink. The conventional ratio is 1:2. The specific solvent consumption is directly related to the company’s on-site management level. Let’s calculate it based on the standards of companies with higher management levels, that is, ink and If the organic solvent ratio is 1:1.5, 2.52 tons of ink and 3.78 tons of solvent will be consumed every day. The solid content of domestic gravure printing inks is generally around 30%, that is, 70% of the ink is solvent. Calculated based on this ratio, the solvent in 2.52 tons of ink is 1.76 tons. The total solvent consumption after adding the two items is about 5.54 tons. Without any treatment, except for a small amount of solvent remaining on flexible packaging products and a small amount being inhaled into the body of the operator in the form of solvent vapor, most of the 5.54 tons of solvent will be emitted. into the atmosphere. In other words, one gravure printing machine emits 5.54 tons of organic solvents into the atmosphere a day, which may sound a bit scary at first!
There are many people who question this conclusion. Of course, there will also be questions about whether the data calculation is one-sided and exaggerated, such as: printing machine speed, door width, daily working hours, unit ink consumption of gravure printing, etc. These seem to be details, but the question that arises after summing up is: Is the pollution of the solvent-based gravure printing process really so great? In fact, the production capacity in the case is not outstanding among domestic large and medium-sized flexible packaging companies. If we say 300 meters/minute The vehicle speed is too high, which may refer specifically to the imported gravure printing machine, which has no typical significance for the flexible packaging industry. Then we use a domestic gravure printing machine with a speed of 250 meters/minute. The door width is 1.2 meters, which is widely used by flexible packaging companies. Besides, the daily production time, whether it is four shifts and three operations, or three shifts and two operations, we must pay attention to the effective use of labor. Very few companies have a workload of only 20 hours a day. The machine does not stop when people are eating, and does not stop when changing shifts. It is normal for the effective printing time to exceed 22 hours. As for the unit ink consumption of gravure printing, the author here proposes 7g/m2 for wet ink. Although some companies require only 3 to 4g/m2, this refers to dry ink rather than wet ink. If it is 30% If you calculate the solid content, you will find that the wet ink is far more than 7g/m2. In this case, the daily printing capacity can reach 396,000 square meters, and the ink consumption will be much more than 2.52 tons. The data of gravure VOCs emission may be even more scary.
If the flexo printing process is used, what is the impact of VOCs? Taking this case as an example, because flexo printing uses a closed scraper, unlike gravure printing which uses an open ink tank, the solvents at the production site Leakage and volatilization are much smaller than gravure printing, and the solvent added during the production process is of course much less. According to production statistics, when gravure printing uses an ink to solvent ratio of 1:2, flexo printing only needs 1:1.5, and companies with better on-site management basically only need 1:1. In addition, the ink film of flexo printing is thin, and the unit ink consumption is often only 2g/m2 of wet ink. When flexo printing reaches a daily production capacity of 360,000 square meters, the ink consumption reaches 720kg. Similarly, based on the 30% solid content of flexo printing ink, the solvent in the ink reaches 504kg. Including the necessary solvent addition amount of 720kg, the total amount is 1.224 tons. Compared with the VOCs emissions of approximately 1.22 tons from flexo printing and 5.54 tons from gravure printing, flexo printing is indeed worthy of the reputation of “environmentally friendly process”, but these 1.2 tons of solvent are still discharged into the air after all, and its hazards must be carefully evaluated. .
Faced with the increasingly prominent VOCs emissions and comprehensive management issues, the flexible packaging industry and the ink industry must start to solve the problem of desolvation of inks and replace solvent inks with water inks. This is the only way for the gravure printing process to fundamentally solve environmental problems.
The U.S. packaging and printing industry has had similar VOCs emission problems. Excessive VOCs emissions are subject to heavy penalties in the U.S., so there are fewer gravure printing plants in the U.S. and more flexo printing plants; there are fewer solvent inks and more ink. There is no VOCs problem with ink, so using water ink instead of solvent ink is a good choice. In the United States, many film-type prints are printed with ink, which not only protects the environment but also reduces costs. This is something our Chinese colleagues should learn from.
Of course, the ink mentioned here refers to products that comply with the environmental standards of HJ/T 371-2007 “Technical Requirements for Environmental Labeling Products Gravure Inks and Flexographic Inks” promulgated by the State Environmental Protection Administration in 2007, that is, ammonia and Ink with compound content ≤3%, methanol content ≤2% (gravure printing) or ≤0.3% (flexo printing), and VOCs content ≤30% (gravure printing) or ≤10% (flexo printing). Therefore, ink ink must be screened for products with low ammonia content and low VOCs content.
Difficulties faced by the research and development and promotion of domestic film ink
The R&D and promotion of ink in China is actually very smooth. The real difficulties are with ink printed on films, whether it is gravure or flexo film ink. Gravure film ink cannot solve the problem of the knife wire during the printing process, nor can it solve the drying speed of high-speed printing. Flexographic film ink encounters more problems. Some so-called mature inks do not have clear solutions to the specific needs of users, and the improvement plans cannot meet the needs of users.
Foreign mature film ink has been stranded because it cannot meet the high requirements of the domestic printing industry. This is the same as the supply of ink.In the research and development and promotion of dynamic film ink, heavy regulations and strong medicine must be used to deal with VOCs pollution in the packaging and printing industry. When the author was asked for opinions on local environmental protection standards in Shanghai some time ago, the advice from the leaders of relevant associations was: You must consider it carefully, otherwise it will affect a large number of packaging and printing companies. The starting point of the leadership is to take into account the shortcomings of the current situation and hope to take care of weak small companies in some industries. But honestly speaking, if so many substandard companies are taken care of, who will take care of our living environment? Of course, Chongdian must It is reasonable and must be serious in maintaining the heavy code. Guangdong Province formulated the DB44/815-2010 standard that year, but the effect was not obvious. Should we learn some experiences and lessons from it?
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