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What is the amount of organic solvent emissions from the gravure process? Give a case description: 1 film gravure printing machine,
printing speed of 300 m / min, effective running time of 20 hours per day, film width of 1 m, daily output of 360,000 square meters, the average ink consumption by gravure process Calculated for 7 grams per square meter (note: wet ink, not dry ink), need to consume 2520000 grams of ink, or 2.52 tons. In the gravure process, it is necessary to adjust the viscosity of the ink with a solvent. The conventional ratio is 1:2, that is, 1 kg of ink requires 2 kg of solvent, which includes both the solvent added to the ink tank and the solvent consumed during cleaning. The specific solvent consumption is directly related to the on-site management level of the enterprise. Generally speaking, the enterprise management level is high, the solvent consumption is small, and vice versa. If we calculate according to the management level of the enterprise, that is, the ratio is 1:1.5, then it consumes 3.78 tons of solvent while consuming 2.52 tons of ink. Since the solid content of solvent-based gravure inks is generally not high, 70% of the 2.52 tons of ink is solvent, or 1.764 tons, calculated at 30%. In this way, the solvent consumption of a gravure press for one day is as high as 5.544 tons. This data is not deliberately enlarged.
This is because: the printing speed of 300 m / min is not the highest in the gravure printing enterprises. According to the author, the speed of the domestic gravure printing machine can reach 250 ~ 280 m / min, not to mention the introduction of the gravure industry in these years. Many imported high-speed gravure printing machines; the effective starting time of 20 hours per day is not the longest. Large and medium-sized gravure printing enterprises do not stop during meals and shifts; 7 g of ink per square meter is still ok, some losses The unit ink consumption of larger gravure printing enterprises has far exceeded this value, but it has not been accurately calculated. The solvent addition amount is actually lower than 1:1.5. The general management level of gravure printing enterprise is almost 1: 2. Moreover, the solid content of the solvent-based gravure ink is already high at 30%. In fact, the solid content of many gravure inks is less than 30% at all, in other words, the solvent content of the 1 kg ink is higher.
Other data can also be used to confirm from the side: In some gravure companies that have been concerned about environmental protection, the large amount of solvent has been treated and recycled, and the economic benefits created by it have become the main aspects of corporate profits. The author once had an understanding of a well-known instant noodle packaging manufacturer. The product of the factory is at the low end of the
flexible packaging industry chain, with an annual output value of several hundred million, but the profit is basically contributed by solvent recycling, so the company has always attached great importance to it. Upgrade and renovate the solvent recovery unit, continuously invest and change and upgrade the solvent recovery unit. With a glimpse of the whole leopard, these organic solvents will be discharged directly without treatment, and the amount of emissions will be huge!
What if this case is switched to the flexo process? The flexo ink film is thinner, and the solvent-based flexo ink has a pigment ratio nearly double that of the gravure ink, and the solid content is slightly higher. It is also calculated at 30%, and the ink consumption per square meter is generally 2 g. Because the film flexo printing machine generally adopts a satellite structure, each printing unit adopts a closed type squeegee, and the ink in the ink tank is transported through the pipeline, which is completely open like the ink tank of the gravure printing machine, so the solvent is volatilized. The amount is small. The ratio of flexo ink to solvent is generally 1:1, and the enterprise with higher management level can even reach 1:0.7. For calculation convenience, it is calculated as 1:1 here. Still in accordance with the above production conditions, the solvent consumption of one flexo press for one day is only 1.224 tons, which is 22% of the gravure printing process. No wonder that solvent-based inks are also used. The industry will list flexo printing as an environmentally friendly process, and gravure printing as a non-environmental process. If the film flexo is using water-based ink, what is the comparison? The results can be imagined.
The author's understanding of the environmental hazards of gravure solvent-based inks began in the early 1990s, when he worked in an 80-year-old state-owned enterprise. Every year, dozens of plastic film calendars were printed in the factory. page. At that time, the printing workshop used a large amount of toluic gravure ink. It is a very busy season every spring and summer. This season, the temperature and humidity are high, the air pressure is low, the exhaust gas is difficult to discharge, and the solvent concentration in the workshop is very high. The people who break into the workshop will be immediately I can't open my eyes and cry. Although I moved to Pudong and expanded the factory, it could not completely solve this problem. For gravure solvent inks, especially aromatic hydrocarbon inks, I hated it but could not do anything about it. In the past 10 years, gravure solvent-based inks have been de-benzeneized, but they cannot be desolvated. History and reality have repeatedly warned us that solvent-based gravure inks must be replaced with water-based inks, albeit with many difficulties. (Editor: Liu Yidong)
The above content is selected from the second issue of “ Printing Technology·Packaging and Decoration †in 2014. More journal content please pay attention to the journal channel, and the latest journal content clicks into the electronic journal channel of Keyin.com.
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