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The inks generally used for thin film printing are about 60% to 80% by weight of solvents such as ethanol, n-propanol, isopropanol, n-propyl acetate, and the like. These solvents are all volatile organic compounds and flammable substances. Some inks and thinners also contain Class F, contaminated wastes such as butanone, iso-acetone, toluene, and ethyl acetate.
The use of water-based inks provides a way to reduce environmental pollution and reduce many of the limitations imposed on printers.
Water is an acceptable control technology
The US Environmental Protection Agency has developed and issued guidelines for national and regional air pollution control agencies to enable them to determine which technology to use to reduce the impact of pollution during production. These guidelines are called Control Technology Guides (CTGs). The control technology guidelines set the minimum allowable air pollution for a specific industry or a specific production process. The basic control technical guide for flexographic printing was promulgated in 1978 and provides three possible control technologies:
1. Add control technology: control by adding catalyst, thermal oxide, carbon absorption technology, or solvent recovery. 60% pollution can be reduced by adding control technology. This is the preferred method for effective control of large amounts of waste. The addition of the control technology requires that the additive must exert at least 90% of the degradative pollution, so that the efficiency of the entire production control process to degrade the pollution can reach 67%.
2. High solid content ink control technology: The volumetric ratio of solvents in high solids inks generally does not exceed 40%. According to the control technical standards of the environmental protection agencies, really high solids inks that use solvents actually do not exist.
3. Water-based ink control technology: The proportion of water in the water-based ink should occupy at least 75% of the ink liquid fraction, which is the volume percentage, not the weight percentage.
Market Status of Water-Based Ink Application
The extent of application of a water-based ink depends on the type of substrate being printed and the end use of the print. Paper and low boards readily accept water-based inks and waterborne coatings. When water-based inks are applied to other non-absorbent substrates, such as films and metal foils, these substrates need to be specially treated so that their surfaces can accept water-based inks or water-based coatings.
As early as in previous years, the printing technology of water-based ink on paper and paperboard has been quite perfect, and it is not difficult to achieve high-quality printing. However, with the advent of thin-film printing, the use of water-based inks for thin-film printing has still some insurmountable problems in some respects. However, with the continuous development of new resins in inks and the use of other advanced technologies, the use of water-based inks for film printing has achieved considerable success.
Printers should note that the reliability of water-based inks has now greatly exceeded that of a few years ago. In the past few years, the technological achievements in Xu Shuiji's ink have been born, which are sufficient to meet the current challenges. In each of the past months, ink manufacturers have brought us many new technological improvements to further meet our customers' requirements for reducing volatile organic compounds. Similarly, changing the surface characteristics of the substrate, using new resins, and changing the additives in the film will also help the substrate accept water-based inks. This also includes other commonly used products that were previously unacceptable for water-based inks.
In practical applications, the key to determining whether a water-based ink can be used is to put a water-based ink into use. However, if printers really want to use water-based inks for printing, they also need to do some necessary improvement work and training printer operators so that water-based inks can be applied well in printing.
Water-based inks used in printing barriers
Since the invention of the flexographic printing technology, water-based inks have been used in flexographic printing presses for paper and board printing. Because of the good absorption properties of paper fibers, the printing of water-based inks on paper and cardboard has been quite successful. Part of the ink and solvent (including water) is absorbed by paper and cardboard, and the other part is evaporated into the surrounding air. But if you place an aqueous solvent on the surface of a film or metal foil, it's like dropping water into the waxed car body - water turns into water droplets and rolls around on the surface of the car. The reason is:
1. The surface tension of the ink and the substrate is not the same—especially the difference between a water-based ink and a solvent-based ink. This requires changing the surface tension characteristics of the substrate so that the water-based ink can be more easily transferred and adhered to. Substrate surface.
2. The addition of a lubricant additive or a dehydrating agent ingredient to the film substrate will further complicate the application of the water-based ink. Lubricant additives are added to the film to facilitate easy opening of the plastic bag during the packaging operation. However, when a water-based ink is printed on the surface of the film, the lubricating additive will permeate to the surface of the film and hinder the adhesion of the water-based ink.
3. The ink used in the printing of flexible bags must be resistant to rough and abrasion. Soft packaging forms can display features that are not found in other paper packaging. Frozen foods, agricultural products, ice cream, and other rigid packaging are all required to withstand shocks, so bags must have films that can withstand these resistances. When the product is packaged in the packaging workshop, chemical reactions may occur to produce ammonia, water vapor, etc. Therefore, the printing ink must be able to resist the effects of chemical reactions.
Overcoming these obstacles is a major challenge that packaging printers must face when choosing water-based ink printing.
Basic conditions for printing with water-based inks
The use of water-based ink technology can cause problems with printing presses and printing operators. This requires a full understanding and corresponding improvement of the functional components of the flexographic printing press. When using water-based inks for printing, the following equipment and settings need to be appropriately modified.
1. Ink transfer device: ink fountain roller on the ink transfer device, ink metering roller and anilox roller composition, it should be noted that the use of water-based ink printing, to ensure that the ink metering roller measurement functions and structural performance can be compatible with water-based ink. Because water-based inks (some similar to high solids inks) use less solvent (ie, water) and are prone to drying, some changes to the ink roller are needed, and close attention is paid to the possible corrosion and wear of the anilox roller material. When printing with water-based inks, the metering roller must be constantly rotated because the water-based ink is very difficult to dry and it is very difficult to re-wet the individual ink rollers. This is of utmost importance when the printer is down. At the same time, after the printing machine is shut down, measures must be taken to separate the plate cylinder and the anilox roller automatically. Otherwise, the dry water-based ink will scratch the ink roller and plate.
The old models generally do not have the above-mentioned functions, so they must be improved in use so that the ink fountain roller and the ink-transmitting anilox roller can continuously rotate and separate from the plate cylinder when there is any reason for the shutdown. Otherwise, the water-based ink It will dry in the ink hole of the anilox roller, and it is very difficult to remove, and it must destroy the ink transfer performance of the ink roller.
In addition, the ink fountain roller and the anilox roller in the ink transfer device must also be replaced with new ink rollers that are advantageous for water based ink applications. The softer rubber ink fountain roller often conveys too much ink and cannot scrape excess ink on the anilox roller and is not conducive to printing. therefore:
Since the role of the ink fountain roller is to transfer the ink in the ink fountain to the metering anilox roller, the harder the rubber used by the ink fountain roller is, the less the transferred ink volume is. The ink fountain roller with solvent-based ink has a standard hardness of Shore 65-75A, while the water-based ink requires a Shore hardness of 85-90A.
The anilox roller is engraved with ink holes for metering and transferring the ink. The finer the mesh (the number of ink holes per inch), the shallower the engraved ink hole, the less ink transferred. For example, a 360 line anilox roller will transfer thinner ink layers and less ink and solvent than a 200 line anilox roller. An anilox roller with the same number of screens, but with a smaller ink volume, will reduce the amount of ink transferred. The use of high-quality water-based inks requires less ink transfer than the commonly used alcohol-based inks, so the ink-receiving volume of the anilox roller is improved to reduce the amount of ink transferred.
2. Drying device: In order to achieve better control of drying and higher discharge rate, the existing drying device must be improved or re-equipped. Drying devices that are suitable for the drying of solvent inks are completely unsuitable for the drying of water-based inks. A typical flexo printing drying box is to introduce air into a strong pressure area and blow it through a slit and a small hole on the intaglio. This type of drying apparatus is suitable for solvent type inks that are rapidly volatile and can be carried away with a slightly higher exhaust gas flow.
However, the use of water-based inks poses two problems. One is that the actual amount of vapor evaporated by heating the aqueous solvent in the water-based ink is 10 times that of the solvent-based ink in the same volume.
The second problem stems from the amines needed to keep the resin and colorants in suspension in the formulation of water-based inks. If the amines are completely transferred by the scraping effect, they will remain in the ink layer to weaken the adhesion of the subsequently overprinted ink layer.
The development of a new generation of drying ovens for drying nozzles and the type of gas flow generated takes a more scientific approach. Its latest design idea is to seek to remove the amine and water by a scraping action from the gas flow, and to be able to remove the evaporated water vapor at a high speed.
Dryness is also a major factor in the speed of printing. Low-speed printers may not require a large amount of drying air, but on high-speed printers, if the flow of dry air is inappropriate, the printing speed will be limited.
Conventional investigations have shown that on existing high-speed printing presses, the use of water-based inks for printing only uses common drying equipment, which will result in a 20% to 30% reduction in printing speed, which is mainly due to the increased need for drying water-based inks. Additional downtime.
3. Substrate surface treatment: The surface of the film must be effectively treated prior to printing on the machine to increase its surface tension. The prepress treatment device (discharge or flame treatment) uses high velocity particles to bombard the surface of the film, making it easier to accept water-based inks. Discharge treatment can not only increase the surface tension of the film, but also make the film more susceptible to ink wetting and adhesion of ink. The principle is to make the lubricious additive not dialysis to the surface of the film temporarily, or remove the additive that has been leached out of the surface, so that the ink can better wet the film.
4. Squeegee blade: The new type of flexographic printing press has become one of the first choices for printers who use water-based inks, namely the use of a closed doctor blade system to replace the traditional two-roller ink transfer device. The latest type of more sophisticated box-type squeegee system can also automatically complete the cleaning of the ink path on the flexographic printing press.
In contrast to the way in which ink was previously transferred from an open ink fountain through a rubber roller to an anilox roller, the doctor blade system consists of an anilox roller, a fixed blade and a doctor blade, and an ink reservoir. composition. When inking, the ink is jetted onto the surface of the anilox roller, and excess ink on the surface is scraped off by a doctor blade, and the anilox roller then transfers the ink to the plate.
The box-type squeegee device not only improves the printing quality, but also eliminates the stacking and flying of ink in the open-type ink transfer system and reduces the evaporation of the solvent during the printing process. And through a more effective method to control the ink layer (and water), make the ink more realistic. The latest improvement of the device is to provide a pneumatic cycle flushing device that can clean the entire unit and the anilox roller, thereby reducing the amount of wasted ink and waste of flushing water (or solvent).
5. Auxiliary devices: In accordance with the reorganization of the above-mentioned main institutions, the auxiliary devices also need to be improved accordingly.
Ink pumps used in solvent-based ink printing are not suitable for water-based inks. This ink pump rotates in high speed 
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