With the rapid development of our country’s economy, people’s requirements for the quality of packaging prints are getting higher and higher, especially aesthetic awareness and environmental protection awareness, which has led to increasingly fierce competition among printing companies. These have raised higher and newer standards for printing companies. The request. As a relatively high-grade printed matter, cigarette marking has attracted close attention both at home and abroad. At present, the topic of cigarette label printing at home and abroad is more and more popular for green printing, including non-polluting, renewable printing materials, inks that are harmless to the human body and production environments that meet quality requirements. It is reported that 95% of the flexographic prints and 80% of intaglio prints in the United States are printed with water-based inks, and the smoke sign is no exception.

As a leader in the national tobacco industry, the Shanghai Tobacco Industry Printing Factory has continued to innovate in order to maintain its brand image and successfully replaced aluminum sulphide paper with aluminum spray paper. This shows that we have taken a big step forward in environmental protection printing. At the same time, in order to further reduce the harm caused by cigarettes to the human body, the company strictly controls the content of VOCs (harmful gases) and prohibits the market of cigarettes with VOC content exceeding the standard. In addition, this year will try to use water-based ink for graphic printing on cigarette labels. The application of water-based inks will not only increase the technical content of Shanghai smoke labels, but will also give consumers greater support. As a member of the main production department of Shanghai Smoke Labels, the author made some analysis and discussion on the characteristics of water-based inks and combined with the quality requirements of smoke labels.

First, the characteristics of water-based ink

Water-based inks are simply referred to as inks and are produced by the composite grinding of water-soluble resins, organic pigments, surfactants and related additives. Its advantage is that the solvent used in the ink is not organic solvent but water. The ink does not contain volatile organic solvents, which greatly reduces the emission of VOC (organic volatiles), thereby reducing air pollution and improving the environment for printing operators. It is good for the health of employees. It can completely eliminate certain toxic and harmful substances in solvent-based inks, eliminate the harm to human body and the pollution to packaged goods, improve the overall environmental quality, and apply to the packaging and printing products with strict requirements for hygienic conditions such as tobacco, alcohol and food. In addition, water-based inks can also reduce the risk of fire and hidden dangers caused by static electricity and flammable solvents.

At present, water-based inks are in the development stage. Whether the imported or domestic water-based inks need to be improved, the high surface free energy of the water components in the ink makes it difficult for the inks to wet and print on the surface of PE-based substrates. Drying time is also an important issue at present, unless the printing press is equipped with enough drying equipment, otherwise the printing speed will be affected. In addition, the gloss of the water-based ink is lower than that of the solvent-based ink, which imposes higher requirements on the choice of the resin. . High quality water-based inks are relatively expensive.

Water-based ink manufacturing processes differ from solvent inks in the choice of pigments and binders. In order to stabilize the printability and improve the water resistance and light fastness of pigments, the pigments used are alkali-soluble and have good dispersibility in water. The PH value of the ink during printing is controlled at 7.5 to 8.5. The binder determines the printability of the ink and the film quality after film formation. In the past, many ink manufacturers' water-based inks failed to meet customer requirements in terms of glossiness and abrasion resistance, making water-based inks have been used in low-grade printing products. The main reason was that the quality of the linking materials did not meet the printing requirements. In recent years, foreign ink manufacturers have succeeded in developing water-soluble acrylic resins. Its application has increased the level of water-based ink prints to a level that is comparable to solvent-based inks. However, the price of water-soluble acrylic resin is relatively expensive, which also increases the manufacturing cost of water-based inks. Water, as a solvent, has a much slower rate of volatilization than conventional organic solvents. A printing unit with a better drying system can be selected, or a small amount of alcohol solvent can be added to increase the drying speed. At the same time, the volatilization of organic amines in the printing process affects the stability of the ink. In the normal production, the stabilizer is often added to the ink, and the main component is an amine salt, which improves the solubility of the resin and ensures the high efficiency of production.

Second, the application of water-based ink in the gravure marking

The successful application of water-based inks on cigarette labels mainly depends on the abrasion resistance and water resistance of the ink film, as well as the glossiness and saturation of the color. The ink-carrying part of the gravure printing plate is concave, so it has a large ink volume, a thick ink layer, and a strong three-dimensional effect. If you use a water-based ink to print a cigarette on a gravure press, you should first consider the structure of the gravure. In addition, the solid content of water-based inks is about 20% higher than that of solvent-based inks. Therefore, the depth of the cell walls should be appropriately reduced when making printing plates. In order to improve the ink leveling, it is best to use laser etching process. For gravure printing, a large area of ​​solid color blocks is difficult to dry, especially on non-absorbing substrates. The drying speed of water is several times or even several times slower than that of organic solvents. During the manufacturing process, the drying speed should be several times higher than the solvent ink. In addition, we can also add a small amount of ethanol, isopropyl alcohol and other solvents in the solvent configuration according to actual production conditions. However, if the ratio is too high, the resolubility of the resin will be reduced, and printing failure such as blocking will occur. The above method ensures that the ink forms a stable ink film when entering the next process. The surface tension of the water is large, the drying speed of the ink is slow, and the printing pressure of the gravure printing itself is relatively large. This causes the gradation outlets in the gravure printing process to be easily expanded, and the tobacco labels with rich tone levels are difficult to achieve satisfactory printing. effect. The characteristics of the gravure printing itself determines that the printed matter is dominated by color blocks, the printing ink layer is thick, and the shallow web printing does not achieve the desired effect.

Third, the difference between the application of water-based ink in gravure and flexo cigarettes

There is a fundamental difference between gravure printing and flexographic printing. Although the flexographic printing graphic part is a convex layer, the ink transfer is better, but the printing plate is an elastic resin material, and it is easy to produce deformation. The improper pressure causes the dot to enlarge. This requires the output personnel to carry out the adjustment and adjustment according to the actual situation. In recent years, with the application of flexo CTP and sleeve technology, flexo platemaking technology has made great progress, but flexographic printing is limited by the structure of the plate material, the amount of ink is small, the printed part of the field is obvious The thickness of the gravure printing cannot be achieved. For this reason, in order to improve the three-dimensional effect in the field, many manufacturers usually adopt the method of printing on the ground twice. At the level of rich tone products, through the adjustment of pre-press output outlets and the control of printing pressure, it is possible to control the increase of outlets and achieve a more sophisticated copying effect. At present, some manufacturers also tend to use UV inks for high-grade printed dot outlets (UV inks have a good development direction because of environmental protection). Such combined printing can achieve better printing results.

Through the above discussion, the successful application of water-based inks on cigarette labels not only requires that the printing companies have good printing equipment and first-rate technical personnel, but also that the actual conditions of production should be taken into account in the design of cigarette labels. Regardless of whether water J gravure printing or water-based flexographic printing is used, the large-area thick layer of solid color blocks and the height of the screen lines should be reduced as much as possible. The light and simple graphic design can be the success of water-based inks on cigarette labels. The application provides convenience. In addition, in order to meet the needs of customers, we can consider the combination of printing. For example, in the gravure printing, alcohol-soluble or UV ink printing dots are used, water-based ink is used to print color blocks and lines; in the flexographic printing, UV ink is used to print dots, water-based ink is used to print non-text areas, and thick solid parts can be connected. Print twice to achieve the desired result. Funds allowable manufacturers may consider buying printing equipment such as flexo, gravure, UV printing units, etc., and reasonably arrange printing color groups according to the layout structure.

At present, the tobacco label of Shanghai Tobacco Group Company is still in the initial stage of printing water-based inks. The vast majority of them use on-line gravure printing. Alcohol-soluble (or solvent-based) inks can be used in combination with aqueous inks. For Chinese gold, peony gold, double happiness gold and other colors, metallic glossy water-based ink is difficult to meet the quality requirements (currently there are water-soluble gold and silver inks on the market, the gloss is higher, but the ink price is very expensive, increasing the number of cigarettes Additional cost). For this reason, the color with high glossiness may not use water-based ink temporarily, and the rest of the water-based inks may completely meet the printing quality requirements. In addition, improving the gloss of the coating oil can also improve the gloss of the aqueous ink. At present, waterborne resins and pigments with high glossiness are expensive, several times that of common ink, which undoubtedly increases the printing cost. We can improve the ink's special gloss and reduce the cost through the discussion with the ink manufacturers' technology and the improvement of the ink manufacturing system, and gradually over-print all the water-based inks. After using water-based ink printed products, after the appearance of the quality requirements, we should also conduct a series of physical and chemical experiments, including ink layer abrasion resistance, water resistance, oil resistance, surface smoothness, and color stability Sex and product indentation after the formation of the ink film flexibility and so on. Through efforts to successfully complete the replacement of solvent-based inks to water-based inks, the quality standards of Shanghai smoke labels have been improved.

Reprinted from: Printed Today