I. Introduction
Since the advent of plastic films in the 1940s, plastic gravure printing and plastic gravure printing inks have appeared. However, China began to develop plastic packaging in the 1960s. Due to the weak foundation of China's petrochemical industry and the related prepress and post-press processing technologies and equipment, the country's plastic packaging and printing technology has developed slowly. As China's economy entered a period of rapid development, by the middle of the 1980s, plastic packaging and printing had developed more rapidly. Its rise has driven the further development of gravure ink. Gravure printing has been widely recognized for its colorful prints and high quality, and it has become even more precarious after entering the 21st century.
Plastic gravure printing provides people with exquisite product packaging, and due to the presence of large amounts of toluene in printing ink, it causes a certain degree of pollution to the environment, and it also brings about a certain degree of damage to the health of operators. As the world economy continues to deepen and changes in sustainable development strategies, the impact of environmental protection surge, consumers put higher and higher requirements on the packaging of goods, green packaging is the development of international environmental protection needs. Corresponding to this, the greenization of plastic flexible packaging has also become an inevitable trend of development, which requires a higher requirement for the composition of a gravure ink and the environmental protection of its own ink.
This article is based on the protection of the environment, actively respond to the road of sustainable development, the current situation and development trend of plastic gravure printing inks.
Second, the composition and structure of traditional plastic gravure ink
For plastic gravure ink, according to the printed parts can be divided into table printed plastic gravure ink and composite plastic gravure ink (in India ink).
Table printed plastic gravure ink, as its name suggests, is printed directly on the surface of the surface of the plastic film; and specifically for composite film packaging materials, plastic gravure printing ink is generally printed on a highly transparent polypropylene film, poly The opposite side of the ester film or cellophane is then compounded with a polyethylene film or other material. The ink layer is sandwiched between two plastic films. The printed pattern text is displayed through the film from the inside, so it is commonly referred to as "lithographic printing ink".
Compared with inks in printing inks, table printing inks must have scratch resistance and gloss. Because the ink is sandwiched between two layers of film, it will not be directly rubbed and scratched, and the gloss will be the same for both good and bad. However, after the film is compounded, the composite bond strength at the ink must reach a certain degree, generally not less than 1.0N/15mm. Otherwise, the packaging bag made of this composite material is slightly kneaded or flexed during packaging or transportation, and it is easy to be released again. But generally speaking, whether it is printing ink or printing ink, the composition is roughly as follows:
Coloring material a pigment 8% to 35%
The binder is a solvent 30%~60%
Fill material system material 0 ~ 5%
Auxiliary agent 0 to 3%
The binder is a synthetic resin 10%~30%
Third, the impact of traditional plastic gravure ink on the environment and human health
From the composition of the gravure ink described above, it is not difficult to see that the traditional plastic gravure ink contains a large amount of volatile organic compounds (VOC), which accounts for almost 50% of the plastic gravure ink. In the printing process, in order to reduce the viscosity of the ink, it is often necessary to add more solvent. At present, these solvents are dried and volatilized during the printing process, and some of them are recovered but most of them are released into the atmosphere. Among them, low-boiling, high-volatile solvents such as xylene and toluene and aromatic hydrocarbons that are toxic and flammable are the main factors that pollute the environment. Therefore, it is necessary to consider the influence of the gravure ink solvent on the working environment and the pollution to the atmospheric geographical environment, as well as the negative impact on safety and health. The characteristic values ​​and toxicity of the main organic solvent used in the plastic gravure ink are shown in Table 1 below.
* The relative volatilization rate when butyl acetate is 100, the larger the value, the faster the drying.
As can be seen from the table, although there are no carcinogenic organic solvents in the existing solvents, there are substances that cause central nerve palsy symptoms. In addition, the gravure printing speed is extremely high, and it is necessary to use fast-drying inks with extremely strong volatility. It is also necessary to rely on electric power or infrared heating for external drying to meet the printing requirements. Therefore, the amount of waste gas discharged from the ambassador is printed on the environmental protection of all printing processes. The problem is particularly acute.
Fourth, the development of new environmentally friendly plastic gravure ink
At present, the production of plastic gravure ink is being restricted by laws and regulations such as Fire Protection Law, Labor Safety Law, and Health Law. It is an inevitable trend to actively develop and apply green gravure inks that meet the requirements of environmental protection. Many authorities in the printing industry believe that gravure printing will lose its competitiveness in the market and will eventually be replaced by other printing methods unless it adopts practical measures to solve the grave problem of gravure printing and improve the environmental performance of gravure printing. Therefore, the development of high-concentration, low-viscosity inks suitable for shallow gravure printing, benzene-free alcohol-soluble inks and water-soluble plastic gravure inks is the development direction of plastic gravure inks.
1, water-based gravure ink
The water-based gravure ink is not a new topic, but a long-lasting issue, especially in the field of penetrating paper or paper, the development of water-based is very rapid. However, the water-based ink in plastic film printing has not yet reached a real practical stage. From an overall point of view, the important reason why water-based gravure inks have not been popularized further is that the printing performance and quality of water-based inks are still not up to the standard for solvent-based gravure inks. This is mainly because of the higher surface tension of water, which makes it difficult to wet the ink. Therefore, it is desirable to use inks that do not use organic solvents at all, and water can be used as the main component (completely water-based inks). However, taking into account the moisture and dryness of the plastic films, the use of alcohol-based organic solvents in the inks is also an impetus. Using water-based ink is a more realistic approach.
To date, to achieve the level of printing quality of water-based inks to the level of solvent-based inks, not only water-based inks themselves require advanced technology, but gravure printing equipment and printing plate rollers also need to be improved. For example, improve the printing plate and make the plate shallower. The laser-engraved plate cylinders with groove depths of approximately 38 to 42 μm that have been etched or engraved are changed to laser-engraved plate cylinders with a groove depth of approximately 24 to 28 μm. Further improvements are required for drying equipment and drainage treatment facilities. These renewal tasks require considerable work. investment.
However, as a regulatory requirement for reducing residual organic solvents, water-based is a very effective means. At present, it is still difficult to completely use water-based inks in the field of plastic film printing, but some of them have already begun trials.
2. Toluene-free printing of gravure ink
Since water-based gravure inks cannot completely replace toluene-based inks, the ink industry has been working hard to develop alcohol-soluble inks that meet environmental requirements. Toluene-free, as its name implies, replaces the toluene in traditional plastic gravure inks with other non-toxic or less toxic solvents, and its printing performance is comparable to that of traditional toluene-based inks, thus achieving green environmental protection requirements. The alcohol-soluble plastic gravure ink has the characteristics of low odor and no benzene, which can effectively reduce the damage of toluene-based ink to human health and solve the effect of residual solvent on the quality of packaged food. In Europe and the United States, the development and application of alcohol-soluble plastic gravure ink has become a trend.
Alcohol-soluble plastic gravure inks had suffered from problems such as pasting, rolling, picking, and inaccurate tone reproduction at the beginning of the market. After the improvement of the ink, the squeegee was processed to improve its quality to toluene. The degree to which inks match. However, alcohol-soluble inks cost 20% more than toluene-based inks. So today, when cost reduction is required, how to reduce the cost of alcohol-soluble inks is the most important issue.
V. Conclusion
In recent years, due to increasing calls for social environmental protection, the state has formulated some relevant environmental protection laws and regulations, and the printing factories pay more and more attention to the health of workers. This has increased the printing industry to various kinds of environmental protection inks. demand. Despite the difficulties, it is urgent to develop green inks that can fully replace the toluene-based plastic gravure inks.
Source: China Plastics Industry Network