In recent years, the light curing (uv) technology in flexographic printing has played an important role in the printing of paper and film materials. The uv technology has moved from narrow-width web relief printing to the flexographic printing market. In offset printing, we have also seen the advantages of the uv ink quick-drying system, which can shorten the printing cycle and reduce the workload. The most important feature of the uv curing system is that it can improve the printing stability (in terms of drying) and shorten the waiting time for oxidative drying during the printing process. In the past 10 years, uv printing has brought a great impact on tradition, mainly for flexographic printing on plastic substrates.
Today, there is a new type of ink-cationic ink. It adds a guarantee for improving the environmental protection and quality of flexographic printing. Compared with free radical systems, cationic inks have the advantages of low volatility and low odor, which can be said to be a very good environmentally friendly ink. The odor of free radical ink is a headache, it is harmful to the health of the operators and the environment. The cationic ink (low volatility ink) has a great advantage in this respect, and now it can even be used in some food packaging industries. Cationic inks also have the advantage of attaching to plastic substrates. Cationic inks and coated glazes exhibit particularly good adhesion to the radii-treated substrates, which is the most critical of all advantages.
Compared with free radical inks, cationic inks have a moderate curing speed (this is slightly inferior to free radical inks), and can be secondary cured (approximately extended to 24 hours), without preventing oxidation, humidity effects are slight, no shrinkage, plastic Features such as excellent sex.
Although in terms of curing speed, free radical ink can be dried under high speed printing, while the curing speed of cationic ink is slightly behind. However, recent research and development shows that the improved cationic ink can also be adapted to printing from 150m / min to 200m / min.
The advantage of secondary curing is that when the printed product is output from the printing machine, the ink film looks as if it has been cured, but there is still some reaction (not dry out). Cationic curing technology can continue to react until most of these materials have reacted. In contrast, radical inks can only be completely dried by exposure to UV light. And this process will lead to higher volatilization, especially low molecular weight components that do not react are more likely to volatilize. The cured polymer usually has a high molecular weight and generally does not volatilize. The volatilization of volatiles is also reflected in the extractable components. The content of extractable ingredients is an increasingly important feature of testing food packaging systems. Especially as an analysis technique, the content of extractable ingredients is one part per billion, and even the content of one part per trillion is now being discussed as an indicator of the content of packaging products. The shrinkage of cationic ink is small, so it has good adhesion characteristics.
In the current situation where the call for green environmental protection is increasing day by day, the packaging and printing field requires products that are suitable for environmental protection. Food packaging should meet the cepe standard in the industry standard. In terms of ink, it is necessary to continuously solve the content of harmful substances such as lead, benzene, aromatic compounds, ethyl glycol, etc. in the ink to ensure its safety to food and supplies and the health of printing personnel. Judging from the results achieved by the ink industry, the results are still very encouraging. In 1974, the lead in the ink pigment was removed; in the late 1970s, the cellosolve (ethyl glycol) was removed; in the early 1980s, the toluene in the food packaging instructions was removed; in the late 1980s, the related benzidine yellow Pigments; in the early 1990s, the use of phthalic acid plasticizers was reduced. In the initial stage of the development of cationic inks (mid-1980s), the content of some of the above harmful substances did not meet the regulatory standards. For example, benzene is a by-product produced by the production of cationic inks. Popular aromatic compounds and so on, these are all prohibited ingredients listed in the printing and food packaging ink regulations. Therefore, the cationic ink has not been widely used in the initial stage. Up to now, some units still adopt a wait-and-see attitude, but after continuous improvement, the content of these harmful substances finally reached the industry standard. For example, benzene, in the cationic inks produced today, its content is extremely low, and it cannot be detected at all using ordinary analytical techniques. Many test results on printed matter and printing environment also show that no benzene is found. The content of these substances is generally in the range of a few parts per billion (usually a single digit), which means that packaging products using photoinitiators no longer produce benzene. Looking at the development prospects of cationic inks, I believe that most printing units will still choose cationic inks with excellent characteristics. Although some customers currently have plans to abandon the use of cationic inks, it shows great advantages in the printing process and will certainly be recognized by customers. We believe that with the development of science and technology and the improvement of the ink industry, we must find a good solution to some of the deficiencies of cationic inks, like the excellent records mentioned above. Therefore, we must all have a positive attitude and technical direction to these and better adapt to the new standards.
(1) Cationic film adhesive
The printing speed of gravure printing is very fast, when it is coated with adhesive afterwards, it may appear that there is no drying (the presence of a solvent), or it needs to wait a day to let it cure to a certain strength. In flexographic printing, an adhesive is generally used on the printing machine unit, and the film is cured and cured at a normal printing speed. Within a few minutes, the printed film can be cured, and it is cut on the printing machine to the finished product. , And then hand it over directly to the customer. In this case, the use of uv adhesives does not have the problem of volatile solvents and harmful odors. The printing plant uses a newly developed white pigment binder to remove the traditional solvent problems caused by back white, and then coats the white ink. Solve the problem of the original solvent retention. Today, using a cationic adhesive coating, it is easy to reduce the residual solvent content per square meter to very low. This kind of coating can be used on materials such as polyethylene, polyether, and metal sheet.
(2) Cationic ink-shrink film
The vast majority of the shrink film market is occupied by solvent-based gravure printing, and very few are derived from solvent-based flexo printing. In fact, anhydrous ink is used. Flexo printers have found that the ink system that achieves the expected quality in flexo printing is uv-curable ink, which has no solvent evaporation and has good printing consistency. But when the shrinkage reaches 70%, the adhesion of free volatile ink and mixed dry ink is poor. The cationic ink has passed this required test and has become a unique ink system for ops, pvc and opp materials. The advantages of cationic inks in management and storage are obvious.
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