All sheet-fed offset press manufacturers in Europe are trying to develop on-line coating technology, and the scope of application is not limited to packaging and label products, but extends to book printing, advertising printing, and commercial printing. The steady increase in sales of printers with dedicated on-line coating units can also indicate this trend.
For example, as early as two years ago, Komori company had realized the rapid development of online sealing and coating, and firmly believed this trend, the company's recent multicolor products have coating devices in 80%, some in the end A printing unit, some with a dedicated in-line coating machine to complete the coating function. Heidelberg’s British companies also saw the same prospects. It is said that their sales of B1 coating units increased by 55% five years ago, and that four-fifths of the Speedmaster CD printers sold each year have at least one coating. Cloth machines, and the application of double coaters and anilox/squeegee systems are becoming more and more common.
"It not only simplifies the traditional processing process, it also enhances the visual effects of spot colors."
This trend is also not limited in large format presses: Heidelberg's printers with B2 coating units have increased sales by 350% in the same amount of time. The company launched the B3 Speedmaster SM52 with coating function two years ago and also has a place in the market.
At present, the total annual sales of European coatings and coatings is 22,030 tons, compared with 72,100 tons in the United States. In addition, the use of paint will increase as a result of factors such as design, economy, and production.
In aesthetics, coating can increase the value of a work and distinguish it from other works. From the perspective of production and cost, coating and printing can be completed at one time, which can shorten the production cycle of the job. At the same time, it means that the printed product can be sent to the post-printing process once it passes through the printing press, which reduces the possibility of scratching and is very suitable for time-critical environments. The coating has a protective function during transport and use, making the product more flexible when it is subjected to friction.
In addition to this, the main reason for the recent rapid growth of European coatings and coatings may be technological advances, making processing operations easier and more effective. For example, there is a clear improvement in the blade coating paper material now used. Recent tests by MAN Roland have shown that the effectiveness of UV coatings depends primarily on the quality of the base material and varnish, and they have a significant effect on the effectiveness of the finished product.
Coatings also have some improvements: not only greatly increase the number of types, even better, and many coatings also increase the solid content.
As with photopolymerization and anilox technology, improvements in the drying system also have an impact. As an alternative to the traditional roller system, the cell doctor and the anilox roller in the flexo printing unit can cover a more precise and uniform surface as the coating is transferred from the cells of the anilox roller to the substrate At the time, the problem of edge bleed in the conventional operation does not occur. In addition, compared with the traditional method, it also has the advantages of reducing the use of paint, speeding up the printing press, reducing downtime, and so on.
The photosensitive resin plate is compatible with all solvents and inks and has a longer life. Although the plates are more expensive, the most important thing is that they have more precise registration capabilities and high resolution, and can be used to print more demanding products such as half tone and false light images.
With the ever-increasing demand for coating, it is not surprising that printer manufacturers are trying to improve production technology. Both MAN Roland and KBA have made tests using UV coatings and mixed inks. As MAN Roland pointed out, the use of UV coatings with traditional inks has a number of advantages: the level of gloss produced is not comparable to that of conventional waterborne coatings, and no dusting device is used, and the UV coating is more wear resistant.
However, there is a problem that the chemical composition of UV coatings is incompatible with conventional offset printing inks. Therefore, up to now, two coating units have been installed on the printing press and two coating technologies have been used: the first one is coated with a water-based coating as the primer layer, and then the UV coating is applied.
It is said that the recently studied hybrid ink has solved this problem. This ink is essentially a 25% UV ink component in traditional inks. Although it is necessary to use a suitable UV ink roller and blanket in order to use such an ink, it is necessary to use a corresponding cleaning agent, but the ink does not have to be coated with a primer first, and it can be used on a printing machine having only one coating unit.
Obviously, the printing machine installed with two coating units has better flexibility and is still the best choice, but the hybrid ink used on one unit is very expensive due to the need of the matching ink roller and blanket.
However, according to a large number of printing tests recently conducted by KBA's Radebeul Printing Center at the company, hybrid inks have other advantages. These tests use hybrid inks produced by Sun Chemicals and Epple, as well as standard oil-based offset inks and Pantone spot color inks. The printers used are also standard in many manufacturers. Through experiments, KBA confirmed that it can produce a plastic sensation on the printed surface. This effect was originally obtained by screen printing, and it is not suitable for medium-to-long-lived printing. Now it can be printed through traditional printing. The unit plus mixed ink printing is implemented. Then, elements such as borders, solids and other image parts can be printed by one or more additional units and oily inks, and the ink is dried by the UV desiccant therein.
After the printed product has been UV coated and dried, the part of the image printed by the hybrid ink will have a higher gloss, previously achieved only by secondary coating. This interaction of traditional inks with UV brightening oils allows images printed with oil-based offset inks to exhibit a three-dimensional, rough, glossy surface that feels like plastic.
This year's KBA calendar called "People and Printing" is a good example of applying this technology. Last year's calendar was completed with two on-line coating machines with a drying unit, which were coated with a base coat and a UV coating, respectively. This year, 10,000 sheets were printed in a single pass through a 41-inch, five-color KBA Rapida 150 “eco” press.
Image elements and numbers were printed using Sun Chemical's four-color hybrid HyBryte ink, and the fifth color of the background was printed using Pantone standard oil-based offset inks. The printed sheets were dried after printing and then printed with a full layer of Vegra UV bright paint with a web coater. A drying device is then installed on the upward slope of the double transfer extension.
As a result, all image elements and unprinted background parts were printed using UV printing and had a high gloss. The background area, due to the use of standard offset printing inks and UV gloss oils, presents a rough, shiny surface that feels like plastic.
Jurgen Veil, manager of Radebeul Printing Center at KBA, improved the new in-line coating technology. He explained that "This technology is not only simpler than usual, but also improves the visual effect of spot colors. It will revolutionize commercial in-line coating. In the process, you don't need to use a second coater and dryer, and if you are using more than five color presses, you're still connected to the coater and extended conveyors, and you can apply existing gears more effectively. You can reduce costs by rationally dispensing photosensitive plates or labor-intensive hand-cut glazing."
Further research on KBA calendar printing shows that the printer can use two different types of ink with a few changes, and it will produce other more interesting effects. For example, even if calendar numbers are printed using ordinary reflective printing, overprinting will still produce a smooth effect. This effect is achieved by printing the background itself with a hybrid ink and a background with Pantone reflective ink. In other words, the mixed ink printed area as well as the unprinted area are reacted with the UV paint to form a high gloss UV coating, and it is ensured that the positioning is as accurate as the printing of the ink itself.
This will mean that a spot coat can be obtained with a single coater without the need for a special gloss stencil. This is significant in large-format printing, because the expensive price of glossy stencils tends to make spotlight oil a waste.
Another possible application is a folding carton, where the glued parts of the carton folds cannot be lightened to ensure long-lasting adhesion. However, if the package is printed with a hybrid ink and ink containing a common adhesive, printing the offset ink and the adhesive at the folds of the carton at the same time, the entire surface can be lightened, because the clear oil can be absorbed by the adhesive. Again, this method does not use expensive bright-oil plates and saves time.
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