Add ultraviolet (UV) coating to ordinary inks (1)
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More than 20 years ago, Manroland was the first printing press manufacturer to recommend linkage coatings to the industry. From then on, it is possible to use coatings to enhance the packaging or high-grade booklets such as gloss and protective layers without additional processes.
In recent years, Manroland continues to expand its range of applications and applications: gold, silver, pearlescent, special gloss or matt, partitioning, embossing, fragrance, etc. - all of these coatings can be applied in conjunction with a specified thickness. These extensions, behind the scenes, come from the emergence of two coater presses that use chamber-type scrapers or textured coating technology.
Ultraviolet (UV) coatings are the most desirable if a particularly high gloss is required. This type of coating is resistant to rubbing and does not provide a good protective layer. Its shiny surface makes it visually appealing. Packaging printers are particularly interested in these advantages. Therefore, when the mid-range model proves the effectiveness of these reforms (two coating units plus multiple dryers for preliminary drying, inter-unit and tail drying), large-format models naturally follow this special reinforcement. combination. For large-format printer users, the production of folding boxes is particularly interesting for the use of ordinary inks and then coating of ultraviolet (UV) coatings.
Process technology research has achieved better results
For best results, there are some prerequisites for the press, coating and drying methods. With the highest ideals, it is the only way to coordinate the elements of the press and the specific requirements of individual customers. Many tests help to understand the impact of many different process parameters. It is extremely important that the test is carried out in close cooperation with the partners in the supply industry.
Chamber knife coating provides uniform film thickness
The chamber knife coating developed in 1993 ensures that the thickness of the coating layer is extremely uniform. Reticulated crucibles with different loadings allow for accurate coating of the coating to be applied and can be repeated. The amount of paint contained in the roll is different for each job. The normal rule is between six and thirty cubic centimeters per square meter.
This is a nominal load. The actual transfer, only 25-35% of the wet paint is transferred to the surface of the substrate. Reticulated different mesh surface, allowing the component of paint transfer to meet the needs. If you regularly take care of the crepe, you can ensure the stability of production quality.
Good circulation of paint is an element
To be able to handle many different coatings, the coating's circulation system must be the most appropriate combination. The quality of the coating layer is uniform, depending on the conveying component, storage component and pumping principle, plus the temperature is stable, etc., they must be matched with the coating machine used.
Figure 1: Process for adding effects using common inks and ultraviolet (UV) coatings, Roland R906
LTTLV printing machine and its influencing factors
As various applications continue to increase, coating units provide solutions for related applications. A coating unit has several completely separate coating circuits that can be quickly and economically transferred from one coating method to another. It not only saves school time, but also saves paint and cleaning agents. Diffusion coatings and UV (UV) coatings are not compatible. At the same time, the replacement of pigmented paints into clear coatings requires thorough cleaning. Hygiene is important to ensure quality stability when converting paints.
How to assess coating quality
The change in brightness is particularly remarkable on large-format flow coating surfaces. Therefore, it is of the utmost importance to uniformly coat the coating to maintain a uniform brightness throughout the surface.
There is a so-called "fading effect" that causes difficulties. The ink layer and the paint layer are dried at different rates due to differences in printing time and different physical processes. When different layers of material are mixed to change the volume, a gas is emitted and the surface is deformed. The resulting structure causes a decrease in gloss, depending on their combination.
Glossy gloss with reflected light
A certain light reflection angle can be used to measure the gloss. A surface like a "mirror" that reflects 100% of the light, or only a portion of the light, depends on the quality of the surface of the coating. Consider the degree of gloss, choose the angle of measurement, and be sure to change the gloss information to provide reliable data. The angle of measurement is important because the pigment penetrates deep and there is dispersion. The human eye responds strongly to the luster in the dark background.
Scratch resistance and adhesion test
The scratch and bond characteristics of the coating are important factors in the finished process and also indicate the durability of the print. Customers sometimes test these features in unscientific ways, such as scratching with a nail or sticking with a sticky tape. These are subjective methods, but mainly rely on customer judgment. There is no data that can be measured or copied, but it can be used as a guide. After production, the adhesion of the coating can only last for several hours if it remains stable after many days. During this time, the ink oxidizes to dry, generating a gas that builds up between the ink layer and the coating layer, breaking the bond. Therefore, it is only reasonable to check the adhesion after several days of printing. Acetone is well suited for testing the degree of cure of ultraviolet (UV) coatings: wiping the coating with a cloth that is wet through acetone, and if the curing is poor, the coating will dissolve.
The German Printing Research Association (FORGA) recommends some test devices to check the resistance of peeling and bonding into blocks. The resistance of printed matter can be tested in accordance with the methods provided by the German Industrial Standards DIN16524 and DIN16525.
Influential parameter
For the relevant elements, we bring together a number of basic conclusions. Pay special attention to the effect structure of the whole system, using multiple test methods to determine: how to affect the results of different substrates, inks, primers, paints and dryers? We use a set of reliable quality judgment factors to ensure test results.
Printing material
We test with ordinary quality folding cardboard. Includes recycled materials (GT and GD) and new fiber materials (GC). These basic materials are not only of different grades, but also the coating quality of the machine. Conventionally, two or three times of powder coating is applied on the machine, and the coating methods include: a rolling blade, an air brush, an air knife, and a laminating machine.
Figure 2: Comparing substrates. Apply five different combinations of different amounts of paint on 100% black:
The first row, a lot of UV; the second row, a small amount of UV; the third to the fifth row, medium amount of UV.
Note: To avoid confusion, we need to have different coatings: paint (powder) added to paper or paperboard in paper mills and paint (glazing) added to paper or paperboard to increase the effect of printing.
Thus, important factors for coating are: the basic materials, the manner in which the machine is coated, and the quality of these elements and their uniform characteristics.
The choice of substrate materials, the technical suitability and economics should be a reasonable balance, with the inks used and glazing coatings to achieve the desired luster.
Basic element of printing material
We tested with eight different quality substrates. Each material has the same thickness and a series of useful tests under the same conditions. On different grades of paper, the number of times the powder is applied has a distinct effect.
The effect of re-engineering the material plus two on-machine coatings is much worse than the three-coating on the machine. The new fiber-made cardboard is coated twice but glued, and its surface is smooth and has a gloss of three times. The hardness of the surface coating applied to the machine also has an effect on the gloss - the pressing tool at the time of coating causes a smooth surface and increases gloss.
The water absorption and oil absorption characteristics do not provide any useful information for predicting the possible gloss. In the laboratory, different grades of paperboard, coated with glazing paint, and the gloss characteristics obtained are useful for evaluating the effect of ultraviolet (UV) coatings on linkage.
Depending on the amount of ink and coating applied, the characteristics of the substrate itself have a very serious effect on the degree of gloss. The smoothness and inhalation characteristics of the powder coated surface determine the effect of the coating. Graded cardboard has a uniform smoothness on the surface. Although slight changes are inevitable, especially paper made from natural materials, it also affects gloss.
The grade of cardboard can affect the result by 30% (see Figure 2). It should be noted that even if the coating weight is increased, the difference in gloss level can be reduced. This test does not depend on the grade of the coating (due to the use of coatings from different manufacturers).
Photographs 1 and 2 clearly show that after coating, the structure and fibers of the coated paperboard on the machine can still be clearly seen. On the other hand, the smooth surface of the coated paperboard on the three machines gives the same amount of paint a better effect. The difference between the coating materials on the three machines can be said to be due to the formulation of the on-machine coating powder, the coating tool, and the processing order.
Ink
Offset inks mainly contain pigments, color developing agents, diluents and additives. The ink is applied to the substrate in the form of water, ink, or film. When the pigment component is increased, the same chromaticity can be achieved with a smaller amount of ink. After printing, the "inhalation condensation" ink component dries in a few seconds, but oxidative drying takes hours or even days to complete.
Choosing the right ink is very important
The ink has two undesirable effects on the glazing layer:
(1) Because of the ink hiding relationship, the printed portion on the printed sheet, the moisture of the diffusing paint for the primer is not sufficiently inhaled, affecting the degree of mixing of the paint and the ink, depending on the flow resistance (viscosity) of the two. .
(2) The ink that has just been applied begins its drying process, and even if the second layer of the coating (ultraviolet (UV) coating) is solid, it continues to proceed below. In this case, the primer layer is deformed and the crucible may be affected by the object released during oxidative drying. These interactions reduce the gloss and break the bond.
As mentioned above, due to the interrelationship between the two, the degree of gloss of the ultraviolet (UV) coating is highly dependent on the type of ink selected. To maintain gloss to a certain level, a fast-inhalation ink is required. However, the quality of the board and the quality required for the print are different, which may result in ink spots and limit the capacity for inhalation. When the first printing unit uses an ultra-fast inhalation ink, the subsequent printing unit, when the ink is split and transferred, ink spots are generated. Therefore, each situation needs to be coordinated individually. Use minimal wetting when printing. This will reduce the accumulation of ink on the tape, thus reducing the risk of ink spots. The ink selected will also have a certain relationship with the counter printing of the delivery pile.