Apply UV coating to common inks (3)

UV coating

Nowadays, most of the offset printing uses chemically strong coatings. These UV coatings contain a color developing agent, a chemically reactive diluent, and a photoinitiator. Under the irradiation of UV light, it acts like a mesh, making the coating solid (cured). The UV light causes the photoinitiator to emit a chemical radical that causes the acrylate to polymerize; that is, it forms a long-chain network bond. Oxygen prevents this reaction.

For cation-firm coatings, UV light induces ions; it is linked to a solid condition. Because of the continuity of curing, it takes a long time but it is completely solid. Although the reaction process is inhibited by moisture, cationic ultraviolet (UV) coating methods are mostly used for food packaging because it has no odor and is completely solid. Our tests focus on chemically solid UV coatings.

Ultraviolet (UV) coating and achievable gloss

Increasing the amount of UV coating can improve the gloss (Photos 9 and 10), but the effect is not as much as increasing the amount of primer. During testing, the amount of UV coatings increased from 20 to 30 cubic centimeters per square meter, and the gloss increased by 10 points regardless of ink coverage. When deciding the amount of UV coating, don't forget that depending on its flow resistance (viscosity), too much coating can be difficult (Photos 7 and 8).

Heating the UV coating to 40 degrees Celsius can increase fluidity and increase gloss.

Reticulate textured geometry also affects paint flow. In addition to carrying capacity, its network conditions also play a role.

Only a non-foamed coating then causes a good gloss effect. When the reticulate nests are filled with paint, fine bubbles form within the paint, resulting in microbubbles. This situation can be enhanced with defoamers, coupled with a properly integrated coating circulation system to ensure that the paint does not stir excessively.

Drying is necessary

In a matter of seconds, the color and glossy materials are applied to the substrate. Although manufacturers try their best to convert these layers from liquids to solids, high speed printing imposes limitations. Therefore, the process must choose the appropriate drying support.

Drying is determined by the speed of production

High-speed production is certainly desirable, but keep in mind that the drying methods described are of limited assistance to the dryer. When the production speed increases, the surface of the printed sheet must maintain an acceptable heat, and it is difficult to completely dry the solid. After printing, this situation directly results in the printed sheets on the delivery pile, and the mutual influence of the paper surface and the paper base. If the effect causes visible conditions, it is called anti-printing. Ultraviolet (UV) coating products stabilize in a few days. The gloss and adhesion quality can still change after 24 hours, depending on the ink and coating used. However, changes may not necessarily be shortcomings. Please refer to Figure VII.

The surface of the coating after the solid beam is to maintain its condition. After drying, do not let it change underneath. Sheets are piled up one by one in the delivery area and are under considerable pressure. Therefore, the printed surface should be solid to ensure that it is not damaged by the contact with the first printed sheet. This solid surface is due to the proper beam energy generated by the UV dryer.

Drying raises the temperature of the take-up pile, causing reverse printing and even causing the paper to clump. Therefore, the combination of the printers, the most important thing is to apply proper drying energy at the appropriate time. Therefore, after the printing and coating machines, there is a real need for infrared (IR) lamps plus cold or warm air and suction support. To dry a water-based dispersion type coating, it is recommended to use two transfer forms of extended drying unit between two coaters. If you think that only the drying time determines the gloss effect, then add a transfer part between the two coaters to ensure that the production speed can be increased by 40% without affecting the gloss. Figure 8 shows that the dryer's output energy must match the production speed. UV's output energy follows the speed, but not the linear mode. IR's output energy is linear.

Production situation: the faster the better?

As the speed of the press increases, the degree of gloss drops depending on the ink coverage. As described above, the stability of the formed "base layer" is determined at intervals between the application of the individual paint layers. The paper moves between the units at a speed of 10,000 sheets per hour, and the ink can penetrate into the paper in less than a second. These tests allow ink to infiltrate at normal production speeds. Comparing the gloss of the first and last applied inks, the results showed that the gloss of the final applied ink was poor. This situation can be used as a reference to arrange the layout of the printing layout and color sequence. However, while the gloss can be increased, the speed of the printing press increases, and the gloss decreases due to the use of ordinary ink. The intrinsic problem of this ink is a fact that cannot be concealed. Nevertheless, selecting and coordinating inks, coatings, and adjusting the dryer can reduce such quality deterioration to the slightest degree.

to sum up

The effect that can be achieved with UV coatings depends primarily on the substrate. The use of a high-gloss diffusion coating on a certain type of substrate provides a good indicator of the intended effect of applying an ultraviolet (UV) coating on the substrate. Ink, especially when the coverage is high, can cause a reduction in gloss, but it can be improved with thicker pigments and inks that are easier to infiltrate. The affinity of the ink composition and its primer material determines the degree of adhesion of the coating layer to them, and the bonding condition is stable for several days after printing. Appropriate selection of the type and weight of the underlying material will have a decisive effect on the degree of gloss that can be achieved. Ultraviolet (UV) coatings are surface layers that help prevent scratches. At the same time, if it is evenly coated, it becomes a shiny surface. Choosing the right combination of machines, especially in the dryer section, plus coordinating the condensation of materials and inks, the press provides a number of prerequisites for optimal results.

The requirements for product quality continue to increase, resulting in a corresponding increase in requirements for the selection of appropriate materials, proper press combinations, and machine operator skills.

The process we studied is a special application. The information provided by the relevant partners can help the printing company to achieve results. This research shows that users and printers, paints, inks, substrates and other manufacturers are extremely important. No company can do it alone, but it can fully apply the maximum benefits provided by this method.

Source: 21st Century Fine Chemicals Network