Add UV (UV) coating to ordinary inks (2)
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In combination with UV (UV) coatings on common inks, it is common to first use a diffusion coating to primer. Ordinary offset inks and ultraviolet (UV) coatings are incompatible chemicals, and this "intermediate coating" needs to be applied to the sheets in a wet, wet form in a short period of time. The water-based diffusion synthesis solution contains about 40 to 45% of a solid, and its flow resistance (viscosity) which varies with temperature can be adjusted by adding moisture.
Once the diffusion coating is applied to the sheet, a significant amount of moisture must be drawn into the substrate and some will disappear due to volatilization. Only at this time, the polymer begins to combine to form a tight coating film. In the linkage process, the primer must be dried as soon as possible.
The drying speed, flexibility, penetration, traction, flow resistance (viscosity), gloss and adhesion can be achieved depending on the base material and the additives used.
Priming as a bonding and balancing element
From the increase in the type and amount of primer used, it is clear that its important function.
Especially in the surface with high ink coverage, there is a change in the amount of components and mixing, which affects the situation of the primer, which is more remarkable. Figures 4 and 5 illustrate these relationships.
Turning 13 cm3 of netting per square meter into 18 cm3 of textured enamel, the UV (UV) coating layer is smoother and has a higher gloss (Photos 3 and 4). This situation is more obvious in places with high coverage.
Different types of primers. The effect is also easily identifiable: comparing photo 5 (left) and photo 6 (right), the primer on the left is relatively hard and has a good luster; the primer on the right contains a soft body developer. Applying a hard, shiny base coat on a 400% ink coverage surface can add 35 gloss points; even on a 100% ink coverage surface, more than 15 gloss points can be measured (Figure six). When using soft body primer, severe paper deformation can only be seen on the surface of 200% of the ground. The hard-wearing primer looks like it already has a smooth surface before it is applied to the UV coating. However, the ability to resist rubbing is weakened. When the relative component is used less, the type of primer is particularly strong.
These tests clearly show that drying between the coating units is extremely important. If the drying time and drying conditions are not sufficient before applying the ultraviolet (UV) coating, the best gloss can not be achieved with the best primer and the most effective amount. For this reason, it is recommended to use two coating units and an extended drying section for high quality coated printing.
Ultraviolet (UV) coating
Today, offset printing mostly uses chemically solid coatings. These ultraviolet (UV) coatings contain a vehicle, a chemical reaction diluent, and a photoinitiator. Under UV light, it reticulates to make the coating firm (cured). The UV light causes the photoinitiator to release chemical roots, causing the acrylate to polymerize; that is, forming a long chain network bond. Oxygen blocks this reaction.
For cationic solid coatings, UV light initiates ions; it interlocks to create a solid condition. Because of the continuity of curing, although it takes a long time, it will be completely solid. Although the reaction process is inhibited by moisture, the cationic ultraviolet (UV) coating method is mostly used for food packaging because it has no odor and is completely solid. Our tests focused on chemical root solid UV (UV) coatings.
Ultraviolet (UV) coating layer and gloss that can be achieved
Increasing the UV (UV) coating component can increase the gloss (Photos 9 and 10), but the effect is less than the weight of the primer. During the test, the amount of the ultraviolet (UV) coating was increased from 20 to 30 cubic centimeters per square meter, and the gloss was increased by 10 points regardless of the coverage of the ink layer. When deciding on the amount of ultraviolet (UV) paint, don't forget that depending on its flow resistance (viscosity), too much is difficult to apply smoothly (Photos 7 and 8).
Heating the UV (UV) coating to 40 degrees Celsius enhances fluidity and increases shine.
The geometry of the textured enamel also affects the smoothness of the paint. In addition to its load, its network cable condition also plays a role.
Only a foam-free coating results in a good gloss. When the pits of the textured enamel are filled with paint, fine bubbles form in the paint, causing micro-foam. This situation can be combined with defoamer improvements, plus a properly combined paint circulation system to ensure that the paint is not over-stirred.
Drying is necessary
Within a few seconds, the color and gloss applied to the substrate. While manufacturers try to make these layers change quickly from liquid to solid, high speed printing imposes limitations. Therefore, the process must choose the appropriate dry support.
Drying is determined by production speed
High-speed production is of course desirable, but keep in mind that the dryers described have limited assistance with the drying methods described. As the production speed increases, the surface of the sheet should maintain an acceptable heat and it is difficult to completely dry the solid. After printing, this situation directly causes the printed sheets to be on the delivery pile, and the paper surface and the paper bottom interact. If the influence causes the situation to be seen, it is called counter printing. Ultraviolet (UV) coating products will only stabilize after a few days. Gloss and bond quality can still vary after 24 hours, depending on the ink used and the glazing coating. However, the change may not necessarily be a disadvantage, please refer to Figure 7.
The surface of the coating after the beam is solid, to maintain its condition. After drying, do not let it change underneath. The sheets are stacked one by one in the delivery section and are subjected to 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 caused by the UV beam producing the proper beam energy.
Drying causes the temperature of the delivery stack to rise, causing reverse printing and even sticking the paper into pieces. Therefore, the most important combination of presses is to apply the appropriate drying energy at the appropriate time. Therefore, after printing and coating machines, there is a real need for infrared (IR) lamps plus cold or warm air and pumping support. To dry water-based diffusion coatings, it is recommended to use two transfer forms of extended drying parts between the two coaters. If it is only the drying time that 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 output energy of the dryer must match the production speed. The output energy of the UV is to follow the machine speed, but not the straight line mode. The output energy of IR is a linear mode.
Production situation: The faster the speed, the better?
As the speed of the printing press increases, the degree of gloss decreases depending on the ink coverage. As described above, the stability of the formed "base layer" is determined at intervals of application of individual coating layers. The paper moves between units at a rate of 10,000 sheets per hour, and the ink can only penetrate into the paper in less than a second. These tests allow the ink to penetrate at normal production speeds. Comparing the gloss of the first and last applied inks, the results show that the gloss of the final applied ink is poor. This situation can be used as a reference to arrange the printing layout and color sequence. However, while the gloss can be increased, the speed of the printing press increases, and the gloss is lowered by the use of ordinary ink. The inherent problem of this ink is a fact that cannot be concealed. However, the selection and coordination of inks, paints and conditioning dryers can reduce such quality degradation to a minimum.
to sum up
The effect that can be achieved with ultraviolet (UV) coatings depends mainly on the substrate. Coating a certain type of substrate with a high gloss diffusion coating provides a good indication of the desired effect of applying an ultraviolet (UV) coating on the substrate. Inks, especially in the case of high coverage, can cause a decrease in gloss, but can be improved with dense pigments and inks that are easily penetrated. The affinity of the ink composition and its primer material determines the degree of adhesion of the coating layer to the coating, which is stable for several days after printing. Proper selection of the type and amount of primer material is decisive for the degree of gloss that can be achieved. Ultraviolet (UV) coatings are applied to the surface to 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 drying section, and coordinating the condensation of materials and inks, the press provides the best results and offers a number of prerequisites.
The demand for product quality continues to increase, and the requirements for selecting the right materials, the appropriate press combination, and the skill of the machine operator are also increased.
The process we are studying is a special application. The information provided by the relevant partners will help the printing company to achieve results. This research shows that cooperation between users and manufacturers of printing presses, coatings, inks, substrates, etc. is extremely important. No company can do it alone, and the full benefits of this approach can be fully applied.