Discussion on UV glazing process in the most popul

2022-08-05
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Discussion on UV glazing process in folding carton printing II.

5 it is very important to select the appropriate ink.

ink has two adverse effects on the glazing coating:

due to the exclusion of ink, the water in the dispersive coating for backing on the printing area cannot be fully absorbed by the substrate. Therefore, the mixing degree of ink and coating depends on their viscosity

the drying process of the newly printed ink begins. Even if the second layer of coating - ultraviolet (UV) coating has hardened, the drying continues below. As a result, the coating surface will be deformed and may be affected by the products generated during oxidation drying. These reactions reduce gloss and destroy adhesion

due to the relationship between the above two, the gloss of ultraviolet (UV) glazing mainly depends on the type of ink selected. In order to ensure a certain gloss, a fast absorbing ink should be used. However, ink spots may occur to limit the absorption. When the first printing unit uses ultra fast absorption ink, in the subsequent printing unit, the ink splits and transfers to the blanket, producing ink spots. Therefore, different situations should be treated separately. When printing, we should use less fountain solution, which can reduce the accumulation of ink on the blanket, thus reducing the risk of ink spots. The selected ink also has a certain relationship with the back rubbing of the receiving stack

6 priming material

online ultraviolet (UV) glazing is carried out on ordinary ink. Usually, dispersive paint is used for priming first. Ordinary offset printing ink and ultraviolet (UV) coating are incompatible chemicals, and this "intermediate coating" needs to be coated on the printing sheet in a wet form in a very short time. The water-based dispersion synthesis solution contains 40% ~ 45% solids, and the viscosity varying with temperature can be adjusted by adding water

once the dispersive coating is applied to the printing sheet, a considerable amount of water must be sucked into the substrate, and some will evaporate. Only at this time did the polymer begin to bind and form a dense coating film. Therefore, in the online production process, the backing material must be able to dry as soon as possible. The drying speed, flexibility, penetration ability, overprint force, viscosity, gloss and adhesion that can be achieved depend on the base material and the additives used

the important functions of priming materials can be clearly seen from the use of different types of priming materials and the increase in the number of priming materials. Especially on the surface with high ink coverage, the effect of backing material is more significant

replace 13m3/m3 corrugated roller with 18cm3/m3 corrugated roller. The UV coating is smooth and has higher gloss. This is particularly true on high coverage surfaces

we can easily identify the effects of different types of priming materials. Severe deformation on 200% of the field surface can only be seen when soft priming materials are used. The hard backing material appears to have a smooth surface before UV glazing. However, the scratch resistance is reduced. The smaller the amount used, the greater the influence of the type of priming material. However, the fatigue testing machine is just the opposite. These tests clearly show that drying between glazing units is extremely important. If the drying time and degree are insufficient before ultraviolet (UV) glazing, the best priming material and the best amount can not achieve the best gloss. Therefore, two glazing units are used for glazing, and one extended drying part is recommended

7 ultraviolet (UV) glazing coating

now, chemical base hardening ultraviolet (UV) glazing coating is widely used in offset printing. These UV coatings contain binders, reactive diluents, and photoinitiators. Under the irradiation of ultraviolet (UV) light, the complexing reaction takes place to cure the coating. Ultraviolet (UV) light causes the photoinitiator to release chemical groups, leading to the polymerization of acrylate, forming a long chain connection. Oxygen blocks the reaction

for cationic hardening coatings, ultraviolet (UV) light triggers ion formation and chain reaction to form hardening. Due to the continuity of curing, although the curing speed is slow, it can be completely cured. The cationic hardening ultraviolet (UV) polishing coating method is often used in food packaging, because they have no smell and harden thoroughly. Our tests focus on chemically hardened UV topcoats

increasing the amount of uvpaint can improve the gloss, but the effect is not as good as increasing the amount of primer. During the test, increase the amount of UV coating from 20cm3/m3 to 30ccm3/m3. No matter how large the ink coverage is, the gloss will increase by at least 10 points. When determining the amount of UV coating, the price is usually 2~3 times that of electronic mechanics testing machine. It should be forgotten that it is difficult to apply smoothly if the amount is too large due to viscosity. Heating the UV coating to 40 ℃ can enhance the fluidity and increase the gloss at the same time

in addition, the geometric shape of the roller also affects the flow of the coating. In addition to carrying capacity, the number of wires also plays a role. Only the coating without foam can produce good gloss effect. When the roll cavity is full of paint, tiny bubbles form micro foam in the paint. This situation can be improved by adding defoamer, and a reasonable combination of paint circulation system can ensure that the paint will not be over stirred

8 drying is the key

within a few seconds, the material that gives color and luster is applied to the substrate. Although the suppliers try their best to make these films change from liquid to solid quickly, the high-speed printing plastic tensile machine brush is limited. Therefore, the glazing process must be supported by the selected drying method

① drying is determined by the production speed.

high speed production is certainly what we want, but it should be remembered that the described drying method only helps the drying device. With the increase of production speed, it is difficult to completely dry and harden. After printing, this situation directly causes the upper and lower sides of the receipt stack to react. If it causes a visible situation, it is called back rubbing. The quality characteristics of UV varnished printed matter can only be stabilized after several days. Based on the different inks and coatings used, the gloss and bonding quality can still change after 24 hours. However, change is not always a drawback

to maintain the stability of the surface of the high-speed hardening coating, do not change its bottom after drying. The printing sheets are piled up one by one in the receiving stack and bear considerable pressure. Therefore, the surface of the printing sheets shall be fully hardened to ensure that they are not damaged due to contact with the back of the previous sheet. This hardened surface is caused by the appropriate beam energy generated by the UV drying device

drying raises the temperature of the receiving pile and how to develop and grow rapidly with the help of the capital market, causing the back to rub dirty and even the paper to stick. Therefore, the most important thing is to apply the appropriate drying energy at the appropriate time. Therefore, after the printing and polishing unit, it really needs infrared (IR) lamp, plus cold air, hot air and air extraction. It is recommended to use two extended drying parts in the form of transfer between two glazing units. If you think that only the drying time determines the gloss effect, then add a transfer part between the two glazing units to ensure that the production speed can be increased by 40% without affecting the gloss effect. The output energy of the drying device must match the production speed. The output energy of UV must follow the speed of the printing press, but the relationship is nonlinear. The output energy of IR is linear

when the printing machine speed increases, the gloss decreases due to the change of ink coverage. As mentioned above, the interval between coating each layer determines the formation of a stable "base layer". The paper moves between printing units at the speed of 10000 sheets per hour, and the ink only penetrates into the paper in less than one second. These tests show that under normal production speed, the gloss of the printing ink on the first and last printing units is compared, and the result is that the gloss of the printing ink on the last unit is poor. These conditions can be used as a reference, which is helpful for us to arrange the layout and determine the printing color sequence. However, when printing with ordinary ink, the gloss decreases with the increase of printing speed, which is an inherent problem of ink. It has been said that the selective combination of ink, coating and drying device can minimize the loss of quality

summary

the effect of ultraviolet (UV) glazing mainly depends on the substrate. The effect of coating a substrate with a high gloss dispersive coating can provide a reference for the expected effect of ultraviolet (UV) glazing on this substrate. The ink with high coverage will reduce the gloss, but the composition of the ink and its affinity with the primer can be improved by using a high concentration of pigment and an ink with good absorption, And how many days after printing is the bonding really stable? Correctly selecting the type and amount of primer plays a decisive role in achieving gloss. Ultraviolet (UV) glazing coating is used as the surface layer, which helps to prevent scratching; At the same time, if the coating is uniform, a bright surface can be formed. Choosing appropriate machine components, especially dry parts, and paying attention to the reasonable collocation of materials are the prerequisites for the printing machine to achieve the best effect

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