1. Application of UV coating technology
After the paper packaging products are treated with UV glazing, they can improve their appearance, make the printing quality thick and full, gloss and moisturize, improve the decorative effect of paper products, and can significantly improve the folding resistance and chemical resistance, and improve their performance. To reduce the loss of products during transportation and storage. For products with high moisture resistance requirements (such as electrical appliances, etc.), the paper packaging products are treated with UV glazing to improve the moisture resistance of the packaging.
UV glazing has developed rapidly in recent years, and its proportion in the packaging and printing industry is gradually increasing, but at the same time, there are still many problems to be solved. The first is security. At present, the active diluents used in UV varnish have certain volatility or irritation, which still pollutes the environment. At present, the water-based UV varnish is under development. Who or thickener is used to replace the active diluent, thus solving the problem of volatility and irritation, it is an ideal environmentally friendly product.
Second is the smell problem. Now it is gradually developing towards low odor. At present, UV-glazed packaging products have not yet been fully recognized by the International Food and Drug Home and cannot be in direct contact with food. Therefore, it is necessary to improve the working conditions and environment, improve the drying effect, and be thoroughly cured, thereby reducing the odor.
The third problem is the adhesion to oxidative polymerization inks. Not only does it have odor and low gloss, but also it is difficult to attach the glue. Now double glazing is often used to improve the quality of UV glazing, but at the same time it also increases the cost. Therefore, it is necessary to improve the adaptability of UV varnish and ink.
Finally, there is the issue of cost reduction. Although the cost has dropped a lot, it is cheaper than the cost of BOPP composite membrane compounding. However, in China, there are many types of UV varnishes with different performances. Therefore, prices vary greatly. In general, the cost is still too high, and it is necessary to further reduce the varnish cost, coating cost and equipment operating expenses.
Second, the advantages of UV coating
1. No environmental pollution, no solvent evaporation, both safe and environmentally friendly.
2. Fast drying speed and high production efficiency. Since the photo-curing reaction can be completed in an instant, the UV varnish can be directly stacked or enter the next process after printing and curing, which speeds up the production process and improves the production efficiency.
3. Not limited by the types of substrates, not only can be used to coat paper, aluminum plate, plastic materials and other surfaces, but also used for polymer board, furniture, metal materials, wireless materials, etc.
4. Save space and energy, because UV varnish does not require auxiliary equipment such as drying oven for ordinary oily varnish during the curing process, and the UV curing machine has a small size and high effective utilization rate, thus greatly saving space and energy , To reduce the investment in early equipment.
5. The quality is good, the surface of the printed matter after UV glazing is smooth and bright, there is no phenomenon of warpage, wrinkling, blistering, etc., and the surface hardness is high, the friction is resistant, the scratch is not easy to appear, and the chemical resistance is also good. Compared with the laminated film, the cost is only about 1 / 4-1 / 3 of the laminated film.
3. Introduction of Double Glazing System
In the past, for those printers who wanted to continue to use standard inks but were unwilling to use UV gloss for certain printing jobs, double gloss was undoubtedly their most suitable choice. The two coating units are usually located at the end of the printing press. In order to eliminate or reduce the possibility of loss of gloss (glazing oil penetrates into the ink or substrate), a layer of water-based glazing oil must be applied between the wet offset ink and the final glazing oil to isolate the offset ink, and infrared light is used Or heat radiation drying, can be used as the basis of UV varnish adhesion. At the same time, each glazing unit must have an integrated drying device, which increases the size and equipment cost of the printing press. But the gloss range that can be achieved by such equipment is larger than that of pure UV printers. In addition to the use of water-based varnish plus UV varnish, these devices can also be used to apply the same water-based varnish twice (for example, in order to improve the final gloss, apply two layers of varnish on the substrate), Or apply two different varnishes (for example, apply standard varnish through the first varnish unit, and apply special effect pigments through the second varnish unit). There is another type of double glaze printing machine, that is, a flexographic printing unit and a drying device are installed before the first offset printing unit, so as to apply an opaque white or special effect primer. [next]
4. Introduction of pure UV coating system
The printing line that uses UV ink and UV varnishing at the end can make the printed matter get extremely high gloss. However, once such a pure UV system is adopted, it is almost impossible to switch to other types of glazing operations.
5. Introduction of compound glazing printing equipment
Unlike pure UV printers, composite printers usually refer to printers that can apply both composite inks and final UV coating, as well as traditional offset inks and water-based coatings. This type of printing machine can be easily and flexibly switched between these two operating modes, and there is no need to replace the rubber roller, blanket and drying device. In order to adapt to different operating modes, the compound printing machine is equipped with IR (infrared), hot air and UV curing devices.
The use of the compound printing machine is wider than that of the pure UV printing machine, and does not require the operator to have UV printing production experience. Generally, the gloss obtained by UV varnishing on composite ink is much higher than that obtained by applying two layers of varnish on standard ink, which can be close to the level of pure UV system. Moreover, the composite printing machine is particularly excellent in the combination of matte and gloss effects. The gloss contrast effect obtained is much higher than the operation of applying a layer of aqueous varnish before UV glazing. And compound glazing provides additional options, such as a mix of particle effects and gloss effects. In addition, if a suitable configuration is adopted, the composite printing machine can print with a small amount of alcohol or even without alcohol, which is a great guarantee for environmental protection.
The compound printing machine is the biggest combination of the two printing equipments of UV printing and double glazing, so the compound printing machine is another ideal tool for the UV printing and glazing market. However, the compound type printing machine can use a small amount to print even without using alcohol, so the environmental certificate obtained is particularly honored.
6. The effect of UV glazing on the color of printed matter
Prints that use UV glazing sometimes appear yellowing. There are two main reasons: one is that the UV glazing oil itself yellows; the second is that during the glazing process, the glazing oil only solidifies on the surface of the printed product. The interior is not completely cured.
The yellowing of varnish is related to the oligomer and reactive diluent used in it have a certain yellow color. Therefore, colorless oligomer and reactive diluent should be used to prepare varnish. In addition, the influence of photoinitiators is also great. Some photoinitiators will make the system yellow after curing, such as benzoin dimethyl ether, so you should avoid using such photoinitiators to prepare varnishes.
During the glazing process, if the interior of the glazing oil is not completely cured, the glazing oil thinner inside it will gradually be absorbed by the ink and paper, and at the same time it will act on the binder in the ink, causing the loss of grease. The pigment is not sufficiently protected, and the pigment particles are free. At this time, the smoothness of the surface of the paper coating and the ink layer will decrease. The rough surface will diffuse light reflection, so adding some white components of the plant to the color will increase the brightness and decrease the saturation, giving the overall feeling of yellowing and lightening of the color. Therefore, the curing speed of UV varnish should be increased or an efficient ultraviolet curing light source should be selected. In addition, the use of water-based UV varnish can avoid the chemical effect of the thinner Liu ink layer and paper coating, and can avoid the yellowing of printed products.
Seven, UV coating method
There are many types of UV coating, and there are many classification methods, mainly the following classification methods:
1. According to the relationship between glazing machine and printing machine, it can be divided into: offline glazing and online glazing. (1) Offline polishing
Offline glazing adopts a special glazing machine to glaze the printed products, that is, printing and glazing are carried out on their own dedicated equipment. This glazing method is more flexible and convenient, and the glazing equipment investment is small, which is more suitable for professional post-press processing manufacturers. However, this glazing method increases the transportation and transfer between printing and glazing processes, and the production efficiency is low.
(2) Online polishing
On-line glazing directly connects the glazing unit to the printing unit, that is, printing and glazing are performed on the same machine. The speed is fast, the production efficiency is high, and the processing cost is low. The various types of quality failures are the future development direction. However, online glazing has high requirements on glazing technology, glazing oil, drying equipment and glazing equipment.
2. According to the glazing method, it can be divided into: roller coating glazing and printing glazing.
(1) Roller coating
Roller coating is the most common method of glazing. The coating roller applies the varnish on the surface of the printed product evenly over the entire surface.
(2) Printing and polishing
Printing glazing The glazing oil is applied to the printed product through the glazing plate, so local glazing can be performed. Currently commonly used are gravure glazing, flexographic glazing, offset printing glazing and silk screen glazing.
3. According to the classification of glazing products, it can be divided into: full-frame surface glazing, partial glazing, extinction glazing and artistic glazing.
(1) Full surface gloss
The main function of full-surface gloss is to protect the printed matter and improve the surface gloss of the printed matter. The full-surface smoothing is generally carried out by roller coating.
(2) Partial polishing
Partial glazing generally glazes the graphic parts to be emphasized on the printed matter. The high-gloss picture of the glazing part is compared with the low-gloss picture without the glazing part to produce a wonderful artistic effect. Partial glazing is carried out by printing and glazing. The film obtained by screen printing is thicker, the effect is more obvious than other methods, and the cost is lower. At present, it is used more in China, but its production efficiency is generally Lower.
(3) Extinction and glazing
The matte glazing uses UV matte oil, which is the opposite of ordinary glazing. It is to reduce the gloss of the surface of the printed matter and thus produce a special effect. Too high gloss has a certain degree of stimulation to human eyes. Therefore, extinction glazing is a popular glazing method at present.
(4) Art glazing
The role of artistic glazing is to obtain special artistic effects on the surface of glazing products. If UV pearlescent glazing oil is used to polish the surface of the printed matter, it will produce a pearlescent effect on the surface of the printed matter and make the printed matter look magnificent, noble and elegant.
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