The advantages of UV glazing Many different methods still need to be scrutinized

UV coating characteristics

Gluing is one of the finishing technologies of printed materials. By coating (or spraying or printing) a layer of colorless transparent coating on the surface of the printed material, the surface of the printed material can be thin and evenly transparent after being leveled, dried, and calendered. Bright layer.

The glazing process can be divided into oxidative polymerization glazing, solvent evaporation glazing, UV glazing and thermal curing glazing according to the glazing drying method. UV varnish is UV curing, using UV varnish, coated on the surface of the printed product, and irradiated with ultraviolet light, the varnish can be cured in a very short time. Compared with other coating methods, UV coating has the following advantages:

(1) Varnish is 100% solids, no solvent evaporation, safe and environmentally friendly.

(2) Fast drying speed and high production efficiency. The general drying speed can reach 100m/min to 300m/min, and the fastest can exceed 500m/min.

(3) Not limited by the type of substrate, not only on the surface of paper, aluminum, plastic materials, etc., but also can be applied to the surface of polymer boards, furniture, metal materials, wireless materials, etc.

(4) Low energy consumption and energy saving.

(5) Working at low temperature, can be used for the printing of heat-sensitive substrates (such as plastic).

(6) The quality is good. After the UV coating, the surface of the printed product is smooth and bright, without any burrs, wrinkles, blisters, etc., and has high surface hardness, resistance to rubbing, difficulty in planning marks, and corrosion resistance to chemicals.

(7) After the polishing, the substrates can be processed immediately, no longer need to be hardened, and have higher adaptability in cutting, forming, folding, and the like.

Therefore, UV glazing, as an important glazing method, has become more and more widely used.

UV coating method

There are many UV glazing methods, and there are many classification methods. There are mainly the following classification methods:

1. According to the classification of the relationship between the polishing machine and the printing press, the coating can be divided into two ways: offline coating and online coating.

Off-line glazing uses a special glazing machine to polish the prints, ie, printing and glazing are performed on their own special equipment.
This kind of 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 the printing and glazing processes, and the production efficiency is low.

Online coating directly connects the glazing unit to the printing unit, ie, printing and glazing are performed on the same machine, which has high speed, high production efficiency, low processing cost, and reduces the handling of the printed matter and overcomes the problem caused by dusting. The various types of quality failures are the future direction of development. However, the on-line coating has high requirements for coating technology, coating oil, drying equipment, and coating equipment.

2. According to the glazing method, glazing can be divided into roller coating and printing glazing.

Roller coating is the most common method of glazing. The coating roll is used to spread the coating on the surface of the printed product. Printing glazing coats lacquer on the prints through a glazing plate so that it can be applied locally. Currently used are gravure coating, flexo coating, offset printing, and screen polishing.

3. According to the type of polishing products, glazing can be divided into full-width light, partial glazing, extinction glazing, and artistic glazing. The main role of full-frame light is to protect prints and improve the surface gloss of prints. Full-frame light is generally applied by roller coating.

Partial glossing is generally used to polish parts of graphics that need to be emphasized in printed matter. The high-gloss picture using the gloss part is compared with the low-gloss picture that has no gloss part, resulting in artistic effects. The partial coating is performed by the method of printing glazing, in which the film obtained by coating with a screen printing method is thicker, the effect is more obvious than other methods, and the cost is relatively low. Currently, it is used more domestically, but its production efficiency is general. Lower.

Extinction coating uses UV matte oil, which has the opposite effect of ordinary coating. It reduces the glossiness of the printed surface and produces a special effect. Extinction coating is a popular glazing method.

The role of artistic glazing is to obtain special artistic effects on the surface of glazing products. If using UV pearlescent coating on the surface of the print, it will produce a pearl effect on the printed surface, making the printed material look grand, elegant and elegant.

UV glazing should pay attention to the problem

In order to ensure the quality of UV coating, the following major issues should be noted when polishing:

1. The choice of polishing oil

The glazing oil should first be selected according to the glazing method. Different glazing methods require different properties of the glazing oil. For this purpose, the varnishes with different properties need to be matched. That is, the application of Varnish for offline coating and in-line coating is different. The coating of the roller is different from that for printing coating. When the coating is applied, the varnish used for different printing methods is also different.

If glazing products need to be post-processed such as bronzing or paste, the varnishes with relatively stable chemical properties should be used.

2. Selection of UV curing light source

Because the curing of the UV coating is based on the photoinitiator absorbing the radiant energy of the ultraviolet light to form free radicals, thereby initiating the polymerization and cross-linking reaction of the monomer and the prepolymer, therefore, the choice of the UV curing light source for the UV coating The drying speed of the oil has an important effect. The following factors should be considered when choosing a UV curing light source:

(1) The absorption spectrum of the photoinitiator is matched with the output spectrum of the light source as much as possible so as to maximize the use of the radiant energy of the light source and generate more free radicals, thereby increasing the drying speed of the UV coating oil.

(2) The efficiency of conversion of electrical energy to ultraviolet light should be high.

(3) The strength should be appropriate, the light is too strong, radicals are generated too fast, the reaction rate is increased when the concentration is too high, and the cross-linking reaction is adversely affected; the intensity is too low, the radicals are generated too slowly, and the oxygen inhibition effect is very high. Strong, these will make the UV coating dry too slowly.

(4) Long service life. The UV lamp will gradually age, and the intensity of the expired UV lamp will decrease a lot, causing the UV coating to dry too slowly.

(5) There should be a very good lampshade condenser, the same lamp, lampshade is good or bad, can make the efficiency difference of more than ten times.

(6) Appropriate shape, can make the light evenly distributed on the printed matter, and easy to install, cheap, safe and reliable. Tube lamps are generally used.

(7) Due to the ozone generated in the air under UV light, there should be ventilation equipment.

3. Control of Varnish Coating Quantity

The coating amount of the varnish must be appropriate and the coating should be uniform. The uniform and appropriate coating surface has high smoothness and high gloss. If the coating amount is too small, the coating oil cannot spread evenly, and the optical defect (smoothness) of the surface of the printed matter is reduced, and the smoothness of the coating surface is poor; if the coating amount is excessive, it is beneficial to the coating oil. Leveling also enhances the offsetting effect on surface defects of printed products, but drying can be difficult and costly.

The coating amount of coating is determined in relation to the type of coating, the surface condition of the printed matter, and the coating conditions. When the coating is determined, it is necessary to take care of each other and make overall arrangements, which not only meets the quality requirements of the coating, but also suits various processes.

In coating, the amount of coating can be changed by adjusting the coating machine control mechanism or changing the coater speed. A small amount of change can also be achieved by changing the viscosity of the coating.

4. Control of glazing speed

The glazing speed, that is, the speed of the coater, should be determined based on the curing speed and coating amount of the coating. Varnish curing speed is faster, the coating machine speed can also be increased, when the coating leveling time is short, the coating is relatively thick, and vice versa. In addition, the speed of the coating machine is also related to factors such as the curing light source of the coating machine and the condition of the printed matter.