Analysis of Surface UV Polishing of Book Prints

UV coating is to complete the surface of printed matter printed on the graphic, according to the design requirements with the relevant graphic printing plate and then overprint one or more different properties of the varnish, so that the surface of the print to obtain a predetermined artistic creative effect of UV light film layer.

UV glazing can enhance the light resistance, dirt resistance and abrasion resistance of the ink layer, increase the ability of the ink layer to prevent heat and moisture, play a role of protecting the imprinting and beautifying the decorative products, and is expected to replace the conventional film coating and part of the embossing effect. And have a certain degree of anti-counterfeiting effect, improve product quality, is currently quite popular print surface decorative arts processing methods. Compared with the surface decoration of other printed materials, the price is low, the process is simple, and it can not only cover the full version of glazing, but also can be partially glazing, single or online production can be.

Common UV coating methods

1. The commonly used UV coating methods are spray coating, printing coating and coating coating machine coating

(1) Spray coating is manual operation. Its working speed is slow, coating quality is poor, but it is easy to operate and has strong flexibility. It is suitable for the coating of printed products with small batches and rough surface. (2) Printing and coating are usually coated with a printing device that has been modified for use in glazing. This method is better than the manual spray coating with good quality and high production efficiency. It can use existing printing equipment. It can be used in a dual-purpose machine and is easy to use. It is suitable for all kinds of printing coating and coating processes. (3) Dedicated Coating with optical coating machine can realize accurate control of coating amount. The coating quality is stable and reliable. It is suitable for glazing coating processing of various grades of printed matter. It is currently the most common coating method.

2. UV coating process can be integrated in different ways

(1) According to the glazing method, it can be divided into an offline glazing process and an on-line glazing process: (2) The products can be divided into glazing, partial glazing, extinction and artistic glazing.

3. When applying UV varnish on paper, it can be printed and then offline

This processing speed is generally 30 ~ 60 m / min, but now in order to increase the processing speed, the use of online is gradually increasing, mainly in the following four ways. (1) blanket printing blanket coating, processing speed of 8000 ~ 11000 / h; (2) gravure rotary printing press last unit coating, processing speed of 100 ~ 200 m / min; (3) flexographic printing The final machine and special coating machine, the processing speed of 100 ~ 200 m / min; (4) screen printing machine coating, processing speed of 15 ~ 70 m / min. The first three methods are high-speed, high-volume, on-line UV light production methods. The fourth type is the preferred process for small-batch, multi-species manual and semi-automatic local UV polishing.

Several problems that UV glazing should pay attention to

1. UV lamp usage requirements

UV light sources generally use high-pressure mercury lamps or metal halide lamps (ideal lamps are preferred), and the output power is generally 80 to 120 W/cm to ensure that the curing time of UV varnish is less than 0.5 seconds. UV lamps have a certain service life. Generally, they should be checked and replaced in about 1000 hours. UV light may cause damage to the skin and eyes, and should be shielded from UV light to irradiate the human body. At the same time, it will eliminate the harm to the human body caused by the ozone generated by UV light, and pay attention to the smooth ventilation in the production environment; in the light yellow light work environment Under production more suitable.

2. Not suitable for the processing of easily permeable paper (such as rough offset paper)

Because the low-molecular materials in the UV varnish can easily penetrate into the paper, causing the paper to become dark and even impregnated, it also affects the gloss of the UV varnish coating. In this case, the speed of UV coating should be accelerated and the number of UV lamps should be increased. In order to prevent the infiltration phenomenon, first apply a thin layer of thin base oil to the printed product to avoid the infiltration phenomenon when applying UV varnish.

3. Adhesion (or UV light oil coating is not dry)

Main reasons: (1) Coating is too thick, and the coating thickness and viscosity should be reduced. For some special artistic effects such as wrinkles and crystals, the coating layer is too thick, so it is relatively long under the irradiation of the same power light source. The influence of the curing of UV varnish, on the other hand, reduces the moisture content of the paper, making the paper brittle and brittle, affecting the wear resistance of the UV varnish layer, and more importantly, prolonged irradiation will cause the temperature to rise. High, causing fire and other accidents. At this point can be divided into two fast UV light curing method, the traffic jam on the traffic jam should be promptly removed. (2) UV lamp power shortage or aging (UV lamp life is generally about 1000 hours, more than this time curing efficiency will decrease), should replace the UV lamp to achieve rated power. (3) The coating oil has expired and should be stopped. (4) Decrease the coating amount and thin the gloss film layer. (5) Improve the coating coating processing temperature to completely cure the coating.

4. Poor adhesion

Main reasons: (1) improper use of printed ink layer crystallization or ink additives and anti-slip agent, should improve the printing process, with or without ink additives; (2) UV light oil viscosity is too low, should adjust the polishing machine and improve Varnish viscosity; (3) Improper use of UV varnish type, so that the scratch resistance of UV varnish coating is not good; (4) UV light is excessively cured by radiation; (5) The ink layer of printed matter is not completely dried The glazing is also the cause of the poor adhesion of the coating coating; (6) UV glazing has been applied to prints covered with the BOPP film, because the surface of the film did not have enough corona treatment in advance, resulting in UV light oil coating Poor work, easy to fall off.

5. UV Varnish is poorly cured on black ink, white ink, and shot blue ink layers

Various unexpected problems often occur when printing black oil, white ink, and blue light ink layers. The pigments in the ink and the photoinitiators in the light oil absorb the same wavelength of UV light, and the two have limited competition. UV light energy, and UV light oil curing requires energy, so the impact of the light oil curing is greater, it may cause the light oil curing is not complete. Solution: Increase the power of the UV lamp, increase the lamp set of the UV lamp in a suitable amount, clean the light reflector to increase the irradiation energy of the UV light, and increase the firmness of the UV.

6. The UV coating layer is white and the crosslink density is low

The main reason is that the thinner is used improperly, because the alcohol solvent volatilizes fast, when the ambient temperature is higher, the diluent should be replaced or the ester diluent or special diluent should be used instead.

7. UV coating layer is yellow

The main reasons for the yellowing of UV varnish after curing are: (1) UV varnish has been left for a long time and has turned yellow. In particular, the yellowing phenomenon of poor quality UV varnish is more serious and the appropriate UV light must be replaced. Oil; (2) Excessive UV light irradiation, UV light oil curing excessively, so it is necessary to moderately reduce the power of UV light source or less UV light group, speed up the speed of light.

8. UV gloss gloss is poor

Main reasons: (1) Poor paper quality or surface roughness, large oil absorption, should be replaced by printing paper with higher smoothness; (2) uneven coating or dilution of coating oil is too thin, viscosity is too low, can be adjusted accordingly Polishing machine to improve the viscosity of the varnish; (3) too much dust printed on the print, affecting the gloss of the UV coating.

9. Scratches, blisters, wrinkles on the UV coating film surface

The main reasons are as follows: (1) If the viscosity of the coating oil is too high, appropriate amount of thinner should be added to reduce the value of coating oil viscosity; (2) The coating amount of coating oil is large, and the coating amount is appropriately reduced: (3) Varnish The wettability of the ink on the surface of the printed matter is poor, and the appropriate UV light oil should be replaced or proportioned; (4) The process conditions in the coating process are not matched with the suitability of the gloss oil, the leveling property is poor, and the process parameters are adjusted to make it the same as the gloss oil. Adaptability; (5) Appeared during cutting and die-cutting to minimize the UV coating design at this location.

10. Pay attention to the effective protection of the operator

(1) In UV polishing, UV light may cause damage to the skin and eyes, so be shielded to prevent UV light from irradiating the human body; (2) UV Varnish must be cleaned with a special cleaning agent or ethyl acetate. With gasoline, kerosene is very difficult to wash off. Pay attention to the skin protection of the operator, otherwise the skin will be stimulated by UV varnish, itching, swelling, pimples, and even peeling, splashing on the skin should be promptly washed with soapy water and change the overalls; (3) At the same time the air The ozone generated after UV light irradiation has a certain degree of harm to the human body, and it is necessary to pay attention to the enhancement of the ventilation of the production environment. When conditions permit, the operator will be forced to arrange to rest in a well ventilated outdoor environment after each continuous UV polishing production operation for 2 hours. 10 to 15 minutes.

11. UV Varnish Storage and Use

(1) UV varnish should be stored in cool or ventilated shade, with a shelf life of usually 1 year; (2) If stored at higher temperatures, it can easily deteriorate or harden; (3) UV varnish cannot be normal The use of varnish, the auxiliary agent can only use the special auxiliary agent for UV varnish, the brand is not suitable for different use; (4) The varnishing fastness of UV varnish varies depending on the substrate type. When replacing the new printing material, it must be It is necessary to test and confirm the adhesion performance first, and then batch glazing; (5) UV varnish is suitable for production under the light yellow light working environment.

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