Analysis of Printing Process and Quality Difference of UV Ink II

Fourth, UV ink types and printing process characteristics

At present, many special effects in printing require the use of UV inks. They are widely used in printing methods such as lithographic printing, flexographic printing, screen printing, gravure transfer printing and even computer inkjet printing. The commonly used UV inks include: UV plastic ink, UV metal ink, and UV. Matte ink, UV fragrance ink, UV ice ink, UV foam ink, UV crystal ink, UV expansion ink, UV transparent ink, UV disc ink, UV refraction ink, UV three-dimensional raster ink, UV wrinkle ink, UV scratch ink, UV Flexible inks, UV reflective inks, UV printed circuit board inks, and more. The UV ink printing process differs from conventional printing in that its main features are as follows:

offset printing

The PS plates, rubber rollers, and rubber blankets used in UV offset printing are different from normal offset printing. The printing unit must be equipped with a complete set of UV ink drying equipment, usually including UV drying device, electric cabinet, water cooling device, exhaust device; UV ink because of its strong corrosive, very high requirements on the rubber roller, ink roller must choose the printing machine must Adaptation with UV ink; can not always change the use of UV inks and general oily inks, if you need to change must be cleaned; UV ink ink balance tolerance is very narrow, easy to cause ink emulsification in the printing, easy to dirty version, affect the stability of the printing quality Sex; UV ink after printing high viscosity, lack of leveling, there will be a rough surface of the ink film; printing speed can not be too fast, controlled at 5000 ~ 8000 printing / hour; four color UV ink drying difficulty is different from the general The order of UV color printing is black, cyan, yellow, and magenta.

Flexo

UV flexo inks require lower viscosity than offset printing inks. UV flexo inks have a slightly higher viscosity than water-based inks or solvent-based flexo inks. When substrates are paper and other permeable substrates, they are often used to prevent penetration. Measures for applying the primer; when using UV flexo ink, the screen angle of the anilox roller is preferably 30° or 60°; the roller must be resistant to UV ink; the plate is preferably printed with better UV ink resistance material.

Silk screen

The most commonly used UV screen printing technology is imitation metal etching, ice texture, refractive index, etc. The printed boxes are colorful, elegant and luxurious, and are deeply loved by consumers. To effectively represent the effect of screen printing UV printing, the design of the manuscript in the printing process, the selection of the screen, the selection of the frame and the determination of the stretching process, the thickness of the photosensitive film, the printing pitch and other printing process parameters have their own Unique process method; other UV lamp wavelength, power, drying time, etc. also have an important impact on the final effect; special effects of the printing pattern from the indentation, die-cut position 2 ~ 3mm, in order to avoid damage when sanding sand; take into account The transparency of sand and ink, the text should not be trapped with sand and ink, can be directly printed on gold and silver paper; when a large area of ​​the same color with the field and small text, in order to reduce the letter edge sawtooth effect, should be chosen different mesh purpose Screen separates plate making.

Gravure

At present, gravure printing plays an increasingly important role in UV printing, because its printing ink film thickness is between screen printing and offset printing. With the improvement of the process of “printing gravure printing”, only silk screen printing can be used before. The imitation metal etching, ice grain texture, and refractive index effect are converted into gravure UV printing, which not only overcomes the shortcomings of slow screen printing speed and low efficiency, but also embodies the advantages of gravure printing in the long version.

Fifth, the factors that affect the UV ink curing quality and quality control methods

UV ink storage is very important because it is prone to gelation. The inks of different ink factories should not be blended with each other. In the printing, pay attention to the parameters of UV light source, irradiation distance and light curing time. UV light source selection must not only consider the UV absorption characteristics of the pigments contained in the system, but also take into account the UV absorption characteristics of the initiator. The greater the power of the UV lamp is, the faster the curing is. However, if the UV light source is too large, UV ink embrittlement may occur. The smaller the irradiation distance, the stronger the light, and the faster the photoinitiator generates free radicals, the faster the ink film cures. The pigment in the UV ink can absorb a part of the radiation energy, and as a result, the curing speed with the color system is reduced. Through the use of various photoinitiators, and by adjusting the ratio of various photoinitiators, an ink film with a fast curing speed and excellent performance is obtained.

In actual production, it often happens that due to the poor surface smoothness of the printing material, the ink transfer rate decreases, and uneven printing appears. At this point, the machine operator will usually increase the amount of ink, in order to print better. This situation is most likely to lead to incomplete ink curing, poor adhesion and other issues. Once the surface roughness of the printing material is not good, it is best to use the diluting agent and then print. The printing speed is slow, the curing time is long, and the curing effect is naturally good. If the print cannot be dried at the normal printing speed, the replacement of the UV lamp must be considered. The UV lamp must be fitted with a shade to reflect and focus on the direction of the print. The reflector must also be cleaned and maintained at all times. If some paper dust or powder dust adheres to the reflector, it will affect the UV lamp reflection function. If the UV lamp is not used for a long time, the UV lamp cover should be closed to prevent dust from entering.

In the UV printing process operation, it must be noted that UV ink curing and UV varnish curing should be different. The UV varnish is a transparent body, and there is no obstacle for the ultraviolet rays to shine from the upper layer to the lower layer, so the ultraviolet light intensity required for curing is weak. Cured UV inks need to use focus reflectors, fast curing with high power lamps; and curing UV Varnish can use astigmatism, parallel light reflectors, slow curing with low power lamps is better.

Sixth, UV ink development trend

There are still some defects in the current UV ink printing, and still need to be improved. The main development directions are: to develop low-stimulating reactive monomers to prevent allergic reactions or burns from ink producers and users; to develop photo-initiators for UV-curing color inks, to increase the efficiency of initiation, and to facilitate the deep curing of color inks; Cationic and cationic free radical UV light curing systems, because the cationic light curing system is free from oxygen inhibition, the surface curability is good, the human skin irritation is small, and the internal stress of the ink layer after curing is smaller than that of the free radical light curing system. Advantages such as small shrinkage, flexibility, and good adhesion; development of water-based UV inks that are non-irritating, non-polluting, and safer; improved adhesion of inks to substrates; research and development of UV inks with small curing shrinkage and strong adhesion . (Author: Zhong Zehui)