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UV printing

Date:2011-07-28 17:39

UV is the abbreviation of Rays Ultraviolet, that is, the ultraviolet ray. Ultraviolet (UV) is invisible to the naked eye, is a purple light outside the visible electromagnetic radiation, the wavelength in the range of 10~400nm.
UV ink: UV ink, refers to the UV ray irradiation instant curing ink. The main components of UV ink include pigment, oligomer, monomer (active diluent), light initiator and various additives. The resin and reactive diluent plays a pigment fixation and to provide the role of membrane properties; pigments give ink moderate color and on the substrate covering power; photo induced agents require in pigment interference still can absorb the photon initiated polymerization.
UV printing application market
From the printing process, UV ink fixing speed, conjunctival performance good, for all kinds of printing material has good adhesion and scratch resistance, wear resistance, acid and alkali properties as compared with ordinary ink. Therefore, although the price than ordinary ink is much more expensive, but was widely used. At present, the use of UV ink printing field has the following categories.
1. Non printing of an absorbent material such as polyethylene (PE) film, PVC film (PVC), polypropylene (PP) film, metal foil and non absorbent of special material. If we use common solvent based inks for printing in the printing material, drying time, usually requires the use of dusting, drying rack device or in the ink adding other additives, and UV ink no such problems.
2 metal material is printed on the surface of the metal material using UV ink, can shorten the curing process and simplify the original curing device. At the same time, UV ink surface good curing and conjunctivitis can not only improve the finishing characteristics, but also improve the appearance of the product quality.
3. Commercial paper commercial paper printing printing printing material and ink is more special, such as non carbon copy paper, thermal paper, magnetic ink, anti-counterfeit ink and ink has a certain resistance to discoloration resistance, heat resistance and stability, it is best to use the UV ink or UV light oil. At the same time, because the bill printing equipment is fast, the amount of ink is less, and it has the advantage of using UV printing ink.
UV printing process adaptability
1.UV printing (offset)
Offset according to the state of the substrate can be divided into sheet fed offset printing and web offset, sheet fed offset printing is suitable for paper, cardboard, plastic sheet and foil printing; rotary offset printing speed faster, suitable for large quantities of books, newspapers, business forms and printing self-adhesive. In offset printing using UV ink, the main consideration from the following several aspects: non absorption of printer materials of ink curing; ink emulsification may will hinder the attachment of ink and substrate; rotary printing machine speed and phase matching ink curing speed and the printing speed, especially using self-adhesive printing and special printing ink security printing, UV ink printing effect better in the resin type printing ink.
Offset printing for printing fine products, UV curing can reduce the tiny dot loss, improved color overprint of ink transfer rate. In the selection of raw materials, to consider the effect of each component on the UV ink, in order to ensure the best printing effect. Because the offset ink film is generally 3 ~ 2 m, although beneficial to light curing, but ink film is thin, pigment on the surface of the covering power will be certain effect, so it is generally to improve the pigment content, and increase the pigment content, ink film thickness will be reduced, is not conducive to UV solid, and ink film itself is thin, pigment, filler easily exposed to ink film surface, affecting ink film gloss, therefore, to choose a better dispersion of pigment. UV offset printing should also pay attention to the following points.
(1) different nature of the substrate should choose a different ink, to take into account the transparency of the ink, curing rate, ink coverage and the surface gloss, etc..
(2) in color printing, the ability of various pigment to absorb UV photons is different, and its transmittance is high to M, Y, C, BK, and so the degree of curing of different color ink is also different. Through the direct effect of the photon on the excitation energy of the photon, the printing color sequence is BK, C, Y, M, so that it can absorb the photons as much as possible, and enhance the curing effect.
(3) use of alcohol dampening system can reduce the surface tension of the ink, accelerates the curing effect, and in the printing process, the fountain solution strengthening treatment on the printing plate oleophobic region (blank), to ensure that the lipophilic region sufficiently Pro ink and hydrophilic regions not dwell. To improve the ink formulation and add the appropriate additives can increase the ink of the hydrophobic, but the strong hydrophobicity will lead to the image edge ink shrinkage, subtle levels of loss, network boundaries are not clear, etc., affecting the quality of printed matter.
(4) UV printing on paper surface strength high, surface strength is easy to occur galling failure, with gold, silver cardboard printing, due to the paper surface smooth, less affinity for ink, the second color overprint easy to out the color Mexican rabbit. Therefore, in the UV printing, we should choose the surface tension of the paper, and reasonable arrangement of the color sequence, adjust the printing process parameters, to avoid and reduce the occurrence of the above phenomenon.

2.UV printing (flexible version)
Flexo printing is a kind of printing technology developed rapidly in recent years, and the printing plate is higher than the non text part, and it is flexible and can be used to express the fine level and the outline of the image and text. In addition, its application of printer materials is very extensive, in addition to the traditional paper, some non absorption of printer materials, such as plastic film, aluminum foil composite paper, glass paper can also use of flexo printing.
UV printing ink for flexo printing, in addition to attention should be paid attention to coloring, curing and adhesion, etc., but also must pay attention to ink composition of ink viscosity, rheological properties, in order to obtain good printing adaptability and stability.
Flexo printing process to determine the use of UV ink should not have a higher viscosity. Traditional flexographic printing ink, there are two kinds of solvent and water, needed a large amount of solvent or water to adjust the viscosity of. Due to the use of a large number of solvent, most flexible printing ink in rheology approximation to Newton fluid, will cause the ink deposition, unstable, so given the flexo printing ink proper thixotropy can prevent pigment flocculation and sedimentation.
UV flexo printing ink is a reactive diluent to reduce the viscosity of the system, therefore, its viscosity may be higher than the solvent based flexo printing ink. Although the UV flexo printing ink viscosity ratio screen printing, offset printing ink is low, but the addition of pigment will increase the viscosity, especially in the wetting, dispersion and stability of the pigment is not HERSHEY'S. In addition, pigment ink flow affect the denaturation is more important, proper thixotropy is beneficial. This is because when internal ink molecules cross-linked to a certain extent and pseudoplastic when no pigment dispersion stabilizer of ink system, in the high-speed operation of the roller, its viscosity will plummet, but from the roller into the rate relatively low printing part, the viscosity will rise rapidly, for the substrate surface wettability is poor and not suitable for printing. And the ink has a certain stability, and its viscosity is not high, after high shear, viscosity recovery is relatively slow, printing adaptability is better.
3.UV printing (screen)
UV printing (screen) ink solid content is 100%, there is no volatile, the ink film thickness is basically unchanged, is conducive to get higher film thickness, printing and curing process easy to control, can avoid blocking version, spots and other failures, reduce downtime.
Although UV screen printed with many advantages, but light initiation determined, effects of ink layer curing quality, improper selection and only in the monlchamus membrane surface curing fast. On the other hand, the UV net has its advantages, although the Jimo film is thick, but the lower pigment content can reach a high hiding power, which is favorable for the bottom curing conditions. Under the premises does not prevent pigment saturation and hiding power, appropriate to add well refraction of light filler, increased ink layer transparent medium concentration, also help to improve the underlying triggered to light absorption agent. Due to the screen printing ink film thickness, printing accuracy is not very high, pigment particle size can be larger, so in the premise of no pigment dispersion, can be appropriate to increase the size of pigment, so that the actual light transmittance increased, in order to facilitate the bottom curing.
UV printing problems
Compared with the traditional ink printing, UV printing does have a great advantage, but the application is still facing some problems must be solved and improved.
1. UV printing ink prices although UV ink has a cure in seconds and conjunctival performance advantages, but the price is relatively expensive must also use a dedicated UV blanket and UV ink roller, greatly improving the product cost.
2.UV printing ink UV ink in the curing, the internal composition of the cross-linked polymerization, the volume of the transient changes in the internal stress, affecting the ink on the substrate adhesion. Although the substrate surface treatment or modification, can improve the problem, but the fundamental solution is to seek and develop good adsorption, shrinkage stress is small, the price of UV ink.
Right 3.UV printing ink fountain solution UV ink is mainly used for non absorption of printer materials, and on different substrates and inks formulated are not the same. Therefore, the fountain solution has a wide adaptability to ensure the printing quality. Despite the above problems in UV printing, but with the development of related technologies and the expansion of the application domain, its rapid development is inevitable, not far in the future, UV printing will be more widely used and popular.

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