UV and EB inks in the printing industry
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Energy curing ink concept
There are many technologies in the printing industry, and one of the fastest growing technologies is energy curing technology. It means that the ink or glazing coating is fixed or hardened on the substrate under irradiation of radiant energy to obtain a dried blot. UV light and accelerated high energy electron beam (EB) are two forms of energy for energy curing technology. Accordingly, inks that are cured using UV light and EB energy, respectively, are referred to as UV inks and EB inks.
Nowadays, UV inks and EB inks are valued by many packaging and printing manufacturers, and the cost has been significantly reduced. The UV ink and EB ink printing processes are more and more worthy of study.
Energy curing ink composition
The main chemical components of UV and EB inks include:
● Monomer (Reactive Diluent): A chemical substance with a low molecular weight that determines the surface characteristics of the ink after drying, such as gloss, degree of hardening, and elasticity. Some other monomers are the source of the harmful effects of energy-curing inks.
● Resin (prepolymer): refers to the chemical skeleton of the ink, which affects the consistency, wetting ability and crosslinking characteristics of the ink.
Photoinitiator: A chemical substance in which the ink becomes a high-energy state under the irradiation of UV light and starts to initiate a curing process. The EB ink does not require a photoinitiator because the high energy electron beam has sufficient energy to initiate the polymerization reaction.
● Additives: including waxes, wetting agents, ink varnishing agents that change the characteristics of inks, etc., to specifically improve the physical and chemical properties of the ink.
● Colorant: The particle size and concentration of the pigment will affect the curing rate of the UV ink. Therefore, not only the color of the pigment but also the wettability of the pigment and the ability to receive UV light should be considered when selecting the colorant. Y and M inks are easier to cure, followed by C and K inks. EB inks do not have to consider this when selecting colorants because the energy of the high-energy electron beam is sufficient to cure the thick ink film layer.
UV/EB ink curing principle
The drying of the ink layer after printing of the common ink is that the binder (solvent, grease) in the ink is absorbed and volatilized by the substrate, and the solid matter (colorant, resin, wax, desiccant, etc.) remains on the surface of the substrate to form A thin layer of ink. The drying of general inks and the fixation of energy-curing inks differ in the chemical composition of the ink/glazing coatings, and secondly whether the printing workshop needs to be equipped with energy curing equipment.
Therefore, it is called energy-curing ink because it contains some chemicals. Under the action of UV light or high-energy electron beam, it generates free radicals or ionic groups. The free radicals or ionic groups are crosslinked with other substances to form a network polymer. . For the curing process of UV ink, the following illustration:
Advantages and disadvantages of UV/EB inks
The first UV/EB ink cure time is very short, usually only 1/10 seconds to dry and fix on the surface of the substrate. For traditional thermosetting inks and sheet-fed inks, the drying time may take a few minutes. Even a few days to thoroughly dry, so the use of energy-curing ink to print offset printing jobs, short delivery time, comparable to flexo, gravure, and greatly improved the production efficiency of offset printing.
Secondly, after the UV ink is printed, the UV glazing is processed, and the obtained print has high gloss and uniform surface uniformity. After the machine is glazed, the packaging process such as die cutting, indentation, gluing and bronzing can be completed immediately.
The third printed matter printed with energy-curable ink has strong resistance. The polymer in the ink forms a polymer three-dimensional network polymer by cross-linking reaction, and the ink surface has strong chemical resistance and friction resistance.
The solid content of the fourth UV/EB ink after curing is close to 100%, and usually does not contain VOC (organic volatiles), which strongly demonstrates that the UV/EB ink system is more environmentally friendly than the conventional ink system. For example, the chemical composition of UV/EB inks is well formulated, and the odor of many ordinary inks dried by oxidized conjunctiva is much smaller, and the surface of the printed matter is clean and free of dirt.
The fifth energy-curing ink is less irritating to human skin and is similar to the irritating ink of a gasoline-containing fraction.
Of course, energy-curing inks/glazing coatings also have some disadvantages. Some require an NBR rubber roller or an EPDM rubber roller. A special blanket may be required for offset printing. The blanket may also require special cleaning agents to prevent over-contraction, expansion or deterioration of the blanket.
Second, its cost is higher than traditional inks. However, the high cost is worthwhile compared to the performance of the final printed product.
In addition, a one-time investment in energy curing equipment requires a certain amount of capital. The price of UV curing equipment, UV lamps, and EB curing equipment is steadily declining, especially the price drop of EB curing equipment is the most obvious. Compared with ten years ago, the cost of EB curing equipment has been reduced by four times. In the past few years, the price of UV curing equipment has also steadily declined, and there is good reason to believe that the price of energy curing equipment will continue to decline in the next few years.
Latest technological advances in UV/EB inks
Although mixed ink products from different manufacturers have some differences in performance, they should generally have the following characteristics:
● Can be applied to all types of ordinary printing presses equipped with a unit curing unit
● No need to replace the various chemicals used in rubber rollers, blankets, plates or printing presses
●High gloss of print can be obtained in the continuous printing process
●Can clean rubber roller, blanket, etc. with conventional cleaning agent
●The printing processing suitability on the printing machine is comparable to that of traditional grease type inks.
Looking ahead to the application prospects of energy-curing inks in the printing industry, it still depends on whether the cost of ink can be reduced to a level close to that of ordinary inks.