Application of EB curing technology in printing
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Various technologies in the printing industry are emerging one after another, 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 print. 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. Due to the good drying effect and low pollution, the cost of use has also been significantly reduced in recent years, so it is increasingly favored by printing manufacturers.
This article will focus on some of the issues related to EB curing inks.
The curing principle of EB ink
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 plant needs to be equipped with energy curing equipment.
Process of drying principles of EB inks and common inks
EB curing is a form of radiation curing. It is a process that uses an electron beam as a source of radiation to induce a rapid conversion of a specially formulated 100% reactive liquid into a solid. The principle is: first, the high-energy electron interacts with the coating or ink molecules to break it down into free radicals; then, the free radical reacts with the C=C double bond to form a growth chain; finally, the growth chain and the rest of the coating or ink The components react to cause cross-linking of the cured coating and increase the crosslink density. Due to the high electron energy of irradiation, the above reactions are often accompanied by negative reactions such as molecular degradation, molecular ion rearrangement and the like. Thus the EB cured coating produced greater branching and higher crosslink density.
EB curing requires special curing equipment. The working principle is as follows: after the electrons are emitted from a set of linear cathode plates, a vertical uniform electric field is accelerated, and a curtain electron beam is obtained under the accelerator irradiation box. Since the irradiated article is closer to the electric field, its accelerating voltage is not high (less than 500 kV), but the power is higher due to the large output current. Linear cathode guns are far more compact than scanning equipment, easier to install on production lines, and easier to shield.
EB curing technology features
As a new curing technology, EB curing has unique advantages compared to traditional curing technology.
The first EB ink cure time is very short, generally 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 or even a few It takes only a day to dry thoroughly, so the use of energy-curing inks to print offset printing jobs is short-lived, comparable to flexo and gravure, and greatly improves the productivity of offset printing.
The EB energy required for the second curing ranges from 150 to 300 keV. It reaches the surface of the cured material at a speed close to the speed of light, not only is not limited by the color of the coating, but also cures the adhesive between the internal coating of the paper or other substrate and the opaque substrate (such as aluminum foil).
The third EB cure allows 100% curing of coatings, inks and adhesives, especially in areas where the cure must be 100%, such as food packaging.
The third print printed with energy-curable ink has strong resistance. The chemical substance in the ink forms a polymer three-dimensional network polymer through cross-linking reaction, and the ink surface has strong chemical resistance and friction resistance.
The solid content of the fourth EB ink after curing is close to 100%, and usually does not contain VOC (organic volatiles), which strongly demonstrates that the EB ink system is more environmentally friendly than the conventional ink system. For example, the chemical composition of 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.
Fifth With the development of technology, the irritating effect of EB-curing ink on human skin is getting smaller and smaller, and it is similar to the ordinary ink containing gasoline fraction.
The sixth energy consumption is low, EB curing energy consumption is 5% of UV curing, and 1% of conventional heat curing. Easy to operate, easy to control, high accuracy and repeatability, no environmental pollution.
Development of EB curing technology and application to printing
Currently, EB curing technology is mainly used in flexographic printing, offset printing and glazing in printing.
EB inks are special inks that cure with electron beam energy. Presses that use EB inks require special rolls, fountain solutions, and cleaners because the surface energy of EB gondola is different from conventional inks.
In the early 1970s, the Ford Company of the United States applied EB curing technology to automotive parts and instrument coatings for the first time, which pioneered the application of EB curing technology to industrial production. During the same period, Album Printing used EB curing inks and coatings on packaging materials.
Early EB curing techniques were limited to printing or glazing of web materials. This is because on a sheet-fed press, the gripper row can interfere with the X-ray shielding produced by the electron beam device. On a web press, the EB curing unit is located at the end of the press and is easily attached to the web material without the support. This problem has now been solved through the continuous efforts of R&D personnel. EB curing technology has been widely used in the field of sheetfed folding cartons, sheetfed commercial printing and the like.
Today, high quality EB curing technology has become the best choice for flexible printing. This is not only because it meets the requirements of environmental protection, but also because of its excellent printing quality and the continuous decline in the price of EB curing equipment (EB curing equipment has dropped from the original more than 1 million US dollars to today's 200,000 US dollars, and also There is a trend of further decline). The biggest breakthrough in EB ink applications is its application on CI (central impression cylinder) label flexo presses. During the printing process, the ink achieves wet-wet overprinting without drying after each color printing is completed. With EB technology, it is only necessary to pass an EB curing system to instantly and thoroughly dry the substrate, that is, a "dryer" replaces multiple drying devices in traditional printing.
In label printing, EB glazing has also been widely used. The main difference between EB varnish and EB ink is that the former does not contain pigment. In UV glazing, in order to obtain good gloss, double coating is often performed. The first varnishing unit coats the substrate with a water-based primer that isolates the offset ink from the UV varnish to prevent chemical reactions and prints the graphic and non-graphic parts of the print. Microscopic bumps are filled in; the second coating unit is coated with UV varnish to give the printed product a better printing effect. This requires up to three hot air blowers to achieve complete drying of the print. EB curing has the outstanding advantage of being able to cure thicker layers. EB glazing replaces the traditional two-layer base-to-multilayer structure with a “single-layer” film, which greatly saves material and greatly reduces production costs. Statistics show that the EB coating alone can reduce production costs by about 10%. In this field, the most effective progress is Suntech's successful development of the low-solubility product Sun Bean. It is allowed to come into direct contact with food and can be used as an internal coating for food packaging. Today, the product has been widely used, such as coating in film paper packaging, multi-layer bags, food boxes and so on. There is also a need to pay attention to compatibility with conventional printing inks when applying EB glazing, as waxes and lubricants in conventional inks can interfere with the wetting of EB varnish.
By using EB curing, the coating layer which originally took a few minutes or even a few days to be completely dried can be dried instantaneously, and the flow-through operation is realized, which greatly improves the production efficiency. The application of EB curing technology greatly shortens the time from printing, storage, glazing to packing and transportation, so that the whole process of printing, glazing and packing transportation can be completed in one day, which truly meets the high aging of the modern era. Sex and requirements.
Application prospect of EB curing technology in printing field
EB inks (varnishes) have many advantages, making EB curing technology show strong vitality in the future development.
(1) It does not contain volatile VOC, has no odor or only a small odor, which reduces the harm to workers' health and has no environmental pollution.
(2) Good resistance, because the chemical substances in the ink form a polymer three-dimensional network polymer through cross-linking reaction, and the ink film has good chemical resistance and abrasion resistance.
(3) The curing time is short, generally only 0.1 seconds to completely dry, compared with the traditional printing takes a few minutes or even a few days to completely dry, greatly improving the production efficiency, and is conducive to scale production.
(4) The pigment has a thick bottom and the printed product has a beautiful appearance, and has a strong gloss and a three-dimensional effect.
(5) Reduce the cleaning time of the printing press. Even if the EB ink in the ink fountain is stored for one night, there will be no skinning and hardening, which will reduce waste.
(6) There is no strong heat that causes deformation of the substrate during curing.
Of course, as a new type of curing technology in development, EB curing technology also has some shortcomings. For example, in recent years, although the price of EB curing equipment has been greatly reduced, the one-time investment of equipment is still large; the price of EB ink is still higher than that of ordinary ink; EB curing is only suitable for flat coating curing. Therefore, the geometry of the cured product is limited; an important characteristic of EB ink is that it has good resistance, but this is a factor that is difficult to deink and hinder recycling when the waste printed matter is recycled, so it is also used in the recovery of printed matter. New research must be done.
In short, the application prospects of EB curing technology in the packaging and printing industry are wonderful. In order to make the EB curing process more convenient and economical, we should actively develop low-cost, compact EB curing equipment, improve the transmission device, and make the product can be rotated and cured, so that radiation curing can be applied to a variety of shapes. It can be asserted that EB curing technology will have greater development in the future due to its low pollution, low energy consumption and high quality.