The principle of EB curing technology and its application in printing

Radiation curing technology is a new curing technology that can effectively control air pollution, especially volatile organic compound (VOC) emissions. The curing mechanism is the electron beam EB (Electron Beam) irradiation of solvent-free liquid chemicals, so that a rapid polymerization reaction occurs, resulting in a three-dimensional network structure to form a solid film. As it basically achieves "zero emission in sustainable development," it is increasingly favored by people.

The principle of EB curing technology

EB curing is a form of radiation curing. It is a process in which an electron beam is used as a radiation source to induce the rapid conversion of a specially formulated 100% reactive liquid to a solid. The principle is: First, high-energy electrons interact with coating or ink molecules to decompose them into free radicals; then, the free radicals react with C=C double bonds to form growth chains; finally, the growth chain and the rest of the paint or ink The components react to crosslink the cured coating and increase the crosslink density. Due to the high electron energy of the irradiation, the above reaction is often accompanied by molecular degradation. Molecular ion rearrangements and other negative reactions. Thus, EB-cured coatings produce greater branching and higher crosslink density.

EB curing requires dedicated curing equipment. Curing equipment main body - electron curtain accelerator structure, its working principle is: electrons emit from a group of linear cathode plates, after accelerating through a vertical uniform electric field, under the accelerator irradiation box get screen electron beam. Since the irradiated product is close to the electric field, its accelerating voltage is not high (below 500 kV), but the power is high due to the large output current. The linear cathode gun is far more compact than the scanning device, and it is easier to install on the production line and also easier to shield.

EB curing technology features

As a new type of curing technology, EB curing has unique advantages over traditional curing technologies.

(1) The printing energy required for curing ranges from 150 to 300 keV. It reaches the surface of the cured material at a speed close to the speed of light and is not only limited by the color of the coating, but it also cures the adhesive between paper and other substrate internal coatings and opaque substrates such as aluminum foil.

(2) EB curing allows 100% curing of coatings, inks, and adhesives, especially in areas where curing must be 100%, such as food packaging.

(3) High productivity and finished product rate create conditions for large-scale production.

(4) Low energy consumption, 5% of EB curing energy is 5% for UV curing, and 1% for traditional thermal curing.

(5) Simple operation, easy control, high accuracy and repeatability, no environmental pollution.

Application of EB curing technology in printing

At present, EB curing technology is mainly used in printing flexo printing, offset printing and coating.

EB inks are special inks that are cured using electron beam energy. Printing machines that use EB inks require special rollers, fountain solutions, and cleaning agents because the surface energy of EB inks is different from conventional inks.

In the early 1970s, Ford Motor Company of the United States applied EB curing technology to automotive parts and instrument coatings for the first time, which created a precedent for the application of EB curing technology in industrial production. During the same period, Album used EB-cured inks and coatings on packaging materials.

Early EB curing techniques were limited to the printing or glazing of web materials. This is because on a sheet-fed press, the gripper bar interferes with X-ray shielding produced by the electron beam device. On a web press, the EB curing device is located at the end of the press and is easily affixed to the top of the web without support. Through the continuous efforts of the R&D personnel, this issue has now been resolved. EB curing technology has been widely used in sheet folding cartons, sheetfed commercial printing and other fields.

Today, high-quality EB curing technology has become the best choice for flexographic 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 one million US dollars to about 200,000 US dollars today, and also There is a further decline.) The biggest breakthrough in EB ink application is its application on CI (central impression cylinder) label flexography. In the printing process, the ink achieves wet-wet imprint without drying after each color printing is completed. With EB technology, it is only necessary to use an EB curing system to instantly and thoroughly dry substrates, ie, a “dryer” replaces multiple sets of drying devices in traditional printing.

In label printing, EB coating has also been widely used. The main difference between EB Varnish and EB Ink is that the former does not contain pigments. In UV glazing, two-layer coating is often performed in order to obtain a good gloss. The first glazing unit coats the substrates with substrates of water quality. This coating isolates offset inks and UV varnish to prevent chemical reactions and to print both graphic and non-graphic components on the prints. Micro concave and convex filled; the second coating unit coated with UV varnish, so that the printing products get a better printing effect. In the middle, up to 3 hot air blowers need to be equipped to achieve thorough drying of printed products. EB curing has the outstanding advantage of being able to cure thicker layers. EB glazing used "single-layer" membranes instead of traditional double-layer or even multi-layer structures, greatly saving materials and greatly reducing production costs. According to statistics, only coating the process, the use of EB coating can reduce production costs by about 10%. In this field, the most effective progress is Sun Chemical's successful development of a product with low solubility, Sun Bean. It is allowed to come in direct contact with food and can be used as an internal coating for food packaging. Today, this product has been widely used, such as coating in film paper packaging, multi-layer cloth bags, food boxes and the like. When applying EB, it is also necessary to pay attention to the compatibility with ordinary printing inks, because the wax and lubricant in common inks will hinder the wetting of EB varnish.

With EB curing, the coating layer, which originally required several minutes or even several days to completely dry, can be dried instantaneously, streamlining operations are realized, and the production efficiency is greatly improved. The application of EB curing technology has greatly shortened the time from printing, storage, glazing to packing and transportation, enabling the entire process of printing, glazing, packing and transportation to be completed within one day, truly meeting the high timeliness of today's times. Sexual requirements.

Application Prospect of EB Curing Technology in Printing Field

EB ink (varnish) has many advantages, making EB curing technology show strong vitality in the future development.

(1) It contains no volatile substance VOC, has no odor or only a small odor, reduces the harm to the health of workers, and has no environmental pollution.

(2) Good resistance, since the chemical substances in the ink form a polymer three-dimensional network polymer through cross-linking reaction, the ink film has good chemical resistance and friction resistance.

(3) The curing time is short. Generally, it takes only 0.1 second to completely dry. Compared with the traditional printing that takes several minutes or even several days to completely dry, it greatly improves the production efficiency and is conducive to scale production.

(4) The pigment concentration is high, the printed product has a beautiful appearance, and has a strong gloss and three-dimensionality.

(5) Reduce the cleaning time of the printing press. Even if the EB ink in the ink fountain is stored for one night, the skinning and hardening phenomenon will not occur and waste will be reduced.

(6) There is no strong heat that causes the substrate to deform when cured.

Of course, as a new developing curing technology, EB curing technology also has some shortcomings. For example, in recent years, although EB curing equipment has been greatly reduced in price, its one-time investment in equipment is still relatively large; the price of EB ink is still higher than the price of ordinary ink; EB curing is only applicable to the 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 causes deinking and hinders recycling in the recycling of waste prints. New research must be done.

In short, the application of EB curing technology in the packaging and printing industry is promising. In order to make the printing and curing process more convenient and economical, it is necessary to actively develop a low-cost, compact EB curing device, and improve the transmission device so that the product can be rotated and cured so that the radiation curing can be applied to various shapes of products. 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.

Source of information: Printing Technology Xi'an University of Technology (Bu Ji Mei Wu Qiu Min)