The basic meaning of radiation curing is to use ultraviolet (UV) or electron beam as energy source to initiate a chemically active liquid formulation to achieve rapid reaction curing process on the surface of the substrate.
Industrial applications of UV/EB curing provide an advanced processing tool for surface curing of materials. The biggest advantage of this curing technology over traditional technologies (such as thermal curing) is that radiation curing uses a high-efficiency energy sourceâ€”ultraviolet light or electron beam as the initiatorâ€”to quickly achieve coating cure.
1. Ultraviolet light and electron beam
Ultraviolet light and electron beam can be regarded as members of a large family of radiation. The difference is that ultraviolet light is an electromagnetic radiation, and the electron beam is an accelerated high-energy electron flow.
The UV-C (100-280 nm), UV-B (280-315 nm), and UV-A (315-380 nm) UV-C areas commonly used in radiation curing are subdivided into UV-C regions. The ultraviolet light source used for radiation curing is generally an ultraviolet lamp excited by electric energy.
Electron beam is also a kind of radiation. It is a group of accelerated electron currents. The energy of particles is much higher than that of ultraviolet light, which can ionize air. Therefore, high-energy electron beams can also be called ionizing radiation. Electron beam curing generally does not require photoinitiators and can initiate chemical reactions directly, and the penetrating power of substances is also much greater than that of ultraviolet light. The device that generates the electron beam is called an electron accelerator. A scan-type electron accelerator used for radiation curing has a basic principle similar to that of a home-use television. In the television, the accelerated electron flow scans the television screen to obtain visual information, and the electron beam of the electron accelerator in the radiation curing scans the surface of the substrate to achieve curing processing.
2. Radiation curing - a system engineering
Radiation curing is a new technology developed on the basis of existing science and technology, so it can be seen as a complex formed by the common structure of multiple technologies, including radiation sources (UV and EB), raw materials, monomers, and oligomers. Materials, photoinitiators, various additives (such as pigments, additives), chemical formulations (coatings, inks, adhesives, etc.), substrates, and coating devices. Radiation curing can only exert its inherent vitality through rational allocation of these technical elements. In fact, these technological elements have formed an interdependent market chain in the process of radiation-curing industry and jointly ensure market competitiveness. Therefore, radiation curing itself is a systematic project.
3. "3E Principle" Promotes the Development of Radiation Curing
The establishment and development of any high and new technology now seems to be subject to the "3E principle" and cannot be avoided. Therefore, the "3E principle" is the foundation and driving force for the survival and development of radiation curing. The so-called "3E" refers to Energy, Ecology, and Economy.
(1)Energy energy radiation curing Starvation energy consumption only needs to ensure that active chemical formulas generate polymerization cross-linking reaction under radiation initiation, and it is not necessary to heat the substrate. Therefore, the energy consumption of UV curing is only that of conventional solvent-based coatings and inks. /5, EB curing energy consumption is smaller, only 1/100 of conventional curing.
(2) The active chemical formula used in ecological radiation curing does not contain (or contains less) volatile solvents and is a zero-emission (or low-emission) technology that is conducive to environmental protection. In addition, the basic energy used for radiation curing is power, no fuel, and no carbon dioxide. Therefore, radiation curing is often referred to as "green technology."
(3) The economic radiation curing device is compact, the processing speed is fast, the space is small, and the production efficiency is high. Therefore, the process itself helps to improve product performance and reduce raw material consumption. All this increases the competitiveness of the technology itself from the economic cost.
In addition, the radiation curing has its own characteristics compared with the traditional curing technology, such as room temperature curing, is conducive to the processing of heat-sensitive materials; curing formulations can be adjusted according to demand, is conducive to improving the adaptability of the process to ensure product performance (such as hardness, flexibility, luster, weather resistance, etc.); radiation curing is easy to realize streamlined work and has a high degree of automation.
The unique technical advantages of radiation curing not only meet the requirements of the "3E principle", but also continue to maintain the traditional market competitiveness in the process of industrialization, making radiation curing has been growing rapidly since the 1960s: the current emergency developed countries (Eg, the United States, Japan, and European countries), the annual growth rate is about 10%, the growth rate of developing countries is faster, and China's average annual growth rate can reach 25%.
It is estimated that the market share of global UV/EB-cured chemical raw materials and formulations is only 3% of the total sales volume of industrial coatings (inks, coatings, and adhesives), so the development prospects of radiation curing are promising.
Ultraviolet curing (about 90%) is dominant in radiation curing. Electron beam curing has a relatively small one-time investment (about 10%) due to the high one-off investment in accelerator devices.
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