Radiation curing

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Radiation hardening refers to a process in which reactive materials are converted from a low-molecular to a high-molecular state with the help of high-energy radiation.

Procedure

In most cases, these are initially liquid coating materials (e.g. paints , printing inks , adhesives, etc.) that change to a solid state within a few seconds via a chemical reaction. With paints, a solid and dry film is formed.

Special UV lamps are usually used as radiation sources. A distinction is made here between doped (e.g. lead, iron, gallium or thallium) and undoped lamps ( mercury vapor lamp ) and flash tubes . Recently, UV-LED lamps have also been offered, which are enjoying growing popularity due to their short switching times and long service life. Electron beams are rarely used because of the high technical complexity and the associated high costs. UV-curing lacquers and inks are therefore simply referred to as UV lacquers or UV inks.

Reaction mechanisms

UV-curing lacquers use reactive acrylates , epoxides , enol ethers and, as a special case, also cyclic amines (e.g. aziridine ) as binders . In the past, unsaturated polyester resins were also often used. There are also photo initiators and auxiliaries such as crosslinkers, leveling agents, antioxidants and pigments . Photoinitiators form radicals or reactive cations ( super acids ) on exposure and induce a polymerization or crosslinking reaction of longer-chain molecules.

The cationic curing systems have complex reaction mechanisms, combinations of chain transfer , start and termination reactions that have not yet been clarified in every detail .

Individual evidence

  1. ↑ panacol.de: Innovation: UV-LED also for surface irradiation (PDF; 274 kB).
  2. ↑ European patent EP0619347: (Meth-) acrylic coatings , applicant: PCI Augsburg GmbH.
  3. ↑ European patent EP0584570: Epoxy resin composition containing sulphonium salts , applicant: Siemens AG.
  4. ↑ Suitability of arendiazonium salts as photoinitiators for cationic photopolymerization , dissertation University of Halle 1999.
  5. ↑ Cationic Polymerization of Cyclic Amines, EJ Goethals, EH bay, P. Bruggeman, Institute of organic chemistry Rijksuniversiteit Gent, B-9000 Gent, Belgium.

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  • Cationic Polymerization of Cyclic Amines, EJ Goethals, EH Schacht, P. Bruggeman, Institute of organic chemistry Rijksuniversiteit Gent, B-9000 Gent, Belgium