Electron Beam (EB)
How is working an Electron Beam Accelerator ?
As electrons have a mass and behave as particles and not waves they are not included in the electromagnetic spectrum like photons. The range of voltage of an electron beam machine used in industrial curing applications is between 80 to 300 kV.
In a typical system, high voltage is applied to tungsten wire filaments inside a vacuum chamber. This voltage heats the filaments to a point where a cloud of electrons is generated. By differing voltage between the cloud of electrons and the titanium exit window of the emitter the electrons are drawn toward the window with great speed (in general 50 to 70 % of light speed) and energy. The electrons continue on through the titanium foil of the window and out of the emitter where they impact the coating. As they exit the emitter the electrons impact the coating passing under that window and cause polymerization and cross-linking.
A titanium window foil supported by a water-cooled copper window is used to isolate the vacuum environment of the cathode from the reaction chamber. Excess electron energy that passes through the reaction chamber is absorbed by the beam absorber which can be a chill roll or cooling plate on a lift table assembly. The beam absorber is also water cooled.
Electron beam curing occurs as the result of energy transfer from the accelerated electrons. Electrons penetrate the product resulting in free-radical polymerization of coatings causing instantaneous curing. Nitrogen is used in many electron beam processes to displace oxygen and reduce ozone generation. Nitrogen inerting is mostly used with curing processes and is entirely contained in the reaction chamber of the machine.
What are the Benefits of Electron Beam ?
The entire process is completed in the time that it takes for the strip to pass through the electron beam. EB equipments are powerful enough to cure at highest speed (500 mpm). At these speeds, the entire process is completed in 0.024 seconds !!
● Minimal Space in Line: The EB equipment length can be very short because the curing occurs so fast. Overall in-line length of the BroadBeam processor is less than 3 meters.
● No Solvents, No VOC’s: Solvents are not used in the coatings. Unlike conventional coatings, the process does not require the removal of solvents in order to create a dry product. In other words, all of the chemicals in the “wet” product remain locked into the “dry” product. This is the reason that no VOC’s are produced, and no incinerators or other devices are needed to treat pollution.
● High Electrical Efficiency : The process for creating the electron beam is highly efficient as is the interaction of the beam with the coatings. The electrical energy is carried directly into the coatings by the electrons, in contrast to heat set dryers in which a large volume of air must be heated and must in turn heat the product. Electron beam dryers can be as much as 100 times more efficient than thermal dryers. This high efficiency contributes to the favorable cost comparison to heat set printing.
● No Strip Heating: Because the electrical energy goes directly into the coatings, and the strip doesn’t dwell in a hot gas, the temperature rise of the strip is typically less than a few degrees.
● Functional and Aesthetic Characteristics: High gloss, scuff resistance, depth of color, and strong bond to substrate are some of the best known properties of E-beam cured coatings. Not as well known is the way in which these features relate to recyclability of the finished product