This device is a low-energy electron accelerator. The technology allows the emission of electrons at different energy values to irradiate the surface of different materials: as a result, it is possible to obtain surface modifications, through the conversion of electrical energy into electrical current.

Electron Beam (EB) technology uses accelerated electrons to treat materials quickly and efficiently. Through an accelerator, a heated tungsten cathode emits electrons that, thanks to a potential difference between the cathode and the anode, are accelerated into a vacuum and then released into the irradiation chamber through a thin titanium window. When the electrons hit the material, they ionize the atoms and promote cross-linking, polymerization, sterilization and surface treatment. Some electrons penetrate deeply, allowing even the internal layers of the material to be treated. One of the main advantages of EB is the ability to obtain almost instantaneous curing and drying, eliminating the need for drying ovens and solvents. The treated products are ready for use immediately after the process, ensuring significant energy savings and a significant reduction in waste. In addition, the plant requires limited space and low consumption, making EB technology a safe, ecological and economically advantageous solution for applications in coatings, bonding, sterilization and production of advanced materials.

Applications

The electron irradiation process allows the modification of the chemical and physical properties of polymeric materials, improving the quality of the product. In our laboratories, the electron beam is used for the following applications:

Polymerization of monomers for incorporation into fabrics
Curing of adhesive films
Non-thermal cross-linking of adhesives
Surface sterilization
Curing of resins on filament winding process
Improvement of the mechanical resistance of composites
Production of multilayer composite materials

Characteristics

Electron beam technology is safe, precise, easily controllable, and unlike radioactive sources, can be turned on/off.

Electron beam energy and output power can be modulated over a wide range. Electron accelerator technology to modify the surface of the material is more environmentally friendly than chemical methods because it does not require solvents or toxic agents.

Technical Details

Our electron accelerator operates using the principle of thermionic emission: a heated tungsten cathode emits a stream of electrons that is then accelerated in a vacuum thanks to a potential difference between the cathode and the anode. This beam is appropriately collimated and deflected, similar to the operation of a cathode ray tube in an analog television. The electrons are accelerated to energies between 150 and 300 KeV, with a maximum current of 30 mA, to reach a maximum dose rate of 202 kGy/s.

The machine, located at NTT, uses a single triode system, equipped with a tungsten cathode and a Wehmelt cylinder, operating in a high vacuum chamber. The emitted beam is adjusted in amplitude and vertical position by an X/Y deflection device, which allows for effective scanning of the output window, measuring 75 x 700 mm. Finally, the electron beam passes from the high vacuum chamber to the external environment through a thin titanium plate, which allows vacuum conditions to be maintained in the cathode area. The vacuum system uses a dual pump configuration, consisting of a turbomolecular pump and a rotational pump, to quickly reach and maintain optimal conditions both inside the electron accelerator and the scanning system.

The high voltage is generated by a series of transformers operating at an average frequency of about 35 kHz, combined with an amplifier, and the high voltage section is housed in a hermetically sealed tank containing transformer oil. The system also integrates a water cooling unit, which is essential to keep the temperature of the beam exit window, the vacuum compartment and the transformer under control. The accelerator is protected by a composite shielding that includes, in sequence, a 4 mm stainless steel sheet for structural support, a lead layer with an average thickness of 35 mm and a final 2 mm stainless steel sheet, which prevents the contact of lead oxides with the materials present in the treatment chamber.

The shielding sizing was calculated considering the worst operating conditions (V = 300 kV, I = 30 mA), and is essential to protect against X-ray emission resulting from irradiation. Finally, the electron gun is integrated into a protective structure made of stainless steel and lead, equipped with specific devices for the continuous processing of flexible materials. The vacuum system is a double pump structure, composed of a turbomolecular pump and an additional rotational pump that allows to quickly reach and maintain vacuum conditions both inside the electron accelerator and the scanning system. The high voltage is produced by a series of transformers with an average frequency of about 35 kHz and an amplifier.

The high voltage section is located in a hermetically sealed transformer oil tank. The system includes a water cooling unit, which is necessary to cool the electron beam exit window, the vacuum system and the transformer. The accelerator is shielded with a composite structure consisting of a 4 mm thick stainless steel sheet (support function), a lead layer (average thickness 35 mm) and an additional 2 mm thick stainless steel sheet that prevents the lead oxides from coming into contact with the materials in the treatment chamber. The shielding structure was designed for worst case conditions (V= 300 KV, I= 30 mA). The shielding is necessary to shield the X-rays emitted as a result of irradiation. The electron gun is integrated into a protective structure made of stainless steel and lead, equipped with suitable devices for the continuous processing of flexible materials. When high energy electrons irradiate a sample, the energy transfer to the chemical bond electrons of the material begins.

The final effect is the generation of free radicals and consequently the increase of the chemical reactivity of the treated sample. As a result, chemical-physical processes such as cross-linking, grafting and polymerization of the treated materials are enabled. The presence of free radicals in the polymer chains increases the functionalization of different groups, therefore it is possible to modify the surface of the polymeric material, consequently improving the mechanical and thermal properties. The beam energy varies depending on the field of application, as well as the types of materials to be treated.