Best sheetfed uv printing: uv lamps and reflectors

UV lamps

The violet line launcher is generally a quartz tube containing mercury in an inert gas atmosphere. The high quality quartz transparency ensures that up to 90% of UV light can pass through and is resistant to temperatures up to 800°C. Mercury is used because the radiation it emits cures the colors commonly used in printing throughout the spectral range. For special applications (eg opaque white, heavy ink film and special colors), doped lamps (cobalt, calcium, indium, iron, lead) are required. UV lamps need a transformer to provide several thousand volts of current.

UV mercury lamps are very reliable, but their output decreases with use. The attenuation is related to (a) the number of hours of operation, (b) the number of starts and shutdowns, (c) the efficiency of the cooling system, and the procedure for cleaning the lamp and reflector plates. In general, depending on the supplier and the type of lamp, the lamp guarantees a service life of 1000 to 1500 hours. The new generation of UV lamps uses a circulating halogen process, which greatly avoids the blackening of the edges (caused by electrode corrosion) and significantly retards the internal contamination of the entire lamp (electrode material deposition) if the lamp is correctly Maintenance can achieve a very long service life.

The high power rating of the lamp does not mean that the system can provide high UV efficiency at a definite energy consumption, producing low heat. Efficiency depends not only on the rating of the lamp power, but also on the quality and system performance of the lamp – this indicator varies according to the supplier and the design, affecting the efficiency of curing and energy, for example:

– To reduce the cost of electrical rest and reduce the risk of fire, the lamp system should be equipped with a shutter that can be automatically shut down when the press is stopped. After the shutter is installed, the luminaire can be positioned as close to the substrate as possible, which increases the efficiency by 20% (it also requires less cooling and less energy than other designs).

– The profile of the reflector should focus the radiation for the highest radiation intensity. The ideal situation is to minimize direct radiation and focus the highest intensity in a narrow area.

– First, a high-strength cure is required because it quickly seals the surface of the ink to reduce the effect of oxygen inhibition (otherwise large amounts of oxygen can distort the gloss surface).

– Avoid pre-irradiation and increase the power required for main curing.

– Post-irradiation is only recommended for heat-sensitive materials that may cause registration problems due to the heat generated by the curing between the units.

Reflective plate

Only about 35% of the luminaire radiation passes directly from the luminaire to the substrate (basic energy). The remaining (secondary) energy is reflected by the reflector back onto the printing material. The efficiency of the entire luminaire is determined by the nature of the reflective material used and the profile of the reflector.

The reflector should provide maximum UV curing radiation with minimal energy consumption and minimal heat build-up. The decisive factor in curing is the amount of UV light that reaches the printing material. The UV module should be as close as possible to the substrate because increasing the distance from the surface of the substrate will greatly reduce UV intensity.

UV reflectors are mostly made of aluminum or glass, and their reflection performance is almost equal. Aluminum is used more often because users can replace the reflectors themselves when the reflectors are dirty (the glass needs to be replaced by a professional technician), and there is no need to worry about the glass falling onto the press when the reflector breaks. For heat-sensitive substrates, a selective mirror with a dichroic reflective coating reflects ultraviolet light and absorbs most of the infrared light.

Modules

The new generation of UV modules optimizes the profile of elliptical reflectors and parabolic reflectors, improves strength, reduces back radiation, and reduces energy consumption (eg, AdGuo-Eltosch's LightGuide). The updated module can easily be moved between docking stations and the time for disassembly is no longer than one minute. The plug-and-play connection allows the module to be used as a UV block drying module for one purpose, and the UV block at the end of the printing press is used for another purpose. The UV lamps themselves also have plug-and-play connections that allow the lamp to be replaced no less than one minute without the use of tools.

cool down

UV lamps can reach a surface temperature of 800°C and require effective cooling to avoid damaging the substrate or printer system. The water-cooled system filters and absorbs most of the energy generated by infrared light. The cooling water is essentially pure (non-mineral) and free of bacteria.

Curing system control

The exact UV dose should match each ink color at various printer speeds. The control system should allow each UV lamp output module to be individually programmed to achieve an extremely accurate dose (especially on the radiation used for heat-sensitive substrates), plus every UV of the printer end UV drying unit Modules can be programmed separately. Other required functions include: stepless output adjustment of the dimmer; an integrated shutter system that prevents radiation from entering the press while the printer is waiting for operation, an intermediate drying unit from standstill to production acceleration, and cooling system monitor.

Special lamps and modules

TwinRay: A new curing concept that combines different UV lamps in a single module to eliminate thermal issues related to infrared energy, including registration, paper wrinkling, high stack temperature and stacking issues, and Heat-sensitive printing materials.

WhiteCure: The UV-cured opaque white used in printing plastic films has a different absorption range than standard UV inks (white pigments absorb better than standard colors in different ranges). This means that when curing, it competes with photoinitiators for energy. Higher energy is usually used to ensure the progress of curing, but this can cause problems on heat-sensitive substrates. Specially-doped WhiteCure UV curing modules (inserted into standard fixtures) can increase opaque white cure performance by 25%.

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