Atmospheric oxygen reduces the effectiveness of UV curing in some inks and coatings. Reducing the oxygen level within the UV lamp housing increases production speeds significantly. Inert gas, typically nitrogen, is introduced to the lamp housing to displace oxygen, reducing it to a very low level.
The GEW solution
GEW has developed a compact system in which an inert curing chamber is built around the UV lamphead and sealed against a chilled roller. Oxygen is purged from the chamber using nitrogen gas, which is introduced in a controlled manner via a “nitrogen knife” at the web inlet and via an injector in the curing chamber. An oxygen sensor within the chamber continuously monitors the oxygen level, which is automatically regulated to the number of parts per million set by the operator.
Under normal conditions, oxygen reacts with the photoinitiators in the ink when it is exposed to UV light, rendering some of them inactive in the curing process and limiting the extent of polymerisation that can occur.
Curing under an inert atmosphere significantly increases the rate and extent of cross-linking, with a corresponding reduction in odour from the finished product. The graph shows how the quality of curing increases as the ppm (parts per million) concentration of oxygen is decreased.
What are the benefits?
Allows curing of low migration inks for food grade applications
Improves the curing speed of all free radical inks
Enables curing of free radical silicone coatings
Reduces ink odour
Commission Regulation (EC) No.2023 / 2006, EU No.10 / 2011 relates to good manufacturing process control of materials and coatings intended to come into contact with food. GEW has developed a system for inert gas curing which supports this regulation by several means:
• Continuous inert gas control with real-time recording.
• Low consumption of inert gas, enabling lower levels of oxygen concentration to be achieved resulting in consistent, thorough and cost-effective curing.
• Continuous measurement and regulation of UV lamp’s dose and intensity output for total process control, where specified.
• Electronic reports of oxygen levels in the curing zone and, where specified, UV dosage and intensity.
GEW’s Process Control package includes a means of recording live system curing performance data on a job by job basis. Data appropriate to the UV system configuration is recorded such as oxygen level (ppm), UV intensity and any warning and fault conditions that occur during the logged period.
Customisable logged data can be transferred to the customer as csv files on a weekly basis. Other data transfer options may be available on request, please contact your sales representative for more information.
UV Dryer – compatible with: E2C – up to 60cm / E4C – up to 130cm / NUVA2 – up to 250cm / LED – Up to 250cm
Inert Gas Curing Chamber – available with water-cooled roller or inline water-cooled heatsink.
Oxygen Analyser: Compact zirconium oxide sensor mounted near to the inert gas chamber for rapid response. Precision pump controls sample rate over sensor with filter to keep sensor clean.
Inert Gas Control Box: Housing all-electronic control for monitoring and controlling inert gas flow. Flow and oxygen level are digitally measured and displayed locally on the HMI with multiple viewing options.
UV Output Sensors: Continuous measurement of the UV intensity and dose when synchronised with the machine speed. Measurements are displayed on the system’s HMI.
RHINO power electronics: Ultimate efficiency, aerospace grade electronic control design is used to power the UV lamp and to control the inert gas system.
HMI: GEW UV Process Control displays real-time oxygen concentration and gas flow rates to each oxygen sensor. Job references can be entered to link oxygen and UV process control to job numbers with daily online reports available as standard. Remote monitoring by GEW gives complete service reassurance.
Nitrogen Gas Feed: Gas feed to control box is a key requirement for success. Approximate consumption figures are shown overleaf with more detailed information available on request.
• Real-time monitoring of oxygen concentration and inert gas flow rate in litres/minute. Recordable for individual curing chambers.
• Closed-loop control. The operator simply enters the setpoint, warning and fault levels and presses the run button. The system does the rest. GEW control logic ensures wastage is reduced at all changes of set parameters.
• Simple HMI view:
Inert gas consumption
Inert gas consumption varies according to:
• Oxygen concentration to be achieved
• Running Speed
• Web width
• Surface texture of substrate
• Curing chamber settings
The following graph gives some indication of likely gas consumption with changes in some of the above variables. For more information please contact GEW directly.
Ask us a question about inert gas curing
If you have any questions you would like to ask us about our inert gas curing systems, then fill in the form below and our sales team will get back to you as soon as possible.