The advantages of modular generators for corona and plasma treatment stations
Corona stations are available in all sizes depending on the application- from 10 inch narrow web lines to wide coating machines and BOPP/BOPET lines of up to 10 meters. Usually, the high frequency high voltage that is needed to power the corona process is provided by generators that have to be upsized with increasing performance requirements.
However, their maximum performance is limited due to the maximum available size of the electrical components in the power inverters. With the maximum performance available on the market – 60kW per generator – and therefore per electrode bar, the limits of the technical possibilities are reached. Not only on extremely wide lines but also at high speed applications or for materials with high demands in terms of corona dosage.
Scaling for pretreatment by means of additional electrodes and a single generator quickly becomes expensive due to larger or additional rollers. A further disadvantage of these large single generators is that a technical defect at a critical part of the inverter can bring an entire web to a standstill.
AFS, from Horgau, Germany, now offers a modular generator design as a solid solution to both problems. AFS’ modular generator overcomes the performance limitations of a single generator and, at the same time, minimizes failure rate.
These generators boast several parallel power inverters, which increase the maximum performance of a single generator to 144kW – more than twice as much as conventional products on the market.
Consequently, modular generators are capable of setting new performance records and are perfectly suited for the power needed for processes with controlled gas, such as plasma treatment systems.
If a module fails, the generator will still operate but with a reduction in power until the module is replaced by a new one – simply “plug and play.” Single modules are identical and thus interchangeable. Clearly, modular generators reduce production line downtime and costly trips by onsite service specialists.
During the development of their modular generator technology, the experts at AFS included the most sophisticated components available, such as a larger TFT color touch screens which employ an intuitive user-interface on the generator similar to the graphics and functions of smartphones and tablets. Operational settings can now be adjusted through the proven rotary knob as well as by means of a touch screen. Additionally, system parameters can be easily adjusted through a password protected area for specific applications.
The pre-treatment of sensitive materials is a challenge for many converters. Plasma treatment is recommended in these cases.
Improved adhesion attained through corona pre-treatment depends largely on choosing the correct corona dosage – the quotient of power and web speed at a given working width. In practice, the process or the material usually determine the web/line speed.
However, every converter who has dealt with the surface treatment of sensitive materials or very low web speeds has been confronted with problem that power can only be reduced to about a third of its maximum performance before the corona discharge can become non-homogenous.
Lowering the power level below this level while maintaining an even corona discharge can be achieved by pulsing the corona. However, the energy of a single pulse can be relatively high which may lead to surface damage or excessive ‘pre-treatment’. The occurrence of streamers, which cannot be avoided in normal corona processes, can be especially damaging to sensitive materials, such as sensitive foams and optical films.
With these challenges in mind, Hamburg-based SOFTAL Corona & Plasma has developed its patented LinearPlasma system. The term LinearPlasma describes an indirect plasma pre-treatment method based on corona treatment. This technology enables the processing of delicate substrates because plasma treatment contains no voltage potential and therefore no steamers or high levels of electric fields. The LinearPlasma process does not cause damage typical of corona treatment on film surfaces due to producing very low energy discharge onto substrates.
Thanks to this indirect plasma technique, surfaces of very thick materials such as foams, plates and glass can be successfully treated as well. A welcome side benefit is that no ozone will emerge from porous materials later down the production line, possibly harming equipment or causing health concerns because plasma treatment does not produce ozone.
Additionally, SOFTAL’s LinearPlasma capabilities include the surface treatment of printed electronics. These sensitive materials, which are increasingly embedded in state-of-the-art packaging and technical film composites and require nonconductive surface treatment because electric circuits inside the film are damaged by corona treatment but this situation is avoided when using plasma treatment which is non-conductive.
SOFTAL’s LinearPlasma process has been engineered for printed electronics and potential-free pre-treatment. This means that these sensitive materials are not subjected to an electrical field and therefore conducting structures remain undamaged – no matter if the electronics are applied on the surface or embedded into the material.
In conclusion, converters can look to SOFTAL’s LinearPlasma system for improved adhesion of ink, glue, laminates, and coatings on delicate materials such as sensitive foams, optical films and printed electronics. Learn more on 3DT’s SOFTAL page or contact us at sales@3DTLLC.com for more information about the LinearPlasma system.
Designing a printing or coating process is a tricky thing. Not only during specification of new lines, but even in existing production lines, the coatings and inks always need to be matched to the surface tension of the substrate. Typically, a substrate is treated with corona, increasing the surface tension of the substrate and, thereby, matching the substrate to the ink or coating. Not only in development, but also in production the question arises, how intense should the corona treatment should be? This is especially the case when using older, pre-treated materials that have lost surface tension due long storage periods and requiring refreshment treatment.
Corona treatment is always characterized by the amount of corona dosage or discharge. The dosage (D) describes the energy put into one m2 of the substrate, measured in [Wmin/m2]. It can be calculated by dividing the applied corona power (P) through the web speed (v) and the electrode width (CB) of the corona system:
The applied Corona dosage couples the corona power to the web speed and can be set in direct relation to the achievable dyne level on the substrate surface. The critical task in designing or optimizing a printing or coating process is to determine the right corona dosage that is high enough to enable the process but not overtreat and thus damage the substrate.
Deciding on the right corona dosage is ideally done on test samples in a lab environment. Here, only small amounts of material are used to determine the dosage parameters, resulting in reduced cost and waste. Importantly, production lines remain open for production instead of time consuming testing and development tasks.
SOFTAL solves these issues in the form of a fully integrated Laboratory Table Corona system, the LTC. The motorized substrate holder moves at speeds up to 50 m/min under the 230mm wide corona electrode. This electrode can provide 10 W up to 400 W of power, enabling dosages from to 1 to over 1500 Wmin/m2. The motor itself guarantees a constant speed under the electrode, hence fully reproducible treatment results. Moreover, generator, transformer, drive and ozone destruction are completely integrated in the system, eliminating any requirement for peripheral equipment. Therefore, all the flexibility that is needed in a process engineered laboratory is given to treat conductive as well as non-conductive samples, specifying the exactly right corona dosage needed for the new product.
Furthermore, by using the LTC, surface treatment knowhow can be substantially increased at the production facility while minimizing uncertainties caused by transport and storage from external laboratories. Old, pre-treated and long stored material can be easily tested on site with minimal waste and assigned the correct dosage for refreshment treatment.