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Endless fibre surface engineering by an industrially viable environmentally friendly plasma


Two sets of parallel-plate electrodes are placed vertically side-by-side to form a single gas tight container save for two open ports, one at the base of each electrode set. Grooved guide rollers are placed, one just below each port and one between the tops of the two electrode sets. The container can be filled with lighter-than-air process gas and high voltage RF applied across both electrode sets so as to generate two regions of plasma, one between each electrode set. The reactor then constitutes a double pass system in which endless fibre can approach the reactor horizontally from an unwind reel, is turned 90° into the vertical by the first guide roller, enters the reactor through a port and passes up through the first plasma region. At the top of the electrode array, the fibre is turned 180° by the second guide roller and passes down through the second plasma region and out through the exit port where it is turned through 90° back into the horizontal from where it can be collected on a rewind. This arrangement can be repeated indefinitely by placing more electrode sets in series so as to give a plasma path of the length necessary to achieve the line speed required while still carrying out the target process.
The technique relates to a method or process for using plasmas at atmospheric and/or ambient pressure in industrial manufacturing, processing and production. The method enables the path length of the plasma in the direction of the moving fibre to be extended to lengths of the order of metres while maintaining constant plasma power density, thus increasing the residence time in the plasma of a fibre element moving at fixed speed through the plasma and thus increasing the total energy per unit area coupled into the fibre by the plasma at constant throughput speed and plasma power density. The technique results in enhanced manufacturability of the resulting equipment by ensuring that the equipment can handle the high line speeds necessary for successful integration into existing production lines. Long plasma path lengths are a key distinguishing feature of new generation of cool Atmospheric Pressure Plasma (APP) technology.
With this photo sensor we can measure the light intensity of our plasma. We can use this sensor for process control, as sometimes it can be that microwave or RF-power is on and no plasma is on. If we don’t use the sensor we think that the samples are treated but they are not treated. So in this case we get an alarm from our sensor. This sensor is nearly useable for all plasma treatments, and for endpoint measuring. During the process the light is changing, and if the process (for example: cleaning process) is done the parts are clean and no more dirt is on the surface so the light is the same.
This microwave source is designed for high etching rates and high coating rates. This is very useful for example in a production line for printed circuit boards. In this industry they can save a lot of money with this technology. In the future there are very small holes so these holes are made by plasma. Etching and cleaning is in one step. With the microwave source we have higher frequency and higher ionisation so that we can have a higher etching rate. We already have very good results by polyimide (Kapton) etching. Here we have etching rates of more than 6 µm per minute. Also we did some tests in the semiconductor industry with etching of polysilizium and nitride instead of wet etching. (HF-etching). We had etching rates of 210 nm/min. With this plasma etching the life time of quartz boats and tubes is minimum three times higher than with wet etching and also the plasma etching is environmentally friendly.
Design, building, commission and operation of an industrial prototype system for the generation of non-thermal equilibrium, atmospheric pressure plasmas (APP) in an industrial fibre processing mode was done. Major innovations were made to: the materials used in electrode fabrication, electrode design and manufacture, electrode geometry (vertical instead of horizontal mode and long plasma path length), thermal management to ensure long electrode lifetime consistent with high plasma power density operation, process gas containment reducing expensive gas consumption by 95%, process gas selection (focusing on Helium as the key carrier gas for all processes). The system was designed as an industrial prototype capable of being integrated into a continuous fibre processing production with a plasma path length of 1m but capable of extension to much greater lengths. The system is powered by a commercial RF generator interfaced with an in-house built high voltage step-up transformer. Process gas handling system allows a mix of 2 gases to be delivered to the plasma region.
A uniform, homogeneous and well-behaved, cool APP suitable for industrial processing of materials is generated between two opposing parallel-plate metal electrodes if the opposing face of one or both electrodes is covered by a glass sheet and a high voltage is applied across the inter-electrode gap. The area of the electrodes and, hence, the plasma can extend to m2 but the gap between them is, typically 3 - 20mm. The applied power is Radio Frequency, typically 10-100kHz and linear or other transformers are used to step up the voltage applied to the electrodes to, typically, between 5 - 25kV. If the applied power is in continuous wave mode, the precursor gas must be dominantly Helium, but, if the applied power is pulsed, other gases can be used. The plasmas so generated are a powerful tool for the surface engineering of industrial materials in a continuous, on-line mode.
The technique relates to a method or process for using non-thermal equilibrium (cool) plasmas at atmospheric and/or ambient pressure in industrial manufacturing, processing and production generated from precursor process gases other than ambient air. The technique uses the relative densities of such process gases to the ambient air to achieve process gas containment and confinement to and near to the plasma region. This enables atmospheric/ambient pressure plasmas generated from non-ambient-air precursor process gases to be run in an open port/perimeter configuration suitable for on-line, continuous processing and manufacture while, firstly, reducing or eliminating loss of process gas from the plasma reactor to the surrounding environment, whose loss is costly and/or hazardous and/or environmentally harmful and, secondly, reducing or eliminating contamination of the plasma by unwanted ambient air and, thirdly, ensuring uniform distribution of process gas throughout large plasma volumes having difficult geometry from the aspect of process gas delivery. The use of non-ambient-air process gases is essential to extend the application of cool atmospheric pressure plasmas into new areas of mainstream industrial processing and is a key distinguishing feature of new generation APP technology.
Computer Integrated Manufacturing requires development of equipment and process states diagnostics capable of in-situ monitoring and real-time, in-line process control. The following suite of diagnostics have been developed for application to new generation APP technology with the capability to feed back into the plasma generation and fibre handling control systems: Digital Video Recording System, Optical Emission Spectroscopy, Electrical power parameters, Process gas monitors, Electrode cooling monitor, Fibre presence detector. All of these provide data outputs suitable for interfacing to a PLC-based monitoring and closed loop control system.
This system can be used in the medical industry for example to activate the catheters before marking with a paint for a better adhesion. The paint cannot come of if they do it in the body, especially if the material is Teflon or also for coating and activating. Some polymer foils in this system. It is against diffusion of oxygen in the food industry or coating with special polymers for different applications (example: PCB- industry, optical industry e.g.)
Many of the analytical methods of surface chemistry and physics involve a solid-gas (or solid-vacuum) interface, while in the case of biomedical devices the working environment is often aqueous (body fluids and so on). Since the beginning of the ‘80s, the Atomic Force Microscope was recognised as a method for the characterisation of the solid-aqueous interface, especially by the measurement of force-separation curves (i.e. by the measurement sensed by the AFM tip as it approaches the solid surface in the nanometers range). Within this project we have made ample use of the existing knowledge and developed it into a consistent approach to the characterisation of the solid-aqueous interface of closely related polymers (i.e. of polymers subjected to quantitatively different but qualitatively identical surface modification treatments). This method could support more conventional approaches (i.e. contact angle measurement) in the surface charcaterisation of polymeric medical devices.
With the combination of a liquid flow controller and a pulsable frequency we can produce a lot of different coatings for different applications. With pulse plasma we don’t damage the functional groups of the monomers during the dark phase. The coating can be used for example in the medical industry for biomedical coating or in the metal industry for antioxidation and also as a primer for good adhesion. We reduce with this process also a lot of wet chemistry. One advance in the plasmatechnology will be the coating technology.
Risk assessment of new generation APP technology has identified three safety hazards, namely electrocution, exposure to RF radiation and exposure to ozone or other exhaust gases emitted by the plasma process. Control measures were designed and implemented comprising a grounded Faraday cage surrounding all high voltage parts, self-diagnostic interlocks in tandem on all access points to hazardous areas and fan extract of the reactor enclosure. Following such measures, the risk level analysis showed a negligible risk from all the above hazards. Furthermore, EMC and environmental regulations were fully complied with.
This technique can also be used for other materials, like on Teflon before bonding on steel or other materials. Only if the glue needs amino groups on the surface. (example: Cyancrylate) we can eliminate the already nearly forbidden wet etching process (Tetra etch). With plasma we only use NH3 in a very small amount (ml/min). This can be washed with a gas scrubber after the vacuum pump. We also don’t damage the surface with plasma. In the smart card industry before bonding the chip into the plastic, they need amino groups on the surface if they use cold glue.
This sensor can be used as a process controller if we cannot use the photo sensor. For example if we use oxygen as process gas we have nearly no light. So sometimes we will have problems with the photo sensor, so we use the electronic sensor. But with this sensor we only can measure if plasma is on or not. This sensor is not for end point detection. We can use this sensor also for different frequencies.
A test method has been developed to evaluate performances of glued catheters connections. In particular, we have identified the most critical standard and have developed a protocol for the characterisation of glued catheters parts. The strength of the adhesive joint is evaluated after double sterilisation and aging test of the pieces (simulation of 2 years shelf life), conditioning of the pieces before testing. This protocol allows to evaluate performances of the glued connections after a very severe stress, and gives reliable results on performances of glued connectors and on the suitability of a given production process.
Polyvynylchloride (PVC) is widely used in the medical device industry. A common problem of PVC parts is the release of diottylphtalate (DOP) a plasticiser contained in PVC, whose role is to improve PVC working properties. The problem of DOP release from PVC, and of its possible adverse effect on human health, is widely debated. The method developed allows to decrease toxic effects due to DOP release in in vitro cytotoxicity tests. We observed a significant decrease of toxicity of PVC parts following plasma treatment in proper conditions. The method can be implemented on a larger scale, with possible benefits to the patient's health. It is not known if decreased cytotoxicity is due to the desruption, by plasma, of DOP, or by the decrease of its ability to diffuse and migrate from PVC to the sourronding environment.
Normally you should have a viewing part on each plasma system but this has to be a special part. At first it should be safe against the atmospheric pressure (so it does not burst) and against high frequency and UV. So we designed a special window with a mash included. This mash does not disturb the view into the chamber. It is also against a microwave leakage. The special material is also against UV because in plasma we also produce UV.