Atmospheric pressure plasma - innovation for surfaces

40 workshops of the atmospheric pressure plasma user group ak-adp in 12 years stand for the scientific interest and industrial relevance of the technology.

Currently not an everyday occurrence: the 40th workshop of the ak-adp was held in Jena on November 10 and 11, 2021. The participants from research & development and industry took the opportunity to discuss application examples of plasma technology at normal pressure for economically and environmentally friendly innovative processes.

The presentations focused on a wide range of functionalizable materials as well as very different possibilities of functionalization itself. In addition to the established functionalization of plastic surfaces for improved bonding and painting, examples include electrolytic plasma polishing, the coating of carbon fibres and the metallization of CFRP components, the surface modification and coating of particles, plasma printing and the antimicrobial coating of fingerprint scanners.

View into the plenum. At the 40th ak-adp workshop in November, the focus was on innovative applications of plasma technology at normal pressureDr.Robert Weigelt - team leader of the Thuringian Cluster Management of Landesentwicklungsgesellschaft (LEG) Thüringen mbH - emphasized the importance of promoting innovation and networking in his welcoming address. A LEG study on the potential of surface technologies shows the increasing variety of industrial applications of atmospheric plasmas. The ak-adp offers access to expert knowledge with interdisciplinary exchange.

Prof. Arne Bender from the Technical University of Lübeck came to give the introductory lecture. He works there in the Department of Mechanical Engineering and Economics in the field of materials testing, surface technology and tribology. In his lecture on "Hydrophobic polymers - better bonding and coating through atmospheric pressure plasma treatments", tests were presented on injection-molded tension rods made of PE and PP, which were treated with plasma sources from Diener electronic GmbH and neoplas GmbH. The tests were carried out as practical experiments for students. This created a large data pool for reliable statistical statements. The student work confirmed that atmospheric plasmas are well suited to increasing the adhesive strength of problematic plastics by increasing the polar component of the surface energies.

Laura Barillas-Mora, employee and doctoral student at the Leibniz Institute for Plasma Science and Technology in Greifswald, presented the very interesting topic "SurfAP3 - Plasma Printing for the local surface modification of biosensors & microfluidics" in her lecture. Atmospheric plasmas are used for biosensitive surfaces, as activation and polymerization is a very fast process with low energy input. When working with a micro-needle, line widths in the µm range can be achieved and variable morphologies can be treated. Other potential applications of local plasma treatments include the production of electrically conductive or thermosensitive structures or 3D printing with high resolution and precise functionalization.

Laura Barillas-Mora from the Leibniz Institute for Plasma Science and TechnologyThefollowing speaker - Tobias Weise, Managing Partner and co-founder of plasotec GmbH - was connected online for his presentation. plasotec GmbH deals with the surface finishing of metallic workpieces and uses plasma polishing for this purpose. Weise provided information on the technology and applications in his presentation "Precise surface finishing using electrolytic plasma polishing for use in medical technology, the food industry and mechanical engineering". Environmentally friendly electrolytes are used. The process times are in the sec range for classic surface smoothing and in the min range for edge rounding and plasma polishing of printed components. Examples of applications include cleaning and deburring processes as well as the removal of tarnish and the creation of smooth, shiny metal surfaces.

Another presentation on innovative plasma processes focused on "Adhesive metallization on CFRP components using cold plasma spraying". CFRP components combine many material advantages such as low weight with high stability and optimized material usage. As the matrix material is a plastic, CFRP components are not electrically conductive. This is where a metallic coating is interesting. Jun Xu is working on this at Innovent e.V. in Jena. Cold plasma spraying, for example, can be used to deposit Cu layers with good electrical conductivity. Another application of Cu coating is the deposition of a thin nucleation layer on plastics for the subsequent deposition of an electroless nickel layer as a diffusion barrier or wear protection layer.

Julian Bloh from the German Institute for Rubber Technology in Hanover uses atmospheric plasmas for the "surface modification of filler particles for elastomers using atmospheric pressure plasma". He works with a reactor with an integrated Plasmatreat system and various precursors. Carbon black is used as a filler for the elastomers. The results of the carbon black modification are characterized using thermogravimetry, TEM and confocal 3D-LSM. When the particles pass through the reactor several times, the fillers are first modified and then coated. The characterization of the filler particles was intensively discussed.

The "Deposition of graphene-like thin films on copper particles for novel composite materials" was the focus of the presentation by Dr. Jörg Ihde from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Bremen. The aim of the R&D work was to increase the burn-off resistance of electrodes by improving heat dissipation. To achieve this, the time-consuming production of Cu-graphene mixed material was replaced by a graphene coating of the Cu particles. Currently, a throughput of 1kg Cu/h is already being realized. The graphene-copper particles produced using atmospheric pressure plasma can be pressed into electrodes/contacts and are characterized by improved thermal conductivity and resistance to ageing as well as improved mechanical and electrical wear resistance.

Plasma coatings on glass were the focus of Tom Trautvetter 's doctoral thesis at the Leibniz Institute of Photonic Technology IPHT and the University of Jena (currently an employee of LEONI Fiber Optics GmbH). LEONI Fiber Optics GmbH deals with preform/glass fiber production for fiber optic switches. The aim of the doctoral thesis was to produce a simultaneously and multi-doped preform for active laser fibers using plasma-based synthesis. This requires a high beam quality with high power extraction and low attenuation losses. The modification of the fiber properties without changing the refractive index curve in the material was achieved by plasma assisted vapor-phase axial deposition (VAD) and by aerosol-based liquid-phase doping on the basis of a TEOS sol. The result is a porous precursor with high dopant homogeneity as a prerequisite for the necessary refractive index homogeneity.

Ann-Kathrin Kirschner and Oliver Deußen spoke about the continuous plasma coating of carbon fibersResultsof the joint ZIM project "Plasmahybrid" were presented by Ann-Kathrin Kirschner from the University of Applied Sciences and Arts HAWK Göttingen and Oliver Deußen from the Institute of Textile Technology Aachen ITA at RWTH Aachen University. The aim of the project is to develop a production system for the continuous plasma coating of carbon fibers. The aim is to produce a meltable and formable carbon fiber material using cold plasma spraying by applying a thermoplastic polymer directly to the fibers with a plasma nozzle. Thermoplastic CFRP is difficult to produce, but can be recycled. The weak point is the fiber-matrix adhesion. Plasma is to be used here for fiber coating. One solution is to spread the filament and coat the spread, tension-free fibers.

Dr. Gill Scheltjens from the Molecular Plasma Group in Foetz, Luxembourg, gave an overview of available plasma technologies and applications in a presentation entitled "The versatility and future prospects of molecular plasma treatment" (online). The young system manufacturer offers a wide range of plasma systems from the Plasma Spot to the Plasma Line and Plasma Powder, a prototype consisting of a Plasma Spot and a fluidized bed reactor for powder treatment. The Plasma Spot can be used to inject liquids, emulsions, suspensions and polymer solutions. The Plasma Line is available in 20 cm, 30 cm and 40 cm widths, whereby several widths can be combined as required.

Roberto Wolfer from Jenetric GmbH Jena had a very interesting application of atmospheric plasmas in his luggage. The company is a manufacturer of fingerprint scanners for sovereign areas with high quality standards. Its expertise lies in the optical/electronic recording of fingerprints. Here, forensic quality faces a risk of infection - contactless scanners are not yet certifiable as compatible. The title of the presentation describes the problem that is particularly acute in the coronavirus pandemic: "Fingerprint scanners and hygiene: a conflict of objectives that is difficult to resolve". The solution lies in an antimicrobial CCVD coating with CuO as a bactericidal component. Tests of the antibacterial effect according to DIN EN ISO 22196 show a good effect after 2 hours. This time must be significantly shortened by combining active ingredients and increasing the concentration of active ingredients in the coatings.

The surface analytics presentation at the workshop highlighted issues relating to "Passive thermography for quality assurance of atmospheric pressure plasma treatments on plastics". Michael Heilig from the South German Plastics Center SKZ Würzburg provided information on the attractively priced and precise, operator-independent measurement method, in which the inherent heat of the object is specifically used for the thermographic measurement. The measured values are recorded using a special IR camera and subsequent line evaluation. Referencing with contact angle measurements and tear-off tests after bonding is possible. For this purpose, tests were carried out with various plasma systems. It is also possible to model the heat input as a function of various plasma treatment parameters.

As part of the workshop, there was the opportunity to visit the laboratory at Innovent e.V.. Here the participants were able to get an overview of the technical equipment of the AD plasma laboratory, the possibilities of flame treatment, sol-gel technology and chemical surface treatment. A wide range of surface analysis services are also available for customers and project partners.

The established regulars' table on the evening of the first day was a welcome meeting place for all workshop participants for culinary delights and a broad exchange of ideas.

The workshop was held in compliance with the applicable hygiene regulations. All participants who had not traveled were able to follow the workshop in hybrid form.