Cleaning process based on thixotropic soil-release gels for the removal strongly adhesive industrial soilings
IGF 15911 N
Industrial cleaning represents an economically important and expandable future market for cleaning enterprises. An example is the cleaning of painting lines: Surface painting is an important production step in several industrial fields. Especially in the automotive industry, but also in mechanical engineering, furniture, building devices and consumer goods industry, surface treatments are done in painting lines. Depending on the painting procedure, part geometry and dimension, 10-90 % of the sprayed paint does not reach the workpiece. Residual paint, the so called overspray, is given off to the surroundings as haze. Although the overspray is partly catched and then utilized or disposed, the painting line surfaces get highly soiled by paint haze. In order to guarantee a high quality of the painting, the cleanliness of painting lines and spray booths is of essential importance. The current cleaning procedures show many disadvantages. Necessarily more efficient cleaning processes have to be developed. An appropriate approach relies on the application of special soil-release polymeric systems. They possess on the one hand certain rheological properties (thixotropy), which allow them not to run-off on walls (vertical surfaces). On the other hand they show high affinity with water (high swelling ratios). These soil-release systems are applicable at room temperature and form on the surface a transparent protective film. After soiling with paint and sprinkling with tape water this film swells because of water take up and thus can be removed easily from the surface without high pressure. Aim of the research project was therefore the development of a cleaning procedure based on thixotropic soil release gels for the removal of strongly adhesive industrial soilings. In order to meet the requirements in practice, several criteria have been considered for the polymer selection: compatibility with the varnishing, convenient thixotropic behaviour as well as easy removal when getting in contact with water. As gelling agents were used both synthetic (polyethylene oxide/ polypropylene oxide copolymers) and natural polymers (cellulose derivatives, xanthan gum, galactomannanes). The thixotropic properties were determined by means of a rotational viscosimeter. The developed soil-release gels were applied on typical surface materials, like stainless steel, galvanized tin, aluminium, float glass, glazed ceramic tile, polycarbonate and polymethylmethacrylate in a spray booth with a spray robot. The soil release films formed after drying were characterized and optimized in terms of drying time, film formation, film homogeneity and adhesion. The coated materials were afterwards soiled well-defined with varnish and investigated with regard to the migration and removal ability. Beside different varnish types and colors (solvent-based and water-based systems, one- and two component systems, synthetic resins varnish, acrylic varnish, hardener and thinner) were used also different practice oriented soiling scenarios. Some of the analysed polymer systems showed an adequate functionality (film adhesion, removal ability, no migration) even after a longer residence time of the varnsih on the soil-release film. The results show that already short drying times of the soil-release polymeric dispersion are sufficient to fulfil the coating functionality. Residual soils like soil-release film or varnish rest take no effect on functionality (adhesion and stripping behaviour) of the soil-release dry film, so in principle a multilayer coating with soil-release film and soiled film is possible without interim cleaning process. On the basis of the project results the costs of the respective cleaning procedures can be reduced.
The IGF-project 15911 N of the research association Europäische Forschungsgemeinschaft Reinigungs- und Hygienetechnologie e.V., Campus Fichtenhain 11, D-47807 Krefeld, was supported via the AiF within the funding programme „Industrielle Gemeinschaftsforschung und –entwicklung (IGF)“ by the Federal Ministry of Economic Affairs and Technology (BMWi) due to a decision of the German Parliament.
The research report is available on request from FRT.