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ePaper created 2014-05-07, 13:23:14 | version 1.30.01
10 0 Costly time-consuming outdoor weathering for new materials The product development cycles for new paints, coatings and other polymeric materials are complex, expensive and time- consuming, above all because of the testing methods used. The material surfaces, especially those for outdoor applica- tions, have to be tested at outdoor weathering locations to determine their resistance to weathering. These tests may take several months or even years; the alternative is several thou- sand hours in weathering chambers with beam sources. If the facilities are certified outdoor weathering locations, the neces- sary testing equipment is, as it were, constantly in use and it is difficult for the developers to obtain test stands for new de- velopments at short notice. Alternatively there is weathering equipment on the market that accelerates these tests. Even so, the test cycles take several thousand hours with this equip- ment too. At the same time, considerable running costs are incurred for electricity and beam sources. In both cases, there are major delays in the material development. In order to develop and market product innovations more quickly, new testing methods need to be developed that per- mit developers to analyze the degradation characteristics of polymer surfaces, within a very short time and with a low con- sumption of energy. These evaluations should be comparable to those obtained with the conventional certified methods. Imitation of natural weathering using plasma processes Plasma-based processes are especially promising for weather- ing purposes. Here, the plasma serves as a source of radiation and particles. The effects of radiation, temperature, erosion and moisture, as well as the changes induced by them on the surfaces of polymers, can be obtained in a single process step with plasma processes. For the treatment the surfaces to be tested are placed in a specially adjusted atmosphere. By ignit- ing a plasma, atoms and molecules are stimulated in the gas phase and partially ionized; existing molecules are fragmented and thus chemically activated. Many particles are stimulated in the plasma and relax under light emission, resulting in a broad electromagnetic spectrum. Radical chemical as well as photochemical reactions take place in the plasma phase and on the surface of the samples exposed to the plasma. If re- quired, plasma ions can also be used to erode the surface. The composition of the plasmas can be controlled via the process parameters (pressure, plasma power, gas flow and gas type, duration of treatment). Fig. 1 shows the numerical ratios of the particles generated in a low-pressure plasma plasma. RAPID TESTING METHODS FOR MATERIAL CHARACTERIZATION – PLASMA WEATHERING OF SURFACES Dr. rer. nat. Jakob Barz 1 CHEMISTRY ∼RF matching network electrode e– R• M* radicals electrones ions UV-radiation stimulated particles vacuum chamber ~105 particles / (s·nm2 ) 2 – 20 ions / (s·nm2 ) ~100 radicals / (s·nm2 ) ~100 metastable particles / (s·nm2 ) –0,2 mbar electrode substrate surface plasma e– e– M* M* M* R• R• R• e– 1 cm 5·1015 particles / s 1010 – 1011 ions / cm3 1011 – 1013 metastable particles / cm3 cathode fall process gas 1 process gas 2 cold trap pump