Oberflächenstrukturierung polymerer Fasern durch UV-Laserbestrahlung. 3. Synergetisches Modell für das Entstehen der Oberflächenstrukturen

A synergetic model is proposed for the development of the surface structure on UV-Laser irradiated polymers and especially synthetic fibres. It is suggested that thermal contributions to the UV-laser-polymer-interaction produce a very thin, highly heated layer of molten material at the ablation limit. The formation of the typical surface structure is then thought to be caused by Marangoni-convection and shrinkage because of intrinsic stress. The parameters of the effect therefore are the absorption coefficient for the corresponding laser wavelength as a measure of the thickness of the molten layer and the existence of the shrinking behaviour.     

Oberflächenstrukturierung polymerer fasern durch UV-laserbestrahlung. 11. Oberflächenstrukturierung von polypropylen-folien und -geweben

It is shown that weakly UV-absorbing polymers like polypropylene (PP) become amenable to laser treatment by impregnation with strong absorbers like benzophenone. The high absorption coefficients of the doped polyolefines allow an efficient etching by laser irradiation. In addition, roll-like structures of the surface are obtained as they are known from laser-treatment of polyester and polyamide fibers. The dimensions of these structures on fibers are in the region of 10 to 25 μm with a depth of about 3 °m. Using biaxially stretched PP-foils, drop-like structures are obtained, thus indicating a predominance of thermal effects. On weakly absorbing systems like dyed PP-fibers only fusions of single filaments are obtainable. By mechanical contact of an undoped PP-foil with poly(ethyleneterephthalate) (PETP) foils laser irradiation creates roll-like structures on the PP-surface.     

Oberflächenstrukturierung polymerer Fasern durch UV-Laserbestrahlung, 15. Beschreibung des Temperaturfeldes in PETP-Polymeren während und nach der Laserbestrahlung mit einem gepulsten UV-Laser

For understanding the generation of UV laser induced surface structures of PETP polymers the temperature field within the irradiated surface is calculated in dependence on the laser irradiation wavelength (193 nm, 248 nm, 308 nm), pulse time, pulse form, the irradiation intensity and depth, using temperature-independent material data of PETP polymers known from literature. For this purpose the solution function of the one-dimensional heat differential equation is used. Depending on the order of magnitude of the absorption coefficient of the polymer for UV light of different wavelengths, surface temperatures of approx. 16 000°C (193 nm), 11 000°C (248 nm) and 500°C (308 nm) are calculated at the end of the laser pulse. The temperature input within the polymer layer is limited to only a very small penetration depth. For the irradiation with the two laser wavelengths of 193 nm and 248 nm this is less then 0.4 μm. The cooling process is considerably slower, reaching the initial temperature after approx. 4 μs.     

Oberflächenstrukturierung polymerer fasern durch UV-laserbestrahlung. 6. Zur vermeidung von vergilbungen bei der laserbehandlung von polymeren

It is shown in this paper, that during laser treatment of polymeric materials the occurrence of discolouring layers of laser crack deposits onto the substrate can be avoided without preventing the formation of a laser-induced microstructuring of the surface. Using water, alcohols, ethers or aqueous surfactant solutions as impregnating media during laser treatment a high degree of whiteness of fabrics can be maintained.     

Optische Methoden zur Charakterisierung von hochpolymeren Fasern. 2. Kennzeichnung von Oberflächen durch Specklemeßmethoden.

The surface roughness of textile materials is of great influence on textile processing and practical applications. Speckle-techniques are common for integral, contactless, and non-destructive characterization of metallic surfaces. The scope of this work was to apply the analysis of the contrast of the speckle patterns and the dichromatic speckle correlation to measurements of the roughness of polymer surfaces. For this purpose it was of importance to study the influence of the optical properties of the polymer samples on the characteristics of the speckle field. Methods for measurements on filaments, yarns, and fabrics are discussed.     

Desaktivierungsverhalten von Arenen und Heteroarenen. II. Fluoreszenzlöschung des Acridiziniumions durch äußeren Schweratomeffekt

Deactivation Behaviour of Arenes and Heteroaenes. II. Fluorescence Quenching of Acridizinium Ion by External Heavy Atom Effect The rate constants of fluorescence quenching of acridizinium ion by aliphatic and aromatic bromides and iodides are outlined by the donor properties of quencher (among the known influence of atomic number). The values of the rate constants determined by using the Stern-Volmer-equation correlate with the ionization potentials of donors and the TAFT -constants. If the ionization potentials of the quenchers are low, a participation of triplet states of quenchers or the formation of an exciplex (deactivating ratationless) is assumed.     

Stand der Technik der Oberflächenveredelung durch Laser

State of the art of surface treatment by lasers . Lasers have a great future in surface treatment. Laser surface treatment should not be regarded as a replacement for existing methods. It cannot compete with mass production methods, but can be used whenever a local need arises for special properties or when conventional methods fail. Some new developments, such as laser gas treatment, are also extremely promising.