The role of surface viscoelasticity in slide coating processes |
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Authors: | H Fruhner K -D Wantke |
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Institution: | Max-Planck-Institut für Kolloidund Grenzfl?chenforschung Am Mühlenberg 1, 14476 Golm Germany, DE
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Abstract: | In the slide hopper coating process for simultaneously applying multiple layers of coating liquids to a moving web, surfactants
must be added to the photographic emulsion to ensure a stable position of the liquid bridge formed between the lower edge
of the slide hopper and the moving web. In slide coating of gelatin solutions without an added surfactant, the liquid bridge
becomes instable and begins to oscillate if critical coating conditions are reached. The addition of anionic surfactants stabilizes
the liquid bridge against oscillations. The action of the added surfactants is a result of their interaction with gelatin.
The degree of binding can be used as a measure of the interaction. The binding of anionic and cationic surfactants to gelatin
was investigated using a surfactant-selective electrode. The binding isotherms of the surfactants to an alkali-processed bone
gelatin were determined and compared with the surface dilational properties of the gelatin/surfactant adsorption layers. The
comparison of surface rheological data obtained by the oscillating bubble method with the results of coating experiments demonstrates
that the viscoelastic properties of gelatin/anionic surfactant adsorption layers are of essential importance to the stabilization
of the liquid bridge against oscillations. Pure elastic adsorption layers are not able to stabilize the liquid bridge. The
mechanism of the stabilizing action is discussed.
Received: 30 October 2000/Revised: 12 February 2001/Accepted: 14 February 2001 |
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Keywords: | Slide coating process Gelatin Surfactant Binding isotherm Surface dilational properties |
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