Stock material or miscellaneous articles – Surface property or characteristic of web – sheet or block – Surface modified glass
Reexamination Certificate
2001-10-15
2003-11-18
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Surface property or characteristic of web, sheet or block
Surface modified glass
C428S409000, C428S429000, C428S447000, C428S450000, C428S696000, C427S276000, C427S355000, C427S387000, C427S256000
Reexamination Certificate
active
06649266
ABSTRACT:
The present invention relates to substrates provided with a microstructured surface, to methods of producing them, and to their use as what are known as easy-to-clean systems having dirt repellency properties.
The cleaning of surfaces is time-consuming and costly, and there is therefore great economic interest in giving surfaces dirt repellency properties. Adhesion mechanisms are generally governed by surface-energy parameters between the two contacting surfaces. As a general rule, the systems attempt to lower their free surface energy, generally by means of polar or chemical interactions. Where the free surface energies between two components are already inherently very low, it may generally be assumed that the adhesion between these two components will be weak, since the sum of the low free surface energies is low. What is important in this case is the relative lowering of the free surface energy. In the case of pairings with a high and a low surface energy, a very important factor is the possibilities for interaction. For example, when water is applied to hydrophobic surfaces, it is not possible to induce any marked lowering of the surface energy. This is evident from the fact that the wetting (determination of the surface angle &THgr; at the triple point) is poor. Perfluorinated hydrocarbons, such as Teflon, have a very low surface energy but at the same time have virtually no possibilities of interaction with any other substances whatsoever, whether they be polar or non-polar. Accordingly, hardly any components whatsoever adhere to such surfaces, and components which have deposited on such surfaces can be removed again very easily. This dirt repellency effect is also termed the easy-to-clean effect.
Nevertheless, such arrangements do not make it possible to suppress the van der Waals interactions, which generally are always active. Accordingly, the adhesion of a component to such a surface is defined substantially by the contact area: in other words, the smaller the contact area, the less the adhesion.
Nature makes use of this phenomenon in order to achieve very low levels of adhesion with respect to water. Thus cabbage leaves, for example, or else fruit, are covered by small wax bumps which, in the non-wetting case, as is the case with wax, very greatly reduce the van der Waals contact area of a water droplet and thus generally cause the water droplets to roll off. Where particles of dirt or dust are enclosed in these water droplets, they roll off too. Faced with wetting components such as oils or surfactants, however, such surfaces react conversely: as a result of the enlargement of the surface, the van der Waals interface is very greatly enlarged and the adhesion is increased. For this reason, such arrangements cannot be used in practice as easy-to-clean systems, since in the face of fats and oils, which cause strongly adhering soiling, they are completely unsuitable and rapidly become soiled specifically on account of their large area. For this reason, the “lotus effect” (wax excretions of this kind occur on lotus leaves as well), which has been widely discussed in recent times, is incapable of solving this problem. Moreover, the abrasion resistance would be inadequate for practical purposes.
The object of the present invention is to furnish substrates provided with a microstructured surface which exhibit dirt repellency properties even with respect to wetting components such as oils, fats or surfactants and which can be used in practice as easy-to-clean systems.
The invention provides substrates which are provided with a microstructured surface and whose surface layer
(a) comprises a composition comprising condensates of one or more hydrolysable compounds of at least one element M from main groups III to V and/or transition groups II to IV of the Periodic Table of the Elements, at least some of these compounds containing not only hydrolysable groups A but also non-hydrolysable, carbon-containing groups B and the total molar ratio of groups A to groups B in the parent monomeric starting compounds being from 10:1 to 1:2, from 0.1 to 100 mol % of the groups B being groups B′ containing on average from 5 to 30 fluorine atoms which are attached to one or more aliphatic carbon atoms distanced from M by at least two atoms, and
(b) has a microstructuring of such kind that the contact angle with respect to water or hexadecane is at least 5° higher than the contact angle of a corresponding smooth surface.
The invention further provides a method of producing such substrates provided with a microstructured surface, characterized in that either
(a) the coating composition applied to the substrate for the surface layer, before or during its drying and/or curing, is embossed with an embossing die which has a non-polar and/or low-energy surface, or
(b) the surface-layer composition includes nanoscale inorganic particulate solids or agglomerates having a particle size of at least 50 nm.
The substrates of the invention provided with a microstructured surface are suitable for use as easy-to-clean systems and, even when soiled by oily, fatty or surfactant substances, can be entirely regenerated again by simple rinsing with plain water. A further substantial advantage is that transparent or translucent surface layers can be produced.
FIG. 1
shows the adhesion properties of different substances on a surface as a function of the composition and structure. The unhatched droplets represent a water droplet without constituents and the hatched droplets represent oil or surfactant-admixed water.
Accordingly,
FIG. 1
shows that a water droplet adheres to a hydrophobic surface (a) but rolls off from a microstructured hydrophobic surface (b). An oil or surfactant/H
2
O droplet adheres very firmly to a microstructured hydrophobic surface and cannot be removed with water (c). In contrast, an oil or surfactant/H
2
O droplet adheres more weakly (d) to a microstructured surface of the invention and can be removed easily with plain water (e). In (f) a clean surface is shown.
By a microstructured surface is meant here, in general terms, a surface which, within a small observed two-dimensional element, is not smooth and even but instead has elevations (pixels) or indentations. For example, in each square millimeter of surface area there may be several thousand to several million pixels having a structural height of, for example, 20 nanometers or more up to one or more (e.g. 4) micrometers (measured by atomic force microscopy—AFM). The pixel spacing in this case may be, for example, from 50 to 100 or several hundred nm. Alternatively, for example, the microstructuring may be in the form of whiskers protruding from the surface.
Wetting is the ability of liquids to form an interface with solids. The wetting tendency may be derived from the contact angle formed between liquid and solid. The larger the contact angle, the lower the tendency of the liquid to wet the solid.
The surface of the substrates of the invention has a microstructuring of such kind that the contact angle both with respect to water and with respect to hexadecane is at least 5°, preferably at least 10°, higher than the contact angle of a corresponding smooth surface. In this case, the contact angle of the microstructured surface with respect to water is preferably at least 120°, while the contact angle with respect to hexadecane is preferably at least 70°. In accordance with the invention it is, surprisingly, possible to achieve contact angles with respect to water of up to 170° or more and at the same time to achieve hitherto unattained contact angles with respect to hexadecane of up to 120° or more.
The coating composition used in accordance with the invention may be applied to virtually any desired substrate. Examples include metals, glass, wood, paper, textiles, carpets, ceramic, plastics, but also building materials such as plasters, screeds, cements, putties, bricks, (natural) stone, porous building materials, insulating materials, and bulk products, powders, granules, etc. Examples that may be mentioned of metals include copp
Gross Frank
Mennig Martin
Oliveira Peter W.
Schmidt Helmut
Sepeur Stefan
Feely Michael J
Heller Ehrman White & McAuliffe LLP
Institut für Neue Materialien gemeinnützige GmbH
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