Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1997-01-29
2003-12-09
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S143000, C428S913000, C428S167000, C428S171000, C428S220000, C428S332000, C428S338000, C264S284000, C264S293000, C427S180000
Reexamination Certificate
active
06660363
ABSTRACT:
The present invention pertains to self-cleaning surfaces of objects and a process for producing same wherein the self-cleaning is preferably effected by the surfaces being exposed from time to time to rain or moving water.
The cleaning of the surfaces of objects is of considerable technical and economical importance, partly for optical and aesthetical reasons, partly for technical reasons, particularly in the case of transparent surfaces which must be cleaned from time to time for preserving their function.
There was no lack of attempts to provide technical surfaces which are dirt-repellent and/or self-cleaning with the aid of rain or moving water. The success of these efforts has been relatively small, however, since the properties of such surfaces are maintained only for a relatively short period of time. Thus, the manufacturers of polymer sheets or polymer boards have tried to solve this problem by producing surfaces which are as smooth as possible and turning these surfaces either extremely hydrophobic or extremely hydrophilic. Examples thereof include surfaces made of extremely hydrophobic Teflon, or the extremely hydrophilic “no-drop coatings” from which water and dirt can flow off without forming drops.
CH-PS-26 82 58 describes water-repellent surfaces which exhibit a contact angle with water of more than 120°. They are obtained by applying powders, such as china clay, talc, clay or silica gel, on a substrate, the powder being first hydrophobized by organic silicon compounds. The application is performed together with curable resins or from solutions in organic solvents. Permanently hydrophobic surfaces cannot be produced in this way. Also, there are no indications as to the grain sizes or grain size distributions of the powders. The properties of the surfaces thus obtained are compared with those of the leaves of nasturtium. With this comparison, it should be noted that it was neither known nor technically analyzable whereon the properties of the leaf surface of nasturtium are based. Studies recently performed have shown that nasturtium has an extremely fine ultrastructure with structural elements smaller than 2 &mgr;m. Such surface structures can hardly be generated artificially, and moreover are extremely sensitive mechanically. Thus, nasturtium is a very unsuitable model. Therefore, such structures are not the subject matter of the present invention.
DE-PS-10 23 217 describes a mold for the preparation of molded parts having rough surfaces. The mold is to serve for the preparation of molded parts made of rubber or plastic and having rough surfaces. To achieve this, the walls of the mold are coated with coarse corundum powder and a stoving paint. The molds yield products having occasional depressions and therefore improved adhesive properties. The usual vulcanization skin is even omitted. The surfaces thus obtained are well inscribable, for example. Thus, the products are surely not self-cleaning with moving water.
JP-A-3-174279 (abstract) describes a process for the preparation of matt, decorative surfaces on paper or plastic sheets. They are prepared with paints which are preliminarily cured by means of ionizing radiation and in which unspecified patterns are stamped in an unspecified way. Then, they are completely cured by further irradiation.
Many years' studies by the Applicant have shown that the surfaces of certain plants are capable of cleaning themselves by rain or moving water and that also no solid dirt particles can be permanently deposited on such surfaces. These dirt-repellent properties have for a long time been assigned to various wax layers on the plant surface. However, more detailed examinations have meanwhile shown that the capability of self-cleaning of the plant surfaces is not so much dependent on the kind of wax, but on the surface structure of such waxes. Further examinations have shown that the capability of self-cleaning can in many cases be destroyed by the use of detergents in the water since this leads to an alteration of the wax particles.
The further detailed examinations of the Applicant have now yielded the surprising result that it is technically possible to artificially render the surfaces of objects self-cleaning by artificially providing them with a surface structure of elevations and depressions, taking care that the distances between the elevations of the surface structure are in the range of from 5 to 200 &mgr;m, preferably from 10 to 100 &mgr;m, and the heights of the elevations are in the range of from 5 to 100 &mgr;m, preferably from 10 to 50 &mgr;m, and taking care that these elevations consist of hydrophobic polymers or permanently hydrophobized materials, and taking care that the elevations cannot be detached by water or by water containing detergents.
Such self-cleaning surfaces can be prepared either by creating the surface structures already in the preparation from hydrophobic polymers, or by creating them subsequently, either by subsequent stamping or etching, or by glueing thereon a powder of the hydrophobic polymers. Finally, it is possible to create such self-cleaning surfaces of objects by subsequent permanent hydrophobizing of preliminarily prepared surfaces having the desired structures. One possibility for the subsequent permanent hydrophobization is subsequent silanization of preliminarily prepared surfaces having the desired structures. Silanization can be performed on all materials which are per se hydrophilic, but which are capable of reacting with the reactive groups of silanes so that the surface ultimately consists of the hydrophobic residues of the silanes.
Of particular technical importance are self-cleaning surfaces of objects which are transparent and which are to retain this transparency for a long time for optical, aesthetical or technical reasons. In particular, these are transparent glassworks of buildings, vehicles, sun collectors etc. Also of economical and technical importance, however, is the preparation of self-cleaning surfaces of house facades, roofs, monuments and tents, and of inner linings of silos, tanks or pipelines which either contain aqueous solutions or can readily be cleaned by moving water without leaving any residues. Also of interest are the outer coatings of vehicles, such as cars, trains or airplanes. It is to be taken care then, however, that these surfaces, when cleaned with moving water, must not be exposed to high mechanical strains since this would result in a leveling or polishing of the surface structures so that they become shining, but lose their capability of self-cleaning.
In order to create the desired surface structures in the preparation from hydrophobic polymers already, the objects can from the start be prepared in molds which have the negative of the desired surface structure. Further, it is possible to apply the hydrophobic polymers in the form of solutions and/or dispersions which result in the desired surface structures when drying and curing. Such structures are generated, for instance, from self-organizing polymers, or under conditions as are per se known from the preparation of matt finish paint surfaces.
If it is not possible or not desired to create the desired surface structures from the beginning, this can also be done later, for example, by subsequent stamping or etching. Stamping can be performed, for instance, by heated or heatable forming punches. Etching can be performed with the known means of chemical etching, or by physical methods, such as ion etching with oxygen or other bombardments which lead to a roughening of the surface and thus to a suitable surface structure according to the invention.
Further, it has been shown that it is also possible to obtain the desired surface structure by glueing a powder of the hydrophobic polymers. Powders of hydrophobic polymers having the desired grain sizes are available. Optimum results are only achieved, however, if powders are employed having a relatively narrow grain size distribution.
It could not have been foreseen that the surface structures according to the invention having elevations and
Jacobson & Holman PLLC
Watkins III William P.
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