Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2000-04-10
2002-05-07
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S429000, C428S446000, C428S447000, C427S162000, C427S163100, C427S164000, C427S167000
Reexamination Certificate
active
06383642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of substrate materials, especially transparent substrates, which have hydrophobic/oleophobic properties with the objective of achieving certain rain-proof/dirt-proof effects. For this purpose, such a substrate is provided, for example, with a coating considering the particular application, out of many applications, in which the substrate is to be used, such as glazing materials for aeronautical, sea-going or overland (railroad, highway) transportation vehicles, for buildings (windows), for urban fixtures (billboards, Abribus, etc.) or for interior appointments (decorative panels, furniture), electrical appliances (refrigerator doors, oven doors, windows, etc., glass ceramic plates), cooking utensils, sanitary fixtures (wash basins, bathtubs, etc.), construction materials, etc.
2. Discussion of the Background
Substrates which have been used in the past for various applications may or may not be transparent and generally have been glass, ceramic, glass ceramic, metal, plastic material (polymethyl methacrylate (PMMA), polyvinylbutyral (PVB), polycarbonate (PC) or polyurethane (PU), thermoplastic ethylene/vinyl acetate copolymer (EVA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate/polyester copolymers, cycloolefin copolymers of the ethylene
orbornene and ethylene/cyclopentadiene type, ionomeric resins such as an ethylene/methacrylic acid copolymer neutralized by a polyamine, thermosetting or thermally crosslinkable compounds such as polyurethane, unsaturated polyester (UPE), ethylene/vinyl acetate copolymer, and the like., or a combination of a plurality of such materials.
The hydrophobic/oleophobic property referred to relates to the fact that polar and nonpolar liquids do not adhere to a substrate to form a troublesome film. A substrate with this property will have little or no tendency to retain dust or dirt or any kind, fingerprints, insects, and the like.
The presence of water and/or dirt on the substrate results in an unesthetic appearance and, in certain cases, to a reduction of transparency of the substrate, as well as to a change of visibility through the substrate. Such effects are particularly troublesome when the substrate is a glazing material used in the transportation field.
The hydrophobic/oleophobic, or non-wettability, property of a substrate is based on the fact that the contact angles between a liquid and a given substrate are high, at least 90° C. in the case of water, for example. The liquid then tends to flow easily over the substrate in the form of drops, by simple gravity, if the substrate is inclined or under the effect of aerodynamic forces in the case of a moving vehicle. Known agents for imparting this hydrophobic/oleophobic property are, for example, fluoroalkylsilanes such as described in European Patent Application Nos. EP 0 492 417, EP 0 492 545 and EP 0 672 779.
Common hydrophobic/oleophobic agents include, in particular, the alkyltrihalosilanes and trialkoxysilanes in which the alkyl group has at least one perfluoro terminal group, or in other words a group comprising F
3
C—(CF
2
)
n
—, in which n is a positive integer or zero, as described in European Patent Application No. EP 0 719 743.
The hydrophobic/oleophobic agents are applied in known manner in solution by standard deposition methods, with or without heating.
One of the most pressing problems in this area of technology is that of the durability of the hydrophobic/oleophobic coating. Such coatings, in fact, have been affected by erosion, which never fails to occur to some extent, for example, during the indispensable operations of periodic cleaning of the substrate, when it is transparent, in order to restore satisfactory visibility through the substrate. There is, therefore, constant motivation to slow the progressive removal of hydrophobic/oleophobic coatings of the cited type, which occurs, in particular, because of the action of windshield wipers, all the more so because such removal can also result by degradation of the coating by ultraviolet radiation.
Heretofore, two main methods have been examined with a view to increasing the durability of coatings while limiting the effects of erosion. These two methods both involve increasing the adhesion of coatings to substrates.
In the first approach as described in European Patent Application No. EP 0 484 746, a substrate is preliminarily treated with a primer of the tetrahalosilane or tetraalkoxysilane type.
In the second approach as described in European Patent Application No. EP 0 497 189, irregularities of dimensions between 1 and 10 microns, for example, are created on the substrate surface either by deposition of particles or by various etching processes such as chemical treatment or sandblasting.
Another commonly observed phenomenon is the progressive disappearance of the hydrophobic/oleophobic property under the effect of prolonged exposure to ultraviolet radiation, which more or less destroys the hydrophobic/oleophobic coatings.
It is further pointed out that, in all cases, reestablishment of a new hydrophobic/oleophobic coating to remedy the erosion of the previous coating does not pose any particular difficulty. Treatments of old coatings can be done, after such a coating has been briefly cleaned. Nevertheless, the merit of postponing this operation as long as possible remains obvious. A need, therefore, continues to exist for hydrophobic/oleophobic coatings of increased durability.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a different technique which is capable of achieving hydrophobic/oleophobic coatings of improved durability, especially under exacting conditions of solid friction and exposure to ultraviolet radiation.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained in a process for the formation of a hydrophobic/oleophobic coating on a substrate, which comprises:
ionizing at least one precursor during deposition on a substrate, while during deposition the substrate temperature decreases from a temperature above 80° C. to a temperature below 80° C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The technique of the present invention makes it possible to form coatings in thin and homogeneous layers with great adhesion to a substrate, while permitting the refractive index of the coated substrate to be adjusted as desired by judicious choice of the precursor or precursors employed in any given coating process, in particular to a value almost identical to that of the glass.
Accordingly, an advantageous embodiment of the present process is that the prepared product is transparent and has the optical qualities of a glazing material. The substrate comprises glass or a plastic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC), coated if necessary with a primer, especially based on silica, to favor adhesion of the overlying coating. The said precursor is a silicon compound. An organometallic precursor, alone or in combination with one or more other precursors, especially silicon-containing compounds as mentioned above, is also a suitable. A particularly suitable and appropriate compound, for example, has proved to be one containing tin oxide groups distributed in a carbon chain.
The following compounds are eminently satisfactory as silicon-containing precursors:
a silane such as tetramethylsilane or hexamethyldisilane;
an alkoxysilane such as an alkoxytrialkylsilane in which the alkyl group is a methyl, ethyl, propyl or isopropyl group, methyl being preferred;
fluorosilane, especially a perfluoroalkylalkyltrialkoxysilane or a perfluoroalkylalkyltrihalosilane;
a siloxane such as hexamethyldisiloxane;
a silazane such as hexamethyldisilazane;
and derivatives thereof.
The precursor is preferably introduced into a chamber in which pulses having a frequency from 10 kHz to 10 GHz and a power from 100 to 2000 W are created for a substrate surface area of 0.4 M
2
w
Bernard Claude
Le Bellac David
Kiliman Leszek
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobain Vitrage
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