Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-02-26
2001-10-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S432000, C428S447000, C428S372000, C428S149000, C428S148000, C428S142000, C428S401000, C427S165000, C427S163100, C427S201000, C427S292000, C427S309000
Reexamination Certificate
active
06299981
ABSTRACT:
The invention relates to substrates, in particular transparent substrates, on which it is desired preferably to confer the properties of hydrophobicity/oleophobicity or of hydrophilicity/oleophilicity with a view to obtaining certain anti-rain/anti-stain or anti-mist effects, respectively. To this end, these substrates are, for example, provided with coatings within the context of the manufacture of glazing for various applications, such as the windows for transportation vehicles or for buildings.
It is known to incorporate the functions of hydrophobicity/oleophobicity or of hydrophilicity/oleophi-licity on the surface of substrates of various types. Both these functions concern the wettability of the substrates.
The hydrophobicity/oleophobicity property of a substrate occurs when the contact angles between a liquid and this substrate are high, for example about 120° in the case of water. The liquid then tends to flow readily, in the form of drops, over the substrate, simply by gravity if the substrate is inclined, or due to the effect of aerodynamic forces in the case of a moving vehicle. Known agents for conferring this hydrophobicity/oleophobicity property are, for example, fluorinated alkylsilanes such as those described in Patent Application EP-A1-0,675,087. They are applied in a known manner in solution using conventional methods of deposition, with or without heating.
In contrast, the hydrophilicity/oleophilicity property of a substrate is manifested by small contact angles between a liquid and this substrate, of about 5° in the case of water on clean glass. This property is conducive to the formation of thin transparent liquid films, to the detriment of that of mist, consisting of minute droplets impairing visibility through a transparent substrate. Many hydrophilic agents, in particular those containing hydroxyl groups, such as poly(hydroxyalkyl (meth)acrylate) polymers, are used for this purpose, in a known manner, for transparent substrates. Some compounds, called photocatalytic compounds, such as TiO
2
, are moreover used, in particular in combination with glass substrates, not only for their hydrophilic character after exposure to light but also for their ability to decompose stains of organic origin by a process of radical oxidation. It is known to deposit coatings with a photocatalytic property, comprising TiO
2
, starting with at least one titanium precursor, if necessary in solution, by liquid-phase pyrolysis, by a sol-gel technique or by chemical vapour deposition.
In accordance with the foregoing, the property of hydrophobicity/oleophobicity is quantitatively assessed by measuring the contact angle formed, most often by a drop of water, on a given substrate. In the absence of further information, this contact angle is measured on a horizontal substrate. In reality, as already mentioned above, it is the dynamic behaviour of drops of liquid which is targeted by the action of conferring hydrophobicity on a substrate. This applies equally well to approximately vertical static substrates, such as exterior windows of buildings or the glazing panels used in showers, as to the windows of transportation vehicles. However, in the case of a drop of liquid on a substrate which is inclined to the horizontal, two different contact angles are observed—the advancing contact angle and the receding contact angle, these being determined at the front and rear, respectively, of the drop with respect to the direction in which it is moving. These angles are values reached at the limit of detachment of the drop. The difference between the advancing contact angle and the receding contact angle is called hysteresis. A drop of water having a high hysteresis or a small receding contact angle will have difficulty in flowing over a substrate. Thus, it may easily be understood that effective hydrophobicity is dependent both on a high advancing contact angle and a low hysteresis.
In this regard, the inventors have specifically obtained excellent results never yet achieved until now. Exceptionally easy and rapid flow of drops of liquid, more specifically of water, has been obtained over a substrate according to the invention, which was subjected beforehand to a hydrophobic treatment. What is more, they were able to verify that the measurements provided in accordance with the invention make it possible, at the very least, to preserve, or even increase, the effects of a hydrophilic treatment applied to a substrate.
According to the invention, this essential objective, consisting in accentuating the hydrophobicity/oleophobicity or hydrophilicity/oleophilicity properties of a substrate, is achieved with a substrate on which irregularities of submicron size have been formed, the sizes of these falling, almost in their entirety, into at least two different classes, the respective representative values of which vary by a factor of at least 5 or of at most 1/5.
A particularly advantageous variant is characterized by the existence of two classes of different sizes, as just defined, the representative values of which vary respectively by a factor of at least 100 or of at most 1/100.
In order to preserve the optical properties, in particular of a transparent substrate, the sizes of the irregularities preferably do not exceed 150 nm, so as to avoid or limit the appearance of diffuse transmission of light.
The irregularities form a bumps-and-hollows relief on the substrate and correspond in general, to a greater or lesser extent, to regular geometric shapes having any orientation with respect to the substrate. The term “bumps and hollows”, used to define the subject of the invention, must be understood in the broad sense as simply meaning, respectively, the presence and the absence of material. The sizes of the irregularities, in the sense of the invention, thus correspond substantially to the diameters of spheres or cylinders, to the heights of cylinders or to the sides of polyhedra, these being oriented, with respect to the plane of the substrate, perpendicular to the latter, parallel to it or in any direction. These sizes may also correspond to the dimensions of a hollow, in particular to the space between two protuberances or to the depth of such a hollow.
According to a first embodiment, the irregularities consist, entirely or partly, of objects incorporated into the surface of the substrate and are each defined by at least two dimensions falling into different classes, as defined above. These objects may be different or identical, but advantageously they consist of identical rods having a single orientation, in particular an orientation perpendicular to the plane of the substrate, or having many orientations.
According to a second embodiment, the bumps-and-hollows relief of the substrate is formed, entirely or partly, by relatively small-size objects which are grafted onto objects falling into a class of larger sizes, in the sense of the invention. Of course, it is necessary to spread out the objects of larger sizes sufficiently well over the substrate in such a way that they do not form a compact cluster in which it is no longer possible to discern their individual size. The same applies to the small-sized objects.
In a third embodiment, differing only slightly from the previous one, the surface irregularities of the substrate consist of agglomerates of relatively small objects, which form objects falling, of course, into a class of larger sizes. As in the previous case, it is important for all the objects to be arranged so as to reveal at the same time the two orders of irregularity sizes. In particular, it is necessary for the small objects in the external layers of the agglomerates to be sufficiently spaced apart.
Within the context of the invention, the substrate, provided with its coating, is advantageously transparent; it may be based on glass or on a plastic such as poly(methyl methacrylate) (PMMA), polyvinyl butyral (PVB), polycarbonate (PC) or polyurethane (PU).
According to an advantageous characteristic, the irregularities are created on the surface of the substrate by forming a textu
Azzopardi Marie-Jose
Delattre Laurent
Talpaert Xavier
Boss Wendy
Jones Deborah
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobain Vitrage
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