Coated transparent substrate making fingerprints invisible

Abstract

Coated transparent substrate (1) making fingerprints invisible, comprising a transparent substrate (2), in particular made of glass, and a so-called external coating (3) which has a contact angle with water of greater than 70 degrees and is oleophilic, characterized in that the external coating (3) has a refractive index of less than 1.5, preferably between 1.3 and 1.4, in particular between 1.34 and 1.38, and most preferably between 1.34 and 1.36.

Description

Description Title of the invention: Coated transparent substrate rendering fingerprints invisible

[0001] The invention relates to a transparent substrate comprising a coating that renders fingerprints invisible.

[0002] The invention will be described more particularly for a glass substrate but can be applied to a plastic substrate.

[0003] It is known to coat a glass substrate with an anti-reflective coating formed by alternating low-index and high-index layers, and then to add a hydrophobic and oleophobic coating. However, although the amount of sebum deposited by a fingerprint is minimized due to the oleophobic properties of the substrate, the remaining sebum droplets remain visible.

[0004] Another solution is to apply a hydrophobic and oleophilic coating to the glass. Fingerprint residue remains, but spreads across the surface like a film, reducing its visibility. However, the application of such a coating is not yet entirely satisfactory, as fingerprints remain visible because the refractive index contrast between the glass surface and the fingerprints remains significant at certain viewing angles.

[0005] The invention therefore aims to provide an improved solution of a coated transparent substrate that makes fingerprints invisible, which does not have the aforementioned disadvantages.

[0006] According to the invention, the coated transparent substrate, with its invisible fingerprint property, comprises a transparent substrate, particularly made of glass, and an external coating (the coating intended for direct contact with the external environment and onto which fingerprints will be applied), having a contact angle with water greater than 70 degrees and being oleophilic. An "oleophilic coating" is defined as a coating having a contact angle with sebum of less than 20°, preferably less than 15°, or even less than 10° after stabilization of the substrate / sebum / air triple line. Furthermore, the external coating of the coated transparent substrate has a refractive index of less than 1.5, preferably between 1.3 and 1.4, particularly between 1.34 and 1.38, and even more preferably between 1.34 and 1.36.

[0007] The contact angle of a water droplet at equilibrium on a flat surface can be conventionally measured using a goniometer on a 3-microliter water droplet. The droplet is observed using a high-speed camera that takes photographs from which the data is then recorded. The contact angle. The higher the contact angle value, the more hydrophobic the surface of the sample being tested is.

[0008] Similarly, the contact angle with sebum can be measured in the same way, this time using a drop of sebum. The lower the contact angle value obtained, the more oleophobic the surface of the tested sample.

[0009] The substrate may be made of glass. The substrate may be coated with a reflective metallic layer with a mirror-like function and, over this metallic layer, comprises the external coating of the invention. Alternatively, the substrate may be made of plastic.

[0010] The inventors have shown that it is unexpectedly essential to adapt not only the contact angle, and therefore the wetting, relative to the external surface of the substrate, but also the refractive index of this external surface. The appropriate combination of wetting and refractive index minimizes the visibility of a fingerprint. Thus, the fingerprint, although present, is rendered invisible or nearly invisible. The inventors have therefore demonstrated that it is necessary to combine two characteristics simultaneously: firstly, sufficient wetting to allow the fingerprint to spread (the coating being oleophilic), and secondly, a reduction in the refractive index of the external coating relative to the refractive index of the substrate. Preferably, the refractive index of the external coating is between 1.34 and 1.36 (to be equivalent to the refractive index of human sebum).This configuration of the coated substrate's outer surface allows, when sebum from a fingerprint has been deposited, a reduction in the reflectivity contrast between the sebum-covered area and the substrate (uncovered by sebum), drastically minimizing the fingerprint's visibility, or even rendering it invisible. Furthermore, the substrate coated with the invention's coating has proven to be significantly easier to clean.

[0011] According to a first embodiment, the external coating forms a monolayer; the composition of the monolayer coating is adapted to provide, in combination, a water contact angle greater than 70 degrees, oleophilic properties, and a refractive index less than 1.5, preferably between 1.3 and 1.4, in particular between 1.34 and 1.38, and even more preferably between 1.34 and 1.36. In the context of the present invention, all refractive indices are measured at 550 nm. A monolayer coating has the advantage of improving the durability of the layer. The thickness of the monolayer is, in particular, on the order of micrometers. The thickness of the monolayer is notably greater than 1 pm and less than 8 pm, preferably between 3 and 5 pm.

[0012] In particular, the outer coating monolayer is a hybrid silica layer based on silane(s), hollow silica beads, and an organosilane-type additive. Specifically, the outer coating monolayer is a hybrid silica layer based on tetraetoxysilane (TEOS) and methyltriethoxysilane (MTEOS), comprising hollow silica beads and an organosilane-type additive. The organosilane-type additive represents, in particular, between 0.005% and 3%, preferably between 0.1% and 1%, of the total components of the layer (excluding the beads). Specifically, the hollow silica beads are on average less than 100 nm in size, preferably less than 20 nm. Specifically, the volume proportion of the beads is between 10% and 50%, preferably between 20% and 40%.For example, TEOS and MTEOS are mixed in a solvent such as 1-methyl-2-propanol and an aqueous solution of pH 2 acidified with HCl. An organosilane additive, such as the commercial product KY-1604 from Shin-Etsu Silicones or InvisiPrint® from NBD Nanotechnologies, is added, typically between 0.005% and 3%, preferably between 0.1% and 1% of the total components of the layer (excluding the beads), along with the porous beads themselves. The volume proportion of pores (volume proportion of pore-forming agents) is therefore typically between 10% and 50%, preferably between 20% and 40%. The porosity of the layer constituent can, for example, be verified by pycnometry.

[0013] According to a second embodiment, the external coating comprises a first layer facing the substrate, called the inner layer, capable of reducing the refractive index of the coated substrate compared to the refractive index of the substrate alone, and a second layer, called the outer layer, which is disposed (directly) on the inner layer and is in contact with the external environment, the outer layer having a contact angle with water greater than 70 degrees and being oleophilic.

[0014] According to a feature of the second embodiment, the inner layer (first layer) of the outer coating is a porous layer. Advantageously, the porous layer allows control of the refractive index of the entire outer coating, and in particular allows lowering the refractive index relative to that of glass, without weakening light transmission. According to a feature of the second embodiment, the porous layer has a thickness adapted so as to fall outside the thickness range that generates colored interference in the visible spectrum. in particular the porous layer has a thickness of at least 1 pm.

[0015] According to a feature of the second embodiment, the porous layer is hybrid, preferably based on an organosilane, or is organic, preferably based on a polymer, and the porous layer incorporates porogenic agents which are of a mineral nature, preferably hollow silica beads.

[0016] In particular, the porous layer is closed-pore. The pores have a submicron dimension, specifically less than 100 nm on average, preferably less than 20 nm. Preferably, the pores have a defined shape, preferably substantially spherical or oval. The surface of the pore-forming agent can be either rough or smooth. The fabrication of a porous layer is known per se.

[0017] In particular, the porous layer exhibits a substantially homogeneous distribution throughout its thickness, from the interface with the substrate to the interface with the external layer. The volume proportion of pores (volume proportion of pore-forming agents) is specifically between 10 and 50%, preferably between 20 and 40%. The porosity of the constituent of said layer can, for example, be verified by pycnometry.

[0018] Numerous chemical elements can form the basis of the hybrid porous layer. The porous layer may include, as an essential constituent material, at least one compound of at least one of the following elements: Si, Ti, Zr, Al, or W, Sb, Hf, Ta, V, Mg, Mn, Co, Ni, Sn, Zn, Ce. This may include a simple or mixed oxide of at least one of the aforementioned elements. The hybrid portion is obtained by using an organosilane in the formulation, for example, 3-(2,3-epoxypropoxy)propyltrimethoxysilane (GLYMO) or (3-aminopropyl)triethoxysilane (APTES), or their derivatives.

[0019] We can thus choose silica produced from tetraetoxysilane (TEOS), hybrid materials obtained from organosilane-type precursors whose general formula is R2 nSi(ORl)4-n, where n is an integer between 0 and 2, RI is an alkyl group of the type CxH2x+1, and R2 is an organic group including, for example, an alkyl, epoxy, acrylate, methacrylate, amine, phenyl, or vinyl group. These hybrid compounds can be used alone or in mixtures, in aqueous solution or in a water / alcohol mixture at an appropriate pH.

[0020] According to a feature of the second embodiment, the inner layer of the outer coating, which is a porous layer, has in particular a thickness between 1 and 10 pm.

[0021] According to a feature of the second embodiment, the outer layer of The external coating has a molecular thickness between 10 and 20 nm (on the order of 10 to 20 nm).

[0022] According to a feature of the second embodiment, the outer (oleophilic) layer of the outer coating is a silane (which bonds very well to glass), in particular an alkylsilane. Examples of alkylsilanes include alkylsilanes, alkylthiols, alkylphosphonates, and alkylcarboxylic acids, in which the alkyl group has at least one terminal alkyl group, i.e., one consisting of an H3C—(CH2) group. n , where n is zero or a positive integer.

[0023] According to a feature of the second embodiment, the outer layer of the external coating is deposited by spraying or dipping or thermal evaporation.

[0024] According to one characteristic, the substrate is glass, silica-based glass, soda-lime, preferably silicosodocalcium, or even aluminosilicate, or borosilicate.

[0025] When the substrate is glass, it can be between 2 and 10 mm thick. The substrate thickness will be adapted to the intended use.

[0026] The substrate can be flat or curved.

[0027] The transparent substrate coated with invisible fingerprints can be used in a vehicle, especially a motor vehicle, or in the building (indoors or outdoors) and in furniture, especially for glass surfaces of glass doors, glass partitions, etc.

[0028] The present invention is now described using a purely illustrative and in no way limiting example of the scope of the invention, and from [Fig. 1] which represents a cross-sectional view of an example of an embodiment of a coated substrate according to the invention with invisible fingerprint properties.

[0029] The coated substrate 1 of the invention illustrated in Figure 1 has invisible fingerprint properties.

[0030] The coated substrate 1 comprises a transparent substrate 2 and an external coating 3 deposited on the substrate 2 and in contact with the external environment. The transparent substrate 2 is made of glass or plastic. In the examples described later, the transparent substrate 2 is made of glass. The external coating 3 is designed to render fingerprints invisible.

[0031] According to the invention, the external coating 3 has the following combined characteristics: it has a contact angle with water greater than 70 degrees, it is oleophilic, and it has a refractive index of less than 1.5, preferably including between 1.3 and 1.4, in particular between 1.34 and 1.38, and even more preferably between 1.34 and 1.36.

[0032] According to a first embodiment, the external coating 3 is single-layer and consists of a composition which provides a contact angle with water greater than 70 degrees, an oleophilic function and a refractive index less than 1.5, preferably between 1.3 and 1.4, in particular between 1.34 and 1.38, and even more preferably between 1.34 and 1.36.

[0033] By way of a non-limiting example for the first embodiment, the external monolayer coating 3 is a hybrid silica layer based on tetraetoxysilane (TEOS) and methyltriethoxysilane (MTEOS) comprising hollow silica beads and an organosilane-type additive such as the commercial product KY-1604 from Shin-Etsu Silicones or the product Invisi-Print® from NBD Nanotechnologies, typically between 0.005 and 3%, preferably between 0.1 and 1% of the total components (excluding the beads). The thickness of the monolayer is in particular greater than 1 µm and less than 8 µm, preferably between 3 and 5 µm.

[0034] According to a second embodiment, such as that illustrated in Figure 1, the external coating 3 comprises a first layer 30, called the inner layer, disposed directly on the substrate 2 and capable of reducing the refractive index of the coating 3, and a second layer 31, called the outer layer, disposed directly on the inner layer 30 and in contact with the external environment. The outer layer 31 has a contact angle with water greater than 70 degrees and is oleophilic. The inner layer 30 functions to reduce the refractive index of the entire coated substrate, and the outer layer 31 has a wetting function.

[0035] By way of a non-limiting example of the second embodiment, the inner layer 30 is a porous layer which is capable of reducing the refractive index of the combination of the inner layer 30 and outer layer 31, and the outer layer 31 has a contact angle greater than 70° with respect to the water and is oleophilic.

[0036] The porous layer (inner layer) 30 advantageously has a thickness between 1 and 10 pm, particularly between 2 and 5 pm, for example 3 pm. This thickness contributes in particular to the absence of contrast between the area of ​​the substrate covered with sebum and the uncovered area, and avoids optical interference effects. The porous layer 30 is designed to lower the refractive index of the outer coating 3 to a refractive index between 1.3 and 1.4, particularly between 1.34 and 1.38, and even more so. preferred between 1.34 and 1.36. The porous layer 30 was for example obtained using a porous hybrid silica matrix, comprising hybrid sol-gel silica SiCh - (3-aminopropyl)triethoxysilane (APTES) with hollow silica spheres less than 100 nm in diameter and occupying a volume of 3 to 50% of the porous layer.

[0037] The outer layer 31 has a thickness of at most 20 nm, particularly between 10 and 20 nm, and especially between 12 and 20 nm. The composition is in the form of a single-molecular-weight layer. The oleophilic outer layer 31 is, for example, a layer resulting from the crosslinking of silanes. The composition is deposited by spraying, dipping, or thermal evaporation. An example of the composition of the outer layer 31 is the commercial product KY-1604 from Shin-Etsu Silicones. The outer layer 31 made of the KY-1604 product has a contact angle of 88° with respect to water.

[0038] Tests were carried out using: 1) of a comparative substrate Cl consisting of a glass substrate without coating; 2) of a comparative substrate C2 of the same glass substrate as substrate Cl and coated with the product Shin Etsu KY-1604 with a thickness of 20 nm; the product Shin Etsu KY-1604 was deposited using a manual gun; 3) of a substrate of the invention S made of the same glass substrate as the substrate Cl and coated by the external coating 3 of the invention comprising according to the second embodiment the porous inner layer 30 which is a TEOS-APTES hybrid layer, of thickness 3 pm, with hollow silica spheres of less than 100 nm in diameter and occupying an air volume of 30% of the layer, and the monomolecular outer layer 31 is the Shin Etsu KY-1604 product with a thickness of 20 nm; the Shin Etsu KY-1604 product was deposited using a manual gun.

[0039] The testing protocol, under reproducible conditions, consisted of: - deposit a fingerprint in the same location on each of the three test substrates, the fingerprint consisting of artificial sebum (such as the commercial product NCZ-APS-0012-20 from Nanochemazone), deposited via a pad at a given application pressure and temperature. The application of the sebum to the pad and then the depositing of the fingerprint by the pad are carried out according to a rigorous protocol in order to obtain maximum repeatability and a consistently identical trace; - to alternately place the substrate with the imprint on a support illuminated with the same lighting. Tests are carried out with, on the one hand, a direct lighting, and on the other hand indirect lighting; - to film the illuminated substrate with or without an imprint at an angle of 5° relative to the direction normal to the plane of the substrate. The relative positions "surface to be measured" / "lighting" / "camera" are fixed.

[0040] Table 1 below summarizes the results of the tests after shooting. [Table 1]

[0041] We can therefore see that the imprint on the comparative substrate Cl is very visible and the imprint on the comparative substrate C2, although less significant, is still visible, while the imprint on the substrate S of the invention is invisible.

[0042] The inventors have thus demonstrated that the substrate of the invention, thanks to its specific external coating 3, allows sebum to spread like a film and drastically reduces, or even eliminates, the contrast between the area coated with the sebum film and the sebum-free substrate. As a result, fingerprints are rendered invisible.

Claims

Demands

1. A transparent coated substrate (1) rendering fingerprints invisible, comprising a transparent substrate (2), in particular made of glass, and an external coating (3) which has a contact angle with water greater than 70 degrees and is oleophilic, characterized in that the external coating (3) has a refractive index of less than 1.5, preferably between 1.3 and 1.4, in particular between 1.34 and 1.38, and even more preferably between 1.34 and 1.

36.

2. Transparent coated substrate according to claim 1, characterized in that the external coating (3) forms a monolayer.

3. Transparent coated substrate according to the preceding claim, characterized in that the monolayer of the external coating (3) is a hybrid silica layer based on TEOS and MTEOS and comprising hollow silica beads and an organosilane-type additive, in particular the organosilane-type additive representing between 0.005 and 3%, preferably between 0.1 and 1%, of the total components of the layer.

4. Transparent coated substrate according to claim 1, characterized in that the external coating (3) comprises a first layer (30) facing the substrate, called the inner layer, capable of decreasing the refractive index of the coated substrate compared to the refractive index of the substrate alone, and a second layer (31) called the outer layer, which is disposed on the inner layer (30) and being in contact with the external environment, the outer layer (31) having a contact angle with water greater than 70 degrees and being oleophilic.

5. Transparent coated substrate according to the preceding claim, characterized in that the inner layer (30) is a porous layer.

6. Transparent coated substrate according to the preceding claim, characterized in that the porous layer (30) is hybrid, preferably based on an organosilane, or is organic, preferably based on a polymer, and the porous layer incorporates porogenous agents which are of a mineral nature, preferably hollow silica beads.

7. A transparent substrate coated according to claim 5 or 6, characterized in that the porous layer (30) comprises a proportion of pore volume between 10 and 50%, preferably between 20 and 40%.

8. Transparent substrate coated according to any one of claims 4 to 7, characterized in that the inner layer (30) has a thickness between 1 and 10 pm and the outermost layer (31) has a molecular thickness between 10 and 20 nm.

9. Transparent substrate coated according to any one of claims 4 to 8, characterized in that the outer layer (31) is a silane, in particular an alkylsilane.

10. Transparent substrate coated according to any one of the preceding claims, characterized in that the substrate is used in a vehicle, in particular a motor vehicle, or is used in building and furniture, in particular for glass surfaces of glass doors, glass partitions.

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