WO2025214995A1

WO2025214995A1 - Hydrophobic coatings for transparent surfaces and processes of producing the same

Info

Publication number: WO2025214995A1
Application number: PCT/EP2025/059547
Authority: WO
Inventors: Phally KONG; Frédéric FONTAINE
Original assignee: Umicore Thin Film Products Ag
Current assignee: Umicore Thin Film Products Ag
Priority date: 2024-04-09
Filing date: 2025-04-08
Publication date: 2025-10-16
Anticipated expiration: 2026-10-09

Abstract

The present invention provides hydrophobic coatings for transparent surfaces and processes of producing the same, whereby the invention is embodied by a transparent multilayer structure, comprising: a transparent substrate having an antireflective coating; a transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating applied onto said transparent substrate; and a hydrophobic coating applied onto the outer layer of said transparent surface coating comprising reactive hydroxyl groups, whereby said hydrophobic coating comprises a fluorine free silicone polymer.

Description

HYDROPHOBIC COATINGS FOR TRANSPARENT SURFACES AND PROCESSES OF PRODUCING THE SAME

TECHNICAL FIELD

The present invention relates to environmentally benign hydrophobic coatings with high water and fat, oil and grease (FOG) repellence on substrates like lenses, while also ensuring optimal light transmission. The invention encompasses a layered approach, typically comprising an anti-reflective coating followed by a durable hydro- phobic layer, to achieve the desired functionality and performance characteristics.

INTRODUCTION

Advances in surface engineering have led to the creation of coatings that significantly reduce the adhesion of contaminants such as dust, water and FOG to transparent substrates such as glass, thereby simplifying the cleaning process and enhancing visual clarity. Focused on improving the user experience, these technologies leverage hydrophobic and oleophobic coatings to repel water and FOG , effectively minimizing smudges and maintaining transparency. Such innovations not only contribute to the durability and longevity of the substrate but also ensure sustained optical performance in varying environmental conditions, marking a pivotal step forward in optical technology.

In this respect, US 2003/0026965 Al discloses a multilayer coating for a transparent substrate, such as glass, plastic, or other transparent material, which increases the durability and weatherability of the substrate. The coating includes a surface-hardening layer of organo-siloxane formed over the substrate. An abrasion-resistant coating comprising a multilayer stack of alternating layers of silicon dioxide and zirconium dioxide is formed over the surface-hardening layer. The multi-layer coating further includes a hydrophobic outer layer of perfluoroalkyl silane formed over the abrasionresistant coating to form an outer moisture-resistant surface. This multi-layer coating configuration increases the abrasion resistance and mechanical strength of the transparent substrate on which it is formed without imparting colour to the transparent substrate. US 2020/0301047 Al discloses a hydrophobic and/or oleophobic coating system for an ophthalmic lens having increased effective thickness and water contact angle. In one embodiment, the hydrophobic and/or oleophobic coating system comprises an anti- reflective coating applied to an ophthalmic lens, the anti-reflective coating comprising alternating layers of high and low index materials with an outer layer of silicon dioxide having exposed hydroxyl groups. A hydrophobic coating is applied to the anti- reflective coating, the hydrophobic coating comprising a silane with a hydrophobic, fluorinated group and fewer than three reactive groups capable of bonding to the exposed hydroxyl groups of the anti-reflective coating.

The use of fluorinated hydrocarbons, however, poses environmental concerns. Therefore, there is a demand for fluorine-free hydrophobic and/or oleophobic coatings that provide a high surface quality and durability.

SUMMARY

The current invention provides a solution for at least one of the above mentioned problems by providing hydrophobic coatings for transparent surfaces, as described in claim 1, and processes of producing the same. The invention provides improved hydrophobic properties for transparent substrates through fluorine-free coatings.

DESCRIPTION OF THE FIGURES

By means of further guidance, figures are included to better appreciate the teaching of the present invention. Said figures are intended to assist the description of the invention and are nowhere intended as a limitation of the presently disclosed invention.

The figures and symbols contained therein have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Figure 1 shows the water contact angle of the different obtained coatings according to Example 1 as a function of effective coating thickness (•) and after abrasion testing (°). DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings:

"A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/- 20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

"Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints. All percentages are to be understood as percentage by weight, abbreviated as "wt.%" or as volume per cent, abbreviated as "vol.%", unless otherwise defined or unless a different meaning is obvious to the person skilled in the art from its use and in the context wherein it is used. In the context of the present invention, the "effective thickness of a thin film" is to be considered synonymous for the term "thickness of a thin film" and is determined using reflectance spectroscopy. A cleaned sample is positioned on a calibrated reflectance spectrometer, which is outfitted with a broad-spectrum light source and a detector. Illumination of the thin film with polychromatic light allows for the capture of the reflected spectrum over various wavelengths. Analysis of this spectrum is conducted using software that applies theoretical models to deduce the optical characteristics of the film. The effective thickness of the film is precisely determined by fitting the experimental data to these models, adjusting for the refractive index and thickness to match observed patterns.

In the context of the present invention, the term "coating" refers to a layer that is applied to the surface of a substrate or an underlying layer. Each coating is intended to completely cover the surface of the layer it is applied onto, ensuring uniform coverage across the entire area. Specifically, the term "outer layer" refers to the topmost coating in the multilayer structure, which is the layer that is exposed to the external environment. For clarity, any reference to the "outer layer" in the claims is intended to mean the coating that is exposed on the surface of the structure, not any partial or internal layer. The coatings are to be applied in a manner that ensures full coverage of the previous layer unless otherwise specified.

In the context of the present invention, the molecular weight of a polymer such as a silicone polymer is to be understood as the number-average molecular weight, and is determined by Gel Permeation Chromatography (GPC), also known as Size Exclusion Chromatography (SEC). Initially, the polymer is dissolved, and the solution is then filtered to eliminate insoluble particles that could affect the analysis. This prepared solution is injected into the GPC system. The elution of polymer fractions is detected using a refractive index (R.I) detector. The molecular weight distribution, including the number-average molecular weight (Mn) and weight-average molecular weight (Mw), is determined by comparing the elution profile with that of known standards.

In a first aspect, the present invention provides a transparent multilayer structure, comprising: i. a transparent substrate having an anti reflective coating; ii. a transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, applied to said transparent substrate; iii. a hydrophobic coating applied to the outer layer of said transparent surface coating.

Specifically, said transparent surface coating comprising reactive hydroxyl groups is applied onto said antireflective coating of said transparent substrate. Specifically, said hydrophobic coating comprises a fluorine-free polymer, such as a silicon polymer. The inventors found that the hydrophobic characteristics of the coating improve with higher molecular weights of the fluorine-free polymer, such as a silicon polymer. Furthermore, the inventors found that hydrophobic characteristics of the coating improve with higher layer thickness of the hydrophobic coating, preferably with an effective thickness of at least 5 nm, or of at least 8 nm, or of 10 nm to 100 nm, as determined by reflectance spectroscopy.

In the context of the present invention, the term "transparent substrate" refers to any solid material capable of allowing light to pass through with minimal distortion or absorption, enabling objects or images to be seen clearly when viewed through the material. Typically, such transparent substrates have a transmission of at least 80%, preferably at least 85% and more preferably at least 90%, as determined in accordance to ANSI Z80.1. Transparent substrates include, but are not limited to, materials such as mineral glasses, sapphire, alumino-silicate glasses and various plastics. Glass substrates with low or high chromatic aberration may include traditional silicate glasses, borosilicate glasses, soda-lime glasses, and other glass compositions known for their clarity and stability. Plastic substrates encompass a range of transparent polymeric materials, including acrylics (such as polymethyl methacrylate), polycarbonates, polyurethanes, and other transparent plastics, which offer versatility in terms of weight, light transmission, impact resistance, and ease of fabrication. Said transparent substrate may have a flat shape or a curved shape, and independent of said shape have a first surface where light enters and a second surface where light exits respective to the light source.

In the context of the present invention, the term "substrate" may refer to the base material of optical elements, which are designed for the correction, protection, or enhancement of vision. This includes, but is not limited to, the lenses in prescription glasses, sunglasses, AR. and VR smart glasses, as well as optical components found in cameras, binoculars, and microscopes. Alternatively, the term "substrate" may refer to a base material engineered to support touch-sensitive functionalities, applicable in devices including but not limited to smartphones, computers, tablets, and other interactive electronic devices. This substrate is characterized by its ability to accurately detect and interpret touch gestures and inputs, and it is typically composed of materials that possess both durability and high optical clarity to facilitate user interaction and display visibility. Materials used for such substrates may include glass, such as chemically strengthened glass or gorilla glass, and transparent conductive polymers, which are selected for their combination of touch sensitivity, scratch resistance, and optical properties that minimize distortion and reflection. Additionally, these substrates are often treated or coated with materials that enhance their conductive, oleophobic, and hydrophobic properties, ensuring the longevity and functionality of the touch screen interface. The term 'touch screen substrate' herein encompasses any such base materials that are employed in the construction of touch- sensitive displays for electronic devices. Further, the term "substrate" may refer to architectural glass, automotive glass and display screens.

In the context of the present invention, the term "anti-reflective coating" refers to a thin film layer or layers applied to the surface of optical elements, designed to minimize the reflection of light at the interface between air and the optical substrate. This coating enhances the transmission of light through the optical element, thereby reducing glare and improving the clarity and contrast of the images perceived through the element. The anti-reflective coating is composed of materials with specific refractive indices that are engineered to cause destructive interference for reflected light waves, effectively reducing the reflection from the surface of the optical element. Such coatings are applicable to a variety of optical devices, including but not limited to eyeglasses, camera lenses, binoculars, microscopes, and screens. The composition, thickness, and layering of the anti-reflective coating are precisely controlled to optimize performance across a desired range of wavelengths and angles of incidence. This specification encompasses any such coatings designed to improve the optical performance of devices by reducing surface reflections, enhancing light transmission, and improving user visibility and device functionality. In one embodiment, an anti- reflective coating may comprise alternating layers of high and low index materials to enhance its effectiveness. Specifically, the high-index layers can be composed of materials such as titanium dioxide (TiO₂), zirconium dioxide (ZrO₂), and hafnium dioxide (HfO₂), while the low-index layers may include silicon dioxide (SiO₂), magnesium fluoride (MgF₂), and aluminium oxide (AI2O3). In a first embodiment said anti-reflec- tive coating comprises alternating layers of silicon dioxide and zirconium dioxide; in a second embodiment said anti reflective coating comprises alternating layers of silicon dioxide and titanium dioxide to optimize optical performance by reducing reflections and improving light transmission through the optical element. Preferably, the low-index layer forms the outer layer or top layer of the anti -reflective coating, meaning that it is located as a top layer, faced away from the underlying transparent substrate. Said transparent substrate has an anti reflective coating on at least one of the said surfaces.

In the context of the present invention the term "transparent surface coating comprising reactive hydroxyl groups" refers to a thin film layer applied to the surface of transparent substrates with the primary function of enhancing the substrate's physical, chemical, and optical properties. This type of coating is characterized by the presence of reactive hydroxyl (-OH) groups, which provide significant chemical functionality, allowing for subsequent modification or interaction with other chemical species. Such coatings may include, but are not limited to, materials like: silicon dioxide, known for its transparency, durability, and ability to improve scratch resistance, reduce reflection, and enhance chemical stability; titanium dioxide (TiC)2), used to enhance optical clarity, provide photocatalytic properties, and offer strong durability; zirconium oxide (ZrO₂), known for their superior hardness, wear resistance, and thermal stability; hafnium oxide (HfC)2), known for their superior hardness, wear resistance, and thermal stability, high refractive index and high thermal and chemical stability, particularly at elevated temperatures; aluminium oxide (AI2O3), used for its excellent hardness, chemical stability, and resistance to corrosion; zinc oxide (ZnO), offering UV-blocking capabilities and high transparency; magnesium fluoride, used to reduce reflection and improve optical clarity; indium tin oxide (ITO), a transparent, conductive oxide; silicon nitride (SisIXh) having surface hydroxyl groups, a durable, scratch-resistant material with excellent optical properties.

The presence of hydroxyl groups on the aforementioned surfaces contributes to increased reactivity, enabling the coating to bond with other materials or undergo further surface treatments to tailor its performance characteristics. These coatings are particularly advantageous for applications requiring high durability, environmental resistance, and optical clarity, such as in optical lenses, display panels, and protective layers for sensitive electronic devices. The coatings may be deposited using various techniques, including chemical vapor deposition (CVD), physical vapor deposition (PVD), sol-gel processes, or other suitable methods, allowing for precise control over thickness, uniformity, surface morphology, and the density of reactive hydroxyl groups. The flexibility of these coatings enables their adaptation to a wide range of substrates and end-use applications, with potential for additional functionalization or post-deposition modifications.

Transparent surface coatings comprising reactive hydroxyl groups are typically applied with a layer thickness of 25 nm to 500 nm, or at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 80 nm, and at most 300 nm, or at most 250 nm, or most 200 nm, or at most 150 nm, or at most 100 nm, as determined by reflectance spectroscopy, whereby the thickness of said surface coating is measured including any top surface, low-index layer of the underlying antireflective coating if said layer has the same refractive index as the surface coating, e.g., the top surface, low-index layer of the antireflective coating and the transparent surface coating comprising reactive hydroxyl groups consist of the same material, or at least have the same refractive index.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent surface coating comprising reactive hydroxyl groups is a silicon dioxide coating. In the context of the present invention, the term "silicon dioxide coating" pertains to a thin film layer applied to the surface of transparent substrates for the purpose of enhancing the substrate's physical and optical properties. This coating is comprised of silicon dioxide, a transparent, durable material known for its ability to improve scratch resistance, reduce reflection, and increase chemical stability of the substrate's surface. Such coatings are particularly advantageous for applications requiring enhanced durability, optical clarity, and environmental resistance. The silicon dioxide coating may be applied through various deposition techniques, including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), and sol-gel processes, allowing for precise control over the coating thickness, uniformity, and surface morphology. In the context of the present invention, the term "hydrophobic coating" pertains to a thin film layer designed to be applied to the surface of a substrate to confer water- repellent properties. This coating is characterized by its ability to significantly reduce the surface energy of the substrate, thereby causing water and other hydrophilic fluids to bead and roll off the surface instead of spreading. The hydrophobic effect is achieved through the incorporation of materials or chemical groups that repel water. The application of this coating enhances the substrate's resistance to water, stains, and dirt accumulation, facilitating easier cleaning and maintenance, and improving visibility in wet conditions.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said hydrophobic coating has an effective thickness of at least 5 nm, or of at least 8 nm, or of 10 nm to 100 nm, such as 5 nm to 50 nm or 10 nm to 50 nm, as determined by reflectance spectroscopy, preferably of 15 nm to 45 nm, more preferably of 18 nm to 40 nm, and most preferably of 20 nm to 40 nm.

In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n higher than 1,000 g/mol, as determined by GPC-SEC, or higher than 2,000 g/mol, or higher than 5,000 g/mol, or higher than 6,000 g/mol, or higher than 7,000 g/mol, or higher than 7,500 g/mol, or higher than 8,000 g/mol, or higher than 9,000 g/mol, or higher than 10,000 g/mol, or higher than 11,000 g/mol, or higher than 12,000 g/mol, or higher than 15,000 g/mol. In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n lower than 200,000 g/mol, as determined by GPC-SEC, or lower than 150,000 g/mol, or lower than 125,000 g/mol, or lower than 100,000 g/mol, or lower than 75,000 g/mol, or lower than 50,000 g/mol, or lower than 40,000 g/mol. In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n between 1,000 g/mol and 200,000 g/mol, preferably between 5,000 g/mol and 100,000 g/mol, preferably between 10,000 g/mol and 50,000 g/mol. The inventors found that higher molecular weights of the fluorine-free polymer yielded better characteristics of the obtained hydrophobic coating.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said fluorine-free polymer comprises an organosilicon polymer. Said organosilicon polymer may have one or more side-chains selected of H, C1-C8 alkyl groups such as but not limited to methyl, ethyl, propyl, isopropyl, butyl, isobutyl groups, and C6-C8 aryl groups and/or silane groups, or may be a copolymer having one or more substituents selected from the group comprising H, C1-C8 alkyl groups, C6-C8 aryl groups and silane groups. The inventors found that aromatic groups provide better heat resistance to the polymeric thin film. Said organosilicon polymer may comprise a blend of one or more organosilicon polymers. Preferably, said organosilicon polymer comprises polydimethylsiloxane. The inventors identified organosilicon polymers as a group of polymers having excellent hydrophobic characteristics and processability. The aforementioned organosilicon polymer may contain one or more reactive trialkoxysilyl functional group on the backbone such as in a grafted polymer, or the chain-ends of the polymer. This said trialkoxysilyl group serves as cross-linker to the substrate surface. The trialkoxysilyl group may comprise trimethoxysilyl, triethoxysilyl, tripropoxysilyl, tributoxysilyl and/or triphenoxysilyl. Linkage may also occur via a divalent linkage, e.g., via saturated hydrocarbon, urea, urethane, ether, ester or amide groups.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is tethered to the outer layer of said transparent surface coating via one or more functional groups provided specifically for this purpose in said fluorine-free polymer, i.e., said organosilicon polymer.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is tethered to the outer layer of said transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, via one or more functional groups, also termed 'anchoring groups.' Thereby, it is meant that the organosilicon polymer used has one or more functional groups that are reactive to form an ionic or a covalent bond, preferably a covalent bond, with the exposed hydroxyl groups of the first coating. Having one or more covalent bonds between the underlying layer and the organosilicon polymer ensures high adhesion and durability of the hydrophobic coating. In the context of the present invention, the anchoring groups of the hydrophobic polymer can be terminal or internal, and are preferably internal.

In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is obtained from a precursor having a copolymer structure A: CH₃-[Si(CH₃)₂O]_x- [Si(CH₃)(R)O]_y-CH₃, wherein R is -CH₂CH₂-Si(OC2H5)3, wherein x > 1, y is between 2 and 7, or y is between 2 and 6, said precursor having an number average molecular weight M_n of about 12,000 g/mol.

In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is obtained from a precursor having a copolymer structure B: (C₂H₅O)3Si-CH₂CH₂- [Si(CH₃)₂O]_n-(Si(CH₃)₂-CH₂CH₂-Si(OC₂H5)3 having an number average molecular weight M_n of about 1,100 g/mol.

In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is obtained from a precursor having a copolymer structure C: (C4H₉)-[Si(CH₃)₂O]n- (Si(CH₃)₂-CH₂CH₂-Si(OC₂H5)3 having an number average molecular weight M_n of about 6,000 g/mol.

In one embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said organosilicon polymer is obtained from a precursor having a copolymer structure D: [R(CH₃)SiO]_n, wherein n > 4, and R is -CH₂CH₂-Si(OC₂H5)3, said structure having an number average molecular weight M_n of about 1,000 g/mol.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, has an effective thickness of 50 nm to 1000 nm, preferably of 80 nm to 500 nm. In one embodiment, said transparent surface coating is provided onto a glass substrate and has an effective thickness of 100 nm to 400 nm, preferably of 150 nm to 300 nm. In another embodiment, said transparent surface coating is provided onto a transparent plastic substrate and has an effective thickness of 90 nm to 200 nm, preferably of 100 nm to 150 nm.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent substrate comprises glass or a transparent polymeric material. Polymeric materials suitable as a transparent substrate may be, but not limited to, poly(allyl)carbonate, polycarbonate, polyurethane, polyethylene terephthalate (PET), and thermoplastic polyurethane (TPU). Examples are CR.-39, Trivex and high-index plastic. Glass suitable as a transparent substrate may be, but not limited to, aluminosilicate glass such as Corning's Gorilla Glass, Corning's Eagle glass, soda-lime glass and ultra-thin glass.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent substrate is an optical element or a touchscreen.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent multilayer structure has a water contact angle of between 90° and 150°. Preferably, said transparent multilayer structure has a water contact angle higher than 95°, higher than 100° or even higher than 105°.

In a preferred embodiment, the present invention provides a transparent multilayer structure according to the first aspect of the invention, wherein said transparent multilayer structure has a hexadecane contact angle of between 30° and 90°.

In a second aspect, the present invention provides a process for preparing a transparent multilayer structure, whereby a hydrophobic coating is applied to an outer layer of a transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, whereby said transparent surface coating is provided onto a transparent substrate having an antireflective coating, and whereby said hydro- phobic coating comprises a fluorine-free polymer, and in that said hydrophobic coating is applied to said outer layer of said transparent surface coating with a layer thickness of at least 5 nm, of at least 8 nm, or of 10 nm to 100 nm, as determined by reflectance spectroscopy.

In a preferred embodiment, the present invention provides a process according to the second aspect of the invention, whereby said hydrophobic coating is applied with a layer thickness of 10 nm to 50 nm, as determined by reflectance spectroscopy, preferably 15 nm to 45 nm, preferably 18 to 40 nm, preferably 20 to 40 nm.

In a preferred embodiment, the present invention provides a process according to the second aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n higher than 1,000 g/mol, as determined by GPC-SEC, or higher than 2,000 g/mol, or higher than 5,000 g/mol, or higher than 7,500 g/mol, or higher than 10,000 g/mol, or higher than 12,000 g/mol, or higher than 15,000 g/mol. In one embodiment, the present invention provides a process according to the second aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n lower than 200,000 g/mol, as determined by GPC-SEC, or lower than 150,000 g/mol, or lower than 125,000 g/mol, or lower than 100,000 g/mol, or lower than 75,000 g/mol, or lower than 50,000 g/mol, or lower than 40,000 g/mol. In one embodiment, the present invention provides a process according to the second aspect of the invention, wherein said fluorine-free polymer has a number average molecular weight M_n between 1,000 g/mol and 200,000 g/mol, preferably between 5,000 g/mol and 100,000 g/mol, preferably between 10,000 g/mol and 50,000 g/mol.

In a preferred embodiment, the present invention provides a process according to the second aspect of the invention, whereby said hydrophobic coating is formed onto said outer layer of said transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, using a dry coating technique, preferably using a vacuum coating technique such as physical vapour deposition. The scope of the invention also encompasses wet coating techniques. Specifically, the process may include, but is not limited to, dipping, spray coating, and spin coating techniques. These additional methods offer versatility in applying the hydrophobic layer, catering to various application requirements and substrate characteristics. In a preferred embodiment, the present invention provides a process according to the second aspect of the invention, whereby said hydrophobic coating is applied to said outer layer of said transparent surface coating comprising reactive hydroxyl groups, such as a silicon dioxide coating, at a temperature of between room temperature and 300°C, preferably between room temperature and 100°C and whereby said hydrophobic coating is applied to said outer layer of said transparent surface coating at a pressure of between 10’⁷ mbar and 10’⁴ mbar, preferably at a pressure of between 10'⁶ mbar and 10'⁵ mbar, more preferably at a pressure of between IO'⁵ mbar and 5 . 10’⁵ mbar. When said hydrophobic coating is applied onto a glass substrate, the temperature is between room temperature and 300°C, preferably between room temperature and 200°C and more preferably between room temperature and 100°C. When said hydrophobic coating is applied onto a plastic substrate, the temperature is at least 20°C lower than the glass transition temperature (T_g) of said plastic substrate, and preferably between room temperature and 180°C, preferably between room temperature and 160°C and more preferably between room temperature and 100°C.

EXAMPLES

The following examples are intended to further clarify the present invention, and are nowhere intended to limit the scope of the present invention.

EXAMPLE 1

Polymer A is coated through physical vapour deposition at room temperature and a pressure of about 2.5 . 10'⁵ mbar on a Corning Eagle glass substrate having an anti- reflective coating consisting of alternating TiOz/SiOz/TiOz/SiOz layers and a transparent surface coating comprising reactive hydroxyl groups, i.e., a silicon dioxide coating. The layer thickness of the surface silicon dioxide layer is about 150 nm, as determined by reflectance spectroscopy. A hydrophobic coating is coated with different effective thickness ranging between 12 nm and 45 nm. The water contact angle of the different obtained coatings as a function of effective thickness is shown in Figure 1 (•). The results show that hydrophobic properties quickly increase significantly with increasing effective thickness in the range of 10 nm to 20 nm. Also at higher effective thickness, the hydrophobic properties stay constant between 104° and 106°. Coatings having an effective thickness of higher than 40 nm do not further improve hydrophobic properties compared to effective thicknesses less than 40 nm.

EXAMPLE 2

The coatings obtained according to the procedure described in Example 1 are subjected to abrasion tests (ISO 9211-4 using microfiber cloth and 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle measurements of the non-abraded and abraded coatings are performed according to the sessile drop method as a function of effective thickness is shown in Figure 1 (°). The results show that good hydrophobic properties are maintained.

EXAMPLE 3

The procedure of Example 1 is repeated with Polymer B to result in a coating having an effective thickness of 25 nm. The water contact angle of the obtained coating was 83°.

EXAMPLE 4

The procedure of Example 1 is repeated with Polymer C to result in a coating having an effective thickness of 25 nm. The water contact angle of the obtained coating was 90°.

EXAMPLE 5

The procedure of Example 1 is repeated with Polymer D to result in a coating having an effective thickness of 25 nm. The water contact angle of the obtained coating was 74°.

EXAMPLE 6

The procedure of Example 1 is repeated with a titanium dioxide coating instead of a silicon dioxide coating. EXAMPLE 7

The procedure of Example 1 is repeated with a polymer of type A having a number average molecular weight M_n of 12,000 g/mol, having an effective thickness of about 15 nm and having an average of 3 anchoring groups. The water contact angle was determined to be 105.0° (±1.8°). The coatings obtained accordingly are subjected to abrasion tests (ISO 9211-4 using microfiber clothand 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle after 1000 cycles was determined to be 99.2° (±0.1°).

EXAMPLE 8

The procedure of Example 7 is repeated with a polymer of type A having a number average molecular weight M_n of 14,000 g/mol, having an effective thickness of about 15 nm and having an average of 6.1 anchoring groups. The water contact angle was determined to be 104.4° (±0.2°). The coatings obtained accordingly are subjected to abrasion tests (ISO 9211-4 using microfiber cloth and 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle after 1000 cycles was determined to be 96.2° (±1.7°).

EXAMPLE 9

The procedure of Example 7 is repeated with a polymer of type A having a number average molecular weight M_n of 17,800 g/mol, having an effective thickness of about 15 nm and having 2 terminal anchoring groups. The water contact angle was determined to be 104.6° (±0.3°). The coatings obtained accordingly are subjected to abrasion tests (ISO 9211-4 using microfiber cloth and 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle after 1000 cycles was determined to be 97.1° (±0.3°).

EXAMPLE 10

The procedure of Example 7 is repeated with a polymer of type A having a number average molecular weight M_n of 24,300 g/mol, having an effective thickness of about 15 nm and having 2 terminal anchoring groups. The water contact angle was determined to be 105.9° (±0.3°). The coatings obtained accordingly are subjected to abrasion tests (ISO 9211-4 using microfiber cloth and 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle after 1000 cycles was determined to be 98.4° (±1.2°).

From these results, it can be derived that a sufficiently high effective thickness, i.e., higher than 5 nm or even higher than 10 nm, of the hydrophobic coating and higher molecular weights, i.e., 5,000 g/mol and higher, of the fluorine-free polymer have a beneficial effect on the hydrophobic properties of the surface. Interestingly, higher molecular weights also did not lead to higher standard deviations in the water contact angle, either before or after abrasion testing. Further, the inventors found that the number of effective anchoring groups anchoring the polymer to the surface did not seem to have a strong impact on the hydrophobicity.

EXAMPLE 11

The procedure of Example 1 is repeated whereby the glass substrate with antireflec- tive coating is provided with a transparent surface coating comprising reactive hydroxyl groups, i.e., an aluminium oxide coating with a layer thickness of the surface coating of about 90 nm, as determined by reflectance spectroscopy. A hydrophobic coating with polymer A is coated with a thickness of 20 nm to 30 nm resulting in a water contact angle of 104° and 106°.

EXAMPLE 12

The procedure of Example 1 is repeated with a polymer of type A having a number average molecular weight M_n of 7,000 g/mol, having an effective thickness of about 15 nm and having an average of 6.4 anchoring groups. The water contact angle was determined to be 103.2° (±0.2°). The coatings obtained accordingly are subjected to abrasion tests (ISO 9211-4 using microfiber cloth and 9 N), and the water contact angle is determined after 1000 abrasion cycles. The water contact angle after 1000 cycles was determined to be 93.1° (±0.6°).

Claims

1. A transparent multilayer structure, comprising: i. a transparent substrate having an anti reflective coating; ii. a transparent surface coating comprising reactive hydroxyl groups applied onto said antireflective coating of said transparent substrate; and iii. a hydrophobic coating comprising a fluorine-free silicone polymer applied onto an outer layer of said transparent surface coating, characterized in that said hydrophobic coating has a thickness of 5 nm to 100 nm, and in that said fluorine-free silicone polymer has a number average molecular weight M_n of at least 5,000 g/mol, as determined by GPC-SEC.

2. Transparent multilayer structure according to claim 1, wherein said hydrophobic coating has a thickness of 10 nm to 50 nm.

3. Transparent multilayer structure according to claim 1 or 2, wherein said fluorine-free silicone polymer has a number average molecular weight M_n of at least 7,000 g/mol, as determined by GPC-SEC.

4. Transparent multilayer structure according to any of claims 1 to 3, wherein said fluorine-free silicone polymer comprises an organosilicon polymer having H and or C1-C8 alkyl and/or C6-C8 aryl groups, preferably said fluorine-free silicone polymer comprises polydimethylsiloxane.

5. Transparent multilayer structure according to claim 4, wherein said organosilicon polymer is tethered to the outer layer of said transparent surface coating via one or more functional groups.

6. Transparent multilayer structure according to any of claims 1 to 5, wherein said transparent surface coating has a thickness of 50 nm to 1000 nm.

7. Transparent multilayer structure according to any of claims 1 to 6, wherein said transparent substrate comprises glass or a polymeric substrate.

8. Transparent multilayer structure according to any of claims 1 to 7, wherein said transparent substrate is an optical element or a touch-screen.

9. Transparent multilayer structure according to any of claims 1 to 8, wherein said transparent multilayer structure has a water contact angle of between 90° and 120°.

10. Transparent multilayer structure according to any of claims 1 to 9, wherein said transparent multilayer structure has a hexadecane contact angle of between 30° and 90°.

11. Process for preparing a transparent multilayer structure, whereby a hydrophobic coating comprising a fluorine-free silicone polymer is applied to an outer layer of a transparent surface coating comprising reactive hydroxyl groups, whereby said transparent surface coating is provided onto a transparent substrate having an antireflective coating, characterized in that said hydrophobic coating is applied to said outer layer of said transparent surface coating with a layer thickness of 5 nm to 100 nm, and in that said fluorine-free silicone polymer has a number average molecular weight M_n of at least 5,000 g/mol, as determined by GPC-SEC.

12. Process according to claim 11, whereby said hydrophobic coating is applied with a layer thickness of 10 nm to 50 nm.

13. Process according to claim 11 or 12, whereby said fluorine-free silicone polymer has a number average molecular weight of at least 7,000 g/mol, as determined by GPC-SEC.

14. Process according to any of claims 11 to 13, whereby said hydrophobic coating is formed onto said outer layer of said transparent surface coating using a dry coating technique, preferably using a vacuum coating technique such as physical vapour deposition.

15. Process according to any of claims 11 to 14, whereby said hydrophobic coating is applied to said outer layer of said transparent surface coating at a temperature of between room temperature and 300°C, and whereby said hydrophobic coating is applied to said outer layer of said transparent surface coating at a pressure of between 10'⁶ mbar and 10'⁴ mbar.