TWI883182B - Oleophilic silanes for fingerprint-resistant coatings featuring high transparency, high abrasion-resistance, and low friction - Google Patents

Abstract

The present invention relates to a coating composition comprising an organosilane compound represented by formula (I) or (II) R¹ _3-n R² _n Si-(CH₂ )_x -Ar (I) R¹ _3-n R² _n Si-(CH₂ )_x -Si(R³ )₂ -Ar (II) wherein R¹ is a hydrolysable group, independently selected from halogen or -OR⁴ ; preferably independently selected from -OR⁴ ; R⁴ is independently selected from H or linear or branched alkyl groups having from 1 to 4 carbon atoms; R² is independently H or a linear or branched alkyl group having from 1 to 4 carbon atoms; n is 0, 1 or 2, preferably 0 or 1, most preferably 0; R³ is independently H or a linear or branched alkyl group having from 1 to 4 carbon atoms; Ar is a substituted ornon-substituted aryl group having from 5 to 10 carbon atoms, wherein the optional substituent(s) is/are independently selected from linear or branched alkyl groups, linear or branched halogenated alkyl groups, such as linear or branched fluorinated or chlorinated alkyl groups, -OR⁵ , -N(R⁵ )₂ , and halogen, such as F or Cl, preferably Ar being anon-substituted aryl group having from 5 to 10 carbon atoms; most preferably Ar being anon-substituted phenyl group; R⁵ is independently H or a linear or branched alkyl group having from 1 to 4 carbon atoms; and x is 6 to 16, preferably 8 to 14; or mixtures thereof; and a solvent, an invisible-fingerprint film originating from said organosilane compound, a method of forming said invisible-fingerprint film and an article comprising said invisible-fingerprint film.

Description

Oleophilic silane for anti-fingerprint coatings with high transparency, high abrasion resistance and low friction characteristics

The present invention relates to a coating composition comprising an organosilane compound according to formula (I) or formula (II) or a mixture thereof as described herein, an invisible fingerprint film comprising the organosilane compound, a method of forming the invisible fingerprint film, and an article comprising the invisible fingerprint film.

Typically, digital telecommunication devices (such as mobile phones, personal computers, navigators, and cash machines) are equipped with displays and touch panels installed in input/output units. These displays and touch panels are usually controlled by finger touch, so that fingerprints are deposited on the surface of the displays and touch panels. Fingerprints are composed of a watery part (i.e., sweat) and an oily part (i.e., sebum) (B. Stoehr et al., Unusual Nature of Fingerprints and the Implications for Easy-to-Clean Coatings, Langmuir 2016, 32, 2, 619-625). The oily components of sebum (e.g., mono-, di-, triglycerides, wax esters, and squalene) do not evaporate under typical environmental conditions due to their high molecular weight. Once sebum is deposited on the surface of a display or touch panel, it tends to bead up to form ridges that strongly scatter light. As a result, the quality of the image visible on the display and touch panel, as well as the aesthetic appearance of the device itself, is reduced.

This problem can be solved by applying thin film coatings to the surfaces of displays and touch panels. Commonly known monofunctional coatings include anti-glare (AG) coatings, anti-fingerprint (AF) coatings, and invisible fingerprint (IF) coatings.

AG coating is a technology based on fine irregularities on the surface of a display or touch panel that reduces specular reflections and can obfuscate fingerprints to a lesser extent. AF coating is a method of forming a hydrophobic layer on the surface of a display or touch panel, for example, by spraying or vapor depositing perfluorinated molecules to provide an easy-to-clean and slippery surface with a smooth touch. IF coating is a method of diffusing fat fingerprint components during or after fingerprint application to reduce scattered reflections and thereby make fingerprint residues inconspicuous.

IF coatings are strongly lipophilic coatings that render oil invisible or nearly invisible by diffusing oil, for example, from fingerprints along the screen surface. The refractive index of sebum oil is about 1.46 (Jaime Wisniak, The Chemistry and Technology of Jojoba Oil, 1987, p. 253), which is similar to or slightly lower than standard screen materials such as glass (1.46-1.52), and light will pass through the flat sebum layer without significant scattering. Even though the fingerprints are still physically present, we still cannot see them without close inspection. Under ambient conditions, human sebum is a heterogeneous viscous nonpolar liquid with a relatively high surface tension of about 25 mN/m, and some components such as squalene even exceed 30 mN/m (E.O.Butcher & A.Coonin, The Physical Properties of Human Sebum, 1948). To diffuse such fats, the surface coating must be nonpolar and have a high surface free energy. Since most surfaces with high surface free energy are actually polar (i.e. hydrophilic), coatings that can diffuse high surface tension fats are very difficult to achieve (D.Janssen et al., Static solvent contact angle measurements, surface free energy and wettability determination of various self-assembled monolayers on silicon dioxide, 2006). At the same time, coatings and coating materials that exhibit good IF properties need to be sufficiently hydrophobic in order to prevent the deposition of the aqueous component of the fingerprint fluid (i.e., sweat). Thus, the total amount of deposited fingerprint fluid can be minimized to a level similar to that of a standard AF coating, while making the inevitable residual fat deposits largely invisible.

Viable IF coatings are thus characterized by high water ( _H2O ) contact angle and low contact angle of hydrophobic liquids with high surface tension, such as diiodomethane (DIM), high clarity, low initial turbidity before applying fingerprints, and low turbidity of fingerprints. Ideally, IF coatings should also have high abrasion resistance and a low coefficient of friction, which indicates a smooth surface that is pleasant to the touch when the coated surface is rubbed. Organosilanes have been identified as suitable components for providing good IF coatings.

EP 2 474 577 A1 discloses IF coating compositions comprising organosilane compounds having at least one hydrolyzable group and at least one hydrophobic group, the at least one hydrophobic group comprising an alkyl group and optionally an ethoxy-based group. These IF coatings exhibit high _H2O contact angles and low DIM contact angles, but were not tested in terms of transparency, haze, abrasion resistance and friction coefficient.

US 2019/0367773 A1 discloses an IF coating composition comprising an alkylsilane compound, a POSS compound or a mixture thereof, wherein the alkylsilane compound comprises at least one alkoxy group and at least one hydrophobic group, and the at least one hydrophobic group comprises an alkyl group. These IF coatings show acceptable H ₂ O contact angle, low DIM contact angle and good abrasion resistance, but have not been tested in terms of transparency, turbidity and friction coefficient.

JP 2011/006653 A, JP 2010/100819 A and JP 2011/068000 A all relate to copolymerizable compositions suitable for IF coatings, comprising a hydrolyzable organosilane as one copolymer and a hydrolyzable organosilane having a π-electron conjugated structure as a second copolymer, the π-electron conjugated structure such as an aryl group, which in some embodiments may be bonded to the Si-atom via a short alkyl group of up to 5 carbon atoms. The cured films and copolymerized films showed relatively low turbidity and surface roughness, but the contact angle and abrasion resistance were not tested.

Therefore, there remains a need in the art for coating compositions suitable for IF coatings that exhibit an improved balance of properties such as high water ( _H2O ) contact angle, low contact angle of hydrophobic liquids such as diiodomethane (DIM contact angle), high clarity, low initial turbidity prior to applying fingerprints and low turbidity of fingerprints, high abrasion resistance, and low coefficient of friction.

It has been surprisingly found that specific organosilane or organobissilane compounds show such an improved balance of properties and are therefore qualified for use in excellent IF coatings. Thus, it was found that incorporating alkyl spacers with specific lengths defines the friction coefficient and the wear resistance that can be achieved. Both phenyl-terminated silanes with spacers are significantly longer than the silanes mentioned in the above examples, and the newly developed dimethylsilylphenyl-terminated silanes show properties that are significantly superior to the current state-of-the-art aromatic silanes (JP 2011/006653 A, JP 2010/100819 A and JP 2011/068000 A).

The present invention relates to a coating composition, which comprises an organic silane compound represented by formula (I) or (II): R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Ar (I) R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Si(R ³ ) ₂ -Ar (II) wherein R ¹ is a hydrolyzable group, which is independently selected from halogen or -OR ⁴ ; preferably independently selected from -OR ⁴ ; R ⁴ is independently selected from H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; R ² is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; n is 0, 1 or 2, preferably 0 or 1, and most preferably 0; R ³ is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected as appropriate are independently selected from: linear or branched alkyl groups; linear or branched halogenated alkyl groups, such as linear or branched fluorinated or chlorinated alkyl groups; -OR ⁵ ; -N(R ⁵ ) ₂ ; and halogens, such as F or Cl, Ar is preferably an unsubstituted aryl group having 5 to 10 carbon atoms; Ar is most preferably an unsubstituted phenyl group; R ⁵ is independently H or a linear or branched alkyl group having 1 to 4 carbon atoms; and x is 6 to 16, preferably 8 to 14; or a mixture thereof; and a solvent is optionally present.

In addition, the present invention relates to an invisible fingerprint film derived from a composition comprising an organosilane compound represented by formula (I) or (II): R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Ar (I) R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Si(R ³ ) ₂ -Ar (II) wherein R ¹ is a hydrolyzable group independently selected from a halogen or -OR ⁴ ; preferably independently selected from -OR ⁴ ; R ⁴ is independently selected from H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; R ² is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; n is 0, 1 or 2, preferably 0 or 1, and most preferably 0; R ^{R 3} is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected as appropriate are independently selected from: a straight or branched chain alkyl group; a straight or branched chain halogenated alkyl group, such as a straight or branched chain fluorinated or chlorinated alkyl group; -OR ⁵ ; -N(R ⁵ ) ² ; and a halogen, such as F or Cl, Ar is preferably an unsubstituted aryl group having 5 to 10 carbon atoms; Ar is most preferably an unsubstituted phenyl group; R ⁵ is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; and x is 6 to 16, preferably 8 to 14; or a mixture thereof.

In addition, the present invention relates to a method for forming an invisible fingerprint film, which comprises the following steps: ●  Providing a coating composition as described above or below; ●  Forming an invisible fingerprint film on the substrate by applying the coating composition to at least one surface of the substrate by immersion, coating (such as spraying, spin coating or rod coating) or vacuum deposition.

In addition, the present invention relates to an article comprising an invisible fingerprint film as described above or below on at least one of its outermost surfaces.

The present invention relates to a coating composition, which comprises an organic silane compound represented by formula (I) or (II): R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Ar (I) R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Si(R ³ ) ₂ -Ar (II) wherein R ¹ is a hydrolyzable group independently selected from halogen or -OR ⁴ ; preferably the halogen is F and Cl, more preferably Cl; however, preferably R ¹ is independently selected from -OR ⁴ ; R ⁴ is independently selected from H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; R ² is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; n is 0, 1 or 2, preferably 0 or 1, and most preferably 0; R ³ is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected as appropriate are independently selected from: a straight or branched chain alkyl group; a straight or branched chain halogenated alkyl group, such as a straight or branched chain fluorinated or chlorinated alkyl group; -OR ⁵ ; -N(R ⁵ ) ₂ ; and a halogen, such as F or Cl, Ar is preferably an unsubstituted aryl group having 5 to 10 carbon atoms; Ar is most preferably an unsubstituted phenyl group; R ⁵ is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; and x is 6 to 16, preferably 8 to 14; or a mixture thereof; and a solvent is optionally present.

The coating composition may include one organic silane compound represented by formula (I) or (II), a mixture of two or more organic silane compounds represented by formula (I), a mixture of two or more organic silane compounds represented by formula (II), or a mixture of two or more organic silane compounds represented by formula (I) and (II).

Preferably, for the organosilane compound represented by formula (I) or (II), R ¹ is independently selected from -OR ⁴ : R ⁴ is independently selected from a straight chain or branched chain alkyl group having 1 to 4 carbon atoms; preferably selected from methyl, ethyl or isopropyl; more preferably selected from methyl or ethyl; n is 0; R ³ is independently a straight chain or branched chain alkyl group having 1 to 4 carbon atoms; preferably methyl, ethyl or isopropyl; more preferably methyl; Ar is an unsubstituted aryl group having 5 to 10 carbon atoms; more preferably, Ar is an unsubstituted phenyl group; and n is 8 to 14, preferably 10 to 12, more preferably 11 or 12.

Particularly preferably, for the organosilane compound represented by formula (I) or (II), ^R1 is independently selected from methoxy, ethoxy or isopropoxy, preferably methoxy or ethoxy; n is 0; ^R3 is independently a _C2H5 group or a _CH3 group, preferably _{a CH3} group; Ar is an unsubstituted aryl group having 5 to 10 carbon atoms, preferably an unsubstituted phenyl group; and x is 8 to 14, preferably 10 to 12, more preferably 11 or 12. Most preferably, for the organosilane compound represented by formula (I) or (II), ^R1 is the same and is selected from methoxy or ethoxy; n is 0; ^R3 is a _CH3 group; Ar is an unsubstituted phenyl group; and n is 11 or 12.

Particularly preferred organosilane compounds represented by formula (I) are phenyldodecyltrimethoxysilane and phenyldodecyltriethoxysilane, with phenyldodecyltriethoxysilane being the most preferred.

Particularly preferred organosilane compounds represented by formula (II) are (trimethoxysilyl)(dimethylphenylsilyl)undecane, (triethoxysilyl)(dimethylphenylsilyl)undecane, (trimethoxysilyl)(dimethylphenylsilyl)dodecane, (triethoxysilyl)(dimethylphenylsilyl)dodecane, (trimethoxysilyl)(dimethylphenylsilyl)octane, (triethoxysilyl)(dimethylphenylsilyl)octane, more preferably (trimethoxysilyl)(dimethylphenylsilyl)undecane, (triethoxysilyl)(dimethylphenylsilyl)undecane, (trimethoxysilyl)(dimethylphenylsilyl)octane, (triethoxysilyl)(dimethylphenylsilyl)octane, and most preferably (trimethoxysilyl)(dimethylphenylsilyl)undecane.

The organic silane compound is preferably selected from phenyldodecyltriethoxysilane, (trimethoxysilyl)(dimethylphenylsilyl)undecane or a mixture thereof.

In a particularly preferred embodiment, the organosilane compound is phenyldodecyltriethoxysilane.

In another particularly preferred embodiment, the organosilane compound is (trimethoxysilyl)(dimethylphenylsilyl)undecane.

The organosilane compound as described herein is preferably present in the coating composition in an amount of 0.01 wt % to 25.0 wt %, more preferably 0.02 to 20.0 wt %, still more preferably 0.05 wt % to 15.0 wt %, even more preferably 0.07 wt % to 10.0 wt %, and most preferably 0.10 wt % to 5.0 wt %, based on the total amount of the coating composition.

The coating composition preferably further comprises a solvent. The solvent is preferably selected from the group consisting of methanol, ethanol, isopropanol, butanol, 1-methoxy-2-propyl acetate (PGMEA), 1-methoxy-2-propanol (PGME), 2-butanone (MEK), hexadecane, octane, hexane, cyclohexane, cyclopentane, toluene, xylene, benzene, carbon tetrachloride, chloroform, dichloromethane and ethylene glycol or a mixture thereof. The particularly preferred solvent is an alcohol selected from the group consisting of methanol, ethanol, isopropanol, 1-methoxy-2-propyl acetate (PGMEA), 1-methoxy-2-propanol (PGME), 2-butanone (MEK) or a mixture thereof.

The solvent as described herein is preferably present in the coating composition in an amount of 75.0 wt % to 99.99 wt %, more preferably 80.0 to 99.98 wt %, still more preferably 85.0 wt % to 99.95 wt %, even more preferably 90.0 wt % to 99.93 wt %, and most preferably 95.0 wt % to 99.90 wt %, based on the total amount of the coating composition.

The coating composition may further comprise an additive such as a lubricant for imparting lubricating properties to the film formed by the coating composition. Suitable lubricants are not particularly limited. Non-limiting examples may be, for example, unsaturated fatty acids such as myristic acid, palmitic acid and oleic acid; saturated fatty acids such as lauric acid, palmitic acid and stearic acid; and hydrocarbon materials such as hydrocarbon oils such as squalene, triolein and jojoba oil; or mixtures thereof. If present, the lubricant may be present in the solvent in an amount up to 50 wt %, such as 0.05 wt % to 50 wt %, preferably 0.1 to 25.0 wt %, based on the total amount of solvent present in the coating composition. Other suitable additives may include antioxidants, UV absorbers, light stabilizers and clarifiers. If present, the amount of such additives generally does not exceed 5 wt %, preferably 2 wt % and most preferably 1 wt % of the total amount of the coating composition.

In another embodiment, the present invention relates to an invisible fingerprint film derived from an organosilane compound represented by formula (I) or (II): R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Ar (I) R ¹ _3-n R ² _n Si-(CH ₂ ) _x -Si(R ³ ) ₂ -Ar (II) wherein R ¹ is a hydrolyzable group independently selected from a halogen or -OR ⁴ ; preferably independently selected from -OR ⁴ ; R ⁴ is independently selected from H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; R ² is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; n is 0, 1 or 2, preferably 0 or 1, and most preferably 0; R ^{R 3} is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected as appropriate are independently selected from: a straight or branched chain alkyl group; a straight or branched chain halogenated alkyl group, such as a straight or branched chain fluorinated or chlorinated alkyl group; -OR ⁵ ; -N(R ⁵ ) ₂ ; and a halogen, such as F or Cl, Ar is preferably an unsubstituted aryl group having 5 to 10 carbon atoms; Ar is most preferably an unsubstituted phenyl group; R ⁵ is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; and x is 6 to 16, preferably 8 to 14; or a mixture thereof.

Preferably, the organosilane compound is the same in all embodiments described above or below for the coating composition according to the present invention.

The term "origin" means that during film formation, the organic silane compound represented by formula (I) or (II) may undergo chemical modifications such as hydrolysis, crosslinking, etc. so that the invisible fingerprint film may contain unmodified organic silane compounds and/or modified organic silane compounds.

It has been unexpectedly found that an invisible fingerprint film derived from a composition comprising an organosilane compound represented by formula (I) or formula (II) as described above or below shows an improved balance of properties with respect to high water (H ₂ O) contact angle, low contact angle of a hydrophobic liquid having high surface tension (such as diiodomethane) (DIM contact angle), high transparency, low initial turbidity (before applying fingerprints) and low turbidity with fingerprints, high abrasion resistance and low friction coefficient. Such features of properties qualify the invisible fingerprint film as a coating that diffuses a hydrophobic liquid (such as sebum) and thereby renders fingerprints virtually invisible. This can be seen, for example, by the low haze difference, Δhaze, which is the difference between the haze with the fingerprint minus the initial haze. The film further exhibits good optical properties with high transparency and low initial haze, which qualifies the film as a coating for displays and touch panels. Additionally, the film exhibits a low coefficient of friction when both a metal weight and a paper cover weight are slid over glass coated with the film of the present invention. The low coefficient of friction enables a smooth surface and reduces the sensation of stickiness when a finger slides over a display or touch panel. Still further, the film exhibits high wear resistance, which can be seen in the high water contact angle maintained after up to 3000 cycles of extensive linear wear. The high wear resistance shows the high durability of the film even under high stresses.

When coated on Gorilla® Glass or other chemically strengthened glass, the invisible fingerprint film according to the present invention preferably has a water contact angle greater than 70°, more preferably at least 80°, even more preferably at least 85°, and most preferably at least 90°. When coated on Gorilla® Glass or other chemically strengthened glass, the upper limit of the water contact angle of the invisible fingerprint film is usually not higher than 120°, more preferably not higher than 110°.

In addition, when coated on float glass, the invisible fingerprint film according to the present invention preferably has a water contact angle greater than 70°, more preferably at least 80°, even more preferably at least 85°, and most preferably at least 90°. When coated on float glass, the upper limit of the water contact angle of the invisible fingerprint film is usually not higher than 120°, more preferably not higher than 110°.

When coated on Gorilla® Glass or other chemically strengthened glass, the invisible fingerprint film according to the present invention preferably has a diiodomethane contact angle of no more than 55°, more preferably no more than 52°, even more preferably no more than 50°, and most preferably no more than 48°. When coated on Gorilla® Glass or other chemically strengthened glass, the lower limit of the diiodomethane contact angle of the invisible fingerprint film is usually at least 15°, more preferably at least 20°.

In addition, when coated on float glass, the invisible fingerprint film according to the present invention preferably has a diiodomethane contact angle of no more than 57°, more preferably no more than 55°, still more preferably no more than 52°, and most preferably no more than 50°. When coated on float glass, the lower limit of the diiodomethane contact angle of the invisible fingerprint film is usually at least 15°, more preferably at least 20°.

The high water contact angle and the low diiodomethane contact angle show the obvious hydrophobicity and high lipophilicity of the membrane according to the present invention.

In addition, the invisible fingerprint film preferably exhibits good abrasion resistance: In addition, the invisible fingerprint film as described herein preferably has a water contact angle of at least 60°, more preferably at least 65°, and most preferably at least 70° after 500 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass. The upper limit of the water contact angle of the invisible fingerprint film after 500 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass is generally not higher than 105°, preferably not higher than 95°. In addition, the invisible fingerprint film has a water contact angle of at least 50°, more preferably at least 55°, and most preferably at least 60° after 3000 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass. The upper limit of the water contact angle after 3000 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass is generally not higher than 105°, preferably not higher than 95°.

Preferably, the invisible fingerprint film has a water contact angle of at least 55°, more preferably at least 65°, and most preferably at least 75° on the coated float glass after 500 cycles of extensive linear abrasion. The upper limit of the water contact angle after 500 cycles of extensive linear abrasion when the invisible fingerprint film is coated on the float glass is usually not higher than 105°, preferably not higher than 95° In addition, the invisible fingerprint film preferably has a water contact angle of at least 50°, more preferably at least 55°, and most preferably at least 60° after 3000 cycles of extensive linear abrasion when coated on the float glass. The upper limit of the water contact angle of the invisible fingerprint film when applied on float glass after 3000 cycles of extensive linear abrasion is usually not higher than 105°, preferably not higher than 95°

"Extensive linear wear" in this context means the wear test as described below in the section on measurement methods. One cycle hereby means one run of the described protocol, 500 cycles means 500 runs of the described protocol and 3000 cycles means 3000 runs of the described protocol. High water contact angles after 500 or even 3000 cycles of extensive linear wear indicate that the hydrophobicity of the membrane is still high after the wear protocol, which indicates that the membrane is not excessively damaged and worn.

Preferably, the difference in water contact angle on the coated Gorilla® Glass or other chemically strengthened glass is no more than 45°, more preferably no more than 35°, and most preferably no more than 30°, the difference being the initial contact angle before the start of the abrasion test on the coated Gorilla® Glass or other chemically strengthened glass minus the water contact angle after 3000 cycles of extensive linear abrasion. In addition, the difference in water contact angles on the coated float glass is not more than 45°, more preferably not more than 30°, and most preferably not more than 20°, the difference being the initial contact angle before the start of the abrasion test on the coated float glass minus the water contact angle after 3000 cycles of extensive linear abrasion.

In addition, the invisible fingerprint film according to the present invention exhibits good optical properties:

Preferably, for an incident angle of 0°, when air is measured as the surrounding medium, the Gorilla® glass or other chemically strengthened glass coated with the invisible fingerprint film has a transparency of at least 90%, more preferably at least 91%, and most preferably at least 92%. The upper limit of the transparency of the coated Gorilla® glass or other chemically strengthened glass is usually 94%, preferably 93.6%.

In addition, for an incident angle of 0°, when air is measured as the surrounding medium, the float glass coated with the invisible fingerprint film has a transparency of at least 90%, more preferably at least 91%, and most preferably at least 92%. The upper limit of the transparency of the coated float glass is usually 93%, preferably 92.6%.

In addition, when measured on coated Gorilla® glass or other chemically strengthened glass, the invisible fingerprint film preferably has a haze of no more than 1.0%, more preferably no more than 0.9%, and most preferably no more than 0.8%. The lower limit of haze for coated Gorilla® glass or other chemically strengthened glass is typically 0.01%, preferably 0.03%.

In addition, when measured on the coated float glass, the invisible fingerprint film preferably has a haze of no more than 1.0%, more preferably no more than 0.9%, and most preferably no more than 0.8%. The lower limit of the haze of the coated float glass is generally 0.01%, preferably 0.03%.

When measured on the coated float glass, the haze of the invisible fingerprint film after applying the fingerprint is preferably no more than 8.0%, more preferably no more than 6.0% and most preferably no more than 5.0%. The lower limit of the haze of the coated float glass after applying the fingerprint is usually 1.0%, preferably 2.0%.

In addition, the invisible fingerprint film has a haze difference on the float glass of no more than 7.5%, more preferably no more than 6.0%, and most preferably no more than 5.0%, which is the difference between the haze with fingerprints and the initial haze.

In addition, the invisible fingerprint film according to the present invention preferably shows a low friction coefficient measured using a metal covered with stainless steel foil or glass paper, which indicates the smooth surface of the glass substrate coated with the film of the present invention: The invisible fingerprint film preferably has a friction coefficient of no more than 0.30, more preferably no more than 0.27 and most preferably no more than 0.25 (stainless steel foil against coated Gorilla® glass or other chemically strengthened glass). The lower limit of the friction coefficient (stainless steel foil against coated Gorilla® glass) is generally 0.05, preferably 0.10.

In addition, the invisible fingerprint film preferably has a friction coefficient of no more than 0.40, more preferably no more than 0.35, and most preferably no more than 0.30 (glass paper against coated Gorilla® glass or other chemically strengthened glass). The lower limit of the friction coefficient (glass paper against coated Gorilla® glass or other chemically strengthened glass) is generally 0.05, preferably 0.10.

The invisible fingerprint film preferably has a friction coefficient of no more than 0.30, more preferably no more than 0.25 and most preferably no more than 0.20 (stainless steel foil against coated float glass). The lower limit of the friction coefficient (stainless steel foil against coated float glass) is usually 0.05, preferably 0.10.

In addition, the invisible fingerprint film preferably has a friction coefficient of no more than 0.40, more preferably no more than 0.30 and most preferably no more than 0.25 (cellophane and coated float glass). The lower limit of the friction coefficient (cellophane and coated float glass) is usually 0.05, preferably 0.10.

Another aspect of the present invention is a method for forming an invisible fingerprint film, which comprises the following steps: ●     Providing a coating composition as described above or below; ●     Applying the coating composition to at least one surface of a substrate by immersion, coating or vacuum deposition to form an invisible fingerprint film on the substrate.

Thus, the coating composition and the invisible fingerprint film are preferably all embodiments of the coating composition and the invisible fingerprint film of the present invention as described above or below.

The substrate is preferably a substrate that is easily contaminated by fingerprints, such as glass, metal, ceramic, plastic, wood, stone and the like. The coating composition may be applied to only one surface of the substrate or to all surfaces of the substrate or to any number of surfaces of the substrate.

At least one surface of the substrate may have functional groups, such as hydroxyl groups, carboxyl groups, thiol groups, sulfonic acid groups or similar groups. If functional groups are not present on at least one surface, the at least one surface may be pretreated to introduce such functional groups. Suitable pretreatment methods are, for example, corona discharge treatment, UV/ozone treatment, oxygen or air plasma treatment, treatment involving chemical oxidants such as potassium permanganate or other similar treatments known in the art (e.g., sulfuric acid or nitric acid treatment), acidic or alkaline piranha cleaning using hydrogen peroxide, RCA cleaning or aqua regia treatment.

The coating composition may be applied to at least one surface of the substrate by any suitable means known in the art, such as immersion, coating or vacuum deposition.

In the immersion method, the substrate is immersed in a liquid coating composition, such as by dip coating, so that at least one surface of the substrate is coated with the liquid coating composition. Thereafter, the coating composition is dried, such as by evaporating the solvent, and an invisible fingerprint film is formed.

In coating methods, a liquid coating composition is applied to at least one surface of a substrate, usually by a method controlled by, for example, spraying or spin coating, as well as other devices such as printing or rod coating. Thereafter, the coating composition is usually dried, for example, by evaporating the solvent, and forms an invisible fingerprint film.

In vacuum deposition methods such as physical vapor deposition, the coating composition is usually evaporated and then deposited onto at least one surface of the substrate. Thereafter, the coating composition is usually dried, for example by evaporating the solvent, and forms an invisible fingerprint film.

In the vacuum deposition method, a coating composition containing a higher amount of the organic silane compound of up to 20.0 wt % or even up to 100 wt % is generally used, while for other methods, a coating composition containing a lower amount of the organic silane compound of not more than 5.0 wt % or even not more than 1.5 wt % is used.

The drying steps in all coating processes are generally carried out at elevated temperatures, such as 80°C to 200°C, preferably 100°C to 175°C, and most preferably 120°C to 150°C, depending on the components of the coating composition.

Coating methods suitable for applying the coating composition to at least one surface of a substrate are well known in the art. After coating and thermal annealing, unbound silane molecules can be removed by washing the treated surface with an organic solvent or wiping with a solvent-soaked cloth or a polishing device.

Yet another aspect of the present invention relates to an article comprising an invisible fingerprint film as described above or below on at least one outermost surface thereof.

Thus, the coating composition and the invisible fingerprint film are preferably all embodiments of the coating composition and the invisible fingerprint film of the present invention as described above or below. In all embodiments as described above or below, the invisible fingerprint film is preferably applied to at least one surface of the product using the method for forming the invisible fingerprint film according to the present invention.

The product may be any product that is easily contaminated by fingerprints, such as a product including a display, a touch panel and/or a smooth and glossy housing, such as a digital communication device, such as a mobile phone, a personal computer, a laptop, a navigator, an ATM, a security system or an information terminal. Such a display may be a CRT, LCD, PDP LED or FED display. Such a housing may be a plastic, glass, ceramic or metal housing. At least one surface of the product including the invisible fingerprint film according to the present invention may be at least one of a display, a touch panel or a housing surface.

Example 1. Measurement Method All measurements listed below were performed at 23 °C and 50 % relative humidity.

a)Turbidity, transparency Measured according to ASTM D 1003 using a BYK Gardner haze-gard i hazemeter.

b)Contact angle ( Water, diiodomethane ) Static contact angles were determined by applying droplets (2-5 µL) of deionized water or diiodomethane, subsequent optical characterization by a digital imaging system, and software-assisted analysis using elliptical fit functions. Common optical contact angle measurement setups based on syringe dosing and integrated systems using liquid needle dosing were found to give similar results. The method is described in detail in Ming Jin, Raymond Sanedrin, Daniel Frese, Carsten Scheithauer, · Thomas Willers, Replacing the solid needle by a liquid one when measuring static and advancing contact angles, Colloid Polym Sci (2016) 294:657-665.

c)Extensive linear wear Use with Minoan^TM Linear wear measurement using a TABER®5900 reciprocating friction tester on rubber (6.4 mm diameter) with a pressure of 0.35 N/mm².

d)Friction coefficient Using ForceBoard by INDUSTRIAL DYNAMICS SWEDEN AB^TM The friction measuring device measures the dynamic coefficient of friction using a procedure adapted from ASTM D1894. For this, a square weight (64×64 mm²) covered with a polished stainless steel foil (thickness approx. 0.1 mm) or glass paper is pulled 50 mm on a coated glass plate at a pulling speed of 2.5 mm/s with a pressure of 1.3 mN/mm².

2.    Example a)Coating composition The following coating compositions were prepared: Comparative composition 1 (CC1):    1.0 wt% phenyltrimethoxysilane in ethanol Comparative composition 2 (CC2):    1.0 wt% phenylethyltrimethoxysilane in ethanol Inventive composition 1 (IC1):       1.0 wt% (trimethoxysilyl)(dimethylphenylsilyl)octane in ethanol Inventive composition 2 (IC2):       1.0 wt% (trimethoxysilyl)(dimethylphenylsilyl)undecane in ethanol Inventive composition 3 (IC3):       1.0 wt% phenyldodecyltriethoxysilane in ethanol Inventive composition 4 (IC4):       0.5 wt% (trimethoxysilyl)(dimethylphenylsilyl)undecane and 0.5 wt% phenyldodecyltriethoxysilane

b)Forming invisible fingerprint film on glass substrate The coating composition disclosed above was acidified with nitric acid (3 mg/mL) and then directly applied to float glass and Gorilla® Glass substrates by spin coating. The coated substrates were dried in an oven at 120°C for 20 min.

The following coated glass substrates were obtained: Comparative substrate 1-CS-F: float glass substrate coated with CC-1 Comparative substrate 2-CS-F: float glass substrate coated with CC-2 Inventive substrate 1-IS-F: float glass substrate coated with IC-1 Inventive substrate 2-IS-F: float glass substrate coated with IC-2 Inventive substrate 3-IS-F: float glass substrate coated with IC-3 Inventive substrate 4-IS-F: float glass substrate coated with IC-4

Comparative Substrate 2-CS-G: Gorilla® glass substrate coated with CC-2 Inventive Substrate 1-IS-G: Gorilla® glass substrate coated with IC-1 Inventive Substrate 2-IS-G: Gorilla® glass substrate coated with IC-2 Inventive Substrate 3-IS-G: Gorilla® glass substrate coated with IC-3 Inventive Substrate 4-IS-G: Gorilla® glass substrate coated with IC-4 Water contact angle and diiodomethane contact angle were measured from the coated glass substrates. The water contact angle (CA H ₂ O) and diiodomethane contact angle (CA DIM) are listed in Table 1.

Table 1: Water contact angle (CA H ₂ O) and diiodomethane contact angle (CA DIM) of coated glass substrate Coated glass substrate CA H ₂ O [°] CA DIM [°] 1-CS-F 67 51 2-CS-F 84 48 1-IS-F 94 50 2-IS-F 93 49 3-IS-F 91 42 4-IS-F 90 47 2-CS-G 85 40 1-IS-G 94 47 2-IS-G 94 48 3-IS-G 93 43 4-IS-G 91 46

The results for the contact angles of the films on float glass and Gorilla® Glass substrates were similar. The best results were obtained for the films comprising organosilanes with the longest (CH ₂ )-spacers (IC-2 and IC-3) and their mixture (IC-4). In addition, the haze and transparency of the coated glass substrates were measured. The results are listed in Table 2.

Table 2: Opacity and transparency of coated glass substrates Coated glass substrate transparency[%] Turbidity [%] 1-CS-F 91.8 0.4 2-CS-F 92.3 0.1 1-IS-F 92.4 0.1 2-IS-F 92.4 0.1 3-IS-F 92.3 0.1 4-IS-F 92.6 0.1 2-CS-G 93.5 0.1 1-IS-G 93.5 0.1 2-IS-G 93.5 0.1 3-IS-G 93.5 0.1 4-IS-G 93.6 0.1

All films showed good optical properties in terms of transparency and haze. The haze of the coated float glass substrates was also measured after applying the fingerprint. In Table 3, the haze measurements before applying the fingerprint (initial haze), the haze measurements after applying the fingerprint (haze with fingerprint (FP)), and the difference between haze with FP and initial haze (dhaze) are listed.

Table 3: Opacity measurements before and after fingerprint application Coated glass substrate Initial turbidity [%] Has FP turbidity d Turbidity Uncoated float glass 1.3 9.7 8.4 2-CS-F 0.8 3.3 2.5 1-IS-F 0.7 5.5 4.8 2-IS-F 0.7 4.2 3.6 3-IS-F 0.7 4.3 3.7

All films showed sufficiently low haze after fingerprinting.

In addition, the coefficient of friction of the coated glass substrate was measured when a steel weight (CoF(steel)) was used and when a steel weight covered with glass paper (CoF(paper)) was used. The results are listed in Table 4.

Table 4: Friction coefficient of coated glass substrate Coated glass substrate CoF(Steel) CoF(paper) 1-CS-F 0.21 0.42 2-CS-F 0.32 0.41 1-IS-F 0.22 0.25 2-IS-F 0.19 0.20 3-IS-F 0.19 0.23 4-IS-F 0.20 0.23 2-CS-G 0.36 0.47 1-IS-G 0.27 0.33 2-IS-G 0.24 0.27 3-IS-G 0.19 0.26 4-IS-G 0.22 0.24

The results for the coefficient of friction of the films on float glass and Gorilla® Glass substrates were similar. The best results were obtained for the films comprising the organosilane with the longest (CH ₂ )-spacers (IC-2 and IC-3) and their mixture (IC-4).

Finally, the abrasion resistance of the coated glass substrates was determined by measuring the water contact angle before applying extensive linear abrasion, after 500 cycles of extensive linear abrasion, after 1000 cycles of extensive linear abrasion, after 2000 cycles of extensive linear abrasion, and after 3000 cycles of extensive linear abrasion. The results for coated substrates 2-CS-F, 3-IS-F, 1-IS-F, 2-IS-F, and 4-IS-F are shown from left to right in FIG. 1 , and coated substrates 2-CS-G, 3-IS-G, 1-IS-G, 2-IS-G, and 4-IS-G are shown from left to right in FIG. 2 .

The best abrasion resistance clearly shows the films comprising organosilanes with the longest (CH ₂ )-spacers (IC-2, IC-3 and IC-4).

FIG. 1 shows the abrasion resistance of the coated float glass substrates of these examples obtained by measuring the water contact angle before applying extensive linear abrasion, after 500 cycles of extensive linear abrasion, after 1000 cycles of extensive linear abrasion, after 2000 cycles of extensive linear abrasion, and after 3000 cycles of extensive linear abrasion for the coated substrates 2-CS-F, 1-IS-F, 2-IS-F, 3-IS-F, and 4-IS-F from left to right.

FIG. 2 shows the abrasion resistance of the coated Gorilla® glass substrates of these examples obtained by measuring the water contact angle before applying extensive linear abrasion, after 500 cycles of extensive linear abrasion, after 1000 cycles of extensive linear abrasion, after 2000 cycles of extensive linear abrasion, and after 3000 cycles of extensive linear abrasion for the coated substrates 2-CS-F, 1-IS-F, 2-IS-F, 3-IS-F, and 4-IS-F from left to right.

Claims (13)

A coating composition comprises an organic silane compound represented by formula (I) or (II) _: ^R13 _- ^nR2nSi- ( _CH2 ) _x -Ar (I) _{R13 -} ^nR2nSi- ( _CH2 ) _x -Si( ^R3 ) ₂ -Ar (II) wherein ^R1 is independently selected from halogen or ^-OR4 ; ^R4 is independently selected from H ^or a linear or branched alkyl group having 1 to 4 carbon atoms; ^R2 is independently H or a linear or branched alkyl group having 1 to 4 carbon atoms; n is 0, 1 or 2; ^R3 is independently H or a linear or branched alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected are independently selected from: linear or branched alkyl; linear or branched halogenated alkyl; -OR ⁵ ; -N(R ⁵ ) ₂ ; and halogen; R ⁵ is independently H or a linear or branched alkyl group having 1 to 4 carbon atoms; and x is 6 to 16; or a mixture thereof; and a solvent is optionally present. The coating composition of claim 1, wherein R ¹ is independently selected from methoxy, ethoxy or isopropoxy; n is 0; R ³ is independently a C ₂ H ₅ group or a CH ₃ group; Ar is an unsubstituted aryl group having 5 to 10 carbon atoms; and x is 8 to 14. The coating composition of claim 1, wherein the organic silane compound is selected from phenyldodecyltrimethoxysilane, phenyldodecyltriethoxysilane, (trimethoxysilyl)(dimethylphenylsilyl)undecane, (triethoxysilyl)(dimethylphenylsilyl)undecane, (trimethoxysilyl)(dimethylphenylsilyl)dodecane, (triethoxysilyl)(dimethylphenylsilyl)dodecane, (trimethoxysilyl)(dimethylphenylsilyl)octane, (triethoxysilyl)(dimethylphenylsilyl)octane; or a mixture thereof. The coating composition of claim 1, wherein the organosilane compound is present in the coating composition in an amount of 0.01 wt % to 25.0 wt % based on the total amount of the coating composition. The coating composition of claim 1, wherein the solvent is selected from the group consisting of methanol, ethanol, isopropanol, butanol, 1-methoxy-2-propyl acetate (PGMEA), 1-methoxy-2-propanol (PGME), 2-butanone (MEK), hexadecane, octane, hexane, cyclohexane, cyclopentane, toluene, xylene, benzene, carbon tetrachloride, chloroform, dichloromethane and ethylene glycol or a mixture thereof. An invisible fingerprint film derived from a composition comprising an organosilane compound represented by formula (I) or (II): ^R13 _{- nR2nSi-} ( _CH2 ) _x -Ar (I) ^{R13 -} nR2nSi-( _CH2 ) _x ^- _Si ( ^R3 ) ₂ - _Ar (II) wherein ^R1 is independently selected from halogen or -OR4; ^R4 is independently selected from H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; ^R2 is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; n is 0, 1 or ² ; ^R3 is independently H or a straight or branched chain alkyl group having 1 to 4 carbon atoms; Ar is a substituted or unsubstituted aryl group having 5 to 10 carbon atoms, wherein the substituents selected as appropriate are independently selected from: linear or branched alkyl; linear or branched halogenated alkyl; -OR ⁵ ; -N(R ⁵ ) ₂ ; and halogen; R ⁵ is independently H or a linear or branched alkyl group having 1 to 4 carbon atoms; and x is 6 to 16; or a mixture thereof. The invisible fingerprint film of claim 6, wherein the organic silane compound is the same as that in the coating composition of any one of claims 2 to 4. The invisible fingerprint film of claim 6 has a water contact angle of more than 70° when coated on Gorilla® Glass or other chemically strengthened glass, and/or has a diiodomethane contact angle of no more than 55° when coated on Gorilla® Glass. The invisible fingerprint film of claim 6 has a water contact angle of at least 60° after 500 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass, and/or has a water contact angle of at least 50° after 3000 cycles of extensive linear abrasion when coated on Gorilla® Glass or other chemically strengthened glass. The invisible fingerprint film of claim 6 has a haze difference of no more than 7.5% on the coated float glass, which is the difference between the haze with fingerprints and the initial haze. The invisible fingerprint film of claim 6 has a friction coefficient of no more than 0.30 measured by using stainless steel foil against coated Gorilla® glass or other chemically strengthened glass and/or a friction coefficient of no more than 0.40 measured by using glass paper against coated Gorilla® glass or other chemically strengthened glass. A method for forming an invisible fingerprint film, comprising the following steps: Providing a coating composition as described in any one of claims 1 to 5; Applying the coating composition to at least one surface of a substrate by immersion, coating or vacuum deposition to form an invisible fingerprint film on the substrate. A product that is easily contaminated by fingerprints, comprising an invisible fingerprint film as claimed in any one of claims 6 to 11 on at least one of its outermost surfaces.