Patent Application
20170101540
The present invention relates to compositions and methods for making a coating with anti-fingerprint performance, and the coated articles resulting thereof. More particularly, the present invention relates to compositions and methods for making a coating layer comprising a stationary phase impregnated with a mobile phase having the ability to diffuse and fade fingerprints, in addition to optionally having a strong liquid repellency that minimizes the deposition of fingerprints and eases the cleaning of the coated articles.
Consumer electronics devices such as mobile phones, tablets, and laptop computers are becoming increasingly indispensable. Surfaces of these devices, including touch screen, display panel, and housing, are easily smudged by fingerprints after frequent touching, making them look dirty and unappealing. The problem is especially more challenging for smooth and glossy finishes, as fingerprints are visually more obvious on these surfaces than on rough and matte finishes.
Fingerprint is a complex mixture of hundreds of compounds, which may vary slightly among individuals. The main components of this emulsion are sweat and sebum. Sweat comprises water and a variety of organic matters and inorganic salts. Sebum is composed of various lipids and oily substances. Depending on the amount of sweat, fingerprint is initially made up of nearly 99% of water (The Fingerprint Sourcebook, U.S. Department of Justice, 2011). Water evaporates away after some time upon contact with the surface. Oily and inorganic residues remain and need to be cleaned off manually.
It is commonly known in the art that a coating of low surface energy can impart fingerprint resistance. Water and oil tend to form large contact angles when deposited onto such a coating, which is said to be both hydrophobic (water repellent) and oleophobic (oil repellent). The coating usually comprises a fluorine- or silicone-containing compound. Further enhancement in hydrophobicity and oleophobicity can be attained by incorporating surface texture or roughness. For example, Application WO 2010/147738 discloses a super non-wetting, anti-fingerprint coating comprising perfluoroalkyl-Si and silica nanoparticles with micro- and nanoscale surface roughness. However, the coating is rough, opaque, and limited to glass substrates.
Owing to the low surface tension of sebum, there is presently no coating material with surface energy that is sufficiently low to completely prevent fingerprints from sticking to a surface, particularly if it is a smooth surface devoid of any textural features. Thus, current art is primarily directed to providing an anti-fingerprint coating that only acts to minimize the deposition of fingerprints and ease the cleaning of fingerprints. For example, U.S. Pat. No. 7,153,563 discloses a hard coat film comprising 100 parts by weight of a curable resin and 0.1 to 10 parts by weight of a non-ionic surfactant with a hydrophile-lipophile balance (HLB) value of 2 to 15. The objects of the hard coat film are limited to suppressing the attachment of fingerprints and enabling the easy wiping of fingerprints.
Current art is also directed to providing a coating that minimizes the appearance of fingerprints. Application WO2012/087661 discloses a coating composition comprising a polymerizable resin and a non-ionic unpolymerizable surfactant having an HLB value ranging from 2 to 6 that exhibits reduced fingerprint visibility. The surfactant is a lipophilic liquid.
There is still a need to develop a coating with improved anti-fingerprint performance. It is important to design the coating by considering the composition of fingerprint, which is normally a water-rich emulsion when initially deposited. None of the patents has disclosed a composition or a method for making a coating layer comprising a stationary phase impregnated with a mobile phase that can readily diffuse and fade this initially water-rich emulsion.
The present invention is directed to anti-fingerprint coating compositions, the coating layers and coated articles formed therefrom, the preparation methods therefor, and the uses thereof. The coating compositions and methods according to the present invention are capable of forming a coating layer with anti-fingerprint performance. The coating layer according to the present invention comprises a stationary phase impregnated with a mobile phase that can diffuse and fade fingerprints, in addition to optionally having strong liquid repellency that minimizes the deposition of fingerprints and eases the cleaning of the coated articles.
The present invention exploits the chemistry of the interaction of a mobile phase with fingerprints to cause the fingerprints to diffuse and fade. The mobile phase is impregnated in a suitable amount in the stationary phase that can migrate to the top surface to interact with fingerprints. The composition of the fingerprint, which is initially a water-rich emulsion, is the selection basis for the mobile phase. The mobile phase is a liquid comprising one or more surfactants that interact readily with the emulsion, facilitating the diffusion and fading of fingerprints.
An advantageous aspect of the present invention is the synergistic action of the mobile phase and the stationary phase. Preferably, the stationary phase according to the present invention may have low surface energy, which provides for high liquid repellency that minimizes fingerprint deposition and eases cleaning. The stationary phase may also comprise channels of a size from nano- to micro-scale that serve both as a reservoir for containing the mobile phase and as a network for the transport and migration of the mobile phase to the top surface. Due to low surface energy of the stationary phase, fingerprints tend to form discrete beads or droplets instead of continuous films when initially deposited onto the surface of the stationary phase. The synergistic effect is manifested by the diffusion of the droplets into many tiny droplets, and then the shrinking and fading of the droplets over time.
When used herein, the term “nano- to micro-scale” is meant to include a length scale from 1 nm to 100 μm.
In one aspect of the invention, a composition for forming a coating on top of a substrate is provided. The composition according to the present invention comprises:
Unless otherwise specified, the term “hydrophile-lipophile balance” or “HLB” is a measure of the degree of hydrophilicity or lipophilicity of a surfactant or a blend of surfactants, according to the definition by Griffin (W. C. Griffin, J. Soc. Cosmet. Chem., 1954, 249-259). Typically, a hydrophilic surfactant has an HLB value of 10 or greater, whereas a lipophilic surfactant has an HLB value smaller than 10.
The quantity and the type of surfactants are selected in accordance with the desired diffusion and fading effectiveness, as well as acceptable performance in other attributes like hardness, transparency, gloss, and the like of the resulting coating layer. Preferably, at least one of the surfactants is a nonionic surfactant, which is an effective mobile phase for diffusing and fading fingerprints according to the present invention. In certain embodiments, a liquid comprising 10 to 50 parts by weight of one or more surfactants with an HLB value greater than 6 is used per 100 parts by weight of a binder. For fingerprints with high content of sweat or water, a liquid comprising one or more hydrophilic surfactants with an HLB value of 10 or greater is preferred. In certain embodiments, if the fingerprints are very oily, the composition may further comprise 10 to 40 parts by weight of one or more lipophilic surfactants with an HLB value of greater than 6 to 10. Suitable surfactants include but are not limited to alcohol ethoxylates, alcohol alkoxylates, phenol ethoxylates, nonyl phenol ethoxylates, amine ethoxylates, amide ethoxylates, alkylpolyglucosides, polyalcohols, polyoxylated alcohols, fatty acid esters, amine and amide derivatives, ethylene oxide/propylene oxide copolymers, and silicone surfactants. Exemplary commercially available surfactants include but are not limited to Berol 260, 266, and 840 from Akzo Nobel Surface Chemistry LLC; Ethylan 185, 1003 1005, 1008, and 25-3 from Akzo Nobel Surface Chemistry LLC; Neodol 91-2.5, 91-5, 91-6, 91-8, and 91-8.4 from Shell Chemicals; Lutensol ON 30, 50, 66, 70, and 80 from BASF; KF-640, KF-642, and KF-643 from Shin-Etsu Chemical Co., Ltd.
The binder may be a monomer, oligomer or polymer selected from the group of resins comprising acrylates, acrylics, alkyds, amines, amides, aminos, isocyanates, polyurethanes, epoxies, acrylic/epoxy hybrids, epoxy esters, polyesters, polyethers, polyvinyl alcohols, phenolics, polyvinyl acetates, styrenes, styrene-butadiene copolymers, silicone, polyvinyl butyrals, hydrocarbon resins, or a mixture thereof. In a preferred embodiment, the binder is selected from a group of meth(acrylate) resins, which may be a mixture of monomers and oligomers having various degrees of functionality (mono-, di-, tri-, tetra-, penta-, and hexafunctionality) and functional groups like urethane (meth)acrylate, polyurethane (meth)acrylate, ester (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, polyether (meth)acrylate, amine modified polyether(meth)acrylate, and acrylic (meth)acrylate. Exemplary commercially available (meth)acrylate resins include but are not limited to hexafunctional urethane acrylate, dipentaerythritol hexaacrylate, dipentaerythritol pentaacrylate, ethoxylated pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, ethoxylated pentaerythritol triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, propoxylated glycerol triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, hexamethylene diacrylate, poly(ethylene)glycol diacrylate, bisphenol-A diacrylate, ethoxylated bisphenol-A diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, neopentylglycol diacrylate, ethoxylated neopentylglycol diacrylate, propoxylated neopentylglycol diacrylate, tripropylene glycol diacrylate, ethylene glycol diacrylate, bisphenol A diacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, isobonyl acrylate, alkyl acrylate, benzyl acrylate, phenyl acrylate, mixtures thereof, and the like.
In a preferred embodiment, the composition may comprise a low surface energy compound selected from fluorine-containing additives, which provides the resulting coating layer with easy-clean performance. Preferably, the fluorine-containing additive comprises at least a perfluoropolyether group. Exemplary commercially available fluorinated additives include but are not limited to Megaface RS-72-K, RS-75, RS-76-E, RS-76-NS, RS-90, F-555, F-558, F-571, and F-552 from DIC Corporation; OPTOOL DAC-HP and DSX from Daikin Industries, Ltd.; Fluorolink MD500, MD700, AD1700, 5101X, 5113X, S10, and Fomblin MD40 from Solvay; KY1203, KY164, and KY108 from Shin-Etsu Chemical Co., Ltd.
In certain embodiments, the composition may further comprise a dispersion of inorganic particles to improve hardness and enhance the formation of channels in the stationary phase. Examples of the inorganic particles include but are not limited to silica, alumina, zirconia, titania, vanadia, chromia, ceria, tin oxide, and mixtures thereof. The average particle size may range from 1 nm to 100 μm, and measurement of the particle size may be made using transmission electron microscopy. For coating of high gloss, the average particle size ranging from 1 to 200 nm is preferred. Particles of a size greater than 200 nm may be used for coating of low gloss. The dispersion medium may be any suitable organic solvents or water selected in accordance with the coating composition. The organic solvent is usually present in an amount of 15 to 90% by weight of the total dispersion. Exemplary commercially available nanoparticle dispersions include but are not limited to Organosilicasol IPA-ST, IPA-ST-L, IPA-UP, IPA-ST-ZL, MEK-ST, MEK-ST-L, MEK-ST-UP, MIBK-ST, MEK-EC-2102, MEK-EC-2104, MEK-AC-2202, MEK-AC-4101, and MIBK-SD from Nissan Chemical Industries, Ltd.; NanoBYK 3650, 3651, 3652, 3605, 3610, 3600, 3601, and 3602 from BYK-Chemie GmbH; Nanopol A710, A720, C764, C784, XP20/0166, XP20/0343, and XP21/1279 from Evonik Degussa GmbH; HighLink Nan0 G from Clariant; and mixtures thereof.
Organic solvents or water may be optionally added as diluent in suitable amount to adjust the coating composition to the appropriate concentration and viscosity. Examples of solvents include but are not limited to alcohols (methanol, ethanol, propanol, isopropyl alcohol, butanol), ketones (methyl isobutyl ketone, methyl ethyl ketone, dimethyl ketone, acetone), esters (ethyl acetate, normal butyl acetate, propylene glycol mono-methyl ether acetate), glycols (ethylene glycol), glycol ethers (ethylene glycol mono n-propyl ether, propylene glycol mono-methyl ether), aromatic hydrocarbons (toluene, xylene), aliphatic hydrocarbons (hexane, heptane, cyclohexane), cellosolves (ethyl cellosolve, butyl cellusolve), and mixtures thereof.
In certain embodiments, ultraviolet (UV) radiation is used for curing the coating composition, and the composition may contain one or more photo-initiators. Examples of photo-initiators include but are not limited to 2-hydroxy-2-methyl-1-phenyl-1-propane, 2,4,6-trimethylbenzoyl diphenyl phosphine, bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide, 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2,2-dialkoxybenzophenone, acetophenone, and mixtures thereof.
Additives typically used to impart other desired properties may be optionally added to the coating composition. Examples include leveling agents, defoamers, absorbers, catalysts, initiators, stabilizers, biocides, matting agents, waxes, rheology modifiers, corrosion inhibitors, adhesion promoters, fire retardants, extenders, fillers, dyes, and pigments, and the like.
In another aspect of the present invention, accordingly, a coating layer is provided. The coating layer according to the present invention comprises:
In accordance with certain embodiments,
The components for forming the stationary phase and the mobile phase have the same meaning as defined above.
In certain embodiments, for fingerprints with high content of sweat or water, the mobile phase is preferably a liquid comprising one or more hydrophilic surfactants with an HLB value of 10 or greater as defined above.
In certain embodiments, for very oily fingerprints, the mobile phase may further comprise 10 to 40 parts by weight of one or more lipophilic surfactants with an HLB value of greater than 6 to 10 as defined above.
In a preferred embodiment, the stationary phase may comprise a low surface energy compound selected from fluorine-containing additives as defined above, to provide the resulting coating layer with easy-clean performance.
In certain embodiments, the stationary phase may further comprise inorganic particles with a size ranging from 1 nm to 100 μm as defined above, to improve hardness and enhance the formation of channels in the stationary phase.
The thickness of the coating layer is preferably from 5 to 100 microns. In certain embodiments, the coating also has the advantage of being high gloss and transparent.
In yet another aspect of the invention, methods for forming an anti-fingerprint coating on top of a substrate, the use of the anti-fingerprint coating to diffuse and fade fingerprints, as well as methods for evaluating and improving the performance of diffusion and fading, are provided.
According to the present invention, the methods for forming an anti-fingerprint coating on top of a substrate comprise the steps of:
In certain embodiments, the coating composition according to the present invention may be directly applied on top of a variety of substrates, including but not limited to plastics (for example, polycarbonate, acrylonitrile-butadiene-styrene, polymethyl methacrylate, polyamide, polyimide, polyethylene, polypropylene, polyvinyl chloride, acrylics, polyester, epoxies, polystyrene, polyurethane, blends, and the like), metals and alloys (for example, stainless steel, aluminum, magnesium, and the like), glass (for example, soda lime, borosilicate, aluminum silicate, lead glass, and the like), ceramics, and composites.
In certain embodiments, the coating composition may be applied as a top coating layer or a clear coating layer over one or more coating layers already deposited onto the substrate. Unless otherwise defined, when used herein, the term “substrate” is meant to include both a substrate without any coating coated thereon, and a substrate that is already coated with one or more coating layers.
In certain embodiments, the coating composition may be applied on top of a substrate by conventional techniques, including but not limited to spray coating, dip coating, flow coating, spin coating, brushing, roll coating, flow coating, bar coating, and knife coating.
In certain embodiments, the coating composition may be dried at ambient or elevated temperatures or cured by conventional curing methods, such as thermal cure, ultraviolet or electron beam, to form a coating layer.
The method for diffusing and fading fingerprints according to the present invention comprises providing a coating layer formed according to the above-discussed methods to contact the fingerprints. Specifically, when in contact with fingerprints, the coating layer according to the present invention is capable of both diffusing and fading the fingerprints.
The method for evaluating and improving the anti-fingerprint performance of the coating layer according to the present invention comprises the steps of:
Specifically, the fingerprint-fading performance may be evaluated by depositing fingerprints onto the coating layer and recording the fading of the fingerprint droplets over time under an optical microscope with a magnification of 5× using a digital camera. The number and the total area of the fingerprint droplets may be computed from the digital images. In certain embodiments, the number of fingerprint droplets decreases by more than 30%, 52%, and 73% after 10 min, 1 h, and 6 h, respectively, and the total area of fingerprint droplets decreases by more than 1%, 5%, and 13% after 10 min, 1 h, and 6 h, respectively.
When used herein, the easy-clean performance of the coating layer is related to liquid repellency, which is typically evaluated by the measurements of water and tetradecane (oil) contact angles using an optical contact angle instrument.
In still another aspect of the invention, articles coated with a coating layer according to the present invention are provided. The coating layer according to the present invention is suitable for use in, for example, consumer electronic devices, which have surfaces like housings, touch screens, and displays that are frequently touched by users' fingers. Specifically, the devices include but are not limited to mobile phones, tablets, personal computers, laptop computers, electronic readers, music players, computer accessories (monitors, mouse, keyboards, portable hard disks, printers), televisions, game consoles, global positioning system devices, wearable devices, and the like. Other applications include automotive interior and exterior parts, and home appliances.
The above and other objectives, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art by being described in embodiments thereof with reference to the accompanying drawings.
The following examples are offered to illustrate, but not to limit the claimed invention.
146 g of a binder mixture (970-CJS-704, available from Akzo Nobel Coatings (Tianjin) Co. Ltd., comprising 100 g of binder, 40 g solvent, and 6 g of photoinitiator), 50 g of an ethoxylated alcohol with an HLB value of 10.5 (Berol 260, available from Akzo Nobel Surface Chemistry LLB), 50 g of a nanosilica dispersion (NanoBYK 3652, available from BYK-Chemie GmbH), 7 g of a fluorinated additive (Megaface RS-75, available from DIC Corporation), and 30 g of isopropyl alcohol were mixed and stirred for 10 minutes at room temperature. The resulting mixture was allowed to rest for 5 min.
146 g of a binder mixture coating solution (970-CJS-704, available from Akzo Nobel Coatings (Tianjin) Co. Ltd., comprising 100 g of binder, 40 g solvent, and 6 g of photoinitiator), 7 g of a fluorinated additive (Megaface RS-75, available from DIC Corporation), and 30 g of isopropyl alcohol were mixed and stirred for 10 minutes at room temperature. The resulting mixture was allowed to rest for 5 min.
The coating composition obtained in Example 1 was applied on top of a polycarbonate substrate by spray coating. The coating was baked at 60° C. for 5 min before being cured twice by UV radiation at a line speed of 10 m/min and a light intensity of 1,000 mJ/cm2. The cured coating layer has a film thickness of about 20 μm.
The procedure of Example 2 was repeated except for using the coating composition obtained in Comparative Example 1.
The coating layers obtained from Example 2 and Comparative Example 2 were evaluated in accordance with the following methods.
Contact angle measurements were performed on the coating layers using an optical contact angle instrument OCA 20 from DataPhysics equipped with a digital camera and the SCA 20 software. First, a 4 μL drop of deionized water was applied to a fresh area on the coating layer, and images of the drop were recorded at a speed of 4 frames per second for 5 min by the software. The procedure was repeated for a 4 μL drop of tetradecane.
The drop images were analyzed using the SCA 20 software to determine the drop parameters like height, base diameter, and contact angle, as illustrated in
Fingerprints were deposited onto the coating layer, and images were recorded as a function of time under an optical microscope with a magnification of 5× using a digital camera. Comparison of the images in
Analysis of the images was performed using the ImageJ 1.46r software from National Institute of Health. The number and the total area of the fingerprint droplets were measured and calculated using standard processing and particle measurement tools available in ImageJ.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CN2014/074371 | Mar 2014 | CN | national |
| 14174651.1 | Jun 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/056671 | 3/27/2015 | WO | 00 |
