The present invention relates to optical coatings. More particularly, this invention relates to optical coatings that improve, for example, the anti-glare performance of transparent substrates and methods for forming such optical coatings.
Anti-glare coatings, and anti-glare panels in general, are desirable in many applications including, portrait glass, privacy glass, and display screen manufacturing. Such optical coatings scatter specular reflections into a wide viewing cone to diffuse glare and reflection. It is difficult to achieve a substrate that simultaneously reduces gloss (i.e., specular reflection) and haze (i.e., diffuse transmittance) while relying on light scattering to obtain anti-glare properties.
Conventional methods of forming anti-glare panels include, for example, wet etching the surface of the substrate, using mechanical rollers with pre-defined textures on substrates to create a surface roughness, and applying thin, polymeric films with texture to the substrates using adhesives. Such methods are expensive, have low throughput (i.e., a low rate of manufacture), and lack of precise control with respect to surface texture, which results in a diffuse scattering coating with poor light transmittance or good light transmittance, but poor reduction of glare.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale.
The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
The term “horizontal” as used herein will be understood to be defined as a plane parallel to the plane or surface of the substrate, regardless of the orientation of the substrate. The term “vertical” will refer to a direction perpendicular to the horizontal as previously defined. Terms such as “above”, “below”, “bottom”, “top”, “side” (e.g. sidewall), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane. The term “on” means there is direct contact between the elements. The term “above” will allow for intervening elements.
Embodiments described herein provide for optical coatings, and methods for forming optical coatings, that improve the anti-glare (and/or the anti-reflective) performance of transparent substrates. In accordance with some embodiments, this is accomplished by forming a layer above transparent substrate with micro-particles (e.g., organic micro-particles) embedded in or near the upper surface thereof. The layer (and/or the substrate as a whole) then undergoes a heat treatment which causes the micro-particles to be “combusted off” (i.e., removed). As a result, the upper surface of the layer has a series of surface features thereon which give the layer an effective surface roughness or texture (e.g., between 0.2 micrometers (μm) and 0.8 μm) that is suitable for providing the layer with anti-glare properties. Effective surface roughness may refer to the average surface roughness that a beam of light encounters upon incidence. Effective roughness may refer to the same concept as average surface roughness for normal beam incidence.
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The components of the sol-gel formulation are mixed (as needed) in a pre-determined manner (i.e., composition, order of addition, temperature during mixing, etc.) for a pre-determined time. The presence of alkyltrialkoxysilane in the formulation may help in providing the ability to prepare a several micron thick gelled layer while reducing the likelihood that the layer will crack during thermal treatment to burn off the micro-particles (see below). In some embodiments, a pre-existing matrix formulation may be used to form the matrix, such as commercially available polysiloxane formulations, polysilazane formulations, polyamide formulations, polyacrylate formulations etc.
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However, in some embodiments, an additional process may be performed to embed, or further embed, the micro-particles 112 into the matrix 106. For example, in some embodiments, the micro-particles 112 are deposited using a wet deposition process in which the micro-particles 112 are suspended in a carrier solvent. The micro-particles 112 may then be pressed into the matrix 104 via a mechanical force, such as by passing a roller 116 over the micro-particles 112, such as that shown in
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In should also be noted that some of the micro-particles 112 may be embedded into the upper surface 110 of the matrix 106 such that after the heat treatment, some pores are formed near the upper surface 110 of the matrix 106. As will be appreciated by one skilled in the art, the presence of the pores may reduce the overall refractive index of the respective portion(s) of the matrix 106, thus also providing the matrix 106 (or anti-glare coating) with anti-reflective properties.
In some embodiments, similar to those described above, a sol-gel formulation is prepared using a 50:50 molar combination of tetraethoxysilane (TEOS) and isooctyltrimethoxysilane (as the alkyltrialkoxysilane referred to as IOTMS) as the matrix (and/or binder) material, n-butanol as the solvent, nitric acid as the catalyst, ORGANOSILICASOL IPA-ST-MS (e.g., particle size ˜10-20 microns) spherical silica particles (available from Nissan Chemical America Corporation of Houston, Tex.) as filler material, and water. The total ash content of the solution is 10% (based on equivalent weight of SiO2 produced). The ratio of alkyltrialkoxysilane-based matrix to silica nano-particle fillers is 90:10 ash content contributions. Pre-mixed silanes and silica nano-particles are mixed with water (e.g., 5 times the molar mixed silane amount), nitric acid (e.g., 0.05 times the molar amount of TEOS combined with IOTMS) and n-butanol. The solution is stirred for 24 hours at room temperature, or at an elevated temperature (e.g., 30° C.-60° C.), and cooled to room temperature before application.
The formulation is spin coated onto a clean, dry glass substrate such that a gelled layer with a thickness of approximately 5 μm is formed thereon. The substrate may then be subjected to a limited low temperature pre-cure (e.g., 50° C.-150° C. for 2 min to 10 min) to remove excess solvent and promote gelation. The substrate is then sprayed with polystyrene particles (e.g., having a mean particle size of 1 μm) dispersed in an organic solvent (e.g., 5% by mass) and allowed to air dry, dry under forced air, and/or dry under forced inert gas, with an application of heat (e.g., 50° C.-150° C. for 2 min), or a combination of these methods to remove excessive solvent.
A roller is used immediately afterwards to embed the polystyrene particles into the top layer of the gelled matrix using a fixed and pre-determined normal force without affecting the structural integrity of the gelled, matrix layer. The glass substrate is then heat treated at 500° C. to 700° C. for 3 min to 20 min to combust off the micro-particles, leaving behind a micro-textured surface (with a rough inorganic coating) with a mean surface roughness of 0.2 to 0.8 μm. The heat treatment also helps in curing the matrix material to a more dense, robust and highly interlinked network leading to additional cohesive and adhesive durability.
In some embodiments, the micro-particles are suspended within the matrix-forming solution before the matrix material is deposited. After deposition onto the substrate, the micro-particles segregate preferentially to the coating-air interface (i.e., the top surface of the matrix layer) to concentrate only in the top layer as discreet particles before gelation occurs. Upon application of a thermal treatment, the micro-particles are combusted off, causing the surface features to be formed on the matrix layer/anti-glare coating.
In some embodiments, the segregation of the micro-particles may be achieved by using micro-particles which are buoyant in the wet coating, by use of micro-particles which are treated with a surface segregating surfactant, or by application of an external electric field which attracts particles with a charged surface to the top of the coating before it gels.
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In the embodiment shown, during the deposition process, the coating mechanism 204 is moved across the transparent substrate 202 (e.g., from right to left in
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The methods described herein allow for controlling the surface roughness of the formed anti-glare coating by, for example, adjusting the size(s) and/or distribution of the micro-particles that are deposited onto and/or embedded in the upper surface of the matrix (or base) layer. This parameter may be easily adjusted and/or consistently reproduced.
In some embodiments, the layer is formed above the substrate and the micro-particles are then deposited onto and then embedded into the layer by, for example, application of a mechanical force. In some embodiments, the micro-particles are dispersed within the material used to form the layer before the layer is deposited. In some embodiments, the layer is a multi-layer coating, and the micro-particles are included in a separate layer, such as a particle dispersion, which is deposited above a sol-gel matrix.
At step 1104, the layer (and/or the substrate) undergoes a heat treatment. The heat treatment causes the micro-particles to be removed (e.g., “combusted off”) from the layer. As a result of the removal of the micro-particles, an upper surface of the layer is provided with an effective surface roughness between 0.2 μm and 0.8 μm. At step 1106, the method 1100 ends with an anti-glare coating having been formed above the substrate.
Thus, in some embodiments, a method of forming an anti-glare coating is provided. A sol-gel matrix is formed above a surface of a substrate. A plurality of organic micro-particles are embedded in a surface of the sol-gel matrix. The plurality of organic micro-particles have a size distribution between about 0.1 micrometers (μm) and 10 μm. A heat treatment is applied to the sol-gel matrix and the embedded plurality of organic micro-particles. Substantially all of the embedded plurality of organic micro-particles are removed during the heat treatment, and after the heat treatment, the sol-gel matrix has an effective surface roughness between 0.2 μm and 0.8 μm.
In some embodiments, a method of forming an anti-glare coating is provided. A sol-gel matrix is formed. The sol-gel matrix comprises a plurality of organic micro-particles having a size distribution between about 0.1 μm and 10 μm. The sol-gel matrix is applied to a surface of a substrate. The plurality of organic micro-particles segregate to a top surface of the sol-gel matrix after the applying of the sol-gel matrix. A heat treatment is applied to the sol-gel matrix. Substantially all of the plurality organic micro-particles are removed from the sol-gel matrix during the heat treatment, and after the heat treatment, the sol-gel matrix formed has an effective surface roughness between 0.2 μm and 0.8 μm.
In some embodiments, a method of forming an anti-glare coating is provided.
A sol-gel matrix if formed. A particle dispersion formulation is formed. The particle dispersion formulation includes a plurality of organic micro-particles having a size distribution between about 0.1 μm and 10 μm. The sol-gel matrix is applied to a surface of a substrate. The particle dispersion formulation is applied to a top surface of the sol-gel matrix. The sol-gel matrix and the particle dispersion formulation jointly form a coating. A heat treatment is applied to the coating. Substantially all of the plurality of organic micro-particles are removed from the coating during the heat treatment, and after the heat treatment, the coating maintains an effective surface roughness between 0.2 μm and 0.8 μm.
Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.
This application claims priority to U.S. Provisional Patent Application No. 61/777,995, filed Mar. 12, 2013, entitled “Sol-Gel Coatings,” which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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61777995 | Mar 2013 | US |