US20140272127A1

US20140272127A1 - Anti-Glare Coatings with Sacrificial Surface Roughening Agents and Methods for Forming the Same

Info

Publication number: US20140272127A1
Application number: US14/064,921
Authority: US
Inventors: Nikhil Kalyankar; Scott Jewhurst
Original assignee: Intermolecular Inc
Current assignee: Intermolecular Inc; Guardian Glass LLC
Priority date: 2013-03-12
Filing date: 2013-10-28
Publication date: 2014-09-18
Also published as: US20140272387A1; US20140272384A1; US9423532B2; WO2014143618A1

Abstract

Embodiments provided herein describe optical coatings, panels having optical coatings thereon, and methods for forming optical coatings and panels. A sol-gel matrix is formed above a surface of a substrate. Organic micro-particles are embedded in a surface of the sol-gel matrix. A heat treatment is applied to the sol-gel matrix and the embedded plurality of organic micro-particles. Substantially all of the organic micro-particles are removed during the heat treatment, and after the heat treatment, the sol-gel matrix has a surface roughness suitable to provide anti-glare properties.

Description

CROSS-REFERENCE TO RELATED APPLICATION

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.

TECHNICAL FIELD

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.

BACKGROUND OF THE INVENTION

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a cross-sectional view of a substrate;

FIG. 2 is cross-sectional view of the substrate of FIG. 1 with a matrix layer formed thereon;

FIG. 3 is a cross-sectional view of the substrate of FIG. 2 with micro-particles deposited onto the matrix layer;

FIG. 4 is a cross-sectional view of the substrate of FIG. 3 illustrating the micro-particles being pressed into the matrix layer with a roller;

FIG. 5 is a cross-sectional view of the substrate of FIG. 4 after the micro-particles have been pressed into the matrix layer;

FIG. 6 is a cross-sectional view of the substrate of FIG. 5 after undergoing a heat treatment to remove the micro-particles;

FIG. 7 is a cross-sectional view of a substrate;

FIG. 8 is a cross-sectional view of the substrate of FIG. 7 illustrating a multi-layer coating being deposited thereon with a coating mechanism;

FIG. 9 is a cross-sectional view of the substrate of FIG. 8 after the multi-layer coating is formed thereon;

FIG. 10 is a cross-sectional view of the substrate of FIG. 9 after undergoing a heat treatment; and

FIG. 11 is a flow chart illustrating a method for forming an anti-glare coating, or a coated article, according to some embodiments.

DETAILED DESCRIPTION

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.
FIGS. 1-6 illustrate a method for forming a coated article (or anti-glare panel) 100 according to some embodiments of the present invention. Referring to FIG. 1, a transparent substrate 102 is shown. In some embodiments, the transparent substrate 102 is made of glass and has a thickness 104 of, for example, between 0.1 and 2.0 centimeters (cm). Although only a portion of the substrate 102 is shown, it should be understood that the substrate 102 may have a width of, for example, between 5.0 cm and 2.0 meters (m). In some embodiments, the substrate 102 is made of a transparent polymer.
As shown in FIG. 2, a matrix (or matrix layer) 106 is formed above the transparent substrate 102. In some embodiments, the matrix 106 is formed directly on the transparent substrate 102. However, in some embodiments, other materials and/or layers may be formed between the substrate 102 and the matrix 106. In some embodiments, the matrix 106 is formed using a sol-gel formulation. The sol-gel formulation may include a combination of matrix forming silanes or siloxanes containing one or more of the following: tetraalkoxysilane, oligomeric alkoxysiloxanes, bis(alkoxysilanes), silesquioxanes, dipodal alkoxysilane and/or (alkyl/aryl)trialkoxysilane. An organic solvent, such as an alcohol, ketone, ester, tetrahydrofuran (THF), etc. may be added which serves as a cosolvent for the ingredients. The formulation may also include an accelerator or a catalyst such as an acid, a base, a metal carboxylate or any other type of chemical which can catalyze the sol-gel reaction and water for hydrolysis of the alkoxide groups of the silanes/siloxanes. Additionally, inorganic nanoparticles (e.g., 3-200 nanometers (nm)) may be added to provide structural rigidity to the matrix, along with a stabilizer, such as a surfactant, and ultraviolet (UV) blocking nanoparticles, such as ZnO, TiO₂, CeO₂.
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.
Still referring to FIG. 2, the formulation is deposited onto the transparent substrate 102 (e.g., via spin coating) to form a gelled or solidified layer (i.e., the matrix layer 106) that has a thickness 108 of, for example, between 1 and 100 micrometers (μm). Most of the solvent is removed during the gelation, leaving a compliant, deformable solid layer (or film). After the solvent is removed, the matrix 106 has a substantially smooth, flat upper surface 110.
As shown in FIG. 3, in some embodiments, a plurality of micro-particles (or micro-crystals) 112 are deposited onto the upper surface 110 of the matrix 106. In some embodiments, the micro-particles 112 are made of organic materials. Exemplary micro-particles 112 include polystyrene beads, polymethylmethacrylate (PMMA) beads, or the like, which may be solid, hollow, or of a core-shell construction. The micro-particles 112 may have a uniform, multi-modal, or random particle size distribution. In some embodiments, the size distribution, or effective particles size, (or widths 114) of micro-particles is between 0.1 and 10 μm. In some embodiments, the micro-particles may be non-spherical such as ellipsoidal, or of random shape and surface features.
As shown in FIG. 3, the micro-particles 112 substantially lie on the upper surface 110 of the matrix 106. However, depending on the method of deposition, the micro-particles 112 may at least partially penetrate the matrix 106. For example, in some embodiments, a high velocity spray deposition is used, which provides sufficient force for the micro-particles to completely penetrate the top surface 110 (which may have a crust-like barrier) of the matrix 106.
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 FIG. 4. In some embodiments, a spray deposition or inkjet of the micro-particles 112 may be used, followed by embedding via a mechanical force applied by a roller (e.g., roller 116 in FIG. 4) or a flat plate. In some embodiments, a wet deposition may be used with simultaneous embedding by an applied a mechanical force using a roll (roller) coating, wire rod coating, draw down coating, doctor blade coating, gravure coating, etc.
FIG. 5 illustrates the coated article 100 after the deposition, and the additional embedding process (if used), of the micro-particles 112. In some embodiments, the micro-particles 112 are nearly completely embedded into the upper surface 110 of the matrix 106. However, as suggested above, the degree to which the micro-particles 112 are embedded into the upper surface 110 of the matrix 104 may vary (i.e., between partially embedded to completely embedded) and may be controlled using process parameters during application as well as the material properties of the gelled matrix and micro-particles.
Referring now to FIG. 6, the coated article 100 then undergoes a thermal treatment to combust away (or “burn out” or “burn off”) substantially all of (e.g., at least 90%) the micro-particles 112. As shown, after the micro-particles 112 have been removed, the thickness 108 of the matrix 106 may vary between, for example, approximately 1 and 50 μm. That is, as shown, the upper surface 110 of the optical coating 104 has a series a surface features 116 (i.e., texturing or roughness) formed thereon, which cause the thickness 108 to vary. Due to the surface features 116, the upper surface 110 of the matrix 104 may have an average effective surface roughness ranging, for example, from 0.2 to 0.8 μm. The thermal treatment may also cure the matrix 106 by aiding in the poly-condensation reactions and removing excessive organics, leaving an inorganic coating with a textured surface. As will be appreciated by one skilled in the art, such an effective surface roughness is suitable to provide the matrix 106 with anti-glare properties. In other words, the matrix 106 now forms an anti-glare coating.
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 SiO₂produced). 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.
FIGS. 7-10 illustrate a method for forming a coated article 200 according to other embodiments of the present invention. Referring to FIG. 7, a transparent substrate 202, which may be similar to the substrate 102 described above, is provided.
Referring to FIG. 8, a coating mechanism 204 is used to simultaneously deposit a base (or matrix) layer and a coating layer, with micro-particles suspended therein. Specifically, the coating mechanism includes a first slot 206 and a second slot 208 which operate simultaneously to deposit a multi-layer coating 210 that includes a base layer 212 and a coating layer 214. In particular, the base layer 212 is dispensed from the first slot 206 of the coating mechanism 206, and the coating layer 214 is dispensed from the second slot 208.
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 FIG. 8) such that the base layer 212 is deposited above (e.g., on) an upper surface 216 of the transparent substrate 202 and the coating layer 214 is deposited above the base layer 212. Although not shown, it should be understood that the coating mechanism 204 and/or the slots 206 and 208 may extend the width of the transparent substrate 202 so that the entire transparent substrate 202 may be covered by the multi-layer coating 210 with only one pass of the coating mechanism 204. In some embodiments, the base layer 212 is made using the same materials and methods as the matrix 106 described above, and the coating layer 214 includes a carrier solvent with micro-particles 218 (similar to embodiments described above) suspended therein.
FIG. 9 illustrates the coated article 200 after the deposition of the multi-layer coating 210. As shown, the micro-particles 218 are completely embedded into an upper surface 220 of the multi-layer coating 210 (and/or the coating layer 214) (because the micro-particles 218 are suspended within the carrier solvent prior to deposition). Although not shown, the multi-layer coating 210 may have a thickness similar to the matrix 104 described above (e.g., between 1 and 100 μm before heat treatment).
Referring to FIG. 10, the coated article 200 then undergoes a heat treatment similar to that described above. The heat treatment combusts off the micro-particles 218 such that a series a surface features 222 (i.e., texturing or roughness) are formed on the upper surface 220 of the coating 210, which cause the thickness thereof to vary. Due to the features 222, the upper surface 220 of the coating 210 may have an average surface roughness ranging from 0.2 to 0.8 μm, thus providing the coating 210 with anti-glare properties (i.e., the coating 210 forms an anti-glare coating).
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.
FIG. 11 illustrates a method 1100 for forming an anti-glare coating (or a coated article) according to some embodiments. At step 1102, a layer is formed above a substrate, such as the transparent substrates described above. The layer is formed with a plurality of organic micro-particles embedded therein. The micro-particles have a size distribution of, for example, between about 0.1 micrometers (μm) and 10 μm.
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.

Claims

What is claimed:

1. A method of forming an anti-glare coating, the method comprising:

forming a sol-gel matrix above a surface of a substrate;

embedding a plurality of organic micro-particles in a surface of the sol-gel matrix, wherein the plurality of organic micro-particles have a size distribution between about 0.1 micrometers (μm) and 10 μm;

applying a heat treatment to the sol-gel matrix and the embedded plurality of organic micro-particles, wherein 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.

2. The method of claim 1 wherein the sol-gel matrix has a thickness between 1 μm and 100 μm.

3. The method of claim 1 wherein the plurality of organic micro-particles comprise polystyrene beads, polymethylmethacrylate (PMMA) beads, or a combination thereof.

4. The method of claim 1 wherein each of the plurality organic micro-particles have one of a solid, hollow, or core-shell construction.

5. The method of claim 1 wherein the embedding of the plurality of organic micro-particles into the surface of the sol-gel matrix is performed using high velocity spray, application of a mechanical force, or a combination thereof.

6. The method of claim 1 wherein the heat treatment comprises heating the sol-gel matrix and the embedded plurality of organic micro-particles to a temperature in the range of 450° C. to 700° C.

7. A method of forming an anti-glare coating, the method comprising:

forming a sol-gel matrix, wherein the sol-gel matrix comprises a plurality of organic micro-particles having a size distribution between about 0.1 μm and 10 μm;

applying the sol-gel matrix to a surface of a substrate, wherein the plurality of organic micro-particles segregate to a top surface of the sol-gel matrix after the applying of the sol-gel matrix;

applying a heat treatment to the sol-gel matrix, wherein 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 has an effective surface roughness between 0.2 μm and 0.8 μm.

8. The method of claim 7 wherein the sol-gel matrix has a thickness between 1 μm and 100 μm.

9. The method of claim 7 wherein the plurality of organic micro-particles comprise polystyrene beads, polymethylmethacrylate (PMMA) beads, or a combination thereof.

10. The method of claim 7 wherein each of the plurality organic micro-particles have one of a solid, hollow, or core-shell construction.

11. The method of claim 7 wherein the heat treatment comprises heating the sol-gel matrix to a temperature in the range of 450° C. to 700° C.

12. The method of claim 7 wherein the segregation of the plurality of organic micro-particles to the top surface of the sol-gel matrix is facilitated by at least one of the use of micro-particles that are buoyant in the sol-gel matrix, a surface segregating surfactant within the sol-gel matrix, or by the application of an external electric field.

13. A method of forming an anti-glare coating, the method comprising:

forming a sol-gel matrix;

forming a particle dispersion formulation, wherein the particle dispersion formulation comprises a plurality of organic micro-particles having a size distribution between about 0.1 μm and 10 μm;

applying the sol-gel matrix to a surface of a substrate;

applying the particle dispersion formulation to a top surface of the sol-gel matrix, the sol-gel matrix and the particle dispersion formulation jointly forming a coating;

applying a heat treatment to the coating, wherein 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 a surface roughness between 0.2 μm and 0.8 μm.

14. The method of claim 13 wherein the coating has a thickness between 1 μm and 100 μm.

15. The method of claim 13 wherein the plurality of organic micro-particles comprise polystyrene beads, polymethylmethacrylate (PMMA) beads, or a combination thereof.

16. The method of claim 13 wherein each of the plurality organic micro-particles have one of a solid, hollow, or core-shell construction.

17. The method of claim 13 wherein the heat treatment comprises heating the coating to a temperature in the range of 450° C. to 700° C.

18. The method of claim 13 wherein the applying of the sol-gel matrix and the applying of the particle dispersion formulation occur simultaneously.

19. The method of claim 13 wherein the applying of the sol-gel matrix and the applying of the particle dispersion formulation are performed with a coating mechanism having a first slot and a second slot, wherein the sol-gel matrix is dispensed from the first slot and the particle dispersion formulation is dispensed from the second slot.

20. The method of claim 13, wherein the plurality of organic micro-particles are completely embedded within the coating.