WO2016044937A1

WO2016044937A1 - Photochromic frit and novel uses thereof

Info

Publication number: WO2016044937A1
Application number: PCT/CA2015/050942
Authority: WO
Inventors: Bryce HAWKINGS
Original assignee: Graf X Glass Inc.
Priority date: 2014-09-23
Filing date: 2015-09-23
Publication date: 2016-03-31

Abstract

Photochromic frit is manufactured, with characteristics relating to photochromic behavior, optical clarity, compatibility with float-glass manufacturing processes, or compatibility with optical or other organic plastic compounds used as coatings or intermediate layers in manufactured glass laminates (such as automotive windshields or certain so-called safety glass panels). The photochromic frit is useful for inclusion in transparent panels or products, as a post-formed coating material, for sheets, shapes such as lenses, laminate layers in automotive or other transparent windows and panels, as a part of a colorant layer or coating for paint, glaze, masonry, cosmetics, clothing, or similar applications, whether during manufacture or screened and printed.

Description

Title: Photochromic Frit and Novel Uses Thereof Inventor: Bryce HAWKINGS, Canada

Background of the Invention [0001] It is known in the prior art to prepare "frit" for use in ceramics and glass-making. "Frit" is a term used in ceramics and glass-making to refer to a mixture of ceramic and other compounds for inclusion in glazing or molten glass during glass-making operations. In this instance, "frit" is used to refer to a modern style of materials which is of ceramic or glass made with specific compounds to provide specific characteristics to the finished product to which it is applied, and which is most usefully ground, pulverized or formed to be of very small, relatively homogenously-sized, particles.

[0002] Frit in the modern prior art is used in paint, ceramic glazes and coatings, and in the making of certain types of optically useful materials such as glass or plastics for lenses. In those cases, the frit is made to a specification, and then applied to the object to be treated, glazed or altered, and is then subjected to conditions such as very high temperatures, so that the frit may form a substantially uniform coating, or may become included in the surface layer of the object. In this way, glass may be made photochromic or tinted, float glass may be coated or colored, ceramic material may come to have a specific surface texture, color, reflectivity, and etc.

[0003] Some examples of the prior art which may be of relevance to the invention of this application are discussed in the following paragraphs.

US 3,208,860 to Armistead et al ('"860"), assigned to Corning Glass Works, discloses specific treatments to permit the use of inorganic silicate glasses with phototropic (photochromic) characteristics in amorphous inorganic glassy matrices (such as float glass) by providing sub-micron (ideally 0.004-0.02 microns) particles of photochromic glass crystal being encased in amorphous clear glass absent any other crystals at concentrations of approximately 0.05-0.1% by volume to provide a reversible photo-reactive or photochromic glass. A variety of means of achieving this result are described, including sprinkling the sub-micron crystalline particles on the surface of the matrix materials to form amorphous transparent glass in manufacturing steps and subjecting the matrix and crystals to high temperature and heat, to cause the crystals to disperse in the glassy matrix, to control the heat cycles applied to the glassy matrix to provide a second amorphous layer of submicroscopic droplets within the matrix of (silver halide, for example) to crystallize in place within the amorphous glassy matrix of the float glass substrate. The processes involved are complex, the products involved are necessarily inorganic glass, and the photochromic/phototropic materials involved are sub-micron crystals, much smaller and more difficult to manufacture and handle than larger conventional "frit"-style substances. [0004] US 4,046,586 to Uhlmann et al. ('"586"), assigned to American Optical Corporation provides for the use of inorganic photochromic crystals of between 0.003-1.0 micron particle size (preferably less than about 0.50 microns) in organic substrates such as films, sheets, filters for cameras, wall panels and ophthalmic lenses. The essence of the invention is to coat the photochromic particles' surfaces with a second inorganic material to protect the photochromic substance of the crystals from reacting with the organic substrate material. The photochromic crystals are by nature silver halide, and may not be glassy. The main advantage of this invention is to provide for photochromic ophthalmic lenses made of lightweight optical plastics by, for example, mixing coated photochromic crystals of silver halide into optical plastic and then forming the plastic to make lens shapes; similarly, the coated crystals can be included by mixing them into thermoplastic resins which may in turn be formed into sheets, injection molded into shapes, or otherwise formed. The key is to coat the crystal particles to prevent diffusion of halogen out of the crystal and into the organic substrate. '586 also discloses formation of the inorganic crystals (which need not be glass) by precipitation from a solution of silver salt, and requires that the coating be less than about 100 times the volume of the crystal, and be impervious to host chemistry [of the substrate in which the coated crystal is to be included]. The protective processing is complex, the photochromic crystals may be of uneven size distribution, and the invention has been used primarily in high-value end-products comprising specialized optical plastics for ophthalmic lenses, with the disadvantage that the process is not amenable to post-formation coating of end-products, but is required to be accomplished during manufacture of the end-product's base material (i.e. the lens is formed with crystals embedded, and not coated post-manufacture). [0005] A process described by Nanocerox, Inc. as the "Nanocerox Ceramic Powder Development Process" discloses a liquid-feed flame pyrolysis methodology to produce fine particles of metal oxide powder from highly volatile gaseous metal chlorides. The process is said to be in development, and to result in nano-oxides of particle sizes between 15-100 nm. The process has been applied to a variety of materials and results in relatively evenly distributed particle sizes without milling, grinding, crushing or other micronization techniques. It is said that the resulting nano-powders can be used in some of the same settings one would expect to see frits in use, for instance in providing ceramic coatings, colorants, surface hardening coatings (zirconia toughened alumina, military style transparent armor (armored glass), and self-cleaning coatings) and the like, but also in forming designed pure garnet crystals of usefully large scale by sintering pure garnet nano-particles to desired shapes (such as for laser manufacture). Another published aim of the Nanocerox research is to provide nano-sized catalyst particles for industrial processes or automotive exhaust treatment. The process is of only passing interest in discussing frit and frit alternatives, and does not contemplate the process being used in photochromic coatings, frit or glass manufacturing. Summary of the Invention

[0006] In this invention, a photochromic frit is manufactured, with

characteristics relating to photochromic behavior, optical clarity, compatibility with float-glass manufacturing processes, or compatibility with optical plastics used as coatings or intermediate layers in manufactured glass laminates (such as

automotive windshields or certain so-called safety glass panels), or other organic and inorganic substrates.

[0007] The invention in one embodiment is a frit or powdered glass or crystal substance with relatively uniform diameter crystal or particle sizes, the frit having photochromic properties,

[0008] In another, the frit comprising silver halide.

[0009] In an embodiment, the frit is comprised of particles with sizes between 0.002 - 1.0 microns in diameter, and the frit can be formed by grinding a precursor silver halide crystal with a ball mill or other mechanism to produce suitable size and size distribution of the frit particles, and the size can be made suitable for inclusion in concrete or fiberglass surface resins.

[0010] In some embodiments, the frit will be comprised of about 0.2-0.7% by weight silver.

[0011] In an embodiment, the photochromic frit is applied to the surface of glassy matrices during float glass manufacturing processes using a controlled deposition process to place the frit onto the surface of molten or semi-molten float glass and the frit bonds with the glass surface to form a micro-thin photochromic surface layer on the float glass; the frit may applied evenly to the glass, or in a pattern onto the glass, and the controlled deposition process can be done by one of: a pyrolytic coating; electrostatic deposition; computer-controlled print-head.

[0012] The frit in another embodiment can added to Polyvinyl Butaryl (PVB) while the PVB is in a liquid state, curing the PVB to a pliable state and the invention comprises forming the PVB with included photochromic frit into a pliable sheet. The pliable frit-including PVB sheet may be used in a laminate with other materials such as glass or solid panels or formed sheets, panes, windows and the like.

[0013] This invention focuses on the design and use of photochromic frit composition, and a process to synthesize frit compositions. Frits are ceramic compositions that, in a conventional process, have been fused and quenched to form granulated glass particles, and are important components in compounding enamels, paints and ceramic glazes.

[0014] The photochromic frits described here consist of an inorganic photochromic nanomaterial that may be homogeneously dispersed within a glass matrix (i.e., micron-sized glass particles) thus enabling a reversible transition from a transparent to a darkened state in the presence of certain wavelengths of visible light, which is imparted to the glass matrix. The frit of this invention has numerous applications in the architectural glass industry. For example, this photochromic frit can be used to produce "smart" laminate or architectural windows for controlling heat flow by radiation, in addition to offering UV protection.

[0015] Windows are a major source of heat transfer in homes and buildings regardless of the climate or season. "Smart" windows developed with novel functional nanomaterials such as photochromic frit may provide benefits to home and building owners in maximizing energy savings, as the photochromic nature of the glass can play a role in the temperature and energy conservation of the building. In an example, a building operator may control the temperature, or energy loss and gain, of a building by setting an appropriate level of darkness of the windows of the building depending upon the amount of light within a certain spectrum range hitting the windows' glass. Furthermore, the operator can be presented with a "cost vs. reward" structure before acquiring the product, to appreciate that the one-time capital expense (purchase of the photochromic window) will represent a profitable investment when the future operating expenses (savings in energy costs) are taken into account. [0016] This technology applies to the smart windows market, and also to existing architectural glass industries, and related frit-based industries, which include ceramic tile, glass for packaging, and the auto glass industry among others, including: innovation materials, construction products, building distribution and packaging. Other industries might also make use of photochromic frit, for example automotive, paints and coatings, plastics and resins, and fabrics. One can conceive of camouflage or artistic designs imparted to fabrics or objects or coatings by application of this frit, which is responsive to ambient lighting conditions.

[0017] This invention is loosely based on previously developed photochromic glass technologies developed by companies such as Corning, Inc. For example, several decades ago, Corning developed a glass technology involving the use of inorganic, photo-reactive materials such as silver halide crystals embedded within a glass matrix, Upon irradiation with light, silver and halide radicals formed, which absorb at a different wavelength than the ground state silver halide crystals, thus causing darkening of the glass. The silver and halide radicals cannot escape the glass matrix and recombine in the absence of light to restore the initial colour of the glass. This invention aims to use similar materials but composed as frit and then deployed in or on coatings, fabrics, lenses, windows, films, sub-layers, or other objects, [0018] Photochromic frit (powders) can be processed easily into a wide range of composite materials that can be incorporated into laminate glass structures or annealed onto the surface of float glass as a glazing to serve a wide range of commercial applications, among other things, and can be applied in patterns, differing densities, or in combinations with different frits with different reaction characteristics.

Brief Description of the Drawings

Figure 1 is a perspective drawing of a window in a wall, 1A showing the frit of the invention prior to photochromic change (or without frit), the window transparent; IB showing the window darkened after photochromic change, where the window's surface is coated or embedded with the frit of the invention; and 1C showing the window with a pattern of applied photochromic frit of the invention applied, in a darkened state. Figure 2 shows a laminate with three layers, the centre layer being a sheet comprising photochromic frit.

Detailed Description

[0019] Architectural glass is provided with photochromic qualities, which may be permanent parts of the glass or temporarily applied coatings or layered additions, and which may be applied to the whole of the glass panel, or to selective parts of the panel for aesthetic or functional purposes.

[0020] Photochromic, in this description, refers to the quality of changing transmissivity in a transparent or translucent panel or layer, responsive to certain frequencies of light or similar radiation. Typically, the transmissivity will decrease (i.e. the panel will darken) responsive to some frequency(ies) of light. This is well- known in personal eye-wear such as prescription or protective eyeglasses.

[0021] In one embodiment, photochromic frit ("PC Frit") is a form of glass, granulated or powdered, that contains photochromic crystals that enable the frit to darken when exposed to the Ultra-Violet (UV) wavelengths in sunlight, and then fade back to clear when not exposed to UV.

[0022] The chemical composition of PC Frit is substantially the same as normal Soda-Lime float glass used almost exclusively in the window and auto glass industries, It contains mainly Silica sand, lesser amounts of Sodium, Calcium and Magnesium, and small amounts of Aluminum and Iron. Silver is typically the main photochromic agent in PC Frit, and is added to the mixture, along with at least one of the halogens Chlorine, Fluorine and Bromine which, when heated to melting and cooled at a controlled rate, form Silver-Halide crystals that are permanently locked within the frit's precursor glass matrix. Once cooled and stabilized, the Silver-Halide crystals undergo a change at the molecular level when electrons are activated by UV and cause the Silver molecule to alter their ability to permit transmission of light, and darken. The electrons return to their original state when the UV light is removed, and the glass frit lightens to its original state. This darkening-fading process is entirely reversible and does not change over time, nor does it require external power sources (other than the UV radiation).

[0023] In the PC Frit manufacturing process, once the PC Frit precursor glass is cooled and fractured into a coarse raw state, it can be ground further into an ultra-fine powder which is the consistency necessary to be used in coatings or as an additive to other materials. The finely ground PC Frit will be clear or white when not exposed to UV, then will darken to black or dark grey when exposed to UV or sunlight. Other colors may be possible using other photochromic and associated materials in the PC Frit's composition. The extent of darkening, as well as the rate of darkening and fading, will depend (in this example) on the amount of Silver and Halogens that are in the frit composition, but the usual Silver content will range from .2 to .7 percent by weight. The amount of Silver and Halogens introduced into the frit mixture will depend on the type of application or end use of the PC Frit, and whether the final product is to allow partial light transmission or to be totally opaque.

[0024] An alternative to formation of frit by manufacturing a glassy matrix and then fracturing and grinding or machining it to a fine powder may include other techniques for formation of small particle-sized oxide powders such as by flame pyrolization, selective precipitation and sediment control, or aerosol, or chemical reaction in small droplets in emulsion or solution followed by flash/evaporation of the solvent; there are also means to provide small spherical frit particles using other mechanisms. One familiar with the art will understand where processes other than mass formation of a matrix and further processing/grinding/pulverization would have possible beneficial application.

[0025] Once manufactured, the PC Frit may be used in many settings. The photochromic frit is useful for inclusion in transparent panels or products, as a post- formed coating material for sheets, shapes such as lenses, laminate layers in automotive or other transparent windows and panels, as a part of a colorant layer or protective coating such as in paint, glaze or similar applications, as an addition to fibre-glass or other resins, cement or concrete/masonry materials whether during manufacture or screened and printed or otherwise applied. Photochromic frit may be used for clothing, and topical skin applications such as cosmetic and/or sunscreen products, where the change in transmissivity reactive to light may have protective or aesthetic value.

[0026] Some examples:

1. During the manufacture of float glass, PC Frit may be evenly distributed on the surface of the glass 1 during manufacture by pyrolytic,

electrostatic or other means of controlled distribution, and then in the process may be incorporated into the near-surface portion of the glass panel 1, bringing a photochromic functionality to the entire glass panel 1. In an example, a window pane 1 may be manufactured to comprise photochromic frit in the pane's body or surface. When the pane is not subjected to the influence of light, and the frit is not activated, the pane 1 is transparent as in Figure 1A; after being exposed to the influence of light, the frit is activated, darkening, as in Figure IB.

2. A similar process can be followed, but placing the PC Frit in a pattern 2 on the surface of the glass 1 during manufacture, which will result in a photochromic function in only portions of the glass panel 2 - this may be desirable as an architectural feature or graphic element for the panel's eventual placement, or to provide some specific function, such as protecting equipment or personnel behind only a portion of the glass panel when deployed.

PC Frit may be incorporated into or on plastic films which are used to coat or wrap, or which may be used as an intermediate layer 4 (or layers) in laminated glass products (windshields, windows, etc), possibly sandwiched between other layers of the laminate 3, 5.

As with the float-glass manufacturing, the PC Frit may be applied to the entire film, or to portions of the film to form patterns. Additionally, the film may be uniformly photochromic but cut to shape for a variety of purposes.

Photochromic Frit may also be used in coatings such as modified clear- coat or paints, to change the reflectivity of surfaces treated with the PC Frit - including coating(s).

It is contemplated that a variety of photo-reactive substances can be used or modified by addition of other elements or compounds, to effect color differences as well as transmissivity differences, responsivity to different frequencies of light, and the like, and that further similar uses will become apparent to the skilled reader.

[0027] As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. The various features and elements of the described invention may be combined in a manner different from the combinations described or claimed herein, without departing from the scope of the invention.

Claims

I, A frit being powdered glass or other particulate crystal substance, the

powder or particulate with relatively uniform diameter crystal or particle sizes, the frit having photochromic properties.

2. The frit of claim 1 comprising silver halide.

3. The frit of claim 1 with particle sizes between 0.002 - 1.0 microns in diameter.

4. The frit of claim 1 formed by grinding a precursor silver halide crystal with a ball mill or other grinder to produce suitable size and size distribution of frit particles.

5. The frit of claim 1 with 0.2-0.7% by weight silver.

6. The frit of claim 1 with particle size suitable for inclusion in surface resins for use on concrete or fiberglass.

7. The frit of claim 1 applied to a surface of a glassy matrix during float glass manufacturing using a controlled deposition process to place the frit onto the surface while the surface is molten or semi-molten glass such that the frit bonds with the surface to form a micro-thin photochromic surface layer on the manufactured float glass.

8. The frit of claim 7 applied evenly to the glass.

9. The frit of claim 7 applied in a pattern to the glass.

10. The frit of claim 7 where the controlled deposition process is one of: a

pyrolytic coating; electrostatic deposition; computer-controlled print-head.

II. The frit of claim 1 added to Polyvinyl Butaryl (PVB) while the PVB is in a

liquid state, curing the PVB to a pliable state and forming the PVB with included photochromic frit into a pliable sheet. The frit of claim 11 where the sheet with included frit is used in manufacture of laminated glass products to make laminated glass with photochromic properties imparted by the frit in the PVB layer.

The frit of claim 1 added to paints or coatings in controlled but variable densities and compositions which when applied to a surface in variable thicknesses, densities, patterns or layers, will impart a photochromically reactive contrast or color appearance to the surface when exposed to light of different characteristics or intensities, and produce aesthetic effects or functional effects such as reactive camouflage.