Optical conversion device accompanied by improved inorganic binder

Abstract

To provide an optical conversion device accompanied by an improved inorganic binder.SOLUTION: There is provided an optical conversion device that comprises a layer formed of an inorganic binder, which includes about 25 to about 80 wt.% of a filler, about 20 to about 75 wt.% of an inorganic adhesive, and an about 0.5 to about 5 wt.% of a dispersant. The inorganic binder can withstand a high temperature, has high light transmissivity and high tension / shear strength, can be applied by a flexible coating process, and also has a low hardening temperature. Such an inorganic binder is advantageously employed for various uses of optical light conversion devices, for example, a light tunnel, a projection display system, a phosphor wheel 100 used in such a system, etc.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present disclosure relates to inorganic binders that possess certain properties that make them particularly suitable for use in projection display systems and optical light conversion devices such as phosphor wheels used in such systems. In particular, the inorganic binders of the present disclosure maintain improved bond strength at temperatures up to 400°C.

Background Art

[0002] Organic adhesives (e.g., epoxy, polyurethane, silicone) are widely used for bonding. For example, in phosphor-containing silicone products, phosphor powder is mixed into a silicone binder or adhesive and then dispensed or printed in a desired pattern. Silicone has gained popularity for bonding metals, glass, and other materials due to its high transparency, high bond strength, lower refractive index, and appropriate viscosity. For example, a popular binder option is Dow Corning(R) OE-6336, a silicone adhesive manufactured by Dow Corning(R), which has a mixed viscosity of 1,425 centipoise (cP), a transparency of 99.6% at 450 nm, a refractive index of 1.4 for a thickness of 1 mm, and a heat curing time of 60 minutes at 150°C.

[0003] However, silicone binders / adhesives have insufficient thermal stability. At temperatures exceeding 200°C, the silicone adhesive will decompose and will typically begin to turn yellow and gradually start to burn. This undesirably leads to a short operating life for the phosphor wheel, and it has been observed that the light conversion efficiency drops sharply (>10%@200°C) due to heat dissipation. In applications involving high brightness (e.g., a 300 W laser power), the operating temperature of the phosphor wheel is generally expected to exceed 200°C, thus making the use of silicone adhesives undesirable. That is, silicone products containing phosphors cannot achieve a long operating life in high-power laser projectors. It has been established that in life tests for such products, the safe operating temperature should be controlled to be below 150°C.

[0004] Therefore, in addition to having a higher temperature resistance (e.g., exceeding 200°C (including 300°C and above, up to 400°C)), it would be desirable to provide an inorganic binder that exhibits the same desirable properties of organic binders, namely, high transparency, high bonding strength, low refractive index, and appropriate viscosity. Such an inorganic binder can advantageously be employed in various applications such as optical tunnels, projection display systems, and optical light conversion devices such as phosphor wheels used within such systems. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0005] The present disclosure relates to an inorganic binder that can be used within a high reflectivity coating for an optical light conversion device (e.g., a phosphor wheel) or as an adhesive used to bond two elements. The inorganic binders possess certain properties that make them particularly suitable for use in high power lighting systems. For example, in certain embodiments, the inorganic binder can withstand high temperatures (e.g., above 200 °C (including 300 °C and up to 400 °C)), have a high light transmittance (e.g., at least 98%), have a high tensile / shear strength (e.g., at least 100 psi at 300 °C), can be applied by a flexible coating process (e.g., dispensing, silk printing, spraying), and have a low curing temperature (e.g., less than 185 °C).

[0006] In one configuration, the composition consists essentially of from about 25 to about 80 weight percent of one or more fillers, from about 20 to about 75 weight percent of one or more inorganic binders, and from about 0.5 to about 5 weight percent of one or more dispersants.

[0007] The inorganic binder can include a first component (e.g., a translucent liquid) and a second component (e.g., a transparent liquid). The ratio of the first component to the second component can be from about 1:1 to about 7:3. The inorganic binder can be prepared by stirring the first component and the second component. The first component and the second component can be stirred for a period of from about 2 hours to about 3 hours. The first component and the second component can be stirred at a temperature of from about 25 °C to about 30 °C. In certain embodiments, the first component has a viscosity of from about 1 mPa·sec to about 50 mPa·sec, a density of from about 0.8 g / cm 3 ~ about 1.3 g / cm 3 and a solids content greater than 10%. In some embodiments, the second component has a viscosity of from 0 mPa·sec to about 50 mPa·sec, a density of from about 0.6 g / cm 3 ~ about 1.0 g / cm 3 and a solids content greater than 10%.

[0008] In one configuration, the coefficient of thermal expansion of the filler is within 20% (±20%) of the coefficient of thermal expansion of the inorganic adhesive. The density of the filler can also be within 20% (±20%) of the density of the inorganic adhesive.

[0009] The filler can be selected from the group consisting of silica, aluminum oxide, and boron nitride. The filler can have a granular, flaky, or fibrous shape. The filler can have a particle size of about 0.1 to about 50 microns.

[0010] In some embodiments, the dispersant is an organic substance (e.g., polyvinylpyrrolidone, polyacrylate, gelatin, polyvinyl alcohol, cellulose, styrene-co-maleic anhydride, or lignosulfonate). In alternative embodiments, the dispersant is an inorganic substance (e.g., hexametaphosphate, silicate, polyphosphate, or fumed silica).

[0011] The method of forming an inorganic binder according to the present disclosure includes performing a first curing at a temperature of about 60°C to about 90°C for a period of about 0.2 hours to about 1 hour, and then performing a second curing at a temperature of about 150°C to about 200°C for a period of about 0.4 hours to about 2 hours.

[0012] Also disclosed herein is a light conversion device, the light conversion device comprising a substrate having an inorganic coating, the inorganic coating comprising about 20 to about 80 wt% filler, about 20 to about 75 wt% inorganic binder, and about 0.5 to about 5 wt% dispersant. In more specific embodiments, the filler is present in an amount of about 60 to about 75 wt% and the inorganic binder is present in an amount of about 20 to about 35 wt%.

[0013] The substrate can be in the shape of a disk. The light conversion device can further comprise a motor arranged to rotate the substrate about an axis normal to the substrate.

[0014] In some embodiments, the filler is a phosphor (e.g., yttrium aluminum garnet, silicate, or nitride). The phosphor can have a particle size of about 10 to about 30 microns.

[0015] In certain embodiments, the filler is a refractive powder having a particle size of about 0.1 micron to about 150 microns. The resulting inorganic coating can have a high reflectivity (e.g., at least 80%, at least 90%, at least 95%, at least 98%, etc.) with respect to light having a wavelength of about 380 nm to about 800 nm. The light conversion device can further comprise a phosphor layer applied over the inorganic coating on the substrate.

[0016] A method of forming a light conversion device according to the present disclosure includes applying an inorganic coating to a substrate by spraying, dispensing, or screen printing, performing a first curing of the inorganic coating at a temperature of about 85° C. over a period of about 0.25 hours, and then performing a second curing of the inorganic coating at a temperature of about 185° C. over a period of about 0.75 hours.

[0017] Further disclosed herein is an optical tunnel comprising a plurality of reflectors joined together by an inorganic adhesive capable of withstanding temperatures above 200° C., the inorganic adhesive comprising about 25 to about 80 weight percent filler, about 20 to about 75 weight percent inorganic adhesive, and about 0.5 to about 5 weight percent dispersant.

[0018] In certain embodiments, the filler can be aluminum oxide. The filler can have a particle size of about 0.5 micron to about 10 microns.

[0019] ​A method of forming an optical tunnel according to the present disclosure includes performing a first curing of an inorganic adhesive at a temperature of about 85° C. over a period of about 0.25 hours, and then performing a second curing of the inorganic adhesive at a temperature of about 185° C. over a period of about 0.75 hours.

[0020] These and other non-limiting features of the present disclosure are disclosed more specifically below.

Brief Description of the Drawings

[0021] The following is a brief description of the drawings, which is presented for the purpose of illustrating exemplary embodiments disclosed herein and is not presented for the purpose of limiting the same.

[0022]

Fig. 1A

[0023]

Fig. 1B

[0024]

Fig. 2A

[0025]

Fig. 2B

[0026]

Fig. 3

Modes for Carrying Out the Invention

[0027] A more complete understanding of the components, processes, and devices disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic diagrams based on the convenience and ease of demonstrating the present disclosure, and thus are not intended to indicate the relative size and dimensions of the present device or its components, and / or to define or limit the scope of the exemplary embodiments.

[0028] Specific terms are used in the following description for clarity, but these terms are intended to refer only to the specific structures of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the present disclosure. It should be understood that in the drawings and the following description below, like numeral designations refer to components of like function.

[0029] Unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include plural referents.

[0030] As used in this specification and the claims, the terms "comprise", "include", "having", "has", "can", "contain", and variations thereof are intended to be non-restrictive transitional phrases, terms, or words that, as used herein, require the presence of the stated inclusion / step and permit the presence of other inclusions / steps. However, such descriptions should also be construed as describing compositions or processes as "consisting of" and "consisting essentially of" the recited inclusions / steps, which allow only the presence of the stated inclusions / steps, excluding other inclusions / steps, in addition to any unavoidable impurities that may result therefrom.

[0031] The numerical values in the specification and claims of this application should be understood to include both the same numerical values rounded to the same number of significant digits for determining the value, and numerical values that differ from the stated value by less than the experimental error of conventional measurement techniques of the type described in this application.

[0032] All ranges disclosed in this specification include the recited endpoints and are combinable independently (e.g., the range of "2 grams to 10 grams" includes the endpoints, i.e., 2 grams and 10 grams, and all intermediate values).

[0033] The terms "about" and "approximately" can be used to include any numerical value that can vary without changing the basic function of that value. When used in conjunction with a range, "about" and "approximately" also disclose the range defined by the absolute values of the two endpoints. For example, "about 2 to about 4" also discloses the range of "2 to 4". Generally, the terms "about" and "approximately" can refer to ±10% of the number shown.

[0034] As used herein, the terms "excitation light" and "excitation wavelength" refer to the input light that is subsequently converted, e.g., light produced by a laser-based illumination source or other light source. The terms "emitted light" and "emission wavelength" refer to the resulting light produced by the phosphor that has been exposed to the excitation light, e.g., the converted light.

[0035] As used herein, the term "inorganic" means that an "inorganic" object does not contain any carbon. For the avoidance of doubt, the terms "inorganic binder", "inorganic adhesive", "inorganic coating", and "inorganic adhesive" of this disclosure do not contain carbon.

[0036] For reference, red typically refers to light having a wavelength of from about 780 nanometers to about 622 nanometers. Green typically refers to light having a wavelength of from about 577 nanometers to about 492 nanometers. Blue typically refers to light having a wavelength of from about 492 nanometers to about 455 nanometers. Yellow typically refers to light having a wavelength of from about 597 nanometers to about 577 nanometers. However, this may be context dependent. For example, these colors are sometimes used to label various components and distinguish those components from one another.

[0037] The present disclosure relates to inorganic binders having certain properties that make them particularly suitable for use in high power lighting systems. The inorganic binder is a composition containing a plurality of inclusions. Some performance characteristics such as conversion light output, color, and lifetime are direct functions of the operating temperature. At higher operating temperatures, the conversion light output can decrease, the color can shift, and the operating lifetime can be reduced. Under normal operating conditions, about 50% - 60% of the input power is output as heat while the remainder of the input power is converted to light. At high input powers, the heat generation during conversion will cause high sustained temperatures above 200 degrees Celsius (200 °C) (including 300 °C and above, up to 400 °C).

[0038] In certain embodiments, the inorganic binders of the present disclosure are capable of withstanding high temperatures (e.g., above 200 °C (including 300 °C and above, up to 400 °C)), have a high light transmittance (e.g., at least 98%), have a high tensile / shear strength (e.g., at least 100 psi at 300 °C), can be applied by a flexible coating process (e.g., dispensing, silk printing, spraying), and have a low cure temperature (e.g., less than 185 °C).

[0039] The inorganic binders of the present disclosure can be used within high power lighting systems such as optical light conversion devices (e.g., phosphor wheels). The inorganic binders can be used in different layers to provide a high reflectivity or to provide a wavelength conversion layer.

[0040] As described in various embodiments of this specification, very generally, an inorganic binder comprises, or consists essentially of, at least one filler, at least one inorganic adhesive, and at least one dispersant.

[0041] The inorganic binder may contain from about 25 to about 80 weight percent filler, based on the weight of the inorganic binder, and may contain from about 60 weight percent to about 75 weight percent or from about 65 weight percent to about 75 weight percent filler. The filler can be used to obtain the desired function of the layer made from the inorganic binder. For example, the filler can be a phosphor for producing a wavelength conversion layer or a refractive powder for producing a reflective coating. One or more different fillers can be present.

[0042] The inorganic binder may contain from about 20 to about 75 weight percent inorganic adhesive, based on the weight of the inorganic binder, and may contain from about 20 weight percent to about 45 weight percent or from about 25 weight percent to about 40 weight percent inorganic adhesive.

[0043] The inorganic binder may contain from about 0.5 to about 5 weight percent dispersant, based on the weight of the inorganic binder, and may contain from about 1 to about 4 weight percent or from about 2 to about 3 weight percent dispersant. One or more dispersants can be used, and these amounts apply to the total dispersant being combined.

[0044] In a specific embodiment, the inorganic binder consists essentially of from about 25 to about 80 weight percent of one or more fillers, from about 20 to about 75 weight percent of one or more inorganic adhesives, and from about 0.5 to about 5 weight percent of one or more dispersants, and the sum of these contents is 100 weight percent.

[0045] In other specific embodiments, the inorganic binder consists essentially of from about 60 to about 75 weight percent of one or more fillers, from about 20 to about 40 weight percent of one or more inorganic adhesives, and from about 0.5 to about 5 weight percent of one or more dispersants, and the sum of these contents is 100 weight percent.

[0046] The addition of fillers to an inorganic adhesive improves the bonding strength of the inorganic binder. In particular, the addition reduces the shrinkage rate of the inorganic binder, reduces or prevents the formation of bubbles or cracks during solidification, thereby reducing the amount and / or effect of stress during use and improving the bonding strength of the inorganic binder. The filler can be selected to have a coefficient of thermal expansion within 20% of that of the inorganic adhesive. Similarly, to avoid layering, the filler can be selected to have a density within 20% of that of the inorganic adhesive. The filler may have any desired shape such as granular, flaky, or fibrous shape. Any suitable filler can be used. For example, specifically, the filler can be assumed to be silica, silicate, aluminate, or phosphate, or diamond powder. The filler can be a metal powder such as aluminum, copper, silver, or gold powder. The filler can be a nitride such as aluminum nitride or borazon. The filler can be an oxide such as aluminum oxide or boron oxide. The filler can be a metal oxide, metal nitride, or metal sulfide. The filler can be any suitable particle size such as from about 0.1 micron to about 50 microns.

[0047] The addition of a dispersant is beneficial to disperse the filler throughout the binder, thereby avoiding undesirable aggregation or sedimentation. Any suitable dispersant can be used. For example, specifically, the dispersant can be assumed to be an organic dispersant such as polyvinylpyrrolidone, polyacrylate, gelatin, polyvinyl alcohol, cellulose, styrene-co-maleic anhydride, or lignosulfonate. Specifically, alternatively, the dispersant can be assumed to be an inorganic dispersant such as hexametaphosphate, silicate, polyphosphate, or fumed silica.

[0048] As described above, inorganic binders are employed in various applications such as coatings and can form one or more layers within an optical light conversion device such as a phosphor wheel. The phosphor wheel is used to continuously generate light of different colors. A light conversion (or wavelength conversion) material such as a phosphor is used on the phosphor wheel. The phosphor wheel typically has several fan segments containing different types of phosphors for converting excitation light to green, yellow, or red. Typically, a blue light laser (having a wavelength of about 440 nm to about 460 nm) is used to excite the phosphor segments on the phosphor wheel. The phosphor wheel can also have one or more gaps for allowing the unconverted blue source light to pass through in an unaltered state.

[0049] Figures 1A and 1B illustrate such an optical light conversion device including a wavelength conversion layer formed from an inorganic binder. In particular, the first exemplary optical light conversion device is a phosphor wheel 100. FIG. 1A is a schematic view of the phosphor wheel 100, and FIG. 1B is a side cross-sectional view of the phosphor wheel 100. The phosphor wheel 100 includes a substrate 110 onto which an inorganic binder is applied to form a wavelength conversion layer 120. The wavelength conversion layer is an inorganic coating essentially composed of a filler 121, an inorganic adhesive 122, and a dispersant (not shown). In this particular embodiment, the wavelength conversion layer essentially consists of about 60 to about 75 wt% filler, about 20 to about 45 wt% inorganic adhesive, and about 0.5 to about 5 wt% dispersant.

[0050] The substrate 110 is typically a metal having high thermal conductivity, such as aluminum or an aluminum alloy, copper or a copper alloy, or another metal having high thermal conductivity. The substrate can also be made from, for example, glass, sapphire, or diamond. For purposes of illustration, the wavelength conversion layer 120 is shown separated from the substrate 110, but in use, the inorganic binder is applied directly to the substrate 110, for example, by spraying, dispensing, or silk printing, to form the wavelength conversion layer.

[0051] In this exemplary embodiment of the phosphor wheel 100, the filler is a phosphor. Suitable phosphors include yttrium aluminum garnet (YAG), silicate, and nitride. The phosphor can have a particle size of about 10 to about 30 microns. In addition to the dispersant, the phosphor filler can then be combined with an inorganic binder (e.g., a liquid transparent inorganic binder) to form an inorganic binder. The inorganic binder is dispersed, sprayed, or silk printed onto the substrate and then thermally cured and solidified to form a wavelength conversion layer 120 such as a concentric pattern when the substrate 110 is in a disk shape. The curing of the inorganic coating 120 can be carried out in a stepwise process. For example, in this exemplary embodiment, the first curing step is carried out at a temperature of about 75°C to about 100°C for a period of about 0.1 hour to about 1 hour, e.g., 0.25 hour. The second curing step is then carried out at a higher temperature of about 150°C to about 200°C for a period of about 0.5 to about 1 hour.

[0052] Turning now to FIGS. 2A and 2B, another optical light conversion device is depicted. In particular, the second exemplary light conversion device is another phosphor wheel 200. FIG. 2A is a schematic view of the phosphor wheel 200, and FIG. 2B is a side cross-sectional view of the phosphor wheel 200. The phosphor wheel 200 includes a substrate 210 on which an inorganic binder is applied to form a reflective layer 220, and a phosphor layer 230 is applied over the reflective layer 220 on the substrate 210. The inorganic coating includes a filler 221, an inorganic binder 222, and a dispersant (not shown). In particular, in this exemplary embodiment of the phosphor wheel 200, the inorganic coating consists essentially of about 65 to about 75 wt% filler, about 20 to about 35 wt% inorganic binder, and about 1 wt% to about 2 wt% dispersant.

[0053] In this embodiment of the phosphor wheel 200, the filler includes one or more refractive powders. The refractive powders can have a particle size of from about 0.1 micron to about 150 microns. In addition to the dispersant, the refractive powders can then be combined with an inorganic binder (e.g., a liquid transparent inorganic binder) to form an inorganic binder. The inorganic binder can then be dispersed, sprayed, or silk printed onto a substrate, and then thermally cured and solidified on the substrate 210 in a concentric pattern or the like when the substrate 210 is in a disk shape, preparing the substrate 210 with a highly reflective layer 220 thereon. For example, the inorganic coating 220 can have a high light reflectivity having a wavelength of from about 380 nm to about 800 nm. The curing of the inorganic binder can be carried out in a stepwise process. For example, in this exemplary embodiment, the first curing step is carried out at a temperature of from about 75 °C to about 100 °C for a period of from about 0.1 hour to about 1 hour, e.g., 0.25 hour. A second curing step is then carried out at a temperature of from about 150 °C to about 200 °C, e.g., 185 °C, for a period of from about 0.5 hour to about 1 hour, e.g., 0.75 hour.

[0054] The phosphor wheel 200 further includes a phosphor layer 230 (e.g., a phosphor powder layer) applied over the highly reflective layer 220 on the substrate 210. The phosphor layer 200 can be applied, for example, by dispensing or silk printing.

[0055] Both the phosphor wheel 100 of FIGS. 1A and 1B and the phosphor wheel 200 of FIGS. 2A and 2B can be created by mounting a substrate on a motor that rotates at high speed. Typically, the substrate is rotated during use, but the device can also be used in a static (non-rotating) configuration, in which case it may not be known as a phosphor wheel. The rotation of the phosphor wheel is depicted in FIGS. 1A and 2A by an arrow that passes through each substrate 110, 210 and rotates around an axis A-A that is normal to the plane of each substrate 110, 210.

[0056] As shown in FIGS. 1A-1B and 2A-2B, excitation light 123 of an excitation wavelength (i.e., excitation or input light) from a light source (not shown) (e.g., a laser-based illumination source) is focused onto an inorganic coating, and radiation light 124 of the excitation wavelength (i.e., emitted or converted light) is generated by the inorganic coating. Thus, the inorganic coating converts the light spectrum from excitation light of spectral wavelengths in a first range to emitted (or re-emitted) light of spectral wavelengths in a second, different range. When light of excitation wavelength 123 (e.g., blue light of a laser beam) is focused onto the inorganic coating, light of emission wavelength 124 (e.g., yellow light) is emitted, reflected by the inorganic coating, and then can be condensed, for example, by a lens. The phosphor wheel can be made of an inorganic coating that includes a plurality of color segments (not shown herein), each of which is used to generate light with a specific color, or can be made to emit any desired color. For example, the inorganic coating may be configured to absorb blue light and / or generate yellow light and / or green light.

[0057] Referring now to FIG. 3, an exemplary optical tunnel that employs an inorganic binder as an adhesive is depicted. The optical tunnel wheel 300 includes a plurality of reflectors 301 arranged to define a hollow tunnel therebetween. An inorganic binder 305 is applied to join the reflectors together. The inorganic binder includes one or more fillers, one or more inorganic adhesives, and one or more dispersants. In particular, in this exemplary embodiment of the optical tunnel 300, the inorganic binder consists essentially of about 60 to about 75 wt% filler, about 20 to about 45 wt% inorganic adhesive, and about 2 wt% to about 3 wt% dispersant.

[0058] In this exemplary embodiment of the tunnel 300, the filler is aluminum oxide (Al2O3). The aluminum oxide filler can have a particle size of about 0.5 to about 10 microns. In addition to the dispersant, the aluminum oxide filler can then be combined with an inorganic adhesive (e.g., a liquid transparent inorganic adhesive) to form an inorganic binder 305. The inorganic binder 305 can be dispensed at the joint between adjacent reflectors 301 to bond them together. The inorganic binder 305 is then thermally cured and solidified. The curing of the inorganic binder 305 can be carried out in a stepwise process. For example, in this exemplary embodiment, the first curing step is carried out at a temperature of about 85°C for a period of about 0.25 hours. The second curing step is then carried out at a temperature of about 185°C for a period of about 0.75 hours.

[0059] The inorganic binder / inorganic binder coating and adhesive of the present disclosure provide many advantages over conventional phosphor-containing silicone optical converters. For example, the phosphor-containing inorganic adhesive coating can maintain the optical conversion efficiency at a temperature of at least 200°C (including 300°C or higher, up to 400°C). The coating should have high transparency at visible wavelengths, a low refractive index, high bonding strength, high thermal stability (i.e., high Tg or maximum operating temperature), a relatively low curing / sintering temperature, good compatibility / miscibility with the phosphor, and / or a desirable viscosity. This will improve the thermal durability of the phosphor wheel at temperatures from 165°C to 400°C.

[0060] Desirably, the inorganic binder is substantially optically transparent (e.g., the inorganic binder has a light transmittance of at least 80%, at least 90%, at least 95%, or at least 98%). This is measured, for example, by using a Lambda 950 spectrophotometer available from Perkin-Elmer. In contrast, many organic binders are opaque. This enables the inorganic binder to be used in transmissive or reflective phosphor wheels.

[0061] Inorganic binders can exhibit higher bonding strength than conventional silicone adhesives. In certain embodiments, the inorganic binders of the present disclosure can have an initial bonding strength of at least 100 psi, or at least 200 psi, or from about 100 psi to about 600 psi. This property is measured using two aluminum test plates with the adhesive applied at the highest temperature at which the adhesive is to be used, for example, 300 °C, with the inorganic binder placed between the two plates at a thickness of 0.1 mm and a bonding area of 169 square mm.

[0062] Inorganic adhesives are typically stable over long periods of time, and thus it has been found that the performance of these devices does not necessarily degrade significantly over time. Also, organic materials can exhibit some gas evolution at high operating temperatures. This can lead to contamination of nearby components within the optical device. Additionally, inorganic binders can be more durable than conventional silicone materials under high-power conditions. They exhibit reliable operation under high laser irradiation and temperature. They can also be flexibly fabricated into various sizes, shapes, and thicknesses. The inorganic binders of the present disclosure can also withstand high operating temperatures, i.e., operating temperatures exceeding 200 °C. They can be used in high-power laser projection display systems where solid-state laser projectors can be equipped with laser powers from about 60 watts to about 300 watts, including those exceeding 100 watts. The operating temperature of such devices can reach above 200 °C (including above 300 °C and up to 400 °C), enabling high emission luminance.

[0063] Inorganic binders are envisioned to be used within phosphor wheels and laser projection display systems. They can also be used in combination with solid-state lighting sources, such as automotive headlights. They can further be used as adhesives for light tunnels, light collection tubes, and the like.

[0064] The following examples are provided to illustrate the processes of the present disclosure. The examples are illustrative only and are not necessarily intended to limit the present disclosure to the materials, conditions, or process parameters described therein.

Example

[0065] (Example 1) In one exemplary embodiment, an inorganic adhesive was formed from a first and a second component. The total dissolved solids (TDS) characteristics of the inorganic adhesive used are provided in the following table.

Table 1

[0066] The inorganic adhesive was prepared by mixing the first and second components and stirring at a temperature of about 25 - 30 °C for a period of about 2 - about 3 hours. The ratio of the first component to the second component was about 1:1 - about 7:3.

[0067] The inorganic binder was then prepared by adding a filler and a dispersant to the inorganic adhesive. The inorganic binder was cured in a step - by - step process. The first curing step was carried out at a temperature of about 60 - about 90 °C for a period of about 0.2 - about 1 hour. The second curing step was then carried out at a temperature of about 150 - about 200 °C for a period of about 0.4 - about 2 hours. It has been shown that the cured inorganic binder exhibits excellent bonding strength at the maximum applied temperature due to the high temperature resistance of the inorganic binder.

[0068] The present disclosure has been described with reference to preferred embodiments. Modifications and variations will occur to those skilled in the art upon a reading and understanding of the foregoing detailed description. The present disclosure is intended to cover all such modifications and variations as fall within the scope of the appended claims or their equivalents. For example, the present invention provides the following items. (Item 1) An optical conversion device comprising a layer formed from an inorganic binder, wherein the inorganic binder is about 25 to about 80% by weight of a filler, about 20 to about 75% by weight of an inorganic adhesive, and about 0.5 to about 5% by weight of a dispersant and an optical conversion device containing the same. (Item 2) The optical conversion device according to Item 1, wherein the inorganic adhesive is made from a first component and a second component, and the ratio of the first component to the second component is about 1:1 to about 7:3. (Item 3) The optical conversion device according to Item 2, wherein the inorganic adhesive is prepared by stirring the first and second components at a temperature of about 25 to about 30 °C for a period of about 2 to about 3 hours. (Item 4) The optical conversion device according to Item 2, wherein the first component is a translucent liquid and the second component is a transparent liquid. (Item 5) The first component has a viscosity of about 1 to about 50 mPa·sec, a density of about 0.8 to about 1.3 g / cm 3 and a solid content exceeding 10%, the second component has a viscosity of about 0 to about 50 mPa·sec, a density of about 0.6 to about 1.0 g / cm 3 and a solid content exceeding 10%, The optical conversion device according to any one of Items 1-4. (Item 6) The optical conversion device according to any one of Items 1-5, wherein the thermal expansion coefficient of the filler is within 20% of the thermal expansion coefficient of the inorganic adhesive, and the density of the filler is within 20% of the density of the inorganic adhesive. (Item 7) The filler is a silicate and an aluminate, Phosphateand a light conversion device according to any one of items 1-6, selected from the group consisting of diamond powder, metal powder, nitride, oxide, and metal sulfide, wherein the filler has a granular, flaky, or fibrous shape and a particle size of about 0.1 micron to about 50 microns. (Item 8) The dispersant is an organic dispersant selected from the group consisting of polyvinylpyrrolidone, polyacrylate, gelatin, polyvinyl alcohol, cellulose, styrene-co-maleic anhydride, and lignosulfonate, The dispersant is an inorganic dispersant selected from the group consisting of hexametaphosphate, silicate, poly Phosphate and fumed silica, A light conversion device according to any one of items 1-7. (Item 9) The inorganic binder is capable of withstanding a temperature exceeding 200°C, has a light transmittance of at least 98%, and has a high tensile / shear strength of at least 100 psi at 300°C, and a light conversion device according to any one of items 1-8. (Item 10) A method of forming a layer of the light conversion device according to item 1, the method comprising: performing a first curing at a temperature of about 60°C to about 90°C for a period of about 0.2 hours to about 1 hour, and then performing a second curing at a temperature of about 150°C to about 200°C for a period of about 0.4 hours to about 2 hours comprising a method. (Item 11) A light conversion device, a substrate, an inorganic coating on the substrate, the inorganic coating comprising: about 25 to about 80% by weight of a filler, about 20 to about 75% by weight of an inorganic binder, about 0.5 to about 5% by weight of a dispersant and an inorganic coating, comprising a light conversion device. (Item 12) The light conversion device according to item 11, wherein the substrate has a disk shape and further includes a motor arranged to rotate the substrate around an axis in the normal direction of the substrate. (Item 13) The light conversion device according to any one of items 11-12, wherein the filler is a phosphor selected from the group consisting of yttrium aluminum garnet, silicate, and nitride, and the phosphor has a particle size of about 10 microns to about 30 microns. (Item 14) The light conversion device according to item 11, wherein the filler is a refractive powder having a particle size of about 0.1 micron to about 150 microns. (Item 15) The light conversion device according to item 14, wherein the inorganic coating has a reflectivity of at least 80% with respect to light having a wavelength of about 380 nm to about 800 nm. (Item 16) The light conversion device according to any one of items 14-15, further comprising a phosphor layer applied over the inorganic coating on the substrate. (Item 17) A method of forming the light conversion device according to item 11, the method comprising: applying the inorganic coating to the substrate; performing a first curing of the inorganic coating at a temperature of about 85°C for a period of about 0.25 hours; and then performing a second curing of the inorganic coating at a temperature of about 185°C for a period of about 0.75 hours. A method including the above steps. (Item 18) An optical tunnel, a plurality of reflectors joined together by an inorganic binder capable of withstanding temperatures above 200°C, the inorganic binder comprising: about 25 to about 80 wt% filler; about 20 to about 75 wt% inorganic adhesive; about 0.5 to about 5 wt% dispersant. A plurality of reflectors including An optical tunnel comprising (Item 19) The optical tunnel according to item 18, wherein the filler is aluminum oxide having a particle size of about 0.5 micron to about 10 microns. (Item 20) A method of forming the optical tunnel according to item 18, the method comprising Performing a first curing of the inorganic binder at a temperature of about 85° C. over a period of about 0.25 hours, Thereafter, performing a second curing of the inorganic binder at a temperature of about 185° C. over a period of about 0.75 hours A method including

Claims

【Claim 1】 High transparency.

Images