阅读说明：本技术 用于波长转换装置的耐高温反射层 (High temperature resistant reflective layer for wavelength conversion devices ) 是由 张文博 梁安生 于 2020-04-16 设计创作，主要内容包括：一种诸如荧光轮之类的波长转换装置(100),包括：基底(110)、反射层(120)和反射层(120)上的波长转换层(130)。反射层(120)包含(A)无机粘结剂或有机硅,和(B)反射性纳米颗粒(122)。纳米颗粒(122)的粒度为约200纳米至约500纳米。反射层(120)具有高的热稳定性。本申请还公开了制造波长转换装置(100)的方法和包括该波长转换装置(100)的光投影系统。(A wavelength converting device (100), such as a fluorescent wheel, comprising: a substrate (110), a reflective layer (120), and a wavelength converting layer (130) on the reflective layer (120). The reflective layer (120) comprises (a) an inorganic binder or silicone, and (B) reflective nanoparticles (122). The nanoparticles (122) have a particle size of about 200 nanometers to about 500 nanometers. The reflective layer (120) has a high thermal stability. Methods of manufacturing the wavelength conversion device (100) and light projection systems comprising the wavelength conversion device (100) are also disclosed.)

1. A wavelength conversion device comprising:

a substrate;

a reflective layer on the substrate, the reflective layer comprising (a) a binder; and (B) reflective titanium dioxide (TiO) having a particle size of from about 200 to about 500 nanometers₂) A nanoparticle; and

a wavelength conversion layer on the reflective layer;

wherein the reflective layer is thermally stable at 250 ℃.

2. The wavelength conversion device according to claim 1, wherein the reflective TiO₂The nanoparticles are prepared by reacting organic alcohol, siloxane, and alumina (A1)₂O₃) Zirconium dioxide (ZrO)₂) Or silicon dioxide (SiO)₂) And (4) surface modification.

3. The wavelength conversion device according to claim 1, wherein the reflective layer has a thickness of about 0.05mm to about 0.15 mm.

4. The wavelength conversion device according to claim 1, wherein the weight ratio of the (B) reflective nanoparticles to the (a) binder is from about 1:2.5 to about 1: 0.8.

5. The wavelength conversion device according to claim 1, wherein the weight ratio of the (B) reflective nanoparticles to the (a) binder is from about 1:10 to about 1: 0.2.

6. The wavelength conversion device according to claim 1, wherein the binder (a) comprises a mixture of a solvent and an inorganic binder material, wherein the weight ratio of solvent to inorganic binder material is from about 10:1 to about 0: 1.

7. The wavelength conversion device according to claim 6, wherein the weight ratio of the (B) reflective nanoparticles to the (A) binder is from about 1:10 to about 1: 0.2.

8. The wavelength conversion device according to claim 1, wherein the binder (a) comprises an inorganic sol-gel made of silica or alumina.

9. The wavelength conversion device according to claim 1, wherein the binder (a) comprises octamethyltrisiloxane.

10. The wavelength conversion device of claim 1, wherein the reflective layer has a reflectivity of at least 95% for light having a wavelength of about 420nm to about 680 nm.

11. The wavelength conversion device according to claim 1, wherein the phosphor layer comprises phosphor particles dispersed in glass, or in crystals, or in a ceramic material.

12. The wavelength conversion device according to claim 1, wherein the substrate is disc-shaped.

13. The wavelength conversion device according to claim 1, further comprising a motor for rotating the substrate.

14. The wavelength conversion device according to claim 1, wherein the substrate is a metal, a non-metallic material, or a composite material.

15. A light projection system comprising the wavelength conversion device of claim 1.

16. A method of manufacturing a wavelength conversion device, comprising:

will be combined into a groupA composition applied to a substrate to form a reflective layer on the substrate, the composition comprising (a) a binder; and (B) reflective titanium dioxide (TiO) having a particle size of from about 200 to about 500 nanometers₂) A nanoparticle; and

forming a wavelength conversion layer on the reflective layer;

wherein the reflective layer is thermally stable at 250 ℃.

17. The method of claim 16, wherein the composition has a viscosity of about 0 centipoise (cP) to about 1500 cP.

18. The method of claim 16, further comprising curing the composition at a temperature of about 85 ℃ to about 150 ℃.

19. The method of claim 16, wherein the weight ratio of the (B) reflective nanoparticles to the (a) binder is from about 1:10 to about 1: 0.2.

20. The method of claim 16, wherein the binder (a) comprises a mixture of a solvent and an inorganic binder material, wherein the weight ratio of solvent to inorganic binder material is from about 10:1 to about 0: 1.

21. The method of claim 20, wherein the weight ratio of the (B) reflective nanoparticles to the (a) binder is from about 1:10 to about 1: 0.2.

22. The method of claim 16, wherein the binder (a) comprises an inorganic sol-gel made of silica or alumina.

23. The method of claim 16, wherein the composition is applied by drip, spray, brush, flow, coating, or screen printing.

24. A wavelength conversion device manufactured by the method of claim 16.

25. A light projection system comprising the wavelength conversion device of claim 24.

Background

The present disclosure relates to wavelength conversion devices, such as fluorescent wheels, having a high temperature resistant reflective layer. Therefore, they are particularly suitable for use in projection display systems and optical light conversion devices employing solid-state lasers as light sources.

The fluorescent wheel may be used to generate light of different wavelengths from a single light source. The wheel includes a circular base having surface segments of different colors. When the wheel is rotated with light (from the light source) incident thereon, the surface segments convert the light to a different wavelength.

For a reflective fluorescent wheel, the substrate reflects light, and thus it is desirable to maximize the reflectivity of the substrate. For wavelengths from about 420nm to about 680nm, aluminum (Al) coated substrates typically have an average reflectivity of 94%, while silver (Ag) coated substrates have an average reflectivity of 98%.

However, stability and durability are also concerns for reflective wavelength conversion devices. After several hundred hours of operation at high temperature (greater than 150 ℃), traces of burning were observed in the laser-incident areas on the Ag-coated substrates. The migration of silver ions in the coating at high temperatures may be responsible for this result. This may result in a loss of optical performance of about 9%.

Silicones with high reflectivity (> 95%) have been used to form the reflective layer of wavelength conversion devices. However, they have poor thermal stability. At temperatures above 200 ℃, the silicone will degrade, typically turning yellow first, and gradually begin to burn. At temperatures in excess of 195 ℃, the phosphor layer on the reflective layer also cracks after about 1000 hours. This undesirably leads to a short service life of the fluorescence wheel, and a drastic drop in the light conversion efficiency (> 10% @200 ℃) due to thermal quenching has been observed. In applications with high brightness (e.g., laser power of 300W), the operating temperature of the fluorescent wheel is expected to be typically greater than 200 ℃, thus making the use of silicone undesirable.

A substrate with high reflectivity throughout its lifetime is desired. It is also desirable to increase the substrate reflectivity while maintaining and improving reliable lifetime performance at low cost. Such substrates and reflective coatings/layers may be advantageously used in various applications, such as light tunnels, projection display systems, and optical light conversion devices used in such systems, such as fluorescent wheels.

Disclosure of Invention

The present disclosure relates to compositions for forming reflective layers in wavelength conversion devices (such as fluorescent or color wheels); a reflective layer comprising certain materials; and wavelength conversion devices comprising such reflective layers. Such reflective layers are resistant to temperature degradation at high operating temperatures (e.g., greater than 200 ℃ and up to 250 ℃). Also disclosed herein are methods for making and using such compositions, layers, and devices.

Disclosed in various embodiments herein are wavelength conversion devices comprising: a substrate; a reflective layer on the substrate; and a wavelength converting layer on the reflective layer. The reflective layer comprises (A) a binder; and (B) reflective nanoparticles having a particle size of about 200 nanometers to about 500 nanometers.

In some embodiments, the reflective nanoparticles are pure titanium dioxide (TiO)₂) Or alumina (A1)₂O₃) Or magnesium oxide (MgO). In other embodiments, the reflective nanoparticles are prepared via organic alcohol, siloxane, alumina (a 1)₂O₃) Zirconium dioxide (ZrO)₂) Or silicon dioxide (SiO)₂) Surface modified titanium dioxide (TiO)₂)。

The reflective layer may have a thickness of about 0.05mm to about 0.15 mm. (B) The weight ratio of the reflective nanoparticles to (a) the binder may be about 1:2.5 to about 1: 0.8.

The binder may be an organic binder or an inorganic binder. Examples of organic binders include silicones such as octamethyltrisiloxane. Examples of inorganic binders include sodium silicate.

Desirably, the reflective layer has a reflectivity of at least 95% for light having a wavelength of about 420nm to about 680 nm. The phosphor layer may comprise phosphor particles dispersed in glass, crystals, or ceramic materials. The substrate may be disc-shaped. The wavelength conversion device may further include a motor for rotating the substrate. The substrate may be a metal, a non-metallic material, or a composite material.

Also disclosed are light projection systems including the wavelength conversion devices described herein.

Also disclosed in various embodiments are methods of making a wavelength conversion device, comprising: applying a composition to a substrate to form a reflective layer on the substrate, the composition comprising (a) a binder; and (B) reflective nanoparticles having a particle size of about 200 nanometers to about 500 nanometers; and forming a wavelength conversion layer on the reflective layer.

The viscosity of the composition can be from about 0 centipoise (cP) to about 1500cP when the composition is applied to a substrate. The method further comprises curing the composition at a temperature of about 85 ℃ to about 150 ℃. The composition may be applied by drop coating, spray coating, brush coating, flow, coating or screen printing.

These and other non-limiting features of the present disclosure are disclosed in more detail below.

Drawings

The following is a brief description of the drawings, which are provided for the purpose of illustrating exemplary embodiments disclosed herein and not for the purpose of limiting the same.

Fig. 1A is a schematic diagram of an exemplary optical light conversion device according to the present disclosure, including a substrate, a high reflectivity layer, and a phosphor layer.

Fig. 1B is a side cross-sectional view of the exemplary optical light conversion device of fig. 1A.

Fig. 1C is an exploded view of the layers of the optical light conversion device.

Fig. 2A is a graph showing a relationship between the reflectance and the thickness of the reflective layer of the first fluorescent wheel of the present disclosure.

Fig. 2B is a graph showing a relationship between the reflectance and the thickness of the reflective layer of the second fluorescent wheel of the present disclosure.

Fig. 3 schematically illustrates the fabrication of a reflective layer according to other embodiments.

Detailed Description

A more complete understanding of the components, methods, and apparatuses disclosed herein may be had by reference to the drawings. These drawings are merely schematic depictions based on convenience and ease of demonstrating the present disclosure and are therefore not intended to show the relative sizes and dimensions of the devices or individual components of the devices and/or to define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description, it is to be understood that like reference numerals refer to like functional parts.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

As used in the specification and claims, the terms "comprising," "including," "having," "can," "containing," and variations thereof are intended to be used herein as open-ended transition words, terms, or words that require the presence of the specified components/steps and allow for the presence of other components/steps. However, such description should also be construed as describing the composition or process as "consisting of and" consisting essentially of the enumerated components/steps, "which allows for the presence of only the named components/steps, along with any inevitable impurities that may result from such components, but excludes other components/steps.

Numerical values in the specification and claims of this application should be understood to include: the same value when reduced to the same number of significant digits; and a value that differs from the set point by less than the experimental error of conventional measurement techniques of the type described in this application for determining the value.

All ranges disclosed herein are inclusive of the stated endpoints and independently combinable (e.g., a range of "from 2 grams to 10 grams" is inclusive of the endpoints 2 grams and 10 grams and all intermediate values).

The terms "about" and "approximately" may be used to include any numerical value that can be varied without changing the basic function of the value. The terms "about" and "approximately" when used within a range also disclose the range defined by the absolute values of the two endpoints, e.g., "about 2 to about 4" also discloses the range "from 2 to 4". In general, the terms "about" and "approximately" may refer to +/-10% of the indicated number.

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

As used herein, the term "inorganic" means that the "inorganic" object does not contain any carbon. For the avoidance of doubt, the terms "inorganic binder", "inorganic binder" and "inorganic coating" of the present disclosure do not comprise carbon.

For reference, red generally refers to light having a wavelength of about 780 nanometers to about 622 nanometers. Green generally refers to light having a wavelength of about 577 nanometers to about 492 nanometers. Blue generally refers to light having a wavelength of about 492 nanometers to about 455 nanometers. Yellow generally refers to light having a wavelength of about 597 nanometers to about 577 nanometers. However, the above may depend on the context. For example, these colors are sometimes used to mark various portions and distinguish the portions from each other.

The present disclosure relates to wavelength conversion devices that include a reflective layer having certain compositions. In particular, the reflective layer comprises (a) a binder, which may be organic or inorganic; and (B) reflective nanoparticles having a particle size of from about 200 nanometers to about 500 nanometers, including from about 350 nanometers to about 450 nanometers. These reflective layers will operate at high temperatures (e.g., greater than 200 ℃ or 250 ℃) while maintaining other optical and mechanical parameters, such as percent total reflectance.

Whether the reflective layer maintains high stability can be determined by either of two methods. In the first method, the fluorescent wheel using the reflective layer is placed in an oven and subjected to an aging treatment at 250 ℃. The reflectivity was tested every 100 hours for a minimum of 500 hours and the reflective layer was observed for the presence of any cracks. The reflective layer is considered to maintain high stability if the reflectance change between the measurements of 300 hours, 400 hours, and 500 hours is less than 2% and there are no cracks in the reflective layer. In the first method, the fluorescent wheel using the reflective layer is placed in an oven and subjected to an aging treatment at 250 ℃. The conversion efficiency of the fluorescent wheel was tested every 100 hours for a minimum of 500 hours and observed for the presence of any cracks in the reflective layer. The reflective layer is considered to maintain high stability if the conversion efficiency between measurements at 300 hours, 400 hours and 500 hours varies by less than 2% and there are no cracks in the reflective layer. The reflective layer is considered to maintain high stability as long as it is by one of the two methods.

Turning now to fig. 1A and 1B, wavelength conversion devices of the present disclosure are depicted. The wavelength conversion device is shown in the form of a fluorescent wheel 100. FIG. 1A is a schematic view of a fluorescent wheel 100, and FIG. 1B is a side cross-sectional view of fluorescent wheel 100. The fluorescent wheel 100 includes a substrate 110 having a reflective layer 120 formed thereon, wherein a phosphor layer 130 is applied on the reflective layer 120. A reflective layer is formed from the composition described further herein. As shown herein, the reflective layer 120 is formed by an inorganic binder or silicone (a) labeled with reference numeral 121 and reflective nanoparticles labeled with reference numeral 122.

The substrate 110 is typically a metal having a high thermal conductivity, such as aluminum or an aluminum alloy, copper or a copper alloy, silver or a silver alloy, or other metals having a high thermal conductivity. For example, the substrate may also be made of a non-metallic material or a composite material, such as glass, sapphire, or diamond. The substrate is generally disk-shaped or ring-shaped. The smoothness or roughness of the substrate surface is not critical. However, it is desirable that the surface of the substrate on which the reflective layer 120 is formed is clean and free of stains, oils, organic residues, or biological residues thereon. For low surface energy surfaces, adhesion can be improved by primers or by special surface treatments such as chemical or plasma etching and ozone cleaning.

The phosphor layer 130 includes at least one phosphor. Examples of suitable phosphors include Yttrium Aluminum Garnet (YAG), silicates, and nitrides. The phosphor may have a particle size of about 10 microns to about 30 microns. The phosphor layer is typically in the form of an annular phosphor segment containing different types of phosphors to convert the excitation light to green, yellow, or red. Typically, a blue laser (having a wavelength of about 440nm to about 460 nm) is used to excite a phosphor segment on the phosphor wheel. The fluorescent wheel may also have one or more gaps to allow the blue source light to pass unconverted.

The fluorescent wheel 100 of fig. 1A and 1B can be used by mounting the substrate on a motor to rotate at high speed. Typically, the substrate rotates during use, although the device may be used in a static (non-rotating) configuration, in which case it may not be referred to as a fluorescence wheel. In FIG. 1A, the rotation of the fluorescence wheel is depicted by an arrow rotating about an axis A-A, which passes through the substrate 110 and is perpendicular to the plane of the substrate 110. As a result, light of different wavelengths is sequentially generated.

As shown in fig. 1A and 1B, excitation light 123 (i.e., excitation light or input light) of an excitation wavelength from a light source (not shown) (e.g., a laser-based illumination source) is focused on the phosphor layer. An emission light 124 (i.e., an emission light or converted light) of an emission wavelength is generated by the phosphor layer. In this way, the phosphor layer converts the spectrum from excitation light of a first spectral wavelength range to emission (or re-emission) light of a second, different spectral wavelength range. When light 123 of an excitation wavelength (e.g., laser beam blue light) is focused on the phosphor layer, light 124 of an emission wavelength (e.g., yellow light) will be emitted in all directions including toward the substrate. The reflective layer 120 serves to reflect and redirect the emitted light away from the substrate such that the emitted light is emitted on the same side of the substrate as the side receiving the excitation light. The emitted light may be collected (e.g., by a lens) and used for subsequent downstream processes.

The reflective layer 120 comprises (a) a binder, which may be organic or inorganic; and (B) reflective nanoparticles having a particle size of about 200 nanometers to about 500 nanometers. In a more particular embodiment, the reflective nanoparticles have a particle size of about 350 nanometers to about 450 nanometers.

For adhesive (A), suitable materials should be usable over a long period of time (at least 20,000 hours) in the temperature range of-45 ℃ to 250 ℃ (-49 ° F to +482 ° F). Desirably, the binder may be used at temperatures above 200 ℃ for such long periods of time. The binder (a) may be an organic binder or an inorganic binder.

One example of an organic binder is a silicone, such as octamethyltrisiloxane, which is a reflective resin. Such silicones are available from Dow or Sumitomo Chemical. Prior to coating, the silicone may be mixed with an organic solvent, which may comprise methylsiloxane. An example of an organic solvent is sold under the trade name OS-20 by Dow Corning Corporation. This is a volatile solvent and acts as a diluent to adjust the solution viscosity. The mixed silicone/solvent is made homogeneous as required by the process, and a silicone oil diluent may be added to adjust the viscosity before the mixture is put into the mixer for mixing.

Alternatively, the binder (a) may be an inorganic binder having certain characteristics. Desirably, the inorganic binder has a Coefficient of Thermal Expansion (CTE) of about 0.5 ppm/deg.C to about 25 ppm/deg.C. In a particular embodiment, the inorganic binder is sodium silicate. Sodium silicate is of the formula (Na)₂SiO₃)_nAnd alternatively may be considered a polymer, as shown in formula (I) below.

Sodium silicate has anhydrous and hydrated forms of Na₂SiO₃·nH₂O, wherein n is 5, 6, 8 or 9. Sodium silicate is characterized by silicon dioxide (SiO)₂) With sodium oxide (Na)₂O) in a weight ratio. SiO 2₂:Na₂The weight ratio of O may be 2:1 to 3.75: 1. In particular embodiments, SiO₂:Na₂The weight ratio of O can be from about 2.5:1 to about 3.75:1, or from about 2:1 to about 3:1. Sodium silicate is typically provided as an aqueous solution.

In other embodiments, the inorganic binder may be made of other inorganic materials than sodium silicate. These inorganic materials may be silicates, aluminates, phosphates, borates or inorganic sol-gels. Examples of inorganic sol-gels include those made of Silica (SiO)₂) Or aluminum oxide (Al)₂O₃) The sol-gel is prepared.

In other exemplary embodiments, the inorganic binder is formed from a first component and a second component. The Total Dissolved Solids (TDS) characteristics of the inorganic binders used are provided in the table below:

such specific inorganic binders are prepared by mixing the first and second components and stirring at a temperature of about 25 ℃ to about 30 ℃ for a period of about 2 hours to about 3 hours. The ratio of the first component to the second component is from about 1:1 to about 7: 3.

Desirably, the inorganic binder (a) is substantially optically transparent (e.g., the inorganic binder has a light transmittance of at least 80%, including 90%, and up to 98%. this is determined, for example, using a spectrophotometer with an optic thickness from about 0.1 mm to about 0.2 mm available from Idea.

In particular embodiments, the inorganic binders of the present disclosure are capable of withstanding high temperatures (e.g., greater than 200 ℃, including 300 ℃ or above, and up to 400 ℃), have high light transmittance (e.g., at least 98%), have high tensile shear strength (e.g., at least 100psi at 300 ℃), are capable of being coated by flexible coating methods (e.g., drop coating, screen printing, spray coating), and have low curing temperatures (e.g., less than 185 ℃).

The reflective layer further comprises reflective nanoparticles (B). It is believed that the presence of the reflective nanoparticles reduces the shrinkage of the binder (a), thereby reducing the formation of cracks and bubbles. This avoids stress during assembly and improves the bonding strength of the reflective layer to the substrate. Ideally, the coefficient of thermal expansion of the reflective nanoparticles should be as close as possible to that of the binder (a), and their density should also be as close as possible to avoid delamination of the components.

The reflective nanoparticles have a particle size of about 200 nanometers to about 500 nanometers, including about 300nm to about 500nm and about 350nm to about 450 nm. The reflective nanoparticles may be made of pure titanium dioxide (TiO)₂) Or modified TiO₂And (4) preparing. Modified TiO₂The nanoparticles can be prepared from organic alcohol, siloxane, and aluminum oxide (A1)₂O₃) Zirconium dioxide (ZrO)₂) Or silicon dioxide (SiO)₂) And (4) surface modification. In a preferred embodiment, the reflective nanoparticles are pure TiO₂。

(B) The weight ratio of reflective nanoparticles to (a) binder can be from about 1:2.5 to about 1:0.8, including from about 1:2 to about 1:1. The reflective nanoparticles (B) should be mixed with the binder (a) and then the mixture may be refrigerated before using it. For example, the nanoparticles may be mixed with the binder twice, each at 800rpm for a period of about 2 minutes, followed by refrigeration at about 4 ℃ for about 24 hours. Desirably, the reflective nanoparticles are uniformly dispersed throughout the mixture such that the reflective nanoparticles are also uniformly dispersed throughout the reflective layer.

Referring to fig. 3, there is shown a further embodiment for preparing a mixture of reflective particles 122 and an inorganic binder for use in forming the reflective layer 120. In this embodiment, the solvent 200 and the inorganic binder material 202 are combined in a mixing cup at a solvent to binder ratio of about 10 to 1 to about 0 to 1 (by weight; alternatively written as about 10:1 to about 0:1) to obtain the mixed liquid binder 204.

Mixing reflective TiO₂The nanoparticles 122 are added to the mixing liquid binder 204 in a ratio of nanoparticles to mixing liquid of about 1 to 10 to about 1 to 0.2 (by weight; alternatively written as about 1:10 to about 1:0.2) and then blended twice, each at 800rpm for a period of 2 minutes, to form the reflective layer mixture 206. The solvent 200 may include, but is not limited to, water, alcohol, one or more ethers, and the likeMixtures of these. As a non-limiting example, a solvent used in paint may be used in the process as solvent 200. The reflective layer mixture 206 is refrigerated at a temperature of 4 ℃ for 24 hours, after which the reflective layer mixture 206 is applied to the substrate 110 by drop coating, printing, spraying, or other suitable process to form the reflective layer 120.

The ratio of solvent to binder has an effect on the properties of the reflective layer mixture 206. The addition of solvents with high boiling points (e.g., boiling point > 100 ℃) helps provide improved flow and leveling. If the solvent to binder ratio is greater than 10 to 1 (corresponding to an excess of solvent), the bond between the reflective layer and the substrate is weak, and the bond between the reflective layer 120 and the phosphor layer 130 is weak. For the reflective layer 120, for example, TiO₂The reflective particles of (a) are not bonded firmly enough, the reflective particles will fall off the reflective layer, and cause contamination.

The ratio of nanoparticles to mixing liquid also has an effect on the reflective layer because it affects the viscosity of the reflective layer mixture 206. In the case where the ratio of the nanoparticles to the mixed liquid is 1 to 10, a delamination phenomenon or a crack is observed. Delamination occurs when the nanoparticles 122 are partially detached, and cracking means that the viscosity of the reflective mixture is too low, 1 to 10, and therefore it cannot be used in the dispensing, printing, spraying process, and results in a reduced reflectivity of the reflective layer. On the other hand, when the ratio of the nanoparticles to the mixed liquid is less than 1 to 0.2, non-uniform dispersion and aggregation are observed to occur, and also cannot be used for the dropping, printing, spraying process.

In any of the preceding embodiments, the reflective layer may be formed by applying a mixture of binder (a) and reflective nanoparticles (B) to the substrate. The mixture may be applied by drop coating, spray coating, brush coating, flow, pattern coating, or screen printing.

In applications where the mixture is applied by drop coating or screen printing, a suitable viscosity for the mixture should be from about 0 centipoise to about 1,500 centipoise (cP), including from about 100cP to about 800cP, or from about 100cP to about 600cP, from about 200cP to about 500cP, or from about 1,000cP to about 1,500 cP. Viscosity determination using a Brookfield DVE SLVTJO viscometer or according to ASTM D1084And (4) degree. The inorganic binder itself (i.e. without TiO)₂Nanoparticles) can also have a suitable viscosity of about 0 centipoise to about 1,500 centipoise (cP), including about 0cP to about 800cP, or about 100cP to about 800 cP.

In some cases, it is contemplated that the reflective layer will be built up by multiple passes of application. For example, in a first pass, a mixture of binder (a) and reflective nanoparticles (B) is agitated and then sprayed onto a substrate to form a reflective layer having a thickness of about 0.025mm to about 0.075 mm. The first layer was then left at room temperature for about 0.5 hours and then cured at about 85 ℃ for about 0.5 hours. In a second round, the mixture of binder (a) and reflective nanoparticles (B) was stirred again and then sprayed on top of the first layer, then left at room temperature for about 0.5 hours and then cured at about 85 ℃ for about 0.5 hours. This results in a total thickness of the final reflective layer of about 0.05mm to about 0.15 mm.

Desirably, the reflective layer is configured to reflect in a wavelength range of about 380nm to about 800nm, more preferably about 420nm to about 680 nm. The reflectivity of the reflective resin layer is typically at least (or greater than) 90%, and more preferably at least (or greater than) 94%, or 95%, or 96%, or 97%, or 98%, or 99%.

The total thickness of the reflective layer may be about 0.05mm to about 0.15 mm. In particular embodiments, the reflective layer has a thickness of about 0.7mm to about 0.12 mm. The thickness may be set to maximize the reflectivity of the light output over the desired wavelength range. Thicker layers provide higher reflectivity but may also lead to long term failure, for example, due to peeling or cracking of the reflective layer. Thus, the optimal thickness may be determined by optimal reflectivity and/or some compromise between reflectivity and durability.

The reflective layer is typically different (and distinguishable) from the phosphor layer by its composition and/or structure. In particular, the reflective layer is typically significantly more reflective than the phosphor layer. The phosphor layer is generally not reflective. Typically, the reflective layer does not include a wavelength converting material (e.g., a phosphor).

The reflective layers of the present disclosure comprising reflective nanoparticles can maintain a total reflectance of at least 95% at temperatures above 200 ℃. The reflective layer may be cured at a relatively low temperature of 85 ℃ to 150 ℃. The reflective layer exhibits reliable operation at high laser irradiance and temperature. The reflective layer can also be flexibly made in various sizes, shapes and thicknesses. The reflective layer is also capable of withstanding high operating temperatures, i.e., operating temperatures in excess of 200 ℃ and up to 250 ℃. The reflective layer may be used in high power laser projection display systems where the solid state laser projector may be equipped with laser power from about 60 watts to about 300 watts, including over 100 watts. The operating temperature of such devices can reach above 200 ℃ to achieve high light emission brightness.

In some embodiments, the reflective layer 120 may also serve as a bonding layer between the substrate 110 and the phosphor layer 130. Alternatively or additionally, an auxiliary bonding layer (e.g., glue or tape) may also be used to bond the phosphor layer to the reflective layer. This is useful for certain solid state phosphor layers made of phosphor particles dispersed, for example, in glass, or in crystals or in ceramic materials.

Referring back to fig. 1A and 1C, it should be noted that the width (measured in the radial direction on the substrate) of the reflective layer 120 can vary. In fig. 1A, the width of the reflective layer 120 is much greater than the width of the phosphor layer 130. However, as shown in FIG. 1C, the width of the reflective layer 120 may be substantially equal to the width of the phosphor layer 130. Generally, the width of the reflective layer 120 is at least equal to the width of the phosphor layer 130, and may be greater than the width of the phosphor layer.

It is contemplated that the reflective layers described herein may be used in fluorescent wheels and laser projection display systems. The reflective layer may also be used in conjunction with solid state illumination sources, such as in automotive headlamps.

The following examples are provided to illustrate the methods of the present disclosure. The examples are illustrative only and are not necessarily intended to limit the disclosure to the materials, conditions, or process parameters described herein.

Examples

Example 1

Prepared by mixing inorganic binder and TiO₂Two fluorescent wheels of the reflecting layer made of nanoparticles. Absence of reflecting layerThe organic binder is formed from a first component and a second component. The Total Dissolved Solids (TDS) characteristics of the inorganic binders used are provided in the table below:

inorganic binder and TiO₂The weight ratio of the nanoparticles was 1: 1.7. TiO used in the first round, labelled PT01₂The nanoparticles have a particle size of 0.4 to 0.45 μm (i.e., 400 to 450 nm). TiO used in the second round, labelled PT02₂The particle size of the nanoparticles was 0.36 μm (i.e., 360 nm).

Mixing inorganic binder and TiO₂The nanoparticles were mixed twice in a mixer for a period of two minutes at 800rpm each to produce an Inorganic Scattering Layer Material (ISLM).

Interestingly, ISLM is a shear thinning fluid, i.e. its viscosity becomes less when the ISLM is stirred. PT02 powder also tends to aggregate, resulting in incomplete absorption of the gum. The ISLM was therefore placed in a refrigerator at 4 ℃ for 24 hours to ensure complete absorption of the inorganic binder by the PT02 powder. After 24 hours, the ISLM was gently stirred by hand to ensure that the mixed material was homogeneous. The viscosity of the ISLM is from 1000 centipoise to 1500 centipoise (cP).

The ISLM is applied using an automatic spray coater (PVA 350). The spraying pressure was adjusted to 3.5 MPa. The ISLM was sprayed twice on the Al disc to obtain a wet reflective layer. The wet layer was left at room temperature for 0.5 hours and cured at 85 ° f for 0.5 hours to obtain a reflective layer having a thickness of 0.045 mm. A second layer was applied on top of the first layer to obtain a reflective layer with a total thickness of 0.09 mm. The reflective layer was cured at 185 ° f for 0.5 hours to ensure complete curing of the layer.

First, the diffuse reflectance of the PT01 and PT02 fluorescent wheels was measured at different reflective layer thicknesses. The results of the PT01 fluorescence wheel are shown in figure 2A and table a below. The results of the PT02 fluorescence wheel are shown in figure 2B and table B below. From these results, it can be seen that the reflectance stabilized at greater than 94% at thicknesses greater than 0.08mm (PT01) or 0.07mm (PT 02).

Table a.pt01

Thickness (mm)	Diffuse reflectance (%)
		0.02	84.2
0.02	90.6
		0.04	92.6
0.08	94.2
		0.09	94.7
0.09	94.4
		0.10	94.5

Table b.pt02

Thickness (mm)	Diffuse reflectance (%)
		0.050	93.0
0.070	94.5
		0.075	94.5
0.080	94.4
		0.082	94.8
0.093	94.6

Next, two fluorescence wheels PT01 and PT02 were compared with two other fluorescence wheels. The first comparative wheel, labeled G1, used only an inorganic binder in the reflective layer (i.e., no TiO)₂Nanoparticles). The second comparative wheel, labeled G1.5, used only organic binder in the reflective layer (no TiO)₂Nanoparticles).

Output power tests were performed at different thicknesses, comparing PT02 wheel and G1 wheel. The results of the PT02 round are shown in Table C. In the last column, 100% is the result obtained with the G1 fluorescent wheel.

Table C.

Thickness (mm)	Diffuse reflectance (%)	Output Power @100W	Percentage of relative G1
				0.07	94.7	48.0	106.3
0.08	94.7	48.2	106.6
				0.09	94.6	48.0	106.2

Next, a reliability test was performed comparing PT02 round and G1 round at 100W and 50W. The test conditions are shown in Table D. Run 3 samples for each test. The results of the PT02 round are shown in Table E. Again, 100% is the result obtained from the G1 fluorescent wheel.

Table D.

Table E.

Input power	Thermal shock	High humidity	Relative output power of G1%
				100W	106.2％	105.9％	106.3％
50W	106.1％	106.1％	106.2％

Finally, PT02 round and G1 round were compared at 100W and 50W. The samples were placed in a muffle furnace at 250 ℃ and tested for output performance over time. The results of the PT02 round are shown in Table F. Again, 100% is the result obtained from the G1 fluorescent wheel. The results show that the PT02 wheel was stable and no cracks occurred between the reflective layer and the phosphor layer.

Table F.

Time (hours)	100W	50W
			0	106.3％	106.2％
115	105.9％	106.0％
			206	106.3％	105.8％
349	106.1％	106.1％
			513	106.0％	105.9％

Output power tests were performed at different thicknesses, comparing PT01 wheel and G1 wheel. The results of the PT01 round are shown in Table G. In the last column, 100% is the result obtained with the G1 fluorescent wheel.

Table G.

Thickness (mm)	Output Power @100W, percentage of G1
		0.08	105.7％
0.09	106.7％
		0.10	106.5％

Next, a reliability test was performed comparing PT01 round and G1 round at 100W and 50W. The test conditions are shown in table D above. Each test run ran 3 samples. The results of the PT01 round are shown in Table H. Again, 100% is the result obtained from the G1 fluorescent wheel.

Table H.

Input power	Thermal shock	High humidity	Low temperature	Work output relative to G1Percentage ratio%
					100W	106.0％	106.1％	106.3％	106.4％
50W	106.0％	105.5％	106.3％	106.1％

Finally, PT01 round and G1 round were compared at 100W and 50W. The samples were placed in a muffle furnace at 250 ℃ and tested for output performance over time. The results of the PT01 round are shown in Table I. Again, 100% is the result obtained from the G1 fluorescent wheel. The results show that the PT01 wheel was stable and no cracks occurred between the reflective layer and the phosphor layer.

Table I.

Time (hours)	100W	50W
			0	106.2％	106.3％
230	106.1％	106.1％
			350	106.1％	106.1％
500	105.4％	106.1％

Example 2

Diffusivity tests were performed with different types of nanoparticles: TiO 2₂、A1₂O₃And Al. The binder is an inorganic binder. Layers of different thicknesses were made and tested for diffusivity (i.e., diffuse reflectance). Table J describes five different mixtures and table K provides the diffusivity results for the three mixtures. It should be noted that a given layer may have a different thickness as the mixture is sprayed by hand.

Table J.

Table K.

The results in Table K show that A1 is obtained when the layer thickness exceeds 0.15mm₂O₃Expansion of nanoparticlesThe scattering rate is more than 94 percent. However, A1₂O₃Is unstable (i.e., varies greatly) and requires a thickness greater than TiO for the same reflectivity₂The thickness of the nanoparticles. A1₂O₃And also easily broken. Therefore, it was concluded that TiO₂Are the best nanoparticles for use in high reflectivity layers.

Example 3

With different TiO from different suppliers₂Nanoparticles and Al (OH)₃And MgO for diffusivity test. The binder is an inorganic binder. Layers of different thicknesses were made and tested for diffusivity. Table L describes six different mixtures, and table M provides the diffusivity results for five mixtures. It should be noted that the MgO particles are large and cannot be uniformly mixed.

Table L.

Table M.

Mixture #	Layer thickness (mm)	Diffusion Rate (%)	Average (%)
				5	0.06-0.07	94.1,93.3,94.7,94.8,94.6	94.3
5	0.05-0.07	93.2,93.2,94.8,94.4,94.1	93.9
				6	0.1	93.7,93.2,92.8,93.1,93.7	93.3
6	0.09-1.2	89.9,93.5,93.8,91.3,91.2	91.8
				9	0.12-0.2	83.7,84.4,84.2,85.3,81.8	83.4
9	0.08-0.11	83.3,84.3,84.8,83.4,86.4	84.5
				10			85-87

Mixture #5 can achieve a diffusivity greater than 94%. The results also show that 0.2 μm and 0.5 μm TiO are used₂The nanoparticles can achieve diffuse reflectance of greater than 90%.

The disclosure has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.