Hyperspectral uniformity acrylic light diffusing material

Abstract

The present invention relates to an acrylic light diffusing material providing spectral uniformity in the visible range (400 nm to 800 nm). The light diffusing material provides uniform light transmission for light engines containing two or more light sources with different spectral emission peaks. Due to its high hiding performance, the light diffusing material of the present invention is particularly suitable for use with LED point sources. The diffusing material contains a transparent polymer matrix, such as acrylic polymers from Arkema, and one or more types of diffusing material, providing an optimal balance of spectral uniformity, light transmission, diffusion and hiding performance.

Description

TECHNICAL FIELD

[0001] The present invention relates to an acrylic light diffusing material providing spectral uniformity in the visible range (defined herein as 400 nm to 800 nm). The light diffusing material provides uniform light transmission for light engines having two or more light sources with different spectral emission peaks. Due to its high hiding performance, the light diffusing material of the present invention is particularly useful for use with LED point sources. The diffusing material contains a transparent polymer matrix and one or more types of diffusing material, providing an optimal balance of spectral uniformity, light transmission, diffusion and hiding performance. BACKGROUND

[0002] Light transmission and diffusion can be managed by using diffusing particles (inorganic and organic particles in a polymer matrix). For example, US 7,547,736 describes the use of particles having an average particle size of 15 to 70 microns to provide a frosted appearance and textured surface, and US 8,163,827 describes a high light transmission diffuser screen having inorganic pigments and particles with a matching refractive index.

[0003] A light emitting device consists of a light source and a cover made of plastic (also called a lens or diffuser), the function of which is to shield and protect the light source while still ensuring good transmission of the light emitted by the light source. The plastic can be colored or can have decorative elements or patterns. The cover also has the function of scattering the emitted light, so that the illumination becomes soft and not glaring. Scattering of the light emitted by the light source is achieved by dispersing scattering particles of organic or mineral nature in the plastic.

[0004] Light emitting diodes (LEDs) are increasingly popular as light sources because they consume much less electricity and produce much less heat than standard incandescent or fluorescent lamps. LEDs provide very bright point sources, but the output tends to appear glaring and causes uncomfortable glare. This is a challenge for lighting designers, because many applications require both illumination and low glare. It is often desirable to hide the light source shape, thereby creating more diffuse illumination.

[0005] Replacing traditional light sources with LEDs leads to a change in the illumination. This is because LEDs, especially those with high luminous flux, exhibit directional illumination, whereas the illumination of, for example, a neon tube is from 0° to 360°. Furthermore, the emission spectrum of LEDs is completely different from that of traditional light sources.

[0006] WO 2006 / 100126 describes a thermoplastic cover having dispersed beads for use with LEDs to form a light emitting device. 3 to 30% of scattering particles are dispersed in a transparent plastic. The particles can be inorganic or organic and have an average diameter of 0.5 to 100 microns. No combination of particle size and loading is described, and no hiding performance is taught.

[0007] The addition of scattering particles helps the effect of softening the LED light source, but the scattering also reduces the light transmission. Some LED lamp shade manufacturers add pigments (such as BaS04) to the shade to increase the hiding performance, but this can significantly reduce the light transmission.

[0008] The hiding performance of LED shades is typically measured by the industry in a qualitative way. Quantitative haze measurements are sometimes used as a proxy, but they do not correlate well enough with hiding performance. The applicant has developed a quantitative hiding method as described in US2015 / 0267891, which is incorporated herein by reference.

[0009] There are several acrylic light diffusing materials currently on the market, including spherical plastic particles dispersed within an acrylic matrix. Almost all commercially available acrylic / PMMA products contain additives that block UV light (200 nm to 400 nm) to increase safety of human exposure, which is the intended application of currently available acrylic light diffusing materials. There are products that do not contain UVA blockers, but these are neither intended for use with LED lamps nor do they contain diffusing particles, such as PMMA sheets for tanning beds (US 7,407,998).

[0010] Multi-channel LEDs are often used to utilize different wavelengths of light, and to provide a broad spectrum of transmitted light.

[0011] Problem :

[0012] Many diffusing sheets, especially those containing organic light diffusing beads, exhibit poor spectral uniformity. For light wavelengths in the near-UV range (380 nm to 420 nm), these diffusing sheets often exhibit a sharp drop in transmission efficiency. Thus, for a typical diffuser, there is a significant loss in transmission for a lighting device with a light source having light in this lower range.

[0013] This is problematic for violet LED disinfection applications, such as disinfecting a surface using 405 nm light. In this case, a diffusing resin with a reduced %LT at 405 nm would reduce the efficiency of the 405 nm LED.

[0014] US 9,333,274 seeks to reduce the reflectance or transmission properties to less than 30% of the energy loss in the 380 nm to 420 nm wavelength range.

[0015] There is a need for a diffusing material that can provide high spectral uniformity for several different point sources of different wavelengths, while also providing high light transmission, high diffusion, and good hiding performance.

[0016] Solution

[0017] Surprisingly, it has now been found that a 0.080" thick diffuser cover having a transparent polymer matrix and 0.1 to 40 weight percent of diffusing particles can be formed to provide greater than 40% and preferably greater than 60% light transmission at each of 400 nm, 500 nm, 600 nm, 700 nm and 800 nm, with an absolute difference in light transmission between 400 nm transmission and 800 nm transmission of less than 6%, while still providing at least 65% of the hiding performance at 400 nm, and preferably at each of these wavelengths.

[0018] Ideally, the transmission at each of 400, 500, 600, 700 and 800 is at least 90%.

[0019] Such a material can be used in a multi-spectral luminaire containing two or more light engines having multiple spectral emission peaks. SUMMARY

[0020] In this specification, embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended that the embodiments can be carried out in ways other than those explicitly described, and that they can be implemented in combinations with, or in the absence of, other features. For example, it will be clear that all the features described anywhere in this specification can be combined in any combination.

[0021] The present invention relates to a light diffuser cover composition for use with two or more point light sources, wherein the light diffuser cover composition comprises:

[0022] a) a transparent or translucent polymer matrix,

[0023] b) 0.1 to 40 weight percent, preferably 0.2 to 20 weight percent, more preferably 0.3 to 10 weight percent of diffusing particles dispersed within the transparent polymer matrix,

[0024] wherein the light diffuser cover composition has the following properties when measured on a 0.080 inch (0.203 cm) thick sheet:

[0025] - a light transmission of light at each of 400 nm, 500 nm, 600 nm, 700 nm and 800 nm wavelengths of light is greater than 40%, preferably greater than 60%;

[0026] - an absolute difference between the light transmission at 400 nm and the light transmission at 800 nm is less than 6%; and

[0027] ​- a diffuse level at 400 nm, preferably 400 nm, 500 nm, 600 nm, 700 nm and 800 nm light wavelengths of at least 65% as measured by the hiding performance metric.

[0028] The transparent or translucent polymer matrix in the light diffusing cover composition can be polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate, glycol modified (PETG), polyvinyl chloride (PVC), impact modified PVC, polyester (PET, PBT, APET, etc.), styrene acrylonitrile (SAN), acrylonitrile-acrylate copolymer, acrylonitrile-methyl methacrylate copolymer, methyl methacrylate-styrene copolymer, methacrylate-butadiene-styrene terpolymer, acrylonitrile-styrene-acrylate (ASA) terpolymer, acrylonitrile butadiene styrene (ABS) terpolymer, polystyrene (PS), high impact polystyrene (HIPS), polyolefin, impact modified polyolefin, polycyclohexylethylene, cyclic olefin copolymer (COC), polyvinylidene fluoride (PVdF), PVdF-acrylic copolymer, imidized acrylic polymer, acrylic polymer, impact modified acrylic polymer, and mixtures thereof.

[0029] The matrix polymer is preferably a (meth)acrylic polymer having at least 70 wt% of methyl methacrylate monomer units.

[0030] The diffusing particles in the light diffusing cover are inorganic, organic or mixtures thereof, can have a spherical, near-spherical or irregular shape, and have a refractive index mismatch with the polymer matrix of + / - 0.01 to 0.25, and can have a lower refractive index than the refractive index of the polymer matrix. The diffusing particles can have a multi-modal particle size distribution, and are preferably made of silicone resin, silicone rubber or mixtures thereof.

[0031] The light diffusing cover composition can additionally contain an impact modifier, and can contain one or more types of UV absorbers. Preferably, the composition contains less than 5 wt%, less than 3 wt%, less than 1 wt%, and most preferably no UV absorbers that absorb light wavelengths above 390 nm, based on the total composition.

[0032] The present invention also relates to a lighting device having two or more point light sources of different wavelengths, and a light diffusing cover made of the light diffusing cover composition of any of the above aspects.

[0033] The light diffusing cover can have a thickness of 200 micrometers to 10 millimeters, and preferably has a rough (textured) surface.

[0034] The light diffuser composition and lighting device described in the foregoing aspects can be used in a continuous environment disinfecting luminaire, a multi-color luminaire, a horticulture lighting luminaire, or an in-vehicle lighting system. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The light transmission vs. wavelength plot for an acrylic resin containing silicone diffuser beads (Particle D) and styrene acrylic diffuser beads (Particle B) is compared.

[0036] Figure 2 The hiding performance vs. wavelength plot for the above resin and diffuser particles is compared.

[0037] Figure 3 The light transmission vs. wavelength plot for an acrylic resin containing silicone diffuser beads (Particle D) and styrene acrylic diffuser beads (Particle A) is compared.

[0038] Figure 4 The hiding performance vs. wavelength plot for an acrylic resin containing silicone diffuser beads (Particle D) and styrene acrylic diffuser beads (Particle A) is compared. DETAILED DESCRIPTION

[0039] All documents cited herein are incorporated by reference. Unless otherwise indicated, all molecular weights are weight average molecular weight as determined by gas permeation chromatography (GPC), and all percentages are weight percent.

[0040] As used herein, the term "copolymer" indicates a polymer composed of two or more different monomeric units, including di-copolymers, terpolymers, and polymers having 3 or more different monomers. Copolymers can be random or blocky, can be heterogeneous or homogeneous, and can be synthesized by batch, semi-batch, or continuous processes.

[0041] As used herein, "point source" refers to a source of electromagnetic radiation of any shape in the range of 4,000 angstroms to 7,700 angstroms. This includes, but is not limited to, incandescent, fluorescent, neon, argon, and LED light sources.

[0042] Those skilled in the art will appreciate that the description herein contains only exemplary embodiments and that the present disclosure is intended to cover all modifications and equivalents.

[0043] Diffusion cover

[0044] The diffuser of the present invention is a transparent polymer matrix containing one or more types of diffusing particles. The diffuser of the present invention provides uniform spectral transmission in the wavelength range of 400 nm to 800 nm. The uniform spectral transmission can also be effectively extended to lower wavelengths of light, including as low as 390 nm, 385 nm, and 375 nm. For example, LED light sources with a peak of 405 nm are known to produce light emissions as low as about 385 nm. Because of the uniform spectral transmission provided, the diffuser compositions of the present invention can be used with point light sources of two or more different wavelengths, and especially when one light source is in the range of 375 nm to 450 nm, while the light transmission of ordinary diffusers generally drops off significantly at shorter wavelengths.

[0045] Polymer matrix composition

[0046] The diffuser matrix polymer is a thermoplastic or thermoset polymeric material having a light transmission in the range of 350 nm to 1000 nm according to ASTM D 1003 standard of at least 50%, preferably at least 70%, more preferably at least 80%, and even more preferably greater than 90% (this is the light transmission of the polymer without the scattering particles). The matrix can be transparent or translucent. A translucent glazing can aid in light scattering and is therefore preferred. The translucency can be created by physical treatment of the glazing surface, or by the addition of particles, particularly particles with a refractive index mismatch of 0.01 to 0.25, more preferably 0.02 to 0.2 positive or negative.

[0047] Useful polymer matrix materials include, but are not limited to, polycarbonates (PC), polyethylene terephthalate, glycol modified (PETG), polyvinyl chloride (PVC), impact modified PVC, polyesters (PET, PBT, APET, etc.), styrene acrylonitrile (SAN), acrylonitrile-acrylate copolymer, acrylonitrile-methyl methacrylate copolymer, methyl methacrylate-styrene copolymer, methacrylate-butadiene-styrene terpolymer, acrylonitrile-styrene-acrylate (ASA) terpolymer, acrylonitrile butadiene styrene (ABS) terpolymer, polystyrene (PS), high impact polystyrene (HIPS), polyolefins, impact modified polyolefins, polycyclohexylethylene, cyclic olefin copolymer (COC), polyvinylidene fluoride (PVdF), PVdF-acrylic copolymer, imidized acrylic polymer, acrylic polymer, impact modified acrylic polymer, etc., or mixtures thereof. Useful thermoset polymer matrices include, but are not limited to, silicones and epoxies.

[0048] Acrylic resins, polystyrene, styrene acrylonitrile, and polycarbonate are preferred polymer matrices because they are easily processed and are commercially available. In addition, these polymers exhibit excellent thermo-mechanical strength. While the energy efficiency of LEDs is much higher than incandescent lamps, some of the energy is still converted to heat.

[0049] Acrylic polymers as used herein are intended to include polymers and copolymers having two or more different monomer units formed from alkyl methacrylate and alkyl acrylate monomers and mixtures thereof. The alkyl methacrylate monomer is preferably methyl methacrylate which can comprise greater than 50% to 100% of the monomer mixture. There can also be present from 0% to less than 50% of other acrylate and methacrylate monomers or other ethylenically unsaturated monomers in the monomer mixture including but not limited to styrene, alpha-methyl styrene, acrylonitrile, and low levels of crosslinking agents. Suitable acrylate and methacrylate comonomers include but are not limited to methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, isooctyl methacrylate and isooctyl acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and isobornyl methacrylate, methoxyethyl acrylate and methoxy methacrylate, 2-ethoxyethyl acrylate and 2-ethoxyethyl methacrylate, and dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate monomers. (Meth)acrylic acids such as methacrylic acid and acrylic acid can be used in the monomer mixture. Most preferably, the acrylic polymers are those having from 70% to 99.5% by weight and more preferably from 80% to 99% by weight of methyl methacrylate units and from 0.5% to 30% by weight of one or more C 1-8 Copolymers of linear or branched alkyl acrylate units.

[0050] The acrylic polymers can be alloys with one or more compatible polymers. Preferred alloys are PMMA / polyvinylidene fluoride (PVDF) alloys and PMMA / poly lactic acid (PLA) alloys. The alloys contain from 2% to 95% by weight, preferably from 5% to 90% by weight, more preferably from 20% to 90% by weight, and more preferably from 51% to 90% by weight of PMMA homopolymer or copolymer, and from 5% to 98% by weight, preferably from 10% to 95% by weight, more preferably from 10% to 80% by weight, and more preferably from 10% to 49% by weight of the compatible polymer.

[0051] Diffusion particles

[0052] The diffusing particles can be organic, inorganic, or a mixture thereof, and can be spherical, approximately spherical, or irregular in shape, or a mixture of these shapes. Particles formed from a suspension or emulsion synthesis are relatively spherical. Particles formed from grinding of a cell-cast sheet will be irregular. In one embodiment, the particles are formed from grinding of a cell-cast sheet and have an irregular shape. The irregular shape can help with light dispersion. The diffusing particles maintain their shape and resist deformation under normal heat and pressure processing conditions during incorporation into the polymeric matrix and subsequent formation into an article.

[0053] The average particle size of the diffusing particles is generally in the range of 500 nanometers to 120 micrometers, preferably in the range of 1 micrometer to 90 micrometers. For a single mode distribution, the most preferred particle size range is 1.5 micrometers to 5 micrometers. The distribution can also be a bimodal or a multimodal distribution. One useful bimodal distribution includes 1 to 20, preferably 2 to 15, parts by weight of small crosslinked diffusing particles having an average particle size of 1 micrometer to 20 micrometers, and 2 to 10 parts by weight of large crosslinked diffusing particles having an average particle size of 30 micrometers to 80 micrometers. This bimodal distribution, in addition to providing good hiding, good transmission, and good diffusion, also produces a textured surface.

[0054] The amount of diffusing particles in the polymeric matrix is 0.1 to 40 weight percent based on the weight of the total glaze, preferably 0.2 to 20 weight percent based on the total polymeric matrix composition, and more preferably 0.2 to 10 weight percent, and most preferably 0.3 to 10 weight percent, and more preferably 0.4 to 6 weight percent. The total diffusing particle level depends on the average particle size, and also on the thickness of the glaze. The particles preferably do not absorb light from 350 nm to 400 nm.

[0055] The particles have a refractive index that is mismatched from the matrix, having a refractive index that differs from the refractive index of the matrix polymer by 0.01 to 0.25, preferably 0.02 to 0.20. While not wishing to be bound by any particular theory, it is believed that diffusing particles having a lower refractive index than the polymer matrix are most preferred for maximum spectral uniformity of light transmitted through the diffusing material. It is believed that diffusing materials containing diffusing particles having a lower refractive index than the matrix will result in less Fresnel reflection loss than diffusing materials containing diffusing particles having a higher refractive index than the matrix. While not wishing to be bound by any particular theory, it is believed that additives or processes that increase the surface roughness of the diffusing material are preferred for maximum spectral uniformity of light transmitted through the diffusing material. The refractive index can be measured by methods known in the art, such as the method in accordance with ASTM D 542. Since particles of different sizes are most effective at diffusing light at particular wavelengths, it is preferred to use two or more different average particle size distributions - or a single average particle size with a very very wide particle distribution - in order to provide good diffusion over the range of light from 400 nm to 800 nm. Smaller size diffusing particles can diffuse shorter wavelength light better, while larger average particle size particles can diffuse longer wavelength light better.

[0056] Examples of useful particles include inorganic particles such as BaS04, Ti02, CaC03, BaTi03, fluorine-containing polymer particles such as poly(tetrafluoroethylene) (PTFE), poly(trifluorochloroethylene) (PCTFE), poly(vinylidene fluoride) (PVDF), ethylene chlorotrifluoroethylene (ECTFE), and copolymers thereof; hydrophobic polymers such as polyalkyl oxides; polystyrene; silicones including but not limited to silicone rubbers, oligomeric siloxane cage-like linkages, and silicone resins; core / shell polymer particles; crosslinked acrylic beads, preferably made by suspension, having a composition of 0% to 99.99% styrene, 0% to 99.99% alkyl methacrylate or alkyl acrylate, or a mixture of the two, and 0.01% to 5% crosslinking agent.

[0057] In one embodiment crosslinked methyl methacrylate particles are used. These comprise more than 50 wt.%, preferably more than 70 wt.% and more preferably more than 80 wt.% of methyl methacrylate units and 0.5 wt.% to 20 wt.%, preferably 1 wt.% to 10 wt.% of a monomer with at least two C=C double bonds as crosslinker. This can be, for example, di(meth)acrylate 1,4-butanediol, di(meth)acrylate ethylene glycol, di(meth)acrylate tetraethylene glycol, di(meth)acrylate propylene glycol, pentaerythritol tetra(meth)acrylate, allyl methacrylate or divinylbenzene. In another embodiment acrylic copolymers containing a major portion of butyl acrylate are used.

[0058] In another embodiment the particles have a core-shell structure with a rubbery alkyl acrylate polymer in the core and at least one polymer shell compatible with the polymer matrix. This outer shell represents only a fraction of the total weight of the particle. The rubbery core typically comprises an alkyl acrylate polymer having a refractive index that differs by at least 0.02 or more units from the refractive index of the matrix polymer.

[0059] In a preferred embodiment some or all of the diffusing particles are silicone - silicone rubber and silicone resin particles. Silicone particles useful in the present application can be obtained in several ways, including: A. Hydrolysis and polycondensation of organotrialkoxysilanes and / or tetraalkoxysilanes, these silanes being described by the formula R 1 Si(OR 2 )3 and Si(OR 2 )4, where R' is for example a substituted or unsubstituted alkyl, alkenyl or phenyl group and the hydrolysable alkoxyl group R is an alkyl group such as methyl, ethyl or butyl, or an alkoxy-substituted hydrocarbon group such as 2-methoxyethyl or 3-ethoxyethyl. Examples of organotrialkoxysilanes are methyltrimethoxysilane, methyltriethoxysilane, methyl-n-propoxysilane, methyltriisopropoxysilane and methyltris(2-methoxyethoxy)silane. These silane compounds and the process to produce spherical silicone particles therefrom are known to the person skilled in the art and can be found in patent specifications EP 1 116 741, JP 63-077940 and JP 2000-186148. B: Chemical crosslinking of polysiloxane chains having an inorganic silicone-oxygen backbone and organic side chains susceptible to chemical crosslinking, such as olefinic groups. For example, US 5,969,039 demonstrates such a process.

[0060] The silicon-containing diffusing particles can be used as the only diffusing particles or can be combined with other types of organic and / or inorganic particles. In the examples below, the silicone particles exhibit similar performance when combined with large organic particles.

[0061] Other additives

[0062] The polymer matrix composition can contain other additives, including impact modifiers, and other additives commonly present in polymer formulations, including but not limited to stabilizers, plasticizers, fillers, colorants, pigments, dyes, antioxidants, antistatic agents, surfactants, toners, refractive index matching additives, additives with specific light diffraction.

[0063] Useful impact modifiers include block copolymers, graft copolymers, and core / shell impact modifiers. The impact modifier can be present at a level of 0 to 80 weight percent, preferably 5 to 60 weight percent, more preferably 10 to 45 weight percent, based on the total layer amount of the matrix polymer and all additives. The level of impact modifier can be adjusted to meet the toughness requirements of the composition's end use. Core-shell impact modifiers are multi-stage, continuously produced polymers having a core / shell particle structure with at least two layers. Preferably, the core-shell modifier comprises three layers consisting of a hard core layer, one or more intermediate elastomeric layers, and a hard shell layer.

[0064] In one embodiment, the impact modifier includes a core made of an acrylate / poly siloxane copolymer and a shell made of a hard resin. In this case, the core is a flexible rubbery material prepared by polymerization of one or more vinyl monomers in the presence of a rubbery polymer obtained from monomers such as alkyl acrylate or alkyl methacrylate, where the alkyl group contains 2 to 10 carbon atoms. Products of this type are sold by Mitsubishi Rayon under the designation Metablen® S-2001. ® S-2001.

[0065] According to another embodiment, the impact modifier is composed of a poly(organosiloxane) core and a thermoplastic resin shell. The organic groups of the poly(organosiloxane) core are preferably alkyl or vinyl groups comprising between 1 and 18 carbons, advantageously between 1 and 6 carbons, or substituted aryl or hydrocarbon. The poly(organosiloxane) comprises one or more of these groups. The siloxane has a variable degree of functionalization defining the degree of crosslinking of the poly(organosiloxane). Preferably, the average degree of functionalization is between 2 and 3, thus forming a partially crosslinked core. The shell is formed from a polymer or copolymer formed from monomers such as alkyl acrylate or alkyl methacrylate, acrylonitrile, styrene, vinylstyrene, vinyl propionate, maleimide, vinyl chloride, ethylene, butadiene, isoprene and chlorobutadiene. The fraction of the core represents between 0.05 and 90% by weight of the particle, preferably between 60 and 80% by weight. The particle size is between 10 nm and 400 nm. As an example of impact modifier of this type, mention can be made of the Genioperl® series of products from Wacker Silicones. ®

[0066] In one embodiment, the impact modifier is a high efficiency impact modifier as described in WO 2020 / 198,179 having a T g > 0°C, a core polymer stage of 10 to 80% by weight g < 0°C, an internal polymer shell of 5 to 50% by weight g > 0°C, wherein the ratio of emulsifier to surface area of said core-shell particle is less than 1.5 x 10 -4 g / m 2 .

[0067] ​Light stabilizing and / or UV absorbing additives can be added to the polymer matrix composition, but any such light stabilizing or UV absorbing additives should not interfere with the transmission of light at 400 nm. UV light stabilizers include UV absorbers and antioxidants. The specific choice and loading level of UV absorbers can control the Δ%LT. Lower loading of light stabilizing or UV absorbing additives should be used in the compositions of the present invention, and one or more additives that absorb only at lower wavelengths, such as 250 nm to 360 nm, are selected. Some typical UV absorbers, such as methyl salicylate (MESAL), have slight absorption up to 390 nm. Useful UV absorbers that absorb UVB and UVC light (200 nm to 320 nm light) include, but are not limited to, phenolic (e.g., methyl salicylate or N-(2-ethoxyphenyl)-N'-(2- ethylphenyl)oxal diamide) and / or (p-methoxybenzylidene) dimethylmalonate (e.g., Hostavin PR-25). Useful light stabilizing additives include, but are not limited to, hindered amine light stabilizers (e.g., Tinuvin 770), and can provide additional free radical scavenging and / or antioxidant effects.

[0068] Some commercially available light stabilizing additives (e.g., Tinuvin® P) exhibit a small degree of absorption in the visible region of the electromagnetic spectrum (>380 nm). If such additives are included in a light diffusing acrylic resin, the spectral uniformity can be decreased (increasing ΔLT (800 nm to 400 nm)). It is known to those skilled in the art that alternative commercially available light stabilizing additives (e.g., Tinuvin® 312) do not exhibit absorption in the visible region (>380 nm), and are therefore preferred for use in light diffusing acrylic formulations to improve spectral uniformity (decrease ΔLT (800 nm to 400 nm)). For example, Examples 10 and 14-18 demonstrate that judicious selection of UV absorbers and UV absorber concentrations can improve spectral uniformity.

[0069] Blending procedure

[0070] The diffuser shells of the present invention can be blended and formed by any process known in the art for forming shells, including but not limited to melt compounding and melt processing (such as extrusion, blow molding, injection molding, etc.), or in a cast polymerization process.

[0071] The diffuser shells of the present invention have a thickness of at least 200 microns, and there is no limit to the maximum thickness other than increasing cost and weight. Preferred thicknesses are from 250 microns to 10 millimeters, and more preferred thicknesses are from 300 microns to 5 millimeters.

[0072] Coating

[0073] In one embodiment, the diffuser hoods of the present application can be coated to provide additional properties to the hoods, such as dirt-shedding and weatherability. Useful dirt-shedding coatings can include fluoropolymers, including polyvinylidene fluoride polymers and copolymers having at least 60 wt% of polyvinylidene fluoride monomer units; silicone coatings, crosslinked acrylic coatings, and other coatings known in the art for improving dirt-shedding and weatherability. The coating should generally not interfere with light transmission in the range of 400 nm to 800 nm. The coating can be added by a coating process, a co-extrusion process, a lamination process, or other processes known in the art.

[0074] Light source

[0075] The light diffusing hoods of the present application are particularly useful when used in lighting devices having more than one point light source. A multi-spectral LED device or luminaire is a device containing at least one LED having a peak spectral emission in the visible spectrum (400-800 nm), and at least one additional LED having a different peak spectral transmission in the range of 250-800 nm. Examples include:

[0076] 1 : Continuous environmental disinfection luminaire. Luminaires such as Visa Lighting's CM2084-D - JASPER™ contain LEDs with different multiple peak emissions in order to selectively disinfect surfaces, or provide illumination to humans. In this case, LEDs with peak emissions at 405 nm can be activated to disinfect surfaces, while LEDs with peak emissions at 500 to 700 provide a soft white light for visibility.

[0077] 2: Multi-color luminaire. Commercially available products and smart lighting, such as Philips' HueStrip, contain multiple LEDs embedded within a diffusing enclosure in order to provide color tunability to the user.

[0078] 3: Horticultural lighting. Some crop growers use multi-spectral LED luminaires to influence crop growth and health. For example, LEDs with peak spectral emissions above 700 nm have been shown to influence the phototropism of plants, while LEDs with peak spectral emissions below 400 nm have been used to promote the production of plant flavonoids and phenylpropanoids. Commercially available luminaires contain 4 to 10 LED types with different spectral emission peaks.

[0079] For multi-spectral luminaire applications involving human exposure in whole or in part, it is preferred to place the LED light engine behind a diffusing material in order to reduce glare. It is also preferred that the diffusing material uniformly transmit light across the entire visible spectrum in order to maximize light transmission from each LED through the diffusing material.

[0080] 4. In-vehicle lighting with various colored LEDs. One application is for the interior of an autonomous vehicle. Embodiments

[0081] Measured by ASTM D 542 (Na-D line at 23°C) Refractive index (R.I.) .

[0082] Number average particle size: Measured using Malvern Multisizer II by laser diffraction particle size analysis (electrical sensing zone method, reporting mean particle size.

[0083] Hiding performance

[0084] The hide performance (HP) of the LED cover of the present invention can be determined by a test comprising the following steps:

[0085] a) Form a plate of the material under test that is uniform in thickness (e.g., 0.080 inch thick);

[0086] b) Measure the light transmittance of light at 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm on the sample on the Perkin Elmer Lambda 950 at 0 inches from the integrating sphere;

[0087] c) Measure the light transmittance of light at 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm on the sample on the Perkin Elmer Lambda 950 at 2 inches from the integrating sphere;

[0088] d) Calculate the hide performance percentage in percent as the difference between the two transmittance measurements (0 inches and 2 inches) divided by the 0 inch transmittance measurement multiplied by 100 to get the hide performance percentage at each of the light wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm.

[0089] Hide performance is somewhat related to haze, but for many samples, the correlation between haze and hide performance is not high. In general, the lighting industry relies on qualitative tests that vary from manufacturer to manufacturer, such as the qualitative test according to ASTM D 1003. In commercially available extruded lenses or covers (2 mm thick), the hide performance should be greater than 40% and preferably greater than 50% and no more than 95%. Below 30%, the light is not effectively diffused at a reasonable distance (2 inches). Above 95%, the transmittance of the lens is compromised, reducing the light output. In thinner lenses of 0.9 mm (injection molded), the hide performance should also be greater than 40%

[0090] It was found that the transmission curve is a function of the distance from the integrating sphere on the Perkin Elmer Lambda 950. However, for different materials, the change in light transmission due to the distance from the integrating sphere is not constant. The calculation of the hiding performance was found to be a function of the distance from the integrating sphere.

[0091] Test: Each composition was first extruded into a 2 inch by 2 inch square, 0.080 in thickness. The sample was placed in the Perkin Elmer Lambda 950 at 0 inches from the integrating sphere and the transmission of light at 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm was measured. The sample was then moved to 2 inches from the integrating sphere and the transmission of light at 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm was measured again. The difference between the two transmission measurements (0 inches and 2 inches) was then divided by the 0 inch transmission measurement, multiplied by 100 to calculate the hiding performance to obtain the hiding performance percentage at each wavelength.

[0092] Example Formulations

[0093] Diffusing material samples were obtained by melt compounding the components described in Table 2 and subsequently sheet extruding 0.080" thick sample plaques. The compounding die temperature was controlled at 200°C to 220°C using a Leistritz 27mm twin screw extruder at a line speed of 50 pounds / hour and screw speed of 250 rpm to 350 rpm under vacuum. Optical characterization was performed on a Lambda 950 UV / VIS spectrophotometer. Light transmission (%LT) and hiding performance (HP) were calculated according to the methods described above. Examples 1-13 were extruded and can exhibit some texture due to the particles, while Examples 14-18 were injection molded in a highly polished mold.

[0094] Resin A is a poly(methyl methacrylate) / ethyl acrylate copolymer with an MFR of 2.3 g / 10 min (measured by ASTM D1238, 230°C / 3.8kg) and a refractive index of 1.489 (measured according to ASTM D 542). Resin A does not contain a UV absorbing additive. Table 1 summarizes the diffusing particle characteristics.

[0095] Table 1: Diffusing particles used in the examples. Refractive index measured according to ASTM D 542

[0096]

[0097] Table 2: Example formulations in weight percent.

[0098] Resin A Particle A Particle B Particle C Particle D Example 1 82.0% 18.0% 0.0% 0.0% 0.0% Example 2 99.5% 0.0% 0.5% 0.0% 0.0% Example 3 99.7% 0.0% 0.0% 0.0% 0.3% Example 4 99.4% 0.0% 0.0% 0.6% 0.0% Example 5 99.4% 0.0% 0.0% 0.0% 0.6% Example 6 99.0% 0.0% 1.0% 0.0% 0.0% Example 7 98.5% 0.0% 1.5% 0.0% 0.0%

[0099] Table 3:

[0100]

[0101] Summary of optical light transmission (%LT), hiding power (HP), and spectral uniformity (Δ%LT) for 0.080" thick example panels measured on a Lambda 950 UV / VIS spectrophotometer.

[0102] Examples 1-7

[0103] This example compares an acrylic light diffusing material containing silicone diffusing particles to a commercially available acrylic light diffusing material containing organic diffusing particles. It was found that the silicone containing diffusing particles provided a more uniform spectral transmission at equivalent or better hiding power.

[0104] Figures 1 to 4 The relationship of percent light transmission (%LT) and / or hiding power to wavelength for different levels of diffusing particles is shown in Table 3.

[0105] Spectral uniformity is defined as the difference between %LT(800 nm) - %LT(400 nm).

[0106] The spectral uniformity for each sample is listed in Table 3. Only the acrylic resins containing silicone resin (Particle D) or silicone rubber (Particle C) diffusing particles exhibited a spectral uniformity of less than 6%. It is expected that one skilled in the art could achieve a spectral uniformity of less than 6% using extremely small concentrations of any diffusing particle, however the hiding power would be very low. Both Particle C and Particle D have a lower refractive index than the refractive index of the Resin A matrix. It is believed that diffusing materials containing diffusing particles having a lower refractive index than the refractive index of the matrix are best for promoting uniform spectral transmission when considering the transmission of light through the diffusing material.

[0107] Figure 1 The acrylic resin containing Particle D was compared to the acrylic resin containing Particle B. At 800 nm, the light transmission of 0.6% and 0.3% of Particle D was equivalent to 1% and 1.5% of Particle B, respectively. At 400 nm, the light transmission of 0.6% and 0.3% of Particle D was up to 10% higher than 1% and 1.5% of Particle B, respectively. Thus, the composition containing Particle D exhibited greater spectral uniformity and provided equivalent or better hiding power. Figure 2 ).

[0108] Table 3 shows that the diffusing resin containing Particle D also exhibited better spectral uniformity than the diffusing resin containing Particle A Figure 3). While both resins have the same %LT at 400 nm, the diffusing resin containing Particle A exhibits poorer spectral uniformity compared to the acrylic resin containing Particle D. In addition, the acrylic resin containing Particle D exhibits significantly better hiding performance compared to the diffusing resin containing Particle A Figure 4

[0109] The diffusing resins containing Particles C and D maintain a spectral uniformity of less than 6% while also exhibiting high light transmission and hiding performance greater than or equal to 85% (Examples 3, 4, and 5). The diffusing resin containing Particle B exhibits a spectral uniformity greater than or equal to 6% and a hiding performance greater than or equal to 66%. The diffusing resin containing Particle A shows a spectral uniformity greater than or equal to 6% and a hiding performance of 77%. In the case of Particle A, the large size of the particles creates a rough surface texture that contributes to the improved hiding performance.

[0110] Examples 8-18

[0111] Resin B is the same as Resin A except that Resin B contains very low levels of UV absorbing additives. Resin C is an impact modified acrylic resin containing UV absorbing additives and having an MFR of 1 g / 10 min (measured by ASTM D1238, 230°C / 3.8 kg). Resin D is the same as Resin C except that Resin D does not contain UV stabilizers.

[0112] Table 4: Example Formulations in weight percent.

[0113]

[0114] Table 5

[0115]

[0116] Summary of optical light transmission (%LT), hiding performance (HP), and spectral uniformity (Δ%LT) for 0.080” thick example plaques measured on a Lambda 950 UV / VIS spectrophotometer.

[0117] Table 6: Additional Example Formulations in weight percent.

[0118]

[0119] Table 7:

[0120]

[0121] ​Summary of optical light transmission (%LT), hiding performance (HP), and spectral uniformity (Δ%LT) for 0.080" thick example panels measured on a Lambda 950 UV / VIS spectrophotometer.

Claims

1. A light diffuser cover composition for use with two or more point light sources, wherein the light diffuser cover composition comprises: a) a transparent or translucent polymeric matrix, b) 0.3 to 6 weight percent of diffusing particles dispersed within the transparent or translucent polymeric matrix, wherein the diffusing particles comprise silicone resin, silicone rubber, or mixtures thereof, and have a refractive index that is 0.01 to 0.25 lower than the refractive index of the transparent or translucent polymeric matrix, and wherein silicone-containing diffusing particles are used as the only diffusing particles, wherein the light diffuser cover composition has the following properties when measured on a 0.080 inch (0.203 cm) thick sheet: - a light transmission of light at each of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm light wavelengths is greater than 40%; - an absolute difference between the light transmission at 400 nm and the light transmission at 800 nm is less than 6%; and - a diffusion level at each of 400 nm light wavelengths, as measured by a hiding performance, is at least 65%.

2. The light diffuser cover composition of claim 1, wherein the light diffuser cover composition has the following properties when measured on a 0.080 inch (0.203 cm) thick sheet: - a light transmission of light at each of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm light wavelengths is greater than 60%.

3. The light diffuser cover composition of claim 1, wherein the transparent or translucent polymeric matrix is selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate, glycol-modified PETG, polyvinyl chloride (PVC), impact-modified PVC, PET, PBT, APET, styrene acrylonitrile (SAN), acrylonitrile-acrylate copolymer, acrylonitrile-methyl methacrylate copolymer, methyl methacrylate-styrene copolymer, methacrylate-butadiene-styrene terpolymer, acrylonitrile-styrene-acrylate (ASA) terpolymer, acrylonitrile butadiene styrene (ABS) terpolymer, polystyrene (PS), high-impact polystyrene (HIPS), polyolefin, impact-modified polyolefin, polycyclohexylethylene, cyclic olefin copolymer (COC), polyvinylidene fluoride (PVdF), PVdF-acrylic copolymer, imidized acrylic polymer, acrylic polymer, impact-modified acrylic polymer, and mixtures thereof.

4. The light diffuser cover composition of claim 1, wherein the polymeric matrix is a (meth)acrylic polymer having at least 70 weight percent methyl methacrylate monomer units.

5. The light diffuser cover composition of claim 1, wherein the diffusing particles have a spherical or irregular shape.

6. The light diffuser cover composition of claim 1, wherein the diffusing particles have a multi-modal particle size distribution.

7. The light diffuser cover composition of claim 1, further comprising 0 wt% to 80 wt% of an impact modifier.

8. The light diffuser cover composition of claim 1, wherein the composition contains one or more types of light stabilizing compounds, wherein the composition contains less than 1 wt% of light stabilizing compounds that absorb light wavelengths above 390 nm.

9. A lighting device comprising two or more point light sources of different wavelengths, and a light diffuser cover made of the light diffuser cover composition of claim 1.

10. The lighting device of claim 9, wherein the light diffuser cover has a thickness of 200 micrometers to 10 millimeters.

11. The lighting device of claim 9, wherein the light diffuser cover has a rough surface.

12. The lighting device of claim 9, wherein the lighting device is used for continuous environment disinfection luminaire, horticulture lighting luminaire, or in-vehicle lighting system.

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