Patent Application
20140132883
In lighting, display, and architectural elements, there is a need for visually attractive surfaces, panels, and luminaires that are good illuminators, provide interesting visual features, or offer both. Light extraction layers, specifically clear or transparent light extraction layers, allow for the design of display or lighting elements that may efficiently extract light while minimally distorting and scattering light. Polymer dispersed liquid crystal layers may impart a high haze appearance while turning transparent after application of voltage to the layer.
In one aspect, the present disclosure describes an optical stack. The optical stack includes a light guide and a light extraction layer optically coupled to the lightguide having first and second regions, the first and second regions being disposed such that the variable index light extraction layer selectively extracts guided mode light from the lightguide based on the geometric arrangement of the first and second regions. The optical stack further includes a polymer dispersed liquid crystal layer optically coupled to the light extraction layer having third and fourth regions, wherein at least one of the third and fourth regions has a haze value dependent on a voltage applied to the at least one of the third and fourth regions of the polymer dispersed liquid crystal layer. In some embodiments, one or more of the first and second regions of the light extraction layer is in registration with one or more of the third and fourth regions of the polymer dispersed liquid crystal layer.
Embodiments of the present disclosure include a lightguide, a light extraction layer optically coupled to the lightguide, where the light extraction layer has first and second regions disposed such that the variable index light extraction layer selectively extracts guided mode light from the lightguide based on the geometric arrangement of the first and second regions. A polymer dispersed liquid crystal layer may be optically coupled to the light extraction layer, where the polymer dispersed liquid crystal layer has third and fourth regions and at least one of the third and fourth regions has a haze value dependent on a voltage applied to the at least one of the third and fourth regions of the polymer dispersed liquid crystal layer. Additionally, in some embodiments of the present disclosure, one or more of the first and second regions of the light extraction layer is in registration with one or more of the third and fourth regions of the polymer dispersed liquid crystal layer.
Lightguide 110 may be any suitable shape and constructed or formed from any suitable material. In some embodiments, lightguide 110 may be formed from a polymer, including homopolymers or copolymers of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic, polycarbonate, cyclo-olefin polymers, and silicons. Many transparent materials are suitable for use as lightguide 110, including viscoelastic materials such as hot melt or pressure sensitive adhesives, as described in, for example, U.S. Patent Publication No. 2011-0176325 A1 (Sherman et al.), entitled “Viscoelastic Lightguide.” Lightguide 110, shown as substantially planar in
One or more light sources 120 may be any number of suitable light sources. In some embodiments, one or more light sources 120 includes a light emitting diode, or LED. In other embodiments, one or more light sources 120 may include an incandescent bulb or a cold cathode fluorescent lamp (CCFL). One or more of the light sources of one or more light sources 120 may be colored or have a certain wavelength. In some applications, it may be desirable to generate colored light for decorative or ornamental purposes. In other applications, a non-visible, e.g., ultraviolet bulb can be used in conjunction with a phosphor which may absorb some of the ultraviolet light and reemit light in the visible spectrum. In some embodiments, multiple light sources emitting different wavelengths may be advantageously used to create the appearance of white light. In some embodiments, one or more light sources 120 may be ambient or natural light.
If one or more light sources 120 is external to lightguide 110, it may be desirable to provide collimation or injection optics, possibly including a structured surface on lightguide 110 to prevent wasteful reflection on an external surface of lightguide 110. Injection optics may allow light incident on lightguide 110 at an otherwise supercritical angle to enter and propagate within lightguide 110.
Exemplary light ray 130 is shown to illustrate the general operational principles of edge-lit system 100. Light ray 130, originating from one or more light sources 120, is propagating within the lightguide. For interfaces where light is going from a higher index of refraction medium to a lower index of refraction medium, a critical angle exists where light incident at supercritical angles is totally internally reflected (reflected through TIR). In
Because little or no light is extracted through the surfaces of lightguide 110, observer 140 will not perceive lightguide 110 being illuminated from one or more light sources 120. If lightguide 110 contains few or no distorting or scattering elements, observer 140 will perceive lightguide 110 as transparent and any object or element on the opposite side of lightguide 110 will be clearly visible. Observer 140, while represented by an eye, need not be a human eye. In some embodiments, observer 140 may be replaced with a remote sensor, detector, or even another optical component, film, or stack.
Non-extracting regions 220 and extracting regions 230 may be different in composition, configuration, or both. In some embodiments, non-extracting regions 220 and extracting regions 230 may have different optical or physical properties. For example, non-extracting regions 220 may have a lower index of refraction than extracting regions 230. Further, non-extracting regions 220 may have a lower index (or effective index) of refraction than lightguide 210 through the use of either low-index materials or substances, high-index material substantially interspersed with low-index materials, including air, or both. These characteristics may allow for light to be selectively extracted based on the geometric arrangement of these regions, as described in, for example, U.S. Patent Application Ser. No. 61/446,712, entitled “Illumination Article and Device for Front-Lighting Reflective Scattering Element” and filed Feb. 25, 2011 and U.S. Provisional Patent Application Ser. No. 61/655,208, entitled “Variable Index Light Extraction Layer with Microreplicated Posts and Methods of Making the Same” and filed Jun. 4, 2012.
Alternatively or additionally, extracting regions 230 may have a structured surface on either major surface (either the same side as lightguide 210 or the opposite side) while non-extracting regions 220 may have a different structured surface or may lack one altogether (i.e., may be smooth). In some embodiments, extraction regions 230 may have diffractive features configured to extract guided mode light from lightguide 210, while non-extracting regions 220 may have a lower diffractive surface feature refractive index, or may lack diffractive features altogether. Configurations of diffractive light extraction layers are described in, for example, U.S. Provisional patent application Ser. No. 13/572,813, entitled “Lighting Devices with Patterned Printing of Diffractive Extraction Features” and filed Aug. 13, 2012.
While non-extracting regions 220 and extracting regions 230 are shown as substantially equal in size, shape, and thickness, this need not be the case for constructions and configurations of light extraction layer 212.
First substance 222 and second substance 232 may be chosen from a wide range of suitable materials, including air. First substance 222 and second substance 232 may be selected in order to impart desired optical characteristics to non-extracting regions 220 and extracting regions 230, respectively. For example, first substance 222 may include a low-index material such as a nanoporous or a nanovoided polymeric material, described in, for example, U.S. Patent Application Ser. No. 61/446,740, entitled “Front-Lit Reflective Display Device and Method of Front-Lighting Reflective Display,” and filed Feb. 25, 2011. When first substance 222 has a lower index of refraction than adjacent lightguide 210 and is configured suitably within non-extracting regions 220, guided mode light propagating in lightguide 210 may undergo total internal reflection at the interface between lightguide 210 and non-extracting regions 220, preventing light from being extracted through those areas. Similarly, second substance 232 may include a higher-index material, including optical adhesives, inks, polymeric substances, organic and inorganic substances, or any other suitable material. In some embodiments, the second substance 232 may be selected to have an index of refraction similar to or greater than lightguide 210. Guided mode light will thereby generally be refracted through extracting regions 230 instead of totally internally reflected, allowing light to pass out through extracting regions 230. It may be desirable in some applications to match the indices of refraction of second substance 232 and lightguide 210 in order to minimize distortion.
Second substance 232 may include the same base material as first substance 222, but with modifications to alter one or more of its properties. For example, second substance 232 may include a nanovoided polymeric material and a high index ink printed into its nanovoids. Examples of printing substances into nanovoided polymeric material is described in, for example, U.S. Patent Application Ser. No. 61/485,881, entitled “Back-Lit Transmissive Display Having Variable Index Light Extraction Layer” and filed May 13, 2011. One or both of first substance 222 and second substance 232 may also be selected for its physical properties, such as melting point, warp resistance, flexibility, or ability to be adhered to easily adhered or attached to other surfaces or films.
Exemplary light ray 350 is propagating through the lightguide as guided mode light. First, exemplary light ray 350 is incident on an interface between lightguide 310 and surrounding air. Because the interface is from a higher index of refraction to a lower index of a refraction and exemplary ray 350 is incident on that interface at a supercritical angle, exemplary ray 350 is totally internally reflected. Likewise, when exemplary ray 350 is incident on the interface between lightguide 310 and non-extracting region 320, the optical properties of non-extracting region 320 are such that exemplary ray 320 is internally reflected at that interface as well. While exemplary ray 350 is depicted as being reflected exactly at the interface between non-extracting regions 320 and lightguide 310, depending on the features or configuration of lightguide 310 and non-extracting regions 320, exemplary ray 350 may be reflected anywhere within non-extraction regions 320.
Exemplary light ray 350 is once again totally internally reflected at the interface between lightguide 310 and surrounding air. Propagating exemplary light ray 350 is subsequently incident on extracting regions 330. In some embodiments, because extracting regions 330 have a higher index of refraction than lightguide 310, incident light is refracted within extracting regions 330 and then extracted out of optical stack 300 such that exemplary ray 350 is no longer propagating within lightguide 310. The refraction of exemplary light ray 350 within extracting regions 330 may be less than depicted in the schematic of
Light extracted out of optical stack 300 through extracting regions 330 may be visible to observer 360. If light extraction layer 312 includes a pattern of non-extracting regions 320 and extracting regions 330 that have sufficiently small dimensions, then from the perspective of observer 360, optical stack 300 may appear to be uniformly emitting light and not in fact patterned. In other words, light extraction layer 312 may appear to have only one extracting region: while lightguide 310 and light extraction layer 312 do not in fact generate any light, it may appear this way to observer 360. Depending on the application, it may be desirable to either arrange light extraction layer 312 such that the arrangement of non-extracting regions 320 and extracting regions 330 are visible or such that they are not visible to observer 360.
Polymer dispersed liquid crystal layer 414 includes droplets of liquid crystal dispersed in a polymer matrix. Polymer dispersed liquid crystal layers function by having an electric field applied across the layer such that a change in the orientation of the dispersed liquid crystal droplets takes place. Control of electric field in such layers may be achieved by sandwiching the polymer dispersed liquid crystal between two transparent conductive films functioning as electrodes, utilizing materials such as indium tin oxide (ITO), which may be patterned or etched to accommodate two or more electrically isolated regions or zones. Transparent spacer beads may be included to preserve the two conductive films from touching each other. In some embodiments, the layer is translucent or has high haze in the “off” state, i.e., without the application of voltage, due to light scattering by the refractive index mismatch between the polymer matrix and the dispersed liquid crystal droplets. When the electric field is applied, i.e., when the layer is in the “on” state, the liquid crystalline droplets align to the electric field, causing the refractive index mismatch between the liquid crystalline droplets and the polymeric matrix to decrease such that the layer become transparent or substantially transparent, or at least has low haze.
Because haze values of portions of polymer dispersed liquid crystal layer 414 may depend on electric fields applied across the layer, portions of polymer dispersed liquid crystal layer 414 may be considered “switchable” or “active.” Depending on the configuration of polymer dispersed liquid crystal layer 414, switchable portions, i.e., portions that may be switched from high-haze zones 430A to low-haze zones 420A, may be arranged in any suitable pattern or configuration. In some embodiments, switchable portions of polymer dispersed liquid crystal layer 414 may be disposed, shaped, or sized such that in some states, indicia may be displayed in high-haze zones 430A, such as a message or company logo. In some embodiments, these indicia may be instead displayed in low-haze zones 420A. Because portions may be controlled independently, one or more indicia may be displayed simultaneously, or different indicia may be displayed in different modes or states. Similarly, in some embodiments, a state may be possible where all of or a significant portion of polymer dispersed liquid crystal layer 414 is substantially transparent or, conversely, highly diffuse and hazy.
In
Second ray 554 is incident on one of low-haze zones 540, corresponding to low-haze zones 430A in
Third ray 556 is within lightguide 510. In some embodiments, third ray 556 is emitted or injected into lightguide 510 by one or more light sources 520. Third ray 556 is incident on one of high-haze zones 530 and, like first ray 550, is diffusely scattered into second scattered light 558. Again, while there may be a component of third ray 556 reflected back into the lightguide, such reflections are not directly relevant to what observer 560 perceives when looking at edge-lit system 500A.
In
The electric field dependence of haze values in portions of polymer dispersed liquid crystal layer 514B may be used to configure or design desired applications with switchable haze values. In some embodiments,
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For both
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Second configuration 1020 depicts an outline-type pattern. As shown in
Third configuration 1030 illustrates an arrangement that uses haze values for contrast. While both shapes are illuminated, and while the light extraction zones correspond tightly with the desired shape, the left triangle provides diffuse, hazy light while the right has a low haze value and may appear transparent. The shapes may be any suitable symbol or indicia, whether identical, similar, or different.
Fourth configuration 1040 illustrates an arrangement that has a polka dot pattern of high-haze zones within a circle of light extraction. While fourth configuration 1040 depicts the hazy dots as being rather large and distinct, in some embodiments the smaller shapes may be sufficiently tiny to remain unresolved by an observer, which may create an appearance of texture or impart an interesting pattern to the area.
In some embodiments, the transparent conductive electrodes of the polymer dispersed liquid crystal layer may be preshaped.
For embodiments of the present disclosure, it is possible to get intermediate levels of haze by overlaying two or more provided polymer dispersed liquid crystal layers to produce a composite PDLC layer.
Using an ESI 5200 laser (available from ESI, Portland, Oreg.) with a 32 mA power setting, patterns as shown in
To a solution containing approximately equal amounts (by mass) of NOA65 adhesive and BL036 liquid crystal was added 2% (by weight of combined NOA65 and BL036) Micro Pearl SP spacer beads having a diameter of either 6 μm or 10 μm depending on the desired cell gap. The resulting solution was sonicated for 1 hour in a 40° C. water bath. During sonication, the pattern was cut from the sheet of ITO on PET. The pattern was affixed to a common (un-patterned ITO sheet) with POST-IT tape and leads were cut out. The pattern-common stack was gently cleaned with isopropanol (IPA) and a stream of air.
After sonication, approximately 1.5 mL of solution was applied across the common (with stack held open) near the point of attachment of the two substrates. Care was taken to apply the solution evenly, although more solution was added near the center. The pattern was laid back down and the stack gently smoothed to spread out the solution. The stack was then laminated between polyester liners using a Laminex 27 inch MINIKOTE laminator (available from Laminex, Fort Mill, S.C.) at 30.5 cm/min (1.0 ft/min). No heat was used during lamination.
After lamination the stack was gently wiped to remove excess solution. The stack was then UV cured (one-sided, on a piece of Lexan) for 10 minutes at 1.0 mW/cm2. After curing the PDLC was cleaned with IPA. Small dots of PELCO were added on the leads of the pattern and the common and allowed to dry.
In a 2 L three neck flask, equipped with a condenser and a thermometer, 750 g of Nalco 2327 colloidal silica and 700 g of 1-methoxy-2-propanol were mixed together under rapid stirring. After that, 61.59 g of Silquest A-174 silane was added, and then the mixture was stirred for 10 min., followed by addition of 400 g of 1-methoxy-2-propanol. The mixture was heated at 85° C. for 6 hours using a heating mantle. The resulting solution was allowed to cool down to room temperature. The water and some of the 1-methoxy-2-propanol was removed under vacuum using a rotary evaporator and a 60° C. water bath. The resulting sol was a clear dispersion that was 43.4% wt A-174 modified 20 nm silica in 1-methoxy-2-propanol.
The following were added in a 1-liter wide-mouth amber bottle: 5.70 g of CN 9893 and 22.40 g of SR 444. The bottle was capped and shaken for 2 hours to dissolve CN 9893 (batch is clear). This solution is referred to as Resin Premix.
The following were added to a 2000 mL poly bottle: 482.84 g of the sol prepared as described above and the Resin Premix. The two components were mixed by transferring the batch back and forth between two bottles, ending with the batch in the 2000 mL bottle. To the 2000 mL bottle was added 5.84 g of IRGACURE 184 and 1.12 g of IRGACURE 819. The solution was shaken for 30 minutes to dissolve photoinitiators. The resulting batch was a translucent, low-viscosity dispersion.
The dispersion was diluted to ˜17.7% solids by weight with a 50/50 blend ethyl acetate and DOWANOL PM.
The above coating formulation was coated onto 50 μm PET film (MELINEX 617) using a slot die at a line speed of 3.1 m/ min. The wet coating thickness was approximately 8.1 μm. In an inert chamber (<50 ppm O2), the wet coating was partially cured in-line at the same line speed with UV radiation at 395 nm and dose of 850 mJ/cm2. (UV radiation was provided by UV-LEDs available from Cree, Inc.). The partially cured coating sample was then dried at 70° C. in a 9 meter oven, and under a nitrogen-purged atmosphere, finally cured with a 236 Watt/cm2 Fusion H bulb (available from Fusion UV Systems, Inc.). The resulting nanovoided polymeric layer had a thickness of 1.3 μm. The transmission was 96.4%, the haze was 1.33% and the clarity was 99.7% as measured using a BYK-Gardner HAZE GARD PLUS (Columbia, Md.). The refractive index of the nanovoided layer was between 1.200 and 1.220 as measured at 589 nm using a Metricon Prism Coupler (Metricon Corporation, Pennington, N.J.).
The nanovoided polymeric layer is printed with a UV curable clear ink (UV OP1005 GP) using an indirect gravure printing process. A flexographic tool having a dot pattern with a density variation chosen to align with a desired pattern in a PDLC layer is fabricated (by Southern Graphics Systems) based on a .pdf image that defines the desired pattern. A gravure roll (pyramidal and 9 cubic μm per square μm) is rated to give a wet coating of approximately 9.65 μm. The printing is done at 10 meters per minute with high intensity UV curing under a nitrogen-purged atmosphere with a 236 Watt/cm2 Fusion H bulb (available from Fusion UV Systems, Inc.) after the printing. The resulting printed layer is an optical film comprising: first regions having a first refractive index and comprising nanovoided polymeric material, and second regions wherein the nanovoids are filled or partially filled with the cured clear ink, the second regions having a second refractive index greater than that of the first regions.
PDLC film was prepared as described in “Preparation of Patterned PDLC” and was laminated onto clear acrylic using 3M 8141 OCA. The pattern consisted of a center circle, two concentric rings and an area outside outermost ring as shown in
The % Transmittance (% T) and % Haze (% H) of the PDLCs were measured at 0V, 32V, and 64V using a HAZE-GARD PLUS meter available from BYK-Gardner Inc. of Silver Springs, Md., which complies with ASTM D1003-07e1 “Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics”. The results are reported in the table below. Each value represents the average of 4 measurements taken from the center circle, on each ring, and on the outside the outer ring.
Extraction Layer
A printed clear extraction layer is prepared as described in “Formation of variable index light extraction layer on transparent substrate.” The printed clear extraction layer is then laminated to the PDLC film using 3M 8141 OCA such that the pattern in the PDLC film and the pattern in the printed clear extraction layer align.
PDLC film patterned in the shape of a bottle was prepared as described in “Preparation of Patterned PDLC.” The bottle shape was cut out of the film using scissors and was laminated to clear acrylic using 3M 8141 OCA.
Extraction Layer
A printed clear extraction layer is prepared as described in Example 1 with the pattern in the printed clear extraction layer selected to match the bottle shape in the PDLC layer. The printed clear extraction layer is then cut to match the shape of the bottle screen and is laminated to the PDLC film using 3M 8141 OCA such that the shape in the PDLC film and the shape of the printed clear extraction layer align.
Two PDLC layers were prepared as described in “Preparation of Patterned PDLC” with a series of parallel lines forming the pattern as illustrated in
Extraction Layer
Printed clear extraction layers are prepared as described in Example 1 with the pattern in the printed clear extraction layers selected to match the line patterns in the PDLC layers. A printed clear extraction layer is then laminated to each of the PDLC films using 3M 8141 OCA such that the patterns in the PDLC films and the patterns in the printed clear extraction layers align. The two patterned layers with extractor layers are laminated together using 3M 8141 OCA with the parallel lines in one layer perpendicular to the parallel lines in the other layer and with the printed extractor side of each layer was facing in the same direction (up). The pattern in each layer are independently switched from clear to hazy by the application of voltage across the leads of each layer.
All U.S. patent applications and publications cited in the present application are incorporated herein by reference as if fully set forth. The present invention should not be considered limited to the particular examples and embodiments described above, as such embodiments are described in detail in order to facilitate explanation of various aspects of the invention. Rather, the present invention should be understood to cover all aspects of the invention, including various modifications, equivalent processes, and alternative devices falling within the scope of the invention as defined by the appended claims and their equivalents.
