The present disclosure is directed toward anti-reflective systems and methods of use on switchable panels, and more particularly to systems and methods for anti-reflective panels using liquid crystal microdroplet (LCMD) devices, suspended particle device (SPD), electrochromic or thermochromic materials. In some embodiments, the disclosure provides improvements related to U.S. Pat. Nos. 9,690,174B2 and 9,921,425B2,
Continued advancements in the field of optoelectronics have led to the development of liquid crystal microdroplet (LCMD) displays. In this type of display, liquid crystal (LC) material is contained in microdroplets embedded in a solid polymer matrix. Birefringence results from a material having a different index of refraction in different directions. The extraordinary index of refraction (ne) of a liquid crystal molecule is defined as that measured along the long axis of the molecule, and the ordinary index of refraction (no) is measured in a plane perpendicular to the long axis. The dielectric anisotropy of liquid crystals is defined as Δε=ε∥−ε⊥, where ε∥ and ε⊥, are parallel and perpendicular dielectric constants, respectively. Liquid crystals having a positive dielectric anisotropy (Δε>0) are called positive-type liquid crystals, or positive liquid crystals, and liquid crystals having a negative dielectric anisotropy (Δε<0) are called negative-type liquid crystals, or negative liquid crystals. The positive liquid crystals orient in the direction of an electric field, whereas the negative liquid crystals orient perpendicular to an electric field. These electro-optical properties of liquid crystals have been widely used in various applications.
One approach to obtaining dispersed microdroplets in a polymer matrix is the method of encapsulating or emulsifying the liquid crystals and suspending the liquid crystals in a film which is polymerized. This approach is described, for example, in U.S. Pat. Nos. 4,435,047; 4,605,284; and 4,707,080. This process includes mixing positive liquid crystals and encapsulating material, in which the liquid crystals are insoluble, and permitting formation of discrete capsules containing the liquid crystals. The emulsion is cast on a substrate, which is precoated with a transparent electrode, such as an indium tin oxide (ITO) coating, to form an encapsulated liquid crystal device.
LCMD displays may also be formed by phase separation of low-molecular weight liquid crystals from a prepolymer or polymer solution to form microdroplets of liquid crystals. This process, described in U.S. Pat. Nos. 4,685,771 and 4,688,900, includes dissolving positive liquid crystals in an uncured resin and then sandwiching the mixture between two substrates which are precoated with transparent electrodes. The resin is then cured so that microdroplets of liquid crystals are formed and uniformly dispersed in the cured resin to form a polymer dispersed liquid crystal (PDLC) device. When an AC voltage is applied between the two transparent electrodes, the positive liquid crystals in microdroplets are oriented and the display is transparent if the refractive index of the polymer matrix (np) is made to equal the ordinary index of the liquid crystals (no). The display scatters light in the absence of the electric field, because the directors (vector in the direction of the long axis of the molecules) of the liquid crystals are random and the refractive index of the polymer cannot match the index of the liquid crystals. Nematic liquid crystals having a positive dielectric anisotropy (Δε>0), large Δn, which may contain a dichroic dye mixture, can be used to form a transparent and an absorbing mode.
LCMD displays may be characterized as normal mode displays or reverse mode displays. A normal mode display containing liquid crystals is non-transparent (scattering or absorbing) in the absence of an electric field and is transparent in the presence of an applied electric field. A reverse mode display is transparent in the absence of an electric field and is non-transparent (scattering or absorbing) in the presence of an applied electric field. A LCMD film usually has following layer structure: transparent film/ITO coating/liquid crystal matrix layer/ITO coating/transparent film. The liquid crystal matrix layer is also called the active layer and is responsible for the switching function. Other types of switchable film, such as for example, suspended particle devices (SPD), electrochromic materials or thermochromic materials, have similar structure but different active layers.
Previously, LCMD could only be used indoors because of concerns about UV stability and moisture sensitivity of components, and narrow temperature ranges for use. However, recent innovations have led to the development of outdoor and projection applications, such as for example, switchable projection windows, building advertising and windows for automobile and cruise ship, as shown in U.S. Pat. No. 9,690,174 B2 and U.S. Pat. No. 9,921,425 B2 and Published US Patent Applications. No. US 2015/0275090 A1 and No. US 2016/0243773 A1.
In order to make LCMD film more durable and useful, a LCMD film is often laminated between two layers of glass with interlayers or assembled into a multi-layer window, as discussed herein. Such a laminated glass panel is often called a smart glass or switchable window. Such a multi-layer panel is called a switchable projection panel or window.
There exists a need for devices that use improved LCMD technologies in projection systems and switchable window systems to provide improved viewing quality with reduced or unnoticeable reflections. These methodologies should also be able to be used to reduce reflections on similar devices like suspended particle device (SPD), electrochromic or thermochromic materials.
In one embodiment, a panel apparatus comprises a liquid crystal microdroplet (LCMD) film switchable between transparent and opaque states in response to a change in an applied electrical voltage, wherein transparent electrode of indium tin oxide (ITO) in the LCMD film is replaced with index matched indium tin oxide (IMITO) to reduce reflections and/or the solid/air or film/air interface is treated with anti-reflective (AR) coating.
In another embodiment, a panel apparatus comprises a laminated switchable glass with a liquid crystal microdroplet (LCMD) film. Two glass layers and two interlayer layers sandwich or laminate the LCMD layer in center. Transparent and conductive electrode ITO in the LCMD film is replaced with IMITO, and/or the glass/air interface is treated with anti-reflective coating.
In another embodiment, a panel apparatus comprises a multi-layered switchable glass panel with a liquid crystal microdroplet (LCMD) film. The apparatus includes first layer or a liquid crystal microdroplet (LCMD) display switchable between transparent and opaque states in response to a change in an applied electrical voltage. Transparent and conductive electrodes of ITO in the LCMD film is replaced with IMITO. The panel apparatus also includes a second layer apart from and coupled to the first layer. The second layer includes a transparent panel or glass layer. Two glass layers sandwich the LCMD film layer in center with an air gap between glass layer and the LCMD film. All of solid/air interfaces including film/air interface and glass/air interfaces may be treated with anti-reflective (AR) coating.
Additional aspects, features, and advantages of the present disclosure will become apparent from the following detailed description.
The present disclosure is best understood from the following detailed description when read with accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purpose only. In fact, the dimension of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
As used herein the term “LCMD device” or “LCMD film” or “LCMD display” means a device or film or display, respectively, formed using various classes of polymer films. For example, an LCMD device may be formed using nematic curvilinear aligned phase (NCAP) films, such as material and devices described in U.S. Pat. No. 4,435,047 filed Sep. 16, 1981 disclosing “Encapsulated Liquid Crystal and Method,” which is incorporated by reference herein in its entirety for all purposes and teachings. An LCMD device may also be formed using polymer dispersed liquid crystal (PDLC) films formed using phase separation in a homogenous polymer matrix, such as material and devices described in U.S. Pat. No. 4,688,900 filed Sep. 17, 1985 disclosing “Light Modulating Material Comprising a Liquid Crystal Dispersion in a Plastic Matrix,” which is incorporated by reference herein in its entirety for all purposes and teachings. An LCMD device may also be formed using a non-homogenous polymer dispersed liquid crystal display (NPD-LCD) formed using a non-homogenous light transmissive copolymer matrix with dispersed droplets of liquid crystal material, such as material and devices described in U.S. Pat. No. 5,270,843 filed Aug. 31, 1992 disclosing “Directly Formed Polymer Dispersed Liquid Crystal Light Shutter Displays,” which is incorporated by reference herein in its entirety for all purposes and teachings. Other forms of liquid crystal microdroplet films may also be suitable. A NPD-LCD device may be configured in one of two modes. In a positive mode, an NPD-LCD device is switchable between an opaque state without an applied electrical voltage and clear state with an applied electrical voltage. In a negative mode, an NPD-LCD device is switchable between a clear state without an applied electrical voltage and an opaque state with an applied electrical voltage.
In the last decade, usage of switchable panels in a variety of applications, such as for energy efficient glazing, privacy windows, automobile windows and projection widow advertising, has increased dramatically. This is largely due to the fact that, the special features provided by these products, such as front or rear projection and no changes to the natural light spectrum during use, are now available to be used for outdoor applications. However, reflection during use of these devices seriously affects many applications such as use as building glass or automobile glass and can impact viewing comfort, performance and safety. Reflection can also impact image quality during display of information in building advertising or window advertising applications. Consequently, reflection on switchable devices remains a primary concern.
Unwanted reflections exist in many kinds of switchable devices. In this disclosure, liquid crystal (LC) switchable devices are used as an exemplary example. The principle and method discussed in this disclosure may apply to other systems. One reason to choose liquid crystal type switchable devices for this detailed discussion is that liquid crystal type switchable device is switchable between opaque and clear modes without a tint and has the highest transparency compared to other types of switchable devices. That is, as devices of this type are most vulnerable to unwanted reflections, any solution that is suitable for liquid crystal-based devices will be suitable for other similar devices as well.
There are three major structures described in this disclosure. These are (1) a switchable film or panel, such as a switchable LCMD film, which has the following layer structure: transparent film/ITO transparent electrode/LC-polymer matrix/ITO transparent electrode/transparent film. The LC-polymer matrix is an optically active layer which is responsible for the switching function; (2) a laminated liquid crystal switchable glass with the following layer structure: glass/interlayer/switchable LCMD film/interlayer/glass; and (3) a switchable projection panel with the following layer structure: glass/air gap/switchable LCMD film/air gap/glass. Other types of switchable film basically have same layer structure but with different optically active layers.
When using these switchable films or panels, reflection reduces transmittance and interferes with viewing during see-through applications and/or reduces the quality of projected images during opaque applications. For example, when an LCMD film is taped onto an existing window for use as a switchable privacy curtain and/or as a projection screen, reflections reduce clarity of see-through during transparent mode and quality of projected images during opaque mode. As another example, when a laminated switchable glass is used as a partition panel between a cab's driver and passenger compartment, the driver can be distracted by reflections from the partition panel visible in the rear-view mirror. The problems caused by reflection on switchable panels have become more and more serous in recent years, as a result of LCMD devices being widely used for outdoor applications made possible by improvements in UV, heat and temperature tolerance, and also because natural light can be much brighter that the brightness generated by artificial light sources such as for example during use in a conference room.
Another example is that when using a switchable projection panel as described in U.S. Pat. Nos. 9,690,174 and 9,921,425 with a normal projector, a strong reflection from a projector will disturb viewing of projected images. Similarly, when a laminated switchable glass is used as a switchable window in transparent mode, such as a partition for hospital operation room or a factory production area, reflections from the laminated switchable glass reduce clarity.
As will be appreciated by one of skill in the art, reflection in switchable panel apparatuses is considered to be a complicated process, impacted not only by reflected light but also by scattered light and refracted light as well as by the variety of interfaces formed by the different materials used in the manufacture of the apparatuses. This is often compounded by the fact that it can be difficult to accurately determine the refractive index of some of these compounds. As discussed below, the contribution of these various components to reflection in switchable panel apparatuses has been difficult to isolate and quantify using traditional methods and instruments, such as various photometers and microscopies. This analysis is made even more complicated by the presence of multiple layers.
Previous attempts to resolve this reflection problem have included use of tinted interlayers and tinted glass. While these treatments reduce unwanted reflections, they have a negative impact on image quality and image brightness. This tinting also changed image color and caused changes to the spectrum of natural light. As is known to those of skill in the art, natural light is better for human health and for indoor plant growth than artificial light. Accordingly, the use of tinted interlayers and tinted glass is not suitable for applications that require high quality lighting such as within hospitals, schools and classrooms.
Another attempt to reduce reflection involved shifting the refractive indexes of the LC-polymer layer such that it was closer to the refractive index of the ITO electrode. However, the higher refractive index was generated by using aromatic compounds in the liquid crystals and the monomers forming the polymers. This reduced the operational temperature range of the LCMD, particularly at the lower end of the temperature range.
Due to great difficulty, this problem remains unsolved for decades. This disclosure first introduces solutions which solve the problems of reflection but does not bring any negative impact to the system.
In order to eliminate or reduce reflection, it is necessary first to understand the interactions between the structures that compose the switchable devices and find out where the reflections are coming from. Referring to
A transparent substance has its refractive index, expressed as “n”. Whether an interface will reflect light or not depends on the relative difference between the refractive indexes of the substances forming the interface, which is expressed as “Δn”. An interface formed by substances with the same refractive indexes does not reflect light at all and does not refract light either. Since this disclosure is mainly dealing with reflection, to simplify the discussion, refractive behavior in the light path is ignored in the drawings. Reflective intensity depends on Δn, or the difference between the refractive indexes of the elements that form the interface. Gases such as air have much smaller reflective indexes than solids, therefore, an untreated solid-air interface usually has a strong reflection, for example, 4% reflection for glass at vertical incident angle. As discussed herein, examples of such solid-air surfaces include the glass surface(s) and the film surface(s) of some constructs. Removing or reducing reflections from such surfaces is a focal point of present disclosure. A solid-solid interface with a large difference between the two refractive indexes may also have a strong reflection, which is another focal point of the present disclosure. A solid-solid interface with a small Δn, or a small difference in refractive indexes, has a weak reflection, which will not be discussed in detail in the present disclosure, because a human's eyes are usually not sensitive enough to detect such weak reflections. The weak reflections also are not shown up in the drawings to simplify the discussion.
Anti-reflection is an active field in the electronic display industry, especially those applications using indium tin oxide (ITO) as a transparent electrode. ITO has a high refractive index, around 2.0, therefore, a reflection on any ITO interface is strong. There are several technologies that have been used to reduce reflection caused by the ITO layer, for example the single layer method and the multi-layer method. The single layer approach reduces the reflective index of ITO to match or get close to the reflective index of the other material that forms the interface. For example, if the other material is glass, the ITO refractive index must be reduced from 2.0 to a refractive index of about 1.5. The reflective index of ITO may be reduced by different ways of sputtering, such as the oblique-angle deposition technique. As the deposition angle increases, the porosity of the ITO film increases and the refractive index decreases. Therefore, the difference between reflective indexes Δn of a film-ITO interface is reduced, thereby achieving a reduction in reflection. The multi-layer (two or more layers) method uses interference to achieve an anti-reflection effect. By using alternating layers of a low-index material and a higher-index material and by controlling thickness of layers to obtain an opposite phase, reflections from the different layers may cancel each other, therefore, an overall reduction in reflection is produced. The word “matching” or “matched” means a result for eliminating or reducing reflection by using a technology such as the single layer technique or multi-layer technique.
Both single layer and multi-layer ITO film products are just available commercially. In present disclosure, our main focus is to use existing anti-reflection products on new systems related to switchable devices such as the laminated LC switchable panel and switchable projection panel. As will be appreciated by one of skill in the art, during outdoor applications, the potential brightness from natural light is significantly stronger, for example, tens of times stronger than the brightness generated by artificial lights, that is, “indoor light”. Because of this increased brightness, the reflection problem reaches an irreconcilable level. Reflection also has a serious impact on many recently developed features related to projection, such as front projection and rear projection, 360 degree viewable display and spherical scattering.
For all of the commercially available anti-reflection ITO film or anti-reflection glass, to simplify discussion in present disclosure, a single layer is used to represent a treated interface without mentioning what technology or principle is used to achieve anti-reflection on film or glass. For example, a single layer may be illustrated in this disclosure as an index matched indium tin oxide (IMITO) layer without distinguishing how the anti-reflection is achieved by using single layer technique or multi-layer technique. A single layer may be also used in claims as an index matched indium tin oxide (IMITO) layer without distinguishing how the anti-reflection is achieved by using single layer technique or multi-layer technique.
There has been very little published about the study of anti-reflection of complicated products such as laminated LC switchable panels. As discussed above, one reason may be the lack of effective tools for studying such complicated products. Although many kinds of photometers and micrometers are known and are useful in the study of liquid crystal display (LCD), these instruments are not helpful in studying reflection on LC switchable panels, because scattered light is mixed with reflected light and refracted light. Furthermore, reflected light changes with switching and under different conditions, and it is difficult to determine the refractive index of the LC-polymer layer. Scattered light may be a disturbing factor on the study with photometers and micrometers, plus different optic behaviors occurs on multi layered structure which are close in nanometers and all of this can change when the status of the switchable panel changes. To resolve reflections on a switchable film or glass, it is necessary first to understand reflection behavior and where these reflections come from and which interface is responsible for which reflection.
After many experiments, a successful experiment has been found that confirms reflective layers and interfaces. This invention will for the first time reveal how to locate reflective layers within a multiple layer structure and explain an optic mechanism of reflection and solve reflection problem on switchable devices like LCMD panels. The present disclosure introduces a very useful way to locate reflective layers. Although this experiment does not directly give an answer about reflecting interface but with a series of obviations, operations and logical analysis, it may clearly verify the predicated reflective surfaces with optic theory.
With reference to
It is necessary point out that the actual observed spot 340 is not like what is illustrated, that is, with a large separation between 340A and 340B. 340A and 340B are very close because the actual thickness of the LC-polymer layer is about 20 micrometers and the thickness of the ITO is about 15 nanometers, therefore, the switching of the panel has the effect of changing the intensity on one spot with a little shape change.
This well-designed experiment not only uses a relatively long distance to successfully isolate reflective lights from scattered lights but also uses different reflection spots in different conditions to confirm actual reflective layers. Observed results with numbers of reflective spots, distances between spots and shapes of spots and brightness of spots can be used for understanding and localizing reflective interfaces with known optics. This experiment confirms that the ITO layers are reflective surfaces and for the first time answers why a LCMD device in the transparent state has stronger reflections than normal glass with both experimental results and optic analysis and, of course, provides specific details for avoiding reflections on LCMD panels. Previously, there were no successful solutions developed for reducing or eliminating reflections that were not accompanied with a negative impact on performance within the industry. (Note: It has mentioned above that this experiment for the first-time answers why a LCMD device in the transparent state has stronger reflections than normal glass with both experimental results and optic analysis)
A reflection is determined by Snell's law and the refractive indexes of the substances. A Fresnel reflection is generated from an interface with Δn greater than zero. The greater the difference in Δn, the stronger the Fresnel reflection. A mismatch in the refractive index between layers will result in a Fresnel reflection and loss of transmittance at each interface. Therefore, refractive index-matched structures will minimize Fresnel reflection losses.
Referring to
Since refractive indexes of ITO is changeable in range of visible wavelength, choosing a green laser with 530 nm wavelength may be close to average of daylight or yellow light at 550 nm. Since reflection is depended on different refractive indexes Δn at an interface. An at different interfaces are listed in table 3.
As shown in table 3 and the laser experiment, three interfaces have large Δn's which may generate strong reflections, specifically, the of Glass/air and PET/ITO and ITO/LC-Polymer interfaces. Other interfaces with small Δn do not generate notable reflections as observed in the experiment and as such are not detected by human eyes. That is why using a black board is used to review reflective spots. If using a white paper or board, weak reflective spots will also be seen in total darkness. However, these spots would not be visible in bright light situation, therefore, involving such weak reflective spots is not helpful for the analysis. Since the thickness of the ITO layer is only a dozen nanometers, the two interfaces of PET/ITO and ITO/LC-Polymer actually generate only one spot of reflection, because they are in such close proximity. Therefore, we know that the two side reflective spots are generated by glass/air interfaces and that the center reflective spot is from interfaces of PET/ITO and ITO/LC-Polymer.
A light path way with strong reflections is illustrated in
Referring to
Anti-reflective glass is commercially available and its optic mechanism of anti-reflection is well-known. Since Δn of glass/PVB interface or glass/interlayer interface is already very small (Δn=0.035), the anti-reflective glass only needs to have anti-reflective coating at one side or outer side for reducing cost. As discussed above, while tinted glass also reduced reflection, the tinted glass also altered the color spectrum of displayed images. However, surprising, the anti-reflective coatings have no effect on the color spectrum, resulting in images that are clear and sharp. As will be appreciated by one of skill in the art, this eliminates the contributions of two factors that were long considered to confound the analysis of reflection in switchable panel device apparatuses: scattered light and the complicated structure of the LCMD device. As discussed above, this test allows for the analysis of reflection in total isolation from scattering lights, which confound the results and analyses of traditional tests. Furthermore, as discussed above, this test has determined that the reflective spot from ITO actually comes from two reflective interfaces. Surprisingly, in this testing, the complicated structure of the LCMD device did not confound or confuse the results, but instead, helped to find the answer. This is because, without a switching function, it would have been hard to determine that a normal ITO reflection was formed by two reflections, and then it would be difficult to explain why the reflection of the LCMD is so strong. The strongness is because it combines two reflections.
Refractive index matched ITO film or IMITO 510 is a relative new product in the market. It is just commercially available in some large coating companies such as Sheldahl. The transmittance of refractive IMITO film may be improved from about 78% to 94%.
By using these two improved parts, or anti-refractive glass and refractive index matched ITO film, the optic quality of a laminated switchable glass is greatly improved as a result of total removal of the noticeable reflections, as illustrated in
Apparatus 500 or laminated LC switchable glass may be any silicon-based glass like annealed glass, clear glass or temped glass, or polymer based glass like acrylic and polycarbonate panel. The film may be organic polymer film such as polyethylene terephthalate (PET) film or polycarbonate film.
Suspended particle device (SPD), electrochromic and thermochromic materials have similar structures and applications as switchable windows or energy saving sunroof and the same problem with unwanted reflections. As discussed here, this methodology will resolve the reflection problems on those devices as well.
Similarly, these technical methods can be used to improve optical quality of traditional Switchable Projection Panel 600, illustrated in
In summary, this disclosure introduces two methods to eliminate or reduce reflections from switchable devices, that is, the use of IMITO to replace regular ITO and to add anti-reflective coating to glass/air interface or film/air interface. The glass layers included in
Suspended particle device (SPD), electrochromic or thermochromic materials has similar applications as switchable windows and have the same problems with unwanted reflections. As discussed herein, this methodology will also resolve the reflection problem on those devices. With basic layer structures described above, a different optically active layer determines a type of switchable panel. An optically active layer maybe selected from LCMD material, SPD material, electrochromic material or thermochromic material.
A switchable film may have following layer structures: transparent film/ITO transparent electrode/optically active layer/ITO transparent electrode/transparent film. In structure of the switchable film, there are two film/air interfaces or outer surfaces of two layers of transparent films. There are two methods to eliminate or reduce reflection on the switchable film, or replacing ITO transparent electrode with IMITO transparent electrode and coating film/air interface with anti-reflective coating. Each method has the effect of reducing reflection, the combination of the two methods is better, but costs are different. These methods and combination of the methods may be selected in different applications.
A switchable panel may have two structures, or laminated switchable panel and switchable projection panel. In structure of the switchable projection panel, there is two types of solid/air interfaces or film/air interface and glass/air interface. In structure of laminated switchable panel, there is only one type of solid/air interface or glass/air interface, because an original film/air interface is replaced with solid/solid interface or film/interlayer interface after lamination. There are two methods to eliminate or reduce reflection, including replacing ITO transparent electrode with IMITO transparent electrode and coating solid/air interface with anti-reflective coating. Each method has the effect of reducing reflection, the combination of the two methods is better, but costs are different. These methods and combination of the methods may be selected in different applications. The solid may be film or glass. Solid/air interface may be film/air interface and glass/air interface.
This application claims the benefit of US provisional patent application Serial Number U.S. 62/762,368 filed May 1, 2018, and PCT Application Serial Number PCT/US2019/027707 filed Apr. 16, 2019, the entire contents of which are incorporated herein by reference for all purposes.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/US2019/027707 | 4/16/2019 | WO | 00 |
Number | Date | Country | |
---|---|---|---|
62762368 | May 2018 | US |